Β-cell Survival Research Articles

Cav1.3 L-type Ca2+ channel modulates pancreatic β-cell electrical activity and survival

Pancreatic β-cells express several high voltage-gated Ca2+ channel (HVCC) isoforms critical for insulin release, cell differentiation, and survival. RNAseq and qPCR analyses demonstrated that CACNA1D gene encoding for CaV1.3-α1D isoform is highly expressed in pancreatic islets of both mice and men. Additionally, CACNA1D genetic polymorphisms were associated with increased susceptibility for diabetes while CaV1.3 gain-of-function mutations cause hyperinsulinemia in humans. Nevertheless, functional evidence for the role of CaV1.3 on β-cell electrical activity, insulin release and β-cell mass is contradictory and largely unknown.

Oleanolic Acid: Extraction, Characterization and Biological Activity.

Oleanolic acid, a pentacyclic triterpenoid ubiquitously present in the plant kingdom, is receiving outstanding attention from the scientific community due to its biological activity against multiple diseases. Oleanolic acid is endowed with a wide range of biological activities with therapeutic potential by means of complex and multifactorial mechanisms. There is evidence suggesting that oleanolic acid might be effective against dyslipidemia, diabetes and metabolic syndrome, through enhancing insulin response, preserving the functionality and survival of β-cells and protecting against diabetes complications. In addition, several other functions have been proposed, including antiviral, anti-HIV, antibacterial, antifungal, anticarcinogenic, anti-inflammatory, hepatoprotective, gastroprotective, hypolipidemic and anti-atherosclerotic activities, as well as interfering in several stages of the development of different types of cancer; however, due to its hydrophobic nature, oleanolic acid is almost insoluble in water, which has led to a number of approaches to enhance its biopharmaceutical properties. In this scenario, the present review aimed to summarize the current knowledge and the research progress made in the last years on the extraction and characterization of oleanolic acid and its biological activities and the underlying mechanisms of action.

HDL functionality in type 1 and type 2 diabetes: new insights.

Purpose of reviewTo critically appraise new insights into HDL structure and function in type 1 diabetes (T1DM) and type 2 diabetes (T2DM).Recent findingsIn young T1DM patients with early renal impairment and a high inflammatory score, both HDL antioxidative activity and endothelial vasodilatory function were impaired, revealing a critical link between HDL dysfunction, subclinical vascular damage, systemic inflammation and end organ damage. HDL may inhibit development of T2DM by attenuating endoplasmic reticulum (ER) stress and apoptotic loss of pancreatic β-cells, an effect due in part to ABC transporter-mediated efflux of specific oxysterols with downstream activation of the hedghehog signalling receptor, Smoothened. The apoM-sphingosine-1-phosphate complex is critical to HDL antidiabetic activity, encompassing protection against insulin resistance, promotion of insulin secretion, enhanced β-cell survival and inhibition of hepatic glucose production. Structure-function studies of HDL in hyperglycemic, dyslipidemic T2DM patients revealed both gain and loss of lipidomic and proteomic components. Such changes attenuated both the optimal protective effects of HDL on mitochondrial function and its capacity to inhibit endothelial cell apoptosis. Distinct structural components associated with individual HDL functions.SummaryExtensive evidence indicates that both the proteome and lipidome of HDL are altered in T1DM and T2DM, with impairment of multiple functions.

Azadirachtin Attenuates Lipopolysaccharide-Induced ROS Production, DNA Damage, and Apoptosis by Regulating JNK/Akt and AMPK/mTOR-Dependent Pathways in Rin-5F Pancreatic Beta Cells.

