Reciprocal interactions between mitral valve endothelial and interstitial cells reduce endothelial-to-mesenchymal transition and myofibroblastic activation

Lineage Tracing Identifies Dynamic Contribution of Endothelial Cells to Cardiac Valve Mesenchyme During Development

Heart valve disease is an important cause of morbidity and mortality among cardiac patients worldwide. However, the pathogenesis of heart valve disease is not clear, and a growing body of evidence hints at the importance of the genetic basis and developmental origins of heart valve disease. Therefore, understanding the developmental mechanisms that underlie the formation of heart valves has important implications for the diagnosis, prevention, and treatment of congenital heart disease. Endothelial to mesenchymal transition is a key step in initiating cardiac valve development. The dynamic changes in the relative localization and proportion of different cell sources in the heart valve mesenchymal population are still not fully understood. Here, we used the Cdh5-CreER;R26R-tdTomato mouse line to trace endocardial cushion-derived endothelial cells to explore the dynamic contribution of these cells to each layer of the valve during valve development. This is beneficial for elaborating on the role of endocardial cells in the process of valve remodeling from a precise angle.

FOXC1 and FOXC2 maintain mitral valve endothelial cell junctions, extracellular matrix, and lymphatic vessels to prevent myxomatous degeneration

Background

Mitral valve (MV) disease including myxomatous degeneration is the most common form of valvular heart disease with an age-dependent frequency. Genetic evidence indicates mutations of the transcription factor FOXC1 are associated with MV defects, including mitral valve regurgitation. In this study, we sought to determine whether murine Foxc1 and its closely related factor, Foxc2, are required in valvular endothelial cells (VECs) for the maintenance of MV leaflets, including VEC junctions and the stratified trilaminar extracellular matrix (ECM).

Methods

Adult mice carrying tamoxifen-inducible, endothelial cell (EC)-specific, compound Foxc1;Foxc2 mutations (i.e., EC-Foxc-DKO mice) were used to study the function of Foxc1 and Foxc2 in the maintenance of mitral valves. The EC-mutations of Foxc1/c2 were induced at 7 - 8 weeks of age by tamoxifen treatment, and abnormalities in the MVs of EC-Foxc-DKO mice were assessed via whole-mount immunostaining, immunohistochemistry, and Movat pentachrome/Masson's Trichrome staining.

Results

EC-deletions of Foxc1 and Foxc2 in mice resulted in abnormally extended and thicker mitral valves by causing defects in regulation of ECM organization with increased proteoglycan and decreased collagen. Notably, reticular adherens junctions were found in VECs of control MV leaflets, and these reticular structures were severely disrupted in EC-Foxc1/c2 mutant mice. PROX1, a key regulator in a subset of VECs on the fibrosa side of MVs, was downregulated in EC-Foxc1/c2 mutant VECs. Furthermore, we determined the precise location of lymphatic vessels in murine MVs, and these lymphatic vessels were aberrantly expanded in EC-Foxc1/c2 mutant mitral valves.

Conclusions

Our results indicate that Foxc1 and Foxc2 are required for maintaining the integrity of the MV, including VEC junctions, ECM organization, and lymphatic vessels to prevent myxomatous mitral valve degeneration.

Biology of mitral valve prolapse: from general mechanisms to advanced molecular patterns-a narrative review

Mitral valve prolapse (MVP) represents the most frequent cause of primary mitral regurgitation. For several years, biological mechanisms underlying this condition attracted the attention of investigators, trying to identify the pathways responsible for such a peculiar condition. In the last ten years, cardiovascular research has moved from general biological mechanisms to altered molecular pathways activation. Overexpression of TGF-β signaling, for instance, was shown to play a key role in MVP, while angiotensin-II receptor blockade was found to limit MVP progression by acting on the same signaling pathway. Concerning extracellular matrix organization, the increased valvular interstitial cells density and dysregulated production of catalytic enzymes (matrix metalloproteinases above all) altering the homeostasis between collagen, elastin and proteoglycan components, have been shown to possibly provide a mechanistic basis contributing to the myxomatous MVP phenotype. Moreover, it has been observed that high levels of osteoprotegerin may contribute to the pathogenesis of MVP by increasing collagen deposition in degenerated mitral leaflets. Although MVP is believed to represent the result of multiple genetic pathways alterations, it is important to distinguish between syndromic and non-syndromic conditions. In the first case, such as in Marfan syndrome, the role of specific genes has been clearly identified, while in the latter a progressively increasing number of genetic loci have been thoroughly investigated. Moreover, genomics is gaining more interest as potential disease-causing genes and loci possibly associated with MVP progression and severity have been identified. Animal models could be of help in better understanding the molecular basis of MVP, possibly providing sufficient information to tackle specific mechanisms aimed at slowing down MVP progression, therefore developing non-surgical therapies impacting on the natural history of this condition. Although continuous progress has been made in this field, further translational studies are advocated to improve our knowledge of biological mechanisms underlying MVP development and progression.

CD45 Is Sufficient to Initiate Endothelial-to-Mesenchymal Transition in Human Endothelial Cells-Brief Report

BACKGROUND

Endothelial-to-mesenchymal transition (EndMT) is a dynamic process in which endothelial cells acquire mesenchymal properties and in turn contribute to tissue remodeling and growth. Previously, we found EndMT associated with mitral valve adaptation after myocardial infarction. Furthermore, mitral valve endothelial cells collected at 6 months post-myocardial infarction expressed the pan-leukocyte marker CD45 and EndMT markers. Additionally, mitral valve endothelial cells induced to undergo EndMT with TGF (transforming growth factor)-β1 strongly coexpressed CD45 but not CD11b or CD14. Pharmacologic inhibition of the CD45 PTPase (protein tyrosine phosphatase) domain in mitral valve endothelial cells blocked TGFβ-induced EndMT. This prompted us to speculate that, downstream of TGFβ, CD45 induces EndMT.

METHODS

We activated the endogenous CD45 promoter in human endothelial colony forming cells (ECFCs) using CRISPR (cluster regularly interspaced short palindromic repeats)/inactive Cas9 (CRISPR-associated protein 9) transcriptional activation. Bulk RNA sequencing was performed on control ECFCs and CD45-positive ECFCs to identify transcriptomic changes. Three functional assays-cellular migration, collagen gel contraction, and transendothelial electrical resistance-were conducted to assess mesenchymal properties in CD45-positive ECFCs.

RESULTS

Activation of the endogenous CD45 promoter in ECFC and 3 additional sources of endothelial cells induced expression of several genes implicated in EndMT. In addition, CD45-positive ECFCs showed increased migration, a hallmark of EndMT, increased collagen gel contraction, a hallmark of mesenchymal cells, and decreased cell-cell barrier integrity, indicating reduced endothelial function.

CONCLUSIONS

CD45 is sufficient to incite an EndMT phenotype and acquisition of mesenchymal cell properties in normal human ECFCs. We speculate that CD45, through its C-terminal PTPase domain, initiates signaling events that drive EndMT.

