Diabetic retinopathy remains the leading cause of blindness in working-age adults. Landmark clinical studies have documented that even after achieving and maintaining good glycemic control for many years, damage instilled by the prior poor glycemic control becomes difficult to undo, and the results have suggested that the prior hyperglycemia leaves a legacy. This `metabolic memory' phenomenon is also duplicated in vitro and in vivo experimental models of diabetic retinopathy. Termination of hyperglycemia in rats does not reverse mitochondrial dysfunction and DNA (mtDNA) damage, DNA repair enzyme MutL homolog 1 (Mlh1) remains subnormal, and impaired mtDNA transcription continues to compromise the electron transport chain (ETC). Stability of both genomic and structure/physiology are important for mitochondrial homeostasis; mitochondrial fusion enzyme mitofusin 2 (Mfn2) also remains subnormal even after cessation of hyperglycemia. Recent studies have documented that genomic functions are also modulated by epigenetic modifications, the modifications that regulate gene expression without changing the DNA sequence. Our recent research has shown that diabetes activates DNA methylation machinery in the retina and its capillary cells, and this activation is not terminated by reversal of hyperglycemia. Thus, the central hypothesis is that due to sustained epigenetic modifications, mitochondrial DNA and structure/function remain damaged. Dysfunctional mitochondria continues to fuel into the vicious cycle of free radicals, and cessation of hyperglycemia fails to arrest the progression of incipient diabetic retinopathy.
Aim 1 will investigate the role of epigenetic modification in mitochondrial genomic stability. Our model predicts that due to sustained Mlh1 promoter DNA hypermethylation, mitochondrial genomic stability remains compromised, and impaired mtDNA transcription continues to damage ETC system, fueling into mitochondrial damage.
Aim 2 will determine how epigenetic modifications regulate mitochondrial structural/physiological homeostasis, and will investigate the role of epigenetic modifications of Mfn2 promoter in continued mitochondrial damage.
Aim 3 will determine the effect of protection of mitochondrial homeostasis in the resistance of diabetic retinopathy to halt by directly inhibiting epigenetic modifications during normal glycemia, which has followed hyperglycemia. The plan will employ in vitro (retinal endothelial cells) and in vivo (retinal microvessels from rodents maintained in varied glycemic control) models of metabolic memory, and will utilize fully optimized molecular biological and pharmacological approaches. Our overall goal is to understand the molecular mechanism responsible for continued mitochondrial damage in the progression of diabetic retinopathy. The proposal is based on a testable central hypothesis, and these innovative studies carry a significant translational impact as they are expected to define the role of epigenetics in continued mitochondrial damage, and identify novel therapeutic targets to inhibit the progression of this sight-threatening disease.

Public Health Relevance

Diabetic retinopathy, a slow progressing disease, is the most frequent cause of blindness among young adults. Clinical and experimental studies have shown that the progression of this devastating disease does not halt after re-institution of intensive glycemic control in diabetic patients/animal models. This proposal is focused on understanding the mechanism responsible for continued damage of retinal mtDNA in the progression of diabetic retinopathy after hyperglycemic insult is terminated. The application represents our continued effort in trying to understand the role of epigenetic modifications, especially DNA methylation, in maintaining mitochondrial genomic and physiological stability. The results obtained from our studies have strong potential to be translated into identifying therapies by offering patients an opportunity to supplement their best possible glycemic control with therapies to ameliorate progression of this sight-threatening complication of diabetes.

National Institute of Health (NIH)
National Eye Institute (NEI)
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Diseases and Pathophysiology of the Visual System Study Section (DPVS)
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Shen, Grace L
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Wayne State University
Schools of Medicine
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Kowluru, Renu A; Mishra, Manish (2018) Therapeutic targets for altering mitochondrial dysfunction associated with diabetic retinopathy. Expert Opin Ther Targets 22:233-245
Mishra, Manish; Duraisamy, Arul J; Kowluru, Renu A (2018) Sirt1: A Guardian of the Development of Diabetic Retinopathy. Diabetes 67:745-754
Duraisamy, Arul J; Mishra, Manish; Kowluru, Renu A (2017) Crosstalk Between Histone and DNA Methylation in Regulation of Retinal Matrix Metalloproteinase-9 in Diabetes. Invest Ophthalmol Vis Sci 58:6440-6448
Devi, Takhellambam Swornalata; Somayajulu, Mallika; Kowluru, Renu Anjan et al. (2017) TXNIP regulates mitophagy in retinal Müller cells under high-glucose conditions: implications for diabetic retinopathy. Cell Death Dis 8:e2777
Mishra, Manish; Kowluru, Renu A (2017) Role of PARP-1 as a novel transcriptional regulator of MMP-9 in diabetic retinopathy. Biochim Biophys Acta Mol Basis Dis 1863:1761-1769
Kowluru, Renu A; Shan, Yang (2017) Role of oxidative stress in epigenetic modification of MMP-9 promoter in the development of diabetic retinopathy. Graefes Arch Clin Exp Ophthalmol 255:955-962
Kowluru, Renu A; Mishra, Manish (2017) Epigenetic regulation of redox signaling in diabetic retinopathy: Role of Nrf2. Free Radic Biol Med 103:155-164
Mishra, Manish; Lillvis, John; Seyoum, Berhane et al. (2016) Peripheral Blood Mitochondrial DNA Damage as a Potential Noninvasive Biomarker of Diabetic Retinopathy. Invest Ophthalmol Vis Sci 57:4035-44
Kowluru, Renu A; Shan, Yang; Mishra, Manish (2016) Dynamic DNA methylation of matrix metalloproteinase-9 in the development of diabetic retinopathy. Lab Invest 96:1040-9
Mishra, Manish; Flaga, Jadwiga; Kowluru, Renu A (2016) Molecular Mechanism of Transcriptional Regulation of Matrix Metalloproteinase-9 in Diabetic Retinopathy. J Cell Physiol 231:1709-18

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