Regeneration of reinnervated rat soleus muscle is accompanied by fiber transition toward a faster phenotype

An Overview of the Molecular Cues and Their Intracellular Signaling Shared by Cancer and the Nervous System: From Neurotransmitters to Synaptic Proteins, Anatomy of an All-Inclusive Cooperation

We propose an overview of the molecular cues and their intracellular signaling involved in the crosstalk between cancer and the nervous system. While "cancer neuroscience" as a field is still in its infancy, the relation between cancer and the nervous system has been known for a long time, and a huge body of experimental data provides evidence that tumor-nervous system connections are widespread. They encompass different mechanisms at different tumor progression steps, are multifaceted, and display some intriguing analogies with the nervous system's physiological processes. Overall, we can say that many of the paradigmatic "hallmarks of cancer" depicted by Weinberg and Hanahan are affected by the nervous system in a variety of manners.

Simvastatin Enhances Muscle Regeneration Through Autophagic Defect-Mediated Inflammation and mTOR Activation in G93ASOD1 Mice

Amyotrophic lateral sclerosis is a fatal neurodegenerative disease characterised by the selective loss of motor neurons, muscular atrophy, and degeneration. Statins, as 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors, are the most widely prescribed drugs to lower cholesterol levels and used for the treatment of cardiovascular and cerebrovascular diseases. However, statins are seldom used in muscular diseases, primarily because of their rare statin-associated myopathy. Recently, statins have been shown to reduce muscular damage and improve its function. Here, we investigated the role of statins in myopathy using G93ASOD1 mice. Our results indicated that simvastatin significantly increased the autophagic flux defect and increased inflammation in the skeletal muscles of G93ASOD1 mice. We also found that increased inflammation correlated with aggravated muscle atrophy and fibrosis. Nevertheless, long-term simvastatin treatment promoted the regeneration of damaged muscle by activating the mammalian target of rapamycin pathway. However, administration of simvastatin did not impede vast muscle degeneration and movement dysfunction resulting from the enhanced progressive impairment of the neuromuscular junction. Together, our findings highlighted that simvastatin exacerbated skeletal muscle atrophy and denervation in spite of promoting myogenesis in damaged muscle, providing new insights into the selective use of statin-induced myopathy in ALS.

Muscle atrophy and regeneration associated with behavioural loss and recovery of function after sciatic nerve crush

AIM

To resolve timing and coordination of denervation atrophy and the re-innervation recovery process to discern correlations indicative of common programs governing these processes.

METHODS

Female Sprague-Dawley (SD) rats had a unilateral sciatic nerve crush. Based on longitudinal behavioural observations, the triceps surae muscle was analysed at different time points post-lesion.

RESULTS

Crush results in a loss of muscle function and mass (-30%) followed by a recovery to almost pre-lesion status at 30 days post-crush (dpc). There was no loss of fibres nor any significant change in the number of nuclei per fibre but a shift in fibres expressing myosins I and II that reverted back to control levels at 30 dpc. A residual was the persistence of hybrid fibres. Early on a CHNR -ε to -γ switch and a re-expression of embryonic MyHC showed as signs of denervation. Foxo1, Smad3, Fbxo32 and Trim63 transcripts were upregulated but not Myostatin, InhibinA and ActivinR2B. Combined this suggests that the mechanism instigating atrophy provides a selectivity of pathway(s) activated. The myogenic differentiation factors (MDFs: Myog, Myod1 and Myf6) were upregulated early on suggesting a role also in the initial atrophy. The regulation of these transcripts returned towards baseline at 30 dpc. The examined genes showed a strong baseline covariance in transcript levels which dissolved in the response to crush driven mainly by the MDFs. At 30 dpc the naïve expression pattern was re-established.

CONCLUSION

Peripheral nerve crush offers an excellent model to assess and interfere with muscle adaptions to denervation and re-innervation.

