Wolfram syndrome 1 (WS1) is a rare genetic disorder caused by WFS1 variants that disrupt wolframin, an endoplasmic reticulum-associated protein essential for cellular stress responses, Ca2+ homeostasis, and autophagy. Here, we investigated how the c.316-1G>A and c.757A>T WFS1 mutations, which yield partially functional wolframin, affect the molecular functions of β-cells and explored the therapeutic potential of the glucagon-like peptide 1 receptor (GLP-1R) agonist liraglutide. Pancreatic β-cells obtained from patient-derived induced pluripotent stem cells (iPSCs) carrying this WFS1 variant exhibited reduced insulin processing and impaired secretory granule maturation, as evidenced by proinsulin accumulation and decreased prohormone convertase PC1/3. Moreover, they exhibited dysregulated Ca2+ fluxes due to altered transcription of Ca2+-related genes, including CACNA1D, and significantly reduced SNAP25 levels, leading to uncoordinated oscillations and poor glucose responsiveness. Affected cells also showed increased autophagic flux and heightened susceptibility to inflammatory cytokine-induced apoptosis. Notably, liraglutide treatment rescued these defects by normalizing Ca2+ handling, enhancing insulin processing and secretion, and reducing apoptosis, likely through modulation of the unfolded protein response. These findings underscore the importance of defining mutation-specific dysfunctions in WS1 and support targeting the GLP-1/GLP-1R axis as a therapeutic strategy.

Gestational diabetes mellitus (GDM) is one of the most common medical complications of pregnancy. It is generally defined as glucose intolerance with onset or first recognition during pregnancy. The pathogenesis of GDM has long been attributed to inadequate pancreatic β-cell compensation for the physiological insulin resistance of pregnancy. This defect is thought to resolve after pregnancy but become manifest in later life as an increased risk of diabetes. Examination of mechanisms underlying GDM does not support this commonly held picture. In this Perspective, we present evidence that, like diabetes outside of pregnancy, GDM has no single etiology. It results from multiple causes of a common physiological manifestation, inadequate β-cell function, which leads to a common clinical manifestation, elevated glucose levels. We provide evidence that GDM often represents detection of chronic and progressive β-cell dysfunction that is temporally but not mechanistically related to pregnancy. We provide detailed characterization of the β-cell defect in one high-risk group, Hispanic Americans. Finally, we address some of the clinical and research implications of these findings.

Since little is known about the disposition index (DI) in autoantibody-positive individuals, we have assessed whether DI has a similar association between insulin secretion and sensitivity to the association observed in other populations. In TrialNet Pathway to Prevention (TNPTP; n = 6,620) and Diabetes Prevention Trial-Type 1 (DPT-1; n = 704) study participants, two secretion-sensitivity pairs, each representing a DI, were analyzed cross-sectionally at baseline: area under the curve (AUC) C-peptide/AUC glucose (AUC ratio) and Matsuda index (MI) from TNPTP oral glucose tolerance tests (oral DI), first-phase insulin response (FPIR), and 1 / fasting insulin (1/FI) from DPT-1 from intravenous glucose tolerance tests (DI). Participants were followed for progression to type 1 diabetes (T1D). Within the normal and diabetes glucose ranges, associations of AUC ratio with MI in TNPTP and FPIR with 1/FI in DPT-1 had inverse curvilinear patterns with convexities to the origin. After logarithmic transformations to linearize the secretion and sensitivity measures, the inverse slope was steeper for the diabetes range (P < 0.0001). In a Cox regression model including the AUC ratio and MI as variables and another model including FPIR and 1/FI, the interaction terms of secretion × sensitivity (i.e., the DI/oral DI) predicted stage 3 T1D in both (P < 0.0001). The DI remained significantly predictive (P < 0.0001) when the DPT-1 risk score was added as a covariate in regression models. In autoantibody-positive populations, insulin secretion is inversely related to sensitivity in a quasi-hyperbolic relationship in normal and diabetes ranges of glucose. The DI can be represented by a statistical and physiologic interaction between secretion and sensitivity that is predictive of stage 3 T1D.

