Islet Beta Cells Research Articles

Exploring pancreatic beta-cell subgroups and their connectivity.

Functional pancreatic islet beta cells are essential to ensure glucose homeostasis across species from zebrafish to humans. These cells show significant heterogeneity, and emerging studies have revealed that connectivity across a hierarchical network is required for normal insulin release. Here, we discuss current thinking and areas of debate around intra-islet connectivity, cellular hierarchies and potential "controlling" beta-cell populations. We focus on methodologies, including comparisons of different cell preparations as well as in vitro and in vivo approaches to imaging and controlling the activity of human and rodent islet preparations. We also discuss the analytical approaches that can be applied to live-cell data to identify and study critical subgroups of cells with a disproportionate role in control Ca2+ dynamics and thus insulin secretion (such as "first responders", "leaders" and "hubs", as defined by Ca2+ responses to glucose stimulation). Possible mechanisms by which this hierarchy is achieved, its physiological relevance and how its loss may contribute to islet failure in diabetes mellitus are also considered. A glossary of terms and links to computational resources are provided.

Mechanisms of spinophilin-dependent pancreas dysregulation in obesity.

Spinophilin is an F-actin binding and protein phosphatase 1 (PP1) targeting protein that acts as a scaffold of PP1 to its substrates. Spinophilin knockout (Spino-/-) mice have decreased fat mass, increased lean mass, and improved glucose tolerance, with no difference in feeding behaviors. Although spinophilin is enriched in neurons, its roles in nonneuronal tissues, such as β cells of the pancreatic islets, are unclear. We have corroborated and expanded upon previous studies to determine that Spino-/- mice have decreased weight gain and improved glucose tolerance in two different models of obesity. We have identified multiple putative spinophilin-interacting proteins isolated from intact pancreas and observed increased interactions of spinophilin with exocrine, ribosomal, and cytoskeletal protein classes that normally act to mediate peptide hormone production, processing, and/or release in Leprdb/db and/or high-fat diet-fed (HFF) models of obesity. In addition, we have found that spinophilin interacts with proteins from similar classes in isolated islets, suggesting a role for spinophilin in the pancreatic islet. Consistent with a pancreatic β cell type-specific role for spinophilin, using our recently described conditional spinophilin knockout mice, we found that loss of spinophilin specifically in pancreatic β cells improved glucose tolerance without impacting body weight in chow-fed mice. Our data further support the role of spinophilin in mediating pathophysiological changes in body weight and whole body metabolism associated with obesity. Our data provide the first evidence that pancreatic spinophilin protein interactions are modulated by obesity and that loss of spinophilin specifically in pancreatic β cells impacts whole body glucose tolerance.NEW & NOTEWORTHY To our knowledge, these data are the first to demonstrate that obesity impacts spinophilin protein interactions in the pancreas and identify spinophilin specifically in pancreatic β cells as a modulator of whole body glucose tolerance.

GLP-1 analogue semaglutide regulates pancreatic beta-cell proliferation via PDX-1 expression control

Semaglutide as an agonist of glucagon-like peptide-1 receptor was shown to potentiate insulin release and suppress food motivation targeting pancreatic islet beta cells and brain region including subfornical organ and hypothalamus, which effectively treats type 2 diabetes and obesity. The investigation of prolonged response with semaglutide on beta cells triggering proliferation and apoptotic resistance is yet to be confirmed. Previous research findings have shown that glucagon-like peptide-1 and liraglutide as agonists for glucagon-like peptide-1 receptors on beta cells result in proliferation through upregulation of PDX-1 transcription factor. Semaglutide is investigated to show whether long-term beta cell survival regulation is achieved through the same downstream signalling pathways. Both in vivo and in vitro methods were designed to show the proliferation effect of the semaglutide in C57BL/6 mice using tissue imaging, cell counting and immunosorbent assay for quantitative analysis of PDX-1 expression. The proliferation effect would broaden the application of semaglutide from insulin augmentation to the sustained benefit of beta cell survival.

