Endothelial-cardiomyocyte crosstalk enhances pharmacological cardioprotection

Optimizing myocardial cell protection with xanthine derivative KMUP-3 potentiates autophagy through the PI3K/Akt/eNOS axis

BACKGROUND

Autophagy can have either beneficial or detrimental effects on various heart diseases. Pharmacological interventions improve cardiac function, which is correlated with enhanced autophagy. To assess whether a xanthine derivative (KMUP-3) treatment coincides with enhanced autophagy while also providing cardio-protection, we investigated the hypothesis that KMUP-3 treatment activation of autophagy through PI3K/Akt/eNOS signalling offered cardioprotective properties.

METHODS

The pro-autophagic effect of KMUP-3 was performed in a neonatal rat model targeting cardiac fibroblasts and cardiomyocytes, and by assessing the impact of KMUP-3 treatment on cardiotoxicity, we used antimycin A-induced cardiomyocytes.

RESULTS

As determined by transmission electron microscopy observation, KMUP-3 enhanced autophagosome formation in cardiac fibroblasts. Furthermore, KMUP-3 significantly increased the expressions of autophagy-related proteins, LC3 and Beclin-1, both in a time- and dose-dependent manner; moreover, the pro-autophagy and nitric oxide enhancement effects of KMUP-3 were abolished by inhibitors targeting eNOS and PI3K in cardiac fibroblasts and cardiomyocytes. Notably, KMUP-3 ameliorated cytotoxic effects induced by antimycin A, demonstrating its protective autophagic response.

CONCLUSION

These findings enable the core pathway of PI3K/Akt/eNOS axis in KMUP-3-enhanced autophagy activation and suggest its principal role in safeguarding against cardiotoxicity.

Two decades of heart regeneration research: Cardiomyocyte proliferation and beyond

Interest in vertebrate cardiac regeneration has exploded over the past two decades since the discovery that adult zebrafish are capable of complete heart regeneration, contrasting the limited regenerative potential typically observed in adult mammalian hearts. Undercovering the mechanisms that both support and limit cardiac regeneration across the animal kingdom may provide unique insights in how we may unlock this capacity in adult humans. In this review, we discuss key discoveries in the heart regeneration field over the last 20 years. Initially, seminal findings revealed that pre-existing cardiomyocytes are the major source of regenerated cardiac muscle, drawing interest into the intrinsic mechanisms regulating cardiomyocyte proliferation. Moreover, recent studies have identified the importance of intercellular interactions and physiological adaptations, which highlight the vast complexity of the cardiac regenerative process. Finally, we compare strategies that have been tested to increase the regenerative capacity of the adult mammalian heart. This article is categorized under: Cardiovascular Diseases > Stem Cells and Development.

The benign nature and rare occurrence of cardiac myxoma as a possible consequence of the limited cardiac proliferative/ regenerative potential: a systematic review

BACKGROUND

Cardiac Myxoma is a primary tumor of heart. Its origins, rarity of the occurrence of primary cardiac tumors and how it may be related to limited cardiac regenerative potential, are not yet entirely known. This study investigates the key cardiac genes/ transcription factors (TFs) and signaling pathways to understand these important questions.

METHODS

Databases including PubMed, MEDLINE, and Google Scholar were searched for published articles without any date restrictions, involving cardiac myxoma, cardiac genes/TFs/signaling pathways and their roles in cardiogenesis, proliferation, differentiation, key interactions and tumorigenesis, with focus on cardiomyocytes.

RESULTS

The cardiac genetic landscape is governed by a very tight control between proliferation and differentiation-related genes/TFs/pathways. Cardiac myxoma originates possibly as a consequence of dysregulations in the gene expression of differentiation regulators including Tbx5, GATA4, HAND1/2, MYOCD, HOPX, BMPs. Such dysregulations switch the expression of cardiomyocytes into progenitor-like state in cardiac myxoma development by dysregulating Isl1, Baf60 complex, Wnt, FGF, Notch, Mef2c and others. The Nkx2-5 and MSX2 contribute predominantly to both proliferation and differentiation of Cardiac Progenitor Cells (CPCs), may possibly serve roles based on the microenvironment and the direction of cell circuitry in cardiac tumorigenesis. The Nkx2-5 in cardiac myxoma may serve to limit progression of tumorigenesis as it has massive control over the proliferation of CPCs. The cardiac cell type-specific genetic programming plays governing role in controlling the tumorigenesis and regenerative potential.

CONCLUSION

The cardiomyocytes have very limited proliferative and regenerative potential. They survive for long periods of time and tightly maintain the gene expression of differentiation genes such as Tbx5, GATA4 that interact with tumor suppressors (TS) and exert TS like effect. The total effect such gene expression exerts is responsible for the rare occurrence and benign nature of primary cardiac tumors. This prevents the progression of tumorigenesis. But this also limits the regenerative and proliferative potential of cardiomyocytes. Cardiac Myxoma develops as a consequence of dysregulations in these key genes which revert the cells towards progenitor-like state, hallmark of CM. The CM development in carney complex also signifies the role of TS in cardiac cells.

Endothelial cell dysfunction in cardiac disease: driver or consequence?

The vascular endothelium is a multifunctional cellular system which directly influences blood components and cells within the vessel wall in a given tissue. Importantly, this cellular interface undergoes critical phenotypic changes in response to various biochemical and hemodynamic stimuli, driving several developmental and pathophysiological processes. Multiple studies have indicated a central role of the endothelium in the initiation, progression, and clinical outcomes of cardiac disease. In this review we synthesize the current understanding of endothelial function and dysfunction as mediators of the cardiomyocyte phenotype in the setting of distinct cardiac pathologies; outline existing in vivo and in vitro models where key features of endothelial cell dysfunction can be recapitulated; and discuss future directions for development of endothelium-targeted therapeutics for cardiac diseases with limited existing treatment options.

Pregnancy hypertension-associated endothelial dysfunction is attenuated by isoflurane anesthesia: Evidence of protective effect related to increases in nitric oxide

AIMS

Pregnancy hypertension-induced endothelial dysfunction associated with impairment of nitric oxide (NO) bioavailability and hemodynamic derangements is a challenging for urgent procedures requiring maternal anesthesia. The volatile anesthetic isoflurane has demonstrated NO-associated protective effects. However, this isoflurane-induced effect is still unclear in pregnancy hypertension. Therefore, the present study examined the potential protective effects of isoflurane anesthesia on endothelial dysfunction and hemodynamic changes induced by hypertensive pregnancy associated with fetal and placental growth restrictions.

MATERIALS AND METHODS

Animals were distributed into four groups: normotensive pregnant rats (Preg), anesthetized pregnant rats (Preg+Iso), hypertensive pregnant rats (HTN-Preg), and anesthetized hypertensive pregnant rats (HTN-Preg+Iso). Systolic and diastolic pressures, mean arterial pressure (MAP), heart rate, fetal and placental weights, vascular contraction, endothelium-derived NO-dependent vasodilation, and NO levels were assessed. The vascular endothelial growth factor (VEGF) levels and endothelial NO synthase (eNOS) Serine (1177) phosphorylation (p-eNOS) expression were also examined.

KEY FINDINGS

Isoflurane produced more expressive hypotensive effects in the HTN-Preg+Iso versus Preg+Iso group, with respective reductions in MAP by 50 ± 13 versus 25 ± 4 mmHg (P < 0.05). Also, HTN-Preg+Iso compared to the HTN-Preg group showed (respectively) preventions against the weight loss of the fetuses (4.0 ± 0.6 versus 2.8 ± 0.6 g, P < 0.05) and placentas (0.37 ± 0.06 versus 0.30 ± 0.06 mg, P < 0.05), hyper-reactive vasocontraction response (1.8 ± 0.4 versus 2.8 ± 0.6 g, P < 0.05), impaired endothelium-derived NO-dependent vasodilation (84 ± 8 versus 50 ± 17 %, P < 0.05), reduced VEGF levels (147 ± 46 versus 25 ± 13 pg/mL, P < 0.05), and decreased p-eNOS expression (0.24 ± 0.07 versus 0.09 ± 0.05 arbitrary units, P < 0.05).

SIGNIFICANCE

Isoflurane anesthesia protects maternal endothelial function in pregnancy hypertension, and possibly endothelium-derived NO is involved.