Pancreatic inflammation and the resulting cellular responses have been implicated in pancreatitis, diabetes, and pancreatic cancer. Inflammatory responses due to the bacterial endotoxin, lipopolysaccharide (LPS), have been demonstrated to alter cellular metabolism, autophagy, apoptosis, and cell proliferation in different cell populations, and hence increases the risks for organ toxicity including cancer. The exact molecular mechanism is however not clear. In the present study, we investigated the role and mechanism of an antioxidant, azadirachtin (AZD), a limonoid extracted from the neem tree (Azadirachta indica), against LPS-induced oxidative stress in the pancreatic β-cell line, Rin-5F. We demonstrated that cells treated with LPS (1 µg/mL for 24 h) showed increased reactive oxygen species (ROS) production, DNA damage, cell cycle arrest, and apoptosis. Our results also showed that LPS induced alterations in the AMP-activated protein kinase (AMPK)/mammalian target of rapamycin (mTOR) pathways, suppressing autophagy and augmenting apoptosis. Treatment with Azadirachtin (25 µM for 24 h), on the other hand, rendered some degree of protection to the pancreatic cells from apoptosis by inducing the autophagy signals required for cell survival. These results may have significance in elucidating the mechanisms of pancreatic β-cell survival and death by balancing the molecular communication between autophagy and apoptosis under inflammatory and pathological conditions.

Gut Metabolite Trimethylamine N-Oxide Protects INS-1 β-Cell and Rat Islet Function under Diabetic Glucolipotoxic Conditions.

Serum accumulation of the gut microbial metabolite trimethylamine N-oxide (TMAO) is associated with high caloric intake and type 2 diabetes (T2D). Impaired pancreatic β-cell function is a hallmark of diet-induced T2D, which is linked to hyperglycemia and hyperlipidemia. While TMAO production via the gut microbiome-liver axis is well defined, its molecular effects on metabolic tissues are unclear, since studies in various tissues show deleterious and beneficial TMAO effects. We investigated the molecular effects of TMAO on functional β-cell mass. We hypothesized that TMAO may damage functional β-cell mass by inhibiting β-cell viability, survival, proliferation, or function to promote T2D pathogenesis. We treated INS-1 832/13 β-cells and primary rat islets with physiological TMAO concentrations and compared functional β-cell mass under healthy standard cell culture (SCC) and T2D-like glucolipotoxic (GLT) conditions. GLT significantly impeded β-cell mass and function by inducing oxidative and endoplasmic reticulum (ER) stress. TMAO normalized GLT-mediated damage in β-cells and primary islet function. Acute 40µM TMAO recovered insulin production, insulin granule formation, and insulin secretion by upregulating the IRE1α unfolded protein response to GLT-induced ER and oxidative stress. These novel results demonstrate that TMAO protects β-cell function and suggest that TMAO may play a beneficial molecular role in diet-induced T2D conditions.

Metabolic Effects of CCN5/WISP2 Gene Deficiency and Transgenic Overexpression in Mice.

CCN5/WISP2 is a matricellular protein, the expression of which is under the regulation of Wnt signaling and IGF-1. Our initial characterization supports the notion that CCN5 might promote the proliferation and survival of pancreatic β-cells and thus improve the metabolic profile of the animals. More recently, the roles of endogenous expression of CCN5 and its ectopic, transgenic overexpression on metabolic regulation have been revealed through two reports. Here, we attempt to compare the experimental findings from those studies, side-by-side, in order to further establish its roles in metabolic regulation. Prominent among the discoveries was that a systemic deficiency of CCN5 gene expression caused adipocyte hypertrophy, increased adipogenesis, and lipid accumulation, resulting in insulin resistance and glucose intolerance, which were further exacerbated upon high-fat diet feeding. On the other hand, the adipocyte-specific and systemic overexpression of CCN5 caused an increase in lean body mass, improved insulin sensitivity, hyperplasia of cardiomyocytes, and increased heart mass, but decreased fasting glucose levels. CCN5 is clearly a regulator of adipocyte proliferation and maturation, affecting lean/fat mass ratio and insulin sensitivity. Not all results from these models are consistent; moreover, several important aspects of CCN5 physiology are yet to be explored.

