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Citation: Di Maggio, G.; Confalonieri,
P.; Salton, F.; Trotta, L.; Ruggero, L.;
Kodric, M.; Geri, P.; Hughes, M.;
Bellan, M.; Gilio, M.; et al.
Biomarkers in Systemic Sclerosis: An
Overview. Curr. Issues Mol. Biol. 2023,
45, 7775–7802. https://doi.org/
10.3390/cimb45100490
Academic Editors: Ilya Nikolaevich
Medvedev, Svetlana Zavalishina and
Vorobieva Nadezhda Viktorovna
Received: 2 September 2023
Revised: 19 September 2023
Accepted: 22 September 2023
Published: 25 September 2023
Copyright: © 2023 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
Review
Biomarkers in Systemic Sclerosis: An Overview
Giuseppe Di Maggio 1, †, Paola Confalonieri 1 ,† , Francesco Salton 1, Liliana Trotta 1, Luca Ruggero 1,
Metka Kodric 1, Pietro Geri 1, Michael Hughes 2, Mattia Bellan 3,4,5 , Michele Gilio 6, Selene Lerda 7,
Elisa Baratella 8, Marco Confalonieri 1, Lucrezia Mondini 1, ‡ and Barbara Ruaro 1, *,‡
1Pulmonology Unit, Department of Medical Surgical and Healt Sciencies, Hospital of Cattinara,
University of Trieste, 34149 Trieste, Italy; giuseppe.dimaggio@studenti.units.it (G.D.M.);
metka.kodric@asugi.sanita.fvg.it (M.K.); pietro.geri@asugi.sanita.fvg.it (P.G.); lmondinifr@gmail.com (L.M.)
2Division of Musculoskeletal and Dermatological Sciences, Faculty of Biology, Medicine and Health,
The University of Manchester & Salford Royal NHS Foundation Trust, Manchester M6 8HD, UK;
michael.hughes-6@manchester.ac.uk
3Department of Translational Medicine, Universitàdel Piemonte Orientale (UPO), 28100 Novara, Italy
4Center for Autoimmune and Allergic Disease (CAAD), Universitàdel Piemonte Orientale (UPO),
28100 Novara, Italy
5Department of Medicine, Azienda Ospedaliero–Universitaria, Maggiore della Carità, 28100 Novara, Italy
6Infectious Disease Unit, San Carlo Hospital, 85100 Potenza, Italy
7Graduate School, University of Milan, 20149 Milano, Italy
8Department of Radiology, Cattinara Hospital, University of Trieste, 34149 Trieste, Italy
*Correspondence: barbara.ruaro@yahoo.it
†These authors contributed equally to this work.
‡These authors contributed equally to this work.
Abstract:
Systemic sclerosis (SSc) is a complex autoimmune disease characterized by significant
fibrosis of the skin and internal organs, with the main involvement of the lungs, kidneys, heart,
esophagus, and intestines. SSc is also characterized by macro- and microvascular damage with
reduced peripheral blood perfusion. Several studies have reported more than 240 pathways and
numerous dysregulation proteins, giving insight into how the field of biomarkers in SSc is still
extremely complex and evolving. Antinuclear antibodies (ANA) are present in more than 90% of SSc
patients, and anti-centromere and anti-topoisomerase I antibodies are considered classic biomarkers
with precise clinical features. Recent studies have reported that trans-forming growth factor
β
(TGF-
β
) plays a central role in the fibrotic process. In addition, interferon regulatory factor 5 (IRF5),
interleukin receptor-associated kinase-1 (IRAK-1), connective tissue growth factor (CTGF), transducer
and activator of transcription signal 4 (STAT4), pyrin-containing domain 1 (NLRP1), as well as genetic
factors, including DRB1 alleles, are implicated in SSc damage. Several interleukins (e.g., IL-1, IL-6,
IL-10, IL-17, IL-22, and IL-35) and chemokines (e.g., CCL 2, 5, 23, and CXC 9, 10, 16) are elevated in
SSc. While adiponectin and maresin 1 are reduced in patients with SSc, biomarkers are important in
research but will be increasingly so in the diagnosis and therapeutic approach to SSc. This review
aims to present and highlight the various biomarker molecules, pathways, and receptors involved in
the pathology of SSc.
Keywords: systemic sclerosis (SSc); autoimmune disease; interleukines; chemokines
1. Introduction
Systemic sclerosis (SSc) is a rare connective tissue disease, characterized by complex
and different pathogenetic pathways, including vasculopathy, abnormal immune activation,
with the production of autoantibodies and fibrosis [
1
–
4
]. The pathogenesis of SSc is complex
and not yet completely understood, however the events involved in SSc pathogenesis
can be schematically summarized in three main phases: (a) vascular damage, mainly
of microcirculation; (b) immune system activation/autoimmunity/inflammation and (c)
Curr. Issues Mol. Biol. 2023,45, 7775–7802. https://doi.org/10.3390/cimb45100490 https://www.mdpi.com/journal/cimb
Curr. Issues Mol. Biol. 2023,45 7776
fibrosis [
4
–
10
]. Fibrosis of the skin and internal organs may be considered the main
clinical hallmark of the disease and it is due to fibroblasts activation and dysfunction
with the acquisition of a “myofibroblast phenotype” [
1
,
2
,
11
–
18
]. Skin manifestations
can be recognized and studied by using the modified Rodnan skin score (mRss), the
validated method for assessing the severity of skin involvement in SSc and distinguishing
the different subsets of skin involvement in SSc [
6
–
10
]. The use of the mRss provides
an assessment of skin thickness and has been used as a primary outcome measure in
most clinical trials. The original score was developed in 1979 by Rodnan et al. [
8
]. In
summary, these are the two main forms into which SSc can be formally classified at
present: 1—limited cutaneous form (lcSSc), characterized by predominantly distal skin
thickening and the presence of anticentromere antibodies, and 2—diffuse cutaneous form
(dcSSc), in which there are diffuse distal and proximal skin changes associated with the
presence of anti-topoisomerase antibodies, anti-RNA-III polymerase antibodies, or other
antibodies with antinuclear pattern [
9
–
14
,
19
–
25
]. The most used biomarkers in SSc are
autoantibodies, and in this case, they have utility for diagnosis, classification, and prognosis
of the disease; it should also be mentioned that biomarkers can be potential therapeutic
targets [
4
,
23
–
30
]. Antinuclear antibodies (ANA) are present in more than 90% of SSc
patients, along with anticentromere, anti-Th/To, and anti-topoisomerase I antibodies,
which are considered the classic biomarkers present in 60% of SSc patients and help
to define precise clinical classifications [
4
,
7
,
29
–
37
]. Other autoantibodies, such as those
directed against the endothelium or fibroblasts, against angiotensin II type 1 receptor,
endothelin-1 type A receptor, platelet-derived growth factor receptor (anti-PDGFR), and
extracellular matrix (ECM) proteins [
16
–
20
,
38
–
45
] are also found in SSc patients. More
complex autoantibody systems against G-protein-coupled receptors, growth factors, and
respective receptors have also been described in SSc [
21
,
45
–
49
]. ANA might not only
represent biomarkers of disease but also play a pathogenic role through immune-mediated
mechanisms and molecular mimicry. ANA (particularly anti-topoisomerase-I and anti-RNA
polymerase III antibodies) appear to be transported within the cell by direct interaction
with intercellular components and receptors, targeting intracellular topoisomerase and
RNA polymerase by the corresponding antibodies [22,23,49–55].
Supporting this evidence is the response of some SSc patients to B-cell-targeted thera-
pies and the role of activated B cells in the success of allogeneic bone marrow transplan-
tation for the treatment of SSc [
24
,
25
,
55
–
60
]. In addition, SSc patients have macro- and
microvascular damage and impaired peripheral blood perfusion [
6
,
48
–
53
]. Nail fold video
capillaroscopy (NVC) plays an important role because it is a noninvasive and reliable
method to detect microvascular involvement. NVC is now formally used to classify SSc
because it plays a diagnostic role in recognizing microvascular involvement [
3
,
4
,
26
,
60
–
68
].
Indeed, the presence of capillaroscopic abnormalities of the nail fold, together with the
presence of ANA and recurrent Raynaud’s phenomenon, are predictive factors for pro-
gression to definitive SSc. Anti-topoisomerase I antibodies are also predictive, in the first
3 years
of disease of the development of diffused skin involvement and digital ulcers (DU),
as well as severe interstitial lung disease (ILD) [66–77].
Anti-centromere autoantibodies (ACA) are associated with pulmonary arterial hy-
pertension (PAH), anti-topoisomerase I autoantibodies (anti-topo I) with ILD, and anti-
ti-RNA polymerase III autoantibodies (anti-RNA Pol III) with scleroderma renal crisis
(SRC). Anti-RNA polymerase III autoantibodies may be a biomarker that predicts the
rapid progression of skin thickening, gastric antral vascular ectasia, SSc-associated tumors,
scleroderma renal crisis, and possibly autoimmune syndromes associated with silicone
breast implants [7,27,28,48–53,77–84] (Table 1).
Curr. Issues Mol. Biol. 2023,45 7777
Table 1. Correlation between autoantibodies, clinical manifestations and skin subset.
Autoantibodies Frequency % Subset Clinical Associations
Anti-Topo I 15–25% dcSSc Cardiac, skin and lung involvement
ACA 10–20% lcSSc CREST, DU, PAH
Anti-RNA Pol III 10–25% dcSSc SRC, tendon friction rubs, cardiac involvement
Anti-U1 RNP 5–30% lcSSc MCTD
Anti-PMScl 3–8% Myositis SSc Inflammatory muscle involvement
Anti-To/To 2–5% lcSSc PAH
Legend. Autoantibodies in SSc and their correlations with skin subset and clinical manifestations;
CREST: Calcinosis
, Raynaud’s phenomenon, Esophageal dysmotility, Sclerodactyly, and Teleangiectasia;
DU: digital
ulcers; PAH: pulmonary hypertension
¸
SRC: scleroderma renal crisis; MCTD: mixed connective
tissue disease.
However, SSc patients may also present with other autoantibodies, such as anti-PMScl
(often associated with inflammatory muscle involvement), anti-Th/To, anti-RNP, and anti-
fibrillarin autoantibodies [
26
–
30
]. Approximately 10% of SSc patients are ANA-negative,
but both ANA-negative and ANA-positive patients may present with novel antibodies,
including anti-elF2B, an-ti-RuvBL1/2 complex, anti-U11/12 RNP, anti-U3RNP, anti-BICD2,
anti-Ku and an-ti-PM/Scl [
7
–
10
,
84
–
91
]. It is unusual to find two different SSc-specific
autoantibodies simultaneously in the same individual [
29
–
33
,
48
–
55
,
92
–
99
]. Mortality in SSc
patients is significantly increased and usually related to the life-threatening manifestations
of SSc, including PAH, ILD, SRC, cardiac involvement, tumors, and infections, which are
also related to immunosuppressive drugs [8,9,34,48,56–58,100–109].
The purpose of this review is to present an overview the various molecules, pathways,
and biomarker receptors involved in SSc pathology.
2. Systemic Sclerosis Pathogenesis
The exact processes of SSc pathogenesis are not clear. However, the pathogenic
processes can be summarized in three main events: the endothelial injury with a consequent
microvasculopathy, followed by the autoimmune response and inflammation and finally
a diffuse fibrosis of skin and internal organs [
1
–
10
,
109
–
118
]. Several studies confirmed
the role of each of these three events and their interaction in SSc pathogenesis. However,
the initial trigger event has not yet been identified. Recent studies supported the role of a
genetic predisposition and both endogenous and/or exogenous environmental triggers may
be promoter for epigenetic mechanisms in genetically predisposed
population [1–10,68–75]
.
Interestingly, a recent study supported the role of infectious triggers in SSc pathogenesis; in
particular, the authors reported a possible role of Parvovirus B19 in this disease [15].
2.1. The Role of Endothelial Injury in Systemic Sclerosis Pathogenesis
Regarding the endothelial injury, several studies reported the presence of an endothe-
lial involvement before the development of fibrosis and this situation support the vascular
origin of SSc [
6
–
13
]. Raynaud’s phenomenon (RP) represents the clinical expression of vaso-
motor instability and tendency to vasospasm [
6
–
13
,
106
–
109
]. The alteration of microvascu-
lar tone may represent a trigger leading to the opening of endothelial junctions increasing
the vessel permeability and recalling inflammatory cells [
6
–
13
,
22
–
25
,
106
–
109
]. The increase
of vessel permeability could be considered responsible for oedema that is present in the
early phase of the disease and is correlated with the presence of puffy
fingers [6–13,106–109]
.
The endothelium is an active tissue with important biologic functions, as the production of
vasodilators (i.e., nitric oxide (NO) and prostacyclin) and vasoconstrictors (i.e., endothelin-1
(ET-1) and plated activating factor) and cell adhesion molecules [
10
,
13
]. In SSc vasculopathy
may assume both destructive (loss of capillaries) and proliferative (hypertrophy of the ves-
sel tunic) characteristics with a consequent decrease in vascular bed and ischemic suffering
of skin and internal organs. The SSc vascular damage is characterized by the presence of a
Curr. Issues Mol. Biol. 2023,45 7778
characteristic processes with a vasomotor instability with an imbalance of vasoactive factors:
overproduction of vasoconstrictors (ET-1) and underproduction of vasodilators (NO and prosta-
cyclin) [
6
–
13
,
22
–
25
,
106
–
109
]. The free radical nitric oxide (NO) is a potent vasodilator and is
synthesized from L-arginine by NO synthase
(NOS) [10–19,22–25,40–48,106–113]
. Endothe-
lial isoforms of NOS (eNOS or
NOS 3
) has been identified with a constitutive expression,
other isoforms are shown in other cell types. Furthermore, an inducible expression (iNOS or
NOS 2) in response to a variety of stimuli is possible, with NO-mediated signalling apparent
in the
skin [10–19,40–48,106–113]
. Several studies reported that NO have a biphasic effect in
physiological and pathological conditions, being both beneficial and detrimental depending
on the concentration and local environment [
10
–
19
,
40
–
48
]. Recently observation proposed
the regulation of NO by endogenous levels of the NOS inhibitor asymmetric dimethy-
larginine
(ADMA) [10–19,22–25,40–48,106–113]
. Regarding the endothelial dysfunction in
SSc, there is evidence of reduced intracellular eNOS production in the SSc endothelium
and increased endothelial activation [10–19,22–25,40–48]. Increased endothelial apoptosis
mediated by anti-endothelial cell antibodies and antibody-dependent cell cytotoxicity has
also been shown to precede inflammatory events and
fibrosis [10–19,22–25,40–48]
. While
the aetiology of endothelial dysfunction is still unclear, free-radical-mediated damage and
immunological insults remain attractive proposals to mediate effects. An interesting study
suggested that SSc serum significantly reduces NO synthase activity, paralleled by decreases
in intracellular cGMP and NO production in the cell medium, and supported the presence
of a factor that inhibits
NOS [10–19,22–25,40–48,106–113]
. These results support the obser-
vations from earlier studies that serum factors influence endothelial dysfunction and apop-
tosis; however, it has been reported that SSc serum alone was ineffective and the additional
presence of natural killer cells was required to mediate
cytotoxicity [10–19,40–48,106–113]
.
In the same work it is also demonstrated that SSc serum alone had no significant effect
on endothelial cytotoxicity and the observations of reduced NO activity and production
were unlikely to be due to decreased cell survival. While free-radical-related mechanisms
and immunological insults evidently mediate endothelial dysfunction, the observations
of some papers also suggest the role of circulating inhibitory factors such as ADMA that
may regulate NOS activity
in vivo
, and account for the observed serum induced decrease
in cGMP and NO production
in vitro
[
10
–
19
,
22
–
25
,
40
–
48
]. In summary, formation of NO is
increased in patients with primary RP or lcSSc, but nitration of proteins and ADMA is a
particular feature of dcSSc and may reflect abnormal NO regulation and/or contribute to
endothelial dysfunction in SSc [10–19,22–25,40–48].
Furthermore, endothelial cells presented an increased expression of adhesion molecules
(VCAM1, ICAM and E-selectin) contributing to the recall of inflammatory cells from
the circulation [
6
–
13
,
22
–
25
,
106
–
109
]. ET-1 also presents proliferative and fibrogenic ef-
fects and may contribute not only to the early response with a rapid and transient cell
contraction but also to a slower process culminating in the remodeling phenotype of
blood
vessels [6–13,106–109]
. This later response also involves perivascular fibroblasts and
smooth muscle cells proliferation leading to the hypertrophy of intimal and medial layers
and adventitial fibrosis of vessel. These processes cause a progressive obliteration of blood ves-
sels contributing to a chronic ischemia, that together with endothelial cells apoptosis lead to a pro-
gressive loss of capillaries in the late phase of SSc [
6
–
13
,
106
–
109
]. In SSc patients, vascular en-
dothelial growth factor (VEGF) is overexpressed leading to vascular malformations includ-
ing giant and bushy capillaries, observed at NVC
evaluation [6–13,106–109]
. In SSc, the lack
of new functional blood vessels is also due to an impaired
vasculogenesis [6–13,106–109]
.
In fact, endothelial progenitors seem decreased in SSc patients leading to an incompetent
vasculogenesis. In addition, pericytes, the vascular mural cells, contribute to the regulation
of vascular development and remodeling, and they seem to be activated from the early
phase of the disease inhibiting angiogenetic processes and being responsible to deposition
of extracellular matrix (ECM) [
6
–
13
,
106
–
109
]. It is important to underline that the stimu-
lation of ECM production and the accumulation of ECM proteins worsen tissue hypoxia
resulting in a vicious circle of hypoxia and fibrosis [6–13,22–25,106–109].
Curr. Issues Mol. Biol. 2023,45 7779
2.2. The Role of Immune System in Systemic Sclerosis Pathogenesis
The activation of immune system appears to be an early event, in SSc patho-
genesis [
6
–
13
,
106
–
109
]. Perivascular infiltrates are mainly composed of T cells, but also
macrophages, mast cells and B lymphocytes can be observed [
6
–
13
,
40
–
47
,
106
–
109
]. An
abnormal immune response is characterized by the activation of T lymphocytes from the
earlier phases of SSc. Although their exact role remains to be clarified, T cells seem to
be involved both in the early inflammatory response and in the late fibrotic process with
the production of cytokines leading to the recall of other cells as macrophages and mast
cells. Recently, a new study confirmed an alteration of T-lymphocyte subset and of their
serum cytokines in SSc patients confirming the role of T cells in the pathogenesis of the
disease [
6
–
13
,
44
–
46
,
106
–
109
]. In SSc, among T cells, type 2 T helper (Th2) cells are more
expressed than Th1 cells [
6
–
13
,
40
–
45
,
106
–
109
]. In the last decade, many studies focused
on the role of T reg cells that in SSc have been described reduced in levels and with a de-
creased functional capacity [
6
–
13
,
106
–
109
]. T cells seem to contribute to the SSc progression
through the secretion of several fibrogenic cytokines and chemokines [
6
–
13
,
44
–
46
,
106
–
109
].
IL-4 and IL-13 are released by Th2 cells and promote fibrosis, in fact IL-4 seems able
to stimulate fibroblasts proliferation, migration and collagen production [
6
–
13
,
106
–
109
].
