Abstract
This study investigates the possible mechanism(s) underlying glutathione (GSH) deficiency in the mouse spinal cord during the course of myelin oligodendrocyte glycoprotein35-55 peptide-induced experimental autoimmune encephalomyelitis (EAE), a commonly used animal model of multiple sclerosis. Using the classical enzymatic recycling method and a newly developed immunodot assay, we first demonstrated that total GSH levels (i.e. free GSH plus all its adducts) are reduced in EAE, suggesting an impaired synthesis. The decline in the levels of this essential antioxidant tripeptide in EAE coincides temporally and in magnitude with a reduction in the amount of γ-glutamylcysteine ligase, the rate-limiting enzyme in GSH synthesis. Other enzymes involved in GSH biosynthesis, whose genes also contain antioxidant-response elements, including glutathione synthetase, cystine/glutamate antiporter, and γ-glutamyl transpeptidase (γ-GT) are diminished in EAE as well. Low levels of γ-glutamylcysteine ligase, glutathione synthetase, and γ-GT are the consequence of reduced mRNA expression, which correlates with diminished expression of the nuclear factor (erythroid-derived 2)-like 2 (Nrf2) in both the cytosol and nucleus. Interestingly, the low Nrf2 expression does not seem to be caused by increased degradation via Kelch-like ECH-associated protein 1-dependent or Kelch-like ECH-associated protein 1-independent mechanisms (such as glycogen synthetase kinase-3β activation), or by reduced levels of Nrf2 mRNA. This suggests that translation of this important transcription factor and/or other still unidentified post-translational processes are altered in EAE. These novel findings are central toward understanding how critical antioxidant and protective responses are lost in inflammatory demyelinating disorders.