Effect of Autophagy Inhibition on the Protection of Ischemia Preconditioning against Myocardial Ischemia/Reperfusion Injury in Diabetic Rats

The UCP2/PINK1/LC3b-mediated mitophagy is involved in the protection of NRG1 against myocardial ischemia/reperfusion injury

Available evidence indicates that neuregulin-1 (NRG-1) can provide a protection against myocardial ischemia/reperfusion (I/R) injury and is involved in various cardioprotective interventions by potential regulation of mitophagy. However, the molecular mechanisms linking NRG-1 and mitophagy remain to be clarified. In this study, both an in vivo myocardial I/R injury model of rats and an in vitro hypoxia/reoxygenation (H/R) model of H9C2 cardiomyocytes were applied to determine whether NRG-1 postconditioning attenuated myocardial I/R injury through the regulation of mitophagy and to explore the underlying mechanisms. In the in vivo experiment, cardioprotective effects of NRG-1 were determined by infarct size, cardiac enzyme and histopathologic examinations. The potential downstream signaling pathways and molecular targets of NRG-1 were screened by the RNA sequencing and the Protein-Protein Interaction Networks. The expression levels of mitochondrial uncoupling protein 2 (UCP2) and mitophagy-related proteins in both the I/R myocardium and H/R cardiomyocytes were measured by immunofluorescence staining and Western blots. The activation of mitophagy was observed with transmission electron microscopy and JC-1 staining. The KEGG and GSEA analyses showed that the mitophagy-related signaling pathways were enriched in the I/R myocardium treated with NRG-1, and UCP2 exhibited a significant correlation between mitophagy and interaction with PINK1. Meanwhile, the treatment with mitophagy inhibitor Mdivi-1 significant eliminated the cardioprotective effects of NRG-1 postconditioning in vivo, and the challenge with UCP2 inhibitor genipin could also attenuate the activating effect of NRG-1 postconditioning on mitophagy. Consistently, the in vitro experiment using H9C2 cardiomyocytes showd that NRG-1 treatment significantly up-regulated the expression levels of UCP2 and mitophagy-related proteins, and activated the mitophagy, whereas the challenge with small interfering RNA-mediated UCP2 knockdown abolished the effects of NRG-1. Thus, it is conclused that NRG-1 postconditioning can produce a protection against the myocardial I/R injury by activating mitophagy through the UCP2/PINK1/LC3B signaling pathway.

Deptor protects against myocardial ischemia-reperfusion injury by regulating the mTOR signaling and autophagy

Deptor knockout mice were constructed by crossing Deptor Floxp3 mice with myh6 Cre mice, establishing a myocardial ischemia-reperfusion (I/R) model. Deptor knockout mice exhibited significantly increased myocardial infarction size and increased myocardial apoptosis in vivo. ELISA analysis indicated that the expression of CK-MB, LDH, and CtnT/I was significantly higher in the Deptor knockout mice. Deptor siRNA significantly reduced cell activity and increased myocardial apoptosis after I/R-induced in vitro. Deptor siRNA also significantly up-regulated the expression of p-mTOR, p-4EBP1, and p62, and down-regulated the expression of LC3 after I/R induction. Immunofluorescence indicated that LC3 dual fluorescence was weakened by Deptor knockout, and was enhanced after transfection with Deptor-overexpression plasmids. Treatment with OSI027, a co-inhibitor of mTORC1 and mTORC2, in either Deptor knockout mice or Deptor knockout H9C2 cells, resulted in a significant reduction in infarction size and apoptotic cardiomyocytes. ELISA analysis also showed that the expression of CK-MB, LDH, and CtnT/I were significantly down-regulated by treatment with OSI027. CCK-8 cell viability indicated that cell viability was enhanced, and the number of apoptotic cells was decreased in vitro following treatment with OSI027. These results revealed that OSI027 exerts a protective effect on myocardial ischemia/reperfusion injury in both an in vivo and in an in vitro model of I/R. These findings demonstrate that Deptor protects against I/R-induced myocardial injury by inhibiting the mTOR pathway and by increasing autophagy.

Mechanisms and Therapeutic Strategies for Myocardial Ischemia-Reperfusion Injury in Diabetic States

In patients with myocardial infarction, one of the complications that may occur after revascularization is myocardial ischemia-reperfusion injury (IRI), characterized by a depleted myocardial oxygen supply and absence of blood flow recovery after reperfusion, leading to expansion of myocardial infarction, poor healing of myocardial infarction and reversal of left ventricular remodeling, and an increase in the risk for major adverse cardiovascular events such as heart failure, arrhythmia, and cardiac cell death. As a risk factor for cardiovascular disease, diabetes mellitus increases myocardial susceptibility to myocardial IRI through various mechanisms, increases acute myocardial infarction and myocardial IRI incidence, decreases myocardial responsiveness to protective strategies and efficacy of myocardial IRI protective methods, and increases diabetes mellitus mortality through myocardial infarction. This Review summarizes the mechanisms, existing therapeutic strategies, and potential therapeutic targets of myocardial IRI in diabetic states, which has very compelling clinical significance.

