An aortic aneurysm is characterized by widening of the aortic lumen diameter with adverse remodelling of the vascular extracellular matrix. A thoracic aortic aneurysm (TAA) is highly prevalent in patients with a bicuspid aortic valve (BAV). We investigated the structural remodelling in the aneurysmal ascending aorta in correlation to molecular alterations in male versus female BAV-TAA patients. Aneurysmal aortic samples (diameter >4.4 cm) from male and female patients were compared to non-aneurysmal non-BAV samples. The diameter of the aneurysmal aorta was smaller in females but comparable to that of male patients when normalized to body mass index. Disorganized elastin fibres and reduced elastin protein were found in samples from males and females with BAV-TAA. However, disarrayed collagen fibres and reduced protein were detected only in aortas from males with BAV-TAA. Elastin and collagen I messenger RNA (mRNA) levels were comparable in the BAV-TAA and control groups of both genders, suggesting post-translation degradation. Total elastase activity was elevated similarly in both genders. The activity of MT1-MMP, a potent collagenase, was increased more in aortic samples from males than females with BAV-TAA samples. MMP8 and MMP13 were lower whereas MMP2 was higher in female compared to samples from male BAV-TAA group. TIMP3 and TIMP4 decreased similarly in both genders, while TIMP2 increased in the female BAV-TAA group. Lower smooth muscle cell density in the medial layer of aortas from males with BAV-TAA samples corresponded to the increased caspase-3 cleavage compared to that of females.
Conclusion: We report a gender-dependent MMP/TIMP axis, collagen remodelling and smooth muscle cell (SMC) survival in the BAV-TAA aorta. The elevated TIMP2 could protect against the collagenolytic activity of MT1-MMP, leading to reduced collagen disarray and degradation in female BAV.
Key message: More collagen degradation/disarray and smooth muscle cell loss in male BAV-TAA patients. Similar elastin degradation/disarray in the aneurysmal aorta of both genders. Reduced collagen and elastin in BAV-TAA due to enhanced degradation, not reduced synthesis. Elevated TIMP2 in female BAV-TAA aortas protects against collagen degradation by MT1-MMP.