MEMBRANE PORES ACT AS SELF-RESEALING LIPID SCRAMBLASES
Biological membranes continuously experience leaflet lipid imbalances during growth, lipid synthesis, and vesicle fusion. To alleviate such imbalances and prevent these asymmetries from compromising membrane integrity, cells rely on lipid scramblases - fast and non-specific lipid channel proteins. Here we show that lipid number asymmetry alone is sufficient to drive spontaneous formation of transient hydrophilic pores that function as self-resealing lipid scramblases. Using giant unilamellar vesicles, living cells, and coarse-grained molecular dynamics simulations, we demonstrate that fusion-induced excess lipids in one leaflet lowers membrane edge tension, generating size-selective pores whose size and lifetime scale with the magnitude of asymmetry. Below a critical threshold, these pores reseal spontaneously; above it, membranes collapse. Strikingly, pore opening enables rapid, non-selective lipid translocation between leaflets, dissipating the asymmetry that nucleates the pore and thereby promoting their own closure. Cholesterol buffers moderate imbalances through spontaneous flip flop before pore formation, whereas pore-mediated lipid scrambling relieves the remaining asymmetry and restores cholesterols initial distribution. Our findings identify transient lipid pores as an intrinsic, protein-independent mechanism that couples membrane destabilization to self-repair, providing a universal physical principle for membrane homeostasis during growth, remodelling, and early cellular evolution.