The endogenous anti-angiogenic family of splice variants of VEGF, VEGF_xxxb, are down-regulated in pre-eclamptic placentae at term

PET (pre-eclamptic toxaemia) has recently been linked with alterations in production of a VEGFR1 [VEGF (vascular endothelial growth factor) receptor 1] splice variant that acts as a circulating inhibitor. We have recently described a family of naturally occurring splice variants of VEGF, termed VEGF_xxxb, that also appear to act as inhibitors of conventional VEGF_xxx-mediated angiogenesis. To determine whether alteration in splicing of VEGF–VEGFR family members extended beyond VEGFR1, we investigated the effect of pre-eclampsia on placental VEGF_xxxb mRNA and protein expression. VEGF_xxx and VEGF_xxxb mRNA and protein were both found in normal human term placentae. VEGF_xxx protein formed the majority of the total VEGF protein (980±195 pg/mg), whereas VEGF_xxxb (11.5 pg/mg) was found to form a small part of the total VEGF protein expression (1.5±0.24%). Evidence for VEGF₁₆₅b, VEGF₁₂₁b and VEGF₁₄₅b expression was found. In pre-eclamptic placentae, there was a significant down-regulation of VEGF_xxxb isoforms, but a small up-regulation of VEGF_xxx isoforms. In normal placenta VEGF_xxxb and VEGF_xxx concentrations were positively correlated (r=0.69, P<0.02), whereas in pre-eclamptic placentae, there was a significant negative correlation between VEGF_xxxb and VEGF_xxx protein expression (r=−0.8, P<0.02), indicating that there was a significant uncoupling of the splicing regulation of the VEGF isoforms. Combined with previous studies showing increased soluble VEGFR1 isoforms in human pre-eclampsia, these data suggest that there may be a common mechanism in pre-eclampsia that involves dysregulation of mRNA splicing of members of the VEGF–VEGFR axis.