The formation of synapses during brain development, which plays a crucial role in learning and memory, is mediated by molecular mechanisms that remain elusive. In November 9 Science Daniela Mauch and colleagues from Max-Delbrück-Center for Molecular Medicine, Berlin, Germany and the Centre de Neurochimie, Strasbourg, France show that a factor derived from glial cells which strongly promotes synapse development is actually a cholesterol molecule complexed to apolipoprotein E (apoE).
Mauch et al. identified apoE (a cholesterol carrier) in the glial cell culture supernatant and observed that it promotes synapse development in a culture of rat retinal ganglion cells (RGC) only when apoE was complexed to cholesterol. In addition, mevastatin — an inhibitor of cholesterol synthesis — diminished the synapse development of RGC; the effect of mevastatin was reversed by the addition of exogenous cholesterol (Science 2001, 294:1354-1357).
These results indicate a new role for glial cells as cholesterol providers and could explain why glial cells secrete cholesterol-rich lipoproteins. "This may [also] explain the neurobehavioral manifestations of defects in cholesterol or lipoprotein homeostasis", concluded the authors.