Canagliflozin attenuates post-resuscitation myocardial dysfunction in diabetic rats by inhibiting autophagy through the PI3K/Akt/mTOR pathway

This study investigated the effects of canagliflozin on myocardial dysfunction after cardiac arrest and cardiopulmonary resuscitation in diabetic rats and the underlying mechanisms. Male rats with type 2 diabetes mellitus (T2DM) were subjected to a modified epicardial fibrillation model. Pretreatment with canagliflozin (10 mg/kg/day) for four weeks improved ATP levels, post-resuscitation ejection fraction, acidosis, and hemodynamics. Canagliflozin also reduced myocardial edema, mitochondrial damage and, post-resuscitation autophagy levels. In vitro analyses showed that canagliflozin significantly reduced reactive oxygen species and preserved mitochondrial membrane potential. Using the PI3K/Akt pathway inhibitor Ly294002, canagliflozin was shown to attenuate hyperautophagy and cardiac injury induced by high glucose and hypoxia-reoxygenation through activation of the PI3K/Akt/mTOR pathway. This study highlights the therapeutic potential of canagliflozin in post-resuscitation myocardial dysfunction in diabetes, providing new insights for clinical treatment and experimental research.

Role of Keap1-Nrf2/ARE signal transduction pathway in protection of dexmedetomidine preconditioning against myocardial ischemia/reperfusion injury

Objective: To explore the role and mechanism of the Kelch sample related protein-1-nuclear factor erythroid-2 related factor 2/antioxidant response element (Keap1-Nrf2/ARE) signaling pathway in protection of dexmedetomidine (DEX) preconditioning against myocardial ischemia/reperfusion injury (MIRI). Methods: A total of 70 male SD rats were randomly divided into seven equal groups (n=10): blank control (S group), ischemia/reperfusion injury (C group), DEX preconditioning (DEX group), tertiary butylhydroquinone (tBHQ) control (tBHQ group), combined tBHQ and DEX preconditioning (tBHQ+DEX group), all-trans retinoic acid (ATRA) control (ATRA group), and combined ATRA and DEX preconditioning (ATRA+DEX group). Serum creatine kinase-MB (CK-MB) and cardiac troponin I (cTnI) concentrations were measured by ELISA kits, and the infarct size (IS) was assessed by Evan’s blue and 2,3,5-triphenyltetrazolium chloride (TTC) staining. Oxidative stress was assessed through Western blotting for expression of Keap1-Nrf2/ARE pathway members and oxidative stress markers. Results: Cardioprotection of DEX, tBHQ, and tBHQ+DEX preconditioning treatments were shown as lower concentrations of serum CK-MB and cTnI and a smaller IS following MIRI in rats compared with those of MIRI rats without pre-treatment. In addition, tBHQ+DEX preconditioning exhibited stronger myocardial protection compared with DEX preconditioning. Mechanistically, the cardioprotection offered by DEX, tBHQ, and tBHQ+DEX preconditioning treatments was mediated via exerting antioxidant stress through activation of the Keap1-Nrf2/ARE signal transduction pathway. Conversely, the protective effects of DEX were diminished by blocking the Keap1-Nrf2/ARE pathway with inhibitor ATRA. Conclusion: DEX preconditioning protects against MIRI by exerting antioxidant stress through activation of the Keap1-Nrf2/ARE signal transduction pathway, while inhibition of the Keap1-Nrf2/ARE signal transduction pathway reverses the protective effect of DEX preconditioning on MIRI.

Soluble guanylate cyclase (sGC) stimulator vericiguat alleviates myocardial ischemia-reperfusion injury by improving microcirculation

Background

This study aimed to verify the effect of soluble guanylate cyclase (sGC) stimulator vericiguat on myocardial ischemia-reperfusion injury and explore its mechanism.

