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The Periostin Activation of Integrin Receptors on Sensory Neurons Induces Allergic Itch
Abstract
Chronic allergic itch is a major symptom that affects millions of people and animals, but its pathogenesis is not fully explained. Here, we show that one of the mediators abundantly present in the skin of patients with atopic dermatitis, periostin, induces itch via sensory neurons in mice, dogs, and monkeys. We identified the periostin receptor, the integrin αvβ3 expressed on a subset of sensory neurons. Using pharmacological and genetic approaches, we inhibited the function of this neuronal integrin αvβ3, which significantly reduced periostin-mediated itch in mice. Furthermore, we showed that the cytokine TSLP, and the application of the AD-causing MC903 (calcipotriol) and house dust mites induced periostin secretion. Finally, we established that the JAK/STAT pathway is a key regulator of periostin secretion in keratinocytes. Overall, our results identified a TSLP-periostin reciprocal activation that links the skin to the central nervous system via peripheral sensory neurons, and we characterized the non-canonical functional role of a neuronal integrin in itch behavior.
... In addition, murine models of AD also exhibit an overexpression of periostin by epidermal keratinocytes (KCs). Their chronic inflammation was robustly attenuated by the depletion of periostin or the blockade of periostin-integrin signals, indicating that one of the functions of periostin in allergic inflammation is to establish sustained chronic inflammation through the amplification of Th2-immune responses Mishra et al., 2020). ...
... Translational human studies have shown that dermal periostin correlates with itch intensities in several pruritic diseases (Hashimoto et al., 2021a(Hashimoto et al., , 2020a. Furthermore, periostin has recently been proved to serve as a pruritogen through the direct stimulation of nerve fibers by its receptor a V b 3 integrin (Mishra et al., 2020). It is also an indirect itch mediator that stimulates immune and/or nonimmune cells to secrete pruritogens. ...
... Periostin is one of the endogenous signaling mediators that is highly upregulated in various skin diseases. Strikingly, intradermal and subcutaneous injections of periostin into mice, dogs, and monkeys lead to robust scratching responses (Mishra et al., 2020). Contrary to the itch evoked by other exogenous and endogenous mediators, the periostin-evoked itch is one of the most conserved among multiple species (Olivry and Bäumer, 2015). ...
Periostin, an extracellular matrix and matricellular protein, binds to several types of integrins that transduce its signals. Its function in allergic inflammation is the establishment of sustained chronic inflammation through an amplification of T helper type 2‒immune responses. In addition, recent studies have shown a significant role of periostin in itch sensation through direct integrin-mediated stimulation of nerve fibers and interaction with immune and nonimmune cells (e.g., macrophages, eosinophils, basophils, and keratinocytes). The objective of this review is to describe the role of periostin in itch induction in human and animal models and its expression in human pruritic conditions.
... Arima et al. [21] found periostin to be expressed in significant amounts in the skin of patients with psoriasis, and the authors confirmed through immunohistochemical analysis that periostin was involved with the development of epidermal hyperplasia in AD and psoriasis patients. Recently, we found that intradermal injection of periostin in mice and dogs and subcutaneous injection in monkeys induced robust scratching behavior; we also found that periostin directly activates integrin receptor avb3 (Fig. 1), which is located on DRG sensory neurons [22]. Furthermore, mice treated with topical applications to induce chronic allergic itch similar to that of AD expressed elevated levels of periostin, indicating that periostin works as an endogenous mediator of itch [22]. ...
... Recently, we found that intradermal injection of periostin in mice and dogs and subcutaneous injection in monkeys induced robust scratching behavior; we also found that periostin directly activates integrin receptor avb3 (Fig. 1), which is located on DRG sensory neurons [22]. Furthermore, mice treated with topical applications to induce chronic allergic itch similar to that of AD expressed elevated levels of periostin, indicating that periostin works as an endogenous mediator of itch [22]. ...
... The authors posit that keratinocytes release TSLP, which activates a subset of sensory neurons that express TRPA1 to evoke itch [23]. TSLP has also been found to activate periostin release from keratinocytes, possibly explaining the vicious cycle of chronic itch in AD where cytokines such as TSLP induce the release of other cytokines, creating a reciprocal loop where increasing amounts of each cytokine are produced [22]. Similarly, a study on mice treated with ovalbumin (OVA) showed that TSLP in keratinocytes is required for allergic inflammation in skin [24]. ...
Millions of people globally suffer from allergic diseases, and the cases have been rising in the past decades. One of the major manifestations of allergic diseases is itch, which is an unpleasant symptom that triggers the urge to scratch and greatly affects the quality of life. Thus, research on how sensation of itch is detected/transmitted from the contact of the allergen to the nervous system is crucial in mitigating itch. Recent studies have attempted to elucidate the mechanisms of itch in allergic diseases. Here, we aim to review the endogenous mediators released from immune/nonimmune skin cells (that are indirectly involved in the propagation of itch) and the sensory neurons that express receptors for these itch mediators that are associated with direct transmission of itch in cutaneous allergic diseases. As the mechanisms for allergic itch become clearer, new therapeutic approaches to relieve itch are likely to be developed. Recent clinical trials are testing numerous compounds that target the endogenous mediators and their receptors. These studies provide the possibility of more effective itch treatment for allergic diseases.
... the induction of IL-31 protein [43]. Interleukin-31 binds to a heterodimeric receptor complex consisting of IL-31 receptor α (IL-31RA) and oncostatin M receptor β (OSMRβ) which is present at epithelial cells including keratinocytes, monocytes/ macrophages, mast cells, dendritic cells, basophils and cutaneous (IL-31RA/TRPV1+/TRPA1+) C fibers and in highest density in dorsal-root ganglia neurons [13,28,38,40,44]. These IL-31-affine dorsal-root ganglia neurons possess sensors for both pruritogens and neurogenic inflammation mediators [13]. ...
... Alongside IL-4 and transforming growth factor β, IL-13 is one of the triggers that upregulates the expression of periostin, a central itch inducing extracellular matrix protein secreted by epithelial and endothelial cells as well as by fibroblasts [44]. Hashimoto et al. recently demonstrated periostin to be enhanced in CNPG compared to healthy controls [40]. ...
Introduction:
Prurigo nodularis (PN) or chronic prurigo of nodular type (CNPG) is a subtype of chronic prurigo with severe pruritus and neuroimmune underlying pathophysiology occurring in a plethora of dermatological, systemic, neurologic, and psychiatric conditions.
Areas covered:
We review the increasing repertoire of biologics in the treatment of CNPG focusing on those targeting interleukins 4, 13, 31, oncostatin M and IgE. Presented information is based on a database research on current clinical trials (clinicaltrials.gov, European Clinical Trials Database (EudraCT), US clinical trial registry ICH-GCP) and a PubMed search for latest publications conducted with the combinations of the terms "chronic prurigo", "prurigo nodularis", "pathophysiology", "treatment", "therapy" and "biologics".
Expert opinion:
CNPG gets more and more attention as new therapeutic targets have been revealed in recent years, thus allowing the use of targeted approaches. The off-label advent of dupilumab offered advanced insight into the pathogenesis of CNPG and showed an impressive relief of pruritus in the vast majority of patients. New therapies including biologics (e.g., nemolizumab, tralokinumab, lebrikizumab), small molecules (e.g., neurokinin-1 receptor antagonists, janus kinase inhibitors) as well as mu-opioid receptor antagonists and nalbuphine, a μ-antagonist/κ-agonist, are in the pipeline and offer new hope for an improved future patient care.
... Several itch mediators and their corresponding receptors are reported to be responsible for itch in AD, including histamine (H) and its H1 and H4 receptors (H1R and H4R), 80 (Table 1). 94 Interestingly, skin inflammation is highly involved in the production of these mediators. Some of the important mediators in atopic itch are mentioned in the following sections. ...
... 105 Because periostin induces TSLP secretion by keratinocytes, an amplification loop involving periostin and TSLP is considered to be a mechanism of the dermal remodeling and epidermal hyperplasia typical of chronic AD. 45,105,106 Recently, it was demonstrated that periostin induced itch in mice, dogs and monkeys and the integrin aVb3 was identified as the periostin neuronal receptor. 94 In addition, given that keratinocytes release periostin in response to TSLP, it was found that an amplification loop involving periostin and TSLP may also be involved in chronic allergic itch. 94 ...
