tRNA-Derived Fragments (tRFs) Regulate Post-Transcriptional Gene Expression via AGO-Dependent Mechanism In IL-1β Stimulated Chondrocytes

Summary OBJECTIVES Recent studies have shown that tRNA-derived RNA fragments (tRFs) are novel regulators of post-transcriptional gene expression. However, the expression profiles and their role in post-transcriptional gene regulation in chondrocytes is unknown. Here, we determined tRFs expression profile and explored tRF-3003a role in post-transcriptional gene regulation in IL-1β stimulated chondrocytes. METHODS We used qPCR arrays to determine tRNAs and tRFs expression in age- and sex-matched primary human OA chondrocytes and TC28/I2 cells stimulated with IL-1β. Chondrocytes were transfected with tRNA-CysGCA overexpression plasmid or tRF-3003a mimic and 3’UTR luciferase reporter plasmids of mRNAs harboring predicted tRF target “seed sequence”. The AGO-RNA-induced silencing complex (AGO-RISC)-dependent repressive activity of tRF-3003a was determined by siRNA-mediated knockdown of AGO2. RESULTS IL-1β increased the expression levels of specific tRNAs and of tRF-3003a, a type 3 tRF produced by the cleavage of tRNA-CysGCA. tRF-3003a “seed sequence” was identified in the 3’UTR of JAK3 mRNA and tRNA-CysGCA overexpression or transfection of a tRF-3003a mimic in chondrocytes downregulated JAK3 expression and significantly reduced the activity of the 3’UTR reporter. RIP assay showed enrichment of tRF-3003a into AGO2/RISC in IL-1β treated chondrocytes. The suppressive effect of tRF-3003a on JAK3 3’UTR reporter was abrogated with siRNA-mediated depletion of AGO2. CONCLUSIONS We demonstrate that under pathological conditions chondrocytes display perturbations in the expression profile of specific tRNAs and tRFs. Furthermore, a specific tRF namely tRF-3003a can post-transcriptionally regulate JAK3 expression via AGO/RISC formation in chondrocytes. Identification of this novel mechanism may be of value in the design of precision therapies for OA.