GW SMHS Researchers Uncover Insights into DiGeorge Syndrome
With a $6.2 million project program grant (PPG) from the Eunice Kennedy Shriver National Institute of Child Health and Human Development, five years, and an ideal animal model – a mouse – researchers at the George Washington University (GW) School of Medicine and Health Sciences (SMHS) have begun to crack open the mystery behind DiGeorge Syndrome.
A rare, genetic syndrome caused by a missing piece on the long arm of chromosome 22, DiGeorge Syndrome, or, appropriately, 22q11.2 Deletion Syndrome, results in an array of symptoms: congenital heart defects, cleft palates and other facial abnormalities, developmental delays, intellectual disabilities, and pediatric dysphagia. In this final symptom, pediatric dysphagia, children have difficulty eating and swallowing, which can prevent weight gain and lead to infections in the sinuses, middle ear, and lung. It’s also a serious complication among children with other neurodevelopmental disorders – and that’s where the researchers at GW SMHS have focused their efforts.
“The goal of the PPG,” says Sally Moody, PhD, professor and chair of the Department of Anatomy and Cell Biology at GW SMHS, “was to integrate the research of our collaborative, multidisciplinary team to define the causes of pediatric dysphagia and identify new targets for effective therapy and prevention using 22q11.2 [Deletion Syndrome] as a model.”
Current therapies for pediatric dysphagia, she adds, are limited to treating symptoms or adjusting food consistency to prevent choking. There are no preventive options, and there is no cure.
“We postulated that the lack of new approaches reflects a fundamental lack of understanding of the neural and oropharyngeal mechanisms that are disrupted in pediatric dysphagia and their developmental causes,” Moody explains. “Our research program strove to provide this fundamental understanding by studying various developmental aspects of feeding and swallowing in a mouse model.”
The mouse model, known as LgDel for its similarly deleted chromosome, was as close to perfect match as possible. Not only did the researchers show that the mouse accurately exhibited features of dysphagia, but they were also able to study specific parts of the mouse’s brain development and function to suss out causes of feeding and swallowing issues.
With the mouse model in hand, the researchers tackled three projects, supported by four cores: the administrative core, led by Moody and Anthony LaMantia, PhD, director of the Center for Neurobiology Research at Virginia Tech and former director of the GW Institute for Neuroscience; the genetic resources core, led by Thomas Maynard, PhD, research associate professor at Virginia Tech and former GW SMHS associate research professor; the genomics and bioinformatics core, led by Norman Lee, PhD, professor of pharmacology and physiology at GW SMHS; and the microscopic imaging and analysis core, led by Anastas Popratiloff, MD, PhD, adjunct professor of anatomy and cell biology at GW SMHS.
The first project investigated whether neuronal circuits controling feeding and swallowing operate differently in LgDel mouse pups after birth. The team, headed by David Mendelowitz, PhD, professor and interim chair of pharmacology and physiology at GW SMHS, had two major findings, according to Moody. In the hindbrain, the part of the brain that regulates the feeding and swallowing movements, researchers confirmed that the electrophysiological features of motor neurons controling tongue movements are different in neonatal LgDel mouse pups, which affects feeding and swallowing. Those feeding and swallowing issues continue into adulthood. About 30% of the mice also had abnormalities in the way the palate and larynx formed. The primary deduction? Both neural and structural anomalies lead to post-natal dysphagia.
In the second project, which focused on abnormalities in the cranial nerves that stimulate the parts of the body that control feeding and swallowing, the team identified cellular, molecular, and transcriptional (when RNA copies parts of DNA) disruptions in the hindbrains of LgDel embryos. In comparing these embryos to wild-type, or “normal” mice, researchers found that the results showed three areas – variable gene expression; disrupted sensory neurogenesis (the formation of new neurons); and imprecise sensory and motor innervation, or stimulation, of the mouth during development – led to the problematic swallowing functions associated with pediatric dysphagia.
The third project looked at maternal diets. Researchers, primarily Maynard and Irene Zohn, PhD, associate professor of pediatrics at GW SMHS, hypothesized that changing the levels of retinoic acid, which comes from vitamin A, and other nutrients in the maternal diet would affect the embryonic and neonatal aspects of dysphagia in LgDel mice. They discovered that higher doses of vitamin A intake in pregnant mice can influence the vascular, lung, and cranial nerve development in LgDel embryos and postnatal mice. More, they determined a deficiency in a gene within the 22q11.2 deletion that regulates levels of retinoic acid can cause the anomalies behind palate and craniofacial defects in LgDel mice.
DiGeorge Syndrome discoveries aside, the PPG also produced a number of new research approaches and technologies. Each core created innovative techniques that moved science one step forward, Moody says.
“For example, the genetic resources core provided a number of novel transgenic mouse lines that made it possible to test the contribution of retinoic acid signaling to DiGeorge phenotypes,” she explains. “The microscopic imaging and analysis core developed novel workflows, as well as imaging approaches, that enhanced every experiment in the project.”
On a macrolevel, the study illustrated the exponential benefits of program project grants in which collaborative efforts across multiple disciplines can yield great value to clinical problems.
“By combining approaches that crossed discipline barriers and involved clinical investigators with basic researchers, we were able to bring cellular and molecular insights into a complicated physiological function – feeding and swallowing,” Moody says. “In five years, we published more than 10 peer-reviewed research papers in top-tier journals and five significant review articles.”
“This collaborative group not only made amazing discoveries, it trained three postdoctoral fellows, two post-baccalaureate researchers, and two undergraduate researchers, all of whom have gone on to exciting scientific and medical careers,” she adds. “We [also] have provided a superb foundation upon which future researchers can design new experiments and treatments to solve this important pediatric problem.”