EX-VIVO VALIDATION OF PLASMA PROTEIN FIBRINOGEN GAMMA

Abstract

The clinical hallmarks of AD become apparent when the disease is advanced, and the challenge is to spot the disease in its infancy, before any symptoms. One avenue being explored is a blood-based biomarker for AD. Recently we demonstrated that a simple test consisting of a reduction in Fibrinogen Gamma Chain (FGG) along with age has potential for predicting neocortical amyloid burden (NAB; Ashton et al., 2015). Recent publications have also shown that a blood test to predict NAB is possible (Burnham et al., 2012; Kiddle et al., 2013). Several publications have reported that Fibrinogen and it's subtypes are normally rejected from the brain by the blood-brain barrier (BBB), yet still have been detected in AD mice models and AD post-mortem human brain tissue (Cortes-Canteli et al., 2010; Ryu., 2009). Furthermore, Fibrinogen has been shown to accumulate over time as AD pathology progresses, co-deposit with Aβ in brain tissue, and enhance aggregation and increase Aβ fibrillisation (Klohs et al., 2012; Ahn et al., 2010). It is encouraging that our blood protein of interest has been independently shown to move across a damaged BBB and directly interact and co-localise with amyloid. We now aim to replicate FGG and other promising plasma biomarker candidates of amyloid pathology in larger cohorts and corroborate deposition in post mortem brain tissue. The study includes multiple time point plasma samples (n=115), with additionall sub-set of post mortem brain tissue and sections (n=30; Braak I-VI). Immunoassays for candidate proteins will be performed on the plasma. Immunohistochemistry will be performed on the brain sections while Western blot will be conducted to quantify levels of the targets in brain homogenates. Statistical analysis will be performed to elucidate the association between plasma and brain FGG. By measuring FGG over multiple time points we have confirmed the protein trajectory and have determined its ability to predict the cases positive for amyloid burden. Post mortem brain tissue and sections have been used to confirm the prediction accuracy of plasma FGG. This study will be the first of its kind to demonstrate the development of a candidate protein from plasma to brain.