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Cited by 24Cholesterol and Lipid MetabolismAlzheimer's disease research and treatmentsLipoproteins and Cardiovascular Health

The DOI matches its Crossref record; 88 of the 89 references it cites were found in a registry or an index; 8 of the 88 sources its claims cite were checked for support.

ApoE3 vs. ApoE4 Astrocytes: A Detailed Analysis Provides New Insights into Differences in Cholesterol Homeostasis

Open access
Staurenghi, Erica, Leoni, Valerio, Lo Iacono, Marco, Sottero, Barbara, Testa, Gabriella, Giannelli, Serena, Leonarduzzi, Gabriella, Gamba, Paola·2022·Antioxidants
DOI 10.3390/antiox11112168PMC PMC9686673
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Abstract

The strongest genetic risk factor for sporadic Alzheimer’s disease (AD) is the presence of the ε4 allele of the apolipoprotein E (ApoE) gene, the major apolipoprotein involved in brain cholesterol homeostasis. Being astrocytes the main producers of cholesterol and ApoE in the brain, we investigated the impact of the ApoE genotype on astrocyte cholesterol homeostasis. Two mouse astrocytic cell lines expressing the human ApoE3 or ApoE4 isoform were employed. Gas chromatography–mass spectrometry (GC-MS) analysis pointed out that the levels of total cholesterol, cholesterol precursors, and various oxysterols are altered in ApoE4 astrocytes. Moreover, the gene expression analysis of more than 40 lipid-related genes by qRT-PCR showed that certain genes are up-regulated (e.g., CYP27A1) and others down-regulated (e.g., PPARγ, LXRα) in ApoE4, compared to ApoE3 astrocytes. Beyond confirming the significant reduction in the levels of PPARγ, a key transcription factor involved in the maintenance of lipid homeostasis, Western blotting showed that both intracellular and secreted ApoE levels are altered in ApoE4 astrocytes, as well as the levels of receptors and transporters involved in lipid uptake/efflux (ABCA1, LDLR, LRP1, and ApoER2). Data showed that the ApoE genotype clearly affects astrocytic cholesterol homeostasis; however, further investigation is needed to clarify the mechanisms underlying these differences and the consequences on neighboring cells. Indeed, drug development aimed at restoring cholesterol homeostasis could be a potential strategy to counteract AD.

Overview

AI snapshot

Written from the paper’s full text.

TL;DR

This study compared immortalized mouse astrocytic cell lines expressing human ApoE3 or ApoE4 and found that ApoE4 astrocytes have altered cholesterol homeostasis, including changes in cholesterol precursors, oxysterols, lipid-related gene expression, and key cholesterol transport proteins. The authors suggest these differences may help explain ApoE4-related Alzheimer’s disease risk and identify cholesterol-homeostasis restoration as a potential therapeutic strategy.

Key findings

  • ApoE4 astrocytes had less than half the intracellular ApoE of ApoE3 astrocytes (p < 0.0001), while secreted ApoE in astrocyte-conditioned media was more than doubled (p < 0.01).
  • GC-MS showed lower total cholesterol (−14%; p < 0.05), higher lanosterol (+54%; p < 0.0001) and lathosterol (+142%; p < 0.0001), and lower desmosterol (−32%; p < 0.01) in ApoE4 astrocytes; oxysterols showed higher 25-OHC (+282%; p < 0.0001) and 27-OHC (+72%; p < 0.001), but lower 24-OHC (−36%; p < 0.0001), 7α-OHC (−51%; p < 0.0001), and 7β-OHC (−52%; p < 0.0001), with no significant change in 7-KC.
  • Among 43 lipid-related genes, ApoE4 astrocytes showed up-regulation of CYP27A1 (p < 0.0001), ALOX15 (p < 0.0001), HMGCS1 (p < 0.0001), and others, and down-regulation of PPARγ (p < 0.0001), LXRα/NR1H3 (p < 0.0001), ABCA1 (p < 0.05), and others.
  • Protein analysis confirmed lower PPARγ, ABCA1, LDLR, LRP1 (all p < 0.0001), and ApoER2 (p < 0.001) in ApoE4 astrocytes; the authors propose a possible shift from the Bloch to the Kandutsch–Russell cholesterol synthesis pathway.

Methods

  • Immortalized mouse astrocytes derived from ApoE-targeted replacement (ApoE-TR) mouse primary astrocytes expressing human ApoE3 or ApoE4 under the control of the endogenous mouse ApoE promoter.
  • Sterols and oxysterols were quantified by isotope dilution GC-MS; gene expression was analyzed by qRT-PCR using a 43-gene lipid-regulated array plus single TaqMan assays; protein levels were assessed by Western blotting and immunocytochemistry.
  • Statistical analysis used Student’s t-test with Welch correction, with significance set at p < 0.05; data are presented as means ± SD.

