Cloning and identification of human Sca as a novel inhibitor of osteoclast formation and bone resorption

Mechanistic Insights into Eosinophilic Esophagitis: Therapies Targeting Pathophysiological Mechanisms

Eosinophilic esophagitis (EoE) is a chronic inflammatory disease characterized by eosinophilic infiltration of the esophagus. It arises from a complex interplay of genetic predisposition (susceptibility loci), environmental triggers (allergens and dietary antigens), and a dysregulated immune response, mainly mediated by type 2 T helper cell (Th2)-released cytokines, such as interleukin (IL)-4, IL-5, and IL-13. These cytokines control eosinophil recruitment and activation as well as tissue remodeling, contributing to the characteristic features of EoE. The pathogenesis of EoE includes epithelial barrier dysfunction, mast cell activation, eosinophil degranulation, and fibrosis. Epithelial barrier dysfunction allows allergen penetration and promotes immune cell infiltration, thereby perpetuating the inflammatory response. Mast cells release proinflammatory mediators and promote eosinophil recruitment and the release of cytotoxic proteins and cytokines, causing tissue damage and remodeling. Prolonged inflammation can lead to fibrosis, resulting in long-term complications such as strictures and dysmotility. Current treatment options for EoE are limited and mainly focus on dietary changes, proton-pump inhibitors, and topical corticosteroids. Novel therapies targeting key inflammatory pathways, such as monoclonal antibodies against IL-4, IL-5, and IL-13, are emerging in clinical trials. A deeper understanding of the complex pathogenetic mechanisms behind EoE will contribute to the development of more effective and personalized therapeutic strategies.

Novel insights of EZH2-mediated epigenetic modifications in degenerative musculoskeletal diseases

Degenerative musculoskeletal diseases (Osteoporosis, Osteoarthritis, Degenerative Spinal Disease and Sarcopenia) are pathological conditions that affect the function and pain of tissues such as bone, cartilage, and muscles, and are closely associated with ageing and long-term degeneration. Enhancer of zeste homolog 2 (EZH2), an important epigenetic regulator, regulates gene expression mainly through the PRC2-dependent trimethylation of histone H3 at lysine 27 (H3K27me3). Increasing evidence suggests that EZH2 is involved in several biological processes closely related to degenerative musculoskeletal diseases, such as osteogenic-adipogenic differentiation of bone marrow mesenchymal stem cells, osteoclast activation, chondrocyte functional status, and satellite cell proliferation and differentiation, mainly through epigenetic regulation (H3K27me3). Therefore, the synthesis and elucidation of the role of EZH2 in degenerative musculoskeletal diseases have attracted increasing attention. In addition, although EZH2 inhibitors have been approved for clinical use, whether they can be repurposed for the treatment of degenerative musculoskeletal diseases needs to be considered. Here, we reviewed the role of EZH2 in the development of degenerative musculoskeletal diseases and brought forward prospects of its pharmacological inhibitors in the improvement of the treatment of the diseases.

Human LY6 gene family: potential tumor-associated antigens and biomarkers of prognosis in uterine corpus endometrial carcinoma

The human Lymphocyte antigen-6 (LY6) gene family has recently gained interest for its possible role in tumor progression. We have carried out in silico analyses of all known LY6 gene expression and amplification in different cancers using TNMplot and cBioportal. We also have analyzed patient survival by Kaplan-Meier plotter after mining the TCGA database. We report that upregulated expression of many LY6 genes is associated with poor survival in uterine corpus endometrial carcinoma (UCEC) cancer patients. Importantly, the expression of several LY6 genes is elevated in UCEC when compared to the expression in normal uterine tissue. For example, LY6K expression is 8.25× higher in UCEC compared to normal uterine tissue, and this high expression is associated with poor survival with a hazard ratio of 2.42 (p-value = 0.0032). Therefore, some LY6 gene products may serve as tumor-associated antigens in UCEC, biomarkers for UCEC detection, and possibly targets for directing UCEC patient therapy. Further analysis of tumor-specific expression of LY6 gene family members and LY6-triggered signaling pathways is needed to uncover the function of LY6 proteins and their ability to endow tumor survival and poor prognosis in UCEC patients.

