Sequence, genomic organization and expression of ghrelin receptor in grass carp, Ctenopharyngodon idellus

Ultrastructural study of neuronal cells and localization of ghrelin-like peptide and its receptor in the ganglia of the golden apple snail (Pomacea canaliculata)

Pomacea canaliculata is an invasive snail species causing major problems in agriculture. The snail biology was then investigated. The main objective of the present study was to investigate the nervous system of the snail. The nervous system comprises pairs of cerebral, buccal, pedal, pleural, parietal ganglia and an unpaired visceral ganglion. Most neurons were concentrated at the periphery of the ganglia. The neurons were classified into four types: NR1, NR2, NR3, and NR4. The percentages of the NR3 and NR4 in the pleural and pedal ganglia were significantly higher than those of other ganglia. Ultrastructural study revealed that nuclei of all neuronal types exhibited mostly euchromatins. Many organelles including ribosomes and endoplasmic reticulum were found in their cytoplasm. However, various mitochondria were found in the NR2 and NR3. The immunohistochemistry revealed immunoreactivity of ghrelin-like peptide in the neurons of the cerebral, pleural and pedal ganglia. However, immunoreactivity of GHS-R1a-like peptide existed only in the neurons of the pleural and pedal ganglia. The present study is the first to demonstrate the existence of ghrelin-like peptide and its receptor in P. canaliculata nervous system.

Expression of the growth hormone secretagogue receptor 1a (GHS-R1a) in the brain

The review presents data on the expression of growth hormone secretagogue receptor 1a (GHS-R1a) in the brain regions in model animals (zebrafish, rodents, primates), and in the human brain. Studies show widespread distribution of the receptor in the brain, which evidences the involvement of the receptor in many physiological processes. Using various organisms, data have been obtained regarding the participation of the GHS-R1a in the regulation of the anti- and pro-inflammatory response, proliferation, and apoptosis. It is known that the receptor plays an important role in eating behavior and is also involved in the pathogenetic mechanisms of drug addiction, obesity, and chronic alcohol consumption. Based on this, research is underway with the use of various therapeutic agents that can be used for the pharmacological correction of these conditions. This review also presents hypothetical pathways of intracellular signaling, in which GHS-R1a may participate. A complete understanding of these mechanisms has not yet been reached. The ghrelin intracellular signaling seem to be specific to brain region and, probably, also depend on the metabolic or stress status of the organism.

Antibacterial activity of erythrocyte from grass carp (Ctenopharyngodon idella) is associated with phagocytosis and reactive oxygen species generation

Red blood cells (RBCs) are widely accepted as their primary function in respiration. Recent studies in mammals have revealed a vital role in immune responses of RBCs; however, little is known about immune function of teleost erythrocytes. Here we demonstrated that RBCs from grass carp (Ctenopharyngodon idella) were capable of binding and aggregating the bacteria with apparent morphological alterations. The phagocytosis by teleost RBCs (erythrophagocytosis) was visualized by confocal, scanning and transmission electron microscopy. Hb-Fe^II of hemoglobin (Hb) could quickly be auto-oxidated to Hb-Fe^III (methemoglobin/metHb) in the presence of oxygen (O₂), and release superoxide radical (O₂^-.) which could be spontaneously dismutated into H₂O₂ that could further oxidize Hb-Fe^III to transient HbFe^IV-OH (ferryl-Hb). Furthermore, bacterial extracellular proteases and pathogen-associated molecular patterns (PAMPs) binding to Hb could synergistically activate pseudoperoxidase, subsequently facilitated the generation of reactive oxygen species (ROS) which were toxic to the bacteria. Our results indicated that erythrocyte pertains anti-bacterial activity using unique ROS generation pathway via oxidation of hemoglobin and associated with its phagocytosis.

Ghrelin and Its Receptors in Gilthead Sea Bream: Nutritional Regulation

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.

