Gangisetty Omkaram, Bekdash Rola, Maglakelidze George, Sarkar Dipak K
Endocrine Program, Department of Animal Sciences, Rutgers University, New Brunswick, New Jersey, United States of America.
PLoS One. 2014 Nov 19;9(11):e113228. doi: 10.1371/journal.pone.0113228. eCollection 2014.
Proopiomelanocortin (POMC) is a precursor gene of the neuropeptide β-endorphin in the hypothalamus and is known to regulate various physiological functions including stress response. Several recent reports showed that fetal alcohol exposure programs the hypothalamus to produce lower levels of POMC gene transcripts and to elevate the hypothalamic-pituitary-adrenal (HPA) axis response to stressful stimuli. We investigated the role of methyl CpG binding protein (MeCP2) in the effects of prenatal ethanol on POMC gene expression and hypothalamic-pituitary-adrenal (HPA) axis function. Pregnant Sprague Dawley rats were fed between GD 7 and 21 with a liquid diet containing 6.7% alcohol, pair-fed with isocaloric liquid diet, or fed ad libitum with rat chow, and their male offsprings were used at 60 days after birth in this study. Fetal alcohol exposure reduced the level of POMC mRNA, but increased the level of DNA methylation of this gene in the arcuate nucleus (ARC) of the hypothalamus where the POMC neuronal cell bodies are located. Fetal alcohol exposed rats showed a significant increase in MeCP2 protein levels in POMC cells, MeCP2 gene transcript levels as well as increased MeCP2 protein binding on the POMC promoter in the arcuate nucleus. Lentiviral delivery of MeCP2 shRNA into the third ventricle efficiently reduced MeCP2 expression and prevented the effect of prenatal ethanol on POMC gene expression in the arcuate nucleus. MeCP2-shRNA treatment also normalized the prenatal ethanol-induced increase in corticotropin releasing hormone (CRH) gene expression in the hypothalamus and elevated plasma adrenocorticotrophic hormone (ACTH) and corticosterone hormone responses to lipopolysaccharide (LPS) challenge. These results suggest that fetal alcohol programming of POMC gene may involve recruitment of MeCP2 on to the methylated promoter of the POMC gene to suppress POMC transcript levels and contribute to HPA axis dysregulation.
阿黑皮素原（POMC）是下丘脑中神经肽β-内啡肽的前体基因，已知其可调节包括应激反应在内的多种生理功能。最近的几份报告显示，胎儿酒精暴露会使下丘脑产生较低水平的POMC基因转录本，并增强下丘脑-垂体-肾上腺（HPA）轴对应激刺激的反应。我们研究了甲基CpG结合蛋白（MeCP2）在产前乙醇对POMC基因表达和下丘脑-垂体-肾上腺（HPA）轴功能影响中的作用。在本研究中，将怀孕的斯普拉格-道利大鼠在妊娠第7天至21天期间喂食含6.7%酒精的液体饲料、与等热量液体饲料配对喂食或随意喂食大鼠饲料，并在其雄性后代出生60天后使用。胎儿酒精暴露降低了POMC mRNA水平，但增加了下丘脑弓状核（ARC）中该基因的DNA甲基化水平，而POMC神经元细胞体就位于此处。胎儿酒精暴露大鼠的POMC细胞中MeCP2蛋白水平、MeCP2基因转录本水平显著增加，且弓状核中MeCP2蛋白与POMC启动子的结合也增加。将MeCP2短发夹RNA（shRNA）通过慢病毒导入第三脑室可有效降低MeCP2表达，并防止产前乙醇对弓状核中POMC基因表达的影响。MeCP2-shRNA处理还使产前乙醇诱导的下丘脑促肾上腺皮质激素释放激素（CRH）基因表达增加正常化，并提高了血浆促肾上腺皮质激素（ACTH）水平以及对脂多糖（LPS）刺激的皮质酮激素反应。这些结果表明，胎儿酒精对POMC基因的编程可能涉及MeCP2募集到POMC基因的甲基化启动子上，以抑制POMC转录水平并导致HPA轴失调。
