Microfluidic Approaches to Study Mechanotransduction in Cell Division and Migration

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Physical forces exerted on cells drive changes in phenotype and define organization and tissue patterning during developmental morphogenesis, normal physiologic function, and under pathologic conditions. The term mechanotransduction refers to the process by which cells transduce mechanical inputs into biological responses. The vascular system provides an ideal model to study mechanotransduction, because cells are continuously exposed to external physical forces including shear stress imposed by blood flow, and tangential stress due to blood pressure. Vascular smooth muscle cells (VSMCs) normally reside within the media in a 3D environment surrounded by extracellular matrix. However after endothelial denudation and with exposure to growth factors like platelet derived growth factor B (PDGF-B) VSMCs undergo a phenotypic switch from contractile to synthetic, and they proliferate and migrate from the media to the intimal layer. As a result the microenvironment of the cell changes dramatically: VSMCs undergo compression and deformation as they migrate through tight fenestrae in the internal elastic lamina, and once on the intimal surface, they are exposed to shear stress from flowing blood. The biochemical signals regulating VSMC migration and proliferation have been studied for many years. However the effects of these physical forces on VSMCs after injury are not well understood, and we seek to understand how cells integrate mechanotransduction signals with changes in the cytoskeleton to influence behavioural decisions to migrate and proliferate. The focus of this grant is to investigate mechanisms of mechanotransduction in VSMCs exposed to fluid shear and compressive stresses using microfluidic devices to mimic the in vivo microenvironment. Rationale and Hypotheses: The cytoskeleton plays an important role in mechanotransduction in migrating VSMCs: it bears the brunt of physical forces imposed upon the cell, is the target of the phenotypic switch, and governs the position of intracellular organelles to accomplish polarity required for proliferation and migration. I hypothesize that alterations in the cytoskeletal organization in VSMCs are due to two distinct physical forces to which the cells are exposed as they migrate into the intimal layer: 1. Shear force exerted by blood flow on cells at the intimal surface. 2. Compressive force which deforms the cell and nucleus as it squeezes through small fenestrae in the internal elastic lamina separating the medial and the intimal layers.