Abstract 18748: Prevention of Skeletal Muscle Atrophy and Fibrosis in Congestive Heart Failure by Skeletal Myoblast-Targeted Overexpression of Angiotensin II Type 2 Receptor

Abstract

Introduction: We have previously shown that angiotensin II (Ang II) type 2 receptor (AT2R) positively regulates skeletal myoblast differentiation. Systemic angiotensin II (Ang II) increase or congestive heart failure suppress AT2R expression, likely contributing to the development of skeletal muscle atrophy and fibrosis associated with these conditions. Hypothesis: We hypothesized that AT2R overexpression in skeletal myoblasts could prevent skeletal muscle atrophy and fibrosis associated with congestive heart failure (CHF). Approach: Two mouse models, systemic Ang II infusion and left anterior descending coronary artery (LAD) ligation were used in this study. Myoblast differentiation, muscle atrophy and muscle fibrosis were assessed by analyzing gene expressions (e.g. myogenin and atrogin-1), myofiber cross sectional area, and the collagen deposition (picrosirius red staining). Primary myoblasts were isolated from mouse hindlimb muscles. Myoblast-specific AT2R-overexpressing transgenic mice were generated by crossing Pax7 CreER/+ mice (tamoxifen-inducible cre recombinase is expressed under Pax7 promoter) and CAG-stop flox -AT2R mice (AT2R is expressed under CMV early enhancer element, chicken β-actin gene promoter upon cre-mediated excision of floxed stop codon). Results: AT2R expression was robustly increased during myoblast differentiation both in vitro and in vivo . siRNA-mediated AT2R knockdown significantly suppressed myoblast differentiation in vitro and skeletal muscle regeneration in vivo . In both Ang II infusion and LAD ligation models, AT2R induction during myoblast differentiation was significantly suppressed, associated with reduced muscle regeneration and increased atrophy and fibrosis. Myoblast-specific AT2R overexpression in vivo restored muscle regenerative capacity, and prevented muscle atrophy and fibrosis. Conclusions: AT2R induction in skeletal myoblast is suppressed in CHF, possibly via increased Ang II. Decreased AT2R expression and its downstream signaling in myoblast lead to lowered muscle regenerative capacity and increased muscle atrophy and fibrosis. Restoration of myoblast AT2R expression could lead to a novel therapy to prevent muscle atrophy and fibrosis in CHF condition.