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Citation: Iranpanah, A.; Kooshki, L.;
Moradi, S.Z.; Saso, L.; Fakhri, S.;
Khan, H. The Exosome-Mediated
PI3K/Akt/mTOR Signaling Pathway
in Neurological Diseases.
Pharmaceutics 2023,15, 1006.
https://doi.org/10.3390/
pharmaceutics15031006
Academic Editors: Ivana Cacciatore
and Elena V. Batrakova
Received: 30 November 2022
Revised: 24 February 2023
Accepted: 17 March 2023
Published: 21 March 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/).
pharmaceutics
Review
The Exosome-Mediated PI3K/Akt/mTOR Signaling Pathway in
Neurological Diseases
Amin Iranpanah 1,2, Leila Kooshki 3, Seyed Zachariah Moradi 1, Luciano Saso 4, Sajad Fakhri 1, *
and Haroon Khan 5, *
1Pharmaceutical Sciences Research Center, Health Institute, Kermanshah University of Medical Sciences,
Kermanshah 6734667149, Iran
2USERN Office, Kermanshah University of Medical Sciences, Kermanshah 6715847141, Iran
3Student Research Committee, Kermanshah University of Medical Sciences, Kermanshah 6714415153, Iran
4Department of Physiology and Pharmacology “Vittorio Erspamer”, Sapienza University, P.le Aldo Moro 5,
00185 Rome, Italy
5Department of Pharmacy, Abdul Wali Khan University, Mardan 23200, Pakistan
*Correspondence: pharmacy.sajad@yahoo.com (S.F.); haroonkhan@awkum.edu.pk (H.K.)
Abstract:
As major public health concerns associated with a rapidly growing aging population,
neurodegenerative diseases (NDDs) and neurological diseases are important causes of disability and
mortality. Neurological diseases affect millions of people worldwide. Recent studies have indicated
that apoptosis, inflammation, and oxidative stress are the main players of NDDs and have critical
roles in neurodegenerative processes. During the aforementioned inflammatory/apoptotic/oxidative
stress procedures, the phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt)/mammalian target of
rapamycin (mTOR) pathway plays a crucial role. Considering the functional and structural aspects
of the blood–brain barrier, drug delivery to the central nervous system is relatively challenging.
Exosomes are nanoscale membrane-bound carriers that can be secreted by cells and carry several
cargoes, including proteins, nucleic acids, lipids, and metabolites. Exosomes significantly take part
in the intercellular communications due to their specific features including low immunogenicity,
flexibility, and great tissue/cell penetration capabilities. Due to their ability to cross the blood–brain
barrier, these nano-sized structures have been introduced as proper vehicles for central nervous
system drug delivery by multiple studies. In the present systematic review, we highlight the potential
therapeutic effects of exosomes in the context of NDDs and neurological diseases by targeting the
PI3K/Akt/mTOR signaling pathway.
Keywords:
exosome; neurological disease; neurodegenerative disease; targeted delivery; PI3K;
Akt; mTOR
1. Introduction
Neurodegenerative diseases (NDDs) are progressive and chronic diseases character-
ized by imperceptible changes in neuronal structure [
1
,
2
]. NDDs are accompanied by
a decrease in the population of specific neurons leading to disability, impaired normal
functioning, dementia, and reduced life expectancy of patients. NDDs and neurological
diseases are classified based on various parameters such as anatomical distribution, main
clinical features, and important molecular abnormalities. Multiple sclerosis (MS), Parkin-
son’s disease (PD), Alzheimer’s disease (AD), amyotrophic lateral sclerosis (ALS), and
Huntington’s disease (HD) are common NDDs/neurological diseases that result in the
progressive deterioration of neurons [
3
,
4
]. The prevalence of neurodegenerative disorders
is rapidly increasing alongside the increase in the aging global population. It is estimated
that the number of dementia cases will increase from 13.5 million in 2000 to 36.7 million in
2050, which is alarming [5,6].
Pharmaceutics 2023,15, 1006. https://doi.org/10.3390/pharmaceutics15031006 https://www.mdpi.com/journal/pharmaceutics
Pharmaceutics 2023,15, 1006 2 of 25
Although the pathogenesis of NDDs has not yet been precisely appreciated, numerous
studies have underscored the undeniable contributions of inflammation, oxidative stress,
apoptosis, and protein aggregation in some cases. The production of free radicals during
both pathological and physiological processes plays a considerable role in several signaling
pathways including phagocytosis, activation of enzymes, and regulation of the cell cycle.
Excessive production of reactive oxygen species (ROS) causes various noxious effects such
as protein and deoxyribonucleic acid (DNA) damage and lipid peroxidation [
6
–
9
]. As
another contributor to the neurological disease, neuroinflammation brings about complex
alterations in the brain’s immune system associated with multiple cellular and molecular
aspects [
6
,
7
]. Such events lead to the alteration of glial cells, as well as augmentation of the
concentration, activity, and levels of several inflammatory mediators including cytokines
(e.g., interleukin-1
β
(IL-1
β
), IL-6, tumor necrosis factor-alpha (TNF-
α
)), chemokines (e.g.,
CCL2, CCL5, CXCL1), in addition to the generation of reactive nitrogen species (RNS)
and ROS [
10
,
11
]. Increased permeability/breakdown of the blood–brain barrier (BBB),
infiltration of peripheral immune cells, and edema are some of the other harmful processes
that come to pass during neuroinflammation. Neuroinflammation contributes significantly
to the development and progression of NDDs and neurological diseases. Therefore, sup-
pression of inflammation could result in the prevention and amelioration of neurological
disorders [6,12].
The phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt)/mammalian target of
rapamycin (mTOR) pathway is one of the key signaling pathways that plays pivotal roles
in several pathological/physiological processes such as cellular migration, proliferation,
apoptosis, and angiogenesis. In addition, according to numerous studies dysregulation of
the PI3K/Akt/mTOR signaling pathway is associated with pathological effects in several
disorders such as cardiovascular diseases [
13
,
14
], Crohn’s disease [
15
], cancer [
16
], and
especially NDDs [9,12,17]. Following the activation of PI3K and phosphorylation of phos-
phatidylinositol 4,5- bisphosphate (PIP2), Akt is recruited to the cell membrane. As another
key mediator, mTOR is associated with physiological neuroregeneration [
18
]. Moreover,
the mTOR pathway is engaged in neuronal response-related signals in the gastrointestinal
tract [
19
]. Additionally, mTOR signaling could be involved in autophagy where dam-
aged mitochondria observed in the oxidative stress process could suppress PI3K signaling
downstream through regulatory pathways such as the phosphatase and tensin homologue
(PTEN) pathways [
20
]. Notably, PI3K/Akt pathway can regulate a wide range of upstream
molecules such as growth factor receptors, G protein-coupled receptors (GPCRs), receptor
tyrosine kinases (RTKs), extracellular signal-regulated kinase (ERK), and cytokines, which
are involved in the attenuation of Janus kinase (JAK)/signal transducer and activator of
transcription (STAT) activation [
9
,
18
,
21
–
24
]. Multiple studies have pointed to the signifi-
cant effects of PI3K/Akt/mTOR signaling on several interconnected molecules implicated
in oxidative stress (e.g., superoxide dismutase (SOD), heme oxygenase-1 (HO-1), ROS,
catalase (CAT), nuclear factor erythroid 2–related factor 2 (Nrf2)), apoptosis (e.g., Bax/Bcl-2,
and caspases), and inflammation (e.g., nuclear factor kappa B (NF-
κ
B), ILs, matrix metallo-
proteinases (MMPs), chemokines, cytokines, and cyclooxygenase (COX)) [8,9,25–27].
Although a definitive treatment has still not been offered for NDDs, rapid fundamental
advances in several new fields of science including nanotechnology, artificial intelligence,
proteomics, stem cell therapy, genomics, gene therapy, exosome, and extracellular vesicles
(EVs) technology combined with multidisciplinary approaches have opened new horizons
for the treatment of NDDs and neurological diseases [
28
–
33
]. EVs are classified into
exosomes (30–150 nm), microvesicles (50–1000 nm), or apoptotic bodies (800–5000 nm)
based on their size and origin [
34
,
35
]. Exosomes originate from multi-vesicular bodies, and
the budding of the plasma membrane is the main source of microvesicles and apoptotic
bodies, which contain ribosomal ribonucleic acid (RNA), histones, and DNA produced
from cells that undergo programmed cell death [
33
,
36
–
39
]. It has been demonstrated that
microvesicles and exosomes play pivotal roles in intercellular communication as they are able
to mediate long-distance transmission of biological information via transferring microRNAs
Pharmaceutics 2023,15, 1006 3 of 25
(miRNAs), lipids, membrane receptors, RNA, and proteins between cells [
33
,
36
–
39
]. The type
of cell and the physiological condition affect exosome composition, which may be strongly
correlated with the development and progression of pathological processes [
40
]. As shown
by recent studies, exosomes produced from cancer tissues can lead to disease progression.
In addition, exosomes have been demonstrated to exert detrimental effects on neuronal
tissues in neurological diseases. However, healthy cell-derived exosomes may possess
therapeutic benefits. As a result, therapeutic strategies aimed to inhibit the production,
uptake, or release of disease-promoting exosomes are of great promise [
33
,
36
–
39
]. There is
already no review on the effects of exosome-mediated PI3K/Akt/mTOR signaling pathway
in NDDs. This is the first systematic review that critically highlights the modulatory effects
of exosomes as effective/safe drug delivery vehicles in the context of neurological diseases
through PI3K/Akt/mTOR pathway.
