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Find video protocols related to scientific articles indexed in Pubmed.
Melanocortin receptor accessory protein 2 (MRAP2) interplays with the zebrafish melanocortin 1 receptor (MC1R) but has no effect on its pharmacological profile.
Gen. Comp. Endocrinol.
PUBLISHED: 03-12-2014
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The melanocortin system is probably one of the most complex hormonal systems since it integrates agonist, encoded in the proopiomelanocortin precursor, endogenous antagonist, agouti signaling protein and agouti-related protein, five different G-protein coupled receptors and two accessory proteins. These accessory proteins interact with melanocortin receptors to allow traffic to the plasma membrane or to regulate the pharmacological profile. The MC1R fill the extension locus, which is primarily responsible for the regulation of pigmentation. In zebrafish, both MC1R and MRAP2 system are expressed in the skin. We demonstrate that zebrafish MC1R physically, or closely, interacts with the MRAP2 system, although this interaction did not result in modification of the studied pharmacological profile. However, progressive fasting induced skin darkening but also an upregulation of the MRAP2 expression in the skin, suggesting an unknown role for MRAP2a that could involve receptor desensitization processes. We also demonstrate that crowding stress induces skin darkening and a downregulation of MC1R expression in the skin.
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Characterization, tissue distribution and regulation by fasting of the agouti family of peptides in the sea bass (Dicentrarchus labrax).
Gen. Comp. Endocrinol.
PUBLISHED: 02-05-2014
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The melanocortin system is one of the most complex hormonal systems in vertebrates. Atypically, the signaling of melanocortin receptors is regulated by the binding of endogenous antagonists, named agouti-signaling protein (ASIP) and agouti-related protein (AGRP). Teleost specific genome duplication (TSGD) rendered new gene copies in teleost fish and up to four different genes of the agouti family of peptides have been characterized. In this paper, molecular cloning was used to characterize mRNA of the agouti family of peptides in sea bass. Four different genes were identified: AGRP1, ASIP1, AGRP2 and ASIP2. The AGRP1 gene is mainly expressed in the brain whereas ASIP1 is mainly expressed in the ventral skin. Both ASIP2 and AGRP2 are expressed in the brain and the pineal gland but also in some peripheral tissues. Immunocytochemical studies demonstrated that AGRP1 is exclusively expressed within the lateral tuberal nucleus, the homologue of the mammalian arcuate nucleus in fish. Long-term fasting (8-29 days) increased the hypothalamic expression of AGRP1 but depressed AGRP2 expression (15-29 days). In contrast, the hypothalamic expression of ASIP2 was upregulated during short-term fasting suggesting that this peptide could be involved in the short term regulation of food intake in the sea bass.
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Evolution of the melanocortin system.
Gen. Comp. Endocrinol.
PUBLISHED: 01-07-2014
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The melanocortin system is one of the most complex of the hormonal systems. It involves different agonists encoded in the multiplex precursor proopiomelanocortin (POMC) or in different genes as ?-defensins, endogenous antagonist, like agouti-signalling protein (ASIP) or agouti-related protein (AGRP), and five different melanocortin receptors (MCRs). Rounds of whole genome duplication events have preceded the functional and molecular diversification of the family in addition some co-evolutionary and tandem duplication processes have been proposed. The evolutionary patterns of the different partners are controversial and different hypotheses have emerged from a study of the sequenced genomes. In this review, we summarize the different evolutionary hypotheses proposed for the different melanocortin partners.
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Melanocortin 4 receptor becomes an ACTH receptor by coexpression of melanocortin receptor accessory protein 2.
Mol. Endocrinol.
