Adenoviral GDNF gene transfer enhances neurofunctional recovery after recurrent laryngeal nerve injury

Development and regeneration of the vagus nerve

The vagus nerve, with its myriad constituent axon branches and innervation targets, has long been a model of anatomical complexity in the nervous system. The branched architecture of the vagus nerve is now appreciated to be highly organized around the topographic and/or molecular identities of the neurons that innervate each target tissue. However, we are only just beginning to understand the developmental mechanisms by which heterogeneous vagus neuron identity is specified, patterned, and used to guide the axons of particular neurons to particular targets. Here, we summarize our current understanding of the complex topographic and molecular organization of the vagus nerve, the developmental basis of neuron specification and patterned axon guidance that supports this organization, and the regenerative mechanisms that promote, or inhibit, the restoration of vagus nerve organization after nerve damage. Finally, we highlight key unanswered questions in these areas and discuss potential strategies to address these questions.

An optimized method for high-quality RNA extraction from distinctive intrinsic laryngeal muscles in the rat model

Challenges related to high-quality RNA extraction from post-mortem tissue have limited RNA-sequencing (RNA-seq) application in certain skeletal muscle groups, including the intrinsic laryngeal muscles (ILMs). The present study identified critical factors contributing to substandard RNA extraction from the ILMs and established a suitable method that permitted high-throughput analysis. Here, standard techniques for tissue processing were adapted, and an effective means to control confounding effects during specimen preparation was determined. The experimental procedure consistently provided sufficient intact total RNA (N = 68) and RIN ranging between 7.0 and 8.6, which was unprecedented using standard RNA purification protocols. This study confirmed the reproducibility of the workflow through repeated trials at different postnatal time points and across the distinctive ILMs. High-throughput diagnostics from 90 RNA samples indicated no sequencing alignment scores below 70%, validating the extraction strategy. Significant differences between the standard and experimental conditions suggest circumvented challenges and broad applicability to other skeletal muscles. This investigation remains ongoing given the prospect of therapeutic insights to voice, swallowing, and airway disorders. The present methodology supports pioneering global transcriptome investigations in the larynx previously unfounded in literature.

Drug delivery to the pediatric upper airway

Pediatric upper airway disorders are frequently life-threatening and require precise assessment and intervention. Targeting these pathologies remains a challenge for clinicians due to the high complexity of pediatric upper airway anatomy and numerous potential etiologies; the most common treatments include systemic delivery of high dose steroids and antibiotics or complex and invasive surgeries. Furthermore, the majority of innovative airway management technologies are only designed and tested for adults, limiting their widespread implementation in the pediatric population. Here, we provide a comprehensive review of the most recent challenges of managing common pediatric upper airway disorders, describe the limitations of current clinical treatments, and elaborate on how to circumvent those limitations via local controlled drug delivery. Furthermore, we propose future advancements in the field of drug-eluting technologies to improve pediatric upper airway management outcomes.

TrkA inhibitor promotes motor functional regeneration of recurrent laryngeal nerve by suppression of sensory nerve regeneration

Recurrent laryngeal nerve (RLN) injury, in which hoarseness and dysphagia arise as a result of impaired vocal fold movement, is a serious complication. Misdirected regeneration is an issue for functional regeneration. In this study, we demonstrated the effect of TrkA inhibitors, which blocks the NGF-TrkA pathway that acts on the sensory/automatic nerves thus preventing misdirected regeneration among motor and sensory nerves, and thereby promoting the regeneration of motor neurons to achieve functional recovery. RLN axotomy rat models were used in this study, in which cut ends of the nerve were bridged with polyglycolic acid-collagen tube with and without TrkA inhibitor (TrkAi) infiltration. Our study revealed significant improvement in motor nerve fiber regeneration and function, in assessment of vocal fold movement, myelinated nerve regeneration, compound muscle action potential, and prevention of laryngeal muscle atrophy. Retrograde labeling demonstrated fewer labeled neurons in the vagus ganglion, which confirmed reduced misdirected regeneration among motor and sensory fibers, and a change in distribution of the labeled neurons in the nucleus ambiguus. Our study demonstrated that TrkAi have a strong potential for clinical application in the treatment of RLN injury.

Current landscape in motoneuron regeneration and reconstruction for motor cranial nerve injuries

