Ghrelin suppresses cardiac fibrosis of post-myocardial infarction heart failure rats by adjusting the activin A-follistatin imbalance

Ghrelin, a growth hormone-releasing peptide, potentially improves cardiac function, but the mechanisms remain unclear. In the study, the rat heart failure (HF) model was established by ligating the left anterior descending coronary artery (LAD) and treated with ghrelin (100μg/kg, subcutaneous injection, bid); neonatal rat cardiomyocytes were cultured and stimulated with Ang II (0.1μM) and ghrelin(0.1μM) to explore the underlying mechanism of ghrelin in myocardial remodeling. Hemodynamic changes and serum brain natriuretic peptide (BNP) concentrations were measured to assess cardiac function. Left ventricular mass index (LVMI), hematoxylin and eosin (HE) staining, and Masson's trichrome staining were performed to evaluate myocardial fibrosis. Interestingly, ghrelin significantly improved cardiac function by inhibiting fibrous tissue proliferation. To further explore the mechanisms by which ghrelin interferes with myocardial fibrosis, the levels of activin A (Act A) and its blocker-follistatin (FS) were examined by immunohistochemistry; Act A levels were significantly increased in the myocardial infarction (MI), and ghrelin administeration downregulated Act A expression. In contrast, FS expression showed no significant change in all experimental groups. Furthermore, ghrelin decreased Ang II-induced Act A expression with no effect on FS expression in primary rat cardiomyocytes in vitro (real-time quantitative PCR and ELISA). Thus, ghrelin corrected the Act A/FS imbalance. Finally, Act A treated cultured primary rat cardiac fibroblasts (CFs) showed increased proliferation [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay] and enhanced expressions of type I and type III collagen (Col I and Col III) (real-time quantitative PCR). These data suggest that ghrelin inhibits myocardial fibrosis, attenuates left ventricular remodeling, and eventually improves cardiac function by adjusting Act A/FS imbalance.