Shuttling Through Inner Space
Complex medical issues like transplants, kidney disease, and cancer may be helped by knowing more about how cells communicate.
When scientists are lucky, what comes into focus under the microscope also clarifies a new horizon in medicine. One such adventure started with platelet dust. In 1967, the author of an article in the British Journal of Haematology, reported seeing the dust, or micro-sized particles, under his microscope in the part of blood called plasma. Peter Wolf, the author and a physician, determined that the particles helped blood to clot.
Other researchers also were finding these microparticles in bodily fluids. But many thought they were the equivalent of cellular trash bags: a membrane sack filled with junk put out for the body to clean up. But the microparticles were much more than trash. Researchers now think they may provide a path forward in treating complex and tricky diseases that have few other options.
FROM TRASH TO TREASURE
In 2013, three researchers won the Nobel Prize for identifying the role this trash-to-treasure plays in cellular communication. By then, the microparticles had been rebranded as “extracellular vesicles,” combining a Latin word for bladder or fluid-filled sac (vesicle) with a description of where it travels (extra, or outside, the cell that created it). Not a name meant for a marquee, perhaps, but certainly better than “dust” and one that speaks
to the deceptively simple nature of this cellular tool.
At Mayo, at least 100 researchers are investigating the role of vesicles in liver and kidney disease; organ transplant; pre-eclampsia; and cancers such as glioblastoma, myeloma and melanoma. Understanding how vesicles are used by cells — or are hijacked by disease — may spark critical advances for patients with rare, complex or chronic conditions.
SAFE TRAVEL GUARANTEE
Explained simply, a vesicle is a bit like a space shuttle, protecting its cargo of information (RNA and DNA) and tools (proteins) from a hostile environment. Cells assemble the molecular cargo, pack it in a protective membrane (vesicle) and push the whole thing out of the cell (extracellular) to travel to another cell. In these tiny intercellular communities, cells get stuff from neighbors with something to give.
This type of communication is found in all cells. Bacteria, plants and people all use vesicles to communicate from cell to cell. Why? Because a lot can happen between when an order is shipped and when it arrives.
The space between cells can be unfriendly to unprotected molecules but with vesicles, a cell can be sure the message gets through. And, by understanding more about those tools and instructions, researchers such as Lilach Lerman, M.D., Ph.D., who studies kidney disease at Mayo, think big strides can be made in medical care.
The job of the kidneys is to filter blood. So, when the arteries that bring blood to the kidneys are blocked, they suffer. And the patient suffers.
“These patients don’t have a lot of therapeutic options,” says Dr. Lerman, a researcher and nephrologist at Mayo. “Clinical trials have shown that, even if you open the stenotic [blocked] renal artery and restore its blood flow, it does not necessarily restore function.”
To find new options for this unmet patient need, Dr. Lerman and her team looked at stem cells. They occur naturally throughout the body, to help heal and regenerate tissue when necessary. Stem cells have anti-inflammatory features and the ability to promote growth of microvessels in damaged tissues. But their use is not without risks, according to researchers. In some cases, stem cells can develop mutations linked to cancer. But stem cells, like all cells, pack and release extracellular vesicles. So the team began investigating if it was possible to get a stem cell-like response with just the vesicles and not the stem cells.
They published their results in Kidney International in 2017. Using an animal model of metabolic syndrome and kidney disease, Dr. Lerman’s team found that the vesicle cargo had arrived in the kidney tissue. After four weeks, the authors recorded some good signs: a decrease in kidney inflammation, improved oxygenation and less development of fibrosis. In the metabolic syndrome model, kidney blood flow and function were better in the animals treated with extracellular vesicles.
“We also found that the cargo of vesicles changes depending on the cell,” says Dr. Lerman. “Stem cells from animals with metabolic syndrome seem to have less anti-inflammatory and more pro-inflammatory messages.”
This is not a good sign. But understanding how extracellular vesicle cargo can be affected by disease is important, Dr. Lerman points out because they are part of a patient’s personal repair system.
“Knowing if they don’t work well means we need to find ways to make them work better,” says Dr. Lerman.
And she’s doing just that. In animal models and through collaborations, Dr. Lerman is investigating how the vesicle cargo is processed when it reaches the target cell.
“The cargo components, like proteins and genetic material, don’t necessarily target the same pathways, so it’s not clear that they’re all there to work together for a certain function,” says Dr. Lerman.
But what is clear is that these cellular cargo shuttles have myriad roles to play in disease and health. And, like Dr. Lerman, Tushar Patel, M.B., Ch.B., a Mayo Clinic researcher, sees both sides of that coin.
FROM LIVER REPAIR TO LIVER CANCER
“We have been involved in studies to understand how these vesicles contribute to cancer growth and response to therapy, and also how they participate in the normal functioning of the liver,” says Dr. Patel, dean for research on Mayo Clinic’s Florida campus. Similar to Dr. Lerman’s research, Dr. Patel and his team have looked at how vesicles from stem cells promote repair or regrowth in the liver.
