Metabolic effects of bile acid sequestration: impact on cardiovascular risk factors

PURPOSE OF REVIEW

This article discusses the impact of bile acid sequestrants (BAS) on cardiovascular risk factors (CVRFs), on the basis of recent (pre)clinical studies assessing the metabolic impact of modulation of enterohepatic bile acid signaling via the bile acid receptors farnesoid X receptor (FXR) and Takeda G-protein-coupled receptor 5 (TGR5).

RECENT FINDINGS

BAS decrease low-density lipoprotein-cholesterol by stimulating de novo hepatic bile acid synthesis and lowering intestinal lipid absorption, and improve glucose homeostasis in type 2 diabetes mellitus, at least in part by increasing GLP-1 production, via intestinal TGR5- and FXR-dependent mechanisms. Intestinal and peripheral FXR and TGR5 modulation also affects peripheral tissues, which can contribute to the reduction of CVRFs.

SUMMARY

Bile acids are regulators of metabolism acting in an integrated interorgan manner via FXR and TGR5. Modulation of the bile acid pool size and composition, and selective interference with their receptors could, therefore, be a therapeutic approach to decrease CVRFs. Even though clinical cardiovascular outcome studies using BAS are still lacking, the existing data point to BAS as an efficacious pharmacological approach to reduce CVRFs.

G protein-coupled receptors: signalling and regulation by lipid agonists for improved glucose homoeostasis

G protein-coupled receptors (GPCRs) play a pivotal role in cell signalling, controlling many processes such as immunity, growth, cellular differentiation, neurological pathways and hormone secretions. Fatty acid agonists are increasingly recognised as having a key role in the regulation of glucose homoeostasis via stimulation of islet and gastrointestinal GPCRs. Downstream cell signalling results in modulation of the biosynthesis, secretion, proliferation and anti-apoptotic pathways of islet and enteroendocrine cells. GPR40 and GPR120 are activated by long-chain fatty acids (>C12) with both receptors coupling to the Gαq subunit that activates the Ca(2+)-dependent pathway. GPR41 and GPR43 are stimulated by short-chain fatty acids (C2-C5), and activation results in binding to Gαi that inhibits the adenylyl cyclase pathway attenuating cAMP production. In addition, GPR43 also couples to the Gαq subunit augmenting intracellular Ca(2+) and activating phospholipase C. GPR55 is specific for cannabinoid endogenous agonists (endocannabinoids) and non-cannabinoid fatty acids, which couples to Gα12/13 and Gαq proteins, leading to enhancing intracellular Ca(2+), extracellular signal-regulated kinase 1/2 (ERK) phosphorylation and Rho kinase. GPR119 is activated by fatty acid ethanolamides and binds to Gαs utilising the adenylate cyclase pathway, which is dependent upon protein kinase A. Current research indicates that GPCR therapies may be approved for clinical use in the near future. This review focuses on the recent advances in preclinical diabetes research in the signalling and regulation of GPCRs on islet and enteroendocrine cells involved in glucose homoeostasis.

Adropin acts in brain to inhibit water drinking: potential interaction with the orphan G protein-coupled receptor, GPR19

Adropin, a recently described peptide hormone produced in the brain and liver, has been reported to have physiologically relevant actions on glucose homeostasis and lipogenesis, and to exert significant effect on endothelial function. We describe a central nervous system action of adropin to inhibit water drinking and identify a potential adropin receptor, the orphan G protein-coupled receptor, GPR19. Reduction in GPR19 mRNA levels in medial basal hypothalamus of male rats resulted in the loss of the inhibitory effect of adropin on water deprivation-induced thirst. The identification of a novel brain action of adropin and a candidate receptor for the peptide should extend and accelerate the study of the potential therapeutic value of adropin or its mimetics for the treatment of metabolic disorders.

