Androgenic down-regulation of urotensin II precursor, urotensin II-related peptide precursor and androgen receptor mRNA in the mouse spinal cord

Dynamic changes of urotensin II and its receptor during ovarian development of olive flounder Paralichthys olivaceus

Urotensin II (UII) is a kind of fish somatostatins cyclic peptide, which was originally extracted from the caudal neurosecretory system (CNSS). The system of UII and UII receptor (UIIR) has been reported to have multiple physiological regulatory functions, such as cardiovascular control, osmoregulation, and lipid metabolism. However, the effect of UII and UIIR on the ovarian development has not been covered. This study investigated the expression pattern of UII and UIIR in the ovarian follicles and explored their impact on ovarian development in olive flounder Paralichthys olivaceus. The results showed that the highest UII and UIIR mRNA levels were observed at stage II and stage III follicles during ovarian development, respectively. In situ hybridization revealed that a strong signal of UII was expressed in the oocyte nuclei of stage II follicles, however, UIIR was found in the follicle cells and oocyte cytoplasm of stage II and stage III follicles. Similarly, immunohistochemistry found positive signal of UII was detected in the oocyte nuclei of stage II follicles. The results from in vitro culture of olive flounder follicles suggested the expression of UII and UIIR mRNA levels significantly increased by 10 IU/ml human chorionic gonadotropin (hCG) for 9 h. Furthermore, the transcriptional expression of UII and UIIR was not statistically significantly changed by 17α, 20β-dihydroxy-4-pregnen-3-one (DHP). These results firstly suggested that UII and UII receptor may play vital roles in regulating ovarian growth in olive flounder.

Urotensin II-related peptide (Urp) is expressed in motoneurons in zebrafish, but is dispensable for locomotion in larva

The urotensin 2 (uts2) gene family consists of four paralogs called uts2, uts2-related peptide (urp), urp1 and urp2. uts2 is known to exert a large array of biological effects, including osmoregulation, control of cardiovascular functions and regulation of endocrine activities. Lately, urp1 and urp2 have been shown to regulate axial straightening during embryogenesis. In contrast, much less is known about the roles of urp. The aim of the present study was to investigate the expression and the functions of urp by using the zebrafish as a model. For this purpose, we determined the expression pattern of the urp gene. We found that urp is expressed in motoneurons of the brainstem and the spinal cord, as in tetrapods. This was confirmed with a new Tg(urp:gfp) fluorescent reporter line. We also generated a urp knockout mutant by using CRISPR/Cas9-mediated genome editing and analysed its locomotor activity in larvae. urp mutant did not exhibit any apparent defect of spontaneous swimming when compared to wild-type. We also tested the idea that urp may represent an intermediary of urp1 and urp2 in their role on axial straightening. We found that the upward bending of the tail induced by the overexpression of urp2 in 24-hpf embryos was not altered in urp mutants. Our results indicate that urp does probably not act as a relay downstream of urp2. In conclusion, the present study showed that zebrafish urp gene is primarily expressed in motoneurons but is apparently dispensable for locomotor activity in the early larval stages.

Characterization of four urotensin II receptors (UTS2Rs) in chickens

Urotensin II receptor (UTS2R) is suggested to mediate the actions of urotensin II (UTS2) and UTS2-related peptide (URP, also called UTS2B) in mammals. However, the information regarding the gene structure, functionality and tissue expression of UTS2/URP receptor remains largely unknown in non-mammalian vertebrates including birds. In this study, using RACE-PCR, we cloned the full-length cDNAs of four chicken UTS2/URP receptors and designated them as cUTS2R1, cUTS2R2, cUTS2R3 and cUTS2R5 respectively, according to their evolutionary origin. The cloned cUTS2R1, cUTS2R2, cUTS2R3 and cUTS2R5 are predicted to encode 7-transmembrane receptors of 382, 343, 331 and 363 amino acids respectively, which show 50-66 % amino acid sequence identity with human UTS2R. Using cell-based luciferase reporter assays and Western blot, we demonstrated that chicken UTS2Rs expressed in HEK293 cells could be effectively activated by synthetic chicken UTS2-12, UTS2-17 and URP peptides, and their activation can elevate intracellular calcium concentration and activate MAPK/ERK signaling cascade, indicating that the four UTS2Rs are functional and capable of mediating UTS2/URP actions in chickens. Quantitative real-time PCR revealed that the four receptors are widely, but differentially, expressed in adult chicken tissues, while cUTS2 and cURP are highly expressed in the hindbrain and spinal cord, and moderately/weakly expressed in other tissues examined including the spleen and gonads. Taken together, our data provide first piece of evidence that all four UTS2Rs are functional in an avian species and help to reveal the conserved roles of UTS2R signaling across vertebrates.

