CD44 Deficiency Improves Healing Tendon Mechanics and Increases Matrix and Cytokine Expression in a Mouse Patellar Tendon Injury Model

CD44 plays an important role in inflammation and healing. Previous studies investigated its role in inflammatory diseases and skin wounds; however, the role of CD44 in tendon healing is unknown. Therefore, we investigated the effect of CD44 in the healing of the patellar tendon in a knockout mouse model. We hypothesized that in comparison to wild-type counterparts, CD44 knockout mice would have decreased material parameters, increased organization, decreased expression of proinflammatory cytokines, and increased expression of matrix components during healing. These hypotheses were tested through an in vivo surgical model and mechanical, organizational, and gene expression analyses. Material strength and tissue organization were significantly improved in the CD44 knockout mouse. This could be attributed to increased expression of cytokines and matrix components that are also elevated in regenerative healing. Our study showed that the absence of CD44 in a mouse patellar tendon injury creates an environment that is conducive to regenerative healing through altered gene expression, resulting in superior material properties and reduced cross-sectional area. Therefore, limiting the role of CD44 may improve healing parameters in adult tendon injury. (C) 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 27:1386-1391, 2009