Β-cell Failure Research Articles

Enhanced BMP Signaling Alters Human β-Cell Identity and Function.

Inflammation contributes to the pathophysiology of diabetes. Identifying signaling pathways involved in pancreatic β-cell failure and identity loss can give insight into novel potential treatment strategies to prevent the loss of functional β-cell mass in diabetes. It is reported earlier that the immunosuppressive drug tacrolimus has a detrimental effect on human β-cell identity and function by activating bone morphogenetic protein (BMP) signaling. Here it is hypothesized that enhanced BMP signaling plays a role in inflammation-induced β-cell failure. Single-cell transcriptomics analyses of primary human islets reveal that IL-1β+IFNγ and IFNα treatment activated BMP signaling in β-cells. These findings are validated by qPCR. Furthermore, enhanced BMP signaling with recombinant BMP2 or 4 triggers a reduced expression of key β-cell maturity genes, associated with increased ER stress, and impaired β-cell function. Altogether, these results indicate that inflammation-activated BMP signaling is detrimental to pancreatic β-cells and that BMP-signaling can be a target to preserve β-cell identity and function in a pro-inflammatory environment.

O-GlcNAcylation modulates mTORC1 and autophagy in β-cells, driving diabetes progression.

Type 2 diabetes (T2D) arises when pancreatic β-cells fail to produce sufficient insulin to control blood glucose appropriately. Aberrant nutrient sensing by O-GlcNAcylation and mTORC1 is linked to T2D and the failure of insulin-producing β-cells. However, the nature of their crosstalk in β-cells remains unexplored. Recently, O-GlcNAcylation, a post-translation modification controlled by enzymes OGT/OGA, emerged as a pivotal regulator for β-cell health; deficiency in either enzyme causes β-cell failure. The present study investigates the previously unidentified connection between nutrient sensor OGT and mTORC1 crosstalk to regulate β-cell mass and function in vivo. We show reduced OGT and mTORC1 activity in islets of preclinical β-cell dysfunction model and obese human islets. Using loss or gain of function of OGT, we identified that O-GlcNAcylation positively regulates mTORC1 signaling in β-cells. O-GlcNAcylation negatively modulates autophagy, as the removal of OGT increases autophagy, while the deletion of OGA decreases it. Increasing mTORC1 signaling, via deletion of TSC2, alleviates the diabetic phenotypes by increasing β-cell mass but not β-cell function in OGT deficient mice. Downstream phospho-protein signaling analysis reveal diverging impact on MKK4 and calmodulin signaling between islets with OGT, TSC2, or combined deletion. These data provide new evidence of OGT's significance as an upstream regulator of mTORC1 and autophagy, crucial for the regulation of β-cell function and glucose homeostasis.

9227 Haptoglobin-related protein (HPR) new role as insulin secretion enhancer

Abstract Disclosure: Carlos Viesi, Ph.D.[1], Ian Tamburini, BS[1], Hosung Bae, Ph.D[1]., Erwin Ilegems, Ph.D.[2], Leandro Velez, Ph.D. [1], Mingqi Zhou, BS[1], Christy Nguyen, Ph.D.[1], Casey Johnson, Ph.D.[1], Cholsoon Jang, Ph.D[1]., Erika Nishimura[2] and Marcus Seldin, Ph.D.[1]. [1]Department of Biological Chemistry, Center for Epigenetics and Metabolism, University of California, Irvine, CA, USA, [2]Departments of Diabetes Protein Engineering, Diabetes Biology & Pharmacology, Medicinal Chemistry, Protein Engineering, Novo Nordisk A/S, Novo Nordisk Park, DK-2760 Måløv, Denmark. Type 2 Diabetes (T2D) affects over 530 million people around the globe. Insulin resistance, encompassing tissues such as muscle, adipose, and liver, is the initial step hallmarked by hyperinsulinemia. Coupled with β-cell failure, these coordinated responses progress to T2D, becoming irreversible and medically challenging. Despite the well-established requirement for communication between pancreas and peripheral tissues in T2D progression, this area remains almost entirely unexplored. Here, we performed a human population genetic screening across 310 individuals to search for new endocrine regulators of pancreas function. Specifically, global gene expression from 18 peripheral tissues was analyzed to identify potential endocrine regulators of insulin secretion. This analysis prioritized liver-specific Haptoglobin-related protein (HPR) as genetically-enriched with islet insulin responses. Mouse models using AAV technology and acute protein administration of HPR showed that this newly secreted protein is sufficient to prevent diet-induced insulin resistance through enhanced beta-cell respiration. When mice were administered soluble HPR, then pancreatic tissue subjected to global RNA-sequencing, enhanced respiration pathways were observed. Next, we generated hepatocyte-specific overexpression models using AAV, which were sufficient to rescue whole-body glucose disposal profiles and weight gain in diet-induced insulin-resistant mice. Altogether, these findings highlight HPR as a novel soluble protein which signals from liver to pancreatic islets. Presentation: 6/3/2024

