Inflammation and axon regeneration

Functional muscle strength recovery from nail gun injury to the primary motor cortex

Aim: Functional recovery following injury to the primary motor cortex is an uncommon phenomenon, given the limited ability of neurons of the adult central nervous system to regenerate. Case description: We report on a patient with near complete functional muscle strength recovery from a marked monoparesis due to nail gun injury to the medial primary motor cortex. Besides surgical decision-making, we discuss possible related mechanisms and current challenges in the regenerative processes responsible for the functional recovery. Discussion: To achieve a favorable outcome, surgical decision-making to prevent secondary damage is of upmost importance. Lesion-induced inflammatory response may potentiate endogenous neurogenesis and neuronal plasticity and potentially contribute to the regenerative process involved.

Effects of bone marrow mononuclear cells on induction of axonal sprouting in cortico-cortical and cortico-striatal pathways in an animal model of cortical ablation

OBJECTIVES

Many therapies have been proposed in order to investigate the mechanisms of neural repair associated with neurological diseases, including bone marrow mononuclear cells (BMMC) transplantation. However, there is evidence that some encephalic injuries are less responsive to neural repair, such as, for example, cortical ablation. On the other hand, some models of cortical ablation have shown functional recovery after BMMC transplantation. Thus, it is relevant to expand the knowledge of BMMC transplantation-induced neuroplasticity in animal models, considering a promising approach for the rehabilitation of patients with neurological diseases. Using an experimental model of cerebral cortex ablation in adult male Wistar rats, which is known to be poorly responsive to neuroplasticity, the aim of this study was to investigate the effects of BMMC on axonal sprouting in cortico-cortical and cortico-striatal pathways synaptic fields. An anterograde neurotracer was used to evaluate the distribution of axonal fibres.

RESULTS

The results showed that BMMC were not able to significantly induce axonal sprouting in the evaluated synaptic fields. Our results reinforced the idea that cortical ablation may be less responsive to neuroplasticity and the beneficial effects of BMMC therapy depend on the particularities of a neural microenvironment intrinsic to a given cortical lesion.

Intra-axonal mechanisms driving axon regeneration

Traumatic injury to the peripheral and central nervous systems very often causes axotomy, where an axon loses connections with its target resulting in loss of function. The axon segments distal to the injury site lose connection with the cell body and degenerate. Axotomized neurons in the periphery can spontaneously mount a regenerative response and reconnect to their denervated target tissues, though this is rarely complete in humans. In contrast, spontaneous regeneration rarely occurs after axotomy in the spinal cord and brain. Here, we concentrate on the mechanisms underlying this spontaneous regeneration in the peripheral nervous system, focusing on events initiated from the axon that support regenerative growth. We contrast this with what is known for axonal injury responses in the central nervous system. Considering the neuropathy focus of this special issue, we further draw parallels and distinctions between the injury-response mechanisms that initiate regenerative gene expression programs and those that are known to trigger axon degeneration.

The Influence of Neuron-Extrinsic Factors and Aging on Injury Progression and Axonal Repair in the Central Nervous System

In the aging western population, the average age of incidence for spinal cord injury (SCI) has increased, as has the length of survival of SCI patients. This places great importance on understanding SCI in middle-aged and aging patients. Axon regeneration after injury is an area of study that has received substantial attention and made important experimental progress, however, our understanding of how aging affects this process, and any therapeutic effort to modulate repair, is incomplete. The growth and regeneration of axons is mediated by both neuron intrinsic and extrinsic factors. In this review we explore some of the key extrinsic influences on axon regeneration in the literature, focusing on inflammation and astrogliosis, other cellular responses, components of the extracellular matrix, and myelin proteins. We will describe how each element supports the contention that axonal growth after injury in the central nervous system shows an age-dependent decline, and how this may affect outcomes after a SCI.

Sensory neurons directly promote angiogenesis in response to inflammation via substance P signaling

Blood vessels and nerves travel together to supply most tissues in the body. However, there is a knowledge gap in the mechanisms underlying the direct regulation of angiogenesis by nerves. In the current study, we examined the regulation of angiogenesis by sensory nerves in response to inflammation using the cornea, a normally avascular and densely innervated ocular tissue, as a model. We used desiccating stress as an inflammatory stimulus in vivo and found that sub-basal and epithelial nerve densities in the cornea were reduced in dry eye disease (DED). We established a co-culture system of trigeminal ganglion sensory neurons and vascular endothelial cells (VEC) and found that neurons isolated from mice with DED directly promoted VEC proliferation and tube formation compared with normal controls. In addition, these neurons expressed and secreted higher levels of substance P (SP), a proinflammatory neuropeptide. SP potently promoted VEC activation in vitro and blockade of SP signaling with spantide I, an antagonist of SP receptor Neurokinin-1, significantly reduced corneal neovascularization in vivo. Spantide I and siRNA knockdown of SP abolished the promotion of VEC activation by DED neurons in vitro. Taken together, our data suggested that sensory neurons directly promote angiogenesis via SP signaling in response to inflammation in the cornea.

Genetic changes in rat proximal nerve stumps after sciatic nerve transection

Background

Peripheral nerves can self-regenerate after traumatic injury, although their self-regeneration ability is limited after severe nerve injury. After peripheral nerve injury, the distal nerve stumps undergo Wallerian degeneration while the proximal nerve stumps undergo a regeneration process.

Methods

Here, to decipher genetic changes and involved biological processes in the proximal nerve stumps after peripheral nerve injury, microarray data (GSE30165) were analyzed. Differentially expressed genes in the proximal nerve stumps at 0.5 h, 1 h, 3 h, 6 h, 9 h, 1 d, 4 d, 7 d, and 14 d after rat sciatic nerve transection were subjected to Ingenuity pathway analysis (IPA) bioinformatic analysis.

Results

Cytokine signaling, cellular immune response, nuclear receptor signaling, disease-specific pathways, and organismal growth and development were significantly activated in the proximal nerve stumps after nerve transection. Organ development, inflammation and immune response, diseases and organ abnormalities, and cellular behavior-related biological functions were highly involved.

Conclusions

The expression levels of differentially expressed genes in biological function "Organismal Injury and Abnormalities" were displayed and validated. Our current study helps to obtain a better understanding of the biological processes of peripheral nerve regeneration, especially the regeneration process in the proximal nerve stumps, and thus may help to discover new therapeutic methods that can promote nerve regeneration.

