Regeneration-associated genes decline in chronically injured rat sciatic motoneurons

Characterization of lncRNA and mRNA profiles in the process of repairing peripheral nerve defects with cell-matrixed nerve grafts

BACKGROUND

Decellularized extracellular matrix (dECM) is an intriguing natural biomaterial that has garnered significant attention due to its remarkable biological properties. In our study, we employed a cell-matrixed nerve graft for the repair of sciatic nerve defects in rats. The efficacy of this approach was assessed, and concurrently, the underlying molecular regulatory mechanisms were explored to elucidate how such grafts facilitate nerve regeneration. Long noncoding RNAs (lncRNAs) regulate mRNA expression via multiple mechanisms, including post-transcriptional regulation, transcription factor effects, and competitive binding with miRNAs. These interactions between lncRNAs and mRNAs facilitate precise control of gene expression, allowing organisms to adapt to varying biological environments and physiological states. By investigating the expression profiles and interaction dynamics of mRNAs and lncRNAs, we can enhance our understanding of the molecular mechanisms through which cell-matrixed nerve grafts influence neural repair. Such studies are pivotal in uncovering the intricate networks of gene regulation that underpin this process.

RESULTS

Weighted gene co-expression network analysis (WGCNA) utilizes clustering algorithms, such as hierarchical clustering, to aggregate genes with similar expression profiles into modules. These modules, which potentially correspond to distinct biological functions or processes, can subsequently be analyzed for their association with external sample traits. By correlating gene modules with specific conditions, such as disease states or responses to treatments, WGCNA enables a deeper understanding of the genetic architecture underlying various phenotypic traits and their functional implications. We identified seven mRNA modules and five lncRNA modules that exhibited associations with treatment or time-related events by WGCNA. We found the blue (mRNAs) module which displayed a remarkable enrichment in "axonal guidance" and "metabolic pathways", exhibited strong co-expression with multiple lncRNA modules, including blue (related to "GnRH secretion" and "pyrimidine metabolism"), green (related to "arginine and proline metabolism"), black (related to "nitrogen metabolism"), grey60 (related to "PPAR signaling pathway"), and greenyellow (related to "steroid hormone biosynthesis"). All of the top 50 mRNAs and lncRNAs exhibiting the strongest correlation were derived from the blue module. Validation of key molecules were performed using immunohistochemistry and qRT-PCR.

CONCLUSION

Revealing the principles and molecular regulatory mechanisms of the interaction between materials and biological entities, such as cells and tissues, is a direction for the development of biomimetic tissue engineering technologies and clinically effective products.

Physiology of Nerve Regeneration: Key Factors Affecting Clinical Outcomes

Functional recovery after peripheral nerve injuries is disappointing despite surgical advances in nerve repair. This review summarizes the relatively short window of opportunity for successful nerve regeneration due to the decline in the expression of growth-associated genes and in turn, the decline in regenerative capacity of the injured neurons and the support provided by the denervated Schwann cells, and the atrophy of denervated muscles. Brief, low-frequency electrical stimulation and post-injury exercise regimes ameliorate these deficits in animal models and patients, but the misdirection of regenerating nerve fibers compromises functional recovery and remains an important area of future research.

Nerve Wrap for Local Delivery of FK506/Tacrolimus Accelerates Nerve Regeneration

Peripheral nerve injuries (PNIs) occur frequently and can lead to devastating and permanent sensory and motor function disabilities. Systemic tacrolimus (FK506) administration has been shown to hasten recovery and improve functional outcomes after PNI repair. Unfortunately, high systemic levels of FK506 can result in adverse side effects. The localized administration of FK506 could provide the neuroregenerative benefits of FK506 while avoiding systemic, off-target side effects. This study investigates the utility of a novel FK506-impregnated polyester urethane urea (PEUU) nerve wrap to treat PNI in a previously validated rat infraorbital nerve (ION) transection and repair model. ION function was assessed by microelectrode recordings of trigeminal ganglion cells responding to controlled vibrissae deflections in ION-transected and -repaired animals, with and without the nerve wrap. Peristimulus time histograms (PSTHs) having 1 ms bins were constructed from spike times of individual single units. Responses to stimulus onsets (ON responses) were calculated during a 20 ms period beginning 1 ms after deflection onset; this epoch captures the initial, transient phase of the whisker-evoked response. Compared to no-wrap controls, rats with PEUU-FK506 wraps functionally recovered earlier, displaying larger response magnitudes. With nerve wrap treatment, FK506 blood levels up to six weeks were measured nearly at the limit of quantification (LOQ ≥ 2.0 ng/mL); whereas the drug concentrations within the ION and muscle were much higher, demonstrating the local delivery of FK506 to treat PNI. An immunohistological assessment of ION showed increased myelin expression for animals assigned to neurorrhaphy with PEUU-FK506 treatment compared to untreated or systemic-FK506-treated animals, suggesting that improved PNI outcomes using PEUU-FK506 is mediated by the modulation of Schwann cell activity.

