Role of human valve interstitial cells in valve calcification and their response to atorvastatin

Directed Differentiation of Human Induced Pluripotent Stem Cells to Heart Valve Cells

BACKGROUND

A main obstacle in current valvular heart disease research is the lack of high-quality homogeneous functional heart valve cells. Human induced pluripotent stem cells (hiPSCs)-derived heart valve cells may help with this dilemma. However, there are no well-established protocols to induce hiPSCs to differentiate into functional heart valve cells, and the networks that mediate the differentiation have not been fully elucidated.

METHODS

To generate heart valve cells from hiPSCs, we sequentially activated the Wnt, BMP4, VEGF (vascular endothelial growth factor), and NFATc1 signaling pathways using CHIR-99021, BMP4, VEGF-165, and forskolin, respectively. The transcriptional and functional similarity of hiPSC-derived heart valve cells compared with primary heart valve cells were characterized. Longitudinal single-cell RNA sequencing was used to uncover the trajectory, switch genes, pathways, and transcription factors of the differentiation.

RESULTS

An efficient protocol was developed to induce hiPSCs to differentiate into functional hiPSC-derived valve endothelial-like cells and hiPSC-derived valve interstitial-like cells. After 6-day differentiation and CD144 magnetic bead sorting, ≈70% CD144+ cells and 30% CD144- cells were obtained. On the basis of single-cell RNA sequencing data, the CD144+ cells and CD144- cells were found to be highly similar to primary heart valve endothelial cells and primary heart valve interstitial cells in gene expression profile. Furthermore, CD144+ cells had the typical function of primary heart valve endothelial cells, including tube formation, uptake of low-density lipoprotein, generation of endothelial nitric oxide synthase, and response to shear stress. Meanwhile, CD144- cells could secret collagen and matrix metalloproteinases, and differentiate into osteogenic or adipogenic lineages like primary heart valve interstitial cells. Therefore, we identified CD144+ cells and CD144- cells as hiPSC-derived valve endothelial-like cells and hiPSC-derived valve interstitial-like cells, respectively. Using single-cell RNA sequencing analysis, we demonstrated that the trajectory of heart valve cell differentiation was consistent with embryonic valve development. We identified the main switch genes (NOTCH1, HEY1, and MEF2C), signaling pathways (TGF-β, Wnt, and NOTCH), and transcription factors (MSX1, SP5, and MECOM) that mediated the differentiation. Finally, we found that hiPSC-derived valve interstitial-like cells might derive from hiPSC-derived valve endothelial-like cells undergoing endocardial-mesenchymal transition.

CONCLUSIONS

In summary, this is the first study to report an efficient strategy to generate functional hiPSC-derived valve endothelial-like cells and hiPSC-derived valve interstitial-like cells from hiPSCs, as well as to elucidate the differentiation trajectory and transcriptional dynamics of hiPSCs differentiated into heart valve cells.

Multiscale computational modeling of aortic valve calcification

Calcific aortic valve disease (CAVD) is a common cardiovascular disease that affects millions of people worldwide. The disease is characterized by the formation of calcium nodules on the aortic valve leaflets, which can lead to stenosis and heart failure if left untreated. The pathogenesis of CAVD is still not well understood, but involves several signaling pathways, including the transforming growth factor beta (TGF β ) pathway. In this study, we developed a multiscale computational model for TGF β -stimulated CAVD. The model framework comprises cellular behavior dynamics, subcellular signaling pathways, and tissue-level diffusion fields of pertinent chemical species, where information is shared among different scales. Processes such as endothelial to mesenchymal transition (EndMT), fibrosis, and calcification are incorporated. The results indicate that the majority of myofibroblasts and osteoblast-like cells ultimately die due to lack of nutrients as they become trapped in areas with higher levels of fibrosis or calcification, and they subsequently act as sources for calcium nodules, which contribute to a polydispersed nodule size distribution. Additionally, fibrosis and calcification processes occur more frequently in regions closer to the endothelial layer where the cell activity is higher. Our results provide insights into the mechanisms of CAVD and TGF β signaling and could aid in the development of novel therapeutic approaches for CAVD and other related diseases such as cancer. More broadly, this type of modeling framework can pave the way for unraveling the complexity of biological systems by incorporating several signaling pathways in subcellular models to simulate tissue remodeling in diseases involving cellular mechanobiology.

Models for calcific aortic valve disease in vivo and in vitro

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

Metformin ameliorates valve interstitial cell calcification by promoting autophagic flux

Calcific aortic valve disease (CAVD) is the most common heart disease of the developed world. It has previously been established that metformin administration reduces arterial calcification via autophagy; however, whether metformin directly regulates CAVD has yet to be elucidated. In the present study we investigated whether metformin alleviates valvular calcification through the autophagy-mediated recycling of Runx2. Calcification was reduced in rat valve interstitial cells (RVICs) by metformin treatment (0.5-1.5 mM) (P < 0.01), with a marked decrease in Runx2 protein expression compared to control cells (P < 0.05). Additionally, upregulated expression of Atg3 and Atg7 (key proteins required for autophagosome formation), was observed following metformin treatment (1 mM). Blocking autophagic flux using Bafilomycin-A1 revealed colocalisation of Runx2 with LC3 puncta in metformin treated RVICs (P < 0.001). Comparable Runx2 accumulation was seen in LC3 positive autolysosomes present within cells that had been treated with both metformin and hydroxychloroquine in combination (P < 0.001). Mechanistic studies employing three-way co-immunoprecipitation with Runx2, p62 and LC3 suggested that Runx2 binds to LC3-II upon metformin treatment in VICs. Together these studies suggest that the utilisation of metformin may represent a novel strategy for the treatment of CAVD.

Vascular calcification: from the perspective of crosstalk

Vascular calcification (VC) is highly correlated with cardiovascular disease morbidity and mortality, but anti-VC treatment remains an area to be tackled due to the ill-defined molecular mechanisms. Regardless of the type of VC, it does not depend on a single cell but involves multi-cells/organs to form a complex cellular communication network through the vascular microenvironment to participate in the occurrence and development of VC. Therefore, focusing only on the direct effect of pathological factors on vascular smooth muscle cells (VSMCs) tends to overlook the combined effect of other cells and VSMCs, including VSMCs-VSMCs, ECs-VMSCs, Macrophages-VSMCs, etc. Extracellular vesicles (EVs) are a collective term for tiny vesicles with a membrane structure that are actively secreted by cells, and almost all cells secrete EVs. EVs docked on the surface of receptor cells can directly mediate signal transduction or transfer their contents into the cell to elicit a functional response from the receptor cells. They have been proven to participate in the VC process and have also shown attractive therapeutic prospects. Based on the advantages of EVs and the ability to be detected in body fluids, they may become a novel therapeutic agent, drug delivery vehicle, diagnostic and prognostic biomarker, and potential therapeutic target in the future. This review focuses on the new insight into VC molecular mechanisms from the perspective of crosstalk, summarizes how multi-cells/organs interactions communicate via EVs to regulate VC and the emerging potential of EVs as therapeutic methods in VC. We also summarize preclinical experiments on crosstalk-based and the current state of clinical studies on VC-related measures.

Influence of Aortic Valve Stenosis and Wall Shear Stress on Platelets Function

Aortic valve stenosis (AS) is a common heart valve disease in the elderly population, and its pathogenesis remains an interesting area of research. The degeneration of the aortic valve leaflets gradually progresses to valve sclerosis. The advanced phase is marked by the presence of extracellular fibrosis and calcification. Turbulent, accelerated blood flow generated by the stenotic valve causes excessive damage to the aortic wall. Elevated shear stress due to AS leads to the degradation of high-molecular weight multimers of von Willebrand factor, which may involve bleeding in the mucosal tissues. Conversely, elevated shear stress has been associated with the release of thrombin and the activation of platelets, even in individuals with acquired von Willebrand syndrome. Moreover, turbulent blood flow in the aorta may activate the endothelium and promote platelet adhesion and activation on the aortic valve surface. Platelets release a wide range of mediators, including lysophosphatidic acid, which have pro-osteogenic effects in AS. All of these interactions result in blood coagulation, fibrinolysis, and the hemostatic process. This review summarizes the current knowledge on high shear stress-induced hemostatic disorders, the influence of AS on platelets and antiplatelet therapy.

