Histology, Lipofuscin

Excerpt

Lipofuscin is a pigmented, heterogenous byproduct of failed intracellular catabolism conventionally found within lysosomes or the cytosol of aging postmitotic cells. Although it is present in virtually any cell type, phenotypically proliferative cells often dilute its concentration to an insignificant level. Hannover first discovered lipofuscin in 1842, but its progressive accumulation with age was unknown until the end of the nineteenth century. While this historical description is still accurate, the literature of the past few decades has shifted focus towards its newly understood function as a photosensitizer of tissue and potentiator of intracellular dyshomeostasis. Because of lipofuscin’s extensively cross-linked tertiary structure and nondegradable nature, it is hypothesized to play a critical role in inhibiting proteasome function, mitophagy, autophagy, lysosomal stability, and the propagating reactive oxygen species.

Lipofuscin is frequently used interchangeably with “ceroid” or “ceroid lipofuscin” as both ceroid and lipofuscin are autofluorescent intracellular accumulations of similar composition. However, this may be misleading as the etymological differentiation between lipofuscin and ceroid was traditionally intended to label the former as a term associated with normal aging, and the latter for pathological conditions. This distinction has become muddied as traditional lipofuscin has continued to gain attention for its risk modification effect on many diseases.