Compressive compared with tensile loading of medial collateral ligament scar in vitro uniquely influences mRNA levels for aggrecan, collagen type II,and collagenase

To test the hypothesis that loading conditions can be used to engineer earl y ligament star behaviors, we used an in vitro system to examine the effect that cyclic hydrostatic compression and cyclic tension applied to 6-week r abbit medial collateral ligament scars had on mRNA levels for matrix molecu les, collagenase, and the proto-oncogenes c-fos and c-jun. Our specific hyp othesis was that tensile stress would promote more normal mRNA expression i n ligament whereas compression mould lead to higher levels of mRNA for cart ilage-like molecules. Femur (injured medial collateral ligament)-tibia comp lexes were subjected to a hydrostatic pressure of 1 MPa or a tensile stress of 1 MPa of 0.5 Hz for 1 minute followed by 14 minutes of rest. On the bas is of a preliminary optimization experiment, this 15-minute testing cycle w as repeated for 4 hours Semiquantitative reverse transcription-polymerase c hain reaction analysis was performed for mechanically treated medial collat eral ligament scars with use of rabbit specific primer sets for types I, II , and III collagen, decorin, biglycan, fibromodulin, versican, aggrecan, co llagenase, c-fos, c-jun, and a housekeeping gene, glyceraldehyde-3-phosphat e dehydrogenase. Cyclic hydrostatic compression resulted in a statistically significant increase in mRNA levels of type-II collagen (171% of nonloaded values) and aggrecan (313% of nonloaded values) but statistically signific ant decreases in collagenase mRNA levels (35% of nonloaded values). Cyclic tension also resulted in a statistically significant decrease in collagenas e mRNA levels (66% of nonloaded values) and an increase in aggrecan mRNA le vels (458% of nonloaded values) but no significant change in the mRNA level s for the other molecules. The results show that it is possible to alter mR NA levels for a subset of genes in scar tissue by supplying unique mechanic al stimuli in vitro and thus that further investigation of scar engineering for potential reimplantation appears feasible.