STRUCTURE OF CHONDROCYTE UNDER TENSILE STRAIN

Abstract

Aim: The aim of this study is to visualize the structural changes of both the matrix collagen meshwork and the chondrocyte cytoskeleton of articular cartilage when it is subjected to tensile strain.

Materials and Methods: Dumbbell-shape specimens were harvested from the articular surface of the femur. Specimens were placed with the articular surface uppermost each in individual mini tension device and subjected to a graded series of tensile strains, whilst being observed with phase contrast light microscopy. Thereafter each specimen was fixed in its particular position of strain, and stained with fluorochrome conjugated primary antibodies specific for actin and vimentin and with DAPI for nuclear staining for observation by confocal laser scanning microscopy (CLSM).

Results: Phase contrast microscopy visualized the reorganization of the matrix which became aligned parallel to the direction of strain, resulting in the deformation of the chondrocyte and their nuclei into an elliptical shape. CLSM demonstrated the reorganization of the matrix and chondrocyte cytoskeleton; at no strain, the vimentin meshwork spanned the cytoplasm from plasma membrane to nuclear membrane. At 20% strain, the vimentin meshwork became aligned parallel to the direction of strain and the nucleus was deformed into elliptical shape.

Discussions: There are two possibilities to explain the structural changes in the chondrocyte under tensile strain. 1.The collagen meshwork becomes aligned parallel to the direction of tensile strain, squeezing the chondrocyte into the observed elliptical shape subsequently with the cytoskeleton reorganizing in response to it. 2.The collagen meshwork transfers the tensile strain through the plasma membrane to the vimentin meshwork which reorganizes and subsequently results in the changes in chondrocyte morphology. Further explanation is required to test the above two hypotheses.