Apelin-13 attenuates ER stress-mediated neuronal apoptosis by activating Gαi/Gαq-CK2 signaling in ischemic stroke

Mechanism of Astragalus mongholicus Bunge ameliorating cerebral ischemia-reperfusion injury: Based on network pharmacology analysis and experimental verification

ETHNOPHARMACOLOGICAL RELEVANCE

Astragalus mongholicus Bunge (AMB) is a herb with wide application in traditional Chinese medicine, exerting a wealth of pharmacological effects. AMB has been proven to have an evident therapeutic effect on ischemic cerebrovascular diseases, including cerebral ischemia-reperfusion injury (CIRI). However, the specific mechanism underlying AMB in CIRI remains unclear.

AIM OF THE STUDY

This study aimed to investigate the potential role of AMB in CIRI through a comprehensive approach of network pharmacology and in vivo experimental research.

METHODS

The intersection genes of drugs and diseases were obtained through analysis of the Traditional Chinese Medicine Systems Pharmacology (TCMSP) database and Gene Expression Omnibus (GEO) database. The protein-protein interaction (PPI) network was created through the string website. Meanwhile, the gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis was carried out using R studio, and thereafter the key genes were screened. Then, the molecular docking prediction was made between the main active ingredients and target genes, and hub genes with high binding energy were obtained. In addition, molecular dynamic (MD) simulation was used to validate the result of molecular docking. Based on the results of network pharmacology, we used animal experiments to verify the predicted hub genes. First, the rat middle cerebral artery occlusion and reperfusion (MACO/R) model was established and the effective dose of AMB in CIRI was determined by behavioral detection and 2,3,5-Triphenyltetrazolium chloride (TTC) staining. Then the target proteins corresponding to the hub genes were measured by Western blot. Moreover, the level of neuronal death was measured using hematoxylin and eosin (HE) and Nissl staining.

RESULTS

Based on the analysis of the TCMSP database and GEO database, a total of 62 intersection target genes of diseases and drugs were obtained. The KEGG enrichment analysis showed that the therapeutic effect of AMB on CIRI might be realized through the advanced glycation endproduct-the receptor of advanced glycation endproduct (AGE-RAGE) signaling pathway in diabetic complications, nuclear factor kappa-B (NF-κB) signaling pathway and other pathways. Molecular docking results showed that the active ingredients of AMB had good binding potential with hub genes that included Prkcb, Ikbkb, Gsk3b, Fos and Rela. Animal experiments showed that AWE (60 g/kg) could alleviate CIRI by regulating the phosphorylation of PKCβ, IKKβ, GSK3β, c-Fos and NF-κB p65 proteins.

CONCLUSION

AMB exerts multi-target and multi-pathway effects against CIRI, and the underlying mechanism may be related to anti-apoptosis, anti-inflammation, anti-oxidative stress and inhibiting calcium overload.

Exploring the intricacies of calcium dysregulation in ischemic stroke: Insights into neuronal cell death and therapeutic strategies

Calcium ion (Ca2+) dysregulation is one of the main causes of neuronal cell death and brain damage after cerebral ischemia. During ischemic stroke, the ability of neurons to maintain Ca2+ homeostasis is compromised. Ca2+ regulates various functions of the nervous system, including neuronal activity and adenosine triphosphate (ATP) production. Disruptions in Ca2+ homeostasis can trigger a cascade of events, including activation of the unfolded protein response (UPR) pathway, which is associated with endoplasmic reticulum (ER) stress and mitochondrial dysfunction. This response occurs when the cell is unable to manage protein folding within the ER due to various stressors, such as a high influx of Ca2+. Consequently, the UPR is initiated to restore ER function and alleviate stress, but prolonged activation can lead to mitochondrial dysfunction and, ultimately, cell death. Hence, precise regulation of Ca2+ within the cell is mandatory. The ER and mitochondria are two such organelles that maintain intracellular Ca2+ homeostasis through various calcium-operating channels, including ryanodine receptors (RyRs), inositol trisphosphate receptors (IP3Rs), sarco/endoplasmic reticulum calcium ATPases (SERCAs), the mitochondrial Na+/Ca2+ exchanger (NCLX), the mitochondrial calcium uniporter (MCU) and voltage-dependent anion channels (VDACs). These channels utilize Ca2+ sequestering and release mechanisms to maintain intracellular Ca2+ homeostasis and ensure proper cellular function and survival. The present review critically evaluates the significance of Ca2+ and its physiological role in cerebral ischemia. We have compiled recent findings on calcium's role and emerging treatment strategies, particularly targeting mitochondria and the endoplasmic reticulum, to address Ca2+ overload in cerebral ischemia.

The biological efficacy of Apelin against focal transient cerebral ischemia-reperfusion injury. A systematic review and meta-analysis of animal studies

BACKGROUND

Apelin has been extensively studied, and emerging experimental evidence suggests that Apelin may have effects on stroke by reducing infarct volume and neurological deficits, inhibiting the apoptosis process and reducing brain water content. However, the credibility of the evidence is uncertain. Thus, we aimed to perform a systematic review and meta-analysis to evaluate preclinical studies that used Apelin for the treatment of transient focal cerebral ischemia.

METHODS

Electronic bibliographic databases including PubMed, EMBASE, Scopus, and Google Scholar were searched for finding relevant studies from January 2000 to July 2023. The methodological quality and risk of bias scores for animal studies were calculated based on the CAMARADES and the SYRCLE's RoB tools, respectively. The effect sizes were assessed using Comprehensive Meta-Analysis (CMA) software.

RESULTS

A total of twelve eligible studies were used for the systematic review and meta-analysis. The median scores of study quality and risk of bias were 7.5 out of 10, and 5 out of 10, respectively. Apelin treatment effectively decreased infarct volume (primary outcome) [Hedges' g = 2.72, 95 % CI (1.93, 3.51), p < 0.001], neurological deficit [Hedges' g = 1.76, 95 % CI (0.96, 2.55), p < 0.001], cleaved caspase 3 [Hedges' g = 2.16, 95 % CI (0.87, 3.44), p = 0.001], and apoptotic cell number [Hedges' g = 4.07, 95 % CI (1.25,6.89), p = 0.005] compared with the control group. According to subgroup analysis, more notable neuroprotective effects were observed with intravenous administration than with intracerebroventricular (ICV) administration. Moreover, we determined that effect size of infarct volume was markedly related to the species. The combined measurement of two studies demonstrated that Apelin could reduce BCL2 and TNF-α levels as well as brain water content compared with the control group. However, pooled measurement of two studies showed that no relevancy was discovered between CHOP and altering infarct volume.

CONCLUSION

The present meta-analysis was conducted to assess preclinical studies related to Apelin treatment in rodent ischemic stroke. Apelin can exert promising neuroprotective effects by reducing infarct volume, neurological deficit, caspase 3, apoptotic cell number, TNF- α and brain water content and increasing BCL2. The current evidence supports the anti-apoptotic and anti-inflammatory properties of Apelin, but its effectiveness in decreasing CHOP level in animal models of ischemic stroke needs further elucidation. This study was registered within the International Prospective Register of Systematic Reviews (PROSPERO) as number CRD42023460926.

Neuroprotective effect of apelin-13 and other apelin forms-a review

Neurodegenerative diseases, which occur when neurons begin to deteriorate, affect millions of people worldwide. These age-related disorders are becoming more common partly because the elderly population has increased in recent years. While no treatments are accessible, every year an increasing number of therapeutic and supportive options become available. Various substances that may have neuroprotective effects are currently being researched. One of them is apelin. This review aims to illustrate the results of research on the neuroprotective effect of apelin amino acid oligopeptide which binds to the apelin receptor and exhibits neuroprotective effects in the central nervous system. The collected data indicate that apelin can protect the central nervous system against injury by several mechanisms. More studies are needed to thoroughly investigate the potential neuroprotective effects of this peptide in neurodegenerative diseases and various other types of brain damage.

Xingnaojing injection alleviates cerebral ischemia/reperfusion injury through regulating endoplasmic reticulum stress in Vivo and in Vitro

Background

Xingnaojing (XNJ) injection, an extract derived from traditional Chinese medicine, is commonly used to treat ischemic stroke (IS). Previous studies have shown that XNJ has the ability to alleviate apoptosis in cerebral ischemia-reperfusion injury. However, the potential mechanisms have not been clarified.

Objective

To identify the neuroprotective effect of XNJ and explore whether XNJ inhibits cell apoptosis associated with endoplasmic reticulum stress (ERS) after IS.