Characterization and pharmacological analysis of two adipokinetic hormone receptor variants of the tsetse fly, Glossina morsitans morsitans

Adipokinetic hormones (AKH) are well known regulators of energy metabolism in insects. These neuropeptides are produced in the corpora cardiaca and perform their hormonal function by interacting with specific G protein-coupled receptors (GPCRs) at the cell membranes of target tissues, mainly the fat body. Here, we investigated the sequences, spatial and temporal distributions, and pharmacology of AKH neuropeptides and receptors in the tsetse fly, Glossina morsitans morsitans. The open reading frames of two splice variants of the Glomo-akh receptor (Glomo-akhr) gene and of the AKH neuropeptide encoding genes, gmmhrth and gmmakh, were cloned. Both tsetse AKHR isoforms show strong sequence conservation when compared to other insect AKHRs. Glomo-AKH prepropeptides also have the typical architecture of AKH precursors. In an in vitro Ca(2+) mobilization assay, Glomo-AKH neuropeptides activated each receptor isoform up to nanomolar concentrations. We identified structural features of tsetse AKH neuropeptides essential for receptor activation in vitro. Gene expression profiles suggest a function for AKH signaling in regulating Glossina energy metabolism, where AKH peptides are released from the corpora cardiaca and activate receptors mainly expressed in the fat body. This analysis of the ligand-receptor coupling, expression, and pharmacology of the two Glomo-AKHR variants facilitates further elucidation of the function of AKH in G. m. morsitans.

Intestinal Bile Acid Composition Modulates Prohormone Convertase 1/3 (PC1/3) Expression and Consequent GLP-1 Production in Male Mice

Besides an established medication for hypercholesterolemia, bile acid binding resins (BABRs) present antidiabetic effects. Although the mechanisms underlying these effects are still enigmatic, glucagon-like peptide-1 (GLP-1) appears to be involved. In addition to a few reported mechanisms, we propose prohormone convertase 1/3 (PC1/3), an essential enzyme of GLP-1 production, as a potent molecule in the GLP-1 release induced by BABRs. In our study, the BABR colestimide leads to a bile acid-specific G protein-coupled receptor TGR5-dependent induction of PC1/3 gene expression. Here, we focused on the alteration of intestinal bile acid composition and consequent increase of total TGR5 agonistic activity to explain the TGR5 activation. Furthermore, we demonstrate that nuclear factor of activated T cells mediates the TGR5-triggered PC1/3 gene expression. Altogether, our data indicate that the TGR5-dependent intestinal PC1/3 gene expression supports the BABR-stimulated GLP-1 release. We also propose a combination of BABR and dipeptidyl peptidase-4 inhibitor in the context of GLP-1-based antidiabetic therapy.

n-3 Fatty Acids Induce Neurogenesis of Predominantly POMC-Expressing Cells in the Hypothalamus

Apoptosis of hypothalamic neurons is believed to play an important role in the development and perpetuation of obesity. Similar to the hippocampus, the hypothalamus presents constitutive and stimulated neurogenesis, suggesting that obesity-associated hypothalamic dysfunction can be repaired. Here, we explored the hypothesis that n-3 polyunsaturated fatty acids (PUFAs) induce hypothalamic neurogenesis. Both in the diet and injected directly into the hypothalamus, PUFAs were capable of increasing hypothalamic neurogenesis to levels similar or superior to the effect of brain-derived neurotrophic factor (BDNF). Most of the neurogenic activity induced by PUFAs resulted in increased numbers of proopiomelanocortin but not NPY neurons and was accompanied by increased expression of BDNF and G-protein-coupled receptor 40 (GPR40). The inhibition of GPR40 was capable of reducing the neurogenic effect of a PUFA, while the inhibition of BDNF resulted in the reduction of global hypothalamic cell. Thus, PUFAs emerge as a potential dietary approach to correct obesity-associated hypothalamic neuronal loss.

