Immune mediators in heart-lung communication.

It is often the case that serious, end-stage manifestations of disease result from secondary complications in organs distinct from the initial site of injury or infection. This is particularly true of diseases of the heart-lung axis, given the tight anatomical connections of the two organs within a common cavity in which they collectively orchestrate the two major, intertwined circulatory pathways. Immune cells and the soluble mediators they secrete serve as effective, and targetable, messengers of signals between different regions of the body but can also contribute to the spread of pathology. In this review, we discuss the immunological basis of interorgan communication between the heart and lung in various common diseases, and in the context of organ crosstalk more generally. Gaining a greater understanding of how the heart and lung communicate in health and disease, and viewing disease progression generally from a more holistic, whole-body viewpoint have the potential to inform new diagnostic approaches and strategies for better prevention and treatment of comorbidities.

Therapeutic Spp1 silencing in TREM2+ cardiac macrophages suppresses atrial fibrillation.

Atrial fibrillation (AFib) and the risk of its lethal complications are propelled by fibrosis, which induces electrical heterogeneity and gives rise to reentry circuits. Atrial TREM2+ macrophages secrete osteopontin (encoded by Spp1), a matricellular signaling protein that engenders fibrosis and AFib. Here we show that silencing Spp1 in TREM2+ cardiac macrophages with an antibody-siRNA conjugate reduces atrial fibrosis and suppresses AFib in mice, thus offering a new immunotherapy for the most common arrhythmia.

Virus-Induced Acute Respiratory Distress Syndrome Causes Cardiomyopathy Through Eliciting Inflammatory Responses in the Heart.

BACKGROUND: Viral infections can cause acute respiratory distress syndrome (ARDS), systemic inflammation, and secondary cardiovascular complications. Lung macrophage subsets change during ARDS, but the role of heart macrophages in cardiac injury during viral ARDS remains unknown. Here we investigate how immune signals typical for viral ARDS affect cardiac macrophage subsets, cardiovascular health, and systemic inflammation. METHODS: We assessed cardiac macrophage subsets using immunofluorescence histology of autopsy specimens from 21 patients with COVID-19 with SARS-CoV-2-associated ARDS and 33 patients who died from other causes. In mice, we compared cardiac immune cell dynamics after SARS-CoV-2 infection with ARDS induced by intratracheal instillation of Toll-like receptor ligands and an ACE2 (angiotensin-converting enzyme 2) inhibitor. RESULTS: In humans, SARS-CoV-2 increased total cardiac macrophage counts and led to a higher proportion of CCR2+ (C-C chemokine receptor type 2 positive) macrophages. In mice, SARS-CoV-2 and virus-free lung injury triggered profound remodeling of cardiac resident macrophages, recapitulating the clinical expansion of CCR2+ macrophages. Treating mice exposed to virus-like ARDS with a tumor necrosis factor α-neutralizing antibody reduced cardiac monocytes and inflammatory MHCIIlo CCR2+ macrophages while also preserving cardiac function. Virus-like ARDS elevated mortality in mice with pre-existing heart failure. CONCLUSIONS: Our data suggest that viral ARDS promotes cardiac inflammation by expanding the CCR2+ macrophage subset, and the associated cardiac phenotypes in mice can be elicited by activating the host immune system even without viral presence in the heart.

Ultrasonographic assessment of pulmonary and Central venous congestion in experimental heart failure.

Pulmonary and systemic congestion as a consequence of heart failure are clinically recognized as alarm signals for clinical outcome and mortality. Although signs and symptoms of congestion are well detectable in patients, monitoring of congestion in small animals with heart failure lacks adequate noninvasive methodology yet. Here, we developed a novel ultrasonography-based scoring system to assess pulmonary and systemic congestion in experimental heart failure, by using lung ultrasound (LUS) and imaging of the inferior vena cava (Cava), termed CavaLUS. CavaLUS was established and tested in a rat model of supracoronary aortic banding and a mouse model of myocardial infarction, providing high sensitivity and specificity while correlating to numerous parameters of cardiac performance and disease severity. CavaLUS, therefore, provides a novel comprehensive tool for experimental heart failure in small animals to noninvasively assess congestion.NEW & NOTEWORTHY As thorough, noninvasive assessment of congestion is not available in small animals, we developed and validated an ultrasonography-based research tool to evaluate pulmonary and central venous congestion in experimental heart failure models.

