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The article focuses on the development of a new decellularization protocol for pig nerves that preserves the nerve extracellular matrix (ECM) and its subsequent use in repairing rat median nerves, demonstrating its potential for treating severe nerve injuries.

The interest in perforator vessels is continuously increasing due to the increasing employment of perforator flaps in reconstructive surgery. While the gross anatomy of perforator pedicles has been extensively described, little is known about their histological organization. To fill this gap, we carried out a light and transmission electron microscopy analysis of superior and inferior epigastric perforator pedicles in the rat and of thoraco-dorsal, intercostal and gluteal perforators in the pig. Results showed that, in both animal models, perforating pedicles have a rather complex histological structure, based on a refined organization of the connective tissue surrounding the vessels. The number of veins accompanying each perforating artery varied among specimens, without a clear relation to the anatomical site. Yet, veins are sometimes very small and difficult to be recognized. Finally, the comparison between rat and pig did not reveal major inter-species histological differences. These results point to the perforator pedicle as quite complex and organized anatomical entity that, also considering the emerging relevance of perforator-based flap surgery, should be referred to as an independent organ rather than a appendix of muscles and skin only. [ABSTRACT FROM AUTHOR]

Sciatic nerve crush injury in rat animal model is one of the most common experimental models used in regenerative research. However, the availability of transgenic mouse for nerve regeneration studies is constantly increasing and, therefore, the shift from rat model to mouse model is, in some cases, necessary. Moreover, since most of the human nerve lesions occur in the upper limb, it is also advantageous to shift from sciatic nerve to median nerve. In this study we described an experimental model which involves lesions of the median nerve in the mouse. Data showed that the finger flexor muscle contraction strength, assessed to evaluate the motor function recovery, and reached values not different from the control already 20 days after injury. The degree of nerve regeneration evaluated with stereological methods in light microscopy showed that, 25 days after injury, the number of regenerated myelinated fibers was comparable to the control, but they were smaller with a thinner myelin thickness. Stereological analysis made in electron microscopy confirmed these results, although the total number of fibers quantified was significantly higher compared to light microscopy analysis, due to the very small size of some fibers that can be detected only in electron microscopy. [ABSTRACT FROM AUTHOR]

Regardless of the nerve defect length, nerve injury is a debilitating condition for the affected patient that results in loss of sensory and motor function. These functional impairments can have a profound impact on the patient's quality of life. Surgical approaches for the treatment of short segment nerve defects are well-established. Autologous nerve transplantation, considered the gold standard, and the use of artificial nerve grafts are safe and successful procedures for short segment nerve defect reconstruction. Long segment nerve defects which extend 3.0 cm or more are more problematic for repair. Methods for reconstruction of long defects are limited. Artificial nerve grafts often fail to regenerate and autologous nerve grafts are limited in length and number. Cadaveric processed/unprocessed nerve allografts are a promising alternative in nerve surgery. This review gives a systematic overview on pre-clinical and clinical approaches in nerve allograft transplantation. [ABSTRACT FROM AUTHOR]

In critical nerve gap repair, decellularized nerve allografts are considered a promising tissue engineering strategy that can provide superior regeneration results compared to nerve conduits. Decellularized nerves offer a well-conserved extracellular matrix component that has proven to play an important role in supporting axonal guiding and peripheral nerve regeneration. Up to now, the known decellularized techniques are time and effort consuming. The present study, performed on rat sciatic nerves, aims at investigating a novel nerve decellularization protocol able to combine an effective decellularization in short time with a good preservation of the extracellular matrix component. To do this, a decellularization protocol proven to be efficient for tendons (DN-P1) was compared with a decellularization protocol specifically developed for nerves (DN-P2). The outcomes of both the decellularization protocols were assessed by a series of in vitro evaluations, including qualitative and quantitative histological and immunohistochemical analyses, DNA quantification, SEM and TEM ultrastructural analyses, mechanical testing, and viability assay. The overall results showed that DN-P1 could provide promising results if tested in vivo, as the in vitro characterization demonstrated that DN-P1 conserved a better ultrastructure and ECM components compared to DN-P2. Most importantly, DN-P1 was shown to be highly biocompatible, supporting a greater number of viable metabolically active cells. [ABSTRACT FROM AUTHOR]