Brief Electrical Stimulation Promotes Recovery after Surgical Repair of Injured Peripheral Nerves

Injured peripheral nerves regenerate their axons in contrast to those in the central nervous system. Yet, functional recovery after surgical repair is often disappointing. The basis for poor recovery is progressive deterioration with time and distance of the growth capacity of the neurons that lose their contact with targets (chronic axotomy) and the growth support of the chronically denervated Schwann cells (SC) in the distal nerve stumps. Nonetheless, chronically denervated atrophic muscle retains the capacity for reinnervation. Declining electrical activity of motoneurons accompanies the progressive fall in axotomized neuronal and denervated SC expression of regeneration-associated-genes and declining regenerative success. Reduced motoneuronal activity is due to the withdrawal of synaptic contacts from the soma. Exogenous neurotrophic factors that promote nerve regeneration can replace the endogenous factors whose expression declines with time. But the profuse axonal outgrowth they provoke and the difficulties in their delivery hinder their efficacy. Brief (1 h) low-frequency (20 Hz) electrical stimulation (ES) proximal to the injury site promotes the expression of endogenous growth factors and, in turn, dramatically accelerates axon outgrowth and target reinnervation. The latter ES effect has been demonstrated in both rats and humans. A conditioning ES of intact nerve days prior to nerve injury increases axonal outgrowth and regeneration rate. Thereby, this form of ES is amenable for nerve transfer surgeries and end-to-side neurorrhaphies. However, additional surgery for applying the required electrodes may be a hurdle. ES is applicable in all surgeries with excellent outcomes.

Intraoperative electrical stimulation promotes the short-term recovery of patients with cubital tunnel syndrome after surgery

BACKGROUND

This study was designed to investigate whether intraoperative electrical nerve stimulation has effects on the short-term recovery of cubital tunnel syndrome patients after ulnar nerve release.

METHODS

Patients diagnosed as cubital tunnel syndrome were selected. At the same time, they received conventional surgery treatment. The patients were divided by a randomized digits table into two groups. The control group underwent conventional surgery, and the electrical stimulation (ES) group underwent intraoperative electrical stimulation. All the patients were tested for sensory and motor functions, grip strength, key pinch strength, motor conductivity velocity (MCV), and maximum compound muscle action potential (CMAP) before operation and 1 month and 6 months after operation.

RESULTS

In patients treated with intraoperative ES, the sensory and motor functions and the strength of muscle were significantly improved after 1-month and 6-month follow-up than the control group. After the follow-up, the patients in the ES group had significantly higher grip strength and key pinch strength than the control group. After the follow-up, the patients in the ES group had significantly higher MCV and CMAP than the control group.

CONCLUSION

Intraoperative electrical stimulation of nerve muscle can significantly promote the short-term recovery of nerve and muscle functions after the surgery in cubital tunnel syndrome patients.

Retrograde labeling correlates with motor unit number estimation in rapid-stretch nerve injury

INTRODUCTION/AIMS

Rapid-stretch nerve injuries represent a substantial treatment challenge. No study has examined motor neuron connection after rapid-stretch injury. Our objective in this study was to characterize the electrophysiological properties of graded rapid-stretch nerve injury and assess motor neuron health using retrograde labeling and muscle adenosine triphosphatase (ATPase) histology.

METHODS

Male C57BL/6 mice (n = 6 per group) were rapid-stretch injured at four levels of severity: sham injury, stretch within elastic modulus, inelastic deformation, and stretch rupture. Serial compound muscle action potential (CMAP) and motor unit number estimation (MUNE) measurements were made for 48 days, followed by retrograde labeling and muscle ATPase histology.

RESULTS

Elastic injuries showed no durable abnormalities. Inelastic injury demonstrated profound initial reduction in CMAP and MUNE (P < .036) on day 2, with partial recovery by day 14 after injury (CMAP: 40% baseline, P = .003; MUNE: 55% baseline, P = .033). However, at the experimental endpoint, CMAP had recovered to baseline with only limited improvement in MUNE. Inelastic injury led to reduced retrograde-labeled neurons and grouped fiber type histology. Rupture injury had severe and nonrecovering electrophysiological impairment, dramatically reducing labeled neurons (P = .005), and atrophic or type 1 muscle fibers. There was an excellent correlation between MUNE and retrograde-labeled tibial motor neurons across injury severities (R²  = 0.96).

DISCUSSION

There was no significant electrophysiological derangement in low-severity injuries but there was recoverable conduction block in inelastic injury with slow recovery, potentially due to collateral sprouting. Rupture injuries yielded permanent failure of injured axons to reinnervate. These results provide insight into the pathophysiology of clinical injuries and recovery.

