How and when do myocytes die during ischemia and reperfusion: the late phase

Extracellular PKM2 Preserves Cardiomyocytes and Reduces Cardiac Fibrosis During Myocardial Infarction

Substantial loss of cardiomyocytes during heart attacks and onset of other cardiovascular diseases is a major cause of mortality. Preservation of cardiomyocytes during cardiac injury would be the most effective strategy to manage these diseases in clinic. However, there is no effective treatment strategy that is able to prevent cardiomyocyte loss. We demonstrate here that the systemic administration of a recombinant PKM2 mutant (G415R) preserves cardiomyocytes and reduces cardiac fibrosis during myocardial infarction. G415R preserves cardiomyocytes by protecting the cardiomyocytes from dying and by promoting cardiomyocyte proliferation. Preservation of cardiomyocytes by extracellular PKM2 (EcPKM2) reduces cardiac fibrosis because of the decreased activation of cardiac fibroblasts. Our experiments show that EcPKM2 (G415R) exerts its action by interacting with integrin avb3 on cardiomyocytes. EcPKM2(G415R) activates the integrin-FAK-PI3K signaling axis, which subsequently suppresses PTEN expression and consequently regulates cardiomyocyte apoptosis resistance and proliferation under hypoxia and oxidative stress conditions. Our studies uncover an important cardiomyocyte protection mechanism. More importantly, the activity/action of EcPKM2 (G415R) in preserving cardiomyocyte suggesting a possible therapeutic strategy and target for the treatment of heart attacks and other cardiovascular diseases.

The Impact of Transfer-Related Ischemia on Free Flap Metabolism and Electrolyte Homeostasis-A New In Vivo Experimental Approach in Pigs

Free flap tissue transfer represents the gold standard for extensive defect reconstruction, although malperfusion due to thrombosis remains the leading risk factor for flap failure. Recent studies indicate an increased immune response and platelet activation in connection with pathologic coagulation. The underlying cellular and molecular mechanisms remain poorly understood, however. The presented study, therefore, aims to investigate if transfer-related ischemia alters intra-flap metabolism and electrolyte concentrations compared to central venous blood after free flap transfer in pigs to establish a novel experimental model. Free transfer of a myocutaneous gracilis flap to the axillary region was conducted in five juvenile male pigs. The flap artery was anastomosed to the axillary artery, and intra-flap venous blood was drained and transfused using a rubber-elastic fixed intravenous catheter. Blood gas analysis was performed to assess the effect of transfer time-induced ischemia on intra-flap electrolyte levels, acid-base balance, and hemoglobin concentrations compared to central venous blood. Time to flap reperfusion was 52 ± 10 min on average, resulting in a continuous pH drop (acidosis) in the flaps' venous blood compared to the central venous system (p = 0.037). Potassium (p = 0.016), sodium (p = 0.003), and chloride (p = 0.007) concentrations were significantly increased, whereas bicarbonate (p = 0.016) and calcium (p = 0.008) significantly decreased within the flap. These observations demonstrate the induction of anaerobic glycolysis and electrolyte displacement resulting in acidosis and hence significant tissue damage already after a short ischemic period, thereby validating the novel animal model for investigating intra-flap metabolism and offering opportunities for exploring various (immuno-) thrombo-hemostatic issues in transplantation surgery.

Stachydrine ameliorates hypoxia reoxygenation injury of cardiomyocyte via enhancing SIRT1-Nrf2 pathway

BACKGROUND

Hypoxia/reoxygenation (H/R)-induced cardiomyocyte cell apoptosis is critical in developing myocardial infarction. Stachydrine (STA), an active constituent of Leonurus heterophyllus sweet, could have a protective effect on myocardial H/R injury, which remains unexplored. Therefore, the study aimed to investigate the protective effects and mechanisms of STA on H/R injury of cardiomyocytes.

METHODS

Rat cardiomyocyte H9c2 cells underwent H/R (hypoxia for 4 h and reoxygenation for 12 h). Cells were pretreated with STA (50 µM) 2 h before H/R. Cardiomyocyte injury was evaluated by CCK-8 assay and lactate dehydrogenase (LDH) release. Apoptosis was assessed by TUNEL staining and caspase-3 activity. Oxidative stress was assessed by lipid oxidation product MDA and a ROS-scavenging enzyme SOD in culture media. Western blot was performed to measure the protein expressions of SIRT1, Nrf2, and heme oxygenase-1 (HO-1).

RESULTS

STA reversed the decrease in cell viability and increased LDH release in H9c2 cells with the H/R insult. STA significantly suppressed oxidative stress, reduced MDA content, and increased SOD activity in H9c2 cells exposed to H/R. STA reduced apoptosis in H9c2 cells exposed to H/R, as evidenced by the reduced TUNEL positive cells and caspase-3 activity. In addition, STA enhanced SIRT1, Nrf2, and HO-1 protein expression in H/R-stimulated H9c2 cells. SIRT1 and Nrf2 involved the protective effect of STA in H/R-exposed H9c2 cells, as the changes in cell viability and caspase-3 activity by STA can be reversed by SIRT1 inhibitor EX-527 or Nrf2 siRNA.

CONCLUSIONS

Our data speculated that STA protects H/R injury and inhibits oxidative stress and apoptosis in cardiomyocytes by activation of the SIRT1-Nrf2 pathway.

Cyclic AMP but Not Calmodulin as a Potential Wasoconstrictor in Simulated Reperfusion

The phenomena of ischemia and reperfusion are associated with the pathological background of cardiovascular diseases. Ischemia is initiated by ischemia reperfusion injury (IRI), which involves disruption of intracellular signaling pathways and causes cell death. The aim of this study was to assess the reactivity of vascular smooth muscle cells in the conditions of induced ischemia and reperfusion, and to determine the mechanisms leading to contractility disorders. This study was conducted using classical pharmacometric methods on an isolated model of the rat caudal artery. The experiment consisted of the analysis of the final and initial perfusate pressure measurements after induction of arterial contraction with phenylephrine in the presence of forskolin and A7 hydrochloride, two ligands modifying the contractility of vascular smooth muscle cells (VSMC). The pharmacometric analysis showed that in simulated reperfusion, cyclic nucleotides have a vasoconstrictive effect, and calmodulin has a vasodilating effect. The responsiveness of vascular smooth muscle cells to the vasopressor effects of α1-adrenomimetics during reperfusion may change uncontrollably, and the effects of secondary messengers may be counter physiological. Further studies are needed to evaluate the function of other second messengers on VSMCs in the process of ischemia and reperfusion.

Silencing of Hsa_circ_0055440 Alleviates Hypoxia-Induced Cardiomyocyte Injury by Regulating the MiR-499b-5p/ACSL1 Axis

Circular RNAs (circRNAs) are a new type of regulatory RNAs, which are involved in various cardiac processes. However, the role of circRNA hsa_circ_0055440 (circ-USP39) in acute myocardial infarction regulation has not been studied yet.This study aims to explore the effect of circ-USP39 on hypoxia-induced cardiomyocyte injury.The head-to-tail splicing of circ-USP39 was verified by agarose gel electrophoresis. AC16 cell viability was detected using 3- (4,5-dimethylthiazol-2-yl) -2,5-diphenyltetrazolium bromide assays. The apoptosis of the AC16 cell was determined by flow cytometry and detection of caspase-3 activity. The levels of creatine kinase-muscle/brain and cTnl were evaluated by specific detection kits. The interactions between miR-499b-5p and circ-USP39 (or acyl-CoA synthetase long-chain family member-1 (ACSL1) ) were verified by luciferase reporter assays.After confirming the circular characteristics of circ-USP39, we further found that the circ-USP39 expression was upregulated in hypoxia-induced cardiomyocytes and the circ-USP39 knockdown facilitated the viability of hypoxia-induced AC16, while suppressing cardiomyocyte apoptosis and injury. Importantly, circ-USP39 negatively regulated miR-499b-5p expression. As a downstream target of miR-499b-5p, ACSL1 partially counteracted the protective effect of circ-USP39 depletion on cardiomyocyte injury.Silencing of circ-USP39 alleviates hypoxia-induced cardiomyocyte injury via the miR-499b-5p/ACSL1 axis.

