The biomarkers connecting obesity and cardiometabolic diseases are not fully understood. We aimed to (i) evaluate the associations between body mass index (BMI), waist circumference (WC), and ∼5,000 plasma proteins (SomaScan v4), (ii) identify protein signatures of BMI and WC, and (iii) evaluate the associations between the protein signatures and cardiometabolic health including metabolically unhealthy obesity and type 2 diabetes incidence in the Singapore Multi-Ethnic Cohort (MEC1). Among 410 BMI-associated and 385 WC-associated proteins, we identified protein signatures of BMI and WC and validated them in an independent dataset across two timepoints and externally in the Atherosclerosis Risk in Communities (ARIC) study. The BMI- and WC-protein signatures were highly correlated with total and visceral body fat, respectively. Furthermore, the protein signatures were significantly associated with cardiometabolic risk factors and metabolically unhealthy obesity. In prospective analyses, the protein signatures were strongly associated with type 2 diabetes risk in MEC1 (odds ratio per SD increment in WC-protein signature = 2.84, 95% CI 2.47 to 3.25) and ARIC (hazard ratio = 1.98, 95% CI 1.88 to 2.08). Our protein signatures have potential uses for the monitoring of metabolically unhealthy obesity.

The accumulation of mitochondria in thermogenic adipose tissue (i.e., brown and beige fat) increases energy expenditure, which can aid in alleviating obesity and metabolic disorders. However, recent studies have shown that knocking out key proteins required to maintain mitochondrial function inhibits the energy expenditure in thermogenic fat, and yet the knockout mice are unexpectedly protected from developing obesity or metabolic disorders when fed a high-fat diet (HFD). In the present study, non-biased sequencing-based screening revealed the importance of YY1 in the transcription of electron transport chain genes and the enhancement of mitochondrial function in thermogenic adipose tissue. Specifically, adipocyte YY1 null (YAKO) mice showed lower energy expenditure and were intolerant to cold stress. Interestingly, YAKO mice showed alleviation of HFD-induced metabolic disorders, which can be attributed to a suppression of adipose tissue inflammation. Metabolomic analysis revealed that blocking YY1 directed glucose metabolism toward lactate, enhanced the uptake of glutamine, and promoted the production of anti-inflammatory spermidine. Conversely, blocking spermidine production in YAKO mice reversed their resistance to HFD-induced disorders. Thus, although blocking adipocyte YY1 impairs the thermogenesis, it promotes spermidine production and alleviates adipose tissue inflammation, therefore leads to an uncoupling of adipose tissue energy expenditure from HFD-induced metabolic disorders.

Embedded in the Developmental Origins of Health and Disease hypothesis, maternal hyperglycemia in utero, from pre-existing diabetes or gestational diabetes mellitus, predisposes the offspring to excess adiposity and heightened risk of prediabetes and type 2 diabetes development. This transmission creates a vicious cycle increasing the presence of diabetes from one generation to another, leading to the question: how can we interrupt this vicious cycle? In this Perspective article, we presented the current state of knowledge on the intergenerational transmission of diabetes from epidemiological life course studies. Then, we discussed the potential mechanisms implicated in the intergenerational transmission of diabetes with a focus on epigenetics. We present novel findings stemming from epigenome-wide associations studies of offspring DNA methylation in blood and placental tissues, which shed light on potential molecular mechanisms implicated in the mother-offspring transmission of diabetes. Lastly, in a perspective on how to break the cycle, we consider interventions to prevent offspring obesity and diabetes development before puberty, as a critical period of the intergenerational cycle.

