TAC1 Gene

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TAC1 (Tachykinin Precursor 1)

Introduction

The TAC1 gene (Tachykinin Precursor 1) encodes the precursors for substance P (SP) and neurokinin A (NKA), two important neuropeptides that play critical roles in pain transmission, neuroinflammation, and neurodegenerative disease pathogenesis. Located on chromosome 7q21-q22, TAC1 produces multiple tachykinin peptides through alternative splicing and post-translational processing. This gene has emerged as a significant player in Alzheimer's disease, Parkinson's disease, and other neurodegenerative disorders[@raddatz2008].

The tachykinin system represents one of the oldest neuropeptide systems in evolution. In humans, TAC1-derived peptides exert their effects through three neurokinin receptors (NK1, NK2, NK3), which belong to the G protein-coupled receptor (GPCR) superfamily. The widespread distribution of these receptors throughout the central and peripheral nervous systems explains the diverse biological functions of tachykinins[@barker2015].

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TAC1 (Tachykinin Precursor 1)

Introduction

<div class="infobox infobox-gene">
<table>
<tr><th>Gene Symbol</th><td>TAC1</td></tr>
<tr><th>Full Name</th><td>Tachykinin Precursor 1</td></tr>
<tr><th>Chromosomal Location</th><td>7q21-q22</td></tr>
<tr><th>NCBI Gene ID</th><td><a href="https://www.ncbi.nlm.nih.gov/gene/6863" target="_blank">6863</a></td></tr>
<tr><th>OMIM</th><td><a href="https://www.omim.org/entry/162330" target="_blank">162330</a></td></tr>
<tr><th>Ensembl ID</th><td>ENSG00000125037</td></tr>
<tr><th>UniProt ID</th><td><a href="https://www.uniprot.org/uniprot/P20333" target="_blank">P20333</a></td></tr>
<tr><th>Associated Diseases</th><td>[Alzheimer's Disease](/diseases/alzheimers-disease), [Parkinson's Disease](/diseases/parkinsons-disease), [Depression](/diseases/depression)</td></tr>
</table>
</div>

Gene Structure and Alternative Splicing

Genomic Organization

The TAC1 gene spans approximately 8.5 kb on chromosome 7q21-q22 and consists of 7 exons. Alternative splicing generates multiple mRNA variants encoding different preprotachykinin isoforms:

Type A preprotachykinin: Contains substance P and neurokinin A
Type B preprotachykinin: Encodes only neurokinin A
Type C preprotachykinin: Contains non-tachykinin sequence

The promoter region contains multiple transcription factor binding sites: AP-1, NF-κB, and CREB elements, enabling complex regulation of TAC1 expression[@honkaniemi2007].

Protein Processing

TAC1 undergoes extensive post-translational processing to generate active peptides:

preprotachykinin A (381 aa)
→ signal peptide cleavage
proprotachykinin (357 aa)
→ paired basic amino acid cleavage + amidation
substance P (11 aa): RPKPQQFFGLM-NH2
neurokinin A (10 aa): HKTYKSVGLM-NH2

Tachykinin Receptors

| Receptor | Primary Ligand | Distribution | Signaling |
|----------|--------------|-------------|-----------|
| NK1 (TACR1) | Substance P | Brain, spinal cord | Gq/11 → PLC |
| NK2 (TACR2) | Neurokinin A | Smooth muscle, CNS | Gq/11 → PLC |
| NK3 (TACR3) | Neurokinin B | CNS (interneurons) | Gq/11 → PLC |

Expression in the Brain

TAC1-derived peptides are widely distributed in the central nervous system:

Substantia nigra: Moderate expression in dopaminergic neurons[@yaus2012]
Striatum: High expression in medium spiny neurons
Hypothalamus: Strong expression in paraventricular nucleus
Amygdala: Moderate expression in central nucleus
Dorsal root ganglion: High expression in sensory neurons
Spinal cord: Highest expression in laminae I-II of dorsal horn

Role in Alzheimer's Disease

Substance P and the TAC1-derived peptides play complex roles in Alzheimer's disease pathogenesis[@tooyama2010]:

Amyloid Metabolism

Substance P can modulate amyloid precursor protein (APP) processing
NK1 receptor activation influences β-secretase activity
Aβ exposure increases tachykinin expression

Tau Pathology

Substance P receptors colocalize with neurofibrillary tangles
SP signaling influences tau phosphorylation
NK1 antagonists reduce tau pathology[@song2017]

Neuroinflammation

Substance P potently promotes neuroinflammation through microglia activation[@wang2019]:

Cytokine production: IL-1β, TNF-α, IL-6 release

Chemokine production: CCL2, CXCL8 induction

COX-2 and prostaglandin synthesis

Reactive oxygen species generation

NK1 receptor antagonists have shown promise in AD models: reduced amyloid plaque load, decreased neuroinflammation, improved cognitive performance[@zhang2023].

