Transcriptional profiling of synovium in a porcine model of early post-traumatic osteoarthritis

Abstract

To determine the transcriptional profile of synovium during the molecular phase of post-traumatic osteoarthritis, anterior cruciate ligament transections (ACL) were performed in 36 Yucatan minipigs. Equal numbers were randomly assigned to no further treatment, ACL reconstruction or repair. Perimeniscal synovium for histopathology and RNA-sequencing was harvested at 1 and 4 weeks post-operatively and from six healthy control animals. Microscopic synovitis scores significantly worsened at 1 (p < 0.001) and 4 weeks (p = 0.003) post-surgery relative to controls, and were driven by intimal hyperplasia and increased stromal cellularity without inflammatory infiltrates. Synovitis scores were similar between no treatment, reconstruction, and repair groups (p ≥ 0.668). Relative to no treatment at 1 week, 88 and 367 genes were differentially expressed in the reconstruction and repair groups, respectively (227 and 277 at 4 weeks). Relative to controls and with the treatment groups pooled, 1,683 transcripts were concordantly differentially expressed throughout the post-surgery time-course. Affected pathways included, proteolysis_connective tissue degradation (including upregulations of protease-encoding MMP1, MMP13, and ADAMTS4), and development_cartilage development (including upregulations of ACAN, SOX9, and RUNX2), among others. Using linear regression, significant associations of post-surgery synovial expression levels of 20 genes with the articular cartilage glycosaminoglycan loss were identified. These genes were predominantly related to embryonic skeletal system development and included RUNX2. In conclusion, this study confirmed an increased synovial expression of genes that may serve as targets to prevent cartilage degradation, including MMP1, MMP13, and ADAMTS4, in knees with microscopic synovitis and cartilage proteoglycan loss. Attractive novel targets include regulators of embryonic developmental processes in synovium. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.

Keywords: ACL; RNA-sequencing; animal model; osteoarthritis; synovium.

Figure 1

The histologic response of synovium to ACL surgery. Hematoxylin and eosin stained frontal plane sections of medial meniscus, attached synovium and capsule, corresponding to medians of the microscopic sum score. Bar indicates 5 mm in overview photomicrographs. An increase in synovial tissue area, intimal thickness and stromal cellularity is apparent post-surgery.

Figure 2

The transcriptional response of synovium to surgical induction of osteoarthritis. (A) 14,173 transcripts were expressed >1 RPKM in at least one of the 7 groups defined by ACL status, time and treatment. Log2 fold-changes compared to INTACT controls are depicted as heatmap. (B) Number of differentially expressed genes by time-point and treatment. Most differentially expressed genes were detected in the comparison of post-surgery groups with intact controls, rather than between the surgical groups (each group with n=6). (C) Number of differentially expressed genes by time-point (with surgical groups pooled, 1W and 4W with n=18 each, Intact with n=6). Vast changes in gene expression were observed between 1 or 4 week post-surgery with controls and between 1 and 4 weeks post-surgery. (D) 1683 transcripts were concordantly differentially expressed in the comparison of 1W and 4W with intact controls (One disconcordant between 1 and 4 weeks). Those transcripts enriched 11 pathways (process network ontology), including terms related to cell cycle, cytoskeleton, cell adhesion, inflammation, proteolysis, development, and signal transduction.