Exercise Preconditioning Alters Markers of Cellular Senescence and Prevents DOX‐Induced Cardiorespiratory Dysfunction

Abstract

Doxorubicin (DOX) is a highly effective chemotherapeutic agent; however its clinical use is limited due to cardiorespiratory complications, including the development of dyspnea, exercise intolerance, and cardiomyopathy. While the mechanisms responsible for DOX‐induced cardiorespiratory dysfunction remain unclear, evidence indicates that DOX administration causes DNA damage and promotes oxidative stress‐induced cellular senescence. Factors shown to contribute to DOX‐induced cellular senescence include cell cycle arrest, driven by signaling through the p16INK4a/Rb and p21/p53 pathways, impaired mitochondrial function, upregulation of pro‐survival pathways, increased lysosomal mass, and expression of the proinflammatory senescence‐associated secretory phenotype (SASP). In contrast, exercise has been shown to prevent cellular senescence in several tissues, leading to the hypothesis that endurance exercise preconditioning is sufficient to prevent senescence induced in the heart and diaphragm muscle following DOX chemotherapy treatment. To determine the relationship between DOX‐induced cardiorespiratory impairment, exercise preconditioning and the impact of accelerated cellular senescence, female Sprague‐Dawley rats underwent two weeks of endurance exercise training (treadmill running, 5 days/week, 60 min/day, 30m/min, 0% grade) before receiving a bolus dose of DOX (20mg/kg IP) or saline treatment. Functional measures were evaluated 48 hours after DOX or saline administration, followed by tissue collection for subsequent analysis of cellular senescence markers. Our results revealed that exercise preconditioning prior to DOX administration prevented diastolic and systolic dysfunction in the heart, with marked improvements in fractional shortening, myocardial performance index, and posterior wall shortening velocity compared to sedentary DOX‐treated animals. DOX‐induced weight loss, reduction in grip strength, and diaphragm weakness were partially rescued with exercise as well, with diaphragm specific force production preserved at frequencies of 60‐160Hz. Finally, both exercise and DOX appear to alter expression of proteins associated with the senescent phenotype in the heart and diaphragm. Therefore, the protective effects of exercise against DOX cardiorespiratory dysfunction may be related to changes in muscle cellular senescence.