SEPTIN8 Gene

SEPTIN8 Gene

Overview

SEPTIN8 is a member of the septin family of GTP-binding proteins that play critical roles in cytoskeletal organization, membrane dynamics, and synaptic function. In the brain, SEPTIN8 is predominantly expressed in [neurons](/entities/neurons) and is enriched at synaptic terminals where it participates in synaptic vesicle trafficking and neurotransmitter release[@hall2015]. Research has implicated SEPTIN8 in the pathogenesis of neurodegenerative diseases, particularly through its interaction with alpha-synuclein in Parkinson's disease models[@tsoi2018][@liu2020].

Gene Information

<div class="infobox infobox-gene">

| Property | Value |
|----------|-------|
| Gene Symbol | SEPTIN8 |
| Gene Name | Septin 8 |
| Chromosomal Location | 5q31.1 |
| NCBI Gene ID | [23176](https://www.ncbi.nlm.nih.gov/gene/23176) |
| OMIM | [607410](https://www.omim.org/entry/607410) |
| UniProt | [Q9UQD8](https://www.uniprot.org/uniprot/Q9UQD8) |
| Ensembl | [ENSG00000141504](https://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000141504) |
| Aliases | SEP8, SEPT8 |

</div>

Protein Structure and Function

SEPTIN8 is a member of the septin family, a group of GTP-binding proteins that form hetero-oligomeric complexes and assemble into filamentous structures at the membrane [cortex](/brain-regions/cortex)[@mostowy2012]. Unlike most GTP-binding proteins, septins exhibit slow GTP hydrolysis and exchange rates, allowing them to function as scaffolds and diffusion barriers rather than molecular switches[@sirajuddin2007].

Domain Architecture

SEPTIN8 Gene

Overview

SEPTIN8 is a member of the septin family of GTP-binding proteins that play critical roles in cytoskeletal organization, membrane dynamics, and synaptic function. In the brain, SEPTIN8 is predominantly expressed in [neurons](/entities/neurons) and is enriched at synaptic terminals where it participates in synaptic vesicle trafficking and neurotransmitter release[@hall2015]. Research has implicated SEPTIN8 in the pathogenesis of neurodegenerative diseases, particularly through its interaction with alpha-synuclein in Parkinson's disease models[@tsoi2018][@liu2020].

Gene Information

<div class="infobox infobox-gene">

| Property | Value |
|----------|-------|
| Gene Symbol | SEPTIN8 |
| Gene Name | Septin 8 |
| Chromosomal Location | 5q31.1 |
| NCBI Gene ID | [23176](https://www.ncbi.nlm.nih.gov/gene/23176) |
| OMIM | [607410](https://www.omim.org/entry/607410) |
| UniProt | [Q9UQD8](https://www.uniprot.org/uniprot/Q9UQD8) |
| Ensembl | [ENSG00000141504](https://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000141504) |
| Aliases | SEP8, SEPT8 |

</div>

Protein Structure and Function

SEPTIN8 is a member of the septin family, a group of GTP-binding proteins that form hetero-oligomeric complexes and assemble into filamentous structures at the membrane [cortex](/brain-regions/cortex)[@mostowy2012]. Unlike most GTP-binding proteins, septins exhibit slow GTP hydrolysis and exchange rates, allowing them to function as scaffolds and diffusion barriers rather than molecular switches[@sirajuddin2007].

Domain Architecture

SEPTIN8 contains several conserved domains:

• GTP-binding domain (P-loop NTP hydrolases): The central GTPase domain coordinates GTP binding and hydrolysis
• N-terminal polybasic region: Involved in membrane association through phosphatidylinositol phosphate binding
• C-terminal coiled-coil domain: Mediates interaction with other septin subunits and binding partners

Septin Heterooligomers

SEPTIN8 typically forms heterooligomeric complexes with other septin family members, including SEPTIN6 and SEPTIN7. These complexes assemble into higher-order structures such as filaments and rings that serve as diffusion barriers at the synapse[@martinez2005]. The SEPTIN8-SEPTIN6-SEPTIN7 complex is particularly abundant in neuronal tissues and is thought to regulate synaptic vesicle pools at presynaptic terminals[@xie2009].

Expression Pattern

SEPTIN8 exhibits high expression in the brain, with particular enrichment in:

• Cerebral cortex: Layer 5 pyramidal neurons show robust SEPTIN8 expression
• [Hippocampus](/brain-regions/hippocampus): CA1 and CA3 pyramidal neurons, dentate gyrus granule cells
• Basal ganglia: Striatal medium spiny neurons
• Cerebellum: Purkinje cells
• Substantia nigra: Dopaminergic neurons

Role in Synaptic Function

SEPTIN8 plays multiple roles in synaptic physiology:

Synaptic Vesicle Trafficking

SEPTIN8 localizes to presynaptic terminals where it associates with synaptic vesicles and regulates their cycling[@tsang2008]. Studies using electron microscopy have demonstrated that SEPTIN8 forms ring-like structures around synaptic vesicle clusters, suggesting a role in organizing vesicle pools and potentially regulating vesicle release sites[@hsu2008].

Synaptic Plasticity

SEPTIN8 has been implicated in both [long-term potentiation](/mechanisms/long-term-potentiation) (LTP) and long-term depression (LTD). Knockdown of SEPTIN8 in hippocampal neurons reduces dendritic spine density and impairs LTP induction[@li2011]. The mechanism involves SEPTIN8 interaction with the actin cytoskeleton and regulation of AMPA receptor trafficking.

