Ghrelin对消化系统功能的调节

Ghrelin是一种生长激素促分泌物受体的内源性配体,具有刺激下丘脑和垂体前叶释放生长激素、增强食欲、调节能量平衡及促进胃酸分泌等作用。Ghrelin及其受体在下丘脑、垂体、肾、胃、胰腺、唾液腺中都有表达,可能是脑与胃肠道之间调节内分泌的一种介质,有望在诊断和治疗某些消化系统疾病中发挥一定的作用。本文就消化系统分泌的ghrelin的调节功能作一简要综述。     

唾液腺能够产生Ghrelin

Ghrelin是最初在胃内分泌细胞中发现的脑肠肽,是生长激素促分泌受体（GHS-R）的内源性配体。近年来的研究证明,除胃肠道外,两栖类动物的下丘脑、心脏、胰腺、肺、胎盘都能产生ghrelin。Ghrelin由28个氨基酸组成,其N端第3位n-辛酰化的丝氨酸是ghrelin与其受体结合并发挥生物学活性的关键部位。Ghrelin主要的生理功能是促进生长激素释放,促进摄食和调节能量代谢。Ghrelin可以作用于胃肠道,     

Ghrelin:一种新发现的生长激素释放肽

Ghrelin是一种新发现的含有28个氨基酸的生长激素释放肽,为生长激素促分泌素受体(growthhormonesecretagoguereceptor,GHSR)的内源性配体。当Ghrelin与其特异性受体(GHSR)结合后会产生一系列生物学效应。Ghrelin具有刺激垂体前叶释放生长激素、增加食欲、调节能量代谢平衡,以及促进胃酸分泌等生物学功能,其作用机制目前尚不清楚。     

脑肠肽Ghrelin-GHSR信号系统与肿瘤的关系

脑肠肽Ghrelin是一种含有28个氨基酸的生长激素释放肽,为生长激素促分泌素受体(growth hormone secretagogue recep-tor,GHSR)的内源性配体。Ghrelin及其功能性受体GHSR-1a广泛分布于中枢和外周组织。此外,在多种肿瘤组织和癌细胞中发现有Ghrelin及其功能性受体GHSR-1a的表达。我们的前期工作和目前的研究发现Ghrelin可与经典的功能性受体GHSR-1a或新型受体结合,通过激活多条信号转导通路,对肿瘤的生物学行为发挥重要的调控作用。因此,脑肠肽Ghrelin-GHSR信号系统可为肿瘤的临床诊断和预后评估发挥重要作用,并为肿瘤的分子治疗提供新靶点。     

Ghrelin与疼痛研究进展

Ghrelin为1999年从大鼠胃粘膜及下丘脑中发现的一种生长激素促分泌素受体(growth hor-mone secretagogue receptor,GHS-Rs)的天然配体,由28个氨基酸残基组成。Ghrelin广泛分布于机体的多个组织器官,如下丘脑、垂体、胃肠道、胰腺、心脏、性腺等。Ghrelin与其受体结合后,具有促进生长激素的释放、增加摄食、刺激胃蠕动和胃酸分泌,改善心血管等多种生物学作用。近年来有研究表明,Ghrelin在中枢神经系统具有广泛分布,并且具有镇痛作用,其主要通过调节与疼痛有关的系统和抑制促炎细胞因子的分泌进而缓解疼痛。现将Ghrelin在疼痛方面的研究做一综述。     

新近发现的一种调节肽——生长素

生长素（ghrelin）是一种新发现的含有28个氨基酸的多肽,1999年日本科学家Kojima最先在小鼠和人胃内分泌细胞中发现。最近又在人的下丘脑和脑干发现一种孤立的G蛋白偶联受体-促生长激素分泌受体（GHS-Rs),是其特异性受体,当生长素与其特异性受体结合后会产生一系列生物学效应,如刺激垂体前叶释放生长激素,增加食欲,调节能量平衡,促进胃酸分泌,抗生长素免疫球蛋白G可明显抑制食欲,神经肽Y（NPY）及刺鼠肽基因相关蛋白（AGRP）的抗体或拮抗剂可阻断生长素的增食欲作用,生长素可使NPY基因表达增高并阻断瘦素引起的降低食欲作用,禁食,低血糖和瘦素能使生长素在胃内表达上调,它可能是生长激素/胰岛素样生长因子-1轴和调节能量平衡的神经内分泌调节之间的一个新的联结纽带,与肥胖等密切相关。     

