The living aortic valve: From molecules to function

Osteopontin stabilization and collagen containment slows amorphous calcium phosphate transformation during human aortic valve leaflet calcification

Calcification of aortic valve leaflets is a growing mortality threat for the 18 million human lives claimed globally each year by heart disease. Extensive research has focused on the cellular and molecular pathophysiology associated with calcification, yet the detailed composition, structure, distribution and etiological history of mineral deposition remains unknown. Here transdisciplinary geology, biology and medicine (GeoBioMed) approaches prove that leaflet calcification is driven by amorphous calcium phosphate (ACP), ACP at the threshold of transformation toward hydroxyapatite (HAP) and cholesterol biomineralization. A paragenetic sequence of events is observed that includes: (1) original formation of unaltered leaflet tissues: (2) individual and coalescing 100's nm- to 1 μm-scale ACP spherules and cholesterol crystals biomineralizing collagen fibers and smooth muscle cell myofilaments; (3) osteopontin coatings that stabilize ACP and collagen containment of nodules preventing exposure to the solution chemistry and water content of pumping blood, which combine to slow transformation to HAP; (4) mm-scale nodule growth via ACP spherule coalescence, diagenetic incorporation of altered collagen and aggregation with other ACP nodules; and (5) leaflet diastole and systole flexure causing nodules to twist, fold their encasing collagen fibers and increase stiffness. These in vivo mechanisms combine to slow leaflet calcification and establish previously unexplored hypotheses for testing novel drug therapies and clinical interventions as viable alternatives to current reliance on surgical/percutaneous valve implants.

Comparison study of surface-initiated hydrogel coatings with distinct side-chains for improving biocompatibility of polymeric heart valves

Polymeric heart valves (PHVs) present a promising alternative for treating valvular heart diseases with satisfactory hydrodynamics and durability against structural degeneration. However, the cascaded coagulation, inflammatory responses, and calcification in the dynamic blood environment pose significant challenges to the surface design of current PHVs. In this study, we employed a surface-initiated polymerization method to modify polystyrene-block-isobutylene-block-styrene (SIBS) by creating three hydrogel coatings: poly(2-methacryloyloxy ethyl phosphorylcholine) (pMPC), poly(2-acrylamido-2-methylpropanesulfonic acid) (pAMPS), and poly(2-hydroxyethyl methacrylate) (pHEMA). These hydrogel coatings dramatically promoted SIBS's hydrophilicity and blood compatibility at the initial state. Notably, the pMPC and pAMPS coatings maintained a considerable platelet resistance performance after 12 h of sonication and 10 000 cycles of stretching and bending. However, the sonication process induced visible damage to the pHEMA coating and attenuated the anti-coagulation property. Furthermore, the in vivo subcutaneous implantation studies demonstrated that the amphiphilic pMPC coating showed superior anti-inflammatory and anti-calcification properties. Considering the remarkable stability and optimal biocompatibility, the amphiphilic pMPC coating constructed by surface-initiated polymerization holds promising potential for modifying PHVs.

Mechanical modeling of the maturation process for tissue-engineered implants: Application to biohybrid heart valves

The development of tissue-engineered cardiovascular implants can improve the lives of large segments of our society who suffer from cardiovascular diseases. Regenerative tissues are fabricated using a process called tissue maturation. Furthermore, it is highly challenging to produce cardiovascular regenerative implants with sufficient mechanical strength to withstand the loading conditions within the human body. Therefore, biohybrid implants for which the regenerative tissue is reinforced by standard reinforcement material (e.g. textile or 3d printed scaffold) can be an interesting solution. In silico models can significantly contribute to characterizing, designing, and optimizing biohybrid implants. The first step towards this goal is to develop a computational model for the maturation process of tissue-engineered implants. This paper focuses on the mechanical modeling of textile-reinforced tissue-engineered cardiovascular implants. First, an energy-based approach is proposed to compute the collagen evolution during the maturation process. Then, the concept of structural tensors is applied to model the anisotropic behavior of the extracellular matrix and the textile scaffold. Next, the newly developed material model is embedded into a special solid-shell finite element formulation with reduced integration. Finally, our framework is used to compute two structural problems: a pressurized shell construct and a tubular-shaped heart valve. The results show the ability of the model to predict collagen growth in response to the boundary conditions applied during the maturation process. Consequently, the model can predict the implant's mechanical response, such as the deformation and stresses of the implant.

Valvulogenesis of a living, innervated pulmonary root induced by an acellular scaffold

Heart valve disease is a major cause of mortality and morbidity worldwide with no effective medical therapy and no ideal valve substitute emulating the extremely sophisticated functions of a living heart valve. These functions influence survival and quality of life. This has stimulated extensive attempts at tissue engineering "living" heart valves. These attempts utilised combinations of allogeneic/ autologous cells and biological scaffolds with practical, regulatory, and ethical issues. In situ regeneration depends on scaffolds that attract, house and instruct cells and promote connective tissue formation. We describe a surgical, tissue-engineered, anatomically precise, novel off-the-shelf, acellular, synthetic scaffold inducing a rapid process of morphogenesis involving relevant cell types, extracellular matrix, regulatory elements including nerves and humoral components. This process relies on specific material characteristics, design and "morphodynamism".

Asymmetry of flow in aortic root and its application in hypertrophic obstructive cardiomyopathy

The aortic root (AR) performs sophisticated functions regulating the blood dynamics during the cardiac cycle. Such complex function depends on the nature of flow in the AR. Here, we investigate the potential of new quantitative parameters of flow asymmetry that could have clinical implications. We developed a MATLAB program to study the AR hemodynamics in each sinus of Valsalva using two-dimensional (2-D) cardiac magnetic resonance imaging during systole and particularly at peak systolic flow in 13 healthy volunteers and compared with 10 patients with hypertrophic obstructive cardiomyopathy (HOCM). We show that the effective area of the aortic jet in healthy volunteers is significantly higher at peak systolic flow and on average during systole. The flow asymmetry index, indicating how the jet is skewed away from the left coronary sinus (LCS), is small in healthy volunteers and much larger in HOCM at peak systole. The average of this index over systole is significantly more different between cohorts. Looking in more detail at the flow in the sinuses during systole, we show that the AR jet in healthy volunteers is more symmetrical, affecting the three sinuses almost equally, unlike the asymmetric AR jet in patients with HOCM that has decreased flow rate in the LCS and increased fractional area of backward flow in the LCS. The percentage of backward flow in the sinuses of Valsalva calculated over systole is a potential indicator of perturbed AR hemodynamics and the distribution of vortical flow and could be used as a measure of flow asymmetry.NEW & NOTEWORTHY The aortic root is a vital organ responsible for performing sophisticated functions to regulate the blood flow dynamics during the cardiac cycle. Such synchronized complex performance affects and is affected by the flow symmetry and type of flow reaching the aorta. Here, we report flow asymmetry in the aortic root which could have clinical implications, and we investigate the potential of various quantitative parameters as measures of flow asymmetry in hypertrophic obstructive cardiomyopathy.

