Correlations Between P11-tPA-BDNF Pathway Factors And Depression And Preliminary Study On The Mechanism Of This Pathway

BackgroundMajor depressive disorder(MDD)is one of the most common mental illnesses in mankind with significant and lasting depressed mood and anhedonia as the main manifestations.There are approximately 350 million MDD patients worldwide.The World Health Organization pointed out that by 2030 depression will be the leading cause of disease burden globally.However,the pathophysiological mechanism of MDD is still poorly understood.For decades,the treatment of MDD is mainly based on the monoamine hypothesis,which believes that the depletion of central monoamine neurotransmitter levels is the basic cause of MDD.However,an estimated 30% of MDD patients do not respond to the commonly used antidepressants based on the monoamine hypothesis.In addition,it still takes two to four weeks before the clinical efficacy occurs,even though these antidepressants alter the monoamine levels in the synaptic cleft within hours.Therefore,there is an urgent need to better understand the cellular and molecular mechanisms of MDD.Recently,the neurotrophin hypothesis has received widespread attention,and brainderived neurotrophic factor(BDNF)is one of the most important neurotrophic factors that is widely studied.The hypothesis proposes that decreased neurotrophic signalling is the major factor underlying the pathophysiology of depression,and its restoration underlie the actions of antidepressant treatment.BDNF has an important role in neuronal survival,neurogenesis and synaptic plasticity.BDNF arises from a glycosylation precursor,precursor BDNF(pro BDNF),which is proteolytically cleaved to produce mature BDNF(m BDNF).The tissue plasminogen activator(tPA)/plasmin system is the most important protease involved in the cleavage of pro BDNF.m BDNF binds predominantly to tyrosine kinase receptor B(TrkB)that have anti-apoptotic properties and promote long-term potentiation.After binding to BDNF,the tyrosine residues in the intracellular domain of TrkB undergo autophosphorylation and trigger the activation of downstream pathways,ultimately leading to the phosphorylation and activation of the factors including transcription factor c AMP response-element binding protein(CREB),which mediates cellular functions such as the transcription of related genes essential for neuron survival and differentiation.Among these factors,neuropeptide VGF(non-acronym)is a neuropeptide precursor that can be highly induced by BDNF,and it is an important neurotrophic factor as well.BDNF may activate VGF expression by inducing CREB to bind to the CREB-binding site in the promoter region of VGF.Studies have shown that VGF is involved in mediating hippocampal synaptic plasticity,regulating of metabolism and energy balance,and may also be implicated in depression pathogenesis and mediating antidepressant responses.However,pro BDNF,in binding preferentially to p75 NTR,has opposite effects to m BDNF and favors neuronal apoptosis and long-term depression.Thus,the proteolytic processing of pro BDNF by the tPA/plasmin system may represent a powerful means of regulating the direction of BDNF action that in turn could be implicated in MDD pathogenesis and in the mechanism of action of antidepressants.p11(also known as S100A10)is an important regulator of tPA activity and is closely related to the etiology of MDD and the mechanism of action of antidepressants.The p11/tPA pathway may be an important pathway that regulates the balance of BDNF and participates in the pathogenesis of MDD and the efficacy of antidepressants.However,very little is known about the role of the tPA-BDNF pathway in depression.Part 1 Correlations between the levels of p11-tPA-BDNF pathway factors and depression and antidepressant treatment1、Changes of serum protein levels of the factors in tPA-BDNF pathway in depression and antidepressant treatmentObjectives: To explore whether the serum protein levels of the main factors of the tPABDNF pathway in MDD patients,including tPA,BDNF,TrkB,pro BDNF,p75NTR and VGF,are changed compared with healthy controls(HC),and to observe whether their expression levels are improved after antidepressant treatment.To analyze the value of these factors in the diagnosis and treatment of MDD.Methods: Serum samples of 35 MDD patients before and after 8 weeks of treatment with antidepressants(escitalopram or duloxetine)and 35 HC were collected.The enzyme-linked immunosorbent assay(ELISA)was used to detect the serum protein concentrations of the main factors in the tPA-BDNF pathway,including tPA,BDNF and its receptor TrkB,and pro BDNF and its receptor p75 NTR.In addition,the levels of tPA-BDNF pathway related protein VGF were detected by ELISA in serum of 26 MDD patients before and after treatment with 8 weeks of antidepressants(escitalopram or duloxetine)and 25 HC.The severity of MDD was assessed by 17-item Hamilton depression rating scale(HDRS-17).Results: Compared with HC group,serum levels of tPA and BDNF and the ratio of BDNF/pro BDNF were significantly decreased in MDD group(tPA: P = 0.006,BDNF: P < 0.001,BDNF/pro BDNF: P < 0.001),whereas the levels of TrkB,pro BDNF and its receptor p75 NTR were significantly increased(TrkB: P < 0.001,pro BDNF: P < 0.001,p75NTR: P < 0.001).After 8 weeks of treatment,compared with baseline,the serum levels of tPA and BDNF and the BDNF/pro BDNF ratio were significantly increased(tPA: P = 0.022,BDNF: P < 0.001,BDNF/pro BDNF: P < 0.001),and pro BDNF levels were significantly decreased(P = 0.015),but p75 NTR levels were significantly increased(P = 0.041),and TrkB levels were not significantly changed(P = 0.131)in MDD group.VGF serum levels were significantly lower in MDD group compared with HC group(P = 0.002),and they were reversed by 8 weeks of drug treatment(P < 0.001).tPA,BDNF,TrkB,pro BDNF and p75 NTR all yielded good diagnostic performance with the area under the curve(AUC)of the receiver operating characteristic curve(ROC)> 80% or 90%.Combination of these five proteins demonstrated much better diagnostic effectiveness with AUC = 97.7%,sensitivity = 88.1%,specificity = 92.7% and accuracy = 90.6%.Conclusions: The tPA-BDNF lysis pathway may be implicated in the pathogenesis of MDD and the mechanism underlying antidepressant therapeutic action.Serum VGF may be involved in the pathogenesis of MDD and the efficacy of antidepressants.Serum tPA,BDNF,TrkB,pro BDNF and p75 NTR all showed good diagnostic value and their combination may have certain value in the diagnosis of MDD.2、Changes of peripheral blood m RNA levels of the factors in p11-tPA-BDNF pathway in depression and antidepressant treatmentObjectives: To explore whether peripheral blood m RNA levels of the main factors in p11-tPA-BDNF pathway is involved in the occurrence and antidepressant treatment of MDD.Methods: We collected venous blood samples of 38 HC and 41 MDD patients,and 17 follow-up MDD patients after 2 weeks of antidepressant treatment.The quantitative real-time PCR was used to detect the m RNA levels of the main factors in the p11-tPABDNF pathway,including p11,tPA,plasminogen activator inhibitor-1(PAI-1),BDNF,TrkB and p75 NTR.The severity of MDD was assessed using the HDRS-17 scale.Results: We found that the m RNA levels of BDNF and TrkB in MDD group were significantly lower than those in HC group(BDNF: P < 0.001,TrkB: P = 0.040),BDNF levels increased significantly after 2 weeks of antidepressant treatment(P = 0.038)and TrkB levels did not change significantly(P = 0.606).Compared with HC group,the m RNA levels of p11 and p75 NTR in MDD group were significantly increased(p11: P < 0.001,p75NTR: P = 0.010),and which were significantly decreased after 2 weeks of drug treatment(p11: P = 0.043,p75NTR: P = 0.007).The m RNA levels of tPA and PAI-1 in MDD group were not significantly different from those in the HC group(tPA: P = 0.346,PAI-1: P = 0.438),and they were not significantly changed after antidepressant treatment(tPA: P = 0.918,PAI-1: P = 0.112).No significant correlations were found between the m RNA levels of the p11-tPA-BDNF pathway factors and the severity of depressive symptoms in MDD patients at both baseline and 2 weeks after drug treatment(P > 0.05).The above 4 factors that are significantly different between the MDD group and the HC group were analyzed individually and in combination with ROC.We found that p11,BDNF,TrkB and p75 NTR all showed good diagnostic value,with AUC of 86.4%,87.1%,79.7% and 83.5%,respectively.The combination of these four factors showed a better diagnostic ability for MDD diagnosis,with 95.9% of AUC,87.8% of sensitivity,89.3% of specificity and 88.0% of accuracy.Conclusions: The peripheral blood m RNA levels of the main factors in p11-tPA-BDNF pathway may be implicated in the pathogenesis of MDD and the potential mechanism of antidepressant efficacy.p11,BDNF,TrkB and p75 NTR all showed good diagnostic value and their combination may have certain value in the diagnosis of MDD.Part 2 Preliminary study on the mechanism of p11-tPA-BDNF pathwayObjectives: To investigate whether p11 participates in depression by regulating tPABDNF pathway,and whether small-molecule agonists of BDNF’s receptor TrkB including 7,8-dihydroxyflavone(7,8-DHF)and N-[2-(5-hydroxy-1H-indol-3-yl)ethyl]-2-oxopiperidine-3-carboxamide(HIOC)can improve depression-like behaviors in p11 gene knockout(KO)mice.Methods: We extracted the hippocampus and prefrontal cortex(PFC)brain regions of adult p11 KO mice(C57BL/6)and matched wild type(WT)mice,and detected the expression of tPA-BDNF pathway related proteins and synapse-associated proteins by western blot.Through intraperitoneal injection of small-molecule agonists of BDNF’s receptor TrkB,7,8-DHF and HIOC,to observe whether they can change the depressionlike behaviors of p11 KO mice.Results: We found that in the hippocampus,compared with WT mice,the levels of BDNF,TrkB and PSD95 decreased significantly(P < 0.05)in the p11 KO mice,while the levels of p-TrkB,pro BDNF,p75 NTR,extracellular regulated protein kinases(ERK),p-ERK,protein kinase B(Akt),p-Akt,CREB,p-CREB and Synapsin 1 were not significantly changed(P > 0.05).In the PFC,pro BDNF levels of p11 KO mice were significantly increased compared with WT mice(P = 0.002),while levels of p75 NTR,BDNF,TrkB,p-TrkB,Akt,p-Akt,CREB and p-CREB were not significantly changed(P > 0.05).7,8-DHF 1 mg/kg,5 mg/kg and 10 mg/kg did not significantly change the latency of WT mice entering the dark box in the passive avoidance test(PAT)(P > 0.05).5 mg/kg of 7,8-DHF in the forced swimming test(FST)did not significantly change the immobility time of WT mice(P = 0.267).MK-801 significantly reduced the latency of WT mice entering the dark box in the PAT test(P = 0.012),while 5 mg/kg of 7,8-DHF did not significantly reverse this change(P = 0.705).Compared with WT mice,the latency of p11 KO mice entering the dark box in the PAT test was significantly reduced(Pgenotype = 0.008),and the immobility time of them in the FST was significantly increased(Pgenotype = 0.028).HIOC did not significantly change the latency of WT mice and p11 KO mice entering the dark box and immobility time in the PAT and FST tests(P > 0.05).Conclusion: p11 may down-regulate the signal transduction of the hippocampal BDNF-TrkB pathway and up-regulate the pro BDNF-related pathways in the PFC brain area,thereby regulating neuroplasticity.The TrkB receptor agonists 7,8-DHF and HIOC did not significantly change the depression-like behaviors of WT mice and p11 KO mice.