The protective effect of apelin on ischemia/reperfusion injury

Effects of apelin on neonatal brain neurogenesis in L-NAME-induced maternal preeclampsia

The aim of this study was to investigate the possible protective effects of apelin, which is known to have antioxidant and anti-inflammatory effects, on changes in neurogenesis in newborns of pregnant rats with L-NAME-induced preeclampsia. Wistar albino female rats were divided into four experimental groups: Control, Apelin, Preeclampsia and Preeclampsia + Apelin. Blood pressure was measured on the 5th, 11th and 17th days of gestation, urine protein was analyzed from urine samples collected for 24 h on the 6th, 12th and 18th days and serum creatinine was analyzed from serum samples. Maternal kidney and placenta tissues were obtained to establish the preeclampsia model, and neonatal brain tissues including the cortex, hippocampus and cerebellum regions were obtained to investigate neurogenesis and examined by histological and immunohistochemical methods. The number of newborns, body weight and brain weight of the newborns were measured. eNOS, IL-10, nNOS and NO levels in the brain analyzed via ELISA. Mean arterial pressure, urine protein and serum creatinine increased in the preeclampsia. Newborn weight decreased in the Preeclampsia group, the values in the Preeclampsia + Apelin group were closer to the Control and Apelin groups. In the Preeclampsia group, edema and dilatation in the proximal and distal tubules of kidneys, perivillous fibrin deposition and increase in syncytial nodules of placenta were observed. VEGF immunoreactivity decreased and iNOS immunoreactivity increased in both kidney and placenta. In neonatal brain tissue examinations, cytotoxic edema accompanied by thinning of cortex, delayed migration and lower cell counts in the hippocampus, and increase in intercellular spaces and EGL thickening in the cerebellum were observed in the preeclampsia. Expression of NeuN, GFAP, MBP, IL-10, eNOS, nNOS and NO levels decreased, whereas expression of Iba-1 increased in the preeclampsia. In the Preeclampsia + Apelin group, these findings were similar to the Control and Apelin groups. Apelin administration was found to be beneficial for preventing the adverse consequences of preeclampsia, but further experimental and clinical studies are needed to better understand these effects.

Preliminary evidence for the presence of programmed cell death in pressure injuries

Pressure injuries (PIs) are a common healthcare problem worldwide and are considered to be the most expensive chronic wounds after arterial ulcers. Although the gross factors including ischemia-reperfusion (I/R) have been identified in the etiology of PIs, the precise cellular and molecular mechanisms contributing to PIs development remain unclear. Various forms of programmed cell death including apoptosis, autophagy, pyroptosis, necroptosis and ferroptosis have been identified in PIs. In this paper, we present a detailed overview on various forms of cell death; discuss the recent advances in the roles of cell death in the occurrence and development of PIs and found much of the evidence is novel and based on animal experiments. Herein, we also state critical evaluation of the existing data and future perspective in the field. A better understanding of the programmed cell death mechanism in PIs may have important implications in driving the development of new preventive and therapeutic strategies.

Diagnostic and prognostic significance of apelin-13, APJ for sepsis in the emergency department: A prospective study

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.

Transcription Factor EB: A Promising Therapeutic Target for Ischemic Stroke

Transcription factor EB (TFEB) is an important endogenous defensive protein that responds to ischemic stimuli. Acute ischemic stroke is a growing concern due to its high morbidity and mortality. Most survivors suffer from disabilities such as numbness or weakness in an arm or leg, facial droop, difficulty speaking or understanding speech, confusion, impaired balance or coordination, or loss of vision. Although TFEB plays a neuroprotective role, its potential effect on ischemic stroke remains unclear. This article describes the basic structure, regulation of transcriptional activity, and biological roles of TFEB relevant to ischemic stroke. Additionally, we explore the effects of TFEB on the various pathological processes underlying ischemic stroke and current therapeutic approaches. The information compiled here may inform clinical and basic studies on TFEB, which may be an effective therapeutic drug target for ischemic stroke.

TSPO exacerbates acute cerebral ischemia/reperfusion injury by inducing autophagy dysfunction

Autophagy is considered a double-edged sword, with a role in the regulation of the pathophysiological processes of the central nervous system (CNS) after cerebral ischemia-reperfusion injury (CIRI). The 18-kDa translocator protein (TSPO) is a highly conserved protein, with its expression level in the nervous system closely associated with the regulation of pathophysiological processes. In addition, the ligand of TSPO reduces neuroinflammation in brain diseases, but the potential role of TSPO in CIRI is largely undiscovered. On this basis, we investigated whether TSPO regulates neuroinflammatory response by affecting autophagy in microglia. In our study, increased expression of TSPO was detected in rat brain tissues with transient middle cerebral artery occlusion (tMCAO) and in BV2 microglial cells exposed to oxygen-glucose deprivation or reoxygenation (OGD/R) treatment, respectively. In addition, we confirmed that autophagy was over-activated during CIRI by increased expression of autophagy activation related proteins with Beclin-1 and LC3B, while the expression of p62 was decreased. The degradation process of autophagy was inhibited, while the expression levels of LAMP-1 and Cathepsin-D were significantly reduced. Results of confocal laser microscopy and transmission electron microscopy (TEM) indicated that autophagy flux was disordered. In contrast, inhibition of TSPO prevented autophagy over-activation both in vivo and in vitro. Interestingly, suppression of TSPO alleviated nerve cell damage by reducing reactive oxygen species (ROS) and pro-inflammatory factors, including TNF-α and IL-6 in microglia cells. In summary, these results indicated that TSPO might affect CIRI by mediating autophagy dysfunction and thus might serve as a potential target for ischemic stroke treatment.

Comparative Study of Elabela and Apelin on Apelin Receptor Activation Through β-Arrestin Recruitment

Apelin receptor (APJ) ligands elabela (ELA) and apelin have divergent distributions and function differently in vitro and in vivo. Whether differences exist in their capacity of recruitment of β-arrestins (ARRBs) to APJ remains unknown. The aim of the current study was to investigate the different effects of ELA and apelin on the interaction between APJ and ARRBs in live cells by NanoBiT®. NanoBiT® system is a new technology for studying protein-protein interaction in real-time in live cells, based on the emission of luminescence when two split components of NanoLuc luciferase, large Bit (LgBit) and small Bit (SmBit), complement each other to form an enzymatically active entity. We tagged the APJ and ARRBs with LgBit or SmBit and then evaluated their interactions in transiently transfected HEK293T cells, and determined the signal strength yielded as a result of the interaction. We also investigated the concentration-dependent response of the APJ-ARRB interaction in response to ELA and apelin. Finally, we assessed the effect of F13A, an APJ antagonist which is structurally very similar to apelin-13, on ELA- and apelin-mediated APJ-ARRB interactions. The NanoLuc® luciferase signal was highest in the pair of APJ-LgBit with SmBit-ARRB1 or SmBit-ARRB2. NanoLuc® luciferase signal increased in a concentration-dependent manner from 0.1 nM to 10 μM in response to ELA or apelin. Interestingly, ELA elicited weaker APJ-ARRB interaction signals than apelin. Pre-treatment with F13A potently reduced the APJ-ARRB interaction in response to both ELA and apelin. Our results demonstrated that both ELA and apelin promoted the interaction of APJ and ARRBs in a concentration-dependent manner, and ELA is less efficacious than apelin in inducing the recruitment of ARRBs to APJ, providing a biased functional aspect of ELA vs. apelin at the receptor signaling level. Additionally, ELA and apelin may share the same binding site(s) or pocket(s) at the APJ level.

