Hematopoietic and stromal DMP1-Cre labeled cells form a unique niche in the bone marrow.

Skeletogenesis and hematopoiesis are interdependent. Niches form between cells of both lineages where microenvironmental cues support specific lineage commitment. Because of the complex topography of bone marrow (BM), the identity and function of cells within specialized niches has not been fully elucidated.

Novel population of human monocyte and osteoclast progenitors from pluripotent stem cells and peripheral blood.

Osteoclasts are multinuclear cells of monocytic lineage, with the ability to resorb bone. Studies in mouse have identified bone marrow clonal progenitors able to generate mature osteoclast cells (OCs) in vitro and in vivo. These osteoclast progenitors (OCPs) can also generate macrophages and dendritic cells.

Osteoclasts Derive Predominantly from Bone Marrow-Resident CXCR1 Precursor Cells in Homeostasis, whereas Circulating CXCR1 Cells Contribute to Osteoclast Development during Fracture Repair.

Osteoclasts (OC) originate from either bone marrow (BM)-resident or circulating myeloid OC progenitors (OCP) expressing the receptor CXCR1. Multiple lines of evidence argue that OCP in homeostasis and inflammation differ. We investigated the relative contributions of BM-resident and circulating OCP to osteoclastogenesis during homeostasis and fracture repair.

PI3K activation increases SDF-1 production and number of osteoclast precursors, and enhances SDF-1-mediated osteoclast precursor migration.

Our previous studies showed that in a mouse model in which PI3K-AKT activation was increased (YF mice), osteoclast numbers and levels of SDF-1, a chemokine, were augmented. The purpose of this study was to delineate the role of PI3K activation in regulating SDF-1 production and examine whether SDF-1 can stimulate differentiation and/or migration of osteoclast precursors. Using flow cytometric analysis, we demonstrated that compared to wild type mice, bone marrow of YF mice had increased numbers of CXCL12 abundant reticular (CAR) cells, that are a major cell type responsible for producing SDF-1.

Splenomegaly, myeloid lineage expansion and increased osteoclastogenesis in osteogenesis imperfecta murine.

Osteogenesis imperfecta (OI) is a disease caused by defects in type I collagen production that results in brittle bones. While the pathology is mainly caused by defects in the osteoblast lineage, there is also elevated bone resorption by osteoclasts resulting in high bone turnover in severe forms of the disease. Osteoclasts originate from hematopoietic myeloid cells, however changes in hematopoiesis have not been previously documented in OI.

Serum Amyloid A3 Secreted by Preosteoclasts Inhibits Parathyroid Hormone-stimulated cAMP Signaling in Murine Osteoblasts.

Continuous parathyroid hormone (PTH) blocks its own osteogenic actions in marrow stromal cell cultures by inducing Cox2 and receptor activator of nuclear factor κB ligand (RANKL) in the osteoblastic lineage cells, which then cause the hematopoietic lineage cells to secrete an inhibitor of PTH-stimulated osteoblast differentiation. To identify this inhibitor, we used bone marrow macrophages (BMMs) and primary osteoblasts (POBs) from WT and Cox2 knock-out (KO) mice. Conditioned medium (CM) from RANKL-treated WT, but not KO, BMMs blocked PTH-stimulated cAMP production in POBs.

CCR2+ Ly6C(hi) inflammatory monocyte recruitment exacerbates acute disability following intracerebral hemorrhage.

Intracerebral hemorrhage (ICH) is a devastating type of stroke that lacks a specific treatment. An intense immune response develops after ICH, which contributes to neuronal injury, disability, and death. However, the specific mediators of inflammation-induced injury remain unclear.

Pannexin1 channels act downstream of P2X 7 receptors in ATP-induced murine T-cell death.

Death of murine T cells induced by extracellular ATP is mainly triggered by activation of purinergic P2X 7 receptors (P2X 7Rs). However, a link between P2X 7Rs and pannexin1 (Panx1) channels, which are non-selective, has been recently demonstrated in other cell types. In this work, we characterized the expression and cellular distribution of pannexin family members (Panxs 1, 2 and 3) in isolated T cells.

