Systemic epothilone D improves hindlimb function after spinal cord contusion injury in rats

Axonal Growth and Fasciculation of Spinal Neurons Promoted by Aldynoglia in Alkaline Fibrin Hydrogel: Influence of Tol-51 Sulfoglycolipid

Traumatic spinal cord injury (tSCI) has complex pathophysiological events that begin after the initial trauma. One such event is fibroglial scar formation by fibroblasts and reactive astrocytes. A strong inhibition of axonal growth is caused by the activated astroglial cells as a component of fibroglial scarring through the production of inhibitory molecules, such as chondroitin sulfate proteoglycans or myelin-associated proteins. Here, we used neural precursor cells (aldynoglia) as promoters of axonal growth and a fibrin hydrogel gelled under alkaline conditions to support and guide neuronal cell growth, respectively. We added Tol-51 sulfoglycolipid as a synthetic inhibitor of astrocyte and microglia in order to test its effect on the axonal growth-promoting function of aldynoglia precursor cells. We obtained an increase in GFAP expression corresponding to the expected glial phenotype for aldynoglia cells cultured in alkaline fibrin. In co-cultures of dorsal root ganglia (DRG) and aldynoglia, the axonal growth promotion of DRG neurons by aldynoglia was not affected. We observed that the neural precursor cells first clustered together and then formed niches from which aldynoglia cells grew and connected to groups of adjacent cells. We conclude that the combination of alkaline fibrin with synthetic sulfoglycolipid Tol-51 increased cell adhesion, cell migration, fasciculation, and axonal growth capacity, promoted by aldynoglia cells. There was no negative effect on the behavior of aldynoglia cells after the addition of sulfoglycolipid Tol-51, suggesting that a combination of aldynoglia plus alkaline fibrin and Tol-51 compound could be useful as a therapeutic strategy for tSCI repair.

Alleviating Severe Cytoskeletal Destruction of Spinal Motor Neurons: Another Effect of Docosahexaenoic Acid in Spinal Cord Injury

Spinal cord injury (SCI) treatment remains a major challenge. Spinal motor neurons (MNs) are seriously injured in the early stage after SCI, but this has not received sufficient attention. Oxidative stress is known to play a crucial role in SCI pathology. Our studies demonstrated that oxidative stress can cause severe damage to the cytoskeleton of spinal MNs. Docosahexaenoic acid (DHA) has been shown to have beneficial effects on SCI, but the mechanism remains unclear, and no study has investigated the effect of DHA on oxidative stress-induced spinal MN injury. Here, we investigated the effect of DHA on spinal MN injury through in vivo and in vitro experiments, focusing on the cytoskeleton. We found that DHA not only promoted spinal MN survival but, more importantly, alleviated the severe cytoskeletal destruction of these neurons induced by oxidative stress in vitro and in mice with SCI in vivo. In addition, the mechanisms involved were investigated and elucidated. These results not only suggested a beneficial role of DHA in spinal MN cytoskeletal destruction caused by oxidative stress and SCI but also indicated the important role of the spinal MN cytoskeleton in the recovery of motor function after SCI. Our study provides new insights for the formulation of SCI treatment.

Coordination function index: A novel indicator for assessing hindlimb locomotor recovery in spinal cord injury rats based on catwalk gait parameters

In preclinical studies of spinal cord injury (SCI), behavioral assessments are crucial for evaluating treatment effectiveness. Commonly used methods include Basso, Beattie, Bresnahan (BBB) score and the Louisville swim scale (LSS), relying on subjective observations. The CatWalk automated gait analysis system is also widely used in SCI studies, providing extensive gait parameters from footprints. However, these parameters are often used independently or combined simply without utilizing the vast amount of data provided by CatWalk. Therefore, it is necessary to develop a novel approach encompassing multiple CatWalk parameters for a comprehensive and objective assessment of locomotor function. In this work, we screened 208 CatWalk XT gait parameters and identified 38 suitable for assessing hindlimb motor function recovery in a rat thoracic contusion SCI model. Exploratory factor analysis was used to reveal structural relationships among these parameters. Weighted scores for Coordination effectively differentiated hindlimb motor function levels, termed as the Coordinated Function Index (CFI). CFI showed high reliability, exhibiting high correlations with BBB scores, LSS, and T2WI lesion area. Finally, we simplified CFI based on factor loadings and correlation analysis, obtaining a streamlined version with reliable assessment efficacy. In conclusion, we developed a systematic assessment indicator utilizing multiple CatWalk parameters to objectively evaluate hindlimb motor function recovery in rats after thoracic contusion SCI.

Methods for evaluating gait associated dynamic balance and coordination in rodents

Balance is the dynamic and unconscious control of the body's centre of mass to maintain postural equilibrium. Regulated by the vestibular system, head movement and acceleration are processed by the brain to adjust joints. Several conditions result in a loss of balance, including Alzheimer's Disease, Parkinson's Disease, Menière's Disease and cervical spondylosis, all of which are caused by damage to certain parts of the vestibular pathways. Studies about the impairment of the vestibular system are challenging to carry out in human trials due to smaller study sizes limiting applications of the results and a lacking understanding of the human balance control mechanism. In contrast, more controlled research can be performed in animal studies which have fewer confounding factors than human models and allow specific conditions that affect balance to be replicated. Balance control can be studied using rodent balance-related behavioural tests after spinal or brain lesions, such as the Basso, Beattie and Bresnahan (BBB) Locomotor Scale, Foot Fault Scoring System, Ledged Beam Test, Beam Walking Test, and Ladder Beam Test, which are discussed in this review article along with their advantages and disadvantages. These tests can be performed in preclinical rodent models of femoral nerve injury, stroke, spinal cord injury and neurodegenerative diseases.

