NINJ1 regulates plasma membrane fragility under mechanical strain

The integrity of the plasma membrane is vital for nearly all aspects of cell functioning¹. Mechanical forces can cause plasma membrane damage², but it is unclear whether there are large molecules that regulate the integrity of the plasma membrane under mechanical strain. Here we constructed a 384-well cellular-stretch system that delivers precise, reproducible strain to cultured cells. Using the system, we screened 10,843 small interfering RNAs (siRNAs) targeting 2,726 multipass transmembrane proteins for strain-induced membrane permeability changes. The screen identified NINJ1-a protein that was recently proposed to regulate pyroptosis and other lytic cell death^3,4-as the top hit. We demonstrate that NINJ1 is a critical regulator of mechanical-strain-induced plasma membrane rupture (PMR), without the need for stimulating any cell death programs. NINJ1 levels on the plasma membrane are inversely correlated with the amount of force required to rupture the membrane. In the pyroptosis context, NINJ1 on its own is not sufficient to fully rupture the membrane, and additional mechanical force is required for full PMR. Our study establishes that NINJ1 functions as a bona fide determinant of membrane biomechanical properties. Our study also suggests that PMR across tissues of distinct mechanical microenvironments is subjected to fine-tuning by differences in NINJ1 expression and external forces.