Submitted to: Alcoholism: Clinical and Experimental
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/22/2010
Publication Date: 6/6/2011
Citation: Orlicky, D.J., Roede, J.R., Bales, E., Greenwood, C., Greenberg, A.S., Petersen, D., Mcmanaman, J.L. 2011. Chronic ethanol consumption in mice alters hepatocyte lipid droplet properties. Alcoholism: Clinical and Experimental. 35(6):1020-1033. Interpretive Summary: In mice and humans increased fat storage within the liver predisposes individuals to the development of liver diseases such as hepatitis, loss of liver function (cirrhosis), and finally liver cancer. One of the major complications of excessive alcohol intake is increased storage of fat in livers. Within cells in the body, fat is stored within specific parts of the cells called lipid droplets. Our laboratory is studying the proteins that coat the surface of lipid droplets within cells. These proteins that coat the lipid droplet often promote fat storage. Alcohol intake is thought to increase fat intake in part by causing specific chemical reactions that promote the expression of proteins that are typically induced when the cells are stressed. To determine which proteins coat lipid droplets with alcohol intake, we compared the effects of a diet with alcohol and without it on liver fat accumulation and proteins that coat the lipid droplets. We identified three proteins that coat lipid droplets in mice with alcohol intake, these proteins are called perilipin, ADRP and TIP47. Also we found that the expression of specific stress proteins were associated with the proteins coating the lipid droplets. These studies will allow us in the future to determine the role of these proteins in promoting fat accumulation in livers with alcohol intake.
Technical Abstract: Background: Hepatosteatosis is a common pathological feature of impaired hepatic metabolism following chronic alcohol consumption. Although often benign and reversible, it is widely believed that steatosis is a risk factor for development of advanced liver pathologies, including steatohepatitis and fibrosis. The hepatocyte alterations accompanying the initiation of steatosis are not yet clearly defined. Methods: Induction of hepatosteatosis by chronic ethanol consumption was investigated using the Lieber-DeCarli (LD) high fat diet model. Effects were assessed by immunohistochemistry and blood and tissue enzymatic assays. Cell culture models were employed for mechanistic studies. Results: Pair feeding mice ethanol (LD-Et) or isocaloric control (LD-Co) diets for 6 weeks progressively increased hepatocyte triglyceride accumulation in morphological, biochemical, and zonally distinct cytoplasmic lipid droplets (CLD). The LD-Et diet induced zone 2-specific triglyceride accumulation in large CLD coated with perilipin, adipophilin (ADPH), and TIP47. In LD-Co-fed mice, CLD were significantly smaller than those in LD-Et-fed mice and lacked perilipin. A direct role of perilipin in formation of large CLD was further suggested by cell culture studies showing that perilipin-coated CLD were significantly larger than those coated with ADPH or TIP47. LD-Co- and LD-Et-fed animals also differed in hepatic metabolic stress responses. In LD-Et but not LD-Co-fed mice, inductions were observed in the following: microsomal ethanol-oxidizing system [cytochrome P-4502E1 (CYP2E1)], hypoxia response pathway (hypoxia-inducible factor 1 alpha, HIF1alpha), endoplasmic reticulum stress pathway (calreticulin), and synthesis of lipid peroxidation products [4-hydroxynonenal (4-HNE)]. CYP2E1 and HIF1 alpha immunostaining localized to zone 3 and did not correlate with accumulation of large CLD. In contrast, calreticulin and 4-HNE immunostaining closely correlated with large CLD accumulation. Importantly, 4-HNE staining significantly colocalized with ADPH and perilipin on the CLD surface. Conclusions: These data suggest that ethanol contributes to macrosteatosis by both altering CLD protein composition and inducing lipid peroxide adduction of CLD-associated proteins.