Methods

A myocardial ischemia-reperfusion injury model of mice was established and intravenous administration was performed 2 minutes before reperfusion. Triphenyltetrazolium chloride (TTC) staining and echocardiography were used to verify the effect of vericiguat on myocardial ischemia-reperfusion injury in the infarct area, and immunofluorescence was used to observe myocardial pathological changes at different time points after reperfusion. Quantitative proteomics was conducted to analysis the main differentially expressed proteins after drug intervention. The distribution of endothelial cells and sGC after myocardial ischemia-reperfusion injury in mice was observed by immunofluorescence. RNA sequencing of endothelial cells was used to search for differentially expressed molecules. Thioflavin-S staining was used to observe the effect of vericiguat on improving the nonrecurrence phenomenon and reducing the infarct size after reperfusion.

Results

The effect of the sGC stimulator vericiguat on myocardial ischemia-reperfusion injury was verified, and myocardial microcirculation significantly increased after drug intervention. Quantitative proteomics found that the protein expression of myocardial tissue in the ischemia-reperfusion area was not significantly different in the drug intervention group, except for increased adenosine triphosphate (ATP) activity. Vericiguat, nitroglycerin, and nitrite did not directly affect apoptosis or cell viability. RNA sequencing of human umbilical vein endothelial cells screened the upregulated antioxidant response.

Conclusions

SGC stimulator vericiguat ameliorated myocardial ischemia-reperfusion injury through indirect pathways of improving microcirculation.

Rosmarinic Acid Ameliorates Pulmonary Ischemia/Reperfusion Injury by Activating the PI3K/Akt Signaling Pathway

Pulmonary ischemia/reperfusion (IR) injury is the leading cause of acute lung injury, which is mainly attributed to reactive oxygen species (ROS) induced cell injuries and apoptosis. Since rosmarinic acid (RA) has been identified as an antioxidant natural ester, this natural compound might protect against pulmonary IR injury. In this study, the mice were given RA daily (50, 75, or 100 mg/kg) by gavage for 7 days before the pulmonary IR injury. We found that hypoxemia, pulmonary edema, and serum inflammation cytokines were aggravated in pulmonary IR injury. RA pretreatment (75 and 100 mg/kg) effectively reversed these parameters, while 50 mg/kg RA pretreatment was less pronounced. Our data also indicated RA pretreatment mitigated the upregulation of pro-oxidant NADPH oxidases (NOX2 and NOX4) and the downregulation of anti-oxidant superoxide dismutases (SOD1 and SOD2) upon IR injury. In vitro studies showed RA preserved the viability of anoxia/reoxygenation (AR)-treated A549 cells (a human lung epithelial cell line), and the results showed the protective effect of RA started at 5 μM concentration, reached its maximum at 15 μM, and gradually decreased at 20–25 μM. Besides, RA pretreatment (15 μM) greatly reduced the lactate dehydrogenase release levels subjected to AR treatment. Moreover, the results of our research revealed that RA eliminated ROS production and reduced alveolar epithelial cell apoptosis through activating the phosphatidylinositol 3 kinase (PI3K)/protein kinase B (Akt) signaling pathway, which was supported by using wortmannin, because in the presence of wortmannin, the RA-mediated protection was blocked. Meanwhile, wortmannin also reversed the protective effects of RA in mice. Together, our results demonstrate the beneficial role of RA in pulmonary IR injury via PI3K/Akt-mediated anti-oxidation and anti-apoptosis, which could be a promising therapeutic intervention for pulmonary IR injury.

Pretreatment of cardiac progenitor cells with bradykinin attenuates H2O2-induced cell apoptosis and improves cardiac function in rats by regulating autophagy

Background

Previous studies have demonstrated that human cardiac c-Kit⁺ progenitor cells (hCPCs) can effectively improve ischemic heart disease. However, the major challenge in applying hCPCs to clinical therapy is the low survival rate of graft hCPCs in the host heart, which limited the benefit of transplanted hCPCs. Bradykinin (BK) is a principal active agent of the tissue kinin-kallikrein system. Our previous studies have highlighted that BK mediated the growth and migration of CPCs by regulating Ca²⁺ influx. However, the protective effect of BK on CPCs, improvement in the survival rate of BK-pretreated hCPCs in the infarcted heart, and the related mechanism remain elusive.

Methods

HCPCs were treated with H₂O₂ to induce cell apoptosis and autophagy, and different concentration of BK was applied to rescue the H₂O₂-induced injury detected by MTT assay, TUNEL staining, flow cytometry, western blotting, and mitoSOX assays. The role of autophagy in the anti-apoptotic effect of BK was chemically activated or inhibited using the autophagy inducer, rapamycin, or the inhibitor, 3-methyladenine (3-MA). To explore the protective effect of BK on hCPCs, 3-MA or BK-pretreated hCPCs were transplanted into the myocardial infarcted rats. An echocardiogram was used to determine cardiac function, H&E and Masson staining were employed to assess pathological characteristics, HLA gene expression was quantified by qRT-PCR, and immunostaining was applied to examine neovascularization using confocal microscopy.