Effects of Epothilone Administration on Locomotion Recovery after Spinal Cord Injury: A Systematic Review of Animal Studies

This is a systematic review and meta-analysis of existing evidence regarding the possible effects of epothilones on spinal cord injury (SCI). This study aimed to investigate the possible effects of epothilone administration on locomotion recovery in animal models of SCI. Despite increasing rates of SCI and its burden on populations, no consensus has been reached about the possible treatment modality for SCI. Meanwhile, low-dose epothilones have been reported to have positive effects on SCI outcomes. Electronic databases of Web of Science, Scopus, Embase, and Medline were searched using keywords related to epothilones and SCI until the end of 2020. Two researchers screened the articles, and extracted data were analyzed using STATA ver. 14.0. Final results are reported as a standardized mean difference (SMD) with a 95% confidence interval (CI). After the screening, five studies were included in the analysis. Rats were used in all the studies. Two types of epothilones were used via intraperitoneal injection and were shown to have positive effects on the motor outcomes of samples with SCI (SMD, 0.87; 95% CI, 0.51 to 1.23; p =0.71). Although a slightly better effect was observed when using epothilone B, the difference was not significant (coefficient, -0.50; 95% CI, -1.52 to 0.52; p =0.246). The results of this study suggest that epothilones have positive effects on the improvement of motor function in rats, when administered intraperitoneally until a maximum of 1 day after SCI. However, current evidence regarding the matter is still scarce.

Rehabilitation enhances epothilone-induced locomotor recovery after spinal cord injury

Microtubule stabilization through epothilones is a promising preclinical therapy for functional recovery following spinal cord injury that stimulates axon regeneration, reduces growth-inhibitory molecule deposition and promotes functional improvements. Rehabilitation therapy is the only clinically validated approach to promote functional improvements following spinal cord injury. However, whether microtubule stabilization can augment the beneficial effects of rehabilitation therapy or act in concert with it to further promote repair remains unknown. Here, we investigated the pharmacokinetic, histological and functional efficacies of epothilone D, epothilone B and ixabepilone alone or in combination with rehabilitation following a moderate contusive spinal cord injury. Pharmacokinetic analysis revealed that ixabepilone only weakly crossed the blood-brain barrier and was subsequently excluded from further investigations. In contrast, epothilones B and D rapidly distributed to CNS compartments displaying similar profiles after either subcutaneous or intraperitoneal injections. Following injury and subcutaneous administration of epothilone B or D, rats were subjected to 7 weeks of sequential bipedal and quadrupedal training. For all outcome measures, epothilone B was efficacious compared with epothilone D. Specifically, epothilone B decreased fibrotic scaring which was associated with a retention of fibronectin localized to perivascular cells in sections distal to the lesion. This corresponded to a decreased number of cells present within the intralesional space, resulting in less axons within the lesion. Instead, epothilone B increased serotonergic fibre regeneration and vesicular glutamate transporter 1 expression caudal to the lesion, which was not affected by rehabilitation. Multiparametric behavioural analyses consisting of open-field locomotor scoring, horizontal ladder, catwalk gait analysis and hindlimb kinematics revealed that rehabilitation and epothilone B both improved several aspects of locomotion. Specifically, rehabilitation improved open-field locomotor and ladder scores, as well as improving the gait parameters of limb coupling, limb support, stride length and limb speed; epothilone B improved these same gait parameters but also hindlimb kinematic profiles. Functional improvements by epothilone B and rehabilitation acted complementarily on gait parameters leading to an enhanced recovery in the combination group. As a result, principal component analysis of gait showed the greatest improvement in the epothilone B plus rehabilitation group. Thus, these results support the combination of epothilone B with rehabilitation in a clinical setting.

Recognition of necrotic regions in MRI images of chronic spinal cord injury based on superpixel

BACKGROUND AND OBJECTIVE

The cystic cavity and its surrounding dense glial scar formed in chronic spinal cord injury (SCI) hinder the regeneration of nerve axons. Accurate location of the necrotic regions formed by the scar and the cavity is conducive to eliminate the re-growth obstacles and promote SCI treatment. This work aims to realize the accurate and automatic location of necrotic regions in the chronic SCI magnetic resonance imaging (MRI).

METHODS

In this study, a method based on superpixel is proposed to identify the necrotic regions of spinal cord in chronic SCI MRI. Superpixels were obtained by a simple linear iterative clustering algorithm, and feature sets were constructed from intensity statistical features, gray level co-occurrence matrix features, Gabor texture features, local binary pattern features and superpixel areas. Subsequently, the recognition effects of support vector machine (SVM) and random forest (RF) classification model on necrotic regions were compared from accuracy (ACC), positive predictive value (PPV), sensitivity (SE), specificity (SP), Dice coefficient and algorithm running time.

RESULTS

The method is evaluated on T1- and T2-weighted MRI spinal cord images of 24 adult female Wistar rats. And an automatic recognition method for spinal cord necrosis regions was established based on the SVM classification model finally. The recognition results were 1.00±0.00 (ACC), 0.89±0.09 (PPV), 0.88±0.12 (SE), 1.00±0.00 (SP) and 0.88±0.07 (Dice), respectively.

