Long telomeres protect against age-dependent cardiac disease caused by NOTCH1 haploinsufficiency

Diseases caused by gene haploinsufficiency in humans commonly lack a phenotype in mice that are heterozygous for the orthologous factor, impeding the study of complex phenotypes and critically limiting the discovery of therapeutics. Laboratory mice have longer telomeres relative to humans, potentially protecting against age-related disease caused by haploinsufficiency. Here, we demonstrate that telomere shortening in NOTCH1-haploinsufficient mice is sufficient to elicit age-dependent cardiovascular disease involving premature calcification of the aortic valve, a phenotype that closely mimics human disease caused by NOTCH1 haploinsufficiency. Furthermore, progressive telomere shortening correlated with severity of disease, causing cardiac valve and septal disease in the neonate that was similar to the range of valve disease observed within human families. Genes that were dysregulated due to NOTCH1 haploinsufficiency in mice with shortened telomeres were concordant with proosteoblast and proinflammatory gene network alterations in human NOTCH1 heterozygous endothelial cells. These dysregulated genes were enriched for telomere-contacting promoters, suggesting a potential mechanism for telomere-dependent regulation of homeostatic gene expression. These findings reveal a critical role for telomere length in a mouse model of age-dependent human disease and provide an in vivo model in which to test therapeutic candidates targeting the progression of aortic valve disease.

Imbalanced expression of Vcan mRNA splice form proteins alters heart morphology and cellular protein profiles

The fundamental importance of the proteoglycan versican to early heart formation was clearly demonstrated by the Vcan null mouse called heart defect (hdf). Total absence of the Vcan gene halts heart development at a stage prior to the heart’s pulmonary/aortic outlet segment growth. This creates a problem for determining the significance of versican’s expression in the forming valve precursors and vascular wall of the pulmonary and aortic roots. This study presents data from a mouse model, Vcan^(tm1Zim), of heart defects that results from deletion of exon 7 in the Vcan gene. Loss of exon 7 prevents expression of two of the four alternative splice forms of the Vcan gene. Mice homozygous for the exon 7 deletion survive into adulthood, however, the inability to express the V2 or V0 forms of versican results in ventricular septal defects, smaller cushions/valve leaflets with diminished myocardialization and altered pulmonary and aortic outflow tracts. We correlate these phenotypic findings with a large-scale differential protein expression profiling to identify compensatory alterations in cardiac protein expression at E13.5 post coitus that result from the absence of Vcan exon 7. The Vcan^(tm1Zim) hearts show significant changes in the relative abundance of several cytoskeletal and muscle contraction proteins including some previously associated with heart disease. These alterations define a protein fingerprint that provides insight to the observed deficiencies in pre-valvular/septal cushion mesenchyme and the stability of the myocardial phenotype required for alignment of the outflow tract with the heart ventricles.

Molecular signatures of cardiac defects in Down syndrome lymphoblastoid cell lines suggest altered ciliome and Hedgehog pathways

Forty percent of people with Down syndrome exhibit heart defects, most often an atrioventricular septal defect (AVSD) and less frequently a ventricular septal defect (VSD) or atrial septal defect (ASD). Lymphoblastoid cell lines (LCLs) were established from lymphocytes of individuals with trisomy 21, the chromosomal abnormality causing Down syndrome. Gene expression profiles generated from DNA microarrays of LCLs from individuals without heart defects (CHD⁻; n = 22) were compared with those of LCLs from patients with cardiac malformations (CHD⁺; n = 21). After quantile normalization, principal component analysis revealed that AVSD carriers could be distinguished from a combined group of ASD or VSD (ASD+VSD) carriers. From 9,758 expressed genes, we identified 889 and 1,016 genes differentially expressed between CHD⁻ and AVSD and CHD⁻ and ASD+VSD, respectively, with only 119 genes in common. A specific chromosomal enrichment was found in each group of affected genes. Among the differentially expressed genes, more than 65% are expressed in human or mouse fetal heart tissues (GEO dataset). Additional LCLs from new groups of AVSD and ASD+VSD patients were analyzed by quantitative PCR; observed expression ratios were similar to microarray results. Analysis of GO categories revealed enrichment of genes from pathways regulating clathrin-mediated endocytosis in patients with AVSD and of genes involved in semaphorin-plexin-driven cardiogenesis and the formation of cytoplasmic microtubules in patients with ASD-VSD. A pathway-oriented search revealed enrichment in the ciliome for both groups and a specific enrichment in Hedgehog and Jak-stat pathways among ASD+VSD patients. These genes or related pathways are therefore potentially involved in normal cardiogenesis as well as in cardiac malformations observed in individuals with trisomy 21.

