Role Of DNA Methyltransferases In Neuropathic Pain Induced Depression

Objective Neuropathic pain(NPP)is a common refractory pain triggered by primary nervous system damage and / or dysfunction,with an incidence of up to23.2%.Depression is a mental illness characterized by persistent depression,slow thinking,decreased will activity,and impaired cognitive function.In China,every8-10 people have a depression patient,which greatly increases the burden on the family and society.Global data shows that 10%-15% of patients with severe depression die of suicide,and depression has undoubtedly become a global problem.The pathogenesis of depression is complex,and it is difficult to explain with a single influencing factor.As a stressor,NPP may lead to depression.Clinically,about 50%of NPP patients will experience depressive symptoms.Depression will also aggravate the pain in turn.The two promote each other and bring great challenge to the treatment of the disease.The mechanism by which NPP induces depression is still unclear.At present,it is generally believed that the combination of stress environment and genes may be the key to depression.DNA methylation is an adaptive change that occurs without changing the gene sequence under the action of the environment,mainly in the role of DNA methyltransferases(DNMTs),binding methyl groups tospecific Bases,which leads to gene silencing or down-regulation of expression.The decreased expression of synaptic plasticity-related genes may be the key to NPP-induced depression.Brain-derived neurotrophic factor(BDNF)has been widely studied as an important factor regulating synaptic plasticity.The regulation of BDNF gene methylation is a direct and key link in regulating gene transcription and expression.The hippocampus plays an important role in the regulation of NPP and depression.Therefore,the purpose of this study is to(1)construct a rat NPP model and observe whether it causes depression-like behaviors;(2)detect changes in the expression level of DNMTs in the hippocampus of NPP rats;(3)verify influence of DNMTs on depressive behavior and BDNF expression level via RG108.Method In this experiment,the commonly used NPP model: Spared nerve injury(SNI)model was used to verify the mechanism of depression caused by NPP.The experiment was divided into two parts: the first part: verify the role and mechanism of rat hippocampal DNMTs in NPP-induced depression.According to the random principle,6-8w male SD rats were divided into 4 groups: sham group,SNI group,SNI+ DMSO group,SNI + RG108 group.Part II: To verify whether ketamine relieves NPP-induced depression symptoms by reducing hippocampal DNMTs.This part is divided into 5 groups: sham group,sham + ket group,SNI group,SNI + sal group,SNI + ket group.The body weights of rats were recorded at 1d before and 21 d after operation,and the mechanical pain threshold was detected at 1d before operation and at 7d,14 d,and 21 d after operation.Open field test(OFT)was used to test the locomotor function of the rats 21 d after modeling and intervention;Forced swimming test(FST)and Sucrase preference test(SPT)were used to detect the 21 d postoperative and depression-like behavior;Real-Time Quantitative polymerase chain reaction(q PCR)and Western blotting(WB)were used to detect DNMTs,BDNF exons I and IV,BDNF and The expression level of pro BDNF.Results There was no significant difference in the basal pain threshold of rats in each group 1d before surgery.The pain threshold of SNI rats decreased significantly on the 7d,14 d,and 21 d postoperatively(P <0.05);on the 21 d,the weight gain of SNI rats was low in the sham group(P <0.05),there was no significant difference in thetotal distance of OFT between the two groups.The percentage of sucrose consumption in the SNI group was significantly reduced(P <0.05),and the immobility time in FST was significantly increased(P <0.05).Molecular biochemical results showed that the expression levels of DNMTs of SNI rats were significantly increased(P <0.05),BDNF exon I level was significantly reduced(P <0.05),and the ratio of pro BDNF / BDNF was significantly increased(P <0.05),The administration of RG108 significantly improved the depression symptoms caused by SNI,and reversed the expression levels of BDNF exon I and BDNF,and the ratio of pro BDNF/ BDNF decreased(P <0.05).Conclusion Chronic NPP can cause depressive symptoms,which may be related to the decrease of BDNF level caused by the increase of DNMTs in the hippocampus.Methyltransferase inhibitor RG108 can reverse the expression of BDNF and improve depressive symptoms.The results of this study indicate that the methylation of BDNF may be the key to NPP-induced depression.