Diabetic corneal neuropathy (DCN) is a common complication of diabetes. However, there are very limited therapeutic options. We investigated the effects of a peroxisome proliferator-activated receptor-α (PPAR-α) agonist, fenofibrate, on 30 patients (60 eyes) with type 2 diabetes. On in vivo confocal microscopy evaluation, there was significant stimulation of corneal nerve regeneration and a reduction in nerve edema after 30 days of oral fenofibrate treatment, as evidenced by significant improvement in corneal nerve fiber density (CNFD) and corneal nerve fiber width, respectively. Corneal epithelial cell morphology also significantly improved in cell circularity. Upon clinical examination, fenofibrate significantly improved patients' neuropathic ocular surface status by increasing tear breakup time along with a reduction of corneal and conjunctival punctate keratopathy. Tear substance P (SP) concentrations significantly increased after treatment, suggesting an amelioration of ocular surface neuroinflammation. The changes in tear SP concentrations was also significantly associated with improvement in CNFD. Quantitative proteomic analysis demonstrated that fenofibrate significantly upregulated and modulated the neurotrophin signaling pathway and linolenic acid, cholesterol, and fat metabolism. Complement cascades, neutrophil reactions, and platelet activation were also significantly suppressed. Our results showed that fenofibrate could potentially be a novel treatment for patients with DCN.

Sedentary people have insulin resistance in their skeletal muscle, but whether this also occurs in fat cells was unknown. Insulin inhibition of hydrolysis of triglycerides (antilipolysis) and stimulation of triglyceride formation (lipogenesis) were investigated in subcutaneous fat cells from 204 sedentary and 336 physically active subjects. Insulin responsiveness (maximum hormone effect) and sensitivity (half-maximal effective concentration) were determined. In 69 women, hyperinsulinemia-induced circulating fatty acid levels were measured. In 128 women, adipose gene expression was analyzed. Responsiveness of insulin for antilipolysis (60% inhibition) and lipogenesis (twofold stimulation) were similar between sedentary and active subjects. Sensitivity for both measures decreased ˜10-fold in sedentary subjects (P < 0.01). However, upon multiple regression analysis, only the association between antilipolysis sensitivity and physical activity remained significant when adjusting for BMI, age, sex, waist-to-hip ratio, fat-cell size, and cardiometabolic disorders. Fatty acid levels decreased following hyperinsulinemia but remained higher in sedentary compared with active women (P = 0.01). mRNA expression of insulin receptor and its substrates 1 and 2 was decreased in sedentary subjects. In conclusion, while the maximum effect is preserved, sensitivity to insulin's antilipolytic effect in subcutaneous fat cells is selectively lower in sedentary subjects.

Despite decades of scientific effort, diabetes continues to represent an incredibly complex and difficult disease to treat. This is due in large part to the multifactorial nature of disease onset and progression and the multiple organ systems affected. An increasing body of scientific evidence indicates that a key mediator of diabetes progression is NRF2, a critical transcription factor that regulates redox, protein, and metabolic homeostasis. Importantly, while experimental studies have confirmed the critical nature of proper NRF2 function in preventing the onset of diabetic outcomes, we have only just begun to scratch the surface of understanding the mechanisms by which NRF2 modulates diabetes progression, particularly across different causative contexts. One reason for this is the contradictory nature of the current literature, which can often be accredited to model discrepancies, as well as whether NRF2 is activated in an acute or chronic manner. Furthermore, despite therapeutic promise, there are no current NRF2 activators in clinical trials for the treatment of patients with diabetes. In this review, we briefly introduce the transcriptional programs regulated by NRF2 as well as how NRF2 itself is regulated. We also review the current literature regarding NRF2 modulation of diabetic phenotypes across the different diabetes subtypes, including a brief discussion of contradictory results, as well as what is needed to progress the NRF2 diabetes field forward.

