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Renu A Kowluru - Top 30 Publications

Atypical antipsychotics, insulin resistance and weight; a meta-analysis of healthy volunteer studies.

Atypical antipsychotics increase the risk of diabetes and cardiovascular disease through their side effects of insulin resistance and weight gain. The populations for which atypical antipsychotics are used carry a baseline risk of metabolic dysregulation prior to medication which has made it difficult to fully understand whether atypical antipsychotics cause insulin resistance and weight gain directly. The purpose of this work was to conduct a systematic review and meta-analysis of atypical antipsychotic trials in healthy volunteers to better understand their effects on insulin sensitivity and weight gain. Furthermore, we aimed to evaluate the occurrence of insulin resistance with or without weight gain and with treatment length by using subgroup and meta-regression techniques. Overall, the meta-analysis provides evidence that atypical antipsychotics decrease insulin sensitivity (standardized mean difference=-0.437, p<0.001) and increase weight (standardized mean difference=0.591, p<0.001) in healthy volunteers. It was found that decreases in insulin sensitivity were potentially dependent on treatment length but not weight gain. Decreases in insulin sensitivity occurred in multi-dose studies <13days while weight gain occurred in studies 14days and longer (max 28days). These findings provide preliminary evidence that atypical antipsychotics cause insulin resistance and weight gain directly, independent of psychiatric disease and may be associated with length of treatment. Further, well-designed studies to assess the co-occurrence of insulin resistance and weight gain and to understand the mechanisms and sequence by which they occur are required.

Sirt1- A Guardian of the Development of Diabetic Retinopathy.

Diabetic retinopathy is a multifactorial disease, and the exact mechanism of its pathogenesis remains obscure. A multifunctional deacetylase Sirtuin 1 (Sirt1), is implicated in regulation of many cellular functions and transcription of genes, and retinal Sirt1 is inhibited in diabetes. Our aim is to determine the role of Sirt1 in the development of diabetic retinopathy, and elucidate the molecular mechanism of its downregulation. Using mice overexpressing Sirt1, diabetic for 8 month, structural, functional and metabolic abnormalities were investigated in vascular and neuronal retina. The role of epigenetics in Sirt1 transcriptional suppression was investigated in the retinal microvessels. Compared to wildtype diabetic mice, retinal vasculature from Sirt1 diabetic mice did not present any increase in the number of apoptotic cells, degenerative capillaries and decrease in vascular density. Sirt1 diabetic mice were also protected from mitochondrial damage, and they had normal ERG responses and ganglion cell layer thickness. Wildtype diabetic mice had Sirt1 promoter DNA hypermethylated, which was alleviated in Sirt1 diabetic mice, suggesting the role of epigenetics in its transcriptional suppression. Thus, strategies targeting amelioration of Sirt1 inhibition have potential to maintain retinal vascular and neuronal homeostasis, providing opportunities to retard the development of diabetic retinopathy in its early stages.

Crosstalk Between Histone and DNA Methylation in Regulation of Retinal Matrix Metalloproteinase-9 in Diabetes.

Diabetes activates matrix metalloproteinase-9 (MMP-9), and MMP-9 via damaging retinal mitochondria, activates capillary cell apoptosis. MMP-9 promoter has binding sites for many transcription factors, and in diabetes its promoter undergoes epigenetic modifications, including histone modifications and DNA methylation. Enhancer of Zeste homolog 2 (Ezh2), which catalyzes dimethylation/trimethylation of histone 3 lysine 27 (H3K27me2 and me3), is also associated with DNA methylation. Our aim was to investigate link(s) between histone and DNA modifications in the regulation of MMP-9.

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.

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.

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.

Erratum to: Role of oxidative stress in epigenetic modification of MMP-9 promoter in the development of diabetic retinopathy.

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

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.

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.

Metabolic Stress Induces Caspase-3 Mediated Degradation and Inactivation of Farnesyl and Geranylgeranyl Transferase Activities in Pancreatic β-Cells.

At least 300 prenylated proteins are identified in the human genome; the majority of which partake in a variety of cellular processes including growth, differentiation, cytoskeletal organization/dynamics and vesicle trafficking. Aberrant prenylation of proteins is implicated in human pathologies including cancer; neurodegenerative diseases, retinitis pigmentosa, and premature ageing syndromes. Original observations from our laboratory have demonstrated that prenylation of proteins [small G-proteins and γ-subunits of trimeric G-proteins] is requisite for physiological insulin secretion. Herein, we assessed the impact of metabolic stress [gluco-, lipotoxicity and ER-stress] on the functional status of protein prenylation pathway in pancreatic β-cells.