Methods

In this study, cultured hippocampal neurons from mouse embryos and Sprague-Dawley rats were assigned randomly to four groups: sham, model, XNJ, and edaravone. The treatment groups were administered 2 h after modelling. Neurological deficit scores and motor performance tests were performed after 24 h of modelling. Additionally, pathomorphology, cell apoptosis and calcium content were evaluated. To ascertain the expression of ERS proteins, western blotting and polymerase chain reaction were employed.

Results

The results indicated that XNJ treatment resulted in a notable decrease in infarct volume, apoptosis and missteps compared with the model group. XNJ also exhibited improvements in neurological function, grip strength and motor time. The calcium content significantly reduced in XNJ group. The XNJ administration resulted in a reduction in the levels of proteins associated with ERS including CHOP, GRP78, Bax, caspase-12, caspase-9, and cleaved-caspase-3, but an increase of the Bcl-2/Bax ratio. Furthermore, the downregulation of mRNA expression of CHOP, GRP78, caspase-12, caspase-9, and caspase-3 was confirmed in both cultured neurons and rat model.

Conclusion

These findings suggest that XNJ may alleviate apoptosis by modulating the ERS-induced apoptosis pathway, making it a potential novel therapeutic approach for ischemic stroke.

Expression, Functional Polymorphism, and Diagnostic Values of MIAT rs2331291 and H19 rs217727 Long Non-Coding RNAs in Cerebral Ischemic Stroke Egyptian Patients

Cerebral ischemic stroke (CIS) is a severe cerebral vascular event. This research aimed to evaluate the role of single-nucleotide polymorphisms (SNPs) of the lncRNAs MIAT rs2331291 and H19 rs217727 and epigenetic methylation in the expression patterns of serum lncRNA H19 in CIS Egyptian patients. It included 80 CIS cases and 40 healthy subjects. Serum MIAT expression levels decreased, whereas serum H19 expression levels increased among CIS compared to controls. For MIAT rs2331291, there were significant differences in the genotypic and allelic frequencies between the CIS and healthy subjects at p = 0.02 and p = 0.0001, respectively. Our findings illustrated a significantly increased MIAT T/T genotype frequency in hypertensive CIS compared to non-hypertensive CIS at p = 0.004. However, H19 rs217727 gene frequency C/C was not significantly higher in non-hypertensive CIS than in hypertensive CIS. The methylation of the H19 gene promoter was significantly higher in CIS patients compared to healthy subjects. The level of MIAT was positively correlated with serum H19 in CIS. Receiver operating characteristics (ROC) analysis revealed that serum MIAT and H19 have a high diagnostic potential for distinguishing CIS subjects from healthy ones. In conclusion, the MIAT-rs2331291 polymorphism might serve as a novel potential indicator of CIS.

Apelin-13: A Protective Role in Vascular Diseases

Vascular disease is a common problem with high mortality all over the world. Apelin-13, a key subtype of apelin, takes part in many physiological and pathological responses via regulating many target genes and target molecules or participating in many signaling pathways. More and more studies have demonstrated that apelin-13 is implicated in the onset and progression of vascular disease in recent years. It has been shown that apelin-13 could ameliorate vascular disease by inhibiting inflammation, restraining apoptosis, suppressing oxidative stress, and facilitating autophagy. In this article, we sum up the progress of apelin-13 in the occurrence and development of vascular disease and offer some insightful views about the treatment and prevention strategies of vascular disease.

The regulatory effects of the apelin/APJ system on depression: A prospective therapeutic target

Depression is a debilitating neuropsychological disorder characterized by high incidence, high recurrence, high suicide, and high disability rates, which poses serious threats to human health and imposes heavy psychological and economic burdens on family and society. The pathogenesis of depression is extremely complex, and its etiology is multifactorial. Mounting evidence suggests that apelin and apelin receptor APJ, which compose the apelin/APJ system, are related to the development of depression. However, the specific mechanism is still unclear, and research in this area in human is still insufficient. Acceleration of research into the regulatory effects and underlying mechanisms of the apelin/APJ system in depression may identify attractive therapeutic targets and contribute to the development of novel intervention strategies against this devastating psychological disorder. In this review, we mainly discuss the regulatory effects of apelin/APJ system on depression and its potential therapeutic applications.

Exposure to copper induces endoplasmic reticulum (ER) stress-mediated apoptosis in chicken (Gallus gallus) myocardium

Copper (Cu), an omnipresent environmental pollutant, can cause potential harm to the public and ecosystems. In order to study the cardiotoxicity caused by Cu, molecular biology techniques were used to analyze the effect of Cu on ER stress-mediated cardiac apoptosis. In vivo investigation, 240 1-day-old chickens were fed with Cu (11, 110, 220, and 330 mg/kg) diet for 7 weeks. The consequence showed that high-Cu can induce ER stress and apoptosis in heart tissue. The vitro experiments, the Cu treatment for 24 h could provoke ultrastructural damage and upregulate the apoptosis rate. Meanwhile, GRP78, GRP94, eIF2α, ATF6, XBP1, CHOP, Bax, Bak1, Bcl2, Caspase-12 and Caspase-3 genes levels, and GRP78, GRP94 and Caspase-3 proteins levels were increased, which indicated that ER stress and apoptosis in cardiomyocytes. But the mRNA level of Bcl2 were decreased after Cu exposure. Conversely, Cu-induced ER stress-mediated apoptosis can be alleviated by treatment with 4-PBA. These findings generally showed that Cu exposure can contribute to ER stress-mediated apoptosis in chicken myocardium, which clarifies the important mechanism link between ER stress and apoptosis, and provides a new perspective for Cu toxicology.

Apelin-13 alleviates contrast-induced acute kidney injury by inhibiting endoplasmic reticulum stress

Contrast-induced acute kidney injury (CI-AKI) is a severe complication associated with significant morbidity and mortality, and effective therapeutic strategies are still lacking. Apelin is an endogenous physiological regulator with antioxidative, anti-inflammatory and antiapoptotic properties. However, the role of apelin-13 in CI-AKI remains unclear. In our study, we found that the protein expression levels of apelin were significantly downregulated in rat kidney tissues and HK-2 cells during contrast media treatment. Moreover, we explored the protective effect of apelin-13 on renal tubule damage using in vitro and in vivo models of CI-AKI. Exogenous apelin-13 ameliorated endoplasmic reticulum stress, reactive oxygen species and apoptosis protein expression in contrast media-treated cells and rat kidney tissues. Mechanistically, the downregulation of endoplasmic reticulum stress contributed critically to the antiapoptotic effect of apelin-13. Collectively, our findings reveal the inherent mechanisms by which apelin-13 regulates CI-AKI and provide a prospective target for the prevention of CI-AKI.

Elabela-apelin-12, 17, 36/APJ system promotes platelet aggregation and thrombosis via activating the PANX1-P2X7 signaling pathway

The elabela-apelin/angiotensin domain type 1 receptor-associated protein (APJ) system is an important regulator in certain thrombosis-related diseases such as atherosclerosis, myocardial infarction, and cerebral infarction. Our previous reports have revealed that apelin exacerbates atherosclerotic lesions. However, the relationship between the elabela-apelin/APJ system and platelet aggregation and atherothrombosis is unclear. The results of the present study demonstrate that elabela and other endogenous ligands such as apelin-12, -17, and -36 induce platelet aggregation and thrombosis by activating the pannexin1(PANX1)-P2X7 signaling pathway. Interestingly, the diuretic, spironolactone, a novel PANX1 inhibitor, alleviated elabela- and apelin isoforms-induced platelet aggregation and thrombosis. Significantly, two potential antithrombotic drugs were screened out by targeting APJ receptors, including the anti-HIV ancillary drug cobicistat and the traditional Chinese medicine monomer Schisandrin A. Both cobicistat and Schisandrin A abolished the effects of elabela and apelin isoforms on platelet aggregation, thrombosis, and cerebral infarction. In addition, cobicistat significantly attenuated thrombosis in a ponatinib-induced zebrafish trunk model. Overall, the elabela-apelin/APJ axis mediated platelet aggregation and thrombosis via the PANX1-P2X7 signaling pathway in vitro and in vivo. Blocking the APJ receptor with cobicistat/Schisandrin A or inhibiting PANX1 with spironolactone may provide novel therapeutic strategies against thrombosis.

