The Genetic Regulation of Aortic Valve Development and Calcific Disease

Multiple cell types including melanocytes contribute to elastogenesis in the developing murine aortic valve

Elastic fibers are crucial for aortic valve (AoV) function and are generated and maintained by valvular interstitial cells (VICs). VICs exhibit diverse phenotypes, yet the specific subpopulation responsible for producing and regulating elastic fibers remains unclear. This gap in knowledge is significant, given that elastin (Eln) abnormalities lead to congenital AoV defects and initiate AoV diseases. This study characterizes the timing of Eln expression in murine AoV, revealing it peaks during late embryogenesis and early postnatal stages, decreasing in adulthood. Spatial transcriptomics and RT-qPCR indicate that Eln expression correlates with genes associated to elastogenesis, including Acta2, a smooth muscle cell marker. While Eln expression is not exclusive to a single VIC subpopulation, RNAscope and immunofluorescence demonstrate a population of Eln-expressing VICs that co-express alpha smooth muscle actin and melanocytic markers. As previously reported in adult mice, we show a relationship between AoV pigment and elastic fiber patterning during early postnatal stages and further show that melanocytes may play a critical role in elastogenesis. In summary, Eln is expressed in the AoV during early postnatal stages by cells co-expressing markers of various types, highlighting the complexity of VICs phenotypes and their role in elastic fiber regulation.

Multimodal Analytical Tools to Enhance Mechanistic Understanding of Aortic Valve Calcification

This review focuses on technologies at the core of calcific aortic valve disease (CAVD) and drug target research advancement, including transcriptomics, proteomics, and molecular imaging. We examine how bulk RNA sequencing and single-cell RNA sequencing have engendered organismal genomes and transcriptomes, promoting the analysis of tissue gene expression profiles and cell subpopulations, respectively. We bring into focus how the field is also largely influenced by increasingly accessible proteome profiling techniques. In unison, global transcriptional and protein expression analyses allow for increased understanding of cellular behavior and pathogenic pathways under pathologic stimuli including stress, inflammation, low-density lipoprotein accumulation, increased calcium and phosphate levels, and vascular injury. We also look at how direct investigation of protein signatures paves the way for identification of targetable pathways for pharmacologic intervention. Here, we note that imaging techniques, once a clinical diagnostic tool for late-stage CAVD, have since been refined to address a clinical need to identify microcalcifications using positron emission tomography/computed tomography and even detect in vivo cellular events indicative of early stage CAVD and map the expression of identified proteins in animal models. Together, these techniques generate a holistic approach to CAVD investigation, with the potential to identify additional novel regulatory pathways.

The Role of Endoplasmic Reticulum Stress in Calcific Aortic Valve Disease

Calcific aortic valve disease (CAVD), which is involved in osteogenic reprogramming of valvular interstitial cells, is the most common form of valve disease. It still lacks effective pharmacologic intervention, as its cellular biological mechanisms remain unclear. Congenital abnormality (bicuspid valve) and older age are considered to be the most powerful risk factors for CAVD. Aortic valve sclerosis (AVS) and calcific aortic stenosis (CAS), 2 subclinical forms of CAVD, represent 2 distinct stages of aortic valve calcification. During the AVS stage, the disease is characterised by endothelial activation/damage, inflammatory response, and lipid infiltration accompanied by microcalcification. The CAS stage is dominated by calcification, resulting in valvular dysfunction and severe obstruction to cardiac outflow, which is life threatening if surgery is not performed in time. Endoplasmic reticulum (ER) stress, a state in which conditions disrupting ER homeostasis cause an accumulation of unfolded and misfolded proteins in the ER lumen, has been shown to promote osteogenic differentiation and aortic valve calcification. Therefore, identifying targets or drugs for suppressing ER stress may be a novel approach for CAVD treatment.

Exploring molecular profiles of calcification in aortic vascular smooth muscle cells and aortic valvular interstitial cells

