Differential susceptibility of lung endothelial and epithelial cells to ceramides‐induced apoptosis

Abstract

Ceramide upregulation may induce paracellular ceramides and alveolar cell apoptosis in both alveolar endothelial and epithelial cells, but their susceptibility to ceramide‐mediated apoptosis are unknown. We hypothesized cell‐type specificity in apoptotic responses to ceramide. Human lung microvascular endothelial (EN)‐, small airway epithelial (SEP)‐, and bronchial epithelial (BEP) cells were treated with ceramides (6:0 or 16:0) or dihydroceramide. Apoptosis and endogenous ceramides were quantified by caspase activation, annexin, mitotracker, cytochrome c, and mass spectrometry, respectively. Alveolar EN manifested susceptibility to both ceramides, which induced caspase‐9 activity 12‐fold. In contrast, SEP exhibited mitochondrial‐mediated apoptosis in response to short‐chain ceramide (30% apoptosis, 6h), whereas BEP were least sensitive to ceramide‐induced apoptosis. All cells upregulated endogenous intra‐ and paracellular ceramides after treatment with ceramides, but only epithelial cells released paracellular ceramides in response to dihydroceramides. Paracellular ceramides had marked pro‐apoptotic effects in EN, blocked by neutralizing ceramide antibodies. Our data suggest alveolar and airway epithelial cells have differential susceptibility to ceramide‐induced apoptosis, characteristic which could be exploited in specific interventions in emphysema. NIH HL077328.