Dysregulation of mixed meal-induced gene expression in skeletal muscle in obesity and type 2 diabetes
Physical inactivity and western diet are the main factors leading to skeletal muscle (and whole-body) insulin resistance – a defect in insulin-mediated glucose uptake and metabolism – and associated metabolic diseases, such as obesity and type 2 diabetes mellitus (T2D).  The study of the response to a mixed meal (normalized for body mass and/or basal metabolic rate) is of particular interest, as it simulates the physiological response to a typical (daily) single meal that depends on both the secretory function of the beta cells (insulin response) and the sensitivity of skeletal muscle signaling to insulin – variables, which markedly changing during development of insulin resistance and T2D.  We aimed to compare the early transcriptomic response to a mixed meal normalized to body mass in skeletal muscle of healthy subjects and obese patients without (Ob) and with T2D (Ob+T2D).  To investigate the early transcriptomic response we took biopsy samples from the vastus lateralis muscle prior to and 1 h after a meal. In the Ob+T2D group the average level and increase in C-peptide and insulin in the blood were comparable with healthy subjects that, apparently, is explained by dysfunction of the beta-cells induced by chronic T2D. At the same time, the Ob+T2D group demonstrated dysregulation of mixed meal-induced gene expression in skeletal muscle: mor? than two times lower number of DEGs and a small overlapping with the gene response in the control group. On the contrary, the postprandial level of C-peptide and insulin in the Ob group was significantly greater than in healthy control that is related to insulin oversecretion associated with insulin resistance.  Despite this, the gene response in skeletal muscle was also significantly dysregulated; moreover, it differed from the response in the Ob+T2D group.  It means that defect in regulation of insulin-induced gene expression (insulin resistance in terms of gene expression) appears at the first stage of the development of metabolic disorders. Overall design: Seven healthy subjects, 7 obese patients, and 7 obese patients with T2D were involved in the study.  Subjects arrived at the laboratory at 09:00 after 12 h overnight fast. The venous blood was drawn from the v. intermedia cubiti using catheter prior to, and at 30, and 60 min after the mixed meal tolerant test (MMTT; nutritional drink Resource 2.0 [Nestle Health Science, France], 3 ml/kg of body mass, protein:lipid:carbohydrate 9:9:21, 840 kJ/100 ml). The plasma concentration of glucose and glycated hemoglobin was evaluated using an automatic analyzer Architect c8000 (Abbott Diagnostics, USA) and by HPLC (analyzer D10, BioRad, USA); the serum concentration of insulin and C-peptide was evaluated using an automatic analyzer Cobas 6000 (Roche, Switzerland). Biopsy samples were taken under local anesthesia (2 ml 2% lidocaine) using a modified Bergström needle with manual suction from the left vastus lateralis muscle prior to and after the MMTT.