Understanding the function and signalling mechanisms of VEGF-A and VEGF-C in optic chiasm development.

Lead Research Organisation: University of Aberdeen
Department Name: School of Medical Sciences

Abstract

During development, the billions of nerve cells in our brains and eyes must make appropriate connections with correct target regions. This is achieved by the directed guidance of neuronal processes along highly specific pathways, which are laid down by chemical cues. Mistakes made during axon pathfinding from the eye to the brain, for example as a result of loss of eye pigmentation in albinism, result in an impaired ability to see in depth. Moreover, defects in axon pathfinding within the brain have been linked to the development of disorders such as autism and schizophrenia. Understanding how brain and eye connections form normally may also help devise novel strategies for nerve regeneration following injury or damage to the adult nervous system, for example following optic nerve damage or stroke. Recently, we discovered that a molecule best characterised as a growth factor for blood vessels, which is known as vascular endothelial growth factor (VEGF-A), affects nerve wiring between the eye and brain. Specifically, we found that VEGF-A is essential for the routing of nerve processes that extend from each eye into the opposite brain hemisphere to help us see objects in depth. More recently, we discovered that a related molecule called VEGF-C also affects nerve wiring between the eye and brain. We now seek funding to determine the precise role of VEGF-C in this process, to investigate how VEGF-A and VEGF-C cooperate in establishing the wiring that is necessary for normal vision, and to establish how their signals are transmitted within the nerve cables. This research will advance our understanding of normal brain wiring and, in the future, will likely advance the development of clinical therapies that promote repair and regeneration following damage to the eye and its brain targets.

Technical Summary

The segregation of retinal ganglion cell (RGC) axons at the optic chiasm into contralateral and ipsilateral projections is a process essential for stereovision and an excellent model system to investigate axon guidance decisions. We have demonstrated recently that the VEGF164 isoform of the classical angiogenic factor VEGF-A binds its receptor neuropilin 1 (NRP1) on RGC axons destined for the contralateral optic tract to help them cross the optic chiasm. Our pilot data suggest that a related molecule known best for its function in the lymphatic vasculature, VEGF-C, also directly regulates axon guidance at the chiasm midline. We now wish to extend these findings to identify the precise role of VEGF-C and its main receptor, VEGFR3 at the optic chiasm and to establish if co-operative interactions between VEGF-A and VEGF-C are important for establishing stereovision. We further wish to understand how NRP1 transmits the VEGF-A signals that control RGC axon guidance. We already know from our pilot experiments that NRP1 requires a co-receptor to transmit VEGF-A signals in RGCs and that this co-receptor is neither of the classical vascular VEGF-A receptors, VEGFR1 or VEGFR2. We will use a combination of expression, genetic, functional and biochemical assays to identify the NRP1 interacting protein(s) that convey VEGF-A signals in RGCs. The proposed programme of work will advance significantly our understanding of the mechanisms that establish stereovision and provide fundamental information on the role of classical vascular factors in neural circuit formation.

Planned Impact

This project will significantly enhance our knowledge of the developmental processes that establish functional brain wiring patterns. Beyond their interest to the academic community, the results will impact on several other identifiable beneficiaries:

Commercial private sector: Because this work will identify novel functions and signalling pathways of VEGF family proteins in neurons, the results are likely to be of interest to the commercial sector involved in developing novel therapeutics for patients with neurodegenerative disorders or neurological injury, as they may be able to capitalise on this new knowledge. For example, companies marketing VEGF-A therapies for other purposes may consider that VEGF-A therapies have new applications in regenerative medicine, or identify VEGF-C as a new commercial target. Accordingly, this project is likely to contribute new knowledge that will lead to more translational research in the medium term, and may benefit regenerative and repair medicine to impact positively on public health in the UK and abroad in the long term. The fields of neurodegenerative disorders and neurological trauma in particular are areas of unmet clinical need with high social and economic importance.

Public: An immediate impact of this project is its opportunity to raise awareness and understanding of science and research through public dissemination of novel findings and explaining their significance. Knowledge of the developmental processes sculpting normal brain and eye development is key to understanding how we carry out everyday tasks, such as those that involve sight, sound, smell, learning and memory, etc. Studies of the mechanisms controlling axon growth and pathfinding will also improve the public's understanding of the origins of neurodevelopmental disorders that have been linked to deficits in brain wiring patterns. These topics will be incorporated in outreach activities to engage with the public about this work.

