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Pharmacological and immunohistochemical characterization of the APJ receptor and its endogenous ligand apelin
Journal of Neurochemistry
Abstract
Apelin peptides have recently been identified to be the endogenous ligands for the G protein-coupled receptor APJ. However, little is known about the physiological roles of this ligand-receptor pairing. In the present study we investigated the pharmacology of several apelin analogues at the human recombinant APJ receptor using radioligand binding and functional assays. This has led to the identification of key residues in the apelin peptide required for functional potency and binding affinity through structure-activity studies. In particular, we have identified that replacement of leucine in position 5, or arginine in position 2 and 4 of the C-terminal apelin peptide, apelin-13, resulted in significant changes in pharmacology. We also investigated the detailed localization of pre-proapelin and APJ receptor mRNA in a wide range of human, rat and mouse tissues using quantitative RT-PCR, and carried out a detailed immunohistochemical study of the distribution of the APJ receptor in rat brain and spinal cord. Interestingly, the APJ receptor was not only co-localized in white matter with GFAP in the spinal cord, but was also clearly localized on neurones in the brain, suggesting that this receptor and its peptide may be involved in a wide range of biological process yet to be determined.
... Even simple modifications of the apelin ligand structure cause significant change in the peptide ligand activation. Substitution of the Leu2, Arg2, Lys8, or Phe13 with Ala results in a decrease of the activation activity of the ligand when binding to APLNR (7). Pyroglutamination of Glu at the N-terminus of the peptide modifies Apelin-13 into pyroglutaminated form -(Pyr 1 ) apelin-13, that is more stable (3). ...
... Striatum (15) (7), (4), (8) 11 (13) Putamen (7) n.Caudatus ...
... Corpus callosum (7), (15) Hippocampus (GD+ CA) ...
Apelin is an endogenous ligand for apelin receptor (APLNR), a G protein-coupled receptor (GPCR). This peptide is derived from a 77aa long pre-proapelin. Upon cleavage by different peptidases, several isoforms that bind to the receptor with different strength and downstream effects are created. Many cellular processes that are regulated by the apelinergic system have been discovered – neural and immune functions, blood pressure regulation, fluid homeostasis, hormonal release, cellular proliferation, etc. Additional research has been also made to elucidate the role of the system in pathological conditions affecting the brain and the peripheral organs. In this review, we summarise the distribution of the apelinergic system components in the mammalian organism. We also include a comparative analysis between three different species - human (Homo sapiens), mouse (Mus mus-culus), and rat (Rattus norvegicus).
... Comme pour la plupart des RCPGs, l'apéline en se fixant sur son récepteur, induit la phosphorylation de l'Apéline-R par des kinases des RCPGs (GRK), puis le recrutement de la ß-arrestine1/2 et l'internalisation de l'Apéline-R via un mécanisme dépendant de la clathrine (Evans et al., 2001;Reaux et al., 2001;Medhurst et al., 2003;Zhou et al., 2003b;Iturrioz et al., 2010), K17F entraînant une internalisation plus massive que pE13F à une plus faible concentration. La sérine en position 348 (Ser 348) à l'extrémité C-terminale de l'Apéline-R représente un site de phosphorylation pour GRK2/5 qui est crucial pour l'interaction de l'Apéline-R avec les ß-arrestines1 et 2, permettant ainsi l'internalisation de l'Apéline-R . ...
... Des études par transcription inverse et amplification génique (RT-PCR) quantitative (Kawamata et al., 2001;Medhurst et al., 2003), hybridation in situ et Northern blot (Lee et al., 2000;O'Carroll et al., 2000) ont montré que les ARNms codant pour la préproapéline ou pour l'Apéline-R sont distribués de façon hétérogène dans diverses structures cérébrales chez le rat et l'Homme. ...
... Les ARNms codant pour la préproapéline, ainsi que pour l'Apéline-R, sont exprimés dans le rein chez le rat et chez l'Homme (Hosoya et al., 2000;O'Carroll et al., 2000;Medhurst et al., 2003). ...
L'apéline, un peptide d'origine neuro-endocrine, et son récepteur (Apéline-R) sont co-localisés avec l'arginine-vasopressine (AVP) dans les neurones magnocellulaires vasopressinergiques. L'Apéline-R est aussi présent dans le rein, dans les canaux collecteurs (CC) avec le récepteur de l'AVP de type 2 (V2-R), responsable de l'effet antidiurétique de l'AVP. L'apéline et l'AVP sont régulées de façon opposée par les stimuli osmotiques pour maintenir l'équilibre hydrique de l'organisme. Les Apéline-R sont aussi exprimés dans les vaisseaux et le coeur. L'apéline-17 (K17F) exerce des effets aquarétique, vasodilatateur et inotrope positif. La demi-vie de l'apéline in vivo étant inférieure à la minute, limitant son usage thérapeutique, nous avons développé un analogue de K17F métaboliquement stable, le LIT01-196, qui se comporte comme un puissant agoniste complet de l'Apéline-R et a une demi-vie dans le plasma de 24 h contre 4,6 min pour K17F. I- Nous avons émis l'hypothèse que l'activation de l'Apéline-R par le LIT01-196 pourrait être bénéfique pour le traitement du Syndrome d'Antidiurèse Inappropriée, dans lequel l'hypersécrétion d'AVP conduit à l'hyponatrémie. Ce travail de thèse montre que le LIT01-196 a une demi-vie in vivo de 156 minutes dans la circulation sanguine après administration par voie sous-cutanée (s.c.) chez le rat. Dans une lignée de cellules immortalisées issues de cellules principales de CC, les cellules mpkCCD qui expriment l'Apéline-R, le V2-R et les canaux à eau (les aquaporines 2, AQP2), le LIT01-196 diminue la production d'AMPc induite par la dDAVP (un agoniste du V2-R) et diminue la translocation des AQP2 phosphorylées à la membrane apicale de ces cellules. Dans un modèle expérimental d'hyponatrémie induite par une perfusion continue d'AVP, le LIT01-196 administré par voie s.c bloque l'effet antidiurétique et l'augmentation de l'osmolalité urinaire induits par l'AVP, ce qui augmente la diurèse aqueuse et induit une amélioration progressive de l'hyponatrémie. Ceci suggère que l'activation de l'Apéline-R par le LIT01-196 pourrait constituer une nouvelle approche pharmacologique pour le traitement de l'hyponatrémie. II- Sachant que l'apéline via son récepteur augmente la contractilité cardiaque, tout en réduisant les résistances vasculaires, nous avons émis l'hypothèse qu'un traitement par le LIT01-196 pourrait être bénéfique pour prévenir le développement de l'insuffisance cardiaque (IC) après infarctus du myocarde (IM). L'IC après IM est associée à une mortalité élevée, malgré l'arsenal thérapeutique disponible à ce jour, elle demeure un problème majeur de santé publique. Nous avons évalué, dans ce travail de thèse, les effets d'un traitement chronique par le LIT01-196 pendant quatre semaines après un IM chez la souris sur la fonction cardiaque, l'hypertrophie et la fibrose cardiaques. Le traitement chronique par le LIT01-196 administré par voie s.c chez des souris après IM, obtenu par ligature de l'artère coronaire, améliore la fonction cardiaque de manière significative en améliorant la fonction systolique et en réduisant les volumes et diamètres du ventricule gauche (VG). Différents biomarqueurs de l'IC, mesurés par RT-PCR quantitative sont également réduits (ANF et BNP). De plus, la mesure des paramètres hémodynamiques a permis d'observer après traitement par le LIT01-196, le maintien de la pression artérielle tout en augmentant la contractilité du myocarde, en diminuant la pression intracardiaque en fin de diastole et en maintenant une pression intracardiaque en fin de systole normale. Le LIT01-196 exerce aussi des effets cardioprotecteurs en diminuant la taille de l'infarctus, l'épaisseur des parois du VG et la fibrose cardiaque. Sachant que l'hyponatrémie aggrave la mortalité chez les patients insuffisants cardiaques et que le LIT01-196 améliore l'hyponatrémie et la fonction cardiaque, l'activation de l'Apéline-R pourrait constituer une approche pharmacologique intéressante pour le traitement de l'IC.
... Apelin receptors and their ligands are widely expressed in the mammalian brain [2][3][4][5][6][7]. Increasing interest in the apelinergic system has led to numerous discoveries and shed light on this system's complex functional diversity. ...
... CD10 (Neprilysin) is capable of inactivating [Pyr 1 ] apelin-13, creating two inactive Apelin-13 isoforms (5-13aa and 6-13aa). On the other hand, Angiotensin-converting enzyme 2 (ACE2) converts Apelin-13 and Apelin-36 to active forms, Apelin-13 (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12) and Apelin-32 . (B). ...
... ELABELA gene codes for a non-functional 54aa-long pro-protein, which generates an active 32aa-long protein upon processing. ELABELA-32 can generate three fragments, ELABELA-11, an inactive form, generated with the help of PCSK3, and two functional ones, ELABELA (1)(2)(3)(4)(5)(6)(7)(8)(9) and , with the activity of unknown proteases. Abbreviations: PCSK3, proprotein convertases subtilisin/kexin type; CD10, Neprilysin; ACE2, Angiotensin Converting enzyme-2; KLKB1, Kallikrein. ...
Apelin, a peptide initially isolated from bovine stomach extract, is an endogenous ligand for the Apelin Receptor (APLNR). Subsequently, a second peptide, ELABELA, that can bind to the receptor has been identified. The Apelin receptor and its endogenous ligands are widely distributed in mammalian organs. A growing body of evidence suggests that this system participates in various signalling cascades that can regulate cell proliferation, blood pressure, fluid homeostasis, feeding behaviour, and pituitary hormone release. Additional research has been done to elucidate the system's potential role in neurogenesis, the pathophysiology of Glioblastoma multiforme, and the protective effects of apelin peptides on some neurological and psychiatric disorders-ischemic stroke, epilepsy, Parkinson's, and Alzheimer's disease. This review discusses the current knowledge on the apelinergic system's involvement in brain physiology in health and disease.
... It is widely known that it produces specific factors called adipokines such as chemerin, visfatin, adiponectin, leptin, resistin and apelin. These molecules can engage expressed in specific hypothalamus and cerebroventricular regions of the brain, pituitary gland, skeletal muscle, kidney, spinal cord, thyroid gland, lungs, heart, adipose tissue and reproductive tract (Medhurst et al. 2003;Carpéné et al. 2007;Falcao-Pires et al. 2010;Mercati et al. 2018;Shokrollahi et al. 2022). In veterinary medicine, apelin was isolated from cow and sow ovaries (Roche et al. 2017) and from canine placenta (Troisi et al. 2020). ...
... It is also involved in angiogenesis during pregnancy (Troisi et al. 2020). APLN and its receptor have recently been detected in the male gonads of human and laboratory animals (Medhurst et al. 2003;Estienne et al. 2019;Kawamata et al. 2001;Pope et al. 2012). More specifically, it has been demonstrated that the intracerebroventricular infusion of apelin in male rats reduces serum testosterone levels thus causing a drastic reduction in the number of testosterone-producing Leydig cells (Sandal et al. 2015). ...
... However, to the best of our knowledge, to date few studies have investigated the role that apelin and apelin receptors play in the male reproductive system (Bertrand et al. 2015;Dupont et al. 2015;Campos et al. 2008). Our results revealed, for the first time, the presence of apelin and its receptor in dog testes which are in agreement with those obtained for humans and mice (Medhurst et al. 2003). In particular, this study concerned the immunohistochemical localization of apelin in the residual bodies, in the apical portion of the seminiferous tubules, and of apelin receptor in the cytoplasm of cells localized in the basal portion of the seminiferous tubules. ...
Apelin, a member of the adipokine family, is a novel endogenous peptide which regulates the male reproductive system of mammals by interacting with a specific receptor. Recent studies have highlighted that apelin may play a role in the regulation of reproduction by reducing testosterone production and inhibiting LH secretion. To the best of our knowledge, there is no available data on the presence of the apelin and its receptor in canine testes. Therefore, the aim of this study was to reveal the presence of apelin and evaluate its distribution in the canine testes using immunohistochemical and RT-PCR techniques. For this purpose, five fertile and healthy male dogs were subjected to elective orchiectomy. The immunohistochemical reaction revealed the presence of apelin and its receptor in the canine testes. Apelin was localized in spermatids and spermatozoa with a positive signal in the “acrosomal bodies”. As regards the apelin receptor, a positive immunoreaction was detected in the cytoplasm of the cells localized near to the basal membrane of the seminiferous tubules and in the cytoplasm of Leydig cells. The RT-PCR analysis showed the presence of transcripts for apelin and apelin receptor in all of the samples under study. A 35kDa band confirmed apelin receptor protein expression in all of the samples analysed. In conclusion, the paracrine and endocrine role of apelin and its cognate receptor on male reproduction reported in humans and laboratory animals could also be hypothesized in dogs.
... APLN and its receptor have been detected in many tissues of numerous mammalian species. In fact, transcript and protein for both molecules are expressed in speci c hypothalamus and cerebroventricular regions of the brain, pituitary gland, skeletal muscle, kidney, spinal cord, thyroid gland, lungs, heart, adipose tissue and reproductive tract (Medhurst et al., 2003;Carpéné et al., 2007;Falcao-Pires et al., 2010;Mercati et al., 2018;Shokrollahi et al., 2022). In veterinary medicine apelin was isolated from cow and sow ovaries (Roche et al., 2017) and from canine placenta (Troisi et al., 2020). ...