Cellular and molecular mechanisms underlying the treatment of depression: focusing on hippocampal G-protein-coupled receptors and voltage-dependent calcium channels

Depression is a brain disorder characterized by severe emotional, cognitive, neuroendocrine and somatic dysfunction. Although the latest generation of antidepressant drugs has improved clinical efficacy and safety, the onset of their clinical effect is significantly delayed after treatment commencement, and a large number of patients exhibit inadequate response to these drugs and/or depression relapse even following initially successful treatment. It is therefore essential to develop new antidepressant drugs and/or adjuncts to existing ones. Recent studies suggest that the beneficial effect of antidepressant drugs is mediated, at least in part, via stimulation of adult hippocampal neurogenesis and subsequent increase in hippocampal plasticity. Since the stimulatory effect of antidepressant drugs on hippocampal neurogenesis involves G-protein coupled receptors (GPCR) and voltage-dependent calcium channels (VDCC), greater efficacy may be available if future antidepressant drugs directly target these specific GPCR and VDCC. The potential advantages and limitations of these treatment strategies are discussed in the article.

Comprehensive Profiling of GPCR Expression in Ghrelin-Producing Cells

To determine the comprehensive G protein-coupled receptor (GPCR) expression profile in ghrelin-producing cells and to elucidate the role of GPCR-mediated signaling in the regulation of ghrelin secretion, we determined GPCR expression profiles by RNA sequencing in the ghrelin-producing cell line MGN3-1 and analyzed the effects of ligands for highly expressed receptors on intracellular signaling and ghrelin secretion. Expression of selected GPCRs was confirmed in fluorescence-activated cell-sorted fluorescently tagged ghrelin-producing cells from ghrelin-promoter CreERT2/Rosa-CAG-LSL-ZsGreen1 mice. Expression levels of GPCRs previously suggested to regulate ghrelin secretion including adrenergic-β1 receptor, GPR81, oxytocin receptor, GPR120, and somatostatin receptor 2 were high in MGN3-1 cells. Consistent with previous reports, isoproterenol and oxytocin stimulated the Gs and Gq pathways, respectively, whereas lactate, palmitate, and somatostatin stimulated the Gi pathway, confirming the reliability of current assays. Among other highly expressed GPCRs, prostaglandin E receptor 4 agonist prostaglandin E2 significantly stimulated the Gs pathway and ghrelin secretion. Muscarine, the canonical agonist of cholinergic receptor muscarinic 4, stimulated both the Gq and Gi pathways. Although muscarine treatment alone did not affect ghrelin secretion, it did suppress forskolin-induced ghrelin secretion, suggesting that the cholinergic pathway may play a role in counterbalancing the stimulation of ghrelin by Gs (eg, by adrenaline). In addition, GPR142 ligand tryptophan stimulated ghrelin secretion. In conclusion, we determined the comprehensive expression profile of GPCRs in ghrelin-producing cells and identified two novel ghrelin regulators, prostaglandin E2 and tryptophan. These results will lead to a greater understanding of the physiology of ghrelin and facilitate the development of ghrelin-modulating drugs.

