Early changes in muscle fiber size and gene expression in response to spinal cord transection and exercise

Electrical Stimulation Prevents Muscular Atrophy and the Decrease of Interleukin-6 in Paralyzed Muscles after Spinal Cord Injury in Rats

Objective  To analyze the muscle trophism and expression of interleukin-6 in the biceps brachii muscle of rats with incomplete cervical spinal cord injury treated with neuromuscular electrical stimulation (NMES). Methods  Adult rats underwent C5-C7 spinal cord hemisection and a 5-week NMES protocol. Trophism of the biceps brachii was assessed using muscle weight/body weight ratio and histological analysis. Interleukin-6 expression from biceps brachii was measured using the enzyme-linked immunosorbent assay technique. Results  Preservation of the biceps brachii muscle trophism was found in the NMES treated group, along with prevention of the reduction of interleukin-6 levels. Conclusion  Spinal cord injury causes muscle atrophy and decreases interleukin-6 levels. These alterations are partially prevented by NMES. The results suggest a possible NMES action mechanism and underscore the clinical use of this therapeutic tool.

Cuproptosis and physical training

Copper is an essential element in the human body, involved in many physiological and metabolic functions, including coagulation, oxidative metabolism, and hormone production. The maintenance of copper homeostasis within cells is a complex procedure that is intrinsically controlled by a multitude of intricate mechanisms. Disorders of copper homeostasis encompass a wide range of pathological conditions, including degenerative neurological diseases, metabolic disorders, cardio-cerebrovascular diseases, and tumors. Cuproptosis, a recently identified non-apoptotic mode of cell death mode, is characterized by copper dependence and the regulation of mitochondrial respiration. Cuproptosis represents a novel form of cell death distinct from the previously described modes, including apoptosis, necrosis, pyroptosis, and ferroptosis. Excess copper has been shown to induce cuproptosis by stimulating protein toxic stress responses via copper-dependent abnormal oligomerization of lipoylation proteins within the tricarboxylic acid cycle and the subsequent reduction of iron-sulfur cluster protein levels. Ferredoxin1 facilitates the lipoacylation of dihydrolipoyl transacetylase, which in turn degrades iron-sulfur cluster proteins by reducing Cu2+ to Cu+, thereby inducing cell death. Furthermore, copper homeostasis is regulated by the copper transporter, and disturbances in this homeostasis result in cuproptosis. Current evidence suggests that cuproptosis plays an important role in the onset and development of several cardiovascular diseases. Copper-chelating agents, including ammonium tetrathiomolybdate (VI) and DL-penicillamine, have been shown to facilitate the alleviation of cardiovascular disease by inhibiting cuproptosis. It is hypothesized that oxidative phosphorylation inhibitors such as physical training may inhibit cuproptosis by inhibiting the protein stress response. In conclusion, the implementation of physical training may be a viable strategy to reducte the incidence of cuproptosis.

Selective Myostatin Inhibition Spares Sublesional Muscle Mass and Myopenia-Related Dysfunction after Severe Spinal Cord Contusion in Mice

Clinically relevant myopenia accompanies spinal cord injury (SCI), and compromises function, metabolism, body composition, and health. Myostatin, a transforming growth factor (TGF)β family member, is a key negative regulator of skeletal muscle mass. We investigated inhibition of myostatin signaling using systemic delivery of a highly selective monoclonal antibody - muSRK-015P (40 mg/kg) - that blocks release of active growth factor from the latent form of myostatin. Adult female mice (C57BL/6) were subjected to a severe SCI (65 kdyn) at T9 and were then immediately and 1 week later administered test articles: muSRK-015P (40 mg/kg) or control (vehicle or IgG). A sham control group (laminectomy only) was included. At euthanasia, (2 weeks post-SCI) muSRK-015P preserved whole body lean mass and sublesional gastrocnemius and soleus mass. muSRK-015P-treated mice with SCI also had significantly attenuated myofiber atrophy, lipid infiltration, and loss of slow-oxidative phenotype in soleus muscle. These outcomes were accompanied by significantly improved sublesional motor function and muscle force production at 1 and 2 weeks post-SCI. At 2 weeks post-SCI, lean mass was significantly decreased in SCI-IgG mice, but was not different in SCI-muSRK-015P mice than in sham controls. Total energy expenditure (kCal/day) at 2 weeks post-SCI was lower in SCI-immunoglobulin (Ig)G mice, but not different in SCI-muSRK-015P mice than in sham controls. We conclude that in a randomized, blinded, and controlled study in mice, myostatin inhibition using muSRK-015P had broad effects on physical, metabolic, and functional outcomes when compared with IgG control treated SCI animals. These findings may identify a useful, targeted therapeutic strategy for treating post-SCI myopenia and related sequelae in humans.

Daily and short-term application of joint movement for the prevention of infrapatellar fat pad atrophy due to immobilization

[Purpose] To mobilize the knee joint during cast fixation and to determine whether infrapatellar fat pad changes can be prevented. [Materials and Methods] We randomly allocated Wistar rats into 3 groups as follows: normal group, raised in normal conditions (n=5); contracture group, immobilized with cast fixation (n=5); and prevention group, treated with joint movement during immobilization (n=5). We immobilized the right hindlimb using cast fixation. Joint movement in the prevention group was accomplished by repeatedly pulling the right hindlimb caudally and then returning the leg to the bent position for 10 minutes every day for 2 weeks. We used a metronome to maintain a constant speed, with one set lasting 2 seconds (1-second traction and 1-second return). [Results] The contracture group had adipose cells of various sizes and fibrosis in the infrapatellar fat pad. These changes were also found in milder forms in the prevention group. We found significant differences in the cross section of adipose cells and in knee extension restriction between the groups. [Conclusion] Promoting joint movement may not only have a therapeutic effect on adipose cells but also a preventative effect.

One week, but not 12 hours, of cast immobilization alters promotor DNA methylation patterns in the nNOS gene in mouse skeletal muscle

KEY POINTS

DNA methylation may play an important role in regulating gene expression in skeletal muscle to adapt to physical activity and inactivity. Neuronal nitric oxide synthase (nNOS) in skeletal muscle is a key regulator of skeletal muscle mass; however, it is unclear whether nNOS expression is regulated by DNA methylation. We found that 1 week of cast immobilization increased nNOS DNA methylation levels and downregulated nNOS gene expression in atrophic slow-twitch soleus muscle from the mouse leg. These changes were not detected in non-atrophic fast-twitch extensor digitorum longus muscle. Twelve hours of cast immobilization decreased nNOS gene expression, whereas nNOS DNA methylation levels were unchanged, suggesting that downregulation of nNOS gene expression by short-term muscle inactivity is independent of the DNA methylation pattern. These findings contribute to a better understanding of the maintenance of skeletal muscle mass and prevention of muscle atrophy by epigenetic mechanisms via the nNOS/NO pathway.

ABSTRACT

DNA methylation is a mechanism that controls gene expression in skeletal muscle under various environmental stimuli, such as physical activity and inactivity. Neuronal nitric oxide synthase (nNOS) regulates muscle atrophy in skeletal muscle. However, the mechanisms regulating nNOS expression in atrophic muscle remain unclear. We hypothesized that nNOS expression in atrophic muscle is regulated by DNA methylation of the nNOS promotor in soleus (Sol; slow-twitch fibre dominant) and extensor digitorum longus (EDL; fast-twitch fibre dominant) muscles. One week of cast immobilization induced significant muscle atrophy in Sol but not in EDL. We showed that 1 week of cast immobilization increased nNOS DNA methylation levels in Sol, although only a minor change was detected in EDL. Consistent with the increased DNA methylation levels in atrophic Sol, the gene expression levels of total nNOS and nNOSµ (i.e. the major splicing variant of nNOS in skeletal muscle) decreased. The abundance of the nNOS protein and cell membrane (especially type IIa fibre) immunoreactivity also decreased in atrophic Sol. These changes were not observed in EDL after 1 week of cast immobilization. Furthermore, despite the lack of significant atrophy, 12 h of cast immobilization decreased gene expression levels of total nNOS and nNOSµ in Sol. However, no association was detected between nNOS DNA methylation and gene expression. The expression of the nNOSβ gene, another splicing variant of nNOS, in EDL was unchanged by cast immobilization, whereas its expression was not detected in Sol. We concluded that chronic adaptation of nNOS gene expression in cast immobilized muscle may involve nNOS DNA methylation.

