BME PhD Prospectus Defense – Chris Hartman

2:00 pm on Friday, February 14, 2014
44 Cummington Mall, Room 705
Prof. Joyce Wong, Biomedical Engineering (Advisor, Chair)
Prof. Michael Smith, Biomedical Engineering
Prof. Dimitrije Stamenovic, Biomedical Engineering
Prof. Vickery Trinkaus-Randall, School of Medicine, Biochemistry
Prof. Matthew Layne, School of Medicine, Biochemistry

Title: "The Role of Extracellular Matrix Composition in Vascular Smooth Muscle Cell Durotaxis"

Atherosclerotic plaque formation is characterized by progressive stiffening of the extracellular matrix (ECM) as well as significant changes in the relative abundance of extracellular matrix proteins present in the vessel wall. Both environmental changes have been implicated in driving phenotypic changes in vascular smooth muscle cells (VSMCs) from a quiescent, contractile state to a proliferative and migratory synthetic state associated with cardiovascular disease. Previous work has shown VSMCs are capable of sensing gradients in substrate stiffness and migrating towards regions of elevated stiffness. However, the role of the ECM in the VSMC migratory response to stiffness gradients has not been investigated. In this work, we seek to demonstrate that the ECM presented modulates VSMC migration in response to stiffness gradients, i.e. durotaxis. Specifically, we hypothesize that durotaxis is observed more strongly on matrix proteins that increase in abundance in diseased vessels (fibronectin, collagen 1, vitronectin) and is not observed on matrix typically abundant in normal vessels (laminin, collagen 4). Additionally, we will investigate whether differences in migratory behavior can be explained by the interactions of specific integrins expressed in VSMCs (αvβ3, α2β1) with the ECM.
To this end, we have developed and characterized a polyacrylamide hydrogel culture platform featuring highly tunable gradients in mechanical stiffness and control over ECM composition that allows us to analyze vascular smooth muscle cell behavior in an environment that isolates the individual and combined effects of mechanical and biological signals. Using this system, we will track VSMC migration in vitro and quantitatively analyze differences in migratory behavior as a function of ECM composition. Traction forces from VSMCs migrating on different substrates will be analyzed to determine if differences in traction force generation on different ECMs are responsible for differences in migration behavior. Furthermore, we will use immunofluorescence to quantify the localization of integrins in VSMCs on gradient gels and utilize antibody-based integrin blocking to identify integrins required for sensing mechanical gradients. The results of these investigations will provide enhanced understanding of the role of ECM in VSMC responses to stiffness and will direct further investigation into the mechanotransduction pathways downstream of the receptors required for durotaxis.