Urotensin-related gene transcripts mark developmental emergence of the male forebrain vocal control system in songbirds

Songbirds communicate through learned vocalizations, using a forebrain circuit with convergent similarity to vocal-control circuitry in humans. This circuit is incomplete in female zebra finches, hence only males sing. We show that the UTS2B gene, encoding Urotensin-Related Peptide (URP), is uniquely expressed in a key pre-motor vocal nucleus (HVC), and specifically marks the neurons that form a male-specific projection that encodes timing features of learned song. UTS2B-expressing cells appear early in males, prior to projection formation, but are not observed in the female nucleus. We find no expression evidence for canonical receptors within the vocal circuit, suggesting either signalling to other brain regions via diffusion or transduction through other receptor systems. Urotensins have not previously been implicated in vocal control, but we find an annotation in Allen Human Brain Atlas of increased UTS2B expression within portions of human inferior frontal cortex implicated in human speech and singing. Thus UTS2B (URP) is a novel neural marker that may have conserved functions for vocal communication.

Histomorphological changes in the common carotid artery of the male rat in induced hypogonadism

The role of androgens in the development of cardiovascular diseases remains controversial. The current study therefore sought to determine the changes in the histomorphology of the common carotid artery of the male rat in orchidectomy-induced hypogonadism. Twenty-two Rattus norvegicus male rats aged 2 months were used. The rats were randomly assigned into baseline (n=4), experimental (n=9), and control (n=9) groups. Hypogonadism was surgically induced in the experimental group by bilateral orchiectomy under local anesthesia. At experiment weeks 3, 6, and 9, three rats from each group (experimental and control) were euthanized, their common carotid artery harvested, and routine processing was done for paraffin embedding, sectioning, and staining. The photomicrographs were taken using a digital photomicroscope for morphometric analysis. Orchidectomy resulted in the development of vascular fibrosis, with a significant increase in collagen fiber density and decrease in smooth muscle and elastic fiber density. Moreover, there was development of intimal hyperplasia, with fragmentation of medial elastic lamellae in the common carotid artery of the castrated rats. Orchidectomy induces adverse changes in structure of the common carotid artery of the male rat. These changes may impair vascular function, therefore constituting a possible structural basis for the higher incidences of cardiovascular diseases observed in hypogonadism.

International Union of Basic and Clinical Pharmacology. XCII. Urotensin II, urotensin II-related peptide, and their receptor: from structure to function

Urotensin II (UII) is a cyclic neuropeptide that was first isolated from the urophysis of teleost fish on the basis of its ability to contract the hindgut. Subsequently, UII was characterized in tetrapods including humans. Phylogenetic studies and synteny analysis indicate that UII and its paralogous peptide urotensin II-related peptide (URP) belong to the somatostatin/cortistatin superfamily. In mammals, the UII and URP genes are primarily expressed in cholinergic neurons of the brainstem and spinal cord. UII and URP mRNAs are also present in various organs notably in the cardiovascular, renal, and endocrine systems. UII and URP activate a common G protein-coupled receptor, called UT, that exhibits relatively high sequence identity with somatostatin, opioid, and galanin receptors. The UT gene is widely expressed in the central nervous system (CNS) and in peripheral tissues including the retina, heart, vascular bed, lung, kidney, adrenal medulla, and skeletal muscle. Structure-activity relationship studies and NMR conformational analysis have led to the rational design of a number of peptidic and nonpeptidic UT agonists and antagonists. Consistent with the wide distribution of UT, UII has now been shown to exert a large array of biologic activities, in particular in the CNS, the cardiovascular system, and the kidney. Here, we review the current knowledge concerning the pleiotropic actions of UII and discusses the possible use of antagonists for future therapeutic applications.

