Regulation of matrix metalloproteinase-9 by epigenetic modifications and the development of diabetic retinopathy

Personalized epigenetic management of diabetes

The novel genome-wide assays of epigenetic marks have resulted in a greater understanding of how genetics and the environment interact in the development and inheritance of diabetes. Chronic hyperglycemia induces epigenetic changes in multiple organs, contributing to diabetic complications. Specific epigenetic-modifying compounds have been developed to erase these modifications, possibly slowing down the onset of diabetes-related complications. The current review is an update of the previously published paper, describing the most recent advances in the epigenetics of diabetes.

Imbalance between matrix metalloproteinases and their tissue inhibitors in preeclampsia and gestational trophoblastic diseases

The invasion cascade exhibited by placental trophoblasts and cancerous cells bears many similarities, and it is attributed to extracellular matrix degradation mediated by matrix metalloproteinases (MMPs). Although proper and controlled invasion by trophoblasts into the maternal uterus is an essential requirement for maintenance of normal pregnancy, any abnormality in this phenomenon results in the development of invasion-related disorders such as gestational trophoblastic diseases (GTDs) and preeclampsia. We studied the epigenetic basis of differential expression of two placental MMPs (MMP2 and MMP9) and tissue inhibitors of metalloproteinases (TIMP2 and TIMP1) during normal gestation and invasion-related disorders, i.e., preeclampsia and GTDs. Our study suggests the association of H3K9/27me3 with differential expression of these MMPs and their inhibitors, which regulate the placental invasion during normal pregnancy, whereas no role of CpG methylation was observed in the differential expression of MMPs/TIMPs. Further, development of GTDs was associated with abnormally higher expression of these MMPs and lower levels of their inhibitors, whereas the reverse trends were observed for MMPs and their TIMPs in case of preeclampsia, in association with abnormal changes in H3K9/27me3. These results suggest the involvement of higher levels of MMPs in an aggressive invasive behavior depicted by GTDs, whereas lower levels of these MMPs in shallow and poor invasive phenotype associated with preeclampsia. Thus, our study shows the significance of a proper balance regulated by histone trimethylation between differential expression of MMPs and their TIMPs for maintaining normal pregnancy and its deregulation as a contributing factor for pathogenesis of invasive disorders during pregnancy.

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.

Metalloproteinases as mediators of inflammation and the eyes: molecular genetic underpinnings governing ocular pathophysiology

There are many vision threatening diseases of the eye affecting millions of people worldwide. In this article, we are summarizing potential role of various matrix metalloproteinases (MMPs); the Zn (2+)-dependent endoproteases in eye health along with pathogenesis of prominent ocular diseases such as macular degeneration, diabetic retinopathy, and glaucoma via understanding MMPs regulation in affected patients, interactions of MMPs with their substrate molecules, and key regulatory functions of tissue inhibitor of metalloproteinases (TIMPs) towards maintaining overall homeostasis.

Diabetic retinopathy: reversibility of epigenetic modifications and new therapeutic targets

In recent years, considerable progress has been made in the molecular mechanisms of epigenetics in disease development and progression, the reversible characteristics of epigenetic modification provide new insights for the treatment of such diseases. The pathogenesis of diabetic retinopathy (DR) has not yet been fully understood, treatment of refractory and recurrent diabetic macular edema remains a big change in clinical practice. This review emphasizes that reversibility of epigenetic modification could provide a new strategy for the prevention and treatment of diseases.

Diabetic retinopathy, metabolic memory and epigenetic modifications

Retinopathy, a sight-threatening disease, remains one of the most feared complications of diabetes. Although hyperglycemia is the main initiator, progression of diabetic retinopathy continues even after re-institution of normal glycemic control in diabetic patients, and the deleterious effects of prior hyperglycemic insult depend on the duration and the severity of this insult, suggesting a 'metabolic memory' phenomenon. Metabolic memory phenomenon is successfully duplicated in the experimental models of diabetic retinopathy. Hyperglycemia, in addition to initiating many other biochemical and functional abnormalities and altering expression of genes associated with them, also increases oxidative stress. Increased production of cytosolic reactive oxygen species dysfunctions the mitochondria, and a compromised antioxidant defense system becomes overwhelmed to neutralize free radicals. With the duration of diabetes extending, mitochondrial DNA (mtDNA) is also damaged, and transcription of mtDNA-encoded genes, important for function of the electron transport chain, is compromised. This fuels into a 'self-propagating' vicious cycle of free radicals, and retinopathy continues to progress. Hyperglycemic insult also affects the enzymatic machinery responsible for epigenetic modifications; these modifications alter gene expression without affecting the DNA sequence. Histones and/or DNA modifications of many enzymes, important in mitochondrial homeostasis, affect their activities and disturb mitochondrial homeostasis. Experimental models have shown that these epigenetic modifications have potential to halt only if normal glycemia is maintained from the day of induction of diabetes (streptozotocin) in rats, but if hyperglycemia is allowed to proceed even for couple months before initiation of normal glycemia, these epigenetic modification resist reversal. Supplementation of a therapy targeted to prevent increased oxidative stress or epigenetic modifications, during the normal glucose phase, which has followed high glucose insult, however, helps ameliorate these abnormalities and prevents the progression of diabetic retinopathy. Thus, without undermining the importance of tight glycemic control for a diabetic patient, supplementation of their 'best possible' glycemic control with such targeted therapies has potential to retard further progression of this blinding disease.

The Role of DNA Methylation in the Metabolic Memory Phenomenon Associated With the Continued Progression of Diabetic Retinopathy

Purpose

Clinical and experimental studies have shown that diabetic retinopathy progression does not halt after termination of hyperglycemia, suggesting a “metabolic memory” phenomenon. DNA is highly dynamic, and cytosine methylation changes can last for several years. In diabetes, DNA methylation regulates expression of many genes associated with retinal mitochondrial homeostasis. Our aim was to investigate the role of DNA methylation in the metabolic memory.

Methods

Reversal of 4 days of 20 mM glucose by 4 to 8 days of 5 mM glucose, in the presence/absence of Dnmt inhibitor (5-aza-2′-deoxycytidine), was investigated on DNA methylation and its machinery in human retinal endothelial cells. The key parameters were confirmed in the retina from diabetic rats maintained in good glycemic control (glycated hemoglobin ∼6%) for 3 months after 3 months of poor control (glycated hemoglobin >10%).

Results

DNA methyltransferase 1 (Dnmt 1) remained active after 4 days of normal glucose that followed 4 days of high glucose, and mtDNA stayed hypermethylated with impaired transcription. Hydroxymethylating enzyme Tet2, and matrix metalloproteinase-9 (regulated by hydroxymethylation) also remained upregulated. But, 8 days of normal glucose after 4 days of high glucose ameliorated mtDNA methylation and MMP-9 hydroxymethylation. Direct Dnmt targeting by Aza during the reversal period benefited methylation status of mtDNA and MMP-9 DNA. Similarly, reinstitution of good control after 3 months of poor control in rats did not reverse diabetes-induced increase in retinal Dnmt1 and Tet2, and alter the methylation status of mtDNA and MMP-9.

Conclusions

Retinal DNA methylation-hydroxymethylation machinery does not benefit immediately from reversal of hyperglycemia. Maintenance of good glycemic control for longer duration, and/or direct targeting DNA methylation ameliorates continuous mitochondrial damage, and could retard/halt diabetic retinopathy progression.

