Islet stress, degradation and autoimmunity

Proinsulin degradation and presentation of a proinsulin B-chain autoantigen involves ER-associated protein degradation (ERAD)-enzyme UBE2G2

Type 1 diabetes (T1D) is characterized by HLA class I-mediated presentation of autoantigens on the surface of pancreatic β-cells. Recognition of these autoantigens by CD8+ T cells results in the destruction of pancreatic β-cells and, consequently, insulin deficiency. Most epitopes presented at the surface of β-cells derive from the insulin precursor molecule proinsulin. The intracellular processing pathway(s) involved in the generation of these peptides are poorly defined. In this study, we show that a proinsulin B-chain antigen (PPIB5-14) originates from proinsulin molecules that are processed by ER-associated protein degradation (ERAD) and thus originate from ER-resident proteins. Furthermore, screening genes encoding for E2 ubiquitin conjugating enzymes, we identified UBE2G2 to be involved in proinsulin degradation and subsequent presentation of the PPIB10-18 autoantigen. These insights into the pathway involved in the generation of insulin-derived peptides emphasize the importance of proinsulin processing in the ER to T1D pathogenesis and identify novel targets for future T1D therapies.

Applications of Genome-Editing Technologies for Type 1 Diabetes

Type 1 diabetes (T1D) is a chronic autoimmune disease characterized by the destruction of insulin-producing pancreatic β-cells by the immune system. Although conventional therapeutic modalities, such as insulin injection, remain a mainstay, recent years have witnessed the emergence of novel treatment approaches encompassing immunomodulatory therapies, such as stem cell and β-cell transplantation, along with revolutionary gene-editing techniques. Notably, recent research endeavors have enabled the reshaping of the T-cell repertoire, leading to the prevention of T1D development. Furthermore, CRISPR-Cas9 technology has demonstrated remarkable potential in targeting endogenous gene activation, ushering in a promising avenue for the precise guidance of mesenchymal stem cells (MSCs) toward differentiation into insulin-producing cells. This innovative approach holds substantial promise for the treatment of T1D. In this review, we focus on studies that have developed T1D models and treatments using gene-editing systems.

β Cell Stress and Endocrine Function During T1D: What Is Next to Discover?

Canonically, type 1 diabetes (T1D) is a disease characterized by autoreactive T cells as perpetrators of endocrine dysfunction and β cell death in the spiral toward loss of β cell mass, hyperglycemia, and insulin dependence. β Cells have mostly been considered as bystanders in a flurry of autoimmune processes. More recently, our framework for understanding and investigating T1D has evolved. It appears increasingly likely that intracellular β cell stress is an important component of T1D etiology/pathology that perpetuates autoimmunity during the progression to T1D. Here we discuss the emerging and complex role of β cell stress in initiating, provoking, and catalyzing T1D. We outline the bridges between hyperglycemia, endoplasmic reticulum stress, oxidative stress, and autoimmunity from the viewpoint of intrinsic β cell (dys)function, and we extend this discussion to the potential role for a therapeutic β cell stress-metabolism axis in T1D. Lastly, we mention research angles that may be pursued to improve β cell endocrine function during T1D. Biology gleaned from studying T1D will certainly overlap to innovate therapeutic strategies for T2D, and also enhance the pursuit of creating optimized stem cell-derived β cells as endocrine therapy.

IFNɣ but not IFNα increases recognition of insulin defective ribosomal product-derived antigen to amplify islet autoimmunity

AIMS/HYPOTHESIS

The inflammatory milieu characteristic of insulitis affects translation fidelity and generates defective ribosomal products (DRiPs) that participate in autoimmune beta cell destruction in type 1 diabetes. Here, we studied the role of early innate cytokines (IFNα) and late immune adaptive events (IFNɣ) in insulin DRiP-derived peptide presentation to diabetogenic CD8+ T cells.

METHODS

Single-cell transcriptomics of human pancreatic islets was used to study the composition of the (immuno)proteasome. Specific inhibition of the immunoproteasome catalytic subunits was achieved using siRNA, and antigenic peptide presentation at the cell surface of the human beta cell line EndoC-βH1 was monitored using peptide-specific CD8 T cells.

RESULTS

We found that IFNγ induces the expression of the PSMB10 transcript encoding the β2i catalytic subunit of the immunoproteasome in endocrine beta cells, revealing a critical role in insulin DRiP-derived peptide presentation to T cells. Moreover, we showed that PSMB10 is upregulated in a beta cell subset that is preferentially destroyed in the pancreases of individuals with type 1 diabetes.

CONCLUSIONS/INTERPRETATION

Our data highlight the role of the degradation machinery in beta cell immunogenicity and emphasise the need for evaluation of targeted immunoproteasome inhibitors to limit beta cell destruction in type 1 diabetes.

DATA AVAILABILITY

The single-cell RNA-seq dataset is available from the Gene Expression Omnibus (GEO) using the accession number GSE218316 ( https://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE218316 ).

Autoimmune susceptible HLA class II motifs facilitate the presentation of modified neoepitopes to potentially autoreactive T cells

Rheumatoid arthritis (RA), multiple sclerosis (MS), type 1 diabetes (T1D), and celiac disease (CD), are strongly associated with susceptible HLA class II haplotypes. The peptide-binding pockets of these molecules are polymorphic, thus each HLA class II protein presents a distinct set of peptides to CD4⁺ T cells. Peptide diversity is increased through post-translational modifications, generating non-templated sequences that enhance HLA binding and/or T cell recognition. The high-risk HLA-DR alleles that confer susceptibility to RA are notable for their ability to accommodate citrulline, promoting responses to citrullinated self-antigens. Likewise, HLA-DQ alleles associated with T1D and CD favor the binding of deamidated peptides. In this review, we discuss structural features that promote modified self-epitope presentation, provide evidence supporting the relevance of T cell recognition of such antigens in disease processes, and make a case that interrupting the pathways that generate such epitopes and reprogramming neoepitope-specific T cells are key strategies for effective therapeutic intervention.

