Pancreatic Beta-cell Differentiation Research Articles

Controlling spheroid attachment improves pancreatic beta cell differentiation from human iPS cells.

Regenerative medicine using human induced pluripotent stem cells (hiPSCs) is available for treating type 1 diabetes; however, the efficiency and maturation of hiPSC differentiation into pancreatic beta cells requires improvement. Various protocols, including three-dimensional (3D) culture, have been developed to improve differentiation efficiency and maturation. Several methods for 3D culture have been reported; however, they require costly and complicated equipment, special materials, and complicated operations. To solve these problems, we developed a simple 3D culture method under static conditions using a cyclo-olefin polymer (COP) characterized by high moisture barrier properties, low surface energy, and hydrophobicity. Using this 3D method and our simple and low-cost protocol, we found that differentiation into the definitive endoderm (DE) was better when the spheroids were attached. Therefore, upon the addition of Y-27632, attached spheroids with unique shapes and cavities were formed, and the differentiation efficiency into DE increased. During DE differentiation, the attachment of spheroids to the substrate and their subsequent floating improved differentiation efficiency. We found that the amount of C-peptide in spheroids differentiated using COP dishes was greater than that in rotary culture. Furthermore, INSULIN was highly expressed in areas with low cell density, suggesting that the unique shape of the spheroids made from COP dishes improved differentiation efficiency. Our study suggests that a device-free, simple 3D culture method that controls spheroid attachment improves the efficiency of hiPSC differentiation into pancreatic beta cells.

Differentiation of Pancreatic Beta Cells: Dual Acting of Inflammatory Factors.

In the past decades, scientists have made outstanding efforts to treat diabetes. However, diabetes treatment is still far from satisfactory due to the complex nature of the disease and the challenges encountered in resolving it. Inflammatory factors are key regulators of the immune system's response to pathological insults, organ neogenesis, rejuvenation of novel cells to replace injured cells and overwhelming disease conditions. Currently, the available treatments for type 1 diabetes include daily insulin injection, pancreatic beta cell or tissue transplantation, and gene therapy. Cell therapy, exploiting differentiation, and reprogramming various types of cells to generate pancreatic insulin-producing cells are novel approaches for the treatment of type 1 diabetes. A better understanding of the inflammatory pathways offers valuable and improved therapeutic options to provide more advanced and better treatments for diabetes. In this review, we investigated different types of inflammatory factors that participate in the pathogenesis of type 1 diabetes, their possible dual impacts on the differentiation, reprogramming, and fusion of other stem cell lines into pancreatic insulin-producing beta cells, and the possibility of applying these factors to improve the treatment of this disease.

LBSUN310 Developmental Programming: Gestational Bpa Treatment Leads To Pancreatic Beta Cell Compromise

