Studying the role of TDP-43 induced damage to the VAPB-PTPIP51 ER-mitochondria tethers in fronto-temporal dementia/amyotrophic lateral sclerosis

Alzheimer's disease and related dementias, Parkinson's disease and motor neuron disease are major neurodegenerative diseases that afflict large proportions of our population and exert huge burdens on our healthcare system and economy. There are no cures for any of these diseases and for dementia and motor neuron disease there are not even effective ways of slowing disease progression. There is thus an urgent need to identify new therapeutic targets for treating these diseases.

A number of cellular processes are perturbed in all of these neurodegenerative diseases. These include damage to calcium concentrations in nerve cells, fat metabolism, mitochondria (the energy producers of the cell), transport of proteins and mitochondria within nerve cells, activation of cellular stress responses and alterations to a process termed autophagy which removes damaged proteins from cells. Finally, inflammation is seen in all of these diseases. The conundrum is how damage to all these apparently disparate cellular processes occurs collectively in neurodegenerative diseases. Moreover, the diversity of these damaged features makes devising new treatment strategies difficult; which damaged cellular function should be prioritized as a therapeutic target?

Several recent studies have focused attention on how two components of the cell, the endoplasmic reticulum (ER) and mitochondria, communicate with each other in neurodegenerative diseases. This is because ER-mitochondria communications impact upon most of the cellular processes described above that are damaged in these diseases. We and others have shown that ER-mitochondria communications are perturbed in dementia, Parkinson's disease and motor neuron disease. Importantly, we have identified a mechanism by which ER and mitochondria communicate. It involves binding of the ER protein VAPB to the mitochondrial protein PTPIP51; this binding acts to tether the two cellular components so as to facilitate communication. We have gone on to show that the VAPB-PTPIP51 tethers are damaged in some neurodegenerative diseases.

This project focuses on fronto-temporal dementia (FTD) and amyotrophic lateral sclerosis (ALS). FTD is the second most common cause of presenile dementia after Alzheimer's disease and ALS is the most common cause of motor neuron disease. FTD and ALS are clinically linked with many patients displaying aspects of both diseases. TDP-43 is a protein that is strongly associated with FTD/ALS; abnormal TDP-43 deposits are seen in affected neurons in most FTD/ALS patients and mutations in the TDP-43 gene are the cause of some inherited forms of the disease. TDP-43 is also linked to Alzheimer's and Parkinson's diseases. Notably, we have shown that TDP-43 disrupts the VAPB-PTPIP51 tethers and ER-mitochondria signaling.

The aim of this project is to determine whether damage to ER-mitochondria signaling and the VAPB-PTPIP51 tethers represent pathogenic events that contribute to disease in TDP-43 linked FTD/ALS. The Objectives are:
1. To determine the temporal sequence of ER-mitochondria signaling disruption in some animal models of FTD/ALS. This will reveal whether damage to ER-mitochondria signaling represents an early feature of disease.
2. To determine whether ER-mitochondria signaling is disrupted in human patient derived neurons carrying pathogenic TDP-43 mutations. This will provide clinical relevance to the findings in the animal models.
3. To determine whether correcting TDP-43 induced loosening of ER-mitochondria contacts via overexpression of VAPB or PTPIP51 is protective in cell models.
If we find that TDP-43 induced damage to the VAPB-PTPIP51 tethers is an early disease feature which also occurs in the patient neurons, and that correcting this damage is protective, it will lend strong support for developing drugs which remedy damaged ER-mitochondria signaling in disease.

Fronto-temporal dementia (FTD) and amyotrophic lateral sclerosis (ALS) are major neurodegenerative diseases that are known to be linked. Recently, we and others have investigated ER-mitochondria signaling in FTD/ALS. This is because many functions damaged in FTD/ALS are regulated by this signaling. These studies demonstrate that ER-mitochondria signaling is perturbed by a number of FTD/ALS associated insults. Notably, we have shown that TDP-43, a protein intimately linked to FTD/ALS disrupts ER-mitochondria signaling and that this involves breaking of the VAPB-PTPIP51 ER-mitochondria tethering proteins.