Biomedical importance of the ubiquitin-proteasome system in diabetes and metabolic transdifferentiation of pancreatic duct epithelial cells into β-cells

The ubiquitin-proteasome system (UPS) is a major pathway for cellular protein degradation. The molecular function of the UPS is the removal of damaged proteins, and this function is applied in many biological processes, including inflammation, proliferation, and apoptosis. Accumulating evidence also suggests that the UPS also has a key role in pancreatic β-cell transdifferentiation in diabetes and can be targeted for treatment of diabetic diseases. In this review, we summarized the mechanistic roles of the UPS in the biochemical activities of pancreatic β-cells, including the role of the UPS in insulin synthesis and secretion, as well as β-cell degradation. Also, we discuss how the UPS mediates the transdifferentiation of pancreatic duct epithelial cells into β-cells as the experimental basis for the development of new strategies for the treatment of diabetes in regenerative medicine.

Sox9 is required in regeneration of pancreatic β cells following injury

The reduction of insulin secretion due to pancreatic β cell injury caused by autoimmune reaction is the pathological basis of Type 1 diabetes mellitus (T1DM). Therefore, seeking new molecular targets for alleviating pancreatic β cell injury will provide experimental basis for the prevention and treatment of T1DM. SRY-box 9 (Sox9) is not only an important molecule regulating the development of various organs, but also its high expression can aggravate the pathological process of various diseases. In addition, Sox9⁺ cells are also pancreatic progenitor cells, participating in pancreatic repair reaction induced by injury. In our study, elevated blood glucose and lack of pancreatic β cells almost returned to normal over time after streptozotocin (STZ)-induced pancreatic β cell damage, implying that pancreatic β cells were regenerated after STZ-induced injury. In particular, the expression of Sox9 was significantly elevated during pancreatic β cell regeneration. On this basis, we conducted in vitro experiments to verify whether overexpression of Sox9 could inhibit the damage of pancreatic β cells by inflammatory factors. Our results showed that overexpression of Sox9 alleviated the damage of pancreatic β cells by inflammatory factors and improved the inhibitory effect of inflammatory factors on insulin secretion of pancreatic β cells. Unsurprising, blood glucose levels, insulin content and pancreatic β cell number failed to return to near-normal levels timely after pancreatic β cells specific knockout Sox9 mice were treated with STZ, further confirming the importance of Sox9 in facilitating pancreatic β cell repair or regeneration. Our study indicate that enhanced Sox9 activity might protect pancreatic β cells from autoimmune induced damage and thus improve the pathological process of T1DM.

Differential Expression and Bioinformatics Analysis of Plasma-Derived Exosomal circRNA in Type 1 Diabetes Mellitus

Backgrounds

Both exosome and circular RNA (circRNA) have been reported to participate in the pathogenesis of type 1 diabetes mellitus (T1DM). However, the exact role of exosomal circRNA in T1DM is largely unknown. Here, we identified the exosomal circRNA expression profiles in the plasma of T1DM patients and explored their potential function using bioinformatics analysis. Material and Methods . Exosomes were extracted by the size exclusion chromatography method from plasma of 10 T1DM patients and 10 age- and sex- matched control subjects. Illumina Novaseq6000 platform was used to detect the exosomal circRNA expression profiles. Multiple bioinformatics analysis was applied to investigate the potential biological functions of exosomal circRNAs.

Results

A total of 784 differentially expressed exosomal circRNAs have been identified in T1DM patients, of which 528 were upregulated and 256 were downregulated. Gene Ontology analysis enriched terms such as protein ubiquitination involved in ubiquitin-dependent protein catabolic protein (GO:0042787), membrane (GO:0016020), and GTPase activator activity (GO:0005096). The most enriched pathway in Kyoto Encyclopedia of Genes and Genomes was ubiquitin-mediated proteolysis (ko04120). The miRNA-targeting prediction method was used to identify the miRNAs that bind to circRNAs, and circRNA-miRNA-mRNA pathways were constructed, indicating that interactions between circRNA, miRNA, and gene might be involved in the disease progression.

Conclusions

The present study identified the exosomal circRNA expression profiles in T1DM for the first time. Our results threw novel insights into the molecular mechanisms of T1DM.

Ubiquitin-proteasome system in diabetic retinopathy

Diabetic retinopathy (DR) is the most common complication of diabetes, being the most prevalent reason for blindness among the working-age population in the developed world. Despite constant improvement of understanding of the pathogenesis of DR, identification of novel biomarkers of DR is needed for improvement of patient risk stratification and development of novel prevention and therapeutic approaches. The ubiquitin-proteasome system (UPS) is the primary protein quality control system responsible for recognizing and degrading of damaged proteins. This review aims to summarize literature data on modifications of UPS in diabetes and DR. First, we briefly review the structure and functions of UPS in physiological conditions. We then describe how UPS is involved in the development and progression of diabetes and touch upon the association of UPS genetic factors with diabetes and its complications. Further, we focused on the effect of diabetes-induced hyperglycemia, oxidative stress and hypoxia on UPS functioning, with examples of studies on DR. In other sections, we discussed the association of several other mechanisms of DR (endoplasmic reticulum stress, neurodegeneration etc) with UPS modifications. Finally, UPS-affecting drugs and remedies are reviewed. This review highlights UPS as a promising target for the development of therapies for DR prevention and treatment and identifies gaps in existing knowledge and possible future study directions.

miR-25 and miR-92b regulate insulin biosynthesis and pancreatic β-cell apoptosis

PURPOSE

Pancreatic β-cell failure is a central hallmark of the pathogenesis of diabetes mellitus; however, the molecular basis underlying chronic inflammation-caused β-cell failure remains unclear. This study reported here specifically assessed the association between miR-25/miR-92b family and β-cell failure in diabetes.

METHODS

IL-1β and two additional ER stress activators, palmitate and tunicamycin were applied to evaluate the expression level miR-25 by Taqman^® RT-PCR. Glucose- and potassium-stimulated insulin secretion assays were performed to assess β-cell function. Dual-luciferase activity, and western blotting assays were utilized for miR-25 target gene verification. CCK-8 and TUNEL staining were used to evaluate β-cell viability and apoptosis.

