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.

Targeting ß-Cell Plasticity: A Promising Approach for Diabetes Treatment.

The ß-cells within the pancreas play a pivotal role in insulin production and secretion, responding to fluctuations in blood glucose levels. However, factors like obesity, dietary habits, and prolonged insulin resistance can compromise ß-cell function, contributing to the development of Type 2 Diabetes (T2D). A critical aspect of this dysfunction involves ß-cell dedifferentiation and transdifferentiation, wherein these cells lose their specialized characteristics and adopt different identities, notably transitioning towards progenitor or other pancreatic cell types like α-cells. This process significantly contributes to ß-cell malfunction and the progression of T2D, often surpassing the impact of outright ß-cell loss. Alterations in the expressions of specific genes and transcription factors unique to ß-cells, along with epigenetic modifications and environmental factors such as inflammation, oxidative stress, and mitochondrial dysfunction, underpin the occurrence of ß-cell dedifferentiation and the onset of T2D. Recent research underscores the potential therapeutic value for targeting ß-cell dedifferentiation to manage T2D effectively. In this review, we aim to dissect the intricate mechanisms governing ß-cell dedifferentiation and explore the therapeutic avenues stemming from these insights.

Reg2 treatment is protective but the induced Reg2 autoantibody is destructive to the islets in NOD mice.

Regenerating family protein 2 (Reg2) is a trophic factor which stimulates ß-cell replication and resists islet destruction. However, Reg2 also serves as an islet autoantigen, which makes it complicated to judge the effectiveness in treating diabetes. How Reg2 treatment behaves in non-obese diabetic (NOD) mice is to be investigated. NOD mice were treated with recombinant Reg2 protein, Complete Freund's adjuvant (CFA) + PBS and CFA+Reg2 vaccinations, CFA+PBS- and CFA+Reg2-immunized antisera, and single chain variable fragment (scFv)-Reg2 and mIgG2a-Reg2 antibodies. Glycemic level, bodyweight, serum Reg2 antibody titer, glucose tolerance, and insulin secretion were determined. Islet morphological characteristics, insulitis, cell apoptosis, islet cell components, and T cell infiltration were analyzed by histological examinations. The autoantigenicity of constructed Reg2C and Reg2X fragments was determined in healthy BALB/c mice, and the bioactivity in stimulating cell proliferation and survival was assessed in insulinoma MIN6 cells. Reg2 administration alleviated diabetes in NOD mice with improved glucose tolerance and insulin secretion but elevated serum Reg2 autoantibodies. Histomorphometry showed reduced inflammatory area, TUNEL signal and CD8 + T cell infiltration, and increased ß-cell proportion in support of the islet-protective effect of Reg2 treatment. CFA+PBS and CFA+Reg2 immunizations prevented diabetic onset and alleviated insulitis while injections of the antisera offered mild protections. Antibody treatments accelerated diabetic onset without increasing the overall incidence. Reg2C fragment depletes antigenicity, but reserves protective activity in streptozotocin (STZ)-treated MIN6 cells. In conclusion, Reg2 treatment alleviates type 1 diabetes (T1D) by preserving islet ß-cells, but induces Reg2 autoantibody production which poses a potential risk of accelerating diabetic progression.

Ca2+ signaling and metabolic stress-induced pancreatic ß-cell failure.

Early in the development of Type 2 diabetes (T2D), metabolic stress brought on by insulin resistance and nutrient overload causes ß-cell hyperstimulation. Herein we summarize recent studies that have explored the premise that an increase in the intracellular Ca2+ concentration ([Ca2+]i), brought on by persistent metabolic stimulation of ß-cells, causes ß-cell dysfunction and failure by adversely affecting ß-cell function, structure, and identity. This mini-review builds on several recent reviews that also describe how excess [Ca2+]i impairs ß-cell function.

Bromodomain Protein Inhibition Protects ß-Cells from Cytokine-Induced Death and Dysfunction via Antagonism of NF-κB Pathway.