2. Study Design and Methods
The current systematic review was performed based on Preferred Reporting Items
for Systematic Reviews and Meta-Analysis (PRISMA) criteria. The keywords (“brain”
OR “neuron” OR “Alzheimer’s disease” OR “dementia” OR “Parkinson’s disease” OR
“multiple sclerosis” OR “spinal cord injury” OR “stroke” OR “depression” OR “aging” OR
“seizure” OR “autism” OR “Amyotrophic lateral sclerosis” OR “ALS” OR “Huntington’s
disease” OR “epilepsy”) AND (“PI3K” OR “phosphatidylinositol-3-kinase” OR “PKB”
OR “Akt” OR “protein kinase B” OR “mTOR” OR “m-TOR” OR “mammalian target of
rapamycin”) AND (“exosome”) were searched in [title/abstract/keywords] of the electronic
databases, including Scopus, PubMed, and Web of Science. All pathways/factors related to
PI3K/Akt/mTOR and exosomes were considered in the whole text. Data were collected
without time limitation until September 2022. Only English language studies were included.
Two independent researchers (S.Z.M. and A.I.) performed the search screening. Of the
786 articles collected via systematic search in aforementioned electronic databases, 276 and
222 articles were excluded due to being reviews and duplication, respectively. Moreover,
171 articles were excluded according to their title/abstract, 63 articles were excluded
according to their full-text information, and 8 articles were excluded because they were
not in English. Ultimately, 46 papers were included in this systematic review (Figure 1). In
completing the search strategy, manual search of citations and reference lists falling within
the authors’ expertise were also employed in the PI3K/Akt/mTOR signaling pathway as a
pivotal therapeutic target in neurological diseases.
Pharmaceutics 2023,15, 1006 4 of 25
Pharmaceutics 2023, 15, x 4 of 24
Figure 1. Flowchart of the process of literature search and selection of relevant reports.
3. Neurodegenerative Diseases, Neurological Disorders, and Exosomes: Focusing on
Pivotal Functions of PI3k/Akt/mTOR Signaling Pathway
Over the last few years, several studies demonstrated a promising future for EVs,
especially exosomes for targeting neurological diseases. Concentrating on the pivotal
PI3K/Akt/mTOR signaling pathway and associated factors, exosomes could combat AD,
stroke, SCI, traumatic brain injury (TBI), ALS, optic nerve crush (ONC) injury, and other
central nervous systems (CNS) injuries.
3.1. Exosomes and Alzheimer’s Disease, Cognition, Learning and Memory
AD is characterized as a common neurodegenerative disorder with a close relation-
ship with dementia development. Reportedly, the prevalence of AD is conspicuous in the
aged population and affects quality of life and social activities. In addition, AD pathology
is associated with amyloid beta (Aβ) accumulation, tau protein hyperphosphorylation,
neuroinflammation, and oxidative stress [41–43]. Based on the previous evidence,
PI3K/Akt/mTOR axis is considered to be one of the most significant signaling pathways
in the pathogenesis of NDDs. Indeed, this regulatory pathway displays critical functions
in biological processes such as metabolism, cell proliferation, apoptosis, and angiogenesis
[23]. Several lines of evidence have proposed that there is a correlation between exosome
therapy and PI3K/Akt/mTOR signaling with neuronal damage. Reportedly, adipose mes-
enchymal stem cell-derived exosomes (ADSC-Exo) were shown to be effective in improv-
ing PC12 cell migration/proliferation and could repress apoptosis through boosting
PI3K/Akt signaling pathway. In this line, ADSC-Exo treatment led to the overexpression
Figure 1. Flowchart of the process of literature search and selection of relevant reports.
3. Neurodegenerative Diseases, Neurological Disorders, and Exosomes: Focusing on
Pivotal Functions of PI3k/Akt/mTOR Signaling Pathway
Over the last few years, several studies demonstrated a promising future for EVs,
especially exosomes for targeting neurological diseases. Concentrating on the pivotal
PI3K/Akt/mTOR signaling pathway and associated factors, exosomes could combat AD,
stroke, SCI, traumatic brain injury (TBI), ALS, optic nerve crush (ONC) injury, and other
central nervous systems (CNS) injuries.
3.1. Exosomes and Alzheimer’s Disease, Cognition, Learning and Memory
AD is characterized as a common neurodegenerative disorder with a close relation-
ship with dementia development. Reportedly, the prevalence of AD is conspicuous in
the aged population and affects quality of life and social activities. In addition, AD
pathology is associated with amyloid beta (A
β
) accumulation, tau protein hyperphospho-
rylation, neuroinflammation, and oxidative stress [
41
–
43
]. Based on the previous evidence,
PI3K/Akt/mTOR axis is considered to be one of the most significant signaling pathways
in the pathogenesis of NDDs. Indeed, this regulatory pathway displays critical functions in
biological processes such as metabolism, cell proliferation, apoptosis, and angiogenesis [
23
].
Several lines of evidence have proposed that there is a correlation between exosome therapy
and PI3K/Akt/mTOR signaling with neuronal damage. Reportedly, adipose mesenchy-
mal stem cell-derived exosomes (ADSC-Exo) were shown to be effective in improving
PC12 cell migration/proliferation and could repress apoptosis through boosting PI3K/Akt
signaling pathway. In this line, ADSC-Exo treatment led to the overexpression of CD29,
Pharmaceutics 2023,15, 1006 5 of 25
CD44, CD73, and CD105 as mesenchymal stem cell surface markers while reducing the
expression of CD45 and HLA-DR [
44
]. In another study, bone marrow mesenchymal
stromal cells (BMSCs)-Exo containing growth differentiation factor-15 (GDF-15) could
exert a protective effect on A
β42
-induced SH-SY5Y cell injury through amelioration of the
Akt/glycogen synthase kinase-3 beta (GSK-3
β
)/
β
-catenin signaling pathway. Of note,
though this method of therapy promoted cell viability, it attenuated TNF-
α
, IL-6, IL-1
β
,
IL-8 (as inflammatory cytokines), and apoptosis in A
β42
-induced SH-SY5Y cell damage [
45
].
In addition, a recent study illustrated that exosomes carrying curcumin (Exo-cur) signifi-
cantly improved BBB crossing and ameliorated learning and memory deficits in okadaic
acid (OA)-induced AD under both
in vitro
and
in vivo
models. Exo-cur also attenuated
neural death and OA-induced tau hyperphosphorylation by stimulating the Akt/GSK-3
β
signaling pathway. Thus, Exo-cur represents a promising treatment through deactivation
of microglia and mitigation of the OA-induced apoptosis of neuron cells. In addition, it led
to improved neuronal function and alleviated AD symptoms [
46
]. According to an
in vitro
study, MSC-derived exosomal miR-223 (when applying 2 µg exosome-based on exosomal
protein content per 1
×
10
5
recipient cells) could target PTEN and stimulated PI3K/Akt
signaling pathway in an
in vitro
model of AD. Thus MSC-derived exosomes can increase
cell migration and decrease neuronal apoptosis and inflammatory mediators including
IL-6, IL-1
β
, and TNF-
α
[
47
]. Other studies suggested that neural stem cell (NSC)-derived
exosomes (NSC-Exo) prevented high-fat diet (HFD)-dependent memory deficits in male
C57BL/6 mice by restoring the cAMP response element-binding protein (CREB)/brain-
derived neurotrophic factor (BDNF)/tropomyosin receptor kinase B (TrkB) signaling and
the expression of synaptic plasticity-associated genes. Taken together, treatment with
NSC-Exo (1.5
µ
g per nostril, three times per week) could upregulate CREB/BDNF/TrkB
signaling in the hippocampus of HFD mice, underscoring the treatment as a potential ther-
apy for metabolic disease-related cognitive impairment [
48
]. Furthermore, it was shown
that MSCs-miR-132-3p-Exo improved cognitive decline and synaptic dysfunction as well as
promoted dendritic spine density and neuron numbers by activating the Ras/Akt/GSK-3
β
pathway in vascular dementia under in vitro and in vivo models [49].
Overall, exosomes play critical roles in circumventing cognitive/memory dysfunction
through affecting the PI3K/Akt/mTOR pathway and its associated markers (Table 1). In
summary, although more
in vitro
and
in vivo
studies are necessary to accurately prove the
role of exosomes in AD, according to the mentioned reports, exosomes could be regarded
to be a promising candidate for the prevention or treatment of AD, cognition, learning, and
memory deficit. Additionally, exosomes could be used in combination with other drugs,
which requires comprehensive pre-clinical and clinical studies. Future clinical applications
should also focus on the usefulness of exosomes in predicting the emerging symptoms of
AD. Additionally, application of the microfluidic technique will show the road to diagnosis
of the primary symptoms of AD before the late stages of the disease. High biocompatibility,
high BBB penetration, long blood circulation, prevention of degradation, and tissue tar-
geting are additional advantages of exosomes to be used in AD [
50
]. Due to the capacity
of exosomes in RNA transport, stability, and their BBB-crossing capability, exosomes are
appropriate carriers in combating AD [
51
]. Additionally, neuron-derived exosomes could
make A
β
conformational modifications to non-toxic fibrils and cause increased microglia
uptake [
52
]. Altogether, exosomes are promising drug/enzyme/miRNA delivery vehicles,
and also play a critical role in scavenging waste neurotoxic agents. The neuroprotective
potential of exosomes is also closely linked with their ability to block NF-κB.
Pharmaceutics 2023,15, 1006 6 of 25
Table 1. Exosomes circumvent AD and stroke via PI3K/Akt/mTOR and associated pathways.
