- 33 - Time-Course of Exercise and Apoptosis in Dystrophin-Deficient Muscle of Mice Katia Rossini (1) , Andrea Donà (1) , Marco Sandri (1, 2) , Chiara Destro (1) , Massimo Donà (1) and Ugo Carraro (1) (1) C.N.R. Unit for Muscle Biology and Physiopathology, Department of Biomedi- cal Sciences, University of Padova, Padova, Italy and (2) Institute of Experimental and Laboratory Medicine, University of Padova, Padova, Italy Abstract Apoptosis is a process of cell death occurring in many tissues. That apoptosis precedes ne- crosis in death of dystrophin-deficient muscle fibers of mdx is now accepted. Furthermore, we were the first to describe an increase of apoptotic myonuclei in mdx mice two days after spontaneous running exercise. To investigate the role of apoptosis in muscular dystrophy and to determine minimal time/characteristics of physical exercise able to induce a bout of muscle apoptosis, in the present work we studied contribution of apoptosis to exercise- induced death of muscle fiber by a time-course analysis in mdx mice. The runners were housed in a cage with an exercise wheel and allowed to run spontaneously for two hours or for an entire night (about 12 hours) and, the morning after, Tibialis Anterior of both hindlimbs removed. We checked the activity of mice by monitoring the covered distance and the time when the wheel was moving. Apoptosis was assessed by the terminal deoxynucleotidyl transferase assay and expressed as number of apoptotic nuclei for mm 3 of muscle tissue, and by electron microscopy for mor- fological features. In 12-hours running groups mdx mice present a significant minor activity (18±0.7) in com- parison with 2-hours mdx runners (36±3.5 p < 0.001). Consequently, it seems that mdx mi- ce have an activity peak after 2-hours exercise and then it decreases maybe because mdx muscular fibers are frailer, more fatiguable and susceptible at exercise-induced damage. Control non-runner mdx mice present 40±13 apoptotic myonuclei/mm 3 , 2-hours runner mice 84±13 (p = 0.04 against control) and 12-hours mice 158±32 (p = 0.04 against control; p = 0.23 against 2-hours), while in 12-hours mdx runners interstitial nuclei/mm 3 (188±46) significantly decrease in comparison with 2-hours group (348±50). Electron microscopy confirm that apoptotic myonuclei increase after 2-hours running in comparison with seden- tary and some more after 12-hours running. Besides it shows that apoptotic process involves satellite cells. Besides confirming that apoptosis present in mdx mice at rest dramatically increases after exercise, results suggest that inflammation and interstitial apoptosis increase during a short- time exercise while the apoptotic process in myofibers (doubled in 2-hours runners in com- parison with sedentary group) becomes more manifested after a long-term exercise, even if mdx mice activity decreases. Key words: apoptosis, Duchenne muscular dystrophy, muscle, programmed cell death. Basic Appl Myol 10 (1&2): 33-38, 2000 Apoptosis is a process of individual cell death regu- lated by activation of specific genes [34]. Characteristic morphological features of apoptosis include nuclear and cytoplasmatic condensation, fragmentation of cell into apoptotic bodies which become engulfed by phagocytes, and local absence of inflammation. These changes are due to activation of nuclear endonucleases and cyto- plasmatic proteases, while the death program is modu- lated by several regulatory genes with pro- and anti- apoptotic function [13]. During embryonic development,