Duke University Tissue Engineering Team Grows Self-Healing Muscle in Laboratory

Scientists have grown living muscle in the lab. While this is nothing new, this new advance has succeeded in making muscle that not only looks and works like genuine skeletal muscle, but also heals by itself, which is a significant advance in the field of tissue engineering.

This ultimate goal of this research is to use lab-grown muscle repair muscle damage in human patients. To date, preclinical trials have shown that lab-grown muscle properly regenerated damaged muscle in laboratory mice.

This research comes from Duke University, and the research team responsible for this work thinks that their success was due to the culture environment that they have created to grow muscle in the laboratory. Their well-developed contractile muscle fibers also contained a pool of satellite cells, which are an immature stem cell population in skeletal muscle that are activated when the muscle is damaged. Satellite cells can divide and differentiate into normal muscle tissue in order to heal muscle damage.

Cultured Muscle

Laboratory tests showed that the lab-grown muscle was as strong and good at contracting as muscle isolated from living organism. Also, the laboratory-grown muscle was able to use its satellite cell population to repair itself when the muscle was damaged with toxic chemicals.

Muscle satellite cells

When it was grafted into laboratory mice, the muscle properly integrate into the rest of the surrounding tissue and functioned beautifully when called upon to do so.

The Duke team, however, stresses that more tests must be conducted before this work can be translated into human patients.

The lead researcher for this work, Nenad Bursac, Associate Professor of Biomedical Engineering at Duke University, said: “The muscle we have made represents an important advance for the field. It’s the first time engineered muscle has been created that contracts as strongly as native neonatal [newborn] skeletal muscle.”

UK expert in skeletal muscle tissue engineering Prof Mark Lewis, from Loughborough University, said: “A number of researchers have ‘grown’ muscles in the laboratory and shown that they can behave in similar ways to that seen in the human body. However, transplantation of these grown muscles into a living creature, which continue to function as if they were native muscle has been taken to the next level by the current work.”

Tissue engineering seeks to use stem cells to fashion new organs and tissues from cultured stem cells. Tissue engineering and stem cell biology will certainly transform regenerative medicine, and in many ways it is already doing so. Scientists have already made mini-livers and kidneys in the lab using stem cells, and others are using stem cells to heal damaged heart muscles. Even though some cures and treatments are still some years away, advances continue to pile up. The future of medicine is upon us.

Pluristem’s Phase I/II Muscle Injury Trial Shows that Placental Stem Cells Augment Muscle Healing After Surgery

Pluristem Therapeutics Inc. a leading developer of placenta-based cell therapies, has announced top-line results from its Phase I/II clinical trial that accesses the safety and efficacy of PLacental eXpanded (PLX-PAD) cells in the treatment of muscle injury. This clinical trial showed that PLX-PAD cells were safe and effective. These results provide evidence that PLX cells may be efficacious in the treatment of orthopedic injuries including muscles and tendons.

This Phase I/II trial was a randomized, placebo-controlled, double-blinded study conducted at the Orthopedic Clinic of the Charité University Medical School under the auspices of the Paul-Ehrlich-Institute (PEI), Germany’s health authority. The injured muscle studied was the gluteus medius muscle in the buttock. Hip-replacement patients undergo a surgical procedure that injuries the gluteus medius muscle healing of this muscle after hip replacement surgery is crucial for joint stability and function.

Gluteal Muscles

The 20 patients in the study were randomized into three treatment groups. Each patient received an injection in the gluteal muscle that had been traumatized during surgery. One group was treated with 150 million PLX-PAD cells per dose (n=7), the second was administered 300 million PLX-PAD cells per dose (n=6), and the third received placebo (n=7).

The primary safety endpoint was clearly met since no serious adverse events were reported at either dose level. The study showed that PLX-PAD cells were safe and well tolerated.

The primary efficacy endpoint of the study (how well the stem cells worked) was the change in maximal voluntary isometric contraction force of the gluteal muscle at six months after surgery. Efficacy was shown in both PLX-PAD-treated patient groups. The group that received a dose of 150 million cells showed a statistically significant 500% improvement over the placebo group in the change of the maximal contraction force of the gluteal muscle (p=0.0067). Patients who received the lower dose (300 million cells) showed a 300% improvement over the placebo (p=0.18).

An analysis of the overall structure of the gluteal muscle using magnetic resonance imaging (MRI) indicated an increase in muscle volume in those patients treated with PLX-PAD cells versus the placebo group. The patients who had received the 150 million cell dose displayed a statistically significant superiority over the placebo group. Patients treated at the 150 million cell dose showed an approximate 300% improvement over the placebo in the analysis of muscle volume (p=0.004). Patients treated at the 300 million cell dose showed an approximate 150% improvement over the placebo in the change of muscle volume (p=0.19).

The study’s Senior Scientist, Dr. Tobias Winkler of the Center for Musculoskeletal Surgery, Julius Wolff Institute Berlin, Charité – Universitaetsmedizin Berlin, Germany, commented, “I am very impressed with the magnitude of the efficacy results seen in this trial. PLX cells demonstrated safety and suggested that the increase in muscle volume could be a mechanism for the improvement of contraction force.”