Abstract Developmental exposure to endocrine disrupting chemicals (EDC) such as bisphenol A (BPA) have been shown to be associated with many metabolic defects in humans. Studies in animals have documented detrimental effects of fetal exposure to BPA on metabolic variables such as insulin resistance, adiposity, and cardiac function. For instance, developmental exposure of sheep to bisphenol A (BPA), a ubiquitously present EDC, causes insulin resistance and compensatory hyperinsulinemia but the underlying mechanism of it is not fully understood. To determine if pancreatic hyperplasia or hypertrophy contributes to the hyperinsulinemic status and the ontogeny of these effects, pregnant Suffolk sheep were administered daily subcutaneous injections of BPA (0. 05, 0 .5 or 5 mg/Kg BW) in corn oil from days (D) 30-90 of gestation (term 147 days). Controls received corn oil during the same period. Pancreas were taken at Day 65 and 90 of gestation from control and 0.5mg/kg BPA (environmental exposure level)-treated female fetuses, and control and prenatal BPA-treated female offspring at 2 years of age (all 3 doses) during synchronized follicular phase of the cycle. Immunohistochemistry was used to determine beta cell number, size, and islet insulin content. In addition, to determine if the pancreas was fibrotic, islet collagen content was determined by Picro Sirius red staining and whole pancreas collagen content was measured with scroll collagen assay. Data were analyzed by ANOVA (Y2) and Students's t-test (D65 and D90), and magnitude of response by Cohen's Effect Size analysis. Findings showed large magnitude reduction of islet insulin content at day 65, significant decrease in islet insulin and beta cell count at D90 along with large magnitude decrease in pancreas/fetal weight. In contrast, in the Y2 sheep prenatal BPA treatment induced a large magnitude decrease in beta cell count (0. 05mg/kg dose group), a large magnitude increase in islet insulin content (5mg/kg dose group) and large magnitude increase in islet collagen content (all 3 BPA doses). The decrease in insulin in the D65 and D90 sheep along with the decrease in beta cells and pancreas/fetal weight at D90 indicates adverse developmental impact of BPA exposure on pancreatic beta cell differentiation. Increase in collagen accumulation in Y2 sheep likely contributes to the beta cell loss reflected as decrease in beta cell number seen in 0. 05 mg/kg dose of BPA. Absence of beta cell loss in 0.5 and 5mg/kg dose in the face of increased collagen is consistent with the nonmonotonic responses these EDCs manifest. Taken together, these results highlight the risks posed by developmental exposure to BPA on beta cell function and the corresponding risk for beta cell loss as animals age. Supported by NIH R01 grants ES016541 and ES030374 Presentation: Sunday, June 12, 2022 12:30 p.m. - 2:30 p.m.

TET1 dioxygenase is required for FOXA2-associated chromatin remodeling in pancreatic beta-cell differentiation

Existing knowledge of the role of epigenetic modifiers in pancreas development has exponentially increased. However, the function of TET dioxygenases in pancreatic endocrine specification remains obscure. We set out to tackle this issue using a human embryonic stem cell (hESC) differentiation system, in which TET1/TET2/TET3 triple knockout cells display severe defects in pancreatic β-cell specification. The integrative whole-genome analysis identifies unique cell-type-specific hypermethylated regions (hyper-DMRs) displaying reduced chromatin activity and remarkable enrichment of FOXA2, a pioneer transcription factor essential for pancreatic endoderm specification. Intriguingly, TET depletion leads to significant changes in FOXA2 binding at the pancreatic progenitor stage, in which gene loci with decreased FOXA2 binding feature low levels of active chromatin modifications and enriches for bHLH motifs. Transduction of full-length TET1 but not the TET1-catalytic-domain in TET-deficient cells effectively rescues β-cell differentiation accompanied by restoring PAX4 hypomethylation. Taking these findings together with the defective generation of functional β-cells upon TET1-inactivation, our study unveils an essential role of TET1-dependent demethylation in establishing β-cell identity. Moreover, we discover a physical interaction between TET1 and FOXA2 in endodermal lineage intermediates, which provides a mechanistic clue regarding the complex crosstalk between TET dioxygenases and pioneer transcription factors in epigenetic regulation during pancreas specification.

Enhancement of the Differentiation Potential of Adipose Tissue-Derived Mesenchymal Stem Cells into Insulin-Producing Cells Using Flavonoid Compounds in Diabetic Rats