PUBLISHED: 10-01-2013
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Melanocortin 2 receptor (MC2R) is the only canonical ACTH receptor. Its functional expression requires the presence of an accessory protein, known as melanocortin receptor 2 accessory protein 1 (MRAP1). The vertebrate genome exhibits a paralogue gene called MRAP2, which is duplicated in zebrafish (MRAP2a and MRAP2b), although its function remains unknown. In this paper, we demonstrate that MRAP2a enables MC4R, a canonical MSH receptor, to be activated by ACTH with a similar sensitivity to that exhibited by MC2R. Both proteins physically interact and are coexpressed in the neurons of the preoptic area, a key region in the control of the energy balance and hypophyseal secretion in fish. ACTH injections inhibit food intake in wild-type zebrafish but not in fish lacking functional MC4R. Both MRAP1 and MRAP2a are hormonally regulated, suggesting that these proteins are substrates for feed-back regulatory pathways of melanocortin signaling. Fasting has no effect on the central expression of MRAP2a but stimulates MRAP2b expression. This protein interacts and is colocalized with MC4R in the tuberal hypothalamic neurons but has no effect on the pharmacologic profile of MC4R. However, MRPA2b is able to decrease basal reporter activity in cell lines expressing MC4R. It is plausible that MRAP2b decreases the constitutive activity of the MC4R during fasting periods, driving the animal toward a positive energy balance. Our data indicate that MRAP2s control the activity of MC4R, opening up new pathways for the regulation of melanocortin signaling and, by extension, for the regulation of the energy balance and obesity.
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Characterization of sea bass FSH? 5 flanking region: transcriptional control by 17?-estradiol.
Fish Physiol. Biochem.
PUBLISHED: 07-10-2013
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The sea bass follicle-stimulating hormone 5 flanking region (sbFSH? 5 FR) was cloned and characterized in order to study the molecular mechanisms underlying transcriptional regulation of the sbFSH? gene. Analysis of the ~3.5 kb of this region revealed the presence of several putative cis-acting elements, including steroid hormone response elements, cAMP response elements, pituitary-specific transcription factor response elements, activator protein-1 response elements and TATA sequence. Deleted constructs containing ~3.5 kb of the sbFSH? 5 FR fused to a luciferase reporter gene were transiently transfected into human embryonic kidney (HEK 293) and mouse mature gonadotrope (L?T2) cell lines. The sbFSH? 5 FR was efficiently expressed under basal conditions in L?T2 but not in HEK 293, pointing to both positive and negative regulatory elements. In order to elucidate the estrogen-mediated sbFSH? transcriptional activity, in vitro treatments with 17?-estradiol were carried out on primary cultures of pituitary cells and L?T2 cells transiently expressing luciferase under the control of sbFSH? 5 FR. Overall, these results demonstrate that 17?-estradiol inhibits sbFSH? gene expression directly at the level of the pituitary. However, it was also shown that estrogen did not induce changes of the sbFSH promoter-directed luciferase activity, suggesting that sbFSH? 5FR (~3.5 kb) activity is cell type dependent and its estrogen regulation could require cis-acting elements located upstream of the promoter region, which is characterized in this article.
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Effects of dopaminergic system activation on feeding behavior and growth performance of the sea bass (Dicentrarchus labrax): a self-feeding approach.
Horm Behav
PUBLISHED: 01-08-2013
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Dopamine is synthesized from l-dopa and subsequently processed into norepinephrine and epinephrine. Any excess neurotransmitter can be taken up again by the neurons to be broken down enzymatically into DOPAC. The effect of dopamine on mammalian food intake is controversial. Mice unable to synthesize central dopamine die of starvation. However, studies have also shown that central injection of dopamine inhibits food intake. The effect of dopaminergic system in the fish feeding behavior has been scarcely explored. We report that the inclusion of l-dopa in the diets results in the activation of sea bass central dopaminergic system but also in the significant increase of the hypothalamic serotonin levels. Dietary l-dopa induces a decrease of food intake and feed conversion efficiency that drives a decline of all growth parameters tested. No behavioral effects were observed after l-dopa treatment. l-dopa treatment stimulated central expression of NPY and CRF. It suggests that CRF might mediate l-dopa effects on food intake but also that CRF neurons lie downstream of NPY neurons in the hierarchical forebrain system, thus controlling energy balance. Unexpectedly, dietary administration of haloperidol, a D2-receptor antagonist, cannot block dopamine effects but also induces a decline of the food intake. This decrease seems to be a side effect of haloperidol treatment since fish exhibited a decreased locomotor activity. We conclude that oral l-dopa inhibits sea bass food intake and growth. Mechanism could also involve an increase of hypothalamic serotoninergic tone.
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Morphological and molecular characterization of dietary-induced pseudo-albinism during post-embryonic development of Solea senegalensis (Kaup, 1858).
