Cardiac tissue. Image credit: Fayette A Reynolds M.S. (CC0)
Cardiovascular diseases are one of the world’s biggest killers. Even for patients who survive a heart attack, recovery can be difficult. This is because – unlike some amphibians and fish – humans lack the ability to produce enough new heart muscle cells to replace damaged tissue after a heart injury. In other words, the human heart cannot repair itself.
Molecules known as messenger RNA (mRNA) carry the ‘instructions’ from the DNA inside the cell nucleus to its protein-making machinery in the cytoplasm of the cell. These messenger molecules can also be altered by different enzymes that attach or remove chemical groups. These modifications can change the stability of the mRNA, or even ‘silence’ it altogether by stopping it from interacting with the protein-making machinery, thus halting production of the protein it encodes.
For example, a protein called Mettl3 can attach a methyl group to a specific part of the mRNA, causing a reversible mRNA modification known as m6A. This type of alteration has been shown to play a role in many conditions, including heart disease, but it has been unclear whether m6A could also be important for the regeneration of heart tissue.
To find out more, Jiang, Liu, Chen et al. studied heart injury in mice of various ages. Newborn mice can regenerate their heart muscle for a short time, but adult mice lack this ability, which makes them a useful model to study heart disease.
Analyses of the proteins and mRNAs in mouse heart cells confirmed that both Mettl3 and m6A-modified mRNAs were present. The amount of each also increased with age. Next, experiments in genetically manipulated mice revealed that removing Mettl3 greatly improved tissue repair after heart injury in both newborn and adult mice. In contrast, mouse hearts that produced abnormally high quantities of Mettl3 were unable to regenerate – even if the mice were young. Moreover, a detailed analysis of gene activity revealed that Mettl3 was suppressing heart regeneration by decreasing the production of a growth-promoting protein called FGF16.
These results reveal a key biological mechanism controlling the heart’s ability to repair itself after injury. In the future, Jiang et al. hope that Mettl3 can be harnessed for new, effective therapies to promote heart regeneration in patients suffering from heart disease.
