MAPT Human
Description
Definition and Basic Characteristics of MAPT Human
Microtubule-associated protein tau (MAPT) is a neuronal protein encoded by the MAPT gene located on chromosome 17q21. It plays a critical role in stabilizing microtubules, promoting neuronal polarity, and facilitating axonal transport . In humans, MAPT exists as six isoforms generated by alternative splicing of exons 2, 3, and 10, resulting in variations in N-terminal inserts (0, 1, or 2) and microtubule-binding repeats (3R or 4R) . Recombinant human MAPT (e.g., isoform-4) is produced in E. coli as a non-glycosylated polypeptide (1–352 amino acids) fused to a His-tag for purification .
Key Features
Pathogenic Role in Neurodegenerative Diseases
Hyperphosphorylated MAPT aggregates into neurofibrillary tangles (NFTs), a hallmark of Alzheimer’s disease (AD), frontotemporal dementia (FTD), and other tauopathies . Key mechanisms include:
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Microtubule Destabilization: Phosphorylation reduces MAPT’s affinity for microtubules, impairing axonal transport .
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Conformational Changes: Mutations (e.g., V337M, R406W) induce Alzheimer-like tau filaments with a "fold" structure, accelerating aggregation .
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Seeding and Propagation: Pathological tau spreads transneuronally, contributing to disease progression .
4.1. Knock-In Mouse Models
Humanized MAPT knock-in mice express all six isoforms under endogenous promoters, enabling studies on tau pathology. These models show:
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No Spontaneous Pathology: No NFTs or neuronal loss up to 2 years .
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Accelerated Tau Propagation: AD-derived tau injection induces widespread AT8-immunoreactive species .
The long non-coding RNA MAPT-AS1 is neuron-specific but does not regulate tau expression in vitro or in vivo. Its reduced expression in AD brains correlates with neuronal loss rather than direct pathogenicity .
Product Specs
Q&A
What is the MAPT gene and how does it differ between humans and mice?
The MAPT gene encodes Tau protein, a member of the microtubule-associated protein family. In humans, alternative splicing of MAPT results in six tau isoforms, classified according to whether they contain three (3R) or four (4R) microtubule-binding domains. Adult human brains express all six isoforms, while adult mice normally express only 4R isoforms . This key difference has implications for modeling Alzheimer's disease and other tauopathies in mice, as the differences in mouse and human tau may partially explain the challenges in replicating human disease phenotypes in mouse models .
How is MAPT expression regulated in the human brain?
MAPT expression is regulated through complex mechanisms involving both transcriptional and post-transcriptional processes. The gene shows tissue-specific expression patterns, with enrichment in the brain . Expression data from GTex and FANTOM 5 CAGE datasets demonstrate that MAPT is highly expressed in neuronal tissues and its expression correlates with neuronal maturation markers . Research in human iPSC-derived neurons shows that MAPT expression increases during neuronal differentiation and maturation, suggesting developmental regulation . The expression can also be influenced by epigenetic modifications and potentially by non-coding RNAs, though the specific regulatory mechanisms require further investigation.
How do MAPT isoform expression patterns change during human neuronal development?
Studies using NGN2-induced human iPSC-derived neurons demonstrate that MAPT expression follows a clear temporal pattern during neuronal differentiation and maturation. When examining specific MAPT mRNA isoforms during differentiation at days 0, 3, 9, 16, 23, and 30, researchers observed progressive increases in expression as neurons mature . This maturation-dependent increase aligns with the expression of neuronal markers, confirming that MAPT expression is developmentally regulated in human neurons. Tau protein levels, measured using full-length Tau protein MSD assays, similarly increase with neuronal maturation .
What is the relationship between MAPT expression and neurodegenerative disease pathology?
Analysis of post-mortem brain samples from Alzheimer's disease patients and age-matched controls reveals that MAPT mRNA levels are reduced in the entorhinal cortex of AD brains compared to controls . This reduction may be attributed to neuronal loss that occurs in AD patients at advanced Braak stages rather than direct dysregulation of MAPT transcription. Supporting this interpretation, expression of neuronal markers RBFOX3 and TUBB3 is also reduced in these brain regions, while neuroinflammatory markers TREM2 and GFAP show increased expression . This pattern of expression changes reflects the progressive neurodegeneration and inflammatory response characteristic of AD pathology.
What is MAPT-AS1 and how is it related to MAPT gene expression?
