Targeting Neurite Growth Inhibitors to Induce CNS Regeneration

Bridging the gap: a translational perspective in spinal cord injury

Traumatic spinal cord injury (SCI) is a devastating and complex condition to treat with no curative options. In the past few decades, rapid advancements in our understanding of SCI pathophysiology as well as the mergence of new treatments has created more optimism. Focusing on clinical translation, this paper provides a comprehensive overview of SCI through its epidemiology, pathophysiology, currently employed management strategies, and emerging therapeutic approaches. Additionally, it emphasizes the importance of addressing the heavy quality of life (QoL) challenges faced by SCI patients and their desires, providing a basis to tailor patient-centric forms of care. Furthermore, this paper discusses the frequently encountered barriers in translation from preclinical models to clinical settings. It also seeks to summarize significant completed and ongoing SCI clinical trials focused on neuroprotective and neuroregenerative strategies. While developing a cohesive regenerative treatment strategy remains challenging, even modest improvements in sensory and motor function can offer meaningful benefits and motivation for patients coping with this highly debilitating condition.

The factors affecting neurogenesis after stroke and the role of acupuncture

Stroke induces a state of neuroplasticity in the central nervous system, which can lead to neurogenesis phenomena such as axonal growth and synapse formation, thus affecting stroke outcomes. The brain has a limited ability to repair ischemic damage and requires a favorable microenvironment. Acupuncture is considered a feasible and effective neural regulation strategy to improve functional recovery following stroke via the benign modulation of neuroplasticity. Therefore, we summarized the current research progress on the key factors and signaling pathways affecting neurogenesis, and we also briefly reviewed the research progress of acupuncture to improve functional recovery after stroke by promoting neurogenesis. This study aims to provide new therapeutic perspectives and strategies for the recovery of motor function after stroke based on neurogenesis.

HUCMSCs transplantation combined with ultrashort wave therapy attenuates neuroinflammation in spinal cord injury through NUR77/ NF-κB pathway

AIMS

Spinal cord injury (SCI) is a major cause of long-term physical impairment. Currently, treatment for SCI is limited to supportive measures, which can lead to permanent disability, representing a serious social burden. The present study aimed to evaluate the inflammatory microenvironment effects of human umbilical cord mesenchymal stem cells (HUCMSCs)+ Ultrashort Wave (USW) therapy on SCI and reveal possible mechanisms.

MAIN METHODS

Low-dose USW was treated one day after SCI, and HUCMSCs suspension was transferred to the lesion using a micro-syringe 7 days after SCI. The functional effects of HUCMSCs and USW, separately and combinedly, were measured, together with the infiltration of CD3⁺ cells, formation of A1 astrocytes and activation of NUR77/ NF-κB pathway.

KEY FINDINGS

Our results showed that HUCMSCs+USW therapy improved motor function of SCI rat, together with decreased infiltration of CD3⁺ T cells, and decreased induction of microglia and A1 astrocytes. And also USW treatment played a very important role on decreasing the infiltration of CD3⁺ T cells and IBA-1⁺ cells. Reduced production of pro-inflammatory cytokines IL-1β and IL-6 was also observed in rats receiving HUCMSCs+USW therapy, medicated by NUR77/NF-κB pathway.

SIGNIFICANCE

These findings indicated that HUCMSCs+USW therapy could attenuate inflammatory microenvironment through NUR77/NF-κB signaling pathway, which might contribute to its better outcome.

Photobiomodulation Optimization for Spinal Cord Injury Rat Phantom Model

Spinal Cord Injury (SCI) causes interruption along the severed axonal tract(s) resulting in complete or partial loss of sensation and motor function. SCI can cause tetraplegia or paraplegia. Both these conditions can have lifelong excessive medical costs, as well as can reduce life expectancy. Preclinical research showed that Photobiomodulation therapy (PBMT), also known as Low-level laser (light) therapy (LLLT), possesses reparative and regenerative capabilities that have the potential to be used as a complimentary or supplementary SCI therapy. Despite the promising effects of PBMT, there are still no standardized irradiation parameters (i.e. different wavelengths, power, fluence, irradiance, beam type, beam diameters, and irradiation time) and there is also a lack of standardized experimental protocol(s), which makes it difficult to compare different studies. It is, nonetheless, essential to standardize such irradiation parameters in order to provide better PBMTs. The aim of this study, therefore, is to evaluate the delivery of light in a 3D voxelated SCI rat model for PBMT using different irradiation parameters (wavelengths: 660, 810, and 980 nm; beam types: Gaussian and Flat beam; and beam diameters: 0.04-1.2 cm) using Monte Carlo simulation. This study also aids in providing standardization for preclinical research for PBMT, which will eventually translate into clinical standardization upon clinical research studies and results.

