The aortic valve microenvironment and its role in calcific aortic valve disease

Long noncoding RNA MALAT1 mediates fibrous topography-driven pathologic calcification through trans-differentiation of myoblasts

Prosthesis-induced pathological calcification is a significant challenge in biomaterial applications and is often associated with various reconstructive medical procedures. It is uncertain whether the fibrous extracellular matrix (ECM) adjacent to biomaterials directly triggers osteogenic trans-differentiation in nearby cells. To investigate this possibility, we engineered a heterogeneous polystyrene fibrous matrix (PSF) designed to mimic the ECM. Our findings revealed that the myoblasts grown on this PSF acquired osteogenic properties, resulting in mineralization both in vitro and in vivo. Transcriptomic analyses indicated a notable upregulation in the expression of the long noncoding RNA metastsis-associated lung adenocarcinoma transcript 1 (Malat1) in the C2C12 myoblasts cultured on PSF. Intriguingly, silencing Malat1 curtailed the PSF-induced mineralization and downregulated the expression of bone morphogenetic proteins (Bmps) and osteogenic markers. Further, we found that PSF prompted the activation of Yap1 signaling and epigenetic modifications in the Malat1 promoter, crucial for the expression of Malat1. These results indicate that the fibrous matrix adjacent to biomaterials can instigate Malat1 upregulation, subsequently driving osteogenic trans-differentiation in myoblasts and ectopic calcification through its transcriptional regulation of osteogenic genes, including Bmps. Our findings point to a novel therapeutic avenue for mitigating prosthesis-induced pathological calcification, heralding new possibilities in the field of biomaterial-based therapies.

Computational study of transcatheter aortic valve replacement based on patient-specific models-rapid surgical planning for self-expanding valves

Transcatheter aortic valve replacement (TAVR) is a minimally invasive interventional solution for treating aortic stenosis. The complex post-TAVR complications are associated with the type of valve implanted and the position of the implantation. The study aimed to establish a rapid numerical research method for TAVR to assess the performance differences of self-expanding valves released at various positions. It also aimed to calculate the risks of postoperative paravalvular leak and atrioventricular conduction block, comparing these risks to clinical outcomes to verify the method's effectiveness and accuracy. Based on medical images, six cases were established, including the aortic wall, native valve and calcification; one with a bicuspid aortic valve and five with tricuspid aortic valves. The parameters for the stent materials used by the patients were customized. High strain in the contact area between the stent and the valve annulus may lead to atrioventricular conduction block. Postoperatively, the self-expanding valve maintained a circular cross-section, reducing the risk of paravalvular leak and demonstrating favorable hemodynamic characteristics, consistent with clinical observations. The outcomes of the six simulations showed no significant difference in valve frame morphology or paravalvular leak risk compared to clinical results, thereby validating the numerical simulation process proposed for quickly selecting valve models and optimal release positions, aiding in TAVR preoperative planning based on patients'geometric characteristics.

Models for calcific aortic valve disease in vivo and in vitro

Calcific Aortic Valve Disease (CAVD) is prevalent among the elderly as the most common valvular heart disease. Currently, no pharmaceutical interventions can effectively reverse or prevent CAVD, making valve replacement the primary therapeutic recourse. Extensive research spanning decades has contributed to the establishment of animal and in vitro cell models, which facilitates a deeper understanding of the pathophysiological progression and underlying mechanisms of CAVD. In this review, we provide a comprehensive summary and analysis of the strengths and limitations associated with commonly employed models for the study of valve calcification. We specifically emphasize the advancements in three-dimensional culture technologies, which replicate the structural complexity of the valve. Furthermore, we delve into prospective recommendations for advancing in vivo and in vitro model studies of CAVD.

A Comprehensive Review of Management Strategies for Bicuspid Aortic Valve (BAV): Exploring Epidemiology, Aetiology, Aortopathy, and Interventions in Light of Recent Guidelines

OBJECTIVE

bicuspid aortic valve (BAV) stands as the most prevalent congenital heart condition intricately linked to aortic pathologies encompassing aortic regurgitation (AR), aortic stenosis, aortic root dilation, and aortic dissection. The aetiology of BAV is notably intricate, involving a spectrum of genes and polymorphisms. Moreover, BAV lays the groundwork for an array of structural heart and aortic disorders, presenting varying degrees of severity. Establishing a tailored clinical approach amid this diverse range of BAV-related conditions is of utmost significance. In this comprehensive review, we delve into the epidemiology, aetiology, associated ailments, and clinical management of BAV, encompassing imaging to aortic surgery. Our exploration is guided by the perspectives of the aortic team, spanning six distinct guidelines.

METHODS

We conducted an exhaustive search across databases like PubMed, Ovid, Scopus, and Embase to extract relevant studies. Our review incorporates 84 references and integrates insights from six different guidelines to create a comprehensive clinical management section.

RESULTS

BAV presents complexities in its aetiology, with specific polymorphisms and gene disorders observed in groups with elevated BAV prevalence, contributing to increased susceptibility to other cardiovascular conditions. The altered hemodynamics inherent to BAV instigate adverse remodelling of the aorta and heart, thus fostering the development of epigenetically linked aortic and heart diseases. Employing TTE screening for first-degree relatives of BAV patients might be beneficial for disease tracking and enhancing clinical outcomes. While SAVR is the primary recommendation for indicated AVR in BAV, TAVR might be an option for certain patients endorsed by adept aortic teams. In addition, proficient teams can perform aortic valve repair for AR cases. Aortic surgery necessitates personalized evaluation, accounting for genetic makeup and risk factors. While the standard aortic replacement threshold stands at 55 mm, it may be tailored to 50 mm or even 45 mm based on patient-specific considerations.

CONCLUSION

This review reiterates the significance of considering the multifactorial nature of BAV as well as the need for further research to be carried out in the field.

Pathophysiology, emerging techniques for the assessment and novel treatment of aortic stenosis

Our perspectives on aortic stenosis (AS) are changing. Evolving from the traditional thought of a passive degenerative disease, developing a greater understanding of the condition's mechanistic underpinning has shifted the paradigm to an active disease process. This advancement from the 'wear and tear' model is a result of the growing economic and health burden of AS, particularly within industrialised countries, prompting further research. The pathophysiology of calcific AS (CAS) is complex, yet can be characterised similarly to that of atherosclerosis. Progressive remodelling involves lipid-protein complexes, with lipoprotein(a) being of particular interest for diagnostics and potential future treatment options.There is an unmet clinical need for asymptomatic patient management; no pharmacotherapies are proven to slow progression and intervention timing varies. Novel approaches are developing to address this through: (1) screening with circulating biomarkers; (2) development of drugs to slow disease progression and (3) early valve intervention guided by medical imaging. Existing biomarkers (troponin and brain natriuretic peptide) are non-specific, but cost-effective predictors of ventricular dysfunction. In addition, their integration with cardiovascular MRI can provide accurate risk stratification, aiding aortic valve replacement decision making. Currently, invasive intervention is the only treatment for AS. In comparison, the development of lipoprotein(a) lowering therapies could provide an alternative; slowing progression of CAS, preventing left ventricular dysfunction and reducing reliance on surgical intervention.The landscape of AS management is rapidly evolving. This review outlines current understanding of the pathophysiology of AS, its management and future perspectives for the condition's assessment and treatment.

Single-cell RNA sequencing reveals the diversity and biology of valve cells in cardiac valve disease

From highly aligned extracellular fibrils to the cells, a multilevel ordered hierarchy in valve leaflets is crucial for their biological function. Cardiac valve pathology most frequently involves a disruption in normal structure-function correlations through abnormal and complex interaction of cells, extracellular matrix, and their environment. At present, effective treatment for valve disease is limited and frequently ends with surgical repair or replacement with a mechanical or artificial biological cardiac valve, which comes with insuperable complications for many high-risk patients including aged and pediatric populations. Therefore, there is a critical need to fully appreciate the pathobiology of valve disease in order to develop better, alternative therapies. To date, the majority of studies have focused on delineating valve disease mechanisms at the cellular level. However, the cellular heterogeneity and function is still unclear. In this review, we summarize the body of work on valve cells, with a particular focus on the discoveries about valve cells heterogeneity and functions using single-cell RNA sequencing. We conclude by discussing state-of-the-art strategies for deciphering heterogeneity of these complex cell types, and argue this knowledge could translate into the improved personalized treatment of cardiac valve disease.