The intricate anatomy and physiology of cranial nerves have inspired clinicians and scientists to study their roles in the nervous system. Damage to motor cranial nerves may result from a variety of organic or iatrogenic insults and causes devastating functional impairment and disfigurement. Surgical innovations directed towards restoring function to injured motor cranial nerves and their associated organs have evolved to include nerve repair, grafting, substitution, and muscle transposition. In parallel with this progress, research on tissue-engineered constructs, development of bioelectrical interfaces, and modulation of the regenerative milieu through cellular, immunomodulatory, or neurotrophic mechanisms has proliferated to enhance the available repertoire of clinically applicable reconstructive options. Despite these advances, patients continue to suffer from functional limitations relating to inadequate cranial nerve regeneration, aberrant reinnervation, or incomplete recovery of neuromuscular function. These shortfalls have profound quality of life ramifications and provide an impetus to further elucidate mechanisms underlying cranial nerve denervation and to improve repair. In this review, we summarize the literature on reconstruction and regeneration of motor cranial nerves following various injury patterns. We focus on seven cranial nerves with predominantly efferent functions and highlight shared patterns of injuries and clinical manifestations. We also present an overview of the existing reconstructive approaches, from facial reanimation, laryngeal reinnervation, to variations of interposition nerve grafts for reconstruction. We discuss ongoing endeavors to promote nerve regeneration and to suppress aberrant reinnervation and the development of synkinesis. Insights from these studies will shed light on recent progress and new horizons in understanding the biomechanics of peripheral nerve neurobiology, with emphasis on promising strategies for optimizing neural regeneration and identifying future directions in the field of motor cranial neuron research.

Recurrent laryngeal nerve transection in mice results in translational upper airway dysfunction

The recurrent laryngeal nerve (RLN) is responsible for normal vocal-fold (VF) movement, and is at risk for iatrogenic injury during anterior neck surgical procedures in human patients. Injury, resulting in VF paralysis, may contribute to subsequent swallowing, voice, and respiratory dysfunction. Unfortunately, treatment for RLN injury does little to restore physiologic function of the VFs. Thus, we sought to create a mouse model with translational functional outcomes to further investigate RLN regeneration and potential therapeutic interventions. To do so, we performed ventral neck surgery in 21 C57BL/6J male mice, divided into two groups: Unilateral RLN Transection (n = 11) and Sham Injury (n = 10). Mice underwent behavioral assays to determine upper airway function at multiple time points prior to and following surgery. Transoral endoscopy, videofluoroscopy, ultrasonic vocalizations, and whole-body plethysmography were used to assess VF motion, swallow function, vocal function, and respiratory function, respectively. Affected outcome metrics, such as VF motion correlation, intervocalization interval, and peak inspiratory flow were identified to increase the translational potential of this model. Additionally, immunohistochemistry was used to investigate neuronal cell death in the nucleus ambiguus. Results revealed that RLN transection created ipsilateral VF paralysis that did not recover by 13 weeks postsurgery. Furthermore, there was evidence of significant vocal and respiratory dysfunction in the RLN transection group, but not the sham injury group. No significant differences in swallow function or neuronal cell death were found between the two groups. In conclusion, our mouse model of RLN injury provides several novel functional outcome measures to increase the translational potential of findings in preclinical animal studies. We will use this model and behavioral assays to assess various treatment options in future studies.

Gene Therapy for Recurrent Laryngeal Nerve Injury

Recurrent laryngeal nerve (RLN) injury has considerable clinical implications, including voice and swallowing dysfunction, which may considerably impair the patient’s quality of life. Recovery of vocal fold movement is an essential novel treatment option for RLN injury. The potential of gene therapy for addressing this issue is highly promising. The target sites for RLN gene therapy are the central nervous system, nerve fibers, laryngeal muscles, and vocal cord mucosa. Gene transduction has been reported in each site using viral or non-viral methods. The major issues ensuing after RLN injury are loss of motoneurons in the nucleus ambiguus, degeneration and poor regeneration of nerve fibers and motor end plates, and laryngeal muscle atrophy. Gene therapy using neurotrophic factors has been assessed for most of these issues, and its efficacy has been reported. Another important matter for functional vocal fold movement recovery is misdirected regeneration, in which the wrong neurons may innervate other laryngeal muscles, where even if innervation is reestablished, proper motor function is not restored. Novel strategies involving gene therapy bear promise for overcoming this issue and further investigations are underway.

Hepatocyte Growth Factor (HGF) Promotes Peripheral Nerve Regeneration by Activating Repair Schwann Cells

During the peripheral nerve regeneration process, a variety of neurotrophic factors play roles in nerve repair by acting on neuronal or non-neuronal cells. In this report, we investigated the role(s) of hepatocyte growth factor (HGF) and its receptor, c-met, in peripheral nerve regeneration. When mice were subjected to sciatic nerve injury, the HGF protein level was highly increased at the injured and distal sites. The level of both total and phosphorylated c-met was also highly upregulated, but almost exclusively in Schwann cells (SCs) distal from the injury site. When mice were treated with a c-met inhibitor, PHA-665752, myelin thickness and axon regrowth were decreased indicating that re-myelination was hindered. HGF promoted the migration and proliferation of cultured SCs, and also induced the expression of various genes such as GDNF and LIF, presumably by activating ERK pathways. Furthermore, exogenous supply of HGF around the injury site, by intramuscular injection of a plasmid DNA expressing human HGF, enhanced the myelin thickness and axon diameter in injured nerves. Taken together, our results indicate that HGF and c-met play important roles in Schwann cell-mediated nerve repair, and also that HGF gene transfer may provide a useful tool for treating peripheral neuropathy.