Maternally inherited diabetes and deafness (MIDD) is a monogenic mitochondrial disorder caused by a pathogenic variant in the MT-TL1 gene encoding for a leucine transfer RNA. We propose a new hypothesis that explains how the MT-TL1 variant causes impaired glucose tolerance and diabetes in MIDD. We suggest that diabetes in MIDD primarily depends on a variable combination of insulin resistance and impaired beta cell function that seems more likely to occur in the presence of high skeletal muscle heteroplasmy and moderate beta cell heteroplasmy for m.3243A>G. The underlying genetic defect generates oxidative stress and disrupts the tricarboxylic acid cycle, leading to mTORC1 hyperactivity and modifying mitochondrial retrograde signalling. mTORC1 hyperactivity contributes to insulin resistance and beta cell dysfunction and to an increased load of the m.3243A>G phenotypic variant. Abnormal mitochondrial signalling affects the nuclear epigenome and influences MIDD phenotype. Despite being an apparent pathogenic factor, we highlight evidence showing that heteroplasmy in the blood and in tissues, does not fully explain the phenotypic variability of this condition, and that other factors, including mtDNA copy number, additional nuclear or mitochondrial variants, environmental factors and metabolic characteristics of the patient may be contributing factors. A better understanding of the mechanisms leading to MIDD diabetes will help inform novel management strategies for this form of diabetes.

High-affinity islet autoantibodies predict type 1 diabetes in mice and humans and implicate germinal centers (GCs) in type 1 diabetes pathogenesis. T follicular helper (Tfh) cells are increased in type 1 diabetic individuals and alterations in Tfh-like cells in the peripheral blood predicted individual responses to abatacept. Tfh cells support GC responses and depend on the transcriptional repressor BCL6 for their maturation. We therefore hypothesized that CD4-driven deletion of Bcl6 would disrupt essential T-B lymphocyte interactions in GCs to prevent type 1 diabetes. To test this hypothesis, we generated Bcl6fl/fl-CD4.Cre.NOD mice and found they were completely protected against diabetes. Insulitis severity and tertiary lymphoid structure organization were preserved in the pancreas of Bcl6fl/fl-CD4.Cre.NOD mice, which did not show decreases in CD4+, CD8+, and B cell numbers in the pancreas and draining lymph nodes, relative to control Bcl6fl/fl.NOD mice. CD4-driven loss of functional BCL6 resulted in significantly reduced GC B cell and Tfh cell numbers in the pancreatic lymph nodes and pancreas at late prediabetic intervals. Spontaneous anti-insulin autoantibody was blunted in Bcl6fl/fl-CD4.Cre.NOD mice. These data highlight BCL6 as a novel therapeutic target in type 1 diabetes.

Identified genetic loci for C-peptide and age at diagnosis (AAD) in individuals with type 1 diabetes (T1D) explain only a small proportion of their variation. Here, we aimed to perform large metagenome-wide association studies (GWAS) of C-peptide and AAD in T1D; and to identify the HLA allele/haplotypes associated with C-peptide and AAD. 7,252 and 7,923 European individuals with T1D were included in C-peptide and AAD GWAS, respectively. HLA-DQB1*06:02 which is strongly protective against T1D was associated with higher C-peptide. HLA-DQB1*03:02, HLADRB1*03:01 and HLA-A*24:02 which increase T1D risk were independently associated with younger AAD. HLA-DR3-DR4 haplotype combination, the strongest T1D susceptibility factor, was associated with younger AAD. Outside HLA region, rs115673528 on Chr5 (GABRG2) was associated with C-peptide, and an indel, rs111970692, on Chr15 within CTSH, a known T1D locus, was associated with AAD. Genetically predicted CTSH expression, methylation and protein levels were associated with AAD; Mendelian randomization analysis suggested that higher levels of procathepsin H reduce AAD. In conclusion, some HLA allele/haplotypes associated with T1D also contribute to variability of C-peptide and AAD. Outside HLA, T1D loci are generally not associated with C-peptide or AAD. CTSH could be a potential therapeutic target to delay development/progression of type 1 diabetes.

Shared medical appointments (SMAs) for diabetes and group prenatal care (GPC) for pregnant patients, have emerged as innovative care delivery models. They have the potential to transform diabetes care by overcoming many of the time limitations of traditional one-on-one clinical visits. There is compelling evidence that SMAs improve glycemic control for non-pregnant patients with diabetes, GPC reduces Black/White health disparities in preterm birth, and Diabetes Group Prenatal Care increase postpartum glucose tolerance test uptake among patients with gestational diabetes mellitus. GPC models standout as one of few interventions that reduce racial health disparities, which we hypothesize occurs because they inadvertently exert their effect on both the patient and clinician through a 20+ hour meaningful shared experience. This Perspective explores the evidence for SMA and GPC in diabetes and pregnancy, theoretical underpinnings of the models, their potential to promote more equitable care, and future directions from my Perspective, as a high-risk obstetrician and 2019 ADA Pathway Accelerator award recipient.