Valve Endothelial Cell Exposure to High Levels of Flow Oscillations Exacerbates Valve Interstitial Cell Calcification

The aortic valve facilitates unidirectional blood flow to the systemic circulation between the left cardiac ventricle and the aorta. The valve’s biomechanical function relies on thin leaflets to adequately open and close over the cardiac cycle. A monolayer of valve endothelial cells (VECs) resides on the outer surface of the aortic valve leaflet. Deeper within the leaflet are sublayers of valve interstitial cells (VICs). Valve tissue remodeling involves paracrine signaling between VECs and VICs. Aortic valve calcification can result from abnormal paracrine communication between these two cell types. VECs are known to respond to hemodynamic stimuli, and, specifically, flow abnormalities can induce VEC dysfunction. This dysfunction can subsequently change the phenotype of VICs, leading to aortic valve calcification. However, the relation between VEC-exposed flow oscillations under pulsatile flow to the progression of aortic valve calcification by VICs remains unknown. In this study, we quantified the level of flow oscillations that VECs were exposed to under dynamic culture and then immersed VICs in VEC-conditioned media. We found that VIC-induced calcification was augmented under maximum flow oscillations, wherein the flow was fully forward for half the cardiac cycle period and fully reversed for the other half. We were able to computationally correlate this finding to specific regions of the aortic valve that experience relatively high flow oscillations and that have been shown to be associated with severe calcified deposits. These findings establish a basis for future investigations on engineering calcified human valve tissues and its potential for therapeutic discovery of aortic valve calcification.

Prioritization of Candidate Biomarkers for Degenerative Aortic Stenosis through a Systems Biology-Based In-Silico Approach

Degenerative aortic stenosis is the most common valve disease in the elderly and is usually confirmed at an advanced stage when the only treatment is surgery. This work is focused on the study of previously defined biomarkers through systems biology and artificial neuronal networks to understand their potential role within aortic stenosis. The goal was generating a molecular panel of biomarkers to ensure an accurate diagnosis, risk stratification, and follow-up of aortic stenosis patients. We used in silico studies to combine and re-analyze the results of our previous studies and, with information from multiple databases, established a mathematical model. After this, we prioritized two proteins related to endoplasmic reticulum stress, thrombospondin-1 and endoplasmin, which have not been previously validated as markers for aortic stenosis, and analyzed them in a cell model and in plasma from human subjects. Large-scale bioinformatics tools allow us to extract the most significant results after using high throughput analytical techniques. Our results could help to prevent the development of aortic stenosis and open the possibility of a future strategy based on more specific therapies.

Bioinformatics and Machine Learning Methods to Identify FN1 as a Novel Biomarker of Aortic Valve Calcification

Aim

The purpose of this study was to identify potential diagnostic markers for aortic valve calcification (AVC) and to investigate the function of immune cell infiltration in this disease.

Methods

The AVC data sets were obtained from the Gene Expression Omnibus. The identification of differentially expressed genes (DEGs) and the performance of functional correlation analysis were carried out using the R software. To explore hub genes related to AVC, a protein–protein interaction network was created. Diagnostic markers for AVC were then screened and verified using the least absolute shrinkage and selection operator, logistic regression, support vector machine-recursive feature elimination algorithms, and hub genes. The infiltration of immune cells into AVC tissues was evaluated using CIBERSORT, and the correlation between diagnostic markers and infiltrating immune cells was analyzed. Finally, the Connectivity Map database was used to forecast the candidate small molecule drugs that might be used as prospective medications to treat AVC.

Results

A total of 337 DEGs were screened. The DEGs that were discovered were mostly related with atherosclerosis and arteriosclerotic cardiovascular disease, according to the analyses. Gene sets involved in the chemokine signaling pathway and cytokine–cytokine receptor interaction were differently active in AVC compared with control. As the diagnostic marker for AVC, fibronectin 1 (FN1) (area the curve = 0.958) was discovered. Immune cell infiltration analysis revealed that the AVC process may be mediated by naïve B cells, memory B cells, plasma cells, activated natural killer cells, monocytes, and macrophages M0. Additionally, FN1 expression was associated with memory B cells, M0 macrophages, activated mast cells, resting mast cells, monocytes, and activated natural killer cells. AVC may be reversed with the use of yohimbic acid, the most promising small molecule discovered so far.

Conclusion

FN1 can be used as a diagnostic marker for AVC. It has been shown that immune cell infiltration is important in the onset and progression of AVC, which may benefit in the improvement of AVC diagnosis and treatment.

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.

Midkine Prevents Calcification of Aortic Valve Interstitial Cells via Intercellular Crosstalk

Calcified aortic valve disease (CAVD), the most common valvular heart disease, lacks pharmaceutical treatment options because its pathogenesis remains unclear. This disease with a complex macroenvironment characterizes notable cellular heterogeneity. Therefore, a comprehensive understanding of cellular diversity and cell-to-cell communication are essential for elucidating the mechanisms driving CAVD progression and developing therapeutic targets. In this study, we used single-cell RNA sequencing (scRNA-seq) analysis to describe the comprehensive transcriptomic landscape and cell-to-cell interactions. The transitional valvular endothelial cells (tVECs), an intermediate state during the endothelial-to-mesenchymal transition (EndMT), could be a target to interfere with EndMT progression. Moreover, matrix valvular interstitial cells (mVICs) with high expression of midkine (MDK) interact with activated valvular interstitial cells (aVICs) and compliment-activated valvular interstitial cells (cVICs) through the MK pathway. Then, MDK inhibited calcification of VICs that calcification was validated by Alizarin Red S staining, real-time quantitative polymerase chain reaction (RT-qPCR), and Western blotting assays in vitro. Therefore, we speculated that mVICs secreted MDK to prevent VICs’ calcification. Together, these findings delineate the aortic valve cells’ heterogeneity, underlining the importance of intercellular cross talk and MDK, which may offer a potential therapeutic strategy as a novel inhibitor of CAVD.

Local and global growth and remodeling in calcific aortic valve disease and aging

Aging and calcific aortic valve disease (CAVD) are the main factors leading to aortic stenosis. Both processes are accompanied by growth and remodeling pathways that play a crucial role in aortic valve pathophysiology. Herein, a computational growth and remodeling (G&R) framework was developed to investigate the effects of aging and calcification on aortic valve dynamics. Particularly, an algorithm was developed to couple the global growth and stiffening of the aortic valve due to aging and the local growth and stiffening due to calcification with the aortic valve transient dynamics. The aortic valve dynamics during baseline were validated with available data in the literature. Subsequently, the changes in aortic valve dynamic patterns during aging and CAVD progression were studied. The results revealed the patterns in geometric orifice area reduction and an increase in the valve stress during local and global growth and remodeling of the aortic valve. The proposed algorithm provides a framework to couple mechanobiology models of disease growth with tissue-scale transient structural mechanics models to study the biomechanical changes during cardiovascular disease growth and aging.

Calcific Aortic Stenosis-A Review on Acquired Mechanisms of the Disease and Treatments

Calcific aortic stenosis is a progressive disease that has become more prevalent in recent decades. Despite advances in research to uncover underlying biomechanisms, and development of new generations of prosthetic valves and replacement techniques, management of calcific aortic stenosis still comes with unresolved complications. In this review, we highlight underlying molecular mechanisms of acquired aortic stenosis calcification in relation to hemodynamics, complications related to the disease, diagnostic methods, and evolving treatment practices for calcific aortic stenosis.