Engineered neuronal microtissue provides exogenous axons for delayed nerve fusion and rapid neuromuscular recovery in rats

Nerve injury requiring surgical repair often results in poor functional recovery due to the inability of host axons to re-grow long distances and reform meaningful connections with the target muscle. While surgeons can re-route local axon fascicles to the target muscle, there are no technologies to provide an exogenous source of axons without sacrificing healthy nerves. Accordingly, we have developed tissue engineered neuromuscular interfaces (TE-NMIs) as the first injectable microtissue containing motor and sensory neurons in an anatomically-inspired architecture. TE-NMIs provide axon tracts that are intended to integrate with denervated distal structures and preserve regenerative capacity during prolonged periods without host innervation. Following implant, we found that TE-NMI axons promoted Schwann cell maintenance, integrated with distal muscle, and preserved an evoked muscle response out to 20-weeks post nerve transection in absence of innervation from host axons. By repopulating the distal sheath with exogenous axons, TE-NMIs also enabled putative delayed fusion with proximal host axons, a phenomenon previously not achievable in delayed repair scenarios due to distal axon degeneration. Here, we found immediate electrophysiological recovery after fusion with proximal host axons and improved axon maturation and muscle reinnervation at 24-weeks post-transection (4-weeks following delayed nerve fusion). These findings show that TE-NMIs provide the potential to improve functional recovery following delayed nerve repair.

Traumatic peripheral nerve injuries: diagnosis and management

PURPOSE OF REVIEW

To review advances in the diagnostic evaluation and management of traumatic peripheral nerve injuries.

RECENT FINDINGS

Serial multimodal assessment of peripheral nerve injuries facilitates assessment of spontaneous axonal regeneration and selection of appropriate patients for early surgical intervention. Novel surgical and rehabilitative approaches have been developed to complement established strategies, particularly in the area of nerve grafting, targeted rehabilitation strategies and interventions to promote nerve regeneration. However, several management challenges remain, including incomplete reinnervation, traumatic neuroma development, maladaptive central remodeling and management of fatigue, which compromise functional recovery.

SUMMARY

Innovative approaches to the assessment and treatment of peripheral nerve injuries hold promise in improving the degree of functional recovery; however, this remains a complex and evolving area.

Simultaneous Quantification of Anisotropic Microcirculation and Microstructure in Peripheral Nerve

Peripheral nerve injury is a significant public health challenge, and perfusion in the nerve is a potential biomarker for assessing the injury severity and prognostic outlook. Here, we applied a novel formalism that combined intravoxel incoherent motion (IVIM) and diffusion tensor imaging (DTI) to simultaneously characterize anisotropic microcirculation and microstructure in the rat sciatic nerve. Comparison to postmortem measurements revealed that the in vivo IVIM-DTI signal contained a fast compartment (2.32 ± 0.04 × 10−3 mm2/s mean diffusivity, mean ± sem, n = 6, paired t test p < 0.01) that could be attributed to microcirculation in addition to a slower compartment that had similar mean diffusivity as the postmortem nerve (1.04 ± 0.01 vs. 0.96 ± 0.05 × 10−3 mm2/s, p > 0.05). Although further investigation and technical improvement are warranted, this preliminary study demonstrates both the feasibility and potential for applying the IVIM-DTI methodology to peripheral nerves for quantifying perfusion in the presence of anisotropic tissue microstructure.

Recovering the regenerative potential in chronically injured nerves by using conditioning electrical stimulation

OBJECTIVE

Chronically injured nerves pose a significant clinical challenge despite surgical management. There is no clinically feasible perioperative technique to upregulate a proregenerative environment in a chronic nerve injury. Conditioning electrical stimulation (CES) significantly improves sensorimotor recovery following acute nerve injury to the tibial and common fibular nerves. The authors' objective was to determine if CES could foster a proregenerative environment following chronically injured nerve reconstruction.

METHODS

The tibial nerve of 60 Sprague Dawley rats was cut, and the proximal ends were inserted into the hamstring muscles to prevent spontaneous reinnervation. Eleven weeks postinjury, these chronically injured animals were randomized, and half were treated with CES proximal to the tibial nerve cut site. Three days later, 24 animals were killed to evaluate the effects of CES on the expression of regeneration-associated genes at the cell body (n = 18) and Schwann cell proliferation (n = 6). In the remaining animals, the tibial nerve defect was reconstructed using a 10-mm isograft. Length of nerve regeneration was assessed 3 weeks postgrafting (n = 16), and functional recovery was evaluated weekly between 7 and 19 weeks of regeneration (n = 20).

RESULTS

Three weeks after nerve isograft surgery, tibial nerves treated with CES prior to grafting had a significantly longer length of nerve regeneration (p < 0.01). Von Frey analysis identified improved sensory recovery among animals treated with CES (p < 0.01). Motor reinnervation, assessed by kinetics, kinematics, and skilled motor tasks, showed significant recovery (p < 0.05 to p < 0.001). These findings were supported by immunohistochemical quantification of motor endplate reinnervation (p < 0.05). Mechanisms to support the role of CES in reinvigorating the regenerative response were assessed, and it was demonstrated that CES increased the proliferation of Schwann cells in chronically injured nerves (p < 0.05). Furthermore, CES upregulated regeneration-associated gene expression to increase growth-associated protein-43 (GAP-43), phosphorylated cAMP response element binding protein (pCREB) at the neuronal cell bodies, and upregulated glial fibrillary acidic protein expression in the surrounding satellite glial cells (p < 0.05 to p < 0.001).

