Mechanically stimulated bone cells secrete paracrine factors that regulate osteoprogenitor recruitment, proliferation, and differentiation

Brady, Robert T.; O’Brien, Fergal J.; Hoey, David A.

doi:10.1016/j.bbrc.2015.02.080

Cited by 54 publications

(53 citation statements)

References 31 publications

(42 reference statements)

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“…Although the signaling mechanisms of load‐induced cell proliferation or activation remain unknown, it is well‐established that osteocytes are mechanosensor cells that play a role in the anabolic response to loading . Recent in vitro evidence indicates mechanically stimulated osteocytes secrete factors that stimulate osteoblast and mesenchymal progenitor cell migration and proliferation . Although our in vivo study did not investigate this phenomenon, it offers a possible mechanism for loading‐induced periosteal cell proliferation.…”

Section: Discussionmentioning

confidence: 72%

Proliferation and Activation of Osterix‐Lineage Cells Contribute to Loading‐Induced Periosteal Bone Formation in Mice

Zannit

Silva

2019

JBMR Plus

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Mechanical loading stimulates bone formation. Bone‐lining‐cell activation and cell proliferation have been implicated in this process. However, the origin of osteoblasts that form bone following mechanical stimulation remains unknown. Our objective was to identity the contributions of activation, differentiation, and proliferation of osteoblast lineage cells to loading‐induced periosteal bone formation. Tamoxifen‐inducible Osx‐Cre‐ERT2;Ai9/TdTomato reporter mice (male and female) were aged to young adult (5 months) and middle age (12 months), and were administered tamoxifen for 5 consecutive days to label osterix‐lineage cells. Following a 3‐week clearance period, mice were subjected to five consecutive bouts of unilateral axial tibial compression. We first confirmed this protocol stimulated an increase in periosteal bone formation that was primarily lamellar apposition. Next, mice received 5‐bromo‐2′‐deoxyuridine (BrdU) in their drinking water daily to label proliferating cells; calcein was given to label active mineralizing surfaces. Tibias were harvested after the fifth loading day and processed for frozen undecalcified histology. The middiaphyseal periosteal surface in the region of peak bone formation was analyzed. Histology revealed both nonloaded and loaded tibias were covered in osterix positive (Osx+) cells on the periosteal surface of both 5‐ and 12‐month‐old animals. There was a significant increase in the mineralizing surface (calcein+) covered with Osx+ cells in loaded versus control limbs. Furthermore, nearly all of the mineralizing surfaces (>95%) were lined with Osx+ cells. We also observed approximately 30% of Osx+ cells were also BrdU+, indicating they arose via proliferation. These results show that following mechanical loading, pre‐existing cells of the Osx lineage cover the vast majority of surfaces where there is active loading‐induced bone formation, and a portion of these cells proliferated in the 5‐day loading period. We conclude the initial anabolic response after mechanical loading is based on the activation and proliferation of Osx lineage cells, not the differentiation of progenitor cells. © 2019 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

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Section: Discussionmentioning

confidence: 72%

Proliferation and Activation of Osterix‐Lineage Cells Contribute to Loading‐Induced Periosteal Bone Formation in Mice

Zannit

Silva

2019

JBMR Plus

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“…We have performed PCR and Western blotting analyses for FGF23 expression, whereas no detectable FGF23 gene or protein expression was observed in MLO‐Y4 cells. Many previous studies have also reported that the expression levels of FGF23 in the MLO‐Y4 cell line were negligible/undetectable (Woo et al, ; Atkins et al, ; Sun et al, ; Brady et al, ), which represents an important limitation of the MLO‐Y4 cell line. OCN is an abundant noncollagenous component of the organic bone matrix secreted mainly by osteocytes and osteoblasts (Florencio‐Silva et al, ; Zhang et al, ).…”

Section: Discussionmentioning

confidence: 98%

Fluid shear stress improves morphology, cytoskeleton architecture, viability, and regulates cytokine expression in a time‐dependent manner in MLO‐Y4 cells