PLoS ONE
PUBLISHED: 01-01-2013
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The appearance of the pseudo-albino phenotype was investigated in developing Senegalese sole (Solea senegalensis, Kaup 1858) larvae at morphological and molecular levels. In order to induce the development of pseudo-albinos, Senegalese sole larvae were fed Artemia enriched with high levels of arachidonic acid (ARA). The development of their skin pigmentation was compared to that of a control group fed Artemia enriched with a reference commercial product. The relative amount of skin melanophores, xanthophores and iridophores revealed that larval pigmentation developed similarly in both groups. However, results from different relative proportions, allocation patterns, shapes and sizes of skin chromatophores revealed changes in the pigmentation pattern between ARA and control groups from 33 days post hatching onwards. The new populations of chromatophores that should appear at post-metamorphosis were not formed in the ARA group. Further, spatial patterns of distribution between the already present larval xanthophores and melanophores were suggestive of short-range interaction that seemed to be implicated in the degradation of these chromatophores, leading to the appearance of the pseudo-albino phenotype. The expression profile of several key pigmentation-related genes revealed that melanophore development was promoted in pseudo-albinos without a sufficient degree of terminal differentiation, thus preventing melanogenesis. Present results suggest the potential roles of asip1 and slc24a5 genes on the down-regulation of trp1 expression, leading to defects in melanin production. Moreover, gene expression data supports the involvement of pax3, mitf and asip1 genes in the developmental disruption of the new post-metamorphic populations of melanophores, xanthophores and iridophores.
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Molecular characterization and functional regulation of melanocortin 2 receptor (MC2R) in the sea bass. A putative role in the adaptation to stress.
PLoS ONE
PUBLISHED: 01-01-2013
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The activation of melanocortin 2 receptor (MC2R) by ACTH mediates the signaling cascade leading to steroid synthesis in the interrenal tissue (analogous to the adrenal cortex in mammals) of fish. However, little is known about the functional regulation of this receptor in fish. In this work described, we cloned sea bass MC2R from a liver cDNA. SbMC2R requires the melanocortin 2 receptor accessory protein (MRAP) for its functional expression. Dietary cortisol but not long-term stress protocols downregulated interrenal sbMC2R expression. Data suggest the existence of a negative feedback on interrenal sbMC2R expression imposed by local or systemic glucocorticoids. This feedback could be involved in long-term stress adaptation by regulating interrenal sensitivity to ACTH. ACTH-induced MC2R activation stimulates hepatic lipolysis, suggesting that ACTH may mediate stress-induced effects upstream of cortisol release.
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Oleuropein ameliorates acute colitis in mice.
J. Agric. Food Chem.
PUBLISHED: 12-05-2011
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Oleuropein, the major secoiridoid in olive tree leaves, possesses a wide range of health promoting properties. It has recently been shown to exhibit anti-inflammatory activity. We have evaluated the effect of oleuropein on dextran sulfate sodium (DSS)-induced experimental colitis in mice in order to provide insight into its mechanisms of action. Oral administration of oleuropein notably attenuated the extent and severity of acute colitis while reducing neutrophil infiltration; production of NO, IL-1?, IL-6, and TNF-?; expression of iNOS, COX-2, and MMP-9; and the translocation of the NF-?B p65 subunit to the nucleus in colon tissue. In LPS-stimulated peritoneal macrophages, the oleuropein metabolite, hydroxytyrosol, was shown to inhibit NO production, iNOS expression, NF-?B p65 subunit translocation, mRNA expression, and the release of IL-1?, IL-6, and TNF-?. These results suggest that the effect of oleuropein on DSS-induced colitis is associated with a decrease in the production of interleukins and expression of proteins, principally through reduction of NF-?B activation.
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Stress-induced effects on feeding behavior and growth performance of the sea bass (Dicentrarchus labrax): a self-feeding approach.
J. Comp. Physiol. B, Biochem. Syst. Environ. Physiol.
PUBLISHED: 05-02-2011
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Repetitive aquaculture-related protocols may act as cyclic stressors that induce chronic stress in cultured fish. The sea bass is particularly sensitive to stressful conditions and the mere presence of humans will disturb feeding behavior. In this paper, we study whether chronic stress induced by repetition of acute stress protocols affects long-term feeding behavior and growth performance in sea bass and whether exogenous cortisol may induce stress-like changes in these parameters. We demonstrate that both chronic stress and dietary cortisol decrease food intake and have a negative effect on feed conversion efficiency, severely impairing sea bass performance. Both experimental approaches induced changes in the daily feeding activity by lengthening the active feeding periods. Fish subjected to a cyclic stressor modify their daily feeding pattern in an attempt to avoid interference with the time of the stressor. The delay in feeding when fish are acutely and repeatedly stressed could be of substantial adaptive importance.
