engleski

Accumulation of cholesterol in Niemann Pick type C cells alters APP distribution within endosome compartments

Dysfunction of NPC1 protein causes Niemann Pick type C disease (NPC) and is characterized by accumulation of cholesterol and glycosphingolipids in endosomal/lysosomal compartments. It has been recently demonstrated that NPC disease exhibits an Alzheimer’s disease-like pathology showing tau hyperphosphorylation1 and increased amyloid-beta peptide (Abeta) levels2-4, in addition to a shift in presenilin 1 (PS1) distribution towards early/late endosomes3, 5. In this work we analyzed endocytic trafficking and internalization of the β-amyloid precursor protein (APP) and PS1 in NPC cells. We hypothesized that cholesterol accumulation upon NPC1 dysfunction leads to increased APP and PS1 distribution within endosome compartments and, thus, increased Abeta generation. Endosome compartmentalization of APP and PS1 in CHOwt and CHO NPC1-null cells (NPC cells) was monitored by endosome fractionation and by confocal microscopy. Endosome fractionation was performed in a 25-35% sucrose gradient. Early and late endosome fractions were detected by EEA1 (early) and Rab7 (late) staining. The same antibodies were used to analyze colocalization of endogenous APP and PS1 in early or late endosomes by confocal microscopy. Biotinylation assay was performed to monitor internalization of APP/PS1 between wt and NPC cells. Endosome fractionation showed that in NPC cells there is more APP and PS1 within late endosomal compartments compared to wt cells. In addition, we observed increased APP/PS1 internalization in NPC compared to wt cells. Our results show that loss of NPC1 function causes increased internalization and increased distribution of APP and PS1 towards late endosome compartments. Finding increased compartmentalization of APP and PS1 within late endosomes in NPC cells, suggests that increased Abeta in NPC disease may be due to increased coupling of presenilin 1 and its substrate APP in endosome compartments.

Alzheimer’s disease; APP; cholesterol; endosome; Niemann Pick type C disease; NPC1

nije evidentirano