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      Reactive Astrocytes in Neurodegenerative Diseases

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          Abstract

          Astrocytes, the largest and most numerous glial cells in the central nervous system (CNS), play a variety of important roles in regulating homeostasis, increasing synaptic plasticity and providing neuroprotection, thus helping to maintain normal brain function. At the same time, astrocytes can participate in the inflammatory response and play a key role in the progression of neurodegenerative diseases. Reactive astrocytes are strongly induced by numerous pathological conditions in the CNS. Astrocyte reactivity is initially characterized by hypertrophy of soma and processes, triggered by different molecules. Recent studies have demonstrated that neuroinflammation and ischemia can elicit two different types of reactive astrocytes, termed A1s and A2s. However, in the case of astrocyte reactivity in different neurodegenerative diseases, the recently published research issues remain a high level of conflict and controversy. So far, we still know very little about whether and how the function or reactivity of astrocytes changes in the progression of different neurodegenerative diseases. In this review, we aimed to briefly discuss recent studies highlighting the complex contribution of astrocytes in the process of various neurodegenerative diseases, which may provide us with new prospects for the development of an excellent therapeutic target for neurodegenerative diseases.

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          Most cited references80

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          Thrombospondins are astrocyte-secreted proteins that promote CNS synaptogenesis.

          The establishment of neural circuitry requires vast numbers of synapses to be generated during a specific window of brain development, but it is not known why the developing mammalian brain has a much greater capacity to generate new synapses than the adult brain. Here we report that immature but not mature astrocytes express thrombospondins (TSPs)-1 and -2 and that these TSPs promote CNS synaptogenesis in vitro and in vivo. TSPs induce ultrastructurally normal synapses that are presynaptically active but postsynaptically silent and work in concert with other, as yet unidentified, astrocyte-derived signals to produce functional synapses. These studies identify TSPs as CNS synaptogenic proteins, provide evidence that astrocytes are important contributors to synaptogenesis within the developing CNS, and suggest that TSP-1 and -2 act as a permissive switch that times CNS synaptogenesis by enabling neuronal molecules to assemble into synapses within a specific window of CNS development.
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            GABA from reactive astrocytes impairs memory in mouse models of Alzheimer's disease.

            In Alzheimer's disease (AD), memory impairment is the most prominent feature that afflicts patients and their families. Although reactive astrocytes have been observed around amyloid plaques since the disease was first described, their role in memory impairment has been poorly understood. Here, we show that reactive astrocytes aberrantly and abundantly produce the inhibitory gliotransmitter GABA by monoamine oxidase-B (Maob) and abnormally release GABA through the bestrophin 1 channel. In the dentate gyrus of mouse models of AD, the released GABA reduces spike probability of granule cells by acting on presynaptic GABA receptors. Suppressing GABA production or release from reactive astrocytes fully restores the impaired spike probability, synaptic plasticity, and learning and memory in the mice. In the postmortem brain of individuals with AD, astrocytic GABA and MAOB are significantly upregulated. We propose that selective inhibition of astrocytic GABA synthesis or release may serve as an effective therapeutic strategy for treating memory impairment in AD.
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              Multiple sclerosis: a complicated picture of autoimmunity.

              Understanding of autoimmune diseases, including multiple sclerosis, has expanded considerably in recent years. New insights have been provided by not only animal models but also studies of patients, often in conjunction with experimental therapies. It is accepted that autoimmune T cells mediate the early steps of new multiple sclerosis lesions, and although uncertainties remain about the specific targets of autoreactive T cells, several studies indicate myelin antigens. Recent findings obtained with both animal models and patients with multiple sclerosis indicate involvement of a T helper cell with a T(H)-17 phenotype, in contrast to previous data indicating that T helper type 1 cells are critical. Evidence has also been presented for CD8(+) and regulatory T cell populations, although their involvement remains to be established. Despite evidence supporting the idea that autoreactive T cells are involved in disease induction, cells of myeloid lineage, antibodies and complement as well as processes intrinsic to the central nervous system seem to determine the effector stages of tissue damage. Careful analysis of the alterations in immune processes should further advance knowledge of the relationship between the inflammatory component of this disease and the more diffuse degeneration of progressive multiple sclerosis.
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                Author and article information

                Journal
                Aging Dis
                Aging Dis
                Aging and Disease
                JKL International LLC
                2152-5250
                June 2019
                01 June 2019
                : 10
                : 3
                : 664-675
                Affiliations
                [1-ad-10-3-664] 1Department of Anatomy, Histology and Embryology, School of Basic Medical Sciences, Fudan University, Shanghai 200032, China.
                [2-ad-10-3-664] 2Center for Translational Neurodegeneration and Regenerative Therapy, Shanghai Tenth People’s Hospital affiliated to Tongji University School of Medicine, Shanghai, China.
                Author notes
                [* ]Correspondence should be addressed to: Dr. Song Qin, Department of Anatomy, Histology and Embryology, School of Basic Medical Sciences, Fudan University, Shanghai 200032, China. Email: sqin@ 123456fudan.edu.cn.
                Article
                ad-10-3-664
                10.14336/AD.2018.0720
                6538217
                31165009
                5f91888a-2b66-494f-a8f6-e56bc423deae
                Copyright: © 2019 Li et al.

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution and reproduction in any medium provided that the original work is properly attributed.

                History
                : 11 May 2018
                : 12 July 2018
                : 20 July 2018
                Categories
                Review

                reactive astrocytes,neuroinflammation,neurodegenerative diseases

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