Heart disease is the world’s leading cause of death. More than 650,000 people in the United States alone die from the condition every year. Compounding that loss of life is the economic impact, which is measured in the hundreds of billions.
Heart failure, which often follows a heart attack, occurs when the heart is unable pump sufficient volumes of blood to the rest of body. That diminished pumping power can be felt in the organ and traced all the way down to the protein level.
Cardiac muscle contraction is generated by interactions between actin and myosin, proteins that enable movement at the molecular level by converting energy-rich molecules of ATP into muscle power. ISCRM faculty member Mike Regnier PhD studies how dATP (a natural variant of ATP) can be used to promote stronger heart function. In recent years, Regnier and his team have shown how small changes in protein structure translate to improvements in performance at multiple scales – specifically, at the whole muscle, muscle cell, and the molecular levels.
Now Regnier, who is the Director of the UW Medicine Center for Translational Muscle Research, has received a four-year, $3.3 million NIH grant that will help him and his collaborators in the Murry Lab translate these discoveries into new ways to help patients recover from heart attacks – and avoid the often-fatal consequences of heart disease.
In his lab, Regnier is pursuing a two-pronged approach to treating injured hearts by stimulating the body to generate increased quantities of dATP. One strategy involves using gene therapy to create more of the enzyme that produces dATP. The approach, which is the focus of the grant, uses a combination of gene-editing and stem cell technologies to accomplish the same goal.
The work of healing hearts is done by what Regnier calls small molecule factory and delivery cells. “We engineer stem cells to manufacture the enzyme that makes the dATP. These cells are differentiated into cardiac muscle cells, then transplanted into the heart, where they deliver the nucleotides into the heart muscle.” Regnier adds that insights his team gained from designing the vectors used in the experimental gene therapy influenced the design of the stem cells used in the cell therapy.
At the same time, researchers led by ISCRM Director Chuck Murry, MD, PhD, have demonstrated in large animal models that cardiomyocytes derived from human stem cells can help regenerate damaged or lost heart muscle tissue – a promising therapy that is moving toward human clinical trials.
Regnier explains that the gene edits designed to supercharge dATP production will dovetail with the cell therapy led by the Murry Lab. “This is a way for our labs to make an even better cell. We’re delivering a molecule that will help lead to regeneration and greater gains in function for the heart, which means greater overall recovery for the patient.”
The grant will also fund a collaborative effort by the Regnier Lab and its research partners to understand the complex molecular mechanisms by which dATP increases contractility. This undertaking is based on the premise that the effects of heart failure span many spatial and temporal scales, a holistic, multi-scale research strategy is the best way to develop the next generation of therapeutics.
Using CTMR capabilities, the researchers will perform computational modeling at the protein, cell, and organ levels. The team will also use X-ray diffraction of heart muscle, conducted at the Argonne National Laboratory, to reveal how dATP affects the shape of the myosin protein and high-resolution microscopy in collaboration with investigators at the University of Kent in the UK to determine how dATP affects the complex interaction of proteins in the contractile units of heart muscle.
Three floors up from the Regnier Lab and the CTMR, an effort is underway with ISCRM colleague David Mack, PhD, Associate Professor of Rehabilitation Medicine, to understand and treat a very different group of muscle disorders. Known collectively as congenital contractures, these rare but devastating conditions occur during embryonic development when a mutation in one subtype of myosin impedes fetal muscles to have difficulty relaxing. Depending on the severity of the disease, sustained muscle contraction can cause babies to be born with curved bones, leading to severe mobility impairments.
The current research builds on a long-standing partnership between Regnier and Mike Bamshad, MD, a Professor of Pediatrics, and a physician at Seattle Children’s Hospital. Over the last decade, Bamshad’s team made pioneering discoveries that aided in the diagnosis of different subtypes of congenital contractures and identified the underlying causes. One of the goals of this three-way partnership is to have information flow from the clinic into the laboratory and back to the patients as quickly as possible.
Babies born with one subtype called Freeman Sheldon Syndrome (FSS), have contractures of the hands and feet, contracted facial muscles and eye alignment problems. To create a model of the disease in the laboratory, Christian Mandrycky, PhD, a postdoc co-mentored by Regnier and Mack, has created a line of patient-derived stem cells and is using CRISPR gene-editing technology to engineer a line of FSS mutation-bearing stem cells that differentiate into skeletal muscle, representing two ways to generate insights that could someday help patients.
“A core challenge in studying FSS is that the disease-causing mutation is very active during embryonic development but is more or less dormant in adult tissue,” says Mandrycky. “By using stem cells to model this embryonic phase of muscle development, it gives us the unique opportunity to study these mutations during the period when they’re most damaging and possibly most susceptible to intervention.”