Genetics and pathophysiology of mitral valve prolapse

Mitral valve prolapse (MVP) is a common condition affecting 2-3% of the general population, and the most complex form of valve pathology, with a complication rate up to 10-15% per year in advanced stages. Complications include mitral regurgitation which can lead to heart failure and atrial fibrillation, but also life-threatening ventricular arrhythmia and cardiovascular death. Sudden death has been recently brought to the forefront of MVP disease, increasing the complexity of management and suggesting that MVP condition is not properly understood. MVP can occur as part of syndromic conditions such as Marfan syndrome, but the most common form is non-syndromic, isolated or familial. Although a specific X-linked form of MVP was initially identified, autosomal dominant inheritance appears to be the primary mode of transmission. MVP can be stratified into myxomatous degeneration (Barlow), fibroelastic deficiency, and Filamin A-related MVP. While FED is still considered a degenerative disease associated with aging, myxomatous MVP and FlnA-MVP are recognized as familial pathologies. Deciphering genetic defects associated to MVP is still a work in progress; although FLNA, DCHS1, and DZIP1 have been identified as causative genes in myxomatous forms of MVP thanks to familial approaches, they explain only a small proportion of MVP. In addition, genome-wide association studies have revealed the important role of common variants in the development of MVP, in agreement with the high prevalence of this condition in the population. Furthermore, a potential genetic link between MVP and ventricular arrhythmia or a specific type of cardiomyopathy is considered. Animal models that allow to advance in the genetic and pathophysiological knowledge of MVP, and in particular those that can be easily manipulated to express a genetic defect identified in humans are detailed. Corroborated by genetic data and animal models, the main pathophysiological pathways of MVP are briefly addressed. Finally, genetic counseling is considered in the context of MVP.

Perspectives on pediatric congenital aortic valve stenosis: Extracellular matrix proteins, post translational modifications, and proteomic strategies

In heart valve biology, organization of the extracellular matrix structure is directly correlated to valve function. This is especially true in cases of pediatric congenital aortic valve stenosis (pCAVS), in which extracellular matrix (ECM) dysregulation is a hallmark of the disease, eventually leading to left ventricular hypertrophy and heart failure. Therapeutic strategies are limited, especially in pediatric cases in which mechanical and tissue engineered valve replacements may not be a suitable option. By identifying mechanisms of translational and post-translational dysregulation of ECM in CAVS, potential drug targets can be identified, and better bioengineered solutions can be developed. In this review, we summarize current knowledge regarding ECM proteins and their post translational modifications (PTMs) during aortic valve development and disease and contributing factors to ECM dysregulation in CAVS. Additionally, we aim to draw parallels between other fibrotic disease and contributions to ECM post-translational modifications. Finally, we explore the current treatment options in pediatrics and identify how the field of proteomics has advanced in recent years, highlighting novel characterization methods of ECM and PTMs that may be used to identify potential therapeutic strategies relevant to pCAVS.

The Role of Transforming Growth Factor-β Signaling in Myxomatous Mitral Valve Degeneration

Mitral valve prolapse (MVP) due to myxomatous degeneration is one of the most important chronic degenerative cardiovascular diseases in people and dogs. It is a common cause of heart failure leading to significant morbidity and mortality in both species. Human MVP is usually classified into primary or non-syndromic, including Barlow’s Disease (BD), fibro-elastic deficiency (FED) and Filamin-A mutation, and secondary or syndromic forms (typically familial), such as Marfan syndrome (MFS), Ehlers-Danlos syndrome, and Loeys–Dietz syndrome. Despite different etiologies the diseased valves share pathological features consistent with myxomatous degeneration. To reflect this common pathology the condition is often called myxomatous mitral valve degeneration (disease) (MMVD) and this term is universally used to describe the analogous condition in the dog. MMVD in both species is characterized by leaflet thickening and deformity, disorganized extracellular matrix, increased transformation of the quiescent valve interstitial cell (qVICs) to an activated state (aVICs), also known as activated myofibroblasts. Significant alterations in these cellular activities contribute to the initiation and progression of MMVD due to the increased expression of transforming growth factor-β (TGF-β) superfamily cytokines and the dysregulation of the TGF-β signaling pathways. Further understanding the molecular mechanisms of MMVD is needed to identify pharmacological manipulation strategies of the signaling pathway that might regulate VIC differentiation and so control the disease onset and development. This review briefly summarizes current understanding of the histopathology, cellular activities, molecular mechanisms and pathogenesis of MMVD in dogs and humans, and in more detail reviews the evidence for the role of TGF-β.

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.

Valvular Endothelial Cell Response to the Mechanical Environment-A Review

Heart valve leaflets are complex structures containing valve endothelial cells, interstitial cells, and extracellular matrix. Heart valve endothelial cells sense mechanical stimuli, and communicate amongst themselves and the surrounding cells and extracellular matrix to maintain tissue homeostasis. In the presence of abnormal mechanical stimuli, endothelial cell communication is triggered in defense and such processes may eventually lead to cardiac disease progression. This review focuses on the role of mechanical stimuli on heart valve endothelial surfaces-from heart valve development and maintenance of tissue integrity to disease progression with related signal pathways involved in this process.

Endothelial-Mesenchymal Transition in Cardiovascular Disease

Endothelial-to-mesenchymal transition is a dynamic process in which endothelial cells suppress constituent endothelial properties and take on mesenchymal cell behaviors. To begin the process, endothelial cells loosen their cell-cell junctions, degrade the basement membrane, and migrate out into the perivascular surroundings. These initial endothelial behaviors reflect a transient modulation of cellular phenotype, that is, a phenotypic modulation, that is sometimes referred to as partial endothelial-to-mesenchymal transition. Loosening of endothelial junctions and migration are also seen in inflammatory and angiogenic settings such that endothelial cells initiating endothelial-to-mesenchymal transition have overlapping behaviors and gene expression with endothelial cells responding to inflammatory signals or sprouting to form new blood vessels. Reduced endothelial junctions increase permeability, which facilitates leukocyte trafficking, whereas endothelial migration precedes angiogenic sprouting and neovascularization; both endothelial barriers and quiescence are restored as inflammatory and angiogenic stimuli subside. Complete endothelial-to-mesenchymal transition proceeds beyond phenotypic modulation such that mesenchymal characteristics become prominent and endothelial functions diminish. In proadaptive, regenerative settings the new mesenchymal cells produce extracellular matrix and contribute to tissue integrity whereas in maladaptive, pathologic settings the new mesenchymal cells become fibrotic, overproducing matrix to cause tissue stiffness, which eventually impacts function. Here we will review what is known about how TGF (transforming growth factor) β influences this continuum from junctional loosening to cellular migration and its relevance to cardiovascular diseases.

Integration of Functional Imaging, Cytometry, and Unbiased Proteomics Reveals New Features of Endothelial-to-Mesenchymal Transition in Ischemic Mitral Valve Regurgitation in Human Patients

Background: Following myocardial infarction, mitral regurgitation (MR) is a common complication. Previous animal studies demonstrated the association of endothelial-to-mesenchymal transition (EndMT) with mitral valve (MV) remodeling. Nevertheless, little is known about how MV tissue responds to ischemic heart changes in humans.