Limitations

  • The paper states that it is aware of limitations of the employed experimental model and that further investigation is needed to clarify mechanisms and consequences on neighboring cells; it also notes that more in-depth analysis is needed to understand whether ApoE3 and ApoE4 astrocytes synthesize cholesterol through different pathways, and that PPARγ response networks are complex and require further study.
  • Evident from the text: the study uses immortalized mouse astrocytic cell lines rather than human primary astrocytes or in vivo brain tissue, and some genes (LPL, ALOX5, ABCG1, IL1β) were undetectable, preventing calculation of exact down-regulation or significance for those genes.
  • The text does not report functional outcomes such as neuronal effects, Aβ clearance, or cognitive measures, so the downstream consequences of the observed metabolic differences remain to be established.

Model-written summary. Check it against the paper before relying on it.

Integrity signals

Registry

Crossref · 10.3390/antiox11112168

Cites

88 of 88 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Verification

Claims the paper makes

8 of 88 cited sources checked · 1 supported · 2 flagged · accuracy not yet measured

  • Findingown data

    ApoE4 astrocytes contain significantly lower levels of all three receptors (LDLR, LRP1, ApoER2).

    “Data showed that ApoE4 astrocytes contain significantly lower levels of all three receptors (Figure 5), although conflicting data regarding some of them have been obtained in primary and hiPSC-derived ApoE4 astrocytes [15,24,73].”
    Quote in the paperSubstantial claim3 of 3 sources checked
    • cites [15] Tcw, 2022, Cholesterol and matrisome pathways dysregulated in astrocytes and microglia, Cell source

      The Results section on impaired cholesterol trafficking reports significantly more LDL binding to cell-surface receptors, including LDLRs, in APOE4 astrocytes—the opposite direction from the claimed decrease for LDLR. Our copy does not report lower levels of LRP1 or ApoER2 in those cells; the reported decreases concern APOE protein and the ABCA1/ABCA7 transporters. Page numbers were not available in the indexed passages. (LLM, conf=0.76)

      Checked by a reasoning model — may be wrong.

      Experimental — accuracy not yet measured
    • cites [24] Kirschner, 2022, APOE2, E3, and E4 differentially modulate cellular homeostasis, cholesterol metabolism, and inflammatory response in isogenic iPSC-derived astrocytes, Stem Cell Rep. source

      The Results section (page unavailable) reports no significant difference in LRP1 levels across genotypes, contrary to the claim that APOE4 astrocytes have significantly lower levels of all three receptors. The paper measured VLDLR alongside LRP1, not LDLR and ApoER2. It does support the citing sentence’s caveat that some receptor findings conflict. (LLM, conf=0.90)

      Checked by a reasoning model — may be wrong.

      Experimental — accuracy not yet measured
    • cites [73] Prasad, 2018, Amyloid clearance defect in ApoE4 astrocytes is reversed by epigenetic correction of endosomal pH, Proc. Natl. Acad. Sci. USA source

      The section “Surface expression of LRP1 receptor is severely reduced in ApoE4 astrocytes” reports about 50% lower surface LRP1 in ApoE4 than ApoE3 astrocytes, but no difference in total LRP1 protein. Our copy does not establish significantly lower LDLR or ApoER2 levels, so it does not support the claim about all three receptors. (LLM, conf=0.89)

      Experimental — accuracy not yet measured
  • Interpretationcitation

    The pronounced reduction in these receptors in ApoE4 astrocytes could be one of the reasons for the increased ApoE levels detected in ACM.

    “the pronounced reduction in these receptors in ApoE4 astrocytes could be one of the reasons for the increased ApoE levels detected in ACM (Figure 1), as suggested by other studies [49,50].”
    Quote in the paperSubstantial claim1 of 2 sources checked
    • cites [49] Fryer, 2005, The low density lipoprotein receptor regulates the level of central nervous system human and murine apolipoprotein E but does not modify amyloid plaque pathology in PDAPP mice, J. Biol. Chem. source
    • cites [50] Basak, 2012, Low-density lipoprotein receptor represents an apolipoprotein E-independent pathway of Abeta uptake and degradation by astrocytes, J. Biol. Chem. source
  • Premisecitation

    LXRα is a key regulator of ABCA1 expression.

    “a key regulator of ABCA1 expression [51]”
    Quote in the paperSubstantial claim1 of 1 sources checked
    • cites [51] Courtney, 2016, LXR Regulation of Brain Cholesterol: From Development to Disease, Trends Endocrinol. Metab. source

      The “Cholesterol homeostasis in the CNS” section identifies LXR as a direct transcriptional regulator of ABCA1. The paper distinguishes LXRα from LXRβ in its section on LXR isoforms, but does not specifically identify LXRα as the key regulator of ABCA1 expression. (LLM, conf=0.83)

      Experimental — accuracy not yet measured
  • Findingown data

    The levels of ApoE released in astrocyte-conditioned media by the ApoE4 cell line are more than doubled compared to those secreted by the ApoE3 cell line.

