Ovarian hormone status and skeletal muscle inflammation during recovery from disuse in rats

From inflammation to bone formation: the intricate role of neutrophils in skeletal muscle injury and traumatic heterotopic ossification

Neutrophils are emerging as an important player in skeletal muscle injury and repair. Neutrophils accumulate in injured tissue, thus releasing inflammatory factors, proteases and neutrophil extracellular traps (NETs) to clear muscle debris and pathogens when skeletal muscle is damaged. During the process of muscle repair, neutrophils can promote self-renewal and angiogenesis in satellite cells. When neutrophils are abnormally overactivated, neutrophils cause collagen deposition, functional impairment of satellite cells, and damage to the skeletal muscle vascular endothelium. Heterotopic ossification (HO) refers to abnormal bone formation in soft tissue. Skeletal muscle injury is one of the main causes of traumatic HO (tHO). Neutrophils play a pivotal role in activating BMPs and TGF-β signals, thus promoting the differentiation of mesenchymal stem cells and progenitor cells into osteoblasts or osteoclasts to facilitate HO. Furthermore, NETs are specifically localized at the site of HO, thereby accelerating the formation of HO. Additionally, the overactivation of neutrophils contributes to the disruption of immune homeostasis to trigger HO. An understanding of the diverse roles of neutrophils will not only provide more information on the pathogenesis of skeletal muscle injury for repair and HO but also provides a foundation for the development of more efficacious treatment modalities for HO.

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.

tRNA-derived small RNA, 5'tiRNA-Gly-CCC, promotes skeletal muscle regeneration through the inflammatory response

BACKGROUND

Increasing evidence shows that tRNA-derived small RNAs (tsRNAs) are not only by-products of transfer RNAs, but they participate in numerous cellular metabolic processes. However, the role of tsRNAs in skeletal muscle regeneration remains unknown.

METHODS

Small RNA sequencing revealed the relationship between tsRNAs and skeletal muscle injury. The dynamic expression level of 5'tiRNA-Gly after muscle injury was confirmed by real-time quantitative PCR (q-PCR). In addition, q-PCR, flow cytometry, the 5-ethynyl-2'-deoxyuridine (Edu), cell counting kit-8, western blotting and immunofluorescence were used to explore the biological function of 5'tiRNA-Gly. Bioinformatics analysis and dual-luciferase reporter assay were used to further explore the mechanism of action under the biological function of 5'tiRNA-Gly.

RESULTS

Transcriptome analysis revealed that tsRNAs were significantly enriched during inflammatory response immediately after muscle injury. Interestingly, we found that 5'tiRNA-Gly was significantly up-regulated after muscle injury (P < 0.0001) and had a strong positive correlation with inflammation in vivo. In vitro experiments showed that 5'tiRNA-Gly promoted the mRNA expression of proinflammatory cytokines (IL-1β, P = 0.0468; IL-6, P = 0.0369) and the macrophages of M1 markers (TNF-α, P = 0.0102; CD80, P = 0.0056; MCP-1, P = 0.0002). On the contrary, 5'tiRNA-Gly inhibited the mRNA expression of anti-inflammatory cytokines (IL-4, P = 0.0009; IL-10, P = 0.0007; IL-13, P = 0.0008) and the mRNA expression of M2 markers (TGF-β1, P = 0.0016; ARG1, P = 0.0083). Flow cytometry showed that 5'tiRNA-Gly promoted the percentage of CD86⁺ macrophages (16%, P = 0.011) but inhibited that of CD206⁺ macrophages (10.5%, P = 0.012). Immunofluorescence showed that knockdown of 5'tiRNA-Gly increased the infiltration of M2 macrophages to the skeletal muscles (13.9%, P = 0.0023) and inhibited the expression of Pax7 (P = 0.0089) in vivo. 5'tiRNA-Gly promoted myoblast the expression of myogenic differentiation marker genes (MyoD, P = 0.0002; MyoG, P = 0.0037) and myotube formation (21.3%, P = 0.0016) but inhibited the positive rate of Edu (27.7%, P = 0.0001), cell viability (22.6%, P = 0.003) and the number of myoblasts in the G2 phase (26.3%, P = 0.0016) in vitro. Mechanistically, we found that the Tgfbr1 gene is a direct target of 5'tiRNA-Gly mediated by AGO1 and AGO3. 5'tiRNA-Gly dysregulated the expression of downstream genes related to inflammatory response, activation of satellite cells and differentiation of myoblasts through the TGF-β signalling pathway by targeting Tgfbr1.

CONCLUSIONS

These results reveal that 5'tiRNA-Gly potentially regulated skeletal muscle regeneration by inducing inflammation via the TGF-β signalling pathway. The findings of this study uncover a new potential target for skeletal muscle regeneration treatment.

Skeletal muscle wasting: the estrogen side of sexual dimorphism

The importance of defining sex differences across various biological and physiological mechanisms is more pervasive now than it has been over the past 15-20 years. As the muscle biology field pushes to identify small molecules and interventions to prevent, attenuate, or even reverse muscle wasting, we must consider the effect of sex as a biological variable. It should not be assumed that a therapeutic will affect males and females with equal efficacy or equivalent target affinities under conditions where muscle wasting is observed. With that said, it is not surprising to find that we have an unclear or even a poor understanding of the effects of sex or sex hormones on muscle wasting conditions. Although recent investigations are beginning to establish experimental approaches that will allow investigators to assess the impact of sex-specific hormones on muscle wasting, the field still needs rigorous scientific tools that will allow the community to address critical hypotheses centered around sex hormones. The focus of this review is on female sex hormones, specifically estrogens, and the roles that these hormones and their receptors play in skeletal muscle wasting conditions. With the overall review goal of assembling the current knowledge in the area of sexual dimorphism driven by estrogens with an effort to provide insights to interested physiologists on necessary considerations when trying to assess models for potential sex differences in cellular and molecular mechanisms of muscle wasting.

