Scientists convert human skin cells directly into brain cells
Date: Oct-24-2014 By exposing skin cells to a particular combination of cell
programming molecules, scientists managed to convert them into brain cells
that behave like native cells.
Human skin cells (top) can be converted into medium spiny neurons (bottom) with exposure to the right combination of microRNAs and transcription factors, according to work by Andrew Yoo and colleagues.
Image credit: Yoo Lab
The study is unusual because, unlike many cell conversion techniques, the
cells did not return to a stem cell stage first - they converted directly
into brain cells - thus avoiding the risk of producing many other types of
cells.
And the study is unique, because the team managed to reprogram the skin
cells to become a particular type of brain cell instead of a range of brain
cells.
Writing in the journal Neuron, researchers from Washington
University School of Medicine in St. Louis (WUSTL), MO, report how they used
a particular combination of microRNAs and transcription factors to reprogram
the skin cells into a particular type of brain cell known as medium
spiny neurons.
The medium spiny neurons they produced - which survived for at least 6
months after injection into the brains of mice - are important for
controlling movement and are the main type affected in Huntington's
disease.
Huntington's disease is an inherited genetic disease that causes involuntary
movements and gradual decline of mental ability. Patients with the disease -
which usually starts in middle age - can live for 20 years after symptoms
begin, although these gradually get worse.
Converted cells showed properties of native cells
Senior author Dr. Andrew S. Yoo, assistant professor of developmental
biology at WUSTL, says not only did the new cells survive in the mouse
brain, but they also showed properties similar to native cells:
"These cells are known to extend projections into certain brain regions.
And we found the human transplanted cells also connected to these distant
targets in the mouse brain. That's a landmark point about this paper."
Because they used adult human skin cells in the study - and not mouse
cells or human cells at an earlier stage of development - the team believes
the work shows the potential for using patients' own cells in regenerative
medicine. This is important because therapies can use readily available
cells and also avoid the problem of immune rejection.
For their study, Dr. Yoo and colleagues cultured the skin cells in an
environment that mimics that of brain cells. In previous work, they had already discovered that exposing
skin cells to two small RNA molecules called miR-9 and miR-124 can turn them
into different types of brain cell.
Although they are still trying to work out exactly what happens, the
team believes the two small RNA molecules open up the tightly packed DNA
inside cells that holds instructions for making brain cells, allowing the
genes particular to their development and function to be switched on.
Having proved that exposure to these small RNA molecules converts skin
cells into a mix of brain cells, the team began fine-tuning the chemical
signals. They did this by adding molecules called transcription factors
that they already knew were present in the part of the brain where medium
spiny neurons are abundant.
Transcription factors guide the cells to become a specific type
Co-first author Matheus B. Victor, a graduate student in neuroscience,
says they believe the small RNA molecules are "doing the heavy lifting,"
and:
"They are priming the skin cells to become neurons. The transcription
factors we add then guide the skin cells to become a specific subtype, in
this case medium spiny neurons. We think we could produce different types of
neurons by switching out different transcription factors."
The team also showed that when the skin cells are exposed to the
transcription factors alone, without the small RNA molecules, the skin cells
do not convert successfully.
The team also carried out extensive tests to show the new brain cells had
the hallmarks of native medium spiny neurons. They expressed the right genes
for their specific type and did not express genes for other types of
neurons.
And, when transplanted into the brains of mice, the converted cells
looked like native medium spiny neurons and behaved like them.
The team is now using skin cells from patients with Huntington's disease
and converting them into medium spiny neurons using their new approach. They
also plan to inject the cells into mice with the disease.
The study was funded by various bodies, including the National Institutes
of Health (NIH).
Written by Catharine Paddock PhD
Not to be reproduced without permission.
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Courtesy: Medical News Today
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