Next-Generation Sequencing of Protein-Coding and Long Non-protein-Coding RNAs in Two Types of Exosomes Derived from Human Whole Saliva.

Exosomes are small extracellular vesicles containing microRNAs and mRNAs that are produced by various types of cells. We previously used ultrafiltration and size-exclusion chromatography to isolate two types of human salivary exosomes (exosomes I, II) that are different in size and proteomes. We showed that salivary exosomes contain large repertoires of small RNAs. However, precise information regarding long RNAs in salivary exosomes has not been fully determined. In this study, we investigated the compositions of protein-coding RNAs (pcRNAs) and long non-protein-coding RNAs (lncRNAs) of exosome I, exosome II and whole saliva (WS) by next-generation sequencing technology. Although 11% of all RNAs were commonly detected among the three samples, the compositions of reads mapping to known RNAs were similar. The most abundant pcRNA is ribosomal RNA protein, and pcRNAs of some salivary proteins such as S100 calcium-binding protein A8 (protein S100-A8) were present in salivary exosomes. Interestingly, lncRNAs of pseudogenes (presumably, processed pseudogenes) were abundant in exosome I, exosome II and WS. Translationally controlled tumor protein gene, which plays an important role in cell proliferation, cell death and immune responses, was highly expressed as pcRNA and pseudogenes in salivary exosomes. Our results show that salivary exosomes contain various types of RNAs such as pseudogenes and small RNAs, and may mediate intercellular communication by transferring these RNAs to target cells as gene expression regulators.