Methods: MVs were obtained by the Cardiothoracic Surgical Trials Network from 17 patients with ischemic mitral regurgitation (IMR). Echo-doppler imaging assessed MV function at time of resection. Cryosections of MVs were analyzed using a multi-faceted histology and immunofluorescence examination of cell populations. MVs were further analyzed using unbiased label-free proteomics. Echo-Doppler imaging, histo-cytometry measures and proteomic analysis were then integrated.

Results: MVs from patients with greater MR exhibited proteomic changes associated with proteolysis-, inflammatory- and oxidative stress-related processes compared to MVs with less MR. Cryosections of MVs from patients with IMR displayed activated valvular interstitial cells (aVICs) and double positive CD31+ αSMA+ cells, a hallmark of EndMT. Univariable and multivariable association with echocardiography measures revealed a positive correlation of MR severity with both cellular and geometric changes (e.g., aVICs, EndMT, leaflet thickness, leaflet tenting). Finally, proteomic changes associated with EndMT showed gene-ontology enrichment in vesicle-, inflammatory- and oxidative stress-related processes. This discovery approach indicated new candidate proteins associated with EndMT regulation in IMR.

Conclusion: We describe an atypical cellular composition and distinctive proteome of human MVs from patients with IMR, which highlighted new candidate proteins implicated in EndMT-related processes, associated with maladaptive MV fibrotic remodeling.

Tumor necrosis factor alpha and interleukin 1 beta suppress myofibroblast activation via nuclear factor kappa B signaling in 3D-cultured mitral valve interstitial cells

Mitral valve disease is a major cause of cardiovascular morbidity throughout the world. Many different mitral valve pathologies feature fibrotic remodeling, often accompanied by an inflammatory state. Mitral valve fibrosis is mediated by valvular interstitial cells (VICs), which reside in the valve leaflets and often differentiate into myofibroblast-like cells during disease conditions. In this study, we investigated the effects of tumor necrosis factor alpha (TNF-α) and interleukin 1 beta (IL-1β) on mitral VICs, since these pro-inflammatory cytokines have been shown to exert pleiotropic effects on various cell types in other fibrotic disorders. Using biomimetic three-dimensional culture systems, we demonstrated that TNF-α and IL-1β suppress myofibroblast differentiation in mitral VICs, as evidenced by gene and protein expression of alpha smooth muscle actin and smooth muscle 22 alpha. Addition of TNF-α and IL-1β also inhibited mitral VIC-mediated contraction of collagen gels. Furthermore, inhibition of NF-κB, which is downstream of TNF-α and IL-1β, reversed these effects. These results reveal targetable pathways for potential development of pharmaceutical treatments for alleviating fibrosis during mitral valve disease. STATEMENT OF SIGNIFICANCE: Mitral valve disease is a common cardiovascular condition that is often accompanied by fibrotic tissue remodeling. Valvular interstitial cells (VICs), the fibroblast-like cells that reside in heart valve leaflets, are thought to drive fibrosis during valve disease by differentiating into activated myofibroblasts. However, the signaling pathways that regulate this process in the mitral valve are not fully understood. In the present study, we cultured mitral VICs in collagen and poly(ethylene glycol) scaffolds designed to mimic the heart valve microenvironment and treated the cell-seeded scaffolds with cytokines. Using these 3D culture models, we found that the pro-inflammatory cytokines TNF-α and IL-1β downregulate myofibroblast and fibrosis markers in mitral VICs via the canonical NF-κB signaling pathway.

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

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

Dissecting Calcific Aortic Valve Disease-The Role, Etiology, and Drivers of Valvular Fibrosis

Calcific aortic valve disease (CAVD) is a highly prevalent and progressive disorder that ultimately causes gradual narrowing of the left ventricular outflow orifice with ensuing devastating hemodynamic effects on the heart. Calcific mineral accumulation is the hallmark pathology defining this process; however, fibrotic extracellular matrix (ECM) remodeling that leads to extensive deposition of fibrous connective tissue and distortion of the valvular microarchitecture similarly has major biomechanical and functional consequences for heart valve function. Significant advances have been made to unravel the complex mechanisms that govern these active, cell-mediated processes, yet the interplay between fibrosis and calcification and the individual contribution to progressive extracellular matrix stiffening require further clarification. Specifically, we discuss (1) the valvular biomechanics and layered ECM composition, (2) patterns in the cellular contribution, temporal onset, and risk factors for valvular fibrosis, (3) imaging valvular fibrosis, (4) biomechanical implications of valvular fibrosis, and (5) molecular mechanisms promoting fibrotic tissue remodeling and the possibility of reverse remodeling. This review explores our current understanding of the cellular and molecular drivers of fibrogenesis and the pathophysiological role of fibrosis in CAVD.

Chromatin Accessibility of Human Mitral Valves and Functional Assessment of MVP Risk Loci

RATIONALE

Mitral valve prolapse (MVP) is a common valvopathy that leads to mitral insufficiency, heart failure, and sudden death. Functional genomic studies in mitral valves are needed to better characterize MVP-associated variants and target genes.

OBJECTIVE

To establish the chromatin accessibility profiles and assess functionality of variants and narrow down target genes at MVP loci.

METHODS AND RESULTS

We mapped the open chromatin regions in nuclei from 11 human pathogenic and 7 nonpathogenic mitral valves by an assay for transposase-accessible chromatin with high-throughput sequencing. Open chromatin peaks were globally similar between pathogenic and nonpathogenic valves. Compared with the heart tissue and cardiac fibroblasts, we found that MV-specific assay for transposase-accessible chromatin with high-throughput sequencing peaks are enriched near genes involved in extracellular matrix organization, chondrocyte differentiation, and connective tissue development. One of the most enriched motifs in MV-specific open chromatin peaks was for the nuclear factor of activated T cells family of TFs (transcription factors) involved in valve endocardial and interstitial cell formation. We also found that MVP-associated variants were significantly enriched (P<0.05) in mitral valve open chromatin peaks. Integration of the assay for transposase-accessible chromatin with high-throughput sequencing data with risk loci, extensive functional annotation, and gene reporter assay suggest plausible causal variants for rs2641440 at the SMG6/SRR locus and rs6723013 at the IGFBP2/IGFBP5/TNS1 locus. CRISPR-Cas9 deletion of the sequence including rs6723013 in human fibroblasts correlated with increased expression only for TNS1. Circular chromatin conformation capture followed by high-throughput sequencing experiments provided evidence for several target genes, including SRR, HIC1, and DPH1 at the SMG6/SRR locus and further supported TNS1 as the most likely target gene on chromosome 2.

CONCLUSIONS

Here, we describe unprecedented genome-wide open chromatin profiles from human pathogenic and nonpathogenic MVs and report specific gene regulation profiles, compared with the heart. We also report in vitro functional evidence for potential causal variants and target genes at MVP risk loci involving established and new biological mechanisms. Graphic Abstract: A graphic abstract is available for this article.

