Characterizing Mechanical Properties of Primary Cilium Using Optical Trapping

The effects of deforming a primary cilium away from its equilibrium position were studied to learn more about a cilium’s mechanical properties. Better understanding of the mechanical properties of this flow-sensing structure can be used to develop therapies and treatments for a variety of disorders (ciliopathies, especially Polycystic Kidney Disease) that currently have no effective treatments. Using an optical trap, the tips of primary cilia expressed by LLC-PK cells were optically trapped and the stochastic position of the trapped tip was measured. Tips of microns-long cilia were displaced by small amounts (ranging between 0.1-1-micron) to see how these displacements would affect the net forces acting on the primary cilium tip. This situation was modeled as a particle held between two springs, where the springs are models of the axoneme of the cilium, which provide a restoring force to bring the tip back to its undeformed position. Data to find the trapping force on the tip of the cilium was obtained for each displacement. While our preliminary results showed that the restoring force provided by the axoneme can be detected and quantified, more work will need to go into refining the model to account for variations in how cilia grow from the cell surface.