    “On the other hand, the levels of ApoE released in ACM by the ApoE4 cell line resulted to be more than doubled compared to that secreted by the ApoE3 cell line (p < 0.01; Figure 1B).”
    Quote in the paperSubstantial claim
  • Findingown data

    25-OHC levels are higher in ApoE4 astrocytes than in ApoE3 astrocytes (+282%; p < 0.0001).

    “Concerning the oxysterols of enzymatic origin, ApoE4 astrocytes have been shown to produce higher levels of 25-OHC (+282%; p < 0.0001) and 27-OHC (+72%; p < 0.001)”
    Quote in the paperSubstantial claim
  • It may state two separate claims as one. 24
  • Probably not a substantial claim. 16

  • It may state two separate claims as one.

    Premisecitation

    Cholesterol homeostasis is impaired in ApoE4 astrocytes, although controversial data concerning intracellular and secreted cholesterol levels are present in the literature depending on the experimental model employed.

    “Recently, it has been shown that cholesterol homeostasis is also impaired in ApoE4 astrocytes, although controversial data concerning intracellular and secreted cholesterol levels are present in literature depending on the different experimental model employed [15,16,24].”
    Quote in the paperSubstantial claim3 of 3 sources checked
    • cites [15] Tcw, 2022, Cholesterol and matrisome pathways dysregulated in astrocytes and microglia, Cell source

      The Results section, “Impaired cholesterol trafficking in APOE4 astrocytes and microglia” (page unavailable), reports increased intracellular cholesterol and reduced cholesterol efflux in APOE4 astrocytes, supporting impaired cholesterol homeostasis. The Discussion contrasts efflux findings from rat and mouse models, but the paper does not establish that reported intracellular and secreted cholesterol levels themselves conflict across experimental models. (LLM, conf=0.84)

      Experimental — accuracy not yet measured
    • cites [16] Lin, 2018, APOE4 Causes Widespread Molecular and Cellular Alterations Associated with Alzheimer’s Disease Phenotypes in Human iPSC-Derived Brain Cell Types, Neuron source

      The Results section (‘APOE4 astrocytes exhibit compromised Aβ uptake’; page unavailable) reports altered cholesterol metabolism and higher cellular and secreted cholesterol in APOE4 than APOE3 iPSC-derived astrocytes. The paper does not establish the claimed controversy over intracellular and secreted cholesterol levels across experimental models; its discussion of conflicting findings concerns APOE protein levels instead. (LLM, conf=0.84)

      Experimental — accuracy not yet measured
    • cites [24] Kirschner, 2022, APOE2, E3, and E4 differentially modulate cellular homeostasis, cholesterol metabolism, and inflammatory response in isogenic iPSC-derived astrocytes, Stem Cell Rep. source

      The Results section, “Cholesterol and lipid metabolism show APOE allele-dependent regulation” (page unavailable), reports reduced cellular and secreted cholesterol in APOE4 iAstrocytes, alongside increased non-membrane-bound cholesterol. This supports altered cholesterol homeostasis, but the paper does not establish that conflicting findings in the literature depend on the experimental model used. (LLM, conf=0.83)

      Experimental — accuracy not yet measured

  • It may state two separate claims as one.

    Findingown data

    The expression levels of 43 lipid-related genes were analysed in both ApoE3 and ApoE4 astrocytes, and several genes were up- or down-regulated in ApoE4 compared to ApoE3 astrocytes.

    “In order to investigate this aspect, the expression levels of 43 lipid-related genes were analysed in both ApoE3 and ApoE4 astrocytes and several genes resulted to be up- or down-regulated in ApoE4 compared to ApoE3 astrocytes (Figure 2).”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim. The paper’s conclusions may not depend on it. It may state two separate claims as one.

    Findingown data

    The two cell lines have a different morphology, with ApoE4 astrocytes being smaller than ApoE3 astrocytes.

    “As shown in Figure 1A, the two cell lines have a different morphology, with ApoE4 astrocytes resulting as smaller compared to ApoE3 astrocytes.”
    Quote in the paperNot a substantial claim

  • It may state two separate claims as one.

    Findingown data

    ApoE intracellular and extracellular content, as well as the levels of the ABCA1 transporter and the receptors LDLR, LRP1, and ApoER2, resulted to be impaired in ApoE4 astrocytes.

    “Moreover, ApoE intracellular and extracellular content, as well as the levels of the ABCA1 transporter and the receptors LDLR, LRP1, and ApoER2 resulted to be impaired in ApoE4 astrocytes.”
    Quote in the paperSubstantial claim
    • Rests on an assumption: One of the main proteins responsible for ApoE lipidation in the CNS is the transporter ABCA1.

  • It may state two separate claims as one.

    Findingown data

    CYP46A1 and CYP7A1 reduction is followed by 24-OHC and 7α-OHC reduction, respectively; conversely, CYP27A1 and CH25H increase is followed by 27-OHC and 25-OHC increase.

    “In fact, CYP46A1 and CYP7A1 reduction is followed by 24-OHC and 7α-OHC reduction, respectively; conversely, CYP27A1 and CH25H increase is followed by 27-OHC and 25-OHC increase (Figure 4B).”
    Quote in the paperSubstantial claim

  • It may state two separate claims as one.

