Sodium butyrate prevents cytokine-induced ß-cell dysfunction through restoration of stromal interaction molecule 1 expression and activation of store-operated calcium entry.

Sodium butyrate (NaB) improves ß-cell function in preclinical models of diabetes; however, the mechanisms underlying these beneficial effects have not been fully elucidated. In this study, we investigated the impact of NaB on ß-cell function and calcium (Ca2+) signaling using ex vivo and in vitro models of diabetes. Our results show that NaB significantly improved glucose-stimulated insulin secretion in islets from human organ donors with type 2 diabetes and in cytokine-treated INS-1 ß cells. Consistently, NaB improved glucose-stimulated Ca2+ oscillations in mouse islets treated with proinflammatory cytokines. Because the oscillatory phenotype of Ca2+ in the ß cell is governed by changes in endoplasmic reticulum (ER) Ca2+ levels, we explored the relationship between NaB and store-operated calcium entry (SOCE), a rescue mechanism that acts to refill ER Ca2+ levels through STIM1-mediated gating of plasmalemmal Orai channels. We found that NaB treatment preserved basal ER Ca2+ levels and restored SOCE in IL-1ß-treated INS-1 cells. Furthermore, we linked these changes with the restoration of STIM1 levels in cytokine-treated INS-1 cells and mouse islets, and we found that NaB treatment was sufficient to prevent ß-cell death in response to IL-1ß treatment. Mechanistic experiments revealed that NaB mediated these beneficial effects in the ß-cell through histone deacetylase (HDAC) inhibition, iNOS suppression, and modulation of AKT-GSK-3 signaling. Taken together, these data support a model whereby NaB treatment promotes ß-cell function and Ca2+ homeostasis under proinflammatory conditions through pleiotropic effects that are linked with maintenance of SOCE. These results also suggest a relationship between ß-cell SOCE and gut microbiome-derived butyrate that may be relevant in the treatment and prevention of diabetes.

Dense but not alpha granules of platelets are required for insulin secretion from pancreatic ß cells.

OBJECTIVES: Platelets, originally described for their role in blood coagulation, are now also recognized as key players in modulating inflammation, tissue regeneration, angiogenesis, and carcinogenesis. Recent evidence suggests that platelets also influence insulin secretion from pancreatic ß cells. The multifaceted functions of platelets are mediated by the factors stored in their alpha granules (AGs) and dense granules (DGs). AGs primarily contain proteins, while DGs are rich in small molecules, and both types of granules are released during blood coagulation. Specific components stored in AGs and DGs are implicated in various inflammatory, regenerative, and tumorigenic processes. However, the relative contributions of AGs and DGs to the regulation of pancreatic ß cell function have not been previously explored. METHODS: In this study, we utilized mouse models deficient in AG content (neurobeachin-like 2 (Nbeal2) -deficient mice) and models with defective DG release (Unc13d-deficiency in bone marrow-derived cells) to investigate the impact of platelet granules on insulin secretion from pancreatic ß cells. RESULTS: Our findings indicate that AG deficiency has little to no effect on pancreatic ß cell function and glucose homeostasis. Conversely, mice with defective DG release exhibited glucose intolerance and reduced insulin secretion. Furthermore, Unc13d-deficiency in hematopoietic stem cells led to a reduction in adipose tissue gain in obese mice. CONCLUSIONS: Obtained data suggest that DGs, but not AGs, mediate the influence of platelets on pancreatic ß cells, thereby modulating glucose metabolism.

Design, synthesis, and biological evaluation of ß-carboline-cinnamic acid derivatives as DYRK1A inhibitors in the treatment of diabetes.

