Minireview: In vivo analysis of Wnt signaling in bone
ABSTRACT Bone remodeling requires osteoblasts and osteoclasts working in concert to maintain a constant bone mass. The dysregulation of signaling pathways that affect osteoblast or osteoclast differentiation or function leads to either osteopenia or high bone mass. The discovery that activating and inactivating mutations in low-density lipoprotein receptor-related protein 5, a putative Wnt coreceptor, led to high bone mass and low bone mass in human beings, respectively, generated a tremendous amount of interest in the possible role of the Wnt signaling pathway in the regulation of bone remodeling. A number of mouse models have been generated to study a collection of Wnt signaling molecules that have been identified as regulators of bone mass. These mouse models help establish the canonical Wnt signaling pathway as a major regulator of chondrogenesis, osteoblastogenesis, and osteoclastogenesis. This review will summarize these advances.
SourceAvailable from: Stefano Menini[Show abstract] [Hide abstract]
ABSTRACT: Vascular calcification is an unfavorable event in the natural history of atherosclerosis that predicts cardiovascular morbidity and mortality. However, increasing evidence suggests that different calcification patterns are associated with different or even opposite histopathological and clinical features, reflecting the dual relationship between inflammation and calcification. In fact, initial calcium deposition in response to pro-inflammatory stimuli results in the formation of spotty or granular calcification ("microcalcification"), which induces further inflammation. This vicious cycle favors plaque rupture, unless an adaptive response prevails, with blunting of inflammation and survival of vascular smooth muscle cells (VSMCs). VSMCs promote fibrosis and also undergo osteogenic transdifferentiation, with formation of homogeneous or sheet-like calcification ("macrocalcification"), that stabilizes the plaque by serving as a barrier towards inflammation. Unfortunately, little is known about the molecular mechanisms regulating this adaptive response. The advanced glycation/lipoxidation endproducts (AGEs/ALEs) have been shown to promote vascular calcification and atherosclerosis. Recent evidence suggests that two AGE/ALE receptors, RAGE and galectin-3, modulate in divergent ways, not only inflammation, but also vascular osteogenesis, by favoring "microcalcification" and "macrocalcification", respectively. Galectin-3 seems essential for VSMC transdifferentiation into osteoblast-like cells via direct modulation of the WNT-β-catenin signaling, thus driving formation of "macrocalcification", whereas RAGE favors deposition of "microcalcification" by promoting and perpetuating inflammation and by counteracting the osteoblastogenic effect of galectin-3. Further studies are required to understand the molecular mechanisms regulating transition from "microcalcification" to "macrocalcification", thus allowing to design therapeutic strategies which favor this adaptive process, in order to limit the adverse effects of established atherosclerotic calcification. Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.Atherosclerosis 12/2014; 238(2):220-230. DOI:10.1016/j.atherosclerosis.2014.12.011 · 3.71 Impact Factor
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ABSTRACT: Objective. To investigate the effects of Toll-like receptors in stem cell osteogenesis. Methods. Bone marrow mesenchymal stem cells (BMSCs) were divided into the blank group, the TLR-3 activated group, and the TLR-4 activated group. After 10 days' osteogenic-promoting culture, expression of type I collagen and osteocalcin was determined by Western blot. Osteoblasts (OBs) were also divided into three groups mentioned above. Alkaline phosphatase (ALP) and alizarin red staining were performed after 10 days' ossification-inducing culture. The expression of β-catenin was investigated by Western blot. Results. Both the TLR-3 and TLR-4 activated groups had increased expression of type I collagen and osteocalcin; the effect of TLR-4 was stronger. The intensity of alizarin red and ALP staining was strongest in the TLR-3 activated group and weakest in the TLR-4 activated group. Activation of TLR-4 decreased the expression of β-catenin, whilst activation of TLR-3 did not affect the expression of β-catenin. Discussion. This study suggested that both TLR-3 and -4 promoted differentiation of BMSCs to OBs. TLR-3 had an inducing effect on the ossification of OBs to osteocytes, whilst the effect of TLR-4 was the opposite because of its inhibitory effect on the Wnt signaling pathway.
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ABSTRACT: Dental pulp/dentin regeneration using dental stem cells combined with odontogenic factors may offer great promise to treat and/or prevent premature tooth loss. Here, we investigate if BMP9 and Wnt/β-catenin act synergistically on odontogenic differentiation. Using the immortalized SCAPs (iSCAPs) isolated from mouse apical papilla tissue, we demonstrate that Wnt3A effectively induces early osteogenic marker alkaline phosphatase (ALP) in iSCAPs, which is reduced by β-catenin knockdown. While Wnt3A and BMP9 enhance each other's ability to induce ALP activity in iSCAPs, silencing β-catenin significantly diminishes BMP9-induced osteo/odontogenic differentiation. Furthermore, silencing β-catenin reduces BMP9-induced expression of osteocalcin and osteopontin and in vitro matrix mineralization of iSCAPs. In vivo stem cell implantation assay reveals that while BMP9-transduced iSCAPs induce robust ectopic bone formation, iSCAPs stimulated with both BMP9 and Wnt3A exhibit more mature and highly mineralized trabecular bone formation. However, knockdown of β-catenin in iSCAPs significantly diminishes BMP9 or BMP9/Wnt3A-induced ectopic bone formation in vivo. Thus, our results strongly suggest that β-catenin may play an important role in BMP9-induced osteo/ondontogenic signaling and that BMP9 and Wnt3A may act synergistically to induce osteo/odontoblastic differentiation of iSCAPs. It's conceivable that BMP9 and/or Wnt3A may be explored as efficacious biofactors for odontogenic regeneration and tooth engineering.Biomaterials 11/2014; DOI:10.1016/j.biomaterials.2014.11.007 · 8.31 Impact Factor