Cytokine-induced ß-cell apoptosis is a major pathogenic mechanism in type 1 diabetes (T1D). Despite significant advances in understanding its underlying mechanisms, few drugs have been translated to protect ß-cells in T1D. Epigenetic modulators such as bromodomain-containing BET (bromo- and extra-terminal) proteins are important regulators of immune responses. Pre-clinical studies have demonstrated a protective effect of BET inhibitors in an NOD (non-obese diabetes) mouse model of T1D. However, the effect of BET protein inhibition on ß-cell function in response to cytokines is unknown. Here, we demonstrate that I-BET, a BET protein inhibitor, protected ß-cells from cytokine-induced dysfunction and death. In vivo administration of I-BET to mice exposed to low-dose STZ (streptozotocin), a model of T1D, significantly reduced ß-cell apoptosis, suggesting a cytoprotective function. Mechanistically, I-BET treatment inhibited cytokine-induced NF-kB signaling and enhanced FOXO1-mediated anti-oxidant response in ß-cells. RNA-Seq analysis revealed that I-BET treatment also suppressed pathways involved in apoptosis while maintaining the expression of genes critical for ß-cell function, such as Pdx1 and Ins1. Taken together, this study demonstrates that I-BET is effective in protecting ß-cells from cytokine-induced dysfunction and apoptosis, and targeting BET proteins could have potential therapeutic value in preserving ß-cell functional mass in T1D.

Epigallocatechin gallate attenuated high glucose-induced pancreatic beta cell dysfunction by modulating DRP1-mediated mitochondrial apoptosis pathways.

Long-term exposure to hyperglycemic conditions leads to ß-cell dysfunction, particularly mitochondrial dysfunction, and inflammatory and oxidative stress responses, which are considered the primary causes of ß-cell death and the hallmarks of diabetes. Plant-active ingredients may play a key role in glycemic control. Epigallocatechin gallate (EGCG) is a characteristic catechin derived from tea that possesses anti-diabetic properties. Nonetheless, its underlying mechanisms remain elusive. Herein, the protective role of EGCG on high glucose (33 mM)-induced pancreatic beta cell dysfunction and its possible molecular mechanisms were investigated. Briefly, MIN6 cells were treated with glucose and EGCG (10 µM, 20 µM, and 40 µM) for 48 h. Our results revealed that EGCG dose-dependently restored mitochondrial membrane potential and concomitantly alleviated cell apoptosis. Mechanistically, the expression level of apoptotic protein BAX and Dynamic related protein 1 (DRP1) was significantly downregulated following EGCG treatment, whereas that of the anti-apoptotic protein BCL-2 was significantly upregulated. Taken together, EGCG alleviated high glucose-induced pancreatic beta cell dysfunction by targeting the DRP1-related mitochondrial apoptosis pathway and thus can serve as a nutritional intervention for the preservation of beta cell dysfunction in patients with type 2 diabetes mellitus.

Endoplasmic reticulum stress in pancreatic ß-cell dysfunctionality and diabetes mellitus: a promising target for generation of functional hPSC-derived ß-cells in vitro.

Diabetes mellitus (DM), is a chronic disorder characterized by impaired glucose homeostasis that results from the loss or dysfunction of pancreatic ß-cells leading to type 1 diabetes (T1DM) and type 2 diabetes (T2DM), respectively. Pancreatic ß-cells rely to a great degree on their endoplasmic reticulum (ER) to overcome the increased secretary need for insulin biosynthesis and secretion in response to nutrient demand to maintain glucose homeostasis in the body. As a result, ß-cells are potentially under ER stress following nutrient levels rise in the circulation for a proper pro-insulin folding mediated by the unfolded protein response (UPR), underscoring the importance of this process to maintain ER homeostasis for normal ß-cell function. However, excessive or prolonged increased influx of nascent proinsulin into the ER lumen can exceed the ER capacity leading to pancreatic ß-cells ER stress and subsequently to ß-cell dysfunction. In mammalian cells, such as ß-cells, the ER stress response is primarily regulated by three canonical ER-resident transmembrane proteins: ATF6, IRE1, and PERK/PEK. Each of these proteins generates a transcription factor (ATF4, XBP1s, and ATF6, respectively), which in turn activates the transcription of ER stress-inducible genes. An increasing number of evidence suggests that unresolved or dysregulated ER stress signaling pathways play a pivotal role in ß-cell failure leading to insulin secretion defect and diabetes. In this article we first highlight and summarize recent insights on the role of ER stress and its associated signaling mechanisms on ß-cell function and diabetes and second how the ER stress pathways could be targeted in vitro during direct differentiation protocols for generation of hPSC-derived pancreatic ß-cells to faithfully phenocopy all features of bona fide human ß-cells for diabetes therapy or drug screening.

