AIM: To investigate the effect and mechanism of Caspase-1 on microglia in oxygen-induced retinal neovascularization in mice.

METHODS: Twelve 7-day-old(P7)C57BL/6J mice were randomly divided into normal group, OIR group and OIR+VX-765 group. OIR models were established in OIR group and OIR+VX-765 group. Caspase-1 inhibitor VX-765(4mg/kg, dissolved in 0.4% polyethylene glycol)or 0.4% polyethylene glycol, were intraperitoneally injected from P12 to P16 into the mice of OIR+VX-765 and OIR groups, respectively. Whole retinal flatmounts of P17 mice were prepared, and Lectin staining was performed to calculate the ratio of avascular and neovascular area to retina area. The frozen sections of the posterior ocular segment were prepared, and the distribution of Caspase-1 and activated microglial cells were detected by immunofluorescence technique. Cultured BV-2 cells were divided into control group, hypoxia group and inhibitor group. The cells of inhibitor and hypoxia groups were pre-treated with VX-765 or 0.4% polyethylene glycol for 3h, and then hypoxic incubated for 24h. The expression levels of Caspase-1, p20(active form of Caspase-1), IL-1β and VEGF were detected by Western blotting. The angiogenesis and migration capacity of cultured RF/6A cells were assessed by endothelial cell tube formation assay and migration assay, after they were incubated with supernatant of those different BV-2 groups.

RESULTS:The distribution and morphology of retinal blood vessels were normal in P17 mice of the normal group, and avascular and new blood vessel cluster were found in the mice of OIR group and OIR+VX-765 group. The ratio of avascular area was 12.23%±1.02% and that of the new blood vessel area was 2.16%±0.52% in the OIR+VX-765 group, which decreased in comparison with 16.58%±1.14% and 4.00%±0.41% of the OIR group(P<0.01). Caspase-1 was rarely detected by immunofluorescence staining in the normal retina of the mice, whereas it was mainly co-located with activated microglial cells in the ganglion cell layer and the inner plexiform layer in the mice of OIR group. The expression of Caspase-1, p20, IL-1β and VEGF increased in BV-2 cells of the hypoxia group, which were down-regulated by VX-765(P<0.05), except Caspase-1. The tube length was 271±12, and the number of migrated cells was 347±34 in RF/6A cells cultured with supernatant of BV-2 cells in the hypoxia group, which significantly decreased to 171±22 and 212±27 with inhibitor of Caspase-1(P<0.05).

CONCLUSION:Caspase-1 promotes retinal neovascularization in the mice with OIR, probably by activating the downstream inflammatory factor IL-1β in microglial cells and accelerating the release of VEGF.