Cardiovascular calcification can occur in vascular and valvular structures and is commonly associated with calcium deposition and tissue mineralization leading to stiffness and dysfunction. Patients with chronic kidney disease and associated hyperphosphatemia have an elevated risk for coronary artery calcification (CAC) and calcific aortic valve disease (CAVD). However, there is mounting evidence to suggest that the susceptibility and pathobiology of calcification in these two cardiovascular structures may be different, yet clinically they are similarly treated. To better understand diversity in molecular and cellular processes that underlie hyperphosphatemia-induced calcification in vascular and valvular structures, we exposed aortic vascular smooth muscle cells (AVSMCs) and aortic valve interstitial cells (AVICs) to high (2.5 mM) phosphate (Ph) conditions in vitro, and examined cell-specific responses. To further identify hyperphosphatemic-specific responses, parallel studies were performed using osteogenic media (OM) as an alternative calcific stimulus. Consistent with clinical observations made by others, we show that AVSMCs are more susceptible to calcification than AVICs. In addition, bulk RNA-sequencing reveals that AVSMCs and AVICs activate robust ossification-programs in response to high phosphate or OM treatments, however, the signaling pathways, cellular processes and osteogenic-associated markers involved are cell- and treatment-specific. For example, compared to VSMCs, VIC-mediated calcification involves biological processes related to osteo-chondro differentiation and down regulation of 'actin cytoskeleton'-related genes, that are not observed in VSMCs. Furthermore, hyperphosphatemic-induced calcification in AVICs and AVSMCs is independent of P13K signaling, which plays a role in OM-treated cells. Together, this study provides a wealth of information suggesting that the pathogenesis of cardiovascular calcifications is significantly more diverse than previously appreciated.

Engineered Extracellular Vesicle-Based Therapies for Valvular Heart Disease

Introduction

Valvular heart disease represents a significant burden to the healthcare system, with approximately 5 million cases diagnosed annually in the US. Among these cases, calcific aortic stenosis (CAS) stands out as the most prevalent form of valvular heart disease in the aging population.  CAS is characterized by the progressive calcification of the aortic valve leaflets, leading to valve stiffening. While aortic valve replacement is the standard of care for CAS patients, the long-term durability of prosthetic devices is poor, calling for innovative strategies to halt  or reverse disease progression. Here, we explor the potential use of novel extracellular vesicle (EV)-based nanocarriers for delivering molecular payloads to the affected valve tissue. This approach aims to reduce inflammation and potentially promote resorption of the calcified tissue.

Methods

Engineered EVs loaded with the reprogramming myeloid transcription factors, CEBPA and Spi1, known to mediate the transdifferentiation of committed endothelial cells into macrophages. We evaluated the ability of these engineered EVs to deliver DNA and transcripts encoding CEBPA and Spil into calcified aortic valve tissue obtained from patients undergoing valve replacement due to aortic stenosis. We also investigated whether these EVs could induce the transdifferentiation of endothelial cells into macrophage-like cells.

Results

Engineered EVs loaded with CEBPA + Spi1 were successfully derived from human dermal fibroblasts. Peak EV loading was found to be at 4 h after nanotransfection of donor cells.  These CEBPA + Spi1 loaded EVs effectively transfected aortic valve cells, resulting in the successful induction of transdifferentiation, both in vitro with  endothelial cells and ex vivo with valvular endothelial cells, leading to the development of anti-inflammatory macrophage-like cells.

Conclusions

Our findings highlight the potential of engineered EVs as a next generation nanocarrier to target aberrant calcifications on diseased heart valves. This development holds promise as a novel therapy for high-risk patients who may not be suitable candidates for valve replacement surgery.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12195-023-00783-x.

Implications of Bicuspid Aortic Valve Disease and Aortic Stenosis/Insufficiency as Risk Factors for Thoracic Aortic Aneurysm

Bicuspid Aortic Valves (BAV) are associated with an increased incidence of thoracic aortic aneurysms (TAA). TAA are a common aortic pathology characterized by enlargement of the aortic root and/or ascending aorta, and may become life threatening when left untreated. Typically occurring as the sole pathology in a patient, TAA are largely asymptomatic. However, in some instances, they are accompanied by aortic valve (AV) diseases: either congenital BAV or acquired in the form of Aortic Insufficiency (AI) or aortic stenosis (AS). When TAA are associated with aortic valve disease, determining an accurate and predictable prognosis becomes especially challenging. Patients with AV disease and concomitant TAA lack a widely accepted diagnostic approach, one that integrates our knowledge on aortic valve pathophysiology and encompasses multi-modality imaging approaches. This review summarizes the most recent scientific knowledge regarding the association between AV diseases (BAV, AI, AS) and ascending aortopathies (dilatation, aneurysm, and dissection). We aimed to pinpoint the gaps in monitoring practices and prediction of disease progression in TAA patients with concomitant AV disease. We propose that a morphological and functional analysis of the AV with multi-modality imaging should be included in aortic surveillance programs. This strategy would allow for improved risk stratification of these patients, and possibly new AV phenotypic-specific guidelines with more vigilant surveillance and earlier prophylactic surgery to improve patient outcomes.

