Genetically programmed selective islet beta-cell loss in diabetic subjects with Wolfram's syndrome

ISR inhibition reverses pancreatic β-cell failure in Wolfram syndrome models

Pancreatic β-cell failure by WFS1 deficiency is manifested in individuals with wolfram syndrome (WS). The lack of a suitable human model in WS has impeded progress in the development of new treatments. Here, human pluripotent stem cell derived pancreatic islets (SC-islets) harboring WFS1 deficiency and mouse model of β cell specific Wfs1 knockout were applied to model β-cell failure in WS. We charted a high-resolution roadmap with single-cell RNA-seq (scRNA-seq) to investigate pathogenesis for WS β-cell failure, revealing two distinct cellular fates along pseudotime trajectory: maturation and stress branches. WFS1 deficiency disrupted β-cell fate trajectory toward maturation and directed it towards stress trajectory, ultimately leading to β-cell failure. Notably, further investigation of the stress trajectory identified activated integrated stress response (ISR) as a crucial mechanism underlying WS β-cell failure, characterized by aberrant eIF2 signaling in WFS1-deficient SC-islets, along with elevated expression of genes in regulating stress granule formation. Significantly, we demonstrated that ISRIB, an ISR inhibitor, efficiently reversed β-cell failure in WFS1-deficient SC-islets. We further validated therapeutic efficacy in vivo with β-cell specific Wfs1 knockout mice. Altogether, our study provides novel insights into WS pathogenesis and offers a strategy targeting ISR to treat WS diabetes.

A novel WFS1 variant associated with severe diabetic retinopathy in Wolfram syndrome type 1

BACKGROUND

Wolfram syndrome type 1 is a rare neurodegenerative disorder including diabetes insipidus, diabetes mellitus, optic atrophy, and deafness, with variable additional findings. The phenotypic spectrum is very heterogeneous, with non-autoimmune juvenile-onset diabetes and optic atrophy as minimal criteria for the diagnosis. Biallelic mutations in the WFS1 gene are the causative genetic anomaly for the syndrome, with, however, no evident genotype-phenotype correlation. Among the clinical features of the disease, diabetic retinopathy depicts a rarely reported microvascular complication. In this report, we describe the clinical and genetic findings in a 26-year-old patient presenting with Wolfram syndrome and severe diabetic retinopathy.

METHODS

The mutation screening was performed by polymerase chain reaction followed by Sanger sequencing of the entire coding sequence of the WFS1 gene.

RESULTS

A novel homozygous missense variant c.1901A>T (p.Lys634Met) was found in the proband and classified as probably pathogenic according to the American College of Medical Genetics and Genomics.

CONCLUSIONS

The molecular study of the WFS1 gene is essential for the diagnostic confirmation, to provide appropriate genetic counseling and a mutational screening in the at-risk relatives. The c.1901A>T (p.Lys634 Met) is a novel variant that could be responsible for a severe form of Wolfram syndrome with early and proliferative diabetic retinopathy.

Urinary Tract Involvement in Wolfram Syndrome: A Narrative Review

Wolfram Syndrome (WS) is a rare neurodegenerative disease with autosomal recessive inheritance and characterized by juvenile onset, non-autoimmune diabetes mellitus and later followed by optic atrophy leading to blindness, diabetes insipidus, hearing loss, and other neurological and endocrine dysfunctions. A wide spectrum of neurodegenerative abnormalities affecting the central nervous system has been described. Among these complications, neurogenic bladder and urodynamic abnormalities also deserve attention. Urinary tract dysfunctions (UTD) up to end stage renal disease are a life-threatening complication of WS patients. Notably, end stage renal disease is reported as one of the most common causes of death among WS patients. UTD have been also reported in affected adolescents. Involvement of the urinary tract occurs in about 90% of affected patients, at a median age of 20 years and with peaks at 13, 21 and 33 years. The aim of our narrative review was to provide an overview of the most important papers regarding urological impairment in Wolfram Syndrome. A comprehensive search on PubMed including Wolfram Syndrome and one or more of the following terms: chronic renal failure, bladder dysfunction, urological aspects, and urinary tract dysfunction, was done. The exclusion criteria were studies not written in English and not including urinary tract dysfunction deep evaluation and description. Studies mentioning general urologic abnormalities without deep description and/or follow-up were not considered. Due to the rarity of the condition, we considered not only papers including pediatric patients, but also papers with pediatric and adult case reports

Wolfram syndrome: clinical and genetic profiling of a cohort from a tertiary care centre with characterization of the primary gonadal failure

BACKGROUND

Wolfram syndrome (WFS) is a rare, monogenic neurodegenerative syndrome characterised by insulin requiring non-autoimmune diabetes mellitus (DM) and optic atrophy which are usually the earliest and commonest manifestations. However, there are other features which are under-recognized, adding to morbidity and premature mortality in these patients.

METHODS

Five patients (three males, two females) with genetically confirmed WFS at a single tertiary care centre were prospectively followed up. Their symptomatology, clinical profile, genetic analysis and radiology were analyzed. Multidisciplinary approach was used for comprehensive clinical care of this cohort. Patients with primary gonadal failure were subjected to biopsy and immunohistochemistry (IHC) for wolframin was performed.

RESULTS

DM was the earliest presenting manifestation at 6.2 ± 1.3 years followed by optic atrophy at 10.4 ± 2.3 years, diabetes insipidus at 12 ± 2.1 years and deafness at 12.8 ± 2.1 years. All patients were autoantibody negative with low C-peptide(<0.6 ng/ml). Hypoglycemic episodes were frequent (upto 60%) but there was no instance of diabetic ketoacidosis. Optic atrophy was present alongwith proliferative diabetic retinopathy and cataract in 40%. Uncommon manifestations included neuropsychiatric features, parasuicide, cystopathy, brainstem atrophy and hypergonadotropic hypogonadism only in adult males (n = 2). Testicular biopsy revealed partly hyalinised seminiferous tubules and prominence of Leydig cells. IHC confirmed the presence of mutated wolframin, which was not significantly different from normal testis specimen on protein quantification.

CONCLUSIONS

WFS requires a multidisciplinary approach with special emphasis on early diagnosis and management of other endocrine and non-endocrine features so as to improve long-term outcomes. Gonadal functions need periodic assessment, especially in adult males.

Calpain inhibitor and ibudilast rescue β cell functions in a cellular model of Wolfram syndrome

Wolfram syndrome is a rare multisystem disease characterized by childhood-onset diabetes mellitus and progressive neurodegeneration. Most cases are attributed to pathogenic variants in a single gene, Wolfram syndrome 1 (WFS1). There currently is no disease-modifying treatment for Wolfram syndrome, as the molecular consequences of the loss of WFS1 remain elusive. Because diabetes mellitus is the first diagnosed symptom of Wolfram syndrome, we aimed to further examine the functions of WFS1 in pancreatic β cells in the context of hyperglycemia. Knockout (KO) of WFS1 in rat insulinoma (INS1) cells impaired calcium homeostasis and protein kinase B/Akt signaling and, subsequently, decreased cell viability and glucose-stimulated insulin secretion. Targeting calcium homeostasis with reexpression of WFS1, overexpression of WFS1's interacting partner neuronal calcium sensor-1 (NCS1), or treatment with calpain inhibitor and ibudilast reversed deficits observed in WFS1-KO cells. Collectively, our findings provide insight into the disease mechanism of Wolfram syndrome and highlight new targets and drug candidates to facilitate the development of a treatment for this disorder and similar diseases.