CONCLUSIONS

The proposed method can accurately and noninvasively identify the necrotic regions in MRI, which is helpful for the pre-intervention assessment and post-intervention evaluation of chronic SCI research and treatments, and promoting the clinical transformation of chronic SCI research.

Bridging the gap of axonal regeneration in the central nervous system: A state of the art review on central axonal regeneration

Neuronal regeneration in the central nervous system (CNS) is an important field of research with relevance to all types of neuronal injuries, including neurodegenerative diseases. The glial scar is a result of the astrocyte response to CNS injury. It is made up of many components creating a complex environment in which astrocytes play various key roles. The glial scar is heterogeneous, diverse and its composition depends upon the injury type and location. The heterogeneity of the glial scar observed in different situations of CNS damage and the consequent implications for axon regeneration have not been reviewed in depth. The gap in this knowledge will be addressed in this review which will also focus on our current understanding of central axonal regeneration and the molecular mechanisms involved. The multifactorial context of CNS regeneration is discussed, and we review newly identified roles for components previously thought to solely play an inhibitory role in central regeneration: astrocytes and p75NTR and discuss their potential and relevance for deciding therapeutic interventions. The article ends with a comprehensive review of promising new therapeutic targets identified for axonal regeneration in CNS and a discussion of novel ways of looking at therapeutic interventions for several brain diseases and injuries.

The Foot Fault Scoring System to Assess Skilled Walking in Rodents: A Reliability Study

The foot fault scoring system of the ladder rung walking test (LRWT) is used to assess skilled walking in rodents. However, the reliability of the LRWT foot fault score has not been properly addressed. This study was designed to address this issue. Two independent and blinded raters analyzed 20 rats and 20 mice videos. Each video was analyzed twice by the same rater (80 analyses per rater). The intraclass correlation coefficient (ICC) and the Kappa coefficient were employed to check the accuracy of agreement and reliability in the intra- and inter-rater analyses of the LRWT outcomes. Excellent intra- and inter-rater agreements were found for the forelimb, hindlimb, and both limbs combined in rats and mice. The agreement level was also excellent for total crossing time, total time stopped, and the number of stops during the walking path. Rating individual scores in the foot fault score system (0–6) ranged from satisfactory to excellent, in terms of the intraclass correlation indexes. Moreover, we showed that experienced and inexperienced raters can obtain reliable results if supervised training is provided. We concluded that the LRWT is a reliable and useful tool to study skilled walking in rodents and can help researchers address walking-related neurobiological questions.

[Protective effect of Epothilone D against traumatic optic nerve injury in rats]

OBJECTIVE

To investigate the therapeutic effect of Epothilone D on traumatic optic neuropathy (TON) in rats.

METHODS

Forty-two SD rats were randomized to receive intraperitoneal injection of 1.0 mg/kg Epothilone D or DMSO (control) every 3 days until day 28, and rat models of TON were established on the second day after the first administration. On days 3, 7, and 28, examination of flash visual evoked potentials (FVEP), immunofluorescence staining and Western blotting were performed to examine the visual pathway features, number of retinal ganglion cells (RGCs), GAP43 expression level in damaged axons, and changes of Tau and pTau-396/404 in the retina and optic nerve.

RESULTS

In Epothilone D treatment group, RGC loss rate was significantly decreased by 19.12% (P=0.032) on day 3 and by 22.67% (P=0.042) on day 28 as compared with the rats in the control group, but FVEP examination failed to show physiological improvement in the visual pathway on day 28 in terms of the relative latency of N2 wave (P=0.236) and relative amplitude attenuation of P2-N2 wave (P=0.441). The total Tau content in the retina of the treatment group was significantly increased compared with that in the control group on day 3 (P < 0.001), showing a consistent change with ptau-396/404 level. In the optic nerve axons, the total Tau level in the treatment group was significantly lower than that in the control group on day 7 (P=0.002), but the changes of the total Tau and pTau-396/404 level did not show an obvious correlation. Epothilone D induced persistent expression of GAP43 in the damaged axons, detectable even on day 28 of the experiment.

CONCLUSION

Epothilone D treatment can protect against TON in rats by promoting the survival of injured RGCs, enhancing Tau content in the surviving RGCs, reducing Tau accumulation in injured axons, and stimulating sustained regeneration of axons.

Microtubules as Regulators of Neural Network Shape and Function: Focus on Excitability, Plasticity and Memory

Neuronal microtubules (MTs) are complex cytoskeletal protein arrays that undergo activity-dependent changes in their structure and function as a response to physiological demands throughout the lifespan of neurons. Many factors shape the allostatic dynamics of MTs and tubulin dimers in the cytosolic microenvironment, such as protein–protein interactions and activity-dependent shifts in these interactions that are responsible for their plastic capabilities. Recently, several findings have reinforced the role of MTs in behavioral and cognitive processes in normal and pathological conditions. In this review, we summarize the bidirectional relationships between MTs dynamics, neuronal processes, and brain and behavioral states. The outcomes of manipulating the dynamicity of MTs by genetic or pharmacological approaches on neuronal morphology, intrinsic and synaptic excitability, the state of the network, and behaviors are heterogeneous. We discuss the critical position of MTs as responders and adaptative elements of basic neuronal function whose impact on brain function is not fully understood, and we highlight the dilemma of artificially modulating MT dynamics for therapeutic purposes.