Comparative distribution and in vitro activities of the urotensin II-related peptides URP1 and URP2 in zebrafish: evidence for their colocalization in spinal cerebrospinal fluid-contacting neurons

Urotensin II (UII) is an evolutionarily conserved neuropeptide initially isolated from teleost fish on the basis of its smooth muscle-contracting activity. Subsequent studies have demonstrated the occurrence of several UII-related peptides (URPs), such that the UII family is now known to include four paralogue genes called UII, URP, URP1 and URP2. These genes probably arose through the two rounds of whole genome duplication that occurred during early vertebrate evolution. URP has been identified both in tetrapods and teleosts. In contrast, URP1 and URP2 have only been observed in ray-finned and cartilaginous fishes, suggesting that both genes were lost in the tetrapod lineage. In the present study, the distribution of urp1 mRNA compared to urp2 mRNA is reported in the central nervous system of zebrafish. In the spinal cord, urp1 and urp2 mRNAs were mainly colocalized in the same cells. These cells were also shown to be GABAergic and express the gene encoding the polycystic kidney disease 2-like 1 (pkd2l1) channel, indicating that they likely correspond to cerebrospinal fluid-contacting neurons. In the hindbrain, urp1-expressing cells were found in the intermediate reticular formation and the glossopharyngeal-vagal motor nerve nuclei. We also showed that synthetic URP1 and URP2 were able to induce intracellular calcium mobilization in human UII receptor (hUT)-transfected CHO cells with similar potencies (pEC50=7.99 and 7.52, respectively) albeit at slightly lower potencies than human UII and mammalian URP (pEC50=9.44 and 8.61, respectively). The functional redundancy of URP1 and URP2 as well as the colocalization of their mRNAs in the spinal cord suggest the robustness of this peptidic system and its physiological importance in zebrafish.

Generation of BAC transgenic tadpoles enabling live imaging of motoneurons by using the urotensin II-related peptide (ust2b) gene as a driver

Xenopus is an excellent tetrapod model for studying normal and pathological motoneuron ontogeny due to its developmental morpho-physiological advantages. In mammals, the urotensin II-related peptide (UTS2B) gene is primarily expressed in motoneurons of the brainstem and the spinal cord. Here, we show that this expression pattern was conserved in Xenopus and established during the early embryonic development, starting at the early tailbud stage. In late tadpole stage, uts2b mRNA was detected both in the hindbrain and in the spinal cord. Spinal uts2b⁺ cells were identified as axial motoneurons. In adult, however, the uts2b expression was only detected in the hindbrain. We assessed the ability of the uts2b promoter to drive the expression of a fluorescent reporter in motoneurons by recombineering a green fluorescent protein (GFP) into a bacterial artificial chromosome (BAC) clone containing the entire X. tropicalis uts2b locus. After injection of this construction in one-cell stage embryos, a transient GFP expression was observed in the spinal cord of about a quarter of the resulting animals from the early tailbud stage and up to juveniles. The GFP expression pattern was globally consistent with that of the endogenous uts2b in the spinal cord but no fluorescence was observed in the brainstem. A combination of histological and electrophysiological approaches was employed to further characterize the GFP⁺ cells in the larvae. More than 98% of the GFP⁺ cells expressed choline acetyltransferase, while their projections were co-localized with α-bungarotoxin labeling. When tail myotomes were injected with rhodamine dextran amine crystals, numerous double-stained GFP⁺ cells were observed. In addition, intracellular electrophysiological recordings of GFP⁺ neurons revealed locomotion-related rhythmic discharge patterns during fictive swimming. Taken together our results provide evidence that uts2b is an appropriate driver to express reporter genes in larval motoneurons of the Xenopus spinal cord.

Molecular evolution of GPCRs: Somatostatin/urotensin II receptors

Somatostatin (SS) and urotensin II (UII) are members of two families of structurally related neuropeptides present in all vertebrates. They exert a large array of biological activities that are mediated by two families of G-protein-coupled receptors called SSTR and UTS2R respectively. It is proposed that the two families of peptides as well as those of their receptors probably derive from a single ancestral ligand-receptor pair. This pair had already been duplicated before the emergence of vertebrates to generate one SS peptide with two receptors and one UII peptide with one receptor. Thereafter, each family expanded in the three whole-genome duplications (1R, 2R, and 3R) that occurred during the evolution of vertebrates, whereupon some local duplications and gene losses occurred. Following the 2R event, the vertebrate ancestor is deduced to have possessed three SS (SS1, SS2, and SS5) and six SSTR (SSTR1-6) genes, on the one hand, and four UII (UII, URP, URP1, and URP2) and five UTS2R (UTS2R1-5) genes, on the other hand. In the teleost lineage, all these have been preserved with the exception of SSTR4. Moreover, several additional genes have been gained through the 3R event, such as SS4 and a second copy of the UII, SSTR2, SSTR3, and SSTR5 genes, and through local duplications, such as SS3. In mammals, all the genes of the SSTR family have been preserved, with the exception of SSTR6. In contrast, for the other families, extensive gene losses occurred, as only the SS1, SS2, UII, and URP genes and one UTS2R gene are still present.

