Using Polyacrylamide Hydrogels to Model Physiological Aortic Stiffness Reveals that Microtubules Are Critical Regulators of Isolated Smooth Muscle Cell Morphology and Contractility.

Vascular smooth muscle cells (VSMCs) are the predominant cell type in the medial layer of the aortic wall and normally exist in a quiescent, contractile phenotype where actomyosin-derived contractile forces maintain vascular tone. However, VSMCs are not terminally differentiated and can dedifferentiate into a proliferative, synthetic phenotype. Actomyosin force generation is essential for the function of both phenotypes. Whilst much is already known about the mechanisms of VSMC actomyosin force generation, existing assays are either low throughput and time consuming, or qualitative and inconsistent. In this study, we use polyacrylamide hydrogels, tuned to mimic the physiological stiffness of the aortic wall, in a VSMC contractility assay. Isolated VSMC area decreases following stimulation with the contractile agonists angiotensin II or carbachol. Importantly, the angiotensin II induced reduction in cell area correlated with increased traction stress generation. Inhibition of actomyosin activity using blebbistatin or Y-27632 prevented angiotensin II mediated changes in VSMC morphology, suggesting that changes in VSMC morphology and actomyosin activity are core components of the contractile response. Furthermore, we show that microtubule stability is an essential regulator of isolated VSMC contractility. Treatment with either colchicine or paclitaxel uncoupled the morphological and/or traction stress responses of angiotensin II stimulated VSMCs. Our findings support the tensegrity model of cellular mechanics and we demonstrate that microtubules act to balance actomyosin-derived traction stress generation and regulate the morphological responses of VSMCs.

Emerging regulators of vascular smooth muscle cell migration.

Vascular smooth muscle cells (VSMCs) are the predominant cell type in the blood vessel wall and normally adopt a quiescent, contractile phenotype. VSMC migration is tightly controlled, however, disease associated changes in the soluble and insoluble environment promote VSMC migration. Classically, studies investigating VSMC migration have described the influence of soluble factors. Emerging data has highlighted the importance of insoluble factors, including extracellular matrix stiffness and porosity. In this review, we will recap on the important signalling pathways that regulate VSMC migration and reflect on the potential importance of emerging regulators of VSMC function.