3140 – A PROTEOMIC APPROACH TO IDENTIFY KLF1-REGULATED PROTEINS IN ERYTHROID ISLAND-LIKE MACROPHAGES

Adult erythropoiesis is known to occur in the bone marrow where erythroid progenitors are produced from haematopoietic stem cells then proliferate, differentiate and mature into red blood cells prior entering the circulation. The later stages take place within the erythroblastic island (EI) niche where differentiating erythroblasts are anchored to a central macrophage via adhesion molecules, supporting erythropoiesis by transferring iron for haemoglobin synthesis, by providing cytokines and engulfing the extruded erythroid nuclei. However, it has been challenging to understand the mechanisms that underlie macrophages and erythroblasts interactions within the human EI niche, due to the difficulties that are encounter to access and isolate those cells in vivo. KLF1 is an essential transcription factor that plays a role in erythropoiesis, both as an intrinsic regulator, since it is highly expressed in erythroid cells, and as an extrinsic factor, being also expressed in EI macrophages. Previously, using a genetically manipulated iPSC line whereby a CAG-KLF1-ERT2 transgene was inserted into the safe harbour, we produced iPSC-derived macrophages where KLF1 could be activated upon tamoxifen induction. Co-culture of KLF1 activated macrophages with CD34+ umbilical cord blood, improved the differentiation and maturation of these erythroid progenitors, in comparison with control macrophages. To establish the molecular mechanisms associated with the interactions between macrophages and erythroid cells in the EI niche we performed a proteomic analysis on the iPSC-derived macrophages in the presence and absence of KLF1 activation. Our main focus now is to determine which of these proteins are responsible for the adhesion and communication between macrophages and erythroblasts that those that play a key role in the erythroid differentiation and maturation within the EI niche.