Alexander Guidry

Introduction. Bicuspid aortic valve (BAV) is the most common congenital heart effect to date.¹ Patients diagnosed with BAV are at higher risk of getting thoracic aneurysms, endocarditis, and aortic valve calcifications.¹ The etiology is mostly unknown though researchers have found that mutated NOTCH1 is the main gene involved.¹ NOTCH1 is transmembrane involved in cell fate and differentiation, specifically endothelial cells in the aortic valves.³ MiRNA, mechanosignaling, and small molecules have an important interaction with NOTCH1 that could be the future of BAV gene therapy.^5,6,7 Methods. A donor was used to Induce pluripotent stem cells in which CRISPR was used to knockout the NOTCH1 gene, examined how smooth muscle cells and aortic valve endothelial cells would differentiate without NOTCH1.⁴ Twenty pregnant mice were injected with valproic acid, measured miRNA-34a and other key NOTCH1 genes.⁵ In a following study, researchers wanted to look at the transcriptional downstream effects of dysregulated NOTCH1, 63 patients with missense mutations in NOTCH1 had blood smears done to calculate circulating miRNA-145 levels.³ To better understand the role of mechanical forces on valvulogenesis, researchers used zebrafish embryos to examine out flow tract growth.⁶ Embryos were fixed at the desired stage in 4% paraformaldehyde overnight at 4°C. Anti-sense probes were used on NOTCH1b and klfa2 to visualize during live imaging.⁶ This allowed the researchers to examine where exactly in the outflow tract NOTCH1b and klfa2 had highest expression.⁶ Lastly, a small machinery algorithm was used to identify if endothelial cells were N1 haploinsufficient or wildtype when combined with small molecules for reversion back to normal phenotype.⁷ Results. Smooth muscle cells were shown to have a significant loss of contractile protein while endothelial cell differentiation was greatly reduced without NOTCH1.⁴ High levels of miRNA-34a showed low levels of NOTCH1 expression, contributing to CHD.⁵ Truncated NOTCH1 lowered the transcriptional activity of mi-RNA145, manifesting immature contractile proteins in smooth muscle.³ Klf2a and Notch signaling are activated specifically in the part of the valve corresponding to where the OFT has the smallest diameter and where shear stress is expected to be the highest.⁶ XCT790 was most efficient small molecule, effectively restoring the transcription of mesoderm and cell cycle checkpoint genes.⁷ Conclusions. Etiology is largely unknown for BAV, but it has been shown that NOTCH1 is the prime target for gene therapy.¹ MiRNA play a major role in manifesting BAV and associated diseases while mechanical forces are also needed to generate correct signaling in valves.^3,5,6 Small molecule inhibitors are the future for preventing calcification in aortic valves.⁷

1. Balistreri CR, Crapanzano F, Schirone L, et al. Deregulation of Notch1 pathway and circulating endothelial progenitor cell (EPC) number in patients with bicuspid aortic valve with and without ascending aorta aneurysm. Sci Rep. 2018;8(1):13834. Published 2018 Sep 14. doi:10.1038/s41598-018-32170-2
2. Debiec R, Hamby SE, Jones PD, et al. Novel loss of function mutation in NOTCH1 in a family with bicuspid aortic valve, ventricular septal defect, thoracic aortic aneurysm, and aortic valve stenosis. Mol Genet Genomic Med. 2020;8(10):e1437. doi:10.1002/mgg3.1437
3. Girdauskas E, Petersen J, Neumann N, et al. MiR-145 expression and rare NOTCH1 variants in bicuspid aortic valve-associated aortopathy. PLoS One. 2018;13(7):e0200205. Published 2018 Jul 30. doi:10.1371/journal.pone.0200205
4. Jiao J, Tian W, Qiu P, et al. Induced pluripotent stem cells with NOTCH1 gene mutation show impaired differentiation into smooth muscle and endothelial cells: Implications for bicuspid aortic valve-related aortopathy. J Thorac Cardiovasc Surg. 2018;156(2):515-522.e1. doi:10.1016/j.jtcvs.2018.02.087
5. Wu KH, Xiao QR, Yang Y, et al. MicroRNA-34a modulates the Notch signaling pathway in mice with congenital heart disease and its role in heart development. J Mol Cell Cardiol. 2018;114:300-308. doi:10.1016/j.yjmcc.2017.11.015
6. Duchemin AL, Vignes H, Vermot J. Mechanically activated piezo channels modulate outflow tract valve development through the Yap1 and Klf2-Notch signaling axis. Elife. 2019;8:e44706. Published 2019 Sep 16. doi:10.7554/eLife.44706
7. Theodoris CV, Zhou P, Liu L, et al. Network-based screen in iPSC-derived cells reveals therapeutic candidate for heart valve disease. Science. 2021;371(6530):eabd0724. doi:10.1126/science.abd0724
8. Theodoris CV, Mourkioti F, Huang Y, et al. Long telomeres protect against age-dependent cardiac disease caused by NOTCH1 haploinsufficiency. J Clin Invest. 2017;127(5):1683-1688. doi:10.1172/JCI90338