β-amyloid induced oxidative stress and its effects on astrocytes and neurons

• Main Author: Abeti, R.
• Published: University College London (University of London) 2011
• Subjects: 570
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.625612

Alzheimer’s disease (AD) is the most common form of dementia. It is characterized by the accumulation of amyloid plaques in the brain, made of β- amyloid (Aβ) fragments which activate NADPH oxidase expressed in astrocytes and microglia, increasing the rate of production of reactive oxygen species (ROS) ultimately leading to neuronal dysfunction and degeneration responsible for the cognitive deficits observed in AD. However, the mechanisms by which Aβ induces toxicity remain elusive. In this thesis I explored the mechanisms by which oxidative stress leads to Aβ-induced neuronal death. Ca2+ signalling is intimately involved in the regulation of glial responses, and can have both protective and detrimental effects on the nervous tissue. Therefore, I have explored the effects of Aβ on cell signalling in primary culture of cortical astrocytes, looking at the interplay between Ca2+ and ROS. My results show that Aβ induces toxicity by causing depletion of the Ca2+ stores (ER) through ROS production. While increased ROS generation may have dramatic consequences on brain physiology, techniques to measure ROS generation remain unsatisfactory and controversial. I therefore began by investigating new probes to measure ROS, such as HSP-FRET and rxYFPgrp1. A complicate cascade of inflammatory events take place in astrocytes during Aβ toxicity, but the cell death that follows is neuronal. Neurons can be protected by antioxidants or inhibitors of NADPH oxidase. Accordingly, I aimed to clarify how the activation of the astrocytic NADPH oxidase results in neuronal death. I found evidence that activation of NADPH oxidase by Aβ causes the upregulation of Poly (ADP-ribose) polymerase 1 (PARP-1) in astrocytes. Under conditions of oxidative stress PARP-1 overactivation depletes NAD+ which causes a loss of mitochondrial oxidative phosphorylation, loss of mitochondrial membrane potential and ultimately ATP depletion, leading to cell death. In summary, the work presented investigates Aβ actions on astrocytes signalling and describes a novel mechanism by which Aβ causes neuronal death.