... APLN and its receptor have recently been detected in the male gonads of human and laboratory animals (Medhurst et al., 2003;Estienne et al., 2019;Kawamata et al., 2001;Pope et al., 2012). More speci cally, it has been demonstrated that the intracerebroventricular infusion of apelin in male rats reduces serum testosterone levels thus causing a drastic reduction in the number of testosterone-producing Leydig cells (Sandal et al., 2015). ...
... However, to the best of our knowledge, to date few studies have investigated the role apelin and apelin receptors play in the male reproductive system (Bertrand et al., 2015;Dupont et al., 2015;Campos et al., 2008). Our results revealed the presence of apelin and its receptor in dog testes in agreement with those obtained for humans and mice (Medhurst et al., 2003), This study concerned the immunohistochemical localization of apelin in spermatids and spermatozoa and the apelin receptor in the cytoplasm of cells localized in the basal portion of the seminiferous tubules. These observations suggest that via paracrine or endocrine mechanims apelin is involved in spermatogenesis as well as other adipokines reported in humans (Thomas et al., 2013). ...
Apelin, a member of the adipokine family, is a novel endogenous peptide which regulates the male reproduction system of men and male laboratory animals by interacting with a specific receptor. Recent studies have highlighted that apelin may play a role in the regulation of reproduction by reducing testerone production and inhibiting LH secretion. To the best of our knowledge, there is no available data on the presence of the apelin and its receptor in canine testes. Therefore, the aim of this study was to reveal its presence and evaluate its distribution in the canine testes using immunohistochemical and RT-PCR techniques. For this purpose, five fertile and healthy male dogs were subjected to elective orchiectomy. The immunohistochemical reaction revealed the presence of apelin and its receptor in the canine testes. Apelin was localized in spermatids and spermatozoa with a positive signal in the “acrosomal bodies”. As regards the apelin receptor, a positive immunoreaction was detected in the cytoplasm of the cells localized near to the basal membrane of the seminiferous tubules and in the cytoplasm of Leydig cells. The RT-PCR analysis showed the presence of transcripts for apelin and apelin receptor in all of the samples under study. A 35 kDa band confirmed apelin receptor protein expression in all of the samples analysed. In conclusion, the paracrine and endocrine role of apelin and its cognate receptor on male reproduction reported in humans and laboratory animals, could also be hypothesized in dogs.
... APLN and its receptor have been detected in many tissues of numerous mammalian species. In fact, transcript and protein for both molecules are expressed in speci c hypothalamus and cerebroventricular regions of the brain, pituitary gland, skeletal muscle, kidney, spinal cord, thyroid gland, lungs, heart, adipose tissue and reproductive tract (Medhurst et al., 2003;Carpéné et al., 2007;Falcao-Pires et al., 2010;Mercati et al., 2018;Shokrollahi et al., 2022). In veterinary medicine apelin was isolated from cow and sow ovaries (Roche et al., 2017) and from canine placenta (Troisi et al., 2020). ...
... APLN and its receptor have recently been detected in the male gonads of human and laboratory animals (Medhurst et al., 2003;Estienne et al., 2019;Kawamata et al., 2001;Pope et al., 2012). More speci cally, it has been demonstrated that the intracerebroventricular infusion of apelin in male rats reduces serum testosterone levels thus causing a drastic reduction in the number of testosterone-producing Leydig cells (Sandal et al., 2015). ...
... However, to the best of our knowledge, to date few studies have investigated the role apelin and apelin receptors play in the male reproductive system (Bertrand et al., 2015;Dupont et al., 2015;Campos et al., 2008). Our results revealed the presence of apelin and its receptor in dog testes in agreement with those obtained for humans and mice (Medhurst et al., 2003), This study concerned the immunohistochemical localization of apelin in spermatids and spermatozoa and the apelin receptor in the cytoplasm of cells localized in the basal portion of the seminiferous tubules. These observations suggest that via paracrine or endocrine mechanims apelin is involved in spermatogenesis as well as other adipokines reported in humans (Thomas et al., 2013). ...
Apelin, a member of the adipokine family, is a new endogenous peptide and it’s involved, by interacting with a specific receptor, in the control of human and laboratory animals’male reproduction. As far as we know, no data is available about the presence of the apelinergic system in dog testicles. Therefore the aim of this study was to show, for the first time, its presence and distribution in the canine testis by immunoistochemistry and molecular biology studies. For this purpose, five fertile and healthy male dogs were used and subjected to elective orchiectomy. The immunohistochemical reaction evidenced the presence of apelin and its receptor in the canine testis. In particular, apelin appeared localized in spermatids and spermatozoa with a positive signal in the “acrosomal bodies”. Regarding to the apelin receptor, a positive immunoreaction was evidenced in the cytoplasm of the cells localized in the basal portion of the seminiferous tubules, likely Sertoli’s cells, and in the cytoplasm of Leydig cells. The RT-PCR analysis showed the presence of transcripts for apelin and apelin receptor in all the samples examined. In conclusion our result allows us to hypothesize that the role of the paracrine and endocrine apelinergic system reported in laboratory animals can also be found in the dog.
... After the discovery of APJ, the analysis of its physiological role was halted by a lack of pharmacological tools to modulate its activity. Later work showed that APJ is expressed across a variety of tissues and organs, including the cardiovascular system, lung, kidney, pancreas, and brain with enrichment in hypothalamus, hippocampus, and spinal cord suggesting its involvement in multifaceted physiological responses (Hosoya et al., 2000;Lee et al., 2000;Medhurst et al., 2003;O'Carroll et al., 2000). ...
... Cloning of Apelin receptor (APJ) and classified as orphan (O'Dowd et al., 1993) Identification of Apelin in stomach extract and pairing with APJ (Tatemoto et al., 1998) Identification of Apelin in different organs and tissues (Hosoya et al., 2000;Lee et al., 2000;Medhurst et al., 2003;O'Carroll et al., 2000) Studies on Apelin-KO and APJ-KO mice display inconsistencies (Charo et al., 2009;Kang et al., 2013;Kuba et al., 2007) Discovery of Elabela/Toddler as a novel endogenous ligand for APJ (Chng et al., 2013;Pauli et al., 2014;Wang et al., 2015) Cannabinoid receptors ...
... Apelin also referred to as APLN, a novel discovered naturally occurring multifunctional peptide ligand, interacts with APJ, a G protein-coupled receptor. The genes responsible for apelin and APJ exhibit broad expression in diverse bodily tissues, and the structure of apelin remains remarkably preserved across various species (21,22). Apelin serves as the innate ligand for APJ and its sequence of amino acids closely resembles that of the angiotensin (Ang) II receptor type-1 receptor (AT1R) and the impact of preproapelin, a precursor composed of 77 amino acids, involves enzymatic cleavage and processing, resulting in various molecular forms across different tissues. ...
... Apelin serves as the innate ligand for APJ and its sequence of amino acids closely resembles that of the angiotensin (Ang) II receptor type-1 receptor (AT1R) and the impact of preproapelin, a precursor composed of 77 amino acids, involves enzymatic cleavage and processing, resulting in various molecular forms across different tissues. Shorter variants, like Apelin-13, demonstrate heightened e cacy compared to their longer counterparts (23) which show the highest level of activity at the receptors (24), and its speci c binding region for the APJ receptor is located at its C-terminal (22). The apelin-APJ system has been identi ed as a contributing factor to the development of several prevalent conditions, including heart failure, hypertension, atherosclerosis, type 2 diabetes mellitus, and ulcerative colitis (25). ...
Background: Given the limited specificity of D-dimer, there is a perceived need to discover a more precise marker for diagnosing individuals who are suspected of having pulmonary embolism (PE). In this study, by Evaluating the increase in the serum level of Apelin-13 and D-dimer, we found valuable findings about Apelin-13, which can be suggested as an auxiliary and non-invasive diagnostic biomarker in individuals with suspected PE, based on the obtained results. Methods: In this case-control study, 52 Iranian individuals with a suspicion of pulmonary embolism, were included and then were separated into two groups based on CT angiography results serving as the gold standard imaging method for diagnosing PE: patients with and without PE. Finally, the serum levels of these markers were compared in these two groups. Results: The mean serum D-dimer levels in patients with PE were significantly elevated (p<0.001) in comparison to those without PE (1102.47 to 456.2 ng/ml). Furthermore, the mean level of Apelin-13 was significantly higher in patients with PE (49.8 to 73.11 ng/L) (p <0.001). The cutoff point of Apelin-13 has been calculated 58.50 ng/ml, with 90.9% sensitivity and 90% specificity. The D-dimer cutoff point was 500 ng/ml, with 95.5% sensitivity and 43.3% specificity. Conclusions: Based on the results of this study, the serum level of Apelin-13 can be used as novel diagnostic and screening biomarker in patients with pulmonary thromboembolism Keywords: Pulmonary embolism, Thromboembolism, Apelin-13, D-dimer.
... The final functionally active protein is formed by processing the C-terminal fragment of the preprotein. Apelin and its receptor (APJ) are expressed in the central and peripheral nervous systems and are linked to various neuropathic pain processes [6][7][8][9]. However, the dynamics of apelin expression in RCT have not been elucidated. ...
... Apelin and its receptor system (APJ) are located in the central and peripheral nervous systems [6,8]. Earlier studies have shown that intrathecal injection of apelin induces hyperalgesia [7], and peripheral injection of apelin-13 enhances pain sensitivity [28]. ...
Objectives:
Inflammatory mediators play important roles in the pain associated with rotator cuff tears (RCTs), but their underlying mechanisms are unclear. Apelin, a neuropeptide, is upregulated under inflammatory conditions and possibly contributes to pain induced by rotator cuff tears. This translational study aimed to examine apelin expression and regulation by tumor necrosis factor alpha (TNF-α) in patients with RCT and in rat RCT models.
Methods:
Synovial tissues were harvested from the glenohumeral joints of the shoulders in 46 patients who underwent arthroscopic Bankart repair for recurrent shoulder dislocations (RSDs) or arthroscopic rotator cuff repair for RCTs. The harvested tissues were extracted and processed by reverse transcriptase-polymerase chain reaction (RT-PCR). Rats underwent sham or RCT surgery; the rotator cuff tissues were extracted 1, 7, 14, 28, and 56 days after surgery and analyzed for mRNA expression levels of the TNF-α and apelin using RT-PCR. The cultured rotator cuff cells (RCCs) were stimulated with TNF-α to examine their role in the regulation of apelin expression.
Results:
Apelin expression was higher in the RCT group than in the RSD group and significantly correlated with pain intensity. In rats, the expression was also higher in RCT. Apelin expression significantly increased during the acute and chronic phases in rats.
Conclusions:
In cultured RCCs, apelin mRNA levels significantly increased after TNF-α stimulation. Apelin levels were regulated by TNF-α and were highly expressed in patients with RCT and rats in RCT models. Thus, apelin may be a new pain management target for RCTs.
... The distribution, expression and binding capacity of different apelin isoforms to APJ differ, among which apelin-13 has the strongest bioactivity and receptor binding capacity, and has multiple biological functions [7,8]. Apelin-13 is the main isoform in the CNS and cardiovascular system, and is widely expressed in the CNS, such as the spinal cord, cerebral cortex, hypothalamus and other regions [9,10]. The extensive tissue distribution of apelin-13 and its receptor system in the CNS suggests that it may play an important physiological role in the CNS. ...
... In 1998, Tatemoto et al. first extracted and purified the endogenous legend of APJ (apelin) from bovine gastric secretions using a reverse pharmacological approach and named it apelin [18]. The human apelin gene is located on the X chromosome and encodes apelin prepropeptide formed by 77 amino acids, whose amino acid sequence is highly homologous across species [10]. The N-terminal part of the apelin prepeptide is a signal peptide sequence of amino acids involved in the regulation of apelin binding to the APJ receptor, and the C-terminal part is a highly conserved amino acid sequence involved in the regulation of apelin biological activity [19]. ...
Apelin is a natural ligand for the G protein-coupled receptor APJ, and the apelin/APJ system is widely distributed in vivo. Among the apelin family, apelin-13 is the major apelin isoform in the central nervous system and cardiovascular system, and is involved in the regulation of various physiopathological mechanisms such as apoptosis, neuroinflammation, angiogenesis, and oxidative stress. Apelin is currently being extensively studied in the nervous system, and apelin-13 has been shown to be associated with the onset and progression of a variety of neurological disorders, including stroke, neurodegenerative diseases, epilepsy, spinal cord injury (SCI), and psychiatric diseases. This study summarizes the pathophysiological roles of apelin-13 in the development and progression of neurological related diseases.
... Apelin-13 is a short peptide consisting of 13 amino acids. The N-terminal of apelin-13 binds to the APJ receptor, while the C-terminal is mainly involved in regulating its biological activity (Kawamata et al., 2001;Medhurst et al., 2003). It is degraded into an inactive form in the presence of ACE2 (Vickers et al., 2002), and is also modified into the more stable and active pyroglutamyl apelin-13. ...
... Xu et al. (2018) Frontiers in Pharmacology frontiersin.org currently the only known apelin-13 receptor so far, and is highly expressed in neurons and glial cytoplasm in caudate nucleus, corpus callosum and hippocampus (Hosoya et al., 2000;Medhurst et al., 2003). APJ relays the signals through Gα subunit (Gαi or Gαq) of G protein. ...
The incidence of cerebral ischemia has increased in the past decades, and the high fatality and disability rates seriously affect human health. Apelin is a bioactive peptide and the ligand of the G protein-coupled receptor APJ. Both are ubiquitously expressed in the peripheral and central nervous systems, and regulate various physiological and pathological process in the cardiovascular, nervous and endocrine systems. Apelin-13 is one of the subtypes of apelin, and the apelin-13/APJ signaling pathway protects against cerebral ischemia by promoting angiogenesis, inhibiting excitotoxicity and stabilizing atherosclerotic plaques. In this review, we have discussed the role of apelin-13 in the regulation of cerebral ischemia and the underlying mechanisms, along with the therapeutic potential of the apelin-13/APJ signaling pathway in cerebral ischemia.
