Hypoxia causes pancreatic ß-cell dysfunction and impairs insulin secretion by activating the transcriptional repressor BHLHE40.

Hypoxia can occur in pancreatic ß-cells in type 2 diabetes. Although hypoxia exerts deleterious effects on ß-cell function, the associated mechanisms are largely unknown. Here, we show that the transcriptional repressor basic helix-loop-helix family member e40 (BHLHE40) is highly induced in hypoxic mouse and human ß-cells and suppresses insulin secretion. Conversely, BHLHE40 deficiency in hypoxic MIN6 cells or ß-cells of ob/ob mice reverses defects in insulin secretion. Mechanistically, BHLHE40 represses the expression of Mafa, encoding the transcription factor musculoaponeurotic fibrosarcoma oncogene family A (MAFA), by attenuating the binding of pancreas/duodenum homeobox protein 1 (PDX1) to its enhancer region. Impaired insulin secretion in hypoxic ß-cells was recovered by MAFA re-expression. Collectively, our work identifies BHLHE40 as a key hypoxia-induced transcriptional repressor in ß-cells that inhibit insulin secretion by suppressing MAFA expression.

Glucotoxicity is mediated by cytoplasmic distribution of RAP1 in pancreatic ß-cells.

Diabetes mellitus (DM) is a group of chronic metabolic disorders characterized by persistent hyperglycemia. In our study, we analyzed the level and location of RAP1 changes in the development of ß-cell dysfunction induced by glucotoxicity. We employed three pancreatic ß-cell lines, namely INS-1, 1.2B4, and NIT-1, as well as a streptozotocin-induced diabetes rat model. We demonstrate that after high glucose treatment, RAP1 is increased, probably through induction by AKT, allowing RAP1 to shuttle from the nucleus to the cytoplasm and activate NF-κB signaling. Furthermore, non-enzymatic post-translational modifications of RAP1, such as advanced glycation end products and carbonylation may affect the function of RAP1, such as activation of the NF-κB signaling. Taken together, we showed that RAP1 is a new player in the mechanism of glucotoxicity in pancreatic ß-cells.

From stem cells to pancreatic ß-cells: strategies, applications, and potential treatments for diabetes.

Loss and functional failure of pancreatic ß-cells results in disruption of glucose homeostasis and progression of diabetes. Although whole pancreas or pancreatic islet transplantation serves as a promising approach for ß-cell replenishment and diabetes therapy, the severe scarcity of donor islets makes it unattainable for most diabetic patients. Stem cells, particularly induced pluripotent stem cells (iPSCs), are promising for the treatment of diabetes owing to their self-renewal capacity and ability to differentiate into functional ß-cells. In this review, we first introduce the development of functional ß-cells and their heterogeneity and then turn to highlight recent advances in the generation of ß-cells from stem cells and their potential applications in disease modeling, drug discovery and clinical therapy. Finally, we have discussed the current challenges in developing stem cell-based therapeutic strategies for improving the treatment of diabetes. Although some significant technical hurdles remain, stem cells offer great hope for patients with diabetes and will certainly transform future clinical practice.

Roles of ß-Cell Hypoxia in the Progression of Type 2 Diabetes.

Type 2 diabetes is a chronic disease marked by hyperglycemia; impaired insulin secretion by pancreatic ß-cells is a hallmark of this disease. Recent studies have shown that hypoxia occurs in the ß-cells of patients with type 2 diabetes and hypoxia, in turn, contributes to the insulin secretion defect and ß-cell loss through various mechanisms, including the activation of hypoxia-inducible factors, induction of transcriptional repressors, and activation of AMP-activated protein kinase. This review focuses on advances in our understanding of the contribution of ß-cell hypoxia to the development of ß-cell dysfunction in type 2 diabetes. A better understanding of ß-cell hypoxia might be useful in the development of new strategies for treating type 2 diabetes.

