Endothelial-derived oxidative stress drives myofibroblastic activation and calcification of the aortic valve

Valve Thrombosis Following Transcatheter Aortic Valve Replacement: State-of-the-Art Review

Transcatheter aortic valve replacement (TAVR) is a well-established treatment for severe aortic stenosis, especially in patients over 75 or those at high surgical risk. While these prosthetic valves have a lower thrombogenic profile than mechanical heart valves, leaflet thrombosis in transcatheter aortic valves (TAV) occurs in an estimated 5%-40% of cases. Most TAV thromboses are subclinical and can be detected via cardiac computed tomography (CCT), which reveals hypo-attenuating leaflet thickening and reduced leaflet motion in asymptomatic patients without elevated transprosthetic gradients on echocardiography. The mechanisms behind TAV thrombosis involve local mechanical triggers, patient predisposing factors, and device and procedure-related aspects. The ideal antithrombotic therapy post-TAVR depends on individual patient characteristics, balancing bleeding risks with the need for oral anticoagulants. Data on the optimal management of TAV thrombosis and the routine use of CT post-TAVR are limited. While anticoagulation effectively resolves clinically significant prosthesis thrombosis, its benefit in subclinical cases is unclear. There is an ongoing debate about whether subclinical leaflet thrombosis precedes clinical valve thrombosis, making the ideal follow-up after valve implantation uncertain. This article aims to provide a comprehensive review, summarizing current data on the incidence of TAVR thrombosis, underlying mechanisms, clinical and imaging diagnosis, management strategies, preventive measures, and long-term follow-up.

Macrophages in Calcific Aortic Valve Disease: Paracrine and Juxtacrine Disease Drivers

A significant role in the pathogenesis of CAVD is played by innate immunity cells, such as macrophages. In stenotic valves, macrophages have enhanced inflammatory activity, and the population's balance is shifted toward pro-inflammatory ones. Pro-inflammatory macrophages release cytokines, chemokines, and microRNA, which can directly affect the resident valvular cells and cause valve calcification. In CAVD patients, macrophages may have more pronounced pro-inflammatory properties, enhanced not only by paracrine signals but also by juxtacrine Notch signaling and epigenetic factors, which influence the maturation of macrophages' progenitors. In this review, we observe the accumulated data on the involvement of macrophages in CAVD development via paracrine and juxtacrine interactions.

Challenges of aortic valve tissue culture - maintenance of viability and extracellular matrix in the pulsatile dynamic microphysiological system

BACKGROUND

Calcific aortic valve disease (CAVD) causes an increasing health burden in the 21st century due to aging population. The complex pathophysiology remains to be understood to develop novel prevention and treatment strategies. Microphysiological systems (MPSs), also known as organ-on-chip or lab-on-a-chip systems, proved promising in bridging in vitro and in vivo approaches by applying integer AV tissue and modelling biomechanical microenvironment. This study introduces a novel MPS comprising different micropumps in conjunction with a tissue-incubation-chamber (TIC) for long-term porcine and human AV incubation (pAV, hAV).

RESULTS

Tissue cultures in two different MPS setups were compared and validated by a bimodal viability analysis and extracellular matrix transformation assessment. The MPS-TIC conjunction proved applicable for incubation periods of 14-26 days. An increased metabolic rate was detected for pulsatile dynamic MPS culture compared to static condition indicated by increased LDH intensity. ECM changes such as an increase of collagen fibre content in line with tissue contraction and mass reduction, also observed in early CAVD, were detected in MPS-TIC culture, as well as an increase of collagen fibre content. Glycosaminoglycans remained stable, no significant alterations of α-SMA or CD31 epitopes and no accumulation of calciumhydroxyapatite were observed after 14 days of incubation.

CONCLUSIONS

The presented ex vivo MPS allows long-term AV tissue incubation and will be adopted for future investigation of CAVD pathophysiology, also implementing human tissues. The bimodal viability assessment and ECM analyses approve reliability of ex vivo CAVD investigation and comparability of parallel tissue segments with different treatment strategies regarding the AV (patho)physiology.

Reciprocal interferences of the left ventricular assist device and the aortic valve competence

Patients suffering from end-stage heart failure tend to have high mortality rates. With growing numbers of patients progressing into severe heart failure, the shortage of available donors is a growing concern, with less than 10% of patients undergoing cardiac transplantation (CTx). Fortunately, the use of left ventricular assist devices (LVADs), a variant of mechanical circulatory support has been on the rise in recent years. The expansion of LVADs has led them to be incorporated into a variety of clinical settings, based on the goals of therapy for patients ailing from heart failure. However, with an increase in the use of LVADs, there are a host of complications that arise with it. One such complication is the development and progression of aortic regurgitation (AR) which is noted to adversely influence patient outcomes and compromise pump benefits leading to increased morbidity and mortality. The underlying mechanisms are likely multifactorial and involve the aortic root-aortic valve (AV) complex, as well as the LVAD device, patient, and other factors, all of them alter the physiological mechanics of the heart resulting in AV dysfunction. Thus, it is imperative to screen patients before LVAD implantation for AR, as moderate or greater AR requires a concurrent intervention at the time of LVADs implantation. No current strict guidelines were identified in the literature search on how to actively manage and limit the development and/or progression of AR, due to the limited information. However, some recommendations include medical management by targeting fluid overload and arterial blood pressure, along with adjusting the settings of the LVADs device itself. Surgical interventions are to be considered depending on patient factors, goals of care, and the underlying pathology. These interventions include the closure of the AV, replacement of the valve, and percutaneous approach via percutaneous occluding device or transcatheter aortic valve implantation. In the present review, we describe the interaction between AV and LVAD placement, in terms of patient management and prognosis. Also it is provided a comprehensive echocardiographic strategy for the precise assessment of AV regurgitation severity.

Enduring Reactive Oxygen Species Emission Causes Aberrant Protein S-Glutathionylation Transitioning Human Aortic Valve Cells from a Sclerotic to a Stenotic Phenotype

Aims: During calcific aortic valve stenosis (CAVS) progression, oxidative stress and endothelial dysfunction mark the initial pathogenic steps with a parallel dysregulation of the antioxidant systems. Here, we tested whether oxidation-induced protein S-glutathionylation (P-SSG) accounts for a phenotypic switch in human aortic valvular tissue, eventually leading to calcium deposition. Next, we tested whether countering this reactive oxygen species (ROS) surge would prevent these perturbations. Results: We employed state-of-the-art technologies, such as electron paramagnetic resonance (EPR), liquid chromatography-tandem mass spectrometry, imaging flow-cytometry, and live-cell imaging on human excised aortic valves and primary valve endothelial cells (VECs). We observed that a net rise in EPR-detected ROS emission marked the transition from fibrotic to calcific in human CAVS specimens, coupled to a progressive increment in P-SSG deposition. In human VECs (hVECs), treatment with 2-acetylamino-3-[4-(2-acetylamino-2-carboxyethylsulfanylthiocarbonylamino)phenylthiocarbamoylsulfanyl]propionic acid triggered highly oxidizing conditions prompting P-SSG accumulation, damaging mitochondria, and inducing endothelial nitric oxide synthase uncoupling. All the events conjured up in morphing these cells from their native endothelial phenotype into a damaged calcification-inducing one. As proof of principle, the use of the antioxidant N-acetyl-L-cysteine prevented these alterations. Innovation: Borne as a compensatory system to face excessive oxidative burden, with time, P-SSG contributes to the morphing of hVECs from their innate phenotype into a damaged one, paving the way to calcium deposition. Conclusion: Our data suggest that, in the human aortic valve, unremitted ROS emission along with a P-SSG build-up occurs and accounts, at least in part, for the morphological/functional changes leading to CAVS. Antioxid. Redox Signal. 37, 1051-1071.

