Olivier HERMINE and Thiago TROVATI

The hematology laboratory at the Imagine Institute covers several aspects of the pathophysiology and treatment of malignant and benign hematologic disorders. The laboratory is part of Inserm Unit U1163 and is affiliated with the Clinical Hematology Department at Necker-Enfants Malades Hospital (AP-HP) as well as with the national reference centers for mastocytosis (CEREMAST), immunodeficiencies (CEREDIH), and hemoglobinopathies.

Our laboratory's primary objectives are:

• to characterize the mechanisms governing the pathophysiology of hematologic disorders;
• to develop therapeutic strategies to treat these diseases;
• to advance clinical research;
• to facilitate technology transfer.

We work in close collaboration with the departments of pathology, biology, cytogenetics, molecular biology, biotherapy, infectious diseases, transplantation, and pediatric immunohaematology at Necker-Enfants Malades Hospital. Regulation of erythropoiesis and clinical applications Our research group has been studying erythropoiesis and erythropoietic disorders for the past several years. We have focused in particular on the molecular mechanisms involved in the positive and negative regulation of erythropoiesis and on the impact of these alterations in hematopoietic diseases. We have demonstrated that caspase activation is crucial for erythroid cell differentiation.

Our current objectives are:

1. to elucidate the mechanisms that trigger caspase activation;
2. to identify the factors that control caspase activity and the downstream caspase targets;
3. to characterize the role of caspases and the proteins that regulate their functions,particularly HSP70 in the pathophysiology of erythroid disorders such as thalassemia, myelodysplastic syndrome (MDS), and congenital erythroblastopenia;
4. to develop therapeutic applications targeting caspases in disorders of erythropoiesis.

In thalassemia, we have identified the TGF-beta family as the primary cause of the failure to regulate erythropoiesis. We are studying the molecular and cellular mechanisms involving these cytokines that may explain the failure of erythropoiesis, developing therapeutic strategies using inhibitors, and extending our findings to several other hematological diseases. We have shown that the transferrin receptor (TfR1) is a signaling molecule capable of effectively regulating erythropoiesis independently of its essential role in iron transport. We are currently characterizing the molecular pathways involved in this process. We have developed mutants in the intracellular tail of the TfR1 receptor to identify other molecules that may be involved in the early stages of cell activation. Our goal is to determine the role of these molecular pathways in erythropoiesis as well as in other hematological disorders.

TfR1 is overexpressed in cancer cells compared to their non-cancerous counterparts, and several studies have suggested the therapeutic value of targeting this receptor. We are currently developing, in collaboration with the startup Inatherys (co-founded by Ivan Moura and Olivier Hermine), an antibody directed against TfR1 for the treatment of cancers.

Recently, we have expanded into a new area of research on the role of serotonin in erythropoiesis and red blood cell survival. To characterize the in vivo action of serotonin (5-hydroxytryptamine, 5-HT), we generated mice with a deletion of the gene encoding tryptophan hydroxylase-1 (Tph1). Our results revealed that 5-HT plays a critical role in normal erythropoiesis and red blood cell (RBC) survival in mice. We will now investigate the regulatory mechanisms of 5-HT and the modes of action of serotonin on erythrocyte differentiation, survival, and proliferation, as well as on iron metabolism. We will pay particular attention to the study of protein serotonylation, the modulation of ROS responses, and the production of members of the TGF-beta family. We will also investigate whether serotonin expression plays a role in erythroid disorders, particularly thalassemia, MDS, and primary myelofibrosis (MF), as our preliminary data suggest that aged Tph1-/- mice develop MF. This research could lead to new therapeutic tools for erythroid disorders. At the same time, we are investigating the role of serotonin in the preservation of red blood cells for blood transfusion.
Red blood cell transfusions are frequently used in the management of these various disorders. However, their impact on the course of these diseases is poorly understood. We are currently studying the role of red blood cell transfusions in the progression of cancer and immune-mediated diseases. Mastocytosis and the role of mast cells in the disease Mastocytosis is a rare disease caused by the accumulation of mast cells in various tissues. The pediatric form of mastocytosis is a clonal disease associated with mutations in the C-Kit gene that can resolve spontaneously. The C-Kit mutations observed differ between adults and children, suggesting that the type of mutations may dictate the course of the disease. We are currently trying to understand how these mutations may explain the phenotype and outcome of the disease and how they can be targeted to treat what is still an incurable disease in adult patients.

Mastocytosis is a common disease in dogs. We have identified mutations in the canine C-kit gene and shown that they are similar to those found in pediatric diseases. In collaboration with a pharmaceutical company (AB Science, co-founded by Oliver Hermine), we have demonstrated that kinase inhibitors that block the KIT protein can reduce mast cell infiltration and the symptoms associated with the release of mast cell mediators in dogs. Clinical trials are currently underway for mastocytosis in humans using kinase inhibitors.

Mast cells may play a key role in various inflammatory, neurological, and neoplastic diseases, and these diseases may be targeted by kinase inhibitors that act on mast cells. We will use naturally occurring neoplastic and inflammatory diseases in dogs as a model to test this hypothesis.