Apelin Promotes Prostate Cancer Metastasis by Downregulating TIMP2 via Increases in miR-106a-5p Expression.

Prostate cancer commonly affects the urinary tract of men and metastatic prostate cancer has a very low survival rate. Apelin belongs to the family of adipokines and is associated with cancer development and metastasis. However, the effects of apelin in prostate cancer metastasis is undetermined. Analysis of the database revealed a positive correlation between apelin level with the progression and metastasis of prostate cancer patients. Apelin treatment facilitates cell migration and invasion through inhibiting tissue inhibitor of metalloproteinase 2 (TIMP2) expression. The increasing miR-106a-5p synthesis via c-Src/PI3K/Akt signaling pathway is controlled in apelin-regulated TIMP2 production and cell motility. Importantly, apelin blockade inhibits prostate cancer metastasis in the orthotopic mouse model. Thus, apelin is a promising therapeutic target for curing metastatic prostate cancer.

Neuroprotective gain of Apelin/APJ system.

Apelin is an endogenous ligand of G protein-coupled receptor APJ. In recent years, many studies have shown that the apelin/APJ system has neuroprotective properties, such as anti-inflammatory, anti-oxidative stress, anti-apoptosis, and regulating autophagy, blocking excitatory toxicity. Apelin/APJ system has been proven to play a role in various neurological diseases and may be a promising therapeutic target for nervous system diseases. In this paper, the neuroprotective properties of the apelin/APJ system and its role in neurologic disorders are reviewed. Further understanding of the pathophysiological effect and mechanism of the apelin/APJ system in the nervous system will help develop new therapeutic interventions for various neurological diseases.

Apelin/APJ relieve diabetic cardiomyopathy by reducing microvascular dysfunction.

Microcirculatory injuries had been reported to be involved in diabetic cardiomyopathy, which was mainly related to endothelial cell dysfunction. Apelin, an adipokine that is upregulated in diabetes mellitus, was reported to improve endothelial cell dysfunction and attenuate cardiac insufficiency induced by ischemia and reperfusion. Therefore, it is hypothesized that apelin might be involved in alleviating endothelial cell dysfunction and followed cardiomyopathy in diabetes mellitus. The results showed that apelin improved endothelial cell dysfunction via decreasing apoptosis and expression of adhesion molecules and increasing proliferation, angiogenesis, and expression of E-cadherin, VEGFR 2 and Tie-2 in endothelial cells, which resulted in the attenuation of the capillary permeability in cardiac tissues and following diabetic cardiomyopathy. Meanwhile, the results from endothelial cell-specific APJ knockout mice and cultured endothelial cells confirmed that the effects of apelin on endothelial cells were dependent on APJ and the downstream NFκB pathways. In conclusion, apelin might reduce microvascular dysfunction induced by diabetes mellitus via improving endothelial dysfunction dependent on APJ activated NFκB pathways.

Evaluation of Apelin/APJ system expression in hepatocellular carcinoma as a function of clinical severity.

Apelin, a peptide of 77 amino acids, and its endogenous ligand, angiotensin-like-receptor 1 (APJ), play a key role in the development of tumors by enhancing angiogenesis, metastasis, cell proliferation, development of cancer stem cells and drug resistance and inhibiting apoptosis of cancer cells. However, little is known about Apelin/APJ system involvement in hepatocellular carcinoma (HCC). The aim of this study was to evaluate Apelin and APJ expression in liver specimens, obtained from subjects with HCV-positive HCC who underwent liver transplantation, according to liver disease severity (liver recipients, LR, n = 14, age 59.4 ± 1.8) and in donors (liver donors, LD, n = 14, age 62.1 ± 17.3). Apelin/APJ axis, apoptotic and inflammatory markers were evaluated by Real-Time PCR analysis. The Apelin/APJ system expression resulted significantly higher in LR in comparison with LD (p < 0.05), in particular in those with more severe liver disease. The apoptotic (Bcl-2, BAX, NOTCH-1, Casp-3) and inflammatory (IL-6, TNF-α) markers were increased as a function of disease severity (p < 0.05). Multiple significant positive correlations were found between Apelin/APJ axis and the other markers. Although further investigations are needed to better understand the role of Apelin/APJ axis in HCC, our result indicated a potential role of this axis in its development and progression as well as in recognizing novel therapeutic targets opening a new avenue for treatment.

