Affect Insulin Secretion Research Articles

Prevalence of Thyroid Dysfunction among Patients with Type II diabetes Mellitus in Tertiary Care Center: A Descriptive Cross-sectional Study

Introduction: Diabetes mellitus (DM) and thyroid dysfunction (TD) are two of the most prevalent endocrine disorders globally. Both conditions have significant effects on metabolism and are known to influence each other. Thyroid hormones play a crucial role in glucose homeostasis by affecting insulin secretion, sensitivity, and glucose metabolism.Conversely, altered glucose metabolism in diabetes can impact thyroid function, leading to a higher prevalence of thyroid disorders in diabetic patients. Understanding this relationship is important for improving the clinical management of patients with Type II DM. However, there is limited data on the prevalence of thyroid dysfunction in diabetic populations within specific regions. Methods: A cross-sectional descriptive study was conducted from February to September 2023 among 209 patients diagnosed with Type II DM at a tertiary care center after obtaining ethical approval from Institutional Review Committee(Reference No: 367 (6-11) E2). Thyroid function was assessed using thyroid-stimulating hormone (TSH), free T3 (FT3), and free T4 (FT4) levels. Thyroid dysfunction was classified into hypothyroidism and hyperthyroidism based on standard clinical and laboratory criteria. Data management involved entry into Microsoft Excel, verification for accuracy, and subsequent analysis using SPSS version 29.Results: The study included 209 patients (61% female, 39% male), with a mean age of 65.87 ± 13.7 years. The prevalence of thyroid disorders was 77(36.8%): 53(25.3%) hypothyroidism,24 (11.4%) hyperthyroidism among patient with type II diabetes mellitus.Conclusions: Our study shows a high prevalence of thyroid disorders, especially subclinical hypothyroidism, in individuals with type 2 diabetes. Poorly controlled blood glucose (HbA1c ≥ 7.5) significantly increases the risk, underscoring the need for routine thyroid screening in T2DM management

Monogenic Defects of Beta Cell Function: From Clinical Suspicion to Genetic Diagnosis and Management of Rare Types of Diabetes

Monogenic defects of beta cell function refer to a group of rare disorders that are characterized by early-onset diabetes mellitus due to a single gene mutation affecting insulin secretion. It accounts for up to 5% of all pediatric diabetes cases and includes transient or permanent neonatal diabetes, maturity-onset diabetes of the young (MODY), and various syndromes associated with diabetes. Causative mutations have been identified in genes regulating the development or function of the pancreatic beta cells responsible for normal insulin production and/or release. To date, more than 40 monogenic diabetes subtypes have been described, with those caused by mutations in HNF1A and GCK genes being the most prevalent. Despite being caused by a single gene mutation, each type of monogenic diabetes, especially MODY, can appear with various clinical phenotypes, even among members of the same family. This clinical heterogeneity, its rarity, and the fact that it shares some features with more common types of diabetes, can make the clinical diagnosis of monogenic diabetes rather challenging. Indeed, several cases of MODY or syndromic diabetes are accurately diagnosed in adulthood, after having been mislabeled as type 1 or type 2 diabetes. The recent widespread use of more reliable sequencing techniques has improved monogenic diabetes diagnosis, which is important to guide appropriate treatment and genetic counselling. The current review aims to summarize the latest knowledge on the clinical presentation, genetic confirmation, and therapeutic approach of the various forms of monogenic defects of beta cell function, using three imaginary clinical scenarios and highlighting clinical and laboratory features that can guide the clinician in reaching the correct diagnosis.

A negative regulatory role of β-cell-derived exosomes in the glucose-stimulated insulin secretion of recipient β-cells.

Exosomes are extracellular vesicles that play a role in intercellular communication through the transportation of their cargo including mRNAs, microRNAs, proteins, and nucleic acids. Exosomes can also regulate glucose homeostasis and insulin secretion under diabetic conditions. However, the role of exosomes in insulin secretion in islet β-cells under physiological conditions remains to be clarified. The aim of this study was to investigate whether exosomes derived from pancreatic islet β-cells could affect insulin secretion in naïve β-cells. We first confirmed that exosomes derived from the RIN-m5f β-cell line interfered with the glucose-stimulated insulin secretion (GSIS) of recipient β-cells without affecting cell viability. The exosomes significantly reduced the protein expression levels of phosphorylated Akt, phosphorylated GSK3α/β, CaMKII, and GLUT2 (insulin-related signaling molecules), and they increased the protein expression levels of phosphorylated NFκB-p65 and Cox-2 (inflammation-related signaling molecules), as determined by a Western blot analysis. A bioinformatics analysis of Next-Generation Sequencing data suggested that exosome-carried microRNAs, such as miR-1224, -122-5p, -133a-3p, -10b-5p, and -423-5p, may affect GSIS in recipient β-cells. Taken together, these findings suggest that β-cell-derived exosomes may upregulate exosomal microRNA-associated signals to dysregulate glucose-stimulated insulin secretion in naïve β-cells.

