· To review research findings and facts on regulation mechanisms of candidate genes for human cardiovascular diseases

· To review nature and prevalence of cardiovascular diseases and its types for human.

The most prevalent CVDs include ischaemic heart disease (heart attack), cerebrovascular disease (stroke), hypertension, inflammatory heart disease and rheumatic heart disease in that order of prevalence 24. These five major CVDs are linked to over 16 million deaths annually, with heart attacks alone affecting 12.7% of the global population, followed by stroke, which affects 9.6% of the global population. The numbers of CVD associated deaths per year are much higher in certain regions than others which were 1,106,000, 1,760,000 and 503,000 per year in Americas, Europe and Africa respectively 24.

Cardiovascular disease includes coronary artery diseases (CAD) such asangina and myocardial infarction (commonly known as a heart attack) 2. Other CVDs include stroke, heart failure, hypertensive heart disease, rheumatic heart disease, cardiomyopathy, heart arrhythmia, congenital heart disease (CHD), valvular heart disease, carditis, aortic aneurysms, peripheral artery disease, thromboembolic disease, andvenous thrombosis 25.

CHD is one of CVD which is the most common type of birth defect, affecting 1% of all live births, and is the leading non-infectious cause of death in the first year of life 26. It has been recognized that environmental factors during fetal development increase risk of CHD, including viral infections with rubella 27, chemical teratogens like retinoic acid, lithium, dilantin 28 and halogenated hydrocarbon 29 and maternal diseases including diabetes and systemic lupus erythematosus 30.

In humans, heart development begins at 15 to 16 days of gestation with the migration of precardiac stem cells, in five steps:(1) migration of precardiac cells from the primitive streak and assembly of the paired cardiac crescents at the myocardial plate, (2) coalescence of the cardiac crescents to form the primitive heart tube, establishing the definitive heart, (3) cardiac looping, assurance of proper alignment of the future cardiac chambers, (4) septation and heart chambers formation, and (5) development of the cardiac conduction system and coronary vasculature 3132.

The establishment of left-right asymmetry is very important to the normal development of heart 33. Secreted FGF, BMP, Nodal, and Wnt act as input signal of symmetric cardiac morphogenesis, BMP2, FGF8, Shh/Ihh, and Nodal function as positive regulators, whereas Wnt and Ser are negative regulators 3435. The cardiogenic plate-specific expressed genes NKX2.5, SRF, GATA4, TBX5, and HAND2, compose the core regulatory network of cardiac morphogenesis, controlling heart looping, left-right symmetry and chambers formation. SRF regulates the differentiation of coronary vascular smooth muscle cells 36.

Specific genes such as the NOTCH receptor, Jagged (JAG), WNT, transforming growth factor beta 2 (TGF ß2) and bone morphogenic proteins have been implicated in cardiac neural crest development in the mouse 37. Complex signal pathways are implicated in the crosstalk between endocardium and myocardium to form endocardial cushion and heart valves, including VEGF, NFATc1, Notch, Wnt/ß-catenin, BMP/TGF-ß, EGF, erbB, NF1 signal pathways 3238. Foxn4 driver gene is expressed in the atrioventricular canal and binds to a tbx2 enhancer domain to drive transcription of tbx2b in the atrioventricular canal defects frequent in humans 39.

Mutation in FBN1gene encoding extracellular matrix protein fibrillin 1, responsible for Marfan’s syndrome 40. When a specific mutation in the fibrillin 1 (FBN1) gene causes Marfan’s syndrome in a family, carriers of the same mutation can display variable clinical manifestations 41.

However, more recent studies suggest that microfibrils normally bind the large latent complex of the cytokine transforming growth factor β (TGF-β) and that failure of this event to occur results in increased TGF-β activation and signaling. Now, investigators are exploring the hypothesis that blocking TGF-β signaling will ameliorate the growth of aortic aneurysms in Marfan’s syndrome.

For further examples of therapeutic approaches derived from the study of Mendelian disorders, we refer the reader to a recent review on this topic 42.

Rare mutations in FBN1cause the thoracic aortic aneurysms and dissections seen in Marfan’s syndrome, whereascommon SNPs in the introns of FBN1are the top association result in a GWAS for spontaneous, non-syndromic thoracic aortic aneurysm and dissection 43. Rare mutations in SCN5A, KCNQ1, KCNH2, KCNE1, and KCNJ2cause monogenic long QT syndrome, whereas common SNPs in these five genes are associated with QT interval measured on electrocardiograms in the population 44.

PTPRC, FYB and FCER1G have been identified as key drivers of an inflammatory gene signature underlying multiple diseases (including CAD) 45. Key driver genes such as SGK1, SIK1 and SLC10A6 (sodium metabolism and hypertension), MT2A and TSC22D3 (glucocorticoid signaling), GADD45G, ERRFI1, GPRC5A, and EGFR (cell growth and apoptosis), and CEBPB, CEBPD, and KCNA5 (heart development and function) 46.

MEF2A disease-causing gene for CAD and MI is highly expressed in the endothelium susceptible to inflammation and the formation of an atherosclerotic plaque, which may result in thrombosis, MI, and sudden death 47.

