Biology subjects

Brett, T. J.

Publications and source records attributed to Brett, T. J..

4 recordsLinked to original sources

bioRxiv2024

Biophysical mapping of TREM2-ligand interactions reveals shared surfaces for engagement of multiple AD ligands

TREM2 is a signaling receptor expressed on microglia that has emerged as an important potential drug target for Alzheimers disease and other neurodegenerative diseases. While a number of TREM2 signaling ligands have been identified, little is known regarding the structural details of how it engages them. To better understand this, we created a protein library of 28 different TREM2 variants and 11 different sTREM2 variants that could be used to map interactions with various ligands using biolayer interferometry (BLI). The variants are located in previously identified putative binding surfaces on TREM2 called the hydrophobic site, basic site, and site 2. We found that mutations to the hydrophobic site ablated binding to apoE4, oAb42, and TDP-43. Competition binding experiments further supported that apoE4 and oAb42 share overlapping binding sites on TREM2. In contrast, binding to IL-34 was mediated by the basic site at a surface centering on R76. Competition binding experiments validated a unique site for IL-34, showing little to no competition with either oAb42 or apoE4. Altogether, our results suggest that TREM2 utilizes the hydrophobic site (consisting of CDR1, CDR2, and CDR3) as a common site to engage multiple ligands, and further implies that pharmaceutical strategies targeting this surface might be effective to modulate TREM2 functions.

biophysics↗

bioRxiv2024

Structural and functional analysis of TREM2 interactions with amyloid beta reveal molecular mechanisms that mediate phagocytosis of oligomeric amyloid beta

The TREM2 receptor is expressed on microglia in the brain, where it plays critical roles regulating microglia function. TREM2 engages a number of ligands involved in Alzheimers disease, and consequent signaling triggers phagocytosis, activation, survival, and proliferation. TREM2 has emerged as a drug target for AD, however very little is known regarding the structural basis for TREM2 microglial functions. Here we investigated the engagement of oligomeric amyloid beta (oA{beta}42) with TREM2. Using familial variants of amyloid beta, we show that mutations in the N-terminal portion of A{beta}, notably residues H6 and D7, disrupt binding to TREM2. We then co-crystallized TREM2 with A{beta}(1-8) peptide and determined the high resolution crystal structure. The structure revealed the peptide binds to the hydrophobic site of TREM2, closest to CDR1. Mutational and binding studies using BLI confirmed that mutations to the hydrophobic site ablate binding to oA{beta}42. Finally, we show that these interactions are critical to triggering phagocytosis of oA{beta}42, as oA{beta}42 variants H6R and D7N are not phagocytosed. Altogether, these data indicate that TREM2 engages oA{beta}42 using the hydrophobic site on TREM2 and the N-terminal portion of A{beta}, and that this interaction is critical to trigger signaling and phagocytosis.

biophysics↗

bioRxiv2020

Functional insights from biophysical study of TREM2 interactions with ApoE and Aβ1-42

INTRODUCTIONTREM2 is an innate immune receptor expressed on myeloid cells including microglia in the brain. How TREM2 engages different ligands remains poorly understood. METHODSWe used comprehensive BLI analysis to investigate the TREM2 interactions with ApoE and monomeric amyloid beta (mA{beta}42). RESULTSTREM2 binding did not depend on ApoE lipidation, and there were only slight differences in affinity observed between ApoE isoforms (E4 > E3 > E2). Surprisingly, disease-linked TREM2 variants within a "basic patch" minimally impact ApoE binding. Instead, TREM2 has a unique hydrophobic surface that can bind to ApoE. This direct engagement requires the hinge region of ApoE. TREM2 directly binds mA{beta}42 and can potently inhibit A{beta}42 polymerization, suggesting a potential mechanism for soluble TREM2 (sTREM2) in preventing AD pathogenesis. DISCUSSIONThese findings demonstrate that TREM2 has at least two separate surfaces to engage ligands and uncovers a potential function for sTREM2 in directly inhibiting A{beta} polymerization.

biophysics↗

bioRxiv2018

The MS4A gene cluster is a key regulator of soluble TREM2 and Alzheimer disease risk

Soluble triggering receptor expressed on myeloid cells 2 (sTREM2) levels in the cerebrospinal fluid (CSF) have been associated with Alzheimer disease (AD) status. TREM2 plays a critical role in microglial activation, survival, and phagocytosis; however, the pathophysiological role of sTREM2 in AD is not well understood. Understanding the role of sTREM2 in AD may help reveal biological mechanisms underlying AD and identify novel therapeutic targets. We performed a genome-wide association study (GWAS) to identify genetic modifiers of CSF sTREM2 levels. Common variants in the membrane-spanning 4-domains subfamily A (MS4A) gene region were associated with higher CSF sTREM2 levels (rs1582763; P = 1.15x10-15) and replicated in independent datasets. The variants associated with increased levels of sTREM2 are also associated with reduced AD risk and delayed age-at-onset. Rs1582763 influences expression of MS4A4A and MS4A6A in multiple tissues, suggesting that one or both of these genes are important for regulating sTREM2. MS4A genes encode transmembrane proteins that may play a role in intracellular protein trafficking in microglia. We used human macrophages to begin to test the relationship between MS4A4A and TREM2 and found that they co-localize intracellularly and that antibody-mediated targeting of MS4A4A reduces sTREM2. Thus, genetic, molecular, and cellular findings suggest that MS4A4A regulates sTREM2. These findings also provide a mechanistic explanation of the original GWAS signal in the MS4A locus for AD risk and indicate that TREM2 is involved in sporadic AD risk in general, not only in TREM2 risk-variant carriers.

genomics↗