Adult Rat Mesenchymal Stem Cells Delay Denervated Muscle Atrophy

To evaluate the function of rat mesenchymal stem cells (rMSCs) on denervated gastrocnemius muscles and to address the role of ciliary neurotrophic factor (CNTF) in rMSCs, denervated Wistar rats were separately injected with culture media (sham control), CNTF protein, 2.5?×?10⁵ siCNTF-treated rMSCs, 2.5?×?10⁵ GFP-transfected rMSCs, or 2.5?×?10⁵ untreated rMSCs. Muscle function was assessed at different time points post-surgery. Tibial nerve and gastrocnemius muscle samples were taken at 4, 8, and 12?weeks for histochemistry, and neuromuscular junction repair was also examined by electron microscopy. Fluorescence immunocytochemistry on tissue sections confirmed neurotrophin expression in rMSCs but with little evidence of neuronal differentiation. The engraftment of rMSCs significantly preserved the function of denervated gastrocnemius muscle based both on evaluation of muscle function and direct examination of muscle tissue. Further, the density and depth of the junctional folds were visibly reduced 12?weeks after surgery and transplantation, especially in control group. Knockdown of CNTF expression in rMSCs failed to block muscle preservation, although administration of CNTF protein alone inhibited muscle atrophy, which indicating that delivery of rMSCs could preserve gastrocnemius muscle function following denervation and post-junctional mechanisms involved in the repairing capability of rMSCs.     

失神经骨骼肌萎缩的研究现状及进展

当今骨科领域,周围神经损伤一直影响着患者疗效。肌萎缩的发生,细胞凋亡导致骨骼肌萎缩,神经-肌肉接头处营养因子的代谢发生障碍,肌卫星细胞的减少,生长因子以及线粒体和各种酶的变化都是失神经骨骼肌萎缩的机制。电刺激法,保护神经元,生长因子,神经植入提高神经再生速度以及被动活动可以有效治疗患者。失神经骨骼肌萎缩的研究进展也趋于完善。     

Ellagic Acid Attenuates Muscle Atrophy in STZ-Induced Diabetic Mice

SummaryDiabetes is closely connected with skeletal muscle dysfunction. Ellagic acid (EA) possesses a variety of bio-effects and is applied to the improvement of diabetes. The purpose of this study was to explore the potential improvement effect and mechanisms of EA in streptozotocin (STZ)-induced diabetic muscle atrophy. The model of diabetic mice was established by intra-peritoneal STZ to evaluate treatment effect of EA (100 mg/kg/d for 8 weeks) on muscle atrophy. Our data exhibited that EA enhanced fiber size and weight of gastrocnemius, and promoted grip strength to relieve STZ-induced muscle lesions. In serum, the levels of Creatine kinase (CK), lactate dehydrogenase (LDH), total cholesterol (TC), triglyceride (TG), low-density lipoprotein cholesterol (LDL) were inhibited, while high-density lipoprotein cholesterol (HDL) level was enhanced by EA treatment in diabetic mice. In gastrocnemius, EA decreased Atrogin-1 and MuRF-1 expressions to relieve STZ-induced muscle atrophy. Moreover, EA increased NRF-1 and PGC-1α expressions to alleviate mitochondrial disorder. Meanwhile, EA suppressed CHOP and GRP-87 levels to relieve ER stress. Lastly, EA inhibited BAX expressions and enhanced Bcl-2 expressions to mitigate apoptosis. In conclusion, EA is preventing the event of STZ-induced gastrocnemia by amelioration of mitochondrial dysfunction, ER stress and apoptosis, and could be used in the protection and therapeutic of muscle atrophy in diabetes.     

Impaired Bone Homeostasis in Amyotrophic Lateral Sclerosis Mice with Muscle Atrophy

There is an intimate relationship between muscle and bone throughout life. However, how alterations in muscle functions in disease impact bone homeostasis is poorly understood. Amyotrophic lateral sclerosis (ALS) is a neuromuscular disease characterized by progressive muscle atrophy. In this study we analyzed the effects of ALS on bone using the well established G93A transgenic mouse model, which harbors an ALS-causing mutation in the gene encoding superoxide dismutase 1. We found that 4-month-old G93A mice with severe muscle atrophy had dramatically reduced trabecular and cortical bone mass compared with their sex-matched wild type (WT) control littermates. Mechanically, we found that multiple osteoblast properties, such as the formation of osteoprogenitors, activation of Akt and Erk1/2 pathways, and osteoblast differentiation capacity, were severely impaired in primary cultures and bones from G93A relative to WT mice; this could contribute to reduced bone formation in the mutant mice. Conversely, osteoclast formation and bone resorption were strikingly enhanced in primary bone marrow cultures and bones of G93A mice compared with WT mice. Furthermore, sclerostin and RANKL expression in osteocytes embedded in the bone matrix were greatly up-regulated, and β-catenin was down-regulated in osteoblasts from G93A mice when compared with those of WT mice. Interestingly, calvarial bone that does not load and long bones from 2-month-old G93A mice without muscle atrophy displayed no detectable changes in parameters for osteoblast and osteoclast functions. Thus, for the first time to our knowledge, we have demonstrated that ALS causes abnormal bone remodeling and defined the underlying molecular and cellular mechanisms.     