Dual-specificity tyrosine phosphorylation-regulated kinase A (DYRK1A) is a potential drug target for diabetes. The DYRK1A inhibitor can promote ß cells proliferation, increase insulin secretion and reduce blood sugar in diabetes. In this paper, a series ß-carboline-cinnamic acid skeletal derivatives were designed, synthesized and evaluated to inhibit the activity of DYRK1A and promote pancreatic islet ß cell proliferation. Pharmacological activity showed that all of the compounds could effectively promote pancreatic islet ß cell proliferation at a concentration of 1 µM, and the cell viability of compound A1, A4 and B4 reached to 381.5 %, 380.2 % and 378.5 %, respectively. Compound A1, A4 and B4 could also inhibit the expression of DYRK1A better than positive drug harmine. Further mechanistic studies showed that compound A1, A4 and B4 could inhibit DYRK1A protein expression via promoting its degradation and thus enhancing the expression of proliferative proteins PCNA and Ki67. Molecular docking showed that ß-carboline scaffold of these three compounds was fully inserted into the ATP binding site and formed hydrophobic interactions with the active pocket. Besides, these three compounds were predicted to possess better drug-likeness properties using SwissADME. In conclusion, compounds A1, A4 and B4 were potent pancreatic ß cell proliferative agents as DYRK1A inhibitors and might serve as promising candidates for the treatment of diabetes.

Maternal Western-style diet in nonhuman primates leads to offspring islet adaptations including altered gene expression and insulin hypersecretion.

Maternal overnutrition is associated with increased susceptibility to type 2 diabetes in the offspring. Rodent models have shown that maternal overnutrition influences islet function in offspring. To determine whether maternal Western-style diet (WSD) alters prejuvenile islet function in a model that approximates that of human offspring, we utilized a well-characterized Japanese macaque model. We compared islet function from offspring exposed to WSD throughout pregnancy and lactation and weaned to WSD (WSD/WSD) compared with islets from offspring exposed only to postweaning WSD (CD/WSD) at 1 yr of age. WSD/WSD offspring islets showed increased basal insulin secretion and an exaggerated increase in glucose-stimulated insulin secretion, as assessed by dynamic ex vivo perifusion assays, relative to CD/WSD-exposed offspring. We probed potential mechanisms underlying insulin hypersecretion using transmission electron microscopy to evaluate ß-cell ultrastructure, qRT-PCR to quantify candidate gene expression, and Seahorse assay to assess mitochondrial function. Insulin granule density, mitochondrial density, and mitochondrial DNA ratio were similar between groups. However, islets from WSD/WSD male and female offspring had increased expression of transcripts known to facilitate stimulus-secretion coupling and changes in the expression of cell stress genes. Seahorse assay revealed increased spare respiratory capacity in islets from WSD/WSD male offspring. Overall, these results show that maternal WSD feeding confers changes to genes governing insulin secretory coupling and results in insulin hypersecretion as early as the postweaning period. The results suggest a maternal diet leads to early adaptation and developmental programming in offspring islet genes that may underlie future ß-cell dysfunction.NEW & NOTEWORTHY Programed adaptations in islets in response to maternal WSD exposure may alter ß-cell response to metabolic stress in offspring. We show that islets from maternal WSD-exposed offspring hypersecrete insulin, possibly due to increased components of stimulus-secretion coupling. These findings suggest that islet hyperfunction is programed by maternal diet, and changes can be detected as early as the postweaning period in nonhuman primate offspring.

cGAS-STING mediates cytoplasmic mitochondrial-DNA-induced inflammatory signal transduction during accelerated senescence of pancreatic ß-cells induced by metabolic stress.