Nitric oxide prevents aortic valve calcification by S-nitrosylation of USP9X to activate NOTCH signaling

Calcific aortic valve disease (CAVD) is an increasingly prevalent condition, and endothelial dysfunction is implicated in its etiology. We previously identified nitric oxide (NO) as a calcification inhibitor by its activation of NOTCH1, which is genetically linked to human CAVD. Here, we show NO rescues calcification by an S-nitrosylation-mediated mechanism in porcine aortic valve interstitial cells and single-cell RNA-seq demonstrated NO regulates the NOTCH pathway. An unbiased proteomic approach to identify S-nitrosylated proteins in valve cells found enrichment of the ubiquitin-proteasome pathway and implicated S-nitrosylation of USP9X (ubiquitin specific peptidase 9, X-linked) in NOTCH regulation during calcification. Furthermore, S-nitrosylated USP9X was shown to deubiquitinate and stabilize MIB1 for NOTCH1 activation. Consistent with this, genetic deletion of Usp9x in mice demonstrated CAVD and human calcified aortic valves displayed reduced S-nitrosylation of USP9X. These results demonstrate a previously unidentified mechanism by which S-nitrosylation-dependent regulation of a ubiquitin-associated pathway prevents CAVD.

Rheumatic Heart Valve Disease Pathophysiology and Underlying Mechanisms

Rheumatic heart valve disease (RHVD) is a post-infectious sequel of acute rheumatic fever resulting from an abnormal immune response to a streptococcal pharyngitis that triggers valvular damage. RHVD is the leading cause of cardiovascular death in children and young adults, mainly in women from low and middle-income countries. It is known that long-term inflammation and high degree of fibrosis leads to valve dysfunction due to anatomic disruption of the valve apparatus. However, since public and private investments in RHVD studies are practically inexistent the number of publications is scarce. This disease shows different natural history and clinical presentations as compared to other degenerative heart valve diseases. Although more than five decades passed after the pioneering studies on the pathogenesis of RHVD, it is still unclear how self-tolerance mechanisms fail in this disease, and how humoral and cellular inflammatory responses are interconnected. Despite that pathological mechanisms have been already proposed for RHVD, none of them are able to explain the preferential involvement of the mitral valve. This review focuses on pathophysiology and underlying mechanisms of RHVD.

The Endocardium and Heart Valves

Endocardial cells are specialized endothelial cells that, during embryogenesis, form a lining on the inside of the developing heart, which is maintained throughout life. Endocardial cells are an essential source for several lineages of the cardiovascular system including coronary endothelium, endocardial cushion mesenchyme, cardiomyocytes, mural cells, fibroblasts, liver vasculature, adipocytes, and hematopoietic cells. Alterations in the differentiation programs that give rise to these lineages has detrimental effects, including premature lethality or significant structural malformations present at birth. Here, we will review the literature pertaining to the contribution of endocardial cells to valvular, and nonvalvular lineages and highlight critical pathways required for these processes. The lineage differentiation potential of embryonic, and possibly adult, endocardial cells has therapeutic potential in the regeneration of damaged cardiac tissue or treatment of cardiovascular diseases.

Vascular calcification: New insights into endothelial cells

Vascular calcification, a common pathological basis of vascular disease, is caused by various diseases and is an independent risk factor for cardiovascular events. Therefore, elucidating the pathogenesis of vascular calcification has significant clinical benefits. It is generally believed that vascular calcification is similar to the processes of bone development and cartilage formation. The transformation of vascular smooth muscle cells into osteoblast- and chondrocyte-like cells is a key event. However, recent studies have found that under certain conditions, endothelial cells participate in vascular calcification via endothelial-mesenchymal transition, cytokine secretion, extracellular vesicle synthesis, angiogenesis regulation and hemodynamics. This review aims to explore the relationship between endothelial cells and vascular calcification and to provide a theoretical basis and new ideas for the active prevention and treatment of vascular calcification in the clinic.

Activation of activin/Smad2 and 3 signaling pathway and the&nbsp;potential involvement of endothelial‑mesenchymal transition in the valvular damage due to rheumatic heart disease

Rheumatic heart disease (RHD) is an autoimmune disease caused by rheumatic fever following group A hemolytic streptococcal infection and primarily affects the mitral valve. RHD is currently a major global health problem. However, the exact pathological mechanisms associated with RHD-induced cardiac valve damage remain to be elucidated. The endothelial-mesenchymal transition (EndMT) serves a key role in a number of diseases with an important role in cardiac fibrosis and the activin/Smad2 and 3 signaling pathway is involved in regulating the EndMT. Nevertheless, there are no studies to date, to the best of the authors' knowledge, investigating the association between RHD and EndMT. Thus, the aim of the current study was to investigate the potential role of EndMT in cardiac valve damage and assess whether activin/Smad2 and 3 signaling was activated during RHD-induced valvular injury in a rat model of RHD induced by inactivated Group A streptococci and complete Freund's adjuvant. Inflammation and fibrosis were assessed by hematoxylin and eosin and Sirius red staining. Serum cytokine and rheumatoid factor levels were measured using ELISA kits. Expression levels of activin/Smad2 and 3 signaling pathway-related factors [activin A, Smad2, Smad3, phosphorylated (p-)Smad2 and p-Smad3], EndMT-related factors [lymphoid enhancer factor-1 (LEF-1), Snail1, TWIST, zinc finger E-box-binding homeobox (ZEB)1, ZEB2, α smooth muscle actin (α-SMA) and type I collagen α 1 (COL1A1)], apoptosis-related markers (BAX and cleaved caspase-3) and valvular inflammation markers (NF-κB and p-NF-κB) were detected using reverse transcription-quantitative PCR and western blot analyses. Compared with the control group, the degree of valvular inflammation and fibrosis, serum levels of IL-6, IL-17, TNF-α and expression of apoptosis-related markers (BAX and cleaved caspase-3) and valvular inflammation marker (p-NF-κB), activin/Smad2 and 3 signaling pathway-related factors (activin A, p-Smad2 and p-Smad3), EndMT-related factors (LEF-1, Snail1, TWIST, ZEB 1, ZEB2, α-SMA and COL1A1) were significantly increased in the RHD group. These results suggested that the activin/Smad2 and 3 signaling pathway was activated during the development of valvular damage caused by RHD and that the EndMT is involved in RHD-induced cardiac valve damage.

Mechanisms of the Osteogenic Switch of Smooth Muscle Cells in Vascular Calcification: WNT Signaling, BMPs, Mechanotransduction, and EndMT

Characterized by the hardening of arteries, vascular calcification is the deposition of hydroxyapatite crystals in the arterial tissue. Calcification is now understood to be a cell-regulated process involving the phenotypic transition of vascular smooth muscle cells into osteoblast-like cells. There are various pathways of initiation and mechanisms behind vascular calcification, but this literature review highlights the wingless-related integration site (WNT) pathway, along with bone morphogenic proteins (BMPs) and mechanical strain. The process mirrors that of bone formation and remodeling, as an increase in mechanical stress causes osteogenesis. Observing the similarities between the two may aid in the development of a deeper understanding of calcification. Both are thought to be regulated by the WNT signaling cascade and bone morphogenetic protein signaling and can also be activated in response to stress. In a pro-calcific environment, integrins and cadherins of vascular smooth muscle cells respond to a mechanical stimulus, activating cellular signaling pathways, ultimately resulting in gene regulation that promotes calcification of the vascular extracellular matrix (ECM). The endothelium is also thought to contribute to vascular calcification via endothelial to mesenchymal transition, creating greater cell plasticity. Each of these factors contributes to calcification, leading to increased cardiovascular mortality in patients, especially those suffering from other conditions, such as diabetes and kidney failure. Developing a better understanding of the mechanisms behind calcification may lead to the development of a potential treatment in the future.

