MafA and MafB regulate genes critical to beta-cells in a unique temporal manner

Various strategies to induce beta cell neogenesis: a comprehensive review for unravelling the potential future therapy for curing diabetes

Pancreatic endocrine cells are categorized in to 5 types (alpha, beta, delta, pancreatic polypeptide cells and epsilon), which expresses glucagon, insulin, somatostatin, pancreatic polypeptide, and ghrelin, respectively. Several studies including lineage tracing in Ins2Akita diabetic mice have been done to investigate the identities of pancreatic endocrine cells which concludes, alpha cells have enormous plasticity, which enables them to be reprogrammed by specific transcription factors into insulin secreting beta like cells. Gene therapy has provided the beneficial outcome. Pdx1, MaFA and PAX4 (the transcription factors) in alpha cells can be over expressed which results in reprogramming the targeted alpha cells into beta cells. This trans-differentiation may be induced by infusing an adeno-associated virus (AAV) loaded with distinct transcription factors in the duct of pancreas. Several researches have demonstrated the successful restoration of enhanced insulin secretion in diabetes induced mice. Additionally ductal neurogenin3 (Ngn3), Sglt2 inhibitors, Igfbp1, GLP1 and several clinical and non-clinical agents has been postulated as a basis of beta cell neogenesis. Alpha cell owing to its high plasticity, on prolonged exposure to GABA reprogrammed into beta-like cell due to downregulation of Arx expression by GABA. The various approaches for beta cell neogenesis open a new window towards the establishment of novel gene therapy accession to treat diabetes. However, broad studies are still needed to improve and optimize this treatment methodology. The potentiality of endogenous pancreatic alpha cell to beta cell conversion methods and its outcomes are invigorating. This accomplishment is presently being under trial in non-human primates.

Modeling diabetic alpha cell dysfunction using stem cell-derived alpha cells

Dysfunction of pancreatic alpha cells contributes to the pathophysiology of diabetes. Features of diabetic alpha cell dysfunction include glucagon hypersecretion, defects in proglucagon processing, and altered transcriptomic profile. The lack of an in vitro human alpha cell model has prevented the investigation, and potential correction, of these dysfunctional phenotypes. Here, we show that induction of endoplasmic reticulum (ER) stress in stem cell-derived alpha (SC-α) cells induces hypersecretion of glucagon. ER stress also increases the secretion of glicentin and the expression of glucagon-like peptide-1 (GLP-1), peptides produced by alternate cleavage of proglucagon by the prohormone convertase 1 (PC1/3) enzyme. Additionally, ER stress establishes a diabetic transcriptional state in SC-α cells characterized by downregulation of MAFB, as well as glycolysis and oxidative phosphorylation pathways. We show that sunitinib, a tyrosine kinase inhibitor, protects SC-α cells against the ER stress-induced glucagon hypersecretion phenotype. Thus, SC-α cell model can advance our knowledge of islets in health and diabetes.

Investigation of the motif activity of transcription regulators in pancreatic β-like cell subpopulations differentiated from human induced pluripotent stem cells

Pancreatic β-cells are composed of different subtypes that play a key role in the control of insulin secretion and thereby control glucose homeostasis. In vitro differentiation of human induced pluripotent stem cells (hiPSCs) into 3D spheroids leads to the generation of β-cell subtypes and thus to the development of islet-like structures. Using this cutting-edge cell model, the aim of the study was to decipher the signaling signature that underlines β-cell subtypes, with a focus on the search for the activity of motifs of important transcription regulators (TRs). The investigation was performed using data from previous single-cell sequencing analysis introduced into the integrated system for motif activity response analysis (ISMARA) of transcription regulators. We extracted the matrix of important TRs activated in the β-cell subpopulation and bi-hormonal-like β-cells. Based on these TRs and their targets, we built specific regulatory networks for main cell subpopulations. Our data confirmed the transcriptomic heterogeneity of the β-cell subtype lineage and suggested a mechanism that could account for the differentiation of β-cell subtypes during pancreas development. We do believe that our findings could be instrumental for understanding the mechanisms that affect the balance of β-cell subtypes, leading to impaired insulin secretion in type 2 diabetes.

Defining unique structural features in the MAFA and MAFB transcription factors that control Insulin gene activity

MAFA and MAFB are related basic-leucine-zipper domain-containing transcription factors which have important overlapping and distinct regulatory roles in a variety of cellular contexts, including hormone production in pancreatic islet cells. Here, we first examined how mutating conserved MAF protein-DNA contact sites obtained from X-ray crystal structure analysis impacted their DNA-binding and Insulin enhancer-driven activity. While most of these interactions were essential and their disruption severely compromised activity, we identified that regions outside of these contact sites also contributed to transcriptional activity. AlphaFold 2 (https://alphafold.ebi.ac.uk), an artificial intelligence-based structural prediction program, was used to determine if there were also differences in the three-dimensional organization of the non-DNA binding/dimerization sequences of MAFA and MAFB. This analysis was conducted on the WT proteins as well as the pathogenic MAFASer64Phe and MAFBSer70Ala transactivation domain mutants, with differences revealed between MAFAWT and MAFBWT as well as between MAFASer64Phe and MAFAWT, but not between MAFBSer70Ala and MAFBWT. Moreover, dissimilarities between these proteins were also observed in their ability to cooperatively stimulate Insulin enhancer-driven activity in the presence of other islet-enriched transcription factors. Analysis of MAFA and MAFB chimeras disclosed that these properties were influenced by their unique C-terminal region structural differences predicted by AlphaFold 2. Our findings have revealed key structural features of these closely related proteins that impact their ability to regulate gene expression.

The SWI/SNF chromatin remodelling complex regulates pancreatic endocrine cell expansion and differentiation in mice in vivo

AIMS/HYPOTHESIS

Strategies to augment functional beta cell mass include directed differentiation of stem cells towards a beta cell fate, which requires extensive knowledge of transcriptional programs governing endocrine progenitor cell differentiation in vivo. We aimed to study the contributions of the Brahma-related gene-1 (BRG1) and Brahma (BRM) ATPase subunits of the SWI/SNF chromatin remodelling complex to endocrine cell development.

METHODS

We generated mice with endocrine progenitor-specific Neurog3-Cre BRG1 removal in the presence of heterozygous (Brg1Δendo;Brm+/-) or homozygous (double knockout: DKOΔendo) BRM deficiency. Whole-body metabolic phenotyping, islet function characterisation, islet quantitative PCR and histological characterisation were performed on animals and tissues postnatally. To test the mechanistic actions of SWI/SNF in controlling gene expression during endocrine cell development, single-cell RNA-seq was performed on flow-sorted endocrine-committed cells from embryonic day 15.5 control and mutant embryos.

RESULTS

Brg1Δendo;Brm+/- mice exhibit severe glucose intolerance, hyperglycaemia and hypoinsulinaemia, resulting, in part, from reduced islet number; diminished alpha, beta and delta cell mass; compromised islet insulin secretion; and altered islet gene expression programs, including reductions in MAFA and urocortin 3 (UCN3). DKOΔendo mice were not recovered at weaning; however, postnatal day 6 DKOΔendo mice were severely hyperglycaemic with reduced serum insulin levels and beta cell area. Single-cell RNA-seq of embryonic day 15.5 lineage-labelled cells revealed endocrine progenitor, alpha and beta cell populations from SWI/SNF mutants have reduced expression of Mafa, Gcg, Ins1 and Ins2, suggesting limited differentiation capacity. Reduced Neurog3 transcripts were discovered in DKOΔendo endocrine progenitor clusters, and the proliferative capacity of neurogenin 3 (NEUROG3)+ cells was reduced in Brg1Δendo;Brm+/- and DKOΔendo mutants.

CONCLUSIONS/INTERPRETATION

Loss of BRG1 from developing endocrine progenitor cells has a severe postnatal impact on glucose homeostasis, and loss of both subunits impedes animal survival, with both groups exhibiting alterations in hormone transcripts embryonically. Taken together, these data highlight the critical role SWI/SNF plays in governing gene expression programs essential for endocrine cell development and expansion.

DATA AVAILABILITY

Raw and processed data for scRNA-seq have been deposited into the NCBI Gene Expression Omnibus (GEO) database under the accession number GSE248369.

