Apelin protects against myocardial ischemic injury by inhibiting dynamin-related protein 1

Adaptive enzyme-responsive self-assembling multivalent apelin ligands for targeted myocardial infarction therapy

Microvascular dysfunction following myocardial infarction exacerbates coronary flow obstruction and impairs the preservation of ventricular function. The apelinergic system, known for its pleiotropic effects on improving vascular function and repairing ischemic myocardium, has emerged as a promising therapeutic target for myocardial infarction. Despite its potential, the natural apelin peptide has an extremely short circulating half-life. Current apelin analogs have limited receptor binding efficacy and poor targeting, which restricts their clinical applications. In this study, we utilized an enzyme-responsive peptide self-assembly technique to develop an enzyme-responsive small molecule peptide that adapts to the expression levels of matrix metalloproteinases in myocardial infarction lesions. This peptide is engineered to respond to the high concentration of matrix metalloproteinases in the lesion area, allowing for precise and abundant presentation of the apelin motif. The changes in hydrophobicity allow the apelin motif to self-assemble into a supramolecular multivalent peptide ligand-SAMP. This self-assembly behavior not only prolongs the residence time of apelin in the myocardial infarction lesion but also enhances the receptor-ligand interaction through increased receptor binding affinity due to multivalency. Studies have demonstrated that SAMP significantly promotes angiogenesis after ischemia, reduces cardiomyocyte apoptosis, and improves cardiac function. This novel therapeutic strategy offers a new approach to restoring coronary microvascular function and improving damaged myocardium after myocardial infarction.

APJ as Promising Therapeutic Target of Peptide Analogues in Myocardial Infarction- and Hypertension-Induced Heart Failure

The widely expressed G protein-coupled apelin receptor (APJ) is activated by two bioactive endogenous peptides, apelin and ELABELA (ELA). The apelin/ELA-APJ-related pathway has been found involved in the regulation of many physiological and pathological cardiovascular processes. Increasing studies are deepening the role of the APJ pathway in limiting hypertension and myocardial ischaemia, thus reducing cardiac fibrosis and adverse tissue remodelling, outlining APJ regulation as a potential therapeutic target for heart failure prevention. However, the low plasma half-life of native apelin and ELABELA isoforms lowered their potential for pharmacological applications. In recent years, many research groups focused their attention on studying how APJ ligand modifications could affect receptor structure and dynamics as well as its downstream signalling. This review summarises the novel insights regarding the role of APJ-related pathways in myocardial infarction and hypertension. Furthermore, recent progress in designing synthetic compounds or analogues of APJ ligands able to fully activate the apelinergic pathway is reported. Determining how to exogenously regulate the APJ activation could help to outline a promising therapy for cardiac diseases.

The Yin and Yang Effect of the Apelinergic System in Oxidative Stress

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.

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.

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.

Meteorin-Like (METRNL) Attenuates Myocardial Ischemia/Reperfusion Injury-Induced Cardiomyocytes Apoptosis by Alleviating Endoplasmic Reticulum Stress via Activation of AMPK-PAK2 Signaling in H9C2 Cells

BACKGROUND Myocardial ischemia mediates the progression of multiple cardiovascular diseases and leads to serious damage to the morphology, function, and metabolism of cardiomyocytes. The serum level of the hormone Meteorin-like (METRNL) was lower in patients with coronary artery disease and was negatively correlated with inflammatory cytokines. The aim of the present study was to determine the relationship between METRNL and myocardial ischemia/reperfusion (MI/R) injury, and investigate the molecular mechanisms implicated the pathogenesis of myocardial ischemia. MATERIAL AND METHODS In the present study, H9C2 cells underwent oxygen-glucose deprivation and reperfusion (OGD/R) treatment to establish a MI/R cell model. Quantitative real-time polymerase chain reaction was performed to analyze the expression of target gene. Western blot was used to evaluate the protein expression. Cell Counting Kit-8 assay was employed to detect the cell viability. Enzyme-linked immunosorbent assay was carried out to determine the levels of inflammatory cytokines. Finally, flow cytometry and TUNEL staining were used to detect the apoptotic levels of cardiomyocytes. RESULTS The results showed that the expression of METRNL was downregulated in H9C2 cells during OGD/R. Interestingly, METRNL overexpression inhibited the inflammation, apoptosis and endoplasmic reticulum stress in H9C2 cells during OGD/R, which were totally reversed by PAK2 silencing. In addition, METRNL overexpression induced activation of AMPK-PAK2 signaling cascade. CONCLUSIONS METRNL attenuates MI/R injury-induced cardiomyocytes apoptosis by alleviating endoplasmic reticulum stress via activation of AMPK-PAK2 signaling in H9C2 cells. Our findings support that METRNL might be a promising target for treatment of myocardial ischemia in the future.

