Cells of the adult human heart.

Cardiovascular disease is the leading cause of death worldwide. Advanced insights into disease mechanisms and therapeutic strategies require a deeper understanding of the molecular processes involved in the healthy heart. Knowledge of the full repertoire of cardiac cells and their gene expression profiles is a fundamental first step in this endeavour. Here, using state-of-the-art analyses of large-scale single-cell and single-nucleus transcriptomes, we characterize six anatomical adult heart regions. Our results highlight the cellular heterogeneity of cardiomyocytes, pericytes and fibroblasts, and reveal distinct atrial and ventricular subsets of cells with diverse developmental origins and specialized properties. We define the complexity of the cardiac vasculature and its changes along the arterio-venous axis. In the immune compartment, we identify cardiac-resident macrophages with inflammatory and protective transcriptional signatures. Furthermore, analyses of cell-to-cell interactions highlight different networks of macrophages, fibroblasts and cardiomyocytes between atria and ventricles that are distinct from those of skeletal muscle. Our human cardiac cell atlas improves our understanding of the human heart and provides a valuable reference for future studies.

Ablation of lysophosphatidic acid receptor 1 attenuates hypertrophic cardiomyopathy in a mouse model.

Myocardial fibrosis is a key pathologic feature of hypertrophic cardiomyopathy (HCM). However, the fibrotic pathways activated by HCM-causing sarcomere protein gene mutations are poorly defined. Because lysophosphatidic acid is a mediator of fibrosis in multiple organs and diseases, we tested the role of the lysophosphatidic acid pathway in HCM. Lysphosphatidic acid receptor 1 (LPAR1), a cell surface receptor, is required for lysophosphatidic acid mediation of fibrosis. We bred HCM mice carrying a pathogenic myosin heavy-chain variant (403+/-) with Lpar1-ablated mice to create mice carrying both genetic changes (403+/- LPAR1 -/-) and assessed development of cardiac hypertrophy and fibrosis. Compared with 403+/- LPAR1WT, 403+/- LPAR1 -/- mice developed significantly less hypertrophy and fibrosis. Single-nucleus RNA sequencing of left ventricular tissue demonstrated that Lpar1 was predominantly expressed by lymphatic endothelial cells (LECs) and cardiac fibroblasts. Lpar1 ablation reduced the population of LECs, confirmed by immunofluorescence staining of the LEC markers Lyve1 and Ccl21a and, by in situ hybridization, for Reln and Ccl21a. Lpar1 ablation also altered the distribution of fibroblast cell states. FB1 and FB2 fibroblasts decreased while FB0 and FB3 fibroblasts increased. Our findings indicate that Lpar1 is expressed predominantly by LECs and fibroblasts in the heart and is required for development of hypertrophy and fibrosis in an HCM mouse model. LPAR1 antagonism, including agents in clinical trials for other fibrotic diseases, may be beneficial for HCM.

Pathogenesis of Cardiomyopathy Caused by Variants in ALPK3, an Essential Pseudokinase in the Cardiomyocyte Nucleus and Sarcomere.

BACKGROUND: ALPK3 encodes α-kinase 3, a muscle-specific protein of unknown function. ALPK3 loss-of-function variants cause cardiomyopathy with distinctive clinical manifestations in both children and adults, but the molecular functions of ALPK3 remain poorly understood. METHODS: We explored the putative kinase activity of ALPK3 and the consequences of damaging variants using isogenic human induced pluripotent stem cell-derived cardiomyocytes, mice, and human patient tissues. RESULTS: Multiple sequence alignment of all human α-kinase domains and their orthologs revealed 4 conserved residues that were variant only in ALPK3, demonstrating evolutionary divergence of the ALPK3 α-kinase domain sequence. Phosphoproteomic evaluation of both ALPK3 kinase domain inhibition and overexpression failed to detect significant changes in catalytic activity, establishing ALPK3 as a pseudokinase. Investigations into alternative functions revealed that ALPK3 colocalized with myomesin proteins (MYOM1, MYOM2) at both the nuclear envelope and the sarcomere M-band. ALPK3 loss-of-function variants caused myomesin proteins to mislocalize and also dysregulated several additional M-band proteins involved in sarcomere protein turnover, which ultimately impaired cardiomyocyte structure and function. CONCLUSIONS: ALPK3 is an essential cardiac pseudokinase that inserts in the nuclear envelope and the sarcomere M-band. Loss of ALPK3 causes mislocalization of myomesins, critical force-buffering proteins in cardiomyocytes, and also dysregulates M-band proteins necessary for sarcomere protein turnover. We conclude that ALPK3 cardiomyopathy induces ventricular dilatation caused by insufficient myomesin-mediated force buffering and hypertrophy by impairment of sarcomere proteostasis.