RESULTS

miRNA ChIP identified the increased level of miR-25 in INS-1 cells by IL-1β treatment. Expression levels of miR-25 were significantly upregulated with the treatment of IL-1β, palmitate or tunicamycin in both INS-1 cells and human islets. Ectopic elevation of miR-25 recapitulated most featured β-cell defects caused by IL-1β, including inhibition of insulin biosynthesis and increased β-cell apoptosis. These detrimental effects of miR-25 relied on its seed sequence recognition and repressed expression of its target genes Neurod1 and Mcl1. The miR-25/NEUROD1 axis reduced insulin biosynthesis via transcriptional regulation of β-cell specific genes. The miR-25/MCL1 axis caused β-cell apoptosis in a CASPASE-3/PARP1-dependent manner. Comparable impairments were generated by miR-92b and miR-25, emphasizing the redundant biological roles of miRNA family members with the same seed sequence.

CONCLUSION

MiR-25/miR-92b family plays a major role in β-cell failure occurring under inflammation and diabetes states.

PTPN2 Regulates the Interferon Signaling and Endoplasmic Reticulum Stress Response in Pancreatic β-Cells in Autoimmune Diabetes

Type 1 diabetes (T1D) results from autoimmune destruction of β-cells in the pancreas. Protein tyrosine phosphatases (PTPs) are candidate genes for T1D and play a key role in autoimmune disease development and β-cell dysfunction. Here, we assessed the global protein and individual PTP profiles in the pancreas from nonobese mice with early-onset diabetes (NOD) mice treated with an anti-CD3 monoclonal antibody and interleukin-1 receptor antagonist. The treatment reversed hyperglycemia, and we observed enhanced expression of PTPN2, a PTP family member and T1D candidate gene, and endoplasmic reticulum (ER) chaperones in the pancreatic islets. To address the functional role of PTPN2 in β-cells, we generated PTPN2-deficient human stem cell-derived β-like and EndoC-βH1 cells. Mechanistically, we demonstrated that PTPN2 inactivation in β-cells exacerbates type I and type II interferon signaling networks and the potential progression toward autoimmunity. Moreover, we established the capacity of PTPN2 to positively modulate the Ca2+-dependent unfolded protein response and ER stress outcome in β-cells. Adenovirus-induced overexpression of PTPN2 partially protected from ER stress-induced β-cell death. Our results postulate PTPN2 as a key protective factor in β-cells during inflammation and ER stress in autoimmune diabetes.

Simvastatin mitigates streptozotocin-induced type 1 diabetes in mice through downregulation of ADAM10 and ADAM17

BACKGROUND

T cell mediates immune response in type 1 diabetes mellitus (T1DM) through its trafficking into pancreatic islets. The role of A Disintigrin And Metalloproteinase 10 (ADAM10) and 17 (ADAM17) in pancreatic T-cells recruitment into the pancreatic islets during T1DM is not known.

AIM

Explore the role of ADAM10 and ADAM17 in the processing of CXCL16 in T1DM and possible protective effect of simvastatin (SIM) in streptozotocin (STZ)-induced T1DM.

MAIN METHODS

Balb/c mice were classified into 4 groups, 10 each. Control group received buffer while SIM group received 50 mg/kg, i.p daily for 12 days starting from day 4 of the experiment. Diabetic group; received STZ (55 mg/kg, i.p.) for 5 consecutive days starting from day 1 of the experiment. SIM + STZ group; received SIM (50 mg/kg, i.p.) daily for 12 days and STZ (55 mg/kg, i.p.) for 5 consecutive days. Biochemical, inflammatory and apoptotic markers as well as expression of CXCL16, ADAM10, NF-κB and pancreatic T-cells expression were analyzed.

KEY FINDINGS

Significant increase in biochemical, inflammatory, apoptotic parameters, expression of ADAM10, ADAM17, CXCL16, NF-κB, and infiltrated T-cells to the pancreatic islets were found in STZ group. SIM treatment in the presence of STZ improved biochemical and inflammatory parameters as well as it reduced the expression of CXCL16, ADAM10, ADAM17, NF-κΒ, T-cells migration and apoptosis in the pancreatic islets.

SIGNIFICANCE

SIM mitigated pancreatic β-cell death induced by STZ through down regulation of ADAM10, ADAM17and CXCL16. Therefore, ADAM10/ADAM17 and CXCL16 may serve as novel therapeutic targets for T1DM.

A Pro-Endocrine Pancreatic Islet Transcriptional Program Established During Development Is Retained in Human Gallbladder Epithelial Cells

BACKGROUND & AIMS

Pancreatic islet β-cells are factories for insulin production; however, ectopic expression of insulin also is well recognized. The gallbladder is a next-door neighbor to the developing pancreas. Here, we wanted to understand if gallbladders contain functional insulin-producing cells.

METHODS

We compared developing and adult mouse as well as human gallbladder epithelial cells and islets using immunohistochemistry, flow cytometry, enzyme-linked immunosorbent assays, RNA sequencing, real-time polymerase chain reaction, chromatin immunoprecipitation, and functional studies.

RESULTS

We show that the epithelial lining of developing, as well as adult, mouse and human gallbladders naturally contain interspersed cells that retain the capacity to actively transcribe, translate, package, and release insulin. We show that human gallbladders also contain functional insulin-secreting cells with the potential to naturally respond to glucose in vitro and in situ. Notably, in a non-obese diabetic (NOD) mouse model of type 1 diabetes, we observed that insulin-producing cells in the gallbladder are not targeted by autoimmune cells. Interestingly, in human gallbladders, insulin splice variants are absent, although insulin splice forms are observed in human islets.

CONCLUSIONS

In summary, our biochemical, transcriptomic, and functional data in mouse and human gallbladder epithelial cells collectively show the evolutionary and developmental similarities between gallbladder and the pancreas that allow gallbladder epithelial cells to continue insulin production in adult life. Understanding the mechanisms regulating insulin transcription and translation in gallbladder epithelial cells would help guide future studies in type 1 diabetes therapy.

