Scientists Change Living Pancreatic Cells Into Insulin Producers
28 Aug 2008

US scientists have discovered a way to transform living pancreatic
cells in mice into another type of cell that produces insulin without
having to revert to the stem cell stage, creating what is now a third
route for cell reprogramming to add to the existing methods of iPS
(induced pluripotent stem cells) and hES (human embryonic stem cells).

The study was the work of Harvard Stem Cell Institute co-director Doug
Melton and post doctoral fellow Qiao "Joe" Zhou , at Harvard
University, Boston, Massachusetts, and colleagues and was published as
an advanced online paper in Nature on 27th August.

Melton and colleagues appear to have attained the "holy grail" of stem
cell research, they have turned one type of adult cell directly into
another type of adult cell, opening the door to living cell
transformation directly in patients.

Using what they called "direct reprogramming," the researchers turned
exocrine cells, which account for around 95 percent of pancreatic
tissue, into rare insulin-producing beta cells, which account for a
much smaller 1 per cent or less of pancreatic cells and are therefore
very precious. Beta cells are the ones that die off in Type I
diabetes.

The feat is being heralded as a major step in developing treatments
for Type 2 and Type 1 diabetes, bringing closer the day when patients
won't have to be checking their blood sugar all the time, or even take
insulin medication. The researchers did however caution that it will
be some time before this is a reality, and there are many difficult
hurdles to overcome before the method can be tested in humans.

For example, as with iPS, Melton's team used viruses to introduce
various transcription factors (bits of DNA that alter the way that
genes express themselves) into the target cells. This is a risky
approach in humans because the viruses could behave in other unplanned
and unpredictable ways. The researchers are looking for safer
alternatives based on chemicals for this reason.

Melton pointed out that direct reprogramming will not remove the need
for iPS and hES, and said his lab will continue to use them as well as
the new techniques.

"We need to attack problems from multiple angles," said Melton.

The researchers had a bit of luck when they discovered they could
directly reprogram adult cells. Usually, as in iPS, you have to use
hundreds of trascription factors to revert a mature cell back into a
pluripotent cell that can then be encouraged to develop into any one
of a range of cells. If you were lucky to pick the right combination
of a much smaller subset of transcription factors, in theory you
should be able to short circuit the iPS route and go straight from one
type of mature cell to another.

That is what happened with Melton's team. With a judicious mix of luck
and two years of constant trial and error they hit on three
transcription factors, Ngn3, Pdx1, and MafA. They just kept asking
themselves the question "What genes do you have to turn on for the
cell to become a beta cell?"

As Melton commented:

"If you want to do reprogramming it doesn't take great insight to
figure out that the key genes are transcription factors - the proteins
that bind DNA and tell cells which genes to turn on and which to turn
off."

He said that a stem cell goes through many steps before it becomes a
particular type of adult cell, each step is like passing through a
door with a specific lock and each lock is a trascription factor. He
and his team asked themselves which "locks" were in the beta cells,
and that gave them 1,100 possible transcription factors. Eventually
they discovered that only 200 of them are expressed in the cells of
the pancreas, so that helped to narrow the field somewhat.

The next step was to find which of the 200 were particular to
pancreatic cells that surrounded the beta cells, and that brought the
number down to a more manageable 28. The 28 became 9 after the did
further "lineage studies", as Joe explained, "my best guess is it's
these nine". And he was right. They then mixed all 9 and injected them
into the pancreas. Then by removing them one by one they discovered it
worked best when only three transcription factors were present, the
other six weren't as important, said Joe.

The luck of fate came when they chose those 9, because if they had not
produced results, Melton and his team would have given up, they said.

Through the experiment Melton and colleagues were able to show that
the newly induced beta-cells were "indistinguishable from endogenous
islet beta-cells in size, shape and ultrastructure".

They expressed genes essential for beta-cell function and were able to
"ameliorate hyperglycaemia by remodelling local vasculature and
secreting insulin".

The researchers concluded that:

"This study provides an example of cellular reprogramming using
defined factors in an adult organ and suggests a general paradigm for
directing cell reprogramming without reversion to a pluripotent stem
cell state."

"In vivo reprogramming of adult pancreatic exocrine cells to beta-
cells."
Qiao Zhou, Juliana Brown, Andrew Kanarek, Jayaraj Rajagopal & Douglas
A. Melton
Nature Advance published online 27 August 2008.
doi:10.1038/nature07314

Click here for Abstract.

Sources: Journal Abstract, Harvard Medical School.

Written by: Catharine Paddock, PhD
Copyright: Medical News Today
Not to be reproduced without permission of Medical News Today