Shotgun Brain Proteomics Reveals Early Molecular Signature in Presymptomatic Mouse Model of Alzheimer's Disease

A beta(pE3-42) (N-terminal truncated amyloid-beta peptide starting with pyroglutamate at the third position) is abundant in Alzheimer's disease (AD) brain and has high aggregation propensity and cellular toxicity. Transgenic TBA42 mice expressing A beta(pE3-42) exhibit a neurological phenotype evident at the age of 12 months. As AD has a long presymptomatic period, early detection of imminent neurodegeneration is highly desirable. In the present work we used four-month-old presymptomatic TBA42 mice and performed a whole-brain proteome analysis in order to elucidate early AD-related pathological changes and the molecular networks involved. At least three proteins were found to be moderately (by 17% to 28%) but statistically significantly upregulated, including: nectin-like molecule 1 involved in cell-cell adhesion; Homer proteins involved in scaffolding, organizing proteins at synapse and regulating intracellular calcium within neurons; and inositol-trisphosphate 3-kinase A, which is important for InsP3 induced calcium signaling in the brain. Analysis of key nodes (regulatory molecules found on pathway intersections) identified Rho-kinase (ROCK), a serine/threonine kinase and one of the major downstream effectors of the small GTPase Rho, as well as three key nodes of the mTOR/p70S6K signaling pathway previously implicated in multiple fundamental biological processes including synaptic plasticity, and upregulated in AD. These data confirm that AD-typical molecular pathways can be detected by whole-brain shotgun proteomics in young presymptomatic mice long before the onset of behavioral changes.