Rac2 is required for alternative macrophage activation and bleomycin induced pulmonary fibrosis; a macrophage autonomous phenotype

• Published in: PloS one 2017-08, Vol.12 (8), p.e0182851
• Main Authors: Joshi, Shweta, Singh, Alok R, Wong, Simon S, Zulcic, Muamera, Jiang, Min, Pardo, Annie, Selman, Moises, Hagood, James S, Durden, Donald L
• Format: Article
• Language: English
• Subjects: Activation; Activation analysis; Angiogenesis; Animals; Biology and Life Sciences; Bleomycin; Bleomycin - toxicity; Cancer; Cell activation; Cells, Cultured; Children & youth; Collagen; Collagen - metabolism; Cytokines; Deposition; Differentiation; Extracellular matrix; Fibrosis; Genetic aspects; Genotype & phenotype; Hospitals; Humans; Idiopathic Pulmonary Fibrosis - etiology; Idiopathic Pulmonary Fibrosis - genetics; Idiopathic Pulmonary Fibrosis - immunology; Inflammation; Integrins; Kinases; Lung diseases; Lungs; Macrophage Activation; Macrophages; Macrophages - immunology; Markers; Medicine and Health Sciences; Mice; Mice, Inbred C57BL; Neutrophils; Pediatrics; Phenotype; Polarization; Proteins; Pulmonary fibrosis; rac GTP-Binding Proteins - genetics; rac GTP-Binding Proteins - metabolism; RAC2 GTP-Binding Protein; Rac2 protein; Research and Analysis Methods; Rodents; Signal transduction
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0182851

Idiopathic pulmonary fibrosis (IPF) is a chronic lung disease characterized by cellular phenotype alterations and deposition of extracellular matrix proteins. The alternative activation of macrophages in the lungs has been associated as a major factor promoting pulmonary fibrosis, however the mechanisms underlying this phenomenon are poorly understood. In the present study, we have defined a molecular mechanism by which signals transmitted from the extracellular matrix via the α4β1 integrin lead to the activation of Rac2 which regulates alternative macrophage differentiation, a signaling axis within the pulmonary macrophage compartment required for bleomycin induced pulmonary fibrosis. Mice deficient in Rac2 were protected against bleomycin-induced fibrosis and displayed diminished collagen deposition in association with lower expression of alternatively activated profibrotic macrophage markers. We have demonstrated a macrophage autonomous process by which the injection of M2 and not M1 macrophages restored the bleomycin induced pulmonary fibrosis susceptibility in Rac2-/- mice, establishing a critical role for a macrophage Rac2 signaling axis in the regulation of macrophage differentiation and lung fibrosis in vivo. We also demonstrate that markers of alternative macrophage activation are increased in patients with IPF. Taken together, these studies define an important role for an integrin-driven Rac2 signaling axis in macrophages, and reveal that Rac2 activation is required for polarization of macrophages towards a profibrotic phenotype and progression of pulmonary fibrosis in vivo.