Characterization of NMB, GRP and their receptors (BRS3, NMBR and GRPR) in chickens

Single nucleus/cell RNA-seq of the chicken hypothalamic-pituitary-ovarian axis offers new insights into the molecular regulatory mechanisms of ovarian development

The hypothalamic-pituitary-ovarian (HPO) axis represents a central neuroendocrine network essential for reproductive function. Despite its critical role, the intrinsic heterogeneity within the HPO axis across vertebrates and the complex intercellular interactions remain poorly defined. This study provides the first comprehensive, unbiased, cell type-specific molecular profiling of all three components of the HPO axis in adult Lohmann layers and Liangshan Yanying chickens. Within the hypothalamus, pituitary, and ovary, seven, 12, and 13 distinct cell types were identified, respectively. Results indicated that the pituitary adenylate cyclase activating polypeptide (PACAP), follicle-stimulating hormone (FSH), and prolactin (PRL) signaling pathways may modulate the synthesis and secretion of gonadotropin-releasing hormone (GnRH), FSH, and luteinizing hormone (LH) within the hypothalamus and pituitary. In the ovary, interactions between granulosa cells and oocytes involved the KIT, CD99, LIFR, FN1, and ANGPTL signaling pathways, which collectively regulate follicular maturation. The SEMA4 signaling pathway emerged as a critical mediator across all three tissues of the HPO axis. Additionally, gene expression analysis revealed that relaxin 3 (RLN3), gastrin-releasing peptide (GRP), and cocaine- and amphetamine regulated transcripts (CART, also known as CARTPT) may function as novel endocrine hormones, influencing the HPO axis through autocrine, paracrine, and endocrine pathways. Comparative analyses between Lohmann layers and Liangshan Yanying chickens demonstrated higher expression levels of GRP, RLN3, CARTPT, LHCGR, FSHR, and GRPR in the ovaries of Lohmann layers, potentially contributing to their superior reproductive performance. In conclusion, this study provides a detailed molecular characterization of the HPO axis, offering novel insights into the regulatory mechanisms underlying reproductive biology.

Pituitary transcriptome profile from laying period to incubation period of Changshun green-shell laying hens

BACKGROUND

Incubation behaviour, an instinct for natural breeding in poultry, is strictly controlled by the central nervous system and multiple neuroendocrine hormones and neurotransmitters, and is closely associated with the cessation of egg laying. Therefore, it is essential for the commercial poultry industry to clarify the molecular regulation mechanism of incubation behaviour. Here, we used high-throughput sequencing technology to examine the pituitary transcriptome of Changshun green-shell laying hen, a local breed from Guizhou province, China, with strong broodiness, in two reproductive stages, including egg-laying phase (LP) and incubation phase (BP). We also analyze the differences in gene expression during the transition from egg-laying to incubation, and identify critical pathways and candidate genes involved in controlling the incubation behaviour in the pituitary.

RESULTS

In this study, we demonstrated that a total of 2089 differently expressed genes (DEGs) were identified in the pituitary, including 842 up-regulated and 1247 down-regulated genes. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis revealed that steroid biosynthesis pathway and neuroactive ligand-receptor interaction were significantly enriched based on DEGs commonly identified in pituitary. Further analysis revealed that SRC, ITGB4, ITGB3, PIK3R3 and DRD2 may play crucial roles in the regulation of incubation behaviour.

CONCLUSIONS

We identified 2089 DEGs and the key signaling pathways which may be closely correlated with incubation in Changshun green-shell laying hens, and clarified the molecular regulation mechanism of incubation behaviour. Our results indicate the complexity and variety of differences in reproductive behaviour of different chicken breeds.

Characterization of relaxin 3 and its receptors in chicken: Evidence for relaxin 3 acting as a novel pituitary hormone

Mammalian relaxin (RLN) family peptides binding their receptors (RXFPs) play a variety of roles in many physiological processes, such as reproduction, stress, appetite regulation, and energy balance. In birds, although two relaxin family peptides (RLN3 and INSL5) and four receptors (RXFP1, RXFP2, RXFP2-like, and RXFP3) were predicated, their sequence features, signal properties, tissue distribution, and physiological functions remain largely unknown. In this study, using chickens as the experimental model, we cloned the cDNA of the cRLN3 gene and two receptor (cRXFP1 and cRXFP3) genes. Using cell-based luciferase reporter assays, we demonstrate that cRLN3 is able to activate both cRXFP1 and cRXFP3 for downstream signaling. cRXFP1, rather than cRXFP3, is a cognate receptor for cRLN3, which is different from the mammals. Tissue distribution analyses reveal that cRLN3 is highly expressed in the pituitary with lower abundance in the hypothalamus and ovary of female chicken, together with the detection that cRLN3 co-localizes with pituitary hormone genes LHB/FSHB/GRP/CART and its expression is tightly regulated by hypothalamic factors (GnRH and CRH) and sex steroid hormone (E2). The present study supports that cRLN3 may function as a novel pituitary hormone involving female reproduction.

