Resistin Hepatic Insulin Sensitivity And ¦Â-cell Function

Part I Resistin induces insulin resistance in rat-derived hepatocytesAim: The aim of the present study was to observe the effects of resistin on insulin sensitivity in rat-derived hepatocytes.Methods: The rat hepatoma cell line H4IIE was cultured and stimulated with resistin, glycogen content was detected. The insulin receptor substrate (IRS-1), protein kinase B/Akt, glycogen synthase kinase-3β(GSK-3β), the suppressor of cytokine signaling 3 (SOCS-3) protein content, as well as the phosphorylation status were assessed by Western blotting. Specific antisense oligodeoxynucleotides directed against SOCS-3 were used to knockdown SOCS-3.Results: Resistin induced insulin resistance in rat hepatoma cell line H4IIE. Resistin attenuated multiple effects of insulin, including insulin-stimulated glycogen synthesis and phosphorylation of IRS, protein kinase B/Akt, as well as GSK-3β. Resistin treatment markedly induced the gene and protein expression of SOCS-3, a known inhibitor of insulin signaling. Furthermore, a specific antisense oligodeoxynucleotide directed against SOCS-3 treatment prevented resistin from antagonizing insulin action.Conclusion: The major function of resistin on liver is to induce insulinresistance. SOCS-3 induction may contribute to the resistin-mediatedinhibition of insulin signaling in H4IIE hepatocytes.Part II Resistin induces apoptosis in RINm5F insulinoma cellsAim: To investigate the functions of resistin and TIMP-1 on beta-cell.Methods: Rat insulinoma cells RINm5F were treated with resistin and TIMP-1. The cell viability was measured by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyltetrazolium bromide (MTT) cytotoxicity assay. Caspase-3 activity and DNA laddering assay were used to identify beta-cell apoptosis. Cell apoptosis related IκB-αprotein content, as well as the phosphorylation status were assessed by Western blotting.Results: Beta-cell viability was down-regulated by resistin. Caspase-3 activity was up-regulated by treatment of resistin. Resistin induced the formation of a DNA ladder. TIMP-1 attenuated these effects of resistin on beta-cell. Resistin induced beta-cell apoptosis may relate with activation of IκB-αphosphorylation, which can also be attenuated by TIMP-1. Conclusion: Resistin induced beta-cell apoptosis can be prevented byTIMP-1.Part III Resistin secretion in 3T3-L1 preadipocytes and diet-induced obesity ratsAim: To investigate the regulation of resistin secretion.Methods: Supernatant Resistin was collected during differentiation of3T3-L1 preadipocytes. Diet-induced obesity rats were used to study the invivo regulation of resistin secretion. Resistin was measured by ELISA.Results: Resistin secretion was enhanced during differentiation 3T3-L1preadipocytes. In diet-induced obese rats serum resistin level was higherthan normal controls.Conclusion: Secretion of resistin in adipocytes related with thedifferentation. Resistin level was higher in obese rats than in normals.