Selective Reprogramming Of General Cells? Compounds For Stem-cell Production Fro

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Selective Reprogramming Of General Cells? Compounds For Stem-cell

Production From Adult Cells Identified

http://medicalnewscenter.com/out/out.cgi?

http://www.sciencedaily.com/releases/2008/11/081105135119.htm

Scientists from the Scripps Research Institute have identified a

combination of small molecules that significantly improve the

reprogramming of general adult cells into pluripotent stem cells,

which can then develop into all cell types.

In the study, the scientists screened known drugs and identified

small molecules that could replace conventional reprogramming genes,

which can have dangerous side effects. This new process offers a new

way to generate stem cells from fibroblasts, a general cell type that

is abundant and easily accessible from various tissues, including

skin.

The study was published in the November 6, 2008 edition (Volume 3,

Issue 5) of the journal Cell Stem Cell.

" Our study shows for the first time that somatic or general cell

types can be reprogrammed with only two genes and small molecules,

and that these small molecules can replace one of the two most

essential reprogramming genes, " said Sheng Ding, a Scripps Research

scientist and Associate Professor in the Department of Chemistry, who

led the study with colleagues from Scripps Research and the Max

Planck Institute for Molecular Biomedicine in Germany. " In this case,

we replaced the Sox2 gene, which had previously always been regarded

as absolutely essential for the reprogramming process. "

The SOX2 gene encodes a transcription factor that plays a critical

role in the regulation of embryonic stem cells.

" This proof-of-principle study leads us one step closer to the

ultimate reprogramming of general cells to pluripotent cells in a

completely chemically defined manner without genetic manipulation, "

he said. " In conjunction with our earlier published studies, it

offers definitive proof that we can make cell reprogramming

technology much more practical than it has been. "

Ding went on to suggest that this drug discovery approach could be

used to identify additional small molecules, which could not only

provide insights into the reprogramming process, but also become

useful in in vivo stem cell biology and, ultimately, the development

of novel therapeutics.

This kind of chemical approach to the generation of useful stem cells

offers more precise control over the process, the study said, and has

distinct advantages over the genetic manipulation of oncogenes that

could introduce harmful genomic changes.

Better Results

The new study builds on an earlier study published by Ding and his

colleagues in the June 5, 2008 issue of the journal Cell Stem Cell.

That study showed for the first time that small, drug-like chemicals

could help turn mouse brain cells back into pluripotent stem cells,

while reducing some major drawbacks of a breakthrough technique

discovered two years ago by Japanese researchers to produce

pluripotent stem cells, once derived only from embryos.

The new study identified two small molecule compounds that improved

reprogramming efficiency and that could effectively compensate for

Sox2: BIX and BayK.

For the first time, the new study showed that BIX, an inhibitor of

enzymes involved in regulating gene expression, enables fibroblast

cell reprogramming in the absence of Sox2 gene overexpression.

However, by itself, BIX's reprogramming efficiency is relatively low.

" As a result, we performed a second screen to find a compound that

would synergize with BIX to further increase the reprogramming

efficiency of general cells " Ding said. " Besides providing an

improvement in reprogramming, we believed that these newly identified

molecules might lead to discovery of different reprogramming

mechanisms. "

The second screen identified BayK, a calcium channel agonist, which

was selected because it had no observable reprogramming activity on

general cells in the absence of BIX. In addition, BayK was not known

to affect the cell directly at the epigenetic level—changes in gene

expression without any DNA or DNA-associated packaging protein

modification—but rather at the cell signal transduction level.

The scientists found that when transduced general cells were treated

with both BIX and BayK, a significant increase in the number of

pluripotent cells resulted compared to transduced general cells

treated with BIX alone. In vitro and in vivo characterizations

confirmed that transduction of only two factors with simultaneous

treatment with small molecules BIX and BayK was sufficient to

reprogram general cells to become pluripotent stem cells.

The fact that BayK doesn't act on its own, but needs the presence of

BIX to exert its effect suggests that cells that are already

undergoing a form of reprogramming, perhaps caused by injury, might

be more susceptible to it.

" Needless to say, more work needs to be done to understand the

precise mechanism by which BayK affects the reprogramming process, "

Ding said. " It's interesting to find that a small molecule, which

acts on signaling pathways that have not been linked to pluripotency

and reprogramming previously can significantly enhance reprogramming

efficiency. So far, it's the first small molecule of its type to show

such an effect. This might allow us to ultimately reprogram the

target cell in a more specific manner, without impacting healthy

cells systemically in an in vivo setting. "

The first authors of the study, Induction of Pluripotent Stem Cells

from Mouse Embryonic Fibroblasts by Oct4 and Klf4 with Small-Molecule

Compounds, are Yan Shi and Caroline Desponts of The Scripps Research

Institute. Other authors of the study include Heung Sik Hahm of The

Scripps Research Institute and Jeong Tae Do and Hans R. Schöler of

the Max Planck Institute for Molecular Biomedicine, Münster, Germany.

The study was supported by The Scripps Research Institute.