Contribution of Oxidative Stress (OS) in Calcific Aortic Valve Disease (CAVD): From Pathophysiology to Therapeutic Targets

Calcific aortic valve disease (CAVD) is a major cause of cardiovascular mortality and morbidity, with increased prevalence and incidence. The underlying mechanisms behind CAVD are complex, and are mainly illustrated by inflammation, mechanical stress (which induces prolonged aortic valve endothelial dysfunction), increased oxidative stress (OS) (which trigger fibrosis), and calcification of valve leaflets. To date, besides aortic valve replacement, there are no specific pharmacological treatments for CAVD. In this review, we describe the mechanisms behind aortic valvular disease, the involvement of OS as a fundamental element in disease progression with predilection in AS, and its two most frequent etiologies (calcific aortic valve disease and bicuspid aortic valve); moreover, we highlight the potential of OS as a future therapeutic target.

Role of oxidative stress in calcific aortic valve disease and its therapeutic implications

Calcific aortic valve disease (CAVD) is the end result of active cellular processes that lead to the progressive fibrosis and calcification of aortic valve leaflets. In western populations, CAVD is a significant cause of cardiovascular morbidity and mortality, and in the absence of effective drugs, it will likely represent an increasing disease burden as populations age. As there are currently no pharmacological therapies available for preventing, treating, or slowing the development of CAVD, understanding the mechanisms underlying the initiation and progression of the disease is important for identifying novel therapeutic targets. Recent evidence has emerged of an important causative role for reactive oxygen species (ROS)-mediated oxidative stress in the pathophysiology of CAVD, inducing the differentiation of valve interstitial cells into myofibroblasts and then osteoblasts. In this review, we focus on the roles and sources of ROS driving CAVD and consider their potential as novel therapeutic targets for this debilitating condition.

Tri-Layered and Gel-Like Nanofibrous Scaffolds with Anisotropic Features for Engineering Heart Valve Leaflets

3D heterogeneous and anisotropic scaffolds that approximate native heart valve tissues are indispensable for the successful construction of tissue engineered heart valves (TEHVs). In this study, novel tri-layered and gel-like nanofibrous scaffolds, consisting of poly(lactic-co-glycolic) acid (PLGA) and poly(aspartic acid) (PASP), are fabricated by a combination of positive/negative conjugate electrospinning and bioactive hydrogel post-processing. The nanofibrous PLGA-PASP scaffolds present tri-layered structures, resulting in anisotropic mechanical properties that are comparable with native heart valve leaflets. Biological tests show that nanofibrous PLGA-PASP scaffolds with high PASP ratios significantly promote the proliferation and collagen and glycosaminoglycans (GAGs) secretions of human aortic valvular interstitial cells (HAVICs), compared to PLGA scaffolds. Importantly, the nanofibrous PLGA-PASP scaffolds are found to effectively inhibit the osteogenic differentiation of HAVICs. Two types of porcine VICs, from young and adult age groups, are further seeded onto the PLGA-PASP scaffolds. The adult VICs secrete higher amounts of collagens and GAGs and undergo a significantly higher level of osteogenic differentiation than young VICs. RNA sequencing analysis indicates that age has a pivotal effect on the VIC behaviors. This study provides important guidance and a reference for the design and development of 3D tri-layered, gel-like nanofibrous PLGA-PASP scaffolds for TEHV applications.

Reactive Oxygen Species in Cardiovascular Calcification: Role of Medicinal Plants

Cardiovascular calcification, including vascular calcification and calcific aortic valve disease (CAVD), is a serious worldwide health problem, especially in older adults. The mechanisms underlying cardiovascular calcifications are complex and multifactorial. An increase in reactive oxygen species (ROS) and oxidative stress play important roles in the initiation and development of cardiovascular calcification. This mini-review summarizes the recent evidence that supports the association of ROS with vascular calcification and CAVD and discusses the role of medicinal plants for the prevention and treatment of cardiovascular calcification.

Uncoupling the Vicious Cycle of Mechanical Stress and Inflammation in Calcific Aortic Valve Disease

Calcific aortic valve disease (CAVD) is a common acquired valvulopathy, which carries a high burden of mortality. Chronic inflammation has been postulated as the predominant pathophysiological process underlying CAVD. So far, no effective medical therapies exist to halt the progression of CAVD. This review aims to outline the known pathways of inflammation and calcification in CAVD, focussing on the critical roles of mechanical stress and mechanosensing in the perpetuation of valvular inflammation. Following initiation of valvular inflammation, dysregulation of proinflammatory and osteoregulatory signalling pathways stimulates endothelial-mesenchymal transition of valvular endothelial cells (VECs) and differentiation of valvular interstitial cells (VICs) into active myofibroblastic and osteoblastic phenotypes, which in turn mediate valvular extracellular matrix remodelling and calcification. Mechanosensitive signalling pathways convert mechanical forces experienced by valve leaflets and circulating cells into biochemical signals and may provide the positive feedback loop that promotes acceleration of disease progression in the advanced stages of CAVD. Mechanosensing is implicated in multiple aspects of CAVD pathophysiology. The mechanosensitive RhoA/ROCK and YAP/TAZ systems are implicated in aortic valve leaflet mineralisation in response to increased substrate stiffness. Exposure of aortic valve leaflets, endothelial cells and platelets to high shear stress results in increased expression of mediators of VIC differentiation. Upregulation of the Piezo1 mechanoreceptor has been demonstrated to promote inflammation in CAVD, which normalises following transcatheter valve replacement. Genetic variants and inhibition of Notch signalling accentuate VIC responses to altered mechanical stresses. The study of mechanosensing pathways has revealed promising insights into the mechanisms that perpetuate inflammation and calcification in CAVD. Mechanotransduction of altered mechanical stresses may provide the sought-after coupling link that drives a vicious cycle of chronic inflammation in CAVD. Mechanosensing pathways may yield promising targets for therapeutic interventions and prognostic biomarkers with the potential to improve the management of CAVD.

