McKnight Robert A, Yost Christian C, Yu Xing, Wiedmeier Julia E, Callaway Christopher W, Brown Ashley S, Lane Robert H, Fung Camille M
Division of Neonatology, Department of Pediatrics, University of Utah School of Medicine, Salt Lake City, Utah; and
Division of Neonatology, Department of Pediatrics, University of Utah School of Medicine, Salt Lake City, Utah; and.
Physiol Genomics. 2015 Dec;47(12):634-43. doi: 10.1152/physiolgenomics.00082.2015. Epub 2015 Oct 20.
Intrauterine growth restriction (IUGR) is a common human pregnancy complication. IUGR offspring carry significant postnatal risk for early-onset metabolic syndrome, which is associated with persistent reduction in IGF-1 protein expression. We have previously shown that preadolescent IUGR male mice have decreased hepatic IGF-1 mRNA and circulating IGF-1 protein at postnatal day 21, the age when growth hormone (GH) normally upregulates hepatic IGF-1 expression. Here we studied nucleosome occupancy and CpG methylation at a putative growth hormone-responsive element in intron 2 (in2GHRE) of the hepatic IGF-1 gene in normal, sham-operated, and IUGR mice. Nucleosome occupancy and CpG methylation were determined in embryonic stem cells (ESCs) and in liver at postnatal days 14, 21, and 42. For CpG methylation, additional time points out to 2 yr were analyzed. We confirmed the putative mouse in2GHRE was GH-responsive, and in normal mice, a single nucleosome was displaced from the hepatic in2GHRE by postnatal day 21, which exposed two STAT5b DNA binding sites. Nucleosome displacement correlated with developmentally programmed CpG demethylation. Finally, IUGR significantly altered the nucleosome-depleted region (NDR) at the in2GHRE of IGF-1 on postnatal day 21, with either complete absence of the NDR or with a shifted NDR exposing only one of two STAT5b DNA binding sites. An NDR shift was also seen in offspring of sham-operated mothers. We conclude that prenatal insult such as IUGR or anesthesia/surgery could perturb the proper formation of a well-positioned NDR at the mouse hepatic IGF-1 in2GHRE necessary for transitioning to an open chromatin state.
宫内生长受限（IUGR）是一种常见的人类妊娠并发症。IUGR后代出生后发生早发性代谢综合征的风险显著增加，这与胰岛素样生长因子-1（IGF-1）蛋白表达持续降低有关。我们之前已经表明，青春期前的IUGR雄性小鼠在出生后第21天肝脏IGF-1 mRNA和循环IGF-1蛋白减少，而在这个年龄生长激素（GH）通常会上调肝脏IGF-1的表达。在这里，我们研究了正常、假手术和IUGR小鼠肝脏IGF-1基因第2内含子（in2GHRE）中一个假定的生长激素反应元件处的核小体占据情况和CpG甲基化。在胚胎干细胞（ESC）以及出生后第14天、21天和42天的肝脏中测定了核小体占据情况和CpG甲基化。对于CpG甲基化，还分析了直至2岁的其他时间点。我们证实假定的小鼠in2GHRE对GH有反应，在正常小鼠中，到出生后第21天，一个单核小体从肝脏in2GHRE上移位，暴露出两个信号转导和转录激活因子5b（STAT5b）DNA结合位点。核小体移位与发育程序化的CpG去甲基化相关。最后，IUGR在出生后第21天显著改变了IGF-1的in2GHRE处的核小体缺失区域（NDR），要么完全没有NDR，要么NDR移位，只暴露出两个STAT5b DNA结合位点中的一个。在假手术母亲的后代中也观察到了NDR移位。我们得出结论，诸如IUGR或麻醉/手术等产前损伤可能会扰乱小鼠肝脏IGF-1的in2GHRE处正常定位的NDR的正确形成，而这对于转变为开放染色质状态是必需的。
