Glucokinase activators (GKA) are a long-sought therapeutic modality for the treatment of Type 2 Diabetes (T2D). However, all GKAs failed clinical trials, with the recent exception of dorzagliatin (Hua Medicine). A comprehensive approach using human islet perfusions, enzyme kinetics, x-ray crystallography, and modeling studies was applied to compare the effects of dorzagliatin with the failed GKA MK-0941 (Merck Pharmaceuticals), which is well-characterized both clinically and mechanistically. Dorzagliatin improves glucose stimulation of insulin secretion (GSIS) in a dose- and glucose-dependent manner, in contrast to MK-0941 which induces maximal insulin secretion at low doses and glucose concentrations. To understand these functional differences, the atomic resolution structure of the dorzagliatin-glucokinase (GK) complex was determined and compared with the GK/MK-0941 structure. MK-0941 binds to a pocket accessible in both open and closed conformations, has a strong interaction with Y214, mutation of which produces the most clinically severe activating mutation, and produces a high energy barrier for the open-to-close transition. In contrast, dorzagliatin only binds favorably to the closed form of glucokinase, interacting primarily with R63, and causing a low energy barrier for the open-to-close 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 fibres. This approach utilises 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 signalling branches within individual muscle fibres. We validated this method across multiple inbred mouse strains and models of insulin resistance, including chronic insulin exposure, palmitate treatment, and high-fat diet-induced obesity. Notably, we identified a selective defect in GLUT4 trafficking in insulin-resistant muscle fibres, 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 underlpin metabolic disease.

We tested genetic variants in GCK, GCKR, and PNPLA3 for association with type 2 diabetes-related phenotypes under the hypothesis they may regulate metabolic balance across the liver and contribute to hepatic steatosis and insulin resistance in a large sample of self-identified Mexican Americans from the BetaGene Study. 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 identify tsRNA-1797, a tRNA-derived small RNA, as a critical regulator of retinal vascular dysfunction. tsRNA-1797 expression was markedly up-regulated 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 diabetic vascular complications.

We aimed to identify distinct axes of obesity using advanced 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 (PCA). 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 correlated with higher risks of metabolic and cardiovascular diseases; the Lower Body Fat Axis appeared protective 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.

The identification of a "rundlichen Häuflein" by Paul Langerhans more than 150 years ago marked the initiation of a global effort to unravel the mysteries of pancreatic islets, an intricate system of nutrient-sensing, hormone-secreting, and signaling cells. In type 1 diabetes, this interconnected network is vulnerable to malfunction and immune attack, with strategies to prevent or repair islet damage still in their infancy. In 2014, the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) established the Human Islet Research Network (HIRN) to accelerate our understanding of the molecular and cellular basis of type 1 diabetes development. In this article, investigators from the HIRN detail pioneering advances, technologies, and systems that contextualize insulin-producing β-cells and other related cells within their physiological environment. Disease models, devices, and therapies are evaluated by the HIRN in light of promising functional and mechanistic data. Collaborative relationships and opportunities within this network are emphasized as a means of enhancing the quality of innovative research and talent in science. Topics are developed through a series of questions, achievements, and milestones, with the 75th anniversary of the NIDDK as an opportunity to reflect on the past, present, and future of type 1 diabetes research.

Cardiovascular disease (CVD) is a leading cause of morbidity and mortality in individuals with diabetes. Individuals with type 1 diabetes have a two- to fourfold higher risk of CVD in comparison with the general population, driven by an earlier onset and increased lifetime incidence of CVD events and mortality. Similarly, type 2 diabetes confers two- to threefold increased CVD risk, usually alongside metabolic syndrome, obesity, and hypertension. Despite advancements in methods for achieving glycemic control, the CVD burden remains disproportionately high in diabetes. The mechanisms driving elevated risk are complex and variably multifactorial, involving hyperglycemia, insulin resistance, dyslipidemia, inflammation, and a hypercoagulable state. Unfortunately, critical gaps in understanding persist on how these factors interact to promote CVD in type 1 versus type 2 diabetes, particularly across disease stages and age. Addressing these knowledge gaps is essential to developing targeted therapies that can effectively mitigate CVD risk. To meet this need, the National Institute of Diabetes and Digestive and Kidney Diseases, in partnership with the National Heart, Lung, and Blood Institute, recently formed the Cardiovascular Repository for Type 1 Diabetes (CaRe-T1D) program. Its mission is to elucidate the molecular and cellular pathways linking diabetes with CVD through the provision of high-quality human tissues for investigator-led analyses using cutting-edge technologies and collaborative data sharing to advance precision medicine and reduce the global burden of diabetes-associated cardiovascular complications.

