Senescence is a β-cell stress response in type 1 diabetes (T1D), the origins of which are not understood. We wanted to determine the role of the T cell-mediated autoimmune process in β-cell senescence during T1D. In the nonobese diabetic mouse model, β-cell senescence largely depended on damage inflicted by autoreactive CD4+ and CD8+ T cells during the development of T1D. Chronic exposure to sublethal doses of proinflammatory cytokines associated with the diabetogenic process was sufficient to elicit stable senescence phenotypes in human islets in culture. Our findings suggest that autoreactive T cells trigger not only β-cell death but also β-cell senescence, potentially via cytokine-dependent mechanisms in T1D. This finding has implications for understanding the mechanisms of action and beneficial impacts of immunotherapy using CD3 antibodies in T1D.

Type 1 diabetes has detrimental effects in white matter microstructure. In a longitudinal study, we investigated whether these reported findings change as children grow and enter puberty. At study entry, there were 143 children with type 1 diabetes and 71 control participants without diabetes, 4-9 years old. Brain MRI using diffusion tensor imaging, neurocognitive, and glycemic assessments were performed four times across 6-8 years of follow-up. Longitudinal mixed-effects modeling was used to examine changes in fractional anisotropy (FA), axial diffusivity (AD) (measures of myelination and fiber integrity), radial diffusivity (RD) (axonal leakage), and mean diffusivity (MD) (average diffusion). Associations with glycemic and cognitive measures were assessed. We observed in 182 children (121 type 1 diabetes vs. 61 control participants) who had testing at time 4 that FA increased, and RD, AD, and MD decreased significantly in both groups, with no differences between groups for FA, RD and MD over time. However, children with diabetes had lower AD than control participants at 6-10 years. Differences were not detected at 12 years (age imputed from data), when in puberty. Higher blood glucose levels are associated with lower FA and higher RD and MD. Higher glucose percentage time-in-range was associated with higher FA, reflecting better fiber integrity and myelination and higher cognitive metrics. Within the diabetes group, AD and MD showed no association with neurocognitive outcomes. In summary, white matter AD was decreased in children with diabetes, less so during puberty, and FA was reciprocally related to hyperglycemia. These data suggest continued negative impact of chronic hyperglycemia in the developing brain.

Gastrointestinal hormones are essential for nutrient handling and regulation of glucose metabolism and may affect postprandial blood redistribution. In a randomized cross-over design in 10 healthy men, the involvement of glucose-dependent insulinotropic polypeptide (GIP) in splanchnic blood flow regulation was investigated using an infusion of GIP receptor antagonist (GIPR-An) GIP(3-30)NH2 during ingestion of oral glucose (75 g). In five separate sessions, we investigated GIP(1-42), GIPR-An with and without oral glucose, oral glucose alone, and a control saline infusion. Blood flow was assessed by phase contrast MRI, hepatic oxygen consumption by T2*, and plasma glucose, insulin, C-peptide, glucagon, GIP, GIPR-An, glucagon-like peptide 2, and bone metabolism markers by frequent blood sampling during all sessions. We found GIP(1-42) to stimulate blood flow in the superior mesenteric artery by ∼10% in the fasting state. Oral glucose alone increased mean blood flow in the superior mesenteric artery by ∼70% and portal vein by ∼40% of baseline. During oral glucose ingestion with concurrent infusion of GIPR-An, blood flow in the superior mesenteric artery was ∼22% lower. The hormone infusions did not affect blood flow in the hepatic artery and the celiac artery. Infusion of GIPR-An during oral glucose ingestion resulted in lower insulin secretion and higher levels of carboxy-terminal collagen crosslinks (bone resorption biomarker) compared with saline infusion, whereas glucagon levels were unaffected by both the injection of GIP and the GIPR-An infusions. We conclude that endogenous GIP increases splanchnic blood flow and contributes to postprandial intestinal hyperemia in healthy men.

