Epigenetics: mechanisms and implications for diabetic complications

Epigenetic processing in cardiometabolic disease

Albeit a consistent body of evidence supports the notion that genes influence cardiometabolic features and outcomes, the "non-genetic regulation" of this process is gaining increasing attention. Plastic chemical changes of DNA/histone complexes - known as epigenetic changes - critically determine gene activity by rapidly modifying chromatin accessibility to transcription factors. In this review, we describe the emerging role of chromatin modifications as fine tuners of gene transcription in adipogenesis, insulin resistance, macrophage polarization, immuno-metabolism, endothelial dysfunction and metabolic cardiomyopathy. Epigenetic processing participates in the dynamic interplay among different organs in the cardiometabolic patient. DNA methylation and post-translational histone modifications in both visceral and subcutaneous adipose tissue enable the transcription of genes implicated in lipo- and adipogenesis, inflammation and insulin resistance. Along the same line, complex networks of chromatin modifying enzymes are responsible for impaired nitric oxide bioavailability and defective insulin signalling in the vasculature, thus leading to reduced capillary recruitment and insulin delivery in the liver, skeletal muscle and adipose tissue. Furthermore, changes in methylation status of IL-4, IFNγ and Forkhead box P3 (Foxp3) gene loci are crucial for the polarization of immune cells, thus leading to adipose tissue inflammation and atherosclerosis. Cell-specific epigenetic information could advance our understanding of cardiometabolic processes, thus leading to individualized risk assessment and personalized therapeutic approaches in patients with cardiometabolic disturbances. The development of new chromatin modifying drugs indicates that targeting epigenetic changes is a promising approach to reduce the burden of cardiovascular disease in this setting.

Activated protein C reverses epigenetically sustained p66Shc expression in plaque-associated macrophages in diabetes

Impaired activated protein C (aPC) generation is associated with atherosclerosis and diabetes mellitus. Diabetes-associated atherosclerosis is characterized by the hyperglycaemic memory, e.g., failure of disease improvement despite attenuation of hyperglycaemia. Therapies reversing the hyperglycaemic memory are lacking. Here we demonstrate that hyperglycaemia, but not hyperlipidaemia, induces the redox-regulator p66Shc and reactive oxygen species (ROS) in macrophages. p66Shc expression, ROS generation, and a pro-atherogenic phenotype are sustained despite restoring normoglycemic conditions. Inhibition of p66Shc abolishes this sustained pro-atherogenic phenotype, identifying p66Shc-dependent ROS in macrophages as a key mechanism conveying the hyperglycaemic memory. The p66Shc-associated hyperglycaemic memory can be reversed by aPC via protease-activated receptor-1 signalling. aPC reverses glucose-induced CpG hypomethylation within the p66Shc promoter by induction of the DNA methyltransferase-1 (DNMT1). Thus, epigenetically sustained p66Shc expression in plaque macrophages drives the hyperglycaemic memory, which-however-can be reversed by aPC. This establishes that reversal of the hyperglycaemic memory in diabetic atherosclerosis is feasible.

Epigenetics and Immunometabolism in Diabetes and Aging

SIGNIFICANCE

A strong relationship between hyperglycemia, impaired insulin pathway, and cardiovascular disease in type 2 diabetes (T2D) is linked to oxidative stress and inflammation. Immunometabolic pathways link these pathogenic processes and pose important potential therapeutic targets. Recent Advances: The link between immunity and metabolism is bidirectional and includes the role of inflammation in the pathogenesis of metabolic disorders such as T2D, obesity, metabolic syndrome, and hypertension and the role of metabolic factors in regulation of immune cell functions. Low-grade inflammation, oxidative stress, balance between superoxide and nitric oxide, and the infiltration of macrophages, T cells, and B cells in insulin-sensitive tissues lead to metabolic impairment and accelerated aging.

CRITICAL ISSUES

Inflammatory infiltrate and altered immune cell phenotype precede development of metabolic disorders. Inflammatory changes are tightly linked to alterations in metabolic status and energy expenditure and are controlled by epigenetic mechanisms.

FUTURE DIRECTIONS

A better comprehension of these mechanistic insights is of utmost importance to identify novel molecular targets. In this study, we describe a complex scenario of epigenetic changes and immunometabolism linking to diabetes and aging-associated vascular disease. Antioxid. Redox Signal. 29, 257-274.

Preservation of renal function in chronic diabetes by enhancing glomerular glucose metabolism

Diabetic nephropathy (DN) affects approximately 30-40% of patients with type 1 (T1DM) and type 2 diabetes (T2DM). It is a major cause of end-stage renal disease (ESRD) for the developed world. Hyperglycemia and genetics are major causal factors for the initiation and progression of DN. Multiple abnormalities in glucose and mitochondrial metabolism induced by diabetes likely contribute to the severity of DN. Recent clinical studies in people with extreme duration of T1DM (> 50 years, Joslin Medalist Study) have supported the importance of endogenous protective factors to neutralize the toxic effects of hyperglycemia on renal and other vascular tissues. Using renal glomeruli from these patients (namely Medalists) with and without DN, we have shown the importance of increased glycolytic flux in decreasing the accumulation of glucose toxic metabolites, improving mitochondrial function, survival of glomerular podocytes, and reducing glomerular pathology. Activation of a key glycolytic enzyme, pyruvate kinase M2 (PKM2), resulted in the normalization of renal hemodynamics and mitochondrial and glomerular dysfunction, leading to the mitigation of glomerular pathologies in several mouse models of DN.

Transient epigenomic changes during pregnancy and early postpartum in women with and without type 2 diabetes

AIM

To investigate epigenomic changes in pregnancy and early postpartum in women with and without type 2 diabetes.

METHODS

Dimethylation of histones H3K4, H3K9, H3K27, H3K36 and H3K79 was measured in white blood cells of women at 30 weeks pregnancy, at 8-10 and 20 weeks postpartum and in never-pregnant women.

RESULTS

Dimethylation levels of all five histones were different between women in pregnancy and early postpartum compared with never-pregnant women and were different between women with and without type 2 diabetes.

CONCLUSION

Histone methylation changes are transient in pregnancy and early postpartum and may represent normal physiological responses to hormones. Different epigenomic profiles in women with type 2 diabetes mellitus may correlate with hormonal responses, leading to high risk pregnancy outcomes.

Stable Oxidative Cytosine Modifications Accumulate in Cardiac Mesenchymal Cells From Type2 Diabetes Patients

Rationale:

Human cardiac mesenchymal cells (CMSCs) are a therapeutically relevant primary cell population. Diabetes mellitus compromises CMSC function as consequence of metabolic alterations and incorporation of stable epigenetic changes.

Objective:

To investigate the role of α-ketoglutarate (αKG) in the epimetabolic control of DNA demethylation in CMSCs.

Methods and Results:

Quantitative global analysis, methylated and hydroxymethylated DNA sequencing, and gene-specific GC methylation detection revealed an accumulation of 5-methylcytosine, 5-hydroxymethylcytosine, and 5-formylcytosine in the genomic DNA of human CMSCs isolated from diabetic donors. Whole heart genomic DNA analysis revealed iterative oxidative cytosine modification accumulation in mice exposed to high-fat diet (HFD), injected with streptozotocin, or both in combination (streptozotocin/HFD). In this context, untargeted and targeted metabolomics indicated an intracellular reduction of αKG synthesis in diabetic CMSCs and in the whole heart of HFD mice. This observation was paralleled by a compromised TDG (thymine DNA glycosylase) and TET1 (ten–eleven translocation protein 1) association and function with TET1 relocating out of the nucleus. Molecular dynamics and mutational analyses showed that αKG binds TDG on Arg275 providing an enzymatic allosteric activation. As a consequence, the enzyme significantly increased its capacity to remove G/T nucleotide mismatches or 5-formylcytosine. Accordingly, an exogenous source of αKG restored the DNA demethylation cycle by promoting TDG function, TET1 nuclear localization, and TET/TDG association. TDG inactivation by CRISPR/Cas9 knockout or TET/TDG siRNA knockdown induced 5-formylcytosine accumulation, thus partially mimicking the diabetic epigenetic landscape in cells of nondiabetic origin. The novel compound (S)-2-[(2,6-dichlorobenzoyl)amino]succinic acid (AA6), identified as an inhibitor of αKG dehydrogenase, increased the αKG level in diabetic CMSCs and in the heart of HFD and streptozotocin mice eliciting, in HFD, DNA demethylation, glucose uptake, and insulin response.

