Peripheral nerve regeneration

Schwann cells secrete IGFBP5 to facilitate the growth of keloids

Keloids (KD) are noncancerous fibroproliferative tumors exhibiting cancer-like traits, encompass aggressive unregulated growth, absence of natural regression, and a significantly high rate of recurrence. The precise molecular mechanisms underlying KD pathology remain poorly understood. In this study, we employed single-cell sequencing to examine the characteristics of cells in KD and normal scar (NS) tissue. We evaluated Schwann cells and their secretory protein IGFBP5 function in KD. Then, the recombinant IGFBP5 protein was employed to elucidate the regulatory roles of IGFBP5 in the proliferation, migration, invasion, angiogenesis, and cell cycle of keloids fibroblasts (KF). The rabbit ear scar model was utilized to ascertain the function of IGFBP5 in vivo. We demonstrated that in KD, the proportion of Schwann cells was 4.13 times that of NS. Besides, the IGFBP5 gene exhibited an expression level that was 8.02 times higher in KD Schwann cells compared to those in NS Schwann cells. High IGFBP5 expression was positively associated with the cell proliferation, migration, invasion, angiogenesis, and cell cycle of KF. Additionally, the p53/p21/Cyclin D1 pathway regulated cell cycle and promoted cell proliferation, which was suppressed after rIGFBP5 administration. These findings suggest that Schwann cells infiltrate in KD and secrete IGFBP5 protein to promote KD growth, and targeting IGFBP5 or Schwann cell infiltration could offer novel therapeutic strategies for KD.

The mechanotransduction protein STOML3 is required for proprioceptor plasticity following peripheral nerve regeneration

Nerve regeneration is associated with the plasticity of sensory neurons such that even muscle afferents directed to the skin form mechanosensitive receptive fields appropriate for the new target. STOML3 is an essential mechanotransduction component in many cutaneous mechanoreceptors. Here, we asked whether STOML3 is required for functional and anatomical plasticity following peripheral nerve regeneration. We used a cross-anastomosis model adapted to the mouse, in which the medial gastrocnemius nerve was redirected to innervate hairy skin previously occupied by the sural nerve. We recorded from muscle afferents innervating the skin and found that in wild-type mice their receptive properties were largely identical to normal skin mechanoreceptors. However, in mice lacking STOML3, muscle afferents largely failed to form functional mechanosensitive receptive fields, despite making anatomically appropriate endings in the skin. Our tracing experiments demonstrated that muscle afferents from both wild-type and stoml3 mutant mice display remarkable anatomical plasticity, forming new somatotopically appropriate synaptic terminals in the region of the dorsal horn representing the sural nerve territory. The dramatic reduction in stimulus-evoked activity from the cross-anastomosed gastrocnemius nerve in stoml3 mutant mice did not prevent central anatomical plasticity. Our results have identified a molecular factor required for functional plasticity following peripheral nerve injury.

Exosomes repairment for sciatic nerve injury: a cell-free therapy

Sciatic nerve injury (SNI) is a common type of peripheral nerve injury typically resulting from trauma, such as contusion, sharp force injuries, drug injections, pelvic fractures, or hip dislocations. It leads to both sensory and motor dysfunctions, characterized by pain, numbness, loss of sensation, muscle atrophy, reduced muscle tone, and limb paralysis. These symptoms can significantly diminish a patient's quality of life. Following SNI, Wallerian degeneration occurs, which activates various signaling pathways, inflammatory factors, and epigenetic regulators. Despite the availability of several surgical and nonsurgical treatments, their effectiveness remains suboptimal. Exosomes are extracellular vesicles with diameters ranging from 30 to 150 nm, originating from the endoplasmic reticulum. They play a crucial role in facilitating intercellular communication and have emerged as highly promising vehicles for drug delivery. Increasing evidence supports the significant potential of exosomes in repairing SNI. This review delves into the pathological progression of SNI, techniques for generating exosomes, the molecular mechanisms behind SNI recovery with exosomes, the effectiveness of combining exosomes with other approaches for SNI repair, and the changes and future outlook for utilizing exosomes in SNI recovery.

Schwann Cells as Orchestrators of Nerve Repair: Implications for Tissue Regeneration and Pathologies

Peripheral nerves exist in a stable state in adulthood providing a rapid bidirectional signaling system to control tissue structure and function. However, following injury, peripheral nerves can regenerate much more effectively than those of the central nervous system (CNS). This multicellular process is coordinated by peripheral glia, in particular Schwann cells, which have multiple roles in stimulating and nurturing the regrowth of damaged axons back to their targets. Aside from the repair of damaged nerves themselves, nerve regenerative processes have been linked to the repair of other tissues and de novo innervation appears important in establishing an environment conducive for the development and spread of tumors. In contrast, defects in these processes are linked to neuropathies, aging, and pain. In this review, we focus on the role of peripheral glia, especially Schwann cells, in multiple aspects of nerve regeneration and discuss how these findings may be relevant for pathologies associated with these processes.

Structured wound angiogenesis instructs mesenchymal barrier compartments in the regenerating nerve

Organ injury stimulates the formation of new capillaries to restore blood supply raising questions about the potential contribution of neoangiogenic vessel architecture to the healing process. Using single-cell mapping, we resolved the properties of endothelial cells that organize a polarized scaffold at the repair site of lesioned peripheral nerves. Transient reactivation of an embryonic guidance program is required to orient neovessels across the wound. Manipulation of this structured angiogenic response through genetic and pharmacological targeting of Plexin-D1/VEGF pathways within an early window of repair has long-term impact on configuration of the nerve stroma. Neovessels direct nerve-resident mesenchymal cells to mold a provisionary fibrotic scar by assembling an orderly system of stable barrier compartments that channel regenerating nerve fibers and shield them from the persistently leaky vasculature. Thus, guided and balanced repair angiogenesis enables the construction of a "bridge" microenvironment conducive for axon regrowth and homeostasis of the regenerated tissue.

Regenerative capacity of neural tissue scales with changes in tissue mechanics post injury

Spinal cord injuries have devastating consequences for humans, as mammalian neurons of the central nervous system (CNS) cannot regenerate. In the peripheral nervous system (PNS), however, neurons may regenerate to restore lost function following injury. While mammalian CNS tissue softens after injury, how PNS tissue mechanics changes in response to mechanical trauma is currently poorly understood. Here we characterised mechanical rat nerve tissue properties before and after in vivo crush and transection injuries using atomic force microscopy-based indentation measurements. Unlike CNS tissue, PNS tissue significantly stiffened after both types of tissue damage. This nerve tissue stiffening strongly correlated with an increase in collagen I levels. Schwann cells, which crucially support PNS regeneration, became more motile and proliferative on stiffer substrates in vitro, suggesting that changes in tissue stiffness may play a key role in facilitating or impeding nervous system regeneration.

Application and underlying mechanism of acupuncture for the nerve repair after peripheral nerve injury: remodeling of nerve system

Peripheral nerve injury (PNI) is a structural event with harmful consequences worldwide. Due to the limited intrinsic regenerative capacity of the peripheral nerve in adults, neural restoration after PNI is difficult. Neurological remodeling has a crucial effect on the repair of the form and function during the regeneration of the peripheral nerve after the peripheral nerve is injured. Several studies have demonstrated that acupuncture is effective for PNI-induced neurologic deficits, and the potential mechanisms responsible for its effects involve the nervous system remodeling in the process of nerve repair. Moreover, acupuncture promotes neural regeneration and axon sprouting by activating related neurotrophins retrograde transport, such as nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), glial cell-derived neurotrophic factor (GDNF), N-cadherin, and MicroRNAs. Peripheral nerve injury enhances the perceptual response of the central nervous system to pain, causing central sensitization and accelerating neuronal cell apoptosis. Together with this, the remodeling of synaptic transmission function would worsen pain discomfort. Neuroimaging studies have shown remodeling changes in both gray and white matter after peripheral nerve injury. Acupuncture not only reverses the poor remodeling of the nervous system but also stimulates the release of neurotrophic substances such as nerve growth factors in the nervous system to ameliorate pain and promote the regeneration and repair of nerve fibers. In conclusion, the neurological remodeling at the peripheral and central levels in the process of acupuncture treatment accelerates nerve regeneration and repair. These findings provide novel insights enabling the clinical application of acupuncture in the treatment of PNI.

