Hearts and bones: shared regulatory mechanisms in heart valve, cartilage, tendon, and bone development

Anatomy, Histology, Aetiology, Development and Functions of Cartilago Cordis: A Systematic Review

INTRODUCTION

The cartilago cordis is a structure present within the cardiac skeleton of some, but not all, vertebrate species. This systematic review compared the presence, structure, and function of the cartilago cordis from published works covering all vertebrate species.

METHODS

Literature searches were conducted to obtain information relating to the anatomical location, morphology, prevalence, number of structures, development, and function.

RESULTS

The cartilago cordis was most commonly composed of hyaline cartilage but its location within the cardiac skeleton, anatomical, and histological structure varied between species. The cartilago cordis has not been documented in every vertebrate species, or every individual within each species, but it is present in 68 vertebrates including an amphibian, and some mammals, reptiles, and birds. The function of the cartilago cordis is unknown, but theories have ranged from an adaptive mechanism to support cardiac tissue through to roles in conduction and contraction, especially in areas of high mechanical stress. Possible links between the presence of a cartilago cordis and cardiac pathologies were also identified.

CONCLUSION

The cartilago cordis varied in prevalence, structure, and location; further research is required to understand the function and development. In addition, it is possible there are more vertebrate species containing cartilago cordis than presently known about given its varying prevalence and sometimes small size.

Systematic analysis identifies a connection between spatial and genomic variations of chromatin states

Chromatin states play important roles in the maintenance of cell identities, yet their spatial patterns remain poorly characterized at the organism scale. We developed a systematic approach to analyzing spatial epigenomic data and then applied it to a recently published spatial-CUT&Tag dataset that was obtained from a mouse embryo. We identified a set of spatial genes whose H3K4me3 patterns delineate tissue boundaries. These genes are enriched with tissue-specific transcription factors, and their corresponding genomic loci are marked by broad H3K4me3 domains. Integrative analysis with H3K27me3 profiles showed coordinated spatial transitions across tissue boundaries, which is marked by the continuous shortening of H3K4me3 domains and expansion of H3K27me3 domains. Motif-based analysis identified transcription factors whose activities change significantly during such transitions. Taken together, our systematic analyses reveal a strong connection between the genomic and spatial variations of chromatin states. A record of this paper's transparent peer review process is included in the supplemental information.

A Meta-Analysis Approach to Gene Regulatory Network Inference Identifies Key Regulators of Cardiovascular Diseases

Cardiovascular diseases (CVDs) represent a major concern for global health, whose mechanistic understanding is complicated by a complex interplay between genetic predisposition and environmental factors. Specifically, heart failure (HF), encompassing dilated cardiomyopathy (DC), ischemic cardiomyopathy (ICM), and hypertrophic cardiomyopathy (HCM), is a topic of substantial interest in basic and clinical research. Here, we used a Partial Correlation Coefficient-based algorithm (PCC) within the context of a meta-analysis framework to construct a Gene Regulatory Network (GRN) that identifies key regulators whose activity is perturbed in Heart Failure. By integrating data from multiple independent studies, our approach unveiled crucial regulatory associations between transcription factors (TFs) and structural genes, emphasizing their pivotal roles in regulating metabolic pathways, such as fatty acid metabolism, oxidative stress response, epithelial-to-mesenchymal transition, and coagulation. In addition to known associations, our analysis also identified novel regulators, including the identification of TFs FPM315 and OVOL2, which are implicated in dilated cardiomyopathies, and TEAD1 and TEAD2 in both dilated and ischemic cardiomyopathies. Moreover, we uncovered alterations in adipogenesis and oxidative phosphorylation pathways in hypertrophic cardiomyopathy and discovered a role for IL2 STAT5 signaling in heart failure. Our findings underscore the importance of TF activity in the initiation and progression of cardiac disease, highlighting their potential as pharmacological targets.

ADAMTSL2 mutations determine the phenotypic severity in geleophysic dysplasia

Geleophysic dysplasia-1 (GD1) is an autosomal recessive disorder caused by ADAMTS-like 2 (ADAMTSL2) variants. It is characterized by distinctive facial features, limited joint mobility, short stature, brachydactyly, and life-threatening cardiorespiratory complications. The clinical spectrum spans from perinatal lethality to milder adult phenotypes. We developed and characterized cellular and mouse models, to replicate the genetic profile of a patient who is compound heterozygous for 2 ADAMTSL2 variants, namely p.R61H and p.A165T. The impairment of ADAMTSL2 secretion was observed in both variants, but p.A165T exhibited a more severe impact. Mice carrying different allelic combinations revealed a spectrum of phenotypic severity, from lethality in knockout homozygotes to mild growth impairment observed in adult p.R61H homozygotes. Homozygous and hemizygous p.A165T mice survived but displayed severe respiratory and cardiac dysfunction. The respiratory dysfunction mainly affected the expiration phase, and some of these animals had microscopic post-obstructive pneumonia. Echocardiograms and MRI studies revealed a significant systolic dysfunction, accompanied by a reduction of the aortic root size. Histology verified the presence of hypertrophic cardiomyopathy with myocyte hypertrophy, chondroid metaplasia, and mild interstitial fibrosis. This study revealed a substantial correlation between the degree of impaired ADAMTSL2 secretion and the severity of the observed phenotype in GD1.

Identification and functional coordination analysis of gene co-expression networks in different tissues of XBP1 cartilage-specific deficient mice

Abnormal differentiation and proliferation of chondrocytes leads to various diseases related to growth and development. The process of chondrocyte differentiation involves a series of complex cellular and molecular interactions. X-box binding protein 1 (XBP1), an essential molecule of the unfolded protein response (UPR) in Endoplasmic Reticulum (ER) stress, participated in cartilage development and causes other related diseases. We previously reported that XBP1 deficiency in cartilage impacts the function and associated diseases of many different tissues including cartilage. However, how differential expression of genes modulates the roles of cartilage and other tissues when XBP1 is lack of in chondrocytes remains unclear. We aimed to screen for differentially expressed (DE) genes in cartilage, brain, heart, and muscle by high-throughput sequencing in XBP1 cartilage-specific knockout (CKO) mice. Further, gene co-expression networks were constructed by weighted gene co-expression network analysis (WGCNA) algorithm and pivot genes were identified in the above four tissues. Protein detection, Hematoxylin-eosin (HE) staining and immunohistochemistry (IHC) experiments have proved that these differentially co-expressed genes participate in the downstream regulatory pathway of different tissues and affect tissue function.Significantly differentially expressed mRNAs [differentially expressed genes (DEGs)] were identified between XBP1 CKO mice and controls in cartilage, brain, heart, and muscle tissues, including 610, 126, 199 and 219 DEGs, respectively. 39 differentially co-expressed genes were identified in the above four tissues, and they were important pivot genes. Comprehensive analysis discovered that XBP1 deficiency in cartilage influences the difference of co-expressed genes between cartilage and other different tissues. These differentially co-expressed genes participate in downstream regulatory pathways of different tissues and affect tissue functions. Collectively, our conclusions may contribute potential biomarkers and molecular mechanisms for the mutual modulation between cartilage and different tissues and the diagnosis and treatment of diseases caused by abnormalities in different tissues. The analysis also provides meaningful insights for future genetic discoveries.

