Mitochondrial morphology, topology, and membrane interactions in skeletal muscle: a quantitative three-dimensional electron microscopy study (original) (raw)

2013, Journal of Applied Physiology

Picard M, White K, Turnbull DM. Mitochondrial morphology, topology, and membrane interactions in skeletal muscle: a quantitative threedimensional electron microscopy study. Dynamic remodeling of mitochondrial morphology through membrane dynamics are linked to changes in mitochondrial and cellular function. Although mitochondrial membrane fusion/fission events are frequent in cell culture models, whether mitochondrial membranes dynamically interact in postmitotic muscle fibers in vivo remains unclear. Furthermore, a quantitative assessment of mitochondrial morphology in intact muscle is lacking. Here, using electron microscopy (EM), we provide evidence of interacting membranes from adjacent mitochondria in intact mouse skeletal muscle. Electron-dense mitochondrial contact sites consistent with events of outer mitochondrial membrane tethering are also described. These data suggest that mitochondrial membranes interact in vivo among mitochondria, possibly to induce morphology transitions, for kiss-and-run behavior, or other processes involving contact between mitochondrial membranes. Furthermore, a combination of freeze-fracture scanning EM and transmission EM in orthogonal planes was used to characterize and quantify mitochondrial morphology. Two subpopulations of mitochondria were studied: subsarcolemmal (SS) and intermyofibrillar (IMF), which exhibited significant differences in morphological descriptors, including form factor (means Ϯ SD for SS: 1.41 Ϯ 0.45 vs. IMF: 2.89 Ϯ 1.76, P Ͻ 0.01) and aspect ratio (1.97 Ϯ 0.83 vs. 3.63 Ϯ 2.13, P Ͻ 0.01) and circularity (0.75 Ϯ 0.16 vs. 0.45 Ϯ 0.22, P Ͻ 0.01) but not size (0.28 Ϯ 0.31 vs. 0.27 Ϯ 0.20 m 2 ). Frequency distributions for mitochondrial size and morphological parameters were highly skewed, suggesting the presence of mechanisms to influence mitochondrial size and shape. In addition, physical continuities between SS and IMF mitochondria indicated mixing of both subpopulations. These data provide evidence that mitochondrial membranes interact in vivo in mouse skeletal muscle and that factors may be involved in regulating skeletal muscle mitochondrial morphology. skeletal muscle mitochondria; myofiber; outer mitochondrial membrane; scanning and transmission electron microscopy; mitochondrial reticulum SKELETAL MUSCLE FIBERS PERFORM energetically demanding functions (contraction, rapid cycles of ion transport, gene expression, and protein synthesis) requiring large amounts of ATP Address for reprint requests and other correspondence: M. PicardFig. 4. Physical interactions between SS and IMF mitochondria. Transmission electron micrograph of myofibers in the transverse plane. A: SS and IMF mitochondria are distinct organelles. B and C: some SS and IMF mitochondria form continuous organelles (arrowheads) that coexist in both subcellular compartments. SS, subsarcolemmal; IMF, intermyofibrillar; PM, plasma membrane (sarcolemma); Myofibr, Myofibrils; Cap, capillary. 166 Skeletal Muscle Mitochondrial Morphology • Picard M et al. DISCLOSURES No conflicts of interest, financial or otherwise, are declared by the authors. AUTHOR CONTRIBUTIONS Author contributions: M.P. conception and design of research; M.P. and K.W. performed experiments; M.P. analyzed data; M.P. and D.M.T. interpreted results of experiments; M.P. prepared figures; M.P. drafted manuscript; M.P., K.W., and D.M.T. edited and revised manuscript; M.P., K.W., and D.M.T. approved final version of manuscript. 170 Skeletal Muscle Mitochondrial Morphology • Picard M et al.