Báo cáo khoa học: Roles of prolactin-releasing peptide and RFamide related peptides in the control of stress and food intake potx

MINIREVIEW Roles of prolactin-releasing peptide and RFamide related peptides in the control of stress and food intake Yuki Takayanagi and Tatsushi Onaka Division of Brain and Neurophysiology, Department of Physiology, Jichi Medical University, Japan Introduction RFamide peptides, defined by their carboxy-terminal arginine (R) and amidated phenylalanine (F) residues (hence RFamide), were originally discovered in inverte- brates [1] and have recently been identified in verte- brates [2]. The first reported RFamide peptides in mammals were neuropeptide FF (NPFF) and neuro- peptide AF, which were later confirmed to be encoded on a single gene [3]. By applying a reverse pharmaco- logical approach, in which orphan G protein-coupled receptor ligands were identified by detecting signal transduction induced in cells expressing a targeted orphan G protein-coupled receptor after stimulation, prolactin-releasing peptide (PrRP) was identified to be a ligand of an orphan G protein-coupled receptor, GPR10 (hGR3 ⁄ UHR-1 ⁄ PRLHR) and to belong to the RFamide peptide [4]. Subsequently, by utilizing DNA databases, another gene for RFamide peptides was identified in mammals [5,6]. The RFamide peptides encoded by the gene were named RFamide related peptide (RFRP)-1 ⁄ NPSF and RFRP-3 ⁄ NPVF, which were found to be orthologs of avian peptide LPLRFa- mide. Thus, RFRPs are allocated into the LPXRFa- mide peptide family (X = L or Q). Several other RFamide peptides also have been discovered by a reverse pharmacological method and by DNA sequence database searching, and there are now five families of RFamide peptides known to exist in mammals: NPFF, PrRP, LPXRFamide, kisspeptin Keywords dorsomedial hypothalamus; energy consumption; energy metabolism; food intake; nucleus tractus solitarii; oxytocin; prolactin-releasing peptide; RFamide peptide; RFamide-related peptide; stress Correspondence T. Onaka, Division of Brain and Neurophysiology, Department of Physiology, Jichi Medical University, Shimotsuke-shi, Tochigi-ken 329-0498, Japan Fax: +81 285 44 8147 Tel: +81 285 58 7318 E-mail: tonaka@jichi.ac.jp (Received 13 June 2010, revised 2 September 2010, accepted 13 October 2010) doi:10.1111/j.1742-4658.2010.07932.x Subsequent to the isolation of the first recognized RFamide neuropeptide, FMRFamide, from the clam, a large number of these peptides have been identified. There are now five groups of RFamide peptides identified in mammals. RFamide peptides show diversity with respect to their N-termi- nal sequence and biological activity. RFamide peptides have been impli- cated in a variety of roles, including energy metabolism, stress and pain modulation, as well as effects in the neuroendocrine and cardiovascular systems. In the present minireview, we focus on prolactin-releasing peptide (PrRP) and RFamide related peptide (RFRP) with respect to their roles in the control of energy metabolism and stress responses. Both food intake and stressful stimuli activate PrRP neurons. The administration of PrRP affects energy metabolism and neuroendocrine systems. PrRP-deficient or PrRP receptor-deficient mice show abnormal energy metabolism and ⁄ or stress responses. On the other hand, RFRP neurons are activated by stress- ful stimuli and the administration of RFRP induces neuroendocrine and behavioral stress responses. Taken together, these data suggests that PrRP and RFRP neurons play a role in the control of energy metabolism and/or stress responses. Abbreviations ACTH, adrenocorticotropic hormone; CCK, cholecystokinin-8; CRH, corticotropin-releasing hormone; NPFF, neuropeptide FF; NTS, nucleus tractus solitarii; PrRP, prolactin-releasing peptide; QFRP, pyroglutamylated RFamide peptide; RFRP, RFamide related peptide. 