G-CSF induces up-regulation of CXCR4 expression in human hematopoietic stem cells by beta-adrenergic agonist

Introduction: C-X-C chemokine receptor type 4/stromal-derived factor-1 (CXCR4/SDF-1) axis dynamically mediates hematopoietic stem cell trafficking in the bone marrow (BM). Granulocyte colony-stimulating factor (G-CSF) as the most effective mobilizing agent induces SDF-1 secretion from BM stromal cells into circulation that recruit CXCR4(+) cells such as hematopoietic stem cells (HSCs) into circulation. However, the direct effect of G-CSF on CXCR4 expression of HSC remains unknown. The nervous system regulates HSC migration with effecting on adrenergic receptors. On the other hand, interaction of G-CSF and catecholamines has been demonstrated; hence, we examined the direct effect of G-CSF and catecholamine on CXCR4 expression. Material and methods: After enrichment of CD34(+) HSCs from the cord blood with magnetic-activated cell sorting (MACS), these cells were exposed to G-CSF (100 ng/ml), epinephrine (10 mu M), isoproterenol (10 mu M), and propranolol (1 mu M) separately and together. Results: Our results showed that G-CSF have no direct effect on CXCR4 expression on human CD34(+) cells in vitro and treating HSCs with epinephrine leads to significantly increased CXCR4 in 1, 3, and 5 hours. Epinephrine and G-CSF-induced up-regulation of CXCR4 mRNA is dependent on beta receptors, so incubation of HSCs with propranolol led to inhibition of such increased expression. In addition, isoproterenol and agonist of beta receptors would significantly increase the expression of CXCR4 approximately 4-and 12-fold after 1-hour incubation, respectively. Discussion: Co-stimulation of enriched HSCs with G-CSF and isoproterenol resulted to a further enhanced CXCR4 levels. In general, G-CSF-induced CXCR4 expression is the indirect mechanism and is specifically regulated through beta-adrenergic receptors.