Spatiotemporal patterns of smooth muscle cell changes in ascending aortic dilatation with bicuspid and tricuspid aortic valve stenosis: focus on cell-matrix signaling

Abstract

Objective: The present study examined temporal and spatial patterns of extracellular matrix and smooth muscle cell changes in the ascending aorta with bicuspid and tricuspid aortic valve stenosis.

Methods: Wall specimens were retrieved from both the greater and the lesser curvature ("convexity" and "concavity") of 14 nonaneurysmal and 12 aneurysmal aortas (aortic ratios 1.2 and 1.5, respectively) and from 3 heart donors (normal). Immunochemistry was performed for detection of apoptotic (terminal deoxynucleotidyl transferase-mediated dUTP nick end labelling [TUNEL]-positive) and proliferating (Ki-67-positive) smooth muscle cells and for semiquantification of matrix proteins (collagens, fibronectin, tenascin, laminin). Co-immunoprecipitation assessed the extent of Bcl-2-modifying factor binding to Bcl-2, indicating a matrix-derived cytoskeleton-mediated proapoptotic signaling. Polymerase chain reaction allowed for quantification of messenger RNA expression for Bcl-2.

Results: In both bicuspid and tricuspid aneurysms, fibrillar collagens were reduced, whereas fibronectin and tenascin were increased compared with those in normal conditions. These matrix alterations were already evident in bicuspid nonaneurysmal aortas at the convexity, with significant elevation of apoptotic indexes (P = .02 bicuspid vs normal; P = .48 tricuspid vs normal). Apoptotic indexes correlated with aortic dimensions only in tricuspid aortas (P = .01). No significant increase in Ki-67 was found. Higher levels of Bcl-2-modifying factor-Bcl-2 binding were found in bicuspid nonaneurysmal aorta versus tricuspid (P = .03) and normal aortas (P = .01). Bcl-2 messenger RNA expression was reduced in the bicuspid aorta versus normal (P = .08).

Conclusions: Smooth muscle cell apoptosis with bicuspid aortic valve stenosis occurred before overt aortic dilation, mainly at the convexity, where wall stress is expectedly higher. In this setting, a matrix-dependent proapoptotic signaling was evidenced by increased Bcl-2-modifying factor-Bcl-2 binding. Stress-dependent bicuspid aortic valve matrix changes may trigger early apoptosis by inducing cytoskeletal rearrangement.