Hyaluronan stimulates mobilization of mature hematopoietic cells but not hematopoietic progenitors.

Hyaluronan (HA) is expressed by cells in bone marrow where it contributes to the regulation of hematopoietic homeostasis. In this study, we have demonstrated that exogenous low molecular weight HA (LMW HA) polymers mobilize leukocytes, but not hematopoietic progenitor cells, to peripheral blood within a 3 hour time period following HA administration. Mobilization of leukocytes correlated with increased extracellular MMP-9 concentrations induced by LMW HA, but not high molecular weight (HMW) HA. In contrast, HMW HA up-regulated TIMP-1 expression in bone marrow cells. In vitro, HMW HA did not influence SDF-1 - mediated chemotaxis of hematopoietic progenitors, whereas LMW HA polymers demonstrated inhibitory activity. These findings suggest that the effects of HA on cell motility depend on the size of the HA polymers and on the type of target cells.