Project description:Hematopoietic 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 cells3, CXCL12-abundant reticular (CAR) cells, leptin-receptor positive stromal cells, and nestin-GFP positive mesenchymal progenitors have all been implicated in HSC maintenance. However, it is unclear if specific hematopoietic progenitor cell (HPC) subsets reside in distinct niches defined by the surrounding stromal cells and the regulatory molecules they produce. CXCL12 (stromal-derived factor-1, SDF-1) 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 includes CAR cells and osteoblasts, results in constitutive HPC mobilization and a loss of B lymphoid progenitors, but HSC function is normal. Cxcl12 deletion in endothelial cells results in a modest loss of long-term repopulating activity. Strikingly, deletion of Cxcl12 in nestin-negative mesenchymal progenitors using Prx1-Cre 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 HPC in the bone marrow, while expression of CXCL12 from stromal cells in the perivascular region, including endothelial cells and mesenchymal progenitors, support HSCs. Total of three samples of two groups analyzed. Replica samples of CXCL12-abundant reticular (CAR) cells from two CXCL12-GFP knock-in mice and a combined sample of PDGFRa+ Sca+ CD45- lineage- cells from three Prx1-Cre Rosa26Ai9/+ Cxcl12gfp/+ mice were used and analyzed.
Project description:Hematopoietic 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 cells3, CXCL12-abundant reticular (CAR) cells, leptin-receptor positive stromal cells, and nestin-GFP positive mesenchymal progenitors have all been implicated in HSC maintenance. However, it is unclear if specific hematopoietic progenitor cell (HPC) subsets reside in distinct niches defined by the surrounding stromal cells and the regulatory molecules they produce. CXCL12 (stromal-derived factor-1, SDF-1) 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 includes CAR cells and osteoblasts, results in constitutive HPC mobilization and a loss of B lymphoid progenitors, but HSC function is normal. Cxcl12 deletion in endothelial cells results in a modest loss of long-term repopulating activity. Strikingly, deletion of Cxcl12 in nestin-negative mesenchymal progenitors using Prx1-Cre 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 HPC in the bone marrow, while expression of CXCL12 from stromal cells in the perivascular region, including endothelial cells and mesenchymal progenitors, support HSCs.
Project description:Cellular competition for limiting hematopoietic factors is a physiologically regulated but poorly understood process. Here, we studied this phenomenon by hampering hematopoietic progenitor access to Leptin receptor+ mesenchymal stem/progenitor cells (MSPCs) and endothelial cells (ECs). We showed that HSC numbers increased by 2-fold when multipotent and lineage-restricted progenitors fail to respond to CXCL12 produced by MSPCs and ECs. HSCs were qualitatively normal, and HSC expansion only occurred when early hematopoietic progenitors but not differentiated hematopoietic cells lacked CXCR4. Furthermore, the MSPC and EC transcriptomic heterogeneity was remarkably stable, suggesting that it is impervious to dramatic changes in hematopoietic progenitor interactions. Instead, HSC expansion was caused by increased availability of membrane-bound stem cell factor (mSCF) on MSPCs and ECs due to reduced consumption by cKit-expressing hematopoietic progenitors. These studies revealed an intricate homeostatic balance between HSCs and proximal hematopoietic progenitors regulated by cell competition for limiting amounts of mSCF.
Project description:Cellular competition for limiting hematopoietic factors is a physiologically regulated but poorly understood process. Here, we studied this phenomenon by hampering hematopoietic progenitor access to Leptin receptor+ mesenchymal stem/progenitor cells (MSPCs) and endothelial cells (ECs). We showed that HSC numbers increased by 2-fold when multipotent and lineage-restricted progenitors fail to respond to CXCL12 produced by MSPCs and ECs. HSCs were qualitatively normal, and HSC expansion only occurred when early hematopoietic progenitors but not differentiated hematopoietic cells lacked CXCR4. Furthermore, the MSPC and EC transcriptomic heterogeneity was remarkably stable, suggesting that it is impervious to dramatic changes in hematopoietic progenitor interactions. Instead, HSC expansion was caused by increased availability of membrane-bound stem cell factor (mSCF) on MSPCs and ECs due to reduced consumption by cKit-expressing hematopoietic progenitors. These studies revealed an intricate homeostatic balance between HSCs and proximal hematopoietic progenitors regulated by cell competition for limiting amounts of mSCF.
