Biorheology - Volume 41, issue 3-4

Authors: Gouttenoire, Jérôme | Valcourt, Ulrich | Ronzière, Marie‐Claire | Aubert‐Foucher, Elisabeth | Mallein‐Gerin, Frédéric | Herbage, Daniel

Article Type: Research Article

Abstract: In osteoarthritic cartilage, chondrocytes are able to present heterogeneous cellular reactions with expression and synthesis of the (pro)collagen types characteristic of prechondrocytes (type IIA), hypertrophic chondrocytes (type X), as well as differentiated (types IIB, IX, XI, VI) and dedifferentiated (types I, III) chondrocytes. The expression of type IIA procollagen in human osteoarthritic cartilage support the assumption that OA chondrocytes reverse their phenotype towards a chondroprogenitor phenotype. Recently, we have shown that dedifferentiation of mouse chondrocytes induced by subculture was associated with the alternative splicing of type II procollagen pre‐mRNA with a switch from the IIB to the IIA form. In …this context, we demonstrated that BMP‐2 favours expression of type IIB whereas TGF‐β1 potentiates expression of type IIA induced by subculture. These data reveal the specific capability of BMP‐2 to reverse the program of chondrocyte dedifferentiation. This interesting feature needs to be tested with human chondrocytes since cell amplification is required for the currently used autologous chondrocyte transplantation. Show more

Keywords: Chondrocyte phenotype, type IIA and IIB procollagen, BMP‐2, TGF‐β1, cartilage repair

Citation: Biorheology, vol. 41, no. 3-4, pp. 535-542, 2004

Authors: Stoltz, J.‐F.

Article Type: Other

Citation: Biorheology, vol. 41, no. 3-4, pp. 565-565, 2004

Authors: Millward‐Sadler, S.J. | Wright, M.O. | Flatman, P.W. | Salter, D.M.

Article Type: Research Article

Abstract: Extracellular nucleotides have been shown to have diverse effects on chondrocyte function, generally acting via P2 purinoceptors. We have previously shown that mechanical stimulation at 0.33 Hz of normal human chondrocyte cultures causes cellular hyperpolarisation, while chondrocytes derived from osteoarthritic (OA) cartilage depolarise. Experiments have been undertaken to establish whether ATP is involved in the response of the chondrocyte to mechanical stimulation. Chondrocytes, isolated from normal and OA cartilage obtained, with consent, from human knee joints following surgery, were cultured in non‐confluent monolayer. Cells were mechanically stimulated at 0.33 Hz for 20 minutes at 37°C in the presence or …absence of inhibitors of ATP signalling, or were stimulated by the addition of exogenous ATP or derivatives, and electrophysiological measurements recorded. Samples of medium bathing the cells were collected before and after mechanical stimulation, and the concentration of ATP in the cell medium was measured. Total RNA was extracted from cultured chondrocytes, reverse‐transcribed and used for RT‐PCR with primers specific for P2Y2 purinoceptors. ATP, UTP 2‐methylthioadenosine and αβ‐methylene adenosine 5′‐triphosphate all induced a hyperpolarisation response in normal human articular chondrocytes. No significant change was observed in the membrane potentials of chondrocytes isolated from OA cartilage following the addition of these nucleotides to the medium. In normal chondrocytes, the hyperpolarisation induced by ATP was blocked by the presence of apamin, indicating the involvement of small‐conductance calcium‐activated potassium channels. Following mechanical stimulation of normal chondrocytes, an increase was observed in ATP concentration in the cell culture medium bathing the cells. The presence within the culture medium of suramin or pyridoxal‐phosphate‐6‐azophenyl‐2′,4′‐disulphonic acid (PPADS) prior to and during the period of mechanical stimulation abolished the hyperpolarisation response in normal chondrocytes. The presence of mRNA for P2Y2 purinoceptors was demonstrated in both normal and OA chondrocytes by RT‐PCR. These results suggest that ATP has a role in the response of normal chondrocytes to mechanical stimulation, via P2Y2 purinoceptors. This response appears to be different in chondrocytes derived from OA cartilage, and may be important in the progression of this disease. Show more

Keywords: Osteoarthritis, mechanical stimulation, signal transduction, purinoceptor

Citation: Biorheology, vol. 41, no. 3-4, pp. 567-575, 2004

Authors: Lima, Eric G. | Mauck, Robert L. | Han, Shelley H. | Park, Seonghun | Ng, Kenneth W. | Ateshian, Gerard A. | Hung, Clark T.

