UNRAVELING THE MOLECULAR PATHOGENESIS OF INEFFECTIVE ERYTHROPOIESIS IN CONGENITAL DYSERYTHROPOIETIC ANEMIA TYPE II: IN VITRO EVALUATION OF RAP-011 TREATMENT

Congenital Dyserythropoietic Anemias (CDAs) are subtypes of bone marrow failure syndromes, hallmarked by ineffective erythropoiesis. The most common form is CDA type II (CDAII), showing moderate/severe anemia, relative reticulocytopenia, jaundice, splenomegaly, and iron overload. It is inherited as an autosomal recessive disorder due to loss-of-function mutations in the SEC23B gene. Molecular pathogenesis of CDA II still has to be investigated because the described animal models did not recapitulate the clinical features observed in humans. To date, treatments for CDAII patients consist of supportive therapy, such as erythrocyte transfusions, or bone marrow transplantation or splenectomy in transfusion-dependent cases. Recently, members of TGF-β superfamily have been studied as potential regulators of erythropoiesis, especially the growth differentiation factor 11 (GDF11). Through the binding of specific receptors, GDF11 leads to an inhibited late-stage erythropoiesis. Indeed, two GDF11 inhibitors, ACE-011 and ACE-536, have been associated with an improvement of hematologic parameters. Studies with the mouse counterpart of ACE-011, RAP-011, on a mouse model of β-thalassemia showed increased differentiation of erythroid cells, improvement of the anemic condition and reduced iron overload in treated mice. The first aim of our study was the establishment of a cellular model of CDA II, that could reproduce the main defects of the disease, such as the lack of the erythroid differentiation due to the low or absent expression of SEC23B gene. For this aim, we selected the K562 cell line and, through short-hairpin RNA-based strategy, we obtained two different clones of K562 showing a stable silencing of SEC23B. Then, we decided to assess the effects of RAP-011 on this CDA II model, by investigating the pathway involved in the GDF11 signaling. This treatment simulated the ligand trap function played by RAP-011 towards GDF11. The administration of RAP-011 resulted in a reduction of SMAD2 phosphorylation induced by GDF11 and, moreover, in an increase of different erythroid differentiation markers.