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Physiopathological mechanisms of two congenical platelet disorders : filaminopathy-A and ANKRD26-related - Thrombocytopenia 5THC2

Abstract : Inherited thrombocytopenias are a class of congenital haematological disorders affecting primarily the megakaryocytic lineage and accomunated by a decrease in platelet numbers. Almost 50 different genes have been associated to inherited platelet disorders, and huge differences exist between each disorder, in regard to clinical manifestation and pathobiology. My research interest have been focused on two different congenital thrombocytopenias: Filaminopathy A and Thrombocytopenia 2. The first disease is a X-linked syndrome associated to mutations in the gene FLNA (Filamin A), and patients display a mild to severe macrothrombocytopenia, associated with a lifelong bleeding tendency. The second disorder is an automal dominant condition caused by mutations in the 5’ UTR of the ANKRD26 gene. It is associated with dysmegakaryopoiesis, mild to severe thrombocytopenia and an increased risk to develop myeloid malignancies. To study the physiopathology of those two rare diseases, we have exploited the induced pluripotent stem cell technology to develop several patient specific cell lines. Those experimental tools revealed invaluable for the understanding of the disease physiopathology, and allowed us to describe in great details the molecular mechanisms underlying the reduction in proplatelet formation for Filaminopathy A and the predisposition to leukemia for Thrombocytopenia 2. To perform such studies, we devised a robust differentiation protocol, recapitulating efficiently the haematopoietic differentiation and easily adapted to the in vitro differentiation of multiple cell lineages. Furthermore, we exploited a genome editing technique to introduce efficiently different protein mutants, in order to dissect the molecular role of Filamin A in megakaryopoiesis. In regard of Filaminopathy A, we have been able to describe an original and novel relationship between a membrane integrin (IIb3), Filamin A and a crucial signalling pathway (RhoA) for megakaryopoiesis. Our data support a model where the absence of FLNa induces an abnormal activity of the RhoA pathway, in response to the integrin IIb3 binding to fibrinogen. Concerning the thrombocytopenia 2, we described a novel mechanism that associated the increased expression of ANKRD26 to a deregulated activity of the G-CSF-dependent signalling pathway. This anomaly impacts the normal granulopoiesis and lead to an abnormal amplification of this cell lineage, possibly increasing the risk of acquiring other mutational hits and progress towards a myeloid malignancy.In conclusion, with this work we offer a proof of concept of the potentiality of disease modeling via induced pluripotent stem cells. Our results pave the way for further studies that could advance our understanding of the physiopathology of inherited platelet disorders.
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Alessandro Donada. Physiopathological mechanisms of two congenical platelet disorders : filaminopathy-A and ANKRD26-related - Thrombocytopenia 5THC2. Human health and pathology. Université Sorbonne Paris Cité, 2018. English. ⟨NNT : 2018USPCC250⟩. ⟨tel-02888804v2⟩

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