Bone Mesenchymal Stromal Cell-Derived Extracellular Vesicles Protect Articular Cartilage Through Regulating tRF-Gln-TTG-019/UBL3.

The tRNA-derived fragments (tRFs) are newly discovered noncoding RNAs enriched in extracellular vesicles (EVs). However, the effects of tRFs as biomarkers have not been investigated in cartilage repair. Bone mesenchymal stromal cells (BMSCs) were isolated from male Sprague Dawley (SD) rats, and high-throughput sequencing was used to select tRFs from EVs derived from BMSC which were cultured in chondrogenic induction medium (induced) or stem cell growth medium (control). We established the rat cartilage defect model of the knee joint, in which physiological changes were examined by immunohistochemistry (IHC), to test the protective effect of BMSC-derived EVs and tRF-related molecules. Primary chondrocytes from rat knee joint treated with oxygen-glucose deprivation/reperfusion (OGD/R) were used to investigate the effect of related EVs and tRF on cell proliferation and apoptosis. BMSC-derived EVs could repair the defected cartilage of rat knee joint. OGD/R significantly reduced chondrocytes proliferation, induced chondrocyte apoptosis and inflammation, while BMSC-derived EVs reversed these effects. Additionally, tRF-Gln-TTG-019 significantly increased in EVs derived from differentiated BMSCs when compared with control group. Knockdown ubiquitin-like 3 (UBL3, a molecular target of tRF-Gln-TTG-019) inhibited chondrocytes apoptosis and inflammation induced by OGD/R, and this effect could be synergistically enhanced when co-cultured with BMSC-EVs, but the protection was partly reversed by tRF-Gln-TTG-019 inhibitor. Then we further validated that suppression of UBL3 could promote the proliferation of chondrocytes, inhibit inflammation, and enhance the repair ability of cartilage tissue in a rat cartilage defect model. Similarly to the previous results, BMSC-derived EVs could synergistically enhance these effects, while tRF-Gln-TTG-019 inhibitor weakened them. Our results indicate that tRF in BMSC-derived EVs modulates the process of cartilage repair by regulating UBL3.