Atopic dermatitis is a common, chronic inflammatory skin disease that is characterized by skin barrier dysfunction, inflammation and intense itch. Although the exact mechanisms behind its pathogenesis remain unclear, it is evident that the complex interplay among barrier dysfunction, inflammation and itch are critical in its development, progression and chronicity. Abnormalities in filaggrin, intercellular lipids and tight junctions induce barrier‐disrupted skin, which produces thymic stromal lymphopoietin, interleukin (IL)‐25 and IL‐33; these in turn promote skin inflammation characterized by type 2 immune deviation. This inflammation then downregulates the expression of filaggrin in keratinocytes and exacerbates epidermal barrier dysfunction. Furthermore, various itch mediators/pruritogens produced during this inflammatory process can act directly on sensory nerves and cause itch. In this review, we summarize the basics and recent advances in our understanding of the pathophysiology of atopic dermatitis focusing on three aspects: barrier dysfunction, skin inflammation and itch.
... These cytokines are believed to rapidly bind to membrane receptor in order to generate innate immune response and therefore prime adaptive immune cells. Strikingly, two recent studies have demonstrated that TSLP directly activates neurons 45,46 . Additionally, our current data highly regulated TSLP in the brain in the settings of EAE coincides with previous study 47 and go beyond by demonstrating that TSLP receptor signals by phosphorylation of JAK2 to activate NLRP3-mediated inflammation in response to MOG administration. ...
Hyperactivation of NLRP3 inflammasome contributes to the neuroinflammation in autoimmune disorders, but the underlying regulating mechanism remains to be elucidated. We here demonstrate that mice lacking thymic stromal lymphopoietin receptor gene (Tslpr-/-) exhibit significant decreases in experimental autoimmune encephalitis (EAE) score, reduced CD4+ T cells infiltration, and restored expression of myelin basic protein (MBP) in the brain after induction of EAE by injection of myelin oligodendrocyte glycoprotein35-55 (MOG35-55) . TSLPR signals through Janus Kinase 2 (JAK2) to activate NLRP3. Tslpr-/- mice of EAE show decreased phosphorylation of JAK2 and expression of NLRP3 in the brain. In wild type (WT) mice after induction of EAE, inhibition of JAK2 by ruxolitinib inflammatory and CD4+ cell infiltration, decreased expression of NLRP3, and restored BMP expression in the brain. Ruxolitinib also decreased levels of IL-1β and TSLP in brain of EAE mouse when compared to that without ruxolitinib treatment. Further results with NLRP3 inhibitor MCC950 in EAE mouse of WT verified the proinflammatory role of NLRP3 by showing decreased inflammatory cells and CD4+ T cells, restored MBP expression, and declined levels of IL-1β and TSLP in the brain. In patients with anti-N-methyl-D-aspartate receptor (NMDAR) encephalitis we found increased level of NLRP3 and IL-1β in CSF when compared to that in control subjects. These findings highlight TSLP as a prospective target for treating JAK2-NLRP3 axis-associated autoimmune inflammatory disorders.
... 50 Finally, a marker of interest is periostin, an extracellular matrix glycoprotein secreted primarily by dermal fibroblasts, which promotes Th2 immunity and fibrosis (Figure 2; box G). 51,52 Its expression was shown to be increased in both serum and skin from individuals with RDEB, 53 while other recent studies demonstrated its relevance in BP, stasis dermatitis and chronic allergic itch. 34,49,54 Role of wound healing in epidermolysis bullosaassociated itch ...
Epidermolysis bullosa (EB) is a highly diverse group of inherited skin disorders, resulting from mutations in genes encoding proteins of the dermal‐epidermal junction (DEJ). Itch (pruritus) is one of the commonest symptoms across all EB subtypes. It occurs in blistered or wounded sites, or manifests as a generalized phenomenon, thereby affecting both intact skin and healing wounds. The mechanism of pruritus in EB is unclear. It is likely that skin inflammation secondary to barrier disruption, wound healing cascades and dysregulated activation of epidermal sensory nerve endings are all involved in its pathophysiology on the molecular and cellular level. Understanding these mechanisms in depth is crucial in developing optimised treatments for people with EB and improving quality of life. This review summarises current evidence on the prevalence, mechanisms and management of itch in EB.
... More recently, Mishra et al. discovered that the extracellular matrix protein periostin can provoke robust itch in multiple mammalian species, including non-human primates (Mishra et al., 2020). The authors demonstrated in mice that the pruritic effect of periostin is mediated by binding its receptor a V b3 on DRG neurons and was dependent on the presence of BNP ( Figure 3). ...
Although the medical definition of itch has been in existence for 360 years, only in the last 20 years have we begun to understand the basic mechanisms that underlie this unique sensation. Therapeutics that specifically target chronic itch as a pathologic entity are currently still not available. Recent seminal advances in itch circuitry within the nervous system have intersected with discoveries in immunology in unexpected ways to rapidly inform emerging treatment strategies. The current review aims to introduce these basic concepts in itch biology and highlight how distinct immunologic pathways integrate with recently identified itch-sensory circuits in the nervous system to inform a major new paradigm of neuroimmunology and therapeutic development for chronic itch.
Itch is a universally experienced sensation, and chronic itch can be as diabolically debilitating as pain. Recent advances have not only identified the neuronal itch sensing circuitry, but also have uncovered the intricate interactions between skin and immune cells that work together with neurons to identify itch-inducing irritants. In this review, we will summarize the fundamental mechanisms of acute itch detection in the skin, as well as highlight the recent discoveries relating to this topic.
Atopic dermatitis (AD) is one of the most common itch-inducing allergic skin diseases in humans and animals (1, 2). Interleukin (IL)-31, a cytokine involved in immune response in inflammatory diseases such as AD, has been demonstrated to cause itch by acting on receptors in a subset of transient receptor potential vanilloid (TRPV1) neurons (3–5). We recently identified a small subset of neurons that function as the primary detectors of chemical pruritic stimuli. We showed that the neuropeptide natriuretic polypeptide b (NPPB) is required for the transmission of itch signals and marks the full complement of itch responsive neurons at the periphery (6). However, it remains unknown how itch signals in AD are transmitted by the primary afferents of the sensory neurons in the dorsal root ganglia (DRG) to the spinal cord. This study is aimed to determine if NPPB is involved as a neuropeptide in IL-31-mediated itch in AD via natriuretic polypeptide receptor A (NPRA) in the spinal cord.
Stimuli that elicit itch are detected by sensory neurons that innervate the skin. This information is processed by the spinal cord; however, the way in which this occurs is still poorly understood. Here we investigated the neuronal pathways for itch neurotransmission, particularly the contribution of the neuropeptide somatostatin. We find that in the periphery, somatostatin is exclusively expressed in Nppb+neurons, and we demonstrate that Nppb+somatostatin+cells function as pruriceptors. Employing chemogenetics, pharmacology and cell-specific ablation methods, we demonstrate that somatostatin potentiates itch by inhibiting inhibitory dynorphin neurons, which results in disinhibition of GRPR+neurons. Furthermore, elimination of somatostatin from primary afferents and/or from spinal interneurons demonstrates differential involvement of the peptide released from these sources in itch and pain. Our results define the neural circuit underlying somatostatin-induced itch and characterize a contrasting antinociceptive role for the peptide.
Atopic dermatitis (AD) is a chronic, pruritic, and allergic skin disease in humans and animals, particularly dogs. Canine AD (cAD) has received attention as a spontaneous atopic animal model because domesticated dogs inhabit a human environment, and cAD shares several clinicopathological features with human AD (hAD). In hAD, periostin (PO) is suggested to play a critical role in the enhancement and chronicity of allergic skin inflammation; however, PO involvement in the pathogenesis of cAD is unknown. Here we aimed to clarify PO involvement in the pathophysiology of cAD and focused on the inducing factor and function of PO in canine atopic skin. Using double-labeled in situ hybridization (ISH), interleukin (IL)-13 mRNA-positive cells were detected near the keratinocytes and dermal fibroblasts expressing PO mRNA in atopic skin. Using an in vitro assay, IL-13 induced PO gene expression in both canine dermal fibroblasts and keratinocytes. PO enhanced in vitro growth of canine keratinocytes. Moreover, among PO-induced genes in cultured canine keratinocytes detected using a microarray, we identified IL-25 as a possible mediator in canine atopic skin. In addition, real time polymerase chain reaction (PCR) analysis revealed upregulation of IL-25 gene expression in PO-stimulated keratinocytes. These data suggest that IL-13 possibly derived from T helper 2 (Th2) cells stimulates PO production in both keratinocytes and fibroblasts, and then PO may play a critical role in the pathophysiology of cAD, particularly in the enhancement and chronicity of skin lesions via IL-25.
