title: Tie2(+)  bone marrow endothelial cells regulate hematopoietic stem cell regeneration following radiation injury.
abstract: Hematopoietic stem cells (HSCs) reside in proximity to bone marrow endothelial cells (BM ECs) and maintenance of the HSC pool is dependent upon EC-mediated c-kit signaling. Here, we used genetic models to determine whether radioprotection of BM ECs could facilitate hematopoietic regeneration following radiation-induced myelosuppression. We developed mice bearing deletion of the proapoptotic proteins, BAK and BAX, in Tie2(+) ECs and HSCs (Tie2Bak/Bax(Fl/-) mice) and compared their hematopoietic recovery following total body irradiation (TBI) with mice which retained Bax in Tie2(+) cells. Mice bearing deletion of Bak and Bax in Tie2(+) cells demonstrated protection of BM HSCs, preserved BM vasculature, and 100% survival following lethal dose TBI. In contrast, mice that retained Bax expression in Tie2(+) cells demonstrated depletion of BM HSCs, disrupted BM vasculature, and 10% survival post-TBI. In a complementary study, VEcadherinBak/Bax(Fl/-) mice, which lack Bak and Bax in VEcadherin(+) ECs, also demonstrated increased recovery of BM stem/progenitor cells following TBI compared to mice which retained Bax in VEcadherin(+) ECs. Importantly, chimeric mice that lacked Bak and Bax in HSCs but retained Bak and Bax in BM ECs displayed significantly decreased HSC content and survival following TBI compared to mice lacking Bak and Bax in both HSCs and BM ECs. These data suggest that the hematopoietic response to ionizing radiation is dependent upon HSC-autonomous responses but is regulated by BM EC-mediated mechanisms. Therefore, BM ECs may be therapeutically targeted as a means to augment hematopoietic reconstitution following myelosuppression.
authors.affiliation: Division of Hematologic Malignancies and Cellular Therapy, Department of Medicine, Duke University, Durham, North Carolina 27710, USA.
authors.forename: Phuong L
authors.initials: PL
authors.lastname: Doan
authors.forename: J Lauren
authors.initials: JL
authors.lastname: Russell
authors.forename: Heather A
authors.initials: HA
authors.lastname: Himburg
authors.forename: Katherine
authors.initials: K
authors.lastname: Helms
authors.forename: Jeffrey R
authors.initials: JR
authors.lastname: Harris
authors.forename: Joseph
authors.initials: J
authors.lastname: Lucas
authors.forename: Kirsten C
authors.initials: KC
authors.lastname: Holshausen
authors.forename: Sarah K
authors.initials: SK
authors.lastname: Meadows
authors.forename: Pamela
authors.initials: P
authors.lastname: Daher
authors.forename: Laura B
authors.initials: LB
authors.lastname: Jeffords
authors.forename: Nelson J
authors.initials: NJ
authors.lastname: Chao
authors.forename: David G
authors.initials: DG
authors.lastname: Kirsch
authors.forename: John P
authors.initials: JP
authors.lastname: Chute
mesh_terms: D000818:Animals; D001854:Bone Marrow Cells / Q000378:metabolism* / Q000473:pathology / Q000528:radiation effects; D015820:Cadherins / Q000235:genetics / Q000378:metabolism; D042783:Endothelial Cells / Q000378:metabolism* / Q000473:pathology / Q000528:radiation effects; D015870:Gene Expression / Q000528:radiation effects; D018380:Hematopoietic Stem Cell Transplantation; D006412:Hematopoietic Stem Cells / Q000378:metabolism* / Q000473:pathology / Q000528:radiation effects; D051379:Mice; D008822:Mice, Transgenic; D011833:Radiation Injuries, Experimental / Q000235:genetics / Q000378:metabolism* / Q000401:mortality / Q000473:pathology; D020794:Receptor Protein-Tyrosine Kinases / Q000235:genetics* / Q000378:metabolism; D042787:Receptor, TIE-2; D012038:Regeneration / Q000528:radiation effects; D015398:Signal Transduction / Q000528:radiation effects; D016019:Survival Analysis; D014916:Whole-Body Irradiation; D050998:bcl-2 Homologous Antagonist-Killer Protein / Q000172:deficiency / Q000235:genetics; D051028:bcl-2-Associated X Protein / Q000172:deficiency / Q000235:genetics
chemical_list: C494773:Bak1 protein, mouse; C494827:Bax protein, mouse; D015820:Cadherins; D050998:bcl-2 Homologous Antagonist-Killer Protein; D051028:bcl-2-Associated X Protein; D020794:Receptor Protein-Tyrosine Kinases; D042787:Receptor, TIE-2; C079086:Tek protein, mouse