Attenuation of Mitophagy Exacerbates the Deleterious Effects of Statins on Skeletal Muscle

Abstract

BackgroundStatins are a family of cholesterol lowering drugs that afford proven cardiovascular benefits. However, due to the complications that arise from developing skeletal muscle myopathy, patient withdrawal remains a significant hurdle to maximizing the potential of this therapy. Thus, work to understand and mitigate the negative effects of statins is significant. We previously showed that statins induce mitophagy in cardiac cells; a phenomenon not explored in skeletal muscle. Here we demonstrate statin‐mediated mitophagy is a protective mechanism that attenuates the deleterious cytotoxic effects statins are known to induce in skeletal muscle. We hypothesize that this homeostatic system of mitochondrial quality control is a major determinant in the etiology of statin‐associated myopathy.MethodsC2C12 myotubes were treated with 2μM simvastatin for 24h. C57BL/6 wild‐type and Parkin knockout mice were given a dose of 20mg/kg simvastatin for 2wks via osmotic mini pumps. Mitochondrial markers (Tom70 and Cox4), and mitophagy adapters p62/SQSTM1, NDP52, and Bnip3 were examined via western blot. Regulators of autophagy (FoxO3 and AMPK) were also examined. Cytotoxicity to statin treatment was determined by monitoring cytosolic cytochrome c levels, caspase 3 activation and LDH release in cells silenced for p62/SQSTM1 or Parkin.ResultsStatins induced mitochondrial loss in both C2C12 myotubes, and in gastrocnemius muscle of mice, evidenced by diminished levels of mitochondrial markers Tom70 and Cox4. AMPK and FoxO3 were both activated by statin treatment, which correlated with increased autophagy and myotube atrophy. Pretreatment of C2C12 cells with bafilomycin 2h before statin administration to inhibit autophagic flux blocked mitochondrial loss. Statins increased translocation of mitophagy adapters such as p62/SQSTM1 and NDP52 to the mitochondria and activation of Bnip3. RNAi knockdown of p62/SQSTM1 or Parkin attenuated statin‐induced mitophagy, but increased cytosolic cytochrome c levels, caspase 3 activation and LDH release. Parkin knockout mice treated with simvastatin for 2wks displayed diminished grip strength, and spontaneous movement and rearing in an open field test when compared to wild‐type mice.ConclusionsHere we show that statins promote mitophagy in skeletal muscle cells, mediated in part by p62/SQSTM1 and Parkin. Attenuating statin‐induced mitochondrial loss, via silencing p62/SQSTM1 or Parkin, led to increased statin‐mediated toxicity in cells. Moreover, Parkin knockout mice displayed increased susceptibility to statin treatment. Our findings reveal the potential importance of mitochondrial quality control in the progression of statin myopathy. Specifically, our findings demonstrate that mitophagy plays protects skeletal muscle against the deleterious effects of statins.Support or Funding InformationAmerican Heart Association ‐ Scientist Development Grant 15SDG23230013 to AA