Cartilage response to mechanical force in high‐density chondrocyte cultures

Abstract

High-density cultures of chick embryonic chondrocytes were exposed to intermittent compressive force (ICF) of physiologic magnitude for 24 hours. Proteoglycan synthesis was significantly increased in chondrocyte cultures exposed to ICF as compared with control cultures. Similar effects were found in explants of epiphyseal cartilage. Proteoglycans extracted with guanidine-HCI from cultures exposed to ICF aggregated better with hyaluronic acid than did control cultures, as shown by Sepharose 2B gel chromatography. In addition, the amount of non-extractable proteoglycans was increased in ICF cultures. We conclude that ICF not only increases the synthesis of proteoglycans but also improves the aggregating capacity of proteoglycans and the coherence of proteoglycans with other matrix components. High-density cultures of epiphyseal chondrocytes provide a suitable model to study the processes involved in the perception of and the subsequent cellular response to compressive force by cartilage.The ability of cartilage to function as a weightbearing tissue is related to its chemical composition and the macromolecular organization of its constituents (1). The extracellular matrix of cartilage is primarily composed of collagen and proteoglycan, which account for 50-60% and 10-40% of the dry weight, respectively (2). Collagen confers tensile strength (3) and proteoglycans provide the elasticity and the ability to resist compression (43). Proteoglycan monomers which have an average molecular weight of 1-2 x lo6 daltons (6) possess a high fixed negative charge density, which renders them highly hydrophilic (7).In cartilage the proteoglycans form predominantly very large aggregates, in which many individual monomers are noncovalently associated with hyaluronic acid (8,9). A proteoglycan monomer consists of a protein core which contains 3 regions: the hyaluronic acid binding region with a few short keratan sulfate chains, an intermediate keratan sulfate-rich fragment, and a chondroitin sulfate-rich fragment of variable size (10,ll). The proteoglycan-hyaluronic acid interaction is stabilized by 2 glycoproteins (9,(12)(13)(14)(15)(16).The initial in vivo response of articular cartilage to repetitive trauma is enhanced matrix production without cell proliferation (17), whereas a decrease in loading provokes degenerative changes in the articular cartilage (18,19). This study reports the in vitro response of high-density chondrocyte cultures to intermittent compression. We reported earlier that under in vitro conditions, intermittent compressive force (ICF) decreased cell proliferation of chondrocytes cultured in a monolayer (20). Matrix production, however, should be studied using high-density chondrocyte cultures (21-25). We developed a suitable model (24) and reported that high-density chondrocyte cultures exposed to intermittent compressive force showed a decrease in cell proliferation and an increase in matrix

Increased calcification of growth plate cartilage as a result of compressive force in vitro

“…The experimental apparatus for applying ICF to metatarsal rudiments is depicted in Figure 1. Essentially, ICF was produced following the procedure described previously (17). Compressed air, reduced at 2 atmospheres, was brought to a 5/2 base plate manifold that was controlled by 2 electromagnetic 3/2 valves (all parts from Enots Pneumatic Products, Lichfield, UK).…”

“…We have reported previously (17) that intermittent compressive force (ICF) increases the synthesis and deposition of proteoglycans in the matrix of chondrocytes in vitro. The compressive force was calculated to be of physiologic magnitude (18).…”

“…The compressive force was calculated to be of physiologic magnitude (18). ICF also improves the aggregating capacity of pro- teoglycans and the coherence of proteoglycans with other matrix components (17). This led to the hypothesis that ICF might modulate the deposition of mineral in hypertrophic cartilage.…”

Biosynthetic response of cartilage explants to dynamic compression

“…Cyclic tensile stretching of high-density 14-day chick chondrocyte cultures increased PG synthesis; the single test condition of 5.5% stretching at 0.2 Hz was thought to impart compressive forces to the cells (13). Another approach has been dynamic pressurization of the gas phase (13% at 0.3 Hz) overlying the culture medium (39,74). To interpret these results, it is necessary to first separate the effects of dynamic changes in partial pressure of gas in the medium from hydrostatic pressure, which alone may also elicit a response depending on the amplitude and frequency of pressure change (25,37,43).…”

Effects of fluid-induced shear stress on articular cartilage regeneration under simulated aspects of microgravity

“…There is a great deal of evidence from these studies that static and low frequency cyclic loading (i.e., below approximately 0.01 Hz) inhibits matrix synthesis (Jones et al, 1982;Lippiello et al, 1985;Gray et al, 1988;Sah et al, 1989;Larsson et al, 1991;Sah et al, 1991;Torzilli et al, 1997). Alternatively, under more dynamic conditions of higher frequency loading, extracellular matrix production has been shown to be promoted (van Kampen et al, 1985;Veldhuijzen et al, 1987;Sah et al, 1989;Larsson et al, 1991;Korvert et al, 1992). Parkkinen et al obtained similar results evaluating hydostatic/dynamic pressurization effects in the physiological range at 5 MPa (Parkkinen et al, 1992).…”