Calcific aortic valve stenosis - comparison of inflammatory lesions in the left, right, and non-coronary cusp

BACKGROUND

Calcific aortic valve stenosis (CAVS) is the most frequent acquired heart valve disease in the developed world and the most common cause of heart valve replacement, particularly in older adults. It is considered a form of atherosclerosis and, like the latter, of inflammatory pathogenesis.

METHODS

The incidence and severity of features of chronic inflammation (vascularization, cellular infiltration, bone metaplasia, calcification) in surgically resected semilunar cusps of a tricuspid aortic valve in 100 patients with CAVS were assessed. A novel method of placing metal clips during the operation by the surgeon to distinguish individual cusps was implemented, allowing the pathologist to associate lesions to particular cusps. The findings were evaluated statistically.

RESULTS

The median age of the cohort was 73 years. There was a male predominance of 3.5:1. Almost all the patients had a medical history of risk factors - hypertension (92x), diabetes (51x), and dyslipidaemia (85x). Statistical evaluation of the pathological findings showed that the left cusp was least affected by calcification, vascularization, and chronic inflammation, compared to both the right and non-coronary cusps. On the other hand, the left cusp was the most common site of bone metaplasia. The reason for these differences is unknown. We speculate about mechanobiological effects of abnormal hemodynamics.

CONCLUSIONS

Chronic inflammation plays a significant role in pathogenesis of CAVS. Distinguishing the resected aortic valve cusps by placing metal clips is a useful method to study potential differences (topography) in the pathology of individual cusps.

A Coupled Multiscale Approach to Modeling Aortic Valve Mechanics in Health and Disease

Mechano-biological processes in the aortic valve span multiple length scales ranging from the molecular and cell to tissue and organ levels. The valvular interstitial cells residing within the valve cusps sense and actively respond to leaflet tissue deformations caused by the valve opening and closing during the cardiac cycle. Abnormalities in these biomechanical processes are believed to impact the matrix-maintenance function of the valvular interstitial cells, thereby initiating valvular disease processes such as calcific aortic stenosis. Understanding the mechanical behavior of valvular interstitial cells in maintaining tissue homeostasis in response to leaflet tissue deformation is therefore key to understanding the function of the aortic valve in health and disease. In this study, we applied a multiscale computational homogenization technique (also known as “FE2”) to aortic valve leaflet tissue to study the three-dimensional mechanical behavior of the valvular interstitial cells in response to organ-scale mechanical loading. We further considered calcific aortic stenosis with the aim of understanding the likely relationship between the valvular interstitial cell deformations and calcification. We find that the presence of calcified nodules leads to an increased strain profile that drives further growth of calcification.

Computational Analysis of Wall Shear Stress Patterns on Calcified and Bicuspid Aortic Valves: Focus on Radial and Coaptation Patterns

Calcification and bicuspid valve formation are important aortic valve disorders that disturb the hemodynamics and the valve function. The detailed analysis of aortic valve hemodynamics would lead to a better understanding of the disease’s etiology. We computationally modeled the aortic valve using simplified three-dimensional geometry and inlet velocity conditions obtained via echocardiography. We examined various calcification severities and bicuspid valve formation. Fluid-structure interaction (FSI) analyses were adapted using ANSYS Workbench to incorporate both flow dynamics and leaflet deformation accurately. Simulation results were validated by comparing leaflet movements in B-mode echo recordings. Results indicate that the biomechanical environment is significantly changed for calcified and bicuspid valves. High flow jet velocities are observed in the calcified valves which results in high transvalvular pressure difference (TPG). Wall shear stresses (WSS) increased with the calcification on both fibrosa (aorta side) and ventricularis (left ventricle side) surfaces of the leaflet. The WSS distribution is regular on the ventricularis, as the WSS values proportionally increase from the base to the tip of the leaflet. However, WSS patterns are spatially complex on the fibrosa side. Low WSS levels and spatially complex WSS patterns on the fibrosa side are considered as promoting factors for further calcification and valvular diseases.

Tumor necrosis factor-α promotes and exacerbates calcification in heart valve myofibroblast populations

Pro-inflammatory cytokines play critical roles in regulating valvular interstitial cell (VIC) phenotypic changes that can cause heart valve fibrosis and calcification. Tumor necrosis factor alpha (TNF-α) is a cytokine known to influence VIC behavior and has been reported at high levels in calcified valves ex vivo. We sought to understand the specific effects of TNF-α on VIC phenotypes (eg, fibroblast, profibrotic activated myofibroblasts) and its link with heart valve disorders. We characterize human aortic valve tissue from patients with valve disorders and identify a high variability of fibrotic and calcific markers between tissues. These results motivated in vitro studies to explore the effects of TNF-α on defined VIC fibroblasts and profibrotic activated myofibroblasts, induced via FGF-2 and TGF-β1 treatment. Using 3D hydrogels to culture VICs, we measure the effect of TNF-α (0.1-10 ng/mL) on key markers of fibrosis (eg, αSMA, COL1A1) and calcification (eg, RUNX2, BMP2, and calcium deposits). We observe calcification in TNF-α-treated VIC activated myofibroblasts and identify the MAPK/ERK signaling cascade as a potential pathway for TNF-α mediated calcification. Conversely, VIC fibroblasts respond to TNF-α with decreased calcification. Treatment of VIC profibrotic activated myofibroblast populations with TNF-α leads to increased calcification. Our in vitro findings correlate with findings in diseased human valves and highlight the importance of understanding the effect of cytokines and signaling pathways on specific VIC phenotypes. Finally, we reveal MAPK/ERK as a potential pathway involved in VIC-mediated matrix calcification with TNF-α treatment, suggesting this pathway as a potential pharmaceutical target for aortic valve disease.

Left Ventricular Assist Device Support-Induced Alteration of Mechanical Stress on Aortic Valve and Aortic Wall

The aim of this study was to evaluate the fluid dynamics in the aortic valve and proximal aorta during continuous-flow left ventricular assist device (LVAD) support using epiaortic echocardiography and vector flow mapping technology. A total of 12 patients who underwent HeartMate 3 implantation between December 2018 and February 2020 were prospectively examined. The wall shear stress (WSS) on the ascending aorta, aortic root, and aortic valve was evaluated before and after LVAD implantation. The median age of the cohort was 62 years and 17% were women. The peak WSS on the ascending aorta (Pre 1.48 [0.86-1.69] [Pascal {Pa}] vs. Post 0.33 [0.21-0.58] [Pa]; p = 0.002), aortic root (Pre 0.46 [0.31-0.58] (Pa) vs. Post 0.18 [0.12-0.25] (Pa); p = 0.001), and ventricularis of the aortic valve (Pre 1.76 [1.59-2.30] (Pa) vs. Post 0.30 [0.10-0.61] (Pa); p = 0.001) was significantly lower after LVAD implantation. No difference in WSS was observed on the fibrosa of the aortic valve (Pre 0.36 [0.22-0.53] (Pa) vs. Post 0.38 [0.38-0.52] (Pa); p = 0.850) before and after implantation. The WSS on the ascending aorta, aortic root, and ventricularis of the aortic valve leaflets was significantly altered by LVAD implantation, providing preliminary data on the potential contribution of fluid dynamics to LVAD-induced aortic insufficiency and root thrombus.

Dissecting Calcific Aortic Valve Disease-The Role, Etiology, and Drivers of Valvular Fibrosis

Calcific aortic valve disease (CAVD) is a highly prevalent and progressive disorder that ultimately causes gradual narrowing of the left ventricular outflow orifice with ensuing devastating hemodynamic effects on the heart. Calcific mineral accumulation is the hallmark pathology defining this process; however, fibrotic extracellular matrix (ECM) remodeling that leads to extensive deposition of fibrous connective tissue and distortion of the valvular microarchitecture similarly has major biomechanical and functional consequences for heart valve function. Significant advances have been made to unravel the complex mechanisms that govern these active, cell-mediated processes, yet the interplay between fibrosis and calcification and the individual contribution to progressive extracellular matrix stiffening require further clarification. Specifically, we discuss (1) the valvular biomechanics and layered ECM composition, (2) patterns in the cellular contribution, temporal onset, and risk factors for valvular fibrosis, (3) imaging valvular fibrosis, (4) biomechanical implications of valvular fibrosis, and (5) molecular mechanisms promoting fibrotic tissue remodeling and the possibility of reverse remodeling. This review explores our current understanding of the cellular and molecular drivers of fibrogenesis and the pathophysiological role of fibrosis in CAVD.

