Decrease in fibronectin occurs coincident with the increased expression of its integrin receptor alpha5beta1 in stress-deprived ligaments.

Abstract

Stress deprivation secondary to immobilization leads to atrophic changes in periarticular soft tissues. The changes in ligaments include a disorganization of collagen and cellular ultrastructure with varied biochemical alterations resulting in a functionally weaker tissue. This study tests the hypothesis that alterations in fibronectin (Fn) and the expression of its integrin receptor alpha5beta1 in ligament fibroblasts accompany the extracellular matrix remodeling which occurs in stress-deprived knee ligaments. The left knees of eighteen New Zealand white rabbits were surgically immobilized in acute flexion. Fibroblasts within three nine week and three twelve week stress-deprived anterior cruciate ligaments (ACLs) and medial collateral ligaments (MCLs) demonstrated markedly increased immunostaining for the beta1 and alpha5 integrin subunits, as compared to fibroblasts in the contralateral unoperated control ligaments. The effects of stress deprivation on the concentration of Fn was measured by competitive ELISA on the remaining twelve rabbits. Decreases in Fn of 54.0 percent and 63.7 percent occurred in the ACL after nine and twelve weeks of stress deprivation when compared to contralateral controls. The MCL had less of a decrease, losing 37.7 percent and 41.7 percent at nine and twelve weeks, respectively. These results suggest an important role for the Fn-specific integrin receptor alpha5beta1 in remodeling stress-deprived periarticular ligamentous tissue, and the importance of maintaining normal stresses on periarticular ligaments to prevent the degradation of extracellular matrix components such as Fn.