Conclusions:

Restoring the epimetabolic control of DNA demethylation cycle promises beneficial effects on cells compromised by environmental metabolic changes.

Role of Tight Glycemic Control during Acute Coronary Syndrome on CV Outcome in Type 2 Diabetes

Both incidence and mortality of acute coronary syndrome (ACS) among diabetic patients are much higher than those among nondiabetics. Actually, there are many studies that addressed glycemic control and CV risk, whilst the literature on the role of tight glycemic control during ACS is currently poor. Therefore, in this review, we critically discussed the studies that investigated this specific topic. Hyperglycemia is implicated in vascular damage and cardiac myocyte death through different molecular mechanisms as advanced glycation end products, protein kinase C, polyol pathway flux, and the hexosamine pathway. Moreover, high FFA concentrations may be toxic in acute ischemic myocardium due to several mechanisms, thus leading to endothelial dysfunction. A reduction in free fatty acid plasma levels and an increased availability of glucose can be achieved by using a glucose-insulin-potassium infusion (GIKi) during AMI. The GIKi is associated with an improvement of either long-term prognosis or left ventricular mechanical performance. DIGAMI studies suggested blood glucose level as a significant and independent mortality predictor among diabetic patients with recent ACS, enhancing the important role of glucose control in their management. Several mechanisms supporting the protective role of tight glycemic control during ACS, as well as position statements of Scientific Societies, were highlighted.

Effect of diabetes status and hyperglycemia on global DNA methylation and hydroxymethylation

Type 2 diabetes mellitus (T2DM) is characterized by oxidative stress that could lead to chronic micro- and macrovascular complications. We hypothesized that some of the target organ damage is mediated by oxidative alterations in epigenetic mechanisms involving DNA methylation (5mC) and DNA hydroxymethylation (5hmC). We analyzed global DNA methylation and hydroxymethylation in peripheral blood cells in well-controlled and poorly controlled patients with T2DM and compared them with healthy controls. We also analyzed microarrays of DNA methylation and gene expression of other important tissues in the context of diabetes from the GEO database repository and then compared these results with our experimental gene expression data. DNA methylation and, more importantly, DNA hydroxymethylation levels were increased in poorly controlled patients compared to well-controlled and healthy individuals. Both 5mC and 5hmC measurements were correlated with the percentage of glycated hemoglobin, indicating a direct impact of hyperglycemia on changes over the epigenome. The analysis of methylation microarrays was concordant, and 5mC levels were increased in the peripheral blood of T2DM patients. However, the DNA methylation levels were the opposite of those in other tissues, such as the pancreas, adipose tissue and skeletal muscle. We hypothesize that a process of DNA oxidation associated with hyperglycemia may explain the DNA demethylation in which the activity of ten-eleven translocation (TET) proteins is not sufficient to complete the process. High levels of glucose lead to cellular oxidation, which triggers the process of DNA demethylation aided by TET enzymes, resulting in epigenetic dysregulation of the damaged tissues.

Epigenetic mechanisms underlying maternal diabetes-associated risk of congenital heart disease

Birth defects are the leading cause of infant mortality, and they are caused by a combination of genetic and environmental factors. Environmental risk factors may contribute to birth defects in genetically susceptible infants by altering critical molecular pathways during embryogenesis, but experimental evidence for gene-environment interactions is limited. Fetal hyperglycemia associated with maternal diabetes results in a 5-fold increased risk of congenital heart disease (CHD), but the molecular basis for this correlation is unknown. Here, we show that the effects of maternal hyperglycemia on cardiac development are sensitized by haploinsufficiency of Notch1, a key transcriptional regulator known to cause CHD. Using ATAC-seq, we found that hyperglycemia decreased chromatin accessibility at the endothelial NO synthase (Nos3) locus, resulting in reduced NO synthesis. Transcription of Jarid2, a regulator of histone methyltransferase complexes, was increased in response to reduced NO, and this upregulation directly resulted in inhibition of Notch1 expression to levels below a threshold necessary for normal heart development. We extended these findings using a Drosophila maternal diabetic model that revealed the evolutionary conservation of this interaction and the Jarid2-mediated mechanism. These findings identify a gene-environment interaction between maternal hyperglycemia and Notch signaling and support a model in which environmental factors cause birth defects in genetically susceptible infants.

Epigenetic programming, early life nutrition and the risk of metabolic disease

Time separates the past from the present, during this period memory are formed - written in code and decoded to be read while other memories are erased - but when it comes to the epigenome some memories are harder to forget than others. Recent studies show chemical information is written in the context of the epigenome and codified on histone and non-histone proteins to regulate nuclear processes such as gene transcription. The genome is also subject to modification in the form of 5-methylcytosine, which has been implicated in metabolic memory. In this review, we examine some of the chemical modifications that signal early life events and explore epigenetic changes that underlie the diabetic vasculature. The fine balance between past and present is discussed, as it pertains to gestational diabetes and obesity in context to the Barker hypothesis. We also examine emerging experimental evidence suggesting the hypothalamus as a central regulator of obesity risk and explore current genomic medicine. As for how cells recall specific chemical information, we examine the experimental evidence implicating chemical cues on the epigenome, providing examples of diet during pregnancy and the increased risk of disease in offspring.

Impact of Glycemic Variability on Chromatin Remodeling, Oxidative Stress, and Endothelial Dysfunction in Patients With Type 2 Diabetes and With Target HbA1c Levels

Intensive glycemic control (IGC) targeting HbA_1c fails to show an unequivocal reduction of macrovascular complications in type 2 diabetes (T2D); however, the underlying mechanisms remain elusive. Epigenetic changes are emerging as important mediators of cardiovascular damage and may play a role in this setting. This study investigated whether epigenetic regulation of the adaptor protein p66^Shc, a key driver of mitochondrial oxidative stress, contributes to persistent vascular dysfunction in patients with T2D despite IGC. Thirty-nine patients with uncontrolled T2D (HbA_1c >7.5%) and 24 age- and sex-matched healthy control subjects were consecutively enrolled. IGC was implemented for 6 months in patients with T2D to achieve a target HbA_1c of ≤7.0%. Brachial artery flow-mediated dilation (FMD), urinary 8-isoprostaglandin F_2α (8-isoPGF_2α), and epigenetic regulation of p66^Shc were assessed at baseline and follow-up. Continuous glucose monitoring was performed to determine the mean amplitude of glycemic excursion (MAGE) and postprandial incremental area under the curve (AUCpp). At baseline, patients with T2D showed impaired FMD, increased urinary 8-isoPGF_2α, and p66^Shc upregulation in circulating monocytes compared with control subjects. FMD, 8-isoPGF_2α, and p66^Shc expression were not affected by IGC. DNA hypomethylation and histone 3 acetylation were found on the p66^Shc promoter of patients with T2D, and IGC did not change such adverse epigenetic remodeling. Persistent downregulation of methyltransferase DNMT3b and deacetylase SIRT1 may explain the observed p66^Shc-related epigenetic changes. MAGE and AUCpp but not HbA_1c were independently associated with the altered epigenetic profile on the p66^Shc promoter. Hence, glucose fluctuations contribute to chromatin remodeling and may explain persistent vascular dysfunction in patients with T2D with target HbA_1c levels.

Oxidative Stress-Induced miR-200c Disrupts the Regulatory Loop Among SIRT1, FOXO1, and eNOS

AIMS

Reactive oxygen species (ROS) play a pivotal role in different pathologic conditions, including ischemia, diabetes, and aging. We previously showed that ROS enhance miR-200c expression, causing endothelial cell (EC) apoptosis and senescence. Herein, we dissect the interaction among miR-200c and three strictly related proteins that modulate EC function and ROS production: sirtuin 1 (SIRT1), endothelial nitric oxide synthase (eNOS), and forkhead box O1 (FOXO1). Moreover, the role of miR-200c on ROS modulation was also investigated.

RESULTS

We demonstrated that miR-200c directly targets SIRT1, eNOS, and FOXO1; via this mechanism, miR-200c decreased NO and increased the acetylation of SIRT1 targets, that is, FOXO1 and p53. FOXO1 acetylation inhibited its transcriptional activity on target genes, that is, SIRT1 and the ROS scavengers, catalase and manganese superoxide dismutase. In keeping, miR-200c increased ROS production and induced p66Shc protein phosphorylation in Ser-36; this mechanism upregulated ROS and inhibited FOXO1 transcription, reinforcing this molecular circuitry. These in vitro results were validated in three in vivo models of oxidative stress, that is, human skin fibroblasts from old donors, femoral arteries from old mice, and a murine model of hindlimb ischemia. In all cases, miR-200c was higher versus control and its targets, that is, SIRT1, eNOS, and FOXO1, were downmodulated. In the mouse hindlimb ischemia model, anti-miR-200c treatment rescued these targets and improved limb perfusion. Innovation and Conclusion: miR-200c disrupts SIRT1/FOXO1/eNOS regulatory loop. This event promotes ROS production and decreases NO, contributing to endothelial dysfunction under conditions of increased oxidative stress such as aging and ischemia. Antioxid. Redox Signal. 27, 328-344.

