St6galnac5 (ST6 N-acetylneuraminic acid alpha-2,6-sialyltransferase)
Overview
<table class="infobox infobox-protein">
<tr>
<th class="infobox-header" colspan="2">St6galnac5 (ST6 N-acetylneuraminic acid alpha-2,6-sialyltransferase)</th>
</tr>
<tr>
<td class="label">Gene Name</td>
<td>ST6GALNAC5</td>
</tr>
<tr>
<td class="label">Full Name</td>
<td>ST6 N-acetylneuraminic acid alpha-2,6-sialyltransferase 5</td>
</tr>
<tr>
<td class="label">Chromosomal Location</td>
<td>Chromosome 9</td>
</tr>
<tr>
<td class="label">Protein Class</td>
<td>Sialyltransferase</td>
</tr>
<tr>
<td class="label">Aliases</td>
<td>SIAT7B, ST6GalNAcV</td>
</tr>
<tr>
<td class="label">Astrocyte Marker</td>
<td>Effect of St6galnac5 Knockdown</td>
</tr>
<tr>
<td class="label">A1 markers (C3, Serping1, etc.)</td>
<td>Decreased</td>
</tr>
<tr>
<td class="label">A2 markers (S100a10, Ptx3, etc.)</td>
<td>Increased</td>
</tr>
<tr>
<td class="label">Neurotoxicity</td>
<td>Reduced</td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">2 edges</a></td>
</tr>
</table>
St6galnac5 is a protein. This page describes its structure, normal nervous system function, role in neurodegenerative disease, and potential as a therapeutic target.
...St6galnac5 (ST6 N-acetylneuraminic acid alpha-2,6-sialyltransferase)
Overview
<table class="infobox infobox-protein">
<tr>
<th class="infobox-header" colspan="2">St6galnac5 (ST6 N-acetylneuraminic acid alpha-2,6-sialyltransferase)</th>
</tr>
<tr>
<td class="label">Gene Name</td>
<td>ST6GALNAC5</td>
</tr>
<tr>
<td class="label">Full Name</td>
<td>ST6 N-acetylneuraminic acid alpha-2,6-sialyltransferase 5</td>
</tr>
<tr>
<td class="label">Chromosomal Location</td>
<td>Chromosome 9</td>
</tr>
<tr>
<td class="label">Protein Class</td>
<td>Sialyltransferase</td>
</tr>
<tr>
<td class="label">Aliases</td>
<td>SIAT7B, ST6GalNAcV</td>
</tr>
<tr>
<td class="label">Astrocyte Marker</td>
<td>Effect of St6galnac5 Knockdown</td>
</tr>
<tr>
<td class="label">A1 markers (C3, Serping1, etc.)</td>
<td>Decreased</td>
</tr>
<tr>
<td class="label">A2 markers (S100a10, Ptx3, etc.)</td>
<td>Increased</td>
</tr>
<tr>
<td class="label">Neurotoxicity</td>
<td>Reduced</td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">2 edges</a></td>
</tr>
</table>
St6galnac5 is a protein. This page describes its structure, normal nervous system function, role in neurodegenerative disease, and potential as a therapeutic target.
St6galnac5 (also known as SIAT7B or ST6GalNAcV) encodes a sialyltransferase enzyme that catalyzes the transfer of sialic acid (N-acetylneuraminic acid) to glycoproteins and glycolipids via an alpha-2,6 linkage. This enzyme is a member of the glycosyltransferase family and plays a critical role in protein sialylation, a fundamental post-translational modification that affects protein folding, stability, cell-cell interactions, and receptor signaling.
Protein Function
Sialyltransferase Activity
St6galnac5 belongs to the ST6 N-acetylneuraminic acid alpha-2,6-sialyltransferase family. The enzyme catalyzes the following reaction:
GDP-N-acetylneuraminic acid + glycoprotein → N-acetylneuraminic acid α2-6-glycoprotein + GDP
This reaction adds sialic acid residues to the terminal positions of glycoconjugates, a process known as protein sialylation. Sialylation is one of the most abundant and biologically significant post-translational modifications, affecting:
- Protein stability and half-life — Sialylated proteins are protected from degradation
- Cell-cell recognition — Sialic acid residues serve as ligands for siglecs and other lectins
- Receptor-ligand interactions — Sialylation modulates the affinity of various receptors
- Immune modulation — Sialylated proteins can regulate immune cell activation
Expression Pattern
In the brain, St6galnac5 is predominantly expressed in astrocytes, where it plays a specialized role in regulating astrocyte-neuron interactions. The enzyme is localized to the Golgi apparatus where it sialylates target proteins destined for secretion or membrane presentation.
