The Nogo signaling pathway for regeneration block

Role and Interplay of Different Signaling Pathways Involved in Sciatic Nerve Regeneration

Regeneration of the sciatic nerve is a sophisticated process that involves the interplay of several signaling pathways that orchestrate the cellular responses critical to regeneration. Among the key pathways are the mitogen-activated protein kinase (MAPK), phosphatidylinositol 3-kinase (PI3K)/AKT, cyclic adenosine monophosphate (cAMP), and Janus kinase/signal transducers and transcription activators (JAK/STAT) pathways. In particular, the cAMP pathway modulates neuronal survival and axonal regrowth. It influences various cellular behaviors and gene expression that are essential for nerve regeneration. MAPK is indispensable for Schwann cell differentiation and myelination, whereas PI3K/AKT is integral to the transcription, translation, and cell survival processes that are vital for nerve regeneration. Furthermore, GTP-binding proteins, including those of the Ras homolog gene family (Rho), regulate neural cell adhesion, migration, and survival. Notch signaling also appears to be effective in the early stages of nerve regeneration and in preventing skeletal muscle fibrosis after injury. Understanding the intricate mechanisms and interactions of these pathways is vital for the development of effective therapeutic strategies for sciatic nerve injuries. This review underscores the need for further research to fill existing knowledge gaps and improve therapeutic outcomes.

Advances in electroactive bioscaffolds for repairing spinal cord injury

Spinal cord injury (SCI) is a devastating neurological disorder, leading to loss of motor or somatosensory function, which is the most challenging worldwide medical problem. Re-establishment of intact neural circuits is the basis of spinal cord regeneration. Considering the crucial role of electrical signals in the nervous system, electroactive bioscaffolds have been widely developed for SCI repair. They can produce conductive pathways and a pro-regenerative microenvironment at the lesion site similar to that of the natural spinal cord, leading to neuronal regeneration and axonal growth, and functionally reactivating the damaged neural circuits. In this review, we first demonstrate the pathophysiological characteristics induced by SCI. Then, the crucial role of electrical signals in SCI repair is introduced. Based on a comprehensive analysis of these characteristics, recent advances in the electroactive bioscaffolds for SCI repair are summarized, focusing on both the conductive bioscaffolds and piezoelectric bioscaffolds, used independently or in combination with external electronic stimulation. Finally, thoughts on challenges and opportunities that may shape the future of bioscaffolds in SCI repair are concluded.

Non-canonical retinoid signaling in neural development, regeneration and synaptic function

Canonical retinoid signaling via nuclear receptors and gene regulation is critical for the initiation of developmental processes such as cellular differentiation, patterning and neurite outgrowth, but also mediates nerve regeneration and synaptic functions in adult nervous systems. In addition to canonical transcriptional regulation, retinoids also exert rapid effects, and there are now multiple lines of evidence supporting non-canonical retinoid actions outside of the nucleus, including in dendrites and axons. Together, canonical and non-canonical retinoid signaling provide the precise temporal and spatial control necessary to achieve the fine cellular coordination required for proper nervous system function. Here, we examine and discuss the evidence supporting non-canonical actions of retinoids in neural development and regeneration as well as synaptic function, including a review of the proposed molecular mechanisms involved.

RhoGDI phosphorylation by PKC promotes its interaction with death receptor p75NTR to gate axon growth and neuron survival

How receptors juggle their interactions with multiple downstream effectors remains poorly understood. Here we show that the outcome of death receptor p75NTR signaling is determined through competition of effectors for interaction with its intracellular domain, in turn dictated by the nature of the ligand. While NGF induces release of RhoGDI through recruitment of RIP2, thus decreasing RhoA activity in favor of NFkB signaling, MAG induces PKC-mediated phosphorylation of the RhoGDI N-terminus, promoting its interaction with the juxtamembrane domain of p75NTR, disengaging RIP2, and enhancing RhoA activity in detriment of NF-kB. This results in stunted neurite outgrowth and apoptosis in cerebellar granule neurons. If presented simultaneously, MAG prevails over NGF. The NMR solution structure of the complex between the RhoGDI N-terminus and p75NTR juxtamembrane domain reveals previously unknown structures of these proteins and clarifies the mechanism of p75NTR activation. These results show how ligand-directed competition between RIP2 and RhoGDI for p75NTR engagement determine axon growth and neuron survival. Similar principles are likely at work in other receptors engaging multiple effectors and signaling pathways.

Do Pharmacological Treatments Act in Collaboration with Rehabilitation in Spinal Cord Injury Treatment? A Review of Preclinical Studies

There is no choice other than rehabilitation as a practical medical treatment to restore impairments or improve activities after acute treatment in people with spinal cord injury (SCI); however, the effect is unremarkable. Therefore, researchers have been seeking effective pharmacological treatments. These will, hopefully, exert a greater effect when combined with rehabilitation. However, no review has specifically summarized the combinatorial effects of rehabilitation with various medical agents. In the current review, which included 43 articles, we summarized the combinatorial effects according to the properties of the medical agents, namely neuromodulation, neurotrophic factors, counteraction to inhibitory factors, and others. The recovery processes promoted by rehabilitation include the regeneration of tracts, neuroprotection, scar tissue reorganization, plasticity of spinal circuits, microenvironmental change in the spinal cord, and enforcement of the musculoskeletal system, which are additive, complementary, or even synergistic with medication in many cases. However, there are some cases that lack interaction or even demonstrate competition between medication and rehabilitation. A large fraction of the combinatorial mechanisms remains to be elucidated, and very few studies have investigated complex combinations of these agents or targeted chronically injured spinal cords.

Functional Hydrogel Co-Remolding Migration and Differentiation Microenvironment for Severe Spinal Cord Injury Repair

Spinal cord injury (SCI) activates nestin+ neural stem cells (NSCs), which can be regarded as potential seed cells for neuronal regeneration. However, the lesion microenvironment seriously hinders the migration of the nestin+ cells to the lesion epicenter and their differentiation into neurons to rebuild neural circuits. In this study, a photosensitive hydrogel scaffold is prepared as drug delivery carrier. Genetically engineered SDF1α and NT3 are designed and the scaffold is binary modified to reshape the lesion microenvironment. The binary modified scaffold can effectively induce the migration and neuronal differentiation of nestin+ NSCs in vitro. When implanted into a rat complete SCI model, many of the SCI-activated nestin+ cells migrate into the lesion site and give rise to neurons in short-term. Meanwhile, long-term repair results also show that implantation of the binary modified scaffold can effectively promote the maturation, functionalization and synaptic network reconstruction of neurons in the lesion site. In addition, animals treated with binary scaffold also showed better improvement in motor functions. The therapeutic strategy based on remolding the migration and neuronal differentiation lesion microenvironment provides a new insight into SCI repair by targeting activated nestin+ cells, which exhibits excellent clinical transformation prospects.

Rodent Models of Spinal Cord Injury: From Pathology to Application

Spinal cord injury (SCI) often has devastating consequences for the patient's physical, mental and occupational health. At present, there is no effective treatment for SCI, and appropriate animal models are very important for studying the pathological manifestations, injury mechanisms, and corresponding treatment. However, the pathological changes in each injury model are different, which creates difficulties in selecting appropriate models for different research purposes. In this article, we analyze various SCI models and introduce their pathological features, including inflammation, glial scar formation, axon regeneration, ischemia-reperfusion injury, and oxidative stress, and evaluate the advantages and disadvantages of each model, which is convenient for selecting suitable models for different injury mechanisms to study therapeutic methods.