Hospital Volume and Outcome after Bilateral Internal Mammary Artery Grafting.

BACKGROUND: Bilateral internal mammary artery (BIMA) grafting largely is underutilized in patients undergoing coronary artery bypass grafting (CABG), partly because of the perceived increased complexity of the procedure. AIMS: In this study, we evaluated whether BIMA grafting can safely be performed also in centers, where this revascularization strategy infrequently is adopted. METHODS: Out of 6,783 patients from the prospective multicenter E-CABG study, who underwent isolated non- emergent CABG from January 2015 to December 2016, 2,457 underwent BIMA grafting and their outcome was evaluated in this analysis. RESULTS: The mean number of BIMA grafting per center was 82 cases/year and hospitals were defined as high or low volume, according to this cutoff value. Six hospitals were considered as centers with a high volume of BIMA grafting (no. of procedures ranging from 120 to 267/year; overall: 2,156; prevalence: 62.2%) and nine hospitals as centers with a low volume of BIMA grafting (no. of procedures ranging from 2 to 39/year; overall: 301; prevalence: 9.1%). Multilevel mixed-effects regression analysis showed that the low- and high-volume cohorts had similar outcomes. Propensity score one-to-one matching analysis of 292 pairs showed that the low-volume cohort had a significantly shorter intensive care unit stay (2.2 ± 2.3 versus 2.9 ± 4.8 days, P = .020). The rates of in-hospital death (1.0% versus 0.3%, P = .625), deep sternal wound infection/mediastinitis (3.8% versus 3.1%, P = .824), and 1-year survival (98.1% versus 99.7%, P = .180) as well as other outcomes were similar between the high- and low-volume cohorts. CONCLUSIONS: BIMA grafting can be safely performed also in centers in which this revascularization strategy is infrequently performed.

Impact of preoperative thrombocytopenia on the outcome after coronary artery bypass grafting.

The impact of thrombocytopenia on postoperative bleeding and other major adverse events after cardiac surgery is unclear. This issue was investigated in a series of patients who underwent isolated coronary artery bypass grafting (CABG) from the prospective, multicenter E-CABG registry. Preoperative thrombocytopenia was defined as preoperative platelet count <150 × 109/L and it was considered moderate-severe when preoperative platelet count was <100 × 109/L. Multilevel mixed-effects regression analysis was performed to adjust the effect of thrombocytopenia on outcomes for baseline and operative covariates as well as for interinstitutional differences in patient-blood management. Among 7189 patients included in this analysis, 599 (8.3%) had preoperative thrombocytopenia. Patient with preoperative thrombocytopenia had an increased chest drainage output at 12 h (mean, 519 vs. 456 mL, adjusted coeff. 39, 95%CI 18-60) and rates of severe-massive bleeding (Universal Definition of Perioperative Bleeding (UDPB) severity grades 3-4: 12.7% vs. 8.1%, adjusted OR 1.47, 95%CI 1.11-1.93; E-CABG bleeding severity grades 2-3: 10.4% vs. 6.1%, adjusted OR 1.78, 95%CI 1.30-2.43). Thrombocytopenia was associated with an increased risk of hospital/30-day death (3.2% vs. 1.9%, adjusted OR 2.02, 95%CI 1.20-3.42), 1-year death (5.7% vs. 3.4%, adjusted HR 1.68, 95%CI 1.16-2.44), deep sternal wound infection (3.5% vs. 2.4%, adjusted OR 1.65, 95%CI 1.02-2.66), acute kidney injury (28.1% vs. 22.2%, OR 1.45, 1.18-1.78), and prolonged stay in the intensive care unit (mean, 3.6 vs 2.8 days, adjusted coeff. 0.74, 95%CI 0.40-1.09). Similar results were observed in a subset of patients with moderate-severe thrombocytopenia (51 patients, 0.7%). In particular, these patients had a markedly higher rate of acute kidney injury (40%, adjusted OR, 1.94, 95%CI 1.05-3.57), resternotomy for bleeding (7.8%, adjusted OR 3.49, 95%CI 1.20-10.21), and severe-massive bleeding (UDPB severity grades 3-4: 23.5%, adjusted OR 3.08, 95%CI 1.52-6.22; E-CABG bleeding severity grades 2-3: 23.5%, adjusted OR 4.43, 95%CI 2.15-9.15) compared to patients with normal preoperative platelet count. Mild preoperative thrombocytopenia is associated with increased risk of severe-massive bleeding, mortality, and other major adverse events after CABG. Such risks are markedly increased in patients with moderate-severe preoperative thrombocytopenia.