Sirtuin 4 regulates nutrient-stimulated insulin secretion by modulating GLP-1 secretion

Sirtuin 4 (SIRT4) is a mitochondrial enzyme that can remove several novel post-translational modifications (PTMs) on target proteins and thereby modify their activity. We and others have previously shown that young mice lacking SIRT4 (SIRT4KO mice) have elevated glucose, leucine, and glutamine-stimulated insulin secretion. As these mice aged, they developed insulin resistance and glucose intolerance. We hypothesize that when these mice are young and eat a mixed nutrient diet, they secrete elevated amounts of insulin in response to each meal and this hyperinsulinemia drives the development of insulin resistance in old age. However, while insulin secretion in response to glucose, leucine, and glutamine individually has been reported in these mice, it has not been shown how much insulin these mice secrete in response to combinations of these nutrients, which would more closely resemble a normal meal. Thus, we sought to characterize insulin secretion in SIRT4KO mice in response to mixed nutrient challenges. Indeed, SIRT4KO mice secrete more insulin response to different combinations of glucose, leucine, and glutamine. In most cases, these increases in insulin secretion were synergistic, rather than just an additive effect of each individual nutrient. In particular, when leucine and glucose were administered together in aged SIRT4KO males, plasma insulin levels were synergistically increased more than 3-fold over glucose or leucine alone. Remarkably, treating aged SIRT4KO mice with leucine during a glucose tolerance test resulted in so much insulin secretion that glucose intolerance was normalized. Importantly, despite these extremely high insulin levels, there were no signs of dangerous hypoglycemia. To determine whether these synergistic effects of glucose and leucine on insulin secretion were due to effects of SIRT4 on pancreatic beta-cells, we treated beta-cell specific SIRT4KO mice with glucose and leucine and found no differences in insulin secretion compared to wild-type mice, suggesting that SIRT4 affects insulin secretion by acting indirectly on the beta-cell. To determine whether SIRT4 may affect insulin secretion by altering incretin secretion, we measured GLP-1 secretion in response glucose and leucine in combination and found that GLP-1 secretion was elevated in SIRT4KO mice compared to wild-type controls. Taken together, our data show that SIRT4 may be a key regulator of insulin secretion in response to mixed nutrients via effects on GLP-1 secretion. NIH Support of Competitive Research (SCORE) Pilot Project Award #SC2GM141997 San Jose State University Department of Biological Sciences Start-up Funds. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Senescence of human pancreatic beta cells enhances functional maturation through chromatin reorganization and promotes interferon responsiveness.

Senescent cells can influence the function of tissues in which they reside, and their propensity for disease. A portion of adult human pancreatic beta cells express the senescence marker p16, yet it is unclear whether they are in a senescent state, and how this affects insulin secretion. We analyzed single-cell transcriptome datasets of adult human beta cells, and found that p16-positive cells express senescence gene signatures, as well as elevated levels of beta-cell maturation genes, consistent with enhanced functionality. Senescent human beta-like cells in culture undergo chromatin reorganization that leads to activation of enhancers regulating functional maturation genes and acquisition of glucose-stimulated insulin secretion capacity. Strikingly, Interferon-stimulated genes are elevated in senescent human beta cells, but genes encoding senescence-associated secretory phenotype (SASP) cytokines are not. Senescent beta cells in culture and in human tissue show elevated levels of cytoplasmic DNA, contributing to their increased interferon responsiveness. Human beta-cell senescence thus involves chromatin-driven upregulation of a functional-maturation program, and increased responsiveness of interferon-stimulated genes, changes that could increase both insulin secretion and immune reactivity.

