| First Author | Toren E | Year | 2023 |
| Journal | Mol Metab | Volume | 76 |
| Pages | 101785 | PubMed ID | 37536498 |
| Mgi Jnum | J:339475 | Mgi Id | MGI:7521340 |
| Doi | 10.1016/j.molmet.2023.101785 | Citation | Toren E, et al. (2023) The SSBP3 co-regulator is required for glucose homeostasis, pancreatic islet architecture, and beta-cell identity. Mol Metab 76:101785 |
| abstractText | OBJECTIVE: Transcriptional complex activity drives the development and function of pancreatic islet cells to allow for proper glucose regulation. Prior studies from our lab and others highlighted that the LIM-homeodomain transcription factor (TF), Islet-1 (Isl1), and its interacting co-regulator, Ldb1, are vital effectors of developing and adult beta-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 beta-cells and primary islets (mouse and human) to impact beta-cell target genes MafA and Glp1R in vitro. 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 has critical roles in pancreatic islet cell function in vivo, similar to the Isl1::Ldb1 complex. METHODS: We first developed a novel SSBP3 LoxP allele mouse line, where Cre-mediated recombination imparts a predicted early protein termination. We bred this mouse with constitutive Cre lines (Pdx1- and Pax6-driven) to recombine SSBP3 in the developing pancreas and islet (SSBP3(DeltaPanc) and SSBP3(DeltaIslet)), respectively. We assessed glucose tolerance and used immunofluorescence to detect changes in islet cell abundance and markers of beta-cell identity and function. Using an inducible Cre system, we also deleted SSBP3 in the adult beta-cell, a model termed SSBP3(Deltabeta-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 SSBP3(Deltabeta-cell) we conducted RNA-Seq and compared our results to published datasets for similar beta-cell specific Ldb1 and Isl1 knockouts to identify commonly regulated target genes. RESULTS: SSBP3(DeltaPanc) and SSBP3(DeltaIslet) neonates present with hyperglycemia. SSBP3(DeltaIslet) mice are glucose intolerant by P21 and exhibit a reduction of beta-cell maturity markers MafA, Pdx1, and UCN3. We observe disruptions in islet cell architecture with an increase in glucagon(+) alpha-cells and ghrelin(+) epsilon-cells at P10. Inducible loss of beta-cell SSBP3 in SSBP3(Deltabeta-cell) causes hyperglycemia, glucose intolerance, and reduced GSIS. Transcriptomic analysis of 14-week-old SSBP3(Deltabeta-cell) islets revealed a decrease in beta-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 beta-cells. CONCLUSIONS: SSBP3 drives proper islet identity and function, where its loss causes altered islet-cell abundance and glucose homeostasis. beta-Cell SSBP3 is required for GSIS and glucose homeostasis, at least partially through shared regulation of Ldb1 and Isl1 target genes. |
