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Bronchoalveolar lavage (BAL) cells in idiopathic pulmonary fibrosis express a complex pro-inflammatory, pro-repair, angiogenic activation pattern, likely associated with macrophage iron accumulation

PLoS One. 2018 Apr 12;13(4):e0194803. doi: 10.1371/journal.pone.0194803. eCollection 2018.

Abstract

Idiopathic pulmonary fibrosis (IPF) is a chronic lung disease of unknown cause characterized by alveolar epithelial damage, patchy interstitial fibrosis and diffuse microvascular abnormalities. In IPF, alveolar clustering of iron-laden alveolar macrophages-a common sign of microhemorrhage, has been associated with vascular abnormalities and worsening of pulmonary hypertension. As iron-dependent ROS generation has been shown to induce unrestrained macrophage activation in disease models of vascular damage, we explored alveolar macrophage activation phenotype in IPF patients (n = 16) and healthy controls (CTR, n = 7) by RNA sequencing of bronchoalveolar lavage (BAL) cells. The frequencies of macrophages in BAL cells were 86+4% and 83.4+8% in IPF and CTR groups, respectively (p-value = 0.41). In IPF patients, BAL cells showed increased iron-dependent ROS generation (p-value<0.05 vs CTR). Gene expression analysis showed overrepresentation of Gene Ontology processes/functions and KEGG pathways enriched in upregulated M1-type inflammatory (p-value<0.01), M2-type anti-inflammatory/tissue remodeling (p-value<0.0001), and MTPP-type chronic inflammatory/angiogenic (p-value<0.0001) chemokine and cytokine genes. The ex vivo finding was confirmed by the induction of iron-dependent ROS generation and chemokine/cytokine overexpression of Ccl4, Cxcl10 (M1), Il1rn (M2), Cxcl2, and Cxcl7 (MTPP) in MH-S murine immortalized alveolar macrophages exposed to ferric ammonium citrate in culture (p-value<0.05 vs CTR). The data show alveolar macrophage expression of a pro-inflammatory, tissue remodeling and angiogenic complex activation pattern, suggesting that iron accumulation may play a role in macrophage activation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Bronchoalveolar Lavage Fluid / cytology*
  • Chemokines / metabolism
  • Female
  • Gene Expression Profiling
  • Humans
  • Idiopathic Pulmonary Fibrosis / metabolism*
  • Inflammation / metabolism*
  • Iron / metabolism*
  • Macrophages / metabolism*
  • Male
  • Middle Aged
  • Neovascularization, Pathologic*
  • Phenotype
  • Reactive Oxygen Species / metabolism
  • Sequence Analysis, RNA

Substances

  • Chemokines
  • Reactive Oxygen Species
  • Iron

Grants and funding

This study was supported by University of Florida Departmental funds (UF project #00127916(C.S.) and #00045513(M.L.B)), by funds from the Department of Biomedicine and Prevention, University of Roma by PAINCAGE FP7 #603191 (I.A.). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.