Glia Proteins

2BScientific Guide to Glia Proteins

Introduction to Glia Proteins

Initially the role of Glia cells was greatly underestimated. It was thought that they were just the “glue”- glia is the Greek word for glue, which holds the neurons together. Glia cells are non-neuronal cells in the nervous system that have a multitude of tasks, e.g. maintain homeostasis, form myelin, and provide support and protection for the neuronal cells.

Recently it was discovered that they are also important players in neurotransmission, memory formation and brain development. The population of glia cells in the CNS consists of four main groups; astrocytes, oligodendrocytes, microglia and ependymal cells.

Astrocytes:

This cell type represents the most abundant fraction of non-neuronal cells in the brain. The name of the star-shaped astrocytes is derived from the Greek words astron which means star and cyte which means cell. They perform many functions, including regulating the environment of the neurons by removing excess neurotransmitters and recycle them, controlling the blood- brain barrier permeability and providing nutrients for the neurons, but they also have a role in synaptogenesis and neurogenesis.

Often used marker proteins for astrocytes are: GFAP, S100B and Glutamine synthetase (GS)

Oligodendrocytes:

Their main function is to provide support and insulation to axons in the Central Nervous system (CNS) by coating them with a specialized membrane differentiation called myelin. This myelin sheath allows electrical signals in axons to propagate quicker than in non-myelinated axons. Loss of myelin causes diseases like multiple sclerosis and various leukodystrophies.

Often used marker proteins for oligodendrocytes are: CNP1, MOG, MBP, NG2 and OSP

Microglia:

One of the main functions of the microglia is to act like a “police force” in the CNS. They are the resident form of macrophages in the CNS and build the immune defense in the brain and spinal cord. They remove infectious agents, plaques, damaged or unnecessary synapses and neurons. But they are more than just scavengers removing the debris they are also important in shaping the developing CNS and in normal brain function.

Often used marker proteins for microglia are: IBA1, P2RY12 and TMEM119

Ependymal cells:

These cells line the ventricular system of the brain and the central canal of the spinal cord. They are involved in the creation and secretion of the cerebrospinal fluid (CSF). They are mostly barrel-shaped with cilia at the apical end. With this cilia they help to circulate the CSF. Recent research implies that they can also act as neural stem cells.

Often used marker proteins are: GFAP and Foxj1

Target	SKU	Host	Applications	Reactivity	Clone	Size
Oligodendrocytes
CNP1	355-011	Ms	WB, ICC, IHC	Rt, Ms	335C6	100ug
MBP	295-002	Rb	WB,IHC, IHC-P	HU, Rt, Ms		100ul
Astrocytes
GFAP	173-011	Ms	WB, IP, ICC, IHC, IHC-P, ELISA	HU, Rt, Ms	134B1	100ug
S100B	287-111	Ms	ICC, IHC, IHC-P	Rt, Ms	86D7E4	50UG
Microglia
IBA1 (AIF)	234-003	Rb	WB, IP, ICC, IHC, IHC-P	HU, Rt, Ms	195H4	100ul
TMEM119	400-011	Ms	IHC, IHC-P	Ms	195H4	100ul
TMEM119	400-211	Ms	IHC, IHC-P	Rt	97G1C1	100ug

CNP 1

The 2’, 3’-cyclic nucleotide 3’-phosphodiesterase CNP 1, also referred to as CNPase or CNP, is one of the most abundant membrane-associated enzymes in the myelin sheath of the vertebrate nervous system. In the Central Nervous System (CNS), the protein is exclusively expressed in oligodendrocytes which makes it a valuable marker for this cell type. The enzyme catalyzes the hydrolysis of 2’, 3’-cyclic nucleotides to produce 2’-nucleotides.

It is assumed that CNP 1 participates in RNA metabolism of myelinating oligodendrocytes. The protein also binds to tubulin heterodimers and plays a role in tubulin polymerization and oligodendrocyte process outgrowth.

Myelin basic protein

A major component of the myelin sheath

The myelin sheath is a multi-layered membrane composed of several pro- teins like PLP, claudin 11, and myelin basic protein (MBP), which is specific for the nervous system. MBP functions as an insulator and increases the velocity of axonal impulse conduction.