Roflumilast reduces myocardial ischemia reperfusion injury in vivo and in vitro by activating the AMPK signaling pathway

Myocardial tissue cell damage induced by myocardial ischemia/reperfusion (MI/R) notably elevates the mortality rate, increases the complications of patients with myocardial infarction and decreases reperfusion benefit in patients suffering from acute myocardial infarction. Roflumilast protect against cardiotoxicity. Therefore, the present study aimed to investigate the effect of roflumilast on MI/R injury and the underlying mechanisms. To simulate MI/R in vivo and in vitro, the rat model of MI/R was established and H9C2 cells were subjected to hypoxia/reoxygenation (H/R) induction, respectively. The myocardial infarction areas were observed by 2,3,5-triphenyltetrazolium chloride staining. The myocardial enzyme levels in serum and levels of inflammatory cytokines and oxidative stress markers in cardiac tissue were assessed by corresponding assay kits. The cardiac damage was observed by hematoxylin and eosin staining. The mitochondrial membrane potential in cardiac tissue and H9C2 cells was detected using the JC-1 staining kit. The viability and apoptosis of H9C2 cells were detected by Cell Counting Kit-8 and TUNEL assay, respectively. The levels of inflammatory cytokines, oxidative stress markers and ATP in H/R-induced H9C2 cells were analyzed by corresponding assay kits. Western blotting was used for the estimation of AMP-activated protein kinase (AMPK) signaling pathway-, apoptosis- and mitochondrial regulation-associated protein levels. The mPTP opening was detected using a calcein-loading/cobalt chloride-quenching system. The results indicated that roflumilast decreased MI/R-induced myocardial infarction by alleviating myocardial injury and mitochondrial damage through the activation of the AMPK signaling pathway. In addition, roflumilast mitigated viability damage, alleviated oxidative stress, attenuated the inflammatory response and decreased mitochondrial damage in H/R-induced H9C2 cells by activating the AMPK signaling pathway. However, compound C, an inhibitor of the AMPK signaling pathway, reversed the effect of roflumilast on H/R-induced H9C2 cells. In conclusion, roflumilast alleviated myocardial infarction in MI/R rats and attenuated H/R-induced oxidative stress, inflammatory response and mitochondrial damage in H9C2 cells by activating the AMPK signaling pathway.

Newly Developed Di-Block Copolymer-Based Cell Membrane Stabilizers Protect Mouse Coronary Artery Endothelial Cells against Hypoxia/Reoxygenation Injury

Reperfusion after ischemia causes additional cellular damage, known as reperfusion injury, for which there is still no effective remedy. Poloxamer (P)188, a tri-block copolymer-based cell membrane stabilizer (CCMS), has been shown to provide protection against hypoxia/reoxygenation (HR) injury in various models by reducing membrane leakage and apoptosis and improving mitochondrial function. Interestingly, substituting one of its hydrophilic poly-ethylene oxide (PEO) blocks with a (t)ert-butyl terminus added to the hydrophobic poly-propylene oxide (PPO) block yields a di-block compound (PEO-PPOt) that interacts better with the cell membrane lipid bi-layer and exhibits greater cellular protection than the gold standard tri-block P188 (PEO75-PPO30-PEO75). For this study, we custom-made three different new di-blocks (PEO113-PPO10t, PEO226-PPO18t and PEO113-PPO20t) to systemically examine the effects of the length of each polymer block on cellular protection in comparison to P188. Cellular protection was assessed by cell viability, lactate dehydrogenase release, and uptake of FM1-43 in mouse artery endothelial cells (ECs) following HR injury. We found that di-block CCMS were able to provide the same or better EC protection than P188. Our study provides the first direct evidence that custom-made di-block CCMS can be superior to P188 in improving EC membrane protection, raising their potential in treating cardiac reperfusion injury.

Relationship between ferroptosis and mitophagy in cardiac ischemia reperfusion injury: a mini-review

Cardiovascular diseases (CVD), with high morbidity and mortality, seriously affect people's life and social development. Clinically, reperfusion therapy is typically used to treat ischemic cardiomyopathy, such as severe coronary heart disease and acute myocardial infarction. However, reperfusion therapy can lead to myocardial ischemia reperfusion injury (MIRI), which can affect the prognosis of patients. Studying the mechanisms of MIRI can help us improve the treatment of MIRI. The pathological process of MIRI involves many mechanisms such as ferroptosis and mitophagy. Ferroptosis can exacerbate MIRI, and regulation of mitophagy can alleviate MIRI. Both ferroptosis and mitophagy are closely related to ROS, but there is no clear understanding of the relationship between ferroptosis and mitophagy. In this review, we analyzed the relationship between ferroptosis and mitophagy according to the role of mTOR, NLPR3 and HIF. In addition, simultaneous regulation of mitophagy and ferroptosis may be superior to single therapy for MIRI. We summarized potential drugs that can regulate mitophagy and/or ferroptosis, hoping to provide reference for the development of drugs and methods for MIRI treatment.

KDM3A Attenuates Myocardial Ischemic and Reperfusion Injury by Ameliorating Cardiac Microvascular Endothelial Cell Pyroptosis

Cardiac microvascular endothelial cell ischemia-reperfusion (CMEC I/R) injury occurs in approximately 50% of acute myocardial infarction patients subjected to successful revascularization therapy. This injury leads to cardiac microcirculatory system dysfunctions, which seriously affect cardiac functions and long-term prognostic outcomes. Previously, we elucidated the role of lysine-specific demethylase 3A (KDM3A) in protecting cardiomyocytes from I/R injury; however, its roles in CMEC I/R injuries have yet to be fully established. In this study, hypoxia/reoxygenation (H/R) treatment significantly impaired CMEC functions and induced their pyroptosis, accompanied by KDM3A downregulation. Then, gain- and loss-of-function assays were performed to investigate the roles of KDM3A in CMEC H/R injury in vitro. KDM3A knockout enhanced CMEC malfunctions and accelerated the expressions of pyroptosis-associated proteins, such as NLRP3, cleaved-caspase-1, ASC, IL-1β, GSDMD-N, and IL-18. Conversely, KDM3A overexpression developed ameliorated alternations in CMEC H/R injury. In vivo, KDM3A knockout resulted in the deterioration of cardiac functions and decreased the no-reflow area as well as capillary density. Mechanistically, KDM3A activated the PI3K/Akt signaling pathway and ameliorated I/R-mediated CMEC pyroptosis. In conclusion, KDM3A is a promising treatment target for alleviating CMEC I/R injury.

Regulatory role of TIGAR on endothelial metabolism and angiogenesis

Endothelial glycolytic metabolism plays an important role in the process of angiogenesis. TP53-induced glycolysis and apoptosis regulator (TIGAR) is a significant mediator of cellular energy homeostasis. However, the role of TIGAR in endothelial metabolism, angiogenesis, and coronary flow reserve (CFR) has not been studied. The present study investigated whether knockout (KO) of TIGAR improves endothelial glycolytic function and angiogenesis. In vitro, aortic endothelial cells (ECs) from TIGAR KO mice exhibited increased expression of 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase isoform-3 (PFKFB3) and increased glycolytic function. These were accompanied by increased mitochondrial basal/maximal respiration and ATP production. Furthermore, knockout of TIGAR in ECs enhanced endothelial proliferation, migration, and tube formation. Knockout of TIGAR also significantly increased aortic sprouting ex vivo. In vivo, knockout of TIGAR increased the expression of proangiogenic factor, angiopoietin-1 (Ang-1) in mouse hearts. Knockout of TIGAR also significantly increased coronary capillary density with enhanced CFR in these hearts. Furthermore, TIGAR KO mice subjected to pressure overload (PO), a common model to study angiogenesis and cardiac hypertrophy, exhibited elevated expression of Ang-1, VEGF, and PFKFB3 than that of the wild-type (WT) mice. WT mice subjected to PO exhibited a significant reduction of coronary capillary density and impaired CFR, but TIGAR KO mice did not. In addition, knockout of TIGAR blunted TAC-induced cardiac hypertrophy and dysfunction seen in the WT mice. In conclusion, knockout of TIGAR improves endothelial angiogenetic capabilities by enhancing the endothelial glycolytic function, mitochondrial respiration, and proangiogenic signaling, which leads to increased coronary capillary density and vascular function and protects against chronic stress.

Disturbed Blood Flow Acutely Increases Endothelial Microparticles and Decreases Flow Mediated Dilation in Patients With Heart Failure With Reduced Ejection Fraction

Introduction

Disturbed blood flow, characterized by high retrograde and oscillatory shear rate (SR), is associated with a proatherogenic phenotype. The impact of disturbed blood flow in patients with heart failure with reduced ejection fraction (HFrEF) remains unknown. We tested the hypothesis that acute elevation to retrograde and oscillatory SR provoked by local circulatory occlusion would increase endothelial microparticles (EMPs) and decrease brachial artery flow-mediated dilation (FMD) in patients with HFrEF.

