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 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.

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 Enhanced amyloid-β generation by γ-secretase complex in DRM microdomains with reduced cholesterol levels

2019 ◽  
Vol 29 (3) ◽  
pp. 382-393 ◽  
Author(s):  
Saori Hata ◽  
Anqi Hu ◽  
Yi Piao ◽  
Tadashi Nakaya ◽  
Hidenori Taru ◽  
...  
Keyword(s):  
Cultured Cells ◽  
Late Onset ◽  
Senile Plaques ◽  
Amyloid Β ◽  
Cholesterol Content ◽  
Amyloid Β Protein ◽  
Tissue Samples ◽  
Β Protein ◽  
Aβ Generation ◽  
Carboxy Terminal

Abstract A neuropathologic hallmark of Alzheimer’s disease (AD) is the presence of senile plaques that contain neurotoxic amyloid-β protein (Aβ) species, which are generated by the cleavage of amyloid β-protein precursor by secretases such as the γ-secretase complex, preferentially located in detergent-resistant membrane (DRM) regions and comprising endoproteolysed amino- and carboxy-terminal fragments of presenilin, nicastrin, anterior pharynx defective 1 and presenilin enhancer 2. Whereas some of familial AD patients harbor causative PSEN mutations that lead to more generation of neurotoxic Aβ42, the contribution of Aβ generation to sporadic/late-onset AD remains unclear. We found that the carboxy-terminal fragment of presenilin 1 was redistributed from DRM regions to detergent-soluble membrane (non-DRM) regions in brain tissue samples from individuals with sporadic AD. DRM fractions from AD brain sample had the ability to generate significantly more Aβ and had a lower cholesterol content than DRM fractions from non-demented control subjects. We further demonstrated that lowering the cholesterol content of DRM regions from cultured cells contributed to the redistribution of γ-secretase components and Aβ production. Taken together, the present analyses suggest that the lowered cholesterol content in DRM regions may be a cause of sporadic/late-onset AD by enhancing overall Aβ generation.

Precholesterol Sterols Accumulate in Lipid Rafts of Patients with Smith-Lemli-Opitz Syndrome and X-Linked Dominant Chondrodysplasia Punctata

2008 ◽  
Vol 11 (2) ◽  
pp. 128-132 ◽  
Author(s):  
Dinesh Rakheja ◽  
Richard L. Boriack
Keyword(s):  
Lipid Rafts ◽  
Hedgehog Signaling ◽  
Cholesterol Biosynthesis ◽  
Membrane Lipid ◽  
Chondrodysplasia Punctata ◽  
Autopsy Material ◽  
Cholesterol Levels ◽  
Abnormal Accumulation ◽  
Hedgehog Proteins ◽  
Opitz Syndrome

Systemic fetal dysmorphogenesis in disorders of postsqualene cholesterol biosynthesis is thought to be caused by disruption of Hedgehog signaling. Because precholesterol sterols such as 7-dehydrocholesterol and lathosterol can replace cholesterol in the activation of Hedgehog proteins, it is currently believed that cholesterol deficiency-related Hedgehog signaling block occurs further downstream, probably at the level of Smoothened. Experimentally, such a block in Hedgehog signaling occurs at sterol levels of <40 μg/mg protein. Recently, we studied autopsy material from 2 infants with fatal cholesterol biosynthetic disorders (Smith-Lemli-Opitz syndrome and X-linked dominant chondrodysplasia punctata) in which the hepatic cholesterol levels were far greater. In this study, we demonstrate abnormal accumulation of sterol precursors of cholesterol in membrane lipid rafts (detergent resistance membranes) prepared from liver tissues of these 2 infants: 8-dehydrocholesterol and 7-dehydrocholesterol in lipid rafts of the infant with Smith-Lemli-Opitz syndrome and cholest-8(9)-ene-3β-ol in lipid rafts of the infant with X-linked dominant chondrodysplasia punctata. We suggest that such alterations in the lipid raft sterol environment may affect the biology of cells and the development of fetuses with cholesterol biosynthetic disorders.

scholarly journals NRF2/ARE pathway negatively regulates BACE1 expression and ameliorates cognitive deficits in mouse Alzheimer’s models

2019 ◽  
Vol 116 (25) ◽  
pp. 12516-12523 ◽  
Author(s):  
Gahee Bahn ◽  
Jong-Sung Park ◽  
Ui Jeong Yun ◽  
Yoon Jee Lee ◽  
Yuri Choi ◽  
...  
Keyword(s):  
Cognitive Deficits ◽  
Redox Regulation ◽  
Amyloid Β ◽  
Antioxidant Response ◽  
Related Factor ◽  
Bace1 Expression ◽  
Nrf2 Activation ◽  
Antioxidant Response Elements ◽  
Aβ Generation ◽  
Aβ Production