Secondary analysis of REPRISE III trial: The Lotus valve's persistence after withdrawal

INTRODUCTION

Aortic stenosis (AS) is the leading heart valve disease in developed countries, often caused by calcific degeneration. In low-and-middle-income countries, it's primarily due to RHD. Prevalence of AS increases with age and up to 22.8% of those affected over the age of 75. While surgical aortic valve replacement is standard treatment for AS, many older individuals are not ideal candidates. Transcatheter aortic valve replacement (TAVR) offers an alternative. The REPRISE III trial showed the Lotus valve outperformed the CoreValve/EvolutR TAVR valves in various metrics over 2 years. Despite its success and over 10,000 implantations, the Lotus valve was pulled from the market, highlighting the need to understand its long-term outcomes. Study and results: In the REPRISE III trial, the long-term outcomes of TAVR using the Lotus valve were compared to the CoreValve/EvolutR over 5 years across 55 global centers. Of the participants, 581 (95.7%) used the Lotus valve and 285 (93.4%) used CoreValve/EvolutR. Event rates for all-cause mortality were similar between the groups, but the Lotus valve group had lower rates of disabling stroke and pacemaker implantation. The Lotus valve showed a higher aortic gradient but lower effective orifice area. Additionally, the Lotus valve had reduced mild PVL, valve malpositioning, and the need for a second valve. Both groups showed comparable long-term improvements in heart and cardiomyopathy assessments.

LESSONS LEARNED

The REPRISE III analysis highlights the favourable long-term outcomes of the Lotus valve and CoreValve/EvolutR for high-risk surgical patients. These findings underscore the importance of ongoing management post-valve procedure and the potential advantages of the Lotus valve design. Further studies comparing these valves to surgery will inform aortic stenosis management and potentially expand TAVR indications. The future goal is to develop a tissue-engineered living heart valve to improve survival and quality of life.

Calcific aortic valve disease: mechanisms, prevention and treatment

Calcific aortic valve disease (CAVD) is the most common disorder affecting heart valves and is characterized by thickening, fibrosis and mineralization of the aortic valve leaflets. Analyses of surgically explanted aortic valve leaflets have shown that dystrophic mineralization and osteogenic transition of valve interstitial cells co-occur with neovascularization, microhaemorrhage and abnormal production of extracellular matrix. Age and congenital bicuspid aortic valve morphology are important and unalterable risk factors for CAVD, whereas additional risk is conferred by elevated blood pressure and plasma lipoprotein(a) levels and the presence of obesity and diabetes mellitus, which are modifiable factors. Genetic and molecular studies have identified that the NOTCH, WNT-β-catenin and myocardin signalling pathways are involved in the control and commitment of valvular cells to a fibrocalcific lineage. Complex interactions between valve endothelial and interstitial cells and immune cells promote the remodelling of aortic valve leaflets and the development of CAVD. Although no medical therapy is effective for reducing or preventing the progression of CAVD, studies have started to identify actionable targets.

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

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

Understanding Pulmonary Autograft Remodeling After the Ross Procedure: Stick to the Facts

The Ross, or pulmonary autograft, procedure presents a fascinating mechanobiological scenario. Due to the common embryological origin of the aortic and pulmonary root, the conotruncus, several authors have hypothesized that a pulmonary autograft has the innate potential to remodel into an aortic phenotype once exposed to systemic conditions. Most of our understanding of pulmonary autograft mechanobiology stems from the remodeling observed in the arterial wall, rather than the valve, simply because there have been many opportunities to study the walls of dilated autografts explanted at reoperation. While previous histological studies provided important clues on autograft adaptation, a comprehensive understanding of its determinants and underlying mechanisms is needed so that the Ross procedure can become a widely accepted aortic valve substitute in select patients. It is clear that protecting the autograft during the early adaptation phase is crucial to avoid initiating a sequence of pathological remodeling. External support in the freestanding Ross procedure should aim to prevent dilatation while simultaneously promoting remodeling, rather than preventing dilatation at the cost of vascular atrophy. To define the optimal mechanical properties and geometry for external support, the ideal conditions for autograft remodeling and the timeline of mechanical adaptation must be determined. We aimed to rigorously review pulmonary autograft remodeling after the Ross procedure. Starting from the developmental, microstructural and biomechanical differences between the pulmonary artery and aorta, we review autograft mechanobiology in relation to distinct clinical failure mechanisms while aiming to identify unmet clinical needs, gaps in current knowledge and areas for further research. By correlating clinical and experimental observations of autograft remodeling with established principles in cardiovascular mechanobiology, we aim to present an up-to-date overview of all factors involved in extracellular matrix remodeling, their interactions and potential underlying molecular mechanisms.

Native Aortic Valve Disease Progression and Bioprosthetic Valve Degeneration in Patients With Transcatheter Aortic Valve Implantation

Supplemental Digital Content is available in the text.

Background:

Major uncertainties remain regarding disease activity within the retained native aortic valve, and regarding bioprosthetic valve durability, after transcatheter aortic valve implantation (TAVI). We aimed to assess native aortic valve disease activity and bioprosthetic valve durability in patients with TAVI in comparison with subjects with bioprosthetic surgical aortic valve replacement (SAVR).

