Investigation of the molecular mechanism of VGF-derived peptides in the pain pathway

Pain is the major reason patients seek for medical care. Neuropathic pain is a form of chronic pain associated with neuropathy, which remains an area of considerable therapeutic need. The lack of effective therapeutic treatment for neuropathic pain is largely due to the fact that the underlying mechanism is incompletely understood. Recent studies revealed vgf is the commonly upregulated gene in different animal models of neuropathic pain. In addition, VGF-derived peptides, TLQP-21, LQEQ-19 and TLQP-62 have recently been demonstrated to modulate pain pathways when applied in vivo. However, the precise underlying mechanisms of VGF-derived peptides in neuropathic pain and the molecular identity of the receptor for VGF-derived peptides have not yet been investigated. Here, I demonstrated that TLQP-21, but not LQEQ-19 nor TLQP-62, acts on the primary macrophage in a calcium-dependent and dose-dependent manner. The peptide induces release of calcium from the intracellular stores, and repetitive treatment of TLQP-21 desensitises the calcium response in macrophages. In addition, intraplantar injection of TLQP-21-treated macrophages to the rat hind paw is demonstrated to elicit mechanical hypersensitivity. I have also verified GC1qR, the globular heads of the C1q receptor, is the potential receptor for TLQP-21 on macrophages by neutralising antibody and siRNA knock-down techniques. Moreover, application of the GC1qR neutralising antibody to partial sciatic nerve ligation model of neuropathic pain is shown to potentially delay the onset of mechanical hypersensitivity in vivo. Furthermore, I demonstrated TLQP-21 treatment induces differential gene expression in the primary macrophages by microarray. The results presented in this thesis highlighted the importance of VGF-deriveid peptide, TLQP-21 and its receptor, GC1qR, in the neuropathic pain development through, at least partly, activation of macrophages. The findings furthered our current understanding of the peripheral mechanism of neuropathic pain development, thus suggesting new potential target, and shed lights, for new neuropathic pain analgesic development.Open Acces