Smad2/3-pathway ligand trap luspatercept enhances erythroid differentiation in murine β-thalassaemia by increasing GATA-1 availability

Abstract

In beta-thalassaemia, anaemia results from ineffective erythropoiesis characterized by inhibition of late-stage erythroid differentiation. We earlier used luspatercept and RAP-536 protein traps for certain Smad2/3-pathway ligands to implicate Smad2/3-pathway overactivation in dysregulated erythroid differentiation associated with murine beta-thalassaemia and myelodysplasia. Importantly, luspatercept alleviates anaemia and has been shown to reduce transfusion burden in patients with beta-thalassaemia or myelodysplasia. Here, we investigated the molecular mechanisms underlying luspatercept action and pSmad2/3-mediated inhibition of erythroid differentiation. In murine erythroleukemic (MEL) cells in vitro, ligand-mediated overactivation of the Smad2/3 pathway reduced nuclear levels of GATA-1 (GATA-binding factor-1) and its transcriptional activator TIF1 gamma (transcription intermediary factor 1 gamma), increased levels of reactive oxygen species, reduced cell viability and haemoglobin levels, and inhibited erythroid differentiation. Co-treatment with luspatercept in MEL cells partially or completely restored each of these. In beta-thalassaemic mice, RAP-536 up-regulated Gata1 and its target gene signature in erythroid precursors determined by transcriptional profiling and gene set enrichment analysis, restored nuclear levels of GATA-1 in erythroid precursors, and nuclear distribution of TIF1 gamma in erythroblasts. Bone marrow cells from beta-thalassaemic mice treated with luspatercept also exhibited restored nuclear availability of GATA-1 ex vivo. Our results implicate GATA-1, and likely TIF1 gamma, as key mediators of luspatercept/RAP-536 action in alleviating ineffective erythropoiesis.