7TM Domain Structure of Adhesion GPCRs

Schematic presentation of the overall adhesion G Protein-Coupled Receptor (aGPCR) structure and functional domains, covering an extracellular N-terminal fragment (NTF), a membrane-spanning C-terminal fragment (CTF) and a GPCR proteolysis site (GPS). (Left side) aGPCR model constructed based on the seven-transmembrane (7TM) structure (blue) of secretin family glucagon receptor (GCGR) (PDB, 4L6R) [11] and the GPCR autoproteolysis inducing (GAIN) domain (magenta) structure of latrophilin 1 (PDB, 4DLQ) [9]. The β-13 strand residues are depicted in green. (Right side) The experimentally validated full-length secretin family GCGR structure combining structural and experimental information from the GCGR 7TM crystal structure (PDB, 4L6R) (blue), the GCGR extracellular domain (ECD) structure (PDB, 4ERS) (magenta) and the ECD structure of glucagon-like peptide-1 (GLP-1)-bound glucagon-like peptide-1 receptor (GLP-1R) (PDB, 3IOL) (green), complemented by site-directed mutagenesis, electron microscopy (EM), hydrogen-deuterium exchange (HDX) and cross-linking studies [11-13]) Despite the recent breakthroughs in the elucidation of the three-dimensional structures of the seven transmembrane (7TM) domain of the G protein-coupled receptor (GPCR) superfamily, a corresponding structure of a member of the adhesion GPCR (aGPCR) family has not yet been solved. In this chapter, we give an overview of the current knowledge of the 7TM domain of aGPCRs by comparative structure-based sequence similarity analyses between aGPCRs and GPCRs with known crystal structure. Of the GPCR superfamily, only the secretin family shares some sequence similarity with aGPCRs. This chapter will therefore emphasize on the comparison of these two GPCR families. Two 7TM domain structures of secretin family GPCRs are known that provide insight into the structure-function relationships of conserved sequence motifs that play important roles and are also present in most aGPCRs. This suggests that the 7TM domains of aGPCRs and secretin family GPCRs share a similar structural fold and that the conserved residues in both families may be involved in similar intermolecular interaction networks and facilitate similar conformational changes. Comparison of the residues that line the large peptide hormone binding pocket in the 7TM domain of secretin family GPCRs with corresponding residues in aGPCRs indicates that in the latter, the corresponding pocket in the 7TM domain is relatively hydrophobic and may be even larger. Improved knowledge on these conserved sequence motifs will help to understand the interactions of the aGPCR 7TM domain with ligands and gain insight into the activation mechanism of aGPCRs.

The Estrogen Receptors: An Overview from Different Perspectives

The estrogen receptors, ERα, ERβ, and GPER, mediate the effects of estrogenic compounds on their target tissues. Estrogen receptors are located in the tissues of the female reproductive tract and breast as one would expect, but also in tissues as diverse as bone, brain, liver, colon, skin, and salivary gland. The purpose of this discussion of the estrogen receptors is to provide a brief overview of the estrogen receptors and estrogen action from perspectives such as the historical, physiological, pharmacological, pathological, structural, and ligand perspectives.

Versatile Signaling Activity of Adhesion GPCRs

The adhesion G protein-coupled receptors (aGPCRs) are a family of 33 receptors in humans that are widely expressed in various tissues and involved in many diverse biological processes. These receptors possess extremely large N-termini (NT) containing a variety of adhesion domains. A distinguishing feature of these receptors is the presence within the NT of a highly conserved GPCR autoproteolysis-inducing (GAIN) domain, which mediates autoproteolysis of the receptors into N-terminal and C-terminal fragments that stay non-covalently associated. The downstream signaling pathways and G protein-coupling preferences of many aGPCRs have recently been elucidated, and putative endogenous ligands for some aGPCRs have also been discovered and characterized in recent years. A pivotal observation for aGPCRs has been that deletion or removal of the NT up the point of GAIN cleavage results in constitutive receptor activation. For at least some aGPCRs, this activation is dependent on the unmasking of specific agonistic peptide sequences within the N-terminal stalk region (i.e., the region between the site of GAIN domain cleavage and the first transmembrane domain). However, the specific peptide sequences involved and the overall importance of the stalk region for activation can vary greatly from receptor to receptor. An emerging theme of work in this area is that aGPCRs are capable of versatile signaling activity that may be fine-tuned to suit the specific physiological roles played by the various members of this family.

[Cellular and molecular mechanisms of action of bitter compounds: recent knowledge and perspective]

This overview paper describes in its introductory part bitter-tasting herbal drugs in the context of their traditional use in the loss of appetite and digestive disorders. Then, it mentions current knowledge on signals origin in bitter taste receptors leading to different, unexpected physiological processes. Newly observed biological effects of bitter tastants are correlated with modern trends of their complex study with an aim to develop new drugs primarily acting on bitter taste receptors.Key words: T2R bitter taste receptors GPCR bitters glucose homeostasis asthma ghrelin GLP-1 solitary chemosensory cells.