Mitochondria to plasma membrane redox signaling is essential for fatty acid ß-oxidation-driven insulin secretion.

We asked whether acute redox signaling from mitochondria exists concomitantly to fatty acid- (FA-) stimulated insulin secretion (FASIS) at low glucose by pancreatic ß-cells. We show that FA ß-oxidation produces superoxide/H2O2, providing: i) mitochondria-to-plasma-membrane redox signaling, closing KATP-channels synergically with elevated ATP (substituting NADPH-oxidase-4-mediated H2O2-signaling upon glucose-stimulated insulin secretion); ii) activation of redox-sensitive phospholipase iPLA2γ/PNPLA8, cleaving mitochondrial FAs, enabling metabotropic GPR40 receptors to amplify insulin secretion (IS). At fasting glucose, palmitic acid stimulated IS in wt mice; palmitic, stearic, lauric, oleic, linoleic, and hexanoic acids also in perifused pancreatic islets (PIs), with suppressed 1st phases in iPLA2γ/PNPLA8-knockout mice/PIs. Extracellular/cytosolic H2O2-monitoring indicated knockout-independent redox signals, blocked by mitochondrial antioxidant SkQ1, etomoxir, CPT1 silencing, and catalase overexpression, all inhibiting FASIS, keeping ATP-sensitive K+-channels open, and diminishing cytosolic [Ca2+]-oscillations. FASIS in mice was a postprandially delayed physiological event. Redox signals of FA ß-oxidation are thus documented, reaching the plasma membrane, essentially co-stimulating IS.

The protective effect of imatinib against pancreatic ß-cell apoptosis induced by dexamethasone via increased GSTP1 expression and reduced oxidative stress.

Glucocorticoids (GCs) are known to stimulate pancreatic beta (ß)-cell apoptosis via several mechanisms, including oxidative stress. Our previous study suggested an increase in dexamethasone-induced pancreatic ß-cell apoptosis via a reduction of glutathione S-transferase P1 (GSTP1), which is an antioxidant enzyme. Imatinib, which is a tyrosine kinase inhibitor, also exerts antioxidant effect. This study aims to test our hypothesis that imatinib would prevent pancreatic ß-cell apoptosis induced by dexamethasone via increased GSTP1 expression and reduced oxidative stress. Our results revealed that dexamethasone significantly increased apoptosis in INS-1 cells when compared to the control, and that imatinib significantly decreased INS-1 cell apoptosis induced by dexamethasone. Moreover, dexamethasone significantly increased superoxide production in INS-1 cells when compared to the control; however, imatinib, when combined with dexamethasone, significantly reduced superoxide production in INS-1 cells. Dexamethasone significantly decreased GSTP1, p-ERK1/2, and BCL2 protein expression, but significantly increased p-JNK, p-p38, and BAX protein expression in INS-1 cells-all compared to control. Importantly, imatinib significantly ameliorated the effect of dexamethasone on the expression of GSTP1, p-ERK1/2, p-JNK, p-p38 MAPK, BAX, and BCL2. Furthermore-6-(7-nitro-2,1,3-benzoxadiazol-4-ylthio) hexanol (NBDHEX), which is a GSTP1 inhibitor, neutralized the protective effect of imatinib against pancreatic ß-cell apoptosis induced by dexamethasone. In conclusion, imatinib decreases pancreatic ß-cell apoptosis induced by dexamethasone via increased GSTP1 expression and reduced oxidative stress.