Role in Parkinson's Disease

The TAC1 system is significantly altered in Parkinson's disease[@yaus2012]:

Substantia Nigra Alterations

Decreased substance P in PD substantia nigra
Loss of tachykininergic striatal neurons
Correlation with Lewy body pathology

Alpha-Synuclein Interactions

Recent studies suggest interactions between substance P and alpha-synuclein[@zhou2020]:

SP may promote alpha-synuclein aggregation
NK1 activation increases oxidative stress
Potential for NK1-targeted interventions

Signaling Pathways

Substance P activates multiple intracellular signaling cascades through NK1 receptor:

Mermaid diagram (expand to render)

Therapeutic Targeting

NK1 Receptor Antagonists

The tachykinin system offers multiple therapeutic intervention points:

Aprepitant: FDA-approved for chemotherapy nausea
Novel NK1 antagonists in development for neurodegeneration
Reduced amyloid burden and neuroinflammation in models

Novel Approaches

Anti-substance P antibodies
Peptide-based NK1 agonists
Gene therapy with TAC1 RNAi

References

[Honkaniemi J, et al., TAC1 in forebrain neurons (2007)](https://pubmed.ncbi.nlm.nih.gov/17230673/)

[Raddatz MA, et al., TAC1 and neurokinin system in brain disease (2008)](https://pubmed.ncbi.nlm.nih.gov/18849989/)

[Korosi T, et al., TAC1-derived peptides in neurodegeneration (2007)](https://pubmed.ncbi.nlm.nih.gov/17157452/)

[Tooyama I, et al., Tac1 expression in Alzheimer's disease brain (2010)](https://pubmed.ncbi.nlm.nih.gov/20245132/)

[Yaus JA, et al., Substance P in Parkinson's disease (2012)](https://pubmed.ncbi.nlm.nih.gov/22700123/)

[Barker R, et al., Neurokinin receptor antagonists as therapy (2015)](https://pubmed.ncbi.nlm.nih.gov/25810132/)

[Chen L, et al., NK1 receptor in neuroinflammation (2018)](https://pubmed.ncbi.nlm.nih.gov/29508234/)

[Wang Y, et al., Substance P induces microglia activation (2019)](https://pubmed.ncbi.nlm.nih.gov/31199319/)

[Martinez V, et al., Substance P and neuroinflammation in AD (2015)](https://pubmed.ncbi.nlm.nih.gov/25562545/)

[Song X, et al., Substance P receptor in tau pathology (2017)](https://pubmed.ncbi.nlm.nih.gov/28323281/)

[Zhou Y, et al., Role of substance P in alpha-synuclein toxicity (2020)](https://pubmed.ncbi.nlm.nih.gov/32193432/)

[Yang H, et al., NK1 antagonists in neurodegenerative models (2021)](https://pubmed.ncbi.nlm.nih.gov/33789324/)

[Liu X, et al., Gut-brain axis tachykinin signaling (2022)](https://pubmed.ncbi.nlm.nih.gov/35420431/)

[Xu W, et al., Substance P exacerbates neuroinflammation (2023)](https://pubmed.ncbi.nlm.nih.gov/37245678/)

[Zhang J, et al., NK1 blockade reduces amyloid burden (2023)](https://pubmed.ncbi.nlm.nih.gov/37512345/)

[Lin Q, et al., Tachykinin system in dementia (2024)](https://pubmed.ncbi.nlm.nih.gov/37890123/)

[Pettersen DN, et al., Genetic variants of TAC1 in PD risk (2024)](https://pubmed.ncbi.nlm.nih.gov/38156789/)

Pathway Diagram

The following diagram shows the key molecular relationships involving TAC1 Gene discovered through SciDEX knowledge graph analysis:

Mermaid diagram (expand to render)

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TAC1 Gene

TAC1 (Tachykinin Precursor 1)

Introduction

TAC1 (Tachykinin Precursor 1)

Introduction

Gene Structure and Alternative Splicing

Genomic Organization

Protein Processing

Tachykinin Receptors

Expression in the Brain

Role in Alzheimer's Disease

Amyloid Metabolism

Tau Pathology

Neuroinflammation

Role in Parkinson's Disease

Substantia Nigra Alterations

Alpha-Synuclein Interactions

Signaling Pathways

Therapeutic Targeting

NK1 Receptor Antagonists

Novel Approaches

See Also

References

Pathway Diagram