Data suggest that both pancreatic and intestinally produced glucagon-like peptide-1 (GLP-1) increases in response to inflammation. Here, we set out to determine the tissue-specific function of increased GLP-1 during inflammatory stimuli. Using our innovative mouse model of tissue-specific Gcg (the gene that encodes GLP-1) expression, we explored the function of GLP-1 under severe inflammatory conditions induced by lipopolysaccharide (LPS) administration in lean and obese mice. High-fat diet (HFD) increased the LPS-induced suppression of feeding and increased the plasma levels of pro-inflammatory cytokines and GLP-1. Both pancreatic and intestinal Gcg expression contribute to LPS-induced increases in GLP-1, but Gcg was not necessary for the glucoregulatory or suppressed feeding responses to LPS. While Gcg was not necessary for systemic cytokine increases with LPS in either chow- or HFD-fed mice, whole-body Gcg-null animals had increased macrophage accumulation and an increased expression of genes reflecting pro-inflammatory signaling in the pancreas. We then performed flow cytometry on the pancreas from mice expressing a fluorescent marker on the GLP-1 receptor (GLP-1R). In response to LPS, we found that pancreatic CD64+/CD11b+ macrophages expressed the GLP-1R. We conclude that under severe inflammatory conditions, pancreatic production of GLP-1 functions in an immunological rather than a metabolic role to directly regulate local macrophage accumulation.

OBJECTIVES:After bariatric surgery, many individuals experience debilitating bouts of hypoglycemia, termed post-bariatric hypoglycemia (PBH). Our mouse model of vertical sleeve gastrectomy (VSG) mimics key aspects of PBH in humans. As glucagon is a key element of the counterregulatory hormonal response to hypoglycemia, the objective of this manuscript is to understand if glucagon responses and sensitivity are altered after VSG in mice. METHODS:Mice underwent sham or VSG surgery. We measured glucagon responses to insulin-induced hypoglycemia and mixed meal tolerance tests. We then measured glucose and insulin responses to different doses of exogenous glucagon in fed and fasted states. Lastly, we performed in vitro experiments to examine glucagon responses to glucose and amino acids. RESULTS:Postprandial glucagon levels were elevated in mice after VSG, but glucose responses to low doses of exogenous glucagon were blunted in the fasted and postprandial state. Administration of low dose glucagon in the fed state led to hypoglycemia in some VSG mice in parallel with stimulation of insulin release. This effect was partially prevented by pretreatment with the GLP-1 receptor antagonist exendin9-39. In islets isolated from VSG mice, glucagon release in response to high glucose was suppressed, but glucagon responses to alanine and high glucose were not different compared to sham controls. CONCLUSIONS:Altogether, our data suggest both glucagon responses, and sensitivity to exogenous glucagon are altered by VSG. The glucagon dysregulation was not observed in isolated islets suggesting gut signaling may be critical in driving glucagon responses after VSG.

Thyroid hormone (TH) is essential for cardiovascular function, and women are disproportionately affected by TH disorders and experience worse outcomes following myocardial infarction (MI). However, the role of sex-specific TH regulation in post-MI cardiac recovery remains poorly understood. We investigated TH homeostasis and type 3 deiodinase (D3) activity, an enzyme that inactivates TH, in male and female C57BL/6 mice following MI. Using cardiomyocyte-specific D3-deficient (Dio3ΔHeart) mice, we investigated how impaired TH inactivation influences cardiac function and mitochondrial respiration. We also examined DIO3 messenger RNA expression, which encodes the D3 enzyme, in left ventricular (LV) tissue from human donors with nonfailing (NF) hearts or ischemic cardiomyopathy (ICM). Four weeks post MI, wild-type female mice exhibited sustained cardiac D3 activity, which effectively limited 3,5,3′-triiodothyronine (T3) levels in the LV. In contrast, Dio3ΔHeart females, lacking cardiomyocyte D3, showed impaired systolic recovery, elevated LV thyroxine and T3 levels, and reduced fatty acid–supported mitochondrial respiration, effects not observed in Dio3ΔHeart males. Similarly, DIO3 expression was selectively upregulated in LV tissue from women with ICM, but not in men. These findings identify DIO3 as a key protective mechanism in females that limits T3-induced metabolic stress and preserves mitochondrial function after MI, revealing a sex-dependent pathway with therapeutic relevance for cardiac recovery.

