Interaction of Rab8 with OCRL1: Synaptic growth function in Frontotemporal Dementia and the Neurodevelopmental Disorder Lowe Syndrome

Frontotemporal dementia (FTD) causes a devastating dementia that strikes around 55-65years of age. This disease accounts for a significant percentage of pre-senile dementias and is a considerable burden on society, in terms of care and costs. In a search for genes that drive the progression of the disease, we found two genes, Rab8 and OCRL1. These genes have been proposed to act together, though the reason and purpose is not known. The OCRL1 gene is known to be dysfunctional in another disease known as Lowe Syndrome (LS). Mutations in OCRL1 lead to cataracts, kidney dysfunction and impaired mental function. This makes our study of fundamental importance to our understanding of both FTD and LS. Until now, study of both of these genes has been difficult in other genetic systems (mouse and zebrafish) due to genes with closely related function being present in the animals and causing redundancy. We are using Drosophila, the fruit fly, because of the advanced genetics that we can use with this organism and because it has a functioning nervous system that we can readily study. We have made mutants in the fly versions of OCRL1 and Rab8 and these mutants have interesting neurological defects. Using our mutants, we can study the function of OCRL1 (important for understanding LS) and the function of Rab8 in the nervous system and this will inform us of events occurring in neurons of FTD affected individuals. We can also use these mutants to understand how the two genes interact, furthering our understanding of FTD. Our labs in Manchester and York are in touch with the Alzheimer's Society and the Lowe Syndrome Trust where we communicate our work. We also interact with schools and run practical classes to demonstrate how fun and effective our experiments can be. Our study is therefore critical to our understanding of two important diseases affecting our society, FTD and LS.

In a genetic screen for enhancers and suppressors of a Frontotemporal Dementia related phenotype in Drosophila, we have identified two regulators of membrane traffic (Rab8 and OCRL1) that are known to physically interact. The physiological and cell biological consequence of the interaction between Rab8 and OCRL1 are as yet unknown. Rab8 is a small GTPase and a known regulator of membrane traffic at the Golgi and recycling endosome. Mutations in OCRL1 give rise to the neurodevelopmental condition Lowe Syndrome (LS). OCRL1 is a phosphoinositide phosphatase known to interact with many Rab proteins, endocytic proteins and actin cytoskeleton regulators to effect changes in membrane traffic. Due to issues of genetic redundancy, studies of Rab8 and OCRL1 have been hampered in model organisms to date. In Drosophila there are no redundancy issues for Rab8 or OCRL1. Using the advanced genetic toolbox of Drosophila we have identified mutants in Rab8 and OCRL1 and are now in a position to study:

1) the physiological, anatomical and cell biological consequence of loss of Rab8 function in neurons,
2) for the first time, study the cell biological, anatomical and physiological consequences of loss of OCRL1 function in neurons (and the whole organism),
3) the physiological role for the Rab8 interaction with OCRL1 in a whole organism. We have already observed dysregulation of TGF-beta and JNK/AP1 signaling at the larval neuromuscular synapse of Rab8 mutants.

Our focus will be on the role of these two important proteins in regulation of membrane traffic at the synapse. This study will inform our understanding of membrane traffic in FTD and LS affected neurons.

Who will benefit from this research?: The proposal is a fundamental research investigation of cellular mechanisms of importance to Frontotemporal Dementia (FTD), Lowe Syndrome (LS) and an understanding of membrane traffic (particularly in neurons). It is of importance therefore to four main constituencies:
1) Dementia patients, their carers and dedicated health professionals.
2) Individuals affected by LS, their carers and dedicated health professionals,
3) Academics involved in the understanding of membrane traffic,
4) Academics and health professionals involves in the study of neurodegenerative disease.

We have put in place the following strategies to maximise impact for the duration of the grant:

Communication with Stakeholders:
A) Contact with the Alzheimer's Society (AS) and Lowe Syndrome Trust. AS funds fundamental research into causes and therapies for Dementia in general. In addition they fund telephone helplines, support groups and community events for Dementia patients, families and carers. They have an extensive lay membership and public outreach. STS is in communication with AS to inform them of the progress and outcome of our FTD related study. Opportunities to engage with the patient and lay communities will be sought at every opportunity.
ML has for many years communicated with the LS UK charity to engage with patients and affected families. This continues to generate contact with health professionals dealing with LS. These activities will continue for the duration of the grant.

B) Academic Communication: We will work where possible through publication in Open Access journals, or pay premiums with journals for open access where this service is offered. We will aim for journals with the highest impact and eigen factors to ensure maximum readership, particularly seeking broad subject journals to ensure the widest readership. We will attend and publicise our work at prominent conferences and meetings in the Dementia, neurodevelopmental and membrane trafficking fields, through posters and talks. The PDRA will be encouraged to talk at meetings to generate profile for the study and their own career progression. Genetic strains and DNA constructs will be disseminated freely, or lodged in not-for-profit stock centres that allow ready (and cheap) purchase. Our Drosophila data will contribute to Flybase entries.

Public Communication. Both STS and ML are well versed with speaking on local radio, both having done so on more than one occasion in the past. Both labs have active schools outreach events that run regularly, both to schools and the public. Such activities are positively encouraged by both Manchester and York Universities. We will use our departmental and laboratory public facing websites to highlight our findings. We will use (as we have done effectively in the past) University press officers to communicate with the press and disseminate news rapidly.

Technological Training and impact: Both PDRAs will be trained in the skills and techniques required for the study. They will be encouraged to give talks locally and internationally to publicise their work. This will help career progression and profile.

Creating Industrial Impact: We are aware that at this point we have a fundamental study that would be difficult to transfer to translational impact. However, throughout the course of the grant we will continually review our data and its implications for potential translational impact and industrial interaction.

These strategies we have in place to ensure maximum impact strategically, scientifically and societally for the results of our proposed study.