Global research on type 1 diabetes: A bibliometric study during 2001-2022

Objective. Type 1 diabetes (T1D) publications have increased over the past three decades. However, there is no study to address and identify gaps in this area and to plan future research. This study aims to analyze the global scientific production of T1D in terms of overall structure and hotspots. Methodology. The research literature on T1D from 2001 to 2022 was obtained and examined from the Scopus database. We then performed bibliometric analysis and network visualization using MS Excel and VOSviewer software. Results and Discussion. The global T1D research comprised 20473 publications, which witnessed 6.19% and 58.91% annual average and 10-year cumulative growth during 2001-2022. These together received 596950 citations, with an average Citation Per Paper (CPP) of 29.16. Of the total global publications, 6030 (29.45%) received external funding support from international agencies and 19553 citations (with an average CPP of 32.43). The global publications were sourced from more than 150 countries and were published in 2665 journals by 63747 authors from 24899 organizations. There is an uneven distribution of countries, organizations, and authors in T1D research, wherein 88.37%, 45.15%, and 20.66% of the global literature was contributed by the top 12 countries and top 30 organizations and authors each. The most productive countries were the USA and UK, with a global share of 30% and 11.1% respectively. The most impactful countries were Finland and the UK regarding CPP & Relative Citation Index (RCI). The Barbara Davis Center for Childhood Diabetes, USA, and the University of Colorado Anschutz Medical Campus, USA, were the most productive organizations, with 735 and 679 publications. Jaeb Center for Health Research, USA (77.03 and 2.64) and Harvard Medical School, USA (67.42 and 2.31) were the most impactful organizations regarding CPP & RCI. Pediatric Diabetes (n=1447) and Diabetes Care (n=1191) were the most productive journals, with 1447 and 1191 papers. Diabetes and Diabetes Care registered the highest CPP (81.54 and 73.88 CPP). The most significant and frequently appearing keywords were “diabetes mellitus, type 1”) (92441), “insulin dependent diabetes mellitus” (95750), “metabolism” (24911), “genetics” (11229), “autoantibodies” (8942), “c peptide” (9931) and “pancreas islet beta cell” (7191). Only 5.54% (1134) of the global publications (considered highly-cited papers) received 100 to 4654 citations since their publications and registered a total of 220.28 CPP. Conclusion. This bibliometric study indicated that most of the contributions came from developed countries and only a meager contribution from developing countries, especially South Asia, despite a significant disease burden. This analysis provides a comprehensive overview of the present status of T1D research. It enables a better understanding of T1D research over the years. It should give the researchers structured information and a comprehensive analysis to help identify gaps in the research and the hot spots in this area of research.

Silencing the FABP3 gene in insulin-secreting cells reduces fatty acid uptake and protects against lipotoxicity.

Long-term exposure of pancreatic islets to fatty acids (FAs), common in obesity, metabolic syndrome, and type 2 diabetes, leads to a compensatory hyperactivity followed by inflammation, apoptosis, dysfunctional beta cells, and results in insulin dependence of the patient. Restriction of fatty uptake by islet beta cells may protect them from lipotoxicity. Pancreatic islet beta cells express the fatty acid binding protein 3 (FABP3) to bind FAs and to orchestrate lipid signals. Based on this, we investigated whether downregulation of FABP3, by Fabp3 silencing, might slow lipid metabolism and protect against lipotoxicity in insulin-secreting cells. Neither Fabp3 silencing, nor overexpression affected the glucose-stimulated insulin secretion in absence of FAs. Fabp3 silencing decreased FA-uptake, lipid droplets formation, and the expression of the lipid accumulation-regulating gene Dgat1 in Ins1E cells. It reduced FA-induced inflammation by deactivation of NF-κB, which was associated with upregulation of IκBα and deactivation of the NF-κB p65 nuclear translocation, and the downregulation of the cytokines ILl-6, IL-1β, and TNFα. Ins1E cells were protected from the FA-induced apoptosis as assessed by different parameters including DNA degradation and cleaved caspase-3 immunoblotting. Furthermore, FABP3 silencing improved the viability, Pdx1 gene expression, and the insulin-secreting function in cells long-term cultured with palmitic acid. All results were confirmed by the opposite action rendered by FABP3 overexpression. The present data reveals that pancreatic beta cells can be protected from lipotoxicity by inhibition of FA-uptake, intracellular utilization and accumulation. FABP3 inhibition, hence, may be a useful pharmaceutical approach in obesity, metabolic syndrome, and type 2 diabetes.

Pathological evaluation of the pathogenesis of diabetes mellitus and diabetic peripheral neuropathy.

