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The Islet-1 Interaction Partner Rnf20 Regulates Glucose Homeostasis and Pancreatic β-cell Identity.

ABSTRACT: Diabetes is characterized by a loss of functional β-cell mass, thereby identifying factors involved in establishing and preserving β-cell identity and function is critical for future therapies aiming to combat rising diabetes incidence. While transcription factors are crucial β-cell regulators, knowledge of the interacting co-regulators facilitating gene expression is limited. Previously, we demonstrated that the Islet-1 (Isl1) transcription factor forms complexes with histone ubiquitin ligases Rnf20 and Rnf40 to regulate β-cell gene expression and insulin secretion in vitro. Here, we investigated whether Rnf20-mediated complexes are required for β-cell function in adult islets using an adult-inducible β-cell-enriched Rnf20 knockout mouse model, termed Rnf20Δβ-cell . Tamoxifen induction of Rnf20 recombination prompted a robust loss of histone 2B monoubiquitination (H2Bub1) in b-cells and imparted severe hyperglycemia and glucose intolerance, reduced plasma insulin levels following a glucose challenge, and an overall reduction in insulin content. Expression of mRNAs and proteins involved in glucose stimulated insulin secretion (GSIS) and β-cell identity were also dysregulated in Rnf20Δβ-cell mice. Furthermore, comparative loss of either Rnf20 or Isl1 yielded a similar differential expression of numerous b-cell factors, supporting that Isl1::Rnf20 complexes and histone H2B mono-ubiquitination are critical regulators of cellular identity and function.

ORGANISM(S): Mus musculus

PROVIDER: GSE281063 | GEO | 2025/08/04

REPOSITORIES: GEO

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Project description:Objective: Transcriptional complex activity drives the development and function of pancreatic islet cells to allow for proper glucose regulation. Our prior work highlighted that the LIM-homeodomain transcription factor (TF), Islet-1 (Isl1), and its interacting co-regulator, Ldb1, are vital effectors of developing and adult β-cells. We further found that a member of the Single Stranded DNA-Binding Protein (SSBP) co-regulator family, SSBP3, interacts with Isl1 and Ldb1 in β-cells and primary islets (mouse and human) to impact β-cell target genes MafA and Glp1R. Members of the SSBP family stabilize TF complexes by binding directly to Ldb1 and protecting the complex from ubiquitin-mediated turnover. In this study, we hypothesized that SSBP3 would have critical roles in pancreatic islet cell development and function in vivo, similar to the Isl1::Ldb1 complex. Methods: We first generated a novel SSBP3 LoxP allele mouse line, where Cre-mediated recombination imparts a predicted early protein termination. We bred this mouse to constitutive Cre lines (Pdx1- and Pax6-driven) to recombine of SSBP3 in the developing pancreas and islet (SSBP3DeltaPanc and SSBP3DeltaIslet), respectively. We assessed glucose tolerance and used immunofluorescence to detect changes in islet cell abundance and markers of β-cell identity and function. Using an inducible Cre system we also deleted SSBP3 in the adult β-cell, a model termed SSBP3Deltaβ-cell. We measured glucose tolerance as well as glucose-stimulated insulin secretion (GSIS), both in vivo and in isolated islets in vitro. Using islets from control and SSBP3Deltaβ-cell we conducted RNA-Seq and compared our results to published datasets for similar β-cell specific Ldb1 and Isl1 knockouts to identify commonly regulated target genes. Results: SSBP3DeltaPanc and SSBP3DeltaIslet neonates present with hyperglycemia. SSBP3DeltaIslet mice are glucose intolerant by P21 and exhibit a reduction of β-cell maturity markers MafA, Pdx1, and UCN3. We observe disruptions in islet cell architecture with an increase in glucagon+ α-cells and ghrelin+ ε-cells at P10. Inducible loss of β-cell SSBP3 in SSBP3Deltaβ-cell causes hyperglycemia, glucose intolerance, and reduced GSIS. Transcriptomic analysis of 14-week SSBP3Deltaβ-cell islets revealed a decrease in β-cell function gene expression (Ins, MafA, Ucn3), increased stress and dedifferentiation markers (Neurogenin-3, Aldh1a3, Gastrin), and shared differentially expressed genes between SSBP3, Ldb1, and Isl1 in adult β-cells. Conclusions: SSBP3 drives proper islet development and identity, where its loss causes altered islet-cell abundance and glucose regulatory function. β-cell SSBP3 is required for GSIS and glucose homeostasis, at least partially through shared regulation of Ldb1 and Isl1 target genes.

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The Islet-1 Interaction Partner Rnf20 Regulates Glucose Homeostasis and Pancreatic β-cell Identity.

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