Pathway-driven identification of therapeutic targets for combatting Alzheimer's disease.

The suffering and financial burden associated with Alzheimer's disease are so great due to the protracted nature of the disease. Beginning with problems remembering things, it progresses through an inability to recognise ones family and friends and to carry out daily tasks, leading to sufferers becoming completely dependent on others, bedridden, and eventually dying often up to 10 years after diagnosis due to pneumonia or other common infections. We have no effective treatment for this insidious disease! Mutations in the APP gene cause the familial or inherited form of Alzheimer's disease. The mutations cause the brain to make more of a substance called beta-amyloid, which aggregates into deposits to form senile plaques. There is growing evidence that these plaques are probably a marker of the disease rather than the cause, even a way for the brain to protect itself from the "soluble", toxic form of beta-amyloid.
Our nerve cells make connections with each other called synapses, through which they communicate and store information. These connections are the basis of how we learn and remember. Among the many toxic effects of beta-amyloid, one of the earliest and most important is its ability to break down the connections between nerve cells: Beta amyloid is said to be synaptotoxic. Very recently we have discovered the "signaling pathway" activated by beta-amyloid in nerve cells, and in the brains of sufferers, that causes several of the characteristic features of the disease, including the loss of synapses. This pathway is called the wnt-planar cell polarity (wnt-PCP) pathway. Quite remarkably, another lab have just discovered that the protein made by the APP gene, from which beta-amyloid is also made (by being cut up into small pieces), is a part of the receptor found on the surface of nerve cells that drives the wnt-PCP pathway. This means that the beta-amyloid "toxicity" pathway we have discovered is controlled by the actions of APP, a gene responsible for the inherited form of Alzheimer's disease. This represents a major breakthrough in our understanding of the disease. We now want to explore this pathway in great detail for two reasons. One, it will tell us a much more about the mechanism driving the disease in the brains of people with the disease. Secondly, by understanding the mechanism and knowing what each component does in it we will be able to work out how to block the processes and slow down, or even halt, the disease. It is only by understanding the mechanism we will be able to identify new therapeutic targets and be able to begin the process of finding drugs that work effectively on them. We propose a project of work to achieve this over the next 3.5 years. We have three lines of "attack". One, we will use a novel peptide array technology to rapidly and cost effectively "map" how specific components in this pathway interact, or bind, with one another, including APP and beta-amyloid. This technique enables us to make small peptides (bits of proteins) that can block these interactions. Two, we will use these peptides and other techniques to work out what each component does in the signaling pathway, in nerve cells, including working out exactly how beta-amyloid exerts its effects on nerve cell connections. Three, having achieved this we will be in the position to determine exactly where the disease mechanism should be attacked in order to prevent the crucial synaptotoxic effects of beta-amyloid. The peptides we will have generated to help identify the best targets will then be used to generate "binding assays" which can be then be optimised for future drug screening purposes aimed at finding drugs that act in the desired way upon the target. All such drug screening activities will be undertaken follow on from this, and will be dependent upon our obtaining further funding to do so.

Our aim is to gain a better understanding of the signaling mechanisms driving beta-amyloid neurotoxicity, to identify effective and tractable novel therapeutic targets in the pathway and to develop assays suitable for future high throughput screening ready to identify small molecules acting on them. We are in a unique position to do this following our discoveries concerning the pathway activated by beta-amyloid, which mediates its neurotoxic properties including; tau phosphorylation, neuronal death, synaptotoxicity and, in vivo, cognitive impairment. This pathway, the wnt-Planar Cell Polarity (wnt-PCP) pathway, is also detectable in the Alzheimer's disease (AD) brain. Of major significance for our understanding of AD pathology, the beta-amyloid precursor protein (APP), from which beta-amyloid is derived, has been identified as a necessary component of the wnt-PCP pathway where it is needed to drive it through recruitment of Abl: Thus, the beta-amyloid induction of wnt-PCP signaling is APP-dependent! Our understanding of the pathway will now enable us to decipher it further and more fully define the roles of APP and beta-amyloid within it. We will employ a range of techniques in cell lines and neurons, and validate findings in tissues from animal models and man. In the process we will identify novel, apt therapeutic targets through which to target the disease. Our adoption of peptide array technology to rapidly and accurately map specific protein-protein interactions, will not only help pathway elucidation but will also generate binding peptides, with which, and their binding partner proteins, we will generate assay suitable for future high throughput screening. Thus at the end of this project we will be in good position to commence small molecule identification with a battery of neuron based assays in place ready to evaluate active compounds. Such undertakings will, of course, be dependent on our obtaining further funding.

In the long term this project is predicated on potential benefit to the general public and the health services through identification of novel therapeutic targets and hence effective therapeutics.
In the medium term the wider beneficiaries include the academic community, both those in our immediate groups and our collaborators but also further afield who will benefit from the data and reagents/tools we will generate.
We have also established collaboration with Astra Zeneca relevant to, but not part of, the current proposal. We have a memorandum of understanding and confidentiality agreement with AZ whereby we propose to co-develop therapeutics based on our early understanding of the pathway we have identified.
One manifestation of this close and growing collaboration is an MRC CASE studentship jointly supervised by Lovestone for KCL and Mene Pangalos for Astra Zeneca where we are transferring all our in vitro experiments that led to the identification of the pathway we are investigating to human neurons derived from induced pluripotent stem cells.
The further work to derive therapeutic targets from the current proposal will strengthen our links with Astra Zeneca and in turn the resources that AZ have already committed and will further consider, will enable rapid application of translational elements of this proposal.