Despite the increasing prevalence of type 2 diabetes in youth, its causal associations with circulating biomarkers remain elusive. We first aimed to identify circulating metabolites causally linked to youth-onset type 2 diabetes using Mendelian randomization (MR). By analyzing 675 metabolites from large metabolomic European genome-wide association studies (GWAS) and data on youth type 2 diabetes from the multiancestry Progress in Diabetes Genetics in Youth (ProDiGY) consortium, we identified 34 candidate metabolites. Among these, phosphatidylcholine (pc) ae C42:3 and propionylcarnitine provided the strongest evidence of association with youth-onset type 2 diabetes, based also on positive genetic colocalization and sensitivity analyses accounting for adiposity. Among the 34 candidate metabolites, 23 were retained following colocalization and a replication MR using independent metabolomic GWAS and testing effects on adult type 2 diabetes. Furthermore, we validated associations of six of these metabolites with glucose metabolism-related traits in an observational study in the Avon Longitudinal Study of Parents and Children (ALSPAC). Notably, pc ae C42:3 levels at age 7 years were linked to dysglycemia and insulin resistance in adolescence. These findings underscore the dynamic role of metabolites in glucose metabolism in childhood, offering insights for future screening and treatment strategies.

In mice, glucagon regulates lipid metabolism by activating receptors in the liver; however, its role in human lipid metabolism is incompletely understood. Here we describe three normal-weight individuals from a consanguineous family with early-onset hepatic steatosis and/or cirrhosis. Using exome sequencing, we found they were homozygous for two missense variants in the glucagon receptor gene (GCGR). In cells, the double GCGR mutation reduced cell membrane expression and signaling, resulting in an almost complete loss of function. Carriers of pathogenic GCGR mutations had substantially elevated circulating glucagon and amino acid levels and increased adiposity. Introducing the double GCGR mutation into human induced pluripotent stem cell-derived hepatocytes using CRISPR/Cas9 caused increased lipid accumulation. Our results provide an explanation for increased liver fat seen in clinical trials of GCGR antagonists and reduced liver fat in people with obesity and steatotic liver disease treated with GCGR agonists.

Pancreatic β-cells undergo senescence and loss during aging; however, the underlying mechanisms remain incompletely understood. This study aimed to investigate what sirtuin 6 (SIRT6) does during β-cell aging. Pancreatic β-cell-specific Sirt6 transgenic (TgSIRT6) mice were generated for this study. DNA damage, cell death, and cell proliferation were analyzed in cell and mouse models. SIRT6 protein levels were decreased in pancreatic β-cells during aging. TgSIRT6 mice exhibited less DNA damage and cell death, including apoptosis, necroptosis, and pyroptosis, in β-cells than control mice. TgSIRT6 mice had increased total islet area and mass in pancreas compared with control mice. As a result, TgSIRT6 mice showed better glucose tolerance and glucose-stimulated insulin secretion than control mice. RRAD and GEM-like GTPase 2 (REM2), an endogenouse inhibitor of high-voltage-activated calcium channels, was negatively regulated by SIRT6. Knockdown of Rem2 in INS-1 cells partially rescued the SIRT6 deficiency- and palmitic acid-induced DNA damage, lipid peroxidation, and cell death. Rem2 β-cell-specific knockout mice had less DNA damage and cell death in β-cells than control mice. Our data suggest that SIRT6 is a critical antiaging factor in pancreatic β-cells and is a potential therapeutic target.

Diabetic retinopathy (DR) is characterized by microvascular damage and increased vascular permeability in the retina. The investigation of visual outcomes in late-stage DR is limited by challenges of maintaining chronically hyperglycemic mice, and most reports are restricted to early-stage DR. In this study, we used carefully managed diabetic mice to longitudinally investigate associations between vascular leakage and visual acuity during early- and late-stage DR. Diabetes was induced in C57BL/6J mice with streptozotocin, and fluorescence angiography with dual fluorescence (FA-DF) was used to assess retinal vascular leakage dynamics in chronically hyperglycemic mice for 12 months. Retinal vascular leakage was evident 180 days after diabetes induction and before reduced visual acuity, measured using the optokinetic response, and vascular leakage continued to increase during DR progression. Mice were also treated with intravitreal injections of antiangiogenic aflibercept at late-stage DR, and reduced leakage was reliably measured using FA-DF and was associated with improved visual acuity. Inflammatory and vascular phenotypes were assessed using immunostaining, which revealed significantly lower retinal macrophage and vascular densities and reduced capillary diameter in association with anti-VEGF treatment compared with age-matched diabetic controls. In conclusion, this is the first longitudinal quantification of retinal vascular leakage in early, intermediate, and late stages of DR in the same cohort of mice in a minimally invasive fashion to demonstrate the associated effect of antiangiogenic therapy in vivo. Our findings also further confirmed the sensitivity of FA-DF in assessing retinal vascular leakage in conjunction with other functional measures in longitudinal studies in the same animals.