Estrogen Regulates the Satellite Cell Compartment in Females

Skeletal muscle mass, strength, and regenerative capacity decline with age, with many measures showing a greater deterioration in females around the time estrogen levels decrease at menopause. Here, we show that estrogen deficiency severely compromises the maintenance of muscle stem cells (i.e., satellite cells) as well as impairs self-renewal and differentiation into muscle fibers. Mechanistically, by hormone replacement, use of a selective estrogen-receptor modulator (bazedoxifene), and conditional estrogen receptor knockout, we implicate 17β-estradiol and satellite cell expression of estrogen receptor α and show that estrogen signaling through this receptor is necessary to prevent apoptosis of satellite cells. Early data from a biopsy study of women who transitioned from peri- to post-menopause are consistent with the loss of satellite cells coincident with the decline in estradiol in humans. Together, these results demonstrate an important role for estrogen in satellite cell maintenance and muscle regeneration in females.

Collins et al. show the loss of estrogen in female mice and post-menopausal women leads to a decrease in skeletal muscle stem cells. Using muscle stem cell-specific mutants, it was demonstrated that ERα is necessary for satellite cell maintenance, self-renewal, and protection from apoptosis, thereby promoting optimal muscle regeneration.

Estrogen signaling effects on muscle-specific immune responses through controlling the recruitment and function of macrophages and T cells

Background

Estrogen signaling is indispensable for muscle regeneration, yet the role of estrogen in the development of muscle inflammation, especially in the intramuscular T cell response, and the influence on the intrinsic immuno-behaviors of myofibers remain largely unknown. We investigated this issue using the mice model of cardiotoxin (CTX)-induced myoinjury, with or without estrogen level adjustment.

Methods

CTX injection i.m. (tibialis anterior, TA) was performed for preparing mice myoinjury model. Injection s.c. of 17β-estradiol (E₂) or estrogen receptor antagonist 4-OHT, or ovariectomy (OVX), was used to change estrogen level of animal models in vivo. Serum E₂ level was evaluated by ELISA. Gene levels of estrogen receptor (ERs) and cytokines/chemokines in inflamed muscle were monitored by qPCR. Inflammatory infiltration was observed by immunofluorescence. Macrophage and T cell phenotypes were analyzed by FACS. Immunoblotting was used to assess protein levels of ERs and immunomolecules in C₂C₁₂ myotubes treated with E₂ or 4-OHT, in the presence of IFN-γ.

Results

We monitored the increased serum E₂ level and the upregulated ERβ in regenerated myofibres after myotrauma. The absence of estrogen in vivo resulted in the more severe muscle inflammatory infiltration, involving the recruitment of monocyte/macrophage and CD4⁺ T cells, and the heightened proinflammatory (M1) macrophage. Moreover, estrogen signaling loss led to Treg cells infiltration decrease, Th1 response elevation in inflamed muscle, and the markedly expression upregulation of immunomolecules in IFN-γ-stimulated C₂C₁₂ myotubes in vitro.

Conclusion

Our data suggest that estrogen is a positive intervention factor for muscle inflammatory response, through its effects on controlling intramuscular infiltration and phenotypes of monocytes/macrophages, on affecting accumulation and function of Treg cells, and on suppressing Th1 response in inflamed muscle. Our findings also imply an inhibition effect of estrogen on the intrinsic immune behaviors of muscle cells.

Fast and slow myosin as markers of muscle regeneration in mangled extremities: a pilot study

Mangled extremities were classically managed by amputation. But over the past few decades, with the advancement in surgical techniques, an increased number of limb salvages have been possible. As muscles usually get damaged in such grievous injuries, a thorough understanding of muscle regeneration may give a better insight into muscle healing in these injuries. Muscles are composed of slow and fast fibers which can be represented by slow and fast myosin, respectively. There are some animal studies which reported differential regeneration of slow and fast muscle fibers during muscle healing. We conducted this pilot study to find out whether the same holds true for muscle healing in mangled extremities also. This pilot study is designed in 15 patients with lower limb mangled extremities presenting to trauma center of PGIMER, Chandigarh, who were operated within 24 h of injury to see whether muscle healing in mangled extremities follows the same pattern. Biopsies were taken during initial surgery conducted within 24 h of injury and on the 7th day of injury when patient was posted again for secondary wound closure procedure or revision amputation. The biopsy samples were subjected to histopathological and immunohistochemistry examination using antibodies against fast and slow myosin. We found that the regenerating muscle fibers in the biopsy sample taken on the 7th day of injury showed only slow muscle fibers with the absence of fast muscle fibers when compared with the initial biopsy results showing differential regeneration of slow muscle fibers.

The inclusion complex of carvacrol and β-cyclodextrin reduces acute skeletal muscle inflammation and nociception in rats

BACKGROUND

Skeletal muscle inflammation is strongly associated with pain and may impair regeneration and functional recovery after injury. Since anti-inflammatory and antinociceptive effects have been described for the inclusion complex of carvacrol and β-cyclodextrin (βCD-carvacrol), this study investigated the effects of βCD-carvacrol in a model of acute skeletal muscle inflammation.

METHODS

Muscle injury was induced in male Wistar rats by injection of 3% carrageenan in the gastrocnemius muscle. Rats were orally pretreated with saline (vehicle) or βCD-carvacrol (20, 40, 80 and 180 mg/kg) one hour before administration of carrageenan.

RESULTS

The injection of carrageenan in the gastrocnemius muscle increased tissue myeloperoxidase (MPO) activity (p < 0.001), edema (p < 0.001) and the levels of tumoral necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6, macrophage inflammatory protein (MIP-2), but not IL-10 levels. Also, it increased mechanical hyperalgesia and decreased the grip force of animals. Pretreatment with βCD-carvacrol (80 or 160 mg/kg) significantly decreased muscle MPO activity and edema 24 h after injury in comparison to vehicle-pretreated group. Animals pretreated with βCD-carvacrol (160 mg/kg) presented significantly lower levels of IL-1β, IL-6 and MIP-2 and higher levels of IL-10 six hours after induction and lower levels of TNF-α and MIP-2 after 24 h when compared to the vehicle group. Pretreatment with βCD-carvacrol also reduced mechanical hyperalgesia and limited the decrease of grip force (80 or 160 mg/kg; p < 0.001) 6 and 24 h after injury.