Source of Exosomes Cargo or Intermediate
Molecule Disease Method (In Vitro/In Vivo) Dose/Route of Administration Mechanism of Actions and Outcomes References
ADSC _____ AD in vitro: PC12 cells 10, 50 and 100 µg/mL
↑p-PI3K, p-Akt, CD29, CD44, CD73, CD105, cell
proliferation, and migration;
↓CD45, HLA-DR, and cell apoptosis
[44]
BMSCs GDF-15 AD in vitro: SH-SY5Y cells _____ ↑
Cell viability, Akt/GSK-3
β
/
β
-catenin pathway;
↓Apoptosis, TNF-α, IL-6, IL-1β, and IL-8 [45]
Macrophage cell line
(RAW 264.7) Curcumin AD in vivo: Okadaic acid-induced
AD in C57BL/6 mice;
in vitro: hCMEC/D3 cells
0.4 mg/kg, single i.v. dose, and
100 µg/mL, i.p. for 7 days
↑Curcumin solubility, stability, bioavailability,
cellular uptake and BBB-crossing, p-Akt, p-Ser9
GSK-3β;
↓
Learning deficiencies, cognitive decline, escape
latency, cell apoptosis, tau
hyperphosphorylation, p-Ser396 tau, neuronal
injury, Bax and c-caspase 3;
[46]
HucMSCs miR-223 AD
in vitro: Aβ1–40 -induced injury
in SH-SY5Y cells under hypoxic
conditions
2µg per 1 ×105recipient cells
↑p-Akt;
↓Apoptosis, scratch area, IL-6, IL-1β, TNF-α,
CRP, and PTEN
[47]
NSC _____ HFD-related
cognitive decline in vivo: male C57BL/6 mice 1.5 µg per nostril, 3 times per
week
↑BDNF, nNOS, Sirt1, Egr3, RelA, and pTrkB;
↓Memory impairment [48]
MSCs miR-132-3p VD in vivo: VD-induced in male
C57BL/6 mice;
in vitro: OGD-injured neurons
1×1010
particles/100 µL, via the tail
vein once every
7 days for 21 days
↑Cognitive function, neuron number, dendritic
spine density, synaptic plasticity, Ras, p-Akt,
p-GSK-3β, and neurite elongation;
↓Aβ, p-tau, RASA1, and apoptosis
[49]
MSCs miR-17-92 Stroke
in vivo: 2 h intraluminal
filament-induced MCAO in
Wistar rats;
Ex-vivo rat organotypic brain
slice culture model
3×1011 particles/rat, i.v.
↑GAP-43 immunoreactivity, cortical and
intracortical axonal density, myelin density,
neuronal plasticity, contralesional axon number
and total length, CST axonal remodeling, and
functional recovery
↓Time to remove the adhesive tabs, mNSS score,
and lowest threshold value of ICMS;
↑MBP+myelin and NFH+,
PTEN/PI3K/Akt/mTOR pathway
[53]
MSCs miR-17–92 Stroke
Wistar rats were subjected to 2 h
intraluminal filament-induced
MCAO
100 µg total exosome protein or
3×1011 particles per rat, i.v.
↑Functional recovery, axonal density, p-NF-H
immunoreactive area, synaptophysin
immunoreactivity, primary and secondary
neurite branching, spine density, dendritic
plasticity, neurogenesis, oligodendrogenesis,
p-Akt, p-mTOR, and p-GSK-3β;
↓mNSS score, number of Foot-fault and
PTEN level
[54]
Pharmaceutics 2023,15, 1006 7 of 25
Table 1. Cont.
Source of Exosomes Cargo or Intermediate
Molecule Disease Method (In Vitro/In Vivo) Dose/Route of Administration Mechanism of Actions and Outcomes References
Healthy rat
serum-derived
exosomes
_____ Stroke
in vivo: Focal cerebral ischemia
induced by the intraluminal
suture
MCAO method in SD rats
in vitro: OGD/R injury model
in bEnd.3 immortalized mouse
brain endothelial cells
800 µg/kg, i.v.
50 µg/mL
↑Neurobehavioral scores, total moving distance,
neuronal spine density, claudin-5, ZO-1,
Bcl-2/Bax ratio, p-Akt/Akt and SQSTM1/p62
expression,
↓
Infarct volumes, %distance and %time in center,
BBB leakage, Evans blue dye extravasation,
MMP-9, cleaved caspase-3 and LC3B-II/LC3B-I
ratio;
↑SQSTM1/p62 expression,
↓Apoptotic cells, TUNEL+/CD31+cells, cleaved
caspase-3 and LC3B-II/LC3B-I ratio
[55]
MSCs miR-132-3p Ischemic stroke
in vivo: Focal ischemic stroke
induced by transient MCAO in
C57BL/6 mice
in vitro: H/R injury model in
mouse brain microvascular
endothelial cells
1
×
10
10
particles/100
µ
L in PBS
via the tail
vein, i.v.
50 µg/mL
↑cMVD and CBF;↓ROS, apoptosis, Evans blue
dye extravasation, brain water content, infarct
volume, NDS, and BBB disruption;
↑Ras, p-PI3K/PI3K, p-Akt/Akt and
p-eNOS/eNOS, ZO-1, and Claudin-5;
↓RASA1, ROS, paracelluar
permeability and apoptosis
[56]
BMSCs miR-146a-5p ICH
in vivo: Collagenase type
IV-induced ICH in male SD rats,
by an intrastriatal injection
100 µg/mL, 100 µg via the tail
vein, i.v.
↑SOD and neurological function;
↓Microglia M1 polarization, iNOS, COX-2,
MCP-1, IRAK1, NFAT5, TNF-α, IL-1β, IL-6,
MPO-positive cells, MDA, OX42-positive cells,
Iba-1+/MHC-II+, apoptotic, and degenerative
neurons
[57]
MSCs miR-133b ICH
in vivo: An autologous arterial
blood ICH model in adult male
SD rats
100 µg via the tail
vein, i.v.,
72 h
after ICH
↑p-ERK1/2/ERK1/2 and p-CREB/CREB;
↓RhoA expression, neuronal apoptosis and
neurodegenerative neurons
[58]
ADSCs miR-140-5p SAH
in vivo: SAH-induced
neurological dysfunction in rat
in vitro: TDP-43-induced
neuronal injury
_____ ↑Cell viability and PI3K/Akt activation;
↓IGFBP5 expression and apoptosis [59]
HucMSCs miR-206-knockdown SAH in vivo: SAH-induced EBI in
double blood injection model in
SD rats
200 µL PBS containing 400 µg
exosomes, i.v. injected into the
femoral vein 1 h after SAH
↑Bcl-2, BDNF, TrkB, and p-CREB;
↓Bax, caspase-8, neurological deficit, brain
edema, and neuronal apoptosis
[60]
Pharmaceutics 2023,15, 1006 8 of 25
Table 1. Cont.
Source of Exosomes Cargo or Intermediate
Molecule Disease Method (In Vitro/In Vivo) Dose/Route of Administration Mechanism of Actions and Outcomes References
SC _____ Cerebral I/R injury
in vivo: Focal cerebral I/R
induced by the improved Longa
method in rats
_____
↑Latency for the novel arm, IFN-γ, and Bcl-2;
↓Novel entries, IL-1α, IL-2, TNF-α, Bax, cleaved
caspase-3, cleaved caspase-9, CytC, PI3K, Akt,
and neural cell apoptosis
[61]
ATCs miR-34c Cerebral I/R injury
in vivo: Wistar rats MCAO
model
in vitro: OGD/R model in N2a
mouse neuroblastoma cells
20 and 30 µg/mL via the tail
vein after ischemia,
20 µM
↑Nissl bodies and c-fos positive cell numbers;
↓Neuronal injury, NDS, infarct volume, brain
water content, IL-6, IL-8, and TNF-α;
↑Cell proliferation, EdU positive cell index, and
TLR7;
↓Bax, cleaved caspase-3, cleaved PARP,
apoptosis, and NF-κB/MAPK axis
[62]
BMSCs _____ Cerebral I/R injury in vitro
: OGD/R model in PC12
cells 10 µg/mL
↑
Cell viability, autophagic flux, p-AMPK/AMPK;
↓LDH, morphological changes, pyroptosis,
NLRP3, ROS, cleaved caspase-1, IL-1β,
GSDMD-N, p-mTOR/mTOR, and P62
[63]
ATCs miR-361 Cerebral I/R injury
in vivo: Wistar rats reversible
MCAO model
in vitro
: OGD/R model in PC12
mouse neuroblastoma cells
2 mL exosomes (30 µg/mL) via
the caudal vein, twice a week
for 2 weeks
30 µg/mL
↑Nissl bodies, C-fos and neuronal viability;
↓Nerve damage, NDS, brain water content,
infarct volume, cerebral edema, apoptosis,
AMPK and mTOR mRNA and protein levels;
↑
Cell activity, cell proliferation, and EdU positive
cell index;
↓Apoptosis, Bax, cleaved caspase-3, cleaved
PARP, CTSB, AMPK and mTOR mRNA and
protein levels
[64]
BMSCs miR-29b-3p Hypoxic-ischemic
brain injury
in vivo: Cerebral ischemia
induced by MCAO method in
SD rats
in vitro: OGD/R injury model
in rat primary cortical neurons
and BMECs
100 µg/kg/day
intracerebroventricular
stereotactic injection 2 h after
the
MCAO model, every day for
3 days
↑Bcl-2, VEGFA, VEGFR2, angiogenesis, and
p-Akt/Akt;
↓Apoptotic cells, Bax, cleaved caspase-3, infarct
volume, MVD, and PTEN;
[65]
Pharmaceutics 2023,15, 1006 9 of 25
Table 1. Cont.
