First evidence for the presence of amino acid sensing mechanisms in the fish gastrointestinal tract

This study aimed to characterize amino acid sensing systems in the gastrointestinal tract (GIT) of the carnivorous fish model species rainbow trout. We observed that the trout GIT expresses mRNAs encoding some amino acid receptors described in mammals [calcium-sensing receptor (CaSR), G protein-coupled receptor family C group 6 member A (GPRC6A), and taste receptors type 1 members 1 and 2 (T1r1, T1r2)], while others [taste receptor type 1 member 3 (T1r3) and metabotropic glutamate receptors 1 and 4 (mGlur1, mGlur4)] could not be found. Then, we characterized the response of such receptors, as well as that of intracellular signaling mechanisms, to the intragastric administration of l-leucine, l-valine, l-proline or l-glutamate. Results demonstrated that casr, gprc6a, tas1r1 and tas1r2 mRNAs are modulated by amino acids in the stomach and proximal intestine, with important differences with respect to mammals. Likewise, gut amino acid receptors triggered signaling pathways likely mediated, at least partly, by phospholipase C β3 and β4. Finally, the luminal presence of amino acids led to important changes in ghrelin, cholecystokinin, peptide YY and proglucagon mRNAs and/or protein levels. Present results offer the first set of evidence in favor of the existence of amino acid sensing mechanisms within the fish GIT.

DOCKING MOLEKULER SENYAWA B-KAROTEN DALAM TANAMAN KELOR (Moringa Oleifera L.) SEBAGAI PENGHAMBAT ENZIM TIROSINASE DENGAN AUTODOCK – VINA

Hydroquinone has been used in cosmetics because of its whitening activity. In previous studies, B-carotene in Moringa plants was also known as an inhibitor of the tyrosinase enzyme. It is necessary to know how the interaction mechanism of B-carotene with tyrosinase (5M8N) and which compounds between hydroquinone and B-carotene provide computationally better activity as whitening. Tyrosinase was prepared using Discovery Studio Visualizer. Ligands were prepared using Autodock 4.2. Autodock-Vina is used for ligand docking between proteins. The result is the binding affinity (kcal/mol) of the ligand to protein. Visualization of docking between ligands and proteins using the Ligplot + Program with a 1 year license. Media used for the docking process is a computer with an Intel Core i7-3770 CPU with a speed of 3.40 GHz 8 cores, 1920x1080p resolution, VGA NVIDIA GeForce GTX 750, 8 GB RAM, Windows 8 64-bit. The docking results showed that the binding affinity of B-carotene to tyrosinase was -11.2 while hydroquinone with tyrosinase was -5.4 with RMSD 0. The results of visualization showed that B-carotene binds more amino acid receptors than hydroquinone. B-carotene in moringa has been shown to be active not only in wet laboratories, but also in dry laboratories.

Glutamine-induced signaling pathways via amino acid receptors in enteroendocrine L cell lines

Glucagon-like peptide-1 (GLP-1), secreted by gastrointestinal enteroendocrine L cells, induces insulin secretion and is important for glucose homeostasis. GLP-1 secretion is induced by various luminal nutrients, including amino acids. Intracellular Ca2+ and cAMP dynamics play an important role in GLP-1 secretion regulation; however, several aspects of the underlying mechanism of amino acid-induced GLP-1 secretion are not well characterized. We investigated the mechanisms underlying the L-glutamine-induced increase in Ca2+ and cAMP intracellular concentrations ([Ca2+]i and [cAMP]i, respectively) in murine enteroendocrine L cell line GLUTag cells. Application of L-glutamine to cells under low extracellular [Na+] conditions, which inhibited the function of the sodium-coupled L-glutamine transporter, did not induce an increase in [Ca2+]i. Application of G protein-coupled receptor family C group 6 member A and calcium-sensing receptor antagonist showed little effect on [Ca2+]i and [cAMP]i; however, taste receptor type 1 member 3 (TAS1R3) antagonist suppressed the increase in [cAMP]i. To elucidate the function of TAS1R3, which forms a heterodimeric umami receptor with taste receptor type 1 member 1 (TAS1R1), we generated TAS1R1 and TAS1R3 mutant GLUTag cells using the CRISPR/Cas9 system. TAS1R1 mutant GLUTag cells exhibited L-glutamine-induced increase in [cAMP]i, whereas some TAS1R3 mutant GLUTag cells did not exhibit L-glutamine-induced increase in [cAMP]i and GLP-1 secretion. These findings suggest that TAS1R3 is important for L-glutamine-induced increase in [cAMP]i and GLP-1 secretion. Thus, TAS1R3 may be coupled with Gs and related to cAMP regulation.

Sensitivity of Olfactory Sensory Neurons to food cues is tuned to nutritional states by Neuropeptide Y signalling

ABSTRACTBackgroundModulation of sensory perception by homeostatic feedback from physiological states is central to innate purposive behaviours. Olfaction is an important predictive modality for feeding-related behaviours and its modulation has been associated with hunger-satiety states. However, the mechanisms mapping internal states to chemosensory processing in order to modify behaviour are poorly understood.ResultsIn the zebrafish olfactory epithelium, a subset of olfactory sensory neurons (OSNs) and the terminal nerve projections express neuropeptide Y (NPY). We find that NPY signalling in the peripheral olfactory system of zebrafish is correlated with its nutritional state and is both necessary and sufficient for the olfactory perception of food related odorants. NPY activity dynamically modulates the microvillar OSN activation thresholds and acts cooperatively with amino acid signalling resulting in a switch-like increase in OSN sensitivity in starved animals. We suggest that cooperative activation of phospholipase C by convergent signalling from NPY and amino acid receptors is central to this heightened sensitivity.ConclusionsThis study provides ethologically relevant, physiological evidence for NPY signalling in peripheral modulation of OSN sensitivity to food-associated amino acid cues. We demonstrate sensory gating directly at the level of OSNs and identify a novel mechanistic framework for tuning olfactory sensitivity to prevailing energy states.

Inhibition of the mitochondrial pyruvate carrier protects from excitotoxic neuronal death

Glutamate is the dominant excitatory neurotransmitter in the brain, but under conditions of metabolic stress it can accumulate to excitotoxic levels. Although pharmacologic modulation of excitatory amino acid receptors is well studied, minimal consideration has been given to targeting mitochondrial glutamate metabolism to control neurotransmitter levels. Here we demonstrate that chemical inhibition of the mitochondrial pyruvate carrier (MPC) protects primary cortical neurons from excitotoxic death. Reductions in mitochondrial pyruvate uptake do not compromise cellular energy metabolism, suggesting neuronal metabolic flexibility. Rather, MPC inhibition rewires mitochondrial substrate metabolism to preferentially increase reliance on glutamate to fuel energetics and anaplerosis. Mobilizing the neuronal glutamate pool for oxidation decreases the quantity of glutamate released upon depolarization and, in turn, limits the positive-feedback cascade of excitotoxic neuronal injury. The finding links mitochondrial pyruvate metabolism to glutamatergic neurotransmission and establishes the MPC as a therapeutic target to treat neurodegenerative diseases characterized by excitotoxicity.