BMP-9-induced osteogenic differentiation of mesenchymal progenitors requires functional canonical Wnt/beta-catenin signalling.
ABSTRACT Bone morphogenetic protein 9 (BMP-9) is a member of the transforming growth factor (TGF)-beta/BMP superfamily, and we have demonstrated that it is one of the most potent BMPs to induce osteoblast differentiation of mesenchymal stem cells (MSCs). Here, we sought to investigate if canonical Wnt/beta-catenin signalling plays an important role in BMP-9-induced osteogenic differentiation of MSCs. Wnt3A and BMP-9 enhanced each other's ability to induce alkaline phosphatase (ALP) in MSCs and mouse embryonic fibroblasts (MEFs). Wnt antagonist FrzB was shown to inhibit BMP-9-induced ALP activity more effectively than Dkk1, whereas a secreted form of LPR-5 or low-density lipoprotein receptor-related protein (LRP)-6 exerted no inhibitory effect on BMP-9-induced ALP activity. beta-Catenin knockdown in MSCs and MEFs diminished BMP-9-induced ALP activity, and led to a decrease in BMP-9-induced osteocalcin reporter activity and BMP-9-induced expression of late osteogenic markers. Furthermore, beta-catenin knockdown or FrzB overexpression inhibited BMP-9-induced mineralization in vitro and ectopic bone formation in vivo, resulting in immature osteogenesis and the formation of chondrogenic matrix. Chromatin immunoprecipitation (ChIP) analysis indicated that BMP-9 induced recruitment of both Runx2 and beta-catenin to the osteocalcin promoter. Thus, we have demonstrated that canonical Wnt signalling, possibly through interactions between beta-catenin and Runx2, plays an important role in BMP-9-induced osteogenic differentiation of MSCs.
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ABSTRACT: The Wnt pathway plays a critical role in development and differentiation of many tissues, such as the gut, hair follicles, and bone. Increasing evidence indicates that Wnts may function as key regulators in osteogenic differentiation of mesenchymal stem cells and bone formation. Conversely, aberrant Wnt signaling is associated with many osteogenic pathologies. For example, genetic alterations in the Wnt signaling pathway lead to osteoporosis and osteopenia, while inactivating mutations of Wnt inhibitors result in a hyperostotic skeleton with increased bone mineral density. Hyperparathyroidism causes osteopenia via induction of the Wnt signaling pathway. Lithium, often used to treat bipolar disorder, blocks a Wnt antagonist, decreasing the patient's risk of fractures. Thus, manipulating the Wnt pathway may offer plenty therapeutic opportunities in treating bone disorders. In fact, induction of the Wnt signaling pathway or inhibition of Wnt antagonists has shown promise in treating bone metabolic disorders, including osteoporosis. For example, antibodies targeting the Wnt inhibitor Sclerostin lead to increased bone mineral density in post-menopausal women. However, such therapies targeting the Wnt pathway are not without risk, as genetic alternations may lead to over-activation of Wnt/β-catenin and its association with many tumors. It is conceivable that targeting Wnt inhibitors may predispose the individuals to tumorigenic phenotypes, at least in bone. Here, we review the roles of Wnt signaling in bone metabolic and pathologic processes, as well as the therapeutic potential for targeting Wnt pathway and its associated risks in bone diseases.Current Molecular Pharmacology 01/2011; 4(1):14-25.
Article: Hepatitis C virus core protein activates Wnt/β-catenin signaling through multiple regulation of upstream molecules in the SMMC-7721 cell line.[show abstract] [hide abstract]
ABSTRACT: The core protein of hepatitis C virus (HCV) has been implicated in HCV-induced liver pathogenesis. Previous data have shown that the HCV core protein has pleiotropic functions, including transcriptional regulation of a number of cellular genes, although the mechanism of gene regulation remains unclear. Wnt/β-catenin signaling is also involved in hepatocellular carcinoma (HCC) tumorigenesis. To elucidate the molecular mechanism of HCV pathogenesis, we examined whether HCV core protein activates Wnt/β-catenin signaling in the hepatoma cell line SMMC-7721. The effects of core protein on Wnt/β-catenin signaling cascades were investigated by luciferase reporter gene assay, immunofluorescence, western blot and RT-PCR analysis. Here, we demonstrate that HCV core protein plays an essential role in activating β-catenin/Tcf-4-dependent transcriptional activity and increases active β-catenin expression and nuclear accumulation in SMMC-7721 cells. An RT-PCR assay indicated that core protein upregulates gene expression of canonical Wnt ligands, such as Wnt2, Wnt3, Wnt3a, Wnt8b, Wnt10a, Wnt10b, frizzled receptors Fzd1, 2, 5, 6, 7, 9, and LRP5/6 co-receptors. However, Wnt antagonists SFRP3, 5 and Dkk1 were moderately repressed. Furthermore, ectopic expression of core protein markedly promoted cell proliferation. The soluble Fzd molecule FrzB or the β-catenin inhibitor siBC efficiently blocked cell growth stimulation by the core gene. Our present findings demonstrate that the HCV core protein activates canonical Wnt signaling through tight regulation of several important molecules upstream of β-catenin and presumably results in promotion of cell proliferation in the SMMC-7721 cell line. Taken together, these data suggested that the core protein may be directly involved in Wnt/β-catenin-mediated liver pathogenesis.Archives of Virology 02/2011; 156(6):1013-23. · 2.11 Impact Factor