Inflammatory and Biomechanical Drivers of Endothelial-Interstitial Interactions in Calcific Aortic Valve Disease

Calcific aortic valve disease is dramatically increasing in global burden, yet no therapy exists outside of prosthetic replacement. The increasing proportion of younger and more active patients mandates alternative therapies. Studies suggest a window of opportunity for biologically based diagnostics and therapeutics to alleviate or delay calcific aortic valve disease progression. Advancement, however, has been hampered by limited understanding of the complex mechanisms driving calcific aortic valve disease initiation and progression towards clinically relevant interventions.

Subject-specific multiscale modeling of aortic valve biomechanics

A Finite Element workflow for the multiscale analysis of the aortic valve biomechanics was developed and applied to three physiological anatomies with the aim of describing the aortic valve interstitial cells biomechanical milieu in physiological conditions, capturing the effect of subject-specific and leaflet-specific anatomical features from the organ down to the cell scale. A mixed approach was used to transfer organ-scale information down to the cell-scale. Displacement data from the organ model were used to impose kinematic boundary conditions to the tissue model, while stress data from the latter were used to impose loading boundary conditions to the cell level. Peak of radial leaflet strains was correlated with leaflet extent variability at the organ scale, while circumferential leaflet strains varied over a narrow range of values regardless of leaflet extent. The dependency of leaflet biomechanics on the leaflet-specific anatomy observed at the organ length-scale is reflected, and to some extent emphasized, into the results obtained at the lower length-scales. At the tissue length-scale, the peak diastolic circumferential and radial stresses computed in the fibrosa correlated with the leaflet surface area. At the cell length-scale, the difference between the strains in two main directions, and between the respective relationships with the specific leaflet anatomy, was even more evident; cell strains in the radial direction varied over a relatively wide range (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$0.36-0.87$$\end{document}0.36-0.87) with a strong correlation with the organ length-scale radial strain (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$R^{2}= 0.95$$\end{document}R2=0.95); conversely, circumferential cell strains spanned a very narrow range (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$0.75-0.88$$\end{document}0.75-0.88) showing no correlation with the circumferential strain at the organ level (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$R^{2}= 0.02$$\end{document}R2=0.02). Within the proposed simulation framework, being able to account for the actual anatomical features of the aortic valve leaflets allowed to gain insight into their effect on the structural mechanics of the leaflets at all length-scales, down to the cell scale.

Harnessing Single-Cell RNA Sequencing to Better Understand How Diseased Cells Behave the Way They Do in Cardiovascular Disease

The transition of healthy arteries and cardiac valves into dense, cell-rich, calcified, and fibrotic tissues is driven by a complex interplay of both cellular and molecular mechanisms. Specific cell types in these cardiovascular tissues become activated following the exposure to systemic stimuli including circulating lipoproteins or inflammatory mediators. This activation induces multiple cascades of events where changes in cell phenotypes and activation of certain receptors may trigger multiple pathways and specific alterations to the transcriptome. Modifications to the transcriptome and proteome can give rise to pathological cell phenotypes and trigger mechanisms that exacerbate inflammation, proliferation, calcification, and recruitment of resident or distant cells. Accumulating evidence suggests that each cell type involved in vascular and valvular diseases is heterogeneous. Single-cell RNA sequencing is a transforming medical research tool that enables the profiling of the unique fingerprints at single-cell levels. Its applications have allowed the construction of cell atlases including the mammalian heart and tissue vasculature and the discovery of new cell types implicated in cardiovascular disease. Recent advances in single-cell RNA sequencing have facilitated the identification of novel resident cell populations that become activated during disease and has allowed tracing the transition of healthy cells into pathological phenotypes. Furthermore, single-cell RNA sequencing has permitted the characterization of heterogeneous cell subpopulations with unique genetic profiles in healthy and pathological cardiovascular tissues. In this review, we highlight the latest groundbreaking research that has improved our understanding of the pathological mechanisms of atherosclerosis and future directions for calcific aortic valve disease.

Fluid-structure coupled biotransport processes in aortic valve disease

Biological transport processes near the aortic valve play a crucial role in calcific aortic valve disease initiation and bioprosthetic aortic valve thrombosis. Hemodynamics coupled with the dynamics of the leaflets regulate these transport patterns. Herein, two-way coupled fluid-structure interaction (FSI) simulations of a 2D bicuspid aortic valve and a 3D mechanical heart valve were performed and coupled with various convective mass transport models that represent some of the transport processes in calcification and thrombosis. Namely, five different continuum transport models were developed to study biochemicals that originate from the blood and the leaflets, as well as residence-time and flow stagnation. Low-density lipoprotein (LDL) and platelet activation were studied for their role in calcification and thrombosis, respectively. Coherent structures were identified using vorticity and Lagrangian coherent structures (LCS) for the 2D and 3D models, respectively. A very close connection between vortex structures and biochemical concentration patterns was shown where different vortices controlled the concentration patterns depending on the transport mechanism. Additionally, the relationship between leaflet concentration and wall shear stress was revealed. Our work shows that blood flow physics and coherent structures regulate the flow-mediated biological processes that are involved in aortic valve calcification and thrombosis, and therefore could be used in the design process to optimize heart valve replacement durability.

Biomaterials in Valvular Heart Diseases

Valvular heart disease (VHD) occurs as the result of valvular malfunction, which can greatly reduce patient's quality of life and if left untreated may lead to death. Different treatment regiments are available for management of this defect, which can be helpful in reducing the symptoms. The global commitment to reduce VHD-related mortality rates has enhanced the need for new therapeutic approaches. During the past decade, development of innovative pharmacological and surgical approaches have dramatically improved the quality of life for VHD patients, yet the search for low cost, more effective, and less invasive approaches is ongoing. The gold standard approach for VHD management is to replace or repair the injured valvular tissue with natural or synthetic biomaterials. Application of these biomaterials for cardiac valve regeneration and repair holds a great promise for treatment of this type of heart disease. The focus of the present review is the current use of different types of biomaterials in treatment of valvular heart diseases.

Bioorthogonal click chemistries enable simultaneous spatial patterning of multiple proteins to probe synergistic protein effects on fibroblast function

Three biorthogonal click reactions, a photoinitiated thiol-yne reaction, an azide-alkyne cycloaddition, and a methyltetrazine-transcyclooctene Diels Alder, were used to independently control the presentation of several bioactive proteins to valvular interstitial cells (VICs) in hydrogel scaffolds. Tethered fibroblast growth factor (FGF-2) was found to suppress myofibroblast activation (from 48 ± 7% to 17 ± 6%) and promote proliferation (from 10 ± 2% to 54 ± 3%) at a concentration of 10 ng/mL. In the presence of the pro-fibrotic cytokine transforming growth factor-beta (TGF-β1), FGF-2 could protect the VIC fibroblast phenotype, even at much higher concentrations of TGF-β1 than that of FGF-2. With respect to the fibrocalcific VIC phenotype, TGF-β1 and bone-morphogenic protein-2 (BMP-2) were found to synergistically promote calcific nodule formation (a five-fold increase in nodules compared to TGF-β1 or BMP-2 alone). Exploiting the orthogonal click reactions, FGF-2, TGF-β1 and BMP-2 combinations were patterned into distinct regions on a hydrogel to control VIC activation and nodule formation. Cellular crosstalk between separate regions of the same scaffold was affected by the size of each region as well as the interfacial area between different regions. Collectively, these results demonstrate the versatility and robustness of a photoinitiated thiol-yne reaction to template pendant functionalities that allow for the bioconjugation of multiple proteins. This approach maintains protein bioactivity, providing an in vitro platform capable of achieving a better understanding of the complex mechanisms involved in tissue fibrosis.