Methods:

In a multicenter cross-sectional observational cohort study, patients with TAVI or bioprosthetic SAVR underwent baseline echocardiography, computed tomography angiography, and ¹⁸F-sodium fluoride (¹⁸F-NaF) positron emission tomography. Participants (n=47) were imaged once with ¹⁸F-NaF positron emission tomography/computed tomography either at 1 month (n=9, 19%), 2 years (n=22, 47%), or 5 years (16, 34%) after valve implantation. Patients subsequently underwent serial echocardiography to assess for changes in valve hemodynamic performance (change in peak aortic velocity) and evidence of structural valve dysfunction. Comparisons were made with matched patients with bioprosthetic SAVR (n=51) who had undergone the same imaging protocol.

Results:

In patients with TAVI, native aortic valves demonstrated ¹⁸F-NaF uptake around the outside of the bioprostheses that showed a modest correlation with the time from TAVI (r=0.36, P=0.023). ¹⁸F-NaF uptake in the bioprosthetic leaflets was comparable between the SAVR and TAVI groups (target-to-background ratio, 1.3 [1.2–1.7] versus 1.3 [1.2–1.5], respectively; P=0.27). The frequencies of imaging evidence of bioprosthetic valve degeneration at baseline were similar on echocardiography (6% versus 8%, respectively; P=0.78), computed tomography (15% versus 14%, respectively; P=0.87), and positron emission tomography (15% versus 29%, respectively; P=0.09). Baseline ¹⁸F-NaF uptake was associated with a subsequent change in peak aortic velocity for both TAVI (r=0.7, P<0.001) and SAVR (r=0.7, P<0.001). On multivariable analysis, ¹⁸F-NaF uptake was the only predictor of peak velocity progression (P<0.001).

Conclusions:

In patients with TAVI, native aortic valves demonstrate evidence of ongoing active disease. Across imaging modalities, TAVI degeneration is of similar magnitude to bioprosthetic SAVR, suggesting comparable midterm durability.

Registration:

URL: https://www.clinicaltrials.gov; Unique identifier: NCT02304276.

Aortic valve disease in diabetes: Molecular mechanisms and novel therapies

Valve disease and particularly calcific aortic valve disease (CAVD) and diabetes (DM) are progressive diseases constituting a global health burden for all aging societies (Progress in Cardiovascular Diseases. 2014;56(6):565: Circulation Research. 2021;128(9):1344). Compared to non‐diabetic individuals (The Lancet. 2008;371(9626):1800: The American Journal of Cardiology. 1983;51(3):403: Journal of the American College of Cardiology. 2017;69(12):1523), the diabetic patients have a significantly greater propensity for cardiovascular disorders and faster degeneration of implanted bioprosthetic aortic valves. Previously, using an original experimental model, the diabetic‐hyperlipemic hamsters, we have shown that the earliest alterations induced by these conditions occur at the level of the aortic valves and, with time these changes lead to calcifications and CAVD. However, there are no pharmacological treatments available to reverse or retard the progression of aortic valve disease in diabetes, despite the significant advances in the field. Therefore, it is critical to uncover the mechanisms of valve disease progression, find biomarkers for diagnosis and new targets for therapies. This review aims at presenting an update on the basic research in CAVD in the context of diabetes. We provide an insight into the accumulated data including our results on diabetes‐induced progressive cell and molecular alterations in the aortic valve, new potential biomarkers to assess the evolution and therapy of the disease, advancement in targeted nanotherapies, tissue engineering and the potential use of circulating endothelial progenitor cells in CAVD.

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.

Air spread through a wetted deformable membrane: Implications for the mechanism of soft valves in plants

Plants have a special structure, torus-margo (TM) pit, which comprises a thickened torus at the center encircled by a highly porous margo. It is regarded as a key evolutionary structure to enable stable water transport, minimizing the air spread in the vessels. However, its valve-like dynamics to regulate two-phase flows still remains unclear even at a single pit level. Here, we study the air spreading dynamics using a bioinspired model of this soft pit valve. We divide it into the initial onset and the consecutive air-spreads, and propose the criteria of TM structures as the valve-like function. To delay the onset of air spread, the margo region should be thin and deformable enough to seal the pit aperture with the torus before the air penetration. Even after the onset, the membranes whose maximum pore size is smaller than its thickness can avoid continuous air-spread. The criteria also fit properly into botanical data on the morphologies of TM pits, implying that their valve-like behaviors may alleviate the tradeoff between hydraulic safety and efficiency at the single pit level. Our study would help to understand of the mechanistic pit-level strategy and also can provide insight into fluidic systems to control interfacial phenomena.

Fluid Flow Characteristics of Healthy and Calcified Aortic Valves Using Three-Dimensional Lagrangian Coherent Structures Analysis

Aortic valve calcification is an important cardiovascular disorder that deteriorates the accurate functioning of the valve leaflets. The increasing stiffness due to the calcification prevents the complete closure of the valve and therefore leads to significant hemodynamic alterations. Computational fluid dynamics (CFD) modeling enables the investigation of the entire flow domain by processing medical images from aortic valve patients. In this study, we computationally modeled and simulated a 3D aortic valve using patient-specific dimensions of the aortic root and aortic sinus. Leaflet stiffness is deteriorated in aortic valve disease due to calcification. In order to investigate the influence of leaflet calcification on flow dynamics, three different leaflet-stiffness values were considered for healthy, mildly calcified, and severely calcified leaflets. Time-dependent CFD results were used for applying the Lagrangian coherent structures (LCS) technique by performing finite-time Lyapunov exponent (FTLE) computations along with Lagrangian particle residence time (PRT) analysis to identify unique vortex structures at the front and backside of the leaflets. Obtained results indicated that the peak flow velocity at the valve orifice increased with the calcification rate. For the healthy aortic valve, a low-pressure field was observed at the leaflet tips. This low-pressure field gradually expanded through the entire aortic sinus as the calcification level increased. FTLE field plots of the healthy and calcified valves showed a variety of differences in terms of flow structures. When the number of fluid particles in the healthy valve model was taken as reference, 1.59 and 1.74 times more particles accumulated in the mildly and severely calcified valves, respectively, indicating that the calcified valves were not sufficiently opened to allow normal mass flow rates.

