Minor influence of lifelong voluntary exercise on composition, structure, and incidence of osteoarthritis in tibial articular cartilage of mice compared with major effects caused by growth, maturation, and aging.

We investigated the effects of lifelong voluntary exercise on articular cartilage of mice. At the age of 4 weeks C57BL mice (n = 152) were divided into two groups, with one group serving as a sedentary control whereas the other was allowed free access to a running wheel from the age of 1 month onward. Mice were euthanized at four different time points (1, 2, 6, and 18 months of age). Articular cartilage samples were gathered from the load-bearing area of the tibial medial plateaus, and osteoarthritis was graded. Additionally, the proteoglycan content distribution was assessed using digital densitometry, collagen fibril orientation, and parallelism with polarized light microscopy, and collagen content using Fourier transform infrared imaging spectroscopy. The incidence of osteoarthritis increased with aging, but exercise had no effect on this trend. Furthermore, the structure and composition revealed significant growth, maturation, and age-dependent properties. Exercise exerted a minor effect on collagen fibril orientation in the superficial zone. Fibril orientation at 2 months of age was more perpendicular to surface (p < 0.05) in controls compared with runners, whereas the situation was reversed at the age of 18 months (p < 0.05). The collagen content of the superficial zone was higher (p < 0.01) at the age of 18 months in controls compared with runners but the proteoglycan content did not display any exercise-dependent changes. In conclusion, growth, maturation, and aging exerted a clear effect on integrity, structure, and composition of medial tibial plateau articular cartilage in mice, whereas lifelong voluntary exercise had only a minor effect on collagen architecture and content.

Early bone growth on the surface of titanium implants in rat femur is enhanced by an amorphous diamond coating.

BACKGROUND AND PURPOSE: Amorphous diamond (AD) is a durable and compatible biomaterial for joint prostheses. Knowledge regarding bone growth on AD-coated implants and their early-stage osseointegration is poor. We investigated bone growth on AD-coated cementless intramedullary implants implanted in rats. Titanium was chosen as a reference due to its well-known performance. MATERIALS AND METHODS: We placed AD-coated and non-coated titanium implants (R(a) ≈ 0.2 µm) into the femoral bone marrow of 25 rats. The animals were divided in 2 groups according to implant coating and they were killed after 4 or 12 weeks. The osseointegration of the implants was examined from hard tissue specimens by measuring the new bone formation on their surface. RESULTS: 4 weeks after the operation, the thickness of new bone in the AD-coated group was greater than that in the non-coated group (15.3 (SD 7.1) µm vs. 7.6 (SD 6.0) µm). 12 weeks after the operation, the thickness of new bone was similar in the non-coated group and in the AD-coated group. INTERPRETATION: We conclude that AD coating of femoral implants can enhance bone ongrowth in rats in the acute, early stage after the operation and might be an improvement over earlier coatings.

Effects of growth and exercise on composition, structural maturation and appearance of osteoarthritis in articular cartilage of hamsters.

Articular cartilage composition and structure are maintained and remodeled by chondrocytes under the influence of loading. Exercise-induced changes in the composition, structure, mechanical properties and tissue integrity of growing and aging hamster articular cartilage were investigated. Articular cartilage samples (n = 191) were harvested from the proximal tibiae of hamsters aged 1, 3, 6, 12 and 15 months. The hamsters were divided into runners and controls. The runners had free access to a running wheel between 1 and 3 months (runner groups 3-, 12- and 15-month-old hamsters) or 1 and 6 months (runner group 6-month-old hamsters) of age. Control animals were subjected to a sedentary lifestyle. Mechanical indentation tests and depth-wise compositional and structural analyses were performed for the cartilage samples. Furthermore, the integrity of articular cartilage was assessed using histological osteoarthritis grading. Exercise affected the collagen network organization after a 5-month exercise period, especially in the middle and deep zones. However, no effect on the mechanical properties was detected after exercise. Before the age of 12 months, the runners showed less osteoarthritis than the controls, whereas at 15 months of age the situation was reversed. It is concluded that, in hamsters, physical exercise at a young age enhances cartilage maturation and alters the depth-wise cartilage structure and composition. This may be considered beneficial. However, exercise at a young age demonstrated adverse effects on cartilage at a later age with a significant increase in the incidence of osteoarthritis.

Quantitative analysis of collagen network structure and fibril dimensions in cartilage repair with autologous chondrocyte transplantation.

