Investigating aberrant neuronal calcium regulation by calpain in Alzheimer s Disease

People who suffer from Alzheimer’s disease (AD) have severe memory loss and dementia. These symptoms are caused by the progressive and relentless death of nerve cells in the brain that we use for memory, recognition and most brain functions that give us our personality.

My research is aimed at investigating why nerve cells die in AD because if we can prevent this cell death then we will have effective treatments for this devastating condition.

I will focus on events that increase the amount of calcium inside nerve cells. Normally there is a balance between the amount of calcium entering and leaving nerve cells, but in AD this process is disrupted and excess calcium inside nerve cells causes them to die.

My project will investigate the reasons for this calcium imbalance. I will also use animal models to test the effectiveness of drugs that should restore the calcium balance to determine whether they can prevent the nerve cell death that is characteristic of AD. This work may lead to a new strategy for treating AD which can be developed by the pharmaceutical industry and could result in a new generation of treatments for this devastating illness.

Alzheimer s disease (AD) affects approximately 750,000 people in the UK and the prevalence is rising each year. With a relatively late onset of symptomatic impairment in AD there is an opportunity for pharmacological intervention, however there is still a need for further investigation into pathogenic mechanisms in AD in order to identify therapeutic targets.
Elevated beta-amyloid (Abeta) levels are thought to initiate a pathogenic cascade in AD. Abeta stimulates calpain activation and there are sustained increases in calpain activation early in AD (Nixon et al., 2003). A tonic level of calpain activation is physiologically important in a number of processes, so it is essential to determine what causes sustained increases in calcium leading to the disease-associated calpain over-activation in AD. Calpain was recently shown to cleave and thus inactivate the sodium/calcium exchanger 3 (NCX3), preventing calcium extrusion from neurons and causing neurotoxicity (Bano et al., 2003). My preliminary data shows that calpain-mediated NCX3 cleavage is induced by Abeta in vitro and that NCX3 cleavage is significantly upregulated in AD brain. The research proposed in this experiment is designed to test the hypothesis that Abeta-induced calpain cleavage of the sodium/calcium exchanger (NCX3) is an early toxic event in the pathogenesis of AD, which consequentially results in neuronal death. To do this I will first establish the mechanism by which Abeta induces the accumulation of toxic concentrations of intraneuronal calcium via calpain-mediated cleavage of the NCX3 pump. I will then examine whether reduced expression of NCX3 sensitises neurons to Abeta-induced neurotoxicity using RNAi to suppress NCX3 expression. Constructs which suppress NCX3 to different degrees will be used to allow correlations between levels of NCX3 expression, intraneuronal calcium concentrations and neuronal death. I will establish whether increased NCX3 cleavage is a specific feature of AD or is common to other neurodegenerative disorders by measuring levels of cleaved protein in diseased brain. If NCX3 cleavage is increased specifically in AD brain I can then investigate whether it may be a good peripheral biomarker by examining cleaved NCX3 protein amounts in lymphocytes. Finally, to determine if calpain is a potential pharmacological target for AD I will treat transgenic mouse models of AD with calpain inhibitors using a novel technique. This research will help to unravel complex and poorly understood mechanisms and may lead to the discovery of a key step in the neurodegenerative pathway, with the potential for therapeutic development.