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Astrocytes are the major glial subtype in the brain and mediate numerous functions ranging from metabolic support to gliotransmitter release through signaling mechanisms controlled by Ca2+. Despite intense interest, the Ca2+ influx pathways in astrocytes remain obscure, hindering mechanistic insights into how Ca2+ signaling is coupled to downstream astrocyte-mediated effector functions. Here, we identified store-operated Ca2+ release-activated Ca2+ (CRAC) channels encoded by Orail and STIM1 as a major route of Ca2+ entry for driving sustained and oscillatory Ca2+ signals in astrocytes after stimulation of metabotropic purinergic and protease-activated receptors. Using synaptopHluorin as an optical reporter, we showed that the opening of astrocyte CRAC channels stimulated vesicular exocytosis to mediate the release of gliotransmitters, including ATP. Furthermore, slice electrophysiological recordings showed that activation of astrocytes by protease-activated receptors stimulated interneurons in the CA1 hippocampus to increase inhibitory postsynaptic currents on CA1 pyramidal cells. These results reveal a central role for CRAC channels as regulators of astrocyte Ca2+ signaling, gliotransmitter release, and astrocyte- mediated tonic inhibition of CA1 pyramidal neurons.

No abstract

Selenium is a nutritionally essential trace element that is important for optimal function of the immune system. It is incorporated into selenoproteins as the amino acid selenocysteine and it is known to inhibit the expression of some viruses. In this study, we show that selenium supplementation for 3 days prior to exposure to tumor necrosis factor alpha (TNF-alpha) partially suppresses the induction of human immunodeficiency virus type 1 (HIV-1) replication in both chronically infected T lymphocytic and monocytic cell lines. In acute HIV-1 infection of T lymphocytes and monocytes in the absence of exogenous TNF-alpha, the suppressive effect of selenium supplementation was not observed. However, selenium supplementation did suppress the enhancing effect of TNF-alpha on HIV-1 replication in vitro in acutely infected human monocytes, but not in T lymphocytes. Selenium supplementation also increased the activities of the selenoproteins, glutathione peroxidase (GPx) and thioredoxin reductase (TR), which serve as cellular antioxidants. Taken together, these results suggest that selenium supplementation may prove beneficial as an adjuvant therapy for AIDS through reinforcement of endogenous antioxidative systems.

No abstract