Calcific aortic valve disease: from molecular and cellular mechanisms to medical therapy

Calcific aortic valve disease (CAVD) is a highly prevalent condition that comprises a disease continuum, ranging from microscopic changes to profound fibro-calcific leaflet remodelling, culminating in aortic stenosis, heart failure, and ultimately premature death. Traditional risk factors, such as hypercholesterolaemia and (systolic) hypertension, are shared among atherosclerotic cardiovascular disease and CAVD, yet the molecular and cellular mechanisms differ markedly. Statin-induced low-density lipoprotein cholesterol lowering, a remedy highly effective for secondary prevention of atherosclerotic cardiovascular disease, consistently failed to impact CAVD progression or to improve patient outcomes. However, recently completed phase II trials provide hope that pharmaceutical tactics directed at other targets implicated in CAVD pathogenesis offer an avenue to alter the course of the disease non-invasively. Herein, we delineate key players of CAVD pathobiology, outline mechanisms that entail compromised endothelial barrier function, and promote lipid homing, immune-cell infiltration, and deranged phospho-calcium metabolism that collectively perpetuate a pro-inflammatory/pro-osteogenic milieu in which valvular interstitial cells increasingly adopt myofibro-/osteoblast-like properties, thereby fostering fibro-calcific leaflet remodelling and eventually resulting in left ventricular outflow obstruction. We provide a glimpse into the most promising targets on the horizon, including lipoprotein(a), mineral-binding matrix Gla protein, soluble guanylate cyclase, dipeptidyl peptidase-4 as well as candidates involved in regulating phospho-calcium metabolism and valvular angiotensin II synthesis and ultimately discuss their potential for a future therapy of this insidious disease.

OCT4-mediated inflammation induces cell reprogramming at the origin of cardiac valve development and calcification

Cell plasticity plays a key role in embryos by maintaining the differentiation potential of progenitors. Whether postnatal somatic cells revert to an embryonic-like naïve state regaining plasticity and redifferentiate into a cell type leading to a disease remains intriguing. Using genetic lineage tracing and single-cell RNA sequencing, we reveal that Oct4 is induced by nuclear factor κB (NFκB) at embyronic day 9.5 in a subset of mouse endocardial cells originating from the anterior heart forming field at the onset of endocardial-to-mesenchymal transition. These cells acquired a chondro-osteogenic fate. OCT4 in adult valvular aortic cells leads to calcification of mouse and human valves. These calcifying cells originate from the Oct4 embryonic lineage. Genetic deletion of Pou5f1 (Pit-Oct-Unc, OCT4) in the endocardial cell lineage prevents aortic stenosis and calcification of ApoE^−/− mouse valve. We established previously unidentified self-cell reprogramming NFκB- and OCT4-mediated inflammatory pathway triggering a dose-dependent mechanism of valve calcification.

Interferons Are Pro-Inflammatory Cytokines in Sheared-Stressed Human Aortic Valve Endothelial Cells

Calcific aortic valve disease (CAVD) is an athero-inflammatory process. Growing evidence supports the inflammation-driven calcification model, mediated by cytokines such as interferons (IFNs) and tumor necrosis factor (TNF)-α. Our goal was investigating IFNs' effects in human aortic valve endothelial cells (VEC) and the potential differences between aortic (aVEC) and ventricular (vVEC) side cells. The endothelial phenotype was analyzed by Western blot, qPCR, ELISA, monocyte adhesion, and migration assays. In mixed VEC populations, IFNs promoted the activation of signal transducers and activators of transcription-1 and nuclear factor-κB, and the subsequent up-regulation of pro-inflammatory molecules. Side-specific VEC were activated with IFN-γ and TNF-α in an orbital shaker flow system. TNF-α, but not IFN-γ, induced hypoxia-inducible factor (HIF)-1α stabilization or endothelial nitric oxide synthase downregulation. Additionally, IFN-γ inhibited TNF-α-induced migration of aVEC. Also, IFN-γ triggered cytokine secretion and adhesion molecule expression in aVEC and vVEC. Finally, aVEC were more prone to cytokine-mediated monocyte adhesion under multiaxial flow conditions as compared with uniaxial flow. In conclusion, IFNs promote inflammation and reduce TNF-α-mediated migration in human VEC. Moreover, monocyte adhesion was higher in inflamed aVEC sheared under multiaxial flow, which may be relevant to understanding the initial stages of CAVD.

Association Between Sleep Apnea and Valvular Heart Diseases

Background: Although sleep respiratory disorders are known as a relevant source of cardiovascular risk, there is a substantial lack of trials aimed to evaluate the eventual occurrence of associations between sleep apnea (SA) and valvular heart diseases (VHD).

Methods: We recruited 411 patients referring to our sleep disorder unit, among which 371 had SA. Ninety-three subjects with SA also suffered from VHD. Physical examination, echocardiography, nocturnal cardio-respiratory monitoring, and laboratory tests were performed in each patient. Patient subgroups were comparatively evaluated through cross-sectional analysis.

Results: A statistically significant increase in the prevalence of VHD was detected in relation to high apnea hypopnea index (AHI) values (p = 0.011). Obstructive sleep apnea occurrence was higher in SA patients without VHD (p < 0.0001). Conversely, central and mixed sleep apneas were more frequent among SA patients with VHD (p = 0.0003 and p = 0.002, respectively). We observed a direct correlation between AHI and BMI values (p < 0.0001), as well as between AHI and serum uric acid levels (p < 0.0001), high sensitivity C-reactive protein (p < 0.0001), and indexed left ventricular end-diastolic volume (p < 0.015), respectively. BMI and VHD resulted to be the main predictors of AHI values (p < 0.0001).

Conclusions: Our study suggests that a significant association can occur between SA and VHD. It is clinically relevant that when compared to SA patients without VHD, higher frequencies of central and mixed apneas were found in subjects with SA and VHD. Moreover, after elevated BMI, VHD represented the second predictor of AHI values.

Impairment of mitophagy and autophagy accompanies calcific aortic valve stenosis favoring cell death and the severity of disease

AIMS

In the last 15 years, some observations tried to shed light on the dysregulation of the cellular self-digestion process in calcific aortic valve stenosis (CAVS), but the results obtained remain still controversial. This work is aimed to definitively establish the trend of autophagy in patients affected by CAVS, to analyze the putative involvement of other determinants which impact on the mitochondrial quality control mechanisms and to explore possible avenues for pharmacological interventions in the treatment of CAVS.

METHODS AND RESULTS

This observational study, performed exclusively in ex vivo human samples (cells and serum), by using biochemical approaches and correlations with clinical data, describes new biological features of the calcified valve in terms of mitochondrial dysfunctions. In detail, we unveiled a significant deficiency in mitochondrial respiration and in ATP production coupled to increased production of lactates. In addition, mitochondrial population in the pathologic group is aged with significant alterations in biogenesis and mitophagy pathways. We are also reporting an updated view about autophagy accompanying the calcification process and advanced stages of the disease. We provided evidence for a rapamycin-based therapeutic strategy to revert the calcified phenotype to the wild type one.

CONCLUSIONS

Our data suggest that the Calcific Aortic Valve Stenosis phenotype is featured by defects in mitochondrial quality control mechanisms and that autophagy is not activated enough to counteract cell death and sustain cell functions. Thus, boosting autophagy and mitophagy from short to long-term revert quite all pathological phenotypes.

