Study uncovers molecular events that reveal pathway toward heart disease therapy

The ability to create new healthy heart muscle cells within a patient’s own ailing heart is how scientists hope to reverse heart disease one day. Today, a new study led by UNC-Chapel Hill researchers reveals key molecular details that should be useful in developing this ambitious approach.

In the study two labs at UNC and a group at Princeton University reprogrammed ordinary cells called fibroblasts into new and healthy heart muscle cells, and recorded the changes that appear to be necessary for this reprogramming.

Commenting on the impact of their findings, Frank Conlon, PhD, professor of genetics in the UNC School of Medicine and professor of biology in the UNC College of Arts and Sciences, said: “From these studies we may be able to define pathways to increase the efficiency of fibroblast reprogramming”.

Heart disease kills more than 600,000 people each year in the United States alone and remains the leading cause of death for both men and women. It typically arises from the narrowing or blockage of coronary arteries and involves the progressive replacement of heart muscle cells (cardiomyocytes) with scar tissue, which leads to a loss of heart function and ultimately heart failure.

This progressive disease process occurs in part because cardiomyocytes have a very limited ability to proliferate and replace damaged heart muscle. Scientists have therefore been experimenting with techniques to transform fibroblasts – collagen-making cells that are abundant in the heart – into new cardiomyocytes. They have shown that they can make this therapeutic cell-reprogramming process work in the diseased hearts of lab mice, thus improving heart function. However, the process isn’t as efficient as it needs to be for clinical use, and scientists are still trying to find the reason for this.

For this study, Conlon‘s lab – in collaboration with the UNC McAllister Heart Institute lab of Li Qian, PhD, and the Princeton lab of Ileana Cristea, PhD – employed advanced techniques to map changes in protein levels in fibroblasts as they underwent reprogramming into cardiomyocytes.

They began by triggering the reprogramming using a technique based on one that Qian developed in 2012. They exposed fibroblasts to an engineered retrovirus that enters the cells and starts producing three key “transcription factor” proteins, which effectively reprogramme gene expression in the cells, causing the cells to turn into cardiomyocytes within a few days.

The researchers examined the levels of thousands of distinct proteins in the cells during the three-day transformation from fibroblasts to cardiomyocytes. In so doing, Conlon said, “We revealed a carefully orchestrated series of molecular events.”

The data suggest that the reprogramming process kicked off at about 48 hours after the viruses entered the fibroblasts and significantly affected the abundance of 23 classes of protein.

One of the most striking changes was a sharp rise in the level of a protein called Agrin, which has been found to promote repair processes in damaged hearts. Agrin also inhibits another signalling pathway called the Hippo pathway, known to be involved in regulating organ size. This finding – one of hundreds of individual clues generated by the study – raises the possibility that inhibition of Hippo signalling is needed for cardiomyocyte reprogramming.

Future studies will determine which of these myriad changes does indeed drive reprogramming and, more importantly, which changes can be enhanced to improve reprogramming efficiency.