CXCR4 and myocardial infarction: First, as shown above, PDGF-BB pretreatment increased the cell surface expression of CXCR4, and UTMD upregulated the expression of SDF-1 in myocardial infarct tissue, while the interaction between CXCR4 and SDF-1 improved the migration and homing abilities of implanted MSCs.