Figure 1.

Long-term physical exercise is detrimental for Col6a1^–/– muscles. (A) Histogram showing the mean distance covered daily by wild-type and Col6a1^–/– mice under voluntary running wheel exercise (*p < 0.001, n = 6 each genotype). Error bars indicate s.e.m. (B) Incidence of apoptosis in TA (left) and diaphragm (right) muscles of 5-mo-old wild-type and Col6a1^–/– mice housed either in standard conditions (no run) or after 3-mo running (3-m run) wheel exercise (*p < 0.001, n = 6 each group). Error bars indicate s.e.m. (C) Representative H & E staining of cross-sections of TA and diaphragm muscles isolated from wild-type and Col6a1^–/– mice in standard conditions (no run) or after 3-mo run wheel exercise. Under standard conditions, Col6a1^–/– muscles display various alterations, with centrally nucleated fibers (black arrowheads) and atrophic myofibers (black arrows) in both diaphragm and TA, and signs of inflammation (white asterisk) in diaphragm. After three months of exercise, only a few degenerating myofibers (white arrows) are detected in wild-type muscles, whereas in Col6a1^–/– TA centrally nucleated, atrophic and degenerated myofibers are markedly increased. Three months of exercise leads to extensive myofiber degeneration in Col6a1^–/– diaphragm. (D) Representative cross-sections of TA and diaphragm muscles stained for SDH. Histochemical reaction for SDH produces a purple-blue staining with a speckled pattern, which is proportional to the number of mitochondria and their oxidative activity. In resting conditions (no run), most myofibers of TA show scattered staining of variable intensities, due to the predominantly glycolytic metabolic activity of this muscle, while the diaphragm shows intense blue staining in all myofibers, reflecting its oxidative metabolism. After exercise (3-m run), Col6a1^–/– mice display several abnormally and poorly stained fibers in TA (red asterisks) and a diffuse pale blue staining of diaphragm. Scale bar, 100 μm. (E) Electron micrographs of diaphragm from wild-type and Col6a1^–/– mice after 3 mo of running wheel exercise. Col6a1^–/– diaphragm displays several ultrastructural defects, while wild-type diaphragm maintains a normal structure. Col6a1^–/– diaphragm presents a marked accumulation of dilated sarcoplasmic reticulum (arrowheads), abnormal mitochondria and apoptotic nuclei (upper panels). Many Col6a1^–/– mitochondria appear fragmented and some of them with altered cristae, while wild-type mitochondria maintain elongated shape and normal cristae morphology (lower panels). Scale bars, 1 μm (upper panels) or 200 nm (lower panels). mit, mitochondria; nu, nuclei; WT, wild-type.