Abstract
Exosomes derived from all nephron segments are present in human urine, where their functionality is incompletely understood. Most studies have focused on biomarker discovery rather than exosome function. Through sequencing we identified the miRNA repertoire of urinary exosomes from healthy volunteers; 276 mature miRNAs and 345 pre-miRNAs were identified (43%/7% of reads). Among the most abundant were members of the miR-10, miR-30 and let-7 families. Targets for the identified miRNAs were predicted using five different databases; genes encoding membrane transporters and their regulators were enriched, highlighting the possibility that these miRNAs could modulate key renal tubular functions in a paracrine manner. As proof of concept, cultured renal epithelial cells were exposed to urinary exosomes and cellular exosomal uptake was confirmed; thereafter, reduced levels of the potassium channel ROMK and kinases SGK1 and WNK1 were observed in a human collecting duct cell line, while SPAK was unaltered. In proximal tubular cells, mRNA levels of the amino acid transporter gene SLC38A2 were diminished and reflected in a significant decrement of its encoded protein SNAT2. Protein levels of the kinase SGK1 did not change. Thus we demonstrated a novel potential function for miRNA in urinary exosomes.
Highlights
The majority of studies concerning urinary exosomes have focused on their potential as biomarkers of disease pathology and progression, including prostate and bladder cancers[14,15,16,17], but their functional significance is being addressed
We aimed to identify the miRNA repertoire of urinary exosomes from healthy individuals using the most efficient methods available for exosomal isolation and small RNA extraction
Amounts of miRNA packaged in the exosomes were 7.3 ± 1.7 ng per 100 ml of urine, and the proportion of miRNA compared to other small RNAs was 50.4 ± 5.7% (Supplementary Table S1)
Summary
The majority of studies concerning urinary exosomes have focused on their potential as biomarkers of disease pathology and progression, including prostate and bladder cancers[14,15,16,17], but their functional significance is being addressed. Bruschi and colleagues demonstrated that urinary exosomes can consume oxygen in order to synthesize ATP aerobically, suggesting metabolic activity[20], and Jiang et al showed that urinary exosomes derived from stem cells may have the potential to inhibit podocyte apoptosis and promote vascular regeneration in the kidney[21]. The lack of efficient methods to isolate small RNAs from vesicles has been a constraint to miRNA profiling, and there is no consensus regarding the optimal method for isolation of exosomes. We aimed to identify the miRNA repertoire of urinary exosomes from healthy individuals using the most efficient methods available for exosomal isolation and small RNA extraction. We investigated the direct effects of exosomal miRNA on gene expression and protein levels of selected predicted targets in kidney-derived cell lines
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
