The coronavirus disease 2019 caused by SARS-CoV-2 infections imposes a major threat for the world's healthcare systems and is leading to thousands of deaths. Angiotensin-converting enzyme 2 (ACE2) has been identified as a potential receptor for SARS coronavirus 1 and is also considered the main receptor for SARS-CoV-2. 2 SARS-CoV-2 binds to ACE2 via its glycosylated outer membrane spike proteins. ACE2 is highly expressed in the lung and heart, and is known for its vital role in the cardiovascular system. 3-5 Although SARS-CoV-2 mainly invades alveolar epithelial cells, it can also cause myocardial injury, as assessed by increased troponin T and NT-proBNP levels accompanying increased cardiovascular symptoms in COVID-19-infected patients. 6,7 It is unclear whether elevated biomarkers of cardiac injury (or long-term effects on the cardiovascular system) are directly caused by viral infection of cardiac tissue or are secondary to hypoxia and systemic inflammation. However, patients with underlying cardiovascular disease represent a significant proportion of the patients who may suffer from a severe course after COVID-19 infection. 8 This situation may be aggravated by findings showing that ACE inhibitors, which are often used to treat cardiovascular diseases, augment the expression of the SARS-CoV-2 receptor ACE2 in lung cells. 9 This is probably mediated by an effect on angiotensin II, which is known to reduce ACE2 expression. 9 Thus, ACE inhibition decreases angiotensin II, leading to an indirect up-regulation of ACE2. 9 The effect of angiotensin II receptor blockers (ARBs), which primarily target the angiotensin receptor 1, is unclear. One may speculate that ARBs indirectly reduce ACE2 levels by augmenting free angiotensin II levels, which in turn is expected to downregulate ACE2 via activating the angiotensin receptor 2. However, the effect of the two different treatments on the expression of ACE2 in the heart requires further investigation.Therefore, we used single nuclei RNA sequencing to determine the expression of ACE and ACE2 in the different cell types of the human heart. Gene expression signatures were detected in cardiac tissues of five patients with aortic stenosis (AS) and two patients with heart failure with reduced ejection fraction (HFrEF) ( Figure 1A) and compared with with samples of one healthy donor heart (age: 63 years, male) that was not used for transplantation. After single nuclei RNA sequencing, data were pooled, and unsupervised clustering was performed with a total of 57 601 nuclei. We found 18 distinct clusters. Using cell type-specific gene markers, major cell types were annotated, including cardiomyocytes (six clusters), fibroblasts (one cluster), endothelial cells (three clusters), leucocytes (two clusters), pericytes (one cluster), and smooth muscle cells (one cluster) ( Figure 1B-D). ACE2 was expressed in cardiomyocytes (Cluster 0 and 1) and mural cells, particularly pericytes (Cluster 4), and was detected at a lower expression level in fibroblasts, endothelial cell, and leucocytes...

Pathological cardiac hypertrophy is a leading cause of heart failure, but knowledge of the full repertoire of cardiac cells and their gene expression profiles in the human hypertrophic heart is missing. Here, by using large-scale single-nucleus transcriptomics, we present the transcriptional response of human cardiomyocytes to pressure overload caused by aortic valve stenosis and describe major alterations in cardiac cellular crosstalk. Hypertrophied cardiomyocytes had reduced input from endothelial cells and fibroblasts. Genes encoding Eph receptor tyrosine kinases, particularly EPHB1, were significantly downregulated in cardiomyocytes of the hypertrophied heart. Consequently, EPHB1 activation by its ligand ephrin (EFN)B2, which is mainly expressed by endothelial cells, was reduced. EFNB2 inhibited cardiomyocyte hypertrophy in vitro, while silencing its expression in endothelial cells induced hypertrophy in co-cultured cardiomyocytes. Our human cell atlas of the hypertrophied heart highlights the importance of intercellular crosstalk in disease pathogenesis and provides a valuable resource.

Coronavirus disease 2019 (COVID-19) spawned a global health crisis in late 2019 and is caused by the novel coronavirus SARS-CoV-2. SARS-CoV-2 infection can lead to elevated markers of endothelial dysfunction associated with higher risk of mortality. It is unclear whether endothelial dysfunction is caused by direct infection of endothelial cells or is mainly secondary to inflammation. Here, we investigate whether different types of endothelial cells are susceptible to SARS-CoV-2. Human endothelial cells from different vascular beds including umbilical vein endothelial cells, coronary artery endothelial cells (HCAEC), cardiac and lung microvascular endothelial cells, or pulmonary arterial cells were inoculated in vitro with SARS-CoV-2. Viral spike protein was only detected in HCAECs after SARS-CoV-2 infection but not in the other endothelial cells tested. Consistently, only HCAEC expressed the SARS-CoV-2 receptor angiotensin-converting enzyme 2 (ACE2), required for virus infection. Infection with the SARS-CoV-2 variants B.1.1.7, B.1.351, and P.2 resulted in significantly higher levels of viral spike protein. Despite this, no intracellular double-stranded viral RNA was detected and the supernatant did not contain infectious virus. Analysis of the cellular distribution of the spike protein revealed that it co-localized with endosomal calnexin. SARS-CoV-2 infection did induce the ER stress gene EDEM1, which is responsible for clearance of misfolded proteins from the ER. Whereas the wild type of SARS-CoV-2 did not induce cytotoxic or pro-inflammatory effects, the variant B.1.1.7 reduced the HCAEC cell number. Of the different tested endothelial cells, HCAECs showed highest viral uptake but did not promote virus replication. Effects on cell number were only observed after infection with the variant B.1.1.7, suggesting that endothelial protection may be particularly important in patients infected with this variant.

Background: Dilated cardiomyopathy (DCM) is a leading cause of death in children with heart failure. The outcome of pediatric heart failure treatment is inconsistent and large cohort studies are lacking. Progress may be achieved through personalized therapy that takes age- and disease-related pathophysiology, pathology and molecular fingerprints into account. We present snRNA-seq from pediatric DCM patients as the next step in identifying cellular signatures. Methods: We performed single nuclei RNA sequencing with heart tissues from six children with DCM with an age of 0.5, 0.75, 5, 6, 12 and 13 years. Unsupervised clustering of 18,211 nuclei led to the identification of 14 distinct clusters with 6 major cell types. Results: The number of nuclei in fibroblast clusters increased with age in DCM patients, a finding that was confirmed by histological analysis and was consistent with an age-related increase in cardiac fibrosis quantified by cardiac magnetic resonance imaging. Fibroblasts of DCM patients over 6 years of age showed a profoundly altered gene expression pattern with enrichment of genes encoding fibrillary collagens, modulation of proteoglycans, switch in thrombospondin isoforms and signatures of fibroblast activation. Additionally, a population of cardiomyocytes with a high pro-regenerative profile was identified in infant DCM patients, but was absent in > 6-year-old children. This cluster showed high expression of cell cycle activators such as cyclin D family members, increased glycolytic metabolism and antioxidative genes and alterations in ß-adrenergic signaling genes. Conclusions: Novel insights into the cellular transcriptomes of hearts from pediatric DCM patients provide remarkable age-dependent changes in the expression patterns of fibroblast and cardiomyocyte genes with less fibrotic but enriched pro-regenerative signatures in infants.