Intraportal islet transplantation to treat insulin-dependent diabetes has been clinically validated. However, the hypoxic environment and sinusoidal architecture of the liver are unsuitable for the long-term survival of transplanted islets, leading to the loss of therapeutic effects within 1 year. The spleen has oxygen levels that meet islet needs, but intense instant blood-mediated inflammatory reactions (IBMIRs) and low extracellular matrix (ECM) concentrations hinder islet engraftment and survival. In this study, we developed constructs of islets encapsulated by hepatocytes and fibroblasts. The hepatocytes and fibroblasts create a protective coating that reduces IBMIRs because of the low expression of von Willebrand factor in hepatocytes and supports normal islet survival through ECM production by fibroblasts. These constructs can be easily injected into the mouse spleen. The hepatocyte-fibroblast encapsulation significantly reduces islet mortality during the posttransplantation stress period, enabling rapid engraftment and vascularization in the spleen. The high-oxygen environment of the spleen then supports long-term (>1 year) islet survival and sustained glycemic regulation. Additionally, this method significantly lowers the critical islet dose required for transplantation. The live cell-shielding strategy developed in this study represents a novel approach in islet transplantation and functional regeneration, demonstrating promising clinical potential.

Circulating glucagon concentrations differ between individuals with no diabetes (ND) and those with type 1 diabetes (T1D). We combined an isotope dilution technique using stable tracers [6,22-13C9,15N1]glucagon and [6,14,19,22-13C9,15N1]glucagon with splanchnic and leg catheterization in participants with ND (n = 8; age 23.1 ± 2.9 years, BMI 26.6 ± 3.5 kg/m2, HbA1c 5.0 ± 0.2% [31 ± 2 mmol/mol]) and T1D (n = 6; 29.0 ± 8.8 years, BMI 26.3 ± 5.0 kg/m2, HbA1c 7.9 ± 0.8% [63 ± 8 mmol/mol]) in the overnight fasted state. After baseline period, exogenous glucagon was infused at rates designed to achieve plasma glucagon concentrations spanning the physiological ranges, to determine the effects of rising glucagon concentrations on splanchnic and leg glucagon balance. At baseline, splanchnic glucagon extraction (SGE) was similar (30.7 ± 2.7 vs. 29.1 ± 2.9%) but leg glucagon extraction (LGE) was lower (27.0 ± 4.2 vs. 40.6 ± 3.1%) in participants with T1D versus those with ND. However, with increasing plasma glucagon concentrations, while SGE remained unchanged within and between groups, LGE fell in participants with ND (41 vs. 31 vs. 24%) but did not change in those with T1D. Despite a numerically lower net splanchnic glucagon production in participants with T1D than in those with ND, no changes were observed with increasing glucagon concentrations within the physiological range in both groups. This is the first human study applying novel glucagon isotopes that describes regional glucagon metabolism in participants with ND and T1D. Our observations provide translational relevance for dual hormone closed-loop systems and provide tools for probing the effects of GLP-1, dual, and triple receptor agonists on pancreatic α-cell functions.

Diabetic peripheral neuropathy (DPN) poses significant clinical challenges due to progressive nerve degeneration and vascular insufficiency. To address both neural and vascular complications simultaneously, we employed an mRNA-based protein replacement therapy. In this study, leveraging mRNA template design, structure-based screening identified NGFR100W as a variant dissociating neuroprotective and nociceptive functions, demonstrating enhanced neuritogenic activity without pain sensitization. Additionally, transcriptome analysis of NGF mutants versus wild type further reveals the potential mechanism by which NGFR100W uncouples neuroprotective and nociceptive pathways. We cotransfected chemically modified NGFR100W mRNA and vascular endothelial growth factor A (VEGFA) mRNA, and the conditioned media collected from this transfection promoted endothelial cell migration, tubulogenesis, and neurite outgrowth. In a diabetic mouse model, combination therapy with lipid nanoparticle codelivery of NGFR100W and VEGFA mRNA significantly improved blood flow in the plantar region and mitigated nerve function decline compared with monotherapy. Histological analysis showed increased microvessel formation and higher intraepidermal nerve fiber density in treated mice. Our findings highlight the therapeutic potential of NGFR100W and VEGFA mRNA coadministration for DPN, suggesting that protein supplementation via mRNA could offer a novel strategy for clinical intervention in some chronic medical conditions.

