Biology of mammalian bombesin-like peptides and their receptors

Antipruritic effects of geraniol on acute and chronic itch via modulating spinal GABA/GRPR signaling

BACKGROUND AND PURPOSE

Itch (pruritus) is a common unpleasant feeling, often accompanied by the urge of scratching the skin. It is the main symptom of many systemic and skin diseases, which can seriously affect the patient's quality of life. Geraniol (GE; trans-3,7-dimethyl-2,6-octadien-1-ol) is a natural monoterpene with diverse effects, including anti-inflammatory, antioxidant, neuroprotective, anti-nociceptive, and anticancer properties. The study aims to examine the effects of GE on acute and chronic itch, and explore the underlying mechanisms.

METHODS

Acute itch was investigated by using Chloroquine and compound 48/80 induced model, followed by manifestation of diphenylcyclopropenone (DCP)-induced allergic contact dermatitis and the acetone-ether-water (AEW)-induced dry skin model in mice. The scratching behavior, skin thickness, c-Fos expression, and GRPR protein expression in the spinal cord were subsequently monitored and evaluated by behavioral tests as well as pharmacological and pharmacogenetic technologies.

RESULTS

Dose-dependent intraperitoneal injection of GE alleviated the acute itch, induced by chloroquine and compound 48/80, as well as increased the spinal c-Fos expression. Intrathecal administration of GE suppressed the GABAA receptor inhibitor bicuculline-induced itch, GRP-induced itch, and the GABAergic neuron inhibition-induced itch. Furthermore, the subeffective dose of bicuculline blocked the anti-pruritic effect of GE on the chloroquine and compound 48/80 induced acute itch. GE also attenuated DCP and AEW-induced chronic itch, as well as the increase of spinal GRPR expression in DCP mice.

CONCLUSION AND IMPLICATIONS

GE alleviates both acute and chronic itch via modulating the spinal GABA/GRPR signaling in mice. Findings of this study reveal that GE may provide promising therapeutic options for itch management. Also, considering the pivotal role of essential oils in aromatherapy, GE has great application potential in aromatherapy for treating skin diseases, and especially the skin with severe pruritus.

Hypothalamic response with PKA/CREB signaling is associated with direct cerebroventricular administration of bombesin-induced scratching

Bombesin (BN) is an itch-specific mediator that causes intense itch-scratching activity in mammals. Although most examinations of BN-induced itch processing have focused on the spinal cord, the involvement of central nervous system mechanisms remains unclear. Here, we investigated how relationships among hypothalamic regions regulate BN-mediated itch-scratch processes. We found that intracerebroventricular (i.c.v.) administration of BN (0.04-4 μg) elicited intense itch scratching in mice, whereas BN (0.4-400 μg) administered via intravenous tail injection failed to evoke a scratching response. Additionally, nalfurafine had no significant effects on BN-induced scratching behavior, indicating that central modulation of BN is distinct from histamine-mediated histaminergic itch and chloroquine-mediated non-histaminergic itch signaling pathways. We labeled BN with a fluorescent tag, 7-nitrobenz-2-oxa-1 (NBD), and traced its fluorescence in the hypothalamus for 30 min following i.c.v. NBD-BN administration. Accordingly, we confirmed that i.c.v. administration of BN enhanced c-Fos expression in the dorsal medial nucleus of the hypothalamus, where neuromedin B receptors and gastrin-releasing peptide receptors are highly expressed. Interestingly, in situ injection of BN into the hypothalamus immediately and robustly induced itch-scratching behavior. Moreover, gene transcripts and western blot assay revealed that BN receptor-dependent PKA/CREB signaling was upregulated in the hypothalamus after i.c.v. administration of BN. Consistently, pretreatment with a PKA inhibitor, Rp-cAMP, significantly reduced BN-induced scratching behavior. Our results indicate that the dorsal medial nucleus of the hypothalamus may be a key nucleus in mediating BN-mediated itch and hypothalamic PKA/CREB signaling is involved in regulating BN-mediated itch.

Regulatory Peptides in Asthma

Numerous regulatory peptides play a critical role in the pathogenesis of airway inflammation, airflow obstruction and hyperresponsiveness, which are hallmarks of asthma. Some of them exacerbate asthma symptoms, such as neuropeptide Y and tachykinins, while others have ameliorating properties, such as nociception, neurotensin or β-defensin 2. Interacting with peptide receptors located in the lungs or on immune cells opens up new therapeutic possibilities for the treatment of asthma, especially when it is resistant to available therapies. This article provides a concise review of the most important and current findings regarding the involvement of regulatory peptides in asthma pathology.

Discovery, Optimization, and Clinical Application of Natural Antimicrobial Peptides

Antimicrobial peptides (AMPs) are widespread in multicellular organisms. These structurally diverse molecules are produced as the first line of defense against pathogens such as bacteria, viruses, fungi, and parasites. Also known as host defense peptides in higher eukaryotic organisms, AMPs display immunomodulatory and anticancer activities. During the last 30 years, technological advances have boosted the research on antimicrobial peptides, which have also attracted great interest as an alternative to tackling the antimicrobial resistance scenario mainly provoked by some bacterial and fungal pathogens. However, the introduction of natural AMPs in clinical trials faces challenges such as proteolytic digestion, short half-lives, and cytotoxicity upon systemic and oral application. Therefore, some strategies have been implemented to improve the properties of AMPs aiming to be used as effective therapeutic agents. In the present review, we summarize the discovery path of AMPs, focusing on preclinical development, recent advances in chemical optimization and peptide delivery systems, and their introduction into the market.

Genomic Analysis of Spontaneous Abortion in Holstein Heifers and Primiparous Cows

Background: The objectives of this study were to identify loci, positional candidate genes, gene-sets, and pathways associated with spontaneous abortion (SA) in cattle and compare these results with previous human SA studies to determine if cattle are a good SA model for humans. Pregnancy was determined at gestation day 35 for Holstein heifers and cows. Genotypes from 43,984 SNPs of 499 pregnant heifers and 498 pregnant cows that calved at full term (FT) were compared to 62 heifers and 28 cows experiencing SA. A genome-wide association analysis, gene-set enrichment analysis–single nucleotide polymorphism, and ingenuity pathway analysis were used to identify regions, pathways, and master regulators associated with SA in heifers, cows, and a combined population. Results: Twenty-three loci and 21 positional candidate genes were associated (p < 1 × 10⁻⁵) with SA and one of these (KIR3DS1) has been associated with SA in humans. Eight gene-sets (NES > 3.0) were enriched in SA and one was previously reported as enriched in human SA. Four master regulators (p < 0.01) were associated with SA within two populations. Conclusions: One locus associated with SA was validated and 39 positional candidate and leading-edge genes and 2 gene-sets were enriched in SA in cattle and in humans.

