Impaired Reorganization of Centrosome Structure Underlies Human Infantile Dilated Cardiomyopathy.

BACKGROUND: During cardiomyocyte maturation, the centrosome, which functions as a microtubule organizing center in cardiomyocytes, undergoes dramatic structural reorganization where its components reorganize from being localized at the centriole to the nuclear envelope. This developmentally programmed process, referred to as centrosome reduction, has been previously associated with cell cycle exit. However, understanding of how this process influences cardiomyocyte cell biology, and whether its disruption results in human cardiac disease, remains unknown. We studied this phenomenon in an infant with a rare case of infantile dilated cardiomyopathy (iDCM) who presented with left ventricular ejection fraction of 18% and disrupted sarcomere and mitochondria structure. METHODS: We performed an analysis beginning with an infant who presented with a rare case of iDCM. We derived induced pluripotent stem cells from the patient to model iDCM in vitro. We performed whole exome sequencing on the patient and his parents for causal gene analysis. CRISPR/Cas9-mediated gene knockout and correction in vitro were used to confirm whole exome sequencing results. Zebrafish and Drosophila models were used for in vivo validation of the causal gene. Matrigel mattress technology and single-cell RNA sequencing were used to characterize iDCM cardiomyocytes further. RESULTS: Whole exome sequencing and CRISPR/Cas9 gene knockout/correction identified RTTN, the gene encoding the centrosomal protein RTTN (rotatin), as the causal gene underlying the patient's condition, representing the first time a centrosome defect has been implicated in a nonsyndromic dilated cardiomyopathy. Genetic knockdowns in zebrafish and Drosophila confirmed an evolutionarily conserved requirement of RTTN for cardiac structure and function. Single-cell RNA sequencing of iDCM cardiomyocytes showed impaired maturation of iDCM cardiomyocytes, which underlie the observed cardiomyocyte structural and functional deficits. We also observed persistent localization of the centrosome at the centriole, contrasting with expected programmed perinuclear reorganization, which led to subsequent global microtubule network defects. In addition, we identified a small molecule that restored centrosome reorganization and improved the structure and contractility of iDCM cardiomyocytes. CONCLUSIONS: This study is the first to demonstrate a case of human disease caused by a defect in centrosome reduction. We also uncovered a novel role for RTTN in perinatal cardiac development and identified a potential therapeutic strategy for centrosome-related iDCM. Future study aimed at identifying variants in centrosome components may uncover additional contributors to human cardiac disease.

Patients with varying courses of single coronary artery: case series.

BACKGROUND: Single coronary artery (SCA) is a rare congenital anomaly where blood to the heart is supplied through a common trunk. Identifying these abnormalities is important because some variants can compromise myocardial blood flow and increase risk of sudden cardiac death. CASE SUMMARY: We present five patients with varying Lipton Group I and Group II SCA subtypes, corroborated on multi-imaging modalities and evaluated with comprehensive non-invasive as well as invasive testing. Their clinical presentations also vary from a spectrum of asymptomatic finding to angina equivalent. The decision for definitive surgical intervention involving unroofing of the involved vessel depends largely on symptoms and evidence of myocardial ischaemia. DISCUSSION: While SCA findings are often incidental and benign, understanding the origin, branching pattern, and course of the anomalous artery has implications in prognosis and treatment. This usually involves a combination of anatomic assessment with imaging such as coronary Computed Tomography Angiography (CTA), Magnetic Resonance Angiography (MRA), and/or coronary angiography as well as functional assessment with invasive testing using tools like instantaneous wave-free ratio and intravascular ultrasound both at rest and with stress. Individualized treatment plans can then be made through a multidisciplinary approach involving adult congenital heart disease specialists and congenital cardiothoracic surgeons.

SARS-CoV-2 Myocarditis: Insights Into Incidence, Prognosis, and Therapeutic Implications.