TRANSLATIONAL PERSPECTIVE

The findings from this study provide evidence for new molecular targets involving mitochondrial quality control mechanisms becoming dysregulated in CAVS. These pathways should be considered as amenable for a combination of new therapies in humans for three reasons: i) no pharmacological treatments are still available to slow down the development of advanced CAVS, ii) being calcification a recurring pathway and iii) the targets proposed are druggable by existing drugs used in the clinic for different purposes. This work also suggests a serum biomarker to be highly related to the stage of disease and the calcification grade of the valve.

Protective Effects of Fucoxanthin on Hydrogen Peroxide-Induced Calcification of Heart Valve Interstitial Cells

Cardiovascular diseases such as atherosclerosis and aortic valve sclerosis involve inflammatory reactions triggered by various stimuli, causing increased oxidative stress. This increased oxidative stress causes damage to the heart cells, with subsequent cell apoptosis or calcification. Currently, heart valve damage or heart valve diseases are treated by drugs or surgery. Natural antioxidant products are being investigated in related research, such as fucoxanthin (Fx), which is a marine carotenoid extracted from seaweed, with strong antioxidant, anti-inflammatory, and anti-tumor properties. This study aimed to explore the protective effect of Fx on heart valves under high oxidative stress, as well as the underlying mechanism of action. Rat heart valve interstitial cells under H₂O₂-induced oxidative stress were treated with Fx. Fx improved cell survival and reduced oxidative stress-induced DNA damage, which was assessed by cell viability analysis and staining with propidium iodide. Alizarin Red-S analysis indicated that Fx has a protective effect against calcification. Furthermore, Western blotting revealed that Fx abrogates oxidative stress-induced apoptosis via reducing the expression of apoptosis-related proteins as well as modulate Akt/ERK-related protein expression. Notably, in vivo experiments using 26 dogs treated with 60 mg/kg of Fx in combination with medical treatment for 0.5 to 2 years showed significant recovery in their echocardiographic parameters. Collectively, these in vitro and in vivo results highlight the potential of Fx to protect heart valve cells from high oxidative stress-induced damage.

Contributions of the Endothelium to Vascular Calcification

Vascular calcification (VC) increases morbidity and mortality and constitutes a significant obstacle during percutaneous interventions and surgeries. On a cellular and molecular level, VC is a highly regulated process that involves abnormal cell transitions and osteogenic differentiation, re-purposing of signaling pathways normally used in bone, and even formation of osteoclast-like cells. Endothelial cells have been shown to contribute to VC through a variety of means. This includes direct contributions of osteoprogenitor cells generated through endothelial-mesenchymal transitions in activated endothelium, with subsequent migration into the vessel wall. The endothelium also secretes pro-osteogenic growth factors, such as bone morphogenetic proteins, inflammatory mediators and cytokines in conditions like hyperlipidemia, diabetes, and renal failure. High phosphate levels caused by renal disease have deleterious effects on the endothelium, and induction of tissue non-specific alkaline phosphatase adds to the calcific process. Furthermore, endothelial activation promotes proteolytic destruction of the internal elastic lamina that serves, among other things, as a stabilizer of the endothelium. Appropriate bone mineralization is highly dependent on active angiogenesis, but it is unclear whether the same relationship exists in VC. Through its location facing the vascular lumen, the endothelium is the first to encounter circulating factor and bone marrow-derived cells that might contribute to osteoclast-like versus osteoblast-like cells in the vascular wall. In the same way, the endothelium may be the easiest target to reach with treatments aimed at limiting calcification. This review provides a brief summary of the contributions of the endothelium to VC as we currently know them.

Leaflet immobility and thrombosis in transcatheter aortic valve replacement

Transcatheter aortic valve replacement (TAVR) has grown exponentially worldwide in the last decade. Due to the higher bleeding risks associated with oral anticoagulation and in patients undergoing TAVR, antiplatelet therapy is currently considered first-line antithrombotic treatment after TAVR. Recent studies suggest that some patients can develop subclinical transcatheter heart valve (THV) thrombosis after the procedure, whereby thrombus forms on the leaflets that can be a precursor to leaflet dysfunction. Compared with echocardiography, multidetector computed tomography is more sensitive at detecting THV thrombosis. Transcatheter heart valve thrombosis can occur while on dual antiplatelet therapy with aspirin and thienopyridine but significantly less with anticoagulation. This review summarizes the incidence and diagnostic criteria for THV thrombosis and discusses the pathophysiological mechanisms that may lead to thrombus formation, its natural history, potential clinical implications and treatment for these patients.

KPT-330 Prevents Aortic Valve Calcification via a Novel C/EBPβ Signaling Pathway

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Side-specific valvular endothelial-interstitial cell mechano-communication via cadherin-11

Calcific aortic valve disease (CAVD) is a condition causing stiffening of the aortic valve, impeding cardiac function and resulting in significant morbidity worldwide. CAVD is thought to be driven by the persistent activation of the predominant cell type in the valve, aortic valve interstitial cells (AVICs), into myofibroblasts, resulting in subsequent calcification and stenosis of the valve. Although much of the research into CAVD focuses on AVICs, the aortic valve endothelial cells (AVECs) have been shown to regulate AVICs and maintain tissue homeostasis. Exposed to distinct flow patterns during the cardiac cycle, the AVECs lining either side of the valve demonstrate crucial differences which could contribute to the preferential formation of calcific nodules on the aorta-facing (fibrosa) side of the valve. Cadherin-11 (CDH11) is a cell-cell adhesion protein which has been previously associated with AVIC myofibroblast activation, nodule formation, and CAVD in mice. In this study, we investigated the role of CDH11 in AVECs and examined side-specific differences. The aorta-facing or fibrosa endothelial cells (fibAVECs) express higher levels of CDH11 than the ventricle-facing or ventricularis endothelial cells (venAVECs). This increase in expression corresponds with increased contraction of a free-floating collagen gel compared to venAVECs. Additionally, co-culture of fibAVECs with AVICs demonstrated decreased contraction compared to an AVIC + AVIC control, but increased contraction compared to the venAVECs co-culture. This aligns with the known preferential formation of calcific nodules on the fibrosa. These results together indicate a potential role for CDH11 expression by AVECs in regulating AVIC contraction and subsequent calcification.

Extracellular Matrix in Calcific Aortic Valve Disease: Architecture, Dynamic and Perspectives

Calcific Aortic Valve Disease (CAVD) is the most common valvular heart disease in developed countries and in the ageing population. It is strongly correlated to median age, affecting up to 13% of the population over the age of 65. Pathophysiological analysis indicates CAVD as a result of an active and degenerative disease, starting with sclerosis and chronic inflammation and then leaflet calcification, which ultimately can account for aortic stenosis. Although CAVD has been firstly recognized as a passive event mostly resulting from a degenerative aging process, much evidences suggests that calcification arises from different active processes, involving both aortic valve-resident cells (valve endothelial cells, valve interstitial cells, mesenchymal stem cells, innate immunity cells) and circulating cells (circulating mesenchymal cells, immunity cells). Moreover, a role for the cell-derived "matrix vesicles" and extracellular matrix (ECM) components has also been recognized. The aim of this work is to review the cellular and molecular alterations occurring in aortic valve during CAVD pathogenesis, focusing on the role of ECM in the natural course of the disease.