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Pigment-dispersing activities and cortisol-releasing activities of melanocortins and their receptors in xanthophores and head kidneys of the goldfish Carassius auratus.
Gen. Comp. Endocrinol.
PUBLISHED: 03-03-2011
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The five subtypes of melanocortin receptors (MCRs) mediate the functions of ?-melanocyte-stimulating hormone (?-MSH) and adrenocorticotropic hormone (ACTH). In fish, these hormones are involved in pigment dispersion and cortisol release, respectively. ?-MSH-related peptides exhibit ACTH-like activity in certain fishes. We recently found that multiple Mcr transcripts are expressed in some cell types in the barfin flounder, which is related to regulation of ?-MSH activities. Similar results were also observed for the cortisol-releasing activity of ?-MSH-related peptides in the head kidney. The present study was undertaken to assess relationship between the expression of multiply expressed Mcrs and ?-MSH activities using goldfish. We also determined if ?-MSH-related peptides exhibit ACTH-like activity in goldfish. The transcripts of Mc1r, but not those of other subtypes, were observed in xanthophores. ?-MSH, which has an acetyl group at the N-terminus, was found to disperse pigment in a dose-dependent manner in xanthophores. This potency was found to be slightly greater than that of desacetyl-?-MSH. These results support our findings that MCR has a higher affinity for ?-MSH when single Mcr subtype is expressed. On the other hand, transcripts of Mc2r, but not those of other subtypes, were observed in the head kidney. ACTH(1-24)-stimulated cortisol release was observed in a dose-dependent manner, while ?-MSH-related peptides showed no activity. It therefore appears that MC2R also acts as an ACTH-specific receptor in goldfish and that association of ?-MSH-related peptides upon release of cortisol is uncommon in fishes.
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Fish melanocortin system.
Eur. J. Pharmacol.
PUBLISHED: 01-03-2011
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Melanocortin signalling is mediated by binding to a family of G protein-coupled receptors that positively couple to adenylyl cyclase. Tetrapod species have five melanocortin (MC(1)-MC(5)) receptors. The number of receptors varies in fish, zebrafish, for example, having six melanocortin receptors, with two copies of the melanocortin MC(5) receptor, while pufferfish have 4 receptors with no melanocortin MC(3) receptor and one copy of melanocortin MC(5) receptor. Fish genomes also exhibit orthologue genes for agouti-signalling protein (ASP) and -related protein (AGRP). AGRP expression is confined to a small area in the hypothalamus but ASP is expressed in the skin. Fish melanocortin MC(2) receptor is specific for ACTH and requires the cooperation of accessory proteins (MRAP) to reach functional expression. The four other melanocortin MC receptors distinctively bind MSHs. The interaction of ?-MSH and melanocortin MC(1) receptor plays a key point in the control of the pigmentation and mutations of melanocortin MC(1) receptor are responsible for reduced melanization. Both melanocortin MC(4) and MC(5) receptor are expressed in the hypothalamus, and central melanocortin MC(4) receptor expression is thought to regulate the energy balance through the modulation of feeding behaviour. In addition, the peripheral melanocortin system also regulates lipid metabolism by acting at hepatic melanocortin MC(2) and MC(5) receptors. Both sea bass melanocortin MC(1) and MC(4) receptors are constitutively expressed in vitro and both ASP and AGRP work as inverse agonists but only after inhibition of the phosphodiesterase system. Accordingly, the overexpression of AGRP and ASP transgenes promotes obesity and reduces melanization in zebrafish, respectively.
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Trans- but not cis-resveratrol impairs angiotensin-II-mediated vascular inflammation through inhibition of NF-?B activation and peroxisome proliferator-activated receptor-gamma upregulation.