MG53 is predominantly expressed in striated muscles. The role of MG53 in diabetes mellitus has been gradually elucidated but is still full of controversy. Some reports have indicated that MG53 is upregulated in animal models with metabolic disorders, and that muscle-specific MG53 upregulation is sufficient to induce whole-body insulin resistance and metabolic syndrome through targeting both the insulin receptor (IR) and IR substrate-1 (IRS-1) for ubiquitin-dependent degradation. Additionally, MG53 has been identified as a myokine/cardiokine that is secreted from striated muscles into the bloodstream and circulating MG53 has further been shown to trigger insulin resistance by binding to the extracellular domain of the IR, thereby allosterically inhibiting insulin signaling. Conversely, other studies have reported findings that contradict these results. Specifically, no significant change in MG53 expression in striated muscles or serum has been observed in diabetic models, and the MG53-mediated degradation of IRS-1 may be insufficient to induce insulin resistance due to the compensatory roles of other IRS subtypes. Furthermore, sustained elevation of MG53 levels in serum or systemic administration of recombinant human MG53 (rhMG53) has shown no impact on metabolic function. In this review, we will fully characterize these two disparate views, strive to provide critical insights into their contrasts and propose several specific experimental approaches that may yield additional evidence. Our goal is to encourage the scientific community to elucidate the effects of MG53 on metabolic diseases and the molecular mechanisms involved, thereby providing the theoretical basis for the treatment of metabolic diseases and the applications of rhMG53.

Dysregulation and loss of immune tolerance towards pancreatic β-cell autoantigens are features of type 1 diabetes (T1D). Until recently, life-long insulin injection was the only approved treatment for T1D, and this does not address the underlying disease pathology. Antigen-specific immunotherapy (ASI) seeks to restore tolerance and holds potential as a new therapeutic strategy for treating autoimmune diseases with well characterised antigens. Peptide ASI using processing independent CD4+ T-cell epitopes (PIPs) shows promising results in several autoimmune diseases. Here we successfully applied the principles of PIP design to the T1D autoantigen glutamate decarboxylase 65 (GAD65). Peptides spanning GAD65 predicted to be pan-HLA-DR binding were selected. Peptide P10 displayed enriched responses in peripheral blood mononuclear cells from people with T1D. The minimal epitope of the P10 peptide was fine mapped using T-cell hybridomas generated from HLA-DRB1*04:01 transgenic mice. This minimal epitope, P10Sol, was demonstrated to induce tolerance to the parent peptide in HLA-DRB1*04:01 transgenic mice using a novel activation-induced marker assay. Finally, we show that GAD65 P10Sol PIP is recognised by CD4+ T-cells from people with T1D who possess a range of HLA-DR alleles and can, therefore, be defined as a pan-DR binding peptide with therapeutic potential.

The gold standard for assessing the function of human islets or β-like cells derived from stem cells involves their engraftment under the kidney capsule of hyperglycemic, immunodeficient mice. Current models, such as Streptozotocin (STZ) treatment of severely immunodeficient mice or the NRG-Akita strain are limited due to unstable and variable hyperglycemia and/or high morbidity of these models. To address these limitations, we developed the IsletTester mouse via CRISPR-Cas9 mediated gene editing of glucokinase (Gck), the glucose sensor of the β-cells, directly in NSG zygotes. IsletTester mice are heterozygous for an Arg345->stop mutation in Gck and present with stable random hyperglycemia (∼250mg/dl; ∼14 mM), normal life span and fertility. We demonstrate the utility of this model through functional engraftment of both human islets and hESC-derived β-like cells. The IsletTester mouse will enable the study of human islet biology over time and under different physiological conditions and can provide a useful preclinical platform to determine the functionality of stem cell-derived islet products.

