Defective NOTCH signaling drives increased vascular smooth muscle cell apoptosis and contractile differentiation in bicuspid aortic valve aortopathy: A review of the evidence and future directions

Abstract

OBJECTIVES: Bicuspid aortic valve disease is common and is associated with ascending aortic aneurysms. Vascular smooth muscle cell (VSMC) apoptosis is characteristic of the ascending aorta of bicuspid patients, and NOTCH1 gene mutations have also been linked to the disease. NOTCH signalling is a fundamental cell signalling pathway, which dictates cell fate decisions including apoptosis. Our objective was to elucidate the role of NOTCH signalling in VSMC apoptosis and differentiation in bicuspid aortopathy. METHODS: Ascending aortic biopsies were obtained from 19 bicuspid and 12 tricuspid aortic valve patients and were sub-classified into 4 groups according to the maximum ascending aortic diameter (aneurysmal > _45 mm). Apoptotic VSMCs were counted by light microscopy using a TUNEL assay. Gene expression of key regulators of NOTCH signalling (NOTCH1 and HES1), apoptosis (BAX and BCL-2) and VSMC differentiation (MYH11, CNN1 and MYH10) were quantified using quantitative real-time PCR. Primary VSMCs were cultured from 2 tricuspid aortic valve and 2 bicuspid aortic valve patients, NOTCH signalling was inhibited with N-[N-(3,5-Difluorophenacetyl)-l-alanyl]-Sphenylglycine t-butyl ester, and the gene expression was again quantified. RESULTS: The apoptotic cell count was significantly higher in bicuspid aortic valve patients (3.2 cells/50 000 lm 2 vs 1.1 cells/50 000 lm 2 ; P = 0.033). There was a trend towards lower apoptotic cell count in the aneurysmal versus non-aneurysmal tricuspid and bicuspid groups and an increased ratio of proapoptotic gene expression, which was not statistically significant. This was associated with a 2.8-fold increase in contractile gene expression (P = 0.026) and a 2.0-fold increase in NOTCH signalling gene expression in bicuspid versus tricuspid aortic valve patients (P = 0.022). NOTCH inhibition in cultured VSMCs induced a similar pattern of increased proapoptotic and procontractile gene expressions. CONCLUSIONS: This preliminary study suggests that NOTCH activation in the non-aneurysmal bicuspid aortas may underlie aortopathy by influencing VSMC apoptosis and differentiation. NOTCH signalling manipulation may provide a therapeutic target for preventing aneurysms in bicuspid patients. Further studies with larger sample sizes are needed to substantiate the present findings.

Divergent effects of canonical and non‐canonical TGF‐β signalling on mixed contractile‐synthetic smooth muscle cell phenotype in human Marfan syndrome aortic root aneurysms

“…Four Notch receptors (Notch 1‐4) have been described in humans and represent large transmembrane proteins that bind ligands expressed on adjacent cells . Because Notch plays a key role in neural crest migration and SMC differentiation during ascending aorta/aortic arch development, abnormal signalling may predispose to aneurysm formation . Although Notch signalling has not been studied in MFS, Notch1 gene mutations have been reported in patients with bicuspid aortic valves (BAV) and BAV aortopathy.…”

A novel de novo dominant mutation of NOTCH1 gene in an Iranian family with non‐syndromic congenital heart disease

“…According to the previous studies 11,[26][27][28] 31 Gerhardt et al generated knockout mice lacking NOTCH1 TAD to investigate the role of this domain, their functional assays displayed the importance of the TAD in mammalian cardiac development. 32 NOTCH1 variants have been observed in several types of CHD including BAV, 33 AS, HLHS, COA, TOF, 34 left ventricular outflow tract obstructive (LVOTO), 35 and pulmonary stenosis (PS). 36 In our pedigree, we found a patient with VSD (IV-1) and other with PDA and AVSD (IV-2).…”

The Development of the Ascending Aortic Wall in Tricuspid and Bicuspid Aortic Valve: A Process from Maturation to Degeneration

“…BAV aortas are characterized by dedifferentiated VSCMs without the ability to undergo a phenotypic switch [18]. Moreover, BAV aortas also exhibit significantly more apoptosis as compared to the TAV [34,35].…”