Pulmonary Endothelial Protein Kinase C-Delta (PKCδ) Regulates Neutrophil Migration in Acute Lung Inflammation

Excessive neutrophil migration across the pulmonary endothelium into the lung and release of oxidants and proteases are key elements in pathogenesis of acute lung injury. Previously, we identified protein kinase C-delta (PKC delta) as an important regulator of proinflammatory signaling in human neutrophils and demonstrated that intratracheal instillation of a TAT-conjugated PKC delta inhibitory peptide (PKC delta-TAT) is lung protective in a rat model of sepsis-induced indirect pulmonary injury (cecal ligation and puncture). In the present study, intratracheal instillation of this PKC delta inhibitor resulted in peptide distribution throughout the lung parenchyma and pulmonary endothelium and decreased neutrophil influx, with concomitant attenuation of sepsis-induced endothelial ICAM-1 and VCAM-1 expression in this model. To further delineate the role of PKC delta in regulating neutrophil migration, we used an in vitro transmigration model with human pulmonary microvascular endothelial cells (PMVECs). Consistent with in vivo findings, inhibition of PMVEC PKC delta decreased IL-1 beta-mediated neutrophil transmigration. PKC delta regulation was stimulus-dependent; PKC delta was required for transmigration mediated by IL-1 beta and fMLP (integrin-dependent), but not IL-8 (integrin-independent). PKC delta was essential for IL-1 beta-mediated neutrophil adherence and NF-kappa B-dependent expression of ICAM-1 and VCAM-1. In PMVECs, IL-1 beta-mediated production of ROS and activation of redox-sensitive NF-kappa B were PKC delta dependent, suggesting an upstream signaling role. Thus, PKC delta has an important role in regulating neutrophil-endothelial cell interactions and recruitment to the inflamed lung.