The Role Of Macrophage-Erythroblast Attacher Maea In Erythropoiesis

The Erythroblastic island（EBI）,formed by a central macrophage and developing erythroblasts,was the first hematopoietic niche to be identified and play a crucial role in erythropoiesis in vivo.EBI macrophages anchor erythroid to the erythroblastic islands and form the microenvironment for erythroid proliferation and differentiation,playing a key role in erythropoiesis.Macrophage-Erythroblast attacher（Maea,also known as Emp）,is an adhesion molecule that mediates the adhesion between EBI macrophages and erythroblasts.However,the exact molecular mechanisms that mediate the interaction between macrophages and erythroblasts remain unclear.To explore the role of Maea in erythropoiesis,we constructed Maea floxp mice and conditionally knocked out Maea in macrophages and erythroid cells using the Epo R-td Tomato-Cre,Gypa-td Tomato-Cre and CD169-td Tomato-Cre mouse models previously constructed by our laboratory.Maea mediates homophilic adhesion of macrophages and erythroblasts.Epo R was previously thought to be an erythroid-specific expressed gene,but recent studies have shown that it is also expressed in EBI macrophages.To explore the role of Maea in erythropoiesis,we first used the Epo R-td Tomato-Cre mouse model constructed in our laboratory and obtained Maea^fl/flEpo R-Cre^+/+conditional knockout mice by editing the Cre/lox P system.The Maea^fl/flEpo R-Cre^+/+mice were viable but died at around 3 months of age and developed anemia,impaired erythropoiesis in the bone marrow,enlarged spleen with compensatory erythropoiesis.The number of EBI macrophages in the bone marrow and spleen was reduced,the proportion of red pulp macrophages was decreased and the formation of erythroblastic islands was impaired in Maea^fl/flEpo R-Cre^+/+mice.However,as Epo R is expressed on both EBI macrophages and erythroblasts.It is not clear whether Maea in erythroblasts or macrophages was responsible.Furthermore,since the results showed a reduction in other hematopoietic lineages and previous studies have shown that Epo R is also expressed in hematopoietic stem cells,we speculate that Maea deficiency may also play an important role in maintaining the hematopoietic stem and progenitor cells.In order to explore the effects of Maea-specific deletion in erythroblasts on erythropoiesis,our laboratory constructed an erythroid-specific Gypa-td Tomato-Cre mouse model and obtained Maea erythroid-specific knockout mice(Maea^fl/flGypa-Cre^+/-).Maea^fl/flGypa-Cre^+/-mice developed mild anemia,and compensatory erythropoiesis occurred in the spleen,but erythropoiesis in the bone marrow was not affected.These results show that specific deletion Maea in erythroid cells lead to mice anemia.To investigate the effect of Maea deletion in macrophages on erythropoiesis,our group constructed CD169-td Tomato-Cre mouse model and obtained Maea conditional knockout mice(Maea^fl/flCD169-Cre^+/-)to investigate the function of Maea in macrophages.Maea^fl/flCD169-Cre^+/-mice showed reduced CD169⁺macrophages and red pulp macrophages in the bone marrow and spleen,defected erythroblastic island formation,impaired erythropoiesis in the bone marrow and compensatory hematopoiesis in the spleen,but no alterations in circulating blood parameters.The results suggest that Maea in macrophages plays a more important role in the erythropoiesis,but the phenotype of Maea^fl/flCD169-Cre^+/-mice is much less severe than that of Maea^fl/flEpo R-Cre^+/+mice,suggesting that Maea also plays an important impact in hematopoietic stem cell development.To explore the function of Maea in hematopoietic stem and progenitor cells,We used flow cytometry to examine hematopoietic stem cells from Maea^fl/flEpo R-Cre^+/+mice and showed that knockout of Maea leaded a reduction in hematopoietic stem cells,multipotent hematopoietic progenitors,myeloid progenitors,megakaryocyte/erythroid progenitors and granulocyte/monocyte progenitors,indicating that Maea is essential for the development of hematopoietic stem and progenitor cells.Taken together,Maea plays an important role not only in the process of erythropoiesis,but also in regulating the directional differentiation and development of hematopoietic stem cells.This project will provide new insights into the study of Maea in adult hematopoiesis and help to provide a theoretical basis and data support to improve the understanding of the complex network of developmental regulation of erythroid lineage.