Non-muscle myosin II regulates aortic stiffness through effects on specific focal adhesion proteins and the non-muscle cortical cytoskeleton.

Non-muscle myosin II (NMII) plays a role in many fundamental cellular processes including cell adhesion, migration, and cytokinesis. However, its role in mammalian vascular function is not well understood. Here, we investigated the function of NMII in the biomechanical and signalling properties of mouse aorta. We found that blebbistatin, an inhibitor of NMII, decreases agonist-induced aortic stress and stiffness in a dose-dependent manner. We also specifically demonstrate that in freshly isolated, contractile, aortic smooth muscle cells, the non-muscle myosin IIA (NMIIA) isoform is associated with contractile filaments in the core of the cell as well as those in the non-muscle cell cortex. However, the non-muscle myosin IIB (NMIIB) isoform is excluded from the cell cortex and colocalizes only with contractile filaments. Furthermore, both siRNA knockdown of NMIIA and NMIIB isoforms in the differentiated A7r5 smooth muscle cell line and blebbistatin-mediated inhibition of NM myosin II suppress agonist-activated increases in phosphorylation of the focal adhesion proteins FAK Y925 and paxillin Y118. Thus, we show in the present study, for the first time that NMII regulates aortic stiffness and stress and that this regulation is mediated through the tension-dependent phosphorylation of the focal adhesion proteins FAK and paxillin.