Elisabeth Manville
May 2, 2012

Mending a broken heart with stem cells and microRNAs

Stem cells and genetics are both showing promise to heal hearts damaged by heart attack.Just like a deep wound causes a scar to form on the skin’s surface, the damage sustained during a heart attack can lead to scarring of the heart’s tissue. This scar tissue does not pump blood through the heart, putting more strain on the remaining normal muscle, leading to heart disease and failure. Currently, this condition is treated through implantable devices and, if necessary, heart transplant. In the past several years, there have been numerous studies examining the healing effects of stem cells on the heart. Earlier this year, a study tracked the success of a technique that uses a patient’s own cardiac stem cells to repair damaged heart muscle. However, the latest development in repairing damaged heart muscles does not use stem cells at all, but rather turns scar tissue into heart muscle with microRNAs.

For the new study, published Thursday in the journal Circulation Research, scientists at Duke University Medical Center created tailored microRNAs, molecules that serve as master regulators for several genes. They then delivered the microRNAs into scar tissue cells called fibroblasts, which develop after a heart attack and can impair heart function. The microRNAs successfully reprogrammed the fibroblasts to resemble cardiomyocytes, the healthy cells that make up heart muscle, in a cell culture and also in a mouse model -- an exciting step toward the technique becoming a regenerative therapy. Using microRNAs in heart regeneration could mean avoiding the drawbacks associated with other genetic methods and stem cell transplants, which have also been the subject of recent clinical trials. Genetic methods can come with complications related to genetic alterations, and stem cells can also be difficult to manage within the body.

While this technique is still in the early stages of research, a stem cell method to reduce scar tissue, which also seeks to remedy some of the problems with traditional stem cell techniques, has already been tested in humans and validated with a one-year follow-up. The procedure, developed by Eduardo Marbán of the Cedars-Sinai Heart Institute and first performed in 2009, involves harvesting a patient’s own cardiac stem cells, multiplying the cells in a lab, and then injecting them back into the patient’s heart. Among 17 patients with damaged muscle who received the treatment, there was an average of 50 percent reduction in the size of their scars after one year, with minimal complications. Eight patients who were part of the control group that received traditional post-heart-attack care showed no reduction in scar size. Because the technique uses a patient’s own cardiac cells, it eliminates most ethical dilemmas and decreases chances of rejection.

Since the microRNA technique is still in its early stages and has not yet been tested in humans, it is hard to say if it would have the same promising results as cardiac stem cell transplants in the heart. However, since it does not involve removing stem cells from a patient and injecting them back in, it could prove to be a less complicated and invasive way to mend a broken heart.