Calcific Aortic Valve Disease-Natural History and Future Therapeutic Strategies

Calcific aortic valve disease (CAVD) is the most frequent heart valve disorder. It is characterized by an active remodeling process accompanied with valve mineralization, that results in a progressive aortic valve narrowing, significant restriction of the valvular area, and impairment of blood flow.The pathophysiology of CAVD is a multifaceted process, involving genetic factors, chronic inflammation, lipid deposition, and valve mineralization. Mineralization is strictly related to the inflammatory process in which both, innate, and adaptive immunity are involved. The underlying pathophysiological pathways that go from inflammation to calcification and, finally lead to severe stenosis, remain, however, incompletely understood. Histopathological studies are limited to patients with severe CAVD and no samples are available for longitudinal studies of disease progression. Therefore, alternative routes should be explored to investigate the pathogenesis and progression of CAVD.Recently, increasing evidence suggests that epigenetic markers such as non-coding RNAs are implicated in the landscape of phenotypical changes occurring in CAVD. Furthermore, the microbiome, an essential player in several diseases, including the cardiovascular ones, has recently been linked to the inflammation process occurring in CAVD. In the present review, we analyze and discuss the CAVD pathophysiology and future therapeutic strategies, focusing on the real and putative role of inflammation, calcification, and microbiome.

Quantifying heart valve interstitial cell contractile state using highly tunable poly(ethylene glycol) hydrogels

Valve interstitial cells (VIC) are the primary cell type residing within heart valve tissues. In many valve pathologies, VICs become activated and will subsequently profoundly remodel the valve tissue extracellular matrix (ECM). A primary indicator of VIC activation is the upregulation of α-smooth muscle actin (αSMA) stress fibers, which in turn increase VIC contractility. Thus, contractile state reflects VIC activation and ECM biosynthesis levels. In general, cell contraction studies have largely utilized two-dimensional substrates, which are a vastly different micro mechanical environment than 3D native leaflet tissue. To address this limitation, hydrogels have been a popular choice for studying cells in a three-dimensional environment due to their tunable properties and optical transparency, which allows for direct cell visualization. In the present study, we extended the use of hydrogels to study the active contractile behavior of VICs. Aortic VICs (AVIC) were encapsulated within poly(ethylene glycol) (PEG) hydrogels and were subjected to flexural-deformation tests to assess the state of AVIC contraction. Using a finite element model of the experimental setup, we determined the effective shear modulus μ of the constructs. An increase in μ resulting from AVIC active contraction was observed. Results further indicated that AVIC contraction had a more pronounced effect on μ in softer gels (72 ± 21% increase in μ within 2.5 kPa gels) and was dependent upon the availability of adhesion sites (0.5-1 mM CRGDS). The transparency of the gel allowed us to image AVICs directly within the hydrogel, where we observed a time-dependent decrease in volume (time constant τ=3.04 min) when the AVICs were induced into a hypertensive state. Our results indicated that AVIC contraction was regulated by both the intrinsic (unseeded) gel stiffness and the CRGDS peptide concentrations. This finding suggests that AVIC contractile state can be profoundly modulated through their local micro environment using modifiable PEG gels in a 3D micromechanical-emulating environment. Moving forward, this approach has the potential to be used towards delineating normal and diseased VIC biomechanical properties using highly tunable PEG biomaterials. STATEMENT OF SIGNIFICANCE.

[The renin-angiotensin-aldosterone system as a potential target for therapy in patients with calcific aortic stenosis: a literature review]

Calcific aortic valve stenosis (CAVS) is a serious socio-economic problem in developed countries because this disease is the most common indication for aortic valve replacement. Currently, there are no methods for non-invasive treatment of CAVS. Nevertheless, it is assumed that effective drug therapy for CAVS can be developed on the basis of modulators of the renin-angiotensin-aldosterone system (RAAS), which is involved in the pathogenesis of this disease. The purpose of this paper is to compile and analyze current information on the role of RAAS in the CAVS pathophysiology. Recent data on the effectiveness of RAAS inhibition are reviewed.

Development of calcific aortic valve disease: Do we know enough for new clinical trials?

Calcific aortic valve disease (CAVD), previously thought to represent a passive degeneration of the valvular extracellular matrix (VECM), is now regarded as an intricate multistage disorder with sequential yet intertangled and interacting underlying processes. Endothelial dysfunction and injury, initiated by disturbed blood flow and metabolic disorders, lead to the deposition of low-density lipoprotein cholesterol in the VECM further provoking macrophage infiltration, oxidative stress, and release of pro-inflammatory cytokines. Such changes in the valvular homeostasis induce differentiation of normally quiescent valvular interstitial cells (VICs) into synthetically active myofibroblasts producing excessive quantities of the VECM and proteins responsible for its remodeling. As a result of constantly ongoing degradation and re-deposition, VECM becomes disorganised and rigid, additionally potentiating myofibroblastic differentiation of VICs and worsening adaptation of the valve to the blood flow. Moreover, disrupted and excessively vascularised VECM is susceptible to the dystrophic calcification caused by calcium and phosphate precipitating on damaged collagen fibers and concurrently accompanied by osteogenic differentiation of VICs. Being combined, passive calcification and biomineralisation synergistically induce ossification of the aortic valve ultimately resulting in its mechanical incompetence requiring surgical replacement. Unfortunately, multiple attempts have failed to find an efficient conservative treatment of CAVD; however, therapeutic regimens and clinical settings have also been far from the optimal. In this review, we focused on interactions and transitions between aforementioned mechanisms demarcating ascending stages of CAVD, suggesting a predisposing condition (bicuspid aortic valve) and drug combination (lipid-lowering drugs combined with angiotensin II antagonists and cytokine inhibitors) for the further testing in both preclinical and clinical trials.

Quest for cardiovascular interventions: precise modeling and 3D printing of heart valves

Digitalization of health care practices is substantially manifesting itself as an effective tool to diagnose and rectify complex cardiovascular abnormalities. For cardiovascular abnormalities, precise non-invasive imaging interventions are being used to develop patient specific diagnosis and surgical planning. Concurrently, pre surgical 3D simulation and computational modeling are aiding in the effective surgery and understanding of valve biomechanics, respectively. Consequently, 3D printing of patient specific valves that can mimic the original one will become an effective outbreak for valvular problems. Printing of these patient-specific tissues or organ components is becoming a viable option owing to the advances in biomaterials and additive manufacturing techniques. These additive manufacturing techniques are receiving a full-fledged support from burgeoning field of computational fluid dynamics, digital image processing, artificial intelligence, and continuum mechanics during their optimization and implementation. Further, studies at cellular and molecular biomechanics have enriched our understanding of biomechanical factors resulting in valvular heart diseases. Hence, the knowledge generated can guide us during the design and synthesis of biomaterials to develop superior extra cellular matrix, mimicking materials that can be used as a bioink for 3D printing of organs and tissues. With this notion, we have reviewed current opportunities and challenges in the diagnosis and treatment of heart valve abnormalities through patient-specific valve design via tissue engineering and 3D bioprinting. These valves can replace diseased valves by preserving homogeneity and individuality of the patients.