Calcitonin Gene-Related Peptide Negatively Regulates Alarmin-Driven Type 2 Innate Lymphoid Cell Responses

Neuroimmune interactions have emerged as critical modulators of allergic inflammation, and type 2 innate lymphoid cells (ILC2s) are an important cell type for mediating these interactions. Here, we show that ILC2s expressed both the neuropeptide calcitonin gene-related peptide (CGRP) and its receptor. CGRP potently inhibited alarmin-driven type 2 cytokine production and proliferation by lung ILC2s both in vitro and in vivo. CGRP induced marked changes in ILC2 expression programs in vivo and in vitro, attenuating alarmin-driven proliferative and effector responses. A distinct subset of ILCs scored highly for a CGRP-specific gene signature after in vivo alarmin stimulation, suggesting CGRP regulated this response. Finally, we observed increased ILC2 proliferation and type 2 cytokine production as well as exaggerated responses to alarmins in mice lacking the CGRP receptor. Together, these data indicate that endogenous CGRP is a critical negative regulator of ILC2 responses in vivo.

How Gastrin-Releasing Peptide Opens the Spinal Gate for Itch

Spinal transmission of pruritoceptive (itch) signals requires transneuronal signaling by gastrin-releasing peptide (GRP) produced by a subpopulation of dorsal horn excitatory interneurons. These neurons also express the glutamatergic marker vGluT2, raising the question of why glutamate alone is insufficient for spinal itch relay. Using optogenetics together with slice electrophysiology and mouse behavior, we demonstrate that baseline synaptic coupling between GRP and GRP receptor (GRPR) neurons is too weak for suprathreshold excitation. Only when we mimicked the endogenous firing of GRP neurons and stimulated them repetitively to fire bursts of action potentials did GRPR neurons depolarize progressively and become excitable by GRP neurons. GRPR but not glutamate receptor antagonism prevented this action. Provoking itch-like behavior by optogenetic activation of spinal GRP neurons required similar stimulation paradigms. These results establish a spinal gating mechanism for itch that requires sustained repetitive activity of presynaptic GRP neurons and postsynaptic GRP signaling to drive GRPR neuron output.

•

Spinal itch relay requires effective communication from GRP to GRP receptor neurons

•

Single action potentials in GRP neurons fail to release sufficient GRP

•

Only burst firing releases enough GRP to prime GRP receptor neurons for activation

•

GRP acts as a volume transmitter probably explaining why itch is hard to localize

Immediate Release of Gastrin-Releasing Peptide Mediates Delayed Radiation-Induced Pulmonary Fibrosis

Radiation-induced pulmonary fibrosis (RTPF) is a progressive, serious condition in many subjects treated for thoracic malignancies or after accidental nuclear exposure. No biomarker exists for identifying the irradiated subjects most susceptible to pulmonary fibrosis (PF). Previously, we determined that gastrin-releasing peptide (GRP) was elevated within days after birth in newborns exposed to hyperoxia who later developed chronic lung disease. The goal of the current study was to test whether radiation (RT) exposure triggers GRP release in mice and whether this contributes to RTPF in vivo. We determined urine GRP levels and lung GRP immunostaining in mice 0 to 24 after post-thoracic RT (15 Gy). Urine GRP levels were significantly elevated between 24 hours post-RT; GRP-blocking monoclonal antibody 2A11, given minutes post-RT, abrogated urine GRP levels by 6 to 12 hours and also altered phosphoprotein signaling pathways at 24 hours post-RT. Strong extracellular GRP immunostaining was observed in lung at 6 hours post-RT. Mice given one dose of GRP monoclonal antibody 2A11 24 hours post-RT had significantly reduced myofibroblast accumulation and collagen deposition 15 weeks later, indicating protection against lung fibrosis. Therefore, elevation of urine GRP could be predictive of RTPF development. In addition, transient GRP blockade could mitigate PF in normal lung after therapeutic or accidental RT exposure.

Involvement of Gastrin-Releasing Peptide Receptor in the Regulation of Adipocyte Differentiation in 3T3-L1 Cells

Gastrin-releasing peptide (GRP), a member of bombesin-like peptides, and its receptor (GRP-R) play an important role in various physiological and pathological conditions. In this work, we investigated the role of GRP-R on adipogenesis in 3T3-L1 adipocytes. The expression of GRP-R was significantly increased during the adipocyte differentiation of 3T3-L1 cells. The inhibition of GRP-R by the antagonist RC-3095 affected adipogenesis in 3T3-L1 cells, which reduced lipid accumulation and regulated the expression of adipogenic genes. Moreover, cyclic AMP response element-binding protein (CREB) directly bound to the GRP-R promoter upon exposure to adipogenic stimuli. The down-regulation of GRP-R by the knockdown of CREB inhibited adipocyte differentiation of 3T3-L1 cells. Together these results suggest that the regulation of GRP-R activity or expression has an influence on adipogenesis through regulating adipogenic related genes.

Gastrin-releasing peptide promotes the migration of vascular smooth muscle cells through upregulation of matrix metalloproteinase-2 and -9

Gastrin-releasing peptide (GRP) has been reported to be implicated in the pathogenesis of inflammatory disorders. The migration and proliferation of vascular smooth muscle cells (VSMCs) are key components of vascular inflammation that leads to the development of atherosclerosis. The present study aimed to investigate the molecular effect of GRP on VSMC proliferation and migration. We report that GRP significantly enhanced the proliferation and migration of rat VSMCs. GRP increased mRNA and protein expression of matrix metalloproteinase-2 and -9 (MMP-2/9) in VSMCs. The induction of MMP-2/9 by GRP was regulated by the activation of the signal transducer and activator of transcription-3 (STAT3). In addition, STAT3-knockdown of VSMCs by siRNA or blockade of the GRP receptor inhibited GRP-induced migration of VSMCs. Taken together, our findings indicate that GRP promotes the migration of VSMCs through upregulation of MMP-2/9 via STAT3 activation.