Endoplasmic Reticulum Exit Sites scale with somato-dendritic size in neurons

Nervous systems exhibit dramatic diversity in cell morphology and size. How neurons regulate their biosynthetic and secretory machinery to support such diversity is not well understood. Endoplasmic reticulum exit sites (ERESs) are essential for maintaining secretory flux, and are required for normal dendrite development, but how neurons of different size regulate secretory capacity remains unknown. In Caenorhabditis elegans, we find that the ERES number is strongly correlated with the size of a neuron's dendritic arbor. The elaborately branched sensory neuron, PVD, has especially high ERES numbers. Asymmetric cell division provides PVD with a large initial cell size critical for rapid establishment of PVD's high ERES number before neurite outgrowth, and these ERESs are maintained throughout development. Maintenance of ERES number requires the cell fate transcription factor MEC-3, C. elegans TOR (ceTOR/let-363), and nutrient availability, with mec-3 and ceTOR/let-363 mutant PVDs both displaying reductions in ERES number, soma size, and dendrite size. Notably, mec-3 mutant animals exhibit reduced expression of a ceTOR/let-363 reporter in PVD, and starvation reduces ERES number and somato-dendritic size in a manner genetically redundant with ceTOR/let-363 perturbation. Our data suggest that both asymmetric cell division and nutrient sensing pathways regulate secretory capacities to support elaborate dendritic arbors.

Medium chain length polyhydroxyalkanoates as potential matrix materials for peripheral nerve regeneration

Polyhydroxyalkanoates are natural, biodegradable, thermoplastic and sustainable polymers with a huge potential in fabrication of bioresorbable implantable devices for tissue engineering. We describe a comparative evaluation of three medium chain length polyhydroxyalkanoates (mcl-PHAs), namely poly(3-hydroxyoctanoate), poly(3-hydroxyoctanoate-co-3-hydoxydecanoate) and poly(3-hydroxyoctanoate-co-3-hydroxydecanoate-co-3-hydroxydodecanoate), one short chain length polyhydroxyalkanoate, poly(3-hydroxybutyrate), P(3HB) and synthetic aliphatic polyesters (polycaprolactone and polylactide) with a specific focus on nerve regeneration, due to mechanical properties of mcl-PHAs closely matching nerve tissues. In vitro biological studies with NG108-15 neuronal cell and primary Schwann cells did not show a cytotoxic effect of the materials on both cell types. All mcl-PHAs supported cell adhesion and viability. Among the three mcl-PHAs, P(3HO-co-3HD) exhibited superior properties with regards to numbers of cells adhered and viable cells for both cell types, number of neurite extensions from NG108-15 cells, average length of neurite extensions and Schwann cells. Although, similar characteristics were observed for flat P(3HB) surfaces, high rigidity of this biomaterial, and FDA-approved polymers such as PLLA, limits their applications in peripheral nerve regeneration. Therefore, we have designed, synthesized and evaluated these materials for nerve tissue engineering and regenerative medicine, the interaction of mcl-PHAs with neuronal and Schwann cells, identifying mcl-PHAs as excellent materials to enhance nerve regeneration and potentially their clinical application in peripheral nerve repair.

Spatio-temporally deciphering peripheral nerve regeneration in vivo after extracellular vesicle therapy under NIR-II fluorescence imaging

Extracellular vesicles (EVs) show potential as a therapeutic tool for peripheral nerve injury (PNI), promoting neurological regeneration. However, there are limited data on the in vivo spatio-temporal trafficking and biodistribution of EVs. In this study, we introduce a new non-invasive near-infrared fluorescence imaging strategy based on glucose-conjugated quantum dot (QDs-Glu) labeling to target and track EVs in a sciatic nerve injury rat model in real-time. Our results demonstrate that the injected EVs migrated from the uninjured site to the injured site of the nerve, with an increase in fluorescence signals detected from 4 to 7 days post-injection, indicating the release of contents from the EVs with therapeutic effects. Immunofluorescence and behavioral tests revealed that the EV therapy promoted nerve regeneration and functional recovery at 28 days post-injection. We also found a relationship between functional recovery and the NIR-II fluorescence intensity change pattern, providing novel evidence for the therapeutic effects of EV therapy using real-time NIR-II imaging at the live animal level. This approach initiates a new path for monitoring EVs in treating PNI under in vivo NIR-II imaging, enhancing our understanding of the efficacy of EV therapy on peripheral nerve regeneration and its mechanisms.

Cryoablation for the treatment of chronic rhinitis: a systematic review

BACKGROUND

ClariFix is a novel intranasal cryotherapy device developed for clinic-based cryosurgical ablation of the posterior nasal nerves region. As a relatively new technology, there is a paucity of studies within the literature assessing the efficacy and safety profile of ClariFix for chronic rhinitis.

METHODS

A systematic review was completed in accordance with PRISMA guidelines. Databases searched included: Ovid Medline, Ovid EMBASE, Pubmed, Cochrane and Web of Science. Inclusion criteria consisted of studies investigating the use of ClariFix in chronic rhinitis (i.e., allergic and non-allergic rhinitis) in patients of all ages.

RESULTS

The initial search identified 1110 studies. Final analysis consisted of 8 articles, evaluating a total of 472 patients. The data showed a significant reduction in scores post-treatment across all studies based on validated outcome measures. In all studies, at all time intervals, there was a significant improvement in outcome scores from baseline. Minor adverse effects included post-procedural pain and discomfort, headache and palate numbness. No major adverse events were identified.

CONCLUSION

ClariFix is a novel intranasal cryotherapy device that was introduced in Canada in 2021. This is the first systematic review evaluating its efficacy and safety profile. Across all studies, there was a significant reduction in validated outcome scores at multiple time intervals. Further, the treatment is safe with only minor adverse effects reported by patients. Overall, the consensus from this study highlights an apparent benefit in using this intervention for chronic rhinitis that is refractory to medical management.

Functional neurological restoration of amputated peripheral nerve using biohybrid regenerative bioelectronics

The development of neural interfaces with superior biocompatibility and improved tissue integration is vital for treating and restoring neurological functions in the nervous system. A critical factor is to increase the resolution for mapping neuronal inputs onto implants. For this purpose, we have developed a new category of neural interface comprising induced pluripotent stem cell (iPSC)-derived myocytes as biological targets for peripheral nerve inputs that are grafted onto a flexible electrode arrays. We show long-term survival and functional integration of a biohybrid device carrying human iPSC-derived cells with the forearm nerve bundle of freely moving rats, following 4 weeks of implantation. By improving the tissue-electronics interface with an intermediate cell layer, we have demonstrated enhanced resolution and electrical recording in vivo as a first step toward restorative therapies using regenerative bioelectronics.

Temperature-controlled radiofrequency neurolysis for treatment of chronic rhinitis: 12-month outcomes after treatment in a randomized controlled trial

BACKGROUND

Temperature-controlled radiofrequency (TCRF) neurolysis of the posterior nasal nerve (PNN) area for the treatment of chronic rhinitis was previously reported as superior to a sham-control procedure at 3 months postprocedure in a randomized controlled trial (RCT). The primary endpoint was a responder rate of ≥30% improvement (decrease) for 24-hour reflective total nasal symptom score (rTNSS) compared with baseline. Herein, 12-month outcomes after active treatment are reported.

METHODS

In this prospective, multicenter, patient-blinded RCT, patients in the index active treatment arm were unblinded at 3 months and followed through 12 months. At 3 months, eligible patients from the sham-control arm of the study were invited to crossover to active treatment. Eligibility criteria included rTNSS ≥6, with moderate-severe rhinorrhea and mild-severe congestion. The TCRF stylus was applied bilaterally to nonoverlapping areas in the region of the PNN.

RESULTS

Patients in the index active treatment arm (n = 77) had a mean baseline rTNSS of 8.3 (95% confidence interval [CI], 7.9-8.7). At 12 months, the responder rate was 80.6% (n = 67) (95% CI, 69.1%-89.2%). At 12 months, the mean change in rTNSS was -4.8 (95% CI, -5.5 to -4.1; p < 0.001), a 57.8% improvement. The available initial rTNSS-based outcomes in the crossover active treatment arm (n = 27) were following the same course as the index treatment arm. No serious adverse events and 8 adverse events related to the device/procedure were reported in the trial to date.

