Muscarinic receptor type-1 of the central nervous system primes hematopoietic stem cells for mobilization from the bone marrow via a glucocorticoid-mediated relay

Abstract

Mobilization of hematopoietic stem cells (HSCs) from the bone marrow (BM) into blood circulation can be elicited by the cytokine granulocyte-colony stimulating factor (GCSF). The mechanism by which G-CSF-elicited mobilization occurs is a complex process who's many cellular and molecular targets may not be fully elucidated as of yet. In this study, we identify that muscarinic receptor type-1 (Chrm1) signaling within the central nervous system (CNS) promotes G-CSF mobilization of HSCs. Blockade of Chrm1 in the CNS, but not in the periphery, resulted in reduced HSC mobilization, similar to that observed in Chrm1-/- mice. Parabiosis of Chrm1 -/- mice with wild-type mice is sufficient to rescue Chrm14 impaired HSC mobilization, suggesting a blood borne factor mediates the relay of central signals. Our studies identified Chrm1-/- mice to have significant reductions in plasma and BM glucocorticoids, leading us to explore its role in HSC mobilization. Exogenous administration of glucocorticoids to Chrm1-/- mice was sufficient to restore HSC mobilization to wild-type levels; conversely, inhibition of glucocorticoid production in wild-type animals significantly reduced HSC mobilization. Mice harboring a glucocorticoid receptor (Nr3c1) deficient hematopoietic system also exhibited reductions in HSC mobilization, further confirming a role for glucocorticoid signals in G-CSF-elicited HSC mobilization. Chrm1 was found to be expressed in the hypothalamus and able to activate the hypothalamic-pituitary-adrenal axis by stimulating production of corticotropoin-releasing hormone in the hypothalamus.;Microarray analysis of Chrm1-/- HSCs indicated that glucocorticoids contribute to the steady state organization of 3D actin structures and indeed, hematopoietic cells isolated from Chrm1-/- and Nr3c1Delta/Delta mice were observed to exhibit reduced polymerized actin by phalloidin staining compared to wild-type cells.;Administration of physiological levels of glucocorticoids to Chrm1-/- mice was sufficient to restore polymerization of actin in steady state hematopoietic cells. This suggests that steady state levels of glucocorticoids in the BM microenvironment prime HSCs for GCSF elicited mobilization through the organization of 3D actin networks. These results uncover a novel long-range regulation of HSC migration.