Decreasing O ‐GlcNAc Levels Reverses Diabetic Nephropathy‐Associated Phenotypes

Diabetic nephropathy (DN) is a leading cause of morbidity and mortality in diabetic patients. DN is characterized by structural changes of the glomeruli in the kidney, such as mesangial cell expansion, podocyte foot process effacement, and apoptosis, with accompanying glomerular hyperfiltration. Hyperglycemia has been shown to initiate these glomeruli structural changes by stimulating flux through the hexosamine biosynthetic pathway (HBP). The major endpoint of the HBP is the formation of uridine diphosphate β‐D‐ N ‐acetylglucosamine (UDP‐GlcNAc), the donor for protein O ‐GlcNAcylation, and complex extracellular glycosylation. O ‐GlcNAcylation is a dynamic nutrient sensitive post‐translational modification that is characterized by the addition of single β‐D‐ N ‐acetylglucosamine ( O ‐GlcNAc) to the serine and/or threonine residues of almost every functional class of protein. O ‐GlcNAc serves as a nutrient/stress sensor regulating signaling, transcription, cytoskeletal dynamics, and cell division. Altered O‐ GlcNAc signaling is directly involved in the pathogenesis of diabetes and may have a role in diabetic complications. However, the molecular mechanisms of how hyperglycemia leads to glomerular dysfunction are largely unknown. Here we report that a dynamic sugar‐protein modification, O ‐GlcNAcylation, which serves as a nutrient sensor, links hyperglycemia to defects in glomerular structure and function. By targeting the enzymes that either add or remove O ‐GlcNAc (OGT and OGA, respectively), we show that O ‐GlcNAcylation regulates mesangial ECM production. Increasing O ‐GlcNAc distorts gene expression, protein expression, and subcellular distribution of key slit diaphragm specific proteins, whereas decreasing O ‐GlcNAcylation, even in hyperglycemic conditions, restore podocytes to normal. Electron microscopy of the slit diaphragm reveals that decreasing O ‐GlcNAc rescues the DN‐associated phenotype. This study provides evidence that O‐GlcNAc plays a role in glomerular structure and function and may contribute to the molecular etiology of DN‐associated phenotypes. Support or Funding Information This work is supported by NIH grants F32DK100199 to S. Peterson and R01DK61671, P01HL107153, and N01‐HV‐00240 to G. Hart.