Attenuation of cocaine-induced locomotor sensitization in rats sustaining genetic or pharmacologic antagonism of ghrelin receptors

Systemic infusions of the orexigenic peptide ghrelin (GHR) increase dopamine levels within the nucleus accumbens and augment cocaine-stimulated locomotion and conditioned place preference in rats; observations that suggest an important role for GHR and GHR receptors (GHR-Rs) in drug reinforcement. In the present studies, we examined the development of cocaine locomotor sensitization in rats, sustaining either pharmacologic antagonism or genetic ablation of GHR-Rs. In a pharmacologic study, adult male rats were injected (i.p.) with either 0, 3 or 6 mg/kg JMV 2959 (a GHR-R1 receptor antagonist), and 20 minutes later, with either vehicle or 10 mg/kg cocaine HCl on each of 7 consecutive days. Rats pretreated with JMV 2959 showed significantly attenuated cocaine-induced hyperlocomotion. In a second study, adult wild-type (WT) or mutant rats sustaining ENU-induced knockout of GHR-R [GHR-R ((-/-) )] received daily injections (i.p.) of vehicle (0.9% saline) or 10.0 mg/kg cocaine HCl for 14 successive days. GHR-R null rats treated repeatedly with cocaine showed diminished development of cocaine locomotor sensitization relative to WT rats treated with cocaine. To verify the lack of GHR-R function in the GHR-R ((-/-) ) rats, a separate feeding experiment was conducted in which WT rats, but not GHR-R ((-/-) ) rats, were noted to eat more after a systemic injection of 15 nmol GHR than after vehicle. These results suggest that GHR-R activity is required for the induction of locomotor sensitization to cocaine and complement an emerging literature implicating central GHR systems in drug reward. GHR is an orexigenic gut peptide that is transported across the blood-brain barrier and interacts with GHR-Rs located on ventral tegmental dopamine neurons.

Brain reinforcement system function is ghrelin dependent: studies in the rat using pharmacological fMRI and intracranial self-stimulation

Ghrelin (GHR) is an orexigenic gut peptide that interacts with brain ghrelin receptors (GHR-Rs) to promote food intake. Recent research suggests that GHR acts as a modulator of motivated behavior, suggesting a direct influence of GHR on brain reinforcement circuits. In the present studies, we investigated the role of GHR and GHR-Rs in brain reinforcement function. Pharmacological magnetic resonance imaging was used to spatially resolve the functional activation produced by systemic administration of an orexigenic GHR dose. The imaging data revealed a focal activation of a network of subcortical structures that comprise brain reinforcement circuits-ventral tegmental area, lateral hypothalamus and nucleus accumbens. We next analyzed whether brain reinforcement circuits require functional GHR-Rs. To this purpose, wild-type (WT) or mutant rats sustaining N-ethyl-N-nitrosourea-induced knockout of GHR-Rs (GHR-R null rats) were implanted with stimulating electrodes aimed at the lateral hypothalamus, shaped to respond for intracranial self-stimulation (ICSS) and then tested using a rate-frequency procedure to examine ICSS response patterns. WT rats were readily shaped using stimulation intensities of 75 µA, whereas GHR-R null rats required 300 µA for ICSS shaping. No differences in rate-frequency curves were noted for WT rats at 75 µA and GHR-R null rats at 300 µA. When current intensity was lowered to 100 µA, GHR-R null rats did not respond for ICSS. Taken collectively, these data suggest that systemic GHR can activate mesolimbic dopaminergic areas, and highlight a facilitative role of GHR-Rs on the activity of brain reinforcement systems.

Ablation of ghrelin receptor in leptin-deficient ob/ob mice has paradoxical effects on glucose homeostasis when compared with ablation of ghrelin in ob/ob mice