Role of PARP-1 as a novel transcriptional regulator of MMP-9 in diabetic retinopathy

In diabetes, matrix metalloproteinase-9 (MMP-9) is activated, which damages mitochondria, resulting in accelerated capillary cell apoptosis. Regulation of MMP-9 is controlled by multiple transcription factors including nuclear factor-kB (NF-kB) and activator protein-1 (AP-1). Binding of these transcription factors, however, can be regulated by poly(ADP-ribose) polymerase-1 (PARP-1), which forms a strong initiation complex at the promoter region and facilitates multiple rounds of gene transcription. This complex formation with the transcription factors is regulated by posttranslational acetylation of PARP-1, and in diabetes, the deacetylating enzyme, Sirt1, is inhibited. Our aim was to understand the role of PARP-1 in transcriptional regulation of MMP-9 in the development of diabetic retinopathy. Using human retinal endothelial cells, the effect of PARP-1 inhibition (pharmacologically by PJ34, 1μM; or genetically by its siRNA) on MMP-9 expression was investigated. The effect of PARP-1 acetylation on its binding at the MMP-9 promoter, and with NF-kB/AP-1, was investigated in the cells transfected with Sirt1. In vitro results were validated in the retinal microvessels from diabetic mice either administered PJ34, or overexpressing Sirt1. Inhibition of PARP-1 ameliorated hyperglycemia-induced increase in the binding of NF-kB/AP-1 at the MMP-9 promoter, decreased MMP-9 expression and ameliorated mitochondrial damage. Overexpression of Sirt1 attenuated diabetes-induced increase in PARP-1 binding at MMP-9 promoter or with NF-kB/AP-1. Thus, PARP-1, via manipulating the binding of NF-kB/AP-1 at the MMP-9 promoter, regulates MMP-9 expression, which helps maintain mitochondrial homeostasis.

Abnormal levels of histone methylation in the retinas of diabetic rats are reversed by minocycline treatment

In this study we quantified the alterations of retinal histone post-translational modifications (PTMs) in diabetic rats using a liquid chromatography - tandem mass spectrometry (LC-MS/MS) approach. Some diabetic rats were subsequently treated with minocycline, a tetracycline antibiotic, which has been shown to inhibit the diabetes-induced chronic inflammation in the retinas of rodents. We quantified 266 differentially modified histone peptides, including 48 out of 83 methylation marks with significantly different abundancein retinas of diabetic rats as compared to non-diabetic controls. About 67% of these marks had their relative abundance restored to non-diabetic levels after minocycline treatment. Mono- and di-methylation states of histone H4 lysine 20 (H4K20me1/me2), markers related to DNA damage response, were found to be up-regulated in the retinas of diabetic rats and restored to control levels upon minocycline treatment. DNA damage response biomarkers showed the same pattern once quantified by western blotting. Collectively, this study indicates that alteration of some histone methylation levels is associated with the development of diabetic retinopathy in rodents, and the beneficial effect of minocycline on the retinas of diabetic rodents is partially through its ability to normalize the altered histone methylation levels.

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.

Oxidative Stress-Related Mechanisms and Antioxidant Therapy in Diabetic Retinopathy

Diabetic retinopathy (DR) is one of the most common microvascular complications of diabetes and is the leading cause of blindness in young adults. Oxidative stress has been implicated as a critical cause of DR. Metabolic abnormalities induced by high-glucose levels are involved in the development of DR and appear to be influenced by oxidative stress. The imbalance between reactive oxygen species (ROS) production and the antioxidant defense system activates several oxidative stress-related mechanisms that promote the pathogenesis of DR. The damage caused by oxidative stress persists for a considerable time, even after the blood glucose concentration has returned to a normal level. Animal experiments have proved that the use of antioxidants is a beneficial therapeutic strategy for the treatment of DR, but more data are required from clinical trials. The aims of this review are to highlight the improvements to our understanding of the oxidative stress-related mechanisms underlying the development of DR and provide a summary of the main antioxidant therapy strategies used to treat the disease.

Epigenetic regulation of redox signaling in diabetic retinopathy: Role of Nrf2

Diabetic retinopathy is a major vision threatening disease among working age adults, and increased oxidative stress is one of the prime causative factors in its pathogenesis. Increased reactive oxygen species (ROS) in the cytosol damage mitochondria, and due to compromised antioxidant signaling system and dysfunctional mitochondria with damaged mitochondrial DNA, ROS continue to pile up, accelerating capillary cell loss. In addition to other cellular and enzymatic defense systems, the retina is also equipped with the nuclear erythroid-2-p45-related factor-2 (Nrf2) antioxidant response element signaling pathway, which controls the expression of genes important in detoxification and elimination of ROS. However, in diabetes, its transcriptional activity is impaired, further exacerbating and exposing the retina to elevated stress. Diabetic milieu also alters epigenetic factors responsible for chromatin modifications and gene regulation, and kelch-like ECH-associated protein 1 (Keap1), important in regulating Nrf2-antioxidant signaling axis, is epigenetically modified, impeding nuclear translocation of Nrf2, and this inhibits the transcription of genes with Antioxidant Response Element. This review discusses antioxidant signaling, especially the role of Nrf2, in diabetic retinopathy, and possible involvement of epigenetic modifications in antioxidant signaling and Nrf2 transcriptional activity. Therapies targeting Nrf2 activation, including epigenetic modifications, have potentional to prevent mitochondrial damage and inhibit the development, and progression of this sight-threatening disease which most of the patients get after 20-25 years of diabetes.

Role of oxidative stress in epigenetic modification of MMP-9 promoter in the development of diabetic retinopathy

BACKGROUND

In the pathogenesis of diabetic retinopathy, damaged retinal mitochondria accelerate apoptosis of retinal capillary cells, and regulation of oxidative stress by manipulating mitochondrial superoxide dismutase (SOD2) protects mitochondrial homeostasis and prevents the development of diabetic retinopathy. Diabetes also activates matrix metalloproteinase-9 (MMP-9), and activated MMP-9 damages retinal mitochondria. Recent studies have shown a dynamic DNA methylation process playing an important role in regulation of retinal MMP-9 transcription in diabetes; the aim of this study is to investigate the role of oxidative stress in MMP-9 transcription.

METHODS

The effect of regulation of mitochondrial superoxide on DNA methylation of MMP-9 promoter region was investigated in retinal endothelial cells incubated in the presence or absence of a MnSOD mimetic MnTBAP, by quantifying the levels of 5 methyl cytosine (5mC) and hydroxyl-methyl cytosine (5hmC). The binding of DNA methylating, and of hydroxymenthylating enzymes (Dnmts and Tets, respectively), at MMP-9 promoter (by chromatin immunoprecipitation) was also evaluated. The in vitro results were confirmed in the retina of diabetic mice overexpressing SOD2.

RESULTS

MnTBAP attenuated glucose-induced decrease in 5mC levels and increase on Dnmt1 binding at the MMP-9 promoter region. MnTBAP also ameliorated alterations in 5hmC levels and Tet binding, regulated MMP-9 transcription, and prevented mitochondrial damage. Similarly, mice overexpressing SOD2 were protected from diabetes-induced alteration in MMP-9 promoter methylation, and its transcription.

CONCLUSIONS

Thus, regulation of oxidative stress by pharmacologic/genetic approaches maintains retinal mitochondrial homeostasis by ameliorating epigenetic modifications in the MMP-9 promoter region.