Chronic Epinephrine-Induced Endoplasmic Reticulum and Oxidative Stress Impairs Pancreatic ß-Cells Function and Fate.

Epinephrine influences the function of pancreatic ß-cells, primarily through the α2A-adrenergic receptor (α2A-AR) on their plasma membrane. Previous studies indicate that epinephrine transiently suppresses insulin secretion, whereas prolonged exposure induces its compensatory secretion. Nonetheless, the impact of epinephrine-induced α2A-AR signaling on the survival and function of pancreatic ß-cells, particularly the impact of reprogramming after their removal from sustained epinephrine stimulation, remains elusive. In the present study, we applied MIN6, a murine insulinoma cell line, with 3 days of high concentration epinephrine incubation and 2 days of standard incubation, explored cell function and activity, and analyzed relevant regulatory pathways. The results showed that chronic epinephrine incubation led to the desensitization of α2A-AR and enhanced insulin secretion. An increased number of docked insulin granules and impaired Syntaxin-2 was found after chronic epinephrine exposure. Growth curve and cell cycle analyses showed the inhibition of cell proliferation. Transcriptome analysis showed the occurrence of endoplasmic reticulum stress (ER stress) and oxidative stress, such as the presence of BiP, CHOP, IRE1, ATF4, and XBP, affecting cellular endoplasmic reticulum function and survival, along with UCP2, OPA1, PINK, and PRKN, associated with mitochondrial dysfunction. Consequently, we conclude that chronic exposure to epinephrine induces α2A-AR desensitization and leads to ER and oxidative stress, impairing protein processing and mitochondrial function, leading to modified pancreatic ß-cell secretory function and cell fate.

Imatinib prevents dexamethasone-induced pancreatic ß-cell apoptosis via decreased TRAIL and DR5.

Prolonged administration of dexamethasone, a potent anti-inflammatory drug, can lead to steroid-induced diabetes. Imatinib, a medication commonly prescribed for chronic myeloid leukemia (CML), has been shown to improve diabetes in CML patients. Our recent study demonstrated that dexamethasone induces pancreatic ß-cell apoptosis by upregulating the expression of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and its receptor, death receptor 5 (DR5). We hypothesized that imatinib may protect against dexamethasone-induced pancreatic ß-cell apoptosis by reducing the expression of TRAIL and DR5, thereby favorably modulating downstream effectors in apoptotic pathways. We test this hypothesis by assessing the effects of imatinib on dexamethasone-induced apoptosis in rat insulinoma cell line cells. As anticipated, dexamethasone treatment led to increased TRAIL and DR5 expression, as well as an elevation in superoxide production. Conversely, expression of the TRAIL decoy receptor (DcR1) was decreased. Moreover, key effectors in the extrinsic and intrinsic apoptosis pathways, such as B-cell lymphoma 2 (BCL-2) associated X (BAX), nuclear factor kappa B (NF-κb), P73, caspase 8, and caspase 9, were upregulated, while the antiapoptotic protein BCL-2 was downregulated. Interestingly and importantly, imatinib at a concentration of 10 µM reversed the effect of dexamethasone on TRAIL, DR5, DcR1, superoxide production, BAX, BCL-2, NF-κB, P73, caspase 3, caspase 8, and caspase 9. Similar effects of imatinib on dexamethasone-induced TRAIL and DR5 expression were also observed in isolated mouse islets. Taken together, our findings suggest that imatinib protects against dexamethasone-induced pancreatic ß-cell apoptosis by reducing TRAIL and DR5 expression and modulating downstream effectors in the extrinsic and intrinsic apoptosis pathways.

Glucagon receptor blockage inhibits ß-cell dedifferentiation through FoxO1.