8258 Haptoglobin-related protein (HPR) new role as insulin secretion enhancer

Abstract Disclosure: C. Viesi: None. Type 2 Diabetes (T2D) affects over 530 million people around the globe. Insulin resistance, encompassing tissues such as muscle, adipose, and liver, is the initial step hallmarked by hyperinsulinemia. Coupled with β-cell failure, these coordinated responses progress to T2D, becoming irreversible and medically challenging. Despite the well-established requirement for communication between pancreas and peripheral tissues in T2D progression, this area remains almost entirely unexplored. Here, we performed a human population genetic screening across 310 individuals to search for new endocrine regulators of pancreas function. Specifically, global gene expression from 18 peripheral tissues was analyzed to identify potential endocrine regulators of insulin secretion. This analysis prioritized liver-specific Haptoglobin-related protein (HPR) as genetically-enriched with islet insulin responses. Mouse models using AAV technology and acute protein administration of HPR showed that this newly secreted protein is sufficient to prevent diet-induced insulin resistance through enhanced beta-cell respiration. When mice were administered soluble HPR, then pancreatic tissue subjected to global RNA-sequencing, enhanced respiration pathways were observed. Next, we generated hepatocyte-specific overexpression models using AAV, which were sufficient to rescue whole-body glucose disposal profiles and weight gain in diet-induced insulin-resistant mice. Altogether, these findings highlight HPR as a novel soluble protein which signals from liver to pancreatic islets. Presentation: 6/3/2024

Metabolic Stress Levels Influence the Ability of Myelin Transcription Factors to Regulate β-Cell Identity and Survival.

A hallmark of type 2 diabetes (T2D) is endocrine islet β-cell failure, which can occur via cell dysfunction, loss-of-identity, and/or death. How each is induced remains largely unknown. Here, we use mouse β-cells that are deficient for Myelin transcription factors (Myt TFs, including Myt1, 2, and 3) to address this question. We have reported that inactivating all three Myt genes in pancreatic progenitor cells (MytPancΔ) causes β-cell failure and late onset diabetes in mice. Their lower expression in human β-cells is correlated with β-cell dysfunction and SNPs in MYT2 and MYT3 are associated in higher risk of T2D. We now show that these Myt TF-deficient postnatal β-cells also de-differentiate by reactivating several progenitor markers. Intriguingly, mosaic Myt TF inactivation in only a portion of islet β-cells does not results in overt diabetes, but this creates a condition where Myt TF-deficient β-cells stay alive while activating several markers of Ppy-expressing islet cells. By transplanting MytPancΔ islets into the anterior eye chambers of immune-compromised mice, we directly show that glycemic and obesity-related conditions influence cell fate, with euglycemia inducing several Ppy+ cell markers while hyperglycemia and insulin resistance inducing additional cell death. These findings suggest that the observed β-cell defects in T2D depend on not only their inherent genetic/epigenetic defects, but also the metabolic load.

2-Hydroxylation is a chemical switch linking fatty acids to glucose-stimulated insulin secretion

