Spontaneous Aortic Regurgitation and Valvular Cardiomyopathy in Mice

Myeloid CCN3 protects against aortic valve calcification

BACKGROUND

Cellular communication network factor 3 (CCN3) has been implicated in the regulation of osteoblast differentiation. However, it is not known if CCN3 can regulate valvular calcification. While macrophages have been shown to regulate valvular calcification, the molecular and cellular mechanisms of this process remain poorly understood. In the present study, we investigated the role of macrophage-derived CCN3 in the progression of calcific aortic valve disease.

METHODS

Myeloid-specific knockout of CCN3 (Mye-CCN3-KO) and control mice were subjected to a single tail intravenous injection of AAV encoding mutant mPCSK9 (rAAV8/D377Y-mPCSK9) to induce hyperlipidemia. AAV-injected mice were then fed a high fat diet for 40 weeks. At the conclusion of high fat diet feeding, tissues were harvested and subjected to histologic and pathologic analyses. In vitro, bone marrow-derived macrophages (BMDM) were obtained from Mye-CCN3-KO and control mice and the expression of bone morphogenic protein signaling related gene were verified via quantitative real-time PCR and Western blotting. The BMDM conditioned medium was cocultured with human valvular intersititial cells which was artificially induced calcification to test the effect of the conditioned medium via Western blotting and Alizarin red staining.

RESULTS

Echocardiography revealed that both male and female Mye-CCN3-KO mice displayed compromised aortic valvular function accompanied by exacerbated valve thickness and cardiac dysfunction. Histologically, Alizarin-Red staining revealed a marked increase in aortic valve calcification in Mye-CCN3-KO mice when compared to the controls. In vitro, CCN3 deficiency augmented BMP2 production and secretion from bone marrow-derived macrophages. In addition, human valvular interstitial cells cultured with conditioned media from CCN3-deficient BMDMs resulted in exaggerated pro-calcifying gene expression and the consequent calcification.

CONCLUSION

Our data uncovered a novel role of myeloid CCN3 in the regulation of aortic valve calcification. Modulation of BMP2 production and secretion in macrophages might serve as a key mechanism for macrophage-derived CCN3's anti-calcification function in the development of CAVD. Video Abstract.

S2 Heart Sound Detects Aortic Valve Calcification Independent of Hemodynamic Changes in Mice

Background

Calcific aortic valve disease (CAVD) is often undiagnosed in asymptomatic patients, especially in underserved populations. Although artificial intelligence has improved murmur detection in auscultation exams, murmur manifestation depends on hemodynamic factors that can be independent of aortic valve (AoV) calcium load and function. The aim of this study was to determine if the presence of AoV calcification directly influences the S2 heart sound.

Methods

Adult C57BL/6J mice were assigned to the following 12-week-long diets: (1) Control group (n = 11) fed a normal chow, (2) Adenine group (n = 4) fed an adenine-supplemented diet to induce chronic kidney disease (CKD), and (3) Adenine + HP (n = 9) group fed the CKD diet for 6 weeks, then supplemented with high phosphate (HP) for another 6 weeks to induce AoV calcification. Phonocardiograms, echocardiogram-based valvular function, and AoV calcification were assessed at endpoint.

Results

Mice on the Adenine + HP diet had detectable AoV calcification (9.28 ± 0.74% by volume). After segmentation and dimensionality reduction, S2 sounds were labeled based on the presence of disease: Healthy, CKD, or CKD + CAVD. The dataset (2,516 S2 sounds) was split subject-wise, and an ensemble learning-based algorithm was developed to classify S2 sound features. For external validation, the areas under the receiver operating characteristic curve of the algorithm to classify mice were 0.9940 for Healthy, 0.9717 for CKD, and 0.9593 for CKD + CAVD. The algorithm had a low misclassification performance of testing set S2 sounds (1.27% false positive, 1.99% false negative).

Conclusion

Our ensemble learning-based algorithm demonstrated the feasibility of using the S2 sound to detect the presence of AoV calcification. The S2 sound can be used as a marker to identify AoV calcification independent of hemodynamic changes observed in echocardiography.