The hypotheses to be tested in the project are that damage to the VAPB-PTPIP51 ER-mitochondria tethers is an early disease feature in TDP-43 linked FTD/ALS and that correcting this damage is protective in disease models. The Objectives are:
1. To determine the temporal sequence of ER-mitochondria signaling disruption in TDP-43 transgenic mice. This will reveal whether damage to ER-mitochondria signaling represents an early feature of disease.
2. To determine whether ER-mitochondria signaling is disrupted in neurons derived from induced pluripotent stem cells from FTD/ALS patients carrying pathogenic TDP-43 mutations. This will provide clinical relevance to the findings in the mouse models.
3. To determine whether correcting TDP-43 induced loosening of ER-mitochondria contacts via overexpression of VAPB or PTPIP51 is protective in cell models of FTD/ALS. This will provide evidence as to whether therapeutic targeting of damaged ER-mitochondria signaling might be beneficial.

The studies will utilise transgenic models of FTD/ALS, iPS cell derived neurons and cell culture models including primary rodent neurons. The cell culture experimental approaches will include manipulation of expression of proteins by transfection and monitoring of phenotypes in all models by biochemical assays and advanced microscopy. All analyses will be performed blinded.

This project is to gain insight into how damage to ER-mitochondria signaling and the VAPB-PTPIP51 tethers contribute to the pathogenesis of TDP-43 linked FTD/ALS. However, ER-mitochondria signaling is disrupted in Alzheimer's and Parkinson's diseases and TDP-43 has also been associated with these diseases. We hypothesise that correcting damaged ER-mitochondria signaling will be therapeutic for FTD/ALS and these other neurodegenerative diseases. Finally disruption to ER-mitochondria signaling is linked to some other diseases such as cancer and diabetes. The beneficiaries of this research and how they will benefit are listed below.
1. Academic scientists and the pharmaceutical industry.
The findings from this research will benefit academic scientists researching into FTD/ALS since it will provide insight into the contribution of damaged ER-mitochondria signaling to the disease process. ER-mitochondria signaling is also perturbed in Alzheimer's and Parkinson's diseases and so the findings will also be of value to scientists working on these diseases. In addition, ER-mitochondria signaling regulates a variety of fundamental cellular functions including calcium homeostasis, phospholipid metabolism, mitochondrial biogenesis, intracellular transport of mitochondria, ER stress, autophagy and inflammation. The research will therefore be of value to researchers working in all of these different disciplines. Our work on ER-mitochondria signaling in neurodegenerative diseases has attracted interest from the pharmaceutical industry who view this signaling as a potential therapeutic target; both AbbVie and AstraZeneca have expressed interest. We have recently concluded MTAs to supply AbbVie with our VAPB and PTPIP51 reagents and AbbVie will use these to screen their compound libraries for small molecules that might correct damaged tethers in dementia. Thus the topic of this research has already generated major interest from the pharmaceutical industry. The knowledge generated on this project will therefore be beneficial to pharmaceutical companies interested in this area of research.
2. Society and the economy. FTD is the second largest cause of presenile dementia and ALS is the most common form of motor neuron disease. The social and economic burdens of FTD/ALS are therefore huge. There are currently no disease-modifying treatments for FTD/ALS or Alzheimer's disease and several recent clinical trials for Alzheimer's disease have failed. There is therefore an urgent need to develop a better understanding of disease mechanisms and to identify new therapeutic targets. The research in this project addresses these issues. In the longer term, the results obtained from this project could therefore have considerable socio-economic impact.
3. Junior scientists.
The post-doctoral researcher employed on the grant will be trained and will develop their skills in a broad range of scientific techniques including advanced microscopy, molecular and cellular neuroscience. He/she will also develop a number of transferrable skills including time management, data analysis, presentation skills and scientific writing. MSc and BSc students from King's College regularly undertake research projects in our groups. Some are likely to choose topics that are linked to this project and these students will obtain training in some of the above research areas. Thus, the project will facilitate training of junior scientists in important scientific areas and techniques.