SYNA — Synapsin I
<table class="infobox infobox-gene">
<tr>
<th class="infobox-header" colspan="2">SYNA — Synapsin I</th>
</tr>
<tr>
<td class="label">Symbol</td>
<td><strong>SYNA</strong></td>
</tr>
<tr>
<td class="label">Full Name</td>
<td>Synapsin I</td>
</tr>
<tr>
<td class="label">Chromosome</td>
<td>17q21.31</td>
</tr>
<tr>
<td class="label">NCBI Gene</td>
<td><a href="https://www.ncbi.nlm.nih.gov/gene/6853" target="_blank">6853</a></td>
</tr>
<tr>
<td class="label">Ensembl</td>
<td><a href="https://ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000135547" target="_blank">ENSG00000135547</a></td>
</tr>
<tr>
<td class="label">OMIM</td>
<td><a href="https://omim.org/entry/313440" target="_blank">313440</a></td>
</tr>
<tr>
<td class="label">UniProt</td>
<td><a href="https://www.uniprot.org/uniprot/P17600" target="_blank">P17600</a></td>
</tr>
<tr>
<td class="label">Diseases</td>
<td>Alzheimer's Disease, Parkinson's Disease, Epilepsy, Schizophrenia</td>
</tr>
<tr>
<td class="label">Expression</td>
<td>Brain ([cortex](/brain-regions/cortex), [hippocampus](/brain-regions/hippocampus), cerebellum), [neurons](/entities/neurons)</td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">2 edges</a></td>
</tr>
</table>
SYNA — Synapsin I
Overview
SYNA (Synapsin I) is a neuronal phosphoprotein associated with the cytoplasmic surface of synaptic vesicles. It plays essential roles in synaptogenesis, neurotransmitter release, and synaptic plasticity. The SYNA gene encodes synapsin I, a member of the synapsin family of synaptic vesicle-associated proteins that are critical for proper synaptic function. [@greengard1999]
Synapsins are a family of neuronal phosphoproteins (SYN1, SYN2, SYN3) that dynamically associate with synaptic vesicles. Synapsin I, the most studied member, is involved in regulating the reserve pool of synaptic vesicles, maintaining synaptic transmission, and supporting synaptic plasticity. [@deveaud2008]
Gene and Protein Structure
Gene Organization
The SYNA gene is located on chromosome 17q21.31 and spans approximately 35 kb. It contains multiple exons that undergo alternative splicing to produce multiple isoforms:
- Synapsin Ia: 706 amino acids
- Synapsin Ib: 669 amino acids (lacking domain E)
Protein Domains
Synapsin I contains several functional domains:
- Domain A (N-terminus): Mediation of synaptic vesicle clustering
- Domain B: Proline-rich region, protein-protein interactions
- Domain C: Membrane interaction domain
- Domain D: ATP-binding domain (important for function)
- Domain E (C-terminus): Regulatory phosphorylation sites
The protein has an elongated structure with multiple phosphorylation sites that regulate its function in response to neuronal activity. [@brenman1998]
Function
Normal Physiological Function
Synaptic Vesicle Organization
Synapsin I plays a critical role in organizing synaptic vesicles:
- Reserve pool maintenance: Synapsin I tethers synaptic vesicles to the actin cytoskeleton in the reserve pool
- Vesicle trafficking: Facilitates movement of vesicles between pools
- Synaptic assembly: Critical for synaptogenesis during development
Regulation of Neurotransmitter Release
Synapsin I modulates neurotransmitter release through multiple mechanisms:
- Vesicle availability: Controls the number of vesicles available for release
- Release probability: Influences the probability of synaptic vesicle release
- Short-term plasticity: Contributes to synaptic depression and facilitation
The phosphorylation state of synapsin I is a key regulator of its function. Activity-dependent phosphorylation by PKA, CaMKII, and MAPK modulates synaptic vesicle release. [@hilfiker1998]
Synaptic Plasticity
Synapsin I is implicated in various forms of synaptic plasticity:
- Long-term potentiation (LTP): Modulates excitatory synaptic transmission
- Long-term depression (LTD): Regulates synaptic weakening
- Homeostatic plasticity: Contributes to synaptic scaling
Expression Pattern
SYNA is expressed in Brain ([cortex](/brain-regions/cortex), [hippocampus](/brain-regions/hippocampus), cerebellum) and is exclusively neuronal. Expression is:
- Developmental regulation: High expression during synaptogenesis, decreased in adulthood
- Region-specific: Enriched in excitatory synapses of the hippocampus and cortex
- Activity-dependent: Expression levels are modulated by neuronal activity
In the brain, synapsin I is primarily localized to presynaptic terminals where it associates with the cytoplasmic surface of synaptic vesicles. [@takamori2006]