Renal protection strategies after heart transplantation.

Renal dysfunction caused by calcineurin inhibitor (CNI) nephrotoxicity occurs often and contributes significantly to late mortality after heart transplantation (HTx). Over the last decades, this has prompted many clinical studies in an effort to develop kidney-protecting immunosuppressive strategies including delayed CNI start, minimization, withdrawal, or even de novo CNI avoidance. In the past, these strategies often failed due to the lack of efficacy. Since 2009, novel CNI-reducing strategies have been under investigation. These strategies minimize renal damage using induction agents such as antithymocyte globulin and alternative immunosuppressive agents such as the mechanistic target of rapamycin inhibitors (sirolimus or everolimus) or mycophenolate. This review outlines the recent results of using these renal protection strategies including their drawbacks. We also discuss alternative approaches to optimize individual immunosuppressive therapies after HTx.

Prognostic Impact of Asymptomatic Carotid Artery Stenosis in Patients Undergoing Coronary Artery Bypass Grafting.

OBJECTIVES: The aim of this study was to evaluate the prognostic impact of untreated asymptomatic carotid artery stenosis (CS) in patients undergoing isolated coronary artery bypass grafting (CABG). METHODS: This was a post hoc analysis of data from a prospective multicentre observational study. Patients without history of stroke or transient ischaemic attack from the multicentre E-CABG registry who were screened for CS before isolated CABG were included. RESULTS: Among 2813 patients screened by duplex ultrasound and who did not undergo carotid intervention for asymptomatic CS, 11.1% had a stenosis of 50-59%, 6.0% of 60-69%, 3.1% of 70-79%, 1.4% of 80-89%, 0.5% of 90-99%, and 1.1% had carotid occlusion. In the screened population post-operative stroke occurred in 25 patients (0.9%), with an incidence of 1.5% among patients with CS ≥ 50% (n = 649). Pre-operative screening had not found a relevant CS in 15 of 25 patients suffering stroke after CABG. Brain imaging identified cerebral ischaemic injury in 20 patients, which was bilateral in five patients (25%), ipsilateral to a CS ≥ 50% in six (30%), and ipsilateral to a CS ≥ 70% in three (15%). In univariable analysis, the severity of CS was associated with a significantly increased risk of stroke (CS < 50%, 0.7%; 50-59%, 1.0%; 60-69%, 0.6%; 70-79%, 1.2%; 80-89%, 5.1%; 90-99%, 7.7%; occluded, 6.7%, p < .001). In multivariable analysis, a CS of 90-99% (OR 12.03, 95% CI 1.34-108.23) and the presence of an occluded internal carotid artery (OR 8.783, 95% CI 1.820-42.40) were independent predictors of stroke along with urgency of the procedure, severe massive bleeding according to the E-CABG classification, and the presence of a porcelain ascending aorta. CONCLUSIONS: Among screened patients with untreated asymptomatic patients, CS ≥ 90% was an independent predictor of post-operative stroke. As this condition has a low prevalence and when left untreated is associated with a relatively low rate of stroke, pre-operative screening of asymptomatic CS before CABG may not be justified. CLINICAL TRIAL REGISTRATION: https://clinicaltrials.gov. Unique identifier: NCT02319083.