Glucagon-secreting pancreatic α-cells play pivotal roles in the development of diabetes. Glucagon promotes insulin secretion from ß-cells. However, the long-term effect of glucagon on the function and phenotype of ß-cells had remained elusive. In this study, we found that long-term glucagon intervention or glucagon intervention with the presence of palmitic acid downregulated ß-cell-specific markers and inhibited insulin secretion in cultured ß-cells. These results suggested that glucagon induced ß-cell dedifferentiation under pathological conditions. Glucagon blockage by a glucagon receptor (GCGR) monoclonal antibody (mAb) attenuated glucagon-induced ß-cell dedifferentiation. In primary islets, GCGR mAb treatment upregulated ß-cell-specific markers and increased insulin content, suggesting that blockage of endogenous glucagon-GCGR signaling inhibited ß-cell dedifferentiation. To investigate the possible mechanism, we found that glucagon decreased FoxO1 expression. FoxO1 inhibitor mimicked the effect of glucagon, whereas FoxO1 overexpression reversed the glucagon-induced ß-cell dedifferentiation. In db/db mice and ß-cell lineage-tracing diabetic mice, GCGR mAb lowered glucose level, upregulated plasma insulin level, increased ß-cell area, and inhibited ß-cell dedifferentiation. In aged ß-cell-specific FoxO1 knockout mice (with the blood glucose level elevated as a diabetic model), the glucose-lowering effect of GCGR mAb was attenuated and the plasma insulin level, ß-cell area, and ß-cell dedifferentiation were not affected by GCGR mAb. Our results proved that glucagon induced ß-cell dedifferentiation under pathological conditions, and the effect was partially mediated by FoxO1. Our study reveals a novel cross talk between α- and ß-cells and is helpful to understand the pathophysiology of diabetes and discover new targets for diabetes treatment.NEW & NOTEWORTHY Glucagon-secreting pancreatic α-cells can interact with ß-cells. However, the long-term effect of glucagon on the function and phenotype of ß-cells has remained elusive. Our new finding shows that long-term glucagon induces ß-cell dedifferentiation in cultured ß-cells. FoxO1 inhibitor mimicks whereas glucagon signaling blockage by GCGR mAb reverses the effect of glucagon. In type 2 diabetic mice, GCGR mAb increases ß-cell area, improves ß-cell function, and inhibits ß-cell dedifferentiation, and the effect is partially mediated by FoxO1.

Vanillic acid potentiates insulin secretion and prevents pancreatic ß-cells cytotoxicity under H2O2-induced oxidative stress.

BACKGROUND: Oxidative stress is known to impair cellular functions and, therefore, plays a significant role in the pathophysiology of various diseases, including diabetes. The persistently elevated glucose levels may cause enhanced mitochondrial reactive oxygen species generation, which in turn can damage the pancreatic ß-cells. In this study, we have investigated the effect of vanillic acid on preventing H2O2-induced ß-cells death and retaining its insulin secretion potentiating effect in the presence of H2O2. METHODS: The insulin secretion from the BRIN-BD11 cells was quantified using ELISA-based assays. The viability of the cells was assessed by estimated by the [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide] (MTT) colorimetric assay and DAPI staining. The expression levels of apoptotic and antioxidant proteins were estimated by western blot experiments. RESULTS: Vanillic acid protected pancreatic ß-cells viability and function under the H2O2 oxidative stress condition. The Erk1/2 activation appears to play an important role in vanillic acid potentiated insulin secretion and protection of the ß-cells in the presence of H2O2. Vanillic acid pretreated cells exhibited enhanced expression of antioxidant enzymes such as catalase and SOD-2 and reduced the expression of proapoptotic markers such as BAX and BAD. In addition, it also enhanced the expression of oxidative stress-sensitive transcription factor Nrf-2 and cell survival protein Akt. CONCLUSION: The present study shows that vanillic acid potentiates insulin secretion and protects pancreatic ß-cells from H2O2-induced oxidative stress.

Glucose Homeostasis and Pancreatic Islet Size Are Regulated by the Transcription Factors Elk-1 and Egr-1 and the Protein Phosphatase Calcineurin.

