Review Article Epigenetic Modifications and Diabetic …downloads.hindawi.com/journals/bmri/2013/635284.pdfthe risk of diabetic retinopathy and nephropathy in diabetic patients [ ]

Hindawi Publishing CorporationBioMed Research InternationalVolume 2013 Article ID 635284 9 pageshttpdxdoiorg1011552013635284

Review ArticleEpigenetic Modifications and Diabetic Retinopathy

Renu A Kowluru Julia M Santos and Manish Mishra

Kresge Eye Institute Wayne State University 4717 St Antoine Detroit MI 48201 USA

Correspondence should be addressed to Renu A Kowluru rkowlurumedwayneedu

Received 2 July 2013 Accepted 15 July 2013

Academic Editor Daniel Petrovic

Copyright copy 2013 Renu A Kowluru et al This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

Diabetic retinopathy remains one of the most debilitating chronic complications but despite extensive research in the fieldthe exact mechanism(s) responsible for how retina is damaged in diabetes remains ambiguous Many metabolic pathways havebeen implicated in its development and genes associated with these pathways are altered Diabetic environment also facilitatesepigeneticsmodifications which can alter the gene expressionwithout permanent changes inDNA sequenceThe role of epigeneticsin diabetic retinopathy is now an emerging area and recent work has shown that genes encoding mitochondrial superoxidedismutase (Sod2) and matrix metalloproteinase-9 (MMP-9) are epigenetically modified activates of epigenetic modificationenzymes histone lysine demethylase 1 (LSD1) and DNA methyltransferase are increased and the micro RNAs responsible forregulating nuclear transcriptional factor and VEGF are upregulated With the growing evidence of epigenetic modifications indiabetic retinopathy better understanding of these modifications has potential to identify novel targets to inhibit this devastatingdisease Fortunately the inhibitors and mimics targeted towards histone modification DNA methylation and miRNAs are nowbeing tried for cancer and other chronic diseases and better understanding of the role of epigenetics in diabetic retinopathy willopen the door for their possible use in combating this blinding disease

1 Introduction

Diabetic retinopathy remains the leading cause of blindnessin young adults affecting over 90 patients with 20 years ofdiabetesThe disease carries a heavy burden on our society asit is responsible for 48 of the 37million cases of eye disease-related blindness worldwide With the incidence of diabetesincreasing at an alarming rate the number of people withdiabetic retinopathy is expected to grow from 1266million in2010 to 1910million by 2030 [1]This slow progressing diseaseis mainly characterized by damage of the microvasculatureof the retina Some of the early histopathological changesof this slow progressing disease include microaneurysmshemorrhages cotton wool spots intraretinal microvascularabnormalities and venous bleeding But in more advancedstages new fragile vessels are formed along the retina andon the posterior surface of the vitreous and if not treatedthey result in the detachment of the retina leading toblindness [2] Although hyperglycemia is the major initiatorof diabetic retinopathy hypertension and dyslipidemia arealso considered significant risk factors in its development andprogression [3ndash5]

Despite extensive research in the field to understand thepathogenesis of diabetic retinopathy the exact mechanism(s)remains elusive making inhibition of the progression ofthis disease a daunting task Some of the possible mecha-nisms implicated in its development include oxidative stressincreased formation of advanced glycation end productsand activation of protein kinase-C polyol production andhexosamine pathways [2 6 7] These pathways appear tobe interlinked [8] which further complicates the strategiesto prevent the developmentprogression of this devastatingcomplication of diabetes

2 Genetics and Diabetic Retinopathy

Pathogenesis of a disease is also influenced by geneticfactors and due to variability in the severity of retinopathyamong diabetic patients with similar risk factors the role ofgenetic factors in diabetic retinopathy should be somewhatpredictable However such genetic associations are not yetclearly established Landmark ldquoGenome-Wide AssociationStudiesrdquo have identified number of genetic variants that

2 BioMed Research International

could explain some of the interindividual variations inthe susceptibility of diabetes [9] A meta-analysis studyto investigate possible genetic associations with diabeticretinopathy which incorporated reports published betweenJanuary 1990 and August 2008 has revealed a significantvariation in the AKR1B1 gene This gene encodes aldo-ketoreductase family 1 member B1 which is the rate limitingenzyme of the polyol pathway [10] one of the pathwaysimplicated in the development of diabetic retinopathy [2 67] Another meta-analysis study has shown that Ala allele ofthe Pro12Ala polymorphism in the peroxisome proliferator-activated receptor-1205742 gene acts as a protective gene in theincidence of retinopathy in type 2 diabetic patients [11] Incontrast recent studies have failed to find any associationsbetween VEGF-related SNPs (rs6921438 and rs10738760) andthe risk of diabetic retinopathy and nephropathy in diabeticpatients [12] Thus the association between genetic factorsand diabetic retinopathy remains to be clarified

3 Epigenetic Modificationsand Gene Regulation

Diabetic environment disturbs metabolic homeostasis andalso alters various genes including genes associated withoxidative stress apoptosis and inflammation [13ndash16] Controlof gene expression (ie the ability of a gene to produce abiologically active protein) in mammals in addition to beingmodulated by transcriptional and translational initiationcan also be controlled by changes ldquoon the toprdquo of thegenes without altering the nucleotide composition of thegenome [17] These ldquoepigeneticrdquo modifications are stable butpotentially reversible and can be passed from generationto generation Recent studies have shown that epigeneticchanges play a major role in many chronic diseases such ascancer and diabetes where small changes in the epigenomeover time are considered to lead to disease manifestationThree major epigenetic mechanisms considered to regulategene expression areDNAmethylation histonemodificationsand noncoding RNA activity [18ndash21]

DNAmethylation addition of amethyl group on position5 of cytosine residues of the cluster of CpG dinucleotides(CpG Island) which is the regulatory region of most genes istypically associated with transcriptional repression [22 23]The methylation process brings in the unintended changesbrought up by the environmental exposures or other life styleand these changes can be passed on for multiple generationsCytosine 5 methylation generates 5-methylcytosine (5mC)and the reaction is catalyzed by a family of enzymesmdashDNA (cytosine-5) methyltransferases (Dnmts) The conver-sion of 5mC to 5-hydroxymethylcytosine (5hmC) is facili-tated by Ten-eleven-translocation enzymes (TETs) [24 25]making these enzymes future targets of pharmacologicalregulation However how the process of DNA methylation-demethylation is balanced remains somewhat unclear Asubfamily of DNA glycosylases are considered to promoteactiveDNAdemethylation by removing the 5-methylcytosinebase followed by cleavage of the DNA backbone at the abasic

site and the methylated cytosine is replaced by an unmethy-lated cytosine In contrast the passive process involvesabsenceinactivation of Dnmt1 resulting in hypomethylatedDNA [26]

