MAPK inhibitors protect against early‑stage osteoarthritis by activating autophagy.

Osteoarthritis (OA) is a chronic, age‑related osteoarthropathy that causes a considerable decline in quality of life, as well as economic losses due to its high incidence and poor prognosis. Mitogen‑activated protein kinases (MAPKs) regulate multiple cellular processes, including proliferation, differentiation and apoptosis, in certain diseases, such as cancer, diabetes and Alzheimer's disease. The present study aimed to investigate the regulatory role of the MAPK signaling pathway in early‑stage OA. A rabbit model of early‑stage OA was induced by treatment with the enzyme papain. U0126 [an extracellular signal‑regulated kinase (ERK) inhibitor], SP600125 [a Jun NH2‑terminal kinase (JNK) inhibitor] and SB203580 (a p38 inhibitor) were administered to the rabbits via intra‑articular injection. The severity of OA was assessed by histological examination using H&E, toluidine blue and safranin‑O/fast green staining, as well by analyzing the glycosaminoglycan (GAG) content and determining the OA Research Society International (OARSI) score. Western blotting was used to detect the protein expression levels of matrix metalloproteinase‑3 (MMP3), ERK, phosphorylated (p)‑ERK, p38, p‑p38, JNK, p‑JNK, Beclin1, UNC‑51‑like kinase 1 (ULK1) and microtubule‑associated protein 1 light chain 3 (LC3)II/I. U0126, SP600125 or SB203580 treatment significantly decreased the OARSI scores and significantly increased the GAG levels in the cartilaginous tissues of OA model rabbits. These results indicated that the MAPK inhibitors reduced the severity of OA‑induced injury at the early stage. Western blotting results demonstrated that MAPK inhibition significantly decreased the protein expression levels of MMP3 in OA cartilage. The protective effect of MAPK inhibitors in OA was mediated via the activation of autophagy, as demonstrated by the increased protein expression levels of LC3II/I, ULK1 and Beclin1. Overall, the data indicated that MAPK inhibitors may exert a protective effect against OA by restoring compromised autophagy. Furthermore, the present study suggested that MAPK inhibitors may represent a potential pharmacological strategy for treating OA in the future.