PURPOSE OF REVIEW: In coronavirus disease 2019 (COVID-19), myocardial injury occurs frequently in severe or critically ill hospitalized patients, yet myocarditis is much less common. In this context, revisiting the definition of myocarditis is appropriate with a specific focus on diagnostic and management considerations in patients infected with SARS-CoV-2. RECENT FINDINGS: Pathologic cardiac specimens from patients with COVID-19 suggest a mixed inflammatory response involving lymphocytes and macrophages, and importantly, cellular injury occurs predominantly at the level of pericytes and endothelial cells, less often involving direct myocyte necrosis. In COVID-19, the diagnosis of myocarditis has understandably been based predominantly on clinical criteria, and the number of patients with clinically suspected myocarditis who would meet diagnostic histological criteria is unclear. Echocardiography and cardiac magnetic resonance are important diagnostic tools, although the prognostic implications of abnormalities are still being defined. Importantly, SARS-CoV2 myocarditis should be diagnosed within an appropriate clinical context and should not be based on isolated imaging findings. Therapies in COVID-19 have focused on the major clinical manifestation of pneumonia, but the promotion of viral clearance early in the disease could prevent the development of myocarditis, and further study of immunosuppressive therapies once myocarditis has developed are indicated. A strict and uniform approach is needed to diagnose myocarditis due to SARS-CoV-2 to better understand the natural history of this disease and to facilitate evaluation of potential therapeutic interventions. A methodological approach will also better inform the incidence of COVID-19 associated myocarditis and potential long-term health effects.

Mavrilimumab in patients with severe COVID-19 pneumonia and systemic hyperinflammation (MASH-COVID): an investigator initiated, multicentre, double-blind, randomised, placebo-controlled trial.

BACKGROUND: In patients with COVID-19, granulocyte-macrophage colony stimulating factor (GM-CSF) might be a mediator of the hyperactive inflammatory response associated with respiratory failure and death. We aimed to evaluate whether mavrilimumab, a monoclonal antibody to the GM-CSF receptor, would improve outcomes in patients with COVID-19 pneumonia and systemic hyperinflammation. METHODS: This investigator-initiated, multicentre, double-blind, randomised trial was done at seven hospitals in the USA. Inclusion required hospitalisation, COVID-19 pneumonia, hypoxaemia, and a C-reactive protein concentration of more than 5 mg/dL. Patients were excluded if they required mechanical ventilation. Patients were randomly assigned (1:1) centrally, with stratification by hospital site, to receive mavrilimumab 6 mg/kg as a single intravenous infusion, or placebo. Participants and all clinical and research personnel were masked to treatment assignment. The primary endpoint was the proportion of patients alive and off supplemental oxygen therapy at day 14. The primary outcome and safety were analysed in the intention-to-treat population. This trial is registered at ClinicalTrials.gov, NCT04399980, NCT04463004, and NCT04492514. FINDINGS: Between May 28 and Sept 15, 2020, 40 patients were enrolled and randomly assigned to mavrilimumab (n=21) or placebo (n=19). A trial of 60 patients was planned, but given slow enrolment, the study was stopped early to inform the natural history and potential treatment effect. At day 14, 12 (57%) patients in the mavrilimumab group were alive and off supplemental oxygen therapy compared with nine (47%) patients in the placebo group (odds ratio 1·48 [95% CI 0·43-5·16]; p=0·76). There were no treatment-related deaths, and adverse events were similar between groups. INTERPRETATION: There was no significant difference in the proportion of patients alive and off oxygen therapy at day 14, although benefit or harm of mavrilimumab therapy in this patient population remains possible given the wide confidence intervals, and larger trials should be completed. FUNDING: Kiniksa Pharmaceuticals.

Double-blind randomized proof-of-concept trial of canakinumab in patients with COVID-19 associated cardiac injury and heightened inflammation.

