PROVIDENCE, R.I. — For the first time, scientists have observed the herpes simplex virus traveling from the nerve ending to the nerve cell body within a living nerve cell, according to a team of researchers led by Elaine Bearer, M.D., at Brown University and the Marine Biological Laboratory at Woods Hole, Mass.
Herpes virus causes diseases ranging from the common cold sore to chicken pox. Genital herpes in women causes a significant of risk of death for newborn babies.
Scientists have known that the herpes virus enters a mucous membrane, such as the lip, at the nerve ending and travels along the string-like nerve to the central nervous system near the brain, where the virus replicates or enters latency.
Until this study, no one had observed and recorded that movement, said Bearer, associate professor in Brown’s Department of Pathology and Laboratory Medicine. Understanding how a virus travels within the nerve cell may lead to better treatment and perhaps cures for potentially lethal viral infections.
“Our ability to directly observe the intracellular movements of the virus will enable us to discover the molecules and mechanisms by which herpes gets into the central nervous system,” Bearer said.
The research is to be published in the July 5 issue of the Proceedings of the National Academy of Sciences. Copies are available from the PNAS news office at (202) 334-2138 or by e-mail at [email protected].
To duplicate the movement from nerve ending to cell nucleus, Bearer and colleagues used a nerve cell from a Woods Hole squid as the model because the animal’s “giant” axon – 7 centimeters in length and 1 millimeter in diameter – was large enough to inject and provided good visibility.
The scientists stripped herpes simplex virus Type I of its envelope and injected the human virus into the squid axon. The study showed that the viral particles travel at an “enormously” fast and consistent speed of 2.2 microns per second, which indicates a single mechanism for movement, Bearer said.
“For a long time, it was believed that herpes traveled back to the central nervous system by infecting other cells in the nerve sheath,” Bearer said. The virus does infect these cells, but this research showed that the virus moves much faster inside the axon.
The discovery of a single transport mechanism means that science has one target to hit with drug therapy, Bearer said. It also means that the transport mechanism could someday be used for sending new genes into the central nervous system for therapy.
The procedure retained two other viral parts, the tegument – genetically labeled with green fluorescent protein – and the capsid. The study showed that the viral envelope is not required for transport of the virus.
In addition, the study showed the transport machinery is highly conserved throughout evolution – that is, it is similar in humans and squid.
The research team included Bearer, Xandra O. Breakefield and Deb Schuback of the Massachusetts General Hospital, Boston; Thomas S. Reese of the National Institute of Neurological Disease and Stroke, Bethesda, Md., and Jennifer H. LaVail of the University of California– San Francisco.
The study was funded by the National Institutes of Health and by the Marine Biological Laboratory.
The Marine Biological Laboratory is an independent scientific institution, founded in 1888, that undertakes the highest level of creative research and education in biology, including the biomedical and environmental sciences.
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