Aims/hypothesis: Microarray-based studies of skeletal muscle from patients with type 2 diabetes and high-risk individuals have demonstrated that insulin resistance and reduced mitochondrial biogenesis co-exist early in the pathogenesis of type 2 diabetes independently of hyperglycaemia and obesity. It is unknown whether reduced mitochondrial biogenesis or other transcriptional alterations co-exist with impaired insulin responsiveness in primary human muscle cells from patients with type 2 diabetes.
Methods: Using cDNA microarray technology and global pathway analysis with the Gene Map Annotator and Pathway Profiler (GenMapp 2.1) and Gene Set Enrichment Analysis (GSEA 2.0.1), we examined transcript levels in myotubes established from obese patients with type 2 diabetes and matched obese healthy participants, who had been extensively metabolically characterised both in vivo and in vitro. We have previously reported reduced basal lipid oxidation and impaired insulin-stimulated glycogen synthesis and glucose oxidation in these diabetic myotubes.
Results: No single gene was differently expressed after correction for multiple testing, and no biological pathway was differently expressed using either method of global pathway analysis. In particular, we found no evidence for differential expression of genes involved in mitochondrial oxidative metabolism. Consistently, there was no difference in mRNA levels of genes known to mediate the transcriptional control of mitochondrial biogenesis (PPARGC1A and NRF1) or in mitochondrial mass between diabetic and control myotubes.
Conclusions/interpretation: These results support the hypothesis that impaired mitochondrial biogenesis is not a primary defect in the sequence of events leading to insulin resistance and type 2 diabetes.