Inhibition of Atrial Natriuretic Peptide Clearance Reduces Myocardial Fibrosis and Improves Cardiac Function in Diabetic Rats

Background: Natriuretic peptides (NP) exert pleotropic effects through the recruitment of cGMP-signaling pathways depending on their bioavailability which is regulated by clearance receptors and peptidases. Here, we tested the hypothesis that increasing myocardial bioavailability of NP has a beneficial effect on heart failure. We studied the effects of a mutated NP, MANP, resistant to neprilysin in a model of diabetic cardiomyopathy characterized by a marked myocardial fibrosis. Methods: Natriuretic peptides as well as sacubritril were delivered via osmotic mini-pumps to high-fat/streptozotocin-induced type-2 diabetic (T2D) rats. Cardiac function was evaluated by echocardiography. Myocardial remodeling was studied by histological approaches, collagen phenotype and measurement of cGMP tissue concentration. Live-cell cGMP biosensing was conducted on cultured rat cardiac fibroblasts to investigate biological effects of NPs. cGMP signaling pathway was studied using various antibody arrays and biochemicals assays in cardiac tissue and cultured fibroblasts. Results: MANP exhibits superior efficacy than ANP in reducing left ventricular dysfunction and to reduce myocardial fibrosis with less extracellular matrix deposition. In vitro, MANP and ANP similarly generated cGMP and activated PKG signaling pathway in cardiac fibroblasts, attenuating SMAD activation, collagen secretion and cell proliferation. Nevertheless, in vivo, MANP enhanced cardiac cGMP accumulation and was more potent than ANP in activating myocardial cGMP/PKG signaling and inhibiting the profibrotic SMAD pathway. Endopeptidase inhibition using sacubitril also led to cardiac cGMP accumulation and reduced myocardial fibrosis Conclusions: Myocardial bioavailability of ANP is a major determinant of peptide efficacy in reducing cardiac fibrosis and improving pump function during diabetic cardiomyopathy.