Integrin signaling in inflammatory and neuropathic pain in the rat

Many painful conditions are associated with alterations in the extracellular matrix (ECM) of affected tissues. While several integrins, the receptors for ECM proteins, are present on sensory neurons that mediate pain, the possible role of these cell adhesion molecules in inflammatory or neuropathic pain has not been explored. We found that the intradermal injection of peptide fragments of domains of laminin and fibronectin important for adhesive signaling selectively inhibited the hyperalgesia caused by prostaglandin E-2 (PGE(2)) and epinephrine (EPI), respectively The block of EPI hyperalgesia was mimicked by other peptides containing the RGD integrin-binding sequence. Monoclonal antibodies (mAbs) against the alpha(1) or alpha(3) integrin subunits, which participate in laminin binding, selectively blocked PGE(2) hyperalgesia, while a mAb against the alpha(5) subunit, which participates in fibronectin binding, blocked only EPI-induced hyperalgesia. A mAb against the beta(1) integrin subunit, common to receptors for both laminin and fibronectin, inhibited hyperalgesia caused by both agents, as did the knockdown of beta(1) integrin expression by intrathecal injection of antisense oligodeoxynucleotides. The laminin peptide, but not the fibronectin peptides, also reversibly abolished the longer lasting inflammatory hyperalgesia induced by carrageenan. Finally, the neuropathic hyperalgesia caused by systemic administration of the cancer chemotherapy agent taxol was reversibly inhibited by antisense knockdown of beta(1) integrin. These results strongly implicate specific integrins in the maintenance of inflammatory and neuropathic hyperalgesia.