The influence of different types of hypobaric hypoxia on histone H3 methylation in rat neocortical and hippocampal neurons

Using the quantitative immunohistochemical method, we analyzed changes in the number of cells that were immunopositive for methylated forms of histone H3 at lysine 4 (H3K4me2,3) and lysine 9 (H3K9me2) in the parietal neocortex and hippocampus (the СА1 and СА3 areas) in rats under the conditions of damaging severe hypobaric hypoxia (SH) and mild adaptogenic hypobaric hypoxia (MH). We found that 3 or 24 hours after SH exposure the quantity of H3K9me2-positive cells (IPC) strongly increased, causing heterochromatin formation and global repression of gene transcription. After three (but not single) MH sessions, as well as after the following SH, the quantity of H3K9me2-positive cells decreased and H3K4me2,3- positive cells increased, causing the formation of euchromatin and an increase in the expression of genes–targets of transcriptional factors and other proadaptive proteins, thus increasing the neuroplasticity and neuroprotection of brain neurons after damage. Thus, we showed that different types of hypobaric hypoxia induce ambiguous changes in immunostaining of various forms of H3 histone methylation in mammalian forebrain structures when applying severe damaging and adaptogenic neuroprotective hypobaric hypoxia.