Endothelial GTPCH (GTP Cyclohydrolase 1) and Tetrahydrobiopterin Regulate Gestational Blood Pressure, Uteroplacental Remodeling, and Fetal Growth

Abstract

Abnormal uteroplacental remodeling leads to placental hypoperfusion, causing fetal growth restriction and pregnancy-related hypertension, which are associated with endothelial dysfunction and markers of reduced vascular NO bioavailability and oxidative stress. Tetrahydrobiopterin (BH4) is a redox cofactor for eNOS (endothelial NO synthase) with a required role in NO generation. Using mice models and human samples, we investigated the physiological requirement for endothelial cell BH4 in uteroplacental vascular adaptation and blood pressure regulation to pregnancy. In pregnant mice, selective maternal endothelial BH4 deficiency resulting from targeted deletion of Gch1 caused progressive hypertension during pregnancy and fetal growth restriction. Maternal endothelial cell Gch1 deletion caused defective functional and structural remodeling in uterine arteries and in spiral arteries, leading to placental insufficiency. Using primary endothelial cells isolated from either normal or hypertensive pregnancies, we found that hypertensive pregnancies are associated with reduced endothelial cell BH4 levels, impaired eNOS activity, and reduced endothelial cell proliferation, mediated by reduced GTPCH (GTP cyclohydrolase 1) protein. In rescue experiments, high blood pressure and fetal growth restriction in pregnant endothelial cell Gch1 deficient mice was not rescued by oral BH4 supplementation, due to systemic oxidation of BH4 to dihydrobiopterin. However, the fully reduced folate, 5-methyltetrahydrofolate prevented BH4 oxidation, reduced blood pressure to normal levels, and normalized fetal growth. We identify a critical requirement for maternal endothelial cell BH4 biosynthesis in uteroplacental vascular remodeling in pregnancy. Restoration of endothelial cell BH4 with reduced folates identifies a novel therapeutic target for the prevention and treatment of pregnancy-related hypertension such as preeclampsia.

Endothelial Cell Vasodilator Dysfunction Mediates Progressive Pregnancy-induced Hypertension in Endothelial Cell Tetrahydrobiopterin Deficient Mice

“…Consistent with our previous reports (Chuaiphichai et al, 2021), we observed a small but significant increase in basal systolic blood pressure (˜5-7 mmHg) in Gch1 fl/fl Tie2cre mice compared with wild-type littermates (WT: 103 +-2 mmHg, vsGch1 fl/fl Tie2cre mice: 110 +-1 mmHg,P <0.05, n=6; Figure 1A). In wild type mice, systolic blood pressure was unchanged during pregnancy (baseline WT: 103 +-2 mmHg, vs pregnant WT: 103 +-3 mmHg, n=6; Figure 1A).…”

“…The enzyme dihydrofolate reductase (DHFR) reduces dihydrofolate to the fully reduced folate, tetrahydrofolate, and can also reduce oxidized BH2 to regenerate BH4. We have previously demonstrated that supplementation of BH4 with 5-MTHF, restored BH4 levels in pregnancy (Chuaiphichai et al, 2021). In this study we show for the first time that that the combination of BH4 + 5-MTHF is sufficient to restore vascular function in Gch1 fl/fl Tie2cre mice.…”

“…Oxidative stress causes oxidation of BH4 to BH2 and B, which are incapable of acting as a cofactor for NOS leading to uncoupled NOS. Markers of oxidative stress are present in the placenta and maternal circulation of patients with pre-eclampsia (Raijmakers, Dechend & Poston, 2004) and we have previously shown reduced BH4 in placental extravascular vesicles from women with hypertensive pregnancies (Chuaiphichai et al, 2021). Yet in a landmark clinical trial the antioxidant vitamins C and E failed to prevent the development of pre-eclampsia in high risk pregnancies (Poston, Briley, Seed, Kelly & Shennan, 2006), and simple strategies attempting to restore or augment NO with NO donors in pre-eclampsia have been disappointing (Meher & Duley, 2007).…”

“…In our previous study, we showed that treatment of pregnantGch1 fl/fl Tie2cre mice with BH4 and 5-MTHF was sufficient to restoration BH4 levels and prevented fetal growth restriction and increased blood pressure in late pregnancy (Chuaiphichai et al, 2021;Landmesser et al, 2003;Williams, Vallance, Neild, Spencer & Imms, 1997). Given the results of our current study we hypothesized that BH4 and 5-MTHF supplementa-tion is acting to restored blood pressure and fetal growth via normalization of pregnancy induced vascular remodelling in Gch1 fl/fl Tie2cre mice.…”

“…However, in this study we found that oral BH4 supplementation alone was not sufficient to restore vascular function in uterine arteries and thus prevent progressive hypertension inGch1 fl/fl Tie2cre mice. We have previously shown that oral supplementation of BH4 is not a consistent approach to increase vascular BH4 levels, either in mice or in patients (Chuaiphichai et al, 2021;Cunnington et al, 2012a;Cunnington et al, 2012b), due to oxidation of BH4 to BH2 and B. Interestingly, vascular supplementation of BH4 can be achieved by combining the BH4 with the 5-methyltetrahydrofoalte. The enzyme dihydrofolate reductase (DHFR) reduces dihydrofolate to the fully reduced folate, tetrahydrofolate, and can also reduce oxidized BH2 to regenerate BH4.…”