Defining a novel molecular mechanism in VEGF-induced vascular hyperpermeability

Blood vessel disease can cause blindness, lung dysfunction, stroke and heart attacks, either because poor blood flow starves tissues of oxygen and nutrients or because blood vessels in oxygen-starved tissues are often leaky and thereby cause tissue swelling and promote inflammation. The therapeutic stimulation of new vessel growth with the growth factor VEGF is a promising treatment for these conditions. However, a side effect of stimulating blood vessel growth with VEGF in adults is increased blood vessel leak that impairs organ function, especially if it occurs in the heart, brain, eye and lung. To understand the mechanism through which VEGF causes either blood vessel growth or blood vessel leak, we have altered its ability to signal through a molecule termed NRP1, which conveys signals from VEGF into the endothelial cells that form the inner lining of blood vessels. Our pilot experiments suggest that NRP1 can be targeted in a specific way to block blood vessel leak without affecting blood vessel growth. To identify the mechanism through which NRP1 causes blood vessel leak, we will alter its function in experimental models that affect eye, skin or lung vessel function and use tissue culture models of endothelial cells to define NRP1's interactions with other signalling molecules that play key roles in vascular leak. Our findings will provide key information on how vessel leak might be stemmed in acute and chronic diseases with dysfunctional blood vessels. This research will not have an immediate clinical impact, but may help other researchers to design better therapies that can stem vessel leak and allow the stimulation of new vessel growth without increasing tissue swelling.

Stimulating therapeutic blood vessel growth with the angiogenic growth factor VEGF is considered a promising treatment for ischemic diseases that significantly impact on human health. However, VEGF also causes excessive vascular permeability and thereby promotes tissue oedema. The VEGF receptor NRP1 is essential for vessel growth through angiogenesis and arteriogenesis, but has also been implicated in vascular hyperpermeability. We previously generated mice expressing a truncated NRP1 protein that retains only the transmembrane and extracellular domains, but lacks the cytoplasmic domain. We reported that these mice have normal angiogenesis, but reduced ischemic arteriogenesis. Our unpublished observations show that these mice are also defective in VEGF-induced vascular permeability, even though the NRP1 cytoplasmic domain is thought to lack signalling capacity. Our pilot data additionally show that the only known binding partner of the NRP1 cytoplasmic domain is dispensable for VEGF-induced vascular leak, suggesting that NRP1 promotes vascular permeability in a mechanism that remains to be identified. Our pilot data also show that loss of the NRP1 cytoplasmic domain attenuates vessel leak in an experimental model of inflammatory disease without perturbing neoangiogenesis. We will combine the use of primary endothelial cells for cell and biochemical studies and small molecule inhibitor screening with vascular permeability assays in skin, eye and other organs of wild type and mutant mice with defective VEGF and NRP1 signalling to define molecular differences in the NRP1-mediated signalling pathways that distinguish VEGF-induced vascular permeability from VEGF-induced angiogenesis and arteriogenesis. We will also examine if perturbing VEGF-induced permeability impacts on leukocyte extravasation. These experiments will establish whether the NRP1 cytoplasmic domain is a novel therapeutic target for the treatment of tissue oedema and inflammation in ischemic disease.

Our research will provide fundamental scientific advances with a range of potential beneficiaries in the academic, commercial and public sectors. To maximise engagement with these stakeholders and deliver the widest possible impact for our findings, we will pursue the following objectives in addition to those listed in the section on academic beneficiaries:
1. Contribute to the economic competitiveness of the UK through enhancement of researcher career development.
2. Investigate potential commercial exploitation of the research outcomes.
3. Promote greater public understanding of science through public engagement activities.
4. Establish formal links with clinicians to translate our findings into therapeutic tools.

The training of researchers impacts on the economic competitiveness of the UK through provision of highly skilled individuals. In addition to training in laboratory techniques, the named researchers will be trained in transferable skills, such as effective communication, team working, networking, personal effectiveness, entrepreneurship and career planning through UCL's Research Staff Development Programme to provide necessary skills for employment in academia and other sectors.

To pursue potential transferable or commercial opportunities emerging from our work, we will seek assistance from UCLB, a UCL subsidiary responsible for protecting and commercialising intellectual property rights arising from research carried out at UCL. Opportunities for commercialisation will be reviewed regularly throughout the project, both with UCLB and directly with potential industrial partners, in particular those with existing links to the UCL Institute of Ophthalmology.

An immediate impact of this project is its opportunity to raise awareness and understanding of science and research, and we will engage with the public in the following ways: We will publish the results from this project in high-impact journals with open access-compliant policies to maximise the availability of our research; we will promote the findings of our studies on our University web page; we will liaise with the UCL Press Office and the MRC media service to disseminate our findings through public websites and national media; we will engage with secondary school children by providing work experience placements through existing links with schools to foster inquisitive minds and inspire a next generation of researchers.

The project is highly relevant to clinical medicine. To enable potential clinical exploitation, we will publish results in a timely manner and present at national and international conferences attended by scientists and clinicians; and we will seek collaborations with clinicians to advance new strategies for translation. Key to achieving this objective is Professor Ruhrberg's location in an environment of academic-health sciences partnerships between UCL and four NHS hospital trusts, such as, but not restricted to, the National Institute for Health Research Biomedical Research Centre in Ophthalmology of UCL and Moorfields Eye Hospital.