High resolution monitoring of valvular interstitial cell driven pathomechanisms in procalcific environment using label-free impedance spectroscopy

Introduction

Fibro-calcific aortic valve disease has high prevalence and is associated with significant mortality. Fibrotic extracellular matrix (ECM) remodeling and calcific mineral deposition change the valvular microarchitecture and deteriorate valvular function. Valvular interstitial cells (VICs) in profibrotic or procalcifying environment are frequently used in vitro models. However, remodeling processes take several days to weeks to develop, even in vitro. Continuous monitoring by real-time impedance spectroscopy (EIS) may reveal new insights into this process.

Methods

VIC-driven ECM remodeling stimulated by procalcifying (PM) or profibrotic medium (FM) was monitored by label-free EIS. Collagen secretion, matrix mineralization, viability, mitochondrial damage, myofibroblastic gene expression and cytoskeletal alterations were analyzed.

Results and Discussion

EIS profiles of VICs in control medium (CM) and FM were comparable. PM reproducibly induced a specific, biphasic EIS profile. Phase 1 showed an initial impedance drop, which moderately correlated with decreasing collagen secretion (r = 0.67, p = 0.22), accompanied by mitochondrial membrane hyperpolarization and cell death. Phase 2 EIS signal increase was positively correlated with augmented ECM mineralization (r = 0.97, p = 0.008). VICs in PM decreased myofibroblastic gene expression (p < 0.001) and stress fiber assembly compared to CM. EIS revealed sex-specific differences. Male VICs showed higher proliferation and in PM EIS decrease in phase 1 was significantly pronounced compared to female VICs (male minimum: 7.4 ± 4.2%, female minimum: 26.5 ± 4.4%, p < 0.01). VICs in PM reproduced disease characteristics in vitro remarkably fast with significant impact of donor sex. PM suppressed myofibroblastogenesis and favored ECM mineralization. In summary, EIS represents an efficient, easy-to-use, high-content screening tool enabling patient-specific, subgroup- and temporal resolution.

Hypoxia-inducible factor activation promotes osteogenic transition of valve interstitial cells and accelerates aortic valve calcification in a mice model of chronic kidney disease

Introduction

Valve calcification (VC) is a widespread complication in chronic kidney disease (CKD) patients. VC is an active process with the involvement of in situ osteogenic transition of valve interstitial cells (VICs). VC is accompanied by the activation of hypoxia inducible factor (HIF) pathway, but the role of HIF activation in the calcification process remains undiscovered.

Methods and result

Using in vitro and in vivo approaches we addressed the role of HIF activation in osteogenic transition of VICs and CKD-associated VC. Elevation of osteogenic (Runx2, Sox9) and HIF activation markers (HIF-1α and HIF-2α) and VC occurred in adenine-induced CKD mice. High phosphate (Pi) induced upregulation of osteogenic (Runx2, alkaline-phosphatase, Sox9, osteocalcin) and hypoxia markers (HIF-1α, HIF-2α, Glut-1), and calcification in VICs. Down-regulation of HIF-1α and HIF-2α inhibited, whereas further activation of HIF pathway by hypoxic exposure (1% O₂) or hypoxia mimetics [desferrioxamine, CoCl₂, Daprodustat (DPD)] promoted Pi-induced calcification of VICs. Pi augmented the formation of reactive oxygen species (ROS) and decreased viability of VICs, whose effects were further exacerbated by hypoxia. N-acetyl cysteine inhibited Pi-induced ROS production, cell death and calcification under both normoxic and hypoxic conditions. DPD treatment corrected anemia but promoted aortic VC in the CKD mice model.

Discussion

HIF activation plays a fundamental role in Pi-induced osteogenic transition of VICs and CKD-induced VC. The cellular mechanism involves stabilization of HIF-1α and HIF-2α, increased ROS production and cell death. Targeting the HIF pathways may thus be investigated as a therapeutic approach to attenuate aortic VC.

Identification of key genes involved in calcific aortic valve disease based on integrated bioinformatics analysis

The calcific aortic valve disease (CAVD) develops as an aortic valve sclerosis and progresses to an advanced form of stenosis. In many biological fields, bioinformatics becomes a fundamental component. The key mechanisms involved in CAVD are discovered with the use of bioinformatics to investigate gene function and pathways. We downloaded the original data (GSE51472) from the Gene Expression Omnibus (GEO) database (http://www.ncbi.nlm.nih.gov/geo/). After standardization, 2978 differentially expressed genes (DEGs) were identified from the data sets GSE51472 containing samples from normal, calcified, and sclerotic aortic valves. Analysis of DEGs based on the series test of clusters (STCs) revealed the two most significant patterns. Based on the result of the STC, the functional enrichment analysis of gene ontology (GO) was conducted to investigate the molecular function (MF), biological process (BP), and cell compound (CC) of the DEGs. With a p value of 0.01, DEGs associated with "chronic inflammation," "T-cell receptor complexes," and "antigen binding" had the highest significance within BP, CC, and MF. DEG enrichment in signaling pathways was analyzed using KEGG pathway enrichment. Using a p < 0.05 level of significance, the most enriched biological pathways related to CAVD were "Chemokine signaling pathway," "Cytokine-cytokine receptor interaction," "Tuberculosis," "PI3K-Akt signaling pathway," and "Transcriptional misregulation in cancer." Finally, the construction of gene co-expression networks and pathway networks illustrated the pathogensis of CAVD. TLR2, CD86, and TYROBP were identified as hub genes for the development of CAVD. Moreover, "MAPK signaling pathway," "Apoptosis," and "Pathways in cancer" were regarded as the core pathways among the samples of normal, sclerotic and calcified aortic valve samples.

Overexpressed Thrombospondin 2 Induced Osteogenic Differentiation of Valve Interstitial Cells via Inhibition of Akt/NF-κB Signaling Pathway to Promote Calcific Aortic Valve Disease Development

Thrombospondin 2 (THBS2) is reported to participate in the development of calcific aortic valve disease (CAVD), while the effects are not elucidated completely. The study aimed to explore the role and mechanism of THBS2 in CAVD. Differentially expressed genes related to stenosis and sclerosis were screened through Limma package based on data from Gene Expression Omnibus (GEO), and the functional enrichment analysis was performed by the Database for Annotation, Visualization and Integrated Discovery (DAVID) database. The immunoreactivity of THBS2 in CAVD and normal samples was detected through immunohistochemistry. Valve interstitial cells (VICs) were transfected with short hairpin RNA against THBS2 (shTHBS2) and THBS2 overexpression plasmid and treated with LY294002 (Akt inhibitor) and induced osteogenic differentiation. The expression of THBS2 in CAVD and normal samples and the levels of THBS2, osteocalcin, Runx2, SPARC, COL1A2, COL1A1, SPP1, CTGF, MMP-2, MMP-13, Akt, p-Akt, p65, p-p65, and nuclear p65 in VICs were tested by qRT-PCR and Western blot. ALP activity was assessed using colorimetry. Calcic nodule formation was measured by Alizarin Red staining. THBS2 and PI3K-Akt pathway were differentially enriched in stenosis samples when compared with those in sclerosis samples. THBS2 expression was upregulated in CAVD and positively correlated with ALP activity, calcic nodule formation, osteogenic differentiation-related (osteocalcin, Runx2, SPARC, COL1A2, COL1A1, SPP1, and CTGF) and extracellular matrix– (ECM–) related (MMP-2 and MMP-13) factors in the process of osteogenic differentiation. ShTHBS2 suppressed ALP activity, calcic nodule formation, and osteogenic differentiation/ECM-related molecules while upregulating p-Akt/Akt, p-p65/p65, and nuclear p65 expressions in VICs during osteogenic differentiation. However, THBS2 overexpression had the opposite effect to shTHBS2, and LY294002 reversed the effect of shTHBS2. Collectively, overexpressed THBS2 induces the osteogenic differentiation of VICs via inhibiting Akt/NF-κB pathway to promote the development of CAVD.

Marine-Derived Piericidin Diglycoside S18 Alleviates Inflammatory Responses in the Aortic Valve via Interaction with Interleukin 37

Calcific aortic valve disease (CAVD) is a valvular disease frequently in the elderly individuals that can lead to the valve dysfunction. Osteoblastic differentiation of human aortic valve interstitial cells (HAVICs) induced by inflammation play a crucial role in CAVD pathophysiological processes. To date, no effective drugs for CAVD have been established, and new agents are urgently needed. Piericidin glycosides, obtained from a marine-derived Streptomyces strain, were revealed to have regulatory effects on mitochondria in previous studies. Here, we discovered that 13-hydroxypiericidin A 10-O-α-D-glucose (1→6)-β-D-glucoside (S18), a specific piericidin diglycoside, suppresses lipopolysaccharide- (LPS) induced inflammatory responses of HAVICs by alleviating mitochondrial stress in an interleukin (IL)-37-dependent manner. Knockdown of IL-37 by siRNA not only exaggerated LPS-induced HAVIC inflammation and mitochondrial stress but also abrogated the anti-inflammatory effect of S18 on HAVICs. Moreover, S18 alleviated aortic valve lesions in IL-37 transgenic mice of CAVD model. Microscale thermophoresis (MST) and docking analysis of five piericidin analogues suggested that diglycosides, but not monoglycosides, exert obvious IL-37-binding activity. These results indicate that S18 directly binds to IL-37 to alleviate inflammatory responses in HAVICs and aortic valve lesions in mice. Piericidin diglycoside S18 is a potential therapeutic agent to prevent the development of CAVD.

