title: Toll-like receptor signaling adapter proteins govern spread of neuropathic pain and recovery following nerve injury in male mice.
abstract: BACKGROUND
  Spinal Toll-like receptors (TLRs) and signaling intermediaries have been implicated in persistent pain states. We examined the roles of two major TLR signaling pathways and selected TLRs in a mononeuropathic allodynia.
  
  
  METHODS
  L5 spinal nerve ligation (SNL) was performed in wild type (WT, C57BL/6) male and female mice and in male Tlr2-/-Tlr3-/-, Tlr4-/-, Tlr5-/-, Myd88-/-, Triflps2, Myd88/Triflps2, Tnf-/-, and Ifnar1-/- mice. We also examined L5 ligation in Tlr4-/- female mice. We examined tactile allodynia using von Frey hairs. Iba-1 (microglia) and GFAP (astrocytes) were assessed in spinal cords by immunostaining. Tactile thresholds were analyzed by 1- and 2-way ANOVA and the Bonferroni post hoc test was used.
  
  
  RESULTS
  In WT male and female mice, SNL lesions resulted in a persistent and robust ipsilateral, tactile allodynia. In males with TLR2, 3, 4, or 5 deficiencies, tactile allodynia was significantly, but incompletely, reversed (approximately 50%) as compared to WT. This effect was not seen in female Tlr4-/- mice. Increases in ipsilateral lumbar Iba-1 and GFAP were seen in mutant and WT mice. Mice deficient in MyD88, or MyD88 and TRIF, showed an approximately 50% reduction in withdrawal thresholds and reduced ipsilateral Iba-1. In contrast, TRIF and interferon receptor null mice developed a profound ipsilateral and contralateral tactile allodynia. In lumbar sections of the spinal cords, we observed a greater increase in Iba-1 immunoreactivity in the TRIF-signaling deficient mice as compared to WT, but no significant increase in GFAP. Removing MyD88 abrogated the contralateral allodynia in the TRIF signaling-deficient mice. Conversely, IFNβ, released downstream to TRIF signaling, administered intrathecally, temporarily reversed the tactile allodynia.
  
  
  CONCLUSIONS
  These observations suggest a critical role for the MyD88 pathway in initiating neuropathic pain, but a distinct role for the TRIF pathway and interferon in regulating neuropathic pain phenotypes in male mice.
authors: Jennifer A
authors: JA
authors: Stokes
authors: Jonathan
authors: J
authors: Cheung
authors: Kelly
authors: K
authors: Eddinger
authors: Maripat
authors: M
authors: Corr
authors: Department of Pharmacology, University of California, 9500 Gilman Dr, MC 0636, La Jolla, San Diego, CA 92093-0636, USA. TYAKSH@UCSD.EDU.
authors: Tony L
authors: TL
authors: Yaksh
mesh_terms: D033942:Adaptor Proteins, Vesicular Transport / Q000378:metabolism*; D000818:Animals; D005260:Female; D006930:Hyperalgesia / Q000378:metabolism; D007150:Immunohistochemistry; D008026:Ligation; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018613:Microscopy, Confocal; D053594:Myeloid Differentiation Factor 88 / Q000378:metabolism*; D009437:Neuralgia / Q000378:metabolism*; D059348:Peripheral Nerve Injuries / Q000378:metabolism*; D013127:Spinal Nerves / Q000293:injuries / Q000378:metabolism; D051193:Toll-Like Receptors / Q000378:metabolism*
chemical_list: D033942:Adaptor Proteins, Vesicular Transport; D053594:Myeloid Differentiation Factor 88; D051193:Toll-Like Receptors; C476286:Ticam1 protein, mouse