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Differential interaction of Apolipoprotein-E isoforms with insulin receptors modulates brain insulin signaling in mutant human amyloid precursor protein transgenic mice.

Chan ES, Chen C, Cole GM, Wong BS - Sci Rep (2015)

Bottom Line: Here, we showed that ApoE3 had greater association with insulin receptor as compared to ApoE4, regardless of Aβ42 concentration.However, in the presence of Aβ42, insulin failed to elicit a downstream response only in ApoE4 hippocampal neurons.Taken together, our data show that ApoE genotypes can modulate this Aβ-mediated insulin signaling impairment.

View Article: PubMed Central - PubMed

Affiliation: Departments of Physiology Yong Loo Lin School of Medicine, National University of Singapore, Singapore.

ABSTRACT
It is unclear how human apolipoprotein E4 (ApoE4) increases the risk for Alzheimer's disease (AD). Although Aβ levels can lead to insulin signaling impairment, these experiments were done in the absence of human ApoE. To examine ApoE role, we crossed the human ApoE-targeted replacement mice with mutant human amyloid precursor protein (APP) mice. In 26 week old mice with lower Aβ levels, the expression and phosphorylation of insulin signaling proteins remained comparable among APP, ApoE3xAPP and ApoE4xAPP mouse brains. When the mice aged to 78 weeks, these proteins were markedly reduced in APP and ApoE4xAPP mouse brains. While Aβ can bind to insulin receptor, how ApoE isoforms modulate this interaction remains unknown. Here, we showed that ApoE3 had greater association with insulin receptor as compared to ApoE4, regardless of Aβ42 concentration. In contrast, ApoE4 bound more Aβ42 with increasing peptide levels. Using primary hippocampal neurons, we showed that ApoE3 and ApoE4 neurons are equally sensitive to physiological levels of insulin. However, in the presence of Aβ42, insulin failed to elicit a downstream response only in ApoE4 hippocampal neurons. Taken together, our data show that ApoE genotypes can modulate this Aβ-mediated insulin signaling impairment.

No MeSH data available.


Related in: MedlinePlus

Aβ42 lowers IRS-1 and Akt phosphorylation in ApoE4 hippocampal neurons.(A) Western and (B–D) densitometric analysis of the effects of insulin treatment (2 nM) on ApoE expression and, IRS-1 and Akt expression and phosphorylation in ApoE3 (E3) and ApoE4 (E4) hippocampal neurons exposed to 500 nM of Aβ42 or scrambled Aβ42. β-actin was immunoblotted to ensure similar gel loading of the starting material in each sample. The blot shown was one of three experiments using different primary hippocampal cultures. Blot images were cropped for comparison. Each value represents the mean ± SEM and the relative value for each treatment was normalized against no treatment (NT) of the same hippocampal cell line. One-way ANOVA revealed significant differences in P-IRS-1 Y608, P-Akt S473 and P-Akt T308 expression among treatments within each cell line (**p < 0.01).
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f5: Aβ42 lowers IRS-1 and Akt phosphorylation in ApoE4 hippocampal neurons.(A) Western and (B–D) densitometric analysis of the effects of insulin treatment (2 nM) on ApoE expression and, IRS-1 and Akt expression and phosphorylation in ApoE3 (E3) and ApoE4 (E4) hippocampal neurons exposed to 500 nM of Aβ42 or scrambled Aβ42. β-actin was immunoblotted to ensure similar gel loading of the starting material in each sample. The blot shown was one of three experiments using different primary hippocampal cultures. Blot images were cropped for comparison. Each value represents the mean ± SEM and the relative value for each treatment was normalized against no treatment (NT) of the same hippocampal cell line. One-way ANOVA revealed significant differences in P-IRS-1 Y608, P-Akt S473 and P-Akt T308 expression among treatments within each cell line (**p < 0.01).

Mentions: We used DIV10 hippocampal neurons cultured from ApoE3 and ApoE4 mice. We decided to use these matured neurons to test the Aβ42 susceptibility in the presence of different ApoE isoforms because AD is an ageing disease and immature neurons were more resistant to neurotoxic insults464748. Insulin treatment (2 nM) activated IRS-1 (Y608) and Akt (S473 and T308) phosphorylation in both cultures (Fig. 5). However, 500 nM Aβ42 or scrambled Aβ42 peptides added to ApoE3 and ApoE4 hippocampal neurons had no effect on IRS-1 and Akt expression and phosphorylation, similar to non-treated neurons. The Aβ42 concentration used in our study is comparable to other studies used on primary neurons4449. In ApoE3 hippocampal neurons, F = 22.98, 16.26, 8.22, (p < 0.01) for P-IRS-1 Y608, P-Akt S473 and P-Akt T308 respectively. In ApoE4 hippocampal neurons, F = 8.27, 17.40, 16.65 (p < 0.01) for P-IRS-1 Y608, P-Akt S473 and P-Akt T308 respectively.


