Intrauterine subclinical inflammation sensitive to hypoxic-ischemia brain damage in newborn rats and the epigenetic relationship

Objective To investigate the effects of subclinical intrauterine infection, postnatal hypoxia-ischemia(HI) alone or in combination on the immature brain development, the changes and significance of histone deacetylases(HDACs) and HDAC1 mRNA after brain injury, and the protective effect of erythropoietin (EPO) on white matter injury. Methods Pregnant SD rats were randomly assigned into lipopolysaccharide(LPS) group or normal saline(NS) group, and were injected LPS(0.3 mg/kg) or the normal saline(NS) intraperitoneally at 15 days after conception, continued to raise until delivery, weighed the birth weight of the pups.The postpartum(P) day 5 rat pups were randomly divided into 4 groups: control group, LPS group, HI group and LPS + HI group; intervention groups were divided into: LPS+ HI+ NS group and LPS+ HI+ EPO group.The brain tissues were observed at the time point of 6 h, 24 h and 7 d after HI.The expressions of tumor necrosis factor-α (TNF-α) and HDACs in the brain homogenate were measured by using enzyme-linked immunosorbent assay(ELISA), the levels of myelinbasicprotein(MBP) and microtubule-associated proteins(MAP)-2 were detected by using immunohistochemistry staining, the expressions of MAP-2 mRNA and HDAC1 mRNA were detected by Real-time PCR. Results The expressions of TNF-α, HDACs and HDAC1 mRNA were highest in LPS+ HI group, but MBP was the lowest, and there were significant differences among LPS+ HI group and the other 3 groups(F=60.20, P 0.05). The expression of MBP in LPS+ HI+ EPO group [integrated optical density(IOD) value: 131.59±2.24] was higher than that in the LPS+ HI+ NS group(IOD value: 103.36±3.62), and the difference was statistically significant(t=16.24, P<0.05). There existed necrosis areas in the cortex of LPS+ HI group by MAP-2 immunohistochemistry staining, which was not found in other 3 groups.The expression of MAP-2 mRNA in LPS+ HI group decreased at 6 h after HI, and it raised gradually, and the difference was statistically significant compared with the other 3 groups(all P<0.05). Conclusions Intrauterine subclinical inflammation is sensitive to HI-Induced injury in the immature rat brain, and may lead to epigenetic changes.EPO plays a protective role to white matter after brain damage. Key words: Immature brain; Subclinical inflammation; Hypoxia-ischemia; Epigenetic; Erythropoietin