Dynamic DNA methylation of matrix metalloproteinase-9 in the development of diabetic retinopathy

Diabetes elevates matrix metalloproteinase-9 (MMP-9) in the retina and its capillary cells, and activated MMP-9 damages mitochondria, accelerating retinal capillary cell apoptosis, a phenomenon which precedes the development of retinopathy. Diabetes also favors epigenetic modifications regulating the expression of many genes. DNA methylation is maintained by methylating-hydroxymethylating enzymes, and retinal DNA methyltransferase (Dnmt) is activated in diabetes. Our aim is to investigate the role of DNA methylation in MMP-9 regulation. The effect of high glucose on 5-methylcytosine (5mC) and 5-hydroxymethyl cytosine (5hmC), and binding of Dnmt1 and hydroxymethylating enzyme (Tet2) on MMP-9 promoter were quantified in retinal endothelial cells. Specific role of Tet2 in MMP-9 activation was validated using Tet2-siRNA. The results were confirmed in the retina from streptozotocin-induced diabetic mouse. Although glucose increased Dnmt1 binding at MMP-9 promoter, it decreased 5mC levels. At the same promoter site, Tet2 binding and 5hmC levels were elevated. Tet2-siRNA ameliorated increase in 5hmC and MMP-9 transcription, and protected mitochondrial damage. Diabetic mice also presented similar dynamic DNA methylation changes in the retinal MMP-9 promoter. Thus, in diabetes transcription of retinal MMP-9 is maintained, in part, by an active DNA methylation-hydroxymethylation process, and regulation of this machinery should help maintain mitochondrial homeostasis and inhibit the development/progression of diabetic retinopathy.

Salusin-β Promotes Vascular Smooth Muscle Cell Migration and Intimal Hyperplasia After Vascular Injury via ROS/NFκB/MMP-9 Pathway

AIMS

Media-to-intima migration of vascular smooth muscle cells (VSMCs) is critical to intimal thickening in atherosclerosis and restenosis after coronary angioplasty. The aim of this study is to determine the effects of salusin-β on VSMC migration and intimal hyperplasia after vascular injury and the underlying mechanism.

RESULTS

In vitro, salusin-β promoted VSMC migration, which was attenuated by matrix metalloproteinase (MMP)-9 inhibition. Inhibition or knockdown of p65-nuclear factor kappa beta (NFκB) in VSMCs suppressed salusin-β-induced MMP-9 expression and VSMC migration. Salusin-β increased NADPH oxidase 2 (NOX2) expression and reactive oxygen species (ROS) production, which were prevented by NOX2-small interfering RNA (siRNA) transfection. Salusin-β-induced p65-NFκB translocation, MMP-9 expression, and VSMC migration were inhibited by ROS scavenger, NADPH oxidase inhibitor, or NOX2-siRNA. In vivo, carotid artery ligation-induced vascular injury resulted in intimal hyperplasia in injured artery in rats. Salusin-β was upregulated in the injured carotid arteries of rats, which was attributed to reduced miR-133a-3p expression. Knockdown of salusin-β with siRNA attenuated the vascular injury-induced intimal thickening, p65-NFκB nuclear translocation, and NOX2 and MMP-9 expressions in rats.

INNOVATION

Salusin-β is a critical modulator in VSMC migration and neointima formation in response to vascular injury.

CONCLUSIONS

Salusin-β promotes VSMC migration and vascular injury-induced intimal hyperplasia via MMP-9 accumulation due to NOX2 activation, followed by ROS production, IκBα phosphorylation and degradation, and p65-NFκB translocation. We propose that salusin-β may be important in the VSMC migration and neointima of some vascular diseases. Antioxid. Redox Signal. 24, 1045-1057.

Emerging roles of the myocardin family of proteins in lipid and glucose metabolism

Members of the myocardin family bind to the transcription factor serum response factor (SRF) and act as coactivators controlling genes of relevance for myogenic differentiation and motile function. Binding of SRF to DNA is mediated by genetic elements called CArG boxes, found often but not exclusively in muscle and growth controlling genes. Studies aimed at defining the full spectrum of these CArG elements in the genome (i.e. the CArGome) have in recent years, unveiled unexpected roles of the myocardin family proteins in lipid and glucose homeostasis. This coactivator family includes the protein myocardin (MYOCD), the myocardin-related transcription factors A and B (MRTF-A/MKL1 and MRTF-B/MKL2) and MASTR (MAMSTR). Here we discuss growing evidence that SRF-driven transcription is controlled by extracellular glucose through activation of the Rho-kinase pathway and actin polymerization. We also describe data showing that adipogenesis is influenced by MLK activity through actions upstream of peroxisome proliferator-activated receptor γ with consequences for whole body fat mass and insulin sensitivity. The recently demonstrated involvement of myocardin coactivators in the biogenesis of caveolae, Ω-shaped membrane invaginations of importance for lipid and glucose metabolism, is finally discussed. These novel roles of myocardin proteins may open the way for new unexplored strategies to combat metabolic diseases such as diabetes, which, at the current incidence, is expected to reach 333 million people worldwide by 2025. This review highlights newly discovered roles of myocardin-related transcription factors in lipid and glucose metabolism as well as novel insights into their well-established role as mediators of stretch-dependent effects in smooth muscle. As co-factors for serum response factor (SRF), MKLs regulates transcription of genes involved in the contractile function of smooth muscle cells. In addition to mechanical stimuli, this regulation has now been found to be promoted by extracellular glucose levels in smooth muscle. Recent reports also suggest that MKLs can regulate a subset of genes involved in the formation of lipid-rich invaginations in the cell membrane called caveolae. Finally, a potential role of MKLs in non-muscle cells has been discovered as they negatively influence adipocyte differentiation.

Salusin-β induces foam cell formation and monocyte adhesion in human vascular smooth muscle cells via miR155/NOX2/NFκB pathway

Vascular smooth muscle cells (VSMCs) are indispensible components in foam cell formation. Salusin-β is a stimulator in the progression of atherosclerosis. Here, we showed that salusin-β increased foam cell formation evidenced by accumulation of lipid droplets and intracellular cholesterol content, and promoted monocyte adhesion in human VSMCs. Salusin-β increased the expressions and activity of acyl coenzyme A:cholesterol acyltransferase-1 (ACAT-1) and vascular cell adhesion molecule-1 (VCAM-1) in VSMCs. Silencing of ACAT-1 abolished the salusin-β-induced lipid accumulation, and silencing of VCAM-1 prevented the salusin-β-induced monocyte adhesion in VSMCs. Salusin-β caused p65-NFκB nuclear translocation and increased p65 occupancy at the ACAT-1 and VCAM-1 promoter. Inhibition of NFκB with Bay 11-7082 prevented the salusin-β-induced ACAT-1 and VCAM-1 upregulation, foam cell formation and monocyte adhesion in VSMCs. Scavenging ROS, inhibiting NADPH oxidase or knockdown of NOX2 abolished the effects of salusin-β on ACAT-1 and VCAM-1 expressions, p65-NFκB nuclear translocation, lipid accumulation and monocyte adhesion in VSMCs. Salusin-β increased miR155 expression, and knockdown of miR155 prevented the effects of salusin-β on ACAT-1 and VCAM-1 expressions, p65-NFκB nuclear translocation, lipid accumulation, monocyte adhesion and ROS production in VSMCs. These results indicate that salusin-β induces foam formation and monocyte adhesion via miR155/NOX2/NFκB-mediated ACAT-1 and VCAM-1 expressions in VSMCs.