CONCLUSION

These results show that βCD-carvacrol reduces inflammation and nociception in a model of acute injury to skeletal muscles.

Comparison between Collagen and Lidocaine Intramuscular Injections in Terms of Their Efficiency in Decreasing Myofascial Pain within Masseter Muscles: A Randomized, Single-Blind Controlled Trial

Background and Objective

A novel option for myofascial pain (MFP) management and muscle regeneration is intramuscular collagen injections. The aim of the study was to evaluate the efficiency of intramuscular injections of collagen and lidocaine in decreasing MFP within masseter muscles.

Methods

Myofascial pain within masseter muscles was diagnosed on the basis of the Diagnostic Criteria for Temporomandibular Disorders (II.1.A. 2 and 3). A total of 43 patients with diagnosed MFP within masseter muscles were enrolled to the study (17 male and 26 female, 40 ± 3.8 years old) and randomly divided into three groups. The first group received injections using 2 ml of collagen MD Muscle (Guna), the second group received 2 ml of 2% lidocaine without a vasoconstrictor, and the third group 2 ml of saline as a control (0.9% NaCl). All patients received repeated injections at one-week intervals (days 0 and 7). The visual analogue scale was used to determine pain intensity changes during each follow-up visit (days 0, 7, and 14) in each group. The masseter muscle activity was measured on each visit (days 0, 7, and 14) with surface electromyography (sEMG) (Neurobit Optima 4, Neurobit Systems).

Results

We found that sEMG masseter muscle activity was significantly decreased in Group I (59.2%), less in Group II (39.3%), and least in Group III (14%). Pain intensity reduction was 53.75% in Group I, 25% in Group II, and 20.1% in Group III.

Conclusions

The study confirmed that intramuscular injection of collagen is a more efficient method for reducing myofascial pain within masseter muscles than intramuscular injection of lidocaine.

Ovarian function's role during cancer cachexia progression in the female mouse

Cachexia is a debilitating condition that occurs with chronic disease, including cancer; our research has shown that some regulation of cancer cachexia progression is affected by sex differences. The Apc^Min/+ mouse is genetically predisposed to develop intestinal tumors; IL-6 signaling and hypogonadism are associated with cachexia severity in the male. This relationship in the female warrants further investigation, as we have shown that the ability of IL-6 to induce cachexia differs between the sexes. Since ovarian reproductive function relies on a complex system of endocrine signaling to affect whole body homeostasis, we examined the relationship between ovarian reproductive function and progression of cancer cachexia in the female Apc^Min/+ mouse. Our study of ovarian reproductive function in female Apc^Min/+ mice showed disease-related cessation of estrous cycling (acyclicity) in 38% of mice. Acyclicity, including morphological and functional losses and enhanced muscle inflammatory gene expression, was associated with severe cachexia. Interestingly, ovariectomy rescued body weight and muscle mass and function but increased muscle sensitivity to systemic IL-6 overexpression. In conclusion, our results provide evidence for a relationship between ovarian reproductive function and cachexia progression in female Apc^Min/+ mice.

Defining the Balance between Regeneration and Pathological Ossification in Skeletal Muscle Following Traumatic Injury

Heterotopic ossification (HO) is characterized by the formation of bone at atypical sites. This type of ectopic bone formation is most prominent in skeletal muscle, most frequently resulting as a consequence of physical trauma and associated with aberrant tissue regeneration. The condition is debilitating, reducing a patient's range of motion and potentially causing severe pathologies resulting from nerve and vascular compression. Despite efforts to understand the pathological processes governing HO, there remains a lack of consensus regarding the micro-environmental conditions conducive to its formation, and attempting to define the balance between muscle regeneration and pathological ossification remains complex. The development of HO is thought to be related to a complex interplay between factors released both locally and systemically in response to trauma. It develops as skeletal muscle undergoes significant repair and regeneration, and is likely to result from the misdirected differentiation of endogenous or systemically derived progenitors in response to biochemical and/or environmental cues. The process can be sequentially delineated by the presence of inflammation, tissue breakdown, adipogenesis, hypoxia, neo-vasculogenesis, chondrogenesis and ossification. However, exactly how each of these stages contributes to the formation of HO is at present not well understood. Our previous review examined the cellular contribution to HO. Therefore, the principal aim of this review will be to comprehensively outline changes in the local tissue micro-environment following trauma, and identify how these changes can alter the balance between skeletal muscle regeneration and ectopic ossification. An understanding of the mechanisms governing this condition is required for the development and advancement of HO prophylaxis and treatment, and may even hold the key to unlocking novel methods for engineering hard tissues.

Codelivery of Infusion Decellularized Skeletal Muscle with Minced Muscle Autografts Improved Recovery from Volumetric Muscle Loss Injury in a Rat Model

Skeletal muscle is capable of robust self-repair following mild trauma, yet in cases of traumatic volumetric muscle loss (VML), where more than 20% of a muscle's mass is lost, this capacity is overwhelmed. Current autogenic whole muscle transfer techniques are imperfect, which has motivated the exploration of implantable scaffolding strategies. In this study, the use of an allogeneic decellularized skeletal muscle (DSM) scaffold with and without the addition of minced muscle (MM) autograft tissue was explored as a repair strategy using a lower-limb VML injury model (n = 8/sample group). We found that the repair of VML injuries using DSM + MM scaffolds significantly increased recovery of peak contractile force (81 ± 3% of normal contralateral muscle) compared to unrepaired VML controls (62 ± 4%). Similar significant improvements were measured for restoration of muscle mass (88 ± 3%) in response to DSM + MM repair compared to unrepaired VML controls (79 ± 3%). Histological findings revealed a marked decrease in collagen dense repair tissue formation both at and away from the implant site for DSM + MM repaired muscles. The addition of MM to DSM significantly increased MyoD expression, compared to isolated DSM treatment (21-fold increase) and unrepaired VML (37-fold) controls. These findings support the further exploration of both DSM and MM as promising strategies for the repair of VML injury.