Current Treatment Options for Bilateral Vocal Fold Paralysis: A State-of-the-Art Review

Vocal fold paralysis (VFP) refers to neurological causes of reduced or absent movement of one or both vocal folds. Bilateral VFP (BVFP) is characterized by inspiratory dyspnea due to narrowing of the airway at the glottic level with both vocal folds assuming a paramedian position. The primary objective of intervention for BVFP is to relieve patients’ dyspnea. Common clinical options for management include tracheostomy, arytenoidectomy and cordotomy. Other options that have been used with varying success include reinnervation techniques and botulinum toxin (Botox) injections into the vocal fold adductors. More recently, research has focused on neuromodulation, laryngeal pacing, gene therapy, and stem cell therapy. These newer approaches have the potential advantage of avoiding damage to the voicing mechanism of the larynx with an added goal of restoring some physiologic movement of the affected vocal folds. However, clinical data are scarce for these new treatment options (i.e., reinnervation and pacing), so more investigative work is needed. These areas of research are expected to provide dramatic improvements in the treatment of BVFP.

Brain-derived and glial cell line-derived neurotrophic factor fusion protein immobilization to laminin

Damage to the recurrent laryngeal nerve often causes hoarseness, dyspnea, dysphagia, and sometimes asphyxia due to vocal cord paralysis which result in a reduction of quality of life. Brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF) play critical roles in peripheral nerve regeneration. However, methods for efficiently delivering these molecules are lacking, which limits their use in clinical applications. The present study reports an effective strategy for targeting BDNF and GDNF to laminin by fusing the N-terminal domains of these molecules with agrin (NtA). More specifically, laminin-binding efficacy was assessed and sustained release assays of the delivery of BDNF or GDNF fused with NtA (LBD-BDNF or LBD-GDNF) to laminin were conducted in vitro. In addition, the bioactivity of LBD-BDNF and LBD-GDNF on laminin in vitro was investigated. LBD-BDNF and LBD-GDNF were each able to specifically bind to laminin and maintain their activity in vitro. Moreover, neurotrophic factors with NtA retained higher concentrations and bioactivity levels compared with those without NtA. The ratio of LBD-BDNF and LBD-GDNF that produced optimal effects was 4:6. BDNF and GDNF fused with NtA were effective in specifically binding to laminin. As laminin is a major component of the extracellular matrix, LBD-BDNF and LBD-GDNF may prove useful in the repair of peripheral nerve injuries.

Recovery of erectile function comparing autologous nerve grafts, unseeded conduits, Schwann-cell-seeded guidance tubes and GDNF-overexpressing Schwann cell grafts

Dissection of the cavernous nerves during radical prostatectomy for prostate cancer eliminates spontaneous erections. Using the rat as an experimental model, we compared the regenerative capacity of autologous nerve grafts and Schwann-cell-seeded nerve guides. After bilateral excision of cavernous nerve segments, cavernous nerves were reconstructed using unseeded silicon tubes, nerve autografts and silicon tubes seeded with either Glial-cell-line-derived (GDNF)-overexpressing or green fluorescent protein (GFP)-expressing Schwann cells (SCs) (16 study nerves per group). Control groups underwent either a sham operation or bilateral excision of cavernous nerve segments without repair. After 12 weeks erectile function was assessed by neurostimulation and intracavernous pressure (ICP) measurement. The reconstructed nerve segments were excised and histologically analyzed. We demonstrated an intact erectile response upon neurostimulation in 25% (4/16) of autologous nerve grafts, in 50% (8/16) of unseeded tubes, in 75% (12/16) of the Schwann-cell-GFP group and in 93.75% (15/16) of the GDNF group. ICP was significantly increased when comparing the Schwann-cell-GFP group with nerve autografts, unseeded conduits and negative controls (P<0.005). In conclusion, Schwann-cell-seeded scaffolds combined with neurotrophic factors are superior to unseeded tubes and autologous nerve grafts. They present a promising therapeutic approach for the repair of erectile nerve gaps.

Functional regeneration of the transected recurrent laryngeal nerve using a collagen scaffold loaded with laminin and laminin-binding BDNF and GDNF

Recurrent laryngeal nerve (RLN) injury remains a challenge due to the lack of effective treatments. In this study, we established a new drug delivery system consisting of a tube of Heal-All Oral Cavity Repair Membrane loaded with laminin and neurotrophic factors and tested its ability to promote functional recovery following RLN injury. We created recombinant fusion proteins consisting of brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF) fused to laminin-binding domains (LBDs) in order to prevent neurotrophin diffusion. LBD-BDNF, LBD-GDNF, and laminin were injected into a collagen tube that was fitted to the ends of the transected RLN in rats. Functional recovery was assessed 4, 8, and 12 weeks after injury. Although vocal fold movement was not restored until 12 weeks after injury, animals treated with the collagen tube loaded with laminin, LBD-BDNF and LBD-GDNF showed improved recovery in vocalisation, arytenoid cartilage angles, compound muscle action potentials and regenerated fibre area compared to animals treated by autologous nerve grafting (p < 0.05). These results demonstrate the drug delivery system induced nerve regeneration following RLN transection that was superior to that induced by autologus nerve grafting. It may have potential applications in nerve regeneration of RLN transection injury.