BACE1 is the rate-limiting enzyme for amyloid-β peptides (Aβ) generation, a key event in the pathogenesis of Alzheimer’s disease (AD). By an unknown mechanism, levels of BACE1 and a BACE1 mRNA-stabilizing antisense RNA (BACE1-AS) are elevated in the brains of AD patients, implicating that dysregulation of BACE1 expression plays an important role in AD pathogenesis. We found that nuclear factor erythroid-derived 2-related factor 2 (NRF2/NFE2L2) represses the expression of BACE1 and BACE1-AS through binding to antioxidant response elements (AREs) in their promoters of mouse and human. NRF2-mediated inhibition of BACE1 and BACE1-AS expression is independent of redox regulation. NRF2 activation decreases production of BACE1 and BACE1-AS transcripts and Aβ production and ameliorates cognitive deficits in animal models of AD. Depletion of NRF2 increases BACE1 and BACE1-AS expression and Aβ production and worsens cognitive deficits. Our findings suggest that activation of NRF2 can prevent a key early pathogenic process in AD.

scholarly journals A TrkA-to-p75NTR molecular switch activates amyloid β-peptide generation during aging

2005 ◽  
Vol 391 (1) ◽  
pp. 59-67 ◽  
Author(s):  
Claudio Costantini ◽  
Richard Weindruch ◽  
Giuliano Della Valle ◽  
Luigi Puglielli
Keyword(s):  
Caloric Restriction ◽  
Late Onset ◽  
Senile Plaques ◽  
Amyloid Β ◽  
Normal Aging ◽  
Neurotrophin Receptor ◽  
Tyrosine Kinase Receptor ◽  
Amyloid Β Peptide ◽  
Aβ Amyloid ◽  
Aβ Generation

Aging is the single most important risk factor for AD (Alzheimer's disease). However, the molecular events that connect normal aging to AD are mostly unknown. The abnormal accumulation of Aβ (amyloid β-peptide) in the form of senile plaques is one of the main characteristics of AD. In the present study, we show that two members of the neurotrophin receptor superfamily, TrkA (tyrosine kinase receptor A) and p75NTR (p75 neurotrophin receptor), differentially regulate the processing of APP (amyloid precursor protein): TrkA reduces, whereas p75NTR activates, β-cleavage of APP. The p75NTR-dependent effect requires NGF (nerve growth factor) binding and activation of the second messenger ceramide. We also show that normal aging activates Aβ generation in the brain by ‘switching’ from the TrkA to the p75NTR receptor system. Such an effect is abolished in p75NTR ‘knockout’ animals, and can be blocked by both caloric restriction and inhibitors of nSMase (neutral sphingomyelinase). In contrast with caloric restriction, which prevents the age-associated up-regulation of p75NTR expression, nSMase inhibitors block the activation of ceramide. When taken together, these results indicate that the p75NTR–ceramide signalling pathway activates the rate of Aβ generation in an age-dependent fashion, and provide a new target for both the understanding and the prevention of late-onset AD.

scholarly journals Regulation of beta-amyloid production in neurons by astrocyte-derived cholesterol

2021 ◽  
Vol 118 (33) ◽  
pp. e2102191118
Author(s):  
Hao Wang ◽  
Joshua A. Kulas ◽  
Chao Wang ◽  
David M. Holtzman ◽  
Heather A. Ferris ◽  
...  
Keyword(s):  
Genetic Risk ◽  
Cholesterol Synthesis ◽  
Amyloid Β ◽  
Cholesterol Transport ◽  
Targeted Deletion ◽  
Superresolution Imaging ◽  
Cholesterol Levels ◽  
Aβ Production

Alzheimer’s disease (AD) is characterized by the presence of amyloid β (Aβ) plaques, tau tangles, inflammation, and loss of cognitive function. Genetic variation in a cholesterol transport protein, apolipoprotein E (apoE), is the most common genetic risk factor for sporadic AD. In vitro evidence suggests that apoE links to Aβ production through nanoscale lipid compartments (lipid clusters), but its regulation in vivo is unclear. Here, we use superresolution imaging in the mouse brain to show that apoE utilizes astrocyte-derived cholesterol to specifically traffic neuronal amyloid precursor protein (APP) in and out of lipid clusters, where it interacts with β- and γ-secretases to generate Aβ-peptide. We find that the targeted deletion of astrocyte cholesterol synthesis robustly reduces amyloid and tau burden in a mouse model of AD. Treatment with cholesterol-free apoE or knockdown of cholesterol synthesis in astrocytes decreases cholesterol levels in cultured neurons and causes APP to traffic out of lipid clusters, where it interacts with α-secretase and gives rise to soluble APP-α (sAPP-α), a neuronal protective product of APP. Changes in cellular cholesterol have no effect on α-, β-, and γ-secretase trafficking, suggesting that the ratio of Aβ to sAPP-α is regulated by the trafficking of the substrate, not the enzymes. We conclude that cholesterol is kept low in neurons, which inhibits Aβ accumulation and enables the astrocyte regulation of Aβ accumulation by cholesterol signaling.

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