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“O-PTIR thus provides the optimal combination of high resolution and label-free imaging capabilities, making it ideal for mapping the chemistry of vascular amyloids.”
Reporting in Acta Neuropathologica, researchers at the University of Alabama have tackled a fundamental challenge in understanding cerebral amyloid angiopathy (CAA), a cerebrovascular disorder characterized by amyloid-β (Aβ) deposition in blood vessel walls.
Despite significant overlap with Alzheimer’s disease through shared Aβ pathology, the specific structural characteristics of Aβ aggregates in CAA and their variations between disease severity stages remained poorly understood. Traditional approaches relying on brain-derived fibrils can potentially overlook the polymorphic heterogeneity and chemical associations within vascular amyloids, creating a critical knowledge gap in CAA research.
The research team employed 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.
Their analysis of 80 vascular amyloid deposits revealed a clear increase in β-sheet content within vascular Aβ deposits corresponding to disease progression. Crucially, they identified a significant presence of antiparallel β-sheet structures, particularly prevalent in moderate/severe CAA cases. The abundance of antiparallel structures showed strong correlation with co-localized lipids, implicating a lipid-mediated aggregation mechanism.
To substantiate their ex-vivo observations, the researchers used nanoscale AFM-IR spectroscopy and demonstrated that Aβ40 aggregated in-vitro with brain-derived lipids adopts antiparallel structural distributions mirroring those found in CAA vascular lesions.
Multivariate Curve Resolution analysis revealed that lipids correlate specifically with antiparallel β-structures but not with overall β-sheet populations, indicating that vascular amyloids contain a mixed structural ensemble of both parallel and antiparallel aggregates, with lipid-mediated pathways specifically contributing to antiparallel structure formation.
The O-PTIR technique proved exceptionally powerful for this application, providing unprecedented insights into amyloid structure directly within native tissue environments. The technique’s sub-diffraction spatial resolution and label-free capabilities enabled researchers to map chemical heterogeneities at the subcellular level while avoiding artifacts from sample processing.
This work demonstrates how O-PTIR can reveal disease-relevant structural polymorphs that may be missed by traditional approaches, offering critical insights into pathogenic mechanisms and potential therapeutic targets.
Authors:
Ana Pacheco de Oliveira, Divya Baghel, Brooke Holcombe, William Chase, Tyler Ward, Shih-Hsiu J. Wang, and Ayanjeet Ghosh
