Myosin heavy chain mRNA and protein distribution in immobilized rat skeletal muscle are not affected by testosterone status

Influence of gonadectomy on muscle health in micro- and partial-gravity environments in rats

Gonadal hormones, such as testosterone and estradiol, modulate muscle size and strength in males and females. However, the influence of sex hormones on muscle strength in micro- and partial-gravity environments (e.g., the Moon or Mars) is not fully understood. The purpose of this study was to determine the influence of gonadectomy (castration/ovariectomy) on progression of muscle atrophy in both micro- and partial-gravity environments in male and female rats. Male and female Fischer rats (n = 120) underwent castration/ovariectomy (CAST/OVX) or sham surgery (SHAM) at 11 wk of age. After 2 wk of recovery, rats were exposed to hindlimb unloading (0 g), partial weight bearing at 40% of normal loading (0.4 g, Martian gravity), or normal loading (1.0 g) for 28 days. In males, CAST did not exacerbate body weight loss or other metrics of musculoskeletal health. In females, OVX animals tended to have greater body weight loss and greater gastrocnemius loss. Within 7 days of exposure to either microgravity or partial gravity, females had detectable changes to estrous cycle, with greater time spent in low-estradiol phases diestrus and metestrus (∼47% in 1 g vs. 58% in 0 g and 72% in 0.4 g animals, P = 0.005). We conclude that in males testosterone deficiency at the initiation of unloading has little effect on the trajectory of muscle loss. In females, initial low estradiol status may result in greater musculoskeletal losses.NEW & NOTEWORTHY We find that removal of gonadal hormones does not exacerbate muscle loss in males or females during exposure to either simulated microgravity or partial-gravity environments. However, simulated micro- and partial gravity did affect females' estrous cycles, with more time spent in low-estrogen phases. Our findings provide important data on the influence of gonadal hormones on the trajectory of muscle loss during unloading and will help inform NASA for future crewed missions to space and other planets.

Approaching Gravity as a Continuum Using the Rat Partial Weight-Bearing Model

For decades, scientists have relied on animals to understand the risks and consequences of space travel. Animals remain key to study the physiological alterations during spaceflight and provide crucial information about microgravity-induced changes. While spaceflights may appear common, they remain costly and, coupled with limited cargo areas, do not allow for large sample sizes onboard. In 1979, a model of hindlimb unloading (HU) was successfully created to mimic microgravity and has been used extensively since its creation. Four decades later, the first model of mouse partial weight-bearing (PWB) was developed, aiming at mimicking partial gravity environments. Return to the Lunar surface for astronauts is now imminent and prompted the need for an animal model closer to human physiology; hence in 2018, our laboratory created a new model of PWB for adult rats. In this review, we will focus on the rat model of PWB, from its conception to the current state of knowledge. Additionally, we will address how this new model, used in conjunction with HU, will help implement new paradigms allowing scientists to anticipate the physiological alterations and needs of astronauts. Finally, we will discuss the outstanding questions and future perspectives in space research and propose potential solutions using the rat PWB model.

Muscle metabolism and atrophy: let's talk about sex

Skeletal muscle health is a strong predictor of overall health and longevity. Pathologies affecting skeletal muscle such as cancer cachexia, intensive care unit treatment, muscular dystrophies, and others are associated with decreased quality of life and increased mortality. Recent research has begun to determine that these muscular pathologies appear to present and develop differently between males and females. However, to our knowledge, there has yet to be a comprehensive review on musculoskeletal differences between males and females and how these differences may contribute to sex differences in muscle pathologies. Herein, we present a review of the current literature on muscle phenotype and physiology between males and females and how these differences may contribute to differential responses to atrophic stimuli. In general, females appear to be more susceptible to disuse induced muscle wasting, yet protected from inflammation induced (such as cancer cachexia) muscle wasting compared to males. These differences may be due in part to differences in muscle protein turnover, satellite cell content and proliferation, hormonal interactions, and mitochondrial differences between males and females. However, more works specifically examining muscle pathologies in females are necessary to more fully understand the inherent sex-based differences in muscle pathologies between the sexes and how they may correspond to different clinical treatments.

