title: CXCL12 in early mesenchymal progenitors is required for haematopoietic stem-cell maintenance.
abstract: Haematopoietic stem cells (HSCs) primarily reside in the bone marrow where signals generated by stromal cells regulate their self-renewal, proliferation and trafficking. Endosteal osteoblasts and perivascular stromal cells including endothelial cells, CXCL12-abundant reticular cells, leptin-receptor-positive stromal cells, and nestin-green fluorescent protein (GFP)-positive mesenchymal progenitors have all been implicated in HSC maintenance. However, it is unclear whether specific haematopoietic progenitor cell (HPC) subsets reside in distinct niches defined by the surrounding stromal cells and the regulatory molecules they produce. CXCL12 (chemokine (C-X-C motif) ligand 12) regulates both HSCs and lymphoid progenitors and is expressed by all of these stromal cell populations. Here we selectively deleted Cxcl12 from candidate niche stromal cell populations and characterized the effect on HPCs. Deletion of Cxcl12 from mineralizing osteoblasts has no effect on HSCs or lymphoid progenitors. Deletion of Cxcl12 from osterix-expressing stromal cells, which include CXCL12-abundant reticular cells and osteoblasts, results in constitutive HPC mobilization and a loss of B-lymphoid progenitors, but HSC function is normal. Cxcl12 deletion from endothelial cells results in a modest loss of long-term repopulating activity. Strikingly, deletion of Cxcl12 from nestin-negative mesenchymal progenitors using Prx1-cre (Prx1 also known as Prrx1) is associated with a marked loss of HSCs, long-term repopulating activity, HSC quiescence and common lymphoid progenitors. These data suggest that osterix-expressing stromal cells comprise a distinct niche that supports B-lymphoid progenitors and retains HPCs in the bone marrow, and that expression of CXCL12 from stromal cells in the perivascular region, including endothelial cells and mesenchymal progenitors, supports HSCs.
authors: Department of Medicine, Washington University School of Medicine, St Louis, Missouri 63110, USA.
authors: Adam
authors: A
authors: Greenbaum
authors: Yen-Michael S
authors: YM
authors: Hsu
authors: Ryan B
authors: RB
authors: Day
authors: Laura G
authors: LG
authors: Schuettpelz
authors: Matthew J
authors: MJ
authors: Christopher
authors: Joshua N
authors: JN
authors: Borgerding
authors: Takashi
authors: T
authors: Nagasawa
authors: Daniel C
authors: DC
authors: Link
mesh_terms: D000818:Animals; D001402:B-Lymphocytes / Q000166:cytology; D001853:Bone Marrow / Q000378:metabolism; D002465:Cell Movement; D054426:Chemokine CXCL2 / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D006412:Hematopoietic Stem Cells / Q000166:cytology* / Q000378:metabolism*; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism; D007381:Intermediate Filament Proteins / Q000172:deficiency; D054503:Lymphoid Progenitor Cells / Q000166:cytology / Q000378:metabolism; D059630:Mesenchymal Stem Cells / Q000166:cytology / Q000378:metabolism*; D051379:Mice; D009419:Nerve Tissue Proteins / Q000172:deficiency; D064231:Nestin; D020796:Receptor, Platelet-Derived Growth Factor alpha / Q000235:genetics / Q000378:metabolism; D055153:Stem Cell Niche / Q000502:physiology
chemical_list: D054426:Chemokine CXCL2; C404915:Cxcl2 protein, mouse; D018398:Homeodomain Proteins; D007381:Intermediate Filament Proteins; D009419:Nerve Tissue Proteins; C577485:Nes protein, mouse; D064231:Nestin; C489936:Prrx1 protein, mouse; D020796:Receptor, Platelet-Derived Growth Factor alpha