Insulin receptor phosphorylation, insulin receptor substrate-1 phosphorylation, and phosphatidylinositol 3-kinase activity are decreased in intact skeletal muscle strips from obese subjects.

Abstract

To determine whether the impaired insulin-stimulated glucose uptake in obese individuals is associated with altered insulin receptor signaling, we measured both glucose uptake and early steps in the insulin action pathway in intact strips of human skeletal muscle. Biopsies of rectus abdominus muscle were taken from eight obese and eight control subjects undergoing elective surgery (body mass index 52.9±3.6 vs 25.7±0.9). Insulin-stimulated 2-deoxyglucose uptake was 53% lower in muscle strips from obese subjects. Additional muscle strips were incubated in the basal state or with i0-7 M insulin for 2, 15, or 30 min. In the lean subjects, tyrosine phosphorylation of the insulin receptor and insulin receptor substrate-i (IRS-1), measured by immunoblotting with anti-phosphotyrosine antibodies, was significantly increased by insulin at all time points. In the skeletal muscle from the obese subjects, insulin was less effective in stimulating tyrosine phosphorylation (maximum receptor and IRS-1 phosphorylation decreased by 35 and 38%, respectively). Insulin stimulation of IRS-1 immunoprecipitable phosphatidylinositol 3-kinase (PI 3-kinase) activity also was markedly lower in obese subjects compared with controls (10-vs 35-fold above basal, respectively). In addition, the obese subjects had a lower abundance of the insulin receptor, IRS-1, and the p85 subunit of PI 3-kinase (55, 54, and 64% of nonobese, respectively). We conclude that impaired insulinstimulated glucose uptake in skeletal muscle from severely obese subjects is accompanied by a deficiency in insulin receptor signaling, which may contribute to decreased insulin action. (J. Clin. Invest. 1995.95:2195-2204 Key words:

Low birthweight is associated with specific changes in muscle insulin-signalling protein expression

“…The major proteins identified as being differentially expressed in control and low-birthweight muscle were PKCζ, p85α (regulatory subunit of PI 3-kinase), p110β (catalytic subunit of PI 3-kinase) and GLUT4. Similar reductions in the expression of PKCζ [10] and p85 [18] have been observed in the skeletal muscle of diabetic subjects, although in the latter case these subjects were also morbidly obese. There are no reports to date on the expression of p110β in muscle from diabetic patients compared to control subjects.…”

IGF-1 receptor signalling determines the mitogenic potency of insulin analogues in human smooth muscle cells and fibroblasts

“…Importantly, these results were strictly donor-specific and correlated with levels of the proteins IGF-1R, InsR and/or IRS-1. It has been shown that IRS-1 and InsR levels vary in different tissues of healthy human individuals [27,28]. Furthermore, we found high variation in IGF-1R levels in monocytes isolated from a randomly chosen group of 16 healthy donors.…”

Insulin signalling in skeletal muscle of subjects with or without Type II-diabetes and first degree relatives of patients with the disease

“…This is also confirmed by our data in the FDR subjects who, despite an increased risk for the development of Type II diabetes, displayed no detectable abnormalities. In the context of other studies, where such alterations were partly found, this could indicate that secondary factors like hyperglycaemia [26], increased NEFA concentrations [27] or obesity [23,54] interfere with PI3′-kinase/Akt signalling in overt diabetes. With the present methodology, it cannot be excluded that despite similar overall activity/phosphorylation of the investigated signalling molecules an altered spatial organisation contributed to an altered signalling in FDR and diabetic subjects.…”