Unknown,Transcriptomics,Genomics,Proteomics

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Calcitonin controls bone formation by inhibiting the release of sphingosine 1-phosphate from osteoclasts

ABSTRACT: The hormone calcitonin (CT) is primarily known for its pharmacologic action as an inhibitor of bone resorption, yet CT-deficient mice display increased bone formation. These findings raised the question about the underlying cellular and molecular mechanism of CT action. Here we show that either ubiquitous or osteoclast-specific inactivation of the murine CT receptor (CTR) causes increased bone formation. CT negatively regulates the osteoclast expression of Spns2 gene, which encodes a transporter for the signaling lipid sphingosine 1-phosphate (S1P). CTR-deficient mice show increased S1P levels, and their skeletal phenotype is normalized by deletion of the S1P receptor S1P3. Finally, pharmacologic treatment with the non-selective S1P receptor agonist FTY720 causes increased bone formation in wildtype, but not in S1P3-deficient mice. This study redefines the role of CT in skeletal biology, confirms that S1P acts as an osteoanabolic molecule in vivo, and provides evidence for a pharmacologically exploitable crosstalk between osteoclasts and osteoblasts. Osteoclasts of wildtype and Calcr-/- C57Bl/6 mice were treated with Calcitonin and compared to the non-treated osteoclasts of wildtype or Calcr-/- mice, respectively.

ORGANISM(S): Mus musculus

SUBMITTER: Thomas Streichert

PROVIDER: E-GEOD-60761 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:Bone remodeling is characterized by the sequential, local tethering of osteoclasts and osteoblasts, and is key to the maintenance of bone integrity. While bone matrix-mobilized growth factors, such as TGF-β, are proposed to regulate remodeling, no in vivo evidence exists that an osteoclast-produced molecule is the enigmatic coupling factor. We have identified Cthrc1, a protein secreted by mature bone-resorbing osteoclasts, that targets stromal cells so as to stimulate osteogenesis. The expression of Cthrc1 is robustly induced when mature osteoclasts are placed on dentin or hydroxyapatite, and also by increasing extracellular calcium. Cthrc1 expression in bone increases in a high turnover state, such as that which is induced by RANKL injections in vivo, whereas it decreases with aging or following alendronate treatment, conditions associated with suppressed bone turnover. The targeted deletion of the Cthrc1 gene eliminates Cthrc1 expression in bone, whereas its deficiency in osteoblasts does not exert any significant effect. Osteoclast-specific deletion of the Cthrc1 gene results in osteopenia due to reduced bone formation: it also impairs the coupling process following resorption induced by RANKL injections, with a resultant impairment of bone mass recovery. Thus, Cthrc1 is an osteoclast-secreted “coupling factor” that regulates bone remodeling and hence, skeletal integrity. Total bone marrow cells were prepared from the femurs and tibias of 8-10-week-old C57BL/6 mice and cultured in the presence of M-CSF (100ng/ml) for 3 days as described previously (Takeshita et al., 2000 JBMR 15:1477-1488). Cells were harvested with 0.02% EDTA/PBS and used as bone marrow macrophages (BMMs). These BMMs were cultured in the presence of M-CSF (100 ng/ml) and RANKL (100ng/ml) for 2 days. TRAP positive mononuclear cells were harvested and used as pre-osteoclasts (pOC). These pOC cells were further cultured in the presence of M-CSF and RANKL for 2 days in normal plastic plate or on dentin slices. After 2 days, multinucleated TRAP positive mature osteoclasts were generated as mature osteoclasts on plate (mOCp) and mature resorbing osteoclasts on dentin (mOCd), respectively. RNAs were extracted from four different stages of osteoclast lineage cells; BMMs, pOC, mOCp and mOCd, and used for microarray analysis.

Project description:Osteoclasts are multinucleated cells specialized in degrading the mineralized bone matrix. Osteoclast differentiation and function are tightly regulated, to prevent excessive or insufficient bone resorption. Several control mechanisms participate in modulating osteoclastogenesis, and an increasing number of reports describe the role of microRNAs (miRNAs) in this process. Disrupting the expression of specific miRNAs can result in alterations of osteoclast formation and bone homeostasis. We and others have previously characterized 9 miRNAs whose levels change during osteoclast differentiation, and identified some of the target genes that mediate their function. However, little is known about changes in the miRNA expression profile during osteoclastogenesis. In this study, we isolated a murine primary bone marrow population enriched for osteoclast precursors, and used the Agilent microarray platform to analyze the expression of mature miRNAs after 1, 3, and 5 days of RANKL-driven differentiation. 93 miRNAs showed greater than 2 fold-change during these early, middle, and late stages of osteoclastogenesis. Many of these miRNAs were detected for the first time in osteoclasts, and we validated the expression of selected miRNAs by quantitative RT-PCR. We identified clusters of differentially expressed miRNAs, and performed computational analyses to predict functional pathways that may be regulated by these miRNAs. Several miRNAs were predicted to regulate genes involved in cytoskeletal remodeling, a crucial mechanism for the migration of osteoclast precursors, their maturation, and bone resorbing activity. Our results suggest that clusters of miRNAs differentially expressed during the course of osteoclastogenesis converge on the regulation of several key functional pathways. Overall, this study identified miRNAs expressed during early, middle and late osteoclastogenesis, contributing to understanding the molecular mechanisms regulating this complex differentiation process. Mouse primary bone marrow cultures were enriched for osteoclast precursors by depletion of B220/CD45R+ and CD3+ cells (B and T lymphocytes, respectively). Cells were differentiated with M-CSF and RANKL, and miRNA expression was analyzed at days 1, 3, and 5. Four biological replicates for each time point were used.

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Calcitonin controls bone formation by inhibiting the release of sphingosine 1-phosphate from osteoclasts

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