Cellular mechanism of insulin resistance in nonalcoholic fatty liver disease.

Abstract

Insulin resistance is associated with nonalcoholic fatty liver disease (NAFLD) and is a major factor in the pathogenesis of type 2 diabetes. The development of hepatic insulin resistance has been ascribed to multiple causes, including inflammation, endoplasmic reticulum (ER) stress, and accumulation of hepatocellular lipids in animal models of NAFLD. However, it is unknown whether these same cellular mechanisms link insulin resistance to hepatic steatosis in humans. To examine the cellular mechanisms that link hepatic steatosis to insulin resistance, we comprehensively assessed each of these pathways by using flash-frozen liver biopsies obtained from 37 obese, nondiabetic individuals and correlating key hepatic and plasma markers of inflammation, ER stress, and lipids with the homeostatic model assessment of insulin resistance index. We found that hepatic diacylglycerol (DAG) content in cytoplasmic lipid droplets was the best predictor of insulin resistance (R = 0.80, P < 0.001), and it was responsible for 64% of the variability in insulin sensitivity. Hepatic DAG content was also strongly correlated with activation of hepatic PKCε (R = 0.67, P < 0.001), which impairs insulin signaling. In contrast, there was no significant association between insulin resistance and other putative lipid metabolites or plasma or hepatic markers of inflammation. ER stress markers were only partly correlated with insulin resistance. In conclusion, these data show that hepatic DAG content in lipid droplets is the best predictor of insulin resistance in humans, and they support the hypothesis that NAFLD-associated hepatic insulin resistance is caused by an increase in hepatic DAG content, which results in activation of PKCε.

• Authors: Naoki Kumashiro, Derek M Erion, Dongyan Zhang, Mario Kahn, Sara A Beddow, Xin Chu, Christopher D Still, Glenn S Gerhard, Xianlin Han, James Dziura, Kitt Falk Petersen, Varman T Samuel, Gerald I Shulman
• Journal: Proceedings of the National Academy of Sciences of the United States of America (Proc Natl Acad Sci U S A) Vol. 108 Issue 39 Pg. 16381-5 (Sep 27 2011) ISSN: 1091-6490 [Electronic] United States
• PMID: 21930939 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, Non-P.H.S.)

Chemical References

• Diglycerides
• Protein Kinase C-epsilon

Topics

• Adult
• Diglycerides (metabolism)
• Enzyme Activation
• Fatty Liver (physiopathology)
• Female
• Humans
• Insulin Resistance
• Male
• Middle Aged
• Protein Kinase C-epsilon (metabolism)