Microtubule Organization Is Essential for Maintaining Cellular Morphology and Function

Microtubules (MTs) are highly dynamic polymers essential for a wide range of cellular physiologies, such as acting as directional railways for intracellular transport and position, guiding chromosome segregation during cell division, and controlling cell polarity and morphogenesis. Evidence has established that maintaining microtubule (MT) stability in neurons is vital for fundamental cellular and developmental processes, such as neurodevelopment, degeneration, and regeneration. To fulfill these diverse functions, the nervous system employs an arsenal of microtubule-associated proteins (MAPs) to control MT organization and function. Subsequent studies have identified that the disruption of MT function in neurons is one of the most prevalent and important pathological features of traumatic nerve damage and neurodegenerative diseases and that this disruption manifests as a reduction in MT polymerization and concomitant deregulation of the MT cytoskeleton, as well as downregulation of microtubule-associated protein (MAP) expression. A variety of MT-targeting agents that reverse this pathological condition, which is regarded as a therapeutic opportunity to intervene the onset and development of these nervous system abnormalities, is currently under development. Here, we provide an overview of the MT-intrinsic organization process and how MAPs interact with the MT cytoskeleton to promote MT polymerization, stabilization, and bundling. We also highlight recent advances in MT-targeting therapeutic agents applied to various neurological disorders. Together, these findings increase our current understanding of the function and regulation of MT organization in nerve growth and regeneration.

Fibrosis in the central nervous system: from the meninges to the vasculature

Formation of a collagenous connective tissue scar after penetrating injuries to the brain or spinal cord has been described and investigated for well over 100 years. However, it was studied almost exclusively in the context of penetrating injuries that resulted in infiltration of meningeal fibroblasts, which raised doubts about translational applicability to most CNS injuries where the meninges remain intact. Recent studies demonstrating the perivascular niche as a source of fibroblasts have debunked the traditional view that a fibrotic scar only forms after penetrating lesions that tear the meninges. These studies have led to a renewed interest in CNS fibrosis not only in the context of axon regeneration after spinal cord injury, but also across a spectrum of CNS disorders. Arising with this renewed interest is some discrepancy about which perivascular cell gives rise to the fibrotic scar, but additional studies are beginning to provide some clarity. Although mechanistic studies on CNS fibrosis are still lacking, the similarities to fibrosis of other organs should provide important insight into how CNS fibrosis can be therapeutically targeted to promote functional recovery.

RhoA drives actin compaction to restrict axon regeneration and astrocyte reactivity after CNS injury

An inhibitory extracellular milieu and neuron-intrinsic processes prevent axons from regenerating in the adult central nervous system (CNS). Here we show how the two aspects are interwoven. Genetic loss-of-function experiments determine that the small GTPase RhoA relays extracellular inhibitory signals to the cytoskeleton by adapting mechanisms set in place during neuronal polarization. In response to extracellular inhibitors, neuronal RhoA restricts axon regeneration by activating myosin II to compact actin and, thereby, restrain microtubule protrusion. However, astrocytic RhoA restricts injury-induced astrogliosis through myosin II independent of microtubules by activating Yes-activated protein (YAP) signaling. Cell-type-specific deletion in spinal-cord-injured mice shows that neuronal RhoA activation prevents axon regeneration, whereas astrocytic RhoA is beneficial for regenerating axons. These data demonstrate how extracellular inhibitors regulate axon regeneration, shed light on the capacity of reactive astrocytes to be growth inhibitory after CNS injury, and reveal cell-specific RhoA targeting as a promising therapeutic avenue.

Nimodipine Promotes Functional Recovery After Spinal Cord Injury in Rats

Spinal cord injury (SCI) is a devastating condition that results in severe motor, sensory, and autonomic dysfunction. The L-/T-type calcium channel blocker nimodipine (NMD) exerts a protective effect on neuronal injury; however, the protective effects of long-term administration of NMD in subjects with SCI remain unknown. Thus, the aim of this study was to evaluate the role of long-term treatment with NMD on a clinically relevant SCI model. Female rats with SCI induced by 25 mm contusion were subcutaneously injected with vehicle or 10 mg/kg NMD daily for six consecutive weeks. We monitored the motor score, hind limb grip strength, pain-related behaviors, and bladder function in this study to assess the efficacy of NMD in rats with SCI. Rats treated with NMD showed improvements in locomotion, pain-related behaviors, and spasticity-like symptoms, but not in open-field spontaneous activity, hind limb grip strength or bladder function. SCI lesion areas and perilesional neuronal numbers, gliosis and calcitonin gene-related peptide (CGRP⁺) fiber sprouting in the lumbar spinal cord and the expression of K⁺–Cl⁻ cotransporter 2 (KCC2) on lumbar motor neurons were also observed to further explore the possible protective mechanisms of NMD. NMD-treated rats showed greater tissue preservation with reduced lesion areas and increased perilesional neuronal sparing. NMD-treated rats also showed improvements in gliosis, CGRP⁺ fiber sprouting in the lumbar spinal cord, and KCC2 expression in lumbar motor neurons. Together, these results indicate that long-term treatment with NMD improves functional recovery after SCI, which may provide a potential therapeutic strategy for the treatment of SCI.

