Response gene to complement 32 deficiency causes impaired placental angiogenesis in mice

The objectives of this study are to determine the role of response gene to complement 32 (RGC-32) in the placental angiogenesis during pregnancy and explore the underlying mechanisms. RGC-32-deficient (RGC32(/)) mice were generated from C57BL/6 embryonic stem cells with deletion of exon 2 and 3 of the RGC-32 gene. Most of the RGC32(/) mice can survive. However, their body sizes were much smaller compared with their wild-type littermates when they were born. By examining the embryo development and placentas at 16.5 days post-coitum, we found that RGC32(/) embryos and foetal placentas were significantly smaller than the wild-type. Further analysis showed that the labyrinth zone of RGC32(/) placenta was smaller with defective angiogenesis. Mechanistically, vascular endothelial growth factor (VEGF) receptor 2 (VEGFR2) and placental growth factor (PlGF) were significantly down-regulated in RGC32(/) placentas, suggesting that VEGFR2 and PlGF may mediate RGC-32 function in placental angiogenesis. Indeed, knockdown of RGC-32 by shRNA inhibited VEGF-induced endothelial cell proliferation, migration, and tube formation while blocking VEGFR2 expression. RGC-32 appeared to regulate VEGFR2 expression via activation of NF-kB. Moreover, RGC-32 regulated trophoblasts proliferation via control of PlGF expression. Absence of RGC-32 caused foetal growth restriction through interrupting the placental angiogenesis, which was due to the decrease in VEGFR2 expression through the NF-kB-dependent pathway in endothelial cells and PlGF expression in trophoblasts.