Research Models

APOE4 knock-in, floxed (Gladstone)

Synonyms: APOE4-fKI

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Species: Mouse
Genes: APOE
Mutations: APOE C130R (ApoE4)
Modification: APOE: Knock-In
Disease Relevance: Alzheimer's Disease
Strain Name: N/A
Genetic Background: C57BL/6
Availability: Direct inquiries to Yadong Huang.

Summary

In these knock-in mice, the mouse Apoe coding sequence was replaced by the human APOE4 coding sequence flanked by LoxP sites. 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. Mice expressing floxed human APOE3 (APOE3-fKI) are also available for comparison.

Compared with APOE3-fKI mice, APOE4-fKI mice show signs of gliosis in the hippocampus, loss of somatostatin-positive hilar interneurons, and deficits in learning and memory in the Morris water maze. Deletion of APOE4 from neurons generally, or GABA interneurons specifically, protected mice from these behavioral deficits and somatostatin neuron loss.

Additionally, the APOE knock-in mice have been crossed with mouse models of amyloidosis or tauopathy, in order to compare the effects of human ApoE3 and ApoE4 on Alzheimer’s-related pathology.

The following description refers to mice homozygous for the humanized APOE alleles.

Expression of ApoE

Levels of ApoE protein in the hippocampus and cortex were lower in APOE4-fKI than APOE3-fKI mice, measured at 6 (Bien-Ly et al., 2012) or 17 (Knoferle et al., 2014) months of age.

ApoE protein was found primarily in astrocytes, as shown by immunohistochemistry performed on hippocampal sections of 6-month-old mice (Bien-Ly et al., 2012). Genetic deletion of APOE from astrocytes confirmed that the majority of ApoE was made by astrocytes: Crossing APOE3-fKI or APOE4-fKI mice with GFAP-Cre mice reduced levels of ApoE protein in the hippocampus and cortex by approximately 80 percent (Knoferle et al., 2014).

Immunostaining also showed ApoE protein in GABA-positive interneurons of APOE4-fKI mice. Genetic deletion of APOE from GABA interneurons—through crosses with mice that express Cre from the Dlx-I12b-Cre enhancer, specific for forebrain GABA interneurons—resulted in a 20 to 30 percent reduction in ApoE protein levels in the hippocampus and cortex of APOE4-fKI mice (Knoferle et al., 2014).

Tauopathy

Tau pathology in the hippocampus, evaluated as immunoreactivity to AT8, did not differ between 10-month-old APOE3-fKI mice and APOE4-fKI mice (Koutsodendris et al., Cell Rep, 2023). (Monoclonal antibody AT8 detects “pretangles,” mature neurofibrillary tangles, and neuropil threads and is a common marker of tauopathy.)

Neurodegeneration

An age-related loss of somatostatin-positive neurons—a subset of GABA inhibitory interneurons—in the hilus of the hippocampus had previously been shown in female mice from another APOE4 knock-in line (Andrews-Zwilling et al., 2010; Leung et al., 2012). Aged female APOE4-fKI mice similarly had fewer somatostatin-positive hilar interneurons than APOE3-fKI mice (Knoferle et al., 2014). Genetic deletion of APOE from neurons generally, or GABA interneurons specifically, prevented the loss of somatostatin-positive hilar interneurons in APOE4-fKI mice, while deletion of APOE from astrocytes had no effect.

Hippocampal volume did not differ between 10-month-old APOE3-fKI mice and APOE4-fKI mice (Koutsodendris et al., Cell Rep, 2023). Immunostaining for myelin basic protein in the stratum radiatum of the hippocampus was also similar in the two genotypes.

Gliosis

APOE4-fKI mice show signs of gliosis in the hippocampus, compared with APOE3-fKI mice: The microglia marker Iba1 and the astrocyte marker GFAP occupied approximately double the area of the hippocampi of APOE4-fKI mice compared with APOE3-fKI mice at 10 months of age (Koutsodendris et al., Cell Rep, 2023).