In one study, Dr. Patel and his team examined liver failure in a mouse model. They found the use of vesicles from bone marrow-derived stem cells could reduce liver damage and increase survival in mice to a dramatic degree, he says.
And, in other research, Dr. Patel’s team looked at how vesicles could help a type of liver injury kicked off when blood flow to the liver stops. For surgery or transplantation, blood vessels are briefly clamped to allow the procedure to take place. But tissues can
be injured during this process. In a mouse model, Dr. Patel and his team found that livers bathed in vesicles were less damaged than those that were not. This, says Dr. Patel, suggests that vesicles could be an important tool to improve surgery and liver transplantation.
Dr. Patel’s lab also has published several influential papers. In one, his team developed methods for the production and use of extracellular vesicle from milk, and used these to target liver cancers. In another, they examine the roles vesicles play in signaling between cancer and other cells within the liver, which is necessary to improve treatment for liver cancer. And that — treatment for liver disease and cancer — is Dr. Patel’s hope for the future of research in extracellular vesicle.
“Our long-term goal is to detect cancer early and to improve treatment for cancer,” says Dr. Patel. “We have been systematically evaluating methods for the isolation of extracellular vesicles and for the detection of their content, specifically their RNA content, for use as a new method for the diagnosis and treatment of liver cancers.”
Because what our cells can do, cancer can, too.
By hijacking vesicles, cancer cells may be able to grow and spread more effectively. That’s the bad news. The good news is researchers are taking apart the vesicles sent out by cancer cells to understand the message those cargo ships carry and silence it.
From melanoma and prostate cancer to glioblastoma and multiple myeloma, Mayo Clinic researchers are part of a surge of scientists examining how vesicles can help identify, treat and stop cancers that typically leave patients with few options.
Diane Jelinek, Ph.D., dean of research on Mayo Clinic’s Arizona campus, investigates a class of immune cells called B cells. These white blood cells start as stem cells and differentiate into cells called plasma cells, which produce antibodies to help eliminate infections. Dr. Jelinek’s lab studies normal B cells and cancers related to B cells, such as multiple myeloma, a cancer that often starts in the bone marrow.
After hearing a presentation on vesicles about five years ago, Dr. Jelinek went back to her lab thinking about this new type of cell signal. At that time, her team was working on a molecule linked to myeloma cells, called CD147.
“Just after hearing this seminar, I went and talked to a research technologist in my lab,” says Dr. Jelinek. “I said, ’Gee, I wonder if CD147 can be found in vesicles from myeloma cells.’”
The first thing they wanted to know is if myeloma cells even released vesicles. If so, they would look for their target — CD147 — to see if myeloma cells were exporting this cancer-fueling molecule to other places. In 2014, they reported that, indeed, myeloma cells shed vesicles enriched for CD147.
“From that, we hypothesized that, maybe, the release of these vesicles, which are so small they can travel systemically, contain cargo that can make other parts of the body a good place to grow in, what’s referred to as a premetastatic niche,” says Dr. Jelinek.
The team wondered if the vesicles themselves provided some kind of assistance or if they altered neighboring cells to make the environment better for a myeloma cell. To examine this hypothesis, Dr. Jelinek is working with Tony Hu, Ph.D., an Arizona State University scientist. Together, they are looking at the protein profile of vesicles made by myeloma cells and comparing them to protein profiles from myeloma’s normal counterpart, the plasma cell.
“Our hope would be to identify a couple of proteins that are expressed uniquely or at a significantly higher level by myeloma cells,” explains Dr. Jelinek.
The goal, Dr. Jelinek says, is a biomarker that can pick up a patient’s transition from premalignant to full-blown myeloma.
“The holy grail for us would be if we could identify one or two proteins that might be selectively overexpressed after malignant progression,” says Dr. Jelinek. “And, if those proteins were also present in circulating vesicles, you start seeing where this could potentially be very powerful as a blood test.”
By understanding the message, Dr. Jelinek and other researchers working on other cancers hope to monitor these cellular communications so they can intervene earlier or change the text of the conversation altogether.
DELIVERING HOPE FOR THE FUTURE
“Extracellular vesicles offer a completely new form of biological therapy,” Dr. Patel says. “There is a major opportunity for the use of vesicles for drug delivery or as therapy. The potential there exists for using them to target many different conditions, such as cancers.”
But, Dr. Patel cautions, there is much research that needs to be done, particularly to ensure that the vesicles are not just effective, but safe, and also that they can be produced in a suitable manner. Stay tuned, though, he says, “Extracellular vesicle research is likely to provide many new and exciting opportunities to improve patient care in the future.”
- Sara Tiner