Duchenne muscular dystrophy (DMD) is a severe degenerative muscle disease caused by mutations in the gene that encodes dystrophin, a protein essential for the strength and durability of muscle fibers.
Onset of DMD, which affects about one in 3,500 male births, occurs in early childhood and leads steadily to lost mobility and life-threatening heart and diaphragm weakness. The average life-expectance for people with DMD is 27-30 years and the best therapies can only alleviate symptoms and slow progression of the disease.
Right now, researchers at the Institute for Stem Cell and Regenerative Medicine (ISCRM) are developing gene therapy strategies to deliver functional, miniaturized versions of dystrophin to degenerating muscle in boys with DMD. The efficacy and safety of that treatment is now being evaluated in several clinical trials.
One common cause of death among DMD patients is heart failure. The disease wears down the ability of the heart to beat with enough force to pump blood throughout the body.
Researchers who hope to study exactly how DMD leads to cardiomyopathy – and to design safe, effective treatments that alleviate the problem – need modeling tools that accurately recreate what is happening to the heart cells. While scientists can recapitulate the muscle-wasting effect of DMD in mice, small rodents exhibit only minor signs of heart disease until they are older than human patients would be.
Induced pluripotent stem cells (iPSC) also allow researchers to study DMD and other diseases. iPSC-derived cardiomyocytes are human tissue, which means they can reveal insights mouse cells cannot, but cardiomyocytes in 2D tissue cultures do not mature the same they would in their natural environment, limiting their usefulness as DMD disease models.
Now, a team of investigators led by ISCRM faculty members David Mack, PhD and Nate Sniadecki, PhD have shown that is possible to recreate DMD with much more complexity in a 3D model of engineered heart tissue, making it a reliable preclinical modeling tool to study cardiomyopathy associated with the disease. The research appears in the Journal of Tissue Engineering.
Mack is an Associate Professor of Rehabilitation Medicine. Sniadecki is a Professor Mechanical Engineering and an Associate Director of ISCRM. The first author of the paper is Samantha Bremner, a PhD student in the Mack and Sniadecki Labs. The article follows a May 2022 review, authored by Bremner, and published in Current Cardiology Reports, that explores the potential of novel drug testing platforms to address shortcomings in the existing drug discovery protocols.
“This investigation is another example of the progress we can make through multidisciplinary collaboration,” says Mack. “By pairing advances in engineering with specialized stem cell-based modeling, we are helping to open the door to new research technologies that we hope will make an impact on DMD patients.”
The study published this month paired two innovative technologies. First, stem cells engineered by the Mack Lab to study neuromuscular diseases like DMD were differentiated into heart cells with a dystrophin mutation. Second, a sophisticated system designed by the Sniadecki Lab to measure the force of engineered heart tissues enabled the researchers to precisely measure how DMD impacts heart contraction.
In the study, the cardiomyocytes were encapsulated in a soft hydrogel environment and strung between two posts – one flexible, and one rigid. As the cells remodel their environment, they align themselves from one post to the other and beat synchronously. The researchers record these contractions, which helps them calculate the amount of force being produced.
Bremner explains the novelty of the study. “This is the first paper to fully demonstrate a multifaceted dystrophic phenotype in a three-dimensional engineered tissue that recapitulates how DMD affects the complex factors involved in heart functioning, including contraction, force kinetics, calcium transients, and beat interval.”
The 3D tool enables close study of another factor, says Bremner. “It was thought that DMD occurred because without the dystrophin protein, cell membranes become fragile and shred when muscles contract. We now are learning that abnormal calcium levels also contribute to the disease. Our system uses fluorescent dyes that change in brightness depending on calcium levels.”
In addition to yielding a more detailed picture of the damage DMD does to the heart, the 3D technology described in the paper would also offer greater efficiency for researchers. Stem cell-derived tissue can be engineered faster than animal models and represents a more rapid, human, and high-throughput option for screening drug candidates and gene therapies.
Bremner believes this system could be integrated into the drug development process to increase confidence in potential therapies making their way through preclinical stages by screening for cardiotoxicity, immunogenicity, and other off-target effects before human patients are involved. “I’ve been working on this for four years. It’s very gratifying to contribute a tool that useful for the field of cardiac disease modeling and engineering.”
The next step is to further validate the tool by using it to screen a variety of micro dystrophin gene therapies for DMD.