THORACIC AORTIC DILATIONS IN PATIENTS WITH BICUSPID AORTIC VALVE DISEASE IS MARKED BY ACCELERATED SMOOTH MUSCLE CELL AGING

Abstract

Individuals with a bicuspid aortic valve (BAV) are at increased risk for ascending aortic dilation and dissection. Loss of aortic medial smooth muscle cells (SMCs) and disruption of the extracellular matrix are well-recognized pathologies, but the underlying cellular mechanisms remain elusive. We tested the hypothesis that the dilated aorta in patients with BAV was marked by accelerated cellular aging. Samples of human ascending aorta were obtained from individuals with BAV undergoing thoracic aorta replacement (n=37, age 54.7±2.2, aortic diameter 4.8±0.9 cm) or patients with a tricuspid aortic valve and non-dilated aorta undergoing heart transplantation or coronary bypass procedures (n=8, age 55.3±8.1, aortic diameter 3.1±0.3 cm). Assessment of fresh aortic samples for senescence-associated β-galactosidase revealed evidence for rare medial cell senescence that was 4.2-fold more prevalent in dilated aortas (0.83±0.10%) than in non-dilated aortas (0.20±0.10%, p=0.048). Expression of p16 was abundantly detected in medial SMCs within dilated aortas (24.0±1.5%) and 3-fold more abundant than in non-dilated aortas (8.2±1.5%, p<0.0001). Interestingly, medial p16 expression did not correlate with telomere length of medial cells, as determined by quantitative and standardized PCR (p=0.35). Immunostaining for γH2A.X (phosphorylated Ser139) interestingly revealed discrete nuclear DNA double-strand breakage signals in 25.7±3.8% of medial cells in dilated aortas from patients with BAV, which was 2.3-fold higher than that found in non-dilated aortas (11.0±4.9, p=0.03). Medial cell outgrowths from BAV patients showed increased senescence-associated ß-galactosidase activity compared to control patient SMC outgrowths (38.9±2.9 vs. 19.5±1.9, p=0.0005). Furthermore, incubation of early passage SMCs with 50nM of angiotensin II for 3 days caused a 1.4-fold increase in senescence-associated ß-galactosidase expressing SMCs from BAV patients (p=0.0006), but elicited no change in senescence-associated ß-galactosidase expression in SMCs from control patients (p=0.83). These findings identify a previously unrecognized phenomenon of accelerated SMC aging in the aortas of patients with BAV, with cellular senescence and unresolved DNA breaks. Accelerated cell aging could thus be a driver of aortic wall degeneration in these patients and a potential therapeutic target.