Background <p>Cellular senescence is an outcome of mitochondrial dysfunction occurring during myocardial ischemia/reperfusion injury (MIRI). Mitochondrial telomerase reverse transcriptase (TERT) is responsible for cardiac protection and can improve MIRI. In this study, the effects of TERT on cardiomyocyte senescence after MIRI were evaluated.</p> Methods <p>Infarct area was examined by EVANS BLUE and TTC combined staining in MIRI mice. HE staining evaluated myocardial injury. Ultrasound electrocardiogram was used to detect cardiac function in mice. mRNA expression of TERT and CK1 was assessed utilizing RT-qPCR. Protein levels of SA-β-gal, TERT, p-TERT and CK1 were measured by Western blot. Mitochondrial membrane potential was determined by JC-1. Immunofluorescence staining detected the expression and localization of p-TERT. Co-immunoprecipitation (Co-IP) determined interaction between CK1 and TERT. Changes in senescence-associated secretory phenotype (SASP) were detected by ELISA assay. Mouse primary cardiomyocytes were exposed to oxygen and glucose deprivation/reoxygenation (OGD/R) condition. Cell viability was assessed by CCK-8.</p> Results <p>In MIRI mice, cardiomyocytes showed increased levels of mitochondrial dysfunction and cellular senescence. After MIRI, mitochondrial aggregation of p-TERT diminished in cardiomyocytes, whereas nuclear aggregation increased. TERT depletion exacerbated myocardial damage in MIRI mice. TERT silencing advanced MIRI progression by enhancing mitochondrial dysfunction and cellular senescence in cardiomyocytes. CK1 phosphorylated TERT at serine 227 and controlled mitochondrial relocation of TERT. CK1 alleviated MIRI and reduced cellular senescence by phosphorylating TERT in mice.</p> Conclusion <p>CK1 regulates TERT phosphorylation and mitochondrial translocation to suppress mitochondrial dysfunction and cell senescence after MIRI, which provides new therapeutic targets for MIRI treatment.</p>