Aims C-type natriuretic peptide (CNP) is an essential endothelium-derived signalling species that governs vascular homoeostasis; CNP is also expressed in the heart but an intrinsic role for the peptide in cardiac function is not established. Herein, we employ unique transgenic strains with cell-specific deletion of CNP to define a central (patho)physiological capacity of CNP in maintaining heart morphology and contractility. Methods and results Cardiac structure and function were explored in wild type (WT), cardiomyocyte (cmCNP−/−), endothelium (ecCNP−/−), and fibroblast (fbCNP−/−)—specific CNP knockout mice, and global natriuretic peptide receptor (NPR)-B−/−, and NPR-C−/− animals at baseline and in experimental models of myocardial infarction and heart failure (HF). Endothelium-specific deletion of CNP resulted in impaired coronary responsiveness to endothelium-dependent- and flow-mediated-dilatation; changes mirrored in NPR-C−/− mice. Ex vivo, global ischaemia resulted in larger infarcts and diminished functional recovery in cmCNP−/− and NPR-C−/−, but not ecCNP−/−, vs. WT. The cardiac phenotype of cmCNP−/−, fbCNP−/−, and NPR-C−/− (but not ecCNP−/− or NPR-B−/−) mice was more severe in pressure overload- and sympathetic hyperactivation-induced HF compared with WT; these adverse effects were rescued by pharmacological CNP administration in WT, but not NPR-C−/−, mice. At a molecular level, CNP/NPR-C signalling is impaired in human HF but attenuates activation of well-validated pro-hypertrophic and pro-fibrotic pathways. Conclusion C-type natriuretic peptide of cardiomyocyte, endothelial and fibroblast origins co-ordinates and preserves cardiac structure, function, and coronary vasoreactivity via activation of NPR-C. Targeting NPR-C may prove an innovative approach to treating HF and ischaemic cardiovascular disorders.

Ventricular arrhythmias are an important cause of mortality in the acute myocardial infarction (MI). To elucidate effect of ivabradine, pure heart rate (HR) reducing drug, on ventricular arrhythmias within 24 h after non-reperfused MI in the rat. ECG was recorded for 24 h after MI in untreated and ivabradine treated rats and episodes of ventricular tachycardia/fibrillation (VT/VF) were identified. Forty-five minutes and twenty-four hours after MI epicardial monophasic action potentials (MAPs) were recorded, cardiomyocyte Ca(2+) handling was assessed and expression and function of ion channels were studied. Ivabradine reduced average HR by 17%. Combined VT/VF incidence and arrhythmic mortality were higher in MI versus MI + Ivabradine rats. MI resulted in (1) increase of Ca(2+) sensitivity of ryanodine receptors 24 h after MI; (2) increase of HCN4 expression in the left ventricle (LV) and funny current (IF) in LV cardiomyocytes 24 h after MI, and (3) dispersion of MAP duration both 45 min and 24 h after MI. Ivabradine partially prevented all these three potential proarrhythmic effects of MI. Ivabradine is antiarrhythmic in the acute MI in the rat. Potential mechanisms include prevention of: diastolic Ca(2+)-leak from sarcoplasmic reticulum, upregulation of IF current in LV and dispersion of cardiac repolarization. Ivabradine could be an attractive antiarrhythmic agent in the setting of acute MI.

SignificanceThe morbidity and mortality associated with heart failure (HF) are unacceptably high. Cyclic guanosine-3′,5′-monophosphate (cGMP) plays a key role in preserving cardiac structure and function, and therapeutically targeting cGMP in HF has shown promise in experimental models and patients. Phosphodiesterases (PDEs) metabolize and curtail the actions of cGMP (and cAMP), and increased PDE activity is thought to contribute to HF pathogenesis. Herein, we show that inhibition of one specific isoform, PDE2, enhances the salutary effects of cGMP in the context of HF, and that this beneficial action facilitates a distinct pathway, driven by nitric oxide, that is impaired in this disorder. These observations validate PDE2 inhibitors as a demonstrable means of boosting cardiac cGMP and advancing HF therapy.

