New source of heart stem cells found: study

Agence France-Presse
PARIS - Researchers in
the United States
have discovered a new
group of stem cells
that can give rise to
heart muscle cells,
known as
cardiomyocytes,
according to a study
published Sunday.
The stem cells are
located in the
outermost layer of
the heart and could
one day play a critical
role in regenerating
injured heart tissue,
the researchers say.
"In heart failure, you
lose cardiomyocytes,
so the only way to
reverse heart failure
is to make more of
these cells," said
William Pu, the
study's lead
researcher and a
pediatric cardiologist
at Children's Hospital
in Boston,
Massachusetts.
The new findings
come on the heels of
two earlier
breakthroughs.
In 2006 scientists
identified another
cardiac stem cell --
marked by the
expression of a gene
called Nkx2-5 -- with
the potential to
become either heart
muscle or cells lining
blood vessels in the
organ's left-sided
chambers.
Gene expression is the
process by which
information encoded
in the DNA of a
particular gene is
transformed into a
protein or RNA, which
plays a key role in
protein synthesis.
In parallel, other US
researchers
discovered a related
progenitor heart cell --
so-called because of
its capacity to
generate different
types of tissue -- that
produces the same
cell types in the right-
sided heart chambers.
Pu's study, published
online in the journal
Nature, shows for the
first time that new
heart stem cells can
also be derived from a
third type of cardiac
stell cell, located
within the surface of
the organ and
identifiable through
its expression of a
gene called Wt1.
The results were
independently verified
by another team of
scientists at the
University of
California in San
Diego, whose research
was published in the
same issue of Nature.
Pu and colleagues
showed that the cells
from the heart's
outer lining, called the
epicardium, can not
only metamorphose
into cardiomyocytes
but also into smooth
muscle cells,
endothelial cells,
which line the interior
of blood vessels, and
fibroblasts, found in
connective tissue.
"If you are going to
regenerate tissue,
you need to
regenerate the whole
tissue, not just the
cardiomyocytes," Pu
said in a statement.
The discovery of the
new stem cells was an
accident. In order to
study the role a
different gene in the
epicardium, the
researchers labeled
cells in live mouse
embryos with red
fluorescent protein.
"Unexpectedly, we saw
that these epicardial
cells were becoming
cardiomycytes -- it
was a lucky
observation," said Pu.
The next challenge, he
added, is trying to
figure out how a
progenitor stem cell
decides to become a
certain type of
functioning cell within
the heart, and then
how to develop
methods to trick the
stem cells into
transforming into the
desired tissue.
"We still don't know
how we can
manipulate these
progenitors," he said.

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