In the last two decades, significant progress has been made toward understanding the genetic basis of type 2 diabetes. An important supporter of this research has been the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), most recently through the Accelerating Medicines Partnership Program for Type 2 Diabetes (AMP T2D) and Accelerating Medicines Partnership Program for Common Metabolic Diseases (AMP CMD). These public-private partnerships of the National Institutes of Health, multiple biopharmaceutical and life sciences companies, and nonprofit organizations, facilitated and managed by the Foundation for the National Institutes of Health, were designed to improve understanding of therapeutically relevant biological pathways for type 2 diabetes. On the occasion of NIDDK's 75th anniversary, we review the history of NIDDK support for these partnerships, which saw the convergence of research directions prioritized by academic consortia, the pharmaceutical industry, and government funders. Although the NIDDK was not the sole originator or funder of these efforts, its support and leadership have been pivotal to the partnerships' success and have enabled their research to be broadly accessible through the AMP Common Metabolic Diseases Knowledge Portal (CMDKP) and the AMP Common Metabolic Diseases Genome Atlas (CMDGA). Findings from AMP CMD align with NIDDK's mission to conduct research and share results with the goal of improving health and quality of life.

This year marks the 75th anniversary of the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) of the National Institutes of Health. NIDDK's long history of research and innovation includes support of four types of collaborative research centers focused on diabetes, endocrinology, and metabolic diseases. The Diabetes Research Centers promote basic and clinical diabetes research, while the Centers for Diabetes Translation Research conduct diabetes research across the translation science spectrum. The Mouse Metabolic Phenotyping Center (MMPC)-Live program provides the research community with standardized phenotyping services for mouse models of diabetes and obesity, and the Cystic Fibrosis Research and Translation Centers advance basic, preclinical, and clinical research for cystic fibrosis. These centers have evolved over time in response to new scientific opportunities and to expand their reach to be an asset to the larger scientific community. Looking to the future, NIDDK will continue to ensure that these centers enhance the research community, foster novel and synergistic scientific collaborations, and promote career development of scientists in the early stages of their careers. We will also ensure that our centers align with NIDDK's goal of improving health outcomes for all people with and at risk for diseases, within our mission.

G protein-coupled receptor 35 (GPR35) is a poorly characterized receptor with unclear intracellular mechanisms in endothelial cells (ECs). Oxidative stress responsive 1 (OXSR1) is a serine/ threonine protein kinase that modulates cell morphology and has recently been found to promote angiogenesis. We hypothesized that GPR35 inhibition promotes EC angiogenesis via augmenting OXSR1 activity and accelerating wound healing in diabetes. Here, we show that active GPR35 contributed to the impaired migration and tube formation of human dermal microvascular endothelial cells (ECs) from type 2 diabetic (T2D) patients or ECs exposed to high glucose. Proximity labeling and coimmunoprecipitation identified OXSR1 as an interacting partner of GPR35 in ECs. GPR35 suppressed OXSR1 from translocating to nuclei to activate SMAD1/5, thereby inhibiting the transcription of angiogenic factors. Furthermore, enhanced wound angiogenic response and accelerated wound closures were observed in induced T2D mice with topical application of GPR35 siRNA, or in T2D models of transgenic mice with either global or endothelial-selective GPR35 deletion. Our data suggest that GPR35 suppresses OXSR1-dependent angiogenic activity in ECs, contributing to poor angiogenesis and delayed wound healing in T2D animals. This study provides both in vitro and in vivo evidence for GPR35 as a potential therapeutic target in tissue repair in patients with diabetes.

In this month's Classics in Diabetes featured article, published in Diabetes in 1993, the description by Kahn et al. of the relationship between insulin secretion and insulin sensitivity in 93 healthy adults without diabetes provided a model for the regulation of glucose tolerance that continues to be used today. In the study, data from a large sample of individuals studied with intravenous glucose tolerance tests demonstrated that in those with normal glucose tolerance, insulin secretion and sensitivity were related by a hyperbolic curve. This relationship supports adaptability between these parameters that maintains a constant amount of insulin action, and glycemia conforming to the normal range. These findings have led to the general view that type 2 diabetes mellitus is fundamentally a failure of β-cells to adequately supply tissues such as the liver, skeletal muscle, and adipose with insulin. This simple conception remains useful for explaining diabetes pathogenesis and interpreting experimental data some 30 years after publication, with impact meriting recognition as a Diabetes classic.