Behavior

Compared with APOE3-fKI mice, 17-month-old APOE4-fKI mice showed deficits in the Morris water maze test of spatial learning and memory (Knoferle et al., 2014). APOE4-fKI mice took longer to find the hidden platform during the training phase. APOE3-fKI mice showed a preference for the target quadrant in probe tests administered 24, 72, and 120 hours after the last training session, while APOE4-fKI mice failed to show a preference on the last (120-hour) probe. (It should be  noted that only female mice were used in this study, and they were the GFAP-Cre-negative littermates of the progeny of crosses between APOE-fKI mice or GFAP-Cre- or Syn-1-Cre-expressing mice that were used to examine the effects of genetic deletion of APOE from astrocytes or neurons, respectively.)

Modification details

The APOE4-fKI mice were created through homologous recombination using a vector containing exons 2 through 4 of the human APOE gene (E4 allele) flanked by LoxP sites.

Applications of the model

Effects of cell-type-specific deletion of APOE on learning and memory. Compared with APOE3-fKI mice, 17-month-old female APOE4-fKI mice showed deficits in learning and memory in the Morris water maze (Knoferle et al., 2014). APOE was deleted from astrocytes, neurons, or GABA interneurons through crosses of APOE-fKI mice with GFAP-Cre, Syn-1-Cre, or Dlx-Cre transgenic mice, respectively. Deletion of APOE4 from neurons generally, or GABA interneurons specifically, protected mice from behavioral deficits induce by ApoE4 (i.e., the performance in the Morris water maze of Syn-1-Cre/APOE4-fKI mice or Dlx-Cre/APOE4-fKI mice was similar to that of APOE3-fKI mice). Deletion of APOE4 from astrocytes did not affect the performance of APOE4-fKI mice, nor did deletion of APOE3 from any of the three cell types affect the performance of APOE3-fKI mice.

Crosses

APOE knock-in, floxed (Gladstone) x J20. APOE3-fKI and APOE4-fKI mice were crossed with J20 mice, which carry a human APP transgene with the Swedish and Indiana mutations linked to AD, to generate models in which to study the effects of human APOE in the context of amyloidosis. Initial studies focused on the effects on Aβ accumulation in the mouse brain (Bien-Ly et al., 2012). Halving the gene dose of APOE reduced Aβ accumulation in the hippocampus at 12 months but not 6 months. Additionally, spatially restricted excision of APOE4 in adult mice via injection of an adenovirus carrying Cre-recombinase reduced levels of insoluble Aβ42 in the injected hippocampus.

APOE knock-in, floxed (Gladstone) x PS19. 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).

 

 

 

 

Last Updated: 17 Sep 2025

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References

Research Models Citations

  1. APOE3 knock-in, floxed (Gladstone)
  2. APOE4 Targeted Replacement
  3. J20 (PDGF-APPSw,Ind)
  4. Tau P301S (Line PS19)

AlzAntibodies Citations

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

Mutations Citations

  1. APP K670_M671delinsNL (Swedish)
  2. APP V717F (Indiana)
  3. MAPT P301S

Paper Citations

  1. Bien-Ly N, Gillespie AK, Walker D, Yoon SY, Huang Y. Reducing human apolipoprotein E levels attenuates age-dependent Aβ accumulation in mutant human amyloid precursor protein transgenic mice. J Neurosci. 2012 Apr 4;32(14):4803-11. PubMed.
  2. Knoferle J, Yoon SY, Walker D, Leung L, Gillespie AK, Tong LM, Bien-Ly N, Huang Y. Apolipoprotein E4 produced in GABAergic interneurons causes learning and memory deficits in mice. J Neurosci. 2014 Oct 15;34(42):14069-78. PubMed.
  3. 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.
  4. Andrews-Zwilling Y, Bien-Ly N, Xu Q, Li G, Bernardo A, Yoon SY, Zwilling D, Yan TX, Chen L, Huang Y. Apolipoprotein E4 causes age- and Tau-dependent impairment of GABAergic interneurons, leading to learning and memory deficits in mice. J Neurosci. 2010 Oct 13;30(41):13707-17. PubMed.
  5. Leung L, Andrews-Zwilling Y, Yoon SY, Jain S, Ring K, Dai J, Wang MM, Tong L, Walker D, Huang Y. Apolipoprotein E4 causes age- and sex-dependent impairments of hilar GABAergic interneurons and learning and memory deficits in mice. PLoS One. 2012;7(12):e53569. PubMed.
  6. 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.

External Citations

  1. GFAP-Cre mice
  2. Syn-1-Cre-expressing mice

Further Reading

No Available Further Reading