Abstract
Reactivation of endogenous hematopoietic stem cells (HSCs) are initiated by stimulation of bone marrow niche triggered by various injury signals. Here, we show that treatment with 5-fluorouracil (5-FU) leads to reconstruction of bone marrow (BM) microenvironment to establish an activated niche stimulating hematopoietic stem cells (HSCs). First, we show that pre-treatment with 5-FU leads to engraftment of donor cells in non-irradiated recipient mice without affecting the homing efficiency of HSCs into BM. The HSC activation effects were reproduced in-vitro by co-culturing hematopoietic cells with CD45-Ter119- stromal cells derived from 5-FU treated BM, but not by co-culture with CD45+ cells or stromal cells obtained from enzymatic digestion of bone from the same mice. Examination of BM mesenchymal cells after 5-FU treatment revealed a rapid emergence of high-proliferating mesenchymal progenitors exhibiting large size colony (CFU-F) and higher self-renewal of colonogenic cells 3-5 days after 5-FU treatment, which was concomitantly associated with regeneration of CD34+Lin-Sca-1+c-kit+ (LSK) cells in the same BM. The cellular changes in mesenchymal stroma was associated with rapid emergence of characteristic mesenchymal cell populations (PDGFR-a+/Leptin receptor+/SSEA-3+: PLS) with 650-folds increase of the PLS cells in BM in 3 days after 5-FU treatment. However, the increase of these PLS mesenchymal cells were not associated with increase in mitotic activity of mesenchymal cells (<5% BrdU+ cells), indicating phenotypic conversion of subpopulation in BM. Moreover, cellular changes in mesenchymal niche were associated with rapid increase of mesenchymal cells expressing cross-talk molecules such as CXCL-12 (20-folds), Jagged-1 (13-folds) and DLL-1 (15-folds). Furthermore, in-vivo administration of chemicals blocking CXCL-12 and notch signaling during the recovery from the 5-FU treatment led to the significant loss of LSK-SLAM cells in the regenerated BM. Interestingly, the BM niche activated by 5-FU exerted a distinct effect on normal and leukemic cells in a manner that it provide higher support on the primitive state of normal HSCs than for MN-1 induced leukemia cells. Thus, leukemic mice engrafted with MN-1 cells exhibited a decrease in primitive leukemic cell (Lin-c-kit+) and higher survival by 5-FU treatment than those treated by radiation. Taken together, our study reveals the cellular reconstruction of mesenchymal niche in BM during stimulus-induced niche activation and provides an insight on the selective niche targeting as a novel therapeutic strategies for hematological diseases. DisclosuresNo relevant conflicts of interest to declare.
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