Spontaneous and Stimulus-Evoked Respiratory Rate Elevation Corresponds to Development of Allodynia in Spinal Cord-Injured Rats

Respiratory complications frequently accompany spinal cord injury (SCI) and slowed breathing has been shown to mitigate pain sensitivity. It is possible that elevated respiratory rates (RRs) signal the emergence of chronic pain after SCI. We previously validated the use of remote electric field sensors to noninvasively track breathing in freely behaving rodents. Here, we examined spontaneous (resting) and stimulus-evoked RRs as potential indices of mechanical hypersensitivity following SCI. Adult male Long-Evans rats received a lower thoracic hemisection or contusion SCI, or sham surgery, and underwent weekly assessments of mechanical and thermal sensitivity using the von Frey and Hargreaves tests, respectively. Resting RRs were recorded with remote sensors prior to nociception assays as well as 1 day post-surgery. Evoked RRs were quantified weekly in response to at-level mechanical stimulation provided by a small brush at various stimulation speeds, including those corresponding to the distinct tuning properties of a sub-population of cutaneous afferents known as C-low threshold mechanoreceptors. SCI rats developed mechanical hypersensitivity, which peaked 2-3 weeks after SCI. Compared with at baseline, hemisection SCI rats showed significantly heightened resting RRs at 1 day and 7 days post-injury, and the latter predicted development of pain hypersensitivity. In contusion SCI rats, resting RR increases were less substantial but occurred at all weekly time-points. Increases in brush-evoked RR coincided with full expression of hypersensitivity at 14 (hemisection) or 21 (contusion) days after SCI, and these effects were restricted to the lowest brush speeds. Our results support the possibility that early changes in RR may convey pain information in rats.

Spinal Cord Injury Leads to Hyperoxidation and Nitrosylation of Skeletal Muscle Ryanodine Receptor-1 Associated with Upregulation of Nicotinamide Adenine Dinucleotide Phosphate Oxidase 4

Spinal cord injury (SCI) results in marked atrophy and dysfunction of skeletal muscle. There are currently no effective treatments for SCI-induced muscle atrophy or the dysfunction of the remaining muscle tissue. Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase-4 (Nox4) produces reactive oxygen species (ROS) in sarcoplasmic reticulum (SR) and has been identified as an important O2 sensor in skeletal muscle. Ryanodine receptors (RyRs) are calcium (Ca2+) channels that are responsible for Ca2+ release from SR. In skeletal muscle, type1 RyR (RyR1) is predominantly functional. RyR1 is regulated by multiple proteins, including calstabin1, which assures that they close appropriately once contraction has ceased. RyR1 function is also regulated by oxidation and redox-dependent cysteine nitrosylation. Excessive oxidation/nitrosylation of RyR1 is associated with dissociation of calstabin1 and reduced muscle force generation. However, whether Nox4 levels in skeletal muscle are elevated or whether RyR1 is oxidized or nitrosylated after SCI has not been determined. In this study, we examined Nox4 expression, oxidation/nitrolysation status, and association of calstabin1 with RyR1 in skeletal muscle derived from rats that were subjected to T4 complete transection (SCI), and observed elevated expression of Nox4 messenger RNA and protein in muscle after SCI associated with enhanced binding of Nox4 to RyR1, increased oxidation and nitrosylation of RyR1, and dissociation of calstabin1 from RyR1 in SCI rat muscle. Our data suggest that RyR1 dysfunction resulting from excessive oxidation/nitrosylation may contribute to reduced specific force after SCI and suggest that Nox4 may be the source of ROS responsible for increased oxidation and nitrosylation of RyR1.

Sternopygus macrurus electric organ transcriptome and cell size exhibit insensitivity to short-term electrical inactivity

Electrical activity is an important regulator of cellular function and gene expression in electrically excitable cell types. In the weakly electric teleost fish Sternopygus macrurus, electrocytes, i.e., the current-producing cells of the electric organ, derive from a striated muscle lineage. Mature electrocytes are larger than muscle fibers, do not contain sarcomeres, and are driven continuously at frequencies higher than those exerted on muscle cells. Previous work showed that the removal of electrical activity by spinal cord transection (ST) for two and five weeks led to an upregulation of some sarcomeric proteins and a decrease in electrocyte size. To test whether changes in gene transcription preceded these phenotypic changes, we determined the sensitivity of electrocyte gene expression to electrical inactivity periods of two and five days after ST. Whole tissue gene expression profiles using deep RNA sequencing showed minimal alterations in the levels of myogenic transcription factor and sarcomeric transcripts after either ST period. Moreover, while analysis of differentially expressed genes showed a transient upregulation of genes associated with proteolytic mechanisms at two days and an increase in mRNA levels of cytoskeletal genes at five days after electrical silencing, electrocyte size was not affected. Electrical inactivity also resulted in the downregulation of genes that were classified into enriched clusters associated with functions of axon migration and synapse structure. Overall, these data demonstrate that unlike tissues in the myogenic lineage in other vertebrate species, regulation of gene transcription and cell size in the muscle-like electrocytes of S. macrurus is highly insensitive to short-term electrical inactivity. Moreover, together with data obtained from control and long-term ST studies, the present data suggest that neural input might influence post-transcriptional processes to affect the mature electrocyte phenotype.

Effects Of treadmill training on hindlimb muscles of spinal cord-injured mice

Introduction: Treadmill training is known to prevent muscle atrophy after spinal cord injury (SCI), but the training duration required to optimize recovery has not been investigated. Methods: Hemisected mice were randomized to 3, 6, or 9 weeks of training or no training. Muscle fiber type composition and fiber cross‐sectional area (CSA) of medial gastrocnemius (MG), soleus (SOL), and tibialis anterior (TA) were assessed using ATPase histochemistry. Results: Muscle fiber type composition of SCI animals did not change with training. However, 9 weeks of training increased the CSA of type IIB and IIX fibers in TA and MG muscles. Conclusions: Nine weeks of training after incomplete SCI was effective in preventing atrophy of fast‐twitch muscles, but there were limited effects on slow‐twitch muscles and muscle fiber type composition. These data provide important evidence of the benefits of exercising paralyzed limbs after SCI. Muscle Nerve, 2016 Muscle Nerve55: 232–242, 2017

Properties of skeletal muscle in the teleost Sternopygus macrurus are unaffected by short-term electrical inactivity

Skeletal muscle is distinguished from other tissues on the basis of its shape, biochemistry, and physiological function. Based on mammalian studies, fiber size, fiber types, and gene expression profiles are regulated, in part, by the electrical activity exerted by the nervous system. To address whether similar adaptations to changes in electrical activity in skeletal muscle occur in teleosts, we studied these phenotypic properties of ventral muscle in the electric fish Sternopygus macrurus following 2 and 5 days of electrical inactivation by spinal transection. Our data show that morphological and biochemical properties of skeletal muscle remained largely unchanged after these treatments. Specifically, the distribution of type I and type II muscle fibers and the cross-sectional areas of these fiber types observed in control fish remained unaltered after each spinal transection survival period. This response to electrical inactivation was generally reflected at the transcript level in real-time PCR and RNA-seq data by showing little effect on the transcript levels of genes associated with muscle fiber type differentiation and plasticity, the sarcomere complex, and pathways implicated in the regulation of muscle fiber size. Data from this first study characterizing the acute influence of neural activity on muscle mass and sarcomere gene expression in a teleost are discussed in the context of comparative studies in mammalian model systems and vertebrate species from different lineages.