MAPT-AS1 is a natural antisense transcript (NAT) associated with the MAPT gene. It belongs to a class of long non-coding RNAs (lncRNAs) that can potentially regulate the expression of their overlapping protein-coding genes at epigenetic, transcriptional, or translational levels . Expression data shows that MAPT-AS1 and MAPT are co-expressed in the brain, suggesting a possible functional relationship . While some studies have proposed that MAPT-AS1 may act as a negative regulator of MAPT expression at the epigenetic level, or that it could repress Tau translation through MIR motifs that are complementary to sequences in the 5' untranslated region of MAPT mRNA, more recent research challenges these hypotheses .
What experimental evidence exists regarding MAPT-AS1's role in regulating Tau expression?
Despite initial reports suggesting MAPT-AS1 might regulate MAPT expression, recent research using multiple experimental approaches has failed to confirm this regulatory relationship. When researchers modulated MAPT-AS1 levels using siRNA-, ASO- and lentiviral-based approaches in multiple human cell lines and in human iPSC-derived neurons, they observed no changes in MAPT transcription or translation . These comprehensive experiments suggest that, contrary to previous hypotheses, MAPT-AS1 does not directly regulate MAPT expression in human neurons in vitro . This finding has important implications for understanding MAPT regulation and for evaluating MAPT-AS1 as a potential therapeutic target for tauopathies.
What are the key features of MAPT knock-in mouse models?
MAPT knock-in mouse models are designed to address the limitations of traditional transgenic models by replacing the entire genomic sequence of murine Mapt (from exon 1 to exon 14) with the human MAPT gene . This approach offers several advantages:
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These mice express all six possible MAPT transcripts, mirroring human tau isoform diversity
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They lack mouse tau that could potentially interact with human tau
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The expression of the transgene is under the control of Mapt's natural regulatory elements, ensuring physiological levels with normal cellular and temporal specificity
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Adult MAPT knock-in mice express both 3R and 4R tau isoforms, with 4R mRNA approximately 70% that of 3R mRNA, similar to human expression patterns
These models show normal axonal localization of tau protein without evidence of increased neuroinflammation, neuronal death, or brain atrophy compared to wild-type mice, at least up to two years of age .
How do MAPT knock-in models compare to traditional MAPT transgenic models for studying tauopathies?
Traditional MAPT transgenic models often utilize random insertion of human MAPT cDNA or genomic fragments, leading to potential issues with expression levels, spatial patterns, and interference from endogenous mouse tau. In contrast, MAPT knock-in models offer several methodological advantages:
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Physiological expression levels and patterns: The human MAPT gene in knock-in models is expressed under endogenous mouse promoter control, preventing artificial overexpression artifacts
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Complete replacement of mouse tau: Eliminates potential confounding interactions between mouse and human tau proteins
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All human tau isoforms: Expresses the complete set of human tau isoforms in appropriate ratios (3R:4R)
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Normal development: Shows normal tau localization and no spontaneous pathology, providing a "clean" background for disease-modifying interventions
When used to study tau propagation, MAPT knock-in mice showed accelerated propagation of pathological tau (AT8-immunoreactive) species after AD-derived tau was injected into the mouse brain, compared to wild-type mice, demonstrating their utility for modeling certain aspects of tauopathies .
What techniques are most effective for analyzing MAPT expression in human brain tissue?
When analyzing MAPT expression in human brain tissue, researchers employ multiple complementary techniques to ensure comprehensive characterization:
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RT-qPCR: For quantifying MAPT mRNA levels relative to endogenous control genes. This allows detection of expression differences between disease and control brain regions as demonstrated in studies of entorhinal cortex and hippocampus from AD patients and controls .
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RNA sequencing: Provides transcriptome-wide context for MAPT expression. The StringTie algorithm on stranded poly(A)+ RNA-sequencing data has been used to identify different MAPT-AS1 isoforms and their relationship to MAPT .
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3'end-sequencing: Used for precise mapping of transcript termination sites, providing insights into transcript isoform diversity .
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CAGE (Cap Analysis Gene Expression) sequencing: For accurate identification of transcription start sites and analysis of promoter usage .
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In situ hybridization: To visualize the spatial distribution of MAPT transcripts in brain sections.
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Protein quantification: ELISA or MSD assays for measuring tau protein levels, as demonstrated in the quantification of full-length Tau protein during neuronal differentiation .
These methodologies should be accompanied by appropriate controls, including measurements of neuronal (RBFOX3, TUBB3) and glial (TREM2, GFAP, P2RY12, ALDH1L1) markers to account for cell-type specific expression patterns and potential neuronal loss in disease samples .