CONCLUSION

TCRF neurolysis of the PNN area is safe and the symptom burden improvement that was superior to a sham procedure at 3 months was sustained through 12 months.

Resurgent neuropathic discharge: an obstacle to the therapeutic use of neuroma resection?

ABSTRACT

Ectopic discharge ("ectopia") in damaged afferent axons is a major contributor to chronic neuropathic pain. Clinical opinion discourages surgical resection of nerves proximal to the original injury site for fear of resurgence of ectopia and exacerbated pain. We tested this concept in a well-established animal neuroma model. Teased-fiber recordings were made of ectopic spontaneous discharge originating in the experimental nerve-end neuroma and associated dorsal root ganglia in rats that underwent either a single transection (with ligation) of the sciatic nerve or 2 consecutive transections separated by 7, 14, 21, or 30 days. Ectopia emerged in afferent A and C fibers after a single cut with kinetics anticipated from previous studies. When resection was performed during the early period of intense A-fiber activity, a brief period of resurgence was observed. However, resection of neuromas of more than 14 days was followed by low levels of activity with no indication of resurgence. This remained the case in trials out to 60 days after the first cut. Similarly, we saw no indication of resurgent ectopia originating in axotomized dorsal root ganglion neuronal somata and no behavioral reflection of resurgence. In summary, we failed to validate the concern that proximal resection of a problematic nerve would lead to intense resurgent ectopic discharge and pain. As the well-entrenched concept of resurgence is based more on case reports and anecdotes than on solid evidence, it may be justified to relax the stricture against resecting neuromas as a therapeutic strategy, at least within the framework of controlled clinical trials.

Repair of Long Peripheral Nerve Defects in Sheep: A Translational Model for Nerve Regeneration

Despite advances in microsurgery, full functional recovery of severe peripheral nerve injuries is not commonly attained. The sheep appears as a good preclinical model since it presents nerves with similar characteristics to humans. In this study, we induced 5 or 7 cm resection in the peroneal nerve and repaired with an autograft. Functional evaluation was performed monthly. Electromyographic and ultrasound tests were performed at 6.5 and 9 months postoperation (mpo). No significant differences were found between groups with respect to functional tests, although slow improvements were seen from 5 mpo. Electrophysiological tests showed compound muscle action potentials (CMAP) of small amplitude at 6.5 mpo that increased at 9 mpo, although they were significantly lower than the contralateral side. Ultrasound tests showed significantly reduced size of tibialis anterior (TA) muscle at 6.5 mpo and partially recovered size at 9 mpo. Histological evaluation of the grafts showed good axonal regeneration in all except one sheep from autograft 7 cm (AG7) group, while distal to the graft there was a higher number of axons than in control nerves. The results indicate that sheep nerve repair is a useful model for investigating long-gap peripheral nerve injuries.

Hydrogen peroxide induced by nerve injury promotes axon regeneration via connective tissue growth factor

Regeneration of the neuromuscular junction (NMJ) leverages on extensive exchange of factors released from motor axon terminals (MATs), muscle fibers and perisynaptic Schwann cells (PSCs), among which hydrogen peroxide (H₂O₂) is a major pro-regenerative signal. To identify critical determinants of NMJ remodeling in response to injury, we performed temporal transcriptional profiling of NMJs from 2 month-old mice during MAT degeneration/regeneration, and cross-referenced the differentially expressed genes with those elicited by H₂O₂ in SCs. We identified an enrichment in extracellular matrix (ECM) transcripts, including Connective Tissue Growth Factor (Ctgf), which is usually expressed during development. We discovered that Ctgf levels are increased in a Yes-associated protein (YAP)-dependent fashion in response to rapid, local H₂O₂ signaling generated by stressed mitochondria in the injured sciatic nerve, a finding highlighting the importance of signals triggered by mechanical force to motor nerve repair. Through sequestration of Ctgf or inactivation of H₂O₂, we delayed the recovery of neuromuscular function by impairing SC migration and, in turn, axon-oriented re-growth. These data indicate that H₂O₂ and its downstream effector Ctgf are pro-regenerative factors that enable axonal growth, and reveal a striking ECM remodeling process during nerve regeneration upon local H₂O₂ signaling. Our study identifies key transcriptomic changes at the regenerating NMJ, providing a rich source of pro-regenerative factors with potential for alleviating the consequences of peripheral nerve injuries.

Sexual dimorphism of early transcriptional reprogramming in degenerating peripheral nerves

Sexual dimorphism is a powerful yet understudied factor that influences the timing and efficiency of gene regulation in axonal injury and repair processes in the peripheral nervous system. Here, we identified common and distinct biological processes in female and male degenerating (distal) nerve stumps based on a snapshot of transcriptional reprogramming 24 h after axotomy reflecting the onset of early phase Wallerian degeneration (WD). Females exhibited transcriptional downregulation of a larger number of genes than males. RhoGDI, ERBB, and ERK5 signaling pathways increased activity in both sexes. Males upregulated genes and canonical pathways that exhibited robust baseline expression in females in both axotomized and sham nerves, including signaling pathways controlled by neuregulin and nerve growth factors. Cholesterol biosynthesis, reelin signaling, and synaptogenesis signaling pathways were downregulated in females. Signaling by Rho Family GTPases, cAMP-mediated signaling, and sulfated glycosaminoglycan biosynthesis were downregulated in both sexes. Estrogens potentially influenced sex-dependent injury response due to distinct regulation of estrogen receptor expression. A crosstalk of cytokines and growth hormones could promote sexually dimorphic transcriptional responses. We highlighted prospective regulatory activities due to protein phosphorylation, extracellular proteolysis, sex chromosome-specific expression, major urinary proteins (MUPs), and genes involved in thyroid hormone metabolism. Combined with our earlier findings in the corresponding dorsal root ganglia (DRG) and regenerating (proximal) nerve stumps, sex-specific and universal early phase molecular triggers of WD enrich our knowledge of transcriptional regulation in peripheral nerve injury and repair.

Use of a bio-electronic device comprising of targeted dual neuromodulation of the hepatic and celiac vagal branches demonstrated enhanced glycemic control in a type 2 diabetic rat model as well as in an Alloxan treated swine model

Background

There is an unmet need for new type 2 diabetes treatments providing improved efficacy, durability and customized to improve patient’s compliance. Bio-electronic neuromodulation of Vagus nerve branches innervating organs that regulate plasma glucose, may be a method for treating type 2 diabetes. The pancreas has been shown to release insulin during Vagus stimulation. The hepatic vagal branch, innervating the liver, has been shown to decrease glucose release and decrease insulin resistance following ligation. However, standalone stimulation of the Vagus nerve has shown mixed results and Vagus nerve ligation has undesirable effects. Little is known; however, of the effect on plasma glucose with combined neuromodulation consisting of stimulation of the celiac branch innervating the pancreas with simultaneous high frequency alternating current (HFAC) blockade of the hepatic branch. This study tested the effects of this approach on increasing glycemic control in rat a model of type 2 diabetes and Alloxan treated swine.

Materials and methods

Zucker obese (fatty) male rats (ZDF fa/fa) were used as a model of type 2 diabetes as well as glucose intolerant Alloxan treated swine. In ZDF rat experiments glycemic control was accessed with an intravenous glucose tolerance test during HFAC-induced hepatic branch block with concurrent celiac stimulation (HFAC + stimulation). In swine experiments glycemic control was accessed by an oral glucose tolerance test during HFAC + stimulation. Insulin measurements were taken prior to and following swine experiments giving insight into beta cell exhaustion. Histopathology was conducted to determine safety of HFAC + stimulation on Vagal branches.

Results

Zucker rats demonstrated a significant improvement to an intravenous glucose tolerance test during HFAC + stimulation compared to sham. There was no significant difference from sham compared to hepatic vagotomy or celiac stimulation. In Alloxan treated swine, when subjected to HFAC + stimulation, there was a significant improvement in glycemic control as measured by an improvement on oral glucose tolerance tests and a decrease in fasting plasma glucose. Insulin responses were similar prior to and following HFAC + stimulation experiments. Histopathology demonstrated healthy swine Vagus nerves.

Conclusion

Electrical blockade of the hepatic Vagus branch with simultaneous stimulation of the celiac Vagus branch may be a novel, adjustable and localized approach for a treatment of type 2 diabetes.

