Increased phosphorylated extracellular signal-regulated kinase immunoreactivity associated with proliferative and morphologic lung alterations after chrysotile asbestos inhalation in mice - PubMed (original) (raw)

Increased phosphorylated extracellular signal-regulated kinase immunoreactivity associated with proliferative and morphologic lung alterations after chrysotile asbestos inhalation in mice

R F Robledo et al. Am J Pathol. 2000 Apr.

Abstract

Activation of extracellular signal-regulated kinases (ERK) has been associated with the advent of asbestos-associated apoptosis and proliferation in mesothelial and alveolar epithelial cells and may be linked to the development of pulmonary fibrosis. The objective of studies here was to characterize the development of inflammation, cellular proliferation, and fibrosis in asbestos-exposed C57Bl/6 mice in relationship to patterns of ERK phosphorylation. Inflammation occurred after 10 and 20 days of asbestos exposure as evidenced by increases in total protein and neutrophils in bronchoalveolar lavage fluid. Increases in cell proliferation were observed at 30 days in bronchiolar epithelia and at 4, 14, and 30 days in the alveolar compartment of the lung. Trichrome-positive focal lesions of pulmonary fibrosis developed at 30 days in the absence of elevations in lung hydroxyproline or procollagen mRNA levels. Striking increases in ERK phosphorylation were observed within pulmonary epithelial cells at sites of developing fibrotic lesions after 14 and 30 days of inhalation. In addition to characterizing a murine inhalation model of asbestosis, we provide the first evidence showing activation of ERK signaling within lung epithelium in vivo, following inhalation of asbestos fibers.

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Figures

Figure 1.

Experimental protocols of National Institute of Environmental Health Sciences chrysotile asbestos inhalation experiments (∼10 mg/m3, 6 hours/day, 5 days/week) in C57Bl/6 mice (n = 5/group/time period).

Figure 2.

Differential cell counts and total protein levels in BAL samples from sham- and chrysotile asbestos-exposed C57Bl/6 mice. No significant differences in total cell numbers were observed between exposure groups (data not shown). Values are means ± SE; n = 4 mice/group. *Significant difference from time-matched control, P ≤ 0.05.

Figure 3.

Representative images of lung tissue sections using Masson’s trichrome staining (A−C) or an antibody to BrdU (D−F). A and D: 30-day sham exposure; B, E, and F: 30-day chrysotile exposure; C: 30-day chrysotile exposure + 28-day recovery period. Focal increases in fibrosis were noted in chrysotile-exposed lungs at 30 days (B) at bronchiolar-alveolar ductal bifurcations (arrowheads). Lesions did not appear to increase in severity or extent in the 30-day chrysotile exposure + 28-day recovery group (C). Note increased BrdU immunostaining (arrows) within a developing alveolar ductal lesion (E) and peribronchiolar lesion (F) after 30 days of chrysotile exposure. Original magnifications,×400 (A, B, D, E) and ×200 (C and F).

Figure 4.

Hydroxyproline content of C57Bl/6 mouse lungs after inhalation of chrysotile asbestos. Values are means ± SE; n = 5 mice/group.

Figure 5.

Quantitative image analysis of BrdU incorporation in proliferating lung cells in C57Bl/6 mice after inhalation of chrysotile asbestos. Values are means ± SE; n = 5 mice/group. *Statistically significant difference from time-matched control, P ≤ 0.05.

Figure 6.

Representative images illustrating phosphorylated-ERK immunoreactivity (arrows) in lung tissue sections: A, 30-day chrysotile exposure (negative staining control); B, mouse intestine (positive staining control); C, 30-day sham exposure; D, 14-day chrysotile exposure; E−H, 30-day chrysotile exposure. Note increased clustering of ERK phosphorylation in bronchiolar epithelial and bifurcation cells after 14 and 30 days of chrysotile exposure (D and E). Increased focal ERK phosphorylation was also noted in developing peribronchiolar fibrotic lesions and alveolar ductal lesions after 30 days of exposure (F−H). Hematoxylin counterstain; original magnifications, ×400 (A, B, D, E, and H) and ×200 (C, F, and G).

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Increased phosphorylated extracellular signal-regulated kinase immunoreactivity associated with proliferative and morphologic lung alterations after chrysotile asbestos inhalation in mice - PubMed (original) (raw)