Mitochondria respond to stress and undergo fusion and fission at variable rates, depending on the cell status. To understand mitochondria behavior during muscle fatigue, we investigated mitochondria ultrastructure and the level of a fission and stress-related protein in fast muscle fibers of mice subjected to fatigue. Mice were forced running at increasing speed till exhaustion at 45’-1 hr. In other mice high-intensity muscle stimulation through the sciatic nerve simulated the forced treadmill exercise. We detect the unusual presence of a rare phenotype characterized by Elongated Mitochondria Constrictions (EMCs) connecting two separate segments of the original organelles. EMCs are rare in resting muscles and their frequency increases, albeit still at low levels, in stimulated muscles. The constrictions are accompanied by higher Drp-1 phosphorylation at Ser616, indicating an increased translocation of Drp-1 to mitochondria membrane. This is indicative of a mitochondrial stress response perhaps leading to or facilitating a long lasting fission event. A close apposition of SR to the constricted areas, detected by both transmission and scanning electron microscopy is highly suggestive of an SR involvement in inducing constrictions.
Elongated Mitochondria Constrictions and fission in muscle fatigue
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Manuela Lavorato, Emanuele Loro, Valentina Debattisti, Tejvir Khurana, Clara Franzini-Armstrong; Elongated Mitochondria Constrictions and fission in muscle fatigue. J Cell Sci 2018; jcs.221028. doi: https://doi.org/10.1242/jcs.221028
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