Supernatant versus exosomal urinary microRNAs. Two fractions with different outcomes in gynaecological cancers

MicroRNAs (miRNAs) are key regulatory molecules implicated in fundamental cell processes. Recent investigations have been focused to investigate their diagnostic potential also in various body fluids. Plasma and serum are widely used for these purposes. Urinary miRNAs, as the easily available type of sample, have been explored particularly in urological diseases recently. However, we have shown previously that differential expression of urinary cell-free miRNAs may be observed also in gynaecological cancers, such as ovarian and endometrial cancers. In the present article, we focus on the differences in particular urine cell-free miRNA abundance among different samples including particularly ovarian and endometrial cancers and rare gynaecological diagnoses involved in the study. Using raw abundance miRNA expression data, we confirmed significant up-regulation of miR-92a in ovarian cancer, and significant down-regulation of miR-106b in endometrial cancers. As miR-21 appeared up-regulated in the endometrial cancer similarly as in the verification process, where also miR-106b resulted in significant down-regulation in ovarian cancer, these miRNAs may be good candidates for further evaluation as novel diagnostics. To find out why supernatant but not exosomal urine miRNAs fraction resulted in significant results in regards to deregulation of expression, we performed a comparison of the same urine samples isolated by these two manners. We show that diagnostic potential of cell-free urinary miRNAs may depend on the urine fraction used for the isolation. While particular urinary miRNAs may be enriched, other may reveal unchanged or diminished expression in the exosomal fraction in comparison with supernatant fraction, giving differences also between cancer and control samples. More research will be needed to further explore which kind of cell-free samples would give better results for diagnostic purposes in various diagnoses using urinary samples and investigating cell-free miRNAs expression. Meanwhile, different urine fractions should be explored for their miRNA expression to establish novel diagnostic urinary miRNA markers.