Species: Mouse
Genes: APOE, MAPT
Mutations: APOE C130R (ApoE4), MAPT P301S
Modification: APOE: Knock-In; MAPT: Transgenic
Disease Relevance: Alzheimer's Disease
Strain Name: N/A
Genetic Background: APOE knock-in, floxed (Gladstone): C57BL/6. PS19: C57BL/6 x C3H
Availability: For APOE knock-in, floxed (Gladstone) mice, direct inquiries to Yadong Huang. PS19 mice are available from The Jackson Lab: Stock# 008169.

Summary

In the APOE knock-in, floxed (Gladstone) lines, the mouse Apoe coding sequence was replaced by the human APOE coding sequence flanked by LoxP sites. Mice expressing either human APOE3 (APOE3-fKI) or APOE4 (APOE4-fKI) are available. Transgenic expression of Cre recombinase—through viral transduction or crosses with mice carrying Cre transgenes under the control of inducible or cell-type-specific promoters—allows researchers to test the effects of disrupting APOE expression at particular times or in selected cell types.

APOE3-fKI and APOE4-fKI mice were crossed with PS19 mice, which carry a human MAPT transgene with the P301S mutation linked to frontotemporal dementia, to generate models in which to study the effects of human APOE in the context of tauopathy.

APOE4 exacerbated tauopathy in PS19 mice—increasing levels of disease-associated hyperphosphorylated tau, gliosis, and neurodegeneration. Selective excision of APOE4 from neurons reduced these pathologies to levels seen in PS19 mice expressing APOE3 (Koutsodendris et al., Nat Aging, 2023).

In the description below, mice hemizygous for the MAPT transgene and homozygous for the floxed APOE3 or APOE4 alleles are referred to as “PS19-E3” and “PS19-E4,” respectively. Animals were studied at 10 months of age, unless stated otherwise.

Tauopathy

Markers of tauopathy were elevated in the hippocampi of PS19-E4 mice, compared with PS19-E3.

Tauopathy was assessed as immunoreactivity to AT8, a monoclonal antibody that recognizes hyperphosphorylated tau found in “pre-tangles,” mature neurofibrillary tangles, and neuropil threads. AT8 burden (percent areal coverage of AT8 immunoreactivity in the hippocampus) determined  immunohistochemically and levels of AT8-immunoreactive tau in hippocampal lysates, measured in Western blots, were higher in PS19-E4 mice than PS19-E3 animals (Koutsodendris et al., Cell Rep, 2023; Koutsodendris et al., Nat Aging, 2023). Additionally, the number of cells stained with Thioflavin S, a marker of fibrillar aggregates, was higher in the mice expressing APOE4 (Koutsodendris et al., Nat Aging, 2023).

Excision of APOE4 from neurons, through crosses of PS19-E4 mice with mice expressing Cre-recombinase under the control of the Synapsin-1 promoter, restored these tauopathy markers to the levels seen in PS19 mice expressing human APOE3 (Koutsodendris et al., Nat Aging, 2023).

Neurodegeneration

PS19 mice expressing endogenous mouse Apoe show hippocampal atrophy accompanied by ventricular enlargement, beginning between 6 and 9 months of age (Yoshiyama et al., 2007). When examined at 10 months, PS19-E4 mice showed signs of possible neurodegeneration, compared with PS19-E3 animals: Hippocampal volumes and the thickness of layer CA1 and the dentate gyrus were greater in PS19-E3 than in PS19-E4, while ventricular volumes were larger in PS19-E4 than PS19-E3 (Koutsodendris et al., Cell Rep, 2023; Koutsodendris et al., Nat Aging, 2023). Oligodendrocyte integrity in PS19-E4 hippocampi also appeared compromised, with reduced immunostaining for myelin basic protein, Olig2 (a marker of mature oligodendrocytes), and NG2 (a marker of oligodendrocyte precursors), compared with PS19-E3 (Koutsodendris et al., Cell Rep, 2023; Koutsodendris et al., Nat Aging, 2023). As these markers were not quantified at younger ages in PS19-APOE mice, a developmental effect of APOE genotype cannot be formally ruled out.

Immunostaining for cleaved caspase-3, a marker for apoptosis in postmitotic neurons, provided  evidence that APOE4 induces neurodegeneration. PS19-E4 mice had a higher proportion of neurons containing cleaved caspase-3 in the hippocampus than did PS19-E3 mice (Koutsodendris et al., Nat Aging, 2023).

Excision of APOE4 from neurons in PS19-E4 mice restored the markers of hippocampal integrity mentioned above to the levels seen in PS19 mice expressing human APOE3 (Koutsodendris et al., Nat Aging, 2023).

Gliosis

Markers of microgliosis (percent areal coverage of Iba1 and CD68 immunoreactivity) and astrogliosis (percent areal coverage of GFAP and S100β immunoreactivity) were elevated in the hippocampi of 10-month-old PS19-E4 mice, compared with PS19-E3 animals (Koutsodendris et al., Cell Rep, 2023; Koutsodendris et al., Nat Aging, 2023). There was a negative correlation between each of the glial markers and hippocampal volume in PS19-E4 mice (Koutsodendris et al., Cell Rep, 2023).

Immunostaining for Iba1 or GFAP did not differ between PS19-E4 and PS19-E3 mice at 6 months of age (Koutsodendris et al., Cell Rep, 2023).