Implications for neutrophils in cardiac arrhythmias.

Cardiac arrhythmias commonly occur as a result of aberrant electrical impulse formation or conduction in the myocardium. Frequently discussed triggers include underlying heart diseases such as myocardial ischemia, electrolyte imbalances, or genetic anomalies of ion channels involved in the tightly regulated cardiac action potential. Recently, the role of innate immune cells in the onset of arrhythmic events has been highlighted in numerous studies, correlating leukocyte expansion in the myocardium to increased arrhythmic burden. Here, we aim to call attention to the role of neutrophils in the pathogenesis of cardiac arrhythmias and their expansion during myocardial ischemia and infectious disease manifestation. In addition, we will elucidate molecular mechanisms associated with neutrophil activation and discuss their involvement as direct mediators of arrhythmogenicity.

Detection and modification of biomarkers of inflammation determining successful rhythm control in patients with atrial fibrillation.

INTRODUCTION: Multiple pathophysiological mechanisms are involved in the pathogenesis of atrial fibrillation (AF). Growing evidence suggests that both local and systemic inflammation plays a key role even in early stages and its progression towards persisting and permanent AF. Rhythm control therapy via pulmonary vein isolation or cardioversion is the cornerstone of AF therapy for most symptomatic patients, yet arrhythmia recurrence after treatment is still common, especially in patients with persistent AF. MATERIAL AND METHODS: In this review, we summarize the current state of knowledge of biomarkers of inflammation with prognostic value in patients with atrial fibrillation as well as anti-inflammatory medication with potential benefits after rhythm control therapy. RESULTS AND DISCUSSION: Both onset of AF, progression and arrhythmia recurrence after rhythm control therapy can be caused by local and systemic inflammation. Various inflammatory biomarkers have been established to predict treatment success. Furthermore, additional anti-inflammatory therapy may significantly improve success rates.

Elastin stabilization prevents impaired biomechanics in human pulmonary arteries and pulmonary hypertension in rats with left heart disease.

Pulmonary hypertension worsens outcome in left heart disease. Stiffening of the pulmonary artery may drive this pathology by increasing right ventricular dysfunction and lung vascular remodeling. Here we show increased stiffness of pulmonary arteries from patients with left heart disease that correlates with impaired pulmonary hemodynamics. Extracellular matrix remodeling in the pulmonary arterial wall, manifested by dysregulated genes implicated in elastin degradation, precedes the onset of pulmonary hypertension. The resulting degradation of elastic fibers is paralleled by an accumulation of fibrillar collagens. Pentagalloyl glucose preserves arterial elastic fibers from elastolysis, reduces inflammation and collagen accumulation, improves pulmonary artery biomechanics, and normalizes right ventricular and pulmonary hemodynamics in a rat model of pulmonary hypertension due to left heart disease. Thus, targeting extracellular matrix remodeling may present a therapeutic approach for pulmonary hypertension due to left heart disease.

Recruited macrophages elicit atrial fibrillation.

Atrial fibrillation disrupts contraction of the atria, leading to stroke and heart failure. We deciphered how immune and stromal cells contribute to atrial fibrillation. Single-cell transcriptomes from human atria documented inflammatory monocyte and SPP1+ macrophage expansion in atrial fibrillation. Combining hypertension, obesity, and mitral valve regurgitation (HOMER) in mice elicited enlarged, fibrosed, and fibrillation-prone atria. Single-cell transcriptomes from HOMER mouse atria recapitulated cell composition and transcriptome changes observed in patients. Inhibiting monocyte migration reduced arrhythmia in Ccr2-∕- HOMER mice. Cell-cell interaction analysis identified SPP1 as a pleiotropic signal that promotes atrial fibrillation through cross-talk with local immune and stromal cells. Deleting Spp1 reduced atrial fibrillation in HOMER mice. These results identify SPP1+ macrophages as targets for immunotherapy in atrial fibrillation.

In-ovo echocardiography for application in cardiovascular research.