Electrical stimulation and testosterone enhance recovery from recurrent laryngeal nerve crush

OBJECTIVE

This study investigated the effects of a combinatorial treatment, consisting of a brief period of nerve electrical stimulation (ES) and systemic supraphysiologic testosterone, on functional recovery following a crush of the recurrent laryngeal nerve (RLN).

STUDY DESIGN

Prospective, controlled animal study.

METHODS

After a crush of the left RLN, adult male Sprague-Dawley rats were divided into four treatment groups: 1) no treatment, 2) ES, 3) testosterone propionate (TP), and 4) ES + TP. Each group was subdivided into 1, 2, 3, or 4 weeks post-operative survival time points. Groups had an n of 4- 9. Recovery of vocal fold mobility (VFM) was assessed.

RESULTS

Brief ES of the proximal nerve alone or in combination with TP accelerated the initiation of functional recovery. TP administration by itself also produced increased VFM scores compared to controls, but there were no statistical differences between the ES-treated and TP-treated animals. Treatment with brief ES alone was sufficient to decrease the time required to recover complete VFM. Animals with complete VFM were seen in treatment groups as early as 1 week following injury; in the untreated group, this was not observed until at least 3 weeks post-injury, translating into a 66% decrease in time to complete recovery.

CONCLUSIONS

Brief ES, alone or in combination with TP, promise to be effective therapeutic interventions for promoting regeneration following RLN injury.

Role of Schwann cells in the regeneration of penile and peripheral nerves

Schwann cells (SCs) are the principal glia of the peripheral nervous system. The end point of SC development is the formation of myelinating and nonmyelinating cells which ensheath large and small diameter axons, respectively. They play an important role in axon regeneration after injury, including cavernous nerve injury that leads to erectile dysfunction (ED). Despite improvement in radical prostatectomy surgical techniques, many patients still suffer from ED postoperatively as surgical trauma causes traction injuries and local inflammatory changes in the neuronal microenvironment of the autonomic fibers innervating the penis resulting in pathophysiological alterations in the end organ. The aim of this review is to summarize contemporary evidence regarding: (1) the origin and development of SCs in the peripheral and penile nerve system; (2) Wallerian degeneration and SC plastic change following peripheral and penile nerve injury; (3) how SCs promote peripheral and penile nerve regeneration by secreting neurotrophic factors; (4) and strategies targeting SCs to accelerate peripheral nerve regeneration. We searched PubMed for articles related to these topics in both animal models and human research and found numerous studies suggesting that SCs could be a novel target for treatment of nerve injury-induced ED.

Neurotrophin expression and laryngeal muscle pathophysiology following recurrent laryngeal nerve transection

Laryngeal palsy often occurs as a result of recurrent laryngeal or vagal nerve injury during oncological surgery of the head and neck, affecting quality of life and increasing economic burden. Reinnervation following recurrent laryngeal nerve (RLN) injury is difficult despite development of techniques, such as neural anastomosis, nerve grafting and creation of a laryngeal muscle pedicle. In the present study, due to the limited availability of human nerve tissue for research, a rat model was used to investigate neurotrophin expression and laryngeal muscle pathophysiology in RLN injury. Twenty-five male Sprague-Dawley rats underwent right RLN transection with the excision of a 5-mm segment. Vocal fold movements, vocalization, histology and immunostaining were evaluated at different time-points (3, 6, 10 and 16 weeks). Although vocalization was restored, movement of the vocal fold failed to return to normal levels following RLN injury. The expression of brain‑derived neurotrophic factor and glial cell line-derived neurotrophic factor differed in the thyroarytenoid (TA) and posterior cricoarytenoid muscles. The number of axons did not increase to baseline levels over time. Furthermore, normal muscle function was unlikely with spontaneous reinnervation. During regeneration following RLN injury, differences in the expression levels of neurotrophic factors may have resulted in preferential reinnervation of the TA muscles. Data from the present study indicated that neurotrophic factors may be applied for restoring the function of the laryngeal nerve following recurrent injury.

Value of a novel PGA-collagen tube on recurrent laryngeal nerve regeneration in a rat model

OBJECTIVES/HYPOTHESIS

Nerbridge (Toyobo Co., Ltd., Osaka, Japan) is a novel polyglycolic acid (PGA) tube that is filled with collagen fibers and that facilitates nerve fiber expansion and blood vessel growth. It is biocompatible and commercially available, with governmental approval for practical use in Japan. We hypothesized that the PGA-collagen tube would promote regeneration of the recurrent laryngeal nerve (RLN). This hypothesis was examined in a rat axotomy model of the RLN.

STUDY DESIGN

Prospective animal study.

METHODS

The axotomy model was established by transection of the left RLN in adult Sprague-Dawley rats. The cut ends of the nerve were bridged using Nerbridge (Toyobo Co., Ltd.) with a 1-mm gap (tube-treatment group) or direct sutures (sutured-control group). Left vocal fold mobility, nerve conduction velocity, morphology, and histology were assessed after 15 weeks.

