scholarly journals Amyloidogenic Processing of APP in Lipid Rafts

2010 ◽  
Vol 3 (1) ◽  
pp. 21-31
Author(s):  
Madepalli K. Lakshmana ◽  
Subhojit Roy ◽  
Kaihong Mi ◽  
David E. Kang
Keyword(s):  
Lipid Rafts ◽  
Lipid Raft ◽  
Amyloid Β ◽  
Convincing Evidence ◽  
Amyloid Β Peptide ◽  
Cholesterol Levels ◽  
Amyloidogenic Processing ◽  
Secretase Inhibitor ◽  
Aβ Generation ◽  
Lipid Raft Microdomains

Increased generation of amyloid β peptide (Aβ) derived from amyloid precursor protein (APP) is the primary pathological characteristic of Alzheimer’s disease (AD). However, the sub cellular compartment in which APP undergoes cleavage by secretases to generate Aβ is not precisely known. Compelling evidences suggest that amyloidogenic processing of APP occurs in lipid rafts. An indirect support for lipid raft processing of APP includes the localization of Aβ, APP C-terminal fragments (CTFs), APP holoprotein and secretases in the lipid raft microdomains, although few studies failed to find APP in the lipid rafts. The indirect support also comes from both experimental and clinical studies involving modulation of cholesterol levels and its effect on Aβ generation. Moderate depletion of cholesterol results in significant reduction in Aβ levels and increased dietary intake of cholesterol leads to higher levels of Aβ production suggesting that amyloidogenic processing of APP strongly depends on cholesterol levels and therefore on lipid raft integrity. More convincing evidence that lipid rafts are critical for amyloidogenic processing of APP comes from studies using antibody-mediated co-patching of APP and BACE1 which results in lipid raft association of APP and BACE1 and increased Aβ generation. Further, an endosome/lipid raft targeting of β-secretase inhibitor by sterol-mediated anchoring leading to reduced Aβ generation also suggests that lipid rafts are pivotal for amyloidogenic processing of APP. In the absence of an effective therapy for AD, proteins responsible for delivery of APP to lipid rafts including LRP, RanBP9 and ApoER2 may be excellent therapeutic targets in AD.

scholarly journals Preferred Endocytosis of Amyloid Precursor Protein from Cholesterol-Enriched Lipid Raft Microdomains

Molecules ◽  
2020 ◽  
Vol 25 (23) ◽  
pp. 5490
Author(s):  
Yoon Young Cho ◽  
Oh-Hoon Kwon ◽  
Sungkwon Chung
Keyword(s):  
Amyloid Precursor Protein ◽  
Lipid Rafts ◽  
Lipid Raft ◽  
Amyloid Β ◽  
Precursor Protein ◽  
Cholesterol Levels ◽  
Elevated Cholesterol ◽  
Aβ Generation ◽  
Lipid Raft Microdomains ◽  
First Time

Amyloid precursor protein (APP) at the plasma membrane is internalized via endocytosis and delivered to endo/lysosomes, where neurotoxic amyloid-β (Aβ) is produced via β-, γ-secretases. Hence, endocytosis plays a key role in the processing of APP and subsequent Aβ generation. β-, γ-secretases as well as APP are localized in cholesterol-enriched lipid raft microdomains. However, it is still unclear whether lipid rafts are the site where APP undergoes endocytosis and whether cholesterol levels affect this process. In this study, we found that localization of APP in lipid rafts was increased by elevated cholesterol level. We also showed that increasing or decreasing cholesterol levels increased or decreased APP endocytosis, respectively. When we labeled cell surface APP, APP localized in lipid rafts preferentially underwent endocytosis compared to nonraft-localized APP. In addition, APP endocytosis from lipid rafts was regulated by cholesterol levels. Our results demonstrate for the first time that cholesterol levels regulate the localization of APP in lipid rafts affecting raft-dependent APP endocytosis. Thus, regulating the microdomain localization of APP could offer a new therapeutic strategy for Alzheimer’s disease.