Role of Apelin/APJ axis in cancer development and progression

Apelin is an endogenous peptide, which is expressed in a vast board of organs such as the brain, placenta, heart, lungs, kidneys, pancreas, testis, prostate and adipose tissues. The apelin receptor, called angiotensin-like-receptor 1 (APJ), is also expressed in the brain, spleen, placenta, heart, liver, intestine, prostate, thymus, testis, ovary, lungs, kidneys, stomach, and adipose tissue. The apelin/APJ axis is involved in a number of physiological and pathological processes. The apelin expression is increased in various kinds of cancer and the apelin/APJ axis plays a key role in the development of tumors through enhancing angiogenesis, metastasis, cell proliferation and also through the development of cancer stem cells and drug resistance. The apelin also stops the apoptosis of cancer cells. The apelin/APJ axis was considered in this review as an attractive therapeutic target for cancer treatment.

MicroRNA-668-3p Protects Against Oxygen-Glucose Deprivation in a Rat H9c2 Cardiomyocyte Model of Ischemia-Reperfusion Injury by Targeting the Stromal Cell-Derived Factor-1 (SDF-1)/CXCR4 Signaling Pathway

Background

Ischemia-reperfusion injury (IRI) results from the restoration of blood supply to ischemic organs, including the heart. Expression of microRNA-668-3p (miR-668-3p) is known to protect the kidney from IRI. This study aimed to investigate the role of miR-668-3p in oxygen-glucose deprivation (OGD) in a rat H9c2 cardiomyocyte model of IRI.

Material/Methods

Rat H9c2 cardiomyocytes were cultured in glucose-free Dulbecco’s modified Eagle’s medium (DMEM) under anaerobic conditions, followed by oxygenation, to create the OGD model of IRI. The luciferase reporter assay evaluated the interaction between stromal cell-derived factor-1 (SDF-1), or CXC motif chemokine 12 (CXCL12), and miR-668-3p. Protein and mRNA levels of SDF-1, CXCR4, Bcl2, Bax, cleaved caspase-3, endothelial nitric oxide synthase (eNOS), and phosphorylated endothelial nitric oxide synthase (p-eNOS) were analyzed by Western blot and quantitative reverse transcription-polymerase chain reaction (RT-qPCR), and apoptosis were assessed by flow cytometry. Enzyme-linked immunosorbent assay (ELISA) measured reactive oxygen species (ROS), including malondialdehyde (MDA), nitric oxide (NO), p-eNOS, and the inflammatory cytokines, tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), IL-6, and monocyte chemoattractant protein-1 (MCP-1) in H9c2 cell supernatants.

Results

In the OGD rat H9c2 cardiomyocyte model of IRI, miR-668-3p levels were reduced. Overexpression of miR-668-3p inhibited SDF-1, CXCR4, the expression of inflammatory cytokines, markers of oxidative stress, and p-eNOS. The overexpression of SDF-1 reversed these findings. Overexpression of SDF-1 promoted cell apoptosis, which was reduced by miR-668-3p.

Conclusions

In the OGD rat H9c2 cardiomyocyte model of IRI, miR-668-3p suppressed mediators of inflammation and oxidative stress and enhanced cell viability through the SDF-1/CXCR4 signaling pathway.

Apelin shorten QT interval by inhibiting Kir2.1/IK1 via a PI3K way in acute myocardial infarction

QT interval prolongation and depolarization of resting membrane potential (RMP) were found in acute myocardial infarction (MI) which is involved in the arrhythmogenic mechanism and raising the risk to initiate torsade de pointes. However, clinical anti-arrhythmic agents that primarily act on QT interval and RMP are not currently available. Our objective was to determine whether Apelin, an endogenous peptide ligand of receptor APJ, affects QT interval and RMP and underlying mechanisms. To test this viewpoint, mice were subjected to MI by ligating the left main coronary artery and Apelin was applied through tail vein at 5 min prior coronary occlusion in tested group. Compared to MI group, pretreatment of Apelin (15 μg/kg) shortened QTc and QT interval induced by MI, significantly elevated RMP and shortened action potential duration (APD) by increased I_K1 currents recorded using whole-cell patch technique from cardiomyocytes underwent MI. In cultured neonatal mouse cardiomyocytes, Apelin (1 μmol/L) restored hypoxia-induced Kir2.1 down-regulation, which was abolished by IP3K inhibitor LY-294002. Additionally, Apelin elicited a time-dependent increase in phosphorylation of Akt leading to increase in PI3-kinase activity. These results showed that Apelin enhanced I_K1/Kir2.1 currents via IP3K pathway as by rescue ischemia- and hypoxia-induced RMP depolarization and prolongation of QT interval, which may prevent or cure acute ischemic-mediated arrhythmias. This study brings new information to anti-arrhythmic theories and provides a potential target for the clinical management of acute ischemia-related arrhythmias.