Evidence for Neuropeptide W Acting as a Physiological Corticotropin-releasing Inhibitory Factor in Male Chickens

In vertebrates, adrenocorticotropin (ACTH), released by the pituitary gland, is a critical part of the stress axis and stress response. Generally, the biosynthesis and secretion of ACTH are controlled by both hypothalamic stimulatory factors and inhibitory factors [eg, ACTH-releasing inhibitory factor (CRIF)], but the identity of this CRIF remains unrevealed. We characterized the neuropeptide B (NPB)/neuropeptide W (NPW) system in chickens and found that NPW could directly target the pituitary to inhibit growth hormone (GH) and prolactin (PRL) secretion via neuropeptide B/W receptor 2 (NPBWR2), which is completely different from the mechanism in mammals. The present study first carried out a series of assays to investigate the possibility that NPW acts as a physiological CRIF in chickens. The results showed that (1) NPW could inhibit ACTH synthesis and secretion by inhibiting the 3',5'-cyclic adenosine 5'-monophosphate/protein kinase A signaling cascade in vitro and in vivo; (2) NPBWR2 was expressed abundantly in corticotrophs (ACTH-producing cells), which are located mainly in cephalic lobe of chicken pituitary, as demonstrated by single-cell RNA-sequencing, immunofluorescent staining, and fluorescence in situ hybridization; (3) dexamethasone could stimulate pituitary NPBWR2 and hypothalamic NPW expression in chicks, which was accompanied by the decease of POMC messenger RNA levels, as revealed by in vitro and subcutaneous injection assays; and (4) the temporal expression profiles of NPW-NPBWR2 pair in hypothalamus-pituitary axis and POMC in pituitary were almost unanimous in chicken. Collectively, these findings provide comprehensive evidence for the first time that NPW is a potent physiological CRIF in chickens that plays a core role in suppressing the activity of the stress axis.

Renin Cell Baroreceptor, a Nuclear Mechanotransducer Central for Homeostasis

[Figure: see text].

Single-Cell RNA Sequencing Analysis of Chicken Anterior Pituitary: A Bird's-Eye View on Vertebrate Pituitary

It is well-established that anterior pituitary contains multiple endocrine cell populations, and each of them can secrete one/two hormone(s) to regulate vital physiological processes of vertebrates. However, the gene expression profiles of each pituitary cell population remains poorly characterized in most vertebrate groups. Here we analyzed the transcriptome of each cell population in adult chicken anterior pituitaries using single-cell RNA sequencing technology. The results showed that: (1) four out of five known endocrine cell clusters have been identified and designated as the lactotrophs, thyrotrophs, corticotrophs, and gonadotrophs, respectively. Somatotrophs were not analyzed in the current study. Each cell cluster can express at least one known endocrine hormone, and novel marker genes (e.g., CD24 and HSPB1 in lactotrophs, NPBWR2 and NDRG1 in corticotrophs; DIO2 and SOUL in thyrotrophs, C5H11ORF96 and HPGDS in gonadotrophs) are identified. Interestingly, gonadotrophs were shown to abundantly express five peptide hormones: FSH, LH, GRP, CART and RLN3; (2) four non-endocrine/secretory cell types, including endothelial cells (expressing IGFBP7 and CFD) and folliculo-stellate cells (FS-cells, expressing S100A6 and S100A10), were identified in chicken anterior pituitaries. Among them, FS-cells can express many growth factors, peptides (e.g., WNT5A, HBEGF, Activins, VEGFC, NPY, and BMP4), and progenitor/stem cell-associated genes (e.g., Notch signaling components, CDH1), implying that the FS-cell cluster may act as a paracrine/autocrine signaling center and enrich pituitary progenitor/stem cells; (3) sexually dimorphic expression of many genes were identified in most cell clusters, including gonadotrophs and lactotrophs. Taken together, our data provides a bird's-eye view on the diverse aspects of anterior pituitaries, including cell composition, heterogeneity, cell-to-cell communication, and gene expression profiles, which facilitates our comprehensive understanding of vertebrate pituitary biology.

The gastrin-releasing peptide/bombesin system revisited by a reverse-evolutionary study considering Xenopus

Bombesin is a putative antibacterial peptide isolated from the skin of the frog, Bombina bombina. Two related (bombesin-like) peptides, gastrin-releasing peptide (GRP) and neuromedin B (NMB) have been found in mammals. The history of GRP/bombesin discovery has caused little attention to be paid to the evolutionary relationship of GRP/bombesin and their receptors in vertebrates. We have classified the peptides and their receptors from the phylogenetic viewpoint using a newly established genetic database and bioinformatics. Here we show, by using a clawed frog (Xenopus tropicalis), that GRP is not a mammalian counterpart of bombesin and also that, whereas the GRP system is widely conserved among vertebrates, the NMB/bombesin system has diversified in certain lineages, in particular in frog species. To understand the derivation of GRP system in the ancestor of mammals, we have focused on the GRP system in Xenopus. Gene expression analyses combined with immunohistochemistry and Western blotting experiments demonstrated that GRP peptides and their receptors are distributed in the brain and stomach of Xenopus. We conclude that GRP peptides and their receptors have evolved from ancestral (GRP-like peptide) homologues to play multiple roles in both the gut and the brain as one of the ‘gut-brain peptide’ systems.

