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Age-dependent Wnt gene expression in bone and during the course of osteoblast differentiation.

ABSTRACT: Wnt signaling is vital for osteoblast differentiation and recently has been associated with aging. Because impaired osteoblastogenesis is a cellular characteristic of age-induced bone loss, we investigated whether this process is associated with an altered expression of Wnt signaling-related proteins in bone and osteoblasts. Bone marrow cells were isolated from male C57BL/6 mice, aged 6 weeks, 6 months, and 18 months, respectively. Osteogenic differentiation was induced for 3 weeks and assessed using alizarin red staining. Gene expression of Wnt1, 3a, 4, 5a, 5b, 7b, 9b, 10b, lipoprotein receptor-related protein (LRP)-5/6, as well as dickkopf-1 (Dkk-1), sclerostin, and secreted frizzled related protein-1 (sFRP-1) was determined in bone tissue and osteoblasts on days 7, 14, and 21 by real-time RT-PCR. Osteoblast differentiation was significantly reduced in aged mice compared with young and adult mice. In bone tissue, expression levels of all genes assessed were decreased in adult and old mice, respectively, compared with young mice. Mature osteoblasts of aged compared with those of young mice showed enhanced expression of Wnt9b, LRP-6, and Dkk-1, and decreased expression of Wnt5a and 7b. In early osteoblasts, mRNA levels of Wnt1, 5a, 5b, and 7b were increased significantly in aged mice. The expression of Wnt3a, 4, LRP-5, and sclerostin was not altered in aged osteoblasts. In conclusion, osteoblastic expression of each Wnt-related protein is regulated individually by aging. The overall decreased expression of Wnt-related proteins in bone tissue of aged mice underlines the newly discovered association of Wnt signaling with aging.

SUBMITTER: Rauner M

PROVIDER: S-EPMC2585653 | biostudies-other | 2008 Dec

REPOSITORIES: biostudies-other

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Project description:Developing novel approaches to treat skeletal disorders requires an understanding of how critical molecular factors regulate osteoblast differentiation and bone remodeling. We have reported that (1) retinoic acid receptor-related orphan receptor beta (Rorβ) is upregulated in bone samples isolated from aged mice and humans in vivo; (2) Rorβ expression is inhibited during osteoblastic differentiation in vitro; and (3) genetic deletion of Rorβ in mice results in preservation of bone mass during aging. These data establish that Rorβ inhibits osteogenesis and that strict control of Rorβ expression is essential for bone homeostasis. Because microRNAs (miRNAs) are known to play important roles in the regulation of gene expression in bone, we explored whether a predicted subset of nine miRNAs regulates Rorβ expression during both osteoblast differentiation and aging. Mouse osteoblastic cells were differentiated in vitro and assayed for Rorβ and miRNA expression. As Rorβ levels declined with differentiation, the expression of many of these miRNAs, including miR-219a-5p, was increased. We further demonstrated that miR-219a-5p was decreased in bone samples from old (24-month) mice, as compared with young (6-month) mice, concomitant with increased Rorβ expression. Importantly, we also found that miR-219a-5p expression was decreased in aged human bone biopsies compared with young controls, demonstrating that this phenomenon also occurs in aging bone in humans. Inhibition of miR-219a-5p in mouse calvarial osteoblasts led to increased Rorβ expression and decreased alkaline phosphatase expression and activity, whereas a miR-219a-5p mimic decreased Rorβ expression and increased osteogenic activity. Finally, we demonstrated that miR-219a-5p physically interacts with Rorβ mRNA in osteoblasts, defining Rorβ as a true molecular target of miR-219a-5p. Overall, our findings demonstrate that miR-219a-5p is involved in the regulation of Rorβ in both mouse and human bone. © 2018 American Society for Bone and Mineral Research.

Project description:IntroductionBreast cancers frequently metastasise to the skeleton where they cause osteolytic bone destruction by stimulating osteoclasts to resorb bone and by preventing osteoblasts from producing new bone. The Runt-related transcription factor 2, Runx2, is an important determinant of bone metastasis in breast cancer. Runx2 is known to mediate activation of osteoclast activity and inhibition of osteoblast differentiation by metastatic breast cancer cells. However, while Runx2-regulated genes that mediate osteoclast activation have been identified, how Runx2 determines inhibition of osteoblasts is unknown.MethodsThe aim of this study was to determine how Runx2 mediates the ability of metastatic breast cancer cells to modulate the activity of bone cells. We have previously demonstrated that Runx2 requires the co-activator core binding factor beta (CBFβ) to regulate gene expression in breast cancer cells. We, therefore, performed independent microarray analyses to identify target genes whose expression is dependent upon both Runx2 and CBFβ. Common target genes, with a role in modulating bone-cell function, were confirmed using a combination of siRNA, quantitative reverse transcriptase PCR (qRT-PCR), ELISA, promoter reporter analysis, Electrophoretic Mobility Shift Assay (EMSA) and chromatin immunoprecipitation (ChIP) assays. The function of Runx2/CBFβ-regulated genes in mediating the ability of MDA-MB-231 to inhibit osteoblast differentiation was subsequently established in primary bone marrow stromal cell cultures and MC-3T3 osteoblast cells.ResultsWe show that Runx2/CBFβ mediates inhibition of osteoblast differentiation by MDA-MB-231 cells through induction of the Wnt signaling antagonist, sclerostin. We demonstrate that MDA-MB-231 cells secrete sclerostin and that sclerostin-expression is critically dependent on both Runx2 and CBFβ. We also identified the osteoclast activators IL-11 and granulocyte-macrophage colony-stimulating factor (GM-CSF) as new target genes of Runx2/CBFβ in metastatic breast cancer cells.ConclusionsThis study demonstrates that Runx2 and CBFβ are required for the expression of genes that mediate the ability of metastatic breast cancer cells to directly modulate both osteoclast and osteoblast function. We also show that Runx2-dependent inhibition of osteoblast differentiation by breast cancer cells is mediated through the Wnt antagonist, sclerostin.

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Age-dependent Wnt gene expression in bone and during the course of osteoblast differentiation.

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