Methods

Eighteen patients with HFrEF aged 55 ± 2 years, with left ventricular ejection fraction (LVEF) 26 ± 1%, and 14 control subjects aged 49 ± 2 years with LVEF 65 ± 1 randomly underwent experimental and control sessions. Brachial artery FMD (Doppler) was evaluated before and after 30 min of disturbed forearm blood flow provoked by pneumatic cuff (Hokanson) inflation to 75 mm Hg. Venous blood samples were collected at rest, after 15 and 30 min of disturbed blood flow to assess circulating EMP levels (CD42b−/CD31+; flow cytometry).

Results

At rest, FMD was lower in patients with HFrEF compared with control subjects (P < 0.001), but blood flow patterns and EMPs had no differences (P > 0.05). The cuff inflation provoked a greater retrograde SR both groups (P < 0.0001). EMPs responses to disturbed blood flow significantly increased in patients with HFrEF (P = 0.03). No changes in EMPs were found in control subjects (P > 0.05). Disturbed blood flow decreased FMD both groups. No changes occurred in control condition.

Conclusion

Collectively, our findings suggest that disturbed blood flow acutely decreases FMD and increases EMP levels in patients with HFrEF, which may indicate that this set of patients are vulnerable to blood flow disturbances.

Targeting the Endothelium to Achieve Cardioprotection

Despite considerable improvements in the treatment of myocardial infarction, it is still a highly prevalent disease worldwide. Novel therapeutic strategies to limit infarct size are required to protect myocardial function and thus, avoid heart failure progression. Cardioprotection is a research topic with significant achievements in the context of basic science. However, translation of the beneficial effects of protective approaches from bench to bedside has proven difficult. Therefore, there is still an unmet need to study new avenues leading to protecting the myocardium against infarction. In line with this, the endothelium is an essential component of the cardiovascular system with multiple therapeutic targets with cardioprotective potential. Endothelial cells are the most abundant non-myocyte cell type in the heart and are key players in cardiovascular physiology and pathophysiology. These cells can regulate vascular tone, angiogenesis, hemostasis, and inflammation. Accordingly, endothelial dysfunction plays a fundamental role in cardiovascular diseases, which may ultimately lead to myocardial infarction. The endothelium is of paramount importance to protect the myocardium from ischemia/reperfusion injury via conditioning strategies or cardioprotective drugs. This review will provide updated information on the most promising therapeutic agents and protective approaches targeting endothelial cells in the context of myocardial infarction.

Cardiomyocyte-derived small extracellular vesicles can signal eNOS activation in cardiac microvascular endothelial cells to protect against Ischemia/Reperfusion injury

Rationale: The crosstalk between cardiac microvascular endothelial cells (CMECs) and cardiomyocytes (CMs) has emerged as a key component in the development of, and protection against, cardiac diseases. For example, activation of endothelial nitric oxide synthase (eNOS) in CMECs, by therapeutic strategies such as ischemic preconditioning, plays a critical role in the protection against myocardial ischemia/reperfusion (I/R) injury. However, much less is known about the signals produced by CMs that are able to regulate CMEC biology. Here we uncovered one such mechanism using Tongxinluo (TXL), a traditional Chinese medicine, that alleviates myocardial ischemia/reperfusion (I/R) injury by activating CMEC eNOS. The aim of our study is to identify the signals produced by CMs that can regulate CMEC biology during I/R. Methods: Ex vivo, in vivo, and in vitro settings of ischemia-reperfusion were used in our study, with the protective signaling pathways activated in CMECs identified using genetic inhibition (p70s6k1 siRNA, miR-145-5p mimics, etc.), chemical inhibitors (the eNOS inhibitor, L-NNA, and the small extracellular vesicles (sEVs) inhibitor, GW4869) and Western blot analyses. TritonX-100 at a dose of 0.125% was utilized to inactivate the eNOS activity in endothelium to investigate the role of CMEC-derived eNOS in TXL-induced cardioprotection. Results: We found that while CMEC-derived eNOS activity was required for the cardioprotection of TXL, activation of eNOS in CMECs by TXL did not occur directly. Instead, eNOS activation in CMECs required a crosstalk between CMs and CMECs through the uptake of CM-derived sEVs. We further demonstrate that TXL induced CM-sEVs contain increased levels of Long Intergenic Non-Protein Coding RNA, Regulator Of Reprogramming (Linc-ROR). Upon uptake into CMECs, linc-ROR downregulates its target miR-145-5p leading to activation of the eNOS pathway by facilitating the expression of p70s6k1 in these cells. The activation of CMEC-derived eNOS works to increase survival in both the CMECs and the CMs themselves. Conclusions: These data uncover a mechanism by which the crosstalk between CMs and CMECs leads to the increased survival of the heart after I/R injury and point to a new therapeutic target for the blunting of myocardial I/R injury.

Endothelial Sirtuin 3 Dictates Glucose Transport to Cardiomyocyte and Sensitizes Pressure Overload-Induced Heart Failure

Background

Alterations of energetic metabolism are suggested to be an important contributor to pressure overload (PO)‐induced heart failure. Our previous study reveals that knockout of endothelial Sirtuin 3 (SIRT3) alters glycolysis and impairs diastolic function. We hypothesize that endothelial SIRT3 regulates glucose utilization of cardiomyocytes and sensitizes PO‐induced heart failure.

Methods and Results

SIRT3 endothelial cell knockout mice and their control SIRT3 LoxP mice were subjected to PO by transverse aortic constriction for 7 weeks. The ratio of heart weight to tibia length was increased in both strains of mice, in which SIRT3 endothelial cell knockout mice+transverse aortic constriction exhibited more severe cardiac hypertrophy. Coronary blood flow and systolic function were significantly decreased in SIRT3 endothelial cell knockout mice+transverse aortic constriction compared with SIRT3 LoxP mice+transverse aortic constriction, as evidenced by lower systolic/diastolic ratio, ejection fraction, and fractional shortening. PO‐induced upregulation of apelin and glucose transporter 4 were significantly reduced in the hearts of SIRT3 endothelial cell knockout mice. In vitro, levels of hypoxia‐inducible factor‐1α and glucose transporter 1 and glucose uptake were significantly reduced in SIRT3 knockout endothelial cells. Furthermore, hypoxia‐induced apelin expression was abolished together with reduced apelin‐mediated glucose uptake in SIRT3 knockout endothelial cells. Exposure of cardiomyocyte with apelin increased expression of glucose transporter 1 and glucose transporter 4. This was accompanied by a significant increase in glycolysis. Supplement of apelin in SIRT3 knockout hypoxic endothelial cell media increased glycolysis in the cardiomyocytes.

Conclusions

Knockout of SIRT3 disrupts glucose transport from endothelial cells to cardiomyocytes, reduces cardiomyocyte glucose utilization via apelin in a paracrine manner, and sensitizes PO‐induced heart failure. Endothelial SIRT3 may regulate cardiomyocyte glucose availability and govern the function of the heart.

Intralipid Increases Nitric Oxide Release from Human Endothelial Cells During Oxidative Stress

BACKGROUND

Intralipid (ILP), a lipid emulsion, protects organs against ischemia/reperfusion (IR) injury. We hypothesized that ILP activates endothelial nitric oxide synthase (eNOS) and increases NO release from endothelial cells (ECs) through a fatty-acid translocase cluster of differentiation (CD36) mediated endocytotic mechanism, acting as a potentially protective paracrine signal during oxidative stress.

METHODS

Human umbilical-vein ECs were exposed to 1% ILP for 2 hours followed by oxidative stress with 0.2-mM hydrogen peroxide for 2 hours. Western blots were conducted with anti-CD36, dynamin-2, src-kinase-1, eNOS, and phospho-eNOS; equal protein loading was confirmed with β-actin. CD36 immunoprecipitation was probed for caveolin-1 to determine if CD36 and caveolin-1 were complexed on the cell membrane. NO was measured by fluorescence of ECs.

RESULTS

ILP caused a 227% increase in CD36 expression vs controls. Immunoprecipitation indicated a CD36/caveolin-1 complex on ECs' membrane with exposure to ILP. Dynamin-2 increased 52% and src-kinase-1 340% after ILP treatment vs control cells. eNOS phosphorylation was confirmed by a 63% increase in the phospho-eNOS/eNOS ratio in ILP-treated cells, and NO fluorescence increased 102%.

CONCLUSION

ILP enters ECs via endocytosis by a CD36/caveolin-1 cell membrane receptor complex, which in turn is pulled into the cell by dynamin-2 activity. Upregulation of src-kinase-1 and eNOS phosphorylation suggest downstream mediators. Subsequent NO release from ECs serve as a paracrine signal to neighboring cells for protection against IR injury. Student t-test was utilized for single comparisons and analysis of variance with Bonferroni-Dunn post hoc modification for multiple comparisons; P < .05 was considered statistically significant.