Regulation of Pancreatic β-Cell Mass by Gene-Environment Interaction

The main pathogenic mechanism of diabetes consists of an increase in insulin resistance and a decrease in insulin secretion from pancreatic β-cells. The number of diabetic patients has been increasing dramatically worldwide, especially in Asian people whose capacity for insulin secretion is inherently lower than that of other ethnic populations. Causally, changes of environmental factors in addition to intrinsic genetic factors have been considered to have an influence on the increased prevalence of diabetes. Particular focus has been placed on "gene-environment interactions" in the development of a reduced pancreatic β-cell mass, as well as type 1 and type 2 diabetes mellitus. Changes in the intrauterine environment, such as intrauterine growth restriction, contribute to alterations of gene expression in pancreatic β-cells, ultimately resulting in the development of pancreatic β-cell failure and diabetes. As a molecular mechanism underlying the effect of the intrauterine environment, epigenetic modifications have been widely investigated. The association of diabetes susceptibility genes or dietary habits with gene-environment interactions has been reported. In this review, we provide an overview of the role of gene-environment interactions in pancreatic β-cell failure as revealed by previous reports and data from experiments.

The etiology and pathogenesis of type 1 diabetes - A personal, non-systematic review of possible causes, and interventions

In this review after a lifelong research career, my personal opinion on the development of type 1 diabetes (T1D) from its very start to clinical manifestation will be described. T1D is a disease of an increased intestinal permeability and a reduced pancreas volume. I am convinced that virus might be the initiator and that this virus could persist on strategically significant locations. Furthermore, intake of gluten is important both in foetal life and at later ages. Disturbances in sphingolipid metabolism may also be of crucial importance. During certain stages of T1D, T cells take over resulting in the ultimate destruction of beta cells, which manifests T1D as an autoimmune disease. Several preventive and early treatment strategies are mentioned. All together this review has more new theories than usually, and it might also be more speculative than ordinarily. But without new ideas and theories advancement is difficult, even though everything might not hold true during the continuous discovery of the etiology and pathogenesis of T1D.

Aberrant expression of transglutaminase 2 in pancreas and thymus of NOD mice underscores the importance of deamidation in neoantigen generation

Post-translational modifications can lead to a break in immune tolerance in autoimmune diseases such as type 1 diabetes (T1D). Deamidation, the conversion of glutamine to glutamic acid by transglutaminase (TGM) enzymes, is a post-translational modification of interest, with deamidated peptides being reported as autoantigens in T1D. However, little is known about how Tgm2, the most ubiquitously expressed Tgm isoform, is regulated and how tolerance against deamidated peptides is lost. Here, we report on the aberrant expression and regulation of Tgm2 in the pancreas and thymus of NOD mice. We demonstrate that Tgm2 expression is induced by the inflammatory cytokines IL1β and IFNγ in a synergistic manner and that murine pancreatic islets of NOD mice have higher Tgm2 levels, while Tgm2 levels in medullary thymic epithelial cells are reduced. We thus provide the first direct evidence to our knowledge that central tolerance establishment against deamidated peptides might be impaired due to lower Tgm2 expression in NOD medullary thymic epithelial cells, which together with the aberrantly high levels of deamidated peptides in NOD β-cells underscores the role of deamidation in amplifying T-cell reactivity.

Environmental Determinants of Type 1 Diabetes: From Association to Proving Causality

The rising incidence of type 1 diabetes (T1D) cannot be ascribed to genetics alone, and causative environmental triggers and drivers must also be contributing. The prospective TEDDY study has provided the greatest contributions in modern time, by addressing misconceptions and refining the search strategy for the future. This review outlines the evidence to date to support the pathways from association to causality, across all stages of T1D (seroconversion to beta cell failure). We focus on infections and vaccinations; infant growth and childhood obesity; the gut microbiome and the lifestyle factors which cultivate it. Of these, the environmental determinants which have the most supporting evidence are enterovirus infection, rapid weight gain in early life, and the microbiome. We provide an infographic illustrating the key environmental determinants in T1D and their likelihood of effect. The next steps are to investigate these environmental triggers, ideally though gold-standard randomised controlled trials and further prospective studies, to help explore public health prevention strategies.

Partners in Crime: Beta-Cells and Autoimmune Responses Complicit in Type 1 Diabetes Pathogenesis

Type 1 diabetes (T1D) is an autoimmune disease characterized by autoreactive T cell-mediated destruction of insulin-producing pancreatic beta-cells. Loss of beta-cells leads to insulin insufficiency and hyperglycemia, with patients eventually requiring lifelong insulin therapy to maintain normal glycemic control. Since T1D has been historically defined as a disease of immune system dysregulation, there has been little focus on the state and response of beta-cells and how they may also contribute to their own demise. Major hurdles to identifying a cure for T1D include a limited understanding of disease etiology and how functional and transcriptional beta-cell heterogeneity may be involved in disease progression. Recent studies indicate that the beta-cell response is not simply a passive aspect of T1D pathogenesis, but rather an interplay between the beta-cell and the immune system actively contributing to disease. Here, we comprehensively review the current literature describing beta-cell vulnerability, heterogeneity, and contributions to pathophysiology of T1D, how these responses are influenced by autoimmunity, and describe pathways that can potentially be exploited to delay T1D.