Hospital Outcome and Risk Indices of Mortality after redo-mitral valve surgery in Potential Candidates for Transcatheter Procedures: Results From a European Registry.

OBJECTIVE: Transcatheter mitral valve-in-valve/valve-in-ring procedures (TM-VIVoR) are increasing. The authors aimed to identify independent predictors for hospital mortality in redo mitral valve surgery as possible future selection criteria for TM-VIVoR. DESIGN: Retrospective multicenter registry. SETTING: Tertiary university and community hospitals. PARTICIPANTS: Two-hundred and sixty patients (out of 920 enrolled) who are potentially candidates for TM-VIVoR undergoing redo-surgery. INTERVENTIONS: Redo mitral surgery. MEASUREMENTS AND MAIN RESULTS: Regression analyzes and receiver operating characteristic (ROC) curves identified independent predictors of death. Patients potentially candidates for TM-VIVoR reported significant hospital mortality (9.2%; EuroSCORE II: 13.2 ± 13.1, Society of Thoracic Surgeons [STS] score: 6.2 ± 3.1) and major morbidity (3.8% acute myocardial infarction, 5% stroke, 16.9% perioperative respiratory failure, 16.5% acute renal insufficiency, 25% massive transfusions). EuroSCORE II (odds ration [OR] 1.06; confidence interval [CI] 1.01-1.10; p = 0.005), STS score (OR 1.58; CI 1.27-1.97; p = 0.001), age at surgery (OR 1.05; CI 1.00-1.15; p = 0.05), preoperative dialysis (OR 2.5; CI 1.8-12.6; p = 0.042), left ventricular ejection fraction (LVEF) <30% (OR 4.8; CI 1.12-37.1; p = 0.021), severe pulmonary hypertension (OR 7.5; CI 1.9-29.4; p = 0.003), and previous coronary artery bypass grafting (CABG) (OR 11.8; CI 1.7-36.9; p = 0.002) were independent predictors of hospital mortality. ROC analyses reported good prediction for EuroSCORE II (AUC: 0.76; cut-off value: >13.1; 70.8% sensitivity and 68.2% specificity) and better prediction for STS score (AUC: 0.81; cut-off value: 7.4; 75.0% sensitivity and 66.2% specificity). Quintiles stratification identified EuroSCORE II ≥18.7 (5th quintile, observed mortality: 19.3%) and STS score >9.1 as strong predictors of death within each risk-categorization (OR 5.9 and 12.1, respectively). CONCLUSIONS: High EuroSCORE II and STS scores, advanced age at surgery, LVEF <30%, previous CABG, severe pulmonary hypertension or preoperative dialysis might represent in the future preferred indications for TM-VIVoR in the redo-mitral surgery scenario.

Meta-Analysis of the Outcome After Postcardiotomy Venoarterial Extracorporeal Membrane Oxygenation in Adult Patients.

OBJECTIVE: This study was planned to pool existing data on outcome and to evaluate the efficacy of postcardiotomy venoarterial extracorporeal membrane oxygenation (VA-ECMO) in adult patients. DESIGN: Systematic review of the literature and meta-analysis. SETTING: Multi-institutional study. PARTICIPANTS: Adult patients with acute heart failure immediately after cardiac surgery. INTERVENTIONS: VA-ECMO after cardiac surgery. Studies evaluating only heart transplant patients were excluded from this analysis. MEASUREMENTS AND MAIN RESULTS: A literature search was performed to identify studies published since 2000. Thirty-one studies reported on 2,986 patients (mean age, 58.1 years) who required postcardiotomy VA-ECMO. The weaning rate from VA-ECMO was 59.5% and hospital survival was 36.1% (95% CI 31.5-40.8). The pooled rate of reoperation for bleeding was 42.9%, major neurological event 11.3%, lower limb ischemia 10.8%, deep sternal wound infection/mediastinitis 14.7%, and renal replacement therapy 47.1%. The pooled mean number of transfused red blood cell units was 17.7 (95% CI 13.3-22.1). The mean stay in the intensive care unit was 13.3 days (95% CI 10.2-16.4). Survivors were significantly younger (mean, 55.7 v 63.6 years, p = 0.015) and their blood lactate level before starting VA-ECMO was lower (mean, 7.7 v 10.7 mmol/L, p = 0.028) than patients who died. One-year survival rate was 30.9% (95% CI 24.3-37.5). CONCLUSIONS: Pooled data showed that VA-ECMO may salvage one-third of patients unresponsive to any other resuscitative treatment after adult cardiac surgery.

