Abstract: BACKGROUND: The blood-brain barrier is an important structure that protects the central nervous system, and the study of the effects of high glucose on the blood-brain barrier is important for the prevention of high glucose-induced damage to the central nervous system. 
OBJECTIVE: To investigate the potential effect of high glucose on the blood-brain barrier function of hCMEC/D3 human brain microvascular endothelial cells.
METHODS: hCMEC/D3 cells were cultured in regular sugar medium (glucose concentration of 25 mmol/L) and high-sugar medium (glucose concentration of 55 mmol/L). The morphology of cells in each group was observed by light microscopy. CCK-8 assay was used to detect changes in cell viability. A monolayer blood-brain barrier model was established using hCMEC/D3 cell line with Transwell chamber device. Changes in cell transmembrane resistance were monitored daily. The permeability of cell monolayers was detected by phenol red permeability. Flow cytometry was used to detect the apoptosis rate of the cells. Western blot assay was used to detect the expression of Bcl-2, Bax, Caspase-3, ZO-1, Occludin, Claudin-1, and histone deacetylase 4. The levels of histone deacetylase in cell supernatant were detected by ELISA. The expression of histone deacetylase 4 in cells was detected by immunofluorescence. 
RESULTS AND CONCLUSION: (1) The cell viability of high sugar group was significantly lower than that of control group (P < 0.000 1). (2) The cells of the control group were in a good growth state, interwoven into a dense mesh, with interconnections between synapses. The cell growth of high glucose group was suppressed, and the connection of inter-cellular synapses was reduced. (3) Compared with the control group, the transmembrane resistance value of the high glucose group was reduced (P < 0.05); phenol-red permeability of the monolayer cell membrane was increased (P < 0.05); cell apoptosis rate was increased (P < 0.01); the expression of Bax protein was increased (P < 0.000 1); the expression of Caspase-3 protein had no significant change (P > 0.05); the expression of Bcl-2, ZO-1, Occludin, Claudin-1, and histone deacetylase 4 proteins was decreased (P < 0.01, P < 0.001, P < 0.01, P < 0.000 1, P < 0.01); the fluorescence expression of histone deacetylase 4 was decreased (P < 0.001) in the high glucose group. (4) The level of histone deacetylase 4 in the cell supernatant of the high glucose group was lower than that of the control group (P < 0.05). The results show that high glucose induces the increased apoptosis and enhances permeability of hCEMCE/D3 cells, and its mechanism may be related to the decreased expression level of histone deacetylase 4.

Key words: high glucose, blood-brain barrier, tight junction, permeability, apoptosis, histone deacetylase 4, engineered tissue construction