Results

The in vitro results showed that BK suppressed H₂O₂-induced hCPCs apoptosis and ROS production in a concentration-dependent manner by promoting pAkt and Bcl-2 expression and reducing cleaved caspase 3 and Bax expression. Moreover, BK restrained the H₂O₂-induced cell autophagy by decreasing LC3II/I, Beclin1, and ATG5 expression and increasing P62 expression. In the in vivo experiment, the transplanted BK- or 3-MA-treated hCPCs were found to be more effectively improved cardiac function by decreasing cardiomyocyte apoptosis, inflammatory infiltration, and myocardial fibrosis, and promoting neovascularization in the infarcted heart, compared to untreated-hCPCs or c-kit^- cardiomyocytes (CPC^- cells).

Conclusions

Our present study established a new method to rescue transplanted hCPCs in the infarcted cardiac area via regulating cell apoptosis and autophagy of hCPCs by pretreatment with BK, providing a new therapeutic option for heart failure.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02503-6.

Neuroprotective Effects of Long-Term Metformin Preconditioning on Rats with Ischemic Brain Injuries

INTRODUCTION

This study is to analyze the neuroprotective effects of long-term metformin (Met) preconditioning on rats with ischemic brain injuries and the related mechanisms.

METHODS

Twenty-five Sprague-Dawley rats were randomly divided into 5 groups: sham group, middle cerebral artery occlusion (MCAO) group, normal saline + MCAO group, pre- Met + MCAO group, and 3-MA + Met + MCAO group. Pathological changes of brain were observed by hematoxylin-eosin staining. Neurobehavior scores were calculated. Infarct area was assessed by 2,3,5-triphenyltetrazolium chloride staining. Apoptosis of neurons was detected by TdT-mediated dUTP Nick-End Labeling (TUNEL). Western blot tested the expression of LC3 (microtubule-associated protein 1 light chain 3), Beclin-1, adenosine 5'-monophosphate ([AMP]-activated protein kinase [AMPK]), and p-AMPK in hippocampal CA1 region.

RESULTS

Compared with the sham group, the MCAO group induced severe pathological changes in the brain. The neurobehavior scores and infarct area in the brain were increased in the MCAO group than in the sham group. The apoptosis level in the MCAO group was also higher than in the sham group. However, after pretreatment with Met, the pathological changes in the brain were attenuated. Compared with the MCAO group, the pre-Met + MCAO group also had decreased neurobehavior scores and infarct area in the brain. Additionally, the apoptosis level in the pre-Met + MCAO group was lower than in the MCAO group. Moreover, the MCAO group had increased levels of LC3 and Beclin-1 than in the sham group. In the pre-Met + MCAO group, their levels were decreased than in the MCAO group. The p-AMPK level in the pre-Met + MCAO group was also increased than in the MCAO group, suggesting activation of p-AMPK by Met.

CONCLUSION

Long-term Met pretreatment has neuroprotective effect on ischemic brain injury, which may be related to the regulation of autophagy-related protein expression and apoptosis.

Inositol pyrophosphates mediated the apoptosis induced by hypoxic injury in bone marrow-derived mesenchymal stem cells by autophagy

Objective

To investigate the potential effect of IP7 on the autophagy and apoptosis of bone marrow mesenchymal stem cells (BM-MSCs) caused by hypoxia.

Methods

BM-MSCs isolated from adult male C57BL/6 mice were exposed to normoxic condition and hypoxic stress for 6 h, 12 h, and 24 h, respectively. Then, flow cytometry detected the characteristics of BM-MSCs. Furthermore, N6-(p-nitrobenzyl) purine (TNP) was administrated to inhibit inositol pyrophosphates (IP7). TUNEL assay determined the apoptosis in BM-MSCs with hypoxia. Meanwhile, RFP-GFP-LC3 plasmid transfection and transmission microscope was used for measuring autophagy. In addition, Western blotting assay evaluated protein expressions.

Results

Hypoxic injury increased the autophagy and apoptosis of BM-MSCs. At the same time, hypoxic injury enhanced the production of IP7. Moreover, hypoxia decreased the activation of Akt/mTOR signaling pathway. At last, TNP (inhibitor of IP7) repressed the increased autophagy and apoptosis of BM-MSCs under hypoxia.

Conclusion

The present study indicated that hypoxia increased autophagy and apoptosis via IP7-mediated Akt/mTOR signaling pathway of BM-MSCs. It may provide a new potential therapy target for myocardial infarction (MI).