Epigenetic regulation of 5-lipoxygenase in the phenotypic plasticity of valvular interstitial cells associated with aortic valve stenosis

Pathological Mechanism and Treatment of Calcified Aortic Stenosis

Calcified aortic stenosis (AS) is one of the most common valvular heart diseases worldwide, characterized by progressive fibrocalcific remodeling and thickening of the leaflets, which ultimately leads to obstruction of blood flow. Its pathobiology is an active and complicated process, involving endothelial cell dysfunction, lipoprotein deposition and oxidation, chronic inflammation, phenotypic transformation of valve interstitial cells, neovascularization, and intravalvular hemorrhage. To date, no targeted drug has been proven to slow down or prevent disease progression. Aortic valve replacement is still the optimal treatment of AS. This article reviews the etiology, diagnosis, and management of calcified aortic stenosis and proposes novel potential therapeutic targets.

Epigenetics: a new warrior against cardiovascular calcification, a forerunner in modern lifestyle diseases

Arterial and aortic valve calcifications are the most prevalent pathophysiological conditions among all the reported cases of cardiovascular calcifications. It increases with several risk factors like age, hypertension, external stimuli, mechanical forces, lipid deposition, malfunction of genes and signaling pathways, enhancement of naturally occurring calcium inhibitors, and many others. Modern-day lifestyle is affected by numerous environmental factors and harmful toxins that impair our health rather than providing benefits. Applying the combinatorial approach or targeting the exact mechanism could be a new strategy for drug designing or attenuating the severity of calcification. Most of the non-communicable diseases are life-threatening; thus, altering the phenotype and not the genotype may reveal the gateway for fighting with upcoming hurdles. Overall, this review summarizes the reason behind the generation of arterial and aortic valve calcification and its related signaling pathways and also the detrimental effects of calcification. In addition, the individual process of epigenetics and how the implementation of this process becomes a novel approach for diminishing the harmful effect of calcification are discussed. Noteworthy, as epigenetics is linked with genetics and environmental factors necessitates further clinical trials for complete and in-depth understanding and application of this strategy in a more specific and prudent manner.

Profiling Genome-Wide DNA Methylation Patterns in Human Aortic and Mitral Valves

Cardiac valves exhibit highly complex structures and specialized functions that include dynamic interactions between cells, extracellular matrix (ECM) and their hemodynamic environment. Valvular gene expression is tightly regulated by a variety of mechanisms including epigenetic factors such as histone modifications, RNA-based mechanisms and DNA methylation. To date, methylation fingerprints of non-diseased human aortic and mitral valves have not been studied. In this work we analyzed the differential methylation profiles of 12 non-diseased aortic and mitral valve tissue samples (in matched pairs). Analysis of methylation data [reduced representation bisulfite sequencing (RRBS)] of 16,101 promoters genome-wide revealed 584 differentially methylated (DM) promoters, of which 13 were reported in endothelial mesenchymal trans-differentiation (EMT), 37 in aortic and mitral valve disease and 7 in ECM remodeling. Both functional classification as well as network analysis showed that the genes associated with the DM promoters were enriched for WNT-, Cadherin-, Endothelin-, PDGF-, HIF-1 and VEGF- signaling implicated in valvular physiology and pathophysiology. Additional enrichment was detected for TGFB-, NOTCH- and Integrin- signaling involved in EMT as well as ECM remodeling. This data provides the first insight into differential regulation of human aortic and mitral valve tissue and identifies candidate genes linked to DM promoters. Our work will improve the understanding of valve biology, valve tissue engineering approaches and contributes to the identification of relevant drug targets.