Repair strategies for traumatic spinal cord injury, with special emphasis on novel biomaterial-based approaches

As a part of the central nervous system (CNS), the adult mammalian spinal cord displays only very poor ability for self-repair in response to traumatic lesions, which mostly lead to more or less severe, life-long disability. While even adult CNS neurons have a certain plastic potential, their intrinsic regenerative capacity highly varies among different neuronal populations and in the end, regeneration is almost completely inhibited due to extrinsic factors such as glial scar and cystic cavity formation, excessive and persistent inflammation, presence of various inhibitory molecules, and absence of trophic support and of a growth-supportive extracellular matrix structure. In recent years, a number of experimental animal models have been developed to overcome these obstacles. Since all those studies based on a single approach have yielded only relatively modest functional recovery, it is now consensus that different therapeutic approaches will have to be combined to synergistically overcome the multiple barriers to CNS regeneration, especially in humans. In this review, we particularly emphasize the hope raised by the development of novel, implantable biomaterials that should favor the reconstruction of the damaged nervous tissue, and ultimately allow for functional recovery of sensorimotor functions. Since human spinal cord injury pathology depends on the vertebral level and the severity of the traumatic impact, and since the timing of application of the different therapeutic approaches appears very important, we argue that every case will necessitate individual evaluation, and specific adaptation of therapeutic strategies.

Toward Functional Restoration of the Central Nervous System: A Review of Translational Neuroscience Principles

Injury to the central nervous system (CNS) can leave patients with devastating neurological deficits that may permanently impair independence and diminish quality of life. Recent insights into how the CNS responds to injury and reacts to critically timed interventions are being translated into clinical applications that have the capacity to drastically improve outcomes for patients suffering from permanent neurological deficits due to spinal cord injury, stroke, or other CNS disorders. The translation of such knowledge into practical and impactful treatments involves the strategic collaboration between neurosurgeons, clinicians, therapists, scientists, and industry. Therefore, a common understanding of key neuroscientific principles is crucial. Conceptually, current approaches to CNS revitalization can be divided by scale into macroscopic (systems-circuitry) and microscopic (cellular-molecular). Here we review both emerging and well-established tenets that are being utilized to enhance CNS recovery on both levels, and we explore the role of neurosurgeons in developing therapies moving forward. Key principles include plasticity-driven functional recovery, cellular signaling mechanisms in axonal sprouting, critical timing for recovery after injury, and mechanisms of action underlying cellular replacement strategies. We then discuss integrative approaches aimed at synergizing interventions across scales, and we make recommendations for the basis of future clinical trial design. Ultimately, we argue that strategic modulation of microscopic cellular behavior within a macroscopic framework of functional circuitry re-establishment should provide the foundation for most neural restoration strategies, and the early involvement of neurosurgeons in the process will be crucial to successful clinical translation.

Decellularized brain matrix enhances macrophage polarization and functional improvements in rat spinal cord injury

Spinal cord injury (SCI) is a devastating lesion lacking effective treatment options currently available in clinics. The inflammatory process exacerbates the extent of the lesion through a secondary injury mechanism, where proinflammatory classically activated macrophages (M1) are prevalent at the lesion site. However, the polarized alternatively activated anti-inflammatory macrophages (M2) are known to play an important role in wound healing and regeneration following SCI. Herein, we introduce porcine brain decellularized extracellular matrix (dECM) to modulate the macrophages in the injured spinal cord. The hydrogels with collagen and dECM at various dECM concentrations (1, 5, and 8 mg/ml) were used to cultivate primary macrophages and neurons. The dECM hydrogels were shown to promote the polarization of macrophages toward M2 phase and the neurite outgrowth of cortical and hippocampal neurons. When the dECM hydrogels were applied to rat SCI models, the proportion of M1 and M2 macrophages in the injured spinal cord was substantially altered. When received dECM concetration of 5 mg/ml, the expression of molecules associated with M2 (CD206, arginase1, and IL-10) was significantly increased. Consistently, the population of total macrophages and cavity area were substantially reduced in the dECM-treated groups. As a result, the locomotor functions of injured spinal cord, as assessed by BBB and ladder scoring, were significantly improved. Collectively, the porcine brain dECM with optimal concentration promotes functional recovery in SCI models through the activation of M2 macrophages, suggesting the promising use of the engineered hydrogels in the treatment of acute SCI. STATEMENT OF SIGNIFICANCE: Spinal cord injury (SCI) is a devastating lesion, lacking effective treatment options currently available in clinics. Here we delineated that the treatment of injured spinal cord with porcine brain decellularized matrix-based hydrogels for the first time, and could modulate the macrophage polarization and the ultimate functional recovery. When appropriate formulations were applied to a contused spinal cord model in rats, the decellularized matrix hydrogels shifted the macrophages to polarize to pro-regenerative M2 phenotype, decreased the size of lesion cavity, and finally promoted the locomotor functions until 8 weeks following the injury. We consider this work can significantly augment the matrix(biomaterial)-based therapeutic options, as an alternative to drug or cell-free approaches, for the treatment of acute injury of spinal cord.

Functional polymeric nerve guidance conduits and drug delivery strategies for peripheral nerve repair and regeneration

Peripheral nerve injuries can be extremely debilitating, resulting in sensory and motor loss-of-function. Endogenous repair is limited to non-severe injuries in which transection of nerves necessitates surgical intervention. Traditional treatment approaches include the use of biological grafts and alternative engineering approaches have made progress. The current article serves as a comprehensive, in-depth perspective on peripheral nerve regeneration, particularly nerve guidance conduits and drug delivery strategies. A detailed background of peripheral nerve injury and repair pathology, and an in-depth look into augmented nerve regeneration, nerve guidance conduits, and drug delivery strategies provide a state-of-the-art perspective on the field.

Immunological considerations and concerns as pertinent to whole eye transplantation

PURPOSE OF REVIEW

The advent of clinical vascularized composite allotransplantation (VCA), offers hope for whole eye transplantation (WET) in patients with devastating vison loss that fails or defies current treatment options. Optic nerve regeneration and reintegration remain the overarching hurdles to WET. However, the realization of WET may indeed be limited by our lack of understanding of the singular immunological features of the eye as pertinent to graft survival and functional vision restoration in the setting of transplantation.

RECENT FINDINGS

Like other VCA, such as the hand or face, the eye includes multiple tissues with distinct embryonic lineage and differential antigenicity. The ultimate goal of vision restoration through WET requires optimal immune modulation of the graft for successful optic nerve regeneration. Our team is exploring barriers to our understanding of the immunology of the eye in the context of WET including the role of immune privilege and lymphatic drainage on rejection, as well as the effects ischemia, reperfusion injury and rejection on optic nerve regeneration.

SUMMARY

Elucidation of the unique immunological responses in the eye and adnexa after WET will provide foundational clues that will help inform therapies that prevent immune rejection without hindering optic nerve regeneration or reintegration.

Corneal Cells: Fine-tuning Nerve Regeneration

The cornea is a transparent outermost structure of the eye anterior segment comprising the highest density of innervated tissue. In the process of corneal innervation, trigeminal ganglion originated corneal nerves diligently traverse different corneal cell types in different corneal layers including the corneal stroma and epithelium. While crossing the stromal and epithelial cell layers during innervation, due to the existing physical contacts, close interactions occur between stromal keratocytes, epithelial cells, resident immune cells and corneal nerves. Furthermore, by producing various trophic and growth factors corneal cells assist in maintaining the growth and function of corneal nerves. Similarly, corneal nerve generated growth factors critically modify the corneal cell function in all the corneal layers. Due to their close association and contacts, on-going cross-communication between these cell types and corneal nerves play a vital role in the modulation of corneal nerve function, regeneration during wound healing. The present review highlights the influence of different corneal cell types and growth factors released from these cells on corneal nerve regeneration and function.