Pioglitazone Protects Against Hypoxia-Induced Cardiomyocyte Apoptosis Through Inhibiting NLRP3/Caspase-1 Pathway in vivo and in vitro

This study aims to explore the underlying mechanisms of how Pioglitazone (Pio) affects myocardial ischemia-reperfusion (I/R) injury. In this study, after pretreatment of Pio, the pathologic change of myocardial tissues was measured via hematoxylin and eosin staining. The release of lactate dehydrogenase (LDH), superoxide dismutase (SOD), and nitric oxide (NO) were measured. The cardiomyocyte apoptosis was detected via TUNEL assay and flow cytometry assay. The mitochondrial membrane potential (ΔΨm) was estimated using the JC-1 probe. The release of cytochrome c in mitochondria and the translocation of cytochrome c in the cytosol were measured using western blot. Additionally, apoptosis-associated molecules and NOD-like receptor pyrin domain containing-3 (NLRP3)/caspase-1 pathway-related molecules were measured using western blot, quantitative real-time-polymerase chain reaction, and immunofluorescence staining. Results showed that the pretreatment of Pio significantly decreased myocardial tissue damage. Pio pretreatment inhibited the release of creatine kinase and LDH but promoted NO release in serum and H9c2 cell supernatants. Moreover, the pretreatment of Pio notably alleviated cardiomyocyte apoptosis. Pio pretreatment also maintained the mitochondrial membrane potential and prevented cytochrome c release in H/R-induced cardiomyocytes. Additionally, we confirmed that Pio pretreatment inhibited cardiomyocyte apoptosis via repressing the NLRP3/caspase-1 pathway. In conclusion, our study demonstrated that Pio could inhibit myocardial I/R injury and cardiomyocyte apoptosis by inhibiting the activation of the NLRP3/caspase-1 signaling pathway.

Non-Coding RNAs: Prevention, Diagnosis, and Treatment in Myocardial Ischemia-Reperfusion Injury

Recent knowledge concerning the role of non-coding RNAs (ncRNAs) in myocardial ischemia/reperfusion (I/R) injury provides new insight into their possible roles as specific biomarkers for early diagnosis, prognosis, and treatment. MicroRNAs (miRNAs) have fewer than 200 nucleotides, while long ncRNAs (lncRNAs) have more than 200 nucleotides. The three types of ncRNAs (miRNAs, lncRNAs, and circRNAs) act as signaling molecules strongly involved in cardiovascular disorders (CVD). I/R injury of the heart is the main CVD correlated with acute myocardial infarction (AMI), cardiac surgery, and transplantation. The expression levels of many ncRNAs and miRNAs are highly modified in the plasma of MI patients, and thus they have the potential to diagnose and treat MI. Cardiomyocyte and endothelial cell death is the major trigger for myocardial ischemia–reperfusion syndrome (MIRS). The cardioprotective effect of inflammasome activation in MIRS and the therapeutics targeting the reparative response could prevent progressive post-infarction heart failure. Moreover, the pharmacological and genetic modulation of these ncRNAs has the therapeutic potential to improve clinical outcomes in AMI patients.

Promising Therapeutic Candidate for Myocardial Ischemia/Reperfusion Injury: What Are the Possible Mechanisms and Roles of Phytochemicals?

Percutaneous coronary intervention (PCI) is one of the most effective reperfusion strategies for acute myocardial infarction (AMI) despite myocardial ischemia/reperfusion (I/R) injury, causing one of the causes of most cardiomyocyte injuries and deaths. The pathological processes of myocardial I/R injury include apoptosis, autophagy, and irreversible cell death caused by calcium overload, oxidative stress, and inflammation. Eventually, myocardial I/R injury causes a spike of further cardiomyocyte injury that contributes to final infarct size (IS) and bound with hospitalization of heart failure as well as all-cause mortality within the following 12 months. Therefore, the addition of adjuvant intervention to improve myocardial salvage and cardiac function calls for further investigation. Phytochemicals are non-nutritive bioactive secondary compounds abundantly found in Chinese herbal medicine. Great effort has been put into phytochemicals because they are often in line with the expectations to improve myocardial I/R injury without compromising the clinical efficacy or to even produce synergy. We summarized the previous efforts, briefly outlined the mechanism of myocardial I/R injury, and focused on exploring the cardioprotective effects and potential mechanisms of all phytochemical types that have been investigated under myocardial I/R injury. Phytochemicals deserve to be utilized as promising therapeutic candidates for further development and research on combating myocardial I/R injury. Nevertheless, more studies are needed to provide a better understanding of the mechanism of myocardial I/R injury treatment using phytochemicals and possible side effects associated with this approach.

HNO Protects the Myocardium against Reperfusion Injury, Inhibiting the mPTP Opening via PKCε Activation

Donors of nitroxyl (HNO), the one electron-reduction product of nitric oxide (NO^.), positively modulate cardiac contractility/relaxation while limiting ischemia-reperfusion (I/R) injury. The mechanisms underpinning HNO anti-ischemic effects remain poorly understood. Using isolated perfused rat hearts subjected to 30 min global ischemia/1 or 2 h reperfusion, here we tested whether, in analogy to NO^., HNO protection requires PKCε translocation to mitochondria and K_ATP channels activation. To this end, we compared the benefits afforded by ischemic preconditioning (IPC; 3 cycles of I/R) with those eventually granted by the NO^. donor, diethylamine/NO, DEA/NO, and two chemically unrelated HNO donors: Angeli’s salt (AS, a prototypic donor) and isopropylamine/NO (IPA/NO, a new HNO releaser). All donors were given for 19 min before I/R injury. In control I/R hearts (1 h reperfusion), infarct size (IS) measured via tetrazolium salt staining was 66 ± 5.5% of the area at risk. Both AS and IPA/NO were as effective as IPC in reducing IS [30.7 ± 2.2 (AS), 31 ± 2.9 (IPA/NO), and 31 ± 0.8 (IPC), respectively)], whereas DEA/NO was significantly less so (36.2 ± 2.6%, p < 0.001 vs. AS, IPA/NO, or IPC). IPA/NO protection was still present after 120 min of reperfusion, and the co-infusion with the PKCε inhibitor (PKCV1-2500 nM) prevented it (IS = 30 ± 0.5 vs. 61 ± 1.8% with IPA/NO alone, p < 0.01). Irrespective of the donor, HNO anti-ischemic effects were insensitive to the K_ATP channel inhibitor, 5-OH decanoate (5HD, 100 μM), that, in contrast, abrogated DEA/NO protection. Finally, both HNO donors markedly enhanced the mitochondrial permeability transition pore (mPTP) ROS threshold over control levels (≅35–40%), an action again insensitive to 5HD. Our study shows that HNO donors inhibit mPTP opening, thus limiting myocyte loss at reperfusion, a beneficial effect that requires PKCε translocation to the mitochondria but not mitochondrial K⁺ channels activation.

Role of miRNA-1 and miRNA-21 in Acute Myocardial Ischemia-Reperfusion Injury and Their Potential as Therapeutic Strategy

Coronary artery disease remains the leading cause of death. Acute myocardial infarction (MI) is characterized by decreased blood flow to the coronary arteries, resulting in cardiomyocytes death. The most effective strategy for treating an MI is early and rapid myocardial reperfusion, but restoring blood flow to the ischemic myocardium can induce further damage, known as ischemia-reperfusion (IR) injury. Novel therapeutic strategies are critical to limit myocardial IR injury and improve patient outcomes following reperfusion intervention. miRNAs are small non-coding RNA molecules that have been implicated in attenuating IR injury pathology in pre-clinical rodent models. In this review, we discuss the role of miR-1 and miR-21 in regulating myocardial apoptosis in ischemia-reperfusion injury in the whole heart as well as in different cardiac cell types with special emphasis on cardiomyocytes, fibroblasts, and immune cells. We also examine therapeutic potential of miR-1 and miR-21 in preclinical studies. More research is necessary to understand the cell-specific molecular principles of miRNAs in cardioprotection and application to acute myocardial IR injury.

Ozone protects cardiomyocytes against ischemia/reperfusion injury: Regulating the heat shock protein 70 (HPS70) expression through activating the JAK2/STAT3 Pathway

Ischemia/reperfusion (I/R) injury causes complications in early coronary artery reperfusion for acute myocardial infarction (AMI). Ozone (O₃) has been reported to be applied for protecting I/R injury, but its detailed mechanism remains unclear. Our study focused on the protective effect of O₃ pretreatment on myocardial I/R injury and JAK2/STAT3 signaling and HSP70 regulation involving in the mediation. The rat hearts which were perfused and isolated as well as the cultured cardiomyocytes of neonatal rat were exposed to hypoxia/reoxygenation (H/R) and different concentrations of O₃ followed by heat shock protein 70 (HSP70) siRNA treatment. The results showed O₃ attenuated the suppression of cell viability induced by H/R and decreased the release of activity of creatine kinase (CK), lactate dehydrogenase (LDH) and apoptosis of cardiomyocytes in vitro. Moreover, O₃ also activated the JAK2/STAT3 signaling, upregulated the expression of HSP70 both in vitro and vivo, and decreased the index of apoptosis of cardiomyocytes caused by I/R as well as myocardial infarct area in vivo. In addition, HSP70 siRNA and JAK2 inhibitor AG490 inhibited the cardioprotective effect of O₃. And the expression of HSP70 increased by ozone was reduced by AG-490. In conclusion, our results demonstrated that ozone protects cardiomyocytes in I/R injury through regulation of the expression of HSP70 by activating the JAK2/STAT3 pathway.