Sex and genetic factors determine osteoblastic differentiation potential of murine bone marrow stromal cells.

Sex and genetic factors determine skeletal mass, and we tested whether bone histomorphometric parameters were sexually dimorphic in femurs from 1 to 6 month old C57BL/6 mice. Trabecular bone volume declined more rapidly in female mice than in male littermates because of enhanced bone resorption. Although bone formation was not different between sexes, female mice exhibited a higher number of osteoblasts than male littermates, suggesting that osteoblasts from female mice may have a reduced ability to form bone.

Transcriptional regulation of IL-15 expression during hematopoiesis.

Dendritic cells (DCs) are the most commonly studied source of the cytokine IL-15. Using an IL-15 reporter transgenic mouse, we have recently shown previously unappreciated differences in the levels of IL-15 expressed by subsets of conventional DCs (CD8⁺ and CD8⁻). In this study, we show that IL-15 promoter activity was differentially regulated in subsets of hematopoietically derived cells with IL-15 expression largely limited to myeloid lineages.

Identification, characterization, and isolation of a common progenitor for osteoclasts, macrophages, and dendritic cells from murine bone marrow and periphery.

Osteoclasts are specialized bone-resorbing cells that derive from monocyte precursors. We have identified three populations of cells with high osteoclastogenic potential in murine bone marrow, which expressed the phenotype B220(-) CD3(-) CD11b(-/low) CD115(+) and either CD117(hi), CD117(intermediate), or CD117(low). We have evaluated these populations for their ability to also generate macrophages and dendritic cells.

Deletion of CD74, a putative MIF receptor, in mice enhances osteoclastogenesis and decreases bone mass.

CD74 is a type II transmembrane protein that can act as a receptor for macrophage migration inhibitory factor (MIF) and plays a role in MIF-regulated responses. We reported that MIF inhibited osteoclast formation and MIF knockout (KO) mice had decreased bone mass. We therefore examined if CD74 was involved in the ability of MIF to alter osteoclastogenesis in cultured bone marrow (BM) from wild-type (WT) and CD74-deficient (KO) male mice.

Chemotactic and immunoregulatory properties of bone cells are modulated by endotoxin-stimulated lymphocytes.

In our study, we explored the bidirectional communication via soluble factors between bone cells and endotoxin-stimulated splenic lymphocytes in an in vitro coculture model that mimics the inflammatory environment. Both the ability of lymphocytes to affect differentiation and immune properties of bone cells, osteoblasts (OBL) and osteoclasts (OCL), and of bone cells to modulate cytokine and activation profile of endotoxin-stimulated lymphocytes were tested. LPS-pulsed lymphocytes enhanced OCL but inhibited OBL differentiation and increased the RANKL/OPG ratio, and, at the same time, upregulated chemotactic properties of bone cells, specifically CCL2, CCL5, and CXCL10 in OCL and CCL5 and CXCL13 in OBL.

Osteoblast-specific overexpression of human interleukin-7 rescues the bone mass phenotype of interleukin-7-deficient female mice.

Interleukin-7 is a critical cytokine for lymphoid development and a direct inhibitor of in vitro osteoclastogenesis in murine bone marrow cultures. To explore the role of IL-7 in bone, we generated transgenic mouse lines bearing the 2.3-kb rat collagen 1α1 promoter driving the expression of human IL-7 specifically in osteoblasts.

A novel population of cells expressing both hematopoietic and mesenchymal markers is present in the normal adult bone marrow and is augmented in a murine model of marrow fibrosis.

Bone marrow (BM) fibrosis is a feature of severe hyperparathyroidism. Consistent with this observation, mice expressing constitutively active parathyroid hormone (PTH)/PTH-related peptide receptors (PPR) in osteoblasts (PPR*Tg) display BM fibrosis. To obtain insight into the nature of BM fibrosis in such a model, a double-mutant mouse expressing constitutively active PPR and green fluorescent protein (GFP) under the control of the type I collagen promoter (PPR*Tg/GFP) was generated.

