More clinically relevant mouse models for neurodegenerative diseases are sorely needed as tools to study disease progression and to develop future therapeutics. At last month's virtual International Conference on Alzheimer’s and Parkinson’s Disease (AD/PD), two separate research groups labs offered some new options.

  • New mouse models replace the mouse tau gene with the human one.
  • Others combine ApoE4, TREM2 R47H, humanized Aβ42, and diet to model LOAD.
  • Both approaches more closely mimic human tauopathies and AD.

Michael Koob, University of Minnesota, Minneapolis, presented data on targeted replacement mice in which he swapped out the mouse MAPT tau gene against the human MAPT gene. His group also produced five strains into which they incorporated a pathogenic variant of the human MAPT gene, enabling scientists to mimic the genetics of different human tauopathies. Adrian Oblak and colleagues at Indiana University, Indianapolis, and at Jackson Laboratory (JAX), Bar Harbor, Maine, used a multi-gene approach to generate mouse models of late-onset AD, aka LOAD, which afflicts people 65 or older. The mice were fed a high-fat Western diet to examine the impact of some environmental influences on disease progression.

Targeted Replacement of MAPT
In 1998, several research groups first discovered pathogenetic variants in the MAPT gene on chromosome 17 as the underlying cause of certain tauopathies (Hutton et al., 1998; Dumanchin et al., 1998; Spillantini et al., 1998; Clark et al., 1998). Twenty-three years later, dozens more pathogenic tau mutations have been reported; however, exactly how any of them leads to dementia remains unknown.

Mouse models incorporating some of these mutations (see Alzforum Research Models database) have focused primarily on disease phenotypes, above all the signature protein deposits, not on the molecular genetic modifications that lead to these traits. “When you model toward the phenotype, you miss a lot of the subtleties,” Koob told Alzforum. In humans, disease phenotypes take 40 to 60 years to develop. “If you model having dementia when the mouse is 4 months old, you probably did something very different than what happens in a human, because that’s just not how that works,” Koob said

To address this problem, the NIH in 2019 funded the AD-related dementias gene replacement project, of which Koob is the PI. It aims to evaluate the impact of MAPT mutations within the context of the genomic sequence. Koob and colleagues developed a gene-replacement technology that allows them to take out the mouse MAPT gene and substitute in the entire human MAPT gene.

They produced two different wild-type versions of the mice. In H1.0, all 190,000 base pairs of the human sequence are of the H1 haplotype; in H2.1, the first 23,000 base pairs are H1, and the next 167,000 base pairs are of the H2 haplotype. The H1 haplotype block is more common, and carries more risk of neurodegeneration than the H2 haplotype (e.g., Mar 2019 news; Sep 2005 news). To induce a disease phenotype in these wild-type mice, the scientists inflicted a mild traumatic brain injury. After one week, they saw an accumulation of phosphorylated tau near the TBI site.

In addition, the scientists generated five pathogenic variant lines with single nucleotide changes in exon 9, exon 10, and intron 10. In people, these mutations lead to diseases including frontotemporal dementia and Pick’s disease.

Previously, researchers at the University of North Carolina, Chapel Hill, had developed a mouse model with targeted replacement of the endogenous murine ApoE gene with each of the human ApoE alleles. These mice have proven useful, for example in studying an anti-ApoE antibody that removes plaques from both the mouse brain's parenchyma and blood vessels without causing ARIA (Feb 2021 news). The mouse model out of Koob’s lab is the first to replace MAPT in a similar way.

Koob plans to make these mice available without restrictions to the research community as soon as possible. For this, Koob’s lab partners with JAX, which already has the H2.1 model available.

“The mouse models expressing human tau developed in the Koob lab will be a great resource for the AD and ADRD research effort,” Mike Sasner wrote to Alzforum. Sasner directs the Model Organism Development & Evaluation for Late-Onset AD, aka MODEL-AD, program. “While transgenic tau models—particularly Peter Davies’ ‘hTAU’ model—have been widely used for many years, the genome replacement mice should be much better models to study the underlying pathophysiology of AD and FTDs and are more translationally relevant for preclinical studies,” Sasner wrote.

