Mechanical stretch and LPS affect the proliferation, extracellular matrix remodeling and viscoelasticity of lung fibroblasts

The present study aimed to investigate the effects of mechanical stretch and lipopolysaccharides (LPS) on the expression of transforming growth factor-β1 (TGF-β1) and collagen and viscoelasticity in human embryonic MRC-5 lung fibroblasts cultured in vitro and to assess the mechanisms of ARDS-associated ventilator-induced lung injury using an in vitro model. Human embryonic MRC-5 lung fibroblasts were treated with different concentrations of LPS to establish an acute respiratory distress syndrome (ARDS) cell injury model, followed by further culture under different mechanical stretch amplitudes using the Flexcell system to establish a cellular mechanical damage model. The proliferation of MRC-5 cells and the protein and gene expression levels of TGF-β1 and collagen were detected by flow cytometry, ELISA and reverse transcription-quantitative PCR, respectively. As the concentration of LPS increased, the proliferation activity of MRC-5 cells gradually decreased. Low concentrations of LPS led to upregulation of the secretion levels of TGF-β1 and collagen I and the expression of their mRNA, TGF-β1 mRNA and collagen type 1, α1. Conversely, high concentrations of LPS reduced TGF-β1 and collagen I levels and their gene expression. Mechanical stimulation with a stretch of 5% increased the cell proliferation activity; however, it had no significant effect on the expression levels of TGF-β1 and collagen. Mechanical stimulation with a stretching force of 10% inhibited the cell proliferation but increased the expression levels of TGF-β1 and collagen I. A higher mechanical stimulation (15 and 20%) had a significantly greater effect. Mechanical stretch and LPS stimulation led to changes in the structure and viscoelastic behavior of human embryonic MRC-5 lung fibroblasts. In terms of cell function, mechanical stretch may cause an increase in the expression of TGF-β1 in MRC-5 cells, in turn affecting the transcription and translation of collagen genes. This present study provides provides cell-level evidence for understand the mechanisms of action behind the ARDS ventilator-induced lung injury and lung structural remodeling.