Gene expression pattern is also dictated by chromatinwhich is a composite structure of histones and nucleic acidHistones act as spools around which DNAwinds and amongthe 4-histone proteins histone 2A and B (H2A and H2B)H3 and H4 form a tetrameric structure the nucleosome [27]Despite such sophisticated DNA packaging N-terminal ofhistones remains vulnerable for posttranslational modifica-tions and can be acetylatedmethylated and phosphorylatedSuch epigenetic modifications alter the chromatin structurewhich subsequently affects the binding of transcription fac-tors and can regulate the selective expression of genes ina particular tissue by acting like switches to control geneactivity [15 28ndash31]

Acetylation is one of the most common modificationswhich is generally associated with gene activation and theprocess relaxes the chromatin structure allowing recruitmentand binding of transcription factor and RNA polymerase II[32] Acetylation is regulated by fine balance between histoneacetylating and deacetylating enzymes histone acetyltrans-ferases (HATs) add acetyl group while histone deacetylase(HDAC) removes the acetyl group Methylation of histoneshowever shows greater variability as methylation can occurat both lysine and arginine residues and can be associatedwith either gene activation or repression Methylation oflysine 4 of histone 3 (H3K4) is typically associated withgene activation while methylation of lysine 9 (H3K9) isassociated with gene repression [33ndash35] Furthermore theoutcome of methylation is also dictated by the specifichistone residue being modified for example mono- or tri-methylation of H3K4 induces activation of gene expression[36 37] While monomethylation of H3K9 induces geneactivation its tri-methylation suppresses the gene activity[38] As with acetylation methylation status of histonesdepends on the final balance between histone methylatingand demethylating enzymes Histone methylating enzymesSET179 help in H3K4 methylation and suppressors ofvariegation 3-9 homolog (SUV39H) methylates lysine 9 ofhistone 3 [39 40] Subsequently in order to protect fromsuch kind of relatively stable methyl modifications andconstitutive expression of genes lysine specific demethylase(LSD1) specifically removes methyl groups from methylatedH3K4 and H3K9 [41 42]

In addition to DNA methylation and histone modifi-cations gene expression is also regulated by microRNAs(miRNA) the small noncoding RNAs that regulate geneexpression posttranscriptionally by binding to complemen-tary sequences in the 31015840 untranslated regions of messengerRNAs [43 44] This cleaves mRNA resulting in decreasedprotein synthesis and expression of the targeted gene Geneswith epigenetic functions in chromatin can be regulated bymiRNAs affecting chromatin remodeling and gene expres-sion Regulation of genes by DNA methylation and miRNAappears to be interrelated as the function of Dnmts dependson histone modification patterns such as H3K9 methylationand histone deacetylation In addition inhibition of Dnmts

BioMed Research International 3

which causes DNA demethylation can reactivate some ofthe miRNAs [45] Overall these epigenetic modificationsare not permanent but their continuous response to thechanging environment such as diabetes and the chances ofthem being inherited to successive generation make themattractive targets for chronic diseases

4 Role of Epigenetic Modifications in Diabetes

It has become clear that both genetic predisposition andenvironmental factors play critical roles in the developmentof metabolic diseases including obesity and type 2 diabetesand epigenetic modifications have important roles in alteringgene expressions in various chronic diseases [46ndash48] Recentstudies have demonstrated the role of epigenetic mechanismsin islet function and have provided an avenue wherebydietary components could accelerate or prevent age-relateddiseases through their effects on epigenetic modifications[49 50] Increased DNA methylation at the promoter of theperoxisome proliferator-activated receptor coactivator 1 genein the pancreatic islets is shown to play a key role in regulatingmitochondrial genes [51] Our studies have shown that indiabetes hyper methylation of the CpG sites at the regulatoryregion of DNA polymerase gamma affects its binding to themtDNA and this compromises the transcriptional activityresulting in decreased copy number [52] Hyper acetylationof histone H4 at the insulin gene promoter influencesglucose-induced insulin secretion [53] Diabetic patients withnephropathy have altered DNA methylation at the key genepromoters compared to those without nephropathy [54] Tis-sue specific DNA methylation is observed in streptozotocin-induced diabetic rats with hypomethylation in the liver butnot in kidney and in the leukocytes of diabetic patientsDnmtis altered [55 56] Furthermore hyperglycemia induces spe-cific and long-lasting epigenetic modifications [14 15 28 2952 57 58] glucose-induced persistent transcriptional activa-tion of p65 in vascular cells is associated with methylation ofH3K4 and hypomethylation of H3K9 and the concomitantactivation of NF-kB is subsequently associated with increasedinflammatory response [14]

Studies using zebrafish as a model of diabetes haveshown that hyperglycemia induces global DNA hypo methy-lation and aberrant gene expression in the tissue after limbamputation and the process is associated with poor woundhealing process [59] Furthermore 120573-cells from young IUGRanimals a model of type 2 diabetes present changes in DNAmethylation resulting in dysregulation of genes associatedwith cellular memory of intrauterine that is associated withadult susceptibility to diabetes [60]Thus epigenetic changescan account for chronic and persistent complications ofdiabetes

Diabetes also affectsmiRNAs it is shown to downregulatemiR133a the miRNA which is implicated in the regulationof the key genes associated with cardiomyocyte hypertrophy[61] In contrast upregulation of miR-320 is observed incardiac microvascular endothelial cells in type 2 diabetic rats[62] miR-25 the miRNA which targets NADPH oxidase 4is implicated in the pathogenesis of diabetic nephropathy via

promoting oxidative stress [63] In addition decreased levelsof miR-192 are also linked with the severity of nephropathyand fibrosis in diabetic patients [64] Better understanding ofregulatory roles of miRNAs in diabetic cardiomyopathy andother disease processes is expected to elucidate new avenuesfor RNA-based therapeutics

5 Diabetic Retinopathyand Epigenetic Modifications

Diabetic retinopathy is a multifactorial disease and a numberof metabolic abnormalities have been associated with itsdevelopment [7 65] However the role of epigenetic modifi-cations in diabetic retinopathy is still not clear SUV39H2 is agene that encodes histone methyltransferase which catalyzesthe methylation of H3K9 and recent results from the FinnishDiabetic Nephropathy Study with sim3000 diabetic patientshave found an association between the polymorphism inSUV39H2 and diabetic microvascular complications includ-ing retinopathy These studies have suggested the role of his-tone modifications in the development of diabetic retinopa-thy [66] Experimental evidence using in vitro and in vivomodels of diabetic retinopathy have shown that the activitiesof HDACs are increased and that of HATs are decreasedin the retina and its capillary cells in diabetes and globalacetylation of histones is decreased [58]However contrary tothis Kadiyala et al have shown significant increase in retinalhistone acetylation in diabetes [67] strengthening furtherinvestigation into the role of histone modifying enzymes inthe development of diabetic retinopathy

