Roxanne Glazier

BME PhD Defense Presentation

Date: Monday, March 9, 2020

Time: 2:00 pm

Location: Atwood Chemistry Center, Room 316, Emory University

Advisor: Khalid Salaita, PhD (Emory)

Committee:

Jennifer Curtis, PhD (GT)

Andrés García, PhD (GT)

Adam Marcus, PhD (Emory)

Philip Santangelo, PhD (GT)

Title: DNA nanotechnology to map and manipulate adhesion forces on supported lipid bilayers

Abstract: Cells transmit piconewton (pN) receptor forces to ligands in the extracellular matrix and on the surface of adjacent cells. These forces regulate a variety of functions, ranging from cell adhesion to blood clotting and the immune response. Whereas adhesion mechanics on rigid substrates have been well characterized, understanding mechanotransduction at cell-cell junctions has remained challenging due to a lack of suitable tools. In this dissertation, we develop and apply new classes of DNA-based force probes to map and manipulate receptor forces on supported lipid bilayers (SLBs), planar membranes that mimic an adjacent cell. Specifically, we use these probes to elucidate force balance in podosomes, which are multipurpose protrusive structures that form at cell-cell and cell-matrix interfaces. Podosomes are critical in cell migration, invasion, and adhesion, and they also carry out specialized functions ranging from antigen scavenging to bone resorption. Podosomes consist of a modular core-ring architecture, and previous works have demonstrated that the podosome’s actin core generates nanonewton protrusive forces. However, the podosome’s tensile landscape remained poorly understood. In Aim 1, we develop and apply Molecular Tension- Fluorescence Lifetime Imaging Microscopy (MT-FLIM) to map integrin receptor forces and clustering on SLBs. Using MT-FLIM, we demonstrate that integrin receptors apply pN tension in podosome rings. These forces are primarily vertical and require actin polymerization. We then introduce photocleavable probes to site-specifically perturb adhesion forces and apply rupturable DNA-based force probes to test the importance of receptor tension in podosome formation and maintenance. These studies confirm a local mechanical feedback between podosome core protrusion and integrin receptor tension. In Aim 2, we investigate tension probe design. We evaluate structure and energy transfer across a library of DNA-based tension probes using spectroscopy and microscopy and demonstrate the functional implications of probe design on cellular imaging. Altogether this work expands our understanding of adhesion forces in podosomes and contributes new tools for studying juxtacrine receptor interactions on fluid interfaces.