Currently, there are more than 10 million patients with diabetes mellitus in Japan. Therefore, the need to explore the pathogenesis of diabetes and the complications leading to its cure is becoming increasingly urgent. Pathological examination of pancreatic tissues from patients with type 2 diabetes reveals a decrease in the volume of beta cells because of a combination of various stresses. In human type 2 diabetes, islet amyloid deposition is a unique pathological change characterized by proinflammatory macrophage (M1) infiltration into the islets. The pathological changes in the pancreas with islet amyloid were different according to clinical factors, which suggests that type 2 diabetes can be further subclassified based on islet pathology. On the other hand, diabetic peripheral neuropathy is the most frequent diabetic complication. In early diabetic peripheral neuropathy, M1 infiltration in the sciatic nerve evokes oxidative stress or attenuates retrograde axonal transport, as clearly demonstrated by in vitro live imaging. Furthermore, islet parasympathetic nerve density and beta cell volume were inversely correlated in type 2 diabetic Goto-Kakizaki rats, suggesting that diabetic peripheral neuropathy itself may contribute to the decrease in beta cell volume. These findings suggest that the pathogenesis of diabetes mellitus and diabetic peripheral neuropathy may be interrelated.

The selective serotonin reuptake inhibitors, sertraline and paroxetine, improve islet beta-cell mass and function in vitro.

To investigate the effects of the selective serotonin reuptake inhibitors (SSRIs) sertraline and paroxetine at therapeutically relevant concentrations on beta-cell mass and function. Viability was quantified in mouse insulinoma (MIN6) beta cells and mouse islets after 48-h exposure to sertraline (1-10 μM) or paroxetine (0.01-1 μM) using the Trypan blue exclusion test. The effects of therapeutic concentrations of these SSRIs on insulin secretion were determined by static incubation and perifusion experiments, while islet apoptosis was investigated by Caspase-Glo 3/7 assay, TUNEL staining and quantitative PCR analysis. Finally, proliferation of MIN6 and mouse islet beta cells was assessed by bromodeoxyuridine (BrdU) enzyme-linked immunosorbent assay and immunofluorescence. Sertraline (0.1-1 μM) and paroxetine (0.01-0.1 μM) were well tolerated by MIN6 beta cells and islets, whereas 10 μM sertraline and 1 μM paroxetine were cytotoxic. Exposure to 1 μM sertraline and 0.1 μM paroxetine significantly potentiated glucose-stimulated insulin secretion from mouse and human islets. Moreover, they showed protective effects against cytokine- and palmitate-induced apoptosis of islets, they downregulated cytokine-induced Stat1 and Traf1 mRNA expression, and they significantly increased proliferation of mouse beta cells. Our data demonstrate that sertraline and paroxetine act directly on beta cells to enhance glucose-stimulated insulin secretion and stimulate beta-cell mass expansion by increasing proliferation and decreasing apoptosis. These drugs are therefore likely to be appropriate for treating depression in people with type 2 diabetes.

Pharmaceutical targeting of the cannabinoid type 1 receptor impacts the crosstalk between immune cells and islets to reduce insulitis in humans

Aims/hypothesisInsulitis, a hallmark of inflammation preceding autoimmune type 1 diabetes, leads to the eventual loss of functional beta cells. However, functional beta cells can persist even in the face of continuous insulitis. Despite advances in immunosuppressive treatments, maintaining functional beta cells to prevent insulitis progression and hyperglycaemia remains a challenge. The cannabinoid type 1 receptor (CB1R), present in immune cells and beta cells, regulates inflammation and beta cell function. Here, we pioneer an ex vivo model mirroring human insulitis to investigate the role of CB1R in this process.MethodsCD4+ T lymphocytes were isolated from peripheral blood mononuclear cells (PBMCs) from male and female individuals at the onset of type 1 diabetes and from non-diabetic individuals, RNA was extracted and mRNA expression was analysed by real-time PCR. Single beta cell expression from donors with type 1 diabetes was obtained from data mining. Patient-derived human islets from male and female cadaveric donors were 3D-cultured in solubilised extracellular matrix gel in co-culture with the same donor PBMCs, and incubated with cytokines (IL-1β, TNF-α, IFN-γ) for 24–48 h in the presence of vehicle or increasing concentrations of the CB1R blocker JD-5037. Expression of CNR1 (encoding for CB1R) was ablated using CRISPR/Cas9 technology. Viability, intracellular stress and signalling were assayed by live-cell probing and real-time PCR. The islet function measured as glucose-stimulated insulin secretion was determined in a perifusion system. Infiltration of immune cells into the islets was monitored by microscopy. Non-obese diabetic mice aged 7 weeks were treated for 1 week with JD-5037, then euthanised. Profiling of immune cells infiltrated in the islets was performed by flow cytometry.ResultsCNR1 expression was upregulated in circulating CD4+ T cells from individuals at type 1 diabetes onset (6.9-fold higher vs healthy individuals) and in sorted islet beta cells from donors with type 1 diabetes (3.6-fold higher vs healthy counterparts). The peripherally restricted CB1R inverse agonist JD-5037 arrested the initiation of insulitis in humans and mice. Mechanistically, CB1R blockade prevented islet NO production and ameliorated the ATF6 arm of the unfolded protein response. Consequently, cyto/chemokine expression decreased in human islets, leading to sustained islet cell viability and function.Conclusions/interpretationThese results suggest that CB1R could be an interesting target for type 1 diabetes while highlighting the regulatory mechanisms of insulitis. Moreover, these findings may apply to type 2 diabetes where islet inflammation is also a pathophysiological factor.Data availabilityTranscriptomic analysis of sorted human beta cells are from Gene Expression Omnibus database, accession no. GSE121863, available at https://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSM3448161.Graphical