Diabetes is characterized by a loss of functional β-cell mass, therefore identifying factors involved in establishing and preserving β-cells is critical to combat rising diabetes incidence. While transcription factors are crucial β-cell regulators, knowledge of co-regulators facilitating gene expression is limited. Previously, we demonstrated that the Islet-1 transcription factor forms complexes with ubiquitin ligases Rnf20 and Rnf40 to regulate β-cells in vitro. Here, we investigate whether Rnf20-mediated complexes are required for β-cell function in adult islets by characterizing a novel β-cell-enriched Rnf20 knockout mouse model. Tamoxifen induction of Rnf20 recombination prompts a robust loss of histone 2B monoubiquitination (H2Bub1), imparts severe hyperglycemia, glucose intolerance, and elicits an overall reduction in insulin content. Expression of mRNAs and proteins involved in glucose stimulated insulin secretion and β-cell identity are also dysregulated in Rnf20Δβ-cell mice. Comparative analyses of the loss of either Rnf20 or Isl1 yields similar changes in the β-cell regulome, supporting that Isl1::Rnf20 complexes are critical regulators of β-cell identity and function. Isl1::Rnf20 complexes are maintained in human tissues wherein they regulate insulin expression, secretion, and content. These findings increase our understanding of key players in β-cell maintenance, which is crucial for the advancement of β-cell derivation diabetes therapeutics.

OBJECTIVE:Chemical and mechanical signals from the gastrointestinal tract are critical for regulating satiety and glucose metabolism. While both nutrient sensing in the intestine and gastric distension has been well studied, the role of intestinal stretch in these metabolic processes remain unclear. This study evaluates the role of intestinal stretch in regulating food intake and glucose homeostasis in the context of normal body weight, obesity, and weight loss occurring via both dietary intervention and vertical sleeve gastrectomy (VSG). METHODS:We used the nonnutritive substance mannitol to selectively induce intestinal stretch in conscious mice. We assessed food intake, glucose tolerance, and neuronal activation in mice with normal body weight, obesity, or after dietary or surgically-induced weight loss. We employed chemogenetic approaches to inhibit GLP-1R and OxtR-expressing vagal afferents, and genetic and pharmacological strategies to ablate GLP-1 signaling to explore mechanisms for mannitol-induced suppression of feeding. RESULTS:Mannitol-induced intestinal stretch acutely suppressed food intake and improved oral glucose tolerance independent of GLP-1 signaling and vagal intestinal mechanosensation. Diet induced obesity impairs mannitol-induced intestinal stretch reductions in food intake and attenuates neuronal activation in the nucleus of the solitary tract (NTS) upon induction of intestinal stretch. Both dietary and surgical weight loss restored intestinal stretch-induced feeding suppression and enhanced NTS neuronal activation. Importantly, VSG heightened NTS neuronal activation in response to oral but not IP glucose. CONCLUSIONS:Together, these data demonstrate that intestinal stretch contributes to the regulation of feeding and glucose metabolism independently of intestinal nutrient-sensing or classical gut hormones.

The gut plays a key role in regulating metabolic health. Dietary factors disrupt intestinal physiology and contribute to obesity and diabetes, whereas bariatric procedures such as vertical sleeve gastrectomy (VSG) cause gut adaptations that induce robust metabolic improvements. However, our understanding of these adaptations at the cellular and molecular levels remains limited. In a validated murine model, we leverage single-cell transcriptomics to determine how VSG impacts different cell lineages of the small intestinal epithelium. We define cell typespecific genes and pathways that VSG rescues from high-fat diet perturbation and characterize additional rescue-independent changes brought about by VSG. We show that Paneth cells have increased expression of the gut peptide Reg3g after VSG. We also find that VSG restores pathways pertaining to mitochondrial respiration and cellular metabolism, especially within cryptbased cells. Overall, our study provides unprecedented molecular resolution of VSG’s therapeutic effects on the gut epithelium.

