IDENTIFICATION OF A NOVEL ANGIOPOIETIN 2 SIGNALLING CENTRE IN THE EMBRYONIC HAEMATOPOIETIC STEM CELL NICHE

Blood stem cells, also known as haematopoietic stem cells (HSCs), are found in adult bone marrow and they give rise to practically all blood cells throughout the entire lifespan. For many years, transplantations of HSCs have been used (~50,000 patients/year worldwide) to restore normal blood formation in patients with blood disorders and cancers. However, there is a significant shortage of donors, only 20-60% of patients on registers find a good genetic match for transplants, which affects treatment options, efficiency and outcomes. There is therefore an urgent need to find alternative sources of HSCs. One solution would be to produce HSCs in the laboratory from other readily available cell types, such as pluripotent stem cells, which are capable of producing any cell type in the body. This approach holds great promise for regenerative medicine, but currently generating HSCs in the laboratory remains a big challenge, mainly because, despite being of fundamental importance for medical sciences, we have only limited understanding of how HSCs first emerge during embryonic development.
Our recent analyses have revealed a novel signaling centre, Angpt2, which we found to be a strong stimulator of HSC emergence in the mouse embryo. We observed a similar expression pattern of this factor in the human embryo, suggesting it could be an important HSC regulatory centre, which has not been described before. In this project, we will use cutting-edge techniques, including cell purification, gene expression profiling, advanced imaging, bioinformatics and transplantations, to perform a detailed investigation into the role of Ang2 signaling in driving HSC emergence in the embryo. Using novel image-based spatial correlation methods we will build the first 3D digital model of this signaling centre in mouse and human embryonic HSC development. These 3D models and associated datasets will be a valuable resource for the research field. We will further test if Angpt2 can enhance haematopoietic cell/ HSC production from pluripotent cells. In the long term, this could help development of protocols to produce HSCs in the laboratory to meet the shortage of HSCs in the clinic.

Transplantations of haematopoietic stem cells (HSC) have been used in the clinic for several decades to treat various blood disorders. However, a significant shortage of donors for some patient groups means there is urgent need to find alternative sources of HSCs. A key goal of current haematology is the search for methods to efficiently produce HSCs in the laboratory. Pluripotent stem cells hold great hope for regenerative medicine, but generating HSCs from them remains a significant challenge, mainly since our current understanding of the mechanisms driving HSC development, particularly in human, is still extremely limited. Understanding how HSCs form in the embryo will be crucial in defining efficient protocols to generate HSCs in vitro.
Our recent global transcriptome analysis revealed a novel signaling centre, Ang2, in the mouse aorta-gonad-mesonephros (AGM) region which we found is a strong stimulator of HSC development. We also observed a similar expression pattern in the human AGM region, suggestive of a previously undescribed important HSC regulatory centre. We propose a detailed investigation into the role of Ang2 signaling in human and mouse HSC development, using a combination of cutting-edge techniques including gene expression profiling of sorted cells, confocal immunophenotyping and loss/gain-of-function experiments followed by functional assays. To explore potential links with intra-aortic clusters in which HSCs form, we will use novel image-based spatial correlation analysis to create the first 3D models of the Ang2 signalling centre in the mouse and human AGM region. These and associated datasets will be a valuable resource for the research field to inform further functional studies. We will test whether Angpt2 can enhance haematopoietic differentiation of mouse and human ES cells. In the long term this could help development of a protocol for generating bone fide HSCs from pluripotent cell sources to meet clinical demands.

Health Impact
One of the key goals in haematology is to find alternative sources of haematopoietic stem cells (HSCs), which are routinely used in the treatment of blood disorders and cancers, but are in short supply. This project will help us gain a deeper understanding of how HSCs are formed in the body and will test the effects of a novel, previously undescribed, signaling centre on haematopiesis in vivo and in vitro. In future, this could lay the foundation for protocols to generate HSCs in the laboratory to meet the shortage in the clinic, as well as improve transplant safety and efficiency. In the long-term these potential outcomes, including improved treatment options, patient outcomes and public health, would have highly positive societal and economic impacts.

Societal Impact
The bioinformatics datasets, functional data and 3D models generated during this project will be rich resources for the global research community, and will provide important insights into fundamental biological processes. As such, this will be of interest to and benefit the wider public as well as patients, clinicians, science communicators, teachers and pupils. The visual and interactive nature of the 3D digital models lend themselves to public engagement and these will help to stimulate discussion and promote public understanding of regenerative medicine and the fundamental processes involved in blood formation. In the longer term these types of output and activities could inspire a new generation of researchers and medics.

Economic Impact
This project will support the training of highly skilled scientific researchers, who will be a highly desirable contribution to the workforce of the science sector and, through continuing to strive for scientific advances, will give lasting economic benefits. Collaborations with leading experts will strengthen multi-disciplinary and international collaborative links. Positive research findings could attract further funding, promote investment and potentially yield exciting commercial opportunities. Translation of the research into the clinic would require specialised teams of experts to build on results and implement fully GMP compliant strategies. These potential long term impacts would not only advance healthcare, but would also benefit the private sector, support the economy and create jobs.