Fall 2009 Issue
Dr. Brenda Schoffstall and her team of student researchers are making fish get physical - all in the hope of healing our ailing hearts
By Jim W. Harper
Getting fish to work out is not easy. They need constant supervision because they might get lazy and stop swimming, and any "slacking off" could ruin the experiment being conducted by Assistant Professor of Biology Dr. Brenda Schoffstall and a group of student researchers in the biology department. They need their little zebrafish to keep swimming vigorously and to feel stress in order to study how their hearts react.
Keeping the fish motivated also saves them from the embarrassment of falling off the treadmill – or in this case, a flume. "If you don't pay attention, the fish are going to get slammed," notes Danamarie Moonoo, a senior biology major working on the experiment. It's the fishy equivalent of a surfer's wipeout.
Avoiding aquatic injuries is the easy part of this experiment; the hard part is figuring out how the reaction of the zebrafishes' tiny hearts could help humans devise new means of dealing with heart disease. After a heart attack, human hearts are impeded from full functioning because of scar tissue that replaces the formerly healthy tissue. It turns out that some fish and amphibians, on the other hand, have a built-in mechanism for repairing a damaged heart.
Studies have demonstrated that the zebrafish (Danio reiro), a common blue-striped variety available in most pet stores, can re-grow heart muscle after it has been surgically removed. This capacity for regeneration, called hyperplasia, allows them to restore the strength of their hearts in a way that humans cannot replicate. But Schoffstall and her students are investigating "the impossible."
It's a short walk down the hallway from her laboratory on the third floor of the Natural and Health Sciences Building to a brightly-lit room that has the narrow, "tubular" feel of the inside of a submarine. Inside, motors hum and filters flow to keep saltwater sea grasses and other organisms growing inside of 10-gallon tanks. The smaller, blue-tinted tanks of freshwater zebrafish take up an entire wall, and inside each mini-tank the fish wag their tails languidly. Neatly labeled and divided, this showcase is Barry University's Core Aquarium Facility.
Zebrafish are easy to breed and raise but their natural environment does not prepare them for the surprise awaiting them when they leave the aquarium and head down the hall to Schoffstall's lab. The surprise is called the flume, and it forces the non-migratory fish onto an aquatic treadmill. Whether they like it or not, it's time for these fish to get physical.
The first week of training seems to be the hardest for the fish, because they are not used to swimming against a constant current. "They're not salmon," explains Schoffstall. "All zebrafish do in the wild is swim around in a pond." In other words, these natural swimmers have no need to train like a Michael Phelps.
In the flume, however, the fish are subjected to the rapids. They are placed inside of a clear cylinder – reminiscent of a drive-thru bank teller's tube – and a large pump sends water flowing towards them at a constant rate. Before reaching them, the water flows through a bundle of straws, and this simple device distributes the current equally and minimizes dead zones where fish could rest and avoid the experiment's mandatory workout.
On the rise
Their primary trainer during the spring semester was Maxime "Max" Jean, a junior biology major who took charge of the 20 fish under his supervision for nine weeks. He explains that it took four weeks to acclimate the fish to a twice-daily regimen of one and a half hours of exercise. This level of exercise continued for another five weeks in order to place an adequate amount of stress on the zebrafish's hearts.
A third student, Julie Cadet, also monitored the experiment's initial group of fish this summer. Cadet and Jean are Haitian, and Moonoo hails from Trinidad. All three student researchers are beneficiaries of a National Institutes of Health grant, MBRS/RISE, that promotes minorities in the sciences and helps to fund the laboratory overall. MBRS (Minority Biomedical Research Support) and RISE (Research Initiative for Scientific Enhancement) pays students majoring in biology and chemistry to conduct research.
After the nine weeks of training, the "in shape" fish were compared against the control group of "couch potato" fish that never exercised. Cadet recalls holding each fish and pulling back its pectoral fins to expose the beating heart. Then she counted the heartbeats of each fish for 30 seconds. The zebra fish are then sacrificed to record the weight of their bodies, skeletons and hearts.
To regenerate or not to regenerate?
How did the hearts of the zebrafish change due to exercise? The preliminary findings are surprising to Schoffstall because the hearts of the buff, worked-out group of fish look, in some aspects, like hearts of humans with heart disease.
"I'm wondering if it's a negative adaptation to stress. It seems like a mixed response," she says, noting that the left ventricle of the fish's heart appears to get worse, which would be similar to the effect of a heart attack in humans. But something else seems to be happening in the fish that does not occur in humans.
In response to the stress, it appears that cells in the zebrafish hearts are dividing and therefore increasing in number. By contrast, the cells of human hearts hardly ever increase. An older human will still have most of the same heart cells that he or she is born with, Schoffstall notes.
Here is where the zebrafish can teach us an invaluable lesson, she explains. If we can figure out how their hearts grow cells and regenerate tissue, this mechanism could be introduced into damaged human hearts.
But first, researchers such as Schoffstall and her students must figure out what is happening in zebrafish at the molecular level.
In all animals, the cells of the heart expand in response to stress, and this reaction is called hypertrophy. Hypertrophy can be positive, as in the heart of a fine-tuned athlete, or it can be pathological, as in the case of a heart attack, Schoffstall explains, holding up a graphic display of two enlarged hearts, with one showing a healthy flow of blood while the other has a constricted left ventricle. The unhealthy constriction may have multiple causes, such as the effects of diabetes or mutations in the proteins of heart tissue. Heart failure and death is often the result.
To get at this life and death issue, the research team is trying to understand the predominant response in the zebrafish heart. Is it regeneration, something that the human heart cannot do, or is it simply an expansion of the cells? Once this question is answered satisfactorily, they can move on to study the all-important molecular signaling pathways.
"If the molecular signaling processes involved in heart muscle regeneration in zebrafish are fully understood, scientists may be able to investigate ways to stimulate the same signaling processes in humans - heart muscle regeneration may be possible after a heart attack," Schoffstall says.
The places you'll go
In the meantime, all those long sometimes tedious hours spent watching tiny fish swim have benefits outside of the lab. Last February, Moonoo and Jean traveled with Schoffstall to Boston to attend the Biophysical Society Meeting, the world's largest convention for biophysicists. This type of experience inspired Moonoo to revise her career path from medicine to biophysical research. Jean also plans to pursue graduate studies in research, with an eye on a combined MD/PhD program. His résumé is rapidly expanding as in addition to his work in Schoffstall's lab, he spent part of this summer researching an HIV protein at the University of Alabama.
"It's exciting to contribute to research," says Jean, who appreciates the value of the laboratory experience and the time he's spent under Schoffstall's tutelage. "She is a very good guide as a research mentor."
And who knows? The heartfelt work of these student researchers, inspired and guided by the power of a little fish to heal itself, may one day save our own ailing hearts.