Background: Differentiation of stem cells into pancreatic beta cells is a global challenge in reconstructive medicine for the treatment of diabetes. Studies have shown that compounds derived from walnut green skin can differentiate stem cells into beta cells. Flavonoid compounds appear to be the main cause of this differentiation. Objectives: This study examined the effect of flavonoid compounds in walnut green skin on the differentiation of pancreatic beta cells. Methods: The present study conducted the differentiation of adipose tissue-derived mesenchymal stem cells (AD-MSCs) into insulin-producing cells under flavonoid extract at doses of 50 and 100 mg/ml for three weeks. For diabetic rats, streptozotocin was injected intraperitoneally at a dose of 60 mg/kg. To evaluate cell differentiation, this study utilized morphology, dithizone (DTZ) staining, insulin-proinsulin production, insulin beta-receptor by the immunofluorescence method, and insulin measurement by the ELISA method. Serum glucose, cholesterol, and lipids were measured by enzymatic colorimetric, enzyme kit, and autoanalyzer, respectively. The expression of pancreatic cell-specific genes, including Pancreatic and Duodenal Homeobox 1 (Pdx1) and Neurogenin-3 (Ngn3), was also assessed by real-time PCR. Results: Differentiated cells transformed from spindle-shaped to circular or clustered cells under the influence of flavonoid compounds with their specific DTZ staining being positive. The expression of insulin-proinsulin markers, beta receptors, and insulin secretion was also confirmed. Decreased blood lipids and glucose, as well as increased expression of Pdx1 and Ngn3 insulin-producing genes, were significant in the treatment groups (P<0.05). Conclusion: The findings showed that flavonoid compounds could effectively induce the differentiation of AD-MSCs into insulin-producing cells.

Generation of an hiPSC-1 knock-in line expressing TY1-tagged MNX1-protein together with mScarlet

MNX1 encodes a homeobox transcription factor with conserved embryonic requirements in spinal motor neuron formation and pancreatic beta-cell differentiation. Mutations in MNX1 are associated with dominantly inherited Currarino syndrome and neonatal diabetes. To better understand embryonic MNX1 functions we generated an hiPSC-1 knock-in line heterozygously expressing MNX1 C-terminally tagged with 2xTY1 together with a T2A-separated red fluorescent reporter mScarlet. The TY1 epitope tag was introduced to enable immunoprecipitation based analyses on molecular MNX1 interactions and mScarlet was included for enrichment of MNX1 expressing cell populations. This cell line shows normal karyotype, pluripotency marker expression and differentiation potential in vitro.

ISX-9 manipulates endocrine progenitor fate revealing conserved intestinal lineages in mouse and human organoids

ObjectiveEnteroendocrine cells (EECs) survey the gut luminal environment and coordinate hormonal, immune and neuronal responses to it. They exhibit well-characterised physiological roles ranging from the control of local gut function to whole body metabolism, but little is known regarding the regulatory networks controlling their differentiation, especially in the human gut. The small molecule isoxazole-9 (ISX-9) has been shown to stimulate neuronal and pancreatic beta-cell differentiation, both closely related to EEC differentiation. Our aim was to use ISX-9 as a tool to explore EEC differentiation. MethodsWe investigated the effects of ISX-9 on EEC differentiation in mouse and human intestinal organoids, using real-time quantitative polymerase chain reaction (RT-qPCR), fluorescent-activated cell sorting, immunostaining and single-cell RNA sequencing. ResultsISX-9 increased the number of neurogenin3-RFP (Ngn3)-positive endocrine progenitor cells and upregulated NeuroD1 and Pax4, transcription factors that play roles in mouse EEC specification. Single-cell analysis showed induction of Pax4 expression in a developmentally late Ngn3+ population of cells and potentiation of genes associated with progenitors biased toward serotonin-producing enterochromaffin (EC) cells. Further, we observed enrichment of organoids with functional EC cells that was partly dependent on stimulation of calcium signalling in a population of cells residing outside the crypt base. Inducible Pax4 overexpression, in ileal organoids, uncovered its importance as a component of early human endocrine specification and highlighted the potential existence of two major endocrine lineages, the early appearing enterochromaffin lineage and the later developing peptidergic lineage which contains classical gut hormone cell types. ConclusionOur data provide proof-of-concept for the controlled manipulation of specific endocrine lineages with small molecules, whilst also shedding new light on human EEC differentiation and its similarity to the mouse. Given their diverse roles, understanding endocrine lineage plasticity and its control could have multiple therapeutic implications.

