Jörg Hanrieder (1,2,3), Wojciech Michno (1), Louise Carlred (3), Andrew Ewing (3), Stina Syvänen (4)
(1) University of Gothenburg, Mölndal, Sweden; (2) University College London, UK; (3) Chalmers University of Technology, Gothenburg, Sweden; (4) Uppsala University, Uppsala, Sweden
The major pathological hallmarks of Alzheimer’s disease (AD) is the progressive accumulation and aggregation of beta-amyloid (Aβ) and phospho-tau, into neurotoxic deposits. However, the exact molecular processes underlying protein aggregation and plaque pathology remains unknown. The primary goal of this project was to employ advanced molecular imaging mass spectrometry (IMS) to probe the chemical and structural aspects of Aβ plaque pathology in experimental AD. MALDI IMS followed by multivariate image analysis reveal region specific accumulation of differently truncated amyloid peptides in various regions of the brain. Moreover, different protein species were selectively regulated in plaque proximity. In conclusion, MS imaging is a promising approach to probe plaque chemistry in Alzheimer's disease.
Alzheimer’s disease is the most common neurodegenerative disorder affecting 12% over 65 (1). The exact mechanisms underlying AD pathogenesis are still not fully understood, significantly hampering the development of therapeutic treatment strategies. In AD, cognitive decline has been linked to formation of β-amyloid (Aβ) deposits as senile plaques as well as intracellular neurofibrillary tangles comprised of hyper-phosphorylated tau protein (2). The neuropathology in genetic- and sporadic AD is similar with respect to protein accumulation. The arctic and swedish mutation (ARCSWE) of amyloid precursor protein (APP) results in significant increase of neurotoxic Aβ peptides and fibrils (3). Changes in peptide truncation and plaque associated protein species have been implicated with proteopathic mechanisms in AD.
The aim of this study was therefore to employ MALDI based molecular imaging mass spectrometry to probe Aβ plaque pathology in tgARCSWE mice with particular focus on associated neuronal protein species and Aβ peptide truncation.
Transgenic C57BL/6-CBA-F1 male mice carrying the swedish double mutation alone (K670M, N671L) and the Arctic mutation (E693G) of human APP were studied. Protein and peptide changes were examined in adult mouse brain (18 month) using MALDI imaging on fresh frozen coronal cryosections at two different bregma (CPu and Hippocampus).
Multivariate image data analysis by means of hierarchical clustering analysis allowed image data segmentation into regions of interest based on their chemical identity. In the corresponding loadings, Aβ peptide signals that annotate different truncations were observed. This includes e.g. the 3-pyroglutamate truncation , which is considered very neurotoxic and promotes extensively oligomerization. The plaque identity was verified with immunohistochemistry. Moreover plaque specific protein regulations were observed in the frontal cortex and the hippocampus, including an increase of histones and thymosin beta 4 and cytochrome C in the frontal cortical plaques, while and Acyl-CoA binding protein was increased selectively in the hippocampus.
The presented data demonstrate that MALDI based molecular imaging is a promising approach to interrogate chemical plaque pathology in Alzheimer’s disease.
(1) Selkoe, D.J. and Schenk D., Annu Rev Pharmacol Toxicol, 2003.43: p. 545-84 , (2) Thal D.R. et al., Neurology, 2002. 58(12): p. 1791-800, (3) Lord, A., et al., Neurobiol Aging, 2006. 27(1): p. 67-77.