Evidence for defects in the trafficking and translocation of GLUT4 glucose transporters in skeletal muscle as a cause of human insulin resistance.

Abstract

Insulin resistance is instrumental in the pathogenesis of type 2 diabetes mellitus and the Insulin Resistance Syndrome. While insulin resistance involves decreased glucose transport activity in skeletal muscle, its molecular basis is unknown. Since muscle GLUT4 glucose transporter levels are normal in type 2 diabetes, we have tested the hypothesis that insulin resistance is due to impaired translocation of intracellular GLUT4 to sarcolemma. Both insulin-sensitive and insulin-resistant nondiabetic subgroups were studied, in addition to type 2 diabetic patients. Biopsies were obtained from basal and insulin-stimulated muscle, and membranes were subfractionated on discontinuous sucrose density gradients to equilibrium or under nonequilibrium conditions after a shortened centrifugation time. In equilibrium fractions from basal muscle, GLUT4 was decreased by 25-29% in both 25 and 28% sucrose density fractions and increased twofold in both the 32% sucrose fraction and bottom pellet in diabetics compared with insulin-sensitive controls, without any differences in membrane markers (phospholemman, phosphalamban, dihydropyridine-binding complex ␣ -1 subunit). Thus, insulin resistance was associated with redistribution of GLUT4 to denser membrane vesicles. No effects of insulin stimulation on GLUT4 localization were observed. In non-equilibrium fractions, insulin led to small GLUT4 decrements in the 25 and 28% sucrose fractions and increased GLUT4 in the 32% sucrose fraction by 2.8-fold over basal in insulin-sensitive but only by 1.5-fold in both insulinresistant and diabetic subgroups. The GLUT4 increments in the 32% sucrose fraction were correlated with maximal in vivo glucose disposal rates ( r ϭ ϩ 0.51, P ϭ 0.026), and, therefore, represented GLUT4 recruitment to sarcolemma or a quantitative marker for this process. Similar to GLUT4, the insulin-regulated aminopeptidase (vp165) was redistributed to a dense membrane compartment and did not translocate in response to insulin in insulin-resistant subgroups.In conclusion, insulin alters the subcellular localization of GLUT4 vesicles in human muscle, and this effect is impaired equally in insulin-resistant subjects with and without diabetes. This translocation defect is associated with abnormal accumulation of GLUT4 in a dense membrane compartment demonstrable in basal muscle. We have previously observed a similar pattern of defects causing insulin resistance in human adipocytes. Based on these data, we propose that human insulin resistance involves a defect in GLUT4 traffic and targeting leading to accumulation in a dense membrane compartment from which insulin is unable to recruit GLUT4 to the cell surface.

Expression of the skeletal muscle dystrophin–dystroglycan complex and syntrophin-nitric oxide synthase complex is severely affected in the type 2 diabetic Goto–Kakizaki rat

“…A combination of genetic and environmental factors is likely to contribute to the pathogenesis of this metabolic disorder (Moller, 2001). Our initial investigation into the subcellular location of the glucose transporter GLUT4 in basal, non-insulin stimulated muscle agrees with previous studies (Garvey et al, 1998) and suggests an abnormal accumulation of GLUT4 vesicles in a dense membrane region, from which insulin signalling may be unable to properly recruit the transporter molecule. Although expression levels of the insulin receptor, GLUT4 and associated signalling molecules are not affected in GK muscles, insulin resistance may result from the inability of a critical amount of GLUT4 units to reach the plasmalemma.…”

“…Subcellular muscle fractions were isolated by a centrifugation method adapted from Garvey et al (1998). This method is a modification of that previously used to demonstrate insulin-mediated translocation of glucose transporters in rat muscle (Klip et al, 1987).…”

Peripheral insulin resistance develops in transgenic rats overexpressing phosphoenolpyruvate carboxykinase in the kidney

“…Tissue-specific regulation of GLUT4 has also been described in animals fed a high fat diet, which resulted in decreased GLUT4 mRNA expression in white adipose tissue but not skeletal muscle [51,52]. Further analysis has suggested that the defect in muscle glucose uptake in patients with Type 2 diabetes could be associated with impairments in trafficking and/or translocation of GLUT4 to the plasma membrane [53,54,55]. In agreement, high fat-induced skeletal muscle insulin resistance in animals has been associated with defects in the translocation and intrinsic activity of GLUT4.…”

Acetylation of TUG Protein Promotes the Accumulation of GLUT4 Glucose Transporters in an Insulin-responsive Intracellular Compartment

“…They are small (ϳ60-nm diameter) and have a characteristic set of cargo proteins, including the insulin-regulated aminopeptidase, IRAP. Some data suggest that GLUT4 and IRAP do not accumulate in a pool of insulin-responsive GSVs in unstimulated muscle and adipose of individuals with insulin resistance (5,7,8). Nevertheless, despite the medical importance of understanding GSVs, the regulated trafficking of these vesicles has remained enigmatic.…”