To Study Knowledge Regarding Healthy Lifestyle Modifications in Middle-Aged Diabetic Population

Background: Lifestyle plays a significant role in helping patients with diabetes control their blood sugar levels. Understanding early complications to prevent further adverse effects from uncontrolled sugar levels and a worsening healthy lifestyle is a prerequisite to knowledge regarding healthy lifestyle modifications. Exercise therapy has long been recommended for use in the management and prevention of type 2 diabetes. Dietary habits play an important role in the control of blood glucose levels in diabetic patients. An increase in calorie intake leads to poor glycemic control. Stress levels can affect the increased glucose levels. Middle-aged adults are at increased risk of developing diabetes, and this population may benefit from targeted interventions to promote healthy lifestyle modifications. Therefore, a study is needed to assess the level of knowledge and awareness of middle-aged diabetic populations regarding healthy lifestyle modifications. Materials and Methods: A validated questionnaire was prepared on Google Forms and distributed among the diabetic population. Data was calculated automatically on Google spreadsheet. Results: Patients with diabetes exhibit little awareness of recommended lifestyle changes. A poor understanding of diabetes and its complications is demonstrated by 83.87 % of the population. 77.41% of persons have a poor understanding of dietary adjustments for diabetes. 86.02% of respondents exhibit insufficient awareness of physical exercise therapies for diabetes. 52.68% of people are unaware of how stress affects insulin secretion. Conclusion: According to the study’s findings, Given the early onset of diabetes problems, middle-aged diabetics have an increasing need for knowledge regarding appropriate lifestyle adjustments due to their higher risk of diabetes.

Novel Angiogenesis Role of GLP-1(32-36) to Rescue Diabetic Ischemic Lower Limbs via GLP-1R-Dependent Glycolysis in Mice.

Restoring the capacity of endothelial progenitor cells (EPCs) to promote angiogenesis is the major therapeutic strategy of diabetic peripheral artery disease. The aim of this study was to investigate the effects of GLP-1 (glucagon-like peptide 1; 32-36)-an end product of GLP-1-on angiogenesis of EPCs and T1DM (type 1 diabetes) mice, as well as its interaction with the classical GLP-1R (GLP-1 receptor) pathway and its effect on mitochondrial metabolism. In in vivo experiments, we conducted streptozocin-induced type 1 diabetic mice as a murine model of unilateral hind limb ischemia to examine the therapeutic potential of GLP-1(32-36) on angiogenesis. We also generated Glp1r-/- mice to detect whether GLP-1R is required for angiogenic function of GLP-1(32-36). In in vitro experiments, EPCs isolated from the mouse bone marrow and human umbilical cord blood samples were used to detect GLP-1(32-36)-mediated angiogenic capability under high glucose treatment. We demonstrated that GLP-1(32-36) did not affect insulin secretion but could significantly rescue angiogenic function and blood perfusion in ischemic limb of streptozocin-induced T1DM mice, a function similar to its parental GLP-1. We also found that GLP-1(32-36) promotes angiogenesis in EPCs exposed to high glucose. Specifically, GLP-1(32-36) has a causal role in improving fragile mitochondrial function and metabolism via the GLP-1R-mediated pathway. We further demonstrated that GLP-1(32-36) rescued diabetic ischemic lower limbs by activating the GLP-1R-dependent eNOS (endothelial NO synthase)/cGMP/PKG (protein kinase G) pathway. Our study provides a novel mechanism with which GLP-1(32-36) acts in modulating metabolic reprogramming toward glycolytic flux in partnership with GLP-1R for improved angiogenesis in high glucose-exposed EPCs and T1DM murine models. We propose that GLP-1(32-36) could be used as a monotherapy or add-on therapy with existing treatments for peripheral artery disease. URL: www.ebi.ac.uk/metabolights/; Unique identifier: MTBLS9543.

Melatonin, Circadian Rhythms, and Type 2 Diabetes Mellitus: A Comprehensive Review of Epidemiology, Molecular Mechanisms, and Therapeutic Implications