Transgenic mice with OIP-1/hSca overexpression targeted to the osteoclast lineage develop an osteopetrosis bone phenotype

Regulatory mechanisms operative in bone-resorbing osteoclasts are complex. We previously defined the Ly-6 gene family member OIP-1/hSca as an inhibitor of osteoclastogenesis in vitro; however, a role in skeletal development is unknown. In this study, we developed transgenic mice with OIP-1/hSca expression targeted to the osteoclast lineage that develop an osteopetrotic bone phenotype. Humeri from OIP-1 mice showed a significant increase in bone mineral density and bone mineral content. microCT analysis showed increased trabecular thickness and bone volume. OIP-1 mice have dense sclerotic cortical bone with absence of spongiosa and inadequate formation of marrow spaces compared to wild-type mice. Moreover, complete inhibition of osteoclasts and marrow cavities in calvaria suggests defective bone resorption in these mice. OIP-1 mouse bone marrow cultures demonstrated a significant decrease (41%) in osteoclast progenitors and inhibition (39%) of osteoclast differentiation/bone resorption. Western blot analysis further demonstrated suppression of TRAF-2, c-Fos, p-c-Jun, and NFATc1 levels in RANKL-stimulated osteoclast precursors derived from OIP-1 mice. Therefore, OIP-1 is an important physiological inhibitor of osteoclastogenesis and may have therapeutic value against bone loss in vivo.

Regulation of osteoclast differentiation

The osteoclast (OCL) is derived from the cells in monocyte-macrophage lineage. The earliest identifiable OCL precursor is the granulocyte-macrophage colony-forming unit (CFU-GM), which gives rise to granulocytes, monocytes, and OCL. CFU-GM-derived cells then differentiate to committed OCL precursors, which are post-mitotic cells, and fuse to form multinucleated OCL. A variety of factors both positively and negatively regulate OCL formation and activity. These include growth factors, such as macrophage colony-simulating factor, which simulates the proliferation and prevents apoptosis of early OCL precursors, and RANK ligand (RANKL), which is the primary mediator of OCL formation. Most factors that induce OCL differentiation, such as PTHrP, IL-11, and prostaglandins, do so by inducing expression of RANKL on the surface of immature osteoblasts. Osteoprotegerin is a decoy receptor that blocks RANKL activity. In addition, OCL produce autocrine-paracrine factors that regulate OCL formation, such as IL-6, which is produced at high levels by OCL in Paget's disease and increases OCL formation. We screened human and murine OCL cDNA libraries to identify autocrine-paracrine factors that regulate OCL activity. We identified annexin-II, MIP-1alpha, ADAM8, eosinophil chemotactic factor, and OCL inhibitor factors 1 and 2 as factors involved in OCL formation. Most recently, we have identified the receptor for ADAM8, alpha9beta1 integrin, which appears to be critical for normal OCL activity. OCL differentiation is controlled by exogenous hormones and cytokines as well as autocrine-paracrine factors that positively or negatively regulate OCL proliferation and differentiation.

Eosinophil chemotactic factor-L (ECF-L): a novel osteoclast stimulating factor

Screening a cDNA library enriched for genes expressed in OCLs identified ECF-L. ECF-L enhanced OCL formation without increasing RANKL levels. Anti-ECF-L inhibited RANKL-induced OCL formation. These results support a potent role of ECF-L in osteoclastogenesis.

INTRODUCTION

To investigate the molecular mechanisms that control osteoclastogenesis, we developed an immortalized osteoclast (OCL) precursor cell line that forms mature OCLs in the absence of stromal cells and used it to form pure populations of OCLs.

MATERIALS AND METHODS

Polymerase chain reaction (PCR) selective cDNA subtraction was used to identify genes that are highly expressed in mature OCLs compared with OCL precursors employing OCL and OCL precursors derived from this cell line.

RESULTS

Eosinophil chemotactic factor-L (ECF-L), a previously described chemotactic factor for eosinophils, was one of the genes identified. Conditioned media from 293 cells transfected with mECF-L cDNA, or purified ECF-L Fc protein, increased OCL formation in a dose-dependent manner in mouse bone marrow cultures treated with 10(-10) M 1,25(OH)2D3. OCLs derived from marrow cultures treated with ECF-L conditioned media formed increased pit numbers and resorption area per dentin slice compared with OCLs induced by 1,25(OH)2D3 (p < 0.01). Addition of an antisense S-oligonucleotide to mECF-L inhibited OCL formation in murine bone marrow cultures treated only with 10(-9) M 1,25(OH)2D3 compared with the sense S-oligonucleotide control. Time course studies demonstrated that ECF-L acted at the later stages of OCL formation, and chemotactic assays showed that mECF-L increased migration of OCL precursors. mECF-L mRNA was detectable in mononuclear and multinucleated cells by in situ hybridization. Interestingly, a neutralizing antibody to ECF-L blocked RANKL or 10(-9) M 1,25(OH)2D3-induced OCL formation in mouse bone marrow cultures, although ECF-L did not induce RANKL expression.

CONCLUSIONS

These data show ECF-L is a previously unknown factor that is a potent mediator of OCL formation, which acts at the later stages of OCL formation and enhances the effects of RANKL.