Mechanisms underlying the pathophysiology of heart failure with preserved ejection fraction: the tip of the iceberg

Heart failure with preserved ejection fraction (HFpEF) is a multifaceted syndrome with a complex aetiology often associated with several comorbidities, such as left ventricle pressure overload, diabetes mellitus, obesity, and kidney disease. Its pathophysiology remains obscure mainly due to the complex phenotype induced by all these associated comorbidities and to the scarcity of animal models that adequately mimic HFpEF. Increased oxidative stress, inflammation, and endothelial dysfunction are currently accepted as key players in HFpEF pathophysiology. However, we have just started to unveil HFpEF complexity and the role of calcium handling, energetic metabolism, and mitochondrial function remain to clarify. Indeed, the enlightenment of such cellular and molecular mechanisms represents an opportunity to develop novel therapeutic approaches and thus to improve HFpEF treatment options. In the last decades, the number of research groups dedicated to studying HFpEF has increased, denoting the importance and the magnitude achieved by this syndrome. In the current technological and web world, the amount of information is overwhelming, driving us not only to compile the most relevant information about the theme but also to explore beyond the tip of the iceberg. Thus, this review aims to encompass the most recent knowledge related to HFpEF or HFpEF-associated comorbidities, focusing mainly on myocardial metabolism, oxidative stress, and energetic pathways.

Stress-induced remodelling of the mitral valve: a model for leaflet thickening and superimposed tissue formation in mitral valve disease

AIMS

In mitral valve prolapse (MVP), leaflet thickening has recently been suggested to be due, in addition to a myxomatous degeneration, to the presence of a superimposed tissue (SIT), defined as an additional fibrous layer on top of the original leaflet. The mechanisms of SIT formation are currently unknown. We hypothesized that SIT formation would result from excessive leaflet stress and we used a unique ex vivo model to assess the correlation between leaflet remodelling and the type and location of mechanical stress and to elucidate the mechanisms underlying SIT formation.

METHODS AND RESULTS

Human diseased mitral valves (MVs; n = 21) were histologically analysed for SIT formation and original leaflet thickening. The SIT comprised of various compositions of extracellular matrix and could reach more than 50% of total leaflet thickness. Original leaflet and SIT thickness did not show significant correlation (r = -0.27, P = 0.23), suggesting different regulatory mechanisms. To study the role of the mechanical environment on MV remodelling, mouse MV were cultured in their natural position in the heart and subjected to various haemodynamic conditions representing specific phases of the cardiac cycle and the MVP configuration. SIT formation was induced in the ex vivo model, mostly present on the atrial side, and clearly dependent on the duration, type, and extent of mechanical stress. Specific stainings and lineage tracing experiments showed that SIT comprises of macrophages and myofibroblasts and is associated with the activation of the transforming growth factor-beta and bone morphogenetic protein signalling pathways. Migration of valvular interstitial cells and macrophages through breakages of the endothelial cell lining contributed to SIT formation.

CONCLUSIONS

Mechanical stresses induce specific cellular and molecular changes in the MV that result in SIT formation. These observations provide the first insights in the mechanism of SIT formation and represent an initial step to identify potential novel and early treatment for MVP.

Aortic Valve Regurgitation: Pathophysiology and Implications for Surgical Intervention in the Era of TAVR

Aortic insufficiency (AI) or regurgitation is caused by the malcoaptation of the aortic valve (AV) cusps due to intrinsic abnormalities of the valve itself, a dilatation or geometric distortion of the aortic root, or by some combination thereof. In recent years, there has been an increase in the number of studies suggesting that AI is an active disease process caused by a combination of factors including but not limited to alteration of specific molecular pathways, genetic predisposition, and changes in the mechanotransductive properties of the AV apparatus. As the surgical management of AV disease continues to evolve, increasingly sophisticated surgical and percutaneous techniques for AV repair and replacement, including transcatheter aortic valve replacement (TAVR), have become more commonplace and will likely continue to expand as new devices are introduced. However, these techniques necessitate frequent reappraisal of the biological and mechanobiological mechanisms underlying AV regurgitation to better understand the risk factors for AI development and recurrence following surgical intervention as well as expand our limited knowledge on patient selection for such procedures. The aim of this review is to describe some of the putative mechanisms implicated in the development of AI, dissect some of the cross-talk among known and possible signaling pathways leading to valve remodeling, identify association between these pathways and pharmacological approaches, and discuss the implications for surgical and percutaneous approaches to AV repair in replacement in the TAVR era.

NFκB (Nuclear Factor κ-Light-Chain Enhancer of Activated B Cells) Activity Regulates Cell-Type-Specific and Context-Specific Susceptibility to Calcification in the Aortic Valve

OBJECTIVE

Although often studied independently, little is known about how aortic valve endothelial cells and valve interstitial cells interact collaborate to maintain tissue homeostasis or drive valve calcific pathogenesis. Inflammatory signaling is a recognized initiator of valve calcification, but the cell-type-specific downstream mechanisms have not been elucidated. In this study, we test how inflammatory signaling via NFκB (nuclear factor κ-light-chain enhancer of activated B cells) activity coordinates unique and shared mechanisms of valve endothelial cells and valve interstitial cells differentiation during calcific progression. Approach and Results: Activated NFκB was present throughout the calcific aortic valve disease (CAVD) process in both endothelial and interstitial cell populations in an established mouse model of hypercholesterolemia-induced CAVD and in human CAVD. NFκB activity induces endothelial to mesenchymal transformation in 3-dimensional cultured aortic valve endothelial cells and subsequent osteogenic calcification of transformed cells. Similarly, 3-dimensional cultured valve interstitial cells calcified via NFκB-mediated osteogenic differentiation. NFκB-mediated endothelial to mesenchymal transformation was directly demonstrated in vivo during CAVD via genetic lineage tracking. Genetic deletion of NFκB in either whole valves or valve endothelium only was sufficient to prevent valve-specific molecular and cellular mechanisms of CAVD in vivo despite the persistence of a CAVD inducing environment.

CONCLUSIONS

Our results identify NFκB signaling as an essential molecular regulator for both valve endothelial and interstitial participation in CAVD pathogenesis. Direct demonstration of valve endothelial cell endothelial to mesenchymal transformation transmigration in vivo during CAVD highlights a new cellular population for further investigation in CAVD morbidity. The efficacy of valve-specific NFκB modulation in inhibiting hypercholesterolemic CAVD suggests potential benefits of multicell type integrated investigation for biological therapeutic development and evaluation for CAVD.