Neuromedin B and its receptor silencing suppresses osteoclast generation by modulating precursor proliferation via M-CSF/c-Fms/D-type cyclins

Neuromedin B (NMB), a mammalian bombesin-like peptide, regulates diverse physiological processes, such as energy metabolism, memory and fear behavior, and cellular growth, through its cognate receptor, NMBR. In this study, we report that NMB expression was upregulated during osteoclast development and that silencing NMB or NMBR attenuated osteoclast generation mediated by macrophage colony-stimulating factor (M-CSF) and receptor activator of NF-κB ligand (RANKL). We found that knockdown of NMB or NMBR using a small hairpin RNA suppressed M-CSF-induced proliferation of osteoclast precursor cells without altering osteoclast differentiation. Interestingly, NMB or NMBR knockdown reduced the expression of the M-CSF receptor, c-Fms, which is an important modulator of osteoclast development. Consequently, NMB or NMBR silencing inhibited M-CSF/c-Fms-mediated downstream signaling pathways like activation of ERK and Akt and induction of D-type cyclins, cyclin D1 and D2. Moreover, knockdown of NMB or NMBR accelerated apoptosis in osteoclast lineage cells by inducing caspase-3, caspase-9, and Bim expression. In summary, our study demonstrates that the NMB/NMBR axis plays a pivotal role in osteoclast generation by modulating the proliferation and survival of osteoclast lineage cells.

Gastrin-releasing peptide induces monocyte adhesion to vascular endothelium by upregulating endothelial adhesion molecules

Gastrin-releasing peptide (GRP) is a neuropeptide that plays roles in various pathophysiological conditions including inflammatory diseases in peripheral tissues; however, little is known about whether GRP can directly regulate endothelial inflammatory processes. In this study, we showed that GRP promotes the adhesion of leukocytes to human umbilical vein endothelial cells (HUVECs) and the aortic endothelium. GRP increased the expression of intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) by activating nuclear factor-κB (NF-κB) in endothelial cells. In addition, GRP activated extracellular signal-regulated kinase 1/2 (ERK1/2), p38MAPK, and AKT, and the inhibition of these signaling pathways significantly reduced GRP-induced monocyte adhesion to the endothelium. Overall, our results suggested that GRP may cause endothelial dysfunction, which could be of particular relevance in the development of vascular inflammatory disorders.

Neuromedin B receptor antagonism inhibits migration, invasion, and epithelial-mesenchymal transition of breast cancer cells

Neuromedin B (NMB) acts as an autocrine growth factor and a pro-angiogenic factor. Its receptor, NMB receptor (NMB-R), is overexpressed in solid tumors. In the present study, we showed that an NMB-R antagonist, PD168368, suppresses migration and invasion of the human breast cancer cell line MDA-MB-231. In addition, PD168368 reduced epithelial-mesenchymal transition (EMT) of breast cancer cells by E-cadherin upregulation and vimentin downregulation. Moreover, we found that PD168368 potently inhibits in vivo metastasis of breast cancer. Taken together, these findings suggest that NMB-R antagonism may be an alternative approach to prevent breast cancer metastasis, and targeting NMB-R may provide a novel therapeutic strategy for breast cancer treatment.

Molecular basis for high affinity and selectivity of peptide antagonist, Bantag-1, for the orphan BB3 receptor

Bombesin-receptor-subtype-3 (BB3 receptor) is a G-protein-coupled-orphan-receptor classified in the mammalian Bombesin-family because of high homology to gastrin-releasing peptide (BB2 receptor)/neuromedin-B receptors (BB1 receptor). There is increased interest in BB3 receptor because studies primarily from knockout-mice suggest it plays roles in energy/glucose metabolism, insulin-secretion, as well as motility and tumor-growth. Investigations into its roles in physiological/pathophysiological processes are limited because of lack of selective ligands. Recently, a selective, peptide-antagonist, Bantag-1, was described. However, because BB3 receptor has low-affinity for all natural, Bn-related peptides, little is known of the molecular basis of its high-affinity/selectivity. This was systematically investigated in this study for Bantag-1 using a chimeric-approach making both Bantag-1 loss-/gain-of-affinity-chimeras, by exchanging extracellular (EC) domains of BB3/BB2 receptor, and using site-directed-mutagenesis. Receptors were transiently expressed and affinities determined by binding studies. Bantag-1 had >5000-fold selectivity for BB3 receptor over BB2/BB1 receptors and substitution of the first EC-domain (EC1) in loss-/gain-of affinity-chimeras greatly affected affinity. Mutagenesis of each amino acid difference in EC1 between BB3 receptor/BB2 receptor showed replacement of His(107) in BB3 receptor by Lys(107) (H107K-BB3 receptor-mutant) from BB2 receptor, decreased affinity 60-fold, and three replacements [H107K, E11D, G112R] decreased affinity 500-fold. Mutagenesis in EC1's surrounding transmembrane-regions (TMs) demonstrated TM2 differences were not important, but R127Q in TM3 alone decreased affinity 400-fold. Additional mutants in EC1/TM3 explored the molecular basis for these changes demonstrated in EC1, particularly important is the presence of aromatic-interactions by His(107), rather than hydrogen-bonding or charge-charge interactions, for determining Bantag-1 high affinity/selectivity. In regard to Arg(127) in TM3, both hydrogen-bonding and charge-charge interactions contribute to the high-affinity/selectivity for Bantag-1.

GRPR/PI3Kγ: Partners in Central Transmission of Itch

The gastrin-releasing peptide (GRP) and its receptor (GRPR) are important components of itch transmission. Upstream, but not downstream, aspects of GRPR signaling have been investigated extensively. We hypothesize that GRPR signals in part through the PI3Kγ/Akt pathway. We used pharmacological, electrophysiological, and behavioral approaches to further evaluate GRPR downstream signaling pathways. Our data show that GRP directly activates small-size capsaicin-sensitive DRG neurons, an effect that translates into transient calcium flux and membrane depolarization (∼ 20 mV). GRPR activation also induces Akt phosphorylation, a proxy for PI3Kγ activity, in ex vivo naive mouse spinal cords and in GRPR transiently expressing HEK293 cells. The intrathecal injection of GRP led to intense scratching, an effect largely reduced by either GRPR antagonists or PI3Kγ inhibitor. Scratching behavior was also induced by the intrathecal injection of an Akt activator. In a dry skin model of itch, we show that GRPR blockade or PI3Kγ inhibition reversed the scratching behavior. Altogether, these findings are highly suggestive that GRPR is expressed by the central terminals of DRG nociceptive afferents, which transmit itch via the PI3Kγ/Akt pathway.