Transcription Factor CREM Mediates High Glucose Response in Cardiomyocytes and in a Male Mouse Model of Prolonged Hyperglycemia

This study aims at investigating the epigenetic landscape of cardiomyocytes exposed to elevated glucose levels. High glucose (30 mM) for 72 hours determined some epigenetic changes in mouse HL-1 and rat differentiated H9C2 cardiomyocytes including upregulation of class I and III histone deacetylase protein levels and activity, inhibition of histone acetylase p300 activity, increase in histone H3 lysine 27 trimethylation, and reduction in H3 lysine 9 acetylation. Gene expression analysis focused on cardiotoxicity revealed that high glucose induced markers associated with tissue damage, fibrosis, and cardiac remodeling such as Nexilin (NEXN), versican, cyclic adenosine 5'-monophosphate-responsive element modulator (CREM), and adrenoceptor α2A (ADRA2). Notably, the transcription factor CREM was found to be important in the regulation of cardiotoxicity-associated genes as assessed by specific small interfering RNA and chromatin immunoprecipitation experiments. In CD1 mice, made hyperglycemic by streptozotoicin (STZ) injection, cardiac structural alterations were evident at 6 months after STZ treatment and were associated with a significant increase of H3 lysine 27 trimethylation and reduction of H3 lysine 9 acetylation. Consistently, NEXN, CREM, and ADRA2 expression was significantly induced at the RNA and protein levels. Confocal microscopy analysis of NEXN localization showed this protein irregularly distributed along the sarcomeres in the heart of hyperglycemic mice. This evidence suggested a structural alteration of cardiac Z-disk with potential consequences on contractility. In conclusion, high glucose may alter the epigenetic landscape of cardiac cells. Sildenafil, restoring guanosine 3', 5'-cyclic monophosphate levels, counteracted the increase of CREM and NEXN, providing a protective effect in the presence of hyperglycemia.

Regulation of Matrix Metalloproteinase in the Pathogenesis of Diabetic Retinopathy

Diabetic retinopathy, a progressive disease, is the major cause of acquired blindness in the developed countries. Despite cutting-edge research in the field, the exact mechanism of this multifactorial disease remains elusive. Matrix metalloproteinases (MMPs) degrade extracellular matrix and play significant role in regulating intracellular homeostasis. In the pathogenesis of diabetic retinopathy, activation of gelatinase MMPs (MMP-2 and MMP-9) in the retina is an early event, and activated MMPs damage the mitochondria and augment retinal capillary cell apoptosis, a phenomenon which is observed before histopathology characteristic of diabetic retinopathy can be seen. MMPs are regulated by a number of different mechanisms including cleavage of their zymogens, regulation of their tissue inhibitors, and their gene expressions by transcriptional factors and epigenetic modifications. This chapter reviews the current literature about the role of MMPs in the development of diabetic retinopathy, and describes different mechanisms to regulate their activation. With evolving research implicating MMPs in both preneovascularization and neovascularization stages of diabetic retinopathy, they could be an attractive target to inhibit the development/progression of diabetic retinopathy, a disease which has potential to rob vision during the most productive years of a diabetic patient's life.

Imbalance between HDAC and HAT activities drives aberrant STAT1/MyD88 expression in macrophages from type 1 diabetic mice

AIMS

To investigate the hypothesis that alteration in histone acetylation/deacetylation triggers aberrant STAT1/MyD88 expression in macrophages from diabetics. Increased STAT1/MyD88 expression is correlated with sterile inflammation in type 1 diabetic (T1D) mice.

METHODS

To induce diabetes, we injected low-doses of streptozotocin in C57BL/6 mice. Peritoneal or bone marrow-differentiated macrophages were cultured in 5mM (low) or 25mM (high glucose). ChIP analysis of macrophages from nondiabetic or diabetic mice was performed to determine acetylation of lysine 9 in histone H3 in MyD88 and STAT1 promoter regions. Macrophages from diabetic mice were treated with the histone acetyltransferase inhibitor anacardic acid (AA), followed by determination of mRNA expression by qPCR.

RESULTS

Increased STAT1 and MyD88 expression in macrophages from diabetic but not naive mice cultured in low glucose persisted for up to 6days. Macrophages from diabetic mice exhibited increased activity of histone acetyltransferases (HAT) and decreased histone deacetylases (HDAC) activity. We detected increased H3K9Ac binding to Stat1/Myd88 promoters in macrophages from T1D mice and AA in vitro treatment reduced STAT1 and MyD88 mRNA expression.

CONCLUSIONS/INTERPRETATION

These results indicate that histone acetylation drives elevated Stat1/Myd88 expression in macrophages from diabetic mice, and this mechanism may be involved in sterile inflammation and diabetes comorbidities.

Epigenetic regulation of the thioredoxin-interacting protein (TXNIP) gene by hyperglycemia in kidney

Diabetic kidney disease is the leading cause of end-stage renal disease. Genetic factors have been suggested to contribute to its susceptibility. However, results from genetic studies are disappointing possibly because the role of glucose in diabetic kidney disease predisposed by epigenetic mechanisms has not been taken into account. Since thioredoxin-interacting protein (TXNIP) has been shown to play an important role in the pathogenesis of diabetic kidney disease, we tested whether glucose could induce expression of TXNIP in the kidney by epigenetic mechanisms. In kidneys from diabetic Sur1-E1506K(+/+) mice, hyperglycemia-induced Txnip expression was associated with stimulation of activating histone marks H3K9ac, H3K4me3, and H3K4me1, as well as decrease in the repressive histone mark H3K27me3 at the promoter region of the gene. Glucose also coordinated changes in histone marks and TXNIP gene expression in mouse SV40 MES13 mesangial cells and the normal human mesangial cell line NHMC. The involvement of histone acetylation in glucose-stimulated TXNIP expression was confirmed by reversing or enhancing acetylation using the histone acetyltransferase p300 inhibitor C646 or the histone deacetylase inhibitor trichostatin A. Thus, glucose is a potent inducer of histone modifications, which could drive expression of proinflammatory genes and thereby predispose to diabetic kidney disease.

Molecular targets of developmental exposure to bisphenol A in diabesity: a focus on endoderm-derived organs

Several studies associate foetal human exposure to bisphenol A (BPA) to metabolic/endocrine diseases, mainly diabesity. They describe the role of BPA in the disruption of pancreatic beta cell, adipocyte and hepatocyte functions. Indeed, the complexity of the diabesity phenotype is due to the involvement of different endoderm-derived organs, all targets of BPA. Here, we analyse this point delineating a picture of different mechanisms of BPA toxicity in endoderm-derived organs leading to diabesity. Moving from epidemiological data, we summarize the in vivo experimental data of the BPA effects on endoderm-derived organs (thyroid, pancreas, liver, gut, prostate and lung) after prenatal exposure. Mainly, we gather molecular data evidencing harmful effects at low-dose exposure, pointing to the risk to human health. Although the fragmentation of molecular data does not allow a clear conclusion to be drawn, the present work indicates that the developmental exposure to BPA represents a risk for endoderm-derived organs development as it deregulates the gene expression from the earliest developmental stages. A more systematic analysis of BPA impact on the transcriptomes of endoderm-derived organs is still missing. Here, we suggest in vitro toxicogenomics approaches as a tool for the identification of common mechanisms of BPA toxicity leading to the diabesity in organs having the same developmental origin.

Histone demethylase KDM3a, a novel regulator of vascular smooth muscle cells, controls vascular neointimal hyperplasia in diabetic rats

BACKGROUND AND AIMS

Deregulation of histone demethylase KDM3a, an important regulator for H3K9 methylation, is correlated with obesity and abnormal metabolism in rodent models. However, the function of KDM3a in vascular remodeling under diabetic condition is unknown.

