Effect of ROS/NLRP3/Caspase-1 signaling pathway on the apoptosis of retinal pigment epithelial cells induced by high glucose

Objective

To investigate the effect of the nucleotide-binding domain, leucine-rich-containing family, pyrin domain-containing 3 (NLRP3) inflammasome on the proliferation and apoptosis of human retinal pigment epithelial cell line ARPE-19 exposed to high glucose and its mechanism.

Methods

ARPE-19 cells cultured in vitro were divided into normal control group and high-glucose group, and were cultured in conventional medium and medium containing 30 mmol/L glucose for 48 hours, respectively.The content of reactive oxygen species (ROS) were detected by fluorescent probe, and the activity of superoxide dismutase (SOD) and the concentration of malondialdehyde (MDA) were tested by biochemical assay.The cells of the two groups were cultured with 0, 2, 5, 10, 15 and 20 μmol/L NLRP3 inhibitor CY-09 for 48 hours, respectively.The proliferation rate of ARPE-19 cells under various concentrations of CY-09 treatment was detected by cell counting kit-8, and the appropriate concentration of CY-09 was determined.ARPE-19 cells were divided into normal control group, normal+ CY-09 group, high-glucose group and high glucose+ CY-09 group.The culture medium in the normal+ CY-09 group and high glucose+ CY-09 group was supplemented with 15 μmol/L CY-09. Flow cytometry was used to detect the apoptosis rate of each group, and Western blot was used to detect the relative expression levels of NLRP3, apoptosis-associated point protein (ASC), Caspase-1 precursor (pro-Caspase-1) and active fragments (cleaved-Caspase-1), B lymphocytoma-2 protein (Bcl-2), Bcl-2-associated X protein (Bax), Caspase-3 precursor (pro-Caspase-3) and active fragments (cleaved-Caspase-3).

Results

The intensity of ROS fluorescence and MDA concentration were 120 020±3 245, (4.92±0.09) nmol/mg in the high-glucose group, which were both significantly higher than 35 426±811 and (1.78±0.03) nmol/mg in the normal control group, and the SOD activity was (35.65±1.22) μmol/(min·mg) in the high-glucose group, which was significantly lower than (74.96±1.41) μmol/(min·mg) in the normal control group, showing statistically significant differences between the two groups (t=35.760, 46.960, 29.830; all at P<0.05). The proliferation rate of RPE cells in high-glucose group was significantly lower than that in normal control group, and the difference was statistically significant (t=18.820, P<0.05). With the increase of CY-09 concentration, the proliferation rate of cells in the high-glucose group was gradually increased.The proliferation rates of cells treated with 10, 15 and 20 μmol/L CY-09 were all significantly higher than those treated with 0 μmol/L CY-09, showing statistically significant differences between them (all at P<0.05). The proliferation rates of cells treated with 15 μmol/L and 0 μmol/L CY-09 were not significantly different in the normal control group (P>0.05). The apoptosis rate of cells in the high-glucose group was (21.68±0.41)%, which was significantly higher than (6.67±1.05)% in the normal control group and (13.96±0.07)% in the high-glucose+ CY-09 group, and the differences were statistically significant (both at P<0.05). The relative expression levels of NLRP3, ASC, cleaved-Caspase-1, cleaved-Caspase-3 and Bax proteins were significantly higher and the relative expression levels of Bcl-2 protein was significantly lower in the high-glucose group compared with the normal control group, and the differences were statistically significant (all at P<0.05). The relative expression levels of NLRP3, ASC, the active fragment of cleaved-Caspase-1, Bax and cleaved-Caspase-3 proteins were decreased and the relative expression levels of Bcl-2 protein were increased in the normal+ CY-09 group and high glucose+ CY-09 group compared with the normal control group and high glucose group, and the differences were statistically significant (all at P<0.05).

Conclusions

NLRP3 inflammasome mediates the high glucose induced RPE cells apoptosis through ROS/NLRP3/Caspase-1 signaling pathway.

Oxidative stress; Inflammasomes; NLR family, pyrin domain-containing 3 protein; High glucose; Retinal pigment epithelium