Oncomodulin: The Enigmatic Parvalbumin Protein

EF-hand Ca²⁺-binding protein family members, α- and β-parvalbumins have been studied for decades. Yet, considerable information is lacking distinguishing functional differences between mammalian α-parvalbumin (PVALB) and oncomodulin (OCM), a branded β-parvalbumin. Herein, we provide an overview detailing the current body of work centered around OCM as an EF-Hand Ca²⁺-binding protein and describe potential mechanisms of OCM function within the inner ear and immune cells. Additionally, we posit that OCM is evolutionarily distinct from PVALB and most other β-parvalbumins. This review summarizes recent studies pertaining to the function of OCM and emphasizes OCM as a parvalbumin possessing a unique cell and tissue distribution, Ca²⁺ buffering capacity and phylogenetic origin.

Neuroinflammation and Optic Nerve Regeneration: Where Do We Stand in Elucidating Underlying Cellular and Molecular Players?

Neurodegenerative diseases and central nervous system (CNS) trauma are highly irreversible, in part because adult mammals lack a robust regenerative capacity. A multifactorial problem underlies the limited axonal regeneration potential. Strikingly, neuroinflammation seems able to induce axonal regrowth in the adult mammalian CNS. It is increasingly clear that both blood-borne and resident inflammatory cells as well as reactivated glial cells affect axonal regeneration. The scope of this review is to give a comprehensive overview of the knowledge that links inflammation (with a focus on the innate immune system) to axonal regeneration and to critically reflect on the controversy that still prevails about the cells, molecules and pathways that are dominating the scene. Also, a brief overview is given of what is already known about the crosstalk between and the heterogeneity of cell types that might play a role in axonal regeneration. Recent research indicates that inflammation-induced axonal regrowth is not solely driven by a single-cell population but probably relies on the crosstalk between multiple cell types and the strong regulation of these cell populations in time and space. Moreover, there is growing evidence that the different cell populations are highly heterogeneous and as such can react differently upon injury. This could explain the controversial results that have been obtained over the past years. The primary focus of this manuscript is the retinofugal system of adult mammals, however, when relevant, insights or examples of the spontaneous regenerating zebrafish model and spinal cord research are added.

Demonstration of technical feasibility and viability of whole eye transplantation in a rodent model

INTRODUCTION

Whole eye transplantation (WET) holds promise for vision restoration in devastating/disabling visual loss (congenital or traumatic) not amenable to surgical or neuroprosthetic treatment options. The eye includes multiple tissues with distinct embryonic lineage and differential antigenicity. Anatomically and immunologically, the eye is unique due to its avascular (cornea) and highly vascular (retina) components. Our goal was to establish technical feasibility, demonstrate graft viability, and evaluate histologic changes in ocular tissues/adnexae in a novel experimental model of WET that included globe, adnexal, optic nerve (ON), and periorbital soft tissues.

METHODS

Outbred Sprague-Dawley rats (n = 5) received heterotopic vascularized WET from donors. Each WET included the entire globe, adnexa, ON, and periorbital soft tissues supplied by the common carotid artery and external jugular vein. Viability and perfusion were confirmed by clinical examination, angiography and magnetic resonance imaging (MRI). Globe, adnexal, and periorbital tissues were analyzed for histopathologic changes, and the ON was examined for neuro-regeneration at study endpoint (30 days) or Banff Grade 3 rejection in the periorbital skin (whichever was earlier).

RESULTS

Gross examination confirmed transplant viability and corneal transparency. Average operative duration was 64.0 ± 5.8 min. Average ischemia time was 26.0 ± 4.2 min. MRI revealed loss of globe volume by 36.0 ± 2.8% after transplantation. Histopathology of globe and adnexal tissues showed unique and differential patterns of inflammatory cell infiltration. The ON revealed a neurodegeneration pattern.

CONCLUSION

The present study is the first in the literature to establish an experimental model of WET. This model holds significant potential in investigating mechanistic pathways, monitoring strategies or developing management approaches involving ocular viability, immune rejection, and ON regeneration after WET.

Potential immunotherapy for Alzheimer disease and age-related dementia

Emerging results support the concept that Alzheimer disease (AD) and age-related dementia are affected by the ability of the immune system to contain the brain's pathology. Accordingly, well-controlled boosting, rather than suppression of systemic immunity, has been suggested as a new approach to modify disease pathology without directly targeting any of the brain's disease hallmarks. Here, we provide a short review of the mechanisms orchestrating the cross-talk between the brain and the immune system. We then discuss how immune checkpoint blockade directed against the PD-1/PD-L1 pathways could be developed as an immunotherapeutic approach to combat this disease using a regimen that will address the needs to combat AD.

Differential Glycosylation Expression in Injured Rat Spinal Cord Treated with Immunosuppressive Drug Cyclosporin-A

Glycosylation is ubiquitous throughout the central nervous system and altered following spinal cord injury (SCI). The glial scar that forms following SCI is composed of several chondroitin sulfate proteoglycans, which inhibit axonal regrowth. Cyclosporin-A (CsA), an immunosuppressive therapeutic, has been proposed as a potential treatment after SCI. We investigated CsA treatment in the spinal cord of healthy, contusion injured, and injured CsA-treated rats. Lectin histochemistry using fluorescently labeled lectins, SBA, MAA, SNA-I, and WFA, was performed to identify the terminal carbohydrate residues of glycoconjugates within the spinal cord. SBA staining decreased in gray and white matter following spinal cord injury, whereas staining was increased at the lesion site in CsA-treated animals, indicating an increase in galactose and N-acetylgalactosamine terminal structures. No significant changes in MAA were observed. WFA staining was abundant in gray matter and observed to increase at the lesion site, in agreement with increased expression of chondroitin sulfate proteoglycans. SNA-I-stained blood vessels in all spinal cord regions and dual staining identified a subpopulation of astrocytes in the lesion site, which expressed α-(2,6)-sialic acid. Glycosylation were altered in injured spinal cord treated with CsA, indicating that glycosylation and alteration of particular carbohydrate structures are important factors to consider in the examination of the environment of the spinal cord after injury.