Excision of APOE4 from neurons in PS19-E4 mice restored these glial markers to the levels seen in PS19 mice expressing human APOE3 (Koutsodendris et al., Nat Aging, 2023).

Electrophysiology

Hippocampal network excitability, assessed through input-output curves at Schaffer collateral-CA1 synapses, was increased in PS19-E4 compared with PS19-E3. Excision of APOE4 from neurons in PS19-E4 mice reduced network hyperexcitability (Koutsodendris et al., Nat Aging, 2023).

Modification details

APOE-fKI. The APOE-fKI mice were created through homologous recombination using a vector containing exons 2 through 4 of the human APOE gene (either APOE3 or APOE4) flanked by LoxP sites.

PS19. PS19 transgenic mice express mutant human microtubule-associated protein tau (MAPT) driven by the mouse prion protein (Prnp) promoter. The transgene encodes the disease-associated P301S mutation and includes four microtubule-binding domains and one N-terminal insert (4R/1N). The transgene inserted at Chr3:140354280-140603283 (Build GRCm38/mm10), causing a 249 Kb deletion that does not affect any known genes (Goodwin et al., 2017).

Applications of the model

Effect of removing neuronal APOE4 on HMGB1 translocation and release. Under pathological conditions, the nuclear protein high-mobility group box 1 (HMGB1) has been shown to translocate to the cytoplasm and then enter the extracellular space, where it activates immune cells. In contrast to PS19-E3 mice, PS19-E4 mice showed age-dependent translocation and release of HMGB1. Excision of APOE4 from neurons, through crosses of PS19-E4 mice with mice expressing Cre-recombinase under the control of the Synapsin-1 promoter, reduced HMGB1 translocation and release (Koutsodendris et al., Cell Rep, 2023).

Effect of removing neuronal APOE4 on APOE4-exacerbated tauopathy. As mentioned above, APOE4 exacerbates tauopathy in PS19 mice—increasing levels of disease-associated hyperphosphorylated tau, gliosis, and neurodegeneration—and selective excision of APOE4 from neurons reduced these pathologies to levels seen in PS19 mice expressing APOE3. Transcriptomic analyses showed that removal of neuronal APOE4 also decreased the proportion of cells classified as disease-associated neurons, microglia, astroglia, or oligodendroglia based on gene-expression profiles (Koutsodendris et al., Nat Aging, 2023).

Related Model

The effect of APOE4 on tauopathy—specifically on the propagation of tau—has been studied in APOE-fKI mice in which mutant human tau was expressed from an adeno-associated virus-2 vector (AAV2-tau-P301S).  AAV2-tau-P301S was injected unilaterally into the hippocampi of 10-month-old mice and animals were examined three months later. Compared with APOE3, APOE4 exacerbated the spread of tau: The numbers of cells immunoreactive for total human tau or AT8-immunoreactive tau in the hippocampi contralateral to the injection were greater in APOE4-fKI mice than APOE3-fKI mice. Selective excision of APOE4 from neurons, through crossing APOE4-fKI mice with mice expressing Cre-recombinase under the control of the Synapsin-1 promoter, reduced tau propagation in APOE4-fKI mice to the extent seen in APOE3-fKI mice (Koutsodendris et al., Nat Aging, 2023).

Phenotype Characterization

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References

Research Models Citations

1. APOE3 knock-in, floxed (Gladstone)
2. APOE4 knock-in, floxed (Gladstone)
3. Tau P301S (Line PS19)

Mutations Citations

1. MAPT P301S

AlzAntibodies Citations

1. Tau (AT8); Phospho Tau (Ser 202, Thr 205) 18 May 2022

Paper Citations

1. Koutsodendris N, Blumenfeld J, Agrawal A, Traglia M, Grone B, Zilberter M, Yip O, Rao A, Nelson MR, Hao Y, Thomas R, Yoon SY, Arriola P, Huang Y. Neuronal APOE4 removal protects against tau-mediated gliosis, neurodegeneration and myelin deficits. Nat Aging. 2023 Mar;3(3):275-296. Epub 2023 Feb 20 PubMed.
2. Koutsodendris N, Blumenfeld J, Agrawal A, Traglia M, Yip O, Rao A, Kim MJ, Nelson MR, Wang YH, Grone B, Hao Y, Thomas R, Zilberter M, Yoon SY, Arriola P, Huang Y. APOE4-promoted gliosis and degeneration in tauopathy are ameliorated by pharmacological inhibition of HMGB1 release. Cell Rep. 2023 Oct 31;42(10):113252. Epub 2023 Oct 19 PubMed.
3. Yoshiyama Y, Higuchi M, Zhang B, Huang SM, Iwata N, Saido TC, Maeda J, Suhara T, Trojanowski JQ, Lee VM. Synapse loss and microglial activation precede tangles in a P301S tauopathy mouse model. Neuron. 2007 Feb 1;53(3):337-51. PubMed.
4. Goodwin LO, Splinter E, Davis TL, Urban R, He H, Braun RE, Chesler EJ, Kumar V, van Min M, Ndukum J, Philip VM, Reinholdt LG, Svenson K, White JK, Sasner M, Lutz C, Murray SA. Large-scale discovery of mouse transgenic integration sites reveals frequent structural variation and insertional mutagenesis. bioRχiv preprint first posted online Dec. 18, 2017

External Citations

1. mice
2. The Jackson Lab: Stock# 008169

Further Reading