Contrarily, antifibrotic cytokines (IFN-
γ
, characteristic of Th1, and IL-10, characteristic of
Treg) are decreased, indirectly contributing to fibrogenesis process in SSc. B cells represent
a relatively small subpopulation of perivascular lymphocytes, however the presence of
specific antibodies in almost all SSc patients, suggests a certain role of B cells in SSc patho-
genesis. The exact mechanisms that stimulate the activation of B cells and the induction
of a humoral immune response remain to be understood. There are several hypotheses,
including molecular mimicry, the potential expression of autoantigen peptides and a
B cells
hyperactivity due to intrinsic B cells abnormalities [
6
–
13
,
106
–
109
]. The contribution of the
SSc specific antibodies to the disease development remains to be clarified; however, recent
data suggest a possible role of antibodies on endothelial damage with the interaction with
growth factor (PDGF) receptors and ET-1 receptor [
6
–
13
,
106
–
109
]. In SSc pathogenesis,
the role of B cells is not confined to the production of antibodies, in fact activated B lym-
phocytes may also contribute to fibrosis process stimulating fibroblast through the IL-6
pathway [6–13,106–109].
2.3. The Role of Fibrotic Process in Systemic Sclerosis Pathogenesis
The increased production and deposition of ECM is the most prominent hallmark of
SSc affecting both skin and internal organs. ECM consists of different proteins, as collagens,
proteoglycans, fibronectin and adhesion molecules [
6
–
13
,
42
–
48
,
106
–
109
]. Collagen is the
most important component of ECM. Collagen is produced by fibroblasts that can be
considered the key effectors of fibrosis in SSc, in fact, they presented an activated phenotype
in myofibroblasts and both the early endothelial dysfunction and the innate immune system
activation are crucial in the fibrotic process [
6
–
13
,
106
–
109
]. In addition, recent studies
described a relative resistance to apoptosis of fibroblasts in SSc [
6
–
13
,
106
–
109
]. The TGF
β
stimulation is considered responsible for the activation of fibroblasts. However, it is not
able to explain all the phenotypic characteristics of these cells in SSc. TGF
β
is secreted
by different cells (platelets, monocytes/macrophages, T cells, and fibroblast) and it is not
the only fibrogenic mediators in SSc, also PDGF and CTGF (connective tissue growth
factor) are considered leading actors in the pro-fibrotic process. PDGF is a mitogen and
chemoattractant for fibroblasts, released by endothelial cells, platelets and macrophages.
PDGF seems able to increase the secretion of TGF
β
and IL-6 and to stimulate collagen,
fibronectin and proteoglycan production. CTGF may stimulate fibroblasts growth and
promote the synthesis of part of ECM [6–13,40–45,106–109].
Furthermore, an abnormal pro-fibrotic Th2- polarized T cell response has been pro-
posed to mediate tissue damage and fibrosis in SSc-ILD as Th2 cytokines lead to the
activation of alternative inflammatory pathways and to the transcription of transforming
growth factor (TGF)-
β
, involved in induction and progression of fibrosis [
8
,
9
]. Moreover,
Curr. Issues Mol. Biol. 2023,45 7780
it has been demonstrated that IL-4/IL-13 axis upregulate genes known to be involved in
the mechanisms of wound healing and fibrosis in murine models and
in vitro
, infuencing
the activation of myofbroblasts [
2
–
8
,
40
–
46
]. Several studies reported that Th2 cytokines
contribute to the differentiation and migration of eosinophils, which are involved in sys-
temic inflammatory process in SSc patients [
2
–
8
,
40
–
46
]. At a later stage, fibroblasts pro-
liferation and activation lead to extracellular matrix deposition and fibrosis of the lung
parenchyma [2–8,40–46].
Recent studies shown that alterations in macrophage polarisation are involved among
the possible immune system abnormalities contributing to SSc pathogenesis. Macrophages
have been classified as classically (M1) or alternatively (M2) activated, although growing
evidence indicates that they may exhibit characteristics shared by more than one of the
described phenotypes, in particular an M2 pre-eminent phenotype has been postulated
for SSc monocytes/macrophages [
2
–
8
,
40
–
46
]. Several recent studies demonstrated that
M2 and more significantly cells expressing both M1 and M2 surface markers identified
patients with SSc in comparison of the healthy population; on the contrary, they observed
no differences when only M1 markers were used. The authors of numerous paper demon-
strated that the initial gating strategy based on the CD204+cells resulted the most efficient
to describe monocyte/macrophage phenotype differences between SSc patients and healthy
subjects [2–8,40–46].
Furthermore, the result of other works supported the above observations demonstrat-
ing a remarkable plasticity of circulating monocytes/macrophages, resulting in a ‘spectrum’
of activation states and other papers showed a downregulation of interferon-
γ
response
and IL6/JAK/STAT3 pathway in SSc monocyte-derived macrophages, possibly describing
a ‘SSc specific macrophage’ [2–8,40–46].
3. Biomarkers in Systemic Sclerosis
Recent studies have shown how vast and ever-expanding the field of biomarkers
is in SSc. Biomarkers will become increasingly important in research and, consequently,
in the diagnosis and therapeutic approach to SSc [
30
–
36
,
59
–
67
]. Several studies have
demonstrated the involvement of at least 240 pathways and numerous dysregulated pro-
teins in the pathogenesis of SSc, so the field of biomarkers in this disease is complex and
evolving [
30
–
36
,
59
–
67
]. Cytokeratin 17 (CK17), marginal zone protein B1 (MZB1), and
leucine-rich
α
2-glycoprotein-1 (LRG1) appear to be potential biomarkers for SSc, with CK17
negatively associated with disease severity and higher values of CK17
protective [37,59–67]
.
A potential therapeutic target could be endostatin, which is associated with vascular mani-
festations in SSc and is specifically elevated in progressive SSc; it has been considered a
marker of disease severity [38,62–67].
Periostin is secreted by fibroblasts and epithelial cells and is associated with cell
adhesion, fibrosis, angiogenesis, survival and matrix remodeling [
34
,
39
–
41
]. In SSc, cir-
culating periostin levels are elevated and associated with disease duration, skin fibrosis,
and cardiomyopathy [
39
–
41
]. The chemokine CC2 (CCL2) also appears to be involved in
the development of fibrosis in SSc [
39
–
42
,
62
]. MicroRNAs (miRNAs) are short nucleotide
sequences involved in cellular regulation [
37
,
38
]. The miR-138 and miR-27a microRNAs
suppress major pathways involved in epithelial-to-mesenchymal cell transition and subsequent
fibrosis [
37
,
38
,
45
,
60
–
67
]. The relative expression of miR-138 and miR-27a is significantly
lower in SSc patients than in controls, while only miR-138 is further depressed in dif-
fuse cutaneous SSc, thus potentially both could be used as diagnostic biomarkers with
miR-138 specific to predict severity [
45
,
60
–
67
]. Suppression of carcinogenicity receptor
2 (ST2) binds IL-33 and serum soluble ST2 (sST2) suppresses IL-33 signaling [
45
,
60
–
67
].
Elevated serum sST2 levels are associated with increased joint disease activity and in-
creased hand dysfunction in SSc, indicating that sST2 could be a biomarker to predict SSc
joint involvement [
45
,
60
–
67
]. Angiopoietins (Ang-1 and Ang-2) interact with the specific
receptor tyrosine kinase Tie2 to modulate endothelial cell activation, vascular remodeling,
and angiogenesis [
45
,
60
–
67
]. In SSc patients, Ang-1 decreased while Ang-2 increased,
Curr. Issues Mol. Biol. 2023,45 7781
thus this may contribute to both vascular ablation and new abnormal blood vessel
formation [
41
–
45
,
60
–
67
]. In their interesting study Michalska-Jakubus et al. suggested
for the first time that dysregulation of angiopoietins/VEGF system with shift towards
Ang2 and VEGF and decrease in Ang1 levels may play a role in progression of SSc specific
microangiopathy from capillary enlargement and collapse to aberrant vessel repair and
final loss of angiogenesis [
12
]. The authors reported that VEGF levels seem to be increased
early in SSc but in face of attenuated Ang1 it might lead to ectatic microvessels of increased
permeability as reflected by giants and microhaemorrhages typical for an “Active” NVC
pattern. The researcher supported that elevated levels of VEGF appeared to be sustained
also in advanced stages of microangiopathy and correspond with capillary loss (“Late”
NVC pattern) [
12
]. In conclusions, the results of this study might be partially explained by
the relative advantage of Ang2 that increase later in disease progress and result in advanced
vascular damage. These eminent researchers identified that altered Ang1/Ang2 profile
might underlay loss of angiogenesis in SSc despite increase in VEGF and may be one of
the essential factors promoting SSc specific microangiopathy. Moreover, since Ang1 is an
“endothelial survival factor”, it is possible that its relative insufficiency in SSc patients, as
revealed in this article, might be the mechanism underlying dysfunction and damage of
endothelial cells thought to be a primary event in disease pathogenesis [12].
The IFN-regulated protein sialic acid-binding Ig-like lectin 1 (SIGLEC-1) is upregulated
in SSc compared with controls but is not associated with specific complications [
45
,
60
–
67
].
Increased activation and expression of type 1 interferons are typical of SSc and may provide
a potential therapeutic target [
45
,
60
–
67
]. In SSc, the lack of new functional blood vessels is
also due to impaired vasculogenesis [
2
,
7
,
29
]. Indeed, endothelial progenitors appear to be
reduced in SSc patients, leading to incompetent vasculogenesis. Furthermore, pericytes,
which are mural cells, contribute to the regulation of vascular development and remodeling
and appear to be activated from the early stage of the disease by inhibiting angiogenic
processes and being responsible for the deposition of extracellular matrix
(ECM) [2,7,29]
.
Abnormal accumulation of ECM usually occurs in SSc [
2
,
29
]. ECM catabolism is regulated
by matrix metalloproteinases (MMP-1 to MMP-28) whose activity is in turn inhibited by
tissue MMP inhibitors (TIMP-1 to TIMP-4) [
2
,
29
]. TIMP-4 is increased in SSc patients com-
pared to healthy subjects [
2
,
29
]. Similarly, semaphorins (Sema3A-F) have anti-angiogenic
effects and are increased in SSc patients [2,29]. Cytokines and interleukins (e.g., IL-1, IL-4,
IL-6, IL-13, IL-17B, IL-17E, IL-17F, IL-22, IL-35) and chemokines (e.g., CCL2,3,5,20,21) are
often elevated in SSc [30–38,59–67] (Table 2).
Table 2. Biomarkers in systemic sclerosis.
Biomarker Clinical Association
IL-6↑
[6,81–89,95–98,101,108]
mRSS, early progressive skin sclerosis, poor prognosis, DLco
decline in SSc-ILD
CCL2↑
[30–42,59–67,81–87]ILD (lung dysfunction, CT scores), mRSS
CTGF↑
[81–87]mRSS, ILD
CXCL4↑
[81–87,116–119]mRSS, lung fibrosis, PAH, disease progression
CX3CL1↑
[68,81–87]dcSSc, ILD, digital ulcer
ICAM-1↑
[84–90]
Rapidly progressive disease, digital ulcers, dcSSc, ILD, joint
involvement, renal crisis, predictive of respiratory dysfunction
Von Willebrand factor↑
[118–133]
Raynaud’s phenomenon, disease severity, ILD, predictive of
PAH
Curr. Issues Mol. Biol. 2023,45 7782
Table 2. Cont.
Biomarker Clinical Association
SP-D↑
[81–90]Severity of ILD, maximum fibrosis scores on HRCT
CCL18↑
[81–87]
Activity and severity of ILD, predictive worsening of ILD and
mortality
MMP-7↑
[2,29,81–87]ILD, disease severity
MMP-12↑
[2,29,81–87,116–119]Skin sclerosis, dcSSc, ILD, nailfold bleeding, lower FVC
CRP↑
[2,10,41–50,114–120]
Skin sclerosis, PAH, renal dysfunction, risk of progressive early
ILD, worse pulmonary function
TGF-β↑
[81–87,116–119,134–140]Digital ulcers, dcSSc
TGF-β↓
[81–87,116–119,134–140]dcSSc, mRSS (in dcSSc)
VEGF↑
[6,88,89,95–98,100–108,116–119]
Systemic organ involvement, PAH, shorter disease duration,
skin sclerosis, reduced capillary density of nailfold
VEGF↓
[6,88,89,95–98,100–108,116–119]Digital ulcers
CXCL8↑
[81–87]Predictive of physical dysfunction
CXCL10↑
[19,81–87,141–150]Preclinical/early SSc
VCAM-1↑
[19,141–150]Systemic organ involvement, renal crisis, disease activity
E-selectin↑
[19,116–119,141–150]Systemic organ involvement, renal crisis, disease activity
P-selectin↑
[19,116–119,141–150]Disease activity, predictive of physical disability
Endostatin↑
[38,62–67,116–119]PAH
BNP/NT pro-BNP↑
[116–126,151]Severity, stability, and prognosis of PAH
Endothelin-1↑
[16–20,38–45,116–133,141–153]
PAH, systemic organ involvement, microangiopathy defined by
capillaroscopy
Type I collagen (C-terminal telopeptide)↑
[79–94,116–119]Skin fibrosis, mRSS, pulmonary dysfunction, CRP
Type III collagen (N-terminal peptide)↑
[79–94,116–119]Disease activity, mRSS, HRCT score, prognosis
MMP-9↑
[2,29,116–119]mRSS, dcSSc
MMP-12↑
[2,29,81–87,116–119]Skin sclerosis, dcSSc, ILD, nailfold bleeding, lower FVC
Legend.
↑
, upregulated;
↓
, downregulated; IL-6, interleukin 6; CTGF, connective tissue growth factor; ICAM-1,
intercellular adhesion molecule 1; SP-D, surfactant protein-D; MMP, matrix metalloproteinases; TGF-
β
, trans-
forming growth factor; VEGF, vascular endothelial growth factor; NT-proBNP, N-terminal-pro hormone BNP;
ILD, interstitial lung disease; DLco, diffusing capacity of carbon monoxide; CT, computed tomography; PAH,
pulmonary arterial hypertension; HRCT, high resolution CT; mRSS, modified Rodnan total skin thickness score;
dcSSc, diffuse cutaneous systemic sclerosis; lcSSc, limited cutaneous systemic sclerosis.
Curr. Issues Mol. Biol. 2023,45 7783
In the following sections, the role of disease-relevant biomarkers of specific organ
systems in SSc will be discussed.
4. Biomarkers in Systemic Sclerosis Interstitial Lung Disease
Interstitial lung disease (ILD) is one of the most common manifestations of SSc (SSc-
ILD), affecting approximately 40–60% of patients, and pulmonary hypertension (PH) is the
leading cause of both mortality and disability in SSc [
69
–
75
]. Pulmonary involvement is
responsible for approximately 35% of all SSc-related deaths [70–77].
Risk factors associated with the development of SSc-ILD include male gender, dif-
fuse cutaneous SSc, African American heredity, and the presence of anti-Scl-70 (anti-
topoisomerase I) antibodies [
77
–
84
]. The clinical course, timing of onset, and spectrum of
severity of ILD vary among patients with SSc, making the diagnosis and management of
ILD very difficult. Indeed, in many subjects with SSc pulmonary involvement remains
limited and stable even without treatment [
79
–
87
]. Conversely, some patients may present
with severe and/or rapidly progressive ILD and for this reason, many efforts have been
made to identify patients at risk for ILD and its greater severity. Among these were the
dcSSc subset, African-American race, older age and disease onset, shorter disease duration,
positive abs anti-Mouse I, and absence of ACA [86–94].
Lung endothelial damage is central to the pathogenesis of ILD. Histologically, SSc-ILD
presents as a picture of nonspecific interstitial pneumonia, unlike idiopathic pulmonary fi-
brosis, which is usually characterized by the usual picture of interstitial
pneumonia [93–98]
.
SSc-ILD is characterized by inflammation early in the disease, extensive endothelial dys-
function, and increased deposition of ECM, particularly collagen produced by activated
myofibroblasts in resident tissues [
79
–
87
]. As ECM increases, lung tissue stiffness increases,
leading to restrictive lung disease with reduced lung compliance, decreased lung volumes,
and diffusing capacity, resulting in decreased exercise tolerance, dyspnea, fatigue, hy-
poxia, hypertension lung disease, work disability, and shortened life. expectation. The
disease process is thought to be initiated by repetitive epithelial and endothelial cell in-
jury with activation of the immune system, recruitment of fibroblasts, and phenotypic
transformation of the fibroblast into a myofibroblast which then secretes excessive ECM
resulting in fibrosis [
84
–
90
]. The initial endothelial and epithelial lesions are probably
autoimmune and inflammatory in nature but could also be induced by pathogens and
environmental factors [
88
–
94
]. In some epithelial cells, the apoptotic process takes place,
stripping the alveoli, while other epithelial cells mutate into myofibroblasts with reduced
apoptosis, loss of polarity, increased migration, and increased production of ECM, in-
cluding collagen [
88
–
94
]. The reduced apoptotic capacity of myofibroblasts can cause
an abnormal persistence of these active cells, contributing to progressive fibrosis [
81
–
87
].
Transforming growth factor b (TGF-
β
) is fundamental in the process of accumulation
of ECM and therefore fibrosis, as well as dysregulation of the immune system towards
inflammation [81–87]
. Stimulation of TGF
β
is thought to be responsible for the activation
of fibroblasts, however, it is not able to explain all the phenotypic characteristics of these
cells in SSc. For example, when stimulated by TGF
β
, fibroblasts acquire a myofibroblast
phenotype, however, this process requires other events such as co-expression of the variant
form of fibronectin extra domain (ED-A) [
81
–
87
]. In addition, epithelial cells, pericytes,
and bone marrow-derived cells can differentiate into myofibroblast-like cells. TGF
β
is
secreted by various cells (platelets, monocytes/macrophages, T cells, fibroblasts) and is
not the only fibrogenic mediator in SSc. PDGF and CTGF (connective tissue growth)
are also considered to be major players in the fibrotic process. CTGF can stimulate the
growth of fibroblasts and promote the synthesis of part of the ECM. PDGF is a mitogen
and chemoattractant for fibroblasts, released by endothelial cells, platelets, macrophages
and fibroblasts. It seems able to increase the secretion of TGF
β
and IL-6 and stimulate the
production of collagen, fibronectin and proteoglycans [
81
–
87
]. Other biomarkers typically
implicated in SSc-ILD include specific autoantibodies, signal transducer and activator
of transcription 4 (STAT4), CD226 (DNAX accessory molecule 1), interferon regulatory
Curr. Issues Mol. Biol. 2023,45 7784
factor 5 (IRF5), associated interleukin-1 kinase-1 to the cell receptor (IRAK1), connective
tissue growth factor (CTGF), pyrin-containing domain 1 (NLRP1), T-cell surface zeta-chain
glycoprotein (CD3
ζ
) or CD247, the NLR family, SP-D (surfactant protein), KL-6 (Krebs von
den Lungen-6), IL-8, leucine-rich
α
2-glycoprotein-1 (LRG1) and CCL19, as well as genetic
factors including the -DRB1 allele [
81
–
87
]. SSc-ILD was particularly associated with anti-
topoisomerase I antibodies (anti-Scl-70 antibody), antinuclear antibodies with nucleolar
pattern (including anti-RNA-polymerase III, anti-NOR-90 anti-Th/To, anti- PM/Scl-75,
anti-U3-RNP/fibrillarin or anti-PM/Scl-100 antibodies) [
81
–
87
]. Anti-PM/Scl defines SSc
patients with a high frequency of ILD, calcinosis, dermatomyositis skin changes, and severe
myositis [
81
–
87
]. The biomarkers most associated with active lung disease and progres-
sion specifically in SSc-ILD are KL-6 (Krebs von den Lungen-6), SP-D (surfactant protein),
C-reactive
protein, and CCL19 although other biomarkers are also present non-specific can
be elevated [
81
–
87
]. Th2 lymphocytes produce IL-13 and IL-4 which stimulate fibrob-
lasts and activate pro-fibrotic macrophages M2 which induce TGF-
β
, plaque-derived
growth factor (PDGF), and fibroblast growth factors (FGF) which induce the activation
of myo-fibroblasts [
81
–
87
]. Biomarker chemokines including CCL18, CX3CL1 and CXCL
with and without RNA complexes have recently been associated with SSc-ILD [81–87].
