Neuropathology of Alzheimer’s disease (AD) is characterized by the accumulation and aggregation of Amyloid β (Aβ) peptides into extracellular plaques of the brain. The Aβ peptides are generated from amyloid precursor proteins by β- and γ-secretases. Aβ deposited not only in cerebral parenchyma but also in leptomeningeal and cerebral vessel walls. This has been known as cerebral amyloid angiopathy.
Here, we adopt MALDI-imaging mass spectrometry (MALDI-IMS) on autopsied brain tissues to obtain a comprehensive protein mapping. Human cortical specimens for IMS were obtained from brains that were removed, processed, and stored at -80 ˚C within 8 h postmortem at the Brain bank at Tokyo Metropolitan Institute of Gerontology. Each brain specimen was taken from the occipital cortex of five AD patients and five non-pathological controls. This study was approved by the ethics committee at each hospital or institute. Cryosections were cut and transferred to Indium-Tin-Oxide coated glass slides. Spectra were acquired using the rapifleX in positive linear mode, whereas ions were detected in a mass range of m/z 2,000-20,000 with spatial resolution of 20-100 µm. Matrix was uniformly deposited on the slide using the HTX-sprayer. Visualization and statistical analysis were used flexImaging and SCiLS Lab.
The current analysis clarifies that Aβ1-42 and Aβ1-43 were selectively deposited to senile plaque and shorter Aβ peptides were deposited to leptomeningeal blood vessels. In order to deepen proteomic information with the current specimen, we have dissected a small piece of tissues from leptomeningeal vessels as well as parenchymal area with laser micro dissection and were applied to LC-TIMS-TOF-MS/MS analysis. Data analysis was done with Proteinscape. From single vascular structure and adjacent cortical parenchyma dissected with 0.25-0.5 mm2 yields a thousand of protein annotation. Further analysis including detected peptide fragments as well as immunohistochemistry with a specific epitope recognition will validate the current strategy.