Source of Exosomes Cargo or Intermediate
Molecule Disease Method (In Vitro/In Vivo) Dose/Route of Administration Mechanism of Actions and Outcomes References
Neuron, EC, NPC and
ATC differentiated from
H9 hES
_____ Ischemia OGD-induced injury in H9 hES
derived neurons 100 µg/mL
↑Neuronal survival rate, p-PI3K p85, p-Akt,
p-mTOR, Bcl-2, and basal neuronal synaptic
transmission;
↓Neuronal damage, p-AMPK, COX-2, iNOS,
TNF-α, Bax, and cleaved caspase-3
[66]
EPCs miR-126 Diabetic ischemic
stroke
H/R and HG-induced injury in
human astrocytes 3×109
particles/mL ↓Cytotoxicity, ROS and lipid peroxidation [67]
Abbreviations:
↑
: increase or improvement;
↓
: decrease or loss; AD: Alzheimer’s disease; ADSCs: adipose tissue-originated stromal cells; Akt: protein kinase B; AMPK: AMP-activated
protein kinase; ATCs: astrocytes; A
β
: amyloid beta; BBB: blood–brain barrier; BDNF: brain-derived neurotrophic factor; BMECs: brain microvascular endothelial cells; BMSCs: bone
marrow mesenchymal stem cells; CBF: cerebral blood flow; cMVD: cerebral vascular density; COX-2: cyclooxygenase-2; CREB: cAMP response element-binding protein; CRP: C-reactive
protein; CST: corticospinal tract; CTSB: cathepsin B; CytC: cytochrome C; EBI: early brain injury; eNOS: endothelial nitric oxide synthesis; EPCs: endothelial progenitor cells; ERK1/2:
extracellular signal-regulated kinase 1/2; ES: embryonic stem cell; GDF-15: growth differentiation factor-15; GSDMD-N: N-terminal of gasdermin D; H/R: hypoxia/reoxygenation; hES:
human embryonic stem cell; HFD: high-fat diet; HG: high glucose; HucMSCs: human umbilical cord-derived MSCs; I/R: ischemia/reperfusion; ICH: intracerebral hemorrhage; ICMS:
intracortical microstimulation; IFN-
γ
: interferon-
γ
; IGFBP5: insulin-like growth factor-binding protein 5; IL: interleukin; iNOS: inducible nitric oxide synthase; i.p.: intraperitoneal; IRAK1:
interleukin-1 receptor-associated kinase 1; i.v.: intravenous; MAPK: mitogen-activated protein kinase; MCAO: middle cerebral artery occlusion; MCP-1: monocyte chemoattractant
protein-1; miR: microRNA; mNSS: modified neurological severity score; MPO: myeloperoxidase; MSCs: multipotent mesenchymal stromal cells; mTOR: mammalian target of rapamycin;
MVD: microvessel density; NDS: neurological deficit score; NFAT5: nuclear factor of activated T cells 5; NF-
κ
B: nuclear factor-kappa B; NLRP3: nucleotide-binding domain and
leucine-rich repeat family protein 3; nNOS: neuronal nitric oxide synthase; NPC: neural progenitor cell; NSC: neural stem cells; OGD/R: oxygen glucose deprivation/reperfusion;
PARP: poly-adenosine diphosphate-ribose polymerase; p-CREB: phospho-cAMP response element-binding protein; p-GSK-3
β
: phosphorylated-glycogen synthase kinase-3 beta; PI3K:
phosphoinositide-3-kinase; PTEN: phosphatase and tensin homolog; RASA1: Ras p21 protein activator 1; ROS: reactive oxygen species; SAH: subarachnoid hemorrhage; SC: stem cell;
SD: Sprague–Dawley; SQSTM1: sequestosome 1; TLR7: toll-like receptor 7; TNF-
α
: tumor necrosis factor-
α
; TrkB: tropomyosin-related receptor kinase B; VD: vascular dementia; VEGFA:
vascular endothelial growth factor A; VEGFR2: vascular endothelial growth factor receptor 2.
Pharmaceutics 2023,15, 1006 10 of 25
3.2. Exosomes and Stroke
Stroke is considered the second leading cause of mortality and the third leading cause
of disability worldwide with an increasing growth globally [
68
,
69
]. As a socioeconomic
problem, stroke has a high morbidity and mortality rate [
70
]. Thus, it could decrease the life
quality of patients and impose high economic costs on patients and healthcare systems [
69
].
Its occurrence is predicted to reach 23 million people in the world by 2030 [
71
]. There
are three different types of stroke. Ischemic stroke and hemorrhagic stroke are the major
types of strokes [
69
,
70
]. A transient ischemic attack (TIA) or mini-stroke is another type
of stroke in which symptoms last less than 24 h and can be a warning sign for future
strokes [
68
]. Ischemic stroke or brain ischemia is the most common type of stroke and
occurs due to a blockage of blood flow to the brain. Obstruction is usually caused by blood
clots and results in hypoxia, nutrient deprivation, and the induction of inflammation and
oxidative stress [
69
,
70
,
72
]. Hemorrhagic stroke is caused by a blood vessel rupture, leading
to intracerebral hemorrhage (ICH) or subarachnoid hemorrhage (SAH) [73].
The persistent bleeding from a hemorrhagic stroke causes oxidative stress, neuroin-
flammation, apoptosis, and BBB disruption [
56
,
70
]. In addition, the PI3K/Akt/mTOR
pathway can modulate multiple cellular and molecular events including oxidative stress
factors, inflammatory responses, programmed cell death, and cell survival, and it protects
neurons and the brain from ischemic damages [
9
,
74
,
75
]. Hence, this pathway can be con-
sidered as one a significant signaling pathway and therapeutic target for neuroprotection
against stroke.
Xin et al. illustrated that MSCs-miR-17-92
+
-Exo enhanced PI3K/Akt/mTOR activation
by reducing PTEN expression, which modulated the stroke injury induced by middle
cerebral artery occlusion (MCAO) in rats. In addition, they demonstrated that Exo-miR-
17-92
+
significantly elevated corticospinal tract (CST) axonal remodeling, myelination,
neurological recovery, and reversed MCAO-induced behavioral dysfunctionality [
53
]. In
another similar model, Exo-miR-17-92
+
represented protective effects on brain injury and
increased functional recovery, axonal density, neurogenesis, oligodendrogenesis, and spine
and dendritic plasticity through inhibition of PTEN activity and increases in p-Akt, p-
mTOR, and p-GSK-3
β
activity [
54
]. Healthy rat serum-derived exosomes have also shown
neuroprotective effects in combating stroke injury in
in vitro
(50
µ
g/mL) and
in vivo
(800
µ
g/kg, i.v.) models through elevation of the p-Akt/Akt ratio, claudin-5, zonula
occludens (ZO)-1, the Bcl-2/Bax ratio, and sequestosome 1 (SQSTM1)/p62 expression
while reducing BBB leakage, cell apoptosis, MMP-9, cleaved caspase-3, and LC3B-II/LC3B-
I ratio. Healthy rat serum-derived exosomes also improved the results of behavioral
tests [
55
]. MSCs-miR-132-3p-Exo showed a notable amelioration of infarct volume, BBB
dysfunction, neurological deficit scores (NDS), brain edema, and injury in focal ischemic
stroke induced by transient MCAO in C57BL/6 mice through suppressing the expression
of RASA1, reducing apoptosis and the ROS levels, and upregulating Ras, ZO-1, claudin-5,
and the Ras/PI3K/Akt/endothelial nitric oxide synthesis (eNOS) pathway [56].
In a rat model of ICH, Duan and colleagues showed that BMSC-miR-146a-5p-Exos ame-
liorated neurological function through decreasing oxidative stress and inflammatory medi-
ators interconnected to the PI3K/Akt/mTOR pathway including COX-2, malondialdehyde
(MDA), inducible nitric oxide synthase (iNOS), TNF-
α
, myeloperoxidase (MPO)-positive
cells, monocyte chemoattractant protein-1 (MCP-1), IL-1
β
, and IL-6 and suppression of
microglial M1 polarization. These effects were associated with the downregulation of
nuclear factor of activated T cells 5 (NFAT5) and IL-1 receptor-associated kinase 1 (IRAK1)
expression [
57
]. In another rat model of ICH, MSC exosome-transferred miR-133b (100
µ
g
via the tail vein, i.v., 72 h after ICH) reduced neuronal apoptosis and neurodegeneration
by RhoA downregulation and ERK1/2/CREB pathway activation [
58
]. A recent report
by Wang and colleagues showed that ADSC-Exos could decline neurological deficits and
promote cell viability through suppression of insulin-like growth factor-binding protein
5 (IGFBP5) and increase in the expression of PI3K/Akt signaling pathway components
in
in vitro
and
in vivo
models of SAH [
59
]. Recent studies have shown that BDNF could
Pharmaceutics 2023,15, 1006 11 of 25
confer protection against apoptosis and neuronal injury by activating the ERK and/or
PI3K/Akt pathway to stimulate the phosphorylation of CREB [
76
,
77
]. In another study,
miR-206-knockdown exosomes from human umbilical cord-derived mesenchymal stem
cells (hucMSCs) demonstrated significant
in vivo
therapeutic effects in SAH-induced early
brain injury (EBI) through the BDNF/TrkB/CREB signaling pathway. BDNF/TrkB/CREB
signaling pathway activation inhibited neuronal death and minimized brain edema and
neurological dysfunction. In addition, hucMSCs-derived miR-206-knockdown exosomes
ameliorated Bcl-2/Bax ratio and reduced cleaved caspase-8 induced by brain injury [60].
Stem cell-derived exosomes (SC-Exos) attenuated neuronal apoptosis, augmented
interferon-gamma (IFN-
γ
) and Bcl-2, and decreased IL-1
α
, IL-2, TNF-
α
, Bax, cytochrome
C (CytC), and cleaved caspase-3 and caspase-9 production in rats with cerebral ischemia/
reperfusion (I/R) injury. These mechanisms could be linked to PI3K/Akt pathway-
mediated mitochondrial apoptosis [
61
]. Wu et al. elucidated the
in vitro
and
in vivo
neuroprotective effects of astrocyte-derived exosome (ATC-Exos)-contained miR-34c in
terms of the protection of Neuro 2A (N2a) mouse neuroblastoma cells by increasing toll-like
receptor 7 (TLR7) expression and downregulating the NF-
κ
B/mitogen-activated protein
kinase (MAPK) pathways. It has been shown that treatment with ATC-Exos significantly
reduces infarction volume; brain edema; inflammatory mediators including IL-6, IL-8 and
TNF-
α
; apoptotic factors such as Bax, cleaved caspase-3, and cleaved PARP; and ameliorates
neurological deficits caused by cerebral I/R injury [
62
]. Furthermore, 10
µ
g/mL BMSC-Exos
conferred protective effects on oxygen–glucose deprivation/reperfusion (OGD/R)-induced
injury in PC12 cells and promoted cell viability by targeting the AMP-activated protein
kinase (AMPK)/mTOR pathway [
63
]. In another study, Bu and colleagues showed the
neuroprotective advantages of ATC-Exos contained miR-361 under
in vitro
(30
µ
g/mL)
and 2 mL exosomes (30
µ
g/mL) via the caudal vein, twice a week for 2 weeks) models
of cerebral I/R injury through attenuation of the AMPK/mTOR signaling pathway via
targeting cathepsin B (CTSB). In addition, infarct volume, cerebral edema, cleaved poly
adenosine diphosphate-ribose polymerase (PARP), cleaved caspase-3, and Bax exhibited a
significant decrease in the ATC-Exo-treated groups, while neuronal viability increased [
64
].