J. Immunol.
PUBLISHED: 08-13-2010
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Angiotensin II (Ang-II) displays inflammatory activity and is implicated in several cardiovascular disorders. This study evaluates the effect of cis- and trans (t)-resveratrol (RESV) in two in vivo models of vascular inflammation and identifies the cardioprotective mechanisms that underlie them. In vivo, Ang-II-induced arteriolar leukocyte adhesion was inhibited by 71% by t-RESV (2.1 mg/kg, i.v.), but was not affected by cis-RESV. Because estrogens influence the rennin-angiotensin system, chronic treatment with t-RESV (15 mg/kg/day, orally) inhibited ovariectomy-induced arteriolar leukocyte adhesion by 81%, partly through a reduction of cell adhesion molecule (CAM) expression and circulating levels of cytokine-induced neutrophil chemoattractant, MCP-1, and MIP-1alpha. In an in vitro flow chamber system, t-RESV (1-10 microM) undermined the adhesion of human leukocytes under physiological flow to Ang-II-activated human endothelial cells. These effects were accompanied by reductions in monocyte and endothelial CAM expression, chemokine release, phosphorylation of p38 MAPK, and phosphorylation of the p65 subunit of NF-kappaB. Interestingly, t-RESV increased the expression of peroxisome proliferator-activated receptor-gamma in human endothelial and mononuclear cells. These results demonstrate for the first time that the in vivo anti-inflammatory activity of RESV is produced by its t-RESV, which possibly interferes with signaling pathways that cause the upregulation of CAMs and chemokine release. Upregulation of proliferator-activated receptor-gamma also appears to be involved in the cardioprotective effects of t-RESV. In this way, chronic administration of t-RESV may reduce the systemic inflammatory response associated with the activation of the rennin-angiotensin system, thereby decreasing the risk of further cardiovascular disease.
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Melatonin-synthesizing enzymes in pineal, retina, liver, and gut of the goldfish (Carassius): mRNA expression pattern and regulation of daily rhythms by lighting conditions.
Chronobiol. Int.
PUBLISHED: 07-27-2010
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It has been suggested that melatonin is synthesized in nonphotosensitive organs of vertebrates in addition to the well-known sites of the pineal gland and retina. However, very few studies have demonstrated the gene expression of melatonin-synthesizing enzymes in extrapineal and extraretinal locations. This study focuses on the circadian expression of the two key enzymes of the melatoninergic pathway, arylalkylamine N-acetyltransferase (AANAT) and hydroxyindole-O-methyltransferase (HIOMT), in central and peripheral locations of a teleost fish, the goldfish (Carassius auratus). First, the full-length cDNA sequences corresponding to the goldfish AANAT-2 (gAanat-2) and HIOMT-2 (gHiomt-2) were cloned, showing high similarity with other teleost sequences. Two forms of AANAT exist in teleosts. Here, for the first time, two isoforms of HIOMT are deduced from phylogenetic analysis. Moreover, both HIOMT and AANAT were detected in several peripheral locations, including liver and gut, the present results being the first to find HIOMT in nonphotosensitive structures of a fish species. Second, quantitative real-time polymerase chain reaction (PCR) studies were performed to investigate regulation of gAanat-2 in pineal and peripheral locations of goldfish maintained under different lighting conditions. The current results show circadian rhythms in Aanat-2 and Hiomt-2 transcripts in liver and hindgut, suggesting a local melatonin synthesis in goldfish. Moreover, the analysis of daily expression of gAanat-2 under different lighting conditions, including continuous light (24L) and darkness (24D) revealed light-dependent rhythms in the pineal and retina, as expected, but also in liver and hindgut. The persistence in hindgut of these gAanat-2 rhythms under both constant conditions, 24L and 24D, suggests expression of this transcript is governed by a circadian clock and entrained by nonphotic cues. Finally, the current results support the existence of melatonin synthesis in gut and liver of the goldfish.
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Role of melanocortin receptor accessory proteins in the function of zebrafish melanocortin receptor type 2.
Mol. Cell. Endocrinol.
PUBLISHED: 01-08-2010
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In this paper, we identify three different MRAPs in zebrafish, zfMRAP1, zfMRAP2a and zfMRAP2b, and demonstrate that zfMC2R is not functional in the absence of MRAP expression. ZfMRAP1 expression was restricted to adipose tissue and the anterior kidney whereas MRAP2a and MRAP2b were expressed in all the tissues tested. Quantification of surface receptor and immunofluorescence studies indicated that the receptor is unable to translocate to membrane in the absence of MRAP isoforms. MRAP1 and MRAP2b are localized in the plasma membrane in the absence of zfMC2R expression but MRAP2b is retained in perinuclear position. MRAP1 and MRAP2a displayed an equivalent translocation capacity to the membrane of zfMC2R but only zfMRAP1 expression led to intracellular cAMP increases after ACTH stimulation. ZfMRAP2b had no effect on zfMC2R activity but both zfMRAP2 isoforms enhanced the zfMRAP1-assisted cAMP intracellular increase, suggesting an interaction between zfMRAP1 and zfMRAP2s when regulating zfMC2R activity.
