Erratum: Rapid mobilization of hematopoietic progenitors by AMD3100 and catecholamines is mediated by CXCR4-dependent SDF-1 release from bone marrow stromal cells

Physiologic corticosterone oscillations regulate murine hematopoietic stem/progenitor cell proliferation and CXCL12 expression by bone marrow stromal progenitors

The role of corticosterone (Cort), the immune system's major stress hormone, in the regulation of hematopoietic stem and progenitor cells (HSPCs) and their dynamic bone marrow (BM) microenvironment is currently unknown. We report that corticotropin-releasing factor receptor 1 (CRFR1) mutant mice with chronically low Cort levels showed aberrant HSPC regulation, having higher HSPC numbers and upregulation of the chemokine CXCL12, phenotypes that were restored by Cort supplementation. Expanded stromal progenitors known to support HSPCs were also observed in these low-Cort-containing mice. A similar phenotype was induced in wild-type (WT) mice by Metyrapone, a Cort synthesis inhibitor. Conversely, high Cort exposure induced HSPC apoptosis, reduced long-term BM repopulation and decreased stromal progenitor cell numbers. We documented circadian oscillations of Cort in WT BM but not in CRFR1 mutant mice, leading to diminished circadian BM CXCL12 fluctuations and increased number of circulating HSPCs in these mice. Finally, low Cort induced expansion of stromal progenitors, CXCL12 expression, HSPC proliferation and BM repopulation capacity, involving Notch1 signaling. This was associated with upregulation of the Notch ligand, Jagged1, in BM myeloid cells. Our results suggest that daily physiologic Cort oscillations are critical for balanced HSPC proliferation and function involving Notch1 signaling and their supportive BM microenvironment.

Quantifying hematopoietic stem and progenitor cell mobilization

Allogeneic donor blood cells and autologous peripheral blood leukocytes (PBL), obtained following -clinical mobilization procedures, are routinely used as a major source of hematopoietic stem and progenitor cells (HSPC) for transplantation protocols. It is, therefore, essential to evaluate and to quantify the extent by which the HSPC are mobilized and enriched in the circulation in correlation with their long-term hematopoietic reconstitution capacity. In this chapter, we describe quantitative methods that measure the number of mobilized HSPC according to specific criteria, as well as their functional properties in vitro and in vivo. The described assays are useful for assessment of progenitor cell mobilization as applied to both human and murine HSPC.

Heparin-induced leukocytosis requires 6-O-sulfation and is caused by blockade of selectin- and CXCL12 protein-mediated leukocyte trafficking in mice

Leukocytosis refers to an increase in leukocyte count above the normal range in the blood and is a common laboratory finding in patients. In many cases, the mechanisms underlying leukocytosis are not known. In this study, we examined the effects, the structural determinants, and the underlying mechanisms of heparin-induced leukocytosis, a side effect occurring in 0.44% of patients receiving heparin. We observed that heparin induced both lymphocytosis and neutrophilia, and the effects required heparin to be 6-O-sulfated but did not require its anticoagulant activity. Cell mobilization studies revealed that the lymphocytosis was attributable to a combination of blockage of lymphocyte homing and the release of thymocytes from the thymus, whereas the neutrophilia was caused primarily by neutrophil release from the bone marrow and demargination in the vasculature. Mechanistic studies revealed that heparin inhibits L- and P-selectin, as well as the chemokine CXCL12, leading to leukocytosis. Heparin is known to require 6-O-sulfate to inhibit L- and P-selectin function, and in this study we observed that 6-O-sulfate is required for its interaction with CXCL12. We conclude that heparin-induced leukocytosis requires glucosamine 6-O-sulfation and is caused by blockade of L-selectin-, P-selectin-, and CXCL12-mediated leukocyte trafficking.