Citrullination of glucokinase is linked to autoimmune diabetes

The immunology of type 1 diabetes

Following the seminal discovery of insulin a century ago, treatment of individuals with type 1 diabetes (T1D) has been largely restricted to efforts to monitor and treat metabolic glucose dysregulation. The recent regulatory approval of the first immunotherapy that targets T cells as a means to delay the autoimmune destruction of pancreatic β-cells highlights the critical role of the immune system in disease pathogenesis and tends to pave the way for other immune-targeted interventions for T1D. Improving the efficacy of such interventions across the natural history of the disease will probably require a more detailed understanding of the immunobiology of T1D, as well as technologies to monitor residual β-cell mass and function. Here we provide an overview of the immune mechanisms that underpin the pathogenesis of T1D, with a particular emphasis on T cells.

CD4+ T Cells From Individuals With Type 1 Diabetes Respond to a Novel Class of Deamidated Peptides Formed in Pancreatic Islets

The β-cell plays a crucial role in the pathogenesis of type 1 diabetes, in part through the posttranslational modification of self-proteins by biochemical processes such as deamidation. These neoantigens are potential triggers for breaking immune tolerance. We report the detection by LC-MS/MS of 16 novel Gln and 27 novel Asn deamidations in 14 disease-related proteins within inflammatory cytokine-stressed human islets of Langerhans. T-cell clones responsive against one Gln- and three Asn-deamidated peptides could be isolated from peripheral blood of individuals with type 1 diabetes. Ex vivo HLA class II tetramer staining detected higher T-cell frequencies in individuals with the disease compared with control individuals. Furthermore, there was a positive correlation between the frequencies of T cells specific for deamidated peptides, insulin antibody levels at diagnosis, and duration of disease. These results highlight that stressed human islets are prone to enzymatic and biochemical deamidation and suggest that both Gln- and Asn-deamidated peptides can promote the activation and expansion of autoreactive CD4+ T cells. These findings add to the growing evidence that posttranslational modifications undermine tolerance and may open the road for the development of new diagnostic and therapeutic applications for individuals living with type 1 diabetes.

ARTICLE HIGHLIGHTS

Diabetes mellitus and idiopathic pulmonary fibrosis: a Mendelian randomization study

BACKGROUND

The question as to whether or not diabetes mellitus increases the risk of idiopathic pulmonary fibrosis (IPF) remains controversial. This study aimed to investigate the causal association between type 1 diabetes (T1D), type 2 diabetes (T2D), and IPF using Mendelian randomization (MR) analysis.

METHODS

We used two-sample univariate and multivariate MR (MVMR) analyses to investigate the causal relationship between T1D or T2D and IPF. We obtained genome-wide association study (GWAS) data for T1D and T2D from the European Bioinformatics Institute, comprising 29,652 T1D samples and 101,101 T1D single nucleotide polymorphisms (SNPs) and 655,666 T2D samples and 5,030,727 T2D SNPs. We also used IPF GWAS data from the FinnGen Biobank comprising 198,014 IPF samples and 16,380,413 IPF SNPs. All cases and controls in these datasets were derived exclusively from European populations. In the univariate MR analysis, we employed inverse variance-weighted (IVW), weighted median (WM), and MR-Egger regression methods. For the MVMR analysis, we used the multivariate IVW method primarily, and supplemented it with multivariate MR-Egger and multivariate MR- least absolute shrinkage and selection operator methods. Heterogeneity tests were conducted using the MR-IVW and MR-Egger regression methods, whereas pleiotropic effects were assessed using the MR-Egger intercept. The results of MR and sensitivity analyses were visualized using forest, scatter, leave-one-out, and funnel plots.

RESULTS

Univariate MR revealed a significant causal relationship between T1D and IPF (OR = 1.118, 95% CI = 1.021-1.225, P = 0.016); however, no significant causal relationship was found between T2D and IPF (OR = 0.911, 95% CI = 0.796-1.043, P = 0.178). MVMR analysis further confirmed a causal association between T1D and IPF (OR = 1.133, 95% CI = 1.011-1.270, P = 0.032), but no causal relationship between T2D and IPF (OR = 1.009, 95% CI = 0.790-1.288, P = 0.950). Sensitivity analysis results validated the stability and reliability of our findings.

