Effect of compressive force on the expression of MMPs, PAs, and their inhibitors in osteoblastic Saos-2 cells

Occlusal trauma aggravates periodontitis through the plasminogen/plasmin system

OBJECTIVES

Periodontitis is a common oral disease that is aggravated by occlusal trauma. Fibrin is a protein that participates in blood clotting and is involved in several human diseases. The deposition of fibrin in periodontal tissues can induce periodontitis, while mechanical forces may regulate the degradation of fibrin. Our study investigated how occlusal trauma aggravating periodontitis through regulating the plasminogen/plasmin system and fibrin deposition.

MATERIALS AND METHODS

This study included 84 C57BL/6 mice in which periodontitis was induced with or without occlusal trauma. Micro-computed tomography was used to assess bone resorption. Fibrin, fibrinogen, plasminogen, plasmin, tissue plasminogen activator (t-PA), and urokinase plasminogen activator (u-PA) levels were measured using Frazer-Lendrum staining, quantitative reverse transcription polymerase chain reaction, enzyme-linked immunosorbent assay, western blotting, immunofluorescence staining, and immunohistochemistry staining.

RESULTS

Occlusal trauma aggravated inflammation and bone resorption. The periodontitis group showed significant fibrin deposition. Occlusal trauma increased fibrin deposition and neutrophil aggregation. The periodontitis with occlusal trauma group had decreased fibrinogen, t-PA, and u-PA expression and plasmin and fibrin degradation product levels, as well as increased plasminogen levels.

CONCLUSION

Occlusal trauma promotes excessive fibrin deposition by suppressing the plasminogen/plasmin system, thus exacerbating periodontitis.

Biomechanical Aspects in Bone Tumor Engineering

In the past decades, anticancer drug development brought the field of tumor engineering to a new level by the need of robust test systems. Simulating tumor microenvironment in vitro remains a challenge, and osteosarcoma-the most common primary bone cancer-is no exception. The growing evidence points to the inevitable connection between biomechanical stimuli and tumor chemosensitivity and aggressiveness, thus making this component of the microenvironment a mandatory requirement to the developed models. In this review, we addressed the question: is the "in vivo - in vitro" gap in osteosarcoma engineering bridged from the perspective of biomechanical stimuli? The most notable biomechanical cues in the tumor cell microenvironment are observed and compared in the contexts of in vivo conditions and engineered three-dimensional in vitro models. Impact statement The importance of biomechanical stimuli in three-dimensional in vitro models for drug testing is becoming more pronounced nowadays. This review might assist in understanding the key players of the biophysical environment of primary bone cancer and the current state of bone tumor engineering from this perspective.

Cyclic Stretch-Induced Mechanical Stress Applied at 1 Hz Frequency Can Alter the Metastatic Potential Properties of SAOS-2 Osteosarcoma Cells

Recently, there has been an increasing focus on cellular morphology and mechanical behavior in order to gain a better understanding of the modulation of cell malignancy. This study used uniaxial-stretching technology to select a mechanical regimen able to elevate SAOS-2 cell migration, which is crucial in osteosarcoma cell pathology. Using confocal and atomic force microscopy, we demonstrated that a 24 h 0.5% cyclic elongation applied at 1 Hz induces morphological changes in cells. Following mechanical stimulation, the cell area enlarged, developing a more elongated shape, which disrupted the initial nuclear-to-cytoplasm ratio. The peripheral cell surface also increased its roughness. Cell-based biochemical assays and real-time PCR quantification showed that these morphologically induced changes are unrelated to the osteoblastic differentiative grade. Interestingly, two essential cell-motility properties in the modulation of the metastatic process changed following the 24 h 1 Hz mechanical stimulation. These were cell adhesion and cell migration, which, in fact, were dampened and enhanced, respectively. Notably, our results showed that the stretch-induced up-regulation of cell motility occurs through a mechanism that does not depend on matrix metalloproteinase (MMP) activity, while the inhibition of ion-stretch channels could counteract it. Overall, our results suggest that further research on mechanobiology could represent an alternative approach for the identification of novel molecular targets of osteosarcoma cell malignancy.

