Differential prognostic roles of mitochondrial and genomic tRNA-derived fragments in colorectal liver metastases: A retrospective cohort study
Background: Colorectal liver metastases (CRLM) are the leading cause of colorectal cancer (CRC)-related mortality. Transfer RNA-derived fragments (tRFs), a novel class of small non-coding RNAs (sncRNA), regulate gene expression, stress response, and immune functions in cancer. While tRFs are increasingly implicated in CRC progression, their prognostic significance in CRLM remains unknown. This study investigates the abundance and prognostic value of genomic (ge) and mitochondrial (mt) tRFs in CRLM. Methods: This single-center retrospective cohort study included all CRLM patients who underwent curative liver resection between January 2012 and December 2015. Small RNA sequencing (sRNA-seq) quantified ge- and mt-tRF expression in tumor samples. Event-free survival (EFS) was the primary outcome, and the impact of tRFs on EFS was assessed using Cox regression, spline modeling of the effects of tRFs on EFS, and network analysis. Results: Among 588 screened samples, 40 met eligibility criteria (18 females [45%], median age 64 [42-79]). A total of 432 tRFs were identified, with ge-tRFs (67%) being more abundant than mt-tRFs (33%). Using spline regressions, tRFs were classified into 10 ten prognostic groups. High ge-tRF abundance correlated predominantly with unfavorable EFS (FDR<0.2; 94%), whereas mt-tRFs were significantly (p<0.001; ?2 test) more often associated with favorable EFS (FDR<0.2; 26%). Network analysis of tRF abundance correlations revealed a significantly higher intra-mitochondrial network density compared to the intra-genomic tRF network. However, no significant differences in network structure were observed between prognostically significant vs. non-significant or favorable vs. unfavorable tRFs. Finally, key tRF candidates, such as tRHalve3-His-CAU (mt-tRF) or tRNAleader-Gln-UUG (mt-tRF) paired with tRFmisc-Tyr-GTA (ge-tRF), remained independent prognostic markers after adjustment for clinical covariates. Conclusion: This study provides the first comprehensive characterization of tRF expression in CRLM, revealing distinct prognostic roles for ge- and mt-tRFs. While ge-tRFs were predominantly associated with unfavorable prognosis, a subset of mt-tRFs demonstrated a favorable impact on EFS. These findings highlight the potential of tRFs as novel prognostic biomarkers and therapeutic targets in CRLM, warranting validation in prospective studies. Overall design: From 40 macrodissected FFPE CRLM tissue samples, small RNAs was isolated and small RNA sequencing performed.