Beyond Membrane Protein Structure: Drug Discovery, Dynamics and Difficulties

Most of the previous content of this book has focused on obtaining the structures of membrane proteins. In this chapter we explore how those structures can be further used in two key ways. The first is their use in structure based drug design (SBDD) and the second is how they can be used to extend our understanding of their functional activity via the use of molecular dynamics. Both aspects now heavily rely on computations. This area is vast, and alas, too large to consider in depth in a single book chapter. Thus where appropriate we have referred the reader to recent reviews for deeper assessment of the field. We discuss progress via the use of examples from two main drug target areas; G-protein coupled receptors (GPCRs) and ion channels. We end with a discussion of some of the main challenges in the area.

Docosahexaenoic Acid and Its Role in G-Protein-Coupled Receptor 120 Activation in Children Affected by Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is one of the most important causes of chronic liver disease in children and adults. Recently, therapeutic supplementation with docosahexaenoic acid (DHA) showed an anti-inflammatory and insulin-sensitizing effect in children with NAFLD. The anti-inflammatory effects of DHA depend on its ability to alter phospholipid composition of the cell membrane, to disrupt lipid rafts and to hamper the transcriptional activity of nuclear factor-x03BA;B that controls the expression of proinflammatory cytokines. These effects of DHA are due to the interaction with the G-protein-coupled receptor 120 (GRP120), a lipid-sensing receptor highly expressed in activated macrophages. In fact, DHA may activate GPR120 expression in macrophages causing anti-inflammatory effects, and insulin-sensitizing and antidiabetic effects in vivo. Recently, it has been shown that GPR120 is also expressed by the Kupffer cells of the liver. A diet low in n-3 polyunsaturated fatty acids, as well as the presence of genetic factors, may induce a reduction in the GRP120 signal and the activation of Kupffer cells and inflammation during NAFLD. Therefore, it is conceivable that DHA/GRP120 may play a key role in slowing the progression of liver damage in patients with NAFLD.

The Concise Guide to PHARMACOLOGY 2015/16: G protein-coupled receptors

The Concise Guide to PHARMACOLOGY 2015/16 provides concise overviews of the key properties of over 1750 human drug targets with their pharmacology, plus links to an open access knowledgebase of drug targets and their ligands (www.guidetopharmacology.org), which provides more detailed views of target and ligand properties. The full contents can be found at http://onlinelibrary.wiley.com/doi/10.1111/bph.13348/full. G protein-coupled receptors are one of the eight major pharmacological targets into which the Guide is divided, with the others being: ligand-gated ion channels, voltage-gated ion channels, other ion channels, nuclear hormone receptors, catalytic receptors, enzymes and transporters. These are presented with nomenclature guidance and summary information on the best available pharmacological tools, alongside key references and suggestions for further reading. The Concise Guide is published in landscape format in order to facilitate comparison of related targets. It is a condensed version of material contemporary to late 2015, which is presented in greater detail and constantly updated on the website www.guidetopharmacology.org, superseding data presented in the previous Guides to Receptors & Channels and the Concise Guide to PHARMACOLOGY 2013/14. It is produced in conjunction with NC-IUPHAR and provides the official IUPHAR classification and nomenclature for human drug targets, where appropriate. It consolidates information previously curated and displayed separately in IUPHAR-DB and GRAC and provides a permanent, citable, point-in-time record that will survive database updates.

RF9 Acts as a KISS1R Agonist In Vivo and In Vitro

RF9, a reported antagonist of the mammalian gonadotropin-inhibitory hormone receptor, stimulates gonadotropin secretion in mammals. Recent studies have suggested that the stimulatory effect of RF9 on gonadotropin secretion relies on intact kisspeptin receptor (KISS1R) signaling, but the underlying mechanisms remain to be elucidated. Using Chinese Hamster Ovary cells stably transfected with KISS1R, we show that RF9 binds specifically to KISS1R, with a Kd of 1.6 × 10(-5)M, and stimulates an increase in intracellular calcium and inositol phosphate accumulation in a KISS1R-dependent manner, with EC50 values of 3.0 × 10(-6)M and 1.6 × 10(-7)M, respectively. RF9 also stimulated ERK phosphorylation, with a time course similar to that of kisspeptin-10. RFRP-3, the putative endogenous ligand for NPFFR1, did not stimulate inositol phosphate accumulation or pERK, nor did it alter responses to of kisspeptin-10 or RF9. In agreement with these in vitro data, we found that RF9 stimulated a robust LH increase in Npffr1(-/-) mice, similar to that in wild-type littermates, whereas the stimulatory effect of RF9 was markedly reduced in Kiss1r(-/-) and double Kiss1r(-/-)/Npfrr1(-/-) mice. The stimulatory effect of RF9 on LH secretion was restored by the selective rescue of Kiss1r expression in GnRH neurons, in Kiss1r(-/-T) mice. Taken together, our study demonstrates that RF9 acts primarily as a KISS1R agonist, but not as an allosteric modulator, to stimulate LH secretion. Our findings raise questions regarding the utility of RF9 for assessing NPFF1R function and de-emphasize a predominant role of this signaling system in central regulation of reproduction.