Article Type: Research Article

Abstract: Due to the prevalence of osteoarthritis (OA) and damage to articular cartilage, coupled with the poor intrinsic healing capacity of this avascular connective tissue, there is a great demand for an articular cartilage substitute. As the bearing material of diarthrodial joints, articular cartilage has remarkable functional properties that have been difficult to reproduce in tissue‐engineered constructs. We have previously demonstrated that by using a functional tissue engineering approach that incorporates mechanical loading into the long‐term culture environment, one can enhance the development of mechanical properties in chondrocyte‐seeded agarose constructs. As these gel constructs begin to achieve material properties similar to …that of the native tissue, however, new challenges arise, including integration of the construct with the underlying native bone. To address this issue, we have developed a technique for producing gel constructs integrated into an underlying bony substrate. These osteochondral constructs develop cartilage‐like extracellular matrix and material properties over time in free swelling culture. In this study, as a preliminary to loading such osteochondral constructs, finite element modeling (FEM) was used to predict the spatial and temporal stress, strain, and fluid flow fields within constructs subjected to dynamic deformational loading. The results of these models suggest that while chondral (“gel alone”) constructs see a largely homogenous field of mechanical signals, osteochondral (“gel bone”) constructs see a largely inhomogeneous distribution of mechanical signals. Such inhomogeneity in the mechanical environment may aid in the development of inhomogeneity in the engineered osteochondral constructs. Together with experimental observations, we anticipate that such modeling efforts will provide direction for our efforts aimed at the optimization of applied physical forces for the functional tissue engineering of an osteochondral articular cartilage substitute. Show more

Keywords: Functional tissue engineering, deformational loading, articular cartilage, osteochondral constructs, finite element models

Citation: Biorheology, vol. 41, no. 3-4, pp. 577-590, 2004

Authors: Lammi, Mikko J.

Article Type: Research Article

Abstract: It is well known that physiological forces are essential for the maintenance of normal composition and structure of articular cartilage. Although some of the mechanisms of mechanotransduction are known today, there are certainly many others left unrevealed. In order to understand the complicated systems present in articular cartilage, we have to bring together the data from all fields of cartilage mechanobiology. The 3rd Symposium on Mechanobiology of Cartilage and Chondrocyte was a good effort towards that goal.

Citation: Biorheology, vol. 41, no. 3-4, pp. 593-596, 2004

Authors: Stoltz, J.‐F.

Article Type: Other

Citation: Biorheology, vol. 41, no. 3-4, pp. 597-597, 2004

Authors: Luo, Zong‐Ping | Sun, Yu‐Long | Fujii, Tadashi | An, Kai‐Nan

Article Type: Research Article

Abstract: Type II collagen and hyaluronan are the two major components of extracellular molecules in cartilage and play an important role in mechanical functions of extracellular matrix. Currently, their mechanical properties have been investigated only at the gross‐level. In this study, the mechanical properties of single type II collagen and hyaluronan molecules were directly measured using optical tweezers technique. The persistence length was found to be 11.2±8.4 nm in type II collagen and 4.5±1.2 nm in hyaluronan. This result suggested that type II collagen is stiffer than hyaluronan at the individual molecule level, which supports the general concept that collagen is …responsible for resisting tensile force. The experimental system developed here also provides a powerful tool for quantifying mechanical properties of extracellular matrix at the single molecule level. Show more

Keywords: Type II collagen, hyaluronan, optical tweezers, persistence length, mechanical properties

Citation: Biorheology, vol. 41, no. 3‐4, pp. 247-254, 2004

Authors: Salter, D.M. | Wright, M.O. | Millward‐Sadler, S.J.

