Pseudomonas aeruginosaprotease IV degrades surfactant proteins and inhibits surfactant host defense and biophysical functions

Abstract

Pulmonary surfactant has two distinct functions within the lung: reduction of surface tension at the air-liquid interface and participation in innate host defense. Both functions are dependent on surfactant-associated proteins. Pseudomonas aeruginosa is primarily responsible for respiratory dysfunction and death in cystic fibrosis patients and is also a leading pathogen in nosocomial pneumonia. P. aeruginosa secretes a number of proteases that contribute to its virulence. We hypothesized that P. aeruginosa protease IV degrades surfactant proteins and results in a reduction in pulmonary surfactant host defense and biophysical functions. Protease IV was isolated from cultured supernatant of P. aeruginosa by gel chromatography. Incubation of cell-free bronchoalveolar lavage fluid with protease IV resulted in degradation of surfactant proteins (SP)-A, -D, and -B. SPs were degraded in a time- and dose-dependent fashion by protease IV, and degradation was inhibited by the trypsin-like serine protease inhibitor Nalpha-p-tosyl-L-lysine-chloromethyl ketone (TLCK). Degradation by protease IV inhibited SP-A- and SP-D-mediated bacterial aggregation and uptake by macrophages. Surfactant treated with protease IV was unable to reduce surface tension as effectively as untreated surfactant, and this effect was inhibited by TLCK. We speculate that protease IV may be an important contributing factor to the development and propagation of acute lung injury associated with P. aeruginosa via loss of surfactant function within the lung.

Failure of Respiratory Defenses in the Pathogenesis of Bacterial Pneumonia of Cattle

“…95 Similarly, a protease of Aspergillus fumigatus cleaves several complement proteins and thereby prevents complement activation, 14 while protease IV of P. aeruginosa degrades surfactant proteins. 122 Several Gram-positive pathogens alter the acetylation patterns of peptidoglycan in their cell wall, as a mechanism to resist degradation by lysozyme. 43 The bacterial capsule is important in evading complement 80 but also confers resistance to cathelicidins among some pathogens, including N. meningitidis.…”

Pouring Salt on a Wound: Pseudomonas aeruginosa Virulence Factors Alter Na+ and Cl- Flux in the Lung

“…Protease IV also degrades surfactant proteins A, B, and D, which are important for surface tension and innate immunity (35). The phospholipases PlcB, PlcH, and PlcN target the mucus layer and cell membrane, facilitating bacterial transit through the mucus layer and liberating nutrients exploited by the bacteria (36)(37)(38).…”

Human Pre-Elafin Inhibits a Pseudomonas aeruginosa -Secreted Peptidase and Prevents Its Proliferation in Complex Media

“…AP is also postulated to play a major role in the pathogenesis of acute and chronic lung infections caused by P. aeruginosa (18,32,39). That P. aeruginosa growth is compromised by elafin-directed inhibition of this secreted peptidase therefore constitutes a novel and important finding.…”

“…In addition, due to low membrane permeability, active efflux of drugs, and the presence of ␤-lactamase activity, P. aeruginosa infections are becoming increasingly difficult to treat (17). Hence, the development of novel antimicrobial agents, preferably acting on targets exposed at the bacterial cell surface, is urgently needed.Among the P. aeruginosa virulence factors, the secreted peptidases are thought to play a critical role in tissue invasion, nutrient accessibility, and degradation of the innate host defense molecules and therefore constitute potential therapeutic targets (18)(19)(20). Because opportunistic pathogens are taking advantage of a weakened host protective shield, augmentation therapy with lung natural defense molecules also appears to be a promising avenue for combating P. aeruginosa infections (5,11,44).…”