Abstract
The regulation of the redox status involves the activation of intracellular pathways as Nrf2 which provides hormetic adaptations against oxidative stress in response to environmental stimuli. In the brain, Nrf2 activation upregulates the formation of glutathione (GSH) which is the primary antioxidant system mainly produced by astrocytes. Astrocytes have also been shown to be themselves the target of oxidative stress. However, how changes in the redox status itself could impact the intracellular Ca2+ homeostasis in astrocytes is not known, although this could be of great help to understand the neuronal damage caused by oxidative stress. Indeed, intracellular Ca2+ changes in astrocytes are crucial for their regulatory actions on neuronal networks. We have manipulated GSH concentration in astroglioma cells with selective inhibitors and activators of the enzymes involved in the GSH cycle and analyzed how this could modify Ca2+ homeostasis. IP3-mediated store-operated calcium entry (SOCE), obtained after store depletion elicited by Gq-linked purinergic P2Y receptors activation, are either sensitized or desensitized, following GSH depletion or increase, respectively. The desensitization may involve decreased expression of the proteins STIM2, Orai1, and Orai3 which support SOCE mechanism. The sensitization process revealed by exposing cells to oxidative stress likely involves the increase in the activity of Calcium Release-Activated Channels (CRAC) and/or in their membrane expression. In addition, we observe that GSH depletion drastically impacts P2Y receptor-mediated changes in membrane currents, as evidenced by large increases in Ca2+-dependent K+ currents. We conclude that changes in the redox status of astrocytes could dramatically modify Ca2+ responses to Gq-linked GPCR activation in both directions, by impacting store-dependent Ca2+-channels, and thus modify cellular excitability under purinergic stimulation.
Highlights
Survival depends on the environment for the supply of oxygen, water and essential nutrients
GSH depletion with buthionine sulfoximine (BSO) greatly sensitizes this pathway as evidenced by the unveiling of store-operated calcium entry (SOCE) after the stimulation of Gq-linked P2Y receptors
Enhanced SOCE observed here could result from a rise in Calcium Release-Activated Channels (CRAC) trafficking at the membrane as evidenced by the increased potency of CRAC blocker, this treatment does not appear to result from changes in STIM and Orai proteins expression via genomic actions
Summary
Survival depends on the environment for the supply of oxygen, water and essential nutrients. Living organisms have to adapt continually their metabolic activity to environmental changes in order to keep themselves in homeostatic state Environmental stresses such as caloric restriction, oxygen deprivation, exposure to pollutants, reactive oxygenated species (ROS) are sensed by various systems, socalled hormetic mechanisms, adapting cellular metabolic activity and oxygen consumption to specific conditions. These systems include the Nrf pathway which regulates redox homeostasis (Raefsky and Mattson, 2017) by promoting long-lasting cell protection against oxidative stress (Satoh et al, 2009; RobledinosAntón et al, 2019) via the expression of enzymes involved in ROS scavenging. Invalidating GCL gene results in increased oxidative stress and neuronal death, especially interneurons (Tosic et al, 2006; Kulak et al, 2013; Hardingham and Do, 2016)
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