Impaired Insulin-Stimulated Phosphorylation of Akt and AS160 in Skeletal Muscle of Women With Polycystic Ovary Syndrome Is Reversed by Pioglitazone Treatment

Abstract

OBJECTIVE-Insulin resistance in skeletal muscle is a major risk factor for type 2 diabetes in women with polycystic ovary syndrome (PCOS). However, the molecular mechanisms underlying skeletal muscle insulin resistance and the insulin-sensitizing effect of thiazolidinediones in PCOS in vivo are less well characterized.RESEARCH DESIGN AND METHODS-We determined molecular mediators of insulin signaling to glucose transport in skeletal muscle biopsies of 24 PCOS patients and 14 matched control subjects metabolically characterized by euglycemic-hyperinsulinemic clamps and indirect calorimetry, and we examined the effect of 16 weeks of treatment with pioglitazone in PCOS patients.RESULTS-Impaired insulin-mediated total (R d ) oxidative and nonoxidative glucose disposal (NOGD) was paralleled by reduced insulin-stimulated Akt phosphorylation at Ser473 and Thr308 and AS160 phosphorylation in muscle of PCOS patients. Akt phosphorylation at Ser473 and Thr308 correlated positively with R d and NOGD in the insulin-stimulated state. Serum free testosterone was inversely related to insulin-stimulated R d and NOGD in PCOS. Importantly, the pioglitazone-mediated improvement in insulin-stimulated glucose metabolism, which did not fully reach normal levels, was accompanied by normalization of insulinmediated Akt phosphorylation at Ser473 and Thr308 and AS160 phosphorylation. AMPK activity and phosphorylation were similar in the two groups and did not respond to pioglitazone in PCOS patients.CONCLUSIONS-Impaired insulin signaling through Akt and AS160 in part explains insulin resistance at the molecular level in skeletal muscle in PCOS, and the ability of pioglitazone to enhance insulin sensitivity involves improved signaling through Akt and AS160. Moreover, our data provide correlative evidence that hyperandrogenism in PCOS may contribute to insulin resistance. Diabetes 57:357-366, 2008

Differential aetiology and impact of phosphoinositide 3-kinase (PI3K) and Akt signalling in skeletal muscle on in vivo insulin action

“…In contrast to some [11,12,14,48] and in line with other studies [15,30,43], we saw no association between IRTK as well as IRS-1-PI3K activity and glucose disposal (Fig. 3a, b).…”

“…Multiple defects at several levels in insulin signalling have been described in patients with overt type 2 diabetes [5,[11][12][13][14] and strongly associated diseases [15], but also in conditions predisposing to type 2 diabetes. These conditions include an adverse intrauterine environment as evidenced by low birthweight, which has previously been linked to reduced levels [16] and function [17] of key insulin signalling proteins.…”

Insulin and hyperandrogenism in women with polycystic ovary syndrome

“…Akt is an important mediator of insulin-stimulated GLUT4 translocation and glucose transport [71], and seems to be dependent on the phosphorylation of AS160 at several sites by Akt [72][73][74]. In obese PCOS women, a decrease in insulin-mediated phosphorylation of AS160 and of Akt (at Thr308 and Ser473) has been described [75]. This may be due to dephosphorylation of Akt by protein phosphatases, including protein phosphatase 2A (PP2A), that are activated by ceramide metabolites of palmitate [76].…”

Dual Regulation of Muscle Glycogen Synthase during Exercise by Activation and Compartmentalization

“…SDS-PAGE and Western Blotting-Muscle proteins were separated using 7.5% Tris-HCl gels (Bio-Rad, Denmark), and transferred (semi-dry) to polyvinylidene difluoride membranes (Immobilon Transfer Membrane, Millipore A/S, Denmark) (32). Primary antibodies used for Western blotting: Anti-GS was a polyclonal rabbit antibody (32).…”

“…Primary antibodies used for Western blotting: Anti-GS was a polyclonal rabbit antibody (32). For detection of P-GS3aϩ3b, P-GS2, P-GS2ϩ2a, P-GS1a, and P-GS1b, antibodies were raised against different peptides as described (26,33).…”