O-GlcNAcase deficiency suppresses skeletal myogenesis and insulin sensitivity in mice through the modulation of mitochondrial homeostasis

Abstract

Aims/hypothesis O-GlcNAcylation is implicated in modulating mitochondrial function, which is closely involved in regulating muscle metabolism. The presence of O-GlcNAcase (OGA), the enzyme involved in the removal of O-GlcNAc, in mitochondria was recently confirmed in rats. In the present study, we investigated the regulation of myogenesis and muscle insulin sensitivity to OGA in mice, with a focus on mitochondria. Methods C57BL/6J mice fed a high-fat diet for 4 months were used to observe mitochondrial density, activity and O-GlcNAcylation in muscle. Small interfering RNA and overexpression vectors were used to modulate protein content in vitro. Results High-fat feeding decreased the OGA level and largely increased mitochondrial O-GlcNAcylation in mouse skeletal muscle that was accompanied by decreased levels of peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α), decreased mitochondrial density and disrupted mitochondrial complex activities. Knockdown of OGA in C2C12 myoblasts promoted PGC-1α degradation, resulting in the suppression of mitochondrial biogenesis and myogenesis, whereas neither knockdown of O-GlcNAc transferase nor overexpression of OGA had significant effects on myogenesis. Mitochondrial dysfunction as evidenced by decreased ATP content and increased reactive oxygen species production, and increased lipid and protein oxidation was observed in both myoblasts and myotubes after OGA knockdown. Meanwhile, elevated O-GlcNAcylation through either OGA knockdown or treatment with the OGA inhibitor PUGNAc and the O-GlcNAc transferase substrate D-GlcNAc suppressed myotube insulin signalling transduction and glucose uptake. OGA overexpression had no significant effect on insulin sensitivity but sufficiently improved the insulin resistance induced by D-GlcNAc treatment. Conclusions/interpretation These data suggest that OGA can modulate mitochondrial density via PGC-1α and mitochondrial function via protein O-GlcNAcylation. In this manner, OGA appears to play a key role in myogenesis and the development of muscle insulin resistance.

Obese subcutaneous adipose tissue impairs human myogenesis, particularly in old skeletal muscle, via resistin-mediated activation of NFκB

“…Myogenic differentiation is associated with mitochondrial biogenesis and an increased reliance on oxidative phosphorylation 34 , 39 . Furthermore, alterations in myogenic differentiation capacity and mitochondrial function often coexist 40 – 42 . Therefore, a Seahorse® XF Mito Stress Test was conducted on myotubes that had been differentiated for 8 d with or without the presence of 5 ng/mL recombinant resistin (Fig.…”

“…Furthermore, an increase in lipid content in type I fibres appears to be a feature of sedentary, but not physically active ageing 63 . The effect of IMCL accumulation on skeletal myogenesis is less well established, but O-GlcNAcylation, a post-translational modification that is associated with obesity and diabetes, has a detrimental effect on C2C12 myogenesis 40 . Given these findings, the functional effects of resistin on muscle metabolism we report here may have important implications.…”

O-GlcNAcylation and cardiovascular disease

“…Further studies using comparative O-GlcNAc profiling of mitochondria from control and diabetic rat hearts identified many proteins that had site-specific alterations in O-GlcNAcylation in response to diabetes [60]. These recent insights into O-GlcNAcylation of mitochondrial proteins have provided a better understanding of the mechanisms by which elevated O-GlcNAc levels contribute to the adverse effects of diabetes, but will also usher in new insights into the cardioprotective mechanisms associated with acute increases in O-GlcNAcylation [61]. …”

“…On the other hand, as we begin to understand more about the cellular functions regulated by protein O-GlcNAcylation it is increasingly clear that a more accurate concept would be that O-GlcNAc modification of cardiovascular proteins is a dynamic process that is critical in maintaining normal cardiomyocyte function. This is reinforced by the observations that O-GlcNAcylation of proteins plays a role in regulating fundamental cellular processes ranging from transcription to metabolism; there is also emerging evidence to suggest that protein O-GlcNAcylation also contributes to regulation of autophagy, epigenetics, and mitochondrial biogenesis [4, 51, 61]. Consequently, the context in which O-GlcNAc levels are changed are as specific as the stimuli, cell type or disease state with regard to its effect on cell function.…”

Diverse metabolic effects of O-GlcNAcylation in the pancreas but limited effects in insulin-sensitive organs in mice

“…These observations indicate a potential role for O-GlcNAcylation in glucose metabolism in mammals. Indeed, previous studies in cultured cells have demonstrated that O-GlcNAcylation is involved in glucose metabolism in the liver [11], skeletal muscle [12] and adipose tissues [13], and accelerates insulin secretion in pancreatic beta cells [14]. However, little is known about the physiological roles of this posttranslational modification in glucose metabolism in vivo because congenital Ogt-knockout (KO) mice are embryonic lethal [15].…”