Hematogenous Macrophages: A New Therapeutic Target for Spinal Cord Injury

Spinal cord injury (SCI) is a devastating disease leading to loss of sensory and motor functions, whose pathological process includes mechanical primary injury and secondary injury. Macrophages play an important role in SCI pathology. According to its origin, it can be divided into resident microglia and peripheral monocyte-derived macrophages (hematogenous Mφ). And it can also be divided into M1-type macrophages and M2-type macrophages on the basis of its functional characteristics. Hematogenous macrophages may contribute to the SCI process through infiltrating, scar forming, phagocytizing debris, and inducing inflammatory response. Although some of the activities of hematogenous macrophages are shown to be beneficial, the role of hematogenous macrophages in SCI remains controversial. In this review, following a brief introduction of hematogenous macrophages, we mainly focus on the function and the controversial role of hematogenous macrophages in SCI, and we propose that hematogenous macrophages may be a new therapeutic target for SCI.

Activation and Role of Astrocytes in Ischemic Stroke

Ischemic stroke refers to the disorder of blood supply of local brain tissue caused by various reasons. It has high morbidity and mortality worldwide. Astrocytes are the most abundant glial cells in the central nervous system (CNS). They are responsible for the homeostasis, nutrition, and protection of the CNS and play an essential role in many nervous system diseases’ physiological and pathological processes. After stroke injury, astrocytes are activated and play a protective role through the heterogeneous and gradual changes of their gene expression, morphology, proliferation, and function, that is, reactive astrocytes. However, the position of reactive astrocytes has always been a controversial topic. Many studies have shown that reactive astrocytes are a double-edged sword with both beneficial and harmful effects. It is worth noting that their different spatial and temporal expression determines astrocytes’ various functions. Here, we comprehensively review the different roles and mechanisms of astrocytes after ischemic stroke. In addition, the intracellular mechanism of astrocyte activation has also been involved. More importantly, due to the complex cascade reaction and action mechanism after ischemic stroke, the role of astrocytes is still difficult to define. Still, there is no doubt that astrocytes are one of the critical factors mediating the deterioration or improvement of ischemic stroke.

Transplantation of a vascularized pedicle of hemisected spinal cord to establish spinal cord continuity after removal of a segment of the thoracic spinal cord: A proof-of-principle study in dogs

Introduction

Glial scar formation impedes nerve regeneration/reinnervation after spinal cord injury (SCI); therefore, removal of scar tissue is essential for SCI treatment.

Aims

To investigate whether removing a spinal cord and transplanting a vascularized pedicle of hemisected spinal cord from the spinal cord caudal to the transection can restore motor function, to aid in the treatment of future clinical spinal cord injuries. We developed a canine model. After removal of a 1‐cm segment of the thoracic (T10–T11) spinal cord in eight beagles, a vascularized pedicle of hemisected spinal cord from the first 1.5 cm of the spinal cord caudal to the transection (cut along the posterior median sulcus of the spinal cord) was transplanted to bridge the transected spinal cord in the presence of a fusogen (polyethylene glycol, PEG) in four of the eight dogs. We used various forms of imaging, electron microscopy, and histologic data to determine that after our transplantation of a vascular pedicled hemisection to bridge the transected spinal cord, electrical continuity across the spinal bridge was restored.

Results

Motor function was restored following our transplantation, as confirmed by the re‐establishment of anatomic continuity along with interfacial axonal sprouting.

Conclusion

Taken together, our findings suggest that SCI patients—who have previously been thought to have irreversible damage and/or paralysis—may be treated effectively with similar operative techniques to re‐establish electrical and functional continuity following SCI.

Molecular effects of curcumin on the experimental autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) is an animal model of multiple sclerosis (MS). Previous studies have shown that myelin degradation during MS and EAE resulted in reduced expression of some of the proteins, e.g., the MBP (myelin basic protein), and increased expression of genes such as iNOS (Inducible nitric oxide synthase) and NOGO-A in the affected patients. In the present study, EAE was induced by immunizing Wistar rats (n=12) with homogenized spinal cord of guinea pig and Freund's complete adjuvant. Curcumin is an active ingredient in turmeric with anti-inflammatory properties, which has been studied in this article. In this study, the effect of curcumin administration on the change of the expression of MBP, NOGO-A, and iNOS genes was evaluated using the RT-PCR (Reverse transcription-polymerase chain reaction) technique. The obtained results indicated it could be concluded that curcumin was able to improve EAE by increasing the amount of MBP gene expression and reducing the intensity of NOGO-A expression.

Nogo-A aggravates oxidative damage in oligodendrocytes

Nogo-A is considered one of the most important inhibitors of myelin-associated axonal regeneration in the central nervous system. It is mainly expressed by oligodendrocytes. Although previous studies have found regulatory roles for Nogo-A in neurite outgrowth inhibition, neuronal homeostasis, precursor migration, plasticity, and neurodegeneration, its functions in the process of oxidative injury are largely uncharacterized. In this study, oligodendrocytes were extracted from the cerebral cortex of newborn Sprague-Dawley rats. We used hydrogen peroxide (H₂O₂) to induce an in vitro oligodendrocyte oxidative damage model and found that endogenously expressed Nogo-A is significantly upregulated in oligodendrocytes. After recombinant virus Ad-ZsGreen-rat Nogo-A infection of oligodendrocytes, Nogo-A expression was increased, and the infected oligodendrocytes were more susceptible to acute oxidative insults and exhibited a markedly elevated rate of cell death. Furthermore, knockdown of Nogo-A expression in oligodendrocytes by Ad-ZsGreen-shRNA-Nogo-A almost completely protected against oxidative stress induced by exogenous H₂O₂. Intervention with a Nogo-66 antibody, a LINGO1 blocker, or Y27632, an inhibitor in the Nogo-66-NgR/p75/LINGO-1-RhoA-ROCK pathway, did not affect the death of oligodendrocytes. Ad-ZsGreen-shRNA-Nogo-A also increased the levels of phosphorylated extracellular signal-regulated kinase 1/2 and inhibited BCL2 expression in oligodendrocytes. In conclusion, Nogo-A aggravated reactive oxygen species damage in oligodendrocytes, and phosphorylated extracellular signal-regulated kinase 1/2 and BCL2 might be involved in this process. This study was approved by the Ethics Committee of Peking University People’s Hospital, China (approval No. 2018PHC081) on December 18, 2018.

Astrocytes directly clear myelin debris through endocytosis pathways and followed by excessive gliosis after spinal cord injury

Persisted myelin debris inhibit axon regeneration and contribute to further tissue damage after spinal cord injury (SCI). The traditional view is that myelin debris is mainly cleared by microglia and macrophages, while astrocytes cannot directly engulf myelin debris because they are absent from lesion core. Here, we definitely showed that astrocytes could directly uptake myelin debris both in vitro and in vivo to effectively complement the clearance function. Therefore, it can be shown that astrocytes can exert myelin clearance effect directly and indirectly after spinal cord injury. The damaged myelin debris was transported to lysosomes for degradation through endocytosis pathways, finally resulting in excessive gliosis. This process may be a potential target for regulating neural tissue repair and excessive glia scar formation after SCI.