The role of sex steroid hormones in the pathophysiology and treatment of sarcopenia

Sex steroids influence the maintenance and growth of muscles. Decline in androgens, estrogens and progesterone by aging leads to the loss of muscular function and mass, sarcopenia. These steroid hormones can interact with different signaling pathways through their receptors. To date, sex steroid hormone receptors and their exact roles are not completely defined in skeletal and smooth muscles. Although numerous studies focused on the effects of sex steroid hormones on different types of cells, still many unexplained molecular mechanisms in both skeletal and smooth muscle cells remain to be investigated. In this paper, many different molecular mechanisms that are activated or inhibited by sex steroids and those that influence the growth, proliferation, and differentiation of skeletal and smooth muscle cells are reviewed. Also, the similarities of cellular and molecular pathways of androgens, estrogens and progesterone in both skeletal and smooth muscle cells are highlighted. The reviewed signaling pathways and participating molecules can be targeted in the future development of novel therapeutics.

Influence of ovarian hormones on strength loss in healthy and dystrophic female mice

PURPOSE

The primary objective of this study was to determine whether strength loss and recovery after eccentric contractions are impaired in healthy and dystrophic female mice with low levels of ovarian hormones.

METHODS

Female C57BL/6 (wild-type) or mdx mice were randomly assigned to ovarian-intact (Sham) and ovariectomized (Ovx) groups. Anterior crural muscles were tested for susceptibility to injury from 150 or 50 eccentric contractions in wild-type and mdx mice, respectively. An additional experiment challenged mdx mice with a 2-wk treadmill running protocol followed by an eccentric contraction injury to posterior crural muscles. Functional recovery from injury was evaluated in wild-type mice by measuring isometric torque 3, 7, 14, or 21 d after injury.

RESULTS

Ovarian hormone deficiency in wild-type mice did not affect susceptibility to injury because the ∼50% isometric torque loss after eccentric contractions did not differ between Sham and Ovx mice (P = 0.121). Similarly, in mdx mice, hormone deficiency did not affect the percent of preinjury isometric torque lost by anterior crural muscles after eccentric contractions (P = 0.952), but the percent of preinjury torque in posterior crural muscles was lower in Ovx than in Sham mice (P = 0.014). Recovery from injury in wild-type mice was affected by hormone deficiency. Sham mice recovered preinjury isometric strength by 14 d (96% ± 2%), whereas Ovx mice maintained deficits at 14 and 21 d after injury (80% ± 3% and 84% ± 2%, P < 0.001).

CONCLUSIONS

Ovarian hormone status did not affect the vulnerability of skeletal muscle to strength loss after eccentric contractions. However, ovarian hormone deficiency did impair the recovery of muscle strength in female mice.

Effects of sex steroids on bones and muscles: Similarities, parallels, and putative interactions in health and disease

Estrogens and androgens influence the growth and maintenance of bones and muscles and are responsible for their sexual dimorphism. A decline in their circulating levels leads to loss of mass and functional integrity in both tissues. In the article, we highlight the similarities of the molecular and cellular mechanisms of action of sex steroids in the two tissues; the commonality of a critical role of mechanical forces on tissue mass and function; emerging evidence for an interplay between mechanical forces and hormonal and growth factor signals in both bones and muscles; as well as the current state of evidence for or against a cross-talk between muscles and bone. In addition, we review evidence for the parallels in the development of osteoporosis and sarcopenia with advancing age and the potential common mechanisms responsible for the age-dependent involution of these two tissues. Lastly, we discuss the striking difference in the availability of several drug therapies for the prevention and treatment of osteoporosis, as compared to none for sarcopenia. This article is part of a Special Issue entitled "Muscle Bone Interactions".

Green tea extract attenuates muscle loss and improves muscle function during disuse, but fails to improve muscle recovery following unloading in aged rats

In this study we tested the hypothesis that green tea extract (GTE) would improve muscle recovery after reloading following disuse. Aged (32 mo) Fischer 344 Brown Norway rats were randomly assigned to receive either 14 days of hindlimb suspension (HLS) or 14 days of HLS followed by normal ambulatory function for 14 days (recovery). Additional animals served as cage controls. The rats were given GTE (50 mg/kg body wt) or water (vehicle) by gavage 7 days before and throughout the experimental periods. Compared with vehicle treatment, GTE significantly attenuated the loss of hindlimb plantaris muscle mass (-24.8% vs. -10.7%, P < 0.05) and tetanic force (-43.7% vs. -25.9%, P <0.05) during HLS. Although GTE failed to further improve recovery of muscle function or mass compared with vehicle treatment, animals given green tea via gavage maintained the lower losses of muscle mass that were found during HLS (-25.2% vs. -16.0%, P < 0.05) and force (-45.7 vs. -34.4%, P < 0.05) after the reloading periods. In addition, compared with vehicle treatment, GTE attenuated muscle fiber cross-sectional area loss in both plantaris (-39.9% vs. -23.9%, P < 0.05) and soleus (-37.2% vs. -17.6%) muscles after HLS. This green tea-induced difference was not transient but was maintained over the reloading period for plantaris (-45.6% vs. -21.5%, P <0.05) and soleus muscle fiber cross-sectional area (-38.7% vs. -10.9%, P <0.05). GTE increased satellite cell proliferation and differentiation in plantaris and soleus muscles during recovery from HLS compared with vehicle-treated muscles and decreased oxidative stress and abundance of the Bcl-2-associated X protein (Bax), yet this did not further improve muscle recovery in reloaded muscles. These data suggest that muscle recovery following disuse in aging is complex. Although satellite cell proliferation and differentiation are critical for muscle repair to occur, green tea-induced changes in satellite cell number is by itself insufficient to improve muscle recovery following a period of atrophy in old rats.

