ROS attenuates TET2-dependent ZO-1 epigenetic expression in cerebral vascular endothelial cells

Aims: To investigate whether DNA active demethylase TET regulates the expression of tight junction proteins in endothelial cells of the blood-brain barrier (BBB).

Methods: Correlations between TET2 activity (indicated by its catalytic product 5hmC) and the expression of BBB tight junction proteins were examined in Tet2 knockout mice and post-mortem human brain tissues. In cultured endothelial cells, the impact of changes of TET activity on the expression of tight junction protein, ZO-1, was studied. BBB permeability assays were performed in Tet2 knockout mice.

Results: It was found that the level of 5hmC decreased in brain microvascular endothelial cells of aging mice. In Tet2 knockout mice, the level of 5hmC in endothelial cells was weaker and significantly correlated with the reduced expression of tight junction protein ZO-1. In cultured endothelial cells, H₂O₂ significantly decreased the expression of 5hmC and ZO-1. Tet2 knock-down using siRNA significantly downregulated the expression of ZO-1 in endothelial cells. hMeChip-PCR showed that H₂O₂ decreased the level of 5hmC in the ZO-1 promoter region, which was rescued by N-acetyl cysteine (NAC). Consistently, Tet2 knock-down using siRNA significantly downregulated the level of 5hmC in the ZO-1 promoter region. It was also found that the level of 5hmC decreased in endothelial cells of aging human brains compared with that of adult brains, and the level of ZO-1 was positively correlated with that of 5hmC in microvascular endothelial cells.

Conclusions: These findings suggest that TET activity is essential in regulating ZO-1 expression of BBB. It might be a potential target for neuroprotection during aging and in diverse neurological conditions.