What Are Exosomes? Vesicles With Promising Perspectives
What are exosomes? What makes them so special? Currently, exosomes are a spotlight of medicine, or better say nanomedicine. With time, it becomes more and more clear that a human body can heal itself, and this where exosomes play an important role. What are exosomes and what is their function? Let’s see.
Origin of Exosomes
Exosomes are referred to as extracellular vesicles, so they’re not cells actually, but particles released by the cells. This means that they’re tiny and measured in nanometers.
In general, these vesicles range from 40 to 150 nanometers, making them one of the smallest particles of molecules that can be found in body fluids. With recent advancements in medicine and technologies allowing scientists to analyze and assess even the smallest particles found in our bodies, extracellular vesicles have been proven to have a complex set of functions that help our bodies heal, reverse some negative effects, etc.
The difference in size means differences between exosomes and cells in aspects like contents, purpose, etc. Why are extracellular vesicles so different in their potency and functionality? Since they are released by cells, which can belong to different parts of the body and systems, these nanometric particles serve different functions accordingly, so they are not simply the refuse that cells get rid of, but they are something more being complemented with various benefits that have been and to be discovered.
What are exosomes? Exploring extracellular vesicle content and functionality
What are exosomes? We’ve already defined the exosomes as nanometric vesicles with specific functions of sending a message to other cells, close and distant ones. They can be regarded as mediators between cells, but to understand them better, one should know what is inside these nanometric particles.
Since different cells are capable of releasing vesicles, it means that contents may vary from one particle to another. Thus, exosomes range in size, and among the common contents, they are RNA (micro and messenger) – a piece of genetic data; and they are other types of proteins that include growth factors, receptors, enzymes, and cytokines.
Exosome formation, which is to be discussed later, happens inside the cell, intracellularly. Then, these nanometric particles are released into the body fluid, extracellularly. They serve functions of cargo among cells.
Following this pathway, it can be concluded that after the process that happens in intracellular ambiance, the vesicle becomes a part of extracellular fluid, and this is a way they carry messages from one cell to another, becoming an intercellular circuit.
Besides understanding the exosome definition, it’s more critical to highlight the uses of these extracellular vesicles. Although the discovery of exosomes dates back several decades, it has taken some time to understand the complex structure of these nanometric particles released by cells. Much is still to be researched and discovered, but there are some useful applications that can change a lot in conventional approaches of treatment. Let’s review the exosome purposes further:
Immune System. When people get infected or become ill, the complex immune system is ready to respond. Cells responsible for triggering immune response release exosomes which, in their turn, trigger chain effects that will, in the end, make your body react to a problem causing infection.
A cascade of reactions fights the cause of the infection, and this reaction may be harmful, a kind of hyper reaction, but exosomes alleviate any possible harm by sending suitably matched messages to the cells.
Hair Loss. One of the latest applications of exosomes is to reduce hair loss. Thanks to the abundance of growth factors in the extracellular particles, they trigger the healing effect and positively influence the hair follicles. Exosome therapy is considered to be an innovative and breakthrough treatment option to stop and reverse hair loss.
Lyme Disease. This kind of disease compromises the immune system, the problem lies in the mast cells, and this causes an inflammatory response. Exosomes are employed to reduce such inflammation alongside its effects and help the process of healing to take place faster.
Arthritis. This is another type of inflammatory process occurring in joints and causing pain and discomfort. Even though this condition can be treated with several options, no treatment has been proven to be 100% efficient. However, with the discovery of exosomes in regenerative therapy, much is about to change with more efficient alternatives.
More Possibilities. The two organs that benefit from exosomes to a great extent are the brain and heart. Central Nervous and cardiovascular systems are dependent on nanometric particles released by the cells specific to these systems. Extracellular vesicles released from stem cell culture by means of ultracentrifugation are claimed to progress in medicine.
Formation of exosomes: biogenesis explained
Exosome formation is a complex process that is still to be explained by science. What is an exosome? It’s a very small vesicle that goes outside the cell, or better say, the cell jettisons the vesicles that will have a specific function. How and where are these vesicles formed? Before they start surfing inside the extracellular fluid, they need to be formed inside one cell.
How are exosomes formed: The endocytic origin
Imagine a cell that is full of small compartments. It’s claimed that exosomes have an endocytic origin (endocytic – inside the cell). To become an exosome, a particle should be formed inside a cell. Within an intracellular structure of the cell, there are compartments called an endosome, where the whole process takes place. Going under the complex changes, these compartments become full of small vesicles which then will be jettisoned into the extracellular body fluid.
However, since these vesicles are still inside the cell, they are called intraluminal vesicles. The structure encompassing these intraluminal particles inside endosomes is called the multivesicular body, and as the name suggests, it will have several vesicles inside it. It takes time for these small vesicles to get full of various contents described above. Then, the multivesicular body will fuse with the cell membrane and send out these particles in the body fluid, but does every multivesicular body sends the particles outside the cell structure?
How are exosomes formed: explaining loading principle
Roughly speaking. multivesicular bodies can follow two pathways. One is going to lysosomes, working as a recycling system, and the other way is to go out of the cell and release a vesicle that is known as an exosome.
The sent-out vesicles perform intercellular data exchange with a specific purpose, reprogramming or changing the behavior of the cell. From the definition of exosomes, it’s clear that vesicle carries important content, but how are particles loaded with it? This is where things get even more complicated.
Before releasing the intraluminal vesicles, the cell sends its cargo to them with several pathways. One of the main known ways of such package delivery is ESCRT (endosomal sorting complex required for transport), which is responsible for transferring data to intraluminal vesicles.
According to research, ESCRT was inhibited to understand whether it will stop the formation of exosomes, but they continued to develop. It’s clear that this complex system is still to be explained and analyzed to come up with final conclusions.
