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The ε3 and ε4 alleles of human APOE differentially affect tau phosphorylation in hyperinsulinemic and pioglitazone treated mice.

To AW, Ribe EM, Chuang TT, Schroeder JE, Lovestone S - PLoS ONE (2011)

Bottom Line: Tau phosphorylation was reduced at 3 epitopes (Ser396, Ser202/Thr205 and Thr231) in all HFD, compared to LFD, animals independent of APOE genotype.The introduction of pioglitazone to HFD animals led to a significant reduction in tau phosphorylation at the Ser202/Thr205 epitope in APOEε3 animals only.We found no changes in APP processing however the levels of soluble amyloid beta 40 was reduced in APOE knockout animals treated with pioglitazone.

View Article: PubMed Central - PubMed

Affiliation: King's College London, Institute of Psychiatry, London, United Kingdom.

ABSTRACT

Background: Impaired insulin signalling is increasingly thought to contribute to Alzheimer's disease (AD). The ε4 isoform of the APOE gene is the greatest genetic risk factor for sporadic, late onset AD, and is also associated with risk for type 2 diabetes mellitus (T2DM). Neuropathological studies reported the highest number of AD lesions in brain tissue of ε4 diabetic patients. However other studies assessing AD pathology amongst the diabetic population have produced conflicting reports and have failed to show an increase in AD-related pathology in diabetic brain. The thiazolidinediones (TZDs), peroxisome proliferator-activated receptor gamma agonists, are peripheral insulin sensitisers used to treat T2DM. The TZD, pioglitazone, improved memory and cognitive functions in mild to moderate AD patients. Since it is not yet clear how apoE isoforms influence the development of T2DM and its progression to AD, we investigated amyloid beta and tau pathology in APOE knockout mice, carrying human APOEε3 or ε4 transgenes after diet-induced insulin resistance with and without pioglitazone treatment.

Methods: Male APOE knockout, APOEε3-transgenic and APOEε4-transgenic mice, together with background strain C57BL6 mice were kept on a high fat diet (HFD) or low fat diet (LFD) for 32 weeks, or were all fed HFD for 32 weeks and during the final 3 weeks animals were treated with pioglitazone or vehicle.

Results: All HFD animals developed hyperglycaemia with elevated plasma insulin. Tau phosphorylation was reduced at 3 epitopes (Ser396, Ser202/Thr205 and Thr231) in all HFD, compared to LFD, animals independent of APOE genotype. The introduction of pioglitazone to HFD animals led to a significant reduction in tau phosphorylation at the Ser202/Thr205 epitope in APOEε3 animals only. We found no changes in APP processing however the levels of soluble amyloid beta 40 was reduced in APOE knockout animals treated with pioglitazone.

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Tau phosphorylation is reduced in HFD fed APOE mice, independent of genotype.The frontal cortex from APOE mice were homogenised in sucrose homogenisation buffer, lysates were then immunoblotted with the indicated antibodies. A) Western blot of tau antibodies in frontal cortex of APOE KO, APOEε3, APOEε4 and WT mice fed LFD or HFD. B) Density of phosphorylated tau normalised against total tau. C) Tau phosphorylation is dependent on diet. Phosphorylated tau is normalised to total tau, data is grouped by diet. *p<0.05; **p<0.01; ***p<0.001 by t-test.
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pone-0016991-g004: Tau phosphorylation is reduced in HFD fed APOE mice, independent of genotype.The frontal cortex from APOE mice were homogenised in sucrose homogenisation buffer, lysates were then immunoblotted with the indicated antibodies. A) Western blot of tau antibodies in frontal cortex of APOE KO, APOEε3, APOEε4 and WT mice fed LFD or HFD. B) Density of phosphorylated tau normalised against total tau. C) Tau phosphorylation is dependent on diet. Phosphorylated tau is normalised to total tau, data is grouped by diet. *p<0.05; **p<0.01; ***p<0.001 by t-test.

Mentions: Comparing HFD to LFD animals we found a decrease in tau phosphorylation in the insulin resistant animals at all epitopes examined. This decrease was preserved across all genotypes with a significant decrease in tau phosphorylation in HFD fed WT animals at the Ser202/Thr205 (p = 0.010) and Thr231 epitopes (p = 0.042) and a trend towards reduction at Ser396 (Figure 4A and 4B). Analysis of all genotypes and all epitopes by ANOVA shows a significant interaction between diet and tau phosphorylation (p<0.001) but no effect of genotype. Combining genotypes shows a highly significant effect of tau phosphorylation at all three epitopes (Ser396 p = 0.03, Ser202/Thr205 (AT8) p = 0.0002 and Thr231 (AT180) p = 0.008) (Figure 4C). With respect to levels of soluble Aβ, we observed no significant changes in Aβ40 or Aβ42 according to diet within each APOE genotype nor did we observe changes in APP C-terminal fragments (APP-CTFs) (data not shown). Given the changes in tau phosphorylation we measured the level of active tau kinases and tau phosphatases; GSK-3αβ by using an activity dependent phospho-kinase antibody, Cdk5 by using p35/25 specific antibody and the tau-phosphatase, PP2A. We also measured the activity of Akt, a member of the insulin signalling pathway. No significant changes in the brain were found in GSK-3αβ, Cdk5, PP2A or Akt by APOE genotype or diet (data not shown).


