Extracellular vesicle
Overview
Extracellular vesicles (EVs) are tiny, membrane-bound particles that are released by cells into the extracellular environment. These vesicles are filled with a variety of biomolecules, including proteins, lipids, and nucleic acids, which can be transferred to other cells, influencing their function and behavior. EVs are involved in a wide range of biological processes, from cell-cell communication and immune responses to tissue repair and disease progression.
Classification
Extracellular vesicles can be broadly classified into three main types based on their size, biogenesis, and release pathways: exosomes, microvesicles, and apoptotic bodies.
Exosomes are the smallest type of EVs, typically ranging from 30 to 100 nanometers in diameter. They are formed within the endosomal network of cells and are released when multivesicular bodies (MVBs) fuse with the plasma membrane.
Microvesicles, also known as ectosomes, are slightly larger, with diameters ranging from 100 to 1,000 nanometers. They are formed by the outward budding and fission of the plasma membrane.
Apoptotic bodies are the largest type of EVs, typically measuring 1,000 to 5,000 nanometers in diameter. They are formed during the process of programmed cell death, or apoptosis, and contain cellular debris.
Biogenesis
The biogenesis of extracellular vesicles involves a complex series of events that are tightly regulated by the cell. This process begins with the inward budding of the plasma membrane or endosomal membrane, leading to the formation of intraluminal vesicles within multivesicular bodies or vesicles within the cytoplasm. These vesicles are then released into the extracellular environment when the MVBs or plasma membrane vesicles fuse with the cell membrane.
Cargo Sorting
The cargo of extracellular vesicles, which includes proteins, lipids, and nucleic acids, is not randomly selected. Instead, it is carefully sorted and packaged into the vesicles during their biogenesis. This process is regulated by a variety of mechanisms, including the endosomal sorting complexes required for transport (ESCRT) machinery, lipid rafts, and tetraspanins. The cargo of EVs can reflect the physiological state of the parent cell and can influence the function of recipient cells.
Functions
Extracellular vesicles play a crucial role in cell-cell communication by transferring their cargo to recipient cells. This can influence a wide range of biological processes, from immune responses and inflammation to tissue repair and regeneration. EVs can also contribute to disease progression, including cancer, neurodegenerative diseases, and cardiovascular diseases.
Clinical Applications
Due to their role in cell-cell communication and disease progression, extracellular vesicles have potential applications in both diagnostics and therapeutics. In diagnostics, the cargo of EVs can serve as biomarkers for various diseases, providing a non-invasive method for disease detection and monitoring. In therapeutics, EVs can be engineered to deliver specific cargo to target cells, offering a novel approach for drug delivery.