A novel function of claudin-5 in maintaining the structural integrity of the heart and its implications in cardiac pathology.

This study aims to investigate the role of claudin-5 (Cldn5) in cardiac structural integrity. Proteomic analysis was performed to screen the protein profiles in enlarged left atrium from atrial fibrillation (AF) patients. Cldn5 shRNA adeno-associated virus (AAV) or siRNA was injected into the mouse left ventricle or added into HL1 cells respectively to knockdown Cldn5 in cardiomyocytes to observe whether the change of Cldn5 influences cardiac morphology and function, and affects those protein expressions stem from the proteomic analysis. Mitochondrial density and membrane potential were also measured by Mitotracker staining and JC-1 staining under the confocal microscope in HL1 cells. Cldn5 was reduced in cardiomyocytes from the left atrial appendage of AF patients compared to non-AF donors. Proteomic analysis showed 83 proteins were less abundant and 102 proteins were more abundant in AF patients. KEGG pathway analysis showed less abundant CACNA2D2, CACNB2, MYL2 and MAP6 were highly associated with dilated cardiomyopathy. Cldn5 shRNA AAV injection caused severe cardiac atrophy, dilation and myocardial dysfunction in mice. The decreases in mitochondrial numbers and mitochondrial membrane potentials in HL1 cells were observed after Cldn5 knockdown. We demonstrated for the first time the mechanism of Cldn5 downregulation-induced myocyte atrophy and myocardial dysfunction might be associated with the downregulation of CACNA2D2, CACNB2, MYL2 and MAP6, and mitochondrial dysfunction in cardiomyocytes.

Galangin Attenuates Myocardial Ischemic Reperfusion-Induced Ferroptosis by Targeting Nrf2/Gpx4 Signaling Pathway.

Purpose: Myocardial ischemic reperfusion injury (MIRI) is a crucial clinical problem globally. The molecular mechanisms of MIRI need to be fully explored to develop new therapeutic methods. Galangin (Gal), which is a natural flavonoid extracted from Alpinia Officinarum Hance and Propolis, possesses a wide range of pharmacological activities, but its effects on MIRI remain unclear. This study aimed to determine the pharmacological effects of Gal on MIRI. Methods: C57BL/6 mice underwent reperfusion for 3 h after 45 min of ischemia, and neonatal rat cardiomyocytes (NRCs) subjected to hypoxia and reoxygenation (HR) were cultured as in vivo and in vitro models. Echocardiography and TTC-Evans Blue staining were performed to evaluate the myocardial injury. Transmission electron microscope and JC-1 staining were used to validate the mitochondrial function. Additionally, Western blot detected ferroptosis markers, including Gpx4, FTH, and xCT. Results: Gal treatment alleviated cardiac myofibril damage, reduced infarction size, improved cardiac function, and prevented mitochondrial injury in mice with MIRI. Gal significantly alleviated HR-induced cell death and mitigated mitochondrial membrane potential reduction in NRCs. Furthermore, Gal significantly inhibited ferroptosis by preventing iron overload and lipid peroxidation, as well as regulating Gpx4, FTH, and xCT expression levels. Moreover, Gal up-regulated nuclear transcriptive factor Nrf2 in HR-treated NRCs. Nrf2 inhibition by Brusatol abolished the protective effect of Gal against ferroptosis. Conclusion: This study revealed that Gal alleviates myocardial ischemic reperfusion-induced ferroptosis by targeting Nrf2/Gpx4 signaling pathway.

Research progress on activation transcription factor 3: A promising cardioprotective molecule.

Activation transcription factor 3 (ATF3), a member of the ATF/cyclic adenosine monophosphate response element binding family, can be induced by a variety of stresses. Numerous studies have indicated that ATF3 plays multiple roles in the development and progression of cardiovascular diseases, including atherosclerosis, hypertrophy, fibrosis, myocardial ischemia-reperfusion, cardiomyopathy, and other cardiac dysfunctions. In past decades, ATF3 has been demonstrated to be detrimental to some cardiac diseases. Current studies have indicated that ATF3 can function as a cardioprotective molecule in antioxidative stress, lipid metabolic metabolism, energy metabolic regulation, and cell death modulation. To unveil the potential therapeutic role of ATF3 in cardiovascular diseases, we organized this review to explore the protective effects and mechanisms of ATF3 on cardiac dysfunction, which might provide rational evidence for the prevention and cure of cardiovascular diseases.

