Lipid mediated formation of antiparallel aggregates in cerebral amyloid angiopathy

Cerebral amyloid angiopathy (CAA) is a cerebrovascular disorder marked by amyloid-β (Aβ) deposition in blood vessel walls, leading to hemorrhage and recurring stroke. Despite significant overlap with Alzheimer's disease (AD) through shared Aβ pathology, the specific structural characteristics of Aβ aggregates in CAA and their variations between stages of disease severity are yet to be fully understood. Traditional approaches relying on brain-derived fibrils can potentially overlook the polymorphic heterogeneity and chemical associations within vascular amyloids. This study utilizes sub-diffraction, label-free optical photothermal infrared (O-PTIR) spectroscopic imaging to directly probe the chemical structure and heterogeneity of vascular amyloid aggregates within human brain tissues across different CAA stages. Our results demonstrate a clear increase in β-sheet content within vascular Aβ deposits corresponding to disease progression. Crucially, we identify a significant presence of antiparallel β-sheet structures, particularly prevalent in moderate/severe CAA. The abundance of antiparallel structures correlates strongly with co-localized lipids, implicating a lipid-mediated aggregation mechanism. We substantiate the ex-vivo observations using nanoscale AFM-IR spectroscopy and demonstrate that Aβ40 aggregated in-vitro with brain-derived lipids adopts antiparallel structural distributions mirroring those found in CAA vascular lesions. This work provides critical insights into the structural distributions of Aβ aggregates in CAA, highlighting the presence of polymorphs typically associated with transient intermediates, which may lead to alternate mechanisms for neurotoxicity.