Hormone replacement therapy improves contractile function and myonuclear organization of single muscle fibres from postmenopausal monozygotic female twin pairs - PubMed (original) (raw)

. 2013 May 1;591(9):2333-44.

doi: 10.1113/jphysiol.2012.250092. Epub 2013 Mar 4.

Guillaume Renaud, Yvette Hedstrom, Eija Pöllänen, Paula Ronkainen, Jaakko Kaprio, Markku Alen, Sarianna Sipilä, Konstantin Artemenko, Jonas Bergquist, Vuokko Kovanen, Lars Larsson

Affiliations

Hormone replacement therapy improves contractile function and myonuclear organization of single muscle fibres from postmenopausal monozygotic female twin pairs

Rizwan Qaisar et al. J Physiol. 2013.

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.

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Figures

Figure 1

Figure 1. Confocal microscopy images of single muscle fibres and their representative myonuclei from HRT users and HRT non-users

Type I fibres are typically characterized by deep groove-like structures harbouring long chains of nuclei. Type IIa fibres have a more ordered organization of both spherical and elliptical myonuclei. DAPI stained myonuclei (blue) while rhodamine labelled actin (red). Horizontal bars denote 50 μm (fibre) and 8 μm (nuclei).

Figure 2

Figure 2. Myonuclear domain size (A), nuclei number per unit length (B), and specific tension and stiffness recordings (C) in type I and type IIa fibres in vastus lateralis muscles from HRT using and HRT non-using co-twins

In A and B, * denotes statistically significant difference from non-users (P < 0.05). In C, * and † denote statistically significant difference for the specific force and stiffness, respectively (P < 0.05). All values are mean ± SEM.

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