Background:
It has been reported that topical hypochlorous acid (HOCl) formulations lead to relief of itch in human patients with atopic dermatitis, however the specific anti-pruritic mechanism of action remains unclear.
Objective:
To confirm itch relief and reduction of lesions in a mouse model of atopic dermatitis and to elucidate possible HOCl's mode of action.
Methods:
In this study, the effects of topical administration of HOCl hydrogel (0.05%) on atopic dermatitis-like lesions in NC/Nga mice model as well as in vitro effects of HOCl on dorsal root ganglia neurons and mouse bone marrow derived dendritic cells (mBMDC) were investigated. NC/Nga mice were sensitized with house dust mite allergen and treated topically with HOCl hydrogel both preventively as well as therapeutically against established lesions. Allergen challenge was continued during HOCl hydrogel application.
Results:
Treatment with HOCl hydrogel prevented the development of lesions and scratching bouts during the whole observation period. When administered after full development of lesions, HOCl reduced lesions and scratching behaviour to a similar extent as a positive control 0.1% betamethasone dipropionate ointment. The reduced inflammatory response by HOCl treatment was demonstrated by reduced secretion of inflammatory cytokines in affected skin tissue from NC/Nga mice. In addition, HOCl significantly reduced IL-12 production in mBMDC. The diminished scratching behaviour was confirmed by impaired response to several pruritogens in dorsal root ganglia neurons excised from NC/Nga mice after termination of the studies. The response to the stimuli was also reduced by pre-incubation of sensory neurons from untreated BALB/c mice with 0.0001% HOCl.
Conclusions and clinical relevance:
These data indicate a direct reduction of sensory response by HOCl, leading to significantly reduced itch and inflammation in vivo. This article is protected by copyright. All rights reserved.
Background:
There is a lack of data on the burden of atopic dermatitis (AD) in adults relative to the general population.
Objective:
To characterize the AD burden in adult patients relative to both matched non-AD controls and matched patients with psoriasis in terms of comorbidities, health care resource utilization (HCRU), and costs.
Methods:
Adults (≥18 years) who self-reported a diagnosis of AD or psoriasis and adult non-AD controls were identified from the 2013 US National Health and Wellness Survey. Patients with AD were propensity score-matched with non-AD controls and patients with psoriasis on demographic variables. Patient-reported outcomes were analyzed between matched cohorts.
Results:
Patients with AD had a significantly greater risk for atopic comorbidities, as well as significantly greater HCRU and total cost compared with non-AD controls. The burden of AD was generally comparable to that of psoriasis, although patients with AD reported increased use of emergency room visits compared with patients with psoriasis.
Limitations:
Patient-reported data are susceptible to recall bias and erroneous classification.
Conclusions:
Adult patients with AD reported a substantial disease burden, suggesting an unmet need for more effective AD treatment options.
The trigeminal ganglion contains somatosensory neurons that detect a range of thermal, mechanical and chemical cues and innervate unique sensory compartments in the head and neck including the eyes, nose, mouth, meninges and vibrissae. We used single-cell sequencing and in situ hybridization to examine the cellular diversity of the trigeminal ganglion in mice, defining thirteen clusters of neurons. We show that clusters are well conserved in dorsal root ganglia suggesting they represent distinct functional classes of somatosensory neurons and not specialization associated with their sensory targets. Notably, functionally important genes (e.g. the mechanosensory channel Piezo2 and the capsaicin gated ion channel Trpv1) segregate into multiple clusters and often are expressed in subsets of cells within a cluster. Therefore, the 13 genetically-defined classes are likely to be physiologically heterogeneous rather than highly parallel (i.e., redundant) lines of sensory input. Our analysis harnesses the power of single-cell sequencing to provide a unique platform for in silico expression profiling that complements other approaches linking gene-expression with function and exposes unexpected diversity in the somatosensory system.
Background:
There are sparse and conflicting data regarding the long-term clinical course of atopic dermatitis (AD). Although often described as a childhood disease, newer population-based estimates suggest the prevalence of pediatric and adult disease may be similar.
Methods:
Our objective was to determine whether there is a decline in the prevalence of AD in population-based cohorts of patients followed longitudinally beyond childhood. We conducted a systematic review and meta-analysis including studies assessing AD prevalence across 3 or more points in time. The primary outcome was weighted overall risk difference (percentage decrease in AD prevalence).
Results:
Of 2080 references reviewed, 7 studies with 13 515 participants were included. Participants were assessed at 3-6 time points, ranging from age 3 months to 26 years. The percentage decrease in prevalence after age 12 was 1%, which was not significantly different from zero (95% confidence interval -2%-5%). Similar results were found with other age cut-offs.
Conclusion:
The prevalence of AD in longitudinal birth cohort studies is similar in childhood and adolescence/early adulthood.
Skin is an organ that is susceptible to damage by external injury, chronic inflammation, and autoimmunity. Tissue damage causes alterations in both the configuration and type of cells in lesional skin. This phenomenon, called tissue remodeling, is a universal biological response elicited by programmed cell death, inflammation, immune disorders, and tumorigenic, tumor proliferative, and cytoreductive activity. In this process, changes in the components of the extracellular matrix are required to provide an environment that facilitates tissue remodeling. Among these extracellular matrix components, periostin, a glycoprotein that is predominantly secreted from dermal fibroblasts, has attracted attention. Periostin localizes in the papillary dermis of normal skin, and is aberrantly expressed in the dermis of lesional skin in atopic dermatitis, scar, systemic/limited scleroderma, melanoma, cutaneous T cell lymphoma, and skin damage caused by allergic/autoimmune responses. Periostin induces processes that result in the development of dermal fibrosis, and activate or protract the immune response. The aim of this review was to summarize recent knowledge of the role of periostin in the pathogenesis of dermatoses, and to explore whether periostin is a potential therapeutic target for skin diseases.
We found for the first time that IL-4 and IL-13, signature type 2 cytokines, are able to induce periostin expression. We and others have subsequently shown that periostin is highly expressed in chronic inflammatory diseases-asthma, atopic dermatitis, eosinophilc chronic sinusitis/chronic rhinosinusitis with nasal polyp, and allergic conjunctivitis-and that periostin plays important roles in the pathogenesis of these diseases. The epithelial/mesenchymal interaction via periostin is important for the onset of allergic inflammation, in which periostin derived from fibroblasts acts on epithelial cells or fibroblasts, activating their NF-κB. Moreover, the immune cell/non-immune cell interaction via periostin may be also involved. Now the significance of periostin has been expanded into other inflammatory or fibrotic diseases such as scleroderma and pulmonary fibrosis. The cross-talk of periostin with TGF-β or pro-inflammatory cytokines is important for the underlying mechanism of these diseases. Because of its pathogenic importance and broad expression, diagnostics or therapeutic drugs can be potentially developed to target periostin as a means of treating these diseases.
Background:
Although most patients with atopic dermatitis (AD) are effectively managed with topical medication, a significant minority require systemic therapy. Guidelines for decision making about advancement to systemic therapy are lacking.
Objective:
To guide those considering use of systemic therapy in AD and provide a framework for evaluation before making this therapeutic decision with the patient.
Methods:
A subgroup of the International Eczema Council determined aspects to consider before prescribing systemic therapy. Topics were assigned to expert reviewers who performed a topic-specific literature review, referred to guidelines when available, and provided interpretation and expert opinion.
Results:
We recommend a systematic and holistic approach to assess patients with severe signs and symptoms of AD and impact on quality of life before systemic therapy. Steps taken before commencing systemic therapy include considering alternate or concomitant diagnoses, avoiding trigger factors, optimizing topical therapy, ensuring adequate patient/caregiver education, treating coexistent infection, assessing the impact on quality of life, and considering phototherapy.
Limitations:
Our work is a consensus statement, not a systematic review.
Conclusion:
The decision to start systemic medication should include assessment of severity and quality of life while considering the individual's general health status, psychologic needs, and personal attitudes toward systemic therapies.
