| Toxic injury in the lung can come from a variety of sources. Xenobiotics can act directly in the lung, such as ozone, or may require metabolism into toxic intermediates by Clara cells, the primary metabolically active cells within the lung. Naphthalene (NA), a polycyclic aromatic hydrocarbon abundant in tobacco smoke and the emissions of the internal combustion engine, is a prototypical bioactivated Clara cell toxicant. Much is known about the progression of acute Clara cell injury after a single exposure to NA as well as the in the development of tolerance to repeated exposures to NA. In contrast, relatively little is known about the expression pattern of potentially protective proteins during the acute injury and development of tolerance. The objective of this dissertation was to investigate the expression of one such class of proteins, heat shock proteins (Hsps), in the lung after acute NA-induced Clara cell injury and in the development of the tolerant lung. Further, their expression is related to changes in airway epithelial intracellular glutathione (GSH) pools.; Expression of Hsps in Clara cells after acute NA injury precedes the onset of organelle alterations by ultrastructure, but is closely tied to the onset of GSH depletion and protein adduction by metabolites of NA. Expression is down-regulated after cell exfoliation, during repair. Early in the development of tolerance (1–3 days exposure), there is continued up-regulation of Hsps in the target epithelium. After 4–7 days of consecutive NA exposure Hsps are down-regulated, coincident with the reported up-regulation of GSH biosynthesis. We established the importance of GSH levels to induction of Hsp synthesis in airway epithelial cells. When GSH is depleted from the airway epithelium using the non-toxic chemical depletor diethylmaleate (DEM), there is rapid up-regulation of Hsp 72 in association with intracellular GSH depletion. Lastly, we show that the actin cytoskeleton of Clara cells is altered in response to NA injury. The small Hsp, Hsp 25, co-localizes with the cytoskeletal fraction by Western blot analysis and shifts in distribution in the bronchiolar ciliated cells toward the cell periphery in response to the disrupted Clara cell actin 2hrs post-NA. |
