Using micropost arrays to measure traction forces during dendritic cell motility

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Dendritic cells (DCs) are important regulators of the mammalian immune system and motility is critical to their proper function. Technologies such as cancer immunotherapy critically depend on DC migration. DCs possess multiple chemokine receptors and crawl in response to chemokine gradients, which direct DC positioning throughout the immune system. Ultimately, DCs must integrate multiple signals in order to move in a single direction. The goal of this project is to use a novel biointerfacial tool, micropost array detectors (mPADs), coupled with microfluidic gradient chambers, to apply a time- invariant chemokine gradient to cells, and measure the traction forces exerted by DCs during migration. Our recently published work shows that mPAD arrays are sufficiently sensitive to measure the low traction stresses (0.5 nN per filopod and 20 nN per cell) of migrating DCs. We now use these arrays to understand the components within cells that give rise to directed cell motion and to understand how DCs integrate chemokine signals and convert them to traction stresses and directional motion. The specific aims of the proposal are: 1) to use novel micropost force detector to measure DC motility in well- defined gradients of single chemokines on multiple adhesive ligands; 2) to measure the effects of regulatory proteins HS1 and WASp on DC migration in single chemokine gradients; and 3) to measure the forces of DC migration during turning when the gradient rapidly changes direction. In all aims, post arrays will be calibrated to ensure force maps are independent of post architecture, and we will correlate the direction of motion to the spatio-temporal map of forces that DCs exert. Furthermore, by varying the length of posts, we will determine the relationship between substrate elasticity and directional motion. This project is aided by a wealth of molecular and cellular tools including knock out mice in which chemokine receptors, actin regulatory proteins such as WASp, HS1 and myosin II, and various molecular knockdowns and pharmacological agents. The methods we establish here will yield a comprehensive picture of the forces exerted during DC motility, and the methods established here will have a significant impact on the elucidation of the mechanisms of motility of other fast moving amoeboid cells of the immune system that generate low forces, including T-lymphocytes.