Endoplasmic reticulum stress in pancreatic ß-cell dysfunction: The potential therapeutic role of dietary flavonoids.

Diabetes mellitus (DM) is a global health burden that is characterized by the loss or dysfunction of pancreatic ß-cells. In pancreatic ß-cells, endoplasmic reticulum (ER) stress is a fact of life that contributes to ß-cell loss or dysfunction. Despite recent advances in research, the existing treatment approaches such as lifestyle modification and use of conventional therapeutics could not prevent the loss or dysfunction of pancreatic ß-cells to abrogate the disease progression. Therefore, targeting ER stress and the consequent unfolded protein response (UPR) in pancreatic ß-cells may be a potential therapeutic strategy for diabetes treatment. Dietary phytochemicals have therapeutic applications in human health owing to their broad spectrum of biochemical and pharmacological activities. Flavonoids, which are commonly obtained from fruits and vegetables worldwide, have shown promising prospects in alleviating ER stress. Dietary flavonoids including quercetin, kaempferol, myricetin, isorhamnetin, fisetin, icariin, apigenin, apigetrin, vitexin, baicalein, baicalin, nobiletin hesperidin, naringenin, epigallocatechin 3-O-gallate hesperidin (EGCG), tectorigenin, liquiritigenin, and acacetin have shown inhibitory effects on ER stress in pancreatic ß-cells. Dietary flavonoids modulate ER stress signaling components, chaperone proteins, transcription factors, oxidative stress, autophagy, apoptosis, and inflammatory responses to exert their pharmacological effects on pancreatic ß-cells ER stress. This review focuses on the role of dietary flavonoids as potential therapeutic adjuvants in preserving pancreatic ß-cells from ER stress. Highlights of the underlying mechanisms of action are also presented as well as possible strategies for clinical translation in the management of DM.

Identifying miRNA Signatures Associated with Pancreatic Islet Dysfunction in a FOXA2-Deficient iPSC Model.

The pathogenesis of diabetes involves complex changes in the expression profiles of mRNA and non-coding RNAs within pancreatic islet cells. Recent progress in induced pluripotent stem cell (iPSC) technology have allowed the modeling of diabetes-associated genes. Our recent study using FOXA2-deficient human iPSC models has highlighted an essential role for FOXA2 in the development of human pancreas. Here, we aimed to provide further insights on the role of microRNAs (miRNAs) by studying the miRNA-mRNA regulatory networks in iPSC-derived islets lacking the FOXA2 gene. Consistent with our previous findings, the absence of FOXA2 significantly downregulated the expression of islet hormones, INS, and GCG, alongside other key developmental genes in pancreatic islets. Concordantly, RNA-Seq analysis showed significant downregulation of genes related to pancreatic development and upregulation of genes associated with nervous system development and lipid metabolic pathways. Furthermore, the absence of FOXA2 in iPSC-derived pancreatic islets resulted in significant alterations in miRNA expression, with 61 miRNAs upregulated and 99 downregulated. The upregulated miRNAs targeted crucial genes involved in diabetes and pancreatic islet cell development. In contrary, the absence of FOXA2 in islets showed a network of downregulated miRNAs targeting genes related to nervous system development and lipid metabolism. These findings highlight the impact of FOXA2 absence on pancreatic islet development and suggesting intricate miRNA-mRNA regulatory networks affecting pancreatic islet cell development.

[Mechanism of electroacupuncture regulating nuclear factor-κB pathway to improve the dedifferentiation of pancreatic ß-cells in rats with T2DM].