Differential interaction of Apolipoprotein-E isoforms with insulin receptors modulates brain insulin signaling in mutant human amyloid precursor protein transgenic mice.

Chan ES, Chen C, Cole GM, Wong BS - Sci Rep (2015)

Aβ42 lowers IRS-1 and Akt phosphorylation in ApoE4 hippocampal neurons.(A) Western and (B–D) densitometric analysis of the effects of insulin treatment (2 nM) on ApoE expression and, IRS-1 and Akt expression and phosphorylation in ApoE3 (E3) and ApoE4 (E4) hippocampal neurons exposed to 500 nM of Aβ42 or scrambled Aβ42. β-actin was immunoblotted to ensure similar gel loading of the starting material in each sample. The blot shown was one of three experiments using different primary hippocampal cultures. Blot images were cropped for comparison. Each value represents the mean ± SEM and the relative value for each treatment was normalized against no treatment (NT) of the same hippocampal cell line. One-way ANOVA revealed significant differences in P-IRS-1 Y608, P-Akt S473 and P-Akt T308 expression among treatments within each cell line (**p < 0.01).
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4561911&req=5

f5: Aβ42 lowers IRS-1 and Akt phosphorylation in ApoE4 hippocampal neurons.(A) Western and (B–D) densitometric analysis of the effects of insulin treatment (2 nM) on ApoE expression and, IRS-1 and Akt expression and phosphorylation in ApoE3 (E3) and ApoE4 (E4) hippocampal neurons exposed to 500 nM of Aβ42 or scrambled Aβ42. β-actin was immunoblotted to ensure similar gel loading of the starting material in each sample. The blot shown was one of three experiments using different primary hippocampal cultures. Blot images were cropped for comparison. Each value represents the mean ± SEM and the relative value for each treatment was normalized against no treatment (NT) of the same hippocampal cell line. One-way ANOVA revealed significant differences in P-IRS-1 Y608, P-Akt S473 and P-Akt T308 expression among treatments within each cell line (**p < 0.01).
Mentions: We used DIV10 hippocampal neurons cultured from ApoE3 and ApoE4 mice. We decided to use these matured neurons to test the Aβ42 susceptibility in the presence of different ApoE isoforms because AD is an ageing disease and immature neurons were more resistant to neurotoxic insults464748. Insulin treatment (2 nM) activated IRS-1 (Y608) and Akt (S473 and T308) phosphorylation in both cultures (Fig. 5). However, 500 nM Aβ42 or scrambled Aβ42 peptides added to ApoE3 and ApoE4 hippocampal neurons had no effect on IRS-1 and Akt expression and phosphorylation, similar to non-treated neurons. The Aβ42 concentration used in our study is comparable to other studies used on primary neurons4449. In ApoE3 hippocampal neurons, F = 22.98, 16.26, 8.22, (p < 0.01) for P-IRS-1 Y608, P-Akt S473 and P-Akt T308 respectively. In ApoE4 hippocampal neurons, F = 8.27, 17.40, 16.65 (p < 0.01) for P-IRS-1 Y608, P-Akt S473 and P-Akt T308 respectively.

Bottom Line: Here, we showed that ApoE3 had greater association with insulin receptor as compared to ApoE4, regardless of Aβ42 concentration.However, in the presence of Aβ42, insulin failed to elicit a downstream response only in ApoE4 hippocampal neurons.Taken together, our data show that ApoE genotypes can modulate this Aβ-mediated insulin signaling impairment.

View Article: PubMed Central - PubMed

Affiliation: Departments of Physiology Yong Loo Lin School of Medicine, National University of Singapore, Singapore.

ABSTRACT
It is unclear how human apolipoprotein E4 (ApoE4) increases the risk for Alzheimer's disease (AD). Although Aβ levels can lead to insulin signaling impairment, these experiments were done in the absence of human ApoE. To examine ApoE role, we crossed the human ApoE-targeted replacement mice with mutant human amyloid precursor protein (APP) mice. In 26 week old mice with lower Aβ levels, the expression and phosphorylation of insulin signaling proteins remained comparable among APP, ApoE3xAPP and ApoE4xAPP mouse brains. When the mice aged to 78 weeks, these proteins were markedly reduced in APP and ApoE4xAPP mouse brains. While Aβ can bind to insulin receptor, how ApoE isoforms modulate this interaction remains unknown. Here, we showed that ApoE3 had greater association with insulin receptor as compared to ApoE4, regardless of Aβ42 concentration. In contrast, ApoE4 bound more Aβ42 with increasing peptide levels. Using primary hippocampal neurons, we showed that ApoE3 and ApoE4 neurons are equally sensitive to physiological levels of insulin. However, in the presence of Aβ42, insulin failed to elicit a downstream response only in ApoE4 hippocampal neurons. Taken together, our data show that ApoE genotypes can modulate this Aβ-mediated insulin signaling impairment.

No MeSH data available.


Related in: MedlinePlus