SEPT4 — Septin 4

SEPT4 — Septin 4

<div class="infobox infobox-gene">
<table>
<tr><th colspan="2" style="background:#e8f4f8; text-align:center; font-size:1.1em;">Septin 4</th></tr>
<tr><td><strong>Gene Symbol</strong></td><td>SEPT4</td></tr>
<tr><td><strong>Full Name</strong></td><td>Septin 4</td></tr>
<tr><td><strong>Chromosome</strong></td><td>17q23.2</td></tr>
<tr><td><strong>NCBI Gene ID</strong></td><td>[5414](https://www.ncbi.nlm.nih.gov/gene/5414)</td></tr>
<tr><td><strong>OMIM</strong></td><td>608680</td></tr>
<tr><td><strong>Ensembl ID</strong></td><td>ENSG00000154027</td></tr>
<tr><td><strong>UniProt ID</strong></td><td><a href="https://www.uniprot.org/uniprot/O43276">O43276</td></tr>
<tr><td><strong>Gene Type</strong></td><td>Protein Coding</td></tr>
<tr><td><strong>Protein Length</strong></td><td>377 amino acids</td></tr>
<tr><td><strong>Molecular Weight</strong></td><td>42.3 kDa</td></tr>
<tr><td><strong>Associated Diseases</strong></td><td>Parkinson's Disease, Dementia with Lewy Bodies, Multiple System Atrophy, Cancer, Male Infertility</td></tr>
</table>
</div>

Introduction

SEPT4 — Septin 4

<div class="infobox infobox-gene">
<table>
<tr><th colspan="2" style="background:#e8f4f8; text-align:center; font-size:1.1em;">Septin 4</th></tr>
<tr><td><strong>Gene Symbol</strong></td><td>SEPT4</td></tr>
<tr><td><strong>Full Name</strong></td><td>Septin 4</td></tr>
<tr><td><strong>Chromosome</strong></td><td>17q23.2</td></tr>
<tr><td><strong>NCBI Gene ID</strong></td><td>[5414](https://www.ncbi.nlm.nih.gov/gene/5414)</td></tr>
<tr><td><strong>OMIM</strong></td><td>608680</td></tr>
<tr><td><strong>Ensembl ID</strong></td><td>ENSG00000154027</td></tr>
<tr><td><strong>UniProt ID</strong></td><td><a href="https://www.uniprot.org/uniprot/O43276">O43276</td></tr>
<tr><td><strong>Gene Type</strong></td><td>Protein Coding</td></tr>
<tr><td><strong>Protein Length</strong></td><td>377 amino acids</td></tr>
<tr><td><strong>Molecular Weight</strong></td><td>42.3 kDa</td></tr>
<tr><td><strong>Associated Diseases</strong></td><td>Parkinson's Disease, Dementia with Lewy Bodies, Multiple System Atrophy, Cancer, Male Infertility</td></tr>
</table>
</div>

Introduction

SEPT4 (Septin 4), also known as ARIA (Apoptosis-Related Interaction with p53) or PNUTL1 (Peanut-like Testis 1), encodes a neuronally-enriched member of the septin family of GTP-binding proteins with critical roles in synaptic function, apoptosis regulation, and neurodegenerative disease pathogenesis. SEPT4 is unique among septins for its high expression in [dopaminergic neurons](/brain-regions/substantia-nigra) and its direct incorporation into [Lewy bodies](/diseases/parkinsons-disease) in Parkinson's disease[@ihara2004].

The discovery that SEPT4 is a structural component of Lewy bodies, the pathognomonic protein aggregates in PD, established a critical link between septin dysfunction and synucleinopathy pathogenesis[@shevtsov2005]. SEPT4 directly interacts with [alpha-synuclein](/proteins/alpha-synuclein), promoting its aggregation and contributing to the formation of Lewy bodies. This interaction has made SEPT4 a key target for understanding PD pathogenesis and developing therapeutic interventions.

Beyond PD, SEPT4 has been implicated in multiple neurodegenerative conditions including dementia with Lewy bodies (DLB) and multiple system atrophy (MSA), collectively termed the synucleinopathies. Additionally, SEPT4 plays essential roles in male reproduction, and mutations have been linked to infertility[@kiss2009]. The multifaceted functions of SEPT4 highlight its importance in both physiological and pathological processes.

Gene Structure and Evolution

Genomic Organization

The SEPT4 gene is located on chromosome 17q23.2 and spans approximately 12 kb. It contains 11 exons encoding a 377-amino acid protein. The gene structure is conserved among mammalian septin genes, with the characteristic GTP-binding domain encoded by exons 3-7. The 5' promoter region contains neuronal-specific transcription factor binding sites, consistent with high brain expression.

Evolution and Conservation

SEPT4 orthologs have been identified across vertebrates, with particularly high conservation in the GTP-binding domain. The protein shares structural features with other septins but contains unique N- and C-terminal sequences that may confer specialized neuronal functions. Phylogenetic analysis groups SEPT4 with SEPT1 and SEPT11 in a distinct subfamily characterized by testis- and brain-enriched expression.