METHODS

Adenoviruses expressing KDM3a and lentiviruses expressing KDM3a-targeting siRNA were generated to study the role of KDM3a both in vivo and in vitro. The carotid artery balloon injury model was established in diabetic SD rats to evaluate the significance of KDM3a in vascular injury.

RESULTS

Diabetic vessels were associated with sustained loss of histone H3 lysine 9 di-methylation (H3K9me2) and elevation of KDM3a. This phenomenon was induced by high glucose (HG) and was persistently present even after removal from diabetic condition and high glucose in vascular smooth muscle cells (VSMCs). After 28-day balloon injury, KDM3a overexpression accelerated while KDM3a knockdown reduced neointima formation, following vascular injury in diabetic rats without glucose control. Microarray analysis revealed KDM3a altered the expression of vascular remodeling genes; particularly, it mediated the Rho/ROCK and AngII/AGTR1 pathways. In the in vivo study, HG and Ang II-stimulated proliferation and migration of VSMCs were enhanced by KDM3a overexpression, whereas markedly prevented by KDM3a knockdown. KDM3a regulated the transcription of AGTR1 and ROCK2 via controlling H3K9me2 in the proximal promoter regions.

CONCLUSIONS

Histone demethylase KDM3a promotes vascular neointimal hyperplasia in diabetic rats via AGTR1 and ROCK2 signaling pathways. Targeting KDM3a might represent a promising therapeutic approach for the prevention of coronary artery disease with diabetes.

Diabetes propels the risk for cardiovascular disease: sweet monocytes becoming aggressive?

Diabetes strongly predisposes to cardiovascular disease (CVD), the leading cause of mortality in these patients, as well as in the entire population. Hyperglycemia is an important cardiovascular risk factor as shown by the observation that even transient periods of hyperglycemia, despite return to normoglycemia during follow-up, increase the risk for CVD, a phenomenon termed 'hyperglycemic memory'. The molecular mechanisms underlying this phenomenon remain largely unknown. As inflammation plays an important role in the pathogenesis of atherosclerosis, we propose that long-term functional reprogramming of monocytes and macrophages, induced by hyperglycemia, plays an important role in the phenomenon of hyperglycemic memory leading to cardiovascular complications in patients with diabetes. In this review, we discuss recent insights showing that innate immune cells possess the capacity to reprogram their function through epigenetically mediated rewiring of gene transcription, a process termed 'trained immunity'. The long-term reprogramming of monocytes can be induced by microbial as well as metabolic products, and involves a shift in cellular metabolism from oxidative phosphorylation to aerobic glycolysis. We hypothesize that hyperglycemia in diabetes patients induces long-term activation of monocytes and macrophages through similar mechanisms, thereby contributing to plaque development and subsequent macrovascular complications.

A multicenter clinical study to determine the efficacy of a novel fenugreek seed (Trigonella foenum-graecum) extract (Fenfuro™) in patients with type 2 diabetes

Background

Trigonella foenum-graecum (fenugreek) seeds are known to exhibit potent antioxidant, hypoglycemic, and nephroprotective activities, as well as serve as excellent membrane stabilizers especially because of their content of novel furostanolic saponins. Our previous studies exhibited the broad spectrum safety and efficacy of Fenfuro, a novel T. foenum-graecum seed extract enriched in furostanolic saponins, in type 2 diabetes (T2D) in rats.

Design

This multicenter, randomized, placebo-controlled, double-blind, add-on clinical study evaluated over a period of 90 consecutive days the efficacy of Fenfuro (daily dosage: 500 mg bid) in 154 subjects (male: 108; female: 46; age: 25–60 years) with T2D.

Methods

This study examined the body weight, blood pressure, and pulse rate, as well as the efficacy of Fenfuro on fasting and post-prandial plasma sugar (mg/dL), glycosylated hemoglobin (HbA1c), and fasting and post-prandial C-peptide levels.

Results

Fenfuro caused significant reduction in both fasting plasma and post-prandial blood sugar levels. Approximately 83% of the subjects reported decreases in fasting plasma sugar levels in the Fenfuro-treated group as compared to 62% in the placebo group, while 89% of the subjects demonstrated reduction in post-prandial plasma sugar levels in the Fenfuro-treated group as compared to 72% in the placebo group. HbA1c levels were reduced in both placebo and treatment groups. The decrease in HbA1c levels was significant in both groups as compared to respective baseline values. A significant increase in fasting and post-prandial C-peptide levels compared to the respective baseline values was observed, while no significant changes in fasting and post-prandial C-peptide levels were observed between the two groups. No significant adverse effects were observed by blood chemistry analyses. Furthermore, 48.8% of the subjects reported reduced dosage of anti-diabetic therapy in the Fenfuro-treated group, whereas 18.05% reported reduced dosage of anti-diabetic therapy in the placebo group.

Conclusion

In summary, Fenfuro proved safe and efficacious in ameliorating the symptoms of T2D in humans.

C-peptide protects against hyperglycemic memory and vascular endothelial cell apoptosis

C-peptide exerts protective effects against diabetic complications; however, its role in inhibiting hyperglycemic memory (HGM) has not been elucidated. We investigated the beneficial effect of C-peptide on HGM-induced vascular damage in vitro and in vivo using human umbilical vein endothelial cells and diabetic mice. HGM induced apoptosis by persistent generation of intracellular ROS and sustained formation of ONOO(-) and nitrotyrosine. These HGM-induced intracellular events were normalized by treatment with C-peptide, but not insulin, in endothelial cells. C-peptide also inhibited persistent upregulation of p53 and activation of mitochondrial adaptor p66(shc) after glucose normalization. Further, C-peptide replacement therapy prevented persistent generation of ROS and ONOO(-) in the aorta of diabetic mice whose glucose levels were normalized by the administration of insulin. C-peptide, but not insulin, also prevented HGM-induced endothelial apoptosis in the murine diabetic aorta. This study highlights a promising role for C-peptide in preventing HGM-induced intracellular events and diabetic vascular damage.

A global profile of glucose-sensitive endothelial-expressed long non-coding RNAs

Hyperglycemia-related endothelial dysfunction is believed to be the crux of diabetes-associated micro- and macro-vascular complications. We conducted a systematic transcriptional survey to screen for human endothelial long non-coding RNAs (lncRNAs) regulated by elevated glucose levels. lncRNAs and protein-coding transcripts from human umbilical vein endothelial cells (HUVECs) cultured under high (25 mmol/L) or normal (5 mmol/L) glucose conditions for 24 h were profiled with the Arraystar Human LncRNA Expression Microarray V3.0. Of the 30 586 lncRNAs screened, 100 were significantly upregulated and 186 appreciably downregulated (P < 0.05) in response to high-glucose exposure. In the same HUVEC samples, 133 of the 26 109 mRNAs screened were upregulated and 166 downregulated. Of these 299 differentially expressed mRNAs, 26 were significantly associated with 28 differentially expressed long intergenic non-coding RNAs (P < 0.05). Bioinformatics analyses indicated that the mRNAs most upregulated are primarily enriched in axon guidance signaling pathways; those most downregulated are notably involved in pathways targeting vascular smooth muscle cell contraction, dopaminergic signaling, ubiquitin-mediated proteolysis, and adrenergic signaling. This is the first lncRNA and mRNA transcriptome profile of high-glucose-mediated changes in human endothelial cells. These observations may prove novel insights into novel regulatory molecules and pathways of hyperglycemia-related endothelial dysfunction and, accordingly, diabetes-associated vascular disease.

Insulin promotes vascular smooth muscle cell proliferation and apoptosis via differential regulation of tumor necrosis factor-related apoptosis-inducing ligand

BACKGROUND

Insulin regulates glucose homeostasis but can also promote vascular smooth muscle (VSMC) proliferation, important in atherogenesis. Recently, we showed that tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) stimulates intimal thickening via accelerated growth of VSMCs. The aim of the present study was to determine whether insulin-induced effects on VSMCs occur via TRAIL.

METHODS

Expression of TRAIL and TRAIL receptor in response to insulin and glucose was determined by polymerase chain reaction. Transcriptional activity was assessed using wild-type and site-specific mutations of the TRAIL promoter. Chromatin immunoprecipitation studies were performed. VSMC proliferation and apoptosis was measured.

