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Molecular Characterization and Hypoxia-Induced Upregulation of Neuronal Nitric Oxide Synthase in Atlantic Croaker: Reversal by Antioxidant and Estrogen Treatments
Author(s): Rahman, Md. Saydur; Peter Thomas
NCCOS Center: CSCOR
Name of Publisher: Elsevier
Publication Type: Journal Article
Journal Title: Comparative Biochemistry and Physiology, Part A: Molecular & Integrative Physiology
Date of Publication: 2015
Reference Information: 185:
91-106.
Keywords: Fish; Hypoxia; Neuronal NOS; ROS; Antioxidant; Estradiol-17ß; Atlantic croaker; NGOMEX; free radicals
Abstract: Neuronal nitric oxide synthase (nNOS) catalyzes production of nitric oxide in vertebrate brains. Recent findings indicate that endothelial NOS and reactive oxygen species (ROS) are significantly increased during hypoxic stress and aremodulated by antioxidants. However, the influence of antioxidants and steroids on nNOS upregulation by hypoxia is largely unknown. In this study,we characterized nNOS cDNA and examined the effects of hypoxia and antioxidant and steroid treatments on nNOS expression in Atlantic croaker hypothalamus. Hypoxia exposure (dissolved oxygen, DO: 1.7 mg/L for 2 and/or 4 weeks) caused significant increases in hypothalamic nNOS mRNA, protein and its neuronal expression. Hypothalamic nNOS expression and superoxide radical (O2•-, an index of ROS) production were increased by pharmacological treatment of fish exposed to normoxic conditions with N-ethylmaleimide, an alkene drug which covalently modifies sulfhydryl groups and inhibits aromatase activity. In contrast, treatments with N?-nitro-L-arginine methyl ester, a competitive NOS-inhibitor, or vitamin E, an antioxidant, prevented the upregulation of O2•- production and nNOS expression in hypoxia-exposed (DO: 1.7mg/L for 4 weeks) fish.Moreover, treatmentwith 1,4,6-androstatrien-3,17-dione, an aromatase inhibitor, increased
hypothalamic O2•- production and nNOS expression in normoxic control fish; whereas estradiol-17ß treatment significantly reduced O2•- production and nNOS expression in hypoxia-exposed fish. Doublelabeled immunohistochemical results showed that nNOS and aromatase proteins are co-expressed in the hypothalamus. Taken together, the results suggest that upregulation of nNOS and ROS in the croaker hypothalamus in response to hypoxia is influenced by antioxidant and overall estrogen status.
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