According to a study conducted at Duke University Medical Centre, there could possibly be cells that may help in repairing the damaged heart muscles. It is said that humans have a dismally low ability to stimulate heart muscle cells, which may be the reason why heart attacks that kill cells and scar heart tissues are so fatal.
However, when these scientists studied the highly refined ‘Zebrafish’, they found that there could be a new dimension to clinical research and superior treatment following a heart attack.
Senior scientist Kenneth Poss is of the opinion that, “Our hearts don’t seem so complex that they shouldn’t have the capacity to regenerate.”
The study illustrates that the contribution towards the regeneration of surgically removed heart muscles was from the heart muscles known as ‘cardiomyocytes’. These cells were found near the area where the removal had taken place. To understand it further the team labeled cells in the heart and realized that cells that generated the gata4 gene upon injury finally contributed to regenerating the heart muscle.
The team initially picked a labeled ‘fluorescent reporter’ fish that had the existence of the gata4 gene required to form the heart in the developing embryo. They encountered the fact that the fluorescence was not seen in the zebrafish ventricles, but later when they clipped a small section of the heart, the population of cardiac muscle cells along the outer wall of the ventricles began to glow. A portion of the cells near the removal site began multiplying and amalgamated with the wound thus replacing the damage with a clot.
Scientist Poss adds that, “We don’t know the instructions or the mechanisms yet that mobilize these cells or cause them to proliferate, but we now know that they are the cells that are participating in new muscle growth.”
Kazu Kikuchi, a colleague of Poss retorts that finding a key origin of muscle provides an objective for studies to aide scientists make sense of cardiac muscle regeneration. He further added that by investigating this group of cells, the results expected may be used to cure human heart ailments. The team has stumbled upon several other interesting results as well.
However they still needed to understand if the new cardiomyocytes were combining in a fruitful manner for the muscle that was spared by injury. They found that within two weeks of the injury, the heart cells had started to show normal electrical coupling essential for keeping the heart beating in rhythm. A month on, the electrical coupling was similar to that in a normal heart. Poss commented that this was the first evidence to prove that cardiomyocytes do become electrically coupled. He further added that the situation now had become all the more interesting as the new muscle had to function as well as the existing one.
The study also revealed that the fish heart muscle found a way to work around scar tissue, a fact which could be of worthy importance in the context of the human heart, which obdurately scars after heart muscle dies during a heart attack. The team thought of a genetic way to operate the zebrafish to slow down the regenerative process and form cardiac scars after tissue removal, which otherwise the fish may not normally do. The scientists made the tissue from the scar by blocking a particular genetic signaling pathway and directed the activity of the pathway towards the animal to notice if regeneration could occur after the scar tissue was formed.
The operation on the fish was a success and the team observed the gata4 label in cells near the scar. They could even notice the wall being formed around the scarred tissue removal site. Posh feels that this experiment is highly relevant to many heart attack victims who have developed scars and lived with them for a long time. He also said that by allowing the regeneration to remain active post the development of the scar, there was no sign of removal of the scar tissue, but there was improvement in the tissue near the injuries.
Posh feels that there is still a lot to be learned about the mysterious regenerative abilities of animals like the zebrafish and the salamanders. The scientists want to understand the sources of all of the different cell types in the generated heart tissue and the molecular events responsible for activating those sources.
This study was published in the March 25 issue of ‘Nature’.