Urotensin II receptor (UTR) exists in hyaline chondrocytes: a study of peripheral distribution of UTR in the African clawed frog, Xenopus laevis

Urotensin II (UII) and UII-related peptide (URP) exhibit diverse physiological actions including vasoconstriction, locomotor activity, osmoregulation, and immune response through UII receptor (UTR), which is expressed in the central nervous system and peripheral tissues of fish and mammals. In amphibians, only UII has been identified. As the first step toward elucidating the actions of UII and URP in amphibians, we cloned and characterized URP and UTR from the African clawed frog Xenopus laevis. Functional analysis showed that treatment of UII or URP with Chinese hamster ovary cells transfected with the cloned receptor increased the intracellular calcium concentration in a concentration-dependent manner, whereas the administration of the UTR antagonist urantide inhibited UII- or URP-induced Ca(2+) mobilization. An immunohistochemical study showed that UTR was expressed in the splenocytes and leukocytes isolated from peripheral blood, suggesting that UII and URP are involved in the regulation of the immune system. UTR was also localized in the apical membrane of the distal tubule of the kidney and in the transitional epithelial cells of the urinary bladder. This result supports the view that the UII/URP-UTR system plays an important role in osmoregulation of amphibians. Interestingly, immunopositive labeling for UTR was first detected in the chondrocytes of various hyaline cartilages (the lung septa, interphalangeal joint and sternum). The expression of UTR was also observed in the costal cartilage, tracheal cartilages, and xiphoid process of the rat. These novel findings probably suggest that UII and URP mediate the formation of the cartilaginous matrix.

Characterization of the true ortholog of the urotensin II-related peptide (URP) gene in teleosts

It has been recently established that the urotensin II (UII) family consists of four distinct paralogs in bony vertebrates, namely UII, and the three UII-related peptides (URPs) called URP, URP1 and URP2. These four peptides are encoded by genes which arose from the two rounds of tetraploidization (2R) which took place early during vertebrate evolution. Up to now, three of them, UII, URP1 and URP2, have been identified in teleosts, while only two, UII and URP, have been reported in tetrapods. The fact that fish URP has not been found in previous studies led to the suggestion that the corresponding gene had been lost in the teleost lineage. In the present study, we show that this view is not correct. A search of the most recent release of the Ensembl genome database led us to identify a novel UII/URP-like gene in teleosts. Using synteny analysis, we demonstrate that this gene corresponds to the true ortholog of the tetrapod URP gene. Molecular cloning of the corresponding cDNA in medaka revealed that URP gene encodes a putative peptide, with the primary structure GEPCFWKYCV. In stickleback, tilapia and takifugu, URP exhibited the same sequence while, in tetraodon, it differed by only one amino acid substitution Gly ↔ Ser. In zebrafish, URP appeared totally divergent at its N-terminus with the structure DDTCFWKYCV. In conclusion, the occurrence of a true URP in teleosts shows that the quartet of UII-related genes which arose from 2R has been integrally preserved in this lineage.

Occurrence of two distinct urotensin II-related peptides in zebrafish provides new insight into the evolutionary history of the urotensin II gene family

The urotensin II (UII) family is currently known to consist of two paralogous peptides, namely UII and UII-related peptide (URP). In contrast to UII, which has been identified in all vertebrate classes so far, URP has only been characterized in tetrapods. We report here the occurrence of two distinct URP genes in teleosts, which we have named URP1 and URP2. Synteny analysis revealed that teleost URP1 and URP2 genes and tetrapod URP genes represent three distinct paralog genes that, together with the UII gene, probably arose from the two rounds of tetraploidization, which took place early in vertebrate evolution. The absence of URP in fish indicates that the corresponding gene has been lost in the teleost lineage, whereas it is likely that both the URP1 and URP2 genes have been lost in the tetrapod lineage. Quantitative RT-PCR analysis revealed that the URP2 gene is mainly expressed in the spinal cord and the brain in adult zebrafish. In situ hybridization experiments showed that in zebrafish embryos, URP2 mRNA-containing cells are located in the floor plate of the neural tube. In adult, URP2-expressing cells occur in close contact with the ventral side of the ependymal canal along the whole spinal cord, whereas in the brain, they are located below the fourth ventricle. These URP-expressing cells may correspond to cerebrospinal fluid-contacting neurons. In conclusion, our study reveals the occurrence of four distinct UII paralogous systems in vertebrates that may exert distinct functions, both in tetrapods and teleosts.