The exon copy number variant in the haptoglobin gene is associated with cardiovascular and kidney disease. For stroke, previous research is inconclusive. We aimed to study the relationship between the haptoglobin Hp1/2 genotype and stroke in individuals with type 1 diabetes from the Finnish Diabetic Nephropathy Study. We included two partially overlapping cohorts: one with haptoglobin genotypes determined using genotyping for 179 individuals with stroke and 517 matched control subjects, and the other using haptoglobin genotype imputation for a larger cohort of 500 individuals with stroke and 3,806 individuals without stroke. We observed no difference in the Hp1-1, Hp2-1, and Hp2-2 genotype frequencies between individuals with or without stroke, neither in the genotyping nor the imputation cohorts. Haptoglobin genotypes were also not associated with the ischemic or hemorrhagic stroke subtypes. In our imputed haptoglobin cohort, 61% of individuals with stroke died during follow-up. However, the risk of death was not related to the haptoglobin genotype. Diabetic kidney disease and cardiovascular events were common in the cohort, but the haptoglobin genotypes were not associated with stroke when stratified by these complications. To conclude, the Hp1/2 genotypes did not affect the risk of stroke or survival after stroke in our cohort with type 1 diabetes.

Preferential energy storage in subcutaneous adipose tissue (SAT) confers protection against obesity-induced pathophysiology in females. Females also exhibit distinct immunological responses, relative to males. These differences are often attributed to sex hormones, but reciprocal interactions between metabolism, immunity, and gonadal steroids remain poorly understood. We systematically characterized adipose tissue hypertrophy, sex steroids, and inflammation in male and female mice after increasing durations of high-fat diet (HFD)-induced obesity. After observing that sex differences in adipose tissue distribution before HFD were correlated with lasting protection against inflammation in females, we hypothesized that a priori differences in the ratio of subcutaneous to visceral fat might mediate this relationship. To test this, male and female mice underwent SAT lipectomy (LPX) or sham surgery before HFD challenge, followed by analysis of glial reactivity, adipose tissue inflammation, and reproductive steroids. Because LPX eliminated female resistance to the proinflammatory effects of HFD without changing circulating sex hormones, we conclude that sexually dimorphic organization of subcutaneous and visceral fat determines susceptibility to inflammation in obesity.

Ferroptosis is a newly identified form of regulated cell death that is driven by iron overload and uncontrolled lipid peroxidation, but the role of ferroptosis in cardiac microvascular dysfunction remains unclear. Isorhapontigenin (ISO) is an analog of resveratrol and possesses strong antioxidant capacity and cardiovascular-protective effects. Moreover, ISO has been shown to alleviate iron-induced oxidative damage and lipid peroxidation in mitochondria. Therefore, the current study aimed to explore the benefits of ISO treatment on cardiac microvascular dysfunction in diabetes and the possible mechanisms involved, with a focus on ferroptosis and mitochondria. Our data revealed that ISO treatment improved microvascular density and perfusion in db/db mice by mitigating vascular structural damage, normalizing nitric oxide (NO) production via endothelial NO synthase activation, and enhancing angiogenetic ability via vascular endothelial growth factor receptor 2 phosphorylation. PRDX2 was identified as a downstream target of ISO, and endothelial-specific overexpression of PRDX2 exerted effects on the cardiac microvascular function that were similar to those of ISO treatment. In addition, PRDX2 mediated the inhibitive effects of ISO treatment on ferroptosis by suppressing oxidative stress, iron overload, and lipid peroxidation. Further study suggested that mitochondrial dynamics and dysfunction contributed to ferroptosis, and ISO treatment or PRDX2 overexpression attenuated mitochondrial dysfunction via MFN2-dependent mitochondrial dynamics. Moreover, MFN2 overexpression suppressed the mitochondrial translocation of ACSL4, ultimately inhibiting mitochondria-associated ferroptosis. In contrast, enhancing mitochondria-associated ferroptosis via ACSL4 abolished the protective effects of ISO treatment on cardiac microcirculation. Taken together, the results of the present work demonstrated the beneficial effects of ISO treatment on cardiac microvascular protection in diabetes by suppressing mitochondria-associated ferroptosis through PRDX2-MFN2-ACSL4 pathways.