Capillary contact points determine beta cell polarity, control secretion and are disrupted in the db/db mouse model of diabetes

Aims/hypothesisAlmost all beta cells contact one capillary and insulin granule fusion is targeted to this region. However, there are reports of beta cells contacting more than one capillary. We therefore set out to determine the proportion of beta cells with multiple contacts and the impact of this on cell structure and function.MethodsWe used pancreatic slices in mice and humans to better maintain cell and islet structure than in isolated islets. Cell structure was assayed using immunofluorescence and 3D confocal microscopy. Live-cell two-photon microscopy was used to map granule fusion events in response to glucose stimulation.ResultsWe found that 36% and 22% of beta cells in islets from mice and humans, respectively, have separate contact with two capillaries. These contacts establish a distinct form of cell polarity with multiple basal regions. Both capillary contact points are enriched in presynaptic scaffold proteins, and both are a target for insulin granule fusion. Cells with two capillary contact points have a greater capillary contact area and secrete more, with analysis showing that, independent of the number of contact points, increased contact area is correlated with increased granule fusion. Using db/db mice as a model for type 2 diabetes, we observed changes in islet capillary organisation that significantly reduced total islet capillary surface area, and reduced area of capillary contact in single beta cells.Conclusions/interpretationBeta cells that contact two capillaries are a significant subpopulation of beta cells within the islet. They have a distinct form of cell polarity and both contact points are specialised for secretion. The larger capillary contact area of cells with two contact points is correlated with increased secretion. In the db/db mouse, changes in capillary structure impact beta cell capillary contact, implying that this is a new factor contributing to disease progression.Graphical

Sex-dependent intra-islet structural rearrangements affecting alpha-to-beta cell interactions lead to adaptive enhancements of Ca2+ dynamics in prediabetic beta cells

Aims/hypothesisPrediabetic pancreatic beta cells can adapt their function to maintain normoglycaemia for a limited period of time, after which diabetes mellitus will manifest upon beta cell exhaustion. Understanding sex-specific beta cell compensatory mechanisms and their failure in prediabetes (impaired glucose tolerance) is crucial for early disease diagnosis and individualised treatment. Our aims were as follows: (1) to determine the key time points of the progression from beta cells’ functional adaptations to their failure in vivo; and (2) to mechanistically explain in vivo sex-specific beta cell compensatory mechanisms and their failure in prediabetes.MethodsIslets from male and female transgenic Ins1CreERT2-GCaMP3 mice were transplanted into the anterior chamber of the eye of 10- to 12-week-old sex-matched C57BL/6J mice. Recipient mice were fed either a control diet (CD) or western diet (WD) for a maximum of 4 months. Metabolic variables were evaluated monthly. Beta cell cytoplasmic free calcium concentration ([Ca2+]i) dynamics were monitored in vivo longitudinally by image fluorescence of the GCaMP3 reporter islets. Global islet beta cell [Ca2+]i dynamics in line with single beta cell [Ca2+]i analysis were used for beta cell coordination studies. The glucagon receptor antagonist L-168,049 (4 mmol/l) was applied topically to the transplanted eyes to evaluate in vivo the effect of glucagon on beta cell [Ca2+]idynamics. Human islets from non-diabetic women and men were cultured for 24 h in either a control medium or high-fat/high-glucose medium in the presence or absence of the glucagon receptor antagonist L-168,049. [Ca2+]i dynamics of human islets were evaluated in vitro after 1 h exposure to Fura-10.ResultsMice fed a WD for 1 month displayed increased beta cell [Ca2+]i dynamics linked to enhanced insulin secretion as a functional compensatory mechanism in prediabetes. Recruitment of inactive beta cells in WD-fed mice explained the improved beta cell function adaptation observed in vivo; this occurred in a sex-specific manner. Mechanistically, this was attributable to an intra-islet structural rearrangement involving alpha cells. These sex-dependent cytoarchitecture reorganisations, observed in both mice and humans, induced enhanced paracrine input from adjacent alpha cells, adjusting the glucose setpoint and amplifying the insulin secretion pathway. When WD feeding was prolonged, female mice maintained the adaptive mechanism due to their intrinsically high proportion of alpha cells. In males, [Ca2+]i dynamics progressively declined subsequent to glucose stimulation while insulin secretion continue to increase, suggesting uncoordinated beta cell function as an early sign of diabetes.Conclusions/interpretationWe identified increased coordination of [Ca2+]i dynamics as a beta cell functional adaptation mechanisms in prediabetes. Importantly, we uncovered the mechanisms by which sex-dependent beta cell [Ca2+]i dynamics coordination is orchestrated by an intra-islet structure reorganisation increasing the paracrine input from alpha cells on beta cell function. Moreover, we identified reduced [Ca2+]i dynamics coordination in response to glucose as an early sign of diabetes preceding beta cell secretory dysfunction, with males being more vulnerable. Alterations in coordination capacity of [Ca2+]i dynamics may thus serve as an early marker for beta cell failure in prediabetes.Graphical

