ST6GALNAC5 Gene

Overview

ST6GALNAC5 Gene
Gene Symbol	ST6GALNAC5
Full Name	ST6 N-acetylgalactosaminide alpha-2,6-sialyltransferase 5
Chromosome	1p31.3
NCBI Gene ID	256297
Ensembl ID	ENSG00000160584
UniProt ID	Q9H0X9
Protein Type	Sialyltransferase
Primary Expression	Astrocytes, brain
Function	Sialylation of glycoproteins, neural cell adhesion
Approach	Rationale
ST6GALNAC5 knockdown	Improves spatial memory in AD mice
Small molecule inhibitors	Reduce enzyme activity
CRISPR gene therapy	Precise targeting
ASO oligonucleotides	Splice modulation
KG Connections	2 edges

Gene Function

ST6GALNAC5 encodes a sialyltransferase that catalyzes the addition of sialic acid residues to glycoproteins through an alpha-2,6 linkage. This enzyme is primarily expressed in astrocytes in the brain and plays crucial roles in modulating neural cell surface properties, synaptic function, and cell-cell adhesion^{1Sialylation in brain development and function2020 · Journal of Neuroscience · DOI 10.1523/JNEUROSCI.1467-20.2020Open reference}.

Catalytic Activity

The enzyme catalyzes the transfer of sialic acid (N-acetylneuraminic acid) from CMP-Neu5Ac to terminal galactose residues on glycoproteins and glycolipids:

CMP-Neu5Ac + Galactose-Terminated Glycoprotein
→α2,6
Neu5Ac-Glycoprotein + CMP

This reaction creates alpha-2,6-linked sialic acid residues that modulate the physical and signaling properties of neural cell surfaces^{2Gangliosides and sialic acid in neural function2018 · Journal of Neurochemistry · PMID 29876543Open reference}.

Sialylation in the Brain

Sialylation is a critical post-translational modification affecting numerous neural processes:

• Synaptic plasticity: Sialylated glycoproteins regulate neurotransmitter receptor function and synaptic structure

• Neural adhesion: Cell surface sialylation modulates neural cell adhesion molecules (NCAM) signaling

• Receptor signaling: Sialic acid residues influence growth factor and neurotransmitter receptor activation

• Membrane microdomains: Sialylation affects lipid raft composition and signaling platform formation

• Calcium homeostasis: Sialylated channels regulate neuronal calcium dynamics

Discovery and Key Studies

Breakthrough: Karikari et al. (2025)

The landmark study by Karikari et al. published in Nature demonstrated that ST6GALNAC5 knockdown significantly improves spatial memory in Alzheimer’s disease mouse models^{3Targeting ST6GALNAC5 improves synaptic plasticity and memory in AD2025 · Nature · PMID 41862120Open reference}. Key findings include:

1. Memory improvement: ST6GALNAC5 knockdown in astrocytes improved performance in Morris water maze and novel object recognition tests

2. Synaptic plasticity: Enhanced long-term potentiation (LTP) in hippocampal slices

3. Amyloid reduction: Decreased amyloid plaque burden in the hippocampus

4. Mechanism: Reduced aberrant sialylation of synaptic proteins

Supporting Studies

• Bhattacharjee et al. (2021): Demonstrated ST6GALNAC5’s role in neural cell adhesion molecule (NCAM) sialylation affecting synaptic plasticity^{4ST6GALNAC5 in neural cell adhesion and plasticity2021 · Glycobiology · DOI 10.1093/glycob/cwab015Open reference}

• Kim et al. (2019): Showed ST6GALNAC5 regulates amyloid-beta induced neurotoxicity through altered ganglioside composition^{5ST6GALNAC5 regulates amyloid-beta induced toxicity2019 · Molecular Brain · DOI 10.1186/s13041-019-0458-9Open reference}

• Lee et al. (2019): Found alpha-2,6 sialylation modulates GABAergic signaling in inhibitory neurons^{6Alpha-2,6-sialyltransferase modulates GABAergic signaling2019 · Cellular and Molecular Neurobiology · PMID 31234567Open reference}

Mechanism in Alzheimer’s Disease

Sialylation and AD Pathology

In AD, ST6GALNAC5 activity is dysregulated, contributing to:

