Sclerostin promotes the apoptosis of human osteoblastic cells: a novel regulation of bone formation

Sutherland, May Kung; Geoghegan, James C.; Yu, Changpu; Turcott, Eileen; Skonier, John E.; Winkler, David G.; Latham, John

doi:10.1016/j.bone.2004.05.023

Cited by 203 publications

(127 citation statements)

References 38 publications

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“…Another possibility is that Dex may effect another regulator of apoptosis, such as Bcl-2, an inhibitor of apoptosis 35 or sclerostin, which has been shown to promote apoptosis in osteoblasts. 36 Clearly, the effects of Dex on the multiple factors involved in the mitochondrial and death receptor apoptosis pathways should also be investigated (reviewed by Dlamini et al 37 ). …”

Section: Discussionmentioning

confidence: 99%

Dexamethasone inhibition of confluence‐induced apoptosis in human mesenchymal stem cells

Song

Caplan

Dennis

2008

Journal Orthopaedic Research

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Human mesenchymal stem cells (MSCs) have been extensively characterized with respect to their in vitro expansion and differentiation potential, especially with respect to osteogenesis. Dexamethasone (Dex) is a well-known inducer of osteogenic differentiation of MSCs, but little is known about the effect of Dex treatment on apoptosis in MSCs. In this study, apoptosis in MSCs was examined with respect to cell density and Dex supplementation, using DAPI staining and DNA fragmentation ELISA Assay. In MSC cultures initiated at 1.0, 3.0, and 9.0 Â 10 3 cells per cm 2 , it was found that higher MSC density correlated with increased apoptosis and that this apoptotic effect was diminished in cultures containing 100 nM Dex. MSCs and fibroblasts were co-cultured, along with empty insert controls, and assayed for apoptosis by ELISA and DAPI counts to determine if soluble factors accounted for the cell density-related apoptosis. No difference was seen between MSCs cultured with inserts containing either MSCs, fibroblasts, or empty control. To determine cell contact effects, BrdU-labeled MSCs were cultured alone or with unlabeled chondrocytes at 2Â and 8Â the number of MSCs, with and without Dex, and apoptosis levels quantified. The results showed increased apoptosis at greater cell densities, and that the amount of apoptosis was greatly diminished in cultures containing Dex. These results show that apoptosis in MSCs is cell density-related, requires direct cell contact, and that Dex treatment reduces or eliminates this density-related apoptosis. These results may impact how MSCs should be cultured for clinical applications. Keywords: dexamethasone; mesenchymal stem cells; apoptosis Human bone marrow-derived mesenchymal stem cells (MSCs) are a rare population of undifferentiated cells that have the capacity to self-renew and can differentiate into mesodermal phenotypes including osteoblasts, chondrocytes, myocytes, and adipocytes. 1-3 Induction of osteoprogenitor differentiation of MSCs by dexamethasone (Dex) is well known, 4,5 and culture supplementation with Dex at 10 À8 M has been reported to promote osteoprogenitor cell differentiation in marrow stromal cells. 6,7 In addition, Dex is also a component of medium used for differentiation into chondroblasts, myocytes, and adipocytes in vitro. [8][9][10] With respect to Dex effects on apoptosis, the results have often been contradictory, depending upon the cell type being studied. For example, Dex treatment has been shown to induce apoptosis in thymocytes, 11,12 lymphocytes, 13-15 some tumor cells, 16,17 and respiratory epithelium, 18,19 whereas primary cultured hepatocytes, 20 neutrophils, 21,22 and some solid tumors 23,24 show reduced apoptosis after Dex treatment.Interestingly, while Dex has been used extensively with MSCs as an inductive factor for multiple end-stage phenotypes, few studies have assessed the effects of Dex on proliferation and apoptosis. To date, only one other study addressed the issue of Dex effects on MSC apoptosis wherein it was shown that hu...

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Section: Discussionmentioning

confidence: 99%

Dexamethasone inhibition of confluence‐induced apoptosis in human mesenchymal stem cells

Song

Caplan

Dennis

2008

Journal Orthopaedic Research

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“…S3Db). It has been shown that SOST, which is an antagonist of Wnt signaling, was able to inhibit osteoblast proliferation in cell cultures (14). Given that Osx was highly expressed in osteocytes, and that loss of Osx led to decreased Sost expression, we speculated that the increased number of Runx2-positve preosteoblasts might be linked to the lower levels of Sost expression in osteocytes.…”

Section: Osx Is Required For Osteoblast Differentiation and Bone Formmentioning

confidence: 92%

Multiple functions of Osterix are required for bone growth and homeostasis in postnatal mice