Epicardial deletion of Sox9 leads to myxomatous valve degeneration and identifies Cd109 as a novel gene associated with valve development

Epicardial-derived cells (EPDCs) are involved in the regulation of myocardial growth and coronary vascularization and are critically important for proper development of the atrioventricular (AV) valves. SOX9 is a transcription factor expressed in a variety of epithelial and mesenchymal cells in the developing heart, including EPDCs. To determine the role of SOX9 in epicardial development, an epicardial-specific Sox9 knockout mouse model was generated. Deleting Sox9 from the epicardial cell lineage impairs the ability of EPDCs to invade both the ventricular myocardium and the developing AV valves. After birth, the mitral valves of these mice become myxomatous with associated abnormalities in extracellular matrix organization. This phenotype is reminiscent of that seen in humans with myxomatous mitral valve disease (MVD). An RNA-seq analysis was conducted in an effort to identify genes associated with this myxomatous degeneration. From this experiment, Cd109 was identified as a gene associated with myxomatous valve pathogenesis in this model. Cd109 has never been described in the context of heart development or valve disease. This study highlights the importance of SOX9 in the regulation of epicardial cell invasion-emphasizing the importance of EPDCs in regulating AV valve development and homeostasis-and reports a novel expression profile of Cd109, a gene with previously unknown relevance in heart development.

Broad H3K4me3 Domain Is Associated with Spatial Coherence during Mammalian Embryonic Development

It is well known that the chromatin states play a major role in cell-fate decision and cell-identity maintenance; however, the spatial variation of chromatin states in situ remains poorly characterized. Here, by leveraging recently available spatial-CUT&Tag data, we systematically characterized the global spatial organization of the H3K4me3 profiles in a mouse embryo. Our analysis identified a subset of genes with spatially coherent H3K4me3 patterns, which together delineate the tissue boundaries. The spatially coherent genes are strongly enriched with tissue-specific transcriptional regulators. Remarkably, their corresponding genomic loci are marked by broad H3K4me3 domains, which is distinct from the typical H3K4me3 signature. Spatial transition across tissue boundaries is associated with continuous shortening of the broad H3K4me3 domains as well as expansion of H3K27me3 domains. Our analysis reveals a strong connection between the genomic and spatial variation of chromatin states, which may play an important role in embryonic development.

Perish in the Attempt: Regulated Cell Death in Regenerative and Nonregenerative Tissue

Significance: A cell plays its roles throughout its life span, even during its demise. Regulated cell death (RCD) is one of the key topics in modern biomedical studies. It is considered the main approach for removing stressed and/or damaged cells. Research during the past two decades revealed more roles of RCD, such as coordinating tissue development and driving compensatory proliferation during tissue repair. Recent Advances: Compensatory proliferation, initially identified in primitive organisms during the regeneration of lost tissue, is an evolutionarily conserved process that also functions in mammals. Among various types of RCD, apoptosis is considered the top candidate to induce compensatory proliferation in damaged tissue. Critical Issues: The roles of apoptosis in the recovery of nonregenerative tissue are still vague. The roles of other types of RCD, such as necroptosis and ferroptosis, have not been well characterized in the context of tissue regeneration. Future Directions: In this review article, we attempt to summarize the recent insights on the role of RCD in tissue repair. We focus on apoptosis, with expansion to ferroptosis and necroptosis, in primitive organisms with significant regenerative capacity as well as common mammalian research models. After gathering hints from regenerative tissue, in the second half of the review, we take a notoriously nonregenerative tissue, the myocardium, as an example to discuss the role of RCD in terminally differentiated quiescent cells. Antioxid. Redox Signal. 39, 1053-1069.

PROX1 Inhibits PDGF-B Expression to Prevent Myxomatous Degeneration of Heart Valves

BACKGROUND

Cardiac valve disease is observed in 2.5% of the general population and 10% of the elderly people. Effective pharmacological treatments are currently not available, and patients with severe cardiac valve disease require surgery. PROX1 (prospero-related homeobox transcription factor 1) and FOXC2 (Forkhead box C2 transcription factor) are transcription factors that are required for the development of lymphatic and venous valves. We found that PROX1 and FOXC2 are expressed in a subset of valvular endothelial cells (VECs) that are located on the downstream (fibrosa) side of cardiac valves. Whether PROX1 and FOXC2 regulate cardiac valve development and disease is not known.

METHODS

We used histology, electron microscopy, and echocardiography to investigate the structure and functioning of heart valves from Prox1ΔVEC mice in which Prox1 was conditionally deleted from VECs. Isolated valve endothelial cells and valve interstitial cells were used to identify the molecular mechanisms in vitro, which were tested in vivo by RNAScope, additional mouse models, and pharmacological approaches. The significance of our findings was tested by evaluation of human samples of mitral valve prolapse and aortic valve insufficiency.

RESULTS

Histological analysis revealed that the aortic and mitral valves of Prox1ΔVEC mice become progressively thick and myxomatous. Echocardiography revealed that the aortic valves of Prox1ΔVEC mice are stenotic. FOXC2 was downregulated and PDGF-B (platelet-derived growth factor-B) was upregulated in the VECs of Prox1ΔVEC mice. Conditional knockdown of FOXC2 and conditional overexpression of PDGF-B in VECs recapitulated the phenotype of Prox1ΔVEC mice. PDGF-B was also increased in mice lacking FOXC2 and in human mitral valve prolapse and insufficient aortic valve samples. Pharmacological inhibition of PDGF-B signaling with imatinib partially ameliorated the valve defects of Prox1ΔVEC mice.

CONCLUSIONS

PROX1 antagonizes PDGF-B signaling partially via FOXC2 to maintain the extracellular matrix composition and prevent myxomatous degeneration of cardiac valves.

Cellular and Molecular Mechanisms Underlying Tricuspid Valve Development and Disease

Tricuspid valve (TV) disease is highly prevalent in the general population. For ages considered "the forgotten valve" because of the predominant interest in left-side valve disease, the TV has now received significant attention in recent years, with significant improvement both in diagnosis and in management of tricuspid disease. TV is characterized by complex anatomy, physiology, and pathophysiology, in which the right ventricle plays a fundamental role. Comprehensive knowledge of molecular and cellular mechanisms underlying TV development, TV disease, and tricuspid regurgitation-related right-ventricle cardiomyopathy is necessary to enhance TV disease understanding to improve the ability to risk stratify TR patients, while also predicting valve dysfunction and/or response to tricuspid regurgitation treatment. Scientific efforts are still needed to eventually decipher the complete picture describing the etiopathogenesis of TV and TV-associated cardiomyopathy, and future advances to this aim may be achieved by combining emerging diagnostic imaging modalities with molecular and cellular studies. Overall, basic science studies could help to streamline a new coherent hypothesis underlying both the development of TV during embryogenesis and TV-associated disease and its complications in adult life, providing the conceptual basis for the ultimate and innovative field of valve repair and regeneration using tissue-engineered heart valves.

Association of CT-Derived Extracardiac Features and Aortic Annulus Size in Patients Planned for TAVI

INTRODUCTION

Transcatheter aortic valve implantation (TAVI) is commonly used to treat patients with stenosed aortic valves. CT is one of the crucial steps in planning TAVI to obtain measurements of the aortic annulus to choose an appropriately sized prosthesis. Incorrect measurements can lead to patient-prosthesis mismatch and other complications. However, some patients cannot undergo ECG-gated CT with radiocontrast because of the presence of radiopaque objects in the thorax, arrhythmia, renal failure, etc. Aim: To explore supplementary methods to improve aortic annulus sizing for TAVI by extracardiac measurements.

METHODS

We included all patients who underwent CT as part of TAVI planning. Measurements of femoral and iliac arteries and the femoral head cross-sectional area were performed.

RESULTS

CT scans of 139 patients were included in this study. Sixty-three patients (45%) were males. Mean age of the female patients was 79.6 ± 7.1 years and of the male patients was 81.3 ± 6.1 years. Mean aortic annulus perimeter among female patients was 74.3 ± 6 mm (range 61.9-88.2) and 83 ± 7.9 mm among male patients (range 70.1-74.3 mm). Mean diameters of common iliac, external iliac, and common femoral arteries were 9.2 ± 1.8, 7.6 ± 1, 7.6 ± 1 mm, respectively, for females and 10.2 ± 1.8, 8.5 ± 1.3, and 8.6 ± 1.4 mm for males. Mean perimeter of the femoral head (average value of right and left femoral heads) among the female patients was 137.8 ± 6.3 mm, and among male patients was 155 ± 9.6 mm. A significant correlation was observed between the perimeter of the aortic annulus and the perimeter of the femoral head (Pearson's R² = 0.224). The correlation between the aortic annulus perimeter and the femoral head perimeter was stronger among men than among women (Pearson's R² = 0.66 and 0.19, respectively).