The Expression of MAFB Gene in Circulating Monocytes Is Related to Chronic Inflammatory Status in T2DM Patients

Immune cell-mediated chronic inflammation is one of the causes of type 2 diabetes mellitus (T2DM). Therefore, identifying inflammatory markers in circulating immune cells is highly important for predicting insulin resistance (IR) and the occurrence of T2DM. In this study, we discovered that differentially expressed genes (DEGs) in peripheral blood mononuclear cells (PBMCs) from T2DM patients were associated with innate immunity and chronic inflammatory responses through bulk transcriptome sequencing (bulk RNA-seq). Gene integration analysis revealed that nine DEGs were upregulated, and receiver operating characteristic (ROC) curve analysis revealed that V-maf musculoaponeurotic fibrosarcoma oncogene homolog B (MAFB), a candidate biomarker, has a certain predictive value for T2DM. In population-based cohort studies, we found that MAFB expression was significantly upregulated in the PBMCs of T2DM patients and was significantly correlated with homeostasis model assessment of IR (HOMA-IR), tumor necrosis factor-α (TNF-α), adiponectin (Adipoq), etc. We further evaluated the sensitivity and specificity of MAFB and other clinical parameters for predicting and diagnosing T2DM and found that MAFB expression in PBMCs had a positive effect on the prediction and diagnosis of T2DM. Finally, single-cell RNA sequencing (scRNA-seq) analysis revealed that the increase in MAFB expression was mainly in nonclassical monocytes. Our results suggest that increased MAFB expression in circulating monocytes may mediate chronic inflammatory status in patients with T2DM. Therefore, MAFB gene expression in circulating monocytes has certain clinical significance for predicting and assisting in the diagnosis of T2DM.

Disruption of perinatal myeloid niches impacts the aging clock of pancreatic β cells

Perinatal expansion of pancreatic β cells is critical to metabolic adaptation. Yet, mechanisms surveying the fidelity by which proliferative events generate functional β cell pools remain unknown. We have previously identified a CCR2+ myeloid niche required for peri-natal β cell replication, with β cells dynamically responding to loss and repopulation of these myeloid cells with growth arrest and rebound expansion, respectively. Here, using a timed single-cell RNA-sequencing approach, we show that transient disruption of perinatal CCR2+ macrophages change islet β cell repertoires in young mice to resemble those of aged mice. Gene expression profiling and functional assays disclose prominent mitochondrial defects in β cells coupled to impaired redox states, NAD depletion, and DNA damage, leading to accelerated islets' dysfunction with age. These findings reveal an unexpected vulnerability of mitochondrial β cells' bioenergetics to the disruption of perinatal CCR2+ macrophages, implicating these cells in surveying early in life both the size and energy homeostasis of β cells populations.

GOAT rs10096097 and CREB1 rs6740584 single nucleotide polymorphisms are associated with type 2 diabetes mellitus in Egyptians

Diabetes mellitus (DM) is a chronic disorder that affects nearly half a billion people around the world and causes millions of deaths annually. Treatment of diabetes or related complications represents an economic burden not only for developing countries but also for the developed ones. Hence, new efficient therapeutic and preventive strategies and screening tools are necessary. The current work aimed to assess the potential association of single nucleotide polymorphisms (SNPs) in ghrelin O-acyltransferase (GOAT) rs10096097, cyclic adenosine monophosphate (cAMP) response element binding protein (CREB) rs6740584, and v-maf musculoaponeurotic fibrosarcoma oncogene homolog A (MafA) rs62521874 genes with type 2 DM susceptibility in Egyptians. A total of 96 patients with type 2 DM along with 72 healthy individuals participated in this study. Genotyping was executed via real-time polymerase chain reaction (PCR), and the serum protein levels of GOAT, CREB, and MafA were measured by enzyme-linked immunosorbent assay (ELISA). Genotyping revealed a significant association of GOAT rs10096097 and CREB1 rs6740584 SNPs with type 2 diabetes risk, with significantly higher GOAT rs10096097 G allele and CREB1 rs6740584 T allele frequencies in diabetic patients than in controls. However, insignificant association was identified between the MafA rs62521874 SNP and diabetes in the examined sample of the Egyptian residents. Serum GOAT, CREB1, and MafA protein levels did not vary significantly between diabetic and control individuals. Yet, significant variation in serum GOAT and CREB1 levels was detected between CREB1 rs6740584 genotypes within the diabetic group, with CT and TT genotype carriers showing higher levels than AA genotype patients. GOAT rs10096097 and CREB1 rs6740584, but not MafA rs62521874, SNPs are associated with type 2 diabetes risk in the studied Egyptians.

Defining unique structural features in the MAFA and MAFB transcription factors that control Insulin gene activity

MAFA and MAFB are related basic-leucine-zipper domain containing transcription factors which have important overlapping and distinct regulatory roles in a variety of cellular contexts, including hormone production in pancreatic islet α and β cells. Here we first examined how mutating conserved MAF protein-DNA contacts obtained from X-ray crystal structure analysis impacted their DNA-binding and Insulin enhancer-driven activity. While most of these interactions were essential and their disruption severely compromised activity, we identified that regions outside of the contact areas also contributed to activity. AlphaFold 2, an artificial intelligence-based structural prediction program, was next used to determine if there were also differences in the three-dimensional organization of the non-DNA binding/dimerization sequences of MAFA and MAFB. This analysis was conducted on the wildtype (WT) proteins as well as the pathogenic MAFA Ser64Phe and MAFB Ser70Ala trans -activation domain mutants, with differences revealed between MAFA WT and MAFB WT as well as between MAFA Ser64Phe and MAFA WT , but not between MAFB Ser70Ala and MAFB WT . Moreover, dissimilarities between these proteins were also observed in their ability to cooperatively stimulate Insulin enhancer-driven activity in the presence of other islet-enriched transcription factors. Analysis of MAFA and MAFB chimeras disclosed that these properties were greatly influenced by unique C-terminal region structural differences predicted by AlphaFold 2. Importantly, these results have revealed features of these closely related proteins that are functionally significant in islet biology.

Genetic influences on circulating retinol and its relationship to human health

Retinol is a fat-soluble vitamin that plays an essential role in many biological processes throughout the human lifespan. Here, we perform the largest genome-wide association study (GWAS) of retinol to date in up to 22,274 participants. We identify eight common variant loci associated with retinol, as well as a rare-variant signal. An integrative gene prioritisation pipeline supports novel retinol-associated genes outside of the main retinol transport complex (RBP4:TTR) related to lipid biology, energy homoeostasis, and endocrine signalling. Genetic proxies of circulating retinol were then used to estimate causal relationships with almost 20,000 clinical phenotypes via a phenome-wide Mendelian randomisation study (MR-pheWAS). The MR-pheWAS suggests that retinol may exert causal effects on inflammation, adiposity, ocular measures, the microbiome, and MRI-derived brain phenotypes, amongst several others. Conversely, circulating retinol may be causally influenced by factors including lipids and serum creatinine. Finally, we demonstrate how a retinol polygenic score could identify individuals more likely to fall outside of the normative range of circulating retinol for a given age. In summary, this study provides a comprehensive evaluation of the genetics of circulating retinol, as well as revealing traits which should be prioritised for further investigation with respect to retinol related therapies or nutritional intervention.

Repression of latent NF-κB enhancers by PDX1 regulates β cell functional heterogeneity

Interactions between lineage-determining and activity-dependent transcription factors determine single-cell identity and function within multicellular tissues through incompletely known mechanisms. By assembling a single-cell atlas of chromatin state within human islets, we identified β cell subtypes governed by either high or low activity of the lineage-determining factor pancreatic duodenal homeobox-1 (PDX1). β cells with reduced PDX1 activity displayed increased chromatin accessibility at latent nuclear factor κB (NF-κB) enhancers. Pdx1 hypomorphic mice exhibited de-repression of NF-κB and impaired glucose tolerance at night. Three-dimensional analyses in tandem with chromatin immunoprecipitation (ChIP) sequencing revealed that PDX1 silences NF-κB at circadian and inflammatory enhancers through long-range chromatin contacts involving SIN3A. Conversely, Bmal1 ablation in β cells disrupted genome-wide PDX1 and NF-κB DNA binding. Finally, antagonizing the interleukin (IL)-1β receptor, an NF-κB target, improved insulin secretion in Pdx1 hypomorphic islets. Our studies reveal functional subtypes of single β cells defined by a gradient in PDX1 activity and identify NF-κB as a target for insulinotropic therapy.

