Study On The Mechanism Of MC4R Through JNK Signaling Pathway Mediated Neuropathic Pain

Object:In order to investigate MC4 R antagonist HS014 contributes to chronic constrictive injury-induced neuropathic pain in rats and related mechanisms, searching relationship between MC4 R and JNK singalling pathway to explore the mechanisms of HS014 and SP600125(JNK inhibitor) analgesia, to provide experimental and theoretical basis for the clinical application of HS014.Methods: Ninety-six Sprague Dawley(SD) rats were randomly divided into four groups: Sham surgery group(SHAM group), CCI group(CCI group), CCI +(MC4R antagonist, HS014) group(HS group), CCI+(JNK antagonist,SP600125)(SP group). In the latter two groups, HS014,SP600125 was separately injected intrathecally starting at day 1 after surgery and then lasted for 14 days before the rats were sacrificed. Thermal hyperalgesia and Mechanical thermal pain thresholdwere respectively measured on pre-operative day 1 and postoperative day 3, 7 and 14. In addition, DRG linked to the injury sciatic nerve were isolated for analyzing protein and cytokine levels by immunohistochemistry staining and immunofluorescence assay.The level of p-JNK and MC4 R in the L4- 6 spinal cord horn was tested by western blot and immunofluorescence.Result: Our results show that(1) thermal hyperalgesia were reduced in the HS group and SP group as compared to that in the CCI group.(2) HS014 not only inhibited the expression of MC4 R, but also reduced the p-JNK in DRG and spinal.(3) In DRG and spinal cord of CCI models,Intrathecal injection of SP600125 prevented the activaton of p-JNK but not the expression of M4 CR.(4) In DRG, both MC4 R and JNK singnalling pathway mainly located in the glial cells, especially in the microglia.Conclusion: The mechanisms of neuropathic pain is that HS014 decrease the neuropathic pain related to the inbitition of JNK activation,and at the same time JNK signalling pathwaymay be a downstream of MC4 R in the neuropathic pain induced by CCI.Based on these findings we propose that HS014 attenuates inflammatory pain by suppressing the JNK signalling pathway.