Prognostic Impact of Prolonged Cross-Clamp Time in Coronary Artery Bypass Grafting.

BACKGROUND: The prognostic impact of cross-clamp time (XCT) in patients undergoing isolated coronary artery bypass grafting (CABG) has not been thoroughly investigated. MATERIAL AND METHODS: 2957 patients who underwent on-pump isolated CABG from the prospective multicentre E-CABG study were the subjects of this analysis. RESULTS: The mean XCT in this series was 58±25minutes Cross-clamp time was >60 minutes in 1134 patients (38.3%), >75minutes in 619 patients (20.9%) and >90minutes in 296 patients (10.0%). Multivariate analysis showed that XCT was an independent predictor of 30-day mortality (p<0.0001, OR 1.027, 95%CI 1.015-1.039) along with age (p<0.0001), female gender (p=0.001), pulmonary disease (p=0.001), poor mobility (p=0.002), urgency status (p=0.007), critical preoperative status (p=0.002) and participating centres (p=0.015). Adjusted risk of 30-day mortality was highest for XCT >75minutes (2.9% vs. 1.7%, p=0.002, OR 3.479, 95%CI 1.609-7.520). Analysis of 428 propensity score matched pairs showed that XCT >75minutes was associated with significantly increased risk of early mortality, prolonged use of inotropes, postoperative use of intra-aortic balloon pump, use of extracorporeal membrane oxygenation, atrial fibrillation, prolonged stay in the intensive care unit and of composite major adverse events. CONCLUSIONS: Isolated CABG is currently performed with prolonged XCT in a significant number of patients and this seems to be a determinant of poor early outcome.

Incidence and prognostic impact of bleeding and transfusion after coronary surgery in low-risk patients.

BACKGROUND: Excessive bleeding and blood transfusion are associated with adverse outcome after cardiac surgery, but their mechanistic effects are difficult to disentangle in patients with increased operative risk. This study aimed to evaluate the incidence and prognostic impact of bleeding and transfusion of blood products in low-risk patients undergoing coronary artery bypass grafting (CABG). STUDY DESIGN AND METHODS: Sixteen tertiary European centers of cardiac surgery contributed to the prospective European registry of CABG (E-CABG). The severity of bleeding was defined by the E-CABG bleeding severity classification and universal definition of perioperative bleeding (UDPB) classification. RESULTS: Of 1213 patients with EuroSCORE II of less than 2% (mean, 1.1 ± 0.4%), 18.5% suffered from mild bleeding (E-CABG bleeding Grade 1) and 3.4% experienced severe bleeding (E-CABG bleeding Grade 2-3). Similarly, 19.7% had UDPB Class 2 and 5.9% had UDPB Classes 3 and 4. Mild and severe bleeding defined by the E-CABG and UDPB classifications were associated with an increased risk of several adverse events as adjusted by multiple covariates. The risk of death, stroke, and acute kidney injury was particularly increased in patients with severe bleeding. CONCLUSION: Severe bleeding is rather uncommon in low-risk patients undergoing CABG, but it is associated with an increased risk of major adverse events. Prevention of excessive perioperative bleeding and patient blood management may improve the outcome of cardiac surgery also in low-risk patients.

Glycated Hemoglobin and Risk of Sternal Wound Infection After Isolated Coronary Surgery.

