ApoE4 markedly exacerbates tau-mediated neurodegeneration in a mouse model of tauopathy

Abstract

APOE4 is the strongest genetic risk factor for late-onset Alzheimer disease. ApoE4 increases brain amyloid-β pathology relative to other ApoE isoforms1. However, whether APOE independently influences tau pathology, the other major proteinopathy of Alzheimer disease and other tauopathies, or tau-mediated neurodegeneration, is not clear. By generating P301S tau transgenic mice on either a human ApoE knock-in (KI) or ApoE knockout (KO) background, here we show that P301S/E4 mice have significantly higher tau levels in the brain and a greater extent of somatodendritic tau redistribution by three months of age compared with P301S/E2, P301S/E3, and P301S/EKO mice. By nine months of age, P301S mice with different ApoE genotypes display distinct phosphorylated tau protein (p-tau) staining patterns. P301S/E4 mice develop markedly more brain atrophy and neuroinflammation than P301S/E2 and P301S/E3 mice, whereas P301S/EKO mice are largely protected from these changes. In vitro, E4-expressing microglia exhibit higher innate immune reactivity after lipopolysaccharide treatment. Co-culturing P301S tau-expressing neurons with E4-expressing mixed glia results in a significantly higher level of tumour-necrosis factor-α (TNF-α) secretion and markedly reduced neuronal viability compared with neuron/E2 and neuron/E3 co-cultures. Neurons co-cultured with EKO glia showed the greatest viability with the lowest level of secreted TNF-α. Treatment of P301S neurons with recombinant ApoE (E2, E3, E4) also leads to some neuronal damage and death compared with the absence of ApoE, with ApoE4 exacerbating the effect. In individuals with a sporadic primary tauopathy, the presence of an ε4 allele is associated with more severe regional neurodegeneration. In individuals who are positive for amyloid-β pathology with symptomatic Alzheimer disease who usually have tau pathology, ε4-carriers demonstrate greater rates of disease progression. Our results demonstrate that ApoE affects tau pathogenesis, neuroinflammation, and tau-mediated neurodegeneration independently of amyloid-β pathology. ApoE4 exerts a ‘toxic’ gain of function whereas the absence of ApoE is protective.

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Figure 1: ApoE4 exacerbates neurodegeneration in P301S mice whereas genetic ablation of ApoE is associated with less damage.
Figure 2: ApoE genotypes differentially regulate tau pathology.
Figure 3: ApoE strongly modulates microglial activation.
Figure 4: ApoE4 leads to robust astrocytic activation and promotes neuronal death in vitro whereas the absence of ApoE results in less astrocytic activation and preserves neuronal integrity.

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Acknowledgements

This study was funded by National Institutes of Health (NIH) NS090934 (D.M.H.), P01-AG03991 (D.M.H., J.C.M., A.M.F.), P01-AG026276 (D.M.H., J.C.M., A.M.F.), P50 AG05681 (D.M.H., J.C.M., A.M.F.), the JPB Foundation (D.M.H., B.A.B.), Cure Alzheimer’s Fund (D.M.H.), a grant from AstraZeneca (D.M.H., S.M.P.), NIH AG023501 (W.W.S.), AG019724 (W.W.S.), Consortium for Frontotemporal Dementia Research (W.W.S.), Tau Consortium (W.W.S.), NIH K08 AG052648 (S.S.), NIH AG051812 (O.B.), NS088137 (O.B.), National Multiple Sclerosis Society (5092A1) (O.B.), Nancy Davis Foundation Award (O.B.), Amyotrophic Lateral Sclerosis Association (ALSA2087) (O.B.), and NIH K01 NS096719-01 (G.G.). We thank J. Yu for technical assistance in gene expression analysis; N. Barthélemy for assistance in tau phosphorylation analysis; and S. Schindler for assistance in statistical analysis. Data collection and sharing for this project were funded by the Alzheimer’s Disease Neuroimaging Initiative (ADNI) (NIH Grant U01 AG024904) and Department of Defense ADNI (award number W81XWH-12-2-0012). A full list of ADNI funding information is listed in the Supplementary Information.