Urotensin II, from fish to human

The cyclic peptide urotensin II (UII) was originally isolated from the urophysis of teleost fish on the basis of its ability to contract intestinal smooth muscle. The UII peptide has subsequently been isolated from frog brain and, later on, the pre-proUII cDNA has been characterized in mammals, including humans. A UII paralog called urotensin II-related peptide (URP) has been identified in the rat brain. The UII and URP genes originate from the same ancestral gene as the somatostatin and cortistatin genes. In the central nervous system (CNS) of tetrapods, UII is expressed primarily in motoneurons of the brainstem and spinal cord. The biological actions of UII and URP are mediated through a G protein-coupled receptor, termed UT, that exhibits high sequence similarity with the somatostatin receptors. The UT gene is widely expressed in the CNS and in peripheral organs. Consistent with the broad distribution of UT, UII and URP exert a large array of behavioral effects and regulate endocrine, cardiovascular, renal, and immune functions.

Characterization of urotensin II, distribution of urotensin II, urotensin II-related peptide and UT receptor mRNAs in mouse: evidence of urotensin II at the neuromuscular junction

Urotensin II (UII) and UII-related peptide (URP) are paralog neuropeptides whose existence and distribution in mouse have not yet been investigated. In this study, we showed by HPLC/RIA analysis that the UII-immunoreactive molecule in the mouse brain corresponds to a new UII(17) isoform. Moreover, calcium mobilization assays indicated that UII(17) and URP were equally potent in stimulating UII receptor (UT receptor). Quantitative RT-PCR and in situ hybridization analysis revealed that in the CNS UII and URP mRNAs were predominantly expressed in brainstem and spinal motoneurons. Besides, they were differentially expressed in the medial vestibular nucleus, locus coeruleus and the ventral medulla. In periphery, both mRNAs were expressed in skeletal muscle, testis, vagina, stomach, and gall bladder, whereas only URP mRNA could be detected in the seminal vesicle, heart, colon, and thymus. By contrast, the UT receptor mRNA was widely expressed, and notably, very high amounts of transcript occurred in skeletal muscle and prostate. In the biceps femoris muscle, UII-like immunoreactivity was shown to coexist with synaptophysin in muscle motor end plate regions. Altogether these results suggest that (i) UII and URP may have many redundant biological effects, especially at the neuromuscular junction; (ii) URP may more specifically participate to autonomic, cardiovascular and reproductive functions.

Behavioral actions of urotensin-II

Urotensin-II (U-II) and urotensin-II-related peptide (URP) have been identified as the endogenous ligands of the orphan G-protein-coupled receptor GPR14 now renamed UT. The occurrence of U-II and URP in the central nervous system, and the widespread distribution of UT in the brain suggest that U-II and URP may play various behavioral activities. Studies conducted in rodents have shown that central administration of U-II stimulates locomotion, provokes anxiety- and depressive-like states, enhances feeding activity and increases the duration of paradoxical sleep episodes. These observations indicate that, besides the endocrine/paracrine activities of U-II and URP on cardiovascular and kidney functions, these peptides may act as neurotransmitters and/or neuromodulators to regulate various neurobiological activities.

Comparative distribution of the mRNAs encoding urotensin I and urotensin II in zebrafish

The neural neurosecretory system of fishes produces two biologically active neuropeptides, i.e. the corticotropin-releasing hormone paralog urotensin I (UI) and the somatostatin-related peptide urotensin II (UII). In zebrafish, we have recently characterized two UII variants termed UIIalpha and UIIbeta. In the present study, we have investigated the distribution of UI, UIIalpha and UIIbeta mRNAs in different organs by quantitative RT-PCR analysis and the cellular localization of the three mRNAs in the spinal cord by in situ hybridization (ISH) histochemistry. The data show that the UI gene is mainly expressed in the caudal portion of the spinal cord and, to a lesser extent, in the brain, while the UIIalpha and the UIIbeta genes are exclusively expressed throughout the spinal cord. Single-ISH labeling revealed that UI, UIIalpha and UIIbeta mRNAs occur in large cells, called Dahlgren cells, located in the ventral part of the caudal spinal cord. Double-ISH staining showed that UI, UIIalpha and UIIbeta mRNAs occur mainly in distinct cells, even though a few cells were found to co-express the UI and UII genes. The differential expression of UI, UIIalpha and UIIbeta genes may contribute to the adaptation of Dahlgren cell activity during development and/or in various physiological conditions.