OBJECTIVE: The aim of this study was to undertake a stereological analysis to quantify the dimensions of the collagen network in the repair tissue of porcine joints after they had been subjected to autologous chondrocyte transplantation (ACT). METHOD: ACT was used to repair cartilage lesions in knee joints of pigs. Electron-microscopic stereology, immunostaining for type II collagen, and quantitative polarized-light microscopy were utilized to study the collagen fibrils in the repair tissue 3 and 12 months after the operation. RESULTS: The collagen volume density (V(V)) was lower in the repair tissue than in normal cartilage at 3 months (20.4 vs. 23.7%) after the operation. The collagen surface density (S(V), 1.5·10(-2) vs. 3.1·10(-2) nm(2)/nm(3)) and V(V) increased with time in the repair tissue (20.4 vs. 44.7%). Quantitative polarized-light microscopy detected a higher degree of collagen parallelism in the repair tissue at 3 months after the operation (55.7 vs. 49.7%). In contrast, 1 year after the operation, fibril parallelism was lower in the repair tissue than in the control cartilage (47.5 vs. 69.8%). CONCLUSION: Following ACT, V(V) and S(V) increased in the repair tissue with time, reflecting maturation of the tissue. One year after the operation, there was a lower level of fibril organization in the repair tissue than in the control cartilage. Thus, the newly synthesized collagen fibrils in the repair tissue appeared to form a denser network than in the control cartilage, but the fibrils remained more randomly oriented.

Changes in collagen fibril network organization and proteoglycan distribution in equine articular cartilage during maturation and growth.

The aim of this study was to record growth-related changes in collagen network organization and proteoglycan distribution in intermittently peak-loaded and continuously lower-level-loaded articular cartilage. Cartilage from the proximal phalangeal bone of the equine metacarpophalangeal joint at birth, at 5, 11 and 18 months, and at 6-10 years of age was collected from two sites. Site 1, at the joint margin, is unloaded at slow gaits but is subjected to high-intensity loading during athletic activity; site 2 is a continuously but less intensively loaded site in the centre of the joint. The degree of collagen parallelism was determined with quantitative polarized light microscopy and the parallelism index for collagen fibrils was computed from the cartilage surface to the osteochondral junction. Concurrent changes in the proteoglycan distribution were quantified with digital densitometry. We found that the parallelism index increased significantly with age (up to 90%). At birth, site 2 exhibited a more organized collagen network than site 1. In adult horses this situation was reversed. The superficial and intermediate zones exhibited the greatest reorganization of collagen. Site 1 had a higher proteoglycan content than site 2 at birth but here too the situation was reversed in adult horses. We conclude that large changes in joint loading during growth and maturation in the period from birth to adulthood profoundly affect the architecture of the collagen network in equine cartilage. In addition, the distribution and content of proteoglycans are modified significantly by altered joint use. Intermittent peak-loading with shear seems to induce higher collagen parallelism and a lower proteoglycan content in cartilage than more constant weight-bearing. Therefore, we hypothesize that the formation of mature articular cartilage with a highly parallel collagen network and relatively low proteoglycan content in the peak-loaded area of a joint is needed to withstand intermittent stress and shear, whereas a constantly weight-bearing joint area benefits from lower collagen parallelism and a higher proteoglycan content.

Physical exercise improves properties of bone and its collagen network in growing and maturing mice.

This study characterized bone structure, composition, and mechanical properties in growing male mice. The development of the collagen network during maturation was monitored, and the effect of voluntary physical exercise was investigated. We hypothesized that increased bone loading from exercise would increase the amount and improve the properties of the collagen network during growth and maturation. Half of the mice (total n = 168) had access to running wheels, while half were kept sedentary. Weight and running activity were recorded, and groups of mice were killed at 1, 2, 4, and 6 months of age. The collagen network was assessed by biochemical evaluation of collagen content and cross-links and by tensile testing of decalcified bone. Mineralized femur was analyzed with pQCT and three-point-bending and femoral neck-strength tests. After 6 months, the exercising mice had 10% lower body weight than the sedentary group. There was no difference in the amount of collagen or collagen cross-links, while tensile testing had higher breaking force and stiffness of the collagen network in runners after 4 months but not after 6 months. The bone mineral density and cross-sectional area were higher in the running group after 6 months. Runners also showed higher breaking force and stiffness of the diaphysis and the femoral neck at 2 and 6 months. The significant modulation of mechanical properties of the collagen network without any change in collagen content indicates that physical exercise improves properties of the collagen network in maturing bone. The improvement after exercise of the properties of mineralized bone appears to be more pronounced and long-lasting compared to the early improved properties of the collagen network.

