title: Abrogation of MMP-9 gene protects against the development of retinopathy in diabetic mice by preventing mitochondrial damage.
abstract: OBJECTIVE
  In the development of diabetic retinopathy, mitochondrial dysfunction is considered to play an important role in the apoptosis of retinal capillary cells. Diabetes activates matrix metalloproteinase-9 (MMP-9) in the retina and its capillary cells, and activated MMP-9 becomes proapoptotic. The objective of this study is to elucidate the plausible mechanism by which active MMP-9 contributes to the mitochondrial dysfunction in the retina.
  
  
  METHODS
  Using MMP-9 gene knockout (MMP-KO) mice, we investigated the effect of MMP-9 regulation on diabetes-induced increased retinal capillary cell apoptosis, development of retinopathy, mitochondrial dysfunction and ultrastructure, and mitochondrial DNA (mtDNA) damage. To understand how diabetes increases mitochondrial accumulation of MMP-9, interactions between MMP-9 and chaperone proteins (heat shock protein [Hsp] 70 and Hsp60) were evaluated. The results were confirmed in the retinal mitochondria from human donors with diabetic retinopathy, and in isolated retinal endothelial cells transfected with MMP-9 small interfering RNA (siRNA).
  
  
  RESULTS
  Retinal microvasculature of MMP-KO mice, diabetic for ∼7 months, did not show increased apoptosis and pathology characteristic of retinopathy. In the same MMP-KO diabetic mice, activation of MMP-9 and dysfunction of the mitochondria were prevented, and electron microscopy of the retinal microvasculature region revealed normal mitochondrial matrix and packed lamellar cristae. Damage to mtDNA was protected, and the binding of MMP-9 with Hsp70 or Hsp60 was also normal. As in the retina from wild-type diabetic mice, activation of mitochondrial MMP-9 and alterations in the binding of MMP-9 with chaperone proteins were also observed in the retina from donors with diabetic retinopathy. In endothelial cells transfected with MMP-9 siRNA, high glucose-induced damage to the mitochondria and the chaperone machinery was ameliorated.
  
  
  CONCLUSIONS
  Regulation of activated MMP-9 prevents retinal capillary cells from undergoing apoptosis by protecting mitochondrial ultrastructure and function and preventing mtDNA damage. Thus, MMP-9 inhibitors could have potential therapeutic value in preventing the development of diabetic retinopathy by preventing the continuation of the vicious cycle of mitochondrial damage.
authors.affiliation: Kresge Eye Institute, Wayne State University, Detroit, Michigan, USA. rkowluru@med.wayne.edu
authors.forename: Renu A
authors.initials: RA
authors.lastname: Kowluru
authors.forename: Ghulam
authors.initials: G
authors.lastname: Mohammad
authors.forename: Julia M
authors.initials: JM
authors.lastname: dos Santos
authors.forename: Qing
authors.initials: Q
authors.lastname: Zhong
mesh_terms: D000818:Animals; D017209:Apoptosis; D002478:Cells, Cultured; D018834:Chaperonin 60 / Q000378:metabolism; D004249:DNA Damage; D004272:DNA, Mitochondrial / Q000737:chemistry; D003930:Diabetic Retinopathy / Q000378:metabolism* / Q000473:pathology / Q000517:prevention & control; D004789:Enzyme Activation; D020868:Gene Silencing; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D006801:Humans; D006943:Hyperglycemia / Q000378:metabolism; D008297:Male; D020780:Matrix Metalloproteinase 9 / Q000235:genetics / Q000378:metabolism*; D061965:Matrix Metalloproteinase Inhibitors; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008875:Middle Aged; D008928:Mitochondria / Q000378:metabolism* / Q000648:ultrastructure; D058990:Molecular Targeted Therapy; D012160:Retina / Q000201:enzymology* / Q000648:ultrastructure; D012171:Retinal Vessels / Q000201:enzymology* / Q000473:pathology / Q000648:ultrastructure
chemical_list: D018834:Chaperonin 60; D004272:DNA, Mitochondrial; D018840:HSP70 Heat-Shock Proteins; D061965:Matrix Metalloproteinase Inhibitors; D020780:Matrix Metalloproteinase 9