The uptake of trimethylamine N-oxide (TMAO) and its influence on endothelial cell identity and inflammation

Abstract Background and purpose Trimethylamine N-oxide (TMAO) is associated with a higher risk of atherosclerotic diseases. However, the underlying molecular mechanisms are not completely understood. Inflammation and following endothelial-to-mesenchymal transition (EndMT) – a process where endothelial cells (ECs) lose their function and phenotype and gain a mesenchymal character – contribute to the development of atherosclerosis. We therefore aimed to investigate the potential uptake of TMAO into ECs and its potential impact on inflammation and subsequent EndMT. Methods and results Tandem mass spectrometry revealed a time-dependent uptake of TMAO into primary human endothelial cells of 0.5 nmol/mg protein within the first 30 minutes and of 5.8 nmol/mg within 24 hours. The uptake of TMAO resulted in a significant increase of inflammation as measured by E-selectin expression (+63.8-fold). A prolonged treatment with TMAO for 3 days resulted in an increase of EndMT indicated by a significant increase of the mesenchymal marker genes Versican (+6.8-fold) and Calponin (+11.9-fold), as well as a concomitant decrease of the endothelial marker LYVE1 (−92%). For identification of a potential TMAO transporter in human endothelial cells, we screened for the expression of Solute Carrier Family member transporters in ECs. Through our research, overexpression of the carrier A5 in ECs resulted in a 36% higher intracellular TMAO concentration as early as 30 minutes. In turn, causing a knockdown of A5 prevented TMAO induced inflammation (−77.8% induction of E-Selectin) and EndMT (−98,3% induction of Versican and −461% induction of Calponin). Conclusion Using a large screening approach, we identified A5 as the first TMAO transporter described in ECs. TMAO uptake results in increased inflammation of ECs and induction of EndMT. The data identify a novel mechanism of TMAO uptake into human ECs that may help to better understand lifestyle-mediated effects on atherosclerosis. Funding Acknowledgement Type of funding sources: None.