The progression of calcific aortic valve disease through injury, cell dysfunction, and disruptive biologic and physical force feedback loops

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.

Independent association of aortic stenosis with many known cardiovascular risk factors and many inflammatory diseases

BACKGROUND

Aortic valve stenosis is associated with age, rheumatic fever and bicuspid aortic valve, but its association with other co-morbidities, such as inflammatory disease and race/ethnicity, is less known.

AIM

To investigate any association between aortic stenosis and many co-morbidities.

METHODS

We used the large Nationwide Inpatient Sample database to evaluate any association between aortic stenosis and risk factors. We performed univariate and multivariable analyses, adjusting for co-morbid conditions.

RESULTS

Data were extracted from the first available database that used the International Classification of Diseases, Tenth Revision codes specifically coding for aortic stenosis alone, spanning from 2016 to 2020 (n=112,982,565). A total of 2,322,649 patients had aortic stenosis; the remaining 110,659,916 served as controls. We found a strong and independent significant association between aortic stenosis and coronary artery disease (odds ratio [OR]: 2.11, 95% confidence interval [CI]: 2.09-2.13), smoking (OR: 1.08, 95% CI: 1.07-1.08), diabetes mellitus (OR: 1.15, 95% CI: 1.14-1.16), hypertension (OR: 1.41, 95% CI: 1.4-1.42), hyperlipidaemia (OR: 1.31, 95% CI: 1.3-1.32), renal disease (OR: 1.3, 95% CI: 1.29-1.31), chronic obstructive pulmonary disease (OR: 1.05, 95% CI: 1.04-1.05), obesity (OR: 1.3, 95% CI: 1.29-1.32), white race/ethnicity (OR: 1.47, 95% CI: 1.42-1.52), rheumatoid arthritis (OR: 1.13, 95% CI: 1.11-1.15), scleroderma (OR: 1.93, 95% CI: 1.79-2.09), systemic connective tissue disease (OR: 1.24, 95% CI: 1.2-1.27), polyarteritis nodosa (OR: 1.5, CI: 1.24-1.81) and Raynaud's syndrome (OR: 1.16, 95% CI: 1.09-1.24) (all P<0.001), in addition to known factors, such as age, male sex and bicuspid aortic valve.

CONCLUSION

Using a very large database, we found many new associations with aortic valve stenosis, including race/ethnicity, renal disease, several inflammatory diseases, chronic obstructive pulmonary disease and obesity, in addition to many other known cardiovascular risk factors.

The Impact of Left Ventricular Assist Device Outflow Graft Positioning on Aortic Hemodynamics: Improving Flow Dynamics to Mitigate Aortic Insufficiency

Heart failure is a global health concern with significant implications for healthcare systems. Left ventricular assist devices (LVADs) provide mechanical support for patients with severe heart failure. However, the placement of the LVAD outflow graft within the aorta has substantial implications for hemodynamics and can lead to aortic insufficiency during long-term support. This study employs computational fluid dynamics (CFD) simulations to investigate the impact of different LVAD outflow graft locations on aortic hemodynamics. The introduction of valve morphology within the aorta geometry allows for a more detailed analysis of hemodynamics at the aortic root. The results demonstrate that the formation of vortex rings and subsequent vortices during the high-velocity jet flow from the graft interacted with the aortic wall. Time-averaged wall shear stress (TAWSS) and oscillatory shear index (OSI) indicate that modification of the outflow graft location changes mechanical states within the aortic wall and aortic valve. Among the studied geometric factors, both the height and inclination angle of the LVAD outflow graft are important in controlling retrograde flow to the aortic root, while the azimuthal angle primarily determines the rotational direction of blood flow in the aortic arch. Thus, precise positioning of the LVAD outflow graft emerges as a critical factor in optimizing patient outcomes by improving the hemodynamic environment.

Highly efficient removal of hexavalent chromium by magnetic Fe-C composite from reed straw and electric furnace dust waste

Reed straw and electric furnace dust (EFD) waste were used to prepare magnetic Fe-C composite (EFD&C) by co-precipitation and high-temperature activation method to remove Cr(VI) from water. The magnetic EFD&C owned a large specific surface (536.61 m²/g) and a porous structure (micropores and mesopores), and had an efficient removal capacity for Cr(VI). Under conditions of pH (2), the addition amount of EFD&C (1 g/L), the adsorption time (760 min), and the temperature (45 °C), the maximum adsorption capacity reached 111.94 mg/g. The adsorption mechanism mainly attributed to chemical adsorption (redox), Cr(VI) reduced to Cr(III) by Fe(II) and Fe(0) (from Fe₃O₄ and Fe components in EFD) and surface functional groups of -OH, C = C, C-C and O-C = O (from biochar), and secondary attributed to physical adsorption, Cr(VI) and Cr(III) (from reduced Cr(VI)) adsorbed into the porous structure of EFD&C. This study provided a feasible solution for the preparation of adsorbents for adsorbing heavy metals from iron-containing metallurgical solid waste and biomass waste, which contributed to reducing the environmental pollution and lowering the cost of adsorbent preparation.

NLRP3 inflammasome: The rising star in cardiovascular diseases

Cardiovascular diseases (CVDs) are the prevalent cause of mortality around the world. Activation of inflammasome contributes to the pathological progression of cardiovascular diseases, including atherosclerosis, abdominal aortic aneurysm, myocardial infarction, dilated cardiomyopathy, diabetic cardiomyopathy, heart failure, and calcific aortic valve disease. The nucleotide oligomerization domain-, leucine-rich repeat-, and pyrin domain-containing protein 3 (NLRP3) inflammasome plays a critical role in the innate immune response, requiring priming and activation signals to provoke the inflammation. Evidence shows that NLRP3 inflammasome not only boosts the cleavage and release of IL-1 family cytokines, but also leads to a distinct cell programmed death: pyroptosis. The significance of NLRP3 inflammasome in the CVDs-related inflammation has been extensively explored. In this review, we summarized current understandings of the function of NLRP3 inflammasome in CVDs and discussed possible therapeutic options targeting the NLRP3 inflammasome.