Glial Scar-a Promising Target for Improving Outcomes After CNS Injury

After central nervous system (CNS) injury, a series of stress responses induce astrocytes activation. Reactive astrocytes, which are typically different from astrocytes in normal conditions in altered morphology and gene expression, combine with extracellular matrix (ECM) components to form a glial scar at the lesion site, which walls of the injured region from neighboring healthier tissue. However, as a physical and molecular barrier, glial scar can impede patients' functional recovery in the late period of CNS injury. Thus, inhibiting glial scar formation in the chronic stage after CNS injury may be a promising target to improve outcomes. Since the therapeutic strategies targeting on mediating glial scar formation are regarded as an important part on improving functional recovery after CNS injury, in this review, we focus on the regulating effects of related signaling pathways and other molecules on glial scar, and the process of glial scar formation and the roles that it plays during the acute and chronic stages are also expounded in this article. We hope to get a comprehensive understanding of glial scar during CNS injury based on current researches and to open new perspectives for the therapies to promote functional recovery after CNS injury.

Absence of axonal sprouting following unilateral lesion in 125-day-old rat supraoptic nucleus may be due to age-dependent decrease in protein levels of ciliary neurotrophic factor receptor alpha

Within the supraoptic nucleus (SON) of a 35-day-old rat, we previously demonstrated a collateral sprouting response that reinnervates the partially denervated neural lobe (NL) after unilateral lesion of the hypothalamo-neurohypophysial tract. Others have shown a decreased propensity for axonal sprouting in an aged brain; therefore, to see if the SON exhibits a decreased propensity for axonal sprouting as the animal ages, we performed a unilateral lesion in the 125-day-old rat SON. Ultrastructural analysis of axon profiles in the NL of the 125-day-old rat demonstrated an absence of axonal sprouting following injury. We previously demonstrated that ciliary neurotrophic factor (CNTF) promotes process outgrowth from injured magnocellular neuron axons in vitro. Thus, we hypothesized that the lack of axonal sprouting in the 125-day-old rat SON may be due to a reduction in CNTF or the CNTF receptor components. To this point, we found that as the rat ages there is significantly less CNTF receptor alpha (CNTFRα) protein in the uninjured, 125-day-old rat compared to the uninjured, 35-day-old rat. We also observed that protein levels of CNTF and the CNTF receptor components were increased in the SON and NL following injury in the 35-day-old rat, but there was no difference in the protein levels in the 125-day-old rat. Altogether, the results presented herein demonstrate that the plasticity within the SON is highly dependent on the age of the rat, and that a decrease in CNTFRα protein levels in the 125-day-old rat may contribute to the loss of axonal sprouting following axotomy.

Fastigial nucleus electrostimulation promotes axonal regeneration after experimental stroke via cAMP/PKA pathway

Axon regeneration after cerebral ischemia in mammals is inadequate to restore function, illustrating the need to design better strategies for improving outcomes. Improvement of axon regeneration has been achieved through fastigial nucleus electrostimulation (FNS) in animal researches. However, the mechanisms underlying this neuroprotection remain poorly understood. Increasing the levels of the second messenger cyclic AMP (cAMP) enhances axon regeneration, making it an excellent candidate molecule that has therapeutic potential. In the present study, we examined the expression of cAMP signaling in ischemic brain tissues following focal cerebral ischemia. Adult rats were subjected to ischemia induced by middle cerebral artery occlusion (MCAO). A dipolar electrode was placed into the cerebellum to stimulate the cerebellar fastigial nucleus for 1 h after ischemia. Neurological deficits and the expressions of cAMP, PKA (protein kinase A) and ROCK (Rho-kinase) were determined. Axonal regeneration was measured by upregulation of growth-associated protein 43 (GAP43). The data indicated that FNS significantly enhanced axonal regeneration and motor function recovery after cerebral ischemia. FNS also significantly increased cAMP and PKA levels after ischemic brain injury. All the beneficial effects of FNS were blocked by Rp-cAMP, an antagonist of PKA. Our research suggested that the axonal regeneration conferred by FNS was likely achieved via the regulation of cAMP/PKA pathway.

Scaffold-facilitated locomotor improvement post complete spinal cord injury: Motor axon regeneration versus endogenous neuronal relay formation

Complete transected spinal cord injury (SCI) severely influences the quality of life and mortality rates of animals and patients. In the past decade, many simple and combinatorial therapeutic treatments have been tested in improving locomotor function in animals with this extraordinarily challenging SCI. The potential mechanism for promotion of locomotor function relies either on direct motor axon regeneration through the lesion gap or indirect neuronal relay bridging to functionally reconnect transected spinal stumps. In this review, we first compare the advantages and problems of complete transection SCI animal models with other prevailing SCI models used in motor axon regeneration research. Next, we enumerate some of the popular bio-scaffolds utilized in complete SCI repair in the last decade. Then, the current state of motor axon regeneration as well as its role on locomotor improvement of animals after complete SCI is discussed. Last, the current approach of directing endogenous neuronal relays formation to achieve motor function recovery by well-designed functional bio-scaffolds implantation in complete transected SCI animals is reviewed. Although facilitating neuronal relays formation by bio-scaffolds implantation appears to be more practical and feasible than directing motor axon regeneration in promoting locomotor outcome in animals after complete SCI, there are still challenges in neuronal relays formation, maintaining and debugging for spinal cord regenerative repair.

Bioengineering Human Neurological Constructs Using Decellularized Meningeal Scaffolds for Application in Spinal Cord Injury

Spinal cord injury (SCI) is one of the most devastating conditions echoes with inflammation, enhanced fibrosis and larger axonal gaps due to destruction of neurological cells which has caused continuous increasing mortality rate of SCI patients due to absence of suitable treatment modalities. The restoration of structural and functional aspect of damaged neurological tissues at the lesion site in spinal cord has been challenging. Recent developments have showed tremendous potential of neural stem cell-based strategies to form a neuronal relay circuit across the injury gap which facilitates some levels of improvement in SCI condition. However, to provide better therapeutic responses, critical mass of grafted cells must survive for long-term and differentiate into neuronal cells with well-developed axonal networks. Hence, development of tissue specific biological neuronal constructs is highly desirable to provide mechanical and biological support for long-term survival and function of neurological cells within natural biological niche. In this study, we report development of a tissue specific neuronal constructs by culturing human neural precursor cells on decellularized meningeal scaffolds to provide suitable biological neuronal construct which can be used to support mechanical, structural and functional aspect of damaged spinal cord tissues. This particular tissue specific biological construct is immunologically tolerable and provides precisely orchestral three-dimensional platform to choreograph the long-distance axonal guidance and more organized neuronal cell growth. It passes sufficient mechanical and biological properties enriched with several crucial neurotrophins required for long-term survival and function of neurological cells which is required to form proper axonal bridge to regenerate the damaged axonal connectomes at lesion-site in SCI.

[The role of glial scar on axonal regeneration after spinal cord injury]

The 'glial scar' has been widely studied in the regeneration of spinal cord injury (SCI). For decades, mainstream scientific concept considers glial scar as a 'physical barrier' to impede axonal regeneration after SCI. Moreover, some extracellular molecules produced by glial scar are also regarded as axonal growth inhibitors. With the development of technology and the progress of research, multiple lines of new evidence challenge the pre-existing traditional notions in SCI repair, including the role of glial scar. This review briefly reviewed the history, advance, and controversy of glial scar research in SCI repair since 1930s, hoping to recognize the roles of glial scar and crack the international problem of SCI regeneration.