CONCLUSION

Femoral head diameter is associated with annulus size. This may help size the appropriate prosthesis in cases where the measurements by CT are in the border zone if corroborated by clinically driven data.

Heart morphology during the embryonic development of Podocnemis unifilis Trosquel 1948 (Testudines: Podocnemididae)

Cardiogenesis is similar in all vertebrates, but differences in the valvuloseptal morphogenesis among non-crocodilian reptiles, birds, and mammals are noted. The origin of mesenchymal structures such as valves that regulate the passage of blood and the formation of partial septa that prevent the complete mixing of oxygen-rich and low-oxygen blood present in adult chelonians are essential in the evolutionary understanding of complete septation, endothermy and malformations, even in mammals. In this context, this study analyzed the heart morphogenesis of Podocnemis unifilis (Testudines: Podocnemididae) from the 4th to the 60th day of incubation. We identified the tubular heart stage, folding of the cardiac tube and expansion of the atrial and ventricular compartments followed by atrial septation by the septum primum, ventricle septation by partial septa, outflow tract septation and the formation of bicuspid valves with cartilage differentiation at the base. The formation of the first atrial septum with the mesenchymal cap is noted during the development of the atrial septum, joining the atrioventricular cushion on the 17th day and completely dividing the atria. Small secondary perforations appeared in the mid-cranial part, observed up to the 45th day. Partial ventricle septation into the pulmonary, venous, and arterial subcompartments takes place by trabeculae carneae thickening and grouping on the 15th day. The outflow tract forms the aorticopulmonary and interaortic septa on the 16th day and the bicuspid valves, on the 20th day. Therefore, after the first 20 days, the heart exhibits a general anatomical conformation similar to that of adult turtles.

Increased incidence of mitral valve prolapse in children with pectus chest wall deformity

BACKGROUND

Pectus anomalies constitute 95% of chest anomalies. Pectus carinatum (PC) and excavatum (PE) are often asymptomatic in childhood. However, symptoms and signs such as chest pain, dyspnea, and mitral valve prolapse (MVP) can be seen in pectus anomalies. Demographic characteristics and accompanying cardiac signs in children with pectus deformity were investigated.

METHODS

In this study, the clinical findings for children with pectus deformity, and the incidence of MVP and other concomitant heart diseases detected in echocardiographic examinations were evaluated.

RESULTS

Eighty-two children with PE, 27 with PC, and 107 healthy children were included in this study. In the echocardiographic examination of PE, PC patients, and healthy children, MVP was detected with frequencies of 25%, 33%, and 2% respectively.

CONCLUSIONS

The study showed that pectus anomalies were associated with an increased incidence of MVP. All patients with pectus deformity should therefore undergo a screening echocardiogram in adolescence to assess for the presence of MVP.

Macrophage-extracellular matrix interactions: Perspectives for tissue engineered heart valve remodeling

In situ heart valve tissue engineering approaches have been proposed as promising strategies to overcome the limitations of current heart valve replacements. Tissue engineered heart valves (TEHVs) generated from in vitro grown tissue engineered matrices (TEMs) aim at mimicking the microenvironmental cues from the extracellular matrix (ECM) to favor integration and remodeling of the implant. A key role of the ECM is to provide mechanical support to and attract host cells into the construct. Additionally, each ECM component plays a critical role in regulating cell adhesion, growth, migration, and differentiation potential. Importantly, the immune response to the implanted TEHV is also modulated biophysically via macrophage-ECM protein interactions. Therefore, the aim of this review is to summarize what is currently known about the interactions and signaling networks occurring between ECM proteins and macrophages, and how these interactions may impact the long-term in situ remodeling outcomes of TEMs. First, we provide an overview of in situ tissue engineering approaches and their clinical relevance, followed by a discussion on the fundamentals of the remodeling cascades. We then focus on the role of circulation-derived and resident tissue macrophages, with particular emphasis on the ramifications that ECM proteins and peptides may have in regulating the host immune response. Finally, the relevance of these findings for heart valve tissue engineering applications is discussed.

Activation of AcvR1-Mediated Signaling Results in Semilunar Valve Defects

Calcific aortic valve disease (CAVD) is a common cardiac defect, particularly in the aging population. While several risk factors, such as bi-leaflet valve structure and old age, have been identified in CAVD pathogenesis, molecular mechanisms resulting in this condition are still under active investigation. Bone morphogenetic protein signaling via the activin type I receptor (AcvRI) plays an important role during physiological and pathological processes involving calcification, e.g., bone formation and heterotopic ossification. In addition, AcvRI is required for normal cardiac valve development, yet its role in aortic valve disease, if any, is currently unknown. Here, we induced the expression of constitutively active AcvRI in developing mouse embryos in the endocardium and in cells at the valve leaflet-wall junction that are not of endocardium origin using the Nfac1Cre transgene. The mutant mice were born alive, but showed thickened aortic and pulmonary valve leaflets during the early postnatal period. Adult mutant mice developed aortic stenosis with high frequency, sclerotic aortic valves, and displayed Alcian Blue-positive hypertrophic chondrocyte-like cells at the leaflet-wall junction. Calcification was only seen with low penetrance. In addition, we observed that the expression levels of gene sets associated with inflammation-related cytokine signaling, smooth muscle cell contraction, and cGMP signaling were altered in the mutants when compared with those of the controls. This work shows that, in a mouse model, such continuous AcvRI activity in the Nfatc1Cre recombination domain results in pathological changes in the aortic valve structure and function.

Crosstalk between bone and other organs

Bone has long been considered as a silent organ that provides a reservoir of calcium and phosphorus, traditionally. Recently, further study of bone has revealed additional functions as an endocrine organ connecting systemic organs of the whole body. Communication between bone and other organs participates in most physiological and pathological events and is responsible for the maintenance of homeostasis. Here, we present an overview of the crosstalk between bone and other organs. Furthermore, we describe the factors mediating the crosstalk and review the mechanisms in the development of potential associated diseases. These connections shed new light on the pathogenesis of systemic diseases and provide novel potential targets for the treatment of systemic diseases.

Spontaneous Degenerative Aortic Valve Disease in New Zealand Obese Mice

Background Degenerative aortic valve (AoV) disease and resulting aortic stenosis are major clinical health problems. Murine models of valve disease are rare, resulting in a translational knowledge gap on underlying mechanisms, functional consequences, and potential therapies. Naïve New Zealand obese (NZO) mice were recently found to have a dramatic decline of left ventricular (LV) function at early age. Therefore, we aimed to identify the underlying cause of reduced LV function in NZO mice. Methods and Results Cardiac function and pulmonary hemodynamics of NZO and age-matched C57BL/6J mice were monitored by serial echocardiographic examinations. AoVs in NZO mice demonstrated extensive thickening, asymmetric aortic leaflet formation, and cartilaginous transformation of the valvular stroma. Doppler echocardiography of the aorta revealed increased peak velocity profiles, holodiastolic flow reversal, and dilatation of the ascending aorta, consistent with aortic stenosis and regurgitation. Compensated LV hypertrophy deteriorated to decompensated LV failure and remodeling, as indicated by increased LV mass, interstitial fibrosis, and inflammatory cell infiltration. Elevated LV pressures in NZO mice were associated with lung congestion and cor pulmonale, evident as right ventricular dilatation, decreased right ventricular function, and increased mean right ventricular systolic pressure, indicative for the development of pulmonary hypertension and ultimately right ventricular failure. Conclusions NZO mice demonstrate as a novel murine model to spontaneously develop degenerative AoV disease, aortic stenosis, and the associated end organ damages of both ventricles and the lung. Closely mimicking the clinical scenario of degenerative AoV disease, the model may facilitate a better mechanistic understanding and testing of novel treatment strategies in degenerative AoV disease.

