JCAD couples tight junction condensates to actin and RhoA to maintain the endothelial barrier

How endothelial cell-cell junctions integrate cytoskeletal, adhesive, and local signaling networks to maintain vascular barrier integrity remains incompletely defined. Here, we identify junctional cadherin 5-associated protein (JCAD) as a modular scaffold that organizes endothelial tight junction architecture by coupling junctional condensates to actin and RhoA signaling. Genetic deletion of Jcad in mice does not affect baseline vascular permeability but causes inflammation-dependent barrier hyperpermeability. JCAD depletion in primary human endothelial cells disrupts tight junction continuity and increases paracellular permeability. Mechanistically, JCAD localizes to ZO-1-positive tight junctions independently of VE-cadherin, directly binds filamentous actin, and forms dynamic actin-associated condensates at cell-cell contacts. Structure-function analysis reveals separable domains mediating tight junction targeting and actin binding, establishing a bipartite architecture that distinctly coordinates junctional signaling and cytoskeletal coupling. Together, these findings identify JCAD as a cell-cell adhesion scaffold that integrates the phase-separated tight junction plaque with actin and RhoA-dependent mechanics, enabling endothelial barrier adaptation to inflammatory stress.