RESULTS

Insulin and glucose exposure to VSMC for 24 h stimulated TRAIL mRNA expression. This was also evident at the transcriptional level. Both insulin- and glucose-inducible TRAIL transcriptional activity was blocked by dominant-negative specificity protein-1 (Sp1) overexpression. There are five functional Sp1-binding elements (Sp1-1, Sp1-2, Sp-5/6 and Sp1-7) on the TRAIL promoter. Insulin required the Sp1-1 and Sp1-2 sites, but glucose needed all Sp1-binding sites to induce transcription. Furthermore, insulin (but not glucose) was able to promote VSMC proliferation over time, associated with increased decoy receptor-2 (DcR2) expression. In contrast, chronic 5-day exposure of VSMC to 1 µg/mL insulin repressed TRAIL and DcR2 expression, and reduced Sp1 enrichment on the TRAIL promoter. This was associated with increased cell death.

CONCLUSIONS

The findings of the present study provide a new mechanistic insight into how TRAIL is regulated by insulin. This may have significant implications at different stages of diabetes-associated cardiovascular disease. Thus, TRAIL may offer a novel therapeutic solution to combat insulin-induced vascular pathologies.

"Inflammaging" as a Druggable Target: A Senescence-Associated Secretory Phenotype-Centered View of Type 2 Diabetes

Aging is a complex phenomenon driven by a variety of molecular alterations. A relevant feature of aging is chronic low-grade inflammation, termed “inflammaging.” In type 2 diabetes mellitus (T2DM), many elements of aging appear earlier or are overrepresented, including consistent inflammaging. T2DM patients have an increased death rate, associated with an incremented inflammatory score. The source of this inflammation is debated. Recently, the senescence-associated secretory phenotype (SASP) has been proposed as the main origin of inflammaging in both aging and T2DM. Different pathogenic mechanisms linked to T2DM progression and complications development have been linked to senescence and SASP, that is, oxidative stress and endoplasmic reticulum (ER) stress. Here we review the latest data connecting oxidative and ER stress with the SASP in the context of aging and T2DM, with emphasis on endothelial cells (ECs) and endothelial dysfunction. Moreover, since current medical practice is insufficient to completely suppress the increased death rate of diabetic patients, we propose a SASP-centered view of T2DM as a futuristic therapeutic option, possibly opening new prospects by moving the attention from one-organ studies of diabetes complications to a wider targeting of the aging process.

Epigenomic profiling reveals an association between persistence of DNA methylation and metabolic memory in the DCCT/EDIC type 1 diabetes cohort

We examined whether persistence of epigenetic DNA methylation (DNA-me) alterations at specific loci over two different time points in people with diabetes are associated with metabolic memory, the prolonged beneficial effects of intensive vs. conventional therapy during the Diabetes Control and Complications Trial (DCCT) on the progression of microvascular outcomes in the long-term follow-up Epidemiology of Diabetes Interventions and Complications (EDIC) Study. We compared DNA-me profiles in genomic DNA of whole blood (WB) isolated at EDIC Study baseline from 32 cases (DCCT conventional therapy group subjects showing retinopathy or albuminuria progression by EDIC Study year 10) vs. 31 controls (DCCT intensive therapy group subjects without complication progression by EDIC year 10). DNA-me was also profiled in blood monocytes (Monos) of the same patients obtained during EDIC Study years 16-17. In WB, 153 loci depicted hypomethylation, and 225 depicted hypermethylation, whereas in Monos, 155 hypomethylated loci and 247 hypermethylated loci were found (fold change ≥1.3; P < 0.005; cases vs. controls). Twelve annotated differentially methylated loci were common in both WB and Monos, including thioredoxin-interacting protein (TXNIP), known to be associated with hyperglycemia and related complications. A set of differentially methylated loci depicted similar trends of associations with prior HbA1c in both WB and Monos. In vitro, high glucose induced similar persistent hypomethylation at TXNIP in cultured THP1 Monos. These results show that DNA-me differences during the DCCT persist at certain loci associated with glycemia for several years during the EDIC Study and support an epigenetic explanation for metabolic memory.

Persistent Chromatin Modifications Induced by High Fat Diet

Obesity is a highly heritable complex disease that results from the interaction of multiple genetic and environmental factors. Formerly obese individuals are susceptible to metabolic disorders later in life, even after lifestyle changes are made to mitigate the obese state. This is reminiscent of the metabolic memory phenomenon originally observed for persistent complications in diabetic patients, despite subsequent glycemic control. Epigenetic modifications represent a potential mediator of this observed memory. We previously demonstrated that a high fat diet leads to changes in chromatin accessibility in the mouse liver. The regions of greatest chromatin changes in accessibility are largely strain-dependent, indicating a genetic component in diet-induced chromatin alterations. We have now examined the persistence of diet-induced chromatin accessibility changes upon diet reversal in two strains of mice. We find that a substantial fraction of loci that undergo chromatin accessibility changes with a high fat diet remains in the remodeled state after diet reversal in C57BL/6J mice. In contrast, the vast majority of diet-induced chromatin accessibility changes in A/J mice are transient. Our data also indicate that the persistent chromatin accessibility changes observed in C57BL/6J mice are associated with specific transcription factors and histone post-translational modifications. The persistent loci identified here are likely to be contributing to the overall phenotype and are attractive targets for therapeutic intervention.

miR-23b-3p induces the cellular metabolic memory of high glucose in diabetic retinopathy through a SIRT1-dependent signalling pathway

AIMS/HYPOTHESIS

The mechanisms underlying the cellular metabolic memory induced by high glucose remain unclear. Here, we sought to determine the effects of microRNAs (miRNAs) on metabolic memory in diabetic retinopathy.

METHODS

The miRNA microarray was used to examine human retinal endothelial cells (HRECs) following exposure to normal glucose (N) or high glucose (H) for 1 week or transient H for 2 days followed by N for another 5 days (H→N). Levels of sirtuin 1 (SIRT1) and acetylated-nuclear factor κB (Ac-NF-κB) were examined following transfection with miR-23b-3p inhibitor or with SIRT1 small interfering (si)RNA in the H→N group, and the apoptotic HRECs were determined by flow cytometry. Retinal tissues from diabetic rats were similarly studied following intravitreal injection of miR-23b-3p inhibitor. Chromatin immunoprecipitation (ChIP) analysis was performed to detect binding of NF-κB p65 to the potential binding site of the miR-23b-27b-24-1 gene promoter in HRECs.

RESULTS

High glucose increased miR-23b-3p expression, even after the return to normal glucose. Luciferase assays identified SIRT1 as a target mRNA of miR-23b-3p. Reduced miR-23b-3p expression inhibited Ac-NF-κB expression by rescuing SIRT1 expression and also relieved the effect of metabolic memory induced by high glucose in HRECs. The results were confirmed in the retina using a diabetic rat model of metabolic memory. High glucose facilitated the recruitment of NF-κB p65 and promoted transcription of the miR-23b-27b-24-1 gene, which can be suppressed by decreasing miR-23b-3p expression.

CONCLUSIONS/INTERPRETATION

These studies identify a novel mechanism whereby miR-23b-3p regulates high-glucose-induced cellular metabolic memory in diabetic retinopathy through a SIRT1-dependent signalling pathway.

Epigenetic Mechanisms in Diabetic Kidney Disease

Progressive kidney disease is a common companion to both type 1 and type 2 diabetes. However, the majority of people with diabetes do not develop diabetic kidney disease. This may in part be explained by good control of glucose, blood pressure, obesity and other risk factors for kidney disease. It may also be partly due to their genetic makeup or ethnicity. However, the vast majority of the variability in incident nephropathy remains unaccounted for by conventional risk factors or genetics. Epigenetics has recently emerged as an increasingly powerful paradigm to understand and potentially explain complex non-Mendelian conditions-including diabetic kidney disease. Persistent epigenetic changes can be acquired during development or as adaptations to environmental exposure, including metabolic fluctuations associated with diabetes. These epigenetic modifications-including DNA methylation, histone modifications, non-coding RNAs and other changes in chromatin structure and function-individually and co-operatively act to register, store, retain and recall past experiences in a way to shape the transcription of specific genes and, therefore, cellular functions. This review will explore the emerging evidence for the role of epigenetic modifications in programming the legacy of hyperglycaemia for kidney disease in diabetes.

Metabolic Diseases Downregulate the Majority of Histone Modification Enzymes, Making a Few Upregulated Enzymes Novel Therapeutic Targets--"Sand Out and Gold Stays"

To determine whether the expression of histone modification enzymes is regulated in physiological and pathological conditions, we took an experimental database mining approach pioneered in our labs to determine a panoramic expression profile of 164 enzymes in 19 human and 17 murine tissues. We have made the following significant findings: (1) Histone enzymes are differentially expressed in cardiovascular, immune, and other tissues; (2) our new pyramid model showed that heart and T cells are among a few tissues in which histone acetylation/deacetylation, and histone methylation/demethylation are in the highest varieties; and (3) histone enzymes are more downregulated than upregulated in metabolic diseases and regulatory T cell (Treg) polarization/ differentiation, but not in tumors. These results have demonstrated a new working model of "Sand out and Gold stays," where more downregulation than upregulation of histone enzymes in metabolic diseases makes a few upregulated enzymes the potential novel therapeutic targets in metabolic diseases and Treg activity.