Dominant-negative ALK2 allele associates with congenital heart defects

BACKGROUND

Serious congenital heart defects occur as a result of improper atrioventricular septum (AVS) development during embryogenesis. Despite extensive knowledge of the genetic control of AVS development, few genetic lesions have been identified that are responsible for AVS-associated congenital heart defects.

METHODS AND RESULTS

We sequenced 32 genes known to be important in AVS development in patients with AVS defects and identified 11 novel coding single-nucleotide polymorphisms that are predicted to impair protein function. We focused on variants identified in the bone morphogenetic protein receptor, ALK2, and subjected 2 identified variants to functional analysis. The coding single-nucleotide polymorphisms R307L and L343P are heterozygous missense substitutions and were each identified in single individuals. The L343P allele had impaired functional activity as measured by in vitro kinase and bone morphogenetic protein-specific transcriptional response assays and dominant-interfering activity in vivo. In vivo analysis of zebrafish embryos injected with ALK2 L343P RNA revealed improper atrioventricular canal formation.

CONCLUSIONS

These data identify the dominant-negative allele ALK2 L343P in a patient with AVS defects.

Auricular catecholamine content in ischaemic heart disease

The noradrenaline (NA) content (mean +/- S.D.) of tissue samples from the right atrial appendage in 19 patients with ischaemic heart disease (IHD) was 2.81 +/- 0.94 microng/g and in 7 patients with valvular heart disease (VHD) 2.79 +/- 1.12 microng/g. In 10 patients with uncomplicated atrial septal defect (ASD) the NA content was 1.64 +/- 0.32 microng/g and in 11 patients with congestive heart failure (CHF) 0.75 +/- 0.41 microng/g. The difference in NA content between the IHD group and the ASD and CHF groups is significant (p is less than 0.001). Small amounts of adrenaline and dopamine were found in all groups. There was no significant correlation between auricular NA content and either systemic diastolic blood pressure. The relatively high level of NA in the IHD group is assumed to be a contributory factor in the intracellular metabolic as well as in the systemic changes typical of ischaemia and infarction.

A critical role for the EphA3 receptor tyrosine kinase in heart development

Eph proteins are receptor tyrosine kinases that control changes in cell shape and migration during development. We now describe a critical role for EphA3 receptor signaling in heart development as revealed by the phenotype of EphA3 null mice. During heart development mesenchymal outgrowths, the atrioventricular endocardial cushions, form in the atrioventricular canal. This morphogenetic event requires endocardial cushion cells to undergo an epithelial to mesenchymal transformation (EMT), and results in the formation of the atrioventricular valves and membranous portions of the atrial and ventricular septa. We show that EphA3 knockouts have significant defects in the development of their atrial septa and atrioventricular endocardial cushions, and that these cardiac abnormalities lead to the death of approximately 75% of homozygous EphA3(-/-) mutants. We demonstrate that EphA3 and its ligand, ephrin-A1, are expressed in adjacent cells in the developing endocardial cushions. We further demonstrate that EphA3(-/-) atrioventricular endocardial cushions are hypoplastic compared to wildtype and that EphA3(-/-) endocardial cushion explants give rise to fewer migrating mesenchymal cells than wildtype explants. Thus our results indicate that EphA3 plays a crucial role in the development and morphogenesis of the cells that give rise to the atrioventricular valves and septa.

Blood Cardioplegia Provides Superior Protection in Infant Cardiac Surgery

BACKGROUND

We hypothesized that blood cardioplegia preserves myocardial metabolism and function more effectively than St Thomas' crystalloid cardioplegia in infant cardiac surgery.

METHODS

Thirty infants with atrioventricular septal defects were randomly allocated to either blood or crystalloid intermittent cold (4 degrees C) cardioplegia. Arterial and coronary sinus blood was analyzed for lactate and oxygen. Cardiac output (thermodilution) and left ventricular function (echocardiography) were evaluated.