BACKGROUND: Glycated hemoglobin (HbA1c) is a suspected risk factor for sternal wound infection (SWI) after CABG.Methods and Results:Data on preoperative HbA1c and SWI were available in 2,130 patients undergoing isolated CABG from the prospective E-CABG registry. SWI occurred in 114 (5.4%). Baseline HbA1c was significantly higher in patients with SWI (mean, 54±17 vs. 45±13 mmol/mol, P<0.0001). This difference was also observed in patients without a diagnosis of diabetes (P=0.027), in insulin-dependent diabetic (P=0.023) and non-insulin-dependent diabetic patients (P=0.034). In the overall series, HbA1c >70 mmol/mol (NGSP units, 8.6%) was associated with the highest risk of SWI (20.6% vs. 4.6%; adjusted OR, 5.01; 95% CI: 2.47-10.15). When dichotomized according to the cut-off 53 mmol/mol (NGSP units, 7.0%) as suggested both for diagnosis and optimal glycemic control of diabetes, HbA1c was associated with increased risk of SWI in the overall series (10.6% vs. 3.9%; adjusted OR, 2.09; 95% CI: 1.24-3.52), in diabetic patients (11.7% vs. 5.1%; adjusted OR, 2.69; 95% CI: 1.38-5.25), in patients undergoing elective surgery (9.9% vs. 2.7%; adjusted OR, 2.09; 95% CI: 1.24-3.52) and in patients with bilateral mammary artery grafts (13.7% vs. 4.8%; adjusted OR, 2.35; 95% CI: 1.17-4.69). CONCLUSIONS: Screening for HbA1c before CABG may identify untreated diabetic patients, as well as diabetic patients with suboptimal glycemic control, at high risk of SWI.

Multimodal characterization of dilated cardiomyopathy: Geno- And Phenotyping of PrImary Cardiomyopathy (GrAPHIC).

AIMS: Cardiomyopathies (CMPs) are a heterogeneous group of diseases that are defined by structural and functional abnormalities of the cardiac muscle. Dilated cardiomyopathy (DCM), the most common CMP, is defined by left ventricular dilation and impaired contractility and represents a common cause of heart failure. Different phenotypes result from various underlying genetic and acquired causes with variable effects on disease development and progression, prognosis, and response to medical treatment. Current treatment algorithms do not consider these different aetiologies, due to lack of insights into treatable drivers of cardiac failure in patients with DCM. Our study aims to precisely phenotype and genotype the various subtypes of DCM and hereby lay the foundation for individualized therapy. METHODS AND RESULTS: The Geno- And Phenotyping of PrImary Cardiomyopathy (GrAPHIC) is a currently ongoing prospective observational monocentric cohort study that recruits patients with DCM after exclusion of other causes such as coronary artery disease, valvular dysfunction, myocarditis, exposure to toxins, and peripartum CMP. Patients are enrolled at our heart failure outpatient clinic or during hospitalization at the University Hospital Hamburg. Clinical parameters, multimodal imaging and functional assessment, cardiac biopsies, and blood samples are obtained to enable an integrated genomic, functional, and biomarker analysis. CONCLUSIONS: The GrAPHIC will contribute to a better understanding of the heterogeneous nature of primary CMPs focusing on DCM and provide improved prognostic approaches and more individualized therapies.

Increased endothelial sclerostin caused by elevated DSCAM mediates multiple trisomy 21 phenotypes.

Trisomy 21 (T21), a recurrent aneuploidy occurring in 1:800 births, predisposes to congenital heart disease (CHD) and multiple extracardiac phenotypes. Despite a definitive genetic etiology, the mechanisms by which T21 perturbs development and homeostasis remain poorly understood. We compared the transcriptome of CHD tissues from 49 patients with T21 and 226 with euploid CHD (eCHD). We resolved cell lineages that misexpressed T21 transcripts by cardiac single-nucleus RNA sequencing and RNA in situ hybridization. Compared with eCHD samples, T21 samples had increased chr21 gene expression; 11-fold-greater levels (P = 1.2 × 10-8) of SOST (chr17), encoding the Wnt inhibitor sclerostin; and 1.4-fold-higher levels (P = 8.7 × 10-8) of the SOST transcriptional activator ZNF467 (chr7). Euploid and T21 cardiac endothelial cells coexpressed SOST and ZNF467; however, T21 endothelial cells expressed 6.9-fold more SOST than euploid endothelial cells (P = 2.7 × 10-27). Wnt pathway genes were downregulated in T21 endothelial cells. Expression of DSCAM, residing within the chr21 CHD critical region, correlated with SOST (P = 1.9 × 10-5) and ZNF467 (P = 2.9 × 10-4). Deletion of DSCAM from T21 endothelial cells derived from human induced pluripotent stem cells diminished sclerostin secretion. As Wnt signaling is critical for atrioventricular canal formation, bone health, and pulmonary vascular homeostasis, we concluded that T21-mediated increased sclerostin levels would inappropriately inhibit Wnt activities and promote Down syndrome phenotypes. These findings imply therapeutic potential for anti-sclerostin antibodies in T21.

