The classical form of alpha1-antitrypsin (alpha1AT) deficiency is the most common genetic cause of liver disease in children and emphysema in adults. Liver disease is caused by a gain-of-function mechanism triggered by the retention of aggregated mutant alpha1ATZ the endoplasmic reticulum (ER) of liver cells. Our work has shown that wide variation in the liver disease phenotype among deficient individuals can be explained by genetically- and/or environmentally-determined variation in the relative efficiency of the ER degradation/quality control pathway or of the protective cellular responses activated by ER retention of the mutant protein. Emphysema is caused by a loss-of-function mechanism in which the decrease in alpha1AT molecules available in the lung permits uninhibited proteolytic damage. It is exacerbated by oxidative inactivation of residual alpha1AT function that results from cigarette smoking. However, there is also emerging evidence for marked variability in the lung disease phenotype among alpha1AT-deficient individuals even when cigarette smoking is taken into consideration. In studies over the last three years supported by this grant, we have found that autophagy is one of the mechanisms for degradation of mutant alpha1AT and one of the protective cellular responses activated by ER retention of alpha1ATZ. The autophagic response is a general mechanism whereby cytosol and intracellular organelles, such as ER, are first sequestered from the rest of the cytoplasm by the formation of a vesicle, which then fuses with lysosome for degradation of its contents. It occurs in many cell types, especially during stress states, such as nutrient deprivation, and during the cellular remodeling that accompanies differentiation, morphogenesis and aging. We have also confirmed previous work indicating the alpha1AT is expressed in the respiratory epithelium. Finally, we have established several novel genetically engineered cell culture and transgenic mouse model system including cell lines with inducible expression of alpha1ATZ, an autophagy-deficient cell line with inducible expression of alpha1ATZ and a transgenic mouse model with liver-specific inducible expression of alpha1ATZ. We now propose to use these systems, as well as the GFP-LC3 transgenic mouse which generates fluorescent autophagic vesicles, to provide more information about the mechanisms by which the autophagic response is activated in the alpha1AT-deficient state, and the mechanisms by which autophagy contributes to the disposal of mutant alpha1AT in the ER. We also propose studies designed to determine whether autophagy is induced in the respiratory epithelium and whether there is a reason to believe that the autophagic response plays a role in the variation in liver disease and lung disease phenotypes in alpha1AT deficiency. In the last specific aim, we will use genomic analysis of transgenic mice with inducible expression of alpha1ATZ to provide a comprehensive and unbiased evaluation of how the liver responds to the pathologic state that characterizes alpha1AT deficiency.
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