Numerous studies have examined wound healing and tissue repair after a complete tissue rupture and reported provisional matrix and scar tissue formation in the injury gap. The initial phases of the repair are largely mediated by the coagulation response and a principally extrinsic inflammatory response followed by type III collagen deposition to form scar tissue that may be later remodeled. In this study, we examine subfailure (Grade II sprain) damage to collagenous matrices in which no gross tissue gap is present and a localized concentration of provisional matrix or scar tissue does not form. This results in extracellular matrix remodeling that relies heavily upon type I collagen, and associated proteoglycans, and less heavily on type III scar tissue collagen. For instance, following subfailure tissue damage, collagen I and III expression was suppressed after 1 day, but by day 7 expression of both genes was significantly increased over controls, with collagen I expression significantly larger than type III expression. Concurrent with increased collagen expression were significantly increased expression of the collagen fibrillogenesis supporting proteoglycans fibromodulin, lumican, decorin, the large aggregating proteoglycan versican, and proteases cathepsin K and L. Interestingly, this remodeling process appears intrinsic with little or no inflammation response as damaged tissues show no changes in macrophage or neutrophils levels following injury and expression of the inflammatory markers, tumor necrosis factor-α and tartrate-resistant acid phosphatase were unchanged. Hence, since inflammation plays a large role in wound healing by inducing cell migration and proliferation, and controlling extracellular matrix scar formation, its absence leaves fibroblasts to principally direct tissue remodeling. Therefore, following a Grade II subfailure injury to the collagen matrix, we conclude that tissue remodeling is fibroblast-mediated and occurs without scar tissue formation, but instead with type I collagen fibrillogenesis to repair the tissue. As such, this system provides unique insight into acute tissue damage and offers a potentially powerful model to examine fibroblast behavior.
Bibliographical noteFunding Information:
This work was funded through grants from N.A.S.A. (NAG9-1152), the N.S.F. (CMS9907977), and a N.I.H. Predoctoral Training Grant (#T32 GM07215) in Molecular Biosciences (AAO). The authors thank Dr. David Hart and Carol Reno for assistance with obtaining sample preparation equipment for RNA extraction, Ron McCabe and Anthony Escarcega for technical assistance with laboratory equipment, the Materials Science Center for access to the scanning electron microscope, and Phil Oshel and the Biological and Biomaterial Preparation, Imaging, and Characterization Laboratory (BBPIC) for technical assistance with electron microscopy specimen preparation. Appendix A
- Medial collateral ligament
- Real-time quantitative polymerase chain reaction (real-time QPCR)
- Scar tissue formation
- Subfailure damage