Proteoglycans and Diseases of Soft Tissues

Proteoglycans consist of protein cores to which at least one glycosaminoglycan chain is attached. They play important roles in the physiology and biomechanical function of tendons, ligaments, cardiovascular system, and other systems through their involvement in regulation of assembly and maintenance of extracellular matrix, and through their participation in cell proliferation together with growth factors. They can be divided into two main groups, small and large proteoglycans. The small proteoglycans are also known as small leucine-rich proteoglycans (SLRPs) which are encoded by 18 genes and are further subclassified into Classes I-V. Several members of Class I and II, such as decorin and biglycan from Class I, and Class II fibromodulin and lumican, are known to regulate collagen fibrillogenesis. Decorin limits the diameter of collagen fibrils during fibrillogenesis. The function of biglycan in fibrillogenesis is similar to that of decorin. Though biomechanical function of tendon is compromised in decorin-deficient mice, decorin can substitute for lack of biglycan in biglycan-deficient mice. New data also indicate an important role for biglycan in disorders of the cardiovascular system, including aortic valve stenosis and aortic dissection. Two members of the Class II of SLRPs, fibromodulin and lumican bind to the same site within the collagen molecule and can substitute for each other in fibromodulin- or lumican-deficient mice.Aggrecan and versican are the major representatives of the large proteoglycans. Though they are mainly found in the cartilage where they provide resilience and toughness, they are present also in tensile portions of tendons and, in slightly different biochemical form in fibrocartilage. Degradation by aggrecanase is responsible for the appearance of different forms of aggrecan and versican in different parts of the tendon where these cleaved forms play different roles. In addition, they are important components of the ventricularis of cardiac valves. Mutations in the gene for versican or in the gene for elastin (which binds to versican ) lead to severe disruptions of normal developmental of the heart at least in mice.

Growth Factor Roles in Soft Tissue Physiology and Pathophysiology

Repair and healing of injured and diseased tendons has been traditionally fraught with apprehension and difficulties, and often led to rather unsatisfactory results. The burgeoning research field of growth factors has opened new venues for treatment of tendon disorders and injuries, and possibly for treatment of disorders of the aorta and major arteries as well. Several chapters in this volume elucidate the role of transforming growth factor β (TGFß) in pathogenesis of several heritable disorders affecting soft tissues, such as aorta, cardiac valves, and tendons and ligaments. Several members of the bone morphogenetic group either have been approved by the FDA for treatment of non-healing fractures or have been undergoing intensive clinical and experimental testing for use of healing bone fractures and tendon injuries. Because fibroblast growth factors (FGFs) are involved in embryonic development of tendons and muscles among other tissues and organs, the hope is that applied research on FGF biological effects will lead to the development of some new treatment strategies providing that we can control angiogenicity of these growth factors. The problem, or rather question, regarding practical use of imsulin-like growth factor I (IGF-I) in tendon repair is whether IGF-I acts independently or under the guidance of growth hormone. FGF2 or platelet-derived growth factor (PDGF) alone or in combination with IGF-I stimulates regeneration of periodontal ligament: a matter of importance in Marfan patients with periodontitis. In contrast, vascular endothelial growth factor (VEGF) appears to have rather deleterious effects on experimental tendon healing, perhaps because of its angiogenic activity and stimulation of matrix metalloproteinases-proteases whose increased expression has been documented in a variety of ruptured tendons. Other modalities, such as local administration of platelet-rich plasma (PRP) and/or of mesenchymal stem cells have been explored extensively in tendon healing. Though treatment with PRP and mesenchymal stem cells has met with some success in horses (who experience a lot of tendon injuries and other tendon problems), the use of PRP and mesenchymal stem cells in people has been more problematic and requires more studies before PRP and mesenchymal stem cells can become reliable tools in management of soft tissue injuries and disorders.

Collagen Fibrillogenesis in the Mitral Valve: It's a Matter of Compliance

Collagen fibers are essential structural components of mitral valve leaflets, their tension apparatus (chordae tendineae), and the associated papillary muscles. Excess or lack of collagen fibers in the extracellular matrix (ECM) in any of these structures can adversely affect mitral valve function. The organization of collagen fibers provides a sophisticated framework that allows for unidirectional blood flow during the precise opening and closing of this vital heart valve. Although numerous ECM molecules are essential for the differentiation, growth, and homeostasis of the mitral valve (e.g., elastic fibers, glycoproteins, and glycans), collagen fibers are key to mitral valve integrity. Besides the inert structural components of the tissues, collagen fibers are dynamic structures that drive outside-to-inside cell signaling, which informs valvular interstitial cells (VICs) present within the tissue environment. Diversity of collagen family members and the closely related collagen-like triple helix-containing proteins found in the mitral valve, will be discussed in addition to how defects in these proteins may lead to valve disease.

Role of the Epicardium in the Development of the Atrioventricular Valves and Its Relevance to the Pathogenesis of Myxomatous Valve Disease

This paper is dedicated to the memory of Dr. Adriana "Adri" Gittenberger-de Groot and in appreciation of her work in the field of developmental cardiovascular biology and the legacy that she has left behind. During her impressive career, Dr. Gittenberger-de Groot studied many aspects of heart development, including aspects of cardiac valve formation and disease and the role of the epicardium in the formation of the heart. In this contribution, we review some of the work on the role of epicardially-derived cells (EPDCs) in the development of the atrioventricular valves and their potential involvement in the pathogenesis of myxomatous valve disease (MVD). We provide an overview of critical events in the development of the atrioventricular junction, discuss the role of the epicardium in these events, and illustrate how interfering with molecular mechanisms that are involved in the epicardial-dependent formation of the atrioventricular junction leads to a number of abnormalities. These abnormalities include defects of the AV valves that resemble those observed in humans that suffer from MVD. The studies demonstrate the importance of the epicardium for the proper formation and maturation of the AV valves and show that the possibility of epicardial-associated developmental defects should be taken into consideration when determining the genetic origin and pathogenesis of MVD.

Toward the Effective Bioengineering of a Pathological Tissue for Cardiovascular Disease Modeling: Old Strategies and New Frontiers for Prevention, Diagnosis, and Therapy

Cardiovascular diseases (CVDs) still represent the primary cause of mortality worldwide. Preclinical modeling by recapitulating human pathophysiology is fundamental to advance the comprehension of these diseases and propose effective strategies for their prevention, diagnosis, and treatment. In silico, in vivo, and in vitro models have been applied to dissect many cardiovascular pathologies. Computational and bioinformatic simulations allow developing algorithmic disease models considering all known variables and severity degrees of disease. In vivo studies based on small or large animals have a long tradition and largely contribute to the current treatment and management of CVDs. In vitro investigation with two-dimensional cell culture demonstrates its suitability to analyze the behavior of single, diseased cellular types. The introduction of induced pluripotent stem cell technology and the application of bioengineering principles raised the bar toward in vitro three-dimensional modeling by enabling the development of pathological tissue equivalents. This review article intends to describe the advantages and disadvantages of past and present modeling approaches applied to provide insights on some of the most relevant congenital and acquired CVDs, such as rhythm disturbances, bicuspid aortic valve, cardiac infections and autoimmunity, cardiovascular fibrosis, atherosclerosis, and calcific aortic valve stenosis.