Microenvironment Imbalance of Spinal Cord Injury

Spinal cord injury (SCI), for which there currently is no cure, is a heavy burden on patient physiology and psychology. The microenvironment of the injured spinal cord is complicated. According to our previous work and the advancements in SCI research, ‘microenvironment imbalance’ is the main cause of the poor regeneration and recovery of SCI. Microenvironment imbalance is defined as an increase in inhibitory factors and decrease in promoting factors for tissues, cells and molecules at different times and spaces. There are imbalance of hemorrhage and ischemia, glial scar formation, demyelination and re-myelination at the tissue’s level. The cellular level imbalance involves an imbalance in the differentiation of endogenous stem cells and the transformation phenotypes of microglia and macrophages. The molecular level includes an imbalance of neurotrophic factors and their pro-peptides, cytokines, and chemokines. The imbalanced microenvironment of the spinal cord impairs regeneration and functional recovery. This review will aid in the understanding of the pathological processes involved in and the development of comprehensive treatments for SCI.

Low-level laser therapy for spinal cord injury in rats: effects of polarization

The effects of laser polarization on the efficacy of near-infrared low-level laser therapy for spinal cord injury (SCI) are presented. Rat spinal cords were injured with a weight-drop device, and the lesion sites were directly irradiated with a linearly polarized 808-nm diode laser positioned either perpendicular or parallel to the spine immediately after the injury and daily for five consecutive days. Functional recovery was assessed daily by an open-field test. Regardless of the polarization direction, functional scores of SCI rats that were treated with the 808-nm laser irradiation were significantly higher than those of SCI alone group (Group 1) from day 5 after injury. The locomotive function of SCI rats irradiated parallel to the spinal column (Group 3) was significantly improved from day 10 after injury, compared to SCI rats treated with the linear polarization perpendicular to the spinal column (Group 2). There were no significant differences in ATP contents in the injured tissue among the three groups. We speculate that the higher efficacy with parallel irradiation is attributable to the deeper light penetration into tissue with anisotropic scattering.

Spatio-temporal expression of paired immunoglobulin-like receptor-B in the adult mouse brain after focal cerebral ischaemia

PRIMARY OBJECTIVE

Paired immunoglobulin-like receptor-B (PirB) is another receptor, except for the Nogo receptor, that is involved in inhibition of axons regeneration after central nervous system injury. However, the expression of PirB in focal cerebral ischaemic brain remains unclear. Herein, this study investigated spatial-temporal expression of PirB in the mouse brain following transient focal cerebral ischaemia.

METHODS AND PROCEDURE

Adult male C57BL/6 mice underwent a 60-minute transient occlusion of middle cerebral artery. Mice were killed and brain samples were harvested at 30 minutes, 2 hours, 24 hours, 3 days and 7 days after reperfusion. Expression of PirB in the brain was determined by reverse transcriptase-polymerase chain reaction (RT-PCR), western blot analysis and immunohistochemical staining.

MAIN OUTCOMES AND RESULTS

The results showed that PirB was mainly expressed in ischaemic penumbra. PirB mRNA and protein expression began to increase at 2 hours, peaked at 24 hours and lasted for 7 days after reperfusion in the ischaemic penumbra. By using immunofluorescence, PirB signals were co-localized with NeuN-positive neurons.

CONCLUSION

PirB expression is up-regulated in ischaemic penumbra following transient focal cerebral ischaemia. PirB expression in neurons may play important pathological roles in the inhibition of axonal regeneration after stroke, suggesting that the inhibition of PirB expression may enhance axonal regeneration and functional recovery after stroke.