Neuroprotective Roles of Apelin-13 in Neurological Diseases

Apelin is a natural ligand for the G protein-coupled receptor APJ, and the apelin/APJ system is widely distributed in vivo. Among the apelin family, apelin-13 is the major apelin isoform in the central nervous system and cardiovascular system, and is involved in the regulation of various physiopathological mechanisms such as apoptosis, neuroinflammation, angiogenesis, and oxidative stress. Apelin is currently being extensively studied in the nervous system, and apelin-13 has been shown to be associated with the onset and progression of a variety of neurological disorders, including stroke, neurodegenerative diseases, epilepsy, spinal cord injury (SCI), and psychiatric diseases. This study summarizes the pathophysiological roles of apelin-13 in the development and progression of neurological related diseases.

Feedback Interaction Between Apelin and Endoplasmic Reticulum Stress in the Rat Myocardium

ABSTRACT

Apelin is an endogenous active peptide, playing a crucial role in regulating cardiovascular homeostasis. This study aimed to investigate the interaction between apelin and endoplasmic reticulum stress (ERS). Tunicamycin (Tm) and dithiothreitol (DTT) were used to induce ERS in the ex vivo cultured myocardium of rats. Myocardial injury was determined by the activities of lactate dehydrogenase and creatine kinase-MB in the culture medium. The protein levels of an ERS-associated molecule, apelin, and its receptor angiotensin domain type 1 receptor-associated proteins (APJ) in the myocardium were determined by western blot analysis. The level of apelin in the culture medium was determined by enzyme immunoassay. Administration of Tm and DTT triggered ERS activation and myocardial injury, and led to a decrease in protein levels of apelin and APJ, in a dose-dependent manner. Integrated stress response inhibitor, an inhibitor of eukaryotic initiation factor 2α phosphorylation that is commonly used to prevent activation of protein kinase R-like ER kinase cascades, blocked ERS-induced myocardial injury and reduction of apelin and APJ levels. The ameliorative effect of integrated stress response inhibitor was partially inhibited by [Ala]-apelin-13, an antagonist of APJ. Furthermore, apelin treatment inhibited activation of the 3 branches of ERS induced by Tm and DTT in a dose-dependent manner, thereby preventing Tm-induced or DTT-induced myocardial injury. The negative feedback regulation between ERS activation and apelin/APJ suppression might play a critical role in myocardial injury. Restoration of apelin/APJ signaling provides a potential target for the treatment and prevention of ERS-associated tissue injury and diseases.

The Apelinergic System: Apelin, ELABELA, and APJ Action on Cell Apoptosis: Anti-Apoptotic or Pro-Apoptotic Effect?

The apelinergic system comprises two peptide ligands, apelin and ELABELA, and their cognate G-protein-coupled receptor, the apelin receptor APJ. Apelin is a peptide that was isolated from bovine stomach extracts; the distribution of the four main active forms, apelin-36, -17, -13, and pyr-apelin-13 differs between tissues. The mature form of ELABELA-32 can be transformed into forms called ELABELA-11 or -21. The biological function of the apelinergic system is multifaceted, and includes the regulation of angiogenesis, body fluid homeostasis, energy metabolism, and functioning of the cardiovascular, nervous, respiratory, digestive, and reproductive systems. This review summarises the mechanism of the apelinergic system in cell apoptosis. Depending on the cell/tissue, the apelinergic system modulates cell apoptosis by activating various signalling pathways, including phosphoinositide 3-kinase (PI3K), extracellular signal-regulated protein kinase (ERK1/2), protein kinase B (AKT), 5'AMP-activated protein kinase(AMPK), and protein kinase A (PKA). Apoptosis is critically important during various developmental processes, and any dysfunction leads to pathological conditions such as cancer, autoimmune diseases, and developmental defects. The purpose of this review is to present data that suggest a significant role of the apelinergic system as a potential agent in various therapies.

Mitochondrial unfolded protein response in ischemia-reperfusion injury

Mitochondrial unfolded protein response (UPRmt) is a mitochondrial stress response that activates the transcriptional program of mitochondrial chaperone proteins and proteases to keep protein homeostasis in mitochondria. Ischemia-reperfusion injury results in multiple severe clinical issues linked to high morbidity and mortality in various disorders. The pathophysiology and pathogenesis of ischemia-reperfusion injury are complex and multifactorial. Emerging evidence showed the roles of UPRmt signaling in ischemia-reperfusion injury. Herein, we discuss the regulatory mechanisms underlying UPRmt signaling in C. elegans and mammals. Furthermore, we review the recent studies into the roles and mechanisms of UPRmt signaling in ischemia-reperfusion injury of the heart, brain, kidney, and liver. Further research of UPRmt signaling will potentially develop novel therapeutic strategies against ischemia-reperfusion injury.

Receptor-Interacting Protein 3/Calmodulin-Dependent Kinase II/Proline-Rich Tyrosine Kinase 2 Pathway is Involved in Programmed Cell Death in a Mouse Model of Brain Ischaemic Stroke

Neuronal necroptosis and apoptosis are the most important pathways for programmed cell death after brain ischaemic stroke. Although apoptosis signalling pathways have been extensively studied, molecular mechanisms underlying necroptosis remain unclear. In this study, we found that receptor-interacting protein 3 (RIP3) deficiency reduced cerebral infarction volume, neurological deficits, and neuronal ultrastructural damage in a mouse model of brain ischaemic stroke by inhibiting programmed cell death. RIP3 deficiency inhibited the activation of both calmodulin-dependent kinase II (CaMKII) and proline-rich tyrosine kinase 2 (Pyk2) cascade, decreased the expression of classic necroptotic and apoptotic proteins, and ultimately decreased neuronal necroptosis and apoptosis. We further confirmed that RIP3 deficiency inhibited the decrease of mitochondrial membrane potential, the increase of calcium influx and reactive oxygen species (ROS) production. In addition, compared with WT primary cortical neurons, the decreased expression of CaMKII and Pyk2 was further verified in a Ripk3^-/- primary cortical neurons underlying oxygen and glucose deprivation/reoxygenation (OGD/R) model. In conclusion, we first identified that the RIP3/CaMKII/Pyk2 pathway is involved in programmed cell death after brain ischaemic stroke, which suggests it is a promising therapeutic target in ischaemia-induced neuronal injury.

Levels of Serum and Urine Catecholaminergic and Apelinergic System Members in Acute Ischemic Stroke Patients

Objective: To compare levels of catecholaminergic system members, renalase, cerebellin, and their substrates, epinephrine, norepinephrine, and dopamine, and apelinergic system members, apelin, elabela, and nitric oxide in the blood and urine of patients with acute ischemic stroke and healthy controls. Materials and Methods: 42 patients with acute ischemic stroke and 42 age and sex-matched healthy controls were included in the study. Blood and urine samples were collected simultaneously and within the first 24 hours after the onset of acute stroke clinical manifestations and were measured using an ELISA method. Results: The levels of serum and urine cerebellin, renalase, epinephrine, norepinephrine, dopamine, apelin, elebela, and nitric oxide were similar in ischemic stroke and in control groups (P>0.05). Strong correlations were found between renalase, cerebellin, and catecholamine levels in serum and urine (p

Casein kinase CK2 structure and activities in plants

Casein kinase CK2 is a highly conserved serine/threonine protein kinase and exists in all eukaryotes. It has been demonstrated to be widely involved in the biological processes of plants. The CK2 holoenzyme is a heterotetramer consisting of two catalytic subunits (α and/or α') and two regulatory subunits (β). CK2 in plants is generally encoded by multiple genes, with monomeric and oligomeric forms present in the tissue. Various subunit genes of CK2 have been cloned and characterized from Arabidopsis thaliana, tobacco, maize, wheat, tomato, and other plants. This paper reviews the structural features of CK2, provides a clear classification of its physiological functions and mechanisms of action, and elaborates on the regulation of CK2 activity to provide a knowledge base for subsequent studies of CK2 in plants.

The beneficial roles of apelin-13/APJ system in cerebral ischemia: Pathogenesis and therapeutic strategies

The incidence of cerebral ischemia has increased in the past decades, and the high fatality and disability rates seriously affect human health. Apelin is a bioactive peptide and the ligand of the G protein-coupled receptor APJ. Both are ubiquitously expressed in the peripheral and central nervous systems, and regulate various physiological and pathological process in the cardiovascular, nervous and endocrine systems. Apelin-13 is one of the subtypes of apelin, and the apelin-13/APJ signaling pathway protects against cerebral ischemia by promoting angiogenesis, inhibiting excitotoxicity and stabilizing atherosclerotic plaques. In this review, we have discussed the role of apelin-13 in the regulation of cerebral ischemia and the underlying mechanisms, along with the therapeutic potential of the apelin-13/APJ signaling pathway in cerebral ischemia.

