The genetics of cardiovascular disease: new insights from emerging approaches

Recent Advances in the Critical Role of the Sterol Efflux Transporters ABCG5/G8 in Health and Disease

Cardiovascular disease is characterized by lipid accumulation, inflammatory response, cell death, and fibrosis in the arterial wall and is the leading cause of morbidity and mortality worldwide. Cholesterol gallstone disease is caused by complex genetic and environmental factors and is one of the most prevalent and costly digestive diseases in the USA and Europe. Although sitosterolemia is a rare inherited lipid storage disease, its genetic studies led to identification of the sterol efflux transporters ABCG5/G8 that are located on chromosome 2p21 in humans and chromosome 17 in mice. Human and animal studies have clearly demonstrated that ABCG5/G8 play a critical role in regulating hepatic secretion and intestinal absorption of cholesterol and plant sterols. Sitosterolemia is caused by a mutation in either the ABCG5 or the ABCG8 gene alone, but not in both simultaneously. Polymorphisms in the ABCG5/G8 genes are associated with abnormal plasma cholesterol metabolism and may play a key role in the genetic determination of plasma cholesterol concentrations. Moreover, ABCG5/G8 is a new gallstone gene, LITH9. Gallstone-associated variants in ABCG5/G8 are involved in the pathogenesis of cholesterol gallstones in European, Asian, and South American populations. In this chapter, we summarize the latest advances in the critical role of the sterol efflux transporters ABCG5/G8 in regulating hepatic secretion of biliary cholesterol, intestinal absorption of cholesterol and plant sterols, the classical reverse cholesterol transport, and the newly established transintestinal cholesterol excretion, as well as in the pathogenesis and pathophysiology of ABCG5/G8-related metabolic diseases such as sitosterolemia, cardiovascular disease, and cholesterol gallstone disease.

Differential expression of miRNA in rat myocardial tissues under psychological and physical stress

In the current study, microRNA (miRNA) microarrays were used to detect differentially expressed miRNAs in the myocardial tissues of rat models under stress, to screen target miRNA candidates for miRNA therapy of stress-induced myocardial injury. Rats were bound and suspended in order to induce acute stress (AS) and chronic stress (CS) models. miRNA microarrays were used to detect differentially expressed miRNA in the myocardial tissues of the stressed and control groups. In comparison to the normal control, there were 68 differentially expressed miRNAs in the AS model, of which 32 were upregulated and 36 were downregulated. There were 55 differentially expressed miRNAs in the CS model, of which 20 were upregulated and 35 were downregulated. Of the 123 miRNAs, 15 miRNAs were differentially expressed between the AS and CS groups, of which four were significantly upregulated (rno-miR-296, rno-miR-141, rno-miR-382 and rno-miR-219-5p) and 11 were downregulated (significantly downregulated, rno-miR-135a and rno-miR-466b). The stress of being bound and suspended induces myocardial injury in the rats. Myocardial injury may cause the differential expression of certain miRNAs. Psychological stress may lead to the significant upregulation of rno-miR-296, rno-miR-141, rno-miR-382 and rno-miR-219-5p in addition to the significant downregulation of miR-135a and miR-466b.

Post-transcriptional stimulation of gene expression by microRNAs

MicroRNAs are small noncoding RNA regulatory molecules that control gene expression by guiding associated effector complexes to other RNAs via sequence-specific recognition of target sites. Misregulation of microRNAs leads to a wide range of diseases including cancers, inflammatory and developmental disorders. MicroRNAs were found to mediate deadenylation-dependent decay and translational repression of messages through partially complementary microRNA target sites in the 3'-UTR (untranslated region). A growing series of studies has demonstrated that microRNAs and their associated complexes (microRNPs) elicit alternate functions that enable stimulation of gene expression in addition to their assigned repressive roles. These reports, discussed in this chapter, indicate that microRNA-mediated effects via natural 3' and 5'-UTRs can be selective and controlled, dictated by the RNA sequence context, associated complex, and cellular conditions. Similar to the effects of repression, upregulated gene expression by microRNAs varies from small refinements to significant amplifications in expression. An emerging theme from this literature is that microRNAs have a versatile range of abilities to manipulate post-transcriptional control mechanisms leading to controlled gene expression. These studies reveal new potentials for microRNPs in gene expression control that develop as responses to specific cellular conditions.