Nerve fiber regeneration and complete functional recovery after peripheral nerve injury do not always occur and can be influenced by patient age, gender, lesion site, injury severity, size of the gap between damaged nerve stumps and time interval that elapses before performing surgical repair. The poor outcome occurring after a long delay can be due to loss of the neuron ability to regenerate, loss of the Schwann cell ability to support regeneration and, of course, progressive muscle atrophy. The aim of this study was to investigate the degenerative processes of the denervated distal nerve stump in order to understand which role they can have during delayed nerve regeneration. Morphological and biomolecular analyses carried out on degenerated nerves showed several collagen fibers and fibroblasts, atrophic Schwann cells and a significant reduction of soluble Neuregulin1 (NRG1, an important factor for the survival and activity of Schwann cells) already after 3 months of degeneration. Moreover, functional, morphological, morphometrical and biomolecular analyses were carried out on regenerated distal nerve stumps 6 months after nerve repair (immediate or 3 and 6 months delayed). A rat surgical model of delayed nerve repair consisting of a cross suture between the chronically degenerated median nerve distal stump and the freshly axotomized ulnar proximal stump was used. Functional recovery analysis shows that only the group repaired immediately and not the two delayed-repaired groups, recovered partially. Moreover, quantitative analysis shows that the delayed groups have fewer and smaller myelinated fibers compared to the immediate repair group. Finally, biomolecular analysis performed on the 6-months delayed group shows that soluble NRG1 maintains a low expression also after 6 months of regeneration. These results demonstrate that, despite a delay of 3 or 6 months, the fibers are still able to regenerate, even if they are fewer and smaller than the immediate repaired group. Moreover, the analysis of the NRG1/ErbB system shows a significant decrease of soluble NRG1 in both degenerating and delayed-repaired nerves. Our results suggest that NRG1 plays an important role in Schwann cell activity after denervation, therefore its manipulation could be a good strategy to improve the outcome after delayed nerve repair. [ABSTRACT FROM AUTHOR]

Gut microbiota is responsible for essential functions in human health. Several communication axes between gut microbiota and other organs via neural, endocrine, and immune pathways have been described, and perturbation of gut microbiota composition has been implicated in the onset and progression of an emerging number of diseases. Here, we analyzed peripheral nerves, dorsal root ganglia (DRG), and skeletal muscles of neonatal and young adult mice with the following gut microbiota status: a) germ-free (GF), b) gnotobiotic, selectively colonized with 12 specific gut bacterial strains (Oligo-Mouse-Microbiota, OMM12), or c) natural complex gut microbiota (CGM). Stereological and morphometric analyses revealed that the absence of gut microbiota impairs the development of somatic median nerves, resulting in smaller diameter and hypermyelinated axons, as well as in smaller unmyelinated fibers. Accordingly, DRG and sciatic nerve transcriptomic analyses highlighted a panel of differentially expressed developmental and myelination genes. Interestingly, the type III isoform of Neuregulin1 (NRG1), known to be a neuronal signal essential for Schwann cell myelination, was overexpressed in young adult GF mice, with consequent overexpression of the transcription factor Early Growth Response 2 ( Egr2 ), a fundamental gene expressed by Schwann cells at the onset of myelination. Finally, GF status resulted in histologically atrophic skeletal muscles, impaired formation of neuromuscular junctions, and deregulated expression of related genes. In conclusion, we demonstrate for the first time a gut microbiota regulatory impact on proper development of the somatic peripheral nervous system and its functional connection to skeletal muscles, thus suggesting the existence of a novel 'Gut Microbiota-Peripheral Nervous System-axis.'

Peripheral nerves are frequently affected by lesions caused by trauma (work accidents, car incidents, combat injuries) and following surgical procedures (for instance cancer resection), resulting in loss of motor and sensory function with lifelong impairments. Irrespective of the intrinsic capability of the peripheral nervous system for regeneration, spontaneous or surgically supported regeneration is often unsatisfactory with the limited functional success of nerve repair. For this reason, many efforts have been made to improve the regeneration process. Beyond innovative microsurgical methods that, in certain cases, are necessary to repair nerve injuries, different nonsurgical treatment approaches and adjunctive therapies have been investigated to enhance nerve regeneration. One possibility could be taking advantage of a healthy diet or lifestyle and their relation with proper body functions. Over the years, scientific evidence has been obtained on the benefits of the intake of polyphenols or polyphenol-rich foods in humans, highlighting the neuroprotective effects of these compounds in many neurodegenerative diseases. In order to improve the available knowledge about the potential beneficial role of polyphenols in the process of peripheral nerve regeneration, this review assessed the biological effects of polyphenol administration in supporting and promoting the regenerative process after peripheral nerve injury.

