J. Cardiovasc. Dev. Dis.2014, 1(3), 237-256; doi:10.3390/jcdd1030237 - published 1 December 2014 Show/Hide Abstract
Abstract: Aortic valve disease is a burgeoning public health problem associated with significant mortality. Loss of function mutations in NOTCH1 cause bicuspid aortic valve (BAV) and calcific aortic valve disease. Because calcific nodules manifest on the fibrosa side of the cusp in low fluidic oscillatory shear stress (OSS), elucidating pathogenesis requires approaches that consider both molecular and mechanical factors. Therefore, we examined the relationship between NOTCH loss of function (LOF) and biomechanical indices in healthy and diseased human aortic valve interstitial cells (AVICs). An orbital shaker system was used to apply cyclic OSS, which mimics the cardiac cycle and hemodynamics experienced by AVICs in vivo. NOTCH LOF blocked OSS-induced cell alignment in human umbilical vein endothelial cells (HUVECs), whereas AVICs did not align when subjected to OSS under any conditions. In healthy AVICs, OSS resulted in decreased elastin (ELN) and α-SMA (ACTA2). NOTCH LOF was associated with similar changes, but in diseased AVICs, NOTCH LOF combined with OSS was associated with increased α-SMA expression. Interestingly, AVICs showed relatively higher expression of NOTCH2 compared to NOTCH1. Biomechanical interactions between endothelial and interstitial cells involve complex NOTCH signaling that contributes to matrix homeostasis in health and disorganization in disease.
J. Cardiovasc. Dev. Dis.2014, 1(3), 214-236; doi:10.3390/jcdd1030214 - published 20 November 2014 Show/Hide Abstract
Abstract: The initial heart is composed of a myocardial tube lined by endocardial cells. The TGFβ superfamily is known to play an important role, as BMPs from the myocardium signal to the overlying endocardium to create an environment for EMT. Subsequently, BMP and TGFβ signaling pathways synergize to form primitive valves and regulate myocardial growth. In this study, we investigated the requirement of BMP activity by transgenic over-expression of extracellular BMP antagonist Noggin. Using Nfatc1Cre to drive lineage-restricted Noggin within the endocardium, we show that ectopic Noggin arrests cardiac development in E10.5-11 embryos, resulting in small hearts which beat poorly and die by E12.5. This is coupled with hypoplastic endocardial cushions, reduced trabeculation and fewer mature contractile fibrils in mutant hearts. Moreover, Nfatc1Cre-mediated diphtheria toxin fragment-A expression in the endocardium resulted in genetic ablation and a more severe phenotype with lethality at E11 and abnormal linear hearts. Molecular analysis demonstrated that endocardial Noggin resulted in a specific alteration of TGFβ/BMP-mediated signal transduction, in that, both Endoglin and ALK1 were downregulated in mutant endocardium. Combined, these results demonstrate the cell-autonomous requirement of the endocardial lineage and function of unaltered BMP levels in facilitating endothelium-cardiomyocyte cross-talk and promoting endocardial cushion formation.
J. Cardiovasc. Dev. Dis.2014, 1(3), 201-213; doi:10.3390/jcdd1030201 - published 10 October 2014 Show/Hide Abstract
Abstract: Despite gaining focus, cardiovascular disease (CVD) remains the leading cause of death worldwide. Health promotion agencies have traditionally recommended diets that are low in fat in order to reduce CVD risk however, much debate remains about which dietary approaches are the most efficient for effective disease prevention. Common markers of CVD include elevated plasma triglycerides (TG) and low-density lipoprotein (LDL) cholesterol levels, as well as reduced high-density lipoprotein (HDL) cholesterol levels. While weight loss alone can significantly reduce markers of CVD, manipulating dietary macronutrient content contributes to the beneficial effects of weight loss and furthers the improvement of lipid profiles even without the alteration of total caloric intake. Considering the recent attention to diets that are low in carbohydrates rather than fat, it remains to be elucidated the beneficial effects of each diet type when establishing new recommendations for CVD prevention. This review aims to examine the effects of different macronutrient compositions on lipid markers, thus providing insight into the potential roles of various diet types in the targeted prevention against CVD.