On the Viability and Potential Value of Stem Cells for Repair and Treatment of Central Neurotrauma: Overview and Speculations

Central neurotrauma, such as spinal cord injury or traumatic brain injury, can damage critical axonal pathways and neurons and lead to partial to complete loss of neural function that is difficult to address in the mature central nervous system. Improvement and innovation in the development, manufacture, and delivery of stem-cell based therapies, as well as the continued exploration of newer forms of stem cells, have allowed the professional and public spheres to resolve technical and ethical questions that previously hindered stem cell research for central nervous system injury. Recent in vitro and in vivo models have demonstrated the potential that reprogrammed autologous stem cells, in particular, have to restore functionality and induce regeneration-while potentially mitigating technical issues of immunogenicity, rejection, and ethical issues of embryonic derivation. These newer stem-cell based approaches are not, however, without concerns and problems of safety, efficacy, use and distribution. This review is an assessment of the current state of the science, the potential solutions that have been and are currently being explored, and the problems and questions that arise from what appears to be a promising way forward (i.e., autologous stem cell-based therapies)-for the purpose of advancing the research for much-needed therapeutic interventions for central neurotrauma.

The adhesion and migration of microglia to β-amyloid (Aβ) is decreased with aging and inhibited by Nogo/NgR pathway

Background

Alzheimer’s disease is characterized by progressive accumulation of β-amyloid (Aβ)-containing amyloid plaques, and microglia play a critical role in internalization and degradation of Aβ. Our previous research confirmed that Nogo-66 binding to Nogo receptors (NgR) expressed on microglia inhibits cell adhesion and migration in vitro.

Methods

The adhesion and migration of microglia isolated from WT and APP/PS1 mice from different ages were measured by adhesion assays and transwells. After NEP1-40 (a competitive antagonist of Nogo/NgR pathway) was intracerebroventricularly administered via mini-osmotic pumps for 2 months in APP/PS1 transgenic mice, microglial recruitment toward Aβ deposits and CD36 expression were determined.

Results

In this paper, we found that aging led to a reduction of microglia adhesion and migration to fAβ_1–42 in WT and APP/PS1 mice. The adhesion and migration of microglia to fAβ_1–42 were downregulated by the Nogo, which was mediated by NgR, and the increased inhibitory effects of the Nogo could be observed in aged mice. Moreover, Rho GTPases contributed to the effects of the Nogo on adhesion and migration of microglia to fAβ_1–42 by regulating cytoskeleton arrangement. Furthermore, blocking the Nogo/NgR pathway enhanced recruitment of microglia toward Aβ deposits and expression of CD36 in APP/PS1 mice.

Conclusion

Taken together, Nogo/NgR pathway could take part in Aβ pathology in AD by modulating microglial adhesion and migration to Aβ and the Nogo/NgR pathway might be an important target for treating AD.

Electronic supplementary material

The online version of this article (10.1186/s12974-018-1250-1) contains supplementary material, which is available to authorized users.

EPO-releasing neural precursor cells promote axonal regeneration and recovery of function in spinal cord traumatic injury

Background:

Spinal cord injury (SCI) is a debilitating condition characterized by a complex of neurological dysfunctions ranging from loss of sensation to partial or complete limb paralysis. Recently, we reported that intravenous administration of neural precursors physiologically releasing erythropoietin (namely Er-NPCs) enhances functional recovery in animals following contusive spinal cord injury through the counteraction of secondary degeneration. Er-NPCs reached and accumulated at the lesion edges, where they survived throughout the prolonged period of observation and differentiated mostly into cholinergic neuron-like cells.

Objective:

The aim of this study was to investigate the potential reparative and regenerative properties of Er-NPCs in a mouse experimental model of traumatic spinal cord injury.

Methods and Results:

We report that Er-NPCs favoured the preservation of axonal myelin and strongly promoted the regrowth across the lesion site of monoaminergic and chatecolaminergic fibers that reached the distal portions of the injured cord. The use of an anterograde tracer transported by the regenerating axons allowed us to assess the extent of such a process. We show that axonal fluoro-ruby labelling was practically absent in saline-treated mice, while it resulted very significant in Er-NPCs transplanted animals.

Conclusion:

Our study shows that Er-NPCs promoted recovery of function after spinal cord injury, and that this is accompanied by preservation of myelination and strong re-innervation of the distal cord. Thus, regenerated axons may have contributed to the enhanced recovery of function after SCI.

[Review of the regeneration mechanism of complete spinal cord injury]

Spinal cord injury (SCI), especially the complete SCI, usually results in complete paralysis below the level of the injury and seriously affects the patient's quality of life. SCI repair is still a worldwide medical problem. In the last twenty years, Professor DAI Jianwu and his team pioneered complete SCI model by removing spinal tissue with varied lengths in rodents, canine, and non-human primates to verify therapeutic effect of different repair strategies. Moreover, they also started the first clinical study of functional collagen scaffold on patients with acute complete SCI on January 16th, 2015. This review mainly focusses on the possible mechanisms responsible for complete SCI. In common, recovery of some sensory and motor functions post complete SCI include the following three contributing reasons. ① Regeneration of long ascending and descending axons throughout the lesion site to re-connect the original targets; ② New neural circuits formed in the lesion site by newly generated neurons post injury, which effectively re-connect the transected stumps; ③ The combined effect of ① and ②. The numerous studies have confirmed that neural circuits rebuilt across the injury site by newborn neurons might be the main mechanisms for functional recovery of animals from rodents to dogs. In many SCI model, especially the complete spinal cord transection model, many studies have convincingly demonstrated that the quantity and length of regenerated long descending axons, particularly like CST fibers, are too few to across the lesion site that is millimeters in length to realize motor functional recovery. Hence, it is more feasible in guiding neuronal relays formation by bio-scaffolds implantation than directing long motor axons regeneration in improving motor function of animals with complete spinal cord transection. However, some other issues such as promoting more neuronal relays formation, debugging wrong connections, and maintaining adequate neural circuits for functional recovery are urgent problems to be addressed.

Restorative effects of human neural stem cell grafts on the primate spinal cord

We grafted human spinal cord-derived neural progenitor cells (NPCs) into sites of cervical spinal cord injury in rhesus monkeys (Macaca mulatta). Under three-drug immunosuppression, grafts survived at least 9 months postinjury and expressed both neuronal and glial markers. Monkey axons regenerated into grafts and formed synapses. Hundreds of thousands of human axons extended out from grafts through monkey white matter and synapsed in distal gray matter. Grafts gradually matured over 9 months and improved forelimb function beginning several months after grafting. These findings in a 'preclinical trial' support translation of NPC graft therapy to humans with the objective of reconstituting both a neuronal and glial milieu in the site of spinal cord injury.

Transient activation of Wnt/β-catenin signaling reporter in fibrotic scar formation after compression spinal cord injury in adult mice

After traumatic spinal cord injury (SCI), a scar may form with a fibrotic core (fibrotic scar) and surrounding reactive astrocytes (glial scar) at the lesion site. The scar tissue is considered a major obstacle preventing regeneration both as a physical barrier and as a source for secretion of inhibitors of axonal regeneration. Understanding the mechanism of scar formation and how to control it may lead to effective SCI therapies. Using a compression-SCI model on adult transgenic mice, we demonstrate that the canonical Wnt/β-catenin signaling reporter TOPgal (TCF/Lef1-lacZ) positive cells appeared at the lesion site by 5 days, peaked on 7 days, and diminished by 14 days post injury. Using various representative cell lineage markers, we demonstrate that, these transiently TOPgal positive cells are a group of Fibronectin(+);GFAP(-) fibroblast-like cells in the core scar region. Some of them are proliferative. These results indicate that Wnt/β-catenin signaling may play a key role in fibrotic scar formation after traumatic spinal cord injury.