Preclinical cardiovascular research relies heavily on non-invasive in-vivo echocardiography in mice and rats to assess cardiac function and morphology, since the complex interaction of heart, circulation, and peripheral organs are challenging to mimic ex-vivo. While n-numbers of annually used laboratory animals worldwide approach 200 million, increasing efforts are made by basic scientists aiming to reduce animal numbers in cardiovascular research according to the 3R's principle. The chicken egg is well-established as a physiological correlate and model for angiogenesis research but has barely been used to assess cardiac (patho-) physiology. Here, we tested whether the established in-ovo system of incubated chicken eggs interfaced with commercially available small animal echocardiography would be a suitable alternative test system in experimental cardiology. To this end, we defined a workflow to assess cardiac function in 8-13-day-old chicken embryos using a commercially available high resolution ultrasound system for small animals (Vevo 3100, Fujifilm Visualsonics Inc.) equipped with a high frequency probe (MX700; centre transmit: 50 MHz). We provide detailed standard operating procedures for sample preparation, image acquisition, data analysis, reference values for left and right ventricular function and dimensions, and inter-observer variabilities. Finally, we challenged incubated chicken eggs with two interventions well-known to affect cardiac physiology-metoprolol treatment and hypoxic exposure-to demonstrate the sensitivity of in-ovo echocardiography. In conclusion, in-ovo echocardiography is a feasible alternative tool for basic cardiovascular research, which can easily be implemented into the small animal research environment using existing infrastructure to replace mice and rat experiments, and thus, reduce use of laboratory animals according to the 3R principle.

GPx3 deficiency exacerbates maladaptive right ventricular remodeling in experimental pulmonary artery banding.

The stressed right ventricle (RV) is particularly susceptible to producing and accumulating reactive oxygen species, leading to extracellular matrix deposition and secretion of natriuretic peptides. The role of specific enzymes with antioxidative capacity, like glutathione peroxidase 3 (GPx3), in RV pathogenesis is currently unknown. Here, we use a murine model of pulmonary artery banding (PAB) to study the role of GPx3 in isolated RV pathology. Compared with wild-type (WT) mice undergoing PAB surgery, GPx3-deficient PAB mice presented with higher RV systolic pressure and higher LV eccentricity indices. PAB-induced changes in Fulton's Index, RV free wall thickness, and RV fractional area change were more pronounced in GPx3-deficient mice compared with WT controls. Adverse RV remodeling was enhanced in GPx3-deficient PAB animals, evidenced by increased RV expression levels of connective tissue growth factor (CTGF), transforming growth factor-ß (TGF-ß), and atrial natriuretic peptide (ANP). In summary, GPx3 deficiency exacerbates maladaptive RV remodeling and causes signs of RV dysfunction.

Bone marrow adipocytes fuel emergency hematopoiesis after myocardial infarction.

After myocardial infarction (MI), emergency hematopoiesis produces inflammatory myeloid cells that accelerate atherosclerosis and promote heart failure. Since the balance between glycolysis and mitochondrial metabolism regulates hematopoietic stem cell homeostasis, metabolic cues may influence emergency myelopoiesis. Here, we show in humans and female mice that hematopoietic progenitor cells increase fatty acid metabolism after MI. Blockade of fatty acid oxidation by deleting carnitine palmitoyltransferase (Cpt1A) in hematopoietic cells of Vav1Cre/+Cpt1Afl/fl mice limited hematopoietic progenitor proliferation and myeloid cell expansion after MI. We also observed reduced bone marrow adiposity in humans, pigs and mice following MI. Inhibiting lipolysis in adipocytes using AdipoqCreERT2Atglfl/fl mice or local depletion of bone marrow adipocytes in AdipoqCreERT2iDTR mice also curbed emergency hematopoiesis. Furthermore, systemic and regional sympathectomy prevented bone marrow adipocyte shrinkage after MI. These data establish a critical role for fatty acid metabolism in post-MI emergency hematopoiesis.

Neutrophils incite and macrophages avert electrical storm after myocardial infarction.