Regulation of the Apelinergic System and Its Potential in Cardiovascular Disease: Peptides and Small Molecules as Tools for Discovery

Apelin peptides and the apelin receptor represent a relatively new therapeutic axis for the potential treatment of cardiovascular disease. Several reports suggest apelin receptor activation with apelin peptides results in cardioprotection as noted through positive ionotropy, angiogenesis, reduction of mean arterial blood pressure, and apoptosis. Considering the potential therapeutic benefit attainable through modulation of the apelinergic system, research is expanding to develop novel therapies that limit the inherent rapid degradation of endogenous apelin peptides and produce metabolically stable small molecule agonists and antagonists to more rigorously interrogate the apelin receptor system. This review details the structure-activity relationships for chemically modified apelin peptides and recent disclosures of small molecule agonists and antagonists and summarizes the peer reviewed and patented literature. Development of metabolically stable ligands of apelin receptor and their effects in various models over the coming years will hopefully lead to establishment of this receptor as a validated target for cardiovascular indications.

Alternative Splicing of G Protein-Coupled Receptors: Relevance to Pain Management

Drugs that target G protein-coupled receptors (GPCRs) represent the primary treatment strategy for patients with acute and chronic pain; however, there is substantial individual variability in both the efficacy and adverse effects associated with these drugs. Variability in drug responses is due, in part, to individuals' diversity in alternative splicing of pain-relevant GPCRs. G protein-coupled receptor alternative splice variants often exhibit distinct tissue distribution patterns, drug-binding properties, and signaling characteristics that may impact disease pathology as well as the extent and direction of analgesic effects. We review the importance of GPCRs and their known splice variants to the management of pain.

International Union of Basic and Clinical Pharmacology. XCVII. G Protein-Coupled Estrogen Receptor and Its Pharmacologic Modulators

Estrogens are critical mediators of multiple and diverse physiologic effects throughout the body in both sexes, including the reproductive, cardiovascular, endocrine, nervous, and immune systems. As such, alterations in estrogen function play important roles in many diseases and pathophysiological conditions (including cancer), exemplified by the lower prevalence of many diseases in premenopausal women. Estrogens mediate their effects through multiple cellular receptors, including the nuclear receptor family (ERα and ERβ) and the G protein-coupled receptor (GPCR) family (GPR30/G protein-coupled estrogen receptor [GPER]). Although both receptor families can initiate rapid cell signaling and transcriptional regulation, the nuclear receptors are traditionally associated with regulating gene expression, whereas GPCRs are recognized as mediating rapid cellular signaling. Estrogen-activated pathways are not only the target of multiple therapeutic agents (e.g., tamoxifen, fulvestrant, raloxifene, and aromatase inhibitors) but are also affected by a plethora of phyto- and xeno-estrogens (e.g., genistein, coumestrol, bisphenol A, dichlorodiphenyltrichloroethane). Because of the existence of multiple estrogen receptors with overlapping ligand specificities, expression patterns, and signaling pathways, the roles of the individual receptors with respect to the diverse array of endogenous and exogenous ligands have been challenging to ascertain. The identification of GPER-selective ligands however has led to a much greater understanding of the roles of this receptor in normal physiology and disease as well as its interactions with the classic estrogen receptors ERα and ERβ and their signaling pathways. In this review, we describe the history and characterization of GPER over the past 15 years focusing on the pharmacology of steroidal and nonsteroidal compounds that have been employed to unravel the biology of this most recently recognized estrogen receptor.