Enrichment of Bioactive Lipids in Urinary Extracellular Vesicles and Evidence of Apoptosis in Kidneys of Hypertensive Diabetic Cathepsin B Knockout Mice after Streptozotocin Treatment.

Cathepsin B (CtsB) is a ubiquitously expressed cysteine protease that plays important roles in health and disease. Urinary extracellular vesicles (uEVs) are released from cells associated with urinary organs. The antibiotic streptozotocin (STZ) is known to induce pancreatic islet beta cell destruction, diabetic nephropathy, and hypertension. We hypothesized that streptozotocin-induced diabetic kidney disease and hypertension result in the release of bioactive lipids from kidney cells that induce oxidative stress and renal cell death. Lipidomics was performed on uEVs isolated from CtsB knockout mice treated with or without STZ, and their kidneys were used to investigate changes in proteins associated with cell death. Lysophosphatidylethanolamine (LPE) (18:1), lysophosphatidylserine (LPS) (22:6), and lysophosphatidylglycerol (LPG) (22:5) were among the bioactive lipids enriched in uEVs from CtsB knockout mice treated with STZ compared to untreated CtsB mice (n = 3 uEV preparations per group). Anti-oxidant programming was activated in the kidneys of the CtsB knockout mice treated with STZ, as indicated by increased expression of glutathione peroxidase 4 (GPX4) and the cystine/glutamate antiporter SLC7A11 (XCT) (n = 4 mice per group), which was supported by a higher reactivity to 4-hydroxy-2-nonenal (4-HNE), a marker for oxidative stress (n = 3 mice per group). Apoptosis but not ferroptosis was the ongoing form of cell death in these kidneys as cleaved caspase-3 levels were significantly elevated in the STZ-treated CtsB knockout mice (n = 4 mice per group). There were no appreciable differences in the pro-ferroptosis enzyme acyl-CoA synthetase long-chain family member 4 (ACSL4) or the inflammatory marker CD93 in the kidneys (n = 3 mice per group), which further supports apoptosis as the prevalent mechanism of pathology. These data suggest that STZ treatment leads to oxidative stress, inducing apoptotic injury in the kidneys during the development of diabetic kidney disease and hypertension.

Adenosine kinase inhibits β-cell proliferation by upregulating DNA methyltransferase 3A expression.

To investigate the effects of adenosine kinase (ADK), a key enzyme in determining intracellular adenosine levels, on β cells, and their underlying mechanism. Genetic animal models and transgenic immortalized cells were applied to study the effect of ADK on islet beta-cell proliferation and function. The beta-cell mass and response to glucose were measured in vivo using mice with beta-cell-specific ADK overexpression, and in vitro using ADK-overexpressed immortalized beta-cell. The expression of ADK in human islets at high abundance, especially in β cells, was decreased during the process of β-cell proliferation. Additionally, a transgenic mouse model (ADKtg/tg /Mip-Cre) was generated wherein the mouse Insulin1 gene promoter specifically overexpressed ADK in pancreatic β cells. The ADKtg/tg /Mip-Cre model exhibited impaired glucose tolerance, decreased fasting plasma insulin, loss of β-cell mass, and inhibited β-cell proliferation. Proteomic analysis revealed that ADK overexpression inhibited the expression of several proteins that promote cell proliferation and insulin secretion. Upregulating ADK in the β-cell line inhibited the expression of β-cell related regulatory molecules, including FoxO1, Appl1, Pxn, Pdx-1, Creb and Slc16a3. Subsequent in vitro experiments indicated that the inhibition of β-cell proliferation and the decreased expression of Pdx-1, Creb and Slc16a3 were rescued by DNA methyltransferase 3A (DNMT3A) knockdown in β cells. In this study, we found that the overexpression of ADK decreased the expression of several genes that regulate β cells, resulting in the inhibition of β-cell proliferation and dysfunction by upregulating the expression of DNMT3A.