Elevated β-cell stress levels promote severe diabetes development in mice with MODY4

Maturity-onset diabetes of the young (MODY) is a group of monogenetic forms of diabetes mellitus caused by mutations in genes regulating β-cell development and function. MODY represents a heterogeneous group of non-insulin-dependent diabetes arising in childhood or adult life. Interestingly, clinical heterogeneity in MODY patients like variable disease onset and severity is observed even among individual family members sharing the same mutation, an issue that is not well understood. As high blood glucose levels are a well-known factor promoting β-cell stress and ultimately leading to cell death, we asked whether additional β-cell stress might account for the occurrence of disease heterogeneity in mice carrying a MODY4 mutation. In order to challenge β-cells, we established a MODY4 animal model based on Pdx1 (pancreatic and duodenal homeobox 1) haploinsufficiency, which allows conditional modulation of cell stress by genetic inhibition of the stress-responsive IKK/NF-κB signalling pathway. While Pdx1+/- mice were found glucose intolerant without progressing to diabetes, additional challenge of β-cell function by IKK/NF-κB inhibition promoted rapid diabetes development showing hyperglycaemia, hypoinsulinemia and loss of β-cell mass. Disease pathogenesis was characterized by deregulation of genes controlling β-cell homeostasis and function. Importantly, restoration of normal IKK/NF-κB signalling reverted the diabetic phenotype including normalization of glycaemia and β-cell mass. Our findings implicate that the avoidance of additional β-cell stress can delay a detrimental disease progression in MODY4 diabetes. Remarkably, an already present diabetic phenotype can be reversed when β-cell stress is normalized.

Activation of GLP-1 receptor signalling alleviates cellular stresses and improves beta cell function in a mouse model of Wolfram syndrome

AIMS/HYPOTHESIS

Loss of functional beta cells results in a gradual progression of insulin insufficiency in Wolfram syndrome caused by recessive WFS1 mutations. However, beta cell dysfunction in Wolfram syndrome has yet to be fully characterised, and there are also no specific treatment recommendations. In this study, we aimed to characterise beta cell secretory defects and to examine the potential effects of a glucagon-like peptide-1 (GLP-1) receptor agonist on diabetes in Wolfram syndrome.

METHODS

Insulin secretory function was assessed by the pancreatic perfusion method in mice used as a model of Wolfram syndrome. In addition, granule dynamics in living beta cells were examined using total internal reflection fluorescence microscopy. Acute and chronic effects of exendin-4 (Ex-4) on glucose tolerance and insulin secretion were examined in young Wfs1^-/- mice without hyperglycaemia. Molecular events associated with Ex-4 treatment were investigated using pancreatic sections and isolated islets. In addition, we retrospectively observed a woman with Wolfram syndrome who had been treated with liraglutide for 24 weeks.

RESULTS

Treatment with liraglutide ameliorated our patient's glycaemic control and resulted in a 20% reduction of daily insulin dose along with an off-drug elevation of fasting C-peptide immunoreactivity. Glucose-stimulated first-phase insulin secretion and potassium-stimulated insulin secretion decreased by 53% and 59%, respectively, in perfused pancreases of 10-week-old Wfs1^-/- mice compared with wild-type (WT) mice. The number of insulin granule fusion events in the first phase decreased by 41% in Wfs1^-/- beta cells compared with WT beta cells. Perfusion with Ex-4 increased insulin release in the first and second phases by 3.9-fold and 5.6-fold, respectively, in Wfs1^-/- mice compared with perfusion with saline as a control. The physiological relevance of the effects of Ex-4 was shown by the fact that a single administration potentiated glucose-stimulated insulin secretion and improved glucose tolerance in Wfs1^-/- mice. Four weeks of administration of Ex-4 resulted in an off-drug amelioration of glucose excursions after glucose loading in Wfs1^-/- mice, with insulin secretory dynamics that were indistinguishable from those in WT mice, despite the fact that there was no alteration in beta cell mass. In association with the functional improvements, Ex-4 treatment reversed the increases in phosphorylated eukaryotic initiation factor (EIF2α) and thioredoxin interacting protein (TXNIP), and the decrease in phosphorylated AMP-activated kinase (AMPK), in the beta cells of the Wfs1^-/- mice. Furthermore, Ex-4 treatment modulated the transcription of oxidative and endoplasmic reticulum stress-related markers in isolated islets, implying that it was able to mitigate the cellular stresses resulting from Wfs1 deficiency.

CONCLUSIONS/INTERPRETATION

Our study provides deeper insights into the pathophysiology of beta cell dysfunction caused by WFS1 deficiency and implies that activation of the GLP-1 receptor signal may alleviate insulin insufficiency and aid glycaemic control in Wolfram syndrome.

Natural history and clinical characteristics of 50 patients with Wolfram syndrome

PURPOSE

To describe clinical characteristics of diabetes mellitus (DM) in a group of patients with Wolfram Syndrome (WS).

METHODS

Descriptive, cross-sectional observational design. The sample consisted of 50 patients diagnosed with WS. Clinical criteria contributing to WS diagnosis were analyzed: diabetes mellitus (DM), optic nerve atrophy (OA), sensorineural deafness, urological and neurological dysfunction, among others. These parameters were assessed according to their presence/absence, age of onset, and various clinical-analytical parameters.

RESULTS

All the patients studied presented DM and OA, with a mean age of onset of 5.4 ± .9 (1-14) years and 9 ± .9 (1-16) years, respectively. The remaining criteria were present with a variable frequency: 77% had diabetes insipidus, 66.7% auditory alterations, 77.8% neurogenic bladder, 61.1% neurological involvement, and 27.8% hypogonadism. A 16.7% of the patients had positive albuminuria (urinary albumin/creatinine ratio > 30 mg/g) and 72.2% had hyporreflexia. There were no significant differences in the age of diagnosis nor of the presence of different pathologies according to sex.

CONCLUSIONS

The early presence of a non-autoimmune insulin dependent DM, should alert us of an "infrequent" diabetes syndrome. Wolfram's presumptive diagnosis could be established if juvenile-onset DM occurs concomitantly with OA, and this visual impairment is not attributable to diabetic retinopathy. Despite the long period of evolution of DM and altered values of HbA1c, the prevalence of microvascular complications in the sample are low.

A Randomized Controlled Trial of Dapagliflozin Plus Once-Weekly Exenatide Versus Placebo in Individuals with Obesity and Without Diabetes: Metabolic Effects and Markers Associated with Bodyweight Loss

INTRODUCTION

The sodium-glucose cotransporter 2 inhibitor dapagliflozin and the glucagon-like peptide-1 (GLP-1) receptor agonist exenatide reduce bodyweight via differing and complementary mechanisms. This post hoc analysis investigated the metabolic effects and baseline associations with bodyweight loss on coadministration of dapagliflozin and exenatide once weekly (QW) among adults with obesity and without diabetes.

METHODS

In the primary trial, adults with obesity and without diabetes [n = 50; 18-70 years; body mass index (BMI) 30-45 kg/m²] were randomized to double-blind oral dapagliflozin 10 mg (DAPA) once daily plus subcutaneous long-acting exenatide 2 mg QW (ExQW) or placebo over 24 weeks, followed by an open-label extension from 24-52 weeks during which all participants received active treatment. Primary results have been published previously. This analysis evaluated: (1) the effects of DAPA + ExQW on changes in substrates [free fatty acids (FFAs), glycerol, beta-OH-butyrate, and glucose], hormones (glucagon and insulin), and insulin secretion [insulinogenic index (IGI)] via an oral glucose tolerance test (OGTT) and (2) associations between bodyweight loss and baseline characteristics (e.g., BMI), single-nucleotide polymorphisms (SNPs) associated with the GLP-1 pathway, and markers of glucose regulation.

RESULTS

Compared with placebo at 24 weeks, 2-h FFAs post-OGTT increased (mean difference, +20.4 μmol/l; P < 0.05), and fasting glucose, 2-h glucose post-OGTT, and glucose area under the concentration-time curve (AUC) decreased with DAPA + ExQW [mean differences, -0.68 mmol/l [P < 0.001], -2.20 mmol/l (P < 0.01), and -306 mmol/l min (P < 0.001), respectively]. Glucagon, glycerol, beta-OH-butyrate, and IGI did not differ by treatment group at 24 weeks. Over 52 weeks, DAPA + ExQW decreased fasting insulin, 2-h post-OGTT insulin, and insulin AUC. Among DAPA + ExQW-treated participants, for each copy of the SNP variant rs10010131 A allele (gene WFS1), bodyweight decreased by 2.4 kg (P < 0.05). Lower BMI and a lower IGI were also associated with greater bodyweight loss with DAPA + ExQW.