Glucose-induced expression of the homeotic transcription factor Prep1 is associated with histone post-translational modifications in skeletal muscle

AIMS/HYPOTHESIS

Chronic hyperglycaemia worsens insulin resistance in individuals with type 2 diabetes. Whether this effect is contributed by epigenetic dysregulation and which genes are involved remain unclear. Prep1 (also known as Pknox1) is a gene exerting major effects on the sensitivity of the glucose transport machinery to insulin. Here, we show that dysregulation of Prep1 expression by high glucose levels is associated with histone modifications at its 5' regulatory region.

METHODS

We used mouse and cell models to investigate Prep1 transcriptional regulation by glucose.

RESULTS

Differentiated L6 skeletal muscle cells were grown in the presence of either 5.5 or 25 mmol/l glucose (normal [NG] and high glucose [HG], respectively). The HG exposure increased nuclear factor κ light chain enhancer of activated B cells (NF-κB) p65 binding and recruitment of the su(var)3-9, enhancer-of-zeste, trithorax domain-containing lysine methyltransferase 7 (SET7) histone methyltransferase and p300 acetyltransferase to the 5' region of Prep1, leading to enhanced transcription. In addition, chromatin immunoprecipitation assays revealed concomitantly increased histone H3 mono- and dimethylation and acetylation at Lys4 and Lys9/14, respectively. Skeletal muscle tissue from streptozotocin-treated diabetic mice also showed Prep1 overexpression accompanied by similarly increased recruitment of NF-κB p65 and histone modifications at the 5' region of Prep1. In these same mice, as well as in Prep1-overexpressing L6 cells, Prep1-induced recruitment of the repressor complex myocyte enhancer factor 2 (MEF2)/histone deacetylase 5 (HDAC5) at the Glut4 promoter was also increased, leading to reduced Glut4 expression.

CONCLUSIONS/INTERPRETATION

These studies indicate that HG exposure induces NF-κB recruitment and histone modification at the Prep1 5' region, thereby enhancing the transcription of Prep1 and repressing that of Glut4. Histone changes at the Prep1 gene may contribute to insulin resistance in individuals with type 2 diabetes.

Hyperglycemia: a bad signature on the vascular system

Experimental work has clearly demonstrated that hyperglycemia is able to derail molecular pathways favouring oxidative stress, inflammation and endothelial dysfunction. Consistently, pooled analyses from prospective studies provide strong evidence that glycemic markers, namely glycated haemoglobin (HbA1c), predict cardiovascular risk, with an increase of about 18% in risk for each 1% absolute increase in HbA1c concentration, regardless of classical risk factors. Although the importance of hyperglycemic burden on cardiovascular phenotype, normalization of blood glucose levels in patients with long-standing hyperglycemia does not seem to reduce macrovascular complications. These data suggest that hyperglycemia may exert long-lasting detrimental effects on the cardiovascular system. This emerging phenomenon is defined metabolic or hyperglycemic memory to indicate a long-term persistence of hyperglycemic stress, even after blood glucose normalization. Here, we discuss clinical evidence and potential molecular mechanisms implicated in metabolic memory and, hence, diabetes-related cardiovascular complications.

Understanding type 2 diabetes: from genetics to epigenetics

The known genetic variability (common DNA polymorphisms) does not account either for the current epidemics of type 2 diabetes or for the family transmission of this disorder. However, clinical, epidemiological and, more recently, experimental evidence indicates that environmental factors have an extraordinary impact on the natural history of type 2 diabetes. Some of these environmental hits are often shared in family groups and proved to be capable to induce epigenetic changes which alter the function of genes affecting major diabetes traits. Thus, epigenetic mechanisms may explain the environmental origin as well as the familial aggregation of type 2 diabetes much easier than common polymorphisms. In the murine model, exposure of parents to environmental hits known to cause epigenetic changes reprograms insulin sensitivity as well as beta-cell function in the progeny, indicating that certain epigenetic changes can be transgenerationally transmitted. Studies from different laboratories revealed that, in humans, lifestyle intervention modulates the epigenome and reverts environmentally induced epigenetic modifications at specific target genes. Finally, specific human epigenotypes have been identified which predict adiposity and type 2 diabetes with much greater power than any polymorphism so far identified. These epigenotypes can be recognized in easily accessible white cells from peripheral blood, indicating that, in the future, epigenetic profiling may enable effective type 2 diabetes prediction. This review discusses recent evidence from the literature supporting the immediate need for further investigation to uncover the power of epigenetics in the prediction, prevention and treatment of type 2 diabetes.

The progress in understanding and treatment of diabetic retinopathy

Diabetic retinopathy is the most frequently occurring complication of diabetes mellitus and remains a leading cause of vision loss globally. Its aetiology and pathology have been extensively studied for half a century, yet there are disappointingly few therapeutic options. Although some new treatments have been introduced for diabetic macular oedema (DMO) (e.g. intravitreal vascular endothelial growth factor inhibitors ('anti-VEGFs') and new steroids), up to 50% of patients fail to respond. Furthermore, for people with proliferative diabetic retinopathy (PDR), laser photocoagulation remains a mainstay therapy, even though it is an inherently destructive procedure. This review summarises the clinical features of diabetic retinopathy and its risk factors. It describes details of retinal pathology and how advances in our understanding of pathogenesis have led to identification of new therapeutic targets. We emphasise that although there have been significant advances, there is still a pressing need for a better understanding basic mechanisms enable development of reliable and robust means to identify patients at highest risk, and to intervene effectively before vision loss occurs.

Biomarkers in Diabetic Retinopathy

There is a global diabetes epidemic correlating with an increase in obesity. This coincidence may lead to a rise in the prevalence of type 2 diabetes. There is also an as yet unexplained increase in the incidence of type 1 diabetes, which is not related to adiposity. Whilst improved diabetes care has substantially improved diabetes outcomes, the disease remains a common cause of working age adult-onset blindness. Diabetic retinopathy is the most frequently occurring complication of diabetes; it is greatly feared by many diabetes patients. There are multiple risk factors and markers for the onset and progression of diabetic retinopathy, yet residual risk remains. Screening for diabetic retinopathy is recommended to facilitate early detection and treatment. Common biomarkers of diabetic retinopathy and its risk in clinical practice today relate to the visualization of the retinal vasculature and measures of glycemia, lipids, blood pressure, body weight, smoking, and pregnancy status. Greater knowledge of novel biomarkers and mediators of diabetic retinopathy, such as those related to inflammation and angiogenesis, has contributed to the development of additional therapeutics, in particular for late-stage retinopathy, including intra-ocular corticosteroids and intravitreal vascular endothelial growth factor inhibitors ('anti-VEGFs') agents. Unfortunately, in spite of a range of treatments (including laser photocoagulation, intraocular steroids, and anti-VEGF agents, and more recently oral fenofibrate, a PPAR-alpha agonist lipid-lowering drug), many patients with diabetic retinopathy do not respond well to current therapeutics. Therefore, more effective treatments for diabetic retinopathy are necessary. New analytical techniques, in particular those related to molecular markers, are accelerating progress in diabetic retinopathy research. Given the increasing incidence and prevalence of diabetes, and the limited capacity of healthcare systems to screen and treat diabetic retinopathy, there is need to reliably identify and triage people with diabetes. Biomarkers may facilitate a better understanding of diabetic retinopathy, and contribute to the development of novel treatments and new clinical strategies to prevent vision loss in people with diabetes. This article reviews key aspects related to biomarker research, and focuses on some specific biomarkers relevant to diabetic retinopathy.

Histone deacetylase (HDAC) inhibition improves myocardial function and prevents cardiac remodeling in diabetic mice

BACKGROUND

Recent evidence indicates that inhibition of histone deacetylase (HDAC) protects the heart against myocardial injury and stimulates endogenous angiomyogenesis. However, it remains unknown whether HDAC inhibition produces the protective effect in the diabetic heart. We sought to determine whether HDAC inhibition preserves cardiac performance and suppresses cardiac remodeling in diabetic cardiomyopathy.