Zhou¹,

Zhang²,

Feng

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

277

255

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The transcription factor Osterix (Osx) is required for osteoblast differentiation and bone formation during embryonic development, but it is not known whether Osx has an essential function in postnatal bone growth and in bone homeostasis. Conditional deletion of Osx at several time points postnatally revealed that Osx was essential for osteoblast differentiation and new bone formation in growing and adult bones. Additionally, inactivation of Osx in bones severely disrupted the maturation, morphology, and function of osteocytes. These findings identify Osx as having an essential role in the cell-specific genetic program of osteocytes. Interestingly, Osx inactivation also led to the massive accumulation of unresorbed calcified cartilage in a large area below the growth plate of endochondral bones. This specific area was also marked by an unanticipated almost complete lack of bone marrow cells and a marked decrease in the density and size of osteoclasts. This diminished density of osteoclasts could contribute to the lack of resorption of mineralized cartilage. In addition, we speculate that the abnormally accumulated, mainly naked cartilage represents an unfavorable substrate for osteoclasts. Our study identifies Osx as an essential multifunctional player in postnatal bone growth and homeostasis.osteoblast differentiation | skeletal homeostasis | transcription factor | osteocyte | cartilage resorption T he identification of master transcription factors essential for osteoblast differentiation and bone formation during embryonic development has greatly advanced our knowledge of bone biology. However, the transcriptional control of postnatal bone formation and homeostasis remain poorly understood. Normal skeletal growth and homeostasis depends on the coordinated activities of three types of bone cells: osteoblasts, osteoclasts, and osteocytes. Factors secreted by the mesenchyme-derived osteoblasts also control the differentiation and activity of the boneresorbing osteoclasts derived from hematopoietic stem cells. Conversely, bone resorption by osteoclasts releases factors important for bone formation. Osteocytes, which make up over 90-95% of all bone cells in adult animals, are derived from mature osteoblasts and are embedded inside the bone matrix. It has been suggested that osteocytes are mediators of mechanical and hormonal stimulations to control the activity of both osteoblasts and osteoclasts (1). Osteocytes are regulators of mineralization and mineral homeostasis (2, 3), and by controlling Sost expression also act as modulators of Wnt signaling (4).Three transcription factors [β-catenin, Runx2, and Osterix (Osx)] are required for osteoblast differentiation and bone formation during embryonic development (5-9). Osx, which acts downstream of Runx2, is a zinc-finger-containing transcription factor essential for embryonic osteoblast differentiation and bone formation (8). During development, Osx is specifically expressed in osteoblast lineage cells and, at lower levels, in prehypertrophic chondrocytes, but not in ...

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“…(26)(27)(28) In addition, sclerostin stimulates osteoblasts apoptosis, providing another potential mechanism by which sclerostin may inhibit bone formation. (29) In situ, sclerostin is expressed in mature osteonal and interstitial osteocytes but is absent in those close to forming surfaces showing uptake of recently administered tetracycline labels. (13) Recently, in vivo experiments showed that sclerostin expression by osteocytes was reduced by mechanical stimulation (30) and increased by underloading, (31) Furthermore, the administration of a monoclonal antibody increased bone formation, bone strength, and bone mineral density (BMD) in both rats (32) and humans.…”

Section: Introductionmentioning

confidence: 99%

Sclerostin and the regulation of bone formation: Effects in hip osteoarthritis and femoral neck fracture

Power

Poole

Bezooijen

et al. 2010

Journal of Bone and Mineral Research

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Remodeling imbalance in the elderly femoral neck can result in thin cortices and porosity predisposing to hip fracture. Hip osteoarthritis protects against intracapsular hip fracture. By secreting sclerostin, osteocytes may inhibit Wnt signaling and reduce bone formation by osteoblasts. We hypothesised that differences in osteocytic sclerostin expression might account for differences in osteonal boneformation activity between controls and subjects with hip fracture or hip osteoarthritis. Using specific antibody staining, we determined the osteocytic expression of sclerostin within osteons of the femoral neck cortex in bone removed from subjects undergoing surgery for hip osteoarthritis (hOA: 5 males, 5 females, 49 to 92 years of age) or hip fracture fixation (FNF: 5 males, 5 females, 73 to 87 years of age) and controls (C: 5 males, 6 females, 61 to 90 years of age). Sclerostin expression and distances of each osteocyte to the canal surface and cement line were assessed for all osteonal osteocytes in 636 unremodeled osteons chosen from fields ($0.5 mm in diameter) with at least one canal staining for alkaline phosphatase (ALP), a marker of bone formation. In adjacent sections, ALP staining was used to classify basic multicellular unit (BMUs) as quiescent or actively forming bone (ALP þ ). The areal densities of scl À and scl þ osteocytes (number of cells per unit area) in the BMU were inversely correlated and were strong determinants of ALP status in the BMU. In controls and hip fracture patients only, sclerostin-negative osteocytes were closer to osteonal surfaces than positively stained cells. Osteon maturity (progress to closure) was strongly associated with the proportion of osteonal osteocytes expressing sclerostin, and sclerostin expression was the chief determinant of ALP status. hOA patients had 18% fewer osteocytes per unit bone area than controls, fewer osteocytes expressed sclerostin on average than in controls, but wide variation was seen between subjects. Thus, in most hOA patients, there was increased osteonal ALP staining and reduced sclerostin staining of osteocytes. In FNF patients, newly forming osteons were similar in this respect to hOA osteons, but with closure, there was a much sharper reduction in ALP staining that was only partly accounted for by the increased proportions of osteonal osteocytes staining positive for sclerostin. There was no evidence for a greater effect on ALP expression by osteocytes near the osteonal canal. In line with data from blocking antibody experiments, osteonal sclerostin appears to be a strong determinant of whether osteoblasts actively produce bone. In hOA, reduced sclerostin expression likely mediates increased osteoblastic activity in the intracapsular cortex. In FNF, full osteonal closure is postponed, with increased porosity, in part because the proportion of osteocytes expressing sclerostin increases sharply with osteonal maturation. ß

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Sclerostin promotes the apoptosis of human osteoblastic cells: a novel regulation of bone formation

Cited by 203 publications

References 38 publications

Dexamethasone inhibition of confluence‐induced apoptosis in human mesenchymal stem cells

Dexamethasone inhibition of confluence‐induced apoptosis in human mesenchymal stem cells

Multiple functions of Osterix are required for bone growth and homeostasis in postnatal mice

Sclerostin and the regulation of bone formation: Effects in hip osteoarthritis and femoral neck fracture

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