Effects of Nandrolone in the Counteraction of Skeletal Muscle Atrophy in a Mouse Model of Muscle Disuse: Molecular Biology and Functional Evaluation

Muscle disuse produces severe atrophy and a slow-to-fast phenotype transition in the postural Soleus (Sol) muscle of rodents. Antioxidants, amino-acids and growth factors were ineffective to ameliorate muscle atrophy. Here we evaluate the effects of nandrolone (ND), an anabolic steroid, on mouse skeletal muscle atrophy induced by hindlimb unloading (HU). Mice were pre-treated for 2-weeks before HU and during the 2-weeks of HU. Muscle weight and total protein content were reduced in HU mice and a restoration of these parameters was found in ND-treated HU mice. The analysis of gene expression by real-time PCR demonstrates an increase of MuRF-1 during HU but minor involvement of other catabolic pathways. However, ND did not affect MuRF-1 expression. The evaluation of anabolic pathways showed no change in mTOR and eIF2-kinase mRNA expression, but the protein expression of the eukaryotic initiation factor eIF2 was reduced during HU and restored by ND. Moreover we found an involvement of regenerative pathways, since the increase of MyoD observed after HU suggests the promotion of myogenic stem cell differentiation in response to atrophy. At the same time, Notch-1 expression was down-regulated. Interestingly, the ND treatment prevented changes in MyoD and Notch-1 expression. On the contrary, there was no evidence for an effect of ND on the change of muscle phenotype induced by HU, since no effect of treatment was observed on the resting gCl, restCa and contractile properties in Sol muscle. Accordingly, PGC1α and myosin heavy chain expression, indexes of the phenotype transition, were not restored in ND-treated HU mice. We hypothesize that ND is unable to directly affect the phenotype transition when the specialized motor unit firing pattern of stimulation is lacking. Nevertheless, through stimulation of protein synthesis, ND preserves protein content and muscle weight, which may result advantageous to the affected skeletal muscle for functional recovery.     

Variations of Glucocorticoid Receptors in Intact or Denervated Muscles: Lack of Cause-Effect Relationship with Muscle Atrophy in the Rat

Abstract

The process of muscular atrophy following denervation has been tentatively ascribed to the influence of glucocorticoids (G) because of the rapid increase of cytosolic G receptors (R^G) after sciatic nerve section. It appears however that the level of muscular atrophy is similar: 1. in slow or fast-twitch muscles in spite of huge variations in R^G; 2. in intact or adrenalectomized (ADR-X) rats. Moreover, the protein muscle profile of intact or ADR-X rats after gel electrophoresis is similar but drastically decreased after 3 weeks of denervation. We conclude that there is no causeeffect relationship between muscle atrophy and R^G elevation after nerve section.     

Effect of Estrogen on Denervated Muscle

Abstract: The rate of increase of glucose 6-phosphate dehydrogenase activity in denervated rat extensor digitorum longus muscle shows sexual dimorphism. This phenomenon is further investigated in this report by assessing the effects of ovariectomy, hypophysectomy, hormone replacement therapy, and treatment with an estrogen antagonist, MER-25. The data demonstrate that physiologic doses of estrogens enhance the rate and extent of the increase in glucose 6-phosphate dehydrogenase activity after denervation. The data further indicate that aromatization of androgens may be a significant source of estrogen involved in hormonal modulation of the neural control of glucose 6-phosphate dehydrogenase and other processes in muscle. Furthermore, choline acetyltransferase activity, a marker for the neuromuscular synapse, decreased in rat extensor digitorum longus muscles after denervation, but was unaffected by ovariectomy.     

The Posterior Cricoarytenoid Muscle Is Spared from MuRF1-Mediated Muscle Atrophy in Mice with Acute Lung Injury

Background

Skeletal muscle wasting in acute lung injury (ALI) patients increases the morbidity and mortality associated with this critical illness. The contribution of laryngeal muscle wasting to these outcomes is unknown, though voice impairments and aspiration are common in intensive care unit (ICU) survivors. We evaluated the intrinsic laryngeal abductor (PCA, posterior cricoarytenoid), adductor (CT, cricothyroid) and limb (EDL, extensor digitorum longus) muscles in a mouse model of ALI.