UK and International Research Base: By endowing researchers with both project specific and transferable skills, this project will lead to highly skilled workers that will benefit the UK's economic competitiveness. The project will also lead to new international collaborations and therefore enhance knowledge transfer and increase the international profile of our Universities.

Publications

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Bruce FM (2017) DSCAM promotes axon fasciculation and growth in the developing optic pathway. in Proceedings of the National Academy of Sciences of the United States of America

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Erskine L (2014) Connecting the retina to the brain. in ASN neuro

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Herrera E (2019) Guidance of retinal axons in mammals. in Seminars in cell & developmental biology

 
Description We have gained greater understanding of the mechanisms that control co-patterning of developing nerve and blood vessels in the forming brain, and the importance of interactions between nerves and vessels for normal brain morphology and function. Specifically we have:
1. Identified which of the different forms of VEGF-A (vascular endothelial growth factor-A) are sufficient for VEGF-A signalling in neurons. Whilst it was already known that VEGF164 can act directly on neurons to promote normal development, we now identified a role for VEGF188 that had not been demonstrated previously. This work has been published. This work is important, as VEGF188 binds more tightly to tissue than VEGF164 and might therefore be a more suitable therapeutic reagent for use in regenerative medicine and tissue engineering strategies.
2. Demonstrated that VEGF-A receptor neuropilin-1 is required autonomously in retinal neurons for the normal development of the optic pathway. Together with our previous work, this finding provides direct evidence that the classical angiogenic factor VEGF-A can act directly on neurons to sculpt brain wiring patterns. A manuscript describing these findings is in preparation.
3. Demonstrated that VEGF-A indirectly affects brain wiring patters through its role in orchestrating vascular patterns in the brain. This work has advanced our understanding of the mechanisms that control vessel ingression into the developing brain. Moreover, by providing novel insights into the interactions between nerves and vessels during normal development, our work may help advance the development of more effective regenerative strategies. A manuscript describing these findings is in preparation.
4. Investigated the importance of another VEGF family member termed VEGF-C for normal brain development. We have found that VEGF-C in combination with VEGF-A is important for normal axon patterning and morphology of the developing brain. The finding that VEGF-C in combination with VEGF-A is essential for normal development of brain structure was unexpected, and we have established a collaboration with Dr Jean-Leon Thomas at Yale University, an expert on VEGF-C signalling in neural stem cells, to further investigate this novel finding.
5. Investigated the signalling mechanisms of VEGF-A in neurons. Our previous work had demonstrated that the mechanisms underlying VEGF-A signalling in neurons are distinct from endothelial cells. We also had shown that the VEGF-A receptor neuropilin-1 is essential for VEGF-A signalling in retinal axons and that neuropilin-1 requires a co-receptor for VEGF-A signalling in these cells. We have screened a range of potential co-receptors for neuropilin-1 and identified several possible candidates that we are now validating. We also have identified potential downstream targets of neuropilin-1 that are essential for VEGF-A-dependent patterning of neuronal connections, which we also are now validating. Through identifying the differences in signalling mechanisms of VEGF-A in neurons versus endothelial cells this work may aid in the development of pro- and anti-VEGF-A therapies that can be targeted to these distinct cell types. A grant application is now in preparation to continue this work.

In summary, work funded by this grant has allowed us to publish one manuscript, with several additional manuscripts in the pipeline. We also have published several review articles, presented this work at conferences and participated in a number of public engagement events to disseminate out findings. The staff funded by this grant have also helped to engage and train the next generation of scientists (see relevant sections).
Exploitation Route There are a number of potential beneficiaries of this work:
1. Our findings will be a broad interest to academics working in the fields of axon guidance, VEGF signalling in the nervous system, vascular development and regenerative medicine and may be used by researchers in these and other fields to drive their work forward.
2. Our findings will be of interest to the lay public and may be used to generate greater understanding of normal brain development, in particular the importance of interactions between developing nerves and vessels for establishment of normal brain structure and function.
3. As outlined above, our finding may be utilised by the commercial sector to aid in development of novel or more effective therapeutics and tissue engineering strategies for patients with neurodegenerative disorders or neurological injuries.
Sectors Communities and Social Services/Policy,Education,Pharmaceuticals and Medical Biotechnology