The SSBP3 co-regulator is required for glucose homeostasis, pancreatic islet architecture, and beta-cell identity

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.

Delineating mouse β-cell identity during lifetime and in diabetes with a single cell atlas

Although multiple pancreatic islet single-cell RNA-sequencing (scRNA-seq) datasets have been generated, a consensus on pancreatic cell states in development, homeostasis and diabetes as well as the value of preclinical animal models is missing. Here, we present an scRNA-seq cross-condition mouse islet atlas (MIA), a curated resource for interactive exploration and computational querying. We integrate over 300,000 cells from nine scRNA-seq datasets consisting of 56 samples, varying in age, sex and diabetes models, including an autoimmune type 1 diabetes model (NOD), a glucotoxicity/lipotoxicity type 2 diabetes model (db/db) and a chemical streptozotocin β-cell ablation model. The β-cell landscape of MIA reveals new cell states during disease progression and cross-publication differences between previously suggested marker genes. We show that β-cells in the streptozotocin model transcriptionally correlate with those in human type 2 diabetes and mouse db/db models, but are less similar to human type 1 diabetes and mouse NOD β-cells. We also report pathways that are shared between β-cells in immature, aged and diabetes models. MIA enables a comprehensive analysis of β-cell responses to different stressors, providing a roadmap for the understanding of β-cell plasticity, compensation and demise.

Species-specific roles for the MAFA and MAFB transcription factors in regulating islet β cell identity

Type 2 diabetes (T2D) is associated with compromised identity of insulin-producing pancreatic islet β cells, characterized by inappropriate production of other islet cell-enriched hormones. Here, we examined how hormone misexpression was influenced by the MAFA and MAFB transcription factors, closely related proteins that maintain islet cell function. Mice specifically lacking MafA in β cells demonstrated broad, population-wide changes in hormone gene expression with an overall gene signature closely resembling islet gastrin+ (Gast+) cells generated under conditions of chronic hyperglycemia and obesity. A human β cell line deficient in MAFB, but not one lacking MAFA, also produced a GAST+ gene expression pattern. In addition, GAST was detected in human T2D β cells with low levels of MAFB. Moreover, evidence is provided that human MAFB can directly repress GAST gene transcription. These results support a potentially novel, species-specific role for MafA and MAFB in maintaining adult mouse and human β cell identity, respectively. Here, we discuss the possibility that induction of Gast/GAST and other non-β cell hormones, by reduction in the levels of these transcription factors, represents a dysfunctional β cell signature.

Not the second fiddle: α cell development, identity, and function in health and diabetes

Historic and emerging studies provide evidence for the deterioration of pancreatic α cell function and identity in diabetes mellitus. Increased access to human tissue and the availability of more sophisticated molecular technologies have identified key insights into how α cell function and identity are preserved in healthy conditions and how they become dysfunctional in response to stress. These studies have revealed evidence of impaired glucagon secretion, shifts in α cell electrophysiology, changes in α cell mass, dysregulation of α cell transcription, and α-to-β cell conversion prior to and during diabetes. In this review, we outline the current state of research on α cell identity in health and disease. Evidence in model organisms and humans suggests that in addition to β cell dysfunction, diabetes is associated with a fundamental dysregulation of α cell identity. Importantly, epigenetic studies have revealed that α cells retain more poised and open chromatin at key cell-specific and diabetes-dysregulated genes, supporting the model that the inherent epigenetic plasticity of α cells makes them susceptible to the transcriptional changes that potentiate the loss of identity and function seen in diabetes. Thus, additional research into the maintenance of α cell identity and function is critical to fully understanding diabetes. Furthermore, these studies suggest α cells could represent an alternative source of new β cells for diabetes treatment.

Single-nucleus multi-omics of human stem cell-derived islets identifies deficiencies in lineage specification

Insulin-producing β cells created from human pluripotent stem cells have potential as a therapy for insulin-dependent diabetes, but human pluripotent stem cell-derived islets (SC-islets) still differ from their in vivo counterparts. To better understand the state of cell types within SC-islets and identify lineage specification deficiencies, we used single-nucleus multi-omic sequencing to analyse chromatin accessibility and transcriptional profiles of SC-islets and primary human islets. Here we provide an analysis that enabled the derivation of gene lists and activity for identifying each SC-islet cell type compared with primary islets. Within SC-islets, we found that the difference between β cells and awry enterochromaffin-like cells is a gradient of cell states rather than a stark difference in identity. Furthermore, transplantation of SC-islets in vivo improved cellular identities overtime, while long-term in vitro culture did not. Collectively, our results highlight the importance of chromatin and transcriptional landscapes during islet cell specification and maturation.

Milk Exosomal microRNAs: Postnatal Promoters of β Cell Proliferation but Potential Inducers of β Cell De-Differentiation in Adult Life

Pancreatic β cell expansion and functional maturation during the birth-to-weaning period is driven by epigenetic programs primarily triggered by growth factors, hormones, and nutrients provided by human milk. As shown recently, exosomes derived from various origins interact with β cells. This review elucidates the potential role of milk-derived exosomes (MEX) and their microRNAs (miRs) on pancreatic β cell programming during the postnatal period of lactation as well as during continuous cow milk exposure of adult humans to bovine MEX. Mechanistic evidence suggests that MEX miRs stimulate mTORC1/c-MYC-dependent postnatal β cell proliferation and glycolysis, but attenuate β cell differentiation, mitochondrial function, and insulin synthesis and secretion. MEX miR content is negatively affected by maternal obesity, gestational diabetes, psychological stress, caesarean delivery, and is completely absent in infant formula. Weaning-related disappearance of MEX miRs may be the critical event switching β cells from proliferation to TGF-β/AMPK-mediated cell differentiation, whereas continued exposure of adult humans to bovine MEX miRs via intake of pasteurized cow milk may reverse β cell differentiation, promoting β cell de-differentiation. Whereas MEX miR signaling supports postnatal β cell proliferation (diabetes prevention), persistent bovine MEX exposure after the lactation period may de-differentiate β cells back to the postnatal phenotype (diabetes induction).

mTORC1 is required for epigenetic silencing during β-cell functional maturation

Objective

The mechanistic target of rapamycin complex 1 (mTORC1) is a key molecule that links nutrients, hormones, and growth factors to cell growth/function. Our previous studies have shown that mTORC1 is required for β-cell functional maturation and identity maintenance; however, the underlying mechanism is not fully understood. This work aimed to understand the underlying epigenetic mechanisms of mTORC1 in regulating β-cell functional maturation.

Methods

We performed Microarray, MeDIP-seq and ATAC-seq analysis to explore the abnormal epigenetic regulation in 8-week-old immature βRapKO islets. Moreover, DNMT3A was overexpressed in βRapKO islets by lentivirus, and the transcriptome changes and GSIS function were analyzed.

Results

We identified two major epigenetic silencing mechanisms, DNMT3A-dependent DNA methylation and PRC2-dependent H3K27me3 modification, which are responsible for functional immaturity of Raptor-deficient β-cell. Overexpression of DNMT3A partially reversed the immature transcriptome pattern and restored the impaired GSIS in Raptor-deficient β-cells. Moreover, we found that Raptor directly regulated PRC2/EED and H3K27me3 expression levels, as well as a group of immature genes marked with H3K27me3. Combined with ATAC-seq, MeDIP-seq and ChIP-seq, we identified β-cell immature genes with either DNA methylation and/or H3K27me3 modification.

Conclusion

The present study advances our understanding of the nutrient sensor mTORC1, by integrating environmental nutrient supply and epigenetic modification, i.e., DNMT3A-mediated DNA methylation and PRC2-mediated histone methylation in regulating β-cell identity and functional maturation, and therefore may impact the disease risk of type 2 diabetes.

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Rescued DNMT3A expression in Raptor-deficient islets partially reversed the abnormal induction of immature genes.

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EED/H3K27me3 were impaired in Raptor-ablated β-cell.

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DNA methylation and H3K27me3 are required for mTORC1-dependent epigenetic silencing of immature genes in β-cell.

