Hypoxia-preconditioned mesenchymal stem cells attenuate bleomycin-induced pulmonary fibrosis

Ying-Wei Lan, Kong-Bung Choo, Chuan-Mu Chen, Tsai-Hsien Hung, Young-Bin Chen, Chung-Hsing Hsieh, Han-Pin Kuo, Kowit-Yu Chong

Idiopathic pulmonary fibrosis (IPF) is a progressive diffuse parenchymal lung disorder of unknown etiology. Mesenchymal stem cell (MSC)-based therapy is a novel approach with great therapeutic potentials for the treatment of lung diseases. Despite demonstration of MSC grafting, the populations of engrafted MSCs have been shown to decrease dramatically 24 hours post-transplantation due to exposure to harsh microenvironments. Hypoxia is known to induce expression of cytoprotective genes and also secretion of anti-inflammatory, anti-apoptotic and anti-fibrotic factors. Hypoxic preconditioning is thought to enhance the therapeutic potency and duration of survival of engrafted MSCs. In this work, we aimed to prolong the duration of survival of engrafted MSCs and to enhance the effectiveness of IPF transplantation therapy by the use of hypoxia-preconditioned MSCs. Hypoxic preconditioning was achieved in MSCs under an optimal hypoxic environment. The expression level of cytoprotective factors and its biological effects on damaged alveolar epithelial cells or TGF-beta1-treated fibroblast cells was studied in co-culture experiment in vitro. Furthermore, hypoxia-preconditioned MSCs (HP-MSCs) were intratracheally instilled into bleomycin-induced pulmonary fibrosis mice at day 3, and then lung functions, cellular, molecular and pathological changes were assessed at 7 and 21 days after bleomycin administration. The expression of genes of prosurvival, anti-apoptotic, anti-oxidant and growth factors was upregulated in MSCs under hypoxic conditions. In TGF-beta1-treated MRC-5 fibroblast cells, HP-MSCs attenuated extracellular matrix production through paracrine effects. The pulmonary respiratory functions significant improved for up to 18 days of HP-MSCs treatment. Expression of inflammatory factors and fibrotic factor were all down-regulated in the lung tissues of the HP-MSCs treated mice. Histopathologic examination observed a significant amelioration of the lung fibrosis. Several LacZ-labeled MSCs were observed within the lungs in the HP-MSCs treatment groups at day 21, but no signals were detected in normoxic-MSCs group. Our data further demonstrated that upregulation of hepatocyte growth factor possibly played an important role in mediating the therapeutic effects of transplanted HP-MSCs. Transplantation of hypoxia-preconditioned MSCs exerted better therapeutic effects in bleomycin-induced pulmonary fibrotic mice and enhanced the survival rate of engrafted MSCs, partially due to the upregulation of hepatocyte growth factor.