Wnt/?-catenin Signaling Pathway Regulating Brain-derivd Neurotrophic Factor To Mediate HIV Induced Neuropathic Pain

The nervous system can be directly infected by Human immunodeficiency virus(HIV)which can lead to the neurological dysfunction(HIV/neuroAIDS)in AIDS patients.HIV induced neuropathic pain(HNP)is one of the most common complications of HIV/neuroAIDS.Our previous study has demonstrated that brain-derived neurotophic factor(BDNF)plays an important role in capsaicin-induced pain in mouse.gp120 protein can activate the Wnt/?-catenin signaling pathway which upregulates BDNF expression in microglia BV2.gp120 is a major virulence protein involved in HIV-related neuropathic pain.On this basis,the present study aims to investigate that the role of Wnt/?-catenin signaling pathway regulating BDNF in HNP in vivo.HNP animal model was established by intrathecal injection of(i.t.)gp 120 into mice.The mechanical paw withdrawl threshold(PWT)and the thermal withdrawl latency(TWL)of mice were measured by Von Frey and hot plate method at different time(0,1,2,4,6 h)after gp120 administration.Compared with the control group(i.t.PBS),PWT and TWL of the mice in the intrathecal injection of gp120 group decreased significantly at 1h and reached a volley bottom at 2 h.Correspondingly,the pain in mice was maintained for at least 6 h.The data demonstrated that HNP animal model was successfully established.To confirm whether BDNF is associated with HNP.Western blotting and immunofluorescence(IF)were used to detect the expression of BDNF in the spinal cord of HNP mice.Western blotting analysis showed that the protein expression of BDNF in spinal cord of mice was significantly up-regulated after intrathecal gp120 for 2 h,and 4 h compared with 0 h.Among them,the protein expression of BDNF peaked at 2 h which is about 1.7 times as that of the control group.The results of immunohistochemistry also showed that expression of BDNF in spinal cord of mice was significantly up-regulated after intrathecal injection of gp120 for 2 h.This indicates that BDNF plays a crucial role in HNP.To further determine the relationship between BDNF and HNP,mechanical hyperalgesia tests were performed on mice by intrathecal injection of BDNF blocker TrkB-Fc to block BDNF signaling.The results showed that compared with the PBS+gp120 group,gp120-induced mechanical hyperalgesia was significantly inhibited in the TrkB-Fc+gp 120 group after TrkB-Fc was intrathecally injected at 2 h.The PWT of mice in TrkB-Fc+gp120 group was approximately 4.8 times compared to that of HNP mice.These studies further indicate that BDNF is involved in the development of HNP induced by gp120.At the same time,we found that the expression levels of Wnt3a and ?-catenin were significantly increased in spinal cord of HNP mice,and this trend was similar to that of BDNF upregulation induced by gp120.To further confirm the underlying mechanism of Wnt/?-catenin signaling involved HNP,Wnt/?-catenin signaling pathway was activated by intrathecal injection of Wnt3a.Western blot results showed that expression of ?-catenin and BDNF protein in spinal cord of mice was significantly increased after intrathecal injection of Wnt3a for 2 h,which were 1.7-fold and 2.2-fold,respectively,as that in the control group.This change seemed coincident to that of ?-catenin and BDNF protein in the spinal cord caused by intrathecal gp120.It was also found that intrathecal injection of Wnt3a and gp120 induced mechanical hyperalgesia in mice,and the trend of behavioral changes was similar.The results of this experiment preliminarily indicated that gp120 may induce neuropathic pain in mice by activating wnt/?-catenin signaling pathway to upregulate BDNF expression.To further investigate whether Wnt/?-catenin signaling pathway is involved in expression of BDNF in spinal cord and affecting mechanical allodynia,two inhibitors,IWR-1 and DKK1,were used to block Wnt/?-catenin signaling pathway through different mechanisms,respectively.It was found that ?-catenin expression and BDNF level in spinal cord of HNP mice injected intrathecally with IWR-1 and DKK1 was significantly down-regulated compared to mice administered gp120 alone.Additionally,blocking Wnt signaling pathway by IWR-1 or DKK1 was able to significantly relieve gp120-induced hyperalgesia in mice.Therefore,blocking Wnt/?-catenin signaling pathways can inhibit the expression of BDNF and attenuate gp120-induced mechanical hyperalgesia.In summary,the spinal Wnt/?-catenin signaling pathway is involved in gp120-induced HNP by regulating BDNF expression.This study holds the potential to make significant contribution to improve our understanding of HNP pathological mechanism.It is of great significance for the development of new targeted therapeutic drugs to relieve HNP.