Autophagy can selectively remove damaged organelles, including mitochondria, and in turn protect against mitochondria damage induced-cell death. Acetaminophen (APAP) overdose can cause liver injury in animals and humans by inducing mitochondria damage and subsequent necrosis in hepatocytes. Although many detrimental mechanisms have been reported to be responsible for APAP-induced hepatotoxicity, it is not known whether APAP can modulate autophagy to regulate hepatotoxicity in hepatocytes. To test the hypothesis that autophagy may play a critical protective role against APAP-induced hepatotoxicity, primary cultured mouse hepatocytes and GFP-LC3 transgenic mice were treated with APAP. By using a series of morphological and biochemical autophagic flux assays, we found that APAP induced autophagy both in the in vivo mouse liver and in primary cultured hepatocytes. We also found that APAP treatment might suppress mTOR in hepatocytes and APAP-induced autophagy was suppressed by N-acetylcysteine, suggesting APAP mitochondrial protein binding and the subsequent production of reactive oxygen species may play an important role in APAP-induced autophagy. Pharmacological inhibition of autophagy by 3-methyladenine or chloroquine further exacerbated APAP-induced hepatotoxicity. In contrast, induction of autophagy by rapamycin inhibited APAP-induced hepatotoxicity. Conclusion APAP overdose induces autophagy which attenuates APAP-induced liver cell death by removing damaged mitochondria.

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Fatty acid-induced lipotoxicity plays a critical role in the pathogenesis of nonalcoholic liver disease. Saturated fatty acids and unsaturated fatty acids have differential effects on cell death and steatosis, but the mechanisms responsible for these differences are not known. Using cultured HepG2 cells and primary mouse hepatocytes, we found that unsaturated and saturated fatty acids differentially regulate autophagy and apoptosis. The unsaturated fatty acid, oleic acid, promoted the formation of triglyceride-enriched lipid droplets and induced autophagy but had a minimal effect on apoptosis. In contrast, the saturated fatty acid, palmitic acid, was poorly converted into triglyceride-enriched lipid droplets, suppressed autophagy, and significantly induced apoptosis. Subsequent studies revealed that palmitic acid-induced apoptosis suppressed autophagy by inducing caspase-dependent Beclin 1 cleavage, indicating cross-talk between apoptosis and autophagy. Moreover, our data suggest that the formation of triglyceride-enriched lipid droplets and induction of autophagy are protective mechanisms against fatty acid-induced lipotoxicity. In line with our in vitro findings, we found that high-fat diet-induced hepatic steatosis was associated with autophagy in the mouse liver. Potential modulation of autophagy may be a novel approach that has therapeutic benefits for obesity-induced steatosis and liver injury.

Background:The mechanistic relationship of Parkin and mitofusins in mitochondria quality control is not known. Results: CCCP-induced mitophagy and mitochondrial spheroid formation differentially require Parkin and mitofusins. Conclusion: Parkin and mitofusins reciprocally regulate mitophagy and mitochondrial spheroid formation. Significance: This study revealed a default response of mitochondria to oxidative stress and a molecular mechanism by which Parkin primes the mitochondria for mitophagy.