Human cardiac ischemia-reperfusion injury: Blunted stress response with age

BACKGROUND AND AIM

Autophagy is a cytoprotective recycling mechanism, capable of digesting dysfunctional cellular components, and this process is associated with pro-survival outcomes. Autophagy may decline in the aging myocardium, thereby contributing to cardiac dysfunction. However, it remains to be established how autophagy responds to ischemia-reperfusion stress with age.

METHODS

Samples from the right atrium were collected from young (≤50 years; n = 5) and aged (≥70 years; n = 11) patients before and immediately following cardioplegic arrest during coronary artery bypass grafting surgery, a model of human ischemia-reperfusion injury.

RESULTS

Mitochondrial content, as assessed by a cohort of mitochondrial markers, exhibited an overall decrease in the aging myocardium (p = 0.01). In response to IR, COX-I (0.63 vs. 0.91, p = 0.01) increased in young, but not in aged patients (interaction effect p = 0.08). Reductions in LC3-I (0.48 vs. 0.28, p = 0.02) along with declines in TFEB and TFE3 (0.63 vs. 0.20, p = 0.05; 0.71 vs. 0.20, p = 0.01) were observed with age suggesting an impairment in the aged myocardium. Aged patients also displayed an inability to mount an appropriate response to IR compared to their young counterparts, specifically, increases in v-ATPase and NIX (1.06 vs 0.69, p = .01; 1.15 vs 0.69, p = .001) were not seen in the aged.

CONCLUSION

Our data demonstrate a reduced cardiac mitochondrial content and a blunted mitochondrial response to ischemia with age, accompanied by a possible impairment in mitophagy. These findings support an age-associated inability of the atrial myocardium to mount appropriate adaptive responses to stress.

Pre-clinical Evidence: Berberine as a Promising Cardioprotective Candidate for Myocardial Ischemia/Reperfusion Injury, a Systematic Review, and Meta-Analysis

Objective: Myocardial ischemia/reperfusion (I/R) injury is one of the causes of most cardiomyocyte injuries and deaths. Berberine (BBR) has been suggested a potential to exert protective effects against myocardial I/R injury. This systematic review aims to determine the intrinsic mechanisms of BBR's protective effects in myocardial I/R injury.

Methods: Seven databases were searched for studies performed from inception to July 2020. Methodological quality was assessed by SYRCLE's-RoB tool.

Results: Ten studies including a total of 270 animals were included in this study. The methodology quality scores of the included studies ranged from 5 to 7 points. The meta-analysis we conducted demonstrated that BBR significantly reduced myocardial infarct size and the incidence of ventricular arrhythmia, compared to control groups (P < 0.00001). Cardiac function of animals in the BBR treatment group was also markedly increased (P < 0.00001). The index of myocardial apoptosis and the levels of biomarkers of myocardial infarction (LDH and CK) were also decreased in the BBR treatment groups compared to the control groups (P < 0.00001).

Conclusions: The pre-clinical evidence, according to our study, showed that BBR is a promising therapeutic agent for myocardial I/R injury. However, this conclusion should be further investigated in clinical studies.

Sp1 Targeted PARP1 Inhibition Protects Cardiomyocytes From Myocardial Ischemia-Reperfusion Injury via Downregulation of Autophagy

Myocardial ischemia–reperfusion injury (MIRI), characterized by post-ischemic cardiomyocytes death and reperfusion myocardial damage, is a lethal yet unresolved complication in the treatment of acute myocardial infarction (AMI). Previous studies have demonstrated that poly(ADP-ribose) polymerase-1 (PARP1) participates in the progression of various cardiovascular diseases, and various reports have proved that PARP1 can be a therapeutic target in these diseases, but whether it plays a role in MIRI is still unknown. Therefore, in this study, we aimed to explore the role and mechanism of PARP1 in the development of MIRI. Firstly, we demonstrated that PARP1 was activated during MIRI-induced myocardial autophagy in vitro. Moreover, PARP1 inhibition protected cardiomyocytes from MIRI through the inhibition of autophagy. Next, we discovered that specificity protein1 (Sp1), as a transcription factor of PARP1, regulates its target gene PARP1 through binding to its target gene promoter during transcription. Furthermore, silencing Sp1 protected cardiomyocytes from MIRI via the inhibition of PARP1. Finally, the functions and mechanisms of PARP1 in the development of MIRI were also verified in vivo with SD rats model. Based on these findings, we concluded that PARP1 inhibition protects cardiomyocytes from MIRI through the inhibition of autophagy, which is targeted by Sp1 suppression. Therefore, the utilization of PARP1 exhibits great therapeutic potential for MIRI treatment in future.

PPARγ in Ischemia-Reperfusion Injury: Overview of the Biology and Therapy

Ischemia-reperfusion injury (IRI) is a complex pathophysiological process that is often characterized as a blood circulation disorder caused due to various factors (such as traumatic shock, surgery, organ transplantation, burn, and thrombus). Severe metabolic dysregulation and tissue structure destruction are observed upon restoration of blood flow to the ischemic tissue. Theoretically, IRI can occur in various tissues and organs, including the kidney, liver, myocardium, and brain, among others. The advances made in research regarding restoring tissue perfusion in ischemic areas have been inadequate with regard to decreasing the mortality and infarct size associated with IRI. Hence, the clinical treatment of patients with severe IRI remains a thorny issue. Peroxisome proliferator-activated receptor γ (PPARγ) is a member of a superfamily of nuclear transcription factors activated by agonists and is a promising therapeutic target for ameliorating IRI. Therefore, this review focuses on the role of PPARγ in IRI. The protective effects of PPARγ, such as attenuating oxidative stress, inhibiting inflammatory responses, and antagonizing apoptosis, are described, envisaging certain therapeutic perspectives.

[Lymphotropic therapy in patients after surgical revascularization of lower-limb vessels]

Occlusive and stenotic lesions of lower-limb arteries appear to be amongst the most common manifestations of the pathology of the cardiovascular system and are characterized by various degree of chronic arterial insufficiency. Revascularization is the main stage of treatment for chronic arterial insufficiency of the lower extremities. Performing a reconstructive operation aimed at restoring the arterial blood flow in the ischaemized extremity is accompanied and followed by the development of reperfusion syndrome. The purpose of this study was to assess efficacy of using regional lymphotropic therapy for treatment of reperfusion syndrome in patients with chronic ischaemia of lower limbs in the postoperative period. The study included two groups of patients: the comparison group with standard postoperative treatment and the study group where the standard therapy was supplemented with regional lymphotropic therapy. In the postoperative period, the patients in both groups developed reperfusion oedema of the operated lower limb on day 3 after arterial reconstruction, however, on POD 7 after revascularization, the severity of oedema was apparently less in the study group. Lymphorrhoea after operative treatment in the study group was encountered significantly less often as compared with the control group. According to the findings of ultrasonographic examination of soft tissues in the postoperative period, patients of both groups on POD 3 were found to have pronounced oedema of soft tissues. However, on POD 7 the study group patients demonstrated a dramatic decrease in the thickness of oedema of the subcutaneous fat versus the comparison group patients. Regional lymphotropic therapy after reconstructive operations on arteries of lower limbs promoted a decrease in the severity of reperfusion syndrome on the operated lower limb.