Sexually dimorphic transcriptional programs of early-phase response in regenerating peripheral nerves

The convergence of transcriptional and epigenetic changes in the peripheral nervous system (PNS) reshapes the spatiotemporal gene expression landscape in response to nerve transection. The control of these molecular programs exhibits sexually dimorphic characteristics that remain not sufficiently characterized. In the present study, we recorded genome-wide and sex-dependent early-phase transcriptional changes in regenerating (proximal) sciatic nerve 24 h after axotomy. Male nerves exhibited more extensive transcriptional changes with male-dominant upregulation of cytoskeletal binding and structural protein genes. Regulation of mRNAs encoding ion and ionotropic neurotransmitter channels displayed prominent sexual dimorphism consistent with sex-specific mRNA axonal transport in an early-phase regenerative response. Protein kinases and axonal transport genes showed sexually dimorphic regulation. Genes encoding components of synaptic vesicles were at high baseline expression in females and showed post-injury induction selectively in males. Predictive bioinformatic analyses established patterns of sexually dimorphic regulation of neurotrophic and immune genes, including activation of glial cell line-derived neurotrophic factor Gfra1 receptor and immune checkpoint cyclin D1 (Ccnd1) potentially linked to X-chromosome encoded tissue inhibitor of matrix metallo proteinases 1 (Timp1). Regulatory networks involving Olig1, Pou3f3/Oct6, Myrf, and Myt1l transcription factors were linked to sex-dependent reprogramming in regenerating nerves. Differential expression patterns of non-coding RNAs motivate a model of sexually dimorphic nerve regenerative responses to injury determined by epigenetic factors. Combined with our findings in the corresponding dorsal root ganglia (DRG), unique early-phase sex-specific molecular triggers could enrich the mechanistic understanding of peripheral neuropathies.

Evaluation of Platelet-Rich Plasma Therapy for Peripheral Nerve Regeneration: A Critical Review of Literature

Peripheral nerve injury (PNI) is a common disease in clinic, and the regeneration process of peripheral nerve tissue is slow, and patients with PNI often suffer from the loss of nerve function. At present, related research on the mechanism of peripheral nerve regeneration has become a hot spot, and scholars are also seeking a method that can accelerate the regeneration of peripheral nerve. Platelet-rich plasma (PRP) is a platelet concentrate extracted from autologous blood by centrifugation, which is a kind of bioactive substance. High concentration of platelets can release a variety of growth factors after activation, and can promote the proliferation and differentiation of tissue cells, which can accelerate the process of tissue regeneration. The application of PRP comes from the body, there is no immune rejection reaction, it can promote tissue regeneration with less cost, it is,therefore, widely used in various clinical fields. At present, there are relatively few studies on the application of PRP to peripheral nerve regeneration. This article summarizes the literature in recent years to illustrate the effect of PRP on peripheral nerve regeneration from mechanism to clinical application, and prospects for the application of PRP to peripheral nerve.

Potential of Fibrin Glue and Mesenchymal Stem Cells (MSCs) to Regenerate Nerve Injuries: A Systematic Review

Cell-based therapy is a promising treatment to favor tissue healing through less invasive strategies. Mesenchymal stem cells (MSCs) highlighted as potential candidates due to their angiogenic, anti-apoptotic and immunomodulatory properties, in addition to their ability to differentiate into several specialized cell lines. Cells can be carried through a biological delivery system, such as fibrin glue, which acts as a temporary matrix that favors cell-matrix interactions and allows local and paracrine functions of MSCs. Thus, the aim of this systematic review was to evaluate the potential of fibrin glue combined with MSCs in nerve regeneration. The bibliographic search was performed in the PubMed/MEDLINE, Web of Science and Embase databases, using the descriptors ("fibrin sealant" OR "fibrin glue") AND "stem cells" AND "nerve regeneration", considering articles published until 2021. To compose this review, 13 in vivo studies were selected, according to the eligibility criteria. MSCs favored axonal regeneration, remyelination of nerve fibers, as well as promoted an increase in the number of myelinated fibers, myelin sheath thickness, number of axons and expression of growth factors, with significant improvement in motor function recovery. This systematic review showed clear evidence that fibrin glue combined with MSCs has the potential to regenerate nervous system lesions.

Long-term Outcomes Following Temperature-Controlled Radiofrequency Neurolysis for the Treatment of Chronic Rhinitis

Background

Temperature-controlled radiofrequency neurolysis of the posterior nasal nerve has been shown to reduce the symptom burden of patients with chronic rhinitis.

Objectives

To evaluate the long-term safety and effectiveness of temperature-controlled radiofrequency neurolysis of the posterior nasal nerve for the treatment of chronic rhinitis.

Methods

A prospective extension of a 12-month single-arm study, where reflective total nasal symptom score (rTNSS) and the responses to a study-specific quality of life questionnaire and patient satisfaction survey were collected at 24 months.

Results

Forty-seven patients completed initial 12-month follow-up after treatment with the study device, of which 34 patients were reconsented and completed 24-month follow-up. The mean rTNSS of the long-term follow-up patients improved from 8.4 (95% confidence interval (CI), 7.7 to 9.0) at baseline to 2.9 (95% CI, 2.1 to 3.6), P < .001 at 24 months, a 65.5% improvement. On a 6-point scale (0-5), postnasal drip improved from a mean of 4.1 (95% CI, 3.6 to 4.6) to 2.1 (95% CI, 1.7 to 2.5) and chronic cough improved from 3.2 (95% CI, 2.7 to 3.6) to 0.9 (95% CI, 0.5 to 1.3) from baseline through 24 months; P < .001 for both measures. The proportion of patients achieving a minimal clinically important difference of 30% improvement from baseline at 24 months was 88.2% (95% CI, 73.4%-95.3%). At 24 months, 24% of patients were taking overall fewer and 15% taking overall more rhinitis medication classes than at baseline. Patients reported a higher quality of life in terms of sleep, well-being, and lower oral medication/nasal spray use at 24 months. There were no serious adverse events considered related to the procedure in the 12-24-month period.

Conclusion

Temperature-controlled radiofrequency neurolysis results in a significant and durable reduction in the symptom burden of chronic rhinitis and patients reported improved quality of life through 24 months postprocedure.

Endocytosis-associated patterns in nerve regeneration after peripheral nerve injury

Background

Clearance of myelin debris and remyelination of myelin are necessary steps for peripheral nerve remodeling and regeneration. It has yet to be clarified which genes or proteins are involved in endocytosis or exocytosis in the removal of myelin debris during peripheral nerve repair.

Methods

For this project, a rat model of subacute stage of sciatic nerve injury was established first. Subsequently, normal Schwann cells (NSCs) and activated Schwann cells (ASCs) were harvest before and after peripheral nerve injury (PNI). Following methylated DNA immunoprecipitation sequencing (MeDIP-seq) and tandem mass tags (TMT) labeling analysis of NSCs and ASCs, what common biomarkers changes in peripheral nervous systems remain to be elucidated.

Results

A total of 14,770 different expression genes (DEGs) and 3249 different expression proteins (DEPs) were screened between ASCs and NSCs. For the exosomes, the diameter and particles concentration of exosomes were 141.7 ​nm and 2.97 ​× ​10⁷ particles/mL, respectively. The size distribution of exosomes was 50–200 ​nm. ASCs showed higher cellular uptake ability than the NSCs by cellular uptake test. Moreover, RAB7A, ARF6, ARF1, VPS45, RAB11A, DNM3, and NEDD4 were the core markers and may control the molecular mechanism of the Endocytosis pathway.

Conclusion

These biomarkers may play significant roles in the initiation phase of demyelination and axon regeneration.

The translational potential of this article

This study explores that the endocytosis-associated patterns of Schwann cells may be new therapeutic strategy for nerve tissue engineering and nerve regeneration.

