Hypotonic challenge modulates cell volumes differently in the superficial zone of intact articular cartilage and cartilage explant

Abstract

The objective of this study was to evaluate the effect of sample preparation on the biomechanical behaviour of chondrocytes. We compared the volumetric and dimensional changes of chondrocytes in the superficial zone (SZ) of intact articular cartilage and cartilage explant before and after a hypotonic challenge. Calcein-AM labelled SZ chondrocytes were imaged with confocal laser scanning microscopy through intact cartilage surfaces and through cut surfaces of cartilage explants. In order to clarify the effect of tissue composition on cell volume changes, Fourier Transform Infrared microspectroscopy was used for estimating the proteoglycan and collagen contents of the samples. In the isotonic medium (300 mOsm), there was a significant difference (p < 0.05) in the SZ cell volumes and aspect ratios between intact cartilage samples and cartilage explants. Changes in cell volumes at both short-term (2 min) and long-term (2 h) time points after the hypotonic challenge (180 mOsm) were significantly different (p < 0.05) between the groups. Further, proteoglycan content was found to correlate significantly (r(2) = 0.63, p < 0.05) with the cell volume changes in cartilage samples with intact surfaces. Collagen content did not correlate with cell volume changes. The results suggest that the biomechanical behaviour of chondrocytes following osmotic challenge is different in intact cartilage and in cartilage explant. This indicates that the mechanobiological responses of cartilage and cell signalling may be significantly dependent on the integrity of the mechanical environment of chondrocytes.

Structural and Compositional Changes in Peri- and Extracellular Matrix of Osteoarthritic Cartilage Modulate Chondrocyte Morphology

“…Controlled enzymatic digestions of cartilage could be used to study specifically the effect of collagen or PGs on cell shape changes. 52 This would minimize confounding factors associated with the degeneration process, such as the uncertainty related to the possible lack of the superficial zone in advanced OA.…”

Vibrational spectroscopy of articular cartilage

“…Assignments of NIR (80,84) and FTIR (19,39,50) proteoglycans than the native cartilage (20) and focal degenerative lesions in human osteoarthritic AC contained less proteoglycans than the surrounding healthy tissue (24). The univariate methods are easy to implement, and, therefore, they have been applied in many studies (25)(26)(27)(28)(29)(30)(31)(32). Collagen and proteoglycan concentration and collagen integrity maps produced using the univariate parameters in human tibial AC are shown in Figure 2.…”

Chondrocytic cells express the taurine transporter on their plasma membrane and regulate its expression under anisotonic conditions

“…Taurine transporter promoter activity in dynamically stretched HCS-2/8 cells Osmotic challenges are known to evoke changes in chondrocyte volumes, which create stretching forces in the cell membrane (Turunen et al 2012). Therefore, we tested whether cellular stretching of HCS-2/8 cells would affect taurine transporter promoter activity.…”

“…During a hypertonic challenge, cells actively accumulate small biochemically inert molecules, osmolytes, into the cytosol, and release them to the interstitial matrix under hypotonic conditions. This is a common mechanism through which cells resist volume changes, such as those occurring during osmotic stress (Turunen et al 2012). Taurine is a ubiquitous osmolyte that is involved in cell volume regulation (Hoffmann et al 2009;Lang 2007), and the taurine transport and release mechanism have been one of the most widely studied cellular volume regulation systems (Lambert 2004).…”