Compound Danshen Dripping Pills pretreatment protects the heart from ischemia/reperfusion injury by enhancing autophagic flux

Abstract Compound Danshen Dripping Pills (CDDPs) have been used in clinical treatment to protect the heart from ischemia/reperfusion (IR) injury for many years. However, the underlying mechanism implicated in the protective effects remains to be explored. Here, we determined the effects of CDDPs in Sprague-Dawley rats with the IR model. Cardiac function in vivo was assessed by echocardiography. Transmission electron microscopy, histological and immunohistochemical techniques, Western blotting and recombinant adeno-associated virus 9 transfection were used to illustrate the effects of CDDPs on IR and autophagy. Our results showed that pretreatment with CDDPs decreased the level of serum myocardial enzymes and infarct size in rats after IR. Apoptosis evaluation showed that CDDPs significantly ameliorated the cardiac apoptosis level after IR. Meanwhile, CDDPs pretreatment increased myocardial autophagic flux, with upregulation of LC3B, downregulation of p62, and increased autophagosomes and autolysosomes. Moreover, the autophagic flux inhibitor chloroquine could increase IR injury, while CDDPs could partially reverse the effects. Furthermore, our results showed that the activation of AMPK/mTOR was involved in the cardioprotective effect exerted by CDDPs. Herein, we suggest that CDDPs partially protect the heart from IR injury by enhancing autophagic flux through the activation of AMPK/mTOR.

A novel function of ATF3 in suppression of ferroptosis in mouse heart suffered ischemia/reperfusion.

INTRODUCTION: Ferroptosis, a newly identified type of programmed cell death type, has been proven to contribute to the progression of myocardial ischemia/reperfusion (I/R) injury. However, little is known about ferroptosis regulation in I/R injury. OBJECTIVES: We identified activating transcription factor 3 (ATF3) as a vital regulator of I/R induced ferroptosis and investigated the effects and potential mechanism of ATF3 in cardiac ferroptosis. METHODS: In this study, the dynamic RNA-sequencing (RNA-seq) analysis were performed on mouse hearts exposed to different I/R schedules to identify that ATF3 represents an important modulatory molecule in myocardial I/R injury. Then knockout, rescue and overexpression methods were used in mice and neonatal mouse cells (NMCs) to illustrate the effect of ATF3 on myocardial I/R injury. Loss/gain of function techniques were used both in vivo and in vitro to explore the effects of ATF3 on ferroptosis in I/R injury. Furthermore, chromatin immunoprecipitation sequence (ChIP-seq) analysis was performed in the AC16 human cardiomyocyte cell line to investigate potential genes regulated by ATF3. RESULTS: ATF3 expression reached highest level at early stage of reperfusion, knockout of ATF3 significantly aggravated I/R injury, which could be rescued by ATF3 re-expression. Knockout and the re-expression of ATF3 changed the transcription levels of multiple ferroptosis genes. In addition, results showed that overexpression of ATF3 inhibits cardiomyocyte ferroptosis triggered by erastin and RSL3. Lastly, ChIP-seq and dual luciferase activity analysis revealed ATF3 could bind to the transcription start site of Fanconi anaemia complementation group D2 (FANCD2) and increased the FANCD2 promoter activity. Furthermore, we first demonstrated that overexpression of FANCD2 exerts significant anti-ferroptosis and cardioprotective effect on AC16 cell H/R injury. CONCLUSION: ATF3 inhibits cardiomyocyte ferroptotic death in I/R injury, which might be related with regulating FANCD2. Our study provides new insight into the molecular target for the therapy of myocardial I/R injury.

[Effect of Gegen Qinlian Decoction on cardiac diastolic function of diabetic mice with damp-heat syndrome].