Article Type: Research Article

Abstract: Mechanical forces influence articular cartilage structure by regulating chondrocyte activity. Mechanical stimulation results in activation of an α5β1 integrin dependent intracellular signal cascade involving focal adhesion kinase and protein kinase C, triggering the release of interleukin‐4 from the cell. In normal HAC the response to physiological mechanical stimulation is characterised by increased levels of aggrecan mRNA and a decrease in levels of mRNA for matrix metalloproteinase 3 (MMP‐3), the net result of which would be to maintain and optimise cartilage structure and function. This protective/anabolic response is not seen when chondrocytes from osteoarthritic cartilage are subjected to an identical mechanical …stimulation regime. Following the observation that the neurotransmitter substance P is involved in chondrocyte mechanotransduction the present study was undertaken to establish potential roles for glutamate receptors in the control of chondrocyte mechanical responses. Using immunohistochemistry and RTPCR normal and OA chondrocytes are shown to express NR1 and NR2a subunits of the NMDA receptor. Addition of NMDA receptor agonists to chondrocytes in primary culture resulted in changes in membrane potential consistent with expression of functional receptors. NMDA receptor antagonists inhibited the hyperpolarisation response of normal chondrocytes to mechanical stimulation but had no effect on the depolarisation response of osteoarthritic chondrocytes to mechanical stimulation. These studies indicate that at least one subset of the NMDA receptor family of molecules is expressed in cartilage and may have important modulatory effects on mechanotransduction and cellular responses following mechanical stimulation. Indeed the results suggest that there is an alteration of NMDA receptor signalling in OA chondrocytes, which may be critical in the abnormal response of OA chondrocytes to mechanical stimulation. Thus NMDA receptors appear to be involved in the regulation of human articular chondrocyte responses to mechanical stimulation, and in OA, mechanotransduction pathways may be modified as a result of altered activation and function of these receptors. Show more

Citation: Biorheology, vol. 41, no. 3‐4, pp. 273-281, 2004

Authors: Bailey, Allen J. | Mansell, Jason P. | Sims, Trevor J. | Banse, Xavier

Article Type: Research Article

Abstract: The subchondral bone has long been known to thicken in osteoarthritis. However, recent evidence has demonstrated that the turnover of the bone is increased several fold, and further suggests that the thickening occurs prior to degradation of the articular cartilage, indicating that it plays a role in the pathogenesis of osteoarthritis. The mechanical and biochemical properties of the subchondral bone are therefore of particular interest in any attempt to determine the nature of the factors initiating osteoarthritis. We have shown that the subchondral bone collagen of the femoral head possessed a 20‐fold increase in turnover, as assessed by procollagen …rate of synthesis and metalloproteinase degradation, and a 25% decrease in mineralisation. This increased metabolism and high lysyl hydroxylation leads to narrower and weaker fibres. Additionally the phenotypic expression of the osteoblasts is modified to produce increasing proportions of type I homotrimer in addition to the normal type I heterotrimer, which further reduces the mechanical strength of the bone. Overall, the narrow immature collagen fibres, the reduction in pyrrole cross‐linking, decreased mineralisation, and increased amounts of type I homotrimer, all contribute to a weakening of the mechanical properties of the subchondral bone. Show more

Keywords: Subchondral bone, osteoarthritis, collagen, cross‐linking, metabolism, biomechanics

Citation: Biorheology, vol. 41, no. 3‐4, pp. 349-358, 2004

Authors: Day, J.S. | van der Linden, J.C. | Bank, R.A. | Ding, M. | Hvid, I. | Sumner, D.R. | Weinans, H.

Article Type: Research Article

Abstract: Osteoarthritis is a chronic joint disease with pathological changes in the articulating cartilage and all other tissues that occupy the joint. Radin and coworkers have suggested the involvement of subchondral bone in the disease process. However, evidence for an essential role in the etiology has never been proven. Recent studies showing reduced chemical and mechanical properties of subchondral bone in various stages of the disease have invigorated interest in the role of subchondral bone in the development and progression of the disease. The current study showed that the concept of bone adaptation might explain subchondral stiffening, a process where subchondral …bone becomes typically sclerotic in osteoarthritis. In addition, we report reduced mechanical matrix tissue properties as well as an increase in denatured collagen content. In conclusion, although osteoarthritic bone tissue contains increased denatured collagen and has reduced matrix mechanical properties, the widely accepted concept of subchondral stiffening is compatible with the process of normal bone adaptation. Show more

Citation: Biorheology, vol. 41, no. 3‐4, pp. 359-368, 2004