METHODS

Adult ICR mice received an intraperitoneal injection of either streptozotocin (STZ, 200 mg/kg) to establish the diabetic model or vehicle to serve as control. Once hyperglycemia was confirmed, diabetic mice received sodium butyrate (1%), a specific HDAC inhibitor, in drinking water on a daily basis to inhibit HDAC activity. Mice were randomly divided into following groups, which includes Control, Control + Sodium butyrate (NaBu), STZ and STZ + Sodium butyrate (NaBu), respectively. Myocardial function was serially assessed at 7, 14, 21 weeks following treatments.

RESULTS

Echocardiography demonstrated that cardiac function was depressed in diabetic mice, but HDAC inhibition resulted in a significant functional improvement in STZ-injected mice. Likewise, HDAC inhibition attenuates cardiac hypertrophy, as evidenced by a reduced heart/tibia ratio and areas of cardiomyocytes, which is associated with reduced interstitial fibrosis and decreases in active caspase-3 and apoptotic stainings, but also increased angiogenesis in diabetic myocardium. Notably, glucose transporters (GLUT) 1 and 4 were up-regulated following HDAC inhibition, which was accompanied with increases of GLUT1 acetylation and p38 phosphorylation. Furthermore, myocardial superoxide dismutase, an important antioxidant, was elevated following HDAC inhibition in the diabetic mice.

CONCLUSION

HDAC inhibition plays a critical role in improving cardiac function and suppressing myocardial remodeling in diabetic heart.

Dysregulated post-transcriptional control of COX-2 gene expression in gestational diabetic endothelial cells

BACKGROUND AND PURPOSE

Hyperglycaemic memory describes the progression of diabetic complications during subsequent periods of improved glycaemia. We addressed the hypothesis that transient hyperglycaemia causes aberrant COX-2 expression in HUVEC in response to IL-1β through the induction of long-lasting epigenetic changes involving microRNA-16 (miR-16), a post-transcriptional modulator of COX-2 expression.

EXPERIMENTAL APPROACH

Studies were performed on HUVEC collected from women with gestational diabetes mellitus (GDM) (dHUVEC) and normal women (nHUVEC).

KEY RESULTS

In dHUVEC treated with IL-1β, the expression of COX-2 mRNA and protein was enhanced and generation of prostanoids increased (the most abundant was the promitogenic PGF_2α ). COX-2 mRNA was more stable in dHUVEC and this was associated with miR-16 down-regulation and c-Myc induction (a suppressor of miR expression). dHUVEC showed increased proliferation in response to IL-1β, which was prevented by a COX-2 inhibitor and PGF_2α receptor antagonist. Comparable changes in COX-2 mRNA, miR-16 and c-Myc detected in dHUVEC were produced in nHUVEC exposed to transient high glucose and then stimulated with IL-1β under physiological glucose levels; superoxide anion production was enhanced under these experimental conditions.

CONCLUSIONS AND IMPLICATIONS

Our results describe a possible mechanism operating in GDM that links the enhanced superoxide anion production and epigenetic changes, associated with hyperglycaemic memory, to endothelial dysfunction through dysregulated post-transcriptional control of COX-2 gene expression in response to inflammatory stimuli. The association of conventional therapy for glycaemic control with agents affecting inflammatory responses and oxidative stress might lead to a more effective prevention of the complications associated with GDM.

50 years forward: mechanisms of hyperglycaemia-driven diabetic complications

The advent of insulin treatment in 1923 meant fewer diabetes deaths from acute metabolic deterioration and sepsis and a progressive increase in the burden of disease caused by end-organ damage. These diabetic complications are the major cause of morbidity and premature mortality among diabetic subjects. Over the last 50 years it has become apparent that diabetic complications in disparate tissues may result from a combination of common pathological processes. Pathways activated by initial metabolic insults are promoted by co-factors such as renin-angiotensin-aldosterone system activation, hyperinsulinaemia, underlying genetic susceptibility, and traditional vascular risk factors, particularly hypertension and lipids. These common pathways include AGE formation, reactive oxygen species overproduction, protein kinase C activation, mitochondrial dysfunction and activation of proinflammatory and profibrotic signalling cascades. Once established, these interlinked pathways become self-perpetuating. Many drugs acting against individual downstream targets in these pathways have failed due to lack of efficacy or adverse effects. Gains in the future may be made by better control of existing risk factors, more sophisticated modulation of tissue glucose and insulin signalling, and interventions to improve mitochondrial function and reduce oxidative stress. Epigenetic and microRNA research may lead to methods to disrupt the mechanisms whereby pathological pathways are perpetuated. Expansion in capacity and expertise in biomarker measurement and analysis may allow better targeting of therapies to patients who are most likely to benefit. This is one of a series of commentaries under the banner '50 years forward', giving personal opinions on future perspectives in diabetes, to celebrate the 50th anniversary of Diabetologia (1965-2015).

Diabetic kidney disease

The kidney is arguably the most important target of microvascular damage in diabetes. A substantial proportion of individuals with diabetes will develop kidney disease owing to their disease and/or other co-morbidity, including hypertension and ageing-related nephron loss. The presence and severity of chronic kidney disease (CKD) identify individuals who are at increased risk of adverse health outcomes and premature mortality. Consequently, preventing and managing CKD in patients with diabetes is now a key aim of their overall management. Intensive management of patients with diabetes includes controlling blood glucose levels and blood pressure as well as blockade of the renin-angiotensin-aldosterone system; these approaches will reduce the incidence of diabetic kidney disease and slow its progression. Indeed, the major decline in the incidence of diabetic kidney disease (DKD) over the past 30 years and improved patient prognosis are largely attributable to improved diabetes care. However, there remains an unmet need for innovative treatment strategies to prevent, arrest, treat and reverse DKD. In this Primer, we summarize what is now known about the molecular pathogenesis of CKD in patients with diabetes and the key pathways and targets implicated in its progression. In addition, we discuss the current evidence for the prevention and management of DKD as well as the many controversies. Finally, we explore the opportunities to develop new interventions through urgently needed investment in dedicated and focused research. For an illustrated summary of this Primer, visit: http://go.nature.com/NKHDzg.

Long-lasting partnership between insulin resistance and endothelial dysfunction: role of metabolic memory

BACKGROUND AND PURPOSE

The persistence of deleterious effects of hyperglycaemia even after glucose normalization is referred to as 'metabolic memory'. However, similar persistent effects of the metabolic consequences of a high fat diet (HFD) have not been described.

EXPERIMENTAL APPROACH

Rats were given a normal pellet diet (NPD) or a HFD for 3 months. The animals from the HFD group were then returned to the NPD to observe the long-term effects of insulin resistance. Endothelial dysfunction was assessed by carbachol-mediated vasorelaxation and eNOS phosphorylation.

KEY RESULTS

As expected, HFD consumption resulted in insulin resistance and endothelial dysfunction. Phosphorylation of eNOS at S1177 was decreased in HFD rats, compared with that in the NPD group. Rats on 3 months of HFD showed glucose intolerance and impaired insulin sensitivity and were then switched back to NPD (REV group) . Levels of cholesterol and triglyceride, and adiposity returned to normal in REV rats. However, endothelium-dependent vascular responses to carbachol which were impaired in HFD rats, continued to be impaired in REV rats. Similarly, decreased eNOS phosphorylation after HFD was not improved after 1 or 6 months of REV.

CONCLUSIONS AND IMPLICATIONS

Our data indicate that returning to NPD did not improve the insulin sensitivity or the endothelial dysfunction induced by HFD. Although some biochemical parameters responsible for insulin resistance and endothelial dysfunction were normalized, molecular and vascular abnormalities, involving NO, persisted for several months, highlighting the long-lasting effects of metabolic memory.

Regulation of Nox enzymes expression in vascular pathophysiology: Focusing on transcription factors and epigenetic mechanisms

NADPH oxidases (Nox) represent a family of hetero-oligomeric enzymes whose exclusive biological function is the generation of reactive oxygen species (ROS). Nox-derived ROS are essential modulators of signal transduction pathways that control key physiological activities such as cell growth, proliferation, migration, differentiation, and apoptosis, immune responses, and biochemical pathways. Enhanced formation of Nox-derived ROS, which is generally associated with the up-regulation of different Nox subtypes, has been established in various pathologies, namely cardiovascular diseases, diabetes, obesity, cancer, and neurodegeneration. The detrimental effects of Nox-derived ROS are related to alterations in cell signalling and/or direct irreversible oxidative damage of nucleic acids, proteins, carbohydrates, and lipids. Thus, understanding of transcriptional regulation mechanisms of Nox enzymes have been extensively investigated in an attempt to find ways to counteract the excessive formation of Nox-derived ROS in various pathological states. Despite the numerous existing data, the molecular pathways responsible for Nox up-regulation are not completely understood. This review article summarizes some of the recent advances and concepts related to the regulation of Nox expression in the vascular pathophysiology. It highlights the role of transcription factors and epigenetic mechanisms in this process. Identification of the signalling molecules involved in Nox up-regulation, which is associated with the onset and development of cardiovascular dysfunction may contribute to the development of novel strategies for the treatment of cardiovascular diseases.

