Unveiling the mechanisms of mechanical loading-induced knee osteoarthritis through transcriptomics.

Aims: To establish a novel model of mechanical loading-induced knee osteoarthritis (KOA) and explore its regulatory mechanisms through transcriptomics.

Methods: Knee joints of Sprague-Dawley (SD) rats were mechanically loaded with 13 N, 20 N and 27 N for 2 or 4 weeks to construct mechanically-induced KOA model. Immunohistochemistry (IHC), quantitative real-time polymerase chain reaction (qRT-PCR), Western blot, Safranin O/fast green staining, enzyme-linked immunosorbent assay (ELISA), micro-computed tomography (Micro-CT) and behavioral analysis were used to evaluate damage on the right knee joint. Transcriptomic analysis combined with validation experiments were performed to explore the regulatory mechanism of excessive mechanical loading on KOA development.

Results: A vertical load of 27 N resulted in calf fractures, whereas a 13 N load did not cause remarkable pathological alteration in the knee joint. Notably, applying compression at a load of 20 N for 4 weeks (w) significantly promoted the levels of pro-inflammatory factors IL-6, IL-β, NLRP3, iNOS and TNF-α in serum and joint fluids and markedly minimized the levels of anti-inflammatory factors IL-10 and TGF-β. Immunohistochemistry, qRT-PCR and Western blot analyses suggested that the 20 N load reduced the expression of anabolism markers (ACAN and COL2A1) and escalated the expression of catabolism markers (MMP13 and ADAMTS4). KEGG analysis and validation results showed that PIEZO1-Ca signaling pathway, PI3K-AKT signaling pathway and NF-κB signaling pathway were significantly activated in the 20 N-4 w group.

Conclusion: Continuous loading with 20 N for 4 weeks can induce significant OA-like damage to the cartilage of the right knee in rats, which might be induced through the PIEZO1-Ca/PI3K-AKT/NF-κB signaling pathway.