The Alzheimer's Disease-associated gene CD2AP regulates permeability of endothelial cells and transendothelial migration of immune cells.

Variants at the CD2AP locus, which encodes a branched-actin regulator, are associated with late-onset Alzheimer's disease (AD), and CD2AP-deficient mice show increased blood-brain barrier (BBB) permeability. CD2AP is enriched in endothelial cells, but its function there is poorly understood. In endothelium, branched actin networks maintain cell-cell junctions and are also required for immune cells to cross through individual endothelial cells (transcellular transendothelial migration, TEM). We previously showed that the Arp2/3 activators N-WASP and WAVE2 contribute to these processes, but the capping protein (CP)-interacting proteins involved are unknown. Here we tested whether CD2AP, a CP-interacting protein recruited to cell-cell contacts, regulates both junction integrity and TEM. In primary human microvascular endothelial cells, shRNA knockdown of CD2AP increased TNFα-induced monolayer permeability, measured by transendothelial electrical resistance, and altered VE-cadherin junction morphology. Unexpectedly, on soft hydrogels the same knockdown reduced TEM of NK-92 MI cells, lowering the proportion of transcellular events. Thus, loss of CD2AP weakens the endothelial barrier yet impairs a distinct, actin-dependent route of immune-cell passage. These findings suggest that CD2AP risk variants may affect the BBB through more than permeability, and they identify endothelial immune-cell trafficking as a testable link between CD2AP and AD.