Homozygous PIZZ alpha1-antitrypsin deficiency is the most common genetic cause of liver disease in children and is associated with chronic liver injury and hepatocellular carcinoma in adults. The liver injury results from the hepatotoxic effect of an abnormally folded protein which is unable to traverse the secretory pathway and accumulates in the endoplasmic reticulum (ER) of liver cells. It is unknown, however, why only 15% of the deficient population develop liver injury. We have made the prediction that a subset of the PiZZ population is more susceptible to liver injury by virtue of one or more additional inherited traits or environmental factors that exaggerate the intracellular accumulation of the mutant Z alpha1-AT protein, or exaggerate the cellular pathophysiological consequences of mutant alpha1-AT accumulation. In order to directly examine this prediction, we recently transduced skin fibroblasts from PiZZ individuals with liver disease (""""""""susceptible hosts"""""""") and PiZZ individuals without liver disease (""""""""protected hosts"""""""") with amphotropic retroviral particles designed for constitutive expression of the mutant Z alpha1-AT gene. Human skin fibroblasts do not express the endogenous alpha1-AT gene but presumably express other genes involved in synthesis and postsynthetic processing of secretory proteins. The results indicate that there is a marked delay in ER degradation of the mutant Z alpha1-AT protein after it has accumulated in cells from the susceptible hosts as compared to those from protected hosts. Appropriate disease controls show that the lag in degradation in susceptible hosts is specific for the combination of PiZZ phenotype and liver disease. The results also show that there is a decrease in interaction of mutant alpha1-AT with a resident ER molecular chaperon, a calcium-binding phosphoprotein named calnexin, in a prototype susceptible host when compared to a prototype protected host. Thus, these data provide evidence that other genetic traits that affect the fate of the abnormal Z alpha1-AT molecule, such as a lag in ER degradation, at least in part determine susceptibility to liver disease. in the current proposed project 1 will examine the specificity of the degradative pathway which is defective in PiZZ individuals with liver disease and provide definitive evidence that it is the common ER degradation pathway previously described in model experimental cell systems for T-cell receptor alpha subunits and asialoglycoprotein receptor subunits. For this, I will use amphotropic recombinant retroviral particles to transduce cell lines from prototype susceptible and protected hosts with specific test genes. Finally, I will provide more detailed examination of the lesser degree of interaction between mutant alpha1-AT and calnexin, and examine the possibility that there is heterogeneity in the mechanism for decreased degradation of mutant alpha1-AT within the PiZZ population.
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