Microdevice-based mechanical compression on living cells

Compressive stress enables the investigation of a range of cellular processes in which forces play an important role, such as cell growth, differentiation, migration, and invasion. Such solid stress can be introduced externally to study cell response and to mechanically induce changes in cell morphology and behavior by static or dynamic compression. Microfluidics is a useful tool for this, allowing one to mimic in vivo microenvironments in on-chip culture systems where force application can be controlled spatially and temporally. Here, we review the mechanical compression applications on cells with a broad focus on studies using microtechnologies and microdevices to apply cell compression, in comparison to off-chip bulk systems. Due to their unique features, microfluidic systems developed to apply compressive forces on single cells, in 2D and 3D culture models, and compression in cancer microenvironments are emphasized. Research efforts in this field can help the development of mechanoceuticals in the future.

Magnetic Compression of Tumor Spheroids Increases Cell Proliferation In Vitro and Cancer Progression In Vivo

A growing tumor is submitted to ever-evolving mechanical stress. Endoscopic procedures add additional constraints. However, the impact of mechanical forces on cancer progression is still debated. Herein, a set of magnetic methods is proposed to form tumor spheroids and to subject them to remote deformation, mimicking stent-imposed compression. Upon application of a permanent magnet, the magnetic tumor spheroids (formed from colon cancer cells or from glioblastoma cells) are compressed by 50% of their initial diameters. Such significant deformation triggers an increase in the spheroid proliferation for both cell lines, correlated with an increase in the number of proliferating cells toward its center and associated with an overexpression of the matrix metalloproteinase-9 (MMP-9). In vivo peritoneal injection of the spheroids made from colon cancer cells confirmed the increased aggressiveness of the compressed spheroids, with almost a doubling of the peritoneal cancer index (PCI), as compared with non-stimulated spheroids. Moreover, liver metastasis of labeled cells was observed only in animals grafted with stimulated spheroids. Altogether, these results demonstrate that a large compression of tumor spheroids enhances cancer proliferation and metastatic process and could have implications in clinical procedures where tumor compression plays a role.

Creating In Vitro Three-Dimensional Tumor Models: A Guide for the Biofabrication of a Primary Osteosarcoma Model

Osteosarcoma (OS) is a highly aggressive primary bone tumor. The mainstay for its treatment is multiagent chemotherapy and surgical resection, with a 50-70% 5-year survival rate. Despite the huge effort made by clinicians and researchers in the past 30 years, limited progress has been made to improve patient outcomes. As novel therapeutic approaches for OS become available, such as monoclonal antibodies, small molecules, and immunotherapies, the need for OS preclinical model development becomes equally pressing. Three-dimensional (3D) OS models represent an alternative system to study this tumor: In contrast to two-dimensional monolayers, 3D matrices can recapitulate key elements of the tumor microenvironment (TME), such as the cellular interaction with the bone mineralized matrix. The advancement of tissue engineering and biofabrication techniques enables the incorporation of specific TME aspects into 3D models, to investigate the contribution of individual components to tumor progression and enhance understanding of basic OS biology. The use of biomaterials that mimic the extracellular matrix could also facilitate the testing of drugs targeting the TME itself, allowing a larger range of therapeutics to be tested, while averting the ethical implications and high cost associated with in vivo preclinical models. This review aims at serving as a practical guide by delineating the OS TME ("what it is like") and, in turn, propose various biofabrication strategies to create a 3D model ("how to recreate it"), to improve the in vitro representation of the OS tumor and ultimately generate more accurate drug response profiles.

