Myosin inhibitor reverses hypertrophic cardiomyopathy in genotypically diverse pediatric iPSC-cardiomyocytes to mirror variant correction.

Pathogenic variants in MYH7 and MYBPC3 account for the majority of hypertrophic cardiomyopathy (HCM). Targeted drugs like myosin ATPase inhibitors have not been evaluated in children. We generate patient and variant-corrected iPSC-cardiomyocytes (CMs) from pediatric HCM patients harboring single variants in MYH7 (V606M; R453C), MYBPC3 (G148R) or digenic variants (MYBPC3 P955fs, TNNI3 A157V). We also generate CMs harboring MYBPC3 mono- and biallelic variants using CRISPR editing of a healthy control. Compared with isogenic and healthy controls, variant-positive CMs show sarcomere disorganization, higher contractility, calcium transients, and ATPase activity. However, only MYH7 and biallelic MYBPC3 variant-positive CMs show stronger myosin-actin binding. Targeted myosin ATPase inhibitors show complete rescue of the phenotype in variant-positive CMs and in cardiac Biowires to mirror isogenic controls. The response is superior to verapamil or metoprolol. Myosin inhibitors can be effective in genotypically diverse HCM highlighting the need for myosin inhibitor drug trials in pediatric HCM.

Association between genetic variants in the HIF1A-VEGF pathway and left ventricular regional myocardial deformation in patients with hypertrophic cardiomyopathy.

BACKGROUND: Information on genetic etiology of pediatric hypertrophic cardiomyopathy (HCM) rarely aids in risk stratification and prediction of disease onset. Little data exist on the association between genetic modifiers and phenotypic expression of myocardial performance, hampering an individual precision medicine approach. METHODS: Single-nucleotide polymorphism genotyping for six previously established disease risk alleles in the hypoxia-inducible factor-1α-vascular endothelial growth factor pathway was performed in a pediatric cohort with HCM. Findings were correlated with echocardiographic parameters of systolic and diastolic myocardial deformation measured by two-dimensional (2-D) speckle-tracking strain. RESULTS: Twenty-five children (6.1 ± 4.5 years; 69% male) with phenotypic and genotypic (60%) HCM were included. Out of six risk alleles tested, one, VEGF1 963GG, showed an association with reduced regional systolic and diastolic left ventricular (LV) myocardial deformation. Moreover, LV average and segmental systolic and diastolic strain and strain rate were significantly reduced, as assessed by the standardized difference, in patients harboring the risk allele. CONCLUSIONS: This is the first study to identify an association between a risk allele in the VEGF pathway and regional LV myocardial function, with the VEGF1 963GG allele associated with reduced LV systolic and diastolic myocardial performance. While studies are needed to link this information to adverse clinical outcomes, this knowledge may help in risk stratification and patient management in HCM. IMPACT: Risk allele in the VEGF gene impacts on LV myocardial deformation phenotype in children with HCM. LV 2-D strain is significantly reduced in patients with risk allele compared to non-risk allele patients within HCM patient groups. Describes that deficiencies in LV myocardial performance in children with HCM are associated with a previously identified risk allele in the angiogenic transcription factor VEGF. First study to identify an association between a risk allele in the VEGF pathway and regional LV myocardial deformation measured by 2-D strain in children with HCM.

Machine Learning Identifies Clinical and Genetic Factors Associated With Anthracycline Cardiotoxicity in Pediatric Cancer Survivors.

BACKGROUND: Despite known clinical risk factors, predicting anthracycline cardiotoxicity remains challenging. OBJECTIVES: This study sought to develop a clinical and genetic risk prediction model for anthracycline cardiotoxicity in childhood cancer survivors. METHODS: We performed exome sequencing in 289 childhood cancer survivors at least 3 years from anthracycline exposure. In a nested case-control design, 183 case patients with reduced left ventricular ejection fraction despite low-dose doxorubicin (≤250 mg/m2), and 106 control patients with preserved left ventricular ejection fraction despite doxorubicin >250 mg/m2 were selected as extreme phenotypes. Rare/low-frequency variants were collapsed to identify genes differentially enriched for variants between case patients and control patients. The expression levels of 5 top-ranked genes were evaluated in human induced pluripotent stem cell-derived cardiomyocytes, and variant enrichment was confirmed in a replication cohort. Using random forest, a risk prediction model that included genetic and clinical predictors was developed. RESULTS: Thirty-one genes were differentially enriched for variants between case patients and control patients (p < 0.001). Only 42.6% case patients harbored a variant in these genes compared to 89.6% control patients (odds ratio: 0.09; 95% confidence interval: 0.04 to 0.17; p = 3.98 × 10-15). A risk prediction model for cardiotoxicity that included clinical and genetic factors had a higher prediction accuracy and lower misclassification rate compared to the clinical-only model. In vitro inhibition of gene-associated pathways (PI3KR2, ZNF827) provided protection from cardiotoxicity in cardiomyocytes. CONCLUSIONS: Our study identified variants in cardiac injury pathway genes that protect against cardiotoxicity and informed the development of a prediction model for delayed anthracycline cardiotoxicity, and it also provided new targets in autophagy genes for the development of cardio-protective drugs. (Preventing Cardiac Sequelae in Pediatric Cancer Survivors [PCS2]; NCT01805778).