scholarly journals Preferred endocytosis of amyloid precursor protein from cholesterol-enriched lipid raft microdomains

2020 ◽  
Author(s):  
Yoon Young Cho ◽  
Oh-Hoon Kwon ◽  
Sungkwon Chung
Keyword(s):  
Amyloid Precursor Protein ◽  
Lipid Rafts ◽  
Lipid Raft ◽  
Therapeutic Strategy ◽  
Amyloid Β ◽  
Precursor Protein ◽  
Cholesterol Levels ◽  
Elevated Cholesterol ◽  
Aβ Generation ◽  
Lipid Raft Microdomains

AbstractAmyloid precursor protein (APP) at the plasma membrane is internalized via endocytosis, and delivered to endosomes and lysosomes, where neurotoxic amyloid-β (Aβ) is produced via β-, γ-secretases. Hence, endocytosis plays a key role in the processing of APP and subsequent Aβ generation. β-, γ-secretases as well as APP are localized in cholesterol-enriched lipid raft microdomains. However, it is still unclear whether lipid rafts are the site where APP undergoes endocytosis and whether cholesterol levels affect this process. In this study, we found that localization of APP in lipid rafts was increased by elevated cholesterol level. We also showed that increasing or decreasing cholesterol levels increased or decreased APP endocytosis, respectively. When we labeled cell surface APP, APP localized in lipid rafts preferentially underwent endocytosis compared to non-raft localized APP. In addition, APP endocytosis from lipid rafts was regulated by cholesterol levels. Our results indicate that cholesterol levels regulate the localization of APP in lipid rafts affecting raft-dependent APP endocytosis. Thus, regulating the microdomain localization of APP could offer a new therapeutic strategy for Alzheimer’s disease.

scholarly journals ApoE4-carrying Human Astrocytes Oversupply Cholesterol into Neurons and Promote Aβ Generation

2020 ◽  
Author(s):  
Se-In Lee ◽  
Woojin Jeong ◽  
Sukhee Cho ◽  
Hyein Lee ◽  
Yonghee Jang ◽  
...  
Keyword(s):  
Lipid Rafts ◽  
Late Onset ◽  
Culture Media ◽  
Amyloid Β ◽  
Membrane Lipid ◽  
Conditioned Media ◽  
Cholesterol Levels ◽  
Human Neurons ◽  
Aβ Generation ◽  
Aβ Production

Abstract Background: The onset of Alzheimer’s disease (AD) typically occurs later in life. Recent genetic analysis of patients and unaffected individuals revealed multiple genetic variants associated with late-onset AD. One of the strongest genetic risk factors for AD is 𝜀4 allele of APOE encoding apolipoprotein (ApoE), which is predominantly expressed in astrocytes. The role and mechanism of ApoE in initiating AD-associated pathologies, including amyloid-β (Aβ) accumulation and neurodegeneration in neurons, remains to be elucidated.Methods: Human induced pluripotent stem cells (hiPSCs) from healthy individuals and isogenic cells in which the ApoE 𝜀3 allele was replaced with an 𝜀4 allele were selected to generate human neurons and astrocytes. To investigate the effect of astrocytic ApoE4 on neuronal Aβ production, iPSC-derived neurons carrying the ApoE 𝜀3 allele were cultured in conditioned media from healthy iPSC-derived astrocytes (ApoE3/E4 heterozygote) for five weeks. Then, the media were replaced with either ApoE3 or ApoE4 astrocyte conditioned media (ACM), cultured for four days, and neuronal amyloid precursor protein (APP) expression and Aβ production were measured. To determine potential mechanisms for upregulation of APP in neurons by ApoE4 ACM, changes in plasma membrane lipid rafts were investigated by staining for cholera toxin B. Methyl-b-cyclodextrin (MβCD) was applied to deplete cholesterol in ApoE4 ACM.Results: Secretory factors in conditioned media from hiPSC-derived astrocytes carrying APOE4 significantly increased the levels of APP and Aβ secretion in hiPSC-derived neurons. Increasing cholesterol levels in culture media mimicked the effects of ApoE4 ACM by inducing the formation of lipid rafts that potentially provide a physical platform for APP localization on the membrane. We further found that reducing cholesterol levels in ApoE4 ACM with MβCD abolished its effects on neuronal lipid raft expansion and Aβ generation.Conclusions: Our study suggests that ApoE4 astrocytes contribute to amyloidosis by the expansion of lipid rafts and facilitate neuronal Ab production through oversupply of cholesterol.

