Jiahong Xu

β2‐ but not β1‐adrenoceptor activation modulates intracellular oxygen availability

β‐Adrenoceptors (β‐ARs) play a critical role in the regulation of cardiovascular function. Intracellular oxygen homeostasis is crucial for the survival of cardiomyocytes. However, it is still unclear whether β‐AR activation can modulate intracellular oxygen. Here we used mitochondrial and cytosolic target Renilla luciferase to detect intracellular oxygen concentration. Pharmacological experiments revealed that β2‐AR activation specifically regulates intracellular oxygen in cardiomyocytes and COS7 cells. This effect was abrogated by inhibitory G protein (Gi) inhibition, endothelial nitric oxide synthase (eNOS) blockade, and NO scavenging, implicating that the β2‐AR–Gi–eNOS pathway is involved in this regulation. β2‐AR activation increased the AMP/ATP ratio, AMPK activity, ROS production and prolyl hydroxylase activity. These effects also contribute to the regulation of β2‐AR signalling, thus providing an additional layer of complexity to enforce the specificity of β1‐AR and β2‐AR signalling. Collectively, the study provides novel insight into the modulation of oxygen homeostasis, broadens the scope of β2‐AR function, and may have crucial implications for β2‐AR signalling regulation.

Translocator Protein (18 kDa): A Promising Therapeutic Target and Diagnostic Tool for Cardiovascular Diseases

The translocator protein (18 kDa) (TSPO) is a five transmembrane domain protein in mitochondria, abundantly expressed in a variety of organs and tissues. TSPO contributes to a wide range of biological processes, including cholesterol transportation, mitochondrial membrane potential and respiratory chain regulation, apoptosis, and oxidative stress. Recent studies have demonstrated that TSPO might also be involved in the physiological regulation of cardiac chronotropy and inotropy. Accordingly, TSPO ligands play significant roles in protecting the cardiovascular systems under pathological conditions through cardiac electrical activity retention, intracellular calcium maintenance, mitochondrial energy provision, mitochondrial membrane potential equilibrium, and reactive oxygen species inhibition. This paper focuses on the physiological and pathological characteristics of TSPO in the cardiovascular systems and also summarizes the properties of TSPO ligands. TSPO represents a potential therapeutic target and diagnostic tool for cardiovascular diseases including arrhythmia, myocardial infarction, cardiac hypertrophy, atherosclerosis, myocarditis, and large vessel vasculitis.

Circulating microRNAs as mirrors of acute coronary syndromes: MiRacle or quagMire?

Acute coronary syndrome (ACS), a leading cause of morbidity and mortality worldwide, is among the most serious cardiovascular diseases. Exploring novel approaches, which can complement and improve current strategies for ACS, is continuous. MicroRNAs (miRNAs) are a novel class of small, short non‐coding RNA that post‐transcriptionally regulate genes. The tissue‐ or cell‐specific distribution features of miRNAs and its merit of stably existing in serum and plasma make them attractive biomarkers for ACS. An early and accurate diagnosis is the pre‐requisite to facilitate rapid decision making and treatment and therefore improve outcome in ACS patients. This review highlights and summarizes recent studies using circulating miRNAs as novel biomarkers for ACS including its role in diagnosis, prediction, prognosis and reaction to therapy. In addition, we also discuss the potential function of miRNAs as extracellular communicators in cell‐to‐cell communication. Large multicentre studies are highly needed to pave the road for using circulating miRNAs as biomarkers for ACS from the bench to the bedside. Considering the advantageous properties and the continuously increasing number of studies, circulating miRNAs definitely have the potential to be reasonable diagnostic tools once their infancy has passed.