Emerging Biomarkers, Tools, and Treatments for Diabetic Polyneuropathy

Diabetic neuropathy, with its major clinical sequels, notably neuropathic pain, foot ulcers, and autonomic dysfunction, is associated with substantial morbidity, increased risk of mortality, and reduced quality of life. Despite its major clinical impact, diabetic neuropathy remains underdiagnosed and undertreated. Moreover, the evidence supporting a benefit for causal treatment is weak at least in patients with type 2 diabetes, and current pharmacotherapy is largely limited to symptomatic treatment options. Thus, a better understanding of the underlying pathophysiology is mandatory for translation into new diagnostic and treatment approaches. Improved knowledge about pathogenic pathways implicated in the development of diabetic neuropathy could lead to novel diagnostic techniques that have the potential of improving the early detection of neuropathy in diabetes and prediabetes to eventually embark on new treatment strategies. In this review, we first provide an overview on the current clinical aspects and illustrate the pathogenetic concepts of (pre)diabetic neuropathy. We then describe the biomarkers emerging from these concepts and novel diagnostic tools and appraise their utility in the early detection and prediction of predominantly distal sensorimotor polyneuropathy. Finally, we discuss the evidence for and limitations of the current and novel therapy options with particular emphasis on lifestyle modification and pathogenesis-derived treatment approaches. Altogether, recent years have brought forth a multitude of emerging biomarkers reflecting different pathogenic pathways such as oxidative stress and inflammation and diagnostic tools for an early detection and prediction of (pre)diabetic neuropathy. Ultimately, these insights should culminate in improving our therapeutic armamentarium against this common and debilitating or even life-threatening condition.

Comparisons of SOCS mRNA and protein levels in Xenopus provide insights into optic nerve regenerative success

In vertebrates from fishes to mammals, optic nerve injury induces increased expression ofSuppressor of Cytokine Signaling 3(SOCS3) mRNA, a modulator of cytokine signaling that is known to inhibit CNS axon regeneration. Unlike amniotes, however, anamniotes successfully regenerate optic axons, despite this increase. To address this seeming paradox, we examined the SOCS3 response to optic nerve injury in the frog,Xenopus laevis, at both the mRNA and protein levels. Far from being only transiently induced, SOCS3 mRNA expression increased throughout regeneration in retinal ganglion cells, but immunostaining and Western blots indicated that this increase was reflected at the protein level in regenerating optic axons but not in ganglion cell bodies. Polysome profiling provided additional evidence that SOCS3 protein levels were regulated post-translationally by demonstrating that the mRNA was efficiently translated in the injured eye. In tumor cells, another member of theSOCS gene family,SOCS2, is known to mediate SOCS3 degradation by targeting it for proteasomal degradation. Unlike the SOCS2 response in mammalian optic nerve injury, SOCS2 expression increased inXenopusretinal ganglion cells after injury, at both the mRNA and protein levels; it was, however, largely absent from both uninjured and regenerating optic axons. We propose a similar degradation mechanism may be spatially restricted inXenopusto keep SOCS3 protein levels sufficiently in check within ganglion cell bodies, where SOCS3 would otherwise inhibit transcription of genes needed for regeneration, but allow them to rise within the axons, where SOCS3 has pro-regenerative effects.

Association Between High Neutrophil to Lymphocyte Ratio and Delayed Recovery From Bell's Palsy

Objectives

Factors predictive of the severity of and recovery from Bell’s palsy remain unclear. This study evaluated the association between neutrophil to lymphocyte ratio (NLR) and the severity of and recovery from Bell’s palsy.

Methods

This retrospective study included 51 patients who were hospitalized with Bell’s palsy from 2015 to 2017. Degree of paralysis was assessed by House-Brackmann (H-B) grade. Patients with H-B grades 2–4 were classified as having mild to moderate palsy and patients with H-B grade 5 or 6 were classified as having severe palsy. Patients were evaluated for obesity, hypertension and diabetes mellitus, and blood tests were performed to determine NLR and platelet to lymphocyte ratio. Patients were treated with steroids and antiviral agents. H-B grade was assessed 1 week, 1 month, and 3 months after treatment.

Results

NLR was significantly higher in patients with severe than with mild to moderate palsy (P=0.048). Recovery time was significantly longer in patients with high NLR than low NLR (P=0.045).

Conclusion

Higher NLR in patients with Bell’s palsy was associated with longer recovery time. NLR may be prognostic of recovery time in patients with Bell’s palsy.

Spinal Cord Injury Scarring and Inflammation: Therapies Targeting Glial and Inflammatory Responses

Deficits in neuronal function are a hallmark of spinal cord injury (SCI) and therapeutic efforts are often focused on central nervous system (CNS) axon regeneration. However, secondary injury responses by astrocytes, microglia, pericytes, endothelial cells, Schwann cells, fibroblasts, meningeal cells, and other glia not only potentiate SCI damage but also facilitate endogenous repair. Due to their profound impact on the progression of SCI, glial cells and modification of the glial scar are focuses of SCI therapeutic research. Within and around the glial scar, cells deposit extracellular matrix (ECM) proteins that affect axon growth such as chondroitin sulfate proteoglycans (CSPGs), laminin, collagen, and fibronectin. This dense deposition of material, i.e., the fibrotic scar, is another barrier to endogenous repair and is a target of SCI therapies. Infiltrating neutrophils and monocytes are recruited to the injury site through glial chemokine and cytokine release and subsequent upregulation of chemotactic cellular adhesion molecules and selectins on endothelial cells. These peripheral immune cells, along with endogenous microglia, drive a robust inflammatory response to injury with heterogeneous reparative and pathological properties and are targeted for therapeutic modification. Here, we review the role of glial and inflammatory cells after SCI and the therapeutic strategies that aim to replace, dampen, or alter their activity to modulate SCI scarring and inflammation and improve injury outcomes.

Attenuation of TRPV1 by AMG-517 after nerve injury promotes peripheral axonal regeneration in rats

Aims

The main objective was to investigate the effects of the transient receptor potential cation channel subfamily V member 1 (TRPV1) on nerve regeneration following sciatic transection injury by functional blockage of TRPV1 using AMG-517, a specific blocker of TRPV1.

Methods

AMG-517 was injected into the area surrounding ipsilateral lumbar dorsal root ganglia 30 min after unilateral sciatic nerve transection. The number of sciatic axons and the expression of growth-associated protein-43 (GAP-43) and glial fibrillary acidic protein was examined using semithin sections, Western blot, and immunofluorescence analyses.

Results

Blockage of TRPV1 with AMG-517 markedly promoted axonal regeneration, especially at two weeks after sciatic injury; the number of axons was similar to the uninjured control group. After sciatic nerve transection, expression of glial fibrillary acidic protein was decreased and GAP-43 was increased at the proximal stump. However, the expression of both glial fibrillary acidic protein and GAP-43 increased significantly in AMG-517-treated groups.

Conclusions

TRPV1 may be an important therapeutic target to promote peripheral nerve regeneration after injury.

Monitoring of macrophage recruitment enhanced by Toll-like receptor 4 activation with MR imaging in nerve injury

INTRODUCTION

Macrophage recruitment is critical for nerve regeneration after an injury. The aim of this study was to investigate whether ultrasmall superparamagnetic iron oxide (USPIO) nanoparticle-based MRI could be used to monitor the enhanced macrophage recruitment by Toll-like receptor 4 (TLR4) activation in nerve injury.

