Abusara, ZiadKrawetz, Roman J.Steele, Bridgett L.DuVall, Michael M.Schmidt, Tannin A.Herzog, Walter2018-09-262018-09-262013-04-26Abusara, Z., Krawetz, R., Steele, B., DuVall, M., Schmidt, T., & Herzog, W. (2013). Muscular loading of joints triggers cellular secretion of PRG4 into the joint fluid. Journal of Biomechanics, 46(7), 1225–1230. https://doi.org/10.1016/j.jbiomech.2013.02.0271873-2380http://hdl.handle.net/1880/108060https://doi.org/10.11575/PRISM/43915We developed a novel testing system that allows quantification of joint loading and permits analysis of changes in total protein and PRG4 contents in joint fluid of intact knees in live mice. A sequence of 15 repeat, isometric muscular contractions of "low" intensity (less than 50% of the maximal isometric muscular force), and "high" intensity (greater than 55% of maximal) were applied repeatedly (up to five times with a 15 min rest between contractions) to the mouse knee. Increases in knee joint loading were accompanied with significant increases in total protein (p<0.0001) and PRG4 concentrations in the synovial fluid. Total protein and PRG4 concentrations decreased with repeated "high" intensity loading. However, the addition of cell secretion inhibitors to the knee prior to muscular loading resulted in PRG4 levels that remained below the detection limit for all loading conditions. These results suggest that changes in synovial fluid proteins and PRG4 concentrations upon joint loading are mediated by cells within the joint, and that these changes may be used as quantitative indicators for the intensity and duration of acute joint loading, and might serve as a powerful clinical tool to assess the effectiveness of rehabilitation and prevention exercise programs.enUnless otherwise indicated, this material is protected by copyright and has been made available with authorization from the copyright owner. You may use this material in any way that is permitted by the Copyright Act or through licensing that has been assigned to the document. For uses that are not allowable under copyright legislation or licensing, you are required to seek permission.musclemuscular loadingProteoglycan 4 (PRG4)cartilagesynovial fluidosteoarthritis (OA)journal articlehttp://dx.doi.org/10.1016/j.jbiomech.2013.02.027