Pancreatic ß-cells synthesize and secrete insulin. A key feature of diabetes mellitus is the loss of these cells. A decrease in the number of ß-cells results in decreased biosynthesis of insulin. Increasing the number of ß-cells should restore adequate insulin biosynthesis leading to adequate insulin secretion. Therefore, identifying proteins that regulate the number of ß-cells is a high priority in diabetes research. In this review article, we summerize the results of three sophisticated transgenic mouse models showing that the transcription factors Elk-1 and Egr-1 and the Ca2+/calmodulin-regulated protein phosphatase calcineurin control the formation of sufficiently large pancreatic islets. Impairment of the biological activity of Egr-1 and Elk-1 in pancreatic ß-cells leads to glucose intolerance and dysregulation of glucose homeostasis, the process that maintains glucose concentration in the blood within a narrow range. Transgenic mice expressing an activated calcineurin mutant also had smaller islets and showed hyperglycemia. Calcineurin induces dephosphorylation of Elk-1 which subsequently impairs Egr-1 biosynthesis and the biological functions of Elk-1 and Egr-1 to regulate islet size and glucose homeostasis.

BCL-XL Overexpression Protects Pancreatic ß-Cells against Cytokine- and Palmitate-Induced Apoptosis.

Diabetes is a chronic disease that affects glucose metabolism, either by autoimmune-driven ß-cell loss or by the progressive loss of ß-cell function, due to continued metabolic stresses. Although both α- and ß-cells are exposed to the same stressors, such as proinflammatory cytokines and saturated free fatty acids (e.g., palmitate), only α-cells survive. We previously reported that the abundant expression of BCL-XL, an anti-apoptotic member of the BCL-2 family of proteins, is part of the α-cell defense mechanism against palmitate-induced cell death. Here, we investigated whether BCL-XL overexpression could protect ß-cells against the apoptosis induced by proinflammatory and metabolic insults. For this purpose, BCL-XL was overexpressed in two ß-cell lines-namely, rat insulinoma-derived INS-1E and human insulin-producing EndoC-ßH1 cells-using adenoviral vectors. We observed that the BCL-XL overexpression in INS-1E cells was slightly reduced in intracellular Ca2+ responses and glucose-stimulated insulin secretion, whereas these effects were not observed in the human EndoC-ßH1 cells. In INS-1E cells, BCL-XL overexpression partially decreased cytokine- and palmitate-induced ß-cell apoptosis (around 40% protection). On the other hand, the overexpression of BCL-XL markedly protected EndoC-ßH1 cells against the apoptosis triggered by these insults (>80% protection). Analysis of the expression of endoplasmic reticulum (ER) stress markers suggests that resistance to the cytokine and palmitate conferred by BCL-XL overexpression might be, at least in part, due to the alleviation of ER stress. Altogether, our data indicate that BCL-XL plays a dual role in ß-cells, participating both in cellular processes related to ß-cell physiology and in fostering survival against pro-apoptotic insults.

The De-, Re-, and trans-differentiation of ß-cells: Regulation and function.

Diabetes is a serious, costly, and major health problem worldwide. Whereas diabetes could be alleviated by medication, this disease could not be fully cured at the present time due to the lack of effective therapeutic treatment for ß-cell loss and/or dysfunction. Increased ß-cell mass or volume could be achieved via differentiation of embryonic stem (ES) cells or pluripotent stem cells or through ß-cell renewal, including proliferation, redifferentiation, and transdifferentiation. Data cumulated over the past several years suggest that increased ß-cell dedifferentiation plays a crucial role in the progression of diabetes, shedding new light on potential targets for ß-cell replacement therapy. In this review, we summarize current views on ß-cell dedifferentiation, redifferentiation, and transdifferentiation. We also discuss potential mechanisms regulating these key processes to maintain ß-cell homeostasis. Understanding pancreatic ß-cell differentiation and dedifferentiation could be provide important information on developing effective strategies to cure diabetes.