CONCLUSION

Univariate and multivariate analyses demonstrated a causal relationship between T1D and IPF, whereas no evidence was found to support a causal relationship between T2D and IPF. Therefore, in clinical practice, patients with T1D should undergo lung imaging for early detection of IPF.

Epigenetic Alterations in Alzheimer's Disease: Impact on Insulin Signaling and Advanced Drug Delivery Systems

Alzheimer's disease (AD) is a neurodegenerative condition that predominantly affects the hippocampus and the entorhinal complex, leading to memory lapse and cognitive impairment. This can have a negative impact on an individual's behavior, speech, and ability to navigate their surroundings. AD is one of the principal causes of dementia. One of the most accepted theories in AD, the amyloid β (Aβ) hypothesis, assumes that the buildup of the peptide Aβ is the root cause of AD. Impaired insulin signaling in the periphery and central nervous system has been considered to have an effect on the pathophysiology of AD. Further, researchers have shifted their focus to epigenetic mechanisms that are responsible for dysregulating major biochemical pathways and intracellular signaling processes responsible for directly or indirectly causing AD. The prime epigenetic mechanisms encompass DNA methylation, histone modifications, and non-coding RNA, and are majorly responsible for impairing insulin signaling both centrally and peripherally, thus leading to AD. In this review, we provide insights into the major epigenetic mechanisms involved in causing AD, such as DNA methylation and histone deacetylation. We decipher how the mechanisms alter peripheral insulin signaling and brain insulin signaling, leading to AD pathophysiology. In addition, this review also discusses the need for newer drug delivery systems for the targeted delivery of epigenetic drugs and explores targeted drug delivery systems such as nanoparticles, vesicular systems, networks, and other nano formulations in AD. Further, this review also sheds light on the future approaches used for epigenetic drug delivery.

Non-mutational neoantigens in disease

The ability of mammals to mount adaptive immune responses culminating with the establishment of immunological memory is predicated on the ability of the mature T cell repertoire to recognize antigenic peptides presented by syngeneic MHC class I and II molecules. Although it is widely believed that mature T cells are highly skewed towards the recognition of antigenic peptides originating from genetically diverse (for example, foreign or mutated) protein-coding regions, preclinical and clinical data rather demonstrate that novel antigenic determinants efficiently recognized by mature T cells can emerge from a variety of non-mutational mechanisms. In this Review, we describe various mechanisms that underlie the formation of bona fide non-mutational neoantigens, such as epitope mimicry, upregulation of cryptic epitopes, usage of non-canonical initiation codons, alternative RNA splicing, and defective ribosomal RNA processing, as well as both enzymatic and non-enzymatic post-translational protein modifications. Moreover, we discuss the implications of the immune recognition of non-mutational neoantigens for human disease.

Technical Validation and Utility of an HLA Class II Tetramer Assay for Type 1 Diabetes: A Multicenter Study

CONTEXT

Validated assays to measure autoantigen-specific T-cell frequency and phenotypes are needed for assessing the risk of developing diabetes, monitoring disease progression, evaluating responses to treatment, and personalizing antigen-based therapies.

OBJECTIVE

Toward this end, we performed a technical validation of a tetramer assay for HLA-DRA-DRB1*04:01, a class II allele that is strongly associated with susceptibility to type 1 diabetes (T1D).

METHODS

HLA-DRA-DRB1*04:01-restricted T cells specific for immunodominant epitopes from islet cell antigens GAD65, IGRP, preproinsulin, and ZnT8, and a reference influenza epitope, were enumerated and phenotyped in a single staining tube with a tetramer assay. Single and multicenter testing was performed, using a clone-spiked specimen and replicate samples from T1D patients, with a target coefficient of variation (CV) less than 30%. The same assay was applied to an exploratory cross-sectional sample set with 24 T1D patients to evaluate the utility of the assay.

RESULTS

Influenza-specific T-cell measurements had mean CVs of 6% for the clone-spiked specimen and 11% for T1D samples in single-center testing, and 20% and 31%, respectively, for multicenter testing. Islet-specific T-cell measurements in these same samples had mean CVs of 14% and 23% for single-center and 23% and 41% for multicenter testing. The cross-sectional study identified relationships between T-cell frequencies and phenotype and disease duration, sex, and autoantibodies. A large fraction of the islet-specific T cells exhibited a naive phenotype.

CONCLUSION

Our results demonstrate that the assay is reproducible and useful to characterize islet-specific T cells and identify correlations between T-cell measures and clinical traits.