Fetal reprogramming and senescence in hypoplastic left heart syndrome and in human pluripotent stem cells during cardiac differentiation.

Hypoplastic left heart syndrome (HLHS) is a severe cardiac malformation characterized by left ventricle (LV) hypoplasia and abnormal LV perfusion and oxygenation. We studied hypoxia-associated injury in fetal HLHS and human pluripotent stem cells during cardiac differentiation to assess the effect of microenvironmental perturbations on fetal cardiac reprogramming. We studied LV myocardial samples from 32 HLHS and 17 structurally normal midgestation fetuses. Compared with controls, the LV in fetal HLHS samples had higher nuclear expression of hypoxia-inducible factor-1α but lower angiogenic growth factor expression, higher expression of oncogenes and transforming growth factor (TGF)-ß1, more DNA damage and senescence with cell cycle arrest, fewer cardiac progenitors, myocytes and endothelial lineages, and increased myofibroblast population (P < 0.05 versus controls). Smooth muscle cells (SMCs) had less DNA damage compared with endothelial cells and myocytes. We recapitulated the fetal phenotype by subjecting human pluripotent stem cells to hypoxia during cardiac differentiation. DNA damage was prevented by treatment with a TGF-ß1 inhibitor (P < 0.05 versus nonhypoxic cells). The hypoplastic LV in fetal HLHS samples demonstrates hypoxia-inducible factor-1α up-regulation, oncogene-associated cellular senescence, TGF-ß1-associated fibrosis and impaired vasculogenesis. The phenotype is recapitulated by subjecting human pluripotent stem cells to hypoxia during cardiac differentiation and rescued by inhibition of TGF-ß1. This finding suggests that hypoxia may reprogram the immature heart and affect differentiation and development.

Modeling and rescue of the vascular phenotype of Williams-Beuren syndrome in patient induced pluripotent stem cells.

Elastin haploinsufficiency in Williams-Beuren syndrome (WBS) leads to increased vascular smooth muscle cell (SMC) proliferation and stenoses. Our objective was to generate a human induced pluripotent stem (hiPS) cell model for in vitro assessment of the WBS phenotype and to test the ability of candidate agents to rescue the phenotype. hiPS cells were reprogrammed from skin fibroblasts of a WBS patient with aortic and pulmonary stenosis and healthy control BJ fibroblasts using four-factor retrovirus reprogramming and were differentiated into SMCs. Differentiated SMCs were treated with synthetic elastin-binding protein ligand 2 (EBPL2) (20 µg/ml) or the antiproliferative drug rapamycin (100 nM) for 5 days. We generated four WBS induced pluripotent stem (iPS) cell lines that expressed pluripotency genes and differentiated into all three germ layers. Directed differentiation of BJ iPS cells yielded an 85%-92% pure SMC population that expressed differentiated SMC markers, were functionally contractile, and formed tube-like structures on three-dimensional gel assay. Unlike BJ iPS cells, WBS iPS cells generated immature SMCs that were highly proliferative, showed lower expression of differentiated SMC markers, reduced response to the vasoactive agonists, carbachol and endothelin-1, impaired vascular tube formation, and reduced calcium flux. EBPL2 partially rescued and rapamycin fully rescued the abnormal SMC phenotype by decreasing the smooth muscle proliferation rate and enhancing differentiation and tube formation. WBS iPS cell-derived SMCs demonstrate an immature proliferative phenotype with reduced functional and contractile properties, thereby recapitulating the human disease phenotype. The ability of rapamycin to rescue the phenotype provides an attractive therapeutic candidate for patients with WBS and vascular stenoses.