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Menopause and ovariectomy cause a low grade of systemic inflammation that may be prevented by chronic treatment with low doses of estrogen or losartan.
J. Immunol.
PUBLISHED: 06-24-2009
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The incidence of cardiovascular diseases in premenopausal women is lower than in men or postmenopausal women. This study reports the discovery of a low grade of systemic inflammation, including monocyte adhesion to arterial endothelium, elicited by menopause or estrogen depletion. Chronic treatment with low dose of 17-beta-estradiol or inhibition of the renin-angiotensin system reduced this inflammation. Using an in vitro flow chamber system with human arterial and venous endothelial cells, we found that leukocytes from healthy postmenopausal women were more adhesive to the arterial endothelium than those from premenopausal women regardless of the stimulus used on endothelial cells. Increased circulating levels of IL-8, MCP-1, RANTES, and MIP-1alpha and monocyte CD11b expression were also encountered in postmenopausal vs premenopausal subjects. This translational data led us to investigate the mechanisms in Sprague-Dawley rats. Using intravital microscopy, we imaged mesenteric arterioles and found significant increases in arteriolar leukocyte adhesion, cell adhesion molecule expression, and plasma levels of cytokine-induced neutrophil chemoattractant (CINC/KC), MCP-1, and MIP-1alpha in 1-mo ovariectomized rats. Chronic treatment of ovariectomized rats with low dose of 17-beta-estradiol, losartan, both, or benazepril inhibited ovariectomy-induced arteriolar mononuclear leukocyte adhesion by 77%, 58%, 92%, and 65% respectively, partly by inhibition of cell adhesion molecule up-regulation and the increase in circulating chemokines. These results demonstrate that menopause and ovariectomy generate a low grade of systemic inflammation. Therefore, administration of low doses of estrogens or inhibition of the renin-angiotensin system, at early stages of estrogen deficiency, might prevent the systemic inflammation associated with menopause and decrease the risk of suffering further cardiovascular diseases.
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Sex steroid-induced inhibition of food intake in sea bass (Dicentrarchus labrax).
J. Comp. Physiol. B, Biochem. Syst. Environ. Physiol.
PUBLISHED: 05-02-2009
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This study was conducted to test the sensitivity to gonadal steroids of the systems regulating food intake in sea bass. Animals were treated with silastic implants containing 17-beta-estradiol or testosterone. Self-feeding was recorded for 31 days using computerized demand feeders and unfed-pellet recovery systems. Both steroids strongly decreased self-feeding levels, feed efficiency and specific growth rates. The linear growth of fish treated with testosterone was higher than in 17-beta-estradiol treated fish. In the second experiment, fish were treated with lower 17-beta-estradiol doses and 11-keto-androstenedione, a precursor of the main fish androgen (11-keto-testosterone). The results demonstrated a dose-response effect of estrogen and no effect of non-aromatizable androgens on food intake or growth performance. The inhibitory effect of testosterone on food intake seems to be mediated by its aromatization to estradiol, while linear growth promotion is mediated by the androgen per se. Data suggest that gonadal steroids may be involved in the seasonal feeding pattern of sea bass. The results demonstrate the sensitivity of the mechanisms regulating food intake to estrogenic compounds and point to the risk of including feed containing estrogenic substances in fish diets as well as the risk involved in exposure to "estrogenic environments".
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Phosphodiesterase inhibitor-dependent inverse agonism of agouti-related protein on melanocortin 4 receptor in sea bass (Dicentrarchus labrax).
Am. J. Physiol. Regul. Integr. Comp. Physiol.