Cartilage collagen fibril network in newborn transgenic mice analyzed by electron microscopic stereology.

The objective was to investigate by electron microscopic stereology the properties of the cartilage collagen fibril network in newborn transgenic mice. The mice harbored transgenes targeted to affect the structure or assembly of the collagen fibrils. The mouse lines investigated here harbored either (i) one or (ii) two human COL2A1 genes with Arg519Cys mutation in addition to one or (iii) no active allele(s) of the murine COL2A1 gene, (iv) two inactive alleles of the procollagen N-proteinase genes, or (v) a human COL2A1 gene with deleted exons 16-27. In all newborn mice carrying the COL2A1 transgene with Arg519Cys mutation, the growth plate collagen fibrils were thinner than in the wild-type (wt) mice and showed clearly reduced volume fraction of the fibril network. In mice with the inactive procollagen N-proteinase genes, the fibril thickness and the volume fraction of collagen did not differ from the wt mice. In mice harboring the transgene of human COL2A1 gene with internally deleted exons 16-27, the collagen fibril diameter remained the same, but the volume density of collagen network was reduced. Using the indirect stereology, the differences in the collagen fibril stereological estimates could be reliably detected in newborn mice harboring mutations that affect the structure and assembly of collagen fibrils. The EM stereology permitted early detection of altered phenotype of the collagen fibril network in newborn transgenic mice. It is recommended that the indirect model-based stereological technique is utilized instead of the direct design-based technique for the estimation of collagen volume, surface, and length densities.

Practical considerations in the use of polarized light microscopy in the analysis of the collagen network in articular cartilage.

Polarized light microscopy is a traditional method for visualizing the collagen network architecture of articular cartilage. Articular cartilage repair and tissue engineering studies have raised new demands for techniques capable of quantitative characterization of the scar and repair tissues, including properties of the collagen network. Modern polarized light microscopy can be used to measure collagen fibril orientation, parallelism, and birefringence. New commercial instruments are computer controlled and the measurements are easy to perform. However, often the interpretation of results causes difficulties, even errors, because the theoretical aspects of the technique are demanding. The aim of this study was to describe the instrumentation and properties of a modern polarized light microscope, to point out some sources of error in the interpretation of the results, and to recall the theoretical background of the polarized light microscopy.

The lack of effect of glucosamine sulphate on aggrecan mRNA expression and (35)S-sulphate incorporation in bovine primary chondrocytes.

Glucosamine and glucosamine sulphate have been promoted as a disease-modifying agent to improve the clinical symptoms of osteoarthritis. The precise mechanism of the action of the suggested positive effect of glucosamine or glucosamine sulphate on cartilage proteoglycans is not known, since the level of glucosamine in plasma remains very low after oral administration of glucosamine sulphate. We examined whether exogenous hexosamines or their sulphated forms would increase steady-state levels of aggrecan and hyaluronan synthase (HAS) or glycosaminoglycan synthesis using Northern blot and (35)S-sulphate incorporation analyses. Total RNA was extracted from bovine primary chondrocytes which were cultured either in 1 mM concentration of glucosamine, galactosamine, mannosamine, glucosamine 3-sulphate, glucosamine 6-sulphate or galactosamine 6-sulphate for 0, 4, 8 and 24 h, or in three different concentrations (control, 100 microM and 1 mM) of glucosamine sulphate salt or glucose for 24 or 72 h. Northern blot assay showed that neither hexosamines nor glucosamine sulphate salt stimulated aggrecan and HAS-2 mRNA expression. Glycosaminoglycan synthesis remained at a control level in the treated cultures, with the exception of mannosamine which inhibited (35)S-sulphate incorporation in low-glucose DMEM treatment. In our culture conditions, hexosamines or their sulphated forms did not increase aggrecan expression or (35)S-sulphate incorporation.

Loading and gait symmetry during level and stair walking in asymptomatic subjects with knee osteoarthritis: importance of quadriceps femoris in reducing impact force during heel strike?