Natural isoaspartyl protein modification of ZAP70 alters T cell responses in lupus

Protein posttranslational modifications (PTMs) arise in a number of normal cellular biological pathways and in response to pathology caused by inflammation and/or infection. Indeed, a number of PTMs have been identified and linked to specific autoimmune responses and metabolic pathways. One particular PTM, termed isoaspartyl (isoAsp or isoD) modification, is among the most common spontaneous PTM occurring at physiological pH and temperature. Herein, we demonstrate that isoAsp modifications arise within the ZAP70 protein tyrosine kinase upon T-cell antigen receptor (TCR) engagement. The enzyme protein L-isoaspartate O-methyltransferase (PCMT1, or PIMT, EC 2.1.1.77) evolved to repair isoaspartyl modifications in cells. In this regard, we observe that increased levels of isoAsp modification that arise under oxidative stress are correlated with reduced PIMT activity in patients with systemic lupus erythematosus (SLE). PIMT deficiency leads to T cell hyper-proliferation and hyper-phosphorylation through ZAP70 signaling. We demonstrate that inducing the overexpression of PIMT can correct the hyper-responsive phenotype in lupus T cells. Our studies reveal a phenotypic role of isoAsp modification and phosphorylation of ZAP70 in lupus T cell autoimmunity and provide a potential therapeutic target through the repair of isoAsp modification.

Flexible Bio-Electronic Hybrid Metal-Oxide Channel FET as a Glucose Sensor

A high-sensitivity flexible field-effect transistor (FET) based glucose sensor is fabricated that can surpass the conventional electrochemical glucometers in terms of sensitivity, limit of detection, and other performance parameters. The proposed biosensor is based on the FET operation with the advantage of amplification which provides a high sensitivity and a very low limit of detection. Hybrid metal oxide (ZnO and CuO) nanostructures have been synthesized in the form of hollow spheres (ZnO/CuO-NHS). The FET was fabricated by depositing ZnO/CuO-NHS on the interdigitated electrodes. Glucose oxidase (GOx) was immobilized successfully on the ZnO/CuO-NHS. Three different outputs of the sensor are examined, the FET current, the relative current change, and the drain voltage. The sensitivity of the sensor for each output type has been calculated. The readout circuit can convert the current change to the voltage change that has been used for wireless transmission. The sensor has a very low limit of detection of 30 nM with satisfactory reproducibility, good stability, and high selectivity. The electrical response of the FET biosensor towards the real human blood serum samples demonstrated that it can be offered as a potential device for glucose detection in any medical application.

Regulation of insulin secretion by the post-translational modifications

Post-translational modification (PTM) has a significant impact on cellular signaling and function regulation. In pancreatic β cells, PTMs are involved in insulin secretion, cell development, and viability. The dysregulation of PTM in β cells is clinically associated with the development of diabetes mellitus. Here, we summarized current findings on major PTMs occurring in β cells and their roles in insulin secretion. Our work provides comprehensive insight into understanding the mechanisms of insulin secretion and potential therapeutic targets for diabetes from the perspective of protein PTMs.

Targeting protein modifications in metabolic diseases: molecular mechanisms and targeted therapies

The ever-increasing prevalence of noncommunicable diseases (NCDs) represents a major public health burden worldwide. The most common form of NCD is metabolic diseases, which affect people of all ages and usually manifest their pathobiology through life-threatening cardiovascular complications. A comprehensive understanding of the pathobiology of metabolic diseases will generate novel targets for improved therapies across the common metabolic spectrum. Protein posttranslational modification (PTM) is an important term that refers to biochemical modification of specific amino acid residues in target proteins, which immensely increases the functional diversity of the proteome. The range of PTMs includes phosphorylation, acetylation, methylation, ubiquitination, SUMOylation, neddylation, glycosylation, palmitoylation, myristoylation, prenylation, cholesterylation, glutathionylation, S-nitrosylation, sulfhydration, citrullination, ADP ribosylation, and several novel PTMs. Here, we offer a comprehensive review of PTMs and their roles in common metabolic diseases and pathological consequences, including diabetes, obesity, fatty liver diseases, hyperlipidemia, and atherosclerosis. Building upon this framework, we afford a through description of proteins and pathways involved in metabolic diseases by focusing on PTM-based protein modifications, showcase the pharmaceutical intervention of PTMs in preclinical studies and clinical trials, and offer future perspectives. Fundamental research defining the mechanisms whereby PTMs of proteins regulate metabolic diseases will open new avenues for therapeutic intervention.