CONCLUSIONS

Metabolic effects with DAPA + ExQW included less FFA suppression versus placebo during the OGTT, suggesting compensatory lipid mobilization for energy production when glucose availability was reduced because of glucosuria. The expected increase in glucagon with DAPA did not occur with DAPA + ExQW coadministration. Bodyweight loss with DAPA + ExQW was associated with the SNP variant rs10010131 A allele, lower baseline adiposity (BMI), and lower baseline insulin secretion (IGI). These findings require further validation.

FUNDING

AstraZeneca.

Endoplasmic reticulum stress and eIF2α phosphorylation: The Achilles heel of pancreatic β cells

BACKGROUND

Pancreatic β cell dysfunction and death are central in the pathogenesis of most if not all forms of diabetes. Understanding the molecular mechanisms underlying β cell failure is important to develop β cell protective approaches.

SCOPE OF REVIEW

Here we review the role of endoplasmic reticulum stress and dysregulated endoplasmic reticulum stress signaling in β cell failure in monogenic and polygenic forms of diabetes. There is substantial evidence for the presence of endoplasmic reticulum stress in β cells in type 1 and type 2 diabetes. Direct evidence for the importance of this stress response is provided by an increasing number of monogenic forms of diabetes. In particular, mutations in the PERK branch of the unfolded protein response provide insight into its importance for human β cell function and survival. The knowledge gained from different rodent models is reviewed. More disease- and patient-relevant models, using human induced pluripotent stem cells differentiated into β cells, will further advance our understanding of pathogenic mechanisms. Finally, we review the therapeutic modulation of endoplasmic reticulum stress and signaling in β cells.

MAJOR CONCLUSIONS

Pancreatic β cells are sensitive to excessive endoplasmic reticulum stress and dysregulated eIF2α phosphorylation, as indicated by transcriptome data, monogenic forms of diabetes and pharmacological studies. This should be taken into consideration when devising new therapeutic approaches for diabetes.

Clock Gene Dysregulation Induced by Chronic ER Stress Disrupts β-cell Function

In Wfs1^-/-A^y/a islets, in association with endoplasmic reticulum (ER) stress, D-site-binding protein (Dbp) expression decreased and Nuclear Factor IL-3 (Nfil3)/E4 Promoter-binding protein 4 (E4bp4) expression increased, leading to reduced DBP transcriptional activity. Similar alterations were observed with chemically-induced ER stress. Transgenic mice expressing E4BP4 under the control of the mouse insulin I gene promoter (MIP), in which E4BP4 in β-cells is expected to compete with DBP for D-box, displayed remarkable glucose intolerance with severely impaired insulin secretion. Basal ATP/ADP ratios in MIP-E4BP4 islets were elevated without the circadian oscillations observed in wild-type islets. Neither elevation of the ATP/ADP ratio nor an intracellular Ca2+ response was observed after glucose stimulation. RNA expressions of genes involved in insulin secretion gradually increase in wild-type islets early in the feeding period. In MIP-E4BP4 islets, however, these increases were not observed. Thus, molecular clock output DBP transcriptional activity, susceptible to ER stress, plays pivotal roles in β-cell priming for insulin release by regulating β-cell metabolism and gene expressions. Because ER stress is also involved in the β-cell failure in more common Type-2 diabetes, understanding the currently identified ER stress-associated mechanisms warrants novel therapeutic and preventive strategies for both rare form and common diabetes.

RNA-sequencing of WFS1-deficient pancreatic islets

Wolfram syndrome, an autosomal recessive disorder characterized by juvenile‐onset diabetes mellitus and optic atrophy, is caused by mutations in the WFS1 gene. WFS1 encodes an endoplasmic reticulum resident transmembrane protein. The Wfs1‐null mice exhibit progressive insulin deficiency and diabetes. The aim of this study was to describe the insulin secretion and transcriptome of pancreatic islets in WFS1‐deficient mice. WFS1‐deficient (Wfs1KO) mice had considerably less pancreatic islets than heterozygous (Wfs1HZ) or wild‐type (WT) mice. Wfs1KO pancreatic islets secreted less insulin after incubation in 2 and 10 mmol/L glucose and with tolbutamide solution compared to WT and Wfs1HZ islets, but not after stimulation with 20 mmol/L glucose. Differences in proinsulin amount were not statistically significant although there was a trend that Wfs1KO had an increased level of proinsulin. After incubation in 2 mmol/L glucose solution the proinsulin/insulin ratio in Wfs1KO was significantly higher than that of WT and Wfs1HZ. RNA‐seq from pancreatic islets found melastatin‐related transient receptor potential subfamily member 5 protein gene (Trpm5) to be downregulated in WFS1‐deficient mice. Functional annotation of RNA sequencing results showed that WFS1 deficiency influenced significantly the pathways related to tissue morphology, endocrine system development and function, molecular transport network.

Genome-edited human stem cell-derived beta cells: a powerful tool for drilling down on type 2 diabetes GWAS biology

Type 2 diabetes (T2D) is a disease of pandemic proportions, one defined by a complex aetiological mix of genetic, epigenetic, environmental, and lifestyle risk factors. Whilst the last decade of T2D genetic research has identified more than 100 loci showing strong statistical association with disease susceptibility, our inability to capitalise upon these signals reflects, in part, a lack of appropriate human cell models for study. This review discusses the impact of two complementary, state-of-the-art technologies on T2D genetic research: the generation of stem cell-derived, endocrine pancreas-lineage cells and the editing of their genomes. Such models facilitate investigation of diabetes-associated genomic perturbations in a physiologically representative cell context and allow the role of both developmental and adult islet dysfunction in T2D pathogenesis to be investigated. Accordingly, we interrogate the role that patient-derived induced pluripotent stem cell models are playing in understanding cellular dysfunction in monogenic diabetes, and how site-specific nucleases such as the clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9 system are helping to confirm genes crucial to human endocrine pancreas development. We also highlight the novel biology gleaned in the absence of patient lines, including an ability to model the whole phenotypic spectrum of diabetes phenotypes occurring both in utero and in adult cells, interrogating the non-coding 'islet regulome' for disease-causing perturbations, and understanding the role of other islet cell types in aberrant glycaemia. This article aims to reinforce the importance of investigating T2D signals in cell models reflecting appropriate species, genomic context, developmental time point, and tissue type.

Glycemic variability in patients with Wolfram syndrome is lower than in type 1 diabetes

AIMS

Wolfram syndrome (WFS) is diagnosed as coexistence of diabetes mellitus and optic atrophy, where pancreatic beta cell destruction is associated with neurodegeneration. Typically, WFS necessitates insulin treatment similar to type 1 diabetes (T1D), but the mechanism of beta cell mass reduction leading to hyperglycemia is different.

METHODS

The aim of the study was to assess glycemic variability using the continuous glucose monitoring (CGM) system in seven pediatric patients with genetically confirmed WFS and compare the results with data obtained from 21 propensity score-matched patients with T1D. The "GlyCulator" application was used for the calculation of glycemic variability indices.

RESULTS

CGM recordings showed similarities in glycemic variability among WFS patients, but differing from those of the T1D group. Coefficient of variation (%CV), CONGA4h, and GONGA6h were significantly (p < 0.05) lower in WFS patients (28.08 ± 7.37, 54.96 ± 11.92, and 55.99 ± 10.58) than in T1D patients (37.87 ± 14.24, 74.12 ± 28.74, p = 0.02, and 80.26 ± 35.05, respectively). In WFS patients, the percentage of values above 126 mg/dL was 69.79 (52.08-77.43), whereas in patients with T1D, the percentage was significantly lower-47.22 (35.07-62.85, p = 0.018). Curiously, a tendency toward a lower percentage of measurements below 70 mg/dL was noted in the WFS group [0 (0-7.29)] in comparison with the T1D group [6.25 (0-18.06), p = 0.122]. WFS patients had a significantly higher C-peptide level (0.31 ± 0.2 ng/mL) than T1D patients (0.04 ± 0.04 ng/mL; p = 0.006).

