Astrocytes Prevent Ethanol Induced Apoptosis of Nrf2 Depleted Neurons by Maintaining GSH Homeostasis

Glutathione (GSH), a major cellular antioxidant, is the most abundant intracellular non-protein thiol and anti-oxidant in the body with a concentration of approximately 2 - 3 mM in brain. It can protect cells against oxidative stress injury. It is also vital for guarding normal healthy metabolism as well as defense against a range of disease and toxicity mechanisms by appropriately controlling cellular redox levels, most notably in the central nervous system (CNS).

Nuclear factor erythroid 2-related factor 2 (NFE2L2/Nrf2) is a redox sensitive master regulator of battery of antioxidant enzymes including those involved in GSH antioxidant machinery. In various experimental models of neurodegeneration, neuronal antioxidant defenses (mainly GSH) have been shown to be supported by astrocytes. The authors therefore sought to determine whether astrocytes could render protection to neurons against ethanol (ETOH) toxicity, particularly when the function of Nrf2 was compromised in neurons.

The experimental model consisted of co-culturing PCAs with Nrf2 downregulated PCNs that were exposed with and without 4 mg/mL ETOH for 24 h. Monochlorobimane (MCB) staining followed by FACS analysis showed that astrocytes blocked ETOH induced GSH decrement in Nrf2-silenced neurons as opposed to exaggerated GSH depletion in Nrf2 downregulated PCNs alone. Similarly, the heightened activation of caspase 3/7 observed in Nrf2-compromised neurons was attenuated when co-cultured with astrocytes as measured by luminescence based caspase Glo assay. Furthermore, annexin-V-FITC staining followed by FACS analysis revealed that Nrf2 depleted neurons showed resistance to ETOH induced neuronal apoptosis when co-cultured with astrocytes.

In conclusion, the current study identified a neuroprotective role for cortical astrocytes against ETOH even under a condition when neurons were partially depleted of Nrf2 based antioxidant machinery. Another important finding of the study was that this neuroprotective effect of astrocyte despite partially compromised neuronal Nrf2 could be achieved by GSH supply, a central component mediating redox signaling and cell death progression.

Article by Madhusudhanan Narasimhan, et al, from Texas Tech University Health Sciences Center, Lubbock, USA.

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