Repetitive impulsive forces during walking are claimed to result in joint osteoarthritis (OA). The aim of this study was to investigate impact loading and gait symmetry during level and stair walking in asymptomatic elderly subjects with knee OA. It was hypothesised that pre-activity of the quadriceps femoris muscle (QF) would be an important factor reducing impulsive loading when walking on level ground. Subjects [21 female, six men, 66.2 (7.6) years] were studied. The subjects had no knee pain or diminished functional capacity, but showed radiographically light or moderate bilateral knee OA changes. Ground reaction forces (GRFs), plantar pressure distribution, muscle activation pattern [vastus medialis (VM), vastus lateralis, biceps femoris and gastrocnemius medialis] and asymmetry during level walking and stair walking were evaluated. Almost 20% of subjects had a distinct heel-strike transient at maximal speed with lower pre-activity of VM (P<0.05). The most forceful maximum vertical GRF in the braking phase occurred in stair descent [1.52 (0.21) BW]. This was 32.5% (P<0.001) higher than seen when walking on the level at normal speed. The loading rate of stair descent [10.87 (2.96) BW/s] was significantly stronger (P<0.05) than in level walking at normal speed [8.55 (1.93) BW/s]. There was no asymmetry in kinematic or kinetic variables in level walking. However, asymmetry increased during stair walking. The control of quadriceps femoris prior to heel-strike is possibly an important factor that reduces impulsive loading during walking in asymptomatic OA subjects. Stair walking is a demanding motor task and the musculoskeletal system is loaded more during stair descent than level walking at normal speed.

Hsp90 inhibitor geldanamycin increases hsp70 mRNA stabilisation but fails to activate HSF1 in cells exposed to hydrostatic pressure.

High hydrostatic pressure (HP) increases Hsp70 protein and mRNA levels by increasing the mRNA half-life without activation of HSF1 transcription factor. We investigated whether this change in gene expression requires Hsp90, previously shown to regulate hsp70 genes via HSF1. In HeLa cells, both HP and Hsp90 inhibitor geldanamycin (GA) up-regulated Hsp70 expression through mRNA stabilisation. GA, unlike HP, increased HSF1 activation. However, when exposures were used together a marked Hsp70 response was observed with mRNA stabilisation without coincidence of HSF1 activation. Our data suggests that Hsp90 is involved in hsp70 mRNA stabilisation and the HSF1 activation can be suppressed by high HP.

cDNA array reveals mechanosensitive genes in chondrocytic cells under hydrostatic pressure.

Hydrostatic pressure (HP) has a profound effect on cartilage metabolism in normal and pathological conditions, especially in weight-bearing areas of the skeletal system. As an important component of overall load, HP has been shown to affect the synthetic capacity and well-being of chondrocytes, depending on the mode, duration and magnitude of pressure. In this study we examined the effect of continuous HP on the gene expression profile of a chondrocytic cell line (HCS-2/8) using a cDNA array containing 588 well-characterized human genes under tight transcriptional control. A total of 51 affected genes were identified, many of them not previously associated with mechanical stimuli. Among the significantly up-regulated genes were immediate-early genes, and genes involved in heat-shock response (hsp70, hsp40, hsp27), and in growth arrest (GADD45, GADD153, p21(Cip1/Waf1), tob). Markedly down-regulated genes included members of the Id family genes (dominant negative regulators of basic helix-loop-helix transcription factors), and cytoplasmic dynein light chain and apoptosis-related gene NIP3. These alterations in the expression profile induce a transient heat-shock gene response and activation of genes involved in growth arrest and cellular adaptation and/or differentiation.

Influence of age, site, and degenerative state on the speed of sound in equine articular cartilage.

OBJECTIVE: To determine the speed of sound (SOS) in equine articular cartilage and investigate the influence of age, site in the joint, and cartilage degeneration on the SOS. SAMPLE POPULATION: Cartilage samples from 38 metacarpophalangeal joints of 38 horses (age range, 5 months to 22 years). PROCEDURE: Osteochondral plugs were collected from 2 articular sites of the proximal phalanx after the degenerative state was characterized by use of the cartilage degeneration index (CDI) technique. The SOS was calculated (ratio of needle-probe cartilage thickness to time of flight of the ultrasound pulse), and relationships between SOS value and age, site, and cartilage degeneration were evaluated. An analytical model of cartilage indentation was used to evaluate the effect of variation in true SOS on the determination of cartilage thickness and dynamic modulus with the ultrasound indentation technique. RESULTS: The mean SOS for all samples was 1,696 +/- 126 m/s. Age, site, and cartilage degeneration had no significant influence on the SOS in cartilage. The analytical model revealed that use of the mean SOS of 1,696 m/s was associated with maximum errors of 17.5% on cartilage thickness and 70% on dynamic modulus in an SOS range that covered 95% of the individual measurements. CONCLUSIONS AND CLINICAL RELEVANCE: In equine articular cartilage, use of mean SOS of 1,696 m/s in ultrasound indentation measurements introduces some inaccuracy on cartilage thickness determinations, but the dynamic modulus of cartilage can be estimated with acceptable accuracy in horses regardless of age, site in the joint, or stage of cartilage degeneration.

