The University Record, June 4, 2001

Copper is crucial for embryonic development, study says

By Sally Pobojewski
Medical School Communications

Copper could be more important to the health of a fetus than folic acid, giving up smoking or abstaining from alcohol—according to a new study by scientists at the Medical School.

In the June 5 issue of the Proceedings of the National Academy of Sciences (PNAS), U-M scientists report that copper and a protein called Ctr1, which helps copper get inside cells, is essential for normal embryonic development in mice. Although scientists knew that Ctr1 was involved in copper transport in yeast microorganisms, no one knew exactly how the gene worked in mammals until now.

“Since the genetic structure and function of Ctr1 is nearly identical in mice and humans, it is very likely that Ctr1 is essential for human embryonic development,” says Dennis J. Thiele, professor of biological chemistry, who directed the study.

In recent studies with fruit flies, mice and human cells, Thiele found Ctr1 copper transport proteins and gene sequences in every species. “Ctr1 appears to have been conserved throughout evolutionary development, because it is so effective at bringing copper across membranes and into cells,” he says.

“Ctr1 escorts copper through the cell’s surface membrane and then hands it off to at least three other proteins, which deliver it to specific compartments inside the cell,” Thiele says.

A related paper by scientists from Washington University in St. Louis, published in the same issue of PNAS, describes the role of ATOX1, one of three other proteins in this intracellular copper relay.

“Copper is an essential micronutrient, which is required for vital biochemical reactions within cells,” Thiele says. “Without copper, cells can’t produce energy, metabolize iron or detoxify free radicals. Without copper, we can’t grow blood vessels, synthesize neuropeptides that control muscle contractions or make the collagen that gives our skin its elasticity.”

Thiele studied yeast microorganisms for 17 years to learn how cells process copper. “Our work with yeast, and research by other scientists, was the key to finding the transporter proteins,” he says.

Thiele’s research team found that expression of the Ctr1 gene in human kidney cells stimulated a 30-fold increase in copper uptake by the cells. U-M scientists then used genetic engineering technology to create mice that were missing one of two alleles—or copies of the Ctr1 gene—found in normal mice.

Although these heterozygous mice appeared and acted normal, U-M researchers found that their brains and spleens contained about half as much copper as was found in normal litter mates. Since the ability to metabolize iron—another critical nutrient—depends on copper, it was not a surprise to find that iron levels were lower in organs from heterozygous mice than from normal litter mates.

The big surprise came when U-M researchers bred male and female heterozygous mice to see what would happen to mice without either copy of the Ctr1 gene. Of 378 mouse pups born, not one was found to be missing both copies of the gene. When Thiele examined mouse embryos from these crosses, he discovered that embryos without the Ctr1 gene all died 10–12 days after fertilization. In addition, all these embryos were much smaller than normal and had major abnormalities in organ and cell development.

To test whether copper supplements would help, U-M researchers added it to the drinking water of female experimental mice three weeks before and during their pregnancies. Although they received 50–100 times more copper than control mice, the effect on their embryos was unchanged.

This research was supported by grants from the National Institutes of Health, the International Copper Association and the American Heart Association. Jaekwon Lee, U-M research fellow in biological chemistry, and Joseph R. Prohaska, professor of biochemistry and molecular biology at the University of Minnesota-Duluth, were co-authors.