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

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.

Hyperlipidemia and the development of diabetic retinopathy: Comparison between type 1 and type 2 animal models.

In the pathogenesis of diabetic retinopathy, reactive oxygen species (ROS) are elevated in the retina and the mitochondria are damaged, resulting in accelerated apoptosis. Dyslipidemia is also considered as one of the major factors in its development, and our aim is to investigate the compounding effect of hyperlipidemia in retinopathy.

Peripheral Blood Mitochondrial DNA Damage as a Potential Noninvasive Biomarker of Diabetic Retinopathy.

In the development of diabetic retinopathy, retinal mitochondria become dysfunctional, and mitochondrial DNA (mtDNA) is damaged. Because retinopathy is a progressive disease, and circulating glucose levels are high in diabetes, our aim was to investigate if peripheral blood mtDNA damage can serve as a potential biomarker of diabetic retinopathy.

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.

Diabetic retinopathy and transcriptional regulation of a small molecular weight G-Protein, Rac1.

In diabetic retinopathy, increased cytosolic reactive oxygen species, produced by NADPH oxidase (Nox), damage mitochondria, and this accelerates apoptosis of retinal capillary cells, resulting in the histopathology. Activation of Nox2 is mediated by a small molecular weight GTPase, Rac1, and retinal Rac1 is activated in diabetes. Our goal is to investigate the molecular mechanism responsible for transcriptional activation of Rac1 in the development of diabetic retinopathy. Using retinal microvessels, the site of histopathology associated with diabetic retinopathy, from streptozotocin-induced diabetic rats, we investigated the binding of the nuclear transcriptional factor-kB (NF-kB) at Rac1 promoter. Since activation of NF-kB is regulated by its acetylation-deacetylation, the role of acetylation in Rac1 transcription was confirmed in the retina from diabetic mice overexpressing a deacetylase, Sirtuin 1. Diabetes increased the binding of p65 subunit of NF-kB at the Rac1 promoter. Overexpression of Sirtuin 1 prevented hyper-acetylation of p65, decreased its binding at the Rac1 promoter and ameliorated Rac1-Nox2 mediated mitochondrial damage. Thus, in diabetes Rac1 transcriptional activation in the retina is mediated by acetylation of NF-kB, and modulation of acetylation during the early stages of diabetic retinopathy has potential to inhibit/retard its development.

Molecular Mechanism of Transcriptional Regulation of Matrix Metalloproteinase-9 in Diabetic Retinopathy.

Increase in matrix metalloproteinase-9 (MMP-9) is implicated in retinal capillary cell apoptosis, a phenomenon which precedes the development of diabetic retinopathy. MMP-9 promoter has multiple sites for binding the transcriptional factors, including two for activator protein 1 (AP-1). The binding of AP-1, a heterodimer of c-Jun and c-Fos, is regulated by posttranslational modifications, and in diabetes, deacetylating enzyme, Sirt1, is inhibited. Our aim, is to investigate the molecular mechanism of MMP-9 transcriptional regulation in diabetes. Binding of AP-1 (c-Jun, c-Fos) at the MMP-9 promoter, and AP-1 acetylation were analyzed in retinal endothelial cells incubated in normal or high glucose by chromatin-immunoprecipitation and co-immunoprecipitation respectively. Role of AP-1 in MMP-9 regulation was confirmed by c-Jun or c-Fos siRNAs, and that of its acetylation, by Sirt1 overexpression. In vitro results were validated in the retina from diabetic mice overexpressing Sirt1, and in the retinal microvessels from human donors with diabetic retinopathy. In experimental models, AP-1 binding was increased at the proximal and distal sites of the MMP-9 promoter, and similar phenomenon was confirmed in the retinal microvessels from human donors with diabetic retinopathy. Silencing of AP-1, or overexpression of Sirt1 ameliorated glucose-induced increase in MMP-9 expression and cell apoptosis. Thus, in diabetes, due to Sirt1 inhibition, AP-1 is hyperacetylated, which increases its binding at MMP-9 promoter, and hence, activation of Sirt1 could inhibit the development of diabetic retinopathy by impeding MMP-9-mediated mitochondrial damage. J. Cell. Physiol. 231: 1709-1718, 2016. © 2015 Wiley Periodicals, Inc.