Type 2 diabetes mellitus (T2DM) is an age-related disease characterized by impaired pancreatic ß cell function and insulin resistance. Recent studies have shown that the accumulation of senescent ß cells under metabolic stress conditions leads to the progression of T2DM, while senolysis can improve the prognosis. However, the specific mechanism of ß cell senescence is still unclear. In this study, we found that the increased load of senescence pancreatic ß cells in both older mice and obese mice induced by high-fat diet (HFD) (DIO mice) was accompanied by activation of the Cyclic GMP-AMP synthase (cGAS) - stimulator of interferon genes (STING) pathway and using cGAS or STING small interfering RNA or STING inhibitor C176 to downregulate this pathway reduced the senescence-associated secretion profile (SASP) and senescence of Min6 cells treated with palmitic acid or hydrogen peroxide. C176 intervention in DIO mice also significantly reduced the inflammation and senescence of the islets, thereby protecting the function of pancreatic ß cell and glucose metabolism. Our study further revealed that mitochondrial DNA (mtDNA) leakage under metabolic stress conditions was critical for the activation of the cGAS-STING pathway, which can be reversed by the mtDNA depleting agent ethidium bromide. Consistently, mtDNA leakage was more severe in older mice and was accelerated by a chronic HFD. In conclusion, we demonstrate that cytoplasmic mtDNA activates the cGAS-STING pathway to mediate SASP during the accelerated senescence of pancreatic ß-cells induced by metabolic stress, and this process can be downregulated by the STING inhibitor C176.

TXNIP inhibition in the treatment of type 2 diabetes mellitus: design, synthesis, and biological evaluation of quinazoline derivatives.

Thioredoxin interacting protein (TXNIP) is a potential drug target for type 2 diabetes mellitus (T2DM) treatment. A series of quinazoline derivatives were designed, synthesised, and evaluated to inhibit TXNIP expression and protect from palmitate (PA)-induced ß cell injury. In vitro cell viability assay showed that compounds D-2 and C-1 could effectively protect ß cell from PA-induced apoptosis, and subsequent results showed that these two compounds decreased TXNIP expression by accelerating its protein degradation. Mechanistically, compounds D-2 and C-1 reduced intracellular reactive oxygen species (ROS) production and modulated TXNIP-NLRP3 inflammasome signalling, and thus alleviating oxidative stress injury and inflammatory response under PA insult. Besides, these two compounds were predicted to possess better drug-likeness properties using SwissADME. The present study showed that compounds D-2 and C-1, especially compound D-2, were potent pancreatic ß cell protective agents to inhibit TXNIP expression and might serve as promising lead candidates for the treatment of T2DM.

Ethyl Acetate Fractions of Tectona Grandis Crude Extract Modulate Glucose Absorption and Uptake as Well as Antihyperglycemic Potential in Fructose-Streptozotocin-Induced Diabetic Rats.

Type 2 diabetes (T2D) is a global health challenge with increased morbidity and mortality rates yearly. Herbal medicine has provided an alternative approach to treating T2D with limited access to formal healthcare. Tectona grandis is being used traditionally in the treatment of diabetes. The present study investigated the antidiabetic potential of T. grandis leaves in different solvent extractions, and the crude extract that demonstrated the best activity was further fractionated through solvent-solvent partitioning. The ethyl acetate fraction of the ethanol crude extract showed the best antidiabetic activity in inhibiting α-glucosidase, delaying glucose absorption at the small intestine's lumen, and enhancing the muscle's postprandial glucose uptake. The ethyl acetate fraction was further elucidated for its ability to reduce hyperglycemia in diabetic rats. The ethyl acetate fraction significantly reduced high blood glucose levels in diabetic rats with concomitant modulation in stimulated insulin secretions through improved pancreatic ß-cell function, insulin sensitivity by increasing liver glycogen content, and reduced elevated levels of liver glucose-6-phosphatase activity. These activities could be attributed to the phytochemical constituents of the plant.

IGF-1 ameliorates streptozotocin-induced pancreatic ß cell dysfunction and apoptosis via activating IRS1/PI3K/Akt/FOXO1 pathway.