Two Experimental Strategies to Restore Muscle Mass in Adult Rats Following Spinal Cord Injury

Spinal cord injury decreases muscle mass and is associated with myofiber type trans formations in skeletal muscles. The present study evaluated the potential of motor- assisted cycling exercise or transplantation of fetal spinal cord tissue into the lesion cavity to inhibit or minimize these changes in skeletal muscles of 27 adult female Sprague-Dawley rats. Soleus (SO) and tibialis anterior (TA) muscles were studied 30 to 32 days after injury/intervention in the following groups: uninjured control ani mals (Con); spinal cord injured only (Tx); Tx with a 4-week exercise program con sisting of five weekly 60-minute sessions of cycling exercise initiated 5 days after in jury (TxEx); and Tx with fetal spinal cord tissue transplanted into the lesion cavity at the time of injury (TxTp). SO and TA muscle to body weight ratios were reduced significantly in the Tx group (24-30% decrease vs Con, p < 0.05) but were maintained with regular cycling exercise (6-8% decrease vs Con, no significant difference). The transplant had a beneficial effect on TA muscle mass (16% decrease vs Con, no sig nificant difference) but was not effective in limiting the effects of Tx on SO muscle mass. Immunohistochemistry and Northern analysis of TA and SO muscles revealed a Tx-induced reduction in myofiber cross sectional area (22% and 33% vs Con re spectively, p < 0.05) as well as a conversion in myosin heavy chain (MyHC) expres sion toward faster MyHC isoforms. Moreover, one month after injury, there was an increase in myofibers expressing more than one MyHC. mRNA encoding MyoD, a muscle-specific transcription factor, was increased in SO muscles suggesting that it may be involved in the long-term adaptations following spinal cord transection. Although cycling exercise was effective in preventing the decrease in myofiber area in both TA and SO, it did not inhibit the transformations of myofiber type. TA myofiber area was maintained in transplant recipients, however, this treatment was without conse quence on the size of SO myofibers. These results suggest that some of the normally observed spinal cord injury-induced skeletal muscle adaptations are minimized after one month of cycling exercise or fetal spinal cord tissue transplants. Key Words: Myosin heavy chain—Exercise—MyoD—Fetal tissue transplantation—Fiber types.

Combined Effects of Neurotrophin Secreting Transplants, Exercise, and Serotonergic Drug Challenge Improve Function in Spinal Rats

Objectives. To determine the effects of neurotrophin-secreting transplants combined with exercise and serotonergic drug challenges on recovery of hindlimb function in rats with midthoracic spinal cord transection injuries. Methods. Spinalized animals received transplants of fibroblasts genetically modified to express brain-derived neurotrophic factor and neurotrophin-3 and daily cycling exercise. Hindlimb movement in an open-field test (BBB) was scored weekly. Serotonin agonists were used monthly to further stimulate motor function. Axonal growth was quantified in the transplant and at L5 using immunocytochemical markers. Weights of hindlimb muscles were used to assess muscle atrophy. Results. Neurotrophin-secreting transplants stimulated axonal growth, and cycling prevented muscle atrophy, but individual treatments did not improve motor scores. Combined treatments resulted in improvements in motor function. Serotonergic agonists further improved function in all groups, and transplant groups with exercise achieved weight-supporting levels following drug treatment. Conclusion. Combined treatments, but not individual treatments, improved hindlimb function.

Proteomic and bioinformatic analyses of spinal cord injury‑induced skeletal muscle atrophy in rats

Spinal cord injury (SCI) may result in skeletal muscle atrophy. Identifying diagnostic biomarkers and effective targets for treatment is an important challenge in clinical work. The aim of the present study is to elucidate potential biomarkers and therapeutic targets for SCI‑induced muscle atrophy (SIMA) using proteomic and bioinformatic analyses. The protein samples from rat soleus muscle were collected at different time points following SCI injury and separated by two‑dimensional gel electrophoresis and compared with the sham group. The identities of these protein spots were analyzed by mass spectrometry (MS). MS demonstrated that 20 proteins associated with muscle atrophy were differentially expressed. Bioinformatic analyses indicated that SIMA changed the expression of proteins associated with cellular, developmental, immune system and metabolic processes, biological adhesion and localization. The results of the present study may be beneficial in understanding the molecular mechanisms of SIMA and elucidating potential biomarkers and targets for the treatment of muscle atrophy.

Myogenic regulatory factor (MRF) expression is affected by exercise in postnatal chicken skeletal muscles

The MyoD1, MyoG, Myf5, and Mrf4 proteins belong to the family of muscle regulatory factors (MRFs) and play important roles in skeletal muscle hyperplasia and hypertrophy. We hypothesized that exercise would affect MRF mRNA and protein abundance in postnatal chicken skeletal muscle driving molecular changes that could ultimately lead to increased muscle fiber diameter. At day (d) 43, twelve hundred chickens with similar body weight were randomly assigned to cage, pen, and free-range groups. The MRF mRNA abundance was measured in the pectoralis major and thigh muscle at d56, d70, and d84, and the protein levels of MRFs were determined from the thigh muscle at d84. The results showed no significant difference in mRNA of the MRFs among the three groups at d56 (P>0.05). At d84, chicken in the pen and free-range group showed higher MyoD1, MyoG, Myf5, and Mrf4 mRNA abundance compared to the caged chickens (P<0.05). Free-range chickens had higher Mrf4 and MyoG expression than those in penned ones (P<0.05). Protein abundances of all four factors were lowest in the caged group, and Mrf4 and MyoG protein quantities were greatest in free-range chickens (P<0.05), but Myf5 and MyoD1 protein abundance did not differ between penned and caged groups. The results suggested that exercise up-regulated MRF expression in the postnatal skeletal muscles, which led to an increase in muscle fiber diameter, and eventually affected the meat quality of the skeletal muscles in adult chickens.

Early exercise after spinal cord injury ('Switch-On'): study protocol for a randomised controlled trial

Background

Spinal cord injury (SCI) leads to a profound muscular atrophy, bone loss and bone fragility. While there is evidence that exercising paralysed muscles may lead to reversal of muscle atrophy in the chronic period after SCI, there is little evidence that exercise can prevent muscle changes early after injury. Moreover, whether exercise can prevent bone loss and microarchitectural decay is not clear.

Methods/Design

A multi-centre, parallel group, assessor-blinded randomised controlled trial will be conducted. Fifty participants with acute spinal cord injury will be recruited from four SCI units in Australia and New Zealand. Participants will be stratified by site and AIS status and randomised to an experimental or control group. Experimental participants will receive a 12-week programme of functional electrical stimulation (FES)-assisted cycling. Control participants will receive a 12-week programme of passive cycling. The primary outcome is muscle cross-sectional area of the thigh and calf measured using magnetic resonance images (MRI) of the leg. Secondary outcomes include serum biomarkers of SCI osteoporosis (sclerostin, P1NP and β-CTX), markers of immune function (IL-6, IL-10, FGF2, INF-γ, TNF-α), neurological function, body composition, depression and quality of life. Leg MRIs will be measured by a single blinded assessor based in Melbourne. Serum samples will be analysed in a central laboratory. All other characteristics will be measured at baseline and 12 weeks by blinded and trained assessors at each site. The first participant was randomised on 27 November 2012.

Discussion

The results of this trial will determine the relative effectiveness of a 12-week programme of FES-assisted cycling versus passive cycling in preventing muscle atrophy and maintaining skeletal integrity after spinal cord injury.

Trial registration

ACTRN12611001079932 (18 October 2011)

Neuronal involvement in muscular atrophy

The innervation of skeletal myofibers exerts a crucial influence on the maintenance of muscle tone and normal operation. Consequently, denervated myofibers manifest atrophy, which is preceded by an increase in sarcolemma permeability. Recently, de novo expression of hemichannels (HCs) formed by connexins (Cxs) and other none selective channels, including P2X7 receptors (P2X7Rs), and transient receptor potential, sub-family V, member 2 (TRPV2) channels was demonstrated in denervated fast skeletal muscles. The denervation-induced atrophy was drastically reduced in denervated muscles deficient in Cxs 43 and 45. Nonetheless, the transduction mechanism by which the nerve represses the expression of the above mentioned non-selective channels remains unknown. The paracrine action of extracellular signaling molecules including ATP, neurotrophic factors (i.e., brain-derived neurotrophic factor (BDNF)), agrin/LDL receptor-related protein 4 (Lrp4)/muscle-specific receptor kinase (MuSK) and acetylcholine (Ach) are among the possible signals for repression for connexin expression. This review discusses the possible role of relevant factors in maintaining the normal functioning of fast skeletal muscles and suppression of connexin hemichannel expression.