Role in Alzheimer's Disease
Astrocyte Dysfunction and Neuroinflammation
Recent research has identified St6galnac5 as a critical molecular switch driving astrocytic dysfunction in Alzheimer's disease. Using single-nucleus transcriptomic analysis of human AD brain tissue and the 3xTg-AD mouse model, studies have demonstrated that:
St6galnac5 is upregulated in reactive astrocytes in AD brain tissue
Elevated expression correlates with disease progression and severity
The enzyme drives astrocytes toward a pro-inflammatory, neurotoxic A1 phenotypeEffects on Astrocyte Phenotype
Knockdown of St6galnac5 in astrocytes:
- Reduces expression of A1-associated pro-inflammatory markers
- Increases expression of A2-associated neuroprotective markers
- Alleviates neurite outgrowth deficits in neuron-astrocyte co-cultures
Impact on Synaptic Integrity
One of the most significant findings is that St6galnac5 knockdown preserves synaptic integrity in AD models. In the 3xTg-AD mouse model:
- Synaptic markers are preserved
- Synaptic loss associated with AD pathology is attenuated
- Neuronal connectivity is maintained
Effects on Amyloid and Tau Pathology
Remarkably, St6galnac5 knockdown leads to a marked reduction in both amyloid-β and tau pathologies:
- Amyloid-β: Reduced plaque burden in the brain
- Tau: Decreased tau phosphorylation and neurofibrillary tangle formation
This suggests that astrocyte St6galnac5 plays a role in modulating the processing or clearance of both key AD pathological proteins.
Behavioral Improvements
In female 3xTg-AD mice, AAV-mediated knockdown of St6galnac5 resulted in:
- Improved spatial learning and memory
- Reduced anxiety-like behaviors
- Better performance in memory-related behavioral tasks
Therapeutic Potential
Targeting St6galnac5 in AD
The findings from recent research suggest that targeted inhibition of the St6galnac5 sialylation pathway represents a viable strategy to bolster astrocytic resilience and slow disease progression. Several therapeutic approaches are being considered:
Small molecule inhibitors — Development of selective St6galnac5 inhibitors
Gene therapy — AAV-mediated knockdown as demonstrated in preclinical studies
Antisense oligonucleotides — RNA-based approaches to reduce St6galnac5 expression
Natural compounds — Screening for existing drugs that modulate sialylationAdvantages as a Therapeutic Target
- Astrocyte-specific — Targeting glial dysfunction rather than neuronal mechanisms
- Disease-modifying — Addresses both amyloid and tau pathology
- Behavioral benefit — Demonstrated cognitive improvements in animal models
Pathway Connections
Mermaid diagram (expand to render)
Cross-Links
- [[Astrocytes](/cell-types/astrocytes)](/cell-types/astrocytes)
- [[Alzheimer's Disease](/diseases/alzheimers-disease)](/diseases/alzheimers-disease)
- [Neuroinflammation](/mechanisms/neuroinflammation) — Related pathway
- [Amyloid Cascade Hypothesis](/mechanisms/amyloid-cascade) — Related pathway
- [[Tau Pathology](/mechanisms/tau-pathology)](/proteins/tau)
- [Astrocyte Reactivity](/mechanisms/astrocyte-reactivity) — Related pathway
- [Synaptic Dysfunction](/mechanisms/synaptic-dysfunction) — Related pathway
Summary
St6galnac5 is an astrocyte-expressed sialyltransferase that has emerged as a novel therapeutic target in Alzheimer's disease. By functioning as a molecular switch driving astrocytic dysfunction, St6galnac5 promotes the neurotoxic A1 astrocyte phenotype, contributes to neuroinflammation, and exacerbates both amyloid-β and tau pathologies. Remarkably, knockdown of St6galnac5 not only shifts astrocytes toward a protective A2 phenotype but also reduces amyloid and tau pathology while preserving synaptic integrity and improving cognitive function. This makes St6galnac5 one of the most promising new targets for disease-modifying therapy in AD.
See Also
- [Alzheimer's Disease](/diseases/alzheimers-disease)
- [Neuroinflammation](/mechanisms/neuroinflammation)
- [Amyloid Cascade Hypothesis](/mechanisms/amyloid-cascade)
- [Tau Pathology](/mechanisms/tau-pathology)
- [Astrocyte Reactivity](/mechanisms/astrocyte-reactivity)
- [Synaptic Dysfunction](/mechanisms/synaptic-dysfunction)
External Links
- [PubMed](https://pubmed.ncbi.nlm.nih.gov/)
- [KEGG Pathways](https://www.genome.jp/kegg/pathway.html)
References
[M来电 et al., St6galnac5 drives astrocyte dysfunction in Alzheimer's disease (2024) (2024)](https://pubmed.ncbi.nlm.nih.gov/41862120/)
[Unknown, Varki & Schauer, Sialic Acids (2024) (2024)](https://pubmed.ncbi.nlm.nih.gov/38563778/)
[Liddelow et al., Neurotoxic reactive astrocytes (2017) (2017)](https://pubmed.ncbi.nlm.nih.gov/28450556/)
[Unknown, Hardy & Selkoe, Amyloid hypothesis of AD (2002) (2002)](https://doi.org/10.1126/science.1072994)Pathway Diagram
The following diagram shows the key molecular relationships involving St6galnac5 (ST6 N-acetylneuraminic acid alpha-2,6-sialyltransferase) discovered through SciDEX knowledge graph analysis:
Mermaid diagram (expand to render)