The promotion of neural regeneration in an extreme rat spinal cord injury model using a collagen scaffold containing a collagen binding neuroprotective protein and an EGFR neutralizing antibody

In the treatment of spinal cord injury, implantation of scaffolding biomaterials and the addition of neuroprotective factors will promote neural regeneration. It has been demonstrated in our previous work that linear ordered collagen scaffold (LOCS) will bridge neural regeneration after the injury of spinal cord hemisection, and BDNF fused with a collagen binding domain (CBD-BDNF) can bind to collagen specifically to exert the neuroprotective effect. Besides neuroprotective factors, the lack of axon regeneration of the injured spinal cord has been attributed partially to regeneration inhibitors such as myelin associated proteins and chondroitin sulfate proteoglycans (CSPGs). Epidermal growth factor receptor (EGFR) activation is downstream of the signaling pathways of these inhibitors. Here, the monoclonal antibody, 151IgG that inhibits signaling of EGFR was used to neutralize EGFR. 151IgG was cross-linked to LOCS and CBD-BDNF bound to LOCS to make a triple-functional biomaterial for neural regeneration (bridging, prompting growth and neutralizing growth inhibitors). This triple-functional device was tested in a 6 mm transected SCI model. Results showed that this collagen scaffold with the addition of 151IgG and CBD-BDNF provided effective bridging and stimulation effects for neural regeneration, recovery of electrical transmission of synapses and preventing the formation of glial scars in the extreme transected rat SCI model.

Generation of AcGFP fusion with single-chain Fv selected from a phage display library constructed from mice hyperimmunized against 5-methyl 2'-deoxycytidine

DNA methylation is involved in many diseases such as cancer and autoimmunity. We generated recombinant single-chain Fv (scFv) antibodies against 5-methyl-2'-deoxycytidine (m(5)dCyd) using phage display technology and a hyperimmunized mouse, and the scFv of most interest were constructed as fusion proteins with green fluorescent protein obtained from Aequorea coerulescens GFP (AcGFP). Using RNA isolated from mouse spleens, we constructed a scFv library consisting of λ light chains. The scFv library was selected against m(5)Cyd-BSA and enriched through four rounds of panning. The scFv library was concentrated about 390-fold and an individual clone was reacted with m(5)Cyd-BSA. Two scFvs with high reactivity for m(5)Cyd-BSA termed 1-2 and 1-12 were produced. Furthermore, methylated DNA-binding activities of the scFvs were confirmed using an indirect immunofluorescence assay. Additionally, N- and C-terminal scFv 1-2 fusion with AcGFP were constructed, and we observed the N-terminal AcGFP exhibited much higher fluorescence intensity than the C-terminal fusions. The AcGFP-scFv 1-2 modified N-terminus of scFv with AcGFP had high fluorescence intensity, but the scFv 1-2-AcGFP modified C-terminus of scFv with AcGFP had low fluorescence intensity. The cross-reactivity of AcGFP-scFv 1-2 was similar to scFv 1-2, and thus, AcGFP-scFv 1-2 could be used in a direct immunofluorescence assay. The scFv fusion proteins may be useful for the detection and quantification of cellular methylated DNA in various specimens.

TAT-NEP1-40 as a novel therapeutic candidate for axonal regeneration and functional recovery after stroke

Currently available therapeutics has been less effective in promoting functional recovery from stroke or other injuries in the central nervous system (CNS). Axonal damage is a characteristic pathology seen in CNS injuries. Previously, it was reported that Nogo-A extracellular peptide residues 1-40 (NEP1-40), a competitive antagonist of Nogo-66 receptor (NgR1), has the ability to promote axonal regrowth and functional recovery after CNS injury. However, delivery of the therapeutic proteins into the brain parenchyma is limited due to its inability to cross the blood-brain barrier (BBB). We first generated a biologically active NEP1-40 fusion protein containing the protein transduction domain (PTD) of the transactivator of transcription (TAT), TAT-NEP1-40, which crosses the BBB in vivo after systemic delivery. The TAT-NEP1-40 can protect PC12 cells against oxygen and glucose deprivation (OGD) and promote neurite outgrowth when added exogenously to culture medium. The TAT-NEP1-40 protein transduced into the brain continued to sustain biological activities and protected the brain against ischemia/reperfusion injury through inhibition of neuronal apoptosis. Collectively, our data suggest that TAT-NEP1-40 may be a novel therapeutic candidate for axonal regeneration and functional recovery from CNS injuries such as cerebral hypoxia-ischemia, cerebral hemorrhage, brain trauma, and also for spinal cord injury.