    Findingown data

    ABCA1, LXRα, LPL, and GYK are down-regulated in ApoE4 astrocytes.

    “In addition to LRP1, other genes are regulated by PPARγ such as ABCA1, LXRα, LPL, and GYK [52,83,84], and all were found to be down-regulated in ApoE4 astrocytes (Figure 2 and Figure 5).”
    Quote in the paperSubstantial claim

  • It may state two separate claims as one.

    Premisecitation

    In the brain, most cholesterol is produced de novo by astrocytes and then transported to neurons and other cells by combining with ApoE, mainly synthesized by astrocytes, to form lipoproteins secreted through ATP-binding cassette transporters.

    “In the brain most cholesterol is produced de novo by astrocytes, and then transported to neurons and other cells by combining with ApoE, mainly synthesized by astrocytes, to form lipoproteins that are secreted through the ATP-binding cassette (ABC) transporters [9,10].”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites [9] Holtzman, 2012, Apolipoprotein E and apolipoprotein E receptors: Normal biology and roles in Alzheimer disease, Cold Spring Harb. Perspect. Med. source
    • cites [10] Staurenghi, E., Giannelli, S., Testa, G., Sottero, B., Leonarduzzi, G., and Gamba, P. (2021). Cholesterol Dysmetabolism in Alzheimer’s Disease: A Starring Role for Astrocytes?. Antioxidants, 10. source

  • Probably not a substantial claim. The paper’s conclusions may not depend on it.

    Premisecitation

    The association between cholesterol homeostasis alterations and Alzheimer's disease onset and progression has been evident for many years.

    “The association between cholesterol homeostasis alterations and AD onset and progression has been evident for many years [11,12,13].”
    Quote in the paperNot a substantial claim0 of 3 sources checked
    • cites [11] Gamba, 2015, Oxidized cholesterol as the driving force behind the development of Alzheimer’s disease, Front. Aging Neurosci. source
    • cites [12] Goikolea, 2019, Alterations in cholesterol metabolism as a risk factor for developing Alzheimer’s disease: Potential novel targets for treatment, J. Steroid Biochem. Mol. Biol. source
    • cites [13] Zarrouk, 2018, Lipid Biomarkers in Alzheimer’s Disease, Curr. Alzheimer Res. source

  • Probably not a substantial claim. The paper’s conclusions may not depend on it.

    Premisecitation

    ApoE4 increases the risk of developing Alzheimer's disease by three to twelve times depending on whether the ε4 allele is present in heterozygosis or homozygosis.

    “In contrast to the most common isoform ApoE3, present in 78% of the population, ApoE4 increases the risk of developing AD by three to twelve times depending on whether the ε4 allele is present in heterozygosis or homozygosis [3].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [3] Reiman, 2020, Exceptionally low likelihood of Alzheimer’s dementia in APOE2 homozygotes from a 5000-person neuropathological study, Nat. Commun. source

  • Probably not a substantial claim. The paper’s conclusions may not depend on it.

    Premisecitation

    Cholesterol oxidation products (oxysterols) that accumulate in the brain are key actors in Alzheimer's disease pathogenesis because they lead to neuron dysfunction and degeneration, mainly by enhancing oxidative stress and inflammation.

    “For instance, cholesterol oxidation products (i.e., oxysterols) that accumulate in the brain are key actors in AD pathogenesis because they lead to neuron dysfunction and degeneration, mainly by enhancing oxidative stress and inflammation [11,14].”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites [11] Gamba, 2015, Oxidized cholesterol as the driving force behind the development of Alzheimer’s disease, Front. Aging Neurosci. source
    • cites [14] Bjorkhem, 2009, Oxysterols and neurodegenerative diseases, Mol. Aspects Med. source

  • It may state two separate claims as one.

    Premisecitation

    Changes in lipid metabolism, in particular cholesterol metabolism, predispose to Alzheimer's disease and play a substantial role in different phases of the disease.

    “Indeed, changes in lipid metabolism, in particular that of cholesterol, predispose to AD playing a substantial role in the different phases of the disease [4].”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [4] Kim, 2011, Linking lipids to Alzheimer’s disease: Cholesterol and beyond, Nat. Rev. Neurosci. source

  • Probably not a substantial claim. The paper’s conclusions may not depend on it. It may state two separate claims as one.

    Premisecitation

    The ApoE4 isoform affects lipid and glucose metabolism and many other processes involved in Alzheimer's disease pathology, including Aβ clearance, neuroinflammation, and synaptic function.

    “Indeed, the ApoE4 isoform has been shown to affect lipid and glucose metabolism, but also many other processes involved in AD pathology including Aβ clearance, neuroinflammation, and synaptic function [5]”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [5] Liu, 2013, Apolipoprotein E and Alzheimer disease: Risk, mechanisms and therapy, Nat. Rev. Neurol. source

  • It may state two separate claims as one.

