Research Briefs

Lose Gene, Lose Sleep

Sleep is still a mysterious process. Though scientists have made much progress identifying the brain areas and neurochemicals involved, the molecular basis of this restful state remains unexplored.

In a poster presentation at the annual meeting of the Society for Neuroscience (see p. 1 story), Priyattam Shiromani, (at left) HMS associate professor of psychology at the Brockton Veterans Administration Medical Center, reported the first evidence that a specific gene is involved in inducing sleep. Working with Robert McCarley, a professor of psychiatry at the VA, and others, he found that mice lacking the gene c-fos have insomnia. They need twice as long as normal mice to nod off, and when they finally do, they sleep 30 percent less than their normal cousins.

C-fos is known to become activated in response to many stimuli. For example, thirst activates c-fos in brain cells regulating drinking; light activates c-fos in neurons controlling circadian rhythms. The gene is thought to be an early step in the intracellular signaling cascade that ultimately brings about a behavioral response to a stimulus. It is also active in response to conditions affecting sleep, including stress, pain, even sexual activity, though any molecular connection is unclear.

Shiromani suspects that c-fos builds up a signal during the period of wakefulness that after a certain time induces slumber. Lacking that signal, the knockout mice do not "know" how long they have been awake.

This is just the beginning of the genetic dissection of sleep. Many more genes need to be identified before researchers can understand this process and develop new treatments for the 60 million Americans with insomnia.

One AIDS Vaccine Possible for All HIV Strains?

In the November Journal of Virology, researchers led by Bruce Walker, associate professor of medicine at MGH-East, suggest that it may be possible to develop one AIDS vaccine that is effective against the different versions of the HIV virus found around the globe. The researchers report that the immune system's killer T cells, called cytotoxic T-lymphocytes (CTLs), are able to recognize different strains of HIV.

Previously, there was concern that different HIV strains in different parts of the world would require the development of many vaccines, each targeted to a particular strain.

Cytotoxic T lymphocytes have become a focus of HIV vaccine research, as earlier vaccine strategies based on antibodies against HIV have failed. Recent research has suggested that CTL activity may be key to a successful immune response to HIV. High CTL levels were observed in people who remain healthy despite having been infected for many years, and CTLs specific to HIV also occur in people who resist infection despite repeated exposure to HIV.

Most HIV-infected people in the U.S. and Europe carry strain B of the virus, while strains A, C, D, E, and others predominate in Africa and Asia. The researchers tested whether CTLs from people infected with strain B would recognize viral peptides from all other major strains. Indeed, all of the tested CTLs recognized peptides from at least one non-B strain, and most reacted against peptides from all strains tested. Conversely, the researchers tested CTLs from 14 HIV-infected individuals from Senegal, 10 of whom carried strain A, three carried strain G, and one carried strain C. CTLs from all 14 people reacted against peptides from strain B.

"We were very surprised to see this striking amount of CTL cross-reactivity," says Walker. He notes that CTL-based vaccines are just beginning to be tested in human volunteers, and many questions remain to be answered.

Weight Gain Increases Risk of Breast Cancer After Menopause

Harvard investigators have found strong evidence that gaining weight in adulthood raises the risk of breast cancer in women after menopause, especially in those who are not taking hormone replacement therapy.

As part of the ongoing Brigham-directed Nurses Health Study, Zhiping Huang, a fellow in nutrition at the Harvard School of Public Health, and others, followed 95,256 female nurses, aged 30 to 55, for 16 years and compared their incidence of invasive breast cancer to their body mass index over time. The researchers analyzed separately women who were on hormone replacement therapy from those who were not.

In the November 5 Journal of the American Medical Association, the researchers report that among women who had never used hormones and had gained more than 44 pounds faced almost twice the risk of breast cancer than women with minimal weight gain. Women in this group who had gained 22 to 44 pounds were at 61 percent higher risk.

Overall, 33 percent of the postmenopausal cancer resulted from weight gain, estrogen use, or an interaction of the two. Weight gain alone accounted for 16 percent; estrogen use alone, for 5 percent.

While this number is high, it is also encouraging because, unlike their genes, women can control their weight, researchers from Stanford University School of Medicine and Dartmouth Medical School wrote in a commentary in the same issue of JAMA.

Apoptosis Study Shows How Chemotherapy Causes Female Infertility

Researchers at Massachusetts General Hospital (MGH) and elsewhere have discovered the molecular pathways that lead to the destruction of oocytes by a common chemotherapy drug. The finding, while far from clinical application, eventually could lead to ways for preserving fertility in girls and women treated with anticancer drugs.

In the November Nature Medicine, researchers led by Jonathan Tilly, HMS associate professor of obstetrics, gynecology, and reproductive biology at MGH, working with researchers at Washington University in St. Louis, report that the chemotherapy drug doxorubicin (DXR) causes mouse oocytes to undergo cell suicide, or apoptosis.

"It has been known for years that women treated with chemotherapy become infertile, but we have never known what the mechanisms were," says Tilly.

When the researchers exposed mouse oocytes to doses of DXR equivalent to those present in the blood of cancer patients treated with the drug, they observed the cellular hallmarks of apoptosis, such as cell shrinkage and fragmentation. Mouse zygotes reacted differently to DXR: they halted cell growth and division, but did not die.

Apoptosis is an elaborate process involving the sequential activity of several genes and their proteins. The researchers studied several of these known molecular steps and found that they probably are active in DXR-induced apoptosis. Specifically, the early signal ceramide, the death-promoting gene bax (a member of the bcl-2 gene family), and proteins called caspases (which include ICE, the first mammalian protease identified in apoptosis) all are involved in DXR-induced cell death.

Interestingly, p53-a crucial player in the cell's decision whether to divide, stop dividing, or commit suicide-does not seem to act in the pathway leading to DXR-induced apoptosis in oocytes. This means that anti-cancer drugs that depend on the activity of p53 might successfully destroy tumor cells without damaging oocytes, Tilly suggests.