Maternal hyperglycemia is linked to 19 cord blood DNA methylation biomarkers that predict offspring metabolic dysfunction. These methylation changes, associated with maternal glycemic status, improved the prediction of β-cell dysfunction at 7, 11, and 18 years of age compared with clinical factors alone. Validation in human β-cells and pancreatic ductal epithelial cells confirmed that hyperglycemia influences methylation-dependent gene expression. These findings highlight the role of epigenetic modifications at birth as early indicators of diabetes risk, suggesting that in utero hyperglycemic exposure may mediate long-term metabolic outcomes in offspring.

Diabetes has a large medical and public health impact in American Indians. Studies have used genetic data to distinguish type 1 diabetes (T1D) and type 2 diabetes (T2D) and uncover biologic mechanisms underlying T2D clinical heterogeneity. We applied a T1D polygenic score (PS) to 3,084 American Indians (mean age 56 years, 58% women, 39% diabetes). We also calculated partitioned PS for eight clusters of T2D-associated variants and evaluated their association with 20 cardiometabolic traits and five clinical outcomes. The profile of T1D PS for individuals with diabetes was consistent with T2D. A total T2D PS was significantly associated with early age of T2D onset (P = 3.5 × 10-11). Partitioned PS for T2D clusters were significantly associated with cardiometabolic traits for the obesity cluster (increased measures of body fat and total triglycerides but lower HDL cholesterol), while the lipodystrophy cluster was associated with increased fasting insulin, waist-to-hip ratio, triglycerides, and blood pressure, and lower body fat percentage and HDL cholesterol. T2D clusters were not associated with cardiovascular and kidney outcomes. Our findings support a relationship of cluster-specific T2D partitioned PS with cardiometabolic traits described in other populations, but there are opportunities for developing improved clustering methods using genetic variation from American Indians.

Diabetic cardiomyopathy (DbCM) is a chronic metabolic disorder with few effective treatment strategies. Our previous study demonstrated that activated protein C (aPC), a serine protease, exerts cytoprotective effects in DbCM. However, the mechanisms underlying its role in DbCM require further elucidation. We developed a type 1 diabetic mouse model using thrombomodulin gene point mutation mice (TMP/P) with reduced endogenous aPC generation and investigated the protective effects of aPC on DbCM through intraperitoneal injection of PC. Myocardial functions and structure were assessed by echocardiography and histology. Transcriptomic analysis and immunological evaluation were conducted to investigate the downstream targets. The antisenescence role of aPC was reaffirmed by PC treatment in vivo and aPC intervention in cultured neonatal rat ventricular myocytes in vitro. Endogenous aPC levels were reduced and positively correlated with cardiac diastolic function in diabetic mice. Cardiomyocytes manifested a senescent phenotype in DbCM. With impaired aPC activation, TMP/P mice exhibited aggravated diabetes-induced cardiac dysfunction and cardiomyocyte senescence. Mechanistically, aPC alleviated cardiomyocyte senescence in DbCM by acting on PAR1/PAR3 to restore the interaction between P85 and CaMKIIδ, thereby inhibiting CaMKIIδ phosphorylation and its nuclear translocation. In summary, our study highlights that aPC ameliorates cardiomyocyte senescence in DbCM via the PAR1/PAR3-P85-CaMKIIδ axis.

This study aimed to investigate the relationship between the plasma lipidome and metabolic dysfunction-associated steatotic liver disease (MASLD) in type 2 diabetes. Initially, we conducted a plasma lipidome analysis using supercritical fluid chromatography-tandem mass spectrometry in 143 patients with type 2 diabetes with and without MASLD. Of the 349 lipid species identified, 13 had higher levels and a fold-change ≥2 in the MASLD group than in the non-MASLD group; 10 of these 13 lipids were triglycerides (TGs). The constituent fatty acid (FA) in TGs that exhibited the greatest difference between patients with and without MASLD was myristic acid (FA 14:0). The presence of MASLD was an independent explanatory factor for high FA 14:0 levels in TGs, even after adjusting for covariates. Next, we assessed whether the levels of lipids identified in the initial analysis were influenced by comprehensive diabetes treatment in 26 patients. After comprehensive diabetes treatment of 2 weeks, FA levels in many TGs significantly decreased; especially FA 14:0 levels, and this reduction was more pronounced in patients with MASLD. These results suggest that various plasma lipids, particularly TGs comprising FA 14:0, may be associated with the pathogenesis of MASLD in patients with type 2 diabetes.

