Changes in gene expression of matrix constituents with respect to passage of ligament and tendon fibroblasts.

Trauma to the knee joint often results in injury to one or more supporting soft tissue structures, such as the medial collateral (MCL) and anterior cruciate (ACL) ligaments. Also, a portion of the patellar tendon (PT) is frequently used as a replacement graft for the ACL, resulting in a PT defect. The healing responses of these tissues are dramatically different and range from spontaneous healing to little or no healing. Studies have suggested that native cell behavior could be responsible for differences in healing potential. However, it is difficult to make comparisons as the reported results are based on different cellular passages which could have a dramatic effect on their potential to form healing tissues. Therefore, the objective of this study was to quantify the gene expression of collagen and other matrix constituents of fibroblasts from the MCL, ACL, and PT to document how they change with cell passage. We hypothesized that MCL fibroblasts would possess higher potential for matrix production through passages than ACL and PT cells because the MCL mounts a robust healing response unlike the ACL and PT. These differences in matrix expression would be dependent on passage because at earlier passages all cells would mostly be proliferating while at later passages they would tend to become senescent. Cells were isolated from the MCL, ACL, and PT of three rats and passaged a total of five times (Passage 1 to Passage 5). Using real time RT-PCR, expression of all genes of interest (Collagen Type I (ligament/tendon's main matrix constituent), Collagen Type III, Fibronectin, Metalloprotease-13 [MMP-13], and Tissue Inhibitor of Metallopreotease-1 [TIMP-1]) were quantitatively assessed. It was found that cell number for all three fibroblast types remained high from Passage 1 to Passage 5. There was a statistically significant increase in Collagen Type I of rat MCL fibroblasts throughout passage (p < 0.05). This was evident in the higher relative abundance (to GAPDH) at Passages 3 and 4 (14.5 +/- 2.2 fold and 15.3 +/- 6.9 fold, respectively) than at Passage 1 (3.3 +/- 2.6 fold) (p < 0.05). On the other hand, Collagen Type I expression for ACL and PT fibroblasts were lower than that of MCL fibroblasts and remained at 2.5 +/- 2.0 fold and 1.7 +/- 0.8 fold, respectively. Interestingly, the gene expressions of Collagen Type III, Fibronectin, MMP-13, and TIMP-1 for MCL, ACL, and PT fibroblasts were all relatively constant throughout passage and were not significantly different from one another. The findings of this study indicate that passage does affect the Collagen Type I gene expression of rat MCL fibroblasts and further show that for in vitro ligament tissue engineering efforts, MCL fibroblasts have a more robust potential for ligament remodeling and repair due to the increase in collagen gene expression.