Identifying molecular and functional similarities and differences between human primary cardiac valve interstitial cells and ventricular fibroblasts

Introduction: Fibroblasts are mesenchymal cells that predominantly produce and maintain the extracellular matrix (ECM) and are critical mediators of injury response. In the heart, valve interstitial cells (VICs) are a population of fibroblasts responsible for maintaining the structure and function of heart valves. These cells are regionally distinct from myocardial fibroblasts, including left ventricular cardiac fibroblasts (LVCFBs), which are located in the myocardium in close vicinity to cardiomyocytes. Here, we hypothesize these subpopulations of fibroblasts are transcriptionally and functionally distinct. Methods: To compare these fibroblast subtypes, we collected patient-matched samples of human primary VICs and LVCFBs and performed bulk RNA sequencing, extracellular matrix profiling, and functional contraction and calcification assays. Results: Here, we identified combined expression of SUSD2 on a protein-level, and MEOX2, EBF2 and RHOU at a transcript-level to be differentially expressed in VICs compared to LVCFBs and demonstrated that expression of these genes can be used to distinguish between the two subpopulations. We found both VICs and LVCFBs expressed similar activation and contraction potential in vitro, but VICs showed an increase in ALP activity when activated and higher expression in matricellular proteins, including cartilage oligomeric protein and alpha 2-Heremans-Schmid glycoprotein, both of which are reported to be linked to calcification, compared to LVCFBs. Conclusion: These comparative transcriptomic, proteomic, and functional studies shed novel insight into the similarities and differences between valve interstitial cells and left ventricular cardiac fibroblasts and will aid in understanding region-specific cardiac pathologies, distinguishing between primary subpopulations of fibroblasts, and generating region-specific stem-cell derived cardiac fibroblasts.

Increased TGFβ1 and SMAD3 Contribute to Age-Related Aortic Valve Calcification

Aims

Calcific aortic valve disease (CAVD) is a progressive heart disease that is particularly prevalent in elderly patients. The current treatment of CAVD is surgical valve replacement, but this is not a permanent solution, and it is very challenging for elderly patients. Thus, a pharmacological intervention for CAVD may be beneficial. In this study, we intended to rescue aortic valve (AV) calcification through inhibition of TGFβ1 and SMAD3 signaling pathways.

Methods and Results

The klotho gene, which was discovered as an aging-suppressor gene, has been observed to play a crucial role in AV calcification. The klotho knockout (Kl^–/–) mice have shorter life span (8–12 weeks) and develop severe AV calcification. Here, we showed that increased TGFβ1 and TGFβ-dependent SMAD3 signaling were associated with AV calcification in Kl^–/– mice. Next, we generated Tgfb1- and Smad3-haploinsufficient Kl^–/– mice to determine the contribution of TGFβ1 and SMAD3 to the AV calcification in Kl^–/– mice. The histological and morphometric evaluation suggested a significant reduction of AV calcification in Kl^–/–; Tgfb1^± mice compared to Kl^–/– mice. Smad3 heterozygous deletion was observed to be more potent in reducing AV calcification in Kl^–/– mice compared to the Kl^–/–; Tgfb1^± mice. We observed significant inhibition of Tgfb1, Pai1, Bmp2, Alk2, Spp1, and Runx2 mRNA expression in Kl^–/–; Tgfb1^± and Kl^–/–; Smad3^± mice compared to Kl^–/– mice. Western blot analysis confirmed that the inhibition of TGFβ canonical and non-canonical signaling pathways were associated with the rescue of AV calcification of both Kl^–/–; Tgfb1^± and Kl^–/–; Smad3^± mice.

Conclusion

Overall, inhibition of the TGFβ1-dependent SMAD3 signaling pathway significantly blocks the development of AV calcification in Kl^–/– mice. This information is useful in understanding the signaling mechanisms involved in CAVD.

Parathyroid Hormone Induces Human Valvular Endothelial Cells Dysfunction That Impacts the Osteogenic Phenotype of Valvular Interstitial Cells

Parathyroid hormone (PTH) is a key regulator of calcium, phosphate and vitamin D metabolism. Although it has been reported that aortic valve calcification was positively associated with PTH, the pathophysiological mechanisms and the direct effects of PTH on human valvular cells remain unclear. Here we investigated if PTH induces human valvular endothelial cells (VEC) dysfunction that in turn could impact the switch of valvular interstitial cells (VIC) to an osteoblastic phenotype. Human VEC exposed to PTH were analyzed by qPCR, western blot, Seahorse, ELISA and immunofluorescence. Our results showed that exposure of VEC to PTH affects VEC metabolism and functions, modifications that were accompanied by the activation of p38MAPK and ERK1/2 signaling pathways and by an increased expression of osteogenic molecules (BMP-2, BSP, osteocalcin and Runx2). The impact of dysfunctional VEC on VIC was investigated by exposure of VIC to VEC secretome, and the results showed that VIC upregulate molecules associated with osteogenesis (BMP-2/4, osteocalcin and TGF-β1) and downregulate collagen I and III. In summary, our data show that PTH induces VEC dysfunction, which further stimulates VIC to differentiate into a pro-osteogenic pathological phenotype related to the calcification process. These findings shed light on the mechanisms by which PTH participates in valve calcification pathology and suggests that PTH and the treatment of hyperparathyroidism represent a therapeutic strategy to reduce valvular calcification.

