COL4A1 and myocardial infarction: Human placental mesenchymal stem cell exosomes (HPMSC-Exos) carrying miR-543 increase cardiomyocyte survival by silencing the expression of collagen type IV alpha 1 chain (COL4A1), promote the angiogenesis of cardiac microvascular endothelial cells, relieve MI, and reduce myocardial injury (3).