Date Available

10-31-2015

Year of Publication

2015

Document Type

Doctoral Dissertation

Degree Name

Doctor of Philosophy (PhD)

College

Medicine

Department/School/Program

Pharmacology and Nutritional Sciences

Advisor

Dr. Brett T. Spear

Abstract

The growing obesity epidemic in America carries with it numerous health risks, including diabetes, increased serum lipid levels, and excess fat accumulation in the liver. If these conditions persist or become exacerbated, they may lead to the development of cardiovascular disease, the current leading cause of death among Americans, or to nonalcoholic fatty liver disease (NAFLD) which can progress to hepatocellular carcinoma (HCC), one of the deadliest forms of cancer. Better understanding of the genes involved in these diseases can lead to improved identification of at-risk individuals and treatment strategies.

Our lab previously identified zinc fingers and homeoboxes 2 (Zhx2) as a regulator of hepatic gene expression. The BALB/cJ mouse strain has a hypomorphic mutation in the Zhx2 gene, causing a 95% reduction in Zhx2 protein expression. The near ablation of Zhx2 in BALB/cJ mice confers protection from cardiovascular disease when fed a high fat diet, yet these mice show increased hepatic lipid accumulation and liver damage. Microarray data indicates Zhx2 may be involved in the regulation of numerous genes involved in lipid metabolism. Recent GWAS studies indicate ZHX2 may contribute to the risk of cardiovascular disease and liver damage in humans as well.

In this dissertation, I characterize the role of Zhx2 expression in the liver and how it affects the risk of both cardiovascular disease and liver damage. I generated liver-specific Zhx2 knockout mice and confirmed Zhx2 regulates several novel targets that could contribute to the fatty liver phenotype seen in BALB/cJ mice. Further studies revealed that hepatic Zhx2 expression is necessary for proper sex-specific expression of several Cyptochrome P450 (CYP) genes and could contribute to gender differences in disease susceptibility. Lastly, I performed studies into the functional role of the Zhx2 target gene Elovl3. A mouse model of HCC revealed that Elovl3 is completely repressed in HCC tumors. Cell viability and cell cycle assays indicate that Elovl3 expression slows cell proliferation and may be important for proper cell cycle checkpoints. Together, these data indicate that Zhx2 and/or its targets could be clinically relevant in the detection, prevention, or treatment of cardiovascular disease, fatty liver, and HCC.

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