Ovariectomy differential influence on some hemostatic markers of mice and rats

Rodent ovariectomy is an experimental method to eliminate the main source of sexual steroids. This work explored for the first time the ovariectomy temporal changes induced in the hemostatic coagulation markers: prothrombin time (PT), activated partial thromboplastin time (aPTT), thrombin time (TT), and fibrinogen concentration (FIB) along with uterine weight on adult female CD1 mice and Wistar rats. Uterine weight (Uw) was assessed before ovariectomy (control), and 1, 3, 5, 7, 9, 16, and 21 days after surgery. PT, aPTT, TT and FIB were estimated the same days, using reported standard techniques. Ovariectomy decreased Uw, since day 1; and from day 10 to 21 reached the lowest values for both species. After day 1, mice hemostatic parameters changed (PT +10%, P<0.05; aPTT +53%, P<0.05; TT −24%, P<0.05; FIB +67%, P<0.05). Rats showed significant changes only in TT and FIB (TT −13%, P<0.001; FIB +65%, P<0.001). Neither mice PT, aPTT and TT, recovered control values after 21 days. In the rats from day 5 to 16 aPTT diminished (18–23%, P<0.05) recovering to control values on day 21, TT after 9 days and PT on day 16. In both species, FIB returned to its control values after 9 days. Ovariectomy differentially altered the PT hemostatic parameter of mice and rats indicating a non-equivalence among both species behaviour for experimental studies of blood coagulation.

Decellularized tissue and cell-derived extracellular matrices as scaffolds for orthopaedic tissue engineering

The reconstruction of musculoskeletal defects is a constant challenge for orthopaedic surgeons. Musculoskeletal injuries such as fractures, chondral lesions, infections and tumor debulking can often lead to large tissue voids requiring reconstruction with tissue grafts. Autografts are currently the gold standard in orthopaedic tissue reconstruction; however, there is a limit to the amount of tissue that can be harvested before compromising the donor site. Tissue engineering strategies using allogeneic or xenogeneic decellularized bone, cartilage, skeletal muscle, tendon and ligament have emerged as promising potential alternative treatment. The extracellular matrix provides a natural scaffold for cell attachment, proliferation and differentiation. Decellularization of in vitro cell-derived matrices can also enable the generation of autologous constructs from tissue specific cells or progenitor cells. Although decellularized bone tissue is widely used clinically in orthopaedic applications, the exciting potential of decellularized cartilage, skeletal muscle, tendon and ligament cell-derived matrices has only recently begun to be explored for ultimate translation to the orthopaedic clinic.

Monocarboxylate transporter expression at the onset of skeletal muscle regeneration

The onset of skeletal muscle regeneration is characterized by proliferating myoblasts. Proliferating myoblasts have an increased energy demand and lactate exchange across the sarcolemma can be used to address this increased demand. Monocarboxylate transporters (MCTs) are involved in lactate transport across the sarcolemma and are known to be affected by various physiological stimuli. However, MCT expression at the onset of skeletal muscle regeneration has not been determined. The purpose of this study was to determine if skeletal muscle regeneration altered MCT expression in regenerating tibialis anterior (TA) muscle. Male C57/BL6 mice were randomly assigned to either a control (uninjured) or bupivacaine (injured) group. Three days post injection, the TA was extracted for determination of protein and gene expression. A 21% decrease in muscle mass to tibia length (2.4 ± 0.1 mg/mm vs. 1.9 ± 0.2 mg/mm, P < 0.02) was observed. IGF-1 and MyoD gene expression increased 5.0-fold (P < 0.05) and 3.5-fold (P < 0.05), respectively, 3 days post bupivacaine injection. MCT-1 protein was decreased 32% (P < 0.03); however, MCT-1 gene expression was not altered. There was no difference in MCT4 protein or gene expression. Lactate dehydrogenase (LDH)-A protein expression increased 71% (P < 0.0004). Protein levels of LDH-B and mitochondrial enzyme cytochrome C oxidase subunit decreased 3 days post bupivacaine injection. CD147 and PKC-θ protein increased 64% (P < 0.03) and 79% (P < 0.02), respectively. MCT1 but not MCT4 expression is altered at the onset of skeletal muscle regeneration possibly in an attempt to regulate lactate uptake and use by skeletal muscle cells.

Estrogen replacement and skeletal muscle: mechanisms and population health

There is a growing body of information supporting the beneficial effects of estrogen and estrogen-based hormone therapy (HT) on maintenance and enhancement of muscle mass, strength, and connective tissue. These effects are also evident in enhanced recovery from muscle atrophy or damage and have significant implications particularly for the muscular health of postmenopausal women. Evidence suggests that HT will also help maintain or increase muscle mass, improve postatrophy muscle recovery, and enhance muscle strength in aged females. This is important because this population, in particular, is at risk for a rapid onset of frailty. The potential benefits of estrogen and HT relative to skeletal muscle function and composition combined with other health-related enhancements associated with reduced risk of cardiovascular events, overall mortality, and metabolic dysfunction, as well as enhanced cognition and bone health cumulate in a strong argument for more widespread and prolonged consideration of HT if started proximal to menopausal onset in most women. Earlier reports of increased health risks with HT use in postmenopausal women has led to a decline in HT use. However, recent reevaluation regarding the health effects of HT indicates a general lack of risks and a number of significant health benefits of HT use when initiated at the onset of menopause. Although further research is still needed to fully delineate its mechanisms of action, the general use of HT by postmenopausal women, to enhance muscle mass and strength, as well as overall health, with initiation soon after the onset of menopause should be considered.

Engineering skeletal muscle repair

Healthy skeletal muscle has a remarkable capacity for regeneration. Even at a mature age, muscle tissue can undergo a robust rebuilding process that involves the formation of new muscle cells and extracellular matrix and the re-establishment of vascular and neural networks. Understanding and reverse-engineering components of this process is essential for our ability to restore loss of muscle mass and function in cases where the natural ability of muscle for self-repair is exhausted or impaired. In this article, we will describe current approaches to restore the function of diseased or injured muscle through combined use of myogenic stem cells, biomaterials, and functional tissue-engineered muscle. Furthermore, we will discuss possibilities for expanding the future use of human cell sources toward the development of cell-based clinical therapies and in vitro models of human muscle disease.