Glucagon stimulates hepatic glucose production, in part by promoting the uptake and catabolism of amino acids. Inhibition of the liver glucagon receptor (GCGR) results in elevated plasma amino acids, which triggers the proliferation of pancreatic α-cells, forming a liver-α-cell loop. This study aims to delineate hepatic signaling molecules downstream of GCGR that mediate the liver-α-cell loop. We knocked down liver GCGR, its G-coupled protein GNAS, and two GNAS downstream effectors, PKA and EPAC2 (RAPGEF4). Mice with GCGR, GNAS, and PKA knockdown had similar suppression of hepatic amino acid catabolism genes, hyperaminoacidemia, and α-cell hyperplasia, but those with EPAC2 knockdown did not. We then demonstrated that activating liver PKA was sufficient to reverse hyperaminoacidemia and α-cell hyperplasia caused by GCGR blockade. These results suggest that liver GCGR signals through PKA to control amino acid metabolism and that hepatic PKA plays a critical role in the liver-α-cell loop.

Patients with diabetes are at an increased risk of diabetic cardiomyopathy (DCM) and acute myocardial infarction (AMI). Protecting the heart against AMI is more challenging in DCM than in nondiabetic hearts. We investigated whether intravenous (i.v.) atorvastatin administration during AMI exerts cardioprotection in DCM as seen in nondiabetic hearts. Sprague-Dawley rats were divided into streptozotocin-induced DCM and normoglycemic control groups. Our model of DCM rats exhibited interstitial fibrosis and cardiac dysfunction at 5 weeks. At this time point, all animals underwent AMI induction (coronary ligation for 45 min), receiving i.v. atorvastatin or vehicle during ischemia. Animals were reperfused and sacrificed 24 h later for myocardial infarct size analysis and cardiac tissue sampling. Echocardiography was performed. DCM vehicle rats had larger infarcts than normoglycemic vehicle-treated animals at a comparable area-at-risk. Intravenous atorvastatin reduced infarct size and preserved systolic function in both groups. Compared with vehicle animals, i.v. atorvastatin inhibited RhoA membrane translocation, induced AMPK phosphorylation, prevented apoptosis execution, and improved cardiac remodelling in the infarcted heart of both groups, whereas innate immune cell infiltration was further reduced in i.v. atorvastatin-treated DCM animals. The proven cardioprotective effectiveness of this i.v. statin formulation in the presence of DCM warrants its further development into a clinically therapeutic option.

Recent evidence has shown that adipose tissue eventually develops fibrosis through complex cellular cross talk. Although advances in single-cell transcriptomics have provided new insights into cell diversity during this process, little is known about the interactions among the distinct cell types. In this study, we used single-cell analytical approaches to investigate cell-to-cell communications between macrophages and fibroblasts in the adipose tissue of diet-induced obese mice. Spatial transcriptomics was used to understand local cellular interaction within crown-like structures (CLS), a characteristic histological feature of adipose tissue in obesity driving inflammation and fibrosis. Macrophages and fibroblasts were divided into several subclusters that appeared to interact more intensely and complexly with the degree of obesity. Besides previously reported lipid-associated macrophages (LAMs), we found a small subcluster expressing macrophage-inducible C-type lectin (Mincle), specifically localizing to CLS. Mincle signaling increased the expression of oncostatin M (Osm), suppressing collagen gene expression in adipose tissue fibroblasts. Consistent with these findings, Osm deficiency in immune cells enhanced obesity-induced adipose tissue fibrosis in vivo. Moreover, OSM expression was positively correlated with MINCLE expression in human adipose tissue during obesity. Our results suggest that Osm secreted by Mincle-expressing macrophages is involved in dynamic adipose tissue remodeling in the proximity of CLS.

