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The oestrous cycle and skeletal muscle atrophy: Investigations in rodent models of muscle loss.

ABSTRACT:

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What is the central question of this study? Is the oestrous cycle affected during disuse atrophies and, if so, how are oestrous cycle changes related to musculoskeletal outcomes? What is the main finding and its importance? Rodent oestrous cycles were altered during disuse atrophy, which was correlated with musculoskeletal outcomes. However, the oestrous cycle did not appear to be changed by Lewis lung carcinoma, which resulted in no differences in muscle size in comparison to healthy control animals. These findings suggest a relationship between the oestrous cycle and muscle size during atrophic pathologies.

Abstract

Recent efforts have focused on improving our understanding of female muscle physiology during exposure to muscle atrophic stimuli. A key feature of female rodent physiology is the oestrous cycle. However, it is not known how such stimuli interact with the oestrous cycle to influence muscle health. In this study, we investigated the impact of muscle atrophic stimuli on the oestrous cycle and how these alterations are correlated with musculoskeletal outcomes. A series of experiments were performed in female rodents, including hindlimb unloading (HU), HU followed by 24 h of reloading, HU combined with dexamethasone treatment, and Lewis lung carcinoma. The oestrous cycle phase was assessed throughout each intervention and correlated with musculoskeletal outcomes. Seven or 14 days of HU increased the duration in dioestrus or metoestrus (D/M; low hormones) and was negatively correlated with gastrocnemius mass. Time spent in D/M was also negatively correlated with changes in grip strength and bone density after HU, and with muscle recovery 24 h after the cessation of HU. The addition of dexamethasone strengthened these relationships between time in D/M and reduced musculoskeletal outcomes. However, in animals with Lewis lung carcinoma, oestrous cyclicity did not differ from that of control animals, and time spent in D/M was not correlated with either gastrocnemius mass or tumour burden. In vitro experiments suggested that enhanced protein synthesis induced by estrogen might protect against muscle atrophy. In conclusion, muscle atrophic insults are correlated with changes in the oestrous cycle, which are associated with deterioration in musculoskeletal outcomes. The magnitude of oestrous cycle alterations depends on the atrophic stimuli.

SUBMITTER: Rosa-Caldwell ME

PROVIDER: S-EPMC8639792 | biostudies-literature | 2021 Dec

REPOSITORIES: biostudies-literature

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The oestrous cycle and skeletal muscle atrophy: Investigations in rodent models of muscle loss.

Rosa-Caldwell Megan E ME Mortreux Marie M Kaiser Ursula B UB Sung Dong-Min DM Bouxsein Mary L ML Dunlap Kirsten R KR Greene Nicholas P NP Rutkove Seward B SB

Experimental physiology 20211018 12

<h4>New findings</h4>What is the central question of this study? Is the oestrous cycle affected during disuse atrophies and, if so, how are oestrous cycle changes related to musculoskeletal outcomes? What is the main finding and its importance? Rodent oestrous cycles were altered during disuse atrophy, which was correlated with musculoskeletal outcomes. However, the oestrous cycle did not appear to be changed by Lewis lung carcinoma, which resulted in no differences in muscle size in comparison ...[more]