4-Octyl itaconate suppresses the osteogenic response in aortic valvular interstitial cells via the Nrf2 pathway and alleviates aortic stenosis in mice with direct wire injury

Calcific aortic valve disease (CAVD) is the most prevalent valvular heart disease in older individuals, but there is a lack of drug treatment. The cellular biological mechanisms of CAVD are still unclear. Oxidative stress and endoplasmic reticulum stress (ER stress) have been suggested to be involved in the progression of CAVD. Many studies have demonstrated that 4-octyl itaconate (OI) plays beneficial roles in limiting inflammation and oxidative injury. However, the potential role of OI in CAVD has not been thoroughly explored. Thus, we investigated OI-mediated modulation of ROS generation and endoplasmic reticulum stress to inhibit osteogenic differentiation in aortic valve interstitial cells (VICs). In our study, calcified aortic valves showed increased levels of ER stress and superoxide anion, as well as abnormal expression of Hmox1 and NQO1. In VICs, OI activated the Nrf2 signaling cascade and contributed to Nrf2 stabilization and nuclear translocation, thus augmenting the expression of genes downstream of Nrf2 (Hmox1 and NQO1). Moreover, OI ameliorated osteogenic medium (OM)-induced ROS production, mitochondrial ROS levels and the loss of mitochondrial membrane potential in VICs. Furthermore, OI attenuated the OM-induced upregulation of ER stress markers, osteogenic markers and calcium deposition, which were blocked by the Nrf2-specific inhibitor ML385. Interestingly, we found that OM-induced ER stress and osteogenic differentiation were ROS-dependent and that Hmox1 silencing triggered ROS production, ER stress and elevated osteogenic activity, which were inhibited by NAC. Overexpression of NQO1 mediated by adenovirus vectors significantly suppressed OM-induced ER stress and osteogenic markers. Collectively, these results showed the anti-osteogenic effects of OI on AVICs by regulating the generation of ROS and ER stress by activating the Nrf2 signaling pathway. Furthermore, OI alleviated aortic stenosis in a mouse model with direct wire injury. Due to its antioxidant properties, OI could be a potential drug for the prevention and/or treatment of CAVD.

Reduced Proteolytic Cleavage of von Willebrand Factor Leads to Aortic Valve Stenosis and Load-Dependent Ventricular Remodeling

We hypothesized that excess endothelial-associated von Willebrand factor (vWF) and secondary platelet adhesion contribute to aortic valve stenosis (AS). We studied hyperlipidemic mice lacking ADAMTS13 (LDLR ^-/- AD13 ^-/- ), which cleaves endothelial-associated vWF multimers. On echocardiography and molecular imaging, LDLR ^-/- AD13 ^-/- compared with control strains had increased aortic endothelial vWF and platelet adhesion and developed hemodynamically significant AS, arterial stiffening, high valvulo-aortic impedance, and secondary load-dependent reduction in LV systolic function. Histology revealed leaflet thickening and calcification with valve interstitial cell myofibroblastic and osteogenic transformation, and evidence for TGFβ1 pathway activation. We conclude that valve leaflet endothelial vWF-platelet interactions promote AS through juxtacrine platelet signaling.

Fibroblast growth factor 2 inhibits myofibroblastic activation of valvular interstitial cells

Heart valve disease is a growing problem worldwide. Though very common in older adults, the mechanisms behind the development of the disease aren't well understood, and at present the only therapeutic option is valve replacement. Valvular interstitial cells (VICs) may hold the answer. These cells can undergo pathological differentiation into contractile myofibroblasts or osteoblasts, leading to thickening and calcification of the valve tissue. Our study aimed to characterise the effect of fibroblast growth factor 2 (FGF-2) on the differentiation potential of VICs. We isolated VICs from diseased human valves and treated these cells with FGF-2 and TGF-β to elucidate effect of these growth factors on several myofibroblastic outcomes, in particular immunocytochemistry and gene expression. We used TGF-β as a positive control for myofibroblastic differentiation. We found that FGF-2 promotes a 'quiescent-type' morphology and inhibits the formation of α-smooth muscle actin positive myofibroblasts. FGF-2 reduced the calcification potential of VICs, with a marked reduction in the number of calcific nodules. FGF-2 interrupted the 'canonical' TGF-β signalling pathway, reducing the nuclear translocation of the SMAD2/3 complex. The panel of genes assayed revealed that FGF-2 promoted a quiescent-type pattern of gene expression, with significant downregulations in typical myofibroblast markers α smooth muscle actin, extracellular matrix proteins, and scleraxis. We did not see evidence of osteoblast differentiation: neither matrix-type calcification nor changes in osteoblast associated gene expression were observed. Our findings show that FGF-2 can reverse the myofibroblastic phenotype of VICs isolated from diseased valves and inhibit the calcification potential of these cells.

Models and Techniques to Study Aortic Valve Calcification in Vitro, ex Vivo and in Vivo. An Overview

Aortic valve stenosis secondary to aortic valve calcification is the most common valve disease in the Western world. Calcification is a result of pathological proliferation and osteogenic differentiation of resident valve interstitial cells. To develop non-surgical treatments, the molecular and cellular mechanisms of pathological calcification must be revealed. In the current overview, we present methods for evaluation of calcification in different ex vivo, in vitro and in vivo situations including imaging in patients. The latter include echocardiography, scanning with computed tomography and magnetic resonance imaging. Particular emphasis is on translational studies of calcific aortic valve stenosis with a special focus on cell culture using human primary cell cultures. Such models are widely used and suitable for screening of drugs against calcification. Animal models are presented, but there is no animal model that faithfully mimics human calcific aortic valve disease. A model of experimentally induced calcification in whole porcine aortic valve leaflets ex vivo is also included. Finally, miscellaneous methods and aspects of aortic valve calcification, such as, for instance, biomarkers are presented.

Oxidative Stress in Calcific Aortic Valve Stenosis: Protective Role of Natural Antioxidants

Calcific aortic valve stenosis (CAVS) is the most prevalent heart valvular disease worldwide and a slowly progressive disorder characterized by thickening of the aortic valve, calcification, and subsequent heart failure. Valvular calcification is an active cell regulation process in which valvular interstitial cells involve phenotypic conversion into osteoblasts/chondrocytes-like cells. The underlying pathophysiology is complicated, and there have been no pharmacological treatments for CAVS to date. Recent studies have suggested that an increase in oxidative stress is the major trigger of CAVS, and natural antioxidants could ameliorate the detrimental effects of reactive oxygen species in the pathogenesis of CAVS. It is imperative to review the current findings regarding the role of natural antioxidants in CAVS, as they can be a promising therapeutic approach for managing CAVS, a disorder currently without effective treatment. This review summarizes the current findings on molecular mechanisms associated with oxidative stress in the development of valvular calcification and discusses the protective roles of natural antioxidants in the prevention and treatment of CAVS.

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

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

Role of Extracellular Vesicles as Potential Diagnostic and/or Therapeutic Biomarkers in Chronic Cardiovascular Diseases

Cardiovascular diseases (CVDs) are the first cause of death worldwide. In recent years, there has been great interest in the analysis of extracellular vesicles (EVs), including exosomes and microparticles, as potential mediators of biological communication between circulating cells/plasma and cells of the vasculature. Besides their activity as biological effectors, EVs have been also investigated as circulating/systemic biomarkers in different acute and chronic CVDs. In this review, the role of EVs as potential diagnostic and prognostic biomarkers in chronic cardiovascular diseases, including atherosclerosis (mainly, peripheral arterial disease, PAD), aortic stenosis (AS) and aortic aneurysms (AAs), will be described. Mechanistically, we will analyze the implication of EVs in pathological processes associated to cardiovascular remodeling, with special emphasis in their role in vascular and valvular calcification. Specifically, we will focus on the participation of EVs in calcium accumulation in the pathological vascular wall and aortic valves, involving the phenotypic change of vascular smooth muscle cells (SMCs) or valvular interstitial cells (IC) to osteoblast-like cells. The knowledge of the implication of EVs in the pathogenic mechanisms of cardiovascular remodeling is still to be completely deciphered but there are promising results supporting their potential translational application to the diagnosis and therapy of different CVDs.