Stem cells differentiation into insulin-producing cells (IPCs): recent advances and current challenges

Type 1 diabetes mellitus (T1D) is a chronic disease characterized by an autoimmune destruction of insulin-producing β-pancreatic cells. Although many advances have been achieved in T1D treatment, current therapy strategies are often unable to maintain perfect control of glycemic levels. Several studies are searching for new and improved methodologies for expansion of β-cell cultures in vitro to increase the supply of these cells for pancreatic islets replacement therapy. A promising approach consists of differentiation of stem cells into insulin-producing cells (IPCs) in sufficient number and functional status to be transplanted. Differentiation protocols have been designed using consecutive cytokines or signaling modulator treatments, at specific dosages, to activate or inhibit the main signaling pathways that control the differentiation of induced pluripotent stem cells (iPSCs) into pancreatic β-cells. Here, we provide an overview of the current approaches and achievements in obtaining stem cell-derived β-cells and the numerous challenges, which still need to be overcome to achieve this goal. Clinical translation of stem cells-derived β-cells for efficient maintenance of long-term euglycemia remains a major issue. Therefore, research efforts have been directed to the final steps of in vitro differentiation, aiming at production of functional and mature β-cells and integration of interdisciplinary fields to generate efficient cell therapy strategies capable of reversing the clinical outcome of T1D.

MafB Maintains β -Cell Identity under MafA-Deficient Conditions

The transcription factor MafB plays an essential role in β-cell differentiation during the embryonic stage in rodents. Although MafB disappears from β-cells after birth, it has been reported that MafB can be evoked in β-cells and is involved in insulin⁺β-cell number and islet architecture maintenance in adult mice under diabetic conditions. However, the underlying mechanism by which MafB protects β-cells remains unknown. To elucidate this, we performed RNA sequencing using an inducible diabetes model (A0B^Δpanc mice) that we previously generated. We found that the deletion of Mafb can induce β-cell dedifferentiation, characterized by the upregulation of dedifferentiation markers, Slc5a10 and Cck, as well as several β-cell-disallowed genes, and by the downregulation of mature β-cell markers, Slc2a2 and Ucn3. However, there is no re-expression of well-known progenitor cell markers, Foxo1 and Neurog3. Further, the appearance of ALDH1A3⁺ cells and the disappearance of UCN3⁺ cells also verify the β-cell dedifferentiation state. Collectively, our results suggest that MafB can maintain β-cell identity under certain pathological conditions in adult mice, providing novel insight into the role of MafB in β-cell identity maintenance.

Mafa-dependent GABAergic activity promotes mouse neonatal apneas

While apneas are associated with multiple pathological and fatal conditions, the underlying molecular mechanisms remain elusive. We report that a mutated form of the transcription factor Mafa (Mafa^4A) that prevents phosphorylation of the Mafa protein leads to an abnormally high incidence of breath holding apneas and death in newborn Mafa^4A/4A mutant mice. This apneic breathing is phenocopied by restricting the mutation to central GABAergic inhibitory neurons and by activation of inhibitory Mafa neurons while reversed by inhibiting GABAergic transmission centrally. We find that Mafa activates the Gad2 promoter in vitro and that this activation is enhanced by the mutation that likely results in increased inhibitory drives onto target neurons. We also find that Mafa inhibitory neurons are absent from respiratory, sensory (primary and secondary) and pontine structures but are present in the vicinity of the hypoglossal motor nucleus including premotor neurons that innervate the geniohyoid muscle, to control upper airway patency. Altogether, our data reveal a role for Mafa phosphorylation in regulation of GABAergic drives and suggest a mechanism whereby reduced premotor drives to upper airway muscles may cause apneic breathing at birth.

Apneas are associated with many pathological conditions. Here, the authors show in a mouse model that stabilization of the transcription factor Mafa in brainstem GABAergic neurons may contribute to apnea, by decreasing motor drive to muscles controlling the airways.

Adapting Physiology in Functional Human Islet Organogenesis

Generation of three-dimensional (3D)-structured functional human islets is expected to be an alternative cell source for cadaveric human islet transplantation for the treatment of insulin-dependent diabetes. Human pluripotent stem cells (hPSCs), such as human embryonic stem cells (hESCs) and human induced pluripotent stem cells (hiPSCs), offer infinite resources for newly synthesized human islets. Recent advancements in hPSCs technology have enabled direct differentiation to human islet-like clusters, which can sense glucose and secrete insulin, and those islet clusters can ameliorate diabetes when transplanted into rodents or non-human primates (NHPs). However, the generated hPSC-derived human islet-like clusters are functionally immature compared with primary human islets. There remains a challenge to establish a technology to create fully functional human islets in vitro, which are functionally and transcriptionally indistinguishable from cadaveric human islets. Understanding the complex differentiation and maturation pathway is necessary to generate fully functional human islets for a tremendous supply of high-quality human islets with less batch-to-batch difference for millions of patients. In this review, I summarized the current progress in the generation of 3D-structured human islets from pluripotent stem cells and discussed the importance of adapting physiology for in vitro functional human islet organogenesis and possible improvements with environmental cues.

Urocortin3: Local inducer of somatostatin release and bellwether of beta cell maturity

Urocortin 3 (UCN3) is a peptide hormone expressed in pancreatic islets of Langerhans of both human alpha and human beta cells and solely in murine beta cells. UCN3 signaling acts locally within the islet to activate its cognate receptor, corticotropin releasing hormone receptor 2 (CRHR2), which is expressed by delta cells, to potentiate somatostatin (SST) negative feedback to reduce islet cell hormone output. The functional importance of UCN3 signaling in the islet is to modulate the amount of SST tone allowing for finely tuned regulation of insulin and glucagon secretion. UCN3 signaling is a hallmark of functional beta cell maturation, increasing the beta cell glucose threshold for insulin secretion. In doing so, UCN3 plays a relevant functional role in accurately maintaining blood glucose homeostasis. Additionally, UCN3 acts as an indicator of beta cell maturation and health, as UCN3 is not expressed in immature beta cells and is downregulated in dedifferentiated and dysfunctional beta cell states. Here, we review the mechanistic underpinnings of UCN3 signaling, its net effect on islet cell hormone output, as well as its value as a marker for beta cell maturation and functional status.

Role of the Transcription Factor MAFA in the Maintenance of Pancreatic β-Cells

Pancreatic β-cells are specialized to properly regulate blood glucose. Maintenance of the mature β-cell phenotype is critical for glucose metabolism, and β-cell failure results in diabetes mellitus. Recent studies provide strong evidence that the mature phenotype of β-cells is maintained by several transcription factors. These factors are also required for β-cell differentiation from endocrine precursors or maturation from immature β-cells during pancreatic development. Because the reduction or loss of these factors leads to β-cell failure and diabetes, inducing the upregulation or inhibiting downregulation of these transcription factors would be beneficial for studies in both diabetes and stem cell biology. Here, we discuss one such factor, i.e., the transcription factor MAFA. MAFA is a basic leucine zipper family transcription factor that can activate the expression of insulin in β-cells with PDX1 and NEUROD1. MAFA is indeed indispensable for the maintenance of not only insulin expression but also function of adult β-cells. With loss of MAFA in type 2 diabetes, β-cells cannot maintain their mature phenotype and are dedifferentiated. In this review, we first briefly summarize the functional roles of MAFA in β-cells and then mainly focus on the molecular mechanism of cell fate conversion regulated by MAFA.

Second MAFA Variant Causing a Phosphorylation Defect in the Transactivation Domain and Familial Insulinomatosis

Adult-onset familial insulinomatosis is a rare disorder with recurrent, severe hypoglycemia caused by multiple insulin-secreting pancreatic tumors. The etiology was unclear until the variant p.Ser64Phe in the transcription factor MAFA, a key coordinator of β-cell insulin secretion, was defined as the cause in two families. We here describe detailed genetic, clinical, and family analyses of two sisters with insulinomatosis, aiming to identify further disease causes. Using exome sequencing, we detected a novel, heterozygous missense variant, p.Thr57Arg, in MAFA’s highly conserved transactivation domain. The impact of the affected region is so crucial that in vitro expression studies replacing Thr57 have already been performed, demonstrating a phosphorylation defect with the impairment of transactivation activity and degradation. However, prior to our study, the link to human disease was missing. Furthermore, mild hyperglycemia was observed in six additional, heterozygote family members, indicating that not only insulinomatosis but also MODY-like symptoms co-segregate with p.Thr57Arg. The pre-described MAFA variant, p.Ser64Phe, is located in the same domain, impairs the same phosphorylation cascade, and results in the same symptoms. We confirm MAFA phosphorylation defects are important causes of a characteristic syndrome, thus complementing the pathophysiological and diagnostic disease concept. Additionally, we verify the high penetrance and autosomal dominant inheritance pattern.

