Postsynaptic Proteome of Non-Demented Individuals with Alzheimer's Disease Neuropathology

Abstract

Some individuals, here referred to as Non-Demented with Alzheimer's Neuropathology (NDAN), retain their cognitive function despite the presence of amyloid plaques and tau tangles typical of symptomatic Alzheimer's disease (AD). In NDAN, unlike AD, toxic amyloid-β oligomers do not localize to the postsynaptic densities (PSDs). Synaptic resistance to amyloid-β in NDAN may thus enable these individuals to remain cognitively intact despite the AD-like pathology. The mechanism(s) responsible for this resistance remains unresolved and understanding such protective biological processes could reveal novel targets for the development of effective treatments for AD. The present study uses a proteomic approach to compare the hippocampal postsynaptic densities of NDAN, AD, and healthy age-matched persons to identify protein signatures characteristic for these groups. Subcellular fractionation followed by 2D gel electrophoresis and mass spectrometry were used to analyze the PSDs. We describe fifteen proteins which comprise the unique proteomic signature of NDAN PSDs, thus setting them apart from control subjects and AD patients.

Keywords: Alzheimer’s disease; non-demented with AD-like pathology; postsynaptic density proteome; synapse.

Fig.1

Representative 2DE of proteins identified. The highlighted spots were excised and analyzed in the present study. The x-axis is calibrated in pH units, while y-axis is calibrated in mass units (kDa).

Fig.2

Venn diagram of the total number of proteins with significant differential expression in NDAN versus AD, including the number of proteins that change in AD versus control and NDAN versus control.

Fig.3

Confirmation of proteomic changes for selected proteins. Five cases per group were assayed individually. Case information is provided in Table 4.

Fig.4

Pie chart representing the PANTHER classification of proteins based on protein class. The number of proteins in each category is shown in parenthesis.

Fig.5

IPA identifies twenty proteins from our dataset that are associated with the neurological disease network. A) Upregulated (red) or downregulated (green) proteins from our dataset are highlighted in the network. Solid and dashed lines indicate direct and indirect correlation between proteins, respectively. CAMK2A, calcium/calmodulin-dependent protein kinase type II subunit alpha; PFN2, profilin-2; SYN1, synapsin-1; CNP, 2’,3’-cyclic-nucleotide 3’-phosphodiesterase; PP2A, protein phosphatase 2; ERK1/2, mitogen-activated protein kinase 1/2; DNM1, dynamin-1; Hsp90, heat shock protein 90; TUBB6, tubulin beta-6 chain; VCL, vinculin; ANXA2, annexin 2; TUBA1A, tubulin alpha-1A chain; TUBB2A, tubulin beta-2A chain; TUBA1B, tubulin alpha-1B chain; TUBB4A, tubulin beta-4A chain; SPTAN1, spectrin alpha chain, non-erythrocytic 1; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; CLTA, clathrin light chain A; STXBP1, syntaxin-binding protein 1; KRT10, keratin, type I cytoskeletal 10; CDK4/6, cyclin-dependent kinases 4/6; KRT9, keratin, type I cytoskeletal 9. B) Figure legend for the IPA network. Nodes in the network are depicted by different shapes that represent various functional classes of the proteins. Arrows/lines represent different molecular relationships in the IPA network.