Neuropeptide Y1 receptor antagonism protects β-cells and improves glycemic control in type 2 diabetes

ObjectivesLoss of functional β-cell mass is a key factor contributing to poor glycemic control in advanced type 2 diabetes (T2D). We have previously reported that the inhibition of the neuropeptide Y1 receptor improves the islet transplantation outcome in type 1 diabetes (T1D). The aim of this study was to identify the pathophysiological role of the neuropeptide Y (NPY) system in human T2D and further evaluate the therapeutic potential of using the Y1 receptor antagonist BIBO3304 to improve β-cell function and survival in T2D. MethodsThe gene expression of the NPY system in human islets from nondiabetic subjects and subjects with T2D was determined and correlated with the stimulation index. The glucose-lowering and β-cell-protective effects of BIBO3304, a selective orally bioavailable Y1 receptor antagonist, in high-fat diet (HFD)/multiple low-dose streptozotocin (STZ)-induced and genetically obese (db/db) T2D mouse models were assessed. ResultsIn this study, we identified a more than 2-fold increase in NPY1R and its ligand, NPY mRNA expression in human islets from subjects with T2D, which was significantly associated with reduced insulin secretion. Consistently, the pharmacological inhibition of Y1 receptors by BIBO3304 significantly protected β cells from dysfunction and death under multiple diabetogenic conditions in islets. In a preclinical study, we demonstrated that the inhibition of Y1 receptors by BIBO3304 led to reduced adiposity and enhanced insulin action in the skeletal muscle. Importantly, the Y1 receptor antagonist BIBO3304 treatment also improved β-cell function and preserved functional β-cell mass, thereby resulting in better glycemic control in both HFD/multiple low-dose STZ-induced and db/db T2D mice. ConclusionsOur results revealed a novel causal link between increased islet NPY-Y1 receptor gene expression and β-cell dysfunction and failure in human T2D, contributing to the understanding of the pathophysiology of T2D. Furthermore, our results demonstrate that the inhibition of the Y1 receptor by BIBO3304 represents a potential β-cell-protective therapy for improving functional β-cell mass and glycemic control in T2D.

Lipotoxicity and β-Cell Failure in Type 2 Diabetes: Oxidative Stress Linked to NADPH Oxidase and ER Stress.

A high caloric intake, rich in saturated fats, greatly contributes to the development of obesity, which is the leading risk factor for type 2 diabetes (T2D). A persistent caloric surplus increases plasma levels of fatty acids (FAs), especially saturated ones, which were shown to negatively impact pancreatic β-cell function and survival in a process called lipotoxicity. Lipotoxicity in β-cells activates different stress pathways, culminating in β-cells dysfunction and death. Among all stresses, endoplasmic reticulum (ER) stress and oxidative stress have been shown to be strongly correlated. One main source of oxidative stress in pancreatic β-cells appears to be the reactive oxygen species producer NADPH oxidase (NOX) enzyme, which has a role in the glucose-stimulated insulin secretion and in the β-cell demise during both T1 and T2D. In this review, we focus on the acute and chronic effects of FAs and the lipotoxicity-induced β-cell failure during T2D development, with special emphasis on the oxidative stress induced by NOX, the ER stress, and the crosstalk between NOX and ER stress.

Molecular mechanisms responsible for the sexual dimorphism in pancreatic β-cell insulin release

