Prolonged treatment of primary hepatocytes with oleate induces insulin resistance through p38 mitogen-activated protein kinase.
Free fatty acid (FFA) is believed to be a major environmental factor linking obesity to Type II diabetes. We have recently reported that FFA can induce gluconeogenesis in hepatocytes through p38 mitogen-activated protein kinase (p38). In this study, we have investigated the role of p38 in oleate-induced hepatic insulin resistance. Our results show that a prolonged treatment of primary hepatocytes with oleate blunted insulin suppression of hepatic gluconeogenesis, and decreased insulin-induced phosphorylation of Akt in a p38-dependent manner. Reduction of the insulin-induced Akt phosphorylation by oleate correlated with activation of p38. In the presence of p38 inhibition, prolonged exposure of hepatocytes to oleate failed to reduce insulin-stimulated phosphorylation of Akt. An siRNA against p38alpha prevented oleate suppression of the insulin-induced phosphorylation of Akt. Furthermore, a prolonged exposure of hepatocytes to oleate decreased insulin-induced tyrosine phosphorylation of IRS1/2, while slightly increasing serine phosphorylation of IRS. The decrease of insulin-stimulated tyrosine phosphorylation of IRS1/2 in hepatocytes by oleate was reversed by the inhibition of p38. We further show that a prolonged exposure of primary hepatocytes to oleate elevated the protein level of the phosphatase and tensin homolog deleted on chromosome 10 (PTEN) gene in a p38-dependent manner, but had no effect on the mRNA level of PTEN. Knocking down the PTEN gene prevented oleate to inhibit insulin activation of Akt and insulin suppression of gluconeogenesis. Together, results from this study demonstrate a critical role for p38 in oleate-induced hepatic insulin resistance.
Liu
Hui-Yu
HY
Endocrine Biology Program, The Hamner Institutes for Health Sciences, Research Triangle Park, NC 27709, USA.
Collins
Qu Fan
QF
Xiong
Yan
Y
Moukdar
Fatiha
F
Lupo
Edgar G
EG
Liu
Zhenqi
Z
Cao
Wenhong
W
D000818:Animals; D017209:Apoptosis; D015153:Blotting, Western; D053148:Caspase 3 / Q000378:metabolism; D005943:Gluconeogenesis; D022781:Hepatocytes / Q000187:drug effects* / Q000378:metabolism; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D047468:Immunoprecipitation; D007328:Insulin / Q000494:pharmacology*; D055504:Insulin Receptor Substrate Proteins; D007333:Insulin Resistance; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D019301:Oleic Acid / Q000494:pharmacology*; D051059:PTEN Phosphohydrolase / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D034741:RNA, Small Interfering / Q000494:pharmacology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D014443:Tyrosine / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*
D007004:Hypoglycemic Agents; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D047908:Intracellular Signaling Peptides and Proteins; C526295:Irs1 protein, mouse; C526298:Irs2 protein, mouse; D010750:Phosphoproteins; D034741:RNA, Small Interfering; D019301:Oleic Acid; D014443:Tyrosine; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D051059:PTEN Phosphohydrolase; C487757:Pten protein, mouse; D053148:Caspase 3