Trimethylamine N-oxide induced cognitive impairment through disruption of blood-brain barrier by inhibiting TGF-β...

Growing evidence suggests that trimethylamine N-oxide (TMAO) is closely associated with cognitive impairment. However, the mechanisms by which TMAO causes cognitive impairment remain unclear. TMAO has been reported to regulate blood-brain barrier (BBB) integrity and suppress the expression of tight junction proteins (TJs) in the microvasculature. This study aims to investigate whether disruption of the BBB contributes to TMAO-induced cognitive impairment and to elucidate the underlying molecular mechanisms. Mice recieved an intraperitoneal injection (1.1 mg/kg) of TMAO and underwent the Y-maze test, novel object recognition test, and passive avoidance test 72 h post-treatment. To assess BBB integrity, Evans blue staining, immunofluorescence, western blotting, and qRT-PCR analysis were carried out. Our findings indicated that TMAO treatment induced cognitive impairment and disrupted the BBB integrity in mice. In the hippocampus, TMAO reduced the expression of ZO-1, occludin, claudin1, and CD31 and caused significant ultrastructural changes in the microvasculature. To explore the underlying molecular mechanisms, human cerebral microvascular endothelial cells (hCMEC/D3) were cultured with TMAO. TMAO treatment suppressed TJs and increased monolayer permeability in hCMEC/D3 cells. Transcriptomic analysis revealed that TMAO activated multiple inflammation-related pathways while inhibiting the TGF-β pathway. Moreover, TGF-β1 intervention rescued the down-regulation of TJs and reduced permeability in TMAO-treated hCMEC/D3 cells. Our research demonstrates that TMAO-induced cognitive impairment occurs through the disruption of the BBB by inhibiting the TGF-β pathway in endothelial cells. The current investigation provides new insights into the mechanisms of TMAO neurotoxicity and suggests that increasing TGF-β1 level represents an effective strategy to counteract TMAO-induced cognitive impairment.