Plasticity and stability of visual field maps in adult primary visual cortex

It is important to understand the balance between cortical plasticity and stability in various systems and across spatial scales in the adult brain. Here we review studies of adult plasticity in primary visual cortex (V1), which has a key role in distributing visual information. There are claims of plasticity at multiple spatial scales in adult V1, but a number of inconsistencies in the supporting data raise questions about the extent and nature of such plasticity. Our understanding of the extent of plasticity in V1 is further limited by a lack of quantitative models to guide the interpretation of the data. These problems limit efforts to translate research findings about adult cortical plasticity into significant clinical, educational and policy applications.

Cytokine transport across the injured blood-spinal cord barrier

Spinal cord injury (SCI) induces dynamic changes of the blood-spinal cord barrier and even the more distant blood-brain barrier. Besides an immediate increase of paracellular permeability resulting from the direct impact of the injury, the transport systems for selective cytokines undergo regulatory changes. Since many of the transported molecules play essential roles in neuroregeneration, we propose that this altered peripheral tissue / CNS interaction benefits remodeling of the spinal cord and functional recovery after SCI. This review examines the transport of cytokines and neurotrophic factors into the spinal cord, emphasizing the upregulation of two cytokines--tumor necrosis factor alpha (TNF) and leukemia inhibitory factor (LIF)--during the course of SCI. The increased transport of TNF and LIF after SCI remains saturable and does not coincide with generalized BBB disruption, highlighting a pivotal regulatory role for the blood-spinal cord barrier.

Method to perform IV injections on mice using the facial vein

A novel technique for gaining IV access in a mouse model is presented. Using a cut-down approach, the facial vein is identified through an incision from anterior to the external auditory meatus to posterior to the lateral ispilateral canthus. A small gage needle (30gauge) may be inserted to inject medications. A high success rate (93%) as determined by direct visualization is achieved. The technique would prove especially useful for animals slated for kinematic testing as the incision does not interfere with the animal's ventral surface.

A quantitative method for analysis of in vitro neurite outgrowth

The adult mammalian CNS is extremely limited in its ability to regenerate axons following injury. Glial scar, neuroinflammatory processes and molecules released from myelin impair axonal regrowth and contribute to the lack of neural regeneration. An in vitro assay that quantitates neurite outgrowth from cultured neurons as a model of neuronal regenerative potential is described. Specifically, the neurite outgrowth from primary neurons (rat cerebellar granule neurons; CGNs) and a neuronal cell line (NG108-15) were quantitatively measured after optimization of culture conditions. After cultures were fixed and immunostained to label neurons and nuclei, microscope images were captured and an image analysis algorithm was developed using Image-Pro Plus software to allow quantitative analysis. The algorithm allowed the determination of total neurite length, number of neurons, and number of neurons without neurites. The algorithm also allows for end-user control of thresholds for staining intensity and cell/nuclei size. This assay represents a useful tool for quantification of neurite outgrowth from a variety of neuronal sources with applications that include: (1) assessment of neurite outgrowth potential; (2) identification of molecules that can block or stimulate neurite outgrowth in conventional culture media; and (3) identification of agents that can overcome neurite outgrowth inhibition by inhibitory substrates.

Recovery and Regeneration after Spinal Cord Injury: A Review and Summary of Recent Literature

Introduction: Spinal cord injury (SCI) often results in significant neurologic dysfunction and disability. An annual incidence of 15 to 40 traumatic SCI cases per million population has been reported worldwide, and a conservative estimate for Singapore would be 23 cases per million. With continued improvements in medical care, an increasing prevalence of SCI patients is expected, with corresponding need for comprehensive rehabilitation services led by specialist rehabilitation physicians. Methods: A literature search, review, and summary of findings of recent studies relating to factors associated with recovery, as well as interventions for rehabilitation and promotion of healing of the injured spinal cord was performed. Conclusions: Many SCI patients show improvements in motoric and neurologic level, but those with complete injuries have poor chance of improving American Spinal Injury Association (ASIA) scores. SCI of violent aetiology tends to be more neurologic complete, and those without sacral sparing less likely to improve. Older patients generally do well in activities of daily living. Women have better motor score improvement, although men have better Functional Independence Measure (FIM) scores generally. Electrodiagnostic tests such as somatosensory evoked potentials (SSEPs) and motor evoked potentials (MEPs) can help with prognostication, as can imaging techniques such as magnetic resonance imaging (MRI). Immediate surgery for spinal decompression may improve recovery, but whether routine surgery after SCI improves function remains unclear, as does the timing. Methylprednisolone and similar agents appear to help limit secondary injury processes. Rehabilitation interventions such as functional electrical stimulation (FES) and body-weight supported treadmill ambulation training may be effective, as may neural-controlled prostheses and devices. Substances that promote repair and regeneration of the injured spinal cord such as GM-1, 4-AP, BDNG, GDNF, Nogo and MAG-inhibitors, have been studied. Transplanted tissues and cells, such as blood macrophages, bone marrow transplant with GM-CSF, olfactory ensheathing cells, fetal tissues, stem or progenitor cells, have been reported to produce neurological improvements. Key words: Prognosis, Regeneration, Rehabilitation, Spinal cord injuries