Network modeling predicts personalized gene expression and drug responses in valve myofibroblasts cultured with patient sera

Aortic valve stenosis (AVS) patients experience pathogenic valve leaflet stiffening due to excessive extracellular matrix (ECM) remodeling. Numerous microenvironmental cues influence pathogenic expression of ECM remodeling genes in tissue-resident valvular myofibroblasts, and the regulation of complex myofibroblast signaling networks depends on patient-specific extracellular factors. Here, we combined a manually curated myofibroblast signaling network with a data-driven transcription factor network to predict patient-specific myofibroblast gene expression signatures and drug responses. Using transcriptomic data from myofibroblasts cultured with AVS patient sera, we produced a large-scale, logic-gated differential equation model in which 11 biochemical and biomechanical signals were transduced via a network of 334 signaling and transcription reactions to accurately predict the expression of 27 fibrosis-related genes. Correlations were found between personalized model-predicted gene expression and AVS patient echocardiography data, suggesting links between fibrosis-related signaling and patient-specific AVS severity. Further, global network perturbation analyses revealed signaling molecules with the most influence over network-wide activity, including endothelin 1 (ET1), interleukin 6 (IL6), and transforming growth factor β (TGFβ), along with downstream mediators c-Jun N-terminal kinase (JNK), signal transducer and activator of transcription (STAT), and reactive oxygen species (ROS). Lastly, we performed virtual drug screening to identify patient-specific drug responses, which were experimentally validated via fibrotic gene expression measurements in valvular interstitial cells cultured with AVS patient sera and treated with or without bosentan-a clinically approved ET1 receptor inhibitor. In sum, our work advances the ability of computational approaches to provide a mechanistic basis for clinical decisions including patient stratification and personalized drug screening.

Transcription factor Sp2 promotes TGFB-mediated interstitial cell osteogenic differentiation in bicuspid aortic valves through a SMAD-dependent pathway

Calcification of the bicuspid aortic valve (BAV) involves differential expression of various RNA genes, which is achieved through complex regulatory networks that are controlled in part by transcription factors and microRNAs. We previously found that miR-195-5p regulates the osteogenic differentiation of valvular interstitial cells (VICs) by targeting the TGF-β pathway. However, the transcriptional regulation of miR-195-5p in calcified BAV patients is not yet clear. In this study, stenotic aortic valve tissues from patients with BAVs and tricuspid aortic valves (TAVs) were collected. Candidate transcription factors of miR-195-5p were predicted by bioinformatics analysis and tested in diseased valves and in male porcine VICs. SP2 gene expression and the corresponding protein levels in BAV were significantly lower than those in TAV, and a low SP2 expression level environment in VICs resulted in remarkable increases in RNA expression levels of RUNX2, BMP2, collagen 1, MMP2, and MMP9 and the corresponding proteins. ChIP assays revealed that SP2 directly bound to the transcription promoter region of miR-195-5p. Cotransfection of SP2 shRNA and a miR-195-5p mimic in porcine VICs demonstrated that SP2 repressed SMAD7 expression via miR-195-5p, while knockdown of SP2 increased the mRNA expression of SMAD7 and the corresponding protein and attenuated Smad 2/3 expression. Immunofluorescence staining of diseased valves confirmed that the functional proteins of osteogenesis differentiation, including RUNX2, BMP2, collagen 1, and osteocalcin, were overexpressed in BAVs. In Conclusion, the transcription factor Sp2 is expressed at low levels in VICs from BAV patients, which has a negative impact on miR-195-5p expression by binding its promoter region and partially promotes calcification through a SMAD-dependent pathway.

