This proposal is a competitive renewal of a multiple-PI R01 funded through NIAAA. The goal of the application is to examine how ethanol exposure contributes to fat accumulation in the liver due to altered dynamic properties of the fat storage organelle, the lipid droplet (LD). Specifically we will examine how alcohol exposure compromises both the lipolytic and lipophagic machineries in hepatocytes via disrupting signaling cascades and membrane trafficking effectors, ultimately leading to a fatty liver. During alcoholic liver disease, almost all heavy drinkers develop fatty liver, which is marked by the aberrant and significant accumulation of intrahepatocellular triglycerides in the form of LDs. Understanding the cellular processes contributing to this fat accumulation will provide important information for preventing further progression of injury, as it is known that alcoholic fatty liver is the initial, but entirely reversible stage of liver injury. Our research in the previously- funded R01 examined how LD dynamics in hepatocytes are regulated by several GTPases (dynamins and Rabs in particular) that can act as molecular switches to regulate membrane traffic. We showed that ethanol- induced disruption of these GTPases dramatically increases accumulation of LDs in the liver cell. Preliminary data in support of this continuation application show that the lipolytic machinery of hepatocytes, is activated by agonists of cAMP kinase (isoproterenol, forskolin) but this response is markedly inhibited by ethanol exposure. Additionally, we show that the hepatocyte utilizes sequential mechanisms to catabolize LDs that entail lipolysis followed by lipophagy. Further, it appears that activation of non-receptor tyrosine kinases that reside on the LD-autophagosome (AP) surface function to drive lipophagy, and that alcohol impairs this process. Finally, in addition to engulfment of LDs by APs, removal or ?sampling? of lipids away from LDs seems to occur by a transient, measurable interaction that is sensitive to ethanol exposure. These recent, novel findings provide an excellent foundation for this proposal, and support our central hypothesis that ethanol exposure compromises both the lipolytic and lipophagic machineries in the hepatocyte by disrupting signaling cascades and membrane trafficking events, leading to hepatic steatosis. The two principal investigators directing this project have complementary strengths: Dr. Casey is a biochemist whose expertise is in alcoholic-induced liver damage. Dr. McNiven is a cell biologist whose specialty is membrane-cytoskeleton dynamics. This unique collaborative effort has proven very beneficial to the field of alcoholic liver disease and will continue to result in outcomes otherwise unattainable by individual efforts. The proposed investigation will utilize state-of-the-art membrane trafficking and imaging technologies to quantify specific molecular events that contribute to alcohol- induced fatty liver. Successful completion of these studies will provide novel insights as to how ethanol affects LD dynamics in liver cells, and important information for therapeutic strategies aimed at reducing or eliminating the severity of steatosis and blocking its further progression to alcoholic steatohepatitis, fibrosis and cirrhosis.

Public Health Relevance

The goal of this proposal is to examine how impairments in the metabolism of lipid droplets (LDs), fat storage organelles, can influence LD accumulation in steatosis and contribute to alcohol-induced fatty liver disease. We hypothesize that ethanol exposure leads to hepatic steatosis by altering the disassembly of LDs via attenuation in the lipolytic and lipophagic machineries of LDs in the liver. These defects occur as a result of disrupted membrane trafficking events and impaired signaling cascades. Successful completion of the proposed studies will provide novel insights as to how ethanol affects LD dynamics in hepatocytes, and provide information which could lead to therapeutic strategies that might reduce the severity of steatosis and in this way block the further progression to steatohepatitis, fibrosis and cirrhosis.

Agency
National Institute of Health (NIH)
Institute
National Institute on Alcohol Abuse and Alcoholism (NIAAA)
Type
Research Project (R01)
Project #
5R01AA020735-07
Application #
9319613
Study Section
Hepatobiliary Pathophysiology Study Section (HBPP)
Program Officer
Gao, Peter
Project Start
2011-08-10
Project End
2021-04-30
Budget Start
2017-05-01
Budget End
2018-04-30
Support Year
7
Fiscal Year
2017
Total Cost
Indirect Cost
Name
University of Nebraska Medical Center
Department
Internal Medicine/Medicine
Type
Schools of Medicine
DUNS #
168559177
City
Omaha
State
NE
Country
United States
Zip Code
68198
Schulze, Ryan J; McNiven, Mark A (2018) Fasting Inhibits the Recruitment of Kinesin-1 to Lipid Droplets and Stalls Hepatic Triglyceride Secretion. Hepatology :
Schulze, Ryan J; Rasineni, Karuna; Weller, Shaun G et al. (2017) Ethanol exposure inhibits hepatocyte lipophagy by inactivating the small guanosine triphosphatase Rab7. Hepatol Commun 1:140-152
Schulze, Ryan J; Drižyt?, Kristina; Casey, Carol A et al. (2017) Hepatic Lipophagy: New Insights into Autophagic Catabolism of Lipid Droplets in the Liver. Hepatol Commun 1:359-369
Natarajan, Sathish Kumar; Rasineni, Karuna; Ganesan, Murali et al. (2017) Structure, Function and Metabolism of Hepatic and Adipose Tissue Lipid Droplets: Implications in Alcoholic Liver Disease. Curr Mol Pharmacol 10:237-248
Schott, Micah B; Rasineni, Karuna; Weller, Shaun G et al. (2017) ?-Adrenergic induction of lipolysis in hepatocytes is inhibited by ethanol exposure. J Biol Chem 292:11815-11828
Rasineni, Karuna; Donohue Jr, Terrence M; Thomes, Paul G et al. (2017) Ethanol-induced steatosis involves impairment of lipophagy, associated with reduced Dynamin2 activity. Hepatol Commun 1:501-512
Li, Zhipeng; Schulze, Ryan J; Weller, Shaun G et al. (2016) A novel Rab10-EHBP1-EHD2 complex essential for the autophagic engulfment of lipid droplets. Sci Adv 2:e1601470
Rasineni, Karuna; Penrice, Daniel D; Natarajan, Sathish Kumar et al. (2016) Alcoholic vs non-alcoholic fatty liver in rats: distinct differences in endocytosis and vesicle trafficking despite similar pathology. BMC Gastroenterol 16:27
Schroeder, Barbara; Schulze, Ryan J; Weller, Shaun G et al. (2015) The small GTPase Rab7 as a central regulator of hepatocellular lipophagy. Hepatology 61:1896-907
Rasineni, Karuna; McVicker, Benita L; Tuma, Dean J et al. (2014) Rab GTPases associate with isolated lipid droplets (LDs) and show altered content after ethanol administration: potential role in alcohol-impaired LD metabolism. Alcohol Clin Exp Res 38:327-35

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