Scientists have uncovered the key to how tiny particles, which transport materials between cells through blood and other bodily fluids, maintain their structural integrity. This is thanks to unique proteins that preserve their membranes while adapting to fluctuating electrical signals across various biological settings.
Scientists have uncovered the key to how tiny particles, which transport materials between cells through blood and other bodily fluids, maintain their structural integrity. This is thanks to unique proteins that preserve their membranes while adapting to fluctuating electrical signals across various biological settings.
These particles are known as extracellular vesicles and have garnered interest as potential models for innovative drug delivery systems. However, until recently, researchers lacked a thorough understanding of their functionality.
A recent study led by medical researchers from The Ohio State University discovered that these vesicles include an ion channel—a protein that forms a pathway for electrical charges to move through the protective outer membrane. This process is essential for maintaining a stable internal environment within the vesicles.
Experiments on animals also indicated that the ion channel affects the vesicle’s cargo, suggesting that this protein is crucial not only for the integrity of extracellular vesicles (EVs) but also for their operational capability. When comparing RNA molecules delivered by EVs with and without the ion channel to mice suffering from heart issues, only the molecules from EVs containing ion channels were effective in repairing heart damage.
Harpreet Singh, a professor of physiology and cell biology, and Mahmood Khan, a professor of emergency medicine, both from Ohio State’s College of Medicine, led the study.
“We have not only discovered ion channels in these vesicles; we have successfully recorded functioning ion channels for the first time,” Singh noted. “From initially hypothesizing that these vesicles would have ion channels to demonstrating that they contain various cargo that can either benefit or harm cells—specifically in the case of the heart—we have comprehensively covered the subject.”
The findings were published on January 2 in Nature Communications.
Extracellular vesicles are responsible for transporting proteins and other molecules from one cell to another, influencing biological and physiological responses. Beyond their role in cell communication and maintaining cellular equilibrium, these particles have associations with immune responses, virus spread, cardiovascular diseases, cancer, and neurological disorders.
Drawing from his expertise in ion channels, Singh posited that EVs must possess these channels to safely shuttle molecules between inside cells and the extracellular space. Failing to maintain this balance can lead to membrane rupture due to osmotic stress or disturbance caused by shifting electrical charges.
“Through our extensive experience and a wealth of foundational research over the past century, it’s clear that ion channels are crucial for sustaining any membrane-based structure,” Singh stated.
Consider potassium, a key electrolyte present in high concentrations within cells but significantly lower in the surrounding extracellular fluid.
“When an extracellular vesicle moves from an environment with high potassium to one with low potassium, the inability to maintain ionic equilibrium can lead to osmotic shock,” he explained.
For this research, the team focused on EVs isolated from mice, as provided by Khan, who also leads basic and translational research in the Department of Emergency Medicine and investigates heart repair using stem cell therapy.
Due to the minuscule scale of these particles, scientists developed a technique termed near-field electrophysiology to measure currents within the membranes of the EVs. They identified the presence of a calcium-activated large-conductance potassium channel (BKCa).
Next, they compared EVs from normal mice with those from knockout mice that lack the gene for the BK potassium channel. They discovered that the cargo composition of the EVs from knockout mice differed significantly in both quantity and size, indicating a functional role for the BKCa channel.
Among the cargo of EVs from normal mice, several small RNA segments that regulate gene activation were identified, which are known to aid in protecting the heart against oxidative stress, according to Khan. On the other hand, EVs from knockout mice exhibited a different set of RNA segments called microRNAs.
This discovery prompted subsequent animal trials in Khan’s laboratory, where EVs from both normal and BK gene knockout mice were injected into mice with heart disease.
“EVs from healthy animals offered protection to the heart,” Singh explained. “Conversely, EVs lacking the BK gene did not provide adequate protection and, in fact, made the condition worse. The vesicles missing the channel were enriched with harmful microRNAs.”
“Is the variation in cargo due to differences in packaging, or do the vesicles without the channels simply not survive as well? That remains an open question we are currently exploring.”
Another important unresolved issue is identifying the transport proteins that allow vesicles to maintain ionic stability when moving from the extracellular environment into a cell with high concentrations of potassium.
In addition to enhancing our understanding of extracellular vesicles, Singh believes this research has the potential to improve their therapeutic applications.
“There’s considerable discussion about loading these vesicles with charged molecules—be it drugs, RNA, proteins, or others. If you fill them with charged entities without managing ion homeostasis, you could face adverse effects,” he cautioned. “Our main takeaway is that in bioengineering EVs, achieving the correct balance of ion channels and transporters is essential.”
This research received support from an Ohio State President’s Predoctoral Fellowship, the Department of Physiology and Cell Biology, a Graduate School Alumni Grant, the American Heart Association, and several national institutes focused on health and disease.
Additional co-authors include Shridhar Sanghvi, Divya Sridharan, Parker Evans, Julie Dougherty, Kalina Szteyn, Denis Gabrilovich, Mayukha Dyta, and Jessica Weist from Ohio State; Sandrine Pierre from Marshall University; Shubha Gururaja Rao from Ohio Northern University; Dan Halm from Wright State University; and Tingting Chen, Panagiotis Athanasopoulos, and Amalia Dolga from the University of Groningen.