Pyrrole Plasma Polymer-Coated Electrospun Scaffolds for Neural Tissue Engineering

Promising strategies for neural tissue engineering are based on the use of three-dimensional substrates for cell anchorage and tissue development. In this work, fibrillar scaffolds composed of electrospun randomly- and aligned-oriented fibers coated with plasma synthesized pyrrole polymer, doped and undoped with iodine, were fabricated and characterized. Infrared spectroscopy, thermogravimetric analysis, and X-ray diffraction analysis revealed the functional groups and molecular integration of each scaffold, as well as the effect of plasma polymer synthesis on crystallinity. Scanning microscopy imaging demonstrated the porous fibrillar micrometric structure of the scaffolds, which afforded adhesion, infiltration, and survival for the neural cells. Orientation analysis of electron microscope images confirmed the elongation of neurite-like cell structures elicited by undoped plasma pyrrole polymer-coated aligned scaffolds, without any biochemical stimuli. The MTT colorimetric assay validated the biocompatibility of the fabricated composite materials, and further evidenced plasma pyrrole polymer-coated aligned scaffolds as permissive substrates for the support of neural cells. These results suggest plasma synthesized pyrrole polymer-coated aligned scaffolds are promising materials for tissue engineering applications.

IS THERE NEURAL AND FUNCTIONAL RECOVERY AFTER CLIP REMOVAL IN CERVICAL EXPERIMENTAL SYMPATHECTOMY?

Background:

The surgical treatment of hyperhidrosis by thoracic sympathectomy has brought, in addition to symptomatic relief for many, its main adverse effect: compensatory or reflex sweating. The clipping technique in place of the sympathetic nerve section gave rise to the hope of reversibility, but the positive results showed to be quite divergent, evidencing the academic deficiency regarding the study of this phenomenon.

Aim:

To observe micro and macroscopic damage caused by the polymer clip on sympathetic nerve of rabbits seven days after their clipping and the findings after three weeks of clip removal.

Method:

In this experimental study, 20 rabbits were divided into two groups of 10, group 1 (clipping) and group 2 (de-clipping). The right cervical sympathetic nerve of all animals was clamped with polymeric clip, and in group 2 the nerve was unclipped seven days later. Group 1 rabbits were induced to death on the 7th postoperative day, and group 2 on the 21st after removal of the polymer clip. Macroscopic variables were: clip appearance, presence of discontinuity lesion, infection and adhesions around the nerve. H&E was used in the evaluation of the phases and degree of the inflammatory process and presence of necrosis, and picrosirius red F3BA for quantification of collagen.

Results:

The cervical sympathetic nerve was intact, without necrosis or infection in all animals of the experiment; there were adhesions in both groups, being minimal in eight animals of each group and moderate or intense in two; the clip was completely closed in all animals at the 7th postoperative day; the inflammatory process shown was chronic, with monomorphonuclear predominance. There was no significant difference between groups regarding the intensity the inflammatory process, but the amount of collagen type I and type III was significantly higher in group 2.

Conclusions:

The injury caused by the polymer clip on the sympathetic nerve may be reversible, allowing functional return in the areas involved in the simulated cervical sympathectomy. Clipping of the cervical sympathetic nerve using a polymer clip does not cause discontinuity injury.

Increasing toll-like receptor 2 on astrocytes induced by Schwann cell-derived exosomes promotes recovery by inhibiting CSPGs deposition after spinal cord injury

Background

Traumatic spinal cord injury (SCI) is a severely disabling disease that leads to loss of sensation, motor, and autonomic function. As exosomes have great potential in diagnosis, prognosis, and treatment of SCI because of their ability to easily cross the blood–brain barrier, the function of Schwann cell-derived exosomes (SCDEs) is still largely unknown.

Methods

A T10 spinal cord contusion was established in adult female mice. SCDEs were injected into the tail veins of mice three times a week for 4 weeks after the induction of SCI, and the control group was injected with PBS. High-resolution transmission electron microscope and western blot were used to characterize the SCDEs. Toll-like receptor 2 (TLR2) expression on astrocytes, chondroitin sulfate proteoglycans (CSPGs) deposition and neurological function recovery were measured in the spinal cord tissues of each group by immunofluorescence staining of TLR2, GFAP, CS56, 5-HT, and β-III-tublin, respectively. TLR2^f/f mice were crossed to the GFAP-Cre strain to generate astrocyte specific TLR2 knockout mice (TLR2^−/−). Finally, western blot analysis was used to determine the expression of signaling proteins and IKKβ inhibitor SC-514 was used to validate the involved signaling pathway.

Results

Here, we found that TLR2 increased significantly on astrocytes post-SCI. SCDEs treatment can promote functional recovery and induce the expression of TLR2 on astrocytes accompanied with decreased CSPGs deposition. The specific knockout of TLR2 on astrocytes abolished the decreasing CSPGs deposition and neurological functional recovery post-SCI. In addition, the signaling pathway of NF-κB/PI3K involved in the TLR2 activation was validated by western blot. Furthermore, IKKβ inhibitor SC-514 was also used to validate this signaling pathway.

Conclusion

Thus, our results uncovered that SCDEs can promote functional recovery of mice post-SCI by decreasing the CSPGs deposition via increasing the TLR2 expression on astrocytes through NF-κB/PI3K signaling pathway.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02215-x.

Nerve Suture Combined With ADSCs Injection Under Real-Time and Dynamic NIR-II Fluorescence Imaging in Peripheral Nerve Regeneration in vivo

Peripheral nerve injury gives rise to devastating conditions including neural dysfunction, unbearable pain and even paralysis. The therapeutic effect of current treatment for peripheral nerve injury is unsatisfactory, resulting in slow nerve regeneration and incomplete recovery of neural function. In this study, nerve suture combined with ADSCs injection was adopted in rat model of sciatic nerve injury. Under real-time visualization of the injected cells with the guidance of NIR-II fluorescence imaging in vivo, a spatio-temporal map displaying cell migration from the proximal injection site (0 day post-injection) of the nerve to the sutured site (7 days post-injection), and then to the distal section (14 days post-injection) was demonstrated. Furthermore, the results of electromyography and mechanical pain threshold indicated nerve regeneration and functional recovery after the combined therapy. Therefore, in the current study, the observed ADSCs migration in vivo, electrophysiological examination results and pathological changes all provided robust evidence for the efficacy of the applied treatment. Our approach of nerve suture combined with ADSCs injection in treating peripheral nerve injury under real-time NIR-II imaging monitoring in vivo added novel insights into the treatment for peripheral nerve injury, thus further enhancing in-depth understanding of peripheral nerve regeneration and the mechanism behind.

Evaluation of the Use of Nerve Allograft Preserved in Glycerol

Background:

We aimed to evaluate the use of nerve allograft preserved in glycerol. We compared the efficiency of glycerol-preserved allografts with autogenous nerve grafting, cryopreserved grafts, and detergent-processed grafts in the axonal regeneration. Secondarily, we evaluated the effectiveness of each preservation method in maintaining the extracellular matrix free of cellular components.

Methods:

This was a prospective experimental, longitudinal, unblinded, nonrandomized, controlled animal model study. Three different allograft preservation techniques for the repair of sciatic nerve injuries were compared, including cold preservation, glycerol preservation, and detergent preservation. Functional assessment was performed, and histomorphometric analyses were further performed, which enabled the allograft structure evaluation and an estimation of the nerve regeneration efficacy based on the myelinated axons count and on their diameters.

Results:

After the 14^th week, all groups were already balanced and similar (P = 0.265): all groups present near-zero SFIs, thus confirming their efficiency in promoting nerve regeneration. In the histomorphometric evaluations, all groups were equivalent, presenting a similar efficiency in nerve regeneration (P = 0.716 and P = 0.577, respectively). Similarly, histomorphometric evaluations showed a reduction in the number of axons and in their diameters, but none of them effectively eliminated all cellular debris. Comparing the groups with each other, the groups preserved in glycerol and detergent solution were similar, both presenting better results than the cooled group.

Conclusion:

By evaluating the presence of cell debris after the treatment using glycerol, it was found to be similar to the treatment using detergent and significantly better than the cold-preservation treatment.

Surgical management of pediatric patients with peripheral nerve and plexus lesions caused by stray bullets

PURPOSE

Children and adolescents are frequent victims of gunshot wounds (GSW), either by direct intent or accidentaly. Lesions caused by stray bullets represent a specific type of accidental GSW and are usually associated with urban violence or aerial firing. We thereby present a series of surgically treated pediatric patients with peripheral nerve and brachial plexus lesions caused by stray bullets, referring to their clinical presentation, surgical procedures, and outcomes.