Sudden cardiac death, arising from abnormal electrical conduction, occurs frequently in patients with coronary heart disease. Myocardial ischemia simultaneously induces arrhythmia and massive myocardial leukocyte changes. In this study, we optimized a mouse model in which hypokalemia combined with myocardial infarction triggered spontaneous ventricular tachycardia in ambulatory mice, and we showed that major leukocyte subsets have opposing effects on cardiac conduction. Neutrophils increased ventricular tachycardia via lipocalin-2 in mice, whereas neutrophilia associated with ventricular tachycardia in patients. In contrast, macrophages protected against arrhythmia. Depleting recruited macrophages in Ccr2 -/- mice or all macrophage subsets with Csf1 receptor inhibition increased both ventricular tachycardia and fibrillation. Higher arrhythmia burden and mortality in Cd36 -/- and Mertk -/- mice, viewed together with reduced mitochondrial integrity and accelerated cardiomyocyte death in the absence of macrophages, indicated that receptor-mediated phagocytosis protects against lethal electrical storm. Thus, modulation of leukocyte function provides a potential therapeutic pathway for reducing the risk of sudden cardiac death.

Genetic inhibition of serum glucocorticoid kinase 1 prevents obesity-related atrial fibrillation.

Obesity is an important risk factor for atrial fibrillation (AF), but a better mechanistic understanding of obesity-related atrial fibrillation is required. Serum glucocorticoid kinase 1 (SGK1) is a kinase positioned within multiple obesity-related pathways, and prior work has shown a pathologic role of SGK1 signaling in ventricular arrhythmias. We validated a mouse model of obesity-related AF using wild-type mice fed a high-fat diet. RNA sequencing of atrial tissue demonstrated substantial differences in gene expression, with enrichment of multiple SGK1-related pathways, and we showed upregulated of SGK1 transcription, activation, and signaling in obese atria. Mice expressing a cardiac specific dominant-negative SGK1 were protected from obesity-related AF, through effects on atrial electrophysiology, action potential characteristics, structural remodeling, inflammation, and sodium current. Overall, this study demonstrates the promise of targeting SGK1 in a mouse model of obesity-related AF.

Bone marrow endothelial dysfunction promotes myeloid cell expansion in cardiovascular disease.

Abnormal hematopoiesis advances cardiovascular disease by generating excess inflammatory leukocytes that attack the arteries and the heart. The bone marrow niche regulates hematopoietic stem cell proliferation and hence the systemic leukocyte pool, but whether cardiovascular disease affects the hematopoietic organ's microvasculature is unknown. Here we show that hypertension, atherosclerosis and myocardial infarction (MI) instigate endothelial dysfunction, leakage, vascular fibrosis and angiogenesis in the bone marrow, altogether leading to overproduction of inflammatory myeloid cells and systemic leukocytosis. Limiting angiogenesis with endothelial deletion of Vegfr2 (encoding vascular endothelial growth factor (VEGF) receptor 2) curbed emergency hematopoiesis after MI. We noted that bone marrow endothelial cells assumed inflammatory transcriptional phenotypes in all examined stages of cardiovascular disease. Endothelial deletion of Il6 or Vcan (encoding versican), genes shown to be highly expressed in mice with atherosclerosis or MI, reduced hematopoiesis and systemic myeloid cell numbers in these conditions. Our findings establish that cardiovascular disease remodels the vascular bone marrow niche, stimulating hematopoiesis and production of inflammatory leukocytes.

Cerebrospinal fluid can exit into the skull bone marrow and instruct cranial hematopoiesis in mice with bacterial meningitis.

Interactions between the immune and central nervous systems strongly influence brain health. Although the blood-brain barrier restricts this crosstalk, we now know that meningeal gateways through brain border tissues facilitate intersystem communication. Cerebrospinal fluid (CSF), which interfaces with the glymphatic system and thereby drains the brain's interstitial and perivascular spaces, facilitates outward signaling beyond the blood-brain barrier. In the present study, we report that CSF can exit into the skull bone marrow. Fluorescent tracers injected into the cisterna magna of mice migrate along perivascular spaces of dural blood vessels and then travel through hundreds of sub-millimeter skull channels into the calvarial marrow. During meningitis, bacteria hijack this route to invade the skull's hematopoietic niches and initiate cranial hematopoiesis ahead of remote tibial sites. As skull channels also directly provide leukocytes to meninges, the privileged sampling of brain-derived danger signals in CSF by regional marrow may have broad implications for inflammatory neurological disorders.