Familial combined hyperlipidemia (FCHL) is present in patients of CAD which is elevated serum total cholesterol or triglycerides. USF1 encodes a transcriptional factor belonging to the basic helix-loophelix leucine zipper family and regulates genes involved in glucose and lipid metabolism, including ABCA1 and apolipoproteins CIII, AII, and E48. Also dysregulated biological processes such as cholesterol metabolism and transport can eventually lead to CAD 49.

The work that reported a positive association between a mutation of human ANP gene and the risk of stroke 50. CREBBP gene is mentioned in connection with pathophysiological changes in cerebral vessels predisposing to stroke 51.

There are associations of migraine and stroke with NOS3, EDN and EDNRB regulatory genes52. A candidate gene can be suggested as possibly related to variation in stroke risk. In addition PDE4D6 gene is associated with cardiovascular disease 53.

Some findings have been reported that HDAC9associated with large vessel disease 54 and PITX2and ZFHX3related to cardioembolic stroke 55 and a PITX2variant and cardioembolic stroke 54. ANP is a well-known physiologically important cardiovascular peptide that exerts natriuretic, diuretic, and vasorelaxant properties, and it is expressed in cardiac and cerebral tissues 56. In the search for stroke-related genes, another experimental model was investigated, the SHR with MCAO-induced ischemic stroke 57.

Polymorphisms within the promoter region of the FCN2 gene are associated with plasma levels of this protein in chronic RHD patients and probably prolong the time of infection or repeated streptococcal infections 58.

The interleukin 1 (IL-1) gene cluster located on chromosome 2 includes the genes expressing the proinflammatory cytokines IL-1a and IL-1b and their inhibitor IL-1 receptor antagonist (IL-1RA). The ratio of IL-1RA to IL-1 is important in determining the duration and intensity of the inflammatory response 59. The absence or misrepresentation of two alleles of VNTR from the IL-1RA gene results in a strong inflammatory response. RHD patients with severe carditis had low frequencies of one of these alleles, suggesting the absence of inflammatory control 60.

Mannose-binding lectin is encoded by MBL2 gene, located on the chromosome 61. It is considered an acute-phase reactant 62, whose levels can increase up to threefold during the acute-phase response, mainly due to up-regulation by acute-phase mediators 63. MBL2 is a highly polymorphic gene, exhibiting variants responsible for large variations in both MBL levels and functional activity 64.

It is shown that dilated cardiomyopathy tissues contain elevated levels of p53 and its regulators MDM2 and HAUSP compared to non-failing hearts 65. Also, regulation of MDM2 is critical in cardiac endocardial cushion morphogenesis during heart development 66. It is also shown that GRB2 plays a role in the signaling pathway for cardiac hypertrophy and fibrosis 67.

Inhibition of SMAD2 phosphorylation preserves cardiac function during pressure overload 68. JUN gene is linked to different types of mitral valvular disease (MVD), including mitral regurgitation (MR) and mitral stenosis (MS) 69. It is shown that c-Jun mRNA are upregulated in patients with MS compared with those with MR and that phosphorylated c-Jun N-terminal kinase in the MR group of patients is significantly greater than that in the MS group.

In mammals, four Notch family receptors have been described: NOTCH1 up to NOTCH4; Notch ligands are encoded by the Jagged (JAG1 and JAG2) and Delta-like (DLL1, DLL3 and DLL4) gene families 37.

The formation of bicuspid aortic valve might reflect the role of Notch signaling in regulating the epithelial-mesenchymal transition required for the generation of the heart valves 3774. Recently, mutations in Notch1 in humans have been shown to cause aortic valve defects Additionally, mutations in various Notch signaling pathway genes, including Jagged1, mind bomb 1, Hesr1/Hey1, and Hesr2/Hey2, result I cardiac defects, such as pericardial edema, atrial and ventricular septal defects, cardiac cushion, and valve defects 7576.

MicroRNAs are natural, single-stranded, non–protein-coding small RNA molecules (～22 nucleotides) that regulate gene expression by binding to target mRNAs and suppress its translation or initiate its degradation 77. For example, miR-1 and miR-133 control cardiac and skeletal muscle development 7879. Both genes are under the control of serum response factor, indicating that they are part of a developmental program regulated by cardiac transcription factors. It has been shown that miR-1 targets the cardiac transcription factor HAND2. Deletion of miR-1-2results in heart defects that include VSDs; surviving mice have conduction system defects and increased cardiomyocyte proliferation. Dysregulation of miRNAs might result in congenital heart disease in human 80.

Epigenetics refers to DNA and chromatin modifications that play a critical role in regulation of various genomic functions, cell differentiation and embryonic morphogenesis 8182. In epigenetic, phenotypic differences in monozygous twins could result from their epigenetic differences. BAF60C (also known as SMARCD3), a subunit of Swi/Snf-like chromatin-remodelling complex BAF, physically links cardiac transcription factors to the BAF complex. Loss of BAF60C results in severe defects in cardiac morphogenesis and impaired activation of a subset of cardiac genes. The muscle-restricted histone methyltransferase SMYD1 (also known as BOP) is a crucial regulator of cardiac chamber growth and differentiation. Histone deacetylases have mostly been characterized as having an important role in heart hypertrophy and development 37.