Human Pluripotent Stem Cell-Derived Cardiomyocytes for Assessment of Anticancer Drug-Induced Cardiotoxicity

Cardiotoxicity is a major cause of high attrition rates among newly developed drugs. Moreover, anti-cancer treatment-induced cardiotoxicity is one of the leading reasons of mortality in cancer survivors. Cardiotoxicity screening in vitro may improve predictivity of cardiotoxicity by novel drugs, using human pluripotent stem cell (hPSC)-derived-cardiomyocytes. Anthracyclines, including Doxorubicin, are widely used and highly effective chemotherapeutic agents for the treatment of different forms of malignancies. Unfortunately, anthracyclines cause many cardiac complications early or late after therapy. Anthracyclines exhibit their potent anti-cancer effect primarily via induction of DNA damage during the DNA replication phase in proliferative cells. In contrast, studies in animals and hPSC-cardiomyocytes have revealed that cardiotoxic effects particularly arise from (1) the generation of oxidative stress inducing mitochondrial dysfunction, (2) disruption of calcium homeostasis, and (3) changes in transcriptome and proteome, triggering apoptotic cell death. To increase the therapeutic index of chemotherapeutic Doxorubicin therapy several protective strategies have been developed or are under development, such as (1) reducing toxicity through modification of Doxorubicin (analogs), (2) targeted delivery of anthracyclines specifically to the tumor tissue or (3) cardioprotective agents that can be used in combination with Doxorubicin. Despite continuous progress in the field of cardio-oncology, cardiotoxicity is still one of the major complications of anti-cancer therapy. In this review, we focus on current hPSC-cardiomyocyte models for assessing anthracycline-induced cardiotoxicity and strategies for cardioprotection. In addition, we discuss latest developments toward personalized advanced pre-clinical models that are more closely recapitulating the human heart, which are necessary to support in vitro screening platforms with higher predictivity. These advanced models have the potential to reduce the time from bench-to-bedside of novel antineoplastic drugs with reduced cardiotoxicity.

Vascular endothelial growth factor regulation of endothelial nitric oxide synthase phosphorylation is involved in isoflurane cardiac preconditioning

Aims

Previous studies indicate that nitric oxide derived from endothelial nitric oxide synthase (eNOS) serves as both trigger and mediator in anaesthetic cardiac preconditioning. The mechanisms underlying regulation of eNOS by volatile anaesthetics have not been fully understood. Therefore, this study examined the role of vascular endothelial growth factor (VEGF) in isoflurane cardiac preconditioning.

Methods and results

Wistar rats underwent 30 min of coronary artery occlusion followed by 2 h of reperfusion. Isoflurane given prior to ischaemia/reperfusion significantly decreased myocardial infarct size from 60 ± 1% in control to 40 ± 3% (n = 8 rats/group, P < 0.05). The beneficial effects of isoflurane were blocked by neutralizing antibody against VEGF (nVEGF). Coronary arterial endothelial cells (ECs) alone or together with cardiomyocytes (CMs) were subjected to hypoxia/reoxygenation injury. The expression of VEGF and eNOS was analysed by western blot, and nitric oxide was measured by ozone-based chemiluminescence. In co-cultured CMs and ECs, isoflurane administered before hypoxia/reoxygenation attenuated lactate dehydrogenase activity and increased the ratio of phosphorylated eNOS/eNOS and nitric oxide production. The protective effect of isoflurane on CMs was compromised by nVEGF and after VEGF in ECs was inhibited with hypoxia inducible factor-1α short hairpin RNA (shRNA). The negative effect of hypoxia inducible factor-1α shRNA was restored by recombinant VEGF.

Conclusion

Isoflurane cardiac preconditioning is associated with VEGF regulation of phosphorylation of eNOS and nitric oxide production.

Endothelial-Cell-Derived Human Secretory Leukocyte Protease Inhibitor (SLPI) Protects Cardiomyocytes against Ischemia/Reperfusion Injury

Vascular endothelial cell (EC)-derived factors play an important role in endothelial-cardiomyocyte crosstalk and could save cardiomyocytes (CMs) from injury. The manipulation of endothelial cells to secrete protective factors could enhance cardioprotection. Secretory leukocyte protease inhibitor (SLPI) has been known to protect the heart. The goal of this study was to evaluate the in vitro paracrine protective effect and mechanisms of EC-derived human SLPI on cardiomyocytes subjected to hypoxia/reoxygenation (H/R) injury. Stable endothelial cells overexpressing human SLPI were generated from an endothelial cell line (EA.hy926). The cytoprotective effect was determined by cell survival assay. The results showed that endothelial-derived recombinant human SLPI (rhSLPI) reduced simulated ischemia/reperfusion (I/R)-(81.75% ± 1.42% vs. 60.27% ± 2.52%, p < 0.05) and hypoxia/reoxygenation (H/R)-induced EC injury (83.57% ± 1.78% vs. 63.07% ± 1.93%, p < 0.05). Moreover, co-culture of ECs overexpressing rhSLPI with CMs at ratios 1:1 and 1:3 or treatment with conditioned medium enhanced cell viability by 10.51-16.7% (co-culture) and 15.25-20.45% (conditioned medium) by reducing intracellular reactive oxygen species (ROS) production, the Bax/Bcl-2 expression ratio, caspase-3, and caspase-8, and in preconditioned CMs by activation of p38 MAPK and Akt survival kinase. In conclusion, this study showed for the first time that EC-derived rhSLPI provided cardio-vasculoprotective effects against I/R injury as a possible alternative therapeutic strategy for cardioprotection.

Microenvironment of saphenous vein graft preservation prior to coronary artery bypass grafting

OBJECTIVES

The best preservation solution for a free vascular graft prior to coronary artery bypass grafting (CABG) remains controversial. The aim of this investigation was to evaluate the microenvironment of the human saphenous vein graft when preserved in normal saline (NS) solution or autologous heparinized whole blood (AWB).

METHODS

Between January 2014 and December 2014, 21 patients who underwent CABG were enrolled and a total of 162 saphenous vein graft rings were collected. NS and AWB were used to investigate the influence of the microenvironment. The hypoxia, oxidative stress and vascular apoptosis were assayed by western blot, and endothelial integrity was assessed by immunohistochemical analysis.

RESULTS

The level of PaO2 in AWB was lower than that in NS (median: 100.5 mmHg vs 185.8 mmHg, P = 0.004). This hypoxic condition led to the production of more hypoxia-inducible factor-1 (median: 60.1% vs 15.1%, P = 0.008) and endothelial nitric oxide synthase (median: 52.6% vs 25%, P = 0.046) within 30 min of preservation time. The fact that higher levels of glutathione peroxidase resulted in the preservation of AWB suggests that it is beneficial to boost the vascular antioxidant defense with lower levels of NOX2. AWB led to increased Bcl-2, reduced cytochrome c and cleaved 85 kDa poly ADP-ribose polymerase apoptotic fragments.

CONCLUSIONS

We concluded that AWB possesses a microenvironment that is superior to that of NS for saphenous vein graft preservation prior to CABG.

Over-expression of JAZF1 promotes cardiac microvascular endothelial cell proliferation and angiogenesis via activation of the Akt signaling pathway in rats with myocardial ischemia-reperfusion

Myocardial ischemia-reperfusion (I/R) injury is caused by endothelial dysfunction and enhanced oxidative stress. The overexpression of JAZF1, a zinc finger protein, has been reported to promote cell proliferation and suppress myogenic differentiation in type 2 diabetes. However, the involvement of JAZF1 in myocardial I/R injury remains to be unclear. The current study aims to investigate the role by which JAZF1 influences cardiac microvascular endothelial cells (CMECs) in a rat model of myocardial I/R injury. A total of 50 rats were established as a myocardial I/R model to isolate CMECs, with alterations in JAZF1 expression. After that, the gain- or loss-function of JAZF1 on the proliferation, apoptosis and tube formation ability of CMECs were evaluated by a series of in vitro experiments. Results indicated that JAZF1 was down-regulated in CMECs of rats with myocardial I/R injury. After treatment with JAZF1, the levels of VEGF, Bcl-2, PDGF and p-Akt/Akt were all increased; however, the expression of Bax, caspase-3, caspase-9, p-Bad/Bad, c-caspase-3/caspase-3, c-caspase-9/caspase-9, and p-FKHR/FKHR exhibited decreased levels; CMEC proliferation and angiogenesis were increased, while cell apoptosis was attenuated. CMECs transfected with JAZF1 shRNA exhibited the contrary tendencies. The key findings of this study suggest that the over-expression of JAZF1 alleviates myocardial I/R injury by enhancing proliferation and angiogenesis of CMECs and in turn inhibiting apoptosis of CMECs via the activation of the Akt signaling pathway.