SIGNIFICANCE STATEMENT

Itch is the most common symptom of the skin and is related to noncutaneous diseases. It severely impairs patients' quality of life when it becomes chronic and there is no specific or effective available therapy, mainly because itch pathophysiology is not completely elucidated. Our findings indicate that the enzyme PI3Kγ is a key central mediator of itch transmission. Therefore, we suggest PI3Kγ as an attractive target for the development of new anti-pruritic drugs. With this study, we take a step forward in our understanding of the mechanisms underlying the central transmission of itch sensation.

Bombesin related peptides/receptors and their promising therapeutic roles in cancer imaging, targeting and treatment

INTRODUCTION

Despite remarkable advances in tumor treatment, many patients still die from common tumors (breast, prostate, lung, CNS, colon, and pancreas), and thus, new approaches are needed. Many of these tumors synthesize bombesin (Bn)-related peptides and over-express their receptors (BnRs), hence functioning as autocrine-growth-factors. Recent studies support the conclusion that Bn-peptides/BnRs are well-positioned for numerous novel antitumor treatments, including interrupting autocrine-growth and the use of over-expressed receptors for imaging and targeting cytotoxic-compounds, either by direct-coupling or combined with nanoparticle-technology.

AREAS COVERED

The unique ability of common neoplasms to synthesize, secrete, and show a growth/proliferative/differentiating response due to BnR over-expression, is reviewed, both in general and with regard to the most frequently investigated neoplasms (breast, prostate, lung, and CNS). Particular attention is paid to advances in the recent years. Also considered are the possible therapeutic approaches to the growth/differentiation effect of Bn-peptides, as well as the therapeutic implication of the frequent BnR over-expression for tumor-imaging and/or targeted-delivery.

EXPERT OPINION

Given that Bn-related-peptides/BnRs are so frequently ectopically-expressed by common tumors, which are often malignant and become refractory to conventional treatments, therapeutic interventions using novel approaches to Bn-peptides and receptors are being explored. Of particular interest is the potential of reproducing with BnRs in common tumors the recent success of utilizing overexpression of somatostatin-receptors by neuroendocrine-tumors to provide the most sensitive imaging methods and targeted delivery of cytotoxic-compounds.

Pre-clinical evaluation of eight DOTA coupled gastrin-releasing peptide receptor (GRP-R) ligands for in vivo targeting of receptor-expressing tumors

Background

Overexpression of the gastrin-releasing peptide receptor (GRP-R) has been documented in several human neoplasms such as breast, prostate, and ovarian cancer. There is growing interest in developing radiolabeled peptide-based ligands toward these receptors for the purpose of in vivo imaging and radionuclide therapy of GRP-R-overexpressing tumors. A number of different peptide sequences, isotopes, and labeling methods have been proposed for this purpose. The aim of this work is to perform a direct side-by-side comparison of different GRP-R binding peptides utilizing a single labeling strategy to identify the most suitable peptide sequence.

Methods

Solid-phase synthesis of eight derivatives (BN1-8) designed based on literature analysis was carried out. Peptides were coupled to the DOTA chelator through a PEG4 spacer at the N-terminus. Derivatives were characterized for serum stability, binding affinity on PC-3 human prostate cancer cells, biodistribution in tumor-bearing mice, and gamma camera imaging at 1, 6, and 24 h after injection.

Results

Serum stability was quite variable among the different compounds with half-lives ranging from 16 to 400 min at 37 °C. All compounds tested showed K_d values in the nanomolar range with the exception of BN3 that showed no binding. Biodistribution and imaging studies carried out for compounds BN1, BN4, BN7, and BN8 showed targeting of the GRP-R-positive tumors and the pancreas. The BN8 compound (DOTA-PEG-DPhe-Gln-Trp-Ala-Val-NMeGly-His-Sta-Leu-NH₂) showed high affinity, the longest serum stability, and the highest target-to-background ratios in biodistribution and imaging experiments among the compounds tested.

Conclusions

Our results indicate that the NMeGly for Gly substitution and the Sta-Leu substitution at the C-terminus confer high serum stability while maintaining high receptor affinity, resulting in biodistribution properties that outperform those of the other peptides.

Insights into bombesin receptors and ligands: Highlighting recent advances

This following article is written for Prof. Abba Kastin's Festschrift, to add to the tribute to his important role in the advancement of the role of peptides in physiological, as well as pathophysiological processes. There have been many advances during the 35 years of his prominent role in the Peptide field, not only as editor of the journal Peptides, but also as a scientific investigator and editor of two volumes of the Handbook of Biological Active Peptides [146,147]. Similar to the advances with many different peptides, during this 35 year period, there have been much progress made in the understanding of the pharmacology, cell biology and the role of (bombesin) Bn receptors and their ligands in various disease states, since the original isolation of bombesin from skin of the European frog Bombina bombina in 1970 [76]. This paper will briefly review some of these advances over the time period of Prof. Kastin 35 years in the peptide field concentrating on the advances since 2007 when many of the results from earlier studies were summarized [128,129]. It is appropriate to do this because there have been 280 articles published in Peptides during this time on bombesin-related peptides and it accounts for almost 5% of all publications. Furthermore, 22 Bn publications we have been involved in have been published in either Peptides [14,39,55,58,81,92,93,119,152,216,225,226,231,280,302,309,355,361,362] or in Prof. Kastin's Handbook of Biological Active Peptides [137,138,331].

Bombesin receptor subtype 3 as a potential target for obesity and diabetes

INTRODUCTION

Diabetes mellitus and obesity are important health issues; increasing in prevalence, both in the USA and globally. There are only limited pharmacological treatments, and although bariatric surgery is effective, new effective pharmacologic treatments would be of great value. This review covers one area of increasing interest that could yield new novel treatments of obesity/diabetes mellitus. It involves recognition of the central role the G-protein-coupled receptor, bombesin receptor subtype 3 (BRS-3) plays in energy/glucose metabolism.

AREAS COVERED

Since the initial observation that BRS-3 knockout mice develop obesity, hypertension, impaired glucose metabolism and hyperphagia, there have been numerous studies of the mechanisms involved and the development of selective BRS-3 agonists/antagonists, which have marked effects on body weight, feeding and glucose/insulin homeostasis. In this review, each of these areas is briefly reviewed.

EXPERT OPINION

BRS-3 plays an important role in glucose/energy homeostasis. The development of potent, selective BRS-3 agonists demonstrates promise as a novel approach to treat obesity/diabetic states. One important question that needs to be addressed is whether BRS-3 agonists need to be centrally acting. This is particularly important in light of recent animal and human studies that report transient cardiovascular side effects with centrally acting oral BRS agonists.

