Dystrophin and dystrophin association protein expression decreases with age in vascular smooth muscle

As humans age, the aorta stiffens, diminishing its essential shock absorber function. This increased stiffness transmits higher pressures to downstream vessels in the kidney, brain, and heart, contributing to hypertension and end-organ damage. Although multiple mechanisms involving extracellular matrix (ECM) remodeling and vascular smooth muscle cell (VSMC) contributions to aortic stiffness have been described, additional molecular players likely remain uncharacterized. Dystrophin (DYS) and the dystrophin-associated proteins (DAPs) are cytoskeletal stabilizers known for protecting skeletal muscle cells from contraction-induced damage but are poorly characterized in VSMCs. Loss of DYS has been linked to myocardial stiffness and carotid artery abnormalities. Here, we investigated the function of DYS in biomechanical properties of the mouse aorta. We demonstrated by immunofluorescence that DYS and DAPs are expressed and colocalize in freshly dissociated murine VSMCs. The mdx model, a known dystrophin knockout mouse model, was used to investigate the consequences of lack of dystrophin expression on aortic geometry and biomechanics. In mdx mice, we observed decreased aortic wall thickness but no significant difference in diameter compared to wild-type (WT) mice. This significant difference in aortic geometry is directly related to ex vivo stress and stiffness. We measured aortic stiffness by high-frequency small-amplitude sinusoidal length perturbation and determined dystrophin is essential to maintain normal stiffness and stress at baseline. This suggests that extracellular matrix components in the mdx aorta are contributing to the increased stress and stiffness at baseline. We also determined that DYS is not required to maintain normal stress and stiffness due to the contractile response to depolarization by high K + or alpha-agonist, phenylephrine-induced contraction. Finally, we revealed by Western blot that DYS and alpha-sarcoglycan, a DAP, expression is decreased in aged vascular smooth muscle. Previous studies show that matrix metalloproteinase-2 (MMP2) can degrade DYS in cardiac tissue and that MMP2 activity increases with age in vascular tissue. While we did not directly assess MMP2 in this study, we propose its role as a hypothesis for future exploration. In summary, this study identifies a novel role for DYS in maintaining aortic mechanical integrity and presents evidence that aging diminishes DYS and DAP protein expression in VSMCs.