Background:
Given its public health impact, there is need for broad and representative data on the humanistic burden of atopic dermatitis (AD).
Objective:
To establish the humanistic burden of AD in US adults.
Methods:
Data were from the 2013 US National Health and Wellness Survey; AD self-reports were propensity-matched with non-AD controls and with psoriasis controls. Bivariate analyses were conducted on burden outcomes between the AD and control groups.
Results:
Demographics and baseline characteristics were comparable between matched groups. Subjects with AD (n = 349) versus non-AD controls (n = 698) had significantly higher rates of anxiety, depression, and sleep disorders (29.8%, 31.2%, and 33.2% vs 16.1%, 17.3%, and 19.2%, respectively [all P < .001]); a lower Short Form-36 v2 mental component summary score (44.5 vs 48.0, respectively [P < .001]); a lower physical component summary score (47.6 vs 49.5, respectively [P = .004]), and lower health utilities (0.67 vs 0.72, respectively [P < .001]) in addition to a higher work absenteeism rate (9.9% vs 3.6%, respectively [P < .001]) and activity impairment rate (33.6% vs 25.2%, respectively [P < .001]). Subjects with AD and psoriasis controls (n = 260 each) showed similar impairment in health-related quality of life and productivity.
Limitations:
Data were self-reported.
Conclusion:
AD is associated with a substantial humanistic burden that is similar in magnitude to that of psoriasis, which is also recognized for its debilitating symptoms, indicating the need for more effective treatments for AD.
Itch is an unpleasant cutaneous sensation that can arise following insect bites, exposure to plant ingredients, and some diseases. Itch can also have idiopathic causes. Itch sensations are thought to protect against external insults and toxic substances. Although itch is not directly lethal, chronic and long lasting itch in certain diseases can worsen quality of life. Therefore, the mechanisms responsible for chronic itch require careful investigation. There is a significant amount of basic research concerning itch, and the effect of various itch mediators on primary sensory neurons have been studied. Interestingly, many mediators of itch involve signaling related to transient receptor potential (TRP) channels. TRP channels, especially thermosensitive TRP channels, are expressed by primary sensory neurons and skin keratinocytes, which receive multimodal stimuli, including those that cause itch sensations. Here we review the molecular and cellular mechanisms of itch and the involvement of TRP channels in mediating itch sensations.
The Cre/lox system is widely used in mice to achieve cell-type-specific gene expression. However, a strong and universally responding system to express genes under Cre control is still lacking. We have generated a set of Cre reporter mice with strong, ubiquitous expression of fluorescent proteins of different spectra. The robust native fluorescence of these reporters enables direct visualization of fine dendritic structures and axonal projections of the labeled neurons, which is useful in mapping neuronal circuitry, imaging and tracking specific cell populations in vivo. Using these reporters and a high-throughput in situ hybridization platform, we are systematically profiling Cre-directed gene expression throughout the mouse brain in several Cre-driver lines, including new Cre lines targeting different cell types in the cortex. Our expression data are displayed in a public online database to help researchers assess the utility of various Cre-driver lines for cell-type-specific genetic manipulation.
Periostin is up-regulated in E-NP and is associated with disease severity and Th2 inflammatory markers. Periostin was produced by IgE-stimulated mast cells. Secreted periostin binds to integrin αV on the epithelial cell surface and induces TSLP release from epithelial cells in E-NP.
This study aimed to elucidate the associations between
interleukin-4
(
IL-4
) single nucleotide polymorphisms (SNPs), 590C/T and 589C/T, serum IL-4 levels, and atopic dermatitis (AD) in children.
Methods
. A total of 82 children with AD were randomly selected as the case group and divided into mild group (15 cases), moderate group (46 cases), and severe group (21 cases). Additionally, 100 healthy children were selected as the control group. Genotype frequencies of IL-4 SNPs were detected by PCR-RFLP. Serum IL-4 levels were measured by ELISA.
Results
. Significant differences were shown in genotype distributions and allele frequencies of 589C/T and allele frequencies of 590C/T (all
P
<
0.05
). Serum IL-4 levels in the mild, moderate, and severe groups were significantly higher than those in the control group; significant differences were found among these three groups with increased severity of AD. Serum IL-4 levels of heterozygote and mutant homozygote carriers in the mild, moderate, and severe groups were higher than wild homozygote carriers in those three groups and the control group (all
P
<
0.05
).
Conclusion
. 590T and 589T alleles of
IL-4
gene may be associated with high levels of serum IL-4, which may increase the risk of AD in children.
Keratinocytes are the first cells that come into direct contact with external tactile stimuli; however, their role in touch transduction in vivo is not clear. The ion channel Transient Receptor Potential Ankyrin 1 (TRPA1) is essential for some mechanically-gated currents in sensory neurons, amplifies mechanical responses after inflammation, and has been reported to be expressed in human and mouse skin. Other reports have not detected Trpa1 mRNA transcripts in human or mouse epidermis. Therefore, we set out to determine whether selective deletion of Trpa1 from keratinocytes would impact mechanosensation. We generated K14Cre-Trpa1fl/fl mice lacking TRPA1 in K14-expressing cells, including keratinocytes. Surprisingly, Trpa1 transcripts were very poorly detected in epidermis of these mice or in controls, and detection was minimal enough to preclude observation of Trpa1 mRNA knockdown in the K14Cre-Trpa1fl/fl mice. Unexpectedly, these K14Cre-Trpa1fl/fl mice nonetheless exhibited a pronounced deficit in mechanosensitivity at the behavioral and primary afferent levels, and decreased mechanically-evoked ATP release from skin. Overall, while these data suggest that the intended targeted deletion of Trpa1 from keratin 14-expressing cells of the epidermis induces functional deficits in mechanotransduction and ATP release, these deficits are in fact likely due to factors other than reduction of Trpa1 expression in adult mouse keratinocytes because they express very little, if any, Trpa1.
In this chapter we discuss the many recent discoveries of the mechanisms by which itch is transmitted: the neurotransmitters and the responses they trigger, the mechanisms by which specific neuronal targets are activated, and the specificity of the pathways. Current data reveal that DRG neurons and spinal cord cells use a remarkably selective set of transmitters to convey pruritic information from the periphery to the brain: glutamate and Nppb are released from primary itch-sensory cells; these molecules activate secondary spinal cord pruriceptive specific neurons, which in turn utilize Grp to activate tertiary pruriceptiveselective neurons. Intersecting this basic linear excitatory pathway, inhibitory input from dynorphin and neurons that express the somatostatin receptor modify itch sensation. Cumulatively, these studies paint an elegantly simple picture of how itch signals are transformed and integrated in the spinal cord and open new avenues for research efforts aimed at understanding and better treating itch.
There is currently no properly validated canine model of pruritus to reproduce the itch associated with atopic dermatitis (AD) of dogs and humans. Although a “canine model of atopic pruritus” was published recently, this model (laboratory beagles sensitized to house dust mite [HDM]) showed only inconsistent allergen-induced itch behaviour (1). Similarly, the application of cowhage spicules induces inconsistent itch in Maltese-beagle atopic (MBA) dogs, and this makes such model unsuitable for the evaluation of new therapeutic options (2). Recently, injections of recombinant canine interleukin-31 were found to induce itch in dogs (3). Importantly, modelling itch by stimulating only one pathway is fraught with the risk that interventions tested using such activators might not necessarily translate into clinical efficacy in atopic dogs or humans because of pruritogenic pathway redundancy. There is a model of flea allergy-induced itch, but it is poorly characterized (4). Our objectives were to validate a reproducible model of atopic itch in HDM-sensitized MBA dogs (5) in response to topically applied HDM. Additionally, we evaluated the effect of prednisolone, a standard-of-care anti-allergic drug.