Epigenetics: a new warrior against cardiovascular calcification, a forerunner in modern lifestyle diseases

Arterial and aortic valve calcifications are the most prevalent pathophysiological conditions among all the reported cases of cardiovascular calcifications. It increases with several risk factors like age, hypertension, external stimuli, mechanical forces, lipid deposition, malfunction of genes and signaling pathways, enhancement of naturally occurring calcium inhibitors, and many others. Modern-day lifestyle is affected by numerous environmental factors and harmful toxins that impair our health rather than providing benefits. Applying the combinatorial approach or targeting the exact mechanism could be a new strategy for drug designing or attenuating the severity of calcification. Most of the non-communicable diseases are life-threatening; thus, altering the phenotype and not the genotype may reveal the gateway for fighting with upcoming hurdles. Overall, this review summarizes the reason behind the generation of arterial and aortic valve calcification and its related signaling pathways and also the detrimental effects of calcification. In addition, the individual process of epigenetics and how the implementation of this process becomes a novel approach for diminishing the harmful effect of calcification are discussed. Noteworthy, as epigenetics is linked with genetics and environmental factors necessitates further clinical trials for complete and in-depth understanding and application of this strategy in a more specific and prudent manner.

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.

Innate immune cells in the pathophysiology of calcific aortic valve disease: lessons to be learned from atherosclerotic cardiovascular disease?

Calcific aortic valve disease (CAVD) is the most common valvular disease in the developed world with currently no effective pharmacological treatment available. CAVD results from a complex, multifactorial process, in which valvular inflammation and fibro-calcific remodelling lead to valve thickening and cardiac outflow obstruction. The exact underlying pathophysiology of CAVD is still not fully understood, yet the development of CAVD shows many similarities with the pathophysiology of atherosclerotic cardiovascular disease (ASCVD), such as coronary artery disease. Innate immune cells play a crucial role in ASCVD and might also play a pivotal role in the development of CAVD. This review summarizes the current knowledge on the role of innate immune cells, both in the circulation and in the aortic valve, in the development of CAVD and the similarities and differences with ASCVD. Trained immunity and clonal haematopoiesis of indeterminate potential are proposed as novel immunological mechanisms that possibly contribute to the pathophysiology of CAVD and new possible treatment targets are discussed.

Degenerative changes of the aortic valve during left ventricular assist device support

AIMS

Donor heart shortage leads to increasing use of left ventricular assist device (LVAD) as bridge-to-transplant or destination therapy. Prolonged LVAD support is associated with aortic valve insufficiency, representing a relevant clinical problem in LVAD patients. Nevertheless, the impact of LVAD support on inflammation, remodelling, and chondro-osteogenic differentiation of the aortic valve is still not clearly understood. The aim of the study is to evaluate the impact of LVAD support on structural and molecular alterations of the aortic valve.

METHODS AND RESULTS

During heart transplantation, aortic valves of 63 heart failure patients without (n = 22) and with LVAD support (n = 41) were collected and used for analysis. Data on clinical course as well as echocardiographic data were analysed. Calcification and markers of remodelling, chondro-osteogenic differentiation, and inflammation were evaluated by computed tomography, by mRNA analysis and by histology and immunohistochemistry. Expression of inflammation markers of the LVAD group was analysed with regard to levels of C-reactive protein and driveline infections. Calcium accumulation and mRNA expression of determined markers were correlated with duration of LVAD support. Data were also analysed relating to aortic valve opening and aortic valve insufficiency. There was no difference in the frequency of cardiovascular risk factors or comorbidities between the patient groups. Expression of matrix metalloproteinase-9 (P = 0.007), alpha-smooth muscle actin (P = 0.045), and osteopontin (P = 0.003) were up-regulated in aortic valves of LVAD patients. Histological appearance of the aortic valve was similar in patients with or without LVAD, and computed tomography-based analysis not yet revealed significant difference in tissue calcification. Expression of interferon gamma (P = 0.004), interleukin-1 beta (P < 0.0001), and tumour necrosis factor alpha (P = 0.04) was up-regulated in aortic valves of LVAD patients without concomitant inflammatory cell infiltration and independent from unspecific inflammation. Expression of matrix metalloproteinase-2 (P = 0.038) and transforming growth factor beta (P = 0.0504) correlated negatively with duration of LVAD support. Presence of aortic valve insufficiency led to a significantly higher expression of interferon gamma (P = 0.007) in LVAD patients. There was no alteration in the determined markers in relation to aortic valve opening in LVAD patients.

CONCLUSIONS

Left ventricular assist device support leads to signs of early aortic valve degeneration independent of support duration. Thus, the aortic valve of patients with LVAD support should be closely monitored, particularly in patients receiving destination therapy as well as in the prospect of using aortic valves of LVAD patients as homografts in case of bridge-to-transplant therapy.

Aortic valve cell microenvironment: Considerations for developing a valve-on-chip

Cardiac valves are sophisticated, dynamic structures residing in a complex mechanical and hemodynamic environment. Cardiac valve disease is an active and progressive disease resulting in severe socioeconomic burden, especially in the elderly. Valve disease also leads to a 50% increase in the possibility of associated cardiovascular events. Yet, valve replacement remains the standard of treatment with early detection, mitigation, and alternate therapeutic strategies still lacking. Effective study models are required to further elucidate disease mechanisms and diagnostic and therapeutic strategies. Organ-on-chip models offer a unique and powerful environment that incorporates the ease and reproducibility of in vitro systems along with the complexity and physiological recapitulation of the in vivo system. The key to developing effective valve-on-chip models is maintaining the cell and tissue-level microenvironment relevant to the study application. This review outlines the various components and factors that comprise and/or affect the cell microenvironment that ought to be considered while constructing a valve-on-chip model. This review also dives into the advancements made toward constructing valve-on-chip models with a specific focus on the aortic valve, that is, in vitro studies incorporating three-dimensional co-culture models that incorporate relevant extracellular matrices and mechanical and hemodynamic cues.