Melatonin prevents lung injury by regulating apelin 13 to improve mitochondrial dysfunction

Pulmonary fibrosis is a progressive disease characterized by epithelial cell damage, fibroblast proliferation, excessive extracellular matrix (ECM) deposition, and lung tissue scarring. Melatonin, a hormone produced by the pineal gland, plays an important role in multiple physiological and pathological responses in organisms. However, the function of melatonin in the development of bleomycin-induced pulmonary injury is poorly understood. In the present study, we found that melatonin significantly decreased mortality and restored the function of the alveolar epithelium in bleomycin-treated mice. However, pulmonary function mainly depends on type II alveolar epithelial cells (AECIIs) and is linked to mitochondrial integrity. We also found that melatonin reduced the production of reactive oxygen species (ROS) and prevented apoptosis and senescence in AECIIs. Luzindole, a nonselective melatonin receptor antagonist, blocked the protective action of melatonin. Interestingly, we found that the expression of apelin 13 was significantly downregulated in vitro and in vivo and that this downregulation was reversed by melatonin. Furthermore, ML221, an apelin inhibitor, disrupted the beneficial effects of melatonin on alveolar epithelial cells. Taken together, these results suggest that melatonin alleviates lung injury through regulating apelin 13 to improve mitochondrial dysfunction in the process of bleomycin-induced pulmonary injury.

The hormone melatonin could protect lung cells from the damage associated with respiratory diseases such as pulmonary fibrosis. Several studies have linked such damage with abnormal activity of the mitochondria, with these essential metabolic organelles churning out damaging ‘reactive oxygen species’ (ROS), compounds that induce premature cell aging and death. Melatonin can mitigate ROS production, and researchers led by Haihai Liang at China’s Harbin Medical University have demonstrated that it can prevent injury to airway epithelial cells in a mouse model of lung disease. Melatonin treatment countered much of the damage, resulting in significantly longer survival, and the team identified a target molecule in the mitochondria that may be responsible for this effect. This approach could offer hope for a family of diseases with a poor prognosis and limited treatment options.

Plasma-derived exosomal miR-183 associates with protein kinase activity and may serve as a novel predictive biomarker of myocardial ischemic injury

Myocardial infarction (MI) is primarily caused by ischemic heart or coronary artery disease and is a major cause of mortality worldwide. Thus, it is necessary to establish reliable biochemical markers for the early diagnosis of MI. MicroRNAs (miRNAs or miR) have been demonstrated to circulate in biological fluids and are enclosed in extracellular vesicles, including exosomes. The current study assessed the differential expression of exosomal miRNAs in the plasma of patients with MI and healthy individuals, and the possible mechanism involved. Plasma-derived exosomes were isolated from patients with MI and healthy control individuals, and vesicles with a membrane were observed using transmission electron microscopy. Furthermore, an exosomal miRNA expression profile was compared between patients with MI and healthy individuals using a miRNA microarray. Significantly differentially expressed miRNAs were validated using reverse transcription-quantitative polymerase chain reaction. To the best of our knowledge, the present study was the first to demonstrate that miR-183 was markedly upregulated in patients with MI compared with healthy individuals. In addition, the relative exosomal miR-183 level increased with the degree of myocardial ischemic injury. Additionally, GO and KEGG analyses demonstrated that miR-183 is primarily involved in cell communication, protein kinase activity regulation and adrenergic signaling in cardiomyocytes. Furthermore, a protein-protein interaction network of all the miR-183 target genes was constructed. The results demonstrated that five core genes (PPP2CB, PPP2CA, PRKCA, PPP2CA, PPP2R5C and PPP2R2A) in the PPI network were also associated with protein kinase activity regulation and adrenergic signaling in cardiomyocytes. Taken together, these data demonstrate that exosomal miR-183 derived from the serum of patients with MI may be a novel diagnostic biomarker involved in the regulation of protein kinase activity. miR-183 may therefore be further developed for clinical use to benefit patients with coronary artery diseases.

Apelin-13 Alleviates Early Brain Injury after Subarachnoid Hemorrhage via Suppression of Endoplasmic Reticulum Stress-mediated Apoptosis and Blood-Brain Barrier Disruption: Possible Involvement of ATF6/CHOP Pathway

Neuronal apoptosis plays important roles in the early brain injury after subarachnoid hemorrhage (SAH). This study first showed that inhibition of activating transcription factor 6 (ATF6) by apelin-13 could reduce endoplasmic reticulum (ER)-stress-mediated apoptosis and blood-brain-barrier (BBB) disruption after SAH. We chose apelin-13, ATF6 and CCAAT/enhancer-binding protein (C/EBP) homologous protein (CHOP) siRNAs to verify the hypothesis. Brain water content, neurological behavior and Evans Blue (EB) were assessed at 24 h after SAH. Western blot analysis and reverse transcription-polymerase chain reaction (RT-PCR) were applied to evaluate the expression of targets in both protein and mRNA levels. Neuronal apoptosis was assessed with Terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end labeling (TUNEL) and caspase-3 staining. The results showed that the levels of ATF6, and its downstream protein, CHOP were upregulated and reached the peak at 24 h after SAH. ATF6 was highly expressed in neurons. The administration of apelin-13 could significantly reduce the mRNA and protein levels of ATF6, and its downstream targets, CHOP and caspase-3, but increase the Bcl-2/Bax ratio, Claudin-5, Occludin and ZO-1. What's more, the administration of apelin-13 could reduce brain edema, ameliorate BBB disruption and improve neurological functions. However, the CHOP siRNA could significantly reverse the pro-apoptotic effect induced by the increased ATF6 level after SAH. Apelin-13 could exert its neuroprotective effects via suppression of ATF6/CHOP arm of ER-stress-response pathway in the early brain injury after SAH.