Stem cell therapy and curcumin synergistically enhance recovery from spinal cord injury

Acute traumatic spinal cord injury (SCI) is marked by the enhanced production of local cytokines and pro-inflammatory substances that induce gliosis and prevent reinnervation. The transplantation of stem cells is a promising treatment strategy for SCI. In order to facilitate functional recovery, we employed stem cell therapy alone or in combination with curcumin, a naturally-occurring anti-inflammatory component of turmeric (Curcuma longa), which potently inhibits NF-κB. Spinal cord contusion following laminectomy (T9–10) was performed using a weight drop apparatus (10 g over a 12.5 or 25 mm distance, representing moderate or severe SCI, respectively) in Sprague-Dawley rats. Neural stem cells (NSC) were isolated from subventricular zone (SVZ) and transplanted at the site of injury with or without curcumin treatment. Functional recovery was assessed by BBB score and body weight gain measured up to 6 weeks following SCI. At the conclusion of the study, the mass of soleus muscle was correlated with BBB score and body weight. Stem cell therapy improved recovery from moderate SCI, however, it had a limited effect on recovery after severe SCI. Curcumin stimulated NSC proliferation in vitro, and in combination with stem cell therapy, induced profound recovery from severe SCI as evidenced by improved functional locomotor recovery, increased body weight, and soleus muscle mass. These findings demonstrate that curcumin in conjunction with stem cell therapy synergistically improves recovery from severe SCI. Furthermore, our results indicate that the effect of curcumin extends beyond its known anti-inflammatory properties to the regulation of stem cell proliferation.

Early changes in muscle atrophy and muscle fiber type conversion after spinal cord transection and peripheral nerve transection in rats

Background

Spinal cord transection and peripheral nerve transection cause muscle atrophy and muscle fiber type conversion. It is still unknown how spinal cord transection and peripheral nerve transection each affect the differentiation of muscle fiber type conversion mechanism and muscle atrophy. The aim of our study was to evaluate the difference of muscle weight change, muscle fiber type conversion, and Peroxisome proliferator-activated receptor-γ coactivatior-1α (PGC-1α) expression brought about by spinal cord transection and by peripheral nerve transection.

Methods

Twenty-four Wistar rats underwent surgery, the control rats underwent a laminectomy; the spinal cord injury group underwent a spinal cord transection; the denervation group underwent a sciatic nerve transection. The rats were harvested of the soleus muscle and the TA muscle at 0 week, 1 week and 2 weeks after surgery. Histological examination was assessed using hematoxylin and eosin (H&E) staining and immunofluorescent staing. Western blot was performed with 3 groups.

Results

Both sciatic nerve transection and spinal cord transection caused muscle atrophy with the effect being more severe after sciatic nerve transection. Spinal cord transection caused a reduction in the expression of both sMHC protein and PGC-1α protein in the soleus muscle. On the other hand, sciatic nerve transection produced an increase in expression of sMHC protein and PGC-1α protein in the soleus muscle. The results of the expression of PGC-1α were expected in other words muscle atrophy after sciatic nerve transection is less than after spinal cord transection, however muscle atrophy after sciatic nerve transection was more severe than after spinal cord transection.

Conclusion

In the conclusion, spinal cord transection diminished the expression of sMHC protein and PGC-1α protein in the soleus muscle. On the other hand, sciatic nerve transection enhanced the expression of sMHC protein and PGC-1α protein in the soleus muscle.

Overexpression of insulin-like growth factor-1 attenuates skeletal muscle damage and accelerates muscle regeneration and functional recovery after disuse

Skeletal muscle is a highly dynamic tissue that responds to endogenous and external stimuli, including alterations in mechanical loading and growth factors. In particular, the antigravity soleus muscle experiences significant muscle atrophy during disuse and extensive muscle damage upon reloading. Given that insulin-like growth factor-1 (IGF-1) has been implicated as a central regulator of muscle repair and modulation of muscle size, we examined the effect of virally mediated overexpression of IGF-1 on the soleus muscle following hindlimb cast immobilization and upon reloading. Recombinant IGF-1 cDNA virus was injected into one of the posterior hindlimbs of the mice, while the contralateral limb was injected with saline (control). At 20 weeks of age, both hindlimbs were immobilized for 2 weeks to induce muscle atrophy in the soleus and ankle plantarflexor muscle group. Subsequently, the mice were allowed to reambulate, and muscle damage and recovery were monitored over a period of 2-21 days. The primary finding of this study was that IGF-1 overexpression attenuated reloading-induced muscle damage in the soleus muscle, and accelerated muscle regeneration and force recovery. Muscle T2 assessed by magnetic resonance imaging, a non-specific marker of muscle damage, was significantly lower in IGF-1-injected compared with contralateral soleus muscles at 2 and 5 days reambulation (P<0.05). The reduced prevalence of muscle damage in IGF-1-injected soleus muscles was confirmed on histology, with a lower fractional area of abnormal muscle tissue in IGF-1-injected muscles at 2 days reambulation (33.2±3.3 versus 54.1±3.6%, P<0.05). Evidence of the effect of IGF-1 on muscle regeneration included timely increases in the number of central nuclei (21% at 5 days reambulation), paired-box transcription factor 7 (36% at 5 days), embryonic myosin (37% at 10 days) and elevated MyoD mRNA (7-fold at 2 days) in IGF-1-injected limbs (P<0.05). These findings demonstrate a potential role of IGF-1 in protecting unloaded skeletal muscles from damage and accelerating muscle repair and regeneration.

Paraplegia increases skeletal muscle autophagy

INTRODUCTION

Paraplegia results in significant skeletal muscle atrophy through increases in skeletal muscle protein breakdown. Recent work has identified a novel SIRT1-p53 pathway that is capable of regulating autophagy and protein breakdown.

METHODS

Soleus muscle was collected from 6 male Sprague-Dawley rats 10 weeks after complete T4-5 spinal cord transection (paraplegia group) and 6 male sham-operated rats (control group). We utilized immunoblotting methods to measure intracellular proteins and quantitative real-time polymerase chain reaction to measure the expression of skeletal muscle microRNAs.

RESULTS

SIRT1 protein expression was 37% lower, and p53 acetylation (LYS379) was increased in the paraplegic rats (P < 0.05). Atg7 and Beclin-1, markers of autophagy induction, were elevated in the paraplegia group compared with controls (P < 0.05).

CONCLUSIONS

Severe muscle atrophy resulting from chronic paraplegia appears to increase skeletal muscle autophagy independent of SIRT1 signaling. We conclude that chronic paraplegia may cause an increase in autophagic cell death and negatively impact skeletal muscle protein balance.

Effect of Dipsaci Radix on Hind Limb Muscle Atrophy of Sciatic Nerve Transected Rats

It was reported that Dipsaci radix (DR) has a reinforcement effect on the bone-muscle dysfunction in the oriental medical classics and the experimental animal studies. The muscle atrophy was induced by unilateral transection of the sciatic nerve of the rats. Water-extract of DR was used as treatment once a day for 12 days. The muscle weights of the hind limb, atrophic changes, glycogen contents, compositions and cross-section areas of muscle fiber types in soleus and medial gastrocnemius were investigated. Muscle fiber type was classified to type-I and type-II with MHCf immunohistochemistry. Furthermore, Bax and Bcl-2 expressions were observed with immunohistochemiatry. DR treatment significantly increased muscle weights of soleus, medial gastrocnemius, lateral gastrocnemius, and posterior tibialis of the damaged hind limb. DR treatment reduced apoptotic muscle nuclei and hyaline-degenerated muscle fibers in soleus and medial gastrocnemius of the damaged hind limb. DR treatment also significantly increased glycogen contents in medial gastrocnemius of the damaged hind limb. DR treatment significantly attenuated the slow-to-fast shift in soleus of the damaged hind limb but not in medial gastrocnemius. DR treatment significantly increased cross-section areas of type-I and type-II fibers in soleus and medial gastrocnemius of the damaged hind limb. In soleus and medial gastrocnemius, DR treatment significantly reduced Bax positive muscle nuclei in the damaged hind limb. These results suggest that DR treatment has an anti-atrophic effect and an anti-apoptotic effect against myonuclear apoptosis induced by the peripheral nerve damage.

Characteristics of muscle fibers in rats with limb movements during sleep after spinal cord injury

BACKGROUND/AIMS

Previous studies have demonstrated that spinal cord injury (SCI) results in changes in sleep patterns through increased arousals and limb movements during sleep. Dramatic changes in muscle myosin heavy-chain isoforms have also been reported. The aim of this study was to investigate the characteristics of muscle fibers after SCI in rats with limb movements during sleep.

METHODS

Forty male Wistar rats were divided into four groups: SHAM, SCI 3, 7 and 15 days. Animals were subjected to electrode insertion surgery, 24-hour baseline sleep recording, SCI, and subsequent sleep recording for 3, 7, or 15 consecutive days. In addition, the gastrocnemius muscle and spinal cord were collected for histopathological/histochemical analyses.