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.

MHC Class II Presentation in Autoimmunity

Antigen presentation by major histocompatibility complex class II (MHC-II) molecules is crucial for eliciting an efficient immune response by CD4+ T cells and maintaining self-antigen tolerance. Some MHC-II alleles are known to be positively or negatively associated with the risk of the development of different autoimmune diseases (ADs), including those characterized by the emergence of autoreactive T cells. Apparently, the MHC-II presentation of self-antigens contributes to the autoimmune T cell response, initiated through a breakdown of central tolerance to self-antigens in the thymus. The appearance of autoreactive T cell might be the result of (i) the unusual interaction between T cell receptors (TCRs) and self-antigens presented on MHC-II; (ii) the posttranslational modifications (PTMs) of self-antigens; (iii) direct loading of the self-antigen to classical MHC-II without additional nonclassical MHC assistance; (iv) the proinflammatory environment effect on MHC-II expression and antigen presentation; and (v) molecular mimicry between foreign and self-antigens. The peculiarities of the processes involved in the MHC-II-mediated presentation may have crucial importance in the elucidation of the mechanisms of triggering and developing ADs as well as for clarification on the protective effect of MHC-II alleles that are negatively associated with ADs.

Biomarkers of autoimmunity and beta cell metabolism in type 1 diabetes

Posttranslational protein modifications (PTMs) are an inherent response to physiological changes causing altered protein structure and potentially modulating important biological functions of the modified protein. Besides cellular metabolic pathways that may be dictated by PTMs, the subtle change of proteins also may provoke immune attack in numerous autoimmune diseases. Type 1 diabetes (T1D) is a chronic autoimmune disease destroying insulin-producing beta cells within the pancreatic islets, a result of tissue inflammation to specific autoantigens. This review summarizes how PTMs arise and the potential pathological consequence of PTMs, with particular focus on specific autoimmunity to pancreatic beta cells and cellular metabolic dysfunction in T1D. Moreover, we review PTM-associated biomarkers in the prediction, diagnosis and in monitoring disease activity in T1D. Finally, we will discuss potential preventive and therapeutic approaches of targeting PTMs in repairing or restoring normal metabolic pathways in pancreatic islets.

Carbonyl Posttranslational Modification Associated With Early-Onset Type 1 Diabetes Autoimmunity

Inflammation and oxidative stress in pancreatic islets amplify the appearance of various posttranslational modifications to self-proteins. In this study, we identified a select group of carbonylated islet proteins arising before the onset of hyperglycemia in NOD mice. Of interest, we identified carbonyl modification of the prolyl-4-hydroxylase β subunit (P4Hb) that is responsible for proinsulin folding and trafficking as an autoantigen in both human and murine type 1 diabetes. We found that carbonylated P4Hb is amplified in stressed islets coincident with decreased glucose-stimulated insulin secretion and altered proinsulin-to-insulin ratios. Autoantibodies against P4Hb were detected in prediabetic NOD mice and in early human type 1 diabetes prior to the onset of anti-insulin autoimmunity. Moreover, we identify autoreactive CD4+ T-cell responses toward carbonyl-P4Hb epitopes in the circulation of patients with type 1 diabetes. Our studies provide mechanistic insight into the pathways of proinsulin metabolism and in creating autoantigenic forms of insulin in type 1 diabetes.

The virtues and vices of protein citrullination

The post-translational modification of proteins expands the regulatory scope of the proteome far beyond what is achievable through genome regulation. The field of protein citrullination has seen significant progress in the last two decades. The small family of peptidylarginine deiminase (PADI or PAD) enzymes, which catalyse citrullination, have been implicated in virtually all facets of molecular and cell biology, from gene transcription and epigenetics to cell signalling and metabolism. We have learned about their association with a remarkable array of disease states and we are beginning to understand how they mediate normal physiological functions. However, while the biochemistry of PADI activation has been worked out in exquisite detail in vitro, we still lack a clear mechanistic understanding of the processes that regulate PADIs within cells, under physiological and pathophysiological conditions. This review summarizes and discusses the current knowledge, highlights some of the unanswered questions of immediate importance and gives a perspective on the outlook of the citrullination field.