Parathyroid hormone regulates the distribution and osteoclastogenic potential of hematopoietic progenitors in the bone marrow.

Parathyroid hormone (PTH) increases both the number of osteoclast in bone and the number of early hematopoietic stem cells (HSCs) in bone marrow. We previously characterized the phenotype of multiple populations of bone marrow cells with in vitro osteoclastogenic potential in mice. Here we examined whether intermittent administration of PTH influences these osteoclast progenitor (OCP) populations.

A Phe377del mutation in ANK leads to impaired osteoblastogenesis and osteoclastogenesis in a mouse model for craniometaphyseal dysplasia (CMD).

Craniometaphyseal dysplasia (CMD) is a rare genetic disorder with hyperostosis of craniofacial bones and widened metaphyses in long bones. Patients often suffer from neurological symptoms due to obstruction of cranial foramina. No proven treatment is available and the pathophysiology is largely unknown.

CD13 is dispensable for normal hematopoiesis and myeloid cell functions in the mouse.

The robust and consistent expression of the CD13 cell surface marker on very early as well as differentiated myeloid hematopoietic cells has prompted numerous investigations seeking to define roles for CD13 in myeloid cells. To address the function of myeloid CD13 directly, we created a CD13 null mouse and assessed the responses of purified primary macrophages or DCs from WT and CD13 null animals in cell assays and inflammatory disease models, where CD13 has been implicated previously. We find that mice lacking CD13 develop normally with normal hematopoietic profiles except for an increase in thymic but not peripheral T cell numbers.

gp96, an endoplasmic reticulum master chaperone for integrins and Toll-like receptors, selectively regulates early T and B lymphopoiesis.

Integrins contribute to lymphopoiesis, whereas Toll-like receptors (TLRs) facilitate the myeloid replenishment during inflammation. The combined role of TLRs and integrin on hematopoiesis remains unclear. gp96 (grp94, HSP90b1) is an endoplasmic reticulum master chaperone for multiple TLRs.

Essential role of the RNA-binding protein HuR in progenitor cell survival in mice.

The RNA-binding protein HuR (also known as ELAV1) binds to the 3'-untranslated region of mRNAs and regulates transcript stability and translation. However, the in vivo functions of HuR are not well understood. Here, we report that murine HuR is essential for life; postnatal global deletion of Elavl1 induced atrophy of hematopoietic organs, extensive loss of intestinal villi, obstructive enterocolitis, and lethality within 10 days.

Macrophage migration inhibitory factor inhibits osteoclastogenesis.

MIF is an important regulator of innate and adaptive immunity, which is produced by a variety of cell types including activated T cells and macrophages. We examined the effects of MIF on osteoclastogenesis in bone marrow (BM) cultures from WT and MIF-deficient (KO) mice as well as the bone mass of MIF KO mice. Exogenous MIF inhibited osteoclast formation in BM cultures by decreasing fusion in cells that were treated with M-CSF and RANKL.

Self-antigen prevents CD8 T cell effector differentiation by CD134 and CD137 dual costimulation.

We compared how CD4 vs CD8 cells attain the capacity to express the effector cytokine IFN-gamma under both immunogenic and tolerogenic conditions. Although the Ifng gene locus was epigenetically repressed in naive Ag-inexperienced CD4 cells, it had already undergone partial remodeling toward a transcriptionally competent configuration in naive CD8 cells. After TCR stimulation, CD8 cells fully remodeled the Ifng locus and gained the capacity to express high levels of IFN-gamma more rapidly than CD4 cells.

Use of an alpha-smooth muscle actin GFP reporter to identify an osteoprogenitor population.

Identification of a reliable marker of skeletal precursor cells within calcified and soft tissues remains a major challenge for the field. To address this, we used a transgenic model in which osteoblasts can be eliminated by pharmacological treatment. Following osteoblast ablation a dramatic increase in a population of alpha-smooth muscle actin (alpha-SMA) positive cells was observed.