Biologically inspired approaches to drug delivery for nerve regeneration

As the biological processes governing nerve regeneration have become elucidated over the past decades, interest has developed in manipulating these processes to improve nerve regeneration. Drug delivery to the regenerating nerve has the potential for major clinical applications in neurodegenerative diseases, spinal cord injury and peripheral nerve injury or sacrifice. This article reviews the evolution of the field of drug delivery to the regenerating nerve, from simple local applications of neurotrophic agents in solution and osmotic pump delivery, to the existing approaches involving novel biomaterials and genetically manipulated cell populations. A discussion of the various known nerve growth-promoting agents, and the chemical considerations involved in their delivery, is included. A perspective on the role of tissue engineering approaches for nerve regeneration in the future is offered.

Targeting myelin to optimize plasticity of spared spinal axons

Functional re-innervation of target neurons following neurological damage such as spinal cord injury is an essential requirement of potential therapies. There are at least two avenues by which this can be achieved: (a) through the regeneration of injured axons and (b) through promoting plasticity of those spared by the initial insult. There are several reasons why the latter approach may be more feasible, not the least of which are the inhibitory character of the glial scar, the often long distances over which injured axons must regrow, and the fact that spared axons are often already in the vicinity of denervated targets. The challenge is to unveil the well-recognized intrinsic plasticity of spared axons in a way that avoids complications, such as pain or autonomic dysfunction. One approach that we as well as others have taken is to target growth-suppressing signaling pathways initiated in spared axons by myelin-derived proteins. This article reviews models used for the study of spinal axon plasticity and describes the anatomical and behavioral effects of interfering with myelinderived proteins, their receptors, and components of their intracellular signaling cascades.

Growth-associated gene and protein expression in the region of axonal sprouting in the aged brain after stroke

Aged individuals exhibit reduced functional recovery after stroke. We examined the expression profile in aged animals of a recently identified group of growth-associated genes that underlies post-stroke axonal sprouting in the young adult. Basal levels of most growth-promoting genes are higher in aged cortex compared with young adult, and are further induced after stroke. Compared with the young adult, these genes are induced at later time points after stroke. For growth-inhibitory molecules, myelin-associated glycoprotein and ephrin A5 are uniquely induced in the aged brain; chondroitin sulfate proteoglycans and oligodendrocyte myelin glycoprotein are induced at earlier time points; and Nogo-A, semaphorin IIIa and NG2 decline in aged vs. young adult after stroke. The aged brain does not simply have a reduction in growth-associated molecules after stroke, but a completely unique molecular profile of post-stroke axonal sprouting.

On neural plasticity, new neurons and the postischemic milieu: An integrated view on experimental rehabilitation

This review discusses actual and potential contributors to functional improvement after stroke injuries. Topics that will be covered are neuronal re-organization and sprouting, neural stem/progenitor cell activation and neuronal replacement, as well as the neuronal milieu defined by glia, inflammatory cells and blood vessel supply. It is well established that different types of neuronal plasticity ultimately lead to post-stroke recovery. However, an untapped potential which only recently has started to be extensively explored is neuronal replacement through endogenous or exogenous resources. Major experimental efforts are needed to achieve progress in this burgeoning area. The review stresses the importance of applying neurodevelopmental principles as well as performing a characterization of the role of the postischemic milieu when studying adult brain neural stem/progenitor cells. Integrated and multifaceted experimentation, incorporating actual and possible poststroke function modulators, will be necessary in order to determine future strategies that will ultimately enable considerable progress in the field of neurorehabilitation.