The orexigenic hormone ghrelin is important in diabetes because it has an inhibitory effect on insulin secretion. Ghrelin ablation in leptin-deficient ob/ob (Ghrelin(-/-):ob/ob) mice increases insulin secretion and improves hyperglycemia. The physiologically relevant ghrelin receptor is the growth hormone secretagogue receptor (GHS-R), and GHS-R antagonists are thought to be an effective strategy for treating diabetes. However, since some of ghrelin's effects are independent of GHS-R, we have utilized genetic approaches to determine whether ghrelin's effect on insulin secretion is mediated through GHS-R and whether GHS-R antagonism indeed inhibits insulin secretion. We investigated the effects of GHS-R on glucose homeostasis in Ghsr-ablated ob/ob mice (Ghsr(-/-):ob/ob). Ghsr ablation did not rescue the hyperphagia, obesity, or insulin resistance of ob/ob mice. Surprisingly, Ghsr ablation worsened the hyperglycemia, decreased insulin, and impaired glucose tolerance. Consistently, Ghsr ablation in ob/ob mice upregulated negative β-cell regulators (such as UCP-2, SREBP-1c, ChREBP, and MIF-1) and downregulated positive β-cell regulators (such as HIF-1α, FGF-21, and PDX-1) in whole pancreas; this suggests that Ghsr ablation impairs pancreatic β-cell function in leptin deficiency. Of note, Ghsr ablation in ob/ob mice did not affect the islet size; the average islet size of Ghsr(-/-):ob/ob mice is similar to that of ob/ob mice. In summary, because Ghsr ablation in leptin deficiency impairs insulin secretion and worsens hyperglycemia, this suggests that GHS-R antagonists may actually aggravate diabetes under certain conditions. The paradoxical effects of ghrelin ablation and Ghsr ablation in ob/ob mice highlight the complexity of the ghrelin-signaling pathway.

Effect of ghrelin on glucose regulation in mice

Improvement of glucose metabolism after bariatric surgery appears to be from the composite effect of the alterations in multiple circulating gut hormone concentrations. However, their individual effect on glucose metabolism during different conditions is not clear. The objective of this study was to determine whether ghrelin has an impact on glycogenolysis, gluconeogenesis, and insulin sensitivity (using a mice model). Rate of appearance of glucose, glycogenolysis, and gluconeogenesis were measured in wild-type (WT), ghrelin knockout (ghrelin(-/-)), and growth hormone secretagogue receptor knockout (Ghsr(-/-)) mice in the postabsorptive state. The physiological nature of the fasting condition was ascertained by a short-term fast commenced immediately at the end of the dark cycle. Concentrations of glucose and insulin were measured, and insulin resistance and hepatic insulin sensitivity were calculated. Glucose concentrations were not different among the groups during the food-deprived period. However, plasma insulin concentrations were lower in the ghrelin(-/-) and Ghsr(-/-) than WT mice. The rates of gluconeogenesis, glycogenolysis, and indexes of insulin sensitivity were higher in the ghrelin(-/-) and Ghsr(-/-) than WT mice during the postabsorptive state. Insulin receptor substrate 1 and glucose transporter 2 gene expressions in hepatic tissues of the ghrelin(-/-) and Ghsr(-/-) were higher compared with that in WT mice. This study demonstrates that gluconeogenesis and glycogenolysis are increased and insulin sensitivity is improved by the ablation of the ghrelin or growth hormone secretagogue receptor in mice.

Ghrelinergic system in fish ovaries and ghrelin inhibition of germinal vesicle breakdown in zebrafish oocytes

Ghrelin, the only known orexigenic gut hormone has been proposed to integrate energy balance and reproduction in mammals. There is a large set of data available on the orexigenic and LH stimulatory roles of ghrelin in fish. Ghrelin and ghrelin receptor mRNAs are expressed in the gonads of several fishes. However, the direct roles of ghrelin on fish gonads remain unclear. Our objective was to identify the ghrelinergic system in fish ovaries, at the protein level in the cross sections of paraffin fixed ovaries, and test the direct effects of ghrelin on oocyte maturation. Both ghrelin and ghrelin receptor like immunoreactivity was detected in the follicle cells in the cross section of goldfish and zebrafish ovaries. This agrees with the mRNA expression data and further confirms the presence of the ghrelinergic system in fish ovaries. We found that native ghrelin at 10, 50 and 100 ng/mL concentrations inhibited both basal and maturation-inducing hormone stimulated stage IV germinal vesicle breakdown (GVBD) of zebrafish oocyte maturation in vitro. This result indicates that ghrelin acts directly on zebrafish follicles. When zebrafish follicles were co-incubated with ghrelin and a well-characterized ghrelin receptor antagonist, D-lys(3)-GHRP-6, the inhibitory effects of ghrelin on stage IV GVBD was abolished. This result indicates that ghrelin inhibits stage IV GVBD via its receptor(s). Collectively, our results for the first time indicate a direct role for ghrelin in the ovarian physiology of fish.