This extensive review delves into the epidemiology, risk factors, historical background, and molecular mechanisms of Type 2 Diabetes Mellitus (T2DM). The term "diabetes mellitus" dates back to ancient times and the Greek physician Aertaeus is credited with coining the term. T2DM, which is defined by hyperglycemia, insulin resistance, and relative insulin deficiency, is a global public health concern that affects millions of people worldwide. A combination of genetic, environmental, and lifestyle factors play a role in the development of T2DM. The distinction between Type 1 and Type 2 diabetes was established in 1936, and Type 2 diabetes was identified as a component of the metabolic syndrome in 1988. T2DM is becoming more and more common; it is expected to affect 552 million people by 2030, which means that research and interventions are desperately needed. The risk factors for T2DM include age, genetics, obesity, sedentary lifestyle, and components of the metabolic syndrome. Prediabetes, which is a precursor to T2DM, must be detected early in order to reduce the risk of progression. This review explores the physiological and molecular mechanisms underlying T2DM, with a focus on the complex interactions between melatonin, circadian rhythms, and diabetes. Melatonin, this is primarily synthesized by the pineal gland, is essential for the regulation of circadian rhythms and many other physiological processes. Research has shown how melatonin affects insulin secretion and glucose metabolism, suggesting that it may have therapeutic uses in the treatment of diabetes. Circadian rhythm disturbances, particularly those brought on by shift work, are linked to a higher risk of type 2 diabetes, underscoring the importance of comprehending these intricate relationships. The review highlights the need for more research to fully understand the complex relationships between melatonin, circadian rhythms, and diabetes. Pharmacological interventions, such as the synthetic melatonin agonist agomelatine, offer promising avenues for therapeutic exploration. Thapsigargin, an antagonist of sarco-endoplasmic reticulum Ca2+-ATPase (SERCA), reveals the role of calcium signaling in diabetes research.

NADPH Dynamics: Linking Insulin Resistance and β-Cells Ferroptosis in Diabetes Mellitus.

This review offers an in-depth exploration of Nicotinamide Adenine Dinucleotide Phosphate (NADPH) in metabolic health. It delves into how NADPH affects insulin secretion, influences insulin resistance, and plays a role in ferroptosis. NADPH, a critical cofactor in cellular antioxidant systems and lipid synthesis, plays a central role in maintaining metabolic homeostasis. In adipocytes and skeletal muscle, NADPH influences the pathophysiology of insulin resistance, a hallmark of metabolic disorders such as type 2 diabetes and obesity. The review explores the mechanisms by which NADPH contributes to or mitigates insulin resistance, including its role in lipid and reactive oxygen species (ROS) metabolism. Parallelly, the paper investigates the dual nature of NADPH in the context of pancreatic β-cell health, particularly in its relation to ferroptosis, an iron-dependent form of programmed cell death. While NADPH's antioxidative properties are crucial for preventing oxidative damage in β-cells, its involvement in lipid metabolism can potentiate ferroptotic pathways under certain pathological conditions. This complex relationship underscores the delicate balance of NADPH homeostasis in pancreatic health and diabetes pathogenesis. By integrating findings from recent studies, this review aims to illuminate the nuanced roles of NADPH in different tissues and its potential as a therapeutic target. Understanding these dynamics offers vital insights into the development of more effective strategies for managing insulin resistance and preserving pancreatic β-cell function, thereby advancing the treatment of metabolic diseases.

Zinc deficiency affects insulin secretion and alters insulin-regulated metabolic signaling in rats

BackgroundThe essential trace element zinc is important in stabilizing pancreatic insulin secretion. Zinc not only influences the synthesis of insulin but also affects its activity. Insulin not only exerts a hypoglycemic effect but also regulates glucose and lipid metabolisms in insulin target organs. In this study, we aimed to determine changes to pancreatic β cells and insulin secretion induced by different zinc concentrations and to evaluate the effect of zinc deficiency on glucose intolerance, insulin resistance, and insulin target organs via changing insulin levels. MethodsWe set up two experimental trials. In the first trial, male Sprague Dawley (SD) rats were divided into three groups. Group one (ZnC) received a standard diet, group two (ZnF) was given a zinc-free diet, and group three (ZnFC) was initially fed a zinc-free diet followed by a reversion to the standard diet. After sacrifice, we observed changes in blood parameters, including insulin, and examined alterations in pancreatic tissue using immunostaining, with focus on the localization of pancreatic β-cells. In the second trial, male SD rats were split into two groups, with one receiving a standard diet and the other a zinc-free diet. Oral glucose tolerance and insulin tolerance tests were then performed. After sacrifice, we evaluated changes in lipid and glucose metabolism within insulin target organs using quantitative polymerase chain reaction. ResultsIn the first trial, blood insulin levels and the area of insulin-positive staining in pancreatic β-cells decreased in the ZnF compared to the ZnC group. The ZnFC group did not show recovery in either blood insulin levels or the area of insulin-positive staining in pancreatic β-cells. In the second trial, no differences were observed in glucose tolerance or insulin resistance between the ZnC and ZnF groups. However, changes in the expression of insulin target genes were noted in the liver and adipose tissue in the ZnF group. ConclusionWe reveal that dietary zinc concentrations not only affect the concentration of insulin in the blood but also impact the localization of pancreatic β-cells involved in insulin production. Furthermore, our results suggest that changes in blood insulin levels, induced by different zinc concentrations, could cause metabolic alterations in insulin target organs such as the liver and adipose tissue. This study sheds more light on the role of zinc in insulin-regulated metabolic diseases.