Islet amyloid toxicity: From genesis to counteracting mechanisms.

Islet amyloid polypeptide (IAPP or amylin) is a hormone co-secreted with insulin by pancreatic ß-cells and is the major component of islet amyloid. Islet amyloid is found in the pancreas of patients with type 2 diabetes (T2D) and may be involved in ß-cell dysfunction and death, observed in this disease. Thus, investigating the aspects related to amyloid formation is relevant to the development of strategies towards ß-cell protection. In this sense, IAPP misprocessing, IAPP overproduction, and disturbances in intra- and extracellular environments seem to be decisive for IAPP to form islet amyloid. Islet amyloid toxicity in ß-cells may be triggered in intra- and/or extracellular sites by membrane damage, endoplasmic reticulum stress, autophagy disruption, mitochondrial dysfunction, inflammation, and apoptosis. Importantly, different approaches have been suggested to prevent islet amyloid cytotoxicity, from inhibition of IAPP aggregation to attenuation of cell death mechanisms. Such approaches have improved ß-cell function and prevented the development of hyperglycemia in animals. Therefore, counteracting islet amyloid may be a promising therapy for T2D treatment.

Genetic ablation of the preptin-coding portion of Igf2 impairs pancreatic function in female mice.

Preptin is a 34-amino acid peptide derived from the E-peptide of pro-insulin-like growth factor 2 and is co-secreted with insulin from ß-cells. Little is understood about the effects of endogenous preptin on whole body glucose metabolism. We developed a novel mouse model in which the preptin portion of Igf2 was genetically ablated in all tissues, hereafter referred to as preptin knockout (KO), and tested the hypothesis that the removal of preptin will lead to a decreased insulin response to a metabolic challenge. Preptin KO and wild-type (WT) mice underwent weekly fasting blood glucose measurements, intraperitoneal insulin tolerance tests (ITT) at 9, 29, and 44 wk of age, and an oral glucose tolerance test (GTT) at 45 wk of age. Preptin KO mice of both sexes had similar Igf2 exon 2-3 mRNA expression in the liver and kidney compared with WT mice, but Igf2 exon 3-4 (preptin) expression was not detectable. Western blot analysis of neonatal serum indicated that processing of pro-IGF2 translated from the KO allele may be altered. Preptin KO mice had similar body weight, body composition, ß-cell area, and fasted glucose concentrations compared with WT mice in both sexes up to 47 wk of age. Female KO mice had a diminished ability to mount an insulin response following glucose stimulation in vivo. This effect was absent in male KO mice. Although preptin is not essential for glucose homeostasis, when combined with previous in vitro and ex vivo findings, these data show that preptin positively impacts ß-cell function.NEW & NOTEWORTHY This is the first study to describe a model in which the preptin-coding portion of the Igf2 gene has been genetically ablated in mice. The mice do not show reduced size at birth associated with Igf2 knockout suggesting that IGF2 functionality is maintained, yet we demonstrate a change in the processing of mature Igf2. Female knockout mice have diminished glucose-stimulated insulin secretion, whereas the insulin response in males is not different to wild type.

Morphological alteration of the pancreatic islet in ovariectomized rats fed a high-fat high-fructose diet.