... apelin-13 is identified as the physiological ligand for APJ [12]. Apelin receptor mRNAs are found extensively across various tissues, including the brain, lungs, heart, spinal cord, kidneys, adipose tissue, and skeletal muscle [13][14][15]. In the human kidney, the APJ/apelin system is expressed throughout the renal unit, predominantly in the cortex and vasculature [16,17]. ...
Backgroud
Kidney transplantation is the optimal treatment for end-stage renal disease, yet acute rejection remains a significant challenge to the survival rates of grafts. Ischemia-reperfusion injury (IRI) can initiate an inflammatory response that severely damages the transplanted kidney.
Methods
The APJ/apelin system has been shown to play an anti-inflammatory role across various domains, and in this study, we utilized apelin-13 in a rat kidney transplantation model to investigate its effects on IRI-related inflammation.
Results
Our findings indicate that apelin predominantly localizes in the renal cortex, and following kidney transplantation, there was destruction of tissue structure and an inflammatory response targeting the transplanted kidney. The administration of apelin-13 led to improved kidney function, reduced organizational structure damage, and lower injury and apoptosis indices compared to the control group. Notably, following the administration of apelin-13, the expression levels of pro-inflammatory cytokines, such as TNF-α, IL-6, and IL-1β, were reduced in comparison to the model control group, as determined by immunofluorescence, western blot, and ELISA Manuscript File Click here to view linked References assays. Furthermore, the extent of CD3 T cell infiltration was lower relative to that in the model control group. We specifically examined the classical inflammation signaling pathway, NF-κB. Our results show that, compared to the model group, the administration of apelin-13 reduced the expression of NF-κB signaling pathway proteins, as evidenced by both immunohistochemistry and western blot analyses.
Conclusions
In conclusion, apelin-13 appears to reduce the inflammatory response to ischemia-reperfusion injury following kidney transplantation, partly through the NF-κB signaling pathway.
... Apelin holds significance as an adipokine, with plasma apelin primarily sourced from the vascular endothelial cell lining found in several anatomical locations within the human body, such as the heart, kidney, large conduit vessels, adipocytes, and others [27]. APJ, a prototypical G protein-coupled receptor comprising 380 amino acids and characterized by seven transmembrane domains, exhibits widespread distribution throughout the body [28]. A strong link between apelin and inflammation exists, as demonstrated by Pan et al. [29], who revealed that apelin directly suppresses the synthesis of macrophage MCP-1 and IL-8 after stimulating peritoneal macrophages from rats with LPS. ...
Objectives
This study aimed to assess the diagnostic, risk stratification, and prognostic capabilities of apelin-13 and APJ in comparison to procalcitonin (PCT) for septic patients presenting to the emergency department (ED).
Methods
Two hundred and thirty-eight patients meeting the Third International Consensus Definition (Sepsis-3) criteria were enrolled from Beijing Chaoyang Hospital's ED, along with a control group of forty healthy individuals. Patients were categorized into two groups based on disease severity: those with sepsis or septic shock. Plasma levels of apelin-13, CD4⁺ Th cells, and PCT were measured. The expression levels of plasma APJ mRNA were quantified using real-time fluorescence quantitative PCR (RT-qPCR) methodology. The Sequential Organ Failure Assessment (SOFA) score was determined at the time of enrollment. The prognostic values of apelin-13 and APJ was evaluated in comparison to that of PCT and the SOFA score. All patients were followed up for a duration of 28 days.
Results
The plasma concentrations of apelin-13 and APJ exhibited a positive correlation with the severity of sepsis, while the number of CD4⁺ T cells decreased in septic patients. The areas under the receiver operating characteristic (AUC) curves for apelin-13 and APJ in the diagnosis and prediction of 28-day mortality were greater than that of PCT. In non-survivors at the 28-day follow-up, the plasma levels of apelin-13 and APJ were significantly higher compared to survivors. Furthermore, apelin-13 levels were notably higher in cases of sepsis-induced cardiomyopathy (SICM) than in those without SICM. Apelin-13 and APJ emerged as independent predictors of 28-day mortality among septic patients.
Conclusions
Apelin-13 and APJ demonstrate value in the assessment of risk stratification, early diagnosis, and prognosis of sepsis in the ED. Apelin-13 also proves to be an effective biomarker for assessing the prognosis of SICM in the ED. Sepsis may lead to immune function suppression.
... The exact role of apelin signaling is yet to be investigated. APJ has been detected in the testis of human and laboratory animals such as rats, mice, and dogs (Estienne et al., 2019;Kawamata et al., 2001;Medhurst et al., 2003;Pope et al., 2012;Troisi et al., 2022). ...
The apelin receptor (APJ) belongs to the member of the G protein‐coupled receptor family, and expression of APJ has been reported in the different cell types of testis. The seminiferous tubules in the testis can be identified as different stages (I–XII). It has been also suggested that different factors could be expressed in stage and cell‐specific manner in the seminiferous tubules. Recently, we also shown that expression of APJ is developmentally regulated in the testis from PND1 to PND42. Therefore, we analyzed the expression of APJ in the testis of adult mice by immunohistochemistry. Immunohistochemistry showed that the APJ was highly specific for the round and elongated spermatids with stage‐dependent changes. The seminiferous tubules at stages I–VII showed APJ immunostaining in the spermatid steps 1–8, not steps of 13–16. The seminiferous tubules at stages IX–XII showed APJ immunostaining in the spermatid steps 9–12. These results suggested the possible role of APJ in the spermiogenesis process. The intratesticular administration of APJ antagonist, ML221 showed a few round spermatids in the seminiferous tubules and some of the tubules with complete absence of round spermatid. Overall, we present evidence that APJ expression in spermatid is dependent on the stages of the seminiferous epithelium cycle and APJ could be involved in the differentiation of round spermatid to elongated spermatid.
... Research conducted in some laboratory animals (rats, mice) and human tissues has reported widespread expressions of Apelin and the apelin's receptor in the central nervous system (CNS), cardiovascular, circulatory, digestive, and reproductive systems, as well as in adipose tissue and striated muscles (Kawamata et al., 2001;Medhurst et al., 2003). ...
Recent recognition of various adipokines has redefined white adipose tissue as an endocrine organ intricately involved in overall physiological and metabolic regulation. Apelin, originally known for its cardiovascular and fluid balance effects, is now recognized as an adipokine with broader physiological implications. Apelin, alongside influential factors like leptin and adiponectin, significantly contributes to energy metabolism. Notably, Apelin affects glucose and lipid metabolism and influences insulin secretion. Research consistently shows elevated plasma Apelin concentrations in conditions like type 2 diabetes and obesity.
The discovery of the APJ receptor in 1993, with sequence homology to angiotensin II receptor type 1, revealed its role as a G-protein-coupled receptor (GPCR) named AGTRL1 (Castan – Laurel et al., 2011). Apelin, identified in 1998, acts as the endogenous ligand for the GPCR APJ, producing various isoforms. Apelin is expressed in multiple regions of the central nervous system and peripheral tissues, playing diverse roles based on its tissue presence and bodily fluid localization.
Apelin release in intestinal epithelial cells is initiated by glucose, facilitating glucose transport from the intestinal lumen into the bloodstream. This interaction increases glucose levels in the portal vein, accelerating insulin secretion and enhancing insulin sensitivity. Apelin's stimulation of glucose absorption in the intestinal epithelium contributes to maintaining glucose homeostasis, employing various regulatory pathways, including binding to APJ in central glucose metabolism (Hu et al., 2021).
... Naloxone or apelin antagonist F13A did partial inhibition of seizure, APJ and opioid receptors have a role in apelin-13's antiepileptic effects but the different mechanism may be involved Lv et al., 2012). Apelin's and its receptor's mRNA and protein are located in amygdala, hippocampus and cerebral cortex (Hosoya et al., 2000;Lee et al., 2000;Medhurst et al., 2003). These regions are releated to learning and memory. ...
Apelin, a neuropeptide, is a typical endogenous ligand of G protein-coupled apelin receptor, APJ. Apelin mRNAs, proteins and APJ are commonly found in peripheral tissues and the central nervous system (CNS). Thus apelin-APJ system may be related to many physiological and pathological processes such as epilepsy. Epilepsy is severe chronic neurological disease and affects millions of people worldwide. Disruption of the balance between excitation and inhibition can cause epilepsy. There are few studies about apelin and epilepsy interactions. Clarifying the effect of apelin on epilepsy will be important for the development of treatment.
... Accordingly, the activity of Apelin-13 and Apelin-17 is much stronger than that of Apelin-36, and the different binding affinities for their receptor determine the different APJ signaling pathways activated in cells (30, 31). Therefore, Apelin-13 is considered to be the most biologically active affinity fragment among Apelin subtypes (32), and related research on this form is relatively extensive. ...
Apelin, a novel endogenous ligand of the G-protein-coupled receptor APJ, is encoded by the APLN gene and can be hydrolyzed into multiple subtypes, with Apelin-13 being one of the most active subtypes of the Apelin family. Recent studies have revealed that Apelin-13 functions as an adipokine that participates in the regulation of different biological processes, such as oxidative stress, inflammation, apoptosis, and energy metabolism, thereby playing an important role in the prevention and treatment of various metabolic diseases. However, the results of recent studies on the association between Apelin-13 and various metabolic states remain controversial. Furthermore, Apelin-13 is regulated or influenced by various forms of exercise and could therefore be categorized as a new type of exercise-sensitive factor that attenuates metabolic diseases. Thus, in this review, our purpose was to focus on the relationship between Apelin-13 and related metabolic diseases and the regulation of response movements, with particular reference to the establishment of a theoretical basis for improving and treating metabolic diseases.
... APLNR inhibition induced by endogenous n-3 PUFAs is a novel cardioprotective mechanism after IR APLNR is a GPCR with seven transmembrane domains, first reported in 1993 (O'Dowd et al., 1993). APLNR is found in various organs and tissues, including the heart (Medhurst et al., 2003). This receptor has two known endogenous ligands, apelin and Elabela/ Toddler (Tatemoto et al., 1998;Chng et al., 2013;Pauli et al., 2014). ...
Background: While the protective effects of n-3 polyunsaturated fatty acids (PUFAs) on cardiac ischemia-reperfusion (IR) injury have been previously reported, limited data are available regarding how these fatty acids affect membrane receptors and their downstream signaling following IR injury. We aimed to identify potential receptors activated by n-3 PUFAs in IR hearts to understand the regulatory mechanisms of these receptors.
Methods: We used fat-1 mice, which naturally have elevated levels of n-3 PUFAs, and C57BL/6J mice as a control group to create a myocardial IR injury model through Langendorff perfusion. We assessed the impact of endogenous n-3 PUFAs on left ventricular function, myocardial infarct size, myocardial apoptosis, and ATP production. RNA sequencing (RNA-seq) and bioinformatics analysis were conducted to identify molecular targets affected by n-3 PUFAs. Based on these analyses we then treated IR hearts of WT and fat-1 mice with an antagonist (ML221) or an agonist (apelin-13) for the predicted receptor to assess cardiac contractile function and intracellular signaling pathways. An in vitro hypoxia-reoxygenation (HR) model was also used to confirm the effects of n-3 PUFAs on the examined intracellular signaling pathways.
Results: Endogenous n-3 PUFAs protected cardiac structure and function in post-IR hearts, and modulated phosphorylation patterns in the PI3K-AKT-mTOR signaling pathways. RNA-seq analysis revealed that n-3 PUFAs affected multiple biological processes as well as levels of the apelin receptor (APLNR). Consistent with a role for the PLNNR, ML221 synchronized the activation of the PI3K-AKT-mTOR signaling axis, suppressed the expression of PKCδ and phosphorylated p38α, upregulated PKCε expression, upregulated or restored the phosphorylation of myofilaments, and prevented myocardial injury and contractile dysfunction in WT IR hearts. By contrast, apelin-13 disrupted the PI3K-AKT-mTOR signaling axis in post-IR fat-1 hearts. The phosphorylation signaling targeted by APLNR inhibition in post-IR fat-1 hearts was also observed after treating HR cells with eicosatetraenoic acid (EPA).
Conclusion: Endogenous n-3 PUFAs protect against post-IR injury and preserve cardiac contractile function possibly through APLNR inhibition. This inhibition synchronizes the PI3K-AKT-mTOR axis, suppresses detrimental phosphorylation signaling, and restores or increases myofilament phosphorylation in post-IR hearts. The beneficial effects observed in fat-1 transgenic mouse hearts can be attributed, at least in part, to elevated EPA levels. This study is the first to demonstrate that n-3 PUFAs protect hearts against IR injury through APLNR inhibition.
... Apelin is a peptide that binds to a G protein-coupled receptor (GPCR) called APJ 10 . Apelin and APJ are widely expressed in the central nervous system and peripheral tissues including the hypothalamus, adipose tissue, and skeletal muscle 11 . Apelin regulates several physiological functions such as fluid homeostasis, angiogenesis, and energy metabolism [12][13][14] . ...
