RF04 | PSUN133 Assessment of the Rnf20 Histone Modifier in Regulating Pancreatic Beta-Cell Identity and Function

Abstract

Abstract Type 1 and Type 2 Diabetes are characterized by a loss of functional pancreatic islet β-cells. With the prevalence of diabetes increasing worldwide, a complete understanding of the gene regulatory mechanisms governing the development and function of insulin-producing β-cells is requisite for improving diabetes therapies. Islet 1 (Isl1) is a LIM-homeodomain class transcription factor (TF) required for the maturation, proliferation, function, and survival of islet cells. In our previous study, we identified Isl1 interactions with the ring finger ubiquitin ligases Ring Finger 20 (Rnf20) and Rnf40 in mouse β-cell extracts, mouse islets, and human islets. Rnf20 and Rnf40, exist as homodimeric or heterodimeric complexes to deposit a mono-ubiquitin epigenetic mark on histone (H)2B (i.e., H2Bub1) and regulate gene transcription as a precursor to active H3K4 trimethylation (H3K4me3) and H3K79 methylation (H3K79me) marks. We demonstrated that Rnf20 and Rnf40 are required for the expression of several important β-cell genes and glucose-stimulated insulin secretion in vitro. Specifically, loss of Rnf20and Rnf40 in MIN6 β-cells resulted in a significant dysregulation of β-cell Slc2a2/Glut2 and MafA expression, target genes which were occupied by Rnf20 and H2Bub1. Additionally, using proximity ligation assay (PLA) in MIN6 β-cells, we demonstrated a robust increase in interactions between Isl1 and Rnf20 under high glucose conditions. Based on this, we hypothesize that Rnf20 and/or Rnf40 are required to establish and maintain β-cell identity in adult islets. To begin addressing this, we disrupted Rnf20/Rnf20 and/or Rnf20/Rnf40 complexes in β-cells via generation of adult inducible Rnf20 β-cell-specific knockout mice. In the adult inducible model, 2 weeks following tamoxifen induction (i.e., by 8 weeks of age) both male and female mice became hyperglycemic and severely glucose intolerant. These 8-week-old Rnf20-deficient mice also had reduced plasma insulin following a glucose challenge yet normal insulin sensitivity. Islet RNA exhibited dysregulated mRNAs encoding islet hormones, glucose-stimulated insulin secretion markers, and β-cell identity markers, including Slc2a2/Glut2, Ucn3, and Hb9 . Our findings of similar phenotypes between Isl1 and Rnf20 adult knockout models, a glucose sensitive interaction between Isl1 and Rnf20, and their occupancy of the Slc2a2/Glut2 locus support mechanisms of Isl1-Rnf driven β-cell regulation. Presentation: Saturday, June 11, 2022 1:12 p.m. - 1:17 p.m., Sunday, June 12, 2022 12:30 p.m. - 2:30 p.m.