MafA Regulation in β-Cells: From Transcriptional to Post-Translational Mechanisms

β-cells are insulin-producing cells in the pancreas that maintain euglycemic conditions. Pancreatic β-cell maturity and function are regulated by a variety of transcription factors that enable the adequate expression of the cellular machinery involved in nutrient sensing and commensurate insulin secretion. One of the key factors in this regulation is MAF bZIP transcription factor A (MafA). MafA expression is decreased in type 2 diabetes, contributing to β-cell dysfunction and disease progression. The molecular biology underlying MafA is complex, with numerous transcriptional and post-translational regulatory nodes. Understanding these complexities may uncover potential therapeutic targets to ameliorate β-cell dysfunction. This article will summarize the role of MafA in normal β-cell function and disease, with a special focus on known transcriptional and post-translational regulators of MafA expression.

The Calcium Channel Subunit Gamma-4 as a Novel Regulator of MafA in Pancreatic Beta-Cell Controls Glucose Homeostasis

Impaired fasting glucose (IFG) and impaired glucose tolerance (IGT) are high-risk factors of diabetes development and may be caused by defective insulin secretion in pancreatic beta-cells. Glucose-stimulated insulin secretion is mediated by voltage-gated Ca2+ (CaV) channels in which the gamma-4 subunit (CaVγ4) is required for the beta-cell to maintain its differentiated state. We here aim to explore the involvement of CaVγ4 in controlling glucose homeostasis by employing the CaVγ4-/- mice to study in vivo glucose-metabolism-related phenotypes and glucose-stimulated insulin secretion, and to investigate the underlying mechanisms. We show that CaVγ4-/- mice exhibit perturbed glucose homeostasis, including IFG and IGT. Glucose-stimulated insulin secretion is blunted in CaVγ4-/- mouse islets. Remarkably, CaVγ4 deletion results in reduced expression of the transcription factor essential for beta-cell maturation, MafA, on both mRNA and protein levels in islets from human donors and CaVγ4-/- mice, as well as in INS-1 832/13 cells. Moreover, we prove that CaMKII is responsible for mediating this regulatory pathway linked between CaVγ4 and MafA, which is further confirmed by human islet RNA-seq data. We demonstrate that CaVγ4 is a key player in preserving normal blood glucose homeostasis, which sheds light on CaVγ4 as a novel target for the treatment of prediabetes through correcting the impaired metabolic status.

Gymnemic Acid Ameliorates Pancreatic β-Cell Dysfunction by Modulating Pdx1 Expression: A Possible Strategy for β-Cell Regeneration

BACKGROUND

Endogenous pancreatic β-cell regeneration is a promising therapeutic approach for enhancing β-cell function and neogenesis in diabetes. Various findings have reported that regeneration might occur via stimulating β-cell proliferation, neogenesis, or conversion from other pancreatic cells to β-like cells. Although the current scenario illustrates numerous therapeutic strategies and approaches that concern endogenous β-cell regeneration, all of them have not been successful to a greater extent because of cost effectiveness, availability of suitable donors and rejection in case of transplantation, or lack of scientific evidence for many phytochemicals derived from plants that have been employed in traditional medicine. Therefore, the present study aims to investigate the effect of gymnemic acid (GA) on β-cell regeneration in streptozotocin-induced type 1 diabetic rats and high glucose exposed RIN5-F cells.

METHODS

The study involves histopathological and immunohistochemical analysis to examine the islet's architecture. Quantitative polymerase chain reaction (qPCR) and/or immunoblot were employed to quantify the β-cell regeneration markers and cell cycle proliferative markers.

RESULTS

The immunoexpression of E-cadherin, β-catenin, and phosphoinositide 3-kinases/protein kinase B were significantly increased in GA-treated diabetic rats. On the other hand, treatment with GA upregulated the pancreatic regenerative transcription factor viz. pancreatic duodenal homeobox 1, Neurogenin 3, MafA, NeuroD1, and β-cells proliferative markers such as CDK4, and Cyclin D1, with a simultaneous downregulation of the forkhead box O, glycogen synthase kinase-3, and p21^cip1 in diabetic treated rats. Adding to this, we noticed increased nuclear localization of Pdx1 in GA treated high glucose exposed RIN5-F cells.

CONCLUSION

Our results suggested that GA acts as a potential therapeutic candidate for endogenous β-cell regeneration in treating type 1 diabetes.

MAFA and MAFB regulate exocytosis-related genes in human β-cells

AIMS

Reduced expression of exocytotic genes is associated with functional defects in insulin exocytosis contributing to impaired insulin secretion and type 2 diabetes (T2D) development. MAFA and MAFB transcription factors regulate β-cell physiology, and their gene expression is reduced in T2D β cells. We investigate if loss of MAFA and MAFB in human β cells contributes to T2D progression by regulating genes required for insulin exocytosis.

METHODS

Three approaches were performed: (1) RNAseq analysis with the focus on exocytosis-related genes in MafA^-/- mouse islets, (2) correlational analysis between MAFA, MAFB and exocytosis-related genes in human islets and (3) MAFA and MAFB silencing in human islets and EndoC-βH1 cells followed by functional in vitro studies.

RESULTS

The expression of 30 exocytosis-related genes was significantly downregulated in MafA^-/- mouse islets. In human islets, the expression of 29 exocytosis-related genes correlated positively with MAFA and MAFB. Eight exocytosis-related genes were downregulated in MafA^-/- mouse islets and positively correlated with MAFA and MAFB in human islets. From this analysis, the expression of RAB3A, STXBP1, UNC13A, VAMP2, NAPA, NSF, STX1A and SYT7 was quantified after acute MAFA or MAFB silencing in EndoC-βH1 cells and human islets. MAFA and MAFB silencing resulted in impaired insulin secretion and reduced STX1A, SYT7 and STXBP1 (EndoC-βH1) and STX1A (human islets) mRNA expression. STX1A and STXBP1 protein expression was also impaired in islets from T2D donors which lack MAFA expression.

CONCLUSION

Our data indicate that STXBP1 and STX1A are important MAFA/B-regulated exocytosis genes which may contribute to insulin exocytosis defects observed in MAFA-deficient human T2D β cells.

Clinical implications of cell-of-origin epigenetic characteristics in non-functional pancreatic neuroendocrine tumors

Primary non-functional pancreatic neuroendocrine tumors (NF-PanNETs) are a heterogeneous group of neuroendocrine neoplasms that display highly variable clinical behavior. Therefore, NF-PanNETs often present clinical teams with a dilemma: the uncertain metastatic potential of the tumor has to be weighed against the morbidity associated with surgical resection. Thus, rather than utilizing current radiologic thresholds, there is an urgent need for improved prognostic biomarkers. Recent studies aimed at understanding the epigenetic underpinnings of NF-PanNETs have led to the identification of tumor subgroups based on histone modification and DNA methylation patterns. These molecular profiles tend to resemble the cellular origins of PanNETs. Subsequent retrospective analyses have demonstrated that these molecular signatures are of prognostic value and, importantly, may be useful in the preoperative setting. These studies have highlighted that sporadic NF-PanNETs displaying biomarkers associated with disease progression and poor prognosis, such as alternative lengthening of telomeres, inactivating alpha thalassemia/mental retardation X-linked (ATRX) or death domain-associated protein (DAXX) gene mutations, or copy number variations, more often display alpha cell characteristics. Conversely, NF-PanNETs with beta cell characteristics often lack these unfavorable biomarkers. Alternative lengthening of telomeres, transcription factor protein expression, and possibly DNA methylation can be assessed in endoscopic ultrasound-guided tumor biopsies. Prospective studies focusing on cell-of-origin and epigenetic profile-driven decision making prior to surgery are likely to be routinely implemented into clinical practice in the near future. © 2021 The Authors. The Journal of Pathology published by John Wiley & Sons, Ltd. on behalf of The Pathological Society of Great Britain and Ireland.