A 584 bp deletion in CTRB2 inhibits chymotrypsin B2 activity and secretion and confers risk of pancreatic cancer

Genome-wide association studies (GWASs) have discovered 20 risk loci in the human genome where germline variants associate with risk of pancreatic ductal adenocarcinoma (PDAC) in populations of European ancestry. Here, we fine-mapped one such locus on chr16q23.1 (rs72802365, p = 2.51 × 10-17, OR = 1.36, 95% CI = 1.31-1.40) and identified colocalization (PP = 0.87) with aberrant exon 5-7 CTRB2 splicing in pancreatic tissues (pGTEx = 1.40 × 10-69, βGTEx = 1.99; pLTG = 1.02 × 10-30, βLTG = 1.99). Imputation of a 584 bp structural variant overlapping exon 6 of CTRB2 into the GWAS datasets resulted in a highly significant association with pancreatic cancer risk (p = 2.83 × 10-16, OR = 1.36, 95% CI = 1.31-1.42), indicating that it may underlie this signal. Exon skipping attributable to the deletion (risk) allele introduces a premature stop codon in exon 7 of CTRB2, yielding a truncated chymotrypsinogen B2 protein that lacks chymotrypsin activity, is poorly secreted, and accumulates intracellularly in the endoplasmic reticulum (ER). We propose that intracellular accumulation of a nonfunctional chymotrypsinogen B2 protein leads to ER stress and pancreatic inflammation, which may explain the increased pancreatic cancer risk in carriers of CTRB2 exon 6 deletion alleles.

Long RNA Sequencing and Ribosome Profiling of Inflamed β-Cells Reveal an Extensive Translatome Landscape

Type 1 diabetes (T1D) is an autoimmune disease characterized by autoreactive T cell-mediated destruction of the insulin-producing pancreatic β-cells. Increasing evidence suggest that the β-cells themselves contribute to their own destruction by generating neoantigens through the production of aberrant or modified proteins that escape central tolerance. We recently demonstrated that ribosomal infidelity amplified by stress could lead to the generation of neoantigens in human β-cells, emphasizing the participation of nonconventional translation events in autoimmunity, as occurring in cancer or virus-infected tissues. Using a transcriptome-wide profiling approach to map translation initiation start sites in human β-cells under standard and inflammatory conditions, we identify a completely new set of polypeptides derived from noncanonical start sites and translation initiation within long noncoding RNA. Our data underline the extreme diversity of the β-cell translatome and may reveal new functional biomarkers for β-cell distress, disease prediction and progression, and therapeutic intervention in T1D.

Immunological Monitoring in Beta Cell Replacement: Towards a Pathophysiology-Guided Implementation of Biomarkers

PURPOSE OF REVIEW

Grafted beta cells are lost because of recurrence of T1D and/or allograft rejection, two conditions diagnosed with pancreas graft biopsy, which is invasive and impossible in case of islet transplantation. This review synthetizes the current pathophysiological knowledge and discusses the interest of available immune biomarkers.

RECENT FINDINGS

Despite the central role of auto-(recurrence of T1D) and allo-(T-cell mediated rejection) immune cellular responses, the latter are not directly monitored in routine. In striking contrast, there have been undisputable progresses in monitoring of auto and alloantibodies. Except for pancreas recipients in whom anti-donor HLA antibodies can be directly responsible for antibody-mediated rejection, autoantibodies (and alloantibodies in islet recipients) have no direct pathogenic effect. However, their fluctuation offers a surrogate marker for the activation status of T cells (because antibody generation depends on T cells). This illustrates the necessity to understand the pathophysiology when interpreting a biomarker and selecting the appropriate treatment.

Endoplasmic Reticulum-Mitochondria Crosstalk and Beta-Cell Destruction in Type 1 Diabetes

Beta-cell destruction in type 1 diabetes (T1D) results from the combined effect of inflammation and recurrent autoimmunity. In response to inflammatory signals, beta-cells engage adaptive mechanisms where the endoplasmic reticulum (ER) and mitochondria act in concert to restore cellular homeostasis. In the recent years it has become clear that this adaptive phase may trigger the development of autoimmunity by the generation of autoantigens recognized by autoreactive CD8 T cells. The participation of the ER stress and the unfolded protein response to the increased visibility of beta-cells to the immune system has been largely described. However, the role of the other cellular organelles, and in particular the mitochondria that are central mediator for beta-cell survival and function, remains poorly investigated. In this review we will dissect the crosstalk between the ER and mitochondria in the context of T1D, highlighting the key role played by this interaction in beta-cell dysfunctions and immune activation, especially through regulation of calcium homeostasis, oxidative stress and generation of mitochondrial-derived factors.

A New Hypothesis for Type 1 Diabetes Risk: The At-Risk Allele at rs3842753 Associates With Increased Beta-cell INS Messenger RNA in a Meta-Analysis of Single-Cell RNA-Sequencing Data

OBJECTIVES

Type 1 diabetes is characterized by the autoimmune destruction of insulin-secreting beta cells. Genetic variants upstream at the insulin (INS) locus contribute to ∼10% of type 1 diabetes heritable risk. Previous studies showed an association between rs3842753 C/C genotype and type 1 diabetes susceptibility, but the molecular mechanisms remain unclear. To date, no large-scale studies have looked at the effect of genetic variation at rs3842753 on INS mRNA at the single-cell level.

METHODS

We aligned all human islet single-cell RNA sequencing data sets available to us in year 2020 to the reference genome GRCh38.98 and genotyped rs3842753, integrating 2,315 β cells and 1,223 β-like cells from 13 A/A protected donors, 23 A/C heterozygous donors and 35 C/C at-risk donors, including adults without diabetes and with type 2 diabetes.

RESULTS

INS expression mean and variance were significantly higher in single β cells from females compared with males. On comparing across β cells and β-like cells, we found that rs3842753 C‒containing cells (either homozygous or heterozygous) had the highest INS expression. We also found that β cells with the rs3842753 C allele had significantly higher endoplasmic reticulum stress marker gene expression compared with the A/A homozygous genotype.

CONCLUSIONS

These findings support the emerging concept that inherited risk of type 1 diabetes may be associated with inborn, persistent elevated insulin production, which may lead to β-cell endoplasmic reticulum stress and fragility.

Type 1 diabetes mellitus as a disease of the β-cell (do not blame the immune system?)

