Cell-cell contact in intact bone marrow tissues plays a regulatory role in controlling the secretion of CXCL12 ― a soluble factor required for hematopoietic stem cell homeostasis. This finding, reported online in Nature Immunology, provides additional insight into the mechanisms controlling stem cell mobilization in physiological and clinical situations.
Stromal cells in the bone marrow secrete an array of signaling molecules and create the unique microenvironment required for stem cell maintenance, self-renewal, commitment and differentiation. Tsvee Lapidot and colleagues found that rapid calcium flux between interconnected stromal cells controls CXCL12 secretion. Stress signals, such as mild bleeding or bacterial infection, which might temporarily disturb cell-cell contacts, can block CXCL12 secretion and induce hematopoietic stem cell proliferation and mobilization from their niche.
As part of bone marrow transplantation protocols, the cytokine granulocyte-colony stimulating factor (G-CSF) is repeatedly administrated clinically in order to stimulate stem cell mobilization from the bone marrow to the circulation. G-CSF treatments might act in part by disturbing cell-cell contact between bone marrow stromal cells.