In the progression of SSc-ILD, an important role is played by IL-6, secreted by myofi-
broblasts, M1 macrophages, and B lymphocytes, which increases the expression of IL-4 and
IL-13 receptors, enhancing macrophage polarization M2 and increasing fibrosis [
81
–
87
].
Tocilizumab acts by inhibiting the IL-6 receptor, consequently decreasing the activation of
myofibroblasts and reducing the polarization of M2 macrophages; this underlines the antifi-
brotic effect of this molecule and supports the central role of IL-6 [
81
–
87
]. B cell activation
is also common in SSc, and B cells increase a number of angiogenic factors [
81
–
87
]. B-cell
depletion suppresses pro-fibrotic macrophage differentiation and thereby inhibits fibrosis,
providing the rationale for anti-B-cell agents such as rituximab in SSC-ILD [
81
–
87
]. Among
the biomarkers mentioned above, autoantibodies and C-reactive proteins are the only
biomarkers typically used in routine clinical practice. Anti-Scl-70 antibodies are associated
with an increased incidence of progressive SSc ILD [
81
–
87
]. Additional autoantibodies
against anti-phosphatidylinositol-5-phosphate 4-kinase type 2 beta (PIP4K2B) and AKT
serine/threonine kinase 3 (AKT3) have been linked to increased pulmonary fibrosis in SSc
(114). However, various other biomarkers are under investigation for clinical use, including
KL-6 (Krebs von den Lungen-6), CCL18 (chemokine [C-C motif] ligand 18), MMP7 (ma-
trix metalloproteinase-7), MMP12 (matrix metalloproteinase-12), IL-6, CXCL4 (chemokine
ligand 4 [C-X-C motif]), CXCL3 (chemokine ligand 4 [C-X-C motif]), and chitinase-3-like
protein 1 (YKL-40) as recently reviewed [
81
–
87
]. The presence of MMP-12 has been shown
to be increased in SSc-ILD compared to SSc forms without ILD and correlates with the
degree of pulmonary fibrosis [
81
–
87
]. Sirtuins are NAD-dependent protein deacetylases
that regulate angiogenesis; SIRT1 and SIRT3 correlate with the degree of pulmonary fi-
brosis in SSc [
81
–
87
]. The chemokine CCL2 is increased in SSc and predicts the long-term
progression of SSc-ILD [
81
–
87
]. Jee et al. recently described a composite biomarker index
consisting of SP-D, Ca15-3 and ICAM-1 that identifies SSc-ILD [
84
–
90
]. Cold inducible
RNA binding protein (CIRP) has also been associated with SSc-ILD and may be responsible
for disease activity and response to therapy [81–87].
Histopathologically, SSc-ILD is characterized by an early pulmonary infiltration of
inflammatory cells into the lung parenchyma and can be classified into specific disease
patterns, including non-specific interstitial pneumonia (NSIP), habitual interstitial pneumo-
nia (UIP), organized pneumonia and lymphoid pneumonia [
83
–
90
]. Among the different
patterns of ILD, the most common pattern in SSc is NSIP (50-77% of SSc patients with ILD)
with bilateral involvement typically starting at the bases. The UIP pattern occurs more
rarely during SSc and is characterized by shorter survival than NSIP. SSc-ILD is detected
after diagnosis by high resolution CT (HR-CT) and progression by both HR-CT and pul-
monary function tests (PFT) (Figure 1) [
95
–
98
]. Studies have shown how quantitative CT
Curr. Issues Mol. Biol. 2023,45 7785
scanning can be used to detect early SSc-ILD and differentiate it from interstitial pneumonia
and to follow the progression of SSc-ILD more precisely [95–99].
Curr. Issues Mol. Biol. 2023, 3, FOR PEER REVIEW 11
(chemokine ligand 4 [C-X-C motif]), and chitinase-3-like protein 1 (YKL-40) as recently
reviewed [81–87]. The presence of MMP-12 has been shown to be increased in SSc-ILD
compared to SSc forms without ILD and correlates with the degree of pulmonary fibrosis
[81–87]. Sirtuins are NAD-dependent protein deacetylases that regulate angiogenesis;
SIRT1 and SIRT3 correlate with the degree of pulmonary fibrosis in SSc [81–87]. The
chemokine CCL2 is increased in SSc and predicts the long-term progression of SSc-ILD
[81–87]. Jee et al. recently described a composite biomarker index consisting of SP-D,
Ca15-3 and ICAM-1 that identifies SSc-ILD [84–90]. Cold inducible RNA binding protein
(CIRP) has also been associated with SSc-ILD and may be responsible for disease activity
and response to therapy [81–87].
Histopathologically, SSc-ILD is characterized by an early pulmonary infiltration of
inflammatory cells into the lung parenchyma and can be classified into specific disease
paerns, including non-specific interstitial pneumonia (NSIP), habitual interstitial
pneumonia (UIP), organized pneumonia and lymphoid pneumonia [83–90]. Among the
different paerns of ILD, the most common paern in SSc is NSIP (50-77% of SSc patients
with ILD) with bilateral involvement typically starting at the bases. The UIP paern occurs
more rarely during SSc and is characterized by shorter survival than NSIP. SSc-ILD is
detected after diagnosis by high resolution CT (HR-CT) and progression by both HR-CT
and pulmonary function tests (PFT) (Figure 1) [95–98]. Studies have shown how
quantitative CT scanning can be used to detect early SSc-ILD and differentiate it from
interstitial pneumonia and to follow the progression of SSc-ILD more precisely [95–99].
Figure 1. A 63-year-old female with the diagnosis of SSc. (A) Axial High-resolution CT scan shows
traction bronchiectasis (white arrows) in a back-ground of diffuse ground-glass opacities, related to
a fibrotic nonspecific pneumonia (NSIP) paer. (B) Using the mediastinal window seing the
dilatation of the main pulmonary artery (32 mm) can also be recognized as sign of pulmonary
hypertension, a common complication of the disease. Moreover a dilatation of the esophagus (*) can
be seen (operator E.B., Radiology Unit, University of Trieste, University Hospital of Cainara).
Recently lung ultrasound (LUS) in SSc patients highlighted the role of this technique
in the assessment of ILD. Given ultrasound radiation-free nature and the possibility to
perform this examination at bedside the use of this technique in ILD evaluation has
become increasingly popular in the last decades [95–99]. Through the identification of B-
lines, vertical hyperechogenic lines arising from pleural line, LUS may help to discover
signs of lung interstitial syndrome [97–99] (Figure 2).
Figure 1.
A 63-year-old female with the diagnosis of SSc. (
A
) Axial High-resolution CT scan shows
traction bronchiectasis (white arrows) in a back-ground of diffuse ground-glass opacities, related to a
fibrotic nonspecific pneumonia (NSIP) patter. (
B
) Using the mediastinal window setting the dilatation
of the main pulmonary artery (32 mm) can also be recognized as sign of pulmonary hypertension,
a common complication of the disease. Moreover a dilatation of the esophagus (*) can be seen
(operator E.B., Radiology Unit, University of Trieste, University Hospital of Cattinara).
Recently lung ultrasound (LUS) in SSc patients highlighted the role of this technique
in the assessment of ILD. Given ultrasound radiation-free nature and the possibility to
perform this examination at bedside the use of this technique in ILD evaluation has become
increasingly popular in the last decades [
95
–
99
]. Through the identification of B-lines,
vertical hyperechogenic lines arising from pleural line, LUS may help to discover signs of
lung interstitial syndrome [97–99] (Figure 2).
Curr. Issues Mol. Biol. 2023, 3, FOR PEER REVIEW 12
Figure 2. LUS in SSc. Advanced ILD (B-lines, yellow arrows) using a linear probes (7.5 MHz,
operator F.S., Pulmonology Unit, University of Trieste, University Hospital of Cainara).
Significant or progressive SSc-ILD usually requires therapy [6,88,89,95–98,100–108].
The PFT-based OMERACT (outcome measures in rheumatic diseases) detects progression
of SSc-ILD defined as a ≥10% decline in forced vital functions (FVC) or ≥5% to <10%
decline in FVC with a decline relative ≥15% DLCO [84,87,99–105]. Importantly, with
effective therapy for SSc-ILD, pulmonary fibrosis is stabilized or the rate of decline in lung
function is reduced [84,87,101–106]. Thus, emphasis has accumulated on early diagnosis
and timely therapy of SSc-ILD before significant irreversible lung damage occurs. The
drugs typically used to treat SSc-ILD are non-specific immunosuppressants
(cyclophosphamide, mycophenolate), more specific immunosuppressive drugs including
anti-IL-6 agents (tocilizumab) and anti-B-cell drugs (rituximab), and antifibrotics agents
(nintedanib—a tyrosine kinase inhibitor) [6,88,89,95–98,101–108]. The non-specific
immunosuppressants, mycophenolate, an inhibitor of guanosine nucleotide synthesis,
and cyclophosphamide, an alkylating agent, decrease the proliferation of fibroblasts, T
helper cells and B cells and thus have significant anti-fibrotic effects [6,88,89,95–98,100–
108]. Indeed, mycophenolate is currently considered the standard and baseline therapy
for SSc-ILD. Tocilizumab is increasingly used for SSc-ILD. In particular, the antifibrotic
effect associated with the action of Tocilizumab is linked to the inhibition of the IL-6
receptor, which determines the activation of myofibroblasts and the reduction of the M2
macrophage polarization [6,88,89,95–98,101–108]. In SSc-ILD, anti-B cell agents, such as
Rituximab, are used with the rationale that B cell depletion suppresses pro-fibrotic
macrophage differentiation and consequently inhibits fibrosis [6,88,89,95–98,100–108].
Nintedanib, a tyrosine kinase inhibitor, is an antifibrotic drug that inhibits PDGF, FGF
and vascular endothelial growth factor (VEGF) receptors, reducing fibrosis [6,88,89,95–
98,100–108]. However, among antifibrotics, pirfenidone appears to have less beneficial
effects in SSc, so it has no indication in the treatment of this condition [6,88,89,95–98,100–
108]. Among treatments, autologous hematopoietic stem cell transplantation (AHSCT) is
an alternative for rapidly progressive forms of SSc unresponsive to these agents or for
early SSc-ILD; on the other hand, lung transplantation is the alternative for end-stage lung
disease [6,88,89,95–98,100–108]. In conclusion, multiple arms of the immune system are
Figure 2.
LUS in SSc. Advanced ILD (B-lines, yellow arrows) using a linear probes (7.5 MHz,
operator F.S., Pulmonology Unit, University of Trieste, University Hospital of Cattinara).
Curr. Issues Mol. Biol. 2023,45 7786
Significant or progressive SSc-ILD usually requires therapy [
6
,
88
,
89
,
95
–
98
,
100
–
108
].
The PFT-based OMERACT (outcome measures in rheumatic diseases) detects progression
of SSc-ILD defined as a
≥
10% decline in forced vital functions (FVC) or
≥
5% to <10% de-
cline in FVC with a decline relative
≥
15% DLCO [
84
,
87
,
99
–
105
]. Importantly, with effective
therapy for SSc-ILD, pulmonary fibrosis is stabilized or the rate of decline in lung function
is reduced [
84
,
87
,
101
–
106
]. Thus, emphasis has accumulated on early diagnosis and timely
therapy of SSc-ILD before significant irreversible lung damage occurs. The drugs typically
used to treat SSc-ILD are non-specific immunosuppressants (cyclophosphamide, mycophe-
nolate), more specific immunosuppressive drugs including anti-IL-6 agents (tocilizumab)
and anti-B-cell drugs (rituximab), and antifibrotics agents (nintedanib—a tyrosine kinase
inhibitor) [
6
,
88
,
89
,
95
–
98
,
101
–
108
]. The non-specific immunosuppressants, mycophenolate,
an inhibitor of guanosine nucleotide synthesis, and cyclophosphamide, an alkylating agent,
decrease the proliferation of fibroblasts, T helper cells and B cells and thus have significant
anti-fibrotic effects [
6
,
88
,
89
,
95
–
98
,
100
–
108
]. Indeed, mycophenolate is currently consid-
ered the standard and baseline therapy for SSc-ILD. Tocilizumab is increasingly used for
SSc-ILD. In particular, the antifibrotic effect associated with the action of Tocilizumab is
linked to the inhibition of the IL-6 receptor, which determines the activation of myofi-
broblasts and the reduction of the M2 macrophage polarization [
6
,
88
,
89
,
95
–
98
,
101
–
108
].
In SSc-ILD, anti-B cell agents, such as Rituximab, are used with the rationale that B cell
depletion suppresses pro-fibrotic macrophage differentiation and consequently inhibits
fibrosis [
6
,
88
,
89
,
95
–
98
,
100
–
108
]. Nintedanib, a tyrosine kinase inhibitor, is an antifibrotic
drug that inhibits PDGF, FGF and vascular endothelial growth factor (VEGF) receptors,
reducing fibrosis [
6
,
88
,
89
,
95
–
98
,
100
–
108
]. However, among antifibrotics, pirfenidone ap-
pears to have less beneficial effects in SSc, so it has no indication in the treatment of this
condition [
6
,
88
,
89
,
95
–
98
,
100
–
108
]. Among treatments, autologous hematopoietic stem cell
transplantation (AHSCT) is an alternative for rapidly progressive forms of SSc unrespon-
sive to these agents or for early SSc-ILD; on the other hand, lung transplantation is the
alternative for end-stage lung disease [
6
,
88
,
89
,
95
–
98
,
100
–
108
]. In conclusion, multiple arms
of the immune system are activated in SSc-ILD providing many candidate biomarkers and
potential therapeutic targets.
5. Biomarkers in Systemic Sclerosis Vascular Injury, Focus on Pulmonary
Arterial Hypertension
The most important clinical manifestation of vascular disease in SSc is Raynaud’s phe-
nomenon (RP) and digital ischemia [
6
,
88
,
89
,
95
–
98
,
109
–
115
]. RP is a variable and complex
symptom; it represents a vasospastic condition and is characterized by an initial vasocon-
striction/occlusion of pre-capillary arterioles (pallor/white phase), followed by a cyanotic
phase (purple phase), and finally by post-ischemic hyperaemia (red phase). Cold exposure
and emotional stress are the main triggers of RP. It is often the presenting symptom of the
disease and consists of reversible and transient tissue ischemia, but in SSc it can be persistent
resulting in the formation of digital ulcers (DU) and/or gangrene [
6
,
88
,
89
,
95
–
98
,
109
–
115
].
Digital ulcers are characterized by significant pain and reduced quality of life with hand-
related disability [
6
,
88
,
89
,
95
–
98
,
110
–
116
]. In addition, DUs are burdened with fearsome
complications, such as infection and osteomyelitis.
Among instrumental examinations, NVC is a noninvasive technique to assess capillary
morphology and architecture (Figure 3). As described above, NVC is also included in
the 2013 ACR/EULAR classification criteria. Capillaroscopic abnormalities of SSc include
enlarged (giant) capillaries, microhemorrhages, and capillary leakage [
10
]. Note that
these changes can also be detected in other connective tissue diseases, although they
are more frequent in SSc. RP is followed by telangiectasias, ischemic DU, pitting scars,
periungual microvascular abnormalities, pulmonary arterial hypertension (PAH), and
cardiac disease affecting function and exercise tolerance [
6
,
88
,
89
,
95
–
98
,
110
–
116
]. All are
considered outcomes of vascular damage in SSc.
Curr. Issues Mol. Biol. 2023,45 7787
Curr. Issues Mol. Biol. 2023, 3, FOR PEER REVIEW 13
activated in SSc-ILD providing many candidate biomarkers and potential therapeutic
targets.
5. Biomarkers in Systemic Sclerosis Vascular Injury, Focus on Pulmonary Arterial
Hypertension
The most important clinical manifestation of vascular disease in SSc is Raynaud’s
phenomenon (RP) and digital ischemia [6,88,89,95–98,109–115]. RP is a variable and
complex symptom; it represents a vasospastic condition and is characterized by an initial
vasoconstriction/occlusion of pre-capillary arterioles (pallor/white phase), followed by a
cyanotic phase (purple phase), and finally by post-ischemic hyperaemia (red phase). Cold
exposure and emotional stress are the main triggers of RP. It is often the presenting
symptom of the disease and consists of reversible and transient tissue ischemia, but in SSc
it can be persistent resulting in the formation of digital ulcers (DU) and/or gangrene
[6,88,89,95–98,109–115]. Digital ulcers are characterized by significant pain and reduced
quality of life with hand-related disability [6,88,89,95–98,110–116]. In addition, DUs are
burdened with fearsome complications, such as infection and osteomyelitis.
Among instrumental examinations, NVC is a noninvasive technique to assess
capillary morphology and architecture (Figure 3). As described above, NVC is also
included in the 2013 ACR/EULAR classification criteria. Capillaroscopic abnormalities of
SSc include enlarged (giant) capillaries, microhemorrhages, and capillary leakage [10].
Note that these changes can also be detected in other connective tissue diseases, although
they are more frequent in SSc. RP is followed by telangiectasias, ischemic DU, piing
scars, periungual microvascular abnormalities, pulmonary arterial hypertension (PAH),
and cardiac disease affecting function and exercise tolerance [6,88,89,95–98,110–116]. All
are considered outcomes of vascular damage in SSc.
Figure 3. Nailfold capillaroscopy images (×200). Figure (A) shows the capillaroscopic findings in a
healthy subject with capillaries of normal number and shape, i.e., the so-called U-shaped and
hairpin-like morphology; (B–D) show the capillaroscopic changes in the scleroderma paern in the
early (B), active (C) and late (D) phases, respectively and associated with a progressive distortion of
the architecture of normal capillaries, which gradually deviate from the A paern. In particular in
Figure 3.
Nailfold capillaroscopy images (
×
200). Figure (
A
) shows the capillaroscopic findings in
a healthy subject with capillaries of normal number and shape, i.e., the so-called U-shaped and
hairpin-like morphology; (
B
–
D
) show the capillaroscopic changes in the scleroderma pattern in the
early (
B
), active (
C
) and late (
D
) phases, respectively and associated with a progressive distortion of
the architecture of normal capillaries, which gradually deviate from the A pattern. In particular in
figures (
B
,
D
), megacapillaries (defined as capillaries >50
µ
m) and an increase (
B
) and a subsequent
decrease (
C
) in capillary density, respectively, are observed. The later picture (
D
) is characterised by a
further accentuation of these anomalies, with a greater decrease in capillary density and an additional
number of giant capillaries. In (
B
), there are also areas of microhaemorrhages, observable in the early
phase but also present in the active phase (operators L.M. and B.R, Pulmonology Unit, University of
Trieste, University Hospital of Cattinara).
Pulmonary hypertension (PH) is hemodynamic condition, defined by a mean pul-
monary arterial pressure (mPAP) > 20 mmHg at rest. PAH (pulmonary arterial hyper-
tension) is characterized by a mean pulmonary arterial pressure (mPAP) greater than
20 mmHg
and pulmonary arterial wedge pressure (PAWP) less than 15 mmHg on right
heart catheterization (RHC) (Figure 4) with a PVR > 3 WU in the absence of significant inter-
stitial lung disease (ILD) [
116
–
119
]. PAH is due to vasculopathy of the small and medium
calibre pulmonary arteries (pulmonary arterial hypertension) which leads to vascular re-
modelling and to increase in pulmonary vascular resistance (PVR). PAH occurs in 7% to
19% of SSc patients depending on the population and duration of the disease [116–121].