PUBLISHED: 02-18-2009
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The melanocortin 4 receptor (MC4R) is a G protein-coupled receptor mainly expressed in the central nervous system of vertebrates. Activation of the MC4R leads to a decrease in food intake, whereas inactivating mutations are a genetic cause of obesity. The binding of agouti-related protein (AGRP) reduces not only agonist-stimulated cAMP production (competitive antagonist) but also the basal activity of the receptor, as an inverse agonist. Transgenic zebrafish overexpressing AGRP display increased food intake and linear growth, indicative of a physiological role for the melanocortin system in the control of the energy balance in fish. We report on the cloning, pharmacological characterization, tissue distribution, and detailed brain mapping of a sea bass (Dicentrarchus labrax) MC4R ortholog. Sea bass MC4R is profusely expressed within food intake-controlling pathways of the fish brain. However, the activity of the melanocortin system during progressive fasting does not depend on the hypothalamic/pituitary proopiomelanocortin (POMC) and MC4R expression, which suggests that sea bass MC4R is constitutively activated and regulated by AGRP binding. We demonstrate that AGRP acts as competitive antagonist and reduces MTII-induced cAMP production. AGRP also decreases the basal activity of the receptor as an inverse agonist. This observation suggests that MC4R is constitutively active and supports the evolutionary conservation of the AGRP/MC4R interactions. The inverse agonism, but not the competitive antagonism, depends on the presence of a phosphodiesterase inhibitor (IBMX). This suggests that inverse agonism and competitive antagonism operate through different intracellular signaling pathways, a view that opens up new targets for the treatment of melanocortin-induced metabolic syndrome.
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Beneficial effect of shikonin on experimental colitis induced by dextran sulfate sodium in BALB/c mice.
Evid Based Complement Alternat Med
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The naphthoquinone shikonin, a major component of the root of Lithospermum erythrorhizon, now is studied as an anti-inflammatory agent in the treatment of ulcerative colitis (UC). Acute UC was induced in Balb/C mice by oral administration of 5% dextran sodium sulfate (DSS). The disease activity index was evaluated, and a histologic study was carried out. Orally administered shikonin reduces induced UC in a dose-dependent manner, preventing the shortening of the colorectum and decreasing weight loss by 5% while improving the appearance of feces and preventing bloody stools. The disease activity index score was much lower in shikonin-treated mice than in the colitic group, as well as the myeloperoxidase activity. The expression of cyclooxygenase-2 was reduced by 75%, activation of NF-?B was reduced by 44%, and that of pSTAT-3 by 47%, as well as TNF-?, IL-1?, and IL-6 production. Similar results were obtained in primary macrophages culture. This is the first report of shikonins ability to attenuate acute UC induced by DSS. Shikonin acts by blocking the activation of two major targets: NF-?B and STAT-3, and thus constitutes a promising potential therapeutic agent for the management of the inflammatory bowel disease.
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Transient ectopic overexpression of agouti-signalling protein 1 (asip1) induces pigment anomalies in flatfish.
PLoS ONE
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While flatfish in the wild exhibit a pronounced countershading of the dorso-ventral pigment pattern, malpigmentation is commonly observed in reared animals. In fish, the dorso-ventral pigment polarity is achieved because a melanization inhibition factor (MIF) inhibits melanoblast differentiation and encourages iridophore proliferation in the ventrum. A previous work of our group suggested that asip1 is the uncharacterized MIF concerned. In order to further support this hypothesis, we have characterized asip1 mRNAs in both turbot and sole and used deduced peptide alignments to analyze the evolutionary history of the agouti-family of peptides. The putative asip precursors have the characteristics of a secreted protein, displaying a putative hydrophobic signal. Processing of the potential signal peptide produces mature proteins that include an N-terminal region, a basic central domain with a high proportion of lysine residues as well as a proline-rich region that immediately precedes the C-terminal poly-cysteine domain. The expression of asip1 mRNA in the ventral area was significantly higher than in the dorsal region. Similarly, the expression of asip1 within the unpigmented patches in the dorsal skin of pseudoalbino fish was higher than in the pigmented dorsal regions but similar to those levels observed in the ventral skin. In addition, the injection/electroporation of asip1 capped mRNA in both species induced long term dorsal skin paling, suggesting the inhibition of the melanogenic pathways. The data suggest that fish asip1 is involved in the dorsal-ventral pigment patterning in adult fish, where it induces the regulatory asymmetry involved in precursor differentiation into mature chromatophore. Adult dorsal pseudoalbinism seems to be the consequence of the expression of normal developmental pathways in an inaccurate position that results in unbalanced asip1 production levels. This, in turn, generates a ventral-like differentiation environment in dorsal regions.