The expression of aquaporin-4 is regulated based on innervation in skeletal muscles

Aquaporin-4 (AQP4) is a selective water channel, which expresses on the plasma membrane of myofibers and regulates the osmotic pressure, energy metabolism and morphological changes in myofibers by modulating water transport across sarcolemma in skeletal muscles. Although the physiological roles of AQP4 have been gradually clarified in skeletal muscles, the regulatory mechanisms of AQP4 expression have been poorly understood in skeletal muscles. Recently, it was reported that the expression of AQP4 decreased in atrophied skeletal muscles following sciatic nerve transection, but not tail-suspension. Therefore, expecting that the nerve supply to myofibers would be one of the major regulatory factors regulating AQP4 expression in skeletal muscles, we investigated whether the expression patterns of AQP4 were changed in skeletal muscles by denervation and subsequent reinnervation. As a result, while the APQ4 expression levels were significantly decreased by sciatic nerve freezing-induced denervation, subsequently the expression levels of AQP4 were fully restored during reinnervation in skeletal muscles (p < 0.05, respectively). On the other hand, the expression levels of α1-syntrophin and AQP1, which are respectively structural and functional related AQP4 factors, were stably maintained during the denervation and subsequent reinnervation. Therefore, the present study demonstrated that the expression of AQP4 may be regulated depending on the innervation to skeletal muscles. Moreover, AQP4 regulatory mechanisms may be fundamentally different to those of AQP1 in skeletal muscles.

Terminal Schwann Cells Lead Synapse Remodelling following Injury(1,2)

This commentary article describes the importance and significance of the article recently published by the Kang and colleagues in The Journal of Neuroscience in 2014. Kang and colleagues provided new features of injury induced synapse remodelling.

Biomaterial-based delivery for skeletal muscle repair

Skeletal muscle possesses a remarkable capacity for regeneration in response to minor damage, but severe injury resulting in a volumetric muscle loss can lead to extensive and irreversible fibrosis, scarring, and loss of muscle function. In early clinical trials, the intramuscular injection of cultured myoblasts was proven to be a safe but ineffective cell therapy, likely due to rapid death, poor migration, and immune rejection of the injected cells. In recent years, appropriate therapeutic cell types and culturing techniques have improved progenitor cell engraftment upon transplantation. Importantly, the identification of several key biophysical and biochemical cues that synergistically regulate satellite cell fate has paved the way for the development of cell-instructive biomaterials that serve as delivery vehicles for cells to promote in vivo regeneration. Material carriers designed to spatially and temporally mimic the satellite cell niche may be of particular importance for the complete regeneration of severely damaged skeletal muscle.

Carbon-nanotube-interfaced glass fiber scaffold for regeneration of transected sciatic nerve

Carbon nanotubes (CNTs), with their unique and unprecedented properties, have become very popular for the repair of tissues, particularly for those requiring electrical stimuli. Whilst most reports have demonstrated in vitro neural cell responses of the CNTs, few studies have been performed on the in vivo efficacy of CNT-interfaced biomaterials in the repair and regeneration of neural tissues. Thus, we report here for the first time the in vivo functions of CNT-interfaced nerve conduits in the regeneration of transected rat sciatic nerve. Aminated CNTs were chemically tethered onto the surface of aligned phosphate glass microfibers (PGFs) and CNT-interfaced PGFs (CNT-PGFs) were successfully placed into three-dimensional poly(L/D-lactic acid) (PLDLA) tubes. An in vitro study confirmed that neurites of dorsal root ganglion outgrew actively along the aligned CNT-PGFs and that the CNT interfacing significantly increased the maximal neurite length. Sixteen weeks after implantation of a CNT-PGF nerve conduit into the 10 mm gap of a transected rat sciatic nerve, the number of regenerating axons crossing the scaffold, the cross-sectional area of the re-innervated muscles and the electrophysiological findings were all significantly improved by the interfacing with CNTs. This first in vivo effect of using a CNT-interfaced scaffold in the regeneration process of a transected rat sciatic nerve strongly supports the potential use of CNT-interfaced PGFs at the interface between the nerve conduit and peripheral neural tissues.

