Gene-editing tool successfully reactivates genes in PWS lab study
Scientists hope to translate approach into 'durable therapy' for PWS patients
Researchers have successfully used the gene-editing tool CRISPR to reactivate certain maternally-inherited genes that can compensate for the loss of the corresponding paternally-inherited genes in Prader-Willi syndrome (PWS).
Done using lab-grown human stem cells with a PWS-causing mutation, the work showed that the one-time approach resulted in a sustained effect in the cells, according to the researchers.
“This work provides proof of concept for a therapeutic strategy for PWS by reactivating maternal gene expression [activity] … through targeted [CRISPR]-based … editing,” the team wrote.
Along with her research colleagues, Dahlia Rohm, PhD — who worked on the study as part of her doctoral training at Duke University — noted that a great deal of further investigation still is needed before this strategy can even be tested in humans.
But the lab findings “[lead] us to hope that we can eventually translate this into a durable therapy, not just for Prader-Willi syndrome patients, but for other rare genetic diseases that occur by a similar mechanism,” Rohm said in a university news story.
The findings were described in a study titled “Activation of the imprinted Prader-Willi syndrome locus by CRISPR-based epigenome editing,” which was published in the journal Cell Genomics.
Researchers use CRISPR gene-editing tool to alter epigenetics
All humans have 23 pairs of chromosomes, which are rodlike structures where genes are located. One chromosome is inherited from the mother and one from the father.
PWS is caused by mutations that affect 15q11-13, a specific region in the paternal copy of chromosome 15 that contains genes that control metabolism, appetite, growth, intellectual abilities, and social behavior.
While most people with PWS have a working 15q11-13 region that’s inherited from the mother, the maternally-inherited genes in this region are normally turned off in the brain through a process called imprinting.
“There are many examples of these imprinted regions of the genome, where one copy of a set of genes from either parent is normally silenced,” said Charles Gersbach, PhD, the study’s senior author at Duke and the mentor of Rohm and Josh Black, PhD, who also worked on this research as part of his doctoral training at the North Carolina-based university.
People [with PWS] already have copies of all the genes they need, we just need to figure out a way to turn them on.
To date, “there aren’t really any therapies” for imprinting disorders like PWS, noted Gersbach, the John W. Strohbehn distinguished professor of biomedical engineering at Duke.
But according to Gersbach, “people [with PWS] already have copies of all the genes they need, we just need to figure out a way to turn them on.”
Imprinting involves epigenetic mechanisms, in which chemical tags are added to DNA or histones, influencing genes’ activities without altering their underlying DNA sequence. Histones are the proteins that pack DNA and regulate genes’ accessibility and activity.
CRISPR is a gene-editing technology developed from a system that bacteria evolved to help fight off viruses. Most CRISPR tools work to directly alter the genetic code in a cell’s DNA. Here, the researchers instead utilized this gene-editing tool to alter epigenetics.
Temporary exposure leads to ‘permanent, stable effect’ in lab
The team of scientists first identified two CRISPR-based strategies to activate the maternally-inherited 15q11-13 region. One strategy basically works by recruiting cellular machinery that normally helps to turn on genes. The other works by removing DNA methylation, which is a type of epigenetic modification that normally acts to turn off genes.
Although these two strategies could both turn on genes in the 15q11-13 region in lab-grown human stem cells, they acted on different specific regions of the DNA that act as master regulators for the whole region, the researchers noted.
Black noted that this was the most targeted approach.
“If you wanted to treat this disease through conventional gene therapy, you’d have to deliver many different genes,” Black said. “Our approach to manipulate a master controller of all of these genes that are already present in the imprinted region is a much more straightforward option.”
According to Black, “this is really an ideal use case for the epigenome editing technology we have been focused on.”
Importantly, the researchers found that they could use the methylation-based editing strategy to turn on the maternal 15q11-13 region in lab-grown human stem cells carrying a common PWS-causing mutation. When these cells were allowed to mature into nerve cells, they still had this region activated, even though they hadn’t been directly treated with CRISPR.
Rohm said that “was probably the most exciting result. … That we could use CRISPR as a [temporary] exposure but get a permanent, stable effect.”
Although these results are promising, the team stressed that much more work will be needed to figure out how to deliver these CRISPR-based tools to brain cells in living animals, with the goal of eventually testing this strategy in people.
Further, the reseachers noted that “translating epigenome editing therapies for PWS to the clinic will necessitate further development of safe and efficient delivery of [CRISPR-based] epigenome editors.”
The study was funded in part by the Foundation for Prader Willi Research.
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