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Critical role of fractalkine (CX3CL1) in cigarette smoke-induced mononuclear cell adhesion to the arterial endothelium.
Thorax
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Cigarette smoking is an important risk factor for the development of cardiovascular disease, yet the pathways through which this may operate are poorly understood. Therefore, the mechanism underlying cigarette smoke (CS)-induced arterial endothelial dysfunction and the potential link with fractalkine/CX(3)CL1 upregulation were investigated.
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Identification of distant Agouti-like sequences and re-evaluation of the evolutionary history of the Agouti-related peptide (AgRP).
PLoS ONE
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The Agouti-like peptides including AgRP, ASIP and the teleost-specific A2 (ASIP2 and AgRP2) peptides have potent and diverse functional roles in feeding, pigmentation and background adaptation mechanisms. There are contradictory theories about the evolution of the Agouti-like peptide family as well the nomenclature. Here we performed comprehensive mining and annotation of vertebrate Agouti-like sequences. We identified A2 sequences from salmon, trout, seabass, cod, cichlid, tilapia, gilt-headed sea bream, Antarctic toothfish, rainbow smelt, common carp, channel catfish and interestingly also in lobe-finned fish. Moreover, we surprisingly found eight novel homologues from the kingdom of arthropods and three from fungi, some sharing the characteristic C-x(6)-C-C motif which are present in the Agouti-like sequences, as well as approximate sequence length (130 amino acids), positioning of the motif sequence and sharing of exon-intron structures that are similar to the other Agouti-like peptides providing further support for the common origin of these sequences. Phylogenetic analysis shows that the AgRP sequences cluster basally in the tree, suggesting that these sequences split from a cluster containing both the ASIP and the A2 sequences. We also used a novel approach to determine the statistical evidence for synteny, a sinusoidal Hough transform pattern recognition technique. Our analysis shows that the teleost AgRP2 resides in a chromosomal region that has synteny with Hsa 8, but we found no convincing synteny between the regions that A2, AgRP and ASIP reside in, which would support that the Agouti-like peptides were formed by whole genome tetraplodization events. Here we suggest that the Agouti-like peptide genes were formed through classical subsequent gene duplications where the AgRP is the most distantly related to the three other members of that group, first splitting from a common ancestor to ASIP and A2, and then later the A2 split from ASIP followed by a split resulting in ASIP2 and AgRP2.
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The C-terminal domains of melanocortin-2 receptor (MC2R) accessory proteins (MRAP1) influence their localization and ACTH-induced cAMP production.
Gen. Comp. Endocrinol.
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ACTH binding to the human melanocortin-2 receptor (MC2R) requires the presence of the MC2R accessory protein1 isoforms, MRAP? or MRAP?. This study evaluated the role of the isoform-specific C-terminal domains of MRAP with regard to their cellular localization, topology, interaction with MRAP2 and cAMP production. When stably expressed in HEK293/FRT cells or in B16-G4F mouse melanoma cells (an MSH receptor-deficient cell clone), MRAP? and MRAPdCT (truncated MRAP1, N-terminal only) localized mainly around the nuclear envelope and within dense intracellular endosomes, while MRAP? exhibited a strong localization at the plasma membrane, and partially with rapid recycling endosomes. MRAP? and MRAPdCT both exhibited dual-topology (N(cyto)/C(exo) and N(exo)/C(cyto)) at the plasma membrane whereas MRAP? exhibited only N(cyto)/C(exo) topology at the plasma membrane while adopting dual-topology in intracellular compartments. Both MRAP? and MRAP2 colocalized in intracellular compartments, as opposed to weak colocalization between MRAP? and MRAP2. MRAP2 and MC2R enhanced the expression of MRAP1 isoforms and vice versa. Moreover, in both HEK293/FRT and B16-G4F cells, ACTH failed to activate MC2R unless MRAP1 was present. MRAP1 expression enhanced MC2R cell-surface expression as well as concentration-dependent cAMP accumulation. In the presence of human or zebrafish MC2R, MRAP? induced the highest cAMP accumulation while MRAPdCT induced the lowest. Together, the present findings indicate that the C-terminal domains of MRAP dictate their intracellular localization in addition to regulating ACTH-induced cAMP production. These preferential localizations suggest that MRAP? is involved in MC2R targeting to the plasma membrane, while MRAP? may enhance ACTH-MC2R coupling to cAMP production.
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