T-cells mediate an inhibitory effect of interleukin-4 on osteoclastogenesis

IL-4 is an important cytokine that can influence bone. We identified two distinct actions of IL-4 to inhibit osteoclast formation: one direct on osteoclast progenitors and the second through the production of a novel T-cell surface-associated molecule(s). These data show a new link between the immune system and bone. The Th2 cytokine interleukin (IL)-4 inhibits osteoclast formation in vitro but also acts on other cell types found in bone, including T-cells and macrophages. Because some osteoclastogenesis inhibitors (e.g., IL-12) act indirectly through T-cells, we investigated IL-4 action on osteoclastogenesis in the presence of T-cells. Osteoclast formation from murine spleen cells treated with RANKL and macrophage colony-stimulating factor (M-CSF) was blocked by IL-4 even when spleen cells were depleted of T-cells (Thy 1.2+) and/or B-cells (B220+). Also, IL-4 inhibited osteoclastogenesis in RANKL/M-CSF-stimulated adherent spleen cells, Rag1 -/- (lymphocyte-deficient) spleen cells, and bone marrow macrophages, indicating an action on myelomonocytic cells to block osteoclastogenesis. In contrast, IL-4 did not inhibit osteoclastogenesis in cells from IL-4 receptor null mice (IL-4R -/-). However, when wildtype T-cells were added to IL-4R -/- spleen cell cultures, IL-4 inhibited osteoclast formation, indicating a T-cell-dependent action. Osteoclast formation in RANKL-stimulated RAW 264.7 cells was not inhibited by IL-4 unless T-cells were added to the culture. Separation of RAW 264.7 cells and T-cells by semipermeable membrane ablated this action of IL-4, suggesting the induction of a membrane-associated osteoclastogenesis inhibitor. However, membrane-bound inhibitors thymic shared antigen-1 (TSA-1) and osteoclast inhibitory lectin (OCIL) were not regulated by IL-4. In summary, at least two mechanisms of IL-4 -mediated osteoclastogenesis inhibition exist, including a direct action on myelomonocytic progenitors (from which osteoclasts derive) and an indirect action through T-cells that may involve novel anti-osteoclastic factors.

CytokineRegulation and the signaling mechanism of osteoclast inhibitory peptide-1 (OIP-1/hSca) to inhibit osteoclast formation

The osteoclast (OCL) is the primary bone resorbing cell. OCL formation and activity is regulated by local factors produced in the bone microenvironment. We recently identified OCL inhibitory peptide-1 (OIP-1/ hSca) as a novel inhibitor of OCL formation and bone resorption that is produced by OCLs. OIP-1 is a glycosylphosphatidyl-inositol (GPI)-linked membrane protein (16 kDa) related to the mouse Ly-6 family of hematopoietic proteins. OIP-1 mRNA is expressed in human OCL precursors, granulocyte-macrophage colony-forming unit (GM-CFU), bone marrow cells, and osteoblast cells. We used cycle-dependent reverse transcriptase-polymerase chain reaction (RT-PCR) analysis, which further demonstrated that interferon-gamma (IFN-gamma) strongly enhanced OIP-1/hSca mRNA expression in bone marrow cells and GM-CFU. Similarly, interleukin (IL)-1beta also enhanced OIP-1 mRNA expression in GM-CFU. To determine the participation of OIP-1 in IFN-gamma inhibition of OCL formation, we tested the capacity of a neutralizing antibody specific to OIP-1 c-peptide to inhibit IFN-gamma's effects on OCL-like cell differentiation of mouse macrophages, RAW 264.7 cells. Anti-OIP-1 c-peptide specific antibody partially neutralized IFN-gamma inhibition of OCL differentiation. Furthermore, OIP-1 inhibited phospho-c-Jun (p-c-Jun) kinase activity in RAW 264.7 cells. However, OIP-1/hSca did not affect NF-kappaB activation in these cells. Western blot analysis further demonstrated that OIP-1 significantly decreased TNF receptor associated factor 2 (TRAF-2) expression in RAW 264.7 cells. However, OIP-1 had no effect on TRAF-6 expression in these cells. These data show that IFN-gamma enhances OIP-1/hSca expression in OCL precursors, GM-CFU, and that OIP-1 inhibits OCL formation through suppression of TRAF-2 and p-c-Jun kinase activity.

