Getting stem cells to repair a broken heart

Scientists have discovered how stem cells can be used to prevent a fatal complication of heart attacks known as ventricular tachycardias.

These disturbances of heart rhythm are the most common cause of death following a heart attack and they're caused by abnormal electrical activity in the part of the heart that's been damaged. But now, writing in this week's Nature, Bonn University researcher Wilhelm Roell and his colleagues think they know why, and how to use stem cells to prevent the problem from occurring.

To simulate the damage done by a heart attack the team used a cold probe to make small lesions in the hearts of experimental mice. The animals were then divided into two groups. In one group the damaged region of the heart was immediately injected with stem cells that had been collected from either the developing leg muscles or hearts of embryonic donor mice. To make them easy to identify the donor cells were labelled with a green dye so that the team could follow where they went in the recipient animals. A second group of animals were not injected with stem cells and were followed up as controls. The researchers then tested the susceptibility of the animals to developing potentially fatal ventricular tachycardias (VT). The problem could be provoked in 100% of the control animals and the animals that received injections of muscle stem cells, but in only 39% of the animals that had received heart stem cells, making this group of animals no more susceptible to VT than healthy mice.

When they examined the animals' hearts the team found that the heart-derived stem cells, but not the muscle stem cells, were producing high levels of a protein called connexin 43, which electrically links heart cells together. In this way the donor cells were wiring themselves into the damaged heart and producing an electrical bridge across the injured area, so that the heart rhythm could continue to be conducted normally. To prove that this was the case the researchers then used genetic techniques to make muscle stem cells that were also capable of producing connexin 43. This time, when the cells were injected, the mice were much less vulnerable to VTs. On the basis of these results the team think that this technique could be used to save lives following heart attacks. The connexin gene could be added to stem cells collected from a patient who has just suffered a heart attack, and these cells could be injected into the injured heart, helping to ensure that it remains electrically stable.