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Background & Aims Alcohol abuse is a major cause of liver injury. The pathologic features of alcoholic liver disease develop over prolonged periods, yet the cellular defense mechanisms against the detrimental effects of alcohol are not well understood. We investigated whether macroautophagy, an evolutionarily conserved cellular mechanism that is commonly activated in response to stress, could protect liver cells from ethanol toxicity. Methods Mice were acutely given ethanol by gavage. The effects of ethanol on primary hepatocytes and hepatic cell lines were studied in vitro. Results Ethanol-induced macroautophagy in the livers of mice and cultured cells required ethanol metabolism, generated reactive oxygen species, and inhibited mTOR signaling. Suppression of macroautophagy with pharmacological agents or small interfering RNAs significantly increased hepatocyte apoptosis and liver injury; macroautophagy therefore protected cells from the toxic effects of ethanol. Macroautophagy induced by ethanol seemed to be selective for cells with damaged mitochondria and accumulated lipid droplets, but not long-lived proteins, which could account for its protective effects. Increasing macroautophagy pharmacologically reduced hepatotoxicity and steatosis associated with acute ethanol exposure. Conclusions Macroautophagy protects against ethanol-induced toxicity in livers of mice. Reagents that modify macroautophagy might be developed as therapeutics for patients with alcoholic liver disease.

Autophagy is a cellular response to adverse environment and stress, but its significance in cell survival is not always clear. Here we show that autophagy could be induced in the mammalian cells by chemicals, such as A23187, tunicamycin, thapsigargin, and brefeldin A, that cause endoplasmic reticulum stress. Endoplasmic reticulum stress-induced autophagy is important for clearing polyubiquitinated protein aggregates and for reducing cellular vacuolization in HCT116 colon cancer cells and DU145 prostate cancer cells, thus mitigating endoplasmic reticulum stress and protecting against cell death. In contrast, autophagy induced by the same chemicals does not confer protection in a normal human colon cell line and in the non-transformed murine embryonic fibroblasts but rather contributes to cell death. Thus the impact of autophagy on cell survival during endoplasmic reticulum stress is likely contingent on the status of cells, which could be explored for tumor-specific therapy. Endoplasmic reticulum (ER)3 is critically involved in protein metabolism. Normal ER function is required for the correct folding of many proteins and their post-translational modifications, such as glycosylation and disulfide bond formation. ER stress is induced by the disturbance of the environment in the ER lumen, such as the calcium homeostasis or the redox status, or by the disturbance of ER function, such as glycosylation and transportation to Golgi complex (1). The typical chemicals that induce ER stress include A23187 and thapsigargin, both of which disturb the calcium homeostasis; tunicamycin, which suppresses glycosylation; and brefeldin A, which inhibits transportation to the Golgi complex (1, 2). Thus these chemicals cause protein folding dysfunction, and the accumulated misfolded/unfolded proteins induce ER stress. ER stress is frequently observed in pathological conditions where protein misfolding is caused by genetic mutations either in the molecule to be processed or in the machinery processing the folding (3, 4).The major protective and compensatory mechanism during ER stress is the unfolded protein response (UPR) (1, 5), which leads to translational attenuation and selective up-regulation of a number of bZip transcription factors (1, 5). UPR serves multiple functions, including the assistance of protein folding via the up-regulated ER protein chaperones and the enhanced degradation of misfolded proteins via the up-regulation of molecules involved in the ER-associated degradation pathway (1, 5). However, if the stress is excessive, the compensatory mechanisms may not be able to fully sustain ER function, and ER decompensation could lead to cell death (2, 6). It is not clear whether there are other mechanisms that can regulate ER stress.Macroautophagy (referred as autophagy hereafter) is mainly responsible for the degradation of long-lived proteins and subcellular organelles (7-9). Autophagy is frequently activated in response to adverse environment or stress (10 -13) and has been shown to be involved in many physiological and ...

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