Carnitine, apelin and resveratrol regulate mitochondrial quality control (QC) related proteins and ameliorate acute kidney injury: role of hydrogen peroxide

Mitochondrial impairment is recognised as a prominent feature in kidney diseases. Therefore, we investigated whether the effects of resveratrol, L-carnitine, and apelin in the acute kidney injury model were associated with modulation of mitochondrial quality control (QC) related proteins, intra-renal renin-angiotensin (RAS) activity, adenosine triphosphate (ATP) and Na⁺-K⁺ ATPase gene expression. Rats were randomly assigned to 7 groups: Distilled water injected control group, DMSO injected control group, distilled water injected lipopolysaccharide (LPS) group, DMSO injected LPS group, resveratrol injected LPS group, L-carnitine injected LPS group and apelin 13 injected LPS group. We observed that resveratrol, L-carnitine, and apelin treatments altered mitochondrial (QC) related protein levels (Pink1, Parkin, BNIP-3, Drp1, and PGC1α), decreased intra-renal RAS parameters, increased ATP level and upregulated Na⁺-K⁺ ATPase gene expression in renal tissue. Our results provide new insight into the role of mitochondrial quality control and how different antioxidants exert beneficial effects on acute kidney injury.

High APLN Expression Predicts Poor Prognosis for Glioma Patients

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.

MiRNA-122-5p inhibitor abolishes angiotensin II-mediated loss of autophagy and promotion of apoptosis in rat cardiofibroblasts by modulation of the apelin-AMPK-mTOR signaling

MicroRNAs (miRNAs) have emerged as essential regulators that could have pivotal roles in cardiac homeostasis and pathological remodeling of various cardiovascular diseases. We previously demonstrated that miRNA-122-5p overexpression exacerbated the process of vascular hypertrophy, fibrosis, and dysfunction in hypertensive rats and rat aortic adventitial fibroblasts. However, the exact roles and underlying mechanisms of miRNA-122-5p in myocardial fibroblasts remain largely unknown. In this work, neonatal rat cardiofibroblasts (CFs) were isolated and primarily cultured from the hearts of 2- to 3-d-old Sprague-Dawley rats. Stimulation of angiotensin II (Ang II) resulted in marked increases in cellular proliferation and migration and levels of collagen I, collagen III, CTGF, and TGF-β1 in cultured CFs. Furthermore, Ang II led to promoted expression of P62, Bax, and phosphorylated mTOR as well as downregulation of LC3II, beclin-1, and AMPK-phosphorylated levels, thereby contributing to imbalance of autophagy and apoptosis, and cellular injury in CFs, which were significantly ameliorated by treatment with miRNA-122-5p inhibitor. These changes were associated with decreased levels of collagen I, collagen III, CTGF, and TGF-β1. Furthermore, Ang II-induced loss of autophagy and promotion of apoptosis in CFs were prevented by the treatment with Pyr¹-apelin-13 or AMPK agonist AICAR or mTOR inhibitor rapamycin, respectively. In contrast, administration of miRNA-122-5p mimics and autophagy inhibitor 3-methylademine reversed beneficial roles of Pyr¹-apelin-13. Collectively, these data indicated that miRNA-122-5p is an essential regulator of autophagy and apoptosis in rat CFs via the apelin/AMPK/mTOR signaling pathway, which may be potentially used as a therapeutic target in myocardial fibrosis and related diseases.

Leptomeningeal anastomoses: Mechanisms of pial collateral remodeling in ischemic stroke

Arterial collateralization, as determined by leptomeningeal anastomoses or pial collateral vessels, is a well‐established vital player in cerebral blood flow restoration and neurological recovery from ischemic stroke. A secondary network of cerebral collateral circulation apart from the Circle of Willis, exist as remnants of arteriole development that connect the distal arteries in the pia mater. Recent interest lies in understanding the cellular and molecular adaptations that control the growth and remodeling, or arteriogenesis, of these pre‐existing collateral vessels. New findings from both animal models and human studies of ischemic stroke suggest a multi‐factorial and complex, temporospatial interplay of endothelium, immune and vessel‐associated cell interactions may work in concert to facilitate or thwart arteriogenesis. These valuable reports may provide critical insight into potential predictors of the pial collateral response in patients with large vessel occlusion and may aid in therapeutics to enhance collateral function and improve recovery from stroke.

This article is categorized under:

Neurological Diseases > Molecular and Cellular Physiology

Discriminative Utility of Apelin-to-NT-Pro-Brain Natriuretic Peptide Ratio for Heart Failure with Preserved Ejection Fraction among Type 2 Diabetes Mellitus Patients

BACKGROUND

Apelin is a regulatory vasoactive peptide, which plays a pivotal role in adverse cardiac remodeling and heart failure (HF) with reduced ejection fraction. The purpose of the study was to investigate whether serum levels of apelin is associated with HF with preserved election fraction (HFpEF) in patients with T2DM.

METHODS

The study retrospectively involved 101 T2DM patients aged 41 to 62 years (48 patients with HFpEF and 28 non-HFpEF patients). The healthy control group consisted of 25 individuals with matched age and sex. Data collection included demographic and anthropometric information, hemodynamic performances and biomarkers of the disease. Transthoracic B-mode echocardiography, Doppler and TDI were performed at baseline. Serum levels of N-terminal pro-brain natriuretic peptide (NT-proBNP) and apelin were measured by ELISA in all patients at the study entry.

RESULTS

Unadjusted multivariate logistic model yielded the only apelin to NT-proBNP ratio (OR = 1.44; p = 0.001), BMI > 34 кг/м2 (OR = 1.07; p = 0.036), NT-proBNP > 458 pmol/mL (OR = 1.17; p = 0.042), LAVI > 34 mL/m2 (OR = 1.06; p = 0.042) and E/e' > 11 (OR = 1.04; p = 0.044) remained to be strong predictors for HFpEF. After obesity adjustment, multivariate logistic regression showed that the apelin to NT-proBNP ratio < 0.82 × 10-2 units remained sole independent predictor for HFpEF (OR = 1.44; 95% CI: 1.18-2.77; p = 0.001) HFpEF in T2DM patients. In conclusion, we found that apelin to NT-proBNP ratio < 0.82 × 10-2 units better predicted HFpEF in T2DM patients than apelin and NT-proBNP alone. This finding could open new approach for CV risk stratification of T2DM at higher risk of HF.

