2.10. Destabilization of the medial meniscus (DMM)‐induced experimental osteoarthritis (OA) model

All laboratory procedures related to animal use abided by the provisions of the National Institutes of Health (NIH) Guidelines for the Care and Use of Experimental Animals and were approved by the Animal Care and Use Committee of Zhejiang University (No. 12951). All mice were housed in specific pathogen‐free environment of 22‐24°C and 50%‐60% humidity with 12 hour light/dark cycle. Mice were given free access to standard rodent chow and water ad libitum. The surgical destabilization of the medial meniscus (DMM) closely mimics the clinical manifestations of meniscal injury and has become an important model tool for the study of OA. Thus, the DMM‐induced OA murine model was established to explore the potential therapeutic effect of SO on the progression of OA. A total of seventy‐two 8‐week‐old C57BL/6 mice, 36 females and 36 males, were acquired from the Shanghai Laboratory Animals Centre (SLAC) and raised to the age of three months. Mice were then randomly assigned to one of six groups according to sex (n = 6 mice each), including two groups of Sham‐operated (intragastric administration of PBS only), two groups of DMM surgery and two groups of DMM + SO treatment (intragastric administration of 10 mg/kg SO). For DMM surgery, mice were anaesthetized with chloral hydrate and then subjected to surgical transection of the medial meniscotibial ligament of the right knee as previous described. 22 Sham mice received the same surgical procedure without the transection of the medial meniscotibial ligament. Two days post‐surgery, mice were intragastrically administered with SO (treatment groups) or equivalent volume of PBS (Sham and DMM groups only) every other day for 4 or 8 weeks. No adverse reactions or animal fatalaties were recorded during the treatment period, and all mice exhibited normal behavioural activity. Mice were killed at the respective endpoints and the knee joints were excised, cleaned of soft tissues, fixed in 4% PFA, and then processed for micro‐computed tomography (micro‐CT) and histological assessments.