BACKGROUND AND OBJECTIVE: Type 2 diabetes mellitus (T2DM) is an endocrine disorder with pancreatic ß cell dysfunction and/or reduced insulin sensitivity. IGF-1 is critically involved in pancreatic ß cell growth, differentiation, and insulin secretion. Insulin-mediated IRS1/PI3K/Akt/FOXO1 signaling has been proved to be closely associated with pancreatic ß cell function, hepatic glucose metabolism, and the development of T2DM. This present work was designed to demonstrate the protective role of IGF-1 against pancreatic ß cell dysfunction and to probe into the underlying mechanisms. METHODS: Herein, cell viability, cell apoptosis, insulin secretion, oxidative stress, and glycolysis in STZ-treated INS-1 cells were measured, so as to determine the biological function of IGF-1 against pancreatic ß cell dysfunction in T2DM. Additionally, whether IGF-1 could activate IRS1/PI3K/Akt/FOXO1 signaling pathway to manipulate the progression of T2DM was also investigated. RESULTS: It was discovered that IGF-1 treatment enhanced the viability and suppressed the apoptosis of STZ-treated INS-1 cells. Besides, IGF-1 treatment augmented insulin secretion of INS-1 cells in response to STZ. Moreover, IGF-1 exerted protective role against oxidative damage and displayed inhibitory effect on glycolysis in STZ-treated INS-1 cells. Mechanistically, IGF-1 treatment markedly boosted the activation of IRS1/PI3K/Akt/FOXO1 pathway. Furthermore, treatment with AG1024 (an inhibitor of IGF-1R) partially abolished the actions of IGF-1 on cell viability, cell apoptosis, insulin secretion, oxidative stress, and glycolysis in STZ-treated INS-1 cells. CONCLUSION: To conclude, IGF-1 could improve the viability and inhibit the apoptosis of STZ-treated pancreatic ß cells, induce insulin secretion, alleviate oxidative damage, as well as arrest glycolysis by activating IRS1/PI3K/Akt/FOXO1 pathway.

Cadmium inhibits signal transducer and activator of transcription 6 leading to pancreatic ß cell apoptosis.

The toxic heavy metal cadmium has been proven to cause pancreatic dysfunction and lead to the development of DM. However, the underlying mechanisms have not been completely elucidated. Here, we investigated the effects of cadmium on the pancreatic ß cell line MIN6 and explored the underlying mechanisms. The Cell Counting Kit-8 (CCK8) assay and flow cytometry were used to determine cell viability and apoptosis in MIN6 cells. The expression levels of signal transducer and activator of transcription 6 (STAT6) were assessed by western blotting. We further assessed the effects of cadmium on the function of pancreatic ß cells under high glucose levels using enzyme-linked immunosorbent assay (ELISA) and western blotting. Insulin secretion and expression were decreased by cadmium in MIN6 cells. In addition, cadmium suppressed cell viability and promoted apoptosis of MIN6 cells, downregulated insulin secretion and genesis of MIN6 cells under high glucose conditions, while inhibiting STAT6. Furthermore, after treatment with IL-4, the activator of STAT6, the MIN6 cell viability suppression and apoptosis promotion effect caused by cadmium were blocked. In conclusion, cadmium inhibits pancreatic ß cell MIN6 growth by regulating the activation of STAT6. Our findings reveal a new mechanism of cadmium toxicity in pancreatic ß cells.

Orotic acid protects pancreatic ß cell by p53 inactivation in diabetic mouse model.

Impairment of pancreatic ß cells is a principal driver of the development of diabetes. Restoring normal insulin release from the ß cells depends on the ATP produced by the intracellular mitochondria. In maintaining mitochondrial function, the tumor suppressor p53 has emerged as a novel regulator of metabolic homeostasis and participates in adaptations to nutritional changes. In this study, we used orotic acid, an intermediate in the pathway for de novo synthesis of the pyrimidine nucleotide, to reduce genotoxicity. Administration of orotic acid reduced p53 activation of MIN6 ß cells and subsequently reduced ß cell death in the db/db mouse. Orotic acid intake helped to maintain the islet size, number of ß cells, and protected insulin secretion in the db/db mouse. In conclusion, orotic acid treatment maintained ß cell function and reduced cell death, and may therefore, be a future therapeutic strategy for the prevention and treatment of diabetes.