State-dependent calcium mobilization by urotensin-II in cultured human endothelial cells

Human endothelial cells express urotensin-II (U-II) as well as its receptor GPR14. Using microfluorimetric techniques, the effect of human U-II on cytosolic Ca2+ concentrations [Ca2+]i in cultured human aortic endothelial cells (HAECs) loaded with Fura-2 was evaluated in static or flow conditions. Under the static state, U-II (100 nM) abolished spontaneous Ca2+ oscillations, which occurred in a population of cultured HAEC. Similarly, U-II reduced thrombin-, but not ATP-induced calcium responses, suggesting that the peptide does not alter the Gq/11/IP3 pathway; rather, it modifies the coupling between protease-activated receptors and Gq/11/IP3. Under the flow condition, U-II (1, 10 and 100 nM) produced a dose-dependent increase in [Ca2+]i, which was subjected to desensitization. The result demonstrates a state-dependent effect of U-II in cultured HAEC, which may explain the variable responses to U-II under different experimental conditions.

Another ligand fishing for G protein-coupled receptor 14. Discovery of urotensin II-related peptide in the rat brain

Urotensin II (UII), which was originally isolated from the teleost urophysis, was identified as an endogenous ligand for orphan G protein-coupled receptor 14 (GPR14). The structure of mammalian UII was confirmed by isolation from spinal cord in porcine, or was easily predicted from the sequence of prepro-UII in human. For rat and mouse, however, only the tentative sequences of UII peptides have been demonstrated because the typical processing sites are absent from the amino-terminal region of the mature peptides. Isolation of UII-like immunoreactivity in rat brain revealed the presence of a novel peptide, designated urotensin II-related peptide (URP). URP binds and activates the human and rat urotensin II receptors (GPR14) and has a hypotensive effect when administrated to anesthetized rats. Based on the DNA sequences of the cloned prepro-URP gene, the amino acid sequences of mature URP for mouse and human are identical to that for rat URP. These results suggest that URP is the endogenous and functional ligand for urotensin II receptor in the rat and mouse, and possibly in the human.

Structure-activity relationships of urotensin II and URP

Urotensin II (U-II) and urotensin II-related peptide (URP) are the endogenous ligands for the orphan G-protein-coupled receptor GPR14 now renamed UT. At the periphery, U-II and/or URP exert a wide range of biological effects on cardiovascular tissues, airway smooth muscles, kidney and endocrine glands, while central administration of U-II elicits various behavioral and cardiovascular responses. There is also evidence that U-II and/or URP may be involved in a number of pathological conditions including heart failure, atherosclerosis, renal dysfunction and diabetes. Because of the potential involvement of the urotensinergic system in various physiopathological processes, there is need for the rational design of potent and selective ligands for the UT receptor. Structure-activity relationship studies have shown that the minimal sequence required to retain full biological activity is the conserved U-II(4-11) domain, in particular the Cys5 and Cys10 residues involved in the disulfide bridge, and the Phe6, Lys8 and Tyr9 residues. Free alpha-amino group and C-terminal COOH group are not necessary for the biological activity, and modifications of these radicals may even increase the stability of the analogs. Punctual substitution of native amino acids, notably Phe6 and Trp7, by particular residues generates analogs with antagonistic properties. These studies, which provide crucial information regarding the structural and conformational requirements for ligand-receptor interactions, will be of considerable importance for the design of novel UT ligands with increased selectivity, potency and stability, that may eventually lead to the development of innovative drugs.

Neuropeptide interactions and REM sleep: a role for Urotensin II?

Urotensin II (UII) is a peptide with structural similarity to the somatostatin family with potent vasoconstrictor activity. UII receptor is expressed broadly in the periphery, and most notably in the heart and microvessels. In the brain, the UII receptor can be detected in the spinal cord and in cholinergic nuclei in the brainstem known to be involved in REM sleep regulation. Recent data suggest that, in addition to their vasoactive properties, UII receptor ligands may have excitatory activity on a selective group of neurons that modulate REM sleep. This review focuses on the implications of these findings for the neurobiology of REM sleep regulation and discusses the possible impact of UII and other neuropeptides on the balance of the alternation between sleep states.

