Stimulating microglial neuroinflammation with amyloid-beta oligomers compatible with solid-state NMR structural characterization

Amyloid-beta (Aβ) oligomers are known primary neurotoxic species in Alzheimer's disease, but the connection between oligomer structure and biological activity is not well understood. Current methods for preparing oligomer samples often use toxic detergents, making it difficult to test them in cell-based assays. Researchers have now developed a detergent-free protocol that allows for the isolation and concentration-dependent oligomerization of Aβ42 monomers at 37°C.

This method enables biophysical characterization, including circular dichroism, silver-stained SDS-PAGE, and negative-stain TEM, all of which reveal a β-sheet structure. Solid-state NMR spectroscopy of 13C/15N-labeled oligomers produces well-resolved spectra with β-strand chemical shifts. Two-dimensional 13C-13C DARR and CHHC experiments provide initial inter-residue distance constraints, revealing similarities and differences between the 150 kDa oligomer.

When mouse microglial cells (MMCs) were treated with 50 nM 37°C oligomers, it triggered a stronger pro-inflammatory cytokine response than monomeric Aβ42. Similar results were observed in hiPSC-derived microglia (iMGs) treated with 1 µM oligomers, demonstrating activity in a human cellular model. Importantly, monomeric Aβ42 did not exhibit any activity in these systems, indicating that inflammatory activity depends on the assembly state of Aβ42 rather than the presence of the peptide alone.

The detergent-free Aβ42 oligomer preparation is compatible with solid-state NMR structural characterization and shows biological activity in neuroinflammation assays, providing a valuable platform for studying microglial immune responses to oligomers.