Elucidating the role of PAR2 and gender in a novel model of post-traumatic osteoarthritis
Creators: name: McCulloch, Kendal
Publisher: name: Zenodo
Year: 2024

description: Background: Post-traumatic osteoarthritis (PTOA) is associated with articular cartilage damage and represents a major clinical challenge due to the poor regenerative capability of cartilage. This study presents the development of a novel and robust dual injury murine model of PTOA, which combines destabilisation of the medial meniscus (DMM) and cartilage scratch. This model results in accelerated OA-like symptoms including enhanced osteophyogenesis. Prior studies in the DMM model have demonstrated that loss of proteinase-activated receptor 2 (PAR2) in mice results in significant protection from early OA-like symptoms. For many years it has been recognised that there are significant sex-specific differences in the incidence, prevalence and clinical manifestation of osteoarthritis. Females manifest OA differently from males, with certain areas of the knee being disproportionally affected. However, the reason for, and also mechanisms, contributing to the differences in presentation and progression of OA between sexes have not been extensively investigated. Methods: OA was induced in male and female C57BL/6 wild-type (WT) mice, as well as male PAR2 and PAR2 Col2 KO mice, via (a) DMM, (b) microblade scratches of articular cartilage (CS) or (c) combined DMM and cartilage scratch (DCS). Mice were culled 7, 14 and 28 days post-surgery.Osteophytogenesis and bone changes were monitored using microcomputed tomography, with cartilage damage and synovitis assessed histologically. Dynamic weight bearing was assessed as an indirect measurement of pain at day 14.Results: Osteophytogenesis analysis via microCT revealed that osteophytes were present in all groups at days 7 and 14 post-surgery. However, in DCS, osteophytes were visually larger and more numerous when compared with DMM and CS. Histological assessment of cartilage at day 14 and 28, revealed significantly greater damage in DCS compared with DMM and CS. Furthermore, a significant increase in synovitis was observed in DCS. Finally, at day 14 osteophyte numbers correlated with changes in dynamic weight bearing.Quantification of osteophytes revealed that PAR2-/- mice had significantly smaller osteophytes (p=0.006) with less mineralised bone (p=0.003). Moreover, analysis of metaphyseal trabecular bone on the operated leg showed a significant decrease in % bone volume/tissue volume (BV/TV) (p=0.025). Assessment of pain-related behaviour, using dynamic weight bearing at day 14, demonstrated that PAR2-/- mice exert less load on their front paws.Although females show an increase in both osteophyte size and mineralisation (often related with increased pain) they do not display altered biomechanical loading indicative of OA-like pain as observed in males. Positioning of osteophyte formation is observed to differ between males and females in the DCS model. Male mice present more extensive and severe levels of both subchondral and trabecular osteosclerosis 14 days post-surgery.Conclusion: Joint destabilisation when combined with simultaneous cartilage injury accelerates joint deterioration, as seen in PTOA. Thus, DCS provides a novel and robust model for investigating multiple pathological hallmarks, including osteophytogenesis, cartilage damage, synovitis and OArelated pain. PAR2 plays a role in accelerated OA-like symptoms (i.e., osteophyte formation) in a dual injury model of OA. Furthermore, the loss of PAR2 decreases pain behaviour suggesting that PAR2 is involved in pain sensing. Taken together, these results support the future exploration of PAR2 as a therapeutic target for PTOA. This study further established that sex-differences are present in OA-pathogenesis. The synergistic effects of dual cartilage injury and joint destabilisation observed in male mice were not observed in females to the same extent. Improving our understanding of the mechanisms underlying sex differences in the pathophysiology of OA is instrumental in the development of effective treatments, with the potential of sex specific strategies and therapeutics.