Molecular basis of artery vein differentiation

Lead Research Organisation: University College London
Department Name: UNLISTED

Abstract

Understanding the mechanisms that control growth and differentiation of blood vessels has important clinical implications. For example, abnormal vascular growth in the retina is a major complication in diseases such as diabetic retinopathy or age related macular degeneration and is the leading cause of blindness in the Western world. However, therapeutic intervention can only be achieved if we fully understand the biological principles of vascular development. Progress has been made in the last decade and some of the basic stop-and-go signals of vessel growth have been identified, but the mechanisms that lead to the complexity and diversity of a fully differentiated vascular tree are not well understood.

In this project we investigate how vessels differentiate into arteries or veins. To this end we use mice that have conditional mutations in certain genes, suspected to play a role in this process. The mutations can be activated with a drug (tamoxifen) allowing us to study the function of these genes at specific time points during development. This will help us to understand why the two vessel types behave differently during development and under pathological conditions. Such knowledge will form the basis for future therapies that target only specific blood vessel types and might allow us to manipulate the shape of the vascular tree.

Technical Summary

The vasculature is a highly organized and complex structure on which each and every cell in the body depends. During development, primitive blood vessels form initially simple plexuses that subsequently remodel and differentiate into mature networks consisting of arteries, veins and capillaries. Understanding the molecular mechanisms that guide this process is highly relevant for therapeutic angiogenesis as well as for antiangiogenic therapy. Recent studies in zebrafish have shown that signaling via Notch and vascular endothelial growth factor (VEGF) plays a role in dorsal aorta and cardinal vein formation (the first vessels to develop), but the factors that control artery vein (AV) differentiation later in development are less well understood. A number of genes, suspected to play a role in AV differentiation, have been knocked out in mice but these experiments suffer from the problem that mutations affecting the vasculature usually lead to early embryonic death precluding the study of vascular differentiation in older animals. Here we address this problem by applying an inducible gene deletion method. We recently created mice that express tamoxifen-inducible Cre recombinase specifically in endothelial cells. When they are crossed with mice that contain loxP sites in a particular gene, tamoxifen injection will delete this gene. Preliminary tests have shown that we can target close to 100% of endothelial cells in postnatal animals. We intend to use this system to delete four different genes, involved in Notch and VEGF signaling. We will address the role of VEGF signaling in AV differentiation by deleting VEGF receptor 2 (VEGFR2) and the artery specific VEGF co-receptor Neuropilin-1. We will also study notch signaling (believed to be downstream of VEGF in AV differentiation) by deleting the artery specific notch ligand Delta-like-4 (Dll4). Furthermore, we have previously found evidence that oxygen levels can influence Dll4 expression in arteries and we will therefore target oxygen sensing in arteries by deleting the von-Hippel-Lindau gene. In summary we aim to establish the role of these four genes in postnatal artery vein differentiation but also possible genetic interactions between them.

Publications

10 25 50
 
Description MRC-KHIDI UK-KOREA PARTNERING AWARD
Amount £20,000 (GBP)
Funding ID MC_PC_17104 
Organisation Medical Research Council (MRC) 
Sector Academic/University
Country United Kingdom
Start 06/2017 
End 05/2018
 
Title Pdgfb-CreER mice 
Description These mutant mice allow the inducible deletion of specific genes specifically in the vasculature. They have been developed and characterized in parts during this grant. 
Type Of Material Model of mechanisms or symptoms - mammalian in vivo 
Year Produced 2007 
Provided To Others? Yes  
Impact The mice have been sent so far to more than 15 labs all of which are still in the process of obtaining data with them. As more and more collaborators are using them the reputation for how well the mice are working is increasing and we are getting an increasing number of requests for them. 
 
Description CNS vascular development 
Organisation Stanford University
Department School of Medicine
Country United States 
Sector Academic/University 
PI Contribution We provided transgenic mice that allow the genetic targeting of the developing CNS vasculature.
Impact 21071672
Start Year 2008
 
Description EC metabolism 
Organisation Max Planck Society
Department Max Planck Institute for Heart and Lung Research
Country Germany 
Sector Public 
PI Contribution supplied transgenic mouse strain and helped write manuscript
Collaborator Contribution Used our strain in combination with other mouse strains to study endothelial cell metabolism during angiogenesis
Impact Manuscript under submission
Start Year 2014
 
Description Role of cell adhesion signalling in retinal vessel development 
Organisation Queen Mary University of London
Department Barts and The London School of Medicine and Dentistry
Country United Kingdom 
Sector Academic/University 
PI Contribution We processed and analysed the retinas from mice that were bred by our collaborators.
Collaborator Contribution The collaboration has helped us to rule out some of the genes we suspected to be involved in artery vein differentiation in the retina.
Impact 20339539
Start Year 2008
 
Description Role of jagged1 in angiogenesis 
Organisation Cancer Research UK
Country United Kingdom 
Sector Charity/Non Profit 
PI Contribution We provided our collaborators with endothelial-specific tamoxifen-inucible Cre mice and they provided us with mice containing a floxed Dll4 allele. The first part of this work has been published, the second part is still in preparation.
Collaborator Contribution providing of mutant mice
Impact 19524514
Start Year 2006