J774A. 1 cell apoptosis induced by Leptospira interrogans lipopolysaccharide and apoptotic regulation of associated signaling pathways

Objective To determine the effect of Leptospira interrogans lipopolysaccharide (L-LPS) inducing apoptosis of murine mononuclear-macrophage cell line( J774A. 1 ), and apoptotic regulation of Toll-like receptor(TLR) and associated intracellular signaling pathways. Methods Lipopolysaccharide (L-LPS) of L. interrogans serogroup Icterohaemorrhagiae serovar Lai strain Lai 56601 was prepared using phenol-water method. The effects of L-LPS inducing J774A. 1 cell apoptosis and the apoptosis-blocking with FasL neutralizing antibody were detected by flow cytometry. Real-time fluorescent quantitative RT-PCR (qPCR) and flow cytometry were performed to measure the changes of Fas/FasL mRNA and protein expression levels in J774A. 1 cells before and after L-LPS treatment. The regulations in L-LPS-induced cell apoptosis by TLR2 and TLR4 as well as p38MAPK, JNK, ERK pathways were determined by either TLR2 or TLR4 antibody blocking test, signaling pathway blocking test and flow cytometry. Results 56.50%, 69.28% and 24.35% of the J774A. 1 cells after treatment with 100 ng/ml L-LPS for4, 12 and 24 h were apoptotic,while the apoptosis rates were decreased to 11.21%, 21.58% and 12.70% after the cells blocked by FasL neutralizing antibody(P ＜0.05). The levels of FasL and Fas mRNAs in J774A. 1 cells treated with L-LPS for 4, 12 and 24 h were elevated with 1.34, 2.12, 2.10 times and 2.45, 3.87, 3.12 times compared to those in the L-LPS untreated cells (P ＜ 0. 05 ), respectively, while the expression rates of FasL and Fas proteins were upregulated to 18.61%, 60.13%, 42.75% and 76.34%, 85.70%, 77.92% from 4.82% and 15.32% apoptotic rates in the L-LPS untreated cells, respectively( P ＜0.05 ). The L-LPS-induced apoptosis rate( 11.54% ) of TLR2 antibody blocked J774A. 1 cells was significantly lower than that(66.56% ) of the J774A. 1 cells without TLR2 antibody blocking( P ＜0.05 ), but L-LPS-induced apoptosis rate of TLR4 antibody blocked J774A. 1 cells was as high as 55.27% ( P ＞ 0.05 ). Compared to the apoptosis rate (62.17%) in the p38MAPK and JNK pathway-free J774A. 1 cells, the L-LPS-induced apoptosis rates in p38MAPK blocked cells(20.54% ) and JNK blocked cells(47.98% ) were significantly lower( P ＜0.05 ),and the apoptosis rate in ERK blocked cells was as high as 61.72% ( P ＞ 0.05 ). Conclusion L-LPS was recognized by TLR2 and upregulates both Fas and FasL expression via p38MAPK and JNK pathways, which involving in the process of the L-LPS-induced cell apoptosis. Key words: Leptospira interrogans;  Lipopolysaccharide;  Cell apoptosis;  Fas/FasL;  Toll like receptor