Cigarette smoke exposure reduces leukemia inhibitory factor levels during respiratory syncytial viral infection

Abstract

Background: Viral infections are considered a major driving factor of chronic obstructive pulmonary disease (COPD) exacerbations and thus contribute to disease morbidity and mortality. Respiratory syncytial virus (RSV) is a frequently detected pathogen in the respiratory tract of COPD patients during an exacerbation. We previously demonstrated in a murine model that leukemia inhibitory factor (LIF) expression was increased in the lungs during RSV infection. Subduing LIF signaling in this model enhanced lung injury and airway hypersensitivity. In this study, we investigated lung LIF levels in COPD patient samples to determine the impact of disease status and cigarette smoke exposure on LIF expression.

Materials and methods: Bronchoalveolar lavage fluid (BALF) was obtained from healthy never smokers, smokers, and COPD patients, by written informed consent. Human bronchial epithelial (HBE) cells were isolated from healthy never smokers and COPD patients, grown at the air–liquid interface and infected with RSV or stimulated with polyinosinic:polycytidylic acid (poly (i:c)). Mice were exposed to cigarette smoke daily for 6 months and were subsequently infected with RSV. LIF expression was profiled in all samples.

Results: In human BALF, LIF protein was significantly reduced in both smokers and COPD patients compared to healthy never smokers. HBE cells isolated from COPD patients produced less LIF compared to never smokers during RSV infection or poly (i:c) stimulation. Animals exposed to cigarette smoke had reduced lung levels of LIF and its corresponding receptor, LIFR. Smoke-exposed animals had reduced LIF expression during RSV infection. Two possible factors for reduced LIF levels were increased LIF mRNA instability in COPD epithelia and proteolytic degradation of LIF protein by serine proteases.

Conclusions: Cigarette smoke is an important modulator for LIF expression in the lungs. Loss of LIF expression in COPD could contribute to a higher degree of lung injury during virus-associated exacerbations.

Keywords:

• chronic obstructive pulmonary disease
• leukemia inhibitory factor
• respiratory syncytial virus
• cigarette smoke

Acknowledgments

This work was supported by grants made available to PG (Flight Attendant Medical Research Institute YCSA113380 and CIA160005 and the Alpha-1 Foundation 493373) and to MS (Flight Attendant Medical Research Institute, CIA160011and CIA13033, as well as James & Esther King Biomedical Program of the State of Florida, #5JK02).

Abbreviations list

RSV, respiratory syncytial virus; BALF, bronchoalveolar lavage fluid; HBE, bronchial epithelial; LIF, leukemia inhibitory factor; ARDS, acute respiratory distress syndrome; CXCL, chemokine (C-X-C motif) ligand; CCL, CC chemokine ligands; STAT3, signal transducer and activator of transcription 3; Fap, fibroblast activation protein; IL, interleukin; Tnfs; ALI, air-liquid interface; MOI, multiplicity of infection; PFU, plaque forming units; ETS, E26 transformation-specific; AREs, AU-rich elements; ILF3, Interleukin enhancer binding factor 3; EMT, epithelial-mesenchymal transition; poly (i:c), polyinosinic:polycytidylic acid; siRNA, small interfering RNA; HuR, human antigen R; TTP, tristetraprolin; DICER1, Dcr-1 homolog; NE, neutrophil elastase; AUF-1, AU-rich element-binding factor 1.

Author contributions

All authors contributed toward data analysis, drafting and critically revising the paper, gave final approval of the version to be published, and agree to be accountable for all aspects of the work.

Disclosure

The authors declare that they have no competing interests.