Curr. Issues Mol. Biol. 2023,45 7788
Curr. Issues Mol. Biol. 2023, 3, FOR PEER REVIEW 14
Figures (B,D), megacapillaries (defined as capillaries >50 µm) and an increase (B) and a subsequent
decrease (C) in capillary density, respectively, are observed. The later picture (D) is characterised
by a further accentuation of these anomalies, with a greater decrease in capillary density and an
additional number of giant capillaries. In (B), there are also areas of microhaemorrhages, observable
in the early phase but also present in the active phase (operators L.M. and B.R, Pulmonology Unit,
University of Trieste, University Hospital of Cainara).
Pulmonary hypertension (PH) is hemodynamic condition, defined by a mean
pulmonary arterial pressure (mPAP) > 20 mmHg at rest. PAH (pulmonary arterial
hypertension) is characterized by a mean pulmonary arterial pressure (mPAP) greater
than 20 mmHg and pulmonary arterial wedge pressure (PAWP) less than 15 mmHg on
right heart catheterization (RHC) (Figure 4) with a PVR > 3 WU in the absence of
significant interstitial lung disease (ILD) [116–119]. PAH is due to vasculopathy of the
small and medium calibre pulmonary arteries (pulmonary arterial hypertension) which
leads to vascular remodelling and to increase in pulmonary vascular resistance (PVR).
PAH occurs in 7% to 19% of SSc patients depending on the population and duration of the
disease [116–121].
Figure 4. Graph obtained from a right heart catheterisation procedure performed at our centre in a
68-year-old patient with Systemic Sclerosis with pulmonary involvement and interstitial disease.
Pulmonary hypertension is in fact one of the complications of pulmonary involvement by systemic
sclerosis and affects about 12% of patients with this rheumatological disease. This graph shows on
the y-axis respectively the ECG monitoring (derivation VII) which is performed throughout the
procedure (a), in the picture (b) it is also possible to observe the measurement of the pulmonary
arterial pressure (PAP) and the end-expiratory pulmonary artery wedge pressure (PAWP) in the
picture (c), (operator P.G., Pulmonology Unit, University of Trieste, University Hospital of
Cainara).
Figure 4.
Graph obtained from a right heart catheterisation procedure performed at our centre in
a 68-year-old patient with Systemic Sclerosis with pulmonary involvement and interstitial disease.
Pulmonary hypertension is in fact one of the complications of pulmonary involvement by systemic
sclerosis and affects about 12% of patients with this rheumatological disease. This graph shows
on the y-axis respectively the ECG monitoring (derivation VII) which is performed throughout the
procedure (a), in the picture (b) it is also possible to observe the measurement of the pulmonary
arterial pressure (PAP) and the end-expiratory pulmonary artery wedge pressure (PAWP) in the
picture (c), (operator P.G., Pulmonology Unit, University of Trieste, University Hospital of Cattinara).
The diagnosis of PAH is often made at a late stage, as in the early stages’ patients
may be asymptomatic or complain of nonspecific symptoms. Therefore, patients with
SSc should be screened for PAH, even if asymptomatic, by cardiac echocolordoppler,
respiratory testing, and NT-ProBNP assay. Diagnostic algorithms have been proposed to
identify patients for RHC, which is still the gold standard tool for diagnosing PAH and
PH [
116
–
126
]. Risk factors for PAH include severe Raynaud’s phenomenon, severe digital
ischemia, cutaneous telangiectasias, chronic disease, late onset of the disease, advanced age,
postmenopausal status, reduced diffusing capacity (DLCO < 50%), DLCO/alveolar volume
less than 70%, forced vital capacity/DLCO less than 1.6, and increased right ventricular
systolic pressure greater than 2 mmHg/year [110–119].
Screening should include specific autoantibodies (anti-topoisomerase I (SCL-70), an-ti-
centromere and anti-RNA polymerase III and antiphospholipid antibodies), pulmonary
function tests, echocardiography, pro-terminal brain natriuretic peptide (NT-proBNP), cap-
illaroscopy of nail folds and initial high-resolution CT scan to rule out ILD, and, in case of
PAH, right heart catheterization to determine PA pressure [
118
–
126
,
151
]. Many molecules
have been associated with vascular complications of SSc, so there are many potential
biomarkers for vascular disease and PAH in SSc. Activation, endothelial cell apoptosis,
Curr. Issues Mol. Biol. 2023,45 7789
specific autoantibodies, infectious agents, reactive oxygen species, and other causes that pro-
vide many potential biomarkers may contribute to vascular lesion
formation [121–126,151]
.
Once activated, endothelial cells secrete endothelin-1 (ET-1), von Willebrand factor (vWF),
nitric oxide, and endothelial nitric oxide synthase, resulting in unstable vascular tone,
with decreased vasodilation and increased vasoconstriction causing ischemia and tissue
hypoxia [119–124]
. Endothelin-1 stimulates fibroblasts to convert to activated myofibrob-
lasts with increased ECM secretion, intimal hyperplasia, luminal narrowing, reduced
capillary blood flow vessel obliteration and ischemia [120–126,151].
Local secretion of the von Willebrand factor causes platelet aggregation, hypercoagula-
bility, and fibrin deposition leading to terminal vascular injury [
126
–
133
,
151
]. The endothelial-
mesenchymal transition also favors the formation of
myofibroblasts [128–133,152,153]
. The
activated endothelium also expresses an increase in adhesion molecules and specific
chemokines, recruiting immune cells and perivascular infiltrates leading to further in-
flammation and fibrosis [
128
–
133
,
152
,
153
]. Specifically, the imbalance of cytokines, in-
cluding endothelial growth factor (VEGF), matrix metalloproteinase (MMP)-9, endoglin,
endothelin-1 (ET-1), and the angiostatic pentraxin 3 (PTX3), MMP-12, endostatin, angio-
statin and semaphorin3E (Sema3E) cause dysfunction in angiogenesis and an alteration
in endothelial progenitor cell (EPC) recruitment [
116
–
119
]. Endothelin-1 is secreted by
endothelial cells and activated smooth muscle cells, fibroblasts, epithelial cells, and inflam-
matory cells [
128
–
133
,
152
,
153
]. An increase in ET-1 is present in SSc-PAH compared to SSc
patients without PAH and healthy controls [
116
–
119
]. It was demonstrated that ET-1 levels
were reduced by bosentan treatment in SSc patients with PAH to the levels present in SSc
patients without PAH, indicating that this biomarker could be an indicator of the severity
of vascular damage and response to treatment. bosentan therapy [
154
–
156
]. Pentraxin 3
is a receptor produced by activated endothelial cells, macrophages, smooth muscle cells,
dendritic cells, and fibroblasts [
116
–
119
,
138
,
154
,
157
–
183
]. However, pentraxin 3 levels have
only variable associations with vasculopathy in SSc [
116
–
119
]. Endostatin is an angiostatic
peptide that blocks VEGF activity and has been associated with PAH, scleroderma renal
crisis, and cardiac involvement [
116
–
119
]. Angiostatin antagonizes several growth fac-
tors, including VEGF, and is elevated in patients with more advanced vascular disease
in SSc [
116
–
119
]. Matrix metalloproteinases destroy the ECM and MMP-9 levels were de-
creased in SSc-PAH and increased with bosentin therapy, while MMP-12 was increased in
patients with DU and NVC changes [
116
–
119
]. TGF-
β
remains important for all manifesta-
tions of SSc including PAH [
116
–
119
]. Endoglin (CD105) is an accessory receptor for TGF-
β
and higher circulating endoglin is related suggesting that this was a biomarker for vascular
damage in SSc [
116
–
119
]. Thrombomodulin (TM), CD163, and NT-proBNP are elevated in
SSc-PAH [
116
–
119
]. High levels of maresin 1 are associated with the development of DU in
SSc [
116
–
119
]. Elevated asymmetric dimethylarginine (ADMA) is an endogenous inhibitor
of nitric oxide (NO) that affects endothelial function and is elevated in microvascular disease
in SSc [
116
–
119
]. Hypochromic erythrocytes have been closely associated with the progno-
sis of SSC-PAH [
116
–
119
]. Hemoglobin and ferritin are significantly lower in patients with
pulmonary hypertension (PH) in SSc than in those with pulmonary hypertension, while
uric acid and NT-proBNP are significantly
higher [116–119]
. CCL21 circulating in SSc is a
biomarker associated with PAH and the development of PAH [
128
–
133
,
152
,
153
]. SSc-PAH
is associated with elevated metalloproteinase inhibitors, including TIMP-4 levels, indicating
a cardiopulmonary vasculature-specific role of TIMP-4 activation in
SSc [116–119]
. Neu-
ropilins (NRP1-2) are non-tyrosine kinase glycoprotein receptors expressed on endothelial
cells and are potential predictive biomarkers of PAH, nail fold capillary abnormalities,
and DU [
116
–
119
]. Sirtuins (SIRT1-7) NAD-dependent protein deacetylases that regulate
angiogenesis; SIRT1 and SIRT3 are decreased in SSc and microvascular disease, and SIRT3
is specifically related to the presence of DU [
116
–
119
]. Slit glycoproteins (Slit1-3) are im-
plicated in angiogenesis and are increased in SSc and patients with microvascular disease
(150). Carcinoembryonic antigen-related cell adhesion molecule (CEA-CAM)-positive
monocytes are associated with inflammation and ILD in SSc patients [
116
–
119
]. Circulating
Curr. Issues Mol. Biol. 2023,45 7790
levels of IL-18 are higher and SSc correlates positively with PAH [
116
–
119
]. Similarly, IL33
and soluble carcinogenicity suppression 2 (ST2), are increased in SSc, especially with DU
and PAH [
128
–
133
,
152
,
153
]. IL-32 and macrophage migration inhibitory factor (MIF) are
elevated in SSc patients with PAH [
116
–
119
]. The chemokines CCL20, CCL21, and CCL23
are also elevated in SSc-PAH [
116
–
119
]. Recently elevated CXCL4 levels and decreased
CXCL5 levels have also been associated with SSc-DU [
116
–
119
]. Similarly, the chemokines
CXCL16 and GDF15 are elevated in SSc-PAH [
116
–
119
]. CX3CL1 (fractalkin) is elevated in
SSc with DU (68). Resistin is increased in SSc with DU and in SSc-PAH [
116
–
119
]. Galectin-3
was also higher in SSc patients with DU [
116
–
119
]. Adipsin, visfatin, interferon-gamma
and type 1 interferons are increased in SSc-PAH [
116
–
119
]. Aptamic proteomics of serum
exosomes define patterns that could distinguish primary Raynaud’s disease from early SSc
and, with RNA networks, are potential biomarkers for vascular disease in SSc [116–119].
Treatment of PAH involves a stepwise approach using single agents or combina-
tion therapy with phosphodiesterase type 5 (PDE-5) inhibitors (including sildenafil and
tadalafil), soluble guanylate cyclase (sGC) stimulators (including riociguat), endothelial re-
ceptor antagonists (including bosentan ambrisentan, and macitentan), prostacyclin analogs
(epoprostenol, treprostinil, and iloprost), or selective prostacyclin IP receptor agonists
(selexipag), supported by anticoagulants, diuretics, digoxin, and calcium channel blockers
where appropriate [116–118,154–156].
6. Biomarkers in Systemic Sclerosis Skin Involvement
As previously reported, among the hallmarks of SSc, skin involvement is one of the
pivotal symptoms and is used to classify SSc patients in routine clinical practice into three
different subgroups, limited skin involvement (lcSSc), diffuse skin involvement (dcSSc),
and limited SSc (lSSc) [
1
–
5
]. Although in different sizes and except for patients with SSc
sine Scleroderma (ssSSc), the skin is always involved in SSc. SsSSc is a very rare subgroup
characterized by the complete or partial absence of skin involvement but with the presence
of internal organ involvement and typical serologic abnormalities.
The modified Rodnan skin score (mRss) is the validated method to assess the severity
of skin involvement in SSc and to distinguish, as mentioned above, patients with lcSSc
from those with dcSSc or with lSSc [1–9].
The mRss is a sum of ratings obtained from clinical palpation of 17 skin areas (cheek-
bone, fingers, back of hands, forearms, arms, chest, abdomen, thighs, legs, and feet) [
11
–
13
].
Skin thickness is assessed by palpation and scored on a scale ranging from 0 (normal),
1 (weak), 2 (intermediate) to 3 (severe skin thickening).
The mRss has some disadvantages, for example, it cannot detect small but clinically
relevant changes in skin thickness over time. Recently, several studies have reported
the usefulness of high-frequency skin ultrasound (US) for early identification of skin
involvement in patients with SSc [
6
–
9
]. Most of the authors used a US equipped with a
probe at a frequency of 10–30 MHz, as high frequencies are needed to study skin thickness to
achieve good resolution, even if penetration is poor. This allows good visualization that can
distinguish the epidermis, dermis, and subcutaneous fat, providing a thickness determination
and qualitative assessment of the skin; the authors made a comparison with mRss, the current
gold standard for the study of skin compromise in patients with SSc [17] (Figure 5).
Curr. Issues Mol. Biol. 2023, 3, FOR PEER REVIEW 17
[11–13]. Skin thickness is assessed by palpation and scored on a scale ranging from 0
(normal), 1 (weak), 2 (intermediate) to 3 (severe skin thickening).
The mRss has some disadvantages, for example, it cannot detect small but clinically
relevant changes in skin thickness over time. Recently, several studies have reported the
usefulness of high-frequency skin ultrasound (US) for early identification of skin
involvement in patients with SSc [6–9]. Most of the authors used a US equipped with a
probe at a frequency of 10–30 MHz, as high frequencies are needed to study skin thickness
to achieve good resolution, even if penetration is poor. This allows good visualization that
can distinguish the epidermis, dermis, and subcutaneous fat, providing a thickness
determination and qualitative assessment of the skin; the authors made a comparison with
mRss, the current gold standard for the study of skin compromise in patients with SSc
[17] (Figure 5).
Figure 5. Example of measurement of dermal thickness (yellow arrows) by skin high-frequency US
(18 MHz probe) in a healthy subject (A) and in an SSc patient (B) at the level of arm (operator L.R,
Pulmonology Unit, University of Trieste, University Hospital of Cainara).
Skin involvement in SSc patients has a great impact on patients’ quality of life as it
can cause pruritus, depigmentation, edema, traction ulcers, and movement difficulties;
however, it is not associated with increased mortality. Skin involvement is initially due to
edema caused by microvascular lesions and inflammation, subsequently to increased
collagen deposition. For these reasons, the skin thickens and it is impossible to pinch it in
a normal skin fold. In SSc patients, skin biopsies reveal increased thickness of the dermis
and increased amount of collagen deposition, and the disease usually begins with finger
involvement in a centripetal paern. Skin thickening is universal in SSc and generally
required for a definitive diagnosis with some exceptions [116–119]. There are many
candidate biomarkers for skin disease in SSc. In skin biopsies, the expression levels of
TGF-β1, TGF-βR1 and TGF-βR2 are higher in SSc patients than in healthy subjects [134–
140]. Cutaneous gene expression of macrophage-associated biomarkers (CD14, IL-13RA1)
and TGF-β-associated biomarkers (OSMR SERPINE1, CTGF) is associated with cutaneous
disease progression in SSc [134–140]. Marginal zone protein B1 (MZB1) appears to be a
good biomarker for cutaneous fibrosis [116–119]. Circulating levels of periostin are
elevated in SSc with extensive cutaneous fibrosis [116–119]. Sirtuins are NAD-dependent
protein deacetylases that regulate angiogenesis; SIRT1 and SIRT3 correlate with the
degree of cutaneous fibrosis of the SSc [116–119]. Adiponectin is reduced in skin affected
by SSc [134–140]. The fibrillar collagen molecule COL4A1, the matricellular protein
COMP, the gene encoding spondin-SPON1, and TNC, another ECM protein, have
recently been upregulated in the skin of SSc individuals, and all these molecules
completely distinguish the normal-skinned SSc [116–119]. Other investigators found that
the upregulated genes IL-13RA1, OSMR and SERPINE 1 were the most predictive of
progressive skin disease [134–140].
Skin thickness in SSc often spontaneously improves over time, confounding many
interventional studies, as recently reported with belimumab and nintedanib [184–192].
However, mycophenolate, cyclophosphamide, and methotrexate have been shown to
improve the mRss and reduce skin thickness in SSc [184–192]. Methotrexate has always
been problematic in SSc as it can occasionally cause lung inflammation that can be
confused with SSc-ILD [184–192]. Recently, tofacitinib, although not approved for SSc, has
been shown to be more effective than methotrexate in reducing the mRss, ultrasound skin
Figure 5.
Example of measurement of dermal thickness (yellow arrows) by skin high-frequency US
(18 MHz probe) in a healthy subject (
A
) and in an SSc patient (
B
) at the level of arm (operator L.R,
Pulmonology Unit, University of Trieste, University Hospital of Cattinara).
Curr. Issues Mol. Biol. 2023,45 7791
Skin involvement in SSc patients has a great impact on patients’ quality of life as it can
cause pruritus, depigmentation, edema, traction ulcers, and movement difficulties; how-
ever, it is not associated with increased mortality. Skin involvement is initially due to edema
caused by microvascular lesions and inflammation, subsequently to increased collagen de-
position. For these reasons, the skin thickens and it is impossible to pinch it in a normal skin
fold. In SSc patients, skin biopsies reveal increased thickness of the dermis and increased
amount of collagen deposition, and the disease usually begins with finger involvement
in a centripetal pattern. Skin thickening is universal in SSc and generally required for a
definitive diagnosis with some exceptions [
116
–
119
]. There are many candidate biomarkers
for skin disease in SSc. In skin biopsies, the expression levels of TGF-
β
1, TGF-
β
R1 and
TGF-
β
R2 are higher in SSc patients than in healthy
subjects [134–140]
. Cutaneous gene
expression of macrophage-associated biomarkers (CD14, IL-13RA1) and TGF-
β
-associated
biomarkers (OSMR SERPINE1, CTGF) is associated with cutaneous disease progression
in SSc [
134
–
140
]. Marginal zone protein B1 (MZB1) appears to be a good biomarker for
cutaneous fibrosis [
116
–
119
]. Circulating levels of periostin are elevated in SSc with ex-
tensive cutaneous fibrosis [
116
–
119
]. Sirtuins are NAD-dependent protein deacetylases
that regulate angiogenesis; SIRT1 and SIRT3 correlate with the degree of cutaneous fibro-
sis of the SSc [
116
–
119
]. Adiponectin is reduced in skin affected by SSc [
134
–
140
]. The
fibrillar collagen molecule COL4A1, the matricellular protein COMP, the gene encoding
spondin-SPON1, and TNC, another ECM protein, have recently been upregulated in the
skin of SSc individuals, and all these molecules completely distinguish the normal-skinned
SSc [
116
–
119
]. Other investigators found that the upregulated genes IL-13RA1, OSMR and
SERPINE 1 were the most predictive of progressive skin disease [134–140].
Skin thickness in SSc often spontaneously improves over time, confounding many
interventional studies, as recently reported with belimumab and nintedanib [
184
–
192
].
However, mycophenolate, cyclophosphamide, and methotrexate have been shown to im-
prove the mRss and reduce skin thickness in SSc [
184
–
192
]. Methotrexate has always been
problematic in SSc as it can occasionally cause lung inflammation that can be confused with
SSc-ILD [
184
–
192
]. Recently, tofacitinib, although not approved for SSc, has been shown
to be more effective than methotrexate in reducing the mRss, ultrasound skin thickness,
and musculoskeletal symptoms, and in reducing the biomarker genes regulated by the
interferon in SSc [
184
–
192
]. Ziritaxestat is a selective inhibitor of small autotaxin and re-
duced mRss in SSc, and thus is a promising new agent currently in clinical
trials [184–192]
.
