Endurance exercise is widely recognized for its role in mitigating insulin resistance, yet the precise mechanisms remain unclear. In this Classics in Diabetes article, we revisit the article by Amati et al., "Skeletal Muscle Triglycerides, Diacylglycerols, and Ceramides in Insulin Resistance: Another Paradox in Endurance-Trained Athletes?" Published in the October 2011 issue of Diabetes, this article was among the first to highlight the nuanced roles of exercise-induced changes in bioactive lipids such as ceramide and diacylglycerol (DAG) in insulin signaling. The authors' groundbreaking work challenged some existing paradigms, revealing a more complex relationship between DAGs and insulin resistance than previously thought. Their findings helped lay the foundation for further exploration to unravel the intricate biochemical pathways through which exercise influences insulin sensitivity and metabolic health.

Diabetes leads to a more rapid development of diabetic cardiomyopathy (dbCM) and progression to heart failure in women than in men. Combination of high-fat diet (HFD) and freshly injected streptozotocin (STZ) has been widely used for diabetes induction; however, emerging data show that anomer-equilibrated STZ produces an early-onset and robust diabetes model. We designed a novel protocol using a combination of multiple doses of anomer-equilibrated STZ injections and HFD to develop a stable murine diabetes model featuring dbCM analogous to that in humans. Furthermore, we examined the effect of biological sex on the evolution of cardiometabolic dysfunction in diabetes. Our study included six experimental protocols (8 weeks) in male and female C57BL/6J mice (N = 109): fresh STZ + HFD, anomer-equilibrated STZ + HFD, HFD, fresh STZ, anomer-equilibrated STZ, and control diet + vehicle. Animals were characterized by extensive phenotyping in vivo and ex vivo. Anomer-equilibrated STZ + HFD led to induction of stable experimental murine diabetes characterized by impaired glucose homeostasis, cardiometabolic dysfunction, and altered metabolome of liver, skeletal muscle, kidney, and plasma. dbCM was more severe in female mice, including systolic dysfunction and reduced cardiac energy reserve. This study establishes a novel robust model of inducible murine diabetes and emphasizes the impact of biological sex on diabetes progression and severity.

CD4+ T cells from patients with type 1 diabetes (T1D) have a significant response to post-translationally modified (PTM) deamidated IA-2 peptides; autoantibodies to these PTM neoepitopes remain to be identified in T1D. We aimed to identify autoantibodies specifically targeting reported T-cell reactive, deamidated epitopes of IA-2 and explore their relationship with T1D development. Autoantibodies to deamidated IA-2 were specific to deamidated epitopes and were predominantly present during the late stages of T1D development, challenging the hypothesis that the loss of immune tolerance occurs via post-translational modification of islet antigens. Newly identified autoantibodies to deamidated IA-2 are new biomarkers of islet autoimmunity and have the potential to aid in T1D diagnosis.

Type 1 diabetes (T1D) is an autoimmune disease mediated by autoreactive T cells. Our studies indicate that CD4 T cells reactive to hybrid insulin peptides (HIPs) play a critical role in T-cell-mediated β-cell destruction. We have shown that HIPs form in human islets between fragments of the C-peptide and cleavage products of secretory granule proteins. To identify T-cell specificities contributing to T1D pathogenesis, we tested T-cell reactivity from T1D patients or healthy control individuals using an IFN-γ enzyme-linked immunosorbent spot assay against a library of 240 C-peptide HIPs. We observed elevated T-cell responses to peptide pools containing HIPs that form at the amino acid residues G15, A18, and L26 of C-peptide. In a second cohort of healthy control individuals, at-risk individuals, and T1D patients, T-cell reactivity to HIPs forming at these three residues was monitored. Results indicate that, prior to clinical onset of T1D, there were significantly elevated responses to multiple pools of HIPs, and the magnitude of T-cell reactivity to HIPs forming at residue A18 of the C-peptide was increased. Overall, our study identifies new T-cell specificities in at-risk individuals and indicates that T-cell reactivity to HIPs can be observed before T1D onset.

Cancer survivors who receive cisplatin chemotherapy have an increased risk of type 2 diabetes, but the underlying mechanisms remain unclear. The aim of this study was to investigate whether cisplatin impacts β-cell health and function, thereby contributing to increased type 2 diabetes risk in cancer survivors. In vivo and in vitro cisplatin exposure dysregulated insulin secretion in male and female mice. In vitro cisplatin exposure reduced oxygen consumption, impaired β-cell exocytotic capacity, and altered expression of genes within the insulin secretion pathway in mouse islets. Understanding how chemotherapeutic drugs cause β-cell injury is critical for designing targeted interventions to reduce the risk of cancer survivors developing type 2 diabetes after treatment.