Aims: In coronavirus disease 2019 (COVID-19), myocardial injury is associated with systemic inflammation and higher mortality. Our aim was to perform a proof of concept trial with canakinumab, a monoclonal antibody to interleukin-1ß, in patients with COVID-19, myocardial injury, and heightened inflammation. Methods and results: This trial required hospitalization due to COVID-19, elevated troponin, and a C-reactive protein concentration more than 50 mg/L. The primary endpoint was time to clinical improvement at Day 14, defined as either an improvement of two points on a seven-category ordinal scale or discharge from the hospital. The secondary endpoint was mortality at Day 28. Forty-five patients were randomly assigned to canakinumab 600 mg (n = 15), canakinumab 300 mg (n = 14), or placebo (n = 16). There was no difference in time to clinical improvement compared to placebo [recovery rate ratio (RRR) for canakinumab 600 mg 1.15, 95% confidence interval (CI) 0.46-2.91; RRR for canakinumab 300 mg 0.61, 95% CI 0.23-1.64]. At Day 28, 3 (18.8%) of 15 patients had died in the placebo group, compared with 3 (21.4%) of 14 patients with 300 mg canakinumab, and 1 (6.7%) of 15 patients with 600 mg canakinumab. There were no treatment-related deaths, and adverse events were similar between groups. Conclusion: There was no difference in time to clinical improvement at Day 14 in patients treated with canakinumab, and no safety concerns were identified. Future studies could focus on high dose canakinumab in the treatment arm and assess efficacy outcomes at Day 28.

Canakinumab to reduce deterioration of cardiac and respiratory function in SARS-CoV-2 associated myocardial injury with heightened inflammation (canakinumab in Covid-19 cardiac injury: The three C study).

BACKGROUND: In patients with Covid-19, myocardial injury and increased inflammation are associated with morbidity and mortality. We designed a proof-of-concept randomized controlled trial to evaluate whether treatment with canakinumab prevents progressive respiratory failure and worsening cardiac dysfunction in patients with SARS-CoV2 infection, myocardial injury, and high levels of inflammation. HYPOTHESIS: The primary hypothesis is that canakiumab will shorten time to recovery. METHODS: The three C study (canakinumab in Covid-19 Cardiac Injury, NCT04365153) is a double-blind, randomized controlled trial comparing canakinumab 300 mg IV, 600 mg IV, or placebo in a 1:1:1 ratio in hospitalized Covid-19 patients with elevations in troponin and C-reactive protein (CRP). The primary endpoint is defined as the time in days from randomization to either an improvement of two points on a seven category ordinal scale or discharge from the hospital, whichever occurs first up to 14 days postrandomization. The secondary endpoint is mortality at day 28. A total of 45 patients will be enrolled with an anticipated 5 month follow up period. RESULTS: Baseline characteristics for the first 20 randomized patients reveal a predominantly male (75%), elderly population (median 67 years) with a high prevalence of hypertension (80%) and hyperlipidemia (75%). CRPs have been markedly elevated (median 16.2 mg/dL) with modest elevations in high-sensitivity troponin T (median 21 ng/L), in keeping with the concept of enrolling patients with early myocardial injury. CONCLUSIONS: The three C study will provide insights regarding whether IL-1ß inhibition may improve outcomes in patients with SARS-CoV2 associated myocardial injury and increased inflammation.

Force Generation via ß-Cardiac Myosin, Titin, and α-Actinin Drives Cardiac Sarcomere Assembly from Cell-Matrix Adhesions.

Truncating mutations in the sarcomere protein titin cause dilated cardiomyopathy due to sarcomere insufficiency. However, it remains mechanistically unclear how these mutations decrease sarcomere content in cardiomyocytes. Utilizing human induced pluripotent stem cell-derived cardiomyocytes, CRISPR/Cas9, and live microscopy, we characterize the fundamental mechanisms of human cardiac sarcomere formation. We observe that sarcomerogenesis initiates at protocostameres, sites of cell-extracellular matrix adhesion, where nucleation and centripetal assembly of α-actinin-2-containing fibers provide a template for the fusion of Z-disk precursors, Z bodies, and subsequent striation. We identify that ß-cardiac myosin-titin-protocostamere form an essential mechanical connection that transmits forces required to direct α-actinin-2 centripetal fiber assembly and sarcomere formation. Titin propagates diastolic traction stresses from ß-cardiac myosin, but not α-cardiac myosin or non-muscle myosin II, to protocostameres during sarcomerogenesis. Ablating protocostameres or decoupling titin from protocostameres abolishes sarcomere assembly. Together these results identify the mechanical and molecular components critical for human cardiac sarcomerogenesis.

