P2X4 receptor in the dorsal horn partially contributes to brain-derived neurotrophic factor oversecretion and toll-like receptor-4 receptor activation associated with bone cancer pain

• Published in: Journal of neuroscience research Vol. 92; no. 12; pp. 1690 - 1702
• Main Authors: Jin, Xiao-hong, Wang, Li-Na, Zuo, Jian-Ling, Yang, Jian-Ping, Liu, Si-lan
• Format: Journal Article
• Language: English
• Published: United States Blackwell Publishing Ltd 01.12.2014; Wiley Subscription Services, Inc
• Subjects: Adenosine Triphosphate - pharmacology; Adjuvants, Immunologic - pharmacology; Animals; Bone cancer; Bone Neoplasms - complications; brain-derived neurotrophic factor; Brain-Derived Neurotrophic Factor - secretion; cancer induced bone pain; Carcinoma - complications; Cells, Cultured; Disease Models, Animal; Female; Gene Expression Regulation - drug effects; Lipopolysaccharides - pharmacology; microglia; Microglia - metabolism; P2X4 purinoceptor toll-like receptor-4; p38 Mitogen-Activated Protein Kinases - metabolism; Pain - etiology; Pain - pathology; Pain Measurement; Posterior Horn Cells - metabolism; Rats; Rats, Sprague-Dawley; Receptors, Purinergic P2X4 - genetics; Receptors, Purinergic P2X4 - metabolism; Time Factors; Toll-Like Receptor 4 - genetics; Toll-Like Receptor 4 - metabolism; P2X4 purinoceptor toll-like receptor-4; cancer induced bone pain; brain-derived neurotrophic factor; rats; microglia
• ISSN: 0360-4012; 1097-4547
• DOI: 10.1002/jnr.23443

Previous studies have suggested that the microglial P2X7 purinoceptor is involved in the release of tumor necrosis factor‐α (TNFα) following activation of toll‐like receptor‐4 (TLR4), which is associated with nociceptive behavior. In addition, this progress is evoked by the activation of the P2X4 purinoceptor (P2X4R). Although P2X4R is also localized within spinal microglia in the dorsal horn, little is known about its role in cancer‐induced bone pain (CIBP), which is in some ways unique. With the present rat model of CIBP, we demonstrate a critical role of the microglial P2X4R in the enhanced nociceptive transmission, which is associated with TLR4 activation and secretion of brain‐derived neurotrophic factor (BDNF) and TNFα in the dorsal horn. We assessed mechanical threshold and spontaneous pain of CIBP rats. Moreover, P2X4R small interfering RNA (siRNA) was administered intrathecally, and real‐time PCR, Western blots, immunofluorescence histochemistry, and ELISA were used to detect the expression of P2X4R, TLR4, OX‐42, phosphorylated‐p38 MAPK (p‐p38), BDNF, and TNFα. Compared with controls, intrathecal injection of P2X4R siRNA could prevent nociceptive behavior induced by ATP plus lipopolysaccharide and CIBP and reduce the expression of P2X4R, TLR4, p‐p38, BDNF, and TNFα. In addition, the increase of BDNF protein in rat microglial cells depended on P2X4 receptor signaling, which is partially associated with TLR4 activation. The ability of microglial P2X4R to activate TLR4 in spinal cord leading to behavioral hypersensitivity and oversecretion of BDNF could provide an opportunity for the prevention and treatment of CIBP. © 2014 Wiley Periodicals, Inc.