Adopted protein might be MS culprit.When the fatty, sheaths arachnoid sheath the continuation of the arachnoidea mater around the optic nerve, forming part of its internal sheath. carotid sheath a portion of the cervical fascia enclosing the carotid artery, the internal jugular vein, and the vagus nerve. crural sheath femoral s. that insulate nerve fibers in the brain become damaged, the result is multiple sclerosis (MS). But the cause of this destruction has long baffled researchers. One group now reports that a protein called syncytin might be at fault. Christopher Power of the University of Calgary in Alberta and his colleagues report in the October Nature Neuroscience that brain tissue collected from MS patients at autopsies harbors about three times as much syncytin as does postmortem postmortem /post·mor·tem/ (post-mort´im) performed or occurring after death. post·mor·tem (p st-môr t brain tissue from people without MS. To see what role syncytin might play in MS, the researchers cultured human brain cells in lab dishes. Using a genetically engineered virus that promotes syncytin production, the scientists induced cells called astrocytes astrocyte /as·tro·cyte/ (as´tro-sit) a neuroglial cell of ectodermal origin, characterized by fibrous, protoplasmic, or plasmatofibrous processes. Collectively called astroglia. as·tro·cyte ( to crank out the protein. The cells then released inflammatory proteins and damaging oxidizing compounds called free radicals. This combination killed oligodendrocytes oligodendrocyte /ol·i·go·den·dro·cyte/ (-den´dro-sit) a cell of the oligodendroglia. ol·i·go·den·dro·cyte ( l , brain cells that maintain the myelin sheaths myelin sheathn. that insulate nerve fibers. The insulating envelope of myelin that surrounds the core of a nerve fiber or axon and that facilitates the transmission of nerve impulses, formed from the cell membrane of the Schwann cell in the peripheral nervous system and from oligodendroglia cells. Also called medullary sheath. When the scientists injected the syncytin-promoting virus into the brains of live mice, the viruses invaded astrocytes and caused these cells to produce large amounts of the protein. Within 2 weeks, the mice developed muscle-coordination problems reminiscent of MS symptoms. Mice given an antioxidant recovered. The gene for syncytin is an oddity. Scientists hypothesize that it was captured from retroviruses that invaded the human genome roughly 1 million years ago (SN: 5/13/00, p. 318). The gene is normally quiescent, except when playing a role in placental development, says Mark P. Mattson, a neuroscientist at the National Institute of Aging in Baltimore. "It's not clear why the gene for syncytin is activated in astrocytes of MS patients," he says. Even so, the finding could open up a new strategy for developing treatments for MS.--N.S. |
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