PMID: 34569104

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Project description:Skeletal muscle atrophy is a consequence of many diseases, environmental insults, inactivity, age and injury. Atrophy is characterized by active degradation and removal of contractile proteins and a reduction in fiber size. Animal models have been extensively used to identify pathways leading to atrophic conditions. Here we have used genome-wide expression profiling analysis and quantitative PCR to identify the molecular changes that occur in two clinically relevant animal mouse models of muscle atrophy, hindlimb casting and Achilles tendon laceration (tenotomy). Gastrocnemius muscle samples were collected 2, 7 and 14 days after insult. The total amount of muscle loss as measured by wet weight and muscle fiber size was equivalent between models, although tenotomy resulted in a more rapid induction of muscle atrophy. Furthermore, tentomy resulted in the regulation of significantly more mRNA transcripts then casting. Analysis of the regulated genes and pathways suggest that the mechanism of atrophy is distinct between these models. The degradation following casting appears ubiquitin-proteasome-mediated while degradation following tenotomy appears lysosomal and matrix-metalloproteinase (MMP)-mediated. This data suggests that there are multiple mechanisms leading to muscle atrophy and that specific therapeutic agents may be necessary to combat the atrophy seen under different conditions. Muscle atrophy was induced through two methods; unloading induced by tendon laceration (Tenotomy) and immobilization induced by hindlimb casting (Casting). For the tenotomy, eight week old male C57/B6 mice were anesthetized by ether inhalation and subsequent intramuscular injection of ketamine-xylazine (0.1 ml/g). The right Achilles tendon just proximal to the calcaneus was severed with a sterile scalpel. The mice were allowed to recover and move freely about their cage. An additional cohort of animals was sham operated (Sham) which involved isolation and manipulation of the Achilles tendon without laceration. For the casting, the right hindlimbs of eight week old male C57Bl/6 mice were immobilized through casting. After 2, 7 or 14 days, animals were sacrificed and the left and right gastrocnemius muscles were carefully removed, flash frozen in liquid nitrogen, and stored at -80°C for further processing. The left untreated legs served as controls. A group of naïve animals that received no treatment or manipulation was included as an additional control. Each group consisted of between 5 and 10 samples for a total of 111 individual samples.

Project description:Abstract Background Sarcopenia is a major contributor to frailty and mortality in aging and obesity and is tightly linked to metabolic dysfunction. Imeglimin is a first-in-class oral hypoglycemic agent targeting mitochondrial function; however, despite the central role of mitochondria in skeletal muscle homeostasis, its effects on skeletal muscle under sarcopenia-relevant conditions remain unclear. Methods Imeglimin was administered to male C57BL/6 mice with high-fat diet (HFD)–induced obesity for six weeks and to naturally aged (18-month-old) male mice for 12 weeks. Skeletal muscle fiber morphology and transcriptomic profiles were analyzed in fast- and slow-twitch muscles. In parallel, C2C12 myotubes were exposed to palmitate with or without imeglimin, and inflammatory gene expression and reactive oxygen species (ROS) generation were assessed. Results Imeglimin significantly increased the cross-sectional area (CSA) of Type II fibers in the extensor digitorum longus (EDL) muscle of HFD-fed mice (+66%, P < 0.01 vs. controls). Transcriptomic analyses revealed suppression of conserved molecular signatures of muscle atrophy, including activation of immediate-early genes and inflammatory pathways (-62 to -79%, P < 0.05 vs. HFD-fed mice). In palmitate-treated C2C12 myotubes, imeglimin attenuated lipotoxicity-induced inflammatory gene expression (-28 to -72%, P < 0.05 vs. controls) with reduced ROS generation, consistent with its cell-autonomous effect on myocytes. Notably, in naturally aged mice, 12-week imeglimin treatment preserved EDL muscle fiber size (+14%, P < 0.05 vs. controls) without altering systemic glucose tolerance, accompanied by transcriptomic changes overlapping with those observed in the HFD model (-27 to -82%, P < 0.05 vs. aged controls). Conclusions Imeglimin attenuates skeletal muscle atrophy in obesity and aging, accompanied by coordinated suppression of stress- and inflammation-associated transcriptional programs. These findings indicate that pharmacological regulation of mitochondrial stress responses influences skeletal muscle vulnerability under chronic metabolic stress and identify skeletal muscle as a previously underappreciated target of imeglimin action.

Dataset Information

The oestrous cycle and skeletal muscle atrophy: Investigations in rodent models of muscle loss.

New findings

Abstract

Publications

The oestrous cycle and skeletal muscle atrophy: Investigations in rodent models of muscle loss.

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