A new study by researchers at Cornell University and the University of Bonn has found that even though stem cells can actually replace dead heart tissue after a heart attack very early in life, those same cells lose regenerative ability in adults.

The researchers, using mice as their subjects, came to the conclusion that undifferentiated precursor cells grow new heart cells in a two-day-old mouse, but not in adult mice. This finding settled a decades-old debate whether or not stem cells can play a role in the recovery of the adult mammalian heart after infarction (when heart tissue dies due to a local lack of oxygen).

Stem cells are biological cells found in all multicellular organisms. They are characterized by the ability to divide through mitosis and differentiate into diverse specialized cell types. They can self-renew to produce more stem cells.

Michael Kotlikoff, dean of Cornell’s College of Veterinary Medicine and senior author of the paper that will appear August 29th in the Proceedings of the National Academy of Sciences, said:

“While the existence of these cells in adults is controversial, if one did have fully capable stem cells in adults, why are there no new heart cells after an infarct? Whether this is due to a lack of stem cells or to something special about the infarct that inhibits stem cells from forming new heart cells is the question we addressed, taking advantage of the fact that the newborn mouse has these new cells.”

According to Kotlikoff and team, the two-day old mice were able to grow new heart cells and almost completely recover from infarction, which proved that the injury did not stop stem cells from growing new heart cells. The results also showed that adults do not have the requisite stem cells to create new heart cells, called myocytes, because when when the same procedure was carried out on them, no new heart cells formed. However, new blood vessels were created.

Kotlikoff explained that the stem cells in the adult heart “have lost the ability to become heart cells, and are only capable of forming new vessels.” At the start of life, single stem cells differentiate into all tissues, but as time goes on these cells become “developmentally restricted” or specialized to form only certain tissues.

Written by Sarah Glynn