Chondrocyte deformation within compressed agarose constructs at the cellular and sub-cellular levels

Mechanotransduction events in articular cartilage may be resolved into extr acellular components followed by intracellular signalling events, which fin ally lead to altered cell response. Cell deformation is one of the former c omponents, which has been examined using a model involving bovine chondrocy tes seeded in agarose constructs. Viable fluorescent labels and confocal la ser scanning microscopy were used to examine cellular and sub-cellular morp hology. It was observed that cell size increased up to day 6 in culture, as sociated with an increase in the contents of proteoglycan and collagen. In addition, the organisation of the cytoskeleton components, described using a simple scoring scale, revealed temporal changes for actin fibres, microtu bules and vimentin intermediate filaments. The constructs on day 1 were als o subjected to unconfined compressive strains. A series of confocal scans t hrough the centre of individual cells revealed a change from a spherical to an elliptical morphology. This was demonstrated by a change in diameter ra tio, from a mean value of 1.00 at 0% strain to 0.60 at 25% strain. Using si mple equations, the volume and surface areas were also estimated from the s cans. Although the former revealed little change with increasing construct strain, surface area appeared to increase significantly. However further ex amination, using transmission electron microscopy to reveal fine ultrastruc tural detail at the cell periphery, suggest that this increase may be due t o an unravelling of folds at the cell membrane. Cell deformation was associ ated with a decrease in the nuclear diameter, in the direction of the appli ed strain. The resulting nuclear strain in one direction increased in const ructs compressed at later time points, although its values at all three ass essment times were less than the corresponding values for cell strain. It i s suggested that the nuclear behaviour may be a direct result of temporal c hanges observed in the organisation of the cytoskeleton. The study demonstr ated that the chondrocyte-agarose model provides a useful system for the ex amination of compression events at both cellular and sub-cellular levels. ( C) 1999 Elsevier Science Ltd. All rights reserved.