MicroRNAs as potential biomarkers of smoking-related diseases

MicroRNAs (miRNAs) comprise a family of small, endogenous, noncoding functional RNA molecules that have emerged as key post-transcriptional regulators of gene expression. They inhibit the translation of proteins from mRNA or promote its degradation. Aberrant miRNA expression has been linked to various human diseases and measurement can differentiate between normal and diseased tissue. Expression is tissue-specific and any changes in miRNA expression within a tissue type can be correlated with disease status. Altered miRNA expression has been reported in the smoking-related diseases cancer, chronic obstructive pulmonary disease and cardiovascular disease. Additionally, miRNAs are thought to have vital roles in inflammatory cell differentiation and regulation. miRNAs might, therefore, be useful biomarkers for early detection of disease-related molecular and genetic changes. In this review, we summarize the available scientific evidence for the potential of miRNAs as biomarkers of smoking-related diseases. Studies should be carried out to identify the miRNAs most relevant to specific diseases.

Cardiovascular genomics: a biomarker identification pipeline

Genomic biomarkers are essential for understanding the underlying molecular basis of human diseases such as cardiovascular disease. In this review, we describe a biomarker identification pipeline for cardiovascular disease, which includes 1) high-throughput genomic data acquisition, 2) preprocessing and normalization of data, 3) exploratory analysis, 4) feature selection, 5) classification, and 6) interpretation and validation of candidate biomarkers. We review each step in the pipeline, presenting current and widely used bioinformatics methods. Furthermore, we analyze several publicly available cardiovascular genomics datasets to illustrate the pipeline. Finally, we summarize the current challenges and opportunities for further research.

The Use of High-Throughput Technologies to Investigate Vascular Inflammation and Atherosclerosis

The greatest challenge of scientific research is to understand the causes and consequences of disease. In recent years, great efforts have been devoted to unraveling the basic mechanisms of atherosclerosis (the underlying pathology of cardiovascular disease), which remains a major cause of morbidity and mortality worldwide. Because of the complex and multifactorial pathophysiology of cardiovascular disease, different research techniques have increasingly been combined to unravel genetic aspects, molecular pathways, and cellular functions involved in atherogenesis, vascular inflammation, and dyslipidemia to gain a multifaceted picture addressing this complexity. Thanks to the rapid evolution of high-throughput technologies, we are now able to generate large-scale data on the DNA, RNA, and protein levels. With the help of sophisticated computational tools, these data sets are integrated to enhance information extraction and are being increasingly used in a systems biology approach to model biological processes as interconnected and regulated networks. This review exemplifies the use of high-throughput technologies—such as genomics, transcriptomics, proteomics, and epigenomics—and systems biology to explore pathomechanisms of vascular inflammation and atherosclerosis.

Zebrafish for the study of the biological effects of nicotine

INTRODUCTION

Zebrafish are emerging as a powerful animal model for studying the molecular and physiological effects of nicotine exposure. The zebrafish have many advantageous physical characteristics, including small size, high fecundity rates, and externally developing transparent embryos. When combined with a battery of molecular-genetic tools and behavioral assays, these attributes enable studies to be conducted that are not practical using traditional animal models.

METHODS

We reviewed the literature on the application of the zebrafish model as a preclinical model to study the biological effects of nicotine exposure.

RESULTS

The identified studies used zebrafish to examine the effects of nicotine exposure on early development, addiction, anxiety, and learning. The methods used included green fluorescent protein-labeled proteins to track in vivo nicotine-altered neuron development, nicotine-conditioned place preference, and locomotive sensitization linked with high-throughput molecular and genetic screens and behavioral models of learning and stress response to nicotine. Data are presented on the complete homology of all known human neural nicotinic acetylcholine receptors in zebrafish and on the biological similarity of human and zebrafish dopaminergic signaling.

