Background:Surfactant protein-A (SP-A) contributes to the regulation of sepsis-induced acute kidney injury.In a previous study,we demonstrated that the expression of SP-A in the human renal tubular epithelial (HK-2) cells can be stimulated by lipopolysaccharide (LPS).The present study evaluated the possible signal-transducing mechanisms ofLPS-induced SP-A biosynthesis in the HK-2 cells.Methods:Tetrazolium salt colorimetry (MTT) assay was used to detect cell viability of HK-2 cells after LPS stimulation on different time points.HK-2 cells were stimulated with 100 ng/ml of LPS for different durations to determine the effects of LPS on SP-A and toll-like receptor 4 (TLR4) messenger RNA (mRNA) expression,as well as phosphorylation of mitogen-activated/extracellular signal-regulated kinase (MEK) 1,extracellular signal-regulated kinase 1/2 (ERK1/2),p38 mitogen-activated protein kinase (p38MAPK),and nuclear factor-kappa B (NF-κB) inhibitor-alpha (IkB-α).Then,HK-2 cells were pretreated with CLI-095,a TLR4 inhibitor,to analyze mRNA and protein levels of SP-A and TLR4 and expression of NF-κB in the cytoplasm and nucleus of HK-2 before LPS exposure.Results:HK-2 cells exposed to 100 ng/ml of LPS for 1,6,and 24 h did not affect cell viability which showed no toxic effect of 100 ng/ml LPS on cells (P =0.16);however,the biosynthesis of SP-A mRNA and protein in HK-2 cells was significantly increased (P =0.02).As to the mechanism,LPS enhanced transmembrane receptor TLR4 protein expression.Sequentially,LPS time dependently augmented phosphorylation of MEK1,ERK1/2,and p38MAPK.In addition,levels of phosphorylated IκB-α and nuclear NF-κB were augmented with LPS exposure for 2 h.LPS-induced SP-A and TLR4 mRNA as well as NF-κB expression were significantly inhibited by pretreatment with CLI-095.Conclusions:The present study exhibited that LPS can increase SP-A synthesis in human renal epithelial cells through sequentially activating the TLR4-related MEK1-ERK1/2-NF-κB-dependent pathway.