Pleural fibrosis is a misunderstood disorder which can cause severe restrictive lung disease with high morbidity and even mortality. The condition can develop in response to a large variety of diseases and tissue injury, among them infectious disease, asbestos, drugs, and radiation therapy. There is no efficient treatment to reverse established pleural fibrosis. TGF-β1 is suspected, even if not proven, as a key cytokine in this process. In this study, we used adenoviral gene transfer of TGF-β1 to the pleural mesothelium in rats. We show that local and transient TGF-β1 overexpression induces homogenous, prolonged, and progressive pleural fibrosis without pleurodesis, associated with severe impairment of pulmonary function. We further demonstrate that pleural fibrosis can expand into the lung parenchyma from the visceral layer, but not into the muscle from the parietal layer. We provide evidence that matrix accumulation and fibrosis within the parenchyma evolved through a process involving “mesothelial-fibroblastoid transformation” and suggest that the pleural mesothelial cell may be an important player involved in the development of the subpleural distribution pattern known to be a hallmark of pulmonary fibrosis. This new model of pleural fibrosis will allow us to better understand the mechanisms of progressive fibrogenesis, and to explore novel antifibrotic therapies in the pleural cavity.

The pathological changes in idiopathic pulmonary fibrosis (IPF) typically start in subpleural lung regions, a feature that is currently not explained. IPF, as well as bleomycininduced lung fibrosis, are more common in smokers. We hypothesised that carbon particles, which are major components of cigarette smoke that are transported to alveoli and pleural surface, might be involved in the development of subpleural fibrosis through interaction with pleural mesothelial cells.Carbon particles were administered to mice in combination with bleomycin through intratracheal and/or intrapleural injection and fibrosis was assessed using histomorphometry.Carbon administered to the chest cavity caused severe pleural fibrosis in the presence of bleomycin, whereas bleomycin alone had no fibrogenic effect. The pleural response was associated with progressive fibrosis in subpleural regions, similar to IPF in humans. Matrix accumulation within this area evolved through mesothelial-fibroblastoid transformation, where mesothelial cells acquire myofibroblast characteristics. In contrast, carbon did not exaggerate bleomycin-induced pulmonary fibrosis after combined intratracheal administration.This represents a novel approach to induce a robust experimental model of pleural fibrosis. It also suggests that carbon particles might be involved as a cofactor in the initiation and/or progression of (subpleural) pulmonary and pleural fibrosis. Mesothelial cells appear to be critical contributors to this fibrotic process.

Members of the inhibitor of apoptosis protein (IAP) family have demonstrated functions in cell death, cell signalling, cell migration and mitosis. Several of them are E3 enzymes in the ubiquitination of proteins that leads to their degradation by the proteosomal machinery. We previously reported that one of them, cellular inhibitor of apoptosis protein-1 (c-IAP1), migrated from the nucleus to the surface of the Golgi apparatus in cells undergoing differentiation. Here, we show that c-IAP1 is a client protein of the stress protein HSP90b. In three distinct cellular models, the two proteins interact and migrate from the nucleus to the cytoplasm along the differentiation process through a leptomycin B-sensitive pathway. Inhibition of HSP90 proteins by small chemical molecules and specific depletion of HSP90b isoform by siRNA both lead to auto-ubiquitination of c-IAP1 and its degradation by the proteasome machinery. This chaperone function of HSP90 towards c-IAP1 is specific of its b isoform as specific depletion of HSP90a does not affect c-IAP1 content. Chemical inhibition of HSP90 or siRNA-mediated depletion of HSP90b both inhibit cell differentiation, which can be reproduced by siRNA-mediated depletion of c-IAP1. Altogether, these results suggest that HSP90b prevents auto-ubiquitination and degradation of its client protein c-IAP1, whose depletion would be sufficient to inhibit cell differentiation. Members of the inhibitor of apoptosis protein (IAP) family were initially described as a series of natural inhibitors of cell death. Among the eight human proteins of this family, X-linked IAP (XIAP) demonstrated to be the bona fide caspase inhibitor 1 whereas the others demonstrated, for the most part, functions in cell signalling 2 and mitosis. 3 Several of these proteins harbour a Really Interesting New Gene (RING) domain at the carboxy terminus and function as an E3 enzyme in the cascade of ubiquitination that targets proteins to the ubiquitinproteasome degradation machinery. 4 One of these IAP with a RING domain is cellular IAP1 (c-IAP1) that was initially described as a signalling molecule. 2 Although c-IAP1 has subsequently been described as a direct inhibitor of caspases, this remains a controversial issue. 5,6 Due to its E3 function, c-IAP1 is responsible for the ubiquitination and subsequent degradation of the adaptor protein TNF receptor associated factor 2 7 and the serinethreonine apoptosis signal-regulating kinase 1 8 in the tumour necrosis factor alpha (TNFa) signalling pathway. In this TNFa pathway, c-IAP1 was reported also to interact with the serinethreonine kinases receptor interacting protein 2 and nuclear factor kappaB (NF-kB) essential modifier, upstream of NF-kB, 9 and to block caspase-8 activation, downstream of NF-kB. 10 Deletion experiments in Drosophila melanogaster have revealed other functions of IAPs in cell differentiation, 11 cell migration, 12 and immune response. 13 In mammals, c-IAP1-deficient mice develop normally. However, cells from c-IAP1À/À mice express markedly elevated levels ...

Bleomycin (BLM) is a potent anticancer drug used to treat different malignancies, mainly lymphomas, germ cell tumors, and melanomas. Unfortunately, BLM has major, dose-dependent, pulmonary toxicity that affects 20% of treated individuals. The most severe form of BLM-induced pulmonary toxicity is lung fibrosis. Deglyco-BLM is a molecule derived from BLM in which the sugar residue d-mannosyl-l-glucose disaccharide has been deleted. The objective of this study was to assess the anticancer activity and lung toxicity of deglyco-BLM. We compared the antitumor activity and pulmonary toxicity of intraperitoneally administrated deglyco-BLM and BLM in three rodent models. Pulmonary toxicity was examined in depth after intratracheal administration of both chemotherapeutic agents. The effect of both drugs was further studied in epithelial alveolar cells in vitro. We demonstrated in rodent cancer models, including a human Hodgkin's lymphoma xenograft and a syngeneic melanoma model, that intraperitoneal deglyco-BLM is as effective as BLM in inducing tumor regression. Whereas the antitumor effect of BLM was accompanied by a loss of body weight and the development of pulmonary toxicity, deglyco-BLM did not affect body weight and did not engender lung injury. Both molecules induced lung epithelial cell apoptosis after intratracheal administration, but deglyco-BLM lost the ability to induce caspase-1 activation and the production of ROS (reactive oxygen species), transforming growth factor-β1, and other profibrotic and inflammatory cytokines in the lungs of mice and in vitro. Deglyco-BLM should be considered for clinical testing as a less toxic alternative to BLM in cancer therapy.