Changes in integrin expression are associated with altered homing properties of Lin(-/lo)Thy1.1(lo)Sca-1(+)c-kit(+) hematopoietic stem cells following mobilization by cyclophosphamide/granulocyte colony-stimulating factor.
OBJECTIVE
Although migration of hematopoietic stem cells (HSC) is essential for normal hematopoiesis and successful hematopoietic cell transplantation, little is known about the mechanisms that underlie this movement. We have sought to characterize the factors that regulate HSC migration by analyzing changes in expression of particular adhesion receptors associated with cyclophosphamide/granulocyte colony-stimulating factor (Cy/G-CSF)-induced HSC mobilization.


METHODS
Expression by Lineage(-/lo)Thy1.1(lo)Sca-1(+)c-kit(+) HSC of members of the beta1 integrin family of adhesion molecules was assessed in untreated or Cy/G-CSF-treated mice by multiparameter flow cytometry. In parallel, the in vivo homing properties of normal and mobilized HSC were compared following intravenous transfer of fluorescently marked HSC.


RESULTS
Normal adult HSC express high levels of several beta1 integrin family members. Following Cy/G treatment, bone marrow HSC selectively downregulate alpha 2 integrin expression and upregulate alpha 5 expression. HSC found in the blood following Cy/G-CSF treatment express significantly lower levels of multiple integrins than their bone marrow and/or splenic counterparts. Changes in integrin expression by blood-borne HSC correlate with a 50% decrease in their ability to home to the bone marrow in short-term assays, and with previously observed defects in competitive engraftment by these HSC. Similar reductions in bone marrow (BM) homing are observed for BM HSC treated with alpha 4 integrin function blocking mAb prior to injection. Modulation of integrin expression induced by mobilization was not associated with cell-cycle progression.


CONCLUSIONS
Changes in integrin expression and function are associated with HSC mobilization and likely significantly affect the engraftment potential of hematopoietic stem cells.
Wagers
Amy J
AJ
Department of Pathology, Stanford University School of Medicine, Stanford, CA 94305, USA. awagers@stanford.edu
Allsopp
Richard C
RC
Weissman
Irving L
IL
D000818:Animals; D000950:Antigens, Ly; D002465:Cell Movement / Q000502:physiology*; D003520:Cyclophosphamide / Q000494:pharmacology; D006085:Graft Survival; D016179:Granulocyte Colony-Stimulating Factor / Q000494:pharmacology; D019650:Hematopoietic Stem Cell Mobilization; D018380:Hematopoietic Stem Cell Transplantation; D006412:Hematopoietic Stem Cells / Q000166:cytology* / Q000502:physiology; D007166:Immunosuppressive Agents / Q000494:pharmacology; D016023:Integrins / Q000378:metabolism*; D008565:Membrane Proteins; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D019009:Proto-Oncogene Proteins c-kit; D018800:Thy-1 Antigens
D000950:Antigens, Ly; D007166:Immunosuppressive Agents; D016023:Integrins; C074650:Ly6a protein, mouse; D008565:Membrane Proteins; D018800:Thy-1 Antigens; D016179:Granulocyte Colony-Stimulating Factor; D003520:Cyclophosphamide; D019009:Proto-Oncogene Proteins c-kit