No abstract

Background: Cerebral ischemia, a common cerebrovascular disease, is one of the great threats to human health and new targets for stroke therapy are needed. The transcriptional activity in the cell is regulated by epigenetic processes such as DNA methylation/demethylation, acetylation/deacetylation, histone methylation, etc. Changes in DNA methylation after ischemia can have both neuroprotective and neurotoxic effects depending on the degree of ischemia damage, the time elapsed after injury, and the site of methylation. Methods: In this study, we investigated the changes in the expression and intracellular localization of DNA methyltransferase DNMT1, histone methyltransferases SUV39H1, and G9a in penumbra neurons and astrocytes at 4 and 24 h after stroke in the rat cerebral cortex using photothrombotic stroke (PTS) model. Methods of immunofluorescence microscopy analysis, apoptosis analysis, and immunoblotting were used. Additionally, we have studied the effect of DNMT1 and G9a inhibitors on the volume of PTS-induced infarction and apoptosis of penumbra cells in the cortex of mice after PTS. Results: This study has shown that the level of DNMT1 increased in the nuclear and cytoplasmic fractions of the penumbra tissue at 24 h after PTS. Inhibition of DNMT1 by 5-aza-2′-deoxycytidine protected cells of PTS-induced penumbra from apoptosis. An increase in the level of SUV39H1 in the penumbra was found at 24 h after PTS and G9a was overexpressed at 4 and 24 h after PTS. G9a inhibitors A-366 and BIX01294 protected penumbra cells from apoptosis and reduced the volume of PTS-induced cerebral infarction. Conclusion: Thus, the data obtained show that DNA methyltransferase DNMT1 and histone methyltransferase G9a can be potential protein targets in ischemic penumbra cells, and their inhibitors are potential neuroprotective agents capable of protecting penumbra cells from postischemic damage to the cerebral cortex.

Our studies reveal changes in the expression of the main participants in the processing of amyloid precursor protein (APP) in neurons and astrocytes after photothrombotic stroke (PTS). Here we show the increase in the level of N- and C-terminal fragments of APP in the cytoplasm of ischemic penumbra cells at 24 h after PTS and their co-immunoprecipitation with caveolin-1. The ADAM10 α-secretase level decreased in the rat brain cortex on the first day after PTS. Levels of γ-secretase complex proteins presenilin-1 and nicastrin were increased in astrocytes, but not in neurons, in the penumbra after PTS. Inhibitory analysis showed that these changes lead to neuronal death and activation of astrocytes in the early recovery period after PTS. The caveolin-1 inhibitor daidzein shifted APP processing towards Aβ synthesis, which caused astroglial activation. γ-secretase inhibitor DAPT down-regulated glial fibrillary acidic protein (GFAP) in astrocytes, prevented mouse cerebral cortex cells from PTS-induced apoptosis, and reduced the infarction volume. Thus, new generation γ-secretase inhibitors may be considered as potential agents for the treatment of stroke.

Photothrombotic stroke (PTS) stimulates the level of N- and C-terminal fragments of Amyloid precursor protein (APP) growth in the cytoplasm of ischemic penumbra cells not earlier but at 24 hours. Here we have shown that APP fragments are visualized in thin unmyelinated fibers of neurons, in containing mitochondria large fibers and in synapses but absent in the nuclei. At 24 hours after PTS, some elements of the destroyed tissue accumulated a significant amount of APP protein. The level of ADAM10 α-secretase decreased on the first day after PTS in the rat brain cortex and ADAM-10 co-localized with the lipid raft marker caveolin-1. PTS caused no changes in the level of β-secretase BACE1 either on the first day after PTS or in the early recovery period. The expression of proteins of the γ-secretase complex: presenilin-1 and nicastrin increased in astrocytes, but not in penumbra neurons after PTS. The β-secretase inhibitor LY2886721 did not affect the infarct size of the mouse cerebral cortex and the level of apoptosis of cells in the perifocal region after PTS. Whereas the inhibitor of γ-secretase DAPT reduced the expression of glial fibrillary acidic protein (GFAP) in astrocytes, prevented the growth of apoptosis of mouse cerebral cortex cells reducing the infarct volume on the 7th and 14th days after PTS. DAPT may be considered as a drug for stroke therapy.