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O-GlcNAc Transferase (Ogt) is a nutrient-sensing enzyme important in pancreas organogenesis and beta-cell function. We demonstrated that genetic ablation of Ogt in pancreatic progenitors in mice (OgtKOPanc) caused pancreas hypoplasia, with severe loss of endocrine and exocrine cell mass at birth. However, deletion of Ogt in endocrine progenitors (OgtKOEndo), later in development, led to normal development of beta-cell mass. On postnatal day (p) 23, a portion of OgtKOEndo mice developed hyperglycemia, and all exhibited insulin/glucagon+ bihormonal cells and were overtly diabetic by p60. These results suggest that while Ogt is not required for the formation of pancreatic islets, it is required for the maintenance of islet cell identity. Subsequently, we generated a beta-cell-specific Ogt-deficient mouse model (beta-OgtKO) to test the requirement of Ogt in beta-cell identity. Consistent with the OgtKOEndo, beta-OgtKO mice also displayed an increased incidence of bihormonal cells and a trend towards increased islet alpha-cell gene transcripts but exhibited no differences in beta-cell mass at birth or p30 compared to littermate controls. We hypothesized, mechanistically, that deletion of Ogt perturbed the activity of Pdx1, an Ogt target implicated in the maintenance of beta-cell identity. Indeed, Pdx1 is reduced in beta-OgtKO islets by Western Blot, and morphometric analyses of the islets showed aberrant Pdx1 localization in Ogt-deficient beta-cells. Moreover, studies in Min6 cells treated with Ogt inhibitor Osmi-1 showed a mild decrease in Pdx1 stability, as well as a significant decrease in mRNA transcripts of beta-cell maturity factors Pdx1, MafA, and Urocortin 3. Subsequently, we tested whether Pdx1 reconstitution in beta-OgtKO (beta-OgtKO; PdxTg) is sufficient to rescue beta-cell identity, function and, consequently, blood glucose and the onset of diabetes. Our data suggests that beta-OgtKO;PdxTg mice exhibit transiently improved glucose tolerance at 6 weeks of age. However, both beta-OgtKO and beta-OgtKO;PdxTg developed hyperglycemia at a similar age, suggesting that in addition to normalizing Pdx1 protein, the O-GlcNAcylation of Pdx1 may be essential. Using proximity-directed nanobodies in primary islets, we are testing whether specifically altering O-GlcNAcylation of Pdx1 protein in vitro is sufficient to rescue transcription of key beta-cell genes. Together, these data suggest that Ogt regulates beta-cell identity and function, in part, through Pdx1. This project was funded by the National Institutes of Health. Alicia Wong was supported by T32HL166142-01 and T32GM140936, and Dr. Emilyn Alejandro was supported by R01DK115720 and Regenerative Medicine Minnesota.
Wong et al. (Fri,) studied this question.