For centuries, itch was categorized as a submodality of pain. Recent research over the last decade has led to the realization that itch is in fact a separate and distinct, albeit closely related, sensation. Chronic itch is a common complaint and has numerous etiologies. Various receptors (TRPA1, TRPV1, PAR2, gastrin-releasing peptide receptor (GRPR), Mas-related G proteins), secreted molecules (histamine, nerve growth factor (NGF), substance P (SP), proteases), and cytokines/chemokines (thymic stromal lymphopoietin (TSLP), IL-2, IL-4, IL-13, and IL-31) are implicated as mediators of chronic pruritus. While much remains unknown regarding the mechanisms of chronic itch, this much is certain: there is no singular cause of itch. Rather, itch is caused by a complex interface between skin, keratinocytes, cutaneous nerve fibers, pruritogenic molecules, and the peripheral and central nervous systems. Atopic dermatitis is one of the most itchy skin dermatoses and affects millions worldwide. The sensation of atopic itch is mediated by the interplay between epidermal barrier dysfunction, upregulated immune cascades, and the activation of structures in the central nervous system. Clinicians are in possession of an arsenal of different treatment options ranging from moisturizers, topical immunomodulators, topical anesthetic ion channel inhibitors, systemic immunomodulators, as well as oral drugs capable of reducing neural hypersensitization. Emerging targeted therapies on the horizon, such as dupilumab, promise to usher in a new era of highly specific and efficacious treatments. Alternative medicine, stress reduction techniques, and patient education are also important treatment modalities. This review will focus on the mediators of chronic pruritus mainly associated with atopic dermatitis (atopic itch), as well as numerous different therapeutic options.
Background:
Epidermal hyperplasia is a histological hallmark observed in both atopic dermatitis (AD) and psoriasis, although the clinical features and the underlying immunological disorders of these diseases are different. We previously showed that periostin, a matricellular protein, plays a critical role in epidermal hyperplasia in AD, using a mouse model and a 3-dimensional organotypic coculture system. In this study, we explore the hypothesis that periostin is involved in epidermal hyperplasia in psoriasis.
Methods:
To examine expression of periostin in psoriasis patients, we performed immunohistochemical analysis on skin biopsies from six such patients. To investigate periostin's role in the pathogenesis of psoriasis, we evaluated periostin-deficient mice in a psoriasis mouse model induced by topical treatment with imiquimod (IMQ).
Results:
Periostin was substantially expressed in the dermis of all investigated psoriasis patients. Epidermal hyperplasia induced by IMQ treatment was impaired in periostin-deficient mice, along with decreased skin swelling. However, upon treatment with IMQ, periostin deficiency did not alter infiltration of inflammatory cells such as neutrophils; production of IL-17, -22, or -23; or induction/expansion of IL-17- and IL-22-producing group 3 innate lymphoid cells.
Conclusions:
Periostin plays an important role during epidermal hyperplasia in IMQ-induced skin inflammation, independently of the IL-23-IL-17/IL-22 axis. Periostin appears to be a mediator for epidermal hyperplasia that is common to AD and psoriasis.
Thymic stromal lymphopoietin (TSLP) is an epithelial-derived cytokine similar to IL- 7, whose gene is located on chromosome 5q22.1 and it exerts its biological function through the TSLP-Receptor (TSLP-R). TSLP is expressed primarily by epithelial cells at barrier surfaces such as the skin, gut and lung in response to danger signals. Since it was cloned in 1994, there has been accumulating evidence that TSLP is crucial for the maturation of antigen presenting cells and hematopoietic cells. TSLP genetic variants and its dysregulated expression have been linked to atopic diseases such as atopic dermatitis, asthma, allergic rhinitis and eosinophilic esophagitis.
Extracellular matrix (ECM) is not only involved in the maintenance of normal physiological tissue but also in interactions with other ECM components, tissue remodeling, and modulating immune responses. The skin provides a distinctive environment characterized by rich fibroblasts producing various ECM proteins, epithelial-mesenchymal interactions, and immune responses induced by external stimuli.
Recently, periostin—a matricellular protein—has been highlighted for its pivotal functions in the skin. Analysis of periostin null mice has revealed that periostin contributes to collagen fibrillogenesis, collagen cross-linking, and the formation of ECM meshwork via interactions with other ECM components. Periostin expression is enhanced by mechanical stress or skin injury; this is indicative of the physiologically protective functions of periostin, which promotes wound repair by acting on keratinocytes and fibroblasts. Along with its physiological functions, periostin plays pathogenic roles in skin fibrosis and chronic allergic inflammation. In systemic sclerosis (SSc) patients, periostin levels reflect the severity of skin fibrosis. Periostin null mice have shown reduced skin fibrosis in a bleomycin-induced SSc mouse model, indicating a key role of periostin in fibrosis. Moreover, in atopic dermatitis (AD), attenuated AD phenotype has been observed in periostin null mice in a house dust mite extract-induced AD mouse model. Th2 cytokine-induced periostin acts on keratinocytes to produce inflammatory cytokines that further enhance the Th2 response, thereby sustaining and amplifying chronic allergic inflammation. Thus, periostin is deeply involved in the pathogenesis of AD and other inflammation-related disorders affecting the skin. Understanding the dynamic actions of periostin would be key to dissecting pathogenesis of skin-related diseases and to developing novel therapeutic strategies.
Menthol and other counterstimuli relieve itch, resulting in an antipruritic state that persists for minutes to hours. However, the neural basis for this effect is unclear, and the underlying neuromodulatory mechanisms are unknown. Previous studies revealed that Bhlhb5(-/-) mice, which lack a specific population of spinal inhibitory interneurons (B5-I neurons), develop pathological itch. Here we characterize B5-I neurons and show that they belong to a neurochemically distinct subset. We provide cause-and-effect evidence that B5-I neurons inhibit itch and show that dynorphin, which is released from B5-I neurons, is a key neuromodulator of pruritus. Finally, we show that B5-I neurons are innervated by menthol-, capsaicin-, and mustard oil-responsive sensory neurons and are required for the inhibition of itch by menthol. These findings provide a cellular basis for the inhibition of itch by chemical counterstimuli and suggest that kappa opioids may be a broadly effective therapy for pathological itch.
Periostin, an extracellular matrix protein belonging to the fasciclin family, has been shown to play a critical role in the process of remodeling during tissue/organ development or repair. Periostin functions as a matricellular protein in cell activation by binding to their receptors on cell surface, thereby exerting its biological activities. After we found that periostin is a downstream molecule of interleukin (IL)-4 and IL-13, signature cytokines of type 2 immune responses, we showed that periostin is a component of subepithelial fibrosis in bronchial asthma, the first formal proof that periostin is involved in allergic inflammation. Subsequently, a great deal of evidence has accumulated demonstrating the significance of periostin in allergic inflammation. It is of note that in skin tissues, periostin is critical for amplification and persistence of allergic inflammation by communicating between fibroblasts and keratinocytes. Furthermore, periostin has been applied to development of novel diagnostics or therapeutic agents for allergic diseases. Serum periostin can reflect local production of periostin in inflamed lesions induced by Th2-type immune responses and also can predict the efficacy of Th2 antagonists against bronchial asthma. Blocking the interaction between periostin and its receptor, αv integrin, or down-regulating the periostin expression shows improvement of periostin-induced inflammation in mouse models or in in vitro systems. It is hoped that diagnostics or therapeutic agents targeting periostin will be of practical use in the near future.
Although the cytokine IL-31 has been implicated in inflammatory and lymphoma-associated itch, the cellular basis for its pruritic action is yet unclear.
We sought to determine whether immune cell-derived IL-31 directly stimulates sensory neurons and to identify the molecular basis of IL-31-induced itch.
We used immunohistochemistry and quantitative real-time PCR to determine IL-31 expression levels in mice and human subjects. Immunohistochemistry, immunofluorescence, quantitative real-time PCR, in vivo pharmacology, Western blotting, single-cell calcium imaging, and electrophysiology were used to examine the distribution, functionality, and cellular basis of the neuronal IL-31 receptor α in mice and human subjects.
Among all immune and resident skin cells examined, IL-31 was predominantly produced by TH2 and, to a significantly lesser extent, mature dendritic cells. Cutaneous and intrathecal injections of IL-31 evoked intense itch, and its concentrations increased significantly in murine atopy-like dermatitis skin. Both human and mouse dorsal root ganglia neurons express IL-31RA, largely in neurons that coexpress transient receptor potential cation channel vanilloid subtype 1 (TRPV1). IL-31-induced itch was significantly reduced in TRPV1-deficient and transient receptor channel potential cation channel ankyrin subtype 1 (TRPA1)-deficient mice but not in c-kit or proteinase-activated receptor 2 mice. In cultured primary sensory neurons IL-31 triggered Ca(2+) release and extracellular signal-regulated kinase 1/2 phosphorylation, inhibition of which blocked IL-31 signaling in vitro and reduced IL-31-induced scratching in vivo.
