title: Microglial TIR-domain-containing adapter-inducing interferon-β (TRIF) deficiency promotes retinal ganglion cell survival and axon regeneration via nuclear factor-κB.
abstract: BACKGROUND
  TIR-domain-containing adapter-inducing interferon-β (TRIF) is the sole downstream adaptor of Toll-like receptor (TLR)3, which is one of the major signaling pathways in immune cells leading to neuroinflammation in the central nervous system. Overexpression of TRIF may lead to activation of inflammatory responses, and contribute to pathophysiological progression in both acute and chronic neurodegenerative retinal diseases. In the present study, was aimed to elucidate the contributions of TRIF to optic nerve (ON) regeneration and retinal ganglion cell (RGC) survival following injury to the ON, a widely studied model of central nervous system injury and of degenerative diseases such as glaucoma.
  
  
  METHODS
  We used retrograde labeling with a fluorochrome, hydroxystilbamidine (Fluorogold) to evaluate RGC survival, and immunostaining with growth-associated protein-43 to evaluate axon regeneration in an ON crush model. Changes in microglial cytokines following RGC injury was examined with ELISA and real-time PCR. In vivo studies were carried out in wild-type and trif-/- mice. A Transwell co-culture system and migration test were used to mimic the crosstalk between microglia and RGCs. TRIF-associated downstream adaptors were determined by western blotting.
  
  
  RESULTS
  Compared with wild-type (WT) mice, TRIF knockout (KO) mice displayed a robust ability to regenerate axons 3 or 7 days after nerve injury. In addition, RGC survival was considerably higher in trif-/- than in WT mice. ON lesion induced less microglial activation in trif-/- than in WT mice. and more WT microglia distorted and migrated toward the foramen opticum. In the transwell system, few trif-/- microglia migrated through the membrane when stimulated by the performed lesion on RGC axons in a transwell system. Inactivation of microglial cells in trif-/- mice was associated with reduced production of inflammatory cytokines, as detected with real-time RT-PCR and ELISA. Furthermore western blot analysis showed that activation of known downstream effectors of TRIF, including TBK1, IKKε and NF-κB, were significantly inhibited by TRIF deficiency.
  
  
  CONCLUSIONS
  Our results indicate that TRIF deficiency promotes ON axon regeneration by attenuating microglial activation and consequently reducing the release of harmful cytokines via NF-κB inactivation.
authors.affiliation: Department of Neurobiology, Chongqing Key Laboratory of Neurobiology, Third Military Medical University, Chongqing 400038, PR China.
authors.forename: Sen
authors.initials: S
authors.lastname: Lin
authors.forename: Yajie
authors.initials: Y
authors.lastname: Liang
authors.forename: Jiqiang
authors.initials: J
authors.lastname: Zhang
authors.forename: Chen
authors.initials: C
authors.lastname: Bian
authors.forename: Hongli
authors.initials: H
authors.lastname: Zhou
authors.forename: Qiang
authors.initials: Q
authors.lastname: Guo
authors.forename: Ying
authors.initials: Y
authors.lastname: Xiong
authors.forename: Shurong
authors.initials: S
authors.lastname: Li
authors.forename: Bingyin
authors.initials: B
authors.lastname: Su
mesh_terms: D033942:Adaptor Proteins, Vesicular Transport / Q000172:deficiency*; D000818:Animals; D000831:Animals, Newborn; D001921:Brain / Q000166:cytology; D002478:Cells, Cultured; D016207:Cytokines / Q000235:genetics / Q000378:metabolism; D004195:Disease Models, Animal; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods; D019922:GAP-43 Protein / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D017628:Microglia / Q000378:metabolism*; D009416:Nerve Regeneration / Q000235:genetics* / Q000502:physiology; D009901:Optic Nerve Diseases / Q000473:pathology*; D012165:Retinal Ganglion Cells / Q000473:pathology / Q000502:physiology*; D013266:Stilbamidines
chemical_list: D033942:Adaptor Proteins, Vesicular Transport; D016207:Cytokines; D019922:GAP-43 Protein; D013266:Stilbamidines; C049774:2-hydroxy-4,4'-diamidinostilbene, methanesulfonate salt; C476286:Ticam1 protein, mouse