[Effects of neutrophils alkaline phosphatase on functions of neutrophils in vitro]

To investigate the effects of neutrophils alkaline phosphatase (NAP) on the migration, reactive oxygen species (ROS) generation and apoptosis of neutrophil-like differentiated HL-60 cells.

NAP was overexpressed in HL-60 cells via transfecting coding sequence of NAP by lentivirus. The effectivity of NAP overexpression was confirmed by reverse transcription-polymerase chain reaction (RT-PCR) and Western blotting. HL-60 cells were differentiated into neutrophil-like cells by exposure to 1.5% DMSO. The migration and ROS generation of neutrophil-like cells with NAP overexpression were detected by transwell migration test and flow cytometry, respectively. Cell apoptosis were detected by flow cytometry. The expression of apoptosis-related protein Bax, caspase-3 and caspase-9 in neutrophil-like cells were observed by Western blotting after NAP overexpression.

Over 80% HL-60 cells presented green fluorescence after GFP-NAP infection by lentivirus and screening by puromycin. In addition, the levels of both gene and protein of NAP were up-regulated in these cells. After 5-day culture with 1.5% DMSO, the bulk of induced cell was smaller and the surface appeared many bumps and irregular shape. The ratio of nuclear and cytoplasmic decreased and nucleolus disappeared. The nuclear chromatin changed from dense to loose and the nuclear morphology appeared to be rod and segmented. The percentage of CD11b(+) cell increased from 26.25% to 98.55%. The transwell migration test showed that the number of migrated cells was higher in neutrophil-like cells with NAP overexpression compared with the negative control [(15.30±3.65) ×10(3) vs (8.00±0.78) ×10(3)] (P<0.001). RESULTS of flow cytometry suggested that the mean fluorescence intensity (MFI) of intracellular ROS was significantly higher in neutrophil-like cells with NAP overexpression compared with the negative control (355.70 ± 20.10 vs 103.22 ± 4.71) (P< 0.001). In addition, Western blotting showed that the expressions of apoptosis-related protein Bax, active-caspase-3 and active-caspase-9 were all up-regulated in neutrophil-like cells with NAP overexpression compared with the negative control.

NAP could promote the migration and ROS generation of neutrophil-like cells and accelerate the cell apoptosis.