Identification of O-linked N-acetylglucosamine proteins in rat skeletal muscle using two-dimensional gel electrophoresis and mass spectrometry.

O-linked N-acetylglucosaminylation (O-GlcNAc) is a regulatory post-translational modification of nucleo-cytoplasmic proteins that has a complex interplay with phosphorylation. O-GlcNAc has been described as a nutritional sensor, the level of UDP-GlcNAc that serves as a donor for the uridine diphospho-N-acetylglucosamine:polypeptide beta-N-acetyl-glucosaminyltransferase being regulated by the cellular fate of glucose. Because muscular contraction is both dependent on glucose metabolism and is highly regulated by phosphorylation/dephosphorylation processes, we decided to investigate the identification of O-GlcNAc-modified proteins in skeletal muscle using a proteomic approach. Fourteen proteins were identified as being O-GlcNAc modified. These proteins can be classified in three main classes: i) proteins implicated in the signal transduction and in the translocation between the cytoplasm and the nucleus or structural proteins, ii) proteins of the glycolytic pathway and energetic metabolism, and iii) contractile proteins (myosin heavy chain). A decrease in the O-GlcNAc level was measured in the slow postural soleus muscle after 14-day hindlimb unloading, a model of functional atrophy characterized by a decrease in the force of contraction. These results strongly suggest that O-GlcNAc modification may serve as an important regulation system in skeletal muscle physiology.