The repair of severe nerve injuries requires an autograft or conduit to bridge the gap and avoid axon dispersion. Several conduits are used routinely, but their effectiveness is comparable to that of an autograft only for short gaps. Understanding nerve regeneration within short conduits could help improve their efficacy for longer gaps. Since Schwann cells are known to migrate on endothelial cells to colonize the "nerve bridge", the new tissue spontaneously forming to connect the injured nerve stumps, here we aimed to investigate whether this migratory mechanism drives Schwann cells to also proceed within the nerve conduits used to repair large nerve gaps. Injured median nerves of adult female rats were repaired with 10 mm chitosan conduits and the regenerated nerves within conduits were analyzed at different time points using confocal imaging of sequential thick sections. Our data showed that the endothelial cells formed a dense capillary network used by Schwann cells to migrate from the two nerve stumps into the conduit. We concluded that angiogenesis played a key role in the nerve conduits, not only by supporting cell survival but also by providing a pathway for the migration of newly formed Schwann cells.

Ghrelin is a circulating peptide hormone released by enteroendocrine cells of the gastrointestinal tract as two forms, acylated and unacylated. Acylated ghrelin (AG) binds to the growth hormone secretagogue receptor 1a (GHSR1a), thus stimulating food intake, growth hormone release, and gastrointestinal motility. Conversely, unacylated GHR (UnAG), through binding to a yet unidentified receptor, protects the skeletal muscle from atrophy, stimulates muscle regeneration, and protects cardiomyocytes from ischemic damage. Recently, interest about ghrelin has raised also among neuroscientists because of its effect on the nervous system, especially the stimulation of neurogenesis in spinal cord, brain stem, and hippocampus. However, few information is still available about its effectiveness on peripheral nerve regeneration. To partially fill this gap, the aim of this study was to assess the effect of UnAG on peripheral nerve regeneration after median nerve crush injury and after nerve transection immediately repaired by means of an end-to-end suture. To this end, we exploited FVB1 Myh6/Ghrl transgenic mice in which overexpression of the ghrelin gene (Ghrl) results in selective up-regulation of circulating UnAG levels, but not of AG. Regeneration was assessed by both functional evaluation (grasping test) and morphometrical analysis of regenerated myelinated axons. Results obtained lead to conclude that UnAG could have a role in development of peripheral nerves and during more severe lesions.

Peripheral nerves are highly susceptible to injuries induced from everyday activities such as falling or work and sport accidents as well as more severe incidents such as car and motorcycle accidents. Many efforts have been made to improve nerve regeneration, but a satisfactory outcome is still unachieved, highlighting the need for easy to apply supportive strategies for stimulating nerve growth and functional recovery. Recent focus has been made on the effect of the consumed diet and its relation to healthy and well-functioning body systems. Normally, a balanced, healthy daily diet should provide our body with all the needed nutritional elements for maintaining correct function. The health of the central and peripheral nervous system is largely dependent on balanced nutrients supply. While already addressed in many reviews with different focus, we comprehensively review here the possible role of different nutrients in maintaining a healthy peripheral nervous system and their possible role in supporting the process of peripheral nerve regeneration. In fact, many dietary supplements have already demonstrated an important role in peripheral nerve development and regeneration; thus, a tailored dietary plan supplied to a patient following nerve injury could play a non-negotiable role in accelerating and promoting the process of nerve regeneration.

