Aortic valvular interstitial cells apoptosis and calcification are mediated by TNF-related apoptosis-inducing ligand

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.

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

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

Hypothesis

Calcific aortic valve disease (CAVD) is a common cardiovascular disease in the elderly individuals associated with major morbidity and mortality. The process is characterized by multiple steps: lipid infiltration, inflammation, fibrosis, and calcification. Inhibitors of proprotein convertase subtilisin/kexin type 9 (PCSK9) represent a new therapeutic category of drugs for the treatment of dyslipidemia and atherosclerotic cardiovascular disease. Monoclonal antibodies of PCSK9 can result in substantial reductions in atherogenic lipoprotein cholesterol-carrying particles, especially lipoprotein(a), and thereby hold the potential for further reducing events associated with atherosclerotic cardiovascular disease. In this article, we reviewed the clinical and experimental studies in order to find the evidence of the involvement of PCSK9 in CAVD and the potential benefits of PCSK9 monoclonal antibodies in clinical therapeutics.

MALDI-Imaging Mass Spectrometry: a step forward in the anatomopathological characterization of stenotic aortic valve tissue

Aortic stenosis (AS) is the most common form of valve disease. Once symptoms develop, there is an inexorable deterioration with a poor prognosis; currently there are no therapies capable of modifying disease progression, and aortic valve replacement is the only available treatment. Our goal is to study the progression of calcification by matrix-assisted laser desorption ionization imaging mass spectrometry (MALDI-IMS) and get new insights at molecular level that could help in the understanding of this disease. In this work, we analyzed consecutive slices from aortic valve tissue by MALDI-IMS, to establish the spatial distribution of proteins and peptides directly from the surface of the histological sections. The analysis showed different structures corresponding to regions observed in conventional histology, including large calcification areas and zones rich in collagen and elastic fibers. Peptide extraction from the tissue, followed by liquid chromatography mass spectrometry analysis, provided the identification of collagen VI α-3 and NDRG2 proteins which correlated with the masses obtained by MALDI-IMS and were confirmed by immunohistochemistry. These results highlighted the molecular mechanism implied in AS using MALDI-IMS, a novel technique never used before in this pathology. In addition, we can define specific regions proving a complementary resolution of the molecular histology.

Calcific aortic stenosis

Calcific aortic stenosis (AS) is the most prevalent heart valve disorder in developed countries. It is characterized by progressive fibro-calcific remodelling and thickening of the aortic valve leaflets that, over years, evolve to cause severe obstruction to cardiac outflow. In developed countries, AS is the third-most frequent cardiovascular disease after coronary artery disease and systemic arterial hypertension, with a prevalence of 0.4% in the general population and 1.7% in the population >65 years old. Congenital abnormality (bicuspid valve) and older age are powerful risk factors for calcific AS. Metabolic syndrome and an elevated plasma level of lipoprotein(a) have also been associated with increased risk of calcific AS. The pathobiology of calcific AS is complex and involves genetic factors, lipoprotein deposition and oxidation, chronic inflammation, osteoblastic transition of cardiac valve interstitial cells and active leaflet calcification. Although no pharmacotherapy has proved to be effective in reducing the progression of AS, promising therapeutic targets include lipoprotein(a), the renin-angiotensin system, receptor activator of NF-κB ligand (RANKL; also known as TNFSF11) and ectonucleotidases. Currently, aortic valve replacement (AVR) remains the only effective treatment for severe AS. The diagnosis and staging of AS are based on the assessment of stenosis severity and left ventricular systolic function by Doppler echocardiography, and the presence of symptoms. The introduction of transcatheter AVR in the past decade has been a transformative therapeutic innovation for patients at high or prohibitive risk for surgical valve replacement, and this new technology might extend to lower-risk patients in the near future.

DNA Repair Gene Polymorphism and the Risk of Mitral Chordae Tendineae Rupture

Polymorphisms in Lys939Gln XPC gene may diminish DNA repair capacity, eventually increasing the risk of carcinogenesis. The aim of the present study was to evaluate the significance of polymorphism Lys939Gln in XPC gene in patients with mitral chordae tendinea rupture (MCTR). Twenty-one patients with MCTR and thirty-seven age and sex matched controls were enrolled in the study. Genotyping of XPC gene Lys939Gln polymorphism was carried out using polymerase chain reaction- (PCR-) restriction fragment length polymorphism (RFLP). The frequencies of the heterozygote genotype (Lys/Gln-AC) and homozygote genotype (Gln/Gln-CC) were significantly different in MCTR as compared to control group, respectively (52.4% versus 43.2%, p = 0.049; 38.15% versus 16.2%, p = 0.018). Homozygote variant (Gln/Gln) genotype was significantly associated with increased risk of MCTR (OR = 2.059; 95% CI: 1.097-3.863; p = 0.018). Heterozygote variant (Lys/Gln) genotype was also highly significantly associated with increased risk of MCTR (OR = 1.489; 95% CI: 1.041-2.129; p = 0.049). The variant allele C was found to be significantly associated with MCTR (OR = 1.481; 95% CI: 1.101-1.992; p = 0.011). This study has demonstrated the association of XPC gene Lys939Gln polymorphism with MCTR, which is significantly associated with increased risk of MCTR.