RESULTS

Fifteen weeks after treatment, nerve fiber connections were observed macroscopically in both groups, and more clear myelinated fibers and better prevention of laryngeal muscle atrophy were observed in the tube-treatment group compared with the sutured-control group. However, vocal fold movement recovery was not observed in either group, and the conduction velocity of the RLN did not differ between the two groups.

CONCLUSIONS

Better nerve regeneration was observed in the tube-treatment group. The combination therapy with molecular or gene therapy might be an effective strategy to improve vocal fold movement. The PGA-collagen tube has the potential to promote regeneration of the RLN and to be a scaffold for drug administration in these combination therapies.

LEVEL OF EVIDENCE

N/A. Laryngoscope, 126:E233-E239, 2016.

Is there a role for neurotrophic factors and their receptors in augmenting the neuroprotective effect of (-)-epigallocatechin-3-gallate treatment of sciatic nerve crush injury?

This study analyzed and compared the effects of EGCG treatment on the expression of NTFs and NTF receptors expression in the sciatic nerve and the L3-L6 spinal cord segments at the early phase of regeneration following sciatic nerve crush injury. Analysis of BDNF, GDNF and NT3 neurotropic factors and Trk-B, Trk-C and NGFR-p75 receptors in neurons in the spinal cord of CRUSH and CRUSH + EGGC rats showed significant (p < 0.0001) decrease compared to NAÏVE and SHAM at day 1, 3, 7 and 14 after nerve injury. EGCG treatment significantly (p < 0.0001) increased the BDNF, GDN, NT3, Trk-B, Trk-C and NGFR-p75 immunostaining in the L3-L6 spinal cord compared to CRUSH animals. Also, EGCG treatment significantly increased the Trk-B protein concentration and Trk-B, NT3 and Trk-C gene expression in the spinal cords compared to CRUSH group. However, at day 1 and 3 post nerve injury, EGCG treatment significantly decreased the NGFR-p75 expression compared to CRUSH rats. In the sciatic nerve, EGCG treatment significantly (p < 0.01) increased the Trk-B and NGFR-p75 protein concentration in the controls. EGCG treatment significantly (p < 0.0001) increased the Trk-B, Trk-C and NGFR-p75 mRNA gene expressions in the sciatic nerves compared to CRUSH group. Only at day 1, CRUSH + EGCG animals displayed significant rise in the sciatic nerves NT3 gene expression compared to CRUSH group. Our data suggest that the EGCG neuroprotective effect on the spinal cord neurons may be mediated through the modulation of NTFs and NTF receptors following nerve crush injury in a rat model.

Construction and identification of human glial cell-derived neurotrophic factor gene-modified Schwann cells from rhesus monkeys

The objective of this study was to construct stable rhesus monkey Schwann cells (SCs) modified with the human glial cell-derived neurotrophic factor (hGDNF) gene. hGDNF gene amplification was performed with pUC19-hGDNF as templates, and then the coding sequence of hGDNF was inserted into the eukaryotic expression vector pBABE-puro to obtain the recombinant vector pBABE-puro-hGDNF. The recombinant vector pBABE-puro-hGDNF was identified with restriction enzyme, and then underwent DNA sequencing. SCs from rhesus monkeys were transfected with the recombinant vector pBABE-puro-hGDNF, and then the expression levels of mRNA and protein of the hGDNF gene were determined with real-time fluorescence quantitative PCR and Western blot, respectively, in the transfected SCs. The biological activity of GDNF gene-modified SCs (GDNF-SCs) was assessed by MTT assay. The length of the hGDNF coding sequence of PCR products was 569 bp. After the recombinant eukaryotic expression vectors were digested with restriction enzyme, there was a specific segment of 596 bp. The results of DNA sequencing of the specific segment of 596 bp were the same as that of hGDNF in GenBank, suggesting that the hGDNF gene was successfully inserted into the recombinant retrovirus vectors. The expression levels of mRNA and protein were significantly higher in transfected SCs as compared to nontransfected SCs (p<0.05). MTT assay indicated that the OD value was significantly higher in GDNF-SCs group than in SCs and DMEM groups (p<0.05). hGDNF-SCs can steadily and efficiently release hGDNF. This study provides a basis for cell therapy of nerve injury.

Intravenous mesenchymal stem cell therapy after recurrent laryngeal nerve injury: a preliminary study

OBJECTIVES/HYPOTHESIS

Intravenous administration of mesenchymal stem cells (MSCs) has been recently shown to enhance functional recovery after stroke and spinal cord injury. The therapeutic properties of MSCs are attributed to their secretion of a variety of potent antiinflammatory and neurotrophic factors. We hypothesize that intravenous administration of MSCs after recurrent laryngeal nerve (RLN) injury in the rat may enhance functional recovery.

STUDY DESIGN

Animal Research.

