Fetal alcohol exposure alters proopiomelanocortin gene expression and hypothalamic-pituitary-adrenal axis function via increasing MeCP2 expression in the hypothalamus.

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

Primer sequences.

<p>Forward primer (FP), Reverse primer (RP), Methyl forward primer (MFP), Methyl reverse primer (MRP), Un methyl forward primer (UFP), Un methyl reverse primer (URP), Promoter forward primer (PFP), Promoter reverse primer (PRP).</p><p>Primer sequences.</p

Changes in MeCP2 gene and protein levels in MBH of fetal alcohol exposed rat offspring.

<p><b>A</b>. MeCP2 mRNA levels in MBH of AD, PF and AF rat offspring. MeCP2 mRNA levels were measured by quantitative RT-PCR and the amounts were normalized with GAPDH values and expressed as relative mRNA levels. Data are mean ± SEM (n = 6) and were analyzed using one-way ANOVA with Newman-Keuls post-hoc test; *, <i>P</i><0.05, AF vs. AD or PF. <b>B</b>. A representative western blot gel demonstrating changes in MeCP2 protein levels (top) and actin levels (loading control, bottom) in MBH of AD, PF and AF rat offspring along with quantification measurements were represented as relative protein level (MeCP2/actin). Data are mean ± SEM (n = 6) and were analyzed using one-way ANOVA with Newman-Keuls post-hoc test; **, <i>P</i><0.01, AF vs. AD or PF. <b>C</b>. MeCP2 protein levels in β-endorphin neurons in the ARC of AD, PF and AF rat offspring were measured by double immunofluorescence methods (MeCP2 proteins are shown in green and β-endorphin shown in red). Representative photographs show double-labeled cells in each group. Histograms show the mean ± SEM (n = 6) values of percent β-EP cells expressing MeCP2 and were analyzed using one-way ANOVA with Newman-Keuls post-hoc test; ***, <i>P</i><0.001, AF vs. AD or PF.</p

Changes in MeCP2 binding onto POMC promoter in ARC and PVN of fetal alcohol exposed rat offspring.

<p><b>A</b>. Schematic representation of POMC promoter with CpG sites and primers flanking MeCP2 binding site. <b>B</b>. The levels of MeCP2 binding on POMC promoter in ARC and PVN of AD, PF and AF rat offspring were measured by ChIP assay. MeCP2 bound DNA pulled by its specific antibody was amplified by real time PCR using primers specific for the POMC promoter. MeCP2 enriched DNA was normalized with GAPDH and expressed as fold enrichment (MeCP2/GAPDH). AD and AF are ARC samples of <i>ad libitum</i>-fed and alcohol-fed rats. ADP and AFP are PVN samples of <i>ad libitum</i>-fed and alcohol-fed rats. Data are mean ± SEM (n = 6) and were analyzed using one-way ANOVA with Newman-Keuls post-hoc test; *, <i>P</i><0.05, AF vs. AD; ^a, P<0.001, ADP and AFP versus AD or AF.</p

Effects of lentiviral knockdown of MeCP2 on POMC gene expression levels in fetal alcohol exposed rat offspring.

<p><b>A</b>. A representative western blot gel showing MeCP2 protein levels (top) and actin levels (bottom) in MBH of scr sh (scr) or MeCP2 sh (MeCP) RNA-treated AD, PF and AF rat offspring. Histograms showing MeCP2 and actin ratio values in MBH of AD, PF and AF rats.treated with scr sh or MeCP2 sh RNA. Data are mean ± SEM (n = 6) and were analyzed using one-way ANOVA with Newman-Keuls post-hoc test; *, P<0.05, MeCP2 sh vs. scr-sh; ^a, P<0.05, AF vs. AD or PF. <b>B</b>. POMC mRNA levels in MBH of scr-sh and MeCP2 sh RNA of AD, PF and AF rat offspring. POMC mRNA amounts were normalized with GAPDH and expressed as relative mRNA level. Data are mean ± SEM (n = 6) and were analyzed using one-way ANOVA with Newman-Keuls post-hoc test; *, P<0.05, AF- vs. AD- or PF-scr-sh-treated groups; ^a, P<0.05, MeCP2 sh vs. scr-sh (AF group).</p