The ability to convert cells from one type to another holds great
promise for engineering cells and tissues for therapeutic application,
and a study could help speed research and bring the
technology to the clinic faster.
Researchers at the University of Wisconsin-Madison have developed a
novel strategy to reprogram cells from one type to another in a more
efficient and less biased manner than previous methods.
‘The newly described approach uses a library of artificial transcription factors to switch on genes that convert cells from one type to another.’
The new approach, published this week in the Proceedings of the National Academy of Sciences
(PNAS), uses a library of artificial transcription factors to switch on
genes that convert cells from one type to another.
transcription factors are cellular molecules that bind to DNA to turn
genes on and off. They help determine cell fate, meaning that if a cell
is destined to be a skin cell, a heart cell or an eye cell, different
transcription factors switch on specific sets of genes that program the
cell to attain one state or another.
Using artificial transcription
factors made in the lab, researchers are trying to find which ones best
mimic these natural changes in cell fate.
"Our interest in changing cell fate comes from understanding how
cells selectively use the information in our genomes to make specific
cell types and also from the many therapeutic benefits such knowledge
can offer," says Asuka Eguchi, the study's lead author and a member of
Professor Aseem Ansari's lab in the UW-Madison Department of
Biochemistry. "For example, if a patient needs a certain cell type, the
idea is we can reprogram their own cells to what they need, rather than
relying on donor cells. This allows us to study patient-specific cells
and potentially avoids issues with immune response where a patient's
body could reject the cells."
Conventional methods for finding the correct factors to change cell
fate require scientists to perform a trial-and-error approach. They need
prior knowledge about which combination of the thousands of natural
factors would possibly work within a tightly choreographed timeframe to
program cell fate. It is a slow, laborious, failure-prone process, the
researchers say. The new method utilizes "libraries" of millions of
artificial transcription factors that were designed to bypass natural
controls and switch on genes that might be activated in a given cell
type. In addition, the factors contain an attachment that lets them bind
and work in concert to affect genes, a step not traditionally taken.
By exposing the library of factors to cells, they can see if cell
fate changed in any of them. If so, they can revisit those cells to see
which factors were responsible. For their experiments, the Wisconsin
group started with mice fibroblasts, a cell in connective tissue, and
looked for them to be reprogrammed into what are called induced
pluripotent stem cells. Given proper cues, these types of stem cells can
become any type of cell in an animal's body, including humans. By
reprogramming, the researchers mean that the artificial factors would
trigger all of the right genes to cause the cell to shift from one type
"Imagine you have millions of keys and only a unique key or
combination of keys can turn a motor on," says Ansari, who is also
affiliated with UW-Madison's Genome Center of Wisconsin. "We test all
those keys in parallel and when we see the motor fire up, we go back to
see exactly which key switched it on."
In the process of testing their tool, the researchers discovered
three combinations of the artificial factors that reprogrammed a
fibroblast into a stem cell. The factors played a role similar to that
of a natural transcription factor important in a process, called Oct4.
"In this unbiased approach, we can try to basically cast a wide net
on the whole genome and let the cell tell us if there are important
genes perturbed," Ansari says. "It's a way to induce cell fate
conversions without having to know what genes might be important because
we are able to test so many by using an unbiased library of molecules
that can search nearly every corner of the genome."
The reprogramming of fibroblasts into stem cells has been well
studied. The researchers put their approach to the test in this context
because it places a high-bar and requires significant changes to the
cell. With this proof of concept, the Wisconsin scientists hope other
researchers use their method to discover new genes that can drive more
difficult conversions of cell fate.
"Generating these pluripotent stem cells also helps us avoid having
to make embryonic stem cells, which can be controversial," says Eguchi,
who is a recent graduate of the UW-Madison Cellular and Molecular
Biology Training Program. "We can also start better investigating direct
conversions, which are conversions from one cell type to another
without the need to go to the pluripotent stage first because that can
cause problems in some contexts. This tool opens up the doors to
research these areas more effectively."