Cell therapy for spinal cord injury with olfactory ensheathing glia cells (OECs)

The prospects of achieving regeneration in the central nervous system (CNS) have changed, as most recent findings indicate that several species, including humans, can produce neurons in adulthood. Studies targeting this property may be considered as potential therapeutic strategies to respond to injury or the effects of demyelinating diseases in the CNS. While CNS trauma may interrupt the axonal tracts that connect neurons with their targets, some neurons remain alive, as seen in optic nerve and spinal cord (SC) injuries (SCIs). The devastating consequences of SCIs are due to the immediate and significant disruption of the ascending and descending spinal pathways, which result in varying degrees of motor and sensory impairment. Recent therapeutic studies for SCI have focused on cell transplantation in animal models, using cells capable of inducing axon regeneration like Schwann cells (SchCs), astrocytes, genetically modified fibroblasts and olfactory ensheathing glia cells (OECs). Nevertheless, and despite the improvements in such cell-based therapeutic strategies, there is still little information regarding the mechanisms underlying the success of transplantation and regarding any secondary effects. Therefore, further studies are needed to clarify these issues. In this review, we highlight the properties of OECs that make them suitable to achieve neuroplasticity/neuroregeneration in SCI. OECs can interact with the glial scar, stimulate angiogenesis, axon outgrowth and remyelination, improving functional outcomes following lesion. Furthermore, we present evidence of the utility of cell therapy with OECs to treat SCI, both from animal models and clinical studies performed on SCI patients, providing promising results for future treatments.

Bridging the gap with functional collagen scaffolds: tuning endogenous neural stem cells for severe spinal cord injury repair

Severe spinal cord injury (SCI) induces massive proliferation of spinal cord neural stem cells (NSCs), which are considered a promising cell source for therapeutic neural repair.

Myelin-induced inhibition in a spiral ganglion organ culture - Approaching a natural environment in vitro

The performance of a cochlear implant depends on the defined interaction between afferent neurons of the spiral ganglion and the inserted electrode. Neurite outgrowth can be induced by neurotrophins such as brain-derived neurotrophic factor (BDNF) via tropomyosin kinase receptor B (TrkB). However, neurotrophin signaling through the p75 neurotrophin receptor (p75) inhibits neurite outgrowth in the presence of myelin. Organotypic cultures derived from postnatal (P3-5) mice were used to study myelin-induced inhibition in the cochlear spiral ganglion. Neurite outgrowth was analyzed and quantified utilizing an adapted Sholl analysis. Stimulation of neurite outgrowth was quantified after application of BDNF, the selective TrkB agonist 7,8-dihydroxyflavone (7,8-DHF) and a selective inhibitor of the Rho-associated kinase (Y27632), which inhibits the p75 pathway. Myelin-induced inhibition was assessed by application of myelin-associated glycoprotein (MAG-Fc) to stimulate the inhibitory p75 pathway. Inhibition of neurite outgrowth was achieved by the selective TrkB inhibitor K252a. Stimulation of neurite outgrowth was observed after treatment with BDNF, 7,8 DHF and a combination of BDNF and Y27632. The 7,8-DHF-induced growth effects could be inhibited by K252a. Furthermore, inhibition of neurite outgrowth was observed after supplementation with MAG-Fc. Myelin-induced inhibition could be overcome by 7,8-DHF and the combination of BDNF and Y27632. In this study, myelin-induced inhibition of neurite outgrowth was established in a spiral ganglion model. We reveal that 7,8-DHF is a viable novel compound for the stimulation of neurite outgrowth in a myelin-induced inhibitory environment. The combination of TrkB stimulation and ROCK inhibition can be used to overcome myelin inhibition.

Harnessing cAMP signaling in musculoskeletal regenerative engineering

This paper reviews the most recent findings in the search for small molecule cyclic AMP analogues regarding their potential use in musculoskeletal regenerative engineering.

An Intrinsic Epigenetic Barrier for Functional Axon Regeneration

Mature neurons in the adult peripheral nervous system can effectively switch from a dormant state with little axonal growth to robust axon regeneration upon injury. The mechanisms by which injury unlocks mature neurons' intrinsic axonal growth competence are not well understood. Here, we show that peripheral sciatic nerve lesion in adult mice leads to elevated levels of Tet3 and 5-hydroxylmethylcytosine in dorsal root ganglion (DRG) neurons. Functionally, Tet3 is required for robust axon regeneration of DRG neurons and behavioral recovery. Mechanistically, peripheral nerve injury induces DNA demethylation and upregulation of multiple regeneration-associated genes in a Tet3- and thymine DNA glycosylase-dependent fashion in DRG neurons. In addition, Pten deletion-induced axon regeneration of retinal ganglion neurons in the adult CNS is attenuated upon Tet1 knockdown. Together, our study suggests an epigenetic barrier that can be removed by active DNA demethylation to permit axon regeneration in the adult mammalian nervous system.

Transplantation of hUC-MSCs seeded collagen scaffolds reduces scar formation and promotes functional recovery in canines with chronic spinal cord injury

Spinal cord injury (SCI) can lead to locomotor deficits, and the repair of chronic SCI is considered one of the most challenging clinical problems. Although extensive studies have evaluated treatments for acute SCI in small animals, comparatively fewer studies have been conducted on large-animal SCI in the chronic phase, which is more clinically relevant. Here, we used a collagen-based biomaterial, named the NeuroRegen scaffold, loaded with human umbilical cord-derived mesenchymal stem cells (hUC-MSCs) in a canine chronic SCI model. To generate chronic SCI, the T8 spinal cord segment was removed by complete transection of the spinal cord. Two months later, glial scar tissue was removed and a NeuroRegen scaffold was transplanted into the lesion area. Functionalized NeuroRegen scaffold implantation promoted both locomotor recovery and endogenous neurogenesis in the lesion area. Moreover, some newly generated neurons successfully matured into 5-HT-positive neurons at 1 year post-injury. In addition, many regenerated axon fibers in the lesion area exhibited remyelination and synapse formation at 1 year post-injury in the functionalized NeuroRegen scaffold group. In conclusion, the NeuroRegen scaffold functionalized with hUC-MSCs is a promising potential therapeutic approach to chronic SCI that promotes neuronal regeneration, reduces glial scar formation, and ultimately improves locomotor recovery.

Comparison of RNAi NgR and NEP1-40 in Acting on Axonal Regeneration After Spinal Cord Injury in Rat Models

This study was intended to compare the therapeutic efficacies of NEP1-40 and SiNgR199 on treating spinal cord injury (SCI). Nogo-A, growth associated protein 43 (GAP-43), microtubule associated protein 2 (MAP-2), and amyloid βA4 precursor protein (APP) expressions were determined using western blot and quantitative PCR. Neurite outgrowth detected the growth of neurites, and BDA anterograde tracing was used to label the regenerated axonal. Rats' behavior was assessed with Basso, Beattie, and Bresnahan locomotor rating scale (BBB). Somatosensory evoked potentials (SEPs) and motor evoked potentials (MEPs) were recorded to evaluate the recovery of the sensory and motor systems. Successful establishment of SCI model was verified by immunocytochemical analysis. The increased expression of APP, as well as the decreased expression of GAP-43 and MAP-2, was observed in the SCI model group, but the trends were reversed after the treatments of NEP1-40, siNgR199, and NEP1-40 + siNgR199. Compared with the SCI group, the average neurite length and the BDA-positive fibers were increased in the NEP1-40, siNgR199, and NEP1-40 + siNgR199 groups. The rats in the siNgR199 group and the NEP1-40 + siNgR199 group both showed significantly higher BBB scores than SCI model group and NEP1-40 group. Suggested by electrophysiological evaluation, both the latency and the amplitude of SEPs as well as MEPs had recovered in the NEP1-40, siNgR199, and NEP1-40 + siNgR199 groups after SCI. Both NEP1-40 and siNgR had repairing effects on SCI, suggesting their role in facilitating axonal regeneration after SCI.

