The Studies Of Beta-amyloid Modulates Microglial Responses By Binding To TREM2,and TREM2-targeted Drug Screening

TREM2(Triggering receptor expressed on myeloid cells 2)is a cell surface receptor of the Ig superfamily that is specifically expressed by microglia within the central nervous system(CNS).The R47H mutation in TREM2 constitutes one of the strongest single allele genetic risk factors for AD(Alzheimer’s Disease).A diverse set of potential TREM2 ligands,such as phospholipids and lipoproteins,have been documented.The bona fide endogenous TREM2 ligands associated with AD remain remain to be determined.In this study,we expressed and purified TREM2 protein from the conditioned medium of eukaryotic cell system.We found that oligomeric beta-amyloid specifically bound to TREM2 with high affinity by using solid phase binding,immunoprecipitation and Surface Plasmon Resonance assays.In order to investigate whether Aβ activates TREM2-mediated signaling pathways,we examined the phosphorylation of Syk and Akt in primary microglia as well as TREM2-mediated signaling in a reporter cell system.The stimulation with oAβ induced significantly higher level of p-Syk and p-Akt in wild-type but not Trem2-KO microglia.Furthermore,oAβ selectively activated TREM2 reporter cells but not control cells in a dose-dependent manner.Lastly,the functional outcome of oAβ-TREM2 interaction was tested by examining impacts on microglial migration in vitro and clustering around oAβ1-42-bearing brain areas in vivo.We found that oAp promoted microglial migration in vitro and clustering in vivo in a TREM2-dependent manner.In addition,we have made efforts to screen small molecule compounds that bind to TREM2.We have identified E1 as a candidate that binds to TREM2 with high affinity.However,TREM2 signaling and function remains to be characterized in future studies.It has been widely reported that Aβ is closely involved in progress of AD,and microglia is the major cell type that uptakes and degrades Aβ.Our current study demonstrates that oAβ binds to TREM2 with high affinity and activates TREM2-dependent signaling pathways in microglia.The absence of TREM2 impairs the oAβ-induced microglial migration in vitro and microglial clustering around oAβ-bearing brain regions in vivo.The identification of Aβ as a novel TREM2 ligand links TREM2 to the most prominent pathological features of AD and provides a critical mechanism by which microglia recognize and react to Aβ pathology.