Cleft palate in fetal mice prevented by treating
In addition to shedding light on the biology of cleft palate, the research raises hopes that it may one day be possible to prevent many types of human birth defects by using a similar vaccination-type technique in pregnant women likely to have affected fetuses.
“This is a really important baby step that opens the door to the development of fetal therapies,” said pediatric craniofacial surgeon Michael Longaker, MD. “Our hope and expectation is that patients at Packard Children's and other institutions will benefit as this basic advance is translated into something that will eventually make a significant difference for this and other birth defects.”
Longaker is the senior author of the study, which will be published in the Feb. 11 advance online edition of Nature. The research is the first demonstration that a technique known as chemical genetics in which small molecules are used to modify gene expression or protein activity can reach a fetus when administered to a pregnant animal.
“It's such a cool concept,” said Longaker, professor of medicine and a leader in Stanford's Institute for Stem Cell Biology and Regenerative Medicine. “We injected a small molecule into mom, and it goes into the embryo and works. There are tremendous implications to the idea of preventing conditions in unborn patients rather than trying to treat them after birth.” Cleft defects are the second-most common birth defect worldwide and affect about one in 2,000 births.
Longaker, who spent several years in fetal surgery working to design surgical approaches for life-threatening defects prior to coming to Stanford, said the concept of noninvasively preventing these defects by treating the mother is something that was unthinkable when he first began his work. “This is a great example of expectations changing as technology evolves,” he said.
For this study, co-author and postdoctoral scholar Karen Liu, PhD, used a short amino-acid tag to disrupt the function of a protein called GSK-3 beta. GSK-3 beta function is important in a variety of biological processes, and mice with the tagged protein exhibited many problems in utero, including cleft palates and sternum defects. However, Liu was able to reverse the defects by injecting the pregnant mice with rapamycina small molecule that stabilized the tag and restored the protein's function.
In addition to revealing for the first time that GSK-3 beta is important in palate formation, Liu discovered that the technique could be used to identify the specific times during development that the protein's function is required. For example, maternal rapamycin treatment between embryonic days 13.5 and 15 corrected the palate defect, but normal sternal development required functional protein between days 15.5 and 17. It's likely that the same chemical genetic approach could be applied to a variety of proteins and developmental processes to create a series of molecular snapshots of embryogenesis.
“The beauty of the technique is that it nails down the developmental window for various embryonic events,” said Longaker. “We don't need to treat the mother long term, but just during the time that the organ or structure is forming.”
Although promising, direct human applications of the research will require several key advances: an ability to predict which women are likely to have fetuses with birth defects before the defects occur; knowledge of an effective, small-molecule based therapy that can prevent the defect; and an accurate method of tracking fetal development to allow time-appropriate administration of the therapy.
“Over time, I expect we will have the ability to overcome these obstacles,” said Longaker. “This is the true value of having one of the best children's hospitals in the country integrated within a school of medicine renowned for its research capabilities. With interdisciplinary teamwork, we may be able to develop a whole new way to prevent birth defects.”
Gerald Crabtree, MD, PhD, professor of pathology and developmental biology, collaborated with Longaker and Liu on the study. Liu is supported by an NIH training program in regenerative medicine that fosters the interdisciplinary collaboration that led to the breakthrough research. “We're putting people together in the sandbox who wouldn't normally be playing together,” quipped Longaker about the collaboration.
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