Circ_0010729 regulates hypoxia-induced cardiomyocyte injuries by activating TRAF5 via sponging miR-27a-3p

Ischemic cardiomyopathy is a severe cardiovascular disease with high mortality. Circular RNAs (circRNAs) are widely regulated in diverse human diseases, including Ischemic cardiomyopathy. This study aimed to investigate a novel functional mechanism of circRNA circ_0010729 in hypoxia-induced cardiomyocyte injuries. Human cardiomyocytes (AC16) were exposed to hypoxia to mimic ischemic cardiomyopathy in vitro. Cell viability, apoptosis/necrosis and glycolysis progress, were determined using 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay, flow cytometry assay and glycolysis stress test, respectively. Cell apoptosis was also assessed by the activity of cleaved caspase-3/7. The levels of glycolysis-related proteins and tumor necrosis factor receptor-associated factor 5 (TRAF5) were examined by western blot. The expression of circ_0010729 and miR-27a-3p was measured by real-time quantitative reverse transcription-polymerase chain reaction (qRT-PCR). The prediction about the targeted relationship was verified by dual-luciferase reporter assay, RNA immunoprecipitation (RIP) assay and RNA pull-down assay. As a result, hypoxia treatment inhibited cell viability, induced cell apoptosis and blocked glycolysis, however, these injuries were alleviated by circ_0010729 knockdown. MiR-27a-3p was targeted by circ_0010729, and miR-27a-3p inhibition reversed the role of circ_0010729 knockdown, leading to the deterioration of cell injuries. Further, TRAF5 was a target of miR-27a-3p, and circ_0010729 upregulated the expression of TRAF5 by sponging miR-27a-3p. MiR-27a-3p restoration enhanced cell viability, depleted cell apoptosis and promoted glycolysis of hypoxia-induced AC16 cells, while these effects were abolished by TRAF5 overexpression. In conclusion, circ_0010729 knockdown alleviated hypoxia-induced AC16 cell injuries by mediating the miR-27a-3p/TRAF5 axis.

Prokineticin 2 relieves hypoxia/reoxygenation-induced injury through activation of Akt/mTOR pathway in H9c2 cardiomyocytes

Prokineticin 2 (PK2) was reported to be decreased in the hearts of end-state heart failure patients. Our study aimed to explore the effects of PK2 on hypoxia/reoxygenation (H/R) injury and the underlying mechanism. H9c2 cardiomyocytes were treated with 5 nM PK2 in the presence or absence of 5 mM dual phosphatidylinositol 3-kinase (PI3K)/the mammalian target of rapamycin (mTOR) inhibitor (BEZ235) for 24 h and then subjected to H/R treatment. Cell viability and lactate dehydrogenase (LDH) release were evaluated by CCK-8 and LDH release assays, respectively. Apoptosis was determined by flow cytometry analysis. Oxidative stress was assessed by measuring superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSH-Px) activities and malondialdehyde (MDA) content. Results showed that H/R treatment decreased PK2 expression and inactivated the Akt/mTOR pathway in H9c2 cardiomyocytes. PK2 treatment activated the Akt/mTOR pathway in H/R-exposed H9c2 cardiomyocytes. H/R stimulation suppressed cell viability, increased LDH release, induced apoptosis and oxidative stress in H9c2 cardiomyocytes, while these effects were neutralised by treatment with PK2. However, the inhibitory effects of PK2 on H/R-induced injury in H9c2 cardiomyocytes were abolished by the addition of BEZ235. In conclusion, PK2 relieved H/R-induced injury in H9c2 cardiomyocytes by activation of the Akt/mTOR pathway.

Is REDD1 a metabolic double agent? Lessons from physiology and pathology

The Akt/mechanistic target of rapamycin (mTOR) signaling pathway governs macromolecule synthesis, cell growth, and metabolism in response to nutrients and growth factors. Regulated in development and DNA damage response (REDD)1 is a conserved and ubiquitous protein, which is transiently induced in response to multiple stimuli. Acting like an endogenous inhibitor of the Akt/mTOR signaling pathway, REDD1 protein has been shown to regulate cell growth, mitochondrial function, oxidative stress, and apoptosis. Recent studies also indicate that timely REDD1 expression limits Akt/mTOR-dependent synthesis processes to spare energy during metabolic stresses, avoiding energy collapse and detrimental consequences. In contrast to this beneficial role for metabolic adaptation, REDD1 chronic expression appears involved in the pathogenesis of several diseases. Indeed, REDD1 expression is found as an early biomarker in many pathologies including inflammatory diseases, cancer, neurodegenerative disorders, depression, diabetes, and obesity. Moreover, prolonged REDD1 expression is associated with cell apoptosis, excessive reactive oxygen species (ROS) production, and inflammation activation leading to tissue damage. In this review, we decipher several mechanisms that make REDD1 a likely metabolic double agent depending on its duration of expression in different physiological and pathological contexts. We also discuss the role played by REDD1 in the cross talk between the Akt/mTOR signaling pathway and the energetic metabolism.

Imaging tools for assessment of myocardial fibrosis in humans: the need for greater detail

Myocardial fibrosis is recognized as a key pathological process in the development of cardiac disease and a target for future therapeutics. Despite this recognition, the assessment of fibrosis is not a part of routine clinical practice. This is primarily due to the difficulties in obtaining an accurate assessment of fibrosis non-invasively. Moreover, there is a clear discrepancy between the understandings of myocardial fibrosis clinically where fibrosis is predominately studied with comparatively low-resolution medical imaging technologies like MRI compared with the basic science laboratories where fibrosis can be visualized invasively with high resolution using molecularly specific fluorescence microscopes at the microscopic and nanoscopic scales. In this article, we will first review current medical imaging technologies for assessing fibrosis including echo and MRI. We will then highlight the need for greater microscopic and nanoscopic analysis of human tissue and how this can be addressed through greater utilization of human tissue available through endomyocardial biopsies and cardiac surgeries. We will then describe the relatively new field of molecular imaging that promises to translate research findings to the clinical practice by non-invasively monitoring the molecular signature of fibrosis in patients.

Zishen Huoxue Recipe Protecting Mitochondrial Function of Hypoxic/Reoxygenated Myocardial Cells through mTORC1 Signaling Pathway

Objective

This study focuses on the role of Zishen Huoxue Decoction (ZSHX) in reducing mitochondrial membrane potential and reducing the proportion of apoptosis through the mTORC1 signaling pathway.

Methods

In our experiment, we first constructed an in vitro hypoxia/reoxygenation (H/R) model of H9C2 cells. Then, the cells were divided into control group, model group (hypoxia/reoxygenation, H/R), ZSHX, ZSHX + Rapa, low-dose ZSHX (100 μg/ml), and middle-dose ZSHX. High-dose ZSHX (400 μg/ml) group was treated with Zishen Huoxue Decoction (ZSHX). Western Blot was used to detect the expression of cell-related protein and RT-PCR was used to detect the expression of the cell-related gene in each group. Flow cytometry was used to assay for ROS content and the apoptotic ratio of H9C2 cells, Seahorse Live Cell Energy Meter was used to detect the Mitochondrial Respiratory Function in H9C2 Cells, and confocal laser scanning was used to detect the mitochondrial membrane potential of H9C2 cells.

Results

Western Blot assay showed that the relative expression of mTOR and Raptor in the H/R group was significantly lower than that in the control group (n = 3, P < 0.05). The expression of mTOR and Raptor was upregulated and the relative expression of 4E-BP1 was downregulated in the middle- and high-dose ZSHX groups (n = 3, P < 0.05). In addition, the ROS content of H9C2 cells was detected by flow cytometry, showing the ROS synthesis in H/R group (78.31 + 6.14) higher than that in the control group (34.53 + 6.10) (n = 3, P < 0.01). The ROS value was increased significantly after rapamycin inhibited mTOR (66.18 (+4.03 vs. 52.31 (+6.01), n = 3, P < 0.05). The basal mitochondrial respiration and ATP production in H/R group were significantly lower than those in the control group (38.17 + 17.76); the mitochondrial leakage in H/R model group was significantly higher than that in the control group (H/R: 40.93 + 5.18 vs. Ctrl: 27.17 + 8.92, n = 4, P < 0.05). The apoptotic rate of cardiomyocytes in the H/R model group (70.91 + 4.57) was significantly higher than that in the control group (14.52 + 2.37, n = 3, P < 0.01), and Zishen Huoxue Decoction could decrease the apoptotic rate of hypoxic-reoxygenated cardiomyocytes (ZSHX: 18.24 + 4.17 vs. H/R: 78.91 + 3.48, n = 3, P < 0.01).

Conclusion

ZSHX Decoction has the effects of activating mTORC1, inhibiting the overexpression of 4E-BP1, inhibiting fatty acid oxidation, protecting the respiratory function of mitochondria, reducing ROS and apoptosis, and thus protecting myocardial cells from injury.

