Regulation of RhoGTPase signalling at endothelial junctions and blood vessel integrity

Endothelial cells form a single layer of cells, lining the walls of blood and lymphatic vessels. Individual endothelial cells interact with each other via molecular complexes that mediate adhesion but also function as sensors that transmit information about the environment, such as the presence or absence of neighbouring cells, to the cell interior. Development and function of blood vessel requires endothelia to form functional cell-cell junctions that mediate adhesion and restrict trafficking of cells and molecules along the space in between neighbouring cells. These junctions are essential for blood and lymph vessel integrity, and are highly regulated to enable dynamic developmental processes, such as the growth of new vessels, or during physiological and pathological conditions that can affect vessel wall integrity. Deregulation of endothelial cell junctions occurs in different diseases, such as diabetes or inflammatory conditions, and can lead to vessel leakage or rupture (e.g., haemorrhagic stroke).

This proposal focuses on the identification of molecular mechanisms that regulate endothelial dynamic behaviour via cell-cell junctions and the importance of such mechanisms for blood vessel growth and vascular stability. Our unpublished data indicate that a protein that we previously identified in another cell type is also expressed in endothelial cells and regulates formation of cell-cell junctions and expression of functionally important endothelial genes. We have evidence that this protein is crucial for normal mammalian development and a functional cardiovascular system. Deficiency of this protein leads to internal bleeding and as well as defects in abdominal closure that are reminiscent of a human inherited disease.

The overall aim of this proposal is to understand the role of p114RhoGEF in endothelial cells during normal development and for the function of the vascular system. We also propose experiments designed to determine how this pathway that stabilises cell-cell junctions is regulated with the aim to target this signalling mechanism in the future for possible therapeutic intervention for diseases that lead to vascular leakage.

Knowledge of how cells sense their neighbours and transmit such information to the cell interior is not only important for the understanding of fundamental processes as they occur during the development of the vasculature, organs and tissues, but also to comprehend how different diseases interfere with the normal functioning of our cells. Hence, identifying new mechanisms that guide cell behaviour in response to contact with neighbours will help us to think of new ways to counteract vascular leakage and to treat wide-spread diseases such as cardiovascular conditions, age-related diseases such as diabetes and cancer.

Endothelial cells line the walls of blood and lymphatic vessels. Angiogenesis, vessel integrity and endothelial homoeostasis require endothelial cells to form functional cell-cell junctions. Tight junctions are one of those cell-cell junctions and can be intertwined with adherens junctions in endothelia. This proposal focuses on the role of endothelial tight junctions in blood vessel stability and endothelial homeostasis. We have identified a Rho signalling pathway that is centred on a guanine nucleotide exchange factor that drives junctional actomyosin activation. Our preliminary data indicate that this pathway regulates endothelial junction assembly in vitro and expression of functionally important endothelial genes, and is required for normal development in mouse, a developmental defect that involves vessel stability defects leading to haemorrhages. Our hypothesis is that this Rho signalling pathway regulates junctional actomyosin, endothelial differentiation, vasoprotective responses, and, thereby, epithelial homeostasis and vessel integrity. Aim 1 is to determine the role of this signalling mechanism in endothelial processes and cell-cell tension important for endothelial function and angiogenesis, and employ in vitro angiogenesis models. We also aim to determine how this pathway is regulated and how it affects expression of identified candidate genes and endothelial differentiation. Aim 2 will be to test the in vivo relevance of these findings using loss of function mouse models. Hence, we expect these studies to disclose the role of this Rho signalling mechanism in development and its importance and function in cardiovascular development and vessel integrity. The expected results will be important for the understanding and the development of therapeutic applications for diseases that lead or involve blood vessel leakage, such as diabetes, age-related diseases and inflammation, and haemorrhagic stroke.

Who will benefit from this research?

The immediate beneficiaries will be scientists working in allied fields ranging from developmental biology, tissue engineering, and cardiovascular biology. However, the project is likely to impact medical researchers and translational scientists working on therapeutic applications for various diseases including age-related epithelial degenerations, congenital defects associated with ventral folding morphogenesis, cardiovascular conditions, or diabetes-induced epithelial and endothelial malfunctions. Diseases such as diabetes and age-related conditions represent an increasing burden for the NHS and our society. Hence, insights into the biology and function of endothelial cell junctions will benefit medical scientists, clinicians and, ultimately, patients as well as the NHS and the general public.


How will they benefit from this research?

The research will benefit allied scientists by providing them with the molecular details of a new mechanism that links cell-cell adhesion to the regulation of endothelial cell and tissue dynamics that they can then test in their respective model systems. Translational scientists will benefit in a similar way. In our own research environment, these results can be used to understand many pathological processes that lead to or involve vascular dysfunction, leakage and ruptures. Examples are diabetes, inflammation and haemorrhagic stroke as well as vascular dysplasia and fragility in cerebral cavernous malformation and Clarkson disease (systemic capillary leakage syndrome), a lethal blood vessel disease that has been recently linked to polymorphisms in the p114RhoGEF. This project will also benefit scientist that develop new approaches for tissue engineering and transplantation. Clinicians and patients will then benefit in the longer term by the availability of new approaches to treat common diseases.

The project will also involve training of a postdoctoral fellow that can benefit the private sector as well as public services through the NHS.

The expected results are likely to start to benefit other scientists within the lifetime of this grant.