A New Technique for Shaping the Aortic Sinuses and Conserving Dynamism in the Remodeling Operation

BACKGROUND

Preserving dynamism and recreating the sinuses in the Dacron graft are thought to be important for optimizing results of aortic valve-conserving operations.

METHODS

We describe a novel technique that preserves dynamism and recreates the sinotubular junction. In addition, it tailors 3 sinuses of defined longitudinal and transverse curvatures in a straight Dacron tube during the operation. The technique has been used in 6 patients with varied aortic root pathology. We performed preoperative and postoperative multimodality imaging using computerized image analysis as well as 3-dimensional models.

RESULTS

There was no early or midterm death. Upon discharge, patients were clinically well, with echocardiographic evidence of minimal (3 patients) or mild (3 patients) aortic regurgitation. Computed tomography and cardiac magnetic resonance imaging with extensive image analysis of the aortic root size, shape, and function showed partial or complete normalization of these parameters. This included the shape and dynamism of the aortic annulus and the size and shape of the geometric (effective) orifice. The 4-dimensional magnetic resonance imaging pattern of flow in the sinuses and ascending aorta showed favorable vortices in the sinuses, right-handed helical flow, and marked diminution of energy loss in the ascending aorta.

CONCLUSIONS

The novel technique described here is simple, practical, and cost-effective because it uses a widely available straight Dacron tube. The technique does not use rigid internal or external support. The early results are encouraging. Larger series with longer follow-up are required.

In Situ Remodeling Overrules Bioinspired Scaffold Architecture of Supramolecular Elastomeric Tissue-Engineered Heart Valves

In situ tissue engineering that uses resorbable synthetic heart valve scaffolds is an affordable and practical approach for heart valve replacement; therefore, it is attractive for clinical use. This study showed no consistent collagen organization in the predefined direction of electrospun scaffolds made from a resorbable supramolecular elastomer with random or circumferentially aligned fibers, after 12 months of implantation in sheep. These unexpected findings and the observed intervalvular variability highlight the need for a mechanistic understanding of the long-term in situ remodeling processes in large animal models to improve predictability of outcome toward robust and safe clinical application.

Geometry influences inflammatory host cell response and remodeling in tissue-engineered heart valves in-vivo

Regenerative tissue-engineered matrix-based heart valves (TEM-based TEHVs) may become an alternative to currently-used bioprostheses for transcatheter valve replacement. We recently identified TEM-based TEHVs-geometry as one key-factor guiding their remodeling towards successful long-term performance or failure. While our first-generation TEHVs, with a simple, non-physiological valve-geometry, failed over time due to leaflet-wall fusion phenomena, our second-generation TEHVs, with a computational modeling-inspired design, showed native-like remodeling resulting in long-term performance. However, a thorough understanding on how TEHV-geometry impacts the underlying host cell response, which in return determines tissue remodeling, is not yet fully understood. To assess that, we here present a comparative samples evaluation derived from our first- and second-generation TEHVs. We performed an in-depth qualitative and quantitative (immuno-)histological analysis focusing on key-players of the inflammatory and remodeling cascades (M1/M2 macrophages, α-SMA⁺- and endothelial cells). First-generation TEHVs were prone to chronic inflammation, showing a high presence of macrophages and α-SMA⁺-cells, hinge-area thickening, and delayed endothelialization. Second-generation TEHVs presented with negligible amounts of macrophages and α-SMA⁺-cells, absence of hinge-area thickening, and early endothelialization. Our results suggest that TEHV-geometry can significantly influence the host cell response by determining the infiltration and presence of macrophages and α-SMA⁺-cells, which play a crucial role in orchestrating TEHV remodeling.

Oscillatory fluid-induced mechanobiology in heart valves with parallels to the vasculature

Forces generated by blood flow are known to contribute to cardiovascular development and remodeling. These hemodynamic forces induce molecular signals that are communicated from the endothelium to various cell types. The cardiovascular system consists of the heart and the vasculature, and together they deliver nutrients throughout the body. While heart valves and blood vessels experience different environmental forces and differ in morphology as well as cell types, they both can undergo pathological remodeling and become susceptible to calcification. In addition, while the plaque morphology is similar in valvular and vascular diseases, therapeutic targets available for the latter condition are not effective in the management of heart valve calcification. Therefore, research in valvular and vascular pathologies and treatments have largely remained independent. Nonetheless, understanding the similarities and differences in development, calcific/fibrous pathologies and healthy remodeling events between the valvular and vascular systems can help us better identify future treatments for both types of tissues, particularly for heart valve pathologies which have been understudied in comparison to arterial diseases.

Which Biological Properties of Heart Valves Are Relevant to Tissue Engineering?

Over the last 20 years, the designs of tissue engineered heart valves have evolved considerably. An initial focus on replicating the mechanical and structural features of semilunar valves has expanded to endeavors to mimic the biological behavior of heart valve cells as well. Studies on the biology of heart valves have shown that the function and durability of native valves is underpinned by complex interactions between the valve cells, the extracellular matrix, and the mechanical environment in which heart valves function. The ability of valve interstitial cells to synthesize extracellular matrix proteins and remodeling enzymes and the protective mediators released by endothelial cells are key factors in the homeostasis of valve function. The extracellular matrix provides the mechanical strength and flexibility required for the valve to function, as well as communicating with the cells that are bound within. There are a number of regulatory mechanisms that influence valve function, which include neuronal mechanisms and the tight regulation of growth and angiogenic factors. Together, studies into valve biology have provided a blueprint for what a tissue engineered valve would need to be capable of, in order to truly match the function of the native valve. This review addresses the biological functions of heart valve cells, in addition to the influence of the cells' environment on this behavior and examines how well these functions are addressed within the current strategies for tissue engineering heart valves in vitro, in vivo, and in situ.

