Chondrocyte-extracellular matrix interactions during osmotic swelling

摘要

Cartilage deformation during joint loading results in the exudation of interstitial fluid from the tissue and changes to the fixed charge density (FCD). By the Donnan osmotic effect, FCD changes lead to alterations in the chondrocyte osmotic environment, which can affect cell function. To assess the direct effect of osmotic loading on cartilage biosynthetic activity, researchers have subjected cartilage explants to osmotic loading in culture. A better understanding of the mechanisms which mediate this response may help to elucidate how chondrocytes maintain the structure-function of cartilage under normal or pathologic (e.g., osteoarthritis) conditions. Cartilage swells when placed in a hypotonic medium and shrinks in a hypertonic medium. Performing such explant (osmotic) loading studies, Urban et al. (1993) have reported a decrease of proteoglycan (PG) synthesis in cartilage explants placed in hypertonic culture conditions. To better understand the mechano-electrochemical (MEC) events within the tissue that govern cartilage biosynthetic behavior to osmotic loading, the role of extracellular matrix (ECM) and chondrocyte properties (e.g., elastic modulus, FCD etc.) must be understood. Obviously, this MEC environment is dictated by the relative properties of the cell and ECM. Thus, the objective of this study is to explore how properties of the ECM and chondrocytes might influence the MEC environment when a cartilage explant is subjected to osmotic loading. In this analysis, we will focus particularly on the transient MEC events in the tissue (ECM and cell) which accompany initial application of the osmotic loading.