We have previously shown that activation of the ATP-gated ion channel subtype P2X4 receptors (P2X4Rs) in the spinal cord, the expression of which is upregulated in microglia after nerve injury, is necessary for producing neuropathic pain. The upregulation of P2X4Rs in microglia is, therefore, a key process in neuropathic pain, but the mechanism remains unknown. Here, we find a fibronectin/integrin-dependent mechanism in the upregulation of P2X4Rs. Microglia cultured on dishes coated with fibronectin, an extracellular matrix molecule, expressed a higher level of P2X4R protein when compared with those cultured on control dishes. The increase was suppressed by echistatin, a peptide that selectively blocks β1 and β3-containing integrins, and with a function-blocking antibody of β1 integrin. In in vivo studies, the upregulation of P2X4Rs in the spinal cord after spinal nerve injury was significantly suppressed by intrathecal administration of echistatin. Tactile allodynia in response to nerve injury and intrathecal administration of ATP- and fibronectin-stimulated microglia was inhibited by echistatin. Furthermore, intrathecal administration of fibronectin in normal rats increased the level of P2X4R protein in the spinal cord and produced tactile allodynia. Moreover, the fibronectin-induced allodynia was not observed in mice lacking P2X4R. Taken together with the results of our previous study showing an increase in the spinal fibronectin level after nerve injury, the present results suggest that the fibronectin/integrin system participates in the upregulation of P2X4R expression after nerve injury and subsequent neuropathic pain.
All Science Journal Classification (ASJC) codes
- Cellular and Molecular Neuroscience