Microcurrent electrical nerve stimulation facilitates regrowth of mouse soleus muscle

Microcurrent electrical nerve stimulation (MENS) has been used to facilitate recovery from skeletal muscle injury. However, the effects of MENS on unloading-associated atrophied skeletal muscle remain unclear. Effects of MENS on the regrowing process of unloading-associated atrophied skeletal muscle were investigated. Male C57BL/6J mice (10-week old) were randomly assigned to untreated normal recovery (C) and MENS-treated (M) groups. Mice of both groups are subjected to continuous hindlimb suspension (HS) for 2 weeks followed by 7 days of ambulation recovery. Mice in M group were treated with MENS for 60 min 1, 3, and 5 days following HS, respectively, under anesthesia. The intensity, the frequency, and the pulse width of MENS were set at 10 μA, 0.3 Hz, and 250 msec, respectively. Soleus muscles were dissected before and immediately after, 1, 3 and 7 days after HS. Soleus muscle wet weight and protein content were decreased by HS. The regrowth of atrophied soleus muscle in M group was faster than that in C group. Decrease in the reloading-induced necrosis of atrophied soleus was facilitated by MENS. Significant increases in phosphorylated levels of p70 S6 kinase and protein kinase B (Akt) in M group were observed, compared with C group. These observations are consistent with that MENS facilitated regrowth of atrophied soleus muscle. MENS may be a potential extracellular stimulus to activate the intracellular signals involved in protein synthesis.

Ectopic lipid deposition and the metabolic profile of skeletal muscle in ovariectomized mice

Disruptions of ovarian function in women are associated with increased risk of metabolic disease due to dysregulation of peripheral glucose homeostasis in skeletal muscle. Our previous evidence suggests that alterations in skeletal muscle lipid metabolism coupled with altered mitochondrial function may also develop. The objective of this study was to use an integrative metabolic approach to identify potential areas of dysfunction that develop in skeletal muscle from ovariectomized (OVX) female mice compared with age-matched ovary-intact adult female mice (sham). The OVX mice exhibited significant increases in body weight, visceral, and inguinal fat mass compared with sham mice. OVX mice also had significant increases in skeletal muscle intramyocellular lipids (IMCL) compared with the sham animals, which corresponded to significant increases in the protein content of the fatty acid transporters CD36/FAT and FABPpm. A targeted metabolic profiling approach identified significantly lower levels of specific acyl carnitine species and various amino acids in skeletal muscle from OVX mice compared with the sham animals, suggesting a potential dysfunction in lipid and amino acid metabolism, respectively. Basal and maximal mitochondrial oxygen consumption rates were significantly impaired in skeletal muscle fibers from OVX mice compared with sham animals. Collectively, these data indicate that loss of ovarian function results in increased IMCL storage that is coupled with alterations in mitochondrial function and changes in the skeletal muscle metabolic profile.

Hind limb suspension and long-chain omega-3 PUFA increase mRNA endocannabinoid system levels in skeletal muscle

Muscle disuse has numerous physiological consequences that end up with significant catabolic metabolism and ultimately tissue atrophy. What is not known is how muscle atrophy affects the endocannabinoid (EC) system. Arachidonic acid (AA) is the substrate for anandamide (AEA) and 2-arachidonylgycerol (2-AG), which act as agonists for cannabinoid receptors CB1 and CB2 found in muscle. Diets with n-3 polyunsaturated fatty acids (PUFA) have been shown to reduce tissue levels of AA, AEA and 2-AG. Therefore, we hypothesized that hind limb suspension (HS)-induced muscle atrophy and intake of n-3 PUFA will change mRNA levels of the EC system. Mice were randomized and assigned to a moderate n-3 PUFA [11.7 g/kg eicosapentaenoic acid (EPA)+docosahexaenoic acid (DHA)], high n-3 PUFA (17.6 g/kg EPA+DHA) or control diets for 12 days and then subjected to HS or continued weight bearing (WB) for 14 days. HS resulted in body weight, epididymal fat pad and quadriceps muscle loss compared to WB. Compared to WB, HS had greater mRNA levels of AEA and 2-AG synthesis enzymes and CB2 in the atrophied quadriceps muscle. The high n-3 PUFA diet resulted in greater mRNA levels of EC synthesis enzymes, and CB1 and CB2. The higher mRNA levels for EC with HS and dietary n-3 PUFA suggest that muscle disuse and diet induce changes in the EC system to sensitize muscle in response to metabolic and physiological consequences of atrophy.

Skeletal muscle mass recovery from atrophy in IL-6 knockout mice

AIM

Skeletal muscle interleukin-6 (IL-6) expression is induced by continuous contraction, overload-induced hypertrophy and during muscle regeneration. The loss of IL-6 can alter skeletal muscle's growth and extracellular matrix remodelling response to overload-induced hypertrophy. Insulin-like growth factor-1 (IGF-1) gene expression and related signalling through Akt/mTOR is a critical regulator of muscle mass. The significance of IL-6 expression during the recovery from muscle atrophy is unclear. This study's purpose was to determine the effect of IL-6 loss on mouse gastrocnemius (GAS) muscle mass during recovery from hindlimb suspension (HS)-induced atrophy.

METHODS

Female C57BL/6 [wild type (WT)] and IL-6 knockout (IL-6 KO) mice at 10 weeks of age were assigned to control, HS or HS followed by normal cage ambulation groups.

RESULTS

GAS muscle atrophy was induced by 10 days of HS. HS induced a 20% loss of GAS mass in both WT and IL-6 KO mice. HS+7 days of recovery restored WT GAS mass to cage-control values. GAS mass from IL-6 KO mice did not return to cage-control values until HS+14 days of recovery. Both IGF-1 mRNA expression and Akt/mTOR signalling were increased in WT muscle after 1 day of recovery. In IL-6 KO muscle, IGF-1 mRNA expression was decreased and Akt/mTOR signalling was not induced after 1 day of recovery. MyoD and myogenin mRNA expression were both induced in WT muscle after 1 day of recovery, but not in IL-6 KO muscle.

