Isolation and functional characterization of the arteriole hematopoietic stem cell niche

Hematopoietic stem cells (HSCs) inhabit distinct microenvironments within the adult bone marrow (BM) that govern the delicate balance between HSC quiescence, self-renewal, and differentiation. It has been suggested that quiescent HSCs localize adjacent to BM arteriole endothelial cells in a significant and non-random distribution. This data suggests that the arteriole BM vascular niche may be the primary HSC niche. Because the BM arteriole niche is composed of tightly-associated pericytes, including smooth muscle actin+, LepR+, Nestin+, NG2+, and nonmyelinating Schwann cells, we sought to begin to uncouple the arteriole BM EC niche by examining its capacity to support the maintenance and expansion of HSCs ex vivo and in vivo. We developed a method to isolate and culture BM arteriole endothelial cells in serum-/growth factor-free conditions, allowing for a non-biased approach to examining their instructive function. Utilizing our protocol, we demonstrate that BM endothelial cells, but not BM stromal cells, have the capacity to expand long-term repopulating, multi-lineage HSCs in lieu of complex serum and cytokine supplementation. In addition, transplantation of arteriole endothelial cells promoted rapid hematopoietic recovery and protected HSCs following an LD50 dose of myeloablative irradiation. These data demonstrate that arteriole-derived BM endothelial cells are endowed with the necessary signals to support the self-renewal and regenerative capacity of LT-HSCs and that transplantation of arteriole BM endothelial cells could be used as a therapeutic means to decrease pancytopenias associated with myeloablative treatments to treat a wide array of disease states. Overall design: Transcriptome sequencing of bone marrow endothelial cells and bone marrow stroma, in vitro and in vivo, with and without HSC co-culture.

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Poulos MG, Crowley MJP, Gutkin MC, Ramalingam P, Schachterle W, Thomas JL, Elemento O, Butler JM