Apelin receptor homodimer inhibits apoptosis in vascular dementia

Apelin receptor (APJ), a member of family A of the G protein-coupled receptors (GPCRs), is a potential pharmaceutical target for diseases of the nervous system. Our previous work revealed that human APJ can form a homodimer that has different functional characteristics than the monomer. To investigate the effects of APJ homodimers on neuroprotection in vascular dementia (VD), we established VD model in rats and treated the animals by injecting apelin-13 into the lateral ventricle. In addition, we established an oxygen-glucose deprivation/reoxygenation (OGD/R) model in SH-SY5Y cells treated with apelin-13. After apelin-13 stimulation in the VD rat, the level of APJ and APJ homodimer were elevated. Furthermore, APJ homodimer decreased the level of cleaved caspase-3 and cleaved caspase-9 via the Gα_i3 and Gα_q signaling pathway, thereby increasing the number of neurons and inhibiting apoptosis. Consequently, APJ homodimers may serve as a unique mechanism for neuroprotection against VD and provide new pharmaceutical targets for VD.

Ischemia-induced upregulation of autophagy preludes dysfunctional lysosomal storage and associated synaptic impairments in neurons

Macroautophagy/autophagy is vital for neuronal homeostasis and functions. Accumulating evidence suggest that autophagy is impaired during cerebral ischemia, contributing to neuronal dysfunction and neurodegeneration. However, the outcomes after transient modification in autophagy machinery are not fully understood. This study investigated the effects of ischemic stress on autophagy and synaptic structures using a rat model of oxygen-glucose deprivation (OGD) in hippocampal neurons and a mouse model of middle cerebral artery occlusion (MCAO). Upon acute ischemia, an initial autophagy modification occurred in an upregulation manner. Following, the number of lysosomes increased, as well as lysosomal volume, indicating dysfunctional lysosomal storage. These changes were prevented by inhibiting autophagy via 3-methyladenine (3-MA) treatment or ATG7 (autophagy related 7) knockdown, or were mimicked by rapamycin (RAPA), a known activator of autophagy. This suggests that dysfunctional lysosomal storage is associated with the early burst of autophagy. Dysfunctional lysosomal storage contributed to autophagy dysfunction because the basal level of MTOR-dependent lysosomal biogenesis in the reperfusion was not sufficient to clear undegraded cargoes after transient autophagy upregulation. Further investigation revealed that impairment of synaptic ultra-structures, accompanied by dysfunctional lysosomal storage, may result from a failure in dynamic turnover of synaptic proteins. This indicates a vital role of autophagy-lysosomal machinery in the maintenance of synaptic structures. This study supports previous evidence that dysfunctional lysosomal storage may occur following the upregulation of autophagy in neurons. Appropriate autophagosome-lysosomal functioning is vital for maintenance of neuronal synaptic function and impacts more than the few known synaptic proteins.Abbreviations: 3-MA: 3-methyladenine; ACTB: actin beta; AD: Alzheimer disease; ALR: autophagic lysosome reformation; ATG7: autophagy related 7; CTSB: cathepsin B; CTSD: cathepsin D; DAPI: 4',6-diamidino-2-phenylindole; DEGs: differentially expressed genes; DMEM: Dulbecco's modified Eagle's medium; DMSO: dimethyl sulfoxide; GO: Gene Ontology; HBSS: Hanks' balanced salt solution; HPCA: hippocalcin; i.c.v: intracerebroventricular; KEGG: kyoto encyclopedia of genes and genomes; LAMP1: lysosomal-associated membrane protein 1; MAP1LC3B/LC3: microtubule-associated protein 1 light chain 3 beta; LSDs: lysosomal storage disorders; MAP2: microtubule-associated protein 2; MCAO: middle cerebral artery occlusion; mCTSB: mature CTSB; mCTSD: mature CTSD; MOI: multiplicity of infection; MTOR: mechanistic target of rapamycin kinase; OGD/R: oxygen-glucose deprivation/reoxygenation; PBS: phosphate-buffered saline; PRKAA/AMPKα: protein kinase AMP-activated catalytic subunit alpha; proCTSD: pro-cathepsin D; RAPA: rapamycin; RNA-seq: RNA sequencing; RPS6KB/p70S6K: ribosomal protein S6 kinase; SDS-PAGE: sodium dodecyl sulfate-polyacrylamide gel electrophoresis; SIM: Structured Illumination Microscopy; SNAP25: synaptosomal-associated protein 25; SQSTM1/p62: sequestosome 1; SYN1: synapsin I; SYT1: synaptotagmin I; TBST: tris-buffered saline Tween-20; TEM: transmission electron microscopy; TFEB: transcription factor EB; tMCAO: transient middle cerebral artery occlusion; TTC: 2,3,5-triphenyltetrazolium chloride; TUBB3: tubulin, beta 3 class III.

Apelin-13 protects the lungs from ischemia-reperfusion injury by attenuating inflammatory and oxidative stress

Apelin has been reported to regulate mitochondrial function in myocardial ischemia-reperfusion injury and cerebral ischemia-reperfusion injury. However, the role of apelin-13 in lung ischemia-reperfusion injury (LIRI) remains unclear. This study established an experimental rat model to evaluate the underlying mechanisms of apelin-13 on LIRI. Twenty-four rats were randomly divided to sham operation group (group SM), ischemia/reperfusion group (group IR), and apelin-13 treatment group (group APL). The effects of apelin-13 on LIRI were determined histologically using H&E staining, while the wet/dry weight ratio was used to assess lung edema caused by LIRI. Inflammatory cytokines were also detected in Bronchoalveolar lavage (BAL) fluid by ELISA. The protein expression of UCP2 and the morphological changes of mitochondria were determined by western blotting and electromicroscopy, respectively. The results demonstrated the structural damage of lung tissues and lung edema in group IR. An increased level of inflammatory cytokines including IL-1β, IL-6 and TNF-α was observed in rats with LIRI using ELISA. After that, oxidative stress and morphological damage of mitochondria were also shown in group IR. Yet, the application of apelin-13 reversed all these deleterious effects in group APL. The protective effects of apelin-13 were indicated by decreased reactive oxygen species (ROS) and elevated UCP2 expression levels in rats. In conclusion, this study revealed that apelin-13 had protective effects against LIRI via attenuating lung edema, the production of inflammatory cytokines, oxidative stress and mitochondrial dysfunction.