Volitional Weight-Lifting in Rats Promotes Adaptation via Performance and Muscle Morphology prior to Gains in Muscle Mass

Investigation of volitional animal models of resistance training has been instrumental in our understanding of adaptive training. However, these studies have lacked reactive force measurements, a precise performance measure, and morphological analysis at a distinct phase of training - when initial strength gains precede muscle hypertrophy. Our aim was to expose rats to one month of training (70 or 700 g load) on a custom-designed weight-lifting apparatus for analysis of reactive forces and muscle morphology prior to muscle hypertrophy. Exclusively following 700 g load training, forces increased by 21% whereas muscle masses remained unaltered. For soleus (SOL) and tibialis anterior (TA) muscles, 700 g load training increased muscle fiber number per unit area by ∼20% and decreased muscle fiber area by ∼20%. Additionally, number of muscle fibers per section increased by 18% for SOL muscles. These results establish that distinct morphological alterations accompany early strength gains in a volitional animal model of load-dependent adaptive resistance training.

Improvement of contraction force in injured skeletal muscle after autologous mesenchymal stroma cell transplantation is accompanied by slow to fast fiber type shift

BACKGROUND

Skeletal muscle trauma leads to severe functional deficits, which cannot be addressed by current treatment options. Previous investigation could show the efficacy of a local transplantation (TX) of mesenchymal stroma cells (MSCs) for the therapy of muscle injury. Underlying mechanisms remain to be elucidated. The aim of the present work was to characterize the fiber composition changes following MSC-TX after open crush injury.

METHODS

20 male SD rats received an open crush trauma of the left soleus muscle. 2.5 × 10(6) autologous MSCs were transplanted into the crushed soleus muscle of 10 animals 7 days after trauma (group 1, n = 10). Control animals received an injection of saline solution (group 2, n = 10). Histologic analysis of fibrosis, fiber type composition, and muscle force measurements were performed 28 days after trauma.

RESULTS

MSC-TX improved muscle force significantly (fast-twitch, treated: 0.76 (0.51-1.15), untreated: 0.45 (0.32-0.73); p = 0.01). Tetanic stimulation resulted in a significant increase of force development (treated: 0.63 (0.4-1.21), untreated: 0.34 (0.16-0.48); p = 0.04). Histological analyses showed no differences in the amount of fibrotic tissue (treated vs. untreated, p = 0.42). A shift towards fastMHC-positive fibers was observed following MSC-TX (treated vs. untreated; p = 0.01 (mm(2)) or 0.007 (%)).

CONCLUSION

This study demonstrated an effect of locally administered MSCs in the treatment of skeletal muscle injuries on a structural level. For the first time a fiber type shift towards fastMHC following MSC-TX after crush injury could be demonstrated and related to MSC-TX. These results might open the discussion of an alternative mode of action of MSCs in tissue regeneration.

Acceleration of myofiber formation in culture by a digitized synaptic signal

Developing myofibers require chemical and electrical stimulation to induce functional muscle tissue. Tissue engineering protocols utilize either or both of these to initiate differentiation ex vivo. Current methodologies typically deliver multi-volt electrical signals, which may be hazardous to developing tissues. In attempts to mimic in vivo muscle development, we stimulated cultured muscle precursor cells with a low-voltage (1 mV) digitized synaptic signal derived from cultured cortical neurons. This synaptic signal induced larger and more adherent myofibers, along with markers of myoblast differentiation, compared to those induced following stimulation with a conventional (28 V) square signal. These findings suggest that stimulation with a digitized synaptic signal may be useful in tissue engineering and physical therapy.