    Premisecitation

    ApoE4 has been shown to impact many physiological functions played by astrocytes, affecting their ability to clear Aβ, uptake glutamate, promote neuronal synaptogenesis, and maintain lipid homeostasis.

    “ApoE4 has been shown to impact on many physiological functions played by astrocytes, affecting their ability to clear Aβ, to uptake glutamate, to promote neuronal synaptogenesis, and to maintain lipid homeostasis [15,16,42].”
    Quote in the paperSubstantial claim0 of 3 sources checked
    • cites [15] Tcw, 2022, Cholesterol and matrisome pathways dysregulated in astrocytes and microglia, Cell source
    • cites [16] Lin, 2018, APOE4 Causes Widespread Molecular and Cellular Alterations Associated with Alzheimer’s Disease Phenotypes in Human iPSC-Derived Brain Cell Types, Neuron source
    • cites [42] Zhao, 2017, APOE epsilon4/epsilon4 diminishes neurotrophic function of human iPSC-derived astrocytes, Hum. Mol. Genet. source

  • It may state two separate claims as one.

    Premisecitation

    Significantly reduced ApoE levels were observed in hiPSC-derived ApoE4 astrocytes and in brain homogenates from mouse models expressing the human ApoE4 isoform.

    “In agreement with our data, significantly reduced ApoE levels were also observed in hiPSC-derived ApoE4 astrocytes [15,16,24], as well as in brain homogenates from mouse models expressing the human ApoE4 isoform [43,44].”
    Quote in the paperNot a substantial claim0 of 5 sources checked
    • cites [15] Tcw, 2022, Cholesterol and matrisome pathways dysregulated in astrocytes and microglia, Cell source
    • cites [16] Lin, 2018, APOE4 Causes Widespread Molecular and Cellular Alterations Associated with Alzheimer’s Disease Phenotypes in Human iPSC-Derived Brain Cell Types, Neuron source
    • cites [24] Kirschner, 2022, APOE2, E3, and E4 differentially modulate cellular homeostasis, cholesterol metabolism, and inflammatory response in isogenic iPSC-derived astrocytes, Stem Cell Rep. source
    • cites [43] Sullivan, 2011, Reduced levels of human apoE4 protein in an animal model of cognitive impairment, Neurobiol. Aging source
    • cites [44] Bales, 2009, Human APOE isoform-dependent effects on brain beta-amyloid levels in PDAPP transgenic mice, J. Neurosci. source

  • Probably not a substantial claim. The paper’s conclusions may not depend on it. It may state two separate claims as one.

    Premisecitation

    ApoE4 may contribute to Alzheimer's disease pathogenesis by affecting neuronal structure and function, Aβ production and clearance, tau pathology, and neuroinflammation.

    “Although the role of ApoE4 in AD onset and progression remains unclear, many studies pointed out that ApoE4 may contribute to AD pathogenesis affecting neuronal structure and function, Aβ production and clearance, tau pathology, and neuroinflammation [40].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [40] Koutsodendris, 2022, Apolipoprotein E and Alzheimer’s Disease: Findings, Hypotheses, and Potential Mechanisms, Annu. Rev. Pathol. source

  • Probably not a substantial claim. The paper’s conclusions may not depend on it. It may state two separate claims as one.

    Premisecitation

    The maintenance of cholesterol homeostasis in the brain is essential for neuronal functioning, and abnormal brain cholesterol metabolism is associated with neurodegenerative diseases such as Alzheimer's disease.

    “The maintenance of cholesterol homeostasis in the brain is essential for neuronal functioning and the abnormal brain cholesterol metabolism is associated with neurodegenerative diseases, such as AD [25].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [25] Varma, 2021, Abnormal brain cholesterol homeostasis in Alzheimer’s disease-a targeted metabolomic and transcriptomic study, NPJ Aging Mech. Dis. source

  • It may state two separate claims as one.

    Premisecitation

    7α-OHC, 7β-OHC, and 24-OHC are primarily involved in cholesterol homeostasis regulation, while 25-OHC and 27-OHC are signalling molecules also involved in anti-viral, immunomodulant and inflammatory responses.

    “while 7α-OHC, 7β-OHC, and 24-OHC are primarily involved in cholesterol homeostasis regulation, 25-OHC and 27-OHC are signalling molecules also involved in anti-viral, immunomodulant and inflammatory responses [20]”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [20] Civra, 2019, Antiviral oxysterols are present in human milk at diverse stages of lactation, J. Steroid Biochem. Mol. Biol. source

  • Probably not a substantial claim. The paper’s conclusions may not depend on it. It may state two separate claims as one.

    Premisecitation

    ApoE can be degraded by autophagy and by an LC3-associated endocytosis-like process, and ApoE4 is sequestered in enlarged endosomes.

    “However, it appears that ApoE can be degraded by autophagy and by an LC3-associated endocytosis-like process, and that ApoE4 is sequestered in enlarged endosomes [46].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [46] Fote, 2022, Isoform-dependent lysosomal degradation and internalization of apolipoprotein E requires autophagy proteins, J. Cell Sci. source

  • Probably not a substantial claim. The paper’s conclusions may not depend on it. It may state two separate claims as one.

