Temporal Quantitative Profiling of Newly Synthesized Proteins during Aβ Accumulation

Accumulation
of aggregated amyloid beta (Aβ) in the brain
is believed to impair multiple cellular pathways and play a central
role in Alzheimer’s disease pathology. However, how this process
is regulated remains unclear. In theory, measuring protein synthesis
is the most direct way to evaluate a cell’s response to stimuli,
but to date, there have been few reliable methods to do this. To identify
the protein regulatory network during the development of Aβ
deposition in AD, we applied a new proteomic technique to quantitate
newly synthesized protein (NSP) changes in the cerebral cortex and
hippocampus of 2-, 5-, and 9-month-old APP/PS1 AD transgenic mice.
This bio-orthogonal noncanonical amino acid tagging analysis combined
PALM (pulse azidohomoalanine labeling in mammals) and HILAQ (heavy
isotope labeled AHA quantitation) to reveal a comprehensive dataset
of NSPs prior to and post Aβ deposition, including the identification
of proteins not previously associated with AD, and demonstrated that
the pattern of differentially expressed NSPs is age-dependent. We
also found dysregulated vesicle transportation networks including
endosomal subunits, coat protein complex I (COPI), and mitochondrial
respiratory chain throughout all time points and two brain regions.
These results point to a pathological dysregulation of vesicle transportation
which occurs prior to Aβ accumulation and the onset of AD symptoms,
which may progressively impact the entire protein network and thereby
drive neurodegeneration. This study illustrates key pathway regulation
responses to the development of AD pathogenesis by directly measuring
the changes in protein synthesis and provides unique insights into
the mechanisms that underlie AD.