ABSTRACT
Orexins are hypothalamic peptides that play an important role in maintaining wakefulness in mammals. Permanent deficit in orexinergic function is a pathophysiological hallmark of rodent, canine and human narcolepsy. Here we report that in rats, dogs and humans, somnolence is induced by pharmacological blockade of both orexin OX(1) and OX(2) receptors. When administered orally during the active period of the circadian cycle, a dual antagonist increased, in rats, electrophysiological indices of both non-REM and, particularly, REM sleep, in contrast to GABA(A) receptor modulators; in dogs, it caused somnolence and increased surrogate markers of REM sleep; and in humans, it caused subjective and objective electrophysiological signs of sleep. No signs of cataplexy were observed, in contrast to the rodent, dog or human narcolepsy syndromes. These results open new perspectives for investigating the role of endogenous orexins in sleep-wake regulation.
Subject(s)
Acetamides/pharmacology , Hypothalamus, Posterior/drug effects , Intracellular Signaling Peptides and Proteins/metabolism , Isoquinolines/pharmacology , Neuropeptides/metabolism , Receptors, G-Protein-Coupled/antagonists & inhibitors , Receptors, Neuropeptide/antagonists & inhibitors , Signal Transduction/drug effects , Sleep, REM/drug effects , Tetrahydroisoquinolines/pharmacology , Acetamides/pharmacokinetics , Animals , Dogs , Electroencephalography , Female , Humans , Hypothalamus, Posterior/metabolism , Intracellular Signaling Peptides and Proteins/physiology , Isoquinolines/pharmacokinetics , Male , Neuropeptides/physiology , Orexin Receptors , Orexins , Rats , Sex Factors , Signal Transduction/physiology , Tetrahydroisoquinolines/pharmacokineticsABSTRACT
Urotensin-II (U-II) was identified as the natural ligand of the G protein-coupled receptor GPR14, which has been correspondingly renamed Urotensin-II receptor (U2R). The tissue distribution of U2R and the pharmacological effects of U-II suggest a novel neurohormonal system with potent cardiovascular effects. We here report the human rhabdomyosarcoma cell line TE-671 as the first natural and endogenous source of functional U2R in an immortalized cell line. In TE-671 cells, U-II stimulated extracellular signal regulated kinase phosphorylation and increased c-fos mRNA expression. Furthermore, we demonstrate that the expression of U2R mRNA and functional U-II high affinity binding sites are serum-responsive and that they are specifically up-regulated by interferon gamma (IFNgamma). We propose that IFNgamma contributes to the previously observed increase of U2R density in the heart tissue of congestive heart failure (CHF) patients and we suggest that U2R up-regulation, as a consequence of an inflammatory response, could lead to a clinical worsening of this disease.
Subject(s)
Interferon-gamma/metabolism , Receptors, G-Protein-Coupled/biosynthesis , Up-Regulation , Cell Line, Tumor , Cytokines/metabolism , Dose-Response Relationship, Drug , Humans , Immunoblotting , Inflammation , Mitogen-Activated Protein Kinase 1/metabolism , Mitogen-Activated Protein Kinase 3 , Mitogen-Activated Protein Kinases/metabolism , Phosphorylation , Protein Binding , Proto-Oncogene Proteins c-fos/metabolism , RNA, Messenger/metabolism , Reverse Transcriptase Polymerase Chain Reaction , Signal Transduction , Time Factors , Tissue DistributionABSTRACT
Urotensin-II (U-II), a vasoactive cyclic neuropeptide, was recently identified as the natural ligand for the G-protein coupled receptor GPR14. The expression pattern of U-II and GPR14 are consistent with a role as a neurohormonal regulatory system in cardiovascular homeostasis. Urotensin-II induces a rapid and short-lasting rise in intracellular calcium in recombinant GPR14 expressing cells. In the present study we show that U-II induces signal transduction pathways leading to the long-lasting activation of extracellular signal-regulated kinase 1/2 (ERK1/2) in chinese hamster ovary cells expressing human GPR14 (CHO-GPR14). Furthermore, we observed a growth-stimulating and PD98059 sensitive activity of U-II in CHO-GPR14 cells, but not CHO-K1 cells. The investigation of the GPR14 induced signal transduction pathways leading to ERKI/2 phosphorylation revealed a previously unsuspected role for G(i/o)-protein coupling and showed an involvement of phospatidylinositol-3-kinase, phospholipase C and calcium channel mediated mechanisms. Our results suggest that U-II and its receptor GPR14 may be involved in long-lasting physiological effects such as cardiovascular remodeling.