Targeting local vascular and systemic consequences of inflammation on vascular and cardiac valve calcification

INTRODUCTION

Cardiac valve calcification and vascular calcification (VC) are associated with cardiovascular mortality in the general population and in patients with chronic kidney disease (CKD). CKD, diabetes mellitus, and atherosclerosis are among the causes of systemic inflammation that are associated with VC.

AREAS COVERED

This review collates clinical and experimental evidence that inflammation accelerates VC progression. Specifically, we review the actions of key pro-inflammatory cytokines and inflammation-related transcription factors on VC, and the role played by senescence. Inflammatory cytokines, such as the TNF superfamily and IL-6 superfamily, and inflammation-related transcription factor NF-κB promote calcification in cultured vascular smooth muscle cells, valvular interstitial cells, or experimental animal models through direct effects, but also indirectly by decreasing circulating Fetuin A or Klotho levels.

EXPERT OPINION

Experimental evidence suggests a causal link between inflammation and VC that would change the clinical approach to prevention and treatment of VC. However, the molecular basis remains unclear and little is known about VC in humans treated with drugs targeting inflammatory cytokines. The effect of biologicals targeting TNF-α, RANKL, IL-6, and other inflammatory mediators on VC, in addition to the impact of dietary phosphate in patients with chronic systemic inflammation, requires study.

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

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

Innate and Adaptive Immunity in Calcific Aortic Valve Disease

Calcific aortic valve disease (CAVD) is the most common heart valve disorder. CAVD is a chronic process characterized by a pathologic mineralization of valve leaflets. Ectopic mineralization of the aortic valve involves complex relationships with immunity. Studies have highlighted that both innate and adaptive immunity play a role in the development of CAVD. In this regard, accumulating evidence indicates that fibrocalcific remodelling of the aortic valve is associated with activation of the NF-κB pathway. The expression of TNF-α and IL-6 is increased in human mineralized aortic valves and promotes an osteogenic program as well as the mineralization of valve interstitial cells (VICs), the main cellular component of the aortic valve. Different factors, including oxidized lipid species, activate the innate immune response through the Toll-like receptors. Moreover, VICs express 5-lipoxygenase and therefore produce leukotrienes, which may amplify the inflammatory response in the aortic valve. More recently, studies have emphasized that an adaptive immune response is triggered during CAVD. Herein, we are reviewing the link between the immune response and the development of CAVD and we have tried, whenever possible, to keep a translational approach.

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

Aims

Oxidative stress is present in and contributes to calcification of the aortic valve, but the driving factors behind the initiation of valve oxidative stress are not well understood. We tested whether the valve endothelium acts as an initiator and propagator of oxidative stress in aortic valve disease.

Methods and Results

Calcified human aortic valves showed side-specific elevation of superoxide in the endothelium, co-localized with high VCAM1 expression, linking oxidative stress, inflammation, and valve degeneration. Treatment with inflammatory cytokine TNFα increased superoxide and oxidative stress and decreased eNOS and VE-cadherin acutely over 48 hours in aortic valve endothelial cells (VEC) and chronically over 21 days in ex vivo AV leaflets. Co-treatment of VEC with tetrahydrobiopterin (BH₄) but not apocynin mitigated TNFα-driven VEC oxidative stress. Co-treatment of ex vivo AV leaflets with TNFα+BH₄ or TNFα+peg-SOD rescued endothelial function and mitigated inflammatory responses. Both BH₄ and peg-SOD rescued valve leaflets from the pro-osteogenic effects of TNFα treatment, but only peg-SOD was able to mitigate the fibrogenic effects, including increased collagen and αSMA expression.

Conclusions

Aortic valve endothelial cells are a novel source of oxidative stress in aortic valve disease. TNFα-driven VEC oxidative stress causes loss of endothelial protective function, chronic inflammation, and fibrogenic and osteogenic activation, mitigated differentially by BH₄ and peg-SOD. These mechanisms identify new targets for tailored antioxidant therapy focused on mitigation of oxidative stress and restoration of endothelial protection.

