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The Journal of Neuroscience, November 23, 2005, 25(47):10884-10893; doi:10.1523/JNEUROSCI.2909-05.2005
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Neurobiology of Disease
Choroid Plexus Megalin Is Involved in Neuroprotection by Serum Insulin-Like Growth Factor I
Eva Carro, *
Carlos Spuch, *
Jose Luis Trejo,
Desiré Antequera, and
Ignacio Torres-Aleman
Laboratory of Neuroendocrinology, Cajal Institute, Consejo Superior de Investigaciones Científicas, 28002 Madrid, Spain
The involvement of circulating insulin-like growth factor I (IGF-I) in the beneficial effects of physical exercise on the brain makes this abundant serum growth factor a physiologically relevant neuroprotective signal. However, the mechanisms underlying neuroprotection by serum IGF-I remain primarily unknown. Among many other neuroprotective actions, IGF-I enhances clearance of brain amyloid (A ) by modulating transport/production of A carriers at the blood-brain interface in the choroid plexus. We found that physical exercise increases the levels of the choroid plexus endocytic receptor megalin/low-density lipoprotein receptor-related protein-2 (LRP2), a multicargo transporter known to participate in brain uptake of A carriers. By manipulating choroid plexus megalin levels through viral-directed overexpression and RNA interference, we observed that megalin mediates IGF-I-induced clearance of A and is involved in IGF-I transport into the brain. Through this dual role, megalin participates in the neuroprotective actions of IGF-I including prevention of tau hyperphosphorylation and maintenance of cognitive function in a variety of animal models of cognitive loss. Because we found that in normal aged animals, choroid plexus megalin/LRP2 is decreased, an attenuated IGF-I/megalin input may contribute to increased risk of neurodegeneration, including late-onset Alzheimer's disease.
Key words: megalin-LRP2; insulin-like growth factor I receptor; choroid plexus; amyloidosis; Alzheimer's disease; physical exercise
Received July 14, 2005;
revised September 2, 2005;
accepted October 2, 2005.
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