Recently, Fukasawa and colleagues realized the first single-center trial that assessed the
pharmacokinetics, safety and efficacy of brodalumab, in Japanese patients with SSc. Bro-
dalumab is a fully human anti-IL-17 receptor A monoclonal antibody. Interestingly, all
study patients presented a significant decrease in mRSS, with a reduction in dermal thick-
ness. The authors speculated that, as IL-17 promotes fibroblast proliferation and collagen
production, brodalumab might decrease dermal thickness and mRSS by directly inhibiting
IL-17 action on fibroblasts [
185
]. In conclusions, several studies demonstrated that SSc is
a Th17-dominant disease in Treg/ Th17 balance and the inhibition of the indirect effects
of IL-17 on T and B cell subsets correlated by brodalumab may ameliorate fibrotic skin
lesions [184–191,193,194].
7. Biomarkers in the Gastrointestinal Systemic Sclerosis Impairment
Gastrointestinal (GI) involvement can be found in approximately 80% of SSc patients
(in both the lcSS subgroup and the dcSSc subgroup) and represents a severe manifestation
of the disease. All tracts of the gastrointestinal system can be affected, from micros-
tomia to gastroesophageal reflux and gastrointestinal dysmotility to intestinal pseudo-
obstruction and fecal incontinence [
43
,
195
–
198
]. Gastrointestinal involvement may be
present from the early stage of the disease and may be asymptomatic making its diag-
nosis
difficult [43,195–198]
. Gastrointestinal system involvement in SSc is profound and
includes intestinal and esophageal dysmotility and fibrosis, intestinal ischemia, primary
sclerosing cholangitis, primary biliary cirrhosis, bacterial overgrowth, increase in intesti-
Curr. Issues Mol. Biol. 2023,45 7792
nal malignancies, and intestinal inflammation, among other complications [
43
,
195
–
198
].
Approximately 50% of SSc patients complain of symptoms due to gastric involvement
with early satiety, postprandial fullness, bloating, nausea, and epigastric pain. Another
complication is represented by the so-called “watermelon stomach” due to microvascular
ectasias in the stomach which lead to microhemorrhages and chronic anemia. Patients with
SSc may also present with intestinal malabsorption due to mucosal surface reduction and
bacterial overgrowth, and small bowel involvement may also manifest as intestinal pseudo-
obstruction [
43
,
195
–
198
]. Furthermore, fecal incontinence is frequent among SSc patients.
Treatment of gastrointestinal complications typically focuses on individual problems of
gastroesophageal reflux (proton pump inhibitors, H2-blockers, sucralfate), stenosis (dilata-
tion), dysmotility, and bacterial overgrowth (erythromycin, azithromycin, metoclopramide,
domperidone, cisapride) [
43
,
195
–
198
]. In the line of biomarkers, there are elevated fecal
levels of the inflammatory biomarker calprotectin in SSc, suggesting that fecal calprotectin
could be an effective biomarker for intestinal disease [43,195–198].
8. Biomarkers in Systemic Sclerosis Renal Disease
Scleroderma renal crisis (CRS) is the most frequent renal complication in SSc repre-
senting a medical emergency [
19
,
141
–
150
]. The use of ACE inhibitors has reduced the
occurrence of CRS. CRS is characterized by malignant hypertension, microangiopathic
haemolysis, microthrombosis, thrombocytopenia, vasospasm, and progressive renal failure
which can be caused by a variety of causes, such as various drugs (e.g., corticosteroids,
cyclosporine, and tacrolimus) [
19
,
141
–
150
]. Pathologically, CRS is characterized by rather
bland or subtle findings but may show the typical “onion bulb” findings, hyperplasia of the
juxtaglomerular apparatus, membranous proliferation, renovascular endothelial damage,
intimal proliferation, thrombotic angiopathy, microthrombi of fibrin, hemolysis, vasospasm,
vascular occlusion, ischemia, necrosis, vascular remodeling and possibly fibrosis associated
with hyperreninemia and accelerated hypertension [
19
,
141
–
150
]. Anti-fibrillarin antibodies,
anti-RNA polymerase III antibodies, and speckled pattern ANA have been closely asso-
ciated with the development of SRD; however, anti-topoisomerase antibodies have also
been associated with a high incidence of CRS in some populations [
19
,
141
–
150
]. Antiphos-
pholipid antibodies, especially IgG antiphospholipid antibodies, represent a significant
risk factor for renal disease in SSc compared with antibody-negative patients [
19
,
141
–
150
].
Autoantibodies against methionine sulfoxide reductase A, an enzyme important in antioxi-
dant pathways, have been associated with the development of renal and cardiac disease in
SSc [19,141–150].
Biomarkers of CRS include hypertension, elevated uric acid, decreased renal function,
thrombocytopenia, hemolytic anemia, and elevated levels of serum soluble CD147 and
CD163, renin, mannose-binding lectin, endothelin-1, soluble vascular adhesion molecules,
E- selectin, lipocalin-2, angiogenin, apelin, chemerin, complement components and NT-
proBNP levels [
116
–
119
,
199
]. High amounts of serum uric acid, a purine metabolite, may be
associated with inflammation, endothelial dysfunction, and renal dysfunction [
19
,
141
–
150
].
Giant et al. demonstrated in SSc that uric acid is significantly associated with serum creati-
nine, renal artery resistivity, and decreased glomeruli filtration rate in SSc patients [
141
,
142
].
Elevated serum soluble CD147 (sCD147), an inhibitor of extracellular matrix metallopro-
teinase, and CD163 (sCD163), a cysteine-rich scavenger receptor, have been demonstrated
in patients with CRS [
19
,
141
–
150
]. Similarly, increased endothelin-1 levels and endothe-
lin receptor transport have been associated with CSR [
19
,
141
–
150
]. Furthermore, soluble
vascular adhesion molecules (VCAM-1) and soluble E-selectin have been associated with
SRC [
19
,
141
–
150
]. NT-proBNP is a useful biomarker for CRS and predicts dialysis needs and
renal outcomes [
116
–
119
]. CXCL10 is an IFN-inducible chemokine and a potent chemoat-
tractant for Th1 cells and is found to be elevated in CRS patients [
19
,
141
–
150
]. IL-17B is
specifically increased in SSc with renal abnormalities compared to those without [
116
–
119
].
Treatment of CRS focuses on early diagnosis of CRS, prompt use of angiotensin-converting
Curr. Issues Mol. Biol. 2023,45 7793
enzyme inhibitors, dialysis, and other supportive measures in anticipation of recovery of
renal function [19,141–150].
9. Conclusions
The field of biomarkers in SSc continues to expand in scope and complexity. The sheer
number of molecules, pathways, and receptors involved in the pathology of SSc reflect
the many complexities of the disease. Several biomarkers are intimately involved in both
the pathogenesis and characteristics of the disorder. A biomarker, as broadly defined by
the National Institutes of Health Working Group on Biomarkers, is a measure that can be
applied for purposes as varied as disease diagnosis, staging, prognostication, measuring or
predicting treatment response, and even defining surrogate outcomes [
199
]. Biomarkers are
likely to be of increasing importance for early diagnosis, assessment of disease course and
activity monitoring, as well as therapeutic responses, in SSc patients. Furthermore, the intro-
duction of genomics, proteomics, and metabolomics is deepening our understand-ing of the
pathophysiology and architecture of SSc. With these developments, a breadth of candidate
biomarkers are being studied but the challenge lies in finding readily measurable biomarker
which offer specific diagnostic and prognostic value above that of the actually imaging and
functional techniques. The numerous environmental triggers and epigenetic mechanisms
involved in the pathogenesis of SSc make finding a single biomarker which can accurately
represent SSc a further challenge. Biomarkers in scleroderma are being developed to inform
overall prognosis, predict treatment response, and quantify outcomes which had been
previously defined only clinically. Individual biomarkers such as CXCL4, adiponectin, and
CCL18 are demonstrating prognostic utility for fibrotic and vascular complications to an
extent they may be clinically useful. Furthermore, N-terminal-pro-BNP and BNP have
a well-described association with PAH and systolic pulmonary arterial pressure in SSc,
thought to reflect the increasing stress on the right ventricle with increasing pulmonary
pressures, and subsequent studies have demonstrated a prospective utility of pro-BNP
levels for later development of PAH. Overexpression of type I IFN, TGF-
β
, PPAR-
γ
, PI3K-
Akt, as well as serum levels of adiponectin, MMP-9, MMP-12, LOX, ADAM12, THBS1,
COMP could be used as potential biomarkers of SSc-related skin
fibrosis [40–47,76–87]
.
Moreover, recent studies stressed importance of genetic pathway dependent on TGF-
β
and
serum levels of IL-6, KL-6, SP-D, and CCL18 as prominent biomarkers for assessing the
severity of fibrosis in SSc-related ILD. In the line of biomarkers, there are elevated fecal
levels of the inflammatory biomarker calprotectin in SSc, suggesting that fecal calprotectin
could be an effective biomarker for intestinal disease. The most important biomarkers of
scleroderma renal crisis include increased levels of serum soluble CD147 and CD163, renin,
mannose-binding lectin, endothelin-1, soluble vascular adhesion molecules, E- selectin, lipocalin-
2, angiogenin, apelin, chemerin, complement components and NT-proBNP levels. However,
with the exception of autoantibodies, today there are no routinely measured biomarkers in
SSc and reliable validation of the many potential biomarkers is lacking [
40
–
47
,
76
–
87
,
102
–
110
].
Several studies shown that specific autoantibodies are important serologic markers for
determination subclasses and clinical features of SSc. ANA might not only represent
biomarkers of disease but also play a pathogenic role through immune-mediated mecha-
nisms and molecular mimicry. Moreover, the presence of ANA, NVC abnormalities and
recurrent Raynaud’s phenomenon are predictive factors for progression to definitive SSc.
In particular, anti-topoisomerase I antibodies are predictive, in the first 3 years of disease of
the development of diffused skin involvement and digital ulcers (DU), as well as severe
interstitial lung disease (ILD) [
65
–
74
,
76
–
87
,
119
–
127
]. The anti-centromere autoantibodies
(ACA) are associated with PAH and anti-topoisomerase I autoantibodies with ILD. Finally,
anti-RNA polymerase III autoantibodies may be biomarkers for rapid progression of skin
thickening, gastric antral vascular ectasia, SSc-associated tumors and scleroderma renal
crisis. In summary, identifying biomarkers, which can offer diagnostic and prognostic
certainty, may help SSc patients to receive preventative treatment as part of a personalised
medicine approach. Finally, large randomised controlled trials, which have facilitated new
Curr. Issues Mol. Biol. 2023,45 7794
licensed treatments in SSc, have also offered valuable insight into the response of candidate
biomarkers but further large scale studies focussing on biomarkers are needed to validate
these in order to incorporate them into routine disease stratification.
Author Contributions: Conceptualization, G.D.M., P.C., L.M., F.S. and B.R.; methodology, F.S., M.C.
and M.K.; investigation, L.T., L.R., P.G., E.B., L.M. and B.R.; writing—original draft preparation,
G.D.M. and B.R.; writing—review and editing, S.L.; supervision, M.H., M.B. and M.G. All authors
have read and agreed to the published version of the manuscript.
Funding:
The authors received no financial support for the research, authorship, and/or publication
of this article.
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement:
All the data are available upon reasonable request to the corresponding
author.
Acknowledgments:
The authors thank Chiesi S.P.A. for the support with the capillaroscopy images
acquisition and reproduction. We would also like to thank Dr Lombardi Adriano (from the University
of NiccolòCusano) for the support with the graphic acquisition and reproduction.
Conflicts of Interest: The authors declare no conflict of interest.
References
1.
Varjú, C.; Pauling, J.D.; Saketkoo, L.A. Multi-Organ System Screening, Care, and Patient Support in Systemic Sclerosis. Rheum.
Dis. Clin. 2023,49, 211–248. [CrossRef] [PubMed]
2. Denton, C.P.; Khanna, D. Systemic sclerosis. Lancet 2017,390, 1685–1699. [CrossRef]
3.
Jaeger, V.K.; Tikly, M.; Xu, D.; Siegert, E.; Hachulla, E.; Airò, P.; Valentini, G.; Matucci Cerinic, M.; Distler, O.; Cozzi, F.; et al. Racial
differences in systemic sclerosis disease presentation: A European Scleroderma Trials and Research group study. Rheumatology
2020,59, 1684–1694. [CrossRef]
4.
Smith, V.; Scirè, C.A.; Talarico, R.; Airo, P.; Alexander, T.; Allanore, Y.; Bruni, C.; Codullo, V.; Dalm, V.; De Vries-Bouwstra, J.; et al.
Systemic sclerosis: State of the art on clinical practice guidelines. RMD Open 2018,4(Suppl. 1), e000782. [CrossRef] [PubMed]
5. Gusev, E.; Zhuravleva, Y. Inflammation: A New Look at an Old Problem. Int. J. Mol. Sci. 2022,23, 4596. [CrossRef] [PubMed]
6.
Santiago, T.; Santos, E.; Ruaro, B.; Lepri, G.; Green, L.; Wildt, M.; Watanabe, S.; Lescoat, A.; Hesselstrand, R.; Galdo, F.D.; et al.
Ultrasound and elastography in the assessment of skin involvement in systemic sclerosis: A systematic literature review focusing
on validation and standardization—WSF Skin Ultrasound Group. Semin. Arthritis Rheum. 2022,52, 151954. [CrossRef]
7.
Cutolo, M.; Damjanov, N.; Ruaro, B.; Zekovic, A.; Smith, V. Imaging of connective tissue diseases: Beyond visceral organ imaging?
Best Pract. Res. Clin. Rheumatol. 2016,30, 670–687. [CrossRef] [PubMed]
8.
Rodnan, G.P.; Lipinski, E.; Luksick, J. Skin thickness and collagen content in progressive systemic sclerosis and localized
scleroderma. Arthritis Rheum. 1979,22, 130e40. [CrossRef]
9.
Santiago, T.; Santiago, M.; Ruaro, B.; Salvador, M.J.; Cutolo, M.; da Silva, J.A.P. Ultrasonography for the Assessment of Skin in
Systemic Sclerosis: A Systematic Review. Arthritis Care Res. 2019,71, 563–574. [CrossRef]
10.
Van Den Hoogen, F.; Khanna, D.; Fransen, J.; Johnson, S.R.; Baron, M.; Tyndall, A.; Pope, J.E.2013 classification criteria for systemic
sclerosis: An American College of Rheumatology/European League against Rheumatism collaborative initiative. Arthritis Rheum.
2013,65, 2737–2747. [CrossRef]
11.
Wu, Y.-D.; Sheu, R.-K.; Chung, C.-W.; Wu, Y.-C.; Ou, C.-C.; Hsiao, C.-W.; Chang, H.-C.; Huang, Y.-C.; Chen, Y.-M.; Lo, W.-T.; et al.
Application of Supervised Machine Learning to Recognize Competent Level and Mixed Antinuclear Antibody Patterns Based on
ICAP International Consensus. Diagnostics 2021,11, 642. [CrossRef] [PubMed]
12.
Michalska-Jakubus, M.; Cutolo, M.; Smith, V.; Krasowska, D. Imbalanced serum levels of Ang1, Ang2 and VEGF in systemic
sclerosis: Integrated effects on microvascular reactivity. Microvasc. Res. 2019,125, 103881. [CrossRef]
13.
Benyamine, A.; Bertin, D.; Resseguier, N.; Heim, X.; Bermudez, J.; Launay, D.; Dubucquoi, S.; Hij, A.; Farge, D.; Lescoat, A.; et al.
Quantification of Antifibrillarin (anti-U3 RNP) Antibodies: A New Insight for Patients with Systemic Sclerosis. Diagnostics
2021
,
11, 1064. [CrossRef]
14.
Bellando-Randone, S.; Matucci-Cerinic, M. Very Early Systemic Sclerosis and Pre-systemic Sclerosis: Definition, Recognition,
Clinical Relevance and Future Directions. Curr. Rheumatol. Rep. 2017,19, 65. [CrossRef] [PubMed]
15.
Arvia, R.; Zakrzewska, K.; Giovannelli, L.; Ristori, S.; Frediani, E.; Del Rosso, M.; Mocali, A.; Stincarelli, M.A.; Laurenzana, A.;
Fibbi, G.; et al. Parvovirus B19 induces cellular senescence in human dermal fibroblasts: Putative role in systemic sclerosis-
associated fibrosis. Rheumatology 2022,61, 3864–3874. [CrossRef] [PubMed]
Curr. Issues Mol. Biol. 2023,45 7795
16.
Pellicano, C.; Vantaggio, L.; Colalillo, A.; Pocino, K.; Basile, V.; Marino, M.; Rosato, E. Type 2 cytokines and scleroderma interstitial
lung disease. Clin. Exp. Med. 2023, ahead of print. [CrossRef]
17.
Liem, S.I.; Neppelenbroek, S.; Fehres, C.M.; Wortel, C.; Toes, R.E.; Huizinga, T.W.; de Vries-Bouwstra, J.K. Autoreactive B cell
responses targeting nuclear antigens in systemic sclerosis: Implications for disease pathogenesis. Semin. Arthritis Rheum.
2023
,58,
152136. [CrossRef]
18.
Tsai, C.Y.; Hsieh, S.C.; Wu, T.H.; Li, K.J.; Shen, C.Y.; Liao, H.T.; Yu, C.L. Pathogenic Roles of Autoantibodies and Aberrant
Epigenetic Regulation of Immune and Connective Tissue Cells in the Tissue Fibrosis of Patients with Systemic Sclerosis. Int. J.
Mol. Sci. 2020,21, 3069. [CrossRef]
19.
Graßhoff, H.; Fourlakis, K.; Comdühr, S.; Riemekasten, G. Autoantibodies as Biomarker and Therapeutic Target in Systemic
Sclerosis. Biomedicines 2022,10, 2150. [CrossRef]
20.
Chepy, A.; Bourel, L.; Koether, V.; Launay, D.; Dubucquoi, S.; Sobanski, V. Can Antinuclear Antibodies Have a Pathogenic Role in
Systemic Sclerosis? Front. Immunol. 2022,13, 930970. [CrossRef]
21.
Moroncini, G.; Svegliati Baroni, S.; Gabrielli, A. Agonistic antibodies in systemic sclerosis. Immunol. Lett.
2018
,195, 83–87.
[CrossRef] [PubMed]
22.
Dooley, A.; Gao, B.; Bradley, N.; Abraham, D.J.; Black, C.M.; Jacobs, M.; Bruckdorfer, K.R. Abnormal nitric oxide metabolism
in systemic sclerosis: Increased levels of nitrated proteins and asymmetric dimethylarginine. Rheumatology
2006
,45, 676–684.
[CrossRef]
23.
Chairta, P.P.; Nicolaou, P.; Christodoulou, K. Enrichr in silico analysis of MS-based extracted candidate proteomic biomarkers
highlights pathogenic pathways in systemic sclerosis. Sci. Rep. 2023,13, 1934. [CrossRef]
24.
Zhang, Y.; Zhu, M.; Xie, L.; Zhang, H.; Deng, T. Identification and validation of key immune-related genes with promising
diagnostic and predictive value in systemic sclerosis. Life Sci. 2023,312, 121238. [CrossRef] [PubMed]
25.
Abignano, G.; Del Galdo, F. Biomarkers as an opportunity to stratify for outcome in systemic sclerosis. Eur. J. Rheumatol.
2020
,7
(Suppl. 3), S193–S202. [PubMed]
26.
Sato, S.; Fujimoto, M.; Hasegawa, M.; Komura, K.; Yanaba, K.; Hayakawa, I.; Matsushita, T.; Takehara, K. Serum soluble CTLA-4
levels are increased in diffuse cutaneous systemic sclerosis. Rheumatology 2004,43, 1261–1266. [CrossRef] [PubMed]
27.