Gait Analysis Using Animal Models of Peripheral Nerve and Spinal Cord Injuries

The present review discusses recent data regarding rodent models of spinal cord and peripheral nerve injuries in terms of gait analysis using the CatWalk system (CW), an automated and exceptionally reliable system for assessing gait abnormalities and motor coordination. CW is a good tool for both studying improvements in the walking of animals after suffering a peripheral nerve and spinal cord lesion and to select the best therapies and procedures after tissue destruction, given that it provides objective and quantifiable data. Most studies using CW for gait analysis that were published in recent years focus on injuries inflicted in the peripheral nerve, spinal cord, and brain. CW has been used in the assessment of rodent motor function through high-resolution videos, whereby specialized software was used to measure several aspects of the animal's gait, and the main characteristics of the automated system are presented here. CW was developed to assess footfall and gait changes, and it can calculate many parameters based on footprints and time. However, given the multitude of parameters, it is necessary to evaluate which are the most important under the employed experimental circumstances. By selecting appropriate animal models and evaluating peripheral nerve and spinal cord lesion regeneration using standardized methods, suggestions for new therapies can be provided, which represents the translation of this methodology into clinical application.

Strategies to neutralize RhoA/ROCK pathway after spinal cord injury

Regeneration is bungled following CNS injuries, including spinal cord injury (SCI). Inherent decay of permissive conditions restricts the regrowth of the mature CNS after an injury. Hypertrophic scarring, insignificant intrinsic axon-growth activity, and axon-growth inhibitory molecules such as myelin inhibitors and scar inhibitors constitute a significant hindrance to spinal cord repair. Besides these molecules, a combined absence of various mechanisms responsible for axonal regeneration is the main reason behind the dereliction of the adult CNS to regenerate. The neutralization of specific inhibitors/proteins by stymieing antibodies or encouraging enzymatic degradation results in improved axon regeneration. Previous efforts to induce regeneration after SCI have stimulated axonal development in or near lesion sites, but not beyond them. Several pathways are responsible for the axonal growth obstruction after a CNS injury, including SCI. Herein, we summarize the axonal, glial, and intrinsic factor which impedes the regeneration. We have also discussed the methods to stabilize microtubules and through this to maintain the proper cytoskeletal dynamics of growth cone as disorganized microtubules lead to the failure of axonal regeneration. Moreover, we primarily focus on diverse inhibitors of axonal growth and molecular approaches to counteract them and their downstream intracellular signaling through the RhoA/ROCK pathway.

Upregulation of Apol8 by Epothilone D facilitates the neuronal relay of transplanted NSCs in spinal cord injury

BACKGROUND

Microtubule-stabilizing agents have been demonstrated to modulate axonal sprouting during neuronal disease. One such agent, Epothilone D, has been used to treat spinal cord injury (SCI) by promoting axonal sprouting at the lesion site after SCI. However, the role of Epothilone D in the differentiation of neural stem cells (NSCs) in SCI repair is unknown. In the present study, we mainly explored the effects and mechanisms of Epothilone D on the neuronal differentiation of NSCs and revealed a potential new SCI treatment.

METHODS

In vitro differentiation assays, western blotting, and quantitative real-time polymerase chain reaction were used to detect the effects of Epothilone D on NSC differentiation. Retrograde tracing using a pseudotyped rabies virus was then used to detect neuronal circuit construction. RNA sequencing (RNA-Seq) was valuable for exploring the target gene involved in the neuronal differentiation stimulated by Epothilone D. In addition, lentivirus-induced overexpression and RNA interference technology were applied to demonstrate the function of the target gene. Last, an Apol8-NSC-linear ordered collagen scaffold (LOCS) graft was prepared to treat a mouse model of SCI, and functional and electrophysiological evaluations were performed.

RESULTS

We first revealed that Epothilone D promoted the neuronal differentiation of cultured NSCs and facilitated neuronal relay formation in the injured site after SCI. Furthermore, the RNA-Seq results demonstrated that Apol8 was upregulated during Epothilone D-induced neuronal relay formation. Lentivirus-mediated Apol8 overexpression in NSCs (Apol8-NSCs) promoted NSC differentiation toward neurons, and an Apol8 interference assay showed that Apol8 had a role in promoting neuronal differentiation under the induction of Epothilone D. Last, Apol8-NSC transplantation with LOCS promoted the neuronal differentiation of transplanted NSCs in the lesion site as well as synapse formation, thus improving the motor function of mice with complete spinal cord transection.

CONCLUSIONS

Epothilone D can promote the neuronal differentiation of NSCs by upregulating Apol8, which may provide a promising therapeutic target for SCI repair.

Fidgetin-like 2 negatively regulates axonal growth and can be targeted to promote functional nerve regeneration

The microtubule (MT) cytoskeleton plays a critical role in axon growth and guidance. Here, we identify the MT-severing enzyme fidgetin-like 2 (FL2) as a negative regulator of axon regeneration and a therapeutic target for promoting nerve regeneration after injury. Genetic knockout of FL2 in cultured adult dorsal root ganglion neurons resulted in longer axons and attenuated growth cone retraction in response to inhibitory molecules. Given the axonal growth-promoting effects of FL2 depletion in vitro, we tested whether FL2 could be targeted to promote regeneration in a rodent model of cavernous nerve (CN) injury. The CNs are parasympathetic nerves that regulate blood flow to the penis, which are commonly damaged during radical prostatectomy (RP), resulting in erectile dysfunction (ED). Application of FL2-siRNA after CN injury significantly enhanced functional nerve recovery. Remarkably, following bilateral nerve transection, visible and functional nerve regeneration was observed in 7 out of 8 animals treated with FL2-siRNA, while no control-treated animals exhibited regeneration. These studies identify FL2 as a promising therapeutic target for enhancing regeneration after peripheral nerve injury and for mitigating neurogenic ED after RP - a condition for which, at present, only poor treatment options exist.