[Lipopolysaccharide, TNFα, IL-6, dexamethasone, and insulin increase the expression of GPR54 in the MCF7 breasr cancer cell line]

OBJECTIVE

To investigate the effects of different concentrations of lipopolysaccharide (LPS), tumor necrosis factor α (TNFα), interleukin-6 (IL-6), dexamethasone (Dex), and insulin on the mRNA and protein expressions of GPR54 in the MCF7 cell line in vitro.

METHODS

MCF7 breasr cancer cells were cultured and treated with different concentrations of LPS (10 and 20 µg/ml), TNFα (20 and 100 ng/ml), IL-6 (10 and 20 ng/ml), Dex (10(-6) and 10(-7) mol/L), and insulin (0.01 and 0.1 IU/L). Those treated with culture fluid only served as controls. The mRNA and protein expressions of GPR54 were measured by real-time PCR and Western blot, respectively, after 6, 24, 48, and 72 hours of treatment.

RESULTS

Compared with the blank con- trol, LPS (10 and 20 µg/ml), TNFα (20 and 100 ng/ml), IL-6 (10 and 20 ng/ml), Dex (10(-6) and 10(-7) mol/L), and insulin (0.01 and 0.1 IU/L) significantly increased the expressions of GPR54 mRNA (P < 0.05) and protein (P < 0.05).

CONCLUSION

LPS, TNFα, IL-6, Dex, and insulin evidently increase the expression of GPR54 in the MCF7 cell line, indicating their influence on the function of gonads by regulating the GPR54 level.

Characterization of Imidazopyridine Compounds as Negative Allosteric Modulators of Proton-Sensing GPR4 in Extracellular Acidification-Induced Responses

G protein-coupled receptor 4 (GPR4), previously proposed as the receptor for sphingosylphosphorylcholine, has recently been identified as the proton-sensing G protein-coupled receptor (GPCR) coupling to multiple intracellular signaling pathways, including the G_s protein/cAMP and G₁₃ protein/Rho. In the present study, we characterized some imidazopyridine compounds as GPR4 modulators that modify GPR4 receptor function. In the cells that express proton-sensing GPCRs, including GPR4, OGR1, TDAG8, and G2A, extracellular acidification stimulates serum responsive element (SRE)-driven transcriptional activity, which has been shown to reflect Rho activity, with different proton sensitivities. Imidazopyridine compounds inhibited the moderately acidic pH-induced SRE activity only in GPR4-expressing cells. Acidic pH-stimulated cAMP accumulation, mRNA expression of inflammatory genes, and GPR4 internalization within GPR4-expressing cells were all inhibited by the GPR4 modulator. We further compared the inhibition property of the imidazopyridine compound with psychosine, which has been shown to selectively inhibit actions induced by proton-sensing GPCRs, including GPR4. In the GPR4 mutant, in which certain histidine residues were mutated to phenylalanine, proton sensitivity was significantly shifted to the right, and psychosine failed to further inhibit acidic pH-induced SRE activation. On the other hand, the imidazopyridine compound almost completely inhibited acidic pH-induced action in mutant GPR4. We conclude that some imidazopyridine compounds show specificity to GPR4 as negative allosteric modulators with a different action mode from psychosine, an antagonist susceptible to histidine residues, and are useful for characterizing GPR4-mediated acidic pH-induced biological actions.

