Background: The mouse inbred line C57BL/6J is widely used in mouse genetics and its genome has been incorporated into many genetic reference populations. More recently large initiatives such as the International Knockout Mouse Consortium (IKMC) are using the C57BL/6N mouse strain to generate null alleles for all mouse genes. Hence both strains are now widely used in mouse genetics studies. Here we perform a comprehensive genomic and phenotypic analysis of the two strains to identify differences that may influence their underlying genetic mechanisms. Results: We undertake genome sequence comparisons of C57BL/6J and C57BL/6N to identify SNPs, indels and structural variants, with a focus on identifying all coding variants. We annotate 34 SNPs and 2 indels that distinguish C57BL/6J and C57BL/6N coding sequences, as well as 15 structural variants that overlap a gene. In parallel we assess the comparative phenotypes of the two inbred lines utilizing the EMPReSSslim phenotyping pipeline, a broad based assessment encompassing diverse biological systems. We perform additional secondary phenotyping assessments to explore other phenotype domains and to elaborate phenotype differences identified in the primary assessment. We uncover significant phenotypic differences between the two lines, replicated across multiple centers, in a number of physiological, biochemical and behavioral systems. Conclusions: Comparison of C57BL/6J and C57BL/6N demonstrates a range of phenotypic differences that have the potential to impact upon penetrance and expressivity of mutational effects in these strains. Moreover, the sequence variants we identify provide a set of candidate genes for the phenotypic differences observed between the two strains.

Rationale: Athletes present with atrioventricular node dysfunction manifesting as atrioventricular block. This can necessitate electronic pacemaker implantation, known to be more frequent in athletes with a long training history. Objective: Atrioventricular block in athletes is attributed to high vagal tone. Here, we investigated the alternative hypothesis that electrical remodeling of the atrioventricular node is responsible. Methods and Results: Radiotelemetry ECG data and atrioventricular node biopsies were collected in sedentary and trained Standardbred racehorses, a large-animal model of the athlete’s heart. Trained horses presented with longer PR intervals (that persisted under complete autonomic block) versus sedentary horses, concomitant with reduced expression of key ion channels involved in atrioventricular node conduction: L-type Ca ²⁺ channel subunit Ca _V 1.2 and HCN4 (hyperpolarization-activated cyclic nucleotide-gated channel 4). Atrioventricular node electrophysiology was explored further in mice; prolongation of the PR interval (in vivo and ex vivo), Wenckebach cycle length, and atrioventricular node refractory period were observed in mice trained by swimming versus sedentary mice. Transcriptional profiling in laser-capture microdissected atrioventricular node revealed striking reduction in pacemaking ion channels in trained mice, translating into protein downregulation of Ca _V 1.2 and HCN4. Correspondingly, patch-clamp recordings in isolated atrioventricular node myocytes demonstrated a training-induced reduction in I _{Ca, L} and I _f density that likely contributed to the observed lower frequency of action potential firing in trained cohorts. MicroRNA (miR) profiling and in vitro studies revealed miR-211-5p and miR-432 as direct regulators of Ca _V 1.2 and HCN4. In vivo miRs suppression or detraining restored training-induced PR prolongation and ion channel remodeling. Conclusions: Training-induced atrioventricular node dysfunction is underscored by likely miR-mediated transcriptional remodeling that translates into reduced current density of key ionic currents involved in impulse generation and conduction. We conclude that electrical remodeling is a key mechanism underlying atrioventricular block in athletes.

The purpose of this study was to identify where ultrasmall superparamagnetic particles of iron oxide (USPIO) locate to in myocardium, develop a methodology that differentiates active macrophage uptake of USPIO from passive tissue distribution; and investigate myocardial inflammation in cardiovascular diseases. Myocardial inflammation is hypothesized to be a key pathophysiological mechanism of heart failure (HF), but human evidence is limited, partly because evaluation is challenging. USPIO-magnetic resonance imaging (MRI) potentially allows specific identification of myocardial inflammation but it remains unclear what the USPIO-MRI signal represents. Histological validation was performed using a murine acute myocardial infarction (MI) model. A multiparametric, multi-time-point MRI methodology was developed, which was applied in patients with acute MI (n = 12), chronic ischemic cardiomyopathy (n = 7), myocarditis (n = 6), dilated cardiomyopathy (n = 5), and chronic sarcoidosis (n = 5). USPIO were identified in myocardial macrophages and myocardial interstitium. R1 time-course reflected passive interstitial distribution whereas multi-time-point R2* was also sensitive to active macrophage uptake. R2*/R1 ratio provided a quantitative measurement of myocardial macrophage infiltration. R2* behavior and R2*/R1 ratio were higher in infarcted (p = 0.001) and remote (p = 0.033) myocardium in acute MI and in chronic ischemic cardiomyopathy (infarct: p = 0.008; remote p = 0.010), and were borderline higher in DCM (p = 0.096), in comparison to healthy controls, but were no different in myocarditis or sarcoidosis. An R2*/R1 threshold of 25 had a sensitivity and specificity of 90% and 83%, respectively, for detecting active USPIO uptake. USPIO are phagocytized by cardiac macrophages but are also passively present in myocardial interstitium. A multiparametric multi-time-point MRI methodology specifically identifies active myocardial macrophage infiltration. Persistent active macrophage infiltration is present in infarcted and remote myocardium in chronic ischemic cardiomyopathy, providing a substrate for HF.