Effects of nandrolone on recovery after neurotization of chronically denervated muscle in a rat model

OBJECT

Suboptimal recovery following repair of major peripheral nerves has been partially attributed to denervation atrophy. Administration of anabolic steroids in conjunction with neurotization may improve functional recovery of chronically denervated muscle. The purpose of this study was to evaluate the effect of the administration of nandrolone on muscle recovery following prolonged denervation in a rat model.

METHODS

Eight groups of female Sprague-Dawley rats (15 rats per group, 120 in all) were divided into 3- or 6-month denervated hind limb and sham surgery groups and, then, nandrolone treatment groups and sham treatment groups. Evaluation of treatment effects included nerve conduction, force of contraction, comparative morphology, histology (of muscle fibers), protein electrophoresis (for muscle fiber grouping), and immunohistochemical evaluation.

RESULTS

Although a positive trend was noted, neither reinnervated nor normal muscle showed a statistically significant increase in peak muscle force following nandrolone treatment. Indirect measures, including muscle mass (weight and diameter), muscle cell size, muscle fiber type, and satellite cell counts, all failed to support significant anabolic effect.

CONCLUSIONS

There does not seem to be a functional benefit from nandrolone treatment following reinnervation of either mild or moderately atrophic muscle (related to prolonged denervation) in a rodent model.

Effects of treadmill training on functional recovery following peripheral nerve injury in rats

Exercise, in the form of moderate daily treadmill training following nerve transection and repair leads to enhanced axon regeneration, but its effect on functional recovery is less well known. Female rats were exercised by walking continuously, at a slow speed (10 m/min), for 1 h/day on a level treadmill, beginning 3 days after unilateral transection and surgical repair of the sciatic nerve, and conducted 5 days/wk for 2 wk. In Trained rats, both direct muscle responses to tibial nerve stimulation and H reflexes in soleus reappeared earlier and increased in amplitude more rapidly over time than in Untrained rats. The efficacy of the restored H reflex was greater in Trained rats than in Untrained controls. The reinnervated tibialis anterior and soleus were coactivated during treadmill locomotion in Untrained rats. In Trained animals, the pattern of activation of soleus, but not tibialis anterior, was not significantly different from that found in Intact rats. The overall length of the hindlimb during level and up- and downslope locomotion was conserved after nerve injury in both groups. This conservation was achieved by changes in limb orientation. Limb length was conserved effectively in all rats during downslope walking but only in Trained rats during level and upslope walking. Moderate daily exercise applied immediately after sciatic nerve transection is sufficient to promote axon regeneration, to restore muscle reflexes, and to improve the ability of rats to cope with different biomechanical demands of slope walking.

Gas7-deficient mouse reveals roles in motor function and muscle fiber composition during aging

Background

Growth arrest-specific gene 7 (Gas7) has previously been shown to be involved in neurite outgrowth in vitro; however, its actual role has yet to be determined. To investigate the physiological function of Gas7 in vivo, here we generated a Gas7-deficient mouse strain with a labile Gas7 mutant protein whose functions are similar to wild-type Gas7.

Methodology/Principal Findings

Our data show that aged Gas7-deficient mice have motor activity defects due to decreases in the number of spinal motor neurons and in muscle strength, of which the latter may be caused by changes in muscle fiber composition as shown in the soleus. In cross sections of the soleus of Gas7-deficient mice, gross morphological features and levels of myosin heavy chain I (MHC I) and MHC II markers revealed significantly fewer fast fibers. In addition, we found that nerve terminal sprouting, which may be associated with slow and fast muscle fiber composition, was considerably reduced at neuromuscular junctions (NMJ) during aging.

Conclusions/Significance

These findings indicate that Gas7 is involved in motor neuron function associated with muscle strength maintenance.