Dysregulated Immunity in Pulmonary Hypertension: From Companion to Composer.

Pulmonary hypertension (PH) represents a grave condition associated with high morbidity and mortality, emphasizing a desperate need for innovative and targeted therapeutic strategies. Cumulative evidence suggests that inflammation and dysregulated immunity interdependently affect maladaptive organ perfusion and congestion as hemodynamic hallmarks of the pathophysiology of PH. The role of altered cellular and humoral immunity in PH gains increasing attention, especially in pulmonary arterial hypertension (PAH), revealing novel mechanistic insights into the underlying immunopathology. Whether these immunophysiological aspects display a universal character and also hold true for other types of PH (e.g., PH associated with left heart disease, PH-LHD), or whether there are unique immunological signatures depending on the underlying cause of disease are points of consideration and discussion. Inflammatory mediators and cellular immune circuits connect the local inflammatory landscape in the lung and heart through inter-organ communication, involving, e.g., the complement system, sphingosine-1-phosphate (S1P), cytokines and subsets of, e.g., monocytes, macrophages, natural killer (NK) cells, dendritic cells (DCs), and T- and B-lymphocytes with distinct and organ-specific pro- and anti-inflammatory functions in homeostasis and disease. Perivascular macrophage expansion and monocyte recruitment have been proposed as key pathogenic drivers of vascular remodeling, the principal pathological mechanism in PAH, pinpointing toward future directions of anti-inflammatory therapeutic strategies. Moreover, different B- and T-effector cells as well as DCs may play an important role in the pathophysiology of PH as an imbalance of T-helper-17-cells (TH17) activated by monocyte-derived DCs, a potentially protective role of regulatory T-cells (Treg) and autoantibody-producing plasma cells occur in diverse PH animal models and human PH. This article highlights novel aspects of the innate and adaptive immunity and their interaction as disease mediators of PH and its specific subtypes, noticeable inflammatory mediators and summarizes therapeutic targets and strategies arising thereby.

Pharmacological inhibition of adipose tissue adipose triglyceride lipase by Atglistatin prevents catecholamine-induced myocardial damage.

AIMS: Heart failure (HF) is characterized by an overactivation of ß-adrenergic signalling that directly contributes to impairment of myocardial function. Moreover, ß-adrenergic overactivation induces adipose tissue lipolysis, which may further worsen the development of HF. Recently, we demonstrated that adipose tissue-specific deletion of adipose triglyceride lipase (ATGL) prevents pressure-mediated HF in mice. In this study, we investigated the cardioprotective effects of a new pharmacological inhibitor of ATGL, Atglistatin, predominantly targeting ATGL in adipose tissue, on catecholamine-induced cardiac damage. METHODS AND RESULTS: Male 129/Sv mice received repeated injections of isoproterenol (ISO, 25 mg/kg BW) to induce cardiac damage. Five days prior to ISO application, oral Atglistatin (2 mmol/kg diet) or control treatment was started. Two and twelve days after the last ISO injection cardiac function was analysed by echocardiography. The myocardial deformation was evaluated using speckle-tracking-technique. Twelve days after the last ISO injection, echocardiographic analysis revealed a markedly impaired global longitudinal strain, which was significantly improved by the application of Atglistatin. No changes in ejection fraction were observed. Further studies included histological-, WB-, and RT-qPCR-based analysis of cardiac tissue, followed by cell culture experiments and mass spectrometry-based lipidome analysis. ISO application induced subendocardial fibrosis and a profound pro-apoptotic cardiac response, as demonstrated using an apoptosis-specific gene expression-array. Atglistatin treatment led to a dramatic reduction of these pro-fibrotic and pro-apoptotic processes. We then identified a specific set of fatty acids (FAs) liberated from adipocytes under ISO stimulation (palmitic acid, palmitoleic acid, and oleic acid), which induced pro-apoptotic effects in cardiomyocytes. Atglistatin significantly blocked this adipocytic FA secretion. CONCLUSION: This study demonstrates cardioprotective effects of Atglistatin in a mouse model of catecholamine-induced cardiac damage/dysfunction, involving anti-apoptotic and anti-fibrotic actions. Notably, beneficial cardioprotective effects of Atglistatin are likely mediated by non-cardiac actions, supporting the concept that pharmacological targeting of adipose tissue may provide an effective way to treat cardiac dysfunction.