In humans, type 2 diabetes mellitus (T2DM) has a higher incidence in males compared to females, a phenotype recapitulated by many rodent models. While the sex difference in insulin sensitivity partially accounts for this phenomenon, hitherto uncharacterized differences in pancreatic β-cell insulin release strongly contribute. Here, we show that stepwise increase in extracellular glucose concentration (2, 5, 7.5, 10, 15, 20 mM) induced electrical activity in β cells of both sexes with similar glucose sensitivity (female, EC50 = 9.45 ± 0.15 mM; male, EC50 = 9.42 ± 0.16 mM). However, female β cells' resting membrane potential (RMP) and inter-spike potential (IP) were significantly higher compared to males (e.g., at 15 mM glucose: male RMP = -82.7 ± 6.3, IP = -74.3 ± 6.8 mV; female RMP = -50.0 ± 7.1, IP = -41.2 ± 7.3 mV). Females also showed higher frequency of trains of action potential (AP; at 10 mM glucose: male F = 1.13 ± 0.15 trains/min; female F = 1.78 ± 0.25 trains/min) and longer AP-burst duration (e.g., at 10 mM glucose: male, 241 ± 30.8 ms; female, 419 ± 60.2 ms). The higher RMP in females reduced the voltage-gated calcium channel (CaV) availability by ∼60%. This explains the paradoxical observation that, despite identical CaV expression levels and higher electrical activity, the islet Ca2+ transients were smaller in females compared to males. Interestingly, the different RMPs are not caused by altered KATP, TASK, or TALK K+ currents. However, stromatoxin-1-sensitive KV2.1 K+ current amplitude was almost double in males (IK = 130.93 ± 7.05 pA/pF) compared to females (IK = 75.85 ± 11.3 pA/pF) when measured at +80 mV. Our results are in agreement with previous findings showing that KV2.1 genetic deletion or pharmacological block leads to higher insulin release and β-cell survival. Therefore, we propose the sex-specific expression of KV2.1 to be the mechanism underlying the observed sexual dimorphism in insulin release and the incidence of T2DM.

CaV1.3 L-type Ca2+ channel modulates pancreatic β-cell electrical activity and survival

Pancreatic β cells express several high voltage-gated Ca2+ channel (HVCC) isoforms critical for insulin release, cell differentiation, and survival. RNaseq and qPCR analyses demonstrated that CACNA1D gene encoding for CaV1.3-α1D isoform is highly expressed in pancreatic islets of both mice and men. Additionally, CACNA1D genetic polymorphisms were associated with increased susceptibility for diabetes while CaV1.3 gain-of-function mutations cause hyperinsulinemia in humans. Nevertheless, functional evidence for the role of CaV1.3 on β-cell electrical activity, insulin release, and β-cell mass is contradictory and largely unknown. Here, we show that CaV1.3 deletion led to a sixfold increase in DNA damage and a threefold decrease in proliferation markers in pancreatic β cells of 14-d-old mice, while adult mice were largely unaffected. However, β-cell mass was reduced by ∼20% in both young and old mice, resulting in a diminished sustained insulin release. Voltage-clamp recordings in β-cells of 14-d-old mice showed an ∼20% reduction in total Ca2+ influx (WT Ipeak = -19.76 ± 1.04 pA/pF; CaV1.3-/- Ipeak = -14.84 ± 0.61 pA/pF, P = 0.001) accompanied by slower inactivation and an ∼5 mV rightwards shift in the voltage dependence of activation (WT V1/2 = -7.71 ± 0.82 mV; CaV1.3-/- V1/2 = -2.32 ± 1.09 mV, P = 0.0003). Although to a lower extent, Ca2+ influx in adult CaV1.3-/- β cells was similarly affected. Moreover, current-clamp recordings showed that CaV1.3 deletion delayed the glucose-induced action potential (AP) onset, reduced AP firing frequency (e.g., at 7.5 mM glucose, WT = 4.3 Hz; CaV1.3-/- = 2.1 Hz, P = 0.001) and AP-train frequency (e.g., at 7.5 mM glucose intertrain interval, WT = 49.3 ± 9.6 s; CaV1.3-/- = 120.3 ± 25.5 s, P = 0.04) in both young and adult β cells. Therefore, our data demonstrate that the CaV1.3 channel is required for the initiation of glucose-induced β-cell electrical activity and modulates β-cell mass and insulin release in both young and old mice.

Alleviation of Neuronal Cell Death and Memory Deficit with Chungkookjang Made with Bacillus amyloliquefaciens and Bacillus subtilis Potentially through Promoting Gut-Brain Axis in Artery-Occluded Gerbils.

