Bmal1, a clock gene, is associated with depression, hypertrophy, metabolic syndrome and diabetes. Smad3, which is involved in the TGF-β signaling pathway, plays an important role in the regulation of tumor progression, fibrosis, obesity and diabetes. Our previous report showed that Smad3 has circadian expression in mouse livers. In the current study, we focused on the heart, especially on the myocardial stromal fibroblasts because the roles of Bmal1 and Smad3 in this tissue are poorly understood. Bmal1 and Smad3 have circadian expression in mouse hearts, and their circadian expression patterns were similar. Bmal1 expression decreased in the hearts of whole-body Smad3 knockout mice, whereas Smad3 expression had little effect on heart-specific Bmal1 knockout mice. Both Smad3 knockout and heart-specific Bmal1 knockout mice showed increases in p21, S100A4, CD206 and TNF-α expression in the myocardial stromal fibroblasts and macrophage compared to control mice. We also examined Smad3, Bmal1 and Dec1 expression in human tissue from old myocardial infarctions. Expression of Smad3, Bmal1 and Dec1 decreased in the stromal fibroblasts of tissue from old myocardial infarctions compared to control cases. On the other hand, p21, S100A4 and TNF-α increased in the stromal fibroblasts of tissue from old myocardial infarctions. Furthermore, expression of Smad3, Bmal1 and Dec1 decreased in TNF-α treated-NIH3T3 cells but expression of p21 and S100A4 increased. This new evidence suggests that Smad3 and Bmal1 regulate p21 and S100A4 expression in myocardial stromal fibroblasts through TNF-α.
Keywords: Bmal1; Clock gene; Old myocardial infarction; Smad3; Stromal fibroblasts.