Inflammation and Mechanical Stress Stimulate Osteogenic Differentiation of Human Aortic Valve Interstitial Cells

Background: Aortic valve calcification is an active proliferative process, where interstitial cells of the valve transform into either myofibroblasts or osteoblast-like cells causing valve deformation, thickening of cusps and finally stenosis. This process may be triggered by several factors including inflammation, mechanical stress or interaction of cells with certain components of extracellular matrix. The matrix is different on the two sides of the valve leaflets. We hypothesize that inflammation and mechanical stress stimulate osteogenic differentiation of human aortic valve interstitial cells (VICs) and this may depend on the side of the leaflet. Methods: Interstitial cells isolated from healthy and calcified human aortic valves were cultured on collagen or elastin coated plates with flexible bottoms, simulating the matrix on the aortic and ventricular side of the valve leaflets, respectively. The cells were subjected to 10% stretch at 1 Hz (FlexCell bioreactor) or treated with 0.1 μg/ml lipopolysaccharide, or both during 24 h. Gene expression of myofibroblast- and osteoblast-specific genes was analyzed by qPCR. VICs cultured in presence of osteogenic medium together with lipopolysaccharide, 10% stretch or both for 14 days were stained for calcification using Alizarin Red. Results: Treatment with lipopolysaccharide increased expression of osteogenic gene bone morphogenetic protein 2 (BMP2) (5-fold increase from control; p = 0.02) and decreased expression of mRNA of myofibroblastic markers: α-smooth muscle actin (ACTA2) (50% reduction from control; p = 0.0006) and calponin (CNN1) (80% reduction from control; p = 0.0001) when cells from calcified valves were cultured on collagen, but not on elastin. Mechanical stretch of VICs cultured on collagen augmented the effect of lipopolysaccharide. Expression of periostin (POSTN) was inhibited in cells from calcified donors after treatment with lipopolysaccharide on collagen (70% reduction from control, p = 0.001), but not on elastin. Lipopolysaccharide and stretch both enhanced the pro-calcific effect of osteogenic medium, further increasing the effect when combined for cells cultured on collagen, but not on elastin. Conclusion: Inflammation and mechanical stress trigger expression of osteogenic genes in VICs in a side-specific manner, while inhibiting the myofibroblastic pathway. Stretch and lipopolysaccharide synergistically increase calcification.

Engineering a 3D-Bioprinted Model of Human Heart Valve Disease Using Nanoindentation-Based Biomechanics

In calcific aortic valve disease (CAVD), microcalcifications originating from nanoscale calcifying vesicles disrupt the aortic valve (AV) leaflets, which consist of three (biomechanically) distinct layers: the fibrosa, spongiosa, and ventricularis. CAVD has no pharmacotherapy and lacks in vitro models as a result of complex valvular biomechanical features surrounding resident mechanosensitive valvular interstitial cells (VICs). We measured layer-specific mechanical properties of the human AV and engineered a three-dimensional (3D)-bioprinted CAVD model that recapitulates leaflet layer biomechanics for the first time. Human AV leaflet layers were separated by microdissection, and nanoindentation determined layer-specific Young’s moduli. Methacrylated gelatin (GelMA)/methacrylated hyaluronic acid (HAMA) hydrogels were tuned to duplicate layer-specific mechanical characteristics, followed by 3D-printing with encapsulated human VICs. Hydrogels were exposed to osteogenic media (OM) to induce microcalcification, and VIC pathogenesis was assessed by near infrared or immunofluorescence microscopy. Median Young’s moduli of the AV layers were 37.1, 15.4, and 26.9 kPa (fibrosa/spongiosa/ventricularis, respectively). The fibrosa and spongiosa Young’s moduli matched the 3D 5% GelMa/1% HAMA UV-crosslinked hydrogels. OM stimulation of VIC-laden bioprinted hydrogels induced microcalcification without apoptosis. We report the first layer-specific measurements of human AV moduli and a novel 3D-bioprinted CAVD model that potentiates microcalcification by mimicking the native AV mechanical environment. This work sheds light on valvular mechanobiology and could facilitate high-throughput drug-screening in CAVD.

Conditional deletion of RB1 in the Tie2 lineage leads to aortic valve regurgitation

Objective

Aortic valve disease is a complex process characterized by valve interstitial cell activation, disruption of the extracellular matrix culminating in valve mineralization occurring over many years. We explored the function of the retinoblastoma protein (pRb) in aortic valve disease, given its critical role in mesenchymal cell differentiation including bone development and mineralization.

Approach and results

We generated a mouse model of conditional pRb knockout (cKO) in the aortic valve regulated by Tie2-Cre-mediated excision of floxed RB1 alleles. Aged pRb cKO animals showed significantly more aortic valve regurgitation by echocardiography compared to pRb het control animals. The pRb cKO aortic valves had increased leaflet thickness without increased cellular proliferation. Histologic studies demonstrated intense α-SMA expression in pRb cKO leaflets associated with disorganized extracellular matrix and increased leaflet stiffness. The pRb cKO mice also showed increased circulating cytokine levels.

Conclusions

Our studies demonstrate that pRb loss in the Tie2-lineage that includes aortic valve interstitial cells is sufficient to cause age-dependent aortic valve dysfunction.

In-vitro analysis of early calcification in aortic valvular interstitial cells using Laser-Induced Breakdown Spectroscopy (LIBS)

Calcific aortic valve disease (CAVD) is a major cardiovascular disorder caused by osteogenic differentiation of valvular interstitial cells (VICs) within aortic valves. Conventional methods like colorimetric assays and histology fail to detect small calcium depositions during in-vitro VIC cultures. Laser-induced breakdown spectroscopy (LIBS) is a robust analytical tool used for inorganic materials characterizations, but relatively new to biomedical applications. We employ LIBS, for the first time, for quantitative in-vitro detection of calcium depositions in VICs at various osteogenic differentiation stages. VICs isolated from porcine aortic valves were cultured in osteogenic media over various days. Colorimetric calcium assays based on arsenazo dye and Von Kossa staining measured the calcium depositions within VICs. Simultaneously, LIBS signatures for Ca I (422.67 nm) atomic emission lines were collected for estimating calcium depositions in lyophilized VIC samples. Our results indicate excellent linear correlation between the calcium assay and our LIBS measurements. Furthermore, unlike the assay results, the LIBS results could resolve calcium signals from cell samples with as early as 2 days of osteogenic culture. Quantitatively, the LIBS measurements establish the limit of detection for calcium content in VICs to be ∼0.17±0.04 μg which indicates a 5-fold improvement over calcium assay. Picture: Quantitative LIBS enables in-vitro analysis for early stage detection of calcium deposition within aortic valvular interstitial cells (VICs).

Applications of Cardiac Extracellular Matrix in Tissue Engineering and Regenerative Medicine

The role of the cardiac extracellular matrix (cECM) in providing biophysical and biochemical cues to the cells housed within during disease and development has become increasingly apparent. These signals have been shown to influence many fundamental cardiac cell behaviors including contractility, proliferation, migration, and differentiation. Consequently, alterations to cell phenotype result in directed remodeling of the cECM. This bidirectional communication means that the cECM can be envisioned as a medium for information storage. As a result, the reprogramming of the cECM is increasingly being employed in tissue engineering and regenerative medicine as a method with which to treat disease. In this chapter, an overview of the composition and structure of the cECM as well as its role in cardiac development and disease will be provided. Additionally, therapeutic modulation of cECM for cardiac regeneration as well as bottom-up and top-down approaches to ECM-based cardiac tissue engineering is discussed. Finally, lingering questions regarding the role of cECM in tissue engineering and regenerative medicine are offered as a catalyst for future research.

Hilaire C, Hortells L, Phillippi JA, Sant V, Sant S. Shape-Specific Nanoceria Mitigate Oxidative Stress-Induced Calcification in Primary Human Valvular Interstitial Cell Culture

INTRODUCTION

Lack of effective pharmacological treatment makes valvular calcification a significant clinical problem in patients with valvular disease and bioprosthetic/mechanical valve replacement therapies. Elevated levels of reactive oxygen species (ROS) in valve tissue have been identified as a prominent hallmark and driving factor for valvular calcification. However, the therapeutic value of ROS-modulating agents for valvular calcification remains elusive. We hypothesized that ROS-modulating shape-specific cerium oxide nanoparticles (CNPs) will inhibit oxidative stress-induced valvular calcification. CNPs are a class of self-regenerative ROS-modulating agents, which can switch between Ce3+ and Ce4+ in response to oxidative microen-vironment. In this work, we developed oxidative stress-induced valve calcification model using two patient-derived stenotic valve interstitial cells (hVICs) and investigated the therapeutic effect of shape-specific CNPs to inhibit hVIC calcification.