Cellular lipid storage is regulated by the balance of lipogenesis and lipolysis. The rate-limiting triglyceride hydrolase ATGL (desnutrin/PNPLA2) is critical for lipolysis. The control of ATGL transcription, localization, and activation has been intensively studied, while regulation of the protein stability of ATGL is much less explored. In this study, we showed that the protein stability of ATGL is regulated by the N-end rule in cultured cells and in mice. The N-end rule E3 ligases UBR1 and UBR2 reduce the level of ATGL and affect lipid storage. The N-end rule-resistant ATGL(F2A) mutant, in which the N-terminal phenylalanine (F) of ATGL is substituted by alanine (A), has increased protein stability and enhanced lipolysis activity. ATGLF2A/F2A knock-in mice are protected against high-fat diet (HFD)-induced obesity, hepatic steatosis, and insulin resistance. Hepatic knockdown of Ubr1 attenuates HFD-induced hepatic steatosis by enhancing the ATGL level. Finally, the protein levels of UBR1 and ATGL are negatively correlated in the adipose tissue of obese mice. Our study reveals N-end rule-mediated proteasomal regulation of ATGL, a finding that may potentially be beneficial for treatment of obesity.

To assess the diurnal patterns of postprandial glucose tolerance and insulin sensitivity, 19 subjects with type 2 diabetes (8 women; 60 ± 11 years; BMI 32 ± 5 kg/m2) and 19 anthropometrically matched subjects with no diabetes (ND; 11 women; 53 ± 12 years; BMI 29 ± 5 kg/m2) were studied during breakfast (B), lunch (L), and dinner (D) with identical mixed meals (75 g carbohydrates) on 3 consecutive days in a randomized Latin square design. Three stable isotopes of glucose were ustilized to estimate meal fluxes, and mathematical models were used in estimating indices of insulin action and β-cell function. Postmeal glucose excursions were higher at D versus B and at D versus L in type 2 diabetes (P < 0.05), while in ND they were higher at D versus B (P = 0.025) and at L versus B (P = 0.04). The insulin area under the curve was highest at B compared with L and D in type 2 diabetes, while no differences were observed in ND. Disposition index (DI) was higher at B than at L (P < 0.01) and at D (P < 0.001) in ND subjects, whereas DI was low with unchanging pattern across B-L-D in individuals with type 2 diabetes. Furthermore, between-meal differences in β-cell responsivity to glucose (F) and insulin sensitivity (SI) were concurrent with changes in the DI within groups. Fasting and postmeal glucose, insulin, and C-peptide concentrations, along with estimates of endogenous glucose production (EGP), Rd, SI, F, hepatic extraction of insulin, insulin secretion rate, extracted insulin, and DI, were altered in type 2 diabetes compared with ND (P < 0.011 for all). The data show a diurnal pattern of postprandial glucose tolerance in overweight otherwise glucose-tolerant ND individuals that differs from overweight individuals with type 2 diabetes. The results not only provide valuable insight into management strategies for better glycemic control in people with type 2 diabetes, but also improved understanding of daytime glucose metabolism in overweight individuals without impaired glucose tolerance or overt diabetes.

Identifying the early islet cellular processes of autoimmune type 1 diabetes (T1D) in humans is challenging given the absence of symptoms during this period and the inaccessibility of the pancreas for sampling. In this article, we study temporal events in pancreatic islets in LEW.1WR1 rats, in which autoimmune diabetes can be induced with virus infection, by performing transcriptional analysis of islets harvested during the prediabetic period. Single-cell RNA-sequencing and differential expression analyses of islets from prediabetic rats reveal subsets of β- and α-cells under stress as evidenced by heightened expression, over time, of a transcriptional signature characterized by interferon-stimulated genes, chemokines including Cxcl10, major histocompatibility class I, and genes for the ubiquitin-proteasome system. Mononuclear phagocytes show increased expression of inflammatory markers. RNA-in situ hybridization of rat pancreatic tissue defines the spatial distribution of Cxcl10+ β- and α-cells and their association with CD8+ T cell infiltration, a hallmark of insulitis and islet destruction. Our studies define early islet transcriptional events during immune cell recruitment to islets and reveal spatial associations between stressed β- and α-cells and immune cells. Insights into such early processes can assist in the development of therapeutic and prevention strategies for T1D.