Efficient in vivo genome editing prevents hypertrophic cardiomyopathy in mice.

Dominant missense pathogenic variants in cardiac myosin heavy chain cause hypertrophic cardiomyopathy (HCM), a currently incurable disorder that increases risk for stroke, heart failure and sudden cardiac death. In this study, we assessed two different genetic therapies-an adenine base editor (ABE8e) and a potent Cas9 nuclease delivered by AAV9-to prevent disease in mice carrying the heterozygous HCM pathogenic variant myosin R403Q. One dose of dual-AAV9 vectors, each carrying one half of RNA-guided ABE8e, corrected the pathogenic variant in ≥70% of ventricular cardiomyocytes and maintained durable, normal cardiac structure and function. An additional dose provided more editing in the atria but also increased bystander editing. AAV9 delivery of RNA-guided Cas9 nuclease effectively inactivated the pathogenic allele, albeit with dose-dependent toxicities, necessitating a narrow therapeutic window to maintain health. These preclinical studies demonstrate considerable potential for single-dose genetic therapies to correct or silence pathogenic variants and prevent the development of HCM.

Genetic Contribution to End-Stage Cardiomyopathy Requiring Heart Transplantation.

BACKGROUND: Many cardiovascular disorders propel the development of advanced heart failure that necessitates cardiac transplantation. When treatable causes are excluded, studies to define causes are often abandoned, resulting in a diagnosis of end-stage idiopathic cardiomyopathy. We studied whether DNA sequence analyses could identify unrecognized causes of end-stage nonischemic cardiomyopathy requiring heart transplantation and whether the prevalence of genetic causes differed from ambulatory cardiomyopathy cases. METHODS: We performed whole exome and genome sequencing of 122 explanted hearts from 101 adult and 21 pediatric patients with idiopathic cardiomyopathy from a single center. Data were analyzed for pathogenic/likely pathogenic variants in nuclear and mitochondrial genomes and assessed for nonhuman microbial sequences. The frequency of damaging genetic variants was compared among cardiomyopathy cohorts with different clinical severity. RESULTS: Fifty-four samples (44.3%) had pathogenic/likely pathogenic cardiomyopathy gene variants. The frequency of pathogenic variants was similar in pediatric (42.9%) and adult (43.6%) samples, but the distribution of mutated genes differed (P=8.30×10-4). The prevalence of causal genetic variants was significantly higher in end-stage than in previously reported ambulatory adult dilated cardiomyopathy cases (P<0.001). Among remaining samples with unexplained causes, no damaging mitochondrial variants were identified, but 28 samples contained parvovirus genome sequences, including 2 samples with 6- to 9-fold higher levels than the overall mean levels in other samples. CONCLUSIONS: Pathogenic variants and viral myocarditis were identified in 45.9% of patients with unexplained end-stage cardiomyopathy. Damaging gene variants are significantly more frequent among transplant compared with patients with ambulatory cardiomyopathy. Genetic analyses can help define cause of end-stage cardiomyopathy to guide management and risk stratification of patients and family members.

Pathogenic variants damage cell composition and single cell transcription in cardiomyopathies.