Gastrointestinal peptides and itch sensation

PURPOSE OF REVIEW

To highlight the most recent advances regarding gastrointestinal peptides and their relation to chronic itch, with focus on gastrin-releasing peptide (GRP), substance P, and their respective receptors.

RECENT FINDINGS

GRP and its high-affinity GRP receptor (GRPR) have been identified as key regulators in the spinal cord itch pathway and may be involved in the maintenance of chronic itch sensation. Several neuropeptides including GRP, neuromedin B, and substance P regulate itch signals in a cooperative or inhibitory manner on the spinal level. Small clinical studies show that neurokinin 1 receptor antagonists might be of benefit in the treatment of chronic itch.

SUMMARY

Chronic itch is a burdensome clinical problem, for which no specific treatment is available. Studies on the mechanisms of pruriceptive sensation and its signaling to the central nervous system (CNS) via the spinal cord have elucidated a number of peptides that are implicated in the regulation of itch-specific signaling pathways. Among those, GRP and its high-affinity GRP receptor have been proposed as key elements in the itch-specific neuronal pathways.

Itch mechanisms and circuits

The itch-scratch reflex serves as a protective mechanism in everyday life. However, chronic persistent itching can be devastating. Despite the clinical importance of the itch sensation, its mechanism remains elusive. In the past decade, substantial progress has been made to uncover the mystery of itching. Here, we review the molecules, cells, and circuits known to mediate the itch sensation, which, coupled with advances in understanding the pathophysiology of chronic itching conditions, will hopefully contribute to the development of new anti-itch therapies.

The distribution and frequency of pulmonary neuroendocrine cells in Down syndrome fetal lungs

The pulmonary neuroendocrine cells (PNEC) are located in the epithelial lining of the airways and consist of solitary neuroendocrine cells (NEC) and NEC clusters, the neuroepithelial bodies (NEB). During fetal life, PNEC are the first to differentiate within the primitive airway epithelium, and bombesin expression favors branching of the respiratory tree. We investigated PNEC in Down syndrome (DS), where the lungs often show enlarged and reduced number of alveoli. Immunohistochemistry for bombesin and synaptophysin, PNEC markers, was evaluated in fetal lungs from 15 cases of DS and 11 age-matched controls from the 17th to 23rd week of gestation. Morphometric analysis assessed PNEC in the mucosal lining of each lung, expressed as number/mm. Nonparametric Mann-Whitney U test showed no statistical difference in frequency of PNEC in DS and controls. Our findings suggest that, at least in late second trimester, the distribution and frequency of PNEC in DS fetuses is not altered.

Connecting the dots: potential of data integration to identify regulatory SNPs in late-onset Alzheimer's disease GWAS findings

Late-onset Alzheimer's disease (LOAD) is a multifactorial disorder with over twenty loci associated with disease risk. Given the number of genome-wide significant variants that fall outside of coding regions, it is possible that some of these variants alter some function of gene expression rather than tagging coding variants that alter protein structure and/or function. RegulomeDB is a database that annotates regulatory functions of genetic variants. In this study, we utilized RegulomeDB to investigate potential regulatory functions of lead single nucleotide polymorphisms (SNPs) identified in five genome-wide association studies (GWAS) of risk and age-at onset (AAO) of LOAD, as well as SNPs in LD (r²≥0.80) with the lead GWAS SNPs. Of a total 614 SNPs examined, 394 returned RegulomeDB scores of 1–6. Of those 394 variants, 34 showed strong evidence of regulatory function (RegulomeDB score <3), and only 3 of them were genome-wide significant SNPs (ZCWPW1/rs1476679, CLU/rs1532278 and ABCA7/rs3764650). This study further supports the assumption that some of the non-coding GWAS SNPs are true associations rather than tagged associations and demonstrates the application of RegulomeDB to GWAS data.

Hypoxia regulates the expression of the neuromedin B receptor through a mechanism dependent on hypoxia-inducible factor-1α

The neuromedin B receptor (NMB-R), a member of the mammalian bombesin receptor family, is frequently overexpressed in various tumors. In the present study, we found that exposure to hypoxic conditions increases the levels of NMBR mRNA and protein in breast cancer cells, which are tightly regulated by hypoxia-inducible factor-1α (HIF-1α). We confirmed the effect of HIF-1α on NMBR transcription by performing an NMBR promoter-driven reporter assay and then identified a functional hypoxia-responsive element (HRE) in the human NMBR promoter region. Further, the binding of HIF-1α to the NMBR promoter was corroborated by electrophoretic mobility shift and chromatin immunoprecipitation assays, which showed that HIF-1α specifically and directly bound to the NMBR promoter in response to hypoxia. Immunohistochemical analysis of a xenograft and a human breast cancer tissue array revealed a significant correlation between NMB-R and HIF-1α expression. Taken together, our findings indicate that hypoxia induces NMB-R expression through a novel mechanism to regulate HIF-1α expression in breast cancer cells.

Stress and eating: a dual role for bombesin-like peptides

The current obesity “epidemic” in the developed world is a major health concern; over half of adult Canadians are now classified as overweight or obese. Although the reasons for high obesity rates remain unknown, an important factor appears to be the role stressors play in overconsumption of food and weight gain. In this context, increased stressor exposure and/or perceived stress may influence eating behavior and food choices. Stress-induced anorexia is often noted in rats exposed to chronic stress (e.g., repeated restraint) and access to standard Chow diet; associated reduced consumption and weight loss. However, if a similar stressor exposure takes place in the presence of palatable, calorie dense food, rats often consume an increase proportion of palatable food relative to Chow, leading to weight gain and obesity. In humans, a similar desire to eat palatable or “comfort” foods has been noted under stressful situations; it is thought that this response may potentially be attributable to stress-buffering properties and/or through activation of reward pathways. The complex interplay between stress-induced anorexia and stress-induced obesity is discussed in terms of the overlapping circuitry and neurochemicals that mediate feeding, stress and reward pathways. In particular, this paper draws attention to the bombesin family of peptides (BBs) initially shown to regulate food intake and subsequently shown to mediate stress response as well. Evidence is presented to support the hypothesis that BBs may be involved in stress-induced anorexia under certain conditions, but that the same peptides could also be involved in stress-induced obesity. This hypothesis is based on the unique distribution of BBs in key cortico-limbic brain regions involved in food regulation, reward, incentive salience and motivationally driven behavior.