Genetic determinants of right-ventricular remodeling after tetralogy of Fallot repair.

BACKGROUND: Hypoxia-inducible factor (HIF1A) regulates the myocardial response to hypoxia and hemodynamic load. We investigated the association of HIF1A variants with right-ventricular (RV) remodeling after tetralogy of Fallot (TOF) repair. METHODS: Children with TOF were genotyped for three single-nucleotide polymorphisms in HIF1A. Genotypes were analyzed for association with RV myocardial protein expression and fibrosis at complete repair (n = 42) and RV dilation, fractional area change, and freedom from pulmonary valve/conduit replacement on follow-up. RESULTS: In 180 TOF patients, mean age at repair was 1.0 ± 0.8 y with follow-up at 9.0 ± 3.5 y; 82% had moderate to severe pulmonary insufficiency. Freedom from RV reinterventions at 5, 10, and 15 y was 92, 84, and 67%, respectively. Patients with more functioning HIF1A alleles had higher transforming growth factor ß1 expression and more fibrosis at initial repair as compared with controls (P < 0.05). During follow-up, patients with more functioning HIF1A alleles showed less RV dilation, better preservation of RV function, and greater freedom from RV reinterventions (P < 0.05). This was confirmed in a replication cohort of 69 patients. CONCLUSION: In children who have had TOF repair, a lower number of functioning HIF1A alleles was associated with RV dilation and dysfunction, suggesting that hypoxia adaptation in unrepaired TOF may influence RV phenotype after repair.

Recipient genotype is a predictor of allograft cytokine expression and outcomes after pediatric cardiac transplantation.

OBJECTIVES: This study sought to investigate the influence of recipient renin-angiotensin-aldosterone system (RAAS) genotype on cardiac function, rejection, and outcomes after heart transplantation. BACKGROUND: The RAAS influences cardiac function and up-regulates inflammatory/immune pathways. Little is known about the effect of recipient RAAS polymorphisms in pediatric cardiac transplantation. METHODS: Patients <25 years of age, after cardiac transplantation, were enrolled (2003 to 2008) and genotyped for polymorphisms in genes associated with RAAS upregulation: AGT-G, ACE-D, AGTR1-C, CYP11B2-G, and CMA-A. Presence of at least 1 high-risk allele was defined as a high-risk genotype. Univariable and multivariable associations between genotypes and outcomes were assessed in time-dependent models using survival, logistic, or linear regression models. Biopsy samples were immunostained for interleukin (IL)-6, transforming growth factor (TGF)-beta, and tumor necrosis factor (TNF)-alpha during rejection and quiescence. RESULTS: A total of 145 patients were studied, 103 primary cohort and 42 replication cohort; 81% had rejection, 51% had graft dysfunction, and 13% had vasculopathy, 7% died and 8% underwent re-transplantation. A higher number of homozygous high-risk RAAS genotypes was associated with a higher risk of graft dysfunction (hazard ratio [HR]: 1.5, p = 0.02) and a higher probability of death (HR: 2.5, p = 0.04). The number of heterozygous high-risk RAAS genotypes was associated with frequency of rejection (+0.096 events/year, p < 0.001) and rejection-associated graft dysfunction (+0.37 events/year, p = 0.002). IL-6 and TGF-beta were markedly upregulated during rejection in patients with >/=2 high-risk RAAS genotypes. CONCLUSIONS: Recipient RAAS polymorphisms are associated with a higher risk of rejection, graft cytokine expression, graft dysfunction, and a higher mortality after cardiac transplantation. This may have implications for use of RAAS inhibitors in high-risk patients after transplantation.

LC3-mediated fibronectin mRNA translation induces fibrosarcoma growth by increasing connective tissue growth factor.