Background: Kinase oxidation is a critical signalling mechanism through which changes in the intracellular redox state alter cardiac function. In the myocardium, type-1 protein kinase A (PKARIα) can be reversibly oxidized, forming interprotein disulfide bonds within the holoenzyme complex. However, the effect of PKARIα disulfide formation on downstream signaling in the heart, particularly under states of oxidative stress such as ischemia and reperfusion (I/R), remains unexplored. Methods: Atrial tissue obtained from patients before and after cardiopulmonary bypass and reperfusion and left ventricular (LV) tissue from mice subjected to I/R or sham surgery were used to assess PKARIα disulfide formation by immunoblot. To determine the impact of disulfide formation on PKARIα catalytic activity and sub-cellular localization, live-cell fluorescence imaging and stimulated emission depletion super-resolution microscopy were performed in prkar1 knock-out mouse embryonic fibroblasts, neonatal myocytes or adult LV myocytes isolated from 'redox dead' (Cys17Ser) PKARIα knock-in mice and their wild-type littermates. Comparison of intracellular calcium dynamics between genotypes was assessed in fura2-loaded LV myocytes whereas I/R-injury was assessed ex vivo. Results: In both humans and mice, myocardial PKARIα disulfide formation was found to be significantly increased (2-fold in humans, p=0.023; 2.4-fold in mice, p<0.001) in response to I/R in vivo. In mouse LV cardiomyocytes, disulfide-containing PKARIα was not found to impact catalytic activity, but instead led to enhanced A-kinase-anchoring protein (AKAP) binding with preferential localization of the holoenzyme to the lysosome. Redox-dependent regulation of lysosomal two pore channels (TPC) by PKARIα was sufficient to prevent global calcium release from the sarcoplasmic reticulum in LV myocytes, without affecting intrinsic ryanodine receptor leak or phosphorylation. Absence of I/R-induced PKARIα disulfide formation in "redox dead" knock-in mouse hearts resulted in larger infarcts (2-fold, p<0.001) and a concomitant reduction in LV contractile recovery (1.6-fold, p<0.001), which was prevented by administering the lysosomal TPC inhibitor Ned-19 at the time of reperfusion. Conclusions: Disulfide-modification targets PKARIα to the lysosome where it acts as a gatekeeper for TPC-mediated triggering of global calcium release. In the post-ischemic heart, this regulatory mechanism is critical for protecting from extensive injury and offers a novel target for the design of cardioprotective therapeutics.

Objective: This report describes a mobile outreach influenza immunisation program for vulnerable populations in a resource‐rich setting. It explores vaccine recipients’ demographics, comorbidities and vaccination histories, and the factors influencing their decision to receive vaccine during outreach. Methods: Teams of nurse immunisers visited and provided influenza vaccines to clients from 21 sites (18 community centres for migrants, refugees and the homeless; and three outpatient clinics). Risk factors for severe influenza, vaccination histories and perceived barriers and facilitators to vaccines were collected from vaccine recipients. Results: A total of 1,032 vaccine recipients participated in the survey with responses collected from April to October 2018. Of these, 54% reported at least one risk factor for severe influenza. Sixty per cent of recipients had not received an influenza vaccine in 2017, with most of them reporting ‘not worried about influenza’ as a reason. Pregnant participants most frequently reported a healthcare provider’s recommendation as the reason to receive the vaccine. Conclusion: An outreach program comprising of a means of taking vaccines to the population was a successful strategy to deliver influenza vaccines to high‐risk populations. It needs to be considered in the full range of delivery models to improve influenza vaccine coverage, even in resource‐rich settings. Implication for public health: Strategies reaching out to vulnerable populations are crucial to maximise vaccine uptake.

Introduction: The cofactor tetrahydrobiopterin (BH4) is a critical regulator of nitric oxide synthase (NOS) function and redox signalling, with reduced BH4 implicated in multiple cardiovascular disease states. In the myocardium, augmentation of BH4 levels can impact on cardiomyocyte function, preventing hypertrophy and heart failure. However, the specific role of endothelial cell BH4 biosynthesis in the coronary circulation and its role in cardiac function and the response to ischaemia has yet to be elucidated. Methods/results: Endothelial cell specific Gch1 knock out mice were generated by crossing Gch1fl/f with Tie2cre mice, generating Gch1fl/flTie2cre mice and littermate controls. GTPCH protein and BH4 levels were reduced in heart tissues from Gch1fl/flTie2cre mice, localized to endothelial cells, with normal cardiomyocyte BH4. Deficiency in coronary endothelial cell BH4 led to NOS uncoupling, decreased NO bioactivity, and increased superoxide and hydrogen peroxide production in hearts of Gch1fl/flTie2cre mice. Under physiological condition, loss of endothelial cell-specific BH4 led to mild cardiac hypertrophy in Gch1fl/flTie2cre hearts. Endothelial cell BH4 loss was also associated with increased nNOS protein, loss of eNOS protein and increased phospholamban phosphorylation at Ser17 in cardiomyocytes. Loss of cardiac endothelial cell BH4 led to coronary vascular dysfunction, reduced functional recovery and increased myocardial infarct size following ischemia/reperfusion injury. Conclusion: Taken together, these studies reveal a specific role for endothelial cell Gch1/BH4 biosynthesis in cardiac function and the response to cardiac ischemia/reperfusion injury. Targeting endothelial cell Gch1 and BH4 biosynthesis may provide a novel therapeutic target for the prevention and treatment of cardiac dysfunction and ischaemia-reperfusion injury.

No abstract

No abstract