An injured heart can rarely repair itself. However, a study published in 2011 on Nature reports that a natural protein can activate stem cells in mouse hearts to replace damaged tissue with new muscle cells.
Heart muscle cells, or cardiomyocytes, are irreparably damaged by heart attack. For the heart can continue functioning properly, the damaged cells must be replaced. Heart progenitor cells - cells that can form the various tissues that make up the heart, such as blood vessels and muscle - do exist, but in adults are not active enough to repair damage. So Paul Riley at University College London Institute of Child Health and his colleagues have found a way to wake them up.
Riley and his team used a small protein called thymosin β4 (Tβ4), which is found in many tissues and regulates cell structure and mobility. He and his team injected mice with Tβ4 every day for a week, then anaesthetized the animals and stitched together one of their arteries, mimicking a heart attack. Mice survive this procedure, making it possible to study the way their hearts respond to treatment.
The researchers examined the hearts of mice at various time points after the operation. Two weeks after surgery they found some new heart cells that looked just like cardiomyocytes.
Riley and his team are still working out exactly how Tβ4 switches stem-cell genes in the heart cells back on; they think that the injury provides a trigger for the stem cells to go ahead and divide, making healthy new muscle cells. The researchers are also trying to work out what that injury signal actually is. Riley thinks that Tβ4, or another molecule of similar effect, might become a daily preventative treatment for people who have a family history of heart disease, much as cholesterol-lowering drugs and anti-clotting agents have done.
Although further experiments and clinical trials are needed to show whether Tβ4 works the same way in human hearts, and whether treatment is most effective before or after a heart injury, the scientists agree that self-repair is the best medicine for a broken heart.
[Adapted from «Stem cells patch up ‘broken’ heart» by Marian Turner, NatureNews (June 8, 2011).]