scholarly journals O-GlcNAcylation Inhibits Endocytosis of Amyloid Precursor Protein by Decreasing Its Localization in Lipid Raft Microdomains

Membranes ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 909
Author(s):  
Oh-Hoon Kwon ◽  
Yoon Young Cho ◽  
Jung Hee Lee ◽  
Sungkwon Chung
Keyword(s):  
Amyloid Precursor Protein ◽  
Lipid Rafts ◽  
Lipid Raft ◽  
Hippocampal Neurons ◽  
Protein Modification ◽  
Amyloid Β ◽  
Precursor Protein ◽  
App Trafficking ◽  
Lipid Raft Microdomains ◽  
Aβ Production

Like protein phosphorylation, O-GlcNAcylation is a common post-translational protein modification. We already reported that O-GlcNAcylation of amyloid precursor protein (APP) in response to insulin signaling reduces neurotoxic amyloid-β (Aβ) production via inhibition of APP endocytosis. Internalized APP is delivered to endosomes and lysosomes where Aβ is produced. However, the molecular mechanism involved in the effect of APP O-GlcNAcylation on APP trafficking remains unknown. To investigate the relationship between APP O-GlcNAcylation and APP endocytosis, we tested the effects of insulin on neuroblastoma SH-SY5Y cells overexpressing APP and BACE1, and cultured rat hippocampal neurons. The present study showed that APP O-GlcNAcylation translocated APP from lipid raft to non-raft microdomains in the plasma membrane by using immunocytochemistry and discontinuous sucrose gradients method. By using the biotinylation method, we also found that APP preferentially underwent endocytosis from lipid rafts and that the amount of internalized APP from lipid rafts was specifically reduced by O-GlcNAcylation. These results indicate that O-GlcNAcylation can regulate lipid raft-dependent APP endocytosis via translocation of APP into non-raft microdomains. Our findings showed a new functional role of O-GlcNAcylation for the regulation of APP trafficking, offering new mechanistic insight for Aβ production.

scholarly journals Palmitoylation of the Autographa californica Multicapsid Nucleopolyhedrovirus Envelope Glycoprotein GP64: Mapping, Functional Studies, and Lipid Rafts

2003 ◽  
Vol 77 (11) ◽  
pp. 6265-6273 ◽  
Author(s):  
Sandy Xiaoxin Zhang ◽  
Yu Han ◽  
Gary W. Blissard
Keyword(s):  
Cell Surface ◽  
Lipid Rafts ◽  
Lipid Raft ◽  
Envelope Glycoprotein ◽  
Cysteine Residue ◽  
Autographa Californica ◽  
Membrane Microdomains ◽  
Sf9 Cells ◽  
Wild Type ◽  
Lipid Raft Microdomains

