Lipopigment in the aging brain.

Accumulation of lipopigments in neurons, glial, and other cells is the most characteristic change associated with the aging brain. Lipopigments are bipartite granules consisting of an autofluorescent electron-dense pigment and electron-lucent lipid components. Both components are enclosed by a common, continuous unit membrane. Ceroid-lipofuscinosis granules are also autofluorescent and rich in lysosomal enzymes, as seen in aging lipopigments. However, the fingerprint (lamellar) profiles seen in ceroid granules are not present in the aging lipopigment. This is the major morphological difference between these two types of granules. Dolichols are highly enriched in both aging lipopigment and ceroid granules. The accumulation of dolichols in these granules may be an indicator of a decreased turnover rate of lysosomes resulting from a defect of lysosomal metabolism. Unlike brain, liver seems to be spared in ceroid lipofuscinosis. Using an animal model of ceroid lipofuscinosis, we will be able not only to investigate the steps involved in the formation of the lipopigment but also to explore why certain cells and organs are spared and others are affected.