VE‐Cadherin–Actin Regulation Promotes Mechanotransduction and Monolayer Maturation Involving a Tension‐Sensitive Intermediate State

Epithelial and endothelial monolayers maintain homeostasis by adapting to physiological stimuli and injury through conversion processes that remain incompletely understood. Using human umbilical vein endothelial cell cultures (HUVECs), we elucidate how monolayer maturation and mechanotransduction-induced remodeling are molecularly regulated. Maturation involves reduced cell perimeter leading to increased junctional VE-cadherin that recruits junctional actin, integrins and vinculin to establish a quiescent, stable monolayer. Remarkably, we identify a previously unrecognized, rapid and reversible intermediate-state, marked by VE-cadherin linearization (clustering) and actomyosin relaxation via myosin light chain (MLC)-dephosphorylation, that emerges during mechanotransduction-induced activation, triggered by onset or shifts in shear stress-induced mechanical load. This novel tension-mediated intermediate state enhances junctional actin, integrin and vinculin recruitment, thereby strengthening barrier function while protecting endothelial cells from overstimulation and mechanical damage. MLC rephosphorylation dissolves junctional actin, forms stress fibers and induces the formation of "Junction-Associated-Intermittent-Lamellipodia" (JAIL), enabling cell shape change and arterial phenotype remodeling. Overall, junctional VE-cadherin concentration, together with mechanosensitive signaling that reduces actomyosin tension, governs actin recruitment, revealing a tension-sensitive, intermediate state that protects cells and primes endothelial remodeling. The data provide a broader model for endothelial mechanotransduction and stress adaptation.