Leptin: Clue to poor appetite in oxygen-starved fish

Hypoxia is the most widespread deleterious consequence of eutrophication and has become a major cause of fishery decline. One feature of chronic exposure to hypoxia in fish is inhibition of feeding In this study, we investigated if the gene that encodes the appetite-suppressing hormone leptin is regulated by hypoxia in zebrafish (Danio rerio). Exposure of adult zebrafish to hypoxic conditions (1 +/- 0 2 mg O-2 L-1) for 4 and I 0 days significantly increased leptin-a (zlep-a) mRNA levels in the liver. To evaluate the role of hypoxia-inducible factor 1 (HIF-1) in regulating zlep-a expression, zebrafish embryos were exposed to cobalt chloride (CoCl2. a HIF-1 inducer) and overexpressed with HIF-1 alpha mRNA. Both CoCl2 treatment and HIF-1 alpha markedly increased zlep-a expression in developing embryos, indicating the possible involvement of HIF-1 in zlep-a regulation In vivo promoter analysis indicated that zlep-a promoter activity is found in the muscle fibers of zebrafish embryos and enhanced by CoCl2 This is the first report to show that leptin gene expression in fish is regulated by hypoxia possibly via the involvement of HIF-1 (C) 2010 Elsevier Ireland Ltd All rights reserved.