Altered Lipid Droplet Trafficking: Role in Alcoholic Fatty Liver Disease

ABSTRACT
This proposal is a competitive renewal of a multiple-PI R01 funded through NIAAA. The goal of the application
is to examine how ethanol (EtOH) exposure contributes to fat accumulation in the liver due to altered dynamic
properties of the lipid droplet (LD), a fat storage organelle. Almost all heavy drinkers develop fatty liver, which
is marked by the aberrant and significant accumulation of intrahepatocellular triglycerides stored within LDs.
Understanding the cellular processes contributing to this fat accumulation will provide essential information for
preventing further injury progression, as it is known that alcoholic fatty liver is the initial but reversible stage of
liver injury. Here, we propose to provide molecular insights into these critical questions, aimed at
potential treatments that reverse or prevent EtOH-induced steatosis. This proposal combines the expertise of
two senior investigators recognized for their contributions to the study of EtOH-induced cell injury
and hepatic LD biology. We believe this collaborative effort has been beneficial to the field of ALD and will result
in outcomes not attainable by individual efforts alone. This proposal comprises two well-integrated aims. Aim
One: Blockage of ER-Associated Lipophagy by EtOH. We have made the interesting observation that
nascent LDs of a conserved size (170nm) accumulate at the ER surface of EtOH-damaged hepatocytes and
that lysosomal/autophagic compartments subsequently catabolize these ER-associated LDs. Notably, both
chronic EtOH exposure and pharmacologic disruption of lysosome function attenuate this process leading to
hepatocyte steatosis. Aim Two: Disruptive Alterations of the LD Proteome by EtOH. We found that many
components of the LD “surface proteome” are post-translationally modified by ubiquitin, a pathway we posit
directs removal of select proteins to the proteasome for degradation or directs the entire LD to the lysosome for
catabolism. Importantly, we have found that chronic EtOH exposure markedly increases the ubiquitination of the
LD proteome and thus disrupts normal LD degradation/catabolism leading to steatosis. These observations and
specific aims will allow us to pursue the CENTRAL HYPOTHESIS of this study that EtOH promotes
accumulation of both mature and nascent, ER-associated, LDs through alterations of the LD proteome inhibiting
lipophagy and lipid catabolism leading to hepatocyte steatosis. The proposed investigation will utilize state-of-
the-art imaging and proteomic 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 EtOH 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.

Grant Number: 5R01AA020735-15
NIH Institute/Center: NIH
Principal Investigator: Carol Casey