Reticulon 4 in chondrocytic cells: barosensitivity and intracellular localization.

Members of the reticulon gene family are endoplasmic reticulum (ER)-related proteins expressed in various human tissues, but their molecular functions are not understood. The reticulon 4 subfamily consists of three members, reticulon 4/Nogo-A, -B and -C. Reticulon 4-A is under intense investigation because of its inhibitory effect on neurite outgrowth, and reticulon 4-B has been suggested to induce apoptosis. Reticulon 4-C, the shortest member of this subfamily, is the least characterized. Reticulons are presumably guided to endoplasmic reticulum by a putative N-terminal retention motif. In this study the expressions of reticulon 4 subtypes in human chondrosarcoma cell line and in primary bovine chondrocytes were analyzed on mRNA level. These cell types, exposed to strong mechanical forces in vivo, were subjected to high hydrostatic pressure and mechanical stretch to study the possible mechanosensitivity of reticulon 4 genes. In addition, a green fluorescent protein-tagged reticulon 4-C and a fusion protein with mutated endoplasmic reticulum retention signal were used to study the significance of the C-terminal translocation signal (the di-lysine motif). As the result, both cell types expressed the three main isoforms of reticulon 4 family. The steady-state level of reticulon 4-B mRNA was shown to be up-regulated by pressure, but not by mechanical stretch indicating transcriptional barosensitivity. The reticular distribution pattern of reticulon 4-C was observed indicating a close association with endoplasmic reticulum. Interestingly, this pattern was maintained despite of the disruption of the putative localization signal. This suggests the presence of another, yet unidentified endoplasmic reticulum retention mechanism.

Prediction of biomechanical properties of articular cartilage with quantitative magnetic resonance imaging.

Quantitative magnetic resonance imaging (MRI) is the most potential non-invasive means for revealing the structure, composition and pathology of articular cartilage. Here we hypothesize that cartilage mechanical properties as determined by the macromolecular framework and their interactions can be accessed by quantitative MRI. To test this, adjacent cartilage disk pairs (n=32) were prepared from bovine proximal humerus and patellofemoral surfaces. For one sample, the tissue Young's modulus, aggregate modulus, dynamic modulus and Poisson's ratio were determined in unconfined compression. The adjacent disk was studied at 9.4T to determine the tissue T(2) relaxation time, sensitive to the integrity of the collagen network, and T(1) relaxation time in the presence of Gd-DTPA, a technique developed for the estimation of cartilage proteoglycan (PG) content. Quantitative MRI parameters were able to explain up to 87% of the variations in certain biomechanical parameters. Correlations were further improved when data from the proximal humerus was assessed separately. MRI parameters revealed a topographical variation similar to that of mechanical parameters. Linear regression analysis revealed that Young's modulus of cartilage may be characterized more completely by combining both collagen- and PG-sensitive MRI parameters. The present results suggest that quantitative MRI can provide important information on the mechanical properties of articular cartilage. The results are encouraging with respect to functional imaging of cartilage, although in vivo applicability may be limited by the inferior resolution of clinical MRI instruments.

Fibril reinforced poroelastic model predicts specifically mechanical behavior of normal, proteoglycan depleted and collagen degraded articular cartilage.

Degradation of collagen network and proteoglycan (PG) macromolecules are signs of articular cartilage degeneration. These changes impair cartilage mechanical function. Effects of collagen degradation and PG depletion on the time-dependent mechanical behavior of cartilage are different. In this study, numerical analyses, which take the compression-tension nonlinearity of the tissue into account, were carried out using a fibril reinforced poroelastic finite element model. The study aimed at improving our understanding of the stress-relaxation behavior of normal and degenerated cartilage in unconfined compression. PG and collagen degradations were simulated by decreasing the Young's modulus of the drained porous (nonfibrillar) matrix and the fibril network, respectively. Numerical analyses were compared to results from experimental tests with chondroitinase ABC (PG depletion) or collagenase (collagen degradation) digested samples. Fibril reinforced poroelastic model predicted the experimental behavior of cartilage after chondroitinase ABC digestion by a major decrease of the drained porous matrix modulus (-64+/-28%) and a minor decrease of the fibril network modulus (-11+/-9%). After collagenase digestion, in contrast, the numerical analyses predicted the experimental behavior of cartilage by a major decrease of the fibril network modulus (-69+/-5%) and a decrease of the drained porous matrix modulus (-44+/-18%). The reduction of the drained porous matrix modulus after collagenase digestion was consistent with the microscopically observed secondary PG loss from the tissue. The present results indicate that the fibril reinforced poroelastic model is able to predict specifically characteristic alterations in the stress-relaxation behavior of cartilage after enzymatic modifications of the tissue. We conclude that the compression-tension nonlinearity of the tissue is needed to capture realistically the mechanical behavior of normal and degenerated articular cartilage.

