July 30, 2012
Stem cells create new heart cells in baby mice, but not in adults, study shows
Kotlikoff Lab
In a two-day-old mouse, a heart attack causes active stem cells to grow new heart cells; a few months later, the heart is mostly repaired. But in an adult mouse, recovery from such an attack leads to classic after-effects: scar tissue, permanent loss of function and life-threatening arrhythmias.
A new study by Cornell and University of Bonn researchers found that stem cells did not create new heart cells in adult mice after a heart attack, settling a decades-old controversy about whether stem cells play a role in the recovery of the adult mammalian heart following infarction -- the leading cause of sudden death in the developed world -- where heart tissue dies due to artery blockage.
"If you did have fully capable stem cells in adults, why are there no new heart cells after an infarct? And is this due to the lack of stem cells or due to something special about the infarct that inhibits stem cells from forming new heart cells?" asked Michael Kotlikoff, the Austin O. Hooey Dean of Cornell's College of Veterinary Medicine, and senior author of the paper appearing Aug. 29 in the Proceedings of the National Academy of Sciences.
Beating heart cells
This movie shows beating heart cells in culture that originated as stem cells (look closely around the center of the frame). The researchers used a mouse model where heart cells fluoresced red and undifferentiated stem cells fluoresced green. All of the cells shown in the movie were green at the time of culture and they turn red after they become heart cells. There were no red cells to start, indicating that the origin of the beating red cells was green stem cells. Watch video
Co-author Michelle Steffey, a small-animal surgeon in Cornell's veterinary college, developed a procedure to infarct a neonatal mouse heart that is only one-tenth-of-an-inch wide. "It was a tour-de-force technically to infarct and recover those baby mice," said Kotlikoff.
The baby mice grew new heart cells and almost completely recovered from infarction, proving that the infarction 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.
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Stem cells create new heart cells in baby mice, but not in adults, study shows