Tag Archives: #musclegrowth

Bio-inspired Scaffolds Help Promote Muscle Growth (Medicine)

Rice University bioengineers adapt extracellular matrix for electrospinning

Rice University bioengineers are fabricating and testing tunable electrospun scaffolds completely derived from decellularized skeletal muscle to promote the regeneration of injured skeletal muscle.

Their paper in Science Advances shows how natural extracellular matrix can be made to mimic native skeletal muscle and direct the alignment, growth and differentiation of myotubes, one of the building blocks of skeletal muscle. The bioactive scaffolds are made in the lab via electrospinning, a high-throughput process that can produce single micron-scale fibers.

The research could ease the burden of performing an estimated 4.5 million reconstructive surgeries per year to repair injuries suffered by civilians and military personnel.

Current methods of electrospinning decellularized muscle require a copolymer to aid in scaffold fabrication. The Rice process does not.

“The major innovation is the ability to prepare scaffolds that are 100% extracellular matrix,” said bioengineer and principal investigator Antonios Mikos of Rice’s Brown School of Engineering. “That’s very important because the matrix includes all the signaling motifs that are important for the formation of the particular tissue.”

The scaffolds leverage bioactive cues from decellularized muscle with the tunable material properties afforded through electrospinning to create a material rich with biochemical signals and highly specific topography. The material is designed to degrade as it is replaced by new muscle within the body.

Experiments revealed that cells proliferate best when the scaffolds are not saturated with a crosslinking agent, allowing them access to the biochemical cues within the scaffold matrix.

Aligned fibers produced via electrospinning can be used to form a tunable scaffold for growing new muscle, according to Rice University bioengineers. These fibers were fabricated with decellularized skeletal muscle extracellular matrix on a mandrel spinning at 3,000 rotations per minute. Courtesy of the Mikos Research Group

Electrospinning allowed the researchers to modulate crosslink density. They found that intermediate crosslinking led to better retention of fiber alignment during cell culture.

Most decellularized matrix for muscle regeneration comes from such thin membranes as skin or small intestine tissue. “But for muscle, because it’s thick and more complex, you have to cut it smaller than clinically relevant sizes and the original material properties are lost,” said Rice graduate student and lead author Mollie Smoak. “It doesn’t resemble the original material by the time you’re done.

“In our case, electrospinning was the key to make this material very tunable and have it resemble what it once was,” she said.

“It can generate fibers that are highly aligned, very similar to the architecture that one finds in skeletal muscle, and with all the biochemical cues needed to facilitate the creation of viable muscle tissue,” Mikos said.

Mikos said using natural materials rather than synthetic is important for another reason. “The presence of a synthetic material, and especially the degradation products, may have an adverse effect on the quality of tissue that is eventually formed,” he said.

“For eventual clinical application, we may use a skeletal muscle or matrix from an appropriate source because we’re able to very efficiently remove the DNA that may elicit an immune response,” Mikos said. “We believe that may make it suitable to translate the technology for humans.”

Rice University graduate students Katie Hogan, left, and Mollie Smoak prepare to fabricate a scaffold with an electrospinner. The scaffolds derived from decellularized skeletal muscle are designed to promote regeneration of injured skeletal muscle. Photo by Jeff Fitlow

Smoak said the electrospinning process can produce muscle scaffolds in any size, limited only by the machinery.

“We’re fortunate to collaborate with a number of surgeons, and they see promise in this material being used for craniofacial muscle applications in addition to sports- or trauma-induced injuries to large muscles,” she said. “These would include the animation muscles in your face that are very fine and have very precise architectures and allow for things like facial expressions and chewing.”

Co-authors of the paper are Rice graduate student Katie Hogan and Jane Grande-Allen, the Isabel C. Cameron Professor of Bioengineering. Mikos is the Louis Calder Professor of Bioengineering and Chemical and Biomolecular Engineering.

The National Institutes of Health, the National Science Foundation and the Ford Foundation supported the research.

Read the abstract at https://advances.sciencemag.org/lookup/doi/10.1126/sciadv.abg4123.

Featured image: Aligned myotubes formed on electrospun extracellular matrix scaffolds produced at Rice University. The staining with fluorescent tags shows cells’ expression of myogenic marker desmin (green), actin (red) and nuclei (blue) after seven days of growth. Courtesy of the Mikos Research Group


Provided by Rice University

The Key to Proper Muscle Growth (Medicine)

hree oscillating proteins cause new muscle cells to emerge from muscle stem cells in a balanced manner. In a paper being published in the journal “Nature Communications”, a team led by MDC researcher Carmen Birchmeier explains in detail how this process works.

When a muscle grows, because its owner is still growing too or has started exercising regularly, some of the stem cells in this muscle develop into new muscle cells. The same thing happens when an injured muscle starts to heal. At the same time, however, the muscle stem cells must produce further stem cells – i.e., renew themselves – as their supply would otherwise be depleted very quickly. This requires that the cells involved in muscle growth communicate with each other.