The Effects of Vitamin D on Preventing Hyperglycemia and a Novel Approach to Its Treatment

The dietary reference levels for vitamin D were established with an emphasis on its role in bone health; however, with the identification of vitamin D receptors in all body tissues novel associations with other metabolic disorders, such as diabetes, are being researched. Aside from its standard function as the main regulator of calcium absorption, vitamin D also controls the calcium pool, mediates the activity of beta cell calcium-dependent endopeptidases, encourages the conversion of proinsulin to insulin, increases insulin output, and raises insulin activity in peripheral insulin target tissues. Both immune cells and pancreatic beta cells include vitamin D receptors. A deficiency of vitamin D causes glucose intolerance and affects insulin secretion. Different pathogenic characteristics of the disease are linked to a number of vitamin D-related genes. It has been proven that vitamin D supplementation lowers the risk of type 1 and type 2 diabetes and its associated problems. In this article, we discussed a few prospective clinical trials on vitamin D that are necessary to clearly demonstrate the role of vitamin D in the prevention and management of diabetes.

Perfluorooctane sulfonic acid exposure and diabetes: a cross-sectional analysis of American adults and in vitro experiments

BackgroundPerfluorooctane sulfonic acid (PFOS) exposure has a negative impact on the environment and biological health. However, the relationship between PFOS exposure and diabetes in adults is not clear.ObjectiveIn this study, we included two distinct components: (1) in the cross-sectional analysis, we used data from the National Health and Nutrition Inspection Survey (NHANES) from 2015 to 2018 and eventually included 2539 subjects. The association between PFOS exposure and the risk of diabetes in adults was assessed by a logistic regression model, and further subgroup analysis was carried out according to sex, hypertension status and high cholesterol status. We adjusted for all covariates and found that the positive association between higher PFOS exposure and diabetes remained stable. (2) In vitro experiments were conducted as follows, rat insulinoma β cells (INS-1) were used as experimental materials; cell proliferation activity was detected using the MTT assay; quantitative real-time PCR was used to detect the mRNA expression of insulin; and Western blotting was used to detect insulin protein expression levels.ResultsCompared with Q1, the OR of the highest exposure level group (Q4) of PFOS was 1.342(95% CI 0.940, 1.916). We conducted a logistic regression analysis based on sex, hypertension, and high cholesterol stratification. Stratified by sex, we found that the exposure level of PFOS was significantly positively associated with diabetes (P for trend < 0.05). Subgroup analysis showed that the positive association between PFOS exposure and diabetes was more significant in nonhypertensive individuals (P for trend < 0.01) and those with normal cholesterol levels (P for trend < 0.001). To further determine the causal relationship between PFOS exposure and diabetes, we used rat insulinoma β cells (INS-1) as experimental materials to study the effect of PFOS exposure on insulin secretion. We found that PFOS exposure significantly affected insulin secretion and insulin mRNA and protein expression.ConclusionsIn summary, PFOS exposure is positively associated with the risk of diabetes. However, further studies are needed to confirm our results.

The role of the neural NO synthase adapter protein in the pathogenesis of metabolic syndrome and type 2 diabetes mellitus

