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Quantification and Characterization of Type I Myofiber Grouping: the Effect of Aging
Author(s) -
Hammond Kelley G,
Kelly Neil A,
Bickel C. Scott,
Bamman Marcas M
Publication year - 2016
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.30.1_supplement.1245.31
Subject(s) - myocyte , motor unit , denervation , sarcopenia , reinnervation , myosin , immunohistochemistry , biology , neuromuscular junction , muscle hypertrophy , medicine , anatomy , endocrinology , microbiology and biotechnology , neuroscience
Among the neuromuscular changes that occur with aging, older adults may experience neuronal death, which is revealed through sarcopenia and motor unit loss. However, motor unit loss may not always elicit myofiber death, as some denervated myofibers are reinnervated by another local motor neuron and incorporated into that motor unit. This reorganization of motor units can facilitate the integration of type IIa myofibers into a type I motor unit, causing those fibers to express slow myosin heavy chain (MHC; type I). This denervation/reinnervation and subsequent myofiber type shift can result in type I myofiber grouping. PURPOSE To characterize grouped versus ungrouped type I myofibers by morphological and functional features in older adults. METHODS Muscle tissue specimens were collected from the vastus lateralis, and myofibers were assessed by MHC expression (I, IIa, IIx) for type, size, and grouping. Grouping was determined using a statistical model which includes type I distribution and nearest‐neighbor methods. Capillarization was assessed by immunohistochemistry. RESULTS Percent of grouped type I myofibers is higher in Old compared to Young (51.7% vs. 21.4%; p<0.001). The average number of myofibers per group is higher in Old than Young adults (56.6 vs 13.3; p=0.01). In Older adults, grouped type I myofibers are significantly larger than ungrouped (4911 vs. 4335 μm 2 ; p<0.001), and have fewer capillary contacts per myofiber (2.4 vs. 3.7; p<0.001). CONCLUSION Age‐related changes to skeletal muscle includes an increase in type I myofiber grouping. This grouping is characterized by increased myofiber size and decreased capillarity in grouped type I myofibers. Support or Funding Information Supported by NIH Grant T32HD071866 and the UAB Center for Exercise Medicine