Matrix Metalloproteinase-9 in the Culprit Coronary Artery and Myocardial No-Reflow

BACKGROUND

Matrix Metalloproteinases (MMPs) have been implicated in the pathogenesis of acute myocardial infarction (AMI). However, little is known about the association between MMP-9 and myocardial no-reflow. The aim of this study was to evaluate the role of MMP-9 in the culprit coronary artery as a predictor of no-reflow in patients with ST-elevation AMI.

METHODS

Ninety patients with ST-elevation AMI who underwent emergency percutaneous coronary intervention were consecutively recruited in this study. Blood samples were obtained from the extraction catheter placed distal to the culprit lesion at the beginning of percutaneous coronary intervention. No-reflow was defined as a coronary thrombolysis in myocardial infarction flow grade ≤2 after vessel reopening or thrombolysis in myocardial infarction flow 3 with a final myocardial blush grade ≤2.

RESULTS

No-reflow was observed in 25 patients (27.8%). Using multiple logistic regression analysis, local MMP-9 levels (odds ratio [OR] = 3.356; confidence interval [CI]: 1.441-5.881; P = 0.007) were found to be a significant risk factor of no-reflow together with lesion length (OR = 6.985; CI: 2.574-11.533; P = 0.009) and time to balloon (OR = 2.143; CI: 1.216-5.901; P = 0.042).

CONCLUSIONS

Elevation of MMP-9 level in the culprit coronary artery may predict no-reflow in patients with ST-elevation AMI.

Epigenetic Mechanisms of the Aging Human Retina

Degenerative retinal diseases, such as glaucoma, age-related macular degeneration, and diabetic retinopathy, have complex etiologies with environmental, genetic, and epigenetic contributions to disease pathology. Much effort has gone into elucidating both the genetic and the environmental risk factors for these retinal diseases. However, little is known about how these genetic and environmental risk factors bring about molecular changes that lead to pathology. Epigenetic mechanisms have received extensive attention of late for their promise of bridging the gap between environmental exposures and disease development via their influence on gene expression. Recent studies have identified epigenetic changes that associate with the incidence and/or progression of each of these retinal diseases. Therefore, these epigenetic modifications may be involved in the underlying pathological mechanisms leading to blindness. Further genome-wide epigenetic studies that incorporate well-characterized tissue samples, consider challenges similar to those relevant to gene expression studies, and combine the genome-wide epigenetic data with genome-wide genetic and expression data to identify additional potentially causative agents of disease are needed. Such studies will allow researchers to create much-needed therapeutics to prevent and/or intervene in disease progression. Improved therapeutics will greatly enhance the quality of life and reduce the burden of disease management for millions of patients living with these potentially blinding conditions.

The role of pharmacogenetics and advances in gene therapy in the treatment of diabetic retinopathy

Diabetic retinopathy (DR) and its complications such as diabetic macular edema continue to remain a major cause for legal blindness in the developed world. While the introduction of anti-tVEGF agents has significantly improved visual outcomes of patients with DR, unpredictable response, largely due to genetic polymorphisms, appears to be a challenge with this therapy. With advances in identification of various genetic biomarkers, novel therapeutic strategies consisting of gene transfer are being developed and tested for patients with DR. Application of pharmacogenetic principles appears to be a promising futuristic strategy to attenuate diabetes-mediated retinal vasculopathy. In this comprehensive review, data from recent studies in the field of pharmacogenomics for the treatment of DR have been provided.

The epigenetic regulation of podocyte function in diabetes

Chronic hyperglycemia early in the course of diabetes confers a sustained increase in the risk of complications development. In recent years, efforts to understand the molecular basis for this "metabolic memory" have focused on epigenetic mechanisms as a means by which transient high glucose can cause persistent and propagated changes in cell function. For instance, in vascular endothelial cells, smooth muscle cells and peripheral blood cells, temporary exposure to high glucose causes changes in epigenetic marks that promote a shift towards a pro-inflammatory phenotype. However, the influence of epigenetic processes in complications development extends beyond their contribution to metabolic memory. Podocytes, for example, are terminally differentiated cells of the renal glomerulus whose injury is a major contributor to the pathogenesis of nephropathy. Over recent months, several reports have emerged describing the essential actions of histone-modifying enzymes and DNA methylation patterns (the two principal epigenetic mechanisms) in maintaining podocyte integrity, especially under diabetic conditions. Here, we review the known and potential role of epigenetic processes within podocytes, focusing on the evidence linking these processes to oxidative stress, crosstalk with tubule cells, autophagy and slit-pore protein expression. Whether podocytes themselves exhibit a metabolic memory awaits to be seen.

Personalized epigenetic management of diabetes

Epigenetic regulation of gene expression allows the organism to respond/adapt to environmental conditions without changing the gene coding sequence. Epigenetic modifications have also been found to control gene expression in various diseases, including diabetes. Epigenetic changes induced by hyperglycemia in multiple target organs contribute to metabolic memory of diabetic complications. The long-lasting development of diabetic complications even after achieving glucose control has been partly attributed to epigenetic changes in target cells. Specific epigenetic drugs might rescue chromatin conformation associated to hyperglycemia possibly slowing down the onset of diabetes-related complications. The current review will describe the updated epigenetics in diabetes that can be used to personalize a more focused treatment.

Apoptotic effect of mtrix metalloproteinases 9 in the development of diabetic retinopathy

OBJECTIVE

To explore the potential regulatory mechanism of MMP9 in the development of DR.

METHODS

Plasmids pcDNA-MMP9 and pcDNA-Ang2 were transfected into primary rat retinal Müller cells (RMCs) using Lipofectamine 2000. Cell viability and apoptosis were respectively determined by MTT assay and flow cytometry. Moreover, the interaction between MMP9 and Ang2 was explored. Besides, RMCs were treated with MMP-9 under normal glucose and high glucose condition for 2d. Besides, the expression levels of apoptotic proteins, like MMP9, Ang2, Bax2, Bcl2, cleaved PARP and cleaved caspase3 were determined by Western blot.

RESULTS

The cell viability of siRNA-MMP9 group was significantly increased while decreased in MMP9 overexpression group when compared to control group, respectively. The apoptotic cells in MMP9 overexpression group significantly increased while decreased in siRNA-MMP9 group when compared with control group. MMP9 expression was significantly regulated by Ang2 whereas no significant changes occurred in Ang2 expression when MMP9 expression changed. Moreover, MMP9 expression in HG group significantly increased while there were no significant differences between NG group and control group. Besides, the expression of Bax2, Bcl2, cleaved PARP and cleaved caspase3 in HG group increased while there were no significant differences between NG group and control group.

CONCLUSION

Our findings indicate that MMP9 may play an important role via inducing cell apoptosis in the development of DR via regulating by Ang2 or targeting apoptotic proteins, such as Bax2, Bcl2, cleaved PARP and cleaved caspase3.

