PRMT5 inhibition attenuates cartilage degradation by reducing MAPK and NF-κB signaling

OBJECTIVES

A role for the type II arginine methyltransferase PRMT5 in various human diseases has been identified. In this study, the potential mechanism underlying the involvement of PRMT5 in the pathological process leading to osteoarthritis (OA) was investigated.

METHODS

PRMT5 expression in cartilage tissues from patients with OA and control individuals was assessed by immunohistochemical staining. The regulatory and functional roles of PRMT5 in the chondrocytes of patients with OA and control individuals were determined by western blotting and reverse transcription polymerase chain reaction. The effects of the PRMT5 inhibitor EPZ on interleukin-1β-induced inflammation were examined in the chondrocytes of patients with OA and in the destabilized medial meniscus (DMM) of a mouse model of OA.

RESULTS

PRMT5 was specifically upregulated in the cartilage of patients with OA. Moreover, adenovirus-mediated overexpression of PRMT5 in human chondrocytes caused cartilage degeneration. This degeneration was induced by elevated expression levels of matrix-degrading enzymes (matrix metalloproteinase-3 (MMP-3) and matrix metalloproteinase-13 (MMP-13)) in chondrocytes. The activation of the MAPK and nuclear factor κB signaling pathways was evidenced by elevated levels of p-p65, p-p38, and p-JNK. These effects were attenuated by inhibiting the expression of PRMT5. In the mouse model, EPZ inhibited PRMT5 expression, thus protecting mouse cartilage from DMM-induced OA.

CONCLUSIONS

Our results demonstrate that PRMT5 is a crucial regulator of OA pathogenesis, implying that EPZ has therapeutic value in the treatment of this cartilage-destroying disease.

Zhuangguguanjie formulation protects articular cartilage from degeneration in joint instability-induced murine knee osteoarthritis

Zhuangguguanjie formulation (ZG) can provide noticeable relief from joint pain in patients suffering from knee osteoarthritis (OA). However, the underlying mechanism has not been fully described. Male C57BL/6 mice were administered either ZG or normal saline (NS) following surgical destabilization of the medial meniscus (DMM). At weeks 4, 6 and 8 (post-surgery), knee joints were harvested and assessed with Safranin-O staining. Blood serum was collected and tested. In vitro analysis was carried out to evaluate the effects of ZG on the expression of the OA-related genes. DMM mice indicated reduced cartilage destruction and lower blood serum biomarkers of OA (COMP1 and CTX-1) following ZG treatment. Moreover, the femoral condyle and tibial plateau histological scores were significantly reduced following ZG treatment of the DMM mice. ZG could markedly downregulate the expression of OA-related genes namely, ADAMTS5, MMP3 and MMP13, while it simultaneously upregulated collagen II as demonstrated by in vitro assays. Moreover, chondrocyte apoptosis was significantly decreased following ZG treatment. These results may be caused by the up-regulation of p-AKT expression levels, since the anti-apoptotic effects of ZG can be blocked by treatment with an AKT inhibitor. ZG is capable of preventing and/or reducing the progression of OA by inhibiting chondrocyte apoptosis via the p-AKT/Caspase 3 pathway.

Mean Cartilage Attenuation Measured In Situ in an Osteoarthritis Mouse Model Using Contrast-Enhanced Micro-Computed Tomography is Indicative of Cartilage Degeneration

ObjectiveTo develop and validate an in vivo image acquisition protocol for assessment of cartilage degeneration in an osteoarthritis (OA) mouse model using contrast-enhanced micro-computed tomography (CECT).DesignThree-, four-, seven-, and 10-month-old male STR/ort OA (n = 8) and healthy control CBA/1 (n = 8) mice were imaged using synchrotron-radiation micro-computed tomography. Mean attenuation of cartilage and mean attenuation difference between cartilage and contrast agent (mean Δ attenuation), to control for flux, were calculated and correlated to previously published cartilage parameters measured in the same mice. In a second experiment, C57Bl/6 mice underwent destabilization of medial meniscus (DMM) surgery or sham surgery. At 0 (n = 8 DMM), and 4 weeks (n = 10 DMM, n = 6 sham) post-surgery, mice were imaged using CECT. Mean attenuation and Osteoarthritis Research Society International (OARSI) score of cartilage were calculated, and mean attenuation and OARSI score were correlated.ResultsMean Δ attenuation of medial cartilage was lower in STR/ort OA mice compared to healthy control CBA/1 at 3-, 4-, 7-, and 10-months of age. Medial mean Δ attenuation was positively correlated to cartilage volume and thickness and negatively correlated with surface-to-volume ratio and Collins score. The mean attenuation and OARSI score of cartilage in DMM OA mice was higher than in sham controls in the medial tibia. Mean attenuation was positively correlated with OARSI score in the medial tibia.ConclusionsAn in vivo CECT imaging method was developed and validated. Mean attenuation is sensitive to cartilage degeneration in OA mouse models when imaged against a contrast agent as a background and using in vivo compatible image acquisition parameters.