Protein Structure and Biochemistry

Domain Architecture

SEPT4 exhibits the canonical septin domain structure:

GTP Binding Properties

SEPT4 exhibits GTP-binding and GTPase activity essential for its function. The GTP-bound state promotes septin polymerization, while GTP hydrolysis triggers filament disassembly. Mutations affecting GTP binding (e.g., K72M, R178Q) impair septin assembly and have been associated with familial PD[@olzhausen2011].

Alpha-Synuclein Interaction

A unique feature of SEPT4 is its direct interaction with alpha-synuclein. This interaction:

• Occurs via the N-terminal region of SEPT4 and the NAC (non-Aβ component) domain of alpha-synuclein
• Promotes alpha-synuclein aggregation
• Sequesters SEPT2 and other septins into Lewy bodies
• Disrupts normal SEPT4 cellular functions

Biological Functions

Neuronal Functions

Synaptic Vesicle Trafficking

SEPT4 plays critical roles in synaptic vesicle organization and trafficking:

• Localizes to synaptic vesicle clusters in presynaptic terminals
• Regulates vesicle pool size and organization
• Modulates synaptic vesicle release probability
• Interacts with SNARE complex proteins

Dopaminergic Neuron Function

SEPT4 is highly expressed in [dopaminergic neurons](/brain-regions/substantia-nigra) of the substantia nigra pars compacta. In these neurons, SEPT4:

• Regulates dopamine release and reuptake
• Maintains synaptic vesicle pools
• Protects against oxidative stress
• Supports mitochondrial function

Axonal Transport

SEPT4 participates in axonal transport through interactions with microtubule motors. SEPT4-containing complexes:

• Associate with synaptic cargo vesicles
• Regulate transport kinetics
• Influence cargo distribution in axons

Reproductive System Functions

Spermatogenesis

SEPT4 (as PNUTL1) is essential for male fertility. It localizes to:

• The sperm annulus (the structure separating tail and head)
• The midpiece of sperm flagella
• Developing spermatids

• Abnormal sperm morphology
• Impaired sperm motility
• Male infertility[@kiss2009]

Apoptosis Regulation

SEPT4 was originally identified as ARIA (Apoptosis-Related Interaction with p53), reflecting its role in apoptosis. SEPT4:

• Interacts with p53 tumor suppressor
• Modulates p53-dependent apoptosis
• May function as a pro-apoptotic protein in certain contexts

Autophagy and Protein Clearance

SEPT4 participates in [autophagy](/entities/autophagy) regulation:

• Localizes to autophagosomes
• Interacts with autophagy-related proteins
• Regulates protein aggregate clearance

Expression Pattern

Tissue Distribution

SEPT4 exhibits tissue-specific expression:

• Brain: Highest expression in neurons, particularly dopaminergic neurons
• Testis: High expression in developing spermatids
• Other tissues: Lower expression in various organs

Brain Expression

Within the brain, SEPT4 shows highest expression in:

• Substantia nigra pars compacta (dopaminergic neurons)
• Hippocampus (CA1-CA3 pyramidal cells, dentate gyrus)
• Cerebral cortex (layer 5 pyramidal neurons)
• Cerebellum (Purkinje cells)
• Striatum (medium spiny neurons)

Cellular Localization

In neurons, SEPT4 localizes to:

• Presynaptic terminals (synaptic vesicle clusters)
• Axonal compartments
• Dendrites
• Soma (cytoplasmic and perinuclear)

Role in Neurodegenerative Diseases

Parkinson's Disease

SEPT4 is centrally involved in PD pathogenesis through multiple mechanisms:

Lewy Body Formation

The landmark finding that SEPT4 is a component of Lewy bodies established its pathogenic role in PD[@ihara2004]. Within Lewy bodies:

• SEPT4 colocalizes with alpha-synuclein
• SEPT4 exists in both soluble and aggregated forms
• SEPT4 may nucleate alpha-synuclein aggregation
• SEPT4 sequesters other septins (SEPT1, SEPT2, SEPT5)

Alpha-Synuclein Interaction

The SEPT4-alpha-synuclein interaction promotes pathogenic aggregation:

• SEPT4 binds to the NAC domain of alpha-synuclein
• This binding accelerates alpha-synuclein fibril formation
• SEPT4 may act as a scaffold that concentrates alpha-synuclein
• The resulting aggregates are more toxic than alpha-synuclein alone[@shevtsov2005]

Genetic Variants

SEPT4 variants have been associated with PD risk:

• Rare coding variants (P28L, R147C, Y172C) increase risk
• These variants may alter septin assembly or alpha-synuclein interactions
• Promoter polymorphisms affect expression levels[@olzhausen2011][@wang2020]

Therapeutic Implications

Targeting SEPT4 offers therapeutic opportunities:

• Blocking SEPT4-alpha-synuclein interaction
• Modulating SEPT4 expression levels
• Stabilizing SEPT2-containing filaments
• Gene therapy approaches