MBP can be subdivided into a classic group consisting of isoforms 4 to 14 and a non-classic group of MBP comprising the Golli MBPs (isoforms 1 to 3). Differential splicing events and posttranslational modifications give rise to a wide spectrum of isomers with potentially specialized functions. Most isoforms can be found at the plasma membrane but some are located pre- dominately in the nucleus of oligodendrocytes.

Glia Proteins — Indirect immunostaining of PFA fixed rat brain section with mouse monoclonal anti-CNP1 (cat. no.: 355 011, dilution 1:500; red). Nuclei have been visualized by DAPI staining (blue).

GFAP

A glial-specific type-III intermediate filament protein

Glial fibrillary acidic protein GFAP is a glial-specific member of the inter- mediate filament protein family. This group comprises cell type-specific filamentous proteins with similar structure and function as scaffolding for cytoskeleton assembly and maintenance. GFAP and vimentin (also a member of the same protein family) form intermediate filaments in astrocytic glial cells and modulate their motility and shape. Vimentin is expressed more at early developmental stages, while GFAP is more characteristic of differen- tiated and mature brain astrocytes.

Frequently, neural stem cells and ependymal cells also express GFAP during their development. Additionally, many types of brain tumours, which are often derived from astrocytic cells, heavily express GFAP. This protein is also found in the lens epithelium, Kupffer cells of the liver, in some cells in salivary tumours, and others.

Point-mutations in the GFAP gene have been correlated to Alexander disease: a fatal leukoencephalopathy that leads to the dysmyelination or demyelination of the central nervous system.

S100B

A marker for mature astrocytes

The family of S100 proteins comprises more than 20 members. These proteins are EF-hand Ca2+-binding proteins and are widely distributed in mammalian tissue. Since these proteins are soluble in 100% saturated ammonium-sulfate solution, they have been named S100.

S100B is a frequently used marker protein for mature astrocytes, whereas GFAP is also expressed in germinal zone cells that maintained their imma- ture developmental stage. This protein may function in neurite extension, proliferation of melanoma cells, stimulation of Ca2+ fluxes, inhibition of PKC-mediated phosphorylation, astrocytosis and axonal proliferation, and inhibition of microtubule assembly. In the developing CNS, it acts as a neurotrophic factor and neuronal survival protein. In the adult organism, it is usually elevated due to nervous system damage, which makes it a potential clinical marker.

Indirect immunostaining of cultured rat astrocytes and hippocampus neurons with mouse monoclonal anti-GFAP (cat. no.: 173 011, dilution 1:500; red) and rabbit polyclonal anti-synaptotagmin 1/2 (cat. no.: 105 002, dilution 1:1000; green).

IBA 1

A calcium binding protein specific for microglia

Ionized calcium-binding adaptor molecule 1 (IBA1) or allograft inflamma- tory factor 1 (AIF1) is an EF hand calcium binding protein of 17 kDa which is expressed selectively in microglia/macrophages. IBA1/AIF1 is a cyto- solic protein that binds to actin and enhances membrane ruffling and RAC activation. Its expression has been suggested to be associated with the neuroinflammatory response and with transplant rejection.

The AIF1 gene is located within a segment of the major histocompatibility complex class III region. It has been shown that this gene is highly expressed in testis and spleen, but weakly expressed in brain, lung, and kidney. In brain cells, the IBA1 gene was specifically expressed in microglia. Upon activation of microglia due to inflammation, expression of IBA1 is upregulated which allows discrimination between surveilling and activated microglia.

TMEM119

Microglia are resident myeloid cells of the central nervous system (CNS). They are ontogenetically and functionally distinct from monocyte-derived macrophages that infiltrate the CNS under pathological conditions. Trans- membrane protein 119 (TMEM 119), also referred to as OBIF, is a single-pass type I membrane protein that has been identified as a useful, highly selective microglia marker protein.

Microglia are the immune-competent cells in the brain. In addition to their well-known role in pathological conditions, there is emerging evidence that they play an important roles in the development of the Central Nervous System (CNS) and normal brain function. In contrast to other established microglia-marker proteins, TMEM119 is specific in the CNS for microglia and cannot be found on macrophages which in pathologic events can migrate into the brain. Outside of the brain TMEM119 plays an important role in bone formation and normal bone mineralization.

TMEM119 has a high inter-species variability that makes species-specific antibodies necessary.

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