Panax notoginseng saponins provide neuroprotection by regulating NgR1/RhoA/ROCK2 pathway expression, in vitro and in vivo

ETHNOPHARMACOLOGICAL RELEVANCE

Panax notoginseng saponins (PNS) extracted from a traditional Chinese herbal medicine, Panax notoginseng (Burkill) F.H. Chen (Araliaceae), which has been extensively used in treating coronary heart disease, ischemic cerebrovascular disease and hemorrhagic disorders in China over hundreds of years.

AIMS OF THE STUDY

This study explored whether panax notoginseng saponins (PNS) provided neuroprotective effects by inhibiting the expressions of NgR1, RhoA, and ROCK2 following middle cerebral artery occlusion in rats and oxygen-glucose deprivation/reoxygenation (OGD/R) injury in SH-SY5Y cells.

MATERIALS AND METHODS

2,3,5-Triphenyltetrazolium chloride staining was used to determine successful middle cerebral artery occlusion establishment in sham-operated and operated Sprague-Dawley rats 1 day after injury. The rats were randomly separated into sham, model, NEP1-40, PNS, and NEP1-40 plus PNS (N+P) groups. After 7 days of treatment, body mass and neurological deficit scores were analyzed. Tissues were harvested and analyzed by hematoxylin-eosin staining and immunohistochemical analysis, western blotting, and quantitative real-time PCR (qRT-PCR). The optimal drug concentration of NEP1-40 and PNS on SH-SY5Y cells exposed to OGD/R injury was determined by CCK8 analysis. qRT-PCR was used to measure mRNA expression profiles of NgR1, RhoA, and ROCK2 in SH-SY5Y cells subjected to OGD/R.

RESULTS

The results showed that MCAO surgery successfully produced an infarct, and the PNS, NEP1-40, and N+P groups exhibited increased body mass and ameliorated neurological deficits compared with the model group. NEP1-40 treatment markedly reduced NgR1 and RhoA overexpression when compared to the model group, although there was no significant difference in ROCK2 expression. PNS and N+P treatment significantly decreased NgR1, RhoA, and ROCK2 overexpression compared with the model group. However, N+P treatment did not result in a synergistic effect, as assessed by immunohistochemistry, western blotting, and qRT-PCR. Following optimal administration of PNS (160μg/ml) and NEP1-40 (10ng/ml) on SH-SY5Y cells exposed to OGD/R injury, cell viability in the NEP1-40, PNS, and N+P groups significantly increased compared with the model group, as assessed by CCK8 analysis. Additionally, NgR1, RhoA, and ROCK2 mRNA expression profiles were significantly less in the NEP1-40, PNS, and N+P groups compared with the model group.

CONCLUSION

PNS provided neuroprotective effects in a rat model of cerebral ischemia and SH-SY5Y cells exposed to oxygen/glucose deprivation injury by inhibiting the overexpression of NgR1, RhoA, and ROCK2.

Identification of genetic variants of LGI1 and RTN4R (NgR1) linked to schizophrenia that are defective in NgR1-LGI1 signaling

Background

The protein NgR1 is encoded by RTN4R, a gene linked to schizophrenia. We previously reported NgR1 as receptor for the epilepsy‐linked protein LGI1. NgR1 regulates synapse number and synaptic plasticity, whereas LGI1 antagonizes NgR1 signaling and promotes synapse formation. Impairments in synapse formation are common in neurological disease and we hypothesized that an LGI1–NgR1 signaling pathway may contribute to the development of schizophrenia.

Methods

We screened two unrelated schizophrenic populations for variants in RTN4R and LGI1 using whole exome sequencing and Sanger sequencing. We tested the ability of LGI1 to bind rare coding variants of NgR1 using a cell surface binding assays and the signaling ability of NgR1 using COS7 cell‐spreading assays.

Results

We observed a previously reported rare coding variant in RTN4R (c.1195C>T, pR399W). We report the first LGI1 mutations to be identified in individuals with schizophrenia. Three different LGI1 mutations were found, two missense mutations (c.205G>A, p.V69I) and (c.313G>A, V105M), and an intronic variant (g.897T>C) that likely leads to a protein truncation. We found NgR1^R119W and NgR1^277C have a reduced ability to bind LGI1 in a cell surface binding assay. COS7 cell‐spreading assays reveal that NgR1 mutants are impaired in their ability to mediate RhoA activation.

Conclusion

Variants in NgR1 and LGI1 may be associated with schizophrenia and variants in NgR1 found in schizophrenic patients have impaired LGI1–NgR1 signaling. Impaired LGI1–NgR1 signaling may contribute to disease progression.

The blockage of the Nogo/NgR signal pathway in microglia alleviates the formation of Aβ plaques and tau phosphorylation in APP/PS1 transgenic mice

Background

Alzheimer’s disease (AD) is characterized by extracellular β-amyloid (Aβ) plaques, neurofibrillary tangles (NFTs), and microglia-dominated neuroinflammation. The Nogo/NgR signal pathway is involved in AD pathological features, but the detailed mechanism needs further investigation. Our previous studies have confirmed that the activation of NgR on microglia by Nogo promotes the expression of proinflammatory cytokines and inhibits cell adhesion and migration behaviors. In the present study, we investigated the effects of Nogo/NgR signaling pathway on the pathological features of AD and possible mechanisms.

Methods

After NEP1-40 (a competitive antagonist of Nogo/NgR pathway) was intracerebroventricularly administered via mini-osmotic pumps for 2 months in amyloid precursor protein (APP)/PS1 transgenic mice, plaque load, tau phosphorylation, and inflammatory responses were determined. After primary mouse neurons were exposed to the conditioned medium from BV-2 microglia stimulated by Nogo, the production of Aβ and phosphorylation of tau was quantified by ELISA and western blot.

Results

Inhibition of the Nogo/NgR signaling pathway ameliorated pathological features including amyloid plaques and phosphorylated levels of tau in APP/PS1 mice. In addition, after treatment with the conditioned medium from BV-2 microglia stimulated by Nogo, Aβ production and tau phosphorylation in cultured neurons were increased. The conditioned medium also increased the expression of APP, its amyloidogenic processing, and the activity of GSK3β in neurons. The conditioned medium was also proinflammatory medium, and the blockage of the Nogo/NgR pathway improved the neuroinflammatory environment in APP/PS1 mice.

Conclusions

Taken together, the neuroinflammation mediated by Nogo/NgR pathway in microglia could directly take part in the pathological process of AD by influencing the amyloidogenesis and tau phosphorylation. These results contribute to a better understanding of AD pathogenesis and could offer a new therapeutic option for delaying the progression of AD.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-016-0522-x) contains supplementary material, which is available to authorized users.

Modulating Astrocyte Transition after Stroke to Promote Brain Rescue and Functional Recovery: Emerging Targets Include Rho Kinase

Stroke is a common and serious condition, with few therapies. Whilst previous focus has been directed towards biochemical events within neurons, none have successfully prevented the progression of injury that occurs in the acute phase. New targeted treatments that promote recovery after stroke might be a better strategy and are desperately needed for the majority of stroke survivors. Cells comprising the neurovascular unit, including blood vessels and astrocytes, present an alternative target for supporting brain rescue and recovery in the late phase of stroke, since alteration in the unit also occurs in regions outside of the lesion. One of the major changes in the unit involves extensive morphological transition of astrocytes resulting in altered energy metabolism, decreased glutamate reuptake and recycling, and retraction of astrocyte end feed from both blood vessels and neurons. Whilst globally inhibiting transitional change in astrocytes after stroke is reported to result in further damage and functional loss, we discuss the available evidence to suggest that the transitional activation of astrocytes after stroke can be modulated for improved outcomes. In particular, we review the role of Rho-kinase (ROCK) in reactive gliosis and show that inhibiting ROCK after stroke results in reduced scar formation and improved functional recovery.