Biology and Biomechanics of the Heart Valve Extracellular Matrix

Heart valves are dynamic structures that, in the average human, open and close over 100,000 times per day, and 3 × 10⁹ times per lifetime to maintain unidirectional blood flow. Efficient, coordinated movement of the valve structures during the cardiac cycle is mediated by the intricate and sophisticated network of extracellular matrix (ECM) components that provide the necessary biomechanical properties to meet these mechanical demands. Organized in layers that accommodate passive functional movements of the valve leaflets, heart valve ECM is synthesized during embryonic development, and remodeled and maintained by resident cells throughout life. The failure of ECM organization compromises biomechanical function, and may lead to obstruction or leaking, which if left untreated can lead to heart failure. At present, effective treatment for heart valve dysfunction is limited and frequently ends with surgical repair or replacement, which comes with insuperable complications for many high-risk patients including aged and pediatric populations. Therefore, there is a critical need to fully appreciate the pathobiology of biomechanical valve failure in order to develop better, alternative therapies. To date, the majority of studies have focused on delineating valve disease mechanisms at the cellular level, namely the interstitial and endothelial lineages. However, less focus has been on the ECM, shown previously in other systems, to be a promising mechanism-inspired therapeutic target. Here, we highlight and review the biology and biomechanical contributions of key components of the heart valve ECM. Furthermore, we discuss how human diseases, including connective tissue disorders lead to aberrations in the abundance, organization and quality of these matrix proteins, resulting in instability of the valve infrastructure and gross functional impairment.

Inappropriate cathepsin K secretion promotes its enzymatic activation driving heart and valve malformation

Although congenital heart defects (CHDs) represent the most common birth defect, a comprehensive understanding of disease etiology remains unknown. This is further complicated since CHDs can occur in isolation or as a feature of another disorder. Analyzing disorders with associated CHDs provides a powerful platform to identify primary pathogenic mechanisms driving disease. Aberrant localization and expression of cathepsin proteases can perpetuate later-stage heart diseases, but their contribution toward CHDs is unclear. To investigate the contribution of cathepsins during cardiovascular development and congenital disease, we analyzed the pathogenesis of cardiac defects in zebrafish models of the lysosomal storage disorder mucolipidosis II (MLII). MLII is caused by mutations in the GlcNAc-1-phosphotransferase enzyme (Gnptab) that disrupt carbohydrate-dependent sorting of lysosomal enzymes. Without Gnptab, lysosomal hydrolases, including cathepsin proteases, are inappropriately secreted. Analyses of heart development in gnptab-deficient zebrafish show cathepsin K secretion increases its activity, disrupts TGF-β–related signaling, and alters myocardial and valvular formation. Importantly, cathepsin K inhibition restored normal heart and valve development in MLII embryos. Collectively, these data identify mislocalized cathepsin K as an initiator of cardiac disease in this lysosomal disorder and establish cathepsin inhibition as a viable therapeutic strategy.

Mislocalized cathepsin K promotes cardiac disease in a zebrafish model of the lysosomal disorder mucolipidosis II and can be targeted by cathespin inhibition.

Identification of a peripheral blood gene signature predicting aortic valve calcification

Calcific aortic valve disease (CAVD) is a significant cause of illness and death worldwide. Identification of early predictive markers could help optimize patient management. RNA-sequencing was carried out on human fetal aortic valves at gestational weeks 9, 13, and 22 and on a case-control study with adult noncalcified and calcified bicuspid and tricuspid aortic valves. In dimension reduction and clustering analyses, diseased valves tended to cluster with fetal valves at week 9 rather than normal adult valves, suggesting that part of the disease program might be due to reiterated developmental processes. The analysis of groups of coregulated genes revealed predominant immune-metabolic signatures, including innate and adaptive immune responses involving lymphocyte T-cell metabolic adaptation. Cytokine and chemokine signaling, cell migration, and proliferation were all increased in CAVD, whereas oxidative phosphorylation and protein translation were decreased. Discrete immune-metabolic gene signatures were present at fetal stages and increased in adult controls, suggesting that these processes intensify throughout life and heighten in disease. Cellular stress response and neurodegeneration gene signatures were aberrantly expressed in CAVD, pointing to a mechanistic link between chronic inflammation and biological aging. Comparison of the valve RNA-sequencing data set with a case-control study of whole blood transcriptomes from asymptomatic individuals with early aortic valve calcification identified a highly predictive gene signature of CAVD and of moderate aortic valve calcification in overtly healthy individuals. These data deepen and broaden our understanding of the molecular basis of CAVD and identify a peripheral blood gene signature for the early detection of aortic valve calcification.

Aggrecan in Cardiovascular Development and Disease

Aggrecan is a large proteoglycan that forms giant hydrated aggregates with hyaluronan in the extracellular matrix (ECM). The extraordinary resistance of these aggregates to compression explains their abundance in articular cartilage of joints where they ensure adequate load-bearing. In the brain, they provide mechanical buffering and contribute to formation of perineuronal nets, which regulate synaptic plasticity. Aggrecan is also present in cardiac jelly, developing heart valves, and blood vessels during cardiovascular development. Whereas aggrecan is essential for skeletal development, its function in the developing cardiovascular system remains to be fully elucidated. An excess of aggrecan was demonstrated in cardiovascular tissues in aortic aneurysms, atherosclerosis, vascular re-stenosis after injury, and varicose veins. It is a product of vascular smooth muscle and is likely to be an important component of pericellular matrix, where its levels are regulated by proteases. Aggrecan can contribute to specific biophysical and regulatory properties of cardiovascular ECM via the diverse interactions of its domains, and its accumulation is likely to have a significant role in developmental and disease pathways. Here, the established biological functions of aggrecan, its cardiovascular associations, and potential roles in cardiovascular development and disease are discussed.

Aggrecan, the Primary Weight-Bearing Cartilage Proteoglycan, Has Context-Dependent, Cell-Directive Properties in Embryonic Development and Neurogenesis: Aggrecan Glycan Side Chain Modifications Convey Interactive Biodiversity

This review examines aggrecan's roles in developmental embryonic tissues, in tissues undergoing morphogenetic transition and in mature weight-bearing tissues. Aggrecan is a remarkably versatile and capable proteoglycan (PG) with diverse tissue context-dependent functional attributes beyond its established role as a weight-bearing PG. The aggrecan core protein provides a template which can be variably decorated with a number of glycosaminoglycan (GAG) side chains including keratan sulphate (KS), human natural killer trisaccharide (HNK-1) and chondroitin sulphate (CS). These convey unique tissue-specific functional properties in water imbibition, space-filling, matrix stabilisation or embryonic cellular regulation. Aggrecan also interacts with morphogens and growth factors directing tissue morphogenesis, remodelling and metaplasia. HNK-1 aggrecan glycoforms direct neural crest cell migration in embryonic development and is neuroprotective in perineuronal nets in the brain. The ability of the aggrecan core protein to assemble CS and KS chains at high density equips cartilage aggrecan with its well-known water-imbibing and weight-bearing properties. The importance of specific arrangements of GAG chains on aggrecan in all its forms is also a primary morphogenetic functional determinant providing aggrecan with unique tissue context dependent regulatory properties. The versatility displayed by aggrecan in biodiverse contexts is a function of its GAG side chains.

From Shape to Function: The Next Step in Bioprinting

In 2013, the "biofabrication window" was introduced to reflect the processing challenge for the fields of biofabrication and bioprinting. At that time, the lack of printable materials that could serve as cell-laden bioinks, as well as the limitations of printing and assembly methods, presented a major constraint. However, recent developments have now resulted in the availability of a plethora of bioinks, new printing approaches, and the technological advancement of established techniques. Nevertheless, it remains largely unknown which materials and technical parameters are essential for the fabrication of intrinsically hierarchical cell-material constructs that truly mimic biologically functional tissue. In order to achieve this, it is urged that the field now shift its focus from materials and technologies toward the biological development of the resulting constructs. Therefore, herein, the recent material and technological advances since the introduction of the biofabrication window are briefly summarized, i.e., approaches how to generate shape, to then focus the discussion on how to acquire the biological function within this context. In particular, a vision of how biological function can evolve from the possibility to determine shape is outlined.

