Thrombospondin-1 protects against pathogen-induced lung injury by limiting extracellular matrix proteolysis

Abstract

Acute lung injury is characterized by excessive extracellular matrix proteolysis and neutrophilic inflammation. A major risk factor for lung injury is bacterial pneumonia. However, host factors that protect against pathogen-induced and host-sustained proteolytic injury following infection are poorly understood. Pseudomonas aeruginosa (PA) is a major cause of nosocomial pneumonia and secretes proteases to amplify tissue injury. We show that thrombospondin-1 (TSP-1), a matricellular glycoprotein released during inflammation, dose-dependently inhibits PA metalloendoprotease LasB, a virulence factor. TSP-1-deficient (Thbs1-/-) mice show reduced survival, impaired host defense, and increased lung permeability with exaggerated neutrophil activation following acute intrapulmonary PA infection. Administration of TSP-1 from platelets corrects the impaired host defense and aberrant injury in Thbs1-/- mice. Although TSP-1 is cleaved into 2 fragments by PA, TSP-1 substantially inhibits Pseudomonas elastolytic activity. Administration of LasB inhibitor, genetic disabling of the PA type II secretion system, or functional deletion of LasB improves host defense and neutrophilic inflammation in mice. Moreover, TSP-1 provides an additional line of defense by directly subduing host-derived proteolysis, with dose-dependent inhibition of neutrophil elastase from airway neutrophils of mechanically ventilated critically ill patients. Thus, a host matricellular protein provides dual levels of protection against pathogen-initiated and host-sustained proteolytic injury following microbial trigger.

Increased Alternative Complement Pathway Function and Improved Survival during Critical Illness

“…pneumoniae strain (43816; American Type Culture Collection) or KPC5. Necropsy with lung and spleen colony-forming unit counts; and, in select experiments, serum, BAL fluid, and lung tissue for cytokine analysis were collected at 24 hours postinfection, as previously described ( 31 , 34 , 35 ). Serum cytokine measurement was performed by multiplex assay, as previously described ( see Methods in the online supplement) ( 36 ).…”

Concise Review: The Endothelial Cell Extracellular Matrix Regulates Tissue Homeostasis and Repair

“…The term matricellular has been applied to this group of extracellular proteins that do not contribute directly to the formation of structural ECM elements but serve to modulate cell–matrix interactions and cell function. While they usually have limited expression in adult life, they can become upregulated and released from the ECM during injury and repair . The production and release of matricellular proteins upon injury allows for binding of these proteins to a variety of receptors, growth factors and proteases in the capillary pericellular space, generally reducing cell adhesion and proliferation, and thus tuning ECM remodeling down (Fig.…”

Generation of Xylose-inducible promoter tools forPseudomonasspecies and their use in implicating a role for the Type II secretion system protein XcpQ in inhibition of corneal epithelial wound closure

“…Unlike wild-type PA14 culture filtrates, those from a previously described Δ xcpQ derivative of PA14 (24) were unable to block cell migration (Figure 9). Expression of xcpQ , but not gfp (used as a negative control) from P xut , was able to restore the cell migration inhibition phenotype to the xcpQ mutant in a D-xylose-dependent manner; that is, 50, but not 5 mM D-xylose was sufficient to complement the cell migration inhibition phenotype (Figure 9).…”