Biowire Technology Matures Stem Cell-Derived Heart Cells

Heart research has taken yet another step forward with the invention of a new technique for maturing human heart cells in culture.

Researchers from the University of Toronto have created a fast and reliable method of creating mature human heart muscle patches in a variety of sizes. This technique applies pulsed electric current to the cells that mimics the heart rate of fetal humans.

Milica Radisic, an associate professor at the Institute of Biomaterials and Biomedical Engineering (IBBME), explained the significance of her new discovery: “You cannot obtain human cardiomyocytes (heart cells) from human patients.” However heart cells are vitally important for testing the safety and efficacy of heart drugs, and because human heart muscle cells do not normally divide robustly and form large swaths of heart tissue in culture, finding enough human heart tissue for pharmacological and toxicological test tests has been rather difficult. Tho circumvent this problem, researchers have been using heart muscle cells made from induced pluripotent stem cells (iPSCs). Unfortunately, once these cells are differentiated into heart muscle cells, they form highly immature heart muscle cells that beat too fast to work as a proper model system for adult human heart cells.

As Radisic put it: “The question is, if you want to test drugs or treat adult patients, do you want to use cells that look and function like fetal cardiomyocytes? Can we mature these cells to become more like adult cells?”

Radisic and her co-workers designed the “biowire” culture system for stem cell-derived cardiomyocytes. This system can mature heart muscle cells in culture in a reliable and reproducible manner.

The technique seeds human heart muscle cells along a silk suture, much like the kind used to sew up patients after surgery. The suture directs cells to grow along its length, after which they a treated to cycles of electric pulses. The biowire provides the pulses and acts like a stripped-down pacemaker. The biowire induces the heart muscle cells to increase in size and beat like more mature heart tissue. However the manner in shich the pulses are applied turns out to be very important. Radisic and her team discovered that if the cells were ramped up from zero pulses to 180 pulses per minute to 360 beats per minute, it mimicked the conditions that occur naturally in the developing heart. The fetal heart increases its heart rate prior to birth, and by ramping up the rate at which the pulses were delivered, Radisic and her team exposed the heart cells to the same kind of environment they would have experienced in the fetal heart.

“We found that pushing the cells to their limits over the course of a week derived the best effect,” said Radisic.

Growing the cells on sutures brings an added bonus: They can be sewn directly into a patient, which makes the biowires fully transplantable. Also, the cells can be grown on biodegradable sutures as well, which has practical implications for health care.

“With this discovery we can reduce the costs on the health care system by creating more accurate drug screening.” This discovery brings heart research one step closer to viable heart patches for replacing dead areas of the heart.

The paper’s first author, Sarah Nunes, said this: “One of the greatest challenges of tgransplanting these patches is getting the cells to survive, and for that they need blood vessels. Our next challenge is to put the vascularization together with cardiac cells.” Nunes is a cardiac and a vascular specialist.

Radisic enthusiastically labeled the new technique as a “game changer” in the field of cardiac medicine and it is a sign of how far the field has come in a very short time.

“In 2006 science saw the first derivation of induced pluripotent stem cells from mice. Now we can turn stem cells into cardiac cells and make relatively mature tissue from human samples, without ethical concerns.”

The vascularization part of this should be rather easy, since bone marrow-derived endothelial progenitor cells (EPCs) have been shown to make blood vessels in the heart. Putting these together with the heart patch should provide a winning combination

Inching toward human trials, but definitely making progress!!

Manipulation of a Master Molecular Switch Called 190RhoGAP May Improve Stem Cell Treatment Of Heart Attacks

New research findings have provided vitals clues as to why heart-based stem cells differentiate into muscle or blood vessels. Such a discovery might hold the key to better treatments for heart attacks in the future.

Human heart tissue lacks the capacity to heal after a heart attack and instead of reforming heart muscle; it tends to form a non-contracting heart scar. Stem cells in the heart can augment the healing process and direct the heart to make heart muscle and blood vessels rather than scars, but why this does not normally occur is unclear.