CONCLUSIONS

Regeneration following chronic axotomy is impaired due to downregulation of the proregenerative environment generated following nerve injury. CES delivered to a chronically injured nerve influences the cell body and the nerve to re-upregulate an environment that accelerates axon regeneration, resulting in significant improvements in sensory and motor functional recovery. Percutaneous CES may be a preoperative strategy to significantly improve outcomes for patients undergoing delayed nerve reconstruction.

Myelination, axonal loss and Schwann cell characteristics in axonal polyneuropathy compared to controls

Introduction

Polyneuropathy is a debilitating condition characterized by distal sensory and motor deficits. Schwann cell dysfunction and axonal loss are integral factors in pathophysiology and disease progression of polyneuropathy.

Aims

The aim of this study was the assessment of Schwann cell characteristics, nerve fibers and myelination parameters in polyneuropathy patients compared to controls.

Methods

Nerve tissue was obtained from polyneuropathy patients (n = 10) undergoing diagnostic sural nerve biopsies. Biopsies of healthy peripheral nerves (n = 5) were harvested during elective sural nerve grafting for chronic peripheral nerve lesions. Exclusion criteria for the healthy control group were recent neurological trauma, diabetes, neurological and cardiovascular disease, as well as active malignancies and cytotoxic medication within the last 12 months. The over-all architecture of nerve sections and myelination parameters were histomorphometrically analyzed. Immunofluorescent imaging was used to evaluate Schwann cell phenotypes, senescence markers and myelination parameters.

Results

Histomorphometric analysis of nerve biopsies showed significant axonal loss in polyneuropathy patients compared to controls, which was in accordance with the neuropathological findings. Immunofluorescent staining of Schwann cells and myelin basic protein indicated a significant impairment of myelination and lower Schwann cell counts compared to controls. Phenotypic alterations and increased numbers of non-myelinating p75-positive Schwann cells were found in polyneuropathy patients.

Discussion

This study provided quantitative data of axonal loss, reduced myelination and Schwann cell dysfunction of polyneuropathy patients compared to neurologically healthy controls. Phenotypic alterations of Schwann cells were similar to those seen after peripheral nerve injury, highlighting the clinical relevance of Schwann cell dysfunction.

Green Tea Polyphenols Promote Functional Recovery from Peripheral Nerve Injury in Rats

Background

Peripheral nerve injury (PNI) is a common and progressive disorder with sensory and motor deficits in the peripheral nervous system (PNS). Treatment is difficult, with unfavorable prognosis. Green tea polyphenols (GTPs) exert neuroprotective effects on regeneration of the central nervous system (CNS). However, the effects of GTPs on functional recovery of the PNS have not been fully characterized. Consequently, the present study investigated the effects of GTPs on nerve regeneration of rats with PNI.

Material/Methods

The model of PNI was established in rats by sciatic nerve injury (SNI). Adult male Wistar rats with SNI were randomly divided into a vehicle group and a GTPs group. The compound muscle action potential (CMAP) of rat sciatic nerves (SN) was measured using the CM6240 physiological signal acquisition and processing system. The wet weight of the triceps muscle was determined using an analytical balance. The number of myelinated nerve fibers was counted under an optical microscope. Ultrastructure of the regenerated nerves in SN was observed by transmission electron microscopy. The mRNA and protein expression of nerve growth factor (NGF), growth-associated protein-43 (GAP-43), neurofilament 200 (NF200), and myelin-associated glycoprotein (MAG) in SN stumps were measured by real-time quantification PCR (RT-qPCR) and Western blot, respectively.

Results

In rats with SNI, GTPs relieved the adhesion between nerve anastomosis and surrounding tissues, and significantly increased nerve conduction velocity, wet weight of the triceps muscle, and development and axonal regeneration of myelinated nerve fibers. Moreover, GTPs promoted the mRNA and protein expressions of NGF, GAP-43, NF200, and MAG in SN stumps.

Conclusions

GTPs promotes nerve regeneration in rats with SNI.

Electrical stimulation to enhance peripheral nerve regeneration: Update in molecular investigations and clinical translation

Peripheral nerve injuries are common and frequently result in incomplete functional recovery even with optimal surgical treatment. Permanent motor and sensory deficits are associated with significant patient morbidity and socioeconomic burden. Despite substantial research efforts to enhance peripheral nerve regeneration, few effective and clinically feasible treatment options have been found. One promising strategy is the use of low frequency electrical stimulation delivered perioperatively to an injured nerve at the time of surgical repair. Possibly through its effect of increasing intraneuronal cyclic AMP, perioperative electrical stimulation accelerates axon outgrowth, remyelination of regenerating axons, and reinnervation of end organs, even with delayed surgical intervention. Building on decades of experimental evidence in animal models, several recent, prospective, randomized clinical trials have affirmed electrical stimulation as a clinically translatable technique to enhance functional recovery in patients with peripheral nerve injuries requiring surgical treatment. This paper provides an updated review of the cellular physiology of electrical stimulation and its effects on axon regeneration, Level I evidence from recent prospective randomized clinical trials of electrical stimulation, and ongoing and future directions of research into electrical stimulation as a clinically feasible adjunct to surgical intervention in the treatment of patients with peripheral nerve injuries.

