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author:("Garg, idu")
1.  Endothelial nitric oxide signaling regulates Notch1 in aortic valve disease 
The mature aortic valve is composed of a structured trilaminar extracellular matrix that is interspersed with aortic valve interstitial cells (AVICs) and covered by endothelium. Dysfunction of the valvular endothelium initiates calcification of neighboring AVICs leading to calcific aortic valve disease (CAVD). The molecular mechanism by which endothelial cells communicate with AVICs and cause disease is not well understood. Using a co-culture assay, we show that endothelial cells secrete a signal to inhibit calcification of AVICs. Gain or loss of nitric oxide (NO) prevents or accelerates calcification of AVICs, respectively, suggesting that the endothelial cell-derived signal is NO. Overexpression of Notch1, which is genetically linked to human CAVD, retards the calcification of AVICs that occurs with NO inhibition. In AVICs, NO regulates the expression of Hey1, a downstream target of Notch1, and alters nuclear localization of Notch1 intracellular domain. Finally, Notch1 and NOS3 (endothelial NO synthase) display an in vivo genetic interaction critical for proper valve morphogenesis and the development of aortic valve disease. Our data suggests that endothelial cell-derived NO is a regulator of Notch1 signaling in AVICs in the development of the aortic valve and adult aortic valve disease.
doi:10.1016/j.yjmcc.2013.04.001
PMCID: PMC4058883  PMID: 23583836
3.  Impact of Mendelian Inheritance in Cardiovascular Disease 
Cardiovascular disease is a leading cause of mortality worldwide. While the etiology for the majority of cardiovascular disease is presumed to be a combination of genetic and environmental factors, developments in our understanding of the basic biology of cardiac disorders have been greatly advanced through discoveries made studying heart diseases that exhibit Mendelian forms of inheritance. Most of these diseases primarily affect children and young adults and include cardiomyopathies, arrhythmias, aortic aneurysms and congenital heart defects. The discovery of the genetic etiologies for these diseases have had significant impact on our understanding of more complex forms of cardiovascular disease and in some cases led to novel diagnostic and treatment modalities. In this review, we will summarize these seminal genetic discoveries, highlighting a few that have resulted in significant impact on human disease, and discuss the potential utility of studying Mendelian-inherited heart disease with the development of new genetic technologies and our increased understanding of the human genome.
doi:10.1111/j.1749-6632.2010.05791.x
PMCID: PMC3489013  PMID: 20958326
4.  Congenital Heart Disease–Causing Gata4 Mutation Displays Functional Deficits In Vivo 
PLoS Genetics  2012;8(5):e1002690.
Defects of atrial and ventricular septation are the most frequent form of congenital heart disease, accounting for almost 50% of all cases. We previously reported that a heterozygous G296S missense mutation of GATA4 caused atrial and ventricular septal defects and pulmonary valve stenosis in humans. GATA4 encodes a cardiac transcription factor, and when deleted in mice it results in cardiac bifida and lethality by embryonic day (E)9.5. In vitro, the mutant GATA4 protein has a reduced DNA binding affinity and transcriptional activity and abolishes a physical interaction with TBX5, a transcription factor critical for normal heart formation. To characterize the mutation in vivo, we generated mice harboring the same mutation, Gata4 G295S. Mice homozygous for the Gata4 G295S mutant allele have normal ventral body patterning and heart looping, but have a thin ventricular myocardium, single ventricular chamber, and lethality by E11.5. While heterozygous Gata4 G295S mutant mice are viable, a subset of these mice have semilunar valve stenosis and small defects of the atrial septum. Gene expression studies of homozygous mutant mice suggest the G295S protein can sufficiently activate downstream targets of Gata4 in the endoderm but not in the developing heart. Cardiomyocyte proliferation deficits and decreased cardiac expression of CCND2, a member of the cyclin family and a direct target of Gata4, were found in embryos both homozygous and heterozygous for the Gata4 G295S allele. To further define functions of the Gata4 G295S mutation in vivo, compound mutant mice were generated in which specific cell lineages harbored both the Gata4 G295S mutant and Gata4 null alleles. Examination of these mice demonstrated that the Gata4 G295S protein has functional deficits in early myocardial development. In summary, the Gata4 G295S mutation functions as a hypomorph in vivo and leads to defects in cardiomyocyte proliferation during embryogenesis, which may contribute to the development of congenital heart defects in humans.