Gene Expression Profiles from Heart, Lung and Liver Samples of Total-Body-Irradiated Minipigs: Implications for Predicting Radiation-Induced Tissue Toxicity.

In the event of a major accidental or intentional radiation exposure incident, the affected population could suffer from total- or partial-body exposures to ionizing radiation with acute exposure to organs that would produce life-threatening injury. Therefore, it is necessary to identify markers capable of predicting organ-specific damage so that appropriate directed or encompassing therapies can be applied. In the current work, gene expression changes in response to total-body irradiation (TBI) were identified in heart, lungs and liver tissue of Göttingen minipigs. Animals received 1.7, 1.9, 2.1 or 2.3 Gy TBI and were followed for 45 days. Organ samples were collected at the end of day 45 or sooner if the animal displayed morbidity necessitating euthanasia. Our findings indicate that different organs respond to TBI in a very specific and distinct manner. We also found that the liver was the most affected organ in terms of gene expression changes, and that lipid metabolic pathways were the most deregulated in the liver samples of non-survivors (survival time <45 days). We identified organ-specific gene expression signatures that accurately differentiated non-survivors from survivors and control animals, irrespective of dose and time postirradiation. At what point did these radiation-induced injury markers manifest and how this information could be used for applying intervention therapies are under investigation.

Cardioprotective effect of electroacupuncture in cardiopulmonary bypass through apelin/APJ signaling.

Aim Acupuncture, particularly electroacupuncture (EA), can improve the clinical outcomes of cardiopulmonary bypass (CPB) patients; however, the mechanisms remain unclear. This study aimed to examine the effects of EA pre-treatment on myocardial injury after CPB and investigate its potential mechanisms. MAIN METHODS: Male Sprague-Dawley rats were subjected to CPB and divided into Control (sham-operated), CPB, and EA (CPB + EA) groups. In the EA group, rats were treated with EA at the "PC6" acupoint for 30 min before being subjected to CPB. At 0.5, 1, and 2 h after CPB, the expression levels of plasma cardiac troponin I (cTnI) and lactate dehydrogenase (LDH), and myeloperoxidase (MPO) activity, TNFα, IL-1ß, reduced glutathione (GSH), oxidized glutathione (GSSH), and the ratio of GSH/GSSH in the myocardial tissue were measured. Apoptosis was detected by terminal deoxynucleotidyl transferase dUTP nick-end labelling (TUNEL) staining. The expression of cleaved caspase-3 was detected by immunofluorescence. The expression of apelin, APJ, AKT, p-Akt, ERK1/2, and p-ERK1/2 was determined using western blotting. KEY FINDINGS: Decreased myocardial injury marker levels, myocardial apoptosis, oxidative stress, and the inflammatory response were found in the EA group compared with the CPB group. The expression levels of apelin, APJ, and p-Akt/AKT were increased in the EA group, and the p-ERK1/2/ERK1/2 level was decreased. SIGNIFICANCE: This study showed that EA pre-treatment can protect the heart from damage following CPB, which might be mainly mediated by restoring the apelin/APJ signaling pathway.

Apelin directs endothelial cell differentiation and vascular repair following immune-mediated injury.

Sustained, indolent immune injury of the vasculature of a heart transplant limits long-term graft and recipient survival. This injury is mitigated by a poorly characterized, maladaptive repair response. Vascular endothelial cells respond to proangiogenic cues in the embryo by differentiation to specialized phenotypes, associated with expression of apelin. In the adult, the role of developmental proangiogenic cues in repair of the established vasculature is largely unknown. We found that human and minor histocompatibility-mismatched donor mouse heart allografts with alloimmune-mediated vasculopathy upregulated expression of apelin in arteries and myocardial microvessels. In vivo, loss of donor heart expression of apelin facilitated graft immune cell infiltration, blunted vascular repair, and worsened occlusive vasculopathy in mice. In vitro, an apelin receptor agonist analog elicited endothelial nitric oxide synthase activation to promote endothelial monolayer wound repair and reduce immune cell adhesion. Thus, apelin acted as an autocrine growth cue to sustain vascular repair and mitigate the effects of immune injury. Treatment with an apelin receptor agonist after vasculopathy was established markedly reduced progression of arterial occlusion in mice. Together, these initial data identify proangiogenic apelin as a key mediator of coronary vascular repair and a pharmacotherapeutic target for immune-mediated injury of the coronary vasculature.