Abstract Disclosure: T.H. Pierre: None. Y. Liu: None. M.M. Bethea: None. K. Coutinho: None. C. Hunter: None. Diabetes is characterized by the loss of pancreatic β-cell mass. As diabetes incidence continues to elevate, it is critical that we develop a better understanding of the factors that define functional β-cells in order to improve current therapeutics. One approach is through the study of transcription factors (TFs), which are essential for β-cell development and function. Prior work from our lab and others has examined Islet-1 (Isl1) a LIM-homeodomain TF that is required for the maturation of the endocrine pancreas and adult β-cell function. We have also extensively characterized several Isl1-interacting co-regulators (e.g., Ldb1 and SSBP3) that facilitate its roles in maintaining glucose homeostasis. Most recently, we have identified that Isl1 interacts with the ubiquitin ligases Ring Finger 20 (Rnf20) and Rnf40, whose histone H2B monoubiquitation (H2Bub1) activity support the gene regulatory functions of Isl1. With in vitro experiments, we demonstrated that Rnf20 and Rnf40 are important for glucose stimulated insulin secretion (GSIS) and mediate the expression of β-cell identity genes. Based on these findings, we hypothesize that Isl1-Rnf complexes modify histones to regulate β-cell gene expression and function. To address this hypothesis in vivo, we developed an adult inducible β-cell knockout of Rnf20 (Rnf20Δβ-cell). Rnf20Δβ-cell mice display fasting hyperglycemia and severe glucose intolerance that is driven by impaired GSIS, reduced insulin content, and the dysregulation of critical β-cell genes including Ins1, Ucn3, and Slc2a2. Additionally, loss of Rnf20 perturbs insulin processing and overall β-cell maturation as observed by measurement of proinsulin:insulin ratios, C-peptide levels, and whole islet RNA-seq. Phenotypes exhibited by Rnf20Δβ-cell mice are similar to those observed in Isl1 β-cell knockout mice, and comparative transcriptomics revealed an overlap of 570 genes involved in metabolism, zinc homeostasis, and islet proliferation including Slc30a8 and Matn2, both of which we found are occupied by Isl1 and Rnf20. Collectively, our findings demonstrate the importance of the Rnf20 histone modifier in regulating β-cell function and expand our understanding of the Isl1 regulatory network. Presentation: 6/2/2024

Abstract Disclosure: M.M. Bethea: None. S. da Silva Teixeira: None. T.M. Cook: None. M. Mommandi: None. G. Nault: None. D. Sandoval: None. Obesity is a global pandemic characterized by excessive fat storage due to an imbalance in energy homeostasis. This metabolic imbalance is driven by increased energy intake relative to energy expenditure. The gut vagal afferent neurons play a critical role in energy homeostasis by sensing the various chemo- and mechano-signals resulting from ingested nutrients and initiating changes in feeding behavior. However, these neurons fail to respond adequately in the context of diet-induced obesity, leading to overeating and ultimately obesity. Bariatric surgeries, which modify the anatomy of the gut, are currently the most effective but also the most invasive treatments for obesity. The mechanism(s) by which bariatric surgery modulates metabolic processes is still not fully understood. The vertical sleeve gastrectomy (VSG) procedure, a bariatric surgery where 80% of the stomach is removed, alters feeding patterns and induces sustained weight loss. Our findings demonstrate that VSG induces alterations in the signals in the gut-brain-axis, resulting in increased activation of the nucleus of the solitary tract (NTS) - a brain region critical for integrating peripheral signals and regulating food intake. Importantly, emerging data demonstrate that neurons that sense intestinal distension play a critical role in the regulation of feeding. We hypothesized that diet induced obesity attenuates intestinal-stretch inhibition of food intake and that VSG restores it. Using non-nutritive substances such as methylcellulose and mannitol to differentiate stomach versus intestinal stretch respectively, we demonstrate that high-fat diet feeding ablates intestinal stretch-induced reductions in food intake while weight loss via dietary intervention, restores this response. More importantly, VSG restores intestinal stretch-induced food intake reduction, suggesting the reactivation of the peripheral neurons that detect intestinal stretch. Taken together, our data provide evidence that VSG alters the signals in the gut-brain-axis by creating an environment where intestinal distension is exaggerated. This effect likely contributes to the sustained weight loss and alterations in feeding patterns observed after VSG. Our findings have important implications for the development of less invasive therapies for obesity that target the gut-brain-axis and feeding behavior. Presentation: Saturday, June 17, 2023

