Exosomes Derived From Umbilical Cord MSCs Ameliorate MSC Aging And Their Myocardial Repair Ability

Background:The incidence of myocardial infarction is rapidly rising,seriously endangering human health.At present,autologous stem cells play a crucial role in the repair and regeneration of myocardial tissue.Mesenchymal stem cell(MSC)is a kind of adult stem cells with strong self-proliferation and multi-differentiation potential.They also secrete a variety of growth factors and active substances,which play an important role in maintaining body homeostasis and injury repair,becoming the preferred donor cells for stem cell transplantation to repair infarcted myocardium.However,studies have shown that,compared with young individual-derived MSCs,MSCs derived from older individuals have a significant defect in cell proliferation,differentiation,anti-apoptosis,post-transplant survival,paracrine function,and post-transplant myocardial repair.Therefore,how to improve the myocardial repair capacity of old MSCs has become an urgent problem to be solved.Studies have shown that the activity factors of MSCs isolated from human fetal tissues in vitro culture condition medium can reduce the expression and activity of senescence-associated β-galactosidase in old MSCs,and increase the cell proliferation and osteogenic differentiation potential of old MSCs.It suggests that paracrine factors of MSCs may play an important role in anti-aging process.Exosomes are extracellular vesicles that carry a wide range of contents including nucleic acids,proteins,lipids,mRNAs,and microRNAs.Exosomes can not only reduce tissue damage,but also improve the ability of tissue repair.Previous studies have shown that in rat myocardial infarction models,pretreatment of cardiac stem cells with exosomes derived from MSCs had better survival rates,increased capillary density around the myocardial infarction,reduced cardiac fibrosis,and restored long-term cardiac function.It was suggested that exosomes play an important role in the paracrine secretion of MSCs,but the effect of exosomes secreted by young individual-derived MSCs on MSCs in elderly patients remains unclear and the mechanism remains to be clarified.Objective:We performed this study to investigate whether exosomes derived from human umbilical cord MSCs(UMSCs)can ameliorate the senescent of old MSCs(OMSCs),improve myocardial repair ability and to explore the related mechanism.Methods and results:1.This study first compared senescent phenotypes and biological functional activities of OMSCs(>60 years old)with UMSCs.The results showed that OMSCs was significantly defective in cell proliferation,migration,and anti-apoptosis.It was confirmed that there were differences in the function of MSCs in different age groups.2.Exosomes were extracted from UMSCs culture condition medium.Senescence phenotype and biological function of OMSCs were observed after treated with exosomes derived from UMSCs.We found that UMSCs-derived exosomes can reduce the expression and activity of senescence-associated β-galactosidase in OMSCs and reduce the expression of aging-related factors such as p51,p21,and p16,and increase the proliferation,migration,three-line differentiation potential anti-apoptotic and paracrine functions of aged MSCs.It was confirmed that exosomes secreted by UMSCs can ameliorate the senescence of OMSCs.3.Age-related miRNAs were screened by database and literature,and the expression differences of specific miRNAs in UMSCs,OMSCs,and exosomes-treated OMSCs were detected,which was parallel to the change in exosomes derived from UMSCs and OMSCs.Besides,we found there was higher levels of miR-136 and lower its downstream gene apaf1 in UMSCs and OMSCs cultured with exosomes derived from UMSCs.It was further confirmed that the exosomes secreted by UMSCs carry anti-aging factors.4.By adding miR-136 mimic in OMSCs and miR-136 inhibitor in UMSCs,it was observed whether the exosomes can ameliorate aging and improve the biological function of OMSCs by releasing miR-136.5.Then we injected DMEM,OMSCs,UMSCs and exosomes treated OMSCs into myocardium immediately after performing myocardial infarction model in mouse to observe the difference in myocardial repair after myocardial infarction.The cardiac function,heart fibrosis,and angiogenesis in mice were analyzed at day3,7,14 and 28 after myocardial infarction.It was found that the cardiac function of OMSCs treated with exosomes was significantly improved.Conclusion:Exosomes derived from human umbilical cord MSCs can ameliorate aging of aged MSCs and enhance myocardial repair by releasing exosomal miR-136.