SIRT1 agonism modulates cardiac NLRP3 inflammasome through pyruvate dehydrogenase during ischemia and reperfusion

Nucleotide-binding oligomerization domain-Like Receptor with a Pyrin domain 3 (NLRP3) inflammasome was emerged as a marker of metabolic dysregulation. We revealed that age-related Sirtuin-1 (SIRT1) modulates cardiac metabolism that medicated inflammatory response during ischemia and reperfusion (I/R) stress. We hypothesize that SIRT1 attenuates NLRP3 inflammasome-dependent inflammation and pyroptosis during myocardial I/R through metabolic modulation. C57BL/6J wild type (WT) mice, inducible cardiomyocyte specific SIRT1 knockout (icSIRT1 KO) and inducible cardiomyocyte specific PDH E1α knockout (icPDH E1α KO) mice were subjected to ligation and release of left anterior descending coronary artery for in vivo regional I/R models. The echocardiography measurement demonstrated that SIRT1 agonist SRT1720 (30 μg/g) improved cardiac systolic function during 45 min of ischemia and 6 h of reperfusion in C57BL/6J WT mice. The biochemical analysis showed that I/R triggered activation of cardiac pyruvate dehydrogenase (PDH), while SIRT1 agonist SRT1720 inhibited I/R-induced PDH activity and reduced production of reactive oxygen species (ROS) during myocardial I/R. Moreover, SRT1720 regulates PDH-related glucose oxidative metabolism to reduce NLRP3 inflammasome activation and pyroptosis in an Akt signaling dependent manner during I/R. Furthermore, an impaired Akt signaling was observed in icSIRT1 KO versus SIRT1^fox/flox mice under I/R stress. Intriguingly, we observed lower levels of ROS generation, decreased NLRP3 levels and less pyroptosis occurred in the icPDH E1α KO versus PDH E1α^flox/flox hearts during I/R. Taken together, the results indicate that SIRT1 agonism can inhibit activation of NLRP3 inflammasome via Akt-dependent metabolic regulation during ischemic insults by I/R.

Adverse Cardiac Remodelling after Acute Myocardial Infarction: Old and New Biomarkers

The prevalence of heart failure (HF) due to cardiac remodelling after acute myocardial infarction (AMI) does not decrease regardless of implementation of new technologies supporting opening culprit coronary artery and solving of ischemia-relating stenosis with primary percutaneous coronary intervention (PCI). Numerous studies have examined the diagnostic and prognostic potencies of circulating cardiac biomarkers in acute coronary syndrome/AMI and heart failure after AMI, and even fewer have depicted the utility of biomarkers in AMI patients undergoing primary PCI. Although complete revascularization at early period of acute coronary syndrome/AMI is an established factor for improved short-term and long-term prognosis and lowered risk of cardiovascular (CV) complications, late adverse cardiac remodelling may be a major risk factor for one-year mortality and postponded heart failure manifestation after PCI with subsequent blood flow resolving in culprit coronary artery. The aim of the review was to focus an attention on circulating biomarker as a promising tool to stratify AMI patients at high risk of poor cardiac recovery and developing HF after successful PCI. The main consideration affects biomarkers of inflammation, biomechanical myocardial stress, cardiac injury and necrosis, fibrosis, endothelial dysfunction, and vascular reparation. Clinical utilities and predictive modalities of natriuretic peptides, cardiac troponins, galectin 3, soluble suppressor tumorogenicity-2, high-sensitive C-reactive protein, growth differential factor-15, midregional proadrenomedullin, noncoding RNAs, and other biomarkers for adverse cardiac remodelling are discussed in the review.

miR‑155 inhibition represents a potential valuable regulator in mitigating myocardial hypoxia/reoxygenation injury through targeting BAG5 and MAPK/JNK signaling

Increasing evidence has indicated that miR-155 is closely associated with apoptosis, which may protect the myocardium and diminish the infarct area in myocardial ischemia reperfusion injury (IRI). In addition, studies have revealed that miR-155 serves a leading role in promoting fibroblast inflammation, cardiac dysfunction and other aspects of myocardial injury. The present study aimed to uncover the function and potential biological mechanism of miR-155 in myocardial IRI. The rat H9c2 myocardial cells was treated with hypoxia/reoxygenation (H/R) to simulate IRI in vitro. Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) was used to detect the expression levels of miR-155 mRNA. Cell Counting Kit-8 and flow cytometry assays and western blot analysis were applied to determine the biological behaviors of the H/R-treated cells. The association between miR-155 and BAG family molecular chaperone regulator 5 (BAG5) was predicted by bioinformatics software and was confirmed by dual luciferase assay. RT-qPCR and western blot analysis were used to analyze the expression of BAG5. The key proteins involved in mitogen-activated protein kinase (MAPK)/JNK signaling pathway were detected by western blot analysis. The data from the RT-qPCR assay indicated that the expression of miR-155 was markedly upregulated in the H/R model, and that downregulation of miR-155 may promote cell proliferation and inhibit cell apoptosis, and vice versa. BAG5, which was downregulated in the H/R model, was confirmed as a target of miR-155 and negatively modulated by miR-155. The key proteins involved in MAPK/JNK signaling, which were highly expressed in the H/R model, were suppressed by treatment with the miR-155 inhibitor, and overexpression of BAG5 promoted the protective effect of miR-155 inhibition on cell injury caused by H/R. In addition, the expression patterns of hypoxia-inducible factor 1-α and von Hippel-Lindau were altered following different treatments. Taken together, the data from the present study indicated that miR-155 inhibition represented a potential treatment strategy to improve myocardial H/R injury, which may be associated with targeting BAG5 and inhibition of the MAPK/JNK pathway.

Antithrombin III Alleviates Myocardial Ischemia/Reperfusion Injury by Inhibiting Excessive Autophagy in a Phosphoinositide 3-Kinase/Akt-Dependent Manner

Autophagy is fundamental to myocardial ischemia/reperfusion (I/R) injury. Antithrombin III (AT) has been shown to protect cardiomyocytes against I/R injury; however, it is unknown whether it modulates autophagy. The objective of this study was to investigate whether AT regulates autophagy during I/R injury and, if so, to identify the potential mechanism involved. Our study showed that AT attenuated I/R injury in vivo and hypoxia/reoxygenation (H/R) injury in vitro. Autophagy was increased both in H9C2 cardiomyocytes during H/R injury and in mouse hearts following I/R injury. The stimulation of autophagy by rapamycin attenuated the protective effect of AT against H9C2 cell injury, indicating that autophagy is involved in the protective role of AT. Furthermore, the cardioprotective effects of AT were abolished by A6730, a specific Akt inhibitor. This study shows that AT exhibits cardioprotective effects by modulating autophagy during I/R injury in a phosphoinositide 3-kinase/Akt-dependent manner.

Pharmacologic ATF6 activation confers global protection in widespread disease models by reprograming cellular proteostasis

Pharmacologic activation of stress-responsive signaling pathways provides a promising approach for ameliorating imbalances in proteostasis associated with diverse diseases. However, this approach has not been employed in vivo. Here we show, using a mouse model of myocardial ischemia/reperfusion, that selective pharmacologic activation of the ATF6 arm of the unfolded protein response (UPR) during reperfusion, a typical clinical intervention point after myocardial infarction, transcriptionally reprograms proteostasis, ameliorates damage and preserves heart function. These effects were lost upon cardiac myocyte-specific Atf6 deletion in the heart, demonstrating the critical role played by ATF6 in mediating pharmacologically activated proteostasis-based protection of the heart. Pharmacological activation of ATF6 is also protective in renal and cerebral ischemia/reperfusion models, demonstrating its widespread utility. Thus, pharmacologic activation of ATF6 represents a proteostasis-based therapeutic strategy for ameliorating ischemia/reperfusion damage, underscoring its unique translational potential for treating a wide range of pathologies caused by imbalanced proteostasis.

Exercise and Cardioprotection: A Natural Defense Against Lethal Myocardial Ischemia-Reperfusion Injury and Potential Guide to Cardiovascular Prophylaxis

Similar to ischemic preconditioning, high-intensity exercise has been shown to decrease infarct size following myocardial infarction. In this article, we review the literature on beneficial effects of exercise, exercise requirements for cardioprotection, common methods utilized in laboratories to study this phenomenon, and discuss possible mechanisms for exercise-mediated cardioprotection.