Melanocortin Receptor 4 (MC4R) Signaling System in Nile Tilapia

The melanocortin receptor 4 (MC4R) signaling system consists of MC4R, MC4R ligands [melanocyte-stimulating hormone (MSH), adrenocorticotropin (ACTH), agouti-related protein (AgRP)], and melanocortin-2 receptor accessory protein 2 (MRAP2), and it has been proposed to play important roles in feeding and growth in vertebrates. However, the expression and functionality of this system have not been fully characterized in teleosts. Here, we cloned tilapia MC4R, MRAP2b, AgRPs (AgRP, AgRP2), and POMCs (POMCa1, POMCb) genes and characterized the interaction of tilapia MC4R with MRAP2b, AgRP, α-MSH, and ACTH in vitro. The results indicate the following. (1) Tilapia MC4R, MRAP2b, AgRPs, and POMCs share high amino acid identity with their mammalian counterparts. (2) Tilapia MRAP2b could interact with MC4R expressed in CHO cells, as demonstrated by Co-IP assay, and thus decrease MC4R constitutive activity and enhance its sensitivity to ACTH_1-40. (3) As in mammals, AgRP can function as an inverse agonist and antagonist of MC4R, either in the presence or absence of MRAP2b. These data, together with the co-expression of MC4R, MRAP2b, AgRPs, and POMCs in tilapia hypothalamus, suggest that as in mammals, ACTH/α-MSH, AgRP, and MRAP2 can interact with MC4R to control energy balance and thus play conserved roles in the feeding and growth of teleosts.

Characterization of the neuropeptide FF (NPFF) gene in chickens: evidence for a single bioactive NPAF peptide encoded by the NPFF gene in birds

The 2 structurally related peptides, neuropeptide FF (NPFF) and neuropeptide AF (NPAF), are encoded by the NPFF gene and have been identified as neuromodulators that regulate nociception and opiate-mediated analgesia via NPFF receptor (NPFFR2) in mammals. However, little is known about these 2 peptides in birds. In this study, we examined the structure, tissue expression profile, and functionality of NPAF and NPFF in chickens. Our results showed that: 1) unlike mammalian NPFF, NPFF from chicken and other avian species is predicted to produce a single bioactive NPAF peptide, whereas the putative avian NPFF peptide likely lacks activity due to the absence of functional RFamide motif at its C-terminus; 2) synthetic chicken (c-) NPAF can potently activate cNPFFR2 (and not cNPFFR1) expressed in HEK293 cells, as monitored by 3 cell-based luciferase reporter systems, indicating that cNPAF is a potent ligand for cNPFFR2, which activation could decrease intracellular cAMP levels and stimulate the MAPK/ERK signaling cascade; interestingly, gonadotropin-inhibitory hormone, a peptide sharing high structural similarity to NPAF, could specifically activate cNPFFR1 (but not cNPFFR2); 3) Quantitative real-time PCR revealed that cNPFF mRNA is widely expressed in chicken tissues with the highest level detected in the hypothalamus, whereas cNPFFR2 is expressed in all tissues examined with the highest level noted in the hypothalamus and anterior pituitary. Taken together, our data reveal that avian NPFF encodes a single bioactive NPAF peptide, which preferentially activates NPFFR2, and provides insights into potential structural and functional changes of NPFF-derived peptides during vertebrate evolution.

BRS3 in both MC4R- and SIM1-expressing neurons regulates energy homeostasis in mice

OBJECTIVE

Bombesin-like receptor 3 (BRS3) is an orphan receptor and Brs3 knockout mice develop obesity with increased food intake and reduced resting metabolic rate and body temperature. The neuronal populations contributing to these effects were examined.

METHODS

We studied energy metabolism in mice with Cre-mediated recombination causing 1) loss of BRS3 selectively in SIM1- or MC4R-expressing neurons or 2) selective re-expression of BRS3 from a null background in these neurons.

RESULTS

The deletion of BRS3 in MC4R neurons increased body weight/adiposity, metabolic efficiency, and food intake, and reduced insulin sensitivity. BRS3 re-expression in these neurons caused partial or no reversal of these traits. However, these observations were confounded by an obesity phenotype caused by the Mc4r-Cre allele, independent of its recombinase activity. The deletion of BRS3 in SIM1 neurons increased body weight/adiposity and food intake, but not to the levels of the global null. The re-expression of BRS3 in SIM1 neurons reduced body weight/adiposity and food intake, but not to wild type levels. The deletion of BRS3 in either MC4R- or SIM1-expressing neurons affected body temperature, with re-expression in either population reversing the null phenotype. MK-5046, a BRS3 agonist, increases light phase body temperature in wild type, but not Brs3 null, mice and BRS3 re-expression in either population restored response to MK-5046.