Diabetic peripheral neuropathy (DPN) is a common diabetes complication with no currently available curative treatments. Here, we demonstrated that the protein level of G-protein-coupled receptor 40 (GPR40) is significantly repressed in the sciatic nerves (SNs) of DPN patients, as well as in the peripheral nerves, including dorsal root ganglia (DRG) and SNs, of streptozotocin-induced type 1 diabetic mice and BKS Cg-m+/+Lepr db/J (db/db) type 2 diabetic mice. We identified that amlodipine besylate (AB), a first-line clinical antihypertensive drug, is a GPR40 agonist capable of alleviating DPN-like pathologies in mice. These pathologies include neurological damage, destruction of myelin sheath structures, vascular injury, loss of intraepidermal nerve fibers, and impaired neurite outgrowth in DRG neurons. To elucidate the underlying mechanisms, we generated the DPN mice with GPR40-specific knockdown in SN and DRG tissues using adeno-associated virus 8-GPR40-RNAi. Mechanistically, AB attenuated inflammatory responses via the GPR40/β-arrestin2/NLRP3 pathway and ameliorated mitochondrial dysfunction through the GPR40/LKB1/AMPK/SIRT1/PGC-1α pathway in DPN mice, which were all further validated in primary human Schwann cells. Additionally, AB suppressed the cross talk between Schwann cells and endothelial cells/DRG neurons in DPN mice. Collectively, our findings highlight the potential of AB for the treatment of DPN.

The association between KCNJ5 mutations and the risk of developing new-onset diabetes (NOD) in patients with unilateral primary aldosteronism (uPA) remains underexplored. To investigate this association, we conducted a longitudinal study using data from the Taiwan Primary Aldosteronism Investigation database. Our sample included 360 patients with uPA who underwent adrenalectomy between 2012 and 2017, 191 (53.1%) of whom had KCNJ5 mutations in their adrenal adenomas. We found that patients with uPA harboring KCNJ5 mutations had a higher rate of complete clinical success (69.5% vs. 43.8%; P < 0.01) and complete biochemical success (93.8% vs. 86.6%; P = 0.04) compared with those without KCNJ5 mutations at 6 months to 1 year after adrenalectomy. Over an average follow-up period of 8.5 years, multivariate Cox regression analysis revealed that patients with uPA with KCNJ5 mutations had a significantly lower risk of developing NOD (hazard ratio [HR] 0.41; 95% CI 0.17-0.996; P = 0.049). Additionally, we identified higher BMI (HR 1.23; 95% CI 1.11-1.37; P < 0.01) and lower estimated glomerular filtration rate (eGFR; HR 0.98; 95% CI 0.97-0.99; P = 0.01) as potential predictors of NOD based on baseline characteristics. The association between patients with uPA without KCNJ5 mutations and higher incidence of NOD was less pronounced in subgroups characterized by younger age, higher BMI, higher eGFR, and lower potassium levels. In conclusion, patients with uPA without KCNJ5 mutations had a higher incidence of NOD, with 13.6% affected during long-term follow-up. Our findings suggest that patients with uPA without KCNJ5 mutations may require more frequent follow-up for NOD after adrenalectomy.

Diabetic neuropathic pain is associated with elevated plasma levels of methylglyoxal (MGO). MGO is a metabolite of glycolysis that causes pain hypersensitivity in mice by stimulating the phosphorylation of eukaryotic initiation factor 2α (p-eIF2α) and subsequently activating the integrated stress response (ISR). We first established that Zucker diabetic fatty rats have enhanced MGO signaling, engage ISR, and develop pain hypersensitivity. Since nuclear factor erythroid 2-related factor 2 (Nrf2) regulates the expression of antioxidant proteins that neutralize MGO, we hypothesized that fumarates, like diroximel fumarate (DRF), will stimulate Nrf2 signaling, and prevent MGO-induced ISR and pain hypersensitivity. DRF (100 mg/kg) treated animals were protected from developing MGO (20 ng) induced mechanical and cold hypersensitivity. Mechanistically, DRF treatment protected against MGO-induced increase in p-eIF2α levels in the sciatic nerve and reduced loss of intraepidermal nerve fiber density. Using Nrf2 knockout mice, we demonstrate that Nrf2 is necessary for the antinociceptive effects of DRF. Cotreatment of MGO (1 µmol/L) with monomethyl fumarate (10, 20, and 50 µmol/L), the active metabolite of DRF, prevented ISR in both mouse and human dorsal root ganglia neurons. Our data show that targeting Nrf2 with DRF is a strategy to potentially alleviate pain associated with elevated MGO levels.