Diabetes and its complications are major causes of mortality worldwide. Type 2 diabetes coexists with insulin resistance and ß-cell dysfunction, which are aggravated by overconsumption and estrogen-deprived conditions. However, the morphology of pancreatic islets in a combined condition of excessive caloric intake and estrogen deficiency has never been described. Herein, we examined morphological changes in the pancreatic islets of ovariectomized (OVX) rats fed a high-fat high-fructose diet (HFFD) for 12 weeks. The histological changes in the size and number of pancreatic islets were assessed by hematoxylin-eosin and immunohistochemical staining. Enlarged pancreatic islets with fat deposition in OVX rats were accompanied by whole-body insulin resistance and hyperglycemia. The addition of a HFFD to OVX rats (OVX + HFFD) further aggravated insulin resistance, with a substantial increase in the density of enlarged pancreatic islets and fat accumulation. The augmented number of enlarged islets was correlated with elevated plasma glucose and insulin levels. Intriguingly, unlike the HFFD and OVX alone, the OVX + HFFD markedly expanded the area of insulin-producing ß-cells and glucagon-producing α-cells. Importantly, enlarged islets, pancreatic fat deposits, and diabetic states developing in OVX + HFFD conditions were resolved by estrogen replacement. Collectively, the morphological characteristics of pancreatic islets were influenced in an insulin-resistant state caused by estrogen deficiency and HFFD consumption and were distinct from each factor alone. A combination of estrogen deficiency with HFFD consumption worsened the integrity of pancreatic islets, ultimately resulting in disease progression. These findings expand our understanding of the causal relationship between pancreatic morphology and diabetes development and suggest therapeutic strategies.

Bitter melon fruit extract enhances intracellular ATP production and insulin secretion from rat pancreatic ß-cells.

Bitter melon (Momordica charantia L.) has been shown to have various health-promoting activities, including antidiabetic and hypoglycaemic effects. Improvement in insulin sensitivity and increase in glucose utilisation in peripheral tissues have been reported, but the effect on insulin secretion from pancreatic ß-cells remains unclear. In this study, we investigated the effect of bitter melon fruit on insulin secretion from ß-cells and the underlying mechanism. The green fruit of bitter melon was freeze-dried and extracted with methanol. The bitter melon fruit extract (BMFE) was fractionated using ethyl acetate (fraction A), n-butanol (fraction B) and water (fraction C). Insulin secretory capacity from INS-1 rat insulinoma cell line and rat pancreatic islets, as well as glucose tolerance in rats by oral glucose tolerance test (OGTT), was measured using BMFE and fractions. ATP production in ß-cells was also examined. BMFE augmented insulin secretion from INS-1 cells in a dose-dependent manner. The significant augmentation of insulin secretion was independent of the glucose dose. Fraction A (i.e. hydrophobic fraction), but not fractions B and C, augmented insulin secretion significantly at the same level as that by BMFE. This finding was also observed in pancreatic islets. In OGTT, BMFE and fraction A decreased blood glucose levels and increased serum insulin levels after glucose loading. The decrease in blood glucose levels was also observed in streptozotocin-induced diabetic rats. In addition, BMFE and fraction A increased the ATP content in ß-cells. We concluded that hydrophobic components of BMFE increase ATP production and augment insulin secretion from ß-cells, consequently decreasing blood glucose levels.

Protection of pancreatic ß-cell by phosphocreatine through mitochondrial improvement via the regulation of dual AKT/IRS-1/GSK-3ß and STAT3/Cyp-D signaling pathways.

Diabetes mellitus (DM) is a metabolic syndrome, caused by insufficient insulin secretion or insulin resistance (IR). DM enhances oxidative stress and induces mitochondrial function in different kinds of cell types, including pancreatic ß-cells. Our previous study has showed phosphocreatine (PCr) can advance the mitochondrial function through enhancing the oxidative phosphorylation and electron transport ability in mitochondria damaged by methylglyoxal (MG). Our aim was to explore the potential role of PCr as a molecule to protect mitochondria from diabetes-induced pancreatic ß-cell injury with insulin secretion deficiency or IR through dual AKT/IRS-1/GSK-3ß and STAT3/Cyclophilin D (Cyp-D) signaling pathways. MG-induced INS-1 cell viability, apoptosis, mitochondrial division and fusion, the morphology, and function of mitochondria were suppressed. Flow cytometry was used to detect the production of intracellular reactive oxygen species (ROS) and the changes of intracellular calcium, and the respiratory function was measured by oxygraph-2k. The expressions of AKT, IRS-1, GSK-3ß, STAT3, and Cyp-D were detected using Western blot. The result showed that the oxidative stress-related kinases were significantly restored to the normal level after the pretreatment with PCr. Moreover, PCr pretreatment significantly inhibited cell apoptosis, decreased intracellular calcium, and ROS production, and inhibited mitochondrial division and fusion, and increased ATP synthesis damaged by MG in INS-1 cells. In addition, pretreatment with PCr suppressed Cytochrome C, p-STAT3, and Cyp-D expressions, while increased p-AKT, p-IRS-1, p-GSK-3ß, caspase-3, and caspase-9 expressions. In conclusion, PCr has protective effect on INS-1 cells in vitro and in vivo, relying on AKT mediated STAT3/ Cyp-D pathway to inhibit oxidative stress and restore mitochondrial function, signifying that PCr might become an emerging candidate for the cure of diabetic pancreatic cancer ß-cell damage.