METHODS

Rats received intraperitoneal injections of either lipopolysaccharide (LPS) or phosphate buffered saline (PBS) or no injection (controls) after a sciatic nerve crush injury. After intravenous injection of the USPIOs (LPS and PBS groups) or PBS (control group), MRI was performed and correlated with histological findings.

RESULTS

LPS group showed more remarkable hypointense signals on T2*-weighted imaging and lower T2 values in the crushed nerves than PBS group. The hypointense signal areas were associated with an enhanced recruitment of iron-loaded macrophages to the injured nerves.

DISCUSSION

USPIO-enhanced MRI can be used to monitor the enhanced macrophage recruitment by means of TLR4 signal pathway activation in nerve injury. Muscle Nerve, 2018.

Increased Calcitonin Gene-Related Peptide and Macrophages Are Involved in Astragalus membranaceus-Mediated Peripheral Nerve Regeneration in Rats

Astragalus membranaceus (AM) is one of 50 fundamental herbs in traditional Chinese medicine. Previous studies have shown that AM extract can be a potential nerve growth-promoting factor, being beneficial for the growth of peripheral nerve axons. We further investigated the effects of AM extract on regeneration in a rat sciatic nerve transection model. Rats were divided into three groups ([Formula: see text]): normal saline (intraperitoneal) as the control, and 1.5[Formula: see text]g/kg or 3.0[Formula: see text]g/kg of AM extract (every other day for four weeks), respectively. We evaluated neuronal electrophysiology, neuronal connectivity, macrophage infiltration, expression levels and location of calcitonin gene-related peptide (CGRP), and expression levels of both nerve growth factors (NGFs) and immunoregulatory factors. In the high-dose AM group, neuronal electrophysiological function (measured by nerve conductive velocity and its latency) was significantly improved ([Formula: see text]). Expression levels of CGRP and macrophage density were also drastically enhanced ([Formula: see text]). Expression levels of fibroblast growth factor (FGF), NGF, platelet-derived growth factor (PDGF), transforming growth factor-[Formula: see text], interleukin-1 (IL-1), and interferon (IFN)-[Formula: see text] were reduced in the high-dose AM group ([Formula: see text]), while FGF, NGF, PDGF, IL-1, and IFN-[Formula: see text] were increased in the low-dose AM group ([Formula: see text]). These results suggest that AM can modulate local inflammatory conditions, enhance nerve regeneration, and potentially increase recovery of a severe peripheral nerve injury.

Anastomotic stoma coated with chitosan film as a betamethasone dipropionate carrier for peripheral nerve regeneration

Scar hyperplasia at the suture site is an important reason for hindering the repair effect of peripheral nerve injury anastomosis. To address this issue, two repair methods are often used. Biological agents are used to block nerve sutures and the surrounding tissue to achieve physical anti-adhesion effects. Another agent is glucocorticosteroid, which can prevent scar growth by inhibiting inflammation. However, the overall effect of promoting regeneration of the injured nerve is not satisfactory. In this regard, we envision that these two methods can be combined and lead to shared understanding for achieving improved nerve repair. In this study, the right tibial nerve was transected 1 cm above the knee to establish a rat tibial nerve injury model. The incision was directly sutured after nerve transection. The anastomotic stoma was coated with 0.5 × 0.5 cm2 chitosan sheets with betamethasone dipropionate. At 12 weeks after injury, compared with the control and poly (D, L-lactic acid) groups, chitosan-betamethasone dipropionate film slowly degraded with the shape of the membrane still intact. Further, scar hyperplasia and the degree of adhesion at anastomotic stoma were obviously reduced, while the regenerated nerve fiber structure was complete and arranged in a good order in model rats. Electrophysiological study showed enhanced compound muscle action potential. Our results confirm that chitosan-betamethasone dipropionate film can effectively prevent local scar hyperplasia after tibial nerve repair and promote nerve regeneration.

Highly conserved molecular pathways, including Wnt signaling, promote functional recovery from spinal cord injury in lampreys

In mammals, spinal cord injury (SCI) leads to dramatic losses in neurons and synaptic connections, and consequently function. Unlike mammals, lampreys are vertebrates that undergo spontaneous regeneration and achieve functional recovery after SCI. Therefore our goal was to determine the complete transcriptional responses that occur after SCI in lampreys and to identify deeply conserved pathways that promote regeneration. We performed RNA-Seq on lamprey spinal cord and brain throughout the course of functional recovery. We describe complex transcriptional responses in the injured spinal cord, and somewhat surprisingly, also in the brain. Transcriptional responses to SCI in lampreys included transcription factor networks that promote peripheral nerve regeneration in mammals such as Atf3 and Jun. Furthermore, a number of highly conserved axon guidance, extracellular matrix, and proliferation genes were also differentially expressed after SCI in lampreys. Strikingly, ~3% of differentially expressed transcripts belonged to the Wnt pathways. These included members of the Wnt and Frizzled gene families, and genes involved in downstream signaling. Pharmacological inhibition of Wnt signaling inhibited functional recovery, confirming a critical role for this pathway. These data indicate that molecular signals present in mammals are also involved in regeneration in lampreys, supporting translational relevance of the model.

The dynamic changes of main cell types in the microenvironment of sciatic nerves following sciatic nerve injury and the influence of let-7 on their distribution

Schwann cells (SCs), fibroblasts and macrophages are the main cells in the peripheral nerve stumps.

Efficacy of self-retained cryopreserved amniotic membrane for treatment of neuropathic corneal pain

PURPOSE

Treatment of neuropathic corneal pain (NCP) remains intricate, and involves a long-term combined multistep approach. The self-retained cryopreserved amniotic membrane (PROKERA®, Bio-Tissue, Miami,FL) has been utilized for multiple ocular surface disorders. We evaluate the efficacy, safety, and tolerability of ProKera® Slim [PKS] and ProKera® Clear [PKC] in the treatment of NCP.

METHODS

Retrospective case series of 9 patients who received PKS/PKC for the acute treatment of NCP. Patient demographics, prior therapies, clinical examination, duration of PKS/PKC retention, changes in pain severity, corneal subbasal nerve density and morphology by in vivo confocal microscopy (IVCM; HRT3/RCM, Heidelberg Engineering, Heidelberg, Germany), and adverse events were recorded.

RESULTS

PKS/PKC were placed in 10 eyes of 9 patients. Pain severity improved by 72.5 ± 8.4% (from 6.3 ± 0.8 to 1.9 ± 0.6, scale 1-10, p = 0.0003) after retention for 6.4 ± 1.1 days. Despite shorter retention for 4.0 ± 0.7 days in patients with ring dysesthesia (4 eyes) or premature implant disengagement (2 eyes), pain severity still improved by 63.1 ± 12.5% (from 6.8 ± 1.0 to 2.4 ± 0.9, p = 0.009). During a follow-up of 9.3 ± 0.8 months, two patients reported recurrence of pain after 2.3 and 9.6 months respectively, treated effectively with additional PKS/PKC. IVCM showed a 36.6 ± 17.6% increase in total nerve density, from 17,700.9 ± 1315.7 to 21,891.3 ± 2040.5 μm/mm2 (p = 0.047), while the fellow PKS/PKC-untreated eyes did not show a significant interval change. Main nerve trunk and branch nerve densities were not statistically different. Dendritiform cell density decreased from 46.0 ± 8.2 to 32.0 ± 6.0 cells/mm2 (p = 0.01).