OBJECTIVE: To observe the effects of electroacupuncture (EA) on the expression of serum interleukin-1ß (IL-1ß), tumor necrosis factor-α (TNF-α), and the pancreatic nuclear factor-κB (NF-κB) pathway in type 2 diabetes mellitus (T2DM) rats, and to explore the possible mechanism by which EA improving the dedifferentiation of pancreatic ß-cells in the treatment of T2DM. METHODS: Among 18 SPF-grade male Wistar rats, 6 rats were randomly selected as the control group, and the remaining 12 rats were fed with high-sugar and high-fat diet combined with intraperitoneal injection of 2% streptozotocin solution (35 mg/kg) to establish T2DM model. After successful modeling, the 12 rats were randomly divided into a model group and an EA group, with 6 rats in each group. The EA group received EA at bilateral "Zusanli" (ST 36), "Sanyinjiao" (SP 6), "Weiwanxiashu" (EX-B 3), and "Pishu" (BL 20), with continuous wave, frequency of 15 Hz, current intensity of 2 mA, for 20 min each time, once a day, 6 times a week, for a total of 6 weeks. Fasting blood glucose (FBG) levels were measured before modeling and before and after intervention. After intervention, ELISA was used to detect the serum fasting insulin (FINS), IL-1ß and TNF-α levels, and the ß-cell function index (HOMA-ß) and insulin resistance index (HOMA-IR) were calculated; HE staining was used to observe the morphology of the pancreatic islets; Western blot was used to detect the protein expression of pancreatic forkhead box protein O1 (FoxO1), pancreatic and duodenal homeobox 1 (PDX-1), neurogenin 3 (NGN3), and NF-κB p65. RESULTS: After intervention, the FBG in the model group was higher than that in the control group (P<0.01), and the FBG in the EA group was lower than that in the model group (P<0.01). Compared with the control group, the model group had increased levels of serum FINS, IL-1ß, TNF-α, and HOMA-IR (P<0.01), and decreased HOMA-ß (P<0.01), reduced protein expression of pancreatic FoxO1 and PDX-1 (P<0.01), and increased protein expression of pancreatic NGN3 and NF-κB p65 (P<0.01, P<0.05). Compared with the model group, the EA group had lower serum FINS, IL-1ß, TNF-α levels, and HOMA-IR (P<0.01), higher HOMA-ß (P<0.05), increased protein expression of pancreatic FoxO1 and PDX-1 (P<0.01, P<0.05), and decreased protein expression of pancreatic NGN3 and NF-κB p65 (P<0.01, P<0.05). The control group's pancreatic islets showed no obvious abnormalities; the model group's pancreatic islets were irregular in shape and had unclear boundaries with the surrounding area, with immune cell infiltration, reduced ß-cell nuclei, disordered arrangement of islet cells, and increased intercellular spaces; the EA group showed improvements in islet morphology, immune cell infiltration, ß-cell nuclei count, and the arrangement and spacing of islet cells approaching normal. CONCLUSION: EA could lower the blood glucose levels in T2DM rats, alleviate chronic inflammatory responses in the islets, and improve the dedifferentiation of pancreatic ß-cells, which may be related to the inhibition of pancreatic NF-κB pathway expression.

Characterizing the effects of Dechlorane Plus on ß-cells: a comparative study across models and species.

Epidemiological studies consistently link environmental toxicant exposure with increased Type 2 diabetes risk. Our study investigated the diabetogenic effects of a widely used flame retardant, Dechlorane Plus (DP), on pancreatic ß-cells using rodent and human model systems. We first examined pancreas tissues from male mice exposed daily to oral gavage of either vehicle (corn oil) or DP (10, 100, or 1000 µg/kg per day) and fed chow or high fat diet for 28-days in vivo. DP exposure did not affect islet size or endocrine cell composition in either diet group. Next, we assessed the effect of 48-hour exposure to vehicle (DMSO) or DP (1, 10, or 100 nM) in vitro using immortalized rat ß-cells (INS-1 832/3), primary mouse and human islets, and human stem-cell derived islet-like cells (SC-islets). In INS-1 832/3 cells, DP did not impact glucose-stimulated insulin secretion (GSIS) but significantly decreased intracellular insulin content. DP had no effect on GSIS in mouse islets or SC-islets but had variable effects on GSIS in human islets depending on the donor. DP alone did not affect insulin content in mouse islets, human islets, or SC-islets, but mouse islets co-exposed to DP and glucolipotoxic (GLT) stress conditions (28.7 mM glucose + 0.5 mM palmitate) had reduced insulin content compared to control conditions. Co-exposure of mouse islets to DP + GLT amplified the upregulation of Slc30a8 compared to GLT alone. Our study highlights the importance and challenges of using different in vitro models for studying chemical toxicity.