Combinatrial treatment of anti-High Mobility Group Box-1 monoclonal antibody and epothilone B improves functional recovery after spinal cord contusion injury

Spinal cord injury (SCI) causes motor and sensory deficits and is currently considered an incurable disease. We have previously reported that administration of anti-High Mobility Group Box-1 monoclonal antibody (anti-HMGB1 mAb) preserved lesion area and improved locomotion recovery in mouse model of SCI. In order to further enhance the recovery, we here examined combinatorial treatment of anti-HMGB1 mAb and epothilone B (Epo B), which has been reported to promote axon regeneration. This combinatorial treatment significantly increased hindlimb movement compared with anti-HMGB1 mAb alone, although Epo B alone failed to increase functional recovery. These results are in agreement with that anti-HMGB1 mAb alone was able to decrease the lesion area spreading and increase the surviving neuron numbers around the lesion, whereas Epo B facilitated axon outgrowth only in combination with anti-HMGB1 mAb, suggesting that anti-HMGB1 mAb-dependent tissue preservation is necessary for Epo B to exhibit its therapeutic effect. Taken together, the combinatorial treatment can be considered as a novel and clinically applicable strategy for SCI.

Combination of Defined CatWalk Gait Parameters for Predictive Locomotion Recovery in Experimental Spinal Cord Injury Rat Models

In many preclinical spinal cord injury (SCI) studies, assessment of locomotion recovery is key to understanding the effectiveness of the experimental intervention. In such rat SCI studies, the most basic locomotor recovery scoring system is a subjective observation of animals freely roaming in an open field, the Basso Beattie Bresnahan (BBB) score. In comparison, CatWalk is an automated gait analysis system, providing further parameter specifications. Although together the CatWalk parameters encompass gait, studies consistently report single parameters, which differ in significance from other behavioral assessments. Therefore, we believe no single parameter produced by the CatWalk can represent the fully-coordinated motion of gait. Typically, other locomotor assessments, such as the BBB score, combine several locomotor characteristics into a representative score. For this reason, we ranked the most distinctive CatWalk parameters between uninjured and SC injured rats. Subsequently, we combined nine of the topmost parameters into an SCI gait index score based on linear discriminant analysis (LDA). The resulting combination was applied to assess gait recovery in SCI experiments comprising of three thoracic contusions, a thoracic dorsal hemisection, and a cervical dorsal column lesion model. For thoracic lesions, our unbiased machine learning model revealed gait differences in lesion type and severity. In some instances, our LDA was found to be more sensitive in differentiating recovery than the BBB score alone. We believe the newly developed gait parameter combination presented here should be used in CatWalk gait recovery work with preclinical thoracic rat SCI models.

Efficacy of epothilones in central nervous system trauma treatment: what has age got to do with it?

Central nervous system injury, specifically traumatic brain and spinal cord injury, can have significant long lasting effects. There are no comprehensive treatments to combat the injury and sequalae of events that occurring following a central nervous system trauma. Herein we discuss the potential for the epothilone family of microtubule stabilizing agents to improve outcomes following experimentally induced trauma. These drugs, which are able to cross the blood-brain barrier, may hold great promise for the treatment of central nervous system trauma and the current literature presents the extensive range of beneficial effects these drugs may have following trauma in animal models. Importantly, the effect of the epothilones can vary and our most recent contributions to this field indicate that the efficacy of epothilones following traumatic brain injury is dependent upon the age of the animals. Therefore, we present a case for a greater emphasis to be placed upon age when using an intervention aimed at neural regeneration and highlight the importance of tailoring the therapeutic regime in the clinic to the age of the patient to promote improved patient outcomes.

Chronic neuronal activation increases dynamic microtubules to enhance functional axon regeneration after dorsal root crush injury

After a dorsal root crush injury, centrally-projecting sensory axons fail to regenerate across the dorsal root entry zone (DREZ) to extend into the spinal cord. We find that chemogenetic activation of adult dorsal root ganglion (DRG) neurons improves axon growth on an in vitro model of the inhibitory environment after injury. Moreover, repeated bouts of daily chemogenetic activation of adult DRG neurons for 12 weeks post-crush in vivo enhances axon regeneration across a chondroitinase-digested DREZ into spinal gray matter, where the regenerating axons form functional synapses and mediate behavioral recovery in a sensorimotor task. Neuronal activation-mediated axon extension is dependent upon changes in the status of tubulin post-translational modifications indicative of highly dynamic microtubules (as opposed to stable microtubules) within the distal axon, illuminating a novel mechanism underlying stimulation-mediated axon growth. We have identified an effective combinatory strategy to promote functionally-relevant axon regeneration of adult neurons into the CNS after injury.

Polymer-Based Scaffold Strategies for Spinal Cord Repair and Regeneration

The injury to the spinal cord is among the most complex fields of medical development. Spinal cord injury (SCI) leads to acute loss of motor and sensory function beneath the injury level and is linked to a dismal prognosis. Currently, while a strategy that could heal the injured spinal cord remains unforeseen, the latest advancements in polymer-mediated approaches demonstrate promising treatment forms to remyelinate or regenerate the axons and to integrate new neural cells in the SCI. Moreover, they possess the capacity to locally deliver synergistic cells, growth factors (GFs) therapies and bioactive substances, which play a critical role in neuroprotection and neuroregeneration. Here, we provide an extensive overview of the SCI characteristics, the pathophysiology of SCI, and strategies and challenges for the treatment of SCI in a review. This review highlights the recent encouraging applications of polymer-based scaffolds in developing the novel SCI therapy.

