Non-alcoholic fatty liver disease (NAFLD) is a disorder of liver lipid metabolism in which both cholesterol and fat accumulate in liver cells. A significant fraction of patients with NAFLD progress to liver inflammation, necrosis, and progressive liver fibrosis. NAFLD is now recognized as a leading cause of cirrhosis in the U.S. and in the Veteran's population;and, is poised to soon represent the most common indication for liver transplantation. In addition to its progression to end-stage liver disease, it is frequently associated with diabetes (insulin resistance) and cardiovascular disease. The clustering of these clinical phenotypes is now known as Metabolic Syndrome. Current therapeutic approaches for the treatment of NAFLD inclusive of cholesterol and triglyceride lowering agents, insulin sensitizing agents, anti-oxidants, and life-style modifications have not been found effective in reversing NAFLD. No good treatment approach currently exists. A better understanding of the interplay of liver cell cholesterol, fat, glucose, and bile acid metabolism is crucial in order to develop more effective therapies. The liver is central to total body lipid homeostasis. Our laboratory has identified delivery of cholesterol into the cell's mitochondria for oxidation as a crucial step in the regulation of liver lipid metabolism. We have found that increased expression of the mitochondrial cholesterol delivery protein, StARD1, in hepatocytes (liver cells), down-regulates pathways of cholesterol biosynthesis while up-regulating pathways of cholesterol degradation and secretion. Increasing liver StARD1 expression increases cholesterol oxidation via pathways initiated by mitochondrial enzyme, CYP27A1;and, the resulting oxysterol products are regulatory molecules capable of mediating changes in lipid metabolism. Furthermore, bile acids, the end product of the CYP27A1 initiated pathway of cholesterol metabolism, are important regulatory molecules in their own right;capable of mediating cholesterol and fat intestinal absorption and metabolism through activation of an intestinal and liver nuclear receptor, FXR. The objective of this application is to elucidate the role of the StARD1/CYP27A1 pathway of cholesterol oxidation in the regulation of hepatic lipid and glucose homeostasis. The completion of these studies: 1) will determine if increasing intracellular cholesterol degradation into regulatory oxysterols and FXR activating bile acids is capable of reversing fatty liver in 2 NAFL animal models under conditions which closely simulate a typical American lifestyle;2) will be used to pull apart the activation of FXR mediated pathways by bile acids from the effects of increased regulatory oxysterols;3) to search for undiscovered regulatory oxysterols generated by increasing expression of the StARD1/CYP27A1 pathway that contribute to the profound liver lipid lowering noted in the face of a Western diet;4) to search for novel sites of regulation which control intracellular regulatory oxysterol levels;and, 5) to determine in the presence and absence of high fat/cholesterol intestinal content how naturally occurring FXR agonists (i.e bile acids) vs. synthetic FXR agonists may differentially alter hepatic cholesterol, fat, and glucose metabolism in a Cyp27a1 knockout mouse model;a naturally occurring genetic model of fatty liver lacking CYP27A1 generated oxysterols. Based on our preliminary findings, we believe that used in concert increased selective activation of the FXR and regulatory oxysterol activated pathways can be utilized to reverse NAFL, and, likely, atherogenesis. This proposal brings forth basic science discoveries that lead to novel treatment approaches. As outlined in the proposal, these studies have the potential to offer immediate clinical promise for treatment of NAFLD not only in our Veterans population, but in the U.S. population as a whole.

Public Health Relevance

Significance/Relevance to VA Patient Care Misssion Nonalcoholic fatty liver disease (NAFLD) is a disorder of liver lipid homeostasis in which both cholesterol and triglycerides accumulate in hepatocytes;and, in a significant portion of NAFLD patients this hepatic lipid accumulation is associated with progression to liver necrosis, inflammation, and fibrosis. NAFLD, with an estimated incidence of 17-33%, is now recognized as a leading cause of cirrhosis in the Veteran's population and in the U.S.;and is predicted to represent the leading indication for live transplantation. NAFLD is associated with an insulin resistant state and cardiovascular disease. The studies proposed in this application and as supported by the preliminary findings on cholesterol, fat, and glucose metabolism represent novel approaches to more clearly define the regulation of lipid and glucose metabolism in hepatocytes. They are designed with proof of principle approaches intended toward uncovering viable treatment approaches for NAFLD. These studies have the potential to offer immediate promise for the treatment of NAFLD.

Agency
National Institute of Health (NIH)
Institute
Veterans Affairs (VA)
Type
Non-HHS Research Projects (I01)
Project #
2I01BX000197-05
Application #
8628400
Study Section
Gastroenterology (GAST)
Project Start
2009-04-01
Project End
2017-12-31
Budget Start
2014-01-01
Budget End
2014-12-31
Support Year
5
Fiscal Year
2014
Total Cost
Indirect Cost
Name
VA Veterans Administration Hospital
Department
Type
DUNS #
146678115
City
Richmond
State
VA
Country
United States
Zip Code
23249
Nagahashi, Masayuki; Takabe, Kazuaki; Liu, Runping et al. (2015) Conjugated bile acid-activated S1P receptor 2 is a key regulator of sphingosine kinase 2 and hepatic gene expression. Hepatology 61:1216-26
Sharon, Chetna; Baranwal, Somesh; Patel, Nirmita J et al. (2015) Inhibition of insulin-like growth factor receptor/AKT/mammalian target of rapamycin axis targets colorectal cancer stem cells by attenuating mevalonate-isoprenoid pathway in vitro and in vivo. Oncotarget 6:15332-47
Kakiyama, Genta; Muto, Akina; Takei, Hajime et al. (2014) A simple and accurate HPLC method for fecal bile acid profile in healthy and cirrhotic subjects: validation by GC-MS and LC-MS. J Lipid Res 55:978-90
Calderon-Dominguez, Maria; Gil, Gregorio; Medina, Miguel Angel et al. (2014) The StarD4 subfamily of steroidogenic acute regulatory-related lipid transfer (START) domain proteins: new players in cholesterol metabolism. Int J Biochem Cell Biol 49:64-8
Bajaj, J S; Heuman, D M; Hylemon, P B et al. (2014) Randomised clinical trial: Lactobacillus GG modulates gut microbiome, metabolome and endotoxemia in patients with cirrhosis. Aliment Pharmacol Ther 39:1113-25
Ren, Shunlin; Kim, Jin Koung; Kakiyama, Genta et al. (2014) Identification of novel regulatory cholesterol metabolite, 5-cholesten, 3?,25-diol, disulfate. PLoS One 9:e103621
Liu, Runping; Zhao, Renping; Zhou, Xiqiao et al. (2014) Conjugated bile acids promote cholangiocarcinoma cell invasive growth through activation of sphingosine 1-phosphate receptor 2. Hepatology 60:908-18
Kakiyama, Genta; Hylemon, Phillip B; Zhou, Huiping et al. (2014) Colonic inflammation and secondary bile acids in alcoholic cirrhosis. Am J Physiol Gastrointest Liver Physiol 306:G929-37
Kakiyama, Genta; Pandak, William M; Gillevet, Patrick M et al. (2013) Modulation of the fecal bile acid profile by gut microbiota in cirrhosis. J Hepatol 58:949-55