Glucose-stimulated insulin secretion (GSIS) in pancreatic β-cells is metabolically regulated and progressively diminished during the development of type 2 diabetes (T2D). This dynamic process is tightly coupled with fatty acid metabolism, but the underlying mechanisms remain poorly understood. Fatty acid 2-hydroxylase (FA2H) catalyzes the conversion of fatty acids to chiral specific (R)-2-hydroxy fatty acids ((R)-2-OHFAs), which influences cell metabolism. However, little is known about its potential coupling with GSIS in pancreatic β cells. Here, we showed that Fa2h knockout decreases plasma membrane localization and protein level of glucose transporter 2 (GLUT2), which is essential for GSIS, thereby controlling blood glucose homeostasis. Conversely, FA2H overexpression increases GLUT2 on the plasma membrane and enhances GSIS. Mechanistically, FA2H suppresses the internalization and trafficking of GLUT2 to the lysosomes for degradation. Overexpression of wild-type FA2H, but not its mutant with impaired hydroxylase activity in the pancreatic β-cells, improves glucose tolerance by promoting insulin secretion. Levels of 2-OHFAs and Fa2h gene expression are lower in high-fat diet-induced obese mouse islets with impaired GSIS. Moreover, lower gene expression of FA2H is observed in a set of human T2D islets when the insulin secretion index is significantly suppressed, indicating the potential involvement of FA2H in regulating mouse and human GSIS. Collectively, our results identified an FA chemical switch to maintain the proper response of GSIS in pancreatic β cells and provided a new perspective on the β-cell failure that triggers T2D.

A Position Statement on Diabetes with β-Cell Failure

Diabetes mellitus is a heterogeneous disease that encompasses a wide range of conditions, from mild cases to severe conditions where survival depends on insulin therapy. The Korean Diabetes Association Task Force Team for Diabetes with β-Cell Failure has established the term to classify severe refractory disease with β-cell failure. Individuals with β-cell failure are at high risk of diabetes-related complications. We propose that diabetes with β-cell failure can be diagnosed when individuals treated with multiple daily insulin injections or insulin pumps meet at least one of the following criteria: fasting C-peptide ≤ 0.6 ng/mL, non-fasting C-peptide ≤ 1.8 ng/mL, 24-hour urine C-peptide < 30 μg/day, or spot urine C-peptide/creatinine ratio ≤ 0.6 nmol/mmol. Among cases of diabetes with β-cell failure, β-cell failure with absolute insulin deficiency can be diagnosed when at least one of the following criteria is met: fasting C-peptide < 0.24 ng/mL, non-fasting C-peptide < 0.6 ng/mL, or spot urine C-peptide/ creatinine ratio < 0.2 nmol/mmol. Multiple daily insulin injections with long-acting insulin analogs and rapid-acting insulin analogs or insulin pumps are required for treatment of diabetes with β-cell failure. Continuous glucose monitoring and an automated insulin delivery system, sensor-augmented pump, or smart insulin pen, along with structured education, are necessary. We call for improvements in the relevant systems to ensure that such treatments can be provided.

Association Between Mycobacterium tuberculosis Sensitization and Insulin Resistance Among US Adults Screened for Type 2 Diabetes Mellitus.

Type 2 diabetes mellitus (T2DM) may be a long-term sequela of infection with Mycobacterium tuberculosis (Mtb) by mechanisms that remain to be fully explained. We evaluated the association between Mtb sensitization and T2DM and, via mediation analysis, the extent to which it is mediated by insulin resistance and/or β-cell failure. Adults were assessed for T2DM by fasting plasma glucose, 2-hour oral glucose tolerance testing, and hemoglobin A1c; β-cell dysfunction and insulin resistance by homoeostasis model assessment 2; and Mtb sensitization by tuberculin skin testing. Associations between Mtb sensitization and T2DM were modeled with probit regression and decomposed into indirect effects of β-cell dysfunction and insulin resistance. Analyses were adjusted for sociodemographic, behavioral, and clinical characteristics. We included 1843 adults. Individuals with Mtb sensitization were older than those without Mtb (median [IQR], 54 [39-64] vs 47 [33-62] years). As compared with being uninfected, Mtb sensitization was associated with T2DM (adjusted absolute risk difference, 9.34% [95% CI, 2.38%-15.0%]; P < .001) and increased insulin resistance (adjusted median difference, 0.16 [95% CI, .03-.29]; P = .014) but not β-cell dysfunction (adjusted median difference, -3.1 [95% CI, -10.4 to 4.3]; P = .42). In mediation analyses, insulin resistance mediated 18.3% (95% CI, 3.29%-36.0%; P = .020) of the total effect of the association between Mtb sensitization and T2DM. Definitive prospective studies examining incident T2DM following tuberculosis are warranted. Notwithstanding, our findings suggest that exposure to Mtb may be a novel risk factor for T2DM, likely driven by an increase in insulin resistance.