Solid stress-induced migration is mediated by GDF15 through Akt pathway activation in pancreatic cancer cells

Solid stress is a biomechanical abnormality of the tumor microenvironment that plays a crucial role in tumor progression. When it is applied to cancer cells, solid stress hinders their proliferation rate and promotes cancer cell invasion and metastatic potential. However, the underlying mechanisms of how it is implicated in cancer metastasis is not yet fully understood. Here, we used two pancreatic cancer cell lines and an established in vitro system to study the effect of solid stress-induced signal transduction on pancreatic cancer cell migration as well as the mechanism involved. Our results show that the migratory ability of cells increases as a direct response to solid stress. We also found that Growth Differentiation Factor 15 (GDF15) expression and secretion is strongly upregulated in pancreatic cancer cells in response to mechanical compression. Performing a phosphoprotein screening, we identified that solid stress activates the Akt/CREB1 pathway to transcriptionally regulate GDF15 expression, which eventually promotes pancreatic cancer cell migration. Our results suggest a novel solid stress signal transduction mechanism bringing GDF15 to the centre of pancreatic tumor biology and rendering it a potential target for future anti-metastatic therapeutic innovations.

Defining the Role of Solid Stress and Matrix Stiffness in Cancer Cell Proliferation and Metastasis

Solid tumors are characterized by an abnormal stroma that contributes to the development of biomechanical abnormalities in the tumor microenvironment. In particular, these abnormalities include an increase in matrix stiffness and an accumulation of solid stress in the tumor interior. So far, it is not clearly defined whether matrix stiffness and solid stress are strongly related to each other or they have distinct roles in tumor progression. Moreover, while the effects of stiffness on tumor progression are extensively studied compared to the contribution of solid stress, it is important to ascertain the biological outcomes of both abnormalities in tumorigenesis and metastasis. In this review, we discuss how each of these parameters is evolved during tumor growth and how these parameters are influenced by each other. We further review the effects of matrix stiffness and solid stress on the proliferative and metastatic potential of cancer and stromal cells and summarize the in vitro experimental setups that have been designed to study the individual contribution of these parameters.

Solid Stress Facilitates Fibroblasts Activation to Promote Pancreatic Cancer Cell Migration

Pancreatic fibroblasts are continuously gaining ground as an important component of tumor microenvironment that dynamically interact with cancer cells to promote tumor progression. In addition, these tumor-infiltrated fibroblasts can acquire an activated phenotype and produce excessive amounts of extracellular matrix creating a highly dense stroma, a situation known as desmoplasia. Desmoplasia, along with the uncontrolled proliferation of cancer cells, leads to the development of compressive forces within the tumor, generating the so-called solid stress. Solid stress is previously shown to affect cancer cell proliferation and migration, however there is no pertinent study taking into account the effects of solid stress on fibroblasts and whether these effects contribute to tumor progression. In this work, we applied a defined compressive stress on pancreatic fibroblasts, similar in magnitude to that experienced by cells in native pancreatic tumors. Our results suggest that solid stress stimulates fibroblasts activation and strongly upregulates Growth Differentiation Factor-15 (GDF15) expression. Moreover, co-culture of compression-induced activated fibroblasts with pancreatic cancer cells significantly promotes cancer cell migration, which is inhibited by shRNA-mediated silencing of GDF15 in fibroblasts. Conclusively, our findings highlight the involvement of biophysical factors, such as solid stress, in tumor progression and malignancy revealing a novel role for GDF15.

Relevance of the plasminogen system in physiology, pathology, and regeneration of oral tissues - From the perspective of dental specialties

Plasmin is a proteolytic enzyme that is crucial in fibrinolysis. In oral tissues, the plasminogen system plays an essential role in physiological and pathological processes, which in addition to fibrinolysis include degradation of extracellular matrix, inflammation, immune response, angiogenesis, tissue remodeling, cell migration, and wound healing. Oral tissues reveal a change in the plasminogen system during pathological processes such as periodontitis, peri-implantitis, or pulpitis, as well as in response to mechanical load. The plasminogen system is also a key element in tissue regeneration. The number of studies investigating the plasminogen system in dentistry have grown continuously in recent years, highlighting its increasing relevance in dental medicine. In this review, we present the diverse functions of the plasminogen system in physiology and its importance for dental specialists in pathology and regeneration. We thus provide an overview of the current knowledge on the role of the plasminogen system in the different fields of dentistry, including endodontics, orthodontics, periodontics, and oral surgery.