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.

Epigenetic Modification of Mitochondrial DNA in the Development of Diabetic Retinopathy.

Retinal mitochondria are dysfunctional in diabetes, and mitochondrial DNA (mtDNA) is damaged and its transcription is compromised. Our aim was to investigate the role of mtDNA methylation in the development of diabetic retinopathy.

Protein prenylation in islet β-cell function in health and diabetes: Putting the pieces of the puzzle together.

Post-translational prenylation involves incorporation of 15-(farnesyl) or 20-(geranylgeranyl) carbon derivatives of mevalonic acid into highly conserved C-terminal cysteines of proteins. The farnesyl transferase (FTase) and the geranylgeranyl transferase (GGTase) mediate incorporation of farnesyl and geranylgeranyl groups, respectively. At least 300 proteins are prenylated in the human genome; the majority of these are implicated in cellular processes including growth, differentiation, cytoskeletal function and vesicle trafficking. From a functional standpoint, isoprenylation is requisite for targeting of modified proteins to relevant cellular compartments for regulation of effector proteins. Pharmacological and molecular biological studies have provided compelling evidence for key roles of this signaling pathway in physiological insulin secretion in normal rodent and human islets. Recent evidence indicates that inhibition of prenylation results in mislocalization of unprenylated proteins, and surprisingly, they remain in active (GTP-bound) conformation. Sustained activation of G proteins has been reported in mice lacking GGTase, suggesting alternate mechanisms for the activation of non-prenylated G proteins. These findings further raise an interesting question if mislocalized, non-prenylated and functionally active G proteins cause cellular pathology since aberrant protein prenylation has been implicated in the onset of cardiovascular disease and diabetes. Herein, we overview the existing evidence to implicate prenylation in islet function and potential defects in this signaling pathways in the diabetic β-cell. We will also identify critical knowledge gaps that need to be addressed for the development of therapeutics to halt defects in these signaling steps in β cells in models of impaired insulin secretion, metabolic stress and diabetes.

The Diabetes Visual Function Supplement Study (DiVFuSS).

Diabetes is known to affect visual function before onset of retinopathy (diabetic retinopathy (DR)). Protection of visual function may signal disruption of mechanisms underlying DR.

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.

Lipotoxicity augments glucotoxicity-induced mitochondrial damage in the development of diabetic retinopathy.

Although hyperglycemia is the main instigator in the development of diabetic retinopathy, dyslipidemia is also considered to play an important role. In the pathogenesis of diabetic retinopathy, cytosolic NADPH oxidase 2 (Nox2) is activated before retinal mitochondria are damaged. Our aim was to investigate the effect of lipids in the development of diabetic retinopathy.

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.

Tiam1-Rac1 Axis Promotes Activation of p38 MAP Kinase in the Development of Diabetic Retinopathy: Evidence for a Requisite Role for Protein Palmitoylation.

Evidence in multiple tissues, including retina, suggests generation of reactive oxygen species (ROS) and the ensuing oxidative stress as triggers for mitochondrial defects and cell apoptosis. We recently reported novel roles for Tiam1-Rac1-Nox2 axis in retinal mitochondrial dysfunction and cell death leading to the development of diabetic retinopathy. Herein, we tested the hypothesis that activation of p38 MAP kinase, a stress kinase, represents the downstream signaling event to Rac1-Nox2 activation in diabetes-induced metabolic stress leading to capillary cell apoptosis.

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

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.

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

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.

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.

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

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.

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.

TIAM1-RAC1 signalling axis-mediated activation of NADPH oxidase-2 initiates mitochondrial damage in the development of diabetic retinopathy.

In diabetes, increased retinal oxidative stress is seen before the mitochondria are damaged. Phagocyte-like NADPH oxidase-2 (NOX2) is the predominant cytosolic source of reactive oxygen species (ROS). Activation of Ras-related C3 botulinum toxin substrate 1 (RAC1), a NOX2 holoenzyme member, is necessary for NOX2 activation and ROS generation. In this study we assessed the role of T cell lymphoma invasion and metastasis (TIAM1), a guanine nucleotide exchange factor for RAC1, in RAC1 and NOX2 activation and the onset of mitochondrial dysfunction in in vitro and in vivo models of glucotoxicity and diabetes.