Matters of the heart: Cellular sex differences

Nearly all cardiovascular diseases show sexual dimorphisms in prevalence, presentation, and outcomes. Until recently, most clinical trials were carried out in males, and many animal studies either failed to identify the sex of the animals or combined data obtained from males and females. Cellular sex in the heart is relatively understudied and many studies fail to report the sex of the cells used for in vitro experiments. Moreover, in the small number of studies in which sex is reported, most of those studies use male cells. The observation that cells from males and females are inherently different is becoming increasingly clear - either due to acquired differences from hormones and other factors or due to intrinsic differences in genotype (XX or XY). Because of the likely contribution of cellular sex differences in cardiac health and disease, here, we explore differences in mammalian male and female cells in the heart, including the less-studied non-myocyte cell populations. We discuss how the heart's microenvironment impacts male and female cellular phenotypes and vice versa, including how secretory profiles are dependent on cellular sex, and how hormones contribute to sexually dimorphic phenotypes and cellular functions. Intracellular mechanisms that contribute to sex differences, including gene expression and epigenetic remodeling, are also described. Recent single-cell sequencing studies have revealed unexpected sex differences in the composition of cell types in the heart which we discuss. Finally, future recommendations for considering cellular sex differences in the design of bioengineered in vitro disease models of the heart are provided.

Multi-Omics Approaches to Define Calcific Aortic Valve Disease Pathogenesis

Calcific aortic valve disease sits at the confluence of multiple world-wide epidemics of aging, obesity, diabetes, and renal dysfunction, and its prevalence is expected to nearly triple over the next 3 decades. This is of particularly dire clinical relevance, as calcific aortic valve disease can progress rapidly to aortic stenosis, heart failure, and eventually premature death. Unlike in atherosclerosis, and despite the heavy clinical toll, to date, no pharmacotherapy has proven effective to halt calcific aortic valve disease progression, with invasive and costly aortic valve replacement representing the only treatment option currently available. This substantial gap in care is largely because of our still-limited understanding of both normal aortic valve biology and the key regulatory mechanisms that drive disease initiation and progression. Drug discovery is further hampered by the inherent intricacy of the valvular microenvironment: a unique anatomic structure, a complex mixture of dynamic biomechanical forces, and diverse and multipotent cell populations collectively contributing to this currently intractable problem. One promising and rapidly evolving tactic is the application of multiomics approaches to fully define disease pathogenesis. Herein, we summarize the application of (epi)genomics, transcriptomics, proteomics, and metabolomics to the study of valvular heart disease. We also discuss recent forays toward the omics-based characterization of valvular (patho)biology at single-cell resolution; these efforts promise to shed new light on cellular heterogeneity in healthy and diseased valvular tissues and represent the potential to efficaciously target and treat key cell subpopulations. Last, we discuss systems biology- and network medicine-based strategies to extract meaning, mechanisms, and prioritized drug targets from multiomics datasets.

Omega-3 Polyunsaturated Fatty Acids and the Resolution of Inflammation: Novel Therapeutic Opportunities for Aortic Valve Stenosis?

Inflammation is well-established in cardiovascular disease, including valvular heart disease. Inflammation is a key process in the fibrosis and calcification of the aortic valve leaflets, which ultimately clinically manifest as aortic valve stenosis characterized by valve dysfunction and cardiac obstruction. In the absence of pharmacological treatment, either surgical or transcatheter aortic valve replacement is currently the only available therapeutic strategy for patients with severe aortic valve stenosis. Omega-3 polyunsaturated fatty acids, which exert beneficial effects in several cardiovascular diseases, serve as the substrate for several bioactive lipid mediators that regulate inflammation. Recent findings point to the beneficial effects of omega-3 fatty acids in cardiac valves, being inversely associated with aortic valve calcification and contributing to the resolution of valvular inflammation by means of the pro-resolving mediator resolvin E1 and downstream signaling through its receptor ChemR23.

DNA methylation of a PLPP3 MIR transposon-based enhancer promotes an osteogenic programme in calcific aortic valve disease

Aims

Calcific aortic valve disease (CAVD) is characterized by the osteogenic transition of valve interstitial cells (VICs). In CAVD, lysophosphatidic acid (LysoPA), a lipid mediator with potent osteogenic activity, is produced in the aortic valve (AV) and is degraded by membrane-associated phospholipid phosphatases (PLPPs). We thus hypothesized that a dysregulation of PLPPs could participate to the osteogenic reprograming of VICs during CAVD.