Type 1 diabetes mellitus is believed to result from destruction of the insulin-producing β-cells in pancreatic islets that is mediated by autoimmune mechanisms. The classic view is that autoreactive T cells mistakenly destroy healthy ('innocent') β-cells. We propose an alternative view in which the β-cell is the key contributor to the disease. By their nature and function, β-cells are prone to biosynthetic stress with limited measures for self-defence. β-Cell stress provokes an immune attack that has considerable negative effects on the source of a vital hormone. This view would explain why immunotherapy at best delays progression of type 1 diabetes mellitus and points to opportunities to use therapies that revitalize β-cells, in combination with immune intervention strategies, to reverse the disease. We present the case that dysfunction occurs in both the immune system and β-cells, which provokes further dysfunction, and present the evidence leading to the consensus that islet autoimmunity is an essential component in the pathogenesis of type 1 diabetes mellitus. Next, we build the case for the β-cell as the trigger of an autoimmune response, supported by analogies in cancer and antitumour immunity. Finally, we synthesize a model ('connecting the dots') in which both β-cell stress and islet autoimmunity can be harnessed as targets for intervention strategies.

SMAD-specific E3 ubiquitin ligase 2 promotes angiogenesis by facilitating PTX3 degradation in MSCs from patients with ankylosing spondylitis

Dysregulated angiogenesis of mesenchymal stem cells (MSCs) is closely related to inflammation and disrupted bone metabolism in patients with various autoimmune diseases. However, the role of MSCs in the development of abnormal angiogenesis in patients with ankylosing spondylitis (AS) remains unclear. In this study, we cultured human umbilical vein endothelial cells (HUVECs) with bone marrow-derived MSCs from patients with AS (ASMSCs) or healthy donors (HDMSCs) in vitro. Then, the cocultured HUVECs were assayed using a cell counting kit-8 (CCK-8) to evaluate the cell proliferation. A wound healing assay was performed to investigate cell migration, and a tube formation assay was conducted to determine the angiogenesis efficiency. ASMSCs exhibited increased angiogenesis, and increased expression of SMAD-specific E3 ubiquitin ligase 2 (Smurf2) in MSCs was the main cause of abnormal angiogenesis in patients with AS. Downregulation of Smurf2 in ASMSCs blocked angiogenesis, whereas overexpression of Smurf2 in HDMSCs promoted angiogenesis. The pro-angiogenic effect of Smurf2 was confirmed by the results of a Matrigel plug assay in vivo. By functioning as an E3 ubiquitin ligase in MSCs, Smurf2 regulated the levels of pentraxin 3 (PTX3), which has been shown to suppress angiogenesis through the PTX3-fibroblast growth factor 2 pathway. Moreover, Smurf2 transcription was regulated by activating transcription factor 4-induced endoplasmic reticulum stress. In conclusion, these results identify novel roles of Smurf2 in negatively regulating PTX3 stability and promoting angiogenesis in ASMSCs.

Type 1 diabetes mellitus in patients with recurrent acute and chronic pancreatitis: A case series

BACKGROUND/OBJECTIVES

Pancreatogenic diabetes mellitus has been assumed to result from non-immune beta cell destruction when the pancreas is replaced by fibrotic tissue secondary to acute and chronic pancreatitis. We hypothesize that recurrent episodes of pancreatic inflammation may increase the risk for developing β-cell autoimmunity in susceptible individuals.

METHODS

We describe 11 patients who had both recurrent acute and/or chronic pancreatitis and type 1 diabetes (T1D) requiring insulin therapy.

RESULTS

All 11 patients had positive autoantibodies and 8 patients tested had minimal to undetectable (7/8) or moderate (1/8) stimulated C-peptide at 12 months after T1D onset. Three had biopsy confirmation of insulitis.

CONCLUSIONS

These cases lend support to the theory that pancreatitis may increase risk for T1D. We postulate that the pro-inflammatory conditions of pancreatitis may increase posttranslational protein modifications of β-cell antigens and neoepitope generation, which are potential initiating events for loss of β-cell self-tolerance.

Effects of TNF-α-308G/A Polymorphism on the Risk of Diabetic Nephropathy and Diabetic Retinopathy: An Updated Meta-Analysis

Diabetic nephropathy (DN) and diabetic retinopathy (DR) are the major factors of morbidity and mortality in the patients with diabetes mellitus (DM). Growing studies have investigated the relationship between the TNF-α-308G/A polymorphism and the susceptibility to DN and DR, without achieving consensus. Thus, we conducted this meta-analysis to reach more comprehensive conclusions for these issues. Eligible studies were retrieved through electronic databases such as PubMed, Embase, Web of Science and China National Knowledge Infrastructure. Summary of odds ratios (OR) and 95% confidence intervals (CIs) were generated to evaluate the intensity of the associations. Statistical analyses were performed by STATA 11.0 and RevMan 5.2. There are fourteen eligible publications involving nineteen studies in this meta-analysis. TNF-α-308G/A polymorphism was significantly related to increasing risk of DN under recessive model (OR=1.37, 95% CI=1.03-1.83) and homozygous model (OR=1.54, 95% CI=1.15-2.06). Moreover, the similar results were also obtained in Asian groups for DN (recessive: OR=1.69, 95% CI=1.18-2.42; homozygous: OR=1.99, 95% CI=1.38-2.86; respectively), and significant association was also detected between TNF-α-308G/A and DN susceptibility in type 2 DM in recessive model (OR=1.39, 95% CI=1.02-1.89). No significant association was observed between TNF-α-308G/A and DR susceptibility in total analyses and subgroup analyses by ethnicity and type of DM. TNF-α-308G/A polymorphism may enhance the susceptibility to diabetic nephropathy, especially in Asian population and in T2DM patients, but not diabetic retinopathy.

Pancreatic β-cells in type 1 and type 2 diabetes mellitus: different pathways to failure

Loss of functional β-cell mass is the key mechanism leading to the two main forms of diabetes mellitus - type 1 diabetes mellitus (T1DM) and type 2 diabetes mellitus (T2DM). Understanding the mechanisms behind β-cell failure is critical to prevent or revert disease. Basic pathogenic differences exist in the two forms of diabetes mellitus; T1DM is immune mediated and T2DM is mediated by metabolic mechanisms. These mechanisms differentially affect early β-cell dysfunction and eventual fate. Over the past decade, major advances have been made in the field, mostly delivered by studies on β-cells in human disease. These advances include studies of islet morphology and human β-cell gene expression in T1DM and T2DM, the identification and characterization of the role of T1DM and T2DM candidate genes at the β-cell level and the endoplasmic reticulum stress signalling that contributes to β-cell failure in T1DM (mostly IRE1 driven) and T2DM (mostly PERK-eIF2α dependent). Here, we review these new findings, focusing on studies performed on human β-cells or on samples obtained from patients with diabetes mellitus.

