Project description:We here show that the niche regulates the quality of the hematopoietic stem cells (HSCs) that are regenerated after transplantation. We find that a reduced level of Wnt5a in the niche regenerates dysfunctional HSCs, which do not successfully engraft secondary recipients. In particular, RNA sequencing shows a dysregulated Zeb1-associated gene expression of multiple genes involved in the small GTPase-dependent actin polymerization pathway. Misexpression of these genes results in reduced ability to direct polarized F-actin localization, leading to defects in adhesion, migratory behavior and homing to the bone marrow of secondary recipients. Our study further shows that the Wnt5a-haploinsufficient environment similarly affects BCR-ABLp185+ cells, which, in 42% of the studied recipients, fail to generate leukemia and, in the remaining cases, fail to transfer leukemia to secondary hosts. Thus, we show that Wnt5a in the niche is required to regenerate HSCs and leukemic cells with functional ability to rearrange the actin cytoskeleton which is required for successful engraftment.
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) 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. Transcriptome sequencing of bone marrow endothelial cells and bone marrow stroma, in vitro and in vivo, with and without HSC co-culture.
Project description:The importance of extrinsic regulation of hematopoietic stem cell activity is increasingly acknowledged. Here we report the generation of a new niche system, which supports expansion of mouse hematopoietic stem cells in vitro. Characterization of this niche revealed a transcriptional regulatory network including four critical factors, namely FOS, SPI1, KLF10 and TFEC. Interestingly, these factors are essential for osteoclastogenesis, thus revealing an osteoclastic network that supports hematopoietic stem cell self-renewal. Lentiviral vectors containing putative transcription factors regulating HSC expansion were transfected into GPE cells and gene expression values were compared to empty vector controls.
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:The importance of extrinsic regulation of hematopoietic stem cell activity is increasingly acknowledged. Here we report the generation of a new niche system, which supports expansion of mouse hematopoietic stem cells in vitro. Characterization of this niche revealed a transcriptional regulatory network including four critical factors, namely FOS, SPI1, KLF10 and TFEC. Interestingly, these factors are essential for osteoclastogenesis, thus revealing an osteoclastic network that supports hematopoietic stem cell self-renewal.
Project description:Maintenance of hematopoietic stem cell (HSC) function in the niche is an orchestrated event. Osteomacs (OM), are key cellular components of the niche. Previously, we documented that osteoblasts, OM, and megakaryocytes interact to promote hematopoiesis. Here, we further characterize OM and identify megakaryocyte-induced mediators that augment the role of OM in the niche. Single cell mRNAseq, mass spectrometry, and CyTOF examination of megakaryocyte-stimulated OM suggested that upregulation of CD166 and Embigin on OM augment their hematopoiesis maintenance function. CD166 knockout OM or shRNA-Embigin knockdown OM, confirmed that loss of these molecules significantly reduced OM ability to augment the osteoblast-mediated hematopoietic enhancing activity. Recombinant CD166 and Embigin partially substituted for OM function, characterizing both proteins as critical mediators of OM hematopoietic function. Our data identify Embigin and CD166 as OM-regulated critical components of HSC function in the niche and potential participants in various in vitro manipulations of stem cells.
Project description: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.
Project description:Jak3 is the only non-promiscuous member of the Jak family of secondary messengers. Jak3–/– mice display defective T and NK cell development, which results in a SCID phenotype. As a result, studies to date have focused on understanding and targeting the cell-autonomous role of Jak3 in immunity, while functional Jak3 expression outside the hematopoietic system remains largely unreported. We show that Jak3 is expressed in endothelial cells across hematopoietic and non-hematopoietic organs, with heightened expression in the bone marrow. The bone marrow niche is understood as a network of different cell types that regulate hematopoietic function. We show that the Jak3–/– bone marrow niche is deleterious for the maintenance of long-term repopulating hematopoietic stem cells (LT-HSCs) and that JAK3-overexpressing endothelial cells have increased potential to expand LT-HSCs in vitro. Increased arterial zonation in the bone marrow of Jak3–/– mice further situates Jak3 as a marker of sinusoidal endothelium. This work may serve to identify a novel function for a highly specific tyrosine kinase in the bone marrow vascular niche and to further characterize the LT-HSC function of sinusoidal endothelium.
Project description:Our research has demonstrated that high expression of surface cMPL receptor marks long-term repopulating human hematopoietic stem cells.