Association Between Type 2 Diabetes Mellitus and Alzheimer's Disease: Common Molecular Mechanism and Therapeutic Targets.

Diabetes mellitus (DM) and Alzheimer's disease (AD) rates are rising, mirroring the global trend of an aging population. Numerous epidemiological studies have shown that those with Type 2 diabetes (T2DM) have an increased risk of developing dementia. These degenerative and progressive diseases share some risk factors. To a large extent, the amyloid cascade is responsible for AD development. Neurofibrillary tangles induce neurodegeneration and brain atrophy; this chain reaction begins with hyperphosphorylation of tau proteins caused by progressive amyloid beta (Aβ) accumulation. In addition to these processes, it seems that alterations in brain glucose metabolism and insulin signalling lead to cell death and reduced synaptic plasticity in AD, before the onset of symptoms, which may be years away. Due to the substantial evidence linking insulin resistance in the brain with AD, researchers have coined the name "Type 3 diabetes" to characterize the condition. We still know little about the processes involved, even though current animal models have helped illuminate the links between T2DM and AD. This brief overview discusses insulin and IGF-1 signalling disorders and the primary molecular pathways that may connect them. The presence of GSK-3β in AD is intriguing. These proteins' association with T2DM and pancreatic β-cell failure suggests they might be therapeutic targets for both disorders.

Mitochondrial Dysfunction and Imeglimin: A New Ray of Hope for the Treatment of Type-2 Diabetes Mellitus.

Diabetes is a rapidly growing health challenge and epidemic in many developing countries, including India. India, being the diabetes capital of the world, has the dubious dual distinction of being the leading nations for both undernutrition and overnutrition. Diabetes prevalence has increased in both rural and urban areas, affected the younger population and increased the risk of complications and economic burden. These alarming statistics ring an alarm bell to achieve glycemic targets in the affected population in order to decrease diabetes-related morbidity and mortality. In the recent years, diabetes pathophysiology has been extended from an ominous triad through octet and dirty dozen etc. There is a new scope to target multiple pathways at the molecular level to achieve a better glycemic target and further prevent micro- and macrovascular complications. Mitochondrial dysfunction has a pivotal role in both β-cell failure and insulin resistance. Hence, targeting this molecular pathway may help with both insulin secretion and peripheral tissue sensitization to insulin. Imeglimin is the latest addition to our anti-diabetic armamentarium. As imeglimin targets, this root cause of defective energy metabolism and insulin resistance makes it a new add-on therapy in different diabetic regimes to achieve the proper glycemic targets. Its good tolerability and efficacy profiles in recent studies shows a new ray of hope in the journey to curtail diabetes-related morbidity.

Increased Genetic Risk for β-Cell Failure Is Associated With β-Cell Function Decline in People With Prediabetes.

Partitioned polygenic scores (pPS) have been developed to capture pathophysiologic processes underlying type 2 diabetes (T2D). We investigated the influence of T2D pPS on diabetes-related traits and T2D incidence in the Diabetes Prevention Program. We generated five T2D pPS (β-cell, proinsulin, liver/lipid, obesity, lipodystrophy) in 2,647 participants randomized to intensive lifestyle, metformin or placebo arms. Associations were tested using general linear models and Cox regression adjusted for age, sex, and principal components. Sensitivity analyses included adjustment for BMI. Higher β-cell pPS was associated with lower insulinogenic index and corrected insulin response at one year follow-up adjusted for baseline measures (effect per pPS standard deviation (SD) -0.04, P=9.6 x 10-7; -8.45 uU/mg, P=5.6 x 10-6, respectively) and with increased diabetes incidence adjusted for BMI at nominal significance (HR 1.10 per SD, P=0.035). The liver/lipid pPS was associated with reduced one-year baseline-adjusted triglyceride levels (effect per SD -4.37, P=0.001). There was no significant interaction between T2D pPS and randomized groups. The remaining pPS were associated with baseline measures only. We conclude that despite interventions for diabetes prevention, participants with a high genetic burden of the β-cell cluster pPS had worsening in measures of β-cell function.

Insulin Dynamics and Pathophysiology in Youth-Onset Type 2 Diabetes.

