Hepatic steatosis or fatty liver is considered the key metabolic precursor to non-alcoholic fatty liver disease (NAFLD), the major cause of liver-associated illness and death in the United States. Disease progression in NAFLD is currently thought to be triggered by an acute insult (the "second hit") that is imposed on hepatic steatosis (the "first hit"). However, a precise understanding of the molecular basis by which the "two hits" trigger the transition from reversible steatosis to NAFLD remains elusive. Previously, we revealed a novel liver- specific transcription factor CREBH (cyclic-AMP-response-element-binding protein H), which is activated by endoplasmic reticulum (ER) stress to mediate an acute-phase inflammatory response in the liver. Recently, we have accumulated strong preliminary evidence that CREBH plays a crucial role in regulating hepatic lipid homeostasis under metabolic stress conditions. Saturated fatty acids, inflammatory stimuli, or high-fat feeding can induce cleavage of CREBH in vitro or in vivo, leading to its activation. Deletion of CREBH in mice resulted in decreased expression of key lipogenic enzymes and reduced hepatic lipid accumulation in response to acute ER stress or atherogenic high-fat feeding. After the high-fat feeding for 6 months, CREBH null mice displayed significantly less hepatic steatosis and inflammation but greater insulin sensitivity and glucose tolerance, compared to the control mice. Furthermore, CREBH was found to activate expression of key lipogenic regulators, including CCAAT-enhancer-binding protein beta (C/EBP2) and peroxisome proliferator- activated receptor gamma (PPAR3), in liver hepatocytes under the metabolic stress. These observations lead to the central hypothesis of this proposal: metabolic stress, induced by excessive saturated fatty acids or pro- inflammatory cytokines, activates CREBH;activated CREBH then functions as a lipogenic transcriptional regulator to propagate hepatic steatosis and steatohepatitis. In this grant application, we will elucidate the pathophysiologic role and molecular mechanism of CREBH in regulating hepatic steatosis and the development of NAFLD. To achieve our research goal, we will pursue three complementary specific aims: (1) to delineate the regulatory mechanism by which metabolic factors, including saturated fatty acids and pro- inflammatory cytokines, activate CREBH;(2) to decipher the molecular basis of CREBH-mediated stress signaling in regulating hepatic lipid homeostasis;(3) to determine the role of CREBH in the transition of hepatic steatosis to steatohepatitis under the metabolic stress. This work represents a novel avenue to elucidate ER stress-associated mechanisms in hepatic steatosis and steatohepatitis that are currently poorly understood. Completion of the proposed studies will not only define the molecular basis by which a novel, stress-induced transcription factor regulates hepatic lipid metabolism, but will also be significant for designing new strategies for the prevention and treatment of human NAFLD and its associated metabolic syndromes.

Public Health Relevance

Non-alcoholic fatty liver disease (NAFLD), the major cause of liver-associated illness and deaths, frequently precedes or co-exists with obesity, type II diabetes, and cardiovascular disease. This project will identify the regulatory mechanisms by which a novel stress-inducible transcription factor CREBH promotes fatty liver and progression of NAFLD under metabolic stress. Understanding the stress-induced molecular mechanisms in hepatic lipid accumulation and its associated pathogenesis is a key prerequisite for the development of new diagnostics and therapeutics targeting NAFLD.

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
Research Project (R01)
Project #
5R01DK090313-04
Application #
8600675
Study Section
Hepatobiliary Pathophysiology Study Section (HBPP)
Program Officer
Doo, Edward
Project Start
2011-01-01
Project End
2015-12-31
Budget Start
2014-01-01
Budget End
2014-12-31
Support Year
4
Fiscal Year
2014
Total Cost
$297,540
Indirect Cost
$101,790
Name
Wayne State University
Department
Genetics
Type
Schools of Medicine
DUNS #
001962224
City
Detroit
State
MI
Country
United States
Zip Code
48202
Su, Qiaozhu; Baker, Chris; Christian, Patricia et al. (2014) Hepatic mitochondrial and ER stress induced by defective PPAR? signaling in the pathogenesis of hepatic steatosis. Am J Physiol Endocrinol Metab 306:E1264-73
Kim, Hyunbae; Mendez, Roberto; Zheng, Ze et al. (2014) Liver-enriched transcription factor CREBH interacts with peroxisome proliferator-activated receptor ? to regulate metabolic hormone FGF21. Endocrinology 155:769-82
Mendez, Roberto; Zheng, Ze; Fan, Zhongjie et al. (2013) Exposure to fine airborne particulate matter induces macrophage infiltration, unfolded protein response, and lipid deposition in white adipose tissue. Am J Transl Res 5:224-34
Kemp, Kyeorda L; Lin, Zhenghong; Zhao, Fang et al. (2013) The serine-threonine kinase inositol-requiring enzyme 1* (IRE1*) promotes IL-4 production in T helper cells. J Biol Chem 288:33272-82
Qiu, Quan; Zheng, Ze; Chang, Lin et al. (2013) Toll-like receptor-mediated IRE1* activation as a therapeutic target for inflammatory arthritis. EMBO J 32:2477-90
Zheng, Ze; Xu, Xiaohua; Zhang, Xuebao et al. (2013) Exposure to ambient particulate matter induces a NASH-like phenotype and impairs hepatic glucose metabolism in an animal model. J Hepatol 58:148-54
Zhang, Chunbin; Wang, Guohui; Zheng, Ze et al. (2012) Endoplasmic reticulum-tethered transcription factor cAMP responsive element-binding protein, hepatocyte specific, regulates hepatic lipogenesis, fatty acid oxidation, and lipolysis upon metabolic stress in mice. Hepatology 55:1070-82
Lee, Jin-Sook; Zheng, Ze; Mendez, Roberto et al. (2012) Pharmacologic ER stress induces non-alcoholic steatohepatitis in an animal model. Toxicol Lett 211:29-38