title: Hormone replacement therapy improves contractile function and myonuclear organization of single muscle fibres from postmenopausal monozygotic female twin pairs.
abstract: Ageing is associated with a decline in muscle mass and strength leading to increased physical dependency in old age. Postmenopausal women experience a greater decline than men of similar age in parallel with the decrease in female sex steroid hormone production. We recruited six monozygous female twin pairs (55-59 years old) where only one twin pair was on hormone replacement therapy (HRT use = 7.8 ± 4.3 years) to investigate the association of HRT with the cytoplasmic volume supported by individual myonuclei (myonuclear domain (MND) size,) together with specific force at the single fibre level. HRT use was associated with a significantly smaller (∼27%; P < 0.05) mean MND size in muscle fibres expressing the type I but not the IIa myosin heavy chain (MyHC) isoform. In comparison to non-users, higher specific force was recorded in HRT users both in muscle fibres expressing type I (∼27%; P < 0.05) and type IIa (∼23%; P < 0.05) MyHC isoforms. These differences were fibre-type dependent, i.e. the higher specific force in fast-twitch muscle fibres was primarily caused by higher force per cross-bridge while slow-twitch fibres relied on both a higher number and force per cross-bridge. HRT use had no effect on fibre cross-sectional area (CSA), velocity of unloaded shortening (V0) and relative proportion of MyHC isoforms. In conclusion, HRT appears to have significant positive effects on both regulation of muscle contraction and myonuclei organization in postmenopausal women.
authors: Department of Neuroscience, Clinical Neurophysiology, Uppsala University, Sweden.
authors: Rizwan
authors: R
authors: Qaisar
authors: Guillaume
authors: G
authors: Renaud
authors: Yvette
authors: Y
authors: Hedstrom
authors: Eija
authors: E
authors: Pöllänen
authors: Paula
authors: P
authors: Ronkainen
authors: Jaakko
authors: J
authors: Kaprio
authors: Markku
authors: M
authors: Alen
authors: Sarianna
authors: S
authors: Sipilä
authors: Konstantin
authors: K
authors: Artemenko
authors: Jonas
authors: J
authors: Bergquist
authors: Vuokko
authors: V
authors: Kovanen
authors: Lars
authors: L
authors: Larsson
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001823:Body Composition; D002467:Cell Nucleus; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D020249:Hormone Replacement Therapy; D006801:Humans; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction / Q000187:drug effects; D018485:Muscle Fibers, Skeletal / Q000166:cytology / Q000187:drug effects* / Q000502:physiology; D018995:Myosin Heavy Chains / Q000378:metabolism; D017698:Postmenopause; D011374:Progesterone / Q000494:pharmacology*; D020033:Protein Isoforms / Q000378:metabolism; D014430:Twins, Monozygotic
chemical_list: D020033:Protein Isoforms; D011374:Progesterone; D004958:Estradiol; D018995:Myosin Heavy Chains