This study was designed to explore the effect and mechanism of Gegen Qinlian Decoction(GQD) on cardiac function of diabetic mice with damp-heat syndrome. The db/db diabetic mice were exposed to the damp-heat environment test chamber for inducing the damp-heat syndrome. Forty-eight six-week-old db/db mice were randomly divided into six groups, namely the db/db diabetic model group, db/db diabetic mouse with damp-heat syndrome(db/db-dh) group, db/db diabetic mouse with damp-heat syndrome treated with low-dose GQD(db/db-dh+GQD-L) group, db/db-dh+GQD-M(medium-dose) group, db/db-dh+GQD-H(high-dose) group, and db/db-dh+lipro(liprostatin-1, the inhibitor of ferroptosis) group, with eight six-week-old db/m mice classified into the control group. The results showed that mice presented with the damp-heat syndrome after exposure to the "high-fat diet" and "damp-heat environment", manifested as the elevated fasting blood glucose, reduced food intake, low urine output, diarrhea, listlessness, loose and coarse hair, and dark yellow and lusterless fur. However, the intragastric administration of the high-dose GQD for 10 weeks ameliorated the above-mentioned symptoms, inhibited myocardial hypertrophy and fibrosis, and improved the cardiac diastolic function of db/db-dh mice. qPCR suggested that GQD regulated the expression of ferroptosis-related genes, weakened the lipid peroxidation in the myocardium, and up-regulated glutathione peroxidase 4(GPX4) expression in comparison with those in the db/db-dh group. At the same time, the ferroptosis inhibitor liprostatin-1 significantly improved the cardiac function and reversed the cardiac remodeling of db/db-dh mice. It can be concluded that the damp-heat syndrome may aggravate myocardial ferroptosis and accelerate cardiac remodeling of db/db mice, thus leading to diastolic dysfunction. GQD is able to improve cardiac remodeling and diastolic function in diabetic mice with damp-heat syndrome, which may be related to its inhibition of myocardial ferroptosis.

A Novel Role of Claudin-5 in Prevention of Mitochondrial Fission Against Ischemic/Hypoxic Stress in Cardiomyocytes.

BACKGROUND: Downregulation of claudin-5 in the heart is associated with the end-stage heart failure. However, the underlying mechanism ofclaudin-5 is unclear. Here we investigated the molecular actions of claudin-5 in perspective of mitochondria in cardiomyocytes to better understand the role of claudin-5 in cardioprotection during ischemia. METHODS: Myocardial ischemia/reperfusion (I/R; 30 min/24 h) and hypoxia/reoxygenation (H/R; 24 h/4 h) were used in this study. Confocal microscopy and transmission electron microscope (TEM) were used to observe mitochondrial morphology. RESULTS: Claudin-5 was detected in murine heart tissue and neonatal rat cardiomyocytes (NRCM). Its protein level was severely decreased after myocardial I/R or H/R. Confocal microscopy showedclaudin-5 presented in the mitochondria of NRCM. H/R-induced claudin-5 downregulation was accompanied by mitochondrial fragmentation. The mitofusin 2 (Mfn2) expressionwas dramatically decreased while the dynamin-related protein (Drp) 1 expression was significantly increased after H/R. The TEM indicatedH/R-induced mitochondrial swelling and fission. Adenoviral claudin-5 overexpression reversed these structural disintegration of mitochondria. The mitochondria-centered intrinsic pathway of apoptosis triggered by H/R and indicated by the cytochrome c and cleaved caspase 3 in the cytoplasm of NRCMs was also reduced by overexpressing claudin-5. Claudin-5 overexpression in mouse heart also significantly decreased cleaved caspase 3 and the infarct size in ischemic heart with improved systolic function. CONCLUSION: We demonstrated for the first time the presence of claudin-5 in the mitochondria in cardiomyocytes and provided the firm evidence for the cardioprotective role of claudin-5 in the preservation of mitochondrial dynamics and cell fate against hypoxia- or ischemia-induced stress.

Cardioprotection of pharmacological postconditioning on myocardial ischemia/reperfusion injury.

Acute myocardial infarction is associated with high rates of morbidity and mortality and can cause irreversible myocardial damage. Timely reperfusion is critical to limit infarct size and salvage the ischemic myocardium. However, reperfusion may exacerbate lethal tissue injury, a phenomenon known as myocardial ischemia/reperfusion (I/R) injury. Pharmacological postconditioning (PPC), a strategy involving medication administration before or during the early minutes of reperfusion, is more efficient and flexible than preconditioning or ischemic conditioning. Previous studies have shown that various mechanisms are involved in the effects of PPC. In this review, we summarize the relative effects and potential underlying mechanisms of PPC to provide a foundation for future research attempting to develop novel treatments against myocardial I/R injury.

Neuregulin­1, a microvascular endothelial­derived protein, protects against myocardial ischemia­reperfusion injury (Review).