Preclinical evaluation of a novel ¹¹¹In-labeled bombesin homodimer for improved imaging of GRPR-positive prostate cancer

Rational-designed multimerization of targeting ligands can be used to improve kinetic and thermodynamic properties. Multimeric targeting ligands may be produced by tethering multiple identical or two or more monomeric ligands of different binding specificities. Consequently, multimeric ligands may simultaneously bind to multiple receptor molecules. Previously, multimerization has been successfully applied on radiolabeled RGD peptides, which resulted in an improved tumor targeting activity in animal models. Multimerization of peptide-based ligands may improve the binding characteristics by increasing local ligand concentration and by improving dissociation kinetics. Here, we present a preclinical study on a novel radiolabeled bombesin (BN) homodimer, designated (111)In-DOTA-[(Aca-BN(7-14)]2, that was designed for enhanced targeting of gastrin-releasing peptide receptor (GRPR)-positive prostate cancer cells. A BN homodimer was conjugated with DOTA-NHS and labeled with (111)In. After HPLC purification, the GRPR targeting ability of (111)In-DOTA-[Aca-BN(7-14)]2 was assessed by microSPECT imaging in SCID mice xenografted with the human prostate cancer cell line PC-3. (111)In labeling of DOTA-[(Aca-BN(7-14)]2 was achieved within 30 min at 85 °C with a labeling yield of >40%. High radiochemical purity (>95%) was achieved by HPLC purification. (111)InDOTA-[Aca-BN(7-14)]2 specifically bound to GRPR-positive PC-3 prostate cancer cells with favorable binding characteristics because uptake of 111In-DOTA-[Aca-BN(7-14)]2 in GRPR-positive PC-3 cells increased over time. A maximum peak with 30% radioactivity was observed after 2 h of incubation. The log D value was -1.8 ± 0.1. (111)In-DOTA-[Aca-BN(7-14)]2 was stable in vitro both in PBS and human serum for at least 4 days. In vivo biodistribution analysis and microSPECT/CT scans performed after 1, 4, and 24 h of injection showed favorable binding characteristics and tumor-to-normal tissue ratios. This study identifies (111)In-DOTA-[(Aca-BN(7-14)]2 as a promising radiotracer for nuclear imaging of GRPR in prostate cancer.

Radiation-induced lung injury is mitigated by blockade of gastrin-releasing peptide

Gastrin-releasing peptide (GRP), secreted by pulmonary neuroendocrine cells, mediates oxidant-induced lung injury in animal models. Considering that GRP blockade abrogates pulmonary inflammation and fibrosis in hyperoxic baboons, we hypothesized that ionizing radiation triggers GRP secretion, contributing to inflammatory and fibrotic phases of radiation-induced lung injury (RiLI). Using C57BL/6 mouse model of pulmonary fibrosis developing ≥20 weeks after high-dose thoracic radiation (15 Gy), we injected small molecule 77427 i.p. approximately 1 hour after radiation then twice weekly for up to 20 weeks. Sham controls were anesthetized and placed in the irradiator without radiation. Lung paraffin sections were immunostained and quantitative image analyses performed. Mice exposed to radiation plus PBS had increased interstitial CD68(+) macrophages 4 weeks after radiation and pulmonary neuroendocrine cells hyperplasia 6 weeks after radiation. Ten weeks later radiation plus PBS controls had significantly increased pSmad2/3(+) nuclei/cm(2). GRP blockade with 77427 treatment diminished CD68(+), GRP(+), and pSmad2/3(+) cells. Finally, interstitial fibrosis was evident 20 weeks after radiation by immunostaining for α-smooth muscle actin and collagen deposition. Treatment with 77427 abrogated interstitial α-smooth muscle actin and collagen. Sham mice given 77427 did not differ significantly from PBS controls. Our data are the first to show that GRP blockade decreases inflammatory and fibrotic responses to radiation in mice. GRP blockade is a novel radiation fibrosis mitigating agent that could be clinically useful in humans exposed to radiation therapeutically or unintentionally.

Gastrointestinal hormones stimulate growth of Foregut Neuroendocrine Tumors by transactivating the EGF receptor

Foregut neuroendocrine tumors [NETs] usually pursuit a benign course, but some show aggressive behavior. The treatment of patients with advanced NETs is marginally effective and new approaches are needed. In other tumors, transactivation of the EGF receptor (EGFR) by growth factors, gastrointestinal (GI) hormones and lipids can stimulate growth, which has led to new treatments. Recent studies show a direct correlation between NET malignancy and EGFR expression, EGFR inhibition decreases basal NET growth and an autocrine growth effect exerted by GI hormones, for some NETs. To determine if GI hormones can stimulate NET growth by inducing transactivation of EGFR, we examined the ability of EGF, TGFα and various GI hormones to stimulate growth of the human foregut carcinoid,BON, the somatostatinoma QGP-1 and the rat islet tumor,Rin-14B-cell lines. The EGFR tyrosine-kinase inhibitor, AG1478 strongly inhibited EGF and the GI hormones stimulated cell growth, both in BON and QGP-1 cells. In all the three neuroendocrine cell lines studied, we found EGF, TGFα and the other growth-stimulating GI hormones increased Tyr(1068) EGFR phosphorylation. In BON cells, both the GI hormones neurotensin and a bombesin analogue caused a time- and dose-dependent increase in EGFR phosphorylation, which was strongly inhibited by AG1478. Moreover, we found this stimulated phosphorylation was dependent on Src kinases, PKCs, matrix metalloproteinase activation and the generation of reactive oxygen species. These results raise the possibility that disruption of this signaling cascade by either EGFR inhibition alone or combined with receptor antagonists may be a novel therapeutic approach for treatment of foregut NETs/PETs.

The structures of four bombesins and their cloned precursor-encoding cDNAs from acid-solvated skin secretion of the European yellow-bellied toad, Bombina variegata

Four different bombesins (bombesin, His(6)-bombesin, Phe(13)-bombesin and Asp(2)-, Phe(4)-SAP-bombesin) have been identified by a systematic sequencing study of peptides in reverse phase HPLC fractions of the skin secretion of the European yellow-bellied toad, Bombina variegata, that had been solvated in 0.1% (v/v) aqueous trifluoroacetic acid (TFA) and stored frozen at -20°C for 12 years. By using a 3'- and 5'-RACE PCR strategy, the corresponding biosynthetic precursor-encoding cDNAs of all four peptides were cloned from a cDNA library made from the same long-term frozen, acid-solvated skin secretion sample following thawing and lyophilization. Canonical bombesin and His(6)-bombesin are classical bombesin sub-family members, whereas Phe(13)-bombesin and Asp(2)-, Phe(4)-SAP-bombesin, belong to the litorin/ranatensin sub-family of bombesin-like peptides (BLPs). Assignment of these peptides to respective sub-families, was based upon both their primary structural similarities and their comparative pharmacological activities. An interesting observation in this study, was that the nucleotide sequences of the open-reading frames of cloned cDNAs encoding bombesin and its His(6)-substituted analog, were identical except for a single base that was responsible for the change observed at the position 6 residue in the mature peptide from Asn to His. In contrast, the precursor cDNA nucleotide sequences encoding the Phe(13)-bombesins, exhibited 53 base differences. The pharmacological activities of synthetic replicates of each bombesin were compared using two different mammalian smooth muscle preparations and all four peptides were found to be active. However, there were significant differences in their relative potencies.