Silk fibroin ( Bombyx mori ) was used to manufacture a nerve conduit (SilkBridge TM ) characterized by a novel 3D architecture. The wall of the conduit consists of two electrospun layers (inner and outer) and one textile layer (middle), perfectly integrated at the structural and functional level. The manufacturing technology conferred high compression strength on the device, thus meeting clinical requirements for physiological and pathological compressive stresses. As demonstrated in a previous work, the silk material has proven to be able to provide a valid substrate for cells to grow on, differentiate and start the fundamental cellular regenerative activities in vitro and, in vivo , at the short time point of 2 weeks, to allow the starting of regenerative processes in terms of good integration with the surrounding tissues and colonization of the wall layers and of the lumen with several cell types. In the present study, a 10 mm long gap in the median nerve was repaired with 12 mm SilkBridge TM conduit and evaluated at middle (4 weeks) and at longer time points (12 and 24 weeks). The SilkBridge TM conduit led to a very good functional and morphological recovery of the median nerve, similar to that observed with the reference autograft nerve reconstruction procedure. Taken together, all these results demonstrated that SilkBridge TM has an optimized balance of biomechanical and biological properties, which allowed proceeding with a first-in-human clinical study aimed at evaluating safety and effectiveness of using the device for the reconstruction of digital nerve defects in humans., (Copyright © 2020 Fregnan, Muratori, Bassani, Crosio, Biagiotti, Vincoli, Carta, Pierimarchi, Geuna, Alessandrino, Freddi and Ronchi.)

Nerve regeneration after delayed nerve repair is often unsuccessful. Indeed, the expression of genes associated with regeneration, including neurotrophic and gliotrophic factors, is drastically reduced in the distal stump of chronically transected nerves; moreover, Schwann cells undergo atrophy, losing their ability to sustain regeneration. In the present study, to provide a three-dimensional environment and trophic factors supporting Schwann cell activity and axon re-growth, we combined the use of an effective conduit (a chitosan tube) with a promising intraluminal structure (fresh longitudinal skeletal muscle fibers). This enriched conduit was used to repair a 10-mm rat median nerve gap after 3-month delay and functional and morphometrical analyses were performed 4 months after nerve reconstruction. Our data show that the enriched chitosan conduit is as effective as the hollow chitosan conduit in promoting nerve regeneration, and its efficacy is not statistically different from the autograft, considered the "gold standard" technique for nerve reconstruction. Since hollow tubes not always lead to good results after long defects (> 20 mm), we believe that the conduit enriched with fresh muscle fibers could be a promising strategy to repair longer gaps, as muscle fibers create a favorable three-dimensional environment and release trophic factors. All procedures were approved by the Bioethical Committee of the University of Torino and by the Italian Ministry of Health (approval number: 864/2016/PR) on September 14, 2016., Competing Interests: None

Neuregulin 1 (NRG1) is a growth factor produced by both peripheral nerves and skeletal muscle. In muscle, it regulates neuromuscular junction gene expression, acetylcholine receptor number, muscle homeostasis and satellite cell survival. NRG1 signalling is mediated by the tyrosine kinase receptors ErbB3 and ErbB4 and their co-receptors ErbB1 and ErbB2. The NRG1/ErbB system is well studied in nerve tissue after injury, but little is known about this system in skeletal muscle after denervation/reinnervation processes. Here, we performed a detailed time-course expression analysis of several NRG1 isoforms and ErbB receptors in the rat superficial digitorum flexor muscle after three types of median nerve injuries of different severities. We found that ErbB receptor expression was correlated with the innervated state of the muscle, with upregulation of ErbB2 clearly associated with the denervation state. Interestingly, the NRG1 isoforms were differently regulated depending on the nerve injury type, leading to the hypothesis that both the NRG1α and NRG1β isoforms play a key role in the muscle reaction to injury. Indeed, in vitro experiments with C2C12 atrophic myotubes revealed that both NRG1α and NRG1β treatment influences the best-known atrophic pathways, suggesting that NRG1 might play an anti-atrophic role.

Nerve fibers are attracted by sutureless end-to-side nerve coaptation into the recipient nerve. Opening a window in the epineurium enhances axon attraction and myelination. The authors analyze the features of nerve repair by end-to-side coaptation. They highlight the known mechanisms of axon sprouting and different hypotheses of start up signals (presence or absence of an epineurial window, role of Schwann cells, signaling from the distal trunk). The clinical literature is also presented and differences between experimental and clinical applications are pointed out. The authors propose their point of view and perspectives deriving from recent experimental and clinical experiences., Competing Interests: Conflicts of interest: None declared.