CONCLUSIONS

Tobacco dependence remains a major health problem worldwide. Further understanding of the molecular effects of nicotine exposure and genetic contributions to dependence may lead to improvement in patient treatment strategies. While there are limitations to the use of zebrafish as a preclinical model, it should provide a valuable tool to complement existing model systems. The reviewed studies demonstrate the enormous opportunity zebrafish have to advance the science of nicotine and tobacco research.

Dissection of cardiovascular development and disease pathways in zebrafish

The use of animal models in medicine has contributed significantly to the development of drug treatments and surgical procedures for the last century, in particular for cardiovascular disease. In order to model human disease in an animal, an appreciation of the strengths and limitations of the system are required to interpret results and design the logical sequence of steps toward clinical translation. As the world's population ages, cardiovascular disease will become even more prominent and further progress will be essential to stave off what seems destined to become a massive public health issue. Future treatments will require the imaginative application of current models as well as the generation of new ones. In this review, we discuss the resources available for modeling cardiovascular disease in zebrafish and the varied attributes of this system. We then discuss current zebrafish disease models and their potential that has yet to be exploited.

Calcium handling in zebrafish ventricular myocytes

The zebrafish is an important model for the study of vertebrate cardiac development with a rich array of genetic mutations and biological reagents for functional interrogation. The similarity of the zebrafish (Danio rerio) cardiac action potential with that of humans further enhances the relevance of this model. In spite of this, little is known about excitation-contraction coupling in the zebrafish heart. To address this issue, adult zebrafish cardiomyocytes were isolated by enzymatic perfusion of the cannulated ventricle and were subjected to amphotericin-perforated patch-clamp technique, confocal calcium imaging, and/or measurements of cell shortening. Simultaneous recordings of the voltage dependence of the L-type calcium current (I(Ca,L)) amplitude and cell shortening showed a typical bell-shaped current-voltage (I-V) relationship for I(Ca,L) with a maximum at +10 mV, whereas calcium transients and cell shortening showed a monophasic increase with membrane depolarization that reached a plateau at membrane potentials above +20 mV. Values of I(Ca,L) were 53, 100, and 17% of maximum at -20, +10, and +40 mV, while the corresponding calcium transient amplitudes were 64, 92, and 98% and cell shortening values were 62, 95, and 96% of maximum, respectively, suggesting that I(Ca,L) is the major contributor to the activation of contraction at voltages below +10 mV, whereas the contribution of reverse-mode Na/Ca exchange becomes increasingly more important at membrane potentials above +10 mV. Comparison of the recovery of I(Ca,L) from acute and steady-state inactivation showed that reduction of I(Ca,L) upon elevation of the stimulation frequency is primarily due to calcium-dependent I(Ca,L) inactivation. In conclusion, we demonstrate that a large yield of healthy atrial and ventricular myocytes can be obtained by enzymatic perfusion of the cannulated zebrafish heart. Moreover, zebrafish ventricular myocytes differed from that of large mammals by having larger I(Ca,L) density and a monophasically increasing contraction-voltage relationship, suggesting that caution should be taken upon extrapolation of the functional impact of mutations on calcium handling and contraction in zebrafish cardiomyocytes.

Genetic, epigenetic, and gene-by-diet interaction effects underlie variation in serum lipids in a LG/JxSM/J murine model

Variation in serum cholesterol, free-fatty acids, and triglycerides is associated with cardiovascular disease (CVD) risk factors. There is great interest in characterizing the underlying genetic architecture of these risk factors, because they vary greatly within and among human populations and between the sexes. We present results of a genome-wide scan for quantitative trait loci (QTL) affecting serum cholesterol, free-fatty acids, and triglycerides in an F(16) advanced intercross line of LG/J and SM/J (Wustl:LG,SM-G16). Half of the population was fed a high-fat diet and half was fed a relatively low-fat diet. Context-dependent genetic (additive and dominance) and epigenetic (imprinting) effects were characterized by partitioning animals into sex, diet, and sex-by-diet cohorts. Here we examine genetic, environmental, and genetic-by-environmental interactions of QTL overlapping previously identified loci associated with CVD risk factors, and we add to the serum lipid QTL landscape by identifying new loci.