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Anton E. Tjust, Adam Danielsson, Peter M. Andersen, Thomas Brännström, Fatima Pedrosa Domellöf; Impact of Amyotrophic Lateral Sclerosis on Slow Tonic Myofiber Composition in Human Extraocular Muscles. Invest. Ophthalmol. Vis. Sci. 2017;58(9):3708-3715. doi: https://doi.org/10.1167/iovs.17-22098.
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To analyze the proportion and cross-sectional area of myofibers containing myosin heavy chain slow-twitch (MyHCI) and myosin heavy chain slow tonic (MyHCsto) in extraocular muscles of autopsied amyotrophic lateral sclerosis (ALS) patients with either spinal or bulbar site of disease onset.
Whole-muscle cross sections from the middle portion of the medial rectus were labeled with antibodies against MyHCI or MyHCsto and laminin. Myofibers labeled with the MyHC antibodies (MyHCI+sto) and the total number of myofibers were quantified in the orbital and global layer of 6 control individuals and 18 ALS patients. The cross-sectional area of myofibers labeled for either MyHC was quantified in 130 to 472 fibers/individual in the orbital and in 180 to 573 fibers/individual in the global layer of each specimen.
The proportion of MyHCI+sto myofibers was significantly smaller in the orbital and global layer of ALS compared to control individuals. MyHCI+sto myofibers were significantly smaller in the global layer than in the orbital layer of ALS, whereas they were of similar size in control subjects. The decreased proportion of MyHCI+sto fibers correlated significantly with the age of death, but not disease duration, in patients who had the bulbar-onset variant of ALS but not in patients with spinal variant.
ALS, regardless of site of onset, involves a loss of myofibers containing MyHCI+sto. Only in bulbar-onset cases did aging seem to play a role in the pathophysiological processes underlying the loss of MyHCI+sto fibers.
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