Scientists from the Gladstone Institutes have done it again. They’ve made a better and faster way of generating healthy heart tissue in mice with damaged hearts. With further advancements, their findings could potentially be translated into a new way of treating heart failure in patients.
Previously, the Gladstone team discovered that they could transform scar tissue in the damaged hearts of mice into healthy, beating heart muscle cells by a process called direct reprogramming. The team found that turning on three transcription factors, Gata4, Mef2c and Tbx5 (collectively called GMT), in the damaged hearts of mice activated heart genes that turned scar tissue cells, also known as cardiac fibroblasts, into beating heart cells or cardiomyocytes.
Their GMT direct cardiac reprogramming technology was only able to turn 10 percent of cardiac fibroblasts into cardiomyocytes in mice over the period of six to eight week. In their new CIRM-funded study published in Circulation, they improved upon their original reprogramming method by identifying two chemicals that improved the efficiency of making new heart cells. Not only were they able to create eight times the number of beating cardiomyocytes from mouse cardiac fibroblasts, but they were also able to speed up the reprogramming process to a period of just one week.
To find these chemicals, they screened a library of 5,500 small molecules. The chemicals that looked most promising for cardiac reprogramming were inhibitors of the TGF-β and WNT signaling pathways. The importance of these chemicals was explained in a Gladstone news release:
“The first chemical inhibits a growth factor that helps cells grow and divide and is important for repairing tissue after injury. The second chemical inhibits an important pathway that regulates heart development. By combining the two chemicals with GMT, the researchers successfully regenerated heart muscle and greatly improved heart function in mice that had suffered a heart attack.”
Senior author on the study, Deepak Srivastava, further explained:
“While our original process for direct cardiac reprogramming with GMT has been promising, it could be more efficient. With our screen, we discovered that chemically inhibiting two biological pathways active in embryonic formation improves the speed, quantity, and quality of the heart cells produced from our original process.”
Encouraged by their studies in mice, the scientists also tested their new and improved direct reprogramming method on human cells. Previously they found that while the same GMT transcription factors could reprogram human cardiac fibroblasts into cardiomyocytes, a combination of seven factors was required to make quality cardiomyocytes comparable to those seen in mice. But with the addition of the two inhibitors, they were able to reduce the number of reprogramming factors from seven to four, which included the GMT factors and one additional factor called Myocardin. These four factors plus the two chemical inhibitors were capable of reprograming human cardiac fibroblasts into beating heart cells.
With heart failure affecting more than 20 million people globally, the need for new therapies that can regenerate the heart is pressing. The Gladstone team is hoping to advance their research to a point where it could be tested in human patients with heart failure. First author on the study, Tamer Mohamed, concluded:
“Heart failure afflicts many people worldwide, and we still do not have an effective treatment for patients suffering from this disease. With our enhanced method of direct cardiac reprogramming, we hope to combine gene therapy with drugs to create better treatments for patients suffering from this devastating disease.”