Human Ly-6 antigen E48 (Ly-6D) regulates important interaction parameters between endothelial cells and head-and-neck squamous carcinoma cells

Selectin ligands are crucial components in the interaction between endothelial cells and extravasating cancer cells and, thus, play an important role in metastasis formation. Head-and-neck squamous cell carcinoma (HNSCC) variants expressing high levels of E48, a human Ly-6 protein (E48(hi)), expressed higher levels of the fucose-generating FX enzyme and of the fucosylated E-selectin ligand sLe(a) than cells expressing low levels of E48 (E48(lo)). Signaling through E48 upregulated expression levels of these molecules in HNSCC. In this work, we provide further evidence supporting the E48-FX-sLe(a) link by showing that FX antisense oligonucleotides reduced sLe(a) expression levels in HNSCC. We also show that E48 may be causally involved in regulating expression levels in HNSCC of 2 additional enzymes involved in the biosynthesis of sLe(a), namely, ST-30 and FucTIII. Also, selectin-mediated adhesion of E48(hi) variants to activated HUVECs was significantly higher than that of E48(lo) variants. Transfection experiments utilizing sense or antisense E48 cDNA indicated that E48 may be causally involved in this adhesion. Chemokines are involved in the extravasation process of tumor cells. The release of chemoattractants from HNSCC variants differing in E48 expression was therefore analyzed. HNSCC did not release any chemoattractants but induced the release of such factors from HUVECs. Supernatants from E48(hi) variants were significantly more efficient than E48(lo) cells at inducing the release of chemoattractants from HUVECs. Transfection experiments indicated that E48 may be causally involved in the induction of chemoattractant release from HUVECs. Angiogenesis is an important manifestation of cancer-endothelium interactions. We therefore assayed for the presence of angiogenic factors in culture supernatants of HNSCC. Supernatants from E48(lo) variants contained significantly higher amounts of PDGF than E48(hi) cells. Transfection experiments indicated that E48 may be causally involved. Taken together, our results suggest that E48 controls important interaction parameters between HNSCC and endothelial cells.

Receptors involved in microenvironment-driven molecular evolution of cancer cells

Cells, including cancer cells, communicate with their microenvironment via various types of membrane receptors. An important down-stream effect of such interactions is a change in the molecular phenotype of the cells. The microenvironment-driven molecular evolution of cancer cells may induce either growth arrest or death of the cells or alternatively, boost their malignancy phenotype. In this paper we summarize studies from our own laboratory on interactions of cancer cells with microenvironmental ligands via two types of receptors that are not commonly associated with tumour progression i.e. the receptor for the Fc portion of IgG, and Ly-6 proteins of mouse and human origin. We also review information on interactions of tumour-associated chemokines and chemokine receptors with the corresponding microenvironmental factors. We demonstrate how these interactions may drive the molecular evolution of tumour cells and discuss the possible impact of this evolution on tumour progression.

Identification of the functional domain of osteoclast inhibitory peptide-1/hSca

Osteoclast (OCL) activity is controlled by local factors produced in the bone microenvironment. We previously identified a novel inhibitor of OCL formation that is produced by OCLs (osteoclast inhibitory peptide-1/human Sca [OIP-1/hSca]). OIP-1/hSca is a glycosylphosphatidylinositol (GPI)-linked membrane protein (16 kDa) that is cleaved from the OCL surface. Immunocytochemical staining further confirmed the expression of OIP-1/hSca in OCL formed in mouse bone marrow cultures. However, the structure/function mechanisms responsible for the inhibitory effects of OIP-1/hSca on OCL formation are unknown. Therefore, we expressed deletion mutants of OIP-1 in 293 cells and tested their effects on OCL formation. These studies indicated that the carboxy-terminal peptide (c-peptide) region is critical for OIP-1/hSca activity. A 33 amino acid OIP-1 c-peptide (10-100 ng/ml) significantly inhibited 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] induced OCL formation and pit formation capacity of OCL on dentine slices in human bone marrow cultures. Furthermore, the c-peptide (10-100 ng/ml) significantly inhibited early human OCL precursor (granulocyte-macrophage colony-forming unit [GM-CFU]) colony formation in methylcellulose cultures. The polyclonal antibody against the OIP-1 c-peptide neutralized the inhibitory effect of OIP-1 c-peptide on OCL formation in mouse bone marrow cultures in vitro. These results show that the OIP-1 c-peptide is the functional domain of OIP-1 and that availability of neutralizing antibody specific to the OIP-1 c-peptide should provide important mechanistic insights into OIP-1/hSca inhibition of osteoclastogenesis in the bone microenvironment.