Cell maturation: Hallmarks, triggers, and manipulation

How cells become specialized, or "mature," is important for cell and developmental biology. While maturity is usually deemed a terminal fate, it may be more helpful to consider maturation not as a switch but as a dynamic continuum of adaptive phenotypic states set by genetic and environment programing. The hallmarks of maturity comprise changes in anatomy (form, gene circuitry, and interconnectivity) and physiology (function, rhythms, and proliferation) that confer adaptive behavior. We discuss efforts to harness their chemical (nutrients, oxygen, and growth factors) and physical (mechanical, spatial, and electrical) triggers in vitro and in vivo and how maturation strategies may support disease research and regenerative medicine.

Alpha-to-beta cell trans-differentiation for treatment of diabetes

Diabetes mellitus is a significant cause of morbidity and mortality in the United States and worldwide. According to the CDC, in 2017, ∼34.2 million of the American population had diabetes. Also, in 2017, diabetes was the seventh leading cause of death and has become the number one biomedical financial burden in the United States. Insulin replacement therapy and medications that increase insulin secretion and improve insulin sensitivity are the main therapies used to treat diabetes. Unfortunately, there is currently no radical cure for the different types of diabetes. Loss of β cell mass is the end result that leads to both type 1 and type 2 diabetes. In the past decade, there has been an increased effort to develop therapeutic strategies to replace the lost β cell mass and restore insulin secretion. α cells have recently become an attractive target for replacing the lost β cell mass, which could eventually be a potential strategy to cure diabetes. This review highlights the advantages of using α cells as a source for generating new β cells, the various investigative approaches to convert α cells into insulin-producing cells, and the future prospects and problems of this promising diabetes therapeutic strategy.

Stem/progenitor cells in normal physiology and disease of the pancreas

Though embryonic pancreas progenitors are well characterised, the existence of stem/progenitor cells in the postnatal mammalian pancreas has been long debated, mainly due to contradicting results on regeneration after injury or disease in mice. Despite these controversies, sequencing advancements combined with lineage tracing and organoid technologies indicate that homeostatic and trigger-induced regenerative responses in mice could occur. The presence of putative progenitor cells in the adult pancreas has been proposed during homeostasis and upon different stress challenges such as inflammation, tissue damage and oncogenic stress. More recently, single cell transcriptomics has revealed a remarkable heterogeneity in all pancreas cell types, with some cells showing the signature of potential progenitors. In this review we provide an overview on embryonic and putative adult pancreas progenitors in homeostasis and disease, with special emphasis on in vitro culture systems and scRNA-seq technology as tools to address the progenitor nature of different pancreatic cells.

Acute hypoxia effects on Keap1/Nrf2 (Mafs)-GST pathway related oxidative metabolism in muscle of Japanese flounder (Paralichthys olivaceus)

Acute hypoxia can aggravate the oxidation metabolism of fish muscle tissue. However, the molecular mechanism of oxidative metabolism in fish muscle under acute hypoxia is not very clear. We carried out effects of a typical oxidative metabolism pathway Keap1/Nrf2 (MafG)-GST on muscle oxidative metabolism of Japanese flounder (Paralichthys olivaceus) during acute hypoxia stimulation (1.65 ± 0.05 mg/L; 1 h, 3 h, 6 h, 12 h, 24 h) and reoxygenation (7.30 ± 0.08 mg/L; R12 h, R24 h, R48 h). The mRNAs of Nrf2 and GST in skeletal muscle were found co-existent, and their expressions were significant increase in 3 h and 6 h. The methylation level of CpG island1 in Nrf2 promoter, whose minimum value appeared at 3 h hypoxia treatment group, was affected by acute hypoxia, and it was negatively correlated with Nrf2 expression. The result suggests that environmental factors may regulate gene expression by epigenetic modification. Dual-luciferase reporter assay showed that GST gene was activated by transcription factor Nrf2, whose transcriptional activation binding region in GST promoter was antioxidant response element located near -980 and -852 sites, and Keap1 and MafG were Nrf2 antagonistic and synergistic factor, respectively. Furthermore, the GST activity changed with hypoxia and reoxygenation treatment in muscle, where other oxidative stress factor (MDA), antioxidant factors (T-AOC, GSH) and antioxidant enzyme activities (GST, SOD, CAT) were also changed. The results of MDA and T-AOC being further different between its hypoxia and normoxia groups (P < 0.05) at 6 h demonstrated that hypoxia stimulation lasting for 6 h would deeply affect Japanese flounder. The study illustrated that Japanese flounder responded to acute hypoxia in multiple metabolic levels by changing methylation status and transcription factor activation. It is significant to understand oxidative metabolic mechanism, analyze organism stress response and promote the scientific development of aquaculture.

The Transcriptome and Epigenome Reveal Novel Changes in Transcription Regulation During Pancreatic Rat Islet Maturation

Islet function is critical for normal glucose homeostasis. Unlike adult β cells, fetal and neonatal islets are more proliferative and have decreased insulin secretion in response to stimuli. However, the underlying mechanisms governing functional maturity of islets have not been completely elucidated. Pancreatic islets comprise different cell types. The microenvironment of islets and interactions between these cell types are critical for β-cell development and maturation. Thus, the study of intact islets is optimal to identify novel molecular mechanisms controlling islet functional development. Transcriptomes and genome-wide histone landscapes of H3K4me3, H3K27me3, and H3K27Ac from intact islets isolated from 2- and 10-week-old Sprague-Dawley rats were integrated to elucidate genes and pathways modulating islet development, as well as the contribution of epigenetic regulation. A total of 4489 differentially expressed genes were identified; 2289 and 2200 of them were up- and down-regulated in 10-week islets, respectively. Ingenuity Pathway Analysis revealed critical pathways regulating functional maturation of islets, including nutrient sensing, neuronal function, immune function, cell replication, and extracellular matrix. Furthermore, we identified significant changes in enrichment of H3K4me3, H3K27me3, and H3K27Ac marks, which correlated with expression changes of genes critical for islet function. These histone marks were enriched at critical transcription factor-binding motifs, such as Hoxa9, C/EBP-β, Gata1, Foxo1, E2f1, E2f3, and Mafb. In addition, our chromatin immunoprecipitation sequencing data revealed multiple potential bivalent genes whose poised states changed with maturation. Collectively, our current study identified critical novel pathways for mature islet function and suggested a role for histone modifications in regulating islet development and maturation.

Sex-biased islet β cell dysfunction is caused by the MODY MAFA S64F variant by inducing premature aging and senescence in males

A heterozygous missense mutation of the islet β cell-enriched MAFA transcription factor (p.Ser64Phe [S64F]) is found in patients with adult-onset β cell dysfunction (diabetes or insulinomatosis), with men more prone to diabetes than women. This mutation engenders increased stability to the unstable MAFA protein. Here, we develop a S64F MafA mouse model to determine how β cell function is affected and find sex-dependent phenotypes. Heterozygous mutant males (MafAS64F/+) display impaired glucose tolerance, while females are slightly hypoglycemic with improved blood glucose clearance. Only MafAS64F/+ males show transiently higher MafA protein levels preceding glucose intolerance and sex-dependent changes to genes involved in Ca2+ signaling, DNA damage, aging, and senescence. MAFAS64F production in male human β cells also accelerate cellular senescence and increase senescence-associated secretory proteins compared to cells expressing MAFAWT. These results implicate a conserved mechanism of accelerated islet aging and senescence in promoting diabetes in MAFAS64F carriers in a sex-biased manner.

Combinatorial transcription factor profiles predict mature and functional human islet α and β cells

Islet-enriched transcription factors (TFs) exert broad control over cellular processes in pancreatic α and β cells, and changes in their expression are associated with developmental state and diabetes. However, the implications of heterogeneity in TF expression across islet cell populations are not well understood. To define this TF heterogeneity and its consequences for cellular function, we profiled more than 40,000 cells from normal human islets by single-cell RNA-Seq and stratified α and β cells based on combinatorial TF expression. Subpopulations of islet cells coexpressing ARX/MAFB (α cells) and MAFA/MAFB (β cells) exhibited greater expression of key genes related to glucose sensing and hormone secretion relative to subpopulations expressing only one or neither TF. Moreover, all subpopulations were identified in native pancreatic tissue from multiple donors. By Patch-Seq, MAFA/MAFB-coexpressing β cells showed enhanced electrophysiological activity. Thus, these results indicate that combinatorial TF expression in islet α and β cells predicts highly functional, mature subpopulations.

