First contracting human muscle grown in laboratory

This is a microscopic view of lab-grown human muscle bundles stained to show patterns made by basic muscle units and their associated proteins (red), which are a hallmark of human muscle.
Credit: Nenad Bursac, Duke University

In a laboratory first, Duke researchers have grown human skeletal muscle that contracts and responds just like native tissue to external stimuli such as electrical pulses, biochemical signals and pharmaceuticals.

The lab-grown tissue should soon allow researchers to test new drugs and study diseases in functioning human muscle outside of the human body.

The study was led by Nenad Bursac, associate professor of biomedical engineering at Duke University, and Lauran Madden, a postdoctoral researcher in Bursac's laboratory. It appears January 13 in the open-access journal eLife

"The beauty of this work is that it can serve as a test bed for clinical trials in a dish," said Bursac. "We are working to test drugs' efficacy and safety without jeopardizing a patient's health and also to reproduce the functional and biochemical signals of diseases -- especially rare ones and those that make taking muscle biopsies difficult."

Bursac and Madden started with a small sample of human cells that had already progressed beyond stem cells but hadn't yet become muscle tissue. They expanded these "myogenic precursors" by more than a 1000-fold, and then put them into a supportive, 3D scaffolding filled with a nourishing gel that allowed them to form aligned and functioning muscle fibers.

"We have a lot of experience making bioartifical muscles from animal cells in the laboratory, and it still took us a year of adjusting variables like cell and gel density and optimizing the culture matrix and media to make this work with human muscle cells," said Madden.

Madden subjected the new muscle to a barrage of tests to determine how closely it resembled native tissue inside a human body. She found that the muscles robustly contracted in response to electrical stimuli -- a first for human muscle grown in a laboratory. She also showed that the signaling pathways allowing nerves to activate the muscle were intact and functional.

To see if the muscle could be used as a proxy for medical tests, Bursac and Madden studied its response to a variety of drugs, including statins used to lower cholesterol and clenbuterol, a drug known to be used off-label as a performance enhancer for athletes.

The effects of the drugs matched those seen in human patients. The statins had a dose-dependent response, causing abnormal fat accumulation at high concentrations. Clenbuterol showed a narrow beneficial window for increased contraction. Both of these effects have been documented in humans. Clenbuterol does not harm muscle tissue in rodents at those doses, showing the lab-grown muscle was giving a truly human response.

"One of our goals is to use this method to provide personalized medicine to patients," said Bursac. "We can take a biopsy from each patient, grow many new muscles to use as test samples and experiment to see which drugs would work best for each person."

This goal may not be far away; Bursac is already working on a study with clinicians at Duke Medicine -- including Dwight Koeberl, associate professor of pediatrics -- to try to correlate efficacy of drugs in patients with the effects on lab-grown muscles. Bursac's group is also trying to grow contracting human muscles using induced pluripotent stem cells instead of biopsied cells.

"There are a some diseases, like Duchenne Muscular Dystrophy for example, that make taking muscle biopsies difficult," said Bursac. "If we could grow working, testable muscles from induced pluripotent stem cells, we could take one skin or blood sample and never have to bother the patient again."

Other investigators involved in this study include George Truskey, the R. Eugene and Susie E. Goodson Professor of Biomedical Engineering and senior associate dean for research for the Pratt School of Engineering, and William Krauss, professor of biomedical engineering, medicine and nursing at Duke University.

The research was supported by NIH Grants R01AR055226 and R01AR065873 from the National Institute of Arthritis and Musculoskeletal and Skin Disease and UH2TR000505 from the NIH Common Fund for the Microphysiological Systems Initiative.

Source: Duke University

Predicting the predator threatening a squirrel by analyzing its sounds and tail movements

Thaddeus McRae poses in the Gifford Arboretum with his remote-controlled cat, after being interviewed by WSVN. Credit: University of Miami College of Arts and Sciences

Everyone has watched squirrels playfully climbing trees, gracefully leaping from branch to branch, and scurrying across parks. Thaddeus McRae, Ph.D '12, adjunct assistant research professor of biology in the University of Miami College of Arts Sciences, has taken these observations to a scientific level.

McRae studied squirrel colonies on the Coral Gables campus to see how their sounds and tail movements differ in response to different kinds of threats. He is looking to discover why squirrels interact using both vocalizations and gestures.

"These multimodal signals, which simultaneously send information via two or more sensory modalities to communicate, are ubiquitous," McRae said, adding that people and other mammals, birds, insects and spiders -- and even some plants -- communicate in this manner.

The different sounds, expressions and gestures might "reinforce each other, or maybe they contain different information, or maybe they reach different audiences," he said.

To conduct his research -- the basis of his Ph.D. dissertation -- McRae designed a unique tool: a remote-controlled cat, which he used to chase squirrels while recording their reactions to ground-based predators. Gliders painted to resemble hawks showed the squirrels' responses to threats from the air.

McRae has become somewhat of a local celebrity scientist, with recent and upcoming stories about his study appearing on the Miami New Times "Riptide" blog, and WSVN. He sees three reasons for this media attention.

Squirrels "are often most abundant in the same places people are most abundant," McRae said, adding that they're "cute and fuzzy with a bushy tail, which for some people goes a long way toward earning goodwill."

He also conducted his research in a "very public setting, outdoors on UM's campus in the middle of the city." McRae believes that this helps to breakdown the "mysterious aura" of science, "putting scientific curiosity out there where passersby can see it and become curious themselves."

Finally, he admits that "there's something a little bit humorous" about his research process and his unusual tools.

"To me, this squirrel study isn't cool because I used remote control cats, although enjoying whatever tools you use is nice, it's cool because we learned something about squirrels that we didn't know before," McRae said.

Over two years of observation McRae, working closely with Professor of Biology Steven Green, found that he could quite accurately predict what type of predator was threatening a squirrel by analyzing its sounds and tail movements.

He measured the response of three distinct squirrel sounds: the "kuk" (a short bark), the "quaa" (a longer squeal) and the "moan" (a whistling sound).

He also looked for specific patterns for tail motions in combination with these noises. The "twitch" involves a controlled movement in an arc shape, while the "flag" can take the shape of an arc, figure eight, circle or squiggle.

McRae theorizes that the squirrels use the vocal and tail alarm calls for two purposes -- to let predators know that they have been spotted, and to warn other squirrels of danger in the area. To this end, he is now conducting follow-up research to determine how squirrels react to distress signals from their peers.

For both his current study and his dissertation research, McRae has worked extensively with undergraduate research assistants.

"I try to give them a taste of various steps in the process, from thinking about the organisms and asking questions, to collecting data, to the sometimes tedious task of converting those data into analyzable form, to drawing conclusions. I share with them the joy of discovery," he said.

"Even a small, fast research project can show us something we never knew before. It may not shake the earth, but it's another tiny piece of understanding. ... For a young student to be one of the first handful of people on Earth to share even a small discovery is, frankly, freaking awesome."

Source: University of Miami