Myosin heavy chain expression pattern as a marker for anabolic potency: desoxymethyltestosterone (madol), norandrostenedione and testosterone repress MHC-IIb expression and stimulate MHC-IId/x expression in orchiectomized rat gastrocnemius muscle

Both 19-norandrostenedione (estr-4-ene-3,17-dione, NOR) and desoxymethyltestosterone (17alpha-methyl-5alpha-androst-2-en-17beta-ol, DMT or "madol") are 'designer steroids' misused for doping purposes in the bodybuilding scene. We have previously characterized the pharmacological profile of madol and identified potential adverse side effects. The aim of this study was to investigate the anabolic potency of NOR, madol and the reference substance testosterone propionate (TP). Besides wet weight of the M.levator ani (LA), we examined the effects on muscle fiber type composition and myosin heavy chain (MHC) expression in the M.gastrocnemius (Gas) muscle as additional markers for anabolic potency. A Hershberger assay was performed, where orchiectomized (orchi) male Wistar rats were treated subcutaneously with NOR, madol, TP or vehicle control (all 1 mg/kg BW/day) for 12 days. Wet weights of the Gas, LA, prostate and seminal vesicle were examined to determine anabolic and androgenic effects. Fiber type composition of the Gas muscle was analyzed using ATPase staining, and MHC protein profiles were determined by silver stain and Western blot analysis. NOR and madol exhibited strong anabolic and weak androgenic potency by stimulating growth of the LA but not the prostate and seminal vesicle. Skeletal muscle fiber type composition characterized by ATPase staining was not significantly altered between the treatment groups, although there was a tendency toward lower levels of type IIB and increased type IIA fibers in all treatment groups relative to orchi. MHC protein expression determined by Western blot and silver stain analysis revealed that MHC IId/x was significantly up-regulated, while MHC IIb was significantly down-regulated in NOR, madol and TP groups relative to orchi. There were no significant differences for MHC IIa and MHC I expression between groups. Results suggest that the observed MHC expression shift could serve as a molecular marker to determine anabolic activity of anabolic steroids at least in skeletal muscle of orchi rats. The molecular mechanisms as well as the androgen-dependent regulation of MHC expression in intact skeletal muscle remain to be further investigated.

Short bouts of stretching increase myo-D, myostatin and atrogin-1 in rat soleus muscle

Stretching is widely used in rehabilitation and sports activities to improve joint range-of-motion and flexibility in humans, but the effect of stretching on the gene expression of skeletal muscle is poorly understood. We evaluated the effect of short bouts of passive stretching of rat soleus muscle on myo-D, myostatin, and atrogin-1 gene expressions. Six groups of animals were submitted to a single session of stretching (10 stretches of 1 minute with 30 seconds of rest between them, performed manually) and were evaluated immediately (I), and 8, 24, 48, 72, and 168 hours after the session. To evaluate the effect of repetitive sessions of stretching on the soleus muscle over 1 week, three groups of animals received a single session per day of stretching and the muscle was evaluated immediately after 2, 3, and 7 sessions. The mRNA levels of myo-D, myostatin, and atrogin-1 were determined by real-time polymerase chain reaction. A single session of stretching increased the mRNA levels of myo-D (after 24 h), myostatin (I, and 168 h later), and atrogin-1 (after 48 h). Repeated daily session of stretching over 1 week increased myostatin (after 7 sessions) and atrogin-1 expression (after 2, 3, and 7 sessions). Thus, short bouts of passive stretching are able to increase the gene expression of factors associated with muscle growth (myo-D), negative regulation of muscle mass (myostatin), and atrophy (atrogin-1), indicating muscle remodeling through different pathways.

The effect of 30 minutes of passive stretch of the rat soleus muscle on the myogenic differentiation, myostatin, and atrogin-1 gene expressions

The effect of 30 minutes of passive stretch of the rat soleus muscle on the myogenic differentiation, myostatin, and atrogin-1 gene expressions.

OBJECTIVE

To evaluate the effect of passive stretch, applied for 30 minutes to the rat soleus muscle, on the myogenic differentiation (myoD), myostatin, and atrogin-1 gene expressions.

DESIGN

Case-controlled study.

SETTING

University laboratory.

ANIMALS

Fifty 12-week-old male Wistar rats.

INTERVENTIONS

Six groups of animals were given a single stretch bout and were evaluated immediately and 8, 24, 48, 72, and 168 hours later. Another 3 groups were evaluated immediately after 2, 3, and 7 stretches. An intact control group was also analyzed.

MAIN OUTCOME MEASURES

The messenger ribonucleic acid (mRNA) levels of myoD, myostatin, and atrogin-1 were assessed by real-time polymerase chain reaction.