Alternative Variants of Pax4 Human Transcription Factor: Comparative Transcriptional Activity

MODY is a group of genetically and clinically heterogeneous forms of diabetes characterized by auto-somal dominant inheritance and is subdivided in 13 subtypes dependent on the gene involved. The subtype MODY9 is a very rare form caused by mutations in the gene encoding the PAX4 transcription factor which is engaged in differentiation of pancreatic beta-cells. PAX4 contains two DNA-binding domains-Paired and Homeo. Expression of the human PAX4 gene is tissue-specific. The alternatively spliced mRNA variants encode for protein isoforms which differ within their N- and C-terminal regions. In this study, the transcriptional activities of the human PAX4 variants, both known and new ones, were determined. The full-length PAX4 containing intact DNA-binding domains was found to have maximal activity in transient expression system of the firefly luciferase reporter gene under control of the insulin promoter in HEK293 cells. The transcriptional activity is significantly reduced in the variants lacking eight N-terminal amino acid residues and/or variants whose Homeo domain is truncated from the C-terminus. Similar data were obtained with the glucagon promoter reporter system. The aberrant PAX4 variants were shown to retain stability and nuclear localization.

Role of TGF-β/Smad Pathway in the Transcription of Pancreas-Specific Genes During Beta Cell Differentiation.

Autoimmune destruction of pancreatic beta cells causes absolute insulin deficiency and results in type 1 diabetes mellitus (T1DM). The substitution of healthy pancreatic beta cells for damaged cells would be the ideal treatment for T1DM; thus, the generation of pancreatic beta cells from adult stem cells represents an attractive avenue for research. In this study, a cocktail of factors was used to induce the differentiation of pancreatic beta cells from mesenchymal stem cells (MSCs). The differentiation program was divided into five stages, and the roles of the cocktail factors used during each stage were systematically elucidated. Activin A was found to phosphorylate Smad2 and Smad3 in stage III, thereby activating the TGF-β/Smad pathway. Meanwhile, the endocrine-specific transcription factor, Ngn3, and the pancreas-specific miRNAs, miR-375 and miR-26a, were dramatically elevated in stage III. We next demonstrated that Smad4, an important transcription factor in the TGF-β/Smad pathway, could bind to the promoter sequences of target genes and enhance their transcription to initiate the differentiation of beta cells. Use of SB-431542, an inhibitor of the TGF-β/Smad pathway, demonstrated in vivo and in vitro that this pathway plays a critical role in the production of pancreatic beta cells and in modulating insulin secretion. Thus, the TGF-β/Smad pathway is involved in the production of beta cells from adult stem cells by enhancing the transcription of Ngn3, miR-375, and miR-26a. These findings further underline the significant promise of cell transplant therapies for type 1 diabetes mellitus.

Screening the RFX6-DNA binding domain for potential genetic variants in patients with type 2 diabetes.

BACKGROUNDThe regulatory factor X6 (RFX6), a member of regulatory factor X family, is known to play a key role in the development and differentiation of pancreatic beta cells as well as insulin production and secretion. However, the potential role of RFX6 in type 2 diabetes (T2D) is still unclear.AIMRecent studies have indicated that RFX6 binding to DNA could be disrupted in diabetes. Therefore, in this study we investigated whether genetic mutations are present in the DNA binding domain of RFX6 gene that could abrogate its function in T2D.METHODSA cohort of T2D patients was enrolled in this study, and the gene encoding the DNA binding domain of RFX6 was amplified by polymerase chain reaction and then analysed by direct DNA sequencing.RESULTSThe DNA sequence analysis revealed the absence of any exonic mutation. However, we have identified a new heterozygous single nucleotide polymorphism (IVS6+31 C>T) in the intronic region of DNA binding domain gene that is present in 9.2% and 8.5% of diabetic and control people, respectively (P = 0.97).CONCLUSIONWe report the absence of any significant genetic variant that could affect the function of RFX6-DNA binding domain in T2D.