Oxidative stress, mitochondrial damage and diabetic retinopathy

Diabetes has emerged as an epidemic of the 21st century, and retinopathy remains the leading cause of blindness in young adults and the mechanism of this blinding disease remains evasive. Diabetes-induced metabolic abnormalities have been identified, but a causal relationship between any specific abnormality and the development of this multi-factorial disease is unclear. Reactive oxygen species (ROS) are increased and the antioxidant defense system is compromised. Increased ROS result in retinal metabolic abnormalities, and these metabolic abnormalities can also produce ROS. Sustained exposure to ROS damages the mitochondria and compromises the electron transport system (ETC), and, ultimately, the mitochondrial DNA (mtDNA) is damaged. Damaged mtDNA impairs its transcription, and the vicious cycle of ROS continues to propagate. Many genes important in generation and neutralization of ROS are also epigenetically modified further increasing ROS, and the futile cycle continues to fuel in. Antioxidants have generated beneficial effects in ameliorating retinopathy in diabetic rodents, but limited clinical studies have not been encouraging. With the ongoing use of antioxidants for other chronic diseases, there is a need for a controlled trial to recognize their potential in ameliorating the development of this devastating disease.

Contribution of epigenetics in diabetic retinopathy

Diabetes has become the epidemic of the 21st century, and with over 90% patients with diabetes becoming at a risk of developing retinopathy, diabetic retinopathy has emerged as a major public health concern. In spite of cutting edge research in the field, how retina and its vasculature are damaged by the diabetic milieu remains ambiguous. The environmental factors, life style or disease process can also bring in modifications in the DNA, and these epigenetic modifications either silence or activate a gene without altering the DNA sequence. Diabetic environment up- or downregulates a number of genes in the retina, and emerging research has shown that it also facilitates epigenetic modifications. In the pathogenesis of diabetic retinopathy, the genes associated with important enzymes (e.g., mitochondrial superoxide dismutase, matrix metalloproteinase-9 and thioredoxin interacting protein) and transcriptional factors are epigenetically modified, the enzymes responsible for these epigenetic modifications are either activated or inhibited, and the levels of microRNAs are altered. With epigenetic modifications taking an important place in diabetic retinopathy, it is now becoming critical to evaluate these modifications, and understand their impact on this slow progressing blinding disease.

Oxidative stress and epigenetic modifications in the pathogenesis of diabetic retinopathy

Diabetic retinopathy remains the major cause of blindness among working age adults. Although a number of metabolic abnormalities have been associated with its development, due to complex nature of this multi-factorial disease, a link between any specific abnormality and diabetic retinopathy remains largely speculative. Diabetes increases oxidative stress in the retina and its capillary cells, and overwhelming evidence suggests a bidirectional relationship between oxidative stress and other major metabolic abnormalities implicated in the development of diabetic retinopathy. Due to increased production of cytosolic reactive oxygen species, mitochondrial membranes are damaged and their membrane potentials are impaired, and complex III of the electron transport system is compromised. Suboptimal enzymatic and nonenzymatic antioxidant defense system further aids in the accumulation of free radicals. As the duration of the disease progresses, mitochondrial DNA (mtDNA) is damaged and the DNA repair system is compromised, and due to impaired transcription of mtDNA-encoded proteins, the integrity of the electron transport system is encumbered. Due to decreased mtDNA biogenesis and impaired transcription, superoxide accumulation is further increased, and the vicious cycle of free radicals continues to self-propagate. Diabetic milieu also alters enzymes responsible for DNA and histone modifications, and various genes important for mitochondrial homeostasis, including mitochondrial biosynthesis, damage and antioxidant defense, undergo epigenetic modifications. Although antioxidant administration in animal models has yielded encouraging results in preventing diabetic retinopathy, controlled longitudinal human studies remain to be conducted. Furthermore, the role of epigenetic in mitochondrial homeostasis suggests that regulation of such modifications also has potential to inhibit/retard the development of diabetic retinopathy.

Solar-simulated ultraviolet radiation induces histone 3 methylation changes in the gene promoters of matrix metalloproteinases 1 and 3 in primary human dermal fibroblasts

Molecular signalling pathways delineating the induction of matrix metalloproteinases (MMPs) by ultraviolet radiation (UVR) are currently well-defined; however, the effects of UVR on epigenetic mechanisms of MMP induction are not as well understood. In this study, we examined solar-simulated UVR (ssUVR)-induced gene expression changes and alterations to histone methylation in the promoters of MMP1 and MMP3 in primary human dermal fibroblasts (HDF). Gene expression changes, including the increased expression of MMP1 and MMP3, were observed using Affymetrix GeneChip arrays and confirmed by qRT-PCR. Using ChIP-PCR, we showed for the first time that in HDF irradiated with 12 J/cm(2) ssUVR, the H3K4me3 transcriptional activating mark increased and the H3K9me2 transcriptional silencing mark decreased in abundance in promoters, correlating with the observed elevation of MMP1 and MMP3 mRNA levels following ssUVR exposure. Changes in mRNA levels due to a single exposure were transient and decreased 5 days after exposure.

MKL1 potentiates lung cancer cell migration and invasion by epigenetically activating MMP9 transcription

Malignant tumors are exemplified by excessive proliferation and aggressive migration/invasion contributing to increased mortality of cancer patients. Matrix metalloproteinase 9 (MMP9) expression is positively correlated with lung cancer malignancy. The mechanism underlying an elevated MMP9 expression is not clearly defined. We demonstrate here that the transcriptional modulator megakaryocytic leukemia 1 (MKL1) was activated by hypoxia and transforming growth factor (TGF-β), two prominent pro-malignancy factors, in cultured lung cancer cells. MKL1 levels were also increased in more invasive types of lung cancer in humans. Depletion of MKL1 in lung cancer cells attenuated migration and invasion both in vitro and in vivo. Overexpression of MKL1 potentiated the induction of MMP9 transcription by hypoxia and TGF-β, whereas MKL1 silencing diminished MMP9 expression. Of interest, MKL1 knockdown eliminated histone H3K4 methylation surrounding the MMP9 promoter. Further analyses revealed that MKL1 recruited ASH2, a component of the H3K4 methyltransferase complex, to activate MMP9 transcription. Depletion of ASH2 ameliorated cancer cell migration and invasion in an MMP9-dependent manner. Together our data indicate that MKL1 potentiates lung cancer cell migration and invasion by epigenetically activating MMP9 transcription.

Epigenetic mechanisms in diabetic complications and metabolic memory

The incidence of diabetes and its associated micro- and macrovascular complications is greatly increasing worldwide. The most prevalent vascular complications of both type 1 and type 2 diabetes include nephropathy, retinopathy, neuropathy and cardiovascular diseases. Evidence suggests that both genetic and environmental factors are involved in these pathologies. Clinical trials have underscored the beneficial effects of intensive glycaemic control for preventing the progression of complications. Accumulating evidence suggests a key role for epigenetic mechanisms such as DNA methylation, histone post-translational modifications in chromatin, and non-coding RNAs in the complex interplay between genes and the environment. Factors associated with the pathology of diabetic complications, including hyperglycaemia, growth factors, oxidant stress and inflammatory factors can lead to dysregulation of these epigenetic mechanisms to alter the expression of pathological genes in target cells such as endothelial, vascular smooth muscle, retinal and cardiac cells, without changes in the underlying DNA sequence. Furthermore, long-term persistence of these alterations to the epigenome may be a key mechanism underlying the phenomenon of 'metabolic memory' and sustained vascular dysfunction despite attainment of glycaemic control. Current therapies for most diabetic complications have not been fully efficacious, and hence a study of epigenetic mechanisms that may be involved is clearly warranted as they can not only shed novel new insights into the pathology of diabetic complications, but also lead to the identification of much needed new drug targets. In this review, we highlight the emerging role of epigenetics and epigenomics in the vascular complications of diabetes and metabolic memory.

