A shift in microglial β-amyloid binding in Alzheimer's disease is associated with cerebral amyloid angiopathy

Area of Science:

• Neuroscience
• Immunology
• Neuropathology

Background:

• Alzheimer's disease (AD) and cerebral amyloid angiopathy (CAA) are common neurodegenerative pathologies characterized by beta-amyloid (Aβ) accumulation and neuroinflammation.
• The precise mechanisms underlying Aβ clearance and the role of the complement system in these conditions remain incompletely understood.

Purpose of the Study:

• To investigate the differential expression of microglia-associated Aβ ligands in post-mortem human brains.
• To examine the association of these ligands with complement activation in AD with and without concomitant CAA.

Main Methods:

• Analysis of human post-mortem brain homogenates and microvessel fractions from AD subjects (with and without CAA) and age-matched controls.
• Quantification of C3b, membrane attack complex (MAC), CD11b, and α-2-macroglobulin.
• Immunoprecipitation (IP) to detect CD11b/C3b/Aβ complexes and confocal microscopy to visualize interactions.

Main Results:

• Significantly elevated levels of C3b and MAC were observed in brains with CAA compared to AD-only and control groups.
• Immunoprecipitation revealed increased CD11b/C3b complexes with Aβ in subjects with both AD and CAA.
• MAC was notably associated with CAA-affected blood vessels, unlike in AD-only or control vessels.

Conclusions:

• Findings suggest a microglial CD11b-mediated Aβ clearance pathway that transports Aβ and C3b to blood vessels in AD/CAA.
• This process may contribute to Aβ deposition and complement propagation, leading to MAC formation and potential vascular fragility.