CONCLUSIONS

Patients with WFS show smaller glycemic variability than individuals with T1D, and this may be associated with persistent residual insulin secretion.

Role of Endoplasmic Reticulum Stress and Unfolded Protein Responses in Health and Diseases

Endoplasmic reticulum (ER) is the site of protein synthesis, protein folding, maintainance of calcium homeostasis, synthesis of lipids and sterols. Genetic or environmental insults can alter its function generating ER stress. ER senses stress mainly by three stress sensor pathways, namely protein kinase R-like endoplasmic reticulum kinase-eukaryotic translation-initiation factor 2α, inositol-requiring enzyme 1α-X-box-binding protein 1 and activating transcription factor 6-CREBH, which induce unfolded protein responses (UPR) after the recognition of stress. Recent studies have demonstrated that ER stress and UPR signaling are involved in cancer, metabolic disorders, inflammatory diseases, osteoporosis and neurodegenerative diseases. However, the precise knowledge regarding involvement of ER stress in different disease processes is still debatable. Here we discuss the possible role of ER stress in various disorders on the basis of existing literature. An attempt has also been made to highlight the present knowledge of this field which may help to elucidate and conjure basic mechanisms and novel insights into disease processes which could assist in devising better future diagnostic and therapeutic strategies.

Type 1 diabetes pathogenesis - Prevention???

Pathogenesis of type 1 diabetes is multi-faceted, including, autoimmunity, genetics and environment. Autoimmunity directed against pancreatic islet cells results in slowly progressive selective beta-cell destruction ("Primary autoimmune insulitis"), culminating over years in clinically manifested insulin-dependent diabetes mellitus (IDDM). Circulating serum autoantibodies directed against the endocrine cells of the islets of Langerhans (Islet cell autoantibodies - ICAb) are an important hallmark of this disease. Assays for islet cell autoantibodies have facilitated the investigation and understanding of several facets in the pathogenesis of autoimmune diabetes. Their applications have extended into clinical practice and have opened new avenues for early preclinical prediction and preventive prophylaxis in IDDM/type 1 DM. Recently, surprisingly, differences in insulin content between T1DM islets, as well as, 'patchy' or 'lobular' destruction of islets have been described. These unique pathobiological phenomena, suggest that beta cell destruction may not always be inexorable and inevitably complete/total, and thus raise hopes for possible therapeutic interruption of beta cell autoimmunity - destruction and cure of type 1 diabetes. "Recurrent or secondary autoimmune insulitis" refers to the rapid reappearance of islet cell autoantibodies post pancreas transplant, and selective islet beta cell destruction in the grafted pancreas [never forgetting or "anamnestic" beta cell destructive memory], in the absence of any graft pancreas rejection [monozygotic twin to twin transplantation]. The one definite environmental factor is congenital rubella, because of which a subset of children subsequently develop type 1 diabetes. The putative predisposing factors are viruses, gluten and cow's milk. The putative protective factors include gut flora, helminths, viral infections, and Vitamin D. Prevention of T1DM can include: Primary prevention strategies before the development of autoantibodies and Secondary prevention regimens after autoantibody development. Once islet cell autoantibodies have developed, the goal is to establish a therapeutic regimen to preserve at least 90% of the beta cells, and prevent the development of hyperglycaemia. The targets for T1DM reversal should include autoimmunity, beta cell regeneration and protection of beta cell mass. Anti-CD3 teplizumab and anti-CD3 otelixizumab have been shown to provide C-peptide preservation. The unanswered questions in diabetes research include elimination of autoimmune memory responses, reestablishment of immune self-tolerance, and mechanisms of disease initiation.

Increment of serum C-peptide measured by glucagon test closely correlates with human relative beta-cell area

Pancreatic beta-cell mass contributes to glucose tolerance. The aim of this study was to evaluate the relationships between human beta-cell mass and various clinical parameters, including insulin secretory capacity. The study included 32 Japanese patients who underwent pancreatectomy and were naive to oral hypoglycemic agents and insulin. They were classified into those with normal glucose tolerance (n=13), impaired glucose tolerance (n=9) and diabetes (n=10), and their insulin secretory capacity and insulin resistance were evaluated. Immunohistochemistry was used to determine relative beta-cell area (%) which represented the proportion of insulin-positive cell area to whole pancreatic section. Increment of C-peptide immunoreactivity level by glucagon test (ΔC-peptide, increment of serum C-peptide [nmol/L] at 6 min after intravenous injection of 1-mg glucagon; r=0.64, p=0.002), homeostasis model assessment of beta-cell function (HOMA-beta, fasting immunoreactive insulin [μIU/mL] x 20 / (fasting plasma glucose [mmol/L] - 3.5); r=0.50, p=0.003), C-peptide index (CPI, fasting C-peptide [nmol/L] / fasting plasma glucose [mmol/L]; r=0.36, p=0.042), and fasting immunoreactive insulin (F-IRI [pmol/L]; r=0.36, p=0.044) correlated significantly and positively with the relative beta-cell area. The area under the curve of plasma glucose level from 0 to 120 min by 75 g-OGTT (AUC0-120) also correlated significantly and inversely with the relative beta-cell area (r=-0.36, p=0.045). Stepwise multiple regression analysis identified ΔC-peptide as the only independent and significant determinant of the relative beta-cell area. We conclude that ΔC-peptide, HOMA-beta, CPI, F-IRI and AUC0-120 correlated closely with the relative beta-cell area, and ΔC-peptide was the most valuable index for the prediction of the area.

Genetics of type 2 diabetes: insights into the pathogenesis and its clinical application. Biomed Res Int. 2014;2014:926713. [PMID: 24864266 PMCID: PMC4016836 DOI: 10.1155/2014/926713]

With rapidly increasing prevalence, diabetes has become one of the major causes of mortality worldwide. According to the latest studies, genetic information makes substantial contributions towards the prediction of diabetes risk and individualized antidiabetic treatment. To date, approximately 70 susceptibility genes have been identified as being associated with type 2 diabetes (T2D) at a genome-wide significant level (P < 5 × 10⁻⁸). However, all the genetic loci identified so far account for only about 10% of the overall heritability of T2D. In addition, how these novel susceptibility loci correlate with the pathophysiology of the disease remains largely unknown. This review covers the major genetic studies on the risk of T2D based on ethnicity and briefly discusses the potential mechanisms and clinical utility of the genetic information underlying T2D.

β-cell dysfunction due to increased ER stress in a stem cell model of Wolfram syndrome

Wolfram syndrome is an autosomal recessive disorder caused by mutations in WFS1 and is characterized by insulin-dependent diabetes mellitus, optic atrophy, and deafness. To investigate the cause of β-cell failure, we used induced pluripotent stem cells to create insulin-producing cells from individuals with Wolfram syndrome. WFS1-deficient β-cells showed increased levels of endoplasmic reticulum (ER) stress molecules and decreased insulin content. Upon exposure to experimental ER stress, Wolfram β-cells showed impaired insulin processing and failed to increase insulin secretion in response to glucose and other secretagogues. Importantly, 4-phenyl butyric acid, a chemical protein folding and trafficking chaperone, restored normal insulin synthesis and the ability to upregulate insulin secretion. These studies show that ER stress plays a central role in β-cell failure in Wolfram syndrome and indicate that chemical chaperones might have therapeutic relevance under conditions of ER stress in Wolfram syndrome and other forms of diabetes.

