Influences of Tumor Necrosis Factor-α on Lysyl Oxidases and Matrix Metalloproteinases of Injured Anterior Cruciate Ligament and Medial Collateral Ligament Fibroblasts.

The anterior cruciate ligament (ACL) fails to heal after injury, even after a primary surgical attempt. In contrast, the medial collateral ligament (MCL) can heal relatively well and restore the full joint function. The difference in intrinsic properties of these ligament cells can be due to their different responses to their local factors. TNF-α is considered to be an important chemical mediator in the wound healing of the ligaments. However, TNF-α-induced expression of lysyl oxidases (LOXs) and matrix metalloproteinases (MMPs) after injury is poorly understood. In this study, we use equi-biaxial stretch chamber to realize 12% stretch, which could mimic the injury to the ACL and MCL fibroblasts in vitro, and aim to determine the intrinsic differences between injured ACL and MCL by characterizing the differential expressions of LOXs and MMPs in response to TNF-α. The methods included Semiquantitative PCR, quantitative real-time PCR, Western blot, and zymography. We found that the mRNAs of LOXs had temporal increases in injured ACL and MCL. Moreover, the increases were higher in injured MCL than those in injured ACL (up to 1.77 ± 0.13-fold in LOX, 1.73 ± 0.21-fold in LOXL-1, 2.23 ± 0.27-fold in LOXL-2, 1.95 ± 0.11-fold in LOXL-3, 1.97 ± 0.28-fold in LOXL-4). On the other hand, the expressions of MMPs in injured ACL were much more prominent than those in injured MCL fibroblasts (up to 2.63 ± 0.20-fold in MMP-1, 3.73 ± 0.18-fold MMP-2, 1.58 ± 0.11-fold MMP-3, 4.23 ± 0.31-fold MMP-12). Similar results were observed at the protein level. The differential expression of LOXs and MMPs between the injured ACL and MCL fibroblasts in this study may help explain the healing abilities of the two different ligaments.