Dexmedetomidine preconditioning attenuates ischemia/reperfusion injury in isolated rat hearts with endothelial dysfunction

BACKGROUND AND PURPOSES

Dexmedetomidine preconditioning (DP) can mimic pharmacological preconditioning and induce cardiac protection. There are controversies on the roles of coronary endothelia in cardioprotection of dexmedetomidine. Herein, we tested the hypothesis that protection of dexmedetomidine is not endothelial dependent in heart against myocardial ischemia/reperfusion (I/R) injury.

METHODS

Langendorff-perfused rat hearts were pretreated by 60 mM of potassium to produce endothelial dysfunction (ED), then medicated with dexmedetomidine, and subsequently subjected to 30 min of global ischemia followed by 60 min of reperfusion. To investigate the cardioprotective effect of dexmedetomidine in heart with ED, isolated rat hearts were randomly divided into the following six groups: sham, I/R, DP, ED, ED + I/R, and ED + DP + I/R. Heart rates, left ventricular function, and coronary perfusion pressure were assessed for each heart. Infarct size was evaluated by triphenyltetrazolium chloride staining. High-sensitivity cardiac troponin T (hs-cTNT) of coronary flow perfusion was determined.

RESULTS

After the isolated hearts with pretreatment of 60 mM of potassium chloride, diastolic function of coronary endothelia in performance of response to histamine was significantly decreased (P < 0.05). DP attenuated I/R-induced infarct size of the left ventricle (P < 0.05) and decreased hs-cTNT (P < 0.05). Additionally, left ventricular developed pressure, +dp/dt_max, and -dp/dt_max were elevated in rat hearts pretreated with dexmedetomidine. Furthermore, dexmedetomidine-mediated cardiac protection against I/R injury was still remained in isolated hearts with coronary ED.

CONCLUSION

Continuous perfusion of 60 mM of potassium for 10 min can produce coronary ED in isolated rat hearts. Dexmedetomidine maintains its protective function against I/R injury in heart with coronary ED. Myocardial protection of dexmedetomidine is non-endothelial function dependent in alleviating I/R injury.

Heterocellularity and Cellular Cross-Talk in the Cardiovascular System

Cellular specialization and interactions with other cell types are the essence of complex multicellular life. The orchestrated function of different cell populations in the heart, in combination with a complex network of intercellular circuits of communication, is essential to maintain a healthy heart and its disruption gives rise to pathological conditions. Over the past few years, the development of new biological research tools has facilitated more accurate identification of the cardiac cell populations and their specific roles. This review aims to provide an overview on the significance and contributions of the various cellular components: cardiomyocytes, fibroblasts, endothelial cells, vascular smooth muscle cells, pericytes, and inflammatory cells. It also aims to describe their role in cardiac development, physiology and pathology with a particular focus on the importance of heterocellularity and cellular interaction between these different cell types.

Emerging role of SIRT3 in endothelial metabolism, angiogenesis, and cardiovascular disease

Sirtuin 3 (SIRT3) a mitochondrial enzyme that plays an important role in energy homeostasis, cardiac remodeling, and heart failure (HF). The expression of SIRT3 declines with advanced age, cardiovascular, and metabolic diseases. Accumulating evidence suggests that SIRT3 plays a critical role in protecting the heart from cardiac hypertrophy, cardiac dysfunction associated with HF, and in the protection of cardiac cells from stress-mediated cell death. Clinical studies have demonstrated that HF with preserved ejection fraction (HFpEF) in patients present with abnormalities in coronary microcirculation related to endothelial dysfunction and coronary microvascular rarefaction. Although SIRT3-mediated regulation of mitochondrial homeostasis and heart function has been intensively investigated, the effect of SIRT3 on endothelial cell (EC) glycolytic metabolism and microvascular function has not been well studied. ECs utilize glycolysis for generating ATP rather than oxidative phosphorylation to maintain their normal functions and promote angiogenesis and EC-cardiomyocyte interactions. Emerging evidence indicates that SIRT3 is involved in the regulation of endothelial metabolism and angiogenesis and thus affects the development of cardiovascular diseases associated with aging. This review will discuss the current knowledge of SIRT3 and its functional role on endothelial metabolism, cardiac function, and cardiovascular diseases.

Transcriptome profiling of 3D co-cultured cardiomyocytes and endothelial cells under oxidative stress using a photocrosslinkable hydrogel system

Myocardial infarction (MI) is one of the most common among cardiovascular diseases. Endothelial cells (ECs) are considered to have protective effects on cardiomyocytes (CMs) under stress conditions such as MI; however, the paracrine CM-EC crosstalk and the resulting endogenous cellular responses that could contribute to this protective effect are not thoroughly investigated. Here we created biomimetic synthetic tissues containing CMs and human induced pluripotent stem cell (hiPSC)-derived ECs (iECs), which showed improved cell survival compared to single cultures under conditions mimicking the aftermath of MI, and performed high-throughput RNA-sequencing to identify target pathways that could govern CM-iEC crosstalk and the resulting improvement in cell viability. Our results showed that single cultured CMs had different gene expression profiles compared to CMs co-cultured with iECs. More importantly, this gene expression profile was preserved in response to oxidative stress in co-cultured CMs while single cultured CMs showed a significantly different gene expression pattern under stress, suggesting a stabilizing effect of iECs on CMs under oxidative stress conditions. Furthermore, we have validated the in vivo relevance of our engineered model tissues by comparing the changes in the expression levels of several key genes of the encapsulated CMs and iECs with in vivo rat MI model data and clinical data, respectively. We conclude that iECs have protective effects on CMs under oxidative stress through stabilizing mitochondrial complexes, suppressing oxidative phosphorylation pathway and activating pathways such as the drug metabolism-cytochrome P450 pathway, Rap1 signaling pathway, and adrenergic signaling in cardiomyocytes pathway.

STATEMENT OF SIGNIFICANCE

Heart diseases are the leading cause of death worldwide. Oxidative stress is a common unwanted outcome that especially occurs due to the reperfusion following heart attack or heart surgery. Standard methods of in vivo analysis do not allow dissecting various intermingled parameters, while regular 2D cell culture approaches often fail to provide a biomimetic environment for the physiologically relevant cellular phenotypes. In this research, a systematic genome-wide transcriptome profiling was performed on myocardial cells in a biomimetic 3D hydrogel-based synthetic model tissue, for identifying possible target genes and pathways as protecting regulators against oxidative stress. Identification of such pathways would be very valuable for new strategies during heart disease treatment by reducing the cellular damage due to reperfusion injury.

Cardiac spheroids as promising in vitro models to study the human heart microenvironment

Three-dimensional in vitro cell systems are a promising alternative to animals to study cardiac biology and disease. We have generated three-dimensional in vitro models of the human heart ("cardiac spheroids", CSs) by co-culturing human primary or iPSC-derived cardiomyocytes, endothelial cells and fibroblasts at ratios approximating those present in vivo. The cellular organisation, extracellular matrix and microvascular network mimic human heart tissue. These spheroids have been employed to investigate the dose-limiting cardiotoxicity of the common anti-cancer drug doxorubicin. Viability/cytotoxicity assays indicate dose-dependent cytotoxic effects, which are inhibited by the nitric oxide synthase (NOS) inhibitor L-NIO, and genetic inhibition of endothelial NOS, implicating peroxynitrous acid as a key damaging agent. These data indicate that CSs mimic important features of human heart morphology, biochemistry and pharmacology in vitro, offering a promising alternative to animals and standard cell cultures with regard to mechanistic insights and prediction of toxic effects in human heart tissue.

Engineered myocardium model to study the roles of HIF-1α and HIF1A-AS1 in paracrine-only signaling under pathological level oxidative stress

Studying heart tissue is critical for understanding and developing treatments for cardiovascular diseases. In this work, we fabricated precisely controlled and biomimetic engineered model tissues to study how cell-cell and cell-matrix interactions influence myocardial cell survival upon exposure to pathological level oxidative stress. Specifically, the interactions of endothelial cells (ECs) and cardiomyocytes (CMs), and the role of hypoxia inducible factor-1α (HIF-1α), with its novel alternative regulator, HIF-1α antisense RNA1 (HIF1A-AS1), in these interactions were investigated. We encapsulated CMs in photo-crosslinkable, biomimetic hydrogels with or without ECs, then exposed to oxidative stress followed by normoxia. With precisely controlled microenvironment provided by the model tissues, cell-cell interactions were restricted to be solely through the secreted factors. CM survival after oxidative stress was significantly improved, in the presence of ECs, when cells were in the model tissues that were functionalized with cell attachment motifs. Importantly, the cardioprotective effect of ECs was reduced when HIF-1α expression was knocked down suggesting that HIF-1α is involved in cardioprotection from oxidative damage, provided through secreted factors conferred by the ECs. Using model tissues, we showed that cell survival increased with increased cell-cell communication and enhanced cell-matrix interactions. In addition, whole genome transcriptome analysis showed, for the first time to our knowledge, a possible role for HIF1A-AS1 in oxidative regulation of HIF-1α. We showed that although HIF1A-AS1 knockdown helps CM survival, its effect is overridden by CM-EC bidirectional interactions as we showed that the conditioned media taken from the CM-EC co-cultures improved CM survival, regardless of HIF1A-AS1 expression.