Gene expression profile of human bone marrow stromal cells: high-throughput expressed sequence tag sequencing analysis

Human bone marrow stromal cells (HBMSC) are pluripotent cells with the potential to differentiate into osteoblasts, chondrocytes, myelosupportive stroma, and marrow adipocytes. We used high-throughput DNA sequencing analysis to generate 4258 single-pass sequencing reactions (known as expressed sequence tags, or ESTs) obtained from the 5' (97) and 3' (4161) ends of human cDNA clones from a HBMSC cDNA library. Our goal was to obtain tag sequences from the maximum number of possible genes and to deposit them in the publicly accessible database for ESTs (dbEST of the National Center for Biotechnology Information). Comparisons of our EST sequencing data with nonredundant human mRNA and protein databases showed that the ESTs represent 1860 gene clusters. The EST sequencing data analysis showed 60 novel genes found only in this cDNA library after BLAST analysis against 3.0 million ESTs in NCBI's dbEST database. The BLAST search also showed the identified ESTs that have close homology to known genes, which suggests that these may be newly recognized members of known gene families. The gene expression profile of this cell type is revealed by analyzing both the frequency with which a message is encountered and the functional categorization of expressed sequences. Comparing an EST sequence with the human genomic sequence database enables assignment of an EST to a specific chromosomal region (a process called digital gene localization) and often enables immediate partial determination of intron/exon boundaries within the genomic structure. It is expected that high-throughput EST sequencing and data mining analysis will greatly promote our understanding of gene expression in these cells and of growth and development of the skeleton.

Ly-6A.2 expression regulates antigen-specific CD4+ T cell proliferation and cytokine production

Ly-6 proteins appear to serve cell adhesion and cell signaling function, but the precise role of Ly-6A.2 in CD4+ T lymphocytes is still unclear. Overexpression of Ly-6A.2 in T lymphocytes has allowed us to analyze the influence of elevated Ly-6A.2 expression on T cell function. In this study we report reduced proliferation of CD4+ T cells overexpressing Ly-6A.2 in response to a peptide Ag. Moreover, the Ly-6A.2-overexpressing CD4+ cells generated elevated levels of IL-4, a key factor that propels the differentiation of naive CD4+ T cells into Th2 subset. The hyporesponsiveness of Ly-6A.2 transgenic CD4+ T cells is dependent on the interaction of Ly-6A.2 T cells with the APCs and can be reversed by blocking the interaction between Ly-6A.2 and a recently reported candidate ligand. Overexpression of Ly-6A.2 in CD4+ T cells reduced their Ca(2+) responses to TCR stimulation, therefore suggesting effects of Ly-6A.2 signaling on membrane proximal activation events. In contrast to the observed Ag-specific hyporesponsiveness, the Ly-6A.2 transgenic CD4+ T cells produced IL-4 independent of the interactions between Ly-6A.2 and the candidate Ly-6A.2 ligand. Our results suggest that 1) interaction of Ly-6A.2 with a candidate ligand regulates clonal expansion of CD4+ Th cells in response to an Ag (these results also provide further functional evidence for presence of Ly-6A.2 ligand on APC); and 2) Ly-6A.2 expression on CD4+ T cells promotes production of IL-4, a Th2 differentiation factor.

Antisense inhibition of macrophage inflammatory protein 1-alpha blocks bone destruction in a model of myeloma bone disease

We recently identified macrophage inflammatory protein 1-alpha (MIP-1alpha) as a factor produced by multiple myeloma (MM) cells that may be responsible for the bone destruction in MM (1). To investigate the role of MIP-1alpha in MM bone disease in vivo, the human MM-derived cell line ARH was stably transfected with an antisense construct to MIP-1alpha (AS-ARH) and tested for its capacity to induce MM bone disease in SCID mice. Human MIP-1alpha levels in marrow plasma from AS-ARH mice were markedly decreased compared with controls treated with ARH cells transfected with empty vector (EV-ARH). Mice treated with AS-ARH cells lived longer than controls and, unlike the controls, they showed no radiologically identifiable lytic lesions. Histomorphometric analysis demonstrated that osteoclasts (OCLs) per square millimeter of bone and OCLs per millimeter of bone surface of AS-ARH mice were significantly less than in EV-ARH mice, and the percentage of tumors per total bone area was also significantly decreased. AS-ARH cells demonstrated decreased adherence to marrow stromal cells, due to reduced expression of the alpha(5)beta(1) integrin and diminished homing capacity and survival. These data support an important role for MIP-1alpha in cell homing, survival, and bone destruction in MM.

Osteoclast-stimulating factor interacts with the spinal muscular atrophy gene product to stimulate osteoclast formation