Methods and results

The expression of PLPPs was examined in human control and mineralized AVs and comprehensive analyses were performed to document the gene regulation and impact of PLPPs on the osteogenic transition of VICs. We found that PLPP3 gene and enzymatic activity were downregulated in mineralized AVs. Multidimensional gene profiling in 21 human AVs showed that expression of PLPP3 was inversely correlated with the level of 5-methylcytosine (5meC) located in an intronic mammalian interspersed repeat (MIR) element. Bisulphite pyrosequencing in a larger series of 67 AVs confirmed that 5meC in intron 1 was increased by 2.2-fold in CAVD compared with control AVs. In isolated cells, epigenome editing with clustered regularly interspersed short palindromic repeats-Cas9 system containing a deficient Cas9 fused with DNA methyltransferase (dCas9-DNMT) was used to increase 5meC in the intronic enhancer and showed that it reduced significantly the expression of PLPP3. Knockdown experiments showed that lower expression of PLPP3 in VICs promotes an osteogenic programme.

Conclusions

DNA methylation of a MIR-based enhancer downregulates the expression of PLPP3 and promotes the mineralization of the AV.

The methylation of Notch1 promoter mediates the osteogenesis differentiation in human aortic valve interstitial cells through Wnt/β-catenin signaling

Aortic valve interstitial cells (AVICs) have the potential to undergo calcification, which has been regarded as a critical issue during the pathology of calcific aortic valve disease (CAVD). In the past decade, epigenetics, in particular, DNA methylation dysregulation, has been reported to play a vital role in the occurrence and development of CAVD. In the present study, the expression of Notch1, which can inhibit the osteogenesis differentiation of valve interstitial cells, was downregulated whereas the expression of methyltransferases was upregulated in CAVD tissues, suggesting the potential role of DNA methylation in Notch1 expression and CAVD progression. As revealed by DNA extraction and bisulfite sequencing polymerase chain reaction (PCR), the methylation level in Notch1 promoter was much higher in CAVD tissues and human AVICs on Day 14 of osteogenesis differentiation induction. The silence of Notch1 intercellular domain (NICD) promoted while the treatment of demethylation agent, 5-Aza-dC, inhibited the osteogenesis differentiation. Moreover, NICD overexpression significantly suppressed the transcriptional activity of β-catenin on TCF4, and the expression of osteogenesis differentiation factors, indicating the involvement of Wnt/β-catenin signaling in Notch1 modulating the osteogenesis differentiation in human AVICs (hAVICs). Taken together, Notch1 promoter methylation leads to a decreased Notch1 expression and subsequent decreased release of NICD in the nucleus of hAVICs, therefore promoting the activation of Wnt/β-catenin signaling and the expression of osteogenesis differentiation factors, finally promoting the osteogenesis differentiation in hAVICs. DNA methylation might act as an important bridge to link epigenetic variation and CAVD progression.

The Genetic Regulation of Aortic Valve Development and Calcific Disease

Heart valves are dynamic, highly organized structures required for unidirectional blood flow through the heart. Over an average lifetime, the valve leaflets or cusps open and close over a billion times, however in over 5 million Americans, leaflet function fails due to biomechanical insufficiency in response to wear-and-tear or pathological stimulus. Calcific aortic valve disease (CAVD) is the most common valve pathology and leads to stiffening of the cusp and narrowing of the aortic orifice leading to stenosis and insufficiency. At the cellular level, CAVD is characterized by valve endothelial cell dysfunction and osteoblast-like differentiation of valve interstitial cells. These processes are associated with dysregulation of several molecular pathways important for valve development including Notch, Sox9, Tgfβ, Bmp, Wnt, as well as additional epigenetic regulators. In this review, we discuss the multifactorial mechanisms that contribute to CAVD pathogenesis and the potential of targeting these for the development of novel, alternative therapeutics beyond surgical intervention.