Ghrelin和脑功能

Ghrelin是首先从大鼠胃粘膜发现的一种新的脑-肠肽激素,具有促进生长激素释放的作用。它经辛酰化修饰具有生物学活性后可以通过血脑屏障发挥作用。研究发现,Ghrelin及其受体在脑组织(如下丘脑、大脑皮质、脑干、海马等)分布较广泛。近几年来,人们对Ghrelin和脑功能的研究也越来越多。本文就Ghrelin在学习和记忆、睡眠、焦虑、应激及神经保护等脑功能中所发挥的作用作一综述。     

Ghrelin与内分泌代谢异常

Ghrelin是近年来新发现的一种小分子活性肽, 主要由胃底的X/A 样细胞分泌,是生长激素促分泌物受体(GHS-R)的内源性配体.Ghrelin及其受体也可表达于肠道、胰腺、肾脏、性腺、胎盘、甲状腺、肾上腺、下丘脑、垂体等多种内分泌组织或器官.研究表明,ghrelin与糖代谢、甲状腺疾病、肥胖、多囊卵巢综合征等多种内分泌代谢疾患有关.本文将就ghrelin与内分泌代谢异常的关系的研究进展作简要介绍.     

Ghrelin与生殖系统研究进展

Ghrelin是1999年发现的生长激素促分泌素受体(growth hormone secretagogue receptor,GHS-R)的天然配体,由28个氨基酸残基组成.除具有促进生长激素的释放、增加摄食、刺激胃蠕动和胃酸分泌,尚有其它许多功能.近年来发现Ghrelin及其受体在生殖系统也广泛分布,提示Ghrelin对生殖系统也具有重要的调节作用,进一步的研究发现Ghrelin具有调节生殖激素黄体生成素、催乳素、雌二醇和孕酮的分泌,促进颗粒细胞的增殖等作用.本文就Ghrelin在生殖系统的研究进展做如下综述.     

冷环境、运动与限食通过ghrelin/Goat/GHS-R系统调节能量平衡的研究进展

胃饥饿素(ghrelin)是一种促循环生长激素(GH)释放和诱导食欲的脑肠肽,在被生长素释放肽O-酰基转移酶(Goat)酰基化后,与生长激素促分泌素受体(GHS-R)结合发挥多种生理作用,如作用于下丘脑弓状核发挥中枢促食欲作用,而外周的ghrelin则促进糖异生和脂肪沉积。在机体的能量代谢过程中,ghrelin/Goat/GHS-R系统对能量平衡发挥着重要的调节作用。研究发现,冷环境、运动和限食均能通过该系统调控能量代谢,但目前国内尚未见相关综述报道。本文梳理国内外相关研究报道,在综述ghrein、Goat和GHS-R对调节能量平衡作用的基础上,介绍冷环境、运动和限食对ghrelin/Goat/GHS-R系统的影响,并提出其介导能量平衡的可能机制,为在冷环境与限食条件下运动防治肥胖提供理论依据。     

The role of C-terminal part of ghrelin in pharmacokinetic profile and biological activity in rats

Ghrelin is an endogenous ligand for growth hormone secretagogue receptor 1a (GHS-R1a), and consists of 28 amino acid residues with octanoyl modification at Ser³. The previous studies have revealed that N-terminal part of ghrelin including modified Ser³ is the active core for the activation of GHS-R1a. On the other hand, the role of C-terminal (8-28) region in ghrelin has not been clarified yet. In the present study, we prepared human ghrelin, C-terminal truncated ghrelin derivatives and anamorelin, a small molecular GHS compound which supposedly mimics the N-terminal active core, and examined GHS-R1a agonist activity in vitro, pharmacokinetic (PK) profile and growth hormone (GH) releasing activity in rats. All compounds demonstrated potent GHS-R1a agonist activities in vitro. Although the lack of C-terminal two amino acids did not modify PK profile and GH releasing activity, the deletion of C-terminal 8 and 20 amino acids affected them, and ghrelin(1-7)-Lys-NH₂ exhibited very short plasma half-life and low GH releasing activity in vivo. In rat plasma, ghrelin(1-7)-Lys-NH₂ was degraded more rapidly than ghrelin, suggesting that C-terminal part of ghrelin protected octanoylation of Ser³ from plasma esterases. Subdiaphragmatic vagotomy significantly attenuated GH response to ghrelin but not to anamorelin. These results suggest that the C-terminal part of ghrelin has an important role in the biological activity in vivo. We also found that ghrelin stimulated GH release mainly via a vagal nerve pathway but anamorelin augmented GH release possibly by directly acting on brain in rats.     

