Astrocytes are specialized glial cells that outnumber neurons by over fivefold. They contiguously tile the entire central nervous system (CNS) and exert many essential complex functions in the healthy CNS. Astrocytes respond to all forms of CNS insults through a process referred to as reactive astrogliosis, which has become a pathological hallmark of CNS structural lesions. Substantial progress has been made recently in determining functions and mechanisms of reactive astrogliosis and in identifying roles of astrocytes in CNS disorders and pathologies. A vast molecular arsenal at the disposal of reactive astrocytes is being defined. Transgenic mouse models are dissecting specific aspects of reactive astrocytosis and glial scar formation in vivo. Astrocyte involvement in specific clinicopathological entities is being defined. It is now clear that reactive astrogliosis is not a simple all-or-none phenomenon but is a finely gradated continuum of changes that occur in context-dependent manners regulated by specific signaling events. These changes range from reversible alterations in gene expression and cell hypertrophy with preservation of cellular domains and tissue structure, to long-lasting scar formation with rearrangement of tissue structure. Increasing evidence points towards the potential of reactive astrogliosis to play either primary or contributing roles in CNS disorders via loss of normal astrocyte functions or gain of abnormal effects. This article reviews (1) astrocyte functions in healthy CNS, (2) mechanisms and functions of reactive astrogliosis and glial scar formation, and (3) ways in which reactive astrocytes may cause or contribute to specific CNS disorders and lesions.

/pdf/astrocytes-biology-and-pathology-2hq13zf0bo.pdf

Astrocytes: biology and pathology

https://www.hopkinsmedicine.org/neurology_neurosurgery/research/labs/als_center/_docs/rothstein_c9orf72.pdf

A hexanucleotide repeat expansion in C9ORF72 is the cause of chromosome 9p21-linked ALS-FTD

Microglial cells are the resident macrophages in the central nervous system. These cells of mesodermal/mesenchymal origin migrate into all regions of the central nervous system, disseminate through the brain parenchyma, and acquire a specific ramified morphological phenotype termed "resting microglia." Recent studies indicate that even in the normal brain, microglia have highly motile processes by which they scan their territorial domains. By a large number of signaling pathways they can communicate with macroglial cells and neurons and with cells of the immune system. Likewise, microglial cells express receptors classically described for brain-specific communication such as neurotransmitter receptors and those first discovered as immune cell-specific such as for cytokines. Microglial cells are considered the most susceptible sensors of brain pathology. Upon any detection of signs for brain lesions or nervous system dysfunction, microglial cells undergo a complex, multistage activation process that converts them into the "activated microglial cell." This cell form has the capacity to release a large number of substances that can act detrimental or beneficial for the surrounding cells. Activated microglial cells can migrate to the site of injury, proliferate, and phagocytose cells and cellular compartments.

Physiology of Microglia

This review is directed at understanding how neuronal death occurs in two distinct insults, global ischemia and focal ischemia. These are the two principal rodent models for human disease. Cell dea...

Ischemic Cell Death in Brain Neurons

https://www.cell.com/trends/neurosciences/pdf/S0166-2236(09)00153-2.pdf

Molecular dissection of reactive astrogliosis and glial scar formation.

Knockout of Glutamate Transporters Reveals a Major Role for Astroglial Transport in Excitotoxicity and Clearance of Glutamate

https://www.cell.com/neuron/pdf/S0896-6273(00)80997-6.pdf

Aberrant RNA processing in a neurodegenerative disease: the cause for absent EAAT2, a glutamate transporter, in amyotrophic lateral sclerosis.

Mutations in the gene for Cu/Zn superoxide dismutase (SOD1) have been detected in some families with an autosomal dominant form of amyotrophic lateral sclerosis; these mutations appear to reduce the activity of this enzyme. To determine whether decreased SOD activity could contribute to motor neuron loss, SOD1 was inhibited chronically with either antisense oligodeoxynucleotides or diethyldithiocarbamate in spinal cord organotypic cultures. Chronic inhibition of SOD resulted in the apoptotic degeneration of spinal neurons, including motor neurons, over several weeks. Motor neuron loss was markedly potentiated by the inhibition of glutamate transport. In this paradigm, motor neuron toxicity could be entirely prevented by the antioxidant N-acetylcysteine and, to a lesser extent, by the non-N-methyl-D-aspartate glutamate receptor antagonist 1-(4-aminophenyl)-4-methyl-7,8-methylenedioxy-5H-2,3-benzodiazepine hydrochloride. These data support the hypothesis that the loss of motor neurons in familial amyotrophic lateral sclerosis could be due to a reduction in SOD1 activity, possibly potentiated by inefficient glutamate transport.

Chronic inhibition of superoxide dismutase produces apoptotic death of spinal neurons

Glutamate transport is critical for synaptic inactivation of glutamate and prevention of excitotoxicity The following four glutamate transporters have been identified in human brain: EAAT1, EAAT2, EAAT3, and EAAT4 Deficient glutamate transport has been identified in the motor cortex and the spinal cord of tissue from amyotrophic lateral sclerosis (ALS) patients The defect appears to be due to a selective loss of the astroglial specific glutamate transporter protein EAAT2 In these studies we sought to extend our understanding of glutamate transporters in ALS by examining the mRNA for each transporter subtype in ALS motor cortex All tissue was matched for age and postmortem delay There was no quantitative change in mRNA for EAAT1, EAAT2, or EAAT3 in ALS motor cortex, even in patients with a large loss of EAAT2 protein (95% decrease compared with control) and decreased tissue glutamate transport (73% decrease compared with control) These studies suggest that the dramatic abnormalities in EAAT2 may be due to translational or post-translational processes

Lynn A. Bristol

Papers

Knockout of Glutamate Transporters Reveals a Major Role for Astroglial Transport in Excitotoxicity and Clearance of Glutamate

Aberrant RNA processing in a neurodegenerative disease: the cause for absent EAAT2, a glutamate transporter, in amyotrophic lateral sclerosis.

Chronic inhibition of superoxide dismutase produces apoptotic death of spinal neurons

Glutamate transporter gene expression in amyotrophic lateral sclerosis motor cortex.

TGFβ Trophic Factors Differentially Modulate Motor Axon Outgrowth and Protection from Excitotoxicity