LUNG COLLAGEN CROSSLINKING--BIOSYNTHESIS AND MATURATION

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Previous work performed under this grant has demonstrated the feasibility of studying collagen biosynthesis and maturation in skin, bone, tendon, and lungs of normal rats by in vivo labelling techniques. The present application proposes to extend these studies into a well documented animal model of pulmonary fibrosis, intra-tracheally injected bleomycin in the rat, to study collagen synthesis and maturation in the damaged, (pre)fibrotic lung. We will specifically test the hypothesis that hydroxylation of key lysine residues that take part in collagen crosslinking reactions is a critical step in the biosynthesis of fibrotic lung collagen. Parallel studies in lung tissue from several animal models and in human fibrotic lungs have demonstrated increased hydroxylation of lysine and an increased ratio of the difunctional Schiff base- derived, crosslink DHLNL to HLNL in (Pre)fibrotic (acute fibrosis) lungs. Similarly, we have observed an increased content of the fully hydroxylated trifunctional crosslink OHP in chronic fibrosis of both animal models and human lungs. Thus, we propose to examine the following hypotheses in this proposal: (i) that increased lysine hydroxylation distinguishes "fibrotic collagen" from "normal collagen" in the lung; (ii) that this difference is mediated by increased activity of lysyl hydroxylase in the (pre)fibrotic lung; and (iii) that once crosslinked, "fibrotic collagen" in the lung is not subject to turnover or breakdown, but rather will persist for the lifetime of the host. A combination of in vivo labelling and tissue slice and homogenate experiments will be performed to examine these questions. Correlative studies with human lung tissue, as available, from patients with acute (ARDS, IRDS) and chronic (IPF) lung fibrosis will examine the underlying mechanisms of collagen accumulation in human lung disease, and will perhaps identify potential new targets for rational therapy of these diseases.