Regulation of the friction coefficient of articular cartilage by TGF-β1 and IL-1β
ABSTRACT Articular cartilage functions to provide a low-friction surface for joint movement for many decades of life. Superficial zone protein (SZP) is a glycoprotein secreted by chondrocytes in the superficial layer of articular cartilage that contributes to effective boundary lubrication. In both cell and explant cultures, TGF-beta1 and IL-1beta have been demonstrated to, respectively, upregulate and downregulate SZP protein levels. It was hypothesized that the friction coefficient of articular cartilage could also be modulated by these cytokines through SZP regulation. The friction coefficient between cartilage explants (both untreated and treated with TGF-beta1 or IL-1beta) and a smooth glass surface due to sliding in the boundary lubrication regime was measured with a pin-on-disk tribometer. SZP was quantified using an enzyme-linked immunosorbant assay and localized by immunohistochemistry. Both TGF-beta1 and IL-1beta treatments resulted in the decrease of the friction coefficient of articular cartilage in a location- and time-dependent manner. Changes in the friction coefficient due to the TGF-beta1 treatment corresponded to increased depth of SZP staining within the superficial zone, while friction coefficient changes due to the IL-1beta treatment were independent of SZP depth of staining. However, the changes induced by the IL-1beta treatment corresponded to changes in surface roughness, determined from the analysis of surface images obtained with an atomic force microscope. These findings demonstrate that the low friction of articular cartilage can be modified by TGF-beta1 and IL-1beta treatment and that the friction coefficient depends on multiple factors, including SZP localization and surface roughness.
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ABSTRACT: To assess ovine synovial fluid (oSF) from different post-injury time points for (1) proteoglycan-4 (PRG4) and hyaluronan (HA) concentration, (2) HA molecular weight (MW) distribution, (3) cartilage boundary lubrication function, and (4) lubricant composition-function relationships. The association between cartilage boundary lubrication and gross cartilage changes after injury was also examined. oSF was collected 2, 4, 10, and 20 weeks post anterior cruciate ligament (ACL) transection in 5 skeletally mature sheep. PRG4 and HA concentrations were measured using sandwich enzyme-linked immunosorbent assay, and HA MW distribution by agarose gel electrophoresis. Cartilage boundary lubrication of oSF was assessed using a cartilage-cartilage friction test. Gross damage to articular cartilage was also quantified at 20 weeks using modified Drez scoring protocol. Early (2-4 weeks) after ACL injury, PRG4 concentrations were significantly higher (p = 0.045, p = 0.037), and HA concentrations were substantially lower (p = 0.005, p = 0.005) compared to 20 weeks. The HA MW distribution also shifted towards lower ranges in the early post-injury stage. The kinetic friction coefficients were significantly higher 2-4 weeks post injury (p = 0.008 and p = 0.049) compared to 20 weeks. Poor cartilage boundary lubricating ability early after injury was associated with cartilage damage at 20 weeks. Altered composition and diminished boundary lubrication of oSF early after ACL transection may predispose the articular cartilage to degenerative changes and initiate osteoarthritis (OA). These observations also provide potential motivation for biotherapeutic interventions at earlier time points post injury. Copyright © 2014. Published by Elsevier Ltd.Osteoarthritis and Cartilage 12/2014; 23(4). DOI:10.1016/j.joca.2014.12.017 · 4.66 Impact Factor
Journal of Tribology 01/2011; 133(4):041201. DOI:10.1115/1.4004760 · 0.90 Impact Factor
Frontiers in bioscience (Scholar edition) 01/2012; S4(1):251. DOI:10.2741/S266