Apelin system detection in the reproductive apparatus of ewes grazing on semi-natural pasture.

Apelin (APLN) is an adipokine with pleiotropic effects involved in the regulation of metabolic, cardiovascular, immune, and electrolyte balance function. Recent studies demonstrated a pivotal role in the regulation of male and female reproduction. APLN and its receptor (APLNR) were found in the hypothalamic-pituitary-gonad axis tissues, regulating gonadotropin release and steroidogenesis. However, to date, there are no studies that describe APLN system in the reproductive apparatus of the sheep. The study was performed on 10 Comisana x Appenninica adult dry ewes reared in a semi-natural pasture. Organ samples were collected from five animals in the two pasture functional phases: after maximum pasture flowering (Group 1) and after maximum pasture dryness (Group 2). Experiments were devised to characterize the gene expression and protein localization of the APLN/APLNR system in ewe reproductive apparatus; in addition, the concentration of plasma APLN was evaluated during the trial. Through immunohistochemical analysis, a positive staining for APLN was observed in the large luteal cells, in the epithelial cell coat of the ampulla, in the uterus epithelial lining and in the uterine glands. APLNR was observed in the granulosa cells, in the large luteal cells, in the secreting cells of the ampulla, in the uterus epithelial lining and uterine glands. The transcripts for APLN and APLNR were evidenced in all organ tissues examined. The highest level of APLN mRNA was detected in the Group 2 ewes in the luteal phase of the ovarian cycle compared to Group 1 ewes in the anestrous one. The relative content of APLN transcript was respectively twofold higher in the ovary (P < 0.05) and uterus (P < 0.05) and threefold higher in the ampulla (P < 0.05) in the Group 2 vs Group 1. The same trend of APLN transcript was evaluated for APLNR mRNA in uterus (P < 0.05) and ovary (P < 0.05). No difference was evidenced between Group 1 and Group 2 for APLNR mRNA levels. The plasma APLN level was fairly constant during the trial period. In conclusion, the present data suggest that the apelinergic system is involved in the reproduction function of ewes, being differentially distributed and expressed in the organs of the reproductive apparatus of ewes; these variations could be related to the sexual cycle and to the cyclic activity of the reproductive apparatus.

Apelin-36 mitigates MPTP/MPP+-induced neurotoxicity: Involvement of α-synuclein and endoplasmic reticulum stress.

Parkinson's disease (PD) is characterized by the progressive loss of dopaminergic neurons within the substantia nigra compacta (SNpc) which leads to the behavioral dysfunction. In the present study, we investigated the effect of Apelin-36 on 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridin (MPTP)/1-methyl-4-phenylpyridinium (MPP+)-induced neurotoxicity. The treatment with Apelin-36 significantly alleviated the MPTP-induced the behavioral dysfunction and dopaminergic neurodegeneration in the SNpc of mice, and also remarkably decreased the MPP+-induced cell death of SH-SY5Y cells. Furthermore, Apelin-36 reversed the MPTP/MPP+-induced loss of TH expression and the induction of α-synuclein expression. Additionally, Apelin-36 significantly attenuated the endoplasmic reticulum stress (ERS) indicated by the inhibition of GRP78, CHOP and cleaved caspase-12 expression in MPTP/MPP+ treated mice and cells. Taken together, the results indicated that Apelin-36 attenuates MPTP/MPP+-induced neurotoxicity, and suggested that Apelin-36 could be a potential therapeutic strategy for the treatment of PD.

APLN/APJ pathway: The key regulator of macrophage functions.

Macrophages play key roles during cardiovascular diseases (CVD) and their related complications. Apelin (APLN) is a key molecule, whose roles during CVD have been documented previously. Therefore, it has been hypothesized that APLN may perform its roles via modulation of macrophages. Additionally, due to the widespread distribution of the CVD, more effective therapeutic strategies need to be developed to overcome the related complications. This review article collected recent information regarding the roles of APLN on the macrophages and discusses its potential chance to be a target for molecular/cellular therapy of APLN and the APLN treated macrophages for CVD.