IL-31RA is a functional receptor expressed by a small subpopulation of IL-31RA(+)/TRPV1(+)/TRPA1(+) neurons and is a critical neuroimmune link between TH2 cells and sensory nerves for the generation of T cell-mediated itch. Thus targeting neuronal IL-31RA might be effective in the management of TH2-mediated itch, including atopic dermatitis and cutaneous T-cell lymphoma.
Current knowledge about Periostin biology has expanded from its recognized functions in embryogenesis and bone metabolism to its roles in tissue repair and remodeling and its clinical implications in cancer. Emerging evidence suggests that Periostin plays a critical role in the mechanism of wound healing; however, the paracrine effect of Periostin in epithelial cell biology is still poorly understood. We found that epithelial cells are capable of producing endogenous Periostin that, unlike mesenchymal cell, cannot be secreted. Epithelial cells responded to Periostin paracrine stimuli by enhancing cellular migration and proliferation and by activating the mTOR signaling pathway. Interestingly, biomechanical stimulation of epithelial cells, which simulates tension forces that occur during initial steps of tissue healing, induced Periostin production and mTOR activation. The molecular association of Periostin and mTOR signaling was further dissected by administering rapamycin, a selective pharmacological inhibitor of mTOR, and by disruption of Raptor and Rictor scaffold proteins implicated in the regulation of mTORC1 and mTORC2 complex assembly. Both strategies resulted in ablation of Periostin-induced mitogenic and migratory activity. These results indicate that Periostin-induced epithelial migration and proliferation requires mTOR signaling. Collectively, our findings identify Periostin as a mechanical stress responsive molecule that is primarily secreted by fibroblasts during wound healing and expressed endogenously in epithelial cells resulting in the control of cellular physiology through a mechanism mediated by the mTOR signaling cascade.
Chronic itch is a major symptom of cutaneous T cell lymphoma (CTCL). In this issue of Neuron, Han and colleagues (2018) provide evidence that one of the itch mediators in CTCL is an extracellular miRNA that directly activates TRPA1 on sensory neurons.
Increasing evidence suggests that extracellular miRNAs may serve as biomarkers of diseases, but the physiological relevance of extracellular miRNA is unclear. We find that intradermal cheek injection of miR-711 induces TRPA1-depedent itch (scratching) without pain (wiping) in naive mice. Extracellular perfusion of miR-711 induces TRPA1 currents in both Trpa1-expressing heterologous cells and native sensory neurons through the core sequence GGGACCC. Computer simulations reveal that the core sequence binds several residues at the extracellular S5-S6 loop of TRPA1, which are critical for TRPA1 activation by miR-711 but not allyl isothiocyanate. Intradermal inoculation of human Myla cells induces lymphoma and chronic itch in immune-deficient mice, associated with increased serum levels of miR-711, secreted from cancer cells. Lymphoma-induced chronic itch is suppressed by miR-711 inhibitor and a blocking peptide that disrupts the miR-711/TRPA1 interaction. Our findings demonstrated an unconventional physiological role of extracellular naked miRNAs as itch mediators and ion channel modulators.
Recent studies have highlighted an emerging role for neuro-immune interactions in mediating allergic diseases. Allergies are caused by an overactive immune response to a foreign antigen. The peripheral sensory and autonomic nervous system densely innervates mucosal barrier tissues including the skin, respiratory tract and gastrointestinal (GI) tract that are exposed to allergens. It is increasingly clear that neurons actively communicate with and regulate the function of mast cells, dendritic cells, eosinophils, Th2 cells and type 2 innate lymphoid cells in allergic inflammation. Several mechanisms of cross-talk between the two systems have been uncovered, with potential anatomical specificity. Immune cells release inflammatory mediators including histamine, cytokines or neurotrophins that directly activate sensory neurons to mediate itch in the skin, cough/sneezing and bronchoconstriction in the respiratory tract and motility in the GI tract. Upon activation, these peripheral neurons release neurotransmitters and neuropeptides that directly act on immune cells to modulate their function. Somatosensory and visceral afferent neurons release neuropeptides including calcitonin gene-related peptide, substance P and vasoactive intestinal peptide, which can act on type 2 immune cells to drive allergic inflammation. Autonomic neurons release neurotransmitters including acetylcholine and noradrenaline that signal to both innate and adaptive immune cells. Neuro-immune signaling may play a central role in the physiopathology of allergic diseases including atopic dermatitis, asthma and food allergies. Therefore, getting a better understanding of these cellular and molecular neuro-immune interactions could lead to novel therapeutic approaches to treat allergic diseases.
Integrins modulate chemically-induced nociception in a variety of inflammatory and neuropathic pain models. Yet, the role of integrins in mechanically-induced pain remains undefined, despite its well-known involvement in cell adhesion and mechanotransduction. Excessive spinal facet capsular ligament stretch is a common injury that induces morphological and functional changes in its innervating afferent neurons and can lead to pain. However, the local mechanisms underlying the translation from tissue deformation to pain signaling are unclear, impeding effective treatment. Therefore, the involvement of the integrin subunit β1 in pain signaling from facet injury was investigated in complementary in vivo and in vitro studies. An anatomical study in the rat identified expression of the integrin subunit β1 in dorsal root ganglion (DRG) neurons innervating the facet, with greater expression in peptidergic than non-peptidergic DRG neurons. Painful facet capsule stretch in the rat upregulated the integrin subunit β1 in small- and medium-diameter DRG neurons at day 7. Inhibiting the α2β1 integrin in a DRG-collagen culture prior to its stretch injury prevented strain-induced increases in axonal substance P (SP) in a dose-dependent manner. Together, these findings suggest that integrin subunit β1-dependent pathways may contribute to SP-mediated pain from mechanical injury of the facet capsular ligament.
Mammals have evolved neurophysiologic reflexes, such as coughing and scratching, to expel invading pathogens and noxious environmental stimuli. It is well established that these responses are also associated with chronic inflammatory diseases, including asthma and atopic dermatitis. However, the mechanisms by which inflammatory pathways promote sensations such as itch remain poorly understood. Here, we show that type 2 cytokines directly activate sensory neurons in both mice and humans. Further, we demonstrate that chronic itch is dependent on neuronal IL-4Rα and JAK1 signaling. We also observe that patients with recalcitrant chronic itch that failed other immunosuppressive therapies markedly improve when treated with JAK inhibitors. Thus, signaling mechanisms previously ascribed to the immune system may represent novel therapeutic targets within the nervous system. Collectively, this study reveals an evolutionarily conserved paradigm in which the sensory nervous system employs classical immune signaling pathways to influence mammalian behavior.
Significance
In the United States, the most common cause of allergic contact dermatitis (ACD) is contact with poison ivy. Severe itch and skin inflammation are the major manifestations of poison ivy-induced ACD. In this study, we have established a critical role of IL-33/ST2 (interleukin 33/growth stimulation expressed gene 2) signaling in both itch and skin inflammation of poison ivy-induced ACD and revealed a previously unidentified interaction of IL-33/ST2 signaling with primary sensory neurons that may underlie the pruritic mechanisms of poison ivy-induced ACD. Blocking IL-33/ST2 signaling may represent a therapeutic approach to ameliorate itch and skin inflammation related to poison ivy dermatitis and, possibly, other chronic itch conditions in which IL-33/ST2 signaling may participate.
Integrins are transmembrane receptors composed of one α subunit and one β subunit and involved in cellular growth, differentiation, and apoptosis. The collagen-binding integrins α1β1 and α2β1 have been shown to regulate wound and tumor vascularization by different mechanisms. In this study, we assessed wound and tumor vascularization in mice with genetic ablation of both integrin subunits α1 and α2, which resulted in loss of integrins α1β1 and α2β1. Wound angiogenesis was investigated in excisional wounds that were inflicted on the back skin of control and mice lacking integrin α1β1 and α2β1. Mutant mice displayed reduced wound angiogenesis, which correlated with decreased macrophage numbers at 3 and 7 days after injury, and showed significantly attenuated vascularization of sponge implants. Angiogenesis induced by tumors arising from intradermal injection of B16 F1 melanoma cells was also reduced in comparison to controls 7 days after injection. This reduction in angiogenesis correlated with increased levels and activity of circulating matrix metalloproteinase 9 and elevated angiostatin levels in plasma of mutant mice, which reduced endothelial cell proliferation. Ex vivo mutant aortic ring explants developed significantly fewer and thinner aortic sprouts with fewer branch points than controls because of impaired endothelial cell proliferation. In conclusion, the loss of integrins α1β1 and α2β1 in mice results in reduced wound and tumor angiogenesis by cell-autonomous and extrinsic mechanisms.
