Pseudomonas aeruginosa causes acute lung injury via the catalytic activity of the patatin-like phospholipase domain of ExoU.
OBJECTIVE
Acute lung injury in Pseudomonas aeruginosa pneumonia depends primarily on ExoU toxin being delivered directly into the eukaryotic cell cytosol through the type III secretion system. The amino-acid sequence of ExoU has a potato patatin-like phospholipase domain, similar to the sequence of mammalian Ca-independent phospholipase A2. We examined whether the acute lung injury caused by cytotoxic P. aeruginosa was dependent on the patatin-like phospholipase domain of ExoU.


METHODS
Laboratory investigation using an established mouse model for P. aeruginosa pneumonia with quantitative measurements of acute lung injury and mortality.


METHODS
University experimental research laboratory.


METHODS
Balb/c mice.


METHODS
First, a site-directional mutation was introduced in the predicted catalytically active site of the patatin-like phospholipase domain of recombinant ExoU protein. The effect of the mutation on the catalytic activity of ExoU was tested by the in vitro lysophospholipase A assay. Second, the same site-directional mutation was introduced into the exoU gene of P. aeruginosa PA103. Mice were intratracheally infected with either a wild-type P. aeruginosa strain PA103 or an isogenic mutant containing the mutation in exoU. Acute epithelial lung injury, lung edema, bacteremia, and mortality were evaluated quantitatively.


RESULTS
Recombinant ExoU had lysophospholipase A activity. Site-directional mutations in the predicted catalytic site of ExoU caused a loss of the lysophospholipase A activity. Whereas the airspace instillation of PA103 caused acute lung injury and death of the infected mice, the airspace instillation of isogenic mutants secreting catalytically inactive ExoU were noncytotoxic and did not cause acute lung injury or death of the infected mice.


CONCLUSIONS
Virulent P. aeruginosa causes acute lung injury and death by the cytotoxic activity derived from the patatin-like phospholipase domain of ExoU.
Pankhaniya
Ravi R
RR
Department of Anesthesia and Perioperative Care, School of Medicine, University of California San Francisco, San Francisco, CA 94143-0542, USA.
Tamura
Miki
M
Allmond
Leonard R
LR
Moriyama
Kiyoshi
K
Ajayi
Temitayo
T
Wiener-Kronish
Jeanine P
JP
Sawa
Teiji
T
D000208:Acute Disease; D000595:Amino Acid Sequence; D000818:Animals; D001426:Bacterial Proteins / Q000037:antagonists & inhibitors / Q000502:physiology*; D020134:Catalytic Domain / Q000502:physiology; D003600:Cytosol / Q000382:microbiology / Q000502:physiology; D004195:Disease Models, Animal; D005057:Eukaryotic Cells / Q000382:microbiology / Q000502:physiology; D015151:Immunoblotting; D007249:Inflammation; D008245:Lysophospholipase / Q000032:analysis / Q000037:antagonists & inhibitors / Q000502:physiology*; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed / Q000502:physiology; D018410:Pneumonia, Bacterial / Q000150:complications* / Q000201:enzymology; D017354:Point Mutation; D011552:Pseudomonas Infections / Q000150:complications* / Q000201:enzymology; D011550:Pseudomonas aeruginosa / Q000472:pathogenicity / Q000502:physiology*; D012128:Respiratory Distress Syndrome / Q000382:microbiology* / Q000401:mortality / Q000473:pathology / Q000517:prevention & control; D016415:Sequence Alignment; D015996:Survival Rate
D001426:Bacterial Proteins; C111749:pseudomonas exoprotein A protein, Pseudomonas aeruginosa; D008245:Lysophospholipase