RESULTS

Our results indicate a rapid and progressive decrease in the cross-sectional area of type I fibers in the gastrocnemius muscle (35.76-24.74 μm(2)) after SCI. Additionally, we found SCI-induced changes in sleep patterns. Following SCI, we also observed limb movements in sleeping rats, as well as significant negative moderate correlations between type I fibers and limb movement.

CONCLUSION

Our study strengthened the hypothesis by correlation between changes in types of muscle fiber (decline in type I fibers) and an increase in limb movements during sleep after SCI.

Acute and prolonged hindlimb exercise elicits different gene expression in motoneurons than sensory neurons after spinal cord injury

We examined gene expression in the lumbar spinal cord and the specific response of motoneurons, intermediate gray and proprioceptive sensory neurons after spinal cord injury and exercise of hindlimbs to identify potential molecular processes involved in activity dependent plasticity. Adult female rats received a low thoracic transection and passive cycling exercise for 1 or 4weeks. Gene expression analysis focused on the neurotrophic factors: brain-derived neurotrophic factor (BDNF), glial cell line-derived neurotrophic factor (GDNF), neurotrophin-3 (NT-3), neurotrophin-4 (NT-4), and their receptors because of their potential roles in neural plasticity. We also examined expression of genes involved in the cellular response to injury: heat shock proteins (HSP) -27 and -70, glial fibrillary acidic protein (GFAP) and caspases -3, -7, and -9. In lumbar cord samples, injury increased the expression of mRNA for TrkB, all three caspases and the HSPs. Acute and prolonged exercise increased expression of mRNA for the neurotrophic factors BDNF and GDNF, but not their receptors. It also increased HSP expression and decreased caspase-7 expression, with changes in protein levels complimentary to these changes in mRNA expression. Motoneurons and intermediate gray displayed little change in mRNA expression following injury, but acute and prolonged exercise increased levels of mRNA for BDNF, GDNF and NT-4. In large DRG neurons, mRNA for neurotrophic factors and their receptors were largely unaffected by either injury or exercise. However, caspase mRNA expression was increased by injury and decreased by exercise. Our results demonstrate that exercise affects expression of genes involved in plasticity and apoptosis in a cell specific manner and that these change with increased post-injury intervals and/or prolonged periods of exercise.

Care of rats with complete high-thoracic spinal cord injury

The complications of spinal cord injury (SCI) increase in number and severity with the level of injury. A recent survey of SCI researchers reveals that animal models of high SCI are essential. Despite this consensus, most laboratories continue to work with mid- or low-thoracic SCI. The available data on cervical SCI in animals characterize incomplete injuries; for example, nearly all studies published in 2009 examine discrete, tract-specific lesions that are not clinically-relevant. A primary barrier to developing animal models of severe, higher SCI is the challenge of animal care, a critical determinant of experimental outcome. Currently, many of these practices vary substantially between laboratories, and are passed down anecdotally within institutions. The care of animals with SCI is complex, and becomes much more challenging as the lesion level ascends. In our experience, the care of animals with high-thoracic (T3) SCI is much more demanding than the care of animals with low-thoracic SCI, even though both injuries result in paraplegia. We have developed an animal care regimen for rats with complete high-thoracic SCI. Our practices have been refined over the past 7 years, in collaboration with animal care centre staff and veterinarians. During this time, we have cared for more than 300 rats with T3 complete transection SCI, with experimental end-points of up to 3 months. Here we provide details of our animal care procedures, including acclimatization, housing, diet, antibiotic prophylaxis, surgical procedures, post-operative monitoring, and prevention of complications. In our laboratory, this comprehensive approach consistently produces good outcomes following T3 complete transection SCI: using body weight as an objective indicator of animal health, we have found that our rats typically return to pre-operative weights within 10 days of T3 complete SCI. It is our hope that the information provided here will improve care of experimental animals, and facilitate adoption of models that directly address the complications associated with higher level injuries.

Excitation-transcription coupling in skeletal muscle: the molecular pathways of exercise

Muscle fibres have different properties with respect to force, contraction speed, endurance, oxidative/glycolytic capacity etc. Although adult muscle fibres are normally post-mitotic with little turnover of cells, the physiological properties of the pre-existing fibres can be changed in the adult animal upon changes in usage such as after exercise. The signal to change is mainly conveyed by alterations in the patterns of nerve-evoked electrical activity, and is to a large extent due to switches in the expression of genes. Thus, an excitation-transcription coupling must exist. It is suggested that changes in nerve-evoked muscle activity lead to a variety of activity correlates such as increases in free intracellular Ca²⁺ levels caused by influx across the cell membrane and/or release from the sarcoplasmatic reticulum, concentrations of metabolites such as lipids and ADP, hypoxia and mechanical stress. Such correlates are detected by sensors such as protein kinase C (PKC), calmodulin, AMP-activated kinase (AMPK), peroxisome proliferator-activated receptor δ (PPARδ), and oxygen dependent prolyl hydroxylases that trigger intracellular signaling cascades. These complex cascades involve several transcription factors such as nuclear factor of activated T-cells (NFAT), myocyte enhancer factor 2 (MEF2), myogenic differentiation factor (myoD), myogenin, PPARδ, and sine oculis homeobox 1/eyes absent 1 (Six1/Eya1). These factors might act indirectly by inducing gene products that act back on the cascade, or as ultimate transcription factors binding to and transactivating/repressing genes for the fast and slow isoforms of various contractile proteins and of metabolic enzymes. The determination of size and force is even more complex as this involves not only intracellular signaling within the muscle fibres, but also muscle stem cells called satellite cells. Intercellular signaling substances such as myostatin and insulin-like growth factor 1 (IGF-1) seem to act in a paracrine fashion. Induction of hypertrophy is accompanied by the satellite cells fusing to myofibres and thereby increasing the capacity for protein synthesis. These extra nuclei seem to remain part of the fibre even during subsequent atrophy as a form of muscle memory facilitating retraining. In addition to changes in myonuclear number during hypertrophy, changes in muscle fibre size seem to be caused by alterations in transcription, translation (per nucleus) and protein degradation.

Impact of treadmill locomotor training on skeletal muscle IGF1 and myogenic regulatory factors in spinal cord injured rats

The objective of this study was to determine the impact of treadmill locomotor training on the expression of insulin-like growth factor I (IGF1) and changes in myogenic regulatory factors (MRFs) in rat soleus muscle following spinal cord injury (SCI). Moderate, midthoracic (T(8)) contusion SCIs were produced using a NYU (New York University) impactor. Animals were randomly assigned to treadmill training or untrained groups. Rats in the training group were trained starting at 1 week after SCI, for either 3 bouts of 20 min over 1.5 days or 10 bouts over 5 days. Five days of treadmill training completely prevented the decrease in soleus fiber size resulting from SCI. In addition, treadmill training triggered increases in IGF1, MGF and IGFBP4 mRNA expression, and a concurrent reduction of IGFBP5 mRNA in skeletal muscle. Locomotor training also caused an increase in markers of muscle regeneration, including small muscle fibers expressing embryonic myosin and Pax7 positive nuclei and increased expression of the MRFs, myogenin and MyoD. We concluded that treadmill locomotor training ameliorated muscle atrophy in moderate contusion SCI rats. Training-induced muscle regeneration and fiber hypertrophy following SCI was associated with an increase in IGF1, an increase in Pax7 positive nuclei, and upregulation of MRFs.

Non-assisted treadmill training does not improve motor recovery and body composition in spinal cord-transected mice

STUDY DESIGN

Experiments in a mouse model of complete paraplegia.

OBJECTIVES

To evaluate the effect of non-assisted treadmill training on motor recovery and body composition in completely spinal cord-transected mice.

SETTINGS

Laval University Medical Center, Neuroscience Unit, Quebec City, Quebec, Canada.

METHODS

Following a complete low-thoracic (Th9/10) spinal transection (Tx), mice were divided into two groups that were either untrained or trained with no assistance. Training consisted of placing the mice during 15 min with no further intervention (that is no tail pinching or body weight support) on a motorized treadmill (8-10 cm s(-1)) five times per week for 5 weeks. Locomotor performances were assessed weekly in both groups using two complementary locomotor rating scales. After 5 weeks, all mice were killed and adipose tissue, soleus, and extensor digitorum longus muscles were dissected for analyses.

RESULTS

No significant difference in locomotor performances or in muscle fibre type conversion was found between trained and untrained mice. In contrast, body weight, adipose tissue, whole muscle, and individual fibre cross-sectional area (CSA) values were significantly lower in trained compared with untrained animals.

