Quantification and characterization of grouped type I myofibers in human aging. Issue 1 (7th September 2017)

• Record Type: Journal Article
• Authors: Kelly, Neil A.; Hammond, Kelley G.; Stec, Michael J.; Bickel, C. Scott; Windham, Samuel T.; Tuggle, S. Craig; Bamman, Marcas M.
• Is Part Of: Muscle & nerve. Volume 57:Issue 1(2018)
• Page Start: E52
• Page End: E59
• Publication Date: 2017-09-07
• Subjects: denervation -- motor unit -- myofiber type grouping -- myofiber switching -- reinnervation; Neuromuscular diseases -- Periodicals; Muscles -- Periodicals; Nerves -- Periodicals; 616.74
• DOI: 10.1002/mus.25711
• Languages: English
• ISSNs: 0148-639X

Abstract

ABSTRACT: Introduction: Myofiber type grouping is a histological hallmark of age‐related motor unit remodeling. Despite the accepted concept that denervation–reinnervation events lead to myofiber type grouping, the completeness of those conversions remains unknown. Methods: Type I myofiber grouping was assessed in vastus lateralis biopsies from Young (26 ± 4 years; n = 27) and Older (66 ± 4 years; n = 91) adults. Grouped and ungrouped type I myofibers were evaluated for phenotypic differences. Results: Higher type I grouping in Older versus Young was driven by more myofibers per group (i.e., larger group size) ( P < 0.05). In Older only, grouped type I myofibers displayed larger cross‐sectional area, more myonuclei, lower capillary supply, and more sarco(endo)plasmic reticulum calcium ATPase I (SERCA I) expression ( P < 0.05) than ungrouped type I myofibers. Discussion: Grouped type I myofibers retain type II characteristics suggesting that conversion during denervation–reinnervation events is either progressive or incomplete. Muscle Nerve 57 : E52–E59, 2018