Biological properties and functional determinants of the urotensin II receptor

The urotensin II receptor (UT) is a member of the G protein-coupled receptor (GPCR) family and binds the cyclic undecapeptide urotensin II (U-II) as well as the octapeptide urotensin II-related peptide (URP). The active UT mediates pleiotropic effects through various signal transduction pathways, including coupling to G proteins and activating the mitogen-activated protein kinase pathway. Several highly conserved residues and motifs of class A GPCRs that are important for activity are found in UT. This review highlights some of the putative roles of these motifs in the binding, activation and desensitization of UT.

Effect of GABA A receptor activation on UT-coupled signaling pathways in rat cortical astrocytes

Cultured rat cortical astrocytes express two types of urotensin II (UII) binding sites: a high affinity site corresponding to the UT (GPR14) receptor and a low affinity site that has not been fully characterized. Activation of the high affinity site in astroglial cells stimulates polyphosphoinositide (PIP) turnover and provokes an increase in intracellular calcium concentration. We have hypothesized that the existence of distinct affinity sites for UII in rat cortical astrocytes could be accounted for by a possible cross-talk between UT and the ligand-gated ion channel GABA(A) receptor (GABA A R). Exposure of cultured astrocytes to UII provoked a bell-shaped increase in cAMP production, with an EC50 stimulating value of 0.83+/-0.04 pM, that was totally blocked in the presence of the adenylyl cyclase inhibitor SQ 22,536. In contrast, UII was found to inhibit forskolin-induced cAMP formation. In the presence of the specific PKA inhibitor H89, UII provoked a sustained stimulation of cAMP formation. Inhibition of PKA by H89 strongly reduced the stimulatory effect of UII on PIP metabolism. GABA and the GABA A R agonist isoguvacine provoked a marked inhibition of UII-induced cAMP synthesis and a significant reduction of UII-evoked PIP turnover. These data suggest that functional interaction between UT and GABA(A)R negatively regulates coupling of UT to the classical PLC/IP(3) signaling cascade as well as to the adenylyl cyclase/PKA pathway.

Cardiorenovascular effects of urotensin II and the relevance of the UT receptor

Urotensin II (U-II) is a vasoactive peptide with many potent effects in the cardiorenovascular system. U-II activates a G-protein-coupled receptor termed UT. UT and U-II are highly expressed in the cardiovascular and renal system. Patients with various cardiovascular diseases show high U-II plasma levels. It was demonstrated that elevated U-II plasma levels and increased UT expression seem to play a role in heart failure, end-stage renal disease and atherosclerosis. U-II induces potent changes in vascular tone regulation. In addition, U-II stimulates vascular smooth muscle cell proliferation and cardiomyocyte hypertrophy. Currently several pharmaceutical companies are developing compounds to control the U-II/UT system. There are preclinical and some clinical studies showing potential benefits of inhibiting U-II function in renal disease, heart failure, and diabetes. This article will review both pre- and clinical data concerning cardiorenovascular effects of U-II.

Structure-activity relationships of a novel series of urotensin II analogues: identification of a urotensin II antagonist

Urotensin II (U-II) is a potent vasoconstrictor peptide which has been identified as the endogenous ligand for the orphan G protein-coupled receptor GPR14 now renamed UT receptor. As the C-terminal cyclic hexapeptide of U-II (U-II(4-11), H-Asp-Cys-Phe-Trp-Lys-Tyr-Cys-Val-OH) possesses full biological activity, we have synthesized a series of U-II(4-11) analogues and measured their binding affinity on hGPR14-transfected CHO cells and their contractile activity on de-endothelialized rat aortic rings. The data indicate that a free amino group and a functionalized side-chain at the N-terminal extremity of the peptide are not required for biological activity. In addition, the minimal chemical requirement at position 9 of U-II(4-11) is the presence of an aromatic moiety. Most importantly, replacement of the Phe6 residue by cyclohexyl-Ala (Cha) led to an analogue, [Cha6]U-II(4-11), that was devoid of agonistic activity but was able to dose-dependently suppress the vasoconstrictor effect of U-II on rat aortic rings. These new pharmacological data, by providing further information regarding the structure-activity relationships of U-II analogues, should prove useful for the rational design of potent and nonpeptidic UT receptor agonists and antagonists.

