Protective Effects of Neutrophil Gelatinase-Associated Lipocalin on Hypoxia/Reoxygenation Injury of HK-2 Cells

Background. Neutrophil-gelatinase associated lipocalin (NAGL) was first extracted from neutrophil granules. Our previous study showed that the expression of NGAL mRNA and protein can be induced by hypoxia/reoxygenation. This study was designed to investigate the relationship between NGAL and hypoxia/reoxygenation injury pathologies in HK-2 cells. Methods. The effect of NGAL on the proliferation of HK-2 cell lines was analyzed with a MTT colorimetric assay. Cell-cycle distribution and measurement of the percentage of apoptotic cells were performed by flow cytometry after stained with propidium iodide and annexin V-fluorescein isothiocyanate. The expression of genes for apoptotic proteins Bc1-2, Box, and caspase-3 was analyzed with real-time reverse-transcription polymerase chain reaction (RT-PCR). The expression of NGAL mRNA and protein was analyzed with real-time RT-PCR or Western blot, respectively. Results. HK-2 cells were treated with hypoxia/reoxygenation. HK-2 cells exhibited an increase in the number of cells in the G0/G1 phase and a decrease in the number of cells in the S and G2/M phases. The proliferation index is decreased. When HK-2 cells were treated with 200 ng/mL recombinant NGAL and hypoxia/reoxygenation, there were no effects on cell-cycle distribution. The ratio of early apoptotic cells in the control and hypoxia/reoxygenation groups were 1.1% and 26.5%, respectively. After the addition of 200 ng/mL recombinant NGAL, the ratio of early apoptotic cells in the hypoxia/reoxygenation group dropped to 19.6%. The expression of Bax/Bc1-2 ratio and caspase-3 were significantly higher in the hypoxia/reoxygenation compared with the control group. After the addition of 200 ng/mL recombinant NGAL, the levels of Bax/Bc1-2 ratio and caspase-3 decreased significantly compared with the control group. Conclusions. The action of NGAL against hypoxia/reoxygenation injury was due to inhibiting the apoptosis via inhibition of the expression of the genes of proapoptotic proteins Box, Bc1-2, and caspase-3.