Abstract
Ghrelin is involved in the regulation of growth in vertebrates through controlling different functions, such as feed intake, metabolism, intestinal activity or growth hormone (Gh) secretion. The aim of this work was to identify the sequences of preproghrelin and Ghrelin receptors (ghsrs), and to study their responses to different nutritional conditions in gilthead sea bream (Sparus aurata) juveniles. The structure and phylogeny of S. aurata preproghrelin was analyzed, and a tissue screening was performed. The effects of 21 days of fasting and 2, 5, 24 h, and 7 days of refeeding on plasma levels of Ghrelin, Gh and Igf-1, and the gene expression of preproghrelin, ghsrs and members of the Gh/Igf-1 system were determined in key tissues. preproghrelin and the receptors are well conserved, being expressed mainly in stomach, and in the pituitary and brain, respectively. Twenty-one days of fasting resulted in a decrease in growth while Ghrelin plasma levels were elevated to decrease at 5 h post-prandial when pituitary ghsrs expression was minimum. Gh in plasma increased during fasting and slowly felt upon refeeding, while plasma Igf-1 showed an inverse profile. Pituitary gh expression augmented during fasting reaching maximum levels at 1 day post-feeding while liver igf-1 expression and that of its splice variants decreased to lowest levels. Liver Gh receptors expression was down-regulated during fasting and recovered after refeeding. This study demonstrates the important role of Ghrelin during fasting, its acute down-regulation in the post-prandial stage and its interaction with pituitary Ghsrs and Gh/Igf-1 axis.
Highlights
Ghrelin is a peptide hormone secreted mainly by the stomach in vertebrates, and detected in many other tissues
Results of the preproghrelin and ghsrs gene expression screening are shown in Figures 3A,B, respectively. preproghrelin was mainly expressed in stomach, but weak expression was detected in many other tissues
Brain, pituitary and liver were the tissues with highest expression of both, ghsr1a and ghsr1b, low levels of expression were found in many other
Summary
Ghrelin is a peptide hormone secreted mainly by the stomach in vertebrates, and detected in many other tissues (e.g., intestine, heart, pancreas, and especially pituitary and brain). Kaiya et al [4] reviewed its function in non-mammalian vertebrates and recently, different publications have investigated its role in other fish species [5,6,7,8,9,10,11,12], but very little is known about this hormone in gilthead sea bream (Sparus aurata) [13]. Ghrelin functions through binding to its receptors, which are known as the growth hormone secretagogue receptors (Ghsrs). The Ghsrs are a family of transmembrane G-protein coupled receptors, and the Ghsr1a isoform, discovered a few years before Ghrelin [14], is known as the active form. Since the discovery of these two receptors, the Ghsrs family has been widely studied and other numerous isoforms (splice variants and paralogues) have been described in vertebrates [15, 16]
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