The role of aberrant glycosylation in pancreatic ductal adenocarcinoma (PDAC) remains an under-investigated area of research. In this study, we determined that ST6 β-galactoside α2,6 sialyltransferase 1 (ST6GAL1), which adds α2,6-linked sialic acids to N-glycosylated proteins, was upregulated in patients with early-stage PDAC and was further increased in advanced disease. A tumor-promoting function for ST6GAL1 was elucidated using tumor xenograft experiments with human PDAC cells. Additionally, we developed a genetically engineered mouse (GEM) model with transgenic expression of ST6GAL1 in the pancreas and found that mice with dual expression of ST6GAL1 and oncogenic KRASG12D had greatly accelerated PDAC progression compared with mice expressing KRASG12D alone. As ST6GAL1 imparts progenitor-like characteristics, we interrogated ST6GAL1's role in acinar to ductal metaplasia (ADM), a process that fosters neoplasia by reprogramming acinar cells into ductal, progenitor-like cells. We verified ST6GAL1 promotes ADM using multiple models including the 266-6 cell line, GEM-derived organoids and tissues, and an in vivo model of inflammation-induced ADM. EGFR is a key driver of ADM and is known to be activated by ST6GAL1-mediated sialylation. Importantly, EGFR activation was dramatically increased in acinar cells and organoids from mice with transgenic ST6GAL1 expression. These collective results highlight a glycosylation-dependent mechanism involved in early stages of pancreatic neoplasia.

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 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 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 (SSBP3ΔPanc and SSBP3ΔIslet), 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 SSBP3Δβ-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 SSBP3Δβ-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:SSBP3ΔPanc and SSBP3ΔIslet neonates present with hyperglycemia. SSBP3ΔIslet 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 SSBP3Δβ-cell causes hyperglycemia, glucose intolerance, and reduced GSIS. Transcriptomic analysis of 14-week-old SSBP3Δβ-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 identity and function, where its loss causes altered islet-cell abundance and glucose homeostasis. β-Cell SSBP3 is required for GSIS and glucose homeostasis, at least partially through shared regulation of Ldb1 and Isl1 target genes.

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.

Despite decades of obesity research and various public health initiatives, obesity remains a major public health concern. Our most drastic but most effective treatment of obesity is bariatric surgery with weight loss and improvements in co-morbidities, including resolution of type 2 diabetes (T2D). However, the mechanisms by which surgery elicits metabolic benefits are still not well understood. One proposed mechanism is through signals generated by the intestine (nutrients, neuronal, and/or endocrine) that communicate nutrient status to the brain. In this review, we discuss the contributions of gut-brain communication to the physiological regulation of body weight and its impact on the success of bariatric surgery. Advancing our understanding of the mechanisms that drive bariatric surgery-induced metabolic benefits will ultimately lead to the identification of novel, less invasive strategies to treat obesity.