The peripheral nervous system has an intrinsic capability to regenerate, crucially related to the ability of Schwann cells (SC) to create a permissive environment, for example, through production of regeneration-promoting neurotrophic factors. Survival, proliferation, migration and differentiation of SC into a myelinating phenotype during development and after injury is regulated by different Neuregulin1 (NRG1) isoforms. This study investigates the expression of different NRG1 isoforms and of their ErbB receptors in distal rat median nerve samples under regenerating conditions after a mild (crush) and more severe (end-to-end repair) injury and under degenerating condition. The expression of the NRG1/ErbB system was evaluated at mRNA and protein level, and demonstrated to be specific for distinct and consecutive phases following nerve injury and regeneration or the progress in degeneration. For the first time a detailed analysis of expression profiles not only of soluble and transmembrane NRG1 isoforms, but also of alpha and beta as well as type a, b and c isoforms is presented. The results of mRNA and protein expression pattern analyses were related to nerve ultrastructure changes evaluated by electron microscopy. In particular, transmembrane NRG1 isoforms are differentially regulated and proteolytically processed under regeneration and degeneration conditions. Soluble NRG1 isoforms alpha and beta, as well as type a and b, are strongly upregulated during axonal regrowth, while type c NRG1 isoform is downregulated. This is accompanied by an upregulation of ErbB receptors. This accurate regulation suggests that each molecule plays a specific role that could be clinically exploited to improve nerve regeneration., (© 2015 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

Biosynthetic nerve grafts are developed in order to complement or replace autologous nerve grafts for peripheral nerve reconstruction. Artificial nerve guides currently approved for clinical use are not widely applied in reconstructive surgery as they still have limitations especially when it comes to critical distance repair. Here we report a comprehensive analysis of fine-tuned chitosan nerve guides (CNGs) enhanced by introduction of a longitudinal chitosan film to reconstruct critical length 15 mm sciatic nerve defects in adult healthy Wistar or diabetic Goto-Kakizaki rats. Short and long term investigations demonstrated that the CNGs enhanced by the guiding structure of the introduced chitosan film significantly improved functional and morphological results of nerve regeneration in comparison to simple hollow CNGs. Importantly, this was detectable both in healthy and in diabetic rats (short term) and the regeneration outcome almost reached the outcome after autologous nerve grafting (long term). Hollow CNGs provide properties likely leading to a wider clinical acceptance than other artificial nerve guides and their performance can be increased by simple introduction of a chitosan film with the same advantageous properties. Therefore, the chitosan film enhanced CNGs represent a new generation medical device for peripheral nerve reconstruction., (Copyright © 2015 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Sprouty (Spry) proteins are negative feedback inhibitors of receptor tyrosine kinase signaling. Downregulation of Spry2 has been demonstrated to promote elongative axon growth of cultured peripheral and central neurons. Here, we analyzed Spry2 global knockout mice with respect to axon outgrowth in vitro and peripheral axon regeneration in vivo. Neurons dissociated from adult Spry2 deficient sensory ganglia revealed stronger extracellular signal-regulated kinase activation and enhanced axon outgrowth. Prominent axon elongation was observed in heterozygous Spry2(+/-) neuron cultures, whereas homozygous Spry2(-/-) neurons predominantly exhibited a branching phenotype. Following sciatic nerve crush, Spry2(+/-) mice recovered faster in motor but not sensory testing paradigms (Spry2(-/-) mice did not tolerate anesthesia required for nerve surgery). We attribute the improvement in the rotarod test to higher numbers of myelinated fibers in the regenerating sciatic nerve, higher densities of motor endplates in hind limb muscles and increased levels of GAP-43 mRNA, a downstream target of extracellular regulated kinase signaling. Conversely, homozygous Spry2(-/-) mice revealed enhanced mechanosensory function (von Frey's test) that was accompanied by an increased innervation of the epidermis, elevated numbers of nonmyelinated axons and more IB4-positive neurons in dorsal root ganglia. The present results corroborate the functional significance of receptor tyrosine kinase signaling inhibitors for axon outgrowth during development and nerve regeneration and propose Spry2 as a novel potential target for pharmacological inhibition to accelerate long-distance axon regeneration in injured peripheral nerves., (© 2014 The Authors Developmental Neurobiology Published by Wiley Periodicals, Inc.)