Endoplasmic Reticulum Stress and the Unfolded Protein Response in Cerebral Ischemia/Reperfusion Injury

Ischemic stroke is an acute cerebrovascular disease characterized by sudden interruption of blood flow in a certain part of the brain, leading to serious disability and death. At present, treatment methods for ischemic stroke are limited to thrombolysis or thrombus removal, but the treatment window is very narrow. However, recovery of cerebral blood circulation further causes cerebral ischemia/reperfusion injury (CIRI). The endoplasmic reticulum (ER) plays an important role in protein secretion, membrane protein folding, transportation, and maintenance of intracellular calcium homeostasis. Endoplasmic reticulum stress (ERS) plays a crucial role in cerebral ischemia pathophysiology. Mild ERS helps improve cell tolerance and restore cell homeostasis; however, excessive or long-term ERS causes apoptotic pathway activation. Specifically, the protein kinase R-like endoplasmic reticulum kinase (PERK), activating transcription factor 6 (ATF6), and inositol-requiring enzyme 1 (IRE1) pathways are significantly activated following initiation of the unfolded protein response (UPR). CIRI-induced apoptosis leads to nerve cell death, which ultimately aggravates neurological deficits in patients. Therefore, it is necessary and important to comprehensively explore the mechanism of ERS in CIRI to identify methods for preserving brain cells and neuronal function after ischemia.

Cerebral Glucose Metabolism and Potential Effects on Endoplasmic Reticulum Stress in Stroke

Ischemic stroke is an extremely common pathology with strikingly high morbidity and mortality rates. The endoplasmic reticulum (ER) is the primary organelle responsible for conducting protein synthesis and trafficking as well as preserving intracellular Ca2⁺ homeostasis. Mounting evidence shows that ER stress contributes to stroke pathophysiology. Moreover, insufficient circulation to the brain after stroke causes suppression of ATP production. Glucose metabolism disorder is an important pathological process after stroke. Here, we discuss the relationship between ER stress and stroke and treatment and intervention of ER stress after stroke. We also discuss the role of glucose metabolism, particularly glycolysis and gluconeogenesis, post-stroke. Based on recent studies, we speculate about the potential relationship and crosstalk between glucose metabolism and ER stress. In conclusion, we describe ER stress, glycolysis, and gluconeogenesis in the context of stroke and explore how the interplay between ER stress and glucose metabolism contributes to the pathophysiology of stroke.

Molecular and cellular mechanisms of spastin in neural development and disease (Review)

Spastin is a microtubule (MT)‑severing enzyme identified from mutations of hereditary spastic paraplegia in 1999 and extensive studies indicate its vital role in various cellular activities. In the past two decades, efforts have been made to understand the underlying molecular mechanisms of how spastin is linked to neural development and disease. Recent studies on spastin have unraveled the mechanistic processes of its MT‑severing activity and revealed that spastin acts as an MT amplifier to mediate its remodeling, thus providing valuable insight into the molecular roles of spastin under physiological conditions. In addition, recent research has revealed multiple novel molecular mechanisms of spastin in cellular biological pathways, including endoplasmic reticulum shaping, calcium trafficking, fatty acid trafficking, as well as endosomal fission and trafficking. These processes are closely involved in axonal and dendritic development and maintenance. The current review presents recent biological advances regarding the molecular mechanisms of spastin at the cellular level and provides insight into how it affects neural development and disease.

Endovascular Stem Cell Therapy Post Stroke Rescues Neurons from Endoplasmic Reticulum Stress-Induced Apoptosis by Modulating Brain-Derived Neurotrophic Factor/Tropomyosin Receptor Kinase B Signaling

Ischemic stroke is devastating, with serious long-term disabilities affecting millions of people worldwide. Growing evidence has shown that mesenchymal stem cells (MSCs) administration after stroke provides neuroprotection and enhances the quality of life in stroke patients. Previous studies from our lab have shown that 1 × 10⁵ MSCs administered intra-arterially (IA) at 6 h post stroke provide neuroprotection through the modulation of inflammasome and calcineurin signaling. Ischemic stroke induces endoplasmic reticulum (ER) stress, which exacerbates the pathology. The current study intends to understand the involvement of brain-derived neurotrophic factor/tropomyosin receptor kinase B (BDNF/TrkB) signaling in preventing apoptosis induced by ER stress post stroke following IA MSCs administration. Ischemic stroke was induced in ovariectomized female Sprague Dawley rats. The MSCs were administered IA, and animals were sacrificed at 24 h post stroke. Infarct area, neurological deficit score, motor coordination, and biochemical parameters were evaluated. The expression of various genes and proteins was assessed. An inhibition study was also carried out to confirm the involvement of BDNF/TrkB signaling in ER stress-induced apoptosis. IA-administered MSCs improved functional outcomes, reduced infarct area, increased neuronal survival, and normalized biochemical parameters. mRNA and protein expression of ER stress markers were reduced, while those of BDNF and TrkB were increased. Reduction in ER stress-mediated apoptosis was also observed. The present study shows that IA MSCs administration post stroke provides neuroprotection and can modulate ER stress-mediated apoptosis via the BDNF/TrkB signaling pathway.

Emerging immune and cell death mechanisms in stroke: Saponins as therapeutic candidates

The complexity of the ischemic cascade is based on the integrated crosstalk of every cell type in the neurovascular unit. Depending on the features of the ischemic insult, several cell death mechanisms are triggered, such as apoptosis, necroptosis, ferroptosis/oxytosis, ETosis or pyroptosis, leading to reactive astrogliosis. However, emerging evidence demonstrates a dual role for the immune system in stroke pathophysiology, where it exerts both detrimental and also beneficial functions. In this review, we discuss the relevance of several cell death modalities and the dual role of the immune system in stroke pathophysiology. We also provide an overview of some emerging immunomodulatory therapeutic strategies, amongst which saponins, which are promising candidates that exert multiple pharmacological effects.

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Several cell death mechanisms coexist in stroke pathophysiology.

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Neurons are more vulnerable to necroptosis than glial cells.

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Inhibitors of receptor-interacting protein kinases and of ferroptosis induce neuroprotection.

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Saponins exert modulatory effects on inflammation and neuronal cell death in stroke.

Research Progress on Mechanism of Neuroprotective Roles of Apelin-13 in Prevention and Treatment of Alzheimer's Disease

Alzheimer's disease (AD) is the most common type of dementia. Currently, more than 50 million people live with dementia worldwide, and this number is expected to increase. Some of the typical pathological changes of AD include amyloid plaque, hyperphosphorylation of tau protein, secretion of inflammatory mediators, and neuronal apoptosis. Apelin is a neuroprotective peptide that is widely expressed in the body. Among members of apelin family, apelin-13 is the most abundant with a high neuroprotective function. Apelin-13/angiotensin domain type 1 receptor-associated proteins (APJ) system regulates several physiological and pathophysiological cell activities, such as apoptosis, autophagy, synaptic plasticity, and neuroinflammation. It has also been shown to prevent AD development. This article reviews the research progress on the relationship between apelin-13 and AD to provide new ideas for prevention and treatment of AD.

Apelin-13 attenuates injury following ischemic stroke by targeting matrix metalloproteinases (MMP), endothelin- B receptor, occludin/claudin-5 and oxidative stress

Oxidative stress, an adverse consequence of brain ischemia-reperfusion injury (IRI), activates matrix metalloproteinase enzymes which cause to destruction of extracellular matrix and tight junction proteins. Oxidative stress during stroke increases serum endothelin-1 and endothelin B receptor (ETBR) expression. Apelin-13, an endogenous peptide, is expressed in numerous tissues that regulate diverse physiological and pathological processes. This study aimed to investigate the effect of intravenous (IV) injection of apelin-13 on cerebral vasogenic edema due to brain IRI. Animals were divided into sham, ischemia, and treat groups. IRI model was induced by middle cerebral artery occlusion (MCAO) for 60 min followed by 23 h reperfusion. Apelin-13 was injected into the tail vein 5 min before reperfusion. Neurological defects were evaluated with longa test. Brain water content and BBB permeability were assessed according to cerebral dry-wet weight and brain Evans blue extraction. Malondialdehyde (MDA), superoxide dismutase (SOD), and catalase (CAT) were measured using the colorimetric method. Expression of occludin and claudin-5, matrix metalloproteinase- 2 and 9 (MMP-2 & 9) and, ETBR were evaluated using Western blot. Brain IRI was associated with BBB breakdowns and vasogenic edema. Apelin-13 significantly reduced BBB permeability and vasogenic edema. Apelin-13 significantly attenuated IRI-related oxidative stress. Apelin-13 decreased expression of mmp-2, 9 and ETBR, prevented from decrement of occludin and claudin-5 expersion, which protected BBB integrity and reduced vasogenic edema. In conclusion, our results have suggested that an IV injection of apelin-13 could somehow reduce vasogenic edema via targeting oxidative stress and ETBR expression.

