Reactive astrogliosis is characterized by a profound change in astrocyte phenotype in response to all CNS injuries and diseases. To better understand the reactive astrocyte state, we used Affymetrix GeneChip arrays to profile gene expression in populations of reactive astrocytes isolated at various time points after induction using two mouse injury models, ischemic stroke and neuroinflammation. We find reactive gliosis consists of a rapid, but quickly attenuated, induction of gene expression after insult and identify induced Lcn2 and Serpina3n as strong markers of reactive astrocytes. Strikingly, reactive astrocyte phenotype strongly depended on the type of inducing injury. Although there is a core set of genes that is upregulated in reactive astrocytes from both injury models, at least 50% of the altered gene expression is specific to a given injury type. Reactive astrocytes in ischemia exhibited a molecular phenotype that suggests that they may be beneficial or protective, whereas reactive astrocytes induced by LPS exhibited a phenotype that suggests that they may be detrimental. These findings demonstrate that, despite well established commonalities, astrocyte reactive gliosis is a highly heterogeneous state in which astrocyte activities are altered to respond to the specific injury. This raises the question of how many subtypes of reactive astrocytes exist. Our findings provide transcriptome databases for two subtypes of reactive astrocytes that will be highly useful in generating new and testable hypotheses of their function, as well as for providing new markers to detect different types of reactive astrocytes in human neurological diseases.

https://www.jneurosci.org/content/jneuro/32/18/6391.full.pdf

Genomic Analysis of Reactive Astrogliosis

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Role of WHO.

The blood-brain barrier (BBB) prevents neurotoxic plasma components, blood cells, and pathogens from entering the brain. At the same time, the BBB regulates transport of molecules into and out of t...

/pdf/blood-brain-barrier-from-physiology-to-disease-and-back-1xwjgb63cg.pdf

Blood-Brain Barrier: From Physiology to Disease and Back

Everyone ages, but only some will develop a neurodegenerative disorder in the process. Disease might occur when cells fail to respond adaptively to age-related increases in oxidative, metabolic and ionic stress, thereby resulting in the accumulation of damaged proteins, DNA and membranes. Determinants of neuronal vulnerability might include cell size and location, metabolism of disease-specific proteins and a repertoire of signal transduction pathways and stress resistance mechanisms. Emerging evidence on protein interaction networks that monitor and respond to the normal ageing process suggests that successful neural ageing is possible for most people, but also cautions that cures for neurodegenerative disorders are unlikely in the near future.

http://www.utdallas.edu/~tres/papers/mattson.2006.pdf

Ageing and neuronal vulnerability

Reactive astrocytes are astrocytes undergoing morphological, molecular, and functional remodeling in response to injury, disease, or infection of the CNS. Although this remodeling was first described over a century ago, uncertainties and controversies remain regarding the contribution of reactive astrocytes to CNS diseases, repair, and aging. It is also unclear whether fixed categories of reactive astrocytes exist and, if so, how to identify them. We point out the shortcomings of binary divisions of reactive astrocytes into good-vs-bad, neurotoxic-vs-neuroprotective or A1-vs-A2. We advocate, instead, that research on reactive astrocytes include assessment of multiple molecular and functional parameters-preferably in vivo-plus multivariate statistics and determination of impact on pathological hallmarks in relevant models. These guidelines may spur the discovery of astrocyte-based biomarkers as well as astrocyte-targeting therapies that abrogate detrimental actions of reactive astrocytes, potentiate their neuro- and glioprotective actions, and restore or augment their homeostatic, modulatory, and defensive functions.