The effect of raloxifene, a SERM, on extracellular matrix protein expression of pelvic fibroblasts

INTRODUCTION AND HYPOTHESIS

We hypothesize that the abnormal extracellular matrix (ECM) turnover in pelvic tissues of women with prolapse may be attenuated by raloxifene. We examine the effect of raloxifene on ECM protein expression in pelvic fibroblasts.

METHODS

Pelvic fibroblasts were isolated from cases (N = 6) and controls (N = 3). Cells were treated with raloxifene. Dose-response analyses were performed by ANOVA. mRNA and protein expression of collagen I, III, MMPs, and TIMPs were determined by RT-PCR and Western blot. MMP activity was analyzed by zymography.

RESULTS

The mRNA expression of TIMP-3 and protein expression of TIMP-1 and TIMP-3 were significantly increased by raloxifene in fibroblasts from both cases and controls (P < 0.05). Collagen I, III, and MMP mRNA and protein expressions were not affected.

CONCLUSIONS

Raloxifene selectively attenuates abnormal matrix degradation by increasing inhibitors of proteases, TIMPs, in pelvic fibroblasts. This opens the possibility for SERMs to be used as preventive therapy for pelvic floor disorders.

Expression of matrix metalloproteinase-1 (MMP-1) in Wistar rat's intervertebral disc after experimentally induced scoliotic deformity

Introduction

A scoliotic deformity on intervertebral discs may accelerate degeneration at a molecular level with the production of metalloproteinases (MMPs). In the present experimental study we evaluated the presence of MMP-1 immunohistochemically after application of asymmetric forces in a rat intervertebral disc and the impact of the degree of the deformity on MMP-1 expression.

Material-Method

Thirty female Wistar rats (aged 2 months old, weighted 200 ± 10 grams) were used. All animals were age, weight and height matched. A mini Ilizarov external fixator was applied at the base of a rat tail under anaesthesia in order to create a scoliotic deformity of the intervertebral disc between the 9^th and 10^th vertebrae. Rats were divided into three groups according to the degree of the deformity. In group I, the deformity was 10°, in group II 30° and in group III 50°. The rats were killed 35 days after surgery. The discs were removed along with the neighbouring vertebral bodies, prepared histologically and stained immunohistochemically. Immunopositivity of disc's cells for MMP-1 was determined using a semi-quantitative scored system.

Results

MMP-1 immunopositivity was detected in disc cells of annulus fibrosus of all intervertebral disc specimens examined. The percentage of MMP-1 positive disc cells in annulus fibrosus in group I, II and III were 20%, 43% and 75%, respectively. MMP-1 positivity was significantly correlated with the degree of the deformity (p < 0,001). An increase of chondrocyte-like disc cells was observed in the outer annulus fibrosus and at the margin of the intervertebral disc adjacent to the vertebral end plates. The difference in the proportion of MMP-1 positive disc cells between the convex and the concave side was statistically not significant in group I (p = 0,6), in group II this difference was statistically significant (p < 0,01). In group III the concave side showed a remarkable reduction in the number of disc's cells and a severe degeneration of matrix microstructure.

Conclusion

The present study showed that an experimentally induced scoliotic deformity on a rat tail intervertebral disc results in over-expression of MMP-1, which is dependent on the degree of the deformity and follows a dissimilar distribution between the convex and the concave side.

Gene expression profiles in 3D tumor analogs indicate compressive strain differentially enhances metastatic potential

Non-physiological mechanobiological stimuli typically occur in tumors and are considered to promote cancer spreading. Non-fluid related pressure (solid stress), which arises as tumors grow against adjacent tissues, is among the least studied endogenous stimuli due to challenges in replicating the in vivo environment. To this end, the novel devices well-pressor and the videomicroscopy-compatible optic-pressor were developed to exert precise compressive strain on cells in 3D gels in absence of other mechanical stimuli and soluble gradients. Glioblastoma (U87, HGL21) and breast cancer (MDA-MB-231) cells in 1% agarose hydrogels were exposed to 50% compressive strain for 3 h (0.25-0.05 kPa). Live imaging showed that cells elongate and deflect vertically to the load. This stimulation is shown for the first time to differentially regulate metastasis-associated genes. Furthermore, a group of differentially expressed genes was identified in all cell types, both by microarrays and confirmed by RT-PCR for select genes (caveolin-1, integrin-β1, Rac1), indicating shared response mechanisms. These genes are functionally linked and involved in decreasing cell-cell contact, increasing ECM degradation, and ultimately promoting invasion. Caveolin could orchestrate these responses while the uPA and PI3K/Akt systems could play major roles. Future work will focus on specific molecular partnerships under compression and their impact on cancer progression.