CONCLUSIONS

Non-assisted treadmill training in these conditions did not improve motor performances and contributed to further accentuate body composition changes post-Tx, suggesting that assistance provided manually, robotically, or pharmacologically may be key to spinal learning and recovery of locomotor function and body composition.

Metallothionein deficiency leads to soleus muscle contractile dysfunction following acute spinal cord injury in mice

Metallothionein (MT) is a small molecular weight protein possessing metal binding and free radical scavenging properties. We hypothesized that MT-1/MT-2 null (MT(-/-)) mice would display exacerbated soleus muscle atrophy, oxidative injury, and contractile dysfunction compared with the response of wild-type (WT) mice following acute spinal cord transection (SCT). Four groups of mice were studied: WT laminectomy, WT transection, MT(-/-) laminectomy (MT(-/-) lami), and MT(-/-) transection (MT(-/-) trans). Laminectomy animals served as surgical controls. Mice in SCT groups experienced similar percent body mass (BM) losses at 7 days postinjury. Soleus muscle mass (MM) and MM-to-BM ratio were lower at 7 days postinjury in SCT vs. laminectomy mice, with no differences observed between strains. However, soleus muscles from MT(-/-) trans mice showed reduced maximal specific tension compared with MT(-/-) lami animals. Mean cross-sectional area (microm(2)) of type I and type IIa fibers decreased similarly in SCT groups compared with laminectomy controls, and no difference in fiber distribution was observed. Lipid peroxidation (4-hydroxynoneal) was greater in MT(-/-) trans vs. MT(-/-) lami mice, but protein oxidation (protein carbonyls) was not altered by MT deficiency or SCT. Expression of key antioxidant proteins (catalase, manganese, and copper-zinc superoxide dismutase) was similar between the groups. In summary, MT deficiency did not impact soleus MM loss, but resulted in contractile dysfunction and increased lipid peroxidation following acute SCT. These findings suggest a role of MT in mediating protective adaptations in skeletal muscle following disuse mediated by spinal cord injury.

Muscle after spinal cord injury

The morphological and contractile changes of muscles below the level of the lesion after spinal cord injury (SCI) are dramatic. In humans with SCI, a fiber-type transformation away from type I begins 4-7 months post-SCI and reaches a new steady state with predominantly fast glycolytic IIX fibers years after the injury. There is a progressive drop in the proportion of slow myosin heavy chain (MHC) isoform fibers and a rise in the proportion of fibers that coexpress both the fast and slow MHC isoforms. The oxidative enzymatic activity starts to decline after the first few months post-SCI. Muscles from individuals with chronic SCI show less resistance to fatigue, and the speed-related contractile properties change, becoming faster. These findings are also present in animals. Future studies should longitudinally examine changes in muscles from early SCI until steady state is reached in order to determine optimal training protocols for maintaining skeletal muscle after paralysis.

Forced exercise as a rehabilitation strategy after unilateral cervical spinal cord contusion injury

Evaluation of locomotor training after spinal cord injury (SCI) has primarily focused on hind limb recovery, with evidence of functional and molecular changes in response to exercise. Since trauma at a cervical (C) level is common in human SCI, we used a unilateral C4 contusion injury model in rats to determine whether forced exercise (Ex) would affect spinal cord biochemistry, anatomy, and recovery of fore and hind limb function. SCI was created with the Infinite Horizon spinal cord impactor device at C4 with a force of 200 Kdyne and a mean displacement of 1600-1800 microm in adult female Sprague-Dawley rats that had been acclimated to a motorized exercise wheel apparatus. Five days post-operatively, the treated group began Ex on the wheel for 20 min per day, 5 days per week for 8 weeks. Wheel speed was increased daily according to the abilities of each animal up to 14 m/min. Control rats were handled daily but were not exposed to Ex. In one set of animals experiencing 5 days of Ex, there was a moderate increase in brain-derived neurotrophic factor (BDNF) and heat shock protein-27 (HSP-27) levels in the lesion epicenter and surrounding tissue. Long-term (8 weeks) survival groups were exposed to weekly behavioral tests to assess qualitative aspects of fore limb and hind limb locomotion (fore limb scale, FLS and BBB [Basso, Beattie, and Bresnahan locomotor rating scale]), as well as sensorimotor (grid) and motor (grip) skills. Biweekly assessment of performance during wheel walking examined gross and fine motor skills. The FLS indicated a significant benefit of Ex during weeks 2-4. The BBB test showed no change with Ex at the end of the 8-week period, however hind limb grid performance was improved during weeks 2-4. Lesion size was not affected by Ex, but the presence of phagocytic and reactive glial cells was reduced with Ex as an intervention. These results suggest that Ex alone can influence the evolution of the injury and transiently improve fore and hind limb function during weeks 2-4 following a cervical SCI.

Muscle and bone plasticity after spinal cord injury: review of adaptations to disuse and to electrical muscle stimulation

The paralyzed musculoskeletal system retains a remarkable degree of plasticity after spinal cord injury (SCI). In response to reduced activity, muscle atrophies and shifts toward a fast-fatigable phenotype arising from numerous changes in histochemistry and metabolic enzymes. The loss of routine gravitational and muscular loads removes a critical stimulus for maintenance of bone mineral density (BMD), precipitating neurogenic osteoporosis in paralyzed limbs. The primary adaptations of bone to reduced use are demineralization of epiphyses and thinning of the diaphyseal cortical wall. Electrical stimulation of paralyzed muscle markedly reduces deleterious post-SCI adaptations. Recent studies demonstrate that physiological levels of electrically induced muscular loading hold promise for preventing post-SCI BMD decline. Rehabilitation specialists will be challenged to develop strategies to prevent or reverse musculoskeletal deterioration in anticipation of a future cure for SCI. Quantifying the precise dose of stress needed to efficiently induce a therapeutic effect on bone will be paramount to the advancement of rehabilitation strategies.

Nerve-dependent changes in skeletal muscle myosin heavy chain after experimental denervation and cross-reinnervation and in a demyelinating mouse model of Charcot-Marie-Tooth disease type 1A

Innervation regulates the contractile properties of vertebrate muscle fibers, in part through the effect of electrical activity on expression of distinct myosins. Herein we analyze the role of innervation in regulating the accumulation of the general, maturational, and adult forms of rodent slow myosin heavy chain (MyHC) that are defined by the presence of distinct antigenic epitopes. Denervation increases the number of fibers that express general slow MyHC, but it decreases the adult slow MyHC epitope. Cross-reinnervation of slow muscle by a fast nerve leads to an increase in the number of fibers that express fast MyHC. In both cases, there is an increase in the number of fibers that express slow and fast IIA MyHCs, but without the adult slow MyHC epitope. The data suggest that innervation is required for maturation and maintenance of diversity of both slow and fast fibers. The sequence of slow MyHC epitope transitions is a useful biomarker, and it may play a significant role during nerve-dependent changes in muscle fiber function. We applied this detailed muscle analysis to a transgenic mouse model of human motor and sensory neuropathy IA, also known as Charcot-Marie-Tooth disease type 1A (CMT1A), in which electrical conduction in some motor nerves is poor due to demyelination. The mice display atrophy of some muscle fibers and changes in slow and fast MyHC epitope expression, suggestive of a progressive increase in innervation of muscle fibers by fast motor neurons, even at early stages. The potential role of these early changes in disease pathogenesis is assessed.

Recovery of control of posture and locomotion after a spinal cord injury: solutions staring us in the face

Over the past 20 years, tremendous advances have been made in the field of spinal cord injury research. Yet, consumed with individual pieces of the puzzle, we have failed as a community to grasp the magnitude of the sum of our findings. Our current knowledge should allow us to improve the lives of patients suffering from spinal cord injury. Advances in multiple areas have provided tools for pursuing effective combination of strategies for recovering stepping and standing after a severe spinal cord injury. Muscle physiology research has provided insight into how to maintain functional muscle properties after a spinal cord injury. Understanding the role of the spinal networks in processing sensory information that is important for the generation of motor functions has focused research on developing treatments that sharpen the sensitivity of the locomotor circuitry and that carefully manage the presentation of proprioceptive and cutaneous stimuli to favor recovery. Pharmacological facilitation or inhibition of neurotransmitter systems, spinal cord stimulation, and rehabilitative motor training, which all function by modulating the physiological state of the spinal circuitry, have emerged as promising approaches. Early technological developments, such as robotic training systems and high-density electrode arrays for stimulating the spinal cord, can significantly enhance the precision and minimize the invasiveness of treatment after an injury. Strategies that seek out the complementary effects of combination treatments and that efficiently integrate relevant technical advances in bioengineering represent an untapped potential and are likely to have an immediate impact. Herein, we review key findings in each of these areas of research and present a unified vision for moving forward. Much work remains, but we already have the capability, and more importantly, the responsibility, to help spinal cord injury patients now.