Wolfram syndrome 1 and adenylyl cyclase 8 interact at the plasma membrane to regulate insulin production and secretion

Endoplasmic reticulum (ER) stress causes pancreatic β-cell dysfunction and contributes to β-cell loss and the progression of type 2 diabetes. Wolfram syndrome 1 (WFS1) has been shown to be an important regulator of the ER stress signalling pathway; however, its role in β-cell function remains unclear. Here we provide evidence that WFS1 is essential for glucose- and glucagon-like peptide 1 (GLP-1)-stimulated cyclic AMP production and regulation of insulin biosynthesis and secretion. Stimulation with glucose causes WFS1 translocation from the ER to the plasma membrane, where it forms a complex with adenylyl cyclase 8 (AC8), an essential cAMP-generating enzyme in the β-cell that integrates glucose and GLP-1 signalling. ER stress and mutant WFS1 inhibit complex formation and activation of AC8, reducing cAMP synthesis and insulin secretion. These findings reveal that an ER-stress-related protein has a distinct role outside the ER regulating both insulin biosynthesis and secretion. The reduction of WFS1 protein on the plasma membrane during ER stress is a contributing factor for β-cell dysfunction and progression of type 2 diabetes.

The impact of the unfolded protein response on human disease

A central function of the endoplasmic reticulum (ER) is to coordinate protein biosynthetic and secretory activities in the cell. Alterations in ER homeostasis cause accumulation of misfolded/unfolded proteins in the ER. To maintain ER homeostasis, eukaryotic cells have evolved the unfolded protein response (UPR), an essential adaptive intracellular signaling pathway that responds to metabolic, oxidative stress, and inflammatory response pathways. The UPR has been implicated in a variety of diseases including metabolic disease, neurodegenerative disease, inflammatory disease, and cancer. Signaling components of the UPR are emerging as potential targets for intervention and treatment of human disease.

Diabetes and neurodegeneration in Wolfram syndrome: a multicenter study of phenotype and genotype

OBJECTIVE

To describe the diabetes phenotype in Wolfram syndrome compared with type 1 diabetes, to investigate the effect of glycemic control on the neurodegenerative process, and to assess the genotype-phenotype correlation.

RESEARCH DESIGN AND METHODS

The clinical data of 50 patients with Wolfram syndrome-related diabetes (WSD) were reviewed and compared with the data of 24,164 patients with type 1 diabetes. Patients with a mean HbA1c during childhood and adolescence of ≤7.5 and >7.5% were compared with respect to the occurrence of additional Wolfram syndrome symptoms. The wolframin (WFS1) gene was screened for mutations in 39 patients. WFS1 genotypes were examined for correlation with age at onset of diabetes.

RESULTS

WSD was diagnosed earlier than type 1 diabetes (5.4±3.8 vs. 7.9±4.2 years; P<0.001) with a lower prevalence of ketoacidosis (7 vs. 20%; P=0.049). Mean duration of remission in WSD was 2.3±2.4 vs. 1.6±2.1 in type 1 diabetes (NS). Severe hypoglycemia occurred in 37 vs. 7.9% (P<0.001). Neurologic disease progression was faster in the WSD group with a mean HbA1c>7.5% (P=0.031). Thirteen novel WSF1 mutations were identified. Predicted functional consequence of WFS1 mutations correlated with age at WSD onset (P=0.028).

CONCLUSIONS

Endoplasmic reticulum stress-mediated decline of β-cells in WSD occurs earlier in life than autoimmune-mediated β-cell destruction in type 1 diabetes. This study establishes a role for WFS1 in determining the age at onset of diabetes in Wolfram syndrome and identifies glucose toxicity as an accelerating feature in the progression of disease.

Wolfram syndrome 1 gene (WFS1) product localizes to secretory granules and determines granule acidification in pancreatic beta-cells

Wolfram syndrome is an autosomal recessive disorder characterized by juvenile-onset insulin-dependent diabetes mellitus and optic atrophy. The gene responsible for the syndrome (WFS1) encodes an endoplasmic reticulum (ER) resident transmembrane protein. The Wfs1-null mouse exhibits progressive insulin deficiency causing diabetes. Previous work suggested that the function of the WFS1 protein is connected to unfolded protein response and to intracellular Ca(2+) homeostasis. However, its precise molecular function in pancreatic β-cells remains elusive. In our present study, immunofluorescent and electron-microscopic analyses revealed that WFS1 localizes not only to ER but also to secretory granules in pancreatic β-cells. Intragranular acidification was assessed by measuring intracellular fluorescence intensity raised by the acidotrophic agent, 3-[2,4-dinitroanilino]-3'-amino-N-methyldipropyramine. Compared with wild-type β-cells, there was a 32% reduction in the intensity in WFS1-deficient β-cells, indicating the impairment of granular acidification. This phenotype may, at least partly, account for the evidence that Wfs1-null islets have impaired proinsulin processing, resulting in an increased circulating proinsulin level. Morphometric analysis using electron microscopy evidenced that the density of secretory granules attached to the plasma membrane was significantly reduced in Wfs1-null β-cells relative to that in wild-type β-cells. This may be relevant to the recent finding that granular acidification is required for the priming of secretory granules preceding exocytosis and may partly explain the fact that glucose-induced insulin secretion is profoundly impaired in young prediabetic Wfs1-null mice. These results thus provide new insights into the molecular mechanisms of β-cell dysfunction in patients with Wolfram syndrome.

The binary switch that controls the life and death decisions of ER stressed β cells

Diabetes mellitus is a group of common metabolic disorders defined by hyperglycemia. One of the most important factors contributing to hyperglycemia is dysfunction and death of β cells. Increasing experimental, clinical, and genetic evidence indicates that endoplasmic reticulum (ER) stress plays an important role in β cell dysfunction and death during the progression of type 1 and type 2 diabetes as well as genetic forms of diabetes such as Wolfram syndrome. The mechanisms of ER stress-mediated β cell dysfunction and death are complex and not homogenous. Here we review the recent key findings on the role of ER stress and the unfolded protein response (UPR) in β cells and the mechanisms of ER stress-mediated β cell dysfunction and death. Complete understanding of these mechanisms will lead to novel therapeutic modalities for diabetes.

A switch from life to death in endoplasmic reticulum stressed β-cells

β-Cell death is an important pathogenic component of both type 1 and type 2 diabetes. Recent findings indicate that cell signalling pathways emanating from the endoplasmic reticulum (ER) play an important role in the regulation of β-cell death during the progression of diabetes. Homeostasis within the ER must be maintained to produce properly folded secretory proteins, such as insulin, in response to the body's need for them. However, the sensitive protein-folding environment in the ER can be perturbed by genetic and environmental factors leading to ER stress. To counteract ER stress, β-cells activate cell signalling pathways termed the unfolded protein response (UPR). The UPR functions as a binary switch between life and death, regulating both survival and death effectors. The outcome of this switch depends on the nature of the ER stress condition, the regulation of UPR activation and the expression and activation of survival and death components. This review discusses the mechanisms and the components in this switch and highlights the roles of this UPR's balancing act between life and death in β-cells.

The binary switch between life and death of endoplasmic reticulum-stressed beta cells

PURPOSE OF REVIEW

beta-Cell death is an important pathogenic component of both type 1 and type 2 diabetes. However, the specific molecular pathways and interactions involved in this process are not completely understood. Increasing evidence indicates that a type of cell stress called endoplasmic reticulum stress (ER stress) plays an important role in beta-cell death. In the present article, we discuss a potential paradigm of ER stress-mediated beta-cell death.

RECENT FINDINGS

Upon ER stress conditions, a signaling network termed the unfolded protein response (UPR) is activated. The UPR regulates adaptive effectors to attenuate ER stress and restore ER homeostasis promoting cell survival. Paradoxically the UPR also regulates apoptotic effectors. When adaptive effectors fail to attenuate ER stress, these apoptotic effectors take into effect leading to cell death. The nature of this switch between life and death is currently under study.

SUMMARY

Depending on the nature of the stress condition, the UPR either protects beta cells or promotes their death. The mechanisms of this switch are not well understood but involve the balance between adaptive and apoptotic factors regulated by the UPR. In the present article, we review examples of this UPR balancing act between life and death and the potential mechanisms involved.