Following the trends of the adult obesity epidemic, and worsened by school disruptions during the coronavirus disease 2019 pandemic, childhood obesity prevalence has reached unprecedented levels. The health implications for this generation are especially concerning, as childhood-onset obesity has more severe health consequences than weight gain that begins in adulthood, including increased risk of type 2 diabetes and diabetes-related complications. The complexity of obesity treatment has been challenging, including remarkable heterogeneity in obesity phenotypes and treatment responses among both adults and children. Many in the field have therefore highlighted a need for precision medicine approaches in obesity treatment across age-groups. This includes a need for precision risk stratification to better target treatment intensity, which will require a better understanding of the earliest stages of metabolic syndrome pathophysiology. The health, function, and distribution of adipose tissue have been established as important determinants of metabolic health in both childhood- and adult-onset obesity, making adipose tissue a promising target for understanding phenotypic heterogeneity in obesity. Here, we provide a brief overview of the current limited understanding of adipose tissue biology during childhood development and discuss opportunities for further research into adipose-centric precision medicine approaches in childhood-onset obesity and type 2 diabetes.

Diabetes triggers cell-type-specific responses in the retina, leading to vascular lesions, glial dysfunction, and neurodegeneration, all of which contribute to the progression of diabetic retinopathy (DR). However, the specific cell types involved in disease development and the molecular mechanisms driving their responses have not yet been fully clarified, impeding the creation of effective therapeutic strategies. Recent advancements in single-cell or single-nuclei transcriptomic technologies have provided a systematic approach to profile transcript-level alterations at single-cell resolution, allowing for an in-depth analysis of diabetes-induced retinal transcriptional changes across various animal models for DR. Here, in the context of research funded by the American Diabetes Association Pathway to Stop Diabetes program, we discuss the cell-type-specific responses in the neural retina identified through single-cell transcriptomic analyses. We emphasize new insights into neural retinal responses, potential therapeutic targets, and the limitations and unresolved topics that warrant further investigation. This article is part of a series of perspectives that report on research funded by the American Diabetes Association Pathway to Stop Diabetes program.

The "omnigenic" hypothesis postulates that polygenic effects of common variants on typical complex traits coalesce via trans effects on the expression of a relatively sparse set of "core" effector genes and their encoded proteins in relevant tissues. The objective of this study was to identify core proteins for type 1 diabetes. We used summary statistics for single nucleotide polymorphism associations with plasma levels of 5,130 proteins in three large cohorts, including the UK Biobank, to compute genome-wide aggregated trans effects (GATE) scores for protein levels in two type 1 diabetes case-control studies (6,828 case individuals, 416,000 control individuals). GATE scores for 27 proteins were associated with type 1 diabetes. Of these, 14 were replicated between data sets, 11 had support in Mendelian randomization analysis, and 9 had experimental support in mouse models of autoimmune diabetes. The strongest associations were for immune checkpoints (PDCD1, CD5, TIGIT, and LAG3), chemokines, and innate immune system proteins (NCR1 and KLRB1). While PDCD1 is a known cause of monogenic autoimmune diabetes, neither it nor most of the core proteins identified here were previously reported as genome-wide association study hits for type 1 diabetes. These results identify possible drug targets with genetic support for causality and suggest that programmed cell death protein 1 agonists under development for other indications should be trialed for type 1 diabetes prevention.

An accurate genetic diagnosis of maturity-onset diabetes of the young (MODY) is critical for personalized treatment. To avoid misdiagnosis, only genes with strong evidence of causality must be tested. Heterozygous variants in NEUROD1, PDX1, APPL1, and WFS1 have been implicated in MODY, but strong genetic evidence supporting causality is lacking. We therefore assessed their existing genetic evidence and performed gene-level burden tests in a large MODY cohort, alongside two established MODY genes as positive controls (HNF1A-high penetrance, RFX6-low penetrance). The first reported MODY-associated variants in NEUROD1, PDX1, APPL1, and WFS1 were <1:20,000 frequency. Based on the small number of large published pedigrees per gene (n < 3), MODY-associated variants showed only modest cosegregation in these genes. Crucially, ultra-rare (minor allele frequency <1:10,000) protein-truncating and predicted-damaging missense variants in APPL1 and WFS1 were not enriched in a MODY cohort (n = 2,571) compared with population control individuals (n = 155,501; all P > 0.05). In contrast, variants in NEUROD1 and PDX1 were enriched, albeit at levels comparable to RFX6. Multiple sensitivity analyses corroborated these findings. In summary, rare heterozygous variants in NEUROD1 and PDX1 are low-penetrance causes of MODY, while those in APPL1 and WFS1 lack robust genetic evidence for causality and should not be included in MODY testing panels.