METHODS

Retrospective study of a series of seven pediatric patients treated from 2012 to 2019 for nerve and/or plexus lesions caused by stray bullets at the Peripheral Nerve Unit of the Division of Neurosurgery of Gaffrée e Guinle University Hospital (HUGG). We used the Visual Analog Scale (VAS) to evaluate pain distress and the British Medical Research Council grading system (BMRC) to assess muscle strength.

RESULTS

Patients' ages ranged from 6 to 17 years old (median of 16), and two were female. All presented preoperatively with intense pain, with a median VAS of 9 (range 7 to 10), and six also had neurological deficits. External neurolysis was conducted in all cases, whereas reconstruction with grafts was needed in four patients. All experienced improvement of pain, and those with motor deficits also experienced some level of recovery.

CONCLUSION

Pediatric patients who endure lesions by stray bullets appear to present with debilitating pain, and often with motor deficits. Multidisciplinary management comprising of surgical treatment and physical and occupational therapy may ameliorate symptoms and improve quality of life, as young patients usually fare better after surgery.

Cryosurgical Ablation for Treatment of Rhinitis: Two-Year Results of a Prospective Multicenter Study

Objectives/Hypothesis

To assess the long‐term (12–24 months) safety and effectiveness of cryoablation of the posterior nasal nerve as treatment for chronic rhinitis.

Study Design

A multicenter, prospective, single‐arm clinical study.

Methods

The study was conducted from February 2017 to April 2020. Study endpoints included change from baseline in the reflective Total Nasal Symptom Score (rTNSS), Rhinoconjunctivitis Quality of Life Questionnaire (RQLQ), physician assessment of improvement using the Clinical Global Impression–Improvement (CGI–I), and the incidence of treatment‐related adverse events.

Results

Ninety‐one participants completed the study through the initial 12‐month study period. Sixty‐two participants consented to the long‐term follow‐up with 57 completing the 24‐month follow‐up. Significant improvements in the total rTNSS were reflected in a median change from baseline of −3.0 or −4.0 at all timepoints (P < .001). Greater than 80.0% of participants achieved the minimum clinically important difference (MCID) of improvement by ≥1 point on the rTNSS at all follow‐ups. Total RQLQ scores indicated significant improvement (P < .0001) in quality of life. Over 77% of participants achieved the MCID (≥0.5 points) for the total RQLQ score. According to the CGI–I, ≥83.0% experienced improvement at all but the 12‐month visit (61.9%). One participant experienced two treatment‐related serious adverse events (epistaxis and retained pledget). A total of 29 nonserious treatment‐related AEs were reported in 23 participants; most events were transient and resolved with little to no intervention.

Conclusions

Cryotherapy significantly and clinically improves rhinitis symptoms and quality of life with outcomes that are durable through 24 months after treatment.

Level of Evidence

4 Laryngoscope, 131:1952–1957, 2021

Spider silk nerve graft promotes axonal regeneration on long distance nerve defect in a sheep model

Peripheral nerve injuries with substantial tissue loss require autologous nerve transplantation or alternatively reconstruction with nerve conduits. Axonal elongation after nerve transection is about 1 mm/day. The precise time course of axonal regeneration on an ultrastructural level in nerve gap repair using either autologous or artificial implants has not been described. As peripheral nerve regeneration is a highly time critical process due to deterioration of the neuromuscular junction, this in vivo examination in a large animal model was performed in order to investigate axonal elongation rates and spider silk material degradation in a narrowly delimited time series (20, 30, 40, 50, 90, 120, 150 and 180 days) by using a novel spider silk based artificial nerve graft as a critical prerequisite for clinical translation. Autologous nerves or artificial nerve conduits based on spider silk of the spider species Trichonephila edulis were transplanted in a 6.0 cm nerve defect model in the black headed mutton. At each of the post-implant time point, electrophysiology recordings were performed to assess functional reinnervation of axonal fibers into the implants. Samples were analyzed by histology and immunofluorescence in order to verify the timeline of axonal regeneration including axonal regeneration rates of the spider silk implant and the autologous transplant groups. Spider silk was degraded within 3 month by a light immune response mainly mediated by Langhans Giant cells. In conjunction with behavioral analysis and electrophysiological measurements, the results indicate that the spider silk nerve implant supported an axonal regeneration comparable to an autologous nerve graft which is the current gold standard in nerve repair surgery. These findings indicate that a biomaterial based spider silk nerve conduit is as effective as autologous nerve implants and may be an important approach for long nerve defects.

Recommendations for Therapy following Nerve Transfer for Children with Acute Flaccid Myelitis

AIM

To provide recommendations for pre- and post-operative occupational and physical therapy for children with acute flaccid myelitis (AFM).

METHODS

Writing panel members consisted of an interdisciplinary team of seven healthcare professionals specializing in the care of children with AFM. The panel reviewed background material on AFM, nerve transfer, and rehabilitation principles applied to pediatrics. Recommendations were prioritized if evidence was available. Where there was no known evidence to support a recommendation, this was noted.

RECOMMENDATIONS

Communication and coordination among interprofessional team members are vital to a comprehensive family-centered rehabilitation program. Surgical planning should include team preparation accounting for frequency, duration, and timing of treatment, as well as individual characteristics and developmental status of the child. Recommendations for pre-operative and six phases of post-operative therapy address assessment, strengthening, range of motion, orthoses, performance of functional activity, and support of the family.

CONCLUSION

Rehabilitation following nerve transfer in children with AFM requires interdisciplinary collaboration and a multisystem approach to assessment and treatment. As new evidence becomes available, recommendations may be revised or replaced accordingly.

Morphological and Functional Changes of Corneal Nerves and Their Contribution to Peripheral and Central Sensory Abnormalities

The cornea is the most densely innervated and sensitive tissue in the body. The cornea is exclusively innervated by C- and A-delta fibers, including mechano-nociceptors that are triggered by noxious mechanical stimulation, polymodal nociceptors that are excited by mechanical, chemical, and thermal stimuli, and cold thermoreceptors that are activated by cooling. Noxious stimulations activate corneal nociceptors whose cell bodies are located in the trigeminal ganglion (TG) and project central axons to the trigeminal brainstem sensory complex. Ocular pain, in particular, that driven by corneal nerves, is considered to be a core symptom of inflammatory and traumatic disorders of the ocular surface. Ocular surface injury affecting corneal nerves and leading to inflammatory responses can occur under multiple pathological conditions, such as chemical burn, persistent dry eye, and corneal neuropathic pain as well as after some ophthalmological surgical interventions such as photorefractive surgery. This review depicts the morphological and functional changes of corneal nerve terminals following corneal damage and dry eye disease (DED), both ocular surface conditions leading to sensory abnormalities. In addition, the recent fundamental and clinical findings of the importance of peripheral and central neuroimmune interactions in the development of corneal hypersensitivity are discussed. Next, the cellular and molecular changes of corneal neurons in the TG and central structures that are driven by corneal nerve abnormalities are presented. A better understanding of the corneal nerve abnormalities as well as neuroimmune interactions may contribute to the identification of a novel therapeutic targets for alleviating corneal pain.

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.

Schwann Cell-Like Cells: Origin and Usability for Repair and Regeneration of the Peripheral and Central Nervous System

Functional recovery after neurotmesis, a complete transection of the nerve fiber, is often poor and requires a surgical procedure. Especially for longer gaps (>3 mm), end-to-end suturing of the proximal to the distal part is not possible, thus requiring nerve graft implantation. Artificial nerve grafts, i.e., hollow fibers, hydrogels, chitosan, collagen conduits, and decellularized scaffolds hold promise provided that these structures are populated with Schwann cells (SC) that are widely accepted to promote peripheral and spinal cord regeneration. However, these cells must be collected from the healthy peripheral nerves, resulting in significant time delay for treatment and undesired morbidities for the donors. Therefore, there is a clear need to explore the viable source of cells with a regenerative potential similar to SC. For this, we analyzed the literature for the generation of Schwann cell-like cells (SCLC) from stem cells of different origins (i.e., mesenchymal stem cells, pluripotent stem cells, and genetically programmed somatic cells) and compared their biological performance to promote axonal regeneration. Thus, the present review accounts for current developments in the field of SCLC differentiation, their applications in peripheral and central nervous system injury, and provides insights for future strategies.