Epigenome alterations in aortic valve stenosis and its related left ventricular hypertrophy

Aortic valve stenosis is the most common cardiac valve disease, and with current trends in the population demographics, its prevalence is likely to rise, thus posing a major health and economic burden facing the worldwide societies. Over the past decade, it has become more than clear that our traditional genetic views do not sufficiently explain the well-known link between AS, proatherogenic risk factors, flow-induced mechanical forces, and disease-prone environmental influences. Recent breakthroughs in the field of epigenetics offer us a new perspective on gene regulation, which has broadened our perspective on etiology of aortic stenosis and other aortic valve diseases. Since all known epigenetic marks are potentially reversible this perspective is especially exciting given the potential for development of successful and non-invasive therapeutic intervention and reprogramming of cells at the epigenetic level even in the early stages of disease progression. This review will examine the known relationships between four major epigenetic mechanisms: DNA methylation, posttranslational histone modification, ATP-dependent chromatin remodeling, and non-coding regulatory RNAs, and initiation and progression of AS. Numerous profiling and functional studies indicate that they could contribute to endothelial dysfunctions, disease-prone activation of monocyte-macrophage and circulatory osteoprogenitor cells and activation and osteogenic transdifferentiation of aortic valve interstitial cells, thus leading to valvular inflammation, fibrosis, and calcification, and to pressure overload-induced maladaptive myocardial remodeling and left ventricular hypertrophy. This is especcialy the case for small non-coding microRNAs but was also, although in a smaller scale, convincingly demonstrated for other members of cellular epigenome landscape. Equally important, and clinically most relevant, the reported data indicate that epigenetic marks, particularly certain microRNA signatures, could represent useful non-invasive biomarkers that reflect the disease progression and patients prognosis for recovery after the valve replacement surgery.

Stenotic Bicuspid and Tricuspid Aortic Valves - Micro-Computed Tomography and Biological Indices of Calcification

BACKGROUND

Valve calcification is well estimated by ex-vivo micro-computed tomography (micro-CT). The objective of this study was to investigate the associations between micro-CT findings and biological indices of calcification in aortic stenosis (AS), as well as differences between bicuspid aortic valve (BAV) and tricuspid aortic valve (TAV).Methods and Results:Aortic valves and plasma were obtained from patients undergoing valve surgery. Valves were dissected and underwent micro-CT, genetic analyses, and calcium content assessment. Plasma levels of calcification markers were measured. Forty-two patients with isolated severe AS, including 22 with BAV, were studied. BAV patients had a lower median CT value (140.0 [130.0-152.0] vs. 157.0 [147.0-176.0], P=0.002) and high-density calcification (HDC) fraction (9.3 [5.7-23.3] % vs. 21.3 [14.3-31.2] %, P=0.01), as compared with TAV. Calcification fraction (CF) correlated with AS severity (measured as maximal transvalvular pressure gradient [r=0.34, P=0.03], maximal flow velocity [r=0.38, P=0.02], and indexed aortic valve area [r=-0.37, P=0.02]). For TAV patients only, mRNA expression of integrin-binding sialoprotein correlated with CF (r=0.45, P=0.048), and the receptor activator of the nuclear factor κ-B ligand transcript correlated with HDC corrugation (r=0.54, P=0.01).

CONCLUSIONS

TAV patients with AS present more mineralized calcifications in micro-CT than BAV subjects. The relative volume of calcifications increases with the AS severity. In TAV patients, upregulated expression of genes involved in osteoblastogenesis in AS correlates with leaflet mineralization in micro-CT.