CTRP1 Attenuates Cerebral Ischemia/Reperfusion Injury via the PERK Signaling Pathway

Cerebral ischemic stroke is one of the leading causes of death worldwide. Previous studies have shown that circulating levels of CTRP1 are upregulated in patients with acute ischemic stroke. However, the function of CTRP1 in neurons remains unclear. The purpose of this study was to explore the role of CTRP1 in cerebral ischemia reperfusion injury (CIRI) and to elucidate the underlying mechanism. Middle cerebral artery occlusion/reperfusion (MCAO/R) and oxygen-glucose deprivation/reoxygenation (OGD/R) models were used to simulate cerebral ischemic stroke in vivo and in vitro, respectively. CTRP1 overexpression lentivirus and CTRP1 siRNA were used to observe the effect of CTRP1 expression, and the PERK selective activator CCT020312 was used to activate the PERK signaling pathway. We found the decreased expression of CTRP1 in the cortex of MCAO/R-treated rats and OGD/R-treated primary cortical neurons. CTRP1 overexpression attenuated CIRI, accompanied by the reduction of apoptosis and suppression of the PERK signaling pathway. Interference with CTRP1 expression in vitro aggravated apoptotic activity and increased the expression of proteins involved in the PERK signaling pathway. Moreover, activating the PERK signaling pathway abolished the protective effects of CTRP1 on neuron injury induced by CIRI in vivo and in vitro. In conclusion, CTRP1 protects against CIRI by reducing apoptosis and endoplasmic reticulum stress (ERS) through inhibiting the PERK-dependent signaling pathway, suggesting that CTRP1 plays a crucial role in the pathogenesis of CIRI.

Retracted: Bone marrow mesenchymal stem cells-derived extracellular vesicles carrying microRNA-221-3p protect against ischemic stroke via ATF3

OBJECTIVE

We aim to explore the protective effect of bone marrow mesenchymal stem cells (BMSCs)-derived exosomal microRNA-221-3p (miR-221-3p) on ischemic stroke (IS) by targeting activating transcription factor 3 (ATF3).

METHODS

The middle cerebral artery occlusion (MCAO) mice model and oxygen-glucose deprivation (OGD) neuron model were established. Extracellular vesicles were isolated from BMSCs (BMSC-EVs) and transfected with altered miR-221-3p or ATF3 to treat the MCAO mice and OGD-treated neurons. MiR-221-3p and ATF3 expression were determined, and the contents of inflammatory factors were detected. The pathological changes and apoptosis in mice brain tissues were observed. In cellular experiments, the viability and apoptosis of OGD-treated neurons were evaluated. Binding relationship between miR-221-3p and ATF3 was determined.

RESULTS

MiR-221-3p was down-regulated and ATF3 was up-regulated in MCAO mice and OGD-treated neurons. BMSC-EVs and BMSC-EVs carrying up-regulated miR-221-3p attenuated inflammation, pathological changes and apoptosis in MCAO mice brain tissues, and also promoted viability and repressed apoptosis of OGD-treated neurons. ATF3 was verified as a target of miR-221-3p.

CONCLUSION

BMSC-EVs carrying miR-221-3p protect against IS by inhibiting ATF3. This study may be helpful for exploring therapeutic strategies of IS.

Apelin/APJ system: A novel therapeutic target for locomotor system diseases

Apelin is an endogenous ligand of G protein-coupled receptor APJ. Apelin/APJ system is widely expressed in abundant tissues, especially bone, joint and muscle tissue. This review focus on the effects of apelin/APJ system on locomotor system. An increasing number of evidence suggests that apelin/APJ system plays a crucial role in many physiological and pathological processes of locomotor system. Physiologically, apelin/APJ system promotes bone formation, muscle metabolism and skeletal muscle production. Pathologically, apelin/APJ system exacerbates osteoarthritis pathogenesis, whereas it alleviates osteoporosis. Besides, the level of apelin expression is regulated by different training modes, including continuous aerobic exercise, high-intensity interval training and resistance exercises. More importantly, exercise-induced apelin may be a potent pharmacological agent for the treatment of diseases and the regulation of physiological processes. Considering the pleiotropic effects of apelin on locomotor system, apelin/APJ system may be an important therapeutic target for locomotor system diseases.

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.

Protein kinase CK2: a potential therapeutic target for diverse human diseases

CK2 is a constitutively active Ser/Thr protein kinase, which phosphorylates hundreds of substrates, controls several signaling pathways, and is implicated in a plethora of human diseases. Its best documented role is in cancer, where it regulates practically all malignant hallmarks. Other well-known functions of CK2 are in human infections; in particular, several viruses exploit host cell CK2 for their life cycle. Very recently, also SARS-CoV-2, the virus responsible for the COVID-19 pandemic, has been found to enhance CK2 activity and to induce the phosphorylation of several CK2 substrates (either viral and host proteins). CK2 is also considered an emerging target for neurological diseases, inflammation and autoimmune disorders, diverse ophthalmic pathologies, diabetes, and obesity. In addition, CK2 activity has been associated with cardiovascular diseases, as cardiac ischemia-reperfusion injury, atherosclerosis, and cardiac hypertrophy. The hypothesis of considering CK2 inhibition for cystic fibrosis therapies has been also entertained for many years. Moreover, psychiatric disorders and syndromes due to CK2 mutations have been recently identified. On these bases, CK2 is emerging as an increasingly attractive target in various fields of human medicine, with the advantage that several very specific and effective inhibitors are already available. Here, we review the literature on CK2 implication in different human pathologies and evaluate its potential as a pharmacological target in the light of the most recent findings.

How can a traffic light properly work if it is always green? The paradox of CK2 signaling

CK2 is a constitutively active protein kinase that assuring a constant level of phosphorylation to its numerous substrates supports many of the most important biological functions. Nevertheless, its activity has to be controlled and adjusted in order to cope with the varying needs of a cell, and several examples of a fine-tune regulation of its activity have been described. More importantly, aberrant regulation of this enzyme may have pathological consequences, e.g. in cancer, chronic inflammation, neurodegeneration, and viral infection. Our review aims at summarizing our current knowledge about CK2 regulation. In the first part, we have considered the most important stimuli shown to affect protein kinase CK2 activity/expression. In the second part, we focus on the molecular mechanisms by which CK2 can be regulated, discussing controversial aspects and future perspectives.

A network map of apelin-mediated signaling

The apelin receptor (APLNR) is a class A (rhodopsin-like) G-protein coupled receptor with a wide distribution throughout the human body. Activation of the apelin/APLNR system regulates AMPK/PI3K/AKT/mTOR and RAF/ERK1/2 mediated signaling pathways. APLNR activation orchestrates several downstream signaling cascades, which play diverse roles in physiological effects, including effects upon vasoconstriction, heart muscle contractility, energy metabolism regulation, and fluid homeostasis angiogenesis. We consolidated a network map of the APLNR signaling map owing to its biomedical importance. The curation of literature data pertaining to the APLNR system was performed manually by the NetPath criteria. The described apelin receptor signaling map comprises 35 activation/inhibition events, 38 catalysis events, 4 molecular associations, 62 gene regulation events, 113 protein expression types, and 4 protein translocation events. The APLNR signaling pathway map data is made freely accessible through the WikiPathways Database ( https://www.wikipathways.org/index.php/Pathway:WP5067 ).

Down-Regulation of miR-181a-5p Prevents Cerebral Ischemic Injury by Upregulating En2 and Activating Wnt/β-catenin Pathway

PURPOSE

Cerebral ischemic injury contributes to severe dysfunction of the brain, which triggers extremely high mortality and disability. The role of microRNA (miR)-181a-5p is documented in cerebral ischemic injury. Therefore, this study intended to further figure out the mechanism of miR-181a-5p in cerebral ischemic injury.