Youth-onset type 2 diabetes (T2D) is increasing around the globe. The mounting disease burden of youth-onset T2D portends substantial consequences for the health outcomes of young people and for health care systems. The pathophysiology of this condition is characterized by insulin resistance and initial insulin hypersecretion ± an inherent insulin secretory defect, with progressive loss of stimulated insulin secretion leading to pancreatic β-cell failure. Research studies focusing on youth-onset T2D have illuminated key differences for youth- vs adult-onset T2D, with youth having more profound insulin resistance and quicker progression to loss of sufficient insulin secretion to maintain euglycemia. There is a need for therapies that are targeted to improve both insulin resistance and, importantly, maintain sufficient insulin secretory function over the lifespan in youth-onset T2D.

(-)-Epigallocatechin 3-gallate protects pancreatic β-cell against excessive autophagy-induced injury through promoting FTO degradation

ABSTRACT Excessive macroautophagy/autophagy leads to pancreatic β-cell failure that contributes to the development of diabetes. Our previous study proved that the occurrence of deleterious hyperactive autophagy attributes to glucolipotoxicity-induced NR3C1 activation. Here, we explored the potential protective effects of (-)-epigallocatechin 3-gallate (EGCG) on β-cell-specific NR3C1 overexpression mice in vivo and NR3C1-enhanced β cells in vitro. We showed that EGCG protects pancreatic β cells against NR3C1 enhancement-induced failure through inhibiting excessive autophagy. RNA demethylase FTO (FTO alpha-ketoglutarate dependent dioxygenase) caused diminished m6A modifications on mRNAs of three pro-oxidant genes (Tlr4, Rela, Src) and, hence, oxidative stress occurs; by contrast, EGCG promotes FTO degradation by the ubiquitin-proteasome system in NR3C1-enhanced β cells, which alleviates oxidative stress, and thereby prevents excessive autophagy. Moreover, FTO overexpression abolishes the beneficial effects of EGCG on β cells against NR3C1 enhancement-induced damage. Collectively, our results demonstrate that EGCG protects pancreatic β cells against NR3C1 enhancement-induced excessive autophagy through suppressing FTO-stimulated oxidative stress, which provides novel insights into the mechanisms for the anti-diabetic effect of EGCG. Abbreviation 3-MA: 3-methyladenine; AAV: adeno-associated virus; Ad: adenovirus; ALD: aldosterone; AUC: area under curve; βNR3C1 mice: pancreatic β-cell-specific NR3C1 overexpression mice; Ctrl: control; CHX: cycloheximide; DEX: dexamethasone; DHE: dihydroethidium; EGCG: (-)-epigallocatechin 3-gallate; FTO: FTO alpha-ketoglutarate dependent dioxygenase; GSIS: glucose-stimulated insulin secretion; HFD: high-fat diet; HG: high glucose; i.p.: intraperitoneal; IOD: immunofluorescence optical density; KSIS: potassium-stimulated insulin secretion; m6A: N6-methyladenosine; MeRIP-seq: methylated RNA immunoprecipitation sequencing; NO: nitric oxide; NR3C1/GR: nuclear receptor subfamily 3, group C, member 1; NR3C1-Enhc.: NR3C1-enhancement; NAC: N-acetylcysteine; NC: negative control; PBS: phosphate-buffered saline; PI: propidium iodide; OCR: oxygen consumption rate; Palm.: palmitate; RELA: v-rel reticuloendotheliosis viral oncogene homolog A (avian); RNA-seq: RNA sequencing; O2 .-: superoxide anion; SRC: Rous sarcoma oncogene; ROS: reactive oxygen species; T2D: type 2 diabetes; TEM: transmission electron microscopy; TLR4: toll-like receptor 4; TUNEL: terminal dUTP nick-end labeling; UTR: untranslated region; WT: wild-type.

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

Early in the development of Type 2 diabetes (T2D), metabolic stress brought on by insulin resistance and nutrient overload causes β-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 β-cells, causes β-cell dysfunction and failure by adversely affecting β-cell function, structure, and identity. This mini-review builds on several recent reviews that also describe how excess [Ca2+]i impairs β-cell function.

Atf4 protects islet β-cell identity and function under acute glucose-induced stress but promotes β-cell failure in the presence of free fatty acid.

