Abstract Fibrotic pulmonary and pleural disorders represent a group of intrathoracic disorders with different etiologies and prognoses. A prominent part of both pulmonary and pleural fibrotic disorders remains etiologically unknown. An essential feature for all these disorders is an increase and disarray of many extracellular matrix proteins which take part in the remodeling of the fibrotic tissue. Further, the injury in pulmonary as well as in pleural fibrosis occurs often at the border between the epithelial or mesothelial and the mesenchymal cells breaking the epithelial basement membrane. Tenascin is an oligomeric matrix glycoprotein of the extracellular matrix. The best known isoforms are tenascin -C, -X, -R, -Y and -W. Tenascin-C is synthesized during embryonic development, expressed in a variety of tumors, being absent or scantily expressed in most adult tissues. The function of tenascin-C is still unclear. In lung, tenascin-C has been shown to be expressed in fetal lung during branching morphogenesis, benign and malignant lung tumors, idiopathic pulmonary fibrosis, sarcoidosis and asthma. The aim of the present study was to study tenascin-C (later called tenascin) expression in various types of pulmonary fibrosis such as usual interstitial pneumonia (UIP), desquamative interstitial pneumonia (DIP), nonspecific interstitial pneumonia (NSIP), bronchiolitis obliterans organizing pneumonia (BOOP), sarcoidosis and extrinsic allergic alveolitis as well as in fibrotic and inflammatory disorders of the pleura of different etiologies. Further, the aims were to compare the accumulation of tenascin with the prognosis in UIP, to confirm the immunohistochemical findings in UIP by Western blotting and immunoelectron miscroscopic (immuno-EM) studies, to investigate which cells synthesize tenascin in UIP and in pleural fibrosis by mRNA in situ hybridization, and to determine whether epithelial lining fluid (ELF) and serum tenascin concentration are increased in patients with UIP, sarcoidosis and extrinsic allergic alveolitis. Tenascin was shown to be increased by immunohistochemical studies in all types of pulmonary and pleural fibrotic disorders included in the study. In UIP, increased tenascin expression was associated with a shortened survival time of the patients. In immuno-EM, labeling for tenascin was seen within type II pneumocytes. UIP cases showed reactivity for a polypeptide of Mr = 200 000 by Western blotting. Myofibroblasts and type II pneumocytes were mainly shown to synthesize tenascin in UIP. Also in pleural fibrosis myofibroblasts, and in addition possibly mesothelial cells, were observed to be responsible for its synthesis. ELF and serum tenascin concentrations were increased in UIP, sarcoidosis and extrinsic allergic alveolitis. In conclusion, tenascin expression is increased in pulmonary and pleural fibrotic disorders, especially in newly formed fibrosis. In UIP, tenascin is actively synthesized at the sites of recent epithelial injury, suggesting that it plays an important role in the fibrogenesis in the lung.

La fibrose pulmonaire idiopathique (FPI) est de pronostic sombre et sans traitement efficace. Elle est caractérisée par un début sous pleural et la présence de myofibroblastes responsables de la synthèse excessive de la matrice extracellulaire. La voie de signalisation du Transforming Growth Factor (TGF)-β1, facteur clé de la genèse de la fibrose et sa progression, passe par les Smads, notamment Smad4. Le TGF-β1 induit la différenciation des fibroblastes pulmonaires et des cellules épithéliales et mésothéliales en myofibroblastes. AB-crystallin est une protéine de choc thermique surexprimée dans la fibrose du foie, du rein et la fibrose vasculaire. Elle peut être induite par le TGF-β1. Dans ce travail, nous avons étudié le rôle d’αB-crystallin dans la fibrose pleurale et pulmonaire. Nous montrons qu’αB-crystallin est surexprimée dans les poumons et la plèvre de patients atteints de FPI. In vivo, dans trois modèles de fibrose pulmonaire (bléomycine, surexpression de TGF-β1 ou d’IL-1β) les souris KO pour αB-crystallin sont protégées de la fibrose avec une inhibition de la voie du TGF-β. In vitro, dans les cellules épithéliales, mésothéliales ou les fibroblastes, αB-crystallin augmente la localisation nucléaire de Smad4. En interagissant avec TIF1γ, responsable de l’export nucléaire de Smad4, elle favorise la séquestration nucléaire de Smad4 et son activité pro-fibrosante. Au contraire, son inhibition permet la formation du complexe Smad4/TIF1γ et l’export nucléaire de Smad4 inhibant son activité. Ce travail montre l’importance d’αB-crystallin dans la fibrose pleuro-pulmonaire et son rôle sur la voie du TGF-. AB-crystallin pourrait être une cible thérapeutique de la FPI. / Idiopathic pulmonary fibrosis (IPF) has no effective current treatment. It is characterized by a sub-pleural onset and the presence of myofibroblasts, responsible for the excessive extracellular matrix synthesis. Transforming Growth Factor (TGF)-β1 is considered as the major profibrotic cytokine. Its signaling pathway occurs through the Smads proteins, including Smad4. TGF-β1 allows the differentiation of lung fibroblasts and epithelial and mesothelial cells into myofibroblasts. AB-crystallin is a small heat shock protein overexpressed in liver, renal and vascular fibrosis and can be induced by TGF-β1. In this study, we assessed the role of αB-crystallin in pleural and pulmonary fibrosis. We show that αB-crystallin is overexpressed in the lung and the pleura of IPF patients. In vivo, in three pulmonary fibrosis models (bleomycin, TGF-β1 or IL-1β overexpression) αB-crystallin KO mice are protected from fibrosis with an inhibition of the TGF-β pathway. In vitro, in epithelial and mesothelial cells or fibroblasts, αB-crystallin increases Smad4 nuclear localization. Interacting with TIF1γ, responsible for the nuclear export of Smad4, it promotes the nuclear sequestration of Smad4 and thus its profibrotic activity. Instead, αB-crystallin inhibition allows the formation of the Smad4/TIF1γ complex and promotes Smad4 nuclear export an profibrotic activity. This work shows the importance of αB-crystallin in pleuro-pulmonary fibrosis and its role on the TGF-β1 pathway. AB-crystallin appears as a putative therapeutic target for IPF.