title: Lipopolysaccharide induces lung fibroblast proliferation through Toll-like receptor 4 signaling and the phosphoinositide3-kinase-Akt pathway.
abstract: Pulmonary fibrosis is characterized by lung fibroblast proliferation and collagen secretion. In lipopolysaccharide (LPS)-induced acute lung injury (ALI), aberrant proliferation of lung fibroblasts is initiated in early disease stages, but the underlying mechanism remains unknown. In this study, we knocked down Toll-like receptor 4 (TLR4) expression in cultured mouse lung fibroblasts using TLR4-siRNA-lentivirus in order to investigate the effects of LPS challenge on lung fibroblast proliferation, phosphoinositide3-kinase (PI3K)-Akt pathway activation, and phosphatase and tensin homolog (PTEN) expression. Lung fibroblast proliferation, detected by BrdU assay, was unaffected by 1 mug/mL LPS challenge up to 24 hours, but at 72 hours, cell proliferation increased significantly. This proliferation was inhibited by siRNA-mediated TLR4 knockdown or treatment with the PI3K inhibitor, Ly294002. In addition, siRNA-mediated knockdown of TLR4 inhibited the LPS-induced up-regulation of TLR4, down-regulation of PTEN, and activation of the PI3K-Akt pathway (overexpression of phospho-Akt) at 72 hours, as detected by real-time PCR and Western blot analysis. Treatment with the PTEN inhibitor, bpV(phen), led to activation of the PI3K-Akt pathway. Neither the baseline expression nor LPS-induced down-regulation of PTEN in lung fibroblasts was influenced by PI3K activation state. PTEN inhibition was sufficient to exert the LPS effect on lung fibroblast proliferation, and PI3K-Akt pathway inhibition could reverse this process. Collectively, these results indicate that LPS can promote lung fibroblast proliferation via a TLR4 signaling mechanism that involves PTEN expression down-regulation and PI3K-Akt pathway activation. Moreover, PI3K-Akt pathway activation is a downstream effect of PTEN inhibition and plays a critical role in lung fibroblast proliferation. This mechanism could contribute to, and possibly accelerate, pulmonary fibrosis in the early stages of ALI/ARDS.
authors.affiliation: Department of Anesthesiology, Renji Hospital, Shanghai Jiaotong University School of Medicine, Shanghai, China.
authors.forename: Zhengyu
authors.initials: Z
authors.lastname: He
authors.forename: Yuan
authors.initials: Y
authors.lastname: Gao
authors.forename: Yuxiao
authors.initials: Y
authors.lastname: Deng
authors.forename: Wen
authors.initials: W
authors.lastname: Li
authors.forename: Yongming
authors.initials: Y
authors.lastname: Chen
authors.forename: Shunpeng
authors.initials: S
authors.lastname: Xing
authors.forename: Xianyuan
authors.initials: X
authors.lastname: Zhao
authors.forename: Jia
authors.initials: J
authors.lastname: Ding
authors.forename: Xiangrui
authors.initials: X
authors.lastname: Wang
mesh_terms: D000818:Animals; D049109:Cell Proliferation / Q000187:drug effects; D002478:Cells, Cultured; D002867:Chromones / Q000494:pharmacology; D015536:Down-Regulation / Q000187:drug effects; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism; D008070:Lipopolysaccharides / Q000633:toxicity*; D008168:Lung / Q000166:cytology* / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D009025:Morpholines / Q000494:pharmacology; D009942:Organometallic Compounds / Q000494:pharmacology; D051059:PTEN Phosphohydrolase / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D010618:Phenanthrolines / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D051197:Toll-Like Receptor 4 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D015854:Up-Regulation / Q000187:drug effects
chemical_list: D002867:Chromones; D008070:Lipopolysaccharides; D009025:Morpholines; D009942:Organometallic Compounds; D051059:PTEN Phosphohydrolase; D010618:Phenanthrolines; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D051057:Proto-Oncogene Proteins c-akt; D034741:RNA, Small Interfering; D051197:Toll-Like Receptor 4; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C102120:bisperoxo(1,10-phenanthroline)oxovanadate(1-); C487757:Pten protein, mouse