Metabolic stress elicits functional changes in pancreatic islets, contributing to the pathogenesis of type 2 diabetes. However, the molecular mechanisms underlying overnutrition stress in islet cells is not well understood. In our study, we subjected human islets to overnutrition with 25 mmol/L glucose and 0.5 mmol/L palmitic acid (glucolipotoxicity) or to a control culture condition with 5.1 mmol/L glucose. We used single-cell RNA sequencing to comprehensively characterize the gene expression changes between these two conditions in a cell type-specific manner. We found that among all islet endocrine cell types, α-cells were the most resilient to glucolipotoxicity, while β-cells were the most susceptible. We also observed a reduction in cell-cell interactions within islet endocrine cells under glucolipotoxicity, alongside alterations in gene regulatory networks linked to type 2 diabetes genetic risk. Finally, targeted drug screening underscored the critical role of histone H3K9 methyltransferases G9a (EHMT2) and GLP (EHMT1) in modulating the β-cell cellular response to overnutrition.

Survivors of childhood cancers who received high doses (40-60 Gy) of cranial irradiation (CI) have increased risks of developing obesity, type 2 diabetes, and metabolic syndrome (MetS). Here, we subjected mice to CI of 0, 0.5, or 2 Gy directed to the hypothalamus to explore the effects of low-to-moderate doses of CI on MetS risks. Despite targeting the hypothalamus as a major metabolic control center, we did not detect hypothalamic astrocyte or microglia activation at 2 or 7 days, or at 3 months post-CI. Indirect calorimetry at 2 months post-CI showed no metabolic alterations between groups, yet female mice subjected to CI were unresponsive to leptin compared with sham. Follow-up monitoring over 2 years revealed accelerated weight gain in the 2-Gy female group and glucose intolerance in both sexes following CI. Insulin sensitivity, plasma insulin, and triglycerides remained unaltered, but both male and female 2-Gy groups showed elevated VLDL and lowered HDL cholesterol levels and aberrant hypothalamic mRNA levels of genes involved in synaptic and neuronal function, neuroinflammation, and endoplasmic reticulum stress. Mortality remained unaffected by all doses of CI. These data strongly suggest a significant risk for developing MetS following low-to-moderate doses of CI, and they support tailored clinical risk assessment and monitoring strategies for patients undergoing CI, especially when the hypothalamus is included.

Iron overload (IO) is a common contributing factor to aspects of the metabolic syndrome (MetS), including insulin resistance. Mechanisms of IO-induced insulin resistance include elevated oxidative stress, endoplasmic reticulum (ER) stress and impaired autophagy. Using an Akt biosensor L6 skeletal muscle cell line, we found that the adiponectin receptor agonist ALY688 prevented impaired insulin signaling in response to IO. Mechanistically, ALY688 counteracted IO-dependent effects on ER stress, the unfolded protein response (UPR), and autophagic flux. Importantly, we found that ALY688 induced FAM134B-dependent ER-phagy (reticulophagy) to ameliorate ER stress. The beneficial effects of ALY688 were attenuated in cells lacking Atg7 or FAM134B, highlighting the importance of selective autophagy of the ER by FAM134B in mitigating IO-induced impaired insulin signaling. These findings translated to a mouse model of IO in which ALY688 improved glucose tolerance, insulin sensitivity, UPR activation, FAM134B expression, and autophagy flux. Collectively, our results demonstrate that ALY688 effectively attenuated IO-induced ER stress and insulin resistance in both mice and cellular skeletal muscle models via stimulation of the UPR and ER-phagy.

Diabetes is characterized by a loss of functional β-cell mass; therefore, identifying factors involved in establishing and preserving β-cells is critical to combat rising diabetes incidence. While transcription factors are crucial β-cell regulators, knowledge of coregulators facilitating gene expression is limited. Previously, we demonstrated that the islet-1 (Isl1) transcription factor forms complexes with ubiquitin ligases ring finger 20 (Rnf20) and Rnf40 to regulate β-cells in vitro. Here, we investigated whether Rnf20-mediated complexes are required for β-cell function in adult islets by characterizing a novel β-cell-enriched Rnf20 knockout mouse model. Tamoxifen induction of Rnf20 recombination prompted a robust loss of histone 2B monoubiquitination, imparted severe hyperglycemia and glucose intolerance, and elicited an overall reduction in insulin content. Expression of mRNAs and proteins involved in glucose-stimulated insulin secretion and β-cell identity were also dysregulated in Rnf20Δβ-cell mice. Comparative analyses of the loss of either Rnf20 or Isl1 yielded similar changes in the β-cell regulome, supporting that Isl1::Rnf20 complexes are critical regulators of β-cell identity and function. Isl1::Rnf20 complexes are maintained in human tissues wherein they regulate insulin expression, secretion, and content. These findings increase our understanding of key players in β-cell maintenance, which is crucial for the advancement of β-cell derivation diabetes therapeutics.