Silencing of lncRNA PVT1 ameliorates streptozotocin-induced pancreatic ß cell injury and enhances insulin secretory capacity by regulating miR-181a-5p.

Diabetes mellitus (DM) is a type of metabolic disorder characterized by long-term hyperglycemia. Accumulating evidence shows that long noncoding RNAs (lncRNAs) play significant roles in the occurrence and development of DM. This study intended to investigate the role of lncRNA plasmacytoma variant translocation 1 (PVT1) in rat insulinoma (INS-1) cells damaged by streptozotocin (STZ) and to identify the potential mechanisms. Firstly, PVT1 expression in INS-1 cells was assessed using RT-qPCR after STZ stimulation. After PVT1-knockdown, cell apoptosis, the contents of oxidative stress related markers, and changes in insulin secretion were detected. Results indicated that PVT1 was remarkably upregulated after STZ stimulation. PVT1-knockdown inhibited STZ-induced oxidative stress and apoptosis of INS-1 cells. Moreover, the insulin secretory capacity was notably elevated following PVT1 silencing. Subsequently, a luciferase reporter assay verified that miR-181a-5p was directly targeted by PVT1. The rescue assays revealed that miR-181a-5p inhibitor dramatically abrogated the effects of PVT1 silencing on oxidative stress, apoptosis, and insulin secretion. Taken together, these findings demonstrated that PVT1-knockdown could ameliorate STZ-induced oxidative stress and apoptosis and elevate insulin secretory capacity in pancreatic ß cells by regulating miR-181a-5p, suggesting a promising biomarker in DM diagnosis and treatment.

[Mechanism of Jinqi Jiangtang Tablets in treatment of pancreatic ß cell dysfunction based on network pharmacology and molecular docking technology].

The present study investigated the therapeutic efficacy and potential mechanism of Jinqi Jiangtang Tablets(JQJT) on pancreatic ß cell dysfunction based on network pharmacology and molecular docking technology. TCMSP platform was used to retrieve the chemical components and targets of the three Chinese herbal medicines of JQJT. The genes were converted to gene symbol by the UniProt, and its intersection with targets related to pancreatic ß cell function in GeneCards and CTD databases was obtained. The drugs, active components and common targets were imported into Cytoscape 3.8.2 to plot the drug-component-target network. The main effective components and targets were obtained by software analysis. The drug targets and targets related to pancreatic ß cell function were imported separately into the STRING platform for the construction of protein-protein interaction(PPI) networks. The two PPI networks were merged by Cytoscape 3.8.2 and the key targets were obtained by plug-in CytoNCA. The targets obtained from drug-component-target network and PPI networks were imported into DAVID for GO analysis and KEGG enrichment analysis. AutoDock was used to carry out molecular docking of main active components and core targets and Pymol was used to plot the molecular docking diagram. The results showed that there were 371 active components and 203 targets related to JQJT and 2 523 targets related to pancreatic ß cell damage, covering 136 common targets. The results revealed core targets(such as PTGS2, PTGS1, NOS2, ESR1 and RXRA) and effective key components(such as quercetin, kaempferol, luteolin, ß-carotene and ß-sitosterol). KEGG enrichment analysis indicated that apoptosis, inflammation, and other signaling pathways were mainly involved. Molecular docking results showed that the main active components could spontaneously bind to the targets. This study preliminarily revealed the mechanism of JQJT in improving pancreatic ß cell damage through multi-component, multi-target and multi-pathway, and provided a theoretical basis for JQJT in the treatment of pancreatic ß cell dysfunction.

Improved Tol2-mediated enhancer trap identifies weakly expressed genes during liver and ß cell development and regeneration in zebrafish.

