|
Conventional wisdom holds that the heart,
unlike many other organs in the body, cannot repair itself
by growing new cells after an injury.
But researchers in New York and Italy
have uncovered evidence suggesting that this dogma may not
be true. In an analysis of the hearts of patients who died
after having a heart attack, researchers
detected signs that heart muscle cells called myocytes continued
to divide after a heart attack.
The researchers examined the hearts of
13 people who died within a few days of having a heart attack
and compared them with 10 normal hearts. The researchers screened
the tissue for the expression of Ki-67, a protein that is
present only in dividing cells.
The investigators report that Ki-67 was
present in many of the cells of the diseased hearts. Compared
with normal hearts, the expression of the protein was 84 times
greater in tissue immediately surrounding damaged heart tissue
and 28 times greater in other heart tissue. The researchers
also detected other cell structures linked to the cell-division
process in the hearts of people who had died from a heart
attack.
The major finding of the study is that
the heart's capacity to
regenerate myocytes increases immediately after a heart attack.
The newly formed heart muscle cells may
arise from stem cells -- immature cells that specialize to
form other types of cells -- that reside in the heart. Cardiac
stem cells have not been identified, but similar cells are
present in the brain.
The evidence that the heart can regenerate
muscle cells and the possible existence of cardiac stem cells
raise hope that it may be possible one day to induce cardiac
stem cells to migrate to a damaged area of the heart to repair
it with new cells.
But given the "grim prospects"
for patients after a heart attack, the NEJM editorial suggested
the heart's ability to repair
itself may be limited.
The heart
clearly needs help to deal with the massive injury caused
by a major heart attack.
Help may be on the way, as animal studies
have shown that stem cells taken from adult bone marrow can
regenerate heart cells after a heart attack.
The field has been brought face to face
with the mysterious processes by which the body regenerates,
and the body does not yield its secrets easily.
The New England
Journal of Medicine June 7, 2001; 344: 1750-1757, 1785-1787
|