TFR1 (transferrin receptor 1) plays a critical role in iron transport across cell membranes and is highly expressed in brain endothelial cells, making it an attractive target for drug delivery across the blood–brain barrier. Humanized TAU, encoded by MAPT, is a key pathogenic factor in tauopathies, including Alzheimer’s disease. By co-expressing human TFR1 and MAPT, this model enables integrated investigation of neurodegenerative disease mechanisms and the development of translational CNS therapeutic strategies.

TFR1/TAU humanized mice are genetically engineered mouse models in which both the Tfr1 and Mapt loci are humanized. In this model, exons 4–19 of the mouse Tfr1 gene, which encode the extracellular region responsible for receptor function, are replaced with the corresponding human TFR1 exons.

Simultaneously, exons 2–10 of the mouse Mapt gene are replaced with human MAPT exons 2–15, and the mouse 3′ UTR is substituted with its human counterpart, ensuring physiological expression of human TAU protein. Human MAPT expression is driven by the endogenous mouse promoter, while endogenous mouse Mapt expression is disrupted.

Key Advantages

• Physiological human TFR1 expression:
  Endogenous replacement of mouse Tfr1 exons 4–19 with human TFR1 ensures authentic human receptor expression.
• Human TAU expression:
  Replacement of mouse Mapt exons with human MAPT exons supports neurodegenerative disease–relevant TAU protein expression.
• Dual functional relevance:
  Enables integrated investigation of iron transport regulation and tau pathology, both critical processes in neurodegenerative disorders.
• BBB targeting insights:
  Human TFR1 expression facilitates evaluation of therapeutics designed for receptor-mediated transport across the blood–brain barrier.
• Translational applications:
  Supports pharmacodynamic and mechanistic studies of MAPT- and TFR1-targeted therapeutic strategies.

TFR1

• The exons 4-19 of mouse Tfr1 gene that encode extracellular domain are replaced by human counterparts in TFR1 humanized mice (B-hTFR1 mice). The genomic region of mouse Tfr1 gene that encodes cytoplasmic portion is retained.
• The promoter, 5’UTR and 3’UTR region of the mouse gene are also retained. The chimeric TFR1 expression is driven by endogenous mouse Tfr1 promoter, while mouse Tfr1 gene transcription and translation will be disrupted.

TAU

• The exons 2~10 of mouse Mapt gene that encode the full-length protein were replaced by human MAPT exons 2~15 in TFR1/TAU humanized mice (B-hTFR1/hTAU mice). The 3’UTR region of the mouse gene is replaced by human counterparts.
• The chimeric MAPT expression is driven by endogenous mouse Mapt promoter, while mouse Mapt gene transcription and translation will be disrupted.

• (A) Human TFR1 and MAPT mRNA are exclusively detectable in cortex of homozygous TFR1/TAU humanized mice, but not in wild-type C57BL/6 mice.
• (B) Relative MAPT mRNA expression level in the cortex and hippocampus were comparable between TAU humanized mice and TFR1/TAU humanized mice.

Strain-specific analysis of mouse and human TFR1 and MAPT mRNA expression in wild-type C57BL/6 mice and TFR1/TAU humanized mice by RT-PCR and qRT-PCR. (A) Total RNA was isolated from the cerebral cortex of wild-type C57BL/6 mice (+/+) and homozygous TFR1/TAU humanized mice (H/H). cDNA was synthesized by reverse transcription, followed by PCR amplification using mouse- or human-specific TFR1 and MAPT primers. (B) Relative MAPT mRNA expression levels in the cerebral cortex and hippocampus of male wild-type C57BL/6 mice, homozygous TAU humanized mice, and homozygous TFR1/TAU humanized mice were analyzed by quantitative real-time PCR (qRT-PCR).

• Mouse TFR1 was detected on bone marrow and blood in wild-type C57BL/6 mice, but not in TFR1/TAU humanized mice.
• Human TFR1 was detected on bone marrow and blood in TFR1/TAU humanized mice, but not in wild-type C57BL/6 mice.