Synergistic Effect of Naringin and Glimepiride in Streptozotocin-induced Diabetic Rats.

Evaluation of the synergistic effect of Naringin and Glimepiride in streptozotocin (STZ)-induced diabetic rats. Wistar rats were chosen and divided into five groups (n=6). STZ was used for the induction of diabetes. The combination of naringin and glimepiride was administered to diabetic rats. The changes in fasting blood sugar, body weight, Hb, HbA1c, and creatinine were evaluated, and urine was collected and the volume was observed. The lipid profiles like TC, HDL, LDL, and TG were measured. The biochemical parameters SGOT, SGPT, and ALP were analysed. Besides, endogenous antioxidant parameters like SOD, GSH, and catalase were also assessed. Lastly, the histopathological study of the beta cells in islets of the pancreas, glomerulus, and tubules of kidney and liver cells was conducted in all groups. The result shows significant reduction (p<0.001) of blood sugar in the naringin and glimepiride-treated group when compared with the control group (diabetes). Additionally, the combination of Naringin (100 mg/kg) and Glimepiride (0.1 mg/kg) significantly restores the creatinine levels and urine volumes, SGOT, SGPT, and ALP when compared to a single dose of administration. Further, the abnormal lipid profile levels (TC, LDL, TG, and HDL), and endogenous antioxidant enzymes (SOD, GSH, catalase) in diabetic control rats were restored to normal levels in a significant manner. The histopathological result reveals significant alterations, including hypertrophy of islets and mild degeneration, renal necrosis, and inflammation of hepatocytes. A synergistic effect of Naringin and glimepiride was observed during the estimation of various biochemical parameters like body weight, fasting blood sugar, creatinine, urine level, TG, total cholesterol, SGOT, SGPT, ALP, Insulin, HbA1c, antioxidant parameters like SOD, GSH, and catalase in STZ-induced diabetic rats. Further, the combination of therapy improves the protective effect of the pancreas, kidney, and liver, suggesting a potential antidiabetic effect.

Single-cell RNA sequencing reveals an immunomodulatory population of double negative T-cells in the diabetic NOD mouse

Abstract NOD mice are a widely used model of type 1 diabetes, an inflammatory autoimmune condition characterized by autoreactive T-cells that target insulin producing beta cells of the pancreatic islets. While T cell biology in the context of this disease is important it is unclear why autoreactive T-cells develop in this model or what they do within the islets themselves. We have designed a single cell sequencing experiment where enriched T-cells taken from diabetic and non-diabetic NOD mice are sequenced for mRNA expression and TCR sequence concurrently. The resulting sequencing data shows abnormal representation of Double Negative (DN) T-cells in all tissues and conditions (~30%). We have observed that like CD8+ and CD4+ T-cells, this population displays normal maturation phenotypes, but experience reduced exhaustion of effector subsets after infiltration of the pancreatic islets. Looking at clonal subpopulations of T-cells we have discovered a subset of CD8+ T-cells that have high expression of GzmA even after loss of the survival signal marker, IL7r. Through investigation of these aberrant T-cell populations, we have found that the diabetic NOD mouse pancreatic is highly immunosuppresive and expression of T-cell co-receptors may have a significant impact on diabetic onset.

