Cyclic tensile stress exerts a protective effect on intervertebral disc cells.

Abstract

To examine the mechanisms behind the beneficial effects of motion-based therapies, the hypothesis that physiologic levels of tensile stress have a beneficial effect on annulus fibrosus cells was tested. To examine the roles of mechanical forces and inflammation in the intervertebral disc, changes in gene expression in response to inflammatory stimulus (IL-1 beta) and tensile stress (6% stress at 0.05 Hz) were examined in fibrochondrocytes isolated from the annulus fibrosus of Sprague-Dawley rats. Cells exposed to an inflammatory stimulus demonstrated an increase in catabolic gene expression, which decreased approximately 50% after exposure to both inflammatory stimulus and tensile stress. After exposure of cells to tensile stress alone, only matrix metalloprotease-13 showed a 50% decrease in expression. Collagen II showed a modest decrease in expression in response to tensile stress in the inflammatory environment. The expression of collagen I and aggrecan did not show a significant change under any of the conditions tested. In this in vitro model, our data demonstrate that moderate levels of tensile stress act as a protective signal by decreasing the expression of catabolic mediators under conditions of inflammation. These data suggest that motion-based therapies that create tensile stress on the annulus may exert their beneficial effects through antiinflammatory actions.