We have recently identified and cloned an intracellular peptide termed osteoclast-stimulating factor (OSF) that increases osteoclast (OCL) formation and bone resorption through a cellular signal transduction cascade, possibly through its interaction with c-Src or related family members. To further identify participants in the OSF signaling cascade, we used yeast two-hybrid screening with Saccharomyces cerevisiae, and we found that the 40-kDa spinal muscular atrophy disease-determining gene product, survival motor neuron (SMN), interacts with the OSF-Src homology 3 domain. Reverse transcription-polymerase chain reaction analysis of SMN mRNA expression in cells of the OCL lineage demonstrates that expression of the exon 7 splice variant of SMN is restricted to mature OCLs, whereas the unspliced transcript was expressed in OCL precursors as well as mature OCLs. Treatment of murine bone marrow cultures with conditioned media (5% (v/v)) from 293 cells transiently expressing the SMN cDNA significantly increased OCL formation, compared with treatment with conditioned media from mock-transfected cells. Furthermore, OCL-stimulatory activity by OSF or SMN was abolished by antisense constructs to SMN or OSF, respectively. These data confirm the participation of SMN in the OSF-enhanced expression of an OCL stimulator. OSF-SMN interaction may provide more insights into novel cellular signaling mechanisms that may play an important role in congenital bone fractures associated with type I spinal muscular atrophy disease.

Osteoclast inhibitory peptide 2 inhibits osteoclast formation via its C-terminal fragment

Osteoclast inhibitory peptide 2 (OIP-2) is a novel autocrine/paracrine factor produced by osteoclasts (OCLs) that inhibits bone resorption and OCL formation in vitro and in vivo. It is identical to the asparaginyl endopeptidase legumain. During maturation of OIP-2, a signal peptide and a 17-kDa C-terminal fragment (CTF) are cleaved to produce the mature enzyme. To determine if enzyme activity is required for inhibition of OCL formation or if only the CTF is responsible for these effects, we synthesized His-tagged complementary DNA (cDNA) constructs for the CTF of OIP-2, the proform of OIP-2, and the "mature enzyme" form of OIP-2. The proform or the CTF portion of OIP-2 inhibited OCL formation in a dose-dependent manner in murine bone marrow cultures stimulated with 1,25-dihydroxyvitamin D3 [1,25(OH)2D3]. The mature form of OIP-2, which was enzymatically active, did not inhibit OCL formation. In addition, OIP-2 inhibited OCL formation in cultures of highly purified human OCL precursor cells or RAW264.7 cells stimulated with 10 ng/ml of receptor activator of NF-kappaB (RANK) ligand. Binding studies with His-tagged OIP-2 showed expression of a putative OIP-2 receptor on RAW264.7 cells treated with RANK ligand for 4 days and human marrow cultures treated with 1,25(OH)2D3 for 3 weeks. These data show that the CTF of OIP-2, rather than the mature enzyme, mediates the inhibitory effects of OIP-2 through a putative receptor on OCL precursors.

A novel osteoblast-derived C-type lectin that inhibits osteoclast formation

We have cloned and expressed murine osteoclast inhibitory lectin (mOCIL), a 207-amino acid type II transmembrane C-type lectin. In osteoclast formation assays of primary murine calvarial osteoblasts with bone marrow cells, antisense oligonucleotides for mOCIL increased tartrate-resistant acid phosphatase-positive mononucleate cell formation by 3-5-fold, whereas control oligonucleotides had no effect. The extracellular domain of mOCIL, expressed as a recombinant protein in Escherichia coli, dose-dependently inhibited multinucleate osteoclast formation in murine osteoblast and spleen cell co-cultures as well as in spleen cell cultures treated with RANKL and macrophage colony-stimulating factor. Furthermore, mOCIL acted directly on macrophage/monocyte cells as evidenced by its inhibitory action on adherent spleen cell cultures, which were depleted of stromal and lymphocytic cells. mOCIL completely inhibited osteoclast formation during the proliferative phase of osteoclast formation and resulted in 70% inhibition during the differentiation phase. Osteoblast OCIL mRNA expression was enhanced by parathyroid hormone, calcitriol, interleukin-1alpha and -11, and retinoic acid. In rodent tissues, Northern blotting, in situ hybridization, and immunohistochemistry demonstrated OCIL expression in osteoblasts and chondrocytes as well as in a variety of extraskeletal tissues. The overlapping tissue distribution of OCIL mRNA and protein with that of RANKL strongly suggests an interaction between these molecules in the skeleton and in extraskeletal tissues.

ADAM8: a novel osteoclast stimulating factor

We used polymerase chain reaction (PCR)-selective complementary DNA (cDNA) subtraction hybridization with an immortalized murine osteoclast (OCL) precursor cell line to identify genes that are highly expressed in OCLs compared with OCL precursors and which may be involved in the OCL differentiation process. ADAM8 was one of the 50 genes identified. ADAM (a disintegrin and metalloproteinase) peptides are membrane-bound proteins that can act as cell-to-cell and cell-to-matrix adhesion molecules, degrade the extracellular matrix, and play a role in tissue morphogenesis. Addition of antisense (AS) S-oligonucleotides for ADAM8 (1-10 nM) to mouse bone marrow cultures treated with 10(-9) M 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] significantly inhibited OCL formation compared with treatment with the control S-oligonucleotide. Furthermore, conditioned media from 293 cells transiently transfected with a secretable form of the ADAM8 cDNA increased OCL formation in a dose-dependent manner. In addition, treatment of OCLs with soluble ADAM8 conditioned media significantly increased pit formation per dentin slice compared with control OCLs. Time course studies indicated that ADAM8 increased OCL formation only when it was present during days 4-7 of the 7-day culture period. Structural analysis, using truncated constructs of ADAM8, showed that the cysteine-rich/disintegrin domain was responsible for its OCL stimulatory activity. Western blot analysis confirmed that the soluble form of ADAM8 is present in normal marrow cultures. These data suggest that ADAM8 plays an important role in OCL formation and acts primarily at the later stages of OCL differentiation.