Muscle growth is regulated by the Notch signaling pathway

We have now provided unequivocal evidence (…) that these rhythmic fluctuations in gene expression are actually crucial for transforming stem cells into muscle cells in a balanced and controlled manner.

— Professor Dr. Carmen Birchmeier, head of Developmental Biology / Signal Transduction Lab

Two years ago, a team of researchers led by Professor Carmen Birchmeier, head of the Developmental Biology/Signal Transduction Lab at the Berlin-based Max Delbrück Center for Molecular Medicine in the Helmholtz Association (MDC), showed that the development of stem cells into muscle cells is regulated with the help of two proteins, Hes1 and MyoD, which are produced in the progenitor cells in an oscillatory manner – i.e., there are periodic fluctuations in the number of cells produced.

Both proteins are involved in the Notch signaling pathway, a widespread mechanism by which cells respond to external stimuli and communicate with other cells. The signaling pathway is named after its receptor “Notch,” onto which the ligand “Delta,” a cell surface protein, latches.

A third protein, Delta-like1, plays a crucial role

“In our current study, we have provided unequivocal evidence that oscillation in muscle tissue is not just some strange phenomenon of the cells involved, but that these rhythmic fluctuations in gene expression are actually crucial for transforming stem cells into muscle cells in a balanced and controlled manner,” says Birchmeier.

Immunofluorescence analysis of a group of proliferating stem cells associated with a muscle fiber (grey). The stem cells produce Dll1 (red) and MyoD (green). Two of the cells produces MyoG (blue): They are differentiating to form a new muscle cell. Note that the overlay of blue, green and red appears as white. © Birchmeier Lab, MDC

Together with researchers from Japan and France, Birchmeier and four other scientists at the MDC also uncovered the crucial role of a third protein that, along with Hes1 and MyoD, forms a dynamic network within the cells. As the team reports in the journal Nature Communications, this protein is the Notch ligand Delta-like1, or Dll1 for short. “It is produced in activated muscle stem cells in a periodically fluctuating manner, with the oscillation period lasting two to three hours,” Birchmeier explains, adding: “Whenever a portion of the stem cells expresses more Dll1, the amount in the other cells is correspondingly lower. This rhythmic signaling determines whether a stem cell becomes a new stem cell or develops into a muscle cell.”

The Hes1 protein sets the pace in the stem cells  

Put simply, Hes1 acts as the oscillatory pacemaker, while MyoD increases Dll1 expression.

— Dr. Ines Lahmann, Lead author of the study

In their experiments with isolated stem cells, individual muscle fibers and mice, Birchmeier and her team further investigated how the Hes1 and MyoD proteins are involved in muscle growth. “Put simply, Hes1 acts as the oscillatory pacemaker, while MyoD increases Dll1 expression,” says Dr. Ines Lahmann, a scientist in Birchmeier’s lab and a lead author of the study along with Yao Zhang from the same team. “These findings were demonstrated not only in our experimental analyses, but also in the mathematical models created by Professor Jana Wolf and Dr. Katharina Baum at the MDC,” Birchmeier says.

Experiments with mutant mice provided the decisive proof

With the help of gene-modified mice, the researchers obtained the most important evidence that Dll1 oscillation plays a critical role in regulating the transformation of stem cells into muscle cells. “In these animals, a specific mutation in the Dll1 gene causes production of the protein to occur with a time delay of a few minutes,” Birchmeier explains. “This disrupts the oscillatory production of Dll1 in cell communities, but does not alter the overall amount of the ligand.”

The mutation has severe consequences on the stem cells, propelling them to prematurely differentiate into muscle cells and fibers.

— Yao Zhang, Lead author of the study

“Nevertheless, the mutation has severe consequences on the stem cells, propelling them to prematurely differentiate into muscle cells and fibers,” reports Zhang, who performed a large portion of the experiments. As a result, he says, the stem cells were depleted very quickly, which resulted, among other things, in an injured muscle in the mice’s hind legs regenerating poorly and remaining smaller than it had been before the injury. “Quite obviously, this minimal genetic change manages to disrupt the successful communication – in the form of oscillation – between stem cells,” Zhang says.

This knowledge could lead to better treatments for muscle diseases

“Only when Dll1 binds to the Notch receptor in an oscillatory manner and thus periodically initiates the signaling cascade in the stem cells is there a good equilibrium between self-renewal and differentiation in the cells,” Birchmeier concludes. The MDC researcher hopes that a better understanding of muscle regeneration and growth may one day help create more effective treatments for muscle injuries and diseases.

Featured image: Immunofluorescence analysis of a group of proliferating stem cells associated with a muscle fiber (grey). The stem cells produce Dll1 (red) and MyoD (green). Two of the cells produces MyoG (blue): They are differentiating to form a new muscle cell. Note that the overlay of blue, green and red appears as white. © Birchmeier Lab, MDC


Literature

Yao Zhang et al: “Oscillations of Delta-like1 regulate the balance between differentiation and maintenance of muscle stem cells“, in Nature Communications, DOI: 10.1038/s41467-021-21631-4


Provided by MDC Berlin