Search

Type 2 diabetes (T2D) is associated with a systemic increase in the pro-inflammatory cytokine IL-1β. While transient exposure to low IL-1β concentrations improves insulin secretion and β-cell proliferation in pancreatic islets, prolonged exposure leads to impaired insulin secretion and collective β-cell death. IL-1 is secreted locally by islet-resident macrophages and β-cells; however, it is unknown if and how the two opposing modes may emerge at single islet level. We investigated the duality of IL-1β with a quantitative in silico model of the IL-1 regulatory network in pancreatic islets. We find that the network can produce either transient or persistent IL-1 responses when induced by pro-inflammatory and metabolic cues. This suggests that the duality of IL-1 may be regulated at the single islet level. We use two core feedbacks in the IL-1 regulation to explain both modes: First, a fast positive feedback in which IL-1 induces its own production through the IL-1R/IKK/NF-κB pathway. Second, a slow negative feedback where NF-κB upregulates inhibitors acting at different levels along the IL-1R/IKK/NF-κB pathway-IL-1 receptor antagonist and A20, among others. A transient response ensues when the two feedbacks are balanced. When the positive feedback dominates over the negative, islets transit into the persistent inflammation mode. Consistent with several observations, where the size of islets was implicated in its inflammatory state, we find that large islets and islets with high density of IL-1β amplifying cells are more prone to transit into persistent IL-1β mode. Our results are likely not limited to IL-1β but are general for the combined effect of multiple pro-inflammatory cytokines and chemokines. Generalizing complex regulations in terms of two feedback mechanisms of opposing nature and acting on different time scales provides a number of testable predictions. Taking islet architecture and cellular heterogeneity into consideration, further dynamic monitoring and experimental validation in actual islet samples will be crucial to verify the model predictions and enhance its utility in clinical applications., (© 2024. The Author(s).)

Introduction: Proinflammatory cytokines are implicated in pancreatic ß cell failure in type 1 and type 2 diabetes and are known to stimulate alternative RNA splicing and the expression of nonsense-mediated RNA decay (NMD) components. Here, we investigate whether cytokines regulate NMD activity and identify transcript isoforms targeted in ß cells., Methods: A luciferase-based NMD reporter transiently expressed in rat INS1(832/13), human-derived EndoC-ßH3, or dispersed human islet cells is used to examine the effect of proinflammatory cytokines (Cyt) on NMD activity. The gain- or loss-of-function of two key NMD components, UPF3B and UPF2, is used to reveal the effect of cytokines on cell viability and function. RNA-sequencing and siRNA-mediated silencing are deployed using standard techniques., Results: Cyt attenuate NMD activity in insulin-producing cell lines and primary human ß cells. These effects are found to involve ER stress and are associated with the downregulation of UPF3B. Increases or decreases in NMD activity achieved by UPF3B overexpression (OE) or UPF2 silencing raise or lower Cyt-induced cell death, respectively, in EndoC-ßH3 cells and are associated with decreased or increased insulin content, respectively. No effects of these manipulations are observed on glucose-stimulated insulin secretion. Transcriptomic analysis reveals that Cyt increases alternative splicing (AS)-induced exon skipping in the transcript isoforms, and this is potentiated by UPF2 silencing. Gene enrichment analysis identifies transcripts regulated by UPF2 silencing whose proteins are localized and/or functional in the extracellular matrix (ECM), including the serine protease inhibitor SERPINA1/α-1-antitrypsin, whose silencing sensitizes ß-cells to Cyt cytotoxicity. Cytokines suppress NMD activity via UPR signaling, potentially serving as a protective response against Cyt-induced NMD component expression., Conclusion: Our findings highlight the central importance of RNA turnover in ß cell responses to inflammatory stress., Competing Interests: Author GR is a consultant for, and has received grant funding from, Sun Pharmaceuticals Inc. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The author(s) declared that they were an editorial board member of Frontiers, at the time of submission. This had no impact on the peer review process and the final decision., (Copyright © 2024 Ghiasi, Marchetti, Piemonti, Nielsen, Porse, Mandrup-Poulsen and Rutter.)