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

OBJECTIVE

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

CONCLUSIONS

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

Cardamonin inhibits osteogenic differentiation of human valve interstitial cells and ameliorates aortic valve calcification via interfering in the NF-κB/NLRP3 inflammasome pathway

Cardamonin (CDM) is a natural chalcone with strong anti-inflammatory properties. Inflammation-induced osteogenic changes in valve interstitial cells (VICs) play crucial roles in the development of calcific aortic valve disease (CAVD), a degenerative disease characterized by degeneration, thickening, fibrosis, and calcification of the heart valve tissues. To investigate the anti-osteogenic differentiation role of CDM in human valve interstitial cells (hVICs), which consequently reverses the calcification of the aortic valve, human VICs were exposed to osteogenic induction medium (OM) with CDM for further cell viability, osteogenic gene and protein expression analyses, and anti-calcification testing. mRNA sequencing was utilized to analyze the differentially expressed genes (DEGs) and related signaling pathways as potential molecular targets involved in CDM's anti-calcification activity. Human aortic valve leaflet ex vivo calcific cultures were used to investigate the CDM inhibition of osteogenic differentiation of hVICs at the tissue level. ApoE^-/- mice fed with a high-fat (HF) diet were used to evaluate the effect of CDM on aortic valve calcification. No significant CDM cytotoxicity was seen in the hVICs at 10 μM. The addition of CDM to OM prevented calcified nodule accumulation, and a decrease in the gene/protein expression levels of BMP2, RUNX2, SPP1, TNF-α, and COL1A2 was observed. Venn diagram analysis of the DEGs identified 666 common DEGs and highlighted the NOD-like receptor signaling pathway (ko04621) as an anti-calcification target of CDM. CDM also repressed the activation of p-AKT, p-ERK1/2, and p-IκBα, and prevented the OM-induced nuclear transcription of NF-κB p65. In the in vitro and ex vivo calcific conditional culture experiments, CDM exhibited anti-inflammatory and anti-calcification effects by suppressing the activation of the NLRP3 inflammasome and downregulating IL-1β expression. In vivo, CDM ameliorated aortic valve calcification by interfering with NLRP3 expression. Our study demonstrated that CDM inhibited the phenotypical calcific transformation of hVICs by mediating the inactivation of the NF-κB/NLRP3 inflammasome. Therefore, it is considered to be a promising natural compound for use in preventing the progression of heart valve calcification disease.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Rate of Progression of Aortic Stenosis in Patients With Cancer

Patients with cancer and aortic stenosis (AS) are exposed to several factors that could accelerate the progression of AS. This study aimed to determine the cumulative incidence of AS progression and associated factors in these patients. This retrospective cohort study included patients with cancer, mild or moderate AS and at least two echocardiograms 6 months apart between 1996 and 2016 at MD Anderson Cancer Center. AS progression was defined by an increase in mean gradient of 20 mmHg or peak velocity of 2 m/s by spectral Doppler echocardiography or as requiring aortic valve replacement. Univariate and multivariable Fine-Gray models to account for the competing risk of death were used. One hundred and two patients were included and median follow-up was 7.3 years. Overall, 30 patients (29%) developed AS progression, while 48 (47%) died without it. Yearly rate of mean gradient change was 4.9 ± 3.9 mmHg and yearly rate of peak velocity change was 0.23 ± 0.29 m/s for patients who developed AS progression. In the univariate analysis, coronary artery disease (CAD), dyspnea, prevalent cyclophosphamide and beta-blocker use were associated with AS progression. In multivariable analysis, CAD and prevalent cyclophosphamide use for the time interval of more than 3 years of follow-up remained significantly associated with increased cumulative incidence of AS progression. In conclusion, patients with mild or moderate AS and cancer are more likely to die before having AS progression. AS progression is associated with CAD and prevalent cyclophosphamide use.

Role of Interleukin 17A in Aortic Valve Inflammation in Apolipoprotein E-deficient Mice

Interleukin 17A (IL17A) is reported to be involved in many inflammatory processes, but its role in aortic valve diseases remains unknown. We examined the role of IL17A based on an ApoE^-/- mouse model with strategies as fed with high-fat diet or treated with IL17A monoclonal antibody (mAb). 12 weeks of high-fat diet feeding can elevate cytokines secretion, inflammatory cells infiltration and myofibroblastic transition of valvular interstitial cells (VICs) in aortic valve. Moreover, diet-induction accelerated interleukin 17 receptor A (IL17RA) activation in VICs. In an IL17A inhibition model, the treatment group was intra-peritoneally injected with anti-IL17A mAb while controls received irrelevant antibody. Functional blockade of IL17A markedly reduced cellular infiltration and transition in aortic valve. To investigate potential mechanisms, NF-κB was co-stained in IL17RA⁺ VICs and IL17RA⁺ macrophages, and further confirmed by Western blotting in VICs. High-fat diet could activate NF-κB nuclear translocation in IL17RA⁺ VICs and IL17RA⁺ macrophages and this process was depressed after IL17A mAb-treatment. In conclusion, high-fat diet can lead to IL17A upregulation, VICs myofibroblastic transition and inflammatory cells infiltration in the aortic value of ApoE^-/- mice. Blocking IL17A with IL17A mAb can alleviate aortic valve inflammatory states.

Identification of CD34+/PGDFRα+ Valve Interstitial Cells (VICs) in Human Aortic Valves: Association of Their Abundance, Morphology and Spatial Organization with Early Calcific Remodeling

Aortic valve interstitial cells (VICs) constitute a heterogeneous population involved in the maintenance of unique valvular architecture, ensuring proper hemodynamic function but also engaged in valve degeneration. Recently, cells similar to telocytes/interstitial Cajal-like cells described in various organs were found in heart valves. The aim of this study was to examine the density, distribution, and spatial organization of a VIC subset co-expressing CD34 and PDGFRα in normal aortic valves and to investigate if these cells are associated with the occurrence of early signs of valve calcific remodeling. We examined 28 human aortic valves obtained upon autopsy. General valve morphology and the early signs of degeneration were assessed histochemically. The studied VICs were identified by immunofluorescence (CD34, PDGFRα, vimentin), and their number in standardized parts and layers of the valves was evaluated. In order to show the complex three-dimensional structure of CD34+/PDGFRα+ VICs, whole-mount specimens were imaged by confocal microscopy, and subsequently rendered using the Imaris (Bitplane AG, Zürich, Switzerland) software. CD34+/PDGFRα+ VICs were found in all examined valves, showing significant differences in the number, distribution within valve tissue, spatial organization, and morphology (spherical/oval without projections; numerous short projections; long, branching, occasionally moniliform projections). Such a complex morphology was associated with the younger age of the subjects, and these VICs were more frequent in the spongiosa layer of the valve. Both the number and percentage of CD34+/PDGFRα+ VICs were inversely correlated with the age of the subjects. Valves with histochemical signs of early calcification contained a lower number of CD34+/PDGFRα+ cells. They were less numerous in proximal parts of the cusps, i.e., areas prone to calcification. The results suggest that normal aortic valves contain a subpopulation of CD34+/PDGFRα+ VICs, which might be involved in the maintenance of local microenvironment resisting to pathologic remodeling. Their reduced number in older age could limit the self-regenerative properties of the valve stroma.

