Functioning muscular tissue was first obtained from human stem cells

Researchers from Duke University, USA, have grown the first functioning muscle from stem cells derived from reprogrammed human skin cells. The new technique described in the article, which was published on January 9, 2018 in Nature Communications, will help scientists to expand the capabilities of cell therapy, and to develop individual models of rare diseases of muscle tissue for drug discovery and biological research.

New work based on the results of tests carried out in 2015, when scientists from Duke University have created the first functioning muscle tissue from human cells obtained from muscle biopsies. Now for the creation of muscles used cells that do not have a muscle origin.

“Starting with pluripotent stem cells that are not muscle cells, but can become all existing cells in our body, allows us to grow an unlimited number of myogenic progenitor cells,” – said Nenad Bursac, professor of biomedical engineering at Duke University.

“These progenitor cells resemble adult muscle stem cells called ‘satellite cells’ that can theoretically grow an entire muscle starting from a single cell.”

In his previous work Bursac and his team used samples with a small number of human myoblasts obtained by biopsy. These cells have already progressed beyond the stem cell stage but hadn’t yet become adult muscle fibers. After several passages, myoblast placed on the supporting 3D scaffolding filled with a nourishing gel, that allowed them to form functioning muscle fibers.

In present study, a team of scientists decided to use human induced pluripotent stem cells (iPSC) that were obtained by reprogramming of mature cells of non-muscle tissues, such as skin or blood, to revert to a primordial state. Further, the iPSC were cultured with the addition of Pax7 molecules that stimulate differentiation of cells into muscle cells.

As cell proliferation they became more similar to – but not quite as robust as – adult muscle stem cells. In previous studies, scientists have failed to mature functioning myocytes from these cells with “intermediate” stage of development.

Researchers from Duke University have managed to succeed after several failed attempts.

“It’s taken years of trial and error, making educated guesses and taking baby steps to finally produce functioning human muscle from pluripotent stem cells,” – said Lingjun Rao, a postdoctoral researcher in Bursac’s laboratory and first author of the study. “What made the difference are our unique cell culture conditions and 3D matrix, which allowed cells to grow and develop much faster and longer than the 2D culture approaches that are more typically used.”

Once the cells began to turn into muscle, Bursac and Rao stopped providing the Pax7 signaling molecule and started giving the cells the support and nourishment they needed to fully mature.

Scientists have shown that after two to four weeks of culturing on the 3D culture, the cells form muscle fibers that can contract and respond to external stimuli such as electrical pulses and biochemical signals that mimic the neural signals in natural muscles.

The researchers implanted the newly grown muscle fibers into adult mice and demonstrated that they successfully survive and function for at least three weeks, gradually integrating into the native tissue through vascularization.

However, artificially produced muscle is not as strong as native muscle tissue, and also falls short of the muscle grown in the previous study with cells from muscle biopsy. Despite this, researchers say that these muscles have a greater capacity compared to the previous “version” of muscle tissue.

Muscle fibers derived from iPSC, form the niche of satellite cells, which are essential to normal mature muscle to recover damages, while in the muscles from the previous study had much less satellite cells. In addition, a method based on stem cells is also capable of growing a much larger number of cells from a small initial amount in comparison with the biopsy method.

Both of these advantages indicate the possibility of using the new technique in regenerative therapies, and for creating models of rare diseases for future research and individualized health care.

“The prospect of studying rare diseases is especially exciting for us,” – said Bursac. “When a child’s muscles are already withering away from something like Duchenne muscular dystrophy, it would not be ethical to take muscle samples from them and do further damage. But with this technique, we can just take a small sample of non-muscle tissue, like skin or blood, revert the obtained cells to a pluripotent state, and eventually grow an endless amount of functioning muscle fibers to test.”

The new technique can also be used in conjunction with genetic therapy. Theoretically, researchers could fix genetic disorders in iPSC derived from a patient, and then grow small patches of completely healthy muscle. It could be used in tandem with more widely targeted genetic therapies or to heal more localized problems.