Abstract 2117 Crosstalk between nutrient sensor proteins, O-GlcNAc Transferase and mTORC1, is key to regulation of pancreatic β-cell mass and function

Type 2 diabetes (T2D) is characterized by the failure of β-cells to adequately secrete insulin, in response to nutrient, to tightly regulate blood glucose level. Nutrient sensor, mechanistic target of rapamycin complex 1 (mTORC1) plays a pivotal role in balancing cell growth and degradative processes (autophagy) to sustain β-cell health and function. Alterations in mTORC1 activity and autophagy are associated with T2D and β-cell failure, yet the underlying mechanisms driving these relationships remain unclear. Out recent work underscores the significance of the nutrient sensor O-GlcNAc Transferase (OGT) as a critical regulator of β-cell health. The deletion of β-cell OGT (βOGTKO) leads to diabetes in mice, resulting from severe β-cell mass loss and insulin secretion deficits. In response to fluctuations in nutrient levels, OGT glycosylates key target cytosolic, nuclear, and mitochondrial proteins, impacting various cellular processes. We hypothesize that under nutrient stress, OGT directly modulates the mTORC1 pathway and, consequently, autophagy-dependent β-cell function. βOGTKO islets exhibit reduced mTORC1 activity and increased autophagy. Initially, we investigated whether mTORC1-driven autophagy affects OGT-dependent β-cell function by deleting Unc-51-like autophagy activating kinase 1 (ULK1; an autophagy initiator downstream of mTORC1) in βOGTKO mice. Supporting our hypothesis, βULK1/OGTKO mice displayed partial improvement of glucose tolerance with attenuated hyperglycemia compared to βOGTKO mice, primarily through enhanced β-cell function, without affecting mass. To comprehensively understand the signaling crosstalk between OGT and mTORC1 pathways, we generated a mouse model with increased mTORC1 activity by deleting tuberous sclerosis complex 2 (TSC2; an mTORC1 inhibitor) in βOGTKO mice. The βTSC2/OGTKO mice exhibited delayed development of hyperglycemia compared to βOGTKO mice. Although normalization of blood glucose was associated with a complete rescue of the β-cell mass deficit, no improvements in secretory function were observed, indicating non-overlapping biological processes that are governed by OGT and mTORC1. Mechanistically, a phospho-protein antibody array on islets from these mouse models revealed divergent and differentially regulated MAPK and calmodulin signaling by OGT and mTORC1. In summary, our data unveil a previously unknown and crucial role of OGT as a master nutrient sensor influencing downstream mTORC1 and autophagy, modulating β-cell mass and function. Work supported by 5F31DK131860 (to SJ) and 5R56DK136293, 1R01DK136237, 5R01DK115720 (to EUA).