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-b1 and IL-1b 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-b1 or IL-1b) 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-b1 and IL-1b 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-b1 treatment corresponded to increased depth of SZP staining within the superficial zone, while friction coefficient changes due to the IL-1b treatment were independent of SZP depth of staining. However, the changes induced by the IL-1b 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-b1 and IL-1b treatment and that the friction coefficient depends on multiple factors, including SZP localization and surface roughness. ß

Surface Zone Articular Chondrocytes Modulate the Bulk and Surface Mechanical Properties of the Tissue-Engineered Cartilage

“…26,27 Briefly, a 5 mm punch was taken from the center of each construct, affixed to acrylic pins by ethyl cyanoacrylate, and then brought into contact with a polished glass disk while fully immersed in PBS. Before the initiation of each friction test, the sample was allowed to equilibrate unconfined under the applied load (0.1 MPa) for 2 min to minimize any fluid effects during testing.…”

“…The boundary mode friction coefficient of cartilage either sliding against cartilage or glass in the presence of SZP has been reported to be *0.02 to 0.04. [24][25][26][27] In bovine femoral condyles, SZP synthesis was found to correlate with mechanical loading. 26 In previous studies, self-assembled constructs have been generated from primary chondrocytes isolated from the SZ and MZ of bovine articular cartilage.…”

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“…Участие лубрицина в обеспечении граничной смазки подтверждено результатами исследований генетических нарушений у человека [21], на животных с экспериментальным артритом [22], нокаутированием гена prg4 у грызунов [23] и функциональных трибологических экспериментах [24]. В то время как СЖ, обработанная гиалуронидазой, не теряла своих смазочных свойств, обработка протеазой, что позволяло ликвидировать лубрицин, приводило к полной их потере.…”

“…Так, трансформирующий фактор роста-β и костные морфогенетические белки (BMP) усиливают продукцию этого белка как в хондроцитах поверхностной зоны, так и в синовиоцитах. Эти эффекты синергетичны в обеих популяциях клеток [24,28]. Регуляция продукции SZP/лубрицина в хондроцитах инсулиноподобным фактором роста-1 (который стимулирует экспресии аггрекана) в большей мере зависит от ситуации.…”

Hydrogels and bioreactors for cartilage research and functional tissue engineering

“…These include elasto-hydrodynamic lubrication [75], squeeze film lubrication provided by synovial fluid [76], boundary lubrication between thin molecular films absorbed to the articulating surfaces [77][78][79][80], and fluid pressurization [67,[81][82][83]. The relative contribution of these lubrication mechanisms is influenced by the normal and tangential forces, as well as relative velocities of the contacting surfaces against each other; however, recent findings suggest that fluid pressurization is the most influential mechanism [67].…”