Atf4 is dispensable in β-cells in young miceAtf4 protects β-cells under high glucoseAtf4 exacerbate fatty acid-induced β-cell defectsAtf4 activates translation but depresses lipid-metabolism.

Dysregulation of cholesterol homeostasis is an early signal of β-cell proteotoxicity characteristic of type 2 diabetes.

Type 2 diabetes (T2D) is a common metabolic disease due to insufficient insulin secretion by pancreatic β-cells in the context of insulin resistance. Islet molecular pathology reveals a role for protein misfolding in β-cell dysfunction and loss with islet amyloid derived from islet amyloid polypeptide (IAPP), a protein coexpressed and cosecreted with insulin. The most toxic form of misfolded IAPP is intracellular membrane disruptive toxic oligomers present in β-cells in T2D and in β-cells of mice transgenic for human IAPP (hIAPP). Prior work revealed a high degree of overlap of transcriptional changes in islets from T2D and prediabetic 9- to 10-wk-old mice transgenic for hIAPP with most changes being pro-survival adaptations and therefore of limited therapeutic guidance. Here, we investigated islets from hIAPP transgenic mice at an earlier age (6 wk) to screen for potential mediators of hIAPP toxicity that precede predominance of pro-survival signaling. We identified early suppression of cholesterol synthesis and trafficking along with aberrant intra-β-cell cholesterol and lipid deposits and impaired cholesterol trafficking to cell membranes. These findings align with comparable lipid deposits present in β-cells in T2D and increased vulnerability to develop T2D in individuals taking medications that suppress cholesterol synthesis.NEW & NOTEWORTHY β-Cell failure in type 2 diabetes (T2D) is characterized by β-cell misfolded protein stress due to the formation of toxic oligomers of islet amyloid polypeptide (IAPP). Most transcriptional changes in islets in T2D are pro-survival adaptations consistent with the slow progression of β-cell loss. In the present study, investigation of the islet transcriptional signatures in a mouse model of T2D expressing human IAPP revealed decreased cholesterol synthesis and trafficking as a plausible early mediator of IAPP toxicity.

Atypical KCNQ1/Kv7 channel function in a neonatal diabetes patient: Hypersecretion preceded the failure of pancreatic β-cells

KCNQ1/Kv7, a low-voltage-gated K+ channel, regulates cardiac rhythm and glucose homeostasis. While KCNQ1 mutations are associated with long-QT syndrome and type2 diabetes, its function in human pancreatic cells remains controversial. We identified a homozygous KCNQ1 mutation (R397W) in an individual with permanent neonatal diabetes melitus (PNDM) without cardiovascular symptoms. To decipher the potential mechanism(s), we introduced the mutation into human embryonic stem cells and generated islet-like organoids (SC-islets) using CRISPR-mediated homology-repair. The mutation did not affect pancreatic differentiation, but affected channel function by increasing spike frequency and Ca2+ flux, leading to insulin hypersecretion. With prolonged culturing, the mutant islets decreased their secretion and gradually deteriorated, modeling a diabetic state, which accelerated by high glucose levels. The molecular basis was the downregulated expression of voltage-activated Ca2+ channels and oxidative phosphorylation. Our study provides a better understanding of the role of KCNQ1 in regulating insulin secretion and β-cell survival in hereditary diabetes pathology.

Loss of β-cell identity and dedifferentiation, not an irreversible process?

Type 2 diabetes (T2D) is a polygenic metabolic disorder characterized by insulin resistance in peripheral tissues and impaired insulin secretion by the pancreas. While the decline in insulin production and secretion was previously attributed to apoptosis of insulin-producing β-cells, recent studies indicate that β-cell apoptosis rates are relatively low in diabetes. Instead, β-cells primarily undergo dedifferentiation, a process where they lose their specialized identity and transition into non-functional endocrine progenitor-like cells, ultimately leading to β-cell failure. The underlying mechanisms driving β-cell dedifferentiation remain elusive due to the intricate interplay of genetic factors and cellular stress. Understanding these mechanisms holds the potential to inform innovative therapeutic approaches aimed at reversing β-cell dedifferentiation in T2D. This review explores the proposed drivers of β-cell dedifferentiation leading to β-cell failure, and discusses current interventions capable of reversing this process, thus restoring β-cell identity and function.

