The Effect of Aβ&lt;sub&gt;1-42&lt;/sub&gt; Oligomers on APP Processing and Aβ&lt;sub&gt;1-40&lt;/sub&gt; Generation in Cultured U-373 Astrocytes

Ourdev, Dimitar; Foroutanpay, Bahram V; Wang, Yanlin; Kar, Satyabrata

doi:10.1159/000438923

Cited by 14 publications

(8 citation statements)

References 39 publications

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“…Interestingly, the activities of ADAM10, BACE1 and g-secretase were found to be enhanced in U18666A-treated cultured astrocytes. Although increased level of ADAM10 corresponds with its enzyme activity, a discrepancy between levels and activities of BACE1 and the g-secretase complex, as observed following U18666A treatment, has been reported in some earlier studies (Kodam et al, 2010;Ourdev et al, 2015) and is consistent with the evidence that the four subunits of g-secretase are tightly regulated by their stoichiometric interaction to form stable complexes (Takasugi et al, 2003). Thus, it is likely that enhanced levels and processing of APP may partly contribute to the upregulation of APP-CTFs and Ab 1-40 in U18666A-treated astrocytes as reported in some cultured neurons/cell lines (Boland et al, 2010;Maulik et al, 2015).…”

Section: Discussionmentioning

confidence: 84%

“…The supernatant and the pellets were harvested and used either immediately or stored at −80 °C until further processing. For some experiments, cultured astrocytes were treated with 5 µg/ml U18666A and then exposed to 30 μg/ml protein synthesis inhibitor cycloheximide along with U18666A for 0.5, 2, or 5 hr over a 24 hr experimental paradigm (Ourdev, Foroutanpay, Wang, & Kar, ). In a separate series of experiments, FBS media were delipidated using EDTA and butanol:diisopropyl ether solution (Cham & Knowles, ) and then sterilized by vacuum filtration through 2 μm filters.…”

Section: Methodsmentioning

confidence: 99%

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Effects of cholesterol transport inhibitor U18666A on APP metabolism in rat primary astrocytes

Yang

Wang

Kar

2017

Glia

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Amyloid β (Aβ) peptides generated from the amyloid precursor protein (APP) play an important role in the degeneration of neurons and development of Alzheimer's disease (AD). Current evidence indicates that high levels of cholesterol-which increase the risk of developing AD-can influence Aβ production in neurons. However, it remains unclear how altered level/subcellular distribution of cholesterol in astrocytes can influence APP metabolism. In this study, we evaluated the effects of cholesterol transport inhibitor U18666A-a class II amphiphile that triggers redistribution of cholesterol within the endosomal-lysosomal (EL) system-on APP levels and metabolism in rat primary cultured astrocytes. Our results revealed that U18666A increased the levels of the APP holoprotein and its cleaved products (α-/β-/η-CTFs) in cultured astrocytes, without altering the total levels of cholesterol or cell viability. The cellular levels of Aβ were also found to be markedly increased, while secretory levels of Aβ were decreased in U18666A-treated astrocytes. We further report a corresponding increase in the activity of the enzymes regulating APP processing, such as α-secretase, β-secretase, and γ-secretase as a consequence of U18666A treatment. Additionally, APP-cleaved products are partly accumulated in the lysosomes following cholesterol sequestration within EL system possibly due to decreased clearance. Interestingly, serum delipidation attenuated enhanced levels of APP and its cleaved products following U18666A treatment. Collectively, these results suggest that cholesterol sequestration within the EL system in astrocytes can influence APP metabolism and the accumulation of APP-cleaved products including Aβ peptides, which can contribute to the development of AD pathology.

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Section: Discussionmentioning

confidence: 84%

Section: Methodsmentioning

confidence: 99%

Effects of cholesterol transport inhibitor U18666A on APP metabolism in rat primary astrocytes

Yang

Wang

Kar

2017

Glia

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“…It is possible that Aβ secreted from astrocytes following kainic acid treatment can act directly on neurons to decrease their vulnerability. Alternatively, Aβ peptide secreted from kainic acid‐treated astrocytes may act to increase the levels/processing of APP in neurons leading to enhanced intraneuronal Aβ level which can then decrease neuronal vulnerability.…”

Section: Discussionmentioning

confidence: 99%

A role for astrocyte‐derived amyloid β peptides in the degeneration of neurons in an animal model of temporal lobe epilepsy