Thymic stromal lymphopoietin (TSLP) activates dendritic cells to induce Th2-mediated inflammation. Periostin, an extracellular matrix protein produced by fibroblasts, induces chronic inflammation by stimulating TSLP production. Recently, a reinforcing cycle linking Th2-type immune responses with periostin-induced keratinocyte activation has been proposed in atopic dermatitis pathogenesis. In this study, we investigated the role of TSLP and periostin in the development of cutaneous T cell lymphoma (CTCL), where Th2 cytokines and chemokines are also dominant. TSLP and periostin mRNA expression levels were elevated in CTCL lesional skin, both of which correlated with interleukin (IL)-4 expression levels. In vitro and ex vivo, IL-4 or IL-13 stimulated periostin expression by dermal fibroblasts, and fibroblasts from CTCL lesional skin expressed higher levels of periostin than those from control skin. Serum periostin levels of CTCL patients were also significantly higher than those of healthy individuals. Hut78 and MJ, CTCL cell lines, and peripheral blood mononuclear cells from leukemic CTCL patients expressed the TSLP receptor. TSLP induced production of IL-4 and IL-13 by Hut78 and MJ cells through the activation of signal transducer and activator of transcription 5. Moreover, TSLP induced proliferation of CTCL cells both in vitro and in vivo. These data suggest that periostin-mediated TSLP production by keratinocytes directly stimulates CTCL tumor cell growth in addition to inducing a Th2-dominant tumor environment in CTCL.
Itch is the most common clinical problem seen in dogs with skin diseases. Although an etiological classification of canine pruritus does not yet exist, most causes would likely fall into the IFSI class I (dermatological) itch. One of the most common causes of canine itch is that associated with atopic dermatitis, and there is randomized controlled trial grade evidence of the efficacy of several antipruritic interventions. At this time, the mainstay of treatment of canine atopic itch relies principally on the use of topical and/or oral glucocorticoids and oral cyclosporine. Type 1 receptor antihistamines are notorious in their inconsistency in reducing pruritus in atopic dogs. A new Janus kinase (JAK)-1 inhibitor has recently been approved for treatment of allergic itch in dogs, and its onset of efficacy is remarkably fast. Modeling itch in dogs can be achieved by allergen sensitization (fleas, house dust mites), and challenges that elicit pruritic manifestation can be used for mechanistic studies as well as for testing of novel anti-itch modalities.
Cytokines classically are secreted “messenger” proteins that modulate cellular function of immune cells. Chemokines attract immune cells to the site where they exert various functions in inflammation, autoimmunity or cancer. Increasing evidence is emerging that cytokines or chemokines can act as “neuromodulators” by activating high-affinity receptors on peripheral or central neurons, microglia cells or Schwann cells. Very recently, cytokines have been shown to act as pruritogens in rodents and humans, while a role of chemokines initch has thus far been only demonstrated in mice. Upon stimulation, cytokines are released by skin or immune cells and form a “bridge of communication” between the immune and nervous system. For some cytokines such as IL-31 and TSLP, the evidence for this role is strong in rodents. For cytokines such as IL-4, there is some convincing evidence, while for cytokines such as oncostatin M, IL-2, IL-6, IL-8 and IL-13, direct evidence is currently limited. Current clinical trials support the idea that cytokines and chemokines and their receptors or signalling pathways are promising targets for the future therapy of certain subtypes of itch.
Oncostatin M (OSM) and interleukin-31 (IL-31) are two cytokines belonging to the IL-6 family which share a common signaling receptor subunit, the OSM receptor beta (OSMRβ). Both of them are released by monocytes/macrophages, dendritic cells and T lymphocytes in inflammatory situations and upon binding to their respective receptor complexes they signal mainly via the JAK/STAT pathway. Besides sharing many biochemical properties, both display divergent physiological functions. This review summarizes aspects of cytokine transcription and biosynthesis, cytokine-receptor interactions, cross-species activities, signal transduction and physiology delineated from recent findings in genetic mouse models for both cytokines, OSM and IL-31.
Copyright © 2015. Published by Elsevier Ltd.
TRP channels are expressed in various cells in skin. As an organ system to border the host and environment, many nonneuronal cells, including epidermal keratinocytes and melanocytes, express several TRP channels functionally distinct from sensory processing. TRPV1 and TRPV3 in keratinocytes of the epidermis and hair apparatus inhibit proliferation, induce terminal differentiation, induce apoptosis, and promote inflammation. Activation of TRPV4, 6, and TRPA1 promotes regeneration of the severed skin barriers. TRPA1 also enhances responses in contact hypersensitivity. TRPCs in keratinocytes regulate epidermal differentiation. In human diseases with pertubered epidermal differentiation, the expression of TRPCs are altered. TRPMs, which contribute to melanin production in melanocytes, serve as significant prognosis markers in patients with metastatic melanoma. In summary, not only act in sensory processing, TRP channels also contribute to epidermal differentiation, proliferation, barrier integration, skin regeneration, and immune responses. In diseases with aberrant TRP channels, TRP channels might be good therapeutic targets.
Nociception is the process whereby primary afferent nerve fibers of the somatosensory system detect noxious stimuli. Pungent irritants from pepper, mint, and mustard plants have served as powerful pharmacological tools for identifying molecules and mechanisms underlying this initial step of pain sensation. These natural products have revealed three members of the transient receptor potential (TRP) ion channel family-TRPV1, TRPM8, and TRPA1-as molecular detectors of thermal and chemical stimuli that activate sensory neurons to produce acute or persistent pain. Analysis of TRP channel function and expression has validated the existence of nociceptors as a specialized group of somatosensory neurons devoted to the detection of noxious stimuli. These studies are also providing insight into the coding logic of nociception and how specification of nociceptor subtypes underlies behavioral discrimination of noxious thermal, chemical, and mechanical stimuli. Biophysical and pharmacological characterization of these channels has provided the intellectual and technical foundation for developing new classes of analgesic drugs.
In humans, periostin plays a critical role in the enhancement and chronicity of allergic skin inflammation; however, whether it is involved in the pathogenesis of canine dermatitis remains unknown. The aim of this study was to examine the expression patterns of periostin in healthy, atopic, and nonatopic chronically inflamed canine skin. Biopsy specimens from 47 dogs with skin disease and normal skin tissue from 5 adult beagles were examined by light microscopy, immunohistochemistry, and in situ hybridization. In normal skin, periostin was localized just beneath the epidermis and around the hair follicles. In chronically inflamed skin, periostin expression was most intense in the dermis with inflammatory cell infiltrates. In contrast, low levels of periostin were detected in acutely inflamed and noninflamed skin. Conversely, all canine atopic dermatitis tissues characteristically showed the most intense expression of periostin in the superficial dermis, particularly at the epidermal-dermal junction. In situ hybridization showed that periostin mRNA was broadly expressed in the basal epidermal keratinocytes, outer root sheath cells, and dermal fibroblasts in normal dog skin. High expression of periostin mRNA was observed in fibroblasts in dog skin with chronically inflamed dermatitis. Moreover, in some chronically inflamed skin specimens, periostin mRNA expression was increased in basal keratinocytes. The severity score of chronic pathologic changes and CD3+ cell number in the dermis were correlated with distribution pattern of periostin in the atopic skin. These data suggest that periostin could play a role in the pathophysiology of chronic dermatitis, including atopic dermatitis, in dogs.
© The Author(s) 2015.