Early Oxidative Stress Response in Patients with Severe Aortic Stenosis Undergoing Transcatheter and Surgical Aortic Valve Replacement: A Transatlantic Study

Myocardial ischemia/reperfusion-related oxidative stress as a result of cardiopulmonary bypass is thought to contribute to the adverse clinical outcomes following surgical aortic valve replacement (SAVR). Although the acute response following this procedure has been well characterized, much less is known about the nature and extent of oxidative stress induced by the transcatheter aortic valve replacement (TAVR) procedure. We therefore sought to examine and directly compare the oxidative stress response in patients undergoing TAVR and SAVR. A total of 60 patients were prospectively enrolled in this exploratory study, 38 patients undergoing TAVR and 22 patients SAVR. Reduced and oxidized glutathione (GSH, GSSG) in red blood cells as well as the ferric-reducing ability of plasma (FRAP) and plasma concentrations of 8-isoprostanes were measured at baseline (S1), during early reperfusion (S2), and 6-8 hours (S3) following aortic valve replacement (AVR). TAVR and SAVR were successful in all patients. Patients undergoing TAVR were older (79.3 ± 9.5 vs. 74.2 ± 4.1 years; P < 0.01) and had a higher mean STS risk score (6.6 ± 4.8 vs. 3.2 ± 3.0; P < 0.001) than patients undergoing SAVR. At baseline, FRAP and 8-isoprostane plasma concentrations were similar between the two groups, but erythrocytic GSH concentrations were significantly lower in the TAVR group. After AVR, FRAP was markedly higher in the TAVR group, whereas 8-isoprostane concentrations were significantly elevated in the SAVR group. In conclusion, TAVR appears not to cause acute oxidative stress and may even improve the antioxidant capacity in the extracellular compartment.

Identification of key genes and pathways in calcific aortic valve disease by bioinformatics analysis

Background

Calcific aortic valve disease (CAVD) is the most common type of valvular heart disease in the elderly. This study is aimed to explore molecular mechanism of CAVD via bioinformatics analysis.

Methods

The gene expression profiles of GSE51472 (including 5 normal aortic valve and 5 calcified aortic valve) and GSE83453 (including 8 normal aortic valve and 19 calcified aortic valve) were downloaded from the Gene Expression Omnibus (GEO) database. Differentially expressed genes (DEGs) were screened using the MetaDE package in R software. Functional and pathway enrichment analysis were performed based on Gene ontology (GO) and KEGG pathway database. Then, STRING database, Cytoscape and MCODE were applied to construct the protein-protein interaction (PPI) network and screen hub genes. Pathway enrichment analysis was further performed for hub genes and gene clusters identified via module analysis.

Results

A total of 107 DEGs were identified in CAVD (53 up-regulated genes, and 54 down-regulated genes), and they were mainly enriched in the terms of immune response, extracellular matrix organization, leukocyte transendothelial migration, cell adhesion molecules (CAMs), and fatty acid metabolism. Five hub genes including VCAM1, MMP9, ITGB2, RAC2, and vWF were identified via PPI network, which were mainly enriched in terms of leukocyte transendothelial migration and cell adhesion. An independently down-regulated protein cluster containing ALDH2, HIBCH, ACADVL, ECHDC2, VAT1L, and MAOA was also identified via PPI network.

Conclusions

The present study identified VCAM1, MMP9, ITGB2, RAC2, vWF and ALDH2 as key genes in the progression of CAVD. Immune cells infiltration might play a key role in the progression of CAVD, while ALDH2-mediated detoxification effect might play a protective role in CAVD. Further studies are needed to elucidate the pathogenesis of CAVD.

The Behavior of the Type of Peritoneal Transport in the Inflammatory and Oxidative Status in Adults Under Peritoneal Dialysis

Peritoneal dialysis (PD) is an alternative for managing the end-stage renal disease (ESRD). The peritoneal membrane (PM) is not just a membrane that passively responds to diffusion and convection. The characteristics of PM result in the peritoneal equilibrium test (PET) and with this test is possible to obtain the type of peritoneal transport (PT). The patient on PD can be classified in different types of PT as; Low, Low Average, High Average, and High. The aim of the study was to compare the inflammatory cytokines, oxidants, antioxidants, and oxidative DNA damage markers in the different types of PT. A cross-sectional analytical study of 77 adult PD patients was performed. Levels of lipoperoxides (LPO) were higher in all types of PT vs. healthy volunteer controls (HC) (p < 0.0001). Nitric oxide (NO) levels were found significantly down-regulated in all types of PT (p < 0.0001). The activity of the superoxide dismutase enzyme (SOD) was found to be significantly increased in all types of PT vs. the HC (p < 0.0001). The levels of the DNA repair enzyme were found to be decreased in all types of PT. The levels of the pro-inflammatory cytokines TNF-α, IL-6, the marker of oxidative DNA damage, 8-IP and the total antioxidant capacity (TAC) were all significantly decreased, contrary to the levels in HC, possibly by the clearance in the dialysis fluid in all types of PT or due to down-regulation of their expression. In conclusion, we found significant changes in markers of inflammation, oxidative stress, and oxidative damage to DNA in all types of PT; Low, low average, high average, and high PT in the values of D/P creatinine at 4 h compared to HC.

Impact of Oxidative Stress and Protein S-Glutathionylation in Aortic Valve Sclerosis Patients with Overt Atherosclerosis

Aortic valve sclerosis (AVSc) is characterized by non-uniform thickening of the leaflets without hemodynamic changes. Endothelial dysfunction, also caused by dysregulation of glutathione homeostasis expressed as ratio between its reduced (GSH) and its oxidised form (GSSG), could represent one of the pathogenic triggers of AVSc. We prospectively enrolled 58 patients with overt atherosclerosis and requiring coronary artery bypass grafting (CABG). The incidence of AVSc in the studied population was 50%. The two groups (No-AVSc and AVSc) had similar clinical characteristics. Pre-operatively, AVSc group showed significantly lower GSH/GSSG ratio than No-AVSc group (p = 0.02). Asymmetric dimethylarginine (ADMA) concentration was significantly higher in AVSc patients compared to No-AVSc patients (p < 0.0001). Explanted sclerotic aortic valves presented a significantly increased protein glutathionylation (Pr-SSG) than No-AVSc ones (p = 0.01). In vitro, inhibition of glutathione reductase caused β-actin glutathionylation, activation of histone 2AX, upregulation of α2 smooth muscle actin (ACTA2), downregulation of platelet and endothelial cell adhesion molecule 1 (PECAM1) and cadherin 5 (CDH5). In this study, we showed for the first time that the dysregulation of glutathione homeostasis is associated with AVSc. We found that Pr-SSG is increased in AVSc leaflets and it could lead to EndMT via DNA damage. Further studies are warranted to elucidate the causal role of Pr-SSG in aortic valve degeneration.

The Genetic Regulation of Aortic Valve Development and Calcific Disease

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

CD39 and CD73 in the aortic valve-biochemical and immunohistochemical analysis in valve cell populations and its changes in valve mineralization

BACKGROUND

The calcific aortic valve disease (CAVD) is a common heart pathology that involves inflammation, fibrosis, and calcification of aortic valve leaflets. All these processes could be affected by changes in the extracellular purinergic signaling that depend on the activity of ectonucleotidases, mainly ectonucleoside triphosphate diphosphohydrolase 1 (CD39, eNTPD1) and ecto-5'nucleotidase (CD73, e5NT).

