Objective To investigate the mechanism of tannic acid in promoting mitochondrial autophagy in chondrocytes and improving knee osteoarthritis (KOA) in mice based on PINK1/Parkin signaling pathway. Methods A mouse KOA model was established via destabilization of medial meniscus surgery. Sham group, model group and tannic acid low-, high-dose (25, 50 mg/kg) groups were set up, drugs were given for intervention for eight weeks. Joint cartilage pathology was assessed by imaging, safranin O-fast green staining and toluidine blue staining. Immunohistochemistry was used to detect the expressions of collagen II (Col-II), matrix metalloproteinase 13 (MMP13), interleukin-1β (IL-1β), PINK1, Parkin, p62 and microtubule-associated protein light chain 3B (LC3B) in cartilage tissue. ATDC5 mouse chondrocytes were stimulated with IL-1β and then treated with tannic acid. Cell viability was measured by CCK-8 assay. Western blotting and qRT-PCR were used to detect the protein and mRNA expressions of Col-II, MMP13 and IL-1β. Western blotting was used to detect the expressions of mitophagy-related proteins PINK1, Parkin, p62 and LC3-II/I. Changes in reactive oxygen species (ROS) and mitochondrial membrane potential were detected by immunofluorescence. Mitochondrial autophagy level was observed by transmission electron microscopy. And reverse mechanism validation was performed using the mitochondrial autophagy inhibitor Mdivi-1. Results Compared with sham group, the cartilage of mice in model group was severely worn, OARSI score was significantly increased (P < 0.01), the protein expression levels of Col-II, PINK1, Parkin and LC3B in cartilage tissue were significantly reduced (P < 0.01), while the protein expression levels of IL-1β, MMP13 and p62 were significantly increased (P < 0.01). Compared with model group, the cartilage morphology of mice in tannic acid group was improved, OARSI score was significantly reduced (P < 0.05), the protein expression levels of Col-II, PINK1, Parkin and LC3B in cartilage tissue were significantly increased (P < 0.01), while the protein expression levels of IL-1β, MMP13 and p62 were significantly decreased (P < 0.01). The cell experiment results showed that IL-1β-induced chondrocyte viability was significantly reduced (P < 0.01), IL-1β, MMP13 protein and mRNA expression levels were significantly increased (P < 0.01), Col-II protein and mRNA expression levels were significantly reduced (P < 0.01), LC3-II/I, PINK1, Parkin protein expression levels were significantly reduced (P < 0.05, 0.01), p62 protein expression level was significantly increased (P < 0.05), intracellular ROS accumulation was increased (P < 0.01), mitochondrial membrane potential was decreased (P < 0.01), and autophagosome was decreased. Compared with model group, cell viability in tannic acid group was significantly increased (P < 0.05, 0.01), ROS accumulation significantly was decreased (P < 0.01), mitochondrial membrane potential was recovered (P < 0.05), IL-1β, MMP13 protein and mRNA expression levels were significantly decreased (P < 0.05, 0.01), Col-II protein and mRNA expression levels were significantly increased (P < 0.05, 0.01), p62 protein expression level was significantly decreased (P < 0.01), LC3-II/I, PINK1 and Parkin protein expression levels were significantly increased (P < 0.01). After the combined use of mitochondrial autophagy inhibitor Mdivi-1, the therapeutic effect of tannic acid on chondrocytes was reversed (P < 0.05, 0.01). Conclusion Tannic acid alleviates articular cartilage damage and delays the progression of KOA by promoting chondrocyte mitophagy through PINK1/Parkin signaling pathway.

tannic acid  /  knee osteoarthritis  /  chondrocyte  /  mitophagy  /  PINK1/Parkin pathway