The Biological Characteristics of Astrocytes and Application in Neurological Diseases

The Composition of The Brain Nervous System

The brain spheres are broadly composed of two types of cells: neurons and glial cells[1]. Neurons are the anatomical, functional, and nutritional units of the brain. Although, the size and shape of neurons are quite different, they have common morphological characteristics and are important substances in complex communication networks[2].

Glial cells are vital for maintaining hemostasis, protecting neurons and forming myelin in the Central Nervous System(CNS)[3]. There are mainly three types of glial cells, including microglia, which are essential for the immune response of the central nervous system; oligodendrocytes, which provide myelin and support for neurons; astrocytes, which are crucial for neuron nutrition providing and brain repairing[4]. The study of Buffo et al has shown that during brain injury, astrocytes acquire stem cell properties and hence may contribute in cell repair after brain injury[5].

The Characteristics and Functions of Astrocytes

As a type of glial cells, astrocyte is also called astroglia[6]. Astrocytes are the most abundant subtype of glial cells in the central nervous system (CNS).

Astrocyte classification has largely been restricted to two morphological groupings, fibrous and protoplasmic astrocytes which are found in the white and gray matter of the brain, respectively[7]. They play many roles that support neuronal functions, including synapse formation, transport and induced storage of metabolic substrates[8].

For example, in figure 1 Astrocytes provide cholesterol as well as energy substrates in support of neuronal functions. The provision of energy substrates is primarily in the form of lactate, which is converted from glucose. Neurotransmitters such as glutamate, noradrenaline, histamine and ACh are released from the pre-synaptic terminal. They are capable of binding to post-synaptic receptors or to receptors present on the surface of astrocytic processes. This binding can trigger a calcium response in the astrocyte that results in the release of gliotransmitters such as GABA, ATP and D-serine that will regulate synaptic activity.

Astrocytes couple together synaptic activity with local blood flow to ensure neurons have a sufficient energy supply. Prostaglandin (PG) and nitric oxide (NO) are all released in response to changes in intracellular calcium levels, which cause vasoconstriction or dilation[9].

Therefore, it is of great significance to successfully isolate primary astrocytes from the brain and further study their role in maintaining brain homeostasis.

Fig. 1 The many roles of the astrocyte [9]

Culture Primary Astrocyte

The rich cell culture of primary astrocytes comes from human brain tissue. Tissue samples were collected in astrocyte culture medium DMEM/HAM F10, which was supplemented with 100 units/ml penicillin, 100 μg/ml streptomycin and 10% fetal bovine serum.

How to Isolate Astrocyte?

The isolation of astrocyte was performed as follows: The isolation steps here are referred to the study of Korotkov et al.: meninges and blood vessels were removed, and the tissue was minced and dissociated by incubating with 2.5 mg/ml trypsin at 37℃ for 20 min. Then the trypsin was inactivated by using astrocyte completely culture medium. Strain the tissue through a 70 μm strainer and transfer the cell suspension to a flask containing fresh astrocyte culture medium and keep it in a 5% CO₂ incubator at 37℃. After incubating for 48 hours, the medium was replaced with fresh medium and then refreshed twice a week after 2-3 weeks. Astrocytes can be used at passages 2–5[10].

The key to identify the Extracted Primary Astrocytes.

As shown in figure 2, the shape of astrocytes is star-shaped, and many processes enclose the synapses produced by neurons. The star-astrocyte neurons were identified using astrocytic marker glial fibrillary acidic protein (GFAP). In human brain cell cultures, approximately 90-99% of GD3+ cells were GFAP+ astrocytes[11]. Histological analysis was traditionally used to identify astrocytes that most of which express glial acidic protein (GFAP).

Fig. 2 Fetal human brain cell cultures were stained with mAbs against GD3 in combination with anti-GFAP antiserum. GD3 (c) and GFAP immunolabeling (d)[11].

The Significance of Astrocyte Research

Astrocytoma is a primary intracranial tumor that develops from astrocytes. Low-grade tumors are more common in children and high-grade tumors are more common in adults[12]. In recent years, astrocytes have been found to be important participants in the process of neurological diseases, which may result from glial cell dysfunction[13].

Astrocytes can regulate painful synaptic transmission via neuronal-glial and glial-glial cell interactions, as well as the involvement of spinal and supraspinal astrocytes in the modulation of pain signaling and the maintenance of neuropathic pain[14]. Astrocytes can affect neuronal degeneration or neuroprotection, which further leads to the pathogenesis of neurodegenerative protein diseases [15].

Conclusion:

Astrocytes not only have neuroprotective effects; they may also be the culprits of some diseases. Although some characteristics and functions of astrocytes have been clarified, there is still a lack of research on how they perform multiple functions. Therefore, being able to successfully master a series of technologies such as primary astrocyte models will promote the development of medicine.

AcceGen Astrocytes

Further researches on astrocyte have vast importance to the better understanding of nervous system mechanism and the developing therapy of neurodegenerative disease. Therefore, purified astrocytes culture is vital to the research experiment. As the expert in cells, AcceGen provides Human Astrocytes and a wide range of cell products of nervous system. It is our pleasure to help relative researches to move forward. For more detailed information, please visit our website or contact [email protected].

References:

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7.  Batiuk MY, Martirosyan A, Wahis J, de Vin F, Marneffe C, Kusserow C, Koeppen J, Viana JF, Oliveira JF, Voet T et al: Identification of region-specific astrocyte subtypes at single cell resolution. Nat Commun 2020, 11(1):1220.

8.  Wenzel TJ, Bajwa E, Klegeris A: Cytochrome c can be released into extracellular space and modulate functions of human astrocytes in a toll-like receptor 4-dependent manner. Biochim Biophys Acta Gen Subj 2019, 1863(11):129400.

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