• Eirini Apostolou, Athanasios Stavropoulos, Alexandros Sountoulidis, Charoula Xirakia, Stavros Giaglis, Evdokia Protopapadakis, Konstantinos Ritis, Spyros Mentzelopoulos, Arja Pasternack, Martyn Foster, Olli Ritvos, George E Tzelepis, Evangelos Andreakos, and Paschalis Sideras.
• Biomedical Research Foundation, Academy of Athens, Center for Immunology and Transplantation, Athens, Greece.
• Am. J. Respir. Crit. Care Med.. 2012 Feb 15;185(4):382-91.

RationaleActivin-A is up-regulated in various respiratory disorders. However, its precise role in pulmonary pathophysiology has not been adequately substantiated in vivo.ObjectivesTo investigate in vivo the consequences of dysregulated Activin-A expression in the lung and identify key Activin-A-induced processes that contribute to respiratory pathology.MethodsActivin-A was ectopically expressed in murine lung, and functional, structural, and molecular alterations were extensively analyzed. The validity of Activin-A as a therapeutic target was demonstrated in animals overexpressing Activin-A or treated with intratracheal instillation of LPS. Relevancy to human pathology was substantiated by demonstrating high Activin-A levels in bronchoalveolar lavage (BAL) samples from patients with acute respiratory distress syndrome (ARDS).Measurements And Main ResultsOverexpression of Activin-A in mouse airways caused pulmonary pathology reminiscent of acute lung injury (ALI)/ARDS. Activin-A triggered a lasting inflammatory response characterized by acute alveolar cell death and hyaline membrane formation, sustained up-regulation of high-mobility group box 1, development of systemic hypercoagulant state, reduction of surfactant proteins SpC, SpB, and SpA, decline of lung compliance, transient fibrosis, and eventually emphysema. Therapeutic neutralization of Activin-A attenuated the ALI/ARDS-like pathology induced either by ectopic expression of Activin-A or by intratracheal instillation of LPS. In line with the similarity of the Activin-A-induced phenotype to human ARDS, selective up-regulation of Activin-A was found in BAL of patients with ARDS.ConclusionsOur studies demonstrate for the first time in vivo the pathogenic consequences of deregulated Activin-A expression in the lung, document novel aspects of Activin-A biology that provide mechanistic explanation for the observed phenotype, link Activin-A to ALI/ARDS pathophysiology, and provide the rationale for therapeutic targeting of Activin-A in these disorders.

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