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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

Insulin receptor substrate protein-1 and Akt expression and phosphorylation in 78 week old mouse brain.(A) Western blot and (B–F) densitometric analysis of insulin receptor substrate 1 (IRS-1), phosphorylated IRS-1 (Y608), total Akt, phosphorylated Akt (S473 and T308), and human ApoE levels in the brain of 78 week old APP (dark grey), ApoE3xAPP (E3XAPP, white) and ApoE4xAPP (E4XAPP, grey) mice. β-actin was immunoblotted to ensure similar gel loading of the starting material in each sample. The blot was a representative of six independent experiments. Blot images were cropped for comparison. Densitometry analysis was performed using the NIH ImageJ software and the relative value for ApoE3xAPP and ApoE4xAPP mice was normalized against age-matched APP mice. Each value represents the mean ± SEM for individual mouse brain sample (n = 6 for each mouse line). One-way ANOVA yielded significant differences between groups (*p < 0.05, **p < 0.01). Student’s t test revealed that human ApoE was also significantly lower in ApoE4xAPP mice as compared to ApoE3xAPP mice (*p < 0.05).
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f2: Insulin receptor substrate protein-1 and Akt expression and phosphorylation in 78 week old mouse brain.(A) Western blot and (B–F) densitometric analysis of insulin receptor substrate 1 (IRS-1), phosphorylated IRS-1 (Y608), total Akt, phosphorylated Akt (S473 and T308), and human ApoE levels in the brain of 78 week old APP (dark grey), ApoE3xAPP (E3XAPP, white) and ApoE4xAPP (E4XAPP, grey) mice. β-actin was immunoblotted to ensure similar gel loading of the starting material in each sample. The blot was a representative of six independent experiments. Blot images were cropped for comparison. Densitometry analysis was performed using the NIH ImageJ software and the relative value for ApoE3xAPP and ApoE4xAPP mice was normalized against age-matched APP mice. Each value represents the mean ± SEM for individual mouse brain sample (n = 6 for each mouse line). One-way ANOVA yielded significant differences between groups (*p < 0.05, **p < 0.01). Student’s t test revealed that human ApoE was also significantly lower in ApoE4xAPP mice as compared to ApoE3xAPP mice (*p < 0.05).

Mentions: In the aged mouse brain (78 weeks) however, post-hoc Tukey-Kramer analysis showed that IRS-1 expression and phosphorylation at Tyr-608 (Y608, equivalent to Y612 in human IRS-1), one of the two main PI3K p85 binding motifs, was significantly lower in ApoE4xAPP mouse brain as compared to ApoE3xAPP and APP mouse brain (Fig. 2A,B).


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)

Insulin receptor substrate protein-1 and Akt expression and phosphorylation in 78 week old mouse brain.(A) Western blot and (B–F) densitometric analysis of insulin receptor substrate 1 (IRS-1), phosphorylated IRS-1 (Y608), total Akt, phosphorylated Akt (S473 and T308), and human ApoE levels in the brain of 78 week old APP (dark grey), ApoE3xAPP (E3XAPP, white) and ApoE4xAPP (E4XAPP, grey) mice. β-actin was immunoblotted to ensure similar gel loading of the starting material in each sample. The blot was a representative of six independent experiments. Blot images were cropped for comparison. Densitometry analysis was performed using the NIH ImageJ software and the relative value for ApoE3xAPP and ApoE4xAPP mice was normalized against age-matched APP mice. Each value represents the mean ± SEM for individual mouse brain sample (n = 6 for each mouse line). One-way ANOVA yielded significant differences between groups (*p < 0.05, **p < 0.01). Student’s t test revealed that human ApoE was also significantly lower in ApoE4xAPP mice as compared to ApoE3xAPP mice (*p < 0.05).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f2: Insulin receptor substrate protein-1 and Akt expression and phosphorylation in 78 week old mouse brain.(A) Western blot and (B–F) densitometric analysis of insulin receptor substrate 1 (IRS-1), phosphorylated IRS-1 (Y608), total Akt, phosphorylated Akt (S473 and T308), and human ApoE levels in the brain of 78 week old APP (dark grey), ApoE3xAPP (E3XAPP, white) and ApoE4xAPP (E4XAPP, grey) mice. β-actin was immunoblotted to ensure similar gel loading of the starting material in each sample. The blot was a representative of six independent experiments. Blot images were cropped for comparison. Densitometry analysis was performed using the NIH ImageJ software and the relative value for ApoE3xAPP and ApoE4xAPP mice was normalized against age-matched APP mice. Each value represents the mean ± SEM for individual mouse brain sample (n = 6 for each mouse line). One-way ANOVA yielded significant differences between groups (*p < 0.05, **p < 0.01). Student’s t test revealed that human ApoE was also significantly lower in ApoE4xAPP mice as compared to ApoE3xAPP mice (*p < 0.05).
Mentions: In the aged mouse brain (78 weeks) however, post-hoc Tukey-Kramer analysis showed that IRS-1 expression and phosphorylation at Tyr-608 (Y608, equivalent to Y612 in human IRS-1), one of the two main PI3K p85 binding motifs, was significantly lower in ApoE4xAPP mouse brain as compared to ApoE3xAPP and APP mouse brain (Fig. 2A,B).

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