TGF-beta1 induces the different expressions of lysyl oxidases and matrix metalloproteinases in anterior cruciate ligament and medial collateral ligament fibroblasts after mechanical injury

The anterior cruciate ligament (ACL) is known to have a poor self-healing ability. In contrast, the medial collateral ligament (MCL) can heal relatively well and restore the joint function. Transforming growth factor-beta1 (TGF-β1) is considered to be an important chemical mediator in the wound healing of the ligaments. While the role of TGF-β1-induced expressions of the lysyl oxidases (LOXs) and matrix metalloproteinases (MMPs), which respectively facilitate the extracellular matrix (ECM) repair and degradation, is poorly understood. In this study, we used equibiaxial stretch chamber to mimic mechanical injury of ACL and MCL fibroblasts, and aimed to determine the intrinsic differences between ACL and MCL by characterizing the differential expressions of LOXs and MMPs in response to TGF-β1 after mechanical injury. By using semi-quantitative PCR, quantitative real-time PCR, western blot and zymography, we found TGF-β1 induced injured MCL to express more LOXs than injured ACL (up to 1.85-fold in LOX, 2.21-fold in LOXL-1, 1.71-fold in LOXL-2, 2.52-fold in LOXL-3 and 3.32-fold in LOXL-4). Meanwhile, TGF-β1 induced injured ACL to express more MMPs than injured MCL fibroblasts (up to 2.33-fold in MMP-1, 2.45-fold in MMP-2, 1.89-fold in MMP-3 and 1.50-fold in MMP-12). The further protein results were coincident with the gene expressions above. The different expressions of LOXs and MMPs inferred the intrinsic differences between ACL and MCL, and the intrinsic differences could help to explain their differential healing abilities.