Glucokinase (GK, gene symbol GCK) maturity-onset diabetes of the young (MODY) is caused by heterozygous inactivating mutations in GK and impaired glucose sensing. We investigated effects of dorzagliatin, a novel allosteric GK activator, on insulin secretion rates (ISRs) and β-cell glucose sensitivity (βCGS) in GCK-MODY and recent-onset type 2 diabetes. In a double-blind, randomized, crossover study, 8 participants with GCK-MODY and 10 participants with type 2 diabetes underwent 2-h 12 mmol/L hyperglycemic clamps following a single oral dose of dorzagliatin 75 mg or matched placebo. Effects of dorzagliatin on wild-type and mutant GK enzyme activity were investigated using an NADP+-coupled assay with glucose-6-phosphate dehydrogenase in vitro. In GCK-MODY, dorzagliatin significantly increased absolute and incremental second-phase ISRs versus placebo but not the acute insulin response. Dorzagliatin improved βCGS in GCK-MODY with an upward and leftward shift in ISR-glucose response. Dorzagliatin increased basal ISRs in type 2 diabetes, with smaller changes in second-phase ISRs versus GCK-MODY. In vitro, dorzagliatin directly reduced the glucose half saturation concentration of wild-type GK and selected GK mutants to varying degrees. Dorzagliatin directly restored enzyme activity of select GK mutants and enhanced wild-type GK activity, thereby correcting the primary defect of glucose sensing in GCK-MODY.

Diabetic kidney disease (DKD) is the leading cause of end-stage kidney disease (ESKD). Prognostic biomarkers reflective of underlying molecular mechanisms are critically needed for effective management of DKD. A three-marker panel was derived from a proteomics analysis of plasma samples by an unbiased machine learning approach from participants (N = 58) in the Clinical Phenotyping and Resource Biobank study. In combination with standard clinical parameters, this panel improved prediction of the composite outcome of ESKD or a 40% decline in glomerular filtration rate. The panel was validated in an independent group (N = 68), who also had kidney transcriptomic profiles. One marker, plasma angiopoietin 2 (ANGPT2), was significantly associated with outcomes in cohorts from the Cardiovascular Health Study (N = 3,183) and the Chinese Cohort Study of Chronic Kidney Disease (N = 210). Glomerular transcriptional angiopoietin/Tie (ANG-TIE) pathway scores, derived from the expression of 154 ANG-TIE signaling mediators, correlated positively with plasma ANGPT2 levels and kidney outcomes. Higher receptor expression in glomeruli and higher ANG-TIE pathway scores in endothelial cells corroborated potential functional effects in the kidney from elevated plasma ANGPT2 levels. Our work suggests that ANGPT2 is a promising prognostic endothelial biomarker with likely functional impact on glomerular pathogenesis in DKD.

Clinical studies investigating the benefit of glucose control on the progression of diabetic neuropathy (DN) have come to controversial results in patients with type 2 diabetes (T2D). This study aimed to assess associations of HbA1c levels with parameters of nerve perfusion in patients with T2D with and without DN using dynamic contrast-enhanced magnetic resonance neurography (DCE-MRN) at 3 Tesla. A total of 58 patients with T2D (20 with DN and 38 without DN) took part in this cross-sectional single-center study. Groups were matched for age, BMI, HbA1c, duration of T2D, and renal function. All patients underwent DCE-MRN with subsequent electrophysiologic and serologic testing. The extended Tofts model was used to quantify the sciatic nerve's microvascular permeability (Ktrans), volume fraction of the extracapillary extracellular space, and volume fraction of the plasma space. As a main result, we found that Ktrans correlated positively with HbA1c in patients with DN, while a negative correlation between the two parameters was found in patients without DN. Our results indicate that the effect of glucose control on the capillary permeability of peripheral nerves differs between patients with T2D with and without DN.