Piezo1 is required for outflow tract and aortic valve development

AIMS

During embryogenesis, the onset of circulatory blood flow generates a variety of hemodynamic forces which reciprocally induce changes in cardiovascular development and performance. It has been known for some time that these forces can be detected by as yet unknown mechanosensory systems which in turn promote cardiogenic events such as outflow tract and aortic valve development. PIEZO1 is a mechanosensitive ion channel present in endothelial cells where it serves to detect hemodynamic forces making it an ideal candidate to play a role during cardiac development. We sought to determine whether PIEZO1 is required for outflow tract and aortic valve development.

METHODS AND RESULTS

By analysing heart development in zebrafish we have determined that piezo1 is expressed in the developing outflow tract where it serves to detect hemodynamic forces. Consequently, disrupting Piezo1 signalling leads to defective outflow tract and aortic valve development and indicates this gene may be involved in the etiology of congenital heart diseases. Based on these findings, we analysed genomic data generated from patients who suffer from left ventricular outflow tract obstructions (LVOTO) and identified 3 probands who each harboured potentially pathogenic variants in PIEZO1. Subsequent in vitro and in vivo assays indicates that these variants behave as dominant negatives leading to an inhibition of normal PIEZO1 mechanosensory activity. Expressing these dominant negative PIEZO1 variants in zebrafish endothelium leads to defective aortic valve development.

CONCLUSION

These data indicate that the mechanosensitive ion channel piezo1 is required for outflow tract and aortic valve development.

Impact of high-fat diet and vitamin D3 supplementation on aortic stenosis establishment in waved-2 epidermal growth factor receptor mutant mice

OBJECTIVE

The use of animal models of aortic stenosis (AS) remains essential to further elucidate its pathophysiology and to evaluate new therapeutic strategies. The waved-2 mouse AS model has been proposed; data have indicated that while aortic regurgitation (AR) is effectively induced, development of AS is rare. We aimed to evaluate the effect of high-fat diet (HFD) and vitamin D₃ supplementation in this model.

METHODS

HFD and subcutaneous vitamin D₃ injections were initiated at the age of 6 weeks until the age of 6 (n = 16, 6-month treatment group) and 9 (n = 11, 9-month treatment group) months. Twelve waved-2 mice without supplementation were used as control. Echocardiography was performed at 3, 6 and 9 months. Blood serum analysis (calcium, 1,25(OH)₂D₃ and cholesterol), histology and immunohistochemistry (CD-31, CD-68 and osteopontin) were evaluated at the end of the experiment (6 or 9 months).

RESULTS

Total cholesterol and 1,25(OH)₂D₃ were significantly increased relative to the control group. HFD and vitamin D₃ supplementation did result in improvements to the model, since AS was only detected in 6 (15.3%) mice (2 in the 3 groups) and AR was developed in the remaining animals. Echocardiographic parameters, fibrosis, thickness, inflammation and valvular calcification, were not significantly different between the 6-month treatment and control groups. Similar results were also observed in the 9-month treatment group.

CONCLUSION

These results suggest that HFD and vitamin D₃ supplementation have no effect in the waved-2 mouse model. This model essentially mimics AR and rarely AS. Further studies are needed to find a reliable animal model of AS.

Discovery of an Experimental Model of Unicuspid Aortic Valve

Background

The epithelial growth factor receptor family of tyrosine kinases modulates embryonic formation of semilunar valves. We hypothesized that mice heterozygous for a dominant loss‐of‐function mutation in epithelial growth factor receptor, which are Egfr^Vel/+ mice, would develop anomalous aortic valves, valve dysfunction, and valvular cardiomyopathy.

Methods and Results

Aortic valves from Egfr^Vel/+ mice and control mice were examined by light microscopy at 2.5 to 4 months of age. Additional Egfr^Vel/+ and control mice underwent echocardiography at 2.5, 4.5, 8, and 12 months of age, followed by histologic examination. In young mice, microscopy revealed anatomic anomalies in 79% of Egfr^Vel/+ aortic valves, which resembled human unicuspid aortic valves. Anomalies were not observed in control mice. At 12 months of age, histologic architecture was grossly distorted in Egfr^Vel/+ aortic valves. Echocardiography detected moderate or severe aortic regurgitation, or aortic stenosis was present in 38% of Egfr^Vel/+ mice at 2.5 months of age (N=24) and in 74% by 8 months of age. Left ventricular enlargement, hypertrophy, and reversion to a fetal myocardial gene expression program occurred in Egfr^Vel/+ mice with aortic valve dysfunction, but not in Egfr^Vel/+ mice with near‐normal aortic valve function. Myocardial fibrosis was minimal or absent in all groups.

