Regarding the role of MOZ in healthy blood system, we developed and investigated a mouse model which where MOZ can be specifically deleted in blood cells MOZ in these cells. The other mouse models available so far are lethal during embryogenesis, as MOZ expression is lost in the entire organism. In contrast with our new model, MOZ is still expressed in other tissues where it is probably essential (brain and gut for example), but can be specifically deleted in the blood system. The study of these mice revealed that loss of MOZ is associated with a lack of the so-called Haematopoietic Stem Cells (HSC). These cells, at the top of the hierarchy in the blood system have the capacity to produce all the other blood cells (the white blood cells which fight infection, and the red blood cells which bring oxygen to the body) and to self renew. Interestingly, even though HSCs are lost in these mice, the other cells are present and have a normal activity. This finding suggests that the HSC are not required during normal healthy blood production in adult. This is an exciting finding, as it challenges our understanding of adult haematopoiesis. It is indeed believed that HSCs cells are critical for the formation of the other blood cells. We are now trying to understand in which context these cells are required. For this, mice that do not express MOZ will be submitted to different stresses, that for example mimics haemorrhage or bacterial infection. We expect that the mice won’t be able to cope with these stresses, as HSCs should be required in these conditions. Indeed, in case of infection or important blood loss, the body should produce a huge quantity of blood cells in a very short time, and in this case, HSCs are expected to be the main source of blood cells. In parallel of the study of the blood system of these mice, we also plan to use the cells that do not express MOZ as a tool to study the molecular activity of MOZ. Understanding MOZ function in healthy blood production is crucial to appreciate what is affected when MOZ is mutated in the context of leukaemia.
In the second part of the project, we studied the subtype of leukaemia with mutation of MOZ. We generated a model where normal healthy cells expressed the mutated form of MOZ. These cells became leukaemic, representing an excellent tool to explore how mutated MOZ leads to the development of leukaemia. Leukaemic cells are characterised by a high proliferation rate and by the fact that they are immature, and cannot anymore differentiate to generate mature effective blood cells. Hence, patients with leukaemia accumulate these immature/blastic cells at the expense of functional blood cells. In these MOZ-related leukaemic cells, we studied the modification of chromatin (the structure that enwrapped DNA that MOZ can modify) and we found that mutated MOZ has an aberrant activity on only a very limited sets of regions of the chromatin. Investigating these regions, we found that the mutated version of MOZ induces the expression of a small subset of genes, which are normally not expressed in healthy blood cells. We next treated the leukaemic cells with a molecular inhibitor of one of these genes. The treatment of the leukaemic cells with this inhibitor lead to a loss of proliferation capacities of the leukaemic cells, one of the main characteristics of a blood cancer cell. The decrease in proliferation is explained by both the death of leukemic cells, and by the fact that some of them differentiate into normal blood cells. Finally, we treated cells obtained directly from patients with leukaemia (opposed to the cells produced in our laboratory) with similar results: an impairment of proliferation capacities. Altogether these results suggest that we have identified a novel potential therapeutic agent for the treatment of leukaemia. We are now on the process to develop further this work to identify a more potent inhibitor.