In addition, BMSC-derived exosomal miR-29b-3p [
65
], exosomes from different H9
human embryonic stem cell (hES)-derived cells [
66
], and miR-126 enriched endothelial
progenitor cells (EPCs)-released exosomes [
67
] are among other exosomes with promising
protective activities in combating brain injury through modulation of the PI3K/Akt/mTOR
signaling pathway and the related mediators.
Altogether, the above-mentioned studies highlight the promising protective effects
of exosomes against different types of stroke by employing different mechanisms such
as the modulation of inflammatory cytokines, autophagic molecules, and oxidative and
apoptotic factors. These functions of exosomes typically pass through the PI3K/Akt/mTOR
signaling pathway (Table 1). In addition, these nano-sized structures display different
advantages such as low immunogenicity and high BBB penetration capacity over other
therapeutic modalities. However, there exist several challenges against exploiting EVs
for therapeutic applications including drug interactions with EV components, a lack of
controlled drug release mechanisms, and a lack of specific biomarkers. Exosome therapy
still has various limitations and more studies are needed to find ways to elevate their
circulation half-life, increase the quantity of bioactive molecules loaded in exosomes,
enhance their stay at the disease site, and use them for targeted delivery to highlight their
eligibility in clinical trials to combat stroke. Thus, further studies including extensive
in vitro
and
in vivo
experimentations as well as comprehensive pre-clinical and clinical
trials on exosomes are necessary to introduce exosomes as potential agents for modulating
stroke. Multiple
in vitro
and
in vivo
reports have proven that exosomes could increase
functional recovery, angiogenesis, neurovascular remodeling, and synaptic plasticity and
could be neurorestorative after stroke through transfer of different types of cargoes such as
miRNAs, proteins, lipids, and phytochemicals [78,79].
Pharmaceutics 2023,15, 1006 12 of 25
3.3. Exosomes and Spinal Cord Injury
SCI is a critical insult to the spinal cord that causes temporary or permanent motor
and sensory impairment and disability [
80
,
81
]. SCI affects most of the body’s functions and
can diminish patients’ quality of life [
80
]. SCI is classified as non-traumatic or traumatic
SCI, according to its etiology [
82
]. Recent studies have shown that the PI3K/Akt/mTOR
pathway plays critical roles in the recovery of the spinal cord after injury via regulation
of the release of proinflammatory cytokines, oxidative stress, cell death, neuron growth,
differentiation, and formation of glial scar [
75
,
83
]. Thus, it is critical to consider the roles of
exosomes in the context of SCI via modulation of the PI3K/Akt/mTOR signaling pathway.
In 2021, Chen et al. investigated the advantages of BMSC-miR-26a-Exos in SCI in
in vitro
and
in vivo
models. The results demonstrated that interference of the PTEN/Akt/
mTOR pathway is the major neuroprotective mechanism governing BMSC-miR-26a-Exo-
mediated functional recovery, neurogenesis, axonal regeneration, and attenuation of astro-
cyte inflammation, autophagy, and glial scarring [
84
]. In another report, miR-338-5p overex-
pressing BMSC-derived exosomes showed neuroprotective activities by elevating neuronal
survival, modulating oxidative stress factors, and suppressing SCI-induced cell death in
both
in vitro
and
in vivo
experiments. These effects were attributed to the PI3K/Akt path-
way via downregulation of cannabinoid receptor 1 (Cnr1) and cAMP-mediated Rap1 activa-
tion [
85
]. Furthermore, exosome-shuttled miR-216a-5p from hypoxic BMSCs (200
µ
g/mL)
was shown to deviate microglia/macrophage polarization from M1 pro-inflammatory phe-
notype to M2 anti-inflammatory phenotype, increase IL-4, and IL-10, and decrease iNOS,
TNF-
α
, IL-1
β
, and IL-6 through activation of the PI3K/Akt pathway and TLR4/NF-
κ
B
pathway suppression. These pathophysiological signaling pathways led to improved func-
tional, gait, and motor recovery in a C57BL/6 mice model of SCI [
86
]. Luo and colleagues
showed that exosomes from G protein-coupled receptor kinase 2 interacting protein 1
(GIT1)-overexpressing BMSCs promoted neural regeneration, functional behavioral recov-
ery, and antiapoptotic factors (e.g., Bcl-2) while reducing glial scar formation, inflammatory
mediators (e.g., IL-1
β
, IL-6, and TNF-
α
), and proapoptotic factors (e.g., Bax and cleaved
caspase-3 and -9) which led to the alleviation of apoptosis and neuroinflammation as
evaluated by
in vitro
and
in vivo
experiments. Upregulation of the PI3K/Akt signaling
pathway could be presumed to be one of the major protective mechanisms adopted by
these exosomes in combating traumatic SCI [87].
Wang et al. showed that MSCs-Exo conferred neuroprotection by anti-inflammatory
activities through downregulation of the nuclear translocation of NF-
κ
B p65, TNF-
α
, IL-1
α
,
IL-1
β
, and p-IKB
α
as demonstrated by
in vitro
and
in vivo
experiments [
88
]. In another
study, MSCs-miR-126-Exo enhanced neurogenesis, angiogenesis, functional recovery, con-
nectivity value, and blood vessel numbers and diminished apoptosis and lesion volume
after SCI. Such effects were mediated through inhibition of sprouty-related EVH1 domain-
containing protein 1 (SPRED1) and PI3K regulatory subunit 2 (PIK3R2) [
89
]. Of other
reports on the exosome-mediated regulation of PI3K/Akt/mTOR, neuron-derived exo-
somes transmitting miR-124-3p could remarkably attenuate axonal damage, lesion volume,
M1 microglia and A1 astrocytes activation. In addition, it minimized pro-inflammatory
cytokines (TNF-
α
, IL-1
α
, IL-6, and IL-1
β
), iNOS, and improved functional/gait recovery
through the regulation of PI3K/Akt/NF-
κ
B signaling pathways as assessed by
in vitro
and
in vivo
experiments [
90
]. Chen et al. investigated the therapeutic effect of FTY720-loaded
exosomes derived from nerve stem cells (NSCs) (FTY720-NSCs-Exos) in SCI using
in vitro
and
in vivo
models. In this line, FTY720-NSC-Exos increased p-Akt, Bcl-2, claudin-5, ZO-1,
and locomotor function while reducing PTEN, SCI lesion, edema formation, inflammatory
cell infiltration, and apoptosis of neuronal cells via regulation of the PTEN/Akt pathway
which led to neuroprotective effects [
91
]. Pan and colleagues demonstrated that primary
Schwann cell-derived exosomes (SCDEs) could promote recovery after SCI through mod-
ulation of NF-
κ
B/PI3K [
92
] and epidermal growth factor receptor (EGFR)/Akt/mTOR
signaling pathways as elucidated by
in vitro
and
in vivo
assays [
93
]. Human urine stem
cell (HUSC)-ANGPTL3-Exo exhibited a neuroprotective activity against SCI and increased
Pharmaceutics 2023,15, 1006 13 of 25
angiogenesis, spinal cord regeneration, sensory improvement, vessel volume fraction, and
recovery of neurological functional by interference with the PI3K/Akt signaling pathway
as confirmed by
in vitro
and
in vivo
experiments [
94
]. According to
in vitro
and
in vivo
evidence, hucMSCs-miR-199a-3p/145-5p-Exos diminished neurological symptoms via de-
creasing the inflammation and apoptotic cells and increasing TrkA, p-Akt, and p-Erk, and
interconnected to nerve growth factor (NGF)/TrkA pathway [
95
]. Additional studies dis-
covered that peripheral macrophage (PM)-Exos [
96
], resveratrol-primed exosomes secreted
by primary microglia [
97
], and pericyte exosomes [
98
] possessed neuroprotective properties
in combating SCI through PI3K/Akt/mTOR signaling pathway and related factors.
Therefore, exosomes could be contemplated as possible therapeutic tools for SCI by
modulating neuroapoptosis, neuronal oxidative stress, and neuroinflammation through the
PI3K/Akt/mTOR signaling pathway. Considering the challenges mentioned for exosomes,
it seems that more
in vivo
studies are needed to conduct clinical trials to determine the role
of exosomes in neurological diseases such as SCI. Taken together, these reports suggest
exosomes as new tools for modulating SCI. As natural carriers of biologically active cargoes,
exosomes could not only remarkably ameliorate functional recovery, neural regeneration,
and angiogenesis of animals with SCI, but also notably elevate the expression of antioxidant
factors, anti-apoptotic protein Bcl-2, and anti-inflammatory mediators including IL-4, IL-10,
and IL-13. Exosomes markedly reduced pro-inflammatory factors such as IL-1
β
, IL-6, and
TNF-
α
and the expression of the apoptotic protein Bax. These effects are in a near linkage
with their ability to regulate the PI3K/Akt/mTOR signaling pathway.
Overall, because exosomes can effectively cross the BBB, they could be used for the
treatment and diagnosis of several neurological disorders, such as SCI. In addition, more
studies are required to clarify the specific role of exosomes in SCI and bring hope for clinical
treatment of SCI.