In vitro models of aortic valve calcification: solidifying a system

Calcific aortic valve disease (CAVD) affects 25% of people over 65, and the late-stage stenotic state can only be treated with total valve replacement, requiring 85,000 surgeries annually in the US alone (University of Maryland Medical Center, 2013, http://umm.edu/programs/services/heart-center-programs/cardiothoracic-surgery/valve-surgery/facts). As CAVD is an age-related disease, many of the affected patients are unable to undergo the open-chest surgery that is its only current cure. This challenge motivates the elucidation of the mechanisms involved in calcification, with the eventual goal of alternative preventative and therapeutic strategies. There is no sufficient animal model of CAVD, so we turn to potential in vitro models. In general, in vitro models have the advantages of shortened experiment time and better control over multiple variables compared to in vivo models. As with all models, the hypothesis being tested dictates the most important characteristics of the in vivo physiology to recapitulate. Here, we collate the relevant pieces of designing and evaluating aortic valve calcification so that investigators can more effectively draw significant conclusions from their results.

Gene expression profiling of biological pathway alterations by radiation exposure

Though damage caused by radiation has been the focus of rigorous research, the mechanisms through which radiation exerts harmful effects on cells are complex and not well-understood. In particular, the influence of low dose radiation exposure on the regulation of genes and pathways remains unclear. In an attempt to investigate the molecular alterations induced by varying doses of radiation, a genome-wide expression analysis was conducted. Peripheral blood mononuclear cells were collected from five participants and each sample was subjected to 0.5 Gy, 1 Gy, 2.5 Gy, and 5 Gy of cobalt 60 radiation, followed by array-based expression profiling. Gene set enrichment analysis indicated that the immune system and cancer development pathways appeared to be the major affected targets by radiation exposure. Therefore, 1 Gy radioactive exposure seemed to be a critical threshold dosage. In fact, after 1 Gy radiation exposure, expression levels of several genes including FADD, TNFRSF10B, TNFRSF8, TNFRSF10A, TNFSF10, TNFSF8, CASP1, and CASP4 that are associated with carcinogenesis and metabolic disorders showed significant alterations. Our results suggest that exposure to low-dose radiation may elicit changes in metabolic and immune pathways, potentially increasing the risk of immune dysfunctions and metabolic disorders.

Molecular biology of calcific aortic valve disease: towards new pharmacological therapies

Calcific aortic valve disease (CAVD) is a chronic process leading to fibrosis and mineralization of the aortic valve. Investigations in the last several years have emphasized that key underlying molecular processes are involved in the pathogenesis of CAVD. In this regard, the processing of lipids and their retention has been underlined as an important mechanism that triggers inflammation. In turn, inflammation promotes/enhances the mineralization of valve interstitial cells, the main cellular component of the aortic valve. On the other hand, transformation of valve interstitial cells into myofibroblasts and osteoblast-like cells is determined by several signaling pathways having reciprocal cross-talks. In addition, the mineralization of the aortic valve has been shown to rely on ectonucleotidase and purinergic signaling. In this review, the authors have highlighted key molecular underpinnings of CAVD that may have significant relevance for the development of novel pharmaceutical therapies.

Basic mechanisms of calcific aortic valve disease

Calcific aortic valve disease (CAVD) is the most common heart valve disorder. There is no medical treatment to prevent and/or promote the regression of CAVD. Hence, it is of foremost importance to delineate and understand the key basic underlying mechanisms involved in CAVD. In the past decade our comprehension of the underpinning processes leading to CAVD has expanded at a fast pace. Hence, our understanding of the basic pathobiological processes implicated in CAVD might lead eventually to the development of novel pharmaceutical therapies for CAVD. In this review, we discuss molecular processes that are implicated in fibrosis and mineralization of the aortic valve. Specifically, we address the role of lipid retention, inflammation, phosphate signalling and osteogenic transition in the development of CAVD. Interplays between these different processes and the key regulation pathways are discussed along with their clinical relevance.

The role of TNF-α and TNF superfamily members in the pathogenesis of calcific aortic valvular disease

Calcific aortic valve disease (CAVD) represents a slowly progressive pathologic process associated with major morbidity and mortality. The process is characterized by multiple steps: inflammation, fibrosis, and calcification. Numerous studies focalized on its physiopathology highlighting different "actors" for the multiple "acts." This paper focuses on the role of the tumor necrosis factor superfamily (TNFSF) members in the pathogenesis of CAVD. In particular, we discuss the clinical and experimental studies providing evidence of the involvement of tumor necrosis factor-alpha (TNF-α), receptor activator of nuclear factor-kappa B (NF-κB) ligand (RANKL), its membrane receptor RANK and its decoy receptor osteoprotegerin (OPG), and TNF-related apoptosis-inducing ligand (TRAIL) in valvular calcification.