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Extracellular caspase-6 drives murine inflammatory pain via microglial TNF-? secretion.

ABSTRACT: Increasing evidence indicates that the pathogenesis of neuropathic pain is mediated through spinal cord microglia activation. The intracellular protease caspase-6 (CASP6) is known to regulate neuronal apoptosis and axonal degeneration; however, the contribution of microglia and CASP6 in modulating synaptic transmission and pain is unclear. Here, we found that CASP6 is expressed specifically in C-fiber axonal terminals in the superficial spinal cord dorsal horn. Animals exposed to intraplantar formalin or bradykinin injection exhibited CASP6 activation in the dorsal horn. Casp6-null mice had normal baseline pain, but impaired inflammatory pain responses. Furthermore, formalin-induced second-phase pain was suppressed by spinal injection of CASP6 inhibitor or CASP6-neutralizing antibody, as well as perisciatic nerve injection of CASP6 siRNA. Recombinant CASP6 (rCASP6) induced marked TNF-? release in microglial cultures, and most microglia within the spinal cord expressed Tnfa. Spinal injection of rCASP6 elicited TNF-? production and microglia-dependent pain hypersensitivity. Evaluation of excitatory postsynaptic currents (EPSCs) revealed that rCASP6 rapidly increased synaptic transmission in spinal cord slices via TNF-? release. Interestingly, the microglial inhibitor minocycline suppressed rCASP6 but not TNF-?-induced synaptic potentiation. Finally, rCASP6-activated microglial culture medium increased EPSCs in spinal cord slices via TNF-?. Together, these data suggest that CASP6 released from axonal terminals regulates microglial TNF-? secretion, synaptic plasticity, and inflammatory pain.

PROVIDER: S-EPMC3934175 | BioStudies |

REPOSITORIES: biostudies

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