4998 FEBS Journal 277 (2010) 4998–5005 ª 2010 The Authors Journal compilation ª 2010 FEBS (previously known as metastin) and pyroglutamylated RFamide peptide (QFRP) (Table 1). RFamide peptides show diversity in their N-terminal sequence and, as a result, a broad pattern of biological activities, includ- ing the control of energy metabolism and stress, as well as effects in the neuroendocrine and cardiovascu- lar systems. In the present minireview, we focus on PrRP and RFRP (Table 2) and review recent progress in research investigating the roles of these two peptides in the control of energy metabolism and stress. PrRP PrRP was considered to serve as a hypothalamic- releasing factor and to act on the anterior pituitary to stimulate prolactin release from the pituitary. However, no PrRP immunoreactivity was found in the external layer of the median eminence, from where classic hypothalamic hormones are released into the portal blood to control anterior pituitary hormone release. Thus, PrRP is not a classic hypothalamic hor- mone in mammals. Instead, PrRP appears to play an important role in the control of energy metabolism and stress [7]. Localization of PrRP and its receptors PrRP neurons are localized mostly in the nucleus trac- tus solitarii (NTS), with modest expression in the ven- trolateral medulla regions of the brainstem, and slight expression in the dorsomedial hypothalamus. In the medulla oblongata, PrRP expression is restricted to the Table 1. Summary of mammalian RFamide peptides and their receptors. The effects of administration of RFamide peptides upon stress responses (hormone release) and energy metabolism are also described. Family name Peptide in mammals Receptors Stress responses Energy metabolism Food intake Energy consumption NPFF NPFF NPAF GPR74 (NPFF-2, NPGPR, HLWAR77) Decrease in vasopressin release Decrease [51] Increase PrRP PrRP GPR10 (hGR3, UHR-1, PRLHR) Increase in the release of ACTH, oxytocin, vasopressin and prolactin Decrease Increase LPXRF RFRP-1 (NPSF) RFRP-3 (NPVF) GPR147 (NPFF-1, OT7T022, RFRPR) Increase in the release of ACTH, oxytocin and prolactin Increase ? ? Kisspeptin Kiss1 (metastin) GPR54 (OT7T175, AXOR12, KISS-1R) ? No effects ? QFRP QRFP (26 Rfa, P513) GPR103 (AQ27, SP9155) ? Increase [52,53] ? Table 2. Amino acid sequences of PrRP and RFRP in human, rats and mice are shown. *Deduced from the cDNA sequence. Peptide Species Number of of amino acids Sequence Reference PrRP Human 20 31 TPDINPAWYASRGIRPVGRF-NH 2 SRTHRHSMEIRTPDINPAWYASRGIRPVGRF-NH 2 [4]* [4]* Rat 20 31 TPDINPAWYTGRGIRPVGRF-NH 2 SRAHQHSMETRTPDINPAWYTGRGIRPVGRF-NH 2 [4]* [4]* Mouse 20 31 TPDINPAWYTGRGIRPVGRF-NH 2 SRAHQHSMETRTPDINPAWYTGRGIRPVGRF-NH 2 * * RFRP-1 (NPSF) Human 37 12 SLNFEELKDWGPKNVIKMSTPAVNKMPHSFANLPLRF-NH 2 MPHSFANLPLRF-NH 2 [5]* [5]*, [54] Rat 37 12 SVTFQELKDWGAKKDIKMSPAPANKVPHSAANLPLRF-NH 2 VPHSAANLPLRF-NH 2 [55] [5]* Mouse 37 12 SVSFQELKDWGAKKDIKMSPAPANKVPHSAANLPLRF-NH 2 VPHSAANLPLRF-NH 2 [5]* [5]* RFRP-3 (NPVF) Human 8 17 VPNLPQRF-NH 2 NMEVSLVRRVPNLPQRF-NH 2 [5]*, [54] [5]* Rat 18 ANMEAGTMSHFPSLPQRF-NH 2 [56] Mouse 17 or 18 (V)NMEAGTRSHFPSLPQRF-NH 2 [5]* Y. Takayanagi and T. Onaka PrRP and RFRPs in metabolism and stress FEBS Journal 277 (2010) 4998–5005 ª 2010 The Authors Journal compilation ª 2010 FEBS 4999 caudal A2 and A1 noradrenergic neurons. Immunohis- tochemical studies have shown that PrRP-immunoreac- tive fibers are widely distributed in the brain [8]. The main receptor for PrRP, GPR10, is also widely expressed in the brain (especially in the reticular nucleus of the thalamus, bed nucleus of the stria termi- nalis, preoptic areas, hypothalamic paraventricular nucleus, periventricular nucleus, dorsomedial hypothal- amus, NTS and area postrema) [9]. In addition to GPR10, PrRP has a high affinity for NPFF receptor 2 (also known as GPR74 ⁄ NPGPR ⁄ HLWAR77). NPFF