Particular physicians and their colleagues have shown that introducing heart stem cells into the heart can reduce the formation of heart scar tissue and increase the regeneration of heart muscle. However, uncovering the molecular switch that directs the fate of these cells could result in even more effective treatments for heart patients.

A recent report has shown that scientists who have manipulated a protein called “p190RhoGAP” managed to direct the differentiation of cardiac stem cells to become either blood vessels or heart muscle. Members of this research group even said that altering levels of this protein can affect the activities of these stem cells.

Andre Levchenko, a biomedical engineering professor who supervised the research effort said: “In biology, finding a central regulator like this is like finding a pot of gold.” The lead author of this paper, Kshitiz, said, “Our findings greatly enhance our understanding of stem cell biology and suggest innovative new ways to control the behavior of cardiac stem cells before and after they are transplanted into a patient. This discovery could significantly change the way stem cell therapy is administered in heart patients.”

Earlier in 2012, a medical team at Cedars-Sinai Medical Center in Los Angeles, CA reported reductions of scar tissue in heart attack patients after harvesting some of the patient’s own cardiac stem cells, growing more of these cells in the lab and then transfusing them back into the patient. Using the stem cells from the patient’s own heart prevented the rejection problems that often occur when tissue is transplanted from another person.

The goal of Levchenko’s research is to determine what directs the stem cells, at the molecular level, to change into helpful heart tissue. Answering this question could improve the results from experiments like the one done at Cedars-Sinai and boost regeneration in the heart after a heart attack to an even greater degree.
Levchenko’s team (from Johns Hopkins) tried to change the surface upon which they grew the harvested cardiac stem cells. Surprisingly, growing the cells on a surface that had a similar rigidity to that of heart tissue caused the stem cells to grow faster and to form blood vessels. The increase in growth was substantially greater than that observed with any other protocol with regard to these stem cells. The increased population growth on such a medium also gave prominent hints as to why the formation of a cardiac scar (a structure with very different rigidity), can inhibit stem cells that reside there from regenerating the heart.

By digging further into this phenomenon, the Johns Hopkins group found that the increased cell growth under these conditions was due to decreases in the levels of a protein called p190RhoGAP. This same molecule, when absent, could also direct stem cells to form blood vessels.
Levchenko explained: “It was the kind of master regulator of this process. And an even bigger surprise was that if we directly forced this molecule to disappear, we no longer needed the special heart-matched surfaces. When the master regulator was missing, the stem cells started to form blood vessels, even on glass.”

When Levchenko’s group artificially increased levels of 190RhoGAP, the stem cells formed heart muscle. According to Levchenko, “The stem cells started to turn into cardiac muscle tissue, instead of blood vessels. This told us that this amazing molecule was the master regulator not only of the blood vessel development, but that it also determined whether cardiac muscles and blood vessels would develop from the same cells, even though these types of tissue are quite different.”

Can such findings make a difference in the treatment of living beings? To get a handle on the clinical consequences of this finding, Levchenko’s group limited the production of p190RhoGAP in cardiac stem cells not within a culture dish, but inside the heart of a living animals. The cells with less 190RhoGAP integrated more smoothly into an animal’s blood vessel networks in the aftermath of a heart attack. Also, more of these transplanted heart cells survived, compared to what had occurred in earlier cell-growing procedures.

Kshitiz said that the special heart-like surface on which the cardiac stem cells were grown triggers regulation of the master molecule, and this then guides the next steps in differentiation.

“This single protein can control the cells’ shape, how fast they divide, how they become blood vessel cells and how they start to form a blood vessel network,” he said. “How it performed all of these myriad tasks that require hundreds of other proteins to act in a complex interplay was an interesting mystery to address, and one that rarely occurs in biology. It was like a molecular symphony being played in time, with each beat placed right at the moment before another melody has to start.”
See Matrix Rigidity Controls Endothelial Differentiation and Morphogenesis of Cardiac Precursors;” Kshitiz et al; Science Signaling, 2012; 5 (227): ra41 DOI: 10.1126/scisignal.2003002.