Transcriptomic analysis of liver from grass carp (Ctenopharyngodon idellus) exposed to high environmental ammonia reveals the activation of antioxidant and apoptosis pathways

High concentration of ammonia in aquatic system leads to detrimental effects on the health of aquatic animals. However, the mechanism underlying ammonia-induced toxicity is still not clear. To better understand the mechanism of ammonia toxicity effects on fish, juvenile grass carp was employed in the present study. RNA high-throughput sequencing technique was applied to analyze the total RNAs extracted from the liver of fish after 8 h post exposure to the water containing 2 mM NH₄HCO₃ which experimentally mimicked the high environmental ammonia (HEA). A total of 49,971,114 and 53,826,986 clean reads were obtained in control and 2 mM HEA group, respectively, in which there were 911 differently expressed genes (DEGs) including 563 up-regulated and 348 down-regulated genes. In addition, 10 DEGs were validated by quantitative PCR. These DEGs were involved in several pathways related with oxidative stress or apoptosis. Further analysis on oxidative stress, histopathology and cellular apoptosis in grass carp liver after HEA exposure revealed interesting findings. Increased reactive oxygen species (ROS) content and superoxide dismutase (SOD) activity together with the decreased catalase (CAT) activity were detected, which may be effected by DEGs and related pathways such as FOXO signaling pathway. The histopathology and TUNEL assays results confirmed that apoptosis was induced in liver when fish had suffered HEA. Combined with the results of transcriptomic experiments, c-Myc-Bax-Caspase9 apoptosis pathway could be involved in grass carp liver apoptosis induced by ammonia stress.

Interplay between the endocrine and circadian systems in fishes

The circadian system is responsible for the temporal organisation of physiological functions which, in part, involves daily cycles of hormonal activity. In this review, we analyse the interplay between the circadian and endocrine systems in fishes. We first describe the current model of fish circadian system organisation and the basis of the molecular clockwork that enables different tissues to act as internal pacemakers. This system consists of a net of central and peripherally located oscillators and can be synchronised by the light-darkness and feeding-fasting cycles. We then focus on two central neuroendocrine transducers (melatonin and orexin) and three peripheral hormones (leptin, ghrelin and cortisol), which are involved in the synchronisation of the circadian system in mammals and/or energy status signalling. We review the role of each of these as overt rhythms (i.e. outputs of the circadian system) and, for the first time, as key internal temporal messengers that act as inputs for other endogenous oscillators. Based on acute changes in clock gene expression, we describe the currently accepted model of endogenous oscillator entrainment by the light-darkness cycle and propose a new model for non-photic (endocrine) entrainment, highlighting the importance of the bidirectional cross-talking between the endocrine and circadian systems in fishes. The flexibility of the fish circadian system combined with the absence of a master clock makes these vertebrates a very attractive model for studying communication among oscillators to drive functionally coordinated outputs.

Ghrelin induces clock gene expression in the liver of goldfish in vitro via protein kinase C and protein kinase A pathways

The liver is the most important link between the circadian system and metabolism. As a food-entrainable oscillator, the hepatic clock needs to be entrained by food-related signals. The objective of the present study was to investigate the possible role of ghrelin (an orexigenic peptide mainly synthesized in the gastrointestinal tract) as an endogenous synchronizer of the liver oscillator in teleosts. To achieve this aim, we first examined the presence of ghrelin receptors in the liver of goldfish. Then, the ghrelin regulation of clock gene expression in the goldfish liver was studied. Finally, the possible involvement of the phospholipase C/protein kinase C (PLC/PKC) and adenylate cyclase/protein kinase A (AC/PKA) intracellular signalling pathways was investigated. Ghrelin receptor transcripts, ghs-r1a, are present in the majority of goldfish hepatic cells. Ghrelin induced the mRNA expression of the positive (gbmal1a, gclock1a) and negative (gper genes) elements of the main loop of the molecular clock machinery, as well as grev-erbα (auxiliary loop) in cultured liver. These effects were blocked, at least in part, by a ghrelin antagonist. Incubation of liver with a PLC inhibitor (U73122), a PKC activator (phorbol 12-myristate 13-acetate) and a PKC inhibitor (chelerythrine chloride) demonstrated that the PLC/PKC pathway mediates such ghrelin actions. Experiments with an AC activator (forskolin) and a PKA inhibitor (H89) showed that grev-erbα regulation could be due to activation of PKA. Taken together, the present results show for the first time in vertebrates a direct action of ghrelin on hepatic clock genes and support a role for this hormone as a temporal messenger in the entrainment of liver circadian functions.