The O-GlcNAcylation And Skeletal Muscle Homoeostasis In Insulin Resistance

BackgroundO-Linkedβ-N-acetylglucosaminylation(O-GlcNAcylation),apost-translational modification,changes proteins function and stability through modifying nuclear,cytoplasmic and mitochondrial proteins on serine and threonine residues.O-GlcNAc transferase(OGT)and O-GlcNAcase(OGA)maintain the O-GlcNAcylation balance to keep organisms active.Skeletal muscle disorders mainly including regeneration disorder and glucose metabolism abnormality are accompanied by O-GlcNAcylation abnormality.As a organ with high energy consumption,skeletal muscle is tightly influenced by mitochondria which function as cellular energy station.The detailed mechanisms of O-GlcNAcylation on mitochondrial energy metabolism and skeletal muscle function remain unclear.Aims1.To study O-GlcNAcylation and mitochondrial function of skeletal muscle of C57BL/6J mice with high fat diet(HFD)and db/db mice with normal diet.2.To study effects of OGA on mitochondrial function of C2C12 myoblast and myotube.3.To study effects of OGA on C2C12 myoblast differetiation and insulin sensitivity of C2C12 myotube.Key resultsC57BL/6J mice were fed HFD for 4 months and db/db mice were fed the normal diet for 2months.Then skeletal muscle was used to observe mitochondrial content,activity,and O-GlcNAcylation.Both HFD feeding and db/db mice showed decreased OGA level and increased mitochondrial O-GlcNAcylation in skeletal muscle,accompanied by decreased peroxisome proliferator-activated receptor gamma coactivator 1-alpha(PGC-1α),mitochondrial content,as well as disrupted mitochondrial complex activities.OGA knockdown in C2C12 myoblasts promoted PGC-1αdegradation resulting in suppression of mitochondrial biogenesis and myogenesis,while either knockdown of OGT or overexpression of OGA had no significant effects on myogenesis.Mitochondrial dysfunction as evidenced by decreased ATP content,increased ROS content,increased lipid and protein oxidation was observed in both myoblast and myotube after OGA knockdown.Elevated O-GlcNAcylation through either OGA knockdown or treatment with OGA inhibitor PUGNAc and OGT substrate D-GlcNAc suppressed myotube insulin signaling transduction and glucose uptake.OGA overexpression had no significant effect on insulin sensitivity but sufficiently improved the insulin resistance induced by D-GlcNAc treatment.ConclusionsThese data suggest that OGA can modulate mitochondrial content via PGC-1αand mitochondrial O-GlcNAcylation.In this manner,OGA appears to play a key role in myogensis and insulin sensitity of skeletal muscle.