α-Tocopherol Transfer Protein Is Important for the Normal Development of Placental Labyrinthine Trophoblasts in Mice

Abstract

␣-Tocopherol transfer protein (␣-TTP), a cytosolic protein that specifically binds ␣-tocopherol, is known as a product of the causative gene in patients with ataxia that is associated with vitamin E deficiency. Targeted disruption of the ␣-TTP gene revealed that ␣-tocopherol concentration in the circulation was regulated by ␣-TTP expression levels. Male ␣-TTP ؊/؊ mice were fertile; however, placentas of pregnant ␣-TTP ؊/؊ females were severely impaired with marked reduction of labyrinthine trophoblasts, and the embryos died at mid-gestation even when fertilized eggs of ␣-TTP ؉/؉ mice were transferred into ␣-TTP ؊/؊ recipients. The use of excess ␣-tocopherol or a synthetic antioxidant (BO-653) dietary supplement by ␣-TTP ؊/؊ females prevented placental failure and allowed full-term pregnancies. In ␣-TTP ؉/؉ animals, ␣-TTP gene expression was observed in the uterus, and its level transiently increased after implantation (4.5 days postcoitum). Our results suggest that oxidative stress in the labyrinth region of the placenta is protected by vitamin E during development and that in addition to the hepatic ␣-TTP, which governs plasma ␣-tocopherol level, the uterine ␣-TTP may also play an important role in supplying this vitamin.Vitamin E (␣-tocopherol) is the most potent lipid-soluble antioxidant in biological membranes, where it contributes to membrane stability. Patients with ataxia and isolated vitamin E deficiency (AVED) 1 have low or undetectable serum vitamin E concentrations and exhibit neurological dysfunction and muscular weakness. It is now established that ␣-tocopherol transfer protein (␣-TTP), a cytosolic liver protein known to specifically bind to ␣-tocopherol (1), is defective in AVED patients (2), indicating that ␣-TTP is a major determinant of plasma ␣-tocopherol level. Although ␣-tocopherol was initially identified as an anti-sterility factor to prevent abortion (3), the mechanism of action and the molecules responsible for its antisterility effect remain unknown. One of the reasons for this is that vitamin E is difficult to deplete from tissues and requires elaborate manipulations to cause deficiency symptoms to occur in experimental animals. In this study, we established a mouse model lacking ␣-TTP by targeted mutagenesis. This animal model for human AVED patients is suitable for examination of the complex pathophysiology of diseases associated with vitamin E deficiency and/or caused by oxidative stress. Here we examined the role of ␣-TTP in pregnancy and embryogenesis using our new animal model. MATERIALS AND METHODSGeneration of ␣-TTP Knockout Mice-An ␣-TTP targeting vector was constructed from an 8.8-kb ␣-TTP genome fragment encompassing exon 1. We inserted a fragment of PGK-neo cassette into the SmaI-SmaI site positioned 5Ј and 3Ј to exon 1 and flanked a 1.8-kb fragment of HSV-tk gene downstream of exon 2. AB2.2-Prime ES cells (Lexicon Genetics) or A3-1 ES (4) cells were transfected by electroporation with a linearized targeting vector. G418/gancyclovir-resistant clones were screened by PCR, and...

Prolonged α-Tocopherol Deficiency Decreases Oxidative Stress and Unmasks α-Tocopherol-dependent Regulation of Mitochondrial Function in the Brain

“…*, p Ͻ 0.01. c, levels in Ttp ϩ/ϩ and Ttp Ϫ/Ϫ mice, also maintained on standard chow, were compared. By 10 weeks of age, less than 5% of ␣-tocopherol remained in Ttp Ϫ/Ϫ brain, as previously reported (21,31,32). In Vivo Superoxide Production Is Lower in VED Mice-Our observation that neuroprostane levels are lower with vitamin E deficiency could reflect either a compensatory enhancement of antioxidant defenses or decreased levels of cellular ROS production.…”

“…Both groups reported that liver ␣-tocopherol levels in Ttp Ϫ/Ϫ mice were 30% of Ttp ϩ/ϩ controls but that Ttp Ϫ/Ϫ mice never accumulated ␣-tocopherol in brain, with levels Ͻ5% of controls (21,31,32). This suggests that tocopherol transfer protein may be critical for brain uptake of ␣-tocopherol, an observation consistent with data from humans with the AVED syndrome, who also show greater depletion of ␣-tocopherol in the brain compared with other tissues.…”

Reduced tumorigenesis in p53 knockout mice exposed in utero to low‐dose vitamin E

“…In contrast, in wild-type fetuses, low-dose VE consistently failed to increase a-tocopherol levels in any tissue, which accounts for the absence of any reduction in oxidative DNA damage in þ/þ p53 fetuses. The mechanisms underlying this differential VE disposition in wild-type fetuses are not clear; but, as for the tissue-selective differences, these may include variations in membrane transporters 37,38 and, at least in the liver, metabolism of a-tocopherol by the cytochromes P450 CYP3A4 and CYP4F2, 39,40 which may be expressed the fetus towards the end of gestation. 41,42 The tissue-and p53 genotype-dependent nature of the antioxidative efficacy of low-dose VE may explain, in part, the conflicting published reports of antitumor efficacy of VE for different cancers.…”

The Effects of Mutations in Helices 4 and 6 of ApoA-I on Scavenger Receptor Class B Type I (SR-BI)-mediated Cholesterol Efflux Suggest That Formation of a Productive Complex between Reconstituted High Density Lipoprotein and SR-BI Is Required for Efficient Lipid Transport

“…On binding lipoproteins, SR-BI mediates both selective cholesteryl ester uptake from the lipoprotein to the cells (19,(23)(24)(25) and bi-directional unesterified cholesterol movement (23,26,27). In addition to cholesteryl esters (19), SR-BI can mediate cellular uptake from HDL of free cholesterol (27,28), triglycerides (28,29), phospholipids (30), and vitamin E (31)(32)(33)(34)(35). SR-BI-mediated cholesterol, cholesteryl ester, and triglyceride movement between lipoproteins and cells and the affinity of ligand binding to SR-BI can be influenced by variations in the size and apolipoprotein and lipid compositions of the HDL particles (14, 15, 29, 30, 36 -40).…”