    Premisecitation

    24-OHC is the main oxysterol involved in brain cholesterol homeostasis, derives from cholesterol oxidation by CYP46A1, and regulates the expression and synthesis of proteins involved in cholesterol synthesis and efflux, including ApoE and ABCA1/ABCG1.

    “The main oxysterol involved in this process is 24-OHC, also called cerebrosterol, which derives from cholesterol oxidation by CYP46A1, a cytochrome P-450 enzyme mainly expressed by neurons but also by astrocytes [55].”
    • Also stated in: § 4. Discussion · plain
      “Moreover, 24-OHC, being an LXR ligand, regulates the expression and synthesis of the proteins involved in cholesterol synthesis and efflux, including ApoE and ABCA1/ABCG1 [59].”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites [55] Milagre, 2008, Transcriptional regulation of the human CYP46A1 brain-specific expression by Sp transcription factors, J. Neurochem. source
    • cites [59] Abildayeva, 2006, 24(S)-hydroxycholesterol participates in a liver X receptor-controlled pathway in astrocytes that regulates apolipoprotein E-mediated cholesterol efflux, J. Biol. Chem. source

  • It may state two separate claims as one.

    Interpretationreasoning

    ApoE4 astrocytes undergo differentiation into a microglia-like phenotype, more involved in immune response than in cholesterol supply for neuronal function and development.

    “further suggesting an ApoE4 astrocyte differentiation into a microglia-like phenotype, more involved in immune response than in cholesterol supply for neuronal function and development.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim.

    Premisecitation

    PPARγ regulates the transcription of several genes involved in late-onset AD, including ApoE.

    “Barrera and colleagues showed that PPARγ regulates the transcription of several genes involved in late-onset AD, including ApoE [80].”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [80] Barrera, J., Subramanian, S., and Chiba-Falek, O. (2018). Probing the role of PPARgamma in the regulation of late-onset Alzheimer’s disease-associated genes. PLoS ONE, 13. source

  • Probably not a substantial claim. It may state two separate claims as one.

    Premisecitation

    PPARγ is a ligand-modulated transcription factor which, through heterodimers with RXR, regulates expression of genes involved in lipid and glucose metabolism; it also exerts a neuroprotective and anti-inflammatory role in the CNS.

    “PPARγ is a ligand-modulated transcription factor which, through the formation of heterodimers with the retinoid X receptor (RXR), regulates the expression of genes involved in lipid and glucose metabolism [52]; in addition, it is known to exert a neuroprotective and anti-inflammatory role in the CNS [77,78].”
    Quote in the paperSubstantial claim0 of 3 sources checked
    • cites [52] Ahmadian, 2013, PPARgamma signaling and metabolism: The good, the bad and the future, Nat. Med. source
    • cites [77] Storer, 2005, Peroxisome proliferator-activated receptor-gamma agonists inhibit the activation of microglia and astrocytes: Implications for multiple sclerosis, J. Neuroimmunol. source
    • cites [78] Gillespie, 2011, Role of PPARgamma, a nuclear hormone receptor in neuroprotection, Indian J. Biochem. Biophys.

  • Probably not a substantial claim.

    Premisecitation

    PPARγ regulates LRP1 protein levels in adipocytes and hepatocytes.

    “PPARγ has been shown to regulate LRP1 protein levels in adipocytes and hepatocytes [81,82]”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites [81] Gauthier, 2003, Adipocyte low density lipoprotein receptor-related protein gene expression and function is regulated by peroxisome proliferator-activated receptor gamma, J. Biol. Chem. source
    • cites [82] Gugnani, 2017, High Concentrations of Rosiglitazone Reduce mRNA and Protein Levels of LRP1 in HepG2 Cells, Front. Pharmacol. source

  • Probably not a substantial claim. The paper’s conclusions may not depend on it. It may state two separate claims as one.

    Premisecitation

    LDLR, LRP1 and ApoER2 receptors are also present in astrocytes and have been shown to be involved in Aβ clearance mediated by astrocytes.

    “However, LDLR, LRP1 and ApoER2 receptors are also present in astrocytes [15,24,63] and have been also shown to be involved in the Aβ clearance mediated by astrocytes [50,64].”
    Quote in the paperNot a substantial claim0 of 5 sources checked
    • cites [15] Tcw, 2022, Cholesterol and matrisome pathways dysregulated in astrocytes and microglia, Cell source
    • cites [24] Kirschner, 2022, APOE2, E3, and E4 differentially modulate cellular homeostasis, cholesterol metabolism, and inflammatory response in isogenic iPSC-derived astrocytes, Stem Cell Rep. source
    • cites [63] Fan, 2001, Expression and regulation of apolipoprotein E receptors in the cells of the central nervous system in culture: A review, J. Am. Aging Assoc. source
    • cites [50] Basak, 2012, Low-density lipoprotein receptor represents an apolipoprotein E-independent pathway of Abeta uptake and degradation by astrocytes, J. Biol. Chem. source
    • cites [64] Liu, 2017, Astrocytic LRP1 Mediates Brain Abeta Clearance and Impacts Amyloid Deposition, J. Neurosci. source

  • Probably not a substantial claim. The paper’s conclusions may not depend on it.

