Relative proportions of hybrid fibres are unaffected by 6 weeks of running exercise in mouse skeletal muscles

Glaser, Brian W.; You, Geoffrey; Zhang, Min; Medler, Scott

doi:10.1113/expphysiol.2009.049023

Cited by 32 publications

(53 citation statements)

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“…1 ). This pattern is different from the results reported for rodent MHCs in other studies [Talmadge and Roy, 1993;Di Maso et al, 2000;Caiozzo et al, 2003;Glaser et al, 2010] in that the IIA and IIX isoforms are reversed in their migration order. As we have indicated previously, the result is better separation of the IIA and IIX isoforms .…”

Section: Proportions Of Fiber Types In Ta Br and Sol Musclescontrasting

confidence: 56%

“…In mouse, the overall fiber type distribution is lower than in the rat, being highly skewed toward the fastest IIB fiber type. Nevertheless, certain mouse muscles contain 25-50% of their fibers as hybrids [Glaser et al, 2010;Zhang et al, 2010]. In the muscles of both of these rodents, the most prevalent hybrid fiber types are the IIX/IIB hybrids, which represent roughly 70-90% of all the hybrid fibers [Caiozzo et al, 2003;Glaser et al, 2010;Zhang et al, 2010].…”

Section: Introductionmentioning

confidence: 99%

“…While hybrid fibers can provide an indication of such fiber type transitions [Talmadge et al, 1995[Talmadge et al, , 1999Di Maso et al, 2000;Unguez et al, 2000;Williamson et al, 2000], in many instances hybrid fibers persist as stable fiber phenotypes [Stephenson, 2001;Caiozzo et al, 2003;Acevedo and Rivero, 2006;Glaser et al, 2010]. In human muscles, the proportion of hybrid fibers is variable, but on average about 15-20% hybrid fibers is normal [Andersen et al, 1999;Williamson et al, 2000;Andersen, 2003].…”

Section: Introductionmentioning

confidence: 99%

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Hybrid Fibers Transform into Distinct Fiber Types in Maturing Mouse Muscles

Brummer

Zhang

Piddoubny

et al. 2013

Cells Tissues Organs

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The role of hybrid fibers as intermediates in fiber type transformations is not completely understood. In some cases hybrids are clearly transitional fibers changing from one type to another, but in others they represent phenotypically stable fibers in normal muscles. In the current study, our goal was to understand the fate of hybrid fibers in fiber type transitions that take place during muscle maturation. Previous studies have reported high proportions of hybrid fibers during postnatal development, but few have followed the fate of these fibers past the time of weaning. We quantified proportions of hybrid fibers in three different mouse skeletal muscles from newly weaned to 6-month-old mice. Hybrid fibers were very prevalent in the brachioradialis (BR) and tibialis anterior (TA) muscles from newly weaned mice, where they constituted 50 and 40% of the fibers, respectively. These hybrids declined steadily to about 15-30% over the next several months. In the soleus muscle the proportion of hybrids did not change, but constituted approximately 20% of fibers. The reduction in IIX/IIB hybrids resulted from different processes in the BR and the TA. In the BR, the reduction was coincident with an increase in type IIX fibers. In the TA, the number of IIX/IIB hybrids was inversely correlated with the proportion of IIB fibers. These patterns reveal that the role of hybrid fibers as intermediates in muscle development is complex. Some hybrid fibers in maturing muscles represent transitional fiber types, while others are phenotypically stable. Moreover, the fate of transitional fibers may be distinct among similar fiber types within different muscles.

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Section: Proportions Of Fiber Types In Ta Br and Sol Musclescontrasting

confidence: 56%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Hybrid Fibers Transform into Distinct Fiber Types in Maturing Mouse Muscles

Brummer

Zhang

Piddoubny

et al. 2013

Cells Tissues Organs

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“…The discrepancy between EDL and soleus muscles in the reliance of MLCK on E 2 -induced pRLC could be related to different abundances of MLCK and myosin light chain phosphatase proteins and their activities in the two muscles (50), differences in cellular context for ER-mediated signaling pathways, or myosin isoform differences between the two muscles. In regard to the latter, there is fiber type heterogeneity in the mouse soleus muscle as is it comprised of type I and IIa fibers based on myosin heavy chain isoform expressions (13), whereas mouse EDL muscle is more homogeneous, with only type II fibers (52), and it has been demonstrated that potentiation is greater in type II than in type I fibers (60). How the effects of E 2 may differ among fibers with various isoforms of the myosin heavy and light chains is not presently clear, nor is the impact of estrogen status on expression of the various myosin isoforms.…”

Section: Discussionmentioning

confidence: 99%

Estradiol modulates myosin regulatory light chain phosphorylation and contractility in skeletal muscle of female mice