Biomechanical factors in the biology of aortic wall and aortic valve diseases

The biomechanical factors that result from the haemodynamic load on the cardiovascular system are a common denominator of several vascular pathologies. Thickening and calcification of the aortic valve will lead to reduced opening and the development of left ventricular outflow obstruction, referred to as aortic valve stenosis. The most common pathology of the aorta is the formation of an aneurysm, morphologically defined as a progressive dilatation of a vessel segment by more than 50% of its normal diameter. The aortic valve is exposed to both haemodynamic forces and structural leaflet deformation as it opens and closes with each heartbeat to assure unidirectional flow from the left ventricle to the aorta. The arterial pressure is translated into tension-dominated mechanical wall stress in the aorta. In addition, stress and strain are related through the aortic stiffness. Furthermore, blood flow over the valvular and vascular endothelial layer induces wall shear stress. Several pathophysiological processes of aortic valve stenosis and aortic aneurysms, such as macromolecule transport, gene expression alterations, cell death pathways, calcification, inflammation, and neoangiogenesis directly depend on biomechanical factors.

Valvular osteoclasts in calcification and aortic valve stenosis severity

BACKGROUND

Bone remodeling in calcified aortic valves is thought to originate from microfractures at multiple sites of the valve, at which osteoclasts and osteoblasts are recruited. The aim of the present study was to assess circulating mediators of bone homeostasis, correlate them to the severity of stenosis and explore the spatio-temporal distribution of bone turnover in different parts of calcified aortic valve tissue.

METHODS AND RESULTS

Plasma and explanted aortic valves were obtained from 46 patients undergoing aortic valve replacement surgery. Plasma levels of tartrate-resistant acid phosphatase (TRAP), receptor activator of nuclear-κB (RANK) ligand and Runt-related transcription factor 2 (Runx2/Cbfa1) exhibited a significant correlation to the severity of aortic stenosis. mRNA levels in normal, thickened and calcified parts of aortic valves assessed by quantitative real-time PCR were significantly elevated in calcified parts of valves for TRAP (5.08 ± 1.6-fold, P<0.001) RANK ligand (8.6 ± 4.2-fold, P<0.001) and RANK (1.98 ± 0.78-fold, P=0.015). In an age, gender and aortic valve anatomy-adjusted multivariable regression analysis the local transcript levels of TRAP correlated significantly with echocardiographic parameters quantifying stenosis severity in early stages, whereas the expression level of Runx2/Cbfa1 was a predictor of the stenosis severity in advanced stages.

CONCLUSIONS

These findings suggest a critical role of bone turnover as a determinant of aortic stenosis severity.

Cellular repressor E1A-stimulated genes controls phenotypic switching of adventitial fibroblasts by blocking p38MAPK activation

AIMS

Phenotypic modulation of adventitial fibroblasts (AFs) plays an important role in the pathogenesis of proliferative vascular diseases. The current study aimed to identify the role of cellular repressor E1A-stimulated genes (CREG), a critical mediator in the maintenance of vascular homeostasis, in AF phenotypic modulation and adventitial remodeling.

METHOD AND RESULTS

Using in situ double-immunofluorescence staining, we ascertained that CREG expression was significantly down-regulated in the adventitia after vascular injury, and its expression pattern was conversely correlated with the expression of smooth muscle α-actin (α-SMA), a marker for differentiation of AFs into myofibroblasts. In vitro data confirmed the association of CREG in angiotensin II (Ang II)-induced AF differentiation. Additionally, overexpression of CREG attenuated Ang II-induced α-SMA expression in AFs. CREGoverexpressing AFs showed decreased levels of proliferation on days 2-5 following stimulation by Ang II compared with controls, with changes in the cell cycle profile as shown by BrdU incorporation assay and fluorescence activated cell sorting analysis. Moreover, wound healing assay and transwell migration model demonstrated that upregulation of CREG expression inhibited Ang II-induced AF migration. We found that CREG-mediated its counterbalancing effects in Ang II-induced phenotypic modulation, proliferation and migration by inhibition of the p38MAPK signaling pathway, validated by pharmacological blockade of p38MAPK with SB 203580 and by overexpression of p38MAPK with transfectants expressing constitutively active p38αMAPK.

CONCLUSION

Our findings suggest that CREG is a novel AF phenotypic modulator in a p38MAPK-dependent manner. Modulating CREG on the local vascular wall may become a new therapeutic target against proliferative vascular diseases.