AIMS/HYPOTHESIS: Insulin-mediated glucose transport and utilisation are decreased in skeletal muscle from type 2 diabetic and glucose-intolerant individuals because of alterations in insulin receptor signalling, GLUT4 translocation to the plasma membrane and microvascular blood flow. Catalytic activity of the muscle-specific isoform of neuronal nitric oxide synthase (nNOS) also participates in the regulation of glucose transport and appears to be decreased in a relevant animal model of drastic insulin resistance, the obese Zucker fa/fa rat. Our objective was to determine the molecular mechanisms involved in this defect. METHODS: Isolated rat muscles and primary cultures of myocytes were used for western blot analysis of protein expression, immunohistochemistry, glucose uptake measurements and GLUT4 translocation assays. RESULTS: nNOS expression was reduced in skeletal muscle from fa/fa rats. This was caused by increased ubiquitination of the enzyme and subsequent degradation by the ubiquitin proteasome pathway. The degradation occurred through a greater interaction of nNOS with the chaperone heat-shock protein 70 and the co-chaperone, carboxyl terminus of Hsc70-interacting protein (CHIP). In addition, an alteration in nNOS sarcolemmal localisation was observed. We confirmed the implication of nNOS breakdown in defective insulin-induced glucose transport by demonstrating that blockade of proteasomal degradation or overexpression of nNOS improved basal and/or insulin-stimulated glucose uptake and GLUT4 translocation in primary cultures of insulin-resistant myocytes. CONCLUSIONS/ INTERPRETATION: Recovery of nNOS in insulin-resistant muscles should be considered a potential new approach to address insulin resistance.
AIMS/HYPOTHESIS: Insulin-mediated glucose transport and utilisation are decreased in skeletal muscle from type 2 diabetic and glucose-intolerant individuals because of alterations in insulin receptor signalling, GLUT4 translocation to the plasma membrane and microvascular blood flow. Catalytic activity of the muscle-specific isoform of neuronal nitric oxide synthase (nNOS) also participates in the regulation of glucose transport and appears to be decreased in a relevant animal model of drastic insulin resistance, the obese Zucker fa/fa rat. Our objective was to determine the molecular mechanisms involved in this defect. METHODS: Isolated rat muscles and primary cultures of myocytes were used for western blot analysis of protein expression, immunohistochemistry, glucose uptake measurements and GLUT4 translocation assays. RESULTS:nNOS expression was reduced in skeletal muscle from fa/fa rats. This was caused by increased ubiquitination of the enzyme and subsequent degradation by the ubiquitin proteasome pathway. The degradation occurred through a greater interaction of nNOS with the chaperone heat-shock protein 70 and the co-chaperone, carboxyl terminus of Hsc70-interacting protein (CHIP). In addition, an alteration in nNOS sarcolemmal localisation was observed. We confirmed the implication of nNOS breakdown in defective insulin-induced glucose transport by demonstrating that blockade of proteasomal degradation or overexpression of nNOS improved basal and/or insulin-stimulated glucose uptake and GLUT4 translocation in primary cultures of insulin-resistant myocytes. CONCLUSIONS/ INTERPRETATION: Recovery of nNOS in insulin-resistant muscles should be considered a potential new approach to address insulin resistance.
Authors: Adrienne M Wang; Yoshihiro Morishima; Kelly M Clapp; Hwei-Ming Peng; William B Pratt; Jason E Gestwicki; Yoichi Osawa; Andrew P Lieberman Journal: J Biol Chem Date: 2010-03-26 Impact factor: 5.157
Authors: A Avogaro; F Piarulli; A Valerio; M Miola; M Calveri; P Pavan; P Vicini; C Cobelli; A Tiengo; L Calò; S Del Prato Journal: Diabetes Date: 1997-06 Impact factor: 9.461
Authors: A T Bender; A M Silverstein; D R Demady; K C Kanelakis; S Noguchi; W B Pratt; Y Osawa Journal: J Biol Chem Date: 1999-01-15 Impact factor: 5.157