3.4. Exosomes and Traumatic Brain Injury
TBI is defined as a mechanical injury to the parenchymal tissues and meninges of the
brain associated with inflammatory and oxidative responses [
99
,
100
]. Based on
in vitro
and
in vivo
studies, endothelial colony-forming cells (ECFCs)-derived exosomes rescued
the expression of tight junction (TJ) proteins by targeting the PTEN/Akt pathway. Indeed,
theses exosomes decreased PTEN expression and activated Akt phosphorylation. On the
other hand, pretreatment with exosomes showed beneficial effects in declining MMP-9
expression, Evans blue dye extravasation, and TJ protein degradation in mice with TBI [
101
].
To suppress TBI-related neuroinflammation, microglial exosomes-contained miR-124-3p
could be considered as a potential therapeutic molecule in preventing neuronal inflam-
mation following TBI through targeting phosphodiesterase 4B (PDE4B) and ultimately
repressing the mTOR signaling pathway. Furthermore, elevated miR-124-3p in microglial
exosome-mediated inhibition of neuronal inflammation was associated with improved anti-
inflammatory M2 polarization of microglial cells [
102
]. Growing evidence has indicated
that hADSC-Exo shows neuroprotective effects against
in vivo
TBI models via suppression
of the classical NF-
κ
B and MAPK signaling pathways to restrain microglia/macrophage
activation. Overall, hADSC-Exo administration caused sensorimotor functional recovery in
TBI rats, improved hippocampal neurogenesis, suppressed neuroinflammation, and miti-
gated neuronal apoptosis. Notably,
in vitro
application of hADSC-Exo markedly inhibited
M1 microglial polarization and increased M2 microglial polarization. Hence, intracere-
broventricular hADSC-Exo administration could serve as a precious therapeutic modality
against CNS diseases [
103
]. Further in-depth studies are needed to confirm the effectiveness
of exosomes in TBI. Collectively, exosomes have exhibited a promising future in combating
TBI through modulating the PI3K/Akt/mTOR pathway (Table 2).
Pharmaceutics 2023,15, 1006 14 of 25
Table 2. Exosomes circumvent SCI and TBI via PI3K/Akt/mTOR and associated pathways.
Source of Exosomes Cargo or Intermediate
Molecule Disease Method (In Vitro/
In Vivo) Dose/Route of Administration Mechanism of Actions and Outcomes References
BMSCs miR-26a SCI
in vivo: SCI induced in
SD rats
in vitro: PC12 cells
200 µg in 200 µL PBS via tail
vein injection
20 µg/mL for 48 h
↑Axonal regeneration, neurogenesis, functional recovery,
BBB scores, MEP amplitudes, neurofilament density, Tuj-1,
p-Akt, p-PI3K, p-mTOR, p-S6K, and p62;
↓Glial scarring, GFAP, astrocyte inflammation, autophagy,
p-AMPK, p-ULK1, p-IKB, and p-p65;
↑Neurofilament generation, nerve regeneration, p-Akt,
p-PI3K, and p-mTOR,
↓PTEN, autophagy, p-AMPK, p-ULK1, p-IKB and p-p65
[84]
BMSCs miR-338-5p SCI
in vivo: SCI induced in
SD rats
in vitro: H2O2-induced
oxidative stress injury
in PC12 cells
100 µg (50 µg microinjected to
injured site +50 µg via the tail
vein) in PBS at 5 min and 1 h
after SCI,
100 µg of total protein
↑NF-M and GAP43;
↓MAG and GFAP;
↑Cell viability, SOD, NF-M, GAP43, Bcl-2, cAMP, Rap1,
p-Akt, and p-PI3K;
↓
Apoptosis, ROS, MAG, GFAP, Bax, cleaved caspase-3, and
Cnr1
[85]
BMSCs under hypoxia miR-216a-5p SCI
in vivo: SCI induced in
C57BL/6 mice
in vitro
: LPS-stimulated
BV2 microglial cells and
primary microglia
200 µg of total protein via tail
vein injection
200 µg/mL
↑Functional recovery, BMS score, gait recovery, motor
coordination, NeuN-positive neurons, MEP amplitudes,
IL-4, IL-10, TGF-β, Arg1, CD206, YM1/2, and M1 to M2
polarization;
↓Neurofilament 200, lesion volume, iNOS, TNF-α, IL-1β,
and IL-6;
↑IL-4, IL-10, Arg1, CD206, YM1/2, M1 to M2 polarization,
TGF-β, p-Akt, and p-PI3K;
↓TNF-α, IL-1β, IL-6, iNOS, TLR4, p-P65, and MyD88;
[86]
GIT1-BMSCs _____ SCI
in vivo: SCI induced in
SD rats
in vitro:
Glutamate-induced
injury model in
neuronal cells
200 µg of total protein via tail
vein injection
100 µg/mL
↑Nissl bodies, neural regeneration, BBB score, motor
function, Bcl-2, and P-Akt;
↓Apoptosis, glial scar formation, TNF-α, IL-1β, IL-6, Bax,
and cleaved caspase-3;
↑Bcl-2;
↓TUNEL-positive cells, neural apoptosis, Bax, cleaved
caspase-3, and caspase-9
[87]
MSCs _____ SCI
in vivo: SCI induced in
SD rats
in vitro: Astrocytes
isolated from SCI rats
1×106in 200 µL PBS via tail
vein injection,
5×104
↑Functional recovery, MBP, BBB scores, Syn, and NeuN;
↓Lesion size, morphological phenomena, p65+nuclei, A1
astrocytes, TNF-
α
, IL-1
α
, IL-1
β
, C3, GFAP, TUNEL-positive
cells, p-IKBα, and p-p65
[88]
Pharmaceutics 2023,15, 1006 15 of 25
Table 2. Cont.
Source of Exosomes Cargo or Intermediate
Molecule Disease Method (In Vitro/
In Vivo) Dose/Route of Administration Mechanism of Actions and Outcomes References
MSCs miR-126 SCI
in vivo: SCI induced in
SD rats
in vitro: OGD injury
model in HUVECs
100 µg of total protein in 0.5 mL
PBS via tail vein injection
10 µg
↑Functional recovery, VEGF, angiogenesis, neurogenesis,
blood vessels number and connectivity value, Bcl-2, NeuN,
Sox2, and Nestin positive cells;
↓Lesion volume, incorrect steps, apoptosis, SPRED1,
PIK3R2, Bax and cleaved caspase-3;
↑Angiogenesis and HUVECs migration;
↓SPRED1 and PIK3R2
[89]
Neuron-derived
exosomes miR-124-3p SCI
in vivo: SCI induced in
C57BL/6 mice
in vitro: Primary
microglial cultures and
MCM, primary
astrocyte cultures and
primary neuronal
cultures
200 µg of total protein in 200 µL
of PBS via tail vein injection
200 µg/mL
↑Functional recovery, BMS score, gait recovery, motor
coordination, MEP amplitudes, and hind limb alternation;
↓
Forelimb dependence, axonal damage, TNF-
α
, IL-1
α
, IL-6,
IL-1β, C1q, M1 microglia, iNOS, C3, and A1 astrocytes;
↑p-PI3K and p-Akt;
↓M1 microglia, iNOS, and p-P65
[90]
NSCs FTY720 SCI
in vivo: SCI induced in
SD rats
in vitro: SCMECs
hypoxic model
20
µ
g in 0.3 mL PBS via tail vein
injection
20 µg/mL
↑Locomotor function, complete
tissue structure, claudin-5, and Bcl-2;
↓Edema formation, inflammatory cell infiltration, SCI
lesion, neuronal cell apoptosis, AQP4, and Bax;
↑ZO-1 and p-Akt
↓PTEN and SCMEC permeability
[91]
Primary SCDEs _____ SCI
in vivo: SCI induced in
mice
in vitro: H2O2-induced
injury in spinal cord
astrocytes
0.1
µ
g/
µ
L in 100
µ
L of DPBS via
tail vein injection, three times a
week for 4 weeks
↑
TLR2, functional recovery, GFAP, 5-HT, BMS score, motor
function, and neuron survival;
↓CSPGs deposition, p-PI3K/PI3K, and NF-κB;
↓p-PI3K/PI3K and NF-κB
[92]
Pharmaceutics 2023,15, 1006 16 of 25
Table 2. Cont.
Source of Exosomes Cargo or Intermediate
Molecule Disease Method (In Vitro/
In Vivo) Dose/Route of Administration Mechanism of Actions and Outcomes References
Primary SCDEs _____ SCI
in vivo: SCI induced in
SD rats
in vitro: H2O2-induced
injury in PC12 cells
250 µL
(0.1 µg/µL) in DPBS via tail
vein injection, three times a
week for 4 weeks
↑Autophagy, motor function, myelinated areas, NeuN,
ChAT, LC3-1/2 and Beclin-1, P62;
↓Apoptosis, %cavity size and EGFR;
↑Neuronal survival, LC3-1/2, Beclin-1 and P62;
↓Apoptosis, EGFR, p-Akt, and p-mTOR
[93]
HUSC ANGPTL3 SCI
in vivo: SCI induced in
mice
in vitro: HUVECs
200
µ
g in 200
µ
L of PBS via local
intrathecal injection
200 µg
↑
Spinal cord regeneration, locomotor function, BMS scores,
sensory improvement, MEP amplitudes, angiogenesis,
vessel volume fraction, vascular segment and bifurcation
numbers;
↓Latent period and lesion cavities area;
↑Proliferation rate, cell migration, tube formation,
angiogenic activities, p-Akt, and p-PI3K
[94]
hUC-MSCs miR-199a-3p/145-5p SCI
in vivo: SCI induced in
SD rats
in vitro: LPS-induced
injury in PC12 cells
20 µg/mL
↑TrkA, locomotor function, and BBB score;
↓Lesion size, inflammation, and apoptotic cells
↑Cell viability, NF-H, β-tubulin-III, Neu-N, p-Akt, p-Erk,
neurite outgrowth, and TrkA;
↓Cblb and Cbl expression;
[95]
PMs _____ SCI
in vivo: SCI induced in
SD rats
in vitro: BV2 cells
cultured in DMEM
culture medium
20 and
200 µg/mL via tail vein
injection
20 and
200 µg/mL
↑BBB score, inclined plate angle, Nissl-positive cells, IL-4,
IL-10, and IL-13;
↓Tissue damage, IL-1β, IL-6, and TNF-α;
↑IL-10, CD206, CD163, Arg-1, LC3-II/I, and Beclin-1;
↓p62, mTOR, and Akt protein level;
[96]
Primary microglia Resveratrol SCI
in vivo: SCI induced in
SD rats
in vitro: Mechanical
injury model in primary
spinal cord neurons
0.2 mL of PBS suspension of
40 µM for 14 days
↑Muscle tension, foot functional movements, BBB scores,
motor function, neuron natural morphology and number,
LC3B-positive cells, Beclin-1, and p-PI3K;
↓TUNEL-positive neurons, cleaved caspase-3, and
apoptosis;
[97]
Pericytes _____ SCI
in vivo: SCI induced in
ICR mice
in vitro: SCMECs
hypoxic model
20
µ
g in 0.3 mL PBS via tail vein
injection
20 µg/mL
↑Locomotor function, complete
tissue structure, myelin sheath, Nissl body morphology
and number, blood flow, Bcl-2, local microvascular
disturbances, mean flux, and claudin-5;
↓Inflammatory cell infiltration, TUNEL-positive cells, Bax,
HIF-1α, BSCB disruption, edema formation, MMP-2, and
AQP4;
↑ZO-1 and p-Akt;
↓PTEN;
[98]
Pharmaceutics 2023,15, 1006 17 of 25
Table 2. Cont.
