Ghrelin attenuates myocardial fibrosis after acute myocardial infarction via inhibiting endothelial-to mesenchymal transition in rat model

Ghrelin, a peptide hormone produced in the gastrointestinal tract, has recently been found to be associated with the onset of myocardial fibrosis (MF). The exact mechanism, however, remains elusive. This study sought to identify the function and mechanism of ghrelin on MF after acute myocardial infarction (AMI). AMI was established in Spraque-Dawley rats by ligation of the left anterior descending (LAD). Ghrelin or saline was intraperitoneally injected two times per day for 8 weeks after ligation. The weight of heart (mg) and the weight ratio of heart to body (mg/g) as well as the fibrotic area were increased, while serum level of ghrelin was decreased after AMI. Ghrelin significantly ameliorated MF and decreased deposition of collagens in perivascular fibrosis area. In addition, ghrelin inhibited Endothelial-to-mesenchymal transition (EndMT), a crucial process for MF, in perivascular fibrosis area and TGF-beta 1-induced human coronary artery endothelial cells (HCAECs). Mechanistically, ghrelin persistently decreased the phosphorylation of Smad2/3 and enhanced the expression of Smad7 and p-AMPK in vivo and in vitro. After the abolition of Smad7, GHSR-1a and AMPK pathway, the effect of ghrelin on EndMT was significantly inhibited. In conclusion, these results presented a novel finding that ghrelin attenuated MF after AMI via regulation EndMT in a GHSR-1 a/AMPK/Smad7- dependent manner.