AATF mediates an antiapoptotic effect of the unfolded protein response through transcriptional regulation of AKT1

Endoplasmic reticulum (ER) stress-mediated cell death plays an important role in the pathogenesis of chronic diseases including diabetes and neurodegeneration. Although pro-apoptotic programs activated by ER stress have been extensively studied, identification and characterization of anti-apoptotic programs that counteract ER stress is currently incomplete. Through the gene expression profiling of β-cells lacking WFS1, a causative gene for Wolfram syndrome, we have discovered a novel anti-apoptotic gene of the unfolded protein response (UPR), apoptosis antagonizing transcription factor (AATF). Here we study the regulation of AATF, identify its target genes, and determine the basis for its anti-apoptotic activities in response to ER stress. We show that AATF is induced by ER stress through the PERK-eIF2α pathway and transcriptionally activates the Akt1 gene through Stat3, which sustains Akt1 activation and promotes cell survival. Ectopic expression of AATF or a constitutively active form of AKT1 confers on cells resistance to ER stress-mediated cell death, whereas RNAi-mediated knockdown of AATF or AKT1 renders cells sensitive to ER stress. We also discovered positive crosstalk between the AATF and WFS1 signaling pathways. Thus, WFS1-deficiency or AATF-deficiency mediates a self-perpetuating cycle of cell death. Our results reveal a novel anti-apoptotic program relevant to treatment for diseases caused by ER stress-mediated cell death.

Wolfram syndrome: a clinicopathologic correlation

Wolfram syndrome or DIDMOAD (diabetes insipidus, diabetes mellitus, optic atrophy and deafness) is a neurodegenerative disorder characterized by diabetes mellitus and optic atrophy as well as diabetes insipidus and deafness in many cases. We report the post-mortem neuropathologic findings of a patient with Wolfram syndrome and correlate them with his clinical presentation. In the hypothalamus, neurons in the paraventricular and supraoptic nuclei were markedly decreased and minimal neurohypophyseal tissue remained in the pituitary. The pontine base and inferior olivary nucleus showed gross shrinkage and neuron loss, while the cerebellum was relatively unaffected. The visual system had moderate to marked loss of retinal ganglion neurons, commensurate loss of myelinated axons in the optic nerve, chiasm and tract, and neuron loss in the lateral geniculate nucleus but preservation of the primary visual cortex. The patient's inner ear showed loss of the organ of Corti in the basal turn of the cochleae and mild focal atrophy of the stria vascularis. These findings correlated well with the patient's high-frequency hearing loss. The pathologic findings correlated closely with the patient's clinical symptoms and further support the concept of Wolfram syndrome as a neurodegenerative disorder. Our findings extend prior neuropathologic reports of Wolfram syndrome by providing contributions to our understanding of eye, inner ear and olivopontine pathology in this disease.

Endoplasmic reticulum stress in beta-cells and development of diabetes

The endoplasmic reticulum (ER) is a cellular compartment responsible for multiple important cellular functions including the biosynthesis and folding of newly synthesized proteins destined for secretion, such as insulin. A myriad of pathological and physiological factors perturb ER function and cause dysregulation of ER homeostasis, leading to ER stress. ER stress elicits a signaling cascade to mitigate stress, the unfolded protein response (UPR). As long as the UPR can relieve stress, cells can produce the proper amount of proteins and maintain ER homeostasis. If the UPR, however, fails to maintain ER homeostasis, cells will undergo apoptosis. Activation of the UPR is critical to the survival of insulin-producing pancreatic beta-cells with high secretory protein production. Any disruption of ER homeostasis in beta-cells can lead to cell death and contribute to the pathogenesis of diabetes. There are several models of ER-stress-mediated diabetes. In this review, we outline the underlying molecular mechanisms of ER-stress-mediated beta-cell dysfunction and death during the progression of diabetes.

Increased insulin demand promotes while pioglitazone prevents pancreatic beta cell apoptosis in Wfs1 knockout mice

AIMS/HYPOTHESIS

The WFS1 gene encodes an endoplasmic reticulum (ER) membrane-embedded protein called Wolfram syndrome 1 protein, homozygous mutations of which cause selective beta cell loss in humans. The function(s) of this protein and the mechanism by which the mutations of this gene cause beta cell death are still not fully understood. We hypothesised that increased insulin demand as a result of obesity/insulin resistance causes ER stress in pancreatic beta cells, thereby promoting beta cell death.

METHODS

We studied the effect of breeding Wfs1 ( -/- ) mice on a C57BL/6J background with mild obesity and insulin resistance, by introducing the agouti lethal yellow mutation (A ( y ) /a). We also treated the mice with pioglitazone.

RESULTS

Wfs1 ( -/- ) mice bred on a C57BL/6J background rarely develop overt diabetes by 24 weeks of age, showing only mild beta cell loss. However, Wfs1 ( -/- ) A ( y ) /a mice developed selective beta cell loss and severe insulin-deficient diabetes as early as 8 weeks. This beta cell loss was due to apoptosis. In Wfs1 ( +/+ ) A ( y ) /a islets, levels of ER chaperone immunoglobulin-binding protein (BiP)/78 kDa glucose-regulated protein (GRP78) and phosphorylation of eukaryotic translation initiation factor 2, subunit alpha (eIF2alpha) apparently increased. Levels of both were further increased in Wfs1 ( -/- ) A ( y ) /a murine islets. Electron micrography revealed markedly dilated ERs in Wfs1 (-/-) A ( y ) /a murine beta cells. Interestingly, pioglitazone treatment protected beta cells from apoptosis and almost completely prevented diabetes development.

CONCLUSIONS/INTERPRETATION

Wfs1-deficient beta cells are susceptible to ER stress. Increased insulin demand prompts apoptosis in such cells in vivo. Pioglitazone, remarkably, suppresses this process and prevents diabetes. As common WFS1 gene variants have recently been shown to confer a risk of type 2 diabetes, our findings may be relevant to the gradual but progressive loss of beta cells in type 2 diabetes.

Impact of polymorphisms in WFS1 on prediabetic phenotypes in a population-based sample of middle-aged people with normal and abnormal glucose regulation

AIM/HYPOTHESIS

Recently, variants in WFS1 have been shown to be associated with type 2 diabetes. We aimed to examine metabolic risk phenotypes of WFS1 variants in glucose-tolerant people and in individuals with abnormal glucose regulation.

METHODS

The type 2 diabetes-associated WFS1 variant rs734312 (His611Arg) was studied in the population-based Inter99 cohort involving 4,568 glucose-tolerant individuals and 1,471 individuals with treatment-naive abnormal glucose regulation, and in an additional 3,733 treated type 2 diabetes patients.

RESULTS

The WFS1 rs734312 showed a borderline significant association with type 2 diabetes with directions and relative risks consistent with previous reports. In individuals with abnormal glucose regulation, the diabetogenic risk A allele of rs734312 was associated in an allele-dependent manner with a decrease in insulinogenic index (p = 0.025) and decreased 30-min serum insulin levels (p = 0.047) after an oral glucose load. In glucose-tolerant individuals the same allele was associated with increased fasting serum insulin concentration (p = 0.019) and homeostasis model assessment of insulin resistance (HOMA-IR; p = 0.026). To study the complex interaction of WFS1 rs734312 on insulin release and insulin resistance we introduced Hotelling's T (2) test. Assuming bivariate normal distribution, we constructed standard error ellipses of the insulinogenic index and HOMA-IR when stratified according to glucose tolerance status around the means of each WFS1 rs734312 genotype level. The interaction term between individuals with normal glucose tolerance and abnormal glucose regulation on the insulinogenic index and HOMA-IR was significantly associated with the traits (p = 0.0017).

CONCLUSIONS/INTERPRETATION

Type 2 diabetes-associated risk alleles of WFS1 are associated with estimates of a decreased pancreatic beta cell function among middle-aged individuals with abnormal glucose regulation.