Alteration of the pattern of regenerative corneal subbasal nerves after laser in-situ keratomileusis surgery

PURPOSE

Corneal nerves exhibit high plasticity, which allows successful reinnervation after nerve damage caused by laser in-situ keratomileusis (LASIK) surgery. This study aimed to examine corneal subbasal nerve orientation during regeneration after LASIK.

METHODS

This study involved 20 healthy, myopic subjects who had undergone bilateral Femto-LASIK 12-16 months prior with a superior hinge position. The corneal subbasal nerve plexus at the central, mid-temporal and mid-superior cornea on the right eye were imaged using in vivo confocal microscopy. Global nerve fibre orientation (indicating the overall pattern) and variation of nerve fibre orientation (indicating the consistency of the orientation) was determined using customised MATLAB™ software (www.mathworks.com/products/matlab.html). Differences in nerve orientation variables between groups were examined using the Mann-Whitney U test. Linear mixed models with Bonferroni adjustment were conducted to examine differences between corneal regions, and over time, after LASIK.

RESULTS

There were no differences between post-LASIK and control groups in global nerve orientation at any of the examined corneal regions. The post-LASIK subjects had a greater variation of nerve orientation at the central (p = 0.007) and temporal (p = 0.049) cornea than the controls. There was a difference in global nerve fibre orientation between corneal regions (p < 0.001) in the controls but not in the post-LASIK group. The variation of nerve fibre orientation was higher at the central, compared to the temporal and superior cornea after LASIK (p < 0.001), although there were no differences between corneal regions in controls.

CONCLUSIONS

Our results demonstrate that there was an increased variability in the corneal subbasal innervation patterns following LASIK when compared to controls.

Signals Orchestrating Peripheral Nerve Repair

The peripheral nervous system has retained through evolution the capacity to repair and regenerate after assault from a variety of physical, chemical, or biological pathogens. Regeneration relies on the intrinsic abilities of peripheral neurons and on a permissive environment, and it is driven by an intense interplay among neurons, the glia, muscles, the basal lamina, and the immune system. Indeed, extrinsic signals from the milieu of the injury site superimpose on genetic and epigenetic mechanisms to modulate cell intrinsic programs. Here, we will review the main intrinsic and extrinsic mechanisms allowing severed peripheral axons to re-grow, and discuss some alarm mediators and pro-regenerative molecules and pathways involved in the process, highlighting the role of Schwann cells as central hubs coordinating multiple signals. A particular focus will be provided on regeneration at the neuromuscular junction, an ideal model system whose manipulation can contribute to the identification of crucial mediators of nerve re-growth. A brief overview on regeneration at sensory terminals is also included.

Neuroprotective effect of Hongjing I granules on erectile dysfunction in a rat model of bilateral cavernous nerve injury

Neurogenic erectile dysfunction (NED) is an inevitable postoperative disease of cavernous nerve injury which will lead to various pathophysiological changes in the corpus cavernosum and dorsal penile nerve caused by radical prostatectomy (RP). Although serval years of clinical application of HJIG I granules (HJIG), an innovative formulation, has demonstrated its reliable clinical efficacy against NED, the mechanism of HJIG remains unclear. This study aimed to assess the neuroprotective effect of HJIG, to repair damaged nerves in a rat model of bilateral cavernous nerve injury (BCNI) in vivo and their effects on neurites of major pelvic ganglia (MPG) regeneration and Schwann cells (SCs) proliferation in vitro. Rats were divided into five groups randomly: normal control (NC), BCNI-induced ED model (M), M + low-dose HJIG (HL), M + medium-dose HJIG (HM), and M + high-dose HJIG (HH). All groups were treated with normal saline or the relevant drug for 28 consecutive days after a standard NED animal model. Our data revealed that administration of HJIG improved NED that was detected by intracavernous pressure (ICP) in a dose-dependent manner. The haematoxylin-eosin (HE) and Immunofluorescence (IF) staining demonstrated that HJIG ameliorate the shape of penis and induced the protein synthesis of GAP43, NF200, S100, and nNOS. NF200 and S100 level were also detected by western blotting. Moreover, HJIG (0.78 mg/mL) markedly increased SCs viability and promoted neurites regeneration of MPG. These findings provide new insights into the NED therapy by HJIG.

Retinal Ganglion Cell Survival and Axon Regeneration after Optic Nerve Transection is Driven by Cellular Intravitreal Sciatic Nerve Grafts

Neurotrophic factors (NTF) secreted by Schwann cells in a sciatic nerve (SN) graft promote retinal ganglion cell (RGC) axon regeneration after either transplantation into the vitreous body of the eye or anastomosis to the distal stump of a transected optic nerve. In this study, we investigated the neuroprotective and growth stimulatory properties of SN grafts in which Schwann cells had been killed (acellular SN grafts, ASN) or remained intact (cellular SN grafts, CSN). We report that both intravitreal (ivit) implanted and optic nerve anastomosed CSN promote RGC survival and when simultaneously placed in both sites, they exert additive RGC neuroprotection. CSN and ASN were rich in myelin-associated glycoprotein (MAG) and axon growth-inhibitory ligand common to both the central nervous system (CNS) and peripheral nervous system (PNS) myelin. The penetration of the few RGC axons regenerating into an ASN at an optic nerve transection (ONT) site is limited into the proximal perilesion area, but is increased >2-fold after ivit CSN implantation and increased 5-fold into a CSN optic nerve graft after ivit CSN implantation, potentiated by growth disinhibition through the regulated intramembranous proteolysis (RIP) of p75^NTR (the signalling trans-membrane moiety of the nogo-66 trimeric receptor that binds MAG and associated suppression of RhoGTP). Mϋller cells/astrocytes become reactive after all treatments and maximally after simultaneous ivit and optic nerve CSN/ASN grafting. We conclude that simultaneous ivit CSN plus optic nerve CSN support promotes significant RGC survival and axon regeneration into CSN optic nerve grafts, despite being rich in axon growth inhibitory molecules. RGC axon regeneration is probably facilitated through RIP of p75^NTR, which blinds axons to myelin-derived axon growth-inhibitory ligands present in optic nerve grafts.

Recovery of sensory function after the implantation of oriented-collagen tube into the resected rat sciatic nerve

Introduction

In the present study, we examined the effect of oriented collagen tube (OCT) implantation on the recovery of sensory function of the resected rat sciatic nerve.

Materials and methods

After a 10-mm long portion of the sciatic nerve of a rat was resected, an OCT was placed in the site of nerve defect. Recovery of the sensory function was evaluated using Von Frey test every 3 days after surgery. The regenerated tissue were histologically and ultrastructurally analyzed 2 and 4 weeks after the surgery.

Results

The sensory reflexes of the OCT group were restored to the level of that of the intact group after 15 days. Hematoxylin and eosin staining revealed the cross-linking between the proximal and distal stumps after 2 weeks. After 4 weeks, Luxol Fast Blue and immunohistochemical staining revealed the presence of myelin sheath from the proximal to distal region of the regenerated tissue and S100B staining confirmed the presence of Schwann cells. Interestingly, no myelin sheath was ultrastructurally observed around the regenerated axons at the central region after 2 weeks.

Conclusions

These results suggest that OCTs facilitate the recovery of sensory function. Additionally, the non-myelinated axons contributed to the recovery of the sensory function.

•

Von Frey test results in the OCT group on POD 15 were comparable at the sham group.

•

OCT group showed regeneration of unmyelinated axons in 2 weeks.

•

Myelination was observed from proximal to distal after 4 weeks OCT implantation.

•

In the OCT group, a large number of blood vessels were observed in nerve in 2 weeks.

Restoration of the Topological Organization of the Trigeminal System Following Trigeminal Nerve Root Injury in the Lamprey

Two issues were examined regarding the trigeminal system in larval lampreys: (1) for normal animals, double labeling was used to confirm that the trigeminal system has a topological organization; (2) following trigeminal nerve root transections, double labeling was used to test whether the topological organization of the trigeminal system is restored. First, for normal animals, Alexa 488 dextran amine applied to the medial oral hood (anterior head) labeled trigeminal motoneurons (MNs) in the ventromedial part of the trigeminal motor nuclei (nVm) and axons of trigeminal sensory neurons (SNs) in the ventromedial part of the trigeminal descending tracts (dV). Also, Texas red dextran amine (TRDA) applied to the lateral oral hood labeled trigeminal MNs in the dorsolateral nVm and sensory axons in the dorsolateral dV. These results confirm the topological organization of the trigeminal system of normal lampreys. Second, following trigeminal nerve root transections, the physical integrity of the nerves was restored during growth of trigeminal sensory and motor axons. In addition, double labeling indicated a restoration and refinement of the topological organization of the trigeminal system with increasing recovery times, but mainly for nVm. Despite the paucity of growth of trigeminal sensory axons in dV even at long recovery times (12-16 wks), a substantial percentage of experimental animals recovered trigeminal-evoked swimming responses and trigeminal-evoked synaptic responses in reticulospinal (RS) neurons. Following trigeminal nerve root injury, several mechanisms, including axonal guidance cues, probably contribute to the substantial restoration of the topological organization of the lamprey trigeminal system.