Mitochondria are dysfunctional in the retina and its capil-lary cells in diabetes and superoxide radicals are elevated andthe enzyme responsible for scavenging superoxide radicals inthe mitochondria MnSOD is impaired [68ndash70] Regulationof mitochondrial superoxide levels by maintaining MnSODprotects capillary cell apoptosis and the development ofdiabetic retinopathy in mice [69 71] In the pathogenesis ofdiabetic retinopathy Sod2 theMnSOD encoding gene is epi-geneticallymodifiedwith increasedH4K20me3 acetylH3K9and p65 subunit of NF-kB (p65) at its promoterenhancerWe have shown that increased acetyl H3K9 and p65 at Sod2interact with H4K20me3 and this results in its inactivation[15] However diabetes demethylates H3K4 and the recruit-ment of LSD1 at Sod2 promoter is increased [28]These resultshave strongly suggested that the demethylation of H3K4by LSD1 is also an important factor in the downregulationof Sod2 Furthermore overexpression of MnSOD preventsincrease in H4K20me3 at Sod2 suggesting that superoxideradicals have regulatory role in the epigenetic modificationof Sod2 and SUV4-20h2 [15] This raises the possibility toutilize therapeutic modalities targeted towards regulationof methylation status of histones to prevent inhibition ofMnSOD and protect mitochondrial damage

Matrix metalloproteinase-9 (MMP-9) an enzyme whichis proapoptotic in the development of diabetic retinopathyis also epigenetically modified in the retina in diabetes [2972 73] We have shown that at its promoter H3K9me2 isdecreased and acetyl H3K9 and the recruitment of LSD1 and


p65 of NF-kB are increased In addition regulation of LSD1ameliorates decreases in H3K9me2 and increases in p65 atMMP-9 promoter prevents the activation ofMMP-9 and alsoinhibits the cell apoptosisThe results have suggested that theactivated LSD1 hypomethylated H3K9 at MMP-9 promoterand this frees up the lysine 9 for acetylation AcetylatedH3K9 opens up the chromatin and the accessibility torecruit p65 is increased [29] This ultimately culminates inthe activation of MMP-9 and mitochondria damage Thusthe regulation of LSD1 by molecular or pharmacologicalmeans could possibly have potential to preventretard thedevelopment and progression of retinopathy by regulatingSod2 andMMP-9 and preventing mitochondrial damage andthe accelerated capillary cell apoptosis in diabetic patientsEpigenetic modifications of thioredoxin interacting proteinan endogenous inhibitor of antioxidant thioredoxin areconsidered responsible for sustained Cox2 expression seen inthe retina in diabetes [74] Furthermore in diabetes the CpGsites at the regulatory region of DNA polymerase gammaare hypermethylated affecting their binding to the mtDNAand the activity of Dnmt is increased [52] Because of thismodification the transcriptional activity is compromised andcopy number is decreased Thus there is growing evidencethat histone modifications and DNA methylation play animportant role in the development of diabetic retinopathy

Alterations inmiRNAexpressionhave also been observedin diabetic eyes and miRNAs in the eye including miR200b(one of the VEGF regulatingmiRNAs) is downregulated [75]Diabetes also upregulates some of the key NF-kB responsivemiRNAs including miR-146 miR-155 miR-132 and miR-21[76] upregulation of miR-29b in the early stages of diabetesis considered to be protective against apoptosis of the retinalganglion cells [77] These diabetes-induced alterations inmiRNAs suggest that they can be used as biomarkers to detectearly stages of the disease progression

Thus understanding and characterizing the epigeneticregulators and their role in the pathogenesis of diabeticretinopathy could help identify novel targets to combat thisdisease which is themajor cause of blindness in young adults

6 Oxidative Stressand Epigenetic Modifications

The disruption of the normal redox potential in a cellularenvironment has detrimental effects on cellular componentsincluding proteins lipids and DNA [78ndash80] Oxidative stresshas been shown to alter histone acetylationdeacetylationand methylationdemethylation Histone demethylase LSD1is FAD-dependent amine oxidases and requires oxygen tofunction [81] Oxidative damage to DNA can also result inepigenetic changes in chromatin organization by inhibitingthe binding of the methyl-CpG binding domain of methyl-CpG binding protein 2 [82] Furthermore disruption ofepigenetic mechanisms can result in oxidative stress [83] Inthe pathogenesis of diabetic retinopathy increased oxidativestress is considered to play amajor role [7 65] and our studieshave shown that the control of oxidative stress preventsepigenetic changes in retinal Sod2 [15] Thus it is plausible

that increased oxidative stress could be one of the mecha-nisms responsible formodulating epigeneticmodifications indiabetic retinopathy (Figure 1)

7 Epigenetic Modifications ofMitochondrial DNA

Although epigenetic changes in nuclear DNA (nDNA) arenow emerging as important areas of investigation in manyacquired chronic diseases epigeneticmodification ofmtDNAis still in its incipient stages Recent work has shown thatthe common epigenetic modifications in nDNA such asthe presence of 5mC and 5hmC are also observed in themtDNA and mitochondria are also equipped with Dnmtsand TETs [84] Furthermore mtDNA methylation decreaseswith age and this age-related hypo methylation is linkedwith the decreased transcription capacity of proteins encodedby mtDNA [85] Increase in Dnmt1 in the mitochondria isshown to upregulate the first mtDNA-encoded gene afterits initiation ND1 and downregulate Cytochrome b the lastgene encoded by mtDNA [84] How diabetes affects mtDNAmethylation and the transcription remains to be investigated

In addition to dysfunction of the mitochondria and theirstructural abnormalitiesmtDNA is also damaged in diabetesand the DNA polymerase gamma (POLG1) a key member ofthe DNA replication machinery is downregulated [13 52 7186 87]The CpG sites at the regulatory region of POLG in theretina are hypermethylated and this possibly compromisesits transcriptional activity [52]

Mitochondrial DNA is very small in size and does notcontain histones instead this DNA is covered with proteinsmainly the mitochondrial transcriptional factor A (TFAM)to form nucleoid [88] In diabetic retinopathy the bindingof TFAM to a nonspecific region of mtDNA is decreasedresulting in decreased levelsn of mtDNA-encoded proteinsand damaging the mtDNA [89 90] Since posttranslationalmodification of histones affects nDNA transcription it isplausible that such changes in TFAM structure might affectmtDNA transcription This suggests that by maintainingmitochondria homeostasis bymodulating epigenetic changesusing pharmaceutical or molecular means could help retardfurther progression of diabetic retinopathy