A multilayered valve leaflet promotes cell-laden collagen type I production and aortic valve hemodynamics

Patients with aortic heart valve disease are limited to valve replacements that lack the ability to grow and remodel. This presents a major challenge for pediatric patients who require a valve capable of somatic growth and at a smaller size. A patient-specific heart valve capable of growth and remodeling while maintaining proper valve function would address this major issue. Here, we recreate the native valve leaflet structure composed of poly-ε-caprolactone (PCL) and cell-laden gelatin-methacrylate/poly (ethylene glycol) diacrylate (GelMA/PEGDA) hydrogels using 3D printing and molding, and then evaluate the ability of the multilayered scaffold to produce collagen matrix under physiological shear stress conditions. We also characterized the valve hemodynamics under aortic physiological flow conditions. The valve's fibrosa layer was replicated by 3D printing PCL in a circumferential direction similar to collagen alignment in the native leaflet, and GelMA/PEGDA sustained and promoted cell viability in the spongiosa/ventricularis layers. We found that collagen type I production can be increased in the multilayered scaffold when it is exposed to pulsatile shear stress conditions over static conditions. When the PCL component was mounted onto a valve ring and tested under physiological aortic valve conditions, the hemodynamics were comparable to commercially available valves. Our results demonstrate that a structurally representative valve leaflet can be generated using 3D printing and that the PCL layer of the leaflet can sustain proper valve function under physiological aortic valve conditions.

Differential Leaflet Remodeling of Bone Marrow Cell Pre-Seeded Versus Nonseeded Bioresorbable Transcatheter Pulmonary Valve Replacements

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Bone marrow mononuclear cell pre-seeding of polycarbonate bisurea–based tissue-engineered heart valves has detrimental effects on long-term performance and in situ remodeling and, therefore, should be avoided.

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Leaflet-specific analysis revealed pronounced remodeling differences with regard to cell infiltration, scaffold resorption, and extracellular matrix deposition within the same valve explant.

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The heterogeneity in remodeling of polycarbonate bisurea–based tissue-engineered heart valves may have important safety implications in terms of clinical translation.

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An in-depth understanding of the mechanobiological mechanisms involved in the in situ remodeling is required to limit the risk of unpredictable (maladaptive) remodeling.

This study showed that bone marrow mononuclear cell pre-seeding had detrimental effects on functionality and in situ remodeling of bioresorbable bisurea-modified polycarbonate (PC-BU)-based tissue-engineered heart valves (TEHVs) used as transcatheter pulmonary valve replacement in sheep. We also showed heterogeneous valve and leaflet remodeling, which affects PC-BU TEHV safety, challenging their potential for clinical translation. We suggest that bone marrow mononuclear cell pre-seeding should not be used in combination with PC-BU TEHVs. A better understanding of cell–scaffold interaction and in situ remodeling processes is needed to improve transcatheter valve design and polymer absorption rates for a safe and clinically relevant translation of this approach.

The genetics and biomechanics of thoracic aortic diseases

Thoracic aortic aneurysms and aortic dissections (TAAD) are highly fatal emergencies within cardiothoracic surgery. With increasing age, thoracic aneurysms become more prevalent and pose an even greater threat when they develop into aortic dissections. Both diseases are multifactorial and are influenced by a multitude of physiological and biomechanical processes. Structural stability of aorta can be disrupted by genes, such as those for extracellular matrix and contractile protein, as well as telomere dysfunction, which leads to senescence of smooth muscle and endothelial cells. Biomechanical changes such as increased luminal pressure imposed by hypertension are also very prevalent and lead to structural instability. Furthermore, ageing is associated with a pro-inflammatory state that exacerbates degeneration of vessel wall, facilitating the development of both aortic aneurysms and aortic dissection. This literature review provides an overview of the aetiology and pathophysiology of both thoracic aneurysms and aortic dissections. With an improved understanding, new therapeutic targets may eventually be identified to facilitate treatment and prevention of these diseases.

Human cell-derived tissue-engineered heart valve with integrated Valsalva sinuses: towards native-like transcatheter pulmonary valve replacements

Transcatheter valve replacement indication is currently being extended to younger and lower-risk patients. However, transcatheter prostheses are still based on glutaraldehyde-fixed xenogeneic materials. Hence, they are prone to calcification and long-term structural degeneration, which are particularly accelerated in younger patients. Tissue-engineered heart valves based on decellularized in vitro grown tissue-engineered matrices (TEM) have been suggested as a valid alternative to currently used bioprostheses, showing good performance and remodeling capacity as transcatheter pulmonary valve replacement (TPVR) in sheep. Here, we first describe the in vitro development of human cell-derived TEM (hTEM) and their application as tissue-engineered sinus valves (hTESVs), endowed with Valsalva sinuses for TPVR. The hTEM and hTESVs were systematically characterized in vitro by histology, immunofluorescence, and biochemical analyses, before they were evaluated in a pulse duplicator system under physiological pulmonary pressure conditions. Thereafter, transapical delivery of hTESVs was tested for feasibility and safety in a translational sheep model, achieving good valve performance and early cellular infiltration. This study demonstrates the principal feasibility of clinically relevant hTEM to manufacture hTESVs for TPVR.

Predictors of Aortic Valve Repair Failure

Aortic valve repair is the preferred approach for the treatment of severe aortic insufficiency (AI), as it allows patients to keep their native aortic valve, thus substantially reducing the risk of prosthesis-related complications. Several studies have documented excellent long-term outcomes of aortic valve repair. The major complication of this operation is AI recurrence, with ensuingneed for reoperation. The surgical experience accumulated over the last two decades has allowed for better understanding of the mechanisms of recurrent AI after aortic valve repair. Herein, we review the current state of knowledge on predictors of aortic valve repair failure. These include unaddressed annular dilation, residual cusp prolapse or retraction, commissural orientation, and use of patch material. This enhanced understanding has led to the development of increasingly refined techniques and improved patient outcomes. Continued follow-up and detailed data collection at the time of surgery, together with three-dimensional echo imaging, will allow further improvements in aortic valve repair.