MC4R dimerization in the paraventricular nucleus and GHSR/MC3R heterodimerization in the arcuate nucleus: is there relevance for body weight regulation?

The worldwide obesity epidemic is increasing, yet at this time, no long-acting and specific pharmaceutical therapies are available. Peripheral hormonal signals communicate metabolic status to the hypothalamus by activating their corresponding receptors in the arcuate nucleus (ARC). In this brain region, a variety of G protein-coupled receptors (GPCRs) are expressed that are potentially involved in weight regulation, but so far, the detailed function of most hypothalamic GPCRs is only partially understood. An important and underappreciated feature of GPCRs is the capacity for regulation via di- and heterodimerization. Increasing evidence implicates that heterodimerization of GPCRs results in profound functional consequences. Recently, we could demonstrate that interaction of the melanocortin 3 receptor (MC3R) and the growth hormone secretagogue receptor (GHSR)-1a results in a modulation of function in both receptors. Although the physiological role of GPCR-GPCR interaction in the hypothalamus is yet to be elucidated, this concept promises new avenues for investigation and understanding of hypothalamic functions dependent on GPCR signaling. Since GPCRs are important targets for drugs to combat many diseases, identification of heterodimers may be a prerequisite for highly specific drugs. Therefore, a detailed understanding of the mechanisms and their involvement in weight regulation is necessary. Fundamental to this understanding is the interplay of GPCR-GPCR in the hypothalamic nuclei in energy metabolism. In this review, we summarize the current knowledge on melanocortin receptors and GHSR-1a in hypothalamic weight regulation, especially as they pertain to possible drug targets. Furthermore, we include available evidence for the participation and significance of GPCR dimerization.

Beyond the metabolic role of ghrelin: a new player in the regulation of reproductive function

Ghrelin is a gastric peptide, discovered by Kojima et al. (1999) [55] as a result of the search for an endogenous ligand interacting with the "orphan receptor" GHS-R1a (growth hormone secretagogue receptor type 1a). Ghrelin is composed of 28 aminoacids and is produced mostly by specific cells of the stomach, by the hypothalamus and hypophysis, even if its presence, as well as that of its receptors, has been demonstrated in many other tissues, not least in gonads. Ghrelin potently stimulates GH release and participates in the regulation of energy homeostasis, increasing food intake, decreasing energy output and exerting a lipogenetic effect. Furthermore, ghrelin influences the secretion and motility of the gastrointestinal tract, especially of the stomach, and, above all, profoundly affects pancreatic functions. Despite of these previously envisaged activities, it has recently been hypothesized that ghrelin regulates several aspects of reproductive physiology and pathology. In conclusion, ghrelin not only cooperates with other neuroendocrine factors, such as leptin, in the modulation of energy homeostasis, but also has a crucial role in the regulation of the hypothalamic-pituitary gonadal axis. In the current review we summarize the main targets of this gastric peptide, especially focusing on the reproductive system.

GPR39, a receptor of the ghrelin receptor family, plays a role in the regulation of glucose homeostasis in a mouse model of early onset diet-induced obesity

GPR39, which may function as a Zn(2+) sensor, is a member of the G protein-coupled receptor family that also includes the receptor for the hunger hormone ghrelin. The down-regulation of GPR39 mRNA in adipose tissue of obese type 2 diabetic patients suggests that GPR39 may contribute to the pathogenesis of the disease. The present study aimed to investigate the role of GPR39 in the regulation of energy balance and glucose homeostasis in wild-type (GPR39(+/+) ) and GPR39 knockout mice (GPR39(-/-) ) with obesity-related type 2 diabetes. GPR39 mRNA levels in adipose tissue of fasted GPR39(+/+) mice fed a high-fat diet (HFD) for 30 weeks were reduced and correlated positively with blood glucose levels. Body weight, fat percentage and energy intake were increased in the HFD group but did not differ between both genotypes. Within the HFD group, blood glucose levels were lower in GPR39(-/-) than in GPR39(+/+) mice, despite significant reductions in prandial plasma insulin levels. The latter may not be a result of changes in β-cell hyperplasia because immunohistochemical staining of pancreata of mice on a HFD showed no differences between genotypes. The lower blood glucose levels may involve alterations in insulin sensitivity as revealed by glucose tolerance tests and respiratory quotient measurements that showed a preference of obese GPR39(-/-) mice for the use of carbohydrates as metabolic fuel. The increase in plasma ghrelin levels in GPR39(-/-) mice fed a HFD may contribute to the alterations in glucose homeostasis, whereas changes in gastric emptying or intestinal Zn(2+) absorption are not involved. The results obtained in the present study suggest that GPR39 plays a role in the pathogenesis of obesity-related type 2 diabetes by affecting the regulation of glucose homeostasis.