ABSTRACT Budded virions (BV) of the baculovirus Autographa californica multicapsid nucleopolyhedrovirus (AcMNPV) contain a major envelope glycoprotein known as GP64, which was previously shown to be palmitoylated. In the present study, we used truncation and amino acid substitution mutations to map the palmitoylation site to cysteine residue 503. Palmitoylation of GP64 was not detected when Cys503 was replaced with alanine or serine. Palmitoylation-minus forms of GP64 were used to replace wild-type GP64 in AcMNPV, and these viruses were used to examine potential functions of GP64 palmitoylation in the context of the infection cycle. Analysis by immunoprecipitation and cell surface studies revealed that palmitoylation of GP64 did not affect GP64 synthesis or its transport to the cell surface in Sf9 cells. GP64 proteins lacking palmitoylation also mediated low-pH-triggered membrane fusion in a manner indistinguishable from that of wild-type GP64. Cells infected with viruses expressing palmitoylation-minus forms of GP64 produced infectious virions at levels similar to those from cells infected with wild-type AcMNPV. In combination, these data suggest that virus entry and exit in Sf9 cells were not significantly affected by GP64 palmitoylation. To determine whether GP64 palmitoylation affected the association of GP64 with membrane microdomains, the potential association of GP64 with lipid raft microdomains was examined. These experiments showed that: (i) AcMNPV-infected Sf9 cell membranes contain lipid raft microdomains, (ii) GP64 association with lipid rafts was not detected in infected Sf9 cells, and (iii) GP64 palmitoylation did not affect the apparent exclusion of GP64 from lipid raft microdomains.

The novel β-secretase inhibitor KMI-429 reduces amyloid β peptide production in amyloid precursor protein transgenic and wild-type mice

2006 ◽  
Vol 96 (2) ◽  
pp. 533-540 ◽  
Author(s):  
Masashi Asai ◽  
Chinatsu Hattori ◽  
Nobuhisa Iwata ◽  
Takaomi C. Saido ◽  
Noboru Sasagawa ◽  
...  
Keyword(s):  
Amyloid Precursor Protein ◽  
Amyloid Β ◽  
Precursor Protein ◽  
Amyloid Β Peptide ◽  
The Novel ◽  
Wild Type ◽  
Secretase Inhibitor

Pathways linking Aβ and tau pathologies

2010 ◽  
Vol 38 (4) ◽  
pp. 993-995 ◽  
Author(s):  
Frank M. LaFerla
Keyword(s):  
Alzheimer’S Disease ◽  
Alzheimer's Disease ◽  
Neurological Disorders ◽  
Amyloid Β ◽  
Amyloid Plaques ◽  
Convincing Evidence ◽  
Amyloid Β Peptide ◽  
Tau Pathology ◽  
Aβ Amyloid ◽  
Cellular Compartments

Aβ (amyloid β-peptide) and tau are the main proteins that misfold and accumulate in amyloid plaques and NFTs (neurofibrillary tangles) of Alzheimer's disease and other neurological disorders. Historically, because plaques and NFTs accumulate in diverse cellular compartments, i.e. mainly extracellularly for plaques and intracellularly for NFTs, it was long presumed that the constituent proteins formed these lesions via unrelated pathways. Animal and cell studies over the last decade, however, have provided convincing evidence to show that Aβ can facilitate the development of tau pathology by altering several cell-dependent and -independent mechanisms. In the present article, results are reviewed from several laboratories that show that modulating Aβ pathology can directly affect the development of tau pathology, which has significant implications for the treatment of Alzheimer's disease.

scholarly journals Flotillin-dependent lipid-raft microdomains are required for functional phagolysosomes against fungal infections

2019 ◽  
Author(s):  
Franziska Schmidt ◽  
Andreas Thywißen ◽  
Marie Röcker ◽  
Cristina Cunha ◽  
Zoltán Cseresnyés ◽  
...  
Keyword(s):  
Lipid Rafts ◽  
Lipid Raft ◽  
Fungal Infections ◽  
Pathogenic Fungus ◽  
Cell Transplant ◽  
Hematopoietic Stem ◽  
Essential Components ◽  
Human Pathogenic Fungus ◽  
Lipid Raft Microdomains