OBJECTIVE AND METHODS

We investigated the localization of CD39 and CD73 proteins in human noncalcified and calcified aortic valves using immunohistochemistry together with analysis of NTPDases and e5NT activities in aortic valve homogenates by analysis of substrate into product conversion by high-performance liquid chromatography. We also measured the rates of extracellular nucleotide catabolism on the surface of isolated cultured aortic valve endothelial (hAVECs) and interstitial cells (hAVICs) as well as characterized cellular CD39 and CD73 distribution.

RESULTS

In noncalcified valves, CD39 and CD73 were expressed in both endothelial and interstitial cells, while in calcified valves, the expressions of CD39 and CD73 were significantly down-regulated with the exception of calcified regions where the expression of CD73 was maintained. This correlated with activities in valve homogenates. NTPDase was reduced by 35% and e5NT activity by 50% in calcified vs. noncalcified valve. CD39 and CD73 were present mainly in the cell membrane of hAVECs, but in hAVICs, these proteins were also present intracellularly. The rates of extracellular adenosine triphosphate and adenosine monophosphate hydrolysis in isolated hAVECs and hAVICs were comparable.

CONCLUSION

The presence of ectonucleotidases in valves and especially in aortic valve interstitial cells highlights important local role of purinergic signaling and metabolism. Changes in the local expression and hence the activity of CD39 and CD73 in calcified valves suggest their potential role in CAVD.

Crystallinity of hydroxyapatite drives myofibroblastic activation and calcification in aortic valves

Calcific aortic valve disease (CAVD) is an inexorably degenerative pathology characterized by progressive calcific lesion formation on the valve leaflets. The interaction of valvular cells in advanced lesion environments is not well understood yet highly relevant as clinically detectable CAVD exhibits calcifications composed of non-stoichiometric hydroxyapatite (HA). In this study, Fourier transform infrared spectroscopic imaging was used to spatially analyze mineral properties as a function of disease progression. Crystallinity (size and perfection) increased with increased valve calcification. To study the relationship between crystallinity and cellular behavior in CAVD, valve cells were seeded into 3D mineral-rich collagen gels containing synthetic HA particles, which had varying crystallinities. Lower crystallinity HA drove myofibroblastic activation in both valve interstitial and endothelial cells, as well as osteoblastic differentiation in interstitial cells. Additionally, calcium accumulation within gels depended on crystallinity, and apoptosis was insufficient to explain differences in HA-driven cellular activity. The protective nature of endothelial cells against interstitial cell activation and calcium accumulation was completely inhibited in the presence of less crystalline HA particles. Elucidating valve cellular behavior post-calcification is of vital importance to better predict and treat clinical pathogenesis, and mineral-containing hydrogel models provide a unique 3D platform to evaluate valve cell responses to a later stage of valve disease.

STATEMENT OF SIGNIFICANCE

We implement a 3D in vitro platform with embedded hydroxyapatite (HA) nanoparticles to investigate the interaction between valve interstitial cells, valve endothelial cells, and a mineral-rich extracellular environment. HA nanoparticles were synthesized based on analysis of the mineral properties of calcific regions of diseased human aortic valves. Our findings indicate that crystallinity of HA drives activation and differentiation in interstitial and endothelial cells. We also show that a mineralized environment blocks endothelial protection against interstitial cell calcification. Our HA-containing hydrogel model provides a unique 3D platform to evaluate valve cell responses to a mineralized ECM. This study additionally lays the groundwork to capture the diversity of mineral properties in calcified valves, and link these properties to progression of the disease.

Pathological significance of lipoprotein(a) in aortic valve stenosis

BACKGROUND AND AIMS

Aortic valve stenosis (AVS) affects a significant percentage of our elderly population and younger subjects with familial hypercholesterolemia. Lipoprotein(a) [Lp(a)] has been associated with AVS in recent genetic studies. The purpose of this study was to determine the effects of Lp(a) on human aortic valve interstitial cells (HAVICs), and to identify apolipoproteins and phospholipids in diseased human aortic valves.

METHODS

We examined the effects of Lp(a) on HAVICs mineralization and oxidant formation. Proteomic analyses were used to determine the effects of Lp(a) on downstream intracellular markers. We also used mass spectroscopy to identify the different lipoproteins and oxidized phospholipids in calcified aortic valves.

RESULTS

HAVICs incubated with either LDL or Lp(a) had significantly higher calcium deposition, compared to control (p<0.001), with Lp(a) having the most significant effect (p<0.01) compared to LDL. Proteomic analysis after 10 days of treatment with Lp(a) resulted in enrichment of proteins involved in calcium deposition and vesicle biogenesis. Treatment of HAVICs with Lp(a) significantly increased ROS formation (p<0.05). Patients with calcific aortic stenosis had higher plasma Lp(a) concentrations compared to non-CAD individuals (p<0.001). LC-MS/MS revealed the presence of apolipoproteins and phospholipids in calcified human aortic valves.

CONCLUSIONS

The present study outlines an association between Lp(a) and AVS, and suggests that Lp(a) may serve as a potential target for therapeutic purposes to manage the progression of AVS.

Calcific Aortic Valve Disease: a Developmental Biology Perspective

PURPOSE OF REVIEW

This review aims to highlight the past and more current literature related to the multifaceted pathogenic programs that contribute to calcific aortic valve disease (CAVD) with a focus on the contribution of developmental programs.

RECENT FINDINGS

Calcification of the aortic valve is an active process characterized by calcific nodule formation on the aortic surface leading to a less supple and more stiffened cusp, thereby limiting movement and causing clinical stenosis. The mechanisms underlying these pathogenic changes are largely unknown, but emerging studies have suggested that signaling pathways common to valvulogenesis and bone development play significant roles and include Transforming Growth Factor-β (TGF-β), bone morphogenetic protein (BMP), Wnt, Notch, and Sox9. This comprehensive review of the literature highlights the complex nature of CAVD but concurrently identifies key regulators that can be targeted in the development of mechanistic-based therapies beyond surgical intervention to improve patient outcome.

Effect of adipose-derived mesenchymal stem cell transplantation on vascular calcification in rats with adenine-induced kidney disease

Previous studies have investigated the use of mesenchymal stem cells (MSCs) to treat damaged kidneys. However, the effect of adipose-derived MSCs (ASCs) on vascular calcification in chronic kidney disease (CKD) is still poorly understood. In the present study, we explored the potential of ASCs for the treatment of CKD and vascular calcification. CKD was induced in male Sprague-Dawley rats by feeding them a diet containing 0.75% adenine for 4 weeks. ASCs transplantation significantly reduced serum inorganic phosphorus (Pi) as compared to that in the control. The histopathology of the kidneys showed a greater dilation of tubular lumens and interstitial fibrosis in the control group. Calcium and Pi contents of the aorta in the ASCs transplantation group were lower than those in the control group. Von Kossa staining of the thoracic aorta media revealed that ASCs transplantation suppressed vascular calcification. Thus, this study revealed that autogenic ASCs transplantation inhibits kidney damage and suppresses the progression of vascular calcification in the CKD rat model, suggesting that autogenic ASCs transplantation is a novel approach for preventing the progression of CKD and vascular calcification.

