Exosomes are small membrane vesicles that are secreted by most cells and found in peripheral blood, urine, saliva, ascites, amniotic fluid, and other bodily fluids. Exosomes contain proteins, lipids, and nucleic acids, as well as different types of non-coding RNA (including miRNA, lncRNA, circRNA, etc.). Its contents, such as miRNA, can be swallowed by other cells and used as a means of communication between cells. Exosomes secreted by host cells or tumor cells are increasingly being implicated in tumorigenesis, growth, invasion, and metastasis. Multiple indexes can be identified at the same time since the detection of molecular markers in body fluids such as peripheral blood is non-invasive and repeatable. As a result, the study of exosomes is extremely important for disease diagnosis.
Figure 1. Exosome isolation techniques, contents, and applications. (Li, 2019)
Comprehensive information of exosomal RNA, such as the analysis of miRNA, lncRNA, and circRNA, a promising molecular marker for clinical diagnosis, can be easily and effectively obtained using high-throughput exosomal RNA sequencing and bioinformatics analysis, which is an ideal method for disease diagnosis and follow-up. Exosomes have been linked to nearly every disease and have become a hotbed of research in disease markers, disease mechanisms, drug development, and other fields.
Exosomes primarily contain short RNA, such as mRNA and miRNA, with little or no ribosomal RNA, which is distinct from cellular RNA. Exosomes can transmit these RNAs from one cell to another, regardless of how far apart the cells are. Exosome-mediated RNA transfer is crucial for cell signal transmission. The study of RNAs in exosomes not only offers useful insights into exosome functions but also holds promise for exosomes as disease biomarkers or vectors in gene therapy. Exosomal RNAs can be characterized using next-generation sequencing, which is a powerful tool.
Exosomal RNA sequencing analysis follows a four-step experimental workflow:
- Isolation and enrichment of exosomes
- RNA isolation
- RNA library preparation and next-generation sequencing.
- RNA-Seq data processing, alignment, and analysis.
Exosomal RNA profiling elucidates the function of exosome-associated RNA and allows for the applications listed below.
- Changes in exosomal miRNA during disease states are thought to be a reliable method for discovering sequence signatures for disease diagnosis and prognosis.
- Exosomal mRNA's identity and expression level have been considered an important approach for identifying biomarkers in blood, saliva, and urine biofluid samples.
- Exosomes also contain long noncoding RNAs (lncRNA), which can have distinct expression patterns.
Exosomal RNA sequencing can also be used for the following purposes:
- Analysis of molecular markers, as well as typing and staging research.
- The research of disease mechanisms, as well as the occurrence, progression, and spread of disease, as well as the tumor microenvironment.
- Clinical disease surveillance, auxiliary diagnosis, and prognosis monitoring
- Drug carrier research and development.