Therapeutics effects of [Pyr1] apelin-13 on rat contusion model of spinal cord injury: An experimental study

Spinal cord injury (SCI) can cause various symptoms, including pain, complete or incomplete loss of autonomic, sensory, motor and functions inferior to the site of the damage. Despite wondrous advances in medicine, treating spinal cord injuries remains a thorny issue yet. Recently, the control of inflammatory processes after damage to the nervous system has been noticed as a promising therapeutic target. The goal of the present experiment was to identify the effects of apelin-13 on the histological outcome, inflammatory factors, and functional recovery in the animal contusion model of SCI were analyzed. 40 Female Wistar rats were randomly but equally assigned in laminectomy, contusion, PBS (1 mL PBS, i.p), control group which received apelin-13 (control + apelin, 100 μg/kg, i.p), and apelin-13 treatment groups. In the treatment group, apelin-13 (100 μg/kg) was injected intraperitoneally 30 min after injury. The weight-dropping contusion model was used for inducing SCI. The Basso, Beattie, and Bresnahan scale (BBB), narrow beam test (NBT), rotarod test, and the open-field test was applied to evaluate locomotor and behavioral activity. Real-time polymerase chain reaction (PCR) and ELISA technique was accomplished eight weeks after inducing SCI to measure the level of fibroblast growth factor FGF-1, FGFR1 and the inflammatory factors including interleukin (IL)-1β, tumor necrosis factor-α (TNF-α), IL-6, and IL-10. Furthermore, histological change was estimated by H&E staining. Our results showed that apelin-13 treatment after SCI led to a significant increase in functional recovery and behavioral tests. Stereological estimation illustrated that apelin-13 could reduce significantly central cavity volume and number of glial cells, and also increase significantly spinal cord volume and number of neural cells. PCR and ELISA evaluation shows a significant increase in IL-10 level and decrease in levels of FGF-1, FGF-R1, and pro-inflammatory cytokines (PIC). This study suggested that apelin-13 has neuroprotective effects by regulating the inflammatory process after SCI.

Intravenous injection of apelin-13 improves sensory-motor balance deficits caused by cerebral ischemic reperfusion injury in male wistar rats via restoration of nitric oxide

It has been reported that apelin-13 possesses neuroprotective effects against cerebral ischemia/reperfusion injury (IRI). Disabilities in sense, movement and balance are the major stroke complications which, result in a high rate of mortality. Here, effects of intravenous (IV) injection of apelin-13 on the severity of neural death, infarct volume, neurological defects and its association with nitric oxide (NO) were investigated. A rat model of cerebral IRI was created by middle cerebral artery occlusion (MCAO) for 60 min and restoration of blood flow for 23 h. Animals were randomly assigned into six groups: sham, ischemia (MCAO), vehicle (MCAO + PBS) and three treatment groups (MCAO + apelin-13 in 10, 20, 40 μg/kg doses, IV). All injections were carried out via tail vein injection 5 min before reperfusion. Neural loss and infarct volume were evaluated by Nissl and 2,3,5-triphenyltetrazolium chloride (TTC) staining, respectively. Neurological defects were scored by standard modified criteria. Serum NO was measured by colorimetric method. Apelin-13 in doses of 20 and 40 μg/kg significantly reduced neural death, infarct volume and disturbance of sensory-motor balance compared to control and vehicle groups (p < 0.05). Serum NO levels reduced in MCAO groups compared to sham. Apelin-13 restored serum NO levels at 20 μg/kg dose (p < 0.05). Our data showed beneficial effect of IV injection of apelin-13 on sensory-motor balance defects by reducing neural death and restoration of serum NO levels. The present study shows the validity of apelin-13 in treatment of ischemic stroke in different administration methods.

Pioglitazone protects blood vessels through inhibition of the apelin signaling pathway by promoting KLF4 expression in rat models of T2DM

Apelin, identified as the endogenous ligand of APJ, exerts various cardiovascular effects. However, the molecular mechanism underlying the regulation of apelin expression in vascular cells is poorly described. Pioglitazone (PIO) and Krüppel-like factor 4 (KLF4) exhibit specific biological functions on vascular physiology and pathophysiology by regulating differentiation- and proliferation-related genes. The present study aimed to investigate the roles of PIO and KLF4 in the transcriptional regulation of apelin in a high-fat diet/streptozotocin rat model of diabetes and in PIO-stimulated vascular smooth muscle cells (VSMCs). Immunohistochemistry, qRT-PCR, and Western blotting assays revealed that the aorta of the Type 2 diabetes mellitus (T2DM) rat models had a high expression of apelin, PIO could decrease the expression of apelin in the PIO-treated rats. In vitro, Western blotting assays and immunofluorescent staining results showed that the basal expression of apelin was decreased but that of KLF4 was increased when VSMCs were stimulated by PIO treatment. Luciferase and chromatin immunoprecipitation assay results suggested that KLF4 bound to the GKLF-binding site of the apelin promoter and negatively regulated the transcription activity of apelin in VSMCs under PIO stimulation. Furthermore, qRT-PCR and Western blotting assay results showed that the overexpression of KLF4 markedly decreased the basal expression of apelin, but the knockdown of KLF4 restored the PIO-induced expression of apelin. In conclusion, PIO inhibited the expression of apelin in T2DM rat models to prevent diabetic macroangiopathy, and negatively regulated the gene transcription of apelin by promoting transcription of KLF4 in the apelin promoter.

Intravenous Administration of Pyroglutamyl Apelin-13 Alleviates Murine Inflammatory Pain via the Kappa Opioid Receptor

Apelin is an endogenous neuropeptide, which has wide distribution in central nervous system and peripheral tissues. Pyroglutamyl apelin-13 [(pyr)apelin-13] is the major apelin isoform in human plasma. However, the role of peripheral (pyr)apelin-13 in pain regulation is unknown. The aim of this study was to investigate the effect of the peripheral injection of (pyr)apelin-13 on inflammatory pain using the formalin test as well as to evaluate the mechanistic basis for the effect. Results showed intravenous (i.v.) injection of (pyr)apelin-13 (10, 20 mg/kg) to significantly decrease licking/biting time during the second phase of the mouse formalin test. In contrast, i.v. injection of apelin-13 had no influence on such effect. Intramuscular injection of (pyr)apelin-13 reduced licking/biting time during the second phase only at a dose of 20 mg/kg. The antinociception of i.v. (pyr)apelin-13 was antagonized by the apelin receptor (APJ, angiotensin II receptor-like 1) antagonist, apelin-13(F13A). (pyr)apelin-13 (i.v. 20 mg/kg) markedly upregulated Aplnr and Adcy2 gene expression in the prefrontal cortex, whereas Fos gene expression was downregulated. The antinociception of i.v. (pyr)apelin-13 was blocked by the opioid receptor antagonist naloxone and the specific kappa opioid receptor (KOR) antagonist nor-binaltorphimine (nor-BNI). (pyr)Apelin-13 upregulated the dynorphin and KOR gene expression and protein levels in the mouse prefrontal cortex, not in striatum. (pyr)Apelin-13 did not influence the motor behavior. Our results demonstrate that i.v. injection of (pyr)apelin-13 induces antinociception via the KOR in the inflammatory pain mouse model.