Diabetes and retinal vascular dysfunction

Diabetes predominantly affects the microvascular circulation of the retina resulting in a range of structural changes unique to this tissue. These changes ultimately lead to altered permeability, hyperproliferation of endothelial cells and edema, and abnormal vascularization of the retina with resulting loss of vision. Enhanced production of inflammatory mediators and oxidative stress are primary insults with significant contribution to the pathogenesis of diabetic retinopathy (DR). We have determined the identity of the retinal vascular cells affected by hyperglycemia, and have delineated the cell autonomous impact of high glucose on function of these cells. We discuss some of the high glucose specific changes in retinal vascular cells and their contribution to retinal vascular dysfunction. This knowledge provides novel insight into the molecular and cellular defects contributing to the development and progression of diabetic retinopathy, and will aid in the development of innovative, as well as target specific therapeutic approaches for prevention and treatment of DR.

Posttranslational modification of Sirt6 activity by peroxynitrite

The mammalian sirtuin 6 (Sirt6) is a site-specific histone deacetylase that regulates chromatin structure and many fundamental biological processes. It inhibits endothelial cell senescence and inflammation, prevents development of cardiac hypertrophy and heart failure, modulates glucose metabolism, and represses tumor growth. The basic molecular mechanisms underlying regulation of Sirt6 enzymatic function are largely unknown. Here we hypothesized that Sirt6 function can be regulated via posttranslational modification, focusing on the role of peroxynitrite, one of the major reactive nitrogen species formed by excessive nitric oxide and superoxide generated during disease processes. We found that incubation of purified recombinant Sirt6 protein with 3-morpholinosydnonimine (SIN-1; a peroxynitrite donor that generates nitric oxide and superoxide simultaneously) increased Sirt6 tyrosine nitration and decreased its intrinsic catalytic activity. Similar results were observed in SIN-1-treated Sirt6, which was overexpressed in HEK293 cells, and in endogenous Sirt6 when human retinal microvascular endothelial cells were treated with SIN-1. To further investigate whether Sirt6 nitration occurs under pathological conditions, we determined Sirt6 nitration and activity in retina using a model of endotoxin-induced retinal inflammation. Our data showed that Sirt6 nitration was increased, whereas its activity was decreased, in this model. With mass spectrometry, we identified that tyrosine 257 in Sirt6 was nitrated after SIN-1 treatment. Mutation of tyrosine 257 to phenylalanine caused loss of Sirt6 activity and abolished SIN-1-induced nitration and decrease in its activity. Mass spectrometry analysis also revealed oxidation of methionine and tryptophan in Sirt6 after SIN-1 treatment. Our results demonstrate a novel regulatory mechanism controlling Sirt6 activity through reactive nitrogen species-mediated posttranslational modification under oxidative and nitrosative stress.

Diabetic retinopathy: could the alpha-1 antitrypsin be a therapeutic option?

Diabetic retinopathy is one of the most important causes of blindness. The underlying mechanisms of this disease include inflammatory changes and remodeling processes of the extracellular-matrix (ECM) leading to pericyte and vascular endothelial cell damage that affects the retinal circulation. In turn, this causes hypoxia leading to release of vascular endothelial growth factor (VEGF) to induce the angiogenesis process. Alpha-1 antitrypsin (AAT) is the most important circulating inhibitor of serine proteases (SERPIN). Its targets include elastase, plasmin, thrombin, trypsin, chymotrypsin, proteinase 3 (PR-3) and plasminogen activator (PAI). AAT modulates the effect of protease-activated receptors (PARs) during inflammatory responses. Plasma levels of AAT can increase 4-fold during acute inflammation then is so-called acute phase protein (APPs). Individuals with low serum levels of AAT could develop disease in lung, liver and pancreas. AAT is involved in extracellular matrix remodeling and inflammation, particularly migration and chemotaxis of neutrophils. It can also suppress nitric oxide (NO) by nitric oxide sintase (NOS) inhibition. AAT binds their targets in an irreversible way resulting in product degradation. The aim of this review is to focus on the points of contact between multiple factors involved in diabetic retinopathy and AAT resembling pleiotropic effects that might be beneficial.

Myocardin-Related Transcription Factor A Epigenetically Regulates Renal Fibrosis in Diabetic Nephropathy

Diabetic nephropathy (DN) is one of the most common complications associated with diabetes and characterized by renal microvascular injury along with accelerated synthesis of extracellular matrix proteins causing tubulointerstitial fibrosis. Production of type I collagen, the major component of extracellular matrix, is augmented during renal fibrosis after chronic exposure to hyperglycemia. However, the transcriptional modulator responsible for the epigenetic manipulation leading to induction of type I collagen genes is not clearly defined. We show here that tubulointerstitial fibrosis as a result of DN was diminished in myocardin-related transcription factor A (MRTF-A) -deficient mice. In cultured renal tubular epithelial cells and the kidneys of mice with DN, MRTF-A was induced by glucose and synergized with glucose to activate collagen transcription. Notably, MRTF-A silencing led to the disappearance of prominent histone modifications indicative of transcriptional activation, including acetylated histone H3K18/K27 and trimethylated histone H3K4. Detailed analysis revealed that MRTF-A recruited p300, a histone acetyltransferase, and WD repeat-containing protein 5 (WDR5), a key component of the histone H3K4 methyltransferase complex, to the collagen promoters and engaged these proteins in transcriptional activation. Estradiol suppressed collagen production by dampening the expression and binding activity of MRTF-A and interfering with the interaction between p300 and WDR5 in renal epithelial cells. Therefore, targeting the MRTF-A-associated epigenetic machinery might yield interventional strategies against DN-associated renal fibrosis.

Epigenetic modifications of Keap1 regulate its interaction with the protective factor Nrf2 in the development of diabetic retinopathy

PURPOSE

Diabetes induces oxidative imbalance in the retina and impairs Nrf2-mediated antioxidant response, and elevates Keap1, the cytoplasmic repressor of Nrf2. The goal of this study was to understand the role of epigenetic modifications at Keap1 promoter in regulation of Nrf2 function.

METHODS

The effect of high glucose on the binding of transcriptional factor Sp1 at Keap1 promoter and histone methylation status of the promoter was investigated in retinal endothelial cells. Role of histone methylation was confirmed in cells transfected with siRNA of methyltransferase enzyme Set7/9 (SetD7). In vitro results were confirmed in the retina from streptozotocin-induced diabetic rats. The role of epigenetic modifications of Keap1 promoter in the metabolic memory was examined in rats maintained in poor control for 3 months followed by good control for 3 months.

RESULTS

Hyperglycemia increased the binding of Sp1 at Keap1 promoter, and enriched H3K4me1 and activated SetD7. SetD7-siRNA prevented increase in Sp1 binding at Keap1 promoter and Keap1 expression, and ameliorated decrease in Nrf2-regulated antioxidant genes. Cessation of hyperglycemia failed to attenuate increased binding of Sp1 at Keap1, and the promoter continued to be methylated with increased expression of Keap1 and decreased expression of Nrf2-regulated genes.

CONCLUSIONS

Epigenetic modifications at Keap1 promoter by SetD7 facilitate its binding with Sp1, increasing its expression. Keap1 restrains Nrf2 in the cytosol, impairing its transcriptional activity. Reversal of hyperglycemia fails to provide any benefit to epigenetic modifications of Keap1 promoter, suggesting their role in both the development of diabetic retinopathy and the metabolic memory phenomenon.

