Rat pawing a syringe

Eri Takematsu’s family endures some chronic diseases. Now her research addresses how those could be resolved

Katie Thrasher

As a child, the diseases her grandparents suffered from seemed no different from cataracts or arthritis. Eri Takematsu did not know that diabetes and heart disease were chronic conditions. Or that they limited blood flow to certain parts of the body, ultimately leading to death. She learned all that later.

“My grandma lives with diabetes and my grandpa has had several heart attacks. They are the main reason I do this research,” Takematsu said. Her work now involves finding biochemical solutions for those at risk of Type 2 diabetes, cardiovascular diseases, and stroke.

That work is what culminated in an article published last month in Nature Communications.

Today, Takematsu works at one of Stanford University’s signature terracotta-roofed buildings, ones fringed by palm trees, and by sidewalks where students whiz by at a frenzied clip on bicycles.

As a postdoctoral scholar in plastic and reconstructive surgery, Takematsu is still as driven to improve vascular health through protein therapeutics as she was nearly seven years ago when she stepped into Aaron Baker’s lab at the University of Texas at Austin.

Then a recent graduate from the Tokyo Institute of Technology (where she had worked on reducing an immune response titanium alloy implants) Takematsu was awestruck by Baker, his lab, his work on regenerative therapies, and specifically his research using stem cell factor (SCF) proteins to improve blood vessel growth.

The cure that worked too well

The project was not if or how the SCF therapy would work. There was extensive evidence that it did. Their problem was to address the severe allergic responses seen (due to activation of mast cells, a type of white blood cell important in immune response) in many people with no history of allergies who received a specific SCF therapy.

And so it began. The research. The trials. The waiting.

Takematsu’s team finally discovered what was triggering the mast cell activity. It was a reaction to the rapid delivery of proteins from the soluble stem cell factor. The therapeutic proteins were overwhelming the body and the immune system overreacted as it fought back against the onslaught of proteins. It was as if you had torn open a bag of mini chocolate chips and dumped it directly down your throat.

Eri Takematsu. Pic courtesy Stanford University

The delivery of the SCF proteins had to be slowed. The answer lay in using a transmembrane (spanning the cell membrane) version of SCF that delivered the protein much more slowly than standard SCF. It seemed like a great idea, but the transmembrane SCF (called tmSCF) was insoluble and clumped together when put in a solution for injection.

“It was a puzzle,” Takematsu said. And while it was clear what needed to be done, the path to get there was a labyrinth of unexplored terrain.

Fat as a sorter

So the team developed a carrier system made of fats, or lipids, to prevent the tmSCF from clumping. Measured in nanometers, the tmSCF came packed in either a 450 nm diameter fat bubble (called a liposome), or a 150 nm diameter lipid nanodisc.

Takematsu explained that nanodiscs and liposomes have been used to stabilize protein structure.“We are the first to use the nanodisc as a therapeutic protein delivery system,” she said.

Schematic illustration of tmSCF proteoliposomes (tmSCFPLs) and tmSCF nanodiscs (tmSCFNDs).
Schematic illustration of tmSCF proteoliposomes (tmSCFPLs) and tmSCF nanodiscs (tmSCFNDs). image adapted from Nature Communications

The research team essentially used a bag of mini chips to make chocolate chip cookies. The delivery of the protein was slowed, the body was not overwhelmed.

There were no notable setbacks or fantastic failures or epic disasters, though the process to develop the new delivery system was painstakingly lengthy.

Consider this: One Lego enthusiast – in their amazon.com review of the Lego set – claimed the process of assembling the Death Star’s 4,016 pieces took 12 hours; it took Takematsu’s team 12 months of research and development to fabricate the first transmembrane sphere.

Once the team had successfully placed the tmSCF in their nanocarriers, it was time to see them in action. That work took another year.

Cell tube formation is the initial step in regenerating blood vessels and eventually returning blood flow to affected areas. Accomplishing this step meant that while the transmembrane and lipid nano carriers prevented a mast cell response, it did not interrupt the SCF therapy itself. In fact, the researchers found tmSCF induced a 16-fold increase in cell tube formation over controls.

Mast cells in connective tissue
Mast cell (circled) in connective tissue help can produce an outsize response that can result in a huge allergic response. Shutterstock

The moment of truth

That was what the team saw at the end of a year’s work: visible signs of cell tube formation – at least outside the body. Takematsu remembers the day she saw the formation as, “the first moment I was truly happy.”

Advancements in vascular regeneration in healthcare is important. Heart disease, stroke, and diabetes ranked in the top eight (first, second, and eighth, respectively) causes of death in 2020, according to the Centers for Disease Control and Prevention (CDC). Patients are plagued by ischemia, infection, organ failure, limb amputation and, eventually, death.

In Austin, the researchers were not resting on their laurels. Over the next year, they saw sign after sign that the combination of the nano carriers and the tmSCF worked. They tested the tmSCF nanodiscs (tmSCFND) and proteoliposome (tmSCFPL) on mice.

Neither common (known as wild type) nor mice with genes for obesity from both parents (known as ob/ob mice) that mimic patients with diabetes displayed any signs of mast cell activation or allergy when given the tmSCF therapy.

The second victory came shortly after when, measured over 14 days, blood flow continually improved. This was seen in hindlimb ischemia models (used to test models of peripheral arterial disease) in both the wild and the ob/ob mice given either the tmSCFND or the tmSCFPL therapeutic. These results are illustrated by the large swaths of bright blue hues in the wild mice treated with the encased tmSCF.

Perfusion of blood wild type vs ob/ob
Mice foot images show how control animals compared with those suffering from hindlimb ischemia. Image adapted from Nature Communication

Working without setting off alarms

The team continually collected data in many ways to compare SCF to tmSCFPL and tmSCFND. They tracked the activity of mast cells, endothelial cells (cells that line blood vessels and help regenerate blood flow), and endothelial progenitor cells (cells that circulate to areas of ischemia and help regenerate blood flow) in mice.

Their work showed tmSCFPL and tmSCFND allowed for the regeneration of blood vessels and blood flow without triggering mast cell activity. It also showed better regeneration of the vessels, and increased blood flow.

Takematsu is optimistic that the next phase of research, although not conducted or led by her, could be successful. The next steps involve testing in rabbits, followed by pigs. Eventually, they hope for FDA approval of human trials.

Takematsu and her team’s work could eventually help people like her grandma, who have diabetes and routinely face issues from low blood flow to their legs and feet. Takematsu notes that for ischemia-related illnesses “there are currently no real treatment options.”

Her grandpa and others like him, who suffer repeated heart attacks, could benefit from having better blood flow to their hearts during recovery. Therapeutics could reduce blood pressure, the strain on the heart needs to use to pump blood when ischemia is present, and even heal damage to the heart muscle following a heart attack.

Blood perfusion improved significantly in those animals that were given the stem cell factor in a package
Blood perfusion improved significantly over days in those animals that were given the stem cell factor in a package of fat. Image adapted from Nature Communications

“There are surgical options such as angioplasty or stenting,” Takematsu says, pointing out that those are invasive, limited in results, and are not always an option for elderly or severely ill patients. Having a non-invasive, injectable therapy option could improve the treatment of peripheral artery disease, cardiac care, and stroke recovery. She sees therapeutic SCF as, “the next generation of medical care and treatment.”

Katie Thrasher

Katie Thrasher is a writer, editor, researcher, and student in the science writing program at Johns Hopkins University. She also holds a degree from the College of Human Ecology at The Ohio State University.

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