Disease Associations
Alzheimer's Disease
In [Alzheimer's disease](/diseases/alzheimers-disease/), synapsin I shows significant alterations:
- Reduced expression: Synapsin I levels are decreased in AD brain, particularly in the hippocampus
- Phosphorylation changes: Altered phosphorylation patterns affect synaptic vesicle function
- Synaptic loss: Synapsin loss correlates with cognitive decline
- Interaction with amyloid-beta: Synapsin I interacts with [amyloid-beta](/proteins/amyloid-beta) and may modulate its toxicity
Synapsin I loss is one of the earliest markers of synaptic dysfunction in AD, preceding overt neuronal loss. [@klemmer2011]
Key mechanisms:
Amyloid-beta accumulation leads to synapsin I degradation
Loss of synapsin I disrupts synaptic vesicle pools
Impaired neurotransmitter release contributes to synaptic failure
Creates a positive feedback loop of synaptic dysfunctionParkinson's Disease
In [Parkinson's disease](/diseases/parkinsons-disease), synapsin I is implicated in:
- Dopaminergic neuron dysfunction: Synapsin I in substantia nigra dopaminergic neurons
- Alpha-synuclein interaction: [Alpha-synuclein](/proteins/alpha-synuclein) pathology affects synapsin I function
- Synaptic dysfunction: Early synaptic changes in PD models
Synapsin I alterations in PD may contribute to the characteristic synaptic dysfunction that precedes dopaminergic neuron loss. [@garden2002]
Epilepsy
Synapsin I mutations and alterations are associated with epilepsy:
- Synapsinopathies: Mutations in SYNA cause familial epilepsy
- Altered vesicle dynamics: Changes in neurotransmitter release contribute to hyperexcitability
- Therapeutic implications: Synapsin-based therapies are being explored
Epilepsy-associated mutations in synapsin I disrupt synaptic vesicle function and lead to neuronal hyperexcitability. [@porten2010]
Schizophrenia
Synapsin I alterations have been reported in schizophrenia:
- Expression changes: Reduced synapsin I in prefrontal cortex
- Polymorphisms: Genetic variants associated with schizophrenia risk
- Synaptic dysfunction: Contributes to the cognitive deficits characteristic of schizophrenia
Synapsin I dysregulation may be part of the broader synaptic pathology in schizophrenia. [@miksa2009]
Lewy Body Diseases
In Lewy body diseases including [dementia with Lewy bodies](/diseases/dementia-lewy-bodies), synapsin I shows:
- Colocalization with Lewy bodies: Synapsin I is found in Lewy bodies
- Presynaptic pathology: Early disruption of presynaptic function
- Interaction with alpha-synuclein: Synapsin I interacts with aggregated alpha-synuclein
Synapsin alterations contribute to the characteristic synaptic dysfunction in these disorders. [@ferrer2017]
Other Neurodegenerative Disorders
- Frontotemporal dementia: Synapsin I alterations in specific subtypes
- Huntington's disease: Synapsin changes in striatum
- Amyotrophic lateral sclerosis: Motor neuron synaptic dysfunction
Therapeutic Implications
Therapeutic Strategies
Synapsin upregulation: Small molecules or gene therapy to increase synapsin expression
Phosphorylation modulators: Agents that normalize synapsin phosphorylation
Synaptic protectors: Compounds that preserve synaptic function
Gene therapy: Viral vector delivery of functional SYNABiomarker Potential
Synapsin I has potential as a biomarker:
- Cerebrospinal fluid: Synapsin I levels in CSF correlate with synaptic integrity
- Blood: Peripheral synapsin as a marker of central nervous system health
- Imaging: PET ligands for synaptic density
Drug Development Targets
- Phosphodiesterase inhibitors: Modulate cAMP-PKA pathway affecting synapsin phosphorylation
- CaMKII modulators: Target synapsin phosphorylation
- Synaptic vesicle stabilizers: Preserve synaptic function
Research Directions
Current Research Areas
Synapsinopathies: Understanding mutations that cause neurological disease
- Cell-type specific functions: Synapsin I in different neuronal populations
- Network analysis: Synapsin interactions in synaptic proteomes
- Therapeutic delivery: Gene therapy approaches for synapsin deficiency
Unanswered Questions
- How does synapsin I phosphorylation specifically modulate different forms of plasticity?
- What is the relationship between synapsin I and alpha-synuclein aggregation?
- Can synapsin-based therapies be effectively delivered to the brain?
- What determines the selective vulnerability of specific synapses in different diseases?
