The Mechanism Of Repairing Acute Myocardial Infarction Injury By Exosomes Derived From Human Umbilical Cord Mesenchymal Stem Cells

Objective:Our previous study found that exosomes derived from human umbilical mesenchymal stem cells（hucMSCs-exosomes）can effectively repair myocardial injury induced by acute myocardial infarction（AMI）,however,the exact mechanism is unknown.This study,on the basis of previous experimental studies,was aimed to further explore the potential mechanism of hucMSCs-exosomes repairing myocardial injury.Methods:Cultivation of hucMSCs used the adherent culture method;Using the method of ultrafiltration and sucrose heavy water gradient density centrifugation to separation and purification hucMSCs-exosomes and identified by nanoparticle analysis and Western blot;on the basis of establishing an AMI model of SD rats by ligation of the left anterior descending coronary artery,infusion hucMSCs-exosomes were treated via tail vein,then,echocardiography,HE staining and Western blot were used to detect the effect of hucMSCs-exosomes on the repair of myocardial injury after 2 days and 4 weeks;Constructing H9C2（2-1）cells injury model in vitro,lactate dehydrogenase（LDH）release detection,trypan blue staining and Western blot were used to detect the effect of exosomes on the repair of myocardial injury after adding exosomes 48h;Western blot was used to detect the changes of Smad7 expression during exosomes repairing myocardial injury;and bioinformatics was used to predict miRNAs that regulate Smad7 expression,and validated by quantitative PCR and luciferase reporter assay;H9C2（2-1）cells underwent hypoxia 48h after transfection miR-125b-5p mimics,Western blot was used to detect the expression of Smad7,Bax and Bcl-2,and detect LDH release,analysis possible mechanisms of exosomes repairing myocardial injury.Results:HucMSCs and hucMSCs-exosomes were successfully isolated in this study;Nanoparticles analysis revealed that the hucMSCs-exosomes were about 134nm of diameter,the final concentration was about 4.17±0.22×10¹⁰ particles/ml;expressed exosomes related protein,such as CD9,CD63 and CD81;hucMSCs-exosomes improved cardiac contractility of SD rat AMI model and repaired myocardial injury in vivo;in vitro hucMSCs-exosomes can significantly inhibit H9C2（2-1）cells apoptosis induced by hypoxia-ischemia damage;and the expression of Smad7 was significantly decreased after myocardial injury in vitro and in vivo,but hucMSCs-exosomes upregulated the expression of Smad7 while repairing myocardial injury;Bioinformatics predicted that miR-125b-5p could regulate the expression of Smad7;the transfected H9C2（2-1）cells were maintained under hypoxia for 48h,compared with the MNC+hypoxia group,miR-125b-5p mimics+hypoxia group had more obvious myocardial damage,and the downregulated of Smad7 expression was more obvious,but hucMSCs-exosomes alleviated this phenomenon to some extent.Conclusion:HucMSCs-exosomes can effectively repair myocardial injury,the possible mechanism is that hucMSCs-exosomes may upregulated Smad7 expression via downregulation of miR-125b-5p to improve myocardial repair.