Role of Complement in Neural Crest migration and craniofacial development

Craniofacial disorders are a primary cause of infant mortality and have serious lifetime consequences, devastating for both children and parents. Craniofacial malformations are usually recognized as abnormalities in the underlying structure of the face, such as anomalies in bone and cartilage development. Facial bones and cartilages originate from a cell population called the neural crest, which migrates from the back of the head to form the face during embryonic development. Therefore, craniofacial disorders are usually attributed to problems in neural crest development. There is a large variety of craniofacial anomalies which have a genetic origin but in only a few cases have the mutated genes been identified. Moreover, only in an extremely small proportion of these cases is the function of the affected gene known. In this project we propose to use animal models that are amenable to genetic dissection to study genes that are potentially involved in craniofacial malformations. The data generated in this project will be directly used in subsequent research to test whether mutations in equivalent genes lead to craniofacial anomalies in humans. In order to find these new genes we have extrapolated knowledge from other systems in which cell migration is better understood, as the immune system. Our preliminary data suggests that a well characterised immune response pathway, called complement, may play a key role in neural crest migration. The complement cascade is used by the immune system to control infections and destroy microbes. Our observations show that mutations in specific elements of the complement cascade lead to dramatic defects on neural crest migration. In this project we propose to identify the cellular and molecular mechanisms by which these factors control neural crest development. In spite of complement deficiencies being a relatively common problem in patients, the role of this system in embryonic development, let alone in craniofacial disorders, has been completely neglected. This will be the first time to implicate complement factors in the early phases of development, before any blood or vessels are present in the embryo. Understanding the role of complement in neural crest migration will be a prelude to understanding the origins of some congenital craniofacial defects, and will open the possibility to develop prevention strategies and repair therapies. Importantly, the demostration that the complement system plays a role in normal cranofacial formation will have a profound impact in health policy. The results from our research may suggest that pregnant women should avoid complement inhibitors treatments (to treat autoimmune diseases) during early gestation. These could have devastating consequences for the child, equivalent to the use of thalidomide in the past.

Collective cell migration is a widely recognized mode of migration during embryogenesis and cancer; however, it is not known how mesenchymal cells, which have reduced cell adhesion, are maintained as a cohesive group during migration. By using cephalic neural crest as a model for collective migration we will test the hypothesis that these cells are kept together by a mechanism of mutual attraction. Studying cephalic neural crest migration will also help to understand the origin of craniofacial abnormalities, a devastating phenotype that leads to birth defects and spontaneous abortion. In order to find novel molecular components implicated in neural crest migration we have examined molecular pathways that control migration in the immune system, where cell migration is better understood. We will focus on the complement system; central to this pathway is the C3 factor, a precursor of the chemoattractant C3a. We will analyze the cellular and molecular mechanisms by which C3a controls neural crest collective cell migration. We will test whether C3a is required for mutual attraction between cells; as alternatives we will analyze whether C3a controls cell adhesion or modifies the response of other known neural crest chemoattractant, Sdf1. The role of the complement cascade in neural crest development will be highly novel as no activity has been described for this system during early embryonic stages, before any blood or vessels are present. The results obtained here could be extrapolated to other migratory systems such as cancer and immune cells. In subsequent research we will use the information generated in this project to screen for craniofacial anomalies in human patients with complement deficiencies. Our hypothesis could have important consequences for human health, as it may suggest the avoidance of complement inhibitors to treat immune diseases during pregnancy.

Who will benefit from this research?
The direct beneficiaries will be the whole community, health policy makers, clinicians in the areas of birth defects, cancer and immunology.

How will they benefit from this research?
1. Birth defects: The rate of birth defects in England is 1.1% (UK Health Research), and many of these defects are related to neural crest derivatives. Understanding how neural crest migrates during embryo development will help to develop diagnostic and therapeutics tools for birth defects associated to a failure in neural crest migration. It is important to mention that several trials have been preformed to test complement inhibitors in their efficacy to treat immune disease; however pregnant woman have been excluded from these trials. Our prediction, based on our hypothesis, is that administration of complement inhibitors during the first period of gestation could have devastation consequence for the embryo, from subtle craniofacial abnormalities to more series defects, and even death. In addition, a reduction in complement level has been associated to unexplained spontaneous abortions. Thus, this project could have a high impact in public health policies, by developing a tighter regulation in the use of complement inhibitors. The result of this project will be immediate used to screen for craniofacial abnormalities in complement deficient patients.

2. Cancer: In the UK in 2007, there were 155,484 deaths from cancer (Cancer Research UK), most of these deaths are produced by secondary tumours which are consequence of metastasis of cancerous cells. There is strong evidence that migrating of neural crest cells share many similarities with cancer metastasis. Understanding the basis of neural crest cells migration will allow us to test whether similar principles also operate for cancer metastasis. In this project we specifically will analyze whether attraction between neural crest is required for cell migration. A similar kind of collective cell migration has been described for many cancer metastases. We are currently working with cancer laboratories to test some of the results that will be produced in this project. The identification of the molecular bases of collective cancer migration, will allow developing potential therapies for metastasis.

3. Immunology: In this project we propose to analyze the role that complement has on early embryonic development. Complement has an important function in the protection against external agents such as microbes, but its uncontrolled activation can also have devastating consequences on several autoimmune diseases. Several research centres and biotechnology industries are currently designing inhibitors of the complement to control specific immune diseases. These inhibitors have being designed in the understanding that complement suppression will not have side effects, others that immunodepression. If our work shows that complement is required for normal early development, many of these complement inhibitors should not be used by pregnant women. The results of our project could have a deep impact on human health.

For all these cases in which we anticipate an impact of our project on the community we will ensure that proper people would have the opportunity to benefit from our research by making use of the programs that University College London has (translational research programs and extensive programme of public engagement).