CONCLUSION

  Muscle IL-6 expression appears important for the initial growth response during the recovery from disuse.

Influence of fixed muscle length and contractile properties on atrophy and subsequent recovery in the rat soleus and plantaris muscles

This study examined muscular atrophy and the recovery process induced by hindlimb unloading and joint immobilization in the rat soleus and plantaris muscles. Rats were divided into control, hindlimb unloading (HU), hindlimb unloading with ankle joint immobilization at the maximum dorsiflexion (HUD), and maximum plantarflexion (HUP) groups. The hindlimb was reloaded after fourteen days of unloading, and muscle atrophy and walking ability were assessed at 0, 3, and 7 days of reloading. A cross sectional area of muscle fibers in the soleus muscle on day 0 of reloading revealed sizes in order from the control, HUD, HUP down to the HU group, indicating that the HU group was the most atrophied among the four groups. These values in the plantaris muscle ranged in order from the control, HU, HUD, to HUP groups, the HUP group being the most atrophied among the four groups. These muscles recovered from atrophy in the same descending order, and the values in the HUD and HUP groups slowly recovered during the reloading periods. The HUD and HUP groups showed a central core lesion and reloading-induced lesions in some type I muscle fibers after the immobilization and reloading, one possible reason for the delayed recovery in these groups. The muscle atrophy in the HU, HUD, and HUP groups remained at day 7 although the walking ability appeared to be normal. Accordingly, further rehabilitation therapy might be necessary even if the functional ability appears to be normal.

Estradiol and genistein antagonize the ovariectomy effects on skeletal muscle myosin heavy chain expression via ER-beta mediated pathways

The age-related decline in ovarian sex hormone production following the onset of menopause alters skeletal muscle metabolic, structural and functional characteristics. The myosin heavy chain (MHC) expression pattern defines skeletal muscle contraction velocity and is therefore an important factor in skeletal muscle function. The present study was designed to examine the effects of 17beta estradiol (E2), estrogen receptor (ER) subtype selective agonists (ERalpha, ERbeta) or genistein (Gen) following ovary removal (OVX) in female Wistar rats in combination with a high intensity treadmill-based exercise protocol (Ex) or normal cage-based activity (NoEx) on MHC protein expression patterns in the slow fiber type m.Soleus (Sol) and the fast fiber type m.Gastrocnemius (Gas). Gen and E2 in the Sol significantly stimulated MHC-I expression relative to OVX only in the absence of exercise (NoEx). MHC-IIb expression in the Gas was significantly increased relative to OVX in Gen Ex and E2 Ex and NoEx groups. The estrogenic effects in the Sol and Gas were both predominantly mediated via ERbeta pathways, since the ERbeta agonist induced greater MHC increases than OVX or ERalpha. We therefore propose that high intensity exercise in combination with exposure to E2, Gen, ERalpha or ERbeta agonists in OVX rats exerts differential effects on MHC expression in skeletal muscles composed of mainly slow type I MHC (Sol) or fast type II MHC (Gas). In summary, the data shows that MHC composition is affected by estrogens and exercise in a fiber type specific manner and that these effects are mainly mediated by ER-beta. This is of great importance with respect to skeletal muscle health and potential treatment with ER selective agonists.

The influence of estrogen on skeletal muscle: sex matters

As women enter menopause, the concentration of estrogen and other female hormones declines. This hormonal decrease has been associated with a number of negative outcomes, including a greater incidence of injury as well as a delay in recovery from these injuries. Over the past two decades, our understanding of the protective effects of estrogen against various types of injury and disease states has grown immensely. In skeletal muscle, studies with animals have demonstrated that sex and estrogen may potentially influence muscle contractile properties and attenuate indices of post-exercise muscle damage, including the release of creatine kinase into the bloodstream and activity of the intramuscular lysosomal acid hydrolase, beta-glucuronidase. Furthermore, numerous studies have revealed an estrogen-mediated attenuation of infiltration of inflammatory cells such as neutrophils and macrophages into the skeletal muscles of rats following exercise or injury. Estrogen has also been shown to play a significant role in stimulating muscle repair and regenerative processes, including the activation and proliferation of satellite cells. Although the mechanisms by which estrogen exerts its influence upon indices of skeletal muscle damage, inflammation and repair have not been fully elucidated, it is thought that estrogen may potentially exert its protective effects by: (i) acting as an antioxidant, thus limiting oxidative damage; (ii) acting as a membrane stabilizer by intercalating within membrane phospholipids; and (iii) binding to estrogen receptors, thus governing the regulation of a number of downstream genes and molecular targets. In contrast to animal studies, studies with humans have not as clearly delineated an effect of estrogen on muscle contractile function or on indices of post-exercise muscle damage and inflammation. These inconsistencies have been attributed to a number of factors, including age and fitness level of subjects, the type and intensity of exercise protocols, and a focus on sex differences that typically involve factors and hormones in addition to estrogen. In recent years, hormone replacement therapy (HRT) or estrogen combined with exercise have been proposed as potentially therapeutic agents for postmenopausal women, as these agents may potentially limit muscle damage and inflammation and stimulate repair in this population. While the benefits and potential health risks of long-term HRT use have been widely debated, controlled studies using short-term HRT or other estrogen agonists may provide future new and valuable insights into understanding the effects of estrogen on skeletal muscle, and greatly benefit the aging female population. Recent studies with older females have begun to demonstrate their benefits.