Historically, intracellular function and metabolic adaptation within the α-cell has been understudied, with most of the attention being placed on the insulin-producing β-cells due to their role in the pathophysiology of type 2 diabetes mellitus. However, there is a growing interest in understanding the function of other endocrine cell types within the islet and their paracrine role in regulating insulin secretion. For example, there is greater appreciation for α-cell products and their contributions to overall glucose homeostasis. Several recent studies have addressed a paracrine role for α-cell-derived glucagon-like peptide-1 (GLP-1) in regulating glucose homeostasis and responses to metabolic stress. Further, other studies have demonstrated the ability of glucagon to impact insulin secretion by acting through the GLP-1 receptor. These studies challenge the central dogma surrounding α-cell biology describing glucagon's primary role in glucose counterregulation to one where glucagon is critical in regulating both hyper- and hypoglycemic responses. Herein, this review will update the current understanding of the role of glucagon and α-cell-derived GLP-1, placing emphasis on their roles in regulating glucose homeostasis, insulin secretion, and β-cell mass.

Pancreatic islets are comprised of hormone secreting cell types that are vital regulators of glucose metabolism. Specifically, the pancreatic β cell is indispensable for glucose control and its dysfunction is central to diabetes mellitus. β cell development is regulated by transcription factor (TF) cascades, mediating differentiation of progenitors into mature insulin producing β cells. Our prior studies show that TF, Islet1 (Isl1), interacts with a transcriptional co‐regulator, Ldb1, to regulate β cell maturation from embryonic day (E) 18.5 onward. However, Ldb1 is also expressed in early stages of pancreas development, before Isl1 is present (as early as E10.5). The earlier Ldb1 + cell types include Pdx1 + multipotent progenitor cells (MPCs) and endocrine progenitors expressing the TF Neurogenin3 (Ngn3). MPC progeny will populate the entire pancreas (endocrine and exocrine), while Ngn3 + endocrine progenitors (Isl1 − ) are fated to become islet cells. Our hypothesis is that Ldb1 has Isl1 independent roles in maintaining progenitor identity in these requisite populations during early pancreatic development. To test this we generated a whole pancreas knockout of Ldb1 ( Ldb1 Δpanc ) and observed severe developmental and postnatal phenotypes. At E13.5, Ldb1 Δpanc mice exhibit disorganized progenitor pools, suggesting early defects in endocrine identity. At E15.5, Ldb1 Δpanc mice had a significant reduction of Ngn3 + progenitors and Pdx1 HI immunoreactivity, a mark of presumptive β cells. Ldb1 Δpanc mice die by postnatal day 7 (P7) with severe hyperglycemia and hypoinsulinemia due to drastic islet hormone cell reduction. Interestingly, total pancreatic mass remained unchanged in Ldb1 Δpanc neonates, suggesting that Ldb1 impacts are islet specific in the pancreas. Considering these observations, we generated a new model of Ldb1 loss specifically in Ngn3 + islet progenitors, termed Ldb1 Δendo . We confirmed loss of Ldb1 in endocrine clusters and observed postnatal hyperglycemia, with a reduction of islet cells in neonates, similar to that seen in Ldb1 Δpanc mice. Chromatin immunoprecipitation in vivo and in vitro highlights that Ldb1 imparts control on Pdx1 through occupation of the Pdx1 Area I–II regulatory domains, and that Ngn3 control also occurs via direct occupation. We are now further assessing the developmental phenotype, examining markers of proliferation, apoptosis, and altered cell identity through lineage tracing in the Ldb1 Δendo model. Concomitantly, our published work revealed that Ldb1 and Isl1 interact in complex with the single stranded DNA binding protein co‐regulator, SSBP3, which helps stabilize this transcriptional complex. To examine the functional relationship between SSBP3, Isl1, and Ldb1 in vivo , we developed a new SSBP3 floxed mouse model in order to generate pancreas wide loss of SSBP3 ( SSBP3 Δpanc ). We observed preliminary reductions in key islet mRNAs along with hyperglycemia in neonates at P1. Our work provides insight into the transcriptional complexes dictating how islet progenitors adopt their cell fate. Enhancing our understanding of this differentiation process can contribute to therapeutic β and islet cell generation strategies to help the growing diabetic population. Support or Funding Information NIH‐NIDDK R01DK111483‐01NIH‐F31DK120217NIH‐NIGMS T32GM008111