Epigenetic modifications of Nrf2-mediated glutamate-cysteine ligase: implications for the development of diabetic retinopathy and the metabolic memory phenomenon associated with its continued progression

Diabetes increases oxidative stress in the retina and decreases the levels of the intracellular antioxidant glutathione (GSH). The transcriptional factor Nrf2 regulates the expression of Gclc, the enzyme important in the biosynthesis of GSH, and in diabetes the binding of Nrf2 at the antioxidant response element region 4 (ARE4) is decreased. Our aim was to investigate the role of epigenetic modifications in the decreased Nrf2 binding at Gclc-ARE4 in the development of diabetic retinopathy and in the metabolic memory associated with its continued progression. The effect of hyperglycemia on H3K4 methylation in Nrf2 binding at Gclc-ARE4 was investigated by chromatin immunoprecipitation in the rat retina and was confirmed in retinal endothelial cells in which histone demethylase (LSD1) was manipulated. The role of histone methylation at Gclc-ARE4 in the metabolic memory was examined in rats maintained under poor control for 3 months followed by good control (GC) for 3 months. Although H3K4me2 at Gclc-ARE4 was increased in diabetes, H3K4me3 and H3K4me1 were decreased. LSD1 siRNA abrogated the glucose-induced decrease in H3K4me1 at Gclc-ARE4 and ameliorated decreases in Nrf2 binding at Gclc-ARE4 and Gclc transcripts. Reestablishment of GC failed to provide any benefits to histone methylation, and Nrf2 binding activity remained compromised. Thus, in diabetic retinopathy, histone methylation at Gclc-ARE4 plays an important role in regulating the Nrf2-Gclc-GSH cascade. Targeting histone methylation could help inhibit/slow down this blinding disease.

Retinal mitochondrial DNA mismatch repair in the development of diabetic retinopathy, and its continued progression after termination of hyperglycemia

PURPOSE

Mitochondrial DNA (mtDNA) is damaged in the retina in diabetes, and mitochondria copy numbers are decreased. The displacement-loop (D-loop) of the mtDNA, the region with transcription/replication elements, experiences more damage than other regions of mtDNA. Our aim was to examine the role of DNA mismatch repair (MMR) in mitochondria homeostasis in diabetic retinopathy, and in its continued progression after cessation of hyperglycemia.

METHODS

Effect of hyperglycemia on sequence variants in the D-loop region was investigated in retinal endothelial cells and in the retina from streptozotocin-induced diabetic rats using mismatch-specific surveyor nuclease. The role of MMR machinery in mtDNA damage and mitochondrial respiration was investigated in retinal endothelial cells overexpressing Mlh1, an MMR enzyme mainly associated with mtDNA polymerase gamma, or Msh2 (associated with nuclear polymerase beta).

RESULTS

Hyperglycemia increased sequence variants in the D-loop region. While overexpression of Mlh1 in endothelial cells ameliorated glucose-induced increase in D-loop sequence variants, decrease in respiration rate and increase in apoptosis, overexpression of Msh2 did not protect the mitochondria damage. Termination of hyperglycemia failed to reverse decrease in MMR enzymes and increase in D-loop sequence variants.

CONCLUSIONS

Due to a compromised MMR system, the sequence variants in the D-loop region were not repaired, and that resulted in impaired mtDNA transcription. Mitochondria become dysfunctional, and they continued to be dysfunctional even after hyperglycemia was terminated, contributing to the development, and progression of diabetic retinopathy. Thus, strategies targeting mitochondrial MMR machinery could help maintain mitochondria homeostasis, and inhibit the development of diabetic retinopathy and its continued progression.

Epigenetic modifications and potential new treatment targets in diabetic retinopathy

Retinopathy is a debilitating vascular complication of diabetes. As with other diabetic complications, diabetic retinopathy (DR) is characterized by the metabolic memory, which has been observed both in DR patients and in DR animal models. Evidences have provided that after a period of poor glucose control insulin or diabetes drug treatment fails to prevent the development and progression of DR even when good glycemic control is reinstituted (glucose normalization), suggesting a metabolic memory phenomenon. Recent studies also underline the role of epigenetic chromatin modifications as mediators of the metabolic memory. Indeed, epigenetic changes may lead to stable modification of gene expression, participating in DR pathogenesis. Moreover, increasing evidences suggest that environmental factors such as chronic hyperglycemia are implicated DR progression and may also affect the epigenetic state. Here we review recent findings demonstrating the key role of epigenetics in the progression of DR. Further elucidation of epigenetic mechanisms, acting both at the cis- and trans-chromatin structural elements, will yield new insights into the pathogenesis of DR and will open the way for the discovery of novel therapeutic targets to prevent DR progression.

Sirt1, a negative regulator of matrix metalloproteinase-9 in diabetic retinopathy

PURPOSE

In the pathogenesis of diabetic retinopathy, matrix metalloproteinase (MMP)-9 damages retinal mitochondria, activating the apoptotic machinery. Transcription of MMP-9 is regulated by nuclear factor kappa B (NF-κB), and the activation of NF-κB is modulated by the acetylation of its p65 subunit. Sirtuin 1 (Sirt1), a deacetylase, plays an important role in the acetylation-deacetylation of p65. The goal of this study is to investigate the role of Sirt1 in the activation of MMP-9 in diabetic retinopathy.

METHODS

The effect of hyperglycemia and Sirt1 activator, resveratrol, on acetylation of p65 and its binding at MMP-9 promoter-and mitochondrial damage and apoptosis-was assessed in the retinal endothelial cells. Role of oxidative stress in the regulation of Sirt1 was evaluated in the cells incubated in H2O2. The results were confirmed in the retina from diabetic mice with Sod2 or MMP-9 gene manipulated.

RESULTS

High glucose decreased Sirt1 activity and increased p65 acetylation, and resveratrol prevented increase in p65 acetylation, binding of p65 at MMP-9 promoter and MMP-9 activation, mitochondria damage, and cell apoptosis. While Sirt1 was decreased by H2O2, MMP-9 was significantly increased. Retina from wild-type diabetic mice presented similar decrease in Sirt1, and diabetic mice with Sod2 overexpression or MMP-9 deletion had normal retinal Sirt1. Retinal microvasculature from human donors with established diabetic retinopathy also had decreased Sirt1.

CONCLUSIONS

Thus, in diabetes, increase in oxidative stress inhibits Sirt1 and p65 is hyperacetylated, increasing the binding of p65 at MMP-9 promoter. Prevention of Sirt1 inhibition, via modulating acetylation of p65, should protect activation of MMP-9 and inhibit the development of diabetic retinopathy.

Lysine-specific demethylase 1-mediated demethylation of histone H3 lysine 9 contributes to interleukin 1β-induced microsomal prostaglandin E synthase 1 expression in human osteoarthritic chondrocytes

Introduction

Microsomal prostaglandin E synthase 1 (mPGES-1) catalyzes the terminal step in the biosynthesis of PGE₂, a critical mediator in the pathophysiology of osteoarthritis (OA). Histone methylation plays an important role in epigenetic gene regulation. In this study, we investigated the roles of histone H3 lysine 9 (H3K9) methylation in interleukin 1β (IL-1β)-induced mPGES-1 expression in human chondrocytes.