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Nox is a unique class of enzymes whose sole function is the generation of ROS.

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Nox-derived ROS play a major role in cell physiology.

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Enhanced expression and activation of Nox has been reported in numerous pathologies.

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Nox expression is regulated via complex transcription factor-epigenetic mechanisms.

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Understanding of Nox regulation is essential to counteract ROS-induced cell damage.

Unacylated ghrelin induces oxidative stress resistance in a glucose intolerance and peripheral artery disease mouse model by restoring endothelial cell miR-126 expression

Reactive oxygen species (ROS) are crucial in long-term diabetes complications, including peripheral artery disease (PAD). In this study, we have investigated the potential clinical impact of unacylated ghrelin (UnAG) in a glucose intolerance and PAD mouse model. We demonstrate that UnAG is able to protect skeletal muscle and endothelial cells (ECs) from ROS imbalance in hind limb ischemia-subjected ob/ob mice. This effect translates into reductions in hind limb functional impairment. We show that UnAG rescues sirtuin 1 (SIRT1) activity and superoxide dismutase-2 (SOD-2) expression in ECs. This leads to SIRT1-mediated p53 and histone 3 lysate 56 deacetylation and results in reduced EC senescence in vivo. We demonstrate, using small interfering RNA technology, that SIRT1 is also crucial for SOD-2 expression. UnAG also renews micro-RNA (miR)-126 expression, resulting in the posttranscriptional regulation of vascular cell adhesion molecule 1 expression and a reduced number of infiltrating inflammatory cells in vivo. Loss-of-function experiments that target miR-126 demonstrate that miR-126 also controls SIRT1 and SOD-2 expression, thus confirming its role in driving UnAG-mediated EC protection against ROS imbalance. These results indicate that UnAG protects vessels from ROS imbalance in ob/ob mice by rescuing miR-126 expression, thus emphasizing its potential clinical impact in avoiding limb loss in PAD.

Gallic Acid Decreases Inflammatory Cytokine Secretion Through Histone Acetyltransferase/Histone Deacetylase Regulation in High Glucose-Induced Human Monocytes

Hyperglycemia contributes to diabetes and several diabetes-related complications. Gallic acid is a polyhydroxy phenolic compound found in various natural products. In this study, we investigated the effects and mechanism of gallic acid on proinflammatory cytokine secretion in high glucose-induced human monocytes (THP-1 cells). THP-1 cells were cultured under normoglycemic or hyperglycemic conditions, in the absence or presence of gallic acid. Hyperglycemic conditions significantly induced histone acetylation, nuclear factor-κB (NF-κB) activation, and proinflammatory cytokine release from THP-1 cells, whereas gallic acid suppressed NF-κB activity and cytokine release. It also significantly reduced CREB-binding protein/p300 (CBP/p300, a NF-κB coactivator) gene expression, acetylation levels, and CBP/p300 histone acetyltransferase (HAT) activity. In addition, histone deacetylase 2 (HDAC2) expression was significantly induced. These results suggest that gallic acid inhibits hyperglycemic-induced cytokine production in monocytes through epigenetic changes involving NF-κB. Therefore, gallic acid may have potential for the treatment and prevention of diabetes and its complications.

Adipose-derived stem cells from diabetic mice show impaired vascular stabilization in a murine model of diabetic retinopathy

Diabetic retinopathy is characterized by progressive vascular dropout with subsequent vision loss. We have recently shown that an intravitreal injection of adipose-derived stem cells (ASCs) can stabilize the retinal microvasculature, enabling repair and regeneration of damaged capillary beds in vivo. Because an understanding of ASC status from healthy versus diseased donors will be important as autologous cellular therapies are developed for unmet clinical needs, we took advantage of the hyperglycemic Akimba mouse as a preclinical in vivo model of diabetic retinopathy in an effort aimed at evaluating therapeutic efficacy of adipose-derived stem cells (mASCs) derived either from healthy, nondiabetic or from diabetic mice. To these ends, Akimba mice received intravitreal injections of media conditioned by mASCs or mASCs themselves, subsequent to development of substantial retinal capillary dropout. mASCs from healthy mice were more effective than diabetic mASCs in protecting the diabetic retina from further vascular dropout. Engrafted ASCs were found to preferentially associate with the retinal vasculature. Conditioned medium was unable to recapitulate the vasoprotection seen with injected ASCs. In vitro diabetic ASCs showed decreased proliferation and increased apoptosis compared with healthy mASCs. Diabetic ASCs also secreted less vasoprotective factors than healthy mASCs, as determined by high-throughput enzyme-linked immunosorbent assay. Our findings suggest that diabetic ASCs are functionally impaired compared with healthy ASCs and support the utility of an allogeneic injection of ASCs versus autologous or conditioned media approaches in the treatment of diabetic retinopathy.

Maternal High-Fat Diet Exaggerates Atherosclerosis in Adult Offspring by Augmenting Periaortic Adipose Tissue-Specific Proinflammatory Response

Objective—

Maternal obesity elicits offspring’s metabolic disorders via developmental modifications of visceral adipose tissue; however, its effect on atherogenesis remains undefined. Perivascular adipose tissue has recently been implicated in vascular remodeling and vasoreactivity. We hypothesize that developmental modifications of perivascular adipose tissue by maternal high-fat diet (HFD) exposure promotes atherosclerosis in adult offspring.

Approach and Results—

Eight-week-old female apolipoprotein E-deficient mice were fed an HFD or normal diet (ND) during gestation and lactation. Offspring were fed a high-cholesterol diet from 8 weeks of age. Twenty-week-old male offspring of HFD-fed dams (O-HFD) showed a 2.1-fold increase in atherosclerotic lesion of the entire aorta compared with those of ND-fed dams (O-ND). Although mRNA expressions of interleukin-6, tumor necrosis factor, and monocyte chemotactic protein-1 and accumulation of macrophages in epididymal white adipose tissue were less in O-HFD than in O-ND, thoracic periaortic adipose tissue (tPAT) showed an exaggerated inflammatory response in O-HFD. Intra-abdominal transplantation of tPAT from 8-week-old O-HFD alongside the distal abdominal aorta exaggerated atherosclerosis development of the infrarenal aorta in recipient apolipoprotein E-deficient mice compared with tPAT from O-ND (210%, P <0.01). Although macrophage accumulation was rarely detected in tPAT of 8-week-old offspring, mRNA expression and protein levels of macrophage colony–stimulating factor were markedly elevated in O-HFD (2.3-fold, 3.3-fold, respectively, P <0.05), suggesting that increased macrophage colony–stimulating factor expression contributes to the augmented accumulation of macrophages, followed by the enhanced proinflammatory response.

Conclusions—

Our findings demonstrate that maternal HFD exaggerates atherosclerosis development in offspring by augmenting tPAT-specific inflammatory response proceeded by an increased expression of macrophage colony–stimulating factor.

Personalized medicine and type 2 diabetes: lesson from epigenetics

Similarly to genetic polymorphisms, epigenetic modifications may alter transcriptional activity and contribute to different traits of the Type 2 diabetes phenotype. The establishment of these epigenetic marks may precede diabetes onset and predict the disease. Current evidence now indicates that epigenetic differences represent markers of diabetes risk. Studies on epigenome plasticity revealed that cytokines and other metabolites, by affecting DNA methylation, may acutely reprogram gene expression and contribute to the Type 2 diabetes phenotype even in the adult life. The available evidence further indicates that epigenetic marks across the genome are subject to dynamic variations in response to environmental cues. Finally, different genes responsible for the interindividual variability in antidiabetic drug response are subjected to epigenetic regulation. Determining how specific epigenetic profiles determine diabetes is a challenging task. In the near future, the identification of epigenetic marks predictive of diabetes risk or response to treatment may offer unanticipated opportunities to personalize Type 2 diabetes management.