METHODS

miR-181a-5p expression in middle cerebral artery occlusion (MCAO) mouse model, oxygen-glucose-deprivation/reoxygenation (OGD/R) N2a cell model, and serum from acute ischemic injury (ACI) patients was evaluated using reverse transcription quantitative polymerase chain reaction (RT-qPCR). Gain- and loss-of-function assays were implemented in MCAO mice and OGD/R-induced N2a cells. In mice, the cerebral infarction area was assessed with 2,3,5-triphenyltetrazolium chloride staining, the number of damaged neurons by Nissl staining, and apoptosis by TdT-mediated dUTP-biotin nick end-labeling staining. Moreover, N2a cell apoptosis and proliferation were determined with flow cytometry or 5-ethynyl-2'-deoxyuridine staining, respectively. The expression of En2 and Wnt/β-catenin pathway-related factors was determined with RT-qPCR and Western blot analysis. The targeting relationship between miR-181a-5p and En2 was evaluated by dual luciferase reporter gene assay.

RESULTS

miR-181a-5p was highly expressed in serum of ACI patients, MCAO mice, and OGD/R-induced N2a cells. En2, lowly expressed in MCAO mice, was targeted by miR-181a-5p, and miR-181a-5p down-regulation activated the Wnt/β-catenin pathway. Furthermore, miR-181a-5p inhibition or En2 overexpression reduced cerebral infarction area, the number of damaged neurons, and apoptosis in MCAO mice, and also diminished apoptosis and accelerated proliferation of OGD/R-induced N2a cells.

CONCLUSION

miR-181a-5p suppression activated Wnt/β-catenin pathway and sequentially attenuated cerebral ischemic injury by targeting En2.

Endoplasmic Reticulum Stress Is Involved in Glucocorticoid-Induced Apoptosis in PC12 Cells

Objective

The present study selected PC12 cells to construct a neuronal injury model induced by glucocorticoids (GC) in vitro, aiming to explore whether the endoplasmic reticulum stress (ERS) PKR-like endoplasmic reticulum kinase (PERK)-activating transcription factor 4 (ATF4)-C/EBP-homologous protein (CHOP) and inositol requirement 1 (IRE1)-apoptosis signal regulating kinase 1 (ASK1)-C-Jun amino-terminal kinase (JNK) signaling pathways are associated with the neuronal injury process induced by GC and provide morphological evidence.

Methods

Cell models with different doses and different durations of GC exposure were established. The viability of PC12 cells was detected by the CCK-8 assay, and the apoptosis rate of PC12 cells was detected by the flow cytometry assay. The expression of microtubule-associated protein 2 (Map2); glucocorticoids receptor (GR); cellular oncogene fos (C-fos); and ERS-related proteins, glucose-regulated protein 78 (GRP78), p-PERK, p-IRE1, ATF4, ASK1, JNK, and CHOP, was observed by immunofluorescence staining.

Results

The results of immunofluorescence staining showed that PC12 cells abundantly expressed Map2 and GR. The CCK-8 assay revealed that high-concentration GC exposure significantly inhibited the cell viability of PC12 cells. The flow cytometry assay indicated that high-concentration GC exposure significantly increased the apoptosis rate of PC12 cells. Immunofluorescence staining showed that GC exposure significantly increased the expression of C-fos, GRP78, p-PERK, p-IRE1, ATF4, ASK1, JNK, and CHOP. Treatment with ERS inhibitor 4-phenylbutyric acid (4-PBA) and GR inhibitor RU38486 attenuated related damage and downregulated the expression of the abovementioned proteins.

Conclusion

High-concentration GC exposure can significantly inhibit the viability of PC12 cells and induce apoptosis. PERK-ATF4-CHOP and IRE1-ASK1-JNK pathways are involved in the above damage process.

Mechanism of Action of Xiaoyao San in Treatment of Ischemic Stroke is Related to Anti-Apoptosis and Activation of PI3K/Akt Pathway

OBJECTIVE

The traditional Chinese medicine (TCM) formulation Xiaoyao San (XYS) has a good clinical effect in treating ischemic stroke (IS). We explored the mechanism and material basis of XYS in IS treatment.

METHODS

Network pharmacology was used to construct a network of XYS components and IS targets. R software was used to analyze the biological process and pathway analysis of the targets of XYS in IS treatment. In vitro, a model of apoptosis of PC12 cells induced by oxygen-glucose deprivation/reperfusion (OGD/R) was established to evaluate the neuroprotective effect of XYS and its influence on the expression of apoptotic protein-related genes. The affinity between the potentially active compounds in XYS and apoptotic proteins was evaluated by molecular docking.

RESULTS

XYS was shown to have 136 chemical components that exert potential anti-IS activity by acting on 175 proteins. Bioinformatics analysis showed that apoptosis and the phosphoinositide 3-kinase/protein kinase B (PI3K-Akt) signaling pathway were the main signaling pathways of XYS. In vitro experiments showed that XYS could improve the effect of OGD/R on PC12-cell activity (EC50 = 0.43 mg/mL) and inhibit apoptosis. The main mechanisms were related to the improvement of oxidative stress and regulation of apoptosis-related gene expression. Molecular docking showed that C22, C102 and other components in XYS had a strong affinity with apoptosis-related proteins.

CONCLUSION

Network pharmacology, in vitro experiments, and molecular docking were used, for the first time, to study the material basis and molecular mechanism of XYS in IS treatment from the perspective of multiple targets and multiple pathways. We provided a new approach for the future study of TCM formulations in the treatment of complex diseases.

Apelin ameliorated acute heart failure via inhibiting endoplasmic reticulum stress in rabbits

This study aimed to investigate whether inhibition of endoplasmic reticulum stress (ERS) mediated the ameliorative effect of apelin on acute heart failure (AHF). Rabbit model of AHF was induced by sodium pentobarbital. Cardiac dysfunction and injury were detected in the rabbit models of AHF, including impaired hemodynamic parameters and increased levels of CK-MB and cTnI. Apelin treatment dramatically improved cardiac impairment caused by AHF. ERS, indexed by increased GRP78, CHOP, and cleaved-caspase12 protein levels, was simultaneously attenuated by apelin. Apelin also could ameliorate increased protein levels of cleaved-caspase3 and Bax, and improved decreased protein levels of Bcl-2. Two common ERS stimulators, tunicamycin (Tm) and dithiothreitol (DTT) blocked the ameliorative effect of apelin on AHF. Phosphorylated Akt levels increased after apelin treatment in the rabbit models of AHF. The Akt signaling inhibitors wortmannin and LY294002 could block the cardioprotective effect of apelin, which could be relieved by ERS inhibitor 4-phenyl butyric acid (4-PBA). The aforementioned beneficial effects of apelin could all be blocked by APJ receptor antagonist F13A. 4-PBA and SC79, an Akt activator, can restore the ameliorative effect of apelin on AHF blocked by F13A. Apelin treatment dramatically ameliorated cardiac impairment caused by AHF, which might be mediated by APJ/Akt/ERS signaling pathway. These results will shed new light on AHF therapy.

The Pathology of Morphine-Inhibited Nerve Repair and Morphine-Induced Nerve Damage Is Mediated via Endoplasmic Reticulum Stress

Objective

The aim of the present study was to observe the pathological damage in the cerebral cortex of rats under acute morphine exposure (AME) and different durations of morphine dependence (MD), explore whether endoplasmic reticulum stress (ERS) is involved in the damage process, and assess the effect of morphine exposure on the proliferation and differentiation of newborn neurons.

Methods

Rat models of AME and different durations of MD were established. Pathological changes in cortical neurons were assessed by hematoxylin and eosin (H&E) and thionine staining. The expression of nuclear receptor-related factor 1 (NURR1) and that of the ERS-related proteins glucose-regulated protein 78 (GRP78), p-eIF2α, activating transcription factor 6 (ATF6), and CHOP in cortical neurons was assessed by immunohistochemistry. Double immunofluorescence labeling was used to observe the expression of Ki-67.

Results

H&E and thionine staining revealed that AME resulted in pyknotic changes in cortical neurons. With prolonged morphine exposure, the number of pyknotic neurons was significantly increased, the protein expression of Ki-67 and NURR1 was significantly decreased, and the protein levels of GRP78, p-eIF2α, ATF6, and CHOP showed marked dynamic changes.

Conclusion

AME and different durations of MD caused varying degrees of pathological changes in the cortex. Furthermore, the dynamic changes observed in ERS-related protein expression suggested that ERS may be associated with cortical injury. Different durations of MD inhibited the proliferation, differentiation, and migration of newborn neurons, which may affect the nerve repair process after injury.