    Interpretationcitation

    The shift to the Kandutsch-Russell pathway might reflect a sort of astrocyte polarization to a cell-type more specialized in immune responses.

    “while the Bloch pathway generally appears as typical for astrocytes, microglia cells seem to preferentially resort to the Kandutsch–Russell pathway; thus, the shift to this enzymatic cascade might reflect a sort of astrocyte polarization to a cell-type more specialized in immune responses [53].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [53] Qian, 2022, Balancing cholesterol in the brain: From synthesis to disposal, Explor. Neuroprotective Ther. source

  • Probably not a substantial claim.

    Premisecitation

    ApoE is able to bind various receptors such as LDLR, LRP1, and ApoER2, through which ApoE-containing lipoproteins are taken up by cells.

    “ApoE is able to bind various receptors such as LDLR, LRP1, and ApoER2, through which ApoE-containing lipoproteins are taken up by cells [9].”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [9] Holtzman, 2012, Apolipoprotein E and apolipoprotein E receptors: Normal biology and roles in Alzheimer disease, Cold Spring Harb. Perspect. Med. source

  • It may state two separate claims as one.

    Premisecitation

    Numerous oxysterols accumulate in the brain as AD progresses (e.g., 27-OHC, 25-OHC, 7α- and 7β-OHC, and 7-KC); conversely, 24-OHC levels drop dramatically in late stages of the disease likely due to neuronal loss.

    “it has been demonstrated that numerous oxysterols accumulate in the brain as AD progresses (e.g., 27-OHC, 25-OHC, 7α- and 7β-OHC, and 7-KC); conversely, the levels of 24-OHC drop dramatically in the late stages of the disease likely due to neuronal loss [19,65].”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites [19] Testa, 2016, Changes in brain oxysterols at different stages of Alzheimer’s disease: Their involvement in neuroinflammation, Redox Biol. source
    • cites [65] Hascalovici, 2014, Neural HO-1/sterol interactions in vivo: Implications for Alzheimer’s disease, Neuroscience source

  • It may state two separate claims as one.

    Premisecitation

    Treatment of different mouse models expressing ApoE4 with the ABCA1 agonist CS-6253 or the LXR agonist T0901317 increases ApoE4 lipidation and reduces ApoE4-driven Aβ accumulation and cognitive deficits.

    “the treatment of different mouse models expressing ApoE4 with the ABCA1 agonist CS-6253 or the LXR agonist T0901317 have been shown to increase ApoE4 lipidation, as well as to reduce ApoE4-driven Aβ accumulation and cognitive deficits [71,72].”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites [71] Michaelson, 2014, Reversal of apoE4-driven brain pathology and behavioral deficits by bexarotene, J. Neurosci. source
    • cites [72] Carter, A.Y., Letronne, F., Fitz, N.F., Mounier, A., Wolfe, C.M., Nam, K.N., Reeves, V.L., Kamboh, H., Lefterov, I., and Koldamova, R. (2017). Liver X receptor agonist treatment significantly affects phenotype and transcriptome of APOE3 and APOE4 Abca1 haplo-deficient mice. PLoS ONE, 12. source
    • Rests on an assumption: One of the main proteins responsible for ApoE lipidation in the CNS is the transporter ABCA1.

  • It may state two separate claims as one.

    Premisecitation

    ApoE4 is able to reduce recycling of the three receptors to the cell membrane, likely because of aberrant endosomal acidification that traps receptors within intracellular compartments and leads to their degradation.

    “several studies showed that ApoE4 is able to reduce their recycling to the cell membrane, likely because of the aberrant endosomal acidification that traps receptors within the intracellular compartments and leads to their degradation [73,74,75].”
    Quote in the paperSubstantial claim0 of 3 sources checked
    • cites [73] Prasad, 2018, Amyloid clearance defect in ApoE4 astrocytes is reversed by epigenetic correction of endosomal pH, Proc. Natl. Acad. Sci. USA source
    • cites [74] Kim, M., and Bezprozvanny, I. (2021). Differences in Recycling of Apolipoprotein E3 and E4-LDL Receptor Complexes-A Mechanistic Hypothesis. Int. J. Mol. Sci., 22. source
    • cites [75] Xian, 2018, Reversal of ApoE4-induced recycling block as a novel prevention approach for Alzheimer’s disease, eLife source

  • It may state two separate claims as one.

    Interpretationreasoning

    To avoid lanosterol accumulation, both a switch to the Kandutsch-Russell pathway and a feedback HMGCR downregulation could occur, resulting in a moderate but significant cholesterol decrease.

