In the bone tissue marrow cavity hematopoietic stem cells (HSC) have

In the bone tissue marrow cavity hematopoietic stem cells (HSC) have been shown to reside in the endosteal and subendosteal perivascular ALPHA-RLC niches which perform specific tasks on HSC maintenance. open. In the present report we used our previously explained assay to demonstrate that endosteal and subendosteal stromal populations are very unique concerning skeletal lineage differentiation potential. This was further supported by a microarray-based analysis which also shown that these two stromal populations play unique albeit complementary tasks in HSC market. Both stromal populations were preferentially isolated from your trabecular region and behave distinctly assays and molecular analyses allowed us to identify endosteal stroma (F-OST) cells as fully committed osteoblasts and subendosteal stroma (F-RET) cells as uncommitted mesenchymal cells primarily displayed by perivascular reticular cells expressing high levels of chemokine ligand CXCL12. Interestingly a number of cytokines and growth factors including interleukin-6 (IL-6) IL-7 IL-15 Hepatocyte growth factor (HGF) and stem cell factor (SCF) matrix metalloproteases (MMPs) were also found to be differentially expressed by F-OST and F-RET cells. Further microarray analyses indicated important mechanisms used by the two stromal compartments in order to create and coordinate the “quiescent” and “proliferative” niches in which hematopoietic stem cells and progenitors reside. by Taichman and Emerson (1994a; 1994b; 1996; 1998) and later evidence was acquired by others (Calvi et al. 2003 Zhang et al. 2003 Visnjic et al. 2004 An increased number of osteoblasts in the marrow cavity lead to an increased number of long-term HSC without affecting any other hematopoietic subpopulation in the bone marrow (Calvi et al. 2003 Zhang et al. ENMD-2076 2003 Furthermore osteoblast ablation from the marrow cavity results in a loss of HSCs (Visnjic et al. 2004 These data provide evidence that osteoblasts play a crucial role in HSC maintenance and behavior. HSCs also reside in the perivascular niche (Arai et al. 2004 Kiel et al. 2005 Sugiyama et al. 2006 in the abluminal side of bone marrow sinusoids interacting with the endothelial and perivascular reticular cells. Sugiyama et al.9 ENMD-2076 observed that HSCs residing in the perivascular niche were in close association with reticular cells which express high levels of CXCL12 a chemokine required for HSC maintenance and lodging (Jung et al. 2006 observation demonstrated that most of hematopoietic stem cells are concentrated in the trabecular zone of the marrow cavity which also harbors high numbers of niche osteblasts sinusoids and CXCL12-positive reticular cells (Calvi et al. 2003 Zhang et al. 2003 Sugiyama et al. 2006 Functional assays indicated that HSC maintenance by both endosteal and perivascular niches are at least in part mediated by Jagged-Notch (Calvi ENMD-2076 et al. 2003 and angiopoietin-1-Tie2 interactions (Arai et al. 2004 Several studies demonstrate that fast-cycling HSCs preferentially reside in vascular niche also ENMD-2076 referred as to “the proliferative niche” whereas quiescent/slow-cycling HSCs are found in close association with endosteal osteoblasts which create a “quiescent niche” (Zhang et al. 2003 ENMD-2076 Arai et al. 2004 Wilson and Trumpp 2006 Parmar et al. 2007 Robey 2011). This is evidenced in myelosuppressive models in which HSCs colonizing the vascular niches in the subendosteal region are mostly ablated. Although still controversial and depending on the ablation protocol used almost all HSCs in contact with endosteal osteoblasts are preserved (Arai et al. 2004 Kiel et al. 2007 Whether this heterogeneous distribution and/or HSC cycling behavior regarding the two niches rely upon the part played by both stromal populations can be a query that remains open up. Different markers such as for example Osteopontin and Sca-1 have already been used to distinguish and isolate osteoblasts from other stromal cells (Mayack and Wagers 2008 Winkler et al. 2010 However most of the markers tested are not only expressed by osteoblasts but also mesenchymal cells at distinct stage of differentiation. In our previous work we established a protocol to isolate and culture separately endosteal osteoblasts (F-OST) and subendosteal reticular cells (F-RET) from the marrow cavity of murine long bones (Balduino et al. 2005 and suggested that F-OST and F-RET fractions mainly comprised.