Vascular matrix remodeling in patients with bicuspid aortic valve malformations: Implications for aortic dilatation

Background: Patients with bicuspid aortic valve malformations are at an increased risk of aortic dilatation, aneurysm formation, and dissection. Vascular tissues with deficient fibrillin-1 microfibrils release matrix metalloproteinases, enzymes that weaken the vessel wall by degrading elastic matrix components. In bicuspid aortic valve disease a deficiency of fibrillin-1 and increased matrix metalloproteinase matrix degradation might result in aortic degeneration and dilatation. Methods: Samples of the pulmonary artery and aorta were obtained from surgical patients with bicuspid aortic valves (n = 21) and tricuspid aortic valves (n = 16). Results: Fibrillin-1 content was reduced in bicuspid aortic valve aortas compared with that seen in tricuspid aortic valve aortas (P = .001), whereas the associated matrix components, elastin and collagen, were unchanged (P = .51 and P = .21). Reductions of aortic fibrillin-1 content were independent of valve function and patient age. Compared with tricuspid aortic valve aorta, matrix metalloproteinase 2 activity was increased more than 2-fold in bicuspid aortic valve aortas (P = .04) and correlated positively with aortic diameter (r = 0.74, P =.05). Matrix metalloproteinase 9 activity was not significantly different. Fibrillin-1 content was also reduced in the pulmonary arteries of patients with bicuspid aortic valves (P = .06), suggesting a systemic deficiency of fibrillin-1. Promatrix metalloproteinase 2 was increased (P = .04), reflecting an increased production of matrix metalloproteinase 2 in these fibrillin-1-deficient tissues, whereas active matrix metalloproteinase 2 and matrix metalloproteinase 9 species were unchanged, and correspondingly, the pulmonary arteries were not dilated. Conclusions: Deficient fibrillin-1 content in the vasculature of patients with bicuspid aortic valves might trigger matrix metalloproteinase production, leading to matrix disruption and dilatation. This process of vascular matrix remodeling in patients with bicuspid aortic valves offers novel therapeutic targets to prevent the aortic degeneration and dilatation characteristic of this disease.