Hepatoprotective Role Of Thymosin beta4 In Alcoholic Liver Injury And Fibrosis

by Ruchi D Shah

Institution: The George Washington University
Year: 2017
Keywords: Molecular biology; Cellular biology; Biochemistry
Posted: 02/01/2018
Record ID: 2155275
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Chronic alcohol induced liver disease (ALD) comprises of a spectrum of disease stages progressing from fatty liver, steatohepatitis, fibrosis, to cirrhosis that may eventually lead to death. Although, the early stages of ALD are reversible, 40% of the patients develop advanced stage liver disease characterized by significant hepatic fibrosis and cirrhosis, for which, currently, liver transplantation is the only curative approach. However, the number patients waiting for liver transplantation far exceeds the meager number of available donors resulting in premature mortality of such patients. Hence, there is an urgent need for therapies for not only prevention and early intervention to stop the disease progression, but also to effectively regenerate the remaining healthy liver so that the patient can be reasonably functional before they can fully recover with a liver transplantation. Thus, any biologically natural modulator that can effectively prevent the progression of ALD until the donor liver is available for transplantation would be desirable even if it cannot completely cure the disease. Thymosin 4 (T4) is an immune modulating natural peptide secreted by thymus gland that is known to prevent inflammation and fibrosis, and promote wound healing and regeneration in the eye, skin and heart. Previous work from our laboratory has also shown that T4 protects against carbon tetrachloride induced acute liver injury in rat. However, not much is known of the role of T4 in alcoholic liver injury. Therefore, in this dissertation research, the role of T4 was investigated in acute on chronic ethanol and lipopolysaccharide (LPS) induced hepatic oxidative stress, inflammation, and fibrosis in an in vivo mouse model, as well as its regenerative potential was studied in chronic ethanol fed mice after partial hepatectomy. Furthermore, the underlying molecular mechanism by which T4 exerts its action, particularly on fibrosis was examined using human hepatic stellate cells (HSC), the main fibrogenic cells of the liver. Based on the well accepted two-hit model for ALD, in the hepatocytes, ethanol acts as the first hit and is oxidized to acetaldehyde, the highly toxic first metabolite of ethanol oxidation by alcohol dehydrogenase (ADH) and ethanol-inducible cytochrome P450 2E1 (CYP2E1) leading to the generation of reactive oxygen species (ROS), resulting in oxidative stress. On the other hand, ethanol-induced leaky gut results in the release of endotoxin (LPS) that acts as the second hit and activates nuclear factor Kappa B (NF?B) in the Kupffer cells and the subsequent production of the pro-inflammatory cytokines that propagates liver inflammation. ROS and the pro-inflammatory cytokines act as fibrogenic stimuli for the activation of HSC and their trans-differentiation from quiescent lipid storing phenotype to activated myofibroblasts that express fibrogenic genes and proliferate and migrate to the site of injury and form a fibrous scar, resulting in fibrosis. This is