Gene Expression Profiling in Lung Tissues from Mice Exposed to Cigarette Smoke, Lipopolysaccharide, or Smoke Plus Lipopolysaccharide by Inhalation

Abstract

The purpose of this study was to investigate whether coexposure to lipopolysacchride (LPS) will heighten the inflammatory response and other pulmonary lesions in mice exposed to cigarette smoke, and thus to evaluate the potential use of this LPS-compromised mouse model as a model for chronic obstructive pulmonary disease (COPD) investigation. AKR/J male mice were exposed to HEPA-filtered air (sham control group), cigarette smoke (smoke group), LPS (LPS group), or smoke plus LPS (smoke-LPS group) by nose-only inhalation. Lungs were collected at the end of the 3-wk exposure and processed for microarray analysis. Clustering and network analysis showed decreased heat-shock response and chaperone activity, increased immune and inflammatory response, and increased mitosis in all three exposed groups. Two networks/function modules were exclusively found in the smoke-LPS group, that is, the downregulated muscle development/muscle contraction process and the upregulated reactive oxygen species production process. Notably, the number of genes and function modules/networks associated with inflammation was reduced in the smoke-LPS group compared to the LPS group. The most upregulated gene in the smoke group, MMP12, is a matrix metalloproteinase that preferentially degrades elastin and has been implicated in COPD development. NOXO1, which was upregulated in all three treatment groups, positively regulates the expression of a subunit of NADPH oxidase (NOX1), a major source of reactive oxygen species, and may play an important role in the pathogenesis of COPD. Serum amyloid A1, which is an acute-phase systemic inflammation marker and can be induced by LPS exposure, was significantly upregulated in the LPS and smoke-LPS groups. MARCO, a scavenger receptor expressed in macrophages that may play a significant role in LPS-induced inflammatory response, was upregulated in the LPS group and the smoke-LPS group, but not in the smoke group. In conclusion, gene expression profiling identified genes and function modules that may be related to COPD pathogenesis and may be useful as biomarkers to monitor COPD progression. In addition, an LPS-compromised mouse model showed potential as a useful tool for studying cigarette smoke-associated COPD.

Chronic Endotoxin Exposure Produces Airflow Obstruction and Lung Dendritic Cell Expansion

“…Thus, the 8-week LPS exposure protocol resulted in increased airway resistance, both at baseline and after the methacholine challenge. Interestingly, for the 5-day LPS mice, a significant increase in airway resistance was also evident at 30, 60, and 120 mg/ml of methacholine ( Figure 1B), and a significant difference in airway sensitivity was evident compared with PBS control mice (ED 50 for PBS, 44.8 6 17.9 mg/ml; ED 50 for LPS mice, 11.9 6 4.0 mg/ml; P ¼ 0.034). Although the 8-week LPS mice exhibited an overall increase in airway reactivity compared with PBS control mice, we did not detect significant differences at individual doses of methacholine, and no significant difference was evident in airway sensitivity compared with PBS control mice (ED 50 for PBS control mice, 25.0 6 9.3 mg/ml; ED 50 for LPS mice, 22.0 6 11.1 mg/ml; P ¼ 0.87).…”

Nox enzymes, ROS, and chronic disease: An example of antagonistic pleiotropy

“…Cigarette smoke may also contribute to obstructive pulmonary disease via Nox-generated ROS. Cigarette smoke and the bacterial product LPS both up-regulate NOXO1, the activator of Nox1 [31]. TLR4 deficiency, which causes emphysema in mice, up-regulated Nox3 in lung and endothelial cells resulting in increased oxidant generation and elastolytic activity.…”

NADPH oxidases in lung biology and pathology: Host defense enzymes, and more

“…Myofibroblasts from patients with iodopathic pulmonary fibrosis produce primarily extracellular H 2 O 2 in response to TGF-β1, presumably due to the presence of NOX4 (187). Exposure of mice to cigarette smoke and/or LPS was found to result in increased lung expression of NOXO1, an activator of NOX1 (214), but the potential significance for cigarette smoke-induced emphysema or lung cancer is unclear. Intriguingly, development of pulmonary emphysema in mice due to genetic deficiency of Toll-like receptor (TLR)-4, was recently associated with upregulation of NOX3 in the pulmonary endothelium, which appears to contribute to elastolytic activity (215).…”