Toll-like receptors (TLRs) are best known for their roles in controlling innate immunity (Akira et al. 2006). TLRs are characterized as pattern-recognition receptors (PRRs) to initiate innate immune responses via recognition of pathogen-associated molecular patterns (PAMPs) (Akira et al. 2006). TLRs can also sense endogenous molecules that are released after cellular stress or tissue injury, known as danger-associated molecular patterns (DAMPs). Activation of TLRs in immune cells leads to the synthesis of various proinflammatory cytokines and chemokines via transcriptional regulation. TLRs-mediated innate immune responses are also a prerequisite for the generation of adaptive immune responses (Mills 2011). Thus, TLRs represent the first line of host defense against pathogens and play a key role in both innate and adaptive immunity (Akira et al. 2006). TLRs are also found to be expressed by various cell types in the central nervous system (CNS) and peripheral nervous system (PNS), such as microglia, astrocytes, oligodendrocytes, Schwann cells, and neurons (Okun et al. 2011; Buchanan et al. 2010; Lehnardt 2010). Activation of TLR signaling in the CNS also results in the production of inflammatory cytokines, enzymes, and other inflammatory mediators, which contributes to the pathogenesis of CNS microbial infection (Suh et al. 2009) as well as noninfective disorders, such as stroke (Caso et al. 2007), Alzheimer’s disease (AD) (Tahara et al. 2006), multiple sclerosis (MS) (Prinz et al. 2006), and chronic pain (Guo and Schluesener 2007; Nicotra et al. 2011; Liu et al. 2012b). TLRs are emerging as important players in acute and chronic itch (Liu et al. 2012b). Our recent study demonstrated that TLRs, including TLR3 and TLR7, are expressed by a subset of primary sensory neurons, which coexpress itch signaling components such as transient receptor potential vanilloid subtype 1 (TRPV1) (Liu et al. 2010, 2012a), and play an important role in itch sensation. TLRs are considered as cellular sensors for detecting exogenous and endogenous ligands/agonists in primary sensory neurons to initiate itch sensation associated with skin infection and tissue injury.
Somatic sensory neurons in the dorsal root ganglia (DRG) are composed of a variety of sensory modalities, such as pain-related nociceptors, itch-related pruriceptors, thermoreceptors and mechanoreceptors (Basbaum et al. 2009; Delmas et al. 2011). This chapter will focus on the neurotransmitter basis of somatic sensory information processing. Most, if not all, DRG neurons are glutamatergic excitatory neurons and release glutamate onto postsynaptic neurons in the dorsal horn of the spinal cord (Broman et al. 1993; De Biasi and Rustioni 1988; Schneider and Perl 1988; Yoshimura and Jessell 1990). A subset of DRG neurons additionally release neuropeptide transmitters (Hökfelt 1991). Accordingly, neurons involved with pain, itch, and thermoception are divided into two subtypes, “peptidergic” and “nonpeptidergic.” Peptidergic neurons release one or two “classic” neuropeptides, the substance P (SP) and the calcitonin gene-related peptide (CGRP), whereas many nonpeptidergic neurons bind the isolection B4 or IB4 (Basbaum et al. 2009). This classic definition is, however, not entirely accurate, due to the existence of other neuropeptides. For example, while the gastrin-releasing peptide (GRP) is expressed in putative CGRP(+) pruriceptors, the expression of the GRP-related peptide Neuromendin B (NMB) is associated with both CGRP(+) and IB4(+) neurons (Fleming et al. 2012; Sun and Chen 2007). Here, we will discuss the roles of distinct transmitters in processing itch- and pain-related sensory information.
The itch-scratch reflex serves as a protective mechanism in everyday life. However, chronic persistent itching can be devastating. Despite the clinical importance of the itch sensation, its mechanism remains elusive. In the past decade, substantial progress has been made to uncover the mystery of itching. Here, we review the molecules, cells, and circuits known to mediate the itch sensation, which, coupled with advances in understanding the pathophysiology of chronic itching conditions, will hopefully contribute to the development of new anti-itch therapies. Expected final online publication date for the Annual Review of Biophysics Volume 43 is May 06, 2014. Please see http://www.annualreviews.org/catalog/pubdates.aspx for revised estimates.
Smooth muscle cell (SMC) migration involves interactions of integrin receptors with extracellular matrix (ECM) and is an important process of neointimal formation in atherosclerosis and restenosis after vascular interventions. Previous studies have shown that periostin (PN), a novel ECM protein, is upregulated in rat carotid artery after balloon injury, and growth factor-stimulated expression of PN promotes SMC migration in vitro. Here, we address the mechanism by which PN-integrin interaction mediates SMC migration in vitro. Aortic SMCs isolated from PN null mice exhibited a significantly reduced ability to migrate and proliferate in vitro. Endogenous PN protein was absent and very low in the culture medium from the primary cultures of PN-/- and wildtype SMCs, respectively. In both types of SMCs, adenovirus-mediated overexpression of HA-tagged PN to a similar extent, which induced a robust cell migration concomitantly with an increase in beta3-integrin expression and phosphorylation of FAK (Tyr397). Furthermore, in cultured human SMCs, specific integrin blocking antibodies showed that interactions of PN-alphanubeta3 and PN-alphanubeta5, but not PN-beta1 integrins, are required for SMC migration. Inhibition of FAK signaling by overexpression of an endogenous FAK inhibitor termed FRNK (FAK-related nonkinase) significantly attenuated FAK (Tyr397) phosphorylation and the SMC migration induced by PN. These results reveal a mechanism whereby PN mediates vascular SMC migration through an interaction with alphaV-integrins (mainly alphanubeta3) and subsequent activation of FAK pathway.
Background:
Recent findings indicate that periostin, an extracellular matrix protein induced by T helper 2 cytokines, plays a critical role in the pathogenesis of atopic dermatitis (AD).
Objectives:
To determine whether serum periostin level is associated with clinical phenotype in adult patients with AD.
Methods:
An enzyme-linked immunosorbent assay was performed to determine serum periostin levels in 257 adult patients with AD, 66 patients with psoriasis vulgaris (PV) as a disease control and 25 healthy controls. Serum periostin levels were analysed together with clinical characteristics and laboratory parameters, including thymus and activation-regulated chemokine (TARC), lactate dehydrogenase (LDH), blood eosinophil count and total IgE. Immunohistochemical analysis evaluated the expression of periostin in association with various clinical phenotypes of AD. The effect of treatment on serum periostin level was also assessed.
Results:
Serum periostin was significantly higher in patients with AD than in patients with PV and healthy controls. Periostin level was found to be positively correlated with disease severity, TARC level, LDH level and eosinophil count, but not with IgE level. Higher serum periostin level was observed in patients with extrinsic AD compared with patients with intrinsic AD; the positive correlation of disease severity disappeared in patients with intrinsic AD. Robust expression of periostin was detected in the dermis of patients with AD with erythroderma, lichenification and, to a lesser extent, scaly erythema. Serial measurement of serum periostin revealed decreased levels of periostin after treatment for AD.
Conclusions:
Periostin may play a critical role in disease severity and chronicity in the pathogenesis of AD.
Itch is described as an irritating sensation that triggers a desire to scratch. However, this definition hardly seems fitting for the millions of people who suffer from intractable itch. Indeed, the Buddhist philosopher Nā´áäāgārjuna more aptly stated, "There is pleasure when an itch is scratched. But to be without an itch is more pleasurable still." Chronic itch is widespread and very difficult to treat. In this review we focus on the molecules, cells and circuits in the peripheral and central nervous systems that drive acute and chronic itch transmission. Understanding the itch circuitry is critical to developing new therapies for this intractable disease.
Asthma is a complex disorder of the airways that is characterized by T helper type 2 (Th2) inflammation. The pleiotrophic cytokine TSLP has emerged as an important player involved in orchestrating the inflammation seen in asthma and other atopic diseases. Early research elucidated the role of TSLP on CD4+ T cells, and recent work has revealed the impact of TSLP on multiple cell types. Furthermore, TSLP plays an important role in the sequential progression of atopic dermatitis to asthma, clarifying the key role of TSLP in the pathogenesis of asthma, a finding with therapeutic implications.
Atopic dermatitis (AD) is a chronic itch and inflammatory disorder of the skin that affects one in ten people. Patients suffering from severe AD eventually progress to develop asthma and allergic rhinitis, in a process known as the "atopic march." Signaling between epithelial cells and innate immune cells via the cytokine thymic stromal lymphopoietin (TSLP) is thought to drive AD and the atopic march. Here, we report that epithelial cells directly communicate to cutaneous sensory neurons via TSLP to promote itch. We identify the ORAI1/NFAT calcium signaling pathway as an essential regulator of TSLP release from keratinocytes, the primary epithelial cells of the skin. TSLP then acts directly on a subset of TRPA1-positive sensory neurons to trigger robust itch behaviors. Our results support a model whereby calcium-dependent TSLP release by keratinocytes activates both primary afferent neurons and immune cells to promote inflammatory responses in the skin and airways.