As regards acute myocardial infarction, great success has been achieved in therapies that reduce the effects of myocardial ischemic injury, while few interventions have achieved satisfactory outcomes for myocardial ischemia­reperfusion (IR) injury. Thus, new research is urgently required to achieve breakthroughs in promising treatments. Neuregulin­1 (NRG­1), which is an endothelium­derived protein and the ligand of ErbB receptors, exerts cardioprotective effects and is rapidly upregulated during IR. NRG­1/ErbB activates several downstream signaling pathways in response to myocardial IR injury. Previous studies have revealed the protective effects of NRG­1 during heart failure, and numerous experiments have explored the mechanisms underlying the NRG­1­induced cardioprotective effects against myocardial IR injury. In the present review, the progress made in the research of NRG­1 as a cardioprotective agent during IR and related conditionings is summarized. Furthermore, the potential benefits of NRG­1 against myocardial IR injury are listed with the prospective use of NRG­1 in clinical applications.

Resveratrol pretreatment alleviates myocardial ischemia/reperfusion injury by inhibiting STIM1-mediated intracellular calcium accumulation.

Previous studies have shown that stromal interaction molecule1 (STIM1)-mediated store-operated Ca2+ entry (SOCE) contributes to intracellular Ca2+ accumulation in H9C2 cells subjected to hypoxia/reoxygenation(H/R) injury. The aim of the present study was to investigate the effect of resveratrol on STIM1-mediated intracellular Ca2+ accumulation and subsequent cell death in the context of myocardial ischemia/reperfusion (I/R) injury. C57 BL/6 mice were fed with either saline or resveratrol (50 mg/kg daily for 2 weeks) and then subjected to myocardial I/R injury. TTC/Evans Blue staining and TUNEL assay were performed to quantify the infarct size and apoptosis index. The cardiac function was evaluated by echocardiography. Neonatal rat ventricular cardiomyocytes (NRVCs) underwent hypoxia/reoxygenation (H/R) to establish the in vitro model. To achieve over-expression, NRVCs were transfected with STIM1-adenovirus vector. Apoptosis was analyzed by TUNEL assay. Cell viability was measured using MTS assay and cell necrosis was determined by LDH release assay. Intracellular Ca2+ concentration was detected by laser scanning confocal microscopy using a Fluo-3AM probe. Resveratrol significantly reduced apoptosis, decreased infarct size, and improved cardiac function in mice subjected to myocardial I/R injury. In NRVCs, resveratrol also downregulated STIM1 expression accompanied by decreased intracellular Ca2+ accumulation elicited by H/R injury. In addition, resveratrol reduced cell apoptosis, upregulated the Bcl-2, decreased Bax, and cleaved caspase-3 expression. Furthermore, the effects of resveratrol on STIM1-mediated intracellular Ca2+ accumulation, apoptotic proteins, and H/R-induced cell injury were exacerbated by STIM1 over-expression and were partly abolished by SOCE inhibitor SKF96365 in NRVCs in vitro. Our findings demonstrate that resveratrol exerts anti-apoptotic activity and improves cardiac functional recovery following myocardial I/R by inhibiting STIM1-induced intracellular Ca2+ accumulation.

Honokiol post-treatment ameliorates myocardial ischemia/reperfusion injury by enhancing autophagic flux and reducing intracellular ROS production.

Honokiol (HKL) is a natural low-molecular-weight biphenolic compound derived from the bark of magnolia trees. Previous studies indicate that HKL exerts potent cardioprotective effects on ischemia/reperfusion (I/R) injury; however, evidence of the further relationship between HKL posttreatment and myocardial I/R injury has not been clearly found. In our study, we explored the protective effect of HKL post treatment on myocardial I/R injury in C57BL/6 mice. We also demonstrated that HKL significantly reduced cellular reactive oxygen species production and attenuated mitochondrial damage in neonatal rat cardiomyocytes exposed to hypoxia/reoxygenation (H/R). In addition, HKL was found to enhance autophagy during I/R or H/R; these effects could be partially blocked by the autophagic flux inhibitor chloroquine. Moreover, our results suggested that enhanced autophagic flux is associated with the Akt signaling pathway. Collectively, our results indicate that HKL posttreatment alleviates myocardial I/R injury and suggest a critical cardioprotective role of HKL in promoting autophagic flux.

Spermidine-enhanced autophagic flux improves cardiac dysfunction following myocardial infarction by targeting the AMPK/mTOR signalling pathway.

