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.

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-1β, 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-1β inhibition may improve outcomes in patients with SARS-CoV2 associated myocardial injury and increased inflammation.

Force Generation via β-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 β-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 β-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.

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 β-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.

Abstract 122: A Novel Mutation in a X-linked Gene Causes Human Congenital Dilated Cardiomyopathy

Congenital dilated cardiomyopathy (cDCM) is a rare but often fatal disease. In most cases, there is no family history, and its etiology is unknown. A major hurdle to elucidating a mechanistic understanding of congenital cardiomyopathy, and primary cardiomyopathies in general, has been a lack of access to diseased human cardiac tissues. Recent advances in patient-derived induced pluripotent stem cells (iPSCs) now enable production of human cardiomyocytes (iPSC-CMs) and allows for a systematic study of normal and diseased cardiomyocytes. We hypothesize that cardiomyocytes generated from iPSCs derived from cDCM patients will exhibit cellular and molecular differences from those generated from healthy donor iPSCs and that a rare genetic mutation, or a collection of mutations, plays a critical role in cDCM pathogenesis. To test these hypotheses, we generated cardiomyocytes from iPSCs derived from a 7-month old male with cDCM using a robust cardiac induction protocol based on the “matrigel sandwich” method of Kamp and colleagues. With this remarkably robust induction method, iPSC-CMs from the cDCM patient and a healthy control donor exhibited proteomic profiles that were 99.7% superimposable. Despite the close similarity at the global proteome level, iPSC-CMs from the cDCM patient showed greatly reduced contractility and dramatic structural defects in the sarcomere and the mitochondria. Finally, bioinformatics analyses of the RNAseq data of the patient’s iPSC-CMs discovered a putative causal mutation in an evolutionarily conserved site in a X-linked gene with unknown function. In summary, our work demonstrates that iPSC-based approaches are particularly useful for the study of human congenital heart diseases. We plan to confirm the causality of this mutation using gene editing techniques such as CRISPR/Cas9 and explore the role of this novel gene in cardiomyocyte structure and function.

Abstract 121: Combinatorial Tailored Polymers Enhanced Maturation of Human iPSC-CMs

There is a tremendous interest in human cardiomyocytes generated from patient-derived induced pluripotent stem cells (iPSC-CMs) for the study and possible treatment of human heart diseases. Despite their vast potential, a significant impediment to a broader application of iPSC-CMs to study human myocyte biology is the structural and functional immaturity of iPSC-CMs. Growing evidence indicates that synthetic polymers utilized as extracellular substrates can exert significant effects on in vitro tissue generation, although the underlying mechanisms remain largely unknown. Based on the profound impact of the extracellular matrix of developing embryos on in vivo organogenesis, we hypothesize that engineered polymer substrates will likewise influence in vitro maturation of iPSC-CMs. A subset of combinatorial polymers was synthesized by polymerizing poly(ε-caprolacton) (PCL), polyethylene glycol (PEG), and carboxylated PCL (cPCL), abbreviated as x%PEG-y%PCL-z%cPCL (x, y, and z: molar %). We investigated effects of the polymer composition on maturation of iPSC-CMs with respect to the beating behavior, mitochondrial function and molecular profiles after 30 days in culture on polymer scaffolds. Results showed the 4%PEG-96%PCL scaffold promoted the most active beating in iPSC-CMs at 30 days and further, that the mitochondrial function, as assessed by tetramethyl rhodamine methylester (TMRM) was significantly increased in the iPSC-CMs cultured on 4%PEG-96%PCL over other polymers. Molecular profiling analysis indicates 4%PEG-96%PCL scaffolds enhanced the expression of MYL2 (a commonly accepted marker of mature ventricular myocytes) as well as of components of the intermediate filaments linking the plasma membrane to the myofilament. In summary, although the polymers we used here exhibit similar physicochemical properties, they have divergent effects on iPSC-CM differentiation. Thus, specific chemical compositions of synthetic substrates can exert profound influence on in vitro maturation of hiPSC-CMs. Our work exploring the effects of synthetic biomaterials on human stem cell differentiation could pave the way for a successful translation of ongoing advances in tissue engineering to new treatments for human heart diseases.

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.