Development of the human heart

In 2014, an extensive review discussing the major steps of cardiac development focusing on growth, formation of primary and chamber myocardium and the development of the cardiac electrical system, was published. Molecular genetic lineage analyses have since furthered our insight in the developmental origin of the various component parts of the heart, which currently can be unambiguously identified by their unique molecular phenotype. Moreover, genetic, molecular and cell biological analyses have driven insights into the mechanisms underlying the development of the different cardiac components. Here, we build on our previous review and provide an insight into the molecular mechanistic revelations that have forwarded the field of cardiac development. Despite the enormous advances in our knowledge over the last decade, the development of congenital cardiac malformations remains poorly understood. The challenge for the next decade will be to evaluate the different developmental processes using newly developed molecular genetic techniques to further unveil the gene regulatory networks operational during normal and abnormal cardiac development.

TGF-ß Regulates Cathepsin Activation during Normal and Pathogenic Development

Cysteine cathepsins play roles during development and disease beyond their function in lysosomal protein turnover. Here, we leverage a fluorescent activity-based probe (ABP), BMV109, to track cysteine cathepsins in normal and diseased zebrafish embryos. Using this probe in a model of mucolipidosis II, we show that loss of carbohydrate-dependent lysosomal sorting alters the activity of several cathepsin proteases. The data support a pathogenic mechanism where TGF-β signals enhance the proteolytic processing of pro-Ctsk by modulating the expression of chondroitin 4-sulfate (C4-S). In MLII, elevated C4-S corresponds with TGF-β-mediated increases in chst11 expression. Inhibiting chst11 impairs the proteolytic activation of Ctsk and alleviates the MLII phenotypes. These findings uncover a regulatory loop between TGF-β signaling and Ctsk activation that is altered in the context of lysosomal disease. This work highlights the power of ABPs to identify mechanisms underlying pathogenic development in living animals.

Chondroitin sulfate is a known regulator of cathepsin protease activity. Flanagan-Steet et al. identify a positive feedback mechanism whereby cathepsins secreted from chondrocytes upon loss of lysosomal targeting activate TGF-β signaling in developing cartilage. This increased signaling, in turn, stimulates chondroitin-4 sulfation and enhances cathepsin activity.

A cellular atlas of Pitx2-dependent cardiac development

The Pitx2 gene encodes a homeobox transcription factor that is required for mammalian development. Disruption of PITX2 expression in humans causes congenital heart diseases and is associated with atrial fibrillation; however, the cellular and molecular processes dictated by Pitx2 during cardiac ontogeny remain unclear. To characterize the role of Pitx2 during murine heart development we sequenced over 75,000 single cardiac cell transcriptomes between two key developmental timepoints in control and Pitx2 null embryos. We found that cardiac cell composition was dramatically altered in mutants at both E10.5 and E13.5. Interestingly, the differentiation dynamics of both anterior and posterior second heart field-derived progenitor cells were disrupted in Pitx2 mutants. We also uncovered evidence for defects in left-right asymmetry within atrial cardiomyocyte populations. Furthermore, we were able to detail defects in cardiac outflow tract and valve development associated with Pitx2 Our findings offer insight into Pitx2 function and provide a compilation of gene expression signatures for further detailing the complexities of heart development that will serve as the foundation for future studies of cardiac morphogenesis, congenital heart disease and arrhythmogenesis.

Endothelial to Mesenchymal Transition in Cardiovascular Disease: JACC State-of-the-Art Review

Endothelial to mesenchymal transition (EndMT) is a process whereby an endothelial cell undergoes a series of molecular events that lead to a change in phenotype toward a mesenchymal cell (e.g., myofibroblast, smooth muscle cell). EndMT plays a fundamental role during development, and mounting evidence indicates that EndMT is involved in adult cardiovascular diseases (CVDs), including atherosclerosis, pulmonary hypertension, valvular disease, and fibroelastosis. Therefore, the targeting of EndMT may hold therapeutic promise for treating CVD. However, the field faces a number of challenges, including the lack of a precise functional and molecular definition, a lack of understanding of the causative pathological role of EndMT in CVDs (versus being a "bystander-phenomenon"), and a lack of robust human data corroborating the extent and causality of EndMT in adult CVDs. Here, we review this emerging but exciting field, and propose a framework for its systematic advancement at the molecular and translational levels.

Non-pathological Chondrogenic Features of Valve Interstitial Cells in Normal Adult Zebrafish

In the heart, unidirectional blood flow depends on proper heart valve function. As, in mammals, regulatory mechanisms of early heart valve and bone development are shown to contribute to adult heart valve pathologies, we used the animal model zebrafish (ZF, Danio rerio) to investigate the microarchitecture and differentiation of cardiac valve interstitial cells in the transition from juvenile (35 days) to end of adult breeding (2.5 years) stages. Of note, light microscopy and immunohistochemistry revealed major differences in ZF heart valve microarchitecture when compared with adult mice. We demonstrate evidence for rather chondrogenic features of valvular interstitial cells by histological staining and immunodetection of SOX-9, aggrecan, and type 2a1 collagen. Collagen depositions are enriched in a thin layer at the atrial aspect of atrioventricular valves and the ventricular aspect of bulboventricular valves, respectively. At the ultrastructural level, the collagen fibrils are lacking obvious periodicity and orientation throughout the entire valve.

Dynamic Expression Profiles of Sox9 in Embryonic, Post Natal, and Adult Heart Valve Cell Populations

Heart valves are dynamic structures and abnormalities during embryonic development can lead to premature lethality or congenital malformations present at birth. The transcription factor Sox9 has been shown to be critical for early and late stages of valve formation, but its defined expression pattern throughout embryonic, post natal, and adult growth and maturation is incomplete. Here we use an antibody to detect 1-100 amino acids of Sox9 and show that in the developing embryo, Sox9 is not detected in valve endothelial cells (VECs) lining the primitive valve structures, but is highly expressed in the endothelial-derived valve interstitial cell population following endothelial-to-mesenchymal transformation. Expression is maintained in this cell population after birth, but is additionally detected in VECs from post natal day 1. Using a specific antibody to detect a phosphorylated form of Sox9 at Serine 181 (pSox9), we note enrichment of pSox9 in VECs at post natal days 1 and 10 and this pattern correlates with the known upstream kinase RockI, and downstream target, Aggrecan. The contribution of Sox9 to post natal growth and maturation of the valve is not known, but this study provides insights for future work examining the differential functions of Sox9 protein in valve cell populations. Anat Rec, 302:108-116, 2019. © 2018 Wiley Periodicals, Inc.

The Genetic Regulation of Aortic Valve Development and Calcific Disease

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

Filamin-A as a Balance between Erk/Smad Activities During Cardiac Valve Development

Mitral valve prolapse (MVP) affects 2.4% of the population and has poorly understood etiology. Recent genetic studies have begun to unravel the complexities of MVP and through these efforts, mutations in the FLNA (Filamin-A) gene were identified as disease causing. Our in vivo and in vitro studies have validated these genetic findings and have revealed FLNA as a central regulator of valve morphogenesis. The mechanisms by which FLNA mutations result in myxomatous mitral valve disease are currently unknown, but may involve proteins previously associated with mutated regions of the FLNA protein, such as the small GTPase signaling protein, R-Ras. Herein, we report that Filamin-A is required for R-Ras expression and activation of the Ras-Mek-Erk pathway. Loss of the Ras/Erk pathway correlated with hyperactivation of pSmad2/3, increased extracellular matrix (ECM) production and enlarged mitral valves. Analyses of integrin receptors in the mitral valve revealed that Filamin-A was required for β1-integrin expression and provided a potential mechanism for impaired ECM compaction and valve enlargement. Our data support Filamin-A as a protein that regulates the balance between Erk and Smad activation and an inability of Filamin-A deficient valve interstitial cells to effectively remodel the increased ECM production through a β1-integrin mechanism. As a consequence, loss of Filamin-A function results in increased ECM production and generation of a myxomatous phenotype characterized by improperly compacted mitral valve tissue. Anat Rec, 302:117-124, 2019. © 2018 Wiley Periodicals, Inc.

