Immunoreactivity of neuronal lipofuscin with monoclonal antibodies to the amyloid beta-protein.

Monoclonal antibodies generated against a synthetic peptide corresponding to amino acids 1 to 24 of cerebrovascular amyloid beta-protein do not only stain amyloidotic blood vessels and the amyloid deposits of the (senile) neuritic plaques, but also the neuronal pigment lipofuscin. Staining of lipofuscin is observed in both cerebral and cerebellar cortices, subcortical nuclei as well as the brain stem, and is identical in Alzheimer and normal control brain. Western blots of a lipofuscin enriched fraction show an anti-beta-protein reactive polypeptide migrating at approximately 31 kDa position on SDS-polyacrylamide gel electrophoresis. These results suggest that this polypeptide is associated with lipofuscin and is most likely derived from the predicted amyloid precursor protein. This implicates that, unlike in Alzheimer's disease where this protein is also processed extraneuronally in a manner to release an amyloid fiber forming fragment, the end point of its processing in the nerve cell seems to accumulate on a lipopigment characteristic for normal aging.