snRNA-Seq analysis of islets from WT mice treated with or without 0.5mM Glucosamine

In diabetes, hyperglycemia drives the progression of b-cell failure and multi-organ complications. Prolonged exposure to high glucose stimulates mTORC1, resulting in impaired glucose metabolism and exacerbation of ER stress and inflammation. However, the precise mechanism by which glucose regulates mTORC1 activity in diabetes remains unclear. We performed metabolic labeling with 13C6- glucose in diabetic animals treated with or without the SGLT2 inhibitor (SGLT2i) dapagliflozin or insulin, followed by targeted metabolomics and metabolic flux analysis. We found that tissue glucose concentrations strongly correlate with glucosamine, rather than with other glucose or amino acid metabolites. Plasma glucosamine levels are increased in patients with impaired fasting glucose (IFG) and type 2 diabetes (T2D) and are inversely correlated with b-cell function. Glucosamine is synthesized by amine group transfer from glutamine to glucose, which enhances O-GlcNAcylation (O-GlcN) of mTORC1- regulating proteins, including Raptor, via O-GlcNAc transferase (OGT), subsequently activating mTORC1. We propose that the glucosamine-mTORC1 pathway is a key mediator of glucose toxicity in diabetes. We studied the role of glucosamine in mediating beta-cell glucotoxicity.