Flow cytometry analysis of mouse and human TFR1 protein expression in bone marrow and peripheral blood of TFR1/TAU humanized mice. Bone marrow and blood cells were collected from wild-type C57BL/6 mice and homozygous TFR1/TAU humanized mice. Mouse and human TFR1 protein expression was analyzed by flow cytometry using anti-mouse TFR1 (BioLegend, 113808) and anti-human TFR1 (BioLegend, 334108) antibodies.

• TFR1 was detectable in the cortex, hippocampus, cerebellum and heart of both wild-type C57BL/6 mice and TFR1/TAU humanized mice, as the antibody was cross-reactive between human and mouse.
• TAU was detectable in the cortex, hippocampus and cerebellum of both wild-type C57BL/6 mice and TFR1/TAU humanized mice, as the antibody was cross-reactive between human and mouse.

Western blot analysis of TFR1 and TAU protein expression in brain and heart tissues of wild-type C57BL/6 mice, TFR1 humanized mice, TAU humanized mice, and TFR1/TAU humanized mice. Brain and heart tissues were collected from wild-type C57BL/6 mice, TFR1 humanized mice, TAU humanized mice, and TFR1/TAU humanized mice. TFR1 and TAU protein expression was analyzed by Western blot using an anti-transferrin receptor antibody (Abcam, ab214039) and an anti-TAU antibody (CST, 46687). A total of 40 μg of protein was loaded for Western blot analysis.

• The human MAPT  mRNA in the treatment group was significantly reduced compared to the control group, demonstrating that TFR1/TAU humanized mice provide a powerful preclinical model for in vivo evaluation of human MAPT targeted antibody oligonucleotide conjugate drugs.

The inhibitory efficiency of the antibody oligonucleotide conjugate (AOC) drug against human MAPT in TFR1/TAU humanized mice. TFR1/TAU humanized mice were randomly divided into three groups (n=3/group, 7-week-old, female). The vehicle, antibody oligonucleotide conjugates drug and oligonucleotide drug were administered to TFR1/TAU humanized mice individually on day 0 and day 7. The mice were sacrificed on day 21, and the hippocampus, cortex and spinal cord were collected to detect the expression level of human MAPT mRNA by qPCR. (A) The schematic diagram of experimental processing. (B) The expression of human MAPT mRNA in hippocampus, cortex and spinal cord. Values are expressed as mean ± SEM. Significance was determined by unpaired t test. *P < 0.05.

Note: This experiment was conducted in collaboration with a client using TFR1/TAU humanized mice (B-hTFR1/hTAU mice).

• The human MAPT  mRNA in the treatment group were significantly reduced compared to the control group, demonstrating that TFR1/TAU humanized mice provide a powerful preclinical model for in vivo evaluation of human MAPT targeted antibody oligonucleotide conjugates drug.

The inhibitory efficiency of the antibody oligonucleotide conjugate (AOC) drug against human MAPT in TFR1/TAU humanized mice. TFR1/TAU humanized mice were randomly divided into three groups (n=3/group, 7-week-old, female). The vehicle, antibody oligonucleotide conjugates drug and oligonucleotide drug were administered to TFR1/TAU humanized mice individually on day 0 and day 7. The mice were sacrificed on day 21, and the hippocampus, cortex and spinal cord were collected to detect the expression level of human MAPT mRNA by qPCR. (A) The schematic diagram of experimental processing. (B) The expression of human MAPT mRNA in hippocampus, cortex and spinal cord. Values are expressed as mean ± SEM. Significance was determined by unpaired t test. *P < 0.05.

Note: This experiment was conducted in collaboration with a client using TFR1/TAU humanized mice (B-hTFR1/hTAU mice).

Q: What is the transcript variants in TFR1/TAU humanized mice (B-hTFR1/hTAU mice)?
A: By using different sets of primers, we detected all the six isoforms (including both 3R and 4R forms) in human brain and all were confirmed via Sanger Sequencing.

Q: Are there differences in expression levels between male and female TFR1/TAU humanized mice (B-hTFR1/hTAU mice)?
A: qPCR analysis showed that the expression levels in male and female mice are generally consistent.