STATEMENT OF SIGNIFICANCE

Cardiovascular diseases, most of which are associated with oxidative stress, is the most common cause of death worldwide. Thus, understanding the molecular events as well as the role of intercellular communication under oxidative stress is upmost importance in its prevention. In this study we used 3D engineered tissue models to investigate the role of HIF-1α and its regulation in EC-mediated cardioprotection. We showed that EC-mediated protection is only possible when there is a bidirectional crosstalk between ECs and CMs even without physical cell-cell contact. In addition, this protective effect is at least partially related to cell-ECM interactions and HIF-1α, which is regulated by HIF1A-AS1 under oxidative stress.

Maturation of human pluripotent stem cell derived cardiomyocytes is improved in cardiovascular construct

In order to translate preclinical data into the clinical studies, relevant in vitro models with structure and key functional properties similar to native human tissue should be used. In vitro cardiac models with vascular structures mimic the highly vascularized myocardium and provide interactions between endothelial cells, stromal cells and cardiomyocytes. Currently, human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) have been shown to present immature morphology and fetal-like electrophysiological properties that may limit their use as physiological test platform. The aim of this study was to develop multicellular in vitro cardiovascular construct modeling human heart tissue. In the cardiovascular construct, hPSC-CMs were cultured with a vascular-like network formed by human foreskin fibroblasts and human umbilical vein endothelial cells that served as a platform in the construct. Cardiomyocyte orientation, maturation, electrophysiological properties and drug responses of the cardiovascular construct were characterized and compared to CM monoculture. hPSC-CMs in cardiovascular construct showed elongated morphology and aligned with the vascular-like network. Electrophysiological properties and calcium metabolism of hPSC-CMs as well as response to E-4031 and adrenaline demonstrated normal physiological behavior. Increased expression of cardiac structural proteins and ion channels in cardiovascular construct compared to CM monoculture were detected. In conclusion, vascular-like network supports the structural and functional maturation of hPSC-CMs. Our results suggest that cardiovascular construct presents more mature in vitro cardiac model compared to CM monoculture and could therefore serve as an advanced test system for cardiac safety and efficacy assessment as well as a model system for biomedical research.

Human iPSC-derived myocardium-on-chip with capillary-like flow for personalized medicine

The heart wall tissue, or the myocardium, is one of the main targets in cardiovascular disease prevention and treatment. Animal models have not been sufficient in mimicking the human myocardium as evident by the very low clinical translation rates of cardiovascular drugs. Additionally, current in vitro models of the human myocardium possess several shortcomings such as lack of physiologically relevant co-culture of myocardial cells, lack of a 3D biomimetic environment, and the use of non-human cells. In this study, we address these shortcomings through the design and manufacture of a myocardium-on-chip (MOC) using 3D cell-laden hydrogel constructs and human induced pluripotent stem cell (hiPSC) derived myocardial cells. The MOC utilizes 3D spatially controlled co-culture of hiPSC derived cardiomyocytes (iCMs) and hiPSC derived endothelial cells (iECs) integrated among iCMs as well as in capillary-like side channels, to better mimic the microvasculature seen in native myocardium. We first fully characterized iCMs using immunostaining, genetic, and electrochemical analysis and iECs through immunostaining and alignment analysis to ensure their functionality, and then seeded these cells sequentially into the MOC device. We showed that iECs could be cultured within the microfluidic device without losing their phenotypic lineage commitment, and align with the flow upon physiological level shear stresses. We were able to incorporate iCMs within the device in a spatially controlled manner with the help of photocrosslinkable polymers. The iCMs were shown to be viable and functional within the device up to 7 days, and were integrated with the iECs. The iCMs and iECs in this study were derived from the same hiPSC cell line, essentially mimicking the myocardium of an individual human patient. Such devices are essential for personalized medicine studies where the individual drug response of patients with different genetic backgrounds can be tested in a physiologically relevant manner.

Tongxinluo modulates cytokine secretion by cardiac microvascular endothelial cells in ischemia/reperfusion injury

Cardiac microvascular endothelial cells (CMECs) extensively secrete cytokines during myocardial ischemia/reperfusion injury (MIRI). Tongxinluo (TXL) has been demonstrated to preserve the function of the endothelium and myocardium against MIRI. This study was designed to identify alterations in the paracrine function of CMECs under hypoxia/reoxygenation (H/R) conditions and assess its modulation by TXL. CMECs were exposed to different concentrations of TXL for 30 min and then subjected to hypoxia and reoxygenation for 12 and 2 h, respectively. Apoptosis was measured to determine the optimal TXL concentration. Protein antibody arrays were used to assess changes in cytokines secreted into conditioned medium by CMECs. A Gene Ontology (GO) analysis was applied to interpret the functional implications of changes in cytokines. TXL inhibited CMEC apoptosis in a concentration-dependent manner after H/R, reaching peak efficacy at a concentration of 800 μg/ml. H/R significantly altered 33 cytokines, and TXL (800 μg/ml) changed the levels of 121 different cytokines compared with the H/R group. Among these cytokines, 10 that were increased by H/R were decreased by TXL, five that were decreased by H/R were increased by TXL, and eight that were attenuated by H/R were further decreased by TXL. Insulin-like growth factor binding protein-1 was up-regulated by H/R and was further increased by TXL. Significantly altered factors were found to be involved in cell proliferation, growth and differentiation, as well as chemotaxis and transport. TXL inhibited the apoptosis of CMECs and modulated their paracrine function in MIRI.

Ablation of SIRT3 causes coronary microvascular dysfunction and impairs cardiac recovery post myocardial ischemia

RATIONALE

Sirtuin (SIRT3), a major nicotinamide adenine dinucleotide (NAD(+))-dependent deacetylase in mitochondria, declines with aging and its ablation is associated with accelerated development of cardiovascular diseases. However, the role of SIRT3 in coronary microvascular function and post-MI recovery has not been completely understood.

OBJECTIVE

The goal was to investigate whether ablation of SIRT3 causes coronary microvascular dysfunction, exacerbates post-myocardial ischemia (MI) cardiac dysfunction and impairs cardiac recovery.

METHODS AND RESULTS

Using endothelial cells (ECs) isolated from SIRT3 knockout (KO) mice, we revealed that the angiogenic capabilities were significantly reduced in SIRT3 deficient ECs. SIRT3 KO mice presented a pre-existing coronary microvascular dysfunction and microvascular rarefaction, as evidenced by a reduction in hyperemic peak diastolic blood flow velocity and coronary flow reserve (CFR), accompanied by loss of capillary-pericytes in the heart. Furthermore, SIRT3 KO mice subjected to myocardial ischemia by the ligation of left anterior descending coronary artery (LAD) exhibited more severe cardiac dysfunction together with decreased pericyte/EC coverage than that of wild type (WT) mice. In contrast, overexpression of SIRT3 preserved cardiac function in post-MI mice. Immunoblot analysis further showed that the expression of angiopoietin-1 (Ang-1), vascular endothelial growth factor (VEGF) and 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3 (PFKFB3) were significantly decreased in the SIRT3-deficient ischemic hearts than those of WT ischemic hearts. This was accompanied by higher levels of cleaved caspase-3 and apoptosis.

CONCLUSION

Our results reveal a potential mechanism by which SIRT3 deletion exacerbates post-MI cardiac dysfunction and impairment of cardiac recovery involving microvascular rarefaction and pre-existing coronary microvascular dysfunction.

Towards comprehensive cardiac repair and regeneration after myocardial infarction: Aspects to consider and proteins to deliver

Ischemic heart disease is a leading cause of death worldwide. After the onset of myocardial infarction, many pathological changes take place and progress the disease towards heart failure. Pathologies such as ischemia, inflammation, cardiomyocyte death, ventricular remodeling and dilation, and interstitial fibrosis, develop and involve the signaling of many proteins. Proteins can play important roles in limiting or countering pathological changes after infarction. However, they typically have short half-lives in vivo in their free form and can benefit from the advantages offered by controlled release systems to overcome their challenges. The controlled delivery of an optimal combination of proteins per their physiologic spatiotemporal cues to the infarcted myocardium holds great potential to repair and regenerate the heart. The effectiveness of therapeutic interventions depends on the elucidation of the molecular mechanisms of the cargo proteins and the spatiotemporal control of their release. It is likely that multiple proteins will provide a more comprehensive and functional recovery of the heart in a controlled release strategy.