The ε3 and ε4 alleles of human APOE differentially affect tau phosphorylation in hyperinsulinemic and pioglitazone treated mice.

To AW, Ribe EM, Chuang TT, Schroeder JE, Lovestone S - PLoS ONE (2011)

Tau phosphorylation is reduced in HFD fed APOE mice, independent of genotype.The frontal cortex from APOE mice were homogenised in sucrose homogenisation buffer, lysates were then immunoblotted with the indicated antibodies. A) Western blot of tau antibodies in frontal cortex of APOE KO, APOEε3, APOEε4 and WT mice fed LFD or HFD. B) Density of phosphorylated tau normalised against total tau. C) Tau phosphorylation is dependent on diet. Phosphorylated tau is normalised to total tau, data is grouped by diet. *p<0.05; **p<0.01; ***p<0.001 by t-test.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3037394&req=5

pone-0016991-g004: Tau phosphorylation is reduced in HFD fed APOE mice, independent of genotype.The frontal cortex from APOE mice were homogenised in sucrose homogenisation buffer, lysates were then immunoblotted with the indicated antibodies. A) Western blot of tau antibodies in frontal cortex of APOE KO, APOEε3, APOEε4 and WT mice fed LFD or HFD. B) Density of phosphorylated tau normalised against total tau. C) Tau phosphorylation is dependent on diet. Phosphorylated tau is normalised to total tau, data is grouped by diet. *p<0.05; **p<0.01; ***p<0.001 by t-test.
Mentions: Comparing HFD to LFD animals we found a decrease in tau phosphorylation in the insulin resistant animals at all epitopes examined. This decrease was preserved across all genotypes with a significant decrease in tau phosphorylation in HFD fed WT animals at the Ser202/Thr205 (p = 0.010) and Thr231 epitopes (p = 0.042) and a trend towards reduction at Ser396 (Figure 4A and 4B). Analysis of all genotypes and all epitopes by ANOVA shows a significant interaction between diet and tau phosphorylation (p<0.001) but no effect of genotype. Combining genotypes shows a highly significant effect of tau phosphorylation at all three epitopes (Ser396 p = 0.03, Ser202/Thr205 (AT8) p = 0.0002 and Thr231 (AT180) p = 0.008) (Figure 4C). With respect to levels of soluble Aβ, we observed no significant changes in Aβ40 or Aβ42 according to diet within each APOE genotype nor did we observe changes in APP C-terminal fragments (APP-CTFs) (data not shown). Given the changes in tau phosphorylation we measured the level of active tau kinases and tau phosphatases; GSK-3αβ by using an activity dependent phospho-kinase antibody, Cdk5 by using p35/25 specific antibody and the tau-phosphatase, PP2A. We also measured the activity of Akt, a member of the insulin signalling pathway. No significant changes in the brain were found in GSK-3αβ, Cdk5, PP2A or Akt by APOE genotype or diet (data not shown).

Bottom Line: Tau phosphorylation was reduced at 3 epitopes (Ser396, Ser202/Thr205 and Thr231) in all HFD, compared to LFD, animals independent of APOE genotype.The introduction of pioglitazone to HFD animals led to a significant reduction in tau phosphorylation at the Ser202/Thr205 epitope in APOEε3 animals only.We found no changes in APP processing however the levels of soluble amyloid beta 40 was reduced in APOE knockout animals treated with pioglitazone.

View Article: PubMed Central - PubMed

Affiliation: King's College London, Institute of Psychiatry, London, United Kingdom.

ABSTRACT

Background: Impaired insulin signalling is increasingly thought to contribute to Alzheimer's disease (AD). The ε4 isoform of the APOE gene is the greatest genetic risk factor for sporadic, late onset AD, and is also associated with risk for type 2 diabetes mellitus (T2DM). Neuropathological studies reported the highest number of AD lesions in brain tissue of ε4 diabetic patients. However other studies assessing AD pathology amongst the diabetic population have produced conflicting reports and have failed to show an increase in AD-related pathology in diabetic brain. The thiazolidinediones (TZDs), peroxisome proliferator-activated receptor gamma agonists, are peripheral insulin sensitisers used to treat T2DM. The TZD, pioglitazone, improved memory and cognitive functions in mild to moderate AD patients. Since it is not yet clear how apoE isoforms influence the development of T2DM and its progression to AD, we investigated amyloid beta and tau pathology in APOE knockout mice, carrying human APOEε3 or ε4 transgenes after diet-induced insulin resistance with and without pioglitazone treatment.

Methods: Male APOE knockout, APOEε3-transgenic and APOEε4-transgenic mice, together with background strain C57BL6 mice were kept on a high fat diet (HFD) or low fat diet (LFD) for 32 weeks, or were all fed HFD for 32 weeks and during the final 3 weeks animals were treated with pioglitazone or vehicle.

Results: All HFD animals developed hyperglycaemia with elevated plasma insulin. Tau phosphorylation was reduced at 3 epitopes (Ser396, Ser202/Thr205 and Thr231) in all HFD, compared to LFD, animals independent of APOE genotype. The introduction of pioglitazone to HFD animals led to a significant reduction in tau phosphorylation at the Ser202/Thr205 epitope in APOEε3 animals only. We found no changes in APP processing however the levels of soluble amyloid beta 40 was reduced in APOE knockout animals treated with pioglitazone.

Show MeSH
Related in: MedlinePlus