NEUROD1 Is Required for the Early α and β Endocrine Differentiation in the Pancreas

Diabetes is a metabolic disease that involves the death or dysfunction of the insulin-secreting β cells in the pancreas. Consequently, most diabetes research is aimed at understanding the molecular and cellular bases of pancreatic development, islet formation, β-cell survival, and insulin secretion. Complex interactions of signaling pathways and transcription factor networks regulate the specification, growth, and differentiation of cell types in the developing pancreas. Many of the same regulators continue to modulate gene expression and cell fate of the adult pancreas. The transcription factor NEUROD1 is essential for the maturation of β cells and the expansion of the pancreatic islet cell mass. Mutations of the Neurod1 gene cause diabetes in humans and mice. However, the different aspects of the requirement of NEUROD1 for pancreas development are not fully understood. In this study, we investigated the role of NEUROD1 during the primary and secondary transitions of mouse pancreas development. We determined that the elimination of Neurod1 impairs the expression of key transcription factors for α- and β-cell differentiation, β-cell proliferation, insulin production, and islets of Langerhans formation. These findings demonstrate that the Neurod1 deletion altered the properties of α and β endocrine cells, resulting in severe neonatal diabetes, and thus, NEUROD1 is required for proper activation of the transcriptional network and differentiation of functional α and β cells.

Redox-dependent and independent effects of thioredoxin interacting protein

Thioredoxin interacting protein (TXNIP) is an important physiological inhibitor of the thioredoxin (TXN) redox system in cells. Regulation of TXNIP expression and/or activity not only plays an important role in redox regulation but also exerts redox-independent physiological effects that exhibit direct pathophysiological consequences including elevated inflammatory response, aberrant glucose metabolism, cellular senescence and apoptosis, cellular immunity, and tumorigenesis. This review provides a brief overview of the current knowledge concerning the redox-dependent and independent roles of TXNIP and its relevance to various disease states. The implications for the therapeutic targeting of TXNIP will also be discussed.

Metabolic Adaptations to Pregnancy in Healthy and Gestational Diabetic Pregnancies: The Pancreas - Placenta Axis

Normal pregnancy is associated with increased insulin resistance as a metabolic adaptation to the nutritional demands of the placenta and fetus, and this is amplified in obese mothers. Insulin resistance is normally compensated for by an adaptive increase in pancreatic β-cell mass together with enhanced glucose-stimulated insulin release. Placentally-derived hormones and growth factors are central to the altered pancreatic morphology and function. A failure of β-cells to undergo adaptive change after the first trimester has been linked with gestational diabetes. In the pregnant mouse, an increase in β-cell replication contributes to a 2-3-fold increase in mass peaking in late gestation, depending on the proliferation of existing β-cells, the differentiation of resident progenitor β-cells, or islet cell transdifferentiation. Using mouse models and human studies placenta- and islet of Langerhans-derived molecules have been identified that are likely to contribute to the metabolic adaptations to pregnancy and whose physiology is altered in the obese, glucose-intolerant mother. Maternal obesity during pregnancy can create a pro-inflammatory environment that can disrupt the response of the β-cells to the endocrine signals of pregnancy and limit the adaptive changes in β-cell mass and function, resulting in an increased risk of gestational diabetes.

Generative modeling of single-cell time series with PRESCIENT enables prediction of cell trajectories with interventions

Existing computational methods that use single-cell RNA-sequencing (scRNA-seq) for cell fate prediction do not model how cells evolve stochastically and in physical time, nor can they predict how differentiation trajectories are altered by proposed interventions. We introduce PRESCIENT (Potential eneRgy undErlying Single Cell gradIENTs), a generative modeling framework that learns an underlying differentiation landscape from time-series scRNA-seq data. We validate PRESCIENT on an experimental lineage tracing dataset, where we show that PRESCIENT is able to predict the fate biases of progenitor cells in hematopoiesis when accounting for cell proliferation, improving upon the best-performing existing method. We demonstrate how PRESCIENT can simulate trajectories for perturbed cells, recovering the expected effects of known modulators of cell fate in hematopoiesis and pancreatic β cell differentiation. PRESCIENT is able to accommodate complex perturbations of multiple genes, at different time points and from different starting cell populations, and is available at https://github.com/gifford-lab/prescient .

The MafA-target gene PPP1R1A regulates GLP1R-mediated amplification of glucose-stimulated insulin secretion in β-cells

The amplification of glucose-stimulated insulin secretion (GSIS) through incretin signaling is critical for maintaining physiological glucose levels. Incretins, like glucagon-like peptide 1 (GLP1), are a target of type 2 diabetes drugs aiming to enhance insulin secretion. Here we show that the protein phosphatase 1 inhibitor protein 1A (PPP1R1A), is expressed in β-cells and that its expression is reduced in dysfunctional β-cells lacking MafA and upon acute MafA knock down. MafA is a central regulator of GSIS and β-cell function. We observed a strong correlation of MAFA and PPP1R1A mRNA levels in human islets, moreover, PPP1R1A mRNA levels were reduced in type 2 diabetic islets and positively correlated with GLP1-mediated GSIS amplification. PPP1R1A silencing in INS1 (832/13) β-cells impaired GSIS amplification, PKA-target protein phosphorylation, mitochondrial coupling efficiency and also the expression of critical β-cell marker genes like MafA, Pdx1, NeuroD1 and Pax6. Our results demonstrate that the β-cell transcription factor MafA is required for PPP1R1A expression and that reduced β-cell PPP1R1A levels impaired β-cell function and contributed to β-cell dedifferentiation during type 2 diabetes. Loss of PPP1R1A in type 2 diabetic β-cells may explains the unresponsiveness of type 2 diabetic patients to GLP1R-based treatments.

ZIGIR, a Granule-Specific Zn2+ Indicator, Reveals Human Islet α Cell Heterogeneity

Numerous mammalian cells contain abundant Zn²⁺ in their secretory granules, yet available Zn²⁺ sensors lack the desired specificity and sensitivity for imaging granular Zn²⁺. We developed a fluorescent zinc granule indicator, ZIGIR, that possesses numerous desired properties for live cell imaging, including >100-fold fluorescence enhancement, membrane permeability, and selective enrichment to acidic granules. The combined advantages endow ZIGIR with superior sensitivity and specificity for imaging granular Zn²⁺. ZIGIR enables separation of heterogenous β cells based on their insulin content and sorting of mouse islets into pure α cells and β cells. In human islets, ZIGIR facilitates sorting of endocrine cells into highly enriched α cells and β cells, reveals unexpectedly high Zn²⁺ activity in the somatostatin granule of some δ cells, and uncovers variation in the glucagon content among human α cells. We expect broad applications of ZIGIR for studying Zn²⁺ biology and Zn²⁺-rich secretory granules and for engineering β cells with high insulin content for treating diabetes.

Scrt1, a transcriptional regulator of β-cell proliferation identified by differential chromatin accessibility during islet maturation

Glucose-induced insulin secretion, a hallmark of mature β-cells, is achieved after birth and is preceded by a phase of intense proliferation. These events occurring in the neonatal period are decisive for establishing an appropriate functional β-cell mass that provides the required insulin throughout life. However, key regulators of gene expression involved in functional maturation of β-cells remain to be elucidated. Here, we addressed this issue by mapping open chromatin regions in newborn versus adult rat islets using the ATAC-seq assay. We obtained a genome-wide picture of chromatin accessible sites (~ 100,000) among which 20% were differentially accessible during maturation. An enrichment analysis of transcription factor binding sites identified a group of transcription factors that could explain these changes. Among them, Scrt1 was found to act as a transcriptional repressor and to control β-cell proliferation. Interestingly, Scrt1 expression was controlled by the transcriptional repressor RE-1 silencing transcription factor (REST) and was increased in an in vitro reprogramming system of pancreatic exocrine cells to β-like cells. Overall, this study led to the identification of several known and unforeseen key transcriptional events occurring during β-cell maturation. These findings will help defining new strategies to induce the functional maturation of surrogate insulin-producing cells.

