Background/Aims: Gut microbiota has been reported to correlate with a higher mortality and worse prognosis of cardiovascular diseases. Trimethylamine N-oxide (TMAO) is a gut microbiota-dependent metabolite of specific dietary nutrients, which is linked to cardiac fibrosis. Recent reports have suggested that the activation of Nucleotide-binding oligomerization domain (NOD)-like receptor protein 3 (NLRP3) inflammasome contributed to cardiac fibrosis. However, whether TMAO mediates cardiac fibrosis via activating NLRP3 inflammasome remains unclear. Methods and Results: To determine the role of TMAO–mediated cardiac fibrosis, we established mouse models of doxorubicin (DOX)-induced cardiac fibrosis with or without TMAO in drinking water. TMAO exacerbated DOX-induced cardiac dysfunction, heart weight and cardiac fibrosis manifested by enhanced collagen accumulation, higher profibrotic levels and elevated inflammatory factors as well as NLRP3 inflammasome activation. Using primary cultured mouse cardiac fibroblast, our results indicated that TMAO promoted proliferation, migration and collagen secretion in a dose-dependent manner by TGF-β/Smad3 signaling. Furthermore, TMAO treatment induced NLRP3 inflammasome activation including oxidative stress in cultured cardiac fibroblast. Importantly, the silencing of NLRP3 presented a protection effect against cardiac fibrosis including cellular proliferation, migration and collagen deposition in vitro. Conclusion: Our data suggested that TMAO aggravated DOX-induced mouse cardiac fibrosis, at least in part, through activation of the NLRP3 inflammasome, providing a new potential target for preventing the progression of cardiac fibrosis.

Premature senescence is associated with atrial fibrosis and has an antifibrotic effect in mice. However, the role of senescence in atrial fibrillation (AF) remains unclear. Here, we investigated the association of premature senescence with fibrosis and also determined the role of senescence in the recurrence of AF after surgery ablation. Western blot, Sirius red staining, SA-β-gal staining and immunohistochemistry were performed to detect the degree of atrial fibrosis ,the expression of TGF-β and collagens, and also the senescence markers in 72 tissue specimens of left atrial appendage in this study. Then the patients undergoing successful surgical ablation were followed up for 12 months. The expression of collagens and TGF-β was paralleled by a high level of atrial fibrosis and were increased in AF group, especially in the persistent AF group. Western blotting of P16 and SA-β-gal staining showed an increased premature senescence in the sinus rhythm, paroxysmal AF and persistent AF groups. In addition, positive area of senescence markers, SA-β-gal and P16, was correlated positively with fibrotic lesions. We also found a lower ratio of P16/TGF-β in patients with recurrence of AF than in patients without recurrent AF. In conclusion, premature senescence is associated with atrial fibrosis in AF, and may have an antifibrotic role in AF.