A1-antitrypsin (AT) deficiency (ATD) is the most common genetic cause of liver disease. The classical form of ATD is due to a single missense mutation (Z) that causes the mutant protein (ATZ) to misfold and accumulate within the endoplasmic reticulum (ER) of liver cells as toxic oligomers, polymers or aggregates. However, due to genetic and environmental modifiers, there is marked variation in the incidence and severity of liver disease among homozygotes. Since the only treatment for severe ATZ-induced hepatic injury is liver transplantation, the development of an animal model amenable to pre-clinical, high-throughput drug screening technologies would greatly assist in the discovery of new compounds that reduce or eliminate ATZ-induced hepatotoxicity. The value of the model would be markedly increased if it also possessed genetic tractability to: 1) elucidate the genetic modifiers of both tissue damage and the endogenous proteostasis pathways that protect against protein misfolding-induced injury, and 2) pinpoint which biochemical pathways and/or molecules are targeted by newly discovered compounds. We show that ATZ induced liver disease is modeled accurately in the nematode, C. elegans. Transgenic animals expressing wild-type human AT secreted the protein. In contrast, animals expressing ATZ faithfully recapitulated the ER trafficking defect of ATZ by demonstrating intracellular inclusions (dilated ER cisterna), and becoming unhealthy as shown by slow growth, small brood sizes and decreased longevity. Using this model we developed an automated, live-animal, high-content screening (HOS) assay that rivals that of any cell-based system. We validated this system by discovering -30 hit compounds, including several that reduced ATZ accumulation by enhancing autophagy, a known pathway of ATZ elimination. Using a modification of our HOS strategy, we also developed a semi-automated technology that reduces the labor intensiveness of genome-wide RNAi screens. We identified several potential genetic modifiers/pathways of ATZ accumulation. Taken together, these studies demonstrated that this transgenic C. elegans model is a powerful platform to initiate the discovery of both novel drugs and genes that modify ATZ hepatotoxicity.
The aims of Project 2 are to discover additional hit compounds for the treatment of ATZ-induced disease phenotypes in C. elegans by both HCS and computer-aided molecular modeling, identify disease modifiers of major and minor effect, and to determine whether different mutant disease modifiers alter responsiveness to therapeutic compounds.
Alpha-1-antitrypsin deficiency is a leading genetic cause of liver injury, but lacks effective treatments. The goal of this study is to model this disease in a simple organism, and use this tool to screen a large collection of chemical compounds for novel drugs that block the development of liver injury.
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