Microtubule Stabilization Promotes Microcirculation Reconstruction After Spinal Cord Injury

Spinal cord microcirculation plays an important role in maintaining the function of spinal cord neurons and other cells. Previous studies have largely focused on the ability of microtubule stabilization to inhibit the fibroblast migration and promote axon regeneration after spinal cord injury (SCI). However, the effect of microtubule stabilization treatment on microcirculation reconstruction after SCI remains unclear. By using immunofluorescence, we found that microtubule stabilization treatment improved microcirculation reconstruction via increasing the number of microvessels, pericytes, and the perfused microvessels after SCI. To clarify the underlying mechanisms, rat brain microvascular endothelial cells and pericytes were subjected to glucose oxygen deprivation. By using flow cytometry and western blotting, we found that microtubule stabilization treatment inhibited apoptosis and migration of endothelial cells and pericytes but promoted proliferation and survival of endothelial cells and pericytes through upregulated expression of vascular endothelial growth factor A (VEGFA), VEGF receptor 2, platelet-derived growth factor-B (PDGFB), PDGF receptor β, and angiopoietin-1 after SCI. Taken together, this study provides evidence for the mechanisms underlying the promotion of microcirculation reconstruction after SCI by microtubule stabilization treatment. Importantly, this study suggests the potential of microtubule stabilization as a therapeutic target to reduce microcirculation dysfunction after SCI in the clinic.

The pathologic outcomes and efficacy of epothilone treatment following traumatic brain injury is determined by age

Traumatic brain injury (TBI) can affect individuals at any age, with the potential of causing lasting neurologic consequences. The lack of effective therapeutic solutions and recommendations for patients that acquire a TBI can be attributed, at least in part, to an inability to confidently predict long-term outcomes following TBI, and how the response of the brain differs across the life span. The purpose of this study was to determine how age specifically affects TBI outcomes in a preclinical model. Male Thy1-YFPH mice, that express yellow fluorescent protein in the cytosol of a subset of Layer V pyramidal neurons in the neocortex, were subjected to a lateral fluid percussion injury over the right parietal cortex at distinct time points throughout the life span (1.5, 3, and 12 months of age). We found that the degree of neuronal injury, astrogliosis, and microglial activation differed depending on the age of the animal when the injury occurred. Furthermore, age affected the initial injury response and how it resolved over time. Using the microtubule stabilizing agent Epothilone D, to potentially protect against these pathologic outcomes, we found that the neuronal response was different depending on age. This study clearly shows that age must be taken into account in neurologic studies and preclinical trials involving TBI, and that future therapeutic interventions must be tailored to age.

Therapeutic repair for spinal cord injury: combinatory approaches to address a multifaceted problem

The recent years saw the advent of promising preclinical strategies that combat the devastating effects of a spinal cord injury (SCI) that are progressing towards clinical trials. However, individually, these treatments produce only modest levels of recovery in animal models of SCI that could hamper their implementation into therapeutic strategies in spinal cord injured humans. Combinational strategies have demonstrated greater beneficial outcomes than their individual components alone by addressing multiple aspects of SCI pathology. Clinical trial designs in the future will eventually also need to align with this notion. The scenario will become increasingly complex as this happens and conversations between basic researchers and clinicians are required to ensure accurate study designs and functional readouts.

Exosomes Derived from miR-126-modified MSCs Promote Angiogenesis and Neurogenesis and Attenuate Apoptosis after Spinal Cord Injury in Rats

Spinal cord injury (SCI) is a devastating neurological event that results in incomplete or complete loss of voluntary motor and sensory function. Until recently, there has been no effective curative strategy for SCI. Our previous study showed that microRNA (miR)-126 promoted angiogenesis and attenuated inflammation after SCI; however, the effect of miR-126-based treatment is limited because of the low efficiency of miR delivery in vivo. Recently, accumulating evidence has indicated that exosomes can serve as a valuable therapeutic vehicle for miR delivery to the central nervous system (CNS). Thus, the present study aimed to investigate whether exosomes derived from mesenchymal stem cells (MSCs) can be used to deliver miR-126 to treat SCI. In this study, we found that MSCs can load miR-126 into secreted exosomes. In a rat model of SCI, exosomes transferred miR-126 to the injured site of the spinal cord, reduced the lesion volume and improved functional recovery after SCI. Additionally, miR-126-loaded exosomes promoted angiogenesis post-SCI. Moreover, the administration of miR-126 exosomes promoted neurogenesis and reduced cell apoptosis after SCI. In vitro, we observed that exosomes derived from miR-126-modified MSCs promoted the angiogenesis and migration of human umbilical venous endothelial cells (HUVECs) by inhibiting the expression of Sprouty-related EVH1 domain-containing protein 1 (SPRED1) and phosphoinositide-3-kinase regulatory subunit 2 (PIK3R2). In conclusion, our study demonstrated that exosomes derived from MSCs transfected with miR-126 may promote angiogenesis and neurogenesis, inhibit apoptosis and promote functional recovery after SCI. These findings suggest that exosomes derived from miR-126-modified MSCs may serve as a novel potential therapeutic strategy for treating SCI.

