Multifunctional role of microRNAs in mesenchymal stem cell-derived exosomes in treatment of diseases

Table 1 Exosome isolation methods

Isolation method	Principle	Advantages	Limitations
Ultracentrifugation	Exosomes are purified by physical centrifugation according to their size and specific gravity	(1) The most common method; (2) Bulk extractability; and (3) Low cost	(1) The operation is complex and time-consuming; (2) Increased impurities; (3) Loss due to adsorption on the tube wall; and (4) Expensive equipment is needed[158]
Ultrafiltration	According to the size of exosomes, exosomes are separated by filter membrane	(1) Simple operation; (2) Rapid process; and (3) High yield	(1) Low-purity; and (2) Stress and shear forces can cause exosome damage
Size exclusion chromatography	The biofluid dissolves in the mobile phase and passes through the stationary phase, in which the various components of the mixture move at different speeds and are separated[159]	(1) High recovery rate; and (2) The structural integrity of exosomes is maintained	(1) Time-consuming; and (2) Low-purity
Precipitation[160,161]	By chemical extraction, the exosome liquid is combined with the liquid in the kit, and eventually the exosomes are deposited.	(1) Simple operation; (2) Rapid process; (3) No need for special equipment	Increased impurities
Immune affinity capture	Immune isolation is performed by magnetic bead-specific adsorption of exosome surface antigens	(1) Easy operation; (2) Rapid process; (3) High purity; and (4) High yield	(1) Does not apply to large-volume cell supernatant; and (2) High cost
Microfluidic technologies (ExoChip)	A microfluidic platform based on nano-acoustic filters, viscoelastic fluid separation, lateral displacement, and immune affinity separates exosomes from biological fluids	(1) Rapid separation; (2) High purity; and (3) Saving the sample	The research is not sufficient and is not widely used at present

Table 2 Representative clinical trials of mesenchymal stem cell-derived exosomes

Exosome origin	Diseases	Administration method	Status	miRNAs that may be associated with MSC therapy for this disease
Allogenic mesenchymal stromal cells	Cerebrovascular disorders	Intravenous injection	Completed	MiRNA-184, miRNA-210, miR-133b, miR-17-92[81,82,162]
Allogenic adipose mesenchymal stem cells	COVID-19	Aerosol inhalation	PhaseI	Has not been reported
Allogenic mesenchymal stromal cells	Multiple organ failure	Intravenous injection	Not yet Recruiting	Has not been reported
Human UC-MSCs	Macular holes	Intravitreal injection	PhaseI	Has not been reported
Human UC-MSCs	Dry eyes	Eye drops	Phase II	Has not been reported
Adipose mesenchymal stem cell	Alzheimer’s disease	Nasal drip	Phase II	MiR-146a-5p[79]
Human UC-MSCs	Diabetes mellitus type 1	Intravenous infusion	Phase III	MiR-1908, miR-203a[80]
MSCs	COVID-19	Inhalation	Phase II	Has not been reported
Human UC-MSCs	Chronic ulcer	Applying and closed by transparent dressing	Completed	Has not been reported

UC-MSCs: Umbilical cord mesenchymal stem cells; MSCs: Mesenchymal stem cells; COVID-19: Corona virus disease 2019.

Table 3 Representative articles on inflammatory regulation

Exosome origin	Diseases	MicroRNA	Downstream molecular/pathways	MicroRNA methodology
Placenta-derived mesenchymal stromal cells	Duchenne muscular dystrophy	MiR-29c	TGF-β	Reporter gene assays[106]
Induced pluripotent stem cells	Group 2 innate lymphoid cell-dominant allergic airway	MiR-146a-5p	T helper 2 (Th2) cytokines	Anion-exchange chromatography; RNA sequencing[105]
Mouse BM-MSCs	Peripheral neuropathy in diabetes	MiR-17, miR-23a, and miR-125b	TLR4/NF-κB signaling pathway.	MiRNA array; ultracentrifugation[164]
MSCs	Myocardial ischemia-reperfusion injury	MiR-182	TLR4 pathway	Differential centrifugation; miRNA sequencing[107]
Human UC-MSCs	Burn-induced excessive inflammation	MiR-181c	TLR4 pathway	PureExo Column; miRNA array analysis[164]
LPS-preconditioned MSCs	Wound healing	Let-7b	TLR4 pathway	Gradient centrifugation; miRNA microarray[111]
Human UC-MSCs	Hyperglycemia-induced retinal inflammation	MiR-126	HMGB1 signaling pathway	Ultracentrifugation[165]

BM-MSCs: Bone marrow MSCs; UC-MSCs: Umbilical cord mesenchymal stem cells; MSCs: Mesenchymal stem cells; TGF-β: Transforming growth factor-β; TLR4: Toll-like receptor 4; HMGB1: High-mobility group box-1.

Table 4 Representative studies in which MSC-derived exosomes affect tumors through miRNAs

Exosome origin	Disease	MiRNA	Downstream molecular/pathway(s)	Outcome
BM-MSCs	Osteosarcoma	MiR-208a	Downregulation of PDCD4 and activation of the ERK1/2 pathway	Promoting tumor progression[119]
BM-MSCs	Multiple myeloma	MiR-146a	The Notch pathway	Promoting tumor progression[121]
BM-MSCs	Colon cancer	MiR-142-3p	Downregulation of Numb	Promoting tumor progression
BM-MSCs	Breast cancer	MiR-23b	Decreased MARCKS expression	Inhibiting tumor progression[128]
MiR-122-transfected AMSCs	HCC	MiR-122	without research	Inhibiting tumor progression[129]
BM-MSCs	Prostate cancer	MiR-143	TFF3	Inhibiting tumor progression[70]
MSCs	Breast cancer	MiR-100	VEGF	Inhibiting tumor progression[166]

BM-MSCs: Bone marrow-derived mesenchymal stem cells; AMSCs: Adipose-derived mesenchymal stem cells; MSCs: Mesenchymal stem cells; HCC: Hepatocellular carcinoma; TFF3: Trefoil factor 3; VEGF: Vascular endothelial growth factor.