Unraveling Verapamil's Multidimensional Role in Diabetes Therapy: From ß-Cell Regeneration to Cholecystokinin Induction in Zebrafish and MIN6 Cell-Line Models.

This study unveils verapamil's compelling cytoprotective and proliferative effects on pancreatic ß-cells amidst diabetic stressors, spotlighting its unforeseen role in augmenting cholecystokinin (CCK) expression. Through rigorous investigations employing MIN6 ß-cells and zebrafish models under type 1 and type 2 diabetic conditions, we demonstrate verapamil's capacity to significantly boost ß-cell proliferation, enhance glucose-stimulated insulin secretion, and fortify cellular resilience. A pivotal revelation of our research is verapamil's induction of CCK, a peptide hormone known for its role in nutrient digestion and insulin secretion, which signifies a novel pathway through which verapamil exerts its therapeutic effects. Furthermore, our mechanistic insights reveal that verapamil orchestrates a broad spectrum of gene and protein expressions pivotal for ß-cell survival and adaptation to immune-metabolic challenges. In vivo validation in a zebrafish larvae model confirms verapamil's efficacy in fostering ß-cell recovery post-metronidazole infliction. Collectively, our findings advocate for verapamil's reevaluation as a multifaceted agent in diabetes therapy, highlighting its novel function in CCK upregulation alongside enhancing ß-cell proliferation, glucose sensing, and oxidative respiration. This research enriches the therapeutic landscape, proposing verapamil not only as a cytoprotector but also as a promoter of ß-cell regeneration, thereby offering fresh avenues for diabetes management strategies aimed at preserving and augmenting ß-cell functionality.

Exploring histone deacetylases in type 2 diabetes mellitus: pathophysiological insights and therapeutic avenues.

Diabetes mellitus is a chronic disease that impairs metabolism, and its prevalence has reached an epidemic proportion globally. Most people affected are with type 2 diabetes mellitus (T2DM), which is caused by a decline in the numbers or functioning of pancreatic endocrine islet cells, specifically the ß-cells that release insulin in sufficient quantity to overcome any insulin resistance of the metabolic tissues. Genetic and epigenetic factors have been implicated as the main contributors to the T2DM. Epigenetic modifiers, histone deacetylases (HDACs), are enzymes that remove acetyl groups from histones and play an important role in a variety of molecular processes, including pancreatic cell destiny, insulin release, insulin production, insulin signalling, and glucose metabolism. HDACs also govern other regulatory processes related to diabetes, such as oxidative stress, inflammation, apoptosis, and fibrosis, revealed by network and functional analysis. This review explains the current understanding of the function of HDACs in diabetic pathophysiology, the inhibitory role of various HDAC inhibitors (HDACi), and their functional importance as biomarkers and possible therapeutic targets for T2DM. While their role in T2DM is still emerging, a better understanding of the role of HDACi may be relevant in improving insulin sensitivity, protecting ß-cells and reducing T2DM-associated complications, among others.

Upregulation of α-ENaC induces pancreatic ß-cell dysfunction, ER stress, and SIRT2 degradation.

