A landmark discovery by researchers at Hamilton's McMaster University could radically alter the way scientists attempt to use embryonic stem cells to grow replacement tissues and treat cancer.
The researchers found that human embryonic stem cells – "the great grandmothers" of all the other cells in our bodies – build themselves a nurturing cocoon that feeds them and directs their ability to turn into other types of tissues.
By manipulating the products of this tiny, cellular placenta, it may be possible for scientists to prompt the stem cells to grow into desired tissues and organs, or to switch off tumour growth, says Mickie Bhatia, the lead study author.
The study will appear in an upcoming issue of the scientific journal Nature.
"We think we've introduced now a mechanism or a new approach to control stem cell fate," says Bhatia, scientific director of the McMaster Stem Cell and Cancer Research Institute.
"I think ... it opens up a completely new arena to now think about controlling the growth and differentiation of the human embryonic stem cells that we didn't know existed until now."
The study shows that making replacement tissues to treat disease requires more than just manipulating the stem cell itself. "You have to control the surrounding cells that govern this (transformation) process," Bhatia says.
Dr. Alan Bernstein, one of Canada's top stem cell experts, called the study "very important."
He says it shows the surrounding cells – called "niche" cells – seem to play an important role in determining whether the stem cells become neurons, blood cells or fat cells, for example.
"We know that the niche to some extent influences their behaviour," says Bernstein, president of the federal Canadian Institutes of Health Research.
The institute helped fund the Hamilton study, but Bernstein was not involved in the research.
Scientists hope stem cells might one day be used to grow new nerve cells in the damaged spinal cords of paraplegics, or to introduce insulin-producing cells into a diabetic pancreas.
Currently researchers in regenerative medicine have been attempting to prompt this tissue transformation by targeting the stem cells themselves, Bhatia says. Now they can turn their attention to the nurturing surrounding cells.
Bhatia says scientists have long thought stem cells were coaxed to transform into other types of tissues by the environment or "niche" they found themselves in. Cardiac stem cells, for example develop heart tissue because that's what they're surrounded by.
It makes sense, then, that as the original cells created after conception, embryonic stem cells would need to develop their own niche, Bhatia says.
Bhatia says the niche is made up of cells generated by the embryonic stem cells.
These surrounding cells in turn feed and direct the parent stem cell via the production of special protein "growth factors."
And some of the growth factors created by the niche cells direct the embryonic stem cell to do nothing but make copies of itself.
To coax the stem cell to make other types of tissues, you have to stop this self-replication process, Bhatia says.
"Once we've done that, then we can draw their attention to making (different kinds) of cells."
Bhatia also says researchers should be able to use the growth factors made by the niche cells to create more and better embryonic stem cells for laboratory research.
"Right now with current technology it's very, very difficult to grow human embryonic stem cells and expensive," says Michael Rudnicki, scientific director of the Stem Cell Network in Canada.
"This (study) points to new ways in which we may be able to do this as well as giving us important biological insight into the mechanisms at play that support the growth of these cells."
Bhatia says the study may also have implications for the treatment of cancers since the niche that controls their growth influences stem cells that make malignant tumours.
"We have a rising notion ... that adult tumours come from stem cells. And so what we believe is that the niche that normally controls the stem cells is also part of what goes wrong when tumours grow."
http://www.thestar.com/article/235100
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