CONCLUSIONS

BRS3 in both MC4R- and SIM1-expressing neurons contributes to regulation of body weight/adiposity, insulin sensitivity, food intake, and body temperature.

Characterization of a novel thyrotropin-releasing hormone receptor, TRHR3, in chickens

The physiological roles of thyrotropin-releasing hormone (TRH) are proposed to be mediated by TRH receptors (TRHR), which have been divided into 3 subtypes, namely, TRHR1, TRHR2, and TRHR3, in vertebrates. Although 2 TRH receptors (TRHR1 and TRHR3) have been predicted to exist in birds, it remains unclear whether TRHR3 is a functional TRH receptor similar to TRHR1. Here, we reported the functionality and tissue expression of TRHR3 in chickens. The cloned chicken TRHR3 (cTRHR3) encodes a receptor of 387 amino acids, which shares high-amino-acid identities (63–80%) to TRHR3 of parrots, lizards, Xenopus tropicalis, and tilapia and comparatively lower sequence identities to chicken TRHR1 or mouse TRHR2. Using cell-based luciferase reporter assays and Western blot, we demonstrated that similar to chicken TRHR1 (cTRHR1), cTRHR3 expressed in HEK 293 cells can be potently activated by TRH and that its activation stimulates multiple signaling pathways, indicating both TRH receptors are functional. Quantitative real-time PCR revealed that cTRHR1 and cTRHR3 are widely, but differentially, expressed in chicken tissues, and their expression is likely controlled by promoters located upstream of exon 1, which display strong promoter activities in cultured DF-1 cells. cTRHR1 is highly expressed in the anterior pituitary and testes, while cTRHR3 is highly expressed in the muscle, testes, fat, pituitary, spinal cord, and many brain regions (including hypothalamus). These findings indicate that TRH actions are likely mediated by 2 TRH receptors in chickens. In conclusion, our data provide the first piece of evidence that both cTRHR3 and cTRHR1 are functional TRH receptors, which helps to elucidate the physiological roles of TRH in birds.

Endothelins (EDN1, EDN2, EDN3) and their receptors (EDNRA, EDNRB, EDNRB2) in chickens: Functional analysis and tissue distribution

Endothelins (EDNs) and their receptors (EDNRs) are reported to be involved in the regulation of many physiological/pathological processes, such as cardiovascular development and functions, pulmonary hypertension, neural crest cell proliferation, differentiation and migration, pigmentation, and plumage in chickens. However, the functionality, signaling, and tissue expression of avian EDN-EDNRs have not been fully characterized, thus impeding our comprehensive understanding of their roles in this model vertebrate species. Here, we reported the cDNAs of three EDN genes (EDN1, EDN2, EDN3) and examined the functionality and expression of the three EDNs and their receptors (EDNRA, EDNRB and EDNRB2) in chickens. The results showed that: 1) chicken (c-) EDN1, EDN2, and EDN3 cDNAs were predicted to encode bioactive EDN peptides of 21 amino acids, which show remarkable degree of amino acid sequence identities (91-95%) to their respective mammalian orthologs; 2) chicken (c-) EDNRA expressed in HEK293 cells could be preferentially activated by chicken EDN1 and EDN2, monitored by the three cell-based luciferase reporter assays, indicating that cEDNRA is a functional receptor common for both cEDN1 and cEDN2. In contrast, both cEDNRB and cEDNRB2 could be activated by all three EDN peptides with similar potencies, indicating that both receptors can function as common receptors for the three EDNs and share functional similarity. Moreover, activation of three EDNRs could stimulate intracellular calcium, MAPK/ERK, and cAMP/PKA signaling pathways. 3) qPCR assay revealed that cEDNs and cEDNRs are widely, but differentially, expressed in adult chicken tissues. Taken together, our data establishes a clear molecular basis to uncover the physiological/pathological roles of EDN-EDNR system in birds and helps to reveal the conserved actions of EDN-EDNR signaling across vertebrates.

Gastrin releasing peptide-induced satiety is associated with hypothalamic and brainstem changes in chicks

Gastrin releasing peptide (GRP) is involved in the stimulation of gastric acid release from the stomach. It also mediates effects on feeding behavior. It is associated with anorexigenic effects in both mammalian and avian species, but the mechanism of action is unknown in any species. The aim of the present study was thus to investigate the hypothalamic and brainstem mechanisms mediating GRP-induced satiety in chicks. In Experiment 1, chicks that received intracerebroventricular (ICV) injection of GRP reduced food intake for up to 150 min following injection and reduced water intake up to 120 min following injection. In Experiment 2, chicks that were food restricted following GRP injection did not reduce water intake. Alimentary canal transit time was not affected by GRP in Experiment 3. A behavior analysis was conducted in Experiment 4, revealing that GRP-treated chicks reduced feeding pecks. In Experiment 5, GRP-treated chicks had increased c-Fos immunoreactivity in the lateral hypothalamus, paraventricular nucleus, and arcuate nucleus of the hypothalamus, and the nucleus of the solitary tract. Collectively, these results demonstrate that central GRP causes anorexigenic effects that are associated with hypothalamic changes without affecting other behaviors.