The impact of atmospheric pressure changes on glucose metabolism encountered in aviation on people with type 1 diabetes is controversial. A dual-isotope study was performed in a hypobaric chamber to simulate pressure changes experienced on commercial flights. The fasting and postprandial glucose kinetics of individuals with type 1 diabetes were evaluated across simulated in-flight cabin pressures (550 mmHg; experimental arm) and ground level (750 mmHg; control arm). The impact of ambient pressure on glucose disposal (Rd), endogenous glucose production (EGP), meal glucose appearance (Ra), and insulin concentrations were evaluated. Six male participants, aged 20-61 years, with a median BMI of 26.6 kg/m2, were studied. Baseline glucose Rd, EGP, and meal Ra values were not affected by ambient pressure changes. Postprandial glucose Rd was higher in hypobaric conditions than ground, the percent change in postprandial glucose concentration was lower, but postprandial EGP and meal Ra were not affected. Insulin concentration between 120 and 180 min was higher in the hypobaric simulation. The observed increase in glucose Rd for individuals with type 1 diabetes who were using insulin pumps may be related to the hypoxia and pressure changes experienced during flight. Because glucose profiles were unaffected, there is no evidence that insulin pump therapy is a risk factor in flight.

Individuals with type 1 diabetes (T1D) or permanent neonatal diabetes (PND) due to an INS gene mutation (INS-PND) have a marked reduction in pancreas volume by MRI compared with control individuals with no diabetes (ND). One possible explanation for this is loss of islet-acinar insulin signaling in these forms of severe insulin deficiency. To test the hypothesis that insulin deficiency drives the loss of pancreas volume in diabetes, we used a standardized and validated MRI protocol to measure pancreas volumes in individuals with various forms of monogenic diabetes, including maturity-onset diabetes of the young (MODY) and PND (HNF4A-MODY, GCK-MODY, HNF1A-MODY, HNF1B-MODY, INS-MODY, or INS-PND; n = 37), and compared their pancreas volumes with those of previously reported individuals with T1D (n = 93) or healthy control participants with ND (n = 90). Across all monogenic diabetes groups, individuals receiving insulin therapy had significantly smaller pancreas volume compared with those not requiring insulin. These results support the hypothesis that insulin signaling to the exocrine pancreas determines pancreas volume in multiple types of diabetes.

Glucokinase (GK) activators (GKAs) are a long-sought therapeutic modality for the treatment of type 2 diabetes. However, GKAs have failed in clinical trials, with the recent exception of dorzagliatin (Hua Medicine). A comprehensive approach using human islet perifusions, enzyme kinetics, X-ray crystallography, and modeling studies was applied to compare the effects of dorzagliatin with those of the unsuccessful GKA MK-0941 (Merck Pharmaceuticals), which is well characterized both clinically and mechanistically. Dorzagliatin improved glucose-stimulated insulin secretion in a dose- and glucose-dependent manner, in contrast to MK-0941, which induced maximal insulin secretion at low doses and glucose concentrations. To understand these functional differences, the atomic resolution structure of the dorzagliatin-GK complex was determined and compared with the GK-MK-0941 structure. MK-0941 bound to a pocket accessible in both open and closed conformations; had a strong interaction with Y214, the mutation of which produces the most clinically severe activating mutation; and produced a high energy barrier for the open-to-closed transition. In contrast, dorzagliatin only bound favorably to the closed form of GK, interacting primarily with R63 and causing a low energy barrier for the open-to-closed transition. This provides the molecular rationale for the clinical success of dorzagliatin, which can guide the future development of next-generation allosteric activators of GK.