Potential Non-neoplastic Applications for Polyphenols in Stem Cell Utilization.

While polyphenols may have important effects on pluripotential stem cells that make them noteworthy as potential antineoplastic agents, their action on stem cells may portend other health benefits, such as treatments for cardiovascular and neurocognitive disorders. Resveratrol, the beststudied polyphenol, has been found to enable stem cells to differentiate into cardiomyocytes, neurons, osteocytes, and pancreatic beta cells, as well as facilitating augmentation of stem cell populations and protecting them from toxic injury. Curcumin protects mesenchymal stem cells from toxicity, and prevents them from facilitating chondrocytic hypertrophy. Quercetin enabled osteocytic and pancreatic beta cell differentiation, and protected neuronal stem cells from injury. Epigallocatechin gallate prevented damage to osteocyte precursors and averted differentiation into undesirable adipocytes. Genistein facilitated osteogenesis while preventing adipogenesis. Several other polyphenols, daidzein, caffeic and chlorogenic acid, kaempferol, and piceatannol, protect stems cells from reactive oxygen species and foster stem cells differentiation away from adipocytic and toward osteocytic lineages. Further research should better elucidate the pharmacokinetic profiles of each polyphenol, explore novel delivery systems, and expand investigation beyond rodent models to additional species.

Tub and β-catenin play a key role in insulin and leptin resistance-induced pancreatic beta-cell differentiation

The aim of this study was to investigate the molecular mechanism of pancreatic islet-derived mesenchymal stem cell (PID-MSC) differentiation into beta-cells in the presence of insulin and leptin resistance stimulators. We determined that beta-cell differentiation was stimulated by glucose, insulin, and leptin. Co-administration of insulin and leptin resulted in greater, at a further stage of differentiation but non-functional beta-cell formation. The levels of p-AKT(Ser473) did not change; SOCS3, PTP1B, p-IRS1(Ser307), PTEN levels increased and p-IRS1(Try) levels decreased due to insulin and leptin co-administration. These findings suggest that co-administration of insulin and leptin to PID-MSCs results in the development of both insulin and leptin resistance together. We showed that this differentiation signaling is mainly mediated by AKT/GSK-3β/β-catenin and Tub. Moreover, β-catenin and Tub were linked to each other in the nucleus under this condition. Furthermore, we found that Tub and β-catenin contributes to insulin production by increasing the expression of transcription factors by binding to the promoter regions of ins1, ins2, and pdx1 genes. In addition, Tub is also bound to the promoter region of the MafA gene. These findings demonstrate that when insulin and leptin resistance develop together in rat PID-MSCs beta-cell differentiation increases markedly via β-catenin and Tub. New therapeutic agents that inhibit AKT/GSK-3β/β-catenin and in particular Tub may help prevent the development or retard the progression of type 2 diabetes.

Pancreatic Beta Cell Differentiation From Human Pluripotent Stem Cells.

Insulin-expressing beta cells are crucial for the maintenance of systemic glucose homeostasis. Elucidation of the molecular and cellular mechanisms of beta cell development, expansion, survival, and function are required for full understanding of the molecular pathogenesis of diabetes. However, access to human beta cells for such studies is limited by virtue of the logistics of acquisition, prior medical status of donor, and imperfect culture systems for maintaining beta cell identity and function after isolation from human pancreas. Here, a technique for generation of beta cells from human pluripotent stem cells (hPSCs) by modification of key signaling pathways during islet development is described. Up to 70% C-peptide-positive beta cells can be obtained from endodermal anlagen after 27 days of differentiation with specific growth factors and small molecules. Although 50% of them are monohormonal C-peptide-positive cells and have molecular and cellular characteristics consistent with human beta cells in the Islets of Langerhans, a sub-population co-expressing other endocrine markers are also generated, indicating the immaturity of these cells. © 2018 by John Wiley & Sons, Inc.

