title: Retinal mitochondrial DNA mismatch repair in the development of diabetic retinopathy, and its continued progression after termination of hyperglycemia.
abstract: OBJECTIVE
  Mitochondrial DNA (mtDNA) is damaged in the retina in diabetes, and mitochondria copy numbers are decreased. The displacement-loop (D-loop) of the mtDNA, the region with transcription/replication elements, experiences more damage than other regions of mtDNA. Our aim was to examine the role of DNA mismatch repair (MMR) in mitochondria homeostasis in diabetic retinopathy, and in its continued progression after cessation of hyperglycemia.
  
  
  METHODS
  Effect of hyperglycemia on sequence variants in the D-loop region was investigated in retinal endothelial cells and in the retina from streptozotocin-induced diabetic rats using mismatch-specific surveyor nuclease. The role of MMR machinery in mtDNA damage and mitochondrial respiration was investigated in retinal endothelial cells overexpressing Mlh1, an MMR enzyme mainly associated with mtDNA polymerase gamma, or Msh2 (associated with nuclear polymerase beta).
  
  
  RESULTS
  Hyperglycemia increased sequence variants in the D-loop region. While overexpression of Mlh1 in endothelial cells ameliorated glucose-induced increase in D-loop sequence variants, decrease in respiration rate and increase in apoptosis, overexpression of Msh2 did not protect the mitochondria damage. Termination of hyperglycemia failed to reverse decrease in MMR enzymes and increase in D-loop sequence variants.
  
  
  CONCLUSIONS
  Due to a compromised MMR system, the sequence variants in the D-loop region were not repaired, and that resulted in impaired mtDNA transcription. Mitochondria become dysfunctional, and they continued to be dysfunctional even after hyperglycemia was terminated, contributing to the development, and progression of diabetic retinopathy. Thus, strategies targeting mitochondrial MMR machinery could help maintain mitochondria homeostasis, and inhibit the development of diabetic retinopathy and its continued progression.
authors.affiliation: Kresge Eye Institute, Wayne State University, Detroit, Michigan, United States.
authors.forename: Manish
authors.initials: M
authors.lastname: Mishra
authors.affiliation: Kresge Eye Institute, Wayne State University, Detroit, Michigan, United States.
authors.forename: Renu A
authors.initials: RA
authors.lastname: Kowluru
mesh_terms: D000818:Animals; D002417:Cattle; D004249:DNA Damage; D053843:DNA Mismatch Repair / Q000235:genetics*; D004272:DNA, Mitochondrial / Q000235:genetics*; D003921:Diabetes Mellitus, Experimental; D003930:Diabetic Retinopathy / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D018450:Disease Progression; D004730:Endothelium, Vascular / Q000378:metabolism / Q000473:pathology; D005786:Gene Expression Regulation; D006943:Hyperglycemia / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D008297:Male; D008928:Mitochondria / Q000235:genetics*; D051718:MutS Homolog 2 Protein / Q000096:biosynthesis / Q000235:genetics; D051381:Rats; D017208:Rats, Wistar; D060888:Real-Time Polymerase Chain Reaction; D012160:Retina / Q000378:metabolism* / Q000473:pathology
chemical_list: D004272:DNA, Mitochondrial; C497174:Msh2 protein, rat; D051718:MutS Homolog 2 Protein
keywords: DNA repair; diabetic retinopathy; metabolic memory; mitochondria damage; mtDNA mismatch