title: The role of TLR4 activation in photoreceptor mitochondrial oxidative stress.
abstract: OBJECTIVE
  Herein the authors investigated whether the activation of Toll-like receptors (TLRs) in the innate immune response causes retinal photoreceptor oxidative stress and mitochondrial DNA (mtDNA) damage.
  
  
  METHODS
  On day 5 after injection of complete Freund's adjuvant containing heat-killed Mycobacterium tuberculosis (CFA), retinas were submitted to polymerase chain reaction (PCR) array focused on the TLR signaling, or apoptosis, pathway. CFA-mediated TLR4 activation, oxidative stress, and mtDNA damage were determined in B10.RIII and knockout (KO) mice (recombination activation gene [Rag] 1(KO), TLR4(KO), myeloid differentiation primary response gene 88 [MyD88](KO), tumor necrosis factor [TNF]-α(KO), or caspase 7(KO) mice) using quantitative real-time PCR, enzyme-linked immunosorbent assay, Western blot analysis, and immunohistochemistry. The mycobacterial DNA load on the retina, brain, liver, and spleen was determined by real-time PCR after intracardiac perfusion.
  
  
  RESULTS
  PCR array demonstrated the upregulation of TLRs and their signaling molecules in retinas of CFA-injected mice compared with those of control animals without inflammatory cell infiltration in the retina and uvea. Mycobacterial DNA was detected in the retinas of CFA-injected mice. Retinas of CFA-injected animals showed oxidative stress and mtDNA damage, primarily in the photoreceptor inner segments. Upregulated TLR4 was localized with CD11b(+)MHCII(+) cells but not with GFAP(+) astrocytes. This oxidative stress/damage was similar in CFA-injected Rag1(KO) mice compared with wild-type controls. Such damage was absent in the retinas of CFA-injected TLR4(KO), MyD88(KO), and TNF-α(KO) mice. CFA-mediated inducible nitric oxide synthase expression in the retina was significantly decreased in TNF-α(KO) mice.
  
  
  CONCLUSIONS
  Retinal photoreceptors are susceptible to mitochondrial oxidative stress/mtDNA damage in robust TLR4-mediated innate immune response.
authors.affiliation: Doheny Eye Institute, Department of Ophthalmology, Keck School of Medicine, University of Southern California, Los Angeles, California 90033, USA.
authors.forename: MinHee K
authors.initials: MK
authors.lastname: Ko
authors.forename: Sindhu
authors.initials: S
authors.lastname: Saraswathy
authors.forename: Jignesh G
authors.initials: JG
authors.lastname: Parikh
authors.forename: Narsing A
authors.initials: NA
authors.lastname: Rao
mesh_terms: D000276:Adjuvants, Immunologic / Q000494:pharmacology; D000818:Animals; D000942:Antigens, Bacterial / Q000276:immunology / Q000494:pharmacology; D017209:Apoptosis / Q000502:physiology; D053179:Caspase 7 / Q000235:genetics; D004272:DNA, Mitochondrial / Q000235:genetics; D004195:Disease Models, Animal; D005620:Freund's Adjuvant / Q000276:immunology / Q000494:pharmacology; D018398:Homeodomain Proteins / Q000235:genetics; D007107:Immune System / Q000502:physiology; D008099:Liver / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008928:Mitochondria / Q000276:immunology / Q000378:metabolism*; D053594:Myeloid Differentiation Factor 88 / Q000235:genetics; D018384:Oxidative Stress / Q000502:physiology*; D020419:Photoreceptor Cells, Vertebrate / Q000276:immunology / Q000378:metabolism*; D012164:Retinal Diseases / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D013154:Spleen / Q000378:metabolism; D051197:Toll-Like Receptor 4 / Q000235:genetics* / Q000276:immunology / Q000378:metabolism*; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics
chemical_list: D000276:Adjuvants, Immunologic; D000942:Antigens, Bacterial; D004272:DNA, Mitochondrial; D018398:Homeodomain Proteins; C507780:Myd88 protein, mouse; D053594:Myeloid Differentiation Factor 88; C493487:Tlr4 protein, mouse; D051197:Toll-Like Receptor 4; D014409:Tumor Necrosis Factor-alpha; C064658:RAG-1 protein; C072681:Mycobacterium tuberculosis antigens; D005620:Freund's Adjuvant; C505524:Casp7 protein, mouse; D053179:Caspase 7