The liver and pancreas are two major digestive organs, and among the different cell types in them, hepatocytes and the insulin-producing ß cells have roles in both health and diseases. Accordingly, clinicians and researchers are very interested in the mechanisms underlying the development and regeneration of liver and pancreatic ß cells. Gene and enhancer traps such as the Tol2 transposon-based system are useful for identifying genes potentially involved in developmental processes in the zebrafish model. Here, we developed a strategy that combines a Tol2-mediated enhancer trap and the Cre/loxP system by using loxP-flanked reporters driven by ß cell- or hepatocyte-specific promoters and the upstream activating sequence (UAS)-driving Cre. Two double-transgenic reporter lines, Tg(ins:loxP-CFPNTR-loxP-DsRed; 10×UAS:Cre, cryaa:Venus) and Tg(fabp10:loxP-CFPNTR-loxP-DsRed; 10×UAS:Cre, cryaa:Venus), were established to label pancreatic ß cells and hepatocytes, respectively. These two double-transgenic lines were each crossed with the Tol2-enhancer trap founder lines to screen for and identify genes expressed in the ß cell and hepatocytes during development. This trap system coupled with application of nitroreductase (NTR)/metronidazole (Mtz)-mediated cell ablation could identify genes expressed during regeneration. Of note, pilot enhancer traps captured transiently and weakly expressed genes such as rab3da and ensab with higher efficiencies than traditional enhancer trap systems. In conclusion, through permanent genetic labeling by Cre/loxP, this improved Tol2-mediated enhancer trap system provides a promising method to identify transiently or weakly expressed, but potentially important, genes during development and regeneration.

Obesity-dependent CDK1 signaling stimulates mitochondrial respiration at complex I in pancreatic ß-cells.

ß-Cell mitochondria play a central role in coupling glucose metabolism with insulin secretion. Here, we identified a metabolic function of cyclin-dependent kinase 1 (CDK1)/cyclin B1-the activation of mitochondrial respiratory complex I-that is active in quiescent adult ß-cells and hyperactive in ß-cells from obese (ob/ob) mice. In WT islets, respirometry revealed that 65% of complex I flux and 49% of state 3 respiration is sensitive to CDK1 inhibition. Islets from ob/ob mice expressed more cyclin B1 and exhibited a higher sensitivity to CDK1 blockade, which reduced complex I flux by 76% and state 3 respiration by 79%. The ensuing reduction in mitochondrial NADH utilization, measured with two-photon NAD(P)H fluorescence lifetime imaging (FLIM), was matched in the cytosol by a lag in citrate cycling, as shown with a FRET reporter targeted to ß-cells. Moreover, time-resolved measurements revealed that in ob/ob islets, where complex I flux dominates respiration, CDK1 inhibition is sufficient to restrict the duty cycle of ATP/ADP and calcium oscillations, the parameter that dynamically encodes ß-cell glucose sensing. Direct complex I inhibition with rotenone mimicked the restrictive effects of CDK1 inhibition on mitochondrial respiration, NADH turnover, ATP/ADP, and calcium influx. These findings identify complex I as a critical mediator of obesity-associated metabolic remodeling in ß-cells and implicate CDK1 as a regulator of complex I that enhances ß-cell glucose sensing.

GSTO1 regulates insulin biosynthesis in pancreatic ß cells.

Insulin biosynthesis and secretion by pancreatic ß cells are critical for the maintenance of blood glucose homeostasis. Here, we show that the expression of glutathione S-transferase omega-1 (GSTO1) is upregulated in the primary islet cells of diabetic Goto-Kakizaki (GK) rats. Knocking out GSTO1 upregulated insulin transcripts and increased the insulin content in both INS-1 cells and primary islet cells. In contrast, overexpression of GSTO1 reduced the insulin content. Furthermore, knocking out GSTO1 increased the expression of pancreatic duodenal homeobox-1 (PDX1) at both the transcription and protein levels. These results indicate that GSTO1 may be involved in the regulation of insulin biosynthesis by modulating the transcriptional expression of PDX1.