Quantitative estimation of myelinated nerve fiber number, together with fiber size parameters, is one of the most important tools for nerve regeneration research. In this study we used a design-based stereological method to evaluate the regenerative process in two experimental paradigms: crush injury and autograft repair. Samples were embedded in resin and morphometric counting and measurements were performed using both light and electron microscopes. Results show a significant difference in myelinated fiber number estimation between light and electron microscopes, especially after autograft repair; light microscope significantly underestimates the number of fibers because of the large number of very small axons that can be detected only in electron microscope. The analysis of the size parameters also shows a higher number of small fibers in electron microscopic analysis, especially in regenerated nerves. This comparative study shows that the integration of data obtained in light microscope with those obtained in electron microscope is necessary in revealing very small myelinated fibers that cannot be detected otherwise. Moreover, the difference in the estimation of total number of myelinated fibers between light and electron microscopes must be considered in data analysis to ensure accurate interpretation of the results., (© 2014 Peripheral Nerve Society.)

Background: There is abundant evidence suggesting that growth factors may play a key role in the healing process, especially in the early stages of inflammation. Despite the reported clinical successes with the use of growth factors there is still a lack of knowledge on the biological mechanism underlying the activity of platelet-rich plasma during the process of muscle healing. The aim of this study was to analyse the early effects of platelet- rich plasma in an easily reproducible animal model., Materials and Methods: Wistar male adult rats (n=102) were used in this study. The muscle lesion was created with a scalpel in the flexor sublimis muscles. Platelet-rich plasma was applied immediately after surgery. Treated, untreated and contralateral muscles were analysed by morphological evaluation and western blot assay., Results: Leucocyte infiltration was significantly greater in muscles treated with platelet-rich plasma than in both untreated and contralateral muscles. The latter showed greater leucocyte infiltration when compared to the untreated muscles. Platelet-rich plasma treatment also modified the cellular composition of the leucocyte infiltration leading to increased expression of CD3, CD8, CD19 and CD68 and to decreased CD4 antigen expression in both platelet-rich plasma treated and contralateral muscles. Blood vessel density and blood vessel diameters were not statistically significantly different between the three groups analysed., Discussion: The results of this study showed that treatment with platelet-rich plasma magnified the physiological early inflammatory response following a muscle injury, modifying the pattern of cellular recruitment. Local platelet-rich plasma treatment may exert a direct or, more plausibly, indirect systemic effect on healing processes, at least in the earliest inflammatory phase.

In spite of great recent advancements, the definition of the optimal strategy for bridging a nerve defect, especially across long gaps, still remains an open issue since the amount of autologous nerve graft material is limited while the outcome after alternative tubulization techniques is often unsatisfactory. The aim of this study was to investigate a new tubulization technique based on the employment of vein conduits filled with whole subcutaneous adipose tissue obtained by lipoaspiration. In adult rats, a 1cm-long defect of the left median nerve was repaired by adipose tissue-vein-combined conduits and compared with fresh skeletal muscle tissue-vein-combined conduits and autologous nerve grafts made by the excised nerve segment rotated by 180°. Throughout the postoperative period, functional recovery was assessed using the grasping test. Regenerated nerve samples were withdrawn at postoperative month-6 and processed for light and electron microscopy and stereology of regenerated nerve fibers. Results showed that functional recovery was significantly slower in the adipose tissue-enriched group in comparison to both control groups. Light and electron microscopy showed that a large amount of adipose tissue was still present inside the vein conduits at postoperative month-6. Stereology showed that all quantitative morphological predictors analyzed performed significantly worse in the adipose tissue-enriched group in comparison to the two control groups. On the basis of this experimental study in the rat, the use of whole adipose tissue for tissue engineering of peripheral nerves should be discouraged. Pre-treatment of adipose tissue aimed at isolating stromal vascular fraction and/or adipose derived stem/precursor cells should be considered a fundamental requisite for nerve repair., (Copyright © 2012 Elsevier GmbH. All rights reserved.)