Genetics of GHRH, GHRH-receptor, GH and GH-receptor: its impact on pharmacogenetics

When a child is not following the normal, predicted growth curve, an evaluation for underlying illnesses and central nervous system abnormalities is required and, appropriate consideration should be given to genetic defects causing GH deficiency (GHD). Because Insulin-like-Growth Factor-I (IGF-I) plays a pivotal role, GHD could also be considered as a form of IGF-I deficiency (IGFD). Although IGFD can develop at any level of the GHRH-GH-IGF axis, a differentiation should be made between GHD (absent to low GH in circulation) and IGFD (normal to high GH in circulation). The main focus of this review is on the GH-gene, the various gene alterations and their possible impact on the pituitary gland. However, although transcription factors regulating the pituitary gland development may cause multiple pituitary hormone deficiency they may present initially as GHD. These defects are discussed in various different chapters within this book, whereas, the impact of alterations of the GHRH-, GHRH-receptor- --as well as the GH-receptor (GHR) gene--will be discussed here.

Role of hormonal axis, growth hormone - IGF-1, in the therapeutic effect of ghrelin in the course of cerulein-induced acute pancreatitis

Ghrelin is a ligand for growth hormone secretagogue receptor and stimulates release of growth hormone (GH). Recent studies have shown that treatment with ghrelin exhibits protective and therapeutic effect in the course of experimental pancreatitis. The aim of present study was to examine the role of GH and insulin-like growth factor-1 (IGF-1) in these effects. Acute pancreatitis was induced by cerulein. Study was performed on pituitary-intact hypophysectomized rats. Ghrelin was administered twice a day at the dose of 8 nmol/kg/dose. IGF-1 was given twice a day at the dose of 20 nmol/kg/dose. The severity of acute pancreatitis was assessed 0 h or 1, 2, 3, 5 and 10 days after the last dose of cerulein. Administration of cerulein led to the development of acute edematous pancreatitis. In pituitary-intact rats, treatment with ghrelin reduced biochemical indexes of the severity of acute pancreatitis and morphological signs of pancreatic damage, leading to faster regeneration of the pancreas reduction in serum concentration of pro-inflammatory interleukin-1β and decrease in serum activity of amylase and lipase. These effects were accompanied with an improvement of pancreatic blood flow and an increase in pancreatic DNA synthesis. Hypophysectomy delayed the healing of the pancreas and abolished the therapeutic effect of ghrelin. In hypophysectomized rats with pancreatitis, treatment with IGF-1 exhibits therapeutic effect similar to that observed in ghrelin-treated rats with the intact pituitary. We conclude that therapeutic effect of ghrelin in cerulein-induced pancreatitis is indirect and depends on the release of GH and IGF-1.

Effects of GH secretagogues on contractility and Ca2+ homeostasis of isolated adult rat ventricular myocytes

Ghrelin and its synthetic analogue hexarelin are specific ligands of GH secretagogue receptor (GHS-R) and induce a variety of cardiovascular protective and cardiac positive inotropic effects. The signaling system underlying immediate effects of both GHSs in cardiomyocytes remains undefined. In the present study, we investigated the immediate effects of GHSs on isolated ventricular myocyte shortening, intracellular Ca(2+) ([Ca(2+)](i)) transients, and the L-type Ca(2+) current (I(Ca,L)). Putative intracellular signalling cascades were studied with specific receptor and signalling blockers. In fresh isolated adult Wistar rat ventricular myocytes, GHSs produced a positive inotropic effect in a concentration-dependent manner and increased the amplitude of [Ca(2+)](i) transients and the I(Ca,L). The positive inotropic response was abolished by the GHS-R1a antagonist [D-Lys(3)]-GH-releasing peptide-6 (10 microm). GHS-induced increase in the I(Ca,L) was abolished by [D-Lys(3)]-GH-releasing peptide-6 and protein kinase C inhibitor, chelerythrine chloride (5 microm), but not by protein kinase A inhibitor, KT 5720 (10 microm). We conclude that hexarelin and ghrelin increase the I(Ca,L), through GHS-R1a receptor and protein kinase C signalling cascade, which contribute to its direct positive inotropic effect on cardiomyocytes.