The emerging role of GPR50 receptor in brain

GPR50 receptor one of the member of G protein-coupled receptors (GPCRs) is extensively expressed in the pituitary, hypothalamus,cortex, midbrain, pons, amygdala, and in several brainstem nuclei. The exact function of this receptor in brain is remains unclear. This review presents current knowledge regarding the function of GPR50 receptor in brain, with a focus on role of this receptor in the hypothalamus-pituitary-adrenal (HPA) axis and the glucocorticoid receptor (GR) signaling, leptin signaling, adaptive thermogenesis, torpor, neurite outgrowth, and self-renewal and neuronal differentiation of neural progenitor cells NPCs. Although the results are encouraging, further research is needed to clarify GPR50 role in neurobiology of mood disorders, adaptive thermogenesis, torpor, and in the pathophysiology of neurological disorders.

Functionalized collagen scaffold implantation and cAMP administration collectively facilitate spinal cord regeneration

Previous studies have demonstrated that several mechanisms, including numerous inhibitory molecules, weak neurotrophic stimulation and deficient intrinsic regenerative responses, collectively contribute to the failure of mature spinal cord axon regeneration. Thus, combinatorial therapies targeting multiple mechanisms have attracted much attention. In the present study, a porous collagen scaffold was used to support neuronal attachment and bridge axonal regeneration. The scaffold was specifically functionalized using neutralizing proteins (CBD-EphA4LBD, CBD-PlexinB1LBD and NEP1-40) and collagen-binding neurotrophic factors (CBD-BDNF and CBD-NT3) to simultaneously antagonize myelin inhibitory molecules (ephrinB3, Sema4D and Nogo) and exert neurotrophic protection and stimulation. Cerebellar granular neurons cultured on the functionalized collagen scaffold promoted neurite outgrowth in the presence of myelin. Furthermore, a full combinatorial treatment comprising functionalized scaffold implantation and cAMP administration was developed to evaluate the synergistic repair ability in a rat T10 complete removal spinal cord injury model. The results showed that full combinatorial therapy exhibited the greatest advantage in reducing the volume of cavitation, facilitating axonal regeneration, and promoting neuronal generation. The newborn neurons generated in the lesion area could form the neuronal relay and enhance the locomotion recovery after severe spinal cord injury.

STATEMENT OF SIGNIFICANCE

A porous collagen scaffold was specifically functionalized with neutralizing proteins and neurotrophic factors to antagonize the myelin inhibitory molecules and exert neurotrophic protection and stimulation for spinal cord regeneration. Cerebellar granular neurons seeded on the functionalized collagen scaffold showed enhanced neurite outgrowth ability in vitro. The functionalized scaffold implantation combined with cAMP administration exhibited synergistic repair ability for rat T10 complete spinal cord transection injury.

Axonal regeneration inhibitors: emerging therapeutic options

For the most part, the central nervous system is unable to regenerate. The majority of injuries of vascular, inflammatory, degenerative and traumatic aetiology lead to an irreversible loss of central nervous system function. The paper presents the role of Nogo-A, MAG and OMgp proteins in the inhibition of central nervous system regeneration, and their potential clinical significance.

Multiple Roles for Nogo Receptor 1 in Visual System Plasticity

During the developmental critical period for visual plasticity, discordant vision alters the responsiveness of neurons in visual cortex. The subsequent closure of the critical period not only consolidates neural function but also limits recovery of acuity from preceding abnormal visual experience. Despite species-specific differences in circuitry of the visual system, these characteristics are conserved. The nogo-66 receptor 1 (ngr1) is one of only a small number of genes identified thus far that is essential to closing the critical period. Mice lacking a functional ngr1 gene retain developmental visual plasticity as adults and their visual acuity spontaneously improves after prolonged visual deprivation. Experiments employing conditional mouse genetics have revealed that ngr1 restricts plasticity within distinct circuits for ocular dominance and visual acuity. However, the mechanisms by which NgR1 limits plasticity have not been elucidated, in part because the subcellular localization and signal transduction of the protein are only partially understood. Here we explore potential mechanisms for NgR1 function in relation to manipulations that reactivate visual plasticity in adults and propose lines of investigation to address relevant gaps in knowledge.

The Nogo/Nogo Receptor (NgR) Signal Is Involved in Neuroinflammation through the Regulation of Microglial Inflammatory Activation

Microglia have been proposed to play a pivotal role in the inflammation response of the CNS by expressing a range of proinflammatory enzymes and cytokines under pathological stimulus. Our previous study has confirmed that Nogo receptor (NgR), an axon outgrowth inhibition receptor, is also expressed on microglia and regulates cell adhesion and migration behavior in vitro. In the present study, we further investigated the proinflammatory effects and possible mechanisms of Nogo on microglia in vitro. In this study, Nogo peptide, Nogo-P4, a 25-amino acid core inhibitory peptide sequence of Nogo-66, was used. We found that Nogo-P4 was able to induce the expression of inducible nitric-oxide synthase and cyclooxygenase-2 and the release of proinflammatory cytokines, including IL-1β, TNF-α, NO, and prostaglandin E2 in microglia, which could be reversed by NEP1-40 (Nogo-66(1-40) antagonist peptide), phosphatidylinositol-specificphospholipase C, or NgR siRNA treatment. After Nogo-P4 stimulated microglia, the phosphorylation levels of NF-κB and STAT3 were increased obviously, which further mediated microglia expressing proinflammatory factors induced by Nogo-P4. Taken together, we concluded that Nogo peptide could directly take part in CNS inflammatory process by influencing the expression of proinflammatory factors in microglia, which were related to the NF-κB and STAT3 signal pathways. Besides neurite outgrowth restriction, the Nogo/NgR signal might be involved in multiple processes in various inflammation-associated CNS diseases.

Functionalized Collagen Scaffold Neutralizing the Myelin-Inhibitory Molecules Promoted Neurites Outgrowth in Vitro and Facilitated Spinal Cord Regeneration in Vivo

Research has demonstrated that many myelin-associated inhibitory molecules jointly contribute to the failure of adult spinal cord regeneration. Therapies comprehensively targeting the multiple inhibitory nature of the injured spinal cord are being concerned. Here, two collagen-binding proteins, CBD-EphA4LBD and CBD-PlexinB1LBD, were constructed, respectively, to neutralize the axon guidance molecules ephrinB3 and sema4D that inhibit the regeneration of nerve fibers. The two neutralizing proteins have proven their ability to specifically bind collagen and to continuously release from collagen scaffolds. They could also promote neurites outgrowth of cerebellar granular neurons and dorsal root ganglion neurons in vitro. Subsequently, the functionalized collagen scaffolds by physically absorbing NEP1-40 and immobilizing CBD-EphA4LBD and CBD-PlexinB1LBD were transplanted into a rat T10 complete spinal cord transection model. Our results showed that rats that received the treatment of transplanting the functionalized collagen scaffold exhibited great advantage on axonal regeneration and locomotion recovery after spinal cord injury.

