Homozygous PIZZ alpha-1-anti-trypsin deficiency is the most common genetic cause of liver disease in children and is also associated with chronic liver disease and hepatocellular carcinoma in adults. Population studies in Sweden show that there is wide variability in the liver disease phenotype among PIZZ individuals with 10-15% particularly susceptible to liver injury. Liver injury/carcinogenesis in this deficiency is thought to result from the cytotoxic effect of mutant alpha1-ATZ molecules retained in the endoplasmic reticulum (ER) of liver cells, but little is known about the mechanism of cytotoxicity. In studies over the last five years supported by this grant, we have made four observation that are critical to further understanding the mechanism of liver injury. First, we have established in genetic complementation studies that there is a relative inefficiency in the degradation/quality control pathway for alpha-1-ATZ in the ER, or in the cellular response to ER retention of ?-1-ATZ, in the subgroup of PIZZ individuals that are susceptible to liver disease. Second, we have discovered that the ubiquitin system and the proteasome play an important role in ER degradation of mutant alpha-1-ATZ. Third, we have discovered that ER retention of (alpha-1-ATZ induces the autophagic response and that the autophagic system may also play a role in degradation of alpha-1-ATZ. Fourth, we have detected the presence of mitochondrial autophagy and mitochondrial degeneration in model cell culture systems, in transgenic mouse models and in human liver from alpha-1-AT deficient patients implicating mitochondrial/oxidant mechanisms in this liver disease. In preliminary work we have established cell culture model systems with inducible expression of alpha-1- ATZ and a transgenic mouse model of alpha-1-AT deficiency with liver-specific inducible expression of mutant alpha-1-ATZ and now propose to use these systems to provide further information about how ER retention of ?-1-ATZ induces autophagy and mitochondrial injury. Thus, the studies proposed in this competitive renewal application will address the novel concept that oxidative stress causes, or contributes to, liver cell injury in alpha-1-ATZ deficiency.
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