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Deficient signaling via Alk2 (Acvr1) leads to bicuspid aortic valve development.

ABSTRACT: Bicuspid aortic valve (BAV) is the most common congenital cardiac anomaly in humans. Despite recent advances, the molecular basis of BAV development is poorly understood. Previously it has been shown that mutations in the Notch1 gene lead to BAV and valve calcification both in human and mice, and mice deficient in Gata5 or its downstream target Nos3 have been shown to display BAVs. Here we show that tissue-specific deletion of the gene encoding Activin Receptor Type I (Alk2 or Acvr1) in the cushion mesenchyme results in formation of aortic valve defects including BAV. These defects are largely due to a failure of normal development of the embryonic aortic valve leaflet precursor cushions in the outflow tract resulting in either a fused right- and non-coronary leaflet, or the presence of only a very small, rudimentary non-coronary leaflet. The surviving adult mutant mice display aortic stenosis with high frequency and occasional aortic valve insufficiency. The thickened aortic valve leaflets in such animals do not show changes in Bmp signaling activity, while Map kinase pathways are activated. Although dysfunction correlated with some pro-osteogenic differences in gene expression, neither calcification nor inflammation were detected in aortic valves of Alk2 mutants with stenosis. We conclude that signaling via Alk2 is required for appropriate aortic valve development in utero, and that defects in this process lead to indirect secondary complications later in life.

SUBMITTER: Thomas PS

PROVIDER: S-EPMC3334911 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BACKGROUND: A better understanding of the molecular mechanism of aortic valve development and bicuspid aortic valve (BAV) formation would significantly improve and optimize the therapeutic strategy for treating BAV patients. Over the past decade, the genes involved in aortic valve development and BAV formation has been increasingly recognized. On the other hand, ADAMTS gene family members have been reported to be able to modulate cardiovascular development and diseases. The present study aimed to further investigate the roles of ADAMTS family members in aortic valve development and BAV formation. METHODS: Morpholino-based ADAMTS family gene-targeted screening for zebrafish heart outflow tract phenotypes combined with DNA sequencing in a 304 cohort BAV patient registry study was initially carried out to identify potentially related genes. Both ADAMTS gene-specific fluorescence in situ hybridization assay and genetic tracing experiments were then performed to evaluate the expression pattern in the aortic valve Accordingly, related genetic mouse models (both knock-out and knock-in) were generated using the CRISPR/Cas9 method to further study the roles of ADAMTS family genes. The lineage tracing technique was used again to evaluate how the cellular activity of specific progenitor cells was regulated by ADAMTS genes. Bulk RNA sequencing was used to investigate the signaling pathways involved. Both inducible pluripotent stem cells (iPSC) derived from BAV patients and genetic mouse tissue were used to study the molecular mechanism of the gene. Immunohistochemistry using different antibodies was performed to describe the phenotype of cardiac valve anomalies, especially in the ECM components. RESULTS: ADAMTS genes targeted phenotype screening in zebrafish and targeted DNA sequencing on a cohort of BAV patients identified ADAMTS16 as a BAV-causing gene and found the ADAMTS16 p.H357Q variant in an inherited BAV family. In addition, both in situ hybridization and genetic tracing studies described a unique spatiotemporal pattern of ADAMTS16 expression during aortic valve development. Adamts16+/- and Adamts16+/H355Q mouse models both exhibited an R-NC-type BAV phenotype, with progressive aortic valve thickening associated with raphe formation (fusion of the commissure). Conditional Adamts16 mutant mouse models further demonstrated that Adamts16 deficiency mainly in endothelial lineage cells recapitulated the BAV phenotype. This was confirmed in lineage tracing mouse models in which Adamts16 deficiency affected endothelial and second heart field cells, not the neural crest cells. Accordingly, the changes were mainly detected in the noncoronary and right coronary leaflets. Bulk RNA sequencing using iPSC-induced endothelial cells (iPSC-ECs) and genetic mouse embryonic heart tissue unveiled enhanced FAK signaling, which was accompanied by elevated fibronectin levels. Both in vitro iPSC-ECs culture and ex vivo embryonic outflow tract explant studies validated the altered FAK signaling. CONCLUSIONS: Our present study identified a novel BAV-causing ADAMTS16 p. H357Q variant. ADAMTS16 deficiency led to BAV formation. We then performed gene expression profiling analysis using data obtained from RNA-seq of 15 different tissues of different genetic mice.

Project description:ImportanceThe outcomes of transcatheter aortic valve replacement (TAVR) in low-risk patients with bicuspid aortic valve stenosis have not been studied in a large scale, multicentered, prospective fashion.ObjectiveTo evaluate the procedural safety, efficacy, and 30-day outcomes of TAVR in patients with bicuspid aortic stenosis at low surgical risk.Design, setting, and participantsThe Low Risk Bicuspid Study is a prospective, single-arm trial study with inclusion/exclusion criteria developed from the Evolut Low Risk Randomized Trial. Follow-up is planned for 10 years. Patients underwent TAVR at 25 centers in the United States who were also participating in the Evolut Low Risk Randomized Trial from December 2018 to October 2019. Eligible patients had severe bicuspid aortic valve stenosis and met American Heart Association/American College of Cardiology guideline indications for aortic valve replacement.InterventionsPatients underwent attempted implant of an Evolut or Evolut PRO transcatheter aortic valve, with valve size based on annular measurements.Main outcomes and measuresThe prespecified primary end point was the incidence of all-cause mortality or disabling stroke at 30 days. The prespecified primary efficacy end point was device success defined as the absence of procedural mortality, the correct position of 1 bioprosthetic heart valve in the proper anatomical location, and the absence of more than mild aortic regurgitation postprocedure.ResultsA total of 150 patients underwent an attempted implant. Baseline characteristics include mean age of 70.3 (5.5) years, 48.0% female (n = 72), and a mean Society of Thoracic Surgeons score of 1.4 (0.6%). Most patients (136; 90.7%) had Sievers type I valve morphology. The incidence of all-cause mortality or disabling stroke was 1.3% (95% CI, 0.3%-5.3%) at 30 days. The device success rate was 95.3% (95% CI, 90.5%-98.1%). At 30 days, the mean (SD) AV gradient was 7.6 (3.7) mm Hg and effective orifice area was 2.3 (0.7) cm2. A new permanent pacemaker was implanted in 22 patients (15.1%). No patients had greater than mild paravalvular leak.Conclusions and relevanceTranscatheter aortic valve replacement in low-surgical risk patients with bicuspid aortic valve stenosis achieved favorable 30-day results, with low rates of death and stroke and high device success rate.Trial registrationClinicalTrials.gov Identifier: NCT03635424.

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Deficient signaling via Alk2 (Acvr1) leads to bicuspid aortic valve development.

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