Expression of Placental FLT1 Transcript Variants Relates to Both Gestational Hypertensive Disease and Fetal Growth

Abstract

Abstract-The recent discovery of additional alternative spliced FLT1 transcripts encoding novel soluble (s)FLT1 protein isoforms complicates both the predictive value and functional implications of sFLT1 in preeclampsia. We investigated FLT1 expression levels and splicing patterns in placentas of normotensive and preeclamptic women, and established the tissue specificity of all FLT1 transcript variants. mRNA levels of sFLT1 splice variants were determined by real-time polymerase chain reaction in 21 normal human tissues and placental biopsies from 91 normotensive and 55 preeclamptic women. Cellular localization of placental FLT1 expression was established by RNA in situ hybridization. Of all tissues investigated, placenta has by far the highest FLT1 mRNA expression level, mainly localized in the syncytiotrophoblast layer. More than 80% of placental transcripts correspond to sFLT1_v2. Compared with normotensive placenta, preeclamptic placenta has Ϸ3-fold higher expression of all FLT1 transcript variants (PϽ0.001), with a slight shift in favor of sFLT1_v1. Although to a lesser degree, transcript levels are also increased in placenta from normotensive women that deliver a small for gestational age neonate. We conclude that sFLT isoform-specific assays could potentially improve the accuracy of current sFLT1 assays for the prediction of preeclampsia. However, placental FLT1 transcript levels are increased not only in preeclampsia but also in normotensive pregnancy with a small for gestational age fetus. This may indicate a common pathway involved in the development of both conditions but complicates the use of circulating sFLT1 protein levels for the prediction or diagnosis of preeclampsia alone. (Hypertension. 2011;58:70-76.) • Online Data SupplementKey Words: endothelial growth factors Ⅲ gene expression Ⅲ human Ⅲ preeclampsia Ⅲ pregnancy H ypertension-related disorders are a major cause of pregnancy complications. Preeclampsia in particular, defined as new-onset hypertension in combination with proteinuria after 20 weeks of gestation, is a leading cause of both maternal and fetal mortality and morbidity. 1 Because preeclampsia is a complex disease involving multiple organs, it has been difficult to clearly assign molecular pathways involved in the etiology. Consequently, proper targets for the development of early biomarkers and prophylaxis are scarce.Although the exact model how preeclampsia develops is still a matter of debate, preeclampsia is thought to originate from abnormal placentation followed by a release of placenta-produced factors into the maternal circulation. These in turn provoke dysfunction of the maternal endothelium, resulting in the preeclamptic clinical symptoms. 2,3 The vascular endothelial growth factor (VEGF) ligands/receptors play an essential role in both normal and pathological functioning of the endothelium 4 and have been implicated in the development of preeclampsia. In particular, the soluble truncated version of VEGF receptor 1 (sFLT1) has been shown to be markedly elevated in preecla...

Proton Pump Inhibitors Decrease Soluble fms-Like Tyrosine Kinase-1 and Soluble Endoglin Secretion, Decrease Hypertension, and Rescue Endothelial Dysfunction

“…PPIs also decreased sFlt-1 e15a protein secretion from preeclamptic placental explants ( Figure 1C). sFlt-1 e15a (or sFlt-1 v14) is the main sFlt-1 variant in placenta 15 that has only been described recently. 15,16 Endothelium is another major tissue source of sFlt-1.…”

“…sFlt-1 e15a (or sFlt-1 v14) is the main sFlt-1 variant in placenta 15 that has only been described recently. 15,16 Endothelium is another major tissue source of sFlt-1. When administered to HUVECs, PPIs dose dependently reduced sFlt-1 secretion ( Figure 1D) but not mRNA expression ( Figure S1D and S1E) of the 2 sFlt-1 variants, sFlt-1 e15a and sFlt-1 i13.…”

Heme Oxygenase-1 Is Not Decreased in Preeclamptic Placenta and Does Not Negatively Regulate Placental Soluble fms-Like Tyrosine Kinase-1 or Soluble Endoglin Secretion

“…In both placental and endothelial cells, silencing HO-1 selectively increased sFlt-1 i13 mRNA expression (generically expressed in many tissues and the main sFlt-1 variant in endothelial cells) 28 but not sFlt-1 e15a. Thus, it is possible that HO-1 may be differentially regulating sFlt-1 i13 but not the placental sFlt-1 variant, sFlt-1 e15a.…”

“…28 The remaining sFlt-1 transcripts are sFlt-1 i13, a variant generically expressed not only in many tissues, notably endothelium, but also in brain and liver. 28 Interestingly, silencing HO-1 increased sFlt-1 i13 expression but not sFlt-1 e15a ( Figure 2E and 2F). However, this did not translate to changes in protein secretion of total sFlt-1 ( Figure 2B and 2D-note the sFlt-1 ELISA indiscriminately detects both variants).…”

“…Interestingly, when we examined mRNA expression, we found that silencing HO-1 significantly upregulated sFlt-1 i13 >2-fold (the main sFlt-1 variant in endothelial cells; Figure 4C) but had no effect on sFlt-1 e15a expression (the dominant sFlt-1 splice variant in placenta but minimally expressed in other tissues 28 ; Figure 4D). Thus, it is possible that the fact that HO-1 specifically regulates sFlt-1 i13 (generic sFlt-1 variant and main endothelial-derived sFlt-1) 28 but not placental sFlt-1 variant (sFlt-1 e15a) may explain why silencing HO-1 affects sFlt-1 protein secretion from endothelial cells but not placenta. Silencing HO-1 in HUVECs did not affect sENG secretion ( Figure 4E).…”