Lai

Collins

Colson

et al. 2016

American Journal of Physiology-Endocrinology and Metabolism

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-Impairment of skeletal muscle function has been associated with changes in ovarian hormones, especially estradiol. To elucidate mechanisms of estradiol on skeletal muscle strength, the hormone's effects on phosphorylation of the myosin regulatory light chain (pRLC) and muscle contractility were investigated, hypothesizing an estradiol-specific beneficial impact. In a skeletal muscle cell line, C 2C12, pRLC was increased by 17␤-estradiol (E 2) in a concentration-dependent manner. In skeletal muscles of C57BL/6 mice that were E 2 deficient via ovariectomy (OVX), pRLC was lower than that from ovary-intact, sham-operated mice (Sham). The reduced pRLC in OVX muscle was reversed by in vivo E 2 treatment. Posttetanic potentiation (PTP) of muscle from OVX mice was low compared with that from Sham mice, and this decrement was reversed by acute E 2 treatment, demonstrating physiological consequence. Western blot of those muscles revealed that low PTP corresponded with low pRLC and higher PTP with greater pRLC. We aimed to elucidate signaling pathways affecting E 2-mediated pRLC using a kinase inhibitor library and C 2C12 cells as well as a specific myosin light chain kinase inhibitor in muscles. PI3K/Akt, MAPK, and CamKII were identified as candidate kinases sensitive to E 2 in terms of phosphorylating RLC. Applying siRNA strategy in C 2C12 cells, pRLC triggered by E 2 was found to be mediated by estrogen receptor-␤ and the G protein-coupled estrogen receptor. Together, these results provide evidence that E 2 modulates myosin pRLC in skeletal muscle and is one mechanism by which this hormone can affect muscle contractility in females. estrogen; estrogen receptor; kinase; post tetanic potentiation; RLC OVARIAN HORMONE DEFICIENCY is related to muscle dysfunction and loss of strength. For example, declines in strength are accelerated around the time of menopause (35,41,51), and skeletal muscles of postmenopausal women on estrogen-based hormone therapy are stronger than those not on hormone therapy (10,17,49). In mouse models, contractile characteristics are impaired in muscles of ovariectomized compared with sham-operated mice (16,38,39,53,65). It was suggested (41) and subsequently demonstrated that ovarian hormones influence muscle strength by directly affecting the function of contractile proteins (43,66), particularly the structure and function of myosin (38,39). Among the ovarian hormones, 17␤-estradiol (E 2 ) appears to be the key hormone, because it reverses muscle weakness and contractile protein dysfunction caused by ovariectomy. Specifically, reduced muscle and contractile protein functions were restored when E 2 was administered to ovariectomized mice (16,38,53). In a chemical model of premature aging, of which the ovaries of young adult mice were locally and specifically induced to be senescent, E 2 treatment improved some muscle contractile functions (18). Although these studies have demonstrated that E 2 impacts muscle and myosin functions, the molecular mechanisms by which this hormone affects the structure a...

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“…Mechanical load (13,15), denervation (41,(63)(64)(65), spinal cord transection (63)(64)(65), hormonal manipulation (13,15,19), and chronic electrical stimulation (47) are each capable of producing major changes in the hybrid fiber content of skeletal muscles. The influence of more natural interventions, like aging and exercise, on hybrid skeletal muscle fibers generally appears to be much less dramatic (7,25,27,29,68,69). As data from skeletal muscles under a variety of conditions have accumulated, it has become clear that hybrid fibers often represent stable phenotypes and are common components of normal muscles (16,60).…”

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confidence: 98%

The continuum of hybrid IIX/IIB fibers in normal mouse muscles: MHC isoform proportions and spatial distribution within single fibers

Zhang

Medler

2010

American Journal of Physiology-Regulatory, Integrative and Comp

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Although skeletal muscle fiber types are often defined as belonging to discrete categories, many muscles possess fibers with intermediate phenotypes. These hybrid fiber types can be identified by their expression of two or more myosin heavy chain (MHC) isoforms within the same single fiber. In mouse muscles, the most common hybrid fibers are those coexpressing the IIX and IIB MHC isoforms. In the present study, we focused on these IIX/IIB fibers from normal mouse muscles to determine the relative proportions of MHC isoforms at both the protein and mRNA levels and to examine the longitudinal distribution of isoforms within single fibers. We found that IIX/IIB hybrids represent ∼25 and 50% of the fibers in the mouse tibialis anterior and brachioradialis, respectively. The relative proportion of the IIX and IIB isoforms in these fibers spans a continuum, from predominantly IIB-like hybrids to IIX-like hybrids. Quantitative assessment of mRNA levels using real-time PCR from single fibers indicated that IIB expression dominated over IIX expression in most fibers and that a general correlation existed between mRNA isoform levels and MHC protein content. However, the match between mRNA levels and protein content was not precise. Finally, we measured MHC isoform proportions in adjacent fiber segments and discovered that ∼30% of hybrids possessed significant differences in isoform content along their length. In some instances, the muscle fiber type as defined by MHC content changed completely along the length of a fiber. This pattern of asymmetrical MHC isoform content along the length of single fibers suggests that the multiple myonuclei of a muscle fiber may express distinct myofibrillar isoforms in an uncoordinated fashion.

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Relative proportions of hybrid fibres are unaffected by 6 weeks of running exercise in mouse skeletal muscles

Cited by 32 publications

References 50 publications

Hybrid Fibers Transform into Distinct Fiber Types in Maturing Mouse Muscles

Hybrid Fibers Transform into Distinct Fiber Types in Maturing Mouse Muscles

Estradiol modulates myosin regulatory light chain phosphorylation and contractility in skeletal muscle of female mice

The continuum of hybrid IIX/IIB fibers in normal mouse muscles: MHC isoform proportions and spatial distribution within single fibers

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