title: Down-regulation of Toll-like receptor 4 gene expression by short interfering RNA attenuates bone cancer pain in a rat model.
abstract: BACKGROUND
  This study demonstrates a critical role in CNS innate immunity of the microglial Toll-like receptor 4 (TLR4) in the induction and maintenance of behavioral hypersensitivity in a rat model of bone cancer pain with the technique of RNA interference (RNAi). We hypothesized that after intramedullary injection of Walker 256 cells (a breast cancer cell line) into the tibia, CNS neuroimmune activation and subsequent cytokine expression are triggered by the stimulation of microglial membrane-bound TLR4.
  
  
  RESULTS
  We assessed tactile allodynia and spontaneous pain in female Sprague-Dawley (SD) rats after intramedullary injection of Walker 256 cells into the tibia. In a complementary study, TLR4 small interfering RNA(siRNA) was administered intrathecally to bone cancer pain rats to reduce the expression of spinal TLR4. The bone cancer pain rats treated with TLR4 siRNA displayed significantly attenuated behavioral hypersensitivity and decreased expression of spinal microglial markers and proinflammatory cytokines compared with controls. Only intrathecal injection of TRL4 siRNA at post-inoculation day 4 could prevent initial development of bone cancer pain; intrathecal injection of TRL4 siRNA at post-inoculation day 9 could attenuate, but not completely block, well-established bone cancer pain.
  
  
  CONCLUSIONS
  TLR4 might be the main mediator in the induction of bone cancer pain. Further study of this early, specific, and innate CNS/microglial response, and how it leads to sustained glial/neuronal hypersensitivity, might lead to new therapies for the prevention and treatment of bone cancer pain syndromes.
authors.affiliation: Department of Anesthesiology, The First Affiliated Hospital of Soochow University, Suzhou, Jiangsu 215006, China.
authors.forename: Liu Si
authors.initials: LS
authors.lastname: Lan
authors.forename: Yang Jian
authors.initials: YJ
authors.lastname: Ping
authors.forename: Wang Li
authors.initials: WL
authors.lastname: Na
authors.forename: Jiang
authors.initials: J
authors.lastname: Miao
authors.forename: Qiu Qiao
authors.initials: QQ
authors.lastname: Cheng
authors.forename: Ma Zhen
authors.initials: MZ
authors.lastname: Ni
authors.forename: Liu
authors.initials: L
authors.lastname: Lei
authors.forename: Li Cai
authors.initials: LC
authors.lastname: Fang
authors.forename: Ren Chun
authors.initials: RC
authors.lastname: Guang
authors.forename: Zhou
authors.initials: Z
authors.lastname: Jin
authors.forename: Li
authors.initials: L
authors.lastname: Wei
mesh_terms: D000818:Animals; D001859:Bone Neoplasms / Q000150:complications*; D016207:Cytokines / Q000378:metabolism; D004195:Disease Models, Animal; D015536:Down-Regulation / Q000187:drug effects / Q000235:genetics; D005260:Female; D005786:Gene Expression Regulation / Q000187:drug effects / Q000235:genetics; D015316:Genetic Therapy / Q000379:methods*; D006930:Hyperalgesia / Q000235:genetics / Q000276:immunology / Q000628:therapy; D018836:Inflammation Mediators / Q000378:metabolism; D017628:Microglia / Q000276:immunology / Q000378:metabolism; D009187:Myelitis / Q000235:genetics* / Q000276:immunology / Q000628:therapy; D010147:Pain Measurement; D010148:Intractable Pain / Q000235:genetics* / Q000276:immunology / Q000628:therapy; D034622:RNA Interference / Q000502:physiology; D034741:RNA, Small Interfering / Q000494:pharmacology* / Q000627:therapeutic use; D051381:Rats; D017207:Rats, Sprague-Dawley; D013977:Tibia / Q000473:pathology / Q000503:physiopathology / Q000601:surgery; D051197:Toll-Like Receptor 4 / Q000037:antagonists & inhibitors / Q000235:genetics*; D016896:Treatment Outcome; D014407:Tumor Cells, Cultured
chemical_list: D016207:Cytokines; D018836:Inflammation Mediators; D034741:RNA, Small Interfering; C495347:Tlr4 protein, rat; D051197:Toll-Like Receptor 4