Role of MyoD in denervated, disused, and exercised muscle

The myogenic regulatory factor MyoD plays an important role in embryonic and adult skeletal muscle growth. Even though it is best known as a marker for activated satellite cells, it is also expressed in myonuclei, and its expression can be induced by a variety of different conditions. Several model systems have been used to study the mechanisms behind MyoD regulation, such as exercise, stretch, disuse, and denervation. Since MyoD reacts in a highly muscle-specific manner, and its expression varies over time and between species, universally valid predictions and explanations for changes in MyoD expression are not possible. This review explores the complex role of MyoD in muscle plasticity by evaluating the induction of MyoD expression in the context of muscle composition and electrical and mechanical stimulation.

Treadmill training after spinal cord hemisection in mice promotes axonal sprouting and synapse formation and improves motor recovery

Treadmill training with weight-support is a therapeutic strategy used in human patients after spinal cord injury (SCI). Exercise leads to locomotor improvement in a variety of animal models; however, the effect of exercise on axonal regrowth has not been directly examined. This study used several locomotor tests, including kinematic gait analysis, to analyze the differences between treadmill-trained and untrained mice in the usage of their paretic hindlimb following a low thoracic hemisection. Analysis of muscle atrophy, anterograde axonal tracing and expression of the synaptic markers synaptophysin and PSD95 were used to correlate observed behavioural changes with anatomical data. Treadmill trained mice showed significant improvement in use of their paretic hindlimb after 4 weeks of exercise compared to untrained mice in an open field locomotor test (Basso-Beattie-Bresnahan [BBB] scale), grid walking and climbing and inter-limb coordination tests. Movement of their hip joint started to approximate the pattern of intact mice, with concomitant use of their ankle. Unlike untrained mice, exercised mice showed decreased muscle atrophy, increased axonal regrowth and collateral sprouting proximal to the lesion site, with maintenance of synaptic markers on motor neurons in the ventral horn. However, there was no axonal regeneration into or across the lesion site indicating that the improved behaviour may have been, at least in part, due to enhanced neural activity above the lesion site.

Slow- and fast-twitch rat hind limb skeletal muscle phenotypes 8 months after spinal cord transection and olfactory ensheathing glia transplantation

Paralysed skeletal muscle of rats with spinal cord injury (SCI) undergoes atrophy and a switch in gene expression pattern which leads to faster, more fatigable phenotypes. Olfactory ensheathing glia (OEG) transplants have been reported to promote axonal regeneration and to restore sensory-motor function in animals with SCI. We hypothesized that OEG transplants could attenuate skeletal muscle phenotypic deterioration and that this effect could underlie the functional recovery observed in behavioural tests. A variety of morphological, metabolic and molecular markers were assessed in soleus (SOL) and extensor digitorum longus (EDL) muscles of spinal cord transected (SCT), OEG-transplanted rats 8 months after the intervention and compared with non-transplanted SCT rats and sham-operated (without SCT) controls (C). A multivariate analysis encompassing all the parameters indicated that OEG-transplanted rats displayed skeletal muscle phenotypes intermediate between non-transplanted and sham-operated controls, but different from both. A high correlation was observed between behaviourally tested sensory-motor functional capacity and expression level of slow- and fast-twitch hind limb skeletal muscle phenotypic markers, particularly the histochemical glycerol-3-phosphate dehydrogenase activity (-0.843, P < 0.0001) and the fraction of variant 2s of the slow regulatory myosin light chain isoform (0.848, P < 0.0001) in SOL. Despite the mean overall effect of OEG transplants in patterning skeletal muscle protein expression towards normal, in 6 out of 9 animals they appeared insufficient to overcome fibre type switching and to support a consistent and generalized long-term maintenance of normal skeletal muscle characteristics. The interplay of OEG and exercise-mediated neurotrophic actions is a plausible mechanism underlying OEG transplantation effects on paralysed skeletal muscle.

Spinal cord injury: present and future therapeutic devices and prostheses

A range of passive and active devices are under development or are already in clinical use to partially restore function after spinal cord injury (SCI). Prosthetic devices to promote host tissue regeneration and plasticity and reconnection are under development, comprising bioengineered bridging materials free of cells. Alternatively, artificial electrical stimulation and robotic bridges may be used, which is our focus here. A range of neuroprostheses interfacing either with CNS or peripheral nervous system both above and below the lesion are under investigation and are at different stages of development or translation to the clinic. In addition, there are orthotic and robotic devices which are being developed and tested in the laboratory and clinic that can provide mechanical assistance, training or substitution after SCI. The range of different approaches used draw on many different aspects of our current but limited understanding of neural regeneration and plasticity, and spinal cord function and interactions with the cortex. The best therapeutic practice will ultimately likely depend on combinations of these approaches and technologies and on balancing the combined effects of these on the biological mechanisms and their interactions after injury. An increased understanding of plasticity of brain and spinal cord, and of the behavior of innate modular mechanisms in intact and injured systems, will likely assist in future developments. We review the range of device designs under development and in use, the basic understanding of spinal cord organization and plasticity, the problems and design issues in device interactions with the nervous system, and the possible benefits of active motor devices.

Time-dependent changes in caspase-3 activity and heat shock protein 25 after spinal cord transection in adult rats

Chronic reductions in muscle activation and loading are associated with decreased heat shock protein 25 (Hsp25) expression and phosphorylation (pHsp25) which, in turn, may contribute to elevated caspase-3-mediated muscle protein breakdown. Thus, the purpose of the present study was to determine whether there are any changes in Hsp25, pHsp25 and caspase-3 activity among rat muscles having different fibre type compositions and functions [soleus, adductor longus (AL), plantaris and tibialis anterior (TA)] at 0 (control), 1, 8 or 28 days after a complete spinal cord transection (ST). The Hsp25 levels were unaffected on days 1 and 8 in all muscles, except for a significant reduction on day 8 in plantaris. The Hsp25 levels were lower than control values in all muscles except TA on day 28. The pHsp25 levels were lower than control values after 8 and 28 days in plantaris and AL and after 28 days in soleus, but higher than control in TA after 8 and 28 days. Caspase-3 activity was higher in ST than control rats on day 8 in all muscles except TA. Caspase-3 activity was negatively correlated with muscle mass for all muscles. In plantaris, Hsp25 and pHsp25 were negatively correlated with caspase-3 activity and Hsp25 was correlated with muscle mass. These relationships were not observed in other muscles. Thus, the effects of ST on Hsp25 and caspase-3 are muscle specific and time dependent, factors that should be considered in developing any intervention to maintain muscle mass after a spinal cord injury.

Chronic paraplegia-induced muscle atrophy downregulates the mTOR/S6K1 signaling pathway

Ribosomal S6 kinase 1 (S6K1) is a downstream component of the mammalian target of rapamycin (mTOR) signaling pathway and plays a regulatory role in translation initiation, protein synthesis, and muscle hypertrophy. AMP-activated protein kinase (AMPK) is a cellular energy sensor, a negative regulator of mTOR, and an inhibitor of protein synthesis. The purpose of this study was to determine whether the hypertrophy/cell growth-associated mTOR pathway was downregulated during muscle atrophy associated with chronic paraplegia. Soleus muscle was collected from male Sprague-Dawley rats 10 wk following complete T(4)-T(5) spinal cord transection (paraplegic) and from sham-operated (control) rats. We utilized immunoprecipitation and Western blotting techniques to measure upstream [AMPK, Akt/protein kinase B (PKB)] and downstream components of the mTOR signaling pathway [mTOR, S6K1, SKAR, 4E-binding protein 1 (4E-BP1), and eukaryotic initiation factor (eIF) 4G and 2alpha]. Paraplegia was associated with significant soleus muscle atrophy (174 +/- 8 vs. 240 +/- 13 mg; P < 0.05). There was a reduction in phosphorylation of mTOR, S6K1, and eIF4G (P < 0.05) with no change in Akt/PKB or 4E-BP1 (P > 0.05). Total protein abundance of mTOR, S6K1, eIF2alpha, and Akt/PKB was decreased, and increased for SKAR (P < 0.05), whereas 4E-BP1 and eIF4G did not change (P > 0.05). S6K1 activity was significantly reduced in the paraplegic group (P < 0.05); however, AMPKalpha2 activity was not altered (3.5 +/- 0.4 vs. 3.7 +/- 0.5 pmol x mg(-1) x min(-1), control vs. paraplegic rats). We conclude that paraplegia-induced muscle atrophy in rats is associated with a general downregulation of the mTOR signaling pathway. Therefore, in addition to upregulation of atrophy signaling during muscle wasting, downregulation of muscle cell growth/hypertrophy-associated signaling appears to be an important component of long-term muscle loss.