Insulin is proved to have angiogenic ability thereby may worsen the diabetic retinopathy (DR) progression. Insulin also triggers the expression of endogenous angiogenic peptide, apelin. Since protamine was introduced as an inhibitor of the apelin receptor, we hypothesized that use of protaminated insulin instead of non-protaminated insulin can decrease the negative role of insulin in progression of DR. Firstly, the incidence of DR was compared among three diabetic patient groups: an oral medication, non-protaminated insulin, and protaminated insulin (PIns). Proliferation and migration rate of HUVECs was measured after insulin, apelin, and protamine exposure. In clinical study, the chance of developing DR was 8.5 and 4.1 times higher in insulin group and PIns groups compared with oral group respectively. Insulin group had a chance of 9.5-folds of non-proliferative DR compared to oral group. However, the difference of non-proliferative DR between PIns and oral group wasn’t significant. In-vitro tests showed that concomitant use of insulin and apelin increases viability and migratory potential of HUVECs. However, protamine could reverse this effect. Protamine present in some insulins might show a promising protective role against diabetic retinopathy. Thus, protaminated insulins may be preferable in the treatment of diabetes.
... Apelin and APJ are expressed in many human and rodent tissues, especially in the pulmonary and cardiovascular systems, such as endocardial and vascular endothelial cells, smooth muscle cells, cardiomyocytes, and to a lesser extent, in different parts of the brain and spinal cord, skeletal muscles, adipose tissue, and the thyroid gland [22][23][24]. ...
Apelin and its receptor are expressed in many tissues and play an important role in maintaining the homeostasis of the cardiovascular system and body fluids. Also, the association of this system with many diseases, such as diabetes, hypertension, obesity, cancer, diabetic retinopathy, etc., has been determined. This system is considered a therapeutic goal in many mentioned diseases. G protein-coupled receptors (GPCRs) have the ability to form oligomers and dimers with themselves and other receptors. The formation of these oligomers is associated with a change in the signaling pathways of the receptors. Research on the oligo and dimers of these receptors can revolutionize the principles of pharmacology. The apelin receptor (APJ) is also a GPCR and has been shown to have the ability to form dimers and oligomers. This article discusses the dimerization and oligomerization of this receptor with its own receptor and other receptors, as well as the signaling pathways.
... In addition, the [Pyr 1 ]apelin-13 sequence incorporates an N-terminal RPRL motif that is absolutely necessary for receptor binding. Earlier SAR studies demonstrated that His7 and Met11 substitutions did not affect the binding or function of the ligand 95 . From these SAR studies, it is apparent that modified peptides can be designed that may show G protein or β-arrestin signalling bias, as is exemplified by the macrocyclic peptide MM07 (ReF. ...
... Apelin, a peptide with regulatory functions, interacts with a G-protein-coupled receptor (APJ). Concentrations are high in the brain and spinal cord, as well as in adipose tissue, skeletal muscle, the digestive tract and the ovaries [5][6][7]. Over the past few years, researchers have paid close attention to the Apelin-APJ system because of the potential function it may play in homeostasis, fluid control, cell proliferation and energy related metabolism [8][9][10]. ...
Introduction. Type 2 diabetes mellitus is the root cause of diabetic nephropathy, a condition affecting the kidneys (T2DM). The number of people who have type 2 diabetes is growing.
Aim. To evaluate the differences in Apelin 13 levels between patients with T2DM who had normal or microalbuminuria and those who had microalbuminuria, as well as between these patients and healthy controls. The intent is to better understand its link to microalbumin, haemoglobin A1c, insulin resistance (IR), and other standard measures.
Materials and methods. Sixty individuals with type 2 diabetes, aged 35 to 45, were selected, and their microalbuminuria and normoalbuminuria were compared. Thirty age-matched healthy volunteers were selected to serve as controls. The concentrations of Apelin 13 and insulin in the plasma were measured with ELISA kits. The Turbilatex assay was used to calculate microalbumin concentrations. Measurements of glycosylated haemoglobin (HbA1C) were made via high-performance liquid chromatography.
Results. Patients with type 2 diabetes mellitus had higher levels of the protein Apelin 13 in their plasma than did healthy controls. T2DM patients with microalbuminuria were different from normoalbuminuric patients in another important way. Correlations between plasma Apelin 13 and albuminuria, HbA1c, and HOMA-IR were all positive.
Conclusion. Considering that plasma Apelin 13 is a critical risk factor in Type 2 diabetes mellitus and frequently arises in the early stages of nephropathy, it may be useful for the assessment of vascular issues in type 2 diabetic patients.
... APJ and the preproapelin, consisting of 77 amino acid residues, are expressed in embryo and adult human tissues, including heart, vasculature (particularly in endothelial cells), and lung tissue; white adipose tissue; the gastrointestinal tract and the liver; several regions of the central nervous system; retinas; limbs; the skin; kidneys; mammary glands; and placental tissue [1,[4][5][6][7][8][9][10][11][12][13][14]. The preproapelin can be cleaved from its C-terminal domain to produce several apelin peptides with different polypeptide chain lengths (apelin-36, apelin-17, and apelin-13). ...
The apelinergic system is a highly conserved pleiotropic system. It comprises the apelin receptor apelin peptide jejunum (APJ) and its two peptide ligands, Elabela/Toddler (ELA) and apelin, which have different spatiotemporal localizations. This system has been implicated in the regulation of the adipoinsular axis, in cardiovascular and central nervous systems, in carcinogenesis, and in pregnancy in humans. During pregnancy, the apelinergic system is essential for embryo cardiogenesis and vasculogenesis and for placental development and function. It may also play a role in the initiation of labor. The apelinergic system seems to be involved in the development of placenta-related pregnancy complications, such as preeclampsia (PE) and intrauterine growth restriction, but an improvement in PE-like symptoms and birth weight has been described in murine models after the exogenous administration of apelin or ELA. Although the expression of ELA, apelin, and APJ is altered in human PE placenta, data related to their circulating levels are inconsistent. This article reviews current knowledge about the roles of the apelinergic system in pregnancy and its pathophysiological roles in placenta-related complications in pregnancy. We also discuss the challenges in translating the actors of the apelinergic system into a marker or target for therapeutic interventions in obstetrics.
... Apelin and APJ mRNA are widely expressed in a variety of organs and tissues including the central nervous system (CNS), cardiovascular system, gastrointestinal tract, adipose tissues, placenta, lungs and kidney (Carpéné et al., 2007;Medhurst et al., 2003;Sekerci et al., 2018). Moreover, pre-proapelin mRNA and apelin protein are found in high concentrations in the human mammary gland, suggesting that apelin is produced endogenously in the mammary gland (Wang et al., 2008). ...
Apelin, a regulatory peptide, is an endogenous ligand of the apelin receptor (APJ), which belongs to the G protein-coupled receptor family. The peptide and its receptor are distributed in animal and human tissues, including the cardiovascular and central nervous systems, and studies indicate that apelin signaling could play a role in cytoprotection of cells where it is found. Apelin activity may be modulated by interactions of the APJ receptor with other receptors, resulting in heteromerization. The interaction of the APJ with other receptor systems increases the signaling repertoire of apelin, thereby allowing it to exert a widened degree of control over cellular physiological functions. This article reviews studies which provide evidence for the physiological importance of APJ/Kappa opioid receptor (KOR) heterodimers in several critical cellular processes, including cell proliferation, and results are discussed which support a role of this peptide and the APJ receptor in functioning of the cardiovascular, gastrointestinal and central nervous systems under normal conditions and pathology, as well as novel signal transduction characteristics resulting following the interaction of APJ and KOR. A better understanding of the cellular protective actions of apelin, and the physiological outcomes from interaction of its receptor with other receptor types could lead to new pharmaceutical targets for various diseases affecting among other organs, the heart, the gastrointestinal system and the brain.
... Human APLNR is a member of seventransmembrane G protein-coupled receptors, consisting of 380 amino acid residues. APLN/APLNR mRNA and protein were detected in the central nervous system (CNS) and the peripheral human tissues, such as callosum, cortex, hippocampus, heart, lung, kidney, stomach [3,4]. APLN/APLNR system was involved in a wide range of pathological and physiological processes, including cardiovascular function [5,6], energy metabolism [7,8], obesity [6], endocrine activity [9], ischemia/reperfusion injury [10], liver disease [11], and neuropathy [12]. ...
Apelin (APLN) is an endogenous ligand of the G protein-coupled receptor APJ (APLNR). APLN/APLNR system was involved in a variety of pathological and physiological functions, such as tumorigenesis and development. However, its prognostic roles in patients with central nervous system (CNS) cancers remain unknown. The present study was designed to explore the expression profile, prognostic significance, and interaction network of APLN/APLNR by integrating data from Oncomine, GEPIA, LOGpc, STRING, GeneMANIA, and immunohistochemical staining. The results demonstrated that APLN and APLNR mRNA expression were significantly increased in CNS cancers, including both low-grade glioma (LGG) and glioblastoma (GBM), when compared with normal CNS tissues. The high APLN, but not APLNR, expression was significantly correlated with overall survival (OS), recurrence free survival (RFS), and progression free survival (PFS) of LGG patients. However, neither APLN nor APLNR expression was significantly related to prognostic value in terms of OS, disease free interval (DFI), disease specific survival (DSS), or progression free interval (PFI) for GBM patients. Additionally, immunohistochemistry staining confirmed the increased APLN expression in tissues of LGG patients with grade II than grade I. These results showed that an elevated APLN level could predict poor OS, RFS, and PFS for LGG patients, and it could be a promising prognostic biomarker for LGG.
... 161 This apelin/APJ system is present around the body. 162 The lack of apelin could suppress the Wnt/b-catenin pathway, which is the principal reason why apelin is correlated with osteoporosis. In addition, the lack of apelin decreases lysyl oxidase (LOXL)-3 and LOXL4 expression, 163 which participate in collagen fiber production, and have an impact on osteoblast formation. ...
Adipokines are the principal mediators in adipose signaling. Nevertheless, besides their role in energy storage, these molecules can be produced by other cells, such as immune cells or chondrocytes. Given their pleiotropic effects, research over the past few years has also focused on musculoskeletal diseases, showing that they adipokines might have relevant roles in worsening the disease or improving the treatment response. In this review, we summarize recent advances in our understanding of adipokines and their role in the more prevalent musculoskeletal immune and inflammatory disorders.
... Its biological action is mediated by a high affinity G protein-coupled receptor named APJ. Both Apelin and APJ are found in several peripheral tissues such as kidney, muscle, liver and heart Medhurst et al., 2003;Lee et al., 2001 ;O'Carroll et al., 2000) where they exert positive effects on peripheral energy metabolism by improving lipid oxidation, mitochondrial oxidative capacity and glucose utilization in muscles of HFD fed mice Dray et al., 2008). Evidence demonstrates that Apelin and APJ are also widely present within the brain (O'Carrol et al., 2000). ...
Les études épidémiologiques estiment que le risque de dépression majeure (DM) est plus élevé chez les patients diabétiques comparé à la population générale. Des études plus spécifiques mettent en lumière des corrélations entre la dégradation de certains paramètres métaboliques et les symptômes anxio-dépressifs chez l'humain. C'est notamment le cas pour l'insulino-résistance périphérique qui est positivement corrélée à la sévérité de la DM. En revanche, les conséquences de l'insulino-résistance centrale sur les troubles dépressifs n'ont jamais été étudiés de manière approfondie non seulement en clinique mais également chez l'animal de laboratoire. Compte tenu de la présence du récepteur à l'insuline dans le cerveau, une des hypothèses serait que cette hormone module directement (ou indirectement) l'activité des systèmes monoaminergiques et notamment celle des neurones sérotoninergiques (5-HT) majoritairement regroupé dans le noyau dorsal du raphé (NDR). En effet, si l'influence de l'insuline sur le système dopaminergique et le comportement alimentaire a déjà été montré, très peu d'études se sont intéressées à son impact sur le système 5-HT pourtant clé dans la physiopathologie de la DM. Au cours de ce travail de thèse nous avons pu montrer que le récepteur à l'insuline est présent sur les neurones 5-HT du NDR. Grâce à des techniques d'électrophysiologie ex- et in-vivo et de microdialyse intracérébrale réalisées sur modèle murin, nous avons caractérisé l'effet excitateur de l'insuline sur l'activité électrique des neurones 5-HT. Ces résultats nous ont amené à tester les effets comportementaux de l'insuline et à montrer les effets anxiolytiques de son injection intra-raphé et intra-nasale chez la souris saine. Dans un second temps, afin de se placer dans un contexte pathologique et de mieux comprendre l'impact de la perturbation de la signalisation de l'insuline sur l'humeur, nous avons étudié l'activité du système 5-HT et les comportements de type anxio-dépressifs dans des modèles murins de diabète de type 1 et 2 (DT1/DT2). Dans ces deux modèles, que ce soit dans un contexte d'insulinopénie (DT1) ou d'insulino-résistance (DT2), les souris présentent un phénotype anxieux et certains traits de la DM associés à un diminution de l'activité du système sérotoninergique du NDR. Enfin, nous avons tenté d'identifier l'implication de l'apeline, une adipokine connue pour ses propriétés insulino-sensibilisatrice sur les anomalies comportementales induites par un DT2. Nos résultats montrent que les souris présentant une invalidation génétique de l'apeline, sont plus susceptibles à développer une insulino-résistance en réponse à un régime alimentaire diabétogène et des troubles comportementaux. De manière intéressante le traitement par la metformine, un antidiabétique aux propriétés insulino-sensibilisatrice, ne permet pas l'amélioration des paramètres métaboliques de ces souris mutantes mais améliore leur état anxieux. Ainsi ce travail de thèse a permis de souligner l'existence d'interactions anatomiques et fonctionnelles entre le système insulinergique et sérotoninergique central ainsi que leur importance dans l'anxiété, un trouble psychiatrique souvent annonciateur d'un épisode dépressif. [...]
