Background: Intrauterine growth restriction (IUGR) is associated with adverse metabolic outcomes during adulthood. Histone modifications and changes in DNA methylation-affected genes are important for fetal development. This study aimed to investigate the epigenetic mechanisms in IUGR.
Methods: IUGR models were established in Sprague-Dawley rats using a maternal nutritional restriction approach during pregnancy. The abundance of insulin-like growth factor 2 (IGF2), phosphoinositide 3-kinase (PI3K), AKT serine/threonine kinase 2 (AKT2), and peroxisome proliferators-activated receptor gamma coactivator 1 alpha (PGC-1α) was examined by real-time polymerase chain reaction (RT-PCR) and Western blotting analysis. Chromatin immunoprecipitation RT-PCR was employed to analyze histone modification in CCCTC-binding factor (CTCF) 1-4 binding sites of the Igf2/H19 imprinting control region (ICR). The methylation states of CTCF1-4 binding sites were studied by pyrosequencing.
Results: The IUGR models were constructed successfully. Igf2 mRNA abundance in the placenta, fetal liver, and newborn liver was decreased in the IUGR group ( P <0.01). Meanwhile, as compared with the control group, the expression levels of AKT2, PI3K, and PGC-1α were lower in newborn and 8-week-old livers in the IUGR group ( P <0.05). In addition, knocking down Igf2 reduced the protein expression levels of AKT2-phosphorylation and PGC-1α ( P <0.05). In CTCF binding sites 1-4 of the Igf2/H19 ICR, acetylated histones H3 (AcH3) enrichment was significantly lower in CTCF1-3 in newborn and 8-week-old IUGR rats. Histone H3 tri-methylated lysine 4 (H3K4me3) enrichment was significantly lower in the CTCF1-4 of newborn and 8-week-old IUGR groups ( P <0.01). H3K9me2 enrichment was significantly higher in the IUGR group ( P <0.01). The CpG dinucleotide methylation levels of CTCF1 and CTCF3, but not those of CTCF2 and CTCF4 binding sites in IUGR rat fetal, 4-week old, and 8-week-old livers decreased significantly ( P <0.05).
Conclusion: The methylation status and histone modification in the Igf2/H19 ICR are related to growth and lipid metabolism via the PGC-1α/PI3K/AKT2 pathway in IUGR rats.
Keywords: DNA methylation; Epigenesis, genetic; Fetal growth retardation; Histone code.
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