In conclusion, our study demonstrates that subjects with BAV display a significant deregulation of TLR4 signaling pathway paralleled by a deregulation of Notch-1 pathway, as previously showed.
Mutations in the NOTCH1 gene are one of only a few genetic anomalies identified in BAV disease; however evidence for defective NOTCH signaling, and its involvement in the characteristic histological changes of VSMC apoptosis and differentiation in ascending aortae of BAV patients is lacking.
NOTCH1 gene mutations might potentially contribute to the development of thoracic aortic aneurysms by affecting SMC differentiation in some patients with bicuspid aortic valve.
These findings are the first to our knowledge to demonstrate an SHF lineage-specific role for Notch1 in AscAA and suggest that genes linked to the development of BAV may also contribute to the associated aortopathy.
Furthermore, several mouse models of BAV have been described defining the role of endothelial Notch1 in aortic valve morphogenesis, whereas others have implicated new genes.
Nine genes previously associated with BAV (NOTCH1, AXIN1, EGFR, ENG, GATA5, NKX2-5, NOS3, PDIA2, and TGFBR2) were sequenced in 48 patients with BAV using the Ion Torrent Personal Genome Machine.
All exons and splice junctions of NOTCH1 were sequenced in probands from 13 affected families presenting with bicuspid aortic valve with ascending aortic aneurysm in the absence of valve calcification.
Two novel NOTCH1 mutations were identified in two Italian families with BAV, highlighting the role of a NOTCH1 signaling pathway in BAV and its aortic complications.
Bicuspid aortic valve (BAV) is the commonest congenital heart disease and a highly heritable trait; however, only the NOTCH1 gene has been linked to limited cases of BAV in humans.
We performed a targeted mutational analysis of NOTCH1 using genomic DNA from 48 unrelated subjects with concomitant bicuspid aortic valve and thoracic aortic aneurysm using denaturing high-performance liquid chromatography and DNA sequencing.
Here, we utilized human induced pluripotent stem cell (iPSC)-derived endothelial cells (ECs) to show that heterozygous nonsense mutations in NOTCH1 that cause aortic valve calcification disrupt the epigenetic architecture, resulting in derepression of latent pro-osteogenic and -inflammatory gene networks.
Corroborating previous studies, analysis of the single sporadic patient with calcified aortic valve in the presence of ascending aortic aneurysm revealed a novel heterozygous missense mutation in NOTCH1 resulting in a nonsynonymous amino acid substitution (p.T1090S, c.C3269G) of an evolutionarily conserved residue.
The NOTCH signaling pathway was linked to a molecular pathway for aortic valve calcification, as NOTCH1 was found to repress activation of Runx2 - a transcription factor critical for osteoblast cell fate that is up-regulated in calcified human aortic valves.