... This study demonstrated for the first time that apelin expression was associated with tumor size, stage, histological type, MVD, LVD, lymph node metastasis and poor prognosis. Extensive studies on the expression of apelin have been published in experimental animals [27][28][29]. However, research on apelin in the human normal breast and breast cancer is limited. ...
PurposeApelin has been shown to be a novel angiogenic factor in various cancers. However, there is limited information regarding the role of apelin in breast cancer. The aim of the present study is to examine associations between apelin, clinicopathological variables, and clinical outcome in breast cancer patients.Methods
In this study, we began by investigating the apelin expression in breast cancer with long-term follow-up using immunohistochemistry. We then analyzed the relationship between apelin expression and microvessel density (MVD), lymphatic vessel density (LVD), lymph node status as well as other established clinicopathological parameters. The relationship between apelin expression and prognosis was also studied. In addition, we compared the apelin and its ligant APJ expression between 30 breast cancer samples and normal breast tissues adjacent to the breast tumors using western blot (WB) and RT-PCR.ResultsApelin protein expression was detected in the cytoplasm of the breast carcinoma cells at various intensities. Apelin expression was positive in 59.2% (84/142) of the breast cancer patients and apelin expression was significantly correlated with tumor size (p = 0.030), stage (p = 0.000), histological type (p = 0.009), MVD (p = 0.000), LVD (p = 0.000), and lymph node metastasis (p = 0.041). Survival curves determined by the Kaplan–Meier method and univariate analysis demonstrated that high expression of apelin was associated with both worse disease-free survival (p < 0.001) and overall survival (p < 0.001). Interestingly, a significant difference in apelin and APJ expression by WB as well as RT-PCR was observed between normal breast tissues adjacent to the breast tumors and breast cancer tissues.Conclusions
Our results showed apelin expression was associated with tumor size, stage, histological type, MVD, LVD, lymph node metastasis and poor prognosis. The presence of apelin may be a new prognostic factor and potential therapeutic target for breast cancer.
... However, PTX3 expression, on the other hand, quickly increases in response to inflammatory stimuli in a variety of diseases, including infectious, autoimmune, and degenerative disorders [11,17]. Despite the fact that there are only a few findings on the interaction between PTX3 and exercise, current data shows that there is no difference in PTX3 levels after a 30-min submaximal aerobic exercise [18], although plasma PTX3 levels improve relative to the control group [14]. Similarly, PTX3 levels increased in untrained individuals with acute moderate and intense aerobic exercise [19]. ...
The effects of various strength training intensities on blood cardiovascular risk markers in healthy men Sağlıklı erkeklerde farklı kuvvet egzersizi yoğunluklarının kan kardiyovasküler risk belirteçleri üzerindeki etkileri Abstract Objectives: Regular physical exercise, especially aerobic exercise, is known to have a protective effect on cardio-vascular health. The aim of this research is to look at the impact of two separate resistance training programs on blood biomarkers that are associated with the early detection of cardiac risk. Methods: Forty-five male participants (mean 41 years) were randomly divided into three groups: The low-intensity resistance exercise group (LIEG), the moderate-intensity resistance exercise group (MIEG), and the control group (CG). The programs were implemented three times a week and in two sets. MIEG consisted of 8-10 repeats at 70-80% density of one repetition maximum load (1RM), while LIEG consisted of 15-17 repeats at 50-60% density of 1RM. CG did not participate in any exercise program. Two-factor mixed-design ANOVA assessed the data. Results: Before, fourth week, and after the exercise program in repeated measurements, there was a significant decrease in body mass (−1.7%), body mass index (−1.7%), apelin (−44%), and pentraxin 3 (−39%) levels in MIEG (p < 0.05). Additionally, our study noted a decrease in pentraxin 3 (−25%, p < 0.05) and interleukin 6 (−21%) levels, while there was an increase in creatine kinase (18%), and lactate dehydrogenase (7.4%) levels in LIEG. Strength levels improved significantly in exercise groups. Conclusions: Eight weeks of moderate-resistance training can potentially reduce the cardiovascular risk in healthy men. Öz Amaç: Düzenli fiziksel egzersizin, özellikle aerobik egzersi-zin, kardiyovasküler sağlık üzerinde koruyucu bir etkisi olduğu bilinmektedir. Bu çalışmada amaç, iki farklı yoğun-luktaki direnç egzersiz programının kardiyak riskin erken teşhisinde yer alan kan belirteçleri üzerindeki etkilerini araştırmaktır. Gereç ve Yöntem: Kırk beş erkek katılımcı (ort. 41 yaş) rastgele üç gruba ayrıldı: Düşük yoğunluklu direnç egzersiz grubu (LIEG), orta yoğunluklu direnç egzersiz grubu (MIEG)
The creation of bioactive molecules for the treatment of cardiovascular diseases based on natural peptides stimulates intensive experimental research. In recent years, it has been established that the C-terminal fragments of apelin, an endogenous ligand of the APJ receptor, reduce metabolic and functional disorders in experimental heart damage. The review presents literature data and generalized results of our own experiments on the effect of apelin-13, [Pyr]apelin-13, apelin-12, and their chemically modified analogues on the heart in normal conditions and when modeling pathophysiological conditions in vitro and in vivo. It has been shown that the spectrum of action of apelin peptides on the damaged myocardium covers a decrease in the death of cardiomyocytes from necrosis, a decrease in cardiomyocyte membrane damage, an improvement in the metabolic state of the myocardium, and a decrease in the formation of reactive oxygen species and lipid peroxidation products. The mechanisms of the protective action of these peptides associated with the activation of the APJ receptor and the manifestation of antioxidant properties are discussed. The data presented in the review indicate the promise of molecular design of pharmacological APJ receptor agonists, which can serve as the basis for the development of cardioprotectors that affect the processes of free radical oxidation and metabolic adaptation.
The pituitary gland is a key endocrine gland in all classes of vertebrates, including mammals. The pituitary gland is an important component of hypothalamus–pituitary–target organ hormonal regulatory axes and forms a functional link between the nervous system and the endocrine system. In response to hypothalamic stimuli, the pituitary gland secretes a number of hormones involved in the regulation of metabolism, stress reactions and environmental adaptation, growth and development, as well as reproductive processes and lactation. In turn, hormones secreted by target organs at the lowest levels of the hormonal regulatory axes regulate the functions of the pituitary gland in the process of hormonal feedback. The pituitary also responds to other peripheral signals, including adipose-tissue-derived factors. These substances are a broad group of peptides known as adipocytokines or adipokines that act as endocrine hormones mainly involved in energy homeostasis. Adipokines, including adiponectin, resistin, apelin, chemerin, visfatin, and irisin, are also expressed in the pituitary gland, and they influence the secretory functions of this gland. This review is an overview of the existing knowledge of the relationship between chosen adipose-derived factors and endocrine functions of the pituitary gland, with an emphasis on the pituitary control of reproductive processes.
Creation of bioactive molecules for treatment of cardiovascular diseases based on natural peptides is the focus of intensive experimental research. In the recent years, it has been established that C-terminal fragments of apelin, an endogenous ligand of the APJ receptor, reduce metabolic and functional disorders in experimental heart damage. The review presents literature data and generalized results of our own experiments on the effect of apelin-13, [Pyr]apelin-13, apelin-12, and their chemically modified analogues on the heart under normal and pathophysiological conditions in vitro and in vivo. It has been shown that the spectrum of action of apelin peptides on the damaged myocardium includes decrease in the death of cardiomyocytes from necrosis, reduction of damage to cardiomyocyte membranes, improvement in myocardial metabolic state, and decrease in formation of reactive oxygen species and lipid peroxidation products. The mechanisms of protective action of these peptides associated with activation of the APJ receptor and manifestation of antioxidant properties are discussed. The data presented in the review show promise of the molecular design of APJ receptor peptide agonists, which can serve as the basis for the development of cardioprotectors that affect the processes of free radical oxidation and metabolic adaptation.
Cardiovascular disease is the leading cause of death worldwide. Its prevalence is rising due to ageing populations and the increasing incidence of diseases such as chronic kidney disease, obesity and diabetes which are associated with elevated cardiovascular risk. Despite currently available treatments, there remains a huge burden of cardiovascular disease-associated morbidity for patients and healthcare systems, and newer treatments are needed. The apelin system, comprising the apelin receptor and its two endogenous ligands apelin and elabela, is a broad regulator of physiology that opposes the actions of the renin-angiotensin and vasopressin systems. Activation of the apelin receptor promotes endothelium-dependent vasodilatation and inotropy, lowers blood pressure and promotes angiogenesis. The apelin system appears to protect against arrhythmias, inhibits thrombosis and has broad anti-inflammatory and anti-fibrotic actions. It also promotes aqueous diuresis through direct and indirect (central) effects in the kidney. Thus, the apelin system offers therapeutic promise for a range of cardiovascular, kidney and metabolic diseases. This review will discuss current cardiovascular disease targets of the apelin system and future clinical utility of apelin receptor agonism.
Apelin and Elabela (Ela) are peptides encoded by APLN and APELA, respectively, which act on their receptor APJ and play crucial roles in the body. Recent research has shown that they not only have important effects on the endocrine system, but also promote vascular development and maintain the homeostasis of myocardial cells. From a molecular biology perspective, we explored the roles of Ela and apelin in the cardiovascular system and summarized the mechanisms of apelin-APJ signaling in the progression of myocardial infarction, ischemia-reperfusion injury, atherosclerosis, pulmonary arterial hypertension, preeclampsia, and congenital heart disease. Evidences indicated that apelin and Ela play important roles in cardiovascular diseases, and there are many studies focused on developing apelin, Ela, and their analogues for clinical treatments. However, the literature on the therapeutic potential of apelin, Ela and their analogues and other APJ agonists in the cardiovascular system is still limited. This review summarized the regulatory pathways of apelin/ELA-APJ axis in cardiovascular function and cardiovascular-related diseases, and the therapeutic effects of their analogues in cardiovascular diseases were also included.
In the central nervous system (CNS), the apelin/APJ system is broadly expressed. According to some studies, activation of this system protects against excitotoxicity mediated by N-methyl-D-aspartate (NMDA) receptors and exerts neuroprotective effects. However, the role of this system in epilepsy remains unclear. In the present study, immunofluorescence staining and western blotting were used to assess APJ localization and expression in the brains of mice with recurrent spontaneous seizures induced by kainic acid (KA). Behavior and local field potentials (LFPs) were assessed in mice with KA-induced seizures. Susceptibility to seizures was assessed in a pentylenetetrazole (PTZ)-induced seizure model. Whole-cell patch-clamp recordings were used to evaluate the role of the apelin/APJ system in regulating synaptic transmission in brain slices from mice in which Mg2+-free medium was used to induce seizures. NMDA receptor GluN2B subunit expression and phosphorylation of GluN2B at Ser1480 were measured in the mouse hippocampus. APJ was primarily localized in neurons, and its expression was upregulated in the epileptic brain. APJ activation after KA-induced status epilepticus (SE) reduced epileptic activity, whereas APJ inhibition aggravated epileptic activity. In the PTZ model, APJ activation was reduced, and APJ inhibition increased susceptibility to seizures. The apelin/APJ system affected NMDA receptor-mediated postsynaptic currents in patch-clamp recordings. Moreover, APJ regulated the levels of GluN2B phosphorylated at Ser1480 and the abundance of cell-surface GluN2B in neurons. Furthermore, endocytosis of the NMDA receptor GluN2B subunit was regulated by the apelin/APJ system. Together, our findings indicate that the apelin/APJ system modulates seizure activity and may be a novel therapeutic target for epilepsy.
Heart failure is one of the most significant public health problems faced by millions of medical researchers worldwide. And pathological cardiac hypertrophy is considered one of the possible factors of increasing the risk of heart failure. Here, we introduce apelin/ELABELA-APJ system as a novel therapeutic target for cardiac hypertrophy, bringing about new directions in clinical treatment. Apelin has been proven to regulate cardiac hypertrophy through various pathways. And an increasing number of studies on ELABELA, the newly discovered endogenous ligand, suggest it can alleviate cardiac hypertrophy through mechanisms similar or different to apelin. In this review, we elaborate on the role that apelin/ELABELA-APJ system plays in cardiac hypertrophy and the intricate mechanisms that apelin/ELABELA-APJ affect cardiac hypertrophy. We also illuminate and make comparisons of the newly designed peptides and small molecules as agonists and antagonists for APJ, updating the breakthroughs in this field.
Apelin is an endogenous ligand for the G protein-coupled receptor APJ and has multiple biological activities in human tissues and organs, including the heart, blood vessels, adipose tissue, central nervous system, lungs, kidneys, and liver. This article reviews the crucial role of apelin in regulating oxidative stress-related processes by promoting prooxidant or antioxidant mechanisms. Following the binding of APJ to different active apelin isoforms and the interaction with several G proteins according to cell types, the apelin/APJ system is able to modulate different intracellular signaling pathways and biological functions, such as vascular tone, platelet aggregation and leukocytes adhesion, myocardial activity, ischemia/reperfusion injury, insulin resistance, inflammation, and cell proliferation and invasion. As a consequence of these multifaceted properties, the role of the apelinergic axis in the pathogenesis of degenerative and proliferative conditions (e.g., Alzheimer’s and Parkinson’s diseases, osteoporosis, and cancer) is currently investigated. In this view, the dual effect of the apelin/APJ system in the regulation of oxidative stress needs to be more extensively clarified, in order to identify new potential strategies and tools able to selectively modulate this axis according to the tissue-specific profile.