Arginine vasotocin (AVT)/mesotocin (MT) receptors in chickens: Evidence for the possible involvement of AVT-AVPR1 signaling in the regulation of oviposition and pituitary prolactin expression

Two structurally related peptides, arginine vasotocin (AVT) and mesotocin (MT), are reported to regulate many physiological processes, such as anti-diuresis and oviposition in birds, and their actions are likely mediated by four AVT/MT receptors (AVPR1A, AVPR1B, MTR and AVPR2b), which are orthologous/paralogous to human AVPR1A, AVPR1B, OXTR and AVPR2 respectively. However, our knowledge regarding the functions of these avian AVT/MT receptors has been limited. Here, we examined the functionality and expression of these receptors in chickens and investigated the roles of AVT in the anterior pituitary. Our results showed that 1) AVPR1A, AVPR1B and AVPR2b could be preferentially activated by AVT, monitored by cell-based luciferase reporter assays and/or Western blot, indicating that they are AVT-specific receptors (AVPR1A; AVPR1B) or AVT-preferring receptor (AVPR2b) functionally coupled to intracellular calcium, MAPK/ERK and cAMP/PKA signaling pathways. In contrast, MTR could be activated by AVT and MT with similar potencies, indicating that MTR is a receptor common for both peptides; 2) Using qPCR, differential expression of the four receptors was found in chicken tissues including the oviduct and anterior pituitary. In particular, only AVPR1A is abundantly expressed in the uterus, suggesting its involvement in mediating AVT-induced oviposition. 3) In cultured chick pituitary cells, AVT could stimulate ACTH and PRL expression and secretion, an action likely mediated by AVPR1B and/or AVPR1A abundantly expressed in anterior pituitary. Collectively, our data helps to elucidate the roles of AVT/MT in birds, such as the 'oxytocic action' of AVT, which induces uterine muscle contraction during oviposition.

Regulation of Pituitary Cocaine- and Amphetamine-Regulated Transcript Expression and Secretion by Hypothalamic Gonadotropin-Releasing Hormone in Chickens

There is increasing evidence that cocaine- and amphetamine-regulated transcript (CART) peptide is abundantly expressed in the anterior pituitary of birds and mammals, suggesting that CART peptide may be a novel pituitary hormone and its expression and secretion is likely controlled by the hypothalamic factor(s). To substantiate this hypothesis, using chicken as an animal model, we examined the effects of gonadotropin-releasing hormone (GnRH) on pituitary CART secretion and expression and investigated whether GnRH could modulate plasma CART levels. The results showed that: (1) chicken GnRH (GnRH1 and GnRH2) could potently stimulate CART peptide secretion in intact pituitaries incubated in vitro, as detected by Western blot; (2) GnRH could also stimulate CART mRNA expression in cultured pituitary cells, as revealed by quantitative real-time polymerase chain reaction (qPCR) assay; (3) GnRH actions on pituitary CART expression and secretion are likely mediated by GnRH receptor coupled to the intracellular Ca²⁺, MEK/ERK, and cAMP/PKA signaling pathways; and (4) plasma CART levels are high in chickens at various developmental stages (1.2–3.5 ng/ml) and show an increasing trend towards sexual maturity, as detected by enzyme-linked immunosorbent assay (ELISA). Moreover, plasma CART levels could be significantly induced by intraperitoneal administration of GnRH in chicks. Taken together, our data provide the first collective evidence that CART peptide is a novel pituitary hormone and its expression and secretion are tightly controlled by hypothalamic GnRH, thus likely being an active player in the hypothalamic-pituitary-gonadal (HPG) axis.

Constitutively active BRS3 is a genuinely orphan GPCR in placental mammals

G protein-coupled receptors (GPCRs) play an important role in physiology and disease and represent the most productive drug targets. Orphan GPCRs, with their endogenous ligands unknown, were considered a source of drug targets and consequently attract great interest to identify their endogenous cognate ligands for deorphanization. However, a contrary view to the ubiquitous existence of endogenous ligands for every GPCR is that there might be a significant overlooked fraction of orphan GPCRs that function constitutively in a ligand-independent manner only. Here, we investigated the evolution of the bombesin receptor-ligand family in vertebrates in which one member-bombesin receptor subtype-3 (BRS3)-is a potential orphan GPCR. With analysis of 17 vertebrate BRS3 structures and 10 vertebrate BRS3 functional data, our results demonstrated that nonplacental vertebrate BRS3 still connects to the original ligands-neuromedin B (NMB) and gastrin-releasing peptide (GRP)-because of adaptive evolution, with significantly changed protein structure, especially in three altered key residues (Q127R, P205S, and R294H) originally involved in ligand binding/activation, whereas the placental mammalian BRS3 lost the binding affinity to NMB/GRP and constitutively activates Gs/Gq/G12 signaling in a ligand-independent manner. Moreover, the N terminus of placental mammalian BRS3 underwent positive selection, exhibiting significant structural differences compared to nonplacental vertebrate BRS3, and this domain plays an important role in constitutive activity of placental mammalian BRS3. In conclusion, constitutively active BRS3 is a genuinely orphan GPCR in placental mammals, including human. To our knowledge, this study identified the first example that might represent a new group of genuinely orphan GPCRs that will never be deorphanized by the discovery of a natural ligand and provided new perspectives in addition to the current ligand-driven GPCR deorphanization.