Intrathecally Administered Apelin-13 Alleviated Complete Freund's Adjuvant-Induced Inflammatory Pain in Mice

Apelin is the endogenous ligand for APJ, a G-protein-coupled receptor. Apelin gene and protein are widely distributed in the central nervous system and peripheral tissues. The role of apelin in chronic inflammatory pain is still unclear. In the present study, a mouse model of complete Freund’s adjuvant (CFA)-induced inflammatory pain was utilized, and the paw withdrawal latency/threshold in response to thermal stimulation and Von Frey filament stimulation were recorded after intrathecal (i.t.) injection of apelin-13 (0.1, 1, and 10 nmol/mouse). The mRNA and protein expression, concentration of glutamic acid (Glu), and number of c-Fos immunol staining in lumbar spinal cord (L4/5) were determined. The results demonstrated that Apln gene expression in the lumbar spinal cord was down-regulated in the CFA pain model. Apelin-13 (10 nmol/mouse, i.t.) alleviated CFA-induced inflammatory pain, and it exhibited a more potent antinociceptive effect than apelin-36 and (pyr)apelin-13. The antinociception of apelin-13 could be blocked by APJ antagonist apelin-13(F13A). I.T. apelin-13 attenuated the increased levels of Aplnr, Grin2b, Camk2d, and c-Fos genes expression, Glu concentration, and NMDA receptor 2B (GluN2B) protein expression caused by CFA. Apelin-13 significantly reduced the number of Fos-positive cells in laminae III and IV/V of the dorsal horn. This study indicated that i.t. apelin-13 exerted an analgesic effect against inflammatory pain, which was mediated by activation of APJ, and inhibition of Glu/GluN2B function and neural activity of the spinal dorsal horn.

Improvement of cerebral ischemia/reperfusion injury by daucosterol palmitate-induced neuronal apoptosis inhibition via PI3K/Akt/mTOR signaling pathway

Traditional Chinese medicine has growing importance in the treatment of ischemia stroke due to its abundance and low drug resistance. In this study, we aim to investigate the therapeutic potential of daucosterol palmitate against ischemia stroke, as well as its neuro-protective mechanism. The dose-response effects of daucosterol palmitate in the protection from brain damage were evaluated in a cerebral ischemia/reperfusion (I/R) rat model. The correlation of neuro-protective effects of daucosterol palmitate with apoptosis inhibition was examined and the possible signaling targets were identified. Our findings revealed that daucosterol palmitate treatment after 2 h' ischemia significantly lowered brain damage, and neuronal cell apoptosis caused by I/R injury in a dose-response mode (20, 40 and 80 mg/kg). Western blot analysis indicated that daucosterol palmitate could reverse the effects of I/R injury on protein expression of PI3K and mTOR, and phosphorylation of Akt. Contrarily, inactivation of PI3K using wortmannin dramatically antagonized the effect of daucosterol palmitate for I/R injury. With these findings, it supports the application potential of daucosterol palmitate in the treatment of ischemia stroke. Besides, the PI3K/Akt/mTOR pathway might be potential cellular targets for daucosterol palmitate.

Apelin-36 mediates neuroprotective effects by regulating oxidative stress, autophagy and apoptosis in MPTP-induced Parkinson's disease model mice

Parkinson's disease (PD), a common human neurodegenerative disorder, is characterized by the presence of intraneuronal Lewy bodies composed principally of abnormal aggregated and post-translationally modified α-synuclein. In our previous research, we have demonstrated the neuroprotective effect of Apelin-36, a neuroendocrine peptide in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridin (MPTP)-lesioned PD model mice. Therefore, this study was designed to evaluate the neuroprotective mechanism of Apelin-36 against MPTP-induced neurotoxicity in mice. The results showed that MPTP-induced the depletion of dopamine in the striatum (STR) was partially reversed by Apelin-36. Apelin-36 also improved the activity of antioxidant system including superoxide dismutase (SOD) and glutathione (GSH), and decreased the overproduction of malondialdehyde (MDA) in the substantia nigra pars compacta (SNpc) and STR of MPTP-treated mice. Moreover, Apelin-36 downregulated inducible nitric oxide synthase (iNOS) and nitrated α-synuclein expression. Furthermore, Apelin-36 significantly promoted autophagy indicated by the up-regulation of LC3-II and Beclin1 and inhibition of p62 expression in the SNpc and STR of MPTP-treated mice. The protective effect of Apelin-36 was also associated with the inhibition of the apoptosis signal-regulating kinase 1 (ASK1)/c-Jun N-terminal kinase (JNK) signaling pathway and inactivation of caspase-3. Taken together, our findings demonstrated that the neuroprotective mechanism of Apelin-36 against MPTP-induced neurotoxicity in mice might be related to decreasing the aggregation of nitrated α-synuclein and alleviating oxidative stress as well as promoting autophagy and inhibiting ASK1/JNK/caspase-3 apoptotic pathway, which provides a novel strategy for PD treatment.

Apelin attenuates depressive-like behavior and neuroinflammation in rats co-treated with chronic stress and lipopolysaccharide

Several experimental studies have proved that activation of neuroinflammation pathways may contribute to the development of depression, a neuropsychiatric disorder disease. Our previous studies have shown the antidepressant properties of apelin, but the mechanism was unkown. This study was performed to verify whether the antidepressant effect of apelin was related to its anti-inflammation effect in the central nervous system. To achieve our aim, we selected the co-treatment of chronic stress and LPS to induced an inflammatory process in rats. The effect of this co-treatment was evaluated through the expression of inflammatory markers and glial cell activation. LPS injection co-treated with unpredictable chronic mild stress resulted in the activation of microglial cell and astrocyte, expression of inflammatory markers and depressive behaviors. Treatment with apelin significantly attenuates the deleterious effects in these rats. Our results showed that apelin improved depressive phenotype and decreased the activation of glial cells in stress co-treatment group. The down-regulations of p-NF-κB and p-IKKβ suggested that the effects are possibly mediated by inhibition of the NF-κB-mediated inflammatory response. These findings speculated that intracerebroventricular injection of apelin could be a therapeutic approach for the treatment of depression, and the antidepressant function of apelin may closely associated with its alleviation in neuroinflammation.