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D.M.H., S.M.P., and Y.S. conceived the study. Y.S., K.Y., and D.M.H. designed the study. Y.S. performed most of the experiments and analysed the data, assisted by K.Y., K.W., G.G., L.Z, M.W.W., J.R., G.R., M.B.F., and H.J.; S.T.S., C.B., and O.B. performed the Nanostring microglial gene expression assay; S.A.L. and B.A.B. performed the astrocytic gene expression assay; W.L. performed the microglia LPS stimulation assay; R.M.T., S.S., L.T.G., B.L.M., W.W.S., J.C.R., and A.L.B. performed data analysis for human primary tauopathies; J.D.A., L.M., C.S., C.X., J.C.M., A.F., and C.C. performed data analysis in human patients with Alzheimer disease; P.M.S. provided the ApoE KI mice. Y.S. and D.M.H. wrote the manuscript. All authors discussed the results and commented on the manuscript. A portion of the human Alzheimer disease data used in preparation of this article was obtained from the ADNI database (http://adni.loni.usc.edu). As such, the investigators within the ADNI contributed to the design and implementation of ADNI and/or provided data but did not participate in analysis or writing of this report. A complete listing of ADNI investigators can be found in the Supplementary Information.

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Correspondence to David M. Holtzman.

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Competing interests

D.M.H. co-founded and is on the scientific advisory board of C2N Diagnostics. He consults for Genentech, AbbVie, Eli Lilly, Proclara, GlaxoSmithKline, and Denali. Washington University receives research grants to the laboratory of D.M.H. from C2N Diagnostics, Eli Lilly, AbbVie, and Denali.

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Extended data figures and tables

Extended Data Figure 1 No brain atrophy or brain volume differences in 3-month-old TE mice or 9-month-old non-tau transgenic mice.

a, Representative images of 3-month-old TE mouse brains (WT, n = 10; TE2, n = 10; TE3, n = 10; TE4, n = 10; TEKO, n = 11) b, Quantification of the piriform/entorhinal cortex, hippocampus, and posterior lateral ventricle volume in 3-month-old TE mice. c, Representative images of 9-month-old non-tau transgenic mouse brains (WT, n = 9; E2, n = 8; E3, n = 12; E4, n = 14; EKO, n = 9). d, Quantification of the piriform/entorhinal cortex, hippocampus, posterior lateral ventricle volume in 9-month-old non-tau transgenic mice. Data expressed as mean ± s.e.m.; one-way ANOVA with Tukey’s post hoc test (two-sided) was used for statistical analysis. Kruskal–Wallis test with Dunn’s multiple comparisons test was performed for analysis of posterior lateral ventricle volume. Source data

Extended Data Figure 2 ApoE4 leads to more severe neuronal loss in the CA1 region of hippocampus in 9-month-old P301S mice.

a, Representative images of 9-month-old TE mouse brain stained with cresyl violet. b, Thickness of the CA1 pyramidal neuronal layer (WT, n = 7; TE2, n = 14; TE3, n = 11; TE4, n = 17; TEKO, n = 16). Data expressed as mean ± s.e.m.; one-way ANOVA with Tukey’s post hoc test (two-sided). c, Correlation between CA1 neuronal layer thickness and hippocampal volume. N = 62 biologically independent animals. Pearson correlation analysis (two-sided), P < 0.0001, R2 = 0.35. *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001. Source data

Extended Data Figure 3 Elevated tau level in TE4 mice is not due to tau synthesis differences, and is probably caused by impairment of autophagy-mediated tau clearance.

a, qPCR result for human tau in 9-month-old TE mouse cortex (WT, n = 5; TE2, TE3, TE4, TEKO, n = 7). b, c, Nanostring analysis for autophagy-related gene expression in (b) 9-month-old TE mouse hippocampus and (c) 9-month-old non-tau transgenic ApoEKI or ApoEKO mouse hippocampus (n = 5 or 6 per group). d, Human ApoE levels in the RAB fraction of 3-month-old (WT, n = 2; TE2, n = 15; TE3, n = 11; TE4, n = 12; TEKO, n = 6) and 9-month-old (WT, n = 5; TE2, n = 14; TE3, n = 11; TE4, n = 17; TEKO, n = 7) TE mouse brain lysates were measured by ELISA. e, Nine-month-old TE mouse cortex was lysed in RIPA buffer without fractionation and total ApoE level was assessed by western blot (n = 3). For gel source data, see Supplementary Fig. 2. Data expressed as mean ± s.e.m.; one-way ANOVA with Tukey’s post hoc test (two-sided) was used for statistical analysis. *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001. Source data

Extended Data Figure 4 ApoE4 promotes pathological tau redistribution from axons to cell bodies at an early age.