Identification of a Novel Functional Corticotropin-Releasing Hormone (CRH2) in Chickens and Its Roles in Stimulating Pituitary TSHβ Expression and ACTH Secretion

Corticotropin-releasing hormone (CRH), together with its structurally and functionally related neuropeptides, constitute the CRH family and play critical roles in multiple physiological processes. Recently, a novel member of this family, namely CRH2, was identified in vertebrates, however, its functionality and physiological roles remain an open question. In this study, using chicken (c-) as the animal model, we characterized the expression and functionality of CRH2 and investigated its roles in anterior pituitary. Our results showed that (1) cCRH2 cDNA is predicted to encode a 40-aa mature peptide, which shares a higher amino acid sequence identity to cCRH (63%) than to other CRH family peptides (23-38%); (2) Using pGL3-CRE-luciferase reporter system, we demonstrated that cCRH2 is ~15 fold more potent in activating cCRH receptor 2 (CRHR2) than cCRHR1 when expressed in CHO cells, indicating that cCRH2 is bioactive and its action is mainly mediated by CRHR2; (3) Quantitative real-time PCR revealed that cCRH2 is widely expressed in chicken tissues including the hypothalamus and anterior pituitary, and its transcription is likely controlled by promoters near exon 1, which display strong promoter activity in cultured DF-1 and HEK293 cells; (4) In cultured chick pituitary cells, cCRH2 potently stimulates TSHβ expression and shows a lower potency in inducing ACTH secretion, indicating that pituitary/hypothalamic CRH2 can regulate pituitary functions. Collectively, our data provides the first piece of evidence to suggest that CRH2 play roles similar, but non-identical, to those of CRH, such as its differential actions on pituitary, and this helps to elucidate the roles of CRH2 in vertebrates.

Brs3 neurons in the mouse dorsomedial hypothalamus regulate body temperature, energy expenditure, and heart rate, but not food intake

Bombesin-like receptor 3 (BRS3) is an orphan G protein-coupled receptor that regulates energy homeostasis and heart rate. We report that acute activation of Brs3-expressing neurons in the dorsomedial hypothalamus (DMH^Brs3) increased body temperature (Tb), brown adipose tissue temperature, energy expenditure, heart rate and blood pressure, with no effect on food intake or physical activity. Conversely, activation of Brs3 neurons in the paraventricular nucleus of the hypothalamus (PVH^Brs3) had no effect on Tb or energy expenditure, but suppressed food intake. Inhibition of DMH^Brs3 neurons decreased Tb and energy expenditure, suggesting a necessary role in Tb regulation. We found that the preoptic area provides major input (excitatory and inhibitory) to DMH^Brs3 neurons. Optogenetic stimulation of DMH^Brs3 projections to the raphe pallidus (RPa) increased Tb. Thus, DMH^Brs3→RPa neurons regulate Tb, energy expenditure and heart rate, and PVH^Brs3 neurons regulate food intake. Brs3 expression is a useful marker for delineating energy metabolism regulatory circuitry.

Effects of neuromedin B on steroidogenesis, cell proliferation and apoptosis in porcine Leydig cells

Neuromedin B (NMB), a mammalian bombesin-related peptide, has numerous physiological functions, including regulating hormone secretions, cell growth, and reproduction, by binding to its receptor (NMBR). In this study, we investigated the effects of NMB on testosterone secretion, steroidogenesis, cell proliferation, and apoptosis in cultured primary porcine Leydig cells. NMBR was mainly expressed in the Leydig cells of porcine testes, and a specific dose of NMB significantly promoted the secretion of testosterone in the primary Leydig cells; moreover, NMB increased the expression of mRNA and/or proteins of NMBR and steroidogenic mediators (steroidogenic acute regulatory (STAR), CYP11A1, and HSD3B1) in the Leydig cells. In addition, specific doses of NMB promoted the proliferation of Leydig cells and increased the expression of proliferating cell nuclear antigen and Cyclin B1 proteins, while suppressing Leydig cell apoptosis and decreasing BAX and Caspase-3 protein expression. These results suggest that the NMB/NMBR system might play an important role in regulating boar reproductive function by modulating steroidogenesis and/or cell growth in porcine Leydig cells.