SUMMARYLipid rafts form signaling platforms on biological membranes with incompletely characterized role in immune response to infection. Here we report that lipid raft microdomains are essential components of the phagolysosomal membrane of macrophages. Genetic deletion of the lipidraft chaperons flotillin-1 and flotillin-2 demonstrate that the assembly of both major defense complexes vATPase and NADPH oxidase on the phagolysosomal membrane requires lipid rafts. Furthermore, we discovered a new virulence mechanism leading to the dysregulation of lipid-raft formation by melanized wild-type conidia of the important human-pathogenic fungusAspergillus fumigatus. This results in reduced phagolysosomal acidification. Phagolysosomes with ingested melanized conidia contain a reduced amount of free Ca2+ions as compared to phagolysosomes with melanin-free conidia. In agreement with a role of Ca2+for generation of functional lipid rafts, we show that Ca2+-dependent calmodulin activity is required for lipid-raft formation on the phagolysosome. We identified a single nucleotide polymorphism in the humanFLOT1gene that results in heightened susceptibility for invasive aspergillosis in hematopoietic stem-cell transplant recipients. Collectively, flotillin-dependent lipid rafts on the phagolysosomal membrane play an essential role in protective antifungal immunity in humans.

Preferential Intercalation of Human Amyloid-β Peptide into Interbilayer Region of Lipid-Raft Membrane in Macromolecular Crowding Environment

2018 ◽  
Vol 122 (41) ◽  
pp. 9482-9489 ◽  
Author(s):  
Mitsuhiro Hirai ◽  
Satoshi Ajito ◽  
Shouki Sato ◽  
Noboru Ohta ◽  
Noriyuki Igarashi ◽  
...  
Keyword(s):  
Lipid Raft ◽  
Macromolecular Crowding ◽  
Amyloid Β ◽  
Amyloid Β Peptide

scholarly journals ApoE4-carrying Human Astrocytes Oversupply Cholesterol into Neurons and Promote Aβ Generation

2020 ◽  
Author(s):  
Se-In Lee ◽  
Woojin Jeong ◽  
Sukhee Cho ◽  
Hyein Lee ◽  
Yonghee Jang ◽  
...  
Keyword(s):  
Lipid Rafts ◽  
Pluripotent Stem Cells ◽  
Late Onset ◽  
Culture Media ◽  
Cholesterol Levels ◽  
Human Astrocytes ◽  
Human Neurons ◽  
Induced Pluripotent ◽  
Aβ Generation ◽  
Aβ Production

Abstract The onset of Alzheimer’s disease (AD) typically occurs later in life. Importantly, however, recent genetic analysis of patients and unaffected individuals revealed multiple genetic variants associated with late-onset AD. One of the strongest genetic risk factors for AD is 𝜀4 allele of APOE encoding apolipoprotein (ApoE), which is predominantly expressed in glial cells. One of the overarching questions is whether and how this astrocyte-enriched risk factor initiates AD-associated pathology in neurons such as Aβ accumulation and neurodegeneration. Here, we use human induced pluripotent stem cells (hiPSCs) from healthy individuals and isogenic cells in which the ApoE 𝜀3 allele was replaced with an 𝜀4 allele to generate human neurons and astrocytes. We then investigate the effect of astrocytic ApoE4 on the neuronal Aβ production. We find that secretory factors in conditioned media from hiPSC-derived astrocytes carrying APOE4 significantly increased the levels of APP and Aβ secretion in hiPSC-derived neurons. Increasing cholesterol levels in culture media mimicked the effects of ApoE4 ACM by inducing the formation of lipid rafts that potentially provide a physical platform for APP localization on the membrane. We further found that reducing cholesterol levels in ApoE4 ACM with MβCD abolished its effects on neuronal lipid raft expansion and Aβ generation. Our study suggests that ApoE4 astrocytes contribute to amyloidosis by the expansion of lipid rafts and facilitate neuronal Ab production through oversupply of cholesterol.

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