Effects of low-magnitude high-frequency vibration on osteoblasts are dependent on estrogen receptor α signaling and cytoskeletal remodeling.

Clinical and experimental studies demonstrate the potential of low-magnitude high-frequency vibration (LMHFV) to enhance bone formation in the intact skeleton and during fracture healing. Moreover, it was shown that the effects of vibration therapy during fracture healing are highly dependent on the estrogen status of the vibrated individual and that estrogen receptor (ER) α signaling plays a major role in mechanotransduction of LMHFV. Because it is known that LMHFV can directly act on osteogenic cells, we hypothesize that the differential effects of LMHFV in the presence and absence of estrogen are mediated by ERα signaling in osteoblasts. To prove this hypothesis, we subjected preosteoblastic MC3T3-E1 cells and primary osteoblasts to LMHFV in vitro. We found increased Cox2 gene expression, cell metabolic activity and cell proliferation after LMHFV in the absence of estrogen, whereas the effects were contrary in the presence of estrogen. Blocking of ERα signaling by Esr1-siRNA knockdown or adding the selective ERα antagonist MPP dihydrochloride abolished the effects of LMHFV on osteoblast proliferation and Cox2 expression. Furthermore, primary osteoblasts isolated from ERα-knockout mice did not show a response towards LMHFV in the presence of estrogen. Additionally, blocking of actin cytoskeletal remodeling by adding the p160ROCK inhibitor Y-27632 abolished the effects of LMHFV. In contrast, expression of primary cilium was not necessary for mechanotransduction of LMHFV. These results suggest that direct effects of LMHFV on osteoblasts are dependent on ERα signaling and cytoskeletal remodeling.

[Mechanobiology and bone metabolism: Clinical relevance for fracture treatment]. / Mechanobiologie und Knochenstoffwechsel : Klinische Bedeutung für die Frakturbehandlung.

Mechanical stimuli are known to significantly influence bone metabolism and fracture healing. Various studies have demonstrated the involvement of complex molecular mechanotransduction pathways, such as the Wnt/beta-catenin, bone morphogenetic protein (BMP) and estrogen receptor signaling pathways in mechanotransduction. Mechanotransduction is influenced by aging and the comorbidities of the patient. Pharmacological modulation of signal transduction influences bone formation and the mechanosensitivity of skeletal tissue. The combination of pharmacological and biomechanical therapies may be useful for the treatment of fractures with impaired healing.

Non-resorbing osteoclasts induce migration and osteogenic differentiation of mesenchymal stem cells.

Osteoclast activity has traditionally been regarded as restricted to bone resorption but there is some evidence that also non-resorbing osteoclasts might influence osteoblast activity. The aim of the present study was to further investigate the hypothesis of an anabolic function of non-resorbing osteoclasts by investigating their capability to recruit mesenchymal stem cells (MSC) and to provoke their differentiation toward the osteogenic lineage. Bone-marrow-derived human MSC were exposed to conditioned media (CM) derived from non-resorbing osteoclast cultures, which were generated from human peripheral blood monocytes. Osteogenic marker genes (transcription factor Runx2, bone sialoprotein, alkaline phosphatase (AP), and osteopontin) were significantly increased. Osteogenic differentiation (OD) was also proved by von Kossa and AP staining occurred in the same range as in MSC cultures stimulated with osteogenic supplements. Chemotactic responses of MSC were measured with a modified Boyden chamber assay. CM from osteoclast cultures induced a strong migratory response in MSC, which was greatly reduced in the presence of an anti-human platelet-derived growth factor (PDGF) receptor beta antibody. Correspondingly, significantly increased PDGF-BB concentrations were measured in the CM using a PDGF-BB immunoassay. CM derived from mononuclear cell cultures did not provoke MSC differentiation and had a significantly lower migratory effect on MSC suggesting that the effects were specifically mediated by osteoclasts. In conclusion, it can be suggested that human non-resorbing osteoclasts induce migration and OD of MSC. While effects on MSC migration might be mainly due to PDGF-BB, the factors inducing OD remain to be elucidated.

Tissue engineering of bone: effects of mechanical strain on osteoblastic cells in type I collagen matrices.

