Abstract 18465: Regulation of Collagen Synthesis and Fibrosis Development in Skeletal Muscle by La-Related Protein 6 (LaRP6)

Abstract

Introduction: Excessive extracellular matrix (ECM) accumulation, especially collagens, impairs muscle function in muscular dystrophies, aging and muscle trauma (fibrosis). We have found increased skeletal muscle fibrosis in congestive heart failure (CHF) conditions, likely contributing to the impaired muscle functions. Hypothesis: We hypothesized that LARP6 (La Ribonucleoprotein Domain Family Member 6), an mRNA binding protein that coordinates efficient translation of Collagen I α chains, regulates collagen synthesis during skeletal muscle fibrosis in CHF conditions. Approach: Skeletal muscle fibrosis was analyzed in two mouse models, angiotensin II (Ang II) infusion and left anterior descending artery (LAD) ligation. Expression and subcellular localization of Collagen I, Larp6 and myogenic markers (myogenin and Myh3) were analyzed by qRT-PCR, western blotting, in situ hybridization (RNAScope) and immunostaining in hindlimb muscles in vivo and primary myoblasts and fibro/adipogenic progenitor (FAP) cells in vitro . Collagen I levels were also analyzed by picrosirius red staining (PSR). These analyses were performed in a newly-generated Larp6 knockout (Larp6 -/- ) mice. Results: In both Ang II and LAD ligation models, Collagen I mRNA and protein levels were increased together with LARP6, suggesting that LARP6 may regulate Collagen I synthesis in these conditions. In cultured myoblasts and FAPs, LARP6 protein was co-localized with Col1a1 mRNA at endoplasmic reticulum (ER). TGF-β treatment increased the LARP6 and Col1a1 mRNA co-localization, associated with increased pro-collagen I protein levels. Although Larp6 deficiency did not alter basal Collagen I levels, Collagen I induction in fibrotic conditions was decreased in Larp6 -/- mice. We found that thick collagen fibers were more significantly decreased compared to intermediate or loosely-packed thin collagen fibers (PSR signal analysis under the polarized microscope). Conclusions: These data suggest that LARP6 regulates Collagen I protein synthesis and its filament assembly likely in ER by binding to Col1a1 mRNA upon fibrosis induction. Suppression of LARP6 may be a therapeutic strategy to prevent pathophysiological fibrosis development in skeletal muscle.