Neutrophils are innate immune cells that play a key role in pathogen clearance. They contribute to inflammatory diseases, including diabetes, by releasing pro-inflammatory cytokines, reactive oxygen species, and extracellular traps (NETs). NETs contain a DNA backbone and catalytically active myeloperoxidase (MPO), which produces hypochlorous acid (HOCl). Chlorination of the DNA nucleoside 8-chloro-deoxyguanosine has been reported as an early marker of inflammation in diabetes. In this study, we examined the reactivity of different chlorinated nucleosides, including 5-chloro-(deoxy)cytidine (5ClC, 5CldC), 8-chloro-(deoxy)adenosine (8ClA, 8CldA) and 8-chloro-(deoxy)guanosine (8ClG, 8CldG), with the INS-1E β-cell line. Exposure of INS-1E cells to 5CldC, 8CldA, 8ClA, and 8CldG decreased metabolic activity and intracellular ATP, and, together with 8ClG, induced apoptotic cell death. Exposure to 8ClA, but not the other nucleosides, resulted in sustained endoplasmic reticulum stress, activation of the unfolded protein response, and increased expression of thioredoxin-interacting protein (TXNIP) and heme oxygenase 1 (HO-1). Exposure of INS-1E cells to 5CldC also increased TXNIP and NAD(P)H dehydrogenase quinone 1 (NQO1) expression. In addition, a significant increase in the mRNA expression of NQO1 and GPx4 was seen in INS-1E cells exposed to 8ClG and 8CldA, respectively. However, a significant decrease in intracellular thiols was only observed in INS-1E cells exposed to 8ClG and 8CldG. Finally, a significant decrease in the insulin stimulation index was observed in experiments with all the chlorinated nucleosides, except for 8ClA and 8ClG. Together, these results suggest that increased formation of chlorinated nucleosides during inflammation in diabetes could influence β-cell function and may contribute to disease progression.

Indoor-confined cats are prone to developing obesity due to a sedentary life and an energy intake exceeding energy requirements. As in humans, feline obesity decreases insulin sensitivity and increases the risk of developing feline diabetes mellitus, but the pathophysiological mechanisms are currently poorly understood. Human obesity-related metabolic alterations seem to relate to changes in the expression of genes involved in glucose metabolism, insulin action and inflammation. The objective of the current study was to investigate changes in the expression of genes relating to obesity, glucose metabolism and inflammation in cats with non-experimentally induced obesity. Biopsies from the sartorius muscle and subcutaneous adipose tissue were obtained from 73 healthy, neutered, indoor-confined domestic shorthaired cats ranging from lean to obese. Quantification of obesity-related gene expression levels relative to glyceraldehyde-3-phosphate dehydrogenase was performed by quantitative real-time polymerase chain reaction. A negative association between obesity and adiponectin expression was observed in the adipose tissue (mean ± SD; normal weight, 27.30 × 10 -3  ± 77.14 × 10 -3 ; overweight, 2.89 × 10 -3  ± 0.38 × 10 -3 and obese, 2.93 × 10 -3  ± 4.20 × 10 -3 , p < 0.05). In muscle, the expression of peroxisome proliferative activated receptor-γ2 and plasminogen activator inhibitor-1 was increased in the obese compared to the normal-weight cats, and resistin was increased in the normal-weight compared to the overweight cats. There were no detectable obesity-related changes in the messenger RNA levels of inflammatory cytokines. In conclusion, a possible obesity-related low-grade inflammation caused by increased expression of key proinflammatory regulators was not observed. This could imply that the development of feline obesity and ensuing insulin resistance may not be based on tissue-derived inflammation, but caused by several determining factors, many of which still need further investigation., (© 2023 The Authors. Journal of Animal Physiology and Animal Nutrition published by Wiley-VCH GmbH.)