J. Cardiovasc. Dev. Dis.2014, 1(3), 177-200; doi:10.3390/jcdd1030177 - published 30 September 2014 Show/Hide Abstract
Abstract: There is considerable confusion as to how best describe the components of the arterial valves. It is hardly surprising, therefore, that similar uncertainties apply to concepts for their development. In this review, we describe the anatomy of the arterial valves as seen in the postnatal heart. We suggest that their working components are best described as leaflets, housed in supporting arterial sinuses. The roots surrounding the leaflets, which are hinged in semilunar fashion, can then be defined as extending from a virtual ring at their base to the sinutubular junction. We also discuss the problems related to definition of the valvar “annulus”. Understanding the development of the arterial roots, which are formed in the central part of the embryonic outflow tract, is facilitated by considering the outflow tract itself as possessing three components, as opposed to the traditional “conus” and “truncus”. These three parts can be described as being distal, intermediate, and proximal. The distal part is separated to form the intrapericardial arterial trunks, while the proximal part becomes the ventricular outflow tracts. It is the intermediate component that houses the developing arterial valves, and their supporting valvar sinuses. The distal parts of the cushions that separate the outflow tract into aortic and pulmonary components, along with the intercalated cushions, excavate to form the leaflets. The walls of the sinuses are formed by growth of non-myocardial tissues from the heart-forming area. We then show how these features can be used to interpret the anatomy and development of congenitally malformed arterial valves.
J. Cardiovasc. Dev. Dis.2014, 1(2), 163-176; doi:10.3390/jcdd1020163 - published 23 September 2014 Show/Hide Abstract
Abstract: Heart valves are complex structures composed of a heterogeneous population of valve interstitial cells (VICs), an overlying endothelium and highly organized layers of extracellular matrix. Alterations in valve homeostasis are characteristic of dysfunction and disease, however the mechanisms that initiate and promote valve pathology are poorly understood. Advancements have been largely hindered by the limited availability of tools for gene targeting in heart valve structures during embryogenesis and after birth. We have previously shown that the transcription factors Sox9 and Scleraxis (Scx) are required for heart valve formation and in this study we describe the recombination patterns of Sox9- and Scx-Cre lines at differential time points in aortic and mitral valve structures. In ScxCre; ROSA26GFP mice, recombination is undetected in valve endothelial cells (VECs) and low in VICs during embryogenesis. However, recombination increases in VICs from post natal stages and by 4 weeks side-specific patterns are observed. Using the inducible Sox9CreERT2 system, we observe recombination in VECs and VICs in the embryo, and high levels are maintained through post natal and juvenile stages. These Cre-drivers provide the field with new tools for gene targeting in valve cell lineages during differential stages of embryonic and post natal maturation and maintenance.
J. Cardiovasc. Dev. Dis.2014, 1(2), 146-162; doi:10.3390/jcdd1020146 - published 26 August 2014 Show/Hide Abstract
Abstract: There is continued debate regarding the appropriate cell type to replace valvular interstitial cells (VICs) in tissue engineered heart valves (TEHVs), particularly for pediatric patients. In this work, neonatal human dermal fibroblasts (nhDFFs) were compared to human pediatric VICs (hpVICs), based on their phenotypic and gene expression characteristics when cultured on collagen type I, fibronectin, fibrin, and tissue culture polystyrene (TCP) substrates. Similar confluency was achieved over the culture period on collagen and fibronectin between both cell types, although nhDFFs tended to reach lower confluence on collagen than on any other substrate. Morphologically, hpVICs tended to spread and form multiple extensions, while nhDFFs remained homogenously spindle-shaped on all substrates. PCR results indicated that fibroblasts did not differ significantly from VICs in gene expression when cultured on fibrin, whereas on collagen type I and fibronectin they showed increased α-SMA, xylosyltransferase I, and collagen type I expression (p < 0.05). However, protein expression of these targets, analyzed by immunocytochemistry and Western blotting, was not significantly different between cell types. These results suggest that nhDFFs express similar matrix production and remodeling genes as hpVICs, and the choice of substrate for TEHV construction can affect the growth and expression profile of nhDFFs as compared to native hpVICs.