A New Role for the Aldosterone/Mineralocorticoid Receptor Pathway in the Development of Mitral Valve Prolapse

RATIONALE

Mitral valve prolapse (MVP) is one of the most common valvular disorders. However, the molecular and cellular mechanisms involved in fibromyxomatous changes in the mitral leaflet tissue have not been elucidated. Aldosterone (Aldo) promotes fibrosis in myocardium, and MR (mineralocorticoid receptor) antagonists (MRAs) improve cardiac function by decreasing cardiac fibrosis.

OBJECTIVE

We investigated the role of the Aldo/MR in the fibromyxomatous modifications associated with MVP.

METHODS AND RESULTS

Aldo enhanced valvular interstitial cell activation markers and induced endothelial-mesenchymal transition in valvular endothelial cells, resulting in increased proteoglycan secretion. MRA blocked all the above effects. Cytokine arrays showed CT-1 (cardiotrophin-1) to be a mediator of Aldo-induced valvular interstitial cell activation and proteoglycan secretion and CD (cluster of differentiation) 14 to be a mediator of Aldo-induced endothelial-mesenchymal transition and proteoglycan secretion in valvular endothelial cells. In an experimental mouse model of MVP generated by nordexfenfluramine administration, MRA treatment reduced mitral valve thickness and proteoglycan content. Endothelial-specific MR deletion prevented fibromyxomatous changes induced by nordexfenfluramine administration. Moreover, proteoglycan expression was slightly lower in the mitral valves of MVP patients treated with MRA.

CONCLUSIONS

These findings demonstrate, for the first time, that the Aldo/MR pathway regulates the phenotypic, molecular, and histological changes of valvular interstitial cells and valvular endothelial cells associated with MVP development. MRA treatment appears to be a promising option to reduce fibromyxomatous alterations in MVP.

Reassessing endothelial-to-mesenchymal transition in cardiovascular diseases

Endothelial cells and mesenchymal cells are two different cell types with distinct morphologies, phenotypes, functions, and gene profiles. Accumulating evidence, notably from lineage-tracing studies, indicates that the two cell types convert into each other during cardiovascular development and pathogenesis. During heart development, endothelial cells transdifferentiate into mesenchymal cells in the endocardial cushion through endothelial-to-mesenchymal transition (EndoMT), a process that is critical for the formation of cardiac valves. Studies have also reported that EndoMT contributes to the development of various cardiovascular diseases, including myocardial infarction, cardiac fibrosis, valve calcification, endocardial elastofibrosis, atherosclerosis, and pulmonary arterial hypertension. Conversely, cardiac fibroblasts can transdifferentiate into endothelial cells and contribute to neovascularization after cardiac injury. However, progress in genetic lineage tracing has challenged the role of EndoMT, or its reversed programme, in the development of cardiovascular diseases. In this Review, we discuss the caveats of using genetic lineage-tracing technology to investigate cell-lineage conversion; we also reassess the role of EndoMT in cardiovascular development and diseases and elaborate on the molecular signals that orchestrate EndoMT in pathophysiological processes. Understanding the role and mechanisms of EndoMT in diseases will unravel the therapeutic potential of targeting this process and will provide a new paradigm for the development of regenerative medicine to treat cardiovascular diseases.

Evaluation of canine 2D cell cultures as models of myxomatous mitral valve degeneration

The utility of cells cultured from the mitral valve as models of myxomatous diseases needs to be properly validated. In this study valve interstitial cells (VICs) and valve endothelial cells (VECs) were cultured from normal and diseased canine mitral valves in 2% (v/v) or 10% FBS media, in the presence of TGFβ1, 2 and 3, the TGFβ RI kinase inhibitor SB431542 and TGFβ neutralising antibodies, 5HT and the 5HT2RB antagonist LY272015. Cultures were examined by morphology, transcriptomic profiling, protein expression of the cell specific markers αSMA and SM22α (VICs), and CD31 (VECs), deposition of proteoglycans (PG), the PG versican, and the TGFβs themselves. VECs derived from normal valves were CD31+/αSMA-, but those from diseased valves were αSMA+, indicating endothelial-to-mesenchymal (EndoMT) transition had occurred. The TGFβs induced EndoMT in normal VECs, and this was abolished by SB431542, with significant changes in αSMA, CD31 and HAS2 expression (P<0.05). Normal VICs cultured in 10% FBS media were αSMA+ (activated myofibroblast (disease) phenotype), but were αSMA- when grown in 2% FBS. VICs from diseased dogs were αSMA+ in 2% FBS (retention of the activated myofibroblast disease phenotype), with significantly increased TGFβ1 expression (P<0.05) compared to normal cells. Treatment of normal and diseased VICs with the TGFβs significantly increased expression of αSMA, SM22α, versican, the TGFβs themselves, and deposition of PGs (P<0.05), with TGFβ1 being the most potent activator. These effects were either abolished or markedly reduced by SB431542 and a pan-TGFβ neutralizing antibody (P<0.05). SB431542 also markedly reduced αSMA expression in VICs from diseased valves, but 5HT and LY272015 had no effect on VIC phenotype. Transcriptomic profiling identified clear differences in gene expression for the different conditions and treatments that partially matched that seen in native diseased valve tissue, including changes in expression of ACTA2 (αSMA), 5HTR2B, TAGLN (SM22α) and MYH10 (SMemb), gene ontology terms and canonical signalling pathways. Normal and diseased VICs and normal VECs from canine mitral valves can be successfully grown in culture with retention of phenotype, which can be manipulated using TGFβ1 and the TGFβ RI kinase inhibitor SB431542. This optimized cell system can now be used to model MMVD to elucidate disease mechanisms and identify key regulators of disease progression.

Endothelial Dysfunction in Patients with Severe Mitral Regurgitation

Mitral valve prolapse (MVP) is the most common cause of severe mitral regurgitation. It has been reported that MVP patients—candidates for mitral valve repair (MVRep)—showed an alteration in the antioxidant defense systems as well as in the L-arginine metabolic pathway. In this study, we investigate if oxidative stress and endothelial dysfunction are an MVP consequence or driving factors. Forty-five patients undergoing MVRep were evaluated before and 6 months post surgery and compared to 29 controls. Oxidized (GSSG) and reduced (GSH) forms of glutathione, and L-arginine metabolic pathway were analyzed using liquid chromatography-tandem mass spectrometry methods while osteoprotegerin (OPG) through the ELISA kit and circulating endothelial microparticles (EMP) by flow cytometry. Six-month post surgery, in MVP patients, the GSSG/GSH ratio decreased while symmetric and asymmetric dimethylarginines levels remained comparable to the baseline. Conversely, OPG levels significantly increased when compared to their baseline. Finally, pre-MVRep EMP levels were significantly higher in patients than in controls and did not change post surgery. Overall, these results highlight that MVRep completely restores the increased oxidative stress levels, as evidenced in MVP patients. Conversely, no amelioration of endothelial dysfunction was evidenced after surgery. Thus, therapies aimed to restore a proper endothelial function before and after surgical repair could benefit MVP patients.