PCSK9 inhibition and cholesterol homeostasis in insulin producing ß-cells.

Low-density lipoprotein cholesterol (LDL-C) plays a central role in the pathology of atherosclerotic cardiovascular disease. For decades, the gold standard for LDL-C lowering have been statins, although these drugs carry a moderate risk for the development of new-onset diabetes. The inhibitors of proprotein convertase subtilisin/kexin type 9 (PCSK9) have emerged in the last years as potential alternatives to statins due to their high efficiency and safety without indications for a diabetes risk so far. Both approaches finally eliminate LDL-C from bloodstream by upregulation of LDL receptor surface expression. Due to their low antioxidant capacity, insulin producing pancreatic ß-cells are sensitive to increased lipid oxidation and related generation of reactive oxygen species. Thus, PCSK9 inhibition has been argued to promote diabetes like statins. Potentially, the remaining patients at risk will be identified in the future. Otherwise, there is increasing evidence that loss of circulating PCSK9 does not worsen glycaemia since it is compensated by local PCSK9 expression in ß-cells and other islet cells. This review explores the situation in ß-cells. We evaluated the relevant biology of PCSK9 and the effects of its functional loss in rodent knockout models, carriers of LDL-lowering gene variants and PCSK9 inhibitor-treated patients.

Role of lncRNA-MEG8/miR-296-3p axis in gestational diabetes mellitus.

AIM: Gestational diabetes mellitus (GDM) is the most common complication in pregnancy. This study aimed to investigate the potential mechanism and effects of long-noncoding RNA maternally expressed 8 (lncRNA-MEG8) in GDM. METHODS: Targeted interactions involving lncRNA-MEG8 and miR-296-3p were initially predicted using starBase software and then confirmed using dual-luciferase reporter gene analysis. The expression levels of lncRNA-MEG8 and miR-296-3p in peripheral blood samples from patients with GDM were measured using reverse transcription-quantitative polymerase chain reaction. Enzyme-linked immunosorbent assay was used to evaluate the overall levels of insulin and insulin secretion. Additionally, MTT and flow cytometric methods were used to detect cell viability and apoptosis. Cell apoptosis-associated proteins were determined by western blotting. RESULTS: Our results indicated that lncRNA-MEG8 is a potential target of miR-296-3p. lncRNA-MEG8 level was higher, whereas that of miR-296-3p was lower in patients with GDM than in healthy individuals. LncRNA-MEG8-siRNA promoted insulin content and secretion. Furthermore, MEG8-siRNA increased cell viability and decreased apoptosis. However, these changes were reversed by an miR-296-3p inhibitor. Moreover, a miR-296-3p mimic had the same effect on INS-1 cells as MEG8-siRNA, as evidenced by enhanced insulin secretion, cell viability, and reduced apoptosis. CONCLUSION: LncRNA-MEG8-siRNA promotes pancreatic ß-cell function by upregulating miR-296-3p.