Decrease of MMP-9 activity improves soleus muscle regeneration

The regeneration of skeletal muscles relies on the function of satellite cells that are quiescent myogenic precursors associated with adult skeletal muscle fibers. Upon injury, the satellite cells are activated, divide extensively, and differentiate into new myofibers. These events are accompanied by the remodeling of the surrounding extracellular matrix, which is mediated by variety of factors, including matrix metalloproteinases (MMPs). Regeneration of certain type of muscles, such as Soleus slow twitch muscle, is often inefficient and hindered by the development of fibrosis. Here, we studied the effect of inhibition of MMP-9 and MMP-2 activity on the Soleus muscle regeneration in vivo and on the in vitro differentiation of myoblasts derived from this muscle. Using in situ and in-gel zymography, we tested the activity of these two MMPs in vivo, during regeneration of the muscle, and in vitro, during differentiation of the myoblasts. We also analyzed the histology of regenerating muscles and morphology of differentiating myoblasts. All these analyses showed that treatment with doxycycline and anti-MMP-9, but not MMP-2 antibody, significantly improved Soleus muscle regeneration and ameliorated development of excessive fibrosis, as well as delayed myoblast proliferation and differentiation in vitro.

Regeneration of skeletal muscle

Skeletal muscle has a robust capacity for regeneration following injury. However, few if any effective therapeutic options for volumetric muscle loss are available. Autologous muscle grafts or muscle transposition represent possible salvage procedures for the restoration of mass and function but these approaches have limited success and are plagued by associated donor site morbidity. Cell-based therapies are in their infancy and, to date, have largely focused on hereditary disorders such as Duchenne muscular dystrophy. An unequivocal need exists for regenerative medicine strategies that can enhance or induce de novo formation of functional skeletal muscle as a treatment for congenital absence or traumatic loss of tissue. In this review, the three stages of skeletal muscle regeneration and the potential pitfalls in the development of regenerative medicine strategies for the restoration of functional skeletal muscle in situ are discussed.

Inflammatory Myopathy with Severe Tongue Atrophy in Pembroke Welsh Corgi Dogs

A disease characterized by tongue and facial muscle atrophy has been recognized sporadically among Pembroke Welsh Corgi (PWC) dogs in Japan. The present study describes the pathologic findings of this canine syndrome. Histopathologic examinations were performed in 2 dogs, including a case of muscular biopsy. Identification and characterization of autoantibodies were attempted by fluorescent antibody test (FAT) and Western blot (WB) by using sera from 7 PWC dogs with typical clinical features, 6 PWC dogs with other clinical signs, and 2 from other breeds with polymyositis. Clinically, the 7 affected PWC dogs exhibited dysphagia with severe tongue atrophy, facial muscular atrophy, and occasional walking difficulty. Histopathologic examinations of the 2 dogs with clinical symptoms revealed moderate to severe inflammatory lesions characterized by lymphohistiocytic infiltration and muscular atrophy in the tongue and/or femoral muscles. The tongue lesions were very severe and accompanied by diffuse fatty infiltration. There were no major lesions in the nervous tissues examined. By FAT, an autoantibody against the cross striation of skeletal muscle was detected in sera from 5 affected PWC dogs. By using WB analysis, the autoantibodies recognized a 42-kDa molecule in striated muscle but not in the nervous tissues. All of the findings indicated that the unique disease of PWC dogs might be generalized inflammatory myopathy, whereas the detailed etiology concerning the dominant involvement of tongue muscles and the role of the autoantibody in the canine disease remain to be clarified.

Xenogeneic extracellular matrix as an inductive scaffold for regeneration of a functioning musculotendinous junction

The prevailing dogma in tissue engineering is cell-centric. One shortcoming of this approach is the failure to provide the implanted cells with a suitable in vivo microenvironment that promotes tissue reconstruction. Extracellular matrix (ECM)-based scaffolds provide a three-dimensional microenvironment that can promote constructive and functional tissue remodeling rather than inflammation and scarring even in the absence of any implanted cells. The objective of this study was to determine the ability of an ECM-based scaffold to facilitate functional restoration of the distal gastrocnemius musculotendinous junction in a canine model after complete resection of the tissue. Within 6 months, vascularized, innervated skeletal muscle that was similar to normal muscle tissue had formed at the ECM-scaffold implantation site. This neo-tissue generated 48% of the contractile force of contralateral musculotendinous junction and represents the first report of de novo formation of contractile, vascularized, and innervated skeletal muscle in situ after significant tissue loss.

