Abstract
The nutrient sensor O-GlcNAc transferase (OGT) catalyzes posttranslational addition of O-GlcNAc onto target proteins, influencing signaling pathways in response to cellular nutrient levels. OGT is highly expressed in pancreatic glucagon-secreting cells (α-cells), which secrete glucagon in response to hypoglycemia. The objective of this study was to determine whether OGT is necessary for the regulation of α-cell mass and function in vivo. We utilized genetic manipulation to produce two α-cell specific OGT-knockout models: a constitutive glucagon-Cre (αOGT(KO)) and an inducible glucagon-Cre (i-αOGT(KO)), which effectively delete OGT in α-cells. Using approaches including immunoblotting, immunofluorescent imaging, and metabolic phenotyping in vivo, we provide the first insight on the role of O-GlcNAcylation in α-cell mass and function. αOGT(KO) mice demonstrated normal glucose tolerance and insulin sensitivity but displayed significantly lower glucagon levels during both fed and fasted states. αOGT(KO) mice exhibited significantly lower α-cell glucagon content and α-cell mass at 6 months of age. In fasting, αOGT(KO) mice showed impaired pyruvate stimulated gluconeogenesis in vivo and reduced glucagon secretion in vitro. i-αOGT(KO) mice showed similarly reduced blood glucagon levels, defective in vitro glucagon secretion, and normal α-cell mass. Interestingly, both αOGT(KO) and i-αOGT(KO) mice had no deficiency in maintaining blood glucose homeostasis under fed or fasting conditions, despite impairment in α-cell mass and function, and glucagon content. In conclusion, these studies provide a first look at the role of OGT signaling in the α-cell, its effect on α-cell mass, and its importance in regulating glucagon secretion in hypoglycemic conditions.