Monogenic diabetes associated with PAX4 gene mutations (MODY9): first description in Russia

Maturity-onset diabetes of the young (MODY) is a heterogeneous group of disorders characterised by autosomal dominant type of inheritance and caused by genetic defects leading to dysfunction of pancreatic beta-cells. To date, at least 13 subtypes of MODY have been described in the literature, the most frequent of which are MODY types 13. MODY2 and MODY3 are the most prevalent subtypes, and were previously described in our country, Russia. Several cases of rare MODY subtypes were subsequently described in the Russian literature. The current report is the first in the Russian literature to present clinical and molecular genetic characteristics of two cases of another rare MODY subtypeMODY9. This type of MODY is associated with mutations in the PAX4 gene, which encodes transcription factor PAX4, one of the factors essential for pancreatic beta-cell differentiation. Molecular genetic analysis was performed using next-generation sequencing, a new method recently applied to verify monogenic diseases and, in particular, MODY. This study reports a novel mutation in the PAX4 gene in MODY patients.

Dynamic Proteomic Analysis of Pancreatic Mesenchyme Reveals Novel Factors That Enhance Human Embryonic Stem Cell to Pancreatic Cell Differentiation.

Current approaches in human embryonic stem cell (hESC) to pancreatic beta cell differentiation have largely been based on knowledge gained from developmental studies of the epithelial pancreas, while the potential roles of other supporting tissue compartments have not been fully explored. One such tissue is the pancreatic mesenchyme that supports epithelial organogenesis throughout embryogenesis. We hypothesized that detailed characterization of the pancreatic mesenchyme might result in the identification of novel factors not used in current differentiation protocols. Supplementing existing hESC differentiation conditions with such factors might create a more comprehensive simulation of normal development in cell culture. To validate our hypothesis, we took advantage of a novel transgenic mouse model to isolate the pancreatic mesenchyme at distinct embryonic and postnatal stages for subsequent proteomic analysis. Refined sample preparation and analysis conditions across four embryonic and prenatal time points resulted in the identification of 21,498 peptides with high-confidence mapping to 1,502 proteins. Expression analysis of pancreata confirmed the presence of three potentially important factors in cell differentiation: Galectin-1 (LGALS1), Neuroplastin (NPTN), and the Laminin α-2 subunit (LAMA2). Two of the three factors (LGALS1 and LAMA2) increased expression of pancreatic progenitor transcript levels in a published hESC to beta cell differentiation protocol. In addition, LAMA2 partially blocks cell culture induced beta cell dedifferentiation. Summarily, we provide evidence that proteomic analysis of supporting tissues such as the pancreatic mesenchyme allows for the identification of potentially important factors guiding hESC to pancreas differentiation.

The lncRNA DEANR1 facilitates human endoderm differentiation by activating FOXA2 expression.

Long non-coding RNAs (lncRNAs) regulate diverse biological processes, including cell lineage specification. Here, we report transcriptome profiling of human endoderm and pancreatic cell lineages using purified cell populations. Analysis of the data sets allows us to identify hundreds of lncRNAs that exhibit differentiation-stage-specific expression patterns. As a first step in characterizing these lncRNAs, we focus on an endoderm-specific lncRNA, definitiveendoderm-associated lncRNA1 (DEANR1), and demonstrate that it plays an important role in human endoderm differentiation. DEANR1 contributes to endoderm differentiation by positively regulating expression of the endoderm factor FOXA2. Importantly, overexpression of FOXA2 is able to rescue endoderm differentiation defects caused byDEANR1 depletion. Mechanistically, DEANR1 facilitates FOXA2 activation by facilitating SMAD2/3 recruitment to the FOXA2 promoter. Thus, our studynot only reveals a large set of differentiation-stage-specific lncRNAs but also characterizes a functional lncRNA that is important for endoderm differentiation.

Plant-Derived Compounds Targeting Pancreatic Beta Cells for the Treatment of Diabetes.

