Fibrogenic Lung Injury Induces Non–Cell-Autonomous Fibroblast Invasion

Abstract

Pathologic accumulation of fibroblasts in pulmonary fibrosis appears to depend on their invasion through basement membranes and extracellular matrices. Fibroblasts from the fibrotic lungs of patients with idiopathic pulmonary fibrosis (IPF) have been demonstrated to acquire a phenotype characterized by increased cell-autonomous invasion. Here, we investigated whether fibroblast invasion is further stimulated by soluble mediators induced by lung injury. We found that bronchoalveolar lavage fluids from bleomycin-challenged mice or patients with IPF contain mediators that dramatically increase the matrix invasion of primary lung fibroblasts. Further characterization of this non-cell-autonomous fibroblast invasion suggested that the mediators driving this process are produced locally after lung injury and are preferentially produced by fibrogenic (e.g., bleomycin-induced) rather than nonfibrogenic (e.g., LPS-induced) lung injury. Comparison of invasion and migration induced by a series of fibroblast-active mediators indicated that these two forms of fibroblast movement are directed by distinct sets of stimuli. Finally, knockdown of multiple different membrane receptors, including platelet-derived growth factor receptor-b, lysophosphatidic acid 1, epidermal growth factor receptor, and fibroblast growth factor receptor 2, mitigated the non-cell-autonomous fibroblast invasion induced by bronchoalveolar lavage from bleomycin-injured mice, suggesting that multiple different mediators drive fibroblast invasion in pulmonary fibrosis. The magnitude of this mediator-driven fibroblast invasion suggests that its inhibition could be a novel therapeutic strategy for pulmonary fibrosis. Further elaboration of the molecular mechanisms that drive non-cell-autonomous fibroblast invasion consequently may provide a rich set of novel drug targets for the treatment of IPF and other fibrotic lung diseases.Keywords: idiopathic pulmonary fibrosis; pathogenesis; fibroblast; invasion; migration Idiopathic pulmonary fibrosis (IPF) is a disease of great unmet medical need. Aberrant or overexuberant wound healing responses to chronic lung injury are now thought to be responsible for the excessive fibroblast accumulation and extracellular matrix deposition that distort the lung's architecture and compromise its function in IPF (1, 2). Better characterization of these abnormal responses to lung injury should provide a rich set of therapeutic targets for novel IPF therapies.The abnormal accumulation of fibroblasts is a central hallmark of fibrotic tissues, including the lung in IPF. In addition to fibroblast proliferation, fibroblast accumulation in pulmonary fibrosis appears to fundamentally depend on: (1) the migration of these cells to sites of tissue injury; and (2) their ability to invade extracellular matrix. Although migration

3D pulmospheres serve as a personalized and predictive multicellular model for assessment of antifibrotic drugs

“…There is emerging recognition of the heterogeneity of IPF pathogenesis, including cell-autonomous behavior and chemoinvasive mediators in the local microenvironment (6). This suggests that each individual patient with IPF has numerous factors that contribute to the phenotype of invasive myofibroblasts (30).…”

“…Current animal models, primarily those in rodents, have been disappointing (4), and many promising drugs have failed to demonstrate efficacy in human randomized clinical trials. An ideal preclinical model will need to recapitulate the multitude of factors responsible for the disease phenotype or endotype (1,5,6). Furthermore, it would more accurately predict drug responsiveness, while providing new insights into the pathobiology of the disease.…”

Surfactant replacement therapy reduces acute lung injury and collapse induration-related lung remodeling in the bleomycin model

“…6, B-C) (34). Invading fibroblasts have been shown to be attracted into provisory matrix very effectively by diverse mediators as early as at day 7 after bleomycin challenge (1). Regarding stereological counting, these regions of collapsed alveoli covered by epithelial cells and invaded by cells such as fibroblasts were now counted as one "septal wall" since all structures were engulfed in the tissue underneath an epithelium.…”

“Scar-cinoma”: viewing the fibrotic lung mesenchymal cell in the context of cancer biology

“…A feature of fibroblasts in pulmonary fibrosis is the ability to invade through basement membranes and ECM, and emerging studies demonstrate that IPF lung fibroblasts can be distinguished from normal lung fibroblasts by their acquisition of an invasive phenotype [104–107]. One study showed the lung fibroblasts from mice that are deficient in β-arrestin, which are protected from bleomycin-induced lung fibrosis, migrate normally but have an impaired ability to invade into Matrigel [105].…”

“…Stimulation of TLR9 significantly increased fibroblast expression of CD44 and matrix metalloproteinase-14 while promoting invasion into Matrigel [109]. Finally, a recent study indicates that while fibrotic lung fibroblasts have increased invasiveness at baseline, they also have an amplified invasive response to bronchoalveolar lavage fluid obtained from fibrotic lungs [107]. These studies demonstrate that local invasion of fibroblasts through basement membrane and interstitium can contribute to the pathogenesis of lung fibrosis, including IPF.…”