Clonal hematopoiesis of indeterminate potential (CHIP) is an age-related disorder that is associated with macrovascular diseases, such as coronary artery disease and stroke. However, the effects of CHIP on microvascular complication have not been explored in individuals with type 2 diabetes. We wanted to determine whether CHIP is associated with diabetic microvascular complications (DMCs). CHIP was associated with a high risk of DMCs, specifically, diabetic retinopathy and diabetic kidney disease, but not diabetic neuropathy. Gene-specific analyses suggested that some driver genes were associated with risk of developing DMCs. These findings indicated that CHIP may represent a novel risk factor for DMCs among individuals with type 2 diabetes, distinct from traditional risk factors, which may have implications for prevention and management of DMCs.

Diabetes is a major risk factor for cardiovascular diseases. The mechanisms of hyperglycemia-induced endothelial dysfunction have been elusive. We found that inositol hexakisphosphate kinase 1 (IP6K1) mediates hyperglycemia-induced endothelial senescence by switching liver kinase B1 (LKB1) activation of the AMPK pathway to activation of the p53 pathway. Hyperglycemia upregulates IP6K1, which stabilizes LKB1 by disrupting Hsp/Hsc70 and carboxyl terminus of Hsc70-interacting protein-mediated LKB1 degradation but suppresses LKB1-dependent AMPK activation. Elevated LKB1 binds more to p53, resulting in p53-dependent endothelial senescence. Endothelial cell-specific deletion of IP6K1 attenuates, whereas endothelial cell-specific overexpression of IP6K1 exaggerates, hyperglycemia-induced endothelial senescence.

Impaired cardiac microvascular function is a significant contributor to diabetic cardiomyopathy. Rnd3 expression is notably downregulated in cardiac microvascular endothelial cells under diabetic conditions. Rnd3 overexpression mitigates diabetic myocardial microvascular injury and improves cardiac function through the Rock1/myosin light chain signaling pathway. Rnd3 facilitates the recruitment and interaction with Trim40 to promote Rock1 ubiquitination, thereby preserving endothelial barrier integrity in the diabetic heart.

Intragastric overfeeding reveals insights into the homeostatic recovery from experimental weight gain. Protection against short-term, overfeeding-induced weight gain primarily involves a profound reduction in food intake and possibly an adaptive increase in energy expenditure. UCP1-mediated thermogenesis is not essential for homeostatic protection against short-term, overfeeding-induced weight gain.

New research builds on previous findings that JMJD8 mediates insulin resistance by promoting adipocyte hypertrophy. We identified PLIN2 as a binding partner of JMJD8 using proteomics approaches. This study reveals a physical interaction between JMJD8 and PLIN2, which plays a crucial role in driving adipocyte hypertrophy and insulin resistance. JMJD8 suppresses fasting-induced lipophagy and reduces energy production by inhibiting PLIN2 phosphorylation. These findings highlight the importance of JMJD8 and PLIN2 in regulating lipid droplet homeostasis and suggest a potential mechanism for controlling fat mobilization during energy deprivation.

Pancreatic cystic changes in adults are increasingly identified through advanced cross-sectional imaging. However, the impact of initial/intralobular epithelial remodeling on the local β-cell population remains unclear. In this study, we examined 10 human cadaveric donor pancreases (tail and body regions) via integration of stereomicroscopy, clinical hematoxylin and eosin histology, and three-dimensional (3D) immunohistochemistry, identifying 36 microcysts (size: 1.22 ± 0.56 mm) alongside 54 low-grade pancreatic intraepithelial neoplasias (positive control of epithelial remodeling; size: 2.42 ± 1.05 mm). Both conditions exhibited significant increases in cytokeratin 7 (CK7) and insulin immunoreactive signals compared with normal lobules. Importantly, despite luminal contents of microcysts causing false positives (autofluorescence) in fluorescence imaging, the defined cystic epithelium showed distinct duct-β-cell associations-including β-cells in the epithelium and duct-β-cell clusters-visualized via antifade 3D/Airyscan superresolution imaging in the high-refractive-index polymer. The periluminal β-cells displayed insulin-positive vesicles residing near the basal domain, while the CK7+ cytokeratins in duct cells accumulated in the apical domain, underlining polarized tissue and cellular organizations. Overall, in microcyst formation, we demonstrate local and associated pancreatic exocrine and endocrine tissue remodeling. Because artifacts are a concern in β-cell investigations in a novel environment, our work using 3D-labeled human pancreas with cytokeratin and vesicle resolving powers provides a robust approach for characterizing the duct-β-cell association in a clinically relevant setting.