Methods

Escherichia coli lipopolysaccharides were instilled into the lungs of adult male C57Bl6J mice (ALI mice). Limb and intrinsic laryngeal muscles were analyzed for fiber size, type, protein expression and myosin heavy chain (MyHC) composition by SDS-PAGE and mass spectroscopy.

Results

Marked muscle atrophy occurred in the CT and EDL muscles, while the PCA was spared. The E3 ubiquitin ligase muscle ring finger-1 protein (MuRF1), a known mediator of limb muscle atrophy in this model, was upregulated in the CT and EDL, but not in the PCA. Genetic inhibition of MuRF1 protected the CT and EDL from ALI-induced muscle atrophy. MyHC-Extraocular (MyHC-EO) comprised 27% of the total MyHC in the PCA, distributed as hybrid fibers throughout 72% of PCA muscle fibers.

Conclusion

The vocal cord abductor (PCA) contains a large proportion of fibers expressing MyHC-EO and is spared from muscle atrophy in ALI mice. The lack of MuRF1 expression in the PCA suggests a previously unrecognized mechanism whereby this muscle is spared from atrophy. Atrophy of the vocal cord adductor (CT) may contribute to the impaired voice and increased aspiration observed in ICU survivors. Further evaluation of the sparing of muscles involved in systemic wasting diseases may lead to potential therapeutic targets for these illnesses.     

Tibial Nerve Transection - A Standardized Model for Denervation-induced Skeletal Muscle Atrophy in Mice

The tibial nerve transection model is a well-tolerated, validated, and reproducible model of denervation-induced skeletal muscle atrophy in rodents. Although originally developed and used extensively in the rat due to its larger size, the tibial nerve in mice is big enough that it can be easily manipulated with either crush or transection, leaving the peroneal and sural nerve branches of the sciatic nerve intact and thereby preserving their target muscles. Thus, this model offers the advantages of inducing less morbidity and impediment of ambulation than the sciatic nerve transection model and also allows investigators to study the physiologic, cellular and molecular biologic mechanisms regulating the process of muscle atrophy in genetically engineered mice. The tibial nerve supplies the gastrocnemius, soleus and plantaris muscles, so its transection permits the study of denervated skeletal muscle composed of fast twitch type II fibers and/or slow twitch type I fibers. Here we demonstrate the tibial nerve transection model in the C57Black6 mouse. We assess the atrophy of the gastrocnemius muscle, as a representative muscle, at 1, 2, and 4 weeks post-denervation by measuring muscle weights and fiber type specific cross-sectional area on paraffin-embedded histologic sections immunostained for fast twitch myosin.     

The Ubiquitin Ligase Nedd4-1 Participates in Denervation-Induced Skeletal Muscle Atrophy in Mice

Skeletal muscle atrophy is a consequence of muscle inactivity resulting from denervation, unloading and immobility. It accompanies many chronic disease states and also occurs as a pathophysiologic consequence of normal aging. In all these conditions, ubiquitin-dependent proteolysis is a key regulator of the loss of muscle mass, and ubiquitin ligases confer specificity to this process by interacting with, and linking ubiquitin moieties to target substrates through protein∶protein interaction domains. Our previous work suggested that the ubiquitin-protein ligase Nedd4-1 is a potential mediator of skeletal muscle atrophy associated with inactivity (denervation, unloading and immobility). Here we generated a novel tool, the Nedd4-1 skeletal muscle-specific knockout mouse (myo^Cre;Nedd4-1^flox/flox) and subjected it to a well validated model of denervation induced skeletal muscle atrophy. The absence of Nedd4-1 resulted in increased weights and cross-sectional area of type II fast twitch fibres of denervated gastrocnemius muscle compared with wild type littermates controls, at seven and fourteen days following tibial nerve transection. These effects are not mediated by the Nedd4-1 substrates MTMR4, FGFR1 and Notch-1. These results demonstrate that Nedd4-1 plays an important role in mediating denervation-induced skeletal muscle atrophy in vivo.     

Neurite Outgrowth-Promoting Factors in Extracts of Denervated Chick Skeletal Muscle

1. An extract of denervated skeletal muscle contained activity for promotion of neurite outgrowth from telencephalic neurons, as well as that from neurons in the spinal cord. A factor responsible for the activity was characterized in cultures of dissociated neurons.2. The factor acted on neurons only when they were attached to the surface of culture dishes. Since treatments with proteases and lectins reduced the outgrowth-promoting activity, the factor was thought to be a glycoprotein.3. Among the monoclonal antibodies raised against the partially purified extract, five antibodies were found to inhibit the activity for spinal and telencephalic neurons. The most potent antibody, 4D2a, recognized mainly a 63-kD protein and other minor proteins in the extract. Although the 63-kD protein was confirmed to be chick serum albumin by analysis of amino acid sequence, the purified albumin exhibited no activity.4. From these observations, the factor was found to be a glycoprotein recognized by the neutralizing antibody as one of the minor components of the extract. This factor exhibits its activity in a substrate-bound form but not in a diffusible one.     

