Mechanism Of GLT1-mTOR Autophagy In The Comorbidity Of Major Depressive Disorder And Chronic Pain

Aims: Major depressive disorder(MDD)and chronic pain are two common clinical complex symptoms.It is found that 66% of depression patients are accompanied by chronic pain.About 73.3% of patients with chronic pain can induce depression.Comorbidities are more complex to distinguish,more serious,less effective and more frequent than single disease,which seriously affect people's quality of life and impose a heavy burden on society.The exact cause and mechanism of comorbid of MDD and chronic pain have not been elucidated so far.The current research results are also different or contradictory,resulting in a slow process of studying their etiology.The lack of a reliable animal model of comorbidity is one of the main limitation that restrict the study of its pathological mechanism.The main purpose of present study was to mimic an animal model of comorbidity of MDD and chronic pain,furthermore,to evaluate the effect of the comorbidity model.Based on this comorbid model the regulation mechanism of glutamate transporter-1(GLT1)-mammalian target of rapamycin(mTOR)autophagy was proposed.Methods: 60 six-week-old female C57/BL6 mice were randomly divided into 6 groups,with 10 rats in each group,they were consisted of naive group,Dextran sulfate sodium(DSS)group,chronic unpredictable stress(CUS)group,DSS + CUS group+saline,DSS + duloxetine group,DSS+CUS+experimental drug group.The method of DSS combined with CUS to mimic the comorbidity mouse model of MDD and chronic pain.Using the disease activity index(DAI),Von Frey Test(VF),bdominal withdrawal reflex(AWR),open field test,elevated cross test,forced swimming,tail suspension test,Sugar preference test to justify the surface validity of comorbid model.In order to verify the construct validity of comorbid modle,the expression levels of mRNA and protein such as nuclear factor-?B(NF-?B),c AMP response element-binding protein(CREB)and brain derived neurotrophic factor(BNDF)were detected by Rt-q PCR,western blot and immunohistochemistry.Furthermore,to explore the underlying mechanism of this comorbid model,the protein expression level of the GLT-1,mTOR,P-mTOR,P62,LC3 were tested.Duloxetine was administered intraperitoneally for 10 consecutive days to evaluate the predictive validity.Electrophysiological patch clamp technique was used to measure the excitability of neurons.Results: Compared with other groups,the comorbidity group showed the significantly decreasing with mechanical pain threshold and increasing visceral pain sensitivities in pain test,as well as showed the increasing immovable time in forcing swimming and hanging tail test,furthermore,the reduction of sugar water of consumption,total activity and exploratory behaviors were found in sugar water preference test and open filed test,respectively.More importantly,there is a clear correlation between the degree of pain and the degree of depression.The results of the expression level of NF-?B,I?Ba mRNA and protein in comorbid mice were remarkable up-regulation and the level of BDNF and CREB mRNA and protein notable down-regulation in comorbid model.Duloxetine can reverse these changes of unusual behavior and molecular level.The comorbid mechanism results demonstred that the level of protein expression of GLT-1,p-mTOR,p-70sk6(Thr389),p62 were distinct down-regulation and the level of LC3-?notable up-regulation in meddle prefrontal lobe(m PFC)of comorbidity group.Furthermore,after administration of riluzole,the protein expression of GLT-1,p-mTOR,p-70sk6(Thr389)and p62 were significantly increased and the LC3-?protein was significantly decreased.This molecular change can be effectively reversed by the GLT1 specific blockers dihydrokainic acid(DHK).The excitability of DRG neurons in the comorbidity group decreased with the level of GLT-1 and is less responsive to GLT-1 inhibitors.Conclusion: The comorbidity model of MDD and chronic pain induced by the method of DSS combined was consistent with the comorbidity standard in terms of surface validity,construct validity and predictive validity,furthermore,this model has the characteristics of certainty,repeatability and effectiveness in mimicry of the comorbidity of MDD and chronic pain.More importantly,GLT-1 mediate the mTOR autophagic signaling pathway plays an important role in the comorbidity of MDD and chronic pain,which may be a new target for the treatment of this complex disease.