The role of bone-derived PDGF-AA in age-related pancreatic ß cell proliferation and function.

The occurrence of type 2 diabetes(T2D) increases with age. The platelet-derived growth factor (PDGF) is one of the key factors regulating ß cell proliferation and function, but the contribution of PDGF signaling in ß cells aging and senescence remains unexplored. Here, we showed that the level of both serum and tissue PDGF-AA decreased with age, and the serum PDGF-AA level was positively correlated with ß cell proliferation and function in aging. The decline of PDGF-AA level in aging was partly due to decreased number as well as secretion of osteoblast lineage cells in bone tissue. Conditioned medium from osteoblast lineage cells induced insulinoma ß cells proliferation and insulin secretion in vitro, while addition of PDGF-AA neutralizing antibody attenuated this effect. Transplantation of juvenile osteoblast lineage cells increased serum PDGF-AA level and promoted ß cell proliferation and function in aging mice, which eventually resulted in better glucose tolerance. Taken together, these findings revealed the role of decreased bone-derived PDGF-AA in mediating the disrupted proliferation and function of ß cells in aging.

Epigenetic repression of AT2 receptor is involved in ß cell dysfunction and glucose intolerance of adult female offspring rats exposed to dexamethasone prenatally.

Prenatal exposure to dexamethasone (PDE) impairs pancreatic ß cell development and glucose homeostasis in offspring especially females. To explore the underlying intrauterine programming mechanism, pregnant Wistar rats were subcutaneously administered with dexamethasone (0, 0.2 and 0.8 mg/kg·d) from gestational days (GD) 9 to 20. Female offspring were collected on GD20 (fetus) and in postnatal week 28 (adult), respectively. PDE reduced the serum insulin levels, ß cell mass, and pancreatic insulin expressions in fetuses and adults, causing glucose intolerance after maturity. The persistent suppression of pancreatic angiotensin II receptor type 2 (AT2R) expression before and after birth could be observed in the PDE females, which is accompanied with decreased histone 3 lysine 14 acetylation (H3K14ac) and H3K27ac levels in AT2R promoter. PDE increased the gene expressions of glucocorticoid receptor (GR) and histone deacetylase 2 (HDAC2) in fetal pancreas. Furthermore, dexamethasone inhibited insulin biosynthesis while activated GR and HDAC2 expression in the rat INS-1 cells. The AT2R expression was repressed by dexamethasone in vitro but only H3K27ac levels in AT2R promoter were lowered. Dexamethasone enhanced the interaction between GR and HDAC2 proteins as well as the binding of GR/HDAC2 complex to AT2R promoter. Moreover, overexpression of AT2R could restore the suppressed insulin biosynthesis induced by dexamethasone in vitro, and both GR antagonist and histone deacetylase abolished the decreased H3K27ac level and gene expression of AT2R. In conclusion, continuous epigenetic repression of AT2R before and after birth may be involved in ß cell dysfunction and glucose intolerance of the PDE adult female offspring.

MicroRNA-203a regulates pancreatic ß cell proliferation and apoptosis by targeting IRS2.