RESULTS

Twenty-four hours after a single session of stretch only, the myoD mRNA levels had increased compared with the control group, whereas an increase in the atrogin-1 expression was observed after 2, 3, and 7 stretches.

CONCLUSIONS

A single session of passive stretch increased the myoD gene expression, a factor related to muscle growth. Interestingly, daily stretches increased the atrogin-1 gene expression, a gene primarily associated with muscle atrophy. The results indicated that gene expression was responsive to the number of stretch sessions.

Quantification by real-time PCR of developmental and adult myosin mRNA in rat muscles

A real-time RT-PCR assay using newly designed primers was developed to analyze developmental and adult MHC mRNA expression both in skeletal muscles and single fibers. Only 4 ng of total RNA was necessary for the analysis of the relative mRNA expression of MHC genes. Different validation steps were realized concerning both specificity and sensitivity of each primer set, and linearity and efficiency of each real-time PCR amplification. Then, quantification of MHC mRNA in neonatal and adult muscles as well as in single fibers was done by the deltaC(T) method, with CycA gene as the reference gene. Due to a higher sensitivity than that of a competitive PCR method, we demonstrated that this assay is suitable to study very low level of MHC mRNA expression as developmental MHC in adult muscle and to quantify mRNA from very small samples.

Neuroendocrine facets of human puberty

The unfolding of pubertal growth and maturation entails multisystem collaboration. Most notably, the outflow of gonadotropins and growth hormone (GH) proceeds both independently and jointly. The current update highlights this unique dependency in the human.

The effect of testosterone on gastrocnemius muscle fibres in growing and adult male and female rats: a histochemical, morphometric and ultrastructural study

In this study, the effect of testosterone on gastrocnemius muscle fibres in growing and adult rats (male and female) was examined using histochemical, morphometric and ultrastructural techniques. After physiological saline (PS), olive oil (OvO) or olive oil + testosterone (OvOT) injections on 72 rats (growing and mature, 36 male and 36 female), the sample tissues of fibre types of the gastrocnemius muscle taken were examined by histochemical [alkaline adenosine triphosphatase (alk-ATPase), acid ATPase (ac-ATPase)], morphometric and ultrastructural techniques. In PS-injected control groups, the gastrocnemius muscle of both sexes contained all the fibre types studied [slow-oxidative muscle fibres (type I), fast-oxidative glycolytic muscle fibres (type IIA) and fast-glycolytic muscle fibres (type IIB)]. The type I fibres had the smallest diameter, type IIA had a medium diameter and type IIB fibres had the largest diameter. In OvO-injected groups, it was observed that the OvO had little effect on the gastrocnemius muscles of either sex, although there was significant enlargement of type IIB fibres. After the injection of OvOT, hypertrophy of muscle fibres was determined by morphometric study. The biggest increase in diameter was on type I fibres. In addition, degenerations on some mitochondria, accumulation of lipid droplets on type I and type II fibres, an increase in glycogen particles, bifurcation of myofibrils, an increase in the number and diameter of units resembling T tubules and an increase in ribosomal content were also observed in the same group by transmission electron microscope. Consequently, it was determined that testosterone can induce protein synthesis in gastrocnemius muscle fibres, and induces changes in shape and size, and also can change the appearance and the number of fibres.

Quantifying the temporospatial expression of postnatal porcine skeletal myosin heavy chain genes

Postnatal skeletal muscle fiber type is commonly defined by one of four major myosin heavy chain (MyHC) gene isoforms (slow/I, 2a, 2x, and 2b) that are expressed. We report on the novel use of combined TaqMan quantitative real-time RT-PCR and image analysis of serial porcine muscle sections, subjected to in situ hybridization (ISH) and immunocytochemistry (IHC), to quantify the mRNA expression of each MyHC isoform within its corresponding fiber type, termed relative fiber type-restricted expression. This versatile approach will allow quantitative temporospatial comparisons of each MyHC isoform among muscles from the same or different individuals. Using this approach on porcine skeletal muscles, we found that the relative fiber type-restricted expression of each postnatal MyHC gene showed wide spatial and temporal variation within a given muscle and between muscles. Marked differences were also observed among pig breeds. Notably, of the four postnatal MyHC isoforms, the 2a MyHC gene showed the highest relative fiber type-restricted expression in each muscle examined, regardless of age, breed, or muscle type. This suggests that although 2a fibers are a minor fiber type, they may be disproportionately more important as a determinant of overall muscle function than was previously believed.