Telocytes in exercise‐induced cardiac growth

Exercise can induce physiological cardiac growth, which is featured by enlarged cardiomyocyte cell size and formation of new cardiomyocytes. Telocytes (TCs) are a recently identified distinct interstitial cell type, existing in many tissues and organs including heart. TCs have been shown to form a tandem with cardiac stem/progenitor cells in cardiac stem cell niches, participating in cardiac regeneration and repair. Although exercise‐induced cardiac growth has been confirmed as an important way to promote cardiac regeneration and repair, the response of cardiac TCs to exercise is still unclear. In this study, 4 weeks of swimming training was used to induce robust healthy cardiac growth. Exercise can induce an increase in cardiomyocyte cell size and formation of new cardiomyocytes as determined by Wheat Germ Lectin and EdU staining respectively. TCs were identified by three immunofluorescence stainings including double labelling for CD34/vimentin, CD34/platelet‐derived growth factor (PDGF) receptor‐α and CD34/PDGF receptor‐β. We found that cardiac TCs were significantly increased in exercised heart, suggesting that TCs might help control the activity of cardiac stem/progenitor cells, cardiomyocytes or endothelial cells. Adding cardiac TCs might help promote cardiac regeneration and renewal.

A novel noninvasive method for measuring fractional flow reserve through three-dimensional modeling

Coronary stenosis with lumen diameter reduction greater than 50% is recognized as coronary artery disease (CAD) [1–4]. Fractional flow reserve (FFR) is an epicardial lesion-specific parameter to determine the functional coronary stenosis, which is determined by pressure difference and resistance [5–8]. Previous studies have demonstrated that FFR guided percutaneous coronary intervention (PCI) could improve outcomes compared with anatomical invasive coronary angiography (ICA) guided PCI [6–10]. This study aims to overcome the deficiencies of invasive FFR and create a novel noninvasive FFR (FFRni). A 70-year-old female patient, diagnosed with CAD, stable angina pectoris, cardiac function III, essential hypertension III (very high-risk group), with blood pressure of 140/85 mm Hg, was enrolled in as a pilot study. Coronary computed tomography angiography (CCTA) was performed using multi-detector computed tomography scanners (Lightspeed 16 Pro). Original images were spilt into thin layers and directly exported into imaging control software MIMICS and processed to form an image sequence. Three-dimensional (3D) geometric models of the narrow coronary arteries including the right coronary artery (RCA), left anterior descending coronary (LAD) and left circumflex artery (LCX) were reconstructed and exported. Then, the geometric model was meshed with 3D Flotran elements in ANSYS software. Finite element analysis (FEA) was applied to analyze the velocity and pressure distribution of selected coronary arteries. Given boundary conditions including average velocity measured by transthoracic Doppler echocardiography with an ultrasound system (Sequoia C256) were applied in an inlet of 3D model. By setting the proper iteration time, the calculation went smoothly. ICA, as the “gold standard”, was performed with standard techniques. Invasive coronary angiography indicated that there was around 80% stenosis in the proximal RCA (Figure 1A). Mild (about 30%) stenosis in the proximal LAD and a diffuse lesion of the LCX (the narrowest was 80%) could also be quantified (Figure 2A). Additionally, the coronal section of CCTA images demonstrated moderate (around 60%) obstructive stenosis in the proximal RCA (Figure 1B). The cross-sectional images indicated 30% stenosis in the proximal and first branch segment of the LAD and diffuse patchy calcified plaques in the LCX leading to intermediate (50%) stenosis (Figure 2B). The diagnostic performance of FFRni was generally consistent with the results of ICA and CCTA. The values of proximal RCA, LAD and distal LCX were 0.73, 0.76 and 0.64, respectively, which suggested the severity of lesion-specific functional ischemia in distal myocardium with 0.75 as the cutoff value (Figures 1C and ​and2C2C). Figure 1 Anatomically obstructive stenosis of right coronary artery (RCA) with a lesion causing ischemia. A – Invasive coronary angiography indicates that stenosis is about 80% in the proximal RCA (black arrow). B – Multi-planar reformat of coronary ... Figure 2 Anatomically obstructive stenosis of left anterior descending coronary (LAD) and left circumflex artery (LCX) with/without functional ischemia. A – Invasive coronary angiography indicates that there exist 30% stenosis in proximal LAD (black arrow) ... Recently, FFR computed from CCTA (FFRCT) was reported. A good correlation between FFRCT and invasive FFR was certified through a randomized clinical controlled trial on 159 vessels in 103 patients [11]. The differences in the calculation process of FFRCT and FFRni in our study mainly reflect the following factors. During FFRCT calculation, coronary flow and pressure are unknown. A method to couple lumped parameter models of the microcirculation to the outflow boundaries of the 3D model was adopted. As a result of the cumbersome workload, it takes approximately 5 h/exam. We utilized FEA of the Flotran CFD module to solve the hemodynamic calculation under given boundary conditions. Therefore, it can greatly reduce the computation time to 3 h/exam. The more relaxed equipment requirements and faster inspection time guarantee potential clinical application of FFRni. Fractional flow reserve is a well-evaluated functional index to assess the ischemic significance of coronary lesions, helping making the decision of revascularization [12–14]. Nevertheless, the invasiveness and costliness are two major reasons restricting its further application. Finite element analysis and CFD over digital 3D modeling were applied in this pilot study and created a novel method to evaluate functional coronary stenosis by FFRni, which showed good consistency with ICA and CCTA. The superiority of no invasiveness and cost-effectiveness establishes the foundation of FFRni for its further applications in clinical practice. However, a large randomized clinical controlled trial assessed by FFRni compared with invasive FFR is urgently needed.