METHODS

Twelve 250-gram Sprague-Dawley rats underwent a controlled crush injury to the left RLN. After confirming postoperative vocal fold immobility, each rat was intravenously infused with either green fluorescent protein-expressing MSCs or control media in a randomized and blinded fashion. Videolaryngoscopy was performed weekly. The laryngoscopy video recordings were reviewed and rated by a fellowship-trained laryngologist who remained blinded to the intervention using a 0 to 3 scale.

RESULTS

At 1 week postinjury, the MSC-infused group showed a trend for higher average functional recovery scores compared to the control group (2.2 vs 1.3), but it did not reach statistical significance (P value of 0.06). By 2 weeks, however, both groups exhibited complete return of function.

CONCLUSIONS

These pilot data indicate that with complete nerve transection by crush injury of the RLN in rat, there is complete recovery of vocal fold mobility at 2 weeks. At 1 week postinjury, animals receiving intravenous infusion of MSCs showed a trend for greater functional recovery, suggesting a potential beneficial effect of MSCs; however, this did not reach statistical significance. Therefore, no definite conclusions can be drawn from these data and further study is required.

LEVEL OF EVIDENCE

N/A.

Differential activation of proapoptotic molecules between mouse and rat models of distal motor trigeminal denervation

BACKGROUND

We previously developed a rat trigeminal motor neuron axotomy model involving masseter and temporal muscle resection to study pathological changes of the central nucleus after peripheral nerve injury caused by oral surgery. Because motor neurons are reported to be more vulnerable to axotomy in mice than rats, we compared the degeneration process of the trigeminal motor nucleus in the rat model with a similar mouse model.

METHODS

We removed masseter and temporal muscles of adult mice or rats. Animals were sacrificed at 3, 7, 14, 28, 42, and 56 days post-operation, and the trigeminal motor nuclei were histologically analyzed.

RESULTS

Size reduction, but no neuronal loss, was seen in the trigeminal motor nuclei in both mice and rats. Time-dependent Noxa expression, starting at 1 week post-operation (wpo), was seen in the mouse model. By 8 wpo, mice expressed a higher level of Noxa than rats. Additionally, we noted persistent expression of cleaved caspase-3 in mice but not in rats. Conversely, apoptosis-inducing factor (AIF), which executes DNA fragmentation in the nucleus, was not translocated to the nucleus in either model.

CONCLUSIONS

Our findings indicate differential activation of motor neuron apoptosis pathways after axotomy in mice and rats. Lack of activation of caspase-independent pathways and distal end denervation in our model might be related to the survival of motor neurons after axonal injury. These findings could be relevant to future neuroprotective strategies for peripheral nerve injury caused by oral surgeries.

Nerve surgery and gene therapy: a neurobiological and clinical perspective

Despite major microsurgical improvements the clinical outcome of peripheral nerve surgery is still regarded as suboptimal. Over the past decade several innovative techniques have been developed to extend the armamentarium of the nerve surgeon. This review evaluates the potential of gene therapy in the context of peripheral nerve repair. First the main challenges impeding peripheral nerve regeneration are presented. This is followed by a short introduction to gene therapy and an overview of its most important advantages over the classical delivery of therapeutic proteins. Next, this review focuses on the most promising viral vectors capable of targeting the peripheral nervous system and their first application in animal models. In addition, the challenges of translating these experimental results to the clinic, the limitations of current vectors and the further developments needed, are discussed. Finally, four strategies are presented on how gene therapy could help patients that have to undergo reconstructive nerve surgery in the future.

Targeted gene transfer into rat facial muscles by nanosecond pulsed laser-induced stress waves

We investigate the feasibility of using nanosecond pulsed laser-induced stress waves (LISWs) for gene transfer into rat facial muscles. LISWs are generated by irradiating a black natural rubber disk placed on the target tissue with nanosecond pulsed laser light from the second harmonics (532 nm) of a Q-switched Nd:YAG laser, which is widely used in head and neck surgery and proven to be safe. After injection of plasmid deoxyribose nucleic acid (DNA) coding for Lac Z into rat facial muscles, pulsed laser is used to irradiate the laser target on the skin surface without incision or exposure of muscles. Lac Z expression is detected by X-gal staining of excised rat facial skin and muscles. Strong Lac Z expression is observed seven days after gene transfer, and sustained for up to 14 days. Gene transfer is achieved in facial muscles several millimeters deep from the surface. Gene expression is localized to the tissue exposed to LISWs. No tissue damage from LISWs is observed. LISW is a promising nonviral target gene transfer method because of its high spatial controllability, easy applicability, and minimal invasiveness. Gene transfer using LISW to produce therapeutic proteins such as growth factors could be used to treat nerve injury and paralysis.

Teashirt 3 regulates development of neurons involved in both respiratory rhythm and airflow control

Neonatal breathing in mammals involves multiple neuronal circuits, but its genetic basis remains unclear. Mice deficient for the zinc finger protein Teashirt 3 (TSHZ3) fail to breathe and die at birth. Tshz3 is expressed in multiple areas of the brainstem involved in respiration, including the pre-Bötzinger complex (preBötC), the embryonic parafacial respiratory group (e-pF), and cranial motoneurons that control the upper airways. Tshz3 inactivation led to pronounced cell death of motoneurons in the nucleus ambiguus and induced strong alterations of rhythmogenesis in the e-pF oscillator. In contrast, the preBötC oscillator appeared to be unaffected. These deficits result in impaired upper airway function, abnormal central respiratory rhythm generation, and altered responses to pH changes. Thus, a single gene, Tshz3, controls the development of diverse components of the circuitry required for breathing.