Exploring potential genes and pathways related to calcific aortic valve disease

Calcific aortic valve disease (CAVD) is currently the most prevalent valvular disease. However, the pathological mechanism of CAVD has not yet been fully elucidated, and no drugs can delay or halt the progression of CAVD. This study aimed to screen for potential biomarkers and pathways of CAVD through bioinformatics analysis. The identification of differentially expressed genes (DEGs) between calcific aortic valves and the control group was performed based on four microarray datasets: GSE12644, GSE51472, GSE77287 and GSE83453. Gene Ontology and Kyoto Encyclopaedia of Genes and Genomes (KEGG) pathway enrichment analysis were conducted. Furthermore, the protein-protein interaction network, and microRNA-target interaction was performed, and hub genes were obtained by using twelve cytoHubba algorithms. As a result, 327 DEGs were identified, including 206 up-regulated and 121 down-regulated genes. KEGG analysis showed that these DEGs were mainly enriched in the PI3K-AKT signaling pathway, ECM-receptor interaction, cytokine-cytokine receptor interaction, and chemokine signaling pathway etc. Moreover, we identified 19 hub genes: CXCL8, CXCL12, CSF1R, HCK, PLEK, CCL5, TLR8, VCAM1, CCR1, CCR7, FPR1, TYROBP, CX3CR1, KIT, PPBP, SPP1, SYK, TLR7, and VWF. And multiple potential miRNAs, including miR-141, miR-34a, miR-155, and miR-486, were identified. And western blot was performed to validate the expression level of hub genes. In conclusion, this study identified several promising biomarkers and pathways for CAVD, which may provide novel molecular markers for diagnosis and targeted therapy.

Organ Culture Model of Aortic Valve Calcification

A significant amount of knowledge has been gained with the use of cell-based assays to elucidate the mechanisms that mediate heart valve calcification. However, cells used in these studies lack their association with the extra-cellular matrix or the influence of other cellular components of valve leaflets. We have developed a model of calcification using intact porcine valve leaflets, that relies upon a biological stimulus to drive the formation of calcified nodules within the valve leaflets. Alizarin Red positive regions were formed in response to lipopolysaccharide and inorganic phosphate, which could be quantified when viewed under polarized light. Point analysis and elemental mapping analysis of electron microscope images confirmed the presence of nodules containing calcium and phosphorus. Immunohistochemical staining showed that the development of these calcified regions corresponded with the expression of RUNX2, osteocalcin, NF-kB and the apoptosis marker caspase 3. The formation of calcified nodules and the expression of bone markers were both inhibited by adenosine in a concentration-dependent manner, illustrating that the model is amenable to pharmacological manipulation. This organ culture model offers an increased level of tissue complexity in which to study the mechanisms that are involved in heart valve calcification.

Decreased Glucagon-Like Peptide-1 Is Associated With Calcific Aortic Valve Disease: GLP-1 Suppresses the Calcification of Aortic Valve Interstitial Cells

Objectives: This study explores the concentration and role of glucagon-like peptide-1 (GLP-1) in calcific aortic valve disease (CAVD). Background: Calcific aortic valve disease is a chronic disease presenting with aortic valve degeneration and mineralization. We hypothesized that the level of GLP-1 is associated with CAVD and that it participates in the calcification of aortic valve interstitial cells (AVICs). Methods: We compared the concentration of GLP-1 between 11 calcific and 12 normal aortic valve tissues by immunohistochemical (IHC) analysis. ELISA was used to measure GLP-1 in serum of the Control (n = 197) and CAVD groups (n = 200). The effect of GLP-1 on the calcification of AVICs and the regulation of calcific gene expression were also characterized. Results: The GLP-1 concentration in the calcific aortic valves was 39% less than that in the control non-calcified aortic valves. Its concentration in serum was 19.3% lower in CAVD patients. Multivariable regression analysis demonstrated that GLP-1 level was independently associated with CAVD risk. In vitro, GLP-1 antagonized AVIC calcification in a dose- and time-dependent manner and it down-regulated RUNX2, MSX2, BMP2, and BMP4 expression but up-regulated SOX9 expression. Conclusions: A reduction in GLP-1 was associated with CAVD, and GLP-1 participated in the mineralization of AVICs by regulating specific calcific genes. GLP-1 warrants consideration as a novel treatment target for CAVD.

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

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

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

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

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

Heme-Mediated Activation of the Nrf2/HO-1 Axis Attenuates Calcification of Valve Interstitial Cells

Calcific aortic valve stenosis (CAVS) is a heart disease characterized by the progressive fibro-calcific remodeling of the aortic valves, an actively regulated process with the involvement of the reactive oxygen species-mediated differentiation of valvular interstitial cells (VICs) into osteoblast-like cells. Nuclear factor erythroid 2-related factor 2 (Nrf2) regulates the expression of a variety of antioxidant genes, and plays a protective role in valve calcification. Heme oxygenase-1 (HO-1), an Nrf2-target gene, is upregulated in human calcified aortic valves. Therefore, we investigated the effect of Nrf2/HO-1 axis in VIC calcification. We induced osteogenic differentiation of human VICs with elevated phosphate and calcium-containing osteogenic medium (OM) in the presence of heme. Heme inhibited Ca deposition and OM-induced increase in alkaline phosphatase and osteocalcin (OCN) expression. Heme induced Nrf2 and HO-1 expression in VICs. Heme lost its anti-calcification potential when we blocked transcriptional activity Nrf2 or enzyme activity of HO-1. The heme catabolism products bilirubin, carbon monoxide, and iron, and also ferritin inhibited OM-induced Ca deposition and OCN expression in VICs. This study suggests that heme-mediated activation of the Nrf2/HO-1 pathway inhibits the calcification of VICs. The anti-calcification effect of heme is attributed to the end products of HO-1-catalyzed heme degradation and ferritin.

SPARC-related modular calcium binding 1 regulates aortic valve calcification by disrupting BMPR-II/p-p38 signalling

Aims

Aortic valve calcification is more prevalent in chronic kidney disease accompanied by hypercalcemia. Secreted protein acidic and rich in cysteine (SPARC)-related modular calcium binding 1 (SMOC1) is a regulator of BMP2 signalling, but the role of SMOC1 in aortic valve calcification under different conditions has not been studied. This study aimed to investigate the roles of SMOC1 in aortic valve calcification under normal and high calcium conditions, focusing on the effects on aortic valve interstitial cells (AVICs).

Methods and results

SMOC1 was expressed by aortic valve endothelial cells and secreted into the extracellular matrix in non-calcific valves and downregulated in calcific aortic valves. In vitro studies demonstrated that HUVEC secreted SMOC1 could enter the cytoplasm of AVICs. Overexpression of SMOC1 attenuated warfarin-induced AVIC calcification but promoted high calcium/phosphate or vitamin D-induced AVIC and aortic valve calcification by regulating BMP2 signalling both in vitro and in vivo. Co-immunoprecipitation revealed that SMOC1 binds to BMP receptor II (BMPR-II) and inhibits BMP2-induced phosphorylation of p38 (p-p38) via amino acids 372–383 of its EF-hand calcium-binding domain. Inhibition of p-p38 by the p38 inhibitor SB203580 blocked the effects of SMOC1 on BMP2 signalling and AVIC calcification induced by high calcium/phosphate medium. In high-calcium-treated AVICs, SMOC1 lost its ability to bind to BMPR-II, but not to caveolin-1, promoting p-p38 and cell apoptosis due to increased expression of BMPR-II and enhanced endocytosis.

Conclusions

These observations support that SMOC1 works as a dual-directional modulator of AVIC calcification by regulating p38-dependent BMP2 signalling transduction according to different extracellular calcium concentrations.