What are the most suitable cellular models for studying human MAPT regulation?
Several cellular models have proven valuable for investigating human MAPT regulation:
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Human neuroblastoma cell lines (SK-N-MC and SH-SY5Y): Offer reproducibility and ease of genetic manipulation for mechanistic studies .
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NGN2-induced human iPSC-derived neurons: Provide a more physiologically relevant model that recapitulates neuronal maturation and expresses MAPT in patterns similar to human neurons. These models:
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Primary human brain cultures: When available, offer the most authentic cellular environment for studying MAPT regulation.
When selecting a model system, researchers should consider the specific research question, the importance of human-specific splicing patterns, the need for mature neuronal phenotypes, and the technical requirements for experimental manipulation .
How should researchers approach contradictory findings regarding MAPT-AS1's regulatory role?
When addressing conflicting findings in MAPT-AS1 research, investigators should implement a systematic approach:
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Comprehensive experimental design: Employ multiple methodologies for modulating MAPT-AS1 expression (siRNA, ASO, and lentiviral approaches) across various cellular models as demonstrated in recent studies challenging the regulatory role of MAPT-AS1 .
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Controls for cell-type specificity: Include both neuroblastoma cell lines and human iPSC-derived neurons to account for potential cell-type specific effects .
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Temporal considerations: Examine effects across different time points during neuronal maturation, as regulatory relationships may be development-dependent.
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Cross-validation of findings: Measure both mRNA and protein levels to assess transcriptional and translational effects .
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Critical evaluation of previously published methodologies: Carefully analyze differences in experimental approaches that might explain contradictory results.
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Consideration of context-dependency: The regulatory relationship between MAPT-AS1 and MAPT may be condition-specific, potentially becoming relevant only under particular stress conditions or in specific neuronal subtypes.
The conflicting findings highlight the complexity of gene regulation and underscore the importance of rigorous methodology in lncRNA functional studies .
What experimental design considerations are critical when using MAPT knock-in models for therapeutic development?
When designing experiments with MAPT knock-in models for therapeutic development, researchers should consider:
These considerations will help maximize the translational value of MAPT knock-in models for developing tau-targeted therapeutics.
Product Science Overview
Microtubule-Associated Protein Tau (MAPT), commonly referred to as Tau, is a protein predominantly expressed in neurons of the central nervous system. It plays a crucial role in stabilizing microtubules, which are essential components of the cytoskeleton. The recombinant form of human Tau protein is produced using Escherichia coli (E. coli) expression systems, allowing for detailed studies of its structure and function.
Tau protein is characterized by its ability to bind to microtubules and promote their assembly and stability. The protein has several isoforms resulting from alternative splicing, with the 441 amino acid isoform being one of the most studied. This isoform is known as “2N4R,” “Isoform Tau-F,” “Tau-4,” or "Tau 441" .
The carboxy-terminal domains of Tau associate with microtubules, stabilizing their structure, while other domains interact with the plasma membrane . Tau’s binding to microtubules is highly dynamic and regulated by phosphorylation, with more than 40 potential phosphorylation sites . Properly folded Tau is highly soluble, but when misfolded, it forms insoluble aggregates that can interfere with cellular functions and lead to cell death .
Abnormal phosphorylation of Tau can result in the self-assembly of tangles of paired helical and/or straight filaments. These aggregates are a hallmark of several neurodegenerative diseases, collectively known as tauopathies, which include Alzheimer’s disease . In Alzheimer’s disease, the aggregation of Tau into fibrils correlates with cognitive impairment . Understanding the mechanisms of Tau aggregation and its role in neurodegeneration is crucial for developing therapeutic strategies.
Producing recombinant human Tau protein involves expressing the protein in E. coli and purifying it using various chromatographic techniques. The purification process can be challenging due to Tau’s intrinsically disordered nature and its tendency to degrade . However, protocols have been developed to obtain high-purity, stable preparations of Tau suitable for in vitro studies, including aggregation experiments that mimic neurodegenerative processes .
Recombinant human Tau protein is widely used in research to study its biochemical properties, interactions with microtubules, and role in disease. It is also used in drug discovery efforts aimed at finding compounds that can prevent or reverse Tau aggregation. The availability of recombinant Tau allows researchers to conduct experiments under controlled conditions, providing valuable insights into the protein’s behavior and its implications for neurodegenerative diseases.
