GLUTAREDOXIN1 OVEREXPRESSION AMELIORATES EARLY F-ACTIN LOSS AND COGNITIVE DEFICITS SEEN IN ALZHEIMER’S DISEASE MOUSE MODEL

Abstract

Fibrillar actin (F-actin) is the key cytoskeletal protein that is highly enriched at dendritic spines and defines spine morphology. We recently demonstrated that synaptosomal F-actin levels were significantly decreased in APP/PS1 mice as early as 1 month of age. APP/PS1 mice also showed recall deficit upon contextual fear conditioning (cFC) at 2 months, which was reversed by F-actin stabilizing agent, jasplakinolide. Reactive oxygen species (ROS) generated by β-amyloid (Aβ) has been implicated in Alzheimer's disease (AD) pathogenesis. However, it is unclear whether ROS contributes to F-actin loss in synaptosomes, in vivo, in mice. Therefore, we investigated whether altered redox signaling could contribute to F-actin loss and behavioral deficits seen early in AD. We used age matched WT and APPswe/PS1ΔE9 mice for our experiments. Associative learning and memory test was assessed by cFC. Highly enriched F-Actin and G-Actin fractions were isolated from WT and APP/PS1 mice. We also used AMS-derivatization approach to determine reduced form of F-actin. AAV-glutaredoxin1 viral particles were delivered into hippocampus of mouse brain using stereotaxic injections. Statistical comparisons were performed using unpaired t-tests or ANOVA followed by post-hoc test. Reduced form of F-actin was significantly decreased but not reduced form of G-actin in synaptosomes of APP/PS1 mice as early as 1 month and this loss was sustained until 9 months, when overt symptoms are observed. S-glutathionylation of synaptosomal actin, which is known to hinder F-actin stabilization, was significantly increased in one month APP/PS1 mice. To determine the role of Aβ mediated endogenous ROS levels on F-actin loss and behavioural deficits in APP/PS1 mice we over-expressed glutaredoxin1 in hippocampus of the mouse brain. Remarkably, we found that cFC behavioral deficits seen in APP/PS1 mice was restored by over expression of glutaredoxin1 in AD mice. We demonstrate that Aβ induced ROS-mediated glutathionylation of actin as one of the mechanisms hindering F-actin stabilization in synaptic compartments leading to behavioral deficits in APP/PS1 mice, which can be reversed by over expression of glutaredoxin1. Our findings provide evidence that F-actin loss through oxidative modification at the synapse plays a critical role in synaptic dysfunction in AD pathogenesis.