CBP-mediated Histone Acetylation Involved In The Mechanisms Of Neuropathic Pain

ObjectivesTo investigate the time-dependent variation tendency of pain behavior and spinal expression of CBP in a rat model of sciatic nerve chronic constriction injury (CCI) model. Silence the spinal expression of CBP gene by intrathecal CBP small hairpin RNA (shRNA), to research the effect of CBP in neuropathic pain.Methods1. Thirty male SD rats were randomly divided into group Normal (n=5), Sham (n=5) and group CCI (n=20). In group CCI, left sciatic nerve CCI model were established according to Bennett and Xie, in group Sham, left sciatic nerves were only exposed without ligation. Paw withdrawal threshold to mechanical stimuli(MWT) and paw withdrawal latency to a thermal nociceptive stimulus(TWL) were measured at1day before (baseline) and1,3,5,7,10,12,14,21days after operation. The animals were then sacrificed and the lumbar segment of the spinal cord were isolated at3,7,14,21days after operation to detect the expression of CBP by Immunohistochemistry.2. Forty male SD rats in which intrathecal catheter was successfully placed were chosen to establish CCI model.The rats were randomly divided into4groups (n=10):sham operation+NS group (group Sham),CCI+NS group (group CCI),CCI+RNAi-NC-LV group(group NC) and CCI+CBP RNAi-LV group(group CBP).Intrathecal NS20μl,RNAi-NC-LV20μl or CBP RNAi-LV20μl after operation. MWT and TWL were measured at1day before (baseline) and3,5,7,10,12,14days after operation.The animals were then sacrificed and the lumbar segment of the spinal cord were isolated at14days after operation to detect the expression of CBP, Ac-H3, Ac-H4, COX-2by RT-PCR, western bolt and Immunohistochemistry.Results1. MWT and TWL of the CCI rats were significantly decreased from day1to day21after operation compared with group Sham, the most distinctive point is day7(P<0.05). Immunohistochemistry results showed that CBP immuno-positive cells were most expressed in gray matter of lumbar spinal cord, especially in layer Ⅰ-Ⅲ. The positive particles mainly located in cell nucleus. CBP immuno-positive cells in layer Ⅰ-Ⅲ of CCI rats increased from day3after operation, lasted to day21, with a peak on day7.2. MWT and TWL of the CCI rats were significantly decreased after operation compared with group Sham (P<0.05), the reduction was alleviated by intrathecal CBP RNAi-LV (P<0.05), and the effect was sustained for7days, MWT and TWL of the CCI rats were not affected by intrathecal RNAi-NC-LV (P>0.05). Immuno-positive cells of CBP, Ac-H3, Ac-H4and COX-2, mRNA expression of CBP and COX-2as well as protein expression of COX-2, were upregulated in CCI rats (P<0.05), the increased expression was inhibited by intrathecal CBP RNAi-LV, but the increased expression was not affected by intrathecal RNAi-NC-LV (P>0.05).ConclusionsThe immuno-expression of CBP in spinal cord in the rat model of CCI is corresponding to the pain behavior.Intrathecal CBP shRNA can release pain and inhibit the expression of CBP, Ac-H3, Ac-H4, COX-2in CCI rats, and the mechanism may be related to the inhibition of CBP induced acetylation on Ac-H3and Ac-H4in the spinal cord.