Approximately one out of two patients with diabetes develops diabetic neuropathy; of these, 20% experience neuropathic pain. Risk factors for neuropathic pain are largely unknown; however, DNA methylation was recently associated with neuropathies and degeneration of nerve fibers. The aim of this work was to describe the DNA methylation signature and identify genes associated with neuropathic pain in type 2 diabetes mellitus (T2DM). We discovered distinct DNA methylation signatures that differentiate painful and painless neuropathy phenotypes associated with T2DM and identified genes with potential as therapeutic targets for neuropathic pain, such as GCH1, MYT1L, and MED16. This work can serve as reference hallmark for future studies on painful diabetic neuropathy and other chronic pain conditions.

Postprandial hypotension (PPH) occurs frequently in type 2 diabetes. Metformin has cardiovascular effects independent of its glucose-lowering capacity, which may modulate the risk of PPH. We investigated the effects of metformin on postprandial blood pressure, including PPH events, heart rate, glucose, insulin, glucagon-like peptide 1 (GLP-1), and gastric emptying, in individuals with type 2 diabetes. Metformin attenuated postprandial decrease in blood pressure and reduced PPH events, in association with augmentation of plasma GLP-1, slowed gastric emptying, and increased heart rate, in type 2 diabetes. These findings establish novel cardiovascular effects of metformin that may mitigate the risk of PPH in type 2 diabetes.

Identification of circulating proteins that may play a role in the pathogenesis of type 1 diabetes can provide promising targets for biomarker and drug target identification. Supported by multiple lines of evidence, circulating abundances of CTSH, IL27RA, SIRPG, and PGM1 were associated with the risk of type 1 diabetes. Tissues and cell types with enrichment of target protein-coding gene expression were identified. CTSH, IL27RA, SIRPG, and PGM1 may be explored as biomarkers or drug targets for type 1 diabetes.

Renin-angiotensin system (RAS) activation plays an important role in the progression of diabetic kidney disease (DKD). However, systemic RAS blockade alone is insufficient to reverse DKD progression. We hypothesized that intrarenal renin-angiotensin system (iRAS) activation plays a crucial role in the progression of DKD. We sought to elucidate the role of the iRAS in DKD progression. Selective deletion of angiotensinogen in renal tubules ameliorated the pathological features of DKD. Our study indicates that iRAS inactivation may be a potential approach for preventing DKD disease severity and its progression.

The COVID-19 pandemic has profoundly affected human health; however, the mechanisms underlying its impact on metabolic and vascular systems remain incompletely understood. Clinical evidence suggests that SARS-CoV-2 directly disrupts vascular homeostasis, with perfusion abnormalities observed in various tissues. The pancreatic islet, a key endocrine miniorgan reliant on its microvasculature for optimal function, may be particularly vulnerable. Studies have proposed a link between SARS-CoV-2 infection and islet dysfunction, but the mechanisms remain unclear. Here, we investigated how SARS-CoV-2 spike S1 protein affects human islet microvascular function. Using confocal microscopy and living pancreas slices from organ donors without diabetes, we show that a SARS-CoV-2 spike S1 recombinant protein activates pericytes, key regulators of islet capillary diameter and β-cell function, and induces capillary constriction. These effects are driven by a loss of ACE2 from pericytes' plasma membrane, impairing ACE2 activity and increasing local angiotensin II levels. Our findings highlight islet pericyte dysfunction as a potential contributor to the diabetogenic effects of SARS-CoV-2 and offer new insights into the mechanisms linking COVID-19, vascular dysfunction, and diabetes.

There is an increasing need for new biomarkers to improve prediction of chronic kidney disease (CKD) in individuals with type 2 diabetes (T2D). We aimed to identify blood-based epigenetic biomarkers associated with incident CKD and develop a methylation risk score (MRS) predicting CKD in individuals with newly diagnosed T2D. DNA methylation was analyzed epigenome wide in blood from 487 individuals with newly diagnosed T2D, of whom 88 developed CKD during an 11.5-year follow-up. Weighted Cox regression was used to associate methylation with incident CKD. Weighted logistic models and cross-validation (k = 5) were performed to test whether the MRS could predict CKD. Methylation at 37 sites was associated with CKD development based on a false discovery rate of <5% and absolute methylation differences of ≥5% between individuals with incident CKD and those free of CKD during follow-up. Notably, 15 genes annotated to these sites, e.g., TGFBI, SHISA3, and SLC43A2 (encoding LAT4), have been linked to CKD or related risk factors, including blood pressure, BMI, and estimated glomerular filtration rate. Using an MRS including 37 sites and cross-validation for prediction of CKD, we generated receiver operating characteristic (ROC) curves with an area under the curve (AUC) of 0.82 for the MRS and AUC of 0.87 for the combination of MRS and clinical factors. Importantly, ROC curves including the MRS had significantly better AUCs versus the one only including clinical factors (AUC = 0.72). The combined epigenetic biomarker had high accuracy in identifying individuals free of future CKD (negative predictive value of 94.6%). We discovered a high-performance epigenetic biomarker for predicting CKD, encouraging its potential role in precision medicine, risk stratification, and targeted prevention in T2D.

