Soluble TREM2 inhibits secondary nucleation of Aβ fibrillization and enhances cellular uptake of fibrillar Aβ

Significance Mutations in a microglial protein, TREM2, represents a risk for Alzheimer’s disease (AD). We show that the soluble form of TREM2, sTREM2, can bind and inhibit fibrillization of Aβ peptides. sTREM2 increases uptake of Aβ fibrils into microglial and neuroglioma cell lines. Contrastingly, mutation R47H was found to have little effect on fibril nucleation and binding, but decreased uptake and functional responses. Our findings using integrative molecular modeling based on cross-linking mass spectrometry data for WT sTREM2–Aβ fibril complex demonstrate that TREM2 has at least two ligand-binding surfaces: one binding Aβ fibrils and the other anionic polyvalent ligands. R47H mutation lies on the latter surface. These findings inform mechanisms by which TREM2 modulates key processes in AD progression.