Author Summary
Cardiac malformations occur due to abnormal heart development and are the most prevalent human birth defect. Defects of atrial and ventricular septation are the most common type of congenital heart defect and are the result of incomplete closure of the atrial and ventricular septa, a process required for formation of a four-chambered heart. The molecular mechanisms that underlie atrial and ventricular septal defects are unknown. We previously published a highly penetrant autosomal dominant mutation (G296S) in GATA4, which was associated with atrial and ventricular septal defects in a large kindred. The disease-causing mutation has a spectrum of biochemical deficits affecting both DNA binding and protein–protein interactions. Here, we report the generation and phenotypic characterization of mice harboring the orthologous mutation in Gata4 (G295S). While homozygous mutant mice display embryonic lethality and cardiac defects, the phenotype is less severe than Gata4-null mice. A subset of Gata4 G295S heterozygote mice display a persistent interatrial communication (patent foramen ovale) and stenosis of the semilunar valves. Molecular characterization of the mutant mice suggests that the Gata4 G295S mutant protein results in diminished expression of Gata4 target genes in the heart and functional deficits in cardiomyocyte proliferation. Thus, cardiomyocyte proliferation defects may contribute to defects of cardiac septation found in humans with GATA4 mutations.
doi:10.1371/journal.pgen.1002690
PMCID: PMC3349729  PMID: 22589735
5.  Inhibitory Role of Notch1 in Calcific Aortic Valve Disease 
PLoS ONE  2011;6(11):e27743.
Aortic valve calcification is the most common form of valvular heart disease, but the mechanisms of calcific aortic valve disease (CAVD) are unknown. NOTCH1 mutations are associated with aortic valve malformations and adult-onset calcification in families with inherited disease. The Notch signaling pathway is critical for multiple cell differentiation processes, but its role in the development of CAVD is not well understood. The aim of this study was to investigate the molecular changes that occur with inhibition of Notch signaling in the aortic valve. Notch signaling pathway members are expressed in adult aortic valve cusps, and examination of diseased human aortic valves revealed decreased expression of NOTCH1 in areas of calcium deposition. To identify downstream mediators of Notch1, we examined gene expression changes that occur with chemical inhibition of Notch signaling in rat aortic valve interstitial cells (AVICs). We found significant downregulation of Sox9 along with several cartilage-specific genes that were direct targets of the transcription factor, Sox9. Loss of Sox9 expression has been published to be associated with aortic valve calcification. Utilizing an in vitro porcine aortic valve calcification model system, inhibition of Notch activity resulted in accelerated calcification while stimulation of Notch signaling attenuated the calcific process. Finally, the addition of Sox9 was able to prevent the calcification of porcine AVICs that occurs with Notch inhibition. In conclusion, loss of Notch signaling contributes to aortic valve calcification via a Sox9-dependent mechanism.
doi:10.1371/journal.pone.0027743
PMCID: PMC3218038  PMID: 22110751
6.  Identification of GATA6 sequence variants in patients with congenital heart defects 
Pediatric research  2010;68(4):281-285.
While the etiology for the majority of congenital heart disease (CHD) remains poorly understood, the known genetic causes are often the result of mutations in cardiac developmental genes. GATA6 encodes for a cardiac transcription factor, which is broadly expressed in the developing heart and is critical for normal cardiac morphogenesis, making it a candidate gene for congenital heart defects in humans. The objective of this study was to determine the frequency of GATA6 sequence variants in a population of individuals with a spectrum of cardiac malformations. The coding regions of GATA6 were sequenced in 310 individuals with CHD. We identified two novel sequence variations in GATA6 that altered highly conserved amino acid residues (A178V and L198V) and were not found in a control population. These variants were identified in two individuals (one with tetralogy of Fallot and the other with an atrioventricular septal defect in the setting of complex CHD). Biochemical studies demonstrate that the GATA6 A178V mutant protein results in increased transactivation ability when compared to wildtype GATA6. These data suggest that non-synonymous GATA6 sequence variants are infrequently found in individuals with CHD.
doi:10.1203/PDR.0b013e3181ed17e4
PMCID: PMC2940936  PMID: 20581743
7.  Genetics of Congenital Heart Disease 
Current Cardiology Reviews  2010;6(2):91-97.
