Background: Osteoarthritis (OA) is one of the most prevalent arthritis types globally, with the knee being particularly susceptible due to its frequent and strenuous use. Urolithin B (UB) exhibits various biological properties, with meniscal repair playing an important role in preventing knee OA. This study aimed to explore the impact of UB on meniscal regeneration and OA progression.

Methods: Initially, we explored the effect of UB on meniscal cells. Utilizing the cell counting kit (CCK)-8 assay, we determined the optimum concentration of UB treatment. Enzyme-linked immunosorbent assay (ELISA) was used for detecting inflammation-related interleukin-1beta (IL-1β). Real-time reverse transcriptase-polymerase chain reaction (RT-qPCR) was used for measuring the expression of extracellular matrix (ECM)-related proteins, ECM-degrading enzymes, and genes associated with joint formation in meniscal cells. Furthermore, 5-Bromo-2′-deoxyuridine (BrdU) staining was used to evaluate the proliferation of meniscal cells. Meniscal tissues were cultured in vitro, and western blot analysis was used to detect levels of proliferation-related markers such as proliferating cell nuclear antigen (PCNA) and vascular endothelial growth factor (VEGF), as well as ECM protein collagen-1 (COL-1) and ECM degradation-related matrix metallopeptidase-13 (MMP-13). Mice were subjected to meniscus injury to establish a knee joint model of meniscus injury-induced osteoarthritis (MIOA) and to verify the effect of UB on meniscal cells in vivo. Pathological changes in knee joints were observed using hematoxylin-eosin (H&E) staining. Additionally, western blot was used to assess PCNA, VEGF, COL-1, and MMP-13 levels, while ELISA was used to detect inflammation-related tumor necrosis factor-alpha (TNF-α), IL-1β, IL-6, and interferon-gamma (IFN-γ) in mouse menisci.

Results: At concentrations up to 100 μM, UB exhibited non-toxicity and concomitantly decreased IL-1β in meniscal cells (p < 0.001). Moreover, UB increased the expression of ECM-related proteins (p < 0.001) and genes associated with joint formation (p < 0.001), while concurrently decreasing the expression of ECM-degrading enzymes (p < 0.001) in meniscal cells. UB promoted meniscal cell proliferation (p < 0.001). Additionally, UB increased PCNA, VEGF, and COL-1 while suppressing MMP-13 in menisci cultured in vitro (p < 0.001). Moreover, UB mitigated the pathological alterations observed in knee joints affected by meniscus injury. In murine models, MIOA led to decreased PCNA, VEGF, and COL-1 levels, alongside increased MMP-13, TNF-α, IL-1β, IL-6, and IFN-γ levels (p < 0.001), all of which were effectively reversed by UB treatment (p < 0.001).

Conclusion: UB effectively promotes meniscal regeneration and repair, while protecting against knee OA in mice, suggesting its potential role in clinical OA treatment.