    “As a consequence of the Bloch-pathway inhibition, lanosterol enhances; to avoid accumulation of the latter, both the switch to the Kandutsch–Russell pathway and a feed-back HMGCR downregulation could occur, resulting altogether in a moderate, although significant, cholesterol decrease.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim. The paper’s conclusions may not depend on it. It may state two separate claims as one.

    Premisecitation

    The Bloch pathway generally appears as typical for astrocytes, while microglia cells seem to preferentially resort to the Kandutsch-Russell pathway.

    “while the Bloch pathway generally appears as typical for astrocytes, microglia cells seem to preferentially resort to the Kandutsch–Russell pathway; thus, the shift to this enzymatic cascade might reflect a sort of astrocyte polarization to a cell-type more specialized in immune responses [53].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [53] Qian, 2022, Balancing cholesterol in the brain: From synthesis to disposal, Explor. Neuroprotective Ther. source
31 of 31

  • The paper relies on this without support.

    The molecular mechanisms underlying ApoE4-induced pathogenic processes are not yet clear.

    “however, the molecular mechanisms underlying ApoE4-induced pathogenic processes are not yet clear.”

  • The paper relies on this without support.

    Cholesterol in the brain derives almost exclusively (>95%) from local de novo synthesis by astrocytes.

    “Thus, cholesterol in the brain derives almost exclusively (>95%) from local de novo synthesis by astrocytes from Acetyl-CoA through reactions catalyzed by over 20 enzymes.”

  • The authors state this as an assumption.

    The physiological presence of 24-OHC in the brain is fundamental to guarantee brain health.

    “This leads to the likely assumption that the physiological presence of this oxysterol in the brain is fundamental to guarantee brain health, suggesting the importance of preventing its loss in the brain during the course of AD [67].”

  • The paper relies on this without support.

    One of the main proteins responsible for ApoE lipidation in the CNS is the transporter ABCA1.

    “One of the main proteins responsible for ApoE lipidation in the CNS is the transporter ABCA1.”
4 of 4

Self-check

Percentages, sums and reported differences re-computed from the paper’s own numbers.

Each contradiction between two passages listed here was confirmed by an independent check.

  • Discussion describes CYP7A1 as reduced despite a nonsignificant result

    Minor

    The Results state that CYP7A1 expression did not change significantly, but the Discussion describes a CYP7A1 reduction as accompanying the decrease in 7α-OHC. A nonsignificant directional trend may exist, but the reported result does not establish the reduction claimed in the Discussion.

1 of 1

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Metadata

Authors
Staurenghi, E., Leoni, V., Lo Iacono, M., Sottero, B., Testa, G., Giannelli, S., Leonarduzzi, G., & Gamba, P.
Affiliations
  • University of Turin (IT)
  • University of Milano-Bicocca (IT)
  • Department of Clinical and Biological Sciences, University of Turin, Orbassano, 10043 Turin, Italy
Corresponding author
Gamba, Paola
ORCID
Venue
Antioxidants
Publisher
MDPI AG
Published
2022-11-01
Volume
11
Issue
11
Pages
2168
ISSN
2076-3921 (ISSN-L)
DOI
10.3390/antiox11112168
PMC
PMC9686673
OpenAlex
W4308332976
Cited by
24
References
89
Citations by year
2026: 7 · 2025: 8 · 2024: 8 · 2023: 1
FWCI
1.81
Type
journal article
Language
en
Open access
Licence
Locations
  • Antioxidants (publishedVersion, cc-by)
  • PubMed Central (publishedVersion, cc-by)
  • PubMed (publishedVersion)
  • Institutional Research Information System University of Turin (University of Turin) (submittedVersion, other-oa)
  • BOA (University of Milano-Bicocca) (submittedVersion, cc-by)
  • DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion, cc-by-sa)
Funders
  • University of Turin (LEOG_RILO_21_01, GAMP_RILO_21_01, 2019-ATE-0481)
  • University of Milano-Bicocca (LEOG_RILO_21_01, GAMP_RILO_21_01, 2019-ATE-0481)
Topics
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Biochemistry › Cholesterol and Lipid Metabolism
  • Life Sciences › Neuroscience › Cellular and Molecular Neuroscience › Alzheimer's disease research and treatments
  • Health Sciences › Medicine › Cardiology and Cardiovascular Medicine › Lipoproteins and Cardiovascular Health
Keywords
apolipoprotein E, APOE ε4, APOE3, astrocytes, cholesterol homeostasis, Alzheimer's disease, oxysterols, lipid metabolism genes, PPARγ, liver X receptor alpha, CYP27A1, ApoER2, ABCA1, LDL receptor, LRP1, apoE secretion, lipid transfer proteins

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Registry, retraction, Cites and statistics results are computed, not judged, with one exception: a printed reference that no index lists is read once by a model before it counts as a citation error. Claims are extracted by a model and kept only when their quote appears verbatim in the text; each cited source is then checked, with a model’s help, for whether it says what the claim relies on. Those verdicts can be wrong — read the claim’s quote and the cited source before relying on one.

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