肌萎缩时的蛋白质降解通路

肌萎缩主要是因为蛋白质降解增强,主要涉及到泛素-蛋白酶体系统、依赖于钙离子的蛋白酶系统、溶酶体系统。在肌萎缩时这些蛋白质降解系统可能是平行作用,也可能按多步骤形式进行。弄清其机制无疑对开发抗肌萎缩药物是有帮助的。     

大鼠肌卫星细胞移植失神经骨骼肌的形态学观测

目的探讨大鼠肌卫星细胞移植能否延缓失神经骨骼肌萎缩。方法将16只成年Wistar大鼠分为实验组与对照组,两组均切断大鼠右后肢胫神经,建立腓肠肌失神经动物模型。实验组：将体外培养的同种异体肌卫星细胞悬液0．2mL缓慢注射到失神经腓肠肌内、外侧头中;对照组：则缓慢注射等量的生理盐水于相同部位。术后第4周,采用肌湿重、肌纤维横截面积形态学观测的方法,检测失神经骨骼肌的萎缩变化情况。结果成功地对成年大鼠肌卫星细胞进行了分离、纯化、鉴定、培养和移植。发现实验组与对照组相比,失神经腓肠肌湿重残存率（由手术侧与自身健侧的肌湿重测定值之比得出）：实验组为0．48±0．050,对照组为0．33±0．059,二者存在显著性差异（P〈0．01）;腓肠肌纤维横截面积残存率（由手术侧与自身健侧的肌纤维横截面积测定值之比得出）：实验组为0．58±0．011,对照组为0．50±0．018,二者存在显著性差异（P〈0．01）。结论本实验表明将肌卫星细胞异体移植到失神经骨骼肌内可明显延缓骨骼肌的萎缩进程,为再生神经到达靶器官提供较多的时间,进而为解决再生神经延伸到靶器官前,靶器官已发生不可逆性萎缩,严重制约再生神经效果的临床难题提供一个新的研究思路。     

Nerve Stump Length and Membrane Changes in Denervated Skeletal Muscle

THE effect of nerve stump length on the rate of failure of neuromuscular transmission and on the degeneration of the neuromuscular apparatus has been studied in some detail^1–4 and there is general agreement that neuromuscular transmission fails and the nerve terminals degenerate more rapidly if the nerve is cut close to the muscle than if it is cut far away.     

Dietary Enrichment with Fish Oil Prevents High Fat-Induced Metabolic Dysfunction in Skeletal Muscle in Mice

High saturated fat (HF-S) diets increase intramyocellular lipid, an effect ameliorated by omega-3 fatty acids in vitro and in vivo, though little is known about sex- and muscle fiber type-specific effects. We compared effects of standard chow, HF-S, and 7.5% HF-S replaced with fish oil (HF-FO) diets on the metabolic profile and lipid metabolism gene and protein content in red (soleus) and white (extensor digitorum longus) muscles of male and female C57BL/6 mice (n = 9-12/group). Weight gain was similar in HF-S- and HF-FO-fed groups. HF-S feeding increased mesenteric fat mass and lipid marker, Oil Red O, in red and mixed muscle; HF-FO increased interscapular brown fat mass. Compared to chow, HF-S and HF-FO increased expression of genes regulating triacylglycerol synthesis and fatty acid transport, HF-S suppressed genes and proteins regulating fatty acid oxidation, whereas HF-FO increased oxidative genes, proteins and enzymes and lipolytic gene content, whilst suppressing lipogenic genes. In comparison to HF-S, HF-FO further increased fat transporters, markers of fatty acid oxidation and mitochondrial content, and reduced lipogenic genes. No diet-by-sex interactions were observed. Neither diet influenced fiber type composition. However, some interactions between muscle type and diet were observed. HF-S induced changes in triacylglycerol synthesis and lipogenic genes in red, but not white, muscle, and mitochondrial biogenesis and oxidative genes were suppressed by HF-S and increased by HF-FO in red muscle only. In conclusion, HF-S feeding promotes lipid storage in red muscle, an effect abrogated by the fish oil, which increases mediators of lipolysis, oxidation and thermogenesis while inhibiting lipogenic genes. Greater storage and synthesis, and lower oxidative genes in red, but not white, muscle likely contribute to lipid accretion encountered in red muscle. Despite several gender-dimorphic genes, both sexes exhibited a similar HF-S-induced metabolic and gene expression profile; likewise fish oil was similarly protective in both sexes.