Fixing broken hearts through tissue engineering

Talks ranged from the cutting-edge translational work of Phillippe Menasche, M.D., Ph.D., professor of thoracic and cardiovascular surgery, Paris Descartes University, to the basic biology research of Sean Wu, M.D., Ph.D., an associate professor of medicine, Stanford University School of Medicine. Menasche's work pioneers human treatment with engineered heart tissue. Wu's work opens the door to generating heart chamber-specific cardiomyocytes from human induced pluripotent stem cells, which act similarly to embryonic stem cells, having the potential to differentiate into any type of cell.

Menasche has placed engineered heart tissue derived from embryonic stem cell-derived cardiac cells onto the hearts of six heart attack patients in France in an initial safety study for this engineered tissue approach. Wu has used single-cell RNA sequencing to show 18 categories of cardiomyocytes in the heart, differing by cell type and anatomical location, even though they all derived from the same lineage.

"We are creating a new community of engineer-scientists," said Jay Zhang, M.D., Ph.D., chair and professor of the UAB Department of Biomedical Engineering. In their welcoming remarks, both Selwyn Vickers, M.D., dean of the UAB School of Medicine, and Victor Dzau, M.D., professor of medicine at Duke University School of Medicine and president of the National Academy of Medicine, spoke of the growing convergence between scientists and physicians that is leading to tremendous possibilities to improve patient care.

The tissue engineering field is moving fast.

Cardiac progenitor cells that can contribute to growth or repair injury in the heart were only discovered in 2003, says symposium presenter Michael Davis, Ph.D., associate professor of Medicine, Department of Biomedical Engineering, Georgia Tech College of Engineering and Emory University School of Medicine. In 2006, the Japanese scientist Shinya Yamanaka first showed how to transform adult cells into induced pluripotent stem cells. This potentially provides feedstock for tissue engineering using either pluripotent cells or specific progenitor cells for certain tissue lineages.

One example of the pace of change was given by Bjorn Knollman, M.D., Ph.D., professor of medicine and pharmacology at Vanderbilt University School of Medicine. Knollman noted an "ugly truth" that everyone recognized in 2013 -- that cardiomyocytes derived from induced pluripotent stem cells were nothing like normal adult cardiomyocytes in shape, size and function.

He described the improved steps like culturing the derived cardiomyocytes in a Matrigel mattress and giving them a 14-day hormone treatment that have led to derived cardiomyocytes with greatly improved cell volume, morphology and function. His take-home message: In just four years, from 2013 to 2017, researchers were able to remove the differences between induced pluripotent stem cell-derived cardiomyocytes and normal adult cardiomyocytes.

In other highlights of the symposium, Joäo Soares, Ph.D., a research scientist for the Center for Cardiovascular Simulation, University of Texas at Austin, explained how subjecting engineered heart valve tissue to cyclic flexure as it is grown in a bioreactor leads to improved quantity, quality and distribution of collagen, as opposed to tissue that is not mechanically stressed.

Sumanth Prabhu, M.D., professor and chair of the Division of Cardiovascular Disease, UAB School of Medicine, talked about the role of immune cells in cardiac remodeling and heart failure. He noted the distinct phases after a heart attack -- acute inflammation and dead tissue degradation, zero to four days; the healing phase of resolution and repair, four to 14 days; and the chronic ischemic heart failure that can occur weeks to months later. Prabhu described experiments to show how specialized spleen macrophages -- specifically marginal-zone metallophilic macrophages -- migrate to the heart after a heart attack and are required for heart repair to commence.

Nenad Bursac, Ph.D., professor of Biomedical Engineering, Duke University School of Medicine, described his advances in engineering vascularized heart tissue for repair after a heart attack. Bursac said a better understanding of how to grow the tissue from heart tissue progenitor cells has allowed formation of mature "giga" patches up to 4 centimeters square that have good propagation of heartbeat contractions and spontaneous formation of capillaries from derived-vascular endothelial and smooth muscle cells. These patches are being tested in pigs.

Duke University's Victor Dzau gave a perspective of the paracrine hypothesis over the past 15 years. In 2003, researchers had seen that applying mesenchymal stem cells to a heart attack area led to improved heart function, with beneficial effects seen as early as 72 hours. However, there was little engraftment and survival of the stem cells. Thus was born the hypothesis, which has been worked out in detail since then -- that stem cells do their work by release of biologically active factors that act on other cells, similar to the way that paracrine hormones have their effect only in the vicinity of the gland secreting it.

Joseph Wu, M.D., Ph.D., professor of radiology, Stanford University School of Medicine, showed how heart cells derived from induced pluripotent stem cells could be used to develop personalized medicine approaches for cancer patients. The problem, he explained, is that some cancer patients are susceptible to a deadly cardiotoxicity when treated with the potent drug doxorubicin. Hence, the drug has a black box warning, the strictest warning mandated by the Food and Drug Administration. Wu was able to use a library of induced pluripotent stem cell-derived cardiomyocytes to associate certain genotypes and phenotypes with doxorubicin sensitivity, in what he called a "clinical trial in a dish." From this knowledge, it will be possible to look at the transcriptome profile in patient-specific cardiomyocytes derived from induced pluripotent stem cells to predict patient-specific drug safety and efficacy, thus fulfilling the definition of precision medicine -- the right treatment at the right time to the right person.

In all, UAB's Cardiovascular Tissue Engineering Symposium included more than 30 presentations. The entire symposium will be summarized in a paper for the journal Circulation Research, expected to be published shortly, Zhang says.

Presentations of the 2015 Cardiovascular Tissue Engineering Symposium were published in the journal Science Translational Medicine, and the presentations of the 2016 Cardiovascular Tissue Engineering Symposium were published in the journal Circulation Research.