The pathogenesis of metabolic syndrome (MS) is characterized by obesity, hypertension, dyslipidemia and insulin resistance. MS increases the risk of developing type 2 diabetes mellitus (DM2). The neuronal isoform of nitric oxide synthase (nNOS) is defined by complex protein-protein interactions, since nNOS, unlike other isoforms of NOS,contains a C-terminal PDZ domain, which allows it to conjugate with other proteins and, first of all, to interact with an adapter of neuronal, or type 1, nitric oxide synthase (NOS1AP), also denoted CAPON in our work. Changes in the interaction between nNOS and NOS1AP lead to metabolic disorders in brain, heart, liver and skeletal muscles, which plays a key role in the development of MS and T2DM. NOS1AP, interacting with the PDZ domain of nNOS, competes with the postsynaptic density protein (PSD95) and regulates the stability of subcellular localization of nNOS and enzyme expression during synapse formation. NOS1AP promotes nNOS binding to targets such as small GTPase (Dexras1), synapsines, regulating the formation of dendritic roots, mediates activation of the nNOS-p38MAP kinase pathway during excitotoxicity. It has been shown that single-nucleotide polymorphism of the NOS1AP gene and its overexpression in the myocardium leads to the manifestation of long QT syndrome, which is most clearly manifested in elderly patients with DM2. It was found that the genetic polymorphism of NOS1AP affects insulin secretion when using calcium blockers, and can promote the development of DM2. The functional role of NOS1AP in stabilizing the functions of skeletal muscle nNOS in the cytoskeletal complex associated with dystrophin/utrophin was discovered. The purpose of the review is to provide updated information on the role of NOS1AP and the nNOS/NOS1AP complex in the pathogenesis of MS and DM2. The potential molecular mechanisms of the interaction of NOS1AP with nNOS and with other proteins, which leads to change in nNOS activity, localization and content, are discussed.

SIRT6's function in controlling the metabolism of lipids and glucose in diabetic nephropathy.

Diabetic nephropathy (DN) is a complication of diabetes mellitus (DM) and the main cause of excess mortality in patients with type 2 DM. The pathogenesis and progression of DN are closely associated with disorders of glucose and lipid metabolism. As a member of the sirtuin family, SIRT6 has deacetylation, defatty-acylation, and adenosine diphosphate-ribosylation enzyme activities as well as anti-aging and anticancer activities. SIRT6 plays an important role in glucose and lipid metabolism and signaling, especially in DN. SIRT6 improves glucose and lipid metabolism by controlling glycolysis and gluconeogenesis, affecting insulin secretion and transmission and regulating lipid decomposition, transport, and synthesis. Targeting SIRT6 may provide a new therapeutic strategy for DN by improving glucose and lipid metabolism. This review elaborates on the important role of SIRT6 in glucose and lipid metabolism, discusses the potential of SIRT6 as a therapeutic target to improve glucose and lipid metabolism and alleviate DN occurrence and progression of DN, and describes the prospects for future research.

Role of transcription factor FOXM1 in diabetes and its complications (Review).

Diabetes mellitus is a chronic metabolic disease commonly associated with complications such as cardiovascular disease, nephropathy and neuropathy, the incidence of which is increasing yearly. Transcription factor forkhead box M1 (FOXM1) serves an important role in development of diabetes and its complications. The present study aimed to review the association between FOXM1 with pathogenesis of diabetes and its complications. FOXM1 may be involved in development and progression of diabetes and its complications by regulating cell biological processes such as cell cycle, DNA damage repair, cell differentiation and epithelial‑mesenchymal transition. FOXM1 is involved in regulation of insulin secretion and insulin resistance, and FOXM1 affects insulin secretion by regulating expression of insulin‑related genes and signaling pathways; FOXM1 is involved in the inflammatory response in diabetes, and FOXM1 can regulate key genes associated with inflammatory response and immune cells, which in turn affects occurrence and development of the inflammatory response; finally, FOXM1 is involved in the regulation of diabetic complications such as cardiovascular disease, nephropathy and neuropathy. In summary, the transcription factor FOXM1 serves an important role in development of diabetes and its complications. Future studies should explore the mechanism of FOXM1 in diabetes and find new targets of FOXM1 as a potential treatment for diabetes and its complications.

1750-P: Differential Impacts of Two Novel HNF1A Variants Associated with Familial Young-Onset Diabetes on Protein Function and Insulin Secretion In Vitro

