Myofiber apoptosis occurs in the inflammation and regeneration phase following eccentric contractions in rats

Abstract

Eccentric contractions (ECC) induce myofibrillar collapse, edema, and inflammation in muscle cells. Although apoptosis of myonuclei following ECC is activated during the inflammatory phase, the apoptosis response of the regenerative phase remains to be elucidated. The aim of the present study was to determine the inflammatory and regenerative phase of the apoptosis responses induced by ECC. In anesthetized rats, the tibialis anterior muscles were subjected to ECC repeated 40 times, evoked by surface electric stimulation (100 Hz, 10 V) with mechanical muscle stretch. Apoptosis was examined in the control group and in groups 1, 3, 7, and 14 days after ECC (each group, n = 4-6). Terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL)-positive myonuclei were assessed by further labeling with dystrophin staining and DAPI. The expression of proteins related to apoptosis (Bcl-2 and Bax) was examined by Western blot assay. At 1 and 3 days, focal edema and necrotic myofibers invaded by mononuclear phagocytes were present, whereas regenerated myofibers with central nuclei were detected at 7 and 14 days. The occurrence of TUNEL-positive myonuclei increased significantly at 7 (7.0 +/- 1.5%) and 14 days (5.6 +/- 0.6%) compared with control (0.9 +/- 0.5%). Further we found that myonuclear apoptosis was restricted to the subsarcolemmal space at 7 and 14 days and markedly absent from the central nucleus. The Bax/Bcl-2 ratio was significantly higher at 3 (4.5 +/- 0.9) and 7 days (3.4 +/- 0.5) after ECC. In conclusion, myofiber apoptotic responses following ECC are present not only in the inflammatory phase but also persist during the regenerative phase.

Mesenchymal stem cells contribute to vascular growth in skeletal muscle in response to eccentric exercise

“…We hypothesize that endothelial cells in capillaries and/or arterioles are remodeling in response to increased stretch or tension associated with lengthening contractions (22,26). Previous studies based on morphological assessment using electron microscopy suggest overt capillary damage does not occur in response to eccentric exercise (12).…”

“…Previous studies based on morphological assessment using electron microscopy suggest overt capillary damage does not occur in response to eccentric exercise (12). However, a more recent study has provided evidence that apoptosis occurs in skeletal muscle at 7 days postexercise, almost exclusively in endothelial cells (26). Microvascular remodeling observed by caspase-3 and CD31 coexpression is also commonly observed in rapidly growing tumors and in patients with peripheral artery disease (16,31).…”

Endothelial Progenitor Cell-Derived Microvesicles Improve Neovascularization in a Murine Model of Hindlimb Ischemia

“…Images were acquired from all the injured area of the ischemic limb sections for the count of the total muscle fibers and of the fibers with small-diameter and with multiple central nuclei that are indicative of the regeneration process. Random images from the total non-ischemic limb section were considered as a control (30).…”

Mechanisms of exercise-induced muscle damage and fatigue: Intracellular calcium accumulation

“…Sudo and Kano 58) investigated the time course and spatial resolution of ECC-induced myofiber apoptosis histologically. Given that TUNEL-positive nuclei were detected in fibers deprived of dystrophin or sarcoglycan sarcolemmal staining, following 6 and 24 hours of ECC contractions 59) , the loss of several membrane skeletal proteins after ECC contractions could lead to fiber death by apoptosis or necrosis 58) .…”

“…Sudo and Kano 58) reported that, in myofiber longitudinal sections, myonuclear apoptosis occurs at the subsarcolemmal level, as opposed to the central cytoplasm, at 7 and 14 days after ECC contractions. Furthermore, Stuelsatz et al 63) reported that calpain-3 participates in the establishment of a pool of reserve cells, by decreasing the transcriptional activity of the key myogenic regulator MyoD -a process that occurs via proteolysis, independent of the ubiquitin-proteasome degradation pathway.…”