FGF-2 inhibits contractile properties of valvular interstitial cell myofibroblasts encapsulated in 3D MMP-degradable hydrogels

Valvular interstitial cells (VICs) are responsible for the maintenance of the extracellular matrix in heart valve leaflets and, in response to injury, activate from a quiescent fibroblast to a wound healing myofibroblast phenotype. Under normal conditions, myofibroblast activation is transient, but the chronic presence of activated VICs can lead to valve diseases, such as fibrotic aortic valve stenosis, for which non-surgical treatments remain elusive. We monitored the porcine VIC response to exogenously delivered fibroblast growth factor 2 (FGF-2; 100 ng/ml), transforming growth factor beta 1 (TGF-β1; 5 ng/ml), or a combination of the two while cultured within 3D matrix metalloproteinase (MMP)-degradable 8-arm 40 kDa poly(ethylene glycol) hydrogels that mimic aspects of the aortic valve. Here, we aimed to investigate VIC myofibroblast activation and subsequent contraction or the reparative wound healing response. To this end, VIC morphology, proliferation, gene expression related to the myofibroblast phenotype [alpha smooth muscle actin (α-SMA) and connective tissue growth factor (CTGF)] and matrix remodeling [collagens (COL1A1 and COL3) and MMP1], and contraction assays were used to quantify the cell response. Treatment with FGF-2 resulted in increased cellular proliferation while reducing the myofibroblast phenotype, as seen by decreased expression of CTGF and α-SMA, and reduced contraction relative to untreated control, suggesting that FGF-2 encourages a reparative phenotype, even in the presence of TGF-β1. TGF-β1 treatment predictably led to an increased proportion of VICs exhibiting the myofibroblast phenotype, indicated by the presence of α-SMA, increased gene expression indicative of matrix remodeling, and bulk contraction of the hydrogels. Functional contraction assays and biomechanical analyses were performed on VIC encapsulated hydrogels and porcine aortic valve tissue explants to validate these findings.

Prosthetic Aortic Valves: Challenges and Solutions

Aortic Valve Disease (AVD) is the most common Valvular Heart Disease (VHD), affecting millions of people worldwide. Severe AVD is treated in most cases with prosthetic aortic valve replacement, which involves the substitution of the native aortic valve with a prosthetic one. In this review we will discuss the different types of prosthetic aortic valves available for implantation and the challenges faced by patients, medical doctors, researchers and manufacturers, as well as the approaches that are taken to overcome them.

Human iPSC-derived mesenchymal stem cells encapsulated in PEGDA hydrogels mature into valve interstitial-like cells

Despite recent advances in tissue engineered heart valves (TEHV), a major challenge is identifying a cell source for seeding TEHV scaffolds. Native heart valves are durable because valve interstitial cells (VICs) maintain tissue homeostasis by synthesizing and remodeling the extracellular matrix. This study demonstrates that induced pluripotent stem cells (iPSC)-derived mesenchymal stem cells (iMSCs) can be derived from iPSCs using a feeder-free protocol and then further matured into VICs by encapsulation within 3D hydrogels. The differentiation efficiency was characterized using flow cytometry, immunohistochemistry staining, and trilineage differentiation. Using our feeder-free differentiation protocol, iMSCs were differentiated from iPSCs and had CD90+, CD44+, CD71+, αSMA+, and CD45- expression. Furthermore, iMSCs underwent trilineage differentiation when cultured in induction media for 21 days. iMSCs were then encapsulated in poly(ethylene glycol)diacrylate (PEGDA) hydrogels grafted with adhesion peptide (RGDS) to promote remodeling and further maturation into VIC-like cells. VIC phenotype was assessed by the expression of alpha-smooth muscle actin (αSMA), vimentin, and collagen production after 28 days. When MSC-derived cells were encapsulated in PEGDA hydrogels that mimic the leaflet modulus, a decrease in αSMA expression and increase in vimentin was observed. In addition, iMSCs synthesized collagen type I after 28 days in 3D hydrogel culture. Thus, the results from this study suggest that iMSCs may be a promising cell source for TEHV.

STATEMENT OF SIGNIFICANCE

Developing a suitable cell source is a critical component for the success and durability of tissue engineered heart valves. The significance of this study is the generation of iPSCs-derived mesenchymal stem cells (iMSCs) that have the capacity to mature into valve interstitial-like cells when introduced into a 3D cell culture designed to mimic the layers of the valve leaflet. iMSCs were generated using a feeder-free protocol, which is one major advantage over other methods, as it is more clinically relevant. In addition to generating a potential new cell source for heart valve tissue engineering, this study also highlights the importance of a 3D culture environment to influence cell phenotype and function.

Off-the-shelf tissue engineered heart valves for in situ regeneration: current state, challenges and future directions

INTRODUCTION

Transcatheter aortic valve replacement (TAVR) is continuously evolving and is expected to surpass surgical valve implantation in the near future. Combining durable valve substitutes with minimally invasive implantation techniques might increase the clinical relevance of this therapeutic option for younger patient populations. Tissue engineering offers the possibility to create tissue engineered heart valves (TEHVs) with regenerative and self-repair capacities which may overcome the pitfalls of current TAVR prostheses.

AREAS COVERED

This review focuses on off-the-shelf TEHVs which rely on a clinically-relevant in situ tissue engineering approach and which have already advanced into preclinical or first-in-human investigation.

EXPERT COMMENTARY

Among the off-the-shelf in situ TEHVs reported in literature, the vast majority covers pulmonary valve substitutes, and only few are combined with transcatheter implantation technologies. Hence, further innovations should include the development of transcatheter tissue engineered aortic valve substitutes, which would considerably increase the clinical relevance of such prostheses.

Biomaterial-driven in situ cardiovascular tissue engineering-a multi-disciplinary perspective

There is a persistent and growing clinical need for readily-available substitutes for heart valves and small-diameter blood vessels. In situ tissue engineering is emerging as a disruptive new technology, providing ready-to-use biodegradable, cell-free constructs which are designed to induce regeneration upon implantation, directly in the functional site. The induced regenerative process hinges around the host response to the implanted biomaterial and the interplay between immune cells, stem/progenitor cell and tissue cells in the microenvironment provided by the scaffold in the hemodynamic environment. Recapitulating the complex tissue microstructure and function of cardiovascular tissues is a highly challenging target. Therein the scaffold plays an instructive role, providing the microenvironment that attracts and harbors host cells, modulating the inflammatory response, and acting as a temporal roadmap for new tissue to be formed. Moreover, the biomechanical loads imposed by the hemodynamic environment play a pivotal role. Here, we provide a multidisciplinary view on in situ cardiovascular tissue engineering using synthetic scaffolds; starting from the state-of-the art, the principles of the biomaterial-driven host response and wound healing and the cellular players involved, toward the impact of the biomechanical, physical, and biochemical microenvironmental cues that are given by the scaffold design. To conclude, we pinpoint and further address the main current challenges for in situ cardiovascular regeneration, namely the achievement of tissue homeostasis, the development of predictive models for long-term performances of the implanted grafts, and the necessity for stratification for successful clinical translation.