Introduction: Mutations in the HNF1A are a cause of monogenic diabetes and are usually dominantly inherited. We report in vitro and clinical studies on two novel HNF1A variants to determine pathogenicity: a recessive (homozygous) HNF1A variant (p.A251T) and a dominant HNF1A variant (p.S19L). We also investigated the mechanisms by which the former variant affects insulin secretion using beta cells derived from induced pluripotent stem cells (iPSCs). Methods: Nuclear localization, DNA binding, and transactivation activity were examined using standard techniques. iPSC lines from proband carrying the p.A251T variant were differentiated into beta-like cells according to Sui et al, CPHG, 2018. Ca2+ dynamics were monitored with Cal-520, and insulin secretion was measured by homogeneous time-resolved fluorescence assay compared to wild-type HNF1A (WT). Results: HNF1A p.A251T showed a mild (10.4% ± 7.3, p= 0.16) decrease in transactivation activity compared with WT, and decreased (48% of WT, p=0.12) DNA binding. These reductions were significant in p.S19L (DNA binding 57% of WT, p=0.049). Significant impaired nuclear uptake (63% vs 90% cells for WT, p&amp;lt;0.0001) was only apparent for p.S19L. Glucose-stimulated insulin secretion was decreased in A251T iPSCs compared with WT (0.29% vs. 0.46% of total insulin). In contrast, glucose-induced Ca2+ increases were increased in mutant cells (arbitrary units: 7.39 ± 1.23, mean +/− SD, n=725 cells vs. 4.58 ± 0.77, n=724, p= &amp;lt; 0.001) Conclusion: We demonstrate the value of combining multiple in vitro functional studies to decipher novel HNF1A variant pathogenicity. The recessive p.A251T variant has relatively mild effects on protein function compared to a dominant p.S19L variant. However, when studying proband iPSC derived beta-cell A251T impairs glucose-stimulated insulin secretion despite preserved Ca2+ entry, suggesting a novel mechanism of action not captured by standard tests of HNF1A function. Disclosure I.Cherkaoui: None. G.A.Rutter: Consultant; Sun Pharmaceutical Industries Ltd. Q.Du: None. C.Dion: None. H.Leitch: None. P.L.Chabosseau: None. D.M.Egli: None. D.Sachedina: None. J.Wastin: None. S.Misra: Research Support; Dexcom, Inc. Funding Diabetes UK

199-OR: Optogenetic Control of Pancreatic Delta Cells Reveals Their Central Role in Hormone Release from Pancreatic Islets

Diabetes mellitus is a metabolic disorder resulting from insufficient insulin release and associated with dysregulation of glucagon secretion. Somatostatin secreted from pancreatic δ-cells is a strong paracrine factor for both insulin and glucagon secretion in islets. Here, we developed an optogenetic approach, through specific expressing light-sensitive channels/pumps in δ-cells, to investigate the paracrine control of hormone release from islets. We generated mouse models that express either a light-sensitive cation channel, channelrhodopsin-2 (ChR2), or a chloride pump, halorhodopsin (HR), specifically in the pancreatic δ-cells (SST-ChR2 and SST-HR mouse). Their specific expression was confirmed by immunostaining. Optoactivation of ChR2 at 1mM glucose rapidly depolarized δ-cells by 37mV (n=5) and stimulated electrical activity and somatostatin release. At high glucose or tolbutamide, light activation of HR repolarized δ-cells by 15 mV (n=3), suppressing action potentials. Optoactivation of SST-ChR2 δ-cells suppressed, after a variable delay depending on the distance from δ-cells, action potential firing in neighbouring α-cells, inhibited exocytosis by 30% (n=5) and glucagon secretion by 55% at 1mM glucose (n=7). In a subset (35%) α-cells with no spontaneous action potentials, opto-inhibition of SST-HR δ-cells caused a 9mV depolarization (n=7) and induced action potential firing, which may account for the stimulation of glucagon secretion. Neither optoactivation, nor opto-inhibition of δ-cells affected insulin secretion at hypo- and hyperglycaemia. However, at normoglycaemia (6 mM glucose), optoactivation of δ-cells depolarized neighbouring β-cells (via gap-junctions) and evoked action potential firing, leading to a paradoxical 160% stimulation of insulin secretion (n=9). We conclude that δ-cells play a central role in the regulation of both insulin and glucagon release but that the effects are more complex than appreciated to date. Disclosure H.Dou: None. C.A.Miranda: None. J.Tolö: None. Q.Zhang: None. P.Rorsman: None. Funding Swedish Research Council

Genetic evidence that high BMI in childhood has a protective effect on intermediate diabetes traits, including measures of insulin sensitivity and secretion, after accounting for BMI in adulthood