Unacylated ghrelin rapidly modulates lipogenic and insulin signaling pathway gene expression in metabolically active tissues of GHSR deleted mice

Background

There is increasing evidence that unacylated ghrelin (UAG) improves insulin sensitivity and glucose homeostasis; however, the mechanism for this activity is not fully understood since a UAG receptor has not been discovered.

Methodology/Principal Findings

To assess potential mechanisms of UAG action in vivo, we examined rapid effects of UAG on genome-wide expression patterns in fat, muscle and liver of growth hormone secretagogue receptor (GHSR)-ablated mice using microarrays. Expression data were analyzed using Ingenuity Pathways Analysis and Gene Set Enrichment Analysis. Regulation of subsets of these genes was verified by quantitative PCR in an independent experiment. UAG acutely regulated clusters of genes involved in glucose and lipid metabolism in all three tissues, consistent with enhancement of insulin sensitivity.

Conclusions/Significance

Fat, muscle and liver are central to the control of lipid and glucose homeostasis. UAG rapidly modulates the expression of metabolically important genes in these tissues in GHSR-deleted mice indicating a direct, GHSR-independent, action of UAG to improve insulin sensitivity and metabolic profile.

Cardiovascular and metabolic effects of ghrelin

Ghrelin is an orexigenic peptide hormone secreted into the systemic circulation predominantly by the X/A-like cells in the mucosa of the stomach. In addiction to central effects on food intake and growth hormone release, ghrelin has also important vascular and metabolic actions. Our laboratory has shown that administration of exogenous ghrelin acutely improves endothelial function by increasing nitric oxide bioavailability and normalizing the alterate balance between endothelin 1/nitric oxide (ET-1/NO) within the vasculature of individuals with metabolic syndrome. Additionally, in endothelial cell cultures, it has been shown that ghrelin directly stimulates NO production using a signaling pathway that involves GHSR-1a, PI 3-kinase, Akt, and eNOS. Other cardiovascular effects of ghrelin include lowering of peripheral resistance, improvement of contractility and cardiac output. In addition ghrelin plays a significant role in the regulation of glucose homeostasis, lipid profiles and body composition. Importantly, ghrelin has antinflammatory and antiapoptotic effects both in vivo and in vitro. This review focuses on the physiological roles of ghrelin in regulating metabolic and endothelial function and on the potential of ghrelin as the therapeutic target to treat metabolic and cardiovascular disorders.

Modulation of ingestive behavior and gastrointestinal motility by ghrelin in diabetic animals and humans

Acyl ghrelin, a 28-amino acid peptide hormone, is the endogenous cognate ligand for the growth hormone secretagogue receptor. Ghrelin is involved in stimulating growth hormone release, eliciting feeding behavior, inducing adiposity and stimulating gastrointestinal motility. Ghrelin is unique for its post-translational modification of O-n-octanoylation at serine 3 through ghrelin O-acyltransferase, and is the only peripheral signal to enhance food intake. Plasma ghrelin levels manifest "biphasic changes" in diabetes mellitus (DM). In the early stage of DM, the stomach significantly increases the secretion of ghrelin into the plasma, and elevated plasma ghrelin levels are correlated with diabetic hyperphagic feeding and accelerated gastrointestinal motility. In the late stage of DM, plasma ghrelin levels may be lower, which might be linked with anorexia/muscle wasting, delayed gastrointestinal transit, and even gastroparesis. Therefore, the unique ghrelin system may be the most important player compared to the other hindgut hormones participating in the "entero-insular axis". Further studies using either knockdown or knockout of ghrelin gene products and ghrelin O-acyltransferase may unravel the pathogenesis of DM, and show benefits in combating this disease and metabolic syndrome.

[Ghrelin down-regulates ACAT-1 in THP-1 derived foam cells via growth hormone secretagogue receptor-dependent pathway]

OBJECTIVE

To investigate the effects of Ghrelin on the expression of acyl coenzyme A:cholesterol acyltransferases-1 (ACAT-1) in THP-1 derived foam cells.