Glucose-stimulated beta-cells exhibit synchronized calcium dynamics across the islet that recruit beta-cells to enhance insulin secretion. Compared to calcium dynamics, the formation and cell-to-cell propagation of electrical signals within the islet are poorly characterized. To determine factors that influence the propagation of electrical activity across the islet underlying calcium oscillations and beta-cell synchronization, we used high-resolution CMOS multielectrode arrays (MEA) to measure voltage changes associated with the membrane potential of individual cells within intact C57BL6 mouse islets. We measured fast (milliseconds, spikes) and slow (seconds, waves) voltage dynamics. Single spike activity and wave signal velocity were both glucose-dependent, but only spike activity was influenced by NMDA receptor activation or inhibition. A repeated glucose stimulus revealed a highly responsive subset of cells in terms of spike activity. When islets were pretreated for 72 hours with glucolipotoxic medium, the wave velocity was significantly reduced. Network analysis confirmed that in response to glucolipotoxicity the synchrony of islet cells was affected due to slower propagating electrical waves and not due to altered spike activity. In summary, this approach provided novel insight regarding the propagation of electrical activity and the disruption of cell-to-cell communication due to excessive stimulation.

Thermogenesis of brown adipose tissues (BAT) provides metabolic benefits against pathological conditions such as Type 2 diabetes, obesity, cardiovascular diseases, and cancer. The thermogenic function of BAT relies on mitochondria, but whether mitochondrial remodeling is required for the beneficial effects of BAT remains unclear. We have recently identified FAM210A as a BAT-enriched mitochondrial protein essential for cold-induced thermogenesis through the modulation of OPA1-dependent cristae remodeling. Here we report a key role of FAM210A in the systemic response to high-fat diet (HFD). We discovered that HFD suppressed FAM210A expression, associated with excessive OPA1 cleavage in BAT. Ucp1-Cre-driven BAT-specific Fam210a knockout (Fam210aUKO) similarly elevates OPA1 cleavage, accompanied by whitening of BAT. When subjected to HFD, the Fam210aUKO mice gained similar fat mass as sibling control mice, but developed glucose intolerance, insulin resistance, and liver steatosis. The metabolic dysfunction was associated with an overall increased lipid content in both liver and BAT. Additionally, Fam210aUKO leads to inflammation in white adipose tissues. These data demonstrate that FAM210A in BAT is necessary for counteracting HFD-induced metabolic dysfunction but not obesity.

Glucose tolerance improves significantly upon consuming a second, identical meal later in the day (second meal phenomenon). We previously established that morning hyperinsulinemia primes the liver for increased afternoon hepatic glucose uptake (HGU). Although the route of insulin delivery is an important determinant of the mechanisms by which insulin regulates liver glucose metabolism (direct hepatic vs indirect insulin action), it is not known if insulin's delivery route affects the second meal response. To determine whether morning peripheral insulin delivery (as occurs clinically, i.e. subcutaneous) can enhance afternoon HGU, conscious dogs were treated in the morning with insulin delivered either via the portal vein or peripherally (leg vein), while glucose was infused to maintain euglycemia. Consequently, arterial insulin levels increased similarly in both groups, but relative hepatic insulin deficiency occurred with peripheral insulin delivery. In the afternoon, all animals were challenged with the same hyperinsulinemichyperglycemic clamp to simulate identical postprandial-like conditions. The substantial enhancement of HGU in the afternoon caused by morning portal vein insulin delivery was lost when insulin was delivered peripherally. This indicates that morning insulin does not cause the second meal phenomenon via its indirect actions on the liver, but rather through direct activation of hepatic insulin signaling.

Murine pancreatic endocrinogenesis has been extensively studied, but human data remain scarce due to limited sample availability. Here, we first built a large collection of human embryonic and fetal pancreases covering the first trimester of pregnancy to explore human endocrinogenesis. Using an experimental pipeline combining in toto staining, tissue clearing, and light-sheet fluorescence microscopy, we show that insulin+, glucagon+, and somatostatin+ cells appear simultaneously at Carnegie Stage (CS) 16. This contrasts with rodents where glucagon+ cells appear first, followed by insulin+ and finally somatostatin+ cells and highlights interspecies differences. We also detected bi-hormonal endocrine cells in 7 out of 9 human pancreases between CS16-18, which were no longer detected at later stages. We observed that cell distribution within human fetal islets resembles adult mouse islets, with a core of beta cells surrounded by alpha and delta cells, differing from a more complex arrangement in adult human islets. This, in connection with the small size of human fetal islets when compared to adult, suggests that adult human islets may form by fusion of pre-existing islets, in contrast to the mouse fission model. Together, our study provides a detailed and comprehensive description of the spatiotemporal dynamics of human pancreatic endocrinogenesis.