CONCLUSIONS

PKS/PKC provide a safe and effective treatment approach to achieve sustained pain control in patients with NCP.

A growing field: The regulation of axonal regeneration by Wnt signaling

The canonical Wnt/β-catenin pathway is a highly conserved signaling cascade that plays critical roles during embryogenesis. Wnt ligands regulate axonal extension, growth cone guidance and synaptogenesis throughout the developing central nervous system (CNS). Recently, studies in mammalian and fish model systems have demonstrated that Wnt/β-catenin signaling also promotes axonal regeneration in the adult optic nerve and spinal cord after injury, raising the possibility that Wnt could be developed as a therapeutic strategy. In this review, we summarize experimental evidence that reveals novel roles for Wnt signaling in the injured CNS, and discuss possible mechanisms by which Wnt ligands could overcome molecular barriers inhibiting axonal growth to promote regeneration. A central challenge in the neuroscience field is developing therapeutic strategies that induce robust axonal regeneration. Although adult axons have the capacity to respond to axonal guidance molecules after injury, there are several major obstacles for axonal growth, including extensive neuronal death, glial scars at the injury site, and lack of axonal guidance signals. Research in rodents demonstrated that activation of Wnt/β-catenin signaling in retinal neurons and radial glia induced neuronal survival and axonal growth, but that activation within reactive glia at the injury site promoted proliferation and glial scar formation. Studies in zebrafish spinal cord injury models confirm an axonal regenerative role for Wnt/β-catenin signaling and identified the cell types responsible. Additionally, in vitro and in vivo studies demonstrated that Wnt induces axonal and neurite growth through transcription-dependent effects of its central mediator β-catenin, potentially by inducing regeneration-promoting genes. Canonical Wnt signaling may also function through transcription-independent interactions of β-catenin with cytoskeletal elements, which could stabilize growing axons and control growth cone movement. Therefore, these studies suggest that Wnt-induced pathways responsible for regulating axonal growth during embryogenesis could be repurposed to promote axonal growth after injury.

Treatment with albumin-hydroxyoleic acid complex restores sensorimotor function in rats with spinal cord injury: Efficacy and gene expression regulation

Sensorimotor dysfunction following incomplete spinal cord injury (SCI) is often characterized by paralysis, spasticity and pain. Previously, we showed that intrathecal (i.t.) administration of the albumin-oleic acid (A-OA) complex in rats with SCI produced partial improvement of these symptoms and that oral 2-hydroxyoleic acid (HOA, a non-hydrolyzable OA analogue), was efficacious in the modulation and treatment of nociception and pain-related anxiety, respectively. Here we observed that intrathecal treatment with the complex albumin-HOA (A-HOA) every 3 days following T9 spinal contusion injury improved locomotor function assessed with the Rotarod and inhibited TA noxious reflex activity in Wistar rats. To investigate the mechanism of action of A-HOA, microarray analysis was carried out in the spinal cord lesion area. Representative genes involved in pain and neuroregeneration were selected to validate the changes observed in the microarray analysis by quantitative real-time RT-PCR. Comparison of the expression between healthy rats, SCI rats, and SCI treated with A-HOA rats revealed relevant changes in the expression of genes associated with neuronal morphogenesis and growth, neuronal survival, pain and inflammation. Thus, treatment with A-HOA not only induced a significant overexpression of growth and differentiation factor 10 (GDF10), tenascin C (TNC), aspirin (ASPN) and sushi-repeat-containing X-linked 2 (SRPX2), but also a significant reduction in the expression of prostaglandin E synthase (PTGES) and phospholipases A1 and A2 (PLA1/2). Currently, SCI has very important unmet clinical needs. A-HOA downregulated genes involved with inflammation and upregulated genes involved in neuronal growth, and may serve to promote recovery of function after experimental SCI.

Complement Protein C3 Suppresses Axon Growth and Promotes Neuron Loss

The inflammatory response to spinal cord injury (SCI) involves localization and activation of innate and adaptive immune cells and proteins, including the complement cascade. Complement C3 is important for the classical, alternative, and lectin pathways of complement activation, and its cleavage products C3a and C3b mediate several functions in the context of inflammation, but little is known about the potential functions of C3 on regeneration and survival of injured neurons after SCI. We report that 6 weeks after dorsal hemisection with peripheral conditioning lesion, C3^-/- mice demonstrated a 2-fold increase in sensory axon regeneration in the spinal cord in comparison to wildtype C3^+/+ mice. In vitro, addition of C3 tripled both myelin-mediated neurite outgrowth inhibition and neuron loss versus myelin alone, and ELISA experiments revealed that myelin serine proteases cleave C3 to generate active fragments. Addition of purified C3 cleavage products to cultured neurons suggested that C3b is responsible for the growth inhibitory and neurotoxic or anti-adhesion activities of C3. These data indicate that C3 reduces neurite outgrowth and neuronal viability in vitro and restricts axon regeneration in vivo, and demonstrate a novel, non-traditional role for this inflammatory protein in the central nervous system.

Sevoflurane preconditioning ameliorates traumatic spinal cord injury through caveolin-3-dependent cyclooxygenase-2 inhibition

Acute traumatic spinal cord injury (tSCI) results in a lifetime of paralysis associated with a host of medical complications. The developing secondary complications of tSCI may result in further chronic neurodegenerative diseases. Sevoflurane preconditioning (SF-PreCon) has shown guaranteed protective effects in myocardial or cerebral ischemic/reperfusion injury. However, the role of SF-PreCon in tSCI still remains to be elucidated. Here, we found that SF-PreCon ameliorated the developing secondary complications through reducing the apoptosis rate and the secretion of inflammatory cytokines in injured spinal cord tissues, and therefore enhancing the recovery after tSCI. Notably, we demonstrated that SF-PreCon ameliorates tSCI through inhibiting Cycloxygenase-2 (COX-2). Importantly, we verified that SF-PreCon inhibits the expression of COX-2 and reduces the apoptosis rate after tSCI via the induction of Caveolin-3 (Cav-3). Taken together, our results suggest that SF-PreCon ameliorates tSCI via Cav-3-dependent COX-2 inhibition and provide an economical and practical method against the secondary injury after tSCI.

Colony Stimulating Factor-1 Receptor Expressing Cells Infiltrating the Cornea Control Corneal Nerve Degeneration in Response to HSV-1 Infection

Purpose

Herpes simplex virus type-1 (HSV-1) is a leading cause of neurotrophic keratitis, characterized by decreased or absent corneal sensation due to damage to the sensory corneal innervation. We previously reported the elicited immune response to infection contributes to the mechanism of corneal nerve regression/damage during acute HSV-1 infection. Our aim is to further establish the involvement of infiltrated macrophages in the mechanism of nerve loss upon infection.

