O-GlcNAc is a sensor in the pancreatic beta cell
Durning, Sean Patrick
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O-linked β-N-acetylglucosamine (O-GlcNAc) is a ubiquitous post-translational protein modification found on serine and threonine amino acid residues of intracellular proteins. This inducible and dynamic PTM is mediated by two cycling enzymes, O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA) in response to environmental stimuli. The nucleotide-sugar donor UDP-GlcNAc is the end product of the hexosamine biosynthetic pathway (HBP) and is responsive to glucose levels entering the cell. Provided its proposed role as a cellular nutrient sensor, O-GlcNAc has been implicated in contributing to the progression of type II diabetes. However, the molecular role for this PTM in the glucose-responsive, insulin secreting pancreatic β cell remains unclear. In this dissertation, I set out to study the role of O-GlcNAc in regulating molecular events in the β cell, specifically at the levels of insulin secretion and transcription. Using directed pharmacological approaches in the mouse insulinoma-6 (Min6) cell line, I demonstrate that elevating nuclear O-GlcNAc preserves glucose stimulated insulin secretion during chronic hyperglycemia. This observed secretory effect directly correlates with O-GlcNAc-induced elevation in perinuclear insulin under basal and prolonged hyperglycemic conditions. The molecular mechanism for these observed changes appears to be, at least in part, due to elevated O-GlcNAc-dependent increases in Ins1 and Ins2 mRNA levels via elevations in histone H3 transcriptional activation marks. Further, whole transcriptome shotgun sequencing reveals that hyperglycemia altered gene transcription is restricted to a subset of genes and that the majority of genes regulated by inhibiting OGA levels are similarly regulated by a shift from euglycemic to hyperglycemic conditions. Thus, my work demonstrates a role for O-GlcNAc as a glucose sensor and modulator of gene transcription in pancreatic β cells.