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PLoS One. 2019 Mar 1;14(3):e0212662. doi: 10.1371/journal.pone.0212662. eCollection 2019.

Synovial fluid proteome changes in ACL injury-induced posttraumatic osteoarthritis: Proteomics analysis of porcine knee synovial fluid.

Author information

Department of Orthopaedic Surgery, Boston Children's Hospital, Harvard Medical School, Boston, MA, United States of America.
Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT, United States of America.
MS & Proteomics Resource, W.M. Keck Biotechnology Resource Laboratory, Yale University, New Haven, CT, United States of America.
Department of Orthopaedics, Warren Alpert Medical School of Brown University & Rhode Island Hospital, Providence, RI, United States of America.


Surgical transection of the anterior cruciate ligament (ACL) in the porcine model leads to posttraumatic osteoarthritis if left untreated. However, a recently developed surgical treatment, bridge-enhanced ACL repair, prevents further cartilage damage. Since the synovial fluid bathes all the intrinsic structures of knee, we reasoned that a comparative analysis of synovial fluid protein contents could help to better understand the observed chondroprotective effects of the bridge-enhanced ACL repair. We hypothesized that post-surgical changes in the synovial fluid proteome would be different in the untreated and repaired knees, and those changes would correlate with the degree of cartilage damage. Thirty adolescent Yucatan mini-pigs underwent unilateral ACL transection and were randomly assigned to either no further treatment (ACLT, n = 14) or bridge-enhanced ACL repair (BEAR, n = 16). We used an isotopically labeled high resolution LC MS/MS-based proteomics approach to analyze the protein profile of synovial fluid at 6 and 12 months after ACL transection in untreated and repaired porcine knees. A linear mixed effect model was used to compare the normalized protein abundance levels between the groups at each time point. Bivariate linear regression analyses were used to assess the correlations between the macroscopic cartilage damage (total lesion area) and normalized abundance levels of each of the identified secreted proteins. There were no significant differences in cartilage lesion area or quantitative abundance levels of the secreted proteins between the ACLT and BEAR groups at 6 months. However, by 12 months, greater cartilage damage was seen in the ACLT group compared to the BEAR group (p = 0.005). This damage was accompanied by differences in the abundance levels of secreted proteins, with higher levels of Vitamin K-dependent protein C (p = 0.001), and lower levels of Apolipoprotein A4 (p = 0.021) and Cartilage intermediate layer protein 1 (p = 0.049) in the ACLT group compared to the BEAR group. There were also group differences in the secreted proteins that significantly changed in abundance between 6 and 12 months in ACLT and BEAR knees. Increased concentration of Ig lambda-1 chain C regions and decreased concentration of Hemopexin, Clusterin, Coagulation factor 12 and Cartilage intermediate layer protein 1 were associated with greater cartilage lesion area. In general, ACLT knees had higher concentrations of pro-inflammatory proteins and lower concentrations of anti-inflammatory proteins than BEAR group. In addition, the ACLT group had a lower and declining synovial concentrations of CILP, in contrast to a consistently high abundance of CILP in repaired knees. These differences suggest that the knees treated with bridge-enhanced ACL repair may be maintaining an environment that is more protective of the extracellular matrix, a function which is not seen in the ACLT knees.

Conflict of interest statement

The authors have no competing interests directly related to this study. However, it should be noted that Dr. Murray holds several patents related to the BEAR surgical procedure, and that Drs. Murray and Fleming recently founded a company (Miach Orthopaedics Inc) to translate the BEAR surgical procedure to clinical use. This does not alter our adherence to PLOS ONE policies on sharing data and materials. Patents: - Biologic replacement for fibrin clot (EP US WO Application US20040059416A1 & US WO Application US20020123805A1) - Device for mixing and delivering fluids for tissue repair (CA EP JP US WO Grant US8308681B2) - Methods and procedures for ligament repair (CA EP JP US WO Application WO2007087353A2) - Activation and delivery devices for therapeutic compositions(US Application US20120116300A1) - Methods and collagen products for tissue repair (US EP JP CA WO Application WO2008060361A2) - Biologic replacement for fibrin clot for intra-articular use (WO Application WO2000078370A1 & EP CA Application CA2377595A1) - Indirect method of articular tissue repair (CA WO Application CA3024196A1)

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