Dexmedetomidine protects the heart against ischemia-reperfusion injury by an endothelial eNOS/NO dependent mechanism

The alpha2-adrenergic receptor agonist Dexmedetomidine (Dex) is a sedative medication used by anesthesiologists. Dex protects the heart against ischemia-reperfusion (IR) and can also act as a preconditioning mimetic. The mechanisms involved in Dex-dependent cardiac preconditioning, and whether this action occurs directly or indirectly on cardiomyocytes, still remain unclear. The endothelial nitric oxide synthase (eNOS)/nitric oxide (NO) signaling pathway and endothelial cells are known to play key roles in cardioprotection against IR injury. Therefore, the aims of this work were to evaluate whether the eNOS/NO pathway mediates the pharmacological cardiac effect of Dex, and whether endothelial cells are required in this cardioprotective action. Isolated adult rat hearts were treated with Dex (10nM) for 25min and the dimerization of eNOS and production of NO were measured. Hearts were then subjected to global IR (30/120min) and the role of the eNOS/NO pathway was evaluated. Dex promoted the activation of eNOS and production of NO. Dex reduced the infarct size and improved the left ventricle function recovery, but this effect was reversed when Dex was co-administered with inhibitors of the eNOS/NO/PKG pathway. In addition, Dex was unable to reduce cell death in isolated adult rat cardiomyocytes subjected to simulated IR. Cardiomyocyte death was attenuated by co-culturing them with endothelial cells pre-treated with Dex. In summary, our results show that Dex triggers cardiac protection by activating the eNOS/NO signaling pathway. This pharmacological effect of Dex requires its interaction with the endothelium.

Isoflurane favorably modulates guanosine triphosphate cyclohydrolase-1 and endothelial nitric oxide synthase during myocardial ischemia and reperfusion injury in rats

BACKGROUND

The authors investigated the hypothesis that isoflurane modulates nitric oxide (NO) synthesis and protection against myocardial infarction through time-dependent changes in expression of key NO regulatory proteins, guanosine triphosphate cyclohydrolase (GTPCH)-1, the rate-limiting enzyme involved in the biosynthesis of tetrahydrobiopterin and endothelial nitric oxide synthase (eNOS).

METHODS

Myocardial infarct size, NO production (ozone-mediated chemiluminescence), GTPCH-1, and eNOS expression (real-time reverse transcriptase polymerase chain reaction and western blotting) were measured in male Wistar rats with or without anesthetic preconditioning (APC; 1.0 minimum alveolar concentration isoflurane for 30 min) and in the presence or absence of an inhibitor of GTPCH-1, 2,4-diamino-6-hydroxypyrimidine.

RESULTS

NO2 production (158 ± 16 and 150 ± 13 pmol/mg protein at baseline in control and APC groups, respectively) was significantly (P < 0.05) increased 1.5 ± 0.1 and 1.4 ± 0.1 fold by APC (n = 4) at 60 and 90 min of reperfusion, respectively, concomitantly, with increased expression of GTPCH-1 (1.3 ± 0.3 fold; n = 5) and eNOS (1.3 ± 0.2 fold; n = 5). In contrast, total NO (NO2 and NO3) was decreased after reperfusion in control experiments. Myocardial infarct size was decreased (43 ± 2% of the area at risk for infarction; n = 6) by APC compared with control experiments (57 ± 1%; n = 6). 2, 4-Diamino-6-hydroxypyrimidine decreased total NO production at baseline (221 ± 25 and 175 ± 31 pmol/mg protein at baseline in control and APC groups, respectively), abolished isoflurane-induced increases in NO at reperfusion, and prevented reductions of myocardial infarct size by APC (60 ± 2%; n = 6).

CONCLUSION

APC favorably modulated a NO biosynthetic pathway by up-regulating GTPCH-1 and eNOS, and this action contributed to protection of myocardium against ischemia and reperfusion injury.

Up-regulation of microRNA-21 mediates isoflurane-induced protection of cardiomyocytes

BACKGROUND

Anesthetic cardioprotection reduces myocardial infarct size after ischemia-reperfusion injury. Currently, the role of microRNA in this process remains unknown. MicroRNAs are short, noncoding nucleotide sequences that negatively regulate gene expression through degradation or suppression of messenger RNA. In this study, the authors uncovered the functional role of microRNA-21 (miR-21) up-regulation after anesthetic exposure.

METHODS

MicroRNA and messenger RNA expression changes were analyzed by quantitative real-time polymerase chain reaction in cardiomyocytes after exposure to isoflurane. Lactate dehydrogenase release assay and propidium iodide staining were conducted after inhibition of miR-21. miR-21 target expression was analyzed by Western blot. The functional role of miR-21 was confirmed in vivo in both wild-type and miR-21 knockout mice.

RESULTS

Isoflurane induces an acute up-regulation of miR-21 in both in vivo and in vitro rat models (n = 6, 247.8 ± 27.5% and 258.5 ± 9.0%), which mediates protection to cardiomyocytes through down-regulation of programmed cell death protein 4 messenger RNA (n = 3, 82.0 ± 4.9% of control group). This protective effect was confirmed by knockdown of miR-21 and programmed cell death protein 4 in vitro. In addition, the protective effect of isoflurane was abolished in miR-21 knockout mice in vivo, with no significant decrease in infarct size compared with nonexposed controls (n = 8, 62.3 ± 4.6% and 56.2 ± 3.2%).

CONCLUSIONS

The authors demonstrate for the first time that isoflurane mediates protection of cardiomyocytes against oxidative stress via an miR-21/programmed cell death protein 4 pathway. These results reveal a novel mechanism by which the damage done by ischemia/reperfusion injury may be decreased.

Induction of autophagy by Tongxinluo through the MEK/ERK pathway protects human cardiac microvascular endothelial cells from hypoxia/reoxygenation injury

: In contrast to cardiomyocytes, autophagy in cardiac microvascular endothelial cells (CMECs) during ischemia/reperfusion (I/R) injury has not been fully investigated. Tongxinluo (TXL), a traditional Chinese medicine, was shown to be vascular protective. We aimed to elucidate the role of autophagy and its regulatory mechanisms by TXL in CMECs subjected to I/R injury. CMECs were exposed to different treatments for 30 minutes and subjected to hypoxia/reoxygenation each for 2 hours. The results indicated that hypoxia/reoxygenation significantly induced autophagy, as identified by an increased number of monodansylcadaverine-positive CMECs, increased autophagosome formation, and a higher type II/type I of light chain 3 ratio, but not Beclin-1 expression. Autophagy inhibition using 3-methyladenine was proapoptotic, but rapamycin-induced autophagy was antiapoptotic. TXL enhanced autophagy and decreased apoptosis in a dose-dependent manner, reaching its largest effect at 800 μg/mL. 3-methyladenine attenuated the TXL-promoted autophagy and antiapoptotic effects, whereas rapamycin had no additional effects compared with TXL alone. TXL upregulated mitogen-activated protein kinase and extracellular signal-regulated kinase (ERK) phosphorylation; however, PD98059 abrogated ERK phosphorylation and decreased autophagy and increased apoptosis compared with TXL alone. These results suggest that autophagy is a protective mechanism in CMECs subjected to I/R injury and that TXL can promote autophagy through activation of the mitogen-activated protein kinase/ERK pathway.

Anaesthetics as cardioprotectants: translatability and mechanism

The pharmacological conditioning of the heart with anaesthetics, such as volatile anaesthetics or opioids, is a phenomenon whereby a transient exposure to an anaesthetic agent protects the heart from the harmful consequences of myocardial ischaemia and reperfusion injury. The cellular and molecular mechanisms of anaesthetic conditioning appear largely to mimic those of ischaemic pre- and post-conditioning. Progress has been made on the understanding of the underlying mechanisms although the order of events and the specific targets of anaesthetics that trigger protection are not always clear. In the laboratory, the protection afforded by certain anaesthetics against cardiac ischaemia and reperfusion injury is powerful and reproducible but this has not necessarily translated into similarly robust clinical benefits. Indeed, clinical studies and meta-analyses delivered variable results when comparing in the laboratory setting protective and non-protective anaesthetics. Reasons for this include underlying conditions such as age, obesity and diabetes. Animal models for disease or ageing, human cardiomyocytes derived from stem cells of patients and further clinical studies are employed to better understand the underlying causes that prevent a more robust protection in patients.