METHODS

The human monocytic leukemia cell line (THP-1) was chosen in our study. The differentiation of THP-1 cells into macrophages was induced by phorbol 12-myristate 13-acetate. Macrophages were then incubated with oxidized LDL (ox-LDL) to generate foam cells. Ghrelin and [D-Lys3]-GHRP-6, the special antagonist of growth hormone secretagogue receptor (GHS-R), were treated during foam cells formation. The ACAT-1 protein and mRNA levels were detected by Western blot and RT-PCR. The effect of variance of cholesterol content was measured by zymochemistry via-fluorospectrophotometer.

RESULTS

Ghrelin reduced the content of cholesterol ester in foam cells obviously. ACAT-1 protein and mRNA levels were also decreased. The antagonist of GHS-R inhibited the effects of Ghrelin on ACAT-1 expression in dose-dependent manner. The ACAT-1 mRNA levels of the GHS-R specific antagonist groups (10(-5), 5 x 10(-5), 10(-4) mol/L) were 1.14 +/- 0.04, 1.58 +/- 0.03, 2.40 +/- 0.16, significantly higher than that of the Ghrelin group (0.89 +/- 0.05). And the protein expressions were 1.25 +/- 0.09, 1.77 +/- 0.11, 2.30 +/- 0.09, also higher than that of the Ghrelin group (0.86 +/- 0.08).

CONCLUSIONS

Ghrelin might interfere atherosclerosis by down-regulating the expression of ACAT-1 via GHS-R pathway.

Assessing the role of the growth hormone secretagogue receptor in motivational learning and food intake

The orexigenic neuropeptide ghrelin is an endogeneous ligand for the growth hormone secretagogue receptor (GHS-R). This orexigen is expressed in both the periphery and in the central system, including portions of mesolimbic dopaminergic circuitry that play a role in affective behaviors. Here we examined pharmacological antagonism of GHS-R in motivational incentive learning, as reflected in Pavlovian-to-instrumental transfer (PIT). Furthermore, it is currently unclear whether the previous effects of ghrelin on food intake are mediated by pre- and/or postingestive influences on ingestive behavior. Thus, the authors also conducted detailed analyses of the temporal dynamics of sucrose licking. Mice received low (50 nmol), moderate (100 nmol), and high (200 nmol) intraperitoneal injections of the GHS-R antagonist GHRP-6 [D-Lys3] prior to subsequent transfer and sucrose consumption tests. Low and moderate doses led to an augmentation of PIT, while high dose injections led to generalized performance deficits. In addition, moderate and high doses of the antagonist resulted in reductions in sucrose intake by reducing palatability of the sucrose. These results suggest dissociable functions of GHS-R in its influence over motivational learning and ingestive behavior.

Gastric mammalian target of rapamycin signaling regulates ghrelin production and food intake

Ghrelin, a gastric hormone, provides a hunger signal to the central nervous system to stimulate food intake. Mammalian target of rapamycin (mTOR) is an intracellular fuel sensor critical for cellular energy homeostasis. Here we showed the reciprocal relationship of gastric mTOR signaling and ghrelin during changes in energy status. mTOR activity was down-regulated, whereas gastric preproghrelin and circulating ghrelin were increased by fasting. In db/db mice, gastric mTOR signaling was enhanced, whereas gastric preproghrelin and circulating ghrelin were decreased. Inhibition of the gastric mTOR signaling by rapamycin stimulated the expression of gastric preproghrelin and ghrelin mRNA and increased plasma ghrelin in both wild-type and db/db mice. Activation of the gastric mTOR signaling by l-leucine decreased the expression of gastric preproghrelin and the level of plasma ghrelin. Overexpression of mTOR attenuated ghrelin promoter activity, whereas inhibition of mTOR activity by overexpression of TSC1 or TSC2 increased its activity. Ghrelin receptor antagonist d-Lys-3-GH-releasing peptide-6 abolished the rapamycin-induced increment in food intake despite that plasma ghrelin remained elevated. mTOR is therefore a gastric fuel sensor whose activity is linked to the regulation of energy intake through ghrelin.