Collagen networks within 3D PEG hydrogels support valvular interstitial cell matrix mineralization

Enzymatically degradable hydrogels were designed for the 3D culture of valvular interstitial cells (VICs), and through the incorporation of various functionalities, we aimed to investigate the role of the tissue microenvironment in promoting the osteogenic properties of VICs and matrix mineralization. Specifically, porcine VICs were encapsulated in a poly(ethylene glycol) hydrogel crosslinked with a matrix metalloproteinase (MMP)-degradable crosslinker (KCGPQG↓IWGQCK) and formed via a thiol-ene photoclick reaction in the presence or absence of collagen type I to promote matrix mineralization. VIC-laden hydrogels were treated with osteogenic medium for up to 15 days, and the osteogenic response was characterized by the expression of RUNX2 as an early marker of an osteoblast-like phenotype, osteocalcin (OCN) as a marker of a mature osteoblast-like phenotype, and vimentin (VIM) as a marker of the fibroblast phenotype. In addition, matrix mineralization was characterized histologically with Von Kossa stain for calcium phosphate. Osteogenic response was further characterized biochemically with calcium assays, and physically via optical density measurements. When the osteogenic medium was supplemented with calcium chloride, OCN expression was upregulated and mineralization was discernable at 12 days of culture. Finally, this platform was used to screen various drug therapeutics that were assessed for their efficacy in preventing mineralization using optical density as a higher throughput readout. Collectively, these results suggest that matrix composition has a key role in supporting mineralization deposition within diseased valve tissue.

Expression and function of mechanosensitive ion channels in human valve interstitial cells

Background

The ability of heart valve cells to respond to their mechanical environment represents a key mechanism by which the integrity and function of valve cusps is maintained. A number of different mechanotransduction pathways have been implicated in the response of valve cells to mechanical stimulation. In this study, we explore the expression pattern of several mechanosensitive ion channels (MSC) and their potential to mediate mechanosensitive responses of human valve interstitial cells (VIC).

Methods

MSC presence and function were probed using the patch clamp technique. Protein abundance of key MSC was evaluated by Western blotting in isolated fibroblastic VIC (VIC_FB) and in VIC differentiated towards myofibroblastic (VIC_MB) or osteoblastic (VIC_OB) phenotypes. Expression was compared in non-calcified and calcified human aortic valves. MSC contributions to stretch-induced collagen gene expression and to VIC migration were assessed by pharmacological inhibition of specific channels.

Results

Two MSC types were recorded in VIC_FB: potassium selective and cation non-selective channels. In keeping with functional data, the presence of both TREK-1 and Kir6.1 (potassium selective), as well as TRPM4, TRPV4 and TRPC6 (cationic non-selective) channels was confirmed in VIC at the protein level. Differentiation of VIC_FB into VIC_MB or VIC_OB phenotypes was associated with a lower expression of TREK-1 and Kir6.1, and a higher expression of TRPV4 and TRPC6. Differences in MSC expression were also seen in non-calcified vs calcified aortic valves where TREK-1, TRPM4 and TRPV4 expression were higher in calcified compared to control tissues. Cyclic stretch-induced expression of COL I mRNA in cultured VIC_FB was blocked by RN-9893, a selective inhibitor of TRPV4 channels while having no effect on the stretch-induced expression of COL III. VIC_FB migration was blocked with the non-specific MSC blocker streptomycin and by GSK417651A an inhibitor of TRPC6/3.

Conclusion

Aortic VIC express a range of MSC that play a role in functional responses of these cells to mechanical stimulation. MSC expression levels differ in calcified and non-calcified valves in ways that are in part compatible with the change in expression seen between VIC phenotypes. These changes in MSC expression, and associated alterations in the ability of VIC to respond to their mechanical environment, may form novel targets for intervention during aortic valvulopathies.

MicroRNA Profiles in Calcified and Healthy Aorta Differ: Therapeutic Impact of miR-145 and miR-378

Our goal was to elucidate microRNAs (miRNAs) that may repress the excess bone morphogenetic protein (BMP) signaling observed during pathological calcification in the Klotho mouse model of kidney disease. We hypothesized that restoring healthy levels of miRNAs that post-transcriptionally repress osteogenic calcific factors may decrease aortic calcification. Our relative abundance profiles of miRNAs in healthy aorta differ greatly from those in calcified mouse aorta. Many of these miRNAs are predicted to regulate proteins involved in BMP signaling and may control osteogenesis. Two differentially regulated miRNAs, miR-145 and miR-378, were selected based on three criteria: reduced levels in calcified aorta, the ability to target more than one protein in the BMP signaling pathway, and conservation of targeted sequences between humans and mice. Forced expression using a lentiviral vector demonstrated that restoring normal levels repressed the synthesis of BMP2 and other pro-osteogenic proteins and inhibited pathological aortic calcification in Klotho mice with renal insufficiency. This study identified miRNAs that may impact BMP signaling in both sexes and demonstrated the efficacy of selected miRNAs in reducing aortic calcification in vivo. Calcification of the aorta and the aortic valve resulting from abnormal osteogenesis is common in those with kidney disease, diabetes, and high cholesterol. Such vascular osteogenesis is a clinically significant feature. The calcification modulating miRNAs described here are candidates for biomarkers and "miRNA replacement therapies" in the context of chronic kidney disease and other pro-calcific conditions.

Secreted Factors From Proinflammatory Macrophages Promote an Osteoblast-Like Phenotype in Valvular Interstitial Cells

OBJECTIVE

Resident valvular interstitial cells (VICs) activate to myofibroblasts during aortic valve stenosis progression, which further promotes fibrosis or even differentiate into osteoblast-like cells that can lead to calcification of valve tissue. Inflammation is a hallmark of aortic valve stenosis, so we aimed to determine proinflammatory cytokines secreted from M1 macrophages that give rise to a transient VIC phenotype that leads to calcification of valve tissue. Approach and Results: We designed hydrogel biomaterials as valve extracellular matrix mimics enabling the culture of VICs in either their quiescent fibroblast or activated myofibroblast phenotype in response to the local matrix stiffness. When VIC fibroblasts and myofibroblasts were treated with conditioned media from THP-1-derived M1 macrophages, we observed robust reduction of αSMA (alpha smooth muscle actin) expression, reduced stress fiber formation, and increased proliferation, suggesting a potent antifibrotic effect. We further identified TNF (tumor necrosis factor)-α and IL (interleukin)-1β as 2 cytokines in M1 media that cause the observed antifibrotic effect. After 7 days of culture in M1 conditioned media, VICs began differentiating into osteoblast-like cells, as measured by increased expression of RUNX2 (runt-related transcription factor 2) and osteopontin. We also identified and validated IL-6 as a critical mediator of the observed pro-osteogenic effect.

CONCLUSIONS

Proinflammatory cytokines in M1 conditioned media inhibit myofibroblast activation in VICs (eg, TNF-α and IL-1β) and promote their osteogenic differentiation (eg, IL-6). Together, our work suggests inflammatory M1 macrophages may drive a myofibroblast-to-osteogenic intermediate VIC phenotype, which may mediate the switch from fibrosis to calcification during aortic valve stenosis progression.

Sex-Specific Features of Calcific Aortic Valve Disease

Calcific aortic valve disease (CAVD) is the most common valvular heart disease in developed countries predominantly affecting the elderly population therefore posing a large economic burden. It is a gradually progressive condition ranging from mild valve calcification and thickening, without the hemodynamic obstruction, to severe calcification impairing leaflet motion, known as aortic stenosis (AS). The progression of CAVD occurs over many years, and it is extremely variable among individuals. It is also associated with an increased risk of coronary events and mortality. The recent insights into the CAVD pathophysiology included an important role of sex. Accumulating evidence suggests that, in patients with CAVD, sex can determine important differences in the relationship between valvular calcification process, fibrosis, and aortic stenosis hemodynamic severity between men and women. Consequently, it has implications on the development of different valvular phenotypes, left ventricular hypertrophy, and cardiovascular outcomes in men and women. Along these lines, taking into account the sex-related differences in diagnosis, prognosis, and treatment outcomes is of profound importance. In this review, the sex-related differences in patients with CAVD, in terms of pathobiology, clinical phenotypes, and outcomes were discussed.

Nano-Polyplexes Mediated Transfection of Runx2-shRNA Mitigates the Osteodifferentiation of Human Valvular Interstitial Cells

Calcific aortic valve disease (CAVD) is a progressive disorder that increases in prevalence with age. An important role in aortic valve calcification is played by valvular interstitial cells (VIC), that with age or in pathological conditions acquire an osteoblast-like phenotype that advances the disease. Therefore, pharmacological interventions aiming to stop or reverse the osteoblastic transition of VIC may represent a therapeutic option for CAVD. In this study, we aimed at developing a nanotherapeutic strategy able to prevent the phenotypic switch of human aortic VIC into osteoblast-like cells. We hypothesize that nanocarriers designed for silencing the Runt-related transcription factor 2 (Runx2) will stop the progress or reverse the osteodifferentiation of human VIC, induced by high glucose concentrations and pro-osteogenic factors. We report here the potential of fullerene (C60)-polyethyleneimine (PEI)/short hairpin (sh)RNA-Runx2 nano-polyplexes to efficiently down-regulate Runx2 mRNA and protein expression leading subsequently to a significant reduction in the expression of osteogenic proteins (i.e. ALP, BSP, OSP and BMP4) in osteoblast-committed VIC. The data suggest that the silencing of Runx2 could represent a novel strategy to impede the osteoblastic phenotypic shift of VIC and the ensuing progress of CAVD.

