Cardiac fibrosis plays an important role in cardiac remodeling after myocardial infarction (MI). The molecular mechanisms that promote cardiac fibrosis after MI are well studied; however, the mechanisms by which the progression of cardiac fibrosis becomes attenuated after MI remain poorly understood. Recent reports show the role of cellular senescence in limiting tissue fibrosis. In the present study, we tested whether cellular senescence of cardiac fibroblasts (CFs) plays a role in attenuating the progression of cardiac fibrosis after MI. We found that the number of γH2AX-positive CFs increased up to day 7, whereas the number of proliferating CFs peaked at day 4 after MI. Senescent CFs were also observed at day 7, suggesting that attenuation of CF proliferation occurred simultaneously with the activation of the DNA damage response (DDR) system and the appearance of senescent CFs. We next cultured senescent CFs with non-senescent CFs and showed that senescent CFs suppressed proliferation of the surrounding non-senescent CFs in a juxtacrine manner. We also found that the blockade of DDR by Atm gene deletion sustained the proliferation of CFs and exacerbated the cardiac fibrosis at the early stage after MI. Our results indicate the role of DDR activation and cellular senescence in limiting cardiac fibrosis after MI. Regulation of cellular senescence in CFs may become one of the therapeutic strategies for preventing cardiac remodeling after MI.
Keywords: Atm; Cardiac remodeling; Fibroblast senescence; Juxtacrine.