Biorheology - Volume 40, issue 1-3

Authors: Hung, Clark T. | LeRoux, Michelle A. | Palmer, Glyn D. | Chao, P.‐H. Grace | Lo, Sansan | Valhmu, Wilmot B.

Article Type: Research Article

Abstract: The effects of hypotonic (180 mOsm) and hypertonic (580 mOsm) medium loading on chondrocyte aggrecan gene expression in 2D monolayer and 3D hydrogel culture (agarose or alginate) were studied. Aggrecan promoter activity was monitored using a luciferase reporter gene assay and transient transfection. Osmotic loading was observed to differentially affect promoter activity, with hypotonic loading generally producing at least a 40% elevation in promoter activity, except for the case of alginate where a 50% suppression was observed. Hypertonic loading produced at least a 35% decrease in activity for all cultures. Similar osmolality‐induced changes to aggrecan mRNA levels were observed in …monolayer cells using qPCR. Deletion of exon 1 blocked the sensitivity of monolayer cells to hypertonic but not hypotonic medium changes. Confocal microscopy measurements suggested that the degree of hypotonic swelling in cells encapsulated in 3D matrix was restricted compared to monolayer cells whereas the degree of hypertonic shrinking was similar under both culture conditions. Show more

Citation: Biorheology, vol. 40, no. 1-3, pp. 61-72, 2003

Authors: Hopewell, Bethan | Urban, Jill P.G.

Article Type: Research Article

Abstract: Articular chondrocytes are exposed to a unique osmotic environment, which varies throughout the depth of cartilage, and in response to mechanical loading or pathological conditions. In light of such osmotic variations we investigated the response of chondrocytes cultured in alginate beads to long term hypo‐ and hyperosmotic challenge. Following pre‐incubation at 380 mOsmol, exposure to hyperosmotic conditions (550 mOsmol) initially decreased 35 S‐sulphate incorporation, but after 24 hours of culture, rates had recovered and surpassed their original levels. MAP kinase inhibitors abrogated this response suggesting their involvement in the adaptation mechanism. Hypo‐osmotic challenge caused a decrease in 35 S‐sulphate incorporation …throughout the culture period. These results suggest that osmolality is a powerful regulator of macromolecular synthesis, and that perturbations in the osmotic environment may alter the set point for turnover. Show more

Keywords: Cartilage, MAP kinase, proteoglycan, glycosaminoglycan

Citation: Biorheology, vol. 40, no. 1-3, pp. 73-77, 2003

Authors: Toyoda, Takashi | Seedhom, Bahaa B. | Kirkham, Jennifer | Bonass, William A.

Article Type: Research Article

Abstract: The aim of this study was to investigate the effect of hydrostatic pressure on the expression of messenger ribonucleic acid (mRNA) for specific extracellular matrix proteins in chondrocytes. Chondrocytes obtained from bovine metatarsophalangeal joints were embedded in cylindrical 2% agarose gels. A novel experimental system was used to apply 5 MPa of static hydrostatic pressure to these chondrocytes for 4 hours. The application of hydrostatic pressure caused a significant increase in the level of aggrecan mRNA by almost four fold (p<0.01) as well as a 50% increase in the level of type II collagen mRNA (p<0.05). However, there was no …significant change in the level of TIMP‐1 mRNA. It was suggested that the application of hydrostatic pressure, in the absence of cell deformation, can bring about changes in the matrix components which may play an important role in the homeostasis and mechanical properties of articular cartilage. Show more

Citation: Biorheology, vol. 40, no. 1-3, pp. 79-85, 2003

Authors: Kaarniranta, Kai | Elo, Mika A. | Sironen, Reijo K. | Karjalainen, Hannu M. | Helminen, Heikki J. | Lammi, Mikko J.

Article Type: Research Article

Abstract: 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‐κB (NF‐κB). 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‐κB binding to their target DNA sequences could be shown in the immortalized chondrocytes. Show more

Citation: Biorheology, vol. 40, no. 1-3, pp. 87-92, 2003

Authors: Karjalainen, Hannu M. | Sironen, Reijo K. | Elo, Mika A. | Kaarniranta, Kai | Takigawa, Masaharu | Helminen, Heikki J. | Lammi, Mikko J.

Article Type: Research Article

Abstract: 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 α6 , and matrix metalloproteinase‐3. Among down‐regulated genes were plakoglobin, TGF‐α, retinoic acid receptor‐α 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 αE and β8 , 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. Show more

Citation: Biorheology, vol. 40, no. 1-3, pp. 93-100, 2003

Authors: Giannoni, Paolo | Siegrist, Mark | Hunziker, Ernst B. | Wong, Marcy

Article Type: Research Article

Abstract: Physical forces are known to influence the synthesis, assembly and degradation of the cartilage extracellular matrix. The expression of cartilage oligomeric matrix protein (COMP) was found to be sensitive to long term cyclic compression. Explants of calf articular cartilage as well as cylindrical alginate/chondrocyte constructs were subjected to uniaxial unconfined dynamic compression for 18 hours after which total mRNA was extracted from samples. COMP expression was assessed by means of semi‐quantitative RT–PCR and Northern blot techniques. The COMP transcript was found to be significantly enriched upon compression in both experimental systems. Incubation with anti‐β1 integrin blocking antibodies abolished the mechanosensitivity …of COMP expression. In addition, the presence of a fully developed pericellular matrix was shown to be a prerequisite for enhanced COMP expression with cyclic loading. Cell/matrix interactions are therefore one of the key events in mechanotransduction in chondrocytes. Show more

Citation: Biorheology, vol. 40, no. 1-3, pp. 101-109, 2003

Authors: Blain, Emma J. | Mason, Deborah J. | Duance, Victor C.

