Cholesterol accumulation in Niemann Pick type C (NPC) model cells causes a shift in APP localization to lipid rafts

Abstract

It has been suggested that cholesterol may modulate amyloid-β (Aβ) formation, a causative factor of Alzheimer's disease (AD), by regulating distribution of the three key proteins in the pathogenesis of AD (β-amyloid precursor protein (APP), β-secretase (BACE1) and/or presenilin 1 (PS1)) within lipid rafts. In this work we tested whether cholesterol accumulation upon NPC1 dysfunction, which causes Niemann Pick type C disease (NPC), causes increased partitioning of APP into lipid rafts leading to increased CTF/Aβ formation in these cholesterol-rich membrane microdomains. To test this we used CHO NPC1-/- cells (NPC cells) and parental CHOwt cells. By sucrose density gradient centrifugation we observed a shift in fl-APP/CTF compartmentalization into lipid raft fractions upon cholesterol accumulation in NPC vs. wt cells. Furthermore, γ-secretase inhibitor treatment significantly increased fl-APP/CTF distribution in raft fractions in NPC vs. wt cells, suggesting that upon cholesterol accumulation in NPC1-null cells increased formation of APP-CTF and its increased processing towards Aβ occurs in lipid rafts. Our results support that cholesterol overload, such as in NPC disease, leads to increased partitioning of APP/CTF into lipid rafts resulting in increased amyloidogenic processing of APP in these cholesterol-rich membranes. This work adds to the mechanism of the cholesterol-effect on APP processing and the pathogenesis of Alzheimer's disease and supports the role of lipid rafts in these processes.

Autophagy-Derived Alzheimer’s Pathogenesis

“…Lipid rafts may also facilitate Aβ aggregation (Rushworth & Hooper, 2010) and extracellular Aβ internalization (Lai & McLaurin, 2010). Increased cholesterol accelerates APP localization into lipid rafts and enhances Aβ generation (Kosicek et al, 2010;Michikawa, 2003); consistent with observations that elevated dietary cholesterol uptake or hypercholesterolemia is associated with increased formation of amyloid plaques (Kivipelto et al, 2001). In addition, cholesterol depletion inhibits neuronal Aβ generation ; and cholesterol-reducing statin drugs appear to reduce the risk of dementia (Gibson Wood et al, 2003).…”

N-glycome of the Lysosomal Glycocalyx is Altered in Niemann-Pick Type C Disease (NPC) Model Cells

“…In addition, a 3-fold increase of cholesterol was detected in the isolated lysosomal fractions from NPC1-null compared to CHOwt cells (p<0.01) ( Figure 1C). This result is in agreement with our previous work using this model (7)(8)(9). We next performed MS-based proteomic analysis of the isolated lysosomal fractions.…”

“…To test these two possibilities we measured the levels of fluorescein signal in the cell lysate and in the medium 24 hours after initial uptake. We did not observe significant differences of the intracellular and Table 1 and Notably, in our previous studies we have substantially used this NPC disease cellular model to elucidate the molecular and cellular details of an AD-like phenotype in NPC (7)(8)(9)36). Based on our results we speculate that changes in the N-glycome of the lysosomal membrane proteins may contribute to lysosomal (dys)function in NPC disease.…”

“…Recently, NPC disease has shown to share several pathological features with the most common and complex Alzheimer's disease (AD) (6). Our previous work has suggested that dysfunction of the late endosomal/lysosomal compartments in NPC1-cellular model is, most likely, responsible for the AD-like features in NPC (7,8), and that increased levels of free cholesterol in NPC play an important role in compartmentalization of the key AD-proteins ( -amyloid precursor protein -6 APP and -secretase -BACE1) within lipid rafts (9) or in modulation of membrane stiffness lading to sequestration of both APP and BACE1 within the endolysosomal pathway (10).…”

Altered dynamics of a lipid raft associated protein in a kidney model of Fabry disease

“…Furthermore, changes in raft composition have been described for some lysosomal storage disorders such as Niemann-Pick type C [33], Gaucher disease type I [34], Sandhoff disease [35], Sanfilippo disease [36], neuronal ceroid lypofuscinosis [37], and Krabbe disease [38]. Whether lipid raft structure is altered in Fabry disease is not known, however recent studies have suggested that trafficking of the glycosphingolipid lactosylceramide and of the apical glycoprotein dipeptidylpeptidase IV are perturbed in fibroblasts of Fabry disease patients compared to control fibroblasts [39,40].…”