New Role Of Protein Helps "Glue" Heart Together

Researchers have looked at the role of Tbx5 in heart
development and demonstrated a novel role in epicardium.
Congenital heart defects are the most common birth defect, affecting 8 out of every 1,000 newborns according to the National Heart, Lung and Blood Institute. In the U.S., more than 35,000 babies are born annually with some sort of heart defect. In a study currently published online and appearing later this month in the journal Circulation Research, researcher looked at the role the Tbx5 protein plays in heart development. Specifically, they demonstrated a novel role for Tbx5 in the epicardium, the outermost cell layer of the heart, which is also the predecessor to the coronary vessels that supply blood and nutrients to the heart.

The job of Tbx5 is to target certain genes and regulate their function within a cell at a specific point in time. The Tbx5 protein is expressed in various cells of the heart, and existing research has shown it plays a role in the development of those cells. The protein's effects have been studied in the heart's innermost layer, the endocardium, as well its thick, middle layer,the myocardium, which is responsible for causing the heart to contract during a heartbeat. But prior to this study, the researchers say little was known about Tbx5's role in the epicardium (outermost layer) and pericardium, which makes up the heart's protective sac, and also the coronary vessels.
 
In this study, the researchers used animal models to study the effect of Tbx5 loss on development of the proepicardium, a group of cells in the embryo that give rise to the epicardium, pericardium and coronary vessels. They found that a loss of Tbx5 delayed the "gluing together" of that outer layer to the heart muscle, which can lead to deficiencies in the way the heart is formed.

The researchers note that there are several risk factors associated with abnormally formed coronary vessels, from mild heart arrhythmias to sudden cardiac death. While surgery can be an option for children with born with congenital heart defects, there is often a "second wave" of problems that can occur when those individuals become teenagers or adults.
 
Studying how Tbx5 contributes to formation of the epicardium/pericardium and coronary vessels will provide us with a new perspective on how to treat individuals with congenital heart defects.