Insulin resistance, a hallmark of type 2 diabetes, accelerates muscle breakdown and impairs energy metabolism. However, the role of ubiquitin specific peptidase 2 (USP2), a key regulator of insulin resistance, in sarcopenia remains unclear. Peroxisome proliferator-activated receptor γ (PPAR-γ) plays a critical role in regulating muscle atrophy. The role of deubiquitinase USP2 in mitigating muscle atrophy was investigated. Our findings revealed reduced USP2 expression in skeletal muscles of patients with type 2 diabetes. In mouse models of diabetes- and dexamethasone (DEX)-induced muscle atrophy, USP2 expression was downregulated in skeletal muscles. Usp2 knockout exacerbated muscle loss and functional impairment induced by diabetes or DEX. Moreover, skeletal muscle-specific Usp2 knockout further aggravated muscle loss and functional impairment induced by diabetes. Local injection of adeno-associated virus-Usp2 into the gastrocnemius muscles of diabetic mice increased muscle mass and improved skeletal muscle performance and endurance. It enhanced insulin sensitivity in diabetic mice, shown by lower fasting serum glucose and insulin levels and better glucose tolerance. Mechanistic analysis showed USP2 directly interacted with PPAR-γ by deubiquitinating it, stabilizing its protein levels, enhancing insulin signaling and sensitivity, and maintaining muscle mass. Loss of PPAR-γ abolishes the regulatory effects of USP2 on insulin sensitivity and muscle atrophy. MYOD1 activates USP2 transcription by binding to its promoter region. This study demonstrates the protective role of USP2 in mitigating muscle atrophy by stabilizing PPAR-γ through deubiquitination, particularly in models of diabetic and DEX-induced muscle atrophy. Targeting the USP2-PPAR-γ axis may offer promising therapeutic strategies for metabolic disorders and sarcopenia.

An understanding of cell interactions is needed to identify therapeutic targets for diabetic cutaneous ulcers. We explored extracellular vesicles after treatment with advanced glycation end products (AGEs-EVs) derived from macrophages that can suppress diabetic cutaneous wound healing. We found that a novel miRNA enriched in AGEs-EVs (miR-ERIA) suppresses the migration and tube formation of vascular endothelial cells by targeting helicase with zinc finger 2. miR-ERIA offers a potential therapeutic target for diabetic cutaneous ulcers.

Homeobox C4 (HOXC4) links metabolic pathways and correlates inversely with mouse body weight and positively with Ucp1 expression in mouse adipose tissue. Gain- and loss-of-function experiments in mice demonstrated HOXC4's essential role in promoting adipose thermogenesis and providing metabolic benefits. HOXC4 interacts with the nuclear receptor coactivator 1 cofactor via its hexapeptide motif to activate Ucp1 transcription, revealing a novel mechanism of thermogenic gene regulation.

Genetic screens were performed across PPARG to study how disruptive mutations across the full coding sequence affect function. An alternative translational start site in PPARG generates a truncated isoform, peroxisome proliferator-activated receptor γ (PPARγ) M135, which lacks the N-terminal activation function 1 (AF-1) domain and shows increased agonist-induced transactivation of target genes. In human carriers of rare PPARG variants, AF-1 domain-disrupting genetic variants increase agonist-induced PPARγ activity and decrease metabolic syndrome severity. Targeting the AF-1 domain is a potential therapeutic strategy for insulin sensitization.

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.