Exosomal microRNAs (miRNAs) in blood and urine under physiological conditions: a comparative study

Objectives: Blood and urine are commonly used specimens for clinical testing, and their contents, particularly exosomal microRNA (miRNA), are diverse, reflecting the metabolic activities of tissues and organs in the body. Methods: Blood and urine samples were collected from six healthy adults. Exosomes were then enriched from these samples, followed by sequencing and bioinformatic analysis of exosomal miRNA. Results: The comparative analysis of miRNAs in blood and urine revealed that 41 miRNAs were more abundant in blood, while 61 were found at lower levels. Notably, hsa-miR-934 was among those with higher expression in blood, whereas hsa-miR-425-5p was one of the miRNAs with lower expression. Kyoto Encyclopedia of Genes and Genomes pathway analysis indicated that the target mRNAs of differentially expressed exosomal miRNAs (DEexo-miRNAs) in both blood and urine are implicated in various signaling pathways, including proteoglycans in cancer, axonal guidance, and the regulation of the actin cytoskeleton. Additionally, the target mRNAs associated with DEexo-miRNAs in urine were also linked to processes such as ubiquitin-mediated proteolysis and the phosphatidylinositol signaling system. In contrast, the target mRNAs corresponding to DEexo-miRNAs in blood were involved in the FoxO signaling pathway and chronic myeloid leukemia, among others. Conclusion: This study observed differential expression of exosomal miRNAs in blood and urine, thereby enriching the available library of exosomal miRNA for these two sample types. It also lays the groundwork for the detection of exosomal biomarkers from blood and urine.