Cardioprotective apelin effects and the cardiac-renal axis: review of existing science and potential therapeutic applications of synthetic and native regulated apelin.

First described in 1998, apelin is one of the endogenous ligands of the apelinergic receptor. Since its discovery, its possible role in human physiology and disease has been intensively studied. Apelin is a native cardioprotective agent that the body synthesizes to create atheroprotective, antihypertensive, and regenerative effects in the body. By antagonizing the RAA system, apelin could play an important role in heart failure and hypertension. It is also involved in myocardial protection against ischemia/reperfusion injury, post-ischemic remodeling, and myocardial fibrosis. A small number of studies even suggest that serum apelin levels may be involved the development of life-threatening arrhythmias. All this information generated excitement about potential therapeutic effects in patients with heart failure and myocardial infarction. The therapeutic index of apelin is unknown but is anticipated to be favorable based on the small number of studies. In this review, we summarize the mechanisms by which apelin exerts its cardioprotective effects and its connection with the cardiorenal axis. Also, we report the potential therapeutic applications of synthetic and native regulated apelin. If larger studies can be performed, it is possible that apelin-mediated drug treatment may play a major role for a large number of patients worldwide in the future.

The impact of apelin-36 on isolated rat hearts as a member of apelin family.

BACKGROUND: Apelin is an endogenous adipocytokine that plays an important role in the regulation of cardiovascular function. Apelin-36 is a member of apelin family. However cardiac reports related to apelin-36 are very rare. The purpose of this study is to investigate the impact of apelin-36 on hemodynamic variables of the isolated rat hearts. METHODS: Twenty-eight rats were equally divided into four groups: control, apelin-36 at the following concentrations: 1 nM, 10 nM and 100 nM. The isolated hearts were perfused with modified Krebs-Henseleit solution (mK-Hs) by using the Langendorff method. Cardiac parameters, including left ventricular developed pressure (LVDP), maximal rate of pressure development (+dP/dtmax), heart rate (HR) and coronary flow (CF) were measured. Gene expressions relevant to cardiomyocyte contractility were determined by real-time PCR. RESULTS: 10 and 100 nM doses of apelin-36 perfusion led to positive inotropy with an increase of LVDP and +dP/dtmax, which are the indexes of cardiac contractility. Furthermore both doses of apelin-36 increased endothelial nitric oxide synthase (eNOS), sarco/endoplasmic reticulum Ca2+-ATPase (Serca2a) and ß2-Adrenergic receptors (ß2-AR) mRNA. CONCLUSION:  These results showed that apelin-36 had a positive inotropic effect on the isolated rat heart and can induce eNOS, Serca2a and ß2-AR genes activation that enhances contractility of the heart (Tab. 1, Fig. 2, Ref. 23).

Apelin modulates murine gastric vagal afferent mechanosensitivity.

Gastric vagal afferents play an important role in the peripheral control of food intake. Apelin, a central appetite regulating hormone, is also abundantly released from the stomach. Whether apelin modulates gastric vagal afferent signalling is unknown. We aimed to determine whether apelin modulates gastric vagal afferent signalling under different states of nutrition. Female C57BL/6 mice were fed either a standard laboratory diet (SLD) or a high fat diet (HFD) for 12 weeks. An in vitro gastric vagal afferent preparation was used to determine the effect of apelin on gastric vagal afferent mechanosensitivity in SLD mice, fed ad libitum or fasted overnight, and HFD mice. To determine the signalling pathway of apelin via gastric vagal afferents, we determined the expression of apelin receptor (APJ receptor) in the gastric mucosa, the whole nodose ganglion and in gastric vagal afferent neurons innervating the stomach using retrograde tracing and real-time quantitative reverse-transcription polymerase chain reaction (qRT-PCR). The location of apelin and APJ receptor within the gastric mucosa was determined by immunohistochemistry. Expression of apelin and APJ receptor mRNA in gastric mucosa was determined using qRT-PCR. Apelin inhibited the response of gastric mucosal vagal afferents to mucosal stroking in fasted SLD mice, but not in mice fed ad libitum a SLD or HFD. Apelin inhibited the response of gastric tension sensitive afferents to circular stretch in SLD mice fed ad libitum or fasted, an effect not observed in HFD mice. APJ receptor mRNA was detected in the gastric mucosa and whole nodose ganglion, but not specifically in gastric vagal afferents neurons. In the gastric mucosa, APJ receptor immunoreactive cells were co-localised or closely associated with apelin containing cells and co-localised with serotonin, gastrin, histamine and gastric intrinsic factor containing cells. In conclusion, apelin modulates gastric vagal afferent signalling in a nutritional status dependent manner. Further, apelin modulates gastric vagal afferents through an indirect pathway, possibly through the release of hormones/peptides from the gastric mucosa.

