Exosomes are one of the three major markers in liquid biopsy, and their popularity has continued to rise in research in recent years.
What is Exosomes?
Exosomes are extracellular vesicles produced by all cells that carry nucleic acids, proteins, lipids, and metabolites. They are mediators of short-range communication between cells, affecting every aspect of cell biology. Exosomes have multiple functions and can serve as communication pathways for intercellular substances and signals. Different cells achieve intercellular communication by secreting exosomes with different components. These exosomes are absorbed by the recipient cells and exchange materials and signals through material exchange or release of contents.
Fig.1 Exosomes: A cell-to-cell transit system in the human body with pleiotropic functions (Kalluri R., LeBleu V. S. 2020).
Exosome biogenesis is a complex process. The cytoplasmic membrane invaginates to form early endosomes (ESEs), which can exchange materials with other organelles, or different ESEs fuse to form late endosomes (LSEs), which further form intracellular multimembrane bodies (MVBs), which contain Many intraluminal vesicles (ILVs), these ILVs may eventually be released as exosomes. Cells may degrade MVBs formed by cells by fusion with autophagosomes or lysosomes, or they may release their contents by fusion with the plasma membrane, forming exosomes. Exosomes are generally divided into two categories: ectosomes and exosomes, among which exosomes are derived from endosomes, with a diameter of about 40 to 160 nm.
Function of Exosomes
Exosomes may serve as a pathway for material and signal communication between cells. Different cells achieve intercellular communication by secreting exosomes carrying different components. These exosomes are absorbed by the recipient cells and exchange materials or release their contents. Objects realize the exchange of materials and signals.
Exosomes also play an important role in human reproduction, pregnancy and embryonic development. Semen, amniotic fluid, blood, and breast milk all contain exosomes with putative functions. Seminal plasma-derived exosomes are related to sperm maturation. Exosomes can also inhibit HIV-1 infection, possibly by blocking the recruitment of HIV early protein transcriptional activators and subsequent transcription of HIV-1.
In addition, exosomes are also associated with various diseases. Exosomes may play a role in the emergence of metabolic diseases and cardiovascular health, and may also be involved in the pathogenesis of neurodegenerative diseases. Research on exosomes in cancer is progressing rapidly and has been implicated in tumors, tumor growth and metastasis, paraneoplastic syndromes, and treatment resistance.
Potential Applications of Exosomes in Diagnosis and Therapy
Exosomes have great potential in clinical applications. Exosomes are present in all biological fluids and secreted by all cells, making exosomes attractive in liquid biopsies for longitudinal sampling to track disease progression. The biogenesis of exosomes can capture complex extracellular and intracellular molecules and can be used for comprehensive diagnostic testing. In addition, exosomes have advantages as therapeutic carriers, such as delivering functional substances to diseased cells, low immune clearance rate, and good tolerance.
In summary, exosomes are a highly heterogeneous group with multiple functions and potential clinical applications. The field of exosome research is constantly evolving, and advances in related technologies and experiments will further increase our understanding of exosomes and improve their potential for use in therapeutics and diagnostics.
Reference
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Kalluri R.; LeBleu V. S. The biology, function, and biomedical applications of exosomes. Science. 2020, 367(6478): eaau6977.
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