Distinct secretion pattern of serum proinsulin in different types of diabetes

Background

Latent autoimmune diabetes in adults (LADA) is characterized by autoimmunity, late-onset and intermediate beta-cell deprivation rate between type 2 diabetes mellitus (T2DM) and type 1 diabetes mellitus (T1DM). Herein, we investigated proinsulin (PI) secretion patterns and the endoplasmic reticulum (ER) dysfunction biomarker, PI-to-C-peptide (PI:CP) ratio, to elucidate beta-cell intrinsic pathogenesis mechanisms in different types of diabetes.

Methods

Total serum fasting PI (FPI) were measured in adult-onset and newly-diagnosed diabetes patients, including 60 T1DM, 60 LADA and 60 T2DM. Thirty of each type underwent mixed meal tolerance tests (MMTTs), and hence 120 min postprandial PI (PPI) were detected. PI:CP ratio = PI (pmol/L) ÷ CP (pmol/L) × 100%. PI-related measurements among types of diabetes were compared. Correlation between PI-related measurements and beta-cell autoimmunity were analyzed. The possibility of discriminating LADA from T1DM and T2DM with PI-related measurements were tested.

Results

FPI and PPI were significantly higher in LADA than T1DM (P<0.001 for both comparisons), but lower than those in T2DM (P<0.001 and P=0.026, respectively). Fasting PI:CP ratio was significantly higher in T1DM than both LADA and T2DM (median 3.25% vs. 2.13% and 2.32%, P=0.011 and P=0.017, respectively). In LADA, positive autoantibody numbers increased by both fasting and postprandial PI:CP ratio (P=0.007 and P=0.034, respectively). Areas under receiver operation characteristic curves (AUC_ROC) of FPI and PPI for discriminating LADA from adult-onset T1DM were 0.751 (P<0.001) and 0.838 (P<0.001), respectively. Between LADA and T2DM, AUC_ROC of FPI and PPI were 0.685 (P<0.001) and 0.741 (P=0.001), respectively.

Conclusions

In the development of autoimmune diabetes, interplays between ER stress and beta-cell autoimmunity are potentially responsible for severer beta-cell destruction. PI-related measurements could help in differentiating LADA from adult-onset T1DM and T2DM.

β-Cell Stress Shapes CTL Immune Recognition of Preproinsulin Signal Peptide by Posttranscriptional Regulation of Endoplasmic Reticulum Aminopeptidase 1

The signal peptide of preproinsulin is a major source for HLA class I autoantigen epitopes implicated in CD8 T cell (CTL)-mediated β-cell destruction in type 1 diabetes (T1D). Among them, the 10-mer epitope located at the C-terminal end of the signal peptide was found to be the most prevalent in patients with recent-onset T1D. While the combined action of signal peptide peptidase and endoplasmic reticulum (ER) aminopeptidase 1 (ERAP1) is required for processing of the signal peptide, the mechanisms controlling signal peptide trimming and the contribution of the T1D inflammatory milieu on these mechanisms are unknown. Here, we show in human β-cells that ER stress regulates ERAP1 gene expression at posttranscriptional level via the IRE1α/miR-17-5p axis and demonstrate that inhibition of the IRE1α activity impairs processing of preproinsulin signal peptide antigen and its recognition by specific autoreactive CTLs during inflammation. These results underscore the impact of ER stress in the increased visibility of β-cells to the immune system and position the IRE1α/miR-17 pathway as a central component in β-cell destruction processes and as a potential target for the treatment of autoimmune T1D.

PPARs and the Development of Type 1 Diabetes

Peroxisome proliferator-activated receptors (PPARs) are a family of transcription factors with a key role in glucose and lipid metabolism. PPARs are expressed in many cell types including pancreatic beta cells and immune cells, where they regulate insulin secretion and T cell differentiation, respectively. Moreover, various PPAR agonists prevent diabetes in the non-obese diabetic (NOD) mouse model of type 1 diabetes. PPARs are thus of interest in type 1 diabetes (T1D) as they represent a novel approach targeting both the pancreas and the immune system. In this review, we examine the role of PPARs in immune responses and beta cell biology and their potential as targets for treatment of T1D.

A robust strategy for proteomic identification of biomarkers of invasive phenotype complexed with extracellular heat shock proteins

As an extension of their orchestration of intracellular pathways, secretion of extracellular heat shock proteins (HSPs) is an emerging paradigm of homeostasis imperative to multicellular organization. Extracellular HSP is axiomatic to the survival of cells during tumorigenesis; proportional representation of specific HSP family members is indicative of invasive potential and prognosis. Further significance has been added by the knowledge that all cancer-derived exosomes have surface-exposed HSPs that reflect the membrane topology of cells that secrete them. Extracellular HSPs are also characteristic of chronic inflammation and sepsis. Accordingly, interrogation of extracellular HSPs secreted from cell culture models may represent a facile means of identifying translational biomarker signatures for targeting in situ. In the current study, we evaluated a simple peptide-based multivalent HSP affinity approach using the Vn96 peptide for low speed pelleting of HSP complexes from bioreactor cultures of cell lines with varying invasive phenotype in xenotransplant models: U87 (glioblastoma multiforme; invasive); HELA (choriocarcinoma; minimally invasive); HEK293T (virally transformed immortalized; embryonic). Proteomic profiling by bottom-up mass spectrometry revealed a comprehensive range of candidate biomarkers including primary HSP ligands. HSP complexes were associated with additional chaperones of prognostic significance such as protein disulfide isomerases, as well as pleiotropic metabolic enzymes, established as proportionally reflective of invasive phenotype. Biomarkers of inflammatory and mechanotransductive phenotype were restricted to the most invasive cell model U87, including chitinase CHI3L1, lamin C, amyloid derivatives, and histone isoforms.