Apelin receptor (APJR) is a class A peptide (apelin) binding G protein-coupled receptor (GPCR) that plays a significant role in regulating blood pressure, cardiac output, and maintenance of fluid homeostasis. It is activated by a wide range of endogenous peptide isoforms of apelin and elabela. The apelin peptide isoforms contain distinct structural features that aid in ligand recognition and activation of the receptor. Site-directed mutagenesis and structure-based studies have revealed the involvement of extracellular and transmembrane regions of the receptor in binding to the peptide isoforms. The structural features of APJR activation of the receptor as well as mediating G-protein and β-arrestin-mediated signaling are delineated by multiple mutagenesis studies. There is increasing evidence that the structural requirements of APJR to activate G-proteins and β-arrestins are different, leading to biased signaling. APJR also responds to mechanical stimuli in a ligand-independent manner. A multitude of studies has focused on developing both peptide and non-peptide agonists and antagonists specific to APJR. Apelin/elabela-activated APJR orchestrates major signaling pathways such as extracellular signal-regulated kinase (ERKs), protein kinase B (PKB/Akt), and p70S. This review focuses on the structural and functional characteristics of apelin, elabela, APJR, and their interactions involved in the binding and activation of the downstream signaling cascade. We also focus on the diverse signaling profile of APJR and its ligands and their involvement in various physiological systems.
Postnatal ovarian and uterine development is crucial to accomplished female fertility. Thus, the investigations of factors that present in pre‐pubertal stages are important as it might be responsible for the regulation of ovarian and uterine function. Apelin, an adipokine and its receptor (APJ) are present in female reproductive organs. However, no study has reported its postnatal expression in uterus and ovary. Thus, we investigated the postnatal developmental changes in expression and localization of apelin and APJ in the ovary and uterus of mice. Postnatal ovary and uterus were collected from postnatal day (PND) 1, 7, 14, 21, 42, 65 and performed western blot analysis and immunohistochemistry. Uterine APJ is elevated in PND14 and PND65, whereas, ovarian APJ elevated in PND7, PND14, and PND65. Apelin expression in both ovary and uterus showed intense staining at PND65 and PND14. Our results showed that apelin and APJ abundance was lower at PND21 in uterus and ovary. In conclusion, apelin and APJ are developmentally regulated in the ovary and uterus, and its localization in the different compartments of ovary and uterus suggest its distribution specific physiological role in the uterus and ovary.
Agonism of the apelin receptor (APJ) has demonstrated beneficial effects in models of heart failure. We have previously disclosed compounds such as 4, which showed good APJ agonist activity but were metabolized to the mono-demethylated, non-interconverting atropisomer metabolites. Herein, we detail the design and optimization of a novel series of N-linked APJ agonists with good potency, metabolic stability, and rat pharmacokinetic profile, which are unable to undergo the same metabolic mono-demethylation cleavage.
Verbascum L. (Scrophulariaceae) cinsi, dünya çapında yaklaşık 360 tür içerir. Türkiye'de 130
melez ilavesi ile cins, kısmen yapay 13 gruba ayrılan 246 tür ile temsil edilmektedir. Türkçe
“Sığırkuyruğu” olarak adlandırılan bu cinsin endemizm oranı, 196 endemik tür (%80) ile
oldukça yüksektir. Bu cins 9 takson ile (V. orientale (L.) All., V. agrimoniifolium subsp.
agrimoniifolium (K.Koch) Hub.-Mor., V. laetum Boiss. & Hausskn ex Boiss., V. racemiferum
Boiss. & Hausskn ex Boiss., V. sinuatum subsp. sinuatum var. adenosepalum Murb., V.
geminiflorum Hochst., V. andrusii Post, V. kotschyi Boiss. & Hohen., V. lasianthum Boiss. ex
Benth.) Mardin ilinde doğal olarak yayılış göstermektedir. Taksonlar tek, iki ve çok yıllıktırlar.
Çiçeklenme Mayıs-Temmuz zaman aralığındadır. Habitatları kireçtaşı yamaçları, Quercus
çalılığı, bağlar, nadas tarlaları, taşlı yamaçlar ve tahıl tarlalarıdır. Yayılış gösterdikleri
yükseklik 0-1050 m arasındadır. Akdeniz ve İran-Turan elementidirler. Taksonların Türkiye
dağılımları Güneydoğu Anadolu Bölgesidir. Sığırkuyruğu, geleneksel veya bitkisel tıpta uzun
yıllardan beri kullanılan bitkilerdendir. Özellikle astım, solunum, hemoroit, saç dökülmeleri,
mantar enfeksiyonları, cilt yaraları, romatizmal ağrılar, ishal, lenfosittik lösemi ve grip gibi
hastalıkların tedavisinde kullanıldığı belirtilmiştir. Bunun yanında yapılan araştırmalarda antiinflamatuar aktiviteye sahip olduğu ve çiçeğinin antiviral özellikler taşıdığı tespit edilmiştir.
Bu derlemede, Verbascum üyelerinin Mardin’de yayılış gösteren taksonlarının taksonomik
özellikleri ve tıbbi açıdan da kullanımları derlenmiştir
Apelin, a member of G protein-coupled receptors and also the endogenous ligand of APJ, has been reported to be expressed in various tissues in vivo and exert significant biological effects. Apelin and APJ are expressed in the central nervous system, particularly the hypothalamus and many peripheral tissues. Apelin has been shown to be involved in the regulation of cardiovascular and fluid homeostasis, food intake, cell proliferation and angiogenesis.In addition to being a peptide found in many parts of the body, apelin is also produced and secreted by adipocytes and is therefore considered an adipokine. It has been shown that Apelin is effective on glucose and lipid metabolism and also regulates insulin secretion. In addition, different studies in both animals and humans have shown that plasma apelin concentrations are generally increased during obesity and type 2 diabetes (T2DM). The aim of this review is to provide information about the effects and interactions of apelin and its receptor, APJ, with obesity and obesity-related diseases.
Keywords: Apelin, APJ, Hormone, Obesity, Diabetes
L’apéline, un neuropeptide vasoactif, son récepteur (Apéline-R) et l’arginine-vasopressine (AVP, hormone antidiurétique) sont co-localisés dans les neurones magnocellulaires vasopressinergiques. Dans le rein, l’Apéline-R est présent dans les artérioles glomérulaires et le canal collecteur (CD) où sont aussi localisés les récepteurs de l’AVP de type 2 (V2-R). L’apéline exerce une action aquarétique par son effet inhibiteur sur l’activité électrique phasique des neurones vasopressinergiques et la sécrétion systémique de l’AVP dans la circulation sanguine, et par son action directe au niveau du rein. Dans cet organe, elle augmente la microcirculation locale et inhibe, au niveau du CD, l’effet antidiurétique de l’AVP médié par les V2-R. L’apéline et l’AVP dans le plasma sont inversement régulées par les stimuli osmotiques aussi bien chez l’Homme que chez le rongeur, montrant que l’apéline participe avec l’AVP au maintien de l’équilibre hydrique. Sur le plan clinique, chez les patients atteints du syndrome d’antidiurèse inappropriée (SIAD), l’équilibre apéline/AVP est altéré, ce qui contribue au défaut du métabolisme de l’eau. L’activation de l’Apéline-R par un analogue métaboliquement stable d’une des isoformes de l’apéline, l’apéline-17, en augmentant la diurèse aqueuse et modérément la prise d’eau, et en corrigeant progressivement l’hyponatrémie, pourrait constituer une nouvelle approche pour le traitement de cette pathologie.
Apelin is a small peptide secreted by the adipose tissue notably in conditions of obesity-induced hyper-insulinemia. Apelin exerts a range of physiological functions at the periphery including the improvement of insulin sensitivity and the increase of muscle strength or cardiac contractibility. Interestingly, the brain is endowed with a high density of APJ, the single target of apelin, and growing evidence suggests various central actions of this adipokine. Interestingly, recent studies reported that the intracerebroventricular infusion of apelin modulates emotional states in middle age stressed animals. However, results are so far been mixed and have not allowed for definitive conclusions about the impact of apelin on anxio-depressive-like phenotype. This study aims 1) to evaluate whether serum apelin levels are associated with mood in older adults and 2) to determine the impact of the genetic apelin inactivation in 12-month old mice fed a standard diet (STD) or in 6-month old mice fed a high fat diet (HFD). A higher plasma apelin level was associated with higher depressive symptoms in older adults. In line with these clinical findings, 12-month old apelin knock-out (Ap-/-) mice displayed a spontaneous antidepressant-like phenotype. In a marked contrast, 6-month old Ap-/- mice harbored a higher degree of peripheral insulin resistance than wild-types in response to HFD and were more prone to develop anxiety while the depressive-like state was not modified. We also provided evidence that such anxious behavior was associated with an impairment of central serotonergic and dopaminergic neuronal activities. Finally, although the insulin sensitizing drug metformin failed to reverse HFD-induced insulin resistance in 6-month old Ap-/- mice, it reversed their anxious phenotype.
These results emphasize a complex contribution of apelin in the regulation of emotional state that might depend on the age and the metabolic status of the animals. Further investigations are warranted to highlight the therapeutic potential of manipulating the apelinergic system in mood-related disorders.
Apelin is an endogenous ligand of G protein-coupled receptor (APJ), and they compose apelin/APJ system. Apelin/APJ system is widely distributed in tissues and plays pleiotropic roles. Attractively, more emphasis has recently been placed on the effects of apelin/APJ system in eye diseases, such as retinopathy of prematurity (ROP), diabetic retinopathy (DR) and diabetic macular edema (DME). In this review, we elaborated the roles of apelin/APJ system in the pathophysiological processes of eye. Concretely, apelin/APJ system induces retinal gliosis and angiogenesis. Hypoxia-inducible factors (HIFs) are involved in apelin/APJ system-triggered ROP progress. Apelin/APJ system mediates DR-induced retinopathy. Apelin/APJ system maintains retinal functions and health by protecting Müller cells from apoptosis. Apelin/APJ system suppresses the NMDA-induced retinal ganglion cell (RGC) loss to protect optic nerve damage. Overall, apelin/APJ system is a potential therapeutic target for eye disease.
Background
In ulcerative colitis patients, Elabela levels and the relation of Elabela with laboratory parameters is unknown.AimThe purpose of this study was to investigate the serum Elabela levels in UC patients and its relationship with other clinical and laboratory findings.Methods
Forty-three patients with UC and 40 healthy controls (group I) similar in age and gender were included in the study. Routine patient history, physical examination, and laboratory tests were followed by analysis of serum Elabela levels. Endoscopic activity index (EAI) of patients with UC was calculated. There were two groups of patients: those in remission (group II) and with active disease (group III).ResultsGroups I, II, and III had 40, 22, and 21 participants, respectively. Serum Elabela levels were found to be 3.32 ± 1.25 ng/mL in group I, 3.38 ± 0.88 ng/mL in group II, and 5.48 ± 1.61 ng/mL in group III. Comparing the serum Elabela levels, a statistically significant difference was found between three groups (p < 0.001). Serum Elabela level showed a significant and positive correlation with EAI, leukocyte count, and hs-CRP, while a negative correlation was found with hemoglobin levels in univariate analysis (p < 0.001, for each). In linear regression analysis, these parameters were found to be associated with EAI and hs-CRP (p = 0.049, β = 0.337, and p = 0.015, β = 0.396, respectively).Conclusion
Elabela concentrations in patients with active UC was significantly higher and was associated with EAI and hs-CRP. Blood Elabela concentrations can be useful in the diagnosis and follow-up of patients with active UC.
We previously reported a series of macrocyclic analogues of [Pyr1]-apelin-13 (Ape13) with increased plasma stability and potent APJ agonist properties. Based on the most promising compound in this series, we synthesized and then evaluated novel macrocyclic compounds of Ape13 to identify agonists with specific pharmacological profiles. These efforts led to the development of analogues 39 and 40, which possess reduced molecular weight (MW 1020 Da vs Ape13, 1534 Da). Interestingly, compound 39 (Ki 0.6 nM), which does not activate the Gα12 signaling pathway while maintaining potency and efficacy similar to Ape13 to activate Gαi1 (EC50 0.8 nM) and β-arrestin2 recruitment (EC50 31 nM), still exerts cardiac actions. In addition, analogue 40 (Ki 5.6 nM), exhibiting a favorable Gα12-biased signaling and an increased in vivo half-life (t1/2 3.7 h vs <1 min of Ape13), produces a sustained cardiac response up to 6 h after a single subcutaneous bolus injection.
We have recently identified a new G protein-coupled receptor, X-msr, whose expression is associated with the endothelial lineage in Xenopus laevis (Devic, E., Paquereau, L., Vernier, P., Knibiehler, B., Audigier, Y., 1996. Expression of a new G protein-coupled receptor X-msr is associated with an endothelial lineage in Xenopus laevis. Mech. Dev. 59, 129-140). Based on its structural analogy to the human orphan receptor APJ, we cloned the murine msr/apj receptor and analyzed its expression in developing tissues. As observed for X-msr, msr/apj transcripts are detected in the endothelium of the primary blood vessels and the forming heart. In addition, they are expressed in somites, limb bud and branchial arches. This expression pattern is distinct from that of the Flk1 gene and suggests that the msr/apj gene is expressed in a subpopulation of endothelial precursors and a mesenchymal population derived from paraaxial mesoderm.
