Idiopathic pulmonary fibrosis (IPF) is a relentlessly progressive lung disease characterized by fibrosis of the peribronchiolar interstitium. There is increasing appreciation that IPF represents the chronic consequence of a maladaptive response to acute lung injury. Accordingly, known mediators of acute lung injury and the acute respiratory distress syndrome (ARDS) may have direct relevance to IPF pathogenesis. The laboratory of my mentor, Dr. Eric Schmidt (University of Colorado), has previously demonstrated the importance of heparanase to the onset of ARDS. Heparanase specifically degrades heparan sulfate (HS), a cell-surface glycosaminoglycan essential for homeostatic lung function. Heparanase-mediated degradation of endothelial HS leads to ARDS; however, the relevance of HS degradation to pulmonary fibroblasts and chronic lung injury is relatively unexplored. In preliminary experiments, we observed increased expression of heparanase in lung explants from patients with severe IPF. Heparanase co-localized with activated pulmonary fibroblasts and was associated with loss of cell-surface HS in pulmonary fibroblasts isolated from human IPF explants. This loss of cell-surface HS is profibrotic, as experimental degradation of HS from normal human lung fibroblasts induced expression of pro-fibrotic genes. Intriguingly, this fibroblast activation was associated with nuclear localization of HS fragments released from the degraded cell surface. Nuclear HS translocation was sufficient to induce pro- fibrotic gene expression, as nucleofection of normal mouse lung fibroblasts (MLFs) similarly induced expression of profibrotic genes transforming growth factor ?, collagen 1A1, and ? Smooth Muscle Actin. As nuclear HS has been previously implicated as an inhibitor of histone acetyltransferases, the observed profibrotic activation of pulmonary fibroblasts after degradation of cell-surface HS may reflect the epigenetic consequence of nuclear HS translocation. Based upon these preliminary studies, I hypothesize that injury-induced expression of pulmonary heparanase cleaves fibroblast cell-surface HS, leading to nuclear internalization of HS fragments. Nuclear HS in turn suppresses histone acetyltransferase activity, inducing pro-fibrotic gene expression in IPF. These studies represent a novel, high-impact investigation with robust preliminary data, providing me with a unique and high-yield opportunity for training in diverse field such as glycosaminoglycan biology, lung injury and repair, and state-of-the-art molecular biology techniques. Furthermore, the proposed studies have translational relevance, representing a novel opportunity to therapeutically target lung fibrosis via either the prevention of HS degradation (and release of HS fragments) or the augmentation of histone acetylation.
We propose to determine if heparanase (a known mediator of acute lung injury) contributes to the pathogenesis of the chronic, progressive lung injury characteristic of idiopathic pulmonary fibrosis (IPF). We will test the hypothesis that heparanase-mediated degradation of fibroblast cell-surface heparan sulfate leads to nuclear translocation of heparan sulfate fragments, inducing fibroproliferative gene expression characteristic of IPF.