High pressure may inhibit periprosthetic osteogenesis

Mechanical effects have been demonstrated to activate periprosthetic osteoclasts and hence to promote bone resorption. However, the periprosthetic mechanical effect on osteoblast function is not clearly understood. The purpose of this study was to explore whether the high pressure on bone caused by a prosthesis affects periprosthetic osteoblast function. We applied static pressure of various magnitudes to SV40-transfected human fetal osteoblast cells, then assayed bioactivities compared to cells cultured without pressure (control). The results showed that osteoblast proliferation, differentiation, apoptosis, necrosis, and mineralization were all sensitive to static pressure, and the effects were magnitude dependent. Low-level static pressure (20 kPa) enhanced osteogenesis. Under 50-100 kPa static pressure, proliferation was inhibited and apoptosis was enhanced, but the cellular phenotype could be maintained. High pressure (250-500 kPa) totally inhibited the bioactivity of the osteoblasts and induced necrosis. Mineralization nodules decreased significantly under 100 kPa pressure, while no nodules could be found under 250 and 500 kPa pressure. RUNX2, COL-1, and BGP mRNA expression was significantly downregulated under 250 and 500 kPa. SOX9 expression was significantly upregulated at 100 kPa but significantly downregulated at 250 and 500 kPa. RANKL/OPG expression was increased under pressure, and the differences were significant at 100 and 500 kPa. These results suggest that periprosthetic high pressure may inhibit osteogenesis and promote osteoclastogenesis. Countermeasures should be developed to improve periprosthetic osteogenesis.

Effect of compressive force on the expression of inflammatory cytokines and their receptors in osteoblastic Saos-2 cells

OBJECTIVE

In orthodontic tooth movement, some cytokines released from periodontal ligament fibroblasts and alveolar bone osteoblasts on the pressure side can alter the normal processes of bone remodelling, resulting in physiological bone resorption. We examined the effect of compressive force and interleukin (IL)-1 type I receptor antagonist (IL-1ra) on the expression of inflammatory cytokines that promote osteoclast formation, as well as on their receptors, in osteoblastic Saos-2 cells.

DESIGN

The cells were cultured in Dulbecco's modified Eagle medium containing 10% fetal bovine serum with or without continuous compressive force (0.5-3.0 g/cm(2)) and/or IL-1ra for up to 24h. The gene expression levels of the cytokines and their receptors were estimated by determining mRNA levels using real-time PCR; the protein levels were determined using ELISA or immunohistochemical staining.

RESULTS

The expression of IL-1beta, IL-1 receptor, IL-6, IL-6 receptor, IL-8 receptor, IL-11 and tumor necrosis factor-alpha (TNFalpha) increased depending on the strength and duration of the compressive force, whereas the expression of IL-8, IL-11 receptor and TNFalpha receptor did not change with the application of compressive force. The expression of cytokines and their receptors produced by 3.0 g/cm(2) of compressive force decreased with the simultaneous addition of IL-1ra and the decrease was remarkable in IL-8 receptor, IL-11 and TNFalpha.

CONCLUSION

These results indicate that mechanical stress induces the production of inflammatory cytokines and their receptors in osteoblasts and the phenomenon is enhanced by the autocrine action of IL-1beta, which is increased in amount by mechanical stress.

