Vascular Endothelial Growth Factor and Erythropoietin Show Different Expression Patterns in the Early and Late Hypoxia Preconditioning Phases and May Correlate with DNA Methylation Status in the Mouse Hippocampus

The decrease of GluN2B and its phosphorylation at Tyr-1336 in extrasynaptic subunits is associated with neuroprotection induced by hypoxia preconditioning

Prior research has firmly established that the N-methyl-d-aspartate (NMDA) receptor subunit 2 B (GluN2B) and its phosphorylation contribute to ischemic/hypoxic brain injury. Hypoxic preconditioning (HPC) is an endogenous mechanism that protects the brain from both ischaemic and hypoxic damage. In this study, we explored the effects of HPC on GluN2B and its phosphorylation at two sites (tyrosine residues 1252 and 1336), catalysed by Fyn, in the hippocampus both in vivo and in vitro. Animal and cellular models of HPC were developed by subjecting mice and the mouse hippocampal neuronal cell line HT22 to repeated hypoxia. Levels of GluN2B and its phosphorylation at the tyrosine residues 1336 (pY1336 GluN2B) and 1252 (pY1252 GluN2B) were detected in HPC-treated hippocampi and HT22 cells using western blotting and immunofluorescence. The distributions of GluN2B, pY1336 GluN2B, and pY1252 GluN2B in the synaptic (TxP) and extrasynaptic components (TxS) were analysed by western blotting. Caspase-3 and spectrin, both markers of cellular injury, were further measured using western blotting. HPC downregulated GluN2B and pY1336 GluN2B levels in the hippocampus and HT22 cells. The changes in GluN2B and pY1336 GluN2B levels in the extrasynaptic components were similar to those in the hippocampus and HT22 cells, while the changes in the synaptic components showed the opposite trend which increased after HPC. The downregulation of GluN2B and pY1336 GluN2B may be associated with neuroprotection induced by HPC. Additionally, their localization at synaptic and extrasynaptic sites may play distinct roles in neuroprotection.

MALAT1 and NEAT1 are Neuroprotective During Hypoxic Preconditioning in the Mouse Hippocampus Possibly by Regulation of NR2B

Wang, Liping, Gang Fu, Ruijuan Han, Peijia Fan, Jing Yang, Kerui Gong, Zhijun Zhao, Chunyang Zhang, Kai Sun, and Guo Shao. MALAT1 and NEAT1 are neuroprotective during hypoxic preconditioning in the mouse hippocampus possibly by regulation of NR2B. High Alt Med Biol. 25:285-294, 2024. Background: The regulation of noncoding ribonucleic acid (ncRNA) has been shown to be involved in cellular and molecular responses to hypoxic preconditioning (HPC), a situation created by the induction of sublethal hypoxia in the brain. The ncRNAs metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) and nuclear paraspeckle assembly transcript 1 (NEAT1) are abundantly expressed in the brain, where they regulate the expression of various genes in nerve cells. However, the exact roles of MALAT1 and NEAT1 in HPC are not fully understood. Methods: A mouse model of acute repeated hypoxia was used as a model of HPC, and MALAT1 and NEAT1 levels in the hippocampus were measured using real-time polymerase chain reaction (PCR). The mRNA and protein levels of N-methyl-d-aspartate receptor subunit 2 B (NR2B) in the mouse hippocampus were measured using real-time PCR and western blotting, respectively. HT22 cells knocked-down for MALAT1 and NEAT1 were used for in vitro testing. Expression of NR2B, which is involved in nerve cell injury under ischemic and hypoxic conditions, was also evaluated. The levels of spectrin and cleaved caspase-3 in MALAT1 and NEAT1 knockdown HT22 cells under oxygen glucose deprivation/reperfusion (OGD/R) were determined by western blotting. Results: HPC increased the expression of MALAT1 and NEAT1 and decreased the expression of NR2B mRNA in the mouse hippocampus (p < 0.05). Knockdown of MALAT1 and NEAT1 increased both NR2B mRNA and protein levels nearly twofold and caused damage under OGD/R conditions in HT22 cells (p < 0.05). Conclusion: MALAT1 and NEAT1 exert neuroprotective effects by influencing the expression of NR2B.

Hypoxia preconditioning increases Notch1 activity by regulating DNA methylation in vitro and in vivo

BACKGROUND

Our previous research has demonstrated that hypoxic preconditioning (HPC) can improve spatial learning and memory abilities in adult mice. Adult hippocampal neurogenesis has been associated with learning and memory. The Neurogenic locus notch homolog protein (Notch) was involved in adult hippocampal neurogenesis, as well as in learning and memory. It is currently unclear whether the Notch pathway regulates hippocampal neuroregeneration by modifying the DNA methylation status of the Notch gene following HPC.

METHOD

The HPC animal model and cell model were established through repeated hypoxia exposure using mice and the mouse hippocampal neuronal cell line HT22. Step-down test was conducted on HPC mice. Real-time PCR and Western blot analysis were used to assess the mRNA and protein expression levels of Notch1 and hairy and enhancer of split1 (HES1). The presence of BrdU-positive cells and Notch1 expression in the hippocampal dental gyrus (DG) were examined with confocal microscopy. The methylation status of the Notch1 was analyzed using methylation-specific PCR (MS-PCR). HT22 cells were employed to elucidate the impact of HPC on Notch1 in vitro.

RESULTS

HPC significantly improved the step-down test performance of mice with elevated levels of mRNA and protein expression of Notch1 and HES1 (P < 0.05). The intensities of the Notch1 signal in the control group, the H group and the HPC group were 2.62 ± 0.57 × 107, 2.87 ± 0.84 × 107, and 3.32 ± 0.14 × 107, respectively, and the number of BrdU (+) cells in the hippocampal DG were 1.83 ± 0.54, 3.71 ± 0.64, and 7.29 ± 0.68 respectively. Compared with that in C and H group, the intensity of the Notch1 signal and the number of BrdU (+) cells increased significantly in HPC group (P < 0.05). The methylation levels of the Notch1 promoter 0.82 ± 0.03, 0.65 ± 0.03, and 0.60 ± 0.02 in the C, H, and HPC groups, respectively. The methylation levels of Notch1 decreased significantly (P < 0.05). The effect of HPC on HT22 cells exhibited similarities to that observed in the hippocampus.

CONCLUSION

HPC may confer neuroprotection by activating the Notch1 signaling pathway and regulating its methylation level, resulting in the regeneration of hippocampal neurons.