Lipofuscin

Lipofuscin is a yellow-brown, autofluorescent pigment composed of cross-linked oxidised proteins, peroxidised lipids, sugar adducts and redox-active metals such as iron. It forms within lysosomes from material that escapes complete degradation, particularly under conditions of oxidative stress and limited autophagic flux. Because lipofuscin is essentially non-degradable and cannot be exported from the cell, it accumulates progressively in long-lived post-mitotic cells, including neurons, cardiomyocytes, skeletal muscle fibres and retinal pigment epithelial cells. The accumulating granules occupy lysosomal volume, blunt autophagy and base-line proteolytic capacity, and contribute to age-related declines in proteostasis. Lipofuscin is widely used as a histological biomarker of cellular ageing and senescence and is implicated in age-related macular degeneration and certain neurodegenerative conditions.