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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

ApoE3 binds to insulin receptor stronger than ApoE4.(A) Total brain lysates from 26 (left) and 78 (right) week old APP, ApoE3xAPP (E3XAPP) and ApoE4xAPP (E4XAPP) mice were immunoprecipitated (IP) with anti-ApoE, and were analyzed for human ApoE, insulin receptor (IR), Aβ and mouse IgG. The flow-through refers to the starting material remaining after separation from the agarose beads, and was analyzed for insulin receptor (IR) and β-actin. Each immunoprecipitation for an individual mouse age has been performed on six different mouse brains (n = 6) from each mouse line, and the two blots shown are from two different mouse brain samples. Blot images were cropped for comparison. (B,C) Densitometry analysis was performed using the NIH ImageJ software and the relative value for ApoE4xAPP mice was normalized against age-matched ApoE3xAPP mice. At 26 and 78 weeks, ApoE4 bound less to IR than ApoE3 in ApoExAPP mice (*p < 0.05, **p < 0.01). At 78 weeks, 5-fold more Aβ binding to ApoE was detected in ApoE4xAPP mice as compared to ApoE3xAPP mice (*p < 0.01).
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f3: ApoE3 binds to insulin receptor stronger than ApoE4.(A) Total brain lysates from 26 (left) and 78 (right) week old APP, ApoE3xAPP (E3XAPP) and ApoE4xAPP (E4XAPP) mice were immunoprecipitated (IP) with anti-ApoE, and were analyzed for human ApoE, insulin receptor (IR), Aβ and mouse IgG. The flow-through refers to the starting material remaining after separation from the agarose beads, and was analyzed for insulin receptor (IR) and β-actin. Each immunoprecipitation for an individual mouse age has been performed on six different mouse brains (n = 6) from each mouse line, and the two blots shown are from two different mouse brain samples. Blot images were cropped for comparison. (B,C) Densitometry analysis was performed using the NIH ImageJ software and the relative value for ApoE4xAPP mice was normalized against age-matched ApoE3xAPP mice. At 26 and 78 weeks, ApoE4 bound less to IR than ApoE3 in ApoExAPP mice (*p < 0.05, **p < 0.01). At 78 weeks, 5-fold more Aβ binding to ApoE was detected in ApoE4xAPP mice as compared to ApoE3xAPP mice (*p < 0.01).

Mentions: To determine if ApoE could interact with the insulin signaling proteins, we immunoprecipitated ApoE from 26 and 78 week old brain lysates of our ApoE3xAPP and ApoE4xAPP mice (Fig. 3). We also included the APP mice as a control as it did not express human ApoE. In both the young and aged mouse brain, we detected more IR bound with ApoE3 than IR bound with ApoE4 (26 weeks, t = 3.385, p < 0.01; 78 weeks, t = 2.758, p < 0.05). Similar levels of ApoE were immunoprecipitated with ApoE3 and ApoE4 at 26 weeks. When Aβ levels were increased at 78 weeks, ApoE4 bound more Aβ than ApoE3 (t = 3.599, p < 0.01). This difference was not due to changes in IR expression, as similar IR content was observed in the brain lysates.


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)

ApoE3 binds to insulin receptor stronger than ApoE4.(A) Total brain lysates from 26 (left) and 78 (right) week old APP, ApoE3xAPP (E3XAPP) and ApoE4xAPP (E4XAPP) mice were immunoprecipitated (IP) with anti-ApoE, and were analyzed for human ApoE, insulin receptor (IR), Aβ and mouse IgG. The flow-through refers to the starting material remaining after separation from the agarose beads, and was analyzed for insulin receptor (IR) and β-actin. Each immunoprecipitation for an individual mouse age has been performed on six different mouse brains (n = 6) from each mouse line, and the two blots shown are from two different mouse brain samples. Blot images were cropped for comparison. (B,C) Densitometry analysis was performed using the NIH ImageJ software and the relative value for ApoE4xAPP mice was normalized against age-matched ApoE3xAPP mice. At 26 and 78 weeks, ApoE4 bound less to IR than ApoE3 in ApoExAPP mice (*p < 0.05, **p < 0.01). At 78 weeks, 5-fold more Aβ binding to ApoE was detected in ApoE4xAPP mice as compared to ApoE3xAPP mice (*p < 0.01).
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getmorefigures.php?uid=PMC4561911&req=5

f3: ApoE3 binds to insulin receptor stronger than ApoE4.(A) Total brain lysates from 26 (left) and 78 (right) week old APP, ApoE3xAPP (E3XAPP) and ApoE4xAPP (E4XAPP) mice were immunoprecipitated (IP) with anti-ApoE, and were analyzed for human ApoE, insulin receptor (IR), Aβ and mouse IgG. The flow-through refers to the starting material remaining after separation from the agarose beads, and was analyzed for insulin receptor (IR) and β-actin. Each immunoprecipitation for an individual mouse age has been performed on six different mouse brains (n = 6) from each mouse line, and the two blots shown are from two different mouse brain samples. Blot images were cropped for comparison. (B,C) Densitometry analysis was performed using the NIH ImageJ software and the relative value for ApoE4xAPP mice was normalized against age-matched ApoE3xAPP mice. At 26 and 78 weeks, ApoE4 bound less to IR than ApoE3 in ApoExAPP mice (*p < 0.05, **p < 0.01). At 78 weeks, 5-fold more Aβ binding to ApoE was detected in ApoE4xAPP mice as compared to ApoE3xAPP mice (*p < 0.01).
Mentions: To determine if ApoE could interact with the insulin signaling proteins, we immunoprecipitated ApoE from 26 and 78 week old brain lysates of our ApoE3xAPP and ApoE4xAPP mice (Fig. 3). We also included the APP mice as a control as it did not express human ApoE. In both the young and aged mouse brain, we detected more IR bound with ApoE3 than IR bound with ApoE4 (26 weeks, t = 3.385, p < 0.01; 78 weeks, t = 2.758, p < 0.05). Similar levels of ApoE were immunoprecipitated with ApoE3 and ApoE4 at 26 weeks. When Aβ levels were increased at 78 weeks, ApoE4 bound more Aβ than ApoE3 (t = 3.599, p < 0.01). This difference was not due to changes in IR expression, as similar IR content was observed in the brain lysates.

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