ALVEOLAR BASEMENT MEMBRANE/CELL INTERACTIONS IN THE LUNG

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Type I pneumocytes, which cover over ninety percent of the alveolar surface of the lung, are particularly susceptible to injury, such as that induced by air-borne toxicants or oxidant stress. Replacement/renewal of these cells following injury requires division and differentiation of a second cell, the type II pneumocyte. Interruption or delay of this process results in faulty repair and irreversibly-impaired function in the alveolar region. The mechanism(s) which govern these critical events are not clear, but preliminary evidence suggests that differences in the composition of the extracellular matrix (basement membrane) microdomains associated with the type I cell compared to the type II cell may influence the known responsiveness of the latter to epidermal, and acidic and basic fibroblast growth factors. The hypothesis to be tested in this proposal is that the specific molecular composition of the alveolar basement membrane and, in particular, its unique sulfated characteristics determines the type II cell's capacity to proliferate, differentiate, and regulate/repair its environment by synthesizing extracellular matrix molecules in response to acidic and basic fibroblast growth factors, and epidermal growth factor. We propose to characterize the proliferative, differentiative, and regulative responses of isolated rat type II cells to acidic and basic fibroblast growth factors, and epidermal growth factor, while maintained in culture on different matrix substrata that vary only in their levels of sulfation. The level of sulfation will be specifically reduced in selected, purified matrix preparations by chemical desulfation, or in biosynthesized substrata by interfering with the normal sulfation of matrix components produced by substrata producer cells. Type II cell proliferative responses to different matrix and sulfate compositions will be measured by 5-bromo- deoxyuridine incorporation; differentiation will be defined by morphologic and histochemical characteristics; and regulation/repair of their environment will be measured by type II cell biosynthesis of extracellular matrix components. These studies will elucidate molecular, structural, and functional relationships between epithelial cells, connective tissue matrices, and soluble growth factors in the pulmonary alveolus. They will provide a foundation for defining the mechanisms of extracellular matrix macromolecular regulation of critical re-epithelialization/repair processes in lung tissue following injury and/or disease.