The orphan G protein-coupled receptor 25 (GPR25) is activated by Apelin and Apela in non-mammalian vertebrates

G protein-coupled receptor 25 (GPR25) is an orphan G protein-coupled receptor in vertebrates, that has been implicated to be associated with autoimmune diseases and regulate blood pressure in humans. However, the endogenous ligand of GPR25 remains unknown in vertebrates. Here, we reported that in non-mammalian vertebrates (zebrafish, spotted gars, and pigeons), GPR25 could be activated by Apelin and Apela peptides, which are also the two endogenous ligands of vertebrate Apelin receptor (APLNR). Using the pGL3-CRE-luciferase reporter assay and confocal microscopy, we first demonstrated that like APLNR, zebrafish GPR25 expressing in HEK293 cells could be effectively activated by zebrafish Apelin and Apela peptides, leading to the inhibition of forskolin-stimulated cAMP production and receptor internalization. Like zebrafish GPR25, pigeon and spotted gar GPR25 could also be activated by Apelin and Apela, and their activation could inhibit forskolin-induced cAMP accumulation. Interestingly, unlike zebrafish (/spotted gar/pigeon) GPR25, human GPR25 could not be activated by Apelin and Apela under the same experimental conditions. RNA-seq analysis further revealed that GPR25 is expressed in a variety of tissues, including the testes and intestine of zebrafish/spotted gars/humans, implying the potential roles of GPR25 signaling in many physiological processes in vertebrates. Taken together, our data not only provides the first proof that the orphan receptor GPR25 possesses two potential ligands 'Apelin and Apela' and its activation decreases intracellular cAMP levels in non-mammalian vertebrates, but also facilitates to unravel the physiological roles of GPR25 signaling in vertebrates.

Characterization of neuromedin U (NMU), neuromedin S (NMS) and their receptors (NMUR1, NMUR2) in chickens

Neuromedin U (NMU) and its structurally-related peptide, neuromedin S (NMS), are reported to regulate many physiological processes and their actions are mediated by two NMU receptors (NMUR1, NMUR2) in mammals. However, the information regarding NMU, NMS, and their receptors is limited in birds. In this study, we examined the structure, functionality, and expression of NMS, NMU, NMUR1 and NMUR2 in chickens. The results showed that: 1) chicken (c-) NMU cDNA encodes a 181-amino acid precursor, which may generate two forms of NMU peptide with 9 (cNMU-9) and 25 amino acids (cNMU-25), respectively. 2) Interestingly, two cNMS transcripts encoding two cNMS precursors of different lengths were identified from chicken pituitary, and both cNMS precursors may produce a mature cNMS peptide of 9 amino acids (cNMS-9). 3) cNMU-9, cNMU-25 and cNMS-9 could activate cNMUR1 expressed in HEK293 cells potently, as monitored by three cell-based luciferase reporter systems, indicating that cNMUR1 can act as a receptor common for cNMU and cNMS peptides, whereas cNMUR2 could be potently activated by cNMS-9, but not by cNMU-9/cNMU-25. 4) cNMU and cNMUR1 are widely expressed in chicken tissues with abundant expression noted in the gastrointestinal tract, as detected by quantitative real-time PCR, whereas cNMUR2 expression is mainly restricted to the brain and anterior pituitary, and cNMS is widely expressed in chicken tissues. Collectively, our data helps to elucidate the physiological roles of NMU/NMS peptides in birds and reveal the functional conservation and changes of NMU/NMS-NMUR axis across vertebrates.

Dopamine D2-like receptors (DRD2 and DRD4) in chickens: Tissue distribution, functional analysis, and their involvement in dopamine inhibition of pituitary prolactin expression

Dopamine (DA) D2-like (and D1-like) receptors are suggested to mediate the dopamine actions in the anterior pituitary and/or CNS of birds. However, the information regarding the structure, functionality, and expression of avian D2-like receptors have not been fully characterized. In this study, we cloned two D2-like receptors (cDRD2, cDRD4) from chicken brain using RACE PCR. The cloned cDRD4 is a 378-amino acid receptor, which shows 57% amino acid (a.a.) identity with mouse DRD4. As in mammals, two cDRD2 isoforms, cDRD2L (long isoform, 437 a.a.) and cDRD2S (short isoform, 408 a.a.), which differ in their third intracellular loop, were identified in chickens. Using cell-based luciferase reporter assays or Western blot, we demonstrated that cDRD4, cDRD2L and cDRD2S could be activated by dopamine and quinpirole (a D2-like receptor agonist) dose-dependently, and their activation inhibits cAMP signaling pathway and stimulates MAPK/ERK signaling cascade, indicating that they are functional receptors capable of mediating dopamine actions. Quantitative real-time PCR revealed that cDRD2 and cDRD4 are widely expressed in chicken tissues with abundant expression noted in anterior pituitary, and their expressions are likely controlled by their promoters near exon 1, as demonstrated by dual-luciferase reporter assays in DF-1 cells. In accordance with cDRD2/cDRD4 expression in the pituitary, DA or quinpirole could partially inhibit vasoactive intestinal peptide-induced prolactin expression in cultured chick pituitary cells. Together, our data proves the functionality of DRD2 and DRD4 in birds and aids to uncover the conserved roles of DA/D2-like receptor system in vertebrates, such as its action on the pituitary.