Resolving metabolic heterogeneity in patients with type 2 diabetes mellitus (T2DM) gives them access to precision medicine. Despite ethnic diversity in pathophysiological processes in individuals with T2DM, studies on subtypes of diabetes related to clinical characteristics in Asians are insufficient. This study aims to identify metabolic patterns in middle-aged patients with T2DM in Republic of Korea (Korea) and determine the incidence of diabetes-related complications according to patterns. We analyzed 6,603 patients with T2DM aged 30 to 64 who visited three centers of general hospital in Korea. Three metabolic patterns were derived: Obesity and Hypertension pattern (OH-P), Liver Function-related HyperGlycemia pattern (LFHG-P), and Decreased Kidney Function pattern (DKF-P). The highest tertile of the OH-P score was associated with an increased risk of peripheral vascular disease compared to the lowest tertile (HR = 1.26, 95% CI = 1.02-1.57). The highest tertile of the LFHG-P score was associated with an increased risk of myocardial infarction (HR = 1.79, 95% CI = 1.13-2.82) and atrial fibrillation (HR = 1.54, 95% CI = 1.07-2.23). No association with complications was found in the DKF-P. This study suggests the need for proper management and treatment according to metabolic patterns in patients with T2DM.

Roux-en-Y gastric bypass (RYGB) has been shown to inhibit β-cell apoptosis, but the underlying mechanisms are not yet fully understood. Cytochrome c oxidase subunit 6A2 (COX6A2) is expressed in β-cells. Here, we sought to investigate the role of COX6A2 in β-cell apoptosis, especially following RYGB. We found that RYGB significantly reduced β-cell apoptosis, accompanied by decreased COX6A2 expression in islets from diabetic Goto-Kakizaki (GK) rats. It is noteworthy that overexpression of COX6A2 promoted β-cell apoptosis, whereas COX6A2 deficiency suppressed it, suggesting the pro-apoptotic role of COX6A2 in β-cells. Mechanistically, increased COX6A2 interacted with and upregulated the expression of cyclophilin D (CypD), facilitating the release of cytochrome c from mitochondria to the cytoplasm, thereby promoting β-cell apoptosis. Furthermore, high-glucose-activated ChREBP epigenetically regulated COX6A2 expression by recruiting histone acetyltransferase p300 to augment histone H3 acetylation at the Cox6a2 promoter, a process inhibited by GLP-1 signaling. Given that RYGB enhances GLP-1 signaling, RYGB is likely to deactivate ChREBP by boosting GLP-1/PKA signaling, thereby reducing COX6A2 expression in islets from GK rats. These findings highlight the crucial role of the GLP-1/PKA/ChREBP axis-controlled COX6A2 in β-cell apoptosis, revealing a previously unrecognized mechanism underlying the reduction in β-cell apoptosis induced by RYGB.

Human embryonic stem cell (hESC)-derived pancreatic alpha and beta cells can be used to develop cell replacement therapies to treat diabetes. However, recent published differentiation protocols yield varying amounts of alpha and beta cells amidst heterogeneous cell populations. To visualize and isolate hESC-derived alpha and beta cells, we generated a GLUCAGON-2AmScarlet and INSULIN-2A-EGFP dual fluorescent reporter (INSEGFPGCGmScarlet) hESC line using CRISPR/Cas9. We established robust expression of EGFP and mScarlet fluorescent proteins in insulin- and glucagon-expressing cells respectively without compromising the differentiation or function of these cells. We also showed the insulin- and glucagon-expressing bihormonal population at the maturing endocrine cell stage (Stage 6) of our pancreatic islet differentiation lose insulin expression over time, while maintaining an alpha-like expression profile, suggesting these bihormonal cells are cell autonomously fated to become alpha-like cells. We also demonstrated this cell line can be used to monitor hESC-derived insulin- and glucagonexpressing cells, and hESC-derived islet morphology in vivo by transplanting them into the anterior chamber of the eye in mice. Together, the INSEGFPGCGmScarlet hESC line provides an efficient strategy for tracking populations of hESC-derived beta- and alpha-like cells.