8 Therapies TargetingEpigenetic Modifications

It is now becoming clear that epigenetic factors have a rolein altering gene expression in chronic diseases suggest-ing that epigenetic mechanisms play a pivotal role in anacquired phenotype As mentioned above DNAmethylationis one of the most common epigenetic modifications andmethylation at specific CpG islands can provide insightsinto disease diagnosis Thus methylation of genes associatedwith that disease can be used as a predictor of efficacy forparticular drug treatments The most commonly used DNAmethylation inhibitors are nucleoside analogs these analogs


ARE

ROSROS

ROS

Diabetes

Retinopathy

MeMe

HATHDAC (SIRT1)

DAMLSD1 SET79

Dnmts

Mitochondria

dysfunction

miRNAs

miR200b

Me

AcMe

Ac Me

H2a

H3H2aH3

H2bH4

H2bH4

H2a

H3H2bH4

uarrMMP-9 uarr NF-120581B

uarr VEGF

darr PolG1 darr Sod2 darr GCLC-ARE

Figure 1 Epigenetic modifications and diabetic retinopathy diabetes increases oxidative stress in the retina reactive oxygen species (ROS)modify enzymes responsible for DNAmethylation (Dnmts) and histone modifications (SAT LSD1 HAT andHDAC etc) and also miRNAsDue to epigenetic modifications of various genes and transcription factors the expression of the targeted genes is altered resulting inmitochondrial dysfunction and ultimately in the development of diabetic retinopathy

incorporate into the DNA and trap all DNA methyltrans-ferases Fortunately FDA has approved Dnmt inhibitors 5-azacytidine (5-Aza-CR azacitidine Vidaza) and 5-aza-20-deoxycytidine (5-Aza-CdR decitabineDacogen) formyeloidcancers and cutaneous T cell lymphoma Furthermore DNAdemethylation agent can also enhance the sensitivity of highlychemoresistant cells to chemotherapeutic drugs suggestingtheir use as a promising approach in treating certain cancers[91] However these agents have significant toxicity at highconcentrations due to DNA damage and a group of morepotent and selective Dnmt inhibitors potentially with lesstoxicity is now being under development Zebularine (1-(120573-D-ribofuranosyl)-2(1H)-pyrimidinone) a cytidine lacking 4-amino group of the pyrimidine ring is less toxic and actsby forming a covalent complex with Dnmt and cytidinedeaminase when incorporated into DNA [92] In additionrecent work has shown that the status of methylation ofVEGFR promoter dictates the efficacy of the VEGF-targeteddrugs on the proliferation of cancer tissue suggesting that theepigenetic alteration of VEGFRs could influence the efficacyof VEGF-specific tyrosine kinase inhibitors [93] This is verysignificant for diabetic patients experiencing possibility of

losing vision due to retinopathy as VEGF is considered asone of the major growth factor in the neovascularizationassociated with proliferative diabetic retinopathy

As mentioned above histone modifications can altergene expression modifying the risk for a disease and theprocess is homeostatically balanced by groups of cellularenzymes that add an acetyl or methyl group or remove themEpigallocatechin-3-gallate is a strong HAT inhibitor and itinhibits p65 acetylation-dependent NF-kB activation [94]and in the pathogenesis of diabetic retinopathy activationof NF-kB is considered to accelerate apoptosis of capillarycells suggesting that inhibitor has potential to inhibit thedevelopment of diabetic retinopathy Histone deacetylasesinhibitor can suppress the growth andor survival of tumorcells [95 96] and Vorinostat and Romidepsin are the firstand only histone deacetylases inhibitors approved by FDAfor clinical use [97] However other inhibitors of histonedeacetylases are in clinical trials for other types of cancertreatment

Since miRNAs can regulate gene expression via differ-ent ways including translational repression mRNA cleav-age and deadenylation miRNAs have rapidly emerged as


promising targets for the development of novel therapeuticsDouble-stranded miRNA mimics and antimRNA antisenseoligodeoxyribonucleotide are the two commonly investigatedtechniques to target specific miRNA miRNAs have a specificand defined target in the pathogenic mechanism of thedisease miRNA-based therapy comes with the advantagethat they target multiple genes involved in the same pathwayprocess [98] One of themajor caveats with themiRNA-basedtherapy is their delivery as these modulators must leave thecirculatory system to get into the target tissue and should beable to cross blood-retina barrier The other important issueis their circulatory half-life The advances in drug deliverytechniques however could open up the use of miRNAs fordiabetic retinopathy

As mentioned above epigenetic modifications are influ-enced by environmental and dietary factors many natu-ral compounds have been tested to evaluate their benefi-cial effects on such modifications [99 100] Polyphenolsincluding resveratrol a natural compound found in theskin of red grapes and a constituent of red wine areimplicated in the regulation of histone deacetylases Sirt1[101] Curcumin (diferuloylmethane) a natural compoundcommonly used as a curry spice is shown to modulate anumber of histone modifying enzymes and miRNAs [102103] and our previous work has shown that its curcuminameliorates retinal metabolic abnormalities postulated to beimportant in the development of diabetic retinopathy [104]Thus natural compounds could have potential benefits ininhibiting the development of retinopathy in diabetic patientsvia modulating both metabolic abnormalities and epigeneticmodifications

The role of epigenetic modifications in the pathogen-esis of diabetic retinopathy is an emerging area Recentresearch has shown that the diabetes environment fostersepigenetic modifications of a number of genes implicatedin the pathogenesis of diabetic retinopathy and enzymesresponsible for bringing in the epigenetic changes are alteredThe use of the inhibitors and mimics is targeted to regulatethe histone modification DNAmethylation and miRNAs arebeing targeted for a number of chronic diseases [105ndash107]and the recent advances in the drug delivery to the retinaare now opening up the field for their future testing for thisdevastating disease which a diabetic patient fears the most

References

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[3] L S Lim and T Y Wong ldquoLipids and diabetic retinopathyrdquoExpert Opinion on Biological Therapy vol 12 no 1 pp 93ndash1052012

[4] N Cheung P Mitchell and T Y Wong ldquoDiabetic retinopathyrdquoThe Lancet vol 376 no 9735 pp 124ndash136 2010

[5] W Zhang H Liu M Rojas R W Caldwell and R BCaldwell ldquoAnti-inflammatory therapy for diabetic retinopathyrdquoImmunotherapy vol 3 no 5 pp 609ndash628 2011

[6] M Kitada Z Zhang A Mima and G L King ldquoMolecularmechanisms of diabetic vascular complicationsrdquo Journal ofDiabetes Investigation vol 1 no 3 pp 77ndash89 2010

