Abstract 266: Autophagy Reverses Intramuscular Lipid Accumulation in Myocytes
Autophagy, or “self-eating” of the cell, is a tightly regulated “housekeeping” process involved in the degradation and recycling of protein aggregates and damaged organelles. In the failing heart, autophagy has been shown to be an adaptive response. We have previously demonstrated that a common feature of non-ischemic heart failure is lipid accumulation, which in excess can mediate cardiac dysfunction via lipotoxicity. Since autophagy mediates the clearance of lipids through a specific process, known as lipophagy, in hepatocytes, we wondered whether the activation of autophagy in the failing heart protects myocyte from lipotoxicity. To test this hypothesis, L6 myocytes were incubated over a period of 6 days with long chain fatty acids, either 0.5mM or 1.0mM fatty acids (equimolar mixture of oleate and palmitate). On the sixth day of treatment, an autophagic inhibitor (bafilomycin A1, 200nM) or autophagic activator (rapamycin, 1uM) was added to the cell culture medium for 24 hours. Intracellular triglyceride (TG) accumulation was measured in the cells using enzyme quantification assay as well as Oil Red O stain. Immunoblotting was also performed on protein markers to confirm autophagic flux (LC3 and P62) and cell death (Caspase3) in the myocytes. The results indicated that increasing concentrations of fatty acids gradually increased intracellular TG accumulation. Inhibition of autophagy using bafilomycin increased this effect whereas activation of autophagy using rapamycin reduced lipid accumulation in the L6 myocytes. Moreover, fatty acid mediated cell death was increased when autophagy is inhibited. We conclude that autophagy promotes the clearance of lipids from cultured myocytes. These findings suggest that lipophagy may be a protective mechanism in the myocyte through the decrease and reversal of intracellular lipid accumulation.
- © 2012 by American Heart Association, Inc.