The nature of early astroglial protection—Fast activation and signaling


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Abstract

HighlightsMajor processes and players of excitation-inhibition balance via Glu homeostasis are highlighted.Discussion of a novel, astroglial “sensor” of oxidative hypometabolism, stress and neuroinflammation is submitted.Astrocytes are placed in the centre of Glu metabolism-reliant ammonia homeostasis.Prevalent and invasive traumatic and ischaemic brain injuries are explored to validate the potential of the “gliocentric” concept of early therapeutic intervention.The idea of excitation-dependent pulsing of “nanocapillars” taking shape by the synapse and perisynaptic astrocytic processes is promoted.Our present review is focusing on the uniqueness of balanced astroglial signaling. The balance of excitatory and inhibitory signaling within the CNS is mainly determined by sharp synaptic transients of excitatory glutamate (Glu) and inhibitory γ-aminobutyrate (GABA) acting on the sub-second timescale. Astroglia is involved in excitatory chemical transmission by taking up i) Glu through neurotransmitter-sodium transporters, ii) K+ released due to presynaptic action potential generation, and iii) water keeping osmotic pressure. Glu uptake-coupled Na+ influx may either ignite long-range astroglial Ca2+ transients or locally counteract over-excitation via astroglial GABA release and increased tonic inhibition. Imbalance of excitatory and inhibitory drives is associated with a number of disease conditions, including prevalent traumatic and ischaemic injuries or the emergence of epilepsy. Therefore, when addressing the potential of early therapeutic intervention, astroglial signaling functions combating progress of Glu excitotoxicity is of critical importance. We suggest, that excitotoxicity is linked primarily to over-excitation induced by the impairment of astroglial Glu uptake and/or GABA release. Within this framework, we discuss the acute alterations of Glu-cycling and metabolism and conjecture the therapeutic promise of regulation. We also confer the role played by key carrier proteins and enzymes as well as their interplay at the molecular, cellular, and organ levels. Moreover, based on our former studies, we offer potential prospect on the emerging theme of astroglial succinate sensing in course of Glu excitotoxicity.

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