Short-term fermented soybeans (chungkookjang) with specific Bacillus (B.) spp. have anti-obesity, antidiabetic, and anti-stroke functions. We examined the hypothesis that the long-term consumption of B. amyloliquefaciens SCGB 1 fermented (CKJ1) and B. subtilis SCDB 291 (CKJ291) chungkookjang can alleviate clinical symptoms and hyperglycemia after ischemic stroke by promoting the gut microbiota–brain axis. We examined this hypothesis in Mongolian male gerbils with stroke symptoms induced by carotid artery occlusion. The artery-occluded gerbils were divided into five groups: no supplementation (Control, Normal-control), 4% cooked soybeans (CSB), CKJ1, or CKJ291 in a high-fat diet for 3 weeks. The carotid arteries of gerbils in the Control, CSB, CKJ1, and CKJ291 groups were occluded for 8 min and they then continued on their assigned diets for an additional 3 weeks. Normal-control gerbils had no artery occlusion. The diets in all groups contained an identical macronutrient composition using starch, casein, soybean oil, and dietary fiber. The CSB, CKJ1, and CKJ291 groups exhibited less neuronal cell death than the Control group, while the CKJ1 group produced the most significant reduction among all groups, as much as 85% of the Normal-control group. CKJ1 and CKJ291 increased the blood flow and removal of blood clots, as determined by Doppler, more than the Control. They also showed more improvement in neurological disorders from ischemic stroke. Their improvement showed a similar tendency as neuronal cell death. CKJ1 treatment improved memory impairment, measured with Y maze and passive avoidance tests, similar to the Normal-control. The gerbils in the Control group had post-stroke hyperglycemia due to decreased insulin sensitivity and β-cell function and mass; the CKJ291, CSB, and CKJ1 treatments protected against glucose disturbance after artery occlusion and were similar to the Normal-control. CKJ1 and CKJ291 also reduced serum tumor necrosis factor-α concentrations and hippocampal interleukin-1β expression levels, compared to the Control. CKJ1 and CKJ291 increased the contents of Lactobacillus, Bacillus, and Akkermansia in the cecum feces, similar to the Normal-control. Picrust2 analysis showed that CKJ1 and CKJ291 increased the propionate and butyrate metabolism and the starch and glucose metabolism but reduced the lipopolysaccharide biosynthesis and fatty acid metabolism compared to the Control. In conclusion, daily CKJ1 and CKJ291 intake prevented neuronal cell death and memory dysfunction from the artery occlusion by increasing blood flow and β-cell survival and reducing post-stroke-hyperglycemia through modulating the gut microbiome composition and metabolites to influence the host metabolism, especially inflammation and insulin resistance, protecting against neuronal cell death and brain dysfunction. CKJ1 had better effects than CKJ291.

Expression of CD47 in the pancreatic β-cells of people with recent-onset type 1 diabetes varies according to disease endotype.

We are studying the dialogue between β-cells and the immune system in type 1 diabetes and have identified a cell surface receptor, signal regulatory protein-alpha (SIRPα) as an important component in the regulation of β-cell survival. SIRPα interacts with another protein, CD47, to mediate signalling. In the present work, we have studied the expression and role of CD47 in human islet cells in type 1 diabetes. Clonal EndoC-βH1 cells were employed for functional studies. Cells were exposed to pro-inflammatory cytokines and their viability monitored by flow cytometry after staining with propidium iodide. Targeted knockdown of CD47 or SIRPα was achieved with small interference RNA molecules and the expression of relevant proteins studied by Western blotting or immunocytochemistry. Human pancreas sections were selected from the Exeter Archival Diabetes Biobank and used to examine the expression of CD47 by immunofluorescence labelling. Image analysis was employed to quantify expression. CD47 is abundantly expressed in both α and β cells in human pancreas. In type 1 diabetes, the levels of CD47 are increased in α cells across all age groups, whereas the expression in β-cells varies according to disease endotype. Knockdown of either CD47 or SIRPα in EndoC-βH1 cells resulted in a loss of viability. We conclude that the CD47 plays a previously unrecognised role in the regulation of β-cell viability. This system is dysregulated in type 1 diabetes suggesting that it may be targeted therapeutically to slow disease progression.

