Effects of ozone stimulation of bronchial epithelial cells on proliferation and collagen synthesis of co-cultured lung fibroblasts

Repetitive Ozone Exposures and Evaluation of Pulmonary Inflammation and Remodeling in Diabetic Mouse Strains

BACKGROUND

Epidemiological studies support the hypothesis that diabetes alters pulmonary responses to air pollutants like ozone (O 3 ). The mechanism(s) underlying these associations and potential links among diabetes, O 3 , and lung inflammation and remodeling are currently unknown.

OBJECTIVES

The goal was to determine whether pulmonary responses to repetitive ozone exposures are exacerbated in murine strains that are hyperglycemic and insulin resistant.

METHODS

Normoglycemic and insulin-sensitive C57BL/6J mice; hyperglycemic, but mildly insulin-resistant, KK mice; and hyperglycemic and markedly insulin-resistant KKAy mice were used for ozone exposure studies. All animals were exposed to filtered air (FA) or repetitive ozone (0.5  ppm O 3 , 4 h/d, for 13 consecutive weekdays). Tissue analysis was performed 24 h following the final exposure. This analysis included bronchoalveolar lavage (BAL) for cell and fluid analysis, and tissue for pathology, immunohistology, mRNA, and hydroxyproline.

RESULTS

Following repetitive O 3 exposure, higher bronchoalveolar lavage fluid inflammatory cells were observed in all mice (KKAy > KK > C 57 BL / 6 ), with a notable influx of neutrophils and eosinophils in KK and KKAy mice. Although the lungs of O 3 -exposed C57BL/6J and KK mice had minimal centriacinar histological changes without fibrosis, the lungs of O 3 -exposed KKAy mice contained marked epithelial hyperplasia in proximal alveolar ducts and adjacent alveoli with associated centriacinar fibrosis. Fibrosis in O 3 -exposed KKAy lungs was confirmed with immunohistochemistry, tissue hydroxyproline content, and tissue mRNA expression of fibrosis-associated genes (Ccl11, Il13, and Mmp12). Immunofluorescence staining and confocal microscopy revealed alterations in the structure and composition of the airway and alveolar epithelium in regions of fibrosis.

DISCUSSION

Our results demonstrate that in diabetic animal strains repetitive ambient ozone exposure led to early and exaggerated pulmonary inflammation and remodeling. Changes in distal and interstitial airspaces and the activation of Th2 inflammatory and profibrotic pathways in experimental animals provide a preliminary, mechanistic framework to support the emerging epidemiological associations among air pollution, diabetes, and lung disease. https://doi.org/10.1289/EHP7255.

Immunologic and Non-Immunologic Mechanisms Leading to Airway Remodeling in Asthma

Asthma increases worldwide without any definite reason and patient numbers double every 10 years. Drugs used for asthma therapy relax the muscles and reduce inflammation, but none of them inhibited airway wall remodeling in clinical studies. Airway wall remodeling can either be induced through pro-inflammatory cytokines released by immune cells, or direct binding of IgE to smooth muscle cells, or non-immunological stimuli. Increasing evidence suggests that airway wall remodeling is initiated early in life by epigenetic events that lead to cell type specific pathologies, and modulate the interaction between epithelial and sub-epithelial cells. Animal models are only available for remodeling in allergic asthma, but none for non-allergic asthma. In human asthma, the mechanisms leading to airway wall remodeling are not well understood. In order to improve the understanding of this asthma pathology, the definition of “remodeling” needs to be better specified as it summarizes a wide range of tissue structural changes. Second, it needs to be assessed if specific remodeling patterns occur in specific asthma pheno- or endo-types. Third, the interaction of the immune cells with tissue forming cells needs to be assessed in both directions; e.g., do immune cells always stimulate tissue cells or are inflamed tissue cells calling immune cells to the rescue? This review aims to provide an overview on immunologic and non-immunologic mechanisms controlling airway wall remodeling in asthma.