T2D is associated with reduced pancreatic β-cell mass, in part, by increased apoptosis and identity loss as insulin-producing cells. Nutrient-sensor protein O-GlcNAc Transferase (Ogt) is a regulator of pancreas development and β-cell function. We hypothesized that Ogt also regulates postnatal β-cell identity maintenance, in part, by modulating the activity and localization of key β-cell transcription factors. We genetically ablated Ogt in endocrine progenitors in mice (Ngn3-cre;OgtKOEndo) . While phenotypically normal at birth, at postnatal (p) day 23, normoglycemic OgtKOEndo displayed aberrant islet architecture, along with a significant increase in Ins/Gcg-expressing bihormonal cells. Reduced levels of Pdx1 expression and increased incidence of cytoplasmic Pdx1 localization were observed in islets of OgtKOEndo mice compared to controls. All OgtKOEndo mice were diabetic by p60, with severe reductions in both α and β-cell mass. Next, we generated a β-cell Ogt-deficient mouse model (RIP-cre;OgtKOIns) . Like OgtKOEndo, OgtKOIns mice had increased incidence of bihormonal cells, with a trending increase in α-cell associated gene transcription. α-cell mass and β-cell mass were also reduced at p30 compared to controls. We hypothesized, mechanistically, that deletion of Ogt perturbed the activity of Pdx1, a transcription factor modified by Ogt and a key regulator of β-cell fate and insulin biogenesis. As expected, OgtKOIns islets display reduced Ins1/2 mRNA, total insulin content, and Pdx1 protein. Over-expression of Pdx1 in the OgtKO;PdxOEIns mice rescued islet insulin content, and O-GlcNAc modification of Pdx1 is positively correlated with insulin secretion. However, no rescue in β-cell mass was observed in OgtKO;PdxOEIns mice. Next, we will determine the role of the O-GlcNAc modification of Pdx1 in β-cell identity in vivo using the OgtKO;PdxOEIns mice and in vitro, using a proximity-directed nanobody technology to increase Pdx1 and Ogt interactions.
A.L.Wong: None. B.Akhaphong: None. A.D.Lockridge: None. E.Alejandro: None.
National Institutes of Health (DK115720)