Human Cystic Fibrosis Macrophages Have Defective Calcium-Dependent PKC Activation of the NADPH Oxidase, an Effect Augmented by Burkholderia cenocepacia

Abstract

Macrophage intracellular pathogen killing is defective in cystic fibrosis (CF), despite abundant production of reactive oxygen species (ROS) in lung tissue. Burkholderia species can cause serious infection in CF and themselves affect key oxidase components in murine non-CF cells. However, it is unknown whether human CF macrophages have an independent defect in the oxidative burst and whether Burkholderia contributes to this defect in terms of assembly of the NADPH oxidase complex and subsequent ROS production. Here we analyze CF and non-CF human monocyte-derived macrophages (MDMs) for ROS production, NADPH assembly capacity, protein kinase C (PKC) expression, and calcium release in response to PMA and CF pathogens. CF MDMs demonstrate a nearly 60% reduction in superoxide production following PMA stimulation compared to non-CF MDMs. Although CF MDMs generally have increased total NADPH component protein expression, they demonstrate decreased expression of the calcium-dependent PKC conventional subclass α/β leading to reduced phosphorylation of NADPH oxidase components p47 ^phox & p40 ^phox in comparison to non-CF MDMs. Ingestion of B. cenocepacia independently contributes to and worsens the overall oxidative burst deficits in CF MDMs compared to non-CF MDMs. Together, these results provide evidence for inherent deficits in the CF macrophage oxidative burst due to decreased phosphorylation of NADPH oxidase cytosolic components that are augmented by Burkholderia. These findings implicate a critical role for defective macrophage oxidative responses in persistent bacterial infections in CF and create new opportunities for boosting the macrophage immune response in order to limit infection.