Short-term calorie restriction activates SIRT1–4 and -7 in cardiomyocytes in vivo and in vitro

Calorie restriction (CR) has been shown to increase longevity and mitigate age‑associated diseases in various organisms. Numerous studies have identified that sirtuin 1 (SIRT1) is upregulated by CR. However, the expression of SIRT isoforms 2‑7 in response to CR in cardiomyocytes has yet to be elucidated. Therefore, the present study aimed to investigate the cellular localization and expression of SIRT1‑7 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 normal‑ (4.5 g/l) or low‑ (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, 3‑5 and 7 demonstrated similar localization patterns in H9c2 cells and rat cardiac tissues, with SIRT1 and 7 predominantly located in the nucleus and SIRT3‑5 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 SIRT1‑4 and ‑7 was increased in the CR group. Western blot analysis further revealed that the protein expression of SIRT1‑4 and ‑7 was significantly increased in the cardiac tissues of rats in the CR group. These results suggest that CR may attenuate age‑associated changes through reducing BW. Moreover, short‑term CR may activate SIRT1 as well as SIRT2‑4 and ‑7 expression in cardiomyocytes in vivo and in vitro.