[7] J M Santos G Mohammad Q Zhong and R A KowluruldquoDiabetic retinopathy superoxide damage and antioxidantsrdquoCurrent Pharmaceutical Biotechnology vol 12 no 3 pp 352ndash361 2011

[8] R A Kowluru ldquoDiabetes-induced elevations in retinal oxida-tive stress protein kinase C and nitric oxide are interrelatedrdquoActa Diabetologica vol 38 no 4 pp 179ndash185 2001

[9] J M Torres N J Cox and L H Philipson ldquoGenome wideassociation studies for diabetes perspective on results andchallengesrdquo Pediatric Diabetes vol 14 pp 90ndash96 2013

[10] K C Donaghue S H Margan A K F Chan et al ldquoTheassociation of aldose reductase gene (AKR1B1) polymorphismswith diabetic neuropathy in adolescentsrdquoDiabeticMedicine vol22 no 10 pp 1315ndash1320 2005

[11] J Ma Y Li F Zhou X Xu G Guo and Y Qu ldquoMeta-analysis of association between the Pro12Ala polymorphismof the peroxisome proliferator-activated receptor-1205742 gene anddiabetic retinopathy in Caucasians and Asiansrdquo MolecularVision vol 18 pp 2352ndash2360 2012

[12] A Bonnefond P J Saulnier M G Stathopoulou N Grarup NC Ndiaye R Roussel et al ldquoWhat is the contribution of twogenetic variants regulating VEGF levels to type 2 diabetes riskand to microvascular complicationsrdquo PLoS ONE vol 8 ArticleID e55921 2013

[13] S Tewari J M Santos and R A Kowluru ldquoDamaged mito-chondrial DNA replication system and the development ofdiabetic retinopathyrdquo Antioxidants amp Redox Signaling vol 17pp 492ndash504 2012

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[15] Q Zhong and R A Kowluru ldquoEpigenetic changes inmitochon-drial superoxide dismutase in the retina and the developmentof diabetic retinopathyrdquo Diabetes vol 60 no 4 pp 1304ndash13132011

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[29] Q Zhong and R A Kowluru ldquoRegulation of matrix metallop-eptidase-9 by epigenetic modifications and the developmentof diabetic retinopathyrdquo Diabetes vol 62 no 7 pp 2559ndash25682013

[30] T Vaissiere C Sawan and Z Herceg ldquoEpigenetic interplaybetween histone modifications and DNA methylation in genesilencingrdquoMutation Research vol 659 no 1-2 pp 40ndash48 2008

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[47] R S Dwivedi J G Herman T A McCaffrey and D S C RajldquoBeyond genetics epigenetic code in chronic kidney diseaserdquoKidney International vol 79 no 1 pp 23ndash32 2011

[48] M K Shanmugam and G Sethi ldquoRole of epigenetics ininflammation-associated diseasesrdquo Subcellular Biochemistryvol 61 pp 627ndash657 2012

[49] T X Pham and J Lee ldquoDietary regulation of histone acetylasesand deacetylases for the prevention of metabolic diseasesrdquoNutrients vol 4 pp 1868ndash1886 2012

[50] G-L Ding F-F Wang J Shu et al ldquoTransgenerational glucoseintolerance with Igf2H19 epigenetic alterations in mouse isletinduced by intrauterine hyperglycemiardquo Diabetes vol 61 no 5pp 1133ndash1142 2012

[51] C Ling S Del Guerra R Lupi et al ldquoEpigenetic regulation ofPPARGC1A in human type 2 diabetic islets and effect on insulinsecretionrdquo Diabetologia vol 51 no 4 pp 615ndash622 2008

[52] S Tewari Q Zhong J M Santos and R A KowluruldquoMitochondria DNA replication and DNA methylation in themetabolic memory associated with continued progression ofdiabetic retinopathyrdquo Investigative Ophthalmology amp VisualScience vol 53 pp 4881ndash4888 2012

[53] C Ling and L Groop ldquoEpigenetics a molecular link betweenenvironmental factors and type 2 diabetesrdquoDiabetes vol 58 no12 pp 2718ndash2725 2009

[54] C G Bell A E Teschendorff V K Rakyan A P MaxwellS Beck and D A Savage ldquoGenome-wide DNA methylationanalysis for diabetic nephropathy in type 1 diabetes mellitusrdquoBMCMedical Genomics vol 3 article 33 2010

[55] T Akcay Y Dincer N Celebi and H Ilkova ldquoO6-methylguanine DNA methyltransferase activity in diabeticpatientsrdquo Diabetes Research and Clinical Practice vol 61 pp1ndash6 2003

[56] K T Williams T A Garrow and K L Schalinske ldquoType Idiabetes leads to tissue-specific DNA hypomethylation in maleratsrdquo Journal of Nutrition vol 138 no 11 pp 2064ndash2069 2008

[57] LMVilleneuveM A Reddy L L LantingMWang LMengand R Natarajan ldquoEpigenetic histone H3 lysine 9 methylationin metabolic memory and inflammatory phenotype of vascularsmooth muscle cells in diabetesrdquo Proceedings of the NationalAcademy of Sciences of the United States of America vol 105 no26 pp 9047ndash9052 2008

[58] Q Zhong and R A Kowluru ldquoRole of histone acetylation in thedevelopment of diabetic retinopathy and themetabolicmemoryphenomenonrdquo Journal of Cellular Biochemistry vol 110 no 6pp 1306ndash1313 2010

[59] A S Olsen M P Sarras Jr A Leontovich and R V IntineldquoHeritable transmission of diabetic metabolic memory inzebrafish correlates with DNA hypomethylation and aberrantgene expressionrdquo Diabetes vol 61 no 2 pp 485ndash491 2012


[60] R F Thompson M J Fazzari H Niu N Barzilai R ASimmons and J M Greally ldquoExperimental intrauterine growthrestriction induces alterations in DNA methylation and geneexpression in pancreatic islets of ratsrdquo Journal of BiologicalChemistry vol 285 no 20 pp 15111ndash15118 2010

[61] B Feng S Chen B George Q Feng and S ChakrabartildquomiR133a regulates cardiomyocyte hypertrophy in diabetesrdquoDiabetesMetabolism Research and Reviews vol 26 no 1 pp40ndash49 2010

[62] X H Wang R Z Qian W Zhang S F Chen H M Jin and RM Hu ldquoMicroRNA-320 expression in myocardial microvascu-lar endothelial cells and its relationship with insulin-like growthfactor-1 in type 2 diabetic ratsrdquo Clinical and ExperimentalPharmacology and Physiology vol 36 no 2 pp 181ndash188 2009