receptor 2 is expressed in the dorsal horn of the spinal cord, thalamus, hypothalamus and hippocampus [10]. Although the physiological functions of NPFF recep- tor 2 activated by PrRP remain to be clarified, a recent study has proposed that central cardiovascular effects of PrRP are mediated via NPFF receptor 2 [11]. Role of PrRP in the control of energy metabolism: food intake Intracerebroventricular injection of PrRP reduces food intake [12]. Both PrRP-deficient mice [13] and GPR10- deficient mice [14] show hyperphagia. Acute inhibition of endogenous PrRP signaling by injections of neutral- izing monoclonal antibodies against PrRP also induces hyperphagia [13]. From experiments with PrRP-defi- cient mice or PrRP-neutralizing antibodies, PrRP has been shown to regulate meal size rather than meal fre- quency [13]. Meal size is regulated by satiety signals that terminate each meal, and one important satiety sig- nal is cholecystokinin-8 (CCK). CCK is released from the intestine in response to meals, and acts via the CCK A receptor on afferent vagal fibers that project into the medulla oblongata, which relays information into the hypothalamus. Food intake [13] or the administra- tion of CCK [15] activates PrRP neurons in the NTS. The anorectic effects of CCK are impaired in both PrRP-deficient mice [13] and GPR10-deficient mice [16], suggesting that PrRP relays satiety signaling of CCK. The downstream actions of PrRP neurons remain to be clarified. However, neurons expressing corticotro- pin-releasing hormone (CRH) or oxytocin may relay PrRP signaling to reduce food intake. Anatomical studies have shown that oxytocin neurons in the hypo- thalamus receive direct projections from PrRP neurons in the medulla oblongata. The administration of PrRP activates neurons expressing CRH or oxytocin in the hypothalamus, both of which are anorexic peptides. PrRP-induced anorexia is attenuated by a CRH recep- tor antagonist or oxytocin receptor antagonist [16]. Furthermore, an oxytocin receptor antagonist reduces the anorexic actions of CCK [17,18], and increases meal size [19]. Oxytocin receptor-deficient mice show an increased meal size [20]. Taken together, these results suggest that the PrRP-oxytocin system plays a pivotal role in relaying the satiety signaling of CCK. PrRP neurons in the brainstem and hypothalamus express leptin receptors [21]. Leptin regulates long-term energy metabolism. Leptin induces the expression of phosphorylated signal transducer and activator of transcription protein 3 in PrRP neurons, especially in the dorsomedial hypothalamus [13] (Fig. 1) and the anorectic effects of leptin are impaired in PrRP-defi- cient mice [13]. These data suggest that the anorectic effects of leptin signaling are mediated, at least in part, by PrRP. Role of PrRP in the control of energy metabolism: energy expenditure PrRP has also been associated with energy expendi- ture. An intracerebroventricular injection of PrRP Fig. 1. Activation of PrRP and RFRP neurons in the dorsomedial hypothalamus after stressful stimuli and leptin administration. The number of PrRP-immunoreactive neurons expressing Fos protein (the protein product of the immediate early gene, c-fos) or phos- phorylated signal transducer and activator of transcription 3 (i.e. a transcription factor downstream of leptin) after conditioned fear stimuli or leptin is shown (top). Both conditioned fear stimuli and leptin administration activate PrRP neurons in the dorsomedial hypothalamus. The number of RFRP-immunoreactive neurons expressing Fos protein after footshocks is shown (bottom). Foot- shocks activate RFRP neurons in the dorsomedial hypothalamus. Data are obtained from previous studies [13,27,48]. *P < 0.05, **P < 0.01, ***P < 0.001. PrRP and RFRPs in metabolism and stress Y. Takayanagi and T. Onaka 5000 FEBS Journal 277 (2010) 4998–5005 ª 2010 The