Cardiovascular malformations are the most common type of birth defect and result in significant mortality worldwide. The etiology for the majority of these anomalies remains unknown but genetic factors are being recognized as playing an increasingly important role. Advances in our molecular understanding of normal heart development have led to the identification of numerous genes necessary for cardiac morphogenesis. This work has aided the discovery of an increasing number of monogenic causes of human cardiovascular malformations. More recently, studies have identified single nucleotide polymorphisms and submicroscopic copy number abnormalities as having a role in the pathogenesis of congenital heart disease. This review discusses these discoveries and summarizes our increasing understanding of the genetic basis of congenital heart disease.
doi:10.2174/157340310791162703
PMCID: PMC2892081  PMID: 21532774
Congenital heart disease; genetics; cardiac development.
8.  A novel mutation in LAMIN A/C is associated with isolated early-onset atrial fibrillation and progressive atrioventricular block followed by cardiomyopathy and sudden cardiac death 
doi:10.1016/j.hrthm.2009.01.037
PMCID: PMC2701154  PMID: 19328042
Lamin A/C; genetics; atrial fibrillation; atrioventricular block; dilated cardiomyopathy; sudden cardiac death
9.  Interaction of Gata4 and Gata6 with Tbx5 is critical for normal cardiac development 
Developmental biology  2008;326(2):368-377.
Congenital heart disease is the most common type of birth defect with an incidence of 1%. Previously, we described a point mutation in GATA4 that segregated with cardiac defects in a family with autosomal dominant disease. The mutation (G296S) exhibited biochemical deficits and disrupted a novel interaction between Gata4 and Tbx5. To determine if Gata4 and Tbx5 genetically interact in vivo, we generated mice heterozygous for both alleles. We found that nearly 100% of mice heterozygous for Gata4 and Tbx5 were embryonic or neonatal lethal and had complete atrioventricular (AV) septal defects with a single AV valve and myocardial thinning. Consistent with this phenotype, Gata4 and Tbx5 are co-expressed in the developing endocardial cushions and myocardium. In mutant embryos, cardiomyocyte proliferation deficits were identified compatible with the myocardial hypoplasia. Similar to Gata4, Gata6 and Tbx5 are co-expressed in the embryonic heart, and the transcription factors synergistically activate the atrial natiuretic factor promoter. We demonstrate a genetic interaction between Gata6 and Tbx5 with an incompletely penetrant phenotype of neonatal lethality and thin myocardium. Gene expression analyses were performed on both sets of compound heterozygotes and demonstrated downregulation of α-myosin heavy chain only in Gata4/Tbx5 heterozygotes. These findings highlight the unique genetic interactions of Gata4 and Gata6 with Tbx5 for normal cardiac morphogenesis in vivo.
doi:10.1016/j.ydbio.2008.11.004
PMCID: PMC2651674  PMID: 19084512
cardiac development; congenital heart defects; Gata4; Gata6; Tbx5; transcription factor
10.  Spectrum of Heart Disease Associated with Murine and Human GATA4 Mutation 
The transcription factor GATA4 is essential for heart morphogenesis. Heterozygous mutation of GATA4 causes familial septal defects. However, the phenotypic spectrum of heterozygous GATA4 mutation is not known. In this study, we defined the cardiac phenotypes that result from heterozygous mutation of murine Gata4. We then asked if GATA4 mutation occurs in humans with these forms of congenital heart disease (CHD). In mice, heterozygous Gata4 mutation was associated with atrial and ventricular septal defect (ASD, VSD), endocardial cushion defect (ECD), RV hypoplasia, and cardiomyopathy. Genetic background strongly influenced the expression of ECD and cardiomyopathy, indicating the presence of important genetic modifiers. In humans, non-synonymous GATA4 sequence variants were associated with ECD (2/43), ASD (1/8), and RV hypoplasia in the context of double inlet left ventricle (1/9), forms of CHD that overlapped with abnormalities seen in the mouse model. These variants were not found in at least 500 control chromosomes, and encode proteins with non-conservative amino acid substitutions at phylogenetically conserved positions, suggesting that they are disease-causing mutations. Cardiomyopathy was not associated with GATA4 mutation in humans. These data establish the phenotypic spectrum of heterozygous Gata4 mutation in mice, and suggest that heterozygous GATA4 mutation leads to partially overlapping phenotypes in humans. Additional studies will be required to determine the degree to which GATA4 mutation contributes to human CHD characterized by ECD or RV hypoplasia.
doi:10.1016/j.yjmcc.2007.06.004
PMCID: PMC2573470  PMID: 17643447
animal models; congenital heart defects; cardiac development; genetics ofcongenital heart disease

Results 1-10 (10)