ENERGY DEFICIENCY SELECTS CROWDED LIVE EPITHELIAL CELLS FOR EXTRUSION

Epithelial cells work collectively to provide a protective barrier yet turn over rapidly by<br/> cell division and death. If the numbers of dividing and dying cells do not match, the<br/> barrier would vanish, or tumours can form. Mechanical forces via the stretch-activated ion channel (SAC) Piezo1 link both processes; stretch promotes cell division, whereas crowding triggers live cells to extrude and then die1,2. However, it was not clear what selects a given crowded cell for extrusion. Here, we show that the crowded cells with least energy and membrane potential are selected for extrusion. Crowding triggers sodium entry via the epithelial sodium channel (ENaC), which depolarizes cells. While those with sufficient energy repolarise, those with limited ATP remain depolarised, which, in turn, triggers water egress via voltage-gated potassium channels Kv1.1 and Kv1.2 and the chloride channel SWELL1. Transient water loss causes cell shrinkage, amplifying crowding to activate crowding-induced live cell extrusion. Thus, our findings suggest that ENaC acts as a tension sensor that probes for cells with the least energy to extrude and die, possibly damping inadvertent crowding activation of Piezo1 in background cells. We reveal new crowding sensing mechanisms upstream of Piezo1 that highlight water regulation and ion channels as key regulators of epithelial cell turnover.