The majority of dorsal spinal cord gastrin releasing peptide is synthesized locally whereas neuromedin B is highly expressed in pain- and itch-sensing somatosensory neurons

Background

Itch is one of the major somatosensory modalities. Some recent findings have proposed that gastrin releasing peptide (Grp) is expressed in a subset of dorsal root ganglion (DRG) neurons and functions as a selective neurotransmitter for transferring itch information to spinal cord interneurons. However, expression data from public databases and earlier literatures indicate that Grp mRNA is only detected in dorsal spinal cord (dSC) whereas its family member neuromedin B (Nmb) is highly expressed in DRG neurons. These contradictory results argue that a thorough characterization of the expression of Grp and Nmb is warranted.

Findings

Grp mRNA is highly expressed in dSC but is barely detectable in DRGs of juvenile and adult mice. Anti-bombesin serum specifically recognizes Grp but not Nmb. Grp is present in a small number of small-diameter DRG neurons and in abundance in layers I and II of the spinal cord. The reduction of dSC Grp after dorsal root rhizotomy is significantly different from those of DRG derived markers but similar to that of a spinal cord neuronal marker. Double fluorescent in situ of Nmb and other molecular markers indicate that Nmb is highly and selectively expressed in nociceptive and itch-sensitive DRG neurons.

Conclusion

The majority of dSC Grp is synthesized locally in dorsal spinal cord neurons. On the other hand, Nmb is highly expressed in pain- and itch-sensing DRG neurons. Our findings provide direct anatomic evidence that Grp could function locally in the dorsal spinal cord in addition to its roles in DRG neurons and that Nmb has potential roles in nociceptive and itch-sensitive neurons. These results will improve our understanding about roles of Grp and Nmb in mediating itch sensation.

Neuromedin B and its receptor influence the activity of myometrial primary cells in vitro through regulation of Il6 expression via the Rela/p65 pathway in mice

The neuromedin B receptor (Nmbr) is an important physiological regulator of spontaneous activities and stress responses through different cascades as well as its autocrine and paracrine effects. Previous studies have revealed that neuromedin B (Nmb) and its receptor signal via the Rela (also known as p65)/Il6 pathway in a mouse model of pregnancy. This study investigated the mechanism of Nmbr signaling via the Rela/p65-Il6 pathway and regulation of the concentration of intracellular free calcium ([Ca(2+)](i)) during the onset of labor in primary mouse myometrial cell cultures isolated from mice in term labor. Data demonstrated Nmbr agonist-mediated upregulation of the DNA binding activity of Rela/p65, Il6 expression, and [Ca(2+)](i) in a concentration-dependent manner. Furthermore, a significant correlation was observed between DNA binding activity of Rela/p65 and Il6 expression. Moreover, this up-regulation was blocked by Nmbr and Rela/p65 knockdown, achieved by RNA interference (RNAi) technology. No significant differences were identified in the inhibition of Il6 expression as a result of Nmbr or Rela/p65 knockdown. However, significant differences were observed between the [Ca(2+)](i) in Rela/p65-specific group and that in the Nmbr-specific small interfering RNA (siRNA)-treated groups. These data demonstrated that the Nmb/Nmbr interaction in pregnant myometrial primary cells in vitro predominantly influenced uterine activity through regulation of Il6 expression via the Rela/p65 pathway, although the effects of Nmbr on [Ca(2+)](i) involved several pathways that remain to be elucidated.

Biology and pharmacology of bombesin receptor subtype-3

PURPOSE OF REVIEW

This review summarizes the results of recent studies regarding the biology and pharmacology of novel synthetic agonists and antagonists of the bombesin receptor subtype-3 (BRS-3).

RECENT FINDINGS

All three mammalian bombesin receptors including gastrin-releasing peptide receptor, the neuromedin B receptor, and the BRS-3 have been shown to regulate energy balance and appetite and satiety. Studies indicate that the orphan BRS-3 is an important regulator of body weight, energy expenditure, and glucose homeostasis. Endogenous bombesin-like peptides bombesin, gastrin-releasing peptide, and neuromedin B receptor do not bind to BRS-3 and the endogenous BRS-3 ligand remains unknown. The novel synthesis of selective, high-affinity BRS-3 agonists and antagonists has recently been accomplished and showed that BRS-3 regulates energy balance independent of other established pathways and glucose-stimulated insulin secretion in the pancreatic islet cells. The availability of new BRS-3 selective agonists and antagonists will facilitate further elucidation of its role in energy homeostasis, and provides a potential approach for the pharmacological treatment of obesity and type 2 diabetes.

SUMMARY

The native ligand of the G protein-coupled BRS-3 has not been identified as of now. However, novel synthesis of small-molecule, high-affinity agonists and antagonists on the BRS-3 was used in the recent studies and demonstrated an important role of BRS-3 in the regulation of energy homeostasis and glucose metabolism.

Appetite-modifying effects of bombesin receptor subtype-3 agonists

Studies on bombesin-like peptides (BLP) and their respective mammalian receptors (Bn-r) have demonstrated a significant biological impact on a broad array of physiological and pathophysiological conditions. Pharmacological experiments in vitro and in vivo as well as utilization of genetic rodent models of the gastrin-releasing peptide receptor (GRP-R/BB2-receptor), neuromedin B receptor (NMB-R/BB1-receptor), and the bombesin receptor subtype-3 (BRS-3/BB3-receptor) further delineated their role in health and disease. All three mammalian bombesin receptors have been shown to possess some role in the regulation of energy balance and appetite and satiety. Compelling experimental evidence has accumulated indicating that the orphan BRS-3 is an important regulator of body weight, energy expenditure, and glucose homeostasis. BRS-3 possesses no high affinity to the endogenous bombesin-like peptides (BLP) bombesin, GRP, and NMB, and its endogenous ligand remains unknown. Recently, the synthesis of novel, selective high-affinity BRS-3 agonists and antagonists has been accomplished and has demonstrated that BRS-3 regulates energy balance independent of other established pathways. Accordingly, the availability of new BRS-3 selective agonists and antagonists will facilitate further elucidation of its role in energy homeostasis and provides a potential approach for the pharmacological treatment of obesity.

