Abstract 19045: Impaired Autophagy Induced by Activated mTORC1 Underlies Development of Dystrophic Cardiomyopathy.
Purpose: Heart failure is a main cause of death in patients with Duchenne muscular dystrophy. Here, we hypothesized that impaired autophagy contributes to the cardiac phenotype in muscular dystrophy.
Methods and Results: We first examined whether cardiac autophagy is altered in the dystrophin-deficient mdx mouse (MDX). Heart weight/tibia length (HW/TL) was similar in MDX and age-matched C57BL10 control mice at 22-week-old (wo). Although cardiac mRNA levels of LC3B and p62 were unchanged in MDX, protein levels of LC3-II (+2.2 fold) and p62 (+2.7 fold) were significantly higher in MDX than those in control, suggesting impaired autophagic flux at the later stage, i.e. autophagosome-lysosome fusion and/or lysosomal degradation. Phospho-S6 and phospho-4EBP1 levels were markedly increased in MDX, indicating activation of mTORC1, a negative regulator of autophagy. Although mTORC1 negatively regulates transcription factor EB which promotes lysosome biogenesis, its target genes were not reduced in MDX. We next examined whether activated mTORC1 impairs autophagic flux in H9c2 cardiomyoblasts. Treatment of cells with MHY1485 (5 μM), an mTORC1 activator, resulted in accumulation of LC3-II and p62 proteins, as seen in MDX hearts. MHY1485 did not affect LysoTracker Red fluorescence, suggesting suppression of autophagic flux independent of lysosome function. Finally, to examine the role of impaired autophagy in the cardiac phenotype, we treated MDX with resveratrol (RSV, 400 mg/kg chow), which promotes autophagy, using separate groups of mice. RSV was started at 8-wo, and mice were sacrificed at 65-wo. In echocardiography at 62-wo, LV fractional shortening was higher (38±2% vs. 34±1%, P<0.05), and end-diastolic LV dimension was smaller in RSV-treated MDX than those in untreated MDX. HW/TL was also reduced by RSV. RSV significantly increased autophagy-related genes including LC3B, PINK1, and Rab7, but rather reduced total LC3 protein level, indicating a restoration of autophagic flux by RSV. Phospho-S6 and phospho-4EBP1 levels were not changed by RSV, indicating mTORC1-independent restoration of autophagy.
Conclusion: The findings suggest that impairment of autophagy induced by activated mTORC1 underlies development of dystrophic cardiomyopathy.
Author Disclosures: A. Kuno: None. R. Hosoda: None. R. Sebori: None. Y. Horio: None.
- © 2016 by American Heart Association, Inc.