Project description:The Cxcr4-Cxcl12 axis has been postulated as a critical pathway dictating leukemia stem cell (LSCs) chemoresistance in AML due to its role in controlling cellular egress from the marrow. Nevertheless, the cellular source of Cxcl12 in the AML microenvironment and the mechanism by which Cxcl12 exert its protective role in AML in vivo remain unresolved. We have evaluated the functional role of Cxcl12 secreted by early mesenchymal stromal cells (MSCs) and osteolineage committed cells in acute myeloid leukemia (AML) maintenance in vivo. Our results demonstrate that early MSCs, in contrast to committed osteoblasts, are integral part of the MLL::AF9 derived AML niche and control LSCs maintenance through Cxcl12 secretion. Cxcl12 from MSCs regulates the oxidative state of LSCs and promotes energy metabolism. Furthermore, the protective role of the niche through the activation of the CXCL12-CXCR4 axis, may also represent a biological hallmark in human pediatric and adult AML, hence, reinforcing the notion that targeting the MSCs-derived CXCL12 may help eradicate leukemia.
Project description:Osteoblasts are a key component of the endosteal hematopoietic stem cell (HSC) niche and have long been recognized with strong hematopoietic supporting activity. Osteoblast conditioned media (OCM) enhances the growth of hematopoietic progenitors in culture and modulate their engraftment activity. We aimed to characterize the hematopoietic supporting activity of OCM by comparing the secretome of immature osteoblasts to that of their precursor, mesenchymal stromal cells (MSC). Over 300 secreted proteins were quantified by mass spectroscopy in media conditioned with MSC or osteoblasts, with 47 being differentially expressed.
Project description:HIF-1a and HIF-2a are expressed at high levels in mesenchymal progenitors compared to more committed mesenchymal cells and hematopoietic cells. HIF-factors could therefore have a role in the regulation the biology of mesenchymal progenitors and their functions, like the non cell-autonomous maintenance of hematopoietic progenitors. We used microarrays to detail the global program of gene expression regulated by HIF-1a or HIF-2a in mesenchymal progenitors Mesenchymal progenitors were FACS-sorted and cultured in low oxygen concentration for few days. Once cells started to form CFU-F colonies, we transduced them with shRNAs targeting specifically HIF-1a or HIF-2a. Four days after transduction, cells were collected and RNA extracted for microarray analysis.
Project description:HIF-1a and HIF-2a are expressed at high levels in mesenchymal progenitors compared to more committed mesenchymal cells and hematopoietic cells. HIF-factors could therefore have a role in the regulation the biology of mesenchymal progenitors and their functions, like the non cell-autonomous maintenance of hematopoietic progenitors. We used microarrays to detail the global program of gene expression regulated by HIF-1a or HIF-2a in mesenchymal progenitors
Project description:Osteoblasts are a key component of the endosteal hematopoietic stem cell (HSC) niche and have long been recognized with strong hematopoietic supporting activity. Osteoblast conditioned media (OCM) enhances the growth of hematopoietic progenitors in culture and modulate their engraftment activity. We aimed to characterize the hematopoietic supporting activity of OCM by comparing the secretome of immature osteoblasts to that of their precursor, mesenchymal stromal cells (MSC). Over 300 secreted proteins were quantified by mass spectroscopy in media conditioned with MSC or osteoblasts, with 47 being differentially expressed.
Project description:Hematopoiesis in adult mammals involves cognate interactions between developing hematopoietic cells and bone marrow stromal cell niches. SCF and CXCL12 play key roles in the maintenance of HSC, while early B cell differentiation requires CXCL12 and IL7. In this study, we characterized mouse BM stromal cells expressing IL7 by performing a transcriptomic analysis. We found that SCF, CXCL12 and IL7 were co-expressed by a unique peri-sinusoidal stromal cell subset.