Contrasting effects of P-selectin and E-selectin on the differentiation of murine hematopoietic progenitor cells

Objective The two endothelial selectins, P- and E-selectin, are critically important for adhesion and homing of hematopoietic progenitor cells (HPC) into the bone marrow. Little is known, however, about the roles of these two selectins in hematopoiesis. Here, we demonstrate that the most primitive HPC capable of long-term in vivo repopulation express P-selectin glycoprotein ligand-1/CD162 (PSGL-1), a receptor common to both P- and E-selectin. In addition, we demonstrate that P-selectin delays the differentiation of HPC whereas E-selectin enhances their differentiation along the monocyte/granulocyte pathway, describing different roles for these selectins in the regulation of hematopoiesis. Materials and methods Murine bone marrow HPC were isolated according to their expression of c-kit and PSGL-1, transplanted into lethally irradiated congenic recipients, and chimerism analyzed 6 months posttransplant. Bone marrow lineage-negative (Lin−) Sca-1+c-kit+ cells were then cultured on immobilized P- or E-selectin for 4 weeks in the presence of cytokines. Hematopoietic potential was assessed using in vitro phenotyping and colony-forming assays and in vivo spleen colony-forming unit (CFU-S) and long-term competitive repopulation assays. Results Long-term competitive repopulating HSCs were Lin−c-kitbright and expressed intermediate levels of PSGL-1. Both P- and E-selectin slowed the proliferation of Lin−Sca-1+c-kit+ cells during the first two weeks of liquid culture. After two weeks, however, cells cultured on immobilized P-selectin showed increased proliferation with increased production of both colony-forming cells (CFC) and CFU-S12 compared to the other cultures. In contrast, E-selectin enhanced the differentiation of Lin−Sca-1+c-kit+ cells into cells that expressed the granulocyte maturation marker, Gr-1, accompanied by loss of CFC potential from these cultured cells. Finally, the long-term repopulation potential of these cells was not maintained following culture on either selectin. Conclusion These results suggest that the two endothelial selectins, E-selectin and P-selectin, have very different effects on HPC. E-selectin accelerates the differentiation of maturing HPC towards granulocyte and monocyte lineages while maintaining the production of more immature CFU-S12 in ex vivo liquid suspension culture. In marked contrast, P-selectin delays the differentiation of Lin−Sca-1+c-kit+ cells, allowing enhanced ex vivo expansion of CFC and CFU-S12 but not HSCs.