OZONE-INDUCED AND ENDOTOXIN-INDUCED MUCOUS CELL METAPLASIAS IN RAT AIRWAY EPITHELIUM - NOVEL ANIMAL-MODELS TO STUDY TOXICANT-INDUCED EPITHELIAL TRANSFORMATION IN AIRWAYS

Mucous (goblet) cell proliferation and hypersecretion of airway mucus are important characteristics of human respiratory disorders, especial ly chronic bronchitis and cystic fibrosis. These changes in secretory patterns also occur in animals experimentally exposed to chemical irri tants such as ozone (O3), sulfur dioxide (SO2), and cigarette smoke. T he cellular and molecular mechanisms involved in irritant-induced muco us cell metaplasia (MCM; transformation of airway epithelium, normally devoid of mucous cells, to a secretory epithelium containing numerous mucous cells) are still unclear. We used two experimental models of t oxicant-induced MCM in rat airways to study the cellular and molecular changes that occur during the development of this respiratory tract l esion. MCM can be induced in the nasal transitional epithelium of rats by repeated exposure to ambient levels of ozone. In addition, MCM can be induced in the tracheobronchial airways of rats repeatedly exposed to endotoxin, a lipopolysaccharide-protein molecule found in the oute r walls of Gram-negative bacteria. The pathogenesis of ozone- or endot oxin-induced MCM has been partially characterized using a variety of m orphometric and histochemical techniques. Toxicant-induced changes in the numbers and types of airway epithelial cells have been estimated u sing morphometric methods designed for estimating the abundance of cel l populations. Nasal pulmonary airway tissues are also processed for l ight microscopy and stained with Alcian Blue (pH 2.5)/Periodic Acid Sc hiff (AB/PAS) for detection of acidic and neutral mucosubstances (the specific glycoprotein product of mucous cells), respectively, within t he tissue. Computerized image analysis is used to quantitate the amoun t of the stained mucous product within the airway epithelium. To bette r characterize the molecular and cellular events in the pathogenesis o f ozone- or endotoxin-induced MCM in the rat airway epithelium, we are conducting studies to determine when, and in which epithelial cells, the mucin gene is expressed after exposure to the toxicant. In these s tudies, rats undergo single or repeated exposures to ozone or endotoxi n and are then sacrificed immediately or a few days after the end of t he exposures. Airway tissues are microdissected from specific regions of the exposed respiratory tract, and changes in mucin core polypeptid e mRNA are evaluated by Northern analysis using human and rat mucin cD NA. In future studies using in situ hybridization, we will establish w hen, and in which epithelial cells, the expression of high molecular w eight airway mucin is initiated in response to ozone or endotoxin. The se cellular and molecular analyses are being conducted to better chara cterize the toxicant-induced changes involved in the metaplastic proce ss. Results from these studies will help us to understand the pathogen esis of MCM and may provide insight into methods of treatment for thes e common airway lesions.