Disease-causing variants in key immune homeostasis genes can lead to monogenic autoimmune diabetes. Some individuals carrying disease-causing variants do not develop autoimmune diabetes, even though they develop other autoimmune disease. We aimed to determine whether type 1 diabetes polygenic risk contributes to phenotypic presentation in monogenic autoimmune diabetes. We used a 67 SNP type 1 diabetes genetic risk score (T1D-GRS) to determine polygenic risk in 62 individuals with monogenic autoimmune diabetes and 180 non-autoimmune neonatal diabetes (NDM) controls. We used population-based controls (n=10,405) and individuals with type 1 diabetes (n=285) as a comparator. Individuals with monogenic autoimmune diabetes had higher T1D-GRSs compared to non-autoimmune NDM (mean 11.3 vs. 9.8; P=1.7×10-5) and controls (mean 10.3; P=7.5×10-6) but were markedly lower than type 1 diabetes (14.9; P= 3.3 × 10-21). These differences were explained by monogenic autoimmune diabetes cases having higher Class II HLA genetic risk, specifically from the DRB1*03:01-DQA1*05:01-DQB1*02:01 haplotype (DR3-DQ2) (P<0.01). In the presence of monogenic autoimmunity, the polygenic class II HLA susceptibility contributes to development of autoimmune diabetes. This suggests a role of class II HLA in targeting the dysregulated immune response towards the beta-cell.

Glucagon-like peptide 1 receptor (GLP-1R) agonists fail to reduce weight and improve glucose control in a sizable minority of people with type 2 diabetes. We hypothesized that stimulation of the hypothalamic-pituitary-adrenal (HPA) axis by GLP-1R agonists, thus inducing cortisol secretion, could explain this unresponsiveness to GLP-1R agonists. To assess the effects of GLP-1R agonist treatment on the HPA axis, we selected ten individuals with type 2 diabetes with (5 women/5 men) and nine without (4 women/5 men) an adequate response to GLP-1R agonists and used [68Ga]Ga-NODAGA-exendin-4 positron emission tomography (PET)/computed tomography (CT) to quantify GLP-1R expression in the pituitary. Oral glucose tolerance and 24 h urinary cortisol excretion was measured in all participants. Pituitary tracer uptake was observed in all participants with no significant difference between responders and non-responders. Pituitary tracer uptake correlated with the area under the curve for ACTH, urinary cortisol to creatinine ratio and age. Interestingly, men had higher pituitary tracer uptake than women. In conclusion, this study does not indicate a role for pituitary GLP-1R expression and HPA axis stimulation to explain the difference in treatment response to GLP-1R agonists among individuals with type 2 diabetes. The findings of substantial pituitary GLP-1R expression and the significant sex differences require further research.

The obesity diagnosis by body mass index (BMI) exhibits considerable interindividual heterogeneity in metabolic phenotypes and risk of developing type 2 diabetes (T2D). We investigated the association of proteomic signature of BMI and T2D and examined whether the proteomic signature of BMI improves prediction of T2D risk. This study included 41,427 adults in the UK Biobank who were free of T2D at baseline and had complete data on proteomics metrics assessed by antibody based Olink assay. The main exposure was a proteomic BMI score (pro-BMI score) calculated from 67 pre-identified plasma proteins associated with BMI. During a median follow-up of 13.7 years, 2,030 incident events of T2D were documented. We observed that a higher proteomic BMI (pro-BMI) score was significantly associated with a higher risk of T2D independent of actual BMI, waist-to-hip ratio, and polygenic risk score for BMI (hazard ratio (HR) comparing the highest with the lowest quartiles was 3.81, 95% CI, 3.08 - 4.71). Pro- BMI score significantly increased the C index when added to a reference model with age, sex, and BMI (C index change, 0.023 [95%CI, 0.018 to 0.027]). Proteomic signature of BMI is significantly associated with the risk of T2D independent of BMI, WHR and genetic susceptibility to obesity. When added to actual BMI, the proteomic signature of BMI provides significant but modest improvement in discrimination.