Changes in contraction-induced phosphorylation of AMP-activated protein kinase and mitogen-activated protein kinases in skeletal muscle after ovariectomy

Recent evidence suggests that ovarian hormones contribute to altered function of skeletal muscle, however the signaling processes thought to regulate muscle function remain undefined in females. Thus, the purpose of this investigation is to determine if ovarian hormone status is critical for contraction-induced activation of AMPK or MAPK in skeletal muscle. Female mice were divided into two groups, ovariectomy (OVX) and SHAM, which were then subjected to in situ isometric contractile protocols. AMPK, ERK 1/2, p38, and JNK phosphorylation were measured in the control and contracting limb. In the in situ protocol, OVX muscles were significantly more resistant to fatigue compared to the SHAM animals. In addition, the muscles from OVX mice demonstrated significantly lower levels of normalized AMPK phosphorylation at rest. AMPK phosphorylation was not increased in the muscles from SHAM mice after the in situ contractile protocol, while the OVX demonstrated significant increases in AMPK phosphorylation. After contraction, normalized ERK2 phosphorylation was significantly higher in the OVX group compared to the SHAM group. Both p38 and JNK phosphorylation increased in response to contraction; but no group differences were detected. A second set of SHAM and OVX animals were subjected to fatigue stimulated under in vitro conditions. Significant increases in AMPK and ERK2 phosphorylation were detected, but no differences were found between groups. In conclusion, removal of the ovaries results in different responses to contraction-induced changes in phosphorylation of AMPK and ERK2 in female mice and suggests hormones secreted from the ovaries significantly impacts cellular signaling in skeletal muscle.

A novel hindlimb immobilization procedure for studying skeletal muscle atrophy and recovery in mouse

Skeletal muscle atrophy is a serious concern for patients afflicted by limb restriction due to surgery (e.g., arthrodesis), several articular pathologies (e.g., arthralgia), or simply following cast immobilization. To study the molecular events involved in this immobilization-induced debilitating condition, a convenient mouse model for atrophy is lacking. Here we provide a new immobilization procedure exploiting the normal flexion of the mouse hindlimb using a surgical staple to fix the ventral part of the foot to the distal part of the calf. Histological analysis revealed that our approach induced significant skeletal muscle atrophy by reducing the myofiber size of the tibialis anterior (TA) muscle by 36% compared with the untreated contralateral TA within a few days postimmobilization. Two molecular markers for atrophy, atrogin-1/muscle atrophy F-box (atrogin-1/MAFbx) and muscle ring finger 1 (MuRF-1) mRNAs, were significantly upregulated by 1.9- and 5.9-fold, respectively. Interestingly, our model also revealed the presence of an early inflammatory process during atrophy, characterized by the mRNA upregulation of TNF-α, IL-1, and IL-6 (1.9-, 2.4-, and 3.4-fold, respectively) simultaneously with the upregulation of the common leukocyte marker CD45 (6.1-fold). Moreover, muscle rapidly recovered on remobilization, an event associated with significantly increased levels of uncoupling protein-3 and peroxisome proliferator-activated receptor γ coactivator-1α mRNA, key components of prooxidative muscle metabolism. This model offers unexpected new insights into the molecular events involved in immobilization atrophy.

Effects of 14 days of microgravity on fast hindlimb and diaphragm muscles of the rat

The purpose of the present study was to determine the effects of 14 days of microgravity on specific rat fast-twitch muscles, and to compare these data with previous data from rat fast-twitch muscles exposed to microgravity for 10 days (Kraemer et al. 2000). Hindlimb muscles containing predominately fast fibers [extensor digitorum longus (EDL), superficial "white" (GSW) and deep "red" (GDR) gastrocnemius] and the diaphragm (DIA) were removed from flight and ground-based control animals and analyzed for: muscle mass, fiber type distribution, cross-sectional area, and myosin heavy chain (MHC) isoform content. Gravitational unloading for 14 days caused significant decreases in muscle mass (8-9%) and cross-sectional area of almost all fiber types (10-35%) from both EDL and gastrocnemius muscles. However, microgravity had little effect on fiber type composition in these muscles with significant changes occurring only in the EDL type IID fiber population (9.5% decrease). Similarly, relative MHC isoform content was only slightly altered by exposure to microgravity (increased content of MHCIIa in flight EDL). No changes in area, fiber type percentages, or MHC isoform content were detected in the DIA following the 14-day spaceflight. Similar to data gathered following a 10-day spaceflight (Kraemer et al. 2000), the 14-day flight did not appear to cause significant slow-to-fast (I --> IIA) or fast-to-faster (IIA --> IID --> IIB) transformations in hindlimb muscles containing predominantly fast-twitch fibers. However, the longer period of gravitational unloading did result in additional loss in muscle fiber cross-sectional area with involvement of more major fiber types.

Apocynin attenuates diaphragm oxidative stress and protease activation during prolonged mechanical ventilation

OBJECTIVE

To investigate whether apocynin protects the diaphragm from wasting and oxidative stress during mechanical ventilation (MV).

DESIGN

Prospective, randomized, controlled study.

SETTING

Research laboratory.

SUBJECTS

Adult female Sprague-Dawley rats.

INTERVENTIONS

Rats were randomly assigned to one of five experimental groups: 1) acutely anesthetized control, 2) spontaneous breathing control, 3) spontaneously breathing control with administration of the nicotinamide adenine dinucleotide phosphate oxidase inhibitor, apocynin, 4) mechanically ventilated, and 5) mechanically ventilated with apocynin.

MEASUREMENTS AND MAIN RESULTS

Apocynin attenuated MV-induced diaphragmatic oxidative stress, contractile dysfunction, and type I, type IIa, and type IIb/IIx myofiber atrophy. The apocynin-induced attenuation of MV-induced diaphragmatic atrophy and contractile dysfunction occurred in conjunction with a reduction in the small increase in nicotinamide adenine dinucleotide phosphate oxidase activity as well as the preservation of total glutathione levels, glutathione peroxidase protein abundance, and a decrease in the activation of the cysteine proteases, calpain-1 and caspase-3. Interestingly, independent of MV, apocynin increased diaphragmatic levels of calpastatin, an endogenous calpain inhibitor. Furthermore, treatment of skeletal muscle cells in culture (C2C12 myotubes) with apocynin resulted in an increase in both calpastatin mRNA levels and protein abundance.

CONCLUSIONS

Our results suggest that the protective effects of apocynin on the diaphragm during prolonged MV seem to be linked to both its functions as an antioxidant and role in cellular signaling regulating the cysteine protease inhibitor calpastatin.