Diacylglycerol (DAG) has been proposed to mediate lipid-induced hepatic insulin resistance. Accumulated hepatic DAG activates PKCε which phosphorylates insulin receptor kinase (IRK) at T1160 to inhibit IRK activation and cause insulin resistance. However, the importance of DAG in lipid-induced hepatic insulin resistance remains controversial. To test the physiological effect of acute DAG accumulation on hepatic insulin sensitivity, we used antisense oligonucleotide (ASO) to specifically inhibit hepatic diglyceride acyltransferase 2 (DGAT2) which catalyzes the conversion of DAG to triglyceride. Previously, chronic DGAT2 inhibition was shown to paradoxically decrease hepatic DAG content due to decreased SREBP-1c-mediated lipogenesis and improve hepatic insulin sensitivity. However, we hypothesized that acute DGAT2 inhibition might provide a narrow window to transiently increase hepatic DAG content and allow us to identify the association between DAG, PKCε activation/translocation and hepatic insulin resistance. As hypothesized, an acute (2-day) DGAT2 inhibition increased hepatic DAG content and PKCε activation (cytosol to membrane translocation). DGAT2 ASO-treated rats on regular chow diet displayed impaired insulin-mediated suppression of hepatic glucose production. This defect of hepatic insulin action was at the level of IRK as indicated by impaired insulin-stimulated IRK Y1158/1162 phosphorylation. Furthermore, measured by a novel LC-MS/MS method, hepatic sn-1,2 DAG, which is the DAG stereoisomer capable of activating PKCε, was increased in the subcellular membrane compartment with DGAT2 ASO treatment.
Conclusion: These data support the importance of membrane sn-1,2 DAG in mediating lipid-induced hepatic insulin resistance through “increased membrane sn-1,2 DAG content -> PKCε activation/translocation -> increased IRK T1160 phosphorylation -> decreased IRK Y1158/1162 phosphorylation -> decreased IRK activity” in vivo.
K. Lyu: None. D. Zhang: None. Y. Nozaki: None. Y. Zhang: None. S. Bhanot: Employee; Self; Ionis Pharmaceuticals, Inc.. G. Cline: None. V. Samuel: None. G.I. Shulman: Advisory Panel; Self; AstraZeneca, Janssen Research & Development, Merck & Co., Inc., Novo Nordisk Inc.. Research Support; Self; Gilead Sciences, Inc..