Distribution of Wfs1 protein in the central nervous system of the mouse and its relation to clinical symptoms of the Wolfram syndrome

Mutations in the coding region of the WFS1 gene cause Wolfram syndrome, a rare multisystem neurodegenerative disorder of autosomal recessive inheritance. Patients with Wolfram syndrome display considerable clinical pleiomorphism, and symptoms such as neurological complications and psychiatric disorders are common. In the present study we have characterized Wfs1 expression pattern in the mouse central nervous system by using a combination of immunohistochemistry on wild-type mice and X-Gal staining of Wfs1 knockout mice with targeted insertion of the lacZ reporter. We identified a robust enrichment of Wfs1 protein in the central extended amygdala and ventral striatum. Prominent Wfs1 expression was seen in the hippocampal CA1 region, parasubiculum, superficial part of the second and third layers of the prefrontal cortex and proisocortical areas, hypothalamic magnocellular neurosecretory system, and central auditory pathway. Wfs1 expression was also detected in numerous brainstem nuclei and in laminae VIII and IX of the spinal cord. Wfs1-positive nerve fibers were found in the medial forebrain bundle, reticular part of the substantia nigra, globus pallidus, posterior caudate putamen, lateral lemniscus, alveus, fimbria, dorsal hippocampal commissure, subiculum, and to a lesser extent in the central sublenticular extended amygdala, compact part of substantia nigra, and ventral tegmental area. The neuroanatomical findings suggest that the lack of Wfs1 protein function can be related to several neurological and psychiatric symptoms found in Wolfram syndrome. Enrichment of Wfs1 protein in the central extended amygdala suggests a role in the modulation of anxiety and fear.

Endoplasmic reticulum stress signaling in pancreatic beta-cells

Pancreatic beta-cells are specialized for the production and regulated secretion of insulin to control blood-glucose levels. Increasing evidence indicates that stress-signaling pathways emanating from the endoplasmic reticulum (ER) are important in the maintenance of beta-cell homeostasis. Under physiological conditions, ER stress signaling has beneficial effects on beta-cells. Timely and proper activation of ER stress signaling is crucial for generating the proper amount of insulin in proportion to the need for it. In contrast, chronic and strong activation of ER stress signaling has harmful effects, leading to beta-cell dysfunction and death. Therefore, to dissect the molecular mechanisms of beta-cell failure and death in diabetes, it is necessary to understand the complex network of ER stress-signaling pathways. This review focuses on the function of the ER stress-signaling network in pancreatic beta-cells.

[Wolfram syndrome: from definition to molecular bases]

Wolfram syndrome (WS) is an autosomal recessive progressive neurodegenerative disorder characterized by diabetes mellitus and optic atrophy. Diabetes insipidus and sensorineural deafness are also noted frequently, explaining the acronym DIDMOAD (diabetes insipidus, diabetes mellitus, optic atrophy and deafness) by which the syndrome is also referred. Additional manifestations such as atonic bladder, ataxia, nystagmus and predisposition for psychiatric illness may be present. The Wolfram syndrome gene, WFS1, was mapped to chromosome 4p16.1 by positional cloning. It encodes an 890-amino-acid polypeptide named wolframin. Although the wolframin function is still not completely known, its localization to the endoplasmic reticulum suggests it can play a role in calcium homeostasis, membrane trafficking and protein processing. Knowing the cellular function of wolframin is necessary for understanding the pathophysiology of Wolfram syndrome. This knowledge may lead to development of therapies to prevent or reduce the outcomes of WS.

Recent advancement of understanding pathogenesis of type 1 diabetes and potential relevance to diabetic nephropathy

Type 1 diabetes mellitus is an autoimmune disease characterized by progressive destruction of pancreatic beta cells by genetic and environmental factors which leads to an absolute dependence of insulin for survival and maintenance of health. Although the majority of mechanisms of beta cell destruction remain unclear, many molecules, including proinflammatory cytokines and chemokines such as tumor necrosis factor alpha and monocyte chemoattractant protein-1, are implicated in the development of beta cell damage. Furthermore, beta cell destruction is enhanced by the Th1 and Th17 subsets of CD4+ T cells. In contrast, there are mechanisms involved in the maintenance of peripheral tolerance by regulatory T cells, the function of which depends on the pleiotropic cytokine transforming growth factor beta. Development and progression of renal injuries in patients with diabetic nephropathy are also associated with several growth factors and proinflammatory cytokines, including tumor necrosis factor alpha, insulin-like growth factor-1, monocyte chemoattractant protein-1, vascular endothelial growth factor, and transforming growth factor beta. Although the pathogenic mechanisms underlying type 1 diabetes and diabetic nephropathy are principally different, i.e., autoimmunity and inflammation, some common factors, including susceptibility genes and proinflammatory cytokines, are involved in both mechanisms, including infiltrating cell recruitment, upregulation of other cytokines and chemokines, or apoptosis.

Microvascular diabetes complications in Wolfram syndrome (diabetes insipidus, diabetes mellitus, optic atrophy, and deafness [DIDMOAD]): an age- and duration-matched comparison with common type 1 diabetes

OBJECTIVE

Some previous studies suggested that patients suffering from Wolfram syndrome or DIDMOAD (diabetes insipidus, diabetes mellitus, optic atrophy, and deafness) might be relatively preserved from diabetic retinopathy and nephropathy. However, these data were not conclusive because either observations were only anecdotic or did not match with control type 1 diabetic populations.

RESEARCH DESIGN AND METHODS

A group of 26 French diabetic patients with DIDMOAD was compared with a population of 52 patients with common type 1 diabetes matched for age at diabetes diagnosis (8.62 +/- 1.84 vs. 8.27 +/- 1.30 years; P = NS) and diabetes duration (12.88 +/- 1.58 vs. 12.87 +/- 1.13 years; P = NS) to study the quality of glycemic control and the incidence of microvascular complications.

RESULTS

Glycemic control was significantly better in the DIDMOAD group than in the type 1 diabetic group (A1C: 7.72 +/- 0.21 vs. 8.99 +/- 0.25%, respectively; P = 0.002), with significant lower daily insulin requirements (0.71 +/- 0.07 vs. 0.88 +/- 0.04 UI x kg(-1) x day(-1), respectively; P = 0.0325). The prevalence of microvascular complications in the DIDMOAD group was half that observed in the type 1 diabetic group, but the difference was not significant.

CONCLUSIONS

Diabetes in DIDMOAD patients is more easily controlled despite the presence of other handicaps. This better glycemic control could explain the trend to decreased microvascular diabetes complications observed in previous studies.

Imaging of the brain in children with type I diabetes mellitus

Type 1 diabetes mellitus (DM) affects about 1 in 500 children and can cause damage to multiple organ systems. In recent years, growing attention has been given to the effects of type 1 DM on the brain. In this article we review important imaging features of the brain in children with type 1 DM, including (1) imaging the child in diabetic ketoacidosis and the child with hypoglycemia, (2) syndromes associated with type 1 DM, and (3) long-term effects of type 1 DM on brain structure.

Common variants in WFS1 confer risk of type 2 diabetes

We studied genes involved in pancreatic beta cell function and survival, identifying associations between SNPs in WFS1 and diabetes risk in UK populations that we replicated in an Ashkenazi population and in additional UK studies. In a pooled analysis comprising 9,533 cases and 11,389 controls, SNPs in WFS1 were strongly associated with diabetes risk. Rare mutations in WFS1 cause Wolfram syndrome; using a gene-centric approach, we show that variation in WFS1 also predisposes to common type 2 diabetes.

A novel mutation of WFS1 gene in a Japanese man of Wolfram syndrome with positive diabetes-related antibodies

Wolfram syndrome is a rare, autosomal recessive disorder characterized by early-onset diabetes mellitus, optic atrophy and neurological and endocrinological abnormalities. A 47-year-old Japanese man with frequent severe hypoglycemic episodes was diagnosed as Wolfram syndrome based on clinical features and laboratory data. He had positive glutamic acid decarboxylase (GAD) and insulinoma-associated antigen-2 (IA-2) antibodies, both uncommon in this syndrome. Genetic analysis revealed that WFS1 gene of the patient has a homozygous 5 base pairs (AAGGC) insertion at position 1279 in exon 8, causing a frameshift at codon 371 leading to premature termination at codon 443.

