Role of Lysosome Damage in ALD Pathogenesis

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Abstract: Despite recent advances that have clarified the etiologies of alcohol-associated liver disease (ALD), the cellular and molecular alterations that lead to progressive liver damage are only partially understood. Furthermore, there are currently no FDA-approved therapies that block, or reverse ALD progression. Thus, it is urgent that we identify cellular and molecular mechanisms that contribute to progressive liver damage, to improve disease prognosis, and identify new treatment targets and procedures that alleviate or even prevent ALD. Heavy alcohol consumption affects all tissues, but it causes the greatest damage to the liver. This is because alcohol (ethanol or EtOH) is primarily metabolized in the liver to generate toxic products (acetaldehyde, superoxide, and hydroxyl radicals) that, with continued drinking, damage and impair the structure and function of membrane-bound organelles, including the ER, mitochondrion, and the lysosome. The latter organelle degrades nearly all macromolecules in eukaryotic cells. Our objective is to identify specific alterations induced by EtOH metabolite(s) that cause lysosome damage in hepatocytes and Kupffer cells (resident liver macrophages), and which leads to parenchymal cell death and inflammatory signaling, respectively. Lysosomes have a crucial role in cellular quality control, as they recycle obsolete proteins and dysfunctional organelles, including damaged lysosomes. If cells do not repair/remove damaged lysosomes, they will continue to leak their proteolytic enzymes to trigger cell death and provoke inflammatory signaling by Kupffer cells. We and others previously reported that chronic ethanol (EtOH) consumption causes faulty lysosome biogenesis and lysosomal membrane instability. Here, we show exciting new pilot data indicating that chronic EtOH consumption by both humans and rodents causes lysosomal membrane damage and subsequent leakage of lysosomal cathepsin(s) (and other hydrolases) that contribute to liver cell injury. Furthermore, such damage releases lysosomal membrane components into the circulation, which may be prognostic markers of liver injury. Our pilot data, presented herein, suggest that primary and/or secondary EtOH metabolites damage lysosomes in hepatocytes and Kupffer cells, inducing cathepsin leakage which contribute to cell death and inflammation. These novel observations support our hypothesis that chronic EtOH oxidation damages lysosomes, causing leakage of cytotoxic lysosomal hydrolases, thereby, contributing to liver injury and inflammation. To test our hypothesis, we propose the following Specific Aims: In Aim 1 we will define the mechanisms of EtOH-induced lysosome damage that incite hepatocyte injury. In Aim 2 we will investigate the mechanisms of EtOH-induced lysosome damage that incite inflammatory signaling in Kupffer cells. We anticipate that the outcome of this research will reveal novel mechanisms by which EtOH oxidation promotes the progression of liver pathology by damaging lysosomes.