The Molecular Mechanism Of Ovarian Local Insulin Resistance In Polycystic Ovarian Syndrome Patients

OBJECTIVE: Researchers have lately found that there is ovary local insulin resistance in polycystic ovarian syndrome, and the ovary local insulin resistance is related closely to the inordinate ovary function of polycystic ovaries syndrome. However, the molecular mechanisms of ovary local insulin resistance are unknown. To explore molecular mechanisms of ovary local insulin resistance we determined the tyrosine phosphorylation and protein expression of insulin receptor substrate1 and 2 (IRS-1, IRS-2) in ovarian luteinizing granulosa cells from patients with PCOS. At the same time we studyed the effect of insulin, LH and rosiglitazone on the tyrosine phosphorylation and protein expression of insulin receptor substrate1 and 2 (IRS-1, IRS-2) in luteinizing granulosa cell between polycystic ovaries and regularly cycling controls, to explore the effect of the abnormal increasing LH and Hyperinsulinemic on ovary insulin resistance in PCOS, and to investegate the molecular mechanisms of the rosiglitazone effect on ovarian insulin resistancein polycystic ovarian syndrome (PCOS).METHODS: ovarian luteinizing granulosa cells from PCOS (n= 11) and normally ovulatory(as control, n=15) were obtained in the process of IVF-ET. Serum luteinizing hormone(LH), follicle stimulating hormone(FSH), testosterone(T) and fasting insulin(FIN) were measured by radioimmunoassay. Fasting plasma glucose (FPG) was measured by oxidase assay. Insulin resistance index was calculated using homeostasis model assessment (HOMA). The mRNA expression of insulin receptor substrates (IRS-1, IRS-2) in ovarian luteinizing granulose cells were assessed by semi-quantitative RT-PCR. The protein and phosphorylation expression of insulin receptor substrates (IRS-1, IRS-2) in ovarian luteinizing granulose cells were analyzed by Western blot and immunoprecipitation. And the same time we observed the effect of different concentration insulin(0,10,100,1000mIU/mL), LH(0,20,200,2000mIU/mL)and rosiglitazone(0,10,100,1000,10000 nM/L)on the tyrosine phosphorylation and protein expression of insulin receptor substrate1 and 2 (IRS-1, IRS-2) in ovarian luteinizing granulosa cells from the two groups. RESULT: (1) The levels of LH, LH/FSH, T, FIN and HOMA-IR in PCOS patients were significantly higher than those in contorl group(P<0.05). (2) As compared with control group, luteinizing granulose cells in PCOS patients had higher IRS-1mRNA expression and protein content(P<0.05), but lower IRS-2mRNA expression and protein content(P<0.05).(3) The phosphorylation expression of IRS-1 and IRS-2 of ovarian luteinizing granulose cells in PCOS patients were significantly lower than those in control group(P<0.05).(4) Treated with physiologic dose insulin (10μU/ml), the mRNA expression and protein content of insulin receptor substrates (IRS-1, IRS-2) was unchanged in both PCOS and controls(P>0.05). However, treated with super-physiologic dose insulin (100μU/ml,1000μU/ml), the IRS-1mRNA expression and protein content was increased remarkably(P<0.05) and the IRS-2mRNA expression and protein content was reduced notably(P<0.05) in both PCOS and controls, and the response of luteinizing granulosa cell to insulin between the two groups was not statistic different(P>0.05). (5) LH significantly increased the IRS-1 mRNA and the protein expression of luteinizing granulose cells in patients with PCOS(P<0.05), but had not effect on IRS-2mRNA and protein expression(P>0.05). There was no effect of LH on IRS-1 and IRS-2 mRNA and protein expression in luteinizing granulose cells in normally ovulatory women(P>0.05). (6) Rosiglitazone corrected the abnormal protein expression and improved the tyrosine phosphorylation of insulin receptor substrate1 and 2 (IRS-1, IRS-2) in ovarian luteinizing granulosa cells from patients with PCOS(P<0.05). Rosiglitazone had no effect on the tyrosine phosphorylation and protein expression of insulin receptor substrate1 and 2 (IRS-1, IRS-2) in ovarian luteinizing granulosa cells from normal ovulatory control(P>0.05).CONCLUSION: (1) There is a selective insulin resistance in ovarian luteinizing granulosa cells from patients with PCOS, the reason may be related to abnormal tyrosine phosphorylation and protein expression of insulin receptor substrates. (2) The insulin resistance and hyperinsulinemic may play a role in the inordinate ovary function of PCOS by up-regulated IRS-1 protein expression and decreased IRS-2 protein expression. (3) Elevated LH may participate the selective insulin resistance of PCOS by up-regulated IRS-1 protein expression. (4)Rosiglitazone improved ovarian function of PCOS, the reason may be related to corrected the abnormal protein expression and improved the tyrosine phosphorylation of insulin receptor substrates in ovarian luteinizing granulosa cells.