Lipopolysaccharide induces inflammatory hyperalgesia triggering a TLR4/MyD88-dependent cytokine cascade in the mice paw

PLoS One. 2014 Mar 3;9(3):e90013. doi: 10.1371/journal.pone.0090013. eCollection 2014.

Abstract

Inflammatory pain can be triggered by different stimuli, such as trauma, radiation, antigen and infection. In a model of inflammatory pain caused by infection, injection in the mice paw of lipopolysaccharide (LPS), a Toll-like receptor 4 (TLR4) agonist, produces mechanical hyperalgesia. We identify here the TLR4 linked signaling pathways that elicit this response. Firstly, LPS paw injection in wild type (WT) mice produced mechanical hyperalgesia that was not altered in TRIF-/- mice. On the other hand, this response was absent in TLR4 mutant and MyD88 null mice and reduced in TNFR1 null mice. Either an IL-1 receptor antagonist, anti-KC/CXCL1 antibody, indomethacin or guanethidine injection also lessened this response. Moreover, LPS-induced time dependent increases in TNF-α, KC/CXCL1 and IL-1β expression in the mice paw, which were absent in TLR4 mutant and MyD88 null mice. Furthermore, in TNFR1 deficient mice, the LPS-induced rises in KC/CXCL1 and IL-1β release were less than in their wild type counterpart. LPS also induced increase of myeloperoxidase activity in the paw skin, which was inhibited in TLR4 mutant and MyD88 null mice, and not altered in TRIF-/- mice. These results suggest that LPS-induced inflammatory pain in mice is solely dependent on the TLR4/MyD88 rather than the TLR4/TRIF signaling pathway. This pathway triggers pronociceptive cytokine TNF-α release that in turn mediates rises in KC/CXCL1 and IL-1β expression. Finally, these cytokines might be involved in stimulating production of directly-acting hyperalgesic mediators such as prostaglandins and sympathomimetic amine.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cytokines / metabolism*
  • Foot / pathology
  • Hyperalgesia / chemically induced*
  • Inflammation / chemically induced*
  • Lipopolysaccharides / pharmacology*
  • Male
  • Mice
  • Mice, Inbred C57BL
  • Mice, Knockout
  • Myeloid Differentiation Factor 88 / genetics
  • Myeloid Differentiation Factor 88 / metabolism*
  • Signal Transduction
  • Stress, Mechanical
  • Toll-Like Receptor 4 / genetics
  • Toll-Like Receptor 4 / metabolism*

Substances

  • Cytokines
  • Lipopolysaccharides
  • Myd88 protein, mouse
  • Myeloid Differentiation Factor 88
  • Tlr4 protein, mouse
  • Toll-Like Receptor 4

Grant support

This work was supported by Grants 2011/19670-0 from São Paulo Research Foundation (FAPESP), Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Ministério da Ciência, Tecnologia e Inovação (MCTI), SETI/Fundação Araucária and Parana State Government. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.