[63] Y Fu Y Zhang Z Wang et al ldquoRegulation of NADPHoxidase activity is associated with miRNA-25-mediated NOX4expression in experimental diabetic nephropathyrdquo AmericanJournal of Nephrology vol 32 no 6 pp 581ndash589 2010

[64] A Krupa R Jenkins D DongLuo A Lewis A Phillipsand D Fraser ldquoLoss of microRNA-192 promotes fibrogenesisin diabetic nephropathyrdquo Journal of the American Society ofNephrology vol 21 no 3 pp 438ndash447 2010

[65] S A Madsen-Bouterse and R A Kowluru ldquoOxidative stressand diabetic retinopathy pathophysiological mechanisms andtreatment perspectivesrdquo Reviews in Endocrine and MetabolicDisorders vol 9 no 4 pp 315ndash327 2008

[66] A Syreeni A El-Osta C Forsblom et al ldquoGenetic examinationof SETD7 and SUV39H1H2 methyltransferases and the riskof diabetes complications in patients with type 1 diabetesrdquoDiabetes vol 60 no 11 pp 3073ndash3080 2011

[67] C S Kadiyala L Zheng Y Du E Yohannes H Y Kaoand M Miyagi ldquoAcetylation of retinal histones in diabetesincreases inflammatory proteins effects of minocycline andmanipulation of histone acetyltransferase (HAT) and histonedeacetylase (HDAC)rdquo Journal of Biological Chemistry vol 287pp 25869ndash25880 2012

[68] M Kanwar P-S Chan T S Kern and R A KowluruldquoOxidative damage in the retinalmitochondria of diabeticmicepossible protection by superoxide dismutaserdquo InvestigativeOph-thalmology and Visual Science vol 48 no 8 pp 3805ndash38112007

[69] R A Kowluru L Atasi and Y-S Ho ldquoRole of mitochondrialsuperoxide dismutase in the development of diabetic retinopa-thyrdquo Investigative Ophthalmology ampVisual Science vol 47 no 4pp 1594ndash1599 2006

[70] R A Kowluru V Kowluru Y Xiong and Y-S Ho ldquoOver-expression of mitochondrial superoxide dismutase in miceprotects the retina from diabetes-induced oxidative stressrdquo FreeRadical Biology and Medicine vol 41 no 8 pp 1191ndash1196 2006

[71] S A Madsen-Bouterse Q Zhong G Mohammad Y-S Hoand R A Kowluru ldquoOxidative damage of mitochondrial DNAin diabetes and its protection by manganese superoxide dismu-taserdquo Free Radical Research vol 44 no 3 pp 313ndash321 2010

[72] R A Kowluru ldquoRole of matrix metalloproteinase-9 in thedevelopment of diabetic retinopathy and its regulation by H-Rasrdquo Investigative Ophthalmology amp Visual Science vol 51 no8 pp 4320ndash4326 2010

[73] R A Kowluru GMohammad J M Dos Santos andQ ZhongldquoAbrogation of MMP-9 gene protects against the developmentof retinopathy in diabetic mice by preventing mitochondrialdamagerdquo Diabetes vol 60 no 11 pp 3023ndash3033 2011

[74] L Perrone T S Devi K-I Hosoya T Terasaki and L P SinghldquoThioredoxin interacting protein (TXNIP) induces inflam-mation through chromatin modification in retinal capillaryendothelial cells under diabetic conditionsrdquo Journal of CellularPhysiology vol 221 no 1 pp 262ndash272 2009

[75] K McArthur B Feng Y Wu S Chen and S ChakrabartildquoMicroRNA-200b regulates vascular endothelial growth factor-mediated alterations in diabetic retinopathyrdquo Diabetes vol 60no 4 pp 1314ndash1323 2011

[76] B Kovacs S Lumayag C Cowan and S Xu ldquoMicroRNAs inearly diabetic retinopathy in streptozotocin-induced diabeticratsrdquo Investigative Ophthalmology amp Visual Science vol 52 no7 pp 4402ndash4409 2011

[77] V A O Silva A Polesskaya T A Sousa et al ldquoExpression andcellular localization of microRNA-29b and RAX an activatorof the RNA-dependent protein kinase (PKR) in the retina ofstreptozotocin-induced diabetic ratsrdquo Molecular Vision vol 17pp 2228ndash2240 2011

[78] M Ott V Gogvadze S Orrenius and B Zhivotovsky ldquoMito-chondria oxidative stress and cell deathrdquo Apoptosis vol 12 no5 pp 913ndash922 2007

[79] M Valko H Morris andM T D Cronin ldquoMetals toxicity andoxidative stressrdquoCurrentMedicinal Chemistry vol 12 no 10 pp1161ndash1208 2005

[80] M Valko D Leibfritz J Moncol M T D Cronin M Mazurand J Telser ldquoFree radicals and antioxidants in normal physi-ological functions and human diseaserdquo International Journal ofBiochemistry and Cell Biology vol 39 no 1 pp 44ndash84 2007

[81] J Wang Z Wu D Li N Li S V Dindot and M C SatterfieldldquoNutrition epigenetics andmetabolic syndromerdquoAntioxidantsamp Redox Signaling vol 17 pp 282ndash301 2012

[82] V Valinluck H-H Tsai D K Rogstad A Burdzy A Birdand L C Sowers ldquoOxidative damage to methyl-CpG sequencesinhibits the binding of themethyl-CpG binding domain (MBD)of methyl-CpG binding protein 2 (MeCP2)rdquo Nucleic AcidsResearch vol 32 no 14 pp 4100ndash4108 2004

[83] Y Chervona andM Costa ldquoThe control of histone methylationand gene expression by oxidative stress hypoxia and metalsrdquoFree Radic Biol Med vol 53 pp 1041ndash1047 2012

[84] L S Shock P V Thakkar E J Peterson R G Moran and SM Taylor ldquoDNAmethyltransferase 1 cytosinemethylation andcytosine hydroxymethylation in mammalian mitochondriardquoProceedings of the National Academy of Sciences of the UnitedStates of America vol 108 no 9 pp 3630ndash3635 2011

[85] S Dzitoyeva H Chen and H Manev ldquoEffect of aging on 5-hydroxymethylcytosine in brainmitochondriardquoNeurobiology ofAging 2012

[86] S A Madsen-Bouterse G Mohammad M Kanwar and R AKowluru ldquoRole of mitochondrial DNA damage in the devel-opment of diabetic retinopathy and the metabolic memoryphenomenon associated with its progressionrdquoAntioxidants andRedox Signaling vol 13 no 6 pp 797ndash805 2010