Previously, we related fibronectin (Fn1) mRNA translation to an interaction between an AU-rich element in the Fn1 3' UTR and light chain 3 (LC3) of microtubule-associated proteins 1A and 1B. Since human fibrosarcoma (HT1080) cells produce little fibronectin and LC3, we used these cells to investigate how LC3-mediated Fn1 mRNA translation might alter tumor growth. Transfection of HT1080 cells with LC3 enhanced fibronectin mRNA translation. Using polysome analysis and RNA-binding assays, we show that elevated levels of translation depend on an interaction between a triple arginine motif in LC3 and the AU-rich element in Fn1 mRNA. Wild-type but not mutant LC3 accelerated HT1080 cell growth in culture and when implanted in SCID mice. Comparison of WT LC3 with vector-transfected HT1080 cells revealed increased fibronectin-dependent proliferation, adhesion and invasion. Microarray analysis of genes differentially expressed in WT and vector-transfected control cells indicated enhanced expression of connective tissue growth factor (CTGF). Using siRNA, we show that enhanced expression of CTGF is fibronectin dependent and that LC3-mediated adhesion, invasion and proliferation are CTGF dependent. Expression profiling of soft tissue tumors revealed increased expression of both LC3 and CTGF in some locally invasive tumor types.

Preservation of mitochondrial structure and function after cardioplegic arrest in the neonate using a selective mitochondrial KATP channel opener.

BACKGROUND: Mitochondrial dysfunction may contribute to early postoperative neonatal heart dysfunction. Diazoxide, a mitochondrial-selective adenosine triphosphate-sensitive potassium-channel opener, is associated with mitochondrial preservation after cardioplegic arrest. We evaluated the mitochondrial-protective effect of diazoxide in terms of mitochondrial structure and function after neonatal cardioplegic arrest. METHODS: Newborn piglets (age, approximately 14 days) underwent cardiopulmonary bypass and 60 minutes of cardioplegic arrest using cold crystalloid cardioplegic solution (CCP, n = 5) or cold crystalloid cardioplegic solution with diazoxide (CCP+D, n = 5). After 6 hours of recovery, myocardium was harvested. Control myocardium from piglets that did not undergo cardiopulmonary bypass (non-CPB, n = 5) was obtained. RESULTS: Cardioplegic arrest was associated with translocation of Bax to the mitochondria, which was not prevented by diazoxide. Nevertheless, by electron microscopy, CCP-associated remodeling of mitochondrial structure was subjectively diminished in CCP+D hearts. In addition, CCP-associated mitochondrial permeabilization and cytochrome c release into the cytosol were prevented with CCP+D (p < 0.05). In vitro oxygen consumption of isolated mitochondria demonstrated deficient function of mitochondrial complex I in CCP, but it was preserved in the CCP+D myocardial mitochondria (p < 0.05). Complex II and IV activity was not different among groups. In parallel with impaired complex I function, the cardiac adenosine triphosphate content was diminished in CCP hearts, but well maintained in CCP+D hearts (p < 0.05). CONCLUSIONS: Although early apoptotic signaling events (Bax translocation) are not prevented by diazoxide, addition of the mitochondrial-selective adenosine triphosphate-sensitive potassium-channel opener to the cardioplegic solution is associated with protection of mitochondrial structural and functional integrity in a clinically relevant model of neonatal cardiac surgery. The mitochondrial-protective effects of diazoxide may contribute to improved postoperative myocardial function in the neonate.

Apolipoprotein D inhibits platelet-derived growth factor-BB-induced vascular smooth muscle cell proliferated by preventing translocation of phosphorylated extracellular signal regulated kinase 1/2 to the nucleus.

OBJECTIVE: Elevated apolipoprotein D (apoD) levels are associated with reduced proliferation of cancer cells. We therefore investigated whether apoD, which occurs free or associated with HDL, suppresses vascular smooth muscle cell (VSMC) proliferation, which is related to the pathobiology of disease. METHODS AND RESULTS: Intense immunoreactivity for apoD was observed in human atherosclerotic plaque but not in normal coronary artery. However, an increase in apoD mRNA was seen in quiescent relative to proliferating fetal lamb aortic VSMCs, and in the rat aortic VSMC line (A10), we demonstrated uptake of apoD from serum. Stable transfection of apoD in A10 cells in the absence of serum did not influence VSMC proliferation assessed by [3H]-thymidine incorporation. ApoD, administered at a dose of 100 ng/mL, completely inhibited basal as well as platelet-derived growth factor (PDGF)-BB-induced VSMC proliferation (P<0.01) but had no effect on fibroblast growth factor-induced VSMC proliferation. ApoD did not suppress PDGF-BB or fibroblast growth factor-2-induced phosphorylation of extracellular signal regulated kinase (ERK) 1/2 but selectively inhibited PDGF-BB-mediated ERK1/2 nuclear translocation. CONCLUSIONS: Our data suggest that apoD selectively modulates the proliferative response of VSMC to growth factors by a mechanism related to nuclear translocation of ERK1/2.