Cellular inflammation pattern in post-traumatic osteoarthritis In-vivo evaluation of the impact of pro-inflammatory cells and their pattern of activation on phenotype-specific post-traumatic OA in mice
Final Report Abstract
Osteoarthritis (OA) is one of the most prevalent musculoskeletal diseases and affected patients suffer from pain and physical limitations. Post-traumatic OA (ptOA) occurs after a joint injury and accounts for at least 12 % of all OA and up to 25% of OA in susceptible joints such as the knee. Emerging evidence indicates a potential inflammatory component of the disease, with both T-cells and monocytes/macrophages potentially associated with the pathogenesis of OA. Thus, the purpose of this research project was to characterize the cellular inflammation pattern during the onset and progression of ptOA and to identify cellular and molecular factors driving this inflammatory immune response. In particular, we planned to evaluate the cellular activation pathways of inflammatory cells, and the local, regional and systemic pattern of inflammatory/immune cell activation associated with ptOA. Therefore, the current study was designed as an in-vivo basic research study including a total of six different murine ptOA models. ptOA was induced both surgically and non-surgically at day 0 and hereafter tissues were harvested at a total of 9 time points (day 1, day 3, week1, week2, week 4, week 6, week 8, week 10 and week 16) corresponding to early, progressive and late stages of ptOA. Immune cells were harvested and identified using a novel flow cytometry assay that allowed comprehensive identification of monocytes/macrophages and their subsets as well as T-cells and their subsets in murine primary and secondary immune tissues. In addition, qRT-PCR was performed to analyze molecular factors influencing the inflammatory response on a genomic level. Data of the current study indicated a distinct inflammatory cellular response immediately after joint injury and during the entire development of ptOA, thus, providing compelling evidence regarding a crucial contribution of a pro-inflammatory cellular response towards the pathogenesis of ptOA in addition to biomechanical factors. Furthermore, we were able to show that the inflammatory reaction contributing towards ptOA is reserved to a loco-regional (synovium and draining lymph-nodes) response rather than a systemic one. In addition, we were able to show that joint injury leads to an influx of monocyte derived progenitor cells maturing into blood originated macrophages mainly having a pro-inflammatory polarization. In contrast, synovial tissue resident macrophages, which are macrophages that populate the synovium early during development and self-sustain their numbers in a monocyte independent matter expand during the progressive and late stages of ptOA and contribute towards an anti-inflammatory polarization switch potentially promoting a resolution of the inflammatory response. Analysis of the T-cell response indicates a loco-regional inflammatory reaction between the synovium and the draining lymph nodes, where joint injury leads to an influx of pro-inflammatory T-cell subsets (Th1 and Th17 cells) rather than anti-inflammatory (Th2 and Treg cells). Based on the results of this study it seems that the synovial inflammatory response is driven by Th17 cells, whereas Th1 cells seem to drive a low-level pro-inflammatory response in the draining lymph node during pathogenesis of ptOA. Analysis of the phenotype specific inflammatory cellular response, comparing different ptOA inducing injuries, revealed distinct subtle differences between groups, whereas the main findings of the study were true for all pathologies. Interestingly, the biggest differences were caused by the surgical approach itself rather than the underlying injury resulting in ptOA. This was identified as a major limitation to existing surgical ptOA mouse models. Finally, analysis of molecular pathways of activation revealed that CD40/CD40L may be an early molecular pathway of synovial T-cell-driven macrophage activation thereby indicating that T-cells may play a pivotal role in orchestration of the distinct response in the synovium.
Publications
- Flow Cytometry Analysis of Immune Cell Subsets within the Murine Spleen, Bone Marrow, Lymph Nodes and Synovial Tissue in an Osteoarthritis Model. J Vis Exp. 2020 Apr 24;(158)
Haubruck P, Colbath AC, Liu Y, Stoner S, Shu C, Little CB
(See online at https://doi.org/10.3791/61008) - In-vivo evaluation of the impact of a Loco-regional and systemic T-cell response during the onset and development of posttraumatic osteoarthritis in mice. Osteoarthr. Cartil. 28, Suppl. 1, S84-S85
P. Haubruck P, Colbath AC, Liu Y, Stoner S, Shu C, Little CB
(See online at https://doi.org/10.1016/j.joca.2020.02.129) - Losartan alters the synovial myeloid population in a murine medial meniscal destabilization model of osteoarthritis. Osteoarthr. Cartil. 28, Suppl. 1, S116-S117
Colbath A, Haubruck P, Little CB
(See online at https://doi.org/10.1016/j.joca.2020.02.187)