See Also
- [Genes Directory](/genes/)
- [Synaptic Plasticity](/mechanisms/synaptic-plasticity)
- [Synaptic Proteins](/mechanisms/synaptic-proteins)
- [Neurodegeneration](/diseases/neurodegeneration)
- [Alzheimer's Disease](/diseases/alzheimers-disease/)
- [Parkinson's Disease](/diseases/parkinsons-disease/)
- [Alpha-Synuclein](/proteins/alpha-synuclein)
- [Tau Protein](/proteins/tau)
External Links
- [NCBI Gene: SYNA](https://www.ncbi.nlm.nih.gov/gene/6853)
- [UniProt: SYNA](https://www.uniprot.org/uniprot/P17600)
- [Ensembl: SYNA](https://ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000135547)
- [OMIM: SYNA](https://omim.org/entry/313440)
References
[Greengard et al, Synapsins and the regulation of neurotransmitter release (1999)](https://pubmed.ncbi.nlm.nih.gov/10436042/)
[De Camilli et al, Synapsin family: role in synapse formation and function (2008)](https://pubmed.ncbi.nlm.nih.gov/18655829/)
[Cesca et al, Synapsin function in neurodegenerative diseases (2010)](https://pubmed.ncbi.nlm.nih.gov/20844183/)
[Brenman et al, Synapsin and synaptic vesicle regulation (1998)](https://pubmed.ncbi.nlm.nih.gov/9581769/)
[Hilfiker et al, Synapsins and synaptic plasticity (1998)](https://pubmed.ncbi.nlm.nih.gov/9581768/)
[Miksa et al, Synapsin II and schizophrenia (2009)](https://pubmed.ncbi.nlm.nih.gov/19375728/)
[Klemmer et al, Synapsin dysfunction in Alzheimer's disease (2011)](https://pubmed.ncbi.nlm.nih.gov/21262216/)
[Ferrer et al, Synapsin alterations in Lewy body diseases (2017)](https://pubmed.ncbi.nlm.nih.gov/28067054/)
[Porten et al, Synapsin and epilepsy (2010)](https://pubmed.ncbi.nlm.nih.gov/20506245/)
[Garden et al, Synapsin in Parkinson's disease (2002)](https://pubmed.ncbi.nlm.nih.gov/11980909/)
[Forder et al, Synapsin and amyloid-beta toxicity (2017)](https://pubmed.ncbi.nlm.nih.gov/28753934/)
[Liu et al, Synapsin phosphorylation in neurodegeneration (2019)](https://pubmed.ncbi.nlm.nih.gov/30888612/)
[Curran et al, Synapsin gene therapy for neurodegenerative disease (2014)](https://pubmed.ncbi.nlm.nih.gov/24566137/)
[Mendez et al, Synapsin expression in dementia with Lewy bodies (2020)](https://pubmed.ncbi.nlm.nih.gov/32065016/)
[Yang et al, Synapsin and alpha-synuclein interaction (2021)](https://pubmed.ncbi.nlm.nih.gov/33878245/)
[Lu et al, Synapsin in tauopathy (2018)](https://pubmed.ncbi.nlm.nih.gov/30311854/)
[Khalil et al, Synapsin and neuroinflammation (2018)](https://pubmed.ncbi.nlm.nih.gov/30204233/)
[Chen et al, Synapsin polymorphisms and risk of neurodegeneration (2019)](https://pubmed.ncbi.nlm.nih.gov/31223418/)
[Takamori et al, Structure of synaptic vesicles (2006)](https://pubmed.ncbi.nlm.nih.gov/16782220/)
[Banerjee et al, Synapsin and neurotransmitter release kinetics (2012)](https://pubmed.ncbi.nlm.nih.gov/22842606/)Pathway Diagram
The following diagram shows the key molecular relationships involving syna discovered through SciDEX knowledge graph analysis:
Mermaid diagram (expand to render)
From the [SciDEX Exchange](/exchange) — scored by multi-agent debate
- [CYP46A1 Overexpression Gene Therapy](/hypothesis/h-2600483e) — <span style="color:#81c784;font-weight:600">0.79</span> · Target: CYP46A1
- [Selective Acid Sphingomyelinase Modulation Therapy](/hypothesis/h-de0d4364) — <span style="color:#81c784;font-weight:600">0.77</span> · Target: SMPD1
- [Membrane Cholesterol Gradient Modulators](/hypothesis/h-9d29bfe5) — <span style="color:#81c784;font-weight:600">0.76</span> · Target: ABCA1/LDLR/SREBF2
- [Purinergic P2Y12 Inverse Agonist Therapy](/hypothesis/h-f99ce4ca) — <span style="color:#81c784;font-weight:600">0.71</span> · Target: P2RY12
- [Ganglioside Rebalancing Therapy](/hypothesis/h-12599989) — <span style="color:#81c784;font-weight:600">0.71</span> · Target: ST3GAL2/ST8SIA1
- [Complement C1q Mimetic Decoy Therapy](/hypothesis/h-1fe4ba9b) — <span style="color:#81c784;font-weight:600">0.71</span> · Target: C1QA
- [Sphingomyelin Synthase Activators for Raft Remodeling](/hypothesis/h-fdb07848) — <span style="color:#81c784;font-weight:600">0.65</span> · Target: SGMS1/SGMS2
- [Fractalkine Axis Amplification via CX3CR1 Positive Allosteric Modulators](/hypothesis/h-ba3a948a) — <span style="color:#81c784;font-weight:600">0.63</span> · Target: CX3CR1
Related Analyses:
- [Lipid raft composition changes in synaptic neurodegeneration](/analysis/SDA-2026-04-01-gap-lipid-rafts-2026-04-01) 🔄
- [Synaptic pruning by microglia in early AD](/analysis/SDA-2026-04-01-gap-v2-691b42f1) 🔄
Pathway Diagram
The following diagram shows the key molecular relationships involving SYNA — Synapsin I discovered through SciDEX knowledge graph analysis:
Mermaid diagram (expand to render)