Apelin-36 Protects HT22 Cells Against Oxygen-Glucose Deprivation/Reperfusion-Induced Oxidative Stress and Mitochondrial Dysfunction by Promoting SIRT1-Mediated PINK1/Parkin-Dependent Mitophagy

Oxidative stress and mitochondrial dysfunction are involved in cerebral ischemia/reperfusion injury-induced neuronal apoptosis. Mitophagy is the main method to eliminate dysfunctional mitochondria. Apelin-36, a type of neuropeptide, has been reported to exert protective effects in cerebral I/R (I/R) injury, but its precise mechanisms remain to be elucidated. To study the effects of Apelin-36 on oxidative stress and mitochondrial dysfunction in cerebral I/R injury, the oxygen-glucose deprivation/reperfusion (OGD/R) model with 6 h of ischemia and 6 h of reperfusion was established in HT22 cells. Results demonstrated that Apelin-36 protected against OGD/R injury by improving cell viability, decreasing the apoptotic cells ratio and increasing the ratio of Bcl-2/Bax. In addition, Apelin-36 treatment inhibited oxidative stress by downregulating the level of reactive oxygen species (ROS) and malondialdehyde (MDA) as well as the expression of inducible nitric oxide synthase (iNOS). And Apelin-36 also activated the level of superoxide dismutase (SOD) and glutathione (GSH). Mitochondrial apoptosis was also alleviated with Apelin-36 treatment detected by the mitochondrial membrane potential (MMP) and the expression of Cytochrome c (Cyt c), Cleaved caspase-9, and Cleaved caspase-3. Furthermore, the SIRT1-mediated PINK1/Parkin-dependent mitophagy was activated by Apelin-36 treatment with the downregulation of p62 and upregulation of LC3B-II and Beclin1. Both EX527 and Cyclosporine A (CsA), which are inhibitors of SIRT1 and mitophagy, markedly alleviated the inhibition of oxidative stress and mitochondrial dysfunction caused by Apelin-36. These findings suggest that SIRT1-mediated PINK1/Parkin-dependent mitophagy is involved in the neuroprotective effects of Apelin-36 on OGD/R-induced oxidative stress and mitochondrial dysfunction.

Induced dysregulation of ACE2 by SARS-CoV-2 plays a key role in COVID-19 severity

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), the cause of COVID-19, is reported to increase the rate of mortality worldwide. COVID-19 is associated with acute respiratory symptoms as well as blood coagulation in the vessels (thrombosis), heart attack and stroke. Given the requirement of angiotensin converting enzyme 2 (ACE2) receptor for SARS-CoV-2 entry into host cells, here we discuss how the downregulation of ACE2 in the COVID-19 patients and virus-induced shift in ACE2 catalytic equilibrium, change the concentrations of substrates such as angiotensin II, apelin-13, dynorphin-13, and products such as angiotensin (1–7), angiotensin (1–9), apelin-12, dynorphin-12 in the human body. Substrates accumulation ultimately induces inflammation, angiogenesis, thrombosis, neuronal and tissue damage while diminished products lead to the loss of the anti-inflammatory, anti-thrombotic and anti-angiogenic responses. In this review, we focus on the viral-induced imbalance between ACE2 substrates and products which exacerbates the severity of COVID-19. Considering the roadmap, we propose multiple therapeutic strategies aiming to rebalance the products of ACE2 and to ameliorate the symptoms of the disease.

Apelin-13 inhibits apoptosis and excessive autophagy in cerebral ischemia/reperfusion injury

Apelin-13 is a novel endogenous ligand for an angiotensin-like orphan G-protein coupled receptor, and it may be neuroprotective against cerebral ischemia injury. However, the precise mechanisms of the effects of apelin-13 remain to be elucidated. To investigate the effects of apelin-13 on apoptosis and autophagy in models of cerebral ischemia/reperfusion injury, a rat model was established by middle cerebral artery occlusion. Apelin-13 (50 μg/kg) was injected into the right ventricle as a treatment. In addition, an SH-SY5Y cell model was established by oxygen-glucose deprivation/reperfusion, with cells first cultured in sugar-free medium with 95% N₂ and 5% CO₂ for 4 hours and then cultured in a normal environment with sugar-containing medium for 5 hours. This SH-SY5Y cell model was treated with 10^–7 M apelin-13 for 5 hours. Results showed that apelin-13 protected against cerebral ischemia/reperfusion injury. Apelin-13 treatment alleviated neuronal apoptosis by increasing the ratio of Bcl-2/Bax and significantly decreasing cleaved caspase-3 expression. In addition, apelin-13 significantly inhibited excessive autophagy by regulating the expression of LC3B, p62, and Beclin1. Furthermore, the expression of Bcl-2 and the phosphatidylinositol-3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) pathway was markedly increased. Both LY294002 (20 μM) and rapamycin (500 nM), which are inhibitors of the PI3K/Akt/mTOR pathway, significantly attenuated the inhibition of autophagy and apoptosis caused by apelin-13. In conclusion, the findings of the present study suggest that Bcl-2 upregulation and mTOR signaling pathway activation lead to the inhibition of apoptosis and excessive autophagy. These effects are involved in apelin-13-induced neuroprotection against cerebral ischemia/reperfusion injury, both in vivo and in vitro. The study was approved by the Animal Ethical and Welfare Committee of Jining Medical University, China (approval No. 2018-JS-001) in February 2018.

Inhibition of endoplasmic reticulum stress mediates the ameliorative effect of apelin on vascular calcification

AIMS

Apelin is the endogenous ligand of G protein-coupled receptor APJ and play an important role in the regulation of cardiovascular homeostasis. We aimed to investigate whether apelin ameliorates vascular calcification (VC) by inhibition of endoplasmic reticulum stress (ERS).

METHODS AND RESULTS

VC model in rats was induced by nicotine plus vitamin D, while calcification of vascular smooth muscle cell (VSMC) was induced by beta-glycerophosphate. Alizarin Red S staining showed dramatic calcium deposition in the aorta of rats with VC, while calcium contents and ALP activity also increased in calcified aorta. Protein levels of apelin and APJ were decreased in the calcified aorta. In rats with VC, apelin treatment significantly ameliorated aortic calcification, compliance and stimulation of ERS. The ameliorative effect of apelin on VC and ERS was also observed in calcified VSMCs. ERS stimulator (tunicamycin or DTT) blocked the beneficial effect of apelin. Apelin treatment activated the PI3K/Akt signaling, blockage of which by wortmannin or inhibitor IV prevented the ameliorative effect of apelin, while ERS inhibitor 4-PBA rescued the blockade effect of wortmannin. Akt-induced GSK inhibition prevented the phosphorylation of PERK and IRE1, and the activation of these two major ERS branches. F13A blocked the ameliorative effect of apelin on VC and ERS, which was reversed by treatment with 4-PBA or Akt activator SC79 CONCLUSIONS: Apelin ameliorated VC by binding to APJ and then prevented ERS activation by stimulating Akt signaling. These results might provide new target for therapy and prevention of VC.

Ghrelin mitigates MPP+-induced cytotoxicity: Involvement of ERK1/2-mediated Nrf2/HO-1 and endoplasmic reticulum stress PERK signaling pathway

Parkinson's disease (PD) is a common progressive and multifactorial neurodegenerative disease. Current pharmacological therapies for PD are inadequate and often accompanied by serious side effects. In search of neuroprotective agents being considered to be beneficial to PD therapy. Ghrelin confers neuroprotective effect in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned PD model, but the underlying mechanism remains not fully elucidated. Here, we utilized human neuroblastoma SH-SY5Y cells exposed to MPP⁺ as a PD model to investigate the underlying mechanism of Ghrelin. In our present work, cell viability, cell apoptosis, oxidative stress-related indicators, and the level of Nrf2, HO-1, PERK, eIF2α, ATF4, CHOP, and ERK1/2 were examined. The results showed that Ghrelin attenuated MPP⁺-induced change of cell viability, apoptosis, coupled with decreased Cytochrome c, caspase-9, and caspase-3 expressions. Consistently, Ghrelin suppressed MPP⁺-induced oxidative stress. Moreover, Ghrelin markedly enhanced Nrf2 expression and nuclear accumulation as well as HO-1 induction. Further investigations showed that Ghrelin significantly inhibited the endoplasmic reticulum stress PERK-eIF2α-ATF4-CHOP pathway. Interestingly, we then found that Ghrelin promoted phosphorylation of ERK1/2, and pharmacological inhibition of ERK signaling abolished the cytoprotective effect of Ghrelin. Furthermore, we also found promoting the activation of the Nrf2/ HO-1 pathway and suppressing of the PERK pathway were mediated by ERK1/2. These findings provided novel insights into the underlying mechanisms of Ghrelin exerted protective effect, suggesting its potential as a novel therapeutic strategy against PD.