TGF-β1 activates RSC96 Schwann cells migration and invasion through MMP-2 and MMP-9 activities

Following peripheral nerve injury, remnant Schwann cells adopt a migratory phenotype and remodel the extracellular matrix allowing axonal regrowth. Although much evidence has demonstrated that TGF-β1 promotes glioma cell motility and induces the expression of extracellular matrix proteins, the effects of TGF-β1 on Schwann cell migration has not yet been studied. We therefore investigated the cellular effects and the signal transduction pathways evoked by TGF-β1 in rattus norvegicus neuronal Schwann RSC96 cell. TGF-β1 significantly increased migration and invasion of Schwann cells assessed by the wound-healing assay and by cell invasion assay. TGF-β1-enhanced migration/invasion was blocked by inhibition of MMP-2 and MMP-9. Consistently, by real-time and western blot analyses, we demonstrated that TGF-β1 increased MMP-2 and MMP-9 mRNA and protein levels. TGF-β1 also increased MMPs activities in cell growth medium, as shown by gelatin zymography. The selective TGF-β Type I receptor inhibitor SB431542 completely abrogated any effects by TGF-β1. Indeed, TGF-β1 Type I receptor activation provoked the cytosol-to-nucleus translocation of SMAD2 and SMAD3. SMAD2 knockdown by siRNA blocked MMP-2 induction and cell migration/invasion due to TGF-β1. TGF-β1 also provoked phosphorylation of MAPKs extracellular regulated kinase 1/2 and JNK1/2. Both MAPKs were upstream to p65/NF-kB inasmuch as both MAPKs' inhibitors PD98059 and SP600125 or their down-regulation by siRNA significantly blocked the TGF-β1-induced nuclear translocation of p65/NF-kB. In addition, p65/NF-κB siRNA knockdown inhibited the effects of TGF-β1 on both MMP-9 and cell migration/invasion. We conclude that TGF-β1 controls RSC96 Schwann cell migration and invasion through MMP-2 and MMP-9 activities. MMP-2 is controlled by SMAD2 whilst MMP-9 is controlled via an ERK1/2-JNK1/2-NF-κB dependent pathway.

Regulatory Mechanism of Peripheral Nerve Myelination by Glutamate-Induced Signaling

Regulation of differentiation and proliferation of Schwann cells is an essential part of the regulation of peripheral nerve development, degeneration, and regeneration. ZNRF1, a ubiquitin ligase, is expressed in undifferentiated/repair Schwann cells, directs glutamine synthetase to proteasomal degradation, and thereby increase glutamate levels in Schwann cell environment. Glutamate elicits subcellular signaling in Schwann cells via mGluR2 to modulate Neuregulin-1/ErbB2/3 signaling and thereby promote undifferentiated phenotype of Schwann cell.

Schwann cell plasticity-roles in tissue homeostasis, regeneration, and disease

How tissues are maintained over a lifetime and repaired following injury are fundamental questions in biology with a disruption to these processes underlying pathologies such as cancer and degenerative disorders. It is becoming increasingly clear that each tissue has a distinct mechanism to maintain homeostasis and respond to injury utilizing different types of stem/progenitor cell populations depending on the insult and/or with a contribution from more differentiated cells that are able to dedifferentiate to aid tissue regeneration. Peripheral nerves are highly quiescent yet show remarkable regenerative capabilities. Remarkably, there is no evidence for a classical stem cell population, rather all cell-types within the nerve are able to proliferate to produce new nerve tissue. Co-ordinating the regeneration of this tissue are Schwann cells (SCs), the main glial cells of the peripheral nervous system. SCs exist in architecturally stable structures that can persist for the lifetime of an animal, however, they are not postmitotic, in that following injury they are reprogrammed at high efficiency to a progenitor-like state, with these cells acting to orchestrate the nerve regeneration process. During nerve regeneration, SCs show little plasticity, maintaining their identity in the repaired tissue. However, once free of the nerve environment they appear to exhibit increased plasticity with reported roles in the repair of other tissues. In this review, we will discuss the mechanisms underlying the homeostasis and regeneration of peripheral nerves and how reprogrammed progenitor-like SCs have broader roles in the repair of other tissues with implications for pathologies such as cancer.

Enhancing Schwann cell migration using concentration gradients of laminin-derived peptides

Neuroregeneration following peripheral nerve injury is largely mediated by Schwann cells (SC), the principal glial cell that supports neurons in the peripheral nervous system. Axonal regeneration in vivo is limited by the extent of SC migration into the gap between the proximal and distal nerve, however, little is known regarding the principal driving forces for SC migration. Engineered microenvironments, such as molecular and protein gradients, play a role in the migration of many cell types, including cancer cells and fibroblasts. However, haptotactic strategies have not been applied widely to SC. Herein, a series of tethered laminin-derived peptides were analyzed for their influence on SC adhesion, proliferation, and alignment. Concentration gradient substrates were fabricated using a controlled vapor deposition method, followed by covalent peptide attachment via a thiol-ene reaction, and characterized by X-ray photoelectron spectroscopy (XPS) and MALDI-MS imaging. While tethered RGD peptides supported SC adhesion and proliferation, concentration gradients of RGD had little influence on biased SC directional migration. In contrast, YIGSR promoted less SC attachment than RGD, yet YIGSR peptide gradients directed migration with a strong bias to the concentration profile. With YIGSR peptide, overall speed increased with the steepness of the peptide concentration profile. YIGSR gradients had no haptotactic effect on rat dermal fibroblast migration, in contrast to fibroblast migration on RGD gradients. The response of SC to these tethered peptide gradients will guide the development of translationally relevant constructs designed to facilitate endogenous SC infiltration into defects for nerve regeneration.

Clinical and in vivo confocal microscopic features of neuropathic corneal pain

Aims

To describe clinical and in vivo confocal microscopy (IVCM) features of neuropathic corneal pain (NCP) without clinically visible signs.

Methods

Prospective, observational study of 27 eyes of 14 patients who had continuous severe ocular pain for one or more years, with minimal or no ocular surface signs and were non-responsive to topical lubricants, steroids and/or ciclosporin. All patients were evaluated using Ocular Surface Disease Index, Oxford grading scale, Schirmer test 1, Cochet Bonnet esthesiometry and response to topical anaesthesia. Central and paracentral regions of the cornea of patients and seven healthy controls were studied by IVCM. Corneal epithelial thickness and sub-basal nerve density were measured in patients and controls.

Results

Four patients responded to topical anaesthesia (responsive group (RG)), indicating peripheral NCP while 10 patients did not show any improvement (non-responsive group (NRG)), indicating central NCP. Schirmer-1 test was within normal limits in the RG but significantly greater in the NRG (p<0.001). None of the other clinical parameters nor corneal epithelial thickness were statistically significantly different. The sub-basal nerve density was significantly reduced (p<0.008) in patients compared with controls. Stroma of all patients demonstrated activated keratocytes and spindle, lateral and stump microneuromas. There was a statistically significant greater number of microneuromas (p<0.0001) and activated keratocytes in RG compared with NRG.

Conclusion

NCP without visible clinical signs does not represent typical dry eye disease. Distinct signs demonstrated on IVCM suggest that peripheral NCP, which responds to topical anaesthesia, and central NCP, which does not, are separate entities.

Peripheral nerve mucoid degeneration involving the sciatic nerve

Peripheral nerve mucoid degeneration (PNMD) is a rare non-neoplastic degenerative condition characterized by endoneural deposit of mucoid matrix. Herein, we report a case of PNMD involving the sciatic nerve with preoperative features, surgical treatment and pathological findings.