Effects of chronic spinal cord injury on body weight and body composition in rats fed a standard chow diet

The inability to maintain body weight within prescribed ranges occurs in a significant portion of the human spinal cord injury (SCI) population. Using a rodent model of long-term high thoracic (spinal level T3) spinal cord transection (TX), we aimed to identify derangements in body weight, body composition, plasma insulin, glucose tolerance, and metabolic function, as measured by uncoupling protein 1 (UCP1) expression in interscapular brown adipose tissue (IBAT). Sixteen weeks after SCI, body weights of injured female rats stabilized and were significantly lower than surgical control animals. At the same time point, SCI rats had a significantly lower whole body fat:lean tissue mass ratio than controls, as measured indirectly by NMR. Despite lower body weight and fat mass, the cumulative consumption of standard laboratory chow (4.0 kcal/g) and mean energy intake (kcal.day(-1).100 g body wt(-1)) of chronic SCI rats was significantly more than controls. Glucose tolerance tests indicated a significant enhancement in glucose handling in 16-wk SCI rats, which were coupled with lower serum insulin levels. The post mortem weight of gonadal and retroperitoneal fat pads was significantly reduced after SCI and IBAT displayed significantly lower real-time PCR expression of UCP1 mRNA. The reduced fat mass and IBAT UCP1 mRNA expression are contraindicative of the cumulative caloric intake by the SCI rats. The prolonged postinjury loss of body weight, including fat mass, is not due to hypophagia but possibly to permanent changes in gastrointestinal transit and absorption, as well as whole body homeostatic mechanisms.

Transplantation of porous tubes following spinal cord transection improves hindlimb function in the rat

STUDY DESIGN

Experimental.

OBJECTIVE

To determine the effects of a porous tube transplant in spinal cord transected rats.

SETTING

Acadia University, Wolfville, Nova Scotia, Canada.

METHODS

Female rats were randomly assigned to three experimental groups: control (Con, n=8), spinal cord transected (Tx, n=5) and spinal cord transected with transplant (TxTp, n=7). The rats in the TxTp and Tx groups received a complete spinal cord transection at the T10 level and the TxTp group immediately received a porous tube transplant.

RESULTS

Locomotor activity rated on the Basso, Beattie, Bresnahan scale improved significantly in the TxTp animals over the 4 weeks such that final scores were 21, 1.4 and 7.1 for the Con, Tx and TxTp groups, respectively. As expected, the muscle to body mass ratios of the hindlimb skeletal muscles of the Tx group were decreased (soleus 35%, plantaris 29% and gastrocnemius 29%) and this was also observed in the TxTp group (soleus 33%, plantaris 23% and gastrocnemius 30%). Cytochrome c oxidase (CYTOX) activity in the plantaris was decreased by Tx but maintained in the TxTp group (Con=82.2, Tx=44.8 and TxTp=72.8 U/min/g).

CONCLUSION

Four weeks after the spinal cord transection, plantaris CYTOX activity and locomotor function improved with porous tube implantation.

SPONSORSHIP

Natural Sciences and Engineering Research Council.

Alterations in mRNA expression and protein products following spinal cord injury in humans

We examined the effects of spinal cord injury (SCI) on alterations in gene expression and respective protein products in human skeletal muscle 2 days and 5 days post-SCI. Biopsies were taken from skeletal muscle of 9 men and 1 woman (n = 10) (43.9 +/- 6.7 years) 2 days and 5 days post-SCI and from 5 healthy young men who served as controls (20.4 +/- 0.5 years). Global changes in gene expression were analysed using Affymetrix GeneChips on a subsample of subjects (n = 3). Candidate genes were then pursued via qRT-PCR. Western blotting (WB) was used to quantify protein products of candidate genes. Immunohistochemistry (IHC) was used to localize proteins. Groups of transcripts showing the greatest percentage of altered expression, the most robust fold-changes, and indicative of involvement of an entire pathway using the GeneChip included genes involved in the ubiquitin proteasome pathway (UPP), metallothionein function, and protease inhibition. qRT-PCR analysis confirmed increases in gene expression for UPP components (UBE3C, Atrogin-1, MURF1, and PSMD11), the metallothioneins (MT1A, MT1F, MT1H), and the protease inhibitor, SLPI (P < 0.05) at 2 days and 5 days post-SCI. Protein levels of the proteasome subunit (PSMD11) and the metallothioneins were increased 5 days post-SCI. Protein levels of UBE3C, Atrogin-1, MURF1 and SLPI were unchanged (P > 0.05). IHC showed increased staining for PSMD11 and the metallothioneins 5 days post-SCI, along the peripheral region of the cells. IHC also showed altered staining for Atrogin-1 at 5 days post-SCI along the membrane region. Thus, there was a profound increase in gene expression of UPP components, the metallothioneins, and the protease inhibitor, SLPI, within 5 days of SCI. Increased protein levels for PSMD11 and the metallothioneins 5 days post-SCI, specifically along the cell periphery, indicate that proteins in this region may be early targets for degradation post-SCI.

Satellite cells express distinct patterns of myogenic proteins in immature skeletal muscle

Satellite cells are the myogenic cells lying between the myofiber sarcolemma and basal lamina. The objective of this study was to determine the expression patterns of MyoD, myogenin, and Pax7 within the satellite cell population in the growing rat soleus and extensor digitorum longus (EDL) muscles. Secondly, the expression of the myogenic markers was also studied within the interstitial cell compartment and myonuclei. It was discovered that the soleus contained a higher number of Pax7, MyoD, or myogenin-positive nuclei compared with the EDL. Similarly, myogenin was expressed at a lower level in the myonuclei of the soleus compared with the EDL, and myogenin was expressed at a higher level in the interstitial compartment of the soleus compared with the EDL. When interstitial nuclei, myonuclei, and double-labeled nuclei were used in the estimate of the satellite cell population, it was discovered that approximately of 13% of the myofibers in a transverse section of the soleus muscle and 4.1% of EDL myofibers exhibit a labeled satellite cell nucleus. Overall, results from this study suggest that expression patterns of these markers vary predictably among muscles with different growth dynamics and phenotypic characteristics.

Changes in soleus muscle function and fiber morphology with one week of locomotor training in spinal cord contusion injured rats

The purpose of this study is two-fold: (1) to examine skeletal muscle function in a rat model of midthoracic contusion spinal cord injury (SCI) and (2) to evaluate the therapeutic influence of a short bout (1 week) of treadmill locomotor training on soleus muscle function (peak force, fatigability, contractile properties, fiber types), size (fiber area), and motor deficit and recovery (BBB scores) after SCI. The rats were injured with a moderate T8 spinal cord contusion and were assigned to either receive treadmill locomotor training (TM), starting 1 week after SCI for 5 consecutive days (20 min/trial, 2 trials/day) or not to receive any exercise intervention (no TM). Locomotor training resulted in a significant improvement in overall locomotor function (32% improvement in BBB scores) when compared to no TM. Also, the injured animals that trained for 1 week had 38% greater peak soleus tetanic forces (p < 0.05), a 9% decrease in muscle fatigue (p < 0.05), 23% larger muscle fiber CSA (p < 0.05), and decreased immunoexpression of fast heavy chain fiber types than did rats receiving no TM. In addition, there was a good correlation (0.704) between the BBB scores of injured animals and peak soleus muscle force regardless of group assignment. No significant differences were seen in twitch or time to peak tension values across groups. Collectively, these results indicate that 1 week of treadmill locomotor training, initiated early after SCI, can significantly improve motor recovery following SCI. The magnitude of these changes is remarkable considering the relatively short training interval and clearly illustrates the potential that initiating treadmill locomotor training shortly after injury may have on countering some of the functional deficits resulting from SCI.