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, 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 pneumocyte. Interruption or delay of this process results in local epithelial hyperplasia, faulty re- an irreversibly- impaired function in the alveolar region. The mechanism(s) which govern these critical events are not clear. We have shown that there is a specific relationship between sulfated components of the alveolar basement membrane and certain growth factors by showing that the level of sulfate in extracellular matrix (ECM) substrata directly influences type II cells by either promoting (low sulfate) or retarding (high sulfate responses to fibroblast growth factors (FGFs) in vitro. We now propose that basic (b)FGF and transforming growth factor beta(TGF-beta) act in different ways with sulfated ECMs to regulate type II cell proliferation an capacity to alter its local environment, thereby defining the effectiveness of epithelial repair and alveolar stabilization. The specific hypothesis to be tested in this proposal is: Regions of low levels of sulfate the alveolar basement membrane in concert with TGF-beta promote proliferation of type II cells. Conversely, regions of higher sulfate in concert with TGF~ repress proliferation, promote biosynthesis of the basement membrane components bFGF and heparin sulfate proteoglycan (HSPG), and modify the level of sulfation and sulfated carbohydrate structure of biosynthesized ECMs. These processes constitute a critical mechanism for regulation of cell numbers and their functions under normal an hyperplastic states in the alveolus. We will examine the regulatory mechanisms of proliferation in type II cells exposed to different sulfated ECM substrata in the presence or absence of FGFs and/or TGF-beta Artificial and biosynthesized ECMs that are naturally not sulfated, sulfated, or chemically sulfated/desulfated will be used as culture substrata, and their effects on the cells' capacity to: 1) alter its basement membrane composition through biosynthesis of beta-FGF and specific ECMs, 2) sulfate and modify relevant ECMs, and 3 regulate local proliferative events within regions of cultures measured under different growth factor conditions. These studies will elucidate molecular, structural, and functional relationships between epithelial cells, ECMs and growth factors and how they regulate the regional environment of the alveolus. They will provide essential data for defining the mechanisms of extracellular matrix macromolecular regulation of critical epithelial renewal processes in normal lung tissue, and following injury and/or disease.