Aims/hypothesisDetermining how high BMI at different time points influences the risk of developing type 2 diabetes and affects insulin secretion and insulin sensitivity is critical.MethodsBy estimating childhood BMI in 441,761 individuals in the UK Biobank, we identified which genetic variants had larger effects on adulthood BMI than on childhood BMI, and vice versa. All genome-wide significant genetic variants were then used to separate the independent genetic effects of high childhood BMI from those of high adulthood BMI on the risk of type 2 diabetes and insulin-related phenotypes using Mendelian randomisation. We performed two-sample MR using external studies of type 2 diabetes, and oral and intravenous measures of insulin secretion and sensitivity.ResultsWe found that a childhood BMI that was one standard deviation (1.97 kg/m2) higher than the mean, corrected for the independent genetic liability to adulthood BMI, was associated with a protective effect for seven measures of insulin sensitivity and secretion, including increased insulin sensitivity index (β=0.15; 95% CI 0.067, 0.225; p=2.79×10−4) and reduced fasting glucose levels (β=−0.053; 95% CI −0.089, −0.017; p=4.31×10−3). However, there was little to no evidence of a direct protective effect on type 2 diabetes (OR 0.94; 95% CI 0.85, 1.04; p=0.228) independently of genetic liability to adulthood BMI.Conclusions/interpretationOur results provide evidence of the protective effect of higher childhood BMI on insulin secretion and sensitivity, which are crucial intermediate diabetes traits. However, we stress that our results should not currently lead to any change in public health or clinical practice, given the uncertainty regarding the biological pathway of these effects and the limitations of this type of study.Graphical

Effects of PCSK9 inhibition on glucose metabolism and β-cell function in humans: a pilot study.

Anti-PCSK9 monoclonal antibodies are effective in reducing LDL-C and cardiovascular events by neutralizing circulating PCSK9. PCSK9, however, is also expressed in tissues, including the pancreas, and studies on PCSK9 KO mice have shown impaired insulin secretion. Statin treatment is already known to affect insulin secretion. Our aim was to conduct a pilot study to evaluate the effect of anti-PCSK9 mAb on glucose metabolism and β-cell function in humans. Fifteen non-diabetic subjects, candidates for anti-PCSK9 mAb therapy, were enrolled. All underwent OGTT at baseline and after 6 months of therapy. During OGTT, insulin secretion parameters were derived from C-peptide by deconvolution (β cell glucose sensitivity). Surrogate insulin sensitivity indices were also obtained from OGTT (Matsuda). Glucose levels during OGTT were unchanged after 6 months of anti-PCSK9 mAb treatment, as well as insulin and C-peptide levels. The Matsuda index remained unchanged, while β-cell glucose sensitivity improved post-therapy (before: 85.3 ± 65.4; after: 118.6 ± 70.9 pmol min-1m-2mM-1; p<0.05). Using linear regression, we found a significant correlation between βCGS changes and BMI (p=0.004). Thus, we compared subjects with values above and below the median (27.6 kg/m2) and found that those with higher BMI had a greater increase in βCGS after therapy (before: 85.37 ± 24.73; after: 118.62 ± 26.83 pmol min-1m-2mM-1; p=0.007). There was also a significant correlation between βCGS change and Matsuda index through linear regression (p=0.04), so we analyzed subjects who had values above and below the median (3.8). This subgroup analysis showed a slight though not significant improvement in βCGS in more insulin resistant patients, (before: 131.4 ± 69.8; after: 170.8 ± 92.7 pmol min-1m-2mM-1; p=0.066). Our pilot study demonstrates that six-month treatment with anti-PCSK9 mAb improves β-cell function, and does not alter glucose tolerance. This improvement is more evident in patients with greater insulin-resistance (low Matsuda) and higher BMI.

Glucocorticoid-mediated induction of ZBTB16 affects insulin secretion in human islets and EndoC-βH1 β-cells

Glucocorticoid use is associated with steroid-induced diabetes mellitus and impaired pancreatic β-cell insulin secretion. Here, the glucocorticoid-mediated transcriptomic changes in human pancreatic islets and the human insulin-secreting EndoC-βH1 cells were investigated to uncover genes involved in β-cell steroid stress-response processes. Bioinformatics analysis revealed glucocorticoids to exert their effects mainly on enhancer genomic regions in collaboration with auxiliary transcription factor families including AP-1, ETS/TEAD, and FOX. Remarkably, we identified the transcription factor ZBTB16 as a highly confident direct glucocorticoid target. Glucocorticoid-mediated induction of ZBTB16 was time- and dose-dependent. Manipulation of ZBTB16 expression in EndoC-βH1 cells combined with dexamethasone treatment demonstrated its protective role against glucocorticoid-induced reduction of insulin secretion and mitochondrial function impairment. In conclusion, we determine the molecular impact of glucocorticoids on human islets and insulin-secreting cells and investigate the effects of glucocorticoid targets on β-cell function. Our findings can pave the way for therapies against steroid-induced diabetes mellitus.