The aim of the present study was to investigate the effect of cyclic uniaxial mechanical strain on a human osteoblastic precursor cell line (hFOB 1.19) in three-dimensional type I collagen matrices. Cell seeded collagen constructs were mechanically stretched by a daily application of cyclic uniaxial strain using a special motor-driven apparatus and compared to unstretched controls. Expression of genes involved in cell proliferation and osteoblastic differentiation as well as matrix production were investigated by analyzing the mRNA of histone H4, core binding factor 1, alkaline phosphatase, osteopontin, osteocalcin, and collagen type I (Col I) up to a cultivation period of 3 weeks using real-time PCR. Cyclic stretching of cell seeded Col I matrices at a magnitude occurring in healing bone increased cell proliferation and slightly elevated the expression of nearly all investigated genes over unstrained controls at various time points. It was concluded that mechanical load promotes the proliferation and differentiation of osteoblastic precursor cells in a Col I matrix and that the application of mechanical stimuli may have a beneficial effect on in vitro tissue formation.

The role of midkine in skeletal remodelling.

UNLABELLED: Bone tissue is subjected to continuous remodelling, replacing old or damaged bone throughout life. In bone remodelling, the coordinated activities of bone-forming osteoblasts and bone-resorbing osteoclasts ensure the maintenance of bone mass and strength. In early life, the balance of these cellular activities is tightly regulated by various factors, including systemic hormones, the mechanical environment and locally released growth factors. Age-related changes in the activity of these factors in bone remodelling can result in diseases with low bone mass, such as osteoporosis. Osteoporosis is a systemic and age-related skeletal disease characterized by low bone mass and structural degeneration of bone tissue, predisposing the patient to an increased fracture risk. The growth factor midkine (Mdk) plays a key role in bone remodelling and it is expressed during bone formation and fracture repair. Using a mouse deficient in Mdk, our group have identified this protein as a negative regulator of bone formation and mechanically induced bone remodelling. Thus, specific Mdk antagonists might represent a therapeutic option for diseases characterized by low bone mass, such as osteoporosis. LINKED ARTICLES: This article is part of a themed section on Midkine. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2014.171.issue-4.

[Diclofenac inhibits proliferation and matrix formation of osteoblast cells]. / Diclofenac hemmt die Proliferation und Matrixbildung osteoblastärer Zellen.

Cell culture studies have shown that NSAID may influence osteogenic activities of osteoblast cultures. However, these studies did not consider long-term effects on differentiating cells. The influence of Voltaren with the non-steroidal agent diclofenac on proliferation and gene expression of the osteoblast-like cell line SaOS-2 was investigated 2, 9, and 16 days after incubation. Two days after 24 h of incubation, 50 microg/ml diclofenac reduced the proliferation and collagen type I expression while 9 and 16 days later no effect was found on either of the parameters. In contrast, 50 microg/ml NSAID has no effect on alkaline phosphatase expression 2 days after incubation while 9 and 16 days later expression had been reduced. Lower concentrations (1.56 and 0.19 microg/ml) had no effects on the studied parameters. BrdU and MTT test showed that 50 microg/ml diclofenac reduced proliferative and metabolic activity. Lower concentrations (< or =25 microg/ml) had a lower or no influence. The findings indicate that the NSAID impairment depends on cellular differentiation stage and is not confined to the time during or immediately after NSAID incubation. According to these results in vitro testing of drugs should be performed over a longer time period to detect possible long-term impacts.

[Effects of mechanical strain on human osteoblastic precursor cells in type I collagen matrices]. / Effekte mechanischer Reize auf humane osteoblastäre Zellen in einer dreidimensionalen Kollagen-Typ-I-Matrix.

BACKGROUND: The aim of the present study was to investigate the effect of mechanical strain on human osteoblastic precursor cells in a three-dimensional scaffold. METHODS: Osteoblastic precursor cells were seeded in a collagen type I gel and mechanically stretched by daily application of cyclic uniaxial strain. The expression of histone H4, core binding factor 1, alkaline phosphatase, osteopontin, osteocalcin, and collagen type I was investigated by analysing the mRNA. Cell and matrix orientation were investigated by scanning electron microscopy. RESULTS: Cyclic stretching increased cell proliferation. The expression of osteogenic markers was slightly increased by mechanical strain. The cells and matrix were strictly oriented in the stress direction. CONCLUSION: The application of mechanical load might have a beneficial effect on the quality and quantity of generated bone tissue and might be a important factor in tissue engineering of bone.