B6-htau Mice

Figure 1. Diagram of the gene editing strategy for the generation of B6-htau mice. The sequences from the ATG start codon to ~500bp downstream of the endogenous mouse Mapt gene was replaced with the sequences from the ATG start codon to ~500bp downstream of the human MAPT gene, the humanized regions include 3'UTR.

● Research on Frontotemporal dementia (FTD);

● Research on Alzheimer's disease (AD);

● Research on other neurodegenerative diseases.

1. Detection of human MAPT gene expression

Figure 2. Human MAPT gene expression in the brain and kidney of 6-week-old wild-type mice (WT) and B6-htau mice. The RT-qPCR analysis results indicate significant expression of the human MAPT gene in both the brain and kidneys of B6-htau mice, with slightly higher expression in female mice compared to males. In contrast, WT mice do not express the human MAPT gene.
ND: Not detected

2. Detection of mouse Mapt gene expression

Figure 3. Mouse Mapt gene expression in the brain and kidney of 6-week-old wild-type mice (WT) and B6-htau mice. The RT-qPCR analysis results showed that the mouse Mapt gene was expressed in the brain and kidney of WT mice, while there was no expression of the mouse Mapt gene in B6-htau mice.

3. Detection of human tau protein expression

Figure 4. Human tau protein expression in the brains of B6-htau mice and wild-type mice (WT). Using a human tau protein-specific antibody, the expression of human tau protein in the mouse brain was detected via Western blot. The results indicate clear expression of human tau protein in the brains of B6-htau mice*. The human MAPT gene transcript can generate up to six different tau protein isoforms through alternative splicing [10], and the binding site (aa.159-163) of the human antibody used in this assay is present in these isoforms. Consequently, multiple bands of varying sizes below 78 kDa were observed in the brains of B6-htau mice. However, since wild-type mice lack the human MAPT gene and human tau protein isoforms, these bands were not detected in the results. In addition, there is no significant gender difference in human tau protein expression in the brains of female and male B6-htau mice.

*The human tau protein antibody is Tau Monoclonal Antibody (HT7), Biotin purchased from Thermo Fisher (Catalog No. MN1000). Due to the high homology between mouse and human sequences, the human tau protein target band (approximately 78 kDa) can also be detected in the brains of wild-type mice. Consistently, bands of approximately 150 kDa were detected in both wild-type mice and B6-htau mice, aligning with the reference results provided in the antibody manual.

4. Small interfering RNA (siRNA) drugs can significantly reduce the expression of human MAPT mRNA in B6-htau mice.

Figure 5. Expression of human MAPT gene in the hippocampus and frontal cortex of 14-week-old male homozygous B6-htau mice after treatment with siRNA drug candidate molecules (AD-1637701 and Conjugate 31*)**. Following a single intracerebroventricular (icv) injection of AD-1637701 and Conjugate 31, hippocampus and frontal cortex samples were collected on day 14 for RT-qPCR analysis. The result shows a significant reduction in human MAPT mRNA expression in the hippocampus and frontal cortex of B6-htau mice treated with AD-1637701 and Conjugate 31 (data presented as mean±SD).

*AD-1637701 and Conjugate 31 are both siRNA drug candidate molecules from disclosed patents [11-12].
**Data provided by the client.

1. Basic information about the MAPT gene

2. MAPT Clinical Variants

3. Disease introduction

Frontotemporal Dementia (FTD), also referred to as frontotemporal lobar dementia, is the second most prevalent form of early-onset dementia, following Alzheimer’s disease. The incidence of FTD is estimated to range from 0.1-46.1 per 10,000 individuals. FTD typically exhibits an autosomal dominant inheritance pattern. Pathologically and radiographically, FTD is characterized by selective degeneration of the frontal and temporal lobes, resulting in personality and behavioral changes, language impairments, and executive dysfunction. Approximately 40%-50% of FTD cases have a familial component, with known causative genes including MAPT, FUS, and TARDBP. Of these, MAPT is the earliest discovered and most frequently implicated in FTD, mutations in the MAPT gene are detectable in roughly 30% of familial FTD cases.

4. MAPT gene and mutations

The human MAPT gene is located on chromosome 17 and encodes the microtubule-associated tau protein. Tau protein is primarily localized to neuronal axons and plays a critical role in microtubule stability and assembly. Mutations in the MAPT gene can promote pathological tau protein accumulation and death of glutamatergic cortical neurons. MAPT mutations typically occur in exons 9-12 and their adjacent intronic regions and can be broadly classified into two categories: The first type of mutation affects protein expression, altering the protein’s structure and stability, as well as its expression level. Deletion of the MAPT gene may impair its function and exacerbate abnormal tau protein aggregation, consistent with the acquisition of cytotoxic effects. Similarly, mutations at specific sites can increase the propensity of tau protein to aggregate. The second type of mutation affects pre-mRNA exon splicing, altering the ratio of 3R to 4R tau protein isoforms and increasing the relative production of 4R-tau protein, which is more prone to fibril formation. Common MAPT mutations include P301L, P301S, and Intron10+3 G>A, among others ^[4].

5. Function of non-coding DNA sequences

According to published reports, the pathogenic Intron10+3 G>A mutation in the MAPT intron can result in an increased proportion of 4R isoforms. Treatment with the oligonucleotide drug ASO-001933, which targets the 3’UTR region of MAPT, has been shown to effectively reduce tau protein expression in mice ^[5], non-human primates, and primary cultures of human neurons ^[6].

6. MAPT Targeted Gene Therapy

Therapies targeting the MAPT gene primarily consist of small molecule drugs and monoclonal antibodies, with indications mainly for Alzheimer’s disease (AD) and frontotemporal dementia (FTD). Transgenic mice are frequently used in drug development, and the utilization of humanized animal models can facilitate the translation of promising MAPT-targeted treatments into clinical trials. Ionis’ ASO drug ISIS-814907 (currently in Phase 2 clinical trials) targets and reduces MAPT gene expression to treat disease. Preclinical research for this drug candidate utilized transgenic humanized PS19 mice, in which the human MAPT gene with the P301S mutation was randomly inserted ^[7-8]. ASO-001933 targets the 3’UTR region of MAPT and effectively reduces its expression, In one study, a humanized disease model obtained by crossing transgenic mice (randomly inserting cDNA of the human wild-type MAPT gene) with MAPT-KO mice was used to pharmacologically analyze candidate drug molecules ^[5]. This study was funded by Roche ^[6]. Additionally, Arvinas’ ASO molecule and monoclonal antibody drug targeting the MAPT gene are currently in preclinical research ^[9].

In summary, the MAPT gene represents a significant pathogenic factor in frontotemporal dementia with a complex underlying mechanism. Current gene therapy approaches primarily utilize ASOs, and humanized mice are used in preclinical drug development. Cyagen’s humanized MAPT mice and mutation models based on this humanized strain can be applied to preclinical research on FTD gene therapy. Customized services can also be provided for specific point mutations.