Exosomes are protein-packed biological messengers that our cells use to communicate with one another. Scientists have devised an effective approach to detect the messages these exosomes are carrying.
These spherical exosomes, which are housed in a cell’s internal membrane but eventually move outside to enter another cell, transport big molecules like proteins, which serve as the body’s fundamental building blocks and as catalysts for biological activity, and RNA, which makes proteins.
“This is an ongoing process,” says Dr. Sang-Ho Kwon, cell biologist in the Department of Cellular Biology and Anatomy at the Medical College of Georgia at Augusta University, and there is increasing evidence that it occurs both in states of health and disease.
“We are trying to figure out this puzzle of what exosomes are doing in different scenarios,” says Kwon.
Kwon is the corresponding author of a study published in the Journal of Extracellular Vesicles that describes the labeling method his research group and he created to examine the contents of exosomes from any particular cell type in order to comprehend their function in health and disease.
“Their contents can help tell us what our cells are telling each other,” Kwon says, and likely provide early clues that we are getting sick and help us better understand how we get sick.
The formation of exosomes is thought to begin with the loading of cargo by their precursor endosomes, which are located close to the cell membrane. This process is analogous to loading the mail truck at the post office before it departs on its route. Exosomes will remain there until the cell releases them so they can move to other cells.
Kwon and his team wanted to catch the cargo early in the process.
Exosomes must currently be isolated from their context before being studied, which is a time-consuming process that can produce erratic results. Exosomes are just one sort of the cellular compartments in our bodies that this method may isolate.
This is an ongoing process. We are trying to figure out this puzzle of what exosomes are doing in different scenarios.
Dr. Sang-Ho Kwon
The MCG team has created a more effective technique that makes it possible to study exosome contents exclusively and in their natural environments. They use an ascorbate peroxidase variant linked to another protein that is known to hunt for exosomes as part of their labeling method.
“APEX is kind of the missile that gets me inside,” Kwon says.
APEX has a strong affinity for the B vitamin biotin, which binds to surrounding proteins, including those carried by the growing exosome, labels them, and aids in their identification. Biotin can also cross the cell membrane that exosomes are attached to.
With the aid of analysis offered by mass spectrometry, they are able to purify and precisely identify the protein cargo as well as the RNA that will make future proteins thanks to a further protein, streptavidin, which attaches to biotin in a natural way.
Kwon’s research focuses on kidney damage, and they have demonstrated using their method how the cargo of exosomes produced by kidney cells and seen in urine is altered by oxidative stress, a consequence of oxygen utilization that is excessive and harmful in disease situations. For instance, certain proteins’ expression levels changed, and some proteins completely vanished.
Their method should make it simpler to create databases of various cell types’ typical contents, which will permit comparison investigations of what happens to those contents in various disease states, such as the kidney injury studied by Kwon or cancer.
“It turns out that by looking at the exosomes in the urine or blood, and by looking at what is inside, we can tell whether the cell is injured or a healthy cell,” he says.
In living kidney cells in culture, they used the tagging technique for the first time. In an animal model of renal disease, they now aim to apply it.
According to the research team, the tagging approach can also be used to track changes in exosome composition over time and possibly how diseased cells are reacting to therapy.
It is well recognized that exosomes are essential for cell communication, both between cells of the same type and with cells of other types. Again, there is mounting evidence that exosomes have a role in sickness, possibly even in the transmission of disease by notifying other cells that they are ill.
“It’s not just passing good news. it also passes bad news,” Kwon says.
He points out that their cargo undoubtedly differs in those various situations, making it crucial to be able to identify what exosomes are carrying. Changes may ultimately serve as good way to monitor response to treatment, another aspect of exosome research that is “exploding,” Kwon says.
Exosomes are biological capsules that can be loaded with medication and transported directly to the appropriate place, and scientists are investigating the possibility of employing exosomes to really administer treatment.
In actuality, exosomes are also released by immune cells, which play a crucial role in both health and illness. Additionally, it appears that these biological compartments are crucial in the removal of waste materials from the cells, including cellular debris.
“It’s an emerging field, right now,” says Kwon.
Proteins are the main inhabitants because they have the ability to transmit messages, but they may also bind to other proteins and alter their functionality, according to him. The same is true for RNA, as small microRNA can change gene expression and, in turn, affect how cells function.
Kwon’s interest in exosomes was piqued when, while a postdoc at the University of California, San Francisco, he grew kidney tubules in a dish and discovered evidence that exosomes were crucial to the shifting gene dynamics there. Kidney tubules return essential nutrients to the blood and eliminate undesirables in the urine.
He refers to the focus on exosomes as “reverse science,” since the majority of scientists are more interested in how cells change than in the packets that cells send out to communicate their activities.
Although it might not seem like it to most people, he claims that because you are looking at a smaller package with many fewer proteins, it is actually a less complex way to approach cell function.
The research was supported by the National Institutes of Health.
