tsRNA‐12391‐Modified Adipose Mesenchymal Stem Cell‐Derived Exosomes Mitigate Cartilage Degeneration in Osteoarthritis by Enhancing Mitophagy

Osteoarthritis (OA) is a cartilage-degenerative joint disease. Mitophagy impacts articular cartilage damage. tRNA-derived small RNAs (tsRNAs) are one of the contents of adipose mesenchymal stem cell (AMSC)-derived exosomes (AMSC-exos) and are involved in disease progression. However, whether tsRNAs regulate mitophagy and whether tsRNA-modified AMSC-exos improve OA via mitophagy remain unclear. We performed small RNA sequencing to identify OA-related tsRNAs, which were then loaded into AMSC-exos, exploring the function and mechanisms related to mitophagy in vitro and in vivo. Overall, 53 differentially expressed tsRNAs (DEtsRNAs) were identified between OA and normal cartilage tissues, among which 42 DEtsRNAs, including tsRNA-12391, were downregulated in the OA group. Target genes of tsRNA-12391 mainly participated in mitophagy-related pathways such as Rap1 signaling pathway. Compared to the control group, tsRNA-12391 mimics significantly promoted mitophagy, as shown by the upregulated expression of PINK1 and LC3 and the co-localization of Mito-Tracker Green and PINK1. Furthermore, tsRNA-12391 mimics effectively enhanced chondrogenesis in chondrocytes, as demonstrated by the elevated expression of collagen II and ACAN. AMSC-exos with tsRNA-12391 overexpression also facilitated mitophagy and chondrogenesis in vitro and in vivo. Mechanistically, tsRNA-12391 bound to ATAD3A restricted ATAD31 from degrading PINK1, leading to PINK1 accumulation. ATAD31 overexpression reversed the effects of tsRNA-12391 mimics on mitophagy and chondrogenesis. AMSC-exos loaded with tsRNA-12391 promoted mitophagy and chondrogenesis by interacting with ATAD31; this may be a novel therapeutic strategy for OA.