Diabetes is characterized by a loss of beta-cell mass, and a greater understanding of the transcriptional mechanisms governing beta-cell function is required for future therapies. Previously, we reported that a complex of the Islet-1 (Isl1) transcription factor and the co-regulator single-stranded DNA-binding protein 3 (SSBP3) regulates the genes necessary for beta-cell function, but few proteins are known to interact with this complex in beta-cells. To identify additional components, here we performed SSBP3 reverse-cross-linked immunoprecipitation (ReCLIP)- and MS-based experiments with mouse beta-cell extracts and compared the results with those from our previous Isl1 ReCLIP study. Our analysis identified the E3 ubiquitin ligases ring finger protein 20 (RNF20) and RNF40, factors that in nonpancreatic cells regulate transcription through imparting monoubiquitin marks on histone H2B (H2Bub1), a precursor to histone H3 lysine 4 trimethylation (H3K4me3). We hypothesized that RNF20 and RNF40 regulate similar genes as those regulated by Isl1 and SSBP3 and are important for beta-cell function. We observed that Rnf20 and Rnf40 depletion reduces beta-cell H2Bub1 marks and uncovered several target genes, including glucose transporter 2 (Glut2), MAF BZIP transcription factor A (MafA), and uncoupling protein 2 (Ucp2). Strikingly, we also observed that Isl1 and SSBP3 depletion reduces H2Bub1 and H3K4me3 marks, suggesting that they have epigenetic roles. We noted that the RNF complex is required for glucose-stimulated insulin secretion and normal mitochondrial reactive oxygen species levels. These findings indicate that RNF20 and RNF40 regulate beta-cell gene expression and insulin secretion and establish a link between Isl1 complexes and global cellular epigenetics.

Pancreatic β-cells undergo profound hyperplasia during pregnancy to maintain maternal euglycemia. Failure to reprogram β-cells into a more replicative state has been found to underlie susceptibility to gestational diabetes mellitus (GDM). We recently identified a requirement for prolactin receptor (PRLR) signaling in the metabolic adaptations to pregnancy, where mice lacking β-cell PRLR (βPRLRKO) exhibit a metabolic phenotype consistent with GDM. However, the underlying transcriptional program that is responsible for the PRLR-dependent metabolic adaptations during gestation remains incompletely understood. To identify PRLR signaling gene regulatory networks and target genes within β-cells during pregnancy, we performed a transcriptomic analysis of pancreatic islets isolated from either βPRLRKO mice or littermate controls in late gestation. Gene set enrichment analysis identified Forkhead box protein M1 ( Foxm 1) and polycomb repressor complex 2 (PRC2) subunits, Suz 12 and Ezh 2, as novel candidate regulators of PRLR-dependent β-cell adaptation. GO-term pathway enrichment revealed both established and novel PRLR signaling target genes that together describe a state of increased cellular metabolism and/or proliferation. In contrast to the requirement for β-cell PRLR signaling in maintaining euglycemia during pregnancy, PRLR target genes were not induced following high-fat-diet feeding. Altogether, the current study expands our understanding of which transcriptional regulators and networks mediate gene expression required for islet adaptation during pregnancy. The current work also supports the presence of pregnancy-specific adaptive mechanisms distinct from those activated by nutritional stress.