Inhibition of PP2A enhances the osteogenic differentiation of human aortic valvular interstitial cells via ERK and p38 MAPK pathways

AIMS

To investigate the role of PP2A in calcified aortic valve disease (CAVD).

MATERIALS AND METHODS

The expressions of PP2A subunits were detected by real-time polymerase chain reaction (RT-PCR) and western blot in aortic valves from patients with CAVD and normal controls, the activities of PP2A were analyzed by commercial assay kit at the same time. Aortic valve calcification of mice was evaluated through histological and echocardiographic analysis. ApoE^-/- mice and ApoE^-/- mice injected intraperitoneally with PP2A inhibitor LB100 were fed a high-cholesterol diet for 24 weeks. Immunofluorescent staining was used to locate the cell-type in which PP2A activity was decreased, the PP2A activity of valvular interstitial cells (VICs) treated with osteogenic induction medium was assessed by western blot and commercial assay kit. After changing the activity of VICs through pharmacologic and genetic intervention, the osteoblast differentiation and mineralization were assessed by western blot and Alizarin Red staining. Finally, the mechanism was clarified by using several specific inhibitors.

KEY FINDINGS

PP2A activity was decreased both in calcified aortic valves and human VICs under osteogenic induction. The PP2A inhibitor LB100 aggravated the aortic valve calcification of mice. Furthermore, PPP2CA overexpression inhibited osteogenic differentiation of VICs, whereas PPP2CA knockdown promoted the process. Further study revealed that the ERK/p38 MAPKs signaling pathways mediated the osteogenic differentiation of VICs induced by PP2A inactivation.

SIGNIFICANCE

This study demonstrated that PP2A plays an important role in CAVD pathophysiology, PP2A activation may provide a novel strategy for the pharmacological treatment of CAVD.

Caffeic Acid Phenethyl Ester Ameliorates Calcification by Inhibiting Activation of the AKT/NF-κB/NLRP3 Inflammasome Pathway in Human Aortic Valve Interstitial Cells

Calcific aortic valve disease (CAVD) occurs via a pathophysiological process that includes inflammation-induced osteoblastic differentiation of aortic valvular interstitial cells (AVICs). Here, we investigated the role of the anti-inflammatory compound caffeic acid phenethyl ester (CAPE) in inhibiting CAVD. Human AVICs were isolated and cultured in osteogenic induction medium (OM) with or without 10 μM CAPE. Cell viability was assessed using CCK8 assays and calcified transformation of AVICs was evaluated by Alizarin Red staining and osteogenic gene/protein expression. RNA-sequencing was conducted to identify differentially expressed genes (DEGs) and enrichment in associated pathways, as potential molecular targets through which CAPE inhibits osteogenic induction. The regulatory effects of CAPE on activation of the AKT/NF-κB and NLRP3 inflammasome were evaluated by Western blot analysis and immunofluorescent staining. CAPE slowed the growth of AVICs cultured in OM but did not show significant cytotoxicity. In addition, CAPE markedly suppressed calcified nodule formation and decreased gene/protein expression of RUNX2 and ALP in AVICs. Gene expression profiles of OM-induced AVICs cultured with or without CAPE revealed 518 common DEGs, which were highly enriched in the NOD-like receptor, PI3K-AKT, and NF-κB signaling pathways. Furthermore, CAPE inhibited phosphorylation of AKT, ERK1/2, and NF-κB, and suppressed NLRP3 inflammasome activation in AVICs cultured in OM. Thus, CAPE is implicated as a potent natural product for the prevention of CAVD by inhibiting activation of the AKT/NF-κB pathway and NLRP3 inflammasome.

The Ryanodine Receptor Contributes to the Lysophosphatidylcholine-Induced Mineralization in Valvular Interstitial Cells

PURPOSE

Fibrocalcific aortic valve disease (CAVD) is caused by the deposition of calcific nodules in the aortic valve leaflets, resulting in progressive loss of function that ultimately requires surgical intervention. This process is actively mediated by the resident valvular interstitial cells (VICs), which, in response to oxidized lipids, transition from a quiescent to an osteoblast-like state. The purpose of this study was to examine if the ryanodine receptor, an intracellular calcium channel, could be therapeutically targeted to prevent this phenotypic conversion.

METHODS

The expression of the ryanodine receptor in porcine aortic VICs was characterized by qRT-PCR and immunofluorescence. Next, the VICs were exposed to lysophosphatidylcholine, an oxidized lipid commonly found in low-density lipoprotein, while the activity of the ryanodine receptor was modulated with ryanodine. The cultures were analyzed for markers of cellular mineralization, alkaline phosphatase activity, proliferation, and apoptosis.

RESULTS

Porcine aortic VICs predominantly express isoform 3 of the ryanodine receptors, and this protein mediates the cellular response to LPC. Exposure to LPC caused elevated intracellular calcium concentration in VICs, raised levels of alkaline phosphatase activity, and increased calcific nodule formation, but these changes were reversed when the activity of the ryanodine receptor was blocked.

CONCLUSIONS

Our findings suggest blocking the activity of the ryanodine receptor can attenuate the valvular mineralization caused by LPC. We conclude that oxidized lipids, such as LPC, play an important role in the development and progression of CAVD and that the ryanodine receptor is a promising target for pharmacological intervention.

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.