Yan

Wang

et al. 2018

Cell Biology International

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The effects of load-induced interstitial fluid shear stress (FSS) on instantaneous signaling response of osteocytes (e.g., calcium signaling) have been well documented. FSS can also initiate the release of many important messenger molecules of osteocytes (e.g., ATP and PGE ). However, the effects of FSS on cellular function and bone metabolism-modulating cytokine expression of osteocytes have not been fully identified (some inconsistent/conflicting results have been documented). Herein, osteocyte-like MLO-Y4 cells were stimulated with 1 Pa, 2-h FSS, and the effects of FSS on cellular morphology, cytoskeletal microstructure, biological activity, and gene and protein expression of important cytokines were investigated. SEM and cytoskeleton staining revealed that FSS induced well-organized cytoskeleton and increased filopodia processes. The osteocytic viability was sustained and apoptosis was inhibited via flow cytometry. FSS promoted Wnt3a and β-catenin gene and protein expression in 0-, 3-, and 6-h (sample collection time post FSS) groups. The FSS-stimulated cells in the 3-h group exhibited more significant effects on the promotion of OCN and Cx43 and inhibition of DKK1 and SOST expression than the 0- and 6-h groups. The 3-h group with FSS stimulation also showed the most prominent effects on suppressing RANKL and RANKL/OPG gene and protein expression. This study revealed a direct regulatory effect of FSS on osteocytic morphology and apoptotic characteristics, and showed that osteocyte-secreted bone metabolism-modulating molecule expression was regulated by FSS in a time-dependent manner. This study not only enriches our basic knowledge for understanding osteocytic mechanotransduction, but also provides important evidence for more scientific experimental design.

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“…We observed a decrease in loadinginduced periosteal activation in bone, where the cilium was deleted in the progenitor population and not the osteoblast, which suggests that loading-induced periosteal activation is caused by the recruitment and differentiation of osteogenic progenitors, not dormant osteoblasts. One potential mechanism for recruitment and differentiation is that osteocytes, previously thought to be essential in bone mechanotransduction (26), detect mechanical stimulation and then release paracrine signals, which are detected by progenitor cells (27)(28)(29). Recent work by our group has demonstrated that soluble factors secreted by mechanically stimulated osteocytes can significantly enhance MSC migration in vitro (28); however, an alternative mechanism may be that progenitor cells directly sense these biophysical signals.…”

Section: Discussionmentioning

confidence: 99%

Mechanical signals promote osteogenic fate through a primary cilia‐mediated mechanism

Chen

Hoey²,

Chua³

et al. 2015

FASEB j.

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It has long been suspected, but never directly shown, that bone formed to accommodate an increase in mechanical loading is related to the creation of osteoblasts from skeletal stem cells. Indeed, biophysical stimuli potently regulate osteogenic lineage commitment in vitro. In this study, we transplanted bone marrow cells expressing green fluorescent protein, to enable lineage tracing, and subjected mice to a biophysical stimulus, to elicit a bone-forming response. We detected cells derived from transplanted progenitors embedded within the bone matrix near active bone-forming surfaces in response to loading, demonstrating for the first time, that mechanical signals enhance the homing and attachment of bone marrow cells to bone surfaces and the commitment to an osteogenic lineage of these cells in vivo. Furthermore, we used an inducible Cre/Lox recombination system to delete kinesin family member 3A (Kif3a), a gene that is essential for primary cilia formation, at will in transplanted cells and their progeny, regardless of which tissue may have incorporated them. Disruption of the mechanosensing organelle, the primary cilium in a progenitor population, significantly decreased the amount of bone formed in response to mechanical stimulation. The collective results of our study directly demonstrate that, in a novel experimental stem cell mechanobiology model, mechanical signals enhance osteogenic lineage commitment in vivo and that the primary cilium contributes to this process.-Chen, J. C., Hoey, D. A., Chua, M., Bellon, R., Jacobs, C. R. Mechanical signals promote osteogenic fate through a primary cilia-mediated mechanism. FASEB J. 30, 1504-1511 (2016). www.fasebj.org

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Mechanically stimulated bone cells secrete paracrine factors that regulate osteoprogenitor recruitment, proliferation, and differentiation

Cited by 54 publications

References 31 publications

Proliferation and Activation of Osterix‐Lineage Cells Contribute to Loading‐Induced Periosteal Bone Formation in Mice

Proliferation and Activation of Osterix‐Lineage Cells Contribute to Loading‐Induced Periosteal Bone Formation in Mice

Fluid shear stress improves morphology, cytoskeleton architecture, viability, and regulates cytokine expression in a time‐dependent manner in MLO‐Y4 cells

Mechanical signals promote osteogenic fate through a primary cilia‐mediated mechanism

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