WFS1-deficiency increases endoplasmic reticulum stress, impairs cell cycle progression and triggers the apoptotic pathway specifically in pancreatic beta-cells

Wolfram syndrome, an autosomal recessive disorder associated with diabetes mellitus and optic atrophy, is caused by mutations in the WFS1 gene encoding an endoplasmic reticulum (ER) membrane protein. Herein, we report that pancreatic islets of wfs1-deficient mice exhibit increases in phosphorylation of RNA-dependent protein kinase-like ER kinase, chaperone gene expressions and active XBP1 protein levels, indicating an enhanced ER stress response. We established wfs1-deficient MIN6 clonal beta-cells by crossing wfs1-deficient mice with mice expressing simian virus 40 large T antigen in beta-cells. These cells show essentially the same alterations in ER stress responses as wfs1-deficient islets, which were reversed by re-expression of WFS1 protein or overexpression of GRP78, a master regulator of the ER stress response. In contrast, these changes are not observed in heart, skeletal muscle or brown adipose tissues with WFS1-deficiency. The increased ER stress response was accompanied by reduced BrdU incorporation and increased caspase-3 cleavage, indicating impaired cell cycle progression and accelerated apoptotic processes in the mutant islets. These changes are associated with increased expression of the cell cycle regulator p21(CIP1) in wfs1-deficient islets and clonal beta-cells. Treatment of islets with thapsigargin, an ER stress inducer, caused upregulation of p21(CIP1). In addition, forced expression of p21(CIP1) resulted in reduced MIN6 beta-cell numbers, suggesting the ER stress-induced increase in p21(CIP1) expression to be involved in beta-cell loss in the mutant islets. These data indicate that WFS1-deficiency activates the ER stress response specifically in beta-cells, causing beta-cell loss through impaired cell cycle progression and increased apoptosis.

Mice conditionally lacking the Wolfram gene in pancreatic islet beta cells exhibit diabetes as a result of enhanced endoplasmic reticulum stress and apoptosis

AIMS/HYPOTHESIS

Wolfram syndrome is an autosomal recessive disorder characterised by childhood diabetes mellitus, optic atrophy and severe neurodegeneration, resulting in premature death. The aim of this study was to investigate the mechanisms responsible for the phenotype of carbohydrate intolerance and loss of pancreatic beta cells in this disorder.

MATERIALS AND METHODS

To study the role of the Wolfram gene (Wfs1) in beta cells, we developed a mouse model with conditional deletion of Wfs1 in beta cells by crossing floxed Wfs1 exon 8 animals with mice expressing Cre recombinase under the control of a rat insulin promoter (RIP2-Cre). Complementary experiments using RNA interference of Wfs1 expression were performed in mouse insulinoma (MIN6) cell lines (WfsKD).

RESULTS

Male knockout mice (betaWfs(-/-)) began developing variable and progressive glucose intolerance and concomitant insulin deficiency, compared with littermate controls, by 12 weeks of age. Analysis of islets from betaWfs(-/-) mice revealed a reduction in beta cell mass, enhanced apoptosis, elevation of a marker of endoplasmic reticulum stress (immunoglobulin heavy chain-binding protein [BiP]), and dilated endoplasmic reticulum with decreased secretory granules by electron microscopy. WfsKD cell lines had significantly increased apoptosis and elevated expression of the genes encoding BiP and C/EBP-homologous protein (CHOP), two markers of endoplasmic reticulum stress.

CONCLUSIONS/INTERPRETATION

These results indicate that (1) lack of expression of Wfs1 in beta cells was sufficient to result in the diabetes mellitus phenotype; (2) beta cell death occurred by an accelerated process of apoptosis; and (3) lack of Wfs1 was associated with dilated endoplasmic reticulum and increased markers of endoplasmic reticulum stress, which appears to be a significant contributor to the reduction in beta cell survival.

WFS1 Is a Novel Component of the Unfolded Protein Response and Maintains Homeostasis of the Endoplasmic Reticulum in Pancreatic β-Cells

In Wolfram syndrome, a rare form of juvenile diabetes, pancreatic beta-cell death is not accompanied by an autoimmune response. Although it has been reported that mutations in the WFS1 gene are responsible for the development of this syndrome, the precise molecular mechanisms underlying beta-cell death caused by the WFS1 mutations remain unknown. Here we report that WFS1 is a novel component of the unfolded protein response and has an important function in maintaining homeostasis of the endoplasmic reticulum (ER) in pancreatic beta-cells. WFS1 encodes a transmembrane glyco-protein in the ER. WFS1 mRNA and protein are induced by ER stress. The expression of WFS1 is regulated by inositol requiring 1 and PKR-like ER kinase, central regulators of the unfolded protein response. WFS1 is normally up-regulated during insulin secretion, whereas inactivation of WFS1 in beta-cells causes ER stress and beta-cell dysfunction. These results indicate that the pathogenesis of Wolfram syndrome involves chronic ER stress in pancreatic beta-cells caused by the loss of function of WFS1.

Endoplasmic reticulum stress induces Wfs1 gene expression in pancreatic beta-cells via transcriptional activation

OBJECTIVE

The WFS1 gene encodes an endoplasmic reticulum (ER) membrane-embedded protein. Homozygous WFS1 gene mutations cause Wolfram syndrome, characterized by insulin-deficient diabetes mellitus and optic atropy. Pancreatic beta-cells are selectively lost from the patient's islets. ER localization suggests that WFS1 protein has physiological functions in membrane trafficking, secretion, processing and/or regulation of ER calcium homeostasis. Disturbances or overloading of these functions induces ER stress responses, including apoptosis. We speculated that WFS1 protein might be involved in these ER stress responses.

DESIGN AND METHODS

Islet expression of the Wfs1 protein was analyzed immunohistochemically. Induction of Wfs1 upon ER stress was examined by Northern and Western blot analyses using three different models: human skin fibroblasts, mouse pancreatic beta-cell-derived MIN6 cells, and Akita mouse-derived Ins2 (96Y/Y) insulinoma cells. The human WFS1 gene promoter-luciferase reporter analysis was also conducted.

RESULT

Islet beta-cells were the major site of Wfs1 expression. This expression was also found in delta-cells, but not in alpha-cells. WFS1 expression was transcriptionally up-regulated by ER stress-inducing chemical insults. Treatment of fibroblasts and MIN6 cells with thapsigargin or tunicamycin increased WFS1 mRNA. WFS1 protein also increased in response to thapsigargin treatment in these cells. WFS1 gene expression was also increased in Ins2 (96Y/Y) insulinoma cells. In these cells, ER stress was intrinsically induced by mutant insulin expression. The WFS1 gene promoter-luciferase reporter system revealed that the human WFS1 promoter was activated by chemically induced ER stress in MIN6 cells, and that the promoter was more active in Ins2 (96Y/Y) cells than Ins2 (wild/wild) cells.

CONCLUSION

Wfs1 expression, which is localized to beta- and delta-cells in pancreatic islets, increases in response to ER stress, suggesting a functional link between Wfs1 and ER stress.

Genetic variations in the WFS1 gene in Japanese with type 2 diabetes and bipolar disorder

Diabetic and psychiatric symptoms often appear in patients with Wolfram syndrome, and obligate carriers of WFS1 have increased prevalence of type 2 diabetes and are more likely to require hospitalization for psychiatric illness including bipolar disorder. To identify the polymorphisms in Japanese, we examined a region of approximately 50 kb covering the entire WFS1 gene, and evaluated the patterns of linkage disequilibrium. We found a total of 42 variations including 8 novel coding single nucleotide polymorphisms (A6T, A134A, N159N, T170T, E237K, R383C, V412L, and V503G), 14 novel non-coding polymorphisms, and 2 linkage disequilibrium blocks. We also performed association studies in patients with type 2 diabetes mellitus and patients with bipolar disorder. The haplotype comprising R456 and H611 was most associated with type 2 diabetes (p = 0.013) and the haplotype comprising g. -15503C/T and g. 16226G/A was most associated with bipolar disorder (p = 0.006), but neither reached significant difference after multiple adjustment. These genetic variations and linkage disequilibrium patterns in WFS1 in Japanese should be useful in further investigation of genetic diversities of WFS1 and various related disorders.