Early-life factors contributing to type 1 diabetes

The incidence of type 1 diabetes has increased since the mid-twentieth century at a rate that is too rapid to be attributed to genetic predisposition alone. While the disease can occur at any age, mounting evidence from longitudinal cohort studies of at-risk children indicate that type 1 diabetes associated autoantibodies can be present from the first year of life, and that those who develop type 1 diabetes at a young age have a more aggressive form of the disease. This corroborates the hypothesis that environmental exposures in early life contribute to type 1 diabetes risk, whether related to maternal influences on the fetus during pregnancy, neonatal factors or later effects during infancy and early childhood. Studies to date show a range of environmental triggers acting at different time points, suggesting a multifactorial model of genetic and environmental factors in the pathogenesis of type 1 diabetes, which integrally involves a dialogue between the immune system and pancreatic beta cells. For example, breastfeeding may have a weak protective effect on type 1 diabetes risk, while use of an extensively hydrolysed formula does not. Additionally, exposure to being overweight pre-conception, both in utero and postnatally, is associated with increased risk of type 1 diabetes. Epidemiological, clinical and pathological studies in humans support a role for viral infections, particularly enteroviruses, in type 1 diabetes, but definitive proof is lacking. The role of the early microbiome and its perturbations in islet autoimmunity and type 1 diabetes is the subject of investigation in ongoing cohort studies. Understanding the interactions between environmental exposures and the human genome and metagenome, particularly across ethnically diverse populations, will be critical for the development of future strategies for primary prevention of type 1 diabetes.

Fibrillation of human islet amyloid polypeptide and its toxicity to pancreatic β-cells under lipid environment

BACKGROUND

Previous studies suggested that fibrillar human IAPP (hIAPP) is more likely to deposit in β-cells, resulting in β-cell injury. However, the changes in the conformation of hIAPP in lipid environment and the mechanism involved in β-cell damage are unclear.

METHODS

Synthetic hIAPP was incubated with five types of free fatty acids and phospholipids 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-l-serine (POPS), which constitute the cell membrane. Thioflavin-T fluorescence assay was conducted to analyze the degree of hIAPP fibrosis, and circular dichroism spectroscopy was performed to detect the β-fold formation of hIAPP. Furthermore, INS-1 cells were infected with human IAPP delivered by a GV230-EGFP plasmid. The effects of endogenous hIAPP overexpression induced by sodium palmitate on the survival, endoplasmic reticulum (ER) stress, and apoptosis of INS-1 cells were evaluated.

RESULTS

The five types of free fatty acids can accelerate the fibrosis of hIAPP. Sodium palmitate also maintained the stability of fibrillar hIAPP. POPS, not POPC, accelerated hIAPP fibrosis. Treatment of INS-1 cells with sodium palmitate increased the expression of hIAPP, activated ER stress and ER stress-dependent apoptosis signaling pathways, and increased the apoptotic rate.

CONCLUSION

Free fatty acids and anionic phospholipid can promote β-fold formation and fibrosis in hIAPP. High lipid induced the overexpression of hIAPP and aggravated ER stress and apoptosis in INS-1 cells, which caused β-cell death in high lipid environment.

GENERAL SIGNIFICANCE

Our study reveals free fatty acids and hIAPP synergistically implicated in endoplasmic reticulum stress and apoptosis of islet β-cells.

The Influence of Type 2 Diabetes-Associated Factors on Type 1 Diabetes

Current efforts to prevent progression from islet autoimmunity to type 1 diabetes largely focus on immunomodulatory approaches. However, emerging data suggest that the development of diabetes in islet autoantibody-positive individuals may also involve factors such as obesity and genetic variants associated with type 2 diabetes, and the influence of these factors increases with age at diagnosis. Although these factors have been linked with metabolic outcomes, particularly through their impact on β-cell function and insulin sensitivity, growing evidence suggests that they might also interact with the immune system to amplify the autoimmune response. The presence of factors shared by both forms of diabetes contributes to disease heterogeneity and thus has important implications. Characteristics that are typically considered to be nonimmune should be incorporated into predictive algorithms that seek to identify at-risk individuals and into the designs of trials for disease prevention. The heterogeneity of diabetes also poses a challenge in diagnostic classification. Finally, after clinically diagnosing type 1 diabetes, addressing nonimmune elements may help to prevent further deterioration of β-cell function and thus improve clinical outcomes. This Perspectives in Care article highlights the role of type 2 diabetes-associated genetic factors (e.g., gene variants at transcription factor 7-like 2 [TCF7L2]) and obesity (via insulin resistance, inflammation, β-cell stress, or all three) in the pathogenesis of type 1 diabetes and their impacts on age at diagnosis. Recognizing that type 1 diabetes might result from the sum of effects from islet autoimmunity and type 2 diabetes-associated factors, their interactions, or both affects disease prediction, prevention, diagnosis, and treatment.

Islet stress, degradation and autoimmunity

β-cell destruction in type 1 diabetes (T1D) results from the effect of inflammation and autoimmunity. In response to inflammatory signals, islet cells engage adaptive mechanisms to restore and maintain cellular homeostasis. Among these mechanisms, the unfolded protein response (UPR) leads to a reduction of the general protein translation rate, increased production of endoplasmic reticulum chaperones and the initiation of degradation by activation of the ER associated degradation pathway (ERAD) in which newly synthetized proteins are ubiquitinylated and processed through the proteasome. This adaptive phase is also believed to play a critical role in the development of autoimmunity by the generation of neoantigens. While we have previously investigated the effect of stress on transcription, translation and post-translational events as possible source for neoantigens, the participation of the degradation machinery, yet crucial in the generation of antigenic peptides, remains to be investigated in the context of T1D pathology. In this review, we will describe the relation between the unfolded protein response and the Ubiquitin Proteasome System (UPS) and address the role of the cellular degradation machinery in the generation of antigens. Learning from tumour immunology, we propose how these processes may unmask β-cells by triggering the generation of aberrant peptides recognized by the immune cells.