The effect of physiological stretch and the valvular endothelium on mitral valve proteomes

IMPACT STATEMENT

This work is important to the field of heart valve pathophysiology as it provides new insights into molecular markers of mechanically induced valvular degeneration as well as the protective role of the valvular endothelium. These discoveries reported here advance our current knowledge of the valvular endothelium and how its removal essentially takes valve leaflets into an environmental shock. In addition, it shows that static conditions represent a mild pathological state for valve leaflets, while 10% cyclic stretch provides valvular cell quiescence. These findings impact the field by informing disease stages and by providing potential new drug targets to reverse or slow down valvular change before it affects cardiac function.

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.

Pathological Remodeling of Mitral Valve Leaflets from Unphysiologic Leaflet Mechanics after Undersized Mitral Annuloplasty to Repair Ischemic Mitral Regurgitation

Background Undersized ring annuloplasty is a commonly used surgical repair for ischemic mitral regurgitation, in which annular downsizing corrects regurgitation, but alters valve geometry and elevates tissue stresses. In this study, we investigated if unphysiological leaflet kinematics after annuloplasty might cause pathogenic biological remodeling of the mitral valve leaflets, and if preserving physiologic leaflet kinematics with a better technique can moderate such adverse remodeling. Methods and Results Twenty-nine swine were induced with ischemic mitral regurgitation, and survivors were assigned to groups: 7 underwent annuloplasty, 12 underwent annuloplasty with papillary-muscle approximation, 6 underwent papillary-muscle approximation, and 3 were sham controls. Pre-and post-surgery leaflet kinematics were measured, and valve tissue was explanted after 3 months to assess biological changes. Anterior leaflet excursion was unchanged across groups, but persistent tethering was observed with annuloplasty. Posterior leaflet was vertically immobile after annuloplasty, better mobile with the combined approach, and substantially ( P=0.0028) mobile after papillary-muscle approximation. Procollagen-1 was higher in leaflets from annuloplasty compared with the other groups. Heat shock protein-47 and lysyl oxidase were higher in groups receiving annuloplasty compared with sham. α- SMA was elevated in leaflets from animals receiving an annuloplasty, indicating activation of quiescent valve interstitial cells, paralleled by elevated transforming growth factor-β expression. Conclusions This is the first study to demonstrate that surgical valve repairs that impose unphysiological leaflet mechanics have a deleterious, pathological impact on valve biology. Surgeons may need to consider restoring physiologic leaflet stresses as well as valve competence, while also exploring pharmacological methods to inhibit the abnormal signaling cascades.

Endothelial Cell Lineage Analysis Does Not Provide Evidence for EMT in Adult Valve Homeostasis and Disease

Epithelial-to-mesenchymal transition (EMT) enables stationary epithelial cells to exhibit migratory behavior and is the key step that initiates heart valve development. Recent studies suggest that EMT is reactivated in the pathogenesis of myxomatous valve disease (MVD), a condition that involves the progressive degeneration and thickening of valve leaflets. These studies have been limited to in vitro experimentation and reliance on histologic costaining of epithelial and mesenchymal markers as evidence of EMT in mouse and sheep models of valve disease. However, longitudinal analysis of cell lineage origins and potential pathogenic or reparative contributions of newly generated mesenchymal cells have not been reported previously. In this study, a genetic lineage tracing strategy was pursued by irreversibly labeling valve endothelial cells in the Osteogenesis imperfecta and Marfan syndrome mouse models to determine whether they undergo EMT during valve disease. Tie2-CreER ^T2 and Cdh5(PAC)-CreER ^T2 mouse lines were used in combination with colorimetric and fluorescent reporters for longitudinal assessment of endothelial cells. These lineage tracing experiments showed no evidence of EMT during adult valve homeostasis or valve pathogenesis. Additionally, CD31 and smooth muscle α-actin (αSMA) double-positive cells, used as an indicator of EMT, were not detected, and levels of EMT transcription factors were not altered. Interestingly, contrary to the endothelial cell-specific Cdh5(PAC)-CreER ^T2 driver line, Tie2-CreER ^T2 lineage-derived cells in diseased heart valves also included CD45+ leukocytes. Altogether, our data indicate that EMT is not a feature of valve homeostasis and disease but that increased immune cells may contribute to MVD. Anat Rec, 302:125-135, 2019. © 2018 Wiley Periodicals, Inc.

A Three-Dimensional Collagen-Elastin Scaffold for Heart Valve Tissue Engineering

Since most of the body's extracellular matrix (ECM) is composed of collagen and elastin, we believe the choice of these materials is key for the future and promise of tissue engineering. Once it is known how elastin content of ECM guides cellular behavior (in 2D or 3D), one will be able to harness the power of collagen-elastin microenvironments to design and engineer stimuli-responsive tissues. Moreover, the implementation of such matrices to promote endothelial-mesenchymal transition of primary endothelial cells constitutes a powerful tool to engineer 3D tissues. Here, we design a 3D collagen-elastin scaffold to mimic the native ECM of heart valves, by providing the strength of collagen layers, as well as elasticity. Valve interstitial cells (VICs) were encapsulated in the collagen-elastin hydrogels and valve endothelial cells (VECs) cultured onto the surface to create an in vitro 3D VEC-VIC co-culture. Over a seven-day period, VICs had stable expression levels of integrin β1 and F-actin and continuously proliferated, while cell morphology changed to more elongated. VECs maintained endothelial phenotype up to day five, as indicated by low expression of F-actin and integrin β1, while transformed VECs accounted for less than 7% of the total VECs in culture. On day seven, over 20% VECs were transformed to mesenchymal phenotype, indicated by increased actin filaments and higher expression of integrin β1. These findings demonstrate that our 3D collagen-elastin scaffolds provided a novel tool to study cell-cell or cell-matrix interactions in vitro, promoting advances in the current knowledge of valvular endothelial cell mesenchymal transition.

Resistance a major hindrance to chemotherapy in hepatocellular carcinoma: an insight

Hepatocellular carcinoma (HCC) is one of the leading causes of cancer mortality, accounting for almost 90% of total liver cancer burden. Surgical resection followed by adjuvant and systemic chemotherapy are the most meticulously followed treatment procedures but the complex etiology and high metastatic potential of the disease renders surgical treatment futile in majority of the cases. Another hindrance to the scenario is the acquired resistance to drugs resulting in relapse of the disease. Hence, to provide insights into development of novel therapeutic targets and diagnostic biomarkers, this review focuses on the various molecular mechanisms underlying chemoresistance in HCC. We have provided a comprehensive summary of the various strategies adopted by HCC cells, extending from apoptosis evasion, autophagy activation, drug expulsion to epigenetic transformation as modes of therapy resistance. The role of stem cells in imparting chemoresistance is also discussed. Furthermore, the review also focuses on how this knowledge might be exploited for the development of an effective, prospective therapy against HCC.