MicroRNA-638 inhibits human aortic valve interstitial cell calcification by targeting Sp7

Calcific aortic valve disease (CAVD) is a complex heart valve disease involving a wide range of pathological changes. Emerging evidence indicates that osteogenic differentiation of human aortic valve interstitial cells (hAVICs) plays a key role in valve calcification. In this study, we aimed to investigate the function of miR-638 in hAVICs osteogenesis. Both miRNA microarray assay and qRT-PCR results demonstrating miR-638 was obviously up-regulated in calcific aortic valves compared with non-calcific valves. We also proved that miR-638 was significantly up-regulated during hAVICs osteogenic differentiation. Overexpression of miR-638 suppressed osteogenic differentiation of hAVICs in vitro, whereas down-regulation of miR-638 enhance the process. Target prediction analysis and dual-luciferase reporter assay confirmed that Sp7 transcription factor (Sp7) was a direct target of miR-638. Furthermore, knockdown of Sp7 inhibited osteogenic differentiation of hAVICs, which is similar to the results observed in up-regulation miR-638. Our data indicated that miR-638 plays an inhibitory role in hAVICs osteogenic differentiation, which may act by targeting Sp7. MiR-638 may be a potential therapeutic target for CAVD.

Spatial Regulation of Valve Interstitial Cell Phenotypes within Three-Dimensional Micropatterned Hydrogels

Calcific aortic valve disease (CAVD) is the third leading cause of cardiovascular disease. CAVD exhibits progressive disruption of the normally highly organized and aligned extracellular matrix (ECM) structure within the valve leaflets simultaneously with myofibroblastic and/or osteogenic differentiation of indigenous endogenous valve interstitial cells (VIC). It is unclear how the alignment of VIC within their 3D microenvironment drives VIC phenotype or how alignment affects cellular responses to biochemical cues in physiological or pathological conditions. In this study, we implement a photolithographic technique to control the alignment and elongation of both normal and diseased human aortic VIC (HAVIC) within microengineered 3D hydrogels consisting of methacrylated hyaluronic acid and methacrylated gelatin. Stripe micropatterning created distinct alignment of HAVIC within a 3D culture system, which promoted spreading and enhanced their activation and osteogenic differentiation in pro-osteogenic conditions. HAVIC from a patient with CAVD exhibited greater susceptibility to myofibroblastic and osteogenic differentiation in culture. The roles of conjugated basic fibroblastic growth factor (bFGF) and RhoA/ROCK pathway in regulating HAVIC phenotypes were also investigated in the presence of aligned microtopography. The addition of bFGF was preventative to osteogenic differentiation for healthy HAVIC; however, it promoted osteogenic differentiation in diseased HAVIC. Inhibition of the ROCK pathway only decreased osteogenic differentiation for diseased HAVIC in the aligned formation. Collectively, these results improve our knowledge of the effects that VIC alignment has on VIC phenotypes and valve disease progression. The cell culture platform also enables a better understanding of the interplay between topography, biochemical cues, and VIC differentiation and provides information useful for directing differentiation as well as valve tissue regeneration.

Comparing the Role of Mechanical Forces in Vascular and Valvular Calcification Progression

Calcification is a prevalent disease in most fully developed countries and is predominantly observed in heart valves and nearby vasculature. Calcification of either tissue leads to deterioration and, ultimately, failure causing poor quality of life and decreased overall life expectancy in patients. In valves, calcification presents as Calcific Aortic Valve Disease (CAVD), in which the aortic valve becomes stenotic when calcific nodules form within the leaflets. The initiation and progression of these calcific nodules is strongly influenced by the varied mechanical forces on the valve. In turn, the addition of calcific nodules creates localized disturbances in the tissue biomechanics, which affects extracellular matrix (ECM) production and cellular activation. In vasculature, atherosclerosis is the most common occurrence of calcification. Atherosclerosis exhibits as calcific plaque formation that forms in juxtaposition to areas of low blood shear stresses. Research in these two manifestations of calcification remain separated, although many similarities persist. Both diseases show that the endothelial layer and its regulation of nitric oxide is crucial to calcification progression. Further, there are similarities between vascular smooth muscle cells and valvular interstitial cells in terms of their roles in ECM overproduction. This review summarizes valvular and vascular tissue in terms of their basic anatomy, their cellular and ECM components and mechanical forces. Calcification is then examined in both tissues in terms of disease prediction, progression, and treatment. Highlighting the similarities and differences between these areas will help target further research toward disease treatment.

Cadherin-11 as a regulator of valve myofibroblast mechanobiology

Cadherin-11 (CDH11) is upregulated in a variety of fibrotic diseases, including arthritis and calcific aortic valve disease. Our recent work has identified CDH11 as a potential therapeutic target and shown that treatment with a CDH11 functional blocking antibody can prevent hallmarks of calcific aortic valve disease in mice. The present study investigated the role of CDH11 in regulating the mechanobiological behavior of valvular interstitial cells believed to cause calcification. Aortic valve interstitial cells were harvested from Cdh11^+/+, Cdh11^+/-, and Cdh11^-/- immortomice. Cells were subjected to inflammatory cytokines transforming growth factor (TGF)-β₁ and IL-6 to characterize the molecular mechanisms by which CDH11 regulates their mechanobiological changes. Histology was performed on aortic valves from Cdh11^+/+, Cdh11^+/-, and Cdh11^-/- mice to identify key responses to CDH11 deletion in vivo. We showed that CDH11 influences cell behavior through its regulation of contractility and its ability to bind substrates via focal adhesions. We also show that transforming growth factor-β₁ overrides the normal relationship between CDH11 and smooth muscle α-actin to exacerbate the myofibroblast disease phenotype. This phenotypic switch is potentiated through the IL-6 signaling axis and could act as a paracrine mechanism of myofibroblast activation in neighboring aortic valve interstitial cells in a positive feedback loop. These data suggest CDH11 is an important mediator of the myofibroblast phenotype and identify several mechanisms by which it modulates cell behavior. NEW & NOTEWORTHY Cadherin-11 influences valvular interstitial cell contractility by regulating focal adhesions and inflammatory cytokine secretion. Transforming growth factor-β₁ overrides the normal balance between cadherin-11 and smooth muscle α-actin expression to promote a myofibroblast phenotype. Cadherin-11 is necessary for IL-6 and chitinase-3-like protein 1 secretion, and IL-6 promotes contractility. Targeting cadherin-11 could therapeutically influence valvular interstitial cell phenotypes in a multifaceted manner.

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.