Chronic exposure to incretin metabolites GLP-1(9−36) and GIP(3−42) affect islet morphology and beta cell health in high fat fed mice

The incretin hormones, glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), are rapidly degraded by dipeptidyl peptidase-4 (DPP-4) to their major circulating metabolites GLP-1(9−36) and GIP(3−42). This study investigates the possible effects of these metabolites, and the equivalent exendin molecule Ex(9−39), on pancreatic islet morphology and constituent alpha and beta cells in high-fat diet (HFD) fed mice. Male Swiss TO-mice (6–8 weeks-old) were maintained on a HFD or normal diet (ND) for 4 months and then received twice-daily subcutaneous injections of GLP-1(9−36), GIP(3−42), Ex(9−39) (25 nmol/kg bw) or saline vehicle (0.9% (w/v) NaCl) over a 60-day period. Metabolic parameters were monitored and excised pancreatic tissues were used for immunohistochemical analysis. Body weight and assessed metabolic indices were not changed by peptide administration. GLP-1(9−36) significantly (p<0.001) increased islet density per mm2 tissue, that was decreased (p<0.05) by HFD. Islet, beta and alpha cell areas were increased (p<0.01) following HFD and subsequently reduced (p<0.01-p<0.001) by GIP(3−42) and Ex(9−39) treatment. While GLP-1(9−36) did not affect islet and beta cell areas in HFD mice, it significantly (p<0.01) decreased alpha cell area. Compared to ND and HFD mice, GIP(3−42) treatment significantly (p<0.05) increased beta cell proliferation. Whilst HFD increased (p<0.001) beta cell apoptosis, this was reduced (p<0.01-p<0.001) by both GLP-1(9−36) and GIP(3−42). These data indicate that the major circulating forms of GLP-1 and GIP, namely GLP-1(9−36) and GIP(3−42) previously considered largely inactive, may directly impact pancreatic morphology, with an important protective effect on beta cell health under conditions of beta cell stress.

Modulation of Cardiac Sarcomeric Function in Mouse Models of Hyperglycemia

Diabetes is a major risk factor for developing heart failure (HF) and patients with diabetes and HF have worse outcomes than patients with HF alone. Given that diabetes is associated with multiple metabolic impairments, it is critical to determine the mechanisms that exacerbate and worsen cardiac outcomes. Hyperglycemia has been associated with cardiac diastolic dysfunction, which is characterized by prolonged relaxation. The specific mechanisms underlying hyperglycemia-induced diastolic dysfunction are unclear. It is known that hyperglycemia induces profound perturbations in cardiac metabolism modifying acyl-based post-translational modifications (PTMs), which are a class of PTMs that have been gaining increasing focus as modulators of non-genomic protein function. We hypothesize that hyperglycemia contributes to cardiac dysfunction by modulating acyl-based modifications on sarcomeric proteins; thereby, leading to prolonged myofilament relaxation. We evaluated sarcomeric function and specific PTMs (acetylation, crotonylation, malonylation, propionylation, and hydoxy-butyrylation) on sarcomeric proteins in two mouse models that have elevated glucose without hyperinsulinemia: mice with inducible deletion of beta islet glucokinase and mice treated with streptozotocin (STZ) induced damage of the beta islet cells. In male and female mice of both models, myofibrils isolated from the hearts of animals with hyperglycemia demonstrated prolonged sarcomeric relaxation compared to myofibrils isolated from euglycemic mice. We found that sarcomeric proteins isolated from the hearts of hyperglycemic mice from both models have decreased protein acetylation. While crotonylation, malonylation, propionylation, and hydoxy-butyrylation are not different between hyperglycemic and euglycemic mice. To determine how decreased acetylation impacts sarcomeric mechanical function, myofibrils isolated from male and female euglycemic mice were treated with histone deacetylases decrease acetylation and mechanics were assessed. We found that decreased acetylation of myofibrils leads to prolonged relaxation similar to what was observed in hyperglycemic hearts. These findings indicate that specific modifications of acyl-PTMs on sarcomeric proteins modulate sarcomeric function and may contribute to overall diastolic dysfunction observed in hyperglycemia. This work was supported by the National Institutes of Health [K01AG066845 KCW] the American Heart Association [22CDA937598 KCW] and the University of Colorado Anschutz Medical Campus Ludeman Family Center for Women’s Health and Specialized Center for Research Excellence (SCORE) pilot award [KCW], Colorado Diabetes Research Center Pilot and Feasibility Award [P30DK11607 KCW)]. 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.

Trends in the Application of Stem Cells for the Treatment of Diabetes

Diabetes mellitus is a global epidemic that showed a dramatic worldwide increase in its incidence and has been associated with life threatening complications if not detected and managed properly. Even though, insulin and oral anti-diabetic drugs were used for its management, lots of efforts are made to improve patient’s care by pancreas and islet transplantation along with stem cell therapies like embryonic stem cells, induced pluripotent stem cells and adult mesenchymal stem cells. Adult stem cells, which are also termed as somatic stem cells or resident stem cells, are a type of undifferentiated cells, resided in a differentiated tissue, organ or organism, in a specialized structural local microenvironment, called stem cell niche. The stem cell niche, is the in vivo microenvironment where stem cells are located and receive extrinsic signals interact and integrate to influence stem cell behavior that generally determine their fate. ESC showed unlimited differentiation into insulin producing β-cells with ethical concerns. MSCs possess the capacity to differentiate into islet-like insulin producing cells, to promote the regeneration of pancreatic islet beta cells and protect endogenous pancreatic islet beta cells from apoptosis through immunomodulatory mechanisms.

