Abstract
Painful diabetic neuropathy (PDN) is a severely debilitating chronic pain syndrome. Spinal chemokine CXCL13 and its receptor CXCR5 were recently demonstrated to play a pivotal role in the pathogenesis of chronic pain induced by peripheral tissue inflammation or nerve injury. In this study we investigated whether CXCL13/CXCR5 mediates PDN and the underlying spinal mechanisms. We used the db/db type 2 diabetes mice, which showed obvious hyperglycemia and obese, long-term mechanical allodynia, and increased expression of CXCL13, CXCR5 as well as pro-inflammatory cytokines TNF-α and IL-6 in the spinal cord. Furthermore, in the spinal cord of db/db mice there is significantly increased gliosis and upregulated phosphorylation of cell signaling kinases, including pERK, pAKT and pSTAT3. Mechanical allodynia and upregulated pERK, pAKT and pSTAT3 as well as production of TNF-α and IL-6 were all attenuated by the noncompetitive NMDA receptor antagonist MK-801. If spinal giving U0126 (a selective MEK inhibitor) or AG490 (a Janus kinase (JAK)-STAT inhibitor) to db/db mice, both of them can decrease the mechanical allodynia, but only inhibit pERK (by U0126) or pSTAT3 (by AG490) respectively. Acute administration of CXCL13 in C57BL/6J mice resulted in exacerbated thermal hyperalgesia and mechanical allodynia, activation of the pERK, pAKT and pSTAT3 pathways and increased production of pro-inflammatory cytokines (IL-1β, TNF-α and IL-6), which were all attenuated by knocking out of Cxcr5. In all, our work showed that chemokine CXCL13 and its receptor CXCR5 in spinal cord contribute to the pathogenesis of PDN and may help develop potential novel therapeutic approaches for patients afflicted with PDN.