Methods

Macrophage Fas-Induced Apoptosis (MAFIA) transgenic C57BL/6 mice were systemically treated with AP20187 dimerizer or vehicle (VEH), and their corneas, lymph nodes, and blood were assessed for CD45+CD11b+GFP+ cell depletion by flow cytometry (FC). Mice were ocularly infected with HSV-1 or left uninfected. At 2, 4, and/or 6 days post infection (PI), corneas were assessed for sensitivity and harvested for FC, nerve structure by immunohistochemistry, viral content by plaque assay, soluble factor content by suspension array, and activation of signaling pathways by Western blot analysis. C57BL6 mice were used to compare to the MAFIA mouse model.

Results

MAFIA mice treated with AP20187 had efficient depletion of CD45+CD11b+GFP+ cells in the tissues analyzed. The reduction of CD45+CD11b+GFP+ cells recruited to the infected corneas of AP20187-treated mice correlated with preservation of corneal nerve structure and function, decreased protein concentration of inflammatory cytokines, and decreased STAT3 activation despite no changes in viral content in the cornea compared to VEH-treated animals.

Conclusions

Our results suggest infiltrated macrophages are early effectors in the nerve regression following HSV-1 infection. We propose the neurodegeneration mechanism involves macrophages, local up-regulation of IL-6, and activation of STAT3.

Cell biology of spinal cord injury and repair

Spinal cord injury (SCI) lesions present diverse challenges for repair strategies. Anatomically complete injuries require restoration of neural connectivity across lesions. Anatomically incomplete injuries may benefit from augmentation of spontaneous circuit reorganization. Here, we review SCI cell biology, which varies considerably across three different lesion-related tissue compartments: (a) non-neural lesion core, (b) astrocyte scar border, and (c) surrounding spared but reactive neural tissue. After SCI, axon growth and circuit reorganization are determined by neuron-cell-autonomous mechanisms and by interactions among neurons, glia, and immune and other cells. These interactions are shaped by both the presence and the absence of growth-modulating molecules, which vary markedly in different lesion compartments. The emerging understanding of how SCI cell biology differs across lesion compartments is fundamental to developing rationally targeted repair strategies.

TFOS DEWS II pain and sensation report

Pain associated with mechanical, chemical, and thermal heat stimulation of the ocular surface is mediated by trigeminal ganglion neurons, while cold thermoreceptors detect wetness and reflexly maintain basal tear production and blinking rate. These neurons project into two regions of the trigeminal brain stem nuclear complex: ViVc, activated by changes in the moisture of the ocular surface and VcC1, mediating sensory-discriminative aspects of ocular pain and reflex blinking. ViVc ocular neurons project to brain regions that control lacrimation and spontaneous blinking and to the sensory thalamus. Secretion of the main lacrimal gland is regulated dominantly by autonomic parasympathetic nerves, reflexly activated by eye surface sensory nerves. These also evoke goblet cell secretion through unidentified efferent fibers. Neural pathways involved in the regulation of meibomian gland secretion or mucin release have not been identified. In dry eye disease, reduced tear secretion leads to inflammation and peripheral nerve damage. Inflammation causes sensitization of polymodal and mechano-nociceptor nerve endings and an abnormal increase in cold thermoreceptor activity, altogether evoking dryness sensations and pain. Long-term inflammation and nerve injury alter gene expression of ion channels and receptors at terminals and cell bodies of trigeminal ganglion and brainstem neurons, changing their excitability, connectivity and impulse firing. Perpetuation of molecular, structural and functional disturbances in ocular sensory pathways ultimately leads to dysestesias and neuropathic pain referred to the eye surface. Pain can be assessed with a variety of questionaires while the status of corneal nerves is evaluated with esthesiometry and with in vivo confocal microscopy.

Translational profiling of retinal ganglion cell optic nerve regeneration in Xenopus laevis

Unlike adult mammals, adult frogs regrow their optic nerve following a crush injury, making Xenopus laevis a compelling model for studying the molecular mechanisms that underlie neuronal regeneration. Using Translational Ribosome Affinity Purification (TRAP), a method to isolate ribosome-associated mRNAs from a target cell population, we have generated a transcriptional profile by RNA-Seq for retinal ganglion cells (RGC) during the period of recovery following an optic nerve injury. Based on bioinformatic analysis using the Xenopus laevis 9.1 genome assembly, our results reveal a profound shift in the composition of ribosome-associated mRNAs during the early stages of RGC regeneration. As factors involved in cell signaling are rapidly down-regulated, those involved in protein biosynthesis are up-regulated alongside key initiators of axon development. Using the new genome assembly, we were also able to analyze gene expression profiles of homeologous gene pairs arising from a whole-genome duplication in the Xenopus lineage. Here we see evidence of divergence in regulatory control among a significant proportion of pairs. Our data should provide a valuable resource for identifying genes involved in the regeneration process to target for future functional studies, in both naturally regenerative and non-regenerative vertebrates.

Transcriptional Profiling at High Temporal Resolution Reveals Robust Immune/Inflammatory Responses during Rat Sciatic Nerve Recovery

After peripheral nerve injury, immune/inflammatory responses are triggered, which are critical for nerve regeneration. Despite their importance, the underlying molecular changes in immune/inflammatory responses remain largely unknown. In this study, we systematically analyzed differentially expressed genes in immune/inflammatory-related pathways at high temporal resolution and experimentally validated gene expression changes with RT-PCR following sciatic nerve crush in rats. We found that immune/inflammatory reactions not only occur in the acute injury but also remained activated over two weeks after injury. Detailed bioinformatic studies suggested that multiple immune/inflammatory pathways, including agranulocyte adhesion and diapedesis, granulocyte adhesion and diapedesis, IL-6 signaling, and IL-10 signaling, were sustained activated during nerve degeneration and regeneration. Our current study expands our understanding of the molecular basis of altered immune/inflammatory-related pathways following injury and thus might offer the possibility of targeting related molecules as therapeutic intervention for peripheral nerve regeneration.

Stem Cell-Containing Hyaluronic Acid-Based Spongy Hydrogels for Integrated Diabetic Wound Healing

The detailed pathophysiology of diabetic foot ulcers is yet to be established and improved treatments are still required. We propose a strategy that directs inflammation, neovascularization, and neoinnervation of diabetic wounds. Aiming to potentiate a relevant secretome for nerve regeneration, stem cells were precultured in hyaluronic acid-based spongy hydrogels under neurogenic/standard media before transplantation into diabetic mice full-thickness wounds. Acellular spongy hydrogels and empty wounds were used as controls. Re-epithelialization was attained 4 weeks after transplantation independently of the test groups, whereas a thicker and more differentiated epidermis was observed for the cellular spongy hydrogels. A switch from the inflammatory to the proliferative phase of wound healing was revealed for all the experimental groups 2 weeks after injury, but a significantly higher M2(CD163⁺)/M1(CD86⁺) subtype ratio was observed in the neurogenic preconditioned group that also failed to promote neoinnervation. A higher number of intraepidermal nerve fibers were observed for the unconditioned group probably due to a more controlled transition from the inflammatory to the proliferative phase. Overall, stem cell-containing spongy hydrogels represent a promising approach to enhance diabetic wound healing by positively impacting re-epithelialization and by modulating the inflammatory response to promote a successful neoinnervation.