Morphogenetic activity of silica and bio-silica on the expression of genes controlling biomineralization using SaOS-2 cells

In a previous study (Schröder et al., J Biomed Mater Res B Appl Biomater 75:387-392, 2005) we demonstrated that human SaOS-2 cells, when cultivated on bio-silica matrices, respond with an increased hydroxyapatite deposition. In the present contribution we investigate if silica-based components (Na-silicate, tetraethyl orthosilicate [TEOS], silica-nanoparticles) (1) change the extent of biomineralization in vitro (SaOS-2 cells) and (2) cause an alteration of the expression of the genes amelogenin, ameloblastin, and enamelin, which are characteristic for an early stage of osteogenesis. We demonstrate that the viability of SaOS-2 cells was not affected by the silica-based components. If Na-silicate or TEOS was added together with ss-glycerophosphate, an organic phosphate donor, a significant increase in biomineralization was measured. Finally, expression levels of the amelogenin, ameloblastin, and enamelin genes were determined in SaOS-2 cells during exposure to the silica-based components. After exposure for 2 days, expression levels of amelogenin and enamelin strongly increased in response to the silica-based components, while no significant change was seen for ameloblastin. In contrast, exposure of SaOS-2 cells to ss-glycerophosphate resulted in increased expression of all three genes. We conclude that the levels of the structural molecules of the enamel matrix, amelogenin and enamelin, increase in the presence of silica-based components and substantially contribute to the extent of hydroxyapatite crystallite formation. These results demonstrate that silica-based components augment hydroxyapatite deposition in vitro and suggest that enzymatically synthesized bio-silica (via silicatein) might be a promising route for tooth reconstruction in vivo.

Membrane type-1 matrix metalloproteinase is induced following cyclic compression of in vitro grown bovine chondrocytes

OBJECTIVE

To determine if membrane type-1 matrix metalloproteinase (MT1-MMP) will respond to cyclic compression of chondrocytes grown in vitro and the regulatory mechanisms underlying this response.

METHODS

Cyclic compression (30min, 1kPa, 1Hz) was applied to bovine chondrocytes (6-9-month-old animals) grown on top of a biodegradable substrate within 3 days of initiating culture. Luciferase assays using bovine articular chondrocytes were undertaken to demonstrate the mechanosensitivity of MT1-MMP. Semi-quantitative reverse-transcription polymerase chain reaction (RT-PCR) and western blot analysis were used to establish the time course of gene and protein upregulation in response to cyclic compression. The regulation of MT1-MMP was assessed by electrophoretic mobility shift assays, RT-PCR and western blot analysis. As well, an MT1-MMP decoy oligonucleotide and an extracellular signal-regulated kinase 1/2 (ERK1/2) pharmacological inhibitor were utilized to further characterize MT1-MMP regulation.

RESULTS

After cyclic compression, MT1-MMP showed a rapid and transient increase in gene expression. Elevated protein levels were detected within 2h of stimulation which returned to baseline by 6h. During cyclic compression, phosphorylation of the mitogen activated protein kinase ERK1/2 increased significantly. This was followed by increased gene and protein expression of the transcription factor; early growth factor-1 (Egr-1) and Egr-1 binding to the MT1-MMP promoter. Blocking Egr-1 DNA binding with a decoy MT1-MMP oligonucleotide, downregulated MT1-MMP gene expression. The ERK1/2 inhibitor U0126 also reduced Egr-1 DNA binding activity to MT1-MMP promoter sequences and subsequent transcription of MT1-MMP.

CONCLUSIONS

These data suggest that cyclic compression of chondrocytes in vitro upregulates MT1-MMP via ERK1/2 dependent activation of Egr-1 binding. Delineation of the regulatory pathways activated by mechanical stimulation will further our understating of the mechanisms influencing tissue remodeling.

