Ghrelin Ameliorates Angiotensin II-Induced Myocardial Fibrosis by Upregulating Peroxisome Proliferator-Activated Receptor Gamma in Young Male Rats

Abstract

Angiotensin (Ang) II contributes to the formation and development of myocardial fibrosis. Ghrelin, a gut peptide, has demonstrated beneficial effects against cardiovascular disease. In the present study, we explored the effect and related mechanism of Ghrelin on myocardial fibrosis in Ang II-infused rats. Adult Sprague-Dawley (SD) rats were divided into 6 groups: Control, Ang II (200ng/kg/min, microinfusion), Ang II+Ghrelin (100 μg/kg, subcutaneously twice daily), Ang II+Ghrelin+GW9662 (a specific PPAR-γ inhibitor, 1 mg/kg/d, orally), Ang II+GW9662, and Ghrelin for 4 wks. In vitro, adult rat cardiac fibroblasts (CFs) were pretreated with or without Ghrelin, Ghrelin+GW9662, or anti-Transforming growth factor (TGF)-β1 antibody and then stimulated with or without Ang II (100 nmol/L) for 24 h. Ang II infusion significantly increased myocardial fibrosis, expression of collagen I, collagen III, and TGF-β1, as well as TGF-β1 downstream proteins p-Smad2, p-Smad3, TRAF6, and p-TAK1 (all p<0.05). Ghrelin attenuated these effects. Similar results were seen in Ang II-stimulated rat cardiac fibroblasts in vitro. In addition, Ghrelin upregulated PPAR-γ expression in vivo and in vitro, and treatment with GW9662 counteracted the effects of Ghrelin. In conclusion, Ghrelin ameliorated Ang II-induced myocardial fibrosis by upregulating PPAR-γ and in turn inhibiting TGF-β1signaling.

Regional Differences in the Ghrelin-Growth Hormone Secretagogue Receptor Signalling System in Human Heart Disease

“…In the same study, no differences in GHSR density were observed in the RA or the LV between the ischemic heart disease or dilated cardiomyopathy to the control tissues 30 . Our findings also showed no changes in myocardial GHSR as measured by Cy5-ghrelin (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19), and a relatively weak correlation with ghrelin, suggesting that more dramatic changes in GHSR may occur at the site of vascular tissue injury or dysfunction.…”

“…Biopsy samples from the left ventricle (LV) and right atrium (RA) were obtained from 25 patients with valvular disease (of whom 13 also had coronary artery disease) and preserved left ventricular ejection fraction, and compared to control samples that were obtained via autopsy. Using quantitative confocal fluorescence microscopy, levels of GHSR were determined using a fluorescent peptide analog of ghrelin, Cy5-ghrelin (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19); ghrelin, the heart failure marker natriuretic peptide type-b (BNP), and contractility marker sarcoplasmic reticulum ATPase pump (SERCA2a) were measured by immunofluorescence. A positive correlation between GHSR and ghrelin was apparent in diseased tissue, but not in control tissue.…”

“…Apoptosis is decreased upon GHSR activation through extracellular signal-related kinases 1/2 (ERK1/2) and AKT serine kinases 5,6 and inhibition of caspase-3 and 9 7 . Fibrosis deposition through collagen I and III production is also minimized in the heart after ghrelin administration 8,9 . Therefore, the ghrelin/GHSR axis within the myocardium plays a critical role in the maintenance of cardiomyocyte function and survival.…”

“…Graphs indicate quantification of integrated densities using linear regression between Cy5-ghrelin(1-19) and ghrelin (r = 0.3995; p=0.0318) in the entire patient cohort where each dot represents one patient sample (B). Regional analysis showed a significant linear regression of Cy5-ghrelin(1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19) and ghrelin in the RA (r = 0.4859; p=0.0299) but not the LV (p=ns) (C). In control tissue, there was no correlation between Cy5-ghrelin(1-19) and ghrelin (p=ns) (D).…”

Morphological and Functional Characteristics of Animal Models of Myocardial Fibrosis Induced by Pressure Overload

“…At present, angiotensin is widely used to construct myocardial fibrosis model, but the dosage and time point have not reached a unified standard. Research showed that myocardial fibrosis could be induced by continuous infusion of angiotensin at different rates of 0.2 or 2.0 μg/kg/min (no mice died during the 4 weeks of Ang II infusion) [121], 200 ng/kg/min [122], 1.5 μg/day [123] and 0.83 μg/kg/min [124], 400 ng/kg/min [125], and 0.7 mg/kg/d [126] via an osmotic minipump for 4 weeks. In addition, myocardial fibrosis could also be induced by continuous infusion of angiotensin at the rates of 1.5 mg/kg/day [127], 1000 ng/kg/ min [128], 1.1 mg/kg/day [129],and 800 ng/min/kg [130] via an osmotic minipump for 2 weeks.…”