Anaesthetics as cardioprotectants: translatability and mechanism

The pharmacological conditioning of the heart with anaesthetics, such as volatile anaesthetics or opioids, is a phenomenon whereby a transient exposure to an anaesthetic agent protects the heart from the harmful consequences of myocardial ischaemia and reperfusion injury. The cellular and molecular mechanisms of anaesthetic conditioning appear largely to mimic those of ischaemic pre- and post-conditioning. Progress has been made on the understanding of the underlying mechanisms although the order of events and the specific targets of anaesthetics that trigger protection are not always clear. In the laboratory, the protection afforded by certain anaesthetics against cardiac ischaemia and reperfusion injury is powerful and reproducible but this has not necessarily translated into similarly robust clinical benefits. Indeed, clinical studies and meta-analyses delivered variable results when comparing in the laboratory setting protective and non-protective anaesthetics. Reasons for this include underlying conditions such as age, obesity and diabetes. Animal models for disease or ageing, human cardiomyocytes derived from stem cells of patients and further clinical studies are employed to better understand the underlying causes that prevent a more robust protection in patients.

Differential analysis of transient increases of serum cTnI in response to handling in rats

Serum cardiac troponins are the key biomarkers of myocardial necrosis in humans and in preclinical species. The use of ultrasensitive assays for serum cardiac troponin I (cTnI) as a biomarker in safety studies is hampered by interindividual differences. In this study, we investigated the effect of handling procedures on serum cTnI and explored modeling and simulation approaches to mitigate the impact of these interindividual differences. Femoral-catheterized male Crl:WI(Han) rats (n = 16/group) were left undisturbed in their cages with no handling; subjected to 5 min of isoflurane/O₂ anesthesia (A); or placed into a rodent restrainer followed by simulated tail vein injection (RR). Serum cTnI concentrations were assessed over a 24-h period using an ultrasensitive assay, and the study was repeated for confirmation. The mean serum cTnI concentration pre-procedure was 4.2 pg/mL, and remained stable throughout the duration of the study in the rats submitted to the A procedure. Serum cTnI concentrations increased transiently after the RR procedure with a median time to maximum concentration (T_max), of 1 and 2 h and a mean maximum value concentration (C_max), of 53.0 and 7.2 pg/mL in the initial and repeat studies, respectively. A population pharmacodynamic model identified interindividual, procedure- and study-specific effects on serum cTnI concentrations in rats. It is concluded that a modeling and simulation approach more appropriately describes and statistically analyzes the data obtained with this ultrasensitive assays.

Scaling and systems biology for integrating multiple organs-on-a-chip

Coupled systems of in vitro microfabricated organs-on-a-chip containing small populations of human cells are being developed to address the formidable pharmacological and physiological gaps between monolayer cell cultures, animal models, and humans that severely limit the speed and efficiency of drug development. These gaps present challenges not only in tissue and microfluidic engineering, but also in systems biology: how does one model, test, and learn about the communication and control of biological systems with individual organs-on-chips that are one-thousandth or one-millionth of the size of adult organs, or even smaller, i.e., organs for a milliHuman (mHu) or microHuman (μHu)? Allometric scaling that describes inter-species variation of organ size and properties provides some guidance, but given the desire to utilize these systems to extend and validate human pharmacokinetic and pharmacodynamic (PK/PD) models in support of drug discovery and development, it is more appropriate to scale each organ functionally to ensure that it makes the suitable physiological contribution to the coupled system. The desire to recapitulate the complex organ-organ interactions that result from factors in the blood and lymph places a severe constraint on the total circulating fluid (~5 mL for a mHu and ~5 μL for a μHu) and hence on the pumps, valves, and analytical instruments required to maintain and study these systems. Scaling arguments also provide guidance on the design of a universal cell-culture medium, typically without red blood cells. This review presents several examples of scaling arguments and discusses steps that should ensure the success of this endeavour.

Impairment of endothelial-myocardial interaction increases the susceptibility of cardiomyocytes to ischemia/reperfusion injury

Endothelial-myocardial interactions may be critically important for ischemia/reperfusion injury. Tetrahydrobiopterin (BH4) is a required cofactor for nitric oxide (NO) production by endothelial NO synthase (eNOS). Hyperglycemia (HG) leads to significant increases in oxidative stress, oxidizing BH4 to enzymatically incompetent dihydrobiopterin. How alterations in endothelial BH4 content impact myocardial ischemia/reperfusion injury remains elusive. The aim of this study was to examine the effect of endothelial-myocardial interaction on ischemia/reperfusion injury, with an emphasis on the role of endothelial BH4 content. Langendorff-perfused mouse hearts were treated by triton X-100 to produce endothelial dysfunction and subsequently subjected to 30 min of ischemia followed by 2 h of reperfusion. The recovery of left ventricular systolic and diastolic function during reperfusion was impaired in triton X-100 treated hearts compared with vehicle-treated hearts. Cardiomyocytes (CMs) were co-cultured with endothelial cells (ECs) and subsequently subjected to 2 h of hypoxia followed by 2 h of reoxygenation. Addition of ECs to CMs at a ratio of 1∶3 significantly increased NO production and decreased lactate dehydrogenase activity compared with CMs alone. This EC-derived protection was abolished by HG. The addition of 100 µM sepiapterin (a BH4 precursor) or overexpression of GTP cyclohydrolase 1 (the rate-limiting enzyme for BH4 biosynthesis) in ECs by gene trasfer enhanced endothelial BH4 levels, the ratio of eNOS dimer/monomer, eNOS phosphorylation, and NO production and decreased lactate dehydrogenase activity in the presence of HG. These results demonstrate that increased BH4 content in ECs by either pharmacological or genetic approaches reduces myocardial damage during hypoxia/reoxygenation in the presence of HG. Maintaining sufficient endothelial BH4 is crucial for cardioprotection against hypoxia/reoxygenation injury.

Activation of hypoxia response in endothelial cells contributes to ischemic cardioprotection

Small-molecule inhibition of hypoxia-inducible factor prolyl 4-hydroxylases (HIF-P4Hs) is being explored for the treatment of anemia. Previous studies have suggested that HIF-P4H-2 inhibition may also protect the heart from an ischemic insult. Hif-p4h-2(gt/gt) mice, which have 76 to 93% knockdown of Hif-p4h-2 mRNA in endothelial cells, fibroblasts, and cardiomyocytes and normoxic stabilization of Hif-α, were subjected to ligation of the left anterior descending coronary artery (LAD). Hif-p4h-2 deficiency resulted in increased survival, better-preserved left ventricle (LV) systolic function, and a smaller infarct size. Surprisingly, a significantly larger area of the LV remained perfused during LAD ligation in Hif-p4h-2(gt/gt) hearts than in wild-type hearts. However, no difference was observed in collateral vessels, while the size of capillaries, but not their number, was significantly greater in Hif-p4h-2(gt/gt) hearts than in wild-type hearts. Hif-p4h-2(gt/gt) mice showed increased cardiac expression of endothelial Hif target genes for Tie-2, apelin, APJ, and endothelial nitric oxide (NO) synthase (eNOS) and increased serum NO concentrations. Remarkably, blockage of Tie-2 signaling was sufficient to normalize cardiac apelin and APJ expression and resulted in reversal of the enlarged-capillary phenotype and ischemic cardioprotection in Hif-p4h-2(gt/gt) hearts. Activation of the hypoxia response by HIF-P4H-2 inhibition in endothelial cells appears to be a major determinant of ischemic cardioprotection and justifies the exploration of systemic small-molecule HIF-P4H-2 inhibitors for ischemic heart disease.

Angiogenesis in the infarcted myocardium

SIGNIFICANCE

Proangiogenic therapy appeared a promising strategy for the treatment of patients with acute myocardial infarction (MI), as de novo formation of microvessels, has the potential to salvage ischemic myocardium at early stages after MI, and is also essential to prevent the transition to heart failure through the control of cardiomyocyte hypertrophy and contractility.

RECENT ADVANCES

Exciting preclinical studies evaluating proangiogenic therapies for MI have prompted the initiation of numerous clinical trials based on protein or gene transfer delivery of growth factors and administration of stem/progenitor cells, mainly from bone marrow origin. Nonetheless, these clinical trials showed mixed results in patients with acute MI.

CRITICAL ISSUES

Even though methodological caveats, such as way of delivery for angiogenic growth factors (e.g., protein vs. gene transfer) and stem/progenitor cells or isolation/culture procedure for regenerative cells might partially explain the failure of such trials, it appears that delivery of a single growth factor or cell type does not support angiogenesis sufficiently to promote cardiac repair.

FUTURE DIRECTIONS

Optimization of proangiogenic therapies might include stimulation of both angiogenesis and vessel maturation and/or the use of additional sources of stem/progenitor cells, such as cardiac progenitor cells. Experimental unraveling of the mechanisms of angiogenesis, vessel maturation, and endothelial cell/cardiomyocyte cross talk in the ischemic heart, analysis of emerging pathways, as well as a better understanding of how cardiovascular risk factors impact endogenous and therapeutically stimulated angiogenesis, would undoubtedly pave the way for the development of novel and hopefully efficient angiogenesis targeting therapeutics for the treatment of acute MI.