Bălănescu, P.; Bălănescu, E.; Băicu
s
,
, C.; Bălănescu, A. Circulatory cytokeratin 17, marginal zone B1 protein and leucine-rich
α
2-glycoprotein-1 as biomarkers for disease severity and fibrosis in systemic sclerosis patients. Biochem. Medica
2022
,32, 030707.
[CrossRef]
28.
Kania, G.; Rudnik, M.; Distler, O. Involvement of the myeloid cell compartment in fibrogenesis and systemic sclerosis. Nat. Rev.
Rheumatol. 2019,15, 288–302. [CrossRef]
29.
Utsunomiya, A.; Oyama, N.; Hasegawa, M. Potential Biomarkers in Systemic Sclerosis: A Literature Review and Update. J. Clin.
Med. 2020,9, 3388. [CrossRef]
30.
Wermuth, P.J.; Piera-Velazquez, S.; Jimenez, S.A. Identification of novel systemic sclerosis biomarkers employing aptamer
proteomic analysis. Rheumatology 2018,57, 1698–1706. [CrossRef]
31.
Bellocchi, C.; Assassi, S.; Lyons, M.; Marchini, M.; Mohan, C.; Santaniello, A.; Beretta, L. Proteomic aptamer analysis reveals
serum markers that characterize preclinical systemic sclerosis (SSc) patients at risk for progression toward definite SSc. Arthritis
Res. Ther. 2023,25, 15. [CrossRef]
32.
Colalillo, A.; Pellicano, C.; Rosato, E. Serum-soluble ST2 and systemic sclerosis arthropathy. Clin. Rheumatol.
2023
,42, 871–877.
[CrossRef] [PubMed]
33.
Kii, I. Periostin Functions as a Scaffold for Assembly of Extracellular Proteins. Adv. Exp. Med. Biol.
2019
,1132, 23–32. [PubMed]
34.
El-Adili, F.; Lui, J.K.; Najem, M.; Farina, G.; Trojanowska, M.; Sam, F.; Bujor, A.M. Periostin overexpression in scleroderma cardiac
tissue and its utility as a marker for disease complications. Arthritis Res. Ther. 2022,24, 251. [CrossRef] [PubMed]
35.
Distler, O.; Distler, J.; Kowal-Bielecka, O.; Gay, R.E.; Müller-Ladner, U.; Gay, S. Chemokines and chemokine receptors in the
pathogenesis of systemic sclerosis. Mod. Rheumatol. 2002,12, 107–112. [CrossRef]
36.
Bayati, P.; Poormoghim, H.; Mojtabavi, N. Aberrant expression of miR-138 as a novel diagnostic biomarker in systemic sclerosis.
Biomark. Insights 2022,17, 11772719221135442. [CrossRef]
37.
Bayati, P.; Kalantari, M.; Assarehzadegan, M.A.; Poormoghim, H.; Mojtabavi, N. MiR-27a as a diagnostic biomarker and potential
therapeutic target in systemic sclerosis. Sci. Rep. 2022,12, 18932. [CrossRef]
38.
Wajda, A.; Walczyk, M.; Dudek, E.; Stypi´nska, B.; Lewandowska, A.; Romanowska-Próchnicka, K.; Chojnowski, M.; Olesi´nska, M.;
Paradowska-Gorycka, A. Serum microRNAs in Systemic Sclerosis, Associations with Digital Vasculopathy and Lung Involvement.
Int. J. Mol. Sci. 2022,23, 10731. [CrossRef]
39.
Iannazzo, F.; Pellicano, C.; Colalillo, A.; Ramaccini, C.; Romaniello, A.; Gigante, A.; Rosato, E. Interleukin-33 and soluble
suppression of tumorigenicity 2 in scleroderma cardiac involvement. Clin. Exp. Med. 2022,23, 897–903. [CrossRef]
40.
Kakkar, V.; Assassi, S.; Allanore, Y.; Kuwana, M.; Denton, C.P.; Khanna, D.; Del Galdo, F. Type 1 interferon activation in systemic
sclerosis: A biomarker, a target or the culprit. Curr. Opin. Rheumatol. 2022,34, 357–364. [CrossRef]
41.
Trombetta, A.C.; Soldano, S.; Contini, P.; Tomatis, V.; Ruaro, B.; Paolino, S.; Brizzolara, R.; Montagna, P.; Sulli, A.; Pizzorni, C.;
et al. A circulating cell population showing both M1 and M2 monocyte/macrophage surface markers characterizes systemic
sclerosis patients with lung involvement. Respir. Res. 2018,19, 186. [CrossRef]
Curr. Issues Mol. Biol. 2023,45 7796
42.
Höppner, J.; Casteleyn, V.; Biesen, R.; Rose, T.; Windisch, W.; Burmester, G.R.; Siegert, E. SIGLEC-1 in Systemic Sclerosis: A Useful
Biomarker for Differential Diagnosis. Pharmaceuticals 2022,15, 1198. [CrossRef] [PubMed]
43.
Pawlik, K.K.; Bohdziewicz, A.; Chrab ˛aszcz, M.; Stochmal, A.; Sikora, M.; Alda-Malicka, R.; Czuwara, J.; Rudnicka, L. Biomarkers
of disease activity in systemic sclerosis. Wiad Lek. 2020,73, 2300–2305. [CrossRef] [PubMed]
44.
Loisel, S.; Lansiaux, P.; Rossille, D.; Ménard, C.; Dulong, J.; Monvoisin, C.; Bescher, N.; Bézier, I.; Latour, M.; Cras, A.; et al.
Regulatory B Cells Contribute to the Clinical Response after Bone Marrow-Derived Mesenchymal Stromal Cell Infusion in
Patients With Systemic Sclerosis. Stem Cells Transl. Med. 2023,14, 194–206. [CrossRef]
45.
Tieu, A.; Chaigne, B.; Dunogué, B.; Dion, J.; Régent, A.; Casadevall, M.; Cohen, P.; Legendre, P.; Terrier, B.;
Costedoat-Chalumeau, N.
;
et al. Autoantibodies versus Skin Fibrosis Extent in Systemic Sclerosis: A Case-Control Study of Inverted Phenotypes. Diagnostics
2022,12, 1067. [CrossRef]
46.
Salton, F.; Confalonieri, P.; Campisciano, G.; Cifaldi, R.; Rizzardi, C.; Generali, D.; Pozzan, R.; Tavano, S.; Bozzi, C.; Lapadula, G.;
et al. Cytokine Profiles as Potential Prognostic and Therapeutic Markers in SARS-CoV-2-Induced ARDS. J. Clin. Med.
2022
,11,
2951. [CrossRef]
47.
Leong, E.; Bezuhly, M.; Marshall, J.S. Distinct Metalloproteinase Expression and Functions in Systemic Sclerosis and Fibrosis:
What We Know and the Potential for Intervention. Front. Physiol. 2021,12, 727451. [CrossRef] [PubMed]
48.
Smith, V.; Beeckman, S.; Herrick, A.L.; Decuman, S.; Deschepper, E.; De Keyser, F.; Distler, O.; Foeldvari, I.; Ingegnoli, F.;
Müller-Ladner, U.; et al. An EULAR study group pilot study on reliability of simple capillaroscopic definitions to describe
capillary morphology in rheumatic diseases. Rheumatology 2016,55, 883–890. [CrossRef]
49.
Trombetta, A.C.; Smith, V.; Pizzorni, C.; Meroni, M.; Paolino, S.; Cariti, C.; Ruaro, B.; Sulli, A.; Cutolo, M. Quantitative Alterations
of Capillary Diameter Have a Predictive Value for Development of the Capillaroscopic Systemic Sclerosis Pattern. J. Rheumatol.
2016,43, 599–606. [CrossRef] [PubMed]
50.
D’Oria, M.; Gandin, I.; Riccardo, P.; Hughes, M.; Lepidi, S.; Salton, F.; Ruaro, B. Correlation between Microvascular Damage
and Internal Organ Involvement in Scleroderma: Focus on Lung Damage and Endothelial Dysfunction. Diagnostics
2022
,13, 55.
[CrossRef]
51.
Cutolo, M.; Ruaro, B.; Smith, V. Macrocirculation versus microcirculation and digital ulcers in systemic sclerosis patients.
Rheumatology 2017,56, 1834–1836. [CrossRef]
52.
Soulaidopoulos, S.; Triantafyllidou, E.; Garyfallos, A.; Kitas, G.D.; Dimitroulas, T. The role of nailfold capillaroscopy in the
assessment of internal organ involvement in systemic sclerosis: A critical review. Autoimmun. Rev.
2017
,16, 787–795. [CrossRef]
53.
Ruaro, B.; Smith, V.; Sulli, A.; Pizzorni, C.; Tardito, S.; Patané, M.; Paolino, S.; Cutolo, M. Innovations in the Assessment of Primary
and Secondary Raynaud’s Phenomenon. Front. Pharmacol. 2019,10, 360. [CrossRef]
54.
Romano, E.; Rosa, I.; Fioretto, B.S.; Matucci-Cerinic, M.; Manetti, M. Circulating Neurovascular Guidance Molecules and Their
Relationship with Peripheral Microvascular Impairment in Systemic Sclerosis. Life 2022,12, 1056. [CrossRef] [PubMed]
55.
Fioretto, B.S.; Rosa, I.; Matucci-Cerinic, M.; Romano, E.; Manetti, M. Current Trends in Vascular Biomarkers for Systemic Sclerosis:
A Narrative Review. Int. J. Mol. Sci. 2023,24, 4097. [CrossRef] [PubMed]
56.
Ledoult, E.; Launay, D.; Béhal, H.; Mouthon, L.; Pugnet, G.; Lega, J.C.; Sobanski, V. Early trajectories of skin thickening are
associated with severity and mortality in systemic sclerosis. Arthritis Res. Ther. 2020,22, 30. [CrossRef] [PubMed]
57.
Codullo, V.; Cavazzana, I.; Bonino, C.; Alpini, C.; Cavagna, L.; Cozzi, F.; Montecucco, C. Serologic profile and mortality rates of
scleroderma renal crisis in Italy. J. Rheumatol. 2009,36, 1464–1469. [CrossRef]
58.
Vondenberg, J.A.; Muruganandam, M.; Nunez, S.E.; Emil, N.S.; Sibbitt, W.L., Jr. Increased malignancies in systemic sclerosis. Int.
J. Rheum. Dis. 2022,25, 90–92. [CrossRef]
59.
Kardum, Ž.; Milas-Ahi´c, J.; Šahinovi´c, I.; Masle, A.M.; Urši´c, D.; Kos, M. Serum levels of interleukin 17 and 22 in patients with
systemic sclerosis: A single-center cross-sectional study. Rheumatol. Int. 2023,43, 345–354. [CrossRef]
60.
Robak, E.; Gerlicz-Kowalczuk, Z.; Dziankowska-Bartkowiak, B.; Wozniacka, A.; Bogaczewicz, J. Serum concentrations of IL-17A,
IL-17B, IL-17E and IL-17F in patients with systemic sclerosis. Arch. Med. Sci. 2019,15, 706–712. [CrossRef]
61.
Wu, Q.; Cao, F.; Tao, J.; Li, X.; Zheng, S.G.; Pan, H.F. Pentraxin 3: A promising therapeutic target for autoimmune diseases.
Autoimmun. Rev. 2020,19, 102584. [CrossRef]
62.
Ikawa, T.; Miyagawa, T.; Fukui, Y.; Minatsuki, S.; Maki, H.; Inaba, T.; Hatano, M.; Toyama, S.; Omatsu, J.; Awaji, K.; et al.
Association of serum CCL20 levels with pulmonary vascular involvement and primary biliary cholangitis in patients with
systemic sclerosis. Int. J. Rheum. Dis. 2021,24, 711–718. [CrossRef]
63.
Didriksen, H.; Molberg, Ø.; Mehta, A.; Jordan, S.; Palchevskiy, V.; Fretheim, H.; Gude, E.; Ueland, T.; Brunborg, C.; Garen, T.; et al.
Target organ expression and biomarker characterization of chemokine CCL21 in systemic sclerosis associated pulmonary arterial
hypertension. Front. Immunol. 2022,13, 991743. [CrossRef] [PubMed]
64.
Pellicano, C.; Romaggioli, L.; Miglionico, M.; Colalillo, A.; Ramaccini, C.; Gigante, A.; Muscaritoli, M.; Rosato, E. Maresin1 is a
predictive marker of new digital ulcers in systemic sclerosis patients. Microvasc. Res. 2022,142, 104366. [CrossRef] [PubMed]
65.
Nowaczyk, J.; Blicharz, L.; Zawistowski, M.; Sikora, M.; Zaremba, M.; Czuwara, J.; Rudnicka, L. The Clinical Significance of
Salusins in Systemic Sclerosis-A Cross-Sectional Study. Diagnostics 2023,13, 848. [CrossRef]
66.
Servaas, N.H.; Hiddingh, S.; Chouri, E.; Wichers, C.G.K.; Affandi, A.J.; Ottria, A.; Bekker, C.P.J.; Cossu, M.;
Silva-Cardoso, S.C.
;
van der Kroef, M.
; et al. Nuclear Receptor Subfamily 4A Signaling as a Key Disease Pathway of CD1c+ Dendritic Cell Dysregula-
tion in Systemic Sclerosis. Arthritis Rheumatol. 2023,75, 279–292. [CrossRef] [PubMed]
Curr. Issues Mol. Biol. 2023,45 7797
67.
Manetti, M.; Romano, E.; Rosa, I.; Guiducci, S.; Bellando-Randone, S.; De Paulis, A.; Ibba-Manneschi, L.; Matucci-Cerinic, M.
Endothelial-to-mesenchymal transition contributes to endothelial dysfunction and dermal fibrosis in systemic sclerosis. Ann.
Rheum. Dis. 2017,76, 924–934. [CrossRef]
68.
Lafyatis, R.; Valenzi, E. Assessment of disease outcome measures in systemic sclerosis. Nat. Rev. Rheumatol.
2022
,18, 527–541.
[CrossRef]
69.
Knarborg, M.; Hyldgaard, C.; Bendstrup, E.; Davidsen, J.R.; Løkke, A.; Shaker, S.B.; Hilberg, O. Comorbidity and mortality in
systemic sclerosis and matched controls: Impact of interstitial lung disease. A population based cohort study based on health
registry data. Chronic Respir. Dis. 2023,20, 14799731231195041. [CrossRef]
70.
Volkmann, E.R.; Wilhalme, H.; Assassi, S.; Kim, G.H.J.; Goldin, J.; Kuwana, M.; Tashkin, D.P.; Roth, M.D. Combining Clinical
and Biological Data to Predict. Progressive Pulmonary Fibrosis in Patients With Systemic Sclerosis Despite Immunomodulatory
Therapy. ACR Open Rheumatol. 2023, Online ahead of print. [CrossRef]
71.
Hoffmann-Vold, A.-M.; Allanore, Y.; Alves, M.; Brunborg, C.; Airó, P.; Ananieva, L.P.; Czirják, L.; Guiducci, S.; Hachulla, E.; Li, M.;
et al. Progressive interstitial lung disease in patients with systemic sclerosis-associated interstitial lung disease in the EUSTAR
database. Ann. Rheum. Dis. 2021,80, 219–227. [CrossRef]
72.
Perelas, A.; Silver, R.M.; Arrossi, A.V.; Highland, K.B. Systemic sclerosis-associated interstitial lung disease. Lancet Respir. Med.
2020,8, 304–320. [CrossRef]
73.
Tyndall, A.J.; Bannert, B.; Vonk, M.; Airò, P.; Cozzi, F.; Carreira, P.E.; Walker, U.A. Causes and risk factors for death in systemic
sclerosis: A study from the EULAR Scleroderma Trials and Research (EUSTAR) database. Ann. Rheum. Dis.
2010
,69, 1809–1815.
[CrossRef]
74.
Wangkaew, S.; Euathrongchit, J.; Wattanawittawas, P.; Kasitanon, N.; Louthrenoo, W. Incidence and predictors of interstitial lung
disease (ILD) in Thai patients with early systemic sclerosis: Inception cohort study. Mod. Rheumatol.
2016
,26, 588–593. [CrossRef]
75.
Geroldinger-Simi´c, M.; Bayati, S.; Pohjanen, E.; Sepp, N.; Nilsson, P.; Pin, E. Autoantibodies against PIP4K2B and AKT3 Are
Associated with Skin and Lung Fibrosis in Patients with Systemic Sclerosis. Int. J. Mol. Sci. 2023,24, 5629. [CrossRef]
76.
Wells, A.U.; Denton, C.P. Interstitial lung disease in connective tissue disease-mechanisms and management. Nat. Rev. Rheumatol.
2014,10, 728–739. [CrossRef]
77.
DeMizio, D.J.; Bernstein, E.J. Detection and classification of systemic sclerosis-related interstitial lung disease: A review. Curr.
Opin. Rheumatol. 2019,31, 553–560. [CrossRef]
78.
Stock, C.J.W.; Renzoni, E.A. Genetic predictors of systemic sclerosis-associated interstitial lung disease: A review of recent
literature. Eur. J. Hum. Genet. 2018,26, 765–777. [CrossRef]
79.
Elhai, M.; Avouac, J.; Allanore, Y. Circulating lung biomarkers in idiopathic lung fibrosis and interstitial lung diseases associated
with connective tissue diseases: Where do we stand? Semin. Arthritis Rheum. 2020,50, 480–491. [CrossRef]
80.
Khanna, D.; Lescoat, A.; Roofeh, D.; Bernstein, E.J.; Kazerooni, E.A.; Roth, M.D.; Martinez, F.; Flaherty, K.R.; Denton, C.P. Systemic
Sclerosis-Associated Interstitial Lung Disease: How to Incorporate Two Food and Drug Administration-Approved Therapies in
Clinical Practice. Arthritis Rheumatol. 2022,74, 13–27. [CrossRef]
81.
Bonhomme, O.; André, B.; Gester, F.; de Seny, D.; Moermans, C.; Struman, I.; Guiot, J. Biomarkers in systemic sclerosis-associated
interstitial lung disease: Review of the literature. Rheumatology 2019,58, 1534–1546. [CrossRef]
82.
Elhai, M.; Hoffmann-Vold, A.M.; Avouac, J.; Pezet, S.; Cauvet, A.; Leblond, A.; Allanore, Y. Performance of Candidate Serum
Biomarkers for Systemic Sclerosis-Associated Interstitial Lung Disease. Arthritis Rheumatol. 2019,71, 972–982. [CrossRef]
83.
Lescoat, A.; Huscher, D.; Schoof, N.; Airò, P.; de Vries-Bouwstra, J.; Riemekasten, G.; Hachulla, E.; Doria, A.; Rosato, E.;
Hunzelmann, N.; et al. Autoantibody status according to multiparametric assay accurately estimates connective tissue disease
classification and identifies clinically relevant disease clusters. RMD Open 2023,9, e003365.
84.
Goldin, J.G.; Lynch, D.A.; Strollo, D.C.; Suh, R.D.; Schraufnagel, D.E.; Clements, P.J.; Scleroderma Lung Study Research Group.
High-resolution CT findings in patients with symptomatic scleroderma-related interstitial lung disease. Chest
2008
,134, 358–367.
[CrossRef] [PubMed]
85.
Hoffmann-Vold, A.-M.; Maher, T.M.; Philpot, E.E.; Ashrafzadeh, A.; Barake, R.; Barsotti, S.; Bruni, C.; Carducci, P.; Carreira, P.E.;
Castellví, I.; et al. The identification and management of interstitial lung disease in systemic sclerosis: Evidence-based European
consensus statements. Lancet Rheum. 2020,2, 71–83. [CrossRef]
86.