Authors Journal compilation ª 2010 FEBS increases body temperature and oxygen consumption [12,22], although neither PrRP-deficient [13], nor GPR10- deficient male mice [23] show significant difference in oxygen consumption under basal conditions. PrRP- deficient mice also show no significant difference in core body temperature either at room temperature or after cold exposure [13]. Pair-fed PrRP-deficient mice show no obese phenotype and no significant difference in oxygen consumption [13], suggesting that endoge- nous PrRP is not important for regulating energy expenditure under resting conditions. On the other hand, obese GPR10-deficient female mice show slightly reduced oxygen consumption [23], suggesting that GPR10 might be important for regulating energy expenditure in females. Obesity has been reported to be more pronounced in female than in male GPR10- deficient mice. It is interesting to note that PrRP neu- rons in the brainstem express estrogen receptors and that PrRP expression in the brainstem is higher in female than in male rats [24]. Thus, the function of PrRP-GPR10 system in the control of energy con- sumption might differ between sexes. PrRP has been suggested to be involved in energy consumption under stressful conditions. Stressful stim- uli increase oxygen consumption. This increase in oxy- gen consumption after stressful stimuli is lower in PrRP-deficient mice [25]. Stressful stimuli activate PrRP neurons, and thus it is possible that PrRP increases energy consumption under the conditions in which PrRP neurons are activated. Roles of PrRP in the control of stress responses PrRP neurons in the medulla oblongata and ⁄ or in the dorsomedial hypothalamus are activated by a variety of stressful stimuli [26], including restraint of body movement, conditioned fear [27] (Fig. 1), footshocks, hemorrhage [28], exercise [29] and inflammatory stress (e.g. lipopolysaccharide injection) [30]. PrRP neurons have been suggested to be involved in neuroendocrine responses to stress. PrRP neurons project directly to CRH neurons and oxytocin neurons in the hypothala- mus [31]. An intracerebroventricular injection of PrRP activates CRH neurons and oxytocin neurons in the hypothalamus, and facilitates adrenocorticotropic hor- mone (ACTH) and oxytocin release into the systemic circulation. Blockade of endogenous PrRP signaling by the administration of PrRP-neutralizing antibodies reduces the activation of hypothalamic paraventricular neurons after noxious stimuli (formalin injection) [30] or reduces oxytocin release in response to conditioned fear [27], suggesting that endogenous PrRP has facilita- tive roles in neuroendocrine stress responses. On the other hand, the administration of PrRP-neutralizing antibodies facilitates ACTH release in response to exercise, suggesting that PrRP inhibits ACTH release in response to exercise [29]. Corticosterone release in response to restraint stress has been reported to be enhanced in PrRP-deficient mice [32]. These data sug- gest that PrRP has inhibitory effects on neuroendo- crine responses to stress. At present, the mechanisms underlying these apparent discrepant data remain to be clarified. However, the roles of PrRP in the control of stress responses may depend upon the nature of stressful stimuli used. Stressful stimuli affect food intake and increase energy expenditure. On the other hand, food intake affects stress responses [33]. PrRP-deficient mice show a lower increase in oxygen consumption after stressful stimuli [25], although the effects of stress on food intake and the effects of food intake on stress responses have not yet been examined in PrRP-defi- cient mice. PrRP might be involved in the integration in the control of energy metabolism and stress responses, whereas the underlying detailed mechanisms need further investigation. RFRP The mammalian