Objective: To examine whether iron intake and genetically determined iron overload interact in predisposing to the development of childhood islet autoimmunity (IA) and type 1 diabetes (T1D)., Research Design and Methods: In The Environmental Determinants of Diabetes in the Young (TEDDY) study, 7,770 genetically high-risk children were followed from birth until the development of IA and progression to T1D. Exposures included energy-adjusted iron intake in the first 3 years of life and a genetic risk score (GRS) for increased circulating iron., Results: We found a U-shaped association between iron intake and risk of GAD antibody as the first autoantibody. In children with GRS ≥2 iron risk alleles, high iron intake was associated with an increased risk of IA, with insulin as first autoantibody (adjusted hazard ratio 1.71 [95% CI 1.14; 2.58]) compared with moderate iron intake., Conclusions: Iron intake may alter the risk of IA in children with high-risk HLA haplogenotypes., (© 2023 by the American Diabetes Association.)

Apart from chaperoning, disulfide bond formation, and downstream processing, the molecular sequence of proinsulin folding is not completely understood. Proinsulin requires proline isomerization for correct folding. Since FK506-binding protein 2 (FKBP2) is an ER-resident proline isomerase, we hypothesized that FKBP2 contributes to proinsulin folding. We found that FKBP2 co-immunoprecipitated with proinsulin and its chaperone GRP94 and that inhibition of FKBP2 expression increased proinsulin turnover with reduced intracellular proinsulin and insulin levels. This phenotype was accompanied by an increased proinsulin secretion and the formation of proinsulin high-molecular-weight complexes, a sign of proinsulin misfolding. FKBP2 knockout in pancreatic β-cells increased apoptosis without detectable up-regulation of ER stress response genes. Interestingly, FKBP2 mRNA was overexpressed in β-cells from pancreatic islets of T2D patients. Based on molecular modeling and an in vitro enzymatic assay, we suggest that proline at position 28 of the proinsulin B-chain (P28) is the substrate of FKBP2's isomerization activity. We propose that this isomerization step catalyzed by FKBP2 is an essential sequence required for correct proinsulin folding.

Aim: The voltage-gated potassium channel K v 11.1 is important for repolarizing the membrane potential in excitable cells such as myocytes, pancreatic α- and β-cells. Moxifloxacin blocks the K v 11.1 channel and increases the risk of hypoglycaemia in patients with diabetes. We investigated glucose regulation and secretion of glucoregulatory hormones in young people with and without moxifloxacin, a drug known to block the K v 11.1 channel., Materials and Methods: The effect of moxifloxacin (800 mg/day for 4 days) or placebo on glucose regulation was assessed in a randomized, double-blind, crossover study of young men and women (age 20-40 years and body mass index 18.5-27.5 kg/m 2 ) without chronic disease, using 6-h oral glucose tolerance tests and continuous glucose monitoring., Results: Thirty-eight participants completed the study. Moxifloxacin prolonged the QTcF interval and increased heart rate. Hypoglycaemia was more frequently observed with moxifloxacin, both during the 8 days of continuous glucose monitoring and during the oral glucose tolerance tests. Hypoglycaemia questionnaire scores were higher after intake of moxifloxacin. Moxifloxacin reduced the early plasma-glucose response (AUC 0-30 min ) by 7% (95% CI: -9% to -4%, p < .01), and overall insulin response (AUC 0-360 min ) decreased by 18% (95% CI: -24% to -11%, p < .01) and plasma glucagon increased by 17% (95% CI: 4%-33%, p = .03). Insulin sensitivity calculated as the Matsuda index increased by 11%, and MISI, an index of muscle insulin sensitivity, increased by 34%., Conclusions: In young men and women, moxifloxacin, a drug known to block the K v 11.1 channel, increased QT interval, decreased glucose levels and was associated with increased muscle insulin sensitivity and more frequent episodes of hypoglycaemia., (© 2022 The Authors. Diabetes, Obesity and Metabolism published by John Wiley & Sons Ltd.)