Bioreactor Conditioning of Valve Scaffolds Seeded Internally with Adult Stem Cells

The goal of this study was to test the hypothesis that stem cells, as a response to valve-specific extracellular matrix "niches" and mechanical stimuli, would differentiate into valvular interstitial cells (VICs). Porcine aortic root scaffolds were prepared by decellularization. After verifying that roots exhibited adequate hemodynamics in vitro, we seeded human adipose-derived stem cells (hADSCs) within the interstitium of the cusps and subjected the valves to in vitro pulsatile bioreactor testing in pulmonary pressures and flow conditions. As controls we incubated cell-seeded valves in a rotator device which allowed fluid to flow through the valves ensuring gas and nutrient exchange without subjecting the cusps to significant stress. After 24 days of conditioning, valves were analyzed for cell phenotype using immunohistochemistry for vimentin, alpha-smooth muscle cell actin (SMA) and prolyl-hydroxylase (PHA). Fresh native valves were used as immunohistochemistry controls. Analysis of bioreactor-conditioned valves showed that almost all seeded cells had died and large islands of cell debris were found within each cusp. Remnants of cells were positive for vimentin. Cell seeded controls, which were only rotated slowly to ensure gas and nutrient exchange, maintained about 50% of cells alive; these cells were positive for vimentin and negative for alpha-SMA and PHA, similar to native VICs. These results highlight for the first time the extreme vulnerability of hADSCs to valve-specific mechanical forces and also suggest that careful, progressive mechanical adaptation to valve-specific forces might encourage stem cell differentiation towards the VIC phenotype.

Knitting for heart valve tissue engineering

Knitting is a versatile technology which offers a large portfolio of products and solutions of interest in heart valve (HV) tissue engineering (TE). One of the main advantages of knitting is its ability to construct complex shapes and structures by precisely assembling the yarns in the desired position. With this in mind, knitting could be employed to construct a HV scaffold that closely resembles the authentic valve. This has the potential to reproduce the anisotropic structure that is characteristic of the heart valve with the yarns, in particular the 3-layered architecture of the leaflets. These yarns can provide oriented growth of cells lengthwise and consequently enable the deposition of extracellular matrix (ECM) proteins in an oriented manner. This technique, therefore, has a potential to provide a functional knitted scaffold, but to achieve that textile engineers need to gain a basic understanding of structural and mechanical aspects of the heart valve and in addition, tissue engineers must acquire the knowledge of tools and capacities that are essential in knitting technology. The aim of this review is to provide a platform to consolidate these two fields as well as to enable an efficient communication and cooperation among these two research areas.

Functional Heart Valve Scaffolds Obtained by Complete Decellularization of Porcine Aortic Roots in a Novel Differential Pressure Gradient Perfusion System

There is a great need for living valve replacements for patients of all ages. Such constructs could be built by tissue engineering, with perspective of the unique structure and biology of the aortic root. The aortic valve root is composed of several different tissues, and careful structural and functional consideration has to be given to each segment and component. Previous work has shown that immersion techniques are inadequate for whole-root decellularization, with the aortic wall segment being particularly resistant to decellularization. The aim of this study was to develop a differential pressure gradient perfusion system capable of being rigorous enough to decellularize the aortic root wall while gentle enough to preserve the integrity of the cusps. Fresh porcine aortic roots have been subjected to various regimens of perfusion decellularization using detergents and enzymes and results compared to immersion decellularized roots. Success criteria for evaluation of each root segment (cusp, muscle, sinus, wall) for decellularization completeness, tissue integrity, and valve functionality were defined using complementary methods of cell analysis (histology with nuclear and matrix stains and DNA analysis), biomechanics (biaxial and bending tests), and physiologic heart valve bioreactor testing (with advanced image analysis of open-close cycles and geometric orifice area measurement). Fully acellular porcine roots treated with the optimized method exhibited preserved macroscopic structures and microscopic matrix components, which translated into conserved anisotropic mechanical properties, including bending and excellent valve functionality when tested in aortic flow and pressure conditions. This study highlighted the importance of (1) adapting decellularization methods to specific target tissues, (2) combining several methods of cell analysis compared to relying solely on histology, (3) developing relevant valve-specific mechanical tests, and (4) in vitro testing of valve functionality.

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.

Alginate for cardiac regeneration: From seaweed to clinical trials

Heart failure is a growing endemic in the aging Western population with a prevalence of over 20 million people worldwide¹. Existing heart failure therapies are unable to reverse heart failure and do not address its fundamental cause, the loss of cardiomyocytes². In order to induce myocardial regeneration for the myocardium and the heart valve, facilitate self-repair, improve tissue salvage, reduce or reverse the adverse-remodeling and ultimately achieve long-term functional stabilization and improvement in the heart function, novel strategies for therapeutic regeneration are being developed which are aiming to compensate for the insufficient and low intrinsic regenerative ability of the adult heart³. Similarly, valve replacement with mechanical or biological substitutes meets numerous hurdles. New approaches using multicellular approaches and new material are extensively studied. Most of those strategies depend on biomaterials that help to achieve functional integrated vasculogenesis and myogenesis in the heart/tissue. Especially for failed heart valve function a number of therapeutic approaches are common from corrective intervention to complete replacement⁴. However the complexity of the heart valve tissue and its high physical exposure has led to a variety of approaches, however therapeutic regeneration needs to be established. Beside other approaches alginate has been identified as one building block to achieve therapeutic regeneration.

Alginate is a versatile and adaptable biomaterial that has found numerous biomedical applications which include wound healing, drug delivery and tissue engineering. Due to its biologically favorable properties including the ease of gelation and its biocompatibility, alginate-based hydrogels have been considered a particularly attractive material for the application in cardiac regeneration and valve replacement techniques. Here, we review current applications of alginate in cardiac regeneration as well as perspectives for the alginate-dependent, cardiac regeneration strategies.

