Apolipoprotein B100 Acts as a Molecular Link Between Lipid-Induced Endoplasmic Reticulum Stress and Hepatic Insulin Resistance

Accumulation of unfolded and misfolded proteins in the endoplasmic reticulum (ER) results in ER stress and lipid overload-induced ER stress has been implicated in the development of insulin resistance. Here, evidence is provided for a molecular link between hepatic apolipoprotein B 100 (apoB100), induction of ER stress, and attenuated insulin signaling. First, in vivo upregulation of hepatic apoB100 by a lipogenic diet was found to be closely associated with ER stress and attenuated insulin signaling in the liver. Direct in vivo overexpression of human apoB100 in a mouse transgenic model futher supported the link between excessive apoB100 expression and hepatic ER stress. Human apoB 100 transgenic mice exhibited hypertriglyceridemia and hyper-glycemia. In vitro, accumulation of cellular apoB100 by free fatty acid (oleate) stimulation or constant expression of wild-type or N-glycosylation mutant apoB50 in hepatic cells induced ER stress. This led to perturbed activation of glycogen synthase kinase 3 and glycogen synthase by way of the activation of c-jun N-terminal kinase and suppression of insulin signaling cascade, suggesting that dysregulation of apoB was sufficient to disturb ER homeostasis and induce hepatic insulin resistance. Small interfering (si)RNA-mediated attenuation of elevated apoB level in the apoB50-expressing cells rescued cells from lipid-induced ER stress and reversed insulin insensitivity. Conclusion: These findings implicate apoB100 as a molecular link between lipid-induced ER stress and hepatic insulin resistance. (HEPATOLOGY 2009;50:77-84.)