Microvesicles are tiny packages released by almost all cells in the body, acting as messengers to communicate with other cells. For a long time, these structures were thought to be cellular debris. However, scientific understanding has advanced, revealing that microvesicles are active participants in the biological communication networks that govern our health. Their recognition as dynamic components of biological communication has transformed our view of cellular interactions.
Understanding Microvesicles
Microvesicles are a type of extracellular vesicle (EV) that originate directly from the budding and fission of a cell’s plasma membrane. These vesicles range in size from approximately 30 nanometers (nm) to 1000 nm, making them generally larger than exosomes, another well-known type of EV, which typically measure between 30 nm and 150 nm and arise from internal compartments called multivesicular bodies.
While both microvesicles and exosomes are enveloped by a lipid bilayer, their distinct origins contribute to differences in their molecular content and surface markers. Microvesicles carry a diverse array of molecules, including various lipids, proteins, and nucleic acids such as messenger RNA (mRNA) and microRNA (miRNA). The specific cargo they contain depends on the cell from which they originate and the conditions or signals that trigger their formation.
Their Roles in Cellular Communication
Microvesicles serve as transporters, facilitating communication between cells by delivering their molecular cargo. When released, these vesicles interact with target cells, often by binding to specific receptors on the recipient cell’s membrane. This interaction can lead to the fusion of the microvesicle with the target cell, releasing its contents directly into the recipient cell’s cytoplasm.
The transfer of molecules like mRNA, miRNA, and proteins through microvesicles can influence the behavior and function of the recipient cell. For instance, transferred mRNA can be translated into new proteins within the target cell, altering its protein synthesis and phenotype. Microvesicles also play a role in maintaining cellular health by helping to remove misfolded proteins, cytotoxic agents, and metabolic waste products from their parent cells. This exchange of information and materials contributes to cellular signaling pathways throughout the body.
Microvesicles in Physiological Processes
Microvesicles are involved in a wide array of physiological processes, contributing to the body’s balance and ability to respond to changes. They participate in angiogenesis, the process of forming new blood vessels, which is essential for development, wound healing, and tissue repair. For example, microvesicles released by endothelial progenitor cells can activate quiescent endothelial cells and promote blood vessel formation by transferring specific mRNA molecules.
Microvesicles also contribute to tissue regeneration and repair. Mesenchymal stem cells, for instance, release microvesicles that stimulate the regeneration of various tissues, including kidney, heart, liver, and nervous tissues. These vesicles also modulate the immune system, exhibiting both anti-tumor effects and, in some contexts, contributing to tumor immune suppression. Their ability to carry and deliver different mediators influences broad physiological responses.
Implications in Disease and Medicine
Microvesicles hold implications for understanding human diseases, particularly in cancer. They are involved in the progression and spread of cancer cells, including the process of metastasis where cancer cells migrate to form new tumors in distant parts of the body. Tumor cells, for example, can release microvesicles containing specific proteins and RNA that promote tumor growth, angiogenesis within the tumor, and even drug resistance in recipient cells.
These vesicles are also being explored as potential diagnostic biomarkers for various diseases. Changes in the levels or molecular content of microvesicles can indicate the presence of disease, offering a non-invasive method for early detection and monitoring. For instance, certain microRNAs found within microvesicles have been identified as potential biomarkers for different types of solid tumors, detectable in bodily fluids like serum, plasma, and urine.
In the realm of therapeutics, microvesicles are being investigated as natural vehicles for delivering therapeutic agents. Their inherent ability to carry a variety of cargo, including drugs and genetic material, and to target specific cell types or tissues makes them promising candidates for targeted drug delivery systems. This potential application could lead to more effective and precise treatments for a range of conditions, leveraging the body’s own communication mechanisms.