Roles of Histone Acetylation Modifiers and Other Epigenetic Regulators in Vascular Calcification

Vascular calcification (VC) is characterized by calcium deposition inside arteries and is closely associated with the morbidity and mortality of atherosclerosis, chronic kidney disease, diabetes, and other cardiovascular diseases (CVDs). VC is now widely known to be an active process occurring in vascular smooth muscle cells (VSMCs) involving multiple mechanisms and factors. These mechanisms share features with the process of bone formation, since the phenotype switching from the contractile to the osteochondrogenic phenotype also occurs in VSMCs during VC. In addition, VC can be regulated by epigenetic factors, including DNA methylation, histone modification, and noncoding RNAs. Although VC is commonly observed in patients with chronic kidney disease and CVD, specific drugs for VC have not been developed. Thus, discovering novel therapeutic targets may be necessary. In this review, we summarize the current experimental evidence regarding the role of epigenetic regulators including histone deacetylases and propose the therapeutic implication of these regulators in the treatment of VC.

Aortic Valve Stenosis: From Basic Mechanisms to Novel Therapeutic Targets

Aortic valve stenosis is the most prevalent heart valve disease worldwide. Although interventional treatment options have rapidly improved in recent years, symptomatic aortic valve stenosis is still associated with high morbidity and mortality. Calcific aortic valve stenosis is characterized by a progressive fibro-calcific remodeling and thickening of the aortic valve cusps, which subsequently leads to valve obstruction. The underlying pathophysiology is complex and involves endothelial dysfunction, immune cell infiltration, myofibroblastic and osteoblastic differentiation, and, subsequently, calcification. To date, no pharmacotherapy has been established to prevent aortic valve calcification. However, novel promising therapeutic targets have been recently identified. This review summarizes the current knowledge of pathomechanisms involved in aortic valve calcification and points out novel treatment strategies.

IL-21 promotes osteoblastic differentiation of human valvular interstitial cells through the JAK3/STAT3 pathway

Objectives: This study amied to whether IL-21 promotes osteoblast transdifferentiation of cultured human Valvular interstitial cells (VICs). Methods: We first confirmed that IL-21 alters gene expression between CAVD aortic valve tissue and normal samples by immunohistochemistry, qPCR, and western blotting. VICs were cultured and treated with IL-21. Gene and protein expression levels of the osteoblastic markers ALP and Runx2, which can be blocked by specific JAK3 inhibitors and/or siRNA of STAT3, were measured. Results: IL-21 expression was upregulated in calcified aortic valves and promotes osteogenic differentiation of human VICs. IL-21 accelerated VIC calcification through the JAK3/STAT3 pathway. Conclusion: Our data suggest that IL-21 is a key factor in valve calcification and a promising candidate for targeted therapeutics for CAVD.

MicroRNA-204 Deficiency in Human Aortic Valves Elevates Valvular Osteogenic Activity

Aortic valve interstitial cells (AVICs) play a major role in valvular calcification associated with calcific aortic valve disease (CAVD). Although AVICs from diseased valves display a pro-osteogenic phenotype, the underlying mechanism causing this remains unclear. MicroRNA-204 (miR-204) is a negative regulator of osteoblast differentiation. We sought to analyze miR-204 expression in diseased human aortic valves and determine the role of this miR in AVIC osteogenic activity associated with CAVD pathobiology. In situ hybridization and PCR analysis revealed miR-204 deficiency in diseased valves and in AVICs from diseased valves. MiR-204 mimic suppressed alkaline phosphatase (ALP) expression and calcium deposition in AVICs from diseased valves. MiR-204 antagomir enhanced ALP expression in AVICs from normal valves through induction of Runx2 and Osx, and expression of miR-204 antagomir in mouse aortic valves promoted calcium deposition through up-regulation of Runx2 and Osx. Further, miR-204 mimic suppressed the osteogenic responses to TGF-β1 in AVICs of normal valves. In conclusion, miR-204 deficiency contributes to the mechanism underlying elevated osteogenic activity in diseased aortic valves, and miR-204 is capable of reversing the pro-osteogenic phenotype of AVICs of diseased valves and suppressing AVIC osteogenic response to stimulation. Exogenous miR-204 may have therapeutic potential for inhibiting valvular calcification associated with CAVD progression.

Spatiotemporal Multi-Omics Mapping Generates a Molecular Atlas of the Aortic Valve and Reveals Networks Driving Disease

BACKGROUND

No pharmacological therapy exists for calcific aortic valve disease (CAVD), which confers a dismal prognosis without invasive valve replacement. The search for therapeutics and early diagnostics is challenging because CAVD presents in multiple pathological stages. Moreover, it occurs in the context of a complex, multi-layered tissue architecture; a rich and abundant extracellular matrix phenotype; and a unique, highly plastic, and multipotent resident cell population.

METHODS

A total of 25 human stenotic aortic valves obtained from valve replacement surgeries were analyzed by multiple modalities, including transcriptomics and global unlabeled and label-based tandem-mass-tagged proteomics. Segmentation of valves into disease stage-specific samples was guided by near-infrared molecular imaging, and anatomic layer-specificity was facilitated by laser capture microdissection. Side-specific cell cultures were subjected to multiple calcifying stimuli, and their calcification potential and basal/stimulated proteomes were evaluated. Molecular (protein-protein) interaction networks were built, and their central proteins and disease associations were identified.

RESULTS

Global transcriptional and protein expression signatures differed between the nondiseased, fibrotic, and calcific stages of CAVD. Anatomic aortic valve microlayers exhibited unique proteome profiles that were maintained throughout disease progression and identified glial fibrillary acidic protein as a specific marker of valvular interstitial cells from the spongiosa layer. CAVD disease progression was marked by an emergence of smooth muscle cell activation, inflammation, and calcification-related pathways. Proteins overrepresented in the disease-prone fibrosa are functionally annotated to fibrosis and calcification pathways, and we found that in vitro, fibrosa-derived valvular interstitial cells demonstrated greater calcification potential than those from the ventricularis. These studies confirmed that the microlayer-specific proteome was preserved in cultured valvular interstitial cells, and that valvular interstitial cells exposed to alkaline phosphatase-dependent and alkaline phosphatase-independent calcifying stimuli had distinct proteome profiles, both of which overlapped with that of the whole tissue. Analysis of protein-protein interaction networks found a significant closeness to multiple inflammatory and fibrotic diseases.

CONCLUSIONS

A spatially and temporally resolved multi-omics, and network and systems biology strategy identifies the first molecular regulatory networks in CAVD, a cardiac condition without a pharmacological cure, and describes a novel means of systematic disease ontology that is broadly applicable to comprehensive omics studies of cardiovascular diseases.

Interstitial cells in calcified aortic valves have reduced differentiation potential and stem cell-like properties

Valve interstitial cells (VICs) are crucial in the development of calcific aortic valve disease. The purpose of the present investigation was to compare the phenotype, differentiation potential and stem cell-like properties of cells from calcified and healthy aortic valves. VICs were isolated from human healthy and calcified aortic valves. Calcification was induced with osteogenic medium. Unlike VICs from healthy valves, VICs from calcified valves cultured without osteogenic medium stained positively for calcium deposits with Alizarin Red confirming their calcific phenotype. Stimulation of VICs from calcified valves with osteogenic medium increased calcification (p = 0.02), but not significantly different from healthy VICs. When stimulated with myofibroblastic medium, VICs from calcified valves had lower expression of myofibroblastic markers, measured by flow cytometry and RT-qPCR, compared to healthy VICs. Contraction of collagen gel (a measure of myofibroblastic activity) was attenuated in cells from calcified valves (p = 0.04). Moreover, VICs from calcified valves, unlike cells from healthy valves had lower potential to differentiate into adipogenic pathway and lower expression of stem cell-associated markers CD106 (p = 0.04) and aldehyde dehydrogenase (p = 0.04). In conclusion, VICs from calcified aortic have reduced multipotency compared to cells from healthy valves, which should be considered when investigating possible medical treatments of aortic valve calcification.