A rat study of the use of end-to-side peripheral nerve repair as a "babysitting" technique to reduce the deleterious effect of chronic denervation

OBJECTIVE

Functional recovery is disappointing after surgical repair of nerves that are injured far from their target organs and/or after delayed repair. In the former case, a nerve transfer that transects a distal nerve fascicle to innervate denervated targets is one strategy to promote nerve regeneration and functional recovery. An alternate strategy tested in this study is to perform an end-to-side neurorrhaphy to "babysit" (protect) the denervated distal nerve stump at the time of nerve repair and reduce the deleterious effect of chronic denervation on nerve regeneration.

METHODS

In the hindlimbs of Sprague-Dawley rats, the common peroneal (CP) nerve was transected unilaterally and the distal CP nerve stump inserted through a perineurial window into the intact tibial (TIB) nerve, i.e., CP-TIB end-to-side neurorrhaphy. In the first experiment, TIB nerve motoneurons that had regenerated and/or sprouted axons into the CP nerve within 3 months were stimulated to elicit contractions, and thereafter, identified with retrograde dyes for counting. In the second experiment, the intact TIB nerve was transected and cross-sutured to a 3-month chronically denervated distal CP nerve stump that had either been "protected" by ingrown TIB nerves after CP-TIB neurorrhaphy or remained chronically denervated. Thereafter, the number of retrogradely labeled TIB nerve motoneurons that had regenerated their nerves within 3 months were counted and reinnervated tibialis anterior (TA) muscles weighed.

RESULTS

A mean (± SE) of 231 ± 83 TIB nerve motoneurons grew into the end-to-side CP distal nerve stump with corresponding ankle flexion; 32% regenerated their axons and 24% sprouted axons from the intact TIB nerve, eliciting ankle flexor-extensor co-contraction. In the second experiment, after a 3-month period of TIB nerve regeneration, significantly more TIB motoneurons regenerated their axons into "protected" than "unprotected" CP distal nerve stumps within 3 months (mean 332 ± 43.6 vs 235 ± 39.3 motoneurons) with corresponding and significantly higher numbers of regenerated nerve fibers, resulting in significantly better recovery of reinnervated TA muscle weight.

CONCLUSIONS

These experiments in rats demonstrated that delayed nerve repair is more effective when the deleterious effects of chronic denervation of the distal nerve stump are reduced by protecting the nerve stump with ingrowing nerve fibers across an end-to-side insertion of the distal nerve stump into a neighboring intact nerve. Such an end-to-side neurorrhaphy may be invaluable as a means of preventing the atrophy of distal nerve stumps and target organs after chronic denervation, which allows for effective reinnervation of the protected distal nerve stumps and target organs over distance and time.

Enhanced regeneration and reinnervation following timed GDNF gene therapy in a cervical ventral root avulsion

Avulsion of spinal nerve roots is a severe proximal peripheral nerve lesion. Despite neurosurgical repair, recovery of function in human patients is disappointing, because spinal motor neurons degenerate progressively, axons grow slowly and the distal Schwann cells which are instrumental to supporting axon extension lose their pro-regenerative properties. We have recently shown that timed GDNF gene therapy (dox-i-GDNF) in a lumbar plexus injury model promotes axon regeneration and improves electrophysiological recovery but fails to stimulate voluntary hind paw function. Here we report that dox-i-GDNF treatment following avulsion and re-implantation of cervical ventral roots leads to sustained motoneuron survival and recovery of voluntary function. These improvements were associated with a twofold increase in motor axon regeneration and enhanced reinnervation of the hand musculature. In this cervical model the distal hand muscles are located 6,5 cm from the reimplantation site, whereas following a lumber lesion this distance is twice as long. Since the first signs of muscle reinnervation are observed 6 weeks after the lesion, this suggests that regenerating axons reached the hand musculature before a critical state of chronic denervation has developed. These results demonstrate that the beneficial effects of timed GDNF-gene therapy are more robust following spinal nerve avulsion lesions that allow reinnervation of target muscles within a relatively short time window after the lesion. This study is an important step in demonstrating the potential of timed GDNF-gene therapy to enhance axon regeneration after neurosurgical repair of a severe proximal nerve lesion.