METHODS

Human valvular interstitial cells (hVICs) were obtained from a normal healthy donor and two patients with calcified aortic valves. hVICs were characterized for their phenotypic (mesenchymal, myofibroblast and osteoblast) marker expression by qRT-PCR and antioxidant enzymes activity before and after exposure to hydrogen peroxide (H2O2)-induced oxidative stress. Four shape-specific CNPs (sphere, short rod, long rod, and cube) were synthesized via hydrothermal or ultra-sonication method and characterized for their biocompatibility in hVICs by alamarBlue® assay, and ROS scavenging ability by DCFH-DA assay. H2O2 and inorganic phosphate (Pi) were co-administrated to induce hVIC calcification in vitro as demonstrated by Alizarin Red S staining and calcium quantification. The effect of CNPs on inhibiting H2O2-induced hVIC calcification was evaluated.

RESULTS

hVICs isolated from calcified valves exhibited elevated osteoblast marker expression and decreased antioxidant enzyme activities compared to the normal hVICs. Due to the impaired antioxidant enzyme activities, acute H2O2-induced oxidative stress resulted in higher ROS levels and osteoblast marker expression in both diseased hVICs when compared to the normal hVICs. Shape-specific CNPs exhibited shape-dependent abiotic ROS scavenging ability, and excellent cytocompatibility. Rod and sphere CNPs scavenged H2O2-induced oxidative stress in hVICs in a shape- and dose-dependent manner by lowering intracellular ROS levels and osteoblast marker expression. Further, CNPs also enhanced activity of antioxidant enzymes in hVICs to combat oxidative stress. Cube CNPs were not effective ROS scavengers. The addition of H2O2 in the Pi-induced calcification model further increased calcium deposition in vitro in a time-dependent manner. Co-administration of rod CNPs with Pi and H2O2 mitigated calcification in the diseased hVICs.

CONCLUSIONS

We demonstrated that hVICs derived from calcified valves exhibited impaired antioxidant defense mechanisms and were more susceptible to oxidative stress than normal hVICs. CNPs scavenged H2O2-induced oxidative stress in hVICs in a shape-dependent manner. The intrinsic ROS scavenging ability of CNPs and their ability to induce cellular antioxidant enzyme activities may confer protection from oxidative stress-exacerbated calcification. CNPs represent promising antioxidant therapy for treating valvular calcification and deserve further investigation.

Robust Generation of Quiescent Porcine Valvular Interstitial Cell Cultures

Background

Valvular interstitial cells (VICs) in the healthy aortic valve leaflet exhibit a quiescent phenotype, with <5% of VICs exhibiting an activated phenotype. Yet, in vitro culture of VICs on tissue culture polystyrene surfaces in standard growth medium results in rapid transformation to an activated phenotype in >90% of cells. The inability to preserve a healthy VIC phenotype during in vitro studies has hampered the elucidation of mechanisms involved in calcific aortic valve disease. This study describes the generation of quiescent populations of porcine VICs in 2‐dimensional in vitro culture and their utility in studying valve pathobiology.

Methods and Results

Within 4 days of isolation from fresh porcine hearts, VICs cultured in standard growth conditions were predominantly myofibroblastic (activated VICs). This myofibroblastic phenotype was partially reversed within 4 days, and fully reversed within 9 days, following application of a combination of a fibroblast media formulation with culture on collagen coatings. Specifically, culture in this combination significantly reduced several markers of VIC activation, including proliferation, apoptosis, α‐smooth muscle actin expression, and matrix production, relative to standard growth conditions. Moreover, VICs raised in a fibroblast media formulation with culture on collagen coatings exhibited dramatically increased sensitivity to treatment with transforming growth factor β1, a known pathological stimulus, compared with VICs raised in either standard culture or medium with a fibroblast media formulation.

Conclusions

The approach using a fibroblast media formulation with culture on collagen coatings generates quiescent VICs that more accurately mimic a healthy VIC population and thus has the potential to transform the study of the mechanisms of VIC activation and dysfunction involved in the early stages of calcific aortic valve disease.

A functionally graded material model for the transmural stress distribution of the aortic valve leaflet

Heterogeneities in structure and stress within heart valve leaflets are of significant concern to their functional physiology, as they affect how the tissue constituents remodel in response to pathological and non-pathological (e.g. exercise, pregnancy) alterations in cardiac function. Indeed, valve interstitial cells (VICs) are known to synthesize and degrade leaflet extracellular matrix (ECM) components in a manner specific to their local micromechanical environment. Quantifying local variations in ECM structure and stress is thus necessary to understand homeostatic valve maintenance as well as to develop predictive models of disease progression and post-surgical outcomes. In the aortic valve (AV), transmural variations in stress have previously been investigated by modeling the leaflet as a composite of contiguous but mechanically distinct layers. Based on previous findings about the bonded nature of these layers (Buchanan and Sacks, BMMB, 2014), we developed a more generalized structural constitutive model by treating the leaflet as a functionally graded material (FGM), whose properties vary continuously over the thickness. We informed the FGM model using high-resolution morphological measurements, which demonstrated that the composition and fiber structure change gradually over the thickness of the AV leaflet. For validation, we fit the model against an extensive database of whole-leaflet and individual-layer mechanical responses. The FGM model predicted large stress variations both between and within the leaflet layers at end-diastole, with low-collagen regions bearing significant radial stress. These novel results suggest that the continually varying structure of the AV leaflet has an important purpose with regard to valve function and tissue homeostasis.

Planar biaxial testing of heart valve cusp replacement biomaterials: Experiments, theory and material constants

OBJECTIVES

Aortic valve (AV) repair has become an attractive option to correct aortic insufficiency. Yet, cusp reconstruction with various cusp replacement materials has been associated with greater long-term repair failures, and it is still unknown how such materials mechanically compare with native leaflets. We used planar biaxial testing to characterize six clinically relevant cusp replacement materials, along with native porcine AV leaflets, to ascertain which materials would be best suited for valve repair.

METHODS

We tested at least six samples of: 1) fresh autologous porcine pericardium (APP), 2) glutaraldehyde fixed porcine pericardium (GPP), 3) St Jude Medical pericardial patch (SJM), 4) CardioCel patch (CC), 5) PeriGuard (PG), 6) Supple PeriGuard (SPG) and 7) fresh porcine AV leaflets (PC). We introduced efficient displacement-controlled testing protocols and processing, as well as advanced convexity requirements on the strain energy functions used to describe the mechanical response of the materials under loading.

RESULTS

The proposed experimental and data processing pipeline allowed for a robust in-plane characterization of all the materials tested, with constants determined for two Fung-like hyperelastic, anisotropic strain energy models.

CONCLUSIONS

Overall, CC and SPG (respectively PG) patches ranked as the closest mechanical equivalents to young (respectively aged) AV leaflets. Because the native leaflets as well as CC, PG and SPG patches exhibit significant anisotropic behaviors, it is suggested that the fiber and cross-fiber directions of these replacement biomaterials be matched with those of the host AV leaflets.

STATEMENT OF SIGNIFICANCE

The long-term performance of cusp replacement materials would ideally be evaluated in large animal models for AV disease and cusp repair, and over several months or more. Given the unavailability and impracticality of such models, detailed information on stress-strain behavior, as studied herein, and investigations of durability and valve dynamics will be the best surrogates, as they have been for prosthetic valves. Overall, comparison with Fig. 3 suggests that CC and SPG (respectively PG) patches may be the closest mechanical equivalents to young (respectively aged) AV leaflets. Interestingly, the thicknesses of these materials are close to those reported for porcine and younger human AV leaflets, which may facilitate surgical implantation, by contrast to the thinner APP which has poor handling qualities. Because the native leaflets as well as CC, PG and SPG patches exhibit anisotropic behaviors, from a mechanistic perspective alone, it stands to reason that cardiac surgeons should seek to intraoperatively match the fiber and cross-fiber directions of these replacement biomaterials with those of the repaired AV leaflets.