Cardiac cell proliferation is not necessary for exercise-induced cardiac growth but required for its protection against ischaemia/reperfusion injury

The adult heart retains a limited ability to regenerate in response to injury. Although exercise can reduce cardiac ischaemia/reperfusion (I/R) injury, the relative contribution of cardiac cell proliferation including newly formed cardiomyocytes remains unclear. A 4‐week swimming murine model was utilized to induce cardiac physiological growth. Simultaneously, the antineoplastic agent 5‐fluorouracil (5‐FU), which acts during the S phase of the cell cycle, was given to mice via intraperitoneal injections. Using EdU and Ki‐67 immunolabelling, we showed that exercise‐induced cardiac cell proliferation was blunted by 5‐FU. In addition, the growth of heart in size and weight upon exercise was unaltered, probably due to the fact that exercise‐induced cardiomyocyte hypertrophy was not influenced by 5‐FU as demonstrated by wheat germ agglutinin staining. Meanwhile, the markers for pathological hypertrophy, including ANP and BNP, were not changed by either exercise or 5‐FU, indicating that physiological growth still developed in the presence of 5‐FU. Furthermore, we showed that CITED4, a key regulator for cardiomyocyte proliferation, was blocked by 5‐FU. Meanwhile, C/EBPβ, a transcription factor responsible for both cellular proliferation and hypertrophy, was not altered by treatment with 5‐FU. Importantly, the effects of exercise in reducing cardiac I/R injury could be abolished when cardiac cell proliferation was attenuated in mice treated with 5‐FU. In conclusion, cardiac cell proliferation is not necessary for exercise‐induced cardiac physiological growth, but it is required for exercise‐associated protection against I/R injury.

Urotensin II inhibited the proliferation of cardiac side population cells in mice during pressure overload by JNK-LRP6 signalling