The Transcriptional Signature of Growth in Human Fetal Aortic Valve Development

BACKGROUND

In the second trimester of human fetal development, a tenfold increase in fetal size occurs while cardiac valves grow and retain their function. Patterns of transcription in normally growing human aortic valves are unknown.

METHODS

Discarded human aortic valve samples were collected from the second trimester, 6 from early (14, 15, 17 weeks) and 6 from late (20, 21, 22 weeks) gestation. Network analysis of RNA sequencing data identified subnetworks of significantly increasing and decreasing transcripts. Subsequent cluster analysis identified patterns of transcription through the time course. Pathway enrichment analysis determined the predominant biological processes at each interval.

RESULTS

We observed phasic transcription over the time course, including an early decrease in cell proliferation and developmental genes (14 to 15 weeks). Pattern specification, shear stress, and adaptive immune genes were induced early. Cell adhesion genes were increased from 14 to 20 weeks. A phase involving cell differentiation and apoptosis (17 to 20 weeks) was followed by downregulation of endothelial-to-mesenchymal transformation genes and then by increased extracellular matrix organization and stabilization (20 to 22 weeks).

CONCLUSIONS

We present a unique data set, comprehensively characterizing human valve development after valve primordia are formed, focusing on key processes displayed by normal aortic valves undergoing significant growth. We build a time course of genes and processes in second trimester fetal valve growth and observe the sequential regulation of gene clusters over time. Critical valve growth genes are potential targets for therapeutic intervention in congenital heart disease and have implications for regenerative medicine and tissue engineering.

Keratan sulfate, a complex glycosaminoglycan with unique functional capability

From an evolutionary perspective keratan sulfate (KS) is the newest glycosaminoglycan (GAG) but the least understood. KS is a sophisticated molecule with a diverse structure, and unique functional roles continue to be uncovered for this GAG. The cornea is the richest tissue source of KS in the human body but the central and peripheral nervous systems also contain significant levels of KS and a diverse range of KS-proteoglycans with essential functional roles. KS also displays important cell regulatory properties in epithelial and mesenchymal tissues and in bone and in tumor development of diagnostic and prognostic utility. Corneal KS-I displays variable degrees of sulfation along the KS chain ranging from non-sulfated polylactosamine, mono-sulfated and disulfated disaccharide regions. Skeletal KS-II is almost completely sulfated consisting of disulfated disaccharides interrupted by occasional mono-sulfated N-acetyllactosamine residues. KS-III also contains highly sulfated KS disaccharides but differs from KS-I and KS-II through 2-O-mannose linkage to serine or threonine core protein residues on proteoglycans such as phosphacan and abakan in brain tissue. Historically, the major emphasis on the biology of KS has focused on its sulfated regions for good reason. The sulfation motifs on KS convey important molecular recognition information and direct cell behavior through a number of interactive proteins. Emerging evidence also suggest functional roles for the poly-N-acetyllactosamine regions of KS requiring further investigation. Thus further research is warranted to better understand the complexities of KS.

Calcific Aortic Valve Disease: a Developmental Biology Perspective

PURPOSE OF REVIEW

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

RECENT FINDINGS

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

A human pericardium biopolymeric scaffold for autologous heart valve tissue engineering: cellular and extracellular matrix structure and biomechanical properties in comparison with a normal aortic heart valve

The objective of our study was to compare the cellular and extracellular matrix (ECM) structure and the biomechanical properties of human pericardium (HP) with the normal human aortic heart valve (NAV). HP tissues (from 12 patients) and NAV samples (from 5 patients) were harvested during heart surgery. The main cells in HP were pericardial interstitial cells, which are fibroblast-like cells of mesenchymal origin similar to the valvular interstitial cells in NAV tissue. The ECM of HP had a statistically significantly (p < 0.001) higher collagen I content, a lower collagen III and elastin content, and a similar glycosaminoglycans (GAGs) content, in comparison with the NAV, as measured by ECM integrated density. However, the relative thickness of the main load-bearing structures of the two tissues, the dense part of fibrous HP (49 ± 2%) and the lamina fibrosa of NAV (47 ± 4%), was similar. In both tissues, the secant elastic modulus (Es) was significantly lower in the transversal direction (p < 0.05) than in the longitudinal direction. This proved that both tissues were anisotropic. No statistically significant differences in UTS (ultimate tensile strength) values and in calculated bending stiffness values in the longitudinal or transversal direction were found between HP and NAV. Our study confirms that HP has an advantageous ECM biopolymeric structure and has the biomechanical properties required for a tissue from which an autologous heart valve replacement may be constructed.

Discovery and Preclinical Characterization of GSK1278863 (Daprodustat), a Small Molecule Hypoxia Inducible Factor-Prolyl Hydroxylase Inhibitor for Anemia

Decreased erythropoietin (EPO) production, shortened erythrocyte survival, and other factors reducing the response to EPO contribute to anemia in patients who have a variety of underlying pathologies such as chronic kidney disease. Treatment with recombinant human EPO (rHuEPO) at supraphysiologic concentrations has proven to be efficacious. However, it does not ameliorate the condition in all patients, and it presents its own risks, including cardiovascular complications. The transcription factors hypoxia-inducible factor (HIF) 1α and HIF2α control the physiologic response to hypoxia and invoke a program of increased erythropoiesis. Levels of HIFα are modulated by oxygen tension via the action of a family of HIF-prolyl hydroxylases (PHDs), which tag HIFα for proteasomal degradation. Inhibition of these PHDs simulates conditions of mild hypoxia, leading to a potentially more physiologic erythropoietic response and presenting a potential alternative to high doses of rHuEPO. Here we describe the discovery and characterization of GSK1278863 [2-(1,3-dicyclohexyl-6-hydroxy-2,4-dioxo-1,2,3,4-tetrahydropyrimidine-5-carboxamido) acetic acid], a pyrimidinetrione-glycinamide low nanomolar inhibitor of PHDs 1-3 that stabilizes HIFα in cell lines, resulting in the production of increased levels of EPO. In normal mice, a single dose of GSK1278863 induced significant increases in circulating plasma EPO but only minimal increases in plasma vascular endothelial growth factor (VEGF-A) concentrations. GSK1278863 significantly increased reticulocytes and red cell mass parameters in preclinical species after once-daily oral administration and has demonstrated an acceptable nonclinical toxicity profile, supporting continued clinical development. GSK1278863 is currently in phase 3 clinical trials for treatment of anemia in patients with chronic kidney disease.

Hypoxia promotes primitive glycosaminoglycan-rich extracellular matrix composition in developing heart valves

During postnatal heart valve development, glycosaminoglycan (GAG)-rich valve primordia transform into stratified valve leaflets composed of GAGs, fibrillar collagen, and elastin layers accompanied by decreased cell proliferation as well as thinning and elongation. The neonatal period is characterized by the transition from a uterine environment to atmospheric O2, but the role of changing O2 levels in valve extracellular matrix (ECM) composition or morphogenesis is not well characterized. Here, we show that tissue hypoxia decreases in mouse aortic valves in the days after birth, concomitant with ECM remodeling and cell cycle arrest of valve interstitial cells. The effects of hypoxia on late embryonic valve ECM composition, Sox9 expression, and cell proliferation were examined in chicken embryo aortic valve organ cultures. Maintenance of late embryonic chicken aortic valve organ cultures in a hypoxic environment promotes GAG expression, Sox9 nuclear localization, and indicators of hyaluronan remodeling but does not affect fibrillar collagen content or cell proliferation. Chronic hypoxia also promotes GAG accumulation in murine adult heart valves in vivo. Together, these results support a role for hypoxia in maintaining a primitive GAG-rich matrix in developing heart valves before birth and also in the induction of hyaluronan remodeling in adults.NEW & NOTEWORTHY Tissue hypoxia decreases in mouse aortic valves after birth, and exposure to hypoxia promotes glycosaminoglycan accumulation in cultured chicken embryo valves and adult murine heart valves. Thus, hypoxia maintains a primitive extracellular matrix during heart valve development and promotes extracellular matrix remodeling in adult mice, as occurs in myxomatous disease.