IL-33 promotes the progression of nonrheumatic aortic valve stenosis via inducing differential phenotypic transition in valvular interstitial cells

OBJECTIVE

Interleukin (IL)-33 is a mediator in the pathogenesis of several inflammatory diseases. Its receptor, ST2, is overexpressed in nonrheumatic aortic valve stenosis (NR-AS). This study compared smooth muscle α-actin (α-SMA), osteopontin (OPN), and suppression of tumorigenicity 2 (ST2) expression between specimens from fibrotic and calcific stages of NR-AS and observed the effects and mechanisms of phenotypic transition of porcine valvular interstitial cells (VICs) in the presence of IL-33.

METHODS

Peripheral blood IL-1 family mRNA and protein levels in NR-AS patients and healthy adults were quantified by real-time quantitative polymerase chain reaction (RT-qPCR) and enzyme-linked immunosorbent assay. Immunohistochemistry and immunofluorescence were used to detect the expression and coexpression of α-SMA, OPN, and ST2 in NR-AS specimens. Porcine VICs were stimulated with IL-33, IL-33+SB203580, or IL-33+SC75741. mRNA and protein expression levels of porcine VICs were detected by RT-qPCR and western blot.

RESULTS

The mRNA and protein levels of IL-33 and sST2 in peripheral blood of NR-AS patients were higher than those in healthy adults. Immunohistochemistry and immunofluorescence showed higher expression of α-SMA, OPN, and ST2 in the calcific stage of NR-AS than in the fibrotic stage. Coexpression of ST2/α-SMA or ST2/OPN was found only in the calcific stage. Nuclear factor (NF)-κB and p38 mitogen-activated protein kinase (MAPK) phosphorylation levels were associated with IL-33-induced porcine VIC differentiation into myofibroblasts and osteoblasts, respectively. IL-33 stimulation also promoted the coexpression of ST2/OPN or α-SMA/OPN/ST2.

CONCLUSION

IL-33 might be a potential biomarker for NR-AS. IL-33-induced porcine VIC differential phenotypic transition and differentiation into myofibroblasts and osteoblasts were dependent on the NF-κB and p38 MAPK signaling pathways, respectively.

Oxidized HDL, as a Novel Biomarker for Calcific Aortic Valve Disease, Promotes the Calcification of Aortic Valve Interstitial Cells

Calcific aortic valve disease (CAVD) is characterized by progressive mineralization of the aortic valve. Lipid infiltration and oxidative stress are the driving forces for the initiation and development of this disease. However, it remains unknown whether oxidized high-density lipoprotein (ox-HDL) plays a role in the mineralization of aortic valve interstitial cells (AVICs). Serum ox-HDL levels were determined in 168 severe CAVD patients and 168 age- and gender-matched non-CAVD controls. Results showed that ox-HDL concentrations were significantly increased in CAVD compared with the control group (131.52 ± 30.96 ng/mL vs. 112.58 ± 32.20 ng/mL, P < 0.001) and were correlated with CAVD severity. Multivariable logistic regression revealed that ox-HDL levels were independently associated with CAVD after adjusting for the incidence of coronary artery disease (CAD) (odds ratio 1.019, 95% CI 1.012-1.027, P < 0.001) or atherosclerotic risk factors (odds ratio 1.027, 95% CI 1.017-1.037, P < 0.001). Chronic ox-HDL stimulation of AVICs increased alkaline phosphatase activity (ALP) and calcium deposits in AVICs in vitro. Mechanistic studies further showed that ox-HDL upregulated several osteogenic factors, including BMP-2, Runx2, and Msx2 expressions in AVICs. This is the first study to demonstrate a relationship between increased ox-HDL concentration and CAVD incidence.

Endothelial Cell Mechano-Metabolomic Coupling to Disease States in the Lung Microvasculature

Lungs are the most vascular part of humans, accepting the totality of cardiac output in a volume much smaller than the body itself. Due to this cardiac output, the lung microvasculature is subject to mechanical forces including shear stress and cyclic stretch that vary with the cardiac and breathing cycle. Vessels are surrounded by extracellular matrix which dictates the stiffness which endothelial cells also sense and respond to. Shear stress, stiffness, and cyclic stretch are known to influence endothelial cell state. At high shear stress, endothelial cells exhibit cell quiescence marked by low inflammatory markers and high nitric oxide synthesis, whereas at low shear stress, endothelial cells are thought to "activate" into a pro-inflammatory state and have low nitric oxide. Shear stress' profound effect on vascular phenotype is most apparent in the arterial vasculature and in the pathophysiology of vascular inflammation. To conduct the flow of blood from the right heart, the lung microvasculature must be rigid yet compliant. It turns out that excessive substrate rigidity or stiffness is important in the development of pulmonary hypertension and chronic fibrosing lung diseases via excessive cell proliferation or the endothelial-mesenchymal transition. Recently, a new body of literature has evolved that couples mechanical sensing to endothelial phenotypic changes through metabolic signaling in clinically relevant contexts such as pulmonary hypertension, lung injury syndromes, as well as fibrosis, which is the focus of this review. Stretch, like flow, has profound effect on endothelial phenotype; metabolism studies due to stretch are in their infancy.

Role of p38 MAPK in Atherosclerosis and Aortic Valve Sclerosis

Atherosclerosis and aortic valve sclerosis are cardiovascular diseases with an increasing prevalence in western societies. Statins are widely applied in atherosclerosis therapy, whereas no pharmacological interventions are available for the treatment of aortic valve sclerosis. Therefore, valve replacement surgery to prevent acute heart failure is the only option for patients with severe aortic stenosis. Both atherosclerosis and aortic valve sclerosis are not simply the consequence of degenerative processes, but rather diseases driven by inflammatory processes in response to lipid-deposition in the blood vessel wall and the aortic valve, respectively. The p38 mitogen-activated protein kinase (MAPK) is involved in inflammatory signaling and activated in response to various intracellular and extracellular stimuli, including oxidative stress, cytokines, and growth factors, all of which are abundantly present in atherosclerotic and aortic valve sclerotic lesions. The responses generated by p38 MAPK signaling in different cell types present in the lesions are diverse and might support the progression of the diseases. This review summarizes experimental findings relating to p38 MAPK in atherosclerosis and aortic valve sclerosis and discusses potential functions of p38 MAPK in the diseases with the aim of clarifying its eligibility as a pharmacological target.

Anthraquinone Emodin Inhibits Tumor Necrosis Factor Alpha-Induced Calcification of Human Aortic Valve Interstitial Cells via the NF-κB Pathway

Exploring effective therapies for delaying calcific heart valve disease (CHVD) is the focus of current cardiovascular clinical and scientific research. In this study, human aortic valve interstitial cells (hVICs) were isolated from patients with CHVD. After expansion, cultured hVICs were induced with the tumor necrosis factor-alpha (TNF-α) with or without anthraquinone emodin (EMD) treatments. Cytotoxicity and flow cytometric analysis were used to assess cell growth, while Alizarin Red S staining was used to detect hVICs calcification. Furthermore, RNA-sequencing analysis was utilized to investigate changes in mRNA profiles of cells cultured in TNF-α conditioned medium with or without EMD. Western blotting and qRT-PCR analyses were used for the verification of key selected genes. Our results indicated that EMD had limited influence on hVIC morphology, whereas in a dose-dependent fashion, EMD interfered with hVIC growth under TNF-α conditioned cell culture. Additionally, hVICs treated with TNF-α plus EMD, presented a gradual decrease of positive Alizarin Red S staining, when compared with cells treated with TNF-α only. Notably, cells treated with TNF-α plus EMD showed 1874 differential expression genes (DEGs), among them, 1131 were upregulated and 743 were downregulated. These DEGs displayed an enrichment of biological functions and signaling pathways, among them, BMP2, RELA, TNF, and TRAF1, were found to be significantly suppressed by EMD and selected given their role in mediating hVIC calcification. In conclusion, our study shows that EMD inhibits TNF-α-induced calcification and phenotypical transformation of hVICs via the NF-κB signaling pathway, thereby preventing calcification events stimulated during acute inflammatory responses.

Serotonin and catecholamines in the development and progression of heart valve diseases

Heart valve diseases (HVDs) arise from a number of different processes that affect both the structure and function of the valve apparatus. Despite diverse aetiologies, treatments for HVDs are limited to percutaneous or surgical interventions. The search for medical therapies to prevent or slow the progression of HVDs has been hampered by our poor understanding of the progression from subclinical to symptomatic phases, and our limited knowledge of the molecular signals that control the susceptibility of valve interstitial cells to pathological remodeling. Clinical evidence has suggested a link between certain neurotransmitters and valvular diseases of the heart. The fenfluramine-phentermine appetite suppressants popular in the 1980s were linked to mitral valve dysfunction, and ergot-derived dopamine agonists for Parkinson's disease have been associated with an increased risk of mitral and aortic valve regurgitation. The effect does not appear to be limited to medications, as valvular pathologies have also been observed in patients with carcinoid tumours of serotonin-producing enterochromaffin cells. The role of neurotransmitter molecules in valve pathology has not been adequately characterized and may represent a target for future medical therapies. Here we present current evidence from both clinical and basic science suggesting a link between neurotransmitters and HVDs, opening the door to future research in this area.

