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Heart Cells Grow Throughout Life Span

lectron micrograph of cardiac muscle. Wellcome Images.

Researchers have discovered that the human heart continues to generate new cells throughout its life span. The finding may lead to the creation of new treatments to boost regeneration in people with heart problems, such as heart attack victims.

Scientists have long thought that organs such as the heart, brain and pancreas are unable to create new cells after development. This theory is largely based on the limited ability of these organs to recover after being damaged by illness or injury. In addition, primary cardiac tumors are very rare, suggesting restricted cell growth within the human heart. However, the rate of cell proliferation in the heart had not been directly measured.

Scientists at the Karolinska Institute in Sweden and Dr. Bruce Buchholz at Lawrence Livermore �����鶹��Ƶ Laboratory (LLNL) in California have developed an innovative way to solve this problem. Their method is based on the observation that cells in the body contain a carbon-14 "timestamp."

The atmospheric concentration of carbon-14 was relatively stable until the Cold War, when above-ground testing of nuclear weapons in the late 1950s to early 1960s caused a spike worldwide. This increased the amount of carbon-14 that was incorporated into the DNA of everyone alive on Earth at the time. Since above-ground testing has been banned, the amount of carbon-14 in the atmosphere—and therefore the amount incorporated into new cells—has gradually fallen. Scientists can now pinpoint when a cell was created by measuring its concentration of carbon-14.

In the new study, the researchers performed carbon-14 analyses of DNA from heart muscle cells (cardiomyocytes) at LLNL's �����鶹��Ƶ Resource for Biomedical Accelerator Mass Spectrometry, a research center supported by NIH's �����鶹��Ƶ Center for Research Resources (NCRR). Tissue samples were obtained from people born up to 22 years before the onset of the nuclear bomb tests.

The researchers reported in Science on April 3, 2009, that the samples' carbon-14 levels showed that cells in the human heart are created into adulthood. The scientists next determined the rate of heart cell growth over time by measuring the carbon-14 DNA profile of people born both before and after the 1950s testing. Mathematical modeling of the carbon-14 data revealed that a 50-year-old heart still contains more than half the cells it had at birth but that the turnover slows down with time. A 25-year-old heart replaces about 1% of all its cardiomyocytes over the course of a year, while a 75-year-old heart replaces about half a percent.

These findings raise the possibility that, if the heart produces more cardiomyocytes after a heart attack, techniques could be developed to enhance that process and potentially reverse heart damage.

“The advantage of cardiomyocyte regeneration over current clinical treatments is the possibility of repair,“ Buchholz explains. “Heart attacks produce scar tissue that never functions properly. If the heart could be stimulated to repair the damage with new cells, recovery from heart attack may be much improved.”

—by Nancy Van Prooyen