Article Type: Research Article

Abstract: Osteoarthritis (OA) develops as a consequence of articular cartilage degeneration possibly initiated by excessive or abnormal loading of the joint, and potentially mediated through a proteinase/proteinase inhibitor imbalance. We have shown previously that physiological loads (0.5 MPa, 1 Hz, 3 hour) elicit increased expression and activation of the matrix metalloproteinases (MMPs) in articular cartilage explants in vitro. The objective of this study was to identify mechanically‐regulated genes involved in the observed induction of MMP expression and enhanced activation. Differential RNA Display (DRD) was used to identify mechanically‐regulated genes by comparing DRD products derived from loaded and unloaded cartilage. One gene …up‐regulated in cartilage after 10, 30 and 60 minute loading revealed 83% homology with Mus musculus thymosin β4 which is known to induce MMP gene expression. The identification of mechanically regulated genes will greatly enhance our understanding of matrix turnover providing an exciting future in elucidating the role of mechanically‐regulated genes in the development of OA. Show more

Citation: Biorheology, vol. 40, no. 1-3, pp. 111-117, 2003

Authors: Romanello, Milena | Veronesi, Valentina | D'Andrea, Paola

Article Type: Research Article

Abstract: Mechanically induced intercellular Ca2+ signalling was investigated in differentiated HOBIT osteoblastic cells. HOBIT cells express connexin43 clustered at the cell‐to‐cell boundary and display functional intercellular coupling assessed by intercellular transfer of Lucifer yellow. Mechanical stimulation of single cells, besides leading to an intracellular Ca2+ rise, induced a wave of increased Ca2+ that was radially propagated to surrounding cells. Treatment of cells with thapsigargin blocked mechanically induced signal propagation. Intercellular Ca2+ spreading was inhibited by 18α‐glycyrrhetinic acid, demonstrating the involvement of gap junctions in signal propagation. Suramin and apyrase decreased the extent of wave propagation, suggesting that …ATP‐mediated paracrine stimulation contribute to cell‐to‐cell signalling. The functional expression of gap‐junctional hemichannels was evidenced in experiments of Mn2+ quenching, extracellular dye uptake and intracellular Ca2+ release, activated by uptake of inositol 1,4,5‐trisphosphate from the external medium. Gap‐junctional hemichannels were activated by low extracellular Ca2+ concentrations and inhibited by 18α‐glycyrrhetinic acid. Show more

Citation: Biorheology, vol. 40, no. 1-3, pp. 119-121, 2003

Authors: Frijns, A.J.H. | Huyghe, J.M. | Kaasschieter, E.F. | Wijlaars, M.W.

Article Type: Research Article

Abstract: Cartilage exhibits a swelling and shrinking behaviour that influences the function of the cells inside the tissue. This behaviour is caused by mechanical, chemical and electrical loads. It is described by the electrochemomechanical mixture theory, in which the tissue is represented by four components: a charged porous solid, a fluid, cations and anions. By distinguishing between the cations and anions, electrical phenomena can be modelled. This mixture theory is verified by fitting the deformations and the electrical potentials in a uniaxial confined swelling and compression experiment to a mixed finite element simulation. The fitted stiffness, permeability, diffusion coefficients, and osmotic …coefficients are in the same range as reported in literature. Show more

Keywords: Mixture theory, streaming potential, cartilage, hydrogel, mixed finite element method

Citation: Biorheology, vol. 40, no. 1-3, pp. 123-131, 2003

Authors: Laasanen, M.S. | Töyräs, J. | Korhonen, R.K. | Rieppo, J. | Saarakkala, S. | Nieminen, M.T. | Hirvonen, J. | Jurvelin, J.S.

Article Type: Research Article

Abstract: Structure and properties of knee articular cartilage are adapted to stresses exposed on it during physiological activities. In this study, we describe site‐ and depth‐dependence of the biomechanical properties of bovine knee articular cartilage. We also investigate the effects of tissue structure and composition on the biomechanical parameters as well as characterize experimentally and numerically the compression–tension nonlinearity of the cartilage matrix. In vitro mechano‐optical measurements of articular cartilage in unconfined compression geometry are conducted to obtain material parameters, such as thickness, Young's and aggregate modulus or Poisson's ratio of the tissue. The experimental results revealed significant site‐ and depth‐dependent …variations in recorded parameters. After enzymatic modification of matrix collagen or proteoglycans our results show that collagen primarily controls the dynamic tissue response while proteoglycans affect more the static properties. Experimental measurements in compression and tension suggest a nonlinear compression–tension behavior of articular cartilage in the direction perpendicular to articular surface. Fibril reinforced poroelastic finite element model was used to capture the experimentally found compression–tension nonlinearity of articular cartilage. Show more

Citation: Biorheology, vol. 40, no. 1-3, pp. 133-140, 2003