Toll-Like Receptors, Inflammation, and Calcific Aortic Valve Disease

Inflammation, the primary response of innate immunity, is essential to initiate the calcification process underlying calcific aortic valve disease (CAVD), the most prevalent valvulopathy in Western countries. The pathogenesis of CAVD is multifactorial and includes inflammation, hemodynamic factors, fibrosis, and active calcification. In the development of CAVD, both innate and adaptive immune responses are activated, and accumulating evidences show the central role of inflammation in the initiation and propagation phases of the disease, being the function of Toll-like receptors (TLR) particularly relevant. These receptors act as sentinels of the innate immune system by recognizing pattern molecules from both pathogens and host-derived molecules released after tissue damage. TLR mediate inflammation via NF-κB routes within and beyond the immune system, and play a crucial role in the control of infection and the maintenance of tissue homeostasis. This review outlines the current notions about the association between TLR signaling and the ensuing development of inflammation and fibrocalcific remodeling in the pathogenesis of CAVD. Recent data provide new insights into the inflammatory and osteogenic responses underlying the disease and further support the hypothesis that inflammation plays a mechanistic role in the initiation and progression of CAVD. These findings make TLR signaling a potential target for therapeutic intervention in CAVD.

Matrix vesicles from chondrocytes and osteoblasts: Their biogenesis, properties, functions and biomimetic models

BACKGROUND

Matrix vesicles (MVs) are released from hypertrophic chondrocytes and from mature osteoblasts, the cells responsible for endochondral and membranous ossification. Under pathological conditions, they can also be released from cells of non-skeletal tissues such as vascular smooth muscle cells. MVs are extracellular vesicles of approximately 100-300nm diameter harboring the biochemical machinery needed to induce mineralization.

SCOPE OF THE REVIEW

The review comprehensively delineates our current knowledge of MV biology and highlights open questions aiming to stimulate further research. The review is constructed as a series of questions addressing issues of MVs ranging from their biogenesis and functions, to biomimetic models. It critically evaluates experimental data including their isolation and characterization methods, like lipidomics, proteomics, transmission electron microscopy, atomic force microscopy and proteoliposome models mimicking MVs.

MAJOR CONCLUSIONS

MVs have a relatively well-defined function as initiators of mineralization. They bind to collagen and their composition reflects the composition of lipid rafts. We call attention to the as yet unclear mechanisms leading to the biogenesis of MVs, and how minerals form and when they are formed. We discuss the prospects of employing upcoming experimental models to deepen our understanding of MV-mediated mineralization and mineralization disorders such as the use of reconstituted lipid vesicles, proteoliposomes and, native sample preparations and high-resolution technologies.

GENERAL SIGNIFICANCE

MVs have been extensively investigated owing to their roles in skeletal and ectopic mineralization. MVs serve as a model system for lipid raft structures, and for the mechanisms of genesis and release of extracellular vesicles.

Exploiting novel valve interstitial cell lines to study calcific aortic valve disease

Calcific aortic valve disease (CAVD) involves progressive valve leaflet thickening and severe calcification, impairing leaflet motion. The in vitro calcification of primary rat, human, porcine and bovine aortic valve interstitial cells (VICs) is commonly employed to investigate CAVD mechanisms. However, to date, no published studies have utilised cell lines to investigate this process. The present study has therefore generated and evaluated the calcification potential of immortalized cell lines derived from sheep and rat VICs. Immortalised sheep (SAVIC) and rat (RAVIC) cell lines were produced by transduction with a recombinant lentivirus encoding the Simian virus (SV40) large and small T antigens (sheep), or large T antigen only (rat), which expressed markers of VICs (vimentin and α‑smooth muscle actin). Calcification was induced in the presence of calcium (Ca; 2.7 mM) in SAVICs (1.9 fold; P<0.001) and RAVICs (4.6 fold; P<0.01). Furthermore, a synergistic effect of calcium and phosphate was observed (2.7 mM Ca/2.0 mM Pi) on VIC calcification in the two cell lines (P<0.001). Analysis of SAVICs revealed significant increases in the mRNA expression of two key genes associated with vascular calcification in cells cultured under calcifying conditions, runt related transcription factor‑2 (RUNX2;1.3 fold; P<0.05 in 4.5 mM Ca) and sodium‑dependent phosphate transporter‑1 (PiT1; 1.2 fold; P<0.05 in 5.4 mM Ca). A concomitant decrease in the expression of the calcification inhibitor matrix Gla protein (MGP) was noted at 3.6 mM Ca (1.3 fold; P<0.01). Assessment of RAVICs revealed alterations in Runx2, Pit1 and Mgp mRNA expression levels (P<0.01). Furthermore, a significant reduction in calcification was observed in SAVICs following treatment with established calcification inhibitors, pyrophosphate (1.8 fold; P<0.01) and etidronate (3.2 fold; P<0.01). Overall, the present study demonstrated that the use of immortalised sheep and rat VIC cell lines is a convenient and cost effective system to investigate CAVD in vitro, and will make a useful contribution to increasing current understanding of the pathophysiological process.

Osteocardiology: Defining the Go/No-Go Time Point for Therapy

Recent epidemiological studies have revealed that the risk factors associated with coronary artery calcification (CAC), including male gender, smoking, hypertension, and elevated serum cholesterol, are similar to the risk factors associated with the development of calcific aortic valve disease (CAVD). The results of the experimental and clinical studies demonstrate that traditional risk factors initiate early atherosclerosis which over time differentiates to form bone in the heart causing clinical CAC and CAVD. Understanding the cellular mechanisms of cardiovascular calcification, the end-stage process of the atherosclerosis will help define the specific time point to modify this cellular process of bone formation in the heart termed osteocardiology. This time point between subclinical atherosclerosis and clinical calcification is the go/no-go time point, or the point of no return with severe clinical calcification in the heart. This review will summarize the development of bone formation in the heart termed osteocardiology, to define the go/no-go time point for therapy initiation to slow the progression of cardiovascular calcification.

On the Functional Role of Valve Interstitial Cell Stress Fibers: A Continuum Modeling Approach

The function of the heart valve interstitial cells (VICs) is intimately connected to heart valve tissue remodeling and repair, as well as the onset and progression of valvular pathological processes. There is yet only very limited knowledge and extant models for the complex three-dimensional VIC internal stress-bearing structures, the associated cell-level biomechanical behaviors, and how they change under varying activation levels. Importantly, VICs are known to exist and function within the highly dynamic valve tissue environment, including very high physiological loading rates. Yet we have no knowledge on how these factors affect VIC function. To this end, we extended our previous VIC computational continuum mechanics model (Sakamoto, et al., 2016, "On Intrinsic Stress Fiber Contractile Forces in Semilunar Heart Valve Interstitial Cells Using a Continuum Mixture Model," J. Mech. Behav. Biomed. Mater., 54(244-258)). to incorporate realistic stress-fiber geometries, force-length relations (Hill model for active contraction), explicit α-smooth muscle actin (α-SMA) and F-actin expression levels, and strain rate. Novel micro-indentation measurements were then performed using cytochalasin D (CytoD), variable KCl molar concentrations, both alone and with transforming growth factor β1 (TGF-β1) (which emulates certain valvular pathological processes) to explore how α-SMA and F-actin expression levels influenced stress fiber responses under quasi-static and physiological loading rates. Simulation results indicated that both F-actin and α-SMA contributed substantially to stress fiber force generation, with the highest activation state (90 mM KCL + TGF-β1) inducing the largest α-SMA levels and associated force generation. Validation was performed by comparisons to traction force microscopy studies, which showed very good agreement. Interestingly, only in the highest activation state was strain rate sensitivity observed, which was captured successfully in the simulations. These unique findings demonstrated that only VICs with high levels of αSMA expression exhibited significant viscoelastic effects. Implications of this study include greater insight into the functional role of α-SMA and F-actin in VIC stress fiber function, and the potential for strain rate-dependent effects in pathological states where high levels of α-SMA occur, which appear to be unique to the valvular cellular in vivo microenvironment.