RESUMEN
Uncovering the cellular and molecular mechanisms by which hematopoietic stem cell (HSC) self-renewal is regulated can lead to the development of new strategies for promoting ex vivo HSC expansion. Here, we report the discovery that alternative (M2)-polarized macrophages (M2-MΦs) promote, but classical (M1)-polarized macrophages (M1-MΦs) inhibit, the self-renewal and expansion of HSCs from mouse bone marrow (BM) in vitro. The opposite effects of M1-MΦs and M2-MΦs on mouse BM HSCs were attributed to their differential expression of nitric oxide synthase 2 (NOS2) and arginase 1 (Arg1), because genetic knockout of Nos2 and Arg1 or inhibition of these enzymes with a specific inhibitor abrogated the differential effects of M1-MΦs and M2-MΦs. The opposite effects of M1-MΦs and M2-MΦs on HSCs from human umbilical cord blood (hUCB) were also observed when hUCB CD34+ cells were cocultured with M1-MΦs and M2-MΦs generated from hUCB CD34- cells. Importantly, coculture of hUCB CD34+ cells with human M2-MΦs for 8 days resulted in 28.7- and 6.6-fold increases in the number of CD34+ cells and long-term SCID mice-repopulating cells, respectively, compared with uncultured hUCB CD34+ cells. Our findings could lead to the development of new strategies to promote ex vivo hUCB HSC expansion to improve the clinical utility and outcome of hUCB HSC transplantation and may provide new insights into the pathogenesis of hematological dysfunctions associated with infection and inflammation that can lead to differential macrophage polarization.
Asunto(s)
Proliferación Celular/efectos de los fármacos , Autorrenovación de las Células/efectos de los fármacos , Células Madre Hematopoyéticas/citología , Macrófagos/fisiología , Animales , Arginasa/metabolismo , Técnicas de Cocultivo , Sangre Fetal/citología , Humanos , Masculino , Ratones , Óxido Nítrico Sintasa de Tipo II/metabolismoRESUMEN
Hematopoietic stem cells (HSCs) mature from pre-HSCs that originate in the major arteries of the embryo. To identify HSCs from in vitro sources, it will be necessary to refine markers of HSCs matured ex vivo. We purified and compared the transcriptomes of pre-HSCs, HSCs matured ex vivo, and fetal liver HSCs. We found that HSC maturation in vivo or ex vivo is accompanied by the down-regulation of genes involved in embryonic development and vasculogenesis, and up-regulation of genes involved in hematopoietic organ development, lymphoid development, and immune responses. Ex vivo matured HSCs more closely resemble fetal liver HSCs than pre-HSCs, but are not their molecular equivalents. We show that ex vivo-matured and fetal liver HSCs express programmed death ligand 1 (PD-L1). PD-L1 does not mark all pre-HSCs, but cell surface PD-L1 was present on HSCs matured ex vivo. PD-L1 signaling is not required for engraftment of embryonic HSCs. Hence, up-regulation of PD-L1 is a correlate of, but not a requirement for, HSC maturation.