Cholecystokinin attenuates β-cell apoptosis in both mouse and human islets

Loss of functional pancreatic β-cell mass and increased β-cell apoptosis are fundamental to the pathophysiology of type 1 and type 2 diabetes. Pancreatic islet transplantation has the potential to cure type 1 diabetes but is often ineffective due to the death of the islet graft within the first few years after transplant. Therapeutic strategies to directly target pancreatic β-cell survival are needed to prevent and treat diabetes and to improve islet transplant outcomes. Reducing β-cell apoptosis is also a therapeutic strategy for type 2 diabetes. Cholecystokinin (CCK) is a peptide hormone typically produced in the gut after food intake, with positive effects on obesity and glucose metabolism in mouse models and human subjects. We have previously shown that pancreatic islets also produce CCK. The production of CCK within the islet promotes β-cell survival in rodent models of diabetes and aging. We demonstrate a direct effect of CCK to reduce cytokine-mediated apoptosis in a β-cell line and in isolated mouse islets in a receptor-dependent manner. However, whether CCK can protect human β-cells was previously unknown. Here, we report that CCK can also reduce cytokine-mediated apoptosis in isolated human islets and CCK treatment in vivo decreases β-cell apoptosis in human islets transplanted into the kidney capsule of diabetic NOD/SCID mice. Collectively, these data identify CCK as a novel therapy that can directly promote β-cell survival in human islets and has therapeutic potential to preserve β-cell mass in diabetes and as an adjunct therapy after transplant.

Cathepsin C Regulates Cytokine-Induced Apoptosis in β-Cell Model Systems.

Emerging evidence suggests that several of the lysosomal cathepsin proteases are genetically associated with type 1 diabetes (T1D) and participate in immune-mediated destruction of the pancreatic β cells. We previously reported that the T1D candidate gene cathepsin H is downregulated by pro-inflammatory cytokines in human pancreatic islets and regulates β-cell function, apoptosis, and disease progression in children with new-onset T1D. In the present study, the objective was to investigate the expression patterns of all 15 known cathepsins in β-cell model systems and examine their role in the regulation of cytokine-induced apoptosis. Real-time qPCR screening of the cathepsins in human islets, 1.1B4 and INS-1E β-cell models identified several cathepsins that were expressed and regulated by pro-inflammatory cytokines. Using small interfering RNAs to knock down (KD) the cytokine-regulated cathepsins, we identified an anti-apoptotic function of cathepsin C as KD increased cytokine-induced apoptosis. KD of cathepsin C correlated with increased phosphorylation of JNK and p38 mitogen-activated protein kinases, and elevated chemokine CXCL10/IP-10 expression. This study suggests that cathepsin C is a modulator of β-cell survival, and that immune modulation of cathepsin expression in islets may contribute to immune-mediated β-cell destruction in T1D.

Pancreatic β-Cell O-GlcNAc Transferase Overexpression Increases Susceptibility to Metabolic Stressors in Female Mice.

The nutrient-sensor O-GlcNAc transferase (Ogt), the sole enzyme that adds an O-GlcNAc-modification onto proteins, plays a critical role for pancreatic β-cell survival and insulin secretion. We hypothesized that β-cell Ogt overexpression would confer protection from β-cell failure in response to metabolic stressors, such as high-fat diet (HFD) and streptozocin (STZ). Here, we generated a β-cell-specific Ogt in overexpressing (βOgtOE) mice, where a significant increase in Ogt protein level and O-GlcNAc-modification of proteins were observed in islets under a normal chow diet. We uncovered that βOgtOE mice show normal peripheral insulin sensitivity and glucose tolerance with a regular chow diet. However, when challenged with an HFD, only female βOgtOE (homozygous) Hz mice developed a mild glucose intolerance, despite increased insulin secretion and normal β-cell mass. While female mice are normally resistant to low-dose STZ treatments, the βOgtOE Hz mice developed hyperglycemia and glucose intolerance post-STZ treatment. Transcriptome analysis between islets with loss or gain of Ogt by RNA sequencing shows common altered pathways involving pro-survival Erk and Akt and inflammatory regulators IL1β and NFkβ. Together, these data show a possible gene dosage effect of Ogt and the importance O-GlcNAc cycling in β-cell survival and function to regulate glucose homeostasis.

