Imprinted genes control fetal and placental growth in mice and in rare human syndromes, but the role of these genes in sporadic intrauterine growth restriction (IUGR) is less well-studied. We measured the ratio of mRNA from a maternally expressed imprinted gene, PHLDA2, to that from a paternally expressed imprinted gene, MEST, by Northern blotting in 38 IUGR-associated placentae and 75 non-IUGR placentae and found an increase in the PHLDA2/MEST mRNA ratio in IUGR (p=0.0001). Altered expression of PHLDA2 and MEST was not accompanied by changes in DNA methylation within their imprinting centers, and immunohistochemistry showed PHLDA2 protein appropriately restricted to villous and intermediate cytotrophoblast in the IUGR placentae. We next did a genome-wide survey of mRNA expression in 14 IUGR placentae with maternal vascular under-perfusion compared to 15 non-IUGR placentae using Affymetrix U133A microarrays. In this series six imprinted genes were differentially expressed by ANOVA with a Benjamini-Hochberg false discovery rate of 0.05, with increased expression of PHLDA2 and decreased expression of MEST, MEG3, GATM, GNAS and PLAGL1 in IUGR placentae. At lower significance, we found IGF2 mRNA decreased and CDKN1C mRNA increased in the IUGR cases. We confirmed the significant reduction in MEG3 non-translated RNA in IUGR placentae by Northern blotting. In addition to imprinted genes, the microarray data highlighted non-imprinted genes acting in endocrine signaling (LEP, CRH, HPGD, INHBA), tissue growth (IGF1), immune modulation (INDO, PSG-family genes), oxidative metabolism (GLRX), vascular function (AGTR1, DSCR1) and metabolite transport (SLC-family solute carriers) as differentially expressed in IUGR vs. non-IUGR placentae.
"In mice, hypermethylation in as few as one paternally expressed imprinted gene is sufficient to induce FGR (Murphy et al. 2001, McMinn et al. 2006, Dilworth et al. 2010). Additionally, global methylation changes and altered gene expression in non-imprinted genes have also been identified in FGR placentas (McCarthy et al. 2007, Einstein et al. 2010, Struwe et al. 2010). "
[Show abstract][Hide abstract] ABSTRACT: Fetal growth restriction (FGR) is a major obstetric complication stemming from poor placental development. Previously, we have shown that paternal obesity in mice is associated with impaired embryo development and significantly reduced fetal and placental weights. We hypothesised that the FGR observed in our rodent model of paternal diet-induced obesity is associated with alterations in metabolic, cell signalling and stress pathways. Male C57Bl/6 mice were fed either a normal or high fat diet for 10 weeks prior to sperm collection for IVF and subsequent embryo transfer. On embryonic day 14, placentas were collected and RNA extracted from both male and female placentas to assess mRNA expression of 24 target genes using custom RT-qPCR arrays. Peroxisome proliferator activated receptor alpha (Ppara) and caspase-12 (Casp12) expression were significantly altered in male placentas from obese fathers compared to normal (p<0.05), but not female placentas. PPARA and CASP12 protein was localised within the placenta to trophoblast giant cells by immunohistochemistry, and relative protein abundance was determined by Western Blot analysis. DNA was also extracted from the same placentas to determine methylation status. Global DNA methylation was significantly increased in female placentas from obese fathers compared to normal (p<0.05), but not male placentas. Here we demonstrate for the first time that paternal obesity is associated with changes in gene expression and methylation status of extraembryonic tissue in a sex-specific manner. These findings reinforce the negative consequences of paternal obesity prior to conception, and emphasise the need for more lifestyle advice for prospective fathers.
"However, numerous imprinted genes play a key role in regulating fetal growth and placental development in a dosage-sensitive manner, with paternal silencing primarily of growth-restricting genes and maternal silencing of growthpromoting genes (Tunster et al., 2013), which suggests that aberrant imprinting might underlie more common human growth disorders. Pleckstrin homology-like domain family A member 2 (PHLDA2) was first highlighted as a potential fetal growth restriction gene in a 2006 study that reported elevated expression in the placenta of 9 out of the 38 fetal growth restriction (FGR) placentae (McMinn et al., 2006). Subsequently, several studies have examined PHLDA2 in relation to fetal growth and birth weight (Jensen et al., 2014). "
[Show abstract][Hide abstract] ABSTRACT: PLECKSTRIN HOMOLOGY-LIKE DOMAIN, FAMILY A, MEMBER 2 (PHLDA2) is a maternally expressed imprinted gene whose elevated expression has been linked to fetal growth restriction in a number of human studies. In mice, Phlda2 negatively regulates placental growth and limits the accumulation of placental glycogen. We previously reported that a three-copy transgene spanning the Phlda2 locus drove a fetal growth restriction phenotype late in gestation suggesting a causative role for Phlda2 in human growth restriction. However, in this model Phlda2 was overexpressed by 4-fold alongside over expression of a second imprinted gene, Slc22a18. Here we genetically isolate the role of Phlda2 in driving late fetal growth restriction. We furthermore show that this Phlda2-driven growth restriction is asymmetrical with a relative sparing of the brain followed by rapid catch-up growth after birth, classic features of placental insufficiency. Strikingly, fetal growth restriction showed strain-specific differences being apparent on the 129 genetic background and absent on the BL6 background. A key difference between these two strains is the placenta. Specifically, BL6 placenta possess a more extensive endocrine compartment and substantially greater stores of placental glycogen. Taken together, these data support a direct role for elevated Phlda2 in limiting fetal growth but also suggest that growth restriction may only manifest when there is limited placental reserve. These findings should be taken into account in interpreting the results from human studies.
"It is expressed in islets, and loss of p57KIP2 expression is associated with increased beta cell proliferation in focal congenital hyperinsulinism (Kassem et al., 2001; Henquin et al., 2011). PHLDA2 also exerts a negative effect on cell proliferation, with increased expression in the placenta being associated with intrauterine growth retardation though uteroplacental insufficiency (McMinn et al., 2006). In contrast, decreased expression of PHLDA2 was detected in neuroendocrine tumors relative to normal islet controls, as a downstream effect of losing the tumor suppressor gene MEN1 resulting in Multiple Endocrine Neoplasia type 1 (Dilley et al., 2005). "
[Show abstract][Hide abstract] ABSTRACT: Type 2 diabetes usually ensues from the inability of pancreatic beta cells to compensate for incipient insulin resistance. The loss of beta cell mass, function, and potentially beta cell identity contribute to this dysfunction to extents which are debated. In recent years, long non-coding RNAs (lncRNAs) have emerged as potentially providing a novel level of gene regulation implicating critical cellular processes such as pluripotency and differentiation. With over 1000 lncRNAs now identified in beta cells, there is growing evidence for their involvement in the above processes in these cells. While functional evidence on individual islet lncRNAs is still scarce, we discuss how lncRNAs could contribute to type 2 diabetes susceptibility, particularly at loci identified through genome-wide association studies as affecting disease risk.
Frontiers in Genetics 07/2014; 5:193. DOI:10.3389/fgene.2014.00193
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