Comparison of biomechanical properties in ascending aortic aneurysms of patients with congenital bicuspid aortic valve and Marfan syndrome.

BACKGROUND: In patients with ascending aortic aneurysms (AscAA), biomechanical differences are seen among patients with congenital bicuspid aortic valves (BAV), Marfan syndrome (MFS), and tricuspid aortic valves (TAV). We examined the hemodynamic profiles and ultrastructures of aneurysmal specimens, focusing on vascular remodelling to better understand AscAA pathogenesis. METHODS: A total of 795 patients with BAV (43.97 ±â€¯0.51 years; 93.2% male), 69 with MFS (34.43 ±â€¯1.44 years; 86.2% male), and 90 with TAV (67.27 ±â€¯0.58 years; 60% male) were enrolled, primarily upon admission with AscAA. The biomechanical properties of the aortic root were assessed and intraoperative specimens were analyzed by light-microscopy and two-photon autofluorescence microscopy. RESULTS: Patients with BAV had significantly greater distension of the aortic root, irrespective of age or aneurysmal widening (R2 = 0.543, p < 0.05). This was associated with significantly increase in the size of the tunica media. Patients with MFS displayed significant stiffness in the sinuses that worsened with age (R2 = 0.752, p < 0.001), similar to patients with TAV (R2 = 0.626, p < 0.05). Patients with MFS showed significant root elasticity with aneurysmal growth (R2 = 0.596, p < 0.05) and increased medial degeneration. Patients with TAV maintained biomechanical properties, apart from aneurysmal dimensions and high levels of inflammation. CONCLUSIONS: Among patients with AscAA, those with BAV maintain tissue elasticity in the aortic root, regardless of age. Patients with MFS demonstrate increased sinus stiffness with medial degeneration, both during aging and with aneurysmal growth. Patients with TAV and AscAA present with increased inflammation.

ROBO4 variants predispose individuals to bicuspid aortic valve and thoracic aortic aneurysm.

Bicuspid aortic valve (BAV) is a common congenital heart defect (population incidence, 1-2%)1-3 that frequently presents with ascending aortic aneurysm (AscAA)4. BAV/AscAA shows autosomal dominant inheritance with incomplete penetrance and male predominance. Causative gene mutations (for example, NOTCH1, SMAD6) are known for ≤1% of nonsyndromic BAV cases with and without AscAA5-8, impeding mechanistic insight and development of therapeutic strategies. Here, we report the identification of variants in ROBO4 (which encodes a factor known to contribute to endothelial performance) that segregate with disease in two families. Targeted sequencing of ROBO4 showed enrichment for rare variants in BAV/AscAA probands compared with controls. Targeted silencing of ROBO4 or mutant ROBO4 expression in endothelial cell lines results in impaired barrier function and a synthetic repertoire suggestive of endothelial-to-mesenchymal transition. This is consistent with BAV/AscAA-associated findings in patients and in animal models deficient for ROBO4. These data identify a novel endothelial etiology for this common human disease phenotype.