Neural Stem Cell-based Regenerative Therapy: A New Approach to Diabetes Treatment.

Diabetes mellitus (DM) is the most common metabolic disorder that occurs due to the loss, or impaired function of insulin-secreting pancreatic beta cells, which are of two types - type 1 (T1D) and type 2 (T2D). To cure DM, the replacement of the destroyed pancreatic beta cells of islet of Langerhans is the most widely practiced treatment. For this, isolating neuronal stem cells and cultivating them as a source of renewable beta cells is a significant breakthrough in medicine. The functions, growth, and gene expression of insulin-producing pancreatic beta cells and neurons are very similar in many ways. A diabetic patient's neural stem cells (obtained from the hippocampus and olfactory bulb) can be used as a replacement source of beta cells for regenerative therapy to treat diabetes. The same protocol used to create functional neurons from progenitor cells can be used to create beta cells. Recent research suggests that replacing lost pancreatic beta cells with autologous transplantation of insulin-producing neural progenitor cells may be a perfect therapeutic strategy for diabetes, allowing for a safe and normal restoration of function and a reduction in potential risks and a long-term cure.

Future clinical prospects of C-peptide testing in the early diagnosis of gestational diabetes.

Gestational diabetes is typically diagnosed in the late second or third trimester of pregnancy. It is one of the most common metabolic disorders among expectant mothers, with potential serious short- and long-term complications for both maternal and offspring health. C-peptide is secreted from pancreatic beta-cells into circulation in equimolar amounts with insulin. It is a useful biomarker to estimate the beta-cell function because it undergoes negligible hepatic clearance and consequently it has a longer half-life compared to insulin. Pregnancy induces increased insulin resistance due to physiological changes in hormonal and metabolic homeostasis. Inadequate compensation by islet beta-cells results in hyperglycemia. The standard oral glucose tolerance test at 24-28 wk of gestation sets the diagnosis. Accumulated evidence from prospective studies indicates a link between early pregnancy C-peptide levels and the risk of subsequent gestational diabetes. Elevated C-peptide levels and surrogate glycemic indices at the beginning of pregnancy could prompt appropriate strategies for secondary prevention.

Prophylactic effects of Combretum molle boughs on changes in the hematological, biochemical, and histological parameters in dexamethasone-induced insulin-resistant rats

BackgroundCombretum molle (Combretaceae) is a plant used in Cameroon traditional medicine to treat diabetes mellitus. To our knowledge, no studies have been performed on the preventive effects of C. molle on change in hematological, biochemical, and histological parameters of insulin-resistant rats. The aim of the study was to evaluate the preventive effect of C. molle on changes in the hematological biochemical, and histological parameters of insulin-resistant rats. MethodsInsulin resistance was induced for 10 days by subcutaneous injection of dexamethasone (1 mg/kg), one hour after oral pretreatment of animals with distilled water, metformin (40 mg/kg), and C. molle extract (250 and 500 mg/kg). Hematological profile (red blood cells, white blood cells, platelets and their indices), biomarkers of renal and hepatic function, hepatic glycogen level, activity of hepatic enzymes of carbohydrate metabolism, and histological sections of kidney, liver and pancreas were assessed. ResultsC. molle extract (250 and 500 mg/kg) caused a significant decrease (p < 0.05 to p < 0.001) in white blood cells, platelets count, and the activities of fructose 6-diphosphatase, glucose-6-phosphate dehydrogenase, and transaminases. It also caused significant increase (p < 0.05 to p < 0.001) in red blood cells, hemoglobin, albumin, glycogen, urea, uric acid, and creatinine values, and fructose-1,6-diphospatase and glucokinase activity. Histological examination revealed regeneration of beta-cells of the pancreatic islets and preventive renal and hepatic tissues against damages caused by impact of dexamethasone. ConclusionC. molle extract protected insulin-resistant patients from hematological, biochemical, and histopathological changes, there by validating the merits of the use of this plant in traditional medicine to treat diabetes mellitus and its complications.