TLR4 and myocardial infarction: The main findings of this study are 1) LPS preconditioning can improve the survival of MSCs, promote expression of VEGF and phospho-Akt in infarcted myocardium; 2) LPS-preconditioned MSCs transplantation can enhance cardiac function, reduce apoptosis of myocardium, inhibit fibrosis and elevate vascular density after MI; 3) TLR4 plays an important role in the signal pathway of LPS-induced cardiac protection.