Estrogen regulates Hippo signaling via GPER in breast cancer

The G protein-coupled estrogen receptor (GPER) mediates both the genomic and nongenomic effects of estrogen and has been implicated in breast cancer development. Here, we compared GPER expression in cancerous tissue and adjacent normal tissue in patients with invasive ductal carcinoma (IDC) of the breast and determined that GPER is highly upregulated in cancerous cells. Additionally, our studies revealed that GPER stimulation activates yes-associated protein 1 (YAP) and transcriptional coactivator with a PDZ-binding domain (TAZ), 2 homologous transcription coactivators and key effectors of the Hippo tumor suppressor pathway, via the Gαq-11, PLCβ/PKC, and Rho/ROCK signaling pathways. TAZ was required for GPER-induced gene transcription, breast cancer cell proliferation and migration, and tumor growth. Moreover, TAZ expression positively correlated with GPER expression in human IDC specimens. Together, our results suggest that the Hippo/YAP/TAZ pathway is a key downstream signaling branch of GPER and plays a critical role in breast tumorigenesis.

Short-chain fatty acids and acidic pH upregulate UT-B, GPR41, and GPR4 in rumen epithelial cells of goats

Currently, the mechanism(s) responsible for the regulation of urea transporter B (UT-B) expression levels in the epithelium of the rumen remain unclear. We hypothesized that rumen fermentation products affect ruminal UT-B expression. Therefore, the effects of short-chain fatty acids (SCFA), pH, ammonia, and urea on mRNA and protein levels of UT-B were assayed in primary rumen epithelial cell cultures and in rumen epithelium obtained from intact goats. In vitro, SCFA and acidic pH were found to synergetically stimulate both mRNA and protein expression of UT-B, whereas NH4Cl decreased mRNA and protein levels of UT-B at pH 6.8. Treatment with urea increased both levels at pH 7.4. When goats received a diet rich in nitrogen (N) and nonfiber carbohydrates (NFC), their rumen epithelium had higher levels of UT-B, and the rumen contained higher concentrations of SCFA and NH3-N with a lower pH. An increase in plasma urea-N concentration was also observed compared with the plasma of the goats that received a diet low in N and NFC. In a second feeding trial, goats that received a NFC-rich, but isonitrogenous, diet had higher mRNA and protein levels of UT-B, and higher levels of G protein-coupled receptor (GPR) 41 and GPR4, in their rumen epithelium. The ruminal concentrations of SCFA and NH3-N also increased, while a lower pH was detected. In contrast, the serum urea-N concentrations remained unchanged. These data indicate that ruminal SCFA and pH are key factors, via GPR4 and GPR41, in the dietary regulation of UT-B expression, and they have priority over changes in plasma urea.

Intra-ventral tegmental area microinjections of urotensin II modulate the effects of cocaine

Although the peptide urotensin II (UII) has well studied direct actions on the cardiovascular system, the UII receptor (UIIR) is expressed by neurons of the hindbrain. Specifically, the UIIR is expressed by the cholinergic neurons of the laterodorsal tegmentum (LDTg) and the pedunculopontine tegmentum (PPTg). These neurons send axons to the ventral tegmental area (VTA), for which the PPTg and LDTg are the sole source of acetylcholine. Therefore, it was hypothesized that UIIR activation within the VTA would modulate reward-related behaviors, such as cocaine-induced drug seeking. Intra-VTA microinjections of UII at high concentrations (1 nmole) established conditioned place preference (CPP), but also blocked cocaine-mediated CPP (10 mg/kg). When rats received systemic sub-effectual doses of cocaine (7.5 mg/kg) with intra-VTA injections of 1 or 10 pmole of UII CPP was formed. Furthermore, the second endogenous ligand for the UIIR, urotensin II-related peptide, had the same effect at the 10 pmole dose. The effects of low doses of UII were blocked by pretreatment with the UIIR antagonist SB657510. Furthermore, it was found that intra-VTA UII (10 pmole) further increased cocaine-mediated (7.5 mg/kg) rises in electrically evoked dopamine in the nucleus accumbens. Our study has found that activation of VTA-resident UIIR produces observable behavioral changes in rats, and that UIIR is able to modulate the effects of cocaine. In addition, it was found that UIIR activation within the VTA can potentiate cocaine-mediated neurochemical effects. Therefore, the coincident activation of the UII-system and cocaine administration may increase the liability for drug taking behavior.