Kuwana, M.; Gil-Vila, A.; Selva-O’Callaghan, A. Role of autoantibodies in the diagnosis and prognosis of interstitial lung disease
in autoimmune rheumatic disorders. Ther. Adv. Musculoskelet. Dis. 2021,13, 1759720X211032457. [CrossRef]
87.
Hoffmann-Vold, A.M.; Fretheim, H.; Meier, C.; Maurer, B. Circulating biomarkers of systemic sclerosis—Interstitial lung disease.
J. Scleroderma Relat. Disord. 2020,5(Suppl. 2), 41–47. [CrossRef]
88.
Manetti, M.; Rosa, I.; Fioretto, B.S.; Matucci-Cerinic, M.; Romano, E. Decreased Serum Levels of SIRT1 and SIRT3 Correlate
with Severity of Skin and Lung Fibrosis and Peripheral Microvasculopathy in Systemic Sclerosis. J. Clin. Med.
2022
,11, 1362.
[CrossRef]
89.
Wu, M.; Baron, M.; Pedroza, C.; Salazar, G.A.; Ying, J.; Charles, J.; Agarwal, S.K.; Hudson, M.; Pope, J.; Zhou, X.; et al. CCL2 in the
Circulation Predicts Long-Term Progression of Interstitial Lung Disease in Patients With Early Systemic Sclerosis: Data from Two
Independent Cohorts. Arthritis Rheumatol. 2017,69, 1871–1878. [CrossRef]
Curr. Issues Mol. Biol. 2023,45 7798
90.
Omori, I.; Sumida, H.; Sugimori, A.; Sakakibara, M.; Urano-Takaoka, M.; Iwasawa, O.; Saito, H.; Matsuno, A.; Sato, S. Serum
cold-inducible RNA-binding protein levels as a potential biomarker for systemic sclerosis-associated interstitial lung disease. Sci.
Rep. 2023,13, 5017. [CrossRef]
91.
Jee, A.S.; Stewart, I.; Youssef, P.; Adelstein, S.; Lai, D.; Hua, S.; Stevens, W.; Proudman, S.; Ngian, G.; Glaspole, I.N.; et al. A
composite serum biomarker index for the diagnosis of systemic sclerosis interstitial lung disease: A multicentre, observational,
cohort study. Arthritis Rheumatol. 2023,75, 1424–1433. [CrossRef]
92.
Hoffmann-Vold, A.M.; Maher, T.M.; Philpot, E.E.; Ashrafzadeh, A.; Distler, O. Assessment of recent evidence for the management
of patients with systemic sclerosis-associated interstitial lung disease: A systematic review. ERJ Open Res.
2021
,7, 00235–02020.
[CrossRef]
93.
Ahmed, S.; Handa, R. Management of Connective Tissue Disease-related Interstitial Lung Disease. Curr. Pulmonol. Rep.
2022
,11,
86–98. [CrossRef]
94.
Temiz Karadag, D.; Cakir, O.; San, S.; Yazici, A.; Ciftci, E.; Cefle, A. Association of quantitative computed tomography ındices with
lung function and extent of pulmonary fibrosis in patients with systemic sclerosis. Clin. Rheumatol.
2022
,41, 513–521. [CrossRef]
95.
Murdaca, G.; Caprioli, S.; Tonacci, A.; Billeci, L.; Greco, M.; Negrini, S.; Cittadini, G.; Zentilin, P.; Ventura Spagnolo, E.;
Gangemi, S.
A Machine Learning Application to Predict Early Lung Involvement in Scleroderma: A Feasibility Evaluation. Diagnostics 2021,
11, 1880. [CrossRef]
96.
Gasperini, M.L.; Gigante, A.; Iacolare, A.; Pellicano, C.; Lucci, S.; Rosato, E. The predictive role of lung ultrasound in progression
of scleroderma interstitial lung disease. Clin. Rheumatol. 2020,39, 119–123. [CrossRef]
97.
Ruaro, B.; Baratella, E.; Confalonieri, P.; Confalonieri, M.; Vassallo, F.G.; Wade, B.; Geri, P.; Pozzan, R.; Caforio, G.; Marrocchio, C.;
et al. High-Resolution Computed Tomography and Lung Ultrasound in Patients with Systemic Sclerosis: Which One to Choose?
Diagnostics 2021,11, 2293. [CrossRef]
98.
Bruni, C.; Mattolini, L.; Tofani, L.; Gargani, L.; Landini, N.; Roma, N.; Lepri, G.; Orlandi, M.; Guiducci, S.; Bellando-Randone, S.;
et al. Lung Ultrasound B-Lines in the Evaluation of the Extent of Interstitial Lung Disease in Systemic Sclerosis. Diagnostics
2022
,
12, 1696. [CrossRef]
99.
Kowal-Bielecka, O.; Fransen, J.; Avouac, J.; Becker, M.; Kulak, A.; Allanore, Y.; Distler, O.; Clements, P.; Cutolo, M.; Czirjak, L.; et al.
Update of EULAR recommendations for the treatment of systemic sclerosis. Ann. Rheum. Dis. 2017,76, 1327–1339. [CrossRef]
100.
Campochiaro, C.; De Luca, G.; Lazzaroni, M.G.; Armentaro, G.; Spinella, A.; Vigone, B.; Ruaro, B.; Stanziola, A.; Benfaremo, D.;
De Lorenzis, E.; et al. Real-life efficacy and safety of nintedanib in systemic sclerosis-interstitial lung disease: Data from an Italian
multicentre study. RMD Open 2023,9, e002850. [CrossRef]
101.
Ruaro, B.; Gandin, I.; Pozzan, R.; Tavano, S.; Bozzi, C.; Hughes, M.; Kodric, M.; Cifaldi, R.; Lerda, S.; Confalonieri, M.; et al.
Nintedanib in Idiopathic Pulmonary Fibrosis: Tolerability and Safety in a Real Life Experience in a Single Centre in Patients also
Treated with Oral Anticoagulant Therapy. Pharmaceuticals 2023,16, 307. [CrossRef]
102.
Kuwana, M.; Allanore, Y.; Denton, C.P.; Distler, J.H.W.; Steen, V.; Khanna, D.; Matucci-Cerinic, M.; Mayes, M.D.; Volkmann, E.R.;
Miede, C.; et al. Nintedanib in Patients with Systemic Sclerosis-Associated Interstitial Lung Disease: Subgroup Analyses by
Autoantibody Status and Modified Rodnan Skin Thickness Score. Arthritis Rheumatol. 2022,74, 518–526. [CrossRef]
103.
Denton, C.P.; Ong, V.H.; Xu, S.; Chen-Harris, H.; Modrusan, Z.; Lafyatis, R.; Sornasse, T. Therapeutic interleukin-6 blockade
reverses transforming growth factor-beta pathway activation in dermal fibroblasts: Insights from the faSScinate clinical trial in
systemic sclerosis. Ann. Rheum. Dis. 2018,77, 1362–1371. [CrossRef]
104.
Khanna, D.; Padilla, C.; Tsoi, L.C.; Nagaraja, V.; Khanna, P.P.; Tabib, T.; Kahlenberg, J.M.; Young, A.; Huang, S.; Gudjonsson, J.E.;
et al. Tofacitinib blocks IFN-regulated biomarker genes in skin fibroblasts and keratinocytes in a systemic sclerosis trial. JCI
Insight 2022,7, e159566. [CrossRef]
105.
Acharya, N.; Sharma, S.K.; Mishra, D.; Dhooria, S.; Dhir, V.; Jain, S. Efficacy and safety of pirfenidone in systemic sclerosis-related
interstitial lung disease-a randomised controlled trial. Rheumatol. Int. 2020,40, 703–710. [CrossRef]
106.
Sullivan, K.M.; Goldmuntz, E.A.; Keyes-Elstein, L.; McSweeney, P.A.; Pinckney, A.; Welch, B.; Furst, D.E. Myeloablative
Autologous Stem-Cell Transplantation for Severe Scleroderma. N. Engl. J. Med. 2018,378, 35–47. [CrossRef] [PubMed]
107.
Bernstein, E.J.; Peterson, E.R.; Sell, J.L.; D’Ovidio, F.; Arcasoy, S.M.; Bathon, J.M.; Lederer, D.J. Survival of adults with systemic
sclerosis following lung transplantation: A nationwide cohort study. Arthritis Rheumatol. 2015,67, 1314–1322. [CrossRef]
108.
Herrick, A.L. Raynaud’s phenomenon and digital ulcers: Advances in evaluation and management. Curr. Opin. Rheumatol.
2021
,
33, 453–462. [CrossRef] [PubMed]
109.
Yu, L.; Domsic, R.T.; Saketkoo, L.; Withey, J.; Frech, T.M.; Herrick, A.L.; Hummers, L.K.; Shah, A.A.; Denton, C.P.;
Khanna, D.
; et al.
Assessment of the Systemic Sclerosis-Associated Raynaud’s Phenomenon Questionnaire: Item Bank and Short-form Development.
Arthritis Care Res. 2023,75, 1725–1734. [CrossRef]
110.
Flavahan, N.A. New mechanism-based approaches to treating and evaluating the vasculopathy of scleroderma. Curr. Opin.
Rheumatol. 2021,33, 471–479. [CrossRef]
111.
Hughes, M.; Allanore, Y.; Chung, L.; Pauling, J.D.; Denton, C.P.; Matucci-Cerinic, M. Raynaud phenomenon and digital ulcers in
systemic sclerosis. Nat. Rev. Rheumatol. 2020,16, 208–221. [CrossRef]
112.
Cutolo, M.; Trombetta, A.C.; Melsens, K.; Pizzorni, C.; Sulli, A.; Ruaro, B.; Paolino, S.; Deschepper, E.; Smith, V. Automated
assessment of absolute nailfold capillary number on videocapillaroscopic images: Proof of principle and validation in systemic
sclerosis. Microcirculation 2018,25, e12447. [CrossRef]
Curr. Issues Mol. Biol. 2023,45 7799
113.
Jasionyte, G.; Seskute, G.; Rugiene, R.; Butrimiene, I. The Promising Role of a Superb Microvascular Imaging Technique in the
Evaluation of Raynaud’s Syndrome in Systemic Sclerosis: Theory and Practical Challenges. Diagnostics
2021
,11, 1743. [CrossRef]
[PubMed]
114.
Pellicano, C.; Iannazzo, F.; Romaggioli, L.; Rosato, E. IL33 and sST2 serum level in systemic sclerosis microvascular involvement.
Microvasc. Res. 2022,142, 104344. [CrossRef]
115.
Humbert, M.; Kovacs, G.; Hoeper, M.M.; Badagliacca, R.; Berger, R.M.; Brida, M.; Rosenkranz, S. 2022 ESC/ERS Guidelines for
the diagnosis and treatment of pulmonary hypertension. Eur. Heart J. 2022,43, 3618–3731. [CrossRef] [PubMed]
116.
Huang, W.-C.; Hsieh, S.-C.; Wu, Y.-W.; Hsieh, T.-Y.; Wu, Y.-J.; Li, K.-J.; Charng, M.-J.; Chen, W.-S.; Sung, S.-H.; Tsao, Y.-P.; et al.
2023 Taiwan Society of Cardiology (TSOC) and Taiwan College of Rheumatology (TCR) Joint Consensus on Connective Tissue
Disease-Associated Pulmonary Arterial Hypertension. Acta Cardiol. Sin. 2023,39, 213–241.
117.
Bruni, C.; De Luca, G.; Lazzaroni, M.-G.; Zanatta, E.; Lepri, G.; Airò, P.; Dagna, L.; Doria, A.; Matucci-Cerinic, M. Screening
for pulmonary arterial hypertension in systemic sclerosis: A systematic literature review. Eur. J. Intern. Med.
2020
,78, 17–25.
[CrossRef]
118.
Theodorakopoulou, M.P.; Minopoulou, I.; Sarafidis, P.; Kamperidis, V.; Papadopoulos, C.; Dimitroulas, T.; Boutou, A.K. Vascular
endothelial injury assessed with functional techniques in systemic sclerosis patients with pulmonary arterial hypertension versus
systemic sclerosis patients without pulmonary arterial hypertension: A systematic review and meta-analysis. Rheumatol. Int.
2021,41, 1045–1053. [CrossRef]
119.
Yaqub, A.; Chung, L. Epidemiology and risk factors for pulmonary hypertension in systemic sclerosis. Curr. Rheumatol. Rep.
2013
,
15, 302. [CrossRef]
120.
Zhang, Y.; Qin, D.; Qin, L.; Yang, X.; Luo, Q.; Wang, H. Diagnostic value of cardiac natriuretic peptide on pulmonary hypertension
in systemic sclerosis: A systematic review and meta-analysis. Jt. Bone Spine 2022,89, 105287. [CrossRef]
121.
Jiang, Y.; Turk, M.A.; Pope, J.E. Factors associated with pulmonary arterial hypertension (PAH) in systemic sclerosis (SSc).
Autoimmun. Rev. 2020,19, 102602. [CrossRef]
122.
Lewis, R.A.; Durrington, C.; Condliffe, R.; Kiely, D.G. BNP/NT-proBNP in pulmonary arterial hypertension: Time for point-of-care
testing? Eur. Respir. Rev. 2020,29, 200009. [CrossRef]
123.
Hickey, P.M.; Lawrie, A.; Condliffe, R. Circulating Protein Biomarkers in Systemic Sclerosis Related Pulmonary Arterial Hyper-
tension: A Review of Published Data. Front. Med. 2018,5, 175. [CrossRef]
124.
Moccaldi, B.; De Michieli, L.; Binda, M.; Famoso, G.; Depascale, R.; Perazzolo Marra, M.; Zanatta, E. Serum Biomarkers in
Connective Tissue Disease-Associated Pulmonary Arterial Hypertension. Int. J. Mol. Sci. 2023,24, 4178. [CrossRef]
125.
Kolstad, K.D.; Khatri, A.; Donato, M.; Chang, S.E.; Li, S.; Steen, V.D.; Chung, L. Cytokine signatures differentiate systemic sclerosis
patients at high versus low risk for pulmonary arterial hypertension. Arthritis Res. Ther. 2022,24, 39. [CrossRef]
126.
Sun, C.; Zhu, H.; Wang, Y.; Han, Y.; Zhang, D.; Cao, X.; Wang, D. Serum metabolite differences detected by HILIC UHPLC-Q-TOF
MS in systemic sclerosis. Clin. Rheumatol. 2023,42, 125–134. [CrossRef]
127.
Bauer, Y.; de Bernard, S.; Hickey, P.; Ballard, K.; Cruz, J.; Cornelisse, P.; Lawrie, A. Identifying early pulmonary arterial
hypertension biomarkers in systemic sclerosis: Machine learning on proteomics from the DETECT cohort. Eur. Respir. J.
2021
,57,
2002591. [CrossRef]
128.
Oller-Rodríguez, J.E.; Vicens Bernabeu, E.; Gonzalez-Mazarío, R.; Grau García, E.; Ortiz Sanjuan, F.M.; Román Ivorra, J.A. Utility
of cytokines CXCL4, CXCL8 and GDF15 as biomarkers in systemic sclerosis. Med. Clin. 2022,159, 359–365. [CrossRef]
129.
Nakamura, K.; Asano, Y.; Taniguchi, T.; Minatsuki, S.; Inaba, T.; Maki, H.; Hatano, M.; Yamashita, T.; Saigusa, R.; Ichimura, Y.; et al.
Serum levels of interleukin-18-binding protein isoform a: Clinical association with inflammation and pulmonary hypertension in
systemic sclerosis. J. Dermatol. 2016,43, 912–918. [CrossRef]
130.
Xanthouli, P.; Gordjani, O.; Benjamin, N.; Harutyunova, S.; Egenlauf, B.; Marra, A.M.; Haas, S.; Milde, N.; Blank, N.;
Lorenz, H.-M.
;
et al. Hypochromic red cells as a prognostic indicator of survival among patients with systemic sclerosis screened for pulmonary
hypertension. Arthritis Res. Ther. 2023,25, 38. [CrossRef]
131.
Chikhoune, L.; Brousseau, T.; Morell-Dubois, S.; Farhat, M.M.; Maillard, H.; Ledoult, E.; Lambert, M.; Yelnik, C.; Sanges, S.;
Sobanski, V.; et al. Association between Routine Laboratory Parameters and the Severity and Progression of Systemic Sclerosis. J.
Clin. Med. 2022,11, 5087. [CrossRef]
132.
Xu, B.; Xu, G.; Yu, Y.; Lin, J. The role of TGF-
β
or BMPR2 signaling pathway-related miRNA in pulmonary arterial hypertension
and systemic sclerosis. Arthritis Res. Ther. 2021,23, 288. [CrossRef]
133.
Grignaschi, S.; Sbalchiero, A.; Spinozzi, G.; Palermo, B.L.; Cantarini, C.; Nardiello, C.; Cavagna, L.; Olivieri, C. Endoglin and
Systemic Sclerosis: A PRISMA-driven systematic review. Front. Med. 2022,9, 964526. [CrossRef]
134.
Planas-Cerezales, L.; Fabbri, L.; Pearmain, L. Add-on therapy for pulmonary fibrosis, a forthcoming era with implications for
practice: The BI 101550 and RELIEF trials. Breathe 2023,9, 230090. [CrossRef]
135.
Ruaro, B.; Sulli, A.; Smith, V.; Pizzorni, C.; Paolino, S.; Alessandri, E.; Trombetta, A.C.; Cutolo, M. Advances in nailfold
capillaroscopic analysis in systemic sclerosis. J. Scleroderma Relat. Disord. 2018,3, 122–131. [CrossRef]
136.
Ruaro, B.; Sulli, A.; Smith, V.; Santiago, T.; da Silva, J.A.P.; Pizzorni, C.; Paolino, S.; Alessandri, E.; Cutolo, M. The impact of
transducer frequency in ultrasound evaluation of subclinical skin involvement in limited cutaneous systemic sclerosis patients.
Clin. Exp. Rheumatol. 2019,37, 147–148.
Curr. Issues Mol. Biol. 2023,45 7800
137.
Villanueva-Martin, G.; Acosta-Herrera, M.; Carmona, E.G.; Kerick, M.; Ortego-Centeno, N.; Callejas-Rubio, J.L.; Mages,
N.;
Klages, S.
; Börno, S.; Timmermann, B.; et al. Non-classical circulating monocytes expressing high levels of microsomal
prostaglandin E2 synthase-1 tag an aberrant IFN-response in systemic sclerosis. J. Autoimmun. 2023,140, 103097. [CrossRef]
138.
Lomelí-Nieto, J.A.; Muñoz-Valle, J.F.; Baños-Hernández, C.J.; Navarro-Zarza, J.E.; Godínez-Rubí, J.M.; García-Arellano, S.;
Ramírez-Dueñas, M.G.; Parra-Rojas, I.; Villanueva-Pérez, A.; Hernández-Bello, J. Transforming growth factor beta isoforms and
TGF-βR1 and TGF-βR2 expression in systemic sclerosis patients. Clin. Exp. Med. 2022,23, 471–481. [CrossRef]
139.
Rosendahl, A.-H.; Schönborn, K.; Krieg, T. Pathophysiology of systemic sclerosis (scleroderma). Kaohsiung J. Med. Sci.
2022
,38,
187–195. [CrossRef]
140.
Utsunomiya, A.; Chino, T.; Kasamatsu, H.; Hasegawa, T.; Utsunomiya, N.; Luong, V.H.; Matsushita, T.; Sasaki, Y.; Ogura, D.;
Niwa, S.-I.; et al. The compound lg283 inhibits bleomycin-induced skin fibrosis via antagonizing tgf-
β
signaling. Arthritis Res.