Source of Exosomes Cargo or Intermediate
Molecule Disease Method (In Vitro/
In Vivo) Dose/Route of Administration Mechanism of Actions and Outcomes References
ECFCs _____ TBI
in vivo: TBI induced in
male C57BL/6 mice
in vitro: RBMEC
hypoxia injury model
4×106cell equivalents via the
tail vein at 2 h
after TBI,5 and 10 µg/mL
↑Neurological functional recovery, TJ, p-Akt, CLN5,
occludin, and ZO-1;
↓Brain edema, PTEN, MMP-9, BBB permeability, EB dye
extravasation, and TJ degradation
[101]
Microglia miR-124-3p TBI
in vivo: (r)TBI male
C57BL/6 mouse model
in vitro: Scratch injury
model in pure cortical
neurons
30 µg via tail vein,
3×108exosomes
↑Neurologic outcomes, neurite outgrowth and IL-10;
↓PDE4B, IL-1β, IL-6, TNF-α, mTOR signaling, neuronal
inflammation, PDE4B, p-4E-BP1, and p-P70S6K;
[102]
Human ADSC _____ TBI
in vivo:
Weight-drop-induced
TBI in male SD rats
in vitro: LPS-induced
inflammatory model
20 µg total protein per rat,
2.0 ×1010 particles/mL,
intracerebroventricular injection
↑Functional recovery, neurogenesis, M1 to M2 microglial
polarization, IGF1, arginase1, CD206 and IL-10;
↓Neuroinflammation, neuronal apoptosis,
hippocampal neurogenesis, CD68+ activated
microglia/macrophages, mNSS score, TNF-
α
, iNOS, IL-1
α
,
IL-1β, IL-6, MCP-1, CCL2, CCL3, CCL5, morphological
transformation, p-P38, p-IKKαβ, p-IKBα, p-P68, NF-κB,
and P38/MAPK activation
[103]
Abbreviations:
↑
: increase or improve;
↓
: decrease or loss; Akt: protein kinase B; AMPK: AMP-activated protein kinase; AQP4: aquaporin-4; BAX: bcl-2-associated X protein; BBB: Basso,
Beattie and Bresnahan; Bcl-2: B-cell lymphoma 2; BMS: Basso mouse scale; BMSCs: bone marrow mesenchymal stem cells; C1q: complement component 1q; C3: complement component
3; cAMP: cyclic adenosine monophosphate; CCL2: chemokine ligand 2; ChAT: choline acetyltransferase; Cnr1: cannabinoid receptor 1; CSPG: chondroitin sulfate proteoglycan; ECFCs:
endothelial colony-forming cells; EGFR: epidermal growth factor receptor; GAP43: growth-associated protein-43; GFAP: glial fibrillary acidic protein; GIT1: G protein-coupled receptor
kinase 2 interacting protein 1; H
2
O
2
: hydrogen peroxide; hUC-MSCs: human umbilical cord mesenchymal stem cells; HUSC: human urine stem cell; HUVECs: human umbilical venous
endothelial cells; IGF1: insulin-like growth factor 1; IKB
α
: NF-kappa-B inhibitor alpha; IL: interleukin; iNOS: inducible nitric oxide synthase; i.p.: intraperitoneal; i.v.: intravenous;
LPS: lipopolysaccharide; MAG: myelin associated glycoprotein; MAPK: mitogen-activated protein kinase; MBP: myelin basic protein; MCM: microglia-conditioned medium; MCP-1:
monocyte chemoattractant protein-1MEP: motor-evoked potential; miR: microRNA; MMP-2: matrix metalloproteinase-2; MSCs: mesenchymal stem cells; NeuN: neuronal nuclei;
NF-M: neuro filament-M; NSCs: neural stem cells; PDE4B: phosphodiesterase 4B; PI3K: phosphoinositide 3-kinase; PIK3R2: phosphoinositide-3-kinase regulatory subunit 2; PMs:
peripheral macrophages; PTEN: phosphatase and tensin homolog; ROS: reactive oxygen species; SCDEs: Schwann cell-derived exosomes; SCI: spinal cord injury; SCMECs: spinal cord
microvascular endothelial cells; SD: Sprague-Dawley; SOD: superoxide dismutase; SPRED1: sprouty-related EVH1 domain-containing protein 1; Syn: synaptophysin; TBI: traumatic
brain injury; TGF-
β
: transforming growth factor-
β
; TJ: tight junction; TLR4: toll-like receptor 4; TNF-
α
: tumor necrosis factor-alpha; Tuj-1:
β
-tubulin-3; VEGF: vascular endothelial
growth factor; ZO-1: zonula occludens-1.
Pharmaceutics 2023,15, 1006 18 of 25
Exosomes could be considered powerful biomarkers for the diagnosis of TBI. Exosome
therapies are effective approaches for improving neurological and functional recovery via
increasing neurite growth and neurogenesis by delivery of gene or pharmacological agents
after TBI [
104
,
105
]. Moreover, there are still some challenges with the design, separation,
and purification procedure of exosomes [
106
]. Therefore, future research should explore a
cheap, quick, and simple standardized method for the generation of exosomes and establish
the best strategies for exosome modulation of TBI toward promoting the translation of
preclinical reports outcomes to clinical studies. In conclusion, the evidence shows that
exosomes might have great potential in neurorestorative therapy for TBI.
3.5. Exosomes and Other Neurological Disorders
It is worth mentioning that various types of exosomes could ameliorate several other
neurological diseases via the PI3K/Akt/mTOR pathway and other interconnected signaling
pathways [
107
]. Emerging reports suggest that the PI3K/Akt signaling pathway and the
associated proteins can be targeted by ADSC-Exo administration in ALS. Notably, it has
been reported that treatment with adipose stem cell (ACS) exosomes reduces pro-apoptotic
proteins such as cleaved caspase-3 and Bax while increasing the anti-apoptotic protein
Bcl-2 in an
in vitro
model of ALS. In addition, Western blot analysis revealed increased
p-Akt and SOD1 expression in ASC exosome-treated cells [
108
]. Moreover, another study
provided evidence on the effects of fibroblast-derived exosomes (FD-Exo) (50 ng/mL) on
the promotion of axonal regeneration in the injured CNS by recruiting Wnt10b toward
lipid rafts and subsequently activating mTOR signaling through GSK-3
β
and tuberous
sclerosis complex 2 (TSC2) [
109
]. In an experimental study, researchers found that FD-
miR-673-5p-Exo is associated with peripheral neuron myelination of Schwann cells via
stimulation of the TSC2/mTOR complex 1 (mTORC1)/sterol-regulatory element binding
protein 2 (SREBP2) axis. Indeed, FD-miR-673-5p-Exo can enhance peripheral neuron
myelination in newborn rats and myelin gene expression in Schwann cells [
110
]. In this
context, MSC-exosomes caused improved axonal growth of cortical recipient neurons and
increased the length of distal axons through augmenting p-mTOR and p-GSK-3
β
and
reducing PTEN; it was also found that elevation of miR-17-92 cluster in the exosomes (miR-
17-92 exosomes) further promoted axonal growth [
111
]. According to the reported studies,
exosomes derived from ADSCs (50 ng/mL) show inhibitory effects on lipopolysaccharide
(LPS)-induced injury in SH-SY5Y and BV-2 cells by reducing TNF-
α
, IL-1
β
, IL-6, COX-
2, iNOS, p-P38, p-P65, p-ERK, and p-JNK. In addition, ADSC-exosomes mitigated LPS
cytototoxic effects and suppressed neuroinflammation by repressing the NF-
κ
B and MAPK
signaling pathways. In conclusion, ADSC-exosomes reveal therapeutic effects on neural
injury induced by microglia activation [
112
]. Evidence indicates that exosomes released by
human ADSC (hAMSCs) seem to be a promising therapeutic approach against neural injury
induced by glutamate in PC12 cells by upregulating PI3K/Akt signaling pathway [
113
].
Based on the research, MSC-Exo in a rat model of ONC injury decreased the expression
of pro-inflammatory cytokines such as IL-1
β
, IL-6, IL-8, TNF-
α
, and MCP-1, whereas it
increased the anti-inflammatory mediator IL-10. In addition, MSC-Exo decreased the ONC-
induced apoptosis of the retinal ganglion cells (RGCs) via promotion of the Bcl-2/Bax ratio
and reduction in caspase-3 activity, and Akt phosphorylation/activation was observed
following intravitreal MSC-Exo administration [
114
]. Altogether, the authors demonstrated
that exosomes could serve as potential therapies in the management/treatment of other
neurological diseases via regulating PI3K/Akt/mTOR and associated signaling pathways
(Table 3).