Tgfβ1-Cthrc1 Signaling Plays an Important Role in the Short-Term Reparative Response to Heart Valve Endothelial Injury

OBJECTIVE

Aortic valve disease is a common worldwide health burden with limited treatment options. Studies have shown that the valve endothelium is critical for structure-function relationships, and disease is associated with its dysfunction, damage, or injury. Therefore, therapeutic targets to maintain a healthy endothelium or repair damaged endothelial cells could hold promise. In this current study, we utilize a surgical mouse model of heart valve endothelial cell injury to study the short-term response at molecular and cellular levels. The goal is to determine if the native heart valve exhibits a reparative response to injury and identify the mechanisms underlying this process. Approach and Results: Mild aortic valve endothelial injury and abrogated function was evoked by inserting a guidewire down the carotid artery of young (3 months) and aging (16-18 months) wild-type mice. Short-term cellular responses were examined at 6 hours, 48 hours, and 4 weeks following injury, whereas molecular profiles were determined after 48 hours by RNA-sequencing. Within 48 hours following endothelial injury, young wild-type mice restore endothelial barrier function in association with increased cell proliferation, and upregulation of transforming growth factor beta 1 (Tgfβ1) and the glycoprotein, collagen triple helix repeat containing 1 (Cthrc1). Interestingly, this beneficial response to injury was not observed in aging mice with known underlying endothelial dysfunction.

CONCLUSIONS

Data from this study suggests that the healthy valve has the capacity to respond to mild endothelial injury, which in short term has beneficial effects on restoring endothelial barrier function through acute activation of the Tgfβ1-Cthrc1 signaling axis and cell proliferation.

Self-eating and Heart: The Emerging Roles of Autophagy in Calcific Aortic Valve Disease

Autophagy is a self-degradative pathway by which subcellular elements are broken down intracellularly to maintain cellular homeostasis. Cardiac autophagy commonly decreases with aging and is accompanied by the accumulation of misfolded proteins and dysfunctional organelles, which are undesirable to the cell. Reduction of autophagy over time leads to aging-related cardiac dysfunction and is inversely related to longevity. However, despite the increasing interest in autophagy in cardiac diseases and aging, the process remains an undervalued and disregarded object in calcific valvular disease. Neither the nature through which autophagy is triggered nor the interplay between autophagic machinery and targeted molecules during aortic valve calcification are fully understood. Recently, the upregulation of autophagy has been shown to result in cardioprotective effects against cell death as well as its origin. Here, we review the evidence that shows how autophagy can be both beneficial and detrimental as it pertains to aortic valve calcification in the heart.

NOTCH Signaling in Aortic Valve Development and Calcific Aortic Valve Disease

NOTCH intercellular signaling mediates the communications between adjacent cells involved in multiple biological processes essential for tissue morphogenesis and homeostasis. The NOTCH1 mutations are the first identified human genetic variants that cause congenital bicuspid aortic valve (BAV) and calcific aortic valve disease (CAVD). Genetic variants affecting other genes in the NOTCH signaling pathway may also contribute to the development of BAV and the pathogenesis of CAVD. While CAVD occurs commonly in the elderly population with tri-leaflet aortic valve, patients with BAV have a high risk of developing CAVD at a young age. This observation indicates an important role of NOTCH signaling in the postnatal homeostasis of the aortic valve, in addition to its prenatal functions during aortic valve development. Over the last decade, animal studies, especially with the mouse models, have revealed detailed information in the developmental etiology of congenital aortic valve defects. In this review, we will discuss the molecular and cellular aspects of aortic valve development and examine the embryonic pathogenesis of BAV. We will focus our discussions on the NOTCH signaling during the endocardial-to-mesenchymal transformation (EMT) and the post-EMT remodeling of the aortic valve. We will further examine the involvement of the NOTCH mutations in the postnatal development of CAVD. We will emphasize the deleterious impact of the embryonic valve defects on the homeostatic mechanisms of the adult aortic valve for the purpose of identifying the potential therapeutic targets for disease intervention.

Molecular and Mechanical Mechanisms of Calcification Pathology Induced by Bicuspid Aortic Valve Abnormalities

Bicuspid aortic valve (BAV) is a congenital defect affecting 1-2% of the general population that is distinguished from the normal tricuspid aortic valve (TAV) by the existence of two, rather than three, functional leaflets (or cusps). BAV presents in different morphologic phenotypes based on the configuration of cusp fusion. The most common phenotypes are Type 1 (containing one raphe), where fusion between right coronary and left coronary cusps (BAV R/L) is the most common configuration followed by fusion between right coronary and non-coronary cusps (BAV R/NC). While anatomically different, BAV R/L and BAV R/NC configurations are both associated with abnormal hemodynamic and biomechanical environments. The natural history of BAV has shown that it is not necessarily the primary structural malformation that enforces the need for treatment in young adults, but the secondary onset of premature calcification in ~50% of BAV patients, that can lead to aortic stenosis. While an underlying genetic basis is a major pathogenic contributor of the structural malformation, recent studies have implemented computational models, cardiac imaging studies, and bench-top methods to reveal BAV-associated hemodynamic and biomechanical alterations that likely contribute to secondary complications. Contributions to the field, however, lack support for a direct link between the external valvular environment and calcific aortic valve disease in the setting of BAV R/L and R/NC BAV. Here we review the literature of BAV hemodynamics and biomechanics and discuss its previously proposed contribution to calcification. We also offer means to improve upon previous studies in order to further characterize BAV and its secondary complications.

