Rules of Contact Inhibition of Locomotion for Cells on Suspended Nanofibers

Abstract

Contact inhibition of locomotion (CIL), in which cells repolarize and move away from contact, is now established as a fundamental driving force in development, repair, and disease biology. Much of what we know of CIL stems from studies on 2D substrates that fail to provide an essential biophysical cue - the curvature of extracellular matrix fibers. We discover rules controlling outcomes of cell-cell collisions on suspended nanofibers, and show them to be profoundly different from the stereotyped CIL behavior known on 2D substrates. Two approaching cells attached to a single fiber do not repolarize upon contact but rather usually migrate past one another. Fiber geometry modulates this behavior: when cells are attached to two fibers, reducing their freedom to reorient, only one of a pair of colliding cells repolarizes on contact, leading to the cell pair migrating as a single unit. CIL outcomes also change when one cell has recently divided and moves with high speed- cells more frequently walk past each other. In collisions with division in the two-fiber geometry, we also capture rare events where a daughter cell pushes the non-dividing cell along the fibers. Our computational model of CIL in fiber geometries reproduces the core qualitative results of the experiments robustly to model parameters. Our model shows that the increased speed of post-division cells may be sufficient to explain their increased walk-past rate. Our results suggest that characterizing cell-cell interactions on flat substrates, channels, or micropatterns is not sufficient to predict interactions in a matrix - the geometry of the fiber can generate entirely new behaviors. SignificanceWhen cells heal a wound or invade a new area, they coordinate their motion. Coordination is often studied by looking at what happens after pairs of cells collide. Post-collision, cells often exhibit contact inhibition of locomotion- they turn around and crawl away from the point where they touched. Our knowledge of repolarization on contact comes from studies on flat surfaces, unlike cells in the body, which crawl along fibers. We discover that cells on single fibers walk past one another- but that cells in contact with multiple fibers stick to one another and move as pairs. This outcome changes to walk-past after cell division. Our experiments and models reveal how the environment regulates cell-cell coordination after contact.