Creation of disease-inspired biomaterial environments to mimic pathological events in early calcific aortic valve disease

An insufficient understanding of calcific aortic valve disease (CAVD) pathogenesis remains a major obstacle in developing treatment strategies for this disease. The aim of the present study was to create engineered environments that mimic the earliest known features of CAVD and apply this in vitro platform to decipher relationships relevant to early valve lesion pathobiology. Glycosaminoglycan (GAG) enrichment is a dominant hallmark of early CAVD, but culture of valvular interstitial cells (VICs) in biomaterial environments containing pathological amounts of hyaluronic acid (HA) or chondroitin sulfate (CS) did not directly increase indicators of disease progression such as VIC activation or inflammatory cytokine production. However, HA-enriched matrices increased production of vascular endothelial growth factor (VEGF), while matrices displaying pathological levels of CS were effective at retaining lipoproteins, whose deposition is also found in early CAVD. Retained oxidized low-density lipoprotein (oxLDL), in turn, stimulated myofibroblastic VIC differentiation and secretion of numerous inflammatory cytokines. OxLDL also increased VIC deposition of GAGs, thereby creating a positive feedback loop to further enrich GAG content and promote disease progression. Using this disease-inspired in vitro platform, we were able to model a complex, multistep pathological sequence, with our findings suggesting distinct roles for individual GAGs in outcomes related to valve lesion progression, as well as key differences in cell-lipoprotein interactions compared with atherosclerosis. We propose a pathogenesis cascade that may be relevant to understanding early CAVD and envision the extension of such models to investigate other tissue pathologies or test pharmacological treatments.

Expression of the Frizzled receptors and their co-receptors in calcified human aortic valves

The cellular mechanisms that induce calcific aortic stenosis are yet to be unraveled. Wnt signaling is increasingly being considered as a major player in the disease process. However, the presence of Wnt Frizzled (Fzd) receptors and co-receptors LRP5 and 6 in normal and diseased human aortic valves remains to be elucidated. Immunohistochemistry and quantitative polymerase chain reaction were used to determine Fzd receptor expression in normal and calcified human aortic valve tissue, as well as human aortic valve interstitial cells (HAVICs) isolated from calcified and normal human aortic valves. There was significantly higher mRNA expression of 4 out of the 10 Fzd receptors in calcified aortic valve tissues and 8 out of the 10 in HAVICs, and both LRP5/6 co-receptors in calcified aortic valves (P < 0.05). These results were confirmed by immunohistochemistry, which revealed abundant increase in immunoreactivity for Fzd3, 7, and 8, mainly in areas of lipid core and calcified nodules of diseased aortic valves. The findings of abundant expression of Fzd and LRP5/6 receptors in diseased aortic valves suggests a potential role for both canonical and noncanonical Wnt signaling in the pathogenesis of human aortic valve calcification. Future investigations aimed at targeting these molecules may provide potential therapies for aortic valve stenosis.

Deficiency of CCAAT/enhancer-binding protein homologous protein (CHOP) prevents diet-induced aortic valve calcification in vivo

Aortic valve (AoV) calcification is common in aged populations. Its subsequent aortic stenosis has been linked with increased morbidity, but still has no effective pharmacological intervention. Our previous data show endoplasmic reticulum (ER) stress is involved in AoV calcification. Here, we investigated whether deficiency of ER stress downstream effector CCAAT/enhancer‐binding protein homology protein (CHOP) may prevent development of AoV calcification. AoV calcification was evaluated in Apoe^−/− mice (n = 10) or in mice with dual deficiencies of ApoE and CHOP (Apoe^−/−CHOP^−/−, n = 10) fed with Western diet for 24 weeks. Histological and echocardiographic analysis showed that genetic ablation of CHOP attenuated AoV calcification, pro‐calcification signaling activation, and apoptosis in the leaflets of Apoe^−/− mice. In cultured human aortic valvular interstitial cells (VIC), we found oxidized low‐density lipoprotein (oxLDL) promoted apoptosis and osteoblastic differentiation of VIC via CHOP activation. Using conditioned media (CM) from oxLDL‐treated VIC, we further identified that oxLDL triggered osteoblastic differentiation of VIC via paracrine pathway, while depletion of apoptotic bodies (ABs) in CM suppressed the effect. CM from oxLDL‐exposed CHOP‐silenced cells prevented osteoblastic differentiation of VIC, while depletion of ABs did not further enhance this protective effect. Overall, our study indicates that CHOP deficiency protects against Western diet‐induced AoV calcification in Apoe^−/− mice. CHOP deficiency prevents oxLDL‐induced VIC osteoblastic differentiation via preventing VIC‐derived ABs releasing.

Epigenome alterations in aortic valve stenosis and its related left ventricular hypertrophy

Aortic valve stenosis is the most common cardiac valve disease, and with current trends in the population demographics, its prevalence is likely to rise, thus posing a major health and economic burden facing the worldwide societies. Over the past decade, it has become more than clear that our traditional genetic views do not sufficiently explain the well-known link between AS, proatherogenic risk factors, flow-induced mechanical forces, and disease-prone environmental influences. Recent breakthroughs in the field of epigenetics offer us a new perspective on gene regulation, which has broadened our perspective on etiology of aortic stenosis and other aortic valve diseases. Since all known epigenetic marks are potentially reversible this perspective is especially exciting given the potential for development of successful and non-invasive therapeutic intervention and reprogramming of cells at the epigenetic level even in the early stages of disease progression. This review will examine the known relationships between four major epigenetic mechanisms: DNA methylation, posttranslational histone modification, ATP-dependent chromatin remodeling, and non-coding regulatory RNAs, and initiation and progression of AS. Numerous profiling and functional studies indicate that they could contribute to endothelial dysfunctions, disease-prone activation of monocyte-macrophage and circulatory osteoprogenitor cells and activation and osteogenic transdifferentiation of aortic valve interstitial cells, thus leading to valvular inflammation, fibrosis, and calcification, and to pressure overload-induced maladaptive myocardial remodeling and left ventricular hypertrophy. This is especcialy the case for small non-coding microRNAs but was also, although in a smaller scale, convincingly demonstrated for other members of cellular epigenome landscape. Equally important, and clinically most relevant, the reported data indicate that epigenetic marks, particularly certain microRNA signatures, could represent useful non-invasive biomarkers that reflect the disease progression and patients prognosis for recovery after the valve replacement surgery.