Neuromedin B receptor antagonist suppresses tumor angiogenesis and tumor growth in vitro and in vivo

Neuromedin B (NMB), a member of the mammalian bombesin-like peptide family, and its receptor were aberrantly expressed in vascularized solid tumors. Here, the NMB receptor (NMB-R) antagonist PD168368 specifically inhibited both NMB-induced in vivo and in vitro angiogenesis. In addition, PD168368 showed growth inhibitory effects on MDA-MB-231 breast cancer cells by inducing cell cycle arrest and apoptosis. Furthermore, PD168368 effectively suppressed tumor growth in a xenograft model of breast tumor in vivo. Overall, NMB-R antagonist exhibited a significant antitumor activity by simultaneously inhibiting neovascularization and cancer cell growth, thereby suggesting that NMB-R could be a potential therapeutic target for cancer treatment.

Gastrin releasing peptides increase Fos-like immunoreactivity in the enteric nervous system and the dorsal vagal complex

We and others have shown that gastrin-releasing peptide (GRP) reduces food intake. In this study, we determined the activation of the gastrointestinal and dorsal vagal complex (DVC) neurons by various forms of GRP to determine the pathway involved in this reduction. We found the following: (1) GRP-10, -27 and -29 (2.1 nmol/kg, i.p.) increased the Fos-like immunoreactivity (Fos-LI, a marker for neuronal activation) in the myenteric neurons of the stomach and the area postrema (AP) of the DVC; (2) GRP-27 and GRP-29 increased the Fos-LI in the myenteric plexus of the duodenum; and (3) only GRP-29 increased the Fos-LI in the submucosal plexus of the duodenum. In conclusion, GRP may reduce food intake by activating the area postrema. The enteric neurons may have a potential role in this reduction through the direct activation of the AP or exerting local gut actions, such as the stimulation of gut motility or secretions.

Pharmacology and selectivity of various natural and synthetic bombesin related peptide agonists for human and rat bombesin receptors differs

The mammalian bombesin (Bn)-receptor family [gastrin-releasing peptide-receptor (GRPR-receptor), neuromedin B-receptor (NMB receptor)], their natural ligands, GRP/NMB, as well as the related orphan receptor, BRS-3, are widely distributed, and frequently overexpressed by tumors. There is increased interest in agonists for this receptor family to explore their roles in physiological/pathophysiological processes, and for receptor-imaging/cytotoxicity in tumors. However, there is minimal data on human pharmacology of Bn receptor agonists and most results are based on nonhuman receptor studies, particular rodent-receptors, which with other receptors frequently differ from human-receptors. To address this issue we compared hNMB-/GRP-receptor affinities and potencies/efficacies of cell activation (assessing phospholipase C activity) for 24 putative Bn-agonists (12 natural, 12 synthetic) in four different cells with these receptors, containing native receptors or receptors expressed at physiological densities, and compared the results to native rat GRP-receptor containing cells (AR42J-cells) or rat NMB receptor cells (C6-glioblastoma cells). There were close correlations (r=0.92-99, p<0.0001) between their affinities/potencies for the two hGRP- or hNMB-receptor cells. Twelve analogs had high affinities (≤ 1 nM) for hGRP receptor with 15 selective for it (greatest=GRP, NMC), eight had high affinity/potencies for hNMB receptors and four were selective for it. Only synthetic Bn analogs containing β-alanine(11) had high affinity for hBRS-3, but also had high affinities/potencies for all GRP-/hNMB-receptor cells. There was no correlation between affinities for human GRP receptors and rat GRP receptors (r=0.131, p=0.54), but hNMB receptor results correlated with rat NMB receptor (r=0.71, p<0.0001). These results elucidate the human and rat GRP-receptor pharmacophore for agonists differs markedly, whereas they do not for NMB receptors, therefore potential GRP-receptor agonists for human studies (such as Bn receptor-imaging/cytotoxicity) must be assessed on human Bn receptors. The current study provides affinities/potencies on a large number of potential agonists that might be useful for human studies.

Neuropeptide signaling differentially affects phase maintenance and rhythm generation in SCN and extra-SCN circadian oscillators

Circadian rhythms in physiology and behavior are coordinated by the brain's dominant circadian pacemaker located in the suprachiasmatic nuclei (SCN) of the hypothalamus. Vasoactive intestinal polypeptide (VIP) and its receptor, VPAC(2), play important roles in the functioning of the SCN pacemaker. Mice lacking VPAC(2) receptors (Vipr2(-/-)) express disrupted behavioral and metabolic rhythms and show altered SCN neuronal activity and clock gene expression. Within the brain, the SCN is not the only site containing endogenous circadian oscillators, nor is it the only site of VPAC(2) receptor expression; both VPAC(2) receptors and rhythmic clock gene/protein expression have been noted in the arcuate (Arc) and dorsomedial (DMH) nuclei of the mediobasal hypothalamus, and in the pituitary gland. The functional role of VPAC(2) receptors in rhythm generation and maintenance in these tissues is, however, unknown. We used wild type (WT) and Vipr2(-/-) mice expressing a luciferase reporter (PER2::LUC) to investigate whether circadian rhythms in the clock gene protein PER2 in these extra-SCN tissues were compromised by the absence of the VPAC(2) receptor. Vipr2(-/-) SCN cultures expressed significantly lower amplitude PER2::LUC oscillations than WT SCN. Surprisingly, in Vipr2(-/-) Arc/ME/PT complex (Arc, median eminence and pars tuberalis), DMH and pituitary, the period, amplitude and rate of damping of rhythms were not significantly different to WT. Intriguingly, while we found WT SCN and Arc/ME/PT tissues to maintain a consistent circadian phase when cultured, the phase of corresponding Vipr2(-/-) cultures was reset by cull/culture procedure. These data demonstrate that while the main rhythm parameters of extra-SCN circadian oscillations are maintained in Vipr2(-/-) mice, the ability of these oscillators to resist phase shifts is compromised. These deficiencies may contribute towards the aberrant behavior and metabolism associated with Vipr2(-/-) animals. Further, our data indicate a link between circadian rhythm strength and the ability of tissues to resist circadian phase resetting.