Pannexin 1: a novel regulator of acute hypoxic pulmonary vasoconstriction.

AIMS: Hypoxic pulmonary vasoconstriction (HPV) is a physiological response to alveolar hypoxia that diverts blood flow from poorly ventilated to better aerated lung areas to optimize ventilation-perfusion matching. Yet, the exact sensory and signalling mechanisms by which hypoxia triggers pulmonary vasoconstriction remain incompletely understood. Recently, ATP release via pannexin 1 (Panx1) and subsequent signalling via purinergic P2Y receptors has been identified as regulator of vasoconstriction in systemic arterioles. Here, we probed for the role of Panx1-mediated ATP release in HPV and chronic hypoxic pulmonary hypertension (PH). METHODS AND RESULTS: Pharmacological inhibition of Panx1 by probenecid, spironolactone, the Panx1 specific inhibitory peptide (10Panx1), and genetic deletion of Panx1 specifically in smooth muscle attenuated HPV in isolated perfused mouse lungs. In pulmonary artery smooth muscle cells (PASMCs), both spironolactone and 10Panx1 attenuated the increase in intracellular Ca2+ concentration ([Ca2+]i) in response to hypoxia. Yet, genetic deletion of Panx1 in either endothelial or smooth muscle cells did not prevent the development of PH in mice. Unexpectedly, ATP release in response to hypoxia was not detectable in PASMC, and inhibition of purinergic receptors or ATP degradation by ATPase failed to attenuate HPV. Rather, transient receptor potential vanilloid 4 (TRPV4) antagonism and Panx1 inhibition inhibited the hypoxia-induced [Ca2+]i increase in PASMC in an additive manner, suggesting that Panx1 regulates [Ca2+]i independently of the ATP-P2Y-TRPV4 pathway. In line with this notion, Panx1 overexpression increased the [Ca2+]i response to hypoxia in HeLa cells. CONCLUSION: In the present study, we identify Panx1 as novel regulator of HPV. Yet, the role of Panx1 in HPV was not attributable to ATP release and downstream signalling via P2Y receptors or TRPV4 activation, but relates to a role of Panx1 as direct or indirect modulator of the PASMC Ca2+ response to hypoxia. Panx1 did not affect the development of chronic hypoxic PH.

Deficiency of inactive rhomboid protein 2 (iRhom2) attenuates diet-induced hyperlipidaemia and early atherogenesis.

AIMS: Atherosclerosis is a chronic inflammatory disease of the arterial vessel wall and anti-inflammatory treatment strategies are currently pursued to lower cardiovascular disease burden. Modulation of recently discovered inactive rhomboid protein 2 (iRhom2) attenuates shedding of tumour necrosis factor-alpha (TNF-α) selectively from immune cells. The present study aims at investigating the impact of iRhom2 deficiency on the development of atherosclerosis. METHODS AND RESULTS: Low-density lipoprotein receptor (LDLR)-deficient mice with additional deficiency of iRhom2 (LDLR-/-iRhom2-/-) and control (LDLR-/-) mice were fed a Western-type diet (WD) for 8 or 20 weeks to induce early or advanced atherosclerosis. Deficiency of iRhom2 resulted in a significant decrease in the size of early atherosclerotic plaques as determined in aortic root cross-sections. LDLR-/-iRhom2-/- mice exhibited significantly lower serum levels of TNF-α and lower circulating and hepatic levels of cholesterol and triglycerides compared to LDLR-/- mice at 8 weeks of WD. Analyses of hepatic bile acid concentration and gene expression at 8 weeks of WD revealed that iRhom2 deficiency prevented WD-induced repression of hepatic bile acid synthesis in LDLR-/- mice. In contrast, at 20 weeks of WD, plaque size, plaque composition, and serum levels of TNF-α or cholesterol were not different between genotypes. CONCLUSION: Modulation of inflammation by iRhom2 deficiency attenuated diet-induced hyperlipidaemia and early atherogenesis in LDLR-/- mice. iRhom2 deficiency did not affect diet-induced plaque burden and composition in advanced atherosclerosis in LDLR-/- mice.