Once differentiated, the stem-cell derived skeletal muscle can then be tested using the wide array of tools available through the CTMR. These let researchers compare the performance of muscle across length scales. “From single molecules, all the way up to engineered or intact tissue, we can see how mutations impact the function of muscle in a very granular way,” Mandrycky explains. Using these tools, the team has shown FSS mutated skeletal muscle cells relax more slowly than wild-type cells without the mutation.
Sophisticated technology is also helping the researchers isolate precisely how the myosin mutation leads to muscle weakness and contractures. Saffie Mohran, a Bioengineering Ph.D. student in the Regnier Labs and Mack Labs, specializes in the study of myofibrils, the smallest organelle of contraction that powers contraction and relaxation. Using a force-testing rig, Mohran can directly measure the effect of the mutation on the contractile machinery that fails in FSS patients.
“Understanding what mechanisms are impacted by the mutations provides us with information on how to treat it,” says Mohran. “Once we identify how the underlying mechanisms impact contractile function, we can begin researching potential therapeutics to treat and/or reverse the expressed phenotype.”
The ultimate goal is to use the stem cell-derived skeletal muscle created in the Mack Lab as a platform to discover new drugs that correct the underlying defect as early as possible during fetal development.
“The genetics of FSS present a big challenge because the mutant myosin disrupts normal muscle contraction and relaxation,” says Mack. “So doing simple gene replacement, like we’ve done for myotubular myopathy, won’t work for this disease. And fixing the myosin mutation by CRISPR gene editing faces a delivery problem because it is difficult to get the editing machinery into enough fetal muscle to make a difference.”
However, an alternative therapy designed by computational modeling holds promise. Matt Childers, PhD, a postdoc in the Regnier and Mack labs who is sponsored by the CTMR, has mathematically modeled myosin and identified the deficiencies in myosin motors caused by FSS mutations. “Myosin mutations are like tiny monkey wrenches thrown in a microscopic motor,” says Childers. “The computational models developed in the CTMR are one of the best ways for us to directly visualize the consequences of a mutation.”
These computational models help the investigators better interpret their experiments by providing detailed ‘blueprints’ that explain why the mutation causes the dysfunction at the molecular and atomic scale. Pinpointing the molecular origins of myosin motor dysfunction brings researchers one step closer to designing custom therapeutic molecules that might correct the mutation.
In addition, these computational models can provide a rapid means of screening potential molecules to select the best candidates for therapeutic development. Sequencing in the ISCRM Genomics Core and small-molecule screening in the Quellos High Throughput Screening Core will also provide vital data.
The CTMR is not just accelerating muscle research at UW Medicine by encouraging collaboration and providing access to world-class equipment and expertise. The center also seeds promising research through a pilot grant program that helps investigators gather preliminary data needed for federal grants.
In 2020, ISCRM faculty member Farid Moussavi-Harami, MD, an Assistant Professor, Division of Cardiology, received a CTMR pilot grant to study how genetic mutations impacted contractile force in the hearts of mice. That funding, combined with a Collaborative Science Award from the American Association, allowed Moussavi-Harami and his research partners to receive a five-year, $3.3 million R01 grant from the NIH to pursue personalized treatments for genetic heart diseases.
Joining Moussavi-Harami on the research team are ISCRM faculty members Jen Davis, PhD, Associate Professor, Lab Medicine and Pathology and Bioengineering, Nate Sniadecki, PhD, Professor of Mechanical Engineering, and Tom Daniel, Professor of Biology. Davis and Sniadecki are also Associate Directors of ISCRM.
The researchers are particularly interested in the mechanisms that underpin hypertrophic cardiomyopathy (HCM) and dilated cardiomyopathy (DCM), two genetic conditions that can appear at any stage of life and fatally disrupt the heart’s ability to pump blood. As a practicing cardiologist, Moussavi-Harami is especially aware of the need for more effective preventions and treatments for HCM and DCM.
“Over the last few years, the field has begun to recognize the importance of genetics in heart failure. Our goal is to harness the technology we have available to today to look for patterns in the mutations that cause cardiomyopathies and then to use that information to develop personalized treatments that match an individual patient’s genetic profile.”
Tapping into technology in ISCRM and CTMR computational/quantitative, and mechanical cores, the researchers will use computers to simulate batches of genetic variants that impair heart functioning and to predict the best treatment to restore normal cardiac force generation. The results produced by simulations will then be validated in stem cell and mouse models.
Moussavi-Harami stresses that the time is right for study of the mutations that contribute to cardiomyopathies. “Advances in genetic screening and gene editing mean we can accurately separate benign variants from dangerous ones, which helps us detect and treat problems earlier using the best strategies for each patient.”
While technology is a major driver of the research Moussavi-Harami says the grant, itself would not have been possible without the collaborative spirit of ISCRM and the CTMR. “This is very team-focused effort. It’s a referendum on the institute and the research environment it encourages. As a physician and now an independent researcher, I’m also grateful for the culture of mentorship that supported me throughout the grant process. ”