The Val66Met BDNF Polymorphism and Peripheral Nerve Injury: Enhanced Regeneration in Mouse Met-Carriers Is Not Further Improved With Activity-Dependent Treatment

Activity-dependent treatments to enhance peripheral nerve regeneration after injury have shown great promise, and clinical trials implementing them have begun. Success of these treatments requires activity-dependent release of brain-derived neurotrophic factor (BDNF). A single nucleotide polymorphism (SNP) in the bdnf gene known as Val66Met, which is found in nearly one third of the human population, results in defective activity-dependent BDNF secretion and could impact the effectiveness of these therapies. Here, we used a mouse model of this SNP to test the efficacy of treadmill exercise in enhancing axon regeneration in animals both heterozygous (V/M) and homozygous (M/M) for the SNP. Axon regeneration was studied 4 weeks after complete transection and repair of the sciatic nerve in both male and female animals, using both electrophysiological and histological outcome measures. Regeneration was enhanced significantly without treatment in V/M mice, compared with wild type (V/V) controls. Unlike V/V mice, treatment of both V/M and M/M mice with treadmill exercise did not result in enhanced regeneration. These results were recapitulated in vitro using dissociated neurons containing the light-sensitive cation channel, channelrhodopsin. Three days after plating, neurites of neurons from V/M and M/M mice were longer than those of V/V neurons. In neurons from V/V mice, but not those from V/M or M/M animals, longer neurites were found after optogenetic stimulation. Taken together, Met-carriers possess an intrinsically greater capacity to regenerate axons in peripheral nerves, but this cannot be enhanced further by activity-dependent treatments.

Resveratrol inhibits paclitaxel-induced neuropathic pain by the activation of PI3K/Akt and SIRT1/PGC1α pathway

Background

Phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt) is one of the essential signaling pathways for the development and maintenance of neuropathic pain.

Objective

To investigate the effect of resveratrol (RES) on paclitaxel-induced neuropathic pain in rats and elucidate the underlying molecular mechanisms.

Method

Male Sprague Dawley rats were randomly divided into seven groups (n=10/group): Group C, Group P, Group R, Group R+P, Group LY + R+P, Group LY (the specific inhibitor of PI3K), Group E (the specific inhibitor of sirtuin 1 [SIRT1]). Paw withdrawal mechanical threshold (PWT) and thermal withdrawal latency (TWL) were recorded. Mitochondrial histomorphology was performed by transmission electron microscope. PI3K, p-Akt, and t-Akt expressions were tested using immunohistochemistry. Western blot was used to detect p-Akt, t-Akt, SIRT1, and PGC1α expressions. The apoptosis in the striatum, spinal dorsal horns (SDH), and dorsal root ganglions (DRG) tissues was assayed by TUNEL. ELISA was used to detect the contents of IL-β, IL-10, malondialdehyde (MDA), and superoxide dismutase (SOD) in striatum, SDH, and DRG tissues.

Results

Compared to the control group, PWT and TWL in the P and LY +R+P groups were significantly decreased on 8th and 14th day after paclitaxel administration (P<0.05). The expressions of p-Akt, SIRT1, and PGC1α were decreased in paclitaxel-induced neuropathic rats; however, the expressions of p-Akt, SIRT1, and PGC1α were significantly increased after RES treatment (P<0.05). Furthermore, the expression of p-Akt was decreased by LY294002 (P<0.05), and amount of SIRT1 and PGC1α expression was inhibited by EX-527 (P<0.05). The t-Akt level was not significantly changed in all groups. RES prevented paclitaxel-induced mitochondrial damage by PI3K/Akt. RES improves the pain symptoms of paclitaxel neuralgia rats by increasing the IL-10 and decreasing the expression of IL-1β. RES increases the SOD and reduces the MDA. RES reduces apoptosis by SIRT1/PGC1α signal pathway.

Conclusion

Our results suggest that RES may inhibit paclitaxel-induced neuropathic pain via PI3K/Akt and SIRT1/PGC1α pathways.

Chitosan tubes enriched with fresh skeletal muscle fibers for delayed repair of peripheral nerve defects

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.

Adsorptive properties of graphene oxide on vitamin B12 and their effect on the promotion of peripheral nerve regeneration

OBJECTIVES

To observe whether Graphene oxide (GO) can absorb vitamin B12 (VB12) and Decellularized scaffold - acellular nerve allograft (ANA) modified GO-VB12 promote the repair of ischiadic nervus defects in a rat model.

METHODS

The adsorption of GO on vitamin and the optimum adsorption conditions were investigated by single factor experiment. The adsorption properties of the material were observed by scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS) to determine the success of adsorption on VB12. GO-VB12-ANA was prepared by vibration mixing method and bridged to injured ischiadic nervus. The nerve action potential, wet weight ratio of gastrocnemius muscle and the expression of GAP-43 were investigated by contrast test to detect its effect on nerve regeneration.

RESULTS

The optimized adsorption conditions for GO on VB12 solution were listed as follows: adsorbent dosage was 6 mg, shaking time was 70 min, the pH value was 6, the optimum concentration of VB12 was 50 mg/L and the theoretical saturated adsorption capacity was 21.51 mg/g. The nerve action potential, wet weight ratio of gastrocnemius muscle and the expression of GAP-43 in nerve fiber of GO-VB12-ANA group were close to the normal values and significantly higher than those of ANA and rotation group.

CONCLUSIONS

Based on the adsorption function of GO on VB12, GO-VB12-ANA can promote regeneration of injured ischiadic nervus, providing the experimental basis for the clinical application of nanomaterials.