ADF/Cofilin-Mediated Actin Turnover Promotes Axon Regeneration in the Adult CNS

Injured axons fail to regenerate in the adult CNS, which contrasts with their vigorous growth during embryonic development. We explored the potential of re-initiating axon extension after injury by reactivating the molecular mechanisms that drive morphogenetic transformation of neurons during development. Genetic loss- and gain-of-function experiments followed by time-lapse microscopy, in vivo imaging, and whole-mount analysis show that axon regeneration is fueled by elevated actin turnover. Actin depolymerizing factor (ADF)/cofilin controls actin turnover to sustain axon regeneration after spinal cord injury through its actin-severing activity. This pinpoints ADF/cofilin as a key regulator of axon growth competence, irrespective of developmental stage. These findings reveal the central role of actin dynamics regulation in this process and elucidate a core mechanism underlying axon growth after CNS trauma. Thereby, neurons maintain the capacity to stimulate developmental programs during adult life, expanding their potential for plasticity. Thus, actin turnover is a key process for future regenerative interventions.

Imaging in vivo dynamics of sensory axon responses to CNS injury

Axons in the adult mammalian brain and spinal cord fail to regenerate upon lesion. In vivo imaging serves as a tool to investigate the immediate response of axons to injury and how the same injured axons behave over time. Here, we describe the dynamic changes that injured sensory axons undergo and methods of imaging them in vivo. First, we explain how sensory axons in the dorsal column of the adult mouse spinal cord respond to axotomy. Then, we highlight practical considerations for implementing two-photon based in vivo imaging of these axons. Finally, we describe future directions for this technique, including the possibility of in vivo imaging of subcellular dynamics within the axon.

Knockdown of Fidgetin Improves Regeneration of Injured Axons by a Microtubule-Based Mechanism

Fidgetin is a microtubule-severing protein that pares back the labile domains of microtubules in the axon. Experimental depletion of fidgetin results in elongation of the labile domains of microtubules and faster axonal growth. To test whether fidgetin knockdown assists axonal regeneration, we plated dissociated adult rat DRGs transduced using AAV5-shRNA-fidgetin on a laminin substrate with spots of aggrecan, a growth-inhibitory chondroitin sulfate proteoglycan. This cell culture assay mimics the glial scar formed after CNS injury. Aggrecan is more concentrated at the edge of the spot, such that axons growing from within the spot toward the edge encounter a concentration gradient that causes growth cones to become dystrophic and axons to retract or curve back on themselves. Fidgetin knockdown resulted in faster-growing axons on both laminin and aggrecan and enhanced crossing of axons from laminin onto aggrecan. Strikingly, axons from within the spot grew more avidly against the inhibitory aggrecan concentration gradient to cross onto laminin, without retracting or curving back. We also tested whether depleting fidgetin improves axonal regeneration in vivo after a dorsal root crush in adult female rats. Whereas control DRG neurons failed to extend axons across the dorsal root entry zone after injury, DRG neurons in which fidgetin was knocked down displayed enhanced regeneration of axons across the dorsal root entry zone into the spinal cord. Collectively, these results establish fidgetin as a novel therapeutic target to augment nerve regeneration and provide a workflow template by which microtubule-related targets can be compared in the future.SIGNIFICANCE STATEMENT Here we establish a workflow template from cell culture to animals in which microtubule-based treatments can be tested and compared with one another for their effectiveness in augmenting regeneration of injured axons relevant to spinal cord injury. The present work uses a viral transduction approach to knock down fidgetin from rat neurons, which coaxes nerve regeneration by elevating microtubule mass in their axons. Unlike previous strategies using microtubule-stabilizing drugs, fidgetin knockdown adds microtubule mass that is labile (rather than stable), thereby better recapitulating the growth status of a developing axon.

Repositioning Microtubule Stabilizing Drugs for Brain Disorders

Microtubule stabilizing agents are among the most clinically useful chemotherapeutic drugs. Mostly, they act to stabilize microtubules and inhibit cell division. While not without side effects, new generations of these compounds display improved pharmacokinetic properties and brain penetrance. Neurological disorders are intrinsically associated with microtubule defects, and efforts to reposition microtubule-targeting chemotherapeutic agents for treatment of neurodegenerative and psychiatric illnesses are underway. Here we catalog microtubule regulators that are associated with Alzheimer's and Parkinson's disease, amyotrophic lateral sclerosis, schizophrenia and mood disorders. We outline the classes of microtubule stabilizing agents used for cancer treatment, their brain penetrance properties and neuropathy side effects, and describe efforts to apply these agents for treatment of brain disorders. Finally, we summarize the current state of clinical trials for microtubule stabilizing agents under evaluation for central nervous system disorders.

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

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

Cytoskeleton dynamics in axon regeneration

Recent years have seen cytoskeleton dynamics emerging as a key player in axon regeneration. The cytoskeleton, in particular microtubules and actin, ensures the growth of neuronal processes and maintains the singular, highly polarized shape of neurons. Following injury, adult central axons are tipped by a dystrophic structure, the retraction bulb, which prevents their regeneration. Abnormal cytoskeleton dynamics are responsible for the formation of this growth-incompetent structure but pharmacologically modulating cytoskeleton dynamics of injured axons can transform this structure into a growth-competent growth cone. The cytoskeleton also drives the migration of scar-forming cells after an injury. Targeting its dynamics modifies the composition of the inhibitory environment formed by scar tissue and renders it more permissive for regenerating axons. Hence, cytoskeleton dynamics represent an appealing target to promote axon regeneration. As some of cytoskeleton-targeting drugs are used in the clinics for other purposes, they hold the promise to be used as a basis for a regenerative therapy after a spinal cord injury.