Differences in the Cerebral Amyloid Angiopathy Proteome in Alzheimer's Disease and Mild Cognitive Impairment

Cerebral amyloid angiopathy (CAA) is a disease caused by the deposition of amyloid-beta (Aβ) in cerebral blood vessels. It is common not only in the elderly and almost all patients with Alzheimer’s disease (AD) but can also occur independently of other AD-related pathologies. The presence and severity of CAA promote the progression of AD-related clinical symptoms and are associated with more rapid cognitive decline even in normal elderly subjects. The onset of CAA may lead to cognitive decline either directly by promoting hypoxia and neuronal injury or indirectly by promoting tau pathology. Additionally, CAA is associated with brain hemorrhage and with amyloid-related imaging abnormalities (ARIA), a major complication of AD immunotherapy.

Although certain components of CAA development mechanisms have been revealed, its fundamental pathogenesis remains unclear. Typically, Aβ deposits in CAA in a characteristic patchy manner, appearing spiral and mostly affecting larger arterioles’ adventitia rather than the media, and mainly includes the more soluble Aβ40 rather than Aβ42. To better understand the molecular mechanisms of CAA, this study used laser capture microdissection (LCM) to obtain CAA-positive (CAA(+)) and CAA-negative (CAA(-)) vessels from dissected brain tissues for proteomic analysis. The goal was to identify proteins selectively enriched in CAA(+) vessels and compare these with the CAA proteome in early AD (mild cognitive impairment, MCI) and late-stage AD.

Research Origin

This paper, authored by Dominique Leitner, Tomas Kavanagh, Evgeny Kanshin, and others, was completed in collaboration among institutions such as Rush University and NYU Grossman School of Medicine. It was published in the journal Acta Neuropathologica in 2024. The study was received on April 4, 2024, revised on July 11, 2024, and accepted on July 12, 2024.

Research Process

Study Design and Experimental Methods

Sample Collection and Classification

Brain tissues were obtained under the approval of the Institutional Review Boards (IRB) of NYU Grossman School of Medicine and Rush University. Samples came from the Religious Orders Study (ROS) and the Memory and Aging Project (MAP) cohorts. Samples included age-matched controls (10 cases), MCI cases (4 cases), and AD cases (6 cases), stratified based on combined clinical and neuropathological standards.

Laser Capture Microdissection (LCM)

Eight-micron-thick sections were cut from formalin-fixed, paraffin-embedded (FFPE) tissue and, using LCM, CAA(+) and CAA(-) vessels were captured from the brain tissues of control, MCI, and AD cases. All samples were immunohistochemically stained with 4G8 antibody to detect Aβ proteins, delineating clear CAA(+) and CAA(-) vascular areas, and then vessels were micro-dissected for subsequent mass spectrometry analysis.

Label-Free Quantitative Mass Spectrometry (LFQ-MS)

All samples were extracted, digested, and separated, followed by label-free quantitative mass spectrometry for protein identification and quantification. Mass spectrometry data were analyzed using Spectronaut software and compared against the UniProt reference database for Homo sapiens to identify and quantify proteins in samples. Data analysis was performed using Perseus software, the R environment, and Graphpad Prism.

Study Results

Protein Expression Analysis

The study detected a total of 2026 proteins, with 257 proteins enriched in CAA(+) vessels in MCI and 289 in AD. Principal component analysis (PCA) showed significant separation between CAA(+) and CAA(-) vessel samples, with trends of protein enrichment and reduction in CAA(+) vessels being similar in both MCI and AD cases.

Matrix Proteins and Ribosomal Proteins

In both groups, enriched proteins were particularly associated with collagen-containing extracellular matrix, whereas proteins associated with ribosomal protein complexes were significantly reduced. Key blood-brain barrier (BBB) proteins showed significantly reduced expression in CAA(+) vessels.

Vascular Type Markers

In CAA(+) vessels, capillary markers such as BSG, SLC7A5, and SLC3A2 decreased, whereas venous marker PTGDS increased. Additionally, collagen family proteins significantly increased in CAA(+) vessels in both MCI and AD, suggesting that vascular matrix remodeling may be related to vascular dysfunction.

Venn Diagram Comparison and Validation

By comparing the CAA proteome with published amyloid plaque proteome data, the study found that most proteins were enriched in both CAA and plaques, though some were more pronounced in CAA. SEMA3G was confirmed as a specific marker for CAA.

Conclusion

This study is the first to separately evaluate the proteomes of CAA(+) and adjacent CAA(-) vessels and to assess them in MCI cases, revealing protein changes related to vascular matrix remodeling, translation deficiencies, and BBB disruption. These changes can lead to vascular dysfunction and future mechanistic, therapeutic, and biomarker research. The discovery of SEMA3G, in particular, may provide a potential biomarker for CAA diagnosis and assessing ARIA risk in patients undergoing immunotherapy.

Highlights

1. First Separate Analysis of CAA(+) and CAA(-) Vessel Proteomes: Previous studies did not separately analyze CAA(+) and adjacent CAA(-) vessels, making this innovative approach significantly enhance understanding of the unique proteins specific to CAA.
2. Analysis in MCI Cases: This study evaluated protein changes not only in late-stage AD but also in the vascular of MCI patients for the first time, providing important clues for early tau protein and vascular pathology detection.
3. SEMA3G Validation: The validation of SEMA3G as a CAA-specific marker offers an important tool for future CAA diagnosis.

This study provides new perspectives on vascular pathology in CAA and AD and could drive further developments in related fields.