Cholesterol Helps Brain Cells Communicate
Excerpt By Amy Norton, Reuters Health

NEW YORK (Reuters Health) - It may cause trouble in the blood, but in the brain cholesterol is key to the cell connections needed for memory and learning, scientists have found.

Past research has suggested that brain ``support cells'' known as glial cells produce a substance that allows the brain's nerve cells, or neurons, to communicate. That substance now appears to be cholesterol, according to a report in the November 9th issue of Science.

This does not mean, however, that downing a fatty steak will enhance a person's brain power. Cholesterol levels in the blood do not determine the brain's supply, as blood cholesterol molecules are too large to cross the blood-brain barrier, researchers explain. The blood-brain barrier is a mechanism that strictly controls the type of molecule allowed to enter into the brain from blood vessels.

Instead, glial cells appear to churn out their own cholesterol supply, report Daniela H. Mauch, of the Max-Delbruck-Center for Molecular Medicine in Berlin, Germany, and colleagues.

The researchers zeroed in on cholesterol through experiments with cells in which the lipid triggered the formation of synapses--the connections through which nerve cells communicate.

``Thus,'' Mauch's team writes, ``the availability of cholesterol appears to limit synapse development.''

In addition, the investigators found that, when cultured alone, neurons produced some cholesterol. But only when glial cells were present was there a cholesterol supply abundant enough for ``massive'' synapse formation.

According to the researchers, these findings suggest that any ``genetic or age-related defects'' in the brain's cholesterol use may impair the circuitry behind mental functioning.

Supporting that possibility, one of their findings was that a protein called apolipoprotein E (apoE) was involved in delivering cholesterol from glial cells to neurons. One form of the apoE gene, apoE4, is linked to an increased risk of Alzheimer's disease.

So the question arises as to whether apoE4 differs in its ability to form synapses among neurons, researchers at Stanford University School of Medicine in California note in an accompanying editorial.

One of the editorialists, Dr. Ben A. Barres, told Reuters Health that while ``it is hard to know for sure...one imagines that apoE4 might be associated with less good cholesterol delivery to the synapse.''

Barres explained, ``In Alzheimer's, it is thought that there is a loss of synapses.'' It now seems possible, he noted, that lower-than-normal cholesterol levels in the brain could be behind this loss.

SOURCE: Science 2001;294:1354-1357.

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