Pharmaceutics 2023,15, 1006 19 of 25
Table 3. Exosomes circumvent other neurological diseases via PI3K/Akt/mTOR and associated pathways.
Source of Exosomes Cargo or Intermediate
Molecule Disease Method (In Vitro/In Vivo) Dose/Route of
Administration Mechanism of Actions and Outcomes References
ADSC _____ ALS
in vitro: H2O2-induced
injury in NSC-34 (G93A)
cells
0.2 µg/mL, corresponding
to 6–8 ×105particles/mL
↑
Phospho-Akt, SOD1 gene, Bcl-2
α
, and cell viability;
↓Cleaved caspase 3, Bax, and apoptosis; [108]
Fibroblast _____ CNS injury in vitro: Cultured adult rat
DRGs and RGCs 50 ng/mL
↑Cell survival, neurite growth, axonal growth, and
pS6K;
↓CSPG and Wnt10b;
[109]
Fibroblast miR-673-5p Peripheral neuron
myelinati on
in vivo: One-day-old
newborn rats
in vitro: Schwann cells
5 nmol/rat every 2 days via
hypodermic injection
↑
Myelin gene expression, mTORC1, SREBP2, Hmgcr,
phosphatidylcholine, phosphatidylethanolamine,
phosphatidylserine, diacyl glycerol, cholesterol,
myelin sheath, myelinated axons, and myelin
lamellae;
↓Tsc2 expression;
[110]
MSCs miR-17-92 Axonal growth
in vitro: Primary cortical
neurons under CSPG
conditions
3×108/300 µL and
3×109/300 µL
↑Axonal growth, distal axons length, p-mTOR, and
p-GSK-3β;
↓PTEN;
[111]
ADSCs _____ Neural injury in vitro
: LPS-induced injury
in SH-SY5Y and BV-2 cells 50 µg/mL
↑Cell viability;
↓Neuroinflammation, microglia cells, TNF-α, IL-1β,
IL-6, COX-2, iNOS, cytotoxicity, p-P38, p-P65, p-ERK,
and p-JNK;
[112]
hAMS _____ Neural injury
in vitro: Neural injury
induced by glutamate in
PC12 cells
100 ng/mL ↑Cell survival and PI3K/Akt signaling activating; [113]
MSCs _____ ONC injury in vivo: ONC-induced
injury in SD rats 3×109/5 µL, intravitreal
injection
↑RGCs survival, IL-10, Bcl-2, and p-Akt;
↓IL-1β, IL-6, IL-8, MCP-1, Bax, TNF-α, cleaved
caspase-3, and apoptosis;
[114]
Abbreviations:
↑
: increase or improve;
↓
: decrease or loss; ADSC: adipose-derived stem cells; Akt: protein kinase B; ALS: amyotrophic lateral sclerosis; CNS: central nervous system;
COX-2: cyclooxygenase-2; CSPG: chondroitin sulfate proteoglycan; DRGs: dorsal root ganglia; ERK: extracellular signal-regulated kinase; GSK-3
β
: glycogen synthase kinase-3 beta;
hAMS: human adipose-derived mesenchymal stem cells; Hmgcr: 3-hydroxy-3methylglutaryl coenzyme A; IL: interleukin; iNOS: inducible nitric oxide synthase; JNK: c-Jun N-terminal
kinase; LPS: lipopolysaccharide; MCP-1: monocyte chemoattractant protein-1; MSCs: mesenchymal stem cells; mTOR: mammalian target of rapamycin; mTORC1: mechanistic target of
the rapamycin complex 1; ONC: optic nerve crush; PTEN: phosphatase and tensin homolog; RGCs: retinal ganglion cells; SREBP2: sterol-regulatory element binding protein 2; TNF-
α
:
tumor necrosis factor-α.
Pharmaceutics 2023,15, 1006 20 of 25
4. Conclusions and Future Perspective
A growing number of studies have highlighted the pivotal role of the PI3K/Akt/mTOR
signaling pathway in the CNS and associated dysregulations. In addition, recent re-
ports are demonstrating the modulatory roles of PI3K/Akt/mTOR pathway and the re-
lated inflammatory mediators (e.g., NF-
κ
B, TNF-
α
, ILs, CRP, COX-2, and MMP-9); oxida-
tive/antioxidative factors (e.g., GSH, SOD, CAT, Nrf2/HO-1, and iNOS); apoptotic factors
(e.g., Bax, Bcl-2, caspase-3, and caspase-9); and the interlinked pathways (e.g., MAPK,
CREB/BDNF, GSK-3
β
, ERK1/2, and JAK/STAT) in the progression/treatment of NDDs
and other neurological diseases (Figure 2). Considering the side effects and resistance
mechanisms to conventional neuroprotective drugs, it is of great importance to provide
alternative therapies in combating neurological diseases. Exosomes can be considered to
be promising therapies owing to their specific properties including low immunogenicity,
flexibility, high BBB penetration capacity, and the capability of being used as drug delivery
vehicles that could provide a long-lasting concentration of medication in the CNS while
having few side effects and especially regulating the aforementioned inflammatory, oxida-
tive, and apoptotic pathways/factors. To combat such pathophysiological mechanisms,
it is necessary to consider novel approaches to drug delivery into the CNS using natural
entities with fewer side effects. Exosomes strategically carry drugs and possess suitable
stability and half-life. Understanding the roles that exosomes play in communication
between various cell types at diverse sites provides a critical step forward in revealing
the details of cell communication [
115
]. However, exosome-based therapeutic strategies
and research progress in the field of exosomes face some challenges including difficul-
ties in characterization, lack of controlled drug release mechanisms, inefficient isolation
methods, drug interaction with exosome/EV components, and lack of specific biomarkers.
Exosomes are suitable carriers for various cargoes including proteins, drugs, and natural
products. There are now limitations in the manipulation of exosomes to be used in dis-
eases. Separation, identification, and diagnosis of exosomes are critical steps requiring
future research [
50
]. The optimization of operational procedures is necessary, and the
characterization of exosome cargoes’ mediating therapeutic effects is warranted. New
low-cost techniques to obtain a large amount of high-purity exosomes need to be provided.
Furthermore, increasing the half-life of exosomes and targeting the ability of exosomes
could provide clinical-grade exosomes as promising therapeutic approaches for future
studies [116].
Pharmaceutics 2023, 15, x 19 of 24
requiring future research [50]. The optimization of operational procedures is necessary,
and the characterization of exosome cargoes’ mediating therapeutic effects is warranted.
New low-cost techniques to obtain a large amount of high-purity exosomes need to be
provided. Furthermore, increasing the half-life of exosomes and targeting the ability of
exosomes could provide clinical-grade exosomes as promising therapeutic approaches for
future studies [116].
Figure 2. Exosomes can target the PI3K/Akt/mTOR signaling pathway, thereby modulating various
interconnected events involved in NDDs towards therapeutic application.
Accordingly, considering the critical role of PI3K/Akt/mTOR in NDDs and the mul-
tiple advantages of EVs in the context of effective and safe drug delivery, exosomes could
confer a significant neuroprotective role in combating AD, PD, ALS, stroke, TBI, and other
neuronal disorders [117].
This is the first systematic review with a focus on the pivotal role of PI3K/Akt/mTOR
pathway targeted by exosomes in NDDs. We critically highlighted the modulatory func-
tions of exosomes in NDDs through PI3K/Akt/mTOR pathway. Future investigations
should incorporate extensive in vitro and in vivo experimentations and well-designed
randomized clinical trials on exosomes to clarify in more detail the crucial roles of the
PI3K/Akt/mTOR pathway and the modulatory effects of exosomes in the context of
NDDs.
Author Contributions: Conceptualization, S.F., A.I. and H.K.; drafting the manuscript, A.I., L.K.
and S.Z.M.; software, S.F.; review and editing, L.S., S.F. and H.K. All authors have read and agreed
to the published version of the manuscript.
Funding: This work was supported by the Student Research Committee at the Kermanshah Univer-
sity of Medical Sciences, Kermanshah, Iran (Grant No.50002205).
Conflicts of Interest: The authors declare no conflict of interest.
References
1. Ou, G.-Y.; Lin, W.-W.; Zhao, W.-J. Neuregulins in neurodegenerative diseases. Front. Aging Neurosci. 2021, 13, 170.
2. Dugger, B.N.; Dickson, D.W. Pathology of neurodegenerative diseases. Cold Spring Harb. Perspect. Biol. 2017, 9, a028035.
Figure 2.
Exosomes can target the PI3K/Akt/mTOR signaling pathway, thereby modulating various
interconnected events involved in NDDs towards therapeutic application.
Pharmaceutics 2023,15, 1006 21 of 25
Accordingly, considering the critical role of PI3K/Akt/mTOR in NDDs and the multi-
ple advantages of EVs in the context of effective and safe drug delivery, exosomes could
confer a significant neuroprotective role in combating AD, PD, ALS, stroke, TBI, and other
neuronal disorders [117].
This is the first systematic review with a focus on the pivotal role of PI3K/Akt/mTOR
pathway targeted by exosomes in NDDs. We critically highlighted the modulatory functions
of exosomes in NDDs through PI3K/Akt/mTOR pathway. Future investigations should
incorporate extensive
in vitro
and
in vivo
experimentations and well-designed randomized
clinical trials on exosomes to clarify in more detail the crucial roles of the PI3K/Akt/mTOR
pathway and the modulatory effects of exosomes in the context of NDDs.
Author Contributions:
Conceptualization, S.F., A.I. and H.K.; drafting the manuscript, A.I., L.K. and
S.Z.M.; software, S.F.; review and editing, L.S., S.F. and H.K. All authors have read and agreed to the
published version of the manuscript.
Funding:
This work was supported by the Student Research Committee at the Kermanshah Univer-
sity of Medical Sciences, Kermanshah, Iran (Grant No. 50002205).
Conflicts of Interest: The authors declare no conflict of interest.
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