Effects of Taxol on Regeneration in a Rat Sciatic Nerve Transection Model

Recent studies describe taxol as a candidate treatment for promoting central nerve regeneration. However, taxol has serious side effects including peripheral neurotoxicity, and little information is known about the effect of taxol on peripheral nerve regeneration. We investigated the effects of taxol on regeneration in a rat sciatic nerve transection model. Rats were divided into four groups (n = 10): normal saline (i.p.) as the control, Cremophor EL vehicle, and 2 or 6 mg/kg of taxol in the Cremophor EL solution (four times in day-2, 4, 6, and 8), respectively. We evaluated neuronal electrophysiology, animal behaviour, neuronal connectivity, macrophage infiltration, location and expression levels of calcitonin gene-related peptide (CGRP), and expression levels of both nerve growth factors and immunoregulatory factors. In the high-dose taxol group (6 mg/kg), neuronal electrophysiological function was significantly impaired. Licking latencies were significantly changed while motor coordination was unaffected. Neuronal connectivity, macrophage density, and expression levels of CGRP was dramatically reduced. Expression levels of nerve growth factors and immunoregulatory factors was also reduced, while it was increased in the low-dose taxol group (2 mg/kg). These results indicate that taxol can modulate local inflammatory conditions, impair nerve regeneration, and impede recovery of a severe peripheral nerve injury.

Neuroinflammation as Fuel for Axonal Regeneration in the Injured Vertebrate Central Nervous System

Damage to the central nervous system (CNS) is one of the leading causes of morbidity and mortality in elderly, as repair after lesions or neurodegenerative disease usually fails because of the limited capacity of CNS regeneration. The causes underlying this limited regenerative potential are multifactorial, but one critical aspect is neuroinflammation. Although classically considered as harmful, it is now becoming increasingly clear that inflammation can also promote regeneration, if the appropriate context is provided. Here, we review the current knowledge on how acute inflammation is intertwined with axonal regeneration, an important component of CNS repair. After optic nerve or spinal cord injury, inflammatory stimulation and/or modification greatly improve the regenerative outcome in rodents. Moreover, the hypothesis of a beneficial role of inflammation is further supported by evidence from adult zebrafish, which possess the remarkable capability to repair CNS lesions and even restore functionality. Lastly, we shed light on the impact of aging processes on the regenerative capacity in the CNS of mammals and zebrafish. As aging not only affects the CNS, but also the immune system, the regeneration potential is expected to further decline in aged individuals, an element that should definitely be considered in the search for novel therapeutic strategies.

Engineered neural tissue with Schwann cell differentiated human dental pulp stem cells: potential for peripheral nerve repair?

Despite the spontaneous regenerative capacity of the peripheral nervous system, large gap peripheral nerve injuries (PNIs) require bridging strategies. The limitations and suboptimal results obtained with autografts or hollow nerve conduits in the clinic urge the need for alternative treatments. Recently, we have described promising neuroregenerative capacities of Schwann cells derived from differentiated human dental pulp stem cells (d-hDPSCs) in vitro. Here, we extended the in vitro assays to show the pro-angiogenic effects of d-hDPSCs, such as enhanced endothelial cell proliferation, migration and differentiation. In addition, for the first time we evaluated the performance of d-hDPSCs in an in vivo rat model of PNI. Eight weeks after transplantation of NeuraWrap™ conduits filled with engineered neural tissue (EngNT) containing aligned d-hDPSCs in 15-mm rat sciatic nerve defects, immunohistochemistry and ultrastructural analysis revealed ingrowing neurites, myelinated nerve fibres and blood vessels along the construct. Although further research is required to optimize the delivery of this EngNT, our findings suggest that d-hDPSCs are able to exert a positive effect in the regeneration of nerve tissue in vivo. Copyright © 2017 John Wiley & Sons, Ltd.

Neurotrophic Factors Used to Treat Spinal Cord Injury

The application of neurotrophic factors as a therapy to improve morphological and behavioral outcomes after experimental spinal cord injury (SCI) has been the focus of many studies. These studies vary markedly in the type of neurotrophic factor that is delivered, the mode of administration, and the location, timing, and duration of the treatment. Generally, the majority of studies have had significant success if neurotrophic factors are applied in or close to the lesion site during the acute or the subacute phase after SCI. Comparatively fewer studies have administered neurotrophic factors in order to directly target the somata of injured neurons. The mode of delivery varies between acute injection of recombinant proteins, subacute or chronic delivery using a variety of strategies including osmotic minipumps, cell-mediated delivery, delivery using polymer release vehicles or supporting bridges of some sort, or the use of gene therapy to modify neurons, glial cells, or precursor/stem cells. In this brief review, we summarize the state of play of many of the therapies using these factors, most of which have been undertaken in rodent models of SCI.

Enhancing Nervous System Recovery through Neurobiologics, Neural Interface Training, and Neurorehabilitation

After an initial period of recovery, human neurological injury has long been thought to be static. In order to improve quality of life for those suffering from stroke, spinal cord injury, or traumatic brain injury, researchers have been working to restore the nervous system and reduce neurological deficits through a number of mechanisms. For example, neurobiologists have been identifying and manipulating components of the intra- and extracellular milieu to alter the regenerative potential of neurons, neuro-engineers have been producing brain-machine and neural interfaces that circumvent lesions to restore functionality, and neurorehabilitation experts have been developing new ways to revitalize the nervous system even in chronic disease. While each of these areas holds promise, their individual paths to clinical relevance remain difficult. Nonetheless, these methods are now able to synergistically enhance recovery of native motor function to levels which were previously believed to be impossible. Furthermore, such recovery can even persist after training, and for the first time there is evidence of functional axonal regrowth and rewiring in the central nervous system of animal models. To attain this type of regeneration, rehabilitation paradigms that pair cortically-based intent with activation of affected circuits and positive neurofeedback appear to be required-a phenomenon which raises new and far reaching questions about the underlying relationship between conscious action and neural repair. For this reason, we argue that multi-modal therapy will be necessary to facilitate a truly robust recovery, and that the success of investigational microscopic techniques may depend on their integration into macroscopic frameworks that include task-based neurorehabilitation. We further identify critical components of future neural repair strategies and explore the most updated knowledge, progress, and challenges in the fields of cellular neuronal repair, neural interfacing, and neurorehabilitation, all with the goal of better understanding neurological injury and how to improve recovery.