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Autophagy Induced by Exogenous Bile Acids is Therapeutic in a Model of Alpha-1-AT Deficiency Liver Disease

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AJP Gastrointestinal and Liver Physiology

Published online on

Abstract

The bile acid, nor-ursodeoxycholic acid (norUDCA), has many biological actions, including anti-apoptotic effects. Homozygous PIZZ alpha-1-antitrypsin (A1AT) deficient humans are known to be at risk for liver disease, cirrhosis, and liver cancer as a result of the accumulation of the toxic, A1AT mutant Z protein within hepatocytes. This accumulation triggers cell death in the hepatocytes with the largest mutant Z protein burdens, followed by compensatory proliferation. Proteolysis pathways within the hepatocyte, including autophagy, act to reduce the intracellular burden of A1AT Z protein. We hypothesized that norUDCA would reduce liver cell death and injury in A1AT deficiency. We treated groups of PiZ transgenic mice and WT mice with norUDCA or vehicle, orally, and examined the effects on the liver. The PiZ mouse is the best model of A1AT liver injury and recapitulates many features of the human liver disease. Results: Mice treated with norUDCA demonstrated reduced hepatocellular death by compensatory hepatocellular proliferation as determined by BrdU incorporation (3.8% control, 0.88% treated, p<0.04). Ki-67 staining as a marker for hepatocellular senescence and death was also reduced (p<0.02). Reduced apoptotic signaling was associated with norUDCA, including reduced cleavage of caspases 3, 7, and 8 (all p<0.05). We determined that norUDCA was associated with a >70% reduction in intrahepatic mutant Z protein (p<0.01). A 32% increase in hepatic autophagy associated with norUDCA was the likely mechanism. Conclusions: norUDCA administration is associated with increased autophagy, reduced A1AT protein accumulation and reduced liver injury in a model of A1AT deficiency.