Islet beta cells (ß-cells) produce insulin in response to high blood glucose levels, which is essential for preserving glucose homeostasis. Voltage-gated ion channels in ß-cells, including Na +, K +, and Ca 2+ channels, aid in the release of insulin. The epithelial sodium channel alpha subunit (α-ENaC), a voltage-independent sodium ion channel, is also expressed in human pancreatic endocrine cells. However, there is no reported study on the function of ENaC in the ß-cells. In the current study, we found that α-ENaC was expressed in human pancreatic glandule and pancreatic islet ß-cells. In the pancreas of db/db mice and high-fat diet-induced mice, and in mouse islet ß-cells (MIN6 cells) treated with palmitate, α-ENaC expression was increased. When α-ENaC was overexpressed in MIN6 cells, insulin content and glucose-induced insulin secretion were significantly reduced. On the other hand, palmitate injured islet ß-cells and suppressed insulin synthesis and secretion, but increased α-ENaC expression in MIN6 cells. However, α-ENaC knockout ( Scnn1a -/-) in MIN6 cells attenuated ß-cell disorder induced by palmitate. Furthermore, α-ENaC regulated the ubiquitylation and degradation of sirtuin 2 in ß-cells. α-ENaC also modulated ß-cell function in correlation with the inositol-requiring enzyme 1 alpha/X-box binding protein 1 (IRE1α/XBP1) and protein kinase RNA-like endoplasmic reticulum kinase/C/EBP homologous protein (PERK/CHOP) endoplasmic reticulum stress pathways. These results suggest that α-ENaC may play a novel role in insulin synthesis and secretion in the ß-cells, and the upregulation of α-ENaC promotes islet ß-cell dysfunction. In conclusion, α-ENaC may be a key regulator involved in islet ß-cell damage and a potential therapeutic target for type 2 diabetes mellitus.

Gain of function mutation in K(ATP) channels and resulting upregulation of coupling conductance are partners in crime in the impairment of Ca2+ oscillations in pancreatic ß-cells.

Gain of function mutations in the pore forming Kir6 subunits of the ATP sensitive K+ channels (K(ATP) channels) of pancreatic ß-cells are the major cause of neonatal diabetes in humans. In this study, we show that in insulin secreting mouse ß-cell lines, gain of function mutations in Kir6.1 result in a significant connexin36 (Cx36) overexpression, which form gap junctional connections and mediate electrical coupling between ß-cells within pancreatic islets. Using computational modeling, we show that upregulation in Cx36 might play a functional role in the impairment of glucose stimulated Ca2+ oscillations in a cluster of ß-cells with Kir6.1 gain of function mutations in their K(ATP) channels (GoF-K(ATP) channels). Our results show that without an increase in Cx36 expression, a gain of function mutation in Kir6.1 might not be sufficient to diminish glucose stimulated Ca2+ oscillations in a ß-cell cluster. We also show that a reduced Cx36 expression, which leads to loss of coordination in a wild-type ß-cell cluster, restores coordinated Ca2+ oscillations in a ß-cell cluster with GoF-K(ATP) channels. Our results indicate that in a heterogenous ß-cell cluster with GoF-K(ATP) channels, there is an inverted u-shaped nonmonotonic relation between the cluster activity and Cx36 expression. These results show that in a neonatal diabetic ß-cell model, gain of function mutations in the Kir6.1 cause Cx36 overexpression, which aggravates the impairment of glucose stimulated Ca2+ oscillations.

Pancreatic islet adaptation in pregnancy and postpartum.

Pancreatic islets, particularly insulin-producing ß-cells, are central regulators of glucose homeostasis capable of responding to a variety of metabolic stressors. Pregnancy is a unique physiological stressor, necessitating the islets to adapt to the complex interplay of maternal and fetal-placental factors influencing the metabolic milieu. In this review we highlight studies defining gestational adaptation mechanisms within maternal islets and emerging studies revealing islet adaptations during the early postpartum and lactation periods. These include adaptations in both ß and in 'non-ß' islet cells. We also discuss insights into how gestational and postpartum adaptation may inform pregnancy-specific and general mechanisms of islet responses to metabolic stress and contribute to investigation of gestational diabetes.

Aged garlic extract preserves beta-cell functioning via modulation of nuclear factor kappa-B (NF-κB)/Toll-like receptor (TLR)-4 and sarco endoplasmic reticulum calcium ATPase (SERCA)/Ca2+ in diabetes mellitus.

