[No authors listed]
Calorie restriction (CR) has been shown to increase longevity and mitigate ageâassociated diseases in various organisms. Numerous studies have identified that sirtuin 1 (SIRT1) is upregulated by CR. However, the expression of SIRT isoforms 2â7 in response to CR in cardiomyocytes has yet to be elucidated. Therefore, the present study aimed to investigate the cellular localization and expression of SIRT1â7 in cardiomyocytes. Twenty SD rats were fed either ad libitum (AL) or a CR diet (60% of AL) for three weeks. In addition, H9c2 cells were cultured in Dulbecco's modified Eagle medium (DMEM) supplemented with either normalâ (4.5 g/l) or lowâ (1 g/l) glucose concentrations for 24 h, representing control or CR cells, respectively. CR rats were observed to have significantly lower heart and body weights (BWs) than control rats. Moreover, immunohistochemical analyzes revealed that SIRT1, 3â5 and 7 demonstrated similar localization patterns in H9c2 cells and rat cardiac tissues, with SIRT1 and 7 predominantly located in the nucleus and SIRT3â5 in the cytoplasm. This was in contrast with SIRT2, which was detected exclusively in the cytoplasm in rat cardiac tissues, but was found predominantly in the nucleus in H9c2 cells. The converse was observed for SIRT6. Quantitative polymerase chain reaction revealed that the mRNA expression of SIRT1â4 and â7 was increased in the CR group. Western blot analysis further revealed that the protein expression of SIRT1â4 and â7 was significantly increased in the cardiac tissues of rats in the CR group. These results suggest that CR may attenuate ageâassociated changes through reducing BW. Moreover, shortâterm CR may activate SIRT1 as well as SIRT2â4 and â7 expression in cardiomyocytes in vivo and in vitro.
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