Segmental Aortic Stiffening Is A Mechanism Driving Early Abdominal Aortic Aneurysm Pathogenesis

Stiffening of the aortic wall is a phenomenon consistently observed in abdominal aortic aneurysm (AAA). However, its role in AAA pathophysiology is largely undefined. Using an established murine elastase-induced AAA model, we demonstrate that segmental aortic stiffening (SAS) precedes aneurysm growth. Finite elements analysis (FEA)-based wall stress calculations reveal that early stiffening of the aneurysm-prone aortic segment leads to axial (longitudinal) stress generated by cyclic (systolic) tethering of adjacent, more compliant wall segments. Interventional stiffening of AAA-adjacent segments (via external application of surgical adhesive) significantly reduces aneurysm growth. These changes correlate with reduced segmental stiffness of the AAA-prone aorta (due to equalized stiffness in adjacent aortic segments), reduced axial wall stress, decreased production of reactive oxygen species (ROS), attenuated elastin breakdown, and decreased expression of inflammatory cytokines and macrophage infiltration, as well as attenuated apoptosis within the aortic wall. Cyclic pressurization of stiffened aortic segments ex vivo increases the expression of genes related to inflammation and extracellular matrix (ECM) remodeling. Finally, human ultrasound studies reveal that aging, a significant AAA risk factor, is accompanied by segmental infrarenal aortic stiffening. The present study introduces the novel concept of segmental aortic stiffening (SAS) as an early pathomechanism generating aortic wall stress and thereby triggering AAA growth. Therefore monitoring SAS by ultrasound might help to better identify patients at risk for AAA disease and better predict the susceptibility of small AAA to further growth. Moreover our results suggest that interventional mechanical stiffening of the AAA-adjacent aorta may be further tested as a novel treatment option to limit early AAA growth.