Comparative Evaluation of Chitosan Nerve Guides with Regular or Increased Bendability for Acute and Delayed Peripheral Nerve Repair: A Comprehensive Comparison with Autologous Nerve Grafts and Muscle-in-Vein Grafts

Reconstruction of joint-crossing digital nerves requires the application of nerve guides with a much higher flexibility than used for peripheral nerve repair along larger bones. Nevertheless, collapse-resistance should be preserved to avoid secondary damage to the regrowing nerve tissue. In recent years, we presented chitosan nerve guides (CNGs) to be highly supportive for the regeneration of critical gap length peripheral nerve defects in the rat. Now, we evidently increased the bendability of regular CNGs (regCNGs) by developing a wavy wall structure, that is, corrugated CNGs (corrCNGs). In a comprehensive in vivo study, we compared both types of CNGs with clinical gold standard autologous nerve grafts (ANGs) and muscle-in-vein grafts (MVGs) that have recently been highlighted in the literature as a suitable alternative to ANGs. We reconstructed rat sciatic nerves over a critical gap length of 15 mm either immediately upon transection or after a delay period of 45 days. Electrodiagnostic measurements were applied to monitor functional motor recovery at 60, 90, 120, and 150 (only delayed repair) days postreconstruction. Upon explanation, tube properties were analyzed. Furthermore, distal nerve ends were evaluated using histomorphometry, while connective tissue specimens were subjected to immunohistological stainings. After 120 days (acute repair) or 150 days (delayed repair), respectively, compression-stability of regCNGs was slightly increased while it remained stable in corrCNGs. In both substudies, regCNGs and corrCNGs supported functional recovery of distal plantar muscles in a similar way and to a greater extent when compared with MVGs, while ANGs demonstrated the best support of regeneration. Anat Rec, 301:1697-1713, 2018. © 2018 Wiley Periodicals, Inc.

Irreversible changes occurring in long-term denervated Schwann cells affect delayed nerve repair

OBJECTIVE

Multiple factors may affect functional recovery after peripheral nerve injury, among them the lesion site and the interval between the injury and the surgical repair. When the nerve segment distal to the lesion site undergoes chronic degeneration, the ensuing regeneration (when allowed) is often poor. The aims of the current study were as follows: 1) to examine the expression changes of the neuregulin 1/ErbB system during long-term nerve degeneration; and 2) to investigate whether a chronically denervated distal nerve stump can sustain nerve regeneration of freshly axotomized axons.

METHODS

This study used 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. Before the suture, a segment of long-term degenerated median nerve stump was harvested for analysis. Functional, morphological, morphometric, and biomolecular analyses were performed.

RESULTS

The results showed that neuregulin 1 is highly downregulated after chronic degeneration, as well as some Schwann cell markers, demonstrating that these cells undergo atrophy, which was also confirmed by ultrastructural analysis. After delayed nerve repair, it was observed that chronic degeneration of the distal nerve stump compromises nerve regeneration in terms of functional recovery, as well as the number and size of regenerated myelinated fibers. Moreover, neuregulin 1 is still downregulated after delayed regeneration.

CONCLUSIONS

The poor outcome after delayed nerve regeneration might be explained by Schwann cell impairment and the consequent ineffective support for nerve regeneration. Understanding the molecular and biological changes occurring both in the chronically degenerating nerve and in the delayed nerve repair may be useful to the development of new strategies to promote nerve regeneration. The results suggest that neuregulin 1 has an important role in Schwann cell activity after denervation, indicating that its manipulation might be a good strategy for improving outcome after delayed nerve repair.

An update on addressing important peripheral nerve problems: challenges and potential solutions

From time to time it is thoughtful and productive to review a medical field and reflect upon what are the major issues that need to be addressed and what is being done to do so. This review article is not meant to be all-inclusive but rather focuses on four evolving areas in the field of peripheral nerve disorders and treatments: (1) nerve surgery under ultrasound guidance using a new ultra-minimally invasive thread technique; (2) evolving magnetic resonance imaging (MRI) and ultrasound imaging techniques that are helping to both diagnose and treat a variety of peripheral nerve problems including entrapment neuropathies, traumatic nerve injuries, and masses arising from nerves; (3) promoting recovery after nerve injury using electrical stimulation; and (4) developing animal models to reproduce a severe nerve injury (neurotmetic grade in continuity) that requires a surgical intervention and repair. In each area we first describe the current challenges and then discuss new and emerging techniques and approaches. It is our hope that this article will bring added attention and resources to help better address peripheral nerve problems that remain a challenge for both patients and physicians.