Generation of polyclonal antiserum against the growth hormone secretagogue receptor (GHS-R): evidence that the GHS-R exists in the hypothalamus, pituitary and stomach of rats

Growth hormone (GH) secretagogues (GHSs), which stimulate GH secretion, are synthetic compounds that act through the GHS receptor (GHS-R) which has been recently cloned. We raised an antiserum in a rabbit against a synthetic peptide corresponding to amino acid residues 248-260 of the third intracellular loop of the rat GHS-R. A competitive immunoassay showed that the antiserum had a specific affinity for the target peptide. To confirm the specificity of the antiserum, the GHS-R cDNA was stably expressed in COS-7 cells. In Western blot analysis, the band was detected at 44 kDa in the extracts from COS-7 cells expressing GHS-R (COS-7/tf3-2) but not in those from wild-type COS-7 cells. Furthermore, while COS-7/tf3-2 cells were strongly immunostained for GHS-R, no GHS-R-like immunoreactivity was observed in wild-type COS-7 cells. Immunoreactive bands were also observed at approximately 46 kDa in the extracts from rat hypothalamus, pituitary and stomach by Western blot analysis. These studies are the first to show the existence of GHS-R protein in the stomach. The antiserum for the GHS-R is sensitive and specific, and it would be useful for clarifying the roles of GHS/ghrelin.     

新的生长激素异形体基因的发现及全长cDNA的克隆

在通过大规模 ESTS技术对垂体基因表达谱的研究中 ,从垂体组织产生了 72 2 2个 ESTS,有385个 ESTs是代表生长激素 (GH)基因的 ,其中 1个为中间缺失 1 38bp的 GH异形体基因 ,并经巢式 RT- PCR及测序证实 ;该基因编码 1 71个氨基酸的前肽 ,去除信号肽后 ,其成熟肽由 1 45个氨基酸组成 ;经生物信息学处理 ,其分子量大小约 1 7k D;与正常生长激素分子内有 2个 GH受体结合位点不同 ,该新的 GH异形体分子内仅有一个生长激素受体的结合位点 .研究结果揭示 :正常垂体内存在着新的 GH异形体基因 ,该基因可能编码外周血中 1 6k D的生长激素 ;其功能可能为 2 2k D GH的生理拮挤剂 .     

Bombesin-like peptides stimulate growth hormone secretion mediated by the gastrin-releasing peptide receptor in cattle

This study was designed to determine the effects of bombesin-like peptides (BLPs) on the secretion of growth hormone (GH) and to characterize the receptor subtypes mediating these effects in cattle. Four experiments were conducted: (1) six steers were randomly assigned to receive intravenous (IV) bolus injections of 0, 0.2, 1.0, 12.5 and 50.0μg/kg neuromedin C (NMC); (2) seven pre-weaned calves were IV injected with 1.0μg/kg NMC; (3) six steers were IV injected with 2.5μg/kg bovine gastrin-releasing peptide (GRP), 1.0μg/kg NMC combined with 20.0μg/kg [d-Lys(3)]-GHRP-6 (an antagonist for the GH secretagogue receptor type 1a [GHS-R1a]), 1.0μg/kg NMC combined with 20.0μg/kg N-acetyl-GRP(20-26)-OCH(2)CH(3) (N-GRP-EE, an antagonist for the GRP receptor), 20.0μg/kg N-GRP-EE alone, 1.0μg/kg neuromedin B (NMB); and (4) four rats were IV injected 1.0μg/kg NMC. A serial blood sample was collected before and after injection. Plasma GH levels dose-dependently increased at 5min after NMC injection and the minimal effective dose was 1.0μg/kg. Plasma GH level was elevated by GRP, but not by NMB. The NMC-induced elevation of GH was completely blocked by N-GRP-EE. The administration of NMC elevated GH level in pre-weaned calves but not in rats. Ghrelin level was unaffected by any treatments; and [d-Lys(3)]-GHRP-6 did not block the NMC-induced elevation of GH. The results indicate BLP-induced elevation of GH levels is mediated by the GRP receptor but not through a ghrelin/GHS-R1a pathway in cattle.     