BACKGROUND AND PURPOSE: Spermidine, a natural polyamine, is abundant in mammalian cells and is involved in cell growth, proliferation, and regeneration. Recently, oral spermidine supplements were cardioprotective in age-related cardiac dysfunction, through enhancing autophagic flux. However, the effect of spermidine on myocardial injury and cardiac dysfunction following myocardial infarction (MI) remains unknown. EXPERIMENTAL APPROACH: We determined the effects of spermidine in a model of MI, Sprague-Dawley rats with permanent ligation of the left anterior descending artery, and in cultured neonatal rat cardiomyocytes (NRCs) exposed to angiotensin II (Ang II). Cardiac function in vivo was assessed with echocardiography. In vivo and in vitro studies used histological and immunohistochemical techniques, along with western blots. KEY RESULTS: Spermidine improved cardiomyocyte viability and decreased cell necrosis in NRCs treated with angiotensin II. In rats post-MI, spermidine reduced infarct size, improved cardiac function, and attenuated myocardial hypertrophy. Spermidine also suppressed the oxidative damage and inflammatory cytokines induced by MI. Moreover, spermidine enhanced autophagic flux and decreased apoptosis both in vitro and in vivo. The protective effects of spermidine on cardiomyocyte apoptosis and cardiac dysfunction were abolished by the autophagy inhibitor chloroquine, indicating that spermidine exerted cardioprotective effects at least partly through promoting autophagic flux, by activating the AMPK/mTOR signalling pathway. CONCLUSIONS AND IMPLICATIONS: Our findings suggest that spermidine improved MI-induced cardiac dysfunction by promoting AMPK/mTOR-mediated autophagic flux.

Roles of sleep deprivation in cardiovascular dysfunctions.

It is widely recognized that inadequate sleep is associated with multiple acute and chronic diseases and results in increased mortality and morbidity for cardiovascular diseases. In recent years, there has been increasing interest in sleep related investigations. Emerging evidence indicates that sleep deprivation changes the biological phenotypes of DNA, RNA and protein levels, but the underlying mechanisms are not clear. We summarized the current research on the detrimental roles of sleep deprivation on the heart and elucidated the underlying mechanisms of sleep deficiency to improve our understanding of sleep deprivation and the emerging strategies to target this process for therapeutic benefit.

Gastrodin pretreatment alleviates myocardial ischemia/reperfusion injury through promoting autophagic flux.

Gastrodin (GAS), a monomeric component exacted from the herb Gastrodia elata Bl, may have cardioprotective effects during injury caused by myocardial ischemia/reperfusion (I/R). For the significant role of autophagy in I/R process, we targeted to explore whether autophagy was contributing to the GAS-induced protective effects during I/R procedure. Male C57BL/6 mice were subjected to reversible left coronary artery ligation and cultured neonatal rat cardiomyocytes (NRCs) exposed to hypoxia were preconditioned with GAS prior to ischemia or hypoxia, following reperfusion for 2 h or re-oxygennation for 3 h respectively. Our results demonstrated that GAS pretreatment increased autophagy and reduced apoptosis during I/R, this effect was weakened by co-treatment with the autophagic flux inhibitor chloroquine (Cq). Compared to mice subjected solely to I/R, GAS-pretreated mice had a notably smaller heart infarct size and an elevation in cardiac function. In GAS-pretreated NRCs, WB data showed that autophagy was promoted (expression of p62 was inhibited and LC3II was increased). In addition, tandem fluorescent mRFP-GFP-LC3 assays illustrated that autophagosomes were degraded duo to an increase in autophagic flux. Co-administration of Cq blocked the autophagic flux. Furthermore, GAS pretreatment increased the mitochondrial membrane potential of NRCs with subjected to H/R and increased the cardiomyocyte survival rate. These protective effects were reversed with Cq. Besides, GAS-induced the enhaucement of autophagy may correlated with activating AMP-activated protein kinase (AMPK) phosphorylation and reduced Mammalian target of rapamycin (mTOR) phosphorylation, which was abrogated by Compound C (Com C, AMPK-specific inhibitor). Our results establish that GAS pretreatment attenuates myocardial I/R injury by increasing autophagic flux aimed at eliminating dysfunctional mitochondria, therefore protecting neighbouring mitochondria and cardiomyocytes.