Neuroprotection using gene therapy to induce vascular endothelial growth factor-A expression

Engineered zinc-finger protein (ZFP) transcription factors induce the expression of endogenous genes and can be remotely delivered using adenoviral vectors. One such factor, Ad-32Ep65-Flag (Ad-p65), targets and induces expression of vascular endothelial growth factor (VEGF; also called VEGF-A) splice variants in their normal biological stoichiometry. We show that Ad-p65 transfection of primary motor neurons results in VEGF variant expression and a significant increase in axon outgrowth in these cells. Given the neuroprotective effects of VEGF and its ability to increase neurite outgrowth, we examined the efficacy of Ad-p65 to enhance motor neuron regeneration in vivo using rats that have undergone recurrent laryngeal nerve (RLN)-crush injury. Injection of Ad-p65 after RLN crush accelerated the return of vocal fold mobility and the percentage of nerve-endplate contacts in the thyroarytenoid muscle. Overall, adenoviral delivery of an engineered ZFP transcription factor inducing VEGF-A splice variant expression enhances nerve regeneration. ZFP transcription factor gene therapy to increase expression of the full complement of VEGF-A splice variants is a promising avenue for the treatment of nerve injury and neurodegeneration.

Degenerative and protective reactions of the rat trigeminal motor nucleus after removal of the masseter and temporal muscles

BACKGROUND

Microsurgical reconstruction techniques have allowed treatment of advanced head and neck carcinomas; however, it remains difficult to achieve long-term, functional reconstruction of the faciocervical muscles. To address this issue, in this we developed a rat trigeminal nerve denervation model that closely simulates the effects of oral surgery.

METHODS

The rat trigeminal nerve denervation model was developed by removing the masseter and temporal muscles, and degeneration process of the trigeminal motor nucleus was investigated by immunohistochemistry with particular focus on microglial/astrocytic reactions and motoneuron degeneration.

RESULTS

Atrophy of the trigeminal motor nucleus was observed at 8 weeks after denervation. A microglial reaction peaked at 3 days post-operation, while an astrocytic reaction was evident within 2 weeks, and peaked around 4 weeks post-operation. Expression of the stress protein HSP27 and an autophagy marker Rab24 was also upregulated in the injured trigeminal motor nucleus.

CONCLUSIONS

The results from this study suggest that this model is a practical and useful tool help to develop a further understanding of the pathology of the trigeminal motor nucleus after surgical denervation.

Physiological role of basic FGF in peripheral nerve development and regeneration: potential for reconstruction approaches

According to expression studies and functional analyses in mutant mice and in rats, FGF-2 appears to be specifically involved during development of peripheral nerves and in de-/re-generating processes at the lesion site and in spinal ganglia. In the absence of FGF receptor (FGFR)3, axonal and myelin diameters of peripheral nerves are significantly reduced, suggesting that FGFR3 physiologically regulates axonal development. The normally occurring neuronal cell death in spinal ganglia after peripheral nerve axotomy does not take place in FGF-2 and FGFR3-deleted mice, respectively, suggesting that injury-induced apoptosis is mediated via FGF-2 binding to FGFR3. According to a bimodal function of FGF-2, lesion-induced neuron death in rat spinal ganglia can be prevented by application of FGF-2 to the proximal nerve stump, which could be mediated via FGFR1/2. At the lesion site, FGF-2 appears to be involved in stimulating Schwann cell proliferation, promoting neurite outgrowth, especially of sensory nerve fibers, and regulating remyelination.

Dysfunction of the recurrent laryngeal nerve and the potential of gene therapy

Injury to the recurrent laryngeal nerve causes vocal fold paresis or paralysis resulting in poor voice quality, and possibly swallowing dysfunction and/or airway compromise. Injury can occur as part of a neurodegenerative disease process or can be due to direct nerve trauma or tumor invasion. Management depends upon symptoms, the cause and severity of injury, and the prognosis for recovery of nerve function. Surgical treatment techniques can improve symptoms, but do not restore physiologic motion. Gene therapy may be a useful adjunct to enhance nerve regeneration in the setting of neurodegenerative disease or trauma. Remote injection of viral vectors into the recurrent laryngeal nerve is the least invasive way to deliver neurotrophic factors to the nerve's cell bodies within the nucleus ambiguus, and in turn to promote nerve regeneration and enhance both nuclear and nerve survival. The purpose of this review is to discuss the potential role for gene therapy in treatment of the unsolved problem of vocal fold paralysis.

