Spermidine combined with resistance exercise ameliorates myocardial injury and mitochondrial dysfunction via AMPK-SIRT1-PGC-1α in D-galactose-induced aging rats

Age-related decline in myocardial structure and function is closely linked to dysregulated mitophagy, impaired mitochondrial biogenesis, and elevated apoptosis. Spermidine (SPD), a naturally occurring polyamine, and resistance exercise (RE) are both known to induce autophagy and exert cardioprotective anti-aging effects. In the present study, we investigated whether combined SPD and RE intervention ameliorates myocardial injury and mitochondrial dysfunction in D-galactose-induced aging rats, and explored the underlying mechanisms. With the exception of a control group, all rats received 6 weeks of daily intraperitoneal D-galactose injections to induce aging. Successful model establishment was verified by quantifying expression of the senescence-associated genes p53, p21, and p16, and by conducting hematoxylin–eosin (H&E) and Masson’s trichrome staining. Following model validation, rats in the aging cohort were assigned to three intervention groups treated for 8 weeks: RE alone, RE + vehicle (VRE), and SPD + RE. Myocardial tissues were assessed using H&E staining, Masson’s trichrome staining, and transmission electron microscopy. Myocardial levels of adenosine triphosphate (ATP), citrate synthase (CS), cytochrome c oxidase subunit I (COX I), and mitochondrial membrane potential (MMP) were quantified. Markers of mitochondrial biogenesis, mitophagy, and apoptosis were also quantified. Molecules of the AMPK-SIRT1-PGC-1α pathway were measured using reverse transcription-quantitative polymerase chain reaction (RT-qPCR), Western blotting, and immunohistochemistry. Combined SPD + RE intervention significantly ameliorated pathological myocardial structural alterations, mitochondrial morphological abnormalities, and functional impairment. It elevated myocardial ATP, CS, COX I, and MMP levels, and activated the AMPK-SIRT1-PGC-1α pathway. Specifically, it upregulated p-AMPK, SIRT1, PGC-1α, NRF1, and TFAM to promote mitochondrial biogenesis. Enhanced mitophagy was confirmed by an increased LC3B-II/LC3B-I ratio and reduced p62 expression, while suppressed apoptosis was verified by upregulated Bcl-2 and downregulated Bax. In conclusion, combined SPD and RE intervention ameliorates age-related myocardial injury and mitochondrial dysfunction by activating the AMPK-SIRT1-PGC-1α signaling pathway, promoting mitochondrial biogenesis and mitophagy, and inhibiting apoptosis.