Rapid Screening Method for Osteoclast Differentiation in Vitro That Measures Tartrate-resistant Acid Phosphatase 5b Activity Secreted into the Culture Medium

Background: Osteoclasts secrete tartrate-resistant acid phosphatase (TRAP; EC 3.1.3.2) 5b into the circulation. We studied the release of TRAP 5b from osteoclasts using a mouse in vitro osteoclast differentiation assay.

Methods: We developed and characterized a polyclonal antiserum in rabbits, using purified human osteoclastic TRAP 5b as antigen. The antiserum was specific for TRAP in Western analysis of mouse osteoclast culture medium and was used to develop an immunoassay. We cultured mouse bone marrow-derived osteoclast precursor cells for 3–7 days with or without clodronate in the presence of vitamin D and analyzed the number of osteoclasts formed and the amount of TRAP 5b activity released into the culture medium.

Results: TRAP 5b activity was not secreted from osteoclast precursor cells. Addition of clodronate-containing liposomes decreased in a dose-dependent manner the number of osteoclasts and TRAP 5b activity released in 6-day cultures. The amount of TRAP 5b activity in the medium detected by the immunoassay correlated significantly with the number of osteoclasts formed (r = 0.94; P &lt;0.0001; n = 120).

Conclusions: The TRAP 5b immunoassay can be used to replace the laborious and time-consuming microscopic counting of osteoclasts in the osteoclast differentiation assay and to test the effects of potential therapeutic agents on osteoclast differentiation, enabling fast screening of large amounts of potential therapeutic agents.

Characterization of Ly-6M, a novel member of the Ly-6 family of hematopoietic proteins

The Ly-6 family includes a number of highly homologous, low molecular weight glycophosphatidylinositol-linked proteins expressed on hematopoietic and lymphoid cells. The best characterized family member is Sca-1 (Ly-6A/E), an antigen commonly used for purification of murine pluripotent hematopoietic cells. We sought to characterize the genomic locus surrounding the Sca-1 gene. We identified several overlapping P1 artificial chromosomes containing theSca-1 gene and mapped one of these to mouse chromosome 15D3.1-3.3, the region previously shown to contain members of the murine Ly-6 gene family. We then mapped this clone and found that the Sca-2 gene lies 35.4 kilobase (kb) downstream ofSca-1 in the opposite transcriptional orientation. This is the first direct demonstration of physical linkage of Ly-6 genes. A novel gene, highly homologous to Sca-1 was identified and localized 13.4 kb downstream of Sca-1. This gene, which we designated Ly-6M, shares several structural features conserved among members of the Ly-6 family. Ly-6M messenger RNA (mRNA) is easily detectable in hematopoietic tissue (bone marrow, spleen, thymus, peritoneal macrophages) as well as kidney and lung. No mRNA expression was detected in heart, stomach, liver, small intestine, brain, or skin. Ly-6M protein is detectable on 10% to 15% of peripheral blood leukocytes, including monocytes and a subpopulation of B220+ cells. Ly-6M is broadly distributed in the bone marrow, with prominent expression on monocytes and myeloid precursors. The identification and characterization of Ly-6M adds a new member to a complex family of homologous, tightly linked genes that have proven extremely useful reagents for defining populations within the hematopoietic system.

Characterization of Ly-6M, a novel member of the Ly-6 family of hematopoietic proteins