The main pathogenesis of type 1 diabetes mellitus (T1DM) is autoimmune-mediated apoptosis of pancreatic islet ß cells. We sought to characterize the function of microRNA-203a (miR-203a) on pancreatic islet ß cell proliferation and apoptosis. In situ hybridization was used to detect the expression of miR-203a in islet ß cells in normal and hyperglycaemic non-obese diabetic (NOD) mice. Cell proliferation was measured by cell counting kit eight and cell apoptosis was detected using flow cytometry. Insulin receptor substrate 2 (IRS2/Irs2) was determined to be a direct target of miR-203a by Luciferase reporter assay. We detected the effects of miR-203a overexpression or inhibition on proliferation and apoptosis of IRS2-overexpressing or IRS2-knockdown MIN6 cells respectively, and preliminarily explored the downstream targets of the IRS2 pathway. NOD mice model was used to detect miR-203a inhibitor treatment for diabetes. Our experiment showed miR-203a was upregulated in pancreatic ß cells of hyperglycaemic NOD mice. Elevated miR-203a expression inhibited the proliferation and promoted the apoptosis of MIN6 cells. IRS2/Irs2 is a novel target gene directly regulated by miR-203a and miR-203a overexpression downregulated the expression of IRS2. Irs2 silencing reduced cell proliferation and increased apoptosis. Irs2 overexpression could abolish the pro-apoptotic and anti-proliferative effects of miR-203a on MIN6 cells. Hyperglycemia in newly hyperglycemic NOD mice was under control after treatment with miR-203a inhibitor. Our study suggests that miR-203a regulates pancreatic ß cell proliferation and apoptosis by targeting IRS2, treatment with miR-203a inhibitors and IRS2 might provide a new therapeutic strategy for T1DM.

ATF5 regulates ß-cell survival during stress.

The stress response and cell survival are necessary for normal pancreatic ß-cell function, glucose homeostasis, and prevention of diabetes. The homeodomain transcription factor and human diabetes gene pancreas/duodenum homeobox protein 1 (Pdx1) regulates ß-cell survival and endoplasmic reticulum stress susceptibility, in part through direct regulation of activating transcription factor 4 (Atf4). Here we show that Atf5, a close but less-studied relative of Atf4, is also a target of Pdx1 and is critical for ß-cell survival under stress conditions. Pdx1 deficiency led to decreased Atf5 transcript, and primary islet ChIP-sequencing localized PDX1 to the Atf5 promoter, implicating Atf5 as a PDX1 target. Atf5 expression was stress inducible and enriched in ß cells. Importantly, Atf5 deficiency decreased survival under stress conditions. Loss-of-function and chromatin occupancy experiments positioned Atf5 downstream of and parallel to Atf4 in the regulation of eIF4E-binding protein 1 (4ebp1), a mammalian target of rapamycin (mTOR) pathway component that inhibits protein translation. Accordingly, Atf5 deficiency attenuated stress suppression of global translation, likely enhancing the susceptibility of ß cells to stress-induced apoptosis. Thus, we identify ATF5 as a member of the transcriptional network governing pancreatic ß-cell survival during stress.

Fanconi-Bickel Syndrome: A Review of the Mechanisms That Lead to Dysglycaemia.

Accumulation of glycogen in the kidney and liver is the main feature of Fanconi-Bickel Syndrome (FBS), a rare disorder of carbohydrate metabolism inherited in an autosomal recessive manner due to SLC2A2 gene mutations. Missense, nonsense, frame-shift (fs), in-frame indels, splice site, and compound heterozygous variants have all been identified in SLC2A2 gene of FBS cases. Approximately 144 FBS cases with 70 different SLC2A2 gene variants have been reported so far. SLC2A2 encodes for glucose transporter 2 (GLUT2) a low affinity facilitative transporter of glucose mainly expressed in tissues playing important roles in glucose homeostasis, such as renal tubular cells, enterocytes, pancreatic ß-cells, hepatocytes and discrete regions of the brain. Dysfunctional mutations and decreased GLUT2 expression leads to dysglycaemia (fasting hypoglycemia, postprandial hyperglycemia, glucose intolerance, and rarely diabetes mellitus), hepatomegaly, galactose intolerance, rickets, and poor growth. The molecular mechanisms of dysglycaemia in FBS are still not clearly understood. In this review, we discuss the physiological roles of GLUT2 and the pathophysiology of mutants, highlight all of the previously reported SLC2A2 mutations associated with dysglycaemia, and review the potential molecular mechanisms leading to dysglycaemia and diabetes mellitus in FBS patients.