Myosin heavy chain isoform profiles remain altered at 7 months if the lacerated medial gastrocnemius is poorly reinnervated: a study in rabbits

Lacerated skeletal muscles often do not recover full function after repair. Denervated muscles with altered myosin heavy chain isoform (MHC) profiles are known to result in functional impairment. We studied the functional recovery of lacerated muscles, assessing MHC profile changes in association to the involvement of the intramuscular nerve (IM). We tested three lacerated models using the rabbit's medial gastrocnemius where the IM was either cut (NNR), repaired (NR), or preserved intact (NP). Muscles were assessed 7 months after repair for muscle atrophy, isometric contraction (by electrical stimulation), and fibrosis formation at the lesion site. Changes in myofibrillar actomyosin adenosine triphosphatase activity, MHC profile, regenerating myofibers and reinnervation were assessed by Western blot, histology, or immunohistology. Lacerated muscles with a repaired (NR) or an intact (NP) IM showed good recovery, with no significant changes in the MHC profile. Muscles where the IM was not repaired (NNR) resulted in significant scar area at the lesion site (p < 0.05), muscle atrophy (67%, p < 0.05) and loss in contractile properties (63% of the uninjured side, p < 0.05). At 7 months, all muscles were reinnervated. However, the NNR had an inappropriate (polyneural) and poorly distributed reinnervation, the presence of regenerating myofibers, and demonstrated a fast-to-slow MHC transition (71%:29% to 44%:56%, ANOVA, p = 0.018). This was associated to the cut IM when the NNR muscle was lacerated. Poor reinnervation in lacerated skeletal muscles alters the myosin heavy chain profile permanently. This study provides a rationale to also consider biological solutions to improve nerve regeneration and reinnervation in the surgical repair of lacerated muscles.

TrkB and TrkC agonist antibodies improve function, electrophysiologic and pathologic features in Trembler J mice

Neurotrophic factors have been considered as potential therapeutics for peripheral neuropathies. Previously, we showed that neurotrophin-3 (NT-3) promotes nerve regeneration in Trembler(J) (Tr(J)) mice and in sural nerves from patients with Charcot-Marie-Tooth 1A (CMT1A). The relatively short plasma half-life of NT-3 and other neurotrophins, however, pose a practical difficulty in their clinical application. Therapeutic agonist antibodies (AAb) targeting the neurotrophic receptors may circumvent this obstacle due to their high specificity and long half-life. Using morphological, electrophysiological studies and functional motor testing, we assessed the efficacy of monoclonal TrkC AAb and TrkB AAb in the Tr(J) mice. Treatments of these AAbs individually or in combination over 20 weeks increased compound muscle action potential (CMAP) amplitude, which correlated with improved grip strength, as compared to the PBS control group. Improvements in CMAP amplitude were most prominent with TrkC AAb treatment. In all treatment groups, distal to the crush site of the sciatic nerves exhibited a significantly greater number of myelinated fibers (MFs) indicating improved regenerative response to injury. In the contralateral intact sciatic nerves, the number of MFs as well as the myelin thickness was also increased significantly by the AAb treatments, suggesting that the hypomyelination/amyelination state of the peripheral nerves in Tr(J) improved. Therapeutic response to AAb combination was often, albeit not always, the most prominent, indicating a non-redundant effect of TrkB and TrkC AAbs. An early functional recovery and the correlative morphological changes of enhanced regeneration were seen with TrkC AAb treatment. These results provide evidence for potential therapeutic use of monoclonal agonist antibodies for neurotrophin receptors in CMT1A and other neuropathies.