members of the LPXRFamide peptide family are RFRP-1 and RFRP-3. RFRP-1 and RFRP- 3 are derived from a single precursor protein. Immu- nohistochemical studies have shown that single cells contain both RFRP-1 and RFRP-3. RFRP-1 and RFRP-3 bind with high affinity to a G protein-coupled receptor, GPR147 (also known as OT7T022, NPFF receptor 1 or RFRP receptor). In birds, peptides of the LPXRFamide family are termed gonadotropin inhibitory hormones. RFRPs have also been reported to serve a similar function in mammals [34]. The administration of RFRP-3 sup- presses plasma luteinizing hormone or follicle-stimulat- ing hormone concentrations in mammals. However, the mechanisms are not fully understood. RFRP-3 inhibits the activity of gonadotropin-releasing hormone neurons in the hypothalamus [35–37]. RFRP-3 has been also reported to act on pituitary gonadotrophs to inhibit luteinizing hormone or follicle-stimulating hor- mone release [38–40], although it is currently a matter of controversy as to whether RFRP-3 exerts a hypo- physiotropic role in mammals [37,41]. RFRP mRNA expression is not affected either by estrogen [42] or tes- tosterone [43], whereas RFRP neurons have been reported to express estrogen receptors [35]. The precise physiological roles of RFRP in the mammalian repro- ductive system need further investigation. Y. Takayanagi and T. Onaka PrRP and RFRPs in metabolism and stress FEBS Journal 277 (2010) 4998–5005 ª 2010 The Authors Journal compilation ª 2010 FEBS 5001 Localization of RFRPs and their receptors The RFRP gene is expressed in the caudal hypothala- mus, including the dorsomedial hypothalamus and the periventricular nucleus. Immunohistochemical studies have shown that RFRP-immunoreactive fibers are widely distributed within the brain [44]. Expression of the main receptor for RFRP, GPR147, is broadly dis- tributed within the brain, including the septal areas, amygdala, bed nucleus of the stria terminalis, hypotha- lamic paraventricular nucleus, dorsomedial hypothala- mus, ventromedial hypothalamus and the anterodorsal thalamic nucleus. Roles of RFRP in the control of food intake and stress responses The dorsomedial hypothalamus plays an important role in the control of energy metabolism [45]. Indeed, RFRPs have been suggested to contribute not only to the control of the reproductive system, but also to the control of energy balance. RFRP neurons project directly to cells expressing neuropeptide Y or pro-opio- melanocortin in the arcuate nucleus of the hypothala- mus, both of which are key molecules in the control of energy balance [46]. The administration of RFRPs induces Fos protein in the arcuate nucleus, which is a center for food intake, and stimulates food intake in rats [36,38]. However, food restriction does not change the expression of RFRP in Siberian hamsters [47]. The effects of RFRP upon energy consumption or oxygen consumption are not known. The downstream and physiological significance of orexigenic actions by RFRP remain to be determined. The involvement of RFRP in the control of stress responses has also been reported. The dorsomedial hypothalamus where RFRP neurons exist plays an important role in the control of stress responses as well as food intake [45]. Subsequent to stressful stimuli, the percentage of RFRP neurons expressing Fos protein [48] (Fig. 1) and the expression of RFRP mRNA in the hypothalamus are increased [49]. RFRP fibers are observed in the hypothalamic paraventricular nucleus and appear to project directly to cells containing CRH or oxytocin [46] in the hypothalamus. The administra- tion of RFRP increases Fos expression in the hypotha- lamic paraventricular nucleus and in hypothalamic oxytocin neurons, and facilitates the release of ACTH and oxytocin into the peripheral circulation. Similar patterns of Fos expression and hormone release are observed