Can Heart Muscle Cells Be Produced from Bone Marrow?

Originally Published MDDI April 2003

R&D DIGEST

It has long been believed that, unlike bone or most human tissues, heart cells are unable to repair themselves naturally when damaged. For this reason, researchers have been exploring ways to grow new heart cells or repair damaged ones.

In 2001, scientists at New York Medical College (Valhalla, NY) challenged the belief that heart damage is permanent. They reported their success in finding large-scale replication of heart-muscle cells in two regions of the heart. Other scientists from that institution and from the National Institutes of Health reported that adult stem cells isolated from mouse bone marrow had become functioning muscle cells when injected into a damaged mouse heart. In that same year, animal studies at Beth Israel Deaconess Medical Center (Boston) suggested that embryonic stem cells could be transplanted to help repair damaged heart tissue and improve function.

In March 2003, doctors at William Beaumont Hospital (Royal Oak, MI) infused a 16-year-old patient's heart with his own blood stem cells in an attempt to repair heart damage. The boy had a massive heart attack in February after being shot in the heart with a nail gun. According to one of the boy's physicians, some improvement was seen in a few days.

Now, research at the Mayo Clinic (Rochester, MN) may offer the first proof that cells produced by the bone marrow can form new heart-muscle cells in adults. Their work could provide important support to development of methods to replace tissue damaged by a heart attack.
“Until recently, the heart has been seen as an organ that cannot be healed,” says Noel Caplice, MD, the Mayo Clinic cardiologist who led the study. “Heart attack damage to the myocardium, or heart muscle, was considered irreversible.”

The researchers studied four female patients with leukemia who had survived 35 to 600 days after receiving bone-marrow transplants from male donors. Heart-tissue samples were examined at autopsy using special staining techniques, which showed that a small portion of the heart-muscle cells, or cardiomyocytes, contained male genetic material and had therefore originated from the donor marrow. Out of the more than 80,000 cell nuclei examined, about 1 in 425 (0.23%) contained the y chromosome.

The study is significant because it is the first confirmation that progenitor cells from outside the heart can form new heart-muscle cells. “These progenitor cells are produced by the bone marrow and circulate in the blood,” says Caplice. “They are like stem cells in that they have potential to develop into various kinds of cells. We have now shown that, given the right biological signals, they can become heart cells .”

Caplice says the study has significant implications for future research. “Under normal conditions, with less than 1% of heart-muscle cells originating from these progenitor cells, they obviously are not adding much to the heart's pumping strength. But if we can determine the signaling mechanism that causes progenitor cells to develop into cardiomyocytes, we may be able to boost the response and induce more of them to proceed in that direction. A growth hormone delivered to the heart could perhaps lead to formation of new muscle around an area of scar tissue, so the heart could actually be healed after being damaged by heart attack. This study provides an important validation of the potential for this new line of research,” he adds.

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