Effects of neutrophilic granule protein on the expression of lipocalin 2 in inflammatory macrophages

Abstract

To explore the effects of neutrophilic granule protein (NGP) on the expression of lipocalin 2 (LCN2) in inflammatory macrophages and its mechanism. NGP-high-expressed RAW264.7 cells (NGP/RAW cells) and negative control RAW264.7 cells (NC/RAW cells) were cultured in vitro. Primary peritoneal macrophages of NGP-high-expressed mice and wild-type C57BL/6 mice were extracted, then cultured in vitro. The cell inflammatory model was established by stimulating with 10 mg/L lipopolysaccharide (LPS, LPS group), and the phosphate buffer solution (PBS) control group was set up. Enzyme-linked immunosorbent assay (ELISA) was used to detect the level of LCN2 in different types of cells. The protein expression of phosphorylated signal transduction and activator of transcription 1 (p-STAT1) was detected with Western blotting. Other NGP/RAW cells and NC/RAW cells were treated with 10 mg/L LPS, 5 mg/L STAT1 pathway inhibitor (fludarabine)+10 mg/L LPS, respectively. The PBS control group was set up. ELISA was used to detect the level of LCN2. In different types of cells, the levels of LCN2 were increased significantly after LPS stimulation in the LPS group as compared with those in the PBS control group, and peaked at 24 hours (μmol/L: 25.61±1.02 vs. 0.46±0.02 in NC/RAW cells, 74.51±2.14 vs. 0.25±0.04 in NGP/RAW cells, 10.13±0.22 vs. 0.01±0.01 in primary macrophages of wild-type C57BL/6 mice, 28.35±0.61 vs. 0.08±0.01 in primary macrophages of NGP-high-expressed mice, all P < 0.05), indicating that the expression of LCN2 in macrophages altered during inflammation reaction. The level of LCN2 in NGP/RAW cells was found significantly increased at different time points after LPS stimulation comparing with that in NC/RAW cells (μmol/L: 8.32±0.22 vs. 3.12±0.11 at 6 hours, 23.12±0.86 vs. 8.12±0.32 at 12 hours, 74.51±2.14 vs. 25.61±1.02 at 24 hours, all P < 0.05), along with the expression of p-STAT1 was significantly up-regulated. The level of LCN2 in the primary macrophages of NGP-high-expressed mice was also significantly increased at 24 hours after LPS stimulation comparing with that in the primary macrophages of wild-type C57BL/6 mice (μmol/L: 28.35±0.61 vs. 10.13±0.22, P < 0.05). However, after pretreated with STAT1 pathway inhibitors, the production of LCN2 in NGP/RAW cells was decreased significantly comparing with that in the LPS group (μmol/L: 6.81±0.19 vs. 22.54±0.58, P < 0.05). But the inhibitors had no significant effect on LCN2 production in NC/RAW cells showing no significant difference as compared with LPS group (μmol/L: 8.04±0.20 vs. 7.86±0.15, P > 0.05), indicating that NGP could up-regulate the expression of LCN2 in macrophages stimulated by LPS by promoting STAT1 activation. NGP could positively regulate LCN2 expression in inflammatory macrophages by activating STAT1 pathway.