A link between sugar and heart defects

How a peptide hormone sparks appetite

Et cetera

A DNA “mimic” to repair genes

Boost for protein, gene studies

The Swedish Sea, center panel, by Jim Dine. © ESM-Ed Meneely/Art Resource, NY

A link between sugar and heart defects

Examining role of glucose in cardiac malformation, researchers look for ways to protect the infant heart.

It’s a heart-rending legacy: mothers who have uncontrolled diabetes during pregnancy are three times more likely to give birth to babies with malformed hearts than are mothers whose blood sugar levels are normal. Doctors have known that for some time, but recent work by researchers at Yale and the University of Arizona helps explain how high blood glucose levels in the mother lead to infant heart defects, and may suggest ways to prevent the problem.

“Lack of control of glucose in early pregnancy is a serious problem, because often the woman doesn’t even know she’s pregnant at the time,” said Joseph A. Madri, Ph.D., M.D., HS ’76, FW ’80, professor of pathology and co-director of medical studies. “Yet this period of the first few weeks is critical, because this is when formation of all the organs occurs.”

In earlier work, Madri and co-workers including Emese Pinter, M.D., an associate research scientist in pediatrics, studied the formation of blood vessels of the yolk sac in a mouse model of maternal diabetes. “We found that higher levels of glucose, comparable to what would be found in a diabetic mother, had profound effects on the development of yolk sac vasculature,” said Madri. “The vasculature of the yolk sac, which is important for nutrient, gas and waste exchange in the developing embryo, was arrested when the glucose level was high.” What’s more, glucose levels didn’t have to remain high for long to cause serious problems, the research showed. Even a brief spike could be enough to abort a pregnancy.

In the newer work, published in the February 17 issue of The Journal of Cell Biology, Madri, Pinter and co-workers focused on a slightly later stage of development, when the cardiovascular system begins to form. Normally, this is a multistep process involving the endocardial cushion, a small area in the embryonic heart with two tissue layers, the endocardium and the myocardium.

“For normal development, endocardial cells overlying the cushion area have to dissociate from one another and migrate into the tissue beneath the endocardium called the cardiac jelly,” said Madri. To investigate how the process is disrupted under high-glucose conditions, the researchers used an in vitro model of endocardial cushion formation. With this model, they showed that high glucose levels inhibit dissociation and migration of the endocardial cells and that this disruption occurs during a critical window at the developmental stage when the embryo consists of 20 to 25 somites (block-like segments of tissue). Next, they explored the role of a regulatory molecule that is involved in keeping the cells in a sheet-like layer. In normal development, levels of platelet endothelial cell adhesion molecule-1 (PECAM-1) drop in the endocardial cells overlying the cushion area, allowing the endocardial cells to move apart and migrate into the cardiac jelly to form such structures as the valves and part of the walls between the chambers of the heart. But when glucose levels are elevated, PECAM-1 persists, the researchers found.

“The endocardial cells can’t dissociate from each other and migrate,” said Madri. “The result is a heart with an opening between chambers or one in which there are problems with the structure of the valves.”

Why does PECAM-1 persist when glucose levels are high? The research implicates vascular endothelial growth factor A (VEGF-A), known to be important in the development of new blood vessels and the regulation of associated processes. Typically in diabetic adults, VEGF-A levels rise along with glucose levels. But for reasons Madri, Pinter and co-workers don’t yet understand, in fetuses VEGF-A shows the opposite effect—its levels drop when glucose is high. Because VEGF-A affects the regulation of PECAM-1, low VEGF-A levels mean that PECAM-1 isn’t properly controlled, allowing it to overstay its welcome.

Now, said Madri, “we’re trying to understand how VEGF is controlled in the fetus and how that’s different than in the adult. Once we know this, perhaps we can devise modalities to blunt the effect of excess glucose in the fetus.”

—Nancy Ross-Flanigan

A cross section of the hypothalamus shows ghrelin neurons and axons, in yellow. These molecules coordinate processes including appetite.

From the stomach to the brain: how a peptide hormone sparks appetite

In recent years neurobiologists have taken a keen interest in a peptide hormone called ghrelin. The molecule appears to be involved in activities such as growth hormone release, energy homeostasis and the functioning of the cardiovascular system. Big Pharma sees in it a potential target for diet drugs because of its role in sparking an appetite.

It is also of interest because, although it is produced by the stomach, it is found in the hypothalamus as well. Now researchers at Yale have tracked ghrelin to a group of previously uncharacterized neurons in the brain’s appetite center.

“Ghrelin-producing cells are distributed in the hypothalamus in such a manner that they are in a perfect position to coordinate the activity of the different hypothalamic subnuclei already known to regulate daily energy balance,” said Tamas Horvath, Ph.D., D.V.M. senior author of an article in the February 20 issue of Neuron and associate professor of obstetrics and gynecology and neurobiology.

Studies in rats and humans had already shown that ghrelin signals the brain’s appetite center when energy levels are low. Levels of ghrelin rose before and declined after meals. The mapping of the ghrelin circuit to neurons in the brain offers a new target for regulating appetite and food intake, Horvath said.

“We believe that these neurons are conveying information regarding circadian rhythm and sensory clues as well,” he said. “You could be watching a movie, see food and become hungry, or be in the kitchen and smell something and become hungry, even if your stomach is full. These brain ghrelin neurons may be those that enable these brain processes to dominate over the actual need for energy intake.”

One hypothesis, Horvath said, is that the system that balances food consumption, energy expenditure, body weight and fat stores may be suppressed by events such as stress or pregnancy. The neuronal system that signals olfactory and visual clues would then dominate.

“We are now working to find out how ghrelin from the stomach and from the brain work together or independently to regulate appetite or food intake and other brain mechanisms,” Horvath said.

—John Curtis

Et Cetera

A DNA “mimic” to repair genes

A peptide nucleic acid (PNA) that mimics DNA holds the promise of repairing defective genes, according to Yale radiologists and geneticists.

PNA, which replaces DNA’s phosphodiester backbone with a polyamide one, creates a strong bond with DNA, said Peter M. Glazer, M.D., Ph.D., professor and chair of the Department of Therapeutic Radiology. “If you can bind something to the gene, maybe you can use that to change the gene,” he said. “If you change the gene to a new sequence it is permanently fixed.”
In a study published in December in the Proceedings of the National Academy of Sciences, Glazer, the senior author, described the use of PNA to introduce a specific DNA sequence into a target gene in extracts of human cervical cancer cells. The new DNA sequence corrected a mutation in the target, the authors reported.
PNA, they concluded, could serve as a tool both for research and for repairing genes implicated in hereditary diseases such as sickle cell anemia and cystic fibrosis.
—John Curtis

Boost for protein, gene studies

The Center for Genomics and Proteomics, founded last year with a $200 million investment from the university, awarded $300,000 in seed money this winter to seven groups of scientists on Science Hill and at the medical school.

“We were looking for projects which have prospects of developing into large programs,” said Sherman M. Weissman, M.D., Sterling Professor of Genetics and professor of medicine, co-director of the center. Michael Snyder, Ph.D., the chair and Lewis B. Cullman Professor of Molecular, Cellular and Developmental Biology, is the director of the center. The funded projects will include research in lipids, Arabidopsis proteome chips, genomic microarrays in C. elegans and Drosophila, a cryopreservation facility and profiling of the rice genome.

“The pilot grants are a great way to stimulate integrative and cutting-edge research projects for the center,” said Snyder.

—John Curtis