Biochemical and functional characterization of high-affinity urotensin II receptors in rat cortical astrocytes

The urotensin II (UII) gene is primarily expressed in the central nervous system, but the functions of UII in the brain remain elusive. Here, we show that cultured rat astrocytes constitutively express the UII receptor (UT). Saturation and competition experiments performed with iodinated rat UII ([(125)I]rUII) revealed the presence of high- and low-affinity binding sites on astrocytes. Human UII (hUII) and the two highly active agonists hUII(4-11) and [3-iodo-Tyr9]hUII(4-11) were also very potent in displacing [(125)I]rUII from its binding sites, whereas the non-cyclic analogue [Ser5,10]hUII(4-11) and somatostatin-14 could only displace [(125)I]rUII binding at micromolar concentrations. Reciprocally, rUII failed to compete with [(125)I-Tyr0,D-Trp8]somatostatin-14 binding on astrocytes. Exposure of cultured astrocytes to rUII stimulated [(3)H]inositol incorporation and increased intracellular Ca(2+) concentration in a dose-dependent manner. The stimulatory effect of rUII on polyphosphoinositide turnover was abolished by the phospholipase C inhibitor U73122, but only reduced by 56% by pertussis toxin. The GTP analogue Gpp(NH)p caused its own biphasic displacement of [(125)I]rUII binding and provoked an affinity shift of the competition curve of rUII. Pertussis toxin shifted the competition curve towards a single lower affinity state. Taken together, these data demonstrate that rat astrocytes express high- and low-affinity UII binding sites coupled to G proteins, the high-affinity receptor exhibiting the same pharmacological and functional characteristics as UT.

Urotensin-II expression in the mouse spinal cord

Urotensin-II (UII), a 12 amino acid peptide, was discovered in the teleost fish neurosecretory cells located in the caudal portion of the spinal cord and which project to a neurohemal gland called the urophysis. The distribution of UII and of its prepro-UII mRNA is not limited to fish and was found for example in the rat spinal cord. In view of the potential interest of obtaining transgenic mice, we have therefore characterized the distribution of mouse pro-UII mRNA and UII immunoreactivity, by in situ hybridization and immunohistochemistry, respectively, in the mouse spinal cord. A population of UII-like immunoreactive cell bodies was located in the ventral horn of the different segments. These cells displayed all the features of motoneurons, as confirmed by a double immunohistochemical labelling showing the co-occurrence of UII and vesicular acetylcholine transporter, and by electron microscope immunocytochemistry. Retrograde labelling of motoneurons innervating the bulbocavernosus penile muscle showed that some of them contained UII. In situ hybridization histochemistry revealed that pro-UII mRNA was located in some ventral horn neuronal perikarya. The pro-UII mRNA-containing cell bodies possessed the same motoneuron characteristics, confirming the results of the immunohistochemical studies and showing that the gene of mouse UII is expressed in a subpopulation of motoneurons in the spinal cord. Our results support the assumption that UII peptide characterized as endocrine in fish is also expressed within mammalian motoneurons.

From heart to mind

The discovery of novel biologically active peptides has led to an explosion in our understanding of the molecular mechanisms that underlie the regulation of sleep and wakefulness. Urotensin II (UII), a peptide originally isolated from fish and known for its strong cardiovascular effects in mammals, is another surprising candidate in the regulatory network of sleep. The UII receptor was found to be expressed by cholinergic neurons of laterodorsal and pedunculopontine tegmental nuclei, an area known to be of utmost importance for the on- and offset of rapid eye movement (REM) sleep. Recently, physiological data have provided further evidence that UII is indeed a modulator of REM sleep. The peptide directly excites cholinergic mesopontine neurons and increases the rate of REM sleep episodes. These new results and its emerging behavioral effects establish UII as a neurotransmitter/neuromodulator in mammals and should spark further interest into the neurobiological role of the peptide.

A novel hypothalamic neuroendocrine peptide: URP (urotensin-II-related peptide)?

Urotensin-II-related peptide (URP) is an eight-amino-acid peptide recently isolated from rat brain and considered as the endogenous ligand for the urotensin-II receptor. Immunohistochemical treatment of mouse brain sections with anti-URP antibodies revealed numerous immunopositive fibres in the median eminence and vascular organ of the lamina terminalis as well as labelled cell bodies, mainly in the preoptic area. In consecutive serial sections, in situ hybridization demonstrated URP-mRNA in neuronal perikarya. Double-immunofluorescence labelling showed a co-localization of URP and GnRH in fibres and cell bodies. These results suggest the existence of URP as a novel hypothalamic neuroendocrine peptide co-localized and possible co-released with GnRH.