[Show abstract][Hide abstract] ABSTRACT: Nutritional conditions during fetal life influence the risk of the development of metabolic syndrome and cardiovascular diseases in adult life (metabolic programming). Impaired glucose tolerance and dysregulated fatty acid metabolism are hallmarks of metabolic syndrome.
We aimed to establish a mouse model of metabolic programming focusing on the sex-specific effects of a maternal low-protein diet during gestation on glucose and lipid metabolism in the adult offspring.
Pregnant C57BL/6 mice received a control or a low-protein diet (18% vs 9% casein) throughout gestation. Male and female offspring received a low-fat or a high-fat diet from 6 to 22 weeks of age.
Maternal low-protein diet during gestation led to deteriorated insulin sensitivity on high-fat feeding in female offspring, as determined by biochemical and microarray analyses. Female offspring of control diet-fed dams were relatively resistant to high-fat diet-induced metabolic dysregulation. In contrast, maternal low-protein diet did not specifically affect the metabolic parameters addressed in male offspring. In males, the high-fat diet led to insulin insensitivity regardless of the diet of the dam.
Our findings show that fetal malnutrition has a limited impact on male mouse offspring, yet it does influence the metabolic response to a high-fat diet in females. These findings may have implications for future early diagnostics in metabolic syndrome and for the development of sex-specific treatment regimens.
[Show abstract][Hide abstract] ABSTRACT: The Liver X receptors (LXR) alpha and beta and their target genes such as the ATP-binding cassette (ABC) transporters have been shown to be crucially involved in the regulation of cellular cholesterol homeostasis. The aim of this study was to characterize the role of LXR alpha/beta in the human placenta under normal physiological circumstances and in preeclampsia.
We investigated the expression pattern of the LXRs and their target genes in the human placenta during normal pregnancy and in preeclampsia. Placental explants and cell lines were studied under different oxygen levels and pharmacological LXR agonists.
Gene expressions (Taqman PCR) and protein levels (Western Blot) were combined with immunohistochemistry to analyze the expression of LXR and its target genes.
In the human placenta, LXRA and LXRB expression increased during normal pregnancy. This was paralleled by the expression of their prototypical target genes, e.g., the cholesterol transporter ABCA1. Interestingly, early-onset preeclamptic placentae revealed a significant upregulation of ABCA1. Culture of JAr trophoblast cells and human first trimester placental explants under low oxygen lead to increased expression of LXRA and ABCA1 which was further enhanced by the LXR agonist T0901317.
LXRA together with ABCA1 are specifically expressed in the human placenta and can be regulated by hypoxia. Deregulation of this system in early preeclampsia might be the result of placental hypoxia and hence might have consequences for maternal-fetal cholesterol transport.
[Show abstract][Hide abstract] ABSTRACT: Prenatal nutrition as influenced by the nutritional status of the mother has been identified as a determinant of adult disease. Feeding low-protein diets during pregnancy in rodents is a well-established model to induce programming events in offspring. We hypothesized that protein restriction would influence fetal lipid metabolism by inducing epigenetic adaptations. Pregnant C57BL/6J mice were exposed to a protein-restriction protocol (9% vs. 18% casein). Shortly before birth, dams and fetuses were killed. To identify putative epigenetic changes, CG-dinucleotide-rich region in the promoter of a gene (CpG island) methylation microarrays were performed on DNA isolated from fetal livers. Two hundred four gene promoter regions were differentially methylated upon protein restriction. The liver X-receptor (Lxr) alpha promoter was hypermethylated in protein-restricted pups. Lxr alpha is a nuclear receptor critically involved in control of cholesterol and fatty acid metabolism. The mRNA level of Lxra was reduced by 32% in fetal liver upon maternal protein restriction, whereas expression of the Lxr target genes Abcg5/Abcg8 was reduced by 56% and 51%, respectively, measured by real-time quantitative PCR. The same effect, although less pronounced, was observed in the fetal intestine. In vitro methylation of a mouse Lxra-promoter/luciferase expression cassette resulted in a 24-fold transcriptional repression. Our study demonstrates that, in mice, protein restriction during pregnancy interferes with DNA methylation in fetal liver. Lxra is a target of differential methylation, and Lxra transcription is dependent on DNA methylation. It is tempting to speculate that perinatal nutrition may influence adult lipid metabolism by DNA methylation, which may contribute to the epidemiological relation between perinatal/neonatal nutrition and adult disease.
Full-text · Article · Nov 2009 · AJP Regulatory Integrative and Comparative Physiology
[Show abstract][Hide abstract] ABSTRACT: There is increasing evidence that the metabolic state of the mother during pregnancy affects long-term glucose and lipid metabolism of the offspring. The liver X receptors (LXR)α and -β are key regulators of cholesterol, fatty acid, and glucose metabolism. LXRs are activated by oxysterols and expressed in fetal mouse liver from day 10 of gestation onward. In the present study, we aimed to elucidate whether in utero pharmacological activation of LXR would influence fetal fatty acid and glucose metabolism and whether this would affect lipid homeostasis at adult age. Exposure of pregnant mice to the synthetic LXR agonist T0901317 increased hepatic mRNA expression levels of Lxr target genes and hepatic and plasma triglyceride levels in fetuses and dams. T0901317 treatment increased absolute de novo synthesis and chain elongation of hepatic oleic acid in dams and fetuses. T0901317 exposure in utero influenced lipid metabolism in adulthood in a sex-specific manner; hepatic triglyceride content was increased (+45%) in male offspring and decreased in female offspring (-42%) when they were fed a regular chow diet compared with untreated sex controls. Plasma and hepatic lipid contents and hepatic gene expression patterns in adult male or female mice fed a high-fat diet were not affected by T0901317 pretreatment. We conclude that LXR treatment of pregnant mice induces immediate effects on lipid metabolism in dams and fetuses. Despite the profound changes during fetal life, long-term effects appeared to be rather mild and sex selective without modulating the lipid response to a high-fat diet.