Review: Apelin in disease.

Apelin, a regulatory peptide, is a ligand of the APJ receptor that belongs to the G protein-coupled receptor family. Apelin and APJ are widely distributed in the body and play potential physiological roles in the cytoprotection of many internal organs. This review article summarizes information about the roles of the apelin/APJ system in neurological, metabolic, hypertension, respiratory, gastrointestinal, hepatic, kidney and cancerous diseases. It is suggested that apelin positively affects the treatment of non-cancerous diseases and may be considered as a therapeutic drug in many illnesses. However, in cancers, apelin appears as a tumour growth stimulator, and its suggested role is as a marker in the diagnosis of tumour cancers in tissues. In summary, apelin has certain therapeutic abilities and can be useful in the treatment of, e.g., insulin resistance, hypertension, etc., but it also can sometimes serve as a negative factor.

Apelin in the hypothalamic paraventricular nucleus improves cardiac function in surgical trauma rats.

Apelin is a novel endogenous active peptide. The aim of this study is to investigate whether apelin in the paraventricular nucleus (PVN) can improve the cardiac function in rats subjected to thoracic surgery trauma, and whether it is involved in the protective effect of electro-acupuncture (EA). Sprague-Dawley rats were randomly divided into non-stressed group (control), thoracic surgical trauma stressed group (trauma) and bilateral Neiguan EA applied on thoracic surgical trauma stressed group (trauma + EA-PC 6). The mRNA expressions of apelin receptor (APJR) and apelin in the PVN were detected by real time-PCR. The exogenous apelin-13 (6 mmol/L, 0.1 µL) was microinjected into the rat PVN in the thoracic trauma group, and the effects of apelin-13 on the blood pressure (BP), heart rate (HR) and the discharge of rostral ventrolateral medulla (RVLM) neurons were observed through the simultaneous recording technology by polygraph. The results showed that the APJR mRNA expression was significantly decreased in the rats of trauma group as compared with that in the control group (P < 0.05), and a decline trend of apelin mRNA expression was also observed. EA application at bilateral Neiguan acupoints partially recovered the decline of APJR and apelin mRNA expression by the treatment of thoracic trauma. Both mean arterial pressure and HR in the thoracic surgical trauma group were significantly increased by the microinjection of exogenous apelin-13 into the PVN (P < 0.05), and the single-unit discharge rate of RVLM neurons also had an increasing trend. These results suggest that apelin in the PVN can improve the cardiac function of thoracic surgical trauma rats, and may be involved in the protective effects of EA.

Protective Role of Apelin Against Cyclosporine-Induced Renal Tubular Injury in Rats.