Polysialic acid as an antigen for monoclonal antibody HIgM12 to treat multiple sclerosis and other neurodegenerative disorders

CNS regeneration is a desirable goal for diseases of brain and spinal cord. Current therapeutic strategies for the treatment of multiple sclerosis (MS) aim to eliminate detrimental effects of the immune system, so far without reversing disability or affecting long-term prognosis in patients. Approachable molecular targets that stimulate CNS repair are not part of the clinical praxis or have not been identified yet. The purpose of this study was to identify the molecular target of the human monoclonal antibody HIgM12. HIgM12 reverses motor deficits in chronically demyelinated mice, a model of MS. Here, we identified polysialic acid (PSA) attached to the neural cell adhesion molecule (NCAM) as the antigen for HIgM12 by using different NCAM knockout strains and through PSA removal from the NCAM protein core. Antibody binding to CNS tissue and primary cells, antibody-mediated cell adhesion, and neurite outgrowth on HIgM12-coated nitrocellulose was detected only in the presence of PSA as assessed by western blotting, immunoprecipitation, immunocytochemistry, and histochemistry. We conclude that HIgM12 mediates its in vivo and in vitro effects through binding to PSA and has the potential to be an effective therapy for MS and neurodegenerative diseases. The human antibody HIgM12 stimulates neurite outgrowth in vitro and promotes function in chronically demyelinated mice, a model of multiple sclerosis. The cellular antigen for HIgM12 was undetermined. Here, we identified polysialic acid attached to NCAM (neural cell adhesion molecule) as the cellular target for HIgM12. This includes glial fibrillary acidic protein (GFAP)-positive mouse astrocytes (GFAP, red; HIgM12, green; DAPI, blue) among other cell types of the central nervous system. These findings indicate a new strategy for the treatment of neuro-motor disorders including multiple sclerosis.

Chondroitin sulfate proteoglycans: Key modulators in the developing and pathologic central nervous system

Chondroitin Sulfate Proteoglycans (CSPGs) are a major component of the extracellular matrix in the central nervous system (CNS) and play critical role in the development and pathophysiology of the brain and spinal cord. Developmentally, CSPGs provide guidance cues for growth cones and contribute to the formation of neuronal boundaries in the developing CNS. Their presence in perineuronal nets plays a crucial role in the maturation of synapses and closure of critical periods by limiting synaptic plasticity. Following injury to the CNS, CSPGs are dramatically upregulated by reactive glia which form a glial scar around the lesion site. Increased level of CSPGs is a hallmark of all CNS injuries and has been shown to limit axonal plasticity, regeneration, remyelination, and conduction after injury. Additionally, CSPGs create a non-permissive milieu for cell replacement activities by limiting cell migration, survival and differentiation. Mounting evidence is currently shedding light on the potential benefits of manipulating CSPGs in combination with other therapeutic strategies to promote spinal cord repair and regeneration. Moreover, the recent discovery of multiple receptors for CSPGs provides new therapeutic targets for targeted interventions in blocking the inhibitory properties of CSPGs following injury. Here, we will provide an in depth discussion on the impact of CSPGs in normal and pathological CNS. We will also review the recent preclinical therapies that have been developed to target CSPGs in the injured CNS.

Translating mechanisms of neuroprotection, regeneration, and repair to treatment of spinal cord injury

One of the big challenges in neuroscience that remains to be understood is why the central nervous system is not able to regenerate to the extent that the peripheral nervous system does. This is especially problematic after traumatic injuries, like spinal cord injury (SCI), since the lack of regeneration leads to lifelong deficits and paralysis. Treatment of SCI has improved during the last several decades due to standardized protocols for emergency medical response teams and improved medical, surgical, and rehabilitative treatments. However, SCI continues to result in profound impairments for the individual. There are many processes that lead to the pathophysiology of SCI, such as ischemia, vascular disruption, neuroinflammation, oxidative stress, excitotoxicity, demyelination, and cell death. Current treatments include surgical decompression, hemodynamic control, and methylprednisolone. However, these early treatments are associated with modest functional recovery. Some treatments currently being investigated for use in SCI target neuroprotective (riluzole, minocycline, G-CSF, FGF-2, and polyethylene glycol) or neuroregenerative (chondroitinase ABC, self-assembling peptides, and rho inhibition) strategies, while many cell therapies (embryonic stem cells, neural stem cells, induced pluripotent stem cells, mesenchymal stromal cells, Schwann cells, olfactory ensheathing cells, and macrophages) have also shown promise. However, since SCI has multiple factors that determine the progress of the injury, a combinatorial therapeutic approach will most likely be required for the most effective treatment of SCI.

Effect of retinoic acid on expression of LINGO-1 and neural regeneration after cerebral ischemia

The purpose of this study was to observe the expression of LINGO-1 after cerebral ischemia, investigate the effects of retinoic acid (RA) on the expression of LINGO-1 and GAP-43, and the number of synapses, and to emplore the repressive effect of LINGO-1 on neural regeneration after cerebral ischemia. The model of permanent focal cerebral ischemia was established by the modified suture method of middle cerebral artery occlusion (MCAO) in Sprague-Dawley (SD) rats. The expression of LINGO-1 was detected by Western blotting and that of GAP-43 by immunohistochemistry. The number of synapses was observed by transmission electron microscopy. The SD rats were divided into three groups: sham operation (sham) group, cerebral ischemia (CI) group and RA treatment (RA) group. The results showed that the expression level of LINGO-1 at 7th day after MCAO in sham, CI and RA groups was 0.266 ± 0.019, 1.215 ± 0.063 and 0.702 ± 0.081, respectively (P<0.01). The number of Gap-43-positive nerve cells at 7th day after MCAO in sham, CI and RA group was 0, 59.08 ± 1.76 and 76.20 ± 3.12 per high power field, respectively (P<0.05). The number of synapses at 7th day after MCAO was 8.42 ± 0.13, 1.74 ± 0.37 and 5.39 ± 0.26 per μm², respectively (P<0.05). It is concluded that LINGO-1 expression is up-regulated after cerebral ischemia, and RA inhibits the expression of LINGO-1, promotes the expression of GAP-43 and increases the number of synapses. It suggests that LINGO-1 may be involved in the pathogenesis of cerebral ischemia, which may provide an experimenal basis for LINGO-1 antogonist, RA, for the treatment of cerebral ischemia.

Nogo receptor 1 limits tactile task performance independent of basal anatomical plasticity

The genes that govern how experience refines neural circuitry and alters synaptic structural plasticity are poorly understood. The nogo-66 receptor 1 gene (ngr1) is one candidate that may restrict the rate of learning as well as basal anatomical plasticity in adult cerebral cortex. To investigate if ngr1 limits the rate of learning we tested adult ngr1 null mice on a tactile learning task. Ngr1 mutants display greater overall performance despite a normal rate of improvement on the gap-cross assay, a whisker-dependent learning paradigm. To determine if ngr1 restricts basal anatomical plasticity in the associated sensory cortex, we repeatedly imaged dendritic spines and axonal varicosities of both constitutive and conditional adult ngr1 mutant mice in somatosensory barrel cortex for two weeks through cranial windows with two-photon chronic in vivo imaging. Neither constant nor acute deletion of ngr1 affected turnover or stability of dendritic spines or axonal boutons. The improved performance on the gap-cross task is not attributable to greater motor coordination, as ngr1 mutant mice possess a mild deficit in overall performance and a normal learning rate on the rotarod, a motor task. Mice lacking ngr1 also exhibit normal induction of tone-associated fear conditioning yet accelerated fear extinction and impaired consolidation. Thus, ngr1 alters tactile and motor task performance but does not appear to limit the rate of tactile or motor learning, nor determine the low set point for synaptic turnover in sensory cortex.