Mitogen-activated protein kinase phosphatase 2, MKP-2, regulates early inflammation in acute lung injury

Acute lung injury (ALI) is mediated by an early proinflammatory response resulting from either a direct or indirect insult to the lung mediating neutrophil infiltration and consequent disruption of the alveolar capillary membrane ultimately leading to refractory hypoxemia. The mitogen-activated protein kinase (MAPK) pathways are a key component of the molecular response activated by those insults triggering the proinflammatory response in ALI. The MAPK pathways are counterbalanced by a set of dual-specific phosphatases (DUSP) that deactivate the kinases by removing phosphate groups from tyrosine or threonine residues. We have previously shown that one DUSP, MKP-2, regulates the MAPK pathway in a model of sepsis-induced inflammation; however, the role of MKP-2 in modulating the inflammatory response in ALI has not been previously investigated. We utilized both MKP-2-null (MKP-2−/−) mice and MKP-2 knockdown in a murine macrophage cell line to elucidate the role of MKP-2 in regulating inflammation during ALI. Our data demonstrated attenuated proinflammatory cytokine production as well as decreased neutrophil infiltration in the lungs of MKP-2−/− mice following direct, intratracheal LPS. Importantly, when challenged with a viable pathogen, this decrease in neutrophil infiltration did not impact the ability of MKP-2−/− mice to clear either gram-positive or gram-negative bacteria. Furthermore, MKP-2 knockdown led to an attenuated proinflammatory response and was associated with an increase in phosphorylation of ERK and induction of a related DUSP, MKP-1. These data suggest that altering MKP-2 activity may have therapeutic potential to reduce lung inflammation in ALI without impacting pathogen clearance.