功能性ghrelin受体在内脏迷走和脊髓传入神经通路中的表达

本文在mRNA和蛋白水平观察了功能性ghrelin受体(growth hormone secretagogue receptor type la,GHS-Rla)在大鼠内脏迷走及脊髓传入神经通路中的表达.结果显示:(1)GHS-Rla免疫反应阳性神经元及GHS-Rla mRNA分布于背根神经节(dorsal root ganglion,DRG)及结状神经节(nodose ganglion,NG).(2)应用免疫双标技术观察到DRG和NG中都有一些GHS-Rla免疫反应阳性神经元,同时降钙素基因相关肽(calcitonin gene-related peptide,CGRP)染色呈阳性,显示GHS-Rla和CGRP共存于同一神经元,表明内脏传入神经元存在许多亚核群.(3)应用荧光金(fluorogold)标记的神经逆行追踪技术对从胃投射到DRG和NG的神经元进行免疫组织化学染色,观察到一些表达CGRP的GHS-Rla免疫反应阳性神经元也被荧光金染色.上述实验结果证实了GHS-Rla在迷走神经和脊髓传入神经元中的表达,提示ghrelin参与了胃.脑轴的调节.     

Growth hormone releasing substances: types and their receptors

A series of structurally diverse growth hormone (GH) releasing substances have been synthesized that are distinct from the naturally occurring GH releasing hormone (GHRH). These synthetic molecules range from the family of GH releasing peptides and mimetics such as MK-0677. The physiological importance of these molecules and their receptor is exemplified by studies in the elderly. For example, when MK-0677 was administered chronically to 70- to 90-year-old subjects, once daily, the age-related reduced amplitude of GH pulses was reversed to that of the physiological profile typical of young adults. In 1996, the synthesis of (35)S-MK-0677 was reported and used as a ligand to characterize a common receptor (GH secretagogue receptor [GHS-R]) for the GH releasing substances. The GHS-R is distinct from the GHRH receptor. Subsequently, the GHS-R gene was cloned and shown to encode a unique G-protein coupled receptor with a deduced protein sequence that was 96% identical in human and rat. Because of the physiological importance of the GHS-R, a search for family members (FMs) was initiated and its molecular evolution investigated. Three FMs GPR38, GPR39 and FM3 were isolated from human genomic libraries. To accelerate the identification of other FMs, a vertebrate organism with a compact genome distant in evolutionary terms from humans was exploited. The pufferfish (Spheroides nephelus) genome provides an ideal model for the discovery of human genes. Three distinct full-length clones encoding proteins of significant sequence identity to the human GHS-R were cloned from the pufferfish. Remarkably, the pufferfish gene with highest sequence homology to the human receptor was activated by the hexapeptide and non-peptide ligands. These intriguing results show that the structure and function of the ligand binding pocket of the human GHS-R has been highly conserved in evolution ( approximately 400 million years) and strongly suggests that an endogenous natural ligand has been conserved. This new information is consistent with a natural ligand for the GHS-R playing a fundamentally important and conserved role in physiology.     

Effect of chronic hyperghrelinemia on ingestive action of ghrelin

The stomach hormone ghrelin is the endogenous ligand for the growth hormone secretagogue receptor (GHS-R). Systemic administration of ghrelin will cause elevations in growth hormone (GH) secretion, food intake, adiposity, and body growth. Ghrelin also affects insulin secretion, gastric acid secretion, and gastric motility. Several reports indicate that repeated or continuous activation of GHS-R by exogenous GHSs or ghrelin results in a diminished GH secretory response. The purpose of this study was to examine the extent to which the acute stimulation of food intake by exogenous ghrelin is altered by chronic hyperghrelinemia in transgenic mice that overexpress the human ghrelin gene. The present findings show that the orexigenic action of exogenous ghrelin is not diminished by a chronic hyperghrelinemia and indicate that the food ingestive pathway of the GHS-R is not susceptible to desensitization. In contrast, the epididymal fat pad growth response, like the GH response, to exogenous ghrelin is blunted in ghrelin transgenic mice with chronic hyperghrelinemia.     

