Nonalcoholic fatty liver disease (NAFLD) occurs in patients without significant alcohol consumption and represents a clinico-histopathological entity with histological features that resemble alcohol-induced liver injury. We have used conditional gene targeting in hepatocytes to inactivate the pVHL-E3-ubiquitin ligase, which targets Hypoxia-Inducible-Factor (HIF) for degradation under normoxia. We have discovered that increased HIF activity alters fatty acid metabolism and results in the development of non-alcoholic fatty liver disease in mice. Hypoxia-Inducible Factor-1 and -2 (HIF-1 and HIF-2) are heterodimeric basic-loop-helix transcription factors and are key mediators of cellular adaptation to diminished oxygen supply. Our findings implicate HIF signaling, in particular signaling through HIF-2, in the development of fatty liver disease. In this grant application we propose in vivo and in vitro studies that make use of conditional gene targeting technology and transgenesis to investigate the role of HIF signaling in the regulation of fatty acid uptake, synthesis, beta-oxidation and secretion. Additional in vitro studies are proposed that specifically focus on selected HIF target genes to study their role in lipid metabolism under hypoxia.
In Aim 1 we carry out functional studies in VHL mutant mice, in Aim 2 we investigate the role of HIF activation early in the development of steatosis following acute inactivation of pVHL in the adult, and Aims 3 and 4 investigate the role of HIF-2 in a wild type genetic background with a focus on HIF-2 target genes relevant for the development of steatosis. The proposed studies are not only important for our understanding of basic HIF functions in lipid metabolism, but more importantly have direct clinical relevance. We provide a direct molecular link between hypoxic injury and fatty liver development and establish a novel role for the HIF pathway in the pathogenesis of NAFLD.

Public Health Relevance

This grant application examines the role of low oxygen and signaling through Hypoxia-Inducible Factor (HIF) in the regulation of hepatic fatty acid metabolism. The proposal has relevance for all patients with non-alcoholic fatty liver disease, obesity, diabetes and those that suffer from cardio-pulmonary conditions resulting in chronically low blood oxygen levels.

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
Research Project (R01)
Project #
1R01DK080821-01A1
Application #
7581541
Study Section
Hepatobiliary Pathophysiology Study Section (HBPP)
Program Officer
Doo, Edward
Project Start
2009-04-20
Project End
2014-03-31
Budget Start
2009-04-20
Budget End
2010-03-31
Support Year
1
Fiscal Year
2009
Total Cost
$384,249
Indirect Cost
Name
Vanderbilt University Medical Center
Department
Internal Medicine/Medicine
Type
Schools of Medicine
DUNS #
004413456
City
Nashville
State
TN
Country
United States
Zip Code
37212
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