BACKGROUND: Peripheral insulin resistance and compromised insulin secretion from pancreatic ß-cells are significant factors and pathogenic hallmarks of diabetes mellitus (DM). NF-κß/TLR-4 and SERCA/Ca2+ pathways have been identified as potential pathways regulating insulin synthesis by preserving pancreatic ß-cell functioning. The current study aimed to evaluate the therapeutic effect of aged garlic extract (AGE) against DM in a streptozotocin (STZ)-induced rat model with particular emphasis on pancreatic ß-cell functioning. METHODS: AGE was characterized by gas chromatography-mass spectrometry (GC-MS), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) to evaluate its physio-chemical characteristics followed by in-vitro anti-diabetic and antioxidant potential. This was followed by the induction of DM in laboratory animals for investigating the therapeutic action of AGE by evaluating the role of NF-κß/TLR-4 and the SERCA/Ca2+ pathway. The parameters assessed in the present experimental setup encompassed antioxidant parameters, metabolic indicators, insulin concentration, intracellular calcium levels, apoptotic markers (CCK-8 and Caspase Glo-8), and protein expression (P-62 and APACHE-II). RESULTS: AGE characterization by SEM, GC-MS, and X-ray diffraction (XRD) revealed the presence of phenylalanine, alliin, S-allylmercaptocysteine (SAMC), tryptophan, 1-methyl-1,2,3,4-tetrahydro-ß-carboline-3-carboxylic acid as major bioactive constituents of AGE. Metabolic studies, including intraperitoneal glucose tolerance test (IPGTT), revealed significantly lower blood glucose levels in the AGE group compared to the disease control group. In contrast, the intraperitoneal insulin tolerance test (ITT) exhibited no significant difference in insulin sensitivity between the AGE supplementation group and the DM control group. Interestingly, AGE was found to have no significant effect on fasting glucose and serum insulin levels. In contrast, AGE supplementation was found to cause significant hypoglycaemia in postprandial blood glucose and insulin levels. Importantly, AGE causes restoration of intracellular Ca2+ levels by modulation of SERCA/Ca2 functioning and inhibition NF-κB/TLR-4 pathway. AGE was found to interact with and inhibit the DR-5/ caspase-8/3 apoptotic complex. Furthermore, microscopic studies revealed degeneration and apoptotic changes in pancreatic ß-cells of the DM control group, while supplementation of AGE resulted in inhibition of apoptotic pathway and regeneration of pancreatic ß-cells. CONCLUSION: The current study suggests that AGE enhance glucose homeostasis by exerting their effects on pancreatic ß-cells, without ameliorating peripheral sensitivity. Moreover, AGEs promote an increase in ß-cell mass by mitigating the apoptosis of pancreatic ß-cells. These findings suggest that AGE could aid in developing a viable alternative therapy for diabetes mellitus (DM).

The efficiency of stem cell differentiation into functional beta cells for treating insulin-requiring diabetes: Recent advances and current challenges.

In recent years, the potential of stem cells (SCs) to differentiate into various types of cells, including ß-cells, has led to a significant boost in development. The efficiency of this differentiation process and the functionality of the cells post-transplantation are crucial factors for the success of stem cell therapy in diabetes. Herein, this article reviews the current advances and challenges faced by stem cell differentiation into functional ß-cells for diabetes treatment. In vitro, researchers have sought to enhance the differentiation efficiency of functional ß-cells by mimicking the normal pancreatic development process, using gene manipulation, pharmacological and culture conditions stimulation, three-dimensional (3D) and organoid culture, or sorting for functional ß-cells based on mature islet cell markers. Furthermore, in vivo studies have also looked at suitable transplantation sites, the enhancement of the transplantation microenvironment, immune modulation, and vascular function reconstruction to improve the survival rate of functional ß-cells, thereby enhancing the treatment of diabetes. Despite these advancements, developing stem cells to produce functional ß-cells for efficacious diabetes treatment is a continuous research endeavor requiring significant multidisciplinary collaboration, for the stem-cell-derived beta cells to evolve into an effective cellular therapy.