Conclusions

A new mouse model uniquely recapitulates salient functional, structural, and histologic features of human unicuspid aortic valve disease, which are phenotypically distinct from other forms of congenital aortic valve disease. The new model may be useful for elucidating mechanisms by which congenitally anomalous aortic valves become critically dysfunctional.

Ultrasonographic and histological evaluation of the effects of long-term carotid catheterization on cardiac function in NMRI mice

Catheterization of laboratory mice is commonly performed in biomedical research to infuse substances and for blood sampling. One approach is to catheterize the right common carotid artery and advance the catheter until the tip is positioned in the aorta or the proximal brachiocephalic trunk. Owing to the small body size of the mouse, a catheter tends to occupy a great part of even the larger vessel lumens, and this may increase vascular resistance with potential pathophysiological impacts on the heart. The present study compared cardiac function of catheterized mice, with catheter tip placement in the brachiocephalic trunk, with sham-operated mice and non-operated control mice. During four weeks post-catheterization, M-mode echocardiography measurements of the thickness of the left ventricular anterior wall, left ventricular inner diameter and the thickness of the left ventricular posterior wall were performed. The left ventricular volume, ejection fraction and fractional shortening were calculated. Moreover, aortic recordings of the thickness of the medial and lateral walls as well as the inner diameter were measured. Terminally, histological analysis of the hearts was conducted, and body weights and heart weights were compared between groups. No effects on echocardiography parameters, histology, body weights or cardiac weights could be found between groups. In the present study, implantation of a carotid catheter with catheter tip placement in the proximal brachiocephalic trunk had minimal influence on cardiac and aortic physiology and did not induce significant cardiac changes.

Sequential Ligand-Dependent Notch Signaling Activation Regulates Valve Primordium Formation and Morphogenesis

RATIONALE

The Notch signaling pathway is crucial for primitive cardiac valve formation by epithelial-mesenchymal transition, and NOTCH1 mutations cause bicuspid aortic valve; however, the temporal requirement for the various Notch ligands and receptors during valve ontogeny is poorly understood.

OBJECTIVE

The aim of this study is to determine the functional specificity of Notch in valve development.

METHODS AND RESULTS

Using cardiac-specific conditional targeted mutant mice, we find that endothelial/endocardial deletion of Mib1-Dll4-Notch1 signaling, possibly favored by Manic-Fringe, is specifically required for cardiac epithelial-mesenchymal transition. Mice lacking endocardial Jag1, Notch1, or RBPJ displayed enlarged valve cusps, bicuspid aortic valve, and septal defects, indicating that endocardial Jag1 to Notch1 signaling is required for post-epithelial-mesenchymal transition valvulogenesis. Valve dysmorphology was associated with increased mesenchyme proliferation, indicating that Jag1-Notch1 signaling restricts mesenchyme cell proliferation non-cell autonomously. Gene profiling revealed upregulated Bmp signaling in Jag1-mutant valves, providing a molecular basis for the hyperproliferative phenotype. Significantly, the negative regulator of mesenchyme proliferation, Hbegf, was markedly reduced in Jag1-mutant valves. Hbegf expression in embryonic endocardial cells could be readily activated through a RBPJ-binding site, identifying Hbegf as an endocardial Notch target. Accordingly, addition of soluble heparin-binding EGF-like growth factor to Jag1-mutant outflow tract explant cultures rescued the hyperproliferative phenotype.

CONCLUSIONS

During cardiac valve formation, Dll4-Notch1 signaling leads to epithelial-mesenchymal transition and cushion formation. Jag1-Notch1 signaling subsequently restrains Bmp-mediated valve mesenchyme proliferation by sustaining Hbegf-EGF receptor signaling. Our studies identify a mechanism of signaling cross talk during valve morphogenesis involved in the origin of congenital heart defects associated with reduced NOTCH function.