In a nutshell, coming back to exosome definition and biogenesis, extracellular vesicles are formed inside compartments of cells known as endosomes. A particular set of vesicles inside cells, intraluminal ones, is known to be a multivesicular body, which waits until they are loaded.
When everything is ready, these bodies can go to the cell membrane and fuse, and thus releasing the loaded vesicle which becomes an exosome. These bodies can go to lysosomes to be broken up into pieces and recycled.
How are exosomes formed: the destiny of multivesicular bodies
If to simplify the definition of exosomes and their biogenesis, it can be said that exosomes are vesicles located in the multivesicular bodies inside the cell. However, the number of the extracellular particles is directly linked to these bodies, as their destiny will be the decisive factor in determining the number and size of the exosomes. Although factors contributing to exosome release are not fully understood, there are some studies showing a correlation of their number and releases.
NDRG1 is a protein that affects the multivesicular body and paves the way of its going and fusing cell membrane, resulting in the release of exosomes. Actually, it adversely affects these bodies and sends them to lysosomes, and thus, blocking this protein increases the number of exosomes in the extracellular fluid. Another protein that can increase exosomes is known as Rab27a, but unlike its counterpart NDRG1, it doesn’t send multivesicular bodies to lysosomes but directly induces them to go to the cell membranes and release extracellular vesicles.
Exosome membrane composition
The membrane of extracellular vesicles resembles the composition of the cell membrane. Besides various proteins, it’s important to point out the receptor availability on the structure of the membrane.
Their structure prevents the vesicle from breaking into pieces in extracellular fluid and traveling inside the body until it reaches the target cell, meaning that vesicles have a particular function when they are released instead of being just a simple waste release, leading to the question what are exosomes? Are they more than just simple molecules found in the fluid of the body?
Having specific receptors allows extracellular vesicles to travel throughout the body without being destroyed or broken into pieces and reach the destination, the specified target cells. When they reach their destination, exosomes can bind with their existing receptors to the receptors of the target cells.
Another way how extracellular vesicles can reach their destination is by means of fusion. Thanks to the unique structure of the exosomes, they can travel and pass through the hardest places, for example, the blood-brain barrier.
Another essential point is that they can serve as drug carriers, as exosomes are known to be mediators between cells. In other words, given the composition of vesicle membrane full of various receptors, exosomes can easily carry components of drugs even to the remote cells, with an ability to pass through the blood-brain barrier opening new perspectives on how to deliver some drugs to treat diseases in the Central Nervous System.
The definition of exosomes: understanding what happens after release
From the definition of exosomes and understanding the basics of their formation, it is clear that a critical part of exosomes’ action is what they do after being released. Since their size and capacities can be different, they can undergo some changes.
For example, some smaller extracellular vesicles can be destroyed into even smaller particles, whereas others succeed in surviving. Now that some exosomes survive, their main purpose is to travel through the body and reach their destination of where they are programmed to carry their contents.
Exosomes are about to change or trigger some effects through the interaction with target cells. Two of the ways how the extracellular vesicles reach their address have been explained. One way is through receptor and the other one is through fusion.
Some exosomes interact with the cell’s surface where vesicles are engulfed by the cell membrane and internalized (a process known as endocytosis). The process of reaching the target cell may take place within hours but the effects after interaction can be long-term.
Understanding extracellular vesicles: what happens in the body?
Exosomes have been proven to have more complex roles, and so much is still to be elaborated on by experts in the future. Given the contents of extracellular vesicles, they are proven to change the behavior of the cell by delivering a message to it. Exosomes have an effect of triggering a particular process like in the case of the immune response.
Another significant finding is that exosomes play the role in the connection of mother and fetus. Fetal cells send signals with exosomes signaling that all organs are ready and this triggers more related processes.
Some recent studies have provided information on how exosomes help people recover after MI (myocardial infarction) which is a heart attack. Exosomes released by the cells of the ischemic tissue (damaged tissue) tend to trigger the release of the cells with healing functions.
Changes in Exosomes with Age
When people get older, they undergo many physiological changes, and this is also a case with exosomes. For example, it’s proven that extracellular vesicles promoting inflammatory responses tend to increase, whereas those responsible for rejuvenation and regeneration tend to decrease. In other words, it’s not only about the change in number that aging results in, but there’s a significant change in the types of exosomes being released.
The prevalence of chronic inflammatory diseases in older people can be explained by an abundance of extracellular vesicles that trigger inflammatory responses that increase with aging. However, such prevalence of these vesicles can function as a biomarker that can be ideal for understanding and detecting health problems, making them an indispensable tool in diagnostics.
Stemming from the definition of exosomes, it’s clear that extracellular vesicles have cutting-edge uses in medicine, and one of the main is regenerative medicine. Messengers and micro RNAs, cytokines, and other important contents of the vesicles make them efficient in the treatment of different illnesses.
Many benefits of exosome therapy make it one of the best minimal-invasive treatment options used in treating aging effects, neurodegenerative disorders, joint problems, and more. The uses of extracellular vesicles in medicine are increasing day by day. If you have more questions and doubts about the particle that can change a lot in the future of medicine or you are wondering what therapies we can offer, don’t hesitate to contact our team of experts here. Find answers easily and effectively.
The Bottom Line
From the exosome definition and explanation of biogenesis of nanometric particles, one can conclude that once regarded as something insignificant, extracellular vesicles have been proven to be the hard-working agents carrying important messages to other cells, from proximal to distant ones.
Extracellular vesicles are hard to detect given their nanometric size, but they are great when it comes to their benefits and uses in the treatment of multiple disorders. These enigmatic particles that can break up within a short time may trigger a long cascade of various long-term effects. They are not something to underestimate and you can confirm it as well.