Myocardial fibrosis can lead to ischemic damage of the myocardium, which can be life-threatening in severe cases. Cardiac fibroblast (CF) transdifferentiation is an important process in myocardial fibrosis. Fucoxanthin (FX) plays a key role in ameliorating myocardial fibrosis; however, its mechanism of action is not fully understood. This study investigated the role of FX in the angiotensin II (Ang II)-induced transdifferentiation of CFs and its potential mechanisms of action. We found that FX inhibited Ang II-induced transdifferentiation of CFs. Simultaneously, FX downregulated bromodomain-containing protein 4 (BRD4) expression in CFs and increased nuclear expression of nuclear factorerythroid 2-related factor 2 (Nrf2). FX reverses AngII-induced inhibition of the Keap1/Nrf2/HO-1 pathway and elevates the level of reactive oxygen species (ROS). FX failed to reverse Ang II-induced changes in fibrosis-associated proteins and ROS levels after Nrf2 silencing. BRD4 silencing reversed the inhibitory effect of Ang II on the Keap1/Nrf2/HO-1 antioxidant signalling pathway. In conclusion, we demonstrated that FX inhibited Ang II-induced transdifferentiation of CFs and that this effect may be related to the activation of the Keap1/Nrf2/HO-1 pathway by reducing BRD4 expression and, ultimately, oxidative stress.
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