BRONCHIOLAR CLARA CELLS: A ROLE IN TYPE 2 CELL FUNCTION

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The nonciliated bronchiolar epithelial (Clara) cell of the lung remains an enigma, particularly with respect to its biological role in the small airway and proximal alveoli. A major barrier to identifying tha Clara cell's functional activity is the great difficulty encountered in obtaining significant quantities of these cells for study. In an effort to develop a unique approach to this problem area, we have recently established a murine lung adenoma model in our laboratory -- induced by transplacental exposure to N,ethylnitrosourea. With appropriate manipulation, we have been able to produce benign tumors of the lung that are primarily of Clara cells origin. Our preliminary morphologic studies have confirmed the structural characteristics of thse cells as being those of the murine Clara cell. During our initial investigations, we observed the development of unusual Type 2 cells in the immediate vicinity of Clara cell tumors. These abnormal Type 2 cell accumulate abundant quantities of surfactant-like phospholipid material in cytoplasmic vacuoles. These appear to be directly related to the age and size of the Clara cell tumor -- the older and larger the tumor becames, the more extensive the inclusions per cell and total number of Type 2 cells involved. The studies outlined in this proposal are designed to test the hypothesis that the bronchiolar Clara cell has a defined functional interaction with alveolar epithelial cells; specifically, the modulation of Type 2 cell surfactant synthesis/secretion via a product produced by Clara cells. The major areas of Clara cell biology will be examined. The first involves the isolation, purification and functional characterization of cells obtained from our tumor model. These cells will be examined in the isolated state for biocemical features such as mixed-function oxidase activity, lipid degrading activity (phospholipases), the chemical compositions of their secretory granules and identification of some of the factors regulating synthesis and release of these secretions. The second approach will attempt to develop optimum conditions for maintaining isolated Clara cells in cutlure. Then to establish co-cultures of Clara cells with freshly isolated rat lung Type 2 cells, the A549 human lung cell line, and if necessary, virus transformed rat lung Type 2 cells in an effort to reproduce the Type 2 cell effects we have observed in vivo. The application of the mouse lung Clara cell adenoma model is a unique approach to testing the proposed hypothesis.