Mass urinary screening and follow-up for school children in Taiwan Province

Mass urinary screening has been carried out among the students of public and private elementary and junior high schools in the Province of Taiwan each semester since 1990. About 3 million students were screened each time. The students who had abnormal urine screening results at the first time received a second urine analysis 10 to 15 days later to confirm the abnormal urine analysis. The blood samples of the students with abnormal urine examination were taken and biochemistry examinations including creatinine (Cr) etc. were performed since 1992. All students with abnormal urine screening results were graded by the severity of hematuria and proteinuria, the heavy proteinuria graded as "D". Chronic renal failure (CRF) is defined as impaired renal function with the serum Cr over 1.7 mg/dl. Longitudinal continuous blood and urine examinations were performed each semester for the students of grade "D" and with CRF. CRF was confirmed by either the hospital medical records or telephone visit. The purpose of this study was to delineate the prevalence of heavy proteinuria (grade D) and CRF in the students of elementary and junior high school in the Taiwan Province from 1992 to 1996. The results revealed the number of urinary screening was 10,288,620. There were 5980 cases with heavy proteinuria with four-year prevalence of 5.81 x 10(-4), 4.83 x 10(-4) for boys; 6.87 x 10(-4) for girls. Girls were affected more often than boys. The peak age of girls was 12 years old and boys was 13 years old. The number of CRF cases was 189 with the four-year prevalence of 1.84 x 10(-5), 2.24 x 10(-5) for boys; 1.41 x 10(-5) for girls. The incidence rate increased after the age of 10; the peak age of boys being 14-year-old and of girls 12-year-old. The exact contributing factors, such as location on islet or lack of pediatric nephrologist, need further study. In conclusion, the four-year prevalence of heavy proteinuria in the students of the elementary and junior high schools in Taiwan was higher in girls than in boys. Glomerular nephritis (GN) is still one of the major causes of urinary abnormalities. The most-important secondary GN was systemic lupus erythematosus (SLE) with lupus nephritis. The percentage of SLE patients among anti-nuclear antibody (ANA) positive was 72%. In contrast, the four-year prevalence of CRF disease was higher in boys with the peak age at 14-year-old. GN is still the major cause of urinary screening abnormality. ANA study is indicated in all Chinese students with abnormal urinary screening.

The prevalence of heavy proteinuria and progression risk factors in children undergoing urinary screening

To evaluate the prevalence and incidence density of heavy proteinuria and chronic renal insufficiency (CRI) and the factors related to disease progression, 10,288,620 urinary screenings of elementary and junior high-school students from 1992 to 1996 were studied retrospectively. Urinary screening included pH, protein, occult blood, and glucose measurements. Blood sample analysis included total protein, albumin, A/G ratio, blood urea nitrogen, creatinine (Cr), antistreptolysin O titer, C3, cholesterol, hepatitis B virus surface antigen, IgA, and fasting blood sugar. The results showed that the 4-year prevalence of proteinuria was higher in girls than in boys (6.87x10(-4) vs. 4.83x10(-4) respectively). There were 189 cases with disease progression into CRI among the 10,288,620 students screened and followed continuously, with the prevalence of disease progression into CRI higher in boys than in girls (2.24x10(-5) vs. 1.41x10(-5) respectively). Of the 119 cases (63%) presenting with CRI since the first urine screening and blood sampling, only 14 had serum Cr levels higher than 6.0 mg/dl. There were 1,289 patients (10.5%) with proteinuria in 1992 and 705 patients (7.1%) in 1996. The absolute number of patients with heavy proteinuria decreased. The percentage of underlying glomerulonephritis in children on dialysis also decreased from 63.2% in 1992 to 47.0% in 1996. Logistic regression analysis showed that a persistent serum cholesterol level higher than 220 mg/dl, an albumin level lower than 3.5 g/dl, total protein less than 6 g/dl, and diastolic pressure higher than 90 mmHg were the significant risk factors for disease progression to CRI. We conclude that early detection of students with heavy proteinuria by mass urinary screening, early appropriate treatment, and monitoring of significant risk factors may help to decrease or delay the progression of renal disease, delay the introduction of dialysis in these predialysis CRI patients and maintain their growth and development.