Adoptive transfer of GRP78-treated dendritic cellsalleviates insulitisinNODmice.

The78-kDaglucose-regulated protein (GRP78) has extracellular, anti-inflammatory properties that can aid resolving inflammation. It has been established previously that GRP78 induced myeloid CD11c+ cell differentiation into distinct tolerogenic cells. This tolerance induction makes GRP78 a potential therapeutic agent for transplanted allogeneic grafts and autoimmune diseases, such as type 1 diabetes. In this research, it is revealed that rmGRP78-treated NOD mice bone marrow-derived CD11c+ cells (GRP78-DCs) highly expressed B7-H4 but down-regulated CD86 and CD40, and retained a tolerogenic signature even after stimulation by LPS. In the assessment of in vivo therapeutic efficacy after the adoptive transfer of GRP78-DCs into NOD mice, fluorescent imaging analyses revealed that the transfer specifically homed in inflamed pancreases, promoting β-cell survival and alleviating insulitis in NOD mice. The adoptive transfer of GRP78-DCs also helped reduce Th1, Th17, and CTL, suppressing inflammatory cytokine production in vivo. The findings suggest that adoptive GRP78-DC transfer is critical to resolving inflammation in NOD mice and may have relevance in a clinical setting.

Pharmacological blockade of the EP3 prostaglandin E2 receptor in the setting of type 2 diabetes enhances β-cell proliferation and identity and relieves oxidative damage

ObjectiveType 2 diabetes is characterized by hyperglycemia and inflammation. Prostaglandin E2, which signals through four G protein-coupled receptors (EP1-4), is a mediator of inflammation and is upregulated in diabetes. We have shown previously that EP3 receptor blockade promotes β-cell proliferation and survival in isolated mouse and human islets ex vivo. Here, we analyzed whether systemic EP3 blockade could enhance β-cell mass and identity in the setting of type 2 diabetes using mice with a spontaneous mutation in the leptin receptor (Leprdb). MethodsFour- or six-week-old, db/+, and db/db male mice were treated with an EP3 antagonist daily for two weeks. Pancreata were analyzed for α-cell and β-cell proliferation and β-cell mass. Islets were isolated for transcriptomic analysis. Selected gene expression changes were validated by immunolabeling of the pancreatic tissue sections. ResultsEP3 blockade increased β-cell mass in db/db mice through enhanced β-cell proliferation. Importantly, there were no effects on α-cell proliferation. EP3 blockade reversed the changes in islet gene expression associated with the db/db phenotype and restored the islet architecture. Expression of the GLP-1 receptor was slightly increased by EP3 antagonist treatment in db/db mice. In addition, the transcription factor nuclear factor E2-related factor 2 (Nrf2) and downstream targets were increased in islets from db/db mice in response to treatment with an EP3 antagonist. The markers of oxidative stress were decreased. ConclusionsThe current study suggests that EP3 blockade promotes β-cell mass expansion in db/db mice. The beneficial effects of EP3 blockade may be mediated through Nrf2, which has recently emerged as a key mediator in the protection against cellular oxidative damage.

