Astrocyte markers are essential for studying astrocyte subpopulations and their roles in the central nervous system (CNS). These markers help distinguish astrocyte heterogeneity across different brain regions and are crucial for understanding astrocyte biology. Astrocyte markers are also used to study astrocyte reactivity in response to CNS pathology.

What are astrocytes?

Astrocytes are star-shaped glial cells that serve various functions in the central nervous system. Astrocytes help regulate blood flow and synaptic function in the brain and spinal cord. As a type of glial cell, astrocytes display diverse astrocyte morphology, and their classification as a cell type is based on their unique structural and functional characteristics. They are vital for brain development, physiology, and pathology.

GFAP (glial fibrillary acidic protein)

Glial fibrillary acidic protein (GFAP) is an intermediate filament and major component of the astrocyte cytoskeleton^1-4. GFAP expression is a hallmark of reactive astrocytes and is commonly used as a classical marker for astrocyte identification. GFAP is upregulated during astrocyte activation and in disease states such as amyotrophic lateral sclerosis and multiple sclerosis. GFAP is also used to distinguish mature astrocytes from other glial cell types.

Figure 1. Human hippocampus tissue section stained with anti-GFAP (ab68428).

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EAAT1/GLAST (excitatory amino acid transporter)

Excitatory amino acid transporter 1 (EAAT1) is an astrocyte-specific glutamate transporter. EAAT1 is involved in regulating synaptic transmission and synapse formation, contributing to the functional characteristics of astrocytes in the central nervous system. EAAT1 is commonly used to label astrocytes and to identify astrocytes positive for this marker in brain tissue. It may also be known as glutamate aspartate Transporter (GLAST)^2,4,5,6.

Figure 2. Rat cerebral cortex tissue sections stained with anti-EAAT1 (ab181036).

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EAAT2/GLT-1

Excitatory amino acid transporter 2 (EAAT2) is an astrocyte-specific glutamate transporter. EAAT2 gene expression shows differential expression across astrocyte subtypes, contributing to the functional diversity of astrocytes in the mouse brain. EAAT2 has many alternative names, including solute carrier family 1 member 2 (SLC1A2) and glutamate transporter 1 (GLT-1)^4-7.

Figure 3. Mouse striatum tissue sections stained with anti-EAAT2 (green) (ab205248).

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Glutamine synthetase

This enzyme is involved in the metabolism of nitrogen. In the brain, it is primarily found in astrocytes. Glutamine synthetase is highly expressed in protoplasmic astrocytes, particularly within the cell body and fine astrocyte processes. Regional differences in glutamine synthetase expression have been observed in hippocampal astrocytes and the somatosensory cortex.

Figure 4. Mouse cerebrum tissue sections stained with anti-glutamine synthetase (green) (ab176562).

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S100 beta

S100 beta is a member of the calcium-binding proteins family. It is also found in oligodendrocyte progenitor cells (OPCs) and immature astrocytes. During development, S100 beta is expressed in both astrocytes and oligodendrocyte progenitor cells, as well as in immature astrocytes. Alterations in S100 beta levels have been observed in neurodegenerative diseases, including Alzheimer's disease. Double labeling with NG2 will distinguish the OPCs from the astrocytes.

Figure 5. Rat cerebrum tissue sections stained with anti-S100 beta (green) (ab52642).

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ALDH1L1 (aldehyde dehydrogenase)

Aldehyde dehydrogenase 1 family member L1 is an enzyme that catalyzes the conversion of 10-formyltetrahydrofolate, NADP+ and water to tetrahydrofolate, NADPH and CO₂.

Figure 6. Human kidney tissue sections stained with anti-ALDH1L1 (ab177463).

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References

1. Cahoy, J. D. et al.  A transcriptome database for astrocytes, neurons, and oligodendrocytes: a new resource for understanding brain development and function.  J. Neurosci.   28, 264–278 (2008).

2. Dimou, L. & Götz, M. Glial cells as progenitors and stem cells: new roles in the healthy and diseased brain.  Physiol. Rev.   94, 709–737 (2014).

3. Kriegstein, A. R. & Götz, M. Radial glia diversity: a matter of cell fate.  Glia   43, 37–43 (2003).

4. Medrano, M. C.  et al.  Functional and morphological characterization of glutamate transporters in the rat locus coeruleus.  Br. J. Pharmacol.   170, (2013).

5. Abrahamsen, B.  et al.  Allosteric modulation of an excitatory amino acid transporter: the subtype-selective inhibitor UCPH-101 exerts sustained inhibition of EAAT1 through an intramonomeric site in the trimerization domain.  J. Neurosci.   33, (2013).

6. Shigeri, Y.  et al.  Effects of threo-β-hydroxyaspartate derivatives on excitatory amino acid transporters (EAAT4 and EAAT5).  J. Neurochem.   79, (2001).

7. Lee, S.-G.  et al.  Mechanism of ceftriaxone induction of excitatory amino acid transporter-2 expression and glutamate uptake in primary human astrocytes.  J. Biol. Chem.   283, (2008).