Integrative Analysis of PRKAG2 Cardiomyopathy iPS and Microtissue Models Identifies AMPK as a Regulator of Metabolism, Survival, and Fibrosis.

AMP-activated protein kinase (AMPK) is a metabolic enzyme that can be activated by nutrient stress or genetic mutations. Missense mutations in the regulatory subunit, PRKAG2, activate AMPK and cause left ventricular hypertrophy, glycogen accumulation, and ventricular pre-excitation. Using human iPS cell models combined with three-dimensional cardiac microtissues, we show that activating PRKAG2 mutations increase microtissue twitch force by enhancing myocyte survival. Integrating RNA sequencing with metabolomics, PRKAG2 mutations that activate AMPK remodeled global metabolism by regulating RNA transcripts to favor glycogen storage and oxidative metabolism instead of glycolysis. As in patients with PRKAG2 cardiomyopathy, iPS cell and mouse models are protected from cardiac fibrosis, and we define a crosstalk between AMPK and post-transcriptional regulation of TGFß isoform signaling that has implications in fibrotic forms of cardiomyopathy. Our results establish critical connections among metabolic sensing, myocyte survival, and TGFß signaling.

HEART DISEASE. Titin mutations in iPS cells define sarcomere insufficiency as a cause of dilated cardiomyopathy.

Human mutations that truncate the massive sarcomere protein titin [TTN-truncating variants (TTNtvs)] are the most common genetic cause for dilated cardiomyopathy (DCM), a major cause of heart failure and premature death. Here we show that cardiac microtissues engineered from human induced pluripotent stem (iPS) cells are a powerful system for evaluating the pathogenicity of titin gene variants. We found that certain missense mutations, like TTNtvs, diminish contractile performance and are pathogenic. By combining functional analyses with RNA sequencing, we explain why truncations in the A-band domain of TTN cause DCM, whereas truncations in the I band are better tolerated. Finally, we demonstrate that mutant titin protein in iPS cell-derived cardiomyocytes results in sarcomere insufficiency, impaired responses to mechanical and ß-adrenergic stress, and attenuated growth factor and cell signaling activation. Our findings indicate that titin mutations cause DCM by disrupting critical linkages between sarcomerogenesis and adaptive remodeling.

Combinatorial polymer matrices enhance in vitro maturation of human induced pluripotent stem cell-derived cardiomyocytes.

Cardiomyocytes derived from human induced pluripotent stem cells (iPSC-CMs) hold great promise for modeling human heart diseases. However, iPSC-CMs studied to date resemble immature embryonic myocytes and therefore do not adequately recapitulate native adult cardiomyocyte phenotypes. Since extracellular matrix plays an essential role in heart development and maturation in vivo, we sought to develop a synthetic culture matrix that could enhance functional maturation of iPSC-CMs in vitro. In this study, we employed a library of combinatorial polymers comprising of three functional subunits - poly-ε-caprolacton (PCL), polyethylene glycol (PEG), and carboxylated PCL (cPCL) - as synthetic substrates for culturing human iPSC-CMs. Of these, iPSC-CMs cultured on 4%PEG-96%PCL (each % indicates the corresponding molar ratio) exhibit the greatest contractility and mitochondrial function. These functional enhancements are associated with increased expression of cardiac myosin light chain-2v, cardiac troponin I and integrin alpha-7. Importantly, iPSC-CMs cultured on 4%PEG-96%PCL demonstrate troponin I (TnI) isoform switch from the fetal slow skeletal TnI (ssTnI) to the postnatal cardiac TnI (cTnI), the first report of such transition in vitro. Finally, culturing iPSC-CMs on 4%PEG-96%PCL also significantly increased expression of genes encoding intermediate filaments known to transduce integrin-mediated mechanical signals to the myofilaments. In summary, our study demonstrates that synthetic culture matrices engineered from combinatorial polymers can be utilized to promote in vitro maturation of human iPSC-CMs through the engagement of critical matrix-integrin interactions.

