IntroductionIdiopathic pulmonary fibrosis (IPF) is a progressive and irreversible fibrotic lung disease, resulting in respiratory insufficiency and reduced survival. Pulmonary fibrosis is a result of repeated alveolar epithelial microinjuries, followed by abnormal regeneration and repair processes in the lung. Recently, stem cells and their secretome have been investigated as a novel therapeutic approach in pulmonary fibrosis. We evaluated the potential of induced pluripotent stem cells (iPSC) conditioned media (iPSC-cm) to regenerate and repair the alveolar epithelium in vitro and improve bleomycin induced lung injury in vivo.MethodsIPSC-cm was collected from cultured iPSC derived from human foreskin fibroblasts and its biological effects on alveolar epithelial wound repair was studied in an alveolar wound healing assay in vitro. Furthermore, iPSC-cm was intratracheally instilled 7 days after bleomycin induced injury in the rat lungs and histologically and biochemically assessed 7 days after instillation.ResultsiPSC-cm increased alveolar epithelial wound repair in vitro compared with medium control. Intratracheal instillation of iPSC-cm in bleomycin-injured lungs reduced the collagen content and improved lung fibrosis in the rat lung in vivo. Profibrotic TGFbeta1 and α-smooth muscle actin (α-sma) expression were markedly reduced in the iPSC-cm treated group compared with control. Antifibrotic hepatocyte growth factor (HGF) was detected in iPSC-cm in biologically relevant levels, and specific inhibition of HGF in iPSC-cm attenuated the antifibrotic effect of iPSC-cm, indicating a central role of HGF in iPSC-cm.ConclusioniPSC-cm increased alveolar epithelial wound repair in vitro and attenuated bleomycin induced fibrosis in vivo, partially due to the presence of HGF and may represent a promising novel, cell free therapeutic option against lung injury and fibrosis.Electronic supplementary materialThe online version of this article (doi:10.1186/scrt513) contains supplementary material, which is available to authorized users.

RationaleStem cells have been identified in the human lung; however, their role in lung disease is not clear. We aimed to isolate mesenchymal stem cells (MSC) from human lung tissue and to study their in vitro properties.MethodsMSC were cultured from lung tissue obtained from patients with fibrotic lung diseases (n = 17), from emphysema (n = 12), and normal lungs (n = 3). Immunofluorescence stainings were used to characterize MSC. The effect of MSC-conditioned media (MSC-CM) on fibroblast proliferation and on lung epithelial wound repair was studied.ResultsExpression of CD44, CD90, and CD105 characterized the cells as MSC. Moreover, the cells stained positive for the pluripotency markers Oct3/4 and Nanog. Positive co-stainings of chemokine receptor type 4 (CXCR4) with CD44, CD90 or CD105 indicated the cells are of bone marrow origin. MSC-CM significantly inhibited the proliferation of lung fibroblasts by 29% (p = 0.0001). Lung epithelial repair was markedly increased in the presence of MSC-CM (+ 32%). Significantly more MSC were obtained from fibrotic lungs than from emphysema or control lungs.ConclusionsOur study demonstrates enhanced numbers of MSC in fibrotic lung tissue as compared to emphysema and normal lung. The cells inhibit the proliferation of fibroblasts and enhance epithelial repair in vitro. Further in vivo studies are needed to elucidate their potential role in the treatment of lung fibrosis.

Differentiation of primary alveolar type II epithelial cells (AEC type II) to AEC type I in culture is a major barrier in the study of the alveolar epithelium in vitro. The establishment of an AEC type II cell line derived from induced pluripotent stem cells (iPSC) represents a novel opportunity to study alveolar epithelial cell biology, for instance in the context of lung injury, fibrosis and repair. In the present study, we generated long lasting AECII from iPSC (iPSC-AEC). Long lasting iPSC-AECII (LL)-iPSC-AECII) displayed morphological characteristics of AECII including growth in a cobble stone monolayer, the presence of lamellar bodies and microvilli as shown by electron microscopy. Also, (LL)-iPSC-AECII expressed AEC type II proteins such as cytokeratin, surfactant protein C and lysotracker DND 26 (a marker for lamellar bodies). Furthermore, the (LL)-iPSC-AECII exhibited functional properties of AECII by an increase of transepithelial electrical resistance (TERR) over time, secretion of inflammatory mediators in biologically relevant quantities (interleukin-6, interleukin-8) and efficient in vitro alveolar epithelial wound repair. Consistent with the AECII phenotype, the cell line showed the ability to uptake and release surfactant protein B, to secrete phospholipids and to differentiate into AEC type I. In summary, we established a long lasting, but finite AEC type II cell line derived from iPSC as a novel cellular model to study alveolar epithelial cell biology in lung health and disease.