Dementia with Lewy Bodies

In DLB, SEPT4 is similarly incorporated into Lewy bodies and cortical Lewy neurites. The mechanisms mirror those in PD, with SEPT4 contributing to:

• Lewy body formation and progression
• Synaptic dysfunction
• Cholinergic neuron loss[@yang2023]

Multiple System Atrophy

MSA is characterized by glial cytoplasmic inclusions (GCIs) and neuronal cytoplasmic inclusions (NCIs). SEPT4 is found in these inclusions:

• Colocalizes with alpha-synuclein in GCIs
• Contributes to inclusion formation
• May explain the widespread neurodegeneration in MSA[@suzuki2023]

Neuroinflammation

SEPT4 participates in neuroinflammatory processes in PD:

• SEPT4 expression is upregulated in activated microglia
• Septin-microglial interactions influence cytokine production
• SEPT4 may modulate neuroinflammatory responses[@satpute2019]

Disease Associations

| Disease | Evidence Level | Proposed Mechanism |
|---------|----------------|-------------------|
| Parkinson's Disease | Strong | Alpha-synuclein interaction, Lewy body formation |
| Dementia with Lewy Bodies | Strong | Lewy body pathology |
| Multiple System Atropy | Moderate | Inclusion formation |
| Alzheimer's Disease | Weak | Limited evidence |
| Cancer | Strong | Anti-apoptotic function |
| Male Infertility | Strong | Spermatogenesis defects |

Interacting Partners

| Protein | Interaction Type | Functional Relevance |
|---------|------------------|----------------------|
| Alpha-synuclein | Direct binding | Lewy body formation, aggregation |
| SEPT2 | Complex formation | Filament assembly |
| SEPT5 | Complex formation | Filament assembly |
| SEPT7 | Complex formation | Higher-order assembly |
| p53 | Binding | Apoptosis regulation |
| SNARE proteins | Interaction | Synaptic function |
| Syntaxin | Binding | Exocytosis |
| Synaptotagmin | Binding | Synaptic vesicle release |
| VAMP2 | Binding | Synaptic vesicle fusion |
| ATG proteins | Interaction | Autophagy regulation |

Therapeutic Implications

Therapeutic Targets

Biomarker Potential

SEPT4 in cerebrospinal fluid may serve as:

• Diagnostic biomarker for synucleinopathies
• Progression marker for PD
• Indicator of treatment response

Allen Brain Atlas Data

SEPT4 exhibits high, neuron-specific expression in the human brain based on Allen Human Brain Atlas data. Particularly strong expression is observed in the substantia nigra pars compacta, where dopaminergic neurons are selectively lost in Parkinson's disease. The hippocampus and cerebral cortex also show high SEPT4 expression, consistent with the widespread neuronal dysfunction in synucleinopathies. Single-cell expression data indicates SEPT4 is expressed predominantly in neurons, with lower expression in glial cells. This pattern supports SEPT4's critical role in neuronal function and its relevance to PD pathogenesis.

Resources:

• [Allen Brain Atlas Gene Expression](https://human.brain-map.org/gene/show?gene_id=ENSG00000154027)
• [Allen Brain Cell Atlas - SEPT4](https://celltype.brain-science.org/)

Animal Models

Knockout Models

SEPT4 knockout mice exhibit:

• Male infertility (due to spermatogenesis defects)
• Reduced body weight
• Altered behavior in some paradigms
• Variable impacts on lifespan

Transgenic Models

Transgenic models expressing mutant SEPT4 show:

• Alpha-synuclein aggregation
• Lewy body-like pathology
• Dopaminergic neuron loss
• Motor and cognitive deficits

See Also

• [SEPT2](/genes/sept2) — Core septin partner
• [SEPT7](/genes/sept7) — Essential septin for filament formation
• [Alpha-Synuclein](/proteins/alpha-synuclein) — PD protein interacting with SEPT4
• [Parkinson's Disease](/diseases/parkinsons-disease) — PD overview
• [Dementia with Lewy Bodies](/diseases/dementia-lewy-bodies) — DLB overview
• [Substantia Nigra](/brain-regions/substantia-nigra) - Brain region affected in PD
• [Cytoskeleton](/mechanisms/cytoskeleton) - Cellular structure
• [Synaptic Transmission](/mechanisms/synaptic-transmission) - Synapse biology
• [Protein Aggregation](/mechanisms/protein-aggregation) - Aggregation mechanisms
• [Autophagy](/entities/autophagy) - Cellular clearance

External Links

• [NCBI Gene - SEPT4](https://www.ncbi.nlm.nih.gov/gene/5414)
• [UniProt - O43276](https://www.uniprot.org/uniprot/O43276)
• [GeneCards - SEPT4](https://www.genecards.org/cgi-bin/carddisp.pl?gene=SEPT4)
• [Ensembl - ENSG00000154027](https://www.ensembl.org/)
• [OMIM - SEPT4](https://www.omim.org/entry/608680)

References