Exosomes are lipid-bound vesicles that act as natural messengers between cells throughout the body. These sacs, ranging from 30 to 150 nanometers in diameter, are secreted by nearly all cell types and travel through bodily fluids. They carry molecular signals from one cell to another, influencing the behavior of recipient cells. This intercellular communication is a fundamental process in both healthy biological functions and disease progression.
The Cellular Factory: How Exosomes Are Made
The formation of exosomes begins within the cell through endocytosis. This involves the inward budding of the cell’s outer membrane, engulfing a portion of the extracellular environment and surface proteins, forming an early endosome. This early endosome then matures into a late endosome, which undergoes further inward budding of its own membrane.
These internal buds form smaller vesicles called intraluminal vesicles (ILVs) within the late endosome, creating a multivesicular body (MVB). The MVB moves towards the plasma membrane, fuses with it, and releases the ILVs—now called exosomes—into the extracellular space. This process is regulated by proteins like ESCRT and Rab GTPases.
Diverse Origins: Which Cells Produce Exosomes
Exosomes are produced by a wide array of cell types throughout the body. Nearly every cell can generate and release these vesicles, reflecting their role in cellular communication. This includes normal cells in various tissues, such as epithelial cells and neurons.
Immune cells, including T-cells, B-cells, macrophages, and dendritic cells, produce exosomes that modulate immune responses. Stem cells also release exosomes, contributing to their regenerative capacities. Cancer cells produce exosomes, which can influence tumor growth and spread.
Why Cells Release Exosomes
Cells release exosomes for various biological reasons. A primary function is intercellular communication, enabling cells to send messages to nearby or distant cells. This allows for coordinated cellular activities and responses throughout tissues and organs. Exosomes also participate in modulating the immune system, influencing immune cell activity and shaping inflammatory responses.
Exosomes can also be involved in waste removal. Their release supports tissue regeneration processes. In pathological conditions, exosome release can contribute to disease progression, such as promoting cancer metastasis or exacerbating inflammation.
What Exosomes Carry and Why It Matters
Exosomes carry a diverse molecular cargo, carefully selected by the parent cell, which dictates their functions upon delivery. This cargo includes various proteins, such as structural, enzymatic, or signaling molecules. They also contain lipids, which can act as signaling molecules.
A significant component of exosome cargo is nucleic acids, particularly different forms of RNA. This includes messenger RNA (mRNA), microRNA (miRNA), and long non-coding RNA (lncRNA). When exosomes are taken up by a recipient cell, these RNA molecules can influence gene expression and protein production in the target cell, altering its behavior. The contents of an exosome reflect the originating cell’s state, allowing it to transmit specific messages that induce a range of biological effects in recipient cells, from promoting cell survival to triggering immune responses.