The combined regulation of estrogen and cyclic tension on fibroblast biosynthesis derived from anterior cruciate ligament Chun-Yi Lee a,b , Xuhui Liu b , Carolyn L. Smith c , Xiaoliu Zhang d , Horng-Chaung Hsu a , Der-Yean Wang a , Zong-Ping Luo b, * a Department of Orthopaedic Surgery, China Medical University Hospital, Taichung, Taiwan b Department of Orthopedic Surgery, Baylor College of Medicine, 6550 Fannin, Suite 451, Houston, TX 77030, USA c Department of Cell Biology, Baylor College of Medicine, Houston, TX, USA d Department of Pediatrics—Hematology and Oncology, Baylor College of Medicine, Houston, TX, USA Received 27 November 2003; received in revised form 21 July 2004; accepted 21 July 2004 Abstract 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. D 2004 Elsevier B.V./International Society of Matrix Biology. All rights reserved. Keywords: Anterior cruciate ligament; Estrogen; Cyclic tensile stretch; Collagen 1. Introduction The anterior cruciate ligament (ACL) is the primary ligament in the knee to resist anterior translation and tibial rotation, and it is the foremost vulnerable ligament in sports-related injuries (Ferretti et al., 1992; Hutchinson and Ireland, 1995; Lindenfeld et al., 1994). Female athletes sustain ACL injuries up to eight times more frequently than males (Gray et al., 1985; Hutchinson and Ireland, 1995; Zelisko et al., 1982). Hormones have been considered a major factor attributing to this injury (Charlton et al., 2001; Deie et al., 2002; Wojtys et al., 1998, 2002). As the ligament is critical in maintaining joint stability, mechanical force may also interact with estrogen to regulate ligament function. The purpose of this study was to investigate the gene expression of major extracellular matrix component molecules—collagen type I, type III, and biglycan—of ACL fibroblasts under combined exposure to mechanical loading and various levels of estrogen. This investigation also includes the identification of the estrogen receptors in primary cultured porcine ACL fibroblasts at the mRNA level. The hypotheses were (1) estrogen significantly affects the gene expression of these three molecules, which are dose- dependent, and (2) the effects of estrogen treatment are regulated by mechanical loading. 0945-053X/$ - see front matter D 2004 Elsevier B.V./International Society of Matrix Biology. All rights reserved. doi:10.1016/j.matbio.2004.07.004 * Corresponding author. Tel: +1 713 986 5522; fax: +1 713 986 5521. E-mail address: luo@bcm.tmc.edu (Z.-P. Luo). Matrix Biology 23 (2004) 323 – 329 www.elsevier.com/locate/matbio