Ghrelin receptor (GHS-R)-like receptor and its genomic organisation in rainbow trout, Oncorhynchus mykiss

Ghrelin, a GH-releasing and appetite-regulating peptide that is released from the stomach is an endogenous ligand for growth hormone secretagogue-receptor (GHS-R). Two types of GHS-R are accepted to be present, a functional GHS-R1a and GHS-R1b with unknown function. In this study, we identified cDNA that encodes protein with close sequence similarity to GHS-R and exon–intron organization of the GHS-R genes in rainbow trout, Oncorhynchus mykiss. Two variants of GHS-R1a proteins with 387-amino acids, namely DQTA/LN-type and ERAT/IS-type, were identified. In 3'-RACE PCR and genomic PCR, we also identified three GHS-R1b orthologs that are consisted of 297- or 300-amino acids with different amino acid sequence at the C-terminus, in addition to the DQTA/LN-type and ERAT/IS-type variations. Genomic PCR revealed that the genes are composed of two exons separated by an intron, and that two GHS-R1a and three GHS-R1b variants are generated by three distinct genes. GHS-R1a and GHSR-1b mRNA were predominantly expressed in the pituitary, followed by the brain. Identified DQTA/LN-type or ERAT/IS-type GHS-R1a cDNA was transfected into mammalian cells, and intracellular calcium ion mobilization assay was carried out. However, we did not find any response to rat ghrelin and a homologous ligand, des-VRQ trout ghrelin, of either receptor in vitro. We found that unexpected mRNA splicing had occurred in the transfected cells, suggesting that the full-length, functional receptor protein might not be generated in the cells. Gene structure and characterization of protein sequence identified in this study were closely similar to other GHS-R, but to conclude that it is a GHS-R for rainbow trout, further study is required to confirm activation of GHS-R1a by ghrelin or GHS. Thus we designated the identified receptor proteins in this study as GHS-R-like receptor (GHSR-LR).     

Ablation of ghrelin receptor reduces adiposity and improves insulin sensitivity during aging by regulating fat metabolism in white and brown adipose tissues

Aging is associated with increased adiposity in white adipose tissues and impaired thermogenesis in brown adipose tissues; both contribute to increased incidences of obesity and type 2 diabetes. Ghrelin is the only known circulating orexigenic hormone that promotes adiposity. In this study, we show that ablation of the ghrelin receptor (growth hormone secretagogue receptor, GHS-R) improves insulin sensitivity during aging. Compared to wild-type (WT) mice, old Ghsr(-/-) mice have reduced fat and preserve a healthier lipid profile. Old Ghsr(-/-) mice also exhibit elevated energy expenditure and resting metabolic rate, yet have similar food intake and locomotor activity. While GHS-R expression in white and brown adipose tissues was below the detectable level in the young mice, GHS-R expression was readily detectable in visceral white fat and interscapular brown fat of the old mice. Gene expression profiles reveal that Ghsr ablation reduced glucose/lipid uptake and lipogenesis in white adipose tissues but increased thermogenic capacity in brown adipose tissues. Ghsr ablation prevents age-associated decline in thermogenic gene expression of uncoupling protein 1 (UCP1). Cell culture studies in brown adipocytes further demonstrate that ghrelin suppresses the expression of adipogenic and thermogenic genes, while GHS-R antagonist abolishes ghrelin's effects and increases UCP1 expression. Hence, GHS-R plays an important role in thermogenic impairment during aging. Ghsr ablation improves aging-associated obesity and insulin resistance by reducing adiposity and increasing thermogenesis. Growth hormone secretagogue receptor antagonists may be a new means of combating obesity by shifting the energy balance from obesogenesis to thermogenesis.