Extracellular Histones in Lung Injury and Fibrosis

• Applicant: Professor Dr. Markus Bosmann
• Subject Area: Pneumology, Thoracic Surgery
• Term: from 2013 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 234374316

Nuclear histones are released to the extracellular spaces during acute lung injury and other lung diseases. The cellular sources of extracellular histones are neutrophils and dying non-immune cells. Neutrophils generate extracellular histones in the form of neutrophil extracellular traps (NETs). The process of NET formation requires decondensation of chromatin by histone citrullination catalyzed by the enzyme, peptidyl arginine deiminase, type IV (PAD4). NETs and extracellular histones serve innate immune defenses by trapping and killing microorganisms during infections. On the other hand, extracellular histones are highly cytotoxic for resident cells in lungs and induce strong inflammatory responses. Our previous work has helped to characterize the pleiotropic roles of extracellular histones during acute lung injury. To date the activities of NETs/extracellular histones for the transition of acute tissue injury into an abnormal wound healing response with tissue remodeling and pulmonary fibrosis have only received little attention. In this project proposal, we aim to investigate the cellular sources and functional activities of extracellular histones during experimental bleomycin-induced lung injury and fibrosis. We will use chimeric mice with histone H2B-eGFP fluorescent reporter activity to determine the relative contributions of NETs versus non-myeloid cell derived extracellular histones in injured lungs. The functional relevance of histone citrullination will be studied in cytotoxicity assays of mouse lung epithelial cell lines. Transgenic mouse strains will be employed for selective depletion of neutrophils or neutrophil-specific genetic deletion of PAD4 during bleomycin-induced lung fibrosis. Monoclonal antibodies directed against histone H4 will be used to antagonize the effects of endogenous extracellular histones during lung fibrosis. The endpoints of these studies will include measurements of extracellular matrix accumulation, cytokine/chemokine patterns as well as intra-pulmonal and central T cell subsets. The long-lasting effects of extracellular histones on the adaptive immune system will be guided by a transcriptome analysis of regulatory T cells. In detail, it is proposed to evaluate the role of stress-induced genes in regulatory T cells in dependency of extracellular histones.This project aims to provide a better insight into the cellular and molecular pathways triggered by extracellular histones in the course of lung injury and lung fibrosis. In future, our experimental findings may be advantageous for the evaluation of extracellular histones as potential targets for therapeutic intervention in pulmonary fibrosis.

• DFG Programme: Research Grants
• International Connection: USA
• Cooperation Partners: Professor Dr. Charles Esmon; Professor Dr. Peter A. Ward