Year: 2011
Type: article
Abstract: Hematopoietic stem cells (HSCs) reside in anatomic association with sinusoidal vessels in the bone marrow (BM), but the mechanisms through which BM endothelial cells regulate HSC regeneration remain unknown. We measured the function of BM ECs in regulating hematopoietic regeneration after ionizing radiation by deletion of the pro-apoptotic genes, Bak and Bax, within Tie2+ cells in Tie2Cre;Bak−/−;BaxFl/- mice. Following a lethal dose of total body irradiation (TBI), these mice demonstrated protection of BM HSCs and 100% survival, whereas mice that retained Bax expression in Tie2+ cells demonstrated depletion of BM HSCs and only 10% survival (p < 0.0001). Chimeric mice which lacked Bak and Bax in BM HSCs but retained Bak and Bax in BM ECs demonstrated an intermediate phenotype (42% survival), indicating that the intrinsic pathway of apoptosis regulates HSC survival from radiation in an HSC-autonomous manner and via an EC-dependent mechanism. To determine the mechanism through which Tie2+ BM ECs regulate HSC regeneration, we generated primary BM EC lines from Tie2Cre;Bak−/−;BaxFl/- mice (Bax−/− BM ECs) and Tie2Cre;Bak−/−;BaxFl/+ control mice (Bax+/- BM ECs). BM c-kit+sca-1+lin- (KSL) stem/progenitor cells were irradiated with 300 cGy and then placed in 7 day culture with Bax−/− BM ECs or Bax+/- BM ECs. Culture with Bax−/− BM ECs yielded a 2000-fold increased number of BM KSL cells (p < 0.05) compared to cultures with Bax+/- ECs. This significant expansion of phenotypic BM stem/progenitor cells corresponded to a 4-fold increase in CFU-S12 cells in the Bax−/− EC cultures vs. Bax+/- EC cultures (p = 0.01). Interestingly, following TBI, mice bearing Bak and Bax deletion in BM ECs displayed 18-fold increased concentration of epidermal growth factor (EGF) in BM serum compared to control mice (p = 0.04), and inhibition of EGF signaling blocked the ability of Bax−/− BM ECs to support the expansion of BM HSCs following irradiation compared to culture with Bax−/− ECs alone (p = 0.0002). Moreover, the addition of EGF to Bax+/- BM ECs culture compared to culture with Bax+/- BM ECs alone significantly increased the recovery of BM HSCs and progenitor cells following irradiation (p = 0.0004), which was comparable to the recovery of BM HSCs and progenitor cells observed in Bax−/− BM EC cultures. These data demonstrate that therapeutic protection of the BM vascular niche protects BM HSCs from myelotoxic injury, and this protection is mediated by EGF action on BM HSCs.
Authors: P.L. Doan, J.L. Russell, H.A. Himburg, K. Helms, S.K. Meadows, P. Daher, J.M. Sullivan, L.B. Jeffords, N.J. Chao, D.G. Kirsch, J.P. Chute
Institution: Duke Medical Center
Language: English
Subfield: Hematology
Field: Medicine
Domain: Health Sciences
Open Access status: hybrid
Estimated APC paid: $3,650
OpenAlex ID: W1964997066