Effects of compressive force on the differentiation of pluripotent mesenchymal cells

The purpose of this study was to determine the effect of mechanical stress on the differentiation of the pluripotent mesenchymal cell line C2C12. C2C12 cells were cultured continuously under compressive force (0.25-2.0 g/cm(2)). After mechanical stress loading, the levels of expression of mRNAs and proteins for phenotype-specific markers of osteoblasts (Runx2, Msx2, Dlx5, Osterix, AJ18), chondroblasts (Sox5, Sox9), myoblasts (MyoD), and adipocytes (PPAR gamma) were measured by real-time polymerase chain reaction analysis and Western blot analysis, respectively. The expression of activated p38 mitogen-activated protein kinase (p38 MAPK) was measured by Western blotting and/or ELISA. Loading 0.5 g/cm(2) of compressive force significantly increased the expression levels of Runx2, Msx2, Dlx5, Osterix, Sox5, and Sox9. In contrast, the expression levels of AJ18, MyoD, and PPAR gamma were decreased by exposure to 0.5 g/cm(2) of compressive force. Loading 0.5 g/cm(2) of compressive force also induced the phosphorylation of p38 MAPK. SB203580, which is a specific inhibitor of p38 MAPK, inhibited the compressive force-induced phosphorylation of p38 MAPK and partially blocked compressive force-induced Runx2 mRNA expression. These results demonstrate that compressive force stimulation directs the differentiation pathway of C2C12 cells into the osteoblast and chondroblast lineage via activated phosphorylation of p38 MAPK.

Effect of compressive force on the production of prostaglandin E(2) and its receptors in osteoblastic Saos-2 cells

In orthodontic tooth movement, prostaglandin E(2) (PGE(2)) released from osteoblasts can alter the normal process of bone remodeling. We examined the effect of compressive force (CF) on PGE(2) production, PGE receptors (Ep1-4) expression, phosphorylation of protein kinase A (p-PKA), and calcium content in Saos-2 cells. PGE(2) production increased as CF strength. Applying CF of 98 or 294 Pa caused the cells to produce approximately 700 and 1,400 pg/mL PGE(2), respectively. CF of 98 Pa increased Ep2 gene expression, and 98 and 294 Pa CF increased Ep4. Immunohistochemical staining showed strong expression of Ep2 under 98 Pa and Ep4 under 98 and 294 Pa. The p-PKA increased as the strength of CF or PGE(2) concentration. The calcium content was increased by the addition of 700 pg/mL PGE(2) but was decreased by 1400 pg/mL. Thus, mechanical stress controls bone formation by stimulating PGE(2) production and Ep2 and/or Ep4 expression in osteoblasts.

Nicotine treatment induces expression of matrix metalloproteinases in human osteoblastic Saos-2 cells

Tobacco smoking is an important risk factor for the development of severe periodontitis. Recently, we showed that nicotine affected mineralized nodule formation, and that nicotine and lipopolysaccharide stimulated the formation of osteoclast-like cells by increasing production of macrophage colony-stimulating factor (M-CSF) and prostaglandin E2 (PGE2) by human osteoblastic Saos-2 cells. In the present study, we examined the effects of nicotine on the expression of matrix metalloproteinases (MMPs), tissue inhibitors of matrix metalloproteinases (TIMPs), the plasminogen activation system including the component of tissue-type plasminogen activator (tPA), urokinase-type PA (uPA), and PA inhibitor type 1 (PAI-1), alpha7 nicotine receptor, and c-fos. We also examined the effect of the nicotine antagonist D-tubocurarine on nicotine-induced expression of MMP-1. Gene expression was examined using real-time polymerase chain reaction (PCR) to estimate mRNA levels. In addition, expression of the MMP, TIMP, uPA, tPA, and PAI-1 proteins was determined by Western blotting analysis. Nicotine treatment caused expression of MMP-1, 2, 3, and 13, but not MMP-14, to increase significantly after 5 or 10 d of culture; MMP-14 expression did not change through day 14. Enhancement of MMP-1 expression by nicotine treatment was eliminated by simultaneous treatment with D-tubocurarine. In the presence of nicotine, expression of uPA, PAI-1, or TIMP-1, 2, 3, or 4 did not change over 14 d of culture, whereas expression of tPA increased significantly by day 7. Nicotine also increased expression of the alpha7 nicotine receptor and c-fos genes. These results suggest that nicotine stimulates bone matrix turnover by increasing production of tPA and MMP-1, 2, 3, and 13, thereby tipping the balance between bone matrix formation and resorption toward the latter process.