Stromal cell-derived factor 1 regulates primitive hematopoiesis by suppressing apoptosis and by promoting G0/G1 transition in CD34+ cells:: evidence for an autocrine/paracrine mechanism

The stromal cell-derived factor 1 (SDF-1) chemokine has various effects on hematopoietic, cell functions. Its role in migration and homing of hematopoietic progenitors is currently well established. Previously it was shown that SDF-1 stimulates myeloid progenitor proliferation in synergy with cytokines. Results of this study indicate that SDF-1 alone promotes survival of purified CD34(+) cells from human unmobilized peripheral blood (PB) by counteracting apoptosis as demonstrated by its capacity to reduce DNA fragmentation, annexin-V+ cell number, and APO2.7 detection and to modulate bcl-2 homolog protein expression. The study demonstrates that SDF-1, produced by sorted CD34(+)CD38(+) cells and over-released in response to cell damage, exerts an antiapoptotic effect on CD34(+) cells through an autocrine/paracrine regulatory loop. SDF-1 participates in the autonomous survival of circulating CD34(+) cells and its effect required activation of the phosphotidyl inositol 3 kinase (PI3-K)/Akt axis. Cell sorting based on Hoechst/pyroninY fluorescences shows that SDF-1 production is restricted to cycling CD34(+) cells. SDF-1 triggers Go quiescent cells in G, phase and, in synergy with thrombopoietin or Steel factor, makes CD34(+) cells progress through S+G(2)/M phases of cell cycle. By assessing sorted CD34(+)CD38(-) and CD34(+)CD38(+) in semisolid culture, the study demonstrates that SDF-1 promotes survival of clonogenic progenitors. In conclusion, the results are the first to Indicate a role for endogenous SDF-1 in primitive hematopoiesis regulation as a survival and cell cycle priming factor for circulating CD34(+) cells. The proposal is made that SDF-1 may contribute to hematopoiesis homeostasis by participating in the autonomous survival and cycling of progenitors under physiologic conditions and by protecting them from cell aggression in stress situations. (C) 2002 by The American Society of Hematology.