Protective Effect And Mechanism Of TREM2 In Parkinson’s Disease With Cognitive Impairment By Promoting The Activation Of Diseased Associated Microglia

OBJECTIVE:Parkinson’s disease(PD)with cognitive impairment severely affects patients’ quality of life,but there are currently no effective treatments.Previous studies have shown that Triggering receptor expressed on myeloid cells 2(TREM2)plays a protective role in Alzheimer’s disease by inhibiting neuroinflammation and amyloid protein aggregation.However,it is not clear whether TREM2 plays a protective role in PD with cognitive impairment.The latest research found that anti-inflammaory disease-associated microglia(DAM),regulated by TREM2-dependent,plays a protective role in a variety of neurodegenerative disease.Based on this,this study explored whether TREM2 plays a protective role in PD with cognitive impairment by promoting the activation of DAM.METHODS:First of all,this study analyzed the correlation between soluble TREM2(sTREM2)in cerebrospinal fluid and PD pathological marker and cognition in pataients with PD.In vivo study,Adenovirus was injected into 4-month-old A53Tα-Syn PD mice to silence the expression of TREM2 protein by using stereotactic injection technology.The cognitive status of mice was evaluated by Morris water maze and new object recognition;α-Synuclein(α-Syn)aggregation,microglial activation and expression of inflammatory cytokines,core markers of DAM,MAPK and NF-κB pathway protein were evaluated by Western blot,immunofluorescence,immunohistochemistry and qPCR.In vivo study,firstly,lentivirus was used to silence TREM2 expression,and α-Syn preformed fibril(α-Syn PFF)was further used to stimulate BV2 microglia.We detected the expression of inflammatory cytokines,DAM core markers,MAPK and NF-κB pathway protein by qPCR and Western blot.The culture medium after PFF stimulation of BV2 microglia in each group was further used to stimulate HT22 neurons,and Western blot was used to detect phosphorylation α-Syn expression,CCK8 and flow cytometry were used to detect cell viability and apoptosis.RESULTS:(1)It was found in clinical cases that sTREM2 was increased in cerebrospinal fluid of PD patients with 2 or more years duration,and sTREM2 in PD patients with 2 or more years duration was found to be positively correlated with αSyn;In the cognitive analysis,it was found that sTREM2 PD patients with 2 or more years duration was negatively correlated with cognitive function(MoCA);(2)In vivo study,in 4 months old A53T α-Syn PD mice,the expression of TREM2 in the hippocampus was significantly lower than that of C57 mice,and the expression of ionic calcium binding adapter 1(Iba1)in microglia was increased;(3)After silencing the expression of TREM2 in hippocampus,The expression of synaptic protein(PSD95)and neuronal marker NeuN in A53T α-Syn PD mice decreased without change of α-Syn protein,and cognitive imapairment of A53Tα-Syn PD mice were aggravated;(4)After silencing the expression of TREM2 in hippocampus,the expression of Ibal,and inflammatory cytokines(iNOS,COX2 protein and TNF-α、IL-1β、IL-6 mRNA)were significantly increased;The expression of the core marker of DAM,such as,Itgax protein,and the mRNA of Itgax,APOE,Timp2,Clec7a,CD68,Lpl,Axl,Ctsl,CCL6 and other genes were decreased significantly,and the expression of P-JNK,P-ERK in MAPK pathway and P-P65 in NF-κB pathway were significantly increased;(5)After silencing the expression of TREM2 in BV2 microglia,PFF was administered to stimulate microglia,the expression of inflammatory cytokines(iNOS,COX2 protein and TNF-α,IL-1β,and IL-6 mRNA)were sigificantly increased;the mRNA expression of DAM core biomarkers such as APOE,Timp2 and CST7,which have anti-inflammatory effects,is significantly reduced,and the expression of P-JNK,P-ERK in MAPK pathway and P-P65 protein in NF-κB pathway were significantly increased;(6)After silencing the TREM2 expression in BV2 microglia TREM2,the culture medium after PFF stimulation of microglia was used to stimulate HT22 neurons,Phosphorylated α-Syn expression in neurons was significantly increased,and the activity of neurons were decreased and cell apoptosis was increased;(7)The core marker of DAM,Timp2 mRNA,decreased due to the TREM2 silencing,was increased significantly after the inhibition of ERK1/2 signal pathway.CONCLUSION:The results of this study suggest that in α-Syn-induced neuroinflammation,TREM2 may promote the activation of anti-inflammatory DAM through the ERR1/2 signal pathway,thereby inhibiting neuroinflammation,reducing neuronal damage in the hippocampus,and plays a protective role in PD with cognitive impairment.