Elevation of Stress-Inducible Heat Shock Protein 70 in the Rat Lung After Exposure to Ozone and Particle-Containing Atmospheres

Abstract

Heat shock proteins (HSPs) are elicited as part of a ubiquitous cellular defense mechanism following exposure to a variety of environmental assaults. Ozone (O₃) is a commonly encountered toxic air pollutant that is known to produce a variety of effects in the lung. However, the effects of O₃ exposure on lung HSP expression have not been reported. In this study, the expression and elevation of stress-inducible HSP 70 was examined in rat lungs (group sizes = 7) following inhalation exposure to either (a) 0.2 ppm O₃ or (b) a mixture of 0.2 ppm O₃, 350 ± 75 μg/m³ road dust particles with mass median aerodynamic diameter of 5 μm, 65 ± 14 μg/m³ ammonium sulfate (SO₄⁻²), and 365 ± 35 μm/m³ ammonium nitrate (NO₃⁻¹). Exposures were episodic at 4 h/day, 4 consecutive days per week for 8 wk; control rats inhaled purified air (n = 4). Rats were euthanized at either 4 or 17 days after the last exposures, and samples of the peripheral lung from the right apical lobe were obtained for analysis of stress-inducible HSP 70 levels. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PACE) and subsequent protein immunoblotting revealed that stress-inducible HSP 70 was present constitutively in the control lungs. There were no differences in HSP 70 levels in the 4-day and 17-day sacrifice groups; therefore, the groups were pooled for statistical analysis. Statistical analysis by analysis of variance demonstrated that inhalation of atmospheres containing either O₃ or O₃ in combination with particles significantly elevated rat lung stress-inducible HSP 70 levels (p =.0007) over control animals that inhaled only purified air; a significant difference could be detected between O₃ inhalation and control air (p = .0003) and O₃ with the other particles versus the control animals (p =.0092). Furthermore, analysis of the two groups that inhaled either O₃ or O₃ in combination with other particles showed a significant difference (p =.0071). The data suggests that lung stress-inducible HSP 70 elevation after exposure to airborne pollutants may be important and that changes in HSP 70 levels may be an extremely sensitive indicator of early pulmonary stress and injury.