👤 Torsten Plösch

Obesity and type 2 diabetes have a heritable component that is not attributable to genetic factors. Instead, epigenetic mechanisms may play a role. We have developed a mouse model of intrauterine growth restriction (IUGR) by in utero malnutrition. IUGR mice developed obesity and glucose intolerance with aging. Strikingly, offspring of IUGR male mice also developed glucose intolerance. Here, we show that in utero malnutrition of F1 males influenced the expression of lipogenic genes in livers of F2 mice, partly due to altered expression of Lxra. In turn, Lxra expression is attributed to altered DNA methylation of its 5' UTR region. We found the same epigenetic signature in the sperm of their progenitors, F1 males. Our data indicate that in utero malnutrition results in epigenetic modifications in germ cells (F1) that are subsequently transmitted and maintained in somatic cells of the F2, thereby influencing health and disease risk of the offspring. Show less

Secretion of cholesterol into bile is important for the elimination of cholesterol from the body. Thyroid hormone (TH) increases biliary cholesterol secretion and hepatic gene expression of adenosine triphosphate (ATP)-binding cassette, subfamily G (WHITE), member 5 (ABCG5) and ATP-binding cassette, subfamily G (WHITE), member 8 (ABCG8), two half-transporters that act as a heterodimeric complex promoting sterol secretion. In addition, nuclear liver x receptor-alpha (LXRa), also regulated by TH, induces gene expression of ABCG5/G8. We here investigated if the TH-induced stimulation of biliary cholesterol secretion is mediated by the ABCG5/G8 complex in vivo, and if so, whether LXRa is involved. Mice homozygous for disruption of Abcg5 (Abcg5(-/-) ) or Lxra (Lxra(-/-) ) and their wild-type counterparts were treated with triiodothyronine (T3) for 14 days and compared to untreated mice of corresponding genetic backgrounds. Bile was collected by gallbladder cannulation, and liver samples were analyzed for gene expression levels. Basal biliary cholesterol secretion in Abcg5(-/-) mice was 72% lower than in Abcg5(+/+) mice. T3 treatment increased cholesterol secretion 3.1-fold in Abcg5(+/+) mice, whereas this response was severely blunted in Abcg5(-/-) mice. In contrast, biliary cholesterol secretion in T3-treated Lxra(+/+) and Lxra(-/-) mice was increased 3.5- and 2.6-fold, respectively, and did not differ significantly. TH-induced secretion of cholesterol into bile is largely dependent on an intact ABCG5/G8 transporter complex, whereas LXRa is not critical for this effect. Show less

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 less

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. Show less

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. Show less

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. Show less