mTOR partly mediates insulin resistance by phosphorylation of insulin receptor substrate-1 on serine(307) residues after burn.
Mammalian target of rapamycin (mTOR) is an important mediator for cross talk between nutritional signals and metabolic signals of insulin by downregulating insulin receptor substrate proteins. Therefore, mTOR inhibition could become a therapeutic strategy in insulin-resistant states, including insulin resistance induced by burn. We tested this hypothesis in the rat model of 30% TBSA full thickness burn, using the mTOR inhibitor rapamycin. Rapamycin (0.4 mg/kg, i.p.) was injected 2 h before euglycemic-hyperinsulinemic glucose clamps at 4 days after burn. IRS-1, phospho-serine³⁰⁷, phospho-tyrosine of IRS-1 and phospho-mTOR in muscle tissue were determined by immunoprecipitation and Western blot analysis or immunohistochemistry. Plasma TNF-α, insulin and C-peptide were determined before and after euglycemic-hyperinsulinemic glucose clamps. Our data showed that TNF-α, insulin and C-peptide significantly increased in the early stage after burn (P < 0.01). The infused rates of total 10% glucose (GIR, mg/kg min) significantly decreased at 4 days after burn. The level of IRS-1 serine³⁰⁷ phosphorylation in muscle in vivo significantly increased after burn (P < 0.01), while insulin-induced tyrosine phosphorylation of IRS-1 significantly decreased (P < 0.01). Inhibition of mTOR by rapamycin inhibited the phosphorylation of mTOR, reduced serine³⁰⁷ phosphorylation, elevated tyrosine phosphorylation and partly prevented the decrease of GIR after burn. However, TNF-α, insulin and C-peptide were not decreased by rapamycin treatment postburn. Taken together, these results indicate that the mTOR pathway is an important modulator of the signals involved in the acute regulation of insulin-stimulated glucose metabolism, and at least, partly contributes to burn-induced insulin resistance. mTOR inhibition may become a therapeutic strategy in insulin-resistant states after burn.
Xin-Long
Chen
C
Department of Burn, Taizhou People's Hospital, Medical College of Yangzhou University, Jiangsu Province, Taizhou 225300, People's Republic of China. cxlcxlzxy@hotmail.com
Zhao-Fan
Xia
X
Dao-Feng
Ben
B
Wei
Duo
D
D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D015153:Blotting, Western; D002056:Burns / Q000188:drug therapy / Q000378:metabolism; D002096:C-Peptide / Q000378:metabolism; D004195:Disease Models, Animal; D015309:Glucose Clamp Technique; D007150:Immunohistochemistry; D007328:Insulin / Q000378:metabolism; D055504:Insulin Receptor Substrate Proteins / Q000378:metabolism*; D007333:Insulin Resistance / Q000502:physiology; D018482:Muscle, Skeletal / Q000378:metabolism; D010766:Phosphorylation; D010768:Phosphoserine / Q000032:analysis; D019000:Phosphotyrosine / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D012694:Serine / Q000737:chemistry / Q000378:metabolism*; D020123:Sirolimus / Q000494:pharmacology*; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism
D000900:Anti-Bacterial Agents; D002096:C-Peptide; C526292:IRS1 protein, human; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D014409:Tumor Necrosis Factor-alpha; D010768:Phosphoserine; D019000:Phosphotyrosine; D012694:Serine; C546842:MTOR protein, human; D058570:TOR Serine-Threonine Kinases; D020123:Sirolimus