The combined regulation of estrogen and cyclic tension on fibroblast biosynthesis derived from anterior cruciate ligament.

Female athletes are two to eight times more likely to suffer a knee or ankle ligament injury than male athletes, and sex hormones have been considered to play an important role in the injury. Because ligaments are always under mechanical loading during sports, mechanical force is also a critical factor in ligament injuries. In this study, the effects of estrogen and mechanical loading on the gene expression of three major components of ligament--collagen type I, type III, and biglycan--in primary cultured porcine anterior cruciate ligament (ACL) fibroblasts were investigated individually and collectively using reverse transcript-polymerase chain reaction (RT-PCR). The results revealed that cyclic tensile loading alone increased the messenger RNA expression of collagen I but did not affect that of collagen III and biglycan, and estrogen alone increased the gene expression of collagen I and III but not of biglycan. However, combined administration of estrogen and cyclic loading inhibited the mRNA expression of all the three genes. These results suggested that the inhibition of the gene expression of major extracellular matrix component molecules caused by the combined effects of estrogen and mechanical loading, unique to females, might be responsible for the increased incidence of ligaments injury in female athletes.