[87] J M Santos S Tewari A F X Goldberg and R A KowluruldquoMitochondrial biogenesis and the development of diabeticretinopathyrdquo Free Radical Biology and Medicine vol 51 no 10pp 1849ndash1860 2011

[88] K Ohgaki T Kanki A Fukuoh et al ldquoThe C-terminal tail ofmitochondrial transcription factor A markedly strengthens itsgeneral binding to DNArdquo Journal of Biochemistry vol 141 no2 pp 201ndash211 2007

[89] J M Santos S Tewari and R A Kowluru ldquoA compensatorymechanism protects retinal mitochondria from initial insult in


diabetic retinopathyrdquo Free Radical Biology andMedicine vol 53pp 1729ndash1737 2012

[90] J M Santos and R A Kowluru ldquoImpaired transport of mito-chondrial transcription factor A (TFAM) and the metabolicmemory phenomenon associated with the progression of dia-betic retinopathyrdquo DiabetesMetabolism Research and Reviewsvol 29 pp 204ndash213 2013

[91] R M Eglen and T Reisine ldquoScreening for compoundsthat modulate epigenetic regulation of the transcriptome anoverviewrdquo Journal of Biomolecular Screening vol 16 no 10 pp1137ndash1152 2011

[92] C Champion D Guianvarcrsquoh C Senamaud-Beaufort et alldquoMechanistic insights on the inhibition of C5 DNA methyl-transferases by zebularinerdquo PLoS ONE vol 5 no 8 Article IDe12388 2010

[93] J Kim J Hwang H Jeong et al ldquoPromoter methylationstatus of VEGF receptor genes-a possible epigenetic biomarkerto anticipate the efficacy of intracellular-acting vegf-targeteddrugs in cancer cellsrdquo Epigenetics vol 7 no 2 pp 191ndash200 2012

[94] K-C Choi G J Myung Y-H Lee et al ldquoEpigallocatechin-3-gallate a histone acetyltransferase inhibitor inhibits EBV-induced B lymphocyte transformation via suppression of RelAacetylationrdquo Cancer Research vol 69 no 2 pp 583ndash592 2009

[95] M J Peart KM Tainton A A Ruefli et al ldquoNovelmechanismsof apoptosis induced by histone deacetylase inhibitorsrdquo CancerResearch vol 63 no 15 pp 4460ndash4471 2003

[96] D Khabele D-S Son A K Parl et al ldquoDrug-induced inactiva-tion or gene silencing of class I histone deacetylases suppressesovarian cancer cell growth implications for therapyrdquo CancerBiology andTherapy vol 6 no 5 pp 795ndash801 2007

[97] E Glass and P H Viale ldquoHistone deacetylase inhibitorsnovel agents in cancer treatmentrdquo Clinical Journal of OncologyNursing vol 17 pp 34ndash40 2013

[98] A CaroliM T Cardillo R Galea and LM Biasucci ldquoPotentialtherapeutic role of microRNAs in ischemic heart diseaserdquoJournal of Cardiology vol 61 pp 315ndash320 2013

[99] S I Khan P Aumsuwan I A Khan L A Walker and AK Dasmahapatra ldquoEpigenetic events associated with breastcancer and their prevention by dietary components targetingthe epigenomerdquo Chemical Research in Toxicology vol 25 no 1pp 61ndash73 2012

[100] S Reuter S C Gupta B Park A Goel and B B AggarwalldquoEpigenetic changes induced by curcumin and other naturalcompoundsrdquoGenes and Nutrition vol 6 no 2 pp 93ndash108 2011

[101] S Chung H Yao S Caito J-W Hwang G Arunachalam andI Rahman ldquoRegulation of SIRT1 in cellular functions role ofpolyphenolsrdquo Archives of Biochemistry and Biophysics vol 501no 1 pp 79ndash90 2010

[102] G Bora-Tatar D Dayangac-Erden A S Demir S DalkaraK Yelekci and H Erdem-Yurter ldquoMolecular modificationson carboxylic acid derivatives as potent histone deacetylaseinhibitors activity and docking studiesrdquo Bioorganic and Medic-inal Chemistry vol 17 no 14 pp 5219ndash5228 2009

[103] J C Howell E Chun and A N Farrell ldquoGlobal microRNAexpression profiling curcumin (diferuloylmethane) altersoxidative stress-responsive microRNAs in human ARPE-19cellsrdquoMolecular Vision vol 19 pp 544ndash560 2013

[104] R A Kowluru and M Kanwar ldquoEffects of curcumin on retinaloxidative stress and inflammation in diabetesrdquo Nutrition andMetabolism vol 4 article 8 2007

[105] Q Lu A M Quinn M P Patel S F Semus A P Gravesand D Bandyopadhyay ldquoPerspectives on the discovery ofsmall-molecule modulators for epigenetic processesrdquo Journal ofBiomolecular Screening vol 17 pp 555ndash571 2012

[106] S P Nana-Sinkam and C M Croce ldquoClinical applications formicroRNAs in cancerrdquo Clinical Pharmacology amp Therapeuticsvol 93 pp 98ndash104 2013

[107] YOki and J-P J Issa ldquoReview recent clinical trials in epigenetictherapyrdquo Reviews on Recent Clinical Trials vol 1 no 2 pp 169ndash182 2006

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Anatomy Research International

PeptidesInternational Journal of


Hindawi Publishing Corporation httpwwwhindawicom

International Journal of

Volume 2014

Zoology


Molecular Biology International

GenomicsInternational Journal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014


BioinformaticsAdvances in

Marine BiologyJournal of



Signal TransductionJournal of


BioMed Research International

Evolutionary BiologyInternational Journal of



Biochemistry Research International

ArchaeaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014


Genetics Research International


Advances in

Virolog y

Hindawi Publishing Corporationhttpwwwhindawicom

Nucleic AcidsJournal of

Volume 2014

Stem CellsInternational



Enzyme Research



Microbiology


could explain some of the interindividual variations inthe susceptibility of diabetes [9] A meta-analysis studyto investigate possible genetic associations with diabeticretinopathy which incorporated reports published betweenJanuary 1990 and August 2008 has revealed a significantvariation in the AKR1B1 gene This gene encodes aldo-ketoreductase family 1 member B1 which is the rate limitingenzyme of the polyol pathway [10] one of the pathwaysimplicated in the development of diabetic retinopathy [2 67] Another meta-analysis study has shown that Ala allele ofthe Pro12Ala polymorphism in the peroxisome proliferator-activated receptor-1205742 gene acts as a protective gene in theincidence of retinopathy in type 2 diabetic patients [11] Incontrast recent studies have failed to find any associationsbetween VEGF-related SNPs (rs6921438 and rs10738760) andthe risk of diabetic retinopathy and nephropathy in diabeticpatients [12] Thus the association between genetic factorsand diabetic retinopathy remains to be clarified