Reproducible In Vitro Tissue Culture Model to Study Basic Mechanisms of Calcific Aortic Valve Disease: Comparative Analysis to Valvular Interstitials Cells

The hallmarks of calcific aortic valve disease (CAVD), an active and regulated process involving the creation of calcium nodules, lipoprotein accumulation, and chronic inflammation, are the significant changes that occur in the composition, organization, and mechanical properties of the extracellular matrix (ECM) of the aortic valve (AV). Most research regarding CAVD is based on experiments using two-dimensional (2D) cell culture or artificially created three-dimensional (3D) environments of valvular interstitial cells (VICs). Because the valvular ECM has a powerful influence in regulating pathological events, we developed an in vitro AV tissue culture model, which is more closely able to mimic natural conditions to study cellular responses underlying CAVD. AV leaflets, isolated from the hearts of 6-8-month-old sheep, were fixed with needles on silicon rubber rings to achieve passive tension and treated in vitro under pro-degenerative and pro-calcifying conditions. The degeneration of AV leaflets progressed over time, commencing with the first visible calcified domains after 14 d and winding up with the distinct formation of calcium nodules, heightened stiffness, and clear disruption of the ECM after 56 d. Both the expression of pro-degenerative genes and the myofibroblastic differentiation of VICs were altered in AV leaflets compared to that in VIC cultures. In this study, we have established an easily applicable, reproducible, and cost-effective in vitro AV tissue culture model to study pathological mechanisms underlying CAVD. The valvular ECM and realistic VIC-VEC interactions mimic natural conditions more closely than VIC cultures or 3D environments. The application of various culture conditions enables the examination of different pathological mechanisms underlying CAVD and could lead to a better understanding of the molecular mechanisms that lead to VIC degeneration and AS. Our model provides a valuable tool to study the complex pathobiology of CAVD and can be used to identify potential therapeutic targets for slowing disease progression.

Chromatin Accessibility of Human Mitral Valves and Functional Assessment of MVP Risk Loci

RATIONALE

Mitral valve prolapse (MVP) is a common valvopathy that leads to mitral insufficiency, heart failure, and sudden death. Functional genomic studies in mitral valves are needed to better characterize MVP-associated variants and target genes.

OBJECTIVE

To establish the chromatin accessibility profiles and assess functionality of variants and narrow down target genes at MVP loci.

METHODS AND RESULTS

We mapped the open chromatin regions in nuclei from 11 human pathogenic and 7 nonpathogenic mitral valves by an assay for transposase-accessible chromatin with high-throughput sequencing. Open chromatin peaks were globally similar between pathogenic and nonpathogenic valves. Compared with the heart tissue and cardiac fibroblasts, we found that MV-specific assay for transposase-accessible chromatin with high-throughput sequencing peaks are enriched near genes involved in extracellular matrix organization, chondrocyte differentiation, and connective tissue development. One of the most enriched motifs in MV-specific open chromatin peaks was for the nuclear factor of activated T cells family of TFs (transcription factors) involved in valve endocardial and interstitial cell formation. We also found that MVP-associated variants were significantly enriched (P<0.05) in mitral valve open chromatin peaks. Integration of the assay for transposase-accessible chromatin with high-throughput sequencing data with risk loci, extensive functional annotation, and gene reporter assay suggest plausible causal variants for rs2641440 at the SMG6/SRR locus and rs6723013 at the IGFBP2/IGFBP5/TNS1 locus. CRISPR-Cas9 deletion of the sequence including rs6723013 in human fibroblasts correlated with increased expression only for TNS1. Circular chromatin conformation capture followed by high-throughput sequencing experiments provided evidence for several target genes, including SRR, HIC1, and DPH1 at the SMG6/SRR locus and further supported TNS1 as the most likely target gene on chromosome 2.

CONCLUSIONS

Here, we describe unprecedented genome-wide open chromatin profiles from human pathogenic and nonpathogenic MVs and report specific gene regulation profiles, compared with the heart. We also report in vitro functional evidence for potential causal variants and target genes at MVP risk loci involving established and new biological mechanisms. Graphic Abstract: A graphic abstract is available for this article.