/pdf/reactive-astrocyte-nomenclature-definitions-and-future-30mrcayhyo.pdf

Reactive astrocyte nomenclature, definitions, and future directions

In the past two decades, over 1000 clinical trials have failed to demonstrate a benefit in treating stroke, with the exception of thrombolytics. Although many targets have been pursued, including antioxidants, calcium channel blockers, glutamate receptor blockers, and neurotrophic factors, often the focus has been on neuronal mechanisms of injury. Broader attention to loss and dysfunction of non-neuronal cell types is now required to increase the chance of success. Of the several glial cell types, this review will focus on astrocytes. Astrocytes are the most abundant cell type in the higher mammalian nervous system, and they play key roles in normal CNS physiology and in central nervous system injury and pathology. In the setting of ischemia astrocytes perform multiple functions, some beneficial and some potentially detrimental, making them excellent candidates as therapeutic targets to improve outcome following stroke and in other central nervous system injuries. The older neurocentric view of the central nervous system has changed radically with the growing understanding of the many essential functions of astrocytes. These include K+ buffering, glutamate clearance, brain antioxidant defense, close metabolic coupling with neurons, and modulation of neuronal excitability. In this review, we will focus on those functions of astrocytes that can both protect and endanger neurons, and discuss how manipulating these functions provides a novel and important strategy to enhance neuronal survival and improve outcome following cerebral ischemia.

Astrocytes: targets for neuroprotection in stroke.

Transient global ischemia, as with cardiac arrest, causes loss of CA1 hippocampal neurons 2-4 d later, whereas nearby dentate gyrus (DG) neurons are relatively resistant. Whether differential astrocyte vulnerability in ischemic injury contributes to CA1 neuronal death is uncertain. Here, we find that CA1 astrocytes are more sensitive to ischemia than DG astrocytes. In rats subjected to transient forebrain ischemia, CA1 astrocytes lose glutamate transport activity and immunoreactivity for GFAP, S100beta, and glutamate transporter GLT-1 within a few hours of reperfusion, but without astrocyte cell death. Oxidative stress may contribute to the observed selective CA1 changes, because CA1 astrocytes show early increases in mitochondrial free radicals and reduced mitochondrial membrane potential. Similar changes were not observed in DG astrocytes. Upregulation of GLT-1 expression in astrocytes with ceftriaxone protected CA1 neurons from forebrain ischemia. We suggest that greater oxidative stress and loss of GLT-1 function selectively in CA1 astrocytes is central to the well known delayed death of CA1 neurons.

https://www.jneurosci.org/content/jneuro/27/16/4253.full.pdf

Selective dysfunction of hippocampal CA1 astrocytes contributes to delayed neuronal damage after transient forebrain ischemia.

miR-181 targets multiple Bcl-2 family members and influences apoptosis and mitochondrial function in astrocytes.

miR-181 regulates GRP78 and influences outcome from cerebral ischemia in vitro and in vivo

Chaperones, especially the stress inducible Hsp70, have been studied for their potential to protect the brain from ischemic injury. While they protect from both global and focal ischemia in vivo and cell culture models of ischemia/reperfusion injury in vitro, the mechanism of protection is not well understood. Protein aggregation is part of the etiology of chronic neurodegenerative diseases such as Huntington's and Alzheimer's, and recent data demonstrate protein aggregates in animal models of stroke. We now demonstrate that overexpression of Hsp70 in hippocampal CA1 neurons reduces evidence of protein aggregation under conditions where neuronal survival is increased. We have also demonstrated protection by the cochaperone Hdj-2 in vitro and demonstrated that this is associated with reduced protein aggregation identified by ubiquitin immunostaining. Hdj-2 can prevent protein aggregate formation by itself, but can only facilitate protein folding in conjunction with Hsp70. Pharmacological induction of Hsp70 was found to reduce both apoptotic and necrotic astrocyte death induced by glucose deprivation or oxygen glucose deprivation. Protection from ischemia and ischemia-like injury by chaperones thus involves at least anti-apoptotic, anti-necrotic and anti-protein aggregation mechanisms.

/pdf/chaperones-protein-aggregation-and-brain-protection-from-1nov4c348n.pdf

Yi-Bing Ouyang

Papers

Astrocytes: targets for neuroprotection in stroke.

Selective dysfunction of hippocampal CA1 astrocytes contributes to delayed neuronal damage after transient forebrain ischemia.

miR-181 targets multiple Bcl-2 family members and influences apoptosis and mitochondrial function in astrocytes.

miR-181 regulates GRP78 and influences outcome from cerebral ischemia in vitro and in vivo

Chaperones, protein aggregation, and brain protection from hypoxic/ischemic injury.