Substrate Stiffness Regulates PDGF-Induced Circular Dorsal Ruffle Formation Through MLCK.

As atherosclerosis progresses, vascular smooth muscle cells (VSMCs) invade from the medial layer into the intimal layer and proliferate, contributing to atherosclerotic plaque formation. This migration is stimulated in part by platelet-derived growth factor (PDGF), which is released by endothelial cells and inflammatory cells, and vessel stiffening, which occurs with age and atherosclerosis progression. PDGF induces the formation of circular dorsal ruffles (CDRs), actin-based structures associated with increased cell motility. Here we show that mechanical changes in matrix stiffness enhance the formation of CDRs in VSMCs in response to PDGF stimulation. Our data indicate that matrix stiffness increases cellular contractility, and that intracellular pre-stress is necessary for robust CDR formation. When treated with agonists that promote contractility, cells increase CDR formation, whereas agonists that inhibit contractility lead to decreased CDR formation. Substrate stiffness promotes CDR formation in response to PDGF by upregulating Src activity through myosin light chain kinase. Together, these data indicate that vessel stiffening accompanying atherogenesis may exacerbate VSMC response to PDGF leading to CDR formation.