Pathogenic variants in genes that cause dilated cardiomyopathy (DCM) and arrhythmogenic cardiomyopathy (ACM) convey high risks for the development of heart failure through unknown mechanisms. Using single-nucleus RNA sequencing, we characterized the transcriptome of 880,000 nuclei from 18 control and 61 failing, nonischemic human hearts with pathogenic variants in DCM and ACM genes or idiopathic disease. We performed genotype-stratified analyses of the ventricular cell lineages and transcriptional states. The resultant DCM and ACM ventricular cell atlas demonstrated distinct right and left ventricular responses, highlighting genotype-associated pathways, intercellular interactions, and differential gene expression at single-cell resolution. Together, these data illuminate both shared and distinct cellular and molecular architectures of human heart failure and suggest candidate therapeutic targets.

Isolation of Nuclei from Mammalian Cells and Tissues for Single-Nucleus Molecular Profiling.

Both single-cell RNA sequencing (scRNAseq) and single-nucleus RNA sequencing (snRNAseq) can be used to characterize the transcriptional profile of individual cells, and based on these transcriptional profiles, help define cell type distribution in mixed cell populations. However, scRNAseq analyses are confounded if some of the cells are large (>50 µm) or if some of cells adhere more tightly to some adjacent cells than to others. Further, single cell isolation for scRNAseq requires fresh tissue, which may not be available for human or animal model tissues. Additionally, the current enzymatic and mechanical methods for single-cell dissociation can lead to stress-induced transcriptional artifacts. Nuclei for snRNAseq, on the other hand, can be isolated from any cell, regardless of size, and from either fresh or frozen tissues, and compared to whole cells, they are more resistant to mechanical pressures and appear not to exhibit as many cell isolation-based transcriptional artifacts. Here, we describe a time- and cost-effective procedure to isolate nuclei from mammalian cells and tissues. The protocol incorporates steps to mechanically disrupt samples to release nuclei. Compared to conventional nuclei isolation protocols, the approach described here increases overall efficiency, eliminates risk of contaminant exposure, and reduces volumes of expensive reagents. A series of RNA quality control checks are also incorporated to ensure success and reduce costs of subsequent snRNAseq experiments. Nuclei isolated by this procedure can be separated on the 10× Genomics Chromium system for either snRNAseq and/or Single-Nucleus ATAC-Seq (snATAC-Seq), and is also compatible with other single cell platforms. © 2021 Wiley Periodicals LLC. Basic Protocol 1: Sample preparation and quality control check via RNA Isolation and Analysis Basic Protocol 2: Nuclei Isolation.

Plakophilin-2 truncating variants impair cardiac contractility by disrupting sarcomere stability and organization.

Progressive loss of cardiac systolic function in arrhythmogenic cardiomyopathy (ACM) has recently gained attention as an important clinical consideration in managing the disease. However, the mechanisms leading to reduction in cardiac contractility are poorly defined. Here, we use CRISPR gene editing to generate human induced pluripotent stem cells (iPSCs) that harbor plakophilin-2 truncating variants (PKP2tv), the most prevalent ACM-linked mutations. The PKP2tv iPSC­derived cardiomyocytes are shown to have aberrant action potentials and reduced systolic function in cardiac microtissues, recapitulating both the electrical and mechanical pathologies reported in ACM. By combining cell micropatterning with traction force microscopy and live imaging, we found that PKP2tvs impair cardiac tissue contractility by destabilizing cell-cell junctions and in turn disrupting sarcomere stability and organization. These findings highlight the interplay between cell-cell adhesions and sarcomeres required for stabilizing cardiomyocyte structure and function and suggest fundamental pathogenic mechanisms that may be shared among different types of cardiomyopathies.

SARS-CoV-2 entry factors are highly expressed in nasal epithelial cells together with innate immune genes.

We investigated SARS-CoV-2 potential tropism by surveying expression of viral entry-associated genes in single-cell RNA-sequencing data from multiple tissues from healthy human donors. We co-detected these transcripts in specific respiratory, corneal and intestinal epithelial cells, potentially explaining the high efficiency of SARS-CoV-2 transmission. These genes are co-expressed in nasal epithelial cells with genes involved in innate immunity, highlighting the cells' potential role in initial viral infection, spread and clearance. The study offers a useful resource for further lines of inquiry with valuable clinical samples from COVID-19 patients and we provide our data in a comprehensive, open and user-friendly fashion at www.covid19cellatlas.org.