Modeling Late-Onset Alzheimer's
Another limitation of current mouse models is that many reflect autosomal-dominant, familial AD, which accounts for fewer than 1 percent of people with Alzheimer's. Many of the older models overexpress their transgenes, causing artifactual phenotypes. To address these problems, the NIH started the MODEL-AD consortium (Oct 2019 news; Oblak et al., 2020). 

As part of the MODEL-AD project, Oblak at IU and her team developed several LOAD knock-in mouse strains. Their LOAD1 mice have human ApoE4 and the TREM2 R47H variant knocked in; the LOAD2 mouse expresses knocked-in human ApoE4, TREM2 R47H, and humanized Aβ42.

Using these mice, Oblak and colleagues can ask such questions as how AD progression is influenced by environmental and lifestyle factors such as diet. A high-fat Western diet has been shown to boost TREM2 in microglia (Mar 2016 news). The scientists fed the LOAD1 and 2 mice a 45 percent high-fat and sugary chow from 2 to 12 months of age, collecting fecal and blood samples along the way. At AD/PD, Oblak showed that by 12 months of age, blood glucose and cholesterol levels were up in both mouse strains. The LOAD2 mice also had higher blood concentrations of the proinflammatory cytokines TNFα and IL10, and of neurofilament light chain, than did LOAD1 mice.

Combining risk variants for LOAD AD with environmental exposures such as a high-fat diet can produce a more relevant model for preclinical testing, Oblak said during the conference's live discussion. She believes that just because these models don’t have an overt neuropathological phenotype doesn’t mean they aren’t representative of the human condition.

“These predementia steps can be modeled really well in mice,” said Koob. “But this hasn’t been appreciated, because reviewers are focused on dramatic changes.” He hopes more groups will use the LOAD model.

With ever more models to choose from (peruse at Alzforum Research Models database), the question on many scientists’ minds is: Which one is the best? “There is never going to be one perfect model,” Frank LaFerla, University of California, Irvine, said during the live discussion. “What specific questions you are seeking to address determines which model you would pick.” LaFerla is a member of the MODEL-AD consortium.—Helen Santoro


  1. In most cases, knock-in animal models of genetic variants affecting human disease must be preferable to transgenic models, since the former make fewer assumptions regarding disease mechanism and would be expected to produce fewer artefactual, misleading phenomena. A number of papers indicate that artefactual phenomena are a serious issue with transgenic models of Alzheimer’s disease (Saito et al., 2014Saito et al., 2016; Foley et al., 2015; Hargis and Blalock, 2017). However, no matter whether a knock-in or transgenic approach is used, we need to be careful not to view model organisms as “machines” with components that can be swapped out for human components and expected to work normally. As genes/proteins change with evolutionary time, the other genes/proteins they interact with are under selective pressure to adapt to those changes. For example, if an entire human gene is swapped into a mouse in order to introduce a disease-causing human point mutation, there may be numerous, cryptic gene/protein interactions that are altered simultaneously that are not relevant to the disease but can complicate interpretation of the disease model phenotype.

    The MODEL-AD program making knock-in models of LOAD genetic risk variants should lead to significant advancement in our understanding of AD pathogenesis. But this approach should be expanded by going “back to the future” and using modern ’omics methods to analyze the early onset fAD knock-in mouse models first generated decades ago (e.g., Guo et al., 1999; Kawasumi et al., 2004). I find it rather amazing that there is very little ’omics data available from these models in the public databases. In fact, we cannot find brain transcriptome data from early onset fAD single-mutation heterozygous knock-in mouse models. This is the genetic state imbued with the fewest assumptions regarding disease mechanism as it closely parallels the human genetic fAD state rather than, e.g., analyses of models homozygous for fAD mutations or bearing multiple fAD mutations simultaneously.

