Stem cell factor is selectively secreted by arterial endothelial cells in bone marrow

Endothelial cells (ECs) contribute to haematopoietic stem cell (HSC) maintenance in bone marrow, but the differential contributions of EC subtypes remain unknown, owing to the lack of methods to separate with high purity arterial endothelial cells (AECs) from sinusoidal endothelial cells (SECs). Here we show that the combination of podoplanin (PDPN) and Sca-1 expression distinguishes AECs (CD45− Ter119− Sca-1bright PDPN−) from SECs (CD45− Ter119− Sca-1dim PDPN+). PDPN can be substituted for antibodies against the adhesion molecules ICAM1 or E-selectin. Unexpectedly, prospective isolation reveals that AECs secrete nearly all detectable EC-derived stem cell factors (SCF). Genetic deletion of Scf in AECs, but not SECs, significantly reduced functional HSCs. Lineage-tracing analyses suggest that AECs and SECs self-regenerate independently after severe genotoxic insults, indicating the persistence of, and recovery from, radio-resistant pre-specified EC precursors. AEC-derived SCF also promotes HSC recovery after myeloablation. These results thus uncover heterogeneity in the contribution of ECs in stem cell niches.
Endothelial cells (EC) are known to contribute to haematopoietic stem cell (HSC) maintenance in the bone marrow (BM). Here the authors demonstrate that arterial ECs can be distinguished from sinusoidal ECs by podoplanin and Sca-1 expression, and that specifically arterial, but not sinusoidal ECs maintain HSCs by secreting SCF.