Dynamic shear stimulation of bovine cartilage biosynthesis of proteoglycan 4

Abstract

Objective. The boundary lubrication function of articular cartilage is mediated in part by proteoglycan 4 (PRG4) molecules at the articular surface and in synovial fluid. The objective of this study was to determine the effects of dynamic shear stimulation on PRG4 biosynthesis by bovine cartilage explants.Methods. Cartilage disks with intact articular surfaces were harvested from immature bovines. Some disks were subjected to 24 hours (day 1) of loading, consisting of a step load of 20% static compression either alone or with superimposed dynamic shear (3% amplitude and 0.1 Hz), while other disks were cultured free-swelling as controls. After the 24-hour loading period, disks were terminated or were further incubated for up to 72 hours (days 2-4) in free-swelling culture to assess chondrocyte responses to, and following, unloading. PRG4 products secreted into culture medium were quantified by enzyme-linked immunosorbent assay and characterized by Western blotting. Chondrocytes expressing PRG4 were localized by immunohistochemistry, and depth-associated variations in chondrocyte PRG4 expression were quantified by image analysis.Results. Dynamic shear stimulation increased PRG4 secretion to 3-4 times that of unloaded controls and statically compressed samples. Sheared cartilage secreted more PRG4 of 345 kd relative to smaller molecular weight species, as compared with unloaded controls. Immunohistochemistry revealed that shear stimulation also increased the total number of cells expressing PRG4 by inducing expression by cells at a depth of 200-400 m.Conclusion. The paradigm that certain mechanical stimuli up-regulate biosynthesis in cartilage appears operative not only for load-bearing matrix constituents, but also for PRG4 molecules that mediate lubrication.

Regulation of the friction coefficient of articular cartilage by TGF‐β1 and IL‐1β

“…This culture technique does not exactly mimic the in vivo situation of a rich cytokine environment and associated mechanical loading, both of which can regulate SZP expression. 17,19,21,35,36 This may further explain the loss of SZP in the controls of the 5-day culture media and tissue (Fig. 3B, D).…”

Role of lubricin and boundary lubrication in the prevention of chondrocyte apoptosis

“…Shear stress and compression increase lubricin expression in bovine cartilage when lubricated (37,38), so the viability of lubricin-producing cells in the superficial zone and the availability of lubricin in SF to deposit on the cartilage surface help maintain boundary lubrication (39). The importance of rapid and continuous replenishment of lubricin during joint loading is supported by our studies, which found a significant increase in COF after 30 h of ex vivo joint oscillation under load in Prg4 +/− compared with Prg4 +/+ mouse limbs (22).…”

Experimental measurement and quantification of frictional contact between biological surfaces experiencing large deformation and slip

“…With mechanical loading, the details of such deformation are often governed by the biomechanical interactions between contacting tissue surfaces, and such interactions may also have direct implications for both normal and pathological processes. Shearing of cartilage during joint articulation has been shown to significantly affect the cellular response (Nugent, et al, 2006, Nugent-Derfus, et al, 2007. Such interactions, which take place throughout the body (e.g.…”