Preview · Article · Oct 2009 · AJP Endocrinology and Metabolism
[Show abstract][Hide abstract] ABSTRACT: Cholesterol is critical for several cellular functions and essential for normal fetal development. Therefore, its metabolism is tightly controlled during all life stages. The liver X receptors-alpha (LXRalpha; NR1H3) and -beta (LXRbeta; NR1H2) are nuclear receptors that are of key relevance in coordinating cholesterol and fatty acid metabolism. The aim of this study was to elucidate whether fetal cholesterol metabolism can be influenced in utero via pharmacological activation of LXR and whether this would have long-term effects on cholesterol homeostasis. Administration of the LXR agonist T0901317 to pregnant mice via their diet (0.015% wt/wt) led to induced fetal hepatic expression levels of the cholesterol transporter genes Abcg5/g8 and Abca1, higher plasma cholesterol levels, and lower hepatic cholesterol levels compared with controls. These profound changes during fetal development did not affect cholesterol metabolism in adulthood nor did they influence coping with a high-fat/high-cholesterol diet. This study shows that the LXR system is functional in fetal mice and susceptible to pharmacological activation. Despite massive changes in fetal cholesterol metabolism, regulatory mechanisms involved in cholesterol metabolism return to a "normal" state in offspring and allow coping with a high-fat/high-cholesterol diet.
Preview · Article · Nov 2008 · AJP Endocrinology and Metabolism
[Show abstract][Hide abstract] ABSTRACT: The ATP-binding cassette (ABC) half-transporters ABCG5 and ABCG8 heterodimerize into a functional complex that mediates the secretion of plant sterols and cholesterol by hepatocytes into bile and their apical efflux from enterocytes. We addressed the putative rate-controlling role of Abcg5/Abcg8 in hepatobiliary cholesterol excretion in mice during (maximal) stimulation of this process. Despite similar bile salt (BS) excretion rates, basal total sterol and phospholipid (PL) output rates were reduced by 82% and 35%, respectively, in chow-fed Abcg5(-/-) mice compared with wild-type mice. When mice were infused with the hydrophilic BS tauroursodeoxycholate, similar relative increases in bile flow, BS output, PL output, and total sterol output were observed in wild-type, Abcg5(+/-), and Abcg5(-/-) mice. Maximal cholesterol and PL output rates in Abcg5(-/-) mice were only 15% and 69%, respectively, of wild-type values. An infusion of increasing amounts of the hydrophobic BS taurodeoxycholate increased cholesterol excretion by 3.0- and 2.4-fold in wild-type and Abcg5(-/-) mice but rapidly induced cholestasis in Abcg5(-/-) mice. Treatment with the liver X receptor (LXR) agonist T0901317 increased the maximal sterol excretion capacity in wild-type mice (fourfold), concomitant with the induction of Abcg5/Abcg8 expression, but not in Abcg5(-/-) mice. In a separate study, mice were fed chow containing 1% (wt/wt) cholesterol. As expected, hepatic expression of Abcg5 and Abcg8 was strongly induced (fivefold and fourfold) in wild-type but not LXR-alpha-deficient (Lxra(-/-)) mice. Surprisingly, hepatobiliary cholesterol excretion was increased to the same extent, i.e., 2.2-fold in wild-type mice and 2.0-fold in Lxra(-/-) mice, upon cholesterol feeding. Our data confirm that Abcg5, as part of the Abcg5/Abcg8 heterodimer, strongly controls hepatobiliary cholesterol secretion in mice. However, our data demonstrate that Abcg5/Abcg8 heterodimer-independent, inducible routes exist that can significantly contribute to total hepatobiliary cholesterol output.
Full-text · Article · Oct 2006 · AJP Gastrointestinal and Liver Physiology
[Show abstract][Hide abstract] ABSTRACT: Dietary supplementation with plant sterols, stanols, and their esters reduces intestinal cholesterol absorption, thus lowering plasma LDL cholesterol concentration in humans. It was suggested that these beneficial effects are attributable in part to induction of genes involved in intestinal cholesterol transport, e.g., Abcg5 and Abcg8, via the liver X receptor (LXR), but direct proof is lacking. Male C57BL/6J mice were fed a purified diet (control), diets containing cholesterol (0.12 g/100 g) only, or in combination with either plant sterols or stanols (0.5 g/100 g) for 4 wk. Plant sterols and stanols dramatically increased neutral fecal sterol excretion (2.2 and 1.4-fold, respectively, compared with cholesterol-fed mice; P < 0.05). Cholesterol and cholesterol ester concentrations were higher in livers of mice fed cholesterol compared with controls (+135% and +925%; P < 0.05). Plant sterols and stanols completely prevented cholesterol accumulation as well as induction of LXR target genes in liver. Feeding plant sterols and stanols did not alter intestinal expression of Abcg5, Abcg8, or other LXR target genes nor of Npc1l1. Fractional cholesterol absorption in Abcg5-/- mice was reduced to the same extent by dietary plant sterols (49%) as in wild-type littermates (44%). Plant sterol and stanol-induced reduction of cholesterol absorption in mice is not associated with upregulation of intestinal LXR target genes nor is it influenced by Abcg5-deficiency. Our data indicate that dietary plant sterols and stanols inhibit cholesterol absorption within the intestinal lumen independently of LXR.
Full-text · Article · Aug 2006 · Journal of Nutrition