Exosomes are key to the SOS signal that the heart muscle sends out after a heart attack. Exosomes in the bloodstream carry greatly increased amounts of heart-specific microRNAs — as seen in both mice and humans. These exosomes preferentially go to progenitor cells in the bone marrow. Inside those cells, the microRNAs turn off a specific gene that allows the progenitor cells to leave the bone marrow and travel to the heart to attempt repairs.
