Aβ-Overlapping Ectodomain Binding of the Clinical-Stage TREM2 Agonist VG-3927.

Triggering receptor expressed on myeloid cells 2 (TREM2) is a microglial immune receptor genetically and functionally linked to Alzheimer's disease (AD). VG-3927, the first clinical-stage small-molecule TREM2 agonist, has been proposed to function as a transmembrane molecular glue and positive allosteric modulator (PAM). Whether it directly engages the extracellular ligand-recognition surface of TREM2 remains unknown. Here, we used a deep learning-based blind docking algorithm to map potential VG-3927 binding sites across TREM2 and identified a binding site within the ectodomain hydrophobic groove, a ligand-recognition surface previously implicated in Aβ and apoE binding. Microscale thermophoresis (MST) confirmed direct interaction of VG-3927 with TREM2 under optimized PEG-400 buffer conditions and independently demonstrated binding of Aβ 1-42 to the receptor. Co-incubation with Aβ reduced the VG-3927 thermophoretic response, consistent with interference at an overlapping ectodomain binding surface. Consistently, Aβ induced a rightward shift in the VG-3927 dose-response curve in a Jurkat TREM2-DAP12 NFAT reporter assay and attenuated VG-3927-induced phospho-SYK signaling. Together, these findings support the presence of a previously unrecognized ectodomain interaction mode for VG-3927 and suggest that amyloid-associated ligand occupancy may modulate TREM2 agonist activity within the AD microenvironment.