 
Description Our findings have been used in public engagement events to further the general publics understanding of the mechanisms controlling normal brain development and how this inforamtion may be utilised to develop therapies for repair following brain injury or disease. We also have used the findings from this study to engage with and provide training to school children and encourage them to consider careers in science.
Sector Communities and Social Services/Policy,Education
Impact Types Societal

 
Description Collaboration with Dr Jean-Leon Thomas 
Organisation Yale University
Department School of Medicine
Country United States 
Sector Academic/University 
PI Contribution We have entered into a collaboration with Dr Jean-Leon Thomas sat Yale University to study the role of VEGF signalling in neuronal development. Through work funded by the grant we have identified an essential role for VEGF-A and VEGF-C in sculpting normal brain formation. Dr Thomas is an expert in VEGF-C signalling in neural stem cells, and we will work in collanoration to futher investigate this novel finding.
Collaborator Contribution Assistance with analyses, intellectual contribution, contribution of reagents.
Impact Novel information on the role of VEGF-C and VEGF-A in neuronal development.
Start Year 2015
 
Description Bring your own brain public engagement event 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? Yes
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact Talk to the general public on my work as part of Brain Awareness/National Science and Engineering week.

Provided general public with greater understanding of the processes underlying normal brain development, and how this can sometimes go wrong.
Year(s) Of Engagement Activity 2013
URL http://www.abdn.ac.uk/events/4082/
 
Description Lab in a Lorry 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach local
Primary Audience Schools
Results and Impact Science communicaiton event aimed at High School children

no actual impacts realised to date
Year(s) Of Engagement Activity 2014
 
Description Nuffield Research Placement 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? Yes
Geographic Reach Regional
Primary Audience Schools
Results and Impact Supervision of school pupils undertaking a full-time 5-6 week summer research project funded through the Nuffield Research Placement Scheme.

Students gained a greater understanding of what it is like to work day-to-day in a research lab, and plan their own projects. This experience has heped them make a decision about their future career choices, with several going on to study science at University.
Year(s) Of Engagement Activity 2012,2014
URL http://www.nuffieldfoundation.org/nuffield-research-placements
 
Description Providing work experience for 4th year school pupil 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Schools
Results and Impact Supervised 4th year High School pupil undertaking a 1 week project in my laboratoy to gain experience of working in a science environment.

Stuendt is now actively considering a career in science
Year(s) Of Engagement Activity 2014
 
Description Providing work experience for 5th year school pupil 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Schools
Results and Impact Supervised 5th year High School pupil undertaking a 3 week project in my laboratoy to gain experience of working in a science environment.

Student applied for and was accepted to study Biomedical Science at University.
Year(s) Of Engagement Activity 2013
 
Description Public engagement by Dr Bruce 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? Yes
Geographic Reach Regional
Primary Audience Schools
Results and Impact Participation in Science in a Lorry Scheme over a 3 day period.

Increased interest in science amongst participation students.
Year(s) Of Engagement Activity 2013
URL http://www.labinalorry.org.uk/
 
Description Seminar at the University of Edinburgh 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Participants in your research or patient groups
Results and Impact Research seminar given at the Centre for Integrative Physiology at the University of Edinburgh

no actual impacts realised to date
Year(s) Of Engagement Activity 2012
 
Description Supervision of 5th year work experience students 
Form Of Engagement Activity Participation in an open day or visit at my research institution
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Schools
Results and Impact 4 5th year school pupils worked full timein my lab for 1 week as part of their work experience. This gave them a better understanding of what a career as a scientist invovles, and will aid in their choice of University courses career selection.
Year(s) Of Engagement Activity 2016
 
Description Talk to Scottish Rugby Union 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Supporters
Results and Impact Communication of research to chairman and staff of Scottish Rugby Union

Funding provided by Scottish Rugby Union and Private Donor to support ressarch into nerve repair and regneration at the University of Aberdeen.
Year(s) Of Engagement Activity 2012
URL http://www.abdn.ac.uk/news/6110/
 
Description Undergraduate summer projects 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Undergraduate students
Results and Impact Supervision of undergraduate students undertaking full-time summer research projects in my lab. Some students wree funded (e.g. By ttHe Wellcome Trust), others worked voluntarily. 2 students ere supervised in 2013, 1 in 2014.

Students gained a greater understanding of what a research career in science would entail. Both students supervised in 2013 have now gone on to study for a PhD in Biomedical Sciences (one in USA, one in Bristol).
Year(s) Of Engagement Activity 2013,2014