Zami Aberman Chairman and CEO stated, “This was a very important study not only for Pluristem but for the cell therapy industry in general. The study confirms our pre-clinical findings that PLX-PAD cell therapy can be effective in treating muscle injury. Having a statistically significant result for our primary efficacy endpoint is very encouraging and consistent with our understanding of the mechanism of action associated with cell therapy. Based on these results, we intend to move forward with implementing our strategy towards using PLX cells in orthopedic indications and muscle trauma.”

Using Stem Cells for Muscle Repair

Stem cell treatments for muscular dystrophy and other degenerative diseases of muscle might be a realistic possibility, since scientists have discovered protocols to make muscle cells from human pluripotent stem cells.

Tiziano Barberi, Ph.D., chief investigator in the Australian Regenerative Medicine Institute (ARMI) at Monash University in Clayton, Victoria, and Bianca Borchin, a graduate student in the Barberi laboratory, have developed techniques to generate skeletal muscle cells. Barberi and Borchin isolated muscle precursor cells from human pluripotent stem cells (hPSCs), after which they applied a purification technique that allows these cells to differentiate further into muscle cells.

Pluripotent stem cells, such as embryonic stem cells (ESCs) or induced pluripotent stem cells (iPSCs), have the ability to become any cell in the human body, including skeletal muscles, which control movement. Once the stem cells begin to differentiate, controlling that process is very challenging, but essential in order to produce only the desired cells. Barberi and Borchin used a technique known as fluorescence activated cell sorting (FACS) to identify those cells that contained the precise combination of protein markers that are expressed in muscle precursor cells. FACS also enabled them to successfully isolate those muscle precursor cells.

“There is an urgent need to find a source of muscle cells that could be used to replace the defective muscle fibers in degenerative disease. Pluripotent stem cells could be the source of these muscle cells,” Dr. Barberi said. “Beyond obtaining muscle from hPSCs, we also found a way to isolate the muscle precursor cells we generated, which is a prerequisite for their use in regenerative medicine.”

Borchin said there were existing clinical trials based on the use of specialized cells derived from hPSCs in the treatment of some degenerative diseases, but deriving muscle cells from pluripotent stem cells proved to be challenging. “These results are extremely promising because they mark a significant step towards the use of hPSCs for muscle repair,” she said.

“The production of a large number of pure muscle precursor cells does not only have potential therapeutic applications, but also provides a platform for large-scale screening of new drugs against muscle disease,” Dr. Barberi added.

This study was published early online Nov. 27 in Stem Cell Reports.  This study does not address the immune response against dystrophin that has plagued gene therapy and stem cell-based muscular dystrophy clinical trials that has been noted in previous posts.  The use of embryonic stem cells, in particular, would create muscles that are not tissue matched to the patient and would generate robust inflammation against the implanted muscles.   Thus embryonic stem cells would generate a “cure” that would be much worse than the disease itself.  Nevertheless, adapting the Barberi-Borchin protocol to induced pluripotent stem cells would produce skeletal muscle cells that are tissue matched to the patient.

Allergy-Associated White Blood Cell Triggers Stem Cell-Mediated Muscle Repair

White blood cells help our bodies ward off invasions from microorganisms, but they serve other purposes too. Once white blood cell in particular, the “eosinophil” helps us when we are infected by multicellular parasites (worms and the like). Eosinophils, however, also play a more unpleasant role, and that is in allergies. When we suffer from allergies, eosinophils multiply and move to our lungs and other places, where they mediate inflammation and tissue damage. Thus eosinophils are the white blood cells we all love to hate.

However, researchers at the University of California, San Francisco (UCSF) have generated new data that, in their view, suggests that eosinophils also play an integral role in muscle regeneration.

Ajay Chawla, Associate Professor at the Cardiovascular Research Institute at UCSF and


lead researcher for this study, said, “Eosinophils are needed for the rapid clearance of necrotic debris, a process that is necessary for timely and complete regeneration of tissues.”

Chawla’s laboratory showed that eosinophils serve double duty when it comes to muscle repair. First, they remove the cellular debris that results from damaged tissues. Secondly, eosinophils secrete a protein called “Interleukin 4” or IL-4. IL-4 triggers a specific type of stem cell to replicate and repair muscle tissue.


According to Chawla, “Without eosinophils you cannot regenerate muscle.”

These eosinophil-activated stem cells are known as “fibro/adipogenic progenitors” (FAP). Until recently, the general thinking surrounding FAPs was that they could only form fat tissue (see Natarajan A., Lemos DR, and Rossi FM, Cell Cycle 2010 9(11): 2045-6).  However, when FAPs are exposed to IL-4, they begin to differentiate into muscle fibers.

“They wake up the cells in muscle that divide and form muscle fibers,” said Chawla

“Bites from venomous animals, many toxicants, and parasitic worms all trigger somewhat similar immune responses that cause injury. We want to know if eosinophils and FAPs are universally employed in these situations as a way to get rid of debris without triggering severe reactions such as anaphylactic shock,” said Chawla.