Cardiac side population cells (CSPs) are promising cell resource for the regeneration in diseased heart as intrinsic cardiac stem cells. However, the relative low ratio of CSPs in the heart limited the ability of CSPs to repair heart and improve cardiac function effectively under pathophysiological condition. Which factors limiting the proliferation of CSPs in diseased heart are unclear. Here, we show that urotensin II (UII) regulates the proliferation of CSPs by c‐Jun N‐terminal kinase (JNK) and low density lipoprotein receptor‐related protein 6 (LRP6) signalling during pressure overload. Pressure overload greatly upregulated UII level in plasma, UII receptor (UT) antagonist, urantide, promoted CSPs proliferation and improved cardiac dysfunction during chronic pressure overload. In cultured CSPs subjected to mechanical stretch (MS), UII significantly inhibited the proliferation by UT. Nanofluidic proteomic immunoassay showed that it is the JNK activation, but not the extracellular signal‐regulated kinase signalling, that involved in the UII‐inhibited‐ proliferation of CSPs during pressure overload. Further analysis in vitro indicated UII‐induced‐phospho‐JNK regulates phosphorylation of LRP6 in cultured CSPs after MS, which is important in the inhibitory effect of UII on the CSPs during pressure overload. In conclusion, UII inhibited the proliferation of CSPs by JNK/LRP6 signalling during pressure overload. Pharmacological inhibition of UII promotes CSPs proliferation in mice, offering a possible therapeutic approach for cardiac failure induced by pressure overload.

Preservation of TSPO by chronic intermittent hypobaric hypoxia confers antiarrhythmic activity.

Abnormal activation of mitochondrial translocator protein (TSPO) contributes to arrhythmogenesis during cardiac metabolic compromise; however, its role in the antiarrhythmic activities of chronic hypoxia adaptation remains unclear. Our results demonstrated that 80% of normoxic rats developed ischaemic VF, whereas this condition was seldom observed in rats with 14 days of chronic intermittent hypobaric hypoxia (CIHH). TSPO stimulation or inhibition affected the arrhythmias incidence in normoxic rats, but did not change the CIHH‐mediated antiarrhythmic effects. Abrupt and excessive elevation of TSPO activity was positively linked to ischaemic VF, and CIHH preserved TSPO activity during ischaemia. The preservation of TSPO activity by CIHH also contributed to the maintenance of intracellular Ca homeostasis. These results suggest that the blunt sensitivity of TSPO to ischaemic stress may be responsible for the antiarrhythmic effects by CIHH.

Bioinformatics Analysis Reveals MicroRNAs Regulating Biological Pathways in Exercise-Induced Cardiac Physiological Hypertrophy

Exercise-induced physiological cardiac hypertrophy is generally considered to be a type of adaptive change after exercise training and is beneficial for cardiovascular diseases. This study aims at investigating exercise-regulated microRNAs (miRNAs) and their potential biological pathways. Here, we collected 23 miRNAs from 8 published studies. MirPath v.3 from the DIANA tools website was used to execute the analysis, and TargetScan was used to predict the target genes. Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO) analyses were performed to identify potential pathways and functional annotations associated with exercise-induced physiological cardiac hypertrophy. Various miRNA targets and molecular pathways, such as Fatty acid elongation, Arrhythmogenic right ventricular cardiomyopathy (ARVC), and ECM-receptor interaction, were identified. This study could prompt the understanding of the regulatory mechanisms underlying exercise-induced physiological cardiac hypertrophy.

Serum-Derived Extracellular Vesicles Protect Against Acute Myocardial Infarction by Regulating miR-21/PDCD4 Signaling Pathway

Acute myocardial infarction (AMI) represents a leading cause of morbidity and mortality worldwide. Extracellular vesicles (EVs) are being recognized as a promising therapeutic approach in protecting against MI. Serum is a rich source of EVs, which transports various microRNAs (miRNAs, miRs). EVs from serum have been shown beneficial for protecting against ischemia-reperfusion injury; however, their roles in AMI are unclear. In addition, whether a miRNA might be responsible for the effects of serum EVs on protecting against AMI is undetermined. Here, we demonstrated that serum EVs significantly reduced cardiomyocytes apoptosis in both cellular and mouse models of AMI, and dramatically attenuated the infarct size in mouse hearts after AMI. Inhibition of miR-21 was shown to reduce the protective effects of serum EVs in inhibiting cardiomyocytes apoptosis. miR-21 was decreased in mouse hearts after AMI, while serum EVs increased that. In addition, the programmed cell death 4 (PDCD4) expression was identified as a target gene of miR-21. Therefore, our study showed the protective effects of serum EVs on AMI, and provided a novel strategy for AMI therapy.