after stressful stimuli. Furthermore, the cen- tral application of RFRP-1 or RFRP-3 induces anxi- ety-related behavior [48]. Taken together, these data are consistent with the view that stressful stimuli acti- vate RFRP neurons and that RFRP-1 and RFRP-3 are involved in neuroendocrine and behavioral responses to stressful stimuli. RFRP neurons express glucocorticoid receptors and the administration of glucocorticoid increases the expression of RFRP mRNA in the hypothalamus [49]. Fig. 2. Possible neural pathways controlling stress and food intake by PrRP and RFRP. The PrRP and RFRP systems influence energy homeostasis and stress responses. The dorsomedial hypothalamus has direct connections to and from the limbic areas, other hypothalamic nuclei and the brainstem, which are involved in stress and energy balance. AMY, amygdala; ARC, arcuate nucleus; BST, bed nucleus of the stria terminalis; DMH, dorsomedial hypothalamus; LHA, lateral hypothalamic area; NTS, nucleus tractus solitarii (A2 noradrenergic region); PBN, parabrachial nucleus; POA, preoptic area; PVN, paraventricular nucleus; SCN, suprachiasmatic nucleus; VLM, ventrolateral medulla (A1 noradrenergic region); VMH, ventromedial hypothalamus. PrRP and RFRPs in metabolism and stress Y. Takayanagi and T. Onaka 5002 FEBS Journal 277 (2010) 4998–5005 ª 2010 The Authors Journal compilation ª 2010 FEBS RFRP neurons also express serotonin receptors and the number of RFRP neurons is increased after chronic administration of a selective serotonin reup- take inhibitor, citalopram [50]. Glucocorticoid and serotonin play major roles in the control of food intake and stress responses. The physiological func- tions of these receptors expressed in RFRP neurons remain to be determined. Conclusions Epidemiological studies have shown that both stress and obesity cause deleterious effects on human health. Obesity is caused by a positive energy balance. Stress- ful stimuli affect neurons in the brainstem and hypo- thalamus, and induce neuroendocrine and behavioral responses. Food intake also activates the brainstem and hypothalamus, resulting in the termination of meals and the induction of energy consumption. Energy homeostasis and stress interact with each other. Stress affects food intake and energy expenditure. On the other hand, energy balance conditions affect stress responses. As described in the present minireview, neu- rons expressing RFamide peptides receive information concerning both internal metabolic states and environ- mental conditions, and play a role in energy homeosta- sis and stress responses (Fig. 2). Thus, it is interesting to speculate that RFamide peptides are pivotal in interactions between stress and energy metabolism. 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Pathophys- iology 17, 135–140. 59 Onaka T, Kuramochi M, Saito J, Ueta Y & Yada T (2005) Galanin-like peptide stimulates vasopressin, oxytocin and adrenocorticotropic hormone release in rats. Neuroreport 16, 243–247. 60 Tanaka M (2010) Relaxin-3 ⁄ INSL7, a neuropeptide involved in the stress response and food intake. FEBS J 277, 4990–4997. Y. Takayanagi and T. Onaka PrRP and RFRPs in metabolism and stress FEBS Journal 277 (2010) 4998–5005 ª 2010 The Authors Journal compilation ª 2010 FEBS 5005 . MINIREVIEW Roles of prolactin-releasing peptide and RFamide related peptides in the control of stress and food intake Yuki Takayanagi and Tatsushi Onaka Division of Brain and Neurophysiology,. progress in research investigating the roles of these two peptides in the control of energy metabolism and stress. PrRP PrRP was considered to serve as a hypothalamic- releasing factor and to act on the. hypothalamus and the anterodorsal thalamic nucleus. Roles of RFRP in the control of food intake and stress responses The dorsomedial hypothalamus plays an important role in the control of energy