BACKGROUND: Cyclosporine (CsA) usually reduces glomerular filtration rate (GFR) but also can induce tubular injury without resulting in GFR reduction. Apelin is an endogenous ligand for the apelin receptor and has diverse physiologic roles related to hemodynamic or metabolic processes. We investigated the renoprotective role of apelin against CsA-induced tubular toxicity in rats. METHODS: Rats were given CsA (15 mg/kg/day) and/or apelin-13 (15 µg/kg/day) for 7 days via subcutaneous injection. We performed serum and urinary assays of creatinine and neutrophil gelatinase-associated lipocalin (NGAL) to estimate renal injury and performed Western blotting for endothelial nitric oxide synthase and nuclear factor of activated T-cell cytoplasmic 1 (NFATc1) to document the underlying mechanism. RESULTS: The CsA-treated group showed increased urinary creatinine excretion, polyuria, and renal glycosuria without GFR reduction, suggesting adequate CsA-induced renal tubular injury. Urinary NGAL excretion also increased significantly in the CsA group. Conversely, apelin attenuated CsA-induced tubular injury and had no effect on urinary NGAL excretion. In histopathologic examination, the apelin-treated group had lower tubulo-interstitial injury scores compared with those in the CsA group. Regarding the effects of apelin, our results indicate that apelin provides protection against CsA-induced tubular injury by activating nitric oxide and/or the NFATc1 pathway. Notably, we also found that CsA inhibits renal glucose reabsorption by reducing Na+-K+ ATPase expression and that apelin reverses reduced renal glucose reabsorption by CsA in tubular cells. CONCLUSIONS: Our study demonstrates the renoprotective effect of apelin against CsA-induced renal tubular toxicity and provides novel insights into the effects of CsA and apelin on renal tubular cells.

An overview on biological functions and emerging therapeutic roles of apelin in diabetes mellitus.

Type 2 diabetes mellitus is a common type of diabetes and considered as multifactorial disease. Apelin is an adipokine which secreted from white adipose tissue and involved in various functions such as insulin sensitivity and food intake. Many studies showed that apelin has a crucial role in diabetes and its concentration will change in relation with insulin resistance. In this review, we will discuss the roles of apelin in energy metabolism and pathogenesis of diabetes and explain why apelin can be a good candidate adipokine to promoting insulin sensitivity.

Effects of adipokines and obesity on uterine contractility.

Obesity is a major public health problem. The prevalence of obesity has significantly increased in developed countries, particularly in France with an overall increase of 76% over the last 15 years. In pregnant women, obesity is associated with alterations in the quality of labor, such as delayed onset of labor, a higher rate of prolonged pregnancies, prolonged labor, and higher oxytocin requirements. There is also an increased prevalence of Cesarean sections, particularly during the active phase of labor, and perinatal complications (postpartum hemorrhage). It seems that some of these functional changes and their consequences can be attributed to a disruption of hormonal balance encountered in obese women and involving adipokines (apelin, ghrelin, visfatin, leptin), but also to the interactions between adipose tissue and the "oxytocin (OT) - oxytocin receptor (OTR)". In this review, we detailed mechanisms to understand the impact of specific metabolic alterations in obesity on uterine contractility. Better knowledge of the impact of obesity on labor and delivery pathophysiology should strengthen the prevention of obesity in women of childbearing age and provide a suitable and effective management. The beneficial effect of weight loss and exercise in non-pregnant women on the correction of metabolic disorders secondary to obesity should be studied in populations of overweight women to demonstrate its effectiveness.

Apelinergic System Structure and Function.

Apelin and apela (ELABELA/ELA/Toddler) are two peptide ligands for a class A G-protein-coupled receptor named the apelin receptor (AR/APJ/APLNR). Ligand-AR interactions have been implicated in regulation of the adipoinsular axis, cardiovascular system, and central nervous system alongside pathological processes. Each ligand may be processed into a variety of bioactive isoforms endogenously, with apelin ranging from 13 to 55 amino acids and apela from 11 to 32, typically being cleaved C-terminal to dibasic proprotein convertase cleavage sites. The C-terminal region of the respective precursor protein is retained and is responsible for receptor binding and subsequent activation. Interestingly, both apelin and apela exhibit isoform-dependent variability in potency and efficacy under various physiological and pathological conditions, but most studies focus on a single isoform. Biophysical behavior and structural properties of apelin and apela isoforms show strong correlations with functional studies, with key motifs now well determined for apelin. Unlike its ligands, the AR has been relatively difficult to characterize by biophysical techniques, with most characterization to date being focused on effects of mutagenesis. This situation may improve following a recently reported AR crystal structure, but there are still barriers to overcome in terms of comprehensive biophysical study. In this review, we summarize the three components of the apelinergic system in terms of structure-function correlation, with a particular focus on isoform-dependent properties, underlining the potential for regulation of the system through multiple endogenous ligands and isoforms, isoform-dependent pharmacological properties, and biological membrane-mediated receptor interaction. © 2018 American Physiological Society. Compr Physiol 8:407-450, 2018.