Abnormal Expression of microRNA-296-3p in Type 2 Diabetes Patients and its Role in Pancreatic ß-Cells Function by Targeting Tensin Homolog Deleted on Chromosome Ten.

Diabetes mellitus (DM), a familiar disease, is characterized by high blood glucose levels owing to insulin deficiency. Researches have suggested that the incidence rate of diabetes is increasing and it has become an important global epidemic. The type 2 diabetes mellitus (T2DM) is featured with pancreatic ß-cell loss and lack of insulin release. Nevertheless, the therapeutic methods that was helpful to improve pancreatic ß-cell damage still unclear. Previous report have revealed that tensin homolog deleted on chromosome ten (PTEN) was remarkably enhanced in serum of patients with T2DM, and the lack of PTEN may prevent function deficiency of pancreatic ß-cells in DM. However, the underlying mechanisms are rarely illustrated. Our purpose in this report was to illustrated the roles and potential mechanism of microRNA-296-3p (miR-296-3p) in uric acid (UA)-induced pancreatic ß-cell injury. The direct target of miR-296-3p was predicted and verified by dual-luciferase reporter system and TargetScan assay. Moreover, Min6 cells were induced by 5 mg/dl UA and the cell proliferation, apoptosis, and insulin release were evaluated using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, flow cytometry and glucose-stimulated insulin secretion (GSIS), respectively. Quantitative reverse transcription PCR (qRT-PCR) and western blot assay were adopted to analyze the levels of miR-296-3p, PTEN and apoptosis-related proteins. TargetScan and Dual-luciferase reporter system confirmed that PTEN directly target miR-296-3p. MiR-296-3p was downregulated in UA-induced Min6 cells and the serum of type 2 diabetes patients, while PTEN was upregulated in UA-induced Min6 cells. Upregulation of miR-296-3p by mimic dramatically promoted miR-296-3p level and decreased PTEN level. Besides, PTEN was over-expressed after PTEN-plasmid transfection. UA treatment prominently decreased cell viability, promoted apoptotic cells, enhanced Bax levels, declined Bcl-2 level as well as decreased insulin release in Min6 cells. MiR-296-3p mimic significantly alleviated UA-induced pancreatic ß-cells dysfunction, and PTEN-plasmid eliminated the protective effect of miR-296-3p on insulin release, cell viability, and apoptosis of pancreatic ß-cells in UA-stimulated Min6 cells. In summary, our findings revealed that upregulation of miR-296-3p protected pancreatic ß-cells functions against UA-induced dysfunction by targeting PTEN, which provides a novel agent for type 2 diabetes treatment.

Adipose Tissue Secretion Pattern Influences ß-Cell Wellness in the Transition from Obesity to Type 2 Diabetes.

The dysregulation of the ß-cell functional mass, which is a reduction in the number of ß-cells and their ability to secure adequate insulin secretion, represents a key mechanistic factor leading to the onset of type 2 diabetes (T2D). Obesity is recognised as a leading cause of ß-cell loss and dysfunction and a risk factor for T2D. The natural history of ß-cell failure in obesity-induced T2D can be divided into three steps: (1) ß-cell compensatory hyperplasia and insulin hypersecretion, (2) insulin secretory dysfunction, and (3) loss of ß-cell mass. Adipose tissue (AT) secretes many hormones/cytokines (adipokines) and fatty acids that can directly influence ß-cell function and viability. As this secretory pattern is altered in obese and diabetic patients, it is expected that the cross-talk between AT and pancreatic ß-cells could drive the maintenance of the ß-cell integrity under physiological conditions and contribute to the reduction in the ß-cell functional mass in a dysmetabolic state. In the current review, we summarise the evidence of the ability of the AT secretome to influence each step of ß-cell failure, and attempt to draw a timeline of the alterations in the adipokine secretion pattern in the transition from obesity to T2D that reflects the progressive deterioration of the ß-cell functional mass.