    There is such transcriptome data from the zebrafish models my laboratory has produced. When we compare the young adult brain transcriptomes of the various zebrafish “knock-in” models we have constructed and analyzed, and include data from APOE knock-in mice (Zhao et al., 2020Sullivan et al., 1997), we find that all these models show early changes in expression of genes involved in oxidative phosphorylation. A preprint of our analysis is available on the bioRxiv server (Barthelson et al., 2021). 


    . Comparative analysis of Alzheimer’s disease knock-in model brain transcriptomes implies changes to energy metabolism as a causative pathogenic stress.

    . Systematic review of the relationship between amyloid-β levels and measures of transgenic mouse cognitive deficit in Alzheimer's disease. J Alzheimers Dis. 2015 Jan 1;44(3):787-95. PubMed.

    . Increased vulnerability of hippocampal neurons to excitotoxic necrosis in presenilin-1 mutant knock-in mice. Nat Med. 1999 Jan;5(1):101-6. PubMed.

    . Transcriptional signatures of brain aging and Alzheimer's disease: What are our rodent models telling us?. Behav Brain Res. 2016 May 4; PubMed.

    . Targeted introduction of V642I mutation in amyloid precursor protein gene causes functional abnormality resembling early stage of Alzheimer's disease in aged mice. Eur J Neurosci. 2004 May;19(10):2826-38. PubMed.

    . Single App knock-in mouse models of Alzheimer's disease. Nat Neurosci. 2014 May;17(5):661-3. Epub 2014 Apr 13 PubMed.

    . Calpain Activation in Alzheimer's Model Mice Is an Artifact of APP and Presenilin Overexpression. J Neurosci. 2016 Sep 21;36(38):9933-6. PubMed.

    . Targeted replacement of the mouse apolipoprotein E gene with the common human APOE3 allele enhances diet-induced hypercholesterolemia and atherosclerosis. J Biol Chem. 1997 Jul 18;272(29):17972-80. PubMed.

    . Alzheimer's Risk Factors Age, APOE Genotype, and Sex Drive Distinct Molecular Pathways. Neuron. 2020 Jun 3;106(5):727-742.e6. Epub 2020 Mar 20 PubMed.

Make a Comment

To make a comment you must login or register.


News Citations

  1. Unequal: Some Tau Haplotypes Carry More Risk Than Others
  2. Tau Shows Subtle Hints of Genetic Association
  3. Would ApoE Make a Better Therapeutic Target Than Aβ?
  4. NIH Funds Translational Research Centers to Accelerate AD Drug Discovery
  5. Microglial Marker TREM2 Rises in Early Alzheimer’s and on Western Diet

Research Models Citations

  1. APOE4 Targeted Replacement
  2. htau

Paper Citations

  1. . Association of missense and 5'-splice-site mutations in tau with the inherited dementia FTDP-17. Nature. 1998 Jun 18;393(6686):702-5. PubMed.
  2. . Segregation of a missense mutation in the microtubule-associated protein tau gene with familial frontotemporal dementia and parkinsonism. Hum Mol Genet. 1998 Oct;7(11):1825-9. PubMed.
  3. . Tau pathology in two Dutch families with mutations in the microtubule-binding region of tau. Am J Pathol. 1998 Nov;153(5):1359-63. PubMed.
  4. . Pathogenic implications of mutations in the tau gene in pallido-ponto-nigral degeneration and related neurodegenerative disorders linked to chromosome 17. Proc Natl Acad Sci U S A. 1998 Oct 27;95(22):13103-7. PubMed.
  5. . Model organism development and evaluation for late-onset Alzheimer's disease: MODEL-AD. Alzheimers Dement (N Y). 2020;6(1):e12110. Epub 2020 Nov 23 PubMed.

Other Citations

  1. Alzforum Research Models database

External Citations

  1. AD-related dementias gene replacement project
  2. H2.1 model
  3. MODEL-AD consortium

Further Reading

No Available Further Reading