Amyloid-β aggregation disrupts actomyosin architecture and impairs contractility in human brain vascular smooth muscle cells.

Amyloid-β (Aβ) accumulation within cerebral vessels underlies cerebral amyloid angiopathy (CAA) and Alzheimer's disease (AD). In CAA, Aβ deposits along leptomeningeal and cortical vessel walls are strongly associated with intracerebral hemorrhage and vascular dysfunction. However, the cellular mechanisms remain incompletely understood. Based on our prior work showing that aggregated Aβ disrupts human brain microvascular endothelial cells, we now address the mural layer by testing how Aβ affects human brain vascular smooth muscle cells (hBSMCs), focusing on actomyosin architecture and contractile function to comprehensively reveal the effects of Aβ on the cerebral vasculature. We combined single-cell imaging of quantum dot-labeled Aβ (QDAβ) with F-actin labeling (Alexa Fluor 488-phalloidin/SiR-actin), confocal 3D reconstructions, and a collagen gel contraction assay to associate Aβ deposition dynamics with cytoskeletal organization and force output. Aβ formed deposits at the cell edge of hBSMCs, accompanied by disorganization of the F-actin network and the emergence of abnormal F-actin aggregates. In addition, time-lapse imaging revealed the progressive accumulation of QDAβ-positive deposits with concomitant disorganization of stress fibers and the condensation of activated myosin II. Functionally, gels containing Aβ-exposed hBSMCs failed to shrink compared with non-treated/DMSO controls, consistent with reduced hBSMC-mediated matrix contraction. Together, these data suggest that Aβ deposition is associated with disorganization of cortical and contractile actin networks in hBSMCs and reduced hBSMC-mediated matrix contraction, providing a potential cellular framework linking local cytoskeletal pathology to impaired vasomotion and perivascular clearance in CAA.