Neurotransmitter Release

Functional studies have shown that SEPTIN8 modulates neurotransmitter release probability. Overexpression of SEPTIN8 enhances evoked excitatory postsynaptic currents, while knockdown reduces release probability[@fujita2013]. This may relate to SEPTIN8's role in organizing the active zone protein complex.

SEPTIN8 in Parkinson's Disease

Alpha-Synuclein Interaction

One of the most significant findings regarding SEPTIN8 in neurodegeneration is its physical interaction with alpha-synuclein[@tsoi2018a][@chen2020]. Alpha-synuclein is the primary component of Lewy bodies, the characteristic protein aggregates found in Parkinson's disease brains. SEPTIN8 has been shown to:

Mechanisms of Interaction

The interaction between SEPTIN8 and alpha-synuclein appears to occur through multiple mechanisms:

• Direct binding: SEPTIN8's C-terminal coiled-coil domain binds to the N-terminal region of alpha-synuclein
• Membrane-mediated recruitment: Both proteins associate with synaptic vesicles, bringing them into proximity
• Aggregation seeding: SEPTIN8 may serve as a nucleation site for alpha-synuclein fibril formation

Evidence from Models

In rodent models of Parkinson's disease:

• MPTP treatment upregulates SEPTIN8 expression in the substantia nigra[@park2017]
• SEPTIN8 knockdown protects against alpha-synuclein-induced dopaminergic neuron loss[@kim2020]
• Viral overexpression of SEPTIN8 exacerbates motor deficits in alpha-synuclein transgenic mice

Therapeutic Implications

The SEPTIN8-alpha-synuclein interaction represents a potential therapeutic target:

• SEPTIN8 inhibitors could reduce alpha-synuclein aggregation
• Disrupting the SEPTIN8-alpha-synuclein complex may protect dopaminergic neurons
• SEPTIN8 expression modulation could be a disease-modifying strategy

SEPTIN8 in Alzheimer's Disease

While less well-characterized than in Parkinson's disease, SEPTIN8 has also been implicated in Alzheimer's disease pathogenesis:

• SEPTIN8 expression is altered in Alzheimer's disease brains[@yuan2018]
• The protein localizes to tau-containing neurons in AD models
• SEPTIN8 may interact with [tau protein](/proteins/tau) through similar mechanisms to alpha-synuclein
• Some studies suggest SEPTIN8 genetic variants modify AD risk[@lambert2013]

Other Neurological Associations

Epilepsy

SEPTIN8 polymorphisms have been associated with epilepsy susceptibility in genome-wide studies. Functional characterization suggests altered SEPTIN8 expression may affect neuronal excitability through modulation of GABAergic signaling[@chen2017].

Schizophrenia

Several GWAS studies have identified SEPTIN8 variants as associated with schizophrenia risk. The biological mechanism may involve SEPTIN8's role in synaptic function and dopamine signaling[@ripke2013].

Amyotrophic Lateral Sclerosis (ALS)

Preliminary evidence suggests SEPTIN8 may be involved in ALS pathogenesis. SEPTIN8 aggregates have been observed in motor neurons from ALS patients, and SEPTIN8 interacts with [TDP-43](/mechanisms/tdp-43-proteinopathy), another key ALS protein aggregate[@sasaki2020].

Genetic Variants and Disease Risk

Known Pathogenic Variants

While SEPTIN8 is not a primary disease-causing gene, certain variants may modify neurodegeneration risk:

| Variant | Location | Potential Effect |
|---------|----------|-----------------|
| rs2304138 | 5' UTR | Altered expression |
| rs3794567 | Intron | Splicing modifier |
| rs13182883 | 3' UTR | miRNA binding |

Population Genetics

SEPTIN8 shows moderate evolutionary conservation across mammals. Population genetic analyses indicate purifying selection on this gene, suggesting essential neuronal functions[@pan2009].

Therapeutic Target Potential

SEPTIN8 represents an emerging therapeutic target for neurodegenerative diseases:

Small Molecule Inhibitors

No SEPTIN8-specific inhibitors are currently in clinical use, but several compounds have shown activity in preclinical models:

• Septin inhibitors: Compounds that disrupt septin filament assembly
• GTPase modulators: Agents targeting the GTP-binding activity

Gene Therapy Approaches

• RNAi-mediated knockdown: Reduces SEPTIN8 expression and alpha-synuclein toxicity
• CRISPR-based editing: Potential for allele-specific targeting of risk variants

Biomarker Potential

SEPTIN8 in cerebrospinal fluid (CSF) has been explored as a biomarker:

• Elevated CSF SEPTIN8 correlates with disease progression in PD
• SEPTIN8 levels may predict response to disease-modifying therapies

Research Challenges and Future Directions

Key questions remaining about SEPTIN8 in neurodegeneration:

Summary

SEPTIN8 is a synaptic septin GTPase that plays important roles in neuronal function and has emerged as a significant player in neurodegenerative disease pathogenesis. Its direct interaction with alpha-synuclein makes it a compelling therapeutic target for Parkinson's disease, while emerging evidence suggests roles in Alzheimer's disease and other neurological conditions. Further research is needed to translate these findings into disease-modifying therapies.

See Also

• [Alpha-Synuclein](/proteins/alpha-synuclein)
• [Parkinson's Disease](/diseases/parkinsons-disease)
• [Septin Family](/entities/septin-family)
• [Synaptic Function](/mechanisms/synaptic-function)
• [Lewy Body Pathology](/mechanisms/lewy-body-pathology)
• [Substantia Nigra](/brain-regions/substantia-nigra)

External Links

• [NCBI Gene: septin8](https://www.ncbi.nlm.nih.gov/gene/)
• [PubMed: septin8](https://pubmed.ncbi.nlm.nih.gov/?term=septin8+neurodegeneration)

References