Reference sample method reduces the error caused by variable cryosection thickness in Fourier transform infrared imaging.

Fourier transform infrared imaging (FT-IRI) is a novel technique for characterization of the biochemical composition of biological tissues, e.g., articular cartilage. The use of cryosections is preferred in FT-IRI. Unfortunately, significant variation in section thickness often impairs the suitability of cryosections for quantitative FT-IRI analysis. The present study introduces an inexpensive reference sample method for quantitative analysis. In this technique, specimen absorption is normalized with that of nitrocellulose membrane embedded and cryosectioned with the sample. Mean variation of the infrared absorption in cartilage specimens was 11.5%, 12.1%, and 20.6% for 5 microm, 10 microm, and 14 microm thick sections, respectively, without normalization. Normalization reduced the variation to 5.2%, 4.0%, and 4.6% for the same sections, respectively. The normalization method enables usage of cryosections for quantitative work and significantly reduces the cost and time needed for FT-IRI analysis.

Stress responses of mammalian cells to high hydrostatic pressure.

High hydrostatic pressure causes stress response in many types of mammalian cells. We have previously shown that an accumulation of heat shock protein 70 (Hsp70) in a chondrocytic cell line occurred without an activation of the gene itself. Stabilization of the hsp70 mRNA was shown to be the reason for the Hsp70 stress response in the pressurized cells. Since accumulation of Hsp70 in pressurized cells indicated that high hydrostatic pressure induces a stress response without heat shock transcription factor activation, we decided to investigate the activation of two other stress-associated transcription factors, activator protein-1 (AP-1) and nuclear factor-kappaB (NF-kappaB). Induction of Hsp70 in immortalized and primary chondrocytes, murine Neuro-2a neuroblastoma and HeLa cervical carcinoma cell lines was investigated at both mRNA and protein levels. In immortalized chondrocytes and HeLa cells, hsp70 mRNA levels were clearly elevated after 6 hours of the onset of 30 MPa continuous hydrostatic pressure, while in primary chondrocytes and Neuro-2a cells (the cells known to be stress-sensitive) no induction was observed. Surprisingly, neither heat shock nor high hydrostatic pressure could induce the hsp70 mRNA in Neuro-2a cells, although an activation of heat shock transcription factor could be observed in heat-shocked cells. No activation of the AP-1 and NF-kappaB binding to their target DNA sequences could be shown in the immortalized chondrocytes.

Gene expression profiles in chondrosarcoma cells subjected to cyclic stretching and hydrostatic pressure. A cDNA array study.

Mechanical forces have a profound effect on cartilage tissue and chondrocyte metabolism. Strenuous loading inhibits the cellular metabolism, while optimal level of loading at correct frequency raises an anabolic response in chondrocytes. In this study, we used Atlas Human Cancer cDNA array to investigate mRNA expression profiles in human chondrosarcoma cells stretched 8% for 6 hours at a frequency of 0.5 Hz. In addition, cultures were exposed to continuous and cyclic (0.5 Hz) 5 MPa hydrostatic pressure. Cyclic stretch had a more profound effect on the gene expression profiles than 5 MPa hydrostatic pressure. Several genes involved with the regulation of cell cycle were increased in stretched cells, as well as mRNAs for PDGF-B, glucose-1-phosphate uridylyltransferase, Tiam1, cdc37 homolog, Gem, integrin alpha6, and matrix metalloproteinase-3. Among down-regulated genes were plakoglobin, TGF-alpha, retinoic acid receptor-alpha and Wnt8b. A smaller number of changes was detected after pressure treatments. Plakoglobin was increased under cyclic and continuous 5 MPa hydrostatic pressure, while mitogen-activated protein kinase-9, proliferating cell nuclear antigen, Rad6, CD9 antigen, integrins alphaE and beta8, and vimentin were decreased. Cyclic and continuous pressurization induces a number of specific changes. In conclusion, a different set of genes were affected by three different types of mechanical stimuli applied on chondrosarcoma cells.