The distribution of macrophage subtypes and their relationship to bone morphogenetic protein 2 in calcified aortic valve stenosis

Activation of the osteogenic signaling cascade (OSC) is thought to be involved in aortic valve stenosis. The aim of this study was to clarify the distribution of macrophage (M) subtypes in the calcified aortic valve and to clarify the relationship between osteoblast-like cells (OLC) and OSC activation. Thirty-six cases of calcified aortic valve were set as the calcification group, and six autopsy cases of aortic valve without pathological calcification comprised the noncalcification group. Aortic valve tissues were used in histological studies including single and double immunostaining to identify M subtypes, bone morphogenetic protein 2 (BMP2) and osteopontin, reverse transcription polymerase chain reaction (RT-PCR) for CD206, heme oxygenase-1 (HO-1), and BMP2 mRNAs and in situ RT-PCR for BMP2 mRNA. Ms positive for CD68, CD163, CD206, and HO-1 were significantly higher in the calcification group than in the noncalcification group (P < 0.01). Comparison of the positive cells in each section of the calcification group showed that cells of all M subtypes were found around calcifications. Osteopontin⁺ cells were also observed around calcifications. CD163⁺/CD206⁺ M2 and CD163⁺/HO-1⁺ Mox were significantly higher in the sponge layer in both groups. In double immunofluorescence, CD206⁺ and a portion of HO-1⁺ Ms expressed BMP2, and in RT-PCR, CD206 or HO-1 mRNA was expressed in cases in which BMP2 was expressed. In in situ RT-PCR, expression of BMP2 mRNA was observed around calcifications. This work clarifies the distribution of M subtypes in calcified aortic valves. In addition, the results suggest that CD206⁺ M2 and HO-1⁺ Mox, which express BMP2 in calcified aortic valves, are OLC candidates.

Triglycerides and remnant cholesterol associated with risk of aortic valve stenosis: Mendelian randomization in the Copenhagen General Population Study

Aims

We tested the hypothesis that higher levels of plasma triglycerides and remnant cholesterol are observationally and genetically associated with increased risk of aortic valve stenosis.

Methods and results

We included 108 559 individuals from the Copenhagen General Population Study. Plasma triglycerides, remnant cholesterol (total cholesterol minus low-density lipoprotein and high-density lipoprotein cholesterol), and 16 genetic variants causing such increased or decreased levels were determined. Incident aortic valve stenosis occurred in 1593 individuals. Observationally compared to individuals with triglycerides &lt;1 mmol/L (&lt;89 mg/dL), the multifactorially adjusted hazard ratio for aortic valve stenosis was 1.02 [95% confidence interval (CI) 0.87–1.19] for individuals with triglycerides of 1.0–1.9 mmol/L (89–176 mg/dL), 1.22 (1.02–1.46) for 2.0–2.9 mmol/L (177–265 mg/dL), 1.40 (1.11–1.77) for 3.0–3.9 mmol/L (266–353 mg/dL), 1.29 (0.88–1.90) for 4.0–4.9 mmol/L (354–442 mg/dL), and 1.52 (1.02–2.27) for individuals with triglycerides ≥5 mmol/L (≥443 mg/dL). By age 85, the cumulative incidence of aortic valve stenosis was 5.1% for individuals with plasma triglycerides &lt;2.0 mmol/L (77 mg/dL), 6.5% at 2.0–4.9 mmol/L (177–442 mg/dL), and 8.2% for individuals with plasma triglycerides ≥5.0 mmol/L (443 mg/dL). The corresponding values for remnant cholesterol categories were 4.8% for &lt;0.5 mmol/L (19 mg/dL), 5.6% for 0.5–1.4 mmol/L (19–57 mg/dL), and 7.4% for ≥1.5 mmol/L (58 mg/dL). Genetically, compared to individuals with allele score 13–16, odds ratios for aortic valve stenosis were 1.30 (95% CI 1.20–1.42; Δtriglycerides +12%; Δremnant cholesterol +11%) for allele score 17–18, 1.41 (1.31–1.52; +25%; +22%) for allele score 19–20, and 1.51 (1.22–1.86; +51%; +44%) for individuals with allele score 21–23.

Conclusion

Higher triglycerides and remnant cholesterol were observationally and genetically associated with increased risk of aortic valve stenosis.

An overview of the mechanisms in vascular calcification during chronic kidney disease

PURPOSE OF REVIEW

Chronic kidney disease (CKD) facilitates a unique environment to strongly accelerate vascular calcification - the pathological deposition of calcium-phosphate in the vasculature. These calcifications are associated with the excessive cardiovascular mortality of CKD patients.