MicroRNA-449c-5p inhibits osteogenic differentiation of human VICs through Smad4-mediated pathway

Calcific aortic valve disease (CAVD) is the most common heart valve disorder, yet its mechanism remains poorly understood. Valve interstitial cells (VICs) are the prevalent cells in aortic valve and their osteogenic differentiation may be responsible for calcific nodule formation in CAVD pathogenesis. Emerging evidence shows microRNA (miRNA, or miR) can function as important regulators of many pathological processes, including osteogenic differentiation. Here, we aimed to explore the function of miR-449c-5p in CAVD pathogenesis. In this study, we demonstrated the role of miR-449c-5p in VICs osteogenesis. MiRNA microarray assay and qRT-PCR results revealed miR-449c-5p was significantly down-regulated in calcified aortic valves compared with non-calcified valves. MiR-449c-5p overexpression inhibited VICs osteogenic differentiation in vitro, whereas down-regulation of miR-449c-5p enhanced the process. Target prediction analysis and dual-luciferase reporter assay confirmed Smad4 was a direct target of miR-449c-5p. Furthermore, knockdown of Smad4 inhibited VICs osteogenic differentiation, similar to the effect observed in up-regulation miR-449c-5p. In addition, animal experiments proved indirectly miR-449c-5p could alleviate aortic valve calcification. Our data suggested miR-449c-5p could function as a new inhibitory regulator of VICs osteogenic differentiation, which may act by targeting Smad4. MiR-449c-5p may be a potential therapeutic target for CAVD.

Robust Generation of Quiescent Porcine Valvular Interstitial Cell Cultures

Background

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

Methods and Results

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

Conclusions

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

NOTCH1 Mutations in Aortic Stenosis: Association with Osteoprotegerin/RANK/RANKL

Background. The NOTCH pathway is known to be important in the pathogenesis of calcific aortic valve disease, possibly through regulators of osteoprotegerin (OPG), receptor activator of nuclear factor κB (RANK), and its ligand (RANKL) system. The purpose of the present study was to search for possible associations between NOTCH1 gene mutations and circulating levels of OPG and soluble RANKL (sRANKL) in patients with aortic stenosis (AS). Methods. The study was performed on 61 patients with AS including 31 with bicuspid and 30 with tricuspid aortic valves. We applied a strategy of targeted mutation screening for 10 out of 34 exons of the NOTCH1 gene by direct sequencing. Serum OPG and sRANKL levels were assessed. Results. In total, 6 genetic variants of the NOTCH1 gene including two new mutations were identified in the study group. In an age- and arterial hypertension-adjusted multivariable regression analysis, the serum OPG levels and the OPG/sRANKL ratio were correlated with NOTCH1 missense variants. All studied missense variants in NOTCH1 gene were found in Ca(2+)-binding EGF motif of the NOTCH extracellular domain bound to Delta-like 4. Conclusion. Our results suggest that the OPG/RANKL/RANK system might be directly influenced by genetic variants of NOTCH1 in aortic valve calcification.

Double-stranded RNA upregulates the expression of inflammatory mediators in human aortic valve cells through the TLR3-TRIF-noncanonical NF-κB pathway

Calcific aortic valve disease is a chronic inflammatory condition, and the inflammatory responses of aortic valve interstitial cells (AVICs) play a critical role in the disease progression. Double-stranded RNA (dsRNA) released from damaged or stressed cells is proinflammatory and may contribute to the mechanism of chronic inflammation observed in diseased aortic valves. The objective of this study is to determine the effect of dsRNA on AVIC inflammatory responses and the underlying mechanism. AVICs from normal human aortic valves were stimulated with polyinosinic-polycytidylic acid [poly(I:C)], a mimic of dsRNA. Poly(I:C) increased the production of IL-6, IL-8, monocyte chemoattractant protein-1, and ICAM-1. Poly(I:C) also induced robust activation of ERK1/2 and NF-κB. Knockdown of Toll-like receptor 3 (TLR3) or Toll-IL-1 receptor domain-containing adapter-inducing IFN-β (TRIF) suppressed ERK1/2 and NF-κB p65 phosphorylation and reduced inflammatory mediator production induced by poly(I:C). Inhibition of NF-κB, not ERK1/2, reduced inflammatory mediator production in AVICs exposed to poly(I:C). Interestingly, inhibition of NF-κB by prevention of p50 migration failed to suppress inflammatory mediator production. NF-κB p65 intranuclear translocation induced by the TLR4 agonist was reduced by inhibition of p50 migration; however, poly(I:C)-induced p65 translocation was not, although the p65/p50 heterodimer is present in AVICs. Poly(I:C) upregulates the production of multiple inflammatory mediators through the TLR3-TRIF-NF-κB pathway in human AVICs. The NF-κB activated by dsRNA appears not to be the canonical p65/p50 heterodimers.

Role of Noncanonical Wnt Signaling Pathway in Human Aortic Valve Calcification

OBJECTIVE

The mechanisms underlying the pathogenesis of aortic valve calcification remain unclear. With accumulating evidence demonstrating that valve calcification recapitulates bone development, the crucial roles of noncanonical Wnt ligands WNT5a, WNT5b, and WNT11 in osteogenesis make them critical targets in the study of aortic valve calcification.

APPROACH AND RESULTS

Using immunohistochemistry, real-time qPCR, Western blotting, and tissue culture, we examined the tissue distribution of WNT5a, WNT5b, and WNT11 in noncalcified and calcified aortic valves and their effects on human aortic valve interstitial cells (HAVICs). Only focal strong immunostaining for WNT5a was seen in and around areas of calcification. Abundant immunostaining for WNT5b and WNT11 was seen in inflammatory cells, fibrosis, and activated myofibroblasts in areas of calcified foci. There was significant correlation between WNT5b and WNT11 overall staining and presence of calcification, lipid score, fibrosis, and microvessels (P<0.05). Real-time qPCR and Western blotting revealed abundant expression of both Wnts in stenotic aortic valves, particularly in bicuspid valves. Incubation of HAVICs from noncalcified valves with the 3 noncanonical Wnts significantly increased cell apoptosis and calcification (P<0.05). Treatment of HAVICs with the mitogen-activated protein kinase-38β and GSK3β inhibitors significantly reduced their mineralization (P<0.01). Raman spectroscopy identified the inorganic phosphate deposits as hydroxyapatite and showed a significant increase in hydroxyapatite deposition in HAVICs in response to WNT5a and WNT11 (P<0.05). Similar crystallinity was seen in the deposits found in HAVICs treated with Wnts and in calcified human aortic valves.