Differential Effects of Normoxic and Hyperoxic Reperfusion on Global Myocardial Ischemia-Reperfusion Injury

The objectives were to investigate if after hypoxia or ischemia, normoxic reperfusion is associated with less oxidant stress (OS), inflammation, and myocardial injury than hyperoxic reperfusion. In this study, cardiomyocytes (H9c2 cells) were cultured in hypoxia, followed by reoxygenation in normoxia or hyperoxia. Cardiomyocyte OS, inflammation, and apoptosis were measured. In parallel experiments, rabbits were cannulated for cardiopulmonary bypass (CPB). Following cardioplegic arrest and aortic cross-clamp removal, hearts were reperfused under normoxic or hyperoxic conditions. Left ventricular developed pressure and contractility (LV +dP/dt) were recorded, and blood samples and heart tissues were collected for measurement of OS, inflammation, and cardiac injury. Results showed that H9c2 cells exposed to hyperoxic reoxygenation showed significant increases in OS, inflammation, and apoptosis compared to normoxic reoxygenation. Following CPB and 2-hour hyperoxic reperfusion, LV +dP/dt and left ventricular developed pressure were significantly decreased compared with pre-CPB values (to 36 ± 21%, P = 0.002; and 53 ± 20%, P = 0.02, respectively), associated with significant increases in all plasma and tissue biomarkers for OS, inflammation, and myocardial injury. In contrast, LV +dP/dt was relatively well preserved under normoxic reperfusion conditions (to 70 ± 14% after 2-hour reperfusion), and was associated with an attenuated myocardial OS, inflammatory, apoptotic, and injury response compared to the hyperoxia group (eg, cTn-I: 5.9 ± 1.5 vs 20.2 ± 7.6 ng/mL, respectively, P < 0.0001). Overall, in both in vitro and in vivo experiments, normoxic reperfusion/reoxygenation was associated with less robust OS, inflammation, apoptosis, and myocardial injury compared with hyperoxic reperfusion/reoxygenation. These results suggest that hyperoxia should be avoided to minimize myocardial OS, inflammation, and ventricular dysfunction after CPB.

Mitochondrial membrane potential

The mitochondrial membrane potential (ΔΨm) generated by proton pumps (Complexes I, III and IV) is an essential component in the process of energy storage during oxidative phosphorylation. Together with the proton gradient (ΔpH), ΔΨm forms the transmembrane potential of hydrogen ions which is harnessed to make ATP. The levels of ΔΨm and ATP in the cell are kept relatively stable although there are limited fluctuations of both these factors that can occur reflecting normal physiological activity. However, sustained changes in both factors may be deleterious. A long-lasting drop or rise of ΔΨm vs normal levels may induce unwanted loss of cell viability and be a cause of various pathologies. Among other factors, ΔΨm plays a key role in mitochondrial homeostasis through selective elimination of dysfunctional mitochondria. It is also a driving force for transport of ions (other than H+) and proteins which are necessary for healthy mitochondrial functioning. We propose additional potential mechanisms for which ΔΨm is essential for maintenance of cellular health and viability and provide recommendations how to accurately measure ΔΨm in a cell and discuss potential sources of artifacts.

Lipid Emulsion Inhibits Apoptosis Induced by a Toxic Dose of Verapamil via the Delta-Opioid Receptor in H9c2 Rat Cardiomyoblasts

The goals of this study were to investigate the effects of lipid emulsion (LE) on apoptosis induced by a toxic dose of verapamil in H9c2 cells and to elucidate the associated cellular mechanism. The effects of LE alone and combined with an inhibitor on the decreases in cell counts and viability induced by verapamil and diltiazem were examined using the MTT assay. The effects of verapamil alone, combined LE and verapamil treatment, and combined inhibitor, LE and verapamil treatment on cleaved caspase-3, caspase-8 and Bax expression, were examined using Western blotting. The effects of verapamil alone and combined with LE on the number of TUNEL-positive H9c2 cells were also examined. LE attenuated the decreases in cell counts and viability induced by verapamil and diltiazem. However, the magnitude of the LE-mediated attenuation of decreased cell viability was enhanced by verapamil compared with diltiazem treatment. Naloxone, naltrindole hydrochloride, LY294002 and MK-2206 inhibited the LE-mediated attenuation of increased cleaved caspase-3 and caspase-8 expression induced by verapamil. LE attenuated the increase in the number of TUNEL-positive cell induced by verapamil. These results suggest that LE attenuates apoptosis induced by verapamil via activation of the delta-opioid receptor, phosphoinositide 3-kinase and Akt.

MicroRNA-206 Protects against Myocardial Ischaemia-Reperfusion Injury in Rats by Targeting Gadd45β

MicroRNAs are widely involved in the pathogenesis of cardiovascular diseases through regulating gene expression via translational inhibition or degradation of their target mRNAs. Recent studies have indicated a critical role of microRNA-206 in myocardial ischaemia-reperfusion (I/R) injury. However, the function of miR-206 in myocardial I/R injury is currently unclear. The present study was aimed to identify the specific role of miR-206 in myocardial I/R injury and explore the underlying molecular mechanism. Our results revealed that the expression level of miR-206 was significantly decreased both in rat I/R group and H9c2 cells subjected to hypoxia/reoxygenation (H/R) compared with the corresponding control. Overexpression of miR-206 observably decreased infarct size and inhibited the cardiomyocyte apoptosis induced by I/R injury. Furthermore, bioinformatics analysis, luciferase activity and western blot assay proved that Gadd45β (growth arrest DNA damage-inducible gene 45β) was a direct target gene of miR-206. In addition, the expression of pro-apoptotic-related genes, such as p53, Bax and cleaved caspase3, was decreased in association with the down-regulation of Gadd45β. In summary, this study demonstrates that miR-206 could protect against myocardial I/R injury by targeting Gadd45β.

The cardioprotective effects of (-)-Epicatechin are mediated through arginase activity inhibition in a murine model of ischemia/reperfusion

The production of nitric oxide (NO) by nitric oxide synthases (NOS) depends on the bioavailability of L-arginine as NOS competes with arginase for this common substrate. As arginase activity increases, less NO is produced and adverse cardiovascular consequences can emerge. (-)-Epicatechin (EPI), the most abundant flavonoid in cacao, has been reported to stimulate endothelial and neuronal NOS expression and function leading to enhanced vascular function and cardioprotective effects. However, little is known about the effects of EPI on myocardial arginase activity. The aim of the present study was to determine if EPI is able to interact and modulate myocardial arginase and NOS expression and activity. For this purpose, in silico modeling, in vitro activity assays and a rat model of ischemia/reperfusion injury were used. In silico and in vitro results demonstrate that EPI can interact with arginase and significantly decrease its activity. In vivo, 10 days of EPI pretreatment reduces ischemic myocardium arginase expression while increasing NOS expression and phosphorylation levels. Altogether, these results may partially account for the cardioprotective effects of EPI.

Ischemia/Reperfusion Injury following Acute Myocardial Infarction: A Critical Issue for Clinicians and Forensic Pathologists

Acute myocardial infarction (AMI) is a leading cause of morbidity and mortality. Reperfusion strategies are the current standard therapy for AMI. However, they may result in paradoxical cardiomyocyte dysfunction, known as ischemic reperfusion injury (IRI). Different forms of IRI are recognized, of which only the first two are reversible: reperfusion-induced arrhythmias, myocardial stunning, microvascular obstruction, and lethal myocardial reperfusion injury. Sudden death is the most common pattern for ischemia-induced lethal ventricular arrhythmias during AMI. The exact mechanisms of IRI are not fully known. Molecular, cellular, and tissue alterations such as cell death, inflammation, neurohumoral activation, and oxidative stress are considered to be of paramount importance in IRI. However, comprehension of the exact pathophysiological mechanisms remains a challenge for clinicians. Furthermore, myocardial IRI is a critical issue also for forensic pathologists since sudden death may occur despite timely reperfusion following AMI, that is one of the most frequently litigated areas of cardiology practice. In this paper we explore the literature regarding the pathophysiology of myocardial IRI, focusing on the possible role of the calpain system, oxidative-nitrosative stress, and matrix metalloproteinases and aiming to foster knowledge of IRI pathophysiology also in terms of medicolegal understanding of sudden deaths following AMI.

Roles of miR-17-92 Cluster in Cardiovascular Development and Common Diseases

MicroRNAs (miRNAs and miRs) are a large class of noncoding, single-stranded, small RNA molecules. The precise control of their expression is essential for keeping tissue homeostasis and normal development of organisms. Thus, unbalanced expression of miRNAs is a hallmark of many diseases. Two to dozens of miRNAs can form into a miRNA cluster, and the miR-17-92 cluster is one of them. Although firstly described as an oncogenic miRNA cluster, the miR-17-92 cluster has also been found to play critical role in normal cardiac development and cardiovascular disease. This review focuses on the characteristics and functions of miR-17-92 cluster in heart.