Synthesis of Novel Aryloxyethylamine Derivatives and Evaluation of Their in Vitro and in Vivo Neuroprotective Activities

A series of aryloxyethylamine derivatives were designed, synthesized and evaluated for their biological activity. Their structures were confirmed by ¹ H-NMR, ¹³ C-NMR, FT-IR and HR-ESI-MS. The preliminary screening of neuroprotection of compounds in vitro was detected by MTT, and the anti-ischemic activity in vivo was tested using bilateral common carotid artery occlusion in mice. Most of these compounds showed potential neuroprotective effects against the glutamate-induced cell death in differentiated rat pheochromocytoma cells (PC12 cells), especially for (4-fluorophenyl){1-[2-(4-methoxyphenoxy)ethyl]piperidin-4-yl}methanone, {1-[2-(4-methoxyphenoxy)ethyl]piperidin-4-yl}(4-methoxyphenyl)methanone, (4-bromophenyl){1-[2-(4-methoxyphenoxy)ethyl]piperidin-4-yl}methanone, {1-[2-(4-chlorophenoxy)ethyl]piperidin-4-yl}(4-chlorophenyl)methanone, (4-chlorophenyl)(1-{2-[(naphthalen-2-yl)oxy]ethyl}piperidin-4-yl)methanone, (4-chlorophenyl){1-[2-(4-methoxyphenoxy)ethyl]piperidin-4-yl}methanone and {1-[2-(4-bromophenoxy)ethyl]piperidin-4-yl}(4-chlorophenyl)methanone, which exhibited potent protection of PC12 cells at three doses (0.1, 1.0, 10 μM). Compounds (4-fluorophenyl){1-[2-(4-methoxyphenoxy)ethyl]piperidin-4-yl}methanone, (4-fluorophenyl){1-[2-(naphthalen-2-yloxy)ethyl]piperidin-4-yl}methanone, {1-[2-(4-methoxyphenoxy)ethyl]piperidin-4-yl}(4-methoxyphenyl)methanone and {1-[2-(4-chlorophenoxy)ethyl]piperidin-4-yl}(4-chlorophenyl)methanone possessed the significant prolongation of the survival time of mice subjected to acute cerebral ischemia and decreased the mortality rate at all five doses tested (200, 100, 50, 25, 12.5 mg/kg) and had significant neuroprotective activity. In addition, (4-fluorophenyl){1-[2-(4-methoxyphenoxy)ethyl]piperidin-4-yl}methanone, {1-[2-(4-methoxyphenoxy)ethyl]piperidin-4-yl}(4-methoxyphenyl)methanone and {1-[2-(4-chlorophenoxy)ethyl]piperidin-4-yl}(4-chlorophenyl)methanone possessed outstanding neuroprotection in vitro and in vivo. These compounds can be used as a promising neuroprotective agents for future development of new anti-ischemic stroke agents. Basic structure-activity relationships are also presented.

Endoplasmic reticulum stress mediates osteocyte death under oxygen-glucose deprivation in vitro

As a vascularized organ, bone is known to be susceptible to ischemia. Ischemic osteonecrosis or skeletal unloading lead to ischemia in bone microenvironment that causes osteocytes to suffer hypoxia and nutrition deprivation.

OBJECTIVE

To explore the effects of Oxygen-glucose deprivation (OGD) on osteocytes and the potential mechanism.

METHODS

OGD model was established in cultured MLO-Y4 cell. Cell damage, intracellular oxidative stress and cell apoptosis were detected at different OGD times (0, 2, 4, 8, 12, 24 h), and the changes in endoplasmic reticulum (ER) stress-related indicators were observed. Furthermore, cells were treated with 4-phenylbutyrate sodium (4-PBA) to inhibit ER stress, and cell damage and oxidative stress level were detected.

RESULTS

The cell viability under OGD exhibited a significantly reduced in a time-dependent manner, and the level of intracellular reactive oxygen species (ROS) were increased, cell apoptosis and ER stress was induced. Inhibition of ER stress can reduce cell death and intracellular ROS levels.

CONCLUSION

Our study demonstrated that ER stress regulates OGD-induced apoptotic cell death in MLO-Y4 cells via intracellular ROS.

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.

(-)-Clausenamide alleviated ER stress and apoptosis induced by OGD/R in primary neuron cultures

OBJECTIVE

The endoplasmic reticulum stress (ERS) and ERS-related neuronal apoptosis contribute to the cerebral ischemia/reperfusion (I/R) injury. (-)-Clausenamide has been reported to be nootropic and improve learning and memory in amnesia animal models. However, whether (-)-Clau could protect neurons from ischemic injury and the possible mechanism needed further study. The present study aimed to explore the effects of (-)-Clau on primary cortical neurons treated with oxygen-glucose deprivation/reoxygenation (OGD/R).

METHODS

Rat primary cortical neurons were used to set up an injury model of OGD/R which imitated the clinical I/R injury. Cell viability and apoptosis were measured by CCK-8 assay, LDH detection and TUNEL staining, respectively. The activation of GRP78/eIF2α-ATF4-CHOP signaling pathway, one of the three branches of ERS, and cleaved caspase-3, the apoptotic marker, were assessed by western blotting.

RESULTS

OGD/R induced activation of GRP78/eIF2α-ATF4-CHOP signaling pathway. (-)-Clau significantly attenuated OGD/R-induced decrease in the cellular viability and the activation of GRP78, eIF2α, ATF4 and CHOP. To further confirm the effect of (-)-Clau on OGD/R-induced ERS activation, the ERS inducer Tunicamycin (TM) was applied. TM significantly abolished (-)-Clau's protective effect against ERS and neuronal apoptosis, indicating that the protective effect of (-)-Clau was dependent on inhibiting ERS.

CONCLUSIONS

The present work demonstrated for the first time that (-)-Clau could reverse the activation of GRP78/eIF2α-ATF4-CHOP branch, thus inhibited ERS and the subsequent apoptosis induced by OGD/R and promoted cell viability in vitro. (-)-Clau could serve as a promising therapeutic agent in the treatment for ischemic stroke in the future.

ABBREVIATIONS

ATF4: activating transcription factor-4; ATF6: activating transcription factor-6; CHOP: transcriptional induction of CCAAT/enhancer binding protein homologous protein; (-)-Clau: 3-hydroxy-4-phenyl-5a-hydroxybenzylN-methyl-g-lactam; eIF2α: eukaryotic initiation factor 2α; ER: endoplasmic reticulum; ERS: endoplasmic reticulum stress; GRP78: 78-kDa glucose regulated protein; I/R: ischemia/reperfusion; IRE1: inositol requiring enzyme-1; JNK: c-Jun N-terminal kinase; OGD/R: oxygen-glucose deprivation/reoxygenation; PERK: double-stranded RNA-dependent protein kinase-like ER kinase; TM: Tunicamycin; UPR: unfolded protein response.

Inhibition of IL-32 Expression Ameliorates Cerebral Ischemia-Reperfusion Injury via the NOD/MAPK/NF-κB Signaling Pathway

Cerebral ischemia represents a major cause of disability, yet its precise mechanism remains unknown. In addition, ischemia-reperfusion injury which occurs during the blood recovery process increases the risk of mortality, and is not adequately addressed with current treatment. To improve therapeutic options, it is important to explore the vital substances that play a pivotal role in ischemia-reperfusion injury. This study is the first to investigate the role of IL-32, a vital pro-inflammatory factor, in models of cerebral ischemia-reperfusion injury. The results showed that IL-32 was highly expressed in both in vivo and in vitro models. The proteins of the NOD/MAPK/NF-κB pathway were also up-regulated, indicating a potential signaling pathway mechanism. Inhibition of IL-32 and blocking of the NOD/MAPK/NF-κB pathway increased cell survival, decreased the level of inflammatory factors and inflammasomes, and attenuated nitrosative stress. Taken together, the results show that inhibition of IL-32 expression ameliorates cerebral ischemia-reperfusion injury via the NOD/MAPK/NF-κB signaling pathway. The findings in this study reveal that IL-32 is a vital target of ischemia-reperfusion injury, providing a new avenue for treatment development.