Pancreatic β-cell KATP channel closure underlies electrical excitability and insulin release, but loss or inhibition of KATP channels can lead to paradoxical crossover from hyperinsulinism plus hypoglycemia, to glucose-intolerance or diabetes. We report genotype-phenotype information on a set of patients clinically diagnosed with maturity onset diabetes of the young (MODY), and carrying coding variants in the KATP regulatory subunit gene ABCC8. In contrast to the naïve prediction that diabetes should be associated with KATP gain-of-function (GOF, as in KATP-dependent neonatal diabetes) each mutation caused mild to severe loss-of-function (LOF), through distinct molecular mechanisms, suggesting the affected individuals may have crossed over to glucose intolerance from KATP channel LOF-dependent congenital hyperinsulinism (CHI). Our data provide definitive support for a paradoxical form of MODY in association with KATP channel LOF, genetically and mechanistically distinct from a late diagnosis of diabetes resulting from KATP GOF. To avoid confusion and inappropriate treatment efforts, we argue that diabetes driven by KATP-GOF and KATP-LOF mutations should be officially recognized as distinct diseases.

Accurate measurement of GLUT4 translocation is crucial for understanding insulin resistance in skeletal muscle, a key factor in the development of metabolic diseases. However, current methods rely on overexpressed epitope-tagged GLUT4 constructs or indirect measurements, limiting their physiological relevance and applicability. To overcome these challenges, we developed an innovative high-sensitivity imaging-based method that enables the direct assessment of endogenous GLUT4 translocation in primary skeletal muscle fibers. This approach uses antibodies targeting exofacial epitopes on native GLUT4. Our method allows multiplexed analysis of multiple insulin-sensitive processes, including transferrin receptor trafficking and FOXO nuclear exclusion, alongside mitochondrial oxidative stress. This comprehensive approach provides a unique opportunity to simultaneously assess insulin action across different signaling branches within individual muscle fibers. We validated this method across multiple inbred mouse strains and models of insulin resistance, including chronic insulin exposure, palmitate treatment, and obesity induced by a high-fat diet. Notably, we identified a selective defect in GLUT4 trafficking in insulin-resistant muscle fibers, while other insulin-dependent processes remained intact. By offering a high-fidelity model that maintains physiological relevance, this novel approach represents a significant advancement in the study of skeletal muscle insulin resistance and provides a powerful tool for dissecting gene-environment interactions that underpin metabolic disease.

We tested genetic variants in GCK, GCKR, and PNPLA3 in a large sample of self-identified Mexican Americans from the BetaGene Study for association with type 2 diabetes-related phenotypes under the hypothesis that they may regulate metabolic balance across the liver and contribute to hepatic steatosis and insulin resistance. We further tested whether interactions with dietary fructose and total sugar contributes to the observed associations. GCK rs1799831 was not associated with any type 2 diabetes-related phenotypes either alone or with any interaction tested. We replicated previous associations reported for GCKR rs780094 and PNPLA3 rs738409. We also show the interaction between GCKR rs780094 and dietary fructose is associated with both glucose effectiveness and glucose effectiveness at zero insulin, measures reflective of hepatic glucose uptake. We further show the interaction between GCKR rs780094 and PNPLA3 rs738409 is associated with type 2 diabetes-related traits, including insulin sensitivity. We conclude variations in GCKR and PNPLA3 and their interactions with each other and dietary fructose are partial determinants of hepatic fat, likely due to alterations in relative contributions of different metabolic pathways in the liver. These findings point to both GCKR and PNPLA3 as important therapeutic targets to mitigate hepatic metabolic dysfunction.

