Dkk1-Wnt signalling pathway in synapse degeneration: implication for early stages of Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative condition characterised by a failing memory and loss of the ability to form and retain new memories. These cognitive features are recognised to be dependent on changes in the number and strength of neuronal contacts called synapses. In AD patients, a progressive cognitive decline and deposition of Amyloid-Beta (A-Beta) plaques in the brain are observed. Work from many labs has demonstrated that A-Beta induces neuronal cell death. However, cognitive decline is best correlated with the loss and dysfunction of synapses. Thus, protection of synapses against vulnerability could provide an avenue for early intervention in AD before considerable cognitive decline is evident.

For many years, our lab has been studying the mechanisms that control synapse formation, growth and maturation in the mammalian brain by focusing on the function of a family of secreted proteins called Wnts. We discovered that Wnts promote the formation of synapses during development and are also required for synapse integrity in the adult brain. Studies from our lab and others strongly suggest that A-Beta compromises the function of Wnt proteins. Indeed, we discovered that A-Beta promotes the synthesis of Dickkopf-1 (Dkk1), a secreted Wnt antagonist and this protein mediates the toxic effect(s) of A-Beta on brain synapses. We recently developed a mouse model to study the function of Dkk1. Using these mice, we demonstrated that Dkk1 induces the loss and dysfunction of synapses in the hippocampus, a brain area crucial for learning and memory. Consistently, Dkk1 expression in the adult brain induces long-term memory defects. The proposed programme of research builds upon these findings. Our main aim is to identify molecules that contribute to synapse degeneration induced by Dkk1. We will employ a multidisciplinary strategy that combines cellular, electrophysiological and behavioural approaches to enhance understanding of these devastating pathological processes.

Our studies will lead to a better understanding of the principles that control synapse integrity and the mechanisms that trigger synapse vulnerability. Thus, our findings will permit the development of therapeutic strategies aimed at ameliorating the symptoms and possibly preventing the progression of cognitive decline at the early stages of AD. Our findings would also contribute to the identification of biomarkers for the early detection of AD.

Deficient Wnt signalling has been shown to contribute to Alzheimer's disease (AD). Given the role of Wnts at the synapse, we propose that the secreted Wnt antagonist Dkk1, which is elevated by A-Beta, contributes to synapse failure in AD. Here we will examine the mechanisms responsible for synapse vulnerability and their impact to AD. We address the following specific aims:

1) To investigate the contribution of downstream components of the Wnt pathway in Dkk1-mediated synapse degeneration. Using a candidate approach, we will study key synaptic components of the Wnt pathway, the LRP6 receptor and the scaffold protein Dishevelled-1 (Dvl1). LRP6 is blocked by Dkk1 and has been linked to late onset AD in a genome wide association study. Moreover, Dvl1 is required for excitatory synapse formation and function. Here, we will evaluate the role of these proteins in synapse vulnerability.

2) To identify novel mechanisms contributing to Dkk1-mediated synapse vulnerability. Proteome and transcriptome analyses will be used to identify proteins that contribute to Dkk1-mediated synapse degeneration. Candidate molecules will be selected for functional studies in primary neuronal cultures. In addition, these molecules will be tested for their contribution to Dkk1-mediated synapse vulnerability.

3) To examine the in vivo role of Dkk1 target molecules. The most highly selected candidates identified in our screens will be chosen for in vivo studies. Gain and loss of function of selected candidates will be examined using viral vectors injected into the adult hippocampus of wild-type and transgenic mice expressing Dkk1.

4) To investigate the role of the Dkk1 target molecules in AD models. Behavioural studies will be performed using the most highly selected candidates from our screen to investigate the ability of these new molecules to modulate synapse degeneration in AD animal model.

Who will benefit from this research?

Our research will benefit scientists working on neurodegenerative diseases, synaptic plasticity and synapse biology. In addition, clinical researchers, in particular human geneticists, will benefit by using data generated from our high-throughput screen. Proteins identified in our screen will also inform companies interested in developing targets for the treatment of neurodegenerative diseases and research clinicians working on the identification of biomarkers for the early detection of AD. Ultimately our research program will benefit people suffering from neurodegenerative diseases.
In the long-term, our work might contribute to the early diagnosis and treatment of neurodegenerative diseases. This will have tremendous impact to patients, their carers and the society as a whole by increasing the standard of living of people who suffer from these devastating disorders and also decreasing health care costs.

How will they benefit from this research?

Our program of research will shed new light into the mechanisms that control synapse vulnerability in neurodegenerative diseases. Following the MRC's strategic objective on Genetics and disease, specific genes or proteins identified in our screen will provide invaluable information for the development of better and early diagnosis of AD.
In accordance with the MRC's strategic objective on translation research, our transgenic model (iDkk1 mice) will be beneficial to the pharmaceutical industry to design and test drugs for the protection of synapses in the nervous system.
In the medium and longer term, our studies are likely to contribute to the development of therapies that protect synapses in neurodegenerative diseases but also in other conditions where synapses become vulnerable such as brain injury and stroke.

What will be done to ensure that they benefit?

In addition to publishing in leading scientific journals, we will communicate our results to the scientific community through national and international scientific meetings and seminars.
We will also disseminate our results through our website and funding organisations. Communication with the general public is paramount to inform the public on recent advances in neurobiology and neurodegenerative diseases. We also participate in public events organised by our funding organisations with the aim to inform patients, clinicians and pharmaceutical companies on our recent findings.
We are in the process to initiate collaborations with our colleagues at the Institute of Neurology who plan to establish a drug discovery centre. The aim here is to screen for compounds that modulate Wnt signalling and/or suppress Dkk1 function to protect synapses at early stages of AD.

What research and professional skills will staff working on the project develop which they could apply in all employment sectors?

Scientists working in the project will receive training in a wide range of applicable, state of the art research approaches, which will significantly improve their career prospects and enabling them to apply for independent fellowships and Faculty positions. They will be encouraged to attend national and international meetings. All our staff will be encouraged to take courses offered by UCL on a wide range of courses in communication skills, grant writing, interview techniques and public engagement. They will also participate at public events such as open days at the LMCB (at UCL) and public events held by our funding organisations.

Postdoctoral researchers, undergraduate and postgraduate students and our research technicians in the lab participate at weekly journal clubs and lab meetings. These events enhance their knowledge in our research area, increase their ability to critically evaluate scientific data and improve presentation skills.