Apelin-13 Protects PC12 Cells Against Methamphetamine-Induced Oxidative Stress, Autophagy and Apoptosis

Methamphetamine (METH) is a potent psychomotor stimulant that has a high potential for abuse in humans. In addition, it is neurotoxic, especially in dopaminergic neurons. Long-lasting exposure to METH causes psychosis and increases the risk of Parkinson's disease. Apelin-13 is a novel endogenous ligand which studies have shown that may have a neuroprotective effect. Therefore, we hypothesized that Apelin-13 might adequately prevent METH-induced neurotoxicity via the inhibition of apoptotic, autophagy, and ROS responses. In this study, PC12 cells were exposed to both METH (0.5, 1, 2, 3, 4, 6 mmol/L) and Apelin-13 (0.5, 1.0, 2.0, 4.0, 8.0 μmol/L) in vitro for 24 h to measure determined dose, and then downstream pathways were measured to investigate apoptosis, autophagy, and ROS responses. The results have indicated that Apelin-13 decreased the apoptotic response post-METH exposure in PC12 cells by increasing cell viability, reducing apoptotic rates. In addition, the study has revealed Apelin-13 decreased gene expression of Beclin-1 by Real-Time PCR and LC3-II by western blotting in METH-induced PC12 cells, which demonstrated autophagy is reduced. In addition, this study has shown that Apelin-13 reduces intracellular ROS of METH-induced PC12 cells. These results support Apelin-13 to be investigated as a potential drug for treatment of neurodegenerative diseases. It is suggested that Apelin-13 is beneficial in reducing oxidative stress, which may also play an important role in the regulation of METH-triggered apoptotic response. Hence, these data indicate that Apelin-13 could potentially alleviate METH-induced neurotoxicity via the reduction of oxidative damages, apoptotic, and autophagy cell death.

Can apelin play a role in the etiology of tinnitus?

Background/aim

Tinnitus is seen in 15% of the general population; in 1%–6% of this number, the quality of life is seriously affected by this chronic condition. Chemical, oxidative, and emotional stressors are important in terms of the clinical course of tinnitus. Apelin is an endogenous peptide which is an oxidative stress mediator. It has been shown that the apelin/APJ (apelin junction receptor) system plays various roles in the physiology and pathophysiology of many organs. However, the role of the apelin/APJ system as an oxidative stress mediator in tinnitus is unknown. We investigated the level of apelin in patients with normal hearing and bilateral tinnitus.

Materials and methods

We enrolled patients diagnosed with bilateral idiopathic tinnitus. Tinnitus severity was determined using the tinnitus handicap inventory (THI). We recorded the levels of plasma apelin-13 and biochemical parameters.

Results

The mean apelin level of the control group was higher than that of the patient group (P = 0.002). A significant negative correlation was evident between the apelin level and the THI (r = –0.460, P = 0.003). The triglyceride (TG) level was significantly higher in the patient group than in the control group (P < 0.001).

Conclusion

In our study, we found a negative correlation between apelin and tinnitus severity. Thus, apelin may play a role in the pathophysiology of idiopathic tinnitus, and may be prescribed during follow-up to reduce oxidative stress in the future. Further clinical studies on the effects of the apelin/APJ (apelin junction receptor) system and the effects of antioxidants in patients with inflammatory diseases are required.

Stigmasterol Exerts Neuro-Protective Effect Against Ischemic/Reperfusion Injury Through Reduction Of Oxidative Stress And Inactivation Of Autophagy

PURPOSE

Stroke remains the primary cause of pain, suffering, and death in patients. One of the major thrusts in stroke therapy is to find an effective prevention strategy. Objectives of this study are to testify the neuro-protection effect of stigmasterol in ischemic/reperfusion injury model.

METHODS

The dosage-dependent effects (20, 40, and 80 mg/kg) of stigmasterol on physiological behaviors and oxidative stress biomarkers were investigated. Expression and phosphorylation of beclin1, microtubule-associated protein 1 light chain 3 (LC3), adenosine monophosphate-activated protein kinase (AMPK), mTOR, and N-terminal kinase (JNK) were detected.

RESULTS

The results showed that stigmasterol was able to effectively reduce neurological deficits and infarct damage induced by the ischemic/reperfusion injury, improve histopathology changes, and restore the levels of the endogenous antioxidant defense system in a dose-response mode. Stigmasterol effectively depressed the expression level of beclin1, and the conversion of LC3 I to LC3 II, while promoted the phosphorylation of mTOR, and remarkably inhibited the phosphorylation of AMPK and JNK, as well as the expression of JNK induced by 24 hrs of reperfusion.

CONCLUSION

These findings reveal that stigmasterol has neuro-protective effect against the ischemic/reperfusion injury, possibly associated with reduction of oxidative stress and inactivation of autophagy via AMPK/mTOR and JNK pathways.

Function and regulation of apelin/APJ system in digestive physiology and pathology

Apelin is an endogenous ligand of seven-transmembrane G-protein-coupled receptor APJ. Apelin and APJ are distributed in various tissues, including the heart, lung, liver, kidney, and gastrointestinal tract and even in tumor tissues. Studies show that apelin messenger RNA is widely expressed in gastrointestinal (GI) tissues, including stomach and small intestine, which is closely correlated with GI function. Thus, the apelin/APJ system may exert a broad range of activities in the digestive system. In this paper, we review the role of the apelin/APJ system in the digestive system in physiological conditions, such as gastric acid secretion, control of appetite and food intake, cell proliferation, cholecystokinin secretion and histamine release, gut-brain axis, GI motility, and others. In pathological conditions, the apelin/APJ system plays an important role in the healing process of stress gastric injury, the clinical features and prognosis of patients with gastric cancers, the reduction of inflammatory response to enteritis and pancreatitis, the mediation of liver fibrogenesis, the promotion of liver damage, the inhibition of liver regeneration, the contribution of splanchnic neovascularization in portal hypertension, the treatment of colon cancer, and GI oxidative damage. Overall, the apelin/APJ system plays diversified functions and regulatory roles in digestive physiology and pathology. Further exploration of the relationship between the apelin/APJ system and the digestive system will help to find new and effective drugs for treating and alleviating the pain of digestive diseases.

Oxidative stress contribution to attention deficit hyperactivity disorder in children with epilepsy

Children with epilepsy have a high incidence of attention deficit hyperactivity disorder (ADHD). Oxidation stress and disturbed neurotransmitters are suggested mechanisms; however, their role is not fully explored. This study evaluates the association between circulating malondialdehyde as an oxidation stress marker, apelin neuropeptide, and ADHD in children with epilepsy. Fifty children with epilepsy of unknown etiology, of which 25 have ADHD, as well as 35 healthy children were included. Serum levels of malondialdehyde and apelin were estimated. We investigated the association between seizure severity, response to medications, malondialdehyde, apelin levels, and ADHD in children with epilepsy. Serum malondialdehyde and apelin levels were higher in children with epilepsy, especially those with ADHD. Malondialdehyde and apelin levels have significant positive correlation with the Chalfont Seizure Severity Score. Regression analysis showed that elevated malondialdehyde is an independent risk factor for ADHD in children with epilepsy (OR: 1.401, 95%CI: 1.056-1.859, p= 0.02). No significant association was found between malondialdehyde and apelin levels and the type of epilepsy or ADHD. Longer duration of epilepsy, increased seizure severity, and uncontrolled seizures are associated with increased oxidation stress, which further increased susceptibility for ADHD. In spite of elevated apelin in children with ADHD, the elevation did not increase the risk of ADHD in children with epilepsy.