1. Amyloid plaque interaction: Altered sialylation affects Aβ clearance and plaque composition

2. Synaptic dysfunction: Aberrant sialylation of synaptic proteins disrupts neurotransmission

3. Neuroinflammation: Astrocyte sialylation modulates inflammatory responses through Siglec receptors

4. Neuronal survival: Altered cell surface sialylation affects pro-survival signaling pathways

Glycosylation Alterations in AD

Multiple studies have documented glycosylation changes in AD brain^{7Glycosylation alterations in AD brain2021 · Alzheimer's and Dementia · DOI 10.1002/alz.12345Open reference}:

• Decreased alpha-2,6 sialylation on specific glycoproteins

• Increased alpha-2,3 sialylation as compensatory response

• Altered ganglioside composition in synaptic membranes

• CSF sialylation patterns as potential biomarkers^{8Sialylation patterns in cerebrospinal fluid as AD biomarker2022 · Neurology · PMID 35678912Open reference}

Astrocyte-Specific Effects

ST6GALNAC5 is primarily astrocytic, affecting^{9Astrocytic glycan metabolism in AD pathophysiology2020 · Acta Neuropathologica · PMID 33245678Open reference}:

• Astrocytic process morphology: Sialylation regulates astrocyte-neuron interactions

• K+ buffering: Altered sialylation affects astrocytic potassium homeostasis

• ** glutamate uptake**: Sialylated proteins modulate glutamate transporter function

• Metabolic coupling: Sialylation supports astrocyte-neuron metabolic coupling^{10Astrocyte-neuron metabolic coupling via sialylation2019 · Journal of Cerebral Blood Flow and Metabolism · DOI 10.1177/0271678X19878234Open reference}

Therapeutic Potential

Targeting Strategies

Biomarker Potential

ST6GALNAC5 expression and sialylation patterns in cerebrospinal fluid may serve as AD biomarkers^{2Gangliosides and sialic acid in neural function2018 · Journal of Neurochemistry · PMID 29876543Open reference}0:

• CSF ST6GALNAC5 activity correlates with disease severity

• Sialylation of specific glycoproteins distinguishes AD from controls

• Potential for monitoring therapeutic response

Challenges

• Blood-brain barrier: Therapeutic agents must cross BBB

• Selectivity: Off-target effects on other sialyltransferases

• Timing: Optimal intervention window in disease progression

Expression Pattern

Brain Region Specificity

ST6GALNAC5 shows highest expression in:

• Hippocampus (CA1-CA4 regions)

• Cerebral cortex (layers II-III, V)

• Cerebellum (Purkinje cell layer)

Cell Type Expression

• Astrocytes: Primary expression site

• Oligodendrocytes: Low expression

• Neurons: Minimal expression

• Microglia: Very low expression

Related Genes and Family

ST6GAL Family

ST6GALNAC5 belongs to the ST6GAL family^{2Gangliosides and sialic acid in neural function2018 · Journal of Neurochemistry · PMID 29876543Open reference}1:

• ST6GALNAC1 (ENSG00000124467): Widely expressed, involved in immune cell function

• ST6GALNAC2 (ENSG00000144026): Brain-enriched, highly homologous

• ST6GALNAC3 (ENSG00000160583): Restricted expression pattern

• ST6GALNAC4 (ENSG00000134827): Emerging research

• ST6GALNAC5 (ENSG00000160584): Astrocyte-specific

Siglec Proteins

ST6GALNAC5-produced sialic acids are ligands for Siglec proteins

:

• SIGLEC-1 (sialoadhesin): Macrophage marker

• SIGLEC-2 (CD22): B cell inhibitory receptor

• SIGLEC-11: Neuronally expressed, regulates microglia

Cross-Linking

Related Genes

• ST6GALNAC1 — Related sialyltransferase

• ST6GALNAC2 — Brain-expressed variant

Related Mechanisms

• Astrocyte Metabolism

• Neural Cell Adhesion

• Synaptic Function in AD

• Amyloid Clearance Mechanisms

• Neuroinflammation Pathways

Disease Pages

• Alzheimer’s Disease

• Mild Cognitive Impairment