We have recently identified apelin as the endogenous ligand for human APJ. In rats, the highest expression of APJ mRNA was
detected in the lung, suggesting that APJ and its ligand play an important role in the pulmonary system. When apelin-36 and
its pyroglutamylated C-terminal peptide, [<Glu65]apelin-13, were compared in microphysiometric analyses, the elevation of extracellular acidification induced in cells expressing
APJ by [<Glu65]apelin-13 was transient, whereas that by apelin-36 was sustained. These responses were almost completely inhibited by a specific
inhibitor for Gi or that for Na+/H+ exchanger. 125I -Labeled [<Glu65]apelin-13 analogue specifically bound to APJ with a high affinity, and [<Glu65]apelin-13 was more potent than apelin-36 in competitive inhibition assays. Because pretreatment with apelin-36 but not [<Glu65]apelin-13 drastically reduced the binding of the labeled apelin to APJ, the different patterns of acidification induced by
these two peptides appeared to reflect their dissociation rather than association with APJ. Apelin elicited the migration
of APJ-expressing cells, and [<Glu65]apelin-13 was more potent than apelin-36 in this activity. Heterogeneous molecular forms of apelin corresponding to apelin-36
and [<Glu65]apelin-13 were produced in bovine colostrum. Apelin-36 and [<Glu65]apelin-13 might have different functions in vivo and in vitro.
The orphan G protein-coupled receptor APJ has been shown to be a coreceptor for human and simian immunodeficiency virus (HIV and SIV) strains. We have determined that some HIV and SIV strains use APJ as a coreceptor to infect the brain-derived NP-2/CD4 cells. Because apelin is an endogenous ligand for the APJ receptor, we examined the inhibitory effects of apelin peptides on HIV infection, and found that the apelin peptides inhibit the entry of some HIV-1 and HIV-2 into the NP-2/CD4 cells expressing APJ. The inhibitory efficiency has been found to be in the order of apelin-36>apelin-17>apelin-13>apelin-12.
Apelin, a peptide recently isolated from bovine stomach tissue extracts, has been identified as the endogenous ligand of the human orphan APJ receptor. We established a stable Chinese hamster ovary (CHO) cell line expressing a gene encoding the rat apelin receptor fused to the enhanced green fluorescent protein, to investigate internalization and the pharmacological profile of the apelin receptor. Stimulation of this receptor by the apelin fragments K17F (Lys1-Phe-Arg-Arg-Gln-Arg-Pro-Arg-Leu-Ser-His-Lys-Gly-Pro-Met-Pro-Phe17) and pE13F (pGlu5-Arg-Pro-Arg-Leu-Ser-His-Lys-Gly-Pro-Met-Pro-Phe17) resulted in a dose-dependent inhibition of forskolin-induced cAMP production and promoted its internalization. In contrast, the apelin fragments R10F (Arg8-Leu-Ser-His-Lys-Gly-Pro-Met-Pro-Phe17) and G5F (Gly13-Pro-Met-Pro-Phe17) were inactive. The physiological role of apelin and its receptor was then investigated by showing for the first time in rodent brain: (i) detection of apelin neurons in the supraoptic and paraventricular nuclei by immunohistochemistry with a specific polyclonal anti-apelin K17F antibody; (ii) detection of apelin receptor mRNA in supraoptic vasopressinergic neurons by in situ hybridization and immunohistochemistry; and (iii) a decrease in vasopressin release following intracerebroventricular injection of K17F, or pE13F, but not R10F. Thus, apelin locally synthesized in the supraoptic nucleus could exert a direct inhibitory action on vasopressinergic neuron activity via the apelin receptors synthesized in these cells. Furthermore, central injection of pE13F significantly decreased water intake in dehydrated normotensive rats but did not affect blood pressure. Together, these results suggest that neuronal apelin plays an important role in the central control of body fluid homeostasis.
We have determined the binding characteristics of [125I]-(Pyr1)Apelin-13, a putative ligand for the APJ orphan receptor in human cardiovascular and rat tissue and investigated the functional properties of (Pyr1)Apelin-13 in human saphenous vein.
The binding of [125I]-(Pyr1)Apelin-13 to sections of human heart tissue was time dependent and rapid at 23°C. Data were fitted to a single site model with an association rate constant (kobs) of 0.115 min−1. [125I]-(Pyr1)Apelin-13 also dissociated from a single site with a dissociation rate constant of 0.0105 min−1.
In saturation binding experiments [125I]-(Pyr1)Apelin-13 bound to human left ventricle with a KD value of 0.35±0.08 nM, Bmax of 4.3±0.9 fmol mg−1 protein with a Hill slope of 0.97±0.04 and to the right atria with a KD of 0.33±0.09 nM, Bmax of 3.1±0.6 fmol mg−1 protein and a Hill slope of 0.93±0.05.
[125I]-(Pyr1)Apelin-13 binding sites were localized using autoradiography to human cardiovascular tissue, including coronary artery, aorta and saphenous vein grafts. In rat tissue a high density of receptors were localized to the molecular layer of the rat cerebellum, rat lung, rat heart and low levels in the rat kidney cortex.
(Pyr1)Apelin-13 potently contracted human saphenous vein with a pD2 value of 8.4±0.2 (n=8). The maximum response elicited by the peptide was 22.6±6% of 100 mM KCl.
We provide the first evidence of APJ receptor expression, relative densities and functional properties of (Pyr1)Apelin-13 in human cardiovascular tissue.
British Journal of Pharmacology (2001) 132, 1255–1260; doi:10.1038/sj.bjp.0703939
The apelin peptide was recently discovered and demonstrated to be the endogenous ligand for the G protein-coupled receptor, APJ. A search of the GenBank databases retrieved a rat expressed sequence tag partially encoding the preproapelin sequence. The GenBank search also revealed a human sequence on chromosome Xq25-26.1, containing the gene encoding preproapelin. We have used the rat sequence to screen a rat brain cDNA library to obtain a cDNA encoding the full-length open reading frame of rat preproapelin. This cDNA encoded a protein of 77 amino acids, sharing an identity of 82% with human preproapelin. Northern and in situ hybridization analyses revealed both human and rat apelin and APJ to be expressed in the brain and periphery. Both sequence and mRNA expression distribution analyses revealed similarities between apelin and angiotensin II, suggesting they that share related physiological roles. A synthetic apelin peptide was injected intravenously into male Wistar rats, resulting in immediate lowering of both systolic and diastolic blood pressure, which persisted for several minutes. Intraperitoneal apelin injections induced an increase in drinking behavior within the first 30 min after injection, with a return to baseline within 1 h.
The synthesis of more than fifty 36-residue oligopeptide analogs of neuropeptide Y (NPY) and their affinity to human Y1 and Y2 receptors is described. Each amino acid of the natural sequence was replaced by L-alanine, the four alanine residues at position 12, 14, 18 and 23 were replaced by glycine. Additional residues were exchanged to closely related ones in order to characterize the prerequisites for binding. A combination of automated single and multiple peptide synthesis using fluoren-9-ylmethoxycarbonyl/tert-butoxy strategy was applied. The purified peptides were characterized by electrospray mass spectrometry, analytical HPLC and amino acid analysis. Binding was investigated by displacement of 125I-labelled neuropeptide Y from human neuroblastoma cell lines SK-N-MC and SMS-KAN. Whereas Pro2 and the integrity of the neuropeptide Y loop is important for the binding to the Y1 receptor, exchanges within the C-terminal helix affect the affinity to the Y2 receptor. The C-terminal pentapeptide amide is important for both receptors and probably represents the binding site. However, Arg33 and Arg35 may not be exchanged by L-alanine in the Y1 system, whereas Arg35 and Tyr36 are the most susceptible residues in the Y2 system. In order to distinguish between conformational effects and direct hormone/receptor interaction via the side chains of neuropeptide Y, circular dichroic studies of the alanine-containing peptides were performed and structure affinity relationships are discussed. Comparing the affinities of the neuropeptide Y analogs to Y1 and Y2 receptors significant differences were found for the two binding sites, which suggests a different active conformation of neuropeptide Y at the two subtypes of receptors. Using molecular dynamics calculations, two distinct conformations were identified which are in good agreement with the data obtained by structure/affinity investigations.
To address conflicting reports concerning the number of angiotensin II (AII) receptor type 1 (AT1) coding loci in vertebrates, Southern blot analysis was used to determine the genomic representation of AT1 receptor genes in animals comprising a divergent evolutionary spectrum. The data demonstrate that the AT1 receptor gene is present as a single genomic copy in a broad spectrum of animals including human, monkey, dog, cow, rabbit, and chicken. In contrast, members of the rodent taxonomic order contain two genes in their genomes. These two genes may have arisen in rodents as a consequence of a gene duplication event that occurred during evolution following the branching of rodents from the mammalian phylogenetic tree. In order to investigate the properties of the human AT1 receptor in a pure cell system, the recombinant human AT1 receptor was stably expressed in mouse L cells. An isolated cell line, designated LhAT1-D6, was found to express abundant levels of recombinant receptor [430 +/- 15 fmol/mg] exhibiting high affinity [KD = 0.15 +/- 0.02 nM] for [125I][SAR1, Ile8] angiotensin II (SIA). The pharmacological profile of ligands competing for [125I] SIA binding to the expressed receptor was in accordance with that of the natural receptor. Radioligand binding of the expressed receptor was decreased in the presence of the non-hydrolyzable analog of GTP, guanosine 5'-(gamma-thio) triphosphate [GTP gamma S]. Angiotensin II evoked a rapid efflux of 45Ca2+ from LhAT1-D6 cells that was blocked by AT1 receptor specific antagonists. In addition, AII inhibited forskolin-stimulated cAMP accumulation in these cells which was blocked by the AT-1 antagonist. Thus, the LhAT1-D6 cell line provides a powerful tool to explore the human AT1 receptor regulation.
We report the cloning of a gene, intronless in its coding region, which we have named APJ. This gene was cloned using the polymerase chain reaction (PCR), with a set of primers designed on the basis of the conservation that members of G protein-coupled receptors (GPCR) have in their transmembrane (TM) regions. The putative receptor protein, APJ, shares closest identity to the angiotensin receptor (AT1) ranging from 40 to 50% in the hydrophobic TM regions of these receptors. The transcripts for this gene were detected in many regions of the brain. PCR analysis of somatic cell lines found APJ-related sequences to be only present on chromosome 11, and high-resolution mapping by fluorescence in situ hybridization (FISH) sublocalized APJ on band q12.
We recently reported that the density of mRNA for the dopamine D4 receptor was extremely low in human cerebral cortex but unexpectedly higher in the corpus callosum and spinal cord both of which contain substantial white-matter area. Under low stringency conditions, Northern blot analysis using the D4 probe detected cross-hybridized mRNAs having a similar distributional profile to the D4 mRNA in human brain regions, suggesting the mRNA distributional profile is not peculiar to the D4 receptor. Homology screening revealed one of the mRNAs to be an orphan seven-transmembrane receptor, APJ, abundantly expressed in the corpus callosum and spinal cord. In porcine spinal cord the APJ mRNA was detected at a higher level in white-matter rather than in gray-matter area. These data suggest that a group of seven-transmembrane receptors, including the D4 and APJ receptor, is preferentially expressed in the white-matter area probably in non-neuronal glial cells.
In the search for an endogenous ligand of the orphan G protein-coupled receptor APJ, the presence of the ligand in various tissue extracts was examined by measuring the increase in extracellular acidification rate of the cells expressing the APJ receptor as a specific signal induced by the interaction of the receptor and ligand. By monitoring this activity, we isolated an APJ receptor ligand, designated apelin, from bovine stomach extracts. The structures of bovine and human apelin preproproteins were deduced from the sequences of the corresponding cDNAs. The preproproteins consisted of 77 amino acid residues, and the apelin sequence was encoded in the C-terminal regions. Synthetic peptides derived from the C-terminal amino acid sequence of bovine preproapelin were capable of specifically promoting the acidification rate in the cells expressing the APJ receptor in a range from 10(-7) to 10(-10) M, indicating that apelin is an endogenous ligand for the APJ receptor.
By using a strategy that we have developed to search for the ligands of orphan seven-transmembrane-domain receptors [S. Hinuma et al., Nature 393 (1998) 272-276], we have recently identified a natural ligand, apelin, for the orphan 7TMR, APJ [K. Tatemoto et al., Biochem. Biophys. Res. Commun. 251 (1998) 471-476]. In this paper, we isolated rat and mouse apelin cDNAs, and analyzed the tissue distribution of apelin mRNA in rats. Although apelin mRNA was widely detected in a variety of tissues, the highest expression of apelin mRNA was detected in the mammary gland of pregnant rats. In the mammary gland, biologically active apelin and its mRNA considerably increased during pregnancy and lactation, and reached a maximal level around parturition. Moreover, a large amount of apelin (14-93 pmol/ml) was found to be secreted in the bovine colostrum, and it was still detectable even in commercial bovine milk. Since apelin partially suppressed cytokine production by mouse spleen cells in response to T cell receptor/CD3 cross-linking, the oral intake of apelin in the colostrum and milk might modulate immune responses in neonates.
Uridine 5'-diphosphoglucose (UDP-glucose) has a well established biochemical role as a glycosyl donor in the enzymatic biosynthesis of carbohydrates. It is less well known that UDP-glucose may possess pharmacological activity, suggesting that a receptor for this molecule may exist. Here, we show that UDP-glucose, and some closely related molecules, potently activate the orphan G protein-coupled receptor KIAA0001 heterologously expressed in yeast or mammalian cells. Nucleotides known to activate P2Y receptors were inactive, indicating the distinctly novel pharmacology of this receptor. The receptor is expressed in a wide variety of human tissues, including many regions of the brain. These data suggest that some sugar-nucleotides may serve important physiological roles as extracellular signaling molecules in addition to their familiar role in intermediary metabolism.