Methods

Chondrocytes were stimulated with IL-1β, and the expression of mPGES-1 mRNA was evaluated using real-time RT-PCR. H3K9 methylation and the recruitment of the histone demethylase lysine-specific demethylase 1 (LSD1) to the mPGES-1 promoter were evaluated using chromatin immunoprecipitation assays. The role of LSD1 was further evaluated using the pharmacological inhibitors tranylcypromine and pargyline and small interfering RNA (siRNA)-mediated gene silencing. The LSD1 level in cartilage was determined by RT-PCR and immunohistochemistry.

Results

The induction of mPGES-1 expression by IL-1β correlated with decreased levels of mono- and dimethylated H3K9 at the mPGES-1 promoter. These changes were concomitant with the recruitment of the histone demethylase LSD1. Treatment with tranylcypromine and pargyline, which are potent inhibitors of LSD1, prevented IL-1β-induced H3K9 demethylation at the mPGES-1 promoter and expression of mPGES-1. Consistently, LSD1 gene silencing with siRNA prevented IL-1β-induced H3K9 demethylation and mPGES-1 expression, suggesting that LSD1 mediates IL-1β-induced mPGES-1 expression via H3K9 demethylation. We show that the level of LSD1 was elevated in OA compared to normal cartilage.

Conclusion

These results indicate that H3K9 demethylation by LSD1 contributes to IL-1β-induced mPGES-1 expression and suggest that this pathway could be a potential target for pharmacological intervention in the treatment of OA and possibly other arthritic conditions.

Developments in Ocular Genetics: 2013 Annual Review

PURPOSE

To highlight major advancements in ocular genetics from the year 2013.

DESIGN

Literature review.

METHODS

A literature search was conducted on PubMed to identify articles pertaining to genetic influences on human eye diseases. This review focuses on manuscripts published in print or online in the English language between January 1, 2013 and December 31, 2013. A total of 120 papers from 2013 were included in this review.

RESULTS

Significant progress has been made in our understanding of the genetic basis of a broad group of ocular disorders, including glaucoma, age-related macular degeneration, cataract, diabetic retinopathy, keratoconus, Fuchs' endothelial dystrophy, and refractive error.

CONCLUSIONS

The latest next-generation sequencing technologies have become extremely effective tools for identifying gene mutations associated with ocular disease. These technological advancements have also paved the way for utilization of genetic information in clinical practice, including disease diagnosis, prediction of treatment response and molecular interventions guided by gene-based knowledge.

Epigenetic mechanisms in the pathogenesis of diabetic retinopathy

Diabetic retinopathy (DR), which arises as a result of an increasing incidence of diabetes mellitus, has gradually become a common disease. Due to its complex pathogenesis, the treatment means of DR are very limited. The findings of several studies have shown that instituting tight glycemic control in diabetic patients does not immediately benefit the progression of retinopathy, and the benefits of good control persist beyond the period of good glycemic control. This has led to the concept of persistent epigenetic changes. Epigenetics has now become an increasingly important area of biomedical research. Recently, important roles of various epigenetic mechanisms have been identified in the pathogenesis of diabetes and its complications. The aim of this review is to provide an overview of the epigenetics and epigenetic mechanisms in diabetes and diabetes complications, and the focus is on the emerging evidence for aberrant epigenetic mechanisms in DR.

Posttranslational modification of mitochondrial transcription factor A in impaired mitochondria biogenesis: implications in diabetic retinopathy and metabolic memory phenomenon

Mitochondrial transcription factor A (TFAM) is one of the key regulators of the transcription of mtDNA. In diabetes, despite increase in gene transcripts of TFAM, its protein levels in the mitochondria are decreased and mitochondria copy numbers become subnormal. The aim of this study is to investigate the mechanism(s) responsible for decreased mitochondrial TFAM in diabetes. Using retinal endothelial cells, we have investigated the effect of overexpression of cytosolic chaperone, Hsp70, and TFAM on glucose-induced decrease in mitochondrial TFAM levels, and the transcription of mtDNA-encoded genes, NADH dehydrogenase subunit 6 (ND6) and cytochrome b (Cytb). To investigate the role of posttranslational modifications in subnormal mitochondrial TFAM, ubiquitination of TFAM was assessed, and the results were confirmed in the retina from streptozotocin-induced diabetic rats. While overexpression of Hsp70 failed to prevent glucose-induced decrease in mitochondrial TFAM and transcripts of ND6 and Cytb, overexpression of TFAM ameliorated decrease in its mitochondrial protein levels and transcriptional activity. TFAM was ubiquitinated by high glucose, and PYR-41, an inhibitor of ubiquitination, prevented TFAM ubiquitination and restored the transcriptional activity. Similarly, TFAM was ubiquitinated in the retina from diabetic rats, and it continued to be modified after reinstitution of normal glycemia. Our results clearly imply that the ubiquitination of TFAM impedes its transport to the mitochondria resulting in subnormal mtDNA transcription and mitochondria dysfunction, and inhibition of ubiquitination restores mitochondrial homeostasis. Reversal of hyperglycemia does not provide any benefit to TFAM ubiquitination. Thus, strategies targeting posttranslational modification could provide an avenue to preserve mitochondrial homeostasis, and inhibit the development/progression of diabetic retinopathy.

Epigenetic modifications and diabetic retinopathy

Diabetic retinopathy remains one of the most debilitating chronic complications, but despite extensive research in the field, the exact mechanism(s) responsible for how retina is damaged in diabetes remains ambiguous. Many metabolic pathways have been implicated in its development, and genes associated with these pathways are altered. Diabetic environment also facilitates epigenetics modifications, which can alter the gene expression without permanent changes in DNA sequence. The role of epigenetics in diabetic retinopathy is now an emerging area, and recent work has shown that genes encoding mitochondrial superoxide dismutase (Sod2) and matrix metalloproteinase-9 (MMP-9) are epigenetically modified, activates of epigenetic modification enzymes, histone lysine demethylase 1 (LSD1), and DNA methyltransferase are increased, and the micro RNAs responsible for regulating nuclear transcriptional factor and VEGF are upregulated. With the growing evidence of epigenetic modifications in diabetic retinopathy, better understanding of these modifications has potential to identify novel targets to inhibit this devastating disease. Fortunately, the inhibitors and mimics targeted towards histone modification, DNA methylation, and miRNAs are now being tried for cancer and other chronic diseases, and better understanding of the role of epigenetics in diabetic retinopathy will open the door for their possible use in combating this blinding disease.

Interrelationship between activation of matrix metalloproteinases and mitochondrial dysfunction in the development of diabetic retinopathy

Mitochondria dysfunction plays a significant role in the apoptosis of retinal cells. Diabetes activates retinal matrix metalloproteinases (MMP-9 and MMP-2), damages retinal mitochondria and activates the apoptotic machinery. This study is to investigate the temporal relationship between the activation of retinal MMPs and mitochondria damage in the development of diabetic retinopathy. Time course of activation of cytosolic MMP-9 and MMP-2 was investigated in the retinal endothelial cells incubated in high glucose for 6-96 h, and correlated with their mitochondrial accumulation and mitochondrial damage. This was confirmed in the retina from rats diabetic for 15 days to ~12 months (streptozotocin-induced). The results show that the activation of cytosolic MMP-9 and MMP-2 is an early event, which is followed by their accumulation in the mitochondria. Increased mitochondrial MMPs dysfunction them and begin to damage their DNA, which initiates a vicious cycle of reactive oxygen species. Thus, modulation of these gelatinase MMPs by pharmacological agents during the early stages of diabetes could provide a strategy to inhibit the development of diabetic retinopathy.