Cachexia is a wasting syndrome associated with cancer, AIDS, multiple sclerosis, and several other disease states. It is characterized by weight loss, fatigue, loss of appetite, and skeletal muscle atrophy and is associated with poor patient prognosis, making it an important treatment target. Ghrelin is a peptide hormone that stimulates growth hormone (GH) release and positive energy balance through binding to the receptor GHSR-1a. Only acylated ghrelin (AG), but not the unacylated form (UnAG), can bind GHSR-1a; however, UnAG and AG share several GHSR-1a-independent biological activities. Here we investigated whether UnAG and AG could protect against skeletal muscle atrophy in a GHSR-1a-independent manner. We found that both AG and UnAG inhibited dexamethasone-induced skeletal muscle atrophy and atrogene expression through PI3Kβ-, mTORC2-, and p38-mediated pathways in myotubes. Upregulation of circulating UnAG in mice impaired skeletal muscle atrophy induced by either fasting or denervation without stimulating muscle hypertrophy and GHSR-1a-mediated activation of the GH/IGF-1 axis. In Ghsr-deficient mice, both AG and UnAG induced phosphorylation of Akt in skeletal muscle and impaired fasting-induced atrophy. These results demonstrate that AG and UnAG act on a common, unidentified receptor to block skeletal muscle atrophy in a GH-independent manner.

After peripheral nerve injuries, the process of nerve regeneration and target reinnervation is very complex and depends on many different events occurring not only at the lesion site but also proximally and distally to it. In spite of the recent scientific and technological advancements, the need to find out new strategies to improve clinical nerve repair and regeneration remains. To reach this goal, the therapeutic strategy should thus exert its effects at different levels in order to simultaneously potentiate axonal regeneration, increase neuronal survival, modulate central reorganization, and inhibit or reduce target organ atrophy. It is expected that this multilevel approach might lead to significant improvement in the functional outcome and thus the quality of life of the patients suffering from peripheral nerve injury., (© 2013 Elsevier Inc. All rights reserved.)

Promoting neuromuscular recovery after neural injury is a major clinical issue. While techniques for nerve reconstruction are continuously improving and most peripheral nerve lesions can be repaired today, recovery of the lost function is usually unsatisfactory. This evidence claims for innovative nonsurgical therapeutic strategies that can implement the outcome after neural repair. Although no pharmacological approach for improving posttraumatic neuromuscular recovery has still entered clinical practice, various molecules are explored in experimental models of neural repair. One of such molecules is the circulating peptide hormone ghrelin. This hormone has proved to have a positive effect on neural repair after central nervous system lesion, and very recently its effectiveness has also been demonstrated in preventing posttraumatic skeletal muscle atrophy. By contrast, no information is still available about its effectiveness on peripheral nerve regeneration although preliminary data from our laboratory suggest that this molecule can have an effect also in promoting axonal regeneration after nerve injury and repair. Should this be confirmed, ghrelin might represent an ideal candidate as a therapeutic agent for improving posttraumatic neuromuscular recovery because of its putative effects at all the various structural levels involved in this regeneration process, namely, the central nervous system, the peripheral nerve, and the target skeletal muscle., (© 2013 Elsevier Inc. All rights reserved.)

The need for the continuous research of new tools for improving motor function recovery after nerve injury is justified by the still often unsatisfactory clinical outcome in these patients. It has been previously shown that the combined use of two reconstructive techniques, namely end-to-side neurorrhaphy and direct muscle neurotization in the rat hindlimb model, can lead to good results in terms of skeletal muscle reinnervation. Here we show that, in the rat forelimb model, the combined use of direct muscle neurotization with either end-to-end or end-to-side neurorrhaphy to reinnervate the denervated flexor digitorum muscles, leads to muscle atrophy prevention over a long postoperative time lapse (10 months). By contrast, very little motor recovery (in case of end-to-end neurorrhaphy) and almost no motor recovery (in case of end-to-side neurorrhaphy) were observed in the grasping activity controlled by flexor digitorum muscles. It can thus be concluded that, at least in the rat, direct muscle neurotization after both end-to-end and end-to-side neurorrhaphy represents a good strategy for preventing denervation-related muscle atrophy but not for regaining the lost motor function.