Current stem cell delivery methods for myocardial repair.

Heart failure commonly results from an irreparable damage due to cardiovascular diseases (CVDs), the leading cause of morbidity and mortality in the United States. In recent years, the rapid advancements in stem cell research have garnered much praise for paving the way to novel therapies in reversing myocardial injuries. Cell types currently investigated for cellular delivery include embryonic stem cells (ESCs), induced pluripotent stem cells (iPSCs), and adult stem cell lineages such as skeletal myoblasts, bone-marrow-derived stem cells (BMSCs), mesenchymal stem cells (MSCs), and cardiac stem cells (CSCs). To engraft these cells into patients' damaged myocardium, a variety of approaches (intramyocardial, transendocardial, transcoronary, venous, intravenous, intracoronary artery and retrograde venous administrations and bioengineered tissue transplantation) have been developed and explored. In this paper, we will discuss the pros and cons of these delivery modalities, the current state of their therapeutic potentials, and a multifaceted evaluation of their reported clinical feasibility, safety, and efficacy. While the issues of optimal delivery approach, the best progenitor stem cell type, the most effective dose, and timing of administration remain to be addressed, we are highly optimistic that stem cell therapy will provide a clinically viable option for myocardial regeneration.

Mapping of ionomic traits in Mimulus guttatus reveals Mo and Cd QTLs that colocalize with MOT1 homologues.

Natural variation in the regulation of the accumulation of mineral nutrients and trace elements in plant tissues is crucial to plant metabolism, development, and survival across different habitats. Studies of the genetic basis of natural variation in nutrient metabolism have been facilitated by the development of ionomics. Ionomics is a functional genomic approach for the identification of the genes and gene networks that regulate the elemental composition, or ionome, of an organism. In this study, we evaluated the genetic basis of divergence in elemental composition between an inland annual and a coastal perennial accession of Mimulus guttatus using a recombinant inbred line (RIL) mapping population. Out of 20 elements evaluated, Mo and Cd were the most divergent in accumulation between the two accessions and were highly genetically correlated in the RILs across two replicated experiments. We discovered two major quantitative trait loci (QTL) for Mo accumulation, the largest of which consistently colocalized with a QTL for Cd accumulation. Interestingly, both Mo QTLs also colocalized with the two M. guttatus homologues of MOT1, the only known plant transporter to be involved in natural variation in molybdate uptake.

Five anthocyanin polymorphisms are associated with an R2R3-MYB cluster in Mimulus guttatus (Phrymaceae).

PREMISE OF STUDY: Botanists have long been interested in the reasons for genetic variation among individuals, populations, and species of plants. The anthocyanin pathway is ideal for studying the evolution of such phenotypic variation. METHODS: We used a combination of quantitative trait loci mapping and association studies to understand the genetic basis of variation in five anthocyanin phenotypes including calyx, corolla, and leaf coloration patterns that vary within and among populations of Mimulus guttatus. We then examined what genes might be responsible for this phenotypic variation and whether one of the traits, calyx spotting, is randomly distributed across the geographic range of the species. KEY RESULTS: All five phenotypes in M. guttatus were primarily controlled by the same major locus (PLA1), which contains a tandem array of three R2R3-MYB genes known to be involved in the evolution of flower color in a related species of Mimulus. Calyx spotting was nonrandomly distributed across the range of M. guttatus and correlated with multiple climate variables. CONCLUSIONS: The results of this study suggest that variation in R2R3-MYB genes is the primary cause of potentially important anthocyanin phenotypic variation within and among populations of M. guttatus, a finding consistent with recent theoretical and empirical research on flower color evolution.