Pulmonary arterial hypertension (PAH) is a disease characterised by raised pulmonary vascular resistance. It has a poor prognosis typically resulting in progressive right ventricular failure and death. Treatment in PAH has advanced rapidly over the past decade with the use of Ca²⁺ channel blockers, prostanoids, endothelin receptor antagonists (ERAs) and phosphodiesterase-5 inhibitors [ 1 x [1] Galie, N., Hoeper, M.M., Humbert, M., Torbicki, A., Vachiery, J.L., Barbera, J.A. et al. Guidelines for the diagnosis and treatment of pulmonary hypertension: the Task Force for the Diagnosis and Treatment of Pulmonary Hypertension of the European Society of Cardiology (ESC) and the European Respiratory Society (ERS), endorsed by the International Society of Heart and Lung Transplantation (ISHLT). Eur Heart J. Oct 2009; 30: 2493–2537 Crossref | PubMed | Scopus (2458) | Google Scholar See all References ] [1] . PAH often has an insidious onset, which means that diagnosis and treatment are usually not begun until the disease is advanced. Recent studies have looked at patients with less severe disease (World Health Organisation (WHO) class II), and have shown that early initiation of therapy can delay the progression of the disease [ 2 x [2] Galie, N., Rubin, L., Hoeper, M., Jansa, P., Al-Hiti, H., Meyer, G. et al. Treatment of patients with mildly symptomatic pulmonary arterial hypertension with bosentan (EARLY study): a double-blind, randomised controlled trial. Lancet. 2008; 371: 2093–2100 Abstract | Full Text | Full Text PDF | PubMed | Scopus (645) | Google Scholar See all References ] [2] .

Background: Prolonged activation of angiotensin II is the main mediator that contributes to the development of heart diseases, so converting angiotensin II into angiotensin 1‐7 has emerged as a new strategy to attenuate detrimental effects of angiotensin II. Prolylcarboxypeptidase is a lysosomal pro‐X carboxypeptidase that is able to cleave angiotensin II at a preferential acidic pH optimum. However, insufficient attention has been given to the cardioprotective functions of prolylcarboxylpeptidase. Methods and Results: We established a CRISPR/CRISPR‐associated protein 9–mediated global prolylcarboxylpeptidase‐knockout and adeno‐associated virus serotype 9–mediated cardiac prolylcarboxylpeptidase overexpression mouse models, which were challenged with the angiotensin II infusion (2 mg/kg per day) for 4 weeks, aiming to investigate the cardioprotective effect of prolylcarboxylpeptidase against hypertensive cardiac hypertrophy. Prolylcarboxylpeptidase expression was upregulated after 2 weeks of angiotensin II infusion and then became downregulated afterward in wild‐type mouse myocardium, suggesting its compensatory function against angiotensin II stress. Moreover, angiotensin II–treated prolylcarboxylpeptidase‐knockout mice showed aggravated cardiac remodeling and dampened cardiac contractility independent of hypertension. We also found that prolylcarboxylpeptidase localizes in cardiomyocyte lysosomes, and loss of prolylcarboxylpeptidase led to excessive angiotensin II levels in myocardial tissue. Further screening demonstrated that hypertrophic prolylcarboxylpeptidase‐knockout hearts showed upregulated extracellular signal‐regulated kinases 1/2 and downregulated protein kinase B activities. Importantly, adeno‐associated virus serotype 9–mediated restoration of prolylcarboxylpeptidase expression in prolylcarboxylpeptidase‐knockout hearts alleviated angiotensin II–induced hypertrophy, fibrosis, and cell death. Interestingly, the combination of adeno‐associated virus serotype 9–mediated prolylcarboxylpeptidase overexpression and an antihypertensive drug, losartan, likely conferred more effective protection than a single treatment protocol to mitigate angiotensin II–induced cardiac dysfunction. Conclusions: Our data demonstrate that prolylcarboxylpeptidase protects the heart from angiotensin II–induced hypertrophic remodeling by controlling myocardial angiotensin II levels.

Prenatal hypoxia is a common pregnancy complication that can permanently alter the structure and function of the fetal heart and predispose individuals to cardiovascular disease. However, the interactive effects of prenatal hypoxia and postnatal lifestyle choices are poorly studied. This study investigated the combined effects of prenatal hypoxia and a postnatal high-salt diet on cardiac function in adulthood. Pregnant Wistar rats were exposed to either 21% oxygen (normoxic group, n = 8) or 10.5% oxygen (hypoxic group, n = 8) from days 15 to 20 of gestation. Male offspring were divided into two groups at five weeks of age; normal salt (0.3 % NaCl) and high salt (8% NaCl) chow. Blood pressure and echocardiography measurements were performed at 18 weeks to assess cardiovascular function. Rats from hypoxic pregnancies had signs of pulmonary hypertension and right ventricular thickening, whereas rats fed a postnatal high-salt diet had systemic hypertension, left ventricular wall thickening and impaired relaxation. When prenatal hypoxia was combined with a postnatal high-salt diet, the rats exhibited a combination of the two phenotypes, but there were no significant interactions. Results suggest a poor postnatal diet can put additional strain on the cardiovascular system of offspring from hypoxic pregnancies, which can have significant implications for disease management. This article is part of the discussion meeting issue ‘Pregnancy at high altitude: the challenge of hypoxia’.