Growth and maturation of heart valves leads to changes in endothelial cell distribution, impaired function, decreased metabolism and reduced cell proliferation

Risk factors of heart valve disease are well defined and prolonged exposure throughout life leads to degeneration and dysfunction in up to 33% of the population. While aortic valve replacement remains the most common need for cardiovascular surgery particularly in those aged over 65, the underlying mechanisms of progressive deterioration are unknown. In other cardiovascular systems, a decline in endothelial cell integrity and function play a major role in promoting pathological changes, and while similar mechanisms have been speculated in the valves, studies to support this are lacking. The goal of this study was to examine age-related changes in valve endothelial cell (VEC) distribution, morphology, function and transcriptomes during critical stages of valve development (embryonic), growth (postnatal (PN)), maintenance (young adult) and aging (aging adult). Using a combination of in vivo mouse, and in vitro porcine assays we show that VEC function including, nitric oxide bioavailability, metabolism, endothelial-to-mesenchymal potential, membrane self-repair and proliferation decline with age. In addition, density of VEC distribution along the endothelium decreases and this is associated with changes in morphology, decreased cell-cell interactions, and increased permeability. These changes are supported by RNA-seq analysis showing that focal adhesion-, cell cycle-, and oxidative phosphorylation-associated biological processes are negatively impacted by aging. Furthermore, by performing high-throughput analysis we are able to report the differential and common transcriptomes of VECs at each time point that can provide insights into the mechanisms underlying age-related dysfunction. These studies suggest that maturation of heart valves over time is a multifactorial process and this study has identified several key parameters that may contribute to impairment of the valve to maintain critical structure-function relationships; leading to degeneration and disease.

Valve interstitial cell tensional homeostasis directs calcification and extracellular matrix remodeling processes via RhoA signaling

AIMS

Valve interstitial cells are active and aggressive players in aortic valve calcification, but their dynamic mediation of mechanically-induced calcific remodeling is not well understood. The goal of this study was to elucidate the feedback loop between valve interstitial cell and calcification mechanics using a novel three-dimensional culture system that allows investigation of the active interplay between cells, disease, and the mechanical valve environment.

METHODS & RESULTS

We designed and characterized a novel bioreactor system for quantifying aortic valve interstitial cell contractility in 3-D hydrogels in control and osteogenic conditions over 14 days. Interstitial cells demonstrated a marked ability to exert contractile force on their environment and to align collagen fibers with the direction of tension. Osteogenic environment disrupted interstitial cell contractility and led to disorganization of the collagen matrix, concurrent with increased αSMA, TGF-β, Runx2 and calcific nodule formation. Interestingly, RhoA was also increased in osteogenic condition, pointing to an aberrant hyperactivation of valve interstitial cells mechanical activity in disease. This was confirmed by inhibition of RhoA experiments. Inhibition of RhoA concurrent with osteogenic treatment reduced pro-osteogenic signaling and calcific nodule formation. Time-course correlation analysis indicated a significant correlation between interstitial cell remodeling of collagen fibers and calcification events.

CONCLUSIONS

Interstitial cell contractility mediates internal stress state and organization of the aortic valve extracellular matrix. Osteogenesis disrupts interstitial cell mechanical phenotype and drives disorganization, nodule formation, and pro-calcific signaling via a RhoA-dependent mechanism.

Cadherin-11 Overexpression Induces Extracellular Matrix Remodeling and Calcification in Mature Aortic Valves

OBJECTIVE

Calcific aortic valve (AoV) disease is a significant clinical problem for which the regulatory mechanisms are poorly understood. Enhanced cell-cell adhesion is a common mechanism of cellular aggregation, but its role in calcific lesion formation is not known. Cadherin-11 (Cad-11) has been associated with lesion formation in vitro, but its function during adult valve homeostasis and pathogenesis is not known. This study aims to elucidate the specific functions of Cad-11 and its downstream targets, RhoA and Sox9, in extracellular matrix remodeling and AoV calcification.

APPROACH AND RESULTS

We conditionally overexpressed Cad-11 in murine heart valves using a novel double-transgenic Nfatc1(Cre);R26-Cad11(TglTg) mouse model. These mice developed hemodynamically significant aortic stenosis with prominent calcific lesions in the AoV leaflets. Cad-11 overexpression upregulated downstream targets, RhoA and Sox9, in the valve interstitial cells, causing calcification and extensive pathogenic extracellular matrix remodeling. AoV interstitial cells overexpressing Cad-11 in an osteogenic environment in vitro rapidly form calcific nodules analogous to in vivo lesions. Molecular analyses revealed upregulation of osteoblastic and myofibroblastic markers. Treatment with a Rho-associated protein kinase inhibitor attenuated nodule formation, further supporting that Cad-11-driven calcification acts through the small GTPase RhoA/Rho-associated protein kinase signaling pathway.

CONCLUSIONS

This study identifies one of the underlying molecular mechanisms of heart valve calcification and demonstrates that overexpression of Cad-11 upregulates RhoA and Sox9 to induce calcification and extracellular matrix remodeling in adult AoV pathogenesis. The findings provide a potential molecular target for clinical treatment.

Towards 3D in vitro models for the study of cardiovascular tissues and disease

The field of tissue engineering is developing biomimetic biomaterial scaffolds that are showing increasing therapeutic potential for the repair of cardiovascular tissues. However, a major opportunity exists to use them as 3D in vitro models for the study of cardiovascular tissues and disease in addition to drug development and testing. These in vitro models can span the gap between 2D culture and in vivo testing, thus reducing the cost, time, and ethical burden of current approaches. Here, we outline the progress to date and the requirements for the development of ideal in vitro 3D models for blood vessels, heart valves, and myocardial tissue.

Cells and extracellular matrix interplay in cardiac valve disease: because age matters

Cardiovascular aging is a physiological process affecting all components of the heart. Despite the interest and experimental effort lavished on aging of cardiac cells, increasing evidence is pointing at the pivotal role of extracellular matrix (ECM) in cardiac aging. Structural and molecular changes in ECM composition during aging are at the root of significant functional modifications at the level of cardiac valve apparatus. Indeed, calcification or myxomatous degeneration of cardiac valves and their functional impairment can all be explained in light of age-related ECM alterations and the reciprocal interplay between altered ECM and cellular elements populating the leaflet, namely valvular interstitial cells and valvular endothelial cells, is additionally affecting valve function with striking reflexes on the clinical scenario. The initial experimental findings on this argument are underlining the need for a more comprehensive understanding on the biological mechanisms underlying ECM aging and remodeling as potentially constituting a pharmacological therapeutic target or a basis to improve existing prosthetic devices and treatment options. Given the lack of systematic knowledge on this topic, this review will focus on the ECM changes that occur during aging and on their clinical translational relevance and implications in the bedside scenario.