Stem cells repair hearts early in life, but not in adults

ScienceDaily (July 30, 2012) Stem cells can actually replace dead heart tissue after a heart attack very early in life -- but those same cells lose that regenerative ability in adults, according to researchers at Cornell University and the University of Bonn.

The study, using mice as subjects, found that undifferentiated precursor cells grow new heart cells in a two-day-old mouse, but not in adult mice, settling a decades-old controversy about whether stem cells can play a role in the recovery of the adult mammalian heart following infarction -- where heart tissue dies due to artery blockage.

"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 cells," said Michael Kotlikoff, dean of Cornell's College of Veterinary Medicine and senior author of the paper. The paper will appear Aug. 29 in the Proceedings of the National Academy of Sciences.

Kotlikoff and his fellow researchers found that two-day-old mice grew new heart cells and almost completely recovered from infarction, proving that the injury did not inhibit stem cells from growing new heart cells. The same procedure was carried out on adult mice and no new heart cells formed, confirming that adults do not have the requisite stem cells to create new heart cells, called myocytes, though new blood vessel cells were created.

The stem cells found in the adult heart "have lost the ability to become heart cells, and are only capable of forming new vessels," Kotlikoff said. Single stem cells differentiate into all tissues at the start of life, but over time these cells become "developmentally restricted" or specialized to form only certain tissues.

Sophie Jesty, Michele Steffey, and Frank Lee are the paper's lead authors and the work is part of a long-term collaboration with Professor Bernd Fleischmann's team at the University of Bonn.

The study was funded by the National Institutes of Health, New York State Stem Cell Science and the European Union Seventh Framework Programme.

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Stem cells repair hearts early in life, but not in adults