The Hippocampus is a Critical Site Mediating Antidepressant-like Activity of Apelin-13 in Rats

The peptide apelin and its receptor APJ are found to express in multiple brain regions, especially in the regions such as the hippocampus and hypothalamus that play important roles in stress and depression. The distribution of apelin and APJ suggests that the apelinergic signaling may be a key mediator in the development of stress-related depressive behavior. We recently demonstrated that intracerebroventricular (i.c.v) injection of apelin-13 exerts an antidepressant-like activity in the rat forced swimming test (FST). However, the possible brain region mediating apelin-13's antidepressant-like activity remains unclear. In the present study, we determined whether the hippocampus and hypothalamus are the possible regions mediating antidepressant-like activity of apelin-13. We found that forced swimming exposure upregulated apelin and APJ protein expression levels in the hippocampus but not hypothalamus in rats. Further, intrahippocampal injection of apelin-13 exerted an antidepressant-like activity (as indicated by a decreased immobility behavior), and intrahippocampal infusion of APJ receptor antagonist F13A blocked the antidepressant-like activity produced by i.c.v injection of apelin-13 in the FST. Moreover, intrahypothalamic injection of apelin-13 did not affect the immobility behavior in the FST. These findings suggest that the hippocampus, but not hypothalamus, is a critical site mediating antidepressant-like activity of apelin-13 in rats.

Apelin/APJ system: A key therapeutic target for liver disease

Apelin, a new bioactive peptide, was identified as an endogenous ligand for APJ (Angiotensin II receptor-like 1). Apelin and its receptor have an abundant distribution in central nervous system and peripheral tissues, including liver. Apelin/APJ has diverse physiological and pathological effects, including regulation of cardiovascular function, angiogenesis, fluid homeostasis and so on. Apelin/APJ system may act as a novel potential therapeutic target for liver disease. In this article, we review the role of apelin/APJ system in liver fibrosis, hepatitis, hepatic cirrhosis, liver injury and metabolic liver disease.

Effects of apelin on retinal microglial cells in a rat model of oxygen-induced retinopathy of prematurity

This study explores the effects of apelin on retinal microglial cells in rat models of oxygen-induced retinopathy of prematurity (ROP). Totally, 274 rats were selected for establishing oxygen-induced retinopathy (OIR) models, and 92 healthy rats for control group. OIR rats were assigned into OIR, 10^-5  g/L apelin, 10^-4  g/L apelin, and 10^-3  g/L apelin groups. Immunohistochemistry was employed to determine morphology of microglial cells and cell number. CDllb, ionized calcium-binding adapter molecule 1 (IBA-1), TNF-α, and iNOS mRNA and protein expressions were identified using RT-qPCR and Western blotting, respectively. ELISA was employed to determine the levels of VEGF and glial fibrillary acidic protein (GFAP). The amoeboid microglial cells were found in the OIR and 10^-3  g/L apelin groups, while bipolar microglial cells were found in the normal control, 10^-5  g/L apelin and 10^-4  g/L apelin groups. In the 1, 2, 3, and 4th week after apelin treatment, there were significantly decreased bipolar microglial cells, lower mRNA and protein expressions of CDllb, IBA-1, TNF-α and iNOS, and the levels of VEGF and GFAP in the 10^-4  g/L apelin group than in the OIR, 10^-3  g/L apelin and 10^-5  g/L apelin groups. The differences between the normal control and 10^-4  g/L apelin groups are not significant. Compared with the OIR group, the 10^-5  g/L apelin and 10^-3  g/L apelin groups presented decreased microglial cells and mRNA and protein expressions of CDllb, IBA-1, TNF-α, and iNOS. Appropriate concentration of apelin may reduce retinal microglial cells in a rat model of oxygen-induced ROP.

Load-dependent effects of apelin on murine cardiomyocytes

The apelin peptide is described as one of the most potent inotropic agents, produced endogenously in a wide range of cells, including cardiomyocytes. Despite positive effects on cardiac contractility in multicellular preparations, as well as indications of cardio-protective actions in several diseases, its effects and mechanisms of action at the cellular level are incompletely understood.

Here, we report apelin effects on dynamic mechanical characteristics of single ventricular cardiomyocytes, isolated from mouse models (control, apelin-deficient [Apelin-KO], apelin-receptor KO mouse [APJ-KO]), and rat. Dynamic changes in maximal velocity of cell shortening and relaxation were monitored. In addition, more traditional indicators of inotropic effects, such as maximum shortening (in mechanically unloaded cells) or peak force development (in auxotonic contracting cells, preloaded using the carbon fibre technique) were studied.

The key finding is that, using Apelin-KO cardiomyocytes exposed to different preloads with the 2-carbon fibre technique, we observe a lowering of the slope of the end-diastolic stress-length relation in response to 10 nM apelin, an effect that is preload-dependent. This suggests a positive lusitropic effect of apelin, which could explain earlier counter-intuitive findings on an apelin-induced increase in contractility occurring without matching rise in oxygen consumption.

Inhibition of the apelin/apelin receptor axis decreases cholangiocarcinoma growth

PURPOSE

Cholangiocarcinoma (CCA) is a malignancy of the biliary epithelium that is associated with low five-year survival. The apelin receptor (APLNR), which is activated by the apelin peptide, has not been studied in CCA. The purpose of this study is to determine if inhibition of the apelin/APLNR axis can inhibit CCA growth.

METHODS

Immunohistochemistry, rtPCR, immunofluorescence, flow cytometry, and ELISA was used to measure APLNR expression in human CCA cells and tissues. Mz-ChA-1 cells were treated with increasing concentrations of apelin and ML221, an APLNR antagonist. Expression of proliferative and angiogenic genes were measured via rtPCR. In vivo, Mz-ChA-1 cells were injected into the flanks of nu/nu mice, which were treated with ML221 (150 μg/kg) via tail vein injection.

RESULTS

Expression of the apelin/APLNR axis was increased in CCA. In vitro, CCA proliferation and angiogenesis was inhibited by ML221 treatment. ML221 treatment significantly decreased tumor growth in nu/nu mice.

CONCLUSION

The apelin/APLNR axis regulates CCA proliferation and angiogenesis. Inhibition of the apelin/APLNR axis decreases tumor growth in our xenograft model. Targeting APLNR signaling has the potential to serve as a novel, tumor directed therapy for CCA.

