Tumor necrosis factor-α-induced microvascular endothelial cell hyperpermeability: role of intrinsic apoptotic signaling

Tumor necrosis factor-alpha (TNF-alpha), a pro-apoptotic cytokine, is involved in vascular hyperpermeability, tissue edema, and inflammation. We hypothesized that TNF-alpha induces microvascular hyperpermeability through the mitochondria-mediated intrinsic apoptotic signaling pathway. Rat lung microvascular endothelial cells grown on Transwell inserts, chamber slides, or dishes were treated with recombinant TNF-alpha (10 ng/ml) in the presence or absence of a caspase-3 inhibitor, Z-DEVD-FMK (100 mu M). Fluorescein isothiocyanate (FITC)-albumin (5 mg/ml) was used as a marker of monolayer permeability. Mitochondrial reactive oxygen species (ROS) was determined using dihydrorhodamine 123 and mitochondrial transmembrane potential using JC-1. The adherens junction integrity and actin cytoskeletal organization were studied using beta-catenin immunofluorescence and rhodamine phalloidin, respectively. Caspase-3 activity was measured fluorometrically. The pretreatment with Z-DEVD-FMK (100 mu M) attenuated TNF-alpha-induced (10 ng/ml) disruption of the adherens junctions, actin stress fiber formation, increased caspase-3 activity, and monolayer hyperpermeability (p < 0.05). TNF-alpha (10 ng/ml) treatment resulted in increased mitochondrial ROS formation and decreased mitochondrial transmembrane potential. Intrinsic apoptotic signaling-mediated caspase-3 activation plays an important role in regulating TNF-alpha-induced endothelial cell hyperpermeability.