Valve Endothelial Cell-Derived Tgfβ1 Signaling Promotes Nuclear Localization of Sox9 in Interstitial Cells Associated With Attenuated Calcification

OBJECTIVE

Aortic valve disease, including calcification, affects >2% of the human population and is caused by complex interactions between multiple risk factors, including genetic mutations, the environment, and biomechanics. At present, there are no effective treatments other than surgery, and this is because of the limited understanding of the mechanisms that underlie the condition. Previous work has shown that valve interstitial cells within the aortic valve cusps differentiate toward an osteoblast-like cell and deposit bone-like matrix that leads to leaflet stiffening and calcific aortic valve stenosis. However, the mechanisms that promote pathological phenotypes in valve interstitial cells are unknown.

APPROACH AND RESULTS

Using a combination of in vitro and in vivo tools with mouse, porcine, and human tissue, we show that in valve interstitial cells, reduced Sox9 expression and nuclear localization precedes the onset of calcification. In vitro, Sox9 nuclear export and calcific nodule formation is prevented by valve endothelial cells. However, in vivo, loss of Tgfβ1 in the endothelium leads to reduced Sox9 expression and calcific aortic valve disease.

CONCLUSIONS

Together, these findings suggest that reduced nuclear localization of Sox9 in valve interstitial cells is an early indicator of calcification, and therefore, pharmacological targeting to prevent nuclear export could serve as a novel therapeutic tool in the prevention of calcification and stenosis.

Serum and tissue biomarkers in aortic stenosis

Background: Calcific aortic valve stenosis (CAVS) is seen in a large proportion of individuals over 60 years. It is an active process, influenced by lipid accumulation, mechanical stress, inflammation, and abnormal extracellular matrix turnover. Various biomarkers (BMs) are studied, as regards mechanisms, diagnosis and prognosis. Methods: In the calcified valves calcium deposition, elastin fragmentation and disorganization of cellular matrix were assessed, together with expression of OPN, OPG, osteocalcin (OCN) and RL2.

We prospectively studied the following serum BMs in 60 patients with CAVS and compared them to 20 healthy controls, free from any cardiac disease: Matrix metalloproteinases (MMP) 2 and 9 and tissue inhibitor of metalloproteinase 1 (TIMP1), which regulate collagen turnover, inflammatory factors, i.e. tumor necrosis factor a (TNFa), interleukin 2 (IL2), transforming growth factor β1 (TGF-β1) which regulates fibrosis, fetuin-A (fet-A), osteopontin (OPN), osteoprotegerin (OPG), sclerostin (SOST), and relaxin-2 (RL2) which positively or negatively regulate calcification. Monocyte chemoattractant protein 1 (MCP-1) which regulates migration and infiltration of monocytes/macrophages was also studied as well as malondialdehyde (MDA) an oxidative marker. Results: Extent of tissue valve calcification (Alizarin Red stain) was negatively correlated with tissue elastin, and RL2, and positively correlated with tissue OCN and serum TIMP1 and MCP-1 and negatively with MMP9.

Tissue OCN was positively correlated with OPN and negatively with the elastin. Tissue OPN was negatively correlated with elastin and OPG. Tissue OPN OPG and RL2 were not correlated with serum levels In the serum we found in patients statistically lower TIMP1, fet-A and RL2 levels, while all other BMs were higher compared to the healthy group. Positive correlations between SOST and IL2, OPG and MDA but negative with TNFa and OPN were found; also MMP9 was negatively correlated with TNFa and MCP-1 was negatively correlated with TIMP1. Conclusion: We found that many BMs expressing calcification, collagen breakdown, or formation, and inflammation are increased in the valve tissue and in the serum of patients with CAVS as compared with healthy group. Our findings may give new insights towards diagnosis but also therapy. Thus antisclerostin, and antiflammatory agents could be tried for preventing aortic calcification progression.

Modulation of human valve interstitial cell phenotype and function using a fibroblast growth factor 2 formulation

Valve interstitial cells (VICs) are fibroblastic in nature however in culture it is widely accepted that they differentiate into a myofibroblastic phenotype. This study assessed a fibroblast culture media formulation for its ability to maintain the phenotype and function of VICs as in the intact healthy valve. Normal human VICs were cultured separately in standard DMEM and in fibroblast media consisting of FGF2 (10ng/ml), insulin (50ng/ml) and 2% FCS for at least a week. Cell morphology, aspect ratio, size, levels and distribution of protein expression, proliferation, cell cycle, contraction and migration were assessed. Some VICs and some valve endothelial cells expressed FGF2 in valve tissue and this expression was increased in calcified valves. VICs in DMEM exhibited large, spread cells whereas VICs in fibroblast media were smaller, elongated and spindly. Aspect ratio and size were both significantly higher in DMEM (p<0.01). The level of expression of α-SMA was significantly reduced in fibroblast media at day 2 after isolation (p<0.01) and the expression of α-SMA, SM22 and EDA-fibronectin was significantly reduced in fibroblast media at days 7 and 12 post-isolation (p<0.01). Expression of cytoskeletal proteins, bone marker proteins and extracellular matrix proteins was reduced in fibroblast media. Proliferation of VICs in fibroblast media was significantly reduced at weeks 1 (p<0.05) and 2 (p<0.01). Collagen gel contraction was significantly reduced in fibroblast media (p<0.05). VICs were found to have significantly fewer and smaller focal adhesions in fibroblast media (p<0.01) with significantly fewer supermature focal adhesions in fibroblast media (p<0.001). Ultrastructurally, VICs in fibroblast media resembled native VICs from intact valves. VICs in fibroblast media demonstrated a slower migratory ability after wounding at 72 hours (p<0.01). Treatment of human VICs with this fibroblast media formulation has the ability to maintain and to dedifferentiate the VICs back to a fibroblastic phenotype with phenotypic and functional characteristics ascribed to cells in the intact valve. This methodology is fundamental in the study of normal valve biology, pathology and in the field of tissue engineering.