A Novel Drug Therapy for Recurrent Laryngeal Nerve Injury Using T-588

OBJECTIVES/HYPOTHESIS

We have previously shown that gene therapy using Insulin-like growth factor (IGF)-I, glial cell line-derived neurotrophic factor (GDNF), and brain-derived neurotrophic factor (BDNF), or a combination of these trophic factors, is a treatment option for recurrent laryngeal nerve (RLN) palsy. However, there remain some difficulties preventing this option from becoming a common clinical therapy for RLN injury. Thus, we need to develop novel treatment option that overcomes the problems of gene therapy.R(-)-1-(benzothiophen-5-yl)-2-[2-N,N-diethylamino]ethoxy]ethanol hydrochloride (T-588), a synthetic compound, is known to have neuroprotective effects on neural cells. In the present study, the possibility of new drug treatments using T-588 for RLN injury was assessed using rat models.

STUDY DESIGN

Animal study.

METHODS

Animals were administered T-588 for 4 weeks. The neuroprotective effects of T-588 administration after vagal nerve avulsion and neurofunctional recovery after recurrent laryngeal nerve crush were studied using motoneuron cell counting, evaluation of choline acetyltransferase immunoreactivity, the electrophysiologic examination, and the re-mobilization of the vocal fold.

RESULTS

T-588 administration successfully prevented motoneuron loss and ameliorated the choline acetyltransferase immunoreactivity in the ipsilateral nucleus ambiguus after vagal nerve avulsion. Significant improvements of motor nerve conduction velocity of the RLN and vocal fold movement were observed in the treatment group when compared to controls.

CONCLUSION

These results indicate that oral administration of T-588 might be a promising therapeutic option in treating peripheral nerve injury.

Development and characterisation of an experimental recurrent laryngeal nerve injury model for the study of viral gene therapy

OBJECTIVES

To develop and characterise an experimental model of recurrent laryngeal nerve injury for the study of viral gene therapy.

METHODS

Twenty rats underwent unilateral recurrent laryngeal nerve injury. After vocal fold mobility was observed, larynges were serially sectioned, and immunohistochemical techniques were employed to stain for neurofilament and motor endplates in order for a blinded investigator to determine the percentage of nerve-endplate contact, as a histological indicator of an intact neuromuscular connection.

RESULTS

All animal procedures resulted in complete, ipsilateral vocal fold paralysis that recovered by three weeks. The mean nerve-endplate contact percentage was 11.6 per cent at one week, 53.9 per cent at two weeks, 88.6 per cent at three weeks, 81.7 per cent at four weeks and 86.6 per cent at five weeks. The differences between results at week one and week three were statistically significant (p < 0.01). The mean nerve-endplate contact percentage on the control side was 86.8 per cent.

CONCLUSIONS

There was a dramatic, measurable decrease in nerve-endplate contact percentage following crush injury to the recurrent laryngeal nerve. Spontaneous recovery was observed by three weeks post-injury. This model will be used to investigate the potential therapeutic role of viral gene therapy for the treatment of recurrent laryngeal nerve injury.

Bioengineered nerve regeneration and muscle reinnervation

The peripheral nervous system has the intrinsic capacity to regenerate but the reinnervation of muscles is often suboptimal and results in limited recovery of function. Injuries to nerves that innervate complex organs such as the larynx are particularly difficult to treat. The many functions of the larynx have evolved through the intricate neural regulation of highly specialized laryngeal muscles. In this review, we examine the responses of nerves and muscles to injury, focusing on changes in the expression of neurotrophic factors, and highlight differences between the skeletal limb and laryngeal muscle systems. We also describe how artificial nerve conduits have become a useful tool for delivery of neurotrophic factors as therapeutic agents to promote peripheral nerve repair and might eventually be useful in the treatment of laryngeal nerve injury.

Gene therapy for laryngeal paralysis

OBJECTIVES

The surgical options for laryngeal paralysis only achieve static changes of vocal fold position. Laryngeal reinnervation procedures have had little impact on the return of dynamic laryngeal function. The development of a new treatment for laryngeal paralysis, aimed at the return of dynamic function and neurologic restoration and regeneration, is necessary.

METHODS

To assess the possibility of gene therapy for laryngeal paralysis aiming for the return of dynamic laryngeal function, we investigated the therapeutic effects of gene therapy using rat laryngeal paralysis models.

RESULTS

In a rat vagal nerve avulsion model, we transferred glial cell line-derived neurotrophic factor (GDNF) gene into the nucleus ambiguus using an adenovirus vector. Two and 4 weeks after the GDNF gene transfer, a significantly larger number of surviving motoneurons was observed. These neuroprotective effects of GDNF gene transfer were enhanced by simultaneous brain-derived neurotrophic factor gene transfer. In a rat recurrent laryngeal nerve crush model, we transferred GDNF gene into recurrent laryngeal nerve fibers after crush injury. Two and 4 weeks after GDNF gene transfer, we observed significantly faster nerve conduction velocity and better vocal fold motion recovery.

CONCLUSIONS

These results indicate that gene therapy could be a future treatment strategy for laryngeal paralysis. Further studies will be necessary to demonstrate the safety of the vector before clinical application.