Lipofuscin.

Over time, postmitotic cells accumulate a non-degradable intralysosomal substance, lipofuscin, which forms due to iron-catalyzed oxidation/polymerization of protein and lipid residues. Lipofuscin is often considered a hallmark of aging, showing an accumulation rate that inversely correlates with longevity. There is an emerging impression that lipofuscin, although still typically considered a harmless wear-and-tear product, may have multiple negative effects. By interfering with the important autophagic process, by which most worn out cellular components are degraded, it may prevent cellular renewal and advance the accumulation of damaged cellular constituents. Due to binding of transition metals, such as iron and copper, lipofuscin also seems to sensitize lysosomes and cells to oxidative stress. Of importance for the pathogenesis of age-related macular degeneration, lipofuscin deposition interferes with the phagocytic activity of retinal pigment epithelial cells and also sensitizes their lysosomes to blue light.