Sex-related differences in matrix remodeling and early osteogenic markers in aortic valvular interstitial cells

Calcific aortic valve disease (CAVD) is a major cardiovascular disorder in the developed countries. Male is a known risk factor in this disease; unfortunately, how sex contributes to CAVD is mostly unknown. The objective of this study is to determine whether valvular interstitial cells (VICs) isolated from male versus female aortic valves demonstrate difference in osteogenic differentiation and/or extracellular matrix (ECM) remodeling. VICs were isolated from male and female rat or porcine aortic valves and cultured in osteogenic media for 10, 15 and 20 days. The proliferation among male and female VICs was assessed by a cell growth assay. The matrix remodeling of the VIC samples was quantified using glycosaminoglycan (GAG), collagen type I and gelatin zymography assays. Early osteogenic marker expression was assessed using alkaline phosphatase (ALP) staining and enzyme activity assay and Alizarin Red S staining. Our result showed that proliferation of VICs was significantly greater in female than male after 12 days of culture in regular media. Additionally, male VICs showed elevated amounts of normalized GAG, collagen I, and activated matrix metallopreoteniase-2 expression compared to female. Similarly, ALP content was greater in male VICs than female at all time points. In addition, male VICs formed calcific nodules with greater size, % area and integrated density than females. The results from this research suggest that there is a sex-related difference in the events associated with osteogenic differentiation of the aortic VICs, where male VICs are more prone to calcification.

Calcific Aortic Valve Disease Is Associated with Layer-Specific Alterations in Collagen Architecture

Disorganization of the valve extracellular matrix (ECM) is a hallmark of calcific aortic valve disease (CAVD). However, while microarchitectural features of the ECM can strongly influence the biological and mechanical behavior of tissues, little is known about the ECM microarchitecture in CAVD. In this work, we apply advanced imaging techniques to quantify spatially heterogeneous changes in collagen microarchitecture in CAVD. Human aortic valves were obtained from individuals between 50 and 75 years old with no evidence of valvular disease (healthy) and individuals who underwent valve replacement surgery due to severe stenosis (diseased). Second Harmonic Generation microscopy and subsequent image quantification revealed layer-specific changes in fiber characteristics in healthy and diseased valves. Specifically, the majority of collagen fiber changes in CAVD were found to occur in the spongiosa, where collagen fiber number increased by over 2-fold, and fiber width and density also significantly increased. Relatively few fibrillar changes occurred in the fibrosa in CAVD, where fibers became significantly shorter, but did not otherwise change in terms of number, width, density, or alignment. Immunohistochemical staining for lysyl oxidase showed localized increased expression in the diseased fibrosa. These findings reveal a more complex picture of valvular collagen enrichment and arrangement in CAVD than has previously been described using traditional analysis methods. Changes in fiber architecture may play a role in regulating the pathobiological events and mechanical properties of valves during CAVD. Additionally, characterization of the ECM microarchitecture can inform the design of fibrous scaffolds for heart valve tissue engineering.

Shear-Sensitive Genes in Aortic Valve Endothelium

SIGNIFICANCE

Currently, calcific aortic valve disease (CAVD) is only treatable through surgical intervention because the specific mechanisms leading to the disease remain unclear. In this review, we explore the forces and structure of the valve, as well as the mechanosensors and downstream signaling in the valve endothelium known to contribute to inflammation and valve dysfunction.

RECENT ADVANCES

While the valvular structure enables adaptation to dynamic hemodynamic forces, these are impaired during CAVD, resulting in pathological systemic changes. Mechanosensing mechanisms-proteins, sugars, and membrane structures-at the surface of the valve endothelial cell relay mechanical signals to the nucleus. As a result, a large number of mechanosensitive genes are transcribed to alter cellular phenotype and, ultimately, induce inflammation and CAVD. Transforming growth factor-β signaling and Wnt/β-catenin have been widely studied in this context. Importantly, NADPH oxidase and reactive oxygen species/reactive nitrogen species signaling has increasingly been recognized to play a key role in the cellular response to mechanical stimuli. In addition, a number of valvular microRNAs are mechanosensitive and may regulate the progression of CAVD.

CRITICAL ISSUES

While numerous pathways have been described in the pathology of CAVD, no treatment options are available to avoid surgery for advanced stenosis and calcification of the aortic valve. More work must be focused on this issue to lead to successful therapies for the disease.

FUTURE DIRECTIONS

Ultimately, a more complete understanding of the mechanisms within the aortic valve endothelium will lead us to future therapies important for treatment of CAVD without the risks involved with valve replacement or repair. Antioxid. Redox Signal. 25, 401-414.

Interleukin 18 promotes myofibroblast activation of valvular interstitial cells

BACKGROUND

Calcific aortic valve disease is the main heart valve disease in the elderly. Valvular interstitial cells (VICs) play an important role in the process of valve calcification. Interleukin 18 (IL-18) is expressed in stenosis aortic valves and is positively related with the clinical severity of aortic stenosis. However, the role of IL-18 in aortic valve calcification remains unclear. This study examined whether IL-18 promotes myofibroblast and/or osteoblast transdifferention of VICs. Porcine VICs were isolated and treated with recombinant porcine IL-18.

METHODS

Porcine VICs were cultured and treated with IL-18. Gene and protein expression of myofibroblastic and osteoblastic markers were tested and nuclear factor κB (NF-κB) phosphorylation was also analyzed. Alkaline phosphatase (ALP) staining and activity assay were also performed.

RESULTS

Our experiments demonstrated that IL-18 significantly enhanced alpha-smooth muscle actin (α-SMA) gene and protein expression. IL-18 treatment also promoted the expression of osteopontin (OPN) and runt-related transcription factor 2 (Runx2) mRNA, although OPN and Runx2 protein expressions were not changed. IL-18 could induce ALP activity in the presence of conditioning medium. We also demonstrated that IL-18 markedly enhanced NF-κB p65 phosphorylation in VICs.

CONCLUSIONS

Together these results suggest that IL-18 promotes the myofibroblast differentiation of VICs and accelerates calcification in the presence of conditioning medium via the NF-κB pathway.

Acute pergolide exposure stiffens engineered valve interstitial cell tissues and reduces contractility in vitro

Medications based on ergoline-derived dopamine and serotonin agonists are associated with off-target toxicities that include valvular heart disease (VHD). Reports of drug-induced VHD resulted in the withdrawal of appetite suppressants containing fenfluramine and phentermine from the US market in 1997 and pergolide, a Parkinson's disease medication, in 2007. Recent evidence suggests that serotonin receptor activity affected by these medications modulates cardiac valve interstitial cell activation and subsequent valvular remodeling, which can lead to cardiac valve fibrosis and dysfunction similar to that seen in carcinoid heart disease. Failure to identify these risks prior to market and continued use of similar drugs reaffirm the need to improve preclinical evaluation of drug-induced VHD. Here, we present two complimentary assays to measure stiffness and contractile stresses generated by engineered valvular tissues in vitro. As a case study, we measured the effects of acute (24 h) pergolide exposure to engineered porcine aortic valve interstitial cell (AVIC) tissues. Pergolide exposure led to increased tissue stiffness, but it decreased both basal and active contractile tone stresses generated by AVIC tissues. Pergolide exposure also disrupted AVIC tissue organization (i.e., tissue anisotropy), suggesting that the mechanical properties and contractile functionality of these tissues are governed by their ability to maintain their structure. We expect further use of these assays to identify off-target drug effects that alter the phenotypic balance of AVICs, disrupt their ability to maintain mechanical homeostasis, and lead to VHD.