Exercise alleviates liver senescence but does not outmatch the effect of dietary restriction in diet-induced MASLD
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Background
The present study aims at deciphering the potential benefits of aerobic exercise and dietary restriction on liver senescence, which is an established hallmark of metabolic dysfunction-associated steatotic liver disease (MASLD), a condition with limited therapeutic options.
Methods
C57BL6 mice were subjected to normal diet (ND, 10% of kilocalories from fat) or a high-fat diet (HFD, 60% of kilocalories deriving from fat and water supplemented with 5% High-fructose Corn Syrup, HFCS) for 12 weeks. Then, for additional 8 weeks, the ND group continued with the same diet, while the HFD group was divided into four subgroups: a) mice that continued with the same HFD-5% HFCS in water scheme (HFD), b) mice that continued with the same HFD-5% HFCS in water scheme and underwent supervised aerobic exercise 3-times/week (HFDEX), c) mice that were switched to ND (dietary restriction, DR) and d) mice that were switched to ND while undergoing supervised aerobic exercise 3-times/week (DREX). Phenotypic and histological characterization of obesity and MASLD were performed in all groups. Biomarkers of senescence were analyzed in terms of their mRNA expression levels to assess the impact of all interventions on MASLD-related senescence in the liver. GL13 and p21 immunohistochemical stainings were conducted to examine the protein levels of senescence-associated lipofuscin and p21 WAF1/CIP1 respectively, so as to finally investigate their relationship with the grade of steatosis observed in each individual animal.
Results
DR and DREX groups exhibited significantly reduced features of obesity and MASLD-related hepatic steatosis, to a greater extent than the respective amelioration driven by aerobic exercise-only in HFDEX animals. A statistically significant increase of the mRNA expression of cyclin-dependent kinase p21 WAF1/CIP1 was detected in HFD livers as compared to ND, which was also reversed upon DR-inclusive interventions. In contrast, the gene expression levels of cyclin-dependent kinase p16 INK4a remained similar in all groups even after a combined intervention. Increased hepatic expression of the p27 and p53 components of the p53-p21 CIP/WAF -driven axis of cellular senescence as well as their restoration to ND-like levels upon DR and DREX, suggest an active participation of the p21 WAF1/CIP1 mechanism of senescence in the emergence of MASLD, but also in its reversal through DR or/and EX interventions. Immunohistochemical stainings for GL13 and p21 confirmed the aforementioned alterations of p21 WAF1/CIP1 at the tissular level.
Conclusion
Liver senescence is responsive both to exercise and dietary restriction, but its amelioration in the context of MASLD is more robust upon DR-inclusive interventions.