Cell Cycle Regulation of the Pdx1 Transcription Factor in Developing Pancreas and Insulin-Producing β-Cells

Current evidence indicates that proliferating β-cells express lower levels of some functional cell identity genes, suggesting that proliferating cells are not optimally functional. Pdx1 is important for β-cell specification, function, and proliferation and is mutated in monogenic forms of diabetes. However, its regulation during the cell cycle is unknown. Here we examined Pdx1 protein expression in immortalized β-cells, maternal mouse islets during pregnancy, and mouse embryonic pancreas. We demonstrate that Pdx1 localization and protein levels are highly dynamic. In nonmitotic cells, Pdx1 is not observed in constitutive heterochromatin, nucleoli, or most areas containing repressive epigenetic marks. At prophase, Pdx1 is enriched around the chromosomes before Ki67 coating of the chromosome surface. Pdx1 uniformly localizes in the cytoplasm at prometaphase and becomes enriched around the chromosomes again at the end of cell division, before nuclear envelope formation. Cells in S phase have lower Pdx1 levels than cells at earlier cell cycle stages, and overexpression of Pdx1 in INS-1 cells prevents progression toward G2, suggesting that cell cycle-dependent regulation of Pdx1 is required for completion of mitosis. Together, we find that Pdx1 localization and protein levels are tightly regulated throughout the cell cycle. This dynamic regulation has implications for the dichotomous role of Pdx1 in β-cell function and proliferation.

Functional maturation of immature β cells: A roadblock for stem cell therapy for type 1 diabetes

Type 1 diabetes mellitus (T1DM) is a chronic autoimmune disease caused by the specific destruction of pancreatic islet β cells and is characterized as the absolute insufficiency of insulin secretion. Current insulin replacement therapy supplies insulin in a non-physiological way and is associated with devastating complications. Experimental islet transplantation therapy has been proven to restore glucose homeostasis in people with severe T1DM. However, it is restricted by many factors such as severe shortage of donor sources, progressive loss of donor cells, high cost, etc. As pluripotent stem cells have the potential to give rise to all cells including islet β cells in the body, stem cell therapy for diabetes has attracted great attention in the academic community and the general public. Transplantation of islet β-like cells differentiated from human pluripotent stem cells (hPSCs) has the potential to be an excellent alternative to islet transplantation. In stem cell therapy, obtaining β cells with complete insulin secretion in vitro is crucial. However, after much research, it has been found that the β-like cells obtained by in vitro differentiation still have many defects, including lack of adult-type glucose stimulated insulin secretion, and multi-hormonal secretion, suggesting that in vitro culture does not allows for obtaining fully mature β-like cells for transplantation. A large number of studies have found that many transcription factors play important roles in the process of transforming immature to mature human islet β cells. Furthermore, PDX1, NKX6.1, SOX9, NGN3, PAX4, etc., are important in inducing hPSC differentiation in vitro. The absent or deficient expression of any of these key factors may lead to the islet development defect in vivo and the failure of stem cells to differentiate into genuine functional β-like cells in vitro. This article reviews β cell maturation in vivo and in vitro and the vital roles of key molecules in this process, in order to explore the current problems in stem cell therapy for diabetes.

Functional maturation of immature β cells: A roadblock for stem cell therapy for type 1 diabetes

Type 1 diabetes mellitus (T1DM) is a chronic autoimmune disease caused by the specific destruction of pancreatic islet β cells and is characterized as the absolute insufficiency of insulin secretion. Current insulin replacement therapy supplies insulin in a non-physiological way and is associated with devastating complications. Experimental islet transplantation therapy has been proven to restore glucose homeostasis in people with severe T1DM. However, it is restricted by many factors such as severe shortage of donor sources, progressive loss of donor cells, high cost, etc. As pluripotent stem cells have the potential to give rise to all cells including islet β cells in the body, stem cell therapy for diabetes has attracted great attention in the academic community and the general public. Transplantation of islet β-like cells differentiated from human pluripotent stem cells (hPSCs) has the potential to be an excellent alternative to islet transplantation. In stem cell therapy, obtaining β cells with complete insulin secretion in vitro is crucial. However, after much research, it has been found that the β-like cells obtained by in vitro differentiation still have many defects, including lack of adult-type glucose stimulated insulin secretion, and multi-hormonal secretion, suggesting that in vitro culture does not allows for obtaining fully mature β-like cells for transplantation. A large number of studies have found that many transcription factors play important roles in the process of transforming immature to mature human islet β cells. Furthermore, PDX1, NKX6.1, SOX9, NGN3, PAX4, etc., are important in inducing hPSC differentiation in vitro. The absent or deficient expression of any of these key factors may lead to the islet development defect in vivo and the failure of stem cells to differentiate into genuine functional β-like cells in vitro. This article reviews β cell maturation in vivo and in vitro and the vital roles of key molecules in this process, in order to explore the current problems in stem cell therapy for diabetes.

p43, a Truncated Form of Thyroid Hormone Receptor α, Regulates Maturation of Pancreatic β Cells

P43 is a truncated form of thyroid hormone receptor α localized in mitochondria, which stimulates mitochondrial respiratory chain activity. Previously, we showed that deletion of p43 led to reduction of pancreatic islet density and a loss of glucose-stimulated insulin secretion in adult mice. The present study was designed to determine whether p43 was involved in the processes of β cell development and maturation. We used neonatal, juvenile, and adult p43-/- mice, and we analyzed the development of β cells in the pancreas. Here, we show that p43 deletion affected only slightly β cell proliferation during the postnatal period. However, we found a dramatic fall in p43-/- mice of MafA expression (V-Maf Avian Musculoaponeurotic Fibrosarcoma Oncogene Homolog A), a key transcription factor of beta-cell maturation. Analysis of the expression of antioxidant enzymes in pancreatic islet and 4-hydroxynonenal (4-HNE) (a specific marker of lipid peroxidation) staining revealed that oxidative stress occurred in mice lacking p43. Lastly, administration of antioxidants cocktail to p43-/- pregnant mice restored a normal islet density but failed to ensure an insulin secretion in response to glucose. Our findings demonstrated that p43 drives the maturation of β cells via its induction of transcription factor MafA during the critical postnatal window.

SIX2 and SIX3 coordinately regulate functional maturity and fate of human pancreatic β cells

The physiological functions of many vital tissues and organs continue to mature after birth, but the genetic mechanisms governing this postnatal maturation remain an unsolved mystery. Human pancreatic β cells produce and secrete insulin in response to physiological cues like glucose, and these hallmark functions improve in the years after birth. This coincides with expression of the transcription factors SIX2 and SIX3, whose functions in native human β cells remain unknown. Here, we show that shRNA-mediated SIX2 or SIX3 suppression in human pancreatic adult islets impairs insulin secretion. However, transcriptome studies revealed that SIX2 and SIX3 regulate distinct targets. Loss of SIX2 markedly impaired expression of genes governing β-cell insulin processing and output, glucose sensing, and electrophysiology, while SIX3 loss led to inappropriate expression of genes normally expressed in fetal β cells, adult α cells, and other non-β cells. Chromatin accessibility studies identified genes directly regulated by SIX2. Moreover, β cells from diabetic humans with impaired insulin secretion also had reduced SIX2 transcript levels. Revealing how SIX2 and SIX3 govern functional maturation and maintain developmental fate in native human β cells should advance β-cell replacement and other therapeutic strategies for diabetes.

Retinol-Binding Protein 4 Activates STRA6, Provoking Pancreatic β-Cell Dysfunction in Type 2 Diabetes

Pancreatic β-cell dysfunction plays a decisive role in the progression of type 2 diabetes. Retinol-binding protein 4 (RBP4) is a prominent adipokine in type 2 diabetes, although its effect on β-cell function remains elusive, and the underlying mechanisms are unknown. Here, we found that elevated circulating RBP4 levels were inversely correlated with pancreatic β-cell function in db/db mice across different glycemic stages. RBP4 directly suppressed glucose-stimulated insulin secretion (GSIS) in primary isolated islets and INS-1E cells in a dose- and time-dependent manner. RBP4 transgenic (RBP4-Tg) overexpressing mice showed a dynamic decrease of GSIS, which appeared as early as 8 weeks old, preceding the impairment of insulin sensitivity and glucose tolerance. Islets isolated from RBP4-Tg mice showed a significant decrease of GSIS. Mechanistically, we demonstrated that the stimulated by retinoic acid 6 (STRA6), RBP4's only known specific membrane receptor, is expressed in β-cells and mediates the inhibitory effect of RBP4 on insulin synthesis through the Janus kinase 2/STAT1/ISL-1 pathway. Moreover, decreasing circulating RBP4 level could effectively restore β-cell dysfunction and ameliorate hyperglycemia in db/db mice. These observations revealed a role of RBP4 in pancreatic β-cell dysfunction, which provides new insight into the diabetogenic effect of RBP4.