Table 1.

Some of the important molecular mechanisms underlying ROS-induced pulmonary fibrosis and areas requiring further investigation

What we know	What we need to know
There is increased oxidative stress in the lungs of patients with pulmonary fibrosis.	What is the most reproducible technique to quantitate ROS in tissue and BALF? What is the in vivo relevance of these findings in the context of treating pulmonary fibrosis and which cell(s) should be targeted?
There is decreased antioxidant defenses in the lungs of patients with pulmonary fibrosis.	What is the best way to quantitate anti-oxidant defenses in tissue and BALF? What is the in vivo relevance of these findings in the context of treating pulmonary fibrosis and which cell(s) should be targeted?
Apoptosis of AECs occurs in patients with IPF and asbestosis.	Is AEC apoptosis essential for mediating pulmonary fibrosis?
Pulmonary fibrosis is associated with activation of an ER stress response that may be due partly to ROS production.	What is the causal role of ROS in activating the ER stress response in AEC as well as the in vivo relevance of ER stress in the context of treating pulmonary fibrosis?
ROS cause AEC apoptosis in vitro while AEC apoptosis occurs in patients with IPF and asbestosis.	Is AEC apoptosis essential for mediating pulmonary fibrosis?
Asbestos induces AM Rac1-dependent mitochondrial ROS production that is important in murine asbestosis.	What role does AM Rac1 play in humans with asbestosis, and is it a useful biomarker of pulmonary fibrosis?
p53-dependent transcription mediates ROS/asbestos-induced intrinsic AEC apoptosis in vitro and is evident in gene-profiling studies of normal and malignant cells.	Is p53-depenedent transcription necessary for pulmonary fibrosis following ROS exposure in animal models or humans?
Mitochondrial hOgg1 and ACO2 prevent oxidant-induced AEC mitochondrial dysfunction and intrinsic apoptosis in vitro.	What is the in vivo relevance of these findings in the context of asbestosis and other forms of pulmonary fibrosis?
ROS activate latent TGF-β, induce TGF-β gene expression, and activate fibroblast collagen production	What is the in vivo relevance of these findings in the context of treating pulmonary fibrosis and which cell(s) should be targeted?
ROS activates Nalp3 inflammasomes.	Is Nalp3 activation induced by ROS necessary and sufficient for inducing pulmonary fibrosis, and if so, which cell is responsible?

Abbreviations: ACO2, mitochondrial aconitase; AEC, alveolar epithelial cell; AM, alveolar macrophage; BALF, bronchoalveolar lavage fluid; ER, endoplasmic reticulum; hOgg1, human 8-oxoguanine-DNA glycosylase 1; IPF, idiopathic pulmonary fibrosis; ROS, reactive oxygen