Regulation of SIRT1 on KLF4 and subsequent Claudin 5 expression. (A) Representative western blot images as well as (B) intensity quantification showing reduced binding of SIRT1 to KLF4 in ABCD1 or HSD17B4 silenced HBMECs. (C) Representative western blot images as well as (D) intensity quantification showing increased KLF4 acetylation in ABCD1 or HSD17B4 silenced HBMECs. (E) Representative western blot images as well as (F) intensity quantification showing KLF4 silencing reduced Claudin 5 expression at both mRNA and protein level. *P<0.05 and **P<0.01 vs. NT control group. NT, non-targeting; ABCD, ATP binding cassette subfamily D member 1; HBMECs, human brain microvascular endothelial cells; TNF, tumor necrosis factor; NF, nuclear factor; KLF4, Krüppel-like factor 4; IgG, immunoglobulin G.