tiRNA‐Gly‐GCC‐002 promotes epithelial‐mesenchymal transition and fibrosis in lupus nephritis via FKBP5‐mediated activation of Smad

Background and Purpose Renal interstitial fibrosis is a frequent pathological manifestation of lupus nephritis (LN). tRNA halves (tiRNAs) are acquired from tRNA‐derived small non‐coding RNAs (sncRNAs) and are associated with fibrosis. Our previous study indicated enhanced tiRNA‐Gly‐GCC‐002 (tiRNA002) levels in kidneys were positively related to LN‐related fibrosis. However, the precise molecular mechanism remains unclear. Experimental Approach The mimic and agomiR of tiRNA002 were introduced into tubular epithelial cells (TECs) and MRL/lpr mice by transfection. The levels of gene and protein expressions were quantified using real‐time quantitative polymerase chain reaction (RT‐qPCR), Western blot and immunofluorescence assays. Key Results In TECs treated with LN serum, as well as in the kidneys of MRL/lpr mice, high levels of tiRNA002 directly influenced the epithelial‐mesenchymal transition (EMT) and extracellular matrix (ECM) deposition. Furthermore, tiRNA002 overexpression promoted EMT in TECs and accelerated renal interstitial fibrosis in MRL/lpr mice via Smad signalling. The target gene of tiRNA002, FKBP prolyl isomerase 5 (FKBP5), improved Smad signalling by interacting with phosphorylated Smad2/3. Silencing FKBP5 alleviated LN serum‐ or tiRNA002‐mimic‐induced EMT in TECs. In addition, FKBP5 overexpression reversed the tiRNA002 knockdown‐mediated reduction of EMT and ECM accumulation. Conclusions and Implications These findings indicated that tiRNA002 is markedly increased in LN, which facilitates renal fibrosis by promoting EMT via FKBP5‐mediated Smad signalling. Therefore, targeting tiRNA002 may be an innovative approach to treat renal interstitial fibrosis in LN.