Diabetes is a metabolic disorder associated with an increased risk of systemic vascular complications. Notably, diabetic retinopathy (DR) represents a major microvascular complication and a leading cause of blindness and vision impairment. Despite its clinical significance, the precise molecular mechanisms underlying vascular dysfunction and the associated metabolic disturbances in DR remain incompletely understood. In this study, we identified tsRNA-1797, a transfer RNA-derived small RNA, as a critical regulator of retinal vascular dysfunction. tsRNA-1797 expression was markedly upregulated under diabetic conditions. Functional studies demonstrated that silencing tsRNA-1797 ameliorated endothelial dysfunction in vitro and inhibited retinal vascular dysfunction in vivo. Mechanistically, tsRNA-1797 was found to disrupt purine metabolism by regulating adenosine production through CD73. The tsRNA-1797-CD73-adenosine axis emerged as a key mediator of retinal vascular dysfunction in DR. These findings establish tsRNA-1797 as a novel regulatory factor that links metabolic dysregulation to vascular dysfunction in DR, highlighting its potential as a promising therapeutic target for diabetes-induced vascular complications.

We aimed to identify distinct axes of obesity using advanced magnetic resonance imaging (MRI)-derived phenotypes. We used 24 MRI-derived fat distribution and muscle volume measures (UK Biobank; N = 33,122) to construct obesity axes through principal component analysis. Genome-wide association studies were performed for each axis to uncover genetic factors, followed by pathway enrichment, genetic correlation, and Mendelian randomization analyses to investigate disease associations. Four primary obesity axes were identified: 1) general obesity, reflecting higher fat accumulation in all regions (visceral, subcutaneous, and ectopic fat); 2) muscle dominant, indicating greater muscle volume; 3) peripheral fat, associated with higher subcutaneous fat in abdominal and thigh regions; and 4) lower-body fat, characterized by increased lower-body subcutaneous fat and reduced ectopic fat. Each axis was associated with distinct genetic loci and pathways. For instance, the lower-body fat axis was associated with RSPO3 and COBLL1, which are emerging as promising candidates for therapeutic targeting. Disease risks varied across axes; the general obesity axis was correlated with higher risks of metabolic and cardiovascular diseases, whereas the lower-body fat axis seemed to protect against type 2 diabetes and cardiovascular disease. This study highlights the heterogeneity of obesity through the identification of obesity axes and emphasizes the potential to extend beyond BMI in defining and treating obesity for obesity-related disease management.

Islet cell replacement therapies have evolved as a viable treatment option for type 1 diabetes complicated by problematic hypoglycemia and glycemic lability. Refinements of islet manufacturing, islet transplantation procedures, peritransplant recipient management, and immunosuppressive protocols allowed most recipients to achieve favorable outcomes. Subsequent phase 3 trials of transplantation of deceased donor islets documented the effectiveness of transplanted islets in restoring near-normoglycemia, glycemic stability, and protection from severe hypoglycemia, with an acceptable safety profile for the enrolled high-risk population. Health authorities in several countries have approved deceased donor islet transplantation for treating patients with type 1 diabetes and recurrent severe hypoglycemia. These achievements amplified academic and industry efforts to generate pluripotent stem cell-derived β-cells through directed differentiation for β-cell replacement. Preliminary results of ongoing clinical trials suggest that the transplantation of stem cell-derived β-cells can consistently restore insulin independence in immunosuppressed recipients with type 1 diabetes, thus signaling the profound progress made in generating an unlimited and a uniform supply of cells for transplant. Avoiding the risks of chronic immunosuppression represents the next frontier. Several strategies have entered or are approaching clinical investigation, including immune-isolating islets, engineering immune-privileged islet implantation sites, rendering islets immune evasive, and inducing immune tolerance in transplanted islets. Capitalizing on high-dimensional, multiomic technologies for deep profiling of graft-directed immunity and the fate of the graft will provide new insights that promise to translate into sustaining functional graft survival long-term. Leveraging these parallel progression paths will facilitate the wider clinical adoption of cell replacement therapies in diabetes care.