3 Epigenetic Modificationsand Gene Regulation

Diabetic environment disturbs metabolic homeostasis andalso alters various genes including genes associated withoxidative stress apoptosis and inflammation [13ndash16] Controlof gene expression (ie the ability of a gene to produce abiologically active protein) in mammals in addition to beingmodulated by transcriptional and translational initiationcan also be controlled by changes ldquoon the toprdquo of thegenes without altering the nucleotide composition of thegenome [17] These ldquoepigeneticrdquo modifications are stable butpotentially reversible and can be passed from generationto generation Recent studies have shown that epigeneticchanges play a major role in many chronic diseases such ascancer and diabetes where small changes in the epigenomeover time are considered to lead to disease manifestationThree major epigenetic mechanisms considered to regulategene expression areDNAmethylation histonemodificationsand noncoding RNA activity [18ndash21]

DNAmethylation addition of amethyl group on position5 of cytosine residues of the cluster of CpG dinucleotides(CpG Island) which is the regulatory region of most genes istypically associated with transcriptional repression [22 23]The methylation process brings in the unintended changesbrought up by the environmental exposures or other life styleand these changes can be passed on for multiple generationsCytosine 5 methylation generates 5-methylcytosine (5mC)and the reaction is catalyzed by a family of enzymesmdashDNA (cytosine-5) methyltransferases (Dnmts) The conver-sion of 5mC to 5-hydroxymethylcytosine (5hmC) is facili-tated by Ten-eleven-translocation enzymes (TETs) [24 25]making these enzymes future targets of pharmacologicalregulation However how the process of DNA methylation-demethylation is balanced remains somewhat unclear Asubfamily of DNA glycosylases are considered to promoteactiveDNAdemethylation by removing the 5-methylcytosinebase followed by cleavage of the DNA backbone at the abasic

site and the methylated cytosine is replaced by an unmethy-lated cytosine In contrast the passive process involvesabsenceinactivation of Dnmt1 resulting in hypomethylatedDNA [26]

Gene expression pattern is also dictated by chromatinwhich is a composite structure of histones and nucleic acidHistones act as spools around which DNAwinds and amongthe 4-histone proteins histone 2A and B (H2A and H2B)H3 and H4 form a tetrameric structure the nucleosome [27]Despite such sophisticated DNA packaging N-terminal ofhistones remains vulnerable for posttranslational modifica-tions and can be acetylatedmethylated and phosphorylatedSuch epigenetic modifications alter the chromatin structurewhich subsequently affects the binding of transcription fac-tors and can regulate the selective expression of genes ina particular tissue by acting like switches to control geneactivity [15 28ndash31]

Acetylation is one of the most common modificationswhich is generally associated with gene activation and theprocess relaxes the chromatin structure allowing recruitmentand binding of transcription factor and RNA polymerase II[32] Acetylation is regulated by fine balance between histoneacetylating and deacetylating enzymes histone acetyltrans-ferases (HATs) add acetyl group while histone deacetylase(HDAC) removes the acetyl group Methylation of histoneshowever shows greater variability as methylation can occurat both lysine and arginine residues and can be associatedwith either gene activation or repression Methylation oflysine 4 of histone 3 (H3K4) is typically associated withgene activation while methylation of lysine 9 (H3K9) isassociated with gene repression [33ndash35] Furthermore theoutcome of methylation is also dictated by the specifichistone residue being modified for example mono- or tri-methylation of H3K4 induces activation of gene expression[36 37] While monomethylation of H3K9 induces geneactivation its tri-methylation suppresses the gene activity[38] As with acetylation methylation status of histonesdepends on the final balance between histone methylatingand demethylating enzymes Histone methylating enzymesSET179 help in H3K4 methylation and suppressors ofvariegation 3-9 homolog (SUV39H) methylates lysine 9 ofhistone 3 [39 40] Subsequently in order to protect fromsuch kind of relatively stable methyl modifications andconstitutive expression of genes lysine specific demethylase(LSD1) specifically removes methyl groups from methylatedH3K4 and H3K9 [41 42]

In addition to DNA methylation and histone modifi-cations gene expression is also regulated by microRNAs(miRNA) the small noncoding RNAs that regulate geneexpression posttranscriptionally by binding to complemen-tary sequences in the 31015840 untranslated regions of messengerRNAs [43 44] This cleaves mRNA resulting in decreasedprotein synthesis and expression of the targeted gene Geneswith epigenetic functions in chromatin can be regulated bymiRNAs affecting chromatin remodeling and gene expres-sion Regulation of genes by DNA methylation and miRNAappears to be interrelated as the function of Dnmts dependson histone modification patterns such as H3K9 methylationand histone deacetylation In addition inhibition of Dnmts


























ARE

ROSROS

ROS

Diabetes

Retinopathy

MeMe

HATHDAC (SIRT1)

DAMLSD1 SET79

Dnmts

Mitochondria

dysfunction

miRNAs

miR200b

Me

AcMe

Ac Me

H2a

H3H2aH3

H2bH4

H2bH4

H2a

H3H2bH4


uarr VEGF











References
























































































































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology


























ARE

ROSROS

ROS

Diabetes

Retinopathy

MeMe

HATHDAC (SIRT1)

DAMLSD1 SET79

Dnmts

Mitochondria

dysfunction

miRNAs

miR200b

Me

AcMe

Ac Me

H2a

H3H2aH3

H2bH4

H2bH4

H2a

H3H2bH4


uarr VEGF











References
























































































































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology















ARE

ROSROS

ROS

Diabetes

Retinopathy

MeMe

HATHDAC (SIRT1)

DAMLSD1 SET79

Dnmts

Mitochondria

dysfunction

miRNAs

miR200b

Me

AcMe

Ac Me

H2a

H3H2aH3

H2bH4

H2bH4

H2a

H3H2bH4


uarr VEGF











References
























































































































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology


ARE

ROSROS

ROS

Diabetes

Retinopathy

MeMe

HATHDAC (SIRT1)

DAMLSD1 SET79

Dnmts

Mitochondria

dysfunction

miRNAs

miR200b

Me

AcMe

Ac Me

H2a

H3H2aH3

H2bH4

H2bH4

H2a

H3H2bH4


uarr VEGF











References
























































































































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology





References
























































































































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology

































































































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology



























































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology




























Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology








Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology

Documents

Review Article Epigenetic Modifications and Diabetic …downloads.hindawi.com/journals/bmri/2013/635284.pdfthe risk of diabetic retinopathy and nephropathy in diabetic patients [ ]