Destabilization of the medial meniscus (DMM) mouse model of OA

All procedures were approved by the First Affiliated Hospital of Sun Yat-sen University ([2013]A-110) Animal Research Committee. We procured 25 8-week-old male wild-type (WT) C57BL/6J mice from GemPharmatech, Co. (Jiangsu, China) and housed them in pathogen-free conditions for experimentation at 12 weeks of age. The mice were fed a normal diet and had access to water. At 12 weeks, the mice were operated on to induce OA as described previously [31], after being anesthetized by isoflurane inhalation (2–3% isoflurane for anesthesia induction and 1.5–2% isoflurane for anesthesia maintenance). The mice were subjected to DMM surgery of the right knees to induce OA, with the left knee sham-operated on as control. Starting at 14 weeks, all mice were randomly divided into five groups (n = 5/group) based on treatment received to the right knee: sham, DMM, MSC-Exos (exosomes secreted by MSCs), MSC-circ_0001236-Exos (exosomes secreted by circRNA_0001236-overexpressing MSCs), and MSC-circ_0001236 + miR-3677-3p mimc-Exos. Mice from the DMM, MSC-Exos, MSC-circ_0001236-Exos, and MSC-circ_0001236 + miR-3677-3p mimic-Exos groups were administered multiple intra-articular injections once a week, for 6 weeks, of 10 μL saline, MSC-Exos(500 μg/ml), MSC-circ_0001236-Exos(500 μg/ml), and MSC-circ_0001236 + miR-3677-3p mimic-Exos(500 μg/ml) with a microliter syringe (Hamilton Company, 1702) and 5-mm 30-gauge needles (Hamilton Company, 7803-05). After 4 weeks (about 23 weeks), the mice were sacrificed, and the knee joint tissue was harvested for further analysis by immunohistochemistry (IHC). The inability to rise or ambulate was considered the humane endpoint in this in vivo study; if a mouse suffered severe OA and was unable to access food or water, the mouse was euthanized.