a, AT8 staining for 3-month-old TE mouse hippocampus. Dotted outline surrounds the dentate gyrus (DG) granule cell bodies. b, Quantification of AT8 covered area in the dentate gyrus cell body region (TE2, n = 16; TE3, n = 10; TE4, n = 10; TEKO, n = 14). Data expressed as mean ± s.e.m.; one-way ANOVA with Tukey’s post hoc test (two-sided). *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001. Source data

Extended Data Figure 5 No or minimal change of microglial gene expression in 3-month-old TE mice or 9-month-old non-tau transgenic mice despite significant changes in 9-month-old TE mice.

a, Nanostring analysis for microglial gene expression in 9-month-old TE4 mice and 9-month-old non-tau transgenic mice (n = 5 or 6). Heatmap generated by hierarchical gene clustering on the basis of genotypes (horizontal: 534 microglial genes; vertical: individual mouse samples) b, Z-score of genes from cluster 1 or cluster 2 categories. c, Nanostring analysis for microglial gene expression in 9-month-old and 3-month-old TE mice (n = 5 or 6). d, Z-score of genes from cluster 1 or cluster 2 categories. Kruskal–Wallis test with Dunn’s multiple comparisons test was performed for statistical analysis. Data expressed as mean ± s.e.m. *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001. Source data

Extended Data Figure 6 P-tau staining patterns are associated with distinct microglial activation profiles.

a, Heatmap generated by hierarchical gene clustering on the basis of p-tau staining types for 9-month-old TE mice (n = 7 or 8). b, Principle component analysis (PCA) of microglial gene expression profile for p-tau staining types. c, Z-score of genes from cluster 1 or cluster 2 categories. Kruskal–Wallis test with Dunn’s multiple comparisons test was performed for statistical analysis. Data expressed as mean ± s.e.m. *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001. Source data

Extended Data Figure 7 No activation of A1 astrocytic genes in 9-month-old non-tau transgenic mice.

a, Microfluidic qRT–PCR for activated astrocytic genes in 9-month-old TE4 mice and 9-month-old non-tau transgenic WT and human ApoE KI mice (n = 5). A1-specific: genes activated only by LPS; A2-specific: genes activated only by ischaemia; PAN reactive: genes activated by either LPS or ischaemia.

Extended Data Figure 8 Possession of ε4 allele accelerates the rate of disease progression in patients with Alzheimer disease.

Disease progression rate in a cohort of 592 CSF biomarker confirmed individuals with symptomatic Alzheimer disease from two different longitudinal studies, the Knight Alzheimer’s Disease Research Center (ADRC) at Washington University and the ADNI. Data generated on the basis of the clinical dementia rating sum of boxes (CDR-SB) scores. Possession of the ε4 allele significantly accelerated disease progression (P = 0.02), with one ε4 allele increasing progression rate by 14% and two ε4 alleles increasing the rate by 23% compared with non-carriers (lineal mixed model, two-sided).

Extended Data Figure 9 Schematic summary of hypotheses.

a, ApoE is essential for neuronal death under pathological conditions. With pathological tau accumulation, the presence of ApoE, especially ApoE4, renders the neurons more susceptible to degeneration, whereas the absence of ApoE protects neurons from death, resulting in neurodegeneration (E4 > E3 ≈ E2 >> EKO). Degenerating neurons further induce neuroinflammation, which is augmented by ApoE4 owing to its inherent higher innate immune reactivity, thereby exacerbating neurodegeneration further. Neuroinflammation may concomitantly affect tau pathology13, resulting in various p-tau staining types that could also contribute to neurodegeneration. b, ApoE affects tau pathogenesis, resulting in different p-tau patterns, which may possess distinct neurotoxicity (type4 > type3 ≈ type2 > type1), leading to different levels of neuronal death and brain atrophy (E4 > E3 ≈ E2 >> EKO). Neuroinflammation accompanying neurodegeneration will in turn exacerbate neuronal death. c, ApoE affects tau pathogenesis, resulting in different p-tau patterns that may have different capacities to induce neuroinflammation (type4 > type3 ≈ type2 > type1), which eventually leads to various degrees of neurodegeneration.

Extended Data Table 1 Possession of an ε4 allele exacerbates regional neurodegeneration in human primary tauopathies

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Shi, Y., Yamada, K., Liddelow, S. et al. ApoE4 markedly exacerbates tau-mediated neurodegeneration in a mouse model of tauopathy. Nature 549, 523–527 (2017). https://doi.org/10.1038/nature24016

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