Different Notch signaling in cells from calcified bicuspid and tricuspid aortic valves

AIMS

Calcific aortic valve disease is the most common heart valve disease in the Western world. Bicuspid and tricuspid aortic valve calcifications are traditionally considered together although the dynamics of the disease progression is different between the two groups of patients. Notch signaling is critical for bicuspid valve development and NOTCH1 mutations are associated with bicuspid valve and calcification. We hypothesized that Notch-dependent mechanisms of valve mineralization might be different in the two groups.

METHODS AND RESULTS

We used aortic valve interstitial cells and valve endothelial cells from patients with calcific aortic stenosis with bicuspid or tricuspid aortic valve. Expression of Notch-related genes in valve interstitial cells by qPCR was different between bicuspid and tricuspid groups. Discriminant analysis of gene expression pattern in the interstitial cells revealed that the cells from calcified bicuspid valves formed a separate group from calcified tricuspid and control cells. Interstitial cells from bicuspid calcified valves demonstrated significantly higher sensitivity to stimuli at early stages of induced proosteogenic differentiation and were significantly more sensitive to the activation of proosteogenic OPN, ALP and POSTIN expression by Notch activation. Notch-activated endothelial-to-mesenchymal transition and the corresponding expression of HEY1 and SLUG were also more prominent in bicuspid valve derived endothelial cells compared to the cells from calcified tricuspid and healthy valves.

CONCLUSION

Early signaling events including Notch-dependent mechanisms that are responsible for the initiation of aortic valve calcification are different between the patients with bicuspid and tricuspid aortic valves.

A survey of membrane receptor regulation in valvular interstitial cells cultured under mechanical stresses

Degenerative valvular diseases have been linked to the action of abnormal forces on valve tissues during each cardiac cycle. It is now accepted that the degenerative behavior of valvular cells can be induced mechanically in vitro. This approach of in vitro modeling of valvular cells in culture constitutes a powerful tool to study, characterize, and develop predictors of heart valve degeneration in vivo. Using such in vitro systems, we expect to determine the exact signaling mechanisms that trigger and mediate propagation of degenerative signals. In this study, we aim to uncover the role of mechanosensing proteins on valvular cell membranes. These can be cell receptors and triggers of downstream pathways that are activated upon the action of cyclical tensile strains in pathophysiological conditions. In order to identify mechanosensors of tensile stresses on valvular interstitial cells, we employed biaxial cyclic strain of valvular cells in culture and quantitatively evaluated the expression of cell membrane proteins using a targeted protein array and interactome analyses. This approach yielded a high-throughput screening of all cell surface proteins involved in sensing mechanical stimuli. In this study, we were able to identify the cell membrane proteins which are activated during physiological cyclic tensile stresses of valvular cells. The proteins identified in this study were clustered into four interactomes, which included CC chemokine ligands, thrombospondin (adhesive glycoproteins), growth factors, and interleukins. The expression levels of these proteins generally indicated that cells tend to increase adhesive efforts to counteract the action of mechanical forces. This is the first study of this kind used to comprehensively identify the mechanosensitive proteins in valvular cells.

Activated hepatic stellate cells play pivotal roles in hepatocellular carcinoma cell chemoresistance and migration in multicellular tumor spheroids

Most Hepatocellular carcinoma (HCC) are resistant to conventional chemotherapeutic agents and remain an unmet medical need. Recently, multiple studies on the crosstalk between HCC and their tumor microenvironment have been conducted to overcome chemoresistance in HCC. In this study, we formed multicellular tumor spheroids (MCTS) to elucidate the mechanisms of environment-mediated chemoresistance in HCC. We observed that hepatic stellate cells (HSCs) in MCTS significantly increased the compactness of spheroids and exhibited strong resistance to sorafenib and cisplatin relative to other types of stromal cells. Increased collagen 1A1 (COL1A1) expression was apparent in activated HSCs but not in fibroblasts or vascular endothelial cells in MCTS. Additionally, COL1A1 deficiency, which was increased by co-culture with HSCs, decreased the cell-cell interactions and thereby increased the therapeutic efficacy of anticancer therapies in MCTS. Furthermore, losartan, which can inhibit collagen I synthesis, attenuated the compactness of spheroids and increased the therapeutic efficacy of anticancer therapies in MCTS. Meanwhile, activated HSCs facilitated HCC migration by upregulating matrix metallopeptidase 9 (MMP9) in MCTS. Collectively, crosstalk between HCC cells and HSCs promoted HCC chemoresistance and migration by increasing the expression of COL1A1 and MMP9 in MCTS. Hence, targeting HSCs might represent a promising therapeutic strategy for liver cancer therapy.

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

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

The mechanisms, diagnosis and management of mitral regurgitation in mitral valve prolapse and hypertrophic cardiomyopathy

Valvular disease is a frequent cardiac pathology leading to heart failure and, ultimately, death. Mitral regurgitation, defined as the inability of the two mitral leaflets to coapt, is a common valvular disease and a self sustained pathology. A better understanding of the mitral valve histological layers provides a better understanding of the leaflet and chordae changes in mitral valve prolapse. Mitral valve prolapse may occur in myxomatous degenerative abnormalities, connective tissue disorders or in sporadic isolated cases. It is the most common mitral abnormality of non-ischemic cause leading to severe surgery-requiring mitral regurgitation. In addition to standard echocardiographic investigations, newly implemented three-dimensional techniques are being used and they permit a better visualisation, from the so-called ‘surgical view’, and an improved evaluation of the mitral valve. Hypertrophic cardiomyopathy is the most frequent inherited myocardial disease caused by mutations in various genes encoding proteins of the cardiac sarcomere, leading to a marked left ventricular hypertrophy unexplained by other comorbidities. The pathological echocardiographic hallmarks of hypertrophic cardiomyopathy are left ventricular hypertrophy, left ventricular outflow tract obstruction and systolic anterior motion of the mitral valve. The systolic anterior motion of the mitral valve contributes to the development of mitral regurgitation and further narrows the left ventricular outflow tract, leading to more severe symptomatology. Cardiac magnetic resonance imaging accurately measures the left ventricular mass, the degree of diastolic function and it may also be used to distinguish phenotypic variants. The clinical outcome of patients with these pathologies is mostly determined by the selected option of treatment. The purpose of surgical correction regarding mitral valve involvement is to restore valvular competence. Surgery has proven to be the only useful treatment in preventing heart failure, improving symptomatology and reducing mortality. Our approach wishes to enhance the understanding of the mitral valve’s involvement in hypertrophic cardiomyopathy and mitral valve prolapse from genetic, haemodynamic and clinical perspectives, as well as to present novelties in the grand field of treatment.