CONCLUSIONS

These findings suggest a potential role for noncanonical Wnt signaling in the pathogenesis of aortic valve calcification.

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

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

Morphology, Clinicopathologic Correlations, and Mechanisms in Heart Valve Health and Disease

The clinical and pathological features of the most frequent intrinsic structural diseases that affect the heart valves are well established, but heart valve disease mechanisms are poorly understood, and effective treatment options are evolving. Major advances in the understanding of the structure, function and biology of native valves and the pathobiology, biomaterials and biomedical engineering, and the clinical management of valvular heart disease have occurred over the past several decades. This communication reviews contemporary considerations relative to the pathology of valvular heart disease, including (1) clinical significance and epidemiology of valvular heart disease; (2) functional and dynamic valvular macro-, micro- and ultrastructure; (3) causes, morphology and mechanisms of human valvular heart disease; and (4) pathologic considerations in valve replacement, repair and, potentially, regeneration of the heart valves.

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.

The Role of High Mobility Group Box 1 Protein in Interleukin-18-Induced Myofibroblastic Transition of Valvular Interstitial Cells

BACKGROUND

Increased levels of interleukin-18 (IL-18) and high mobility group box 1 protein (HMGB1) have been reported in patients with calcific aortic valve disease (CAVD). However, the role of IL-18 and HMGB1 in the modulation of the valvular interstitial cell (VIC) phenotype remains unclear. We hypothesized that HMGB1 mediates IL-18-induced myofibroblastic transition of VICs.

METHODS

The expression of IL-18, HMGB1 and α-smooth muscle actin (α-SMA) in human aortic valves was evaluated by immunohistochemical staining, real-time polymerase chain reaction and immunoblotting. Plasma concentrations of IL-18 and HMGB1 were measured using the ELISA kit. Cultured human aortic VICs were used as an in vitro model.

RESULTS

Immunohistochemistry and immunoblotting revealed increased levels of IL-18, HMGB1 and α-SMA in calcific valves. Circulating IL-18 and HMGB1 levels were also higher in CAVD patients. In vitro, IL-18 induced upregulation of HMGB1 and α-SMA in VICs. Moreover, IL-18 induced secretion of HMGB1 to the extracellular space and activation of nuclear factor kappa-B (NF-κB). Blockade of NF-κB abrogated the upregulation and release of HMGB1 induced by IL-18. Whereas HMGB1 inhibition attenuated the IL-18-induced expression of α-SMA, HMGB1 enhanced the effect of IL-18.

CONCLUSIONS

We demonstrated for the first time that both tissue and plasma levels of IL-18 and HMGB1 were increased in patients with CAVD. Mechanically, HMGB1 mediated IL-18-induced VIC myofibroblastic transition.

Heart valve health, disease, replacement, and repair: a 25-year cardiovascular pathology perspective

The past several decades have witnessed major advances in the understanding of the structure, function, and biology of native valves and the pathobiology and clinical management of valvular heart disease. These improvements have enabled earlier and more precise diagnosis, assessment of the proper timing of surgical and interventional procedures, improved prosthetic and biologic valve replacements and repairs, recognition of postoperative complications and their management, and the introduction of minimally invasive approaches that have enabled definitive and durable treatment for patients who were previously considered inoperable. This review summarizes the current state of our understanding of the mechanisms of heart valve health and disease arrived at through innovative research on the cell and molecular biology of valves, clinical and pathological features of the most frequent intrinsic structural diseases that affect the valves, and the status and pathological considerations in the technological advances in valvular surgery and interventions. The contributions of many cardiovascular pathologists and other scientists, engineers, and clinicians are emphasized, and potentially fruitful areas for research are highlighted.

Active tissue stiffness modulation controls valve interstitial cell phenotype and osteogenic potential in 3D culture

Calcific aortic valve disease (CAVD) progression is a highly dynamic process whereby normally fibroblastic valve interstitial cells (VIC) undergo osteogenic differentiation, maladaptive extracellular matrix (ECM) composition, structural remodeling, and tissue matrix stiffening. However, how VIC with different phenotypes dynamically affect matrix properties and how the altered matrix further affects VIC phenotypes in response to physiological and pathological conditions have not yet been determined. In this study, we develop 3D hydrogels with tunable matrix stiffness to investigate the dynamic interplay between VIC phenotypes and matrix biomechanics. We find that VIC populated within hydrogels with valve leaflet like stiffness differentiate towards myofibroblasts in osteogenic media, but surprisingly undergo osteogenic differentiation when cultured within lower initial stiffness hydrogels. VIC differentiation progressively stiffens the hydrogel microenvironment, which further upregulates both early and late osteogenic markers. These findings identify a dynamic positive feedback loop that governs acceleration of VIC calcification. Temporal stiffening of pathologically lower stiffness matrix back to normal level, or blocking the mechanosensitive RhoA/ROCK signaling pathway, delays the osteogenic differentiation process. Therefore, direct ECM biomechanical modulation can affect VIC phenotypes towards and against osteogenic differentiation in 3D culture. These findings highlight the importance of the homeostatic maintenance of matrix stiffness to restrict pathological VIC differentiation.

STATEMENT OF SIGNIFICANCE

We implement 3D hydrogels with tunable matrix stiffness to investigate the dynamic interaction between valve interstitial cells (VIC, major cell population in heart valve) and matrix biomechanics. This work focuses on how human VIC responses to changing 3D culture environments. Our findings identify a dynamic positive feedback loop that governs acceleration of VIC calcification, which is the hallmark of calcific aortic valve disease. Temporal stiffening of pathologically lower stiffness matrix back to normal level, or blocking the mechanosensitive signaling pathway, delays VIC osteogenic differentiation. Our findings provide an improved understanding of VIC-matrix interactions to aid in interpretation of VIC calcification studies in vitro and suggest that ECM disruption resulting in local tissue stiffness decreases may promote calcific aortic valve disease.

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.