RECENT FINDINGS

Vascular calcification is a multifaceted active process, mediated, at least partly, by vascular smooth muscle cells. These cells are able to transdifferentiate into cells with osteo/chondrogenic properties, which exert multiple effects to facilitate vascular tissue mineralization. As the understanding of the underlying pathophysiology increases, first therapeutic concepts begin to emerge.

SUMMARY

This brief review provides an overview on the so far known mechanisms involved in the initiation and progression of vascular calcification in CKD.

Durability of transcatheter aortic valve implantation: A translational review

Until recently, transcatheter aortic valve implantation was restricted to high-risk and inoperable patients. The updated 2017 European Society of Cardiology Guidelines has widened the indication to include intermediate-risk patients, based on two recently published trials (PARTNER 2 and SURTAVI). Moreover, two other recent trials (PARTNER 3 and EVOLUT LOW RISK) have demonstrated similar results with transcatheter aortic valve implantation in low-risk patients. Thus, extension of transcatheter aortic valve implantation to younger patients, who are currently treated by surgical aortic valve replacement, raises the crucial question of bioprosthesis durability. In this translational review, we propose to produce a state-of-the-art overview of the durability of transcatheter aortic valve implantation by integrating knowledge of the basic science of bioprosthesis degeneration (pathophysiology and biomarkers). After summarising the new definition of structural valve deterioration, we will present what is known about the pathophysiology of aortic stenosis and bioprosthesis degeneration. Next, we will consider how to identify a population at risk of early degeneration, and how basic science with the help of biomarkers could identify and predict structural valve deterioration. Finally, we will present data on the differences in durability of transcatheter aortic valve implantation compared with surgical aortic valve replacement.

Fiber Scaffold Patterning for Mending Hearts: 3D Organization Bringing the Next Step

Heart failure (HF) is a leading cause of death worldwide. The most common conditions that lead to HF are coronary artery disease, myocardial infarction, valve disorders, high blood pressure, and cardiomyopathy. Due to the limited regenerative capacity of the heart, the only curative therapy currently available is heart transplantation. Therefore, there is a great need for the development of novel regenerative strategies to repair the injured myocardium, replace damaged valves, and treat occluded coronary arteries. Recent advances in manufacturing technologies have resulted in the precise fabrication of 3D fiber scaffolds with high architectural control that can support and guide new tissue growth, opening exciting new avenues for repair of the human heart. This review discusses the recent advancements in the novel research field of fiber patterning manufacturing technologies for cardiac tissue engineering (cTE) and to what extent these technologies could meet the requirements of the highly organized and structured cardiac tissues. Additionally, future directions of these novel fiber patterning technologies, designs, and applicability to advance cTE are presented.

Increased Expression of miR-146a in Valvular Tissue From Patients With Aortic Valve Stenosis

miR-146a has been implicated in the regulation of the immune response as well as in inflammatory process of atherosclerosis. In the present study, we have investigated the expression of miR-146a and its targets, TLR4 a IRAK1, in aortic valve stenosis. A total of 58 patients with aortic stenosis (non- and atherosclerotic; tissue obtained during standard aortic valve replacement) were enrolled. The relative expression of mir-146a was higher in valvular tissue from patients with atherosclerosis compared to those without atherosclerosis (p = 0.01). Number of the IRAK1 and TLR4 transcripts did not differ between the investigated groups. There was a trend toward elevation of miR-146a expression in context of inflammatory infiltrate observed in the valvular tissue from patients with atherosclerosis (p = 0.06). In conclusion, in line with the acknowledged role of miR-146a in atherosclerotic inflammation, our data suggest it may be extended to the specific location of aortic valves in aortic stenosis.

Correlational study on altered epicardial adipose tissue as a stratification risk factor for valve disease progression through IL-13 signaling

AIMS

Genetic and environmental factors all interact in the risk of progression of valvular dysfunctions. Previous studies reported a relation between valve diseases and epicardial adipose tissue (EAT) thickness. The aim of this study was to verify the possible relationship between the molecular pattern of EAT related to IL-13 fibrogenic cytokine expression and valve dysfunction.

METHODS AND RESULTS

A valvular heart disease (VHD) population was stratified according to their median EAT thickness (7 mm). The molecular expression of IL-13 in EAT is directly related to the molecular expression of genes associated with extracellular matrix (ECM) turnover, macrophage infiltration and promotion of the formation of ectopic calcific nodules involved in aorta coarctation and calcification.

CONCLUSION

IL-13 gene expression in altered EAT is directly related to the expression of genes involved in ECM turnover and the formation of ectopic calcific nodules, suggesting measurements of EAT as a stratification risk factor for valve instability in the VHD patients.