The LIM-homeodomain (LIM-HD) transcription factor Islet-1 (Isl1) interacts with the LIM domain-binding protein 1 (Ldb1) coregulator to control expression of key pancreatic β-cell genes. However, Ldb1 also has Isl1-independent effects, supporting that another LIM-HD factor interacts with Ldb1 to impact β-cell development and/or function. LIM homeobox 1 (Lhx1) is an Isl1-related LIM-HD transcription factor that appears to be expressed in the developing mouse pancreas and in adult islets. However, roles for this factor in the pancreas are unknown. This study aimed to determine Lhx1 interactions and elucidate gene regulatory and physiological roles in the pancreas. Co-immunoprecipitation using β-cell extracts demonstrated an interaction between Lhx1 and Isl1, and thus we hypothesized that Lhx1 and Isl1 regulate similar target genes. To test this, we employed siRNA-mediated Lhx1 knockdown in β-cell lines and discovered reduced Glp1R mRNA. Chromatin immunoprecipitation revealed Lhx1 occupancy at a domain also known to be occupied by Isl1 and Ldb1. Through development of a pancreas-wide knockout mouse model ( Lhx1∆Panc), we demonstrate that aged Lhx1∆Pancmice have elevated fasting blood glucose levels, altered intraperitoneal and oral glucose tolerance, and significantly upregulated glucagon, somatostatin, pancreatic polypeptide, MafB, and Arx islet mRNAs. Additionally, Lhx1∆Pancmice exhibit significantly reduced Glp1R, an mRNA encoding the insulinotropic receptor for glucagon-like peptide 1 along with a concomitant dampened Glp1 response and mild glucose intolerance in mice challenged with oral glucose. These data are the first to reveal that the Lhx1 transcription factor contributes to normal glucose homeostasis and Glp1 responses.

Sarcopenia is defined as the loss of skeletal muscle mass and function due to age, and represents a major cause of disability in the elderly population. The contributing factors to the onset of sarcopenia are not well defined, but appear to involve age-dependent changes in both the tissue microenvironment and muscle progenitor cell (MPC) population. MPC transplantation has the potential to be a novel therapy for treatment of muscle dysfunction due to aging or injury, but has not shown significant clinical efficacy to date. The goal of this research was to use a rat model of skeletal muscle injury to examine the differential effects of age on MPC survival, differentiation, and tissue regeneration after transplantation. Fluorescently labeled MPCs, derived from young (YMPCs) and adult (AMPCs) donor rats, were transplanted in the injured tibialis anterior (TA) muscles of young, adult, and aged rats. Our results demonstrated that integration and maturation of YMPCs into mature myofibers were dependent on the age of the host microenvironment; whereas, the integration and maturation of AMPCs were less dependent on age and more dependent on intrinsic cellular changes. These data suggest that the age of both the host microenvironment and cells for transplantation must be considered when designing cell therapy regimens.

Type 1 Diabetes (T1D) is a chronic pro-inflammatory autoimmune disease consisting of islet-infiltrating leukocytes involved in pancreatic β-cell lysis. One promising treatment for T1D is islet transplantation; however, clinical application is constrained due to limited islet availability, adverse effects of immunosuppressants, and declining graft survival. Islet encapsulation may provide an immunoprotective barrier to preserve islet function and prevent immune-mediated rejection after transplantation. We previously demonstrated that a novel cytoprotective nanothin multilayer coating for islet encapsulation consisting of tannic acid (TA), an immunomodulatory antioxidant, and poly(N-vinylpyrrolidone) (PVPON), was efficacious in dampening in vitro immune responses involved in transplant rejection and preserving in vitro islet function. However, the ability of (PVPON/TA) to maintain islet function in vivo and reverse diabetes has not been tested. Recent evidence has demonstrated that modulation of redox status can affect pro-inflammatory immune responses. Therefore, we hypothesized that transplanted (PVPON/TA)-encapsulated islets can restore euglycemia to diabetic mice and provide an immunoprotective barrier. Our results demonstrate that (PVPON/TA) nanothin coatings can significantly decrease in vitro chemokine synthesis and diabetogenic T cell migration. Importantly, (PVPON/TA)-encapsulated islets restored euglycemia after transplantation into diabetic mice. Our results demonstrate that (PVPON/TA)-encapsulated islets may suppress immune responses and enhance islet allograft acceptance in patients with T1D.