[Progress in biological effects of cortistatin]

Cortistatin, cloned from cerebral cortex in mammal in 1996, is a sort of polypeptide with multiple biological activities and shares high structural homology with somatostatin. It is widely distributed in tissues and organs of human body, such as brain, coronary artery, stomach, kidney, testis, leukocyte and immunological system. A growing evidence indicates that cortistatin exerts many kinds of biological effects including modulating the process of study and memory, inducing sleep, inhibiting inflammation and regulating endocrine metabolism and homeostasis of cardiovascular system. And these effects are mediated by binding somatostatin receptors, grow hormone secretagogues receptor-1a and Mas-related gene X2 receptor. Cortistatin is considered an important factor regulating the balance of body homeostasis.

Expression of ghrelin receptor, GHSR-1a, and its functional role in the porcine ovarian follicles

Recently, we reported stimulatory effect of ghrelin alone and in combination with growth hormone (GH) on estradiol secretion, aromatase activity in parallel with inhibitory effect on cell apoptosis. The aim of this study was to analyze the expression of the functional ghrelin receptor (GHS-R type 1a) and the effect of GH on GHSR-1a expression in cultured whole porcine follicles. Using RT-PCR and Western Blots, we demonstrated the presence of GHSR-1a in prepubertal pig ovary and found no influence of GH on either GHSR-1a protein levels or mRNA expression. Additionally, to show if, noted previously by us action of ghrelin on ovarian follicular function is dependent of its binding to GHSR-1a, we used an antagonist of the ghrelin receptor, (D-Lys-3)-GHRP-6. In cultures treated together ghrelin and (D-Lys-3)-GHRP-6, estradiol secretion, aromatase activity and cell proliferation returned to control levels. Inhibitory action on caspase-3 activity was not reversed by a selective antagonist of GHSR-1a. In conclusion, results of the present data clearly showed: (1) the presence of GHSR-1a in prepubertal pig ovary and found no influence of GH on GHSR-1a protein levels and mRNA expression, and (2) ghrelin effect on estradiol secretion, aromatase activity and cell proliferation dependent of its binding to GHSR-1a, while the effect on cellular apoptosis was independent of its binding to GHSR-1a.

Ghrelin stimulates proliferation of human osteoblastic TE85 cells via NO/cGMP signaling pathway

Ghrelin regulates bone formation and osteoblast proliferation, but the detailed signaling pathway for its action on osteoblasts remains unclear. In human osteoblastic TE85 cells, we observed the effects and intracellular signaling pathway of ghrelin on cell proliferation using BrdU incorporation method. Ghrelin, at 10(-10)-10(-8) M concentration, significantly increased BrdU incorporation into TE85 cells. The action of ghrelin was inhibited by D: -Lys3-GHRP-6, a selective antagonist of GHS-R. Nitric oxide (NO) scavenger hemoglobin and the NO synthase inhibitor NAME eliminated the stimulatory action of ghrelin on proliferation, while NO donor SNAP and NO synthase substrate L-AME stimulated proliferation of osteoblastic TE85 cells. The cGMP analogue, 8-Br-cGMP, stimulated TE85 cell proliferation, and ghrelin did not enhance proliferation in the presence of 8-Br-cGMP. Inhibition of cGMP production by the guanylate cyclase inhibitor prevented ghrelin-induced osteoblastic TE85 cell proliferation. In conclusion, ghrelin stimulates proliferation of human osteoblastic TE85 cells via intracellular NO/cGMP signaling pathway.

Neuroprotective effect of ghrelin is associated with decreased expression of prostate apoptosis response-4

Ghrelin is known to promote neuronal defense and survival against ischemic injury by inhibiting apoptotic processes. In the present study, we investigated the role of prostate apoptosis response-4 (Par-4), a proapoptotic gene the expression of which is increased after ischemic injury, in ghrelin-mediated neuroprotection during middle cerebral artery occlusion (MCAO). Both ghrelin and des-acyl ghrelin protected cortical neurons from ischemic injury. Ghrelin receptor specific antagonist abolished the protective effects of ghrelin, whereas those of des-acyl ghrelin were preserved, suggesting the involvement of a receptor that is distinct from GHS-R1a. The expression of Par-4 was increased by MCAO, which was attenuated by ghrelin and des-acyl ghrelin treatments. Both ghrelin and des-acyl ghrelin increased the Bcl-2/Bax ratio, prevented cytochrome c release, and inhibited caspase-3 activation. Our data indicate that des-acyl ghrelin, as well as ghrelin, protect cortical neurons against ischemic injury through the inhibition of Par-4 expression and apoptotic molecules in mitochondrial pathway.