The Ly-6 family includes a number of highly homologous, low molecular weight glycophosphatidylinositol-linked proteins expressed on hematopoietic and lymphoid cells. The best characterized family member is Sca-1 (Ly-6A/E), an antigen commonly used for purification of murine pluripotent hematopoietic cells. We sought to characterize the genomic locus surrounding the Sca-1 gene. We identified several overlapping P1 artificial chromosomes containing theSca-1 gene and mapped one of these to mouse chromosome 15D3.1-3.3, the region previously shown to contain members of the murine Ly-6 gene family. We then mapped this clone and found that the Sca-2 gene lies 35.4 kilobase (kb) downstream ofSca-1 in the opposite transcriptional orientation. This is the first direct demonstration of physical linkage of Ly-6 genes. A novel gene, highly homologous to Sca-1 was identified and localized 13.4 kb downstream of Sca-1. This gene, which we designated Ly-6M, shares several structural features conserved among members of the Ly-6 family. Ly-6M messenger RNA (mRNA) is easily detectable in hematopoietic tissue (bone marrow, spleen, thymus, peritoneal macrophages) as well as kidney and lung. No mRNA expression was detected in heart, stomach, liver, small intestine, brain, or skin. Ly-6M protein is detectable on 10% to 15% of peripheral blood leukocytes, including monocytes and a subpopulation of B220+ cells. Ly-6M is broadly distributed in the bone marrow, with prominent expression on monocytes and myeloid precursors. The identification and characterization of Ly-6M adds a new member to a complex family of homologous, tightly linked genes that have proven extremely useful reagents for defining populations within the hematopoietic system.

Paget's disease of bone: diagnosis and treatment update

Paget's disease is a metabolic bone disease characterized by excessive bone resorption and formation due to activated osteoclasts. Although Paget's disease is a high bone turnover state, the excess bone that is formed lacks the structural stability of normal bone. Complications from Paget's disease include deformity, fracture, and pain. Although still unclear, both prevalence and severity of Paget's disease seem to be declining. Recent progress has focused on the environmental as well as genetic etiologies for this disease. Many studies indicate a role for viral infectious agents, whereas others point to a recently identified candidate gene on chromosome 18q. Therapy with bisphosphonate drugs is the treatment of choice. With newer and more powerful agents from this family now available, the majority of patients affected by Paget's disease can achieve sustained remission and avoid complications.

Identification of human asparaginyl endopeptidase (legumain) as an inhibitor of osteoclast formation and bone resorption

We screened a human osteoclast (OCL) cDNA expression library for OCL inhibitory factors and identified a clone that blocked both human and murine OCL formation and bone resorption by more than 60%. This clone was identical to human legumain, a cysteine endopeptidase. Legumain significantly inhibited OCL-like multinucleated cell formation induced by 1,25-dihydroxyvitamin D(3) (1,25-(OH)(2)D(3)) and parathyroid hormone-related protein (PTHrP) in mouse and human bone marrow cultures, and bone resorption in the fetal rat long bone assay in a dose-dependent manner. Legumain was detected in freshly isolated marrow plasma from normal donors and conditioned media from human marrow cultures. Furthermore, treatment of human marrow cultures with an antibody to legumain induced OCL formation to levels that were as high as those induced by 1,25-(OH)(2)D(3). Implantation in nude mice of 293 cells transfected with the legumain cDNA and constitutively expressing high levels of the protein significantly reduced hypercalcemia induced by PTHrP by about 50%, and significantly inhibited the increase in OCL surface and in OCL number expressed per mm(2) bone area and per mm bone surface induced by PTHrP. These results suggest that legumain may be a physiologic local regulator of OCL activity that can negatively modulate OCL formation and activity.

Annexin II increases osteoclast formation by stimulating the proliferation of osteoclast precursors in human marrow cultures

Annexin II (AXII), a calcium-dependent phospholipid-binding protein, has been recently found to be an osteoclast (OCL) stimulatory factor that is also secreted by OCLs. In vitro studies showed that AXII induced OCL formation and bone resorption. However, the mechanism of action by which AXII acts as a soluble extracellular protein to induce OCL formation is unknown. In this paper, we demonstrate that AXII gene expression is upregulated by 1,25-dihydroxyvitamin D3 [1, 25-(OH)2D3] and that addition of AXII significantly increased OCL-like multinucleated cell formation. Time-course studies suggested that AXII acted on the proliferative stage of OCL precursors and that AXII increased thymidine incorporation in OCL precursors. Moreover, AXII enhanced the growth of CFU-GM, the earliest identifiable OCL precursor, when bone marrow cultures were treated with low concentrations of GM-CSF. This capacity of AXII to induce OCL precursor proliferation was due to induction of GM-CSF expression, because the addition of neutralizing antibodies to GM-CSF blocked the stimulatory effect of AXII on OCL formation. RT-PCR analysis using RNA from highly purified subpopulations of marrow cells demonstrated that T cells, especially CD4(+) T cells, produced GM-CSF in response to AXII. Furthermore, FACS(R) analysis of T-cell subpopulations treated with fluorescein-labeled AXII suggested that the CD4(+), but not CD8(+), subpopulation of T cells express an AXII receptor. Taken together, these data suggest that AXII stimulates OCL formation by activating T cells through a putative receptor to secrete GM-CSF. GM-CSF then expands the OCL precursor pool to enhance OCL formation.