P3‐296: Assessment of human apolipoprotein E and Aβ clearance rate in vivo through use of stable isotope‐labeling and tandem mass spectrometry
Year: 2008
Type: article
Abstract: Accumulation of amyloid β peptide (Aβ) in brain is hypothesized to initiate pathogenic cascades that eventually culminate in Alzheimer's disease (AD). Apolipoprotein E4 (ApoE4) is associated with an increased risk, whereas ApoE2 is associated with a decreased risk for AD. ApoE is likely to influence risk for AD by acting as an Aβ binding molecule, thereby influencing Aβ fibrillogenesis and clearance. In order to assess ApoE and Aβ clearance rates in vivo, we developed a novel method that couples tandem mass spectrometry (MS)-based quantitation with in vivo stable isotope-labeling (C6-leucine). C6-leucine (200 mg/kg) was injected into young ApoE2 and ApoE4 knock-in mice by a bolus intraperitioneal injection. Human ApoE was immunoprecipitated with an ApoE monoclonal antibody then subjected to trypsin digestion and nanoLC-tandem MS. The fractional clearance rates (FCR) of ApoE from cortex and hippocampus of ApoE knock-in mice were successfully measured by calculating the ratio of labeled-to-unlabeled leucine. A similar method was applied to PS1(delta9)/APPswe transgenic mice to determine the FCR of Aβ. The FCR of ApoE4 was 2.75±0.60% per hour for hippocampus and 5.46±0.50% per hour for cortex (p<0.01). The clearance rate of ApoE in cortex was significantly higher for ApoE4, compared with ApoE2 (FCR: 5.46±0.50% per hour for ApoE4, 2.07±0.25% per hour for ApoE2, p<0.0001). Taken together, our results suggest that there is differential clearance between ApoE isoforms. The FCR of cortical Aβ was 7.62±1.25% per hour. Remarkably, the FCR of soluble Aβ from cortex of transgenic mice is very similar with that seen for Aβ from human CSF previously reported. The methodology developed to assess the relative difference in FCR between ApoE isoforms as well as Aβ in the brain will be an invaluable tool to study ApoE and Aβ metabolism, and may be applied to investigate the metabolism of other proteins implicated in many neurodegenerative diseases that either misfold or influence protein misfolding.
Source: Alzheimer s & Dementia
Institution: Washington University in St. Louis
Language: English
Subfield: Physiology
Field: Medicine
Domain: Health Sciences
Open Access status: bronze
OpenAlex ID: W2072349685