The hormonal component

An early line of defense against West Nile virus

Et cetera

A signal that the end is near

Enzyme linked to epilepsy

The hormonal component

A new study finds a link between stress, high levels of estrogen and certain mood disorders.

The ancients blamed women’s susceptibility to mental illness on low body temperature, which made them prone to “cold” diseases caused by black bile. More recent theories blamed the pressures of balancing a career and family life. A new study suggests that the vulnerability may hinge on hormones.

High levels of estrogen amplify the effects of stress on the prefrontal cortex, an area of the brain associated with mental disorders such as depression and post-traumatic stress disorder, the Yale study found. This could explain why such illnesses occur twice as often in women as in men and why the discrepancy is most marked between puberty and menopause.

For a study published in the May issue of Molecular Psychiatry, neurobiology graduate student Becca Shansky and associate professor of neurobiology Amy Arnsten, Ph.D., exposed rats to different levels of stress and then tested them on a working memory task that depends on the prefrontal cortex. Female rats were more sensitive than males to moderate levels of stress, but only when the females were in the high-estrogen phase of their estrus cycle. The same sensitivity was seen in females that had their ovaries removed and were then implanted with time-release estrogen capsules. It was not observed in females that received a placebo instead of estrogen.

Now Shansky is trying to sort out the mechanism underlying the effect. Previous research in Arnsten’s lab offers a few hints. Stress releases excess dopamine and norepinephrine in the prefrontal cortex, which activate receptors that cause stress-related impairment, says Shansky. “It’s also known that estrogen regulates the expression of these receptors. Now we’re trying to see which one or ones are involved in mediating this activity.”

Research by another group at the University of Pittsburgh Medical Center has added to the picture. Genetic studies of people with depression turned up an alteration in CREB1, a gene that encodes the regulatory protein CREB.

“We really perked up when we heard that, because the very intracellular pathways that impair the prefrontal cortex turn on this gene product,” Arnsten said, adding that in young women with circulating estrogen, “the activity of the intracellular pathway might be sufficient to cause significant prefrontal cortical dysfunction, leading to depression.” Shansky has experiments under way to determine whether female rats with high estrogen are more vulnerable to activation of CREB1 than those with low estrogen.

“It’s very important that our results are not interpreted as saying that women shouldn’t take stressful jobs or expose themselves to stress,” says Shansky. “It’s more a matter of looking at the mechanisms involved to see if we can find new ways of treating depression.” It’s also important to note that these brain changes occur with uncontrollable stress, Arnsten adds. A long history of animal and human research has shown that a sense of control over the stressor protects cognitive and physiological responses.

Though the Yale experiments involve lab animals, they may apply to people, says Arnsten. The genetic studies show changes in the same molecular pathway that we are studying in rats. It is very encouraging.”

—Nancy Ross-Flanigan

Yale scientists identify an early line of defense against West Nile virus

In the five years since the West Nile virus made its first appearance in New York, it has spread to virtually all of the contiguous 48 states. There has been an alarming increase in infections and the most serious cases have resulted in death from encephalitis. The Centers for Disease Control and Prevention reported about 9,000 cases of West Nile infection last year—more than double the number reported in 2002—and more than 200 deaths. Among those looking for ways to prevent and treat West Nile is Erol Fikrig, M.D., professor of medicine (rheumatology), who has spent the past 11 years investigating the biology of arthropod-borne illnesses, including Lyme disease.

Most of those infected with West Nile virus experience only mild illness, and some have no symptoms at all. Only about 30 percent of patients, many of them elderly or with compromised immune systems, succumb to the most serious form of the illness characterized by encephalitis. In a paper published last September in The Journal of Immunology, Fikrig and his colleagues offered a new explanation for why most patients are able to successfully fight off the virus shortly after infection.

In 2001, Fikrig’s group successfully immunized mice against West Nile by injecting the mice with genetically engineered fragments of the protein shell that encapsulates the virus; exposure to the harmless fragments caused the mice to develop antibodies against the virus. But it took three to four days for the vaccinated mice to deploy these antibodies, and clinical experience has shown that time is of the essence in treating West Nile.

Fikrig thought that in mildly ill patients West Nile’s relentless pace might have been stalled by some early immune response that clears the virus and gives these individuals time to marshal an antibody defense. He concluded that understanding these very early immune reactions is crucial to preventing severe illness and death. Talking one day with Joseph E. Craft, M.D., HS ’77, professor of medicine and immunobiology and chief of the Section of Rheumatology, Fikrig learned of an immune cell with all the right characteristics.

Craft, who specializes in autoimmune illnesses such as lupus, has extensively studied gamma delta T cells, which are believed to serve as a bridge between innate immunity, the body’s first line of defense, and later immune reactions. “We thought that gamma delta T cells might play a role in this early time window,” Craft said.

Along with postdoctoral researcher Tian Wang, Ph.D., Fikrig tested the hypothesis. Wang injected West Nile into a strain of mice that lack gamma delta T cells and found that these mutant mice were markedly more susceptible to infection than normal animals, and quicker to develop encephalitis and die once infected. When Wang injected activated gamma delta T cells into the mutants, they fought off the disease.

But Fikrig isn’t yet sure just how gamma delta T cells mount an early defense against West Nile. With the help of Eileen P. Scully, an M.D./Ph.D. student in Craft’s lab, Fikrig showed that the cells multiply dramatically and are activated quickly after infection. Scully also demonstrated a link between early and late immune reactions; gamma delta T cells produce interferon gamma, a potent molecule that attacks viruses and stimulates the immune system to produce antibodies.

Next Fikrig plans to see whether gamma delta T cells work in the same way in humans. If the results hold up, pharmaceutical companies might be able to make antiviral drugs that fight West Nile by boosting gamma delta T cell activity or interferon gamma production.

—Trisha Gura

Et Cetera

A signal that the end is near

A chemotherapeutic agent used against cancer for more than 30 years has a secondary effect of inducing “death signals” that kill neighboring cells, according to Yale scientists.

The agent, cisplatin, disrupts transcription and replication in tumor cells. It helped cyclist Lance Armstrong recover from testicular cancer and also works against lung, neck, cervical and ovarian cancers. In a study published in the Proceedings of the National Academy of Sciences in April, senior author Peter M. Glazer, M.D./Ph.D. ’87, HS ’91, professor and chair of the department of therapeutic radiology, reported that cells affected by cisplatin can produce a death signal that also kills neighboring cells. The phenomenon occurs only when there is a high density of cells that touch each other and communicate through channels called gap junctions. It also appears to require the activation of DNA-PK, an enzyme involved in DNA damage response.

“If we can understand this mechanism,” Glazer said, “it will help us to identify potential targets for manipulation.”

—John Curtis

Enzyme linked to epilepsy

Small amounts of glutamate help the brain to function normally, but high concentrations of the neurotransmitter have been linked to temporal lobe epilepsy (TLE), a common form of epilepsy that is frequently drug-resistant.

A Yale study published in The Lancet has found that people with TLE also have low levels of glutamine synthetase, an enzyme that transforms glutamate into the non-toxic chemical glutamine.

“We don’t know why glutamine synthetase is decreased in TLE, but this is something we are exploring in our laboratory right now,” said lead author Tore Eid, M.D., Ph.D., an associate research scientist in the laboratory of Nihal C. de Lanerolle, D.Phil., associate professor of neurosurgery and neurobiology. “We also want to see if we can stop the seizures and reduce the brain damage in TLE by boosting the activity of glutamine synthetase.” If this turns out to be the case, Eid added, then it is possible that glutamine synthetase could be a new target for drug therapy.

—J.C.