Melanin-concentrating hormone (MCH), a 19 amino acid cyclic peptide, is largely expressed in the hypothalamus. It is implicated in the control of general arousal and goal-orientated behaviours in mammals, and appears to be a key messenger in the regulation of food intake. An understanding of the biological actions of MCH has been so far hampered by the lack of information about its receptor(s) and their location in the brain. We recently identified the orphan G-protein-coupled receptor SLC-1 as a receptor for the neuropeptide MCH. We used in situ hybridization histochemistry and immunohistochemistry to determine the distribution of SLC-1 mRNA and its protein product in the rat brain and spinal cord. SLC-1 mRNA and protein were found to be widely and strongly expressed throughout the brain. Immunoreactivity was observed in areas that largely overlapped with regions mapping positive for mRNA. SLC-1 signals were observed in the cerebral cortex, caudate-putamen, hippocampal formation, amygdala, hypothalamus and thalamus, as well as in various nuclei of the mesencephalon and rhombencephalon. The distribution of the receptor mRNA and immunolabelling was in good general agreement with the previously reported distribution of MCH itself. Our data are consistent with the known biological effects of MCH in the brain, e.g. modulation of the stress response, sexual behaviour, anxiety, learning, seizure production, grooming and sensory gating, and with a role for SLC-1 in mediating these physiological actions.
TaqMan reverse transcription polymerase chain reaction (RT-PCR) is a recently developed technique which allows the measurement of an accumulating PCR product in real time. In the present study we have validated the use of TaqMan RT-PCR for mRNA localisation studies in human and rat tissues, and for the investigation of gene expression changes in CNS animal models. In human brain, D(2) receptor mRNA was enriched in caudate nucleus and putamen, whilst in rat brain, highest levels of D(2) receptor mRNA expression were observed in striatum and nucleus accumbens, consistent with the known distribution of this receptor in basal ganglia. In a rat model of permanent middle cerebral artery occlusion (pMCAO), endogenous interleukin-1 receptor antagonist (IL-1ra) mRNA was upregulated over 30-fold at 24 h post-lesion in both striatum and cortex ipsilateral to artery occlusion. Brain-derived neurotrophic factor (BDNF) mRNA was transiently upregulated 3.7-fold at 3 h, but not at 24 h or 3 days after induction of cortical spreading depression (CSD) in rats. Our observations in these two animal models using TaqMan RT-PCR were consistent with previous reports using other techniques. In conclusion, TaqMan RT-PCR assays provide a rapid and reliable method for semi-quantitative analysis of gene expression in the nervous system.
APJ is a recently described seven-transmembrane (7TM) receptor that is abundantly expressed in the central nervous system (CNS). This suggests an important role for APJ in neural development and/or function, but neither its cellular distribution nor its function have been defined. APJ can also serve as a co-receptor with CD4 for fusion and infection by some strains of human immunodeficiency virus (HIV-1) in vitro, suggesting a role in HIV neuropathogenesis if it were expressed on CD4-positive CNS cells. To address this, we examined APJ expression in cultured neurons, astrocytes, oligodendrocytes, microglia and monocyte-derived macrophages utilizing both immunocytochemical staining with a polyclonal anti-APJ antibody and RT - PCR. We also analyzed the ability of a recently identified APJ peptide ligand, apelin, to induce calcium elevations in cultured neural cells. APJ was expressed at a high level in neurons and oligodendrocytes, and at lower levels in astrocytes. In contrast, APJ was not expressed in either primary microglia or monocyte-derived macrophages. Several forms of the APJ peptide ligand induced calcium elevations in neurons. Thus, APJ is selectively expressed in certain CNS cell types and mediates intracellular signals in neurons, suggesting that APJ may normally play a role in signaling in the CNS. However, the absence of APJ expression in microglia and macrophages, the prinicpal CD4-positive cell types in the brain, indicates that APJ is unlikely to mediate HIV-1 infection in the CNS.
GABA(B) receptors are G-protein-coupled receptors that mediate the slow and prolonged synaptic actions of GABA in the CNS via the modulation of ion channels. Unusually, GABA(B) receptors form functional heterodimers composed of GABA(B1) and GABA(B2) subunits. The GABA(B1) subunit is essential for ligand binding, whereas the GABA(B2) subunit is essential for functional expression of the receptor dimer at the cell surface. We have used real-time reverse transcriptase-polymerase chain reaction to analyse expression levels of these subunits, and their associated splice variants, in the CNS and peripheral tissues of human and rat. GABA(B1) subunit splice variants were expressed throughout the CNS and peripheral tissues, whereas surprisingly GABA(B2) subunit splice variants were neural specific. Using novel antisera specific to individual GABA(B) receptor subunits, we have confirmed these findings at the protein level. Analysis by immunoblotting demonstrated the presence of the GABA(B1) subunit, but not the GABA(B2) subunit, in uterus and spleen. Furthermore, we have shown the first immunocytochemical analysis of the GABA(B2) subunit in the brain and spinal cord using a GABA(B2)-specific antibody. We have, therefore, identified areas of non-overlap between GABA(B1) and GABA(B2) subunit expression in tissues known to contain functional GABA(B) receptors. Such areas are of interest as they may well contain novel GABA(B) receptor subunit isoforms, expression of which would enable the GABA(B1) subunit to reach the cell surface and form functional GABA(B) receptors.
The human APJ receptor is a G protein-coupled receptor which functions as an efficient alternative co-receptor for a number of human immunodeficiency virus type 1 and simian immunodeficiency virus strains. We have cloned the rat APJ receptor, which we term B78/apj, and have mapped the mRNA distribution of both the receptor and its natural ligand apelin in rat tissues. Northern blot analysis showed a similar pattern of expression for B78/apj and apelin mRNAs with hybridising transcripts seen in the lung, heart, skeletal muscle, kidney, brain and liver. In situ hybridisation histochemistry studies revealed intense B78/apj gene expression in the parenchyma of the lung, a sub-population of glomeruli in the kidney, the corpora lutea of the ovary and isolated cells of the anterior lobe of the pituitary. B78/apj mRNA had a striking and unique distribution within the central nervous system (CNS) where receptor expression was found in cells within the meninges around the brain, in the posterior magnocellular and medial parvocellular areas of the hypothalamic paraventricular nucleus and in the supraoptic nucleus. This hypothalamic distribution offers a possible specific role of this receptor in mediating neuroendocrine responses in the CNS.
The peptide apelin, recently isolated from bovine stomach tissue extracts, has been identified as an endogenous ligand of the human putative receptor protein related to the angiotensin receptor AT(1) (APJ). In this article, we report cloning of the rat apelin receptor cDNA. The sequence shares 90% identity with the human APJ receptor and 31% with the rat AT(1A) angiotensin receptor. Subsequently a stable CHO cell line expressing the receptor fused at its C-terminal part with the enhanced green fluorescent protein (EGFP) was established, allowing to verify its cell surface distribution and to determine the affinity of various apelin and angiotensin fragments on the cloned receptor. As shown for the human APJ receptor, the rat apelin receptor expressed in the cell line was negatively coupled to adenylate cyclase. The apelin fragment K17F (Lys(1)-Phe-Arg-Arg-Gln-Arg-Pro-Arg-Leu-Ser-His-Lys-Gly-Pro-Met-Pro-Phe(17)) inhibited forskolin-stimulated cAMP production at sub-nanomolar concentrations whereas angiotensin II and angiotensin III were inactive. N-terminal elongation of K17F with a tyrosine or the N-terminal deletion of the first four amino acids did not modify the inhibitory action of K17F on cAMP production. In contrast, deletion of the first seven amino acids of K17F or substitution of phenylalanine by an alanine residue at the C-terminus completely abolished the activity of the peptide. In situ hybridization analysis of apelin receptor mRNA expression in the adult rat brain showed intense labeling in the hypothalamus, especially in the supraoptic and the paraventricular nuclei. The anterior and intermediate lobes of the pituitary were also highly labeled, as well as the pineal gland. Labeling was also found in extrahypothalamic structures such as the piriform cortex, the nucleus of the lateral olfactory tract, the central grey matter, the pars compacta of the substantia nigra, the dorsal raphe nucleus, the entorhinal cortex, the dentate gyrus and the Ammon's horn. The hypothalamic and hypophyseal distribution of the receptor suggests an involvement of apelin in the control of neuro- and adenohypophyseal hormone release, whereas its presence in the pineal gland and in discrete higher brain structures points out to possible roles in the regulation of circadian rhythms and of water and food intake behavior.
We analyzed the tissue distribution of apelin mRNA in rats by a quantitative reverse transcription-polymerase chain reaction and that of immunoreactive apelin (ir-apelin) by an enzyme immunoassay (EIA) using a monoclonal antibody. The expression levels of apelin mRNA and ir-apelin seemed to be consistent among tissues: they were highly expressed in the lung and mammary gland. By the combination of gel filtration and EIA, we found that the molecular forms of apelin differ among respective tissues: apelin molecules with sizes close to apelin-36 (long forms) were major components in the lung, testis, and uterus, but both long and short (whose sizes were close to [<Glu(65)]apelin-13) forms were detected in the mammary gland. In Scatchard analyses, the radioiodinated apelin-36 analogue bound to the receptor, APJ, with high affinity. In competitive binding assays, apelin-36 and apelin-19 far more efficiently inhibited the binding of the labeled apelin-36 analogue with APJ than [<Glu(65)]apelin-13. In analyses for the dissociation of apelin from APJ, unlabeled apelin-36 replaced more rapidly the labeled apelin-36 analogue bound with APJ than [<Glu(65)]apelin-13. Our results demonstrate that the long and short forms of apelin differently interact with APJ.
Apelin is the recently identified endogenous ligand for the G-protein-coupled receptor, APJ. Preproapelin and APJ mRNA are found in hypothalamic regions known to be important in the regulation of food and water intake, and pituitary hormone release. The effects of intracerebroventricular (ICV) administration of pyroglutamylated apelin-13 on food and water intake and pituitary hormone release in rats were investigated. Apelin-13 had little effect on food intake, but dose-dependently increased drinking behaviour and water intake at 1 h. Apelin-13 (10 nmol) increased water intake by up to sixfold compared to saline. Compared to saline control, apelin-13 (10 nmol) significantly increased plasma ACTH and corticosterone and decreased plasma prolactin, LH and FSH at 30 min. In vitro, apelin-13 stimulated the release of CRH and AVP from hypothalamic explants, but had no effect on NPY release. These results suggest that apelin may play an important role in the hypothalamic regulation of water intake and endocrine axes.
With the use of an antiserum against human apelin-36, apelin-immunoreactivity (irAP) was detected in neurons and cell processes of the supraoptic nucleus (SO), paraventricular nucleus (PVH), accessory neurosecretory nuclei (Acc) and suprachiasmatic nucleus. Strongly labeled cells/processes were noted in the internal layer of the median eminence, infundibular stem, anterior and posterior pituitary. Double-labeling the sections with goat polyclonal neurophysin I-antiserum and rabbit polyclonal apelin-antiserum revealed a population of magnocellular neurons in the PVH, SO and Acc expressing both irAP and neurophysin I-immunoreactivity (irNP), the latter being a marker of oxytocin-containing neurons. By inference, the AP-positive but irNP-negative magnocellular neurons could be vasopressin-containing. The presence of irAP in certain hypothalamic nuclei and pituitary suggests that the peptide may be a signaling molecule released from the hypothalamic-hypophysial axis.
The peptide apelin originating from a larger precursor preproapelin molecule has been recently isolated and identified as the endogenous ligand of the human orphan G protein-coupled receptor, APJ (putative receptor protein related to the angiotensin receptor AT(1)). We have shown recently that apelin and apelin receptor mRNA are expressed in brain and that the centrally injected apelin fragment K17F (Lys(1)-Phe-Arg-Arg-Gln-Arg-Pro-Arg-Leu-Ser-His-Lys-Gly-Pro-Met-Pro-Phe(17)) decreased vasopressin release and altered drinking behavior. Using a specific polyclonal antiserum against K17F for immunohistochemistry, the aim of the present study was to establish the precise topographical distribution of apelin immunoreactivity in colchicine-treated adult rat brain. Immunoreactivity was essentially detected in neuronal cell bodies and fibers throughout the entire neuroaxis in different densities. Cells bodies have been visualized in the preoptic region, the hypothalamic supraoptic and paraventricular nuclei and in the highest density, in the arcuate nucleus. Apelin immunoreactive cell bodies were also seen in the pons and the medulla oblongata. Apelin nerve fibers appear more widely distributed than neuronal apelin cell bodies. The hypothalamus represented, by far, the major site of apelin-positive nerve fibers which were found in the suprachiasmatic, periventricular, dorsomedial, ventromedial nuclei and in the retrochiasmatic area, with the highest density in the internal layer of the median eminence. Fibers were also found innervating other circumventricular organs such as the vascular organ of the lamina terminalis, the subfornical and the subcommissural organs and the area postrema. Apelin was also detected in the septum and the amygdala and in high density in the paraventricular thalamic nucleus, the periaqueductal central gray matter and dorsal raphe nucleus, the parabrachial and Barrington nuclei in the pons and in the nucleus of the solitary tract, lateral reticular, prepositus hypoglossal and spinal trigeminal nuclei. The topographical distribution of apelinergic neurons in the brain suggests multiple roles for apelin especially in the central control of ingestive behaviors, pituitary hormone release and circadian rhythms.
Characterization of apelin, the ligand for the APJ receptor
- D K Lee
- R Cheng
- T Nguyen
- T Fan
- A P Kariyawasam
- Y Liu
- D H Osmond
- S R George
- O Dowd