Adhesion strength differential of human ligament fibroblasts to collagen types I and III

Fibroblasts embedded in the amorphous healing tissue matrix of ligaments mi grate into damaged sites during the inflammatory process that precedes the formation of new connective tissue after ligament injury. Cell motility inv olved in this migration is strongly influenced by cellular adhesion to prot eins of the extracellular matrix. The adhesion mechanism of interest in thi s study is the attachment of fibroblasts from the anterior cruciate and med ial collateral ligaments to types I and III collagen, two fibrillar collage ns secreted by fibroblasts during tissue repair. Types I and III collagen c onstitute a major portion of these ligaments and are assembled by fibroblas ts into long cable-like fibrils in the extracellular space. Tn this study, a micropipette aspiration technique was used to measure the force required to separate fibroblasts of the anterior cruciate and medial collateral liga ments from substrates composed of type I or III collagen, each at a concent ration of 2 or 5 mu g/ml. Approximately 1,200 fibroblasts from the anterior cruciate ligament and 1,600 from the medial collateral ligament were used, and the adhesion force and area of these cells were determined. Fibroblast s from the anterior cruciate ligament exhibited greater adhesion force than did those from the medial collateral ligament for all concentrations of ty pes I and III collagen. In addition, the adhesiveness of fibroblasts from b oth ligaments was dependent on seeding time for all experimental conditions . To determine the adhesiveness per unit area, defined here as the adhesion strength, the adhesion force was normalized by the adhesion area. At early seeding times (15-45 minutes), fibroblasts from the anterior cruciate liga ment exhibited greater adhesion strength on surfaces coated with type-I col lagen than did those from the medial collateral ligament. However, for both collagen substrates, adhesion strength for fibroblasts from the anterior c ruciate ligament decreased with seeding time whereas that for fibroblasts f rom the medial collateral ligament remained relatively constant for all see ding periods (15-75 minutes).