In a paper

published in the June 7 issue of the New England Journal of Medicine,

scientists from New York Medical College in Valhalla, NY report their

success in finding large scale replication of heart muscle cells in two

regions of the heart, and in identifying several other key indicators

of cell regeneration.

"It has

long been assumed that when the heart is damaged such as after a heart

attack heart muscle cells do not regenerate and the damage is permanent.

This assumption has been challenged in recent years by evidence that heart

muscle cells may in fact regenerate. Now, this latest research provides

the most dramatic and clear-cut demonstration to date of heart cell regeneration

after cardiac injury," says Claude Lenfant, M.D., director of the

NHLBI, a component of the National Institutes of Health.

"With

this landmark study, we have a new understanding of the heart that opens

up the possibility of repairing heart muscle damage after a heart attack,"

he adds.

"This

finding, if confirmed, may begin to clarify how hearts respond to the

normal insults of aging through previously undetected repair mechanisms,"

says David Finkelstein, Ph.D., director of basic cardiovascular research

at the NIA.

Piero Anversa,

M.D., professor of medicine and director of the Cardiovascular Research

Institute, and colleagues, studied myocytes (heart muscle cells) from

the hearts of 13 patients, 4 to 12 days after their heart attacks, and

from the hearts of 10 patients who did not have cardiovascular disease.

Samples were obtained from the border zone near the site of the heart

attack and from a more distant site from the damaged tissue.

these areas of the heart with a high resolution confocal microscope, Anversa

and colleagues were able to measure the expression of Ki67, a protein

found in the nucleus of dividing heart muscle cells. Ki67 is expressed

during all phases of a cell's life cycle and is a strong indicator of

cell division.

The scientists

also obtained images of mitotic division and found other evidence of myoctye

replication, including the formation of the "mitotic spindle,"

and "contractile ring," critical structural indicators of cell

division.

Important evidence

of myocardial repair was demonstrated by the mitotic index, a measurement

of the degree of myocyte division. In comparison with normal hearts, the

number of myoctyes multiplying in diseased hearts was 70 times higher

in the border zone and 24 times higher in the remote myocardium.

The next challenge,

according to Anversa, is to find the source of the dividing myoctyes.

"Are these cells a sub-population of known cells that retain the

capacity to divide, or are they multiplying cells that originate from

stem cells present in the heart?" he asks.

"There

are preliminary indications that primitive cells like stem cells exist

in the human heart. Stem cells may have the ability to develop into the

various cardiac cell types and form new healthy functioning myocardium.

If we can prove the existence of cardiac stem cells and make these cells

migrate to the region of tissue damage, we could conceivably improve the

repair of damaged heart muscle and reduce heart failure," says Anversa.

Research on

animal models supports this possibility. In the April 4 issue of Nature,

the Anversa team and a colleague at the NIH reported that adult stem cells

isolated from mouse bone and injected into a damaged mouse heart became

functioning heart muscle by developing into myocytes and coronary vessels.

Moreover, the

newly formed tissue partially restored the heart's ability to pump blood.

Although a

cardiac stem cell has not yet been identified, scientists have identified

a neural stem cell in the brain.

"Why not

the heart?" asks Anversa.

Back

to Healthwise Home Page |