Diabetes is a global health problem and a national economic burden. Although several antidiabetic drugs are available, the need for novel therapeutic agents with improved efficacy and few side effects remains. Drugs derived from natural compounds are more attractive than synthetic drugs because of their diversity and minimal side effects. This review summarizes the most relevant effects of various plant-derived natural compounds on the functionality of pancreatic beta cells. Published data suggest that natural compounds directly enhance insulin secretion, prevent pancreatic beta cell apoptosis, and modulate pancreatic beta cell differentiation and proliferation. It is essential to continuously investigate natural compounds as sources of novel pharmaceuticals. Therefore, more studies into these compounds' mechanisms of action are warranted for their development as potential anti-diabetics.

Role of islet microRNAs in diabetes: which model for which question?

MicroRNAs are important regulators of gene expression. The vast majority of the cells in our body rely on hundreds of these tiny non-coding RNA molecules to precisely adjust their protein repertoire and faithfully accomplish their tasks. Indeed, alterations in the microRNA profile can lead to cellular dysfunction that favours the appearance of several diseases. A specific set of microRNAs plays a crucial role in pancreatic beta cell differentiation and is essential for the fine-tuning of insulin secretion and for compensatory beta cell mass expansion in response to insulin resistance. Recently, several independent studies reported alterations in microRNA levels in the islets of animal models of diabetes and in islets isolated from diabetic patients. Surprisingly, many of the changes in microRNA expression observed in animal models of diabetes were not detected in the islets of diabetic patients and vice versa. These findings are unlikely to merely reflect species differences because microRNAs are highly conserved in mammals. These puzzling results are most probably explained by fundamental differences in the experimental approaches which selectively highlight the microRNAs directly contributing to diabetes development, the microRNAs predisposing individuals to the disease or the microRNAs displaying expression changes subsequent to the development of diabetes. In this review we will highlight the suitability of the different models for addressing each of these questions and propose future strategies that should allow us to obtain a better understanding of the contribution of microRNAs to the development of diabetes mellitus in humans.

Taming the young and restless—epigenetic gene regulation in pancreas and beta‐cell precursors

The in vivo assessment of epigenetic changes during mouse pancreatic beta‐cell differentiation reveals surprising differences to directed, in vitro differentiation of human embryonic stem cells. New findings reported in this issue of The EMBO Journal further identify Ezh2 as a critical determinant of endocrine progenitor number and could instruct improved protocols for stem cell-based therapies.

PPARγ Activation Attenuates Glycated-Serum Induced Pancreatic Beta-Cell Dysfunction through Enhancing Pdx1 and Mafa Protein Stability

Pancreatic-duodenal homeobox-1 (Pdx1) and v-maf musculoaponeurotic fibrosarcoma oncogene homolog A (Mafa) play important roles in sustaining the pancreatic beta-cell differentiation phenotype. Peroxisome proliferator-activated receptor-γ (PPARγ) is also a regulator of cell differentiation. Our previous study revealed that glycated serum (GS) causes beta-cell dedifferentiation by down-regulating beta-cell specific genes, such as insulin and Pdx1. Here, we show that GS enhanced the cellular accumulation of ubiquitin-conjugated proteins, including Pdx1 and Mafa, in pancreatic beta-cells. Pharmacologic inhibition of proteolytic activity restored the protein levels of Pdx1 and Mafa, whereas inhibition of de novo protein synthesis accelerated their degradation. These findings suggest that both Pdx1 and Mafa are regulated at the post-transcriptional level. We further show that activation of PPARγ could restore GS-induced reduction of Pdx1 and Mafa protein levels, leading to improved insulin secretion and synthesis. Moreover, ectopic expression of Bcl-xl, a mitochondrial regulator, also restored Pdx1 and Mafa protein levels, linking mitochondrial function to Pdx1 and Mafa stability. Taken together, our results identify a key role of PPARγ in regulating pancreatic beta-cell function by improving the stability of Pdx1 and Mafa proteins.