The Effects And Mechanisms Of Microglial Proliferation And Activation Regulated By TREM2 In Alzheimer’s Disease

Objective:To investigate the effects of microglial proliferation and polarization regulated by TREM2 and the mechanisms of the regulation in Alzheimer’s disease（AD）.Methods:（1）Primary microglia from wild type（WT）mice or APP/PS1 mice were treated with Aβ_1-42.TREM2 mRNA and protein levels were measured by Q-PCR and Western Blot separately;the proliferation was measured by CCK-8,and the mRNA levels of M1 marker CD86,CD16,iNOS,TNF-α,IL-6,IL-1βand M2 marker Arg,TGF-β,Ym1 were measured by Q-PCR,protein levels of wnt/β-catenin pathway includingβ-catenin、P-AKT,AKT,P-GSK3βand GSK3βwere measured by Western Blot.（2）Primary microglia from WT mice or APP/PS1 mice were transfected with the small interfering RNA of TREM2（TREM2-siRNA）to knockdown the expression of TREM2,and then treated with Aβ_1-42.The proliferation was measured by CCK-8,and the mRNA levels of M1 marker CD86,CD16,TNF-α,IL-6,IL-1βand M2 marker Arg,TGF-β,Ym1 were measured by Q-PCR.Protein levels of Wnt/β-catenin pathway includingβ-catenin,P-AKT,AKT,P-GSK3βand GSK3βwere measured by Western Blot.（3）Primary microglia from WT mice were transfected with the TREM2-siRNA and then treated with Aβ_1-42.The conditioned medium were collected and added to SH-SY5Y cells.The proliferation of SH-SY5Y cells was measured by CCK-8.（4）Collecting the peripheral blood from mild cognitive impairment（MCI）patients,AD patients and healty control（HC）,mRNA levels of TREM2 in PBMC were measured by Q-PCR.Results:1.TREM2 mRNA and protein levels increased in APP/PS1 primary microglia compared with WT.After treated with Aβ_1-42,TREM2 mRNA and protein levels increased in primary microglia.2.The proliferation of APP/PS1 primary microglia was better than that of WT.After treated with Aβ_1-42,the proliferation of primary microglia increased,the mRNA levels of TNF-α,IL-6,IL-1β,CD86 and CD16 decreased,while the mRNA levels of Arg,TGF-βand Ym1 increased.3.The protein levels ofβ-catenin,P-AKT and P-GSK3βin APP/PS1 primary microglia were higher than that in WT.After treated with Aβ_1-42-42 or over expression of APP,the protein levels ofβ-catenin,P-AKT and P-GSK3βin microglia increased.4.After transfected with TREM2-siRNA,the proliferation in primary microglia evidently decreased,the mRNA levels of TNF-α,IL-6,IL-1β,CD86 and CD16 increased and the mRNA levels of Arg,TGF-βand Ym1 decreased.After treated with Aβ_1-42-42 or over expression of APP,the changes were more significant.5.After transfected with TREM2-siRNA,the protein levels ofβ-catenin,P-AKT,P-GSK3βin microglia decreased,Wnt/β-catenin pathway was restrained.Additional treatment with Aβ_1-42 couldn’t induce the expression ofβ-catenin,P-AKT and P-GSK3βeffectively.6.The conditioned medium from WT microglia treated with TREM2-siRNA transfection and Aβ_1-42 stimulation decreased the proliferation of SH-SY5Y cells.7.Compared with HC,the mRNA levels of TREM2 in PBMC from MCI and AD patients were increased,especially in AD patients.Conclusion:In AD pathological process,the up regulation of TREM2 could induce the activation of Wnt/β-catenin pathway,induce the proliferation and phenotype switch to M2in microglia.TREM2 deficiency could not induce the activation of Wnt/β-catenin pathway effectively,the proliferation of microglia decreased and microglial phenotype switched to M1,thus aggravating the neuronal death.Our studies indicated that TREM2 could promote the proliferation and activation to M2 type via the Wnt/β-catenin pathway in AD.