Polycystic ovary syndrome is associated with tissue-specific differences in insulin resistance

Abstract

Objective: The potential differential contributions of skeletal muscle and adipose tissue to whole body insulin resistance were evaluated in subjects with polycystic ovary syndrome (PCOS).

Research design and methods: Forty-two PCOS subjects and 15 body mass index-matched control subjects were studied. Insulin action was evaluated by the hyperinsulinemic/euglycemic clamp procedure. Isolated adipocytes and cultured muscle cells were analyzed for glucose transport activity; adipocytes, muscle tissue, and myotubes were analyzed for the expression and phosphorylation of insulin-signaling proteins.

Results: Fifty-seven per cent of the PCOS subjects had impaired glucose tolerance and the lowest rate of maximal insulin-stimulated whole body glucose disposal compared to controls (P < 0.01). PCOS subjects with normal glucose tolerance had intermediate reduction in glucose disposal rate (P < 0.05 vs. both control and impaired glucose tolerance subjects). However, rates of maximal insulin-stimulated glucose transport (insulin responsiveness) into isolated adipocytes were comparable between all three groups, whereas PCOS subjects displayed impaired insulin sensitivity. In contrast, myotubes from PCOS subjects displayed reduced insulin responsiveness for glucose uptake and normal sensitivity. There were no differences between groups in the expression of glucose transporter 4 or insulin-signaling proteins or maximal insulin stimulation of phosphorylation of Akt in skeletal muscle, myotubes, or adipocytes.

Conclusions: Individuals with PCOS display impaired insulin responsiveness in skeletal muscle and myotubes, whereas isolated adipocytes display impaired insulin sensitivity but normal responsiveness. Skeletal muscle and adipose tissue contribute differently to insulin resistance in PCOS. Insulin resistance in PCOS cannot be accounted for by differences in the expression of selected signaling molecules or maximal phosphorylation of Akt.

Figures

Figure 1

Maximally insulin-stimulated whole body glucose disposal in normal cycling control (cont) and PCOS (NGT and IGT) subjects as determined from the hyperinsulinemic/euglycemic clamp procedure. Results are average + sem; number of subjects is given in Table 1. comb, Combined results for NGT and IGT subgroups. *, P < 0.0001 vs. control; †, P < 0.01 IGT vs. NGT.

Figure 2

Glucose transport in adipocytes isolated from control (cont) and PCOS subjects. A, Absolute rates of 3-OMG transport in the absence (open bars) and presence (solid bars) of a maximally stimulating (8.5 nm) concentration of insulin. B, Insulin sensitivity. Results are presented as percentage of the maximal insulin effect attained in each individual’s cells at a submaximal (0.17 nm) insulin level. Results are average + sem; n = 8 for control, n = 10 for NGT, and n = 16 for IGT. *, P < 0.05 vs. paired basal; †, P < 0.05 vs. control.

Figure 3

Insulin action on glucose uptake in cultured myotubes from control (cont) and PCOS (combined) subjects. A, Absolute values of basal and maximal insulin (33 nm) stimulated glucose uptake. Results represent average + sem; normal, n = 8; PCOS, n = 24. B, Insulin dose-response curves. Results were normalized to maximal effect attained in each individual set of cells. Control, Open symbols, solid line; PCOS, solid symbols, broken line. Results are average ± sem; n = 8 for both control and PCOS. *, P < 0.05 vs. paired basal; †, P < 0.05 vs. control in the same condition.

Figure 4

Insulin stimulation of Akt phosphorylation. Adipocyte and muscle cell proteins extracted after 15-min incubation in the absence (open bars) or presence (solid bars) of insulin. Muscle tissue collected before and after 3-h insulin infusion. Phosphorylation of pS473-Akt (A) or pT308-Akt (B) was determined by Western blotting. Blots were stripped and reprobed for Akt-1/2. Basal and maximal insulin (33 nm) stimulated phosphorylation, results were normalized against the amount of Akt for each individual and condition. Results represent average + sem. For pS-Akt: isolated adipocytes, n = 11 for control, 21 for PCOS; skeletal muscle, n = 9 and 22; muscle cells, n = 6 and 13. For pT-Akt: adipocytes, n = 8 and 17; muscle tissue, n = 9 and 17; myocytes, n = 6 and 17. *, P < 0.05 vs. basal.