RESULTS

The lactate concentration in coronary sinus blood early after bypass was significantly higher after crystalloid cardioplegia than after blood cardioplegia (2.1 +/- 0.3 vs 1.3 +/- 0.1 mmol/L, p = 0.006), with a significant myocardial release of lactate after crystalloid but not after blood cardioplegia. Oxygen extraction (arterial-coronary sinus O2 content) was higher early after crystalloid cardioplegia (3.02 +/- 0.13 vs 2.35 +/- 0.22 mmol/L, p = 0.01), possibly reflecting a difference in oxygen debt. The cardiac index was higher after blood cardioplegia (4.9 +/- 0.3 vs 4.0 +/- 0.3 L/min(-1)/m(-2), p = 0.04) and echocardiographic grading of left ventricular function was better (4.1 +/- 0.17 vs 3.5 +/- 0.22 arbitrary units, p = 0.046).

CONCLUSIONS

This study indicates that blood cardioplegia preserves myocardial metabolism and function more effectively than crystalloid cardioplegia in infant cardiac surgery. The clinical significance of this finding is uncertain, but the more than 20% increase in cardiac index in the critical phase during weaning from bypass may be advantageous.

Metabolites of the L-arginine-NO pathway in patients with left-to-right shunt

OBJECTIVES

The endogenous production of metabolites of the L-arginine-NO pathway has been found to be altered in patients with left-to-right shunt and pulmonary hypertension. The objective of this study was to analyze the influence of age and of the magnitude of the left-to-right shunt on plasma levels of L-arginine, cyclic guanosine monophosphate (cGMP), nitrite and nitrate in children and young adults presenting with left-to-right shunt.

METHODS

Twenty-nine patients with ventricular septal defect (n=18), atrial septal defect (n=6) and atrioventricular canal (n=5) were assigned to group I when the ratio of pulmonary to systemic blood flow (Qp/Qs) was less than 1.5 (n=10) and to group II when Qp/Qs > or = 1.5 (n=19). At cardiac catheterization blood samples were taken from the pulmonary vein or left ventricle. In 33 controls peripheral venous blood was obtained. cGMP levels were determined by radioimmunoassay, L-arginine, nitrite and nitrate by high performance liquid chromatography (HPLC).

RESULTS

L-arginine plasma levels were lower in group II than in controls (51.7 [23.3-82.2] versus 60.5 [32.4-85.9] pmol/l; p < 0.05 by KRUSKAL-WALLIS). Age did not influence the L-arginine plasma levels (p = 0.30). cGMP levels depended on age (p<0.01) and mean pulmonary artery pressure (p <0.01) but not on high pulmonary blood flow (p=0.85; ANOVA). Plasma nitrite and nitrate were not different in both groups and when compared with controls (nitrite: 26.0 [23.5-31.0] micromol/l; nitrate: 26.8 [24.0-32.0] micromol/l).

CONCLUSIONS

Age and pulmonary artery pressure exert important effects on plasma cGMP. Measurement of nitrite and nitrate in plasma alone may not reflect the endogenous NO production. Future studies should evaluate the role of plasma levels of L-arginine in patients with high pulmonary blood flow undergoing repair of their defect.

Morphine pharmacokinetics in children following cardiac surgery: effects of disease and inotropic support

The pharmacokinetics of morphine have not been previously studied in children following cardiac surgery for tetralogy of Fallot (TOF) or transposition of the great arteries (TGA). Morphine steady-state pharmacokinetics were studied in 21 children undergoing repair of TOF, TGA, or atrio-ventricular septal defects (AVSD). Children with TOF or TGA had increased right-sided pressures with no differences between the groups. Children with TOF had significantly faster clearance rates of morphine (1.39 +/- 0.37 L/kg/h) than children following the Fontan procedure (0.86 +/- 0.31 L/kg/h, P < 0.01). When stratifying children by their postsurgical needs for inotropic support, those needing epinephrine, dopamine, or dobutamine at more than 10 micrograms/kg/min had significantly slower clearance rates (0.73 +/- 0.3 L/kg/h) when compared to the rest of the patients (1.5 +/- 0.41 L/kg/h, P < 0.05). Because most children needing inotropic support underwent the Fontan procedure, it is conceivable that their cardiovascular status had a major impact on morphine metabolism. These results suggest a 50% reduction in morphine dosage in children requiring inotropic support following cardiac surgery.

