Changes in circulating small non-coding RNAs after castration in a cohort of prostate cancer patients

Small non-coding RNAs (sncRNAs) can be found in circulation and may carry endocrine signals. Here, we analyse circulating sncRNAs before and after castration to identify sncRNAs that potentially could convey endocrine signals from the testis. In a previous randomized clinical trial, men with advanced prostate cancer (n=57) were treated by either subcapsular orchiectomy (O-arm, n=28) or GnRH-analogue (G-arm, n=29). Blood samples were obtained at baseline (W0) and at 12 (W12) and 24 weeks (W24) post-intervention. Small non-coding RNAs from 169 longitudinally paired serum samples were sequenced using the RealSeq-Biofluids Small RNA kit. A joint analysis of sncRNA reads at W12 and W24 compared to W0 identified 81 and 175 circulating sncRNAs present at significantly (FDR<0.05) different levels in the O-arm and G-arm, respectively. Most sncRNAs were found at lower levels after treatment (n=67 (83%) and n=150 (86%) in the O- and G-arm, respectively). The most prevalent type of sncRNA was piRNAs contributing to 44% (n=36 piRNAs) in the O-arm and 58% (n=101 piRNAs) in the G-arm. When the two treatment arms were analysed together, 16 sncRNAs were found to be consistently altered after castration. Of these sncRNAs, 8 were piRNAs and 4 have previously been reported in the testis, indicating a likely testicular origin. Using RT-qPCR and small RNA in situ hybridisation, we validated a testicular expression of miR-153 and SNORD38A. In conclusion, the circulating sncRNA profiles are altered after castration and with a substantial loss of piRNAs indicating lost secretion of testicular sncRNAs. However, we cannot deduce if these circulating piRNAs mediate an endocrine signal.