Cardiac Ischemia/Reperfusion Injury: The Beneficial Effects of Exercise

Cardiac ischemia reperfusion injury (IRI) occurs when the myocardium is revascularized after an episode of limited or absent blood supply. Many changes, including free radical production, calcium overload, protease activation, altered membrane lipids and leukocyte activation, contribute to IRI-induced myocardium damage. Aerobic exercise is the only countermeasure against IRI that can be sustained on a regular basis in clinical practice. Interestingly, both short-term (3-5 days) and long-term (several weeks) exercise increase myocardial tolerance, reduce infarct size area and arrhythmias induced by IRI. Exercise protects the heart against IRI in a biphasic manner. The early phase of cardioprotection occurs between 30 min and 3 h following an acute exercise bout, whilst the late phase is achieved within 24 h after the exercise bout and persists for several days. As for the exercise intensity, although controversial data exists, it is feasible that the amount of cardioprotection is proportional to exercise intensity and only achieved above a critical threshold. It is known that aerobic exercise produces a cardioprotective phenotype, however the mechanisms responsible for this phenomenon remain unclear. Apparently, aerobic exercise-induced preconditioning is dependent on several factors that work together to protect the heart. Altered nitric oxide (NO) signaling, increased levels of heat shock proteins (HSPs), enhanced function of ATP-sensitive potassium channels, increased activation of opioids system, and enhanced antioxidant capacity may contribute to exercise-induced cardioprotection. Much has been discovered from animal models involving exercise-induced cardioprotection against cardiac IRI, however translating these findings to clinical practice still represents the major challenge in this field.

Ischemia/Reperfusion

Ischemic disorders, such as myocardial infarction, stroke, and peripheral vascular disease, are the most common causes of debilitating disease and death in westernized cultures. The extent of tissue injury relates directly to the extent of blood flow reduction and to the length of the ischemic period, which influence the levels to which cellular ATP and intracellular pH are reduced. By impairing ATPase-dependent ion transport, ischemia causes intracellular and mitochondrial calcium levels to increase (calcium overload). Cell volume regulatory mechanisms are also disrupted by the lack of ATP, which can induce lysis of organelle and plasma membranes. Reperfusion, although required to salvage oxygen-starved tissues, produces paradoxical tissue responses that fuel the production of reactive oxygen species (oxygen paradox), sequestration of proinflammatory immunocytes in ischemic tissues, endoplasmic reticulum stress, and development of postischemic capillary no-reflow, which amplify tissue injury. These pathologic events culminate in opening of mitochondrial permeability transition pores as a common end-effector of ischemia/reperfusion (I/R)-induced cell lysis and death. Emerging concepts include the influence of the intestinal microbiome, fetal programming, epigenetic changes, and microparticles in the pathogenesis of I/R. The overall goal of this review is to describe these and other mechanisms that contribute to I/R injury. Because so many different deleterious events participate in I/R, it is clear that therapeutic approaches will be effective only when multiple pathologic processes are targeted. In addition, the translational significance of I/R research will be enhanced by much wider use of animal models that incorporate the complicating effects of risk factors for cardiovascular disease. © 2017 American Physiological Society. Compr Physiol 7:113-170, 2017.

Rapamycin Reduced Ischemic Brain Damage in Diabetic Animals Is Associated with Suppressions of mTOR and ERK1/2 Signaling

The objectives of the present study are to investigate the activation of mTOR and ERK1/2 signaling after cerebral ischemia in diabetic rats and to examine the neuroprotective effects of rapamycin. Ten minutes transient global cerebral ischemia was induced in straptozotocin-induced diabetic hyperglycemic rats and non-diabetic, euglycemic rats. Brain samples were harvested after 16 h of reperfusion. Rapamycin or vehicle was injected 1 month prior to the induction of ischemia. The results showed that diabetes increased ischemic neuronal cell death and associated with elevations of p-P70S6K and Ras/ERK1/2 and suppression of p-AMPKα. Rapamycin ameliorated diabetes-enhanced ischemic brain damage and suppressed phosphorylation of P70S6K and ERK1/2. It is concluded that diabetes activates mTOR and ERK1/2 signaling pathways in rats subjected to transient cerebral ischemia and inhibition of mTOR by rapamycin reduces ischemic brain damage and suppresses the mTOR and ERK1/2 signaling in diabetic settings.

MicroRNA-128 inhibition attenuates myocardial ischemia/reperfusion injury-induced cardiomyocyte apoptosis by the targeted activation of peroxisome proliferator-activated receptor gamma

The aim of the present study was to investigate the effects of microRNA (miR)-128 inhibition on the targeted activation of peroxisome proliferator-activated receptor gamma (PPARG) and on cardiomyocyte apoptosis induced by myocardial ischemia/reperfusion (I/R) injury. In vitro, the expression of PPARG was detected by reverse transcription-quantitative polymerase chain reaction and western blotting in neonatal rat ventricular myocytes (NRVMs) and HEK293 cells transfected with the mimics or inhibitors of miR-128 or control RNA. Luciferase reporter assays were used to identify whether PPARG is a direct target of miR-128. In vivo, miR-128 was knocked down via ear vein injection of antagomir-128 in a rabbit myocardial I/R injury model. Western blotting investigated the activation of Akt [phosphorylated (p)-Akt] and the expression of total-Akt, PPARG and myeloid leukemia cell differentiation protein-1 (Mcl-1) in the myocardium. Cardiomyocyte apoptosis was examined with transmission electron microscropy and terminal deoxynucleotidyl transferase dUTP nick end labeling staining. PPARG mRNA and protein were downregulated in NRVMs transfected with miR-128 mimics, but upregulated by antagomir-128 compared with control. This indicates that PPARG is a direct miR-128 target. Activation of Akt (p-Akt), Mcl-1 and PPARG expression in the myocardium were increased by miR-128 inhibition. Furthermore, miR-128 antagomirs significantly reduced apoptosis in hearts subjected to I/R injury, which was blocked by the PPARG inhibitor GW9662. In conclusion, miR-128 inhibition attenuated I/R injury-induced cardiomyocyte apoptosis by the targeted activation of PPARG signaling.

Parthenolide-Induced Cytotoxicity in H9c2 Cardiomyoblasts Involves Oxidative Stress

BACKGROUND

Cardiac cellular injury as a consequence of ischemia and reperfusion involves nuclear factor-κB (NF-κ B), amongst other factors, and NF-κ B inhibitors could substantially reduce myocardial infarct size. Parthenolide, a sesquiterpene lactone compound which could inhibit NF-κ B, has been shown to ameliorate myocardial reperfusion injury but may also produce toxic effects in cardiomyocytes at high concentrations. The aim of this study was to examine the cytotoxic effects of this drug on H9c2 cardiomyoblasts, which are precursor cells of cardiomyocytes.

METHODS

Cell viability and apoptosis were examined by MTT and TUNEL assay, respectively, and protein expression was analyzed by western blot. Reactive oxygen species (ROS) production was measured using DCFH-DA as dye. Cytosolic Ca(2+) concentration and mitochondrial membrane potential were measured microfluorimetrically using, respectively, fura 2 and rhodamine 123 as dyes.

RESULTS

Parthenolide caused apoptosis at 30 μ M, as judged by TUNEL assay and Bax and cytochrome c translocation. It also caused collapse of mitochondrial membrane potential and endoplasmic reticulum stress. Parthenolide triggered ROS formation, and vitamin C (antioxidant) partially alleviated parthenolide-induced cell death.

CONCLUSIONS

The results suggested that parthenolide at high concentrations caused cytotoxicity in cardiomyoblasts in part by inducing oxidative stress, and demonstrated the imperative for cautious and appropriate use of this agent in cardioprotection.

KEY WORDS

Cardiomyoblast; Endoplasmic reticulum stress; Oxidative stress; Parthenolide; Reperfusion injury.

NLRP3 inflammasome activation during myocardial ischemia reperfusion is cardioprotective

BACKGROUND

The innate immune receptor NLRP3 recognizes tissue damage and initiates inflammatory processes through formation multiprotein complexes with the adaptor protein ASC and caspase-1, i.e. NLRP3 inflammasomes, which through cleavage of pro-IL-1β mediates release of bioactive IL-1β. We hypothesized that NLRP3 mediates tissue damage during acute myocardial infarction (MI) and sought to investigate the mechanisms herein in an experimental MI model in mice.

METHODS AND RESULTS

The left coronary artery (LCA) of WT, NLRP3(-/-) and ASC(-/-) mice of both genders was ligated for 30 min followed by 3 or 24 h reperfusion. For pre-conditioning studies, the TLR2 agonist Pam3CSK4 or PBS was injected intraperitoneally 60 min prior to LCA ligation. For mechanistic investigations, blood plasmas and left ventricle tissues were collected, and a hypothesis-driven selection of protein or mRNA targets was investigated. Surprisingly, hearts from NLRP3-deficient mice featured larger infarct size than WT mice (p = 0.0048). In general, there were only modest changes with no significant pattern in myocardial infiltration of neutrophils and macrophages and systemic and myocardial cytokine expression between the three genotypes. Preconditioning with the TLR2 agonist Pam3CSK4 induced Akt phosphorylation and reduced infarct size in WT but not NLRP3 -or ASC -deficient hearts.

