Toll-like receptor signaling adapter proteins govern spread of neuropathic pain and recovery following nerve injury in male mice

J Neuroinflammation. 2013 Dec 9;10:148. doi: 10.1186/1742-2094-10-148.

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.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Adaptor Proteins, Vesicular Transport / metabolism*
  • Animals
  • Female
  • Hyperalgesia / metabolism
  • Immunohistochemistry
  • Ligation
  • Male
  • Mice
  • Mice, Inbred C57BL
  • Microscopy, Confocal
  • Myeloid Differentiation Factor 88 / metabolism*
  • Neuralgia / metabolism*
  • Peripheral Nerve Injuries / metabolism*
  • Spinal Nerves / injuries
  • Spinal Nerves / metabolism
  • Toll-Like Receptors / metabolism*

Substances

  • Adaptor Proteins, Vesicular Transport
  • Myeloid Differentiation Factor 88
  • TICAM-1 protein, mouse
  • Toll-Like Receptors