Ascending aorta dilation in association with bicuspid aortic valve: a maturation defect of the aortic wall

Patients with a bicuspid aortic valve have increased susceptibility to the development of ascending aortic dilation and dissection compared with persons with a tricuspid valve. To unravel a possible different mechanism underlying dilation in bicuspidy and tricuspidy, a comparison of the structure of the aortic wall was made.

Ascending aortic wall biopsies were divided into 4 groups: bicuspid (n=36) and tricuspid (n=23) without and with dilation. The expression of vascular smooth muscle cell maturation markers including lamin A/C, which plays a pivotal role in smooth muscle cell differentiation, and its splicing variant progerin indicative of aging, were studied immunohistochemically. Attention was also paid to the inflammatory status.

There is a significant difference in the structure and maturation of the aortic wall in bicuspidy, persisting in the dilated aortic wall, presenting with a thinner intima, lower expression of α smooth muscle actin, smooth muscle 22α, calponin, and almost absent expression of smoothelin. We show for the first time significantly lowered lamin A/C expression in bicuspidy. Progerin was found to be significantly increased in the media of the dilated wall in tricuspidy, also showing increased periaortic inflammation.

The structure of the nondilated and dilated aortic wall in bicuspidy and tricuspidy are intrinsically different, with the latter having more aspects of aging. In bicuspidy there is a defective smooth muscle cell differentiation possibly linked to lowered lamin A/C expression. Based on this vessel wall immaturity and increased susceptibility to dilation, different diagnostic and therapeutic approaches are warranted.