Background: We previously reported that reduced GPR183 expression in blood from tuberculosis (TB) patients with diabetes is associated with more severe TB., Methods: To further elucidate the role of GPR183 and its oxysterol ligands in the lung, we studied dysglycemic mice infected with Mycobacterium tuberculosis (Mtb)., Results: We found upregulation of the oxysterol-producing enzymes CH25H and CYP7B1 and increased concentrations of 25-hydroxycholesterol upon Mtb infection in the lungs of mice. This was associated with increased expression of GPR183 indicative of oxysterol-mediated recruitment of GPR183-expressing immune cells to the lung. CYP7B1 was predominantly expressed by macrophages in TB granulomas. CYP7B1 expression was significantly blunted in lungs from dysglycemic animals, which coincided with delayed macrophage infiltration. GPR183-deficient mice similarly had reduced macrophage recruitment during early infection., Conclusions: Taken together, we demonstrate a requirement of the GPR183/oxysterol axis for positioning of macrophages to the site of infection and add an explanation to more severe TB in diabetes patients., (© The Author(s) 2022. Published by Oxford University Press for the Infectious Diseases Society of America.)

How immune tolerance is lost to pancreatic β-cell peptides triggering autoimmune type 1 diabetes is enigmatic. We have shown that loss of the proinsulin chaperone glucose-regulated protein (GRP) 94 from the endoplasmic reticulum (ER) leads to mishandling of proinsulin, ER stress, and activation of the immunoproteasome. We hypothesize that inadequate ER proinsulin folding capacity relative to biosynthetic need may lead to an altered β-cell major histocompatibility complex (MHC) class-I bound peptidome and inflammasome activation, sensitizing β-cells to immune attack. We used INS-1E cells with or without GRP94 knockout (KO), or in the presence or absence of GRP94 inhibitor PU-WS13 (GRP94i, 20 µM), or exposed to proinflammatory cytokines interleukin (IL)-1β or interferon gamma (IFNγ) (15 pg/mL and 10 ng/mL, respectively) for 24 h. RT1.A (rat MHC I) expression was evaluated using flow cytometry. The total RT1.A-bound peptidome analysis was performed on cell lysates fractionated by reverse-phase high-performance liquid chromatography (RP-HPLC), followed by liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS). The nucleotide-binding oligomerization domain, leucine rich repeat and pyrin domain containing protein (NLRP1), nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor alpha (IκBα), and (pro) IL-1β expression and secretion were investigated by Western blotting. GRP94 KO increased RT1.A expression in β-cells, as did cytokine exposure compared to relevant controls. Immunopeptidome analysis showed increased RT1.A-bound peptide repertoire in GRP94 KO/i cells as well as in the cells exposed to cytokines. The GRP94 KO/cytokine exposure groups showed partial overlap in their peptide repertoire. Notably, proinsulin-derived peptide diversity increased among the total RT1.A peptidome in GRP94 KO/i along with cytokines exposure. NLRP1 expression was upregulated in GRP94 deficient cells along with decreased IκBα content while proIL-1β cellular levels declined, coupled with increased secretion of mature IL-1β. Our results suggest that limiting β-cell proinsulin chaperoning enhances RT1.A expression alters the MHC-I peptidome including proinsulin peptides and activates inflammatory pathways, suggesting that stress associated with impeding proinsulin handling may sensitize β-cells to immune-attack.

Voltage-gated potassium (K v ) channels play an important role in the repolarization of a variety of excitable tissues, including in the cardiomyocyte and the pancreatic beta cell. Recently, individuals carrying loss-of-function (LoF) mutations in KCNQ1, encoding K v 7.1, and KCNH2 (hERG), encoding K v 11.1, were found to exhibit post-prandial hyperinsulinaemia and episodes of hypoglycaemia. These LoF mutations also cause the cardiac disorder long QT syndrome (LQTS), which can be aggravated by hypoglycaemia. Interestingly, patients with LQTS also have a higher burden of diabetes compared to the background population, an apparent paradox in relation to the hyperinsulinaemic phenotype, and KCNQ1 has been identified as a type 2 diabetes risk gene. This review article summarizes the involvement of delayed rectifier K + channels in pancreatic beta cell function, with emphasis on K v 7.1 and K v 11.1, using the cardiomyocyte for context. The functional and clinical consequences of LoF mutations and polymorphisms in these channels on blood glucose homeostasis are explored using evidence from pre-clinical, clinical and genome-wide association studies, thereby evaluating the link between LQTS, hyperinsulinaemia and type 2 diabetes., (© 2022 The Authors. Acta Physiologica published by John Wiley & Sons Ltd on behalf of Scandinavian Physiological Society.)