Advancements in fundus imaging are revealing disruptions in the neurovascular unit in diabetic retinopathy (DR). In the era of anti-vascular endothelial growth factor treatment, a thorough characterization of neurodegeneration is imperative until patients with DR are sufficiently treated. Here, we demonstrate that extracellular mitochondria exacerbate retinal pigment epithelium (RPE) degeneration and inflammation in DR. Extracellular mitochondria increased in the vitreous of patients with DR and were associated with visual impairment but not with proliferative diabetic retinopathy or diabetic macular edema. Animal experiments demonstrated detrimental effects of extracellular mitochondria on RPE and photoreceptors. Lysosomal cell death induced by extracellular mitochondria in RPE cells required mitochondrial DNA but not its pattern recognition receptors. Furthermore, biochemical screening identified candidates for DNA receptors. Among them, DNA-dependent protein kinase was necessary for extracellular mitochondria-induced cell death in both in vitro and in vivo experiments. Extracellular mitochondria further induced interleukin-1β and tumor necrosis factor-α expression in RPE cells in a Toll-like receptor 9-dependent manner. RNA sequencing suggested that extracellular mitochondria exacerbate inflammation by promoting the proliferation and migration of macrophages, at least in part. In summary, extracellular mitochondria are designated as a novel exacerbating factor of RPE degeneration in DR.

Little is known about the population-based mismatch between phenotypic and genetic BMI (BMI-PGM) and its association with type 2 diabetes. We therefore used data from the China Kadoorie Biobank and UK Biobank and calculated BMI-PGM for each participant as the difference between the percentile for adjusted BMI at baseline and the percentile for adjusted polygenic risk score for BMI. Participants were categorized into discordantly low (BMI-PGM < the first quartile), concordant (the first quartile ≤ BMI-PGM < the third quartile), and discordantly high (BMI-PGM ≥ the third quartile) groups. We calculated adjusted hazard ratios (HRs) for the association of BMI-PGM and type 2 diabetes using Cox proportional hazard models in each cohort, and combined HRs using random-effects meta-analyses. During a median follow-up of 12 years for both cohorts, BMI-PGM was associated with the risk of type 2 diabetes, with the discordantly low group showing reduced risk and the discordantly high group showing elevated risk compared with the concordant group, independent of BMI and other conventional risk factors. In addition, normal-weight individuals with discordantly high BMI-PGM faced a higher risk of type 2 diabetes than overweight individuals. These findings suggest that BMI-PGM may play a potential role in reassessing the risk of type 2 diabetes, particularly among normal-weight populations.

Loss-of-function mutations in ATP-sensitive potassium (KATP) channels cause hyperexcitability and insulin hypersecretion, resulting in congenital hyperinsulinism (CHI). Paradoxically, despite the initial insulin hypersecretion, many CHI cases, as well as KATP knockout (KO) animals, eventually "crossover" to undersecretion and even diabetes. Here, we confirm that Sur1 KO islets exhibit higher intracellular concentration of calcium ion ([Ca2+]i) at all concentrations of glucose but show decreased glucose-stimulated insulin secretion. However, when [Ca2+]i is artificially elevated by increasing extracellular [Ca2+], insulin secretion from Sur1 KO islets increases to the same levels as in wild-type (WT) islets. This indicates that a right-shift in [Ca2+]i dependence of insulin secretion, rather than loss of insulin content or intrinsic secretability, is the primary cause for the crossover. Chronic pharmacological inhibition of KATP channel activity by slow release of glibenclamide in pellet-implanted mice causes a very similar crossover to glucose intolerance and impaired insulin secretion seen in Sur1 KO animals. Whole-islet and single-cell transcriptomic analysis reveal markedly reduced Trpm5 in both conditions. Glibenclamide pellet-implanted Trpm5 KO mice also exhibited significant glucose intolerance. However, this was not as severe as in WT animals, which suggests decreased expression of Trpm5 may play a small role in the disruption of insulin secretion with KATP loss.