Ascending aortic adventitial remodeling and fibrosis are ameliorated with Apelin-13 in rats after TAC via suppression of the miRNA-122 and LGR4-β-catenin signaling

Apelin has been proved to be a critical mediator of vascular function and homeostasis. Here, we investigated roles of Apelin in aortic remodeling and fibrosis in rats with transverse aortic constriction (TAC). Male Sprague-Dawley rats were subjected to TAC and then randomized to daily deliver Apelin-13 (50μg/kg) or angiotensin type 1 receptor (AT1) blocker Irbesartan (50mg/kg) for 4 weeks. Pressure overload resulted in myocardial hypertrophy, systolic dysfunction, aortic remodeling and adventitial fibrosis with reduced levels of Apelin in ascending aortas of rat after TAC compared with sham-operated group. These changes were associated with marked increases in levels of miRNA-122, TGFβ1, CTGF, NFAT5, LGR4, and β-catenin. More importantly, Apelin and Irbesartan treatment strikingly prevented TAC-mediated aortic remodeling and adventitial fibrosis in pressure overloaded rats by blocking AT1 receptor and miRNA-122 levels and repressing activation of the CTGF-NFAT5 and LGR4-β-catenin signaling. In cultured primary rat adventitial fibroblasts, exposure to angiotensin II (100nmolL^-1) led to significant increases in cellular migration and levels of TGFβ1, CTGF, NFAT5, LGR4 and β-catenin, which were effectively reversed by pre-treatment with Apelin (100nmolL^-1) and miRNA-122 inhibitor (50nmolL^-1). In conclusion, Apelin counterregulated against TAC-mediated ascending aortic remodeling and angiotensin II-induced promotion of cellular migration by blocking AT1 receptor and miRNA-122 levels and preventing activation of the TGFβ1-CTGF-NFAT5 and LGR4-β-catenin signaling, ultimately contributing to attenuation of aortic adventitial fibrosis. Our data point to Apelin as an important regulator of aortic remodeling and adventitial fibrosis and a promising target for vasoprotective therapies.

Apelin-13 Protects PC12 Cells from Corticosterone-Induced Apoptosis Through PI3K and ERKs Activation

It is widely accepted that environmental stress is a risk factor for mental disorders. Glucocorticoid hormones play a vital role in the regulation of physiological response to stress. High concentrations of corticosterone can induce cellular damage in PC12 cells, which possess typical neuronal features. Apelin and its receptor APJ are widely distributed in the central nervous system including limbic structures involved in stress responses. Previous studies have suggested that apelin has a neuroprotective function. However, the effect of apelin on corticosterone-induced neuronal damage remains to be elucidated. In the present study, we explored the potential protective activity of apelin-13 in PC12 cells treated with corticosterone and its underling mechanisms. The viability of the cells, the apoptosis of the cells, the level of phosphorylation of Akt (p-Akt) and extracellular signal-regulated kinases (p-ERKs) and cleaved caspase-3 expression were detected by MTT, Hoechst staining and flow cytometer assays and Western blotting. Results showed that corticosterone induced cells viability loss, cell apoptosis, down-regulation of p-Akt and p-ERKs and up-regulation of cleaved caspase-3. The effects induced by corticosterone were attenuated by apelin-13 pretreatment. Furthermore, apelin-13-mediated anti-viability loss, antiapoptosis and caspase-3 suppression activities were blocked by specific inhibitors of phosphatidylinositol 3-kinase (PI3K) (LY294002) and ERKs (PD98059). The data suggest that apelin-13 protects PC12 cells from corticosterone-induced apoptosis through activating PI3K/Akt and ERKs signaling pathways.

Apelin-13 exerts antidepressant-like and recognition memory improving activities in stressed rats

Apelin is the endogenous ligand for the G-protein-coupled receptor (APJ). The localization of APJ in limbic structures suggests a potential role for apelin in emotional processes. However, the role of apelin in the regulation of stress-induced responses such as depression and memory impairment is largely unknown. In the present study, we evaluated the role of apelin-13 in the regulation of stress-induced depression and memory impairment in rats. We report that repeated intracerebroventricular injections of apelin-13 reversed behavioral despair (immobility) in the forced swim (FS) test, a model widely used for the selection of new antidepressant agents. Apelin-13 also reversed behavioral deficits (escape failure) in the learned helplessness test. The magnitude of the antiimmobility and anti-escape failure effects of apelin-13 was comparable to that of imipramine, a classic antidepressant used as a positive control. Rats exposed to FS stress showed memory performance impairment in the novel object recognition test, and this impairment was improved by apelin-13 treatment. Apelin-13 did not affect recognition memory performance in non-stressed rats. Furthermore, the pretreatment of LY294002 (PI3K inhibitors) or PD98059 (ERK1/2 inhibitor) blocked apelin-13-mediated activities in FS-stressed rats. These findings suggest that apelin-13 exerts antidepressant-like and recognition memory improving activities through activating PI3K and ERK1/2 signaling pathways in stressed rats.

In silico Therapeutics for Neurogenic Hypertension and Vasovagal Syncope

Neurocardiovascular diseases (NCVD) are the leading cause of death in the developed world and will remain so till 2020. In these diseases the pathologically changed nervous control of cardiovascular system has the central role. The actual NCV syndromes are neurogenic hypertension, representing the sympathetically mediated disorder, and vasovagal syncope, which is the vagally mediated disorders. Vasovagal syncope, the disease far from its etiological treatment, could benefit from recruiting and application of antimuscarinic drugs used in other parasympathetic disorders. The informational spectrum method (ISM), a method widely applied for the characterization of protein-protein interactions in the field of immunology, endocrinology and anti HIV drug discovery, was applied for the first time in the analysis of neurogenic hypertension and vasovagal syncope therapeutic targets. In silico analysis revealed the potential involvement of apelin in neurogenic hypertension. Applying the EIIP/ISM bioinformatics concept in investigation of drugs for treatment of vasovagal syncope suggests that 78% of tested antimuscarinic drugs could have anti vasovagal syncope effect. The presented results confirm that ISM is a promissing method for investigation of molecular mechanisms underlying pathophysiological proceses of NCV syndromes and discovery of therapeutics targets for their treatment.

Microglia-Induced Maladaptive Plasticity Can Be Modulated by Neuropeptides In Vivo

Microglia-induced maladaptive plasticity is being recognized as a major cause of deleterious self-sustaining pathological processes that occur in neurodegenerative and neuroinflammatory diseases. Microglia, the primary homeostatic guardian of the central nervous system, exert critical functions both during development, in neural circuit reshaping, and during adult life, in the brain physiological and pathological surveillance. This delicate critical role can be disrupted by neural, but also peripheral, noxious stimuli that can prime microglia to become overreactive to a second noxious stimulus or worsen underlying pathological processes. Among regulators of microglia, neuropeptides can play a major role. Their receptors are widely expressed in microglial cells and neuropeptide challenge can potently influence microglial activity in vitro. More relevantly, this regulator activity has been assessed also in vivo, in experimental models of brain diseases. Neuropeptide action in the central nervous system has been associated with beneficial effects in neurodegenerative and neuroinflammatory pathological experimental models. This review describes some of the mechanisms of the microglia maladaptive plasticity in vivo and how neuropeptide activity can represent a useful therapeutical target in a variety of human brain pathologies.