CONCLUSION

Absence of NLRP3 results in increased myocardial infarct size after in vivo ischemia reperfusion, seemingly due to dysfunction of the cardioprotective RISK pathway. Our data imply that NLRP3 contributes to cardio-protection during I/R and do not support a role for NLRP3 or ASC inhibition in the management of acute MI including revascularization therapy.

Effect of Elevated Reperfusion Pressure on “No Reflow” Area and Infarct Size in a Porcine Model of Ischemia–Reperfusion

Background:

The “no reflow” phenomenon (microvascular obstruction despite restoration of epicardial blood flow) develops postreperfusion in acute myocardial infarction and is associated with poor prognosis. We hypothesized that increased reperfusion pressure may attenuate the no reflow phenomenon, as it could provide adequate flow to overcome the high resistance of the microvasculature within the no reflow zone. Thus, we investigated the effect of modestly elevated blood pressure during reperfusion on the extent of no reflow area and infarct size in a porcine model of ischemia–reperfusion.

Methods:

Eighteen farm pigs underwent acute myocardial infarction by occlusion of the anterior descending coronary artery for 1 hour, followed by 2 hours of reperfusion. Just prior to reperfusion, animals were randomized into 2 groups: in group 1 (control group, n = 9), no intervention was performed. In group 2 (n = 9), aortic pressure was increased by ∼20% (compared to ischemia) by partial clamping of the ascending aorta during reperfusion. Following 2 hours of reperfusion, animals were euthanized to measure area at risk, infarct size, and area of no reflow.

Results:

Partial clamping of the ascending aorta resulted in modest elevation of blood pressure during reperfusion. The area at risk did not differ between the 2 groups. The no reflow area was significantly increased in group 2 compared to control animals (50% ± 13% vs 37% ± 9% of the area at risk; P = .04). The infarcted area was significantly increased in group 2 compared to control animals (75% ± 17% vs 52% ± 23% of the area at risk; P = .03). Significant positive correlations were observed between systolic aortic pressure and no reflow area, between systolic aortic pressure and infarcted area and between infarcted area and no reflow area during reperfusion.

Conclusions:

Modestly elevated blood pressure during reperfusion is associated with an increase in no reflow area and in infarct size in a clinically relevant porcine model of ischemia–reperfusion.

All-Trans Retinoic Acid Ameliorates Myocardial Ischemia/Reperfusion Injury by Reducing Cardiomyocyte Apoptosis

Myocardial ischemia/reperfusion (I/R) injury interferes with the restoration of blood flow to ischemic myocardium. Oxidative stress-elicited apoptosis has been reported to contribute to I/R injury. All-trans retinoic acid (ATRA) has anti-apoptotic activity as previously reported. Here, we investigated the effects and the mechanism of action of ATRA on myocardial I/R injury both in vivo and in vitro. In vivo, ATRA reduced the size of the infarcted area (17.81±1.05% vs. 24.41±1.03%, P<0.05) and rescued cardiac function loss (ejection fraction 46.42±6.76% vs. 37.18±4.63%, P<0.05) after I/R injury. Flow-cytometric analysis and TUNEL assay demonstrated that the protective role of ATRA on myocardial I/R injury was related to its anti-apoptotic effects. The anti-apoptotic effects of ATRA were associated with partial inhibition of reactive oxygen species (ROS) production and significantly less phosphorylation of mitogen-activated protein kinases (MAPKs) including p38, JNK, and ERK. Western blot analysis also revealed that ATRA pre-treatment increased a disintegrin and metalloproteinase domain-containing protein 10 (ADAM10) expression (0.65 ± 0.20 vs. 0.41±0.02 in vivo) and reduced the level of receptor for advanced glycation end-products (RAGE) (0.38 ± 0.17 vs. 0.52 ± 0.11 in vivo). Concomitantly, the protective role of ATRA on I/R injury was not observed in RAGE-KO mice. The current results indicated that ATRA could prevent myocardial injury and reduced cardiomyocyte apoptosis after I/R effectively. One possible mechanism underlying these effects is that ATRA could increase ADAM10 expression and thus cleave RAGE, which is the main receptor up-stream of MAPKs in myocardial I/R injury, resulting in the down-regulation of MAPK signaling and protective role on myocardial I/R injury.

Ischemia-reperfusion: From cell biology to acute kidney injury

Ischemia reperfusion injury occurs in the kidney when blood supply is interrupted in clinical settings such as kidney transplantation or nephron sparing surgery for renal tumors. These lesions lead to acute kidney injury (AKI) a detrimental situation associated with impaired short-term allograft function (delayed graft function or primary non function) but also long-term transplant survival through the onset of chronic allograft nephropathy. The present review details the cellular and molecular consequences of ischemia reperfusion in a native kidney as well as in a kidney graft after cold ischemia time, giving a comprehensive description of biological pathways involved during the phase of ischemia and during the reperfusion period where the rapid return to normoxia leads to a large burst of reactive oxygen species along with a dramatic reduction in antioxidant defenses. This work also focuses on the distinct susceptibilities of kidney cells to ischemia (endothelial vs epithelial) and the outcome of acute kidney injury.

Vagus nerve stimulation initiated late during ischemia, but not reperfusion, exerts cardioprotection via amelioration of cardiac mitochondrial dysfunction

BACKGROUND

We previously reported that vagus nerve stimulation (VNS) applied immediately at the onset of cardiac ischemia provides cardioprotection against cardiac ischemic-reperfusion (I/R) injury.

OBJECTIVE

This study aimed to determine whether VNS applied during ischemia or at the onset of reperfusion exerts differential cardioprotection against cardiac I/R injury.

METHODS

Twenty-eight swine (25-30 kg) were randomized into 4 groups: Control (sham-operated, no VNS), VNS-ischemia (VNS applied during ischemia), VNS-reperfusion (VNS applied during reperfusion), and VNS-ischemia+atropine (VNS applied during ischemia with 1 mg/kg atropine administration). Ischemia was induced by left anterior descending (LAD) coronary artery occlusion for 60 minutes, followed by 120 minutes of reperfusion. VNS was applied either 30 minutes after LAD coronary artery occlusion or at the onset of reperfusion and continued until the end of reperfusion. Cardiac function, infarct size, myocardial levels of connexin 43, cytochrome c, tumor necrosis factor α, and interleukin 4, and cardiac mitochondrial function were determined.

RESULTS

VNS applied 30 minutes after LAD coronary artery occlusion, but not at reperfusion, markedly reduced ventricular fibrillation incidence and infarct size (~59%), improved cardiac function; attenuated cardiac mitochondrial reactive oxygen species production, depolarization, swelling, and cytochrome c release; and increased the amount of phosphorylated connexin 43 and interleukin 4 as compared with the Control group. These beneficial effects of VNS were abolished by atropine.

CONCLUSION

VNS could provide significant cardioprotective effects even when initiated later during ischemia, but was not effective after reperfusion. These findings indicate the importance of timing of VNS initiation and warrant the potential clinical application of VNS in protecting myocardium at risk of I/R injury.

Inhibition of the cardiomyocyte-specific kinase TNNI3K limits oxidative stress, injury, and adverse remodeling in the ischemic heart

Percutaneous coronary intervention is first-line therapy for acute coronary syndromes (ACS) but can promote cardiomyocyte death and cardiac dysfunction via reperfusion injury, a phenomenon driven in large part by oxidative stress. Therapies to limit this progression have proven elusive, with no major classes of new agents since the development of anti-platelets/anti-thrombotics. We report that cardiac troponin I-interacting kinase (TNNI3K), a cardiomyocyte-specific kinase, promotes ischemia/reperfusion injury, oxidative stress, and myocyte death. TNNI3K-mediated injury occurs through increased mitochondrial superoxide production and impaired mitochondrial function and is largely dependent on p38 mitogen-activated protein kinase (MAPK) activation. We developed a series of small-molecule TNNI3K inhibitors that reduce mitochondrial-derived superoxide generation, p38 activation, and infarct size when delivered at reperfusion to mimic clinical intervention. TNNI3K inhibition also preserves cardiac function and limits chronic adverse remodeling. Our findings demonstrate that TNNI3K modulates reperfusion injury in the ischemic heart and is a tractable therapeutic target for ACS. Pharmacologic TNNI3K inhibition would be cardiac-selective, preventing potential adverse effects of systemic kinase inhibition.