Kodam¹,

Ourdev²,

Maulik

et al. 2018

Brain Pathology

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Kainic acid, an analogue of the excitatory neurotransmitter glutamate, can trigger seizures and neurotoxicity in the hippocampus and other limbic structures in a manner that mirrors the neuropathology of human temporal lobe epilepsy (TLE). However, the underlying mechanisms associated with the neurotoxicity remain unclear. Since amyloid-β (Aβ) peptides, which are critical in the development of Alzheimer's disease, can mediate toxicity by activating glutamatergic NMDA receptors, it is likely that the enhanced glutamatergic transmission that renders hippocampal neurons vulnerable to kainic acid treatment may involve Aβ peptides. Thus, we seek to establish what role Aβ plays in kainic acid-induced toxicity using in vivo and in vitro paradigms. Our results show that systemic injection of kainic acid to adult rats triggers seizures, gliosis and loss of hippocampal neurons, along with increased levels/processing of amyloid precursor protein (APP), resulting in the enhanced production of Aβ-related peptides. The changes in APP levels/processing were evident primarily in activated astrocytes, implying a role for astrocytic Aβ in kainic acid-induced toxicity. Accordingly, we showed that treating rat primary cultured astrocytes with kainic acid can lead to increased Aβ production/secretion without any compromise in cell viability. Additionally, we revealed that kainic acid reduces neuronal viability more in neuronal/astrocyte co-cultures than in pure neuronal culture, and this is attenuated by precluding Aβ production. Collectively, these results indicate that increased production/secretion of Aβ-related peptides from activated astrocytes can contribute to neurotoxicity in kainic acid-treated rats. Since kainic acid administration can lead to neuropathological changes resembling TLE, it is likely that APP/Aβ peptides derived from astrocytes may have a role in TLE pathogenesis.

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“…The supernatant and the pellets were either used immediately or stored at Ϫ80°C until further processing. For some experiments, APPsw cells grown in 5% FBS were exposed to 3 g/ml U18666A and then treated with 30 g/ml cycloheximide along with U18666A for 0.5, 2, or 5 h over a 24-h experiment (101). In parallel, APPsw cells grown in 10% FBS were pretreated with the BACE1 inhibitor BIV (10 M) or autophagy inhibitor 3-MA (250 M) for 24 h prior to treatment with 3 g/ml U18666A for an additional 24 h. Untreated and treated cells were then harvested for further processing as described earlier (28).…”

Section: Methodsmentioning

confidence: 99%

Endosomal-Lysosomal Cholesterol Sequestration by U18666A Differentially Regulates Amyloid Precursor Protein (APP) Metabolism in Normal and APP-Overexpressing Cells

Chung

Phukan

Vergote

et al. 2018

Molecular and Cellular Biology

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Amyloid β (Aβ) peptide, derived from amyloid precursor protein (APP), plays a critical role in the development of Alzheimer's disease. Current evidence indicates that altered levels or subcellular distribution of cholesterol can regulate Aβ production and clearance, but it remains unclear how cholesterol sequestration within the endosomal-lysosomal (EL) system can influence APP metabolism. Thus, we evaluated the effects of U18666A, which triggers cholesterol redistribution within the EL system, on mouse N2a cells expressing different levels of APP in the presence or absence of extracellular cholesterol and lipids provided by fetal bovine serum (FBS). Our results reveal that U18666A and FBS differentially increase the levels of APP and its cleaved products, the α-, β-, and η-C-terminal fragments, in N2a cells expressing normal levels of mouse APP (N2awt), higher levels of human wild-type APP (APPwt), or "Swedish" mutant APP (APPsw). The cellular levels of Aβ/Aβ were markedly increased in U18666A-treated APPwt and APPsw cells. Our studies further demonstrate that APP and its cleaved products are partly accumulated in the lysosomes, possibly due to decreased clearance. Finally, we show that autophagy inhibition plays a role in mediating U18666A effects. Collectively, these results suggest that altered levels and distribution of cholesterol and lipids can differentially regulate APP metabolism depending on the nature of APP expression.

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The Effect of Aβ<sub>1-42</sub> Oligomers on APP Processing and Aβ<sub>1-40</sub> Generation in Cultured U-373 Astrocytes

Cited by 14 publications

References 39 publications

Effects of cholesterol transport inhibitor U18666A on APP metabolism in rat primary astrocytes

Effects of cholesterol transport inhibitor U18666A on APP metabolism in rat primary astrocytes

A role for astrocyte‐derived amyloid β peptides in the degeneration of neurons in an animal model of temporal lobe epilepsy

Endosomal-Lysosomal Cholesterol Sequestration by U18666A Differentially Regulates Amyloid Precursor Protein (APP) Metabolism in Normal and APP-Overexpressing Cells

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