ObjectiveGiven that cellular O-GlcNAcylation levels are thought to be real-time measures of cellular nutrient status and dysregulated O-GlcNAc signaling is associated with insulin resistance, we evaluated the role of O-GlcNAc transferase (OGT), the enzyme that mediates O-GlcNAcylation, in skeletal muscle.MethodsWe assessed O-GlcNAcylation levels in skeletal muscle from obese, type 2 diabetic people, and we characterized muscle-specific OGT knockout (mKO) mice in metabolic cages and measured energy expenditure and substrate utilization pattern using indirect calorimetry. Whole body insulin sensitivity was assessed using the hyperinsulinemic euglycemic clamp technique and tissue-specific glucose uptake was subsequently evaluated. Tissues were used for histology, qPCR, Western blot, co-immunoprecipitation, and chromatin immunoprecipitation analyses.ResultsWe found elevated levels of O-GlcNAc-modified proteins in obese, type 2 diabetic people compared with well-matched obese and lean controls. Muscle-specific OGT knockout mice were lean, and whole body energy expenditure and insulin sensitivity were increased in these mice, consistent with enhanced glucose uptake and elevated glycolytic enzyme activities in skeletal muscle. Moreover, enhanced glucose uptake was also observed in white adipose tissue that was browner than that of WT mice. Interestingly, mKO mice had elevated mRNA levels of Il15 in skeletal muscle and increased circulating IL-15 levels. We found that OGT in muscle mediates transcriptional repression of Il15 by O-GlcNAcylating Enhancer of Zeste Homolog 2 (EZH2).ConclusionsElevated muscle O-GlcNAc levels paralleled insulin resistance and type 2 diabetes in humans. Moreover, OGT-mediated signaling is necessary for proper skeletal muscle metabolism and whole-body energy homeostasis, and our data highlight O-GlcNAcylation as a potential target for ameliorating metabolic disorders.

O‐GlcNAcylation is the addition and removal of UDP‐GlcNAc to proteins by O‐GlcNAc transferase (OGT) and O‐GlcNAcase (OGA), respectively. This process functions as a nutrient sensing pathway because UDP‐GlcNAc, synthesized in the hexosamine biosynthetic pathway, fluctuates with nutrient levels available to the cell. Although previous studies have established the critical role of OGT in metabolism in a variety of cell types, the role of OGT in satellite cells (SCs) remains unknown. In this study, we generated SC‐specific OGT knock‐out (cKO) mice to investigate the functional role of OGT in SC homeostasis. Initially we subjected WT and cKO muscle to cardiotoxin‐induced injury to assess SC regenerative capacity during muscle regeneration. Compared to WT mice, the cKO mice experienced severely impaired regenerative myogenesis. To investigate whether OGT deficiency induced lack of regeneration was caused by changes in SC intrinsic properties, we traced SCs cycling and self‐renewal in vivo by monitoring the turnover rate of green fluorescent protein (GFP) intensity using a H2B‐GFP lineage tracing strategy. Flow cytometry analysis of the GFP labeling revealed that cKO SCs possessed a higher percentage of GFP‐retained subpopulation than WT SCs after a 10‐week chase period, indicating that SCs lacking OGT had impaired self‐renewal. We then assessed SC proliferative capacity in vitro using clone assay and observed SCs from cKO mice had significantly reduced clone size compared to their WT counterparts. Morphologically, cKO SCs exhibited larger cell size and increased complexity compared to WT SCs, suggesting the lack of proliferation may be caused by the impairment of SC's ability to divide. Taken together, our findings suggest that OGT, and thus O‐GlcNAc signaling, plays a critical role in SC self‐renewal, proliferation, and tissue repair through mediating nutrient sensitive cell division.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.