Serum protein of 135-kDa molecular weight--a molecular signal for cardiac hypertrophy

A serum protein, similar to the 135-kDa protein which appears during experimentally induced cardiac hypertrophy in rats, was identified in human serum by Western blot analysis using anti-rat 135-kDa protein antibody. The rat protein antibody gave a very strong positive signal when reacted with sera obtained from cardiac patients, suggesting an induced level of this protein in patients' sera when compared to normal sera from healthy individuals. Multiple injections of polyclonal anti-rat 135-kDa protein antibody to aorta-constricted animals completely inhibited the development of cardiac hypertrophy, suggesting that this protein could be hypertrophy specific. This was further substantiated by the decrease in the expression of a molecular marker such as the beta myosin heavy chain gene in aorta-constricted but antibody-injected animals. Further, the presence of high levels of this protein in first- and third-day neonatal animals is also suggestive of the hypertrophy-specific nature of this protein as the heart is subjected to high pressure overload immediately after birth.

[Myocardial catecholamine levels in patients with congenital and acquired heart defects]

Catecholamine levels were determined in the myocardial slices from 66 patients with congenital and acquired heart diseases by the trihydroxyindole++ method on a Lumilan fluorescence spectrophotometer. The patients were found to have greatly varying epinephrine and norepinephrine levels. The accumulation of catecholamine reflected, to a certain extent, the occurrence of disorders in relation to the functional load, hyperfunctions of the myocardium. Blood hypoxemia and myocardial hypoxia affected the status of the patients.

The influence of a right-to-left cardiac shunt on lidocaine pharmacokinetics

The pharmacokinetics of lidocaine were studied in 1-2-month-old lambs with surgically created, intracardiac right-to-left shunts (RLS) and in age-matched control lambs. Shunts were prepared by anastomosing the pulmonary artery to the left atrial appendage to achieve arterial oxygen saturation of 65-75%. Catheters were implanted both in the right atrium for drug infusion and in the ascending aorta for blood sampling. Lidocaine, 1 mg/kg, injected as a rapid bolus, or 12 mg/kg, injected as a continuous infusion over 15 min, was delivered into the right atrium. Serial samples of arterial blood were obtained every 2.5 s for 1 min following the bolus injection and up to 4 h following the continuous infusion. Samples were analyzed for lidocaine by gas chromatography. Peak arterial whole blood concentration of lidocaine in the shunted animals was 37.0 +/- 2.1 micrograms/ml compared to 21.1 +/- 0.1 microgram/ml in the control animals; P less than .01. The peak arterial concentrations during the lidocaine infusion were 12.6 +/- 3.5 micrograms/ml in the RLS and 5.8 +/- 1.5 micrograms/ml in the controls. Total body clearance of lidocaine was decreased in the shunted animals to 30.7 +/- 13.2 ml.kg-1.min-1 from 68.1 +/- 12.1 ml.kg-1.min-1 in the control animals; P less than .001. The steady-state volume of distribution was also decreased in the shunted animals, 1.0 +/- 0.2 l/kg versus 2.0 +/- 0.7 l/kg in the controls; P less than .02. To induce convulsions 4.75 +/- 0.46 mg/kg of lidocaine was required in the shunted animals and 7.37 +/- 0.44 mg/kg in the control animals (P less than .001).(ABSTRACT TRUNCATED AT 250 WORDS)

[Oxygen consumption in infants and children with congenital heart defects]

Resting oxygen uptake was determined by a diaferometer in 90 children with congenital heart disease and in 39 children without cardiac defects, both groups ranging in age from 1 month to 15 years. The children with cardiac defects were classified according to the kind of the defect. The values of all children were related to body surface area and in every case compared with standards of basal metabolic rate of Karlberg and Fleisch. Although there was a tendency to higher values of resting oxygen uptake in children with cardiac defects, a statistically definite difference to the standard values could not be established. The possibly influencing factors of oxygen uptake in children with cardiac defects, as weight reduction, sedation, heart dynamics and oxygen cost of breathing are discussed regarding the literature.