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.

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.

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.

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.

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.

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.

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.