Expression changes in pelvic organ prolapse: a systematic review and in silico study

Pelvic organ prolapse (POP) is a highly disabling condition common for a vast number of women worldwide. To contribute to existing knowledge in POP pathogenesis, we performed a systematic review of expression studies on both specific gene and whole-genome/proteome levels and an in silico analysis of publicly available datasets related to POP development. The most extensively investigated genes in individual studies were related to extracellular matrix (ECM) organization. Three premenopausal and two postmenopausal sets from two Gene Expression Omnibus (GEO) studies (GSE53868 and GSE12852) were analyzed; Gene Ontology (GO) terms related to tissue repair (locomotion, biological adhesion, immune processes and other) were enriched in all five datasets. Co-expression was higher in cases than in controls in three premenopausal sets. The shared between two or more datasets up-regulated genes were enriched with those related to inflammatory bowel disease (IBD) in the NHGRI GWAS Catalog. ECM-related genes were not over-represented among differently expressed genes. Up-regulation of genes related to tissue renewal probably reflects compensatory mechanisms aimed at repair of damaged tissue. Inefficiency of this process may have different origins including age-related deregulation of gene expression.

Pathophysiology of Aortic Stenosis and Mitral Regurgitation

The global impact of the spectrum of valve diseases is a crucial, fast-growing, and underrecognized health problem. The most prevalent valve diseases, requiring surgical intervention, are represented by calcific and degenerative processes occurring in heart valves, in particular, aortic and mitral valve. Due to the increasing elderly population, these pathologies will gain weight in the global health burden. The two most common valve diseases are aortic valve stenosis (AVS) and mitral valve regurgitation (MR). AVS is the most commonly encountered valve disease nowadays and affects almost 5% of elderly population. In particular, AVS poses a great challenge due to the multiple comorbidities and frailty of this patient subset. MR is also a common valve pathology and has an estimated prevalence of 3% in the general population, affecting more than 176 million people worldwide. This review will focus on pathophysiological changes in both these valve diseases, starting from the description of the anatomical aspects of normal valve, highlighting all the main cellular and molecular features involved in the pathological progression and cardiac consequences. This review also evaluates the main approaches in clinical management of these valve diseases, taking into account of the main published clinical guidelines. © 2017 American Physiological Society. Compr Physiol 7:799-818, 2017.

Effect of altered haemodynamics on the developing mitral valve in chick embryonic heart

Intracardiac haemodynamics is crucial for normal cardiogenesis, with recent evidence showing valvulogenesis is haemodynamically dependent and inextricably linked with shear stress. Although valve anomalies have been associated with genetic mutations, often the cause is unknown. However, altered haemodynamics have been suggested as a pathogenic contributor to bicuspid aortic valve disease. Conversely, how abnormal haemodynamics impacts mitral valve development is still poorly understood. In order to analyse altered blood flow, the outflow tract of the chick heart was constricted using a ligature to increase cardiac pressure overload. Outflow tract-banding was performed at HH21, with harvesting at crucial valve development stages (HH26, HH29 and HH35). Although normal valve morphology was found in HH26 outflow tract banded hearts, smaller and dysmorphic mitral valve primordia were seen upon altered haemodynamics in histological and stereological analysis at HH29 and HH35. A decrease in apoptosis, and aberrant expression of a shear stress responsive gene and extracellular matrix markers in the endocardial cushions were seen in the chick HH29 outflow tract banded hearts. In addition, dysregulation of extracellular matrix (ECM) proteins fibrillin-2, type III collagen and tenascin were further demonstrated in more mature primordial mitral valve leaflets at HH35, with a concomitant decrease of ECM cross-linking enzyme, transglutaminase-2. These data provide compelling evidence that normal haemodynamics are a prerequisite for normal mitral valve morphogenesis, and abnormal blood flow could be a contributing factor in mitral valve defects, with differentiation as a possible underlying mechanism.

Bioinspired Engineering of Poly(ethylene glycol) Hydrogels and Natural Protein Fibers for Layered Heart Valve Constructs

Layered constructs from poly(ethylene glycol) (PEG) hydrogels and chicken eggshell membranes (ESMs) are fabricated, which can be further cross-linked by glutaraldehyde (GA) to form GA-PEG-ESM composites. Our results indicate that ESMs composed of protein fibrous networks show elastic moduli ∼3.3-5.0 MPa and elongation percentages ∼47-56%, close to human heart valve leaflets. Finite element simulations reveal obvious stress concentration on a partial number of fibers in the GA-cross-linked ESM (GA-ESM) samples, which can be alleviated by efficient stress distribution among multiple layers of ESMs embedded in PEG hydrogels. Moreover, the polymeric networks of PEG hydrogels can prevent mineral deposition and enzyme degradation of protein fibers from incorporated ESMs. The fibrous structures of ESMs retain in the GA-PEG-ESM samples after subcutaneous implantation for 4 weeks, while those from ESM and GA-ESM samples show early degradation to certain extent, suggesting the prevention of enzymatic degradation of protein fibers by the polymeric network of PEG hydrogels in vivo. Thus, these GA-PEG-ESM layered constructs show heterogenic structures and mechanical properties comparable to heart valve leaflets, as well as improved functions to prevent progressive calcification and enzymatic degeneration, which are likely used for artificial heart valves.

Bone Mineral Density Is Positively Related to Carotid Intima-Media Thickness: Findings From a Population-Based Study in Adolescents and Premenopausal Women

Osteoporosis and cardiovascular disease (CVD) are both common causes of morbidity and mortality. Previous studies, mainly of people older than 60 years, suggest a relationship between these conditions. Our aim was to determine the association between bone characteristics and CVD markers in younger and middle-aged individuals. Women (n = 3366) and their adolescent offspring (n = 4368) from the UK population-based cohort study, Avon Longitudinal Study of Parents and Children (ALSPAC), were investigated. We measured total body (TB) and hip bone mineral density (BMD), TB bone area (BA) and bone mineral content (BMC) by dual-energy X-ray absorptiometry (DXA), and carotid intima-media thickness (cIMT) by high-resolution ultrasound. Arterial distensibility was calculated as the difference between systolic and diastolic arterial diameters. Linear regression determined associations between bone exposures and cIMT (in adolescents) and both cIMT and arterial distensibility (in women), generating partial correlation coefficients. Mean (SD) age of women was 48 (4.2) years, body mass index (BMI) was 26.2 (5.0) kg/m² , and 71% were premenopausal. In confounder-adjusted analyses (age, height, lean mass, fat mass, menopause, smoking, estrogen replacement, calcium/vitamin D supplementation, and education) TB and hip BMD were both positively associated with cIMT (0.071 [0.030, 0.112], p = 0.001; 0.063 [0.025, 0.101], p = 0.001, respectively). Femoral neck BMD and TB BMD, BMC, and BA were positively associated with arterial distensibility. Mean (SD) age of adolescents was 17 (0.4) years, BMI was 23 (4.1) kg/m² , and 44.5% were male. Total hip and TB measurements were positively associated with cIMT, with similar magnitudes of association to those found in their mothers. In contrast to most published findings, we identified weak positive associations between BMD and cIMT in predominantly premenopausal women and their adolescent offspring. We found greater femoral neck BMD and TB DXA measurements to be associated with reduced arterial stiffness. Rather than a relationship with preclinical atherosclerosis, in these relatively young populations, we speculate our associations between BMD, cIMT, and arterial distensibility may reflect a shared relationship between bone and vascular growth and development. © 2016 American Society for Bone and Mineral Research.