Mitral valve endothelial cells secrete osteoprotegerin during endothelial mesenchymal transition

AIMS

Mitral valve prolapse (MVP) has a prevalence of 3% in the general population, affecting >176 million people worldwide. Despite this, little is known about the molecular and cellular mechanisms involved in the progression of MVP and surgical intervention is the only available option. In this study we investigated the role of osteoprotegerin (OPG) during endothelial to mesenchymal transition (EndMT) in MVP.

METHODS AND RESULTS

VECs and VICs were isolated from posterior mitral valve leaflets of patients undergoing mitral valve repair (n=25). Plasma was collected from 57 subjects (29 controls and 28 MVP patients). Overexpression of OPG during EndMT followed by autocrine effects characterised by reactive oxygen species increment and accelerated migration was documented. In addition, OPG increased VIC proliferation. Finally, OPG plasma levels were significantly higher in MVP patients compared to control subjects and the area under the ROC curve was 0.92.

CONCLUSION

EndMT has been recognised as a possible pathological mechanism for MVP. For the first time, we report the involvement of OPG in cellular and molecular changes in MVP isolated cells. In addition, we detected elevated circulating OPG levels in MVP patients when compared to controls, which supports the hypothesis that OPG is involved in MVP development and progression.

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.

Valve Interstitial Cells Act in a Pericyte Manner Promoting Angiogensis and Invasion by Valve Endothelial Cells

Neovascularization is an understudied aspect of calcific aortic valve disease (CAVD). Within diseased valves, cells along the neovessels' periphery stain for pericyte markers, but it is unclear whether valvular interstitial cells (VICs) can demonstrate a pericyte-like phenotype. This investigation examined the perivascular potential of VICs to regulate valve endothelial cell (VEC) organization and explored the role of Angiopoeitin1-Tie2 signaling in this process. Porcine VECs and VICs were fluorescently tracked and co-cultured in Matrigel over 7 days. VICs regulated early VEC network organization in a ROCK-dependent manner, then guided later VEC network contraction through chemoattraction. Unlike vascular control cells, the valve cell cultures ultimately formed invasive spheroids with 3D angiogenic-like sprouts. VECs co-cultured with VICs displayed significantly more invasion than VECs alone; with VICs generally leading and wrapping around VEC invasive sprouts. Lastly, Angiopoietin1-Tie2 signaling was found to regulate valve cell organization during VEC/VIC spheroid formation and invasion. VICs demonstrated pericyte-like behaviors toward VECs throughout sustained co-culture. The change from a vasculogenic network to an invasive sprouting spheroid suggests that both cell types undergo phenotypic changes during long-term culture in the model angiogenic environment. Valve cells organizing into spheroids and undergoing 3D invasion of Matrigel demonstrated several typical angiogenic-like phenotypes dependent on basal levels of Angiopoeitin1-Tie2 signaling and ROCK activation. These results suggest that the ectopic sustained angiogenic environment during the early stages of valve disease promotes organized activity by both VECs and VICs, contributing to neovessel formation and the progression of CAVD.

Comparison of cellular changes in Cavalier King Charles spaniel and mixed breed dogs with myxomatous mitral valve disease

INTRODUCTION

The aim of this study was to determine if there are differences in cellular changes in Cavalier King Charles spaniel (CKCS) myxomatous mitral valves compared to non-CKCS dogs.

ANIMALS

Cavalier King Charles spaniels (n = 6) and age-matched mixed breed (n = 6) with severe myxomatous mitral valve disease (MMVD), and normal mixed breed (n = 4) dogs.

MATERIALS AND METHODS

Immunohistochemistry staining and qualitative and quantitative analysis of mitral valves sections, examining for the presence of CD11c and CD45, vimentin, alpha smooth muscle actin (α-SMA) and embryonic smooth muscle myosin heavy chain (Smemb), von Willebrand factor and CD31 and Ki-67.

RESULTS

Vimentin positive cell numbers were increased in the MMVD dogs and distributed throughout the valve with greatest density close to the endothelium. There were no significant differences in cell marker expression for the two diseased groups, but cell numbers were significantly increased compared to controls for α-SMA (CKCS only) and Smemb (CKCS and mixed breed: p < 0.05). Alpha smooth muscle actin+ cells were primarily located at the valve edge, with Smemb+ cells similarly located, but also present throughout the valve stroma. A small number of cells close to the valve edge co-expressed α-SMA and Smemb. Endothelial von Willebrand factor expression was identified in all valves, with evidence of disrupted endothelium in the diseased, but was also found in diseased valve stroma. There was no staining for CD11c, CD45 or CD31 in any valve. Ki-67+ cells formed linear clusters at the leaflet tip and were sparsely distributed throughout both myxomatous valve groups.

CONCLUSIONS

The cellular changes notes with advanced stage MMVD appear similar for CKCS when compared to mixed breed dogs.

Mitral valve disease--morphology and mechanisms

Mitral valve disease is a frequent cause of heart failure and death. Emerging evidence indicates that the mitral valve is not a passive structure, but--even in adult life--remains dynamic and accessible for treatment. This concept motivates efforts to reduce the clinical progression of mitral valve disease through early detection and modification of underlying mechanisms. Discoveries of genetic mutations causing mitral valve elongation and prolapse have revealed that growth factor signalling and cell migration pathways are regulated by structural molecules in ways that can be modified to limit progression from developmental defects to valve degeneration with clinical complications. Mitral valve enlargement can determine left ventricular outflow tract obstruction in hypertrophic cardiomyopathy, and might be stimulated by potentially modifiable biological valvular-ventricular interactions. Mitral valve plasticity also allows adaptive growth in response to ventricular remodelling. However, adverse cellular and mechanobiological processes create relative leaflet deficiency in the ischaemic setting, leading to mitral regurgitation with increased heart failure and mortality. Our approach, which bridges clinicians and basic scientists, enables the correlation of observed disease with cellular and molecular mechanisms, leading to the discovery of new opportunities for improving the natural history of mitral valve disease.

Dynamic Heterogeneity of the Heart Valve Interstitial Cell Population in Mitral Valve Health and Disease

The heart valve interstitial cell (VIC) population is dynamic and thought to mediate lay down and maintenance of the tri-laminar extracellular matrix (ECM) structure within the developing and mature valve throughout life. Disturbances in the contribution and distribution of valve ECM components are detrimental to biomechanical function and associated with disease. This pathological process is associated with activation of resident VICs that in the absence of disease reside as quiescent cells. While these paradigms have been long standing, characterization of this abundant and ever-changing valve cell population is incomplete. Here we examine the expression pattern of Smooth muscle α-actin, Periostin, Twist1 and Vimentin in cultured VICs, heart valves from healthy embryonic, postnatal and adult mice, as well as mature valves from human patients and established mouse models of disease. We show that the VIC population is highly heterogeneous and phenotypes are dependent on age, species, location, and disease state. Furthermore, we identify phenotypic diversity across common models of mitral valve disease. These studies significantly contribute to characterizing the VIC population in health and disease and provide insights into the cellular dynamics that maintain valve structure in healthy adults and mediate pathologic remodeling in disease states.