Receptor-specific crosstalk between prostanoid E receptor 3 and bombesin receptor subtype 3

Bombesin receptor subtype 3 (BRS-3) is a GPCR that is expressed in the CNS, peripheral tissues, and tumors. Our understanding of BRS-3's role in physiology and pathophysiology is limited because its natural ligand is unknown. In an attempt to identify this ligand, we screened toad skin ( Bufo bufo gargarizans Cantor) extracts and identified prostaglandins as putative ligands. In BRS-3-transfected human embryonic kidney (HEK) cells, we found that prostaglandins, with prostaglandin E2 (PGE2) being the most potent, fulfill the pharmacologic criteria of affinity, selectivity, and specificity to be considered as agonists to the BRS-3 receptor. However, PGE2 is unable to activate BRS-3 in different cellular environments. We speculated that EP receptors might be the cause of this cellular selectivity, and we found that EP₃ is the receptor primarily responsible for the differential PGE2 effect. Consequently, we reconstituted the HEK environment in Chinese hamster ovary (CHO) cells and found that BRS-3 and EP₃ interact to potentiate PGE2 signaling. This potentiating effect is receptor specific, and it occurs only when BRS-3 is paired to EP₃. Our study represents an example of functional crosstalk between two distantly related GPCRs and may be of clinical importance for BRS-3-targeted therapies.-Zhang, Y., Liu, Y., Wu, L., Fan, C., Wang, Z., Zhang, X., Alachkar, A., Liang, X., Civelli, O. Receptor-specific crosstalk between prostanoid E receptor 3 and bombesin receptor subtype 3.

Characterization of the Apelin/Elabela Receptors (APLNR) in Chickens, Turtles, and Zebrafish: Identification of a Novel Apelin-Specific Receptor in Teleosts

Apelin receptor(s) (APLNR) are suggested to mediate the actions of apelin and Elabela (ELA) peptides in many physiological processes, including cardiovascular development and food intake in vertebrates. However, the functionality of APLNR has not been examined in most vertebrate groups. Here, we characterized two APLNRs APLNR1, APLNR2) in chickens and red-eared sliders, and three APLNRs in zebrafish (APLNR2a, APLNR2b, APLNR3a), which are homologous to human APLNR. Using luciferase-reporter assays or Western blot, we demonstrated that in chickens, APLNR1 (not APLNR2) expressed in HEK293 cells was potently activated by chicken apelin-36 and ELA-32 and coupled to Gi-cAMP and MAPK/ERK signaling pathways, indicating a crucial role of APLNR1 in mediating apelin/ELA actions; in red-eared sliders, APLNR2 (not APLNR1) was potently activated by apelin-36/ELA-32, suggesting that APLNR2 may mediate apelin/ELA actions; in zebrafish, both APLNR2a and APLNR2b were potently activated by apelin-36/ELA-32 and coupled to Gi-cAMP signaling pathway, as previously proposed, whereas the novel APLNR3a was specifically and potently activated by apelin. Similarly, an apelin-specific receptor (APLNR3b) sharing 57% sequence identity with zebrafish APLNR3a was identified in Nile tilapia. Collectively, our data facilitates the uncovering of the roles of APLNR signaling in different vertebrate groups and suggests a key functional switch between APLNR1 and APLNR2/3 in mediating the actions of ELA and apelin during vertebrate evolution.

Bombesin-like receptor 3 (Brs3) expression in glutamatergic, but not GABAergic, neurons is required for regulation of energy metabolism

Objective

Bombesin-like receptor 3 (BRS-3) is an orphan G protein-coupled receptor. Brs3 null mice have reduced resting metabolic rate and body temperature, increased food intake, and obesity. Here we study the role of Brs3 in different neuron types.

Methods

Mice able to undergo Cre recombinase-dependent inactivation or re-expression of Brs3 were generated, respectively Brs3^fl/y and Brs3^loxTB/y. We then studied four groups of mice with Brs3 selectively inactivated or re-expressed in cells expressing Vglut2-Cre or Vgat-Cre.

Results

Deletion of Brs3 in glutamatergic neurons expressing Vglut2 reproduced the global null phenotype for regulation of food intake, metabolic rate, body temperature, adiposity, and insulin resistance. These mice also no longer responded to a BRS-3 agonist, MK-5046. In contrast, deletion of Brs3 in GABAergic neurons produced no detectable phenotype. Conversely, the wild type phenotype was restored by selective re-expression of Brs3 in glutamatergic neurons, with no normalization achieved by re-expressing Brs3 in GABAergic neurons.

Conclusions

Brs3 expression in glutamatergic neurons is both necessary and sufficient for full Brs3 function in energy metabolism. In these experiments, no function was identified for Brs3 in GABAergic neurons. The data suggest that the anti-obesity pharmacologic actions of BRS-3 agonists occur via agonism of receptors on glutamatergic neurons.

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Brs3 in glutamatergic neurons regulates food intake, metabolic rate, and body weight.

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Brs3 in glutamatergic neurons is both necessary and sufficient for these functions.

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No phenotypes were identified by Brs3 loss or re-expression in GABAergic neurons.

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BRS-3 agonists likely act on glutamatergic neurons for their anti-obesity effects.