Ther. 2022,24, 94. [CrossRef]
141. Reggiani, F.; Moroni, G.; Ponticelli, C. Kidney Involvement in Systemic Sclerosis. J. Pers. Med. 2022,12, 1123. [CrossRef]
142. Bose, N.; Chiesa-Vottero, A.; Chatterjee, S. Scleroderma renal crisis. Semin. Arthritis Rheum. 2015,44, 687–694. [CrossRef]
143.
Gigante, A.; Barbano, B.; Barilaro, G.; Quarta, S.; Gasperini, M.L.; Di Mario, F.; Rosato, E. Serum uric acid as a marker of
microvascular damage in systemic sclerosis patients. Microvasc. Res. 2016,106, 39–43. [CrossRef]
144. Farrukh, L.; Steen, V.D.; Shapiro, L.; Mehta, S. Studying the Role of C5-Inhibition Therapy in Scleroderma Renal Crisis-Induced
Thrombotic Microangiopathy - A Review of Literature. Semin. Arthritis Rheum. 2023,63, 152256. [CrossRef]
145.
Tonsawan, P.; Talabthong, K.; Puapairoj, A.; Foocharoen, C. Renal pathology and clinical associations in systemic sclerosis: A
historical cohort study. Int. J. Gen. Med. 2019,12, 323–331. [CrossRef]
146.
Okrój, M.; Johansson, M.; Saxne, T.; Blom, A.M.; Hesselstrand, R. Analysis of complement biomarkers in systemic sclerosis
indicates a distinct pattern in scleroderma renal crisis. Arthritis Res. Ther. 2016,18, 267. [CrossRef]
147.
Almaabdi, K.; Ahmad, Z.; Johnson, S.R. Advanced Autoantibody Testing in Systemic Sclerosis. Diagnostics
2023
,13, 851.
[CrossRef]
148.
Fritzler, M.J.; Bentow, C.; Beretta, L.; Palterer, B.; Perurena-Prieto, J.; Sanz-Martínez, M.T.; Guillen-Del-Castillo, A.; Marín, A.;
Fonollosa-Pla, V.; Callejas-Moraga, E.; et al. Anti-U11/U12 Antibodies as a Rare but Important Biomarker in Patients with
Systemic Sclerosis: A Narrative Review. Diagnostics 2023,13, 1257. [CrossRef]
149.
Mahler, M.; Kim, G.; Roup, F.; Bentow, C.; Fabien, N.; Goncalves, D.; Palterer, B.; Fritzler, M.J.; Villalta, D. Evaluation of a novel
particle-based multi-analyte technology for the detection of anti-fibrillarin antibodies. Immunol. Res.
2021
,69, 239–248. [CrossRef]
150.
Lande, R.; Palazzo, R.; Mennella, A.; Pietraforte, I.; Cadar, M.; Stefanantoni, K.; Conrad, C.; Riccieri, V.; Frasca, L. New
Autoantibody Specificities in Systemic Sclerosis and Very Early Systemic Sclerosis. Antibodies 2021,10, 12. [CrossRef]
151.
Pagkopoulou, E.; Soulaidopoulos, S.; Katsiki, N.; Malliari, A.; Loutradis, C.; Karagiannis, A.; Dimitroulas, T. The role of
asymmetric dimethylarginine in endothelial dysfunction and abnormal nitric oxide metabolism in systemic sclerosis: Results
from a pilot study. Clin. Rheumatol. 2023,42, 1077–1085. [CrossRef]
152.
Odler, B.; Foris, V.; Gungl, A.; Müller,V.; Hassoun, P.M.; Kwapiszewska, G.; Olschewski, H.; Kovacs, G. Biomarkers for Pulmonary
Vascular Remodeling in Systemic Sclerosis: A Pathophysiological Approach. Front. Physiol. 2018,9, 587. [CrossRef]
153.
Kawashiri, S.Y.; Ueki, Y.; Terada, K.; Yamasaki, S.; Aoyagi, K.; Kawakami, A. Improvement of plasma endothelin-1 and nitric
oxide in patients with systemic sclerosis by bosentan therapy. Rheumatol. Int. 2014,34, 221–225. [CrossRef]
154.
Cutolo, M.; Ruaro, B.; Montagna, P.; Brizzolara, R.; Stratta, E.; Trombetta, A.C.; Scabini, S.; Tavilla, P.P.; Parodi, A.; Corallo, C.;
et al. Effects of selexipag and its active metabolite in contrasting the profibrotic myofibroblast activity in cultured scleroderma
skin fibroblasts. Arthritis Res. Ther. 2018,20, 77. [CrossRef]
155.
Giannelli, G.; Iannone, F.; Marinosci, F.; Lapadula, G.; Antonaci, S. The effect of bosentan on matrix metalloproteinase-9 levels in
patients with systemic sclerosis-induced pulmonary hypertension. Curr. Med. Res. Opin. 2005,21, 327–332. [CrossRef]
156.
Manetti, M.; Guiducci, S.; Romano, E.; Bellando-Randone, S.; Conforti, M.L.; Ibba-Manneschi, L.; Matucci-Cerinic, M. Increased
serum levels and tissue expression of matrix metalloproteinase-12 in patients with systemic sclerosis: Correlation with severity of
skin and pulmonary fibrosis and vascular damage. Ann. Rheum. Dis. 2012,71, 1064–1072. [CrossRef]
157.
Pagkopoulou, E.; Soulaidopoulos, S.; Triantafyllidou, E.; Loutradis, C.; Malliari, A.; Kitas, G.D.; Garyfallos, A.; Dimitroulas, T.
Asymmetric dimethylarginine correlates with worsening peripheral microangiopathy in systemic sclerosis. Microvasc. Res.
2023
,
145, 104448. [CrossRef]
158.
Gordon, J.K.; Martyanov, V.; Franks, J.M.; Bernstein, E.J.; Szymonifka, J.; Magro, C.; Spiera, R.F. Belimumab for the Treatment of
Early Diffuse Systemic Sclerosis: Results of a Randomized, Double-Blind, Placebo-Controlled, Pilot Trial. Arthritis Rheumatol.
2018,70, 308–316. [CrossRef]
159.
Wirz, E.G.; Jaeger, V.K.; Allanore, Y.; Riemekasten, G.; Hachulla, E.; Distler, O.; Airò, P.E.; Carreira, P.; Tikly, M.; Vettori, S.; et al.
Incidence and predictors of cutaneous manifestations during the early course of systemic sclerosis: A 10-year longitudinal study
from the EUSTAR database. Ann. Rheum. Dis. 2016,75, 1285–1292. [CrossRef]
160.
Cafaro, G.; Bartoloni, E.; Baldini, C.; Franceschini, F.; Riccieri, V.; Fioravanti, A.; Fornaro, M.; Ghirardello, A.; Palterer, B.;
Infantino, M.; et al. Mycophenolate Mofetil Versus Placebo for Systemic Sclerosis-Related Interstitial Lung Disease: An Analysis
of Scleroderma Lung Studies I and II. Arthritis Rheumatol. 2017,69, 1451–1460.
161.
Johnson, S.R.; Feldman, B.M.; Pope, J.E.; Tomlinson, G.A. Shifting our thinking about uncommon disease trials: The case of
methotrexate in scleroderma. J. Rheumatol. 2009,36, 323–329. [CrossRef]
Curr. Issues Mol. Biol. 2023,45 7801
162. Roden, A.C.; Camus, P. Iatrogenic pulmonary lesions. Semin. Diagn. Pathol. 2018,35, 260–271. [CrossRef]
163.
Karalilova, R.V.; Batalov, Z.A.; Sapundzhieva, T.L.; Matucci-Cerinic, M.; Batalov, A.Z. Tofacitinib in the treatment of skin and
musculoskeletal involvement in patients with systemic sclerosis, evaluated by ultrasound. Rheumatol. Int.
2021
,41, 1743–1753.
[CrossRef] [PubMed]
164.
Khanna, D.; Denton, C.P.; Furst, D.E.; Mayes, M.D.; Matucci-Cerinic, M.; Smith, V.; de Vries, D.; Ford, P.; Bauer, Y.; Randall, M.J.;
et al. A 24-Week, Phase IIa, Randomized, Double-blind, Placebo-controlled Study of Ziritaxestat in Early Diffuse Cutaneous
Systemic Sclerosis (NOVESA). Arthritis Rheumatol. 2023,75, 1434–1444. [CrossRef] [PubMed]
165.
Ruaro, B.; Pizzorni, C.; Paolino, S.; Smith, V.; Ghio, M.; Casabella, A.; Alessandri, E.; Patané, M.; Sulli, A.; Cutolo, M. Correlations
between nailfold microvascular damage and skin involvement in systemic sclerosis patients. Microvasc. Res.
2019
,125, 103874.
[CrossRef] [PubMed]
166.
Ruaro, B.; Soldano, S.; Smith, V.; Paolino, S.; Contini, P.; Montagna, P.; Pizzorni, C.; Casabella, A.; Tardito, S.; Sulli, A.; et al.
Correlation between circulating fibrocytes and dermal thickness in limited cutaneous systemic sclerosis patients: A pilot study.
Rheumatol. Int. 2019,39, 1369–1376. [CrossRef]
167.
Gagliardi, C.; Adinolfi, A.; Belloli, L.; Romano, M.E.; Ughi, N.; Epis, O.M. Sclerodermic hand: A retrospective study on the role of
ultrasonography in the detection of subclinical joint involvement. Clin. Rheumatol. 2023,42, 2873–2879. [CrossRef]
168.
Hu, M.; Yao, Z.; Xu, L.; Peng, M.; Deng, G.; Liu, L.; Jiang, X.; Cai, X. M2 macrophage polarization in systemic sclerosis fibrosis:
Pathogenic mechanisms and therapeutic effects. Heliyon 2023,9, e16206. [CrossRef]
169.
Stifano, G.; Sornasse, T.; Rice, L.M.; Na, L.; Chen-Harris, H.; Khanna, D.; Jahreis, A.; Zhang, Y.; Siegel, J.; Lafyatis, R. Skin
Gene Expression Is Prognostic for the Trajectory of Skin Disease in Patients with Diffuse Cutaneous Systemic Sclerosis. Arthritis
Rheumatol. 2018,70, 912–919. [CrossRef]
170.
Clark, K.E.N.; Csomor, E.; Campochiaro, C.; Galwey, N.; Nevin, K.A.; Morse, M.; Teo, Y.V.; Freudenberg, J.; Ong, V.H.;
Derrett-Smith, E.
; et al. Integrated analysis of dermal blister fluid proteomics and genome-wide skin gene expression in systemic
sclerosis: An observational study. Lancet Rheumatol. 2022,4, e507–e516. [CrossRef]
171.
Volkmann, E.R.; McMahan, Z. Gastrointestinal involvement in systemic sclerosis: Pathogenesis, assessment and treatment. Curr.
Opin. Rheumatol. 2022,34, 328–336. [CrossRef]
172.
Cutolo, M.; Soldano, S.; Smith, V. Pathophysiology of systemic sclerosis: Current understanding and new insights. Expert Rev.
Clin. Immunol. 2019,15, 753–764. [CrossRef]
173.
Lepri, G.; Guiducci, S.; Bellando-Randone, S.; Giani, I.; Bruni, C.; Blagojevic, J.; Carnesecchi, G.; Radicati, A.; Pucciani, F.;
Marco, M.-C.
Evidence for oesophageal and anorectal involvement in very early systemic sclerosis (VEDOSS): Report from a
single VEDOSS/EUSTAR centre. Ann. Rheum. Dis. 2015,74, 124–128. [CrossRef]
174.
Khanna, D.; Hays, R.D.; Maranian, P.; Seibold, J.R.; Impens, A.; Mayes, M.D.; Clements, P.J.; Getzug, T.; Fathi, N.; Bechtel, A.; et al.
Reliability and validity of the University of California, Los Angeles Scleroderma Clinical Trial Consortium Gastrointestinal Tract
Instrument. Arthritis Rheum. 2009,61, 1257–1263. [CrossRef]
175.
Hamberg, V.; Wallman, J.K.; Mogard, E.; Lindqvist, E.; Olofsson, T.; Andréasson, K. Elevated fecal levels of the inflammatory
biomarker calprotectin in early systemic sclerosis. Rheumatol. Int. 2023,43, 961–967. [CrossRef]
176. Gigante, A.; Navarini, L.; Margiotta, D.; Amoroso, A.; Barbano, B.; Cianci, R.; Afeltra, A.; Rosato, E. Angiogenic and angiostatic
factors in renal scleroderma-associated vasculopathy. Microvasc. Res. 2017,114, 41–45. [CrossRef]
177.
Simon, M.; Lücht, C.; Hosp, I.; Zhao, H.; Wu, D.; Heidecke, H.; Witowski, J.; Budde, K.; Riemekasten, G.; Catar, R. Autoantibodies
from Patients with Scleroderma Renal Crisis Promote PAR-1 Receptor Activation and IL-6 Production in Endothelial Cells. Int. J.
Mol. Sci. 2021,22, 11793. [CrossRef]
178.
Macklin, M.; Yadav, S.; Jan, R.; Reid, P. Checkpoint Inhibitor-Associated Scleroderma and Scleroderma Mimics. Pharmaceuticals
2023,16, 259. [CrossRef]
179.
Ida, T.; Ikeda, K.; Ohbe, H.; Nakamura, K.; Furuya, H.; Iwamoto, T.; Furuta, S.; Miyamoto, Y.; Nakajima, M.; Sasabuchi, Y.; et al.
Early initiation of angiotensin-converting enzyme inhibitor in patients with scleroderma renal crisis: A nationwide inpatient
database study. Rheumatology 2023, kead343. [CrossRef]
180.
Kowalska-K˛epczy´nska, A. Systemic Scleroderma—Definition, Clinical Picture and Laboratory Diagnostics. J. Clin. Med.
2022
,11,
2299. [CrossRef]
181.
Romano, E.; Rosa, I.; Manetti, M. Advances in Systemic Sclerosis: From Pathogenetic Pathways toward Novel Therapeutic Targets.
Life 2023,13, 513. [CrossRef]
182.
Berger, M.; Steen, V.D. Role of anti-receptor autoantibodies in pathophysiology of scleroderma. Autoimmun. Rev.
2017
,16,
1029–1035. [CrossRef]
183. Nagaraja, V. Management of scleroderma renal crisis. Curr. Opin. Rheumatol. 2019,31, 223–230. [CrossRef] [PubMed]
184.
Akamata, K.; Asano, Y.; Noda, S.; Taniguchi, T.; Takahashi, T.; Ichimura, Y.; Toyama, T.; Sumida, H.; Kuwano, Y.; Yanaba, K.; et al.
An inverse correlation of serum angiogenin levels with estimated glomerular filtration rate in systemic sclerosis patients with
renal dysfunction. Eur. J. Dermatol. 2013,23, 269–270. [CrossRef] [PubMed]
185.
Fukasawa, T.; Yoshizaki, A.; Ebata, S.; Fukayama, M.; Kuzumi, A.; Norimatsu, Y.; Matsuda, K.M.; Kotani, H.; Sumida, H.;
Yoshizaki-Ogawa, A.; et al. Interleukin-17 pathway inhibition with brodalumab in early systemic sclerosis: Analysis of a
single-arm, open-label, phase 1 trial. J. Am. Acad. Dermatol. 2023,89, 366–369. [CrossRef] [PubMed]
Curr. Issues Mol. Biol. 2023,45 7802
186.
Gusev, E.; Sarapultsev, A. Atherosclerosis and Inflammation: Insights from the Theory of General Pathological Processes. Int. J.
Mol. Sci. 2023,24, 7910. [CrossRef]
187.
Namas, R.; Tashkin, D.P.; Furst, D.E.; Wilhalme, H.; Tseng, C.H.; Roth, M.D.; Carlson, P. Efficacy of Mycophenolate Mofetil and
Oral Cyclophosphamide on Skin Thickness: Post Hoc Analyses from Two Randomized Placebo-Controlled Trials. Arthritis Care
Res. 2018,70, 439–444. [CrossRef]
188.
Morrisroe, K.; Hansen, D.; Stevens, W.; Ross, L.; Sahhar, J.; Ngian, G.S.; Hill, C.L.; Host, L.; Walker, J.; Proudman, S.; et al.
Progressive pulmonary fibrosis and its impact on survival in systemic sclerosis related interstitial lung disease. Rheumatology
2023, kead491, ahead of print.
189.
Sulli, A.; Ruaro, B.; Smith, V.; Pizzorni, C.; Zampogna, G.; Gallo, M.; Cutolo, M. Progression of nailfold microvascular damage
and antinuclear antibody pattern in systemic sclerosis. J. Rheumatol. 2013,40, 634–639. [CrossRef]
190.
Baron, M.; Barbacki, A.; Man, A.; de Vries-Bouwstra, J.K.; Johnson, D.; Stevens, W.; Osman, M.; Wang, M.; Zhang, Y.;
Sahhar, J.
;
et al. Prediction of damage trajectories in systemic sclerosis using group-based trajectory modelling. Rheumatology
2023
,62,
3059–3066. [CrossRef]
191.
Maehara, T.; Kaneko, N.; Perugino, C.A.; Mattoo, H.; Kers, J.; Allard-Chamard, H.; Mahajan, V.S.; Liu, H.; Murphy, S.J.;
Ghebremichael, M.; et al. Cytotoxic CD4+ T lymphocytes may induce endothelial cell apoptosis in systemic sclerosis. J. Clin.
Investig. 2020,130, 2451–2464. [CrossRef]
192.
Frech, T.M.; Frech, M.; Saknite, I.; O’Connell, K.A.; Ghosh, S.; Baba, J.; Tkaczyk, E.R. Novel therapies and innovation for systemic
sclerosis skin ulceration. Best Pract. Res. Clin. Rheumatol. 2023,36, 101813. [CrossRef]
193. Hoa, S.; Stern, E.P.; Denton, C.P.; Hudson, M. Scleroderma Clinical Trials Consortium Scleroderma Renal Crisis Working Group
Investigators of the Scleroderma Clinical Trials Consortium Scleroderma Renal Crisis Working Group. Towards developing
criteria for scleroderma renal crisis: A scoping review. Autoimmun. Rev. 2017,16, 407–415. [CrossRef]
194.
Penn, H.; Quillinan, N.; Khan, K.; Chakravarty, K.; Ong, V.H.; Burns, A.; Denton, C.P. Targeting the endothelin axis in scleroderma
renal crisis: Rationale and feasibility. QJM 2013,106, 839–848. [CrossRef]
195.
Bandini, G.; Alunno, A.; Ruaro, B.; Galetti, I.; Hughes, M.; McMahan, Z.H. Significant gastrointestinal unmet needs in patients
with systemic sclerosis: Insights from a large international patient survey. Rheumatology 2023, kead486, Online ahead of print.
196.
Prasad, R.M.; Bellacosa, A.; Yen, T.J. Clinical and Molecular Features of Anti-CENP-B Autoantibodies. J. Mol. Pathol.
2021
,2,
281–295. [CrossRef]
197.
Ruaro, B.; Pozzan, R.; Confalonieri, P.; Tavano, S.; Hughes, M.; Matucci Cerinic, M.; Baratella, E.; Zanatta, E.; Lerda, S.; Geri, P.; et al.
Gastroesophageal Reflux Disease in Idiopathic Pulmonary Fibrosis: Viewer or Actor? To Treat or Not to Treat? Pharmaceuticals
2022,15, 1033. [CrossRef] [PubMed]
198.
Alqalyoobi, S.; Little, B.B.; Oldham, J.M.; Obi, O.N. The prognostic value of gastroesophageal reflux disorder in interstitial lung
disease related hospitalizations. Respir. Res. 2023,24, 97. [CrossRef] [PubMed]
199.
Biomarkers Definitions Working Group. Biomarkers and surrogate endpoints: Preferred definitions and conceptual framework.
Clin. Pharmacol. Ther. 2001,69, 89–95. [CrossRef] [PubMed]
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