Imeglimin Ameliorates β-Cell Apoptosis by Modulating the Endoplasmic Reticulum Homeostasis Pathway

The effects of imeglimin, a novel antidiabetes agent, on β-cell function remain unclear. Here, we unveiled the impact of imeglimin on β-cell survival. Treatment with imeglimin augmented mitochondrial function, enhanced insulin secretion, promoted β-cell proliferation, and improved β-cell survival in mouse islets. Imeglimin upregulated the expression of endoplasmic reticulum (ER)-related molecules, including Chop (Ddit3), Gadd34 (Ppp1r15a), Atf3, and Sdf2l1, and decreased eIF2α phosphorylation after treatment with thapsigargin and restored global protein synthesis in β-cells under ER stress. Imeglimin failed to protect against ER stress-induced β-cell apoptosis in CHOP-deficient islets or in the presence of GADD34 inhibitor. Treatment with imeglimin showed a significant decrease in the number of apoptotic β-cells and increased β-cell mass in Akita mice. Imeglimin also protected against β-cell apoptosis in both human islets and human pluripotent stem cell-derived β-like cells. Taken together, imeglimin modulates the ER homeostasis pathway, which results in the prevention of β-cell apoptosis both in vitro and in vivo.

SetD7 (Set7/9) is a novel target of PPARγ that promotes the adaptive pancreatic β-cell glycemic response

Loss of functional pancreatic β-cell mass leads to type 2 diabetes (T2D), attributable to modified β-cell-dependent adaptive gene expression patterns. SetD7 is a histone methyltransferase enriched in pancreatic islets that mono- and dimethylates histone-3-lysine-4 (H3K4), promoting euchromatin modifications, and also maintains the regulation of key β-cell function and survival genes. However, the transcriptional regulation of this important epigenetic modifier is unresolved. Here we identified the nuclear hormone receptor peroxisome proliferator-activated receptor-gamma (PPARγ) as a major transcriptional regulator of SetD7 and provide evidence for direct binding and functionality of PPARγ in the SetD7 promoter region. Furthermore, constitutive shRNA-mediated PPARγ knockdown in INS-1 β-cells or pancreas-specific PPARγ deletion in mice led to downregulation of SetD7 expression as well as its nuclear enrichment. The relevance of the SetD7-PPARγ interaction in β-cell adaptation was tested in normoglycemic 60% partial pancreatectomy (Px) and hyperglycemic 90% Px rat models. Whereas a synergistic increase in islet PPARγ and SetD7 expression was observed upon glycemic adaptation post-60% Px, in hyperglycemic 90% Px rats, islet PPARγ, and PPARγ targets SetD7 and Pdx1 were downregulated. PPARγ agonist pioglitazone treatment in 90% Px rats partially restored glucose homeostasis and β-cell mass and enhanced expression of SetD7 and Pdx1. Collectively, these data provide evidence that the SetD7-PPARγ interaction serves as an important element of the adaptive β-cell response.

Nicotinamide-cinnamic acid cocktail exerts pancreatic β-cells survival coupled with insulin secretion through ERK1/2 signaling pathway in an animal model of apoptosis.

Pancreatic β-cells protection is integral to insulin secretion in diabetic conditions. In this context, we investigated cinnamic acid in combination with nicotinamide on the regulation of insulin secretion and apoptosis in pancreatic β-cells using streptozotocin (STZ)-induced apoptotic model in vivo. The pancreata of nicotinamide (NA)-cinnamic acid (CA) treated rats were studied using histopathological, immunofluorescence, molecular docking, and RT-PCR analyses, supported by serum glucose and insulin levels. The biochemical data revealed that the acute treatment of NA and CA in combination significantly increased serum insulin, thereby lowering blood glucose level in vivo. From histological findings, NA-CA pre-treatment displayed significant protection against STZ-apoptotic trends, improved insulin secretion, and recapitulated the STZ-induced morphology to normal control. The upregulated expressions of caspases, caused by STZ-treatments, were significantly downregulated with NA-CA in immunofluorescent detection and their translational levels, respectively. We found dense ERK½-insulin staining and p-ERK½ expression, which was further supported by strong ERK½ residues-ligands interactions based on in silico analysis. From the pre-clinical data, we thus conclude that NA-CA cocktail exerts dual insulin releasing and survival effects in pancreatic β-cells by targeting ERK½ pathway.