Bax Inhibitor-1 preserves pancreatic β-cell proteostasis by limiting proinsulin misfolding and programmed cell death

The prevalence of diabetes steadily increases worldwide mirroring the prevalence of obesity. Endoplasmic reticulum (ER) stress is activated in diabetes and contributes to β-cell dysfunction and apoptosis through the activation of a terminal unfolded protein response (UPR). Our results uncover a new role for Bax Inhibitor-One (BI-1), a negative regulator of inositol-requiring enzyme 1 (IRE1α) in preserving β-cell health against terminal UPR-induced apoptosis and pyroptosis in the context of supraphysiological loads of insulin production. BI-1-deficient mice experience a decline in endocrine pancreatic function in physiological and pathophysiological conditions, namely obesity induced by high-fat diet (HFD). We observed early-onset diabetes characterized by hyperglycemia, reduced serum insulin levels, β-cell loss, increased pancreatic lipases and pro-inflammatory cytokines, and the progression of metabolic dysfunction. Pancreatic section analysis revealed that BI-1 deletion overburdens unfolded proinsulin in the ER of β-cells, confirmed by ultrastructural signs of ER stress with overwhelmed IRE1α endoribonuclease (RNase) activity in freshly isolated islets. ER stress led to β-cell dysfunction and islet loss, due to an increase in immature proinsulin granules and defects in insulin crystallization with the presence of Rod-like granules. These results correlated with the induction of autophagy, ER phagy, and crinophagy quality control mechanisms, likely to alleviate the atypical accumulation of misfolded proinsulin in the ER. In fine, BI-1 in β-cells limited IRE1α RNase activity from triggering programmed β-cell death through apoptosis and pyroptosis (caspase-1, IL-1β) via NLRP3 inflammasome activation and metabolic dysfunction. Pharmaceutical IRE1α inhibition with STF-083010 reversed β-cell failure and normalized the metabolic phenotype. These results uncover a new protective role for BI-1 in pancreatic β-cell physiology as a stress integrator to modulate the UPR triggered by accumulating unfolded proinsulin in the ER, as well as autophagy and programmed cell death, with consequences on β-cell function and insulin secretion.In pancreatic β-cells, BI-1–/– deficiency perturbs proteostasis with proinsulin misfolding, ER stress, terminal UPR with overwhelmed IRE1α/XBP1s/CHOP activation, inflammation, β-cell programmed cell death, and diabetes.

Non-esterified fatty acid palmitate facilitates oxidative endoplasmic reticulum stress and apoptosis of β-cells by upregulating ERO-1α expression

Adipose tissue-derived non-esterified saturated long-chain fatty acid palmitate (PA) decisively contributes to β-cell demise in type 2 diabetes mellitus in part through the excessive generation of hydrogen peroxide (H2O2). The endoplasmic reticulum (ER) as the primary site of oxidative protein folding could represent a significant source of H2O2. Both ER-oxidoreductin-1 (ERO-1) isoenzymes, ERO-1α and ERO-1β, catalyse oxidative protein folding within the ER, generating equimolar amounts of H2O2 for every disulphide bond formed. However, whether ERO-1-derived H2O2 constitutes a potential source of cytotoxic luminal H2O2 under lipotoxic conditions is still unknown. Here, we demonstrate that both ERO-1 isoforms are expressed in pancreatic β-cells, but interestingly, PA only significantly induces ERO-1α. Its specific deletion significantly attenuates PA-mediated oxidative ER stress and subsequent β-cell death by decreasing PA-mediated ER-luminal and mitochondrial H2O2 accumulation, by counteracting the dysregulation of ER Ca2+ homeostasis, and by mitigating the reduction of mitochondrial membrane potential and lowered ATP content. Moreover, ablation of ERO-1α alleviated PA-induced hyperoxidation of the ER redox milieu. Importantly, ablation of ERO-1α did not affect the insulin secretory capacity, the unfolded protein response, or ER redox homeostasis under steady-state conditions. The involvement of ERO-1α-derived H2O2 in PA-mediated β-cell lipotoxicity was corroborated by the overexpression of a redox-active ERO-1α underscoring the proapoptotic activity of ERO-1α in pancreatic β-cells. Overall, our findings highlight the critical role of ERO-1α-derived H2O2 in lipotoxic ER stress and β-cell failure.