A Shift from a Pivotal to Supporting Role for the Growth-Associated Protein (GAP-43) in the Coordination of Axonal Structural and Functional Plasticity

In a number of animal species, the growth-associated protein (GAP), GAP-43 (aka: F1, neuromodulin, B-50, G50, pp46), has been implicated in the regulation of presynaptic vesicular function and axonal growth and plasticity via its own biochemical properties and interactions with a number of other presynaptic proteins. Changes in the expression of GAP-43 mRNA or distribution of the protein coincide with axonal outgrowth as a consequence of neuronal damage and presynaptic rearrangement that would occur following instances of elevated patterned neural activity including memory formation and development. While functional enhancement in GAP-43 mRNA and/or protein activity has historically been hypothesized as a central mediator of axonal neuroplastic and regenerative responses in the central nervous system, it does not appear to be the crucial substrate sufficient for driving these responses. This review explores the historical discovery of GAP-43 (and associated monikers), its transcriptional, post-transcriptional and post-translational regulation and current understanding of protein interactions and regulation with respect to its role in axonal function. While GAP-43 itself appears to have moved from a pivotal to a supporting factor, there is no doubt that investigations into its functions have provided a clearer understanding of the biochemical underpinnings of axonal plasticity.

The role of cAMP and its downstream targets in neurite growth in the adult nervous system

Injured neurons in the adult mammalian central nervous system (CNS) have a very limited capacity for axonal regeneration and neurite outgrowth. This inability to grow new axons or to regrow injured axons is due to the presence of molecules that inhibit axonal growth, and age related changes in the neuron's innate growth capabilities. Available levels of cAMP are thought to have an important role in linking both of these factors. Elevated levels of cAMP in the developing nervous system are important for the guidance and stability of growth cones. As the nervous system matures, cAMP levels decline and the growth promoting effects of cAMP diminish. It has frequently been demonstrated that increasing neuronal cAMP can enhance neurite growth and regeneration. Some methods used to increase cAMP include administration of cAMP agonists, conditioning lesions, or electrical stimulation. Furthermore, it has been proposed that multiple stages of cAMP induced growth exist, one directly caused by its downstream effector Protein Kinase A (PKA) and one caused by the eventual upregulation of gene transcription. Although the role cAMP in promoting axon growth is well accepted, the downstream pathways that mediate cAMP-mediated axonal growth are less clear. This is partly because various key studies that explored the link between PKA and axonal outgrowth relied on the PKA inhibitors KT5720 and H89. More recent studies have shown that both of these drugs are less specific than initially thought and can inhibit a number of other signalling molecules including the Exchange Protein Activated by cAMP (EPAC). Consequently, it has recently been shown that a number of intracellular signalling pathways previously attributed to PKA can now be attributed solely to activation of EPAC specific pathways, or the simultaneous co-activation of PKA and EPAC specific pathways. These new studies open the door to new potential treatments for repairing the injured spinal cord.

Nerve Regeneration: Understanding Biology and Its Influence on Return of Function After Nerve Transfers

Poor functional outcomes are frequent after peripheral nerve injuries despite the regenerative support of Schwann cells. Motoneurons and, to a lesser extent, sensory neurons survive the injuries but outgrowth of axons across the injury site is slow. The neuronal regenerative capacity and the support of regenerating axons by the chronically denervated Schwann cells progressively declines with time and distance of the injury from the denervated targets. Strategies, including brief low-frequency electrical stimulation that accelerates target reinnervation and functional recovery, and the insertion of cross-bridges between a donor nerve and a recipient denervated nerve stump, are effective in promoting functional outcomes after complete and incomplete injuries.

Effects of peripheral nerve injury on parvalbumin expression in adult rat dorsal root ganglion neurons

Background

Parvalbumin (PV) is a calcium binding protein that identifies a subpopulation of proprioceptive dorsal root ganglion (DRG) neurons. Calcitonin gene-related peptide (CGRP) is also expressed in a high proportion of muscle afferents but its relationship to PV is unclear. Little is known of the phenotypic responses of muscle afferents to nerve injury. Sciatic nerve axotomy or L5 spinal nerve ligation and section (SNL) lesions were used to explore these issues in adult rats using immunocytochemistry.

Results

In naive animals, the mean PV expression was 25 % of L4 or L5 dorsal root ganglion (DRG) neurons, and this was unchanged 2 weeks after sciatic nerve axotomy. Colocalization studies with the injury marker activating transcription factor 3 (ATF3) showed that approximately 24 % of PV neurons expressed ATF3 after sciatic nerve axotomy suggesting that PV may show a phenotypic switch from injured to uninjured neurons. This possibility was further assessed using the spinal nerve ligation (SNL) injury model where injured and uninjured neurons are located in different DRGs. Two weeks after L5 SNL there was no change in total PV staining and essentially all L5 PV neurons expressed ATF3. Additionally, there was no increase in PV-ir in the adjacent uninjured L4 DRG cells. Co-labelling of DRG neurons revealed that less than 2 % of PV neurons normally expressed CGRP and no colocalization was seen after injury.

Conclusion

These experiments clearly show that axotomy does not produce down regulation of PV protein in the DRG. Moreover, this lack of change is not due to a phenotypic switch in PV immunoreactive (ir) neurons, or de novo expression of PV-ir in uninjured neurons after nerve injury. These results further illustrate differences that occur when muscle afferents are injured as compared to cutaneous afferents.