Chemokines are perhaps best known for their role in immune responses, but they can also regulate cell migration during embryonic development. A new paper in Development shows that an atypical chemokine receptor sequesters maternal CXCL12 in the placenta to prevent it from entering the embryonic bloodstream, thus ensuring proper haematopoiesis in the embryo. To learn more about the story behind the paper, we caught up with first author Ayumi Fukuoka and corresponding author Gerry Graham, the Gardiner Chair of Immunology at the University of Glasgow, UK.
Gerry Graham (left) and Ayumi Fukuoka (right)
Gerry, can you give us your scientific biography and the questions your lab is trying to answer?
GG: I have spent my career studying chemokines and their receptors. These molecules are typically studied in the context of inflammation and immunity; our work has provided important insights into how these molecules interact, on a selective basis, to regulate inflammation, and we continue to pursue this line of research using complex novel mouse models. Our goal is to develop a clear understanding of chemokine, and chemokine receptor, involvement in inflammation to inform both our biological understanding of this fundamental process, but also to help with the rational development of therapeutics for use in inflammatory disease.
In addition to our studies in inflammation, we have consistently been interested in investigating the roles of chemokines, and their receptors, in other biological contexts. To this end we have studied their involvement in the regulation of stem cell function, embryonic development and placentation. Central to a number of these analyses has been our cloning and biological characterisation of a molecule called ACKR2, which is the prototypic member of the atypical chemokine receptor family. These molecules are 7-transmembrane spanning receptors and (with the exception of ACKR1) are directly genomically linked to other chemokine receptors. They do not signal in the same way as standard chemokine receptors and they are also expressed in unusual cell types, including trophoblasts within the placenta. These receptors scavenge and degrade chemokines and we have spent a considerable amount of time trying to understand how these scavenging receptors function and what their contribution to inflammation, immunity and development is.
Ayumi, how did you come to work in the lab and what drives your research today?
AF: I worked as an immunology researcher in Japan. My husband is also a researcher, and he found a job in Glasgow. When I decided to move to Glasgow, Gerry kindly offered me this project. I did not have experience in embryos and placenta-based research, so I thought it would be a great opportunity to learn new techniques and acquire new knowledge. I appreciate all the opportunities that this project has given me. I would like to continue to work on trying to understand the regulation of the development of the immune system and immune response, focussing on neonates.
One of our major contributions to the chemokine field has been the championing of the atypical chemokine receptor family
Tell us about the background of the field that inspired your work
AF & GG: As mentioned above, one of our major contributions to the chemokine field has been the championing of the atypical chemokine receptor family. We have been intrigued by the fact that a number of the atypical chemokine receptors (ACKR2, ACKR3 and ACKR4) are expressed on trophoblasts within the placenta. This positions them precisely at the interface between the mother and the foetus and suggests that they must play some sort of role in this tissue. We previously demonstrated that ACKR2-knockout embryos display increased levels of inflammatory chemokines in their plasma. This is because trophoblasts lacking ACKR2 cannot scavenge inflammatory chemokines in maternal blood and these chemokines therefore enter the foetal circulation. This then has an impact on leukocyte migration within embryos and significantly interferes with the accumulation of a specific population of macrophages in developing skin. This phenotype is mild but establishes the notion of ‘chemokine compartmentalisation’, where atypical chemokine receptors separate chemokines in maternal blood from those in the embryo.
In our current study, we have turned our attention to the impact of interfering with ACKR3 on trophoblasts. This atypical chemokine receptor scavenges a chemokine called CXCL12 which is, almost certainly, the primordial chemokine from which the entire complex chemokine family has evolved. The ancient, and conserved, role for this chemokine is in the regulation of stem cell migration during embryogenesis. We therefore set about examining what the impact of interfering with ACKR3 function would be for growth and haematopoietic development of offspring.
Can you give us the key results of the paper in a paragraph?
AF & GG: Essentially, our paper demonstrates that interfering with ACKR3, either by pharmacological inhibition or by Cre-mediated knockout in trophoblasts, allows maternal CXCL12 to enter the foetal circulation. This then interferes with the migration of haematopoietic stem cells within the embryo, resulting in impaired bone marrow haematopoiesis. Interfering with ACKR3 also leads to compromised foetal growth, and this compromised growth persists for many weeks following birth. The haematopoietic abnormalities mean that these offspring are born with an impaired ability to raise immune and inflammatory responses, thus making them vulnerable to perinatal infection and inflammation.
ACKR3 expression on mouse trophoblast cells. Mouse placenta from ACKR3 reporter mouse was stained with trophoblast marker, MCT4. ACKR3 is shown in green, MCT4 in red and DAPI in blue.
When doing the research, did you have any particular result or eureka moment that has stuck with you?
AF: I would say that finding impaired immune responses to bacterial stimuli in young pups born to mothers treated with the ACKR3 blocker was a major discovery. This was a big surprise and exciting for me because it showed us how important placental ACKR3 is for offspring health.
Finding impaired immune responses to bacterial stimuli in young pups born to mothers treated with the ACKR3 blocker was a major discovery
And what about the flipside: any moments of frustration or despair?
AF: I felt frustration during the COVID lockdown because many researchers had to stop working in the lab. I had just found a key phenotype in a mouse model when the lockdown started, and I was hampered in my attempts to pursue it by the lack of access to labs and mice. I was also pregnant when the pandemic happened, so I ended up staying home until my maternity leave finished. I was glad to restart the project when I was back in the lab.
Why did you choose to submit this paper to Development?
AF & GG: As mentioned above we have always sought to examine, wherever possible, the role for chemokines and their receptors in unusual biological contexts. One of the most important of these is in development, and we have been the first to demonstrate clear roles for inflammatory chemokines in a range of developmental processes. We are therefore keen to expose our work to criticism from the developmental biology community, and Development is the ideal vehicle for this. In addition, our previous experience in dealing with Development has been very positive, with unfailingly reasoned and supportive editorial decisions. In terms of the processes of submitting, editorial evaluation and review, Development is one of the best journals that we have ever dealt with.
We have been the first to demonstrate clear roles for inflammatory chemokines in a range of developmental processes
Where will this story take your lab next?
GG: The next key questions relate to the impact of interfering with placental ACKR3 on animals as they develop into adulthood. In addition to having an impact on haematopoietic stem cells, CXCL12 is also crucial for the development of primordial germ cells, cortical interneurons and a variety of endothelial progenitors. We therefore predict that the offspring will demonstrate impaired fertility, behavioural abnormalities and potentially other organ-specific phenotypes. We are in the process of analysing older offspring to comprehensively address this question. In addition, we will be looking at polymorphisms in human ACKR3 to see if we can associate these with any obvious abnormalities in offspring. If we could make this connection, it would raise the possibility of suppressing maternal CXCL12 in at-risk mothers to minimise flux into the embryo and attendant developmental problems.
Finally, let's move outside the lab – what do you like to do in your spare time?
GG: Spending time with my family is key. I play the guitar – not well, but well enough to amuse myself! In addition, I enjoy running and cycling and, when I can get away, hiking and Munro-bagging. I'm also very partial to the odd visit to the pub!
AF: I enjoy cooking during my time off. I miss Japanese foods as it's not easy to find real Japanese food in Scotland. Therefore, I cook Japanese cuisines/sweets at home and enjoy them with my family.
Chemokine Research Group, School of Infection and Immunity, College of Medical, Veterinary and Life Sciences, University of Glasgow, 120 University Place, Glasgow G12 8TA, UK.
E-mail: [email protected]
