Blockade of Rho-associated kinase prevents inhibition of axon regeneration of peripheral nerves induced by anti-ganglioside antibodies

Anti-ganglioside antibodies are associated with delayed/poor clinical recovery in Guillain-Barrèsyndrome,mostly related to halted axon regeneration.Cross-linking of cell surface gangliosides by anti-ganglioside antibodies triggers inhibition of nerve repair in in vitro and in vivo paradigms of axon regeneration.These effects involve the activation of the small GTPase Rho A/ROCK signaling pathways,which negatively modulate growth cone cytoskeleton,similarly to well stablished inhibitors of axon regeneration described so far.The aim of this work was to perform a proof of concept study to demonstrate the effectiveness of Y-27632,a selective pharmacological inhibitor of ROCK,in a mouse model of axon regeneration of peripheral nerves,where the passive immunization with a monoclonal antibody targeting gangliosides GD1a and GT1b was previously reported to exert a potent inhibitory effect on regeneration of both myelinated and unmyelinated fibers.Our results demonstrate a differential sensitivity of myelinated and unmyelinated axons to the pro-regenerative effect of Y-27632.Treatment with a total dosage of 9 mg/kg of Y-27632 resulted in a complete prevention of anti-GD1a/GT1b monoclonal antibody-mediated inhibition of axon regeneration of unmyelinated fibers to skin and the functional recovery of mechanical cutaneous sensitivity.In contrast,the same dose showed toxic effects on the regeneration of myelinated fibers.Interestingly,scale down of the dosage of Y-27632 to 5 mg/kg resulted in a significant although not complete recovery of regenerated myelinated axons exposed to anti-GD1a/GT1b monoclonal antibody in the absence of toxicity in animals exposed to only Y-27632.Overall,these findings confirm the in vivo participation of Rho A/ROCK signaling pathways in the molecular mechanisms associated with the inhibition of axon regeneration induced by anti-GD1a/GT1b monoclonal antibody.Our findings open the possibility of therapeutic pharmacological intervention targeting Rho A/Rock pathway in immune neuropathies associated with the presence of anti-ganglioside antibodies and delayed or incomplete clinical recovery after injury in the peripheral nervous system.

Mechanism by which Rab5 promotes regeneration and functional recovery of zebrafish Mauthner axons

Rab5 is a GTPase protein that is involved in intracellular membrane trafficking. It functions by binding to various effector proteins and regulating cellular responses, including the formation of transport vesicles and their fusion with the cellular membrane. Rab5 has been reported to play an important role in the development of the zebrafish embryo;however, its role in axonal regeneration in the central nervous system remains unclear. In this study, we established a zebrafish Mauthner cell model of axonal injury using single-cell electroporation and two-photon axotomy techniques. We found that overexpression of Rab5 in single Mauthner cells promoted marked axonal regeneration and increased the number of intra-axonal transport vesicles. In contrast, treatment of zebrafish larvae with the Rab kinase inhibitor CID-1067700markedly inhibited axonal regeneration in Mauthner cells. We also found that Rab5 activated phosphatidylinositol 3-kinase(PI3K) during axonal repair of Mauthner cells and promoted the recovery of zebrafish locomotor function. Additionally, rapamycin, an inhibitor of the mechanistic target of rapamycin downstream of PI3K, markedly hindered axonal regeneration. These findings suggest that Rab5 promotes the axonal regeneration of injured zebrafish Mauthner cells by activating the PI3K signaling pathway.

DUSP2 deletion with CRISPR/Cas9 promotes Mauthner cell axonal regeneration at the early stage of zebrafish

Axon regeneration of central neurons is a complex process that is tightly regulated by multiple extrinsic and intrinsic factors.The expression levels of distinct genes are changed after central neural system(CNS)injury and affect axon regeneration.A previous study identified dusp2 as an upregulated gene in zebrafish with spinal cord injury.Here,we found that dual specificity phosphatase 2(DUSP2)is a negative regulator of axon regeneration of the Mauthner cell(M-cell).DUSP2 is a phosphatase that mediates the dephosphorylation of JNK.In this study,we knocked out dusp2 by CRISPR/Cas9 and found that M-cell axons of dusp2(-/-)zebrafish had a better regeneration at the early stage after birth(within 8 days after birth),while those of dusp2^(+/-)zebrafish did not.Overexpression of DUSP2 in Tg(Tol 056)zebrafish by single-cell electroporation retarded the regeneration of M-cell axons.Western blotting results showed that DUSP2 knockout slightly increased the levels of phosphorylated JNK.These findings suggest that knocking out DUSP2 promoted the regeneration of zebrafish M-cell axons,possibly through enhancing JNK phosphorylation.

Phosphorylated S6K1 and 4E-BP1 play different roles in constitutively active Rheb-mediated retinal ganglion cell survival and axon regeneration after optic nerve injury

Ras homolog enriched in brain(Rheb) is a small GTPase that activates mammalian target of rapamycin complex 1(mTORC1).Previous studies have shown that constitutively active Rheb can enhance the regeneration of sensory axons after spinal cord injury by activating downstream effectors of mTOR.S6K1 and4E-BP1 are important downstream effectors of mTORC1.In this study,we investigated the role of Rheb/mTOR and its downstream effectors S6K1 and 4E-BP1in the protection of retinal ganglion cells.We transfected an optic nerve crush mouse model with adeno-associated viral 2-mediated constitutively active Rheb and observed the effects on retinal ganglion cell survival and axon regeneration.We found that overexpression of constitutively active Rheb promoted survival of retinal ganglion cells in the acute(14 days) and chronic(21 and 42 days) stages of injury.We also found that either co-expression of the dominant-negative S6K1mutant or the constitutively active 4E-BP1 mutant together with constitutively active Rheb markedly inhibited axon regeneration of retinal ganglion cells.This suggests that mTORC1-mediated S6K1 activation and 4E-BP1 inhibition were necessary components for constitutively active Rheb-induced axon regeneration.However,only S6K1 activation,but not 4E-BP1 knockdown,induced axon regeneration when applied alone.Furthermore,S6K1 activation promoted the survival of retinal ganglion cells at 14 days post-injury,whereas 4E-BP1 knockdown unexpectedly slightly decreased the survival of retinal ganglion cells at 14 days postinjury.Ove rexpression of constitutively active 4E-BP1 increased the survival of retinal ganglion cells at 14 days post-injury.Likewise,co-expressing constitutively active Rheb and constitutively active 4E-BP1 markedly increased the survival of retinal ganglion cells compared with overexpression of constitutively active Rheb alone at 14 days post-injury.These findings indicate that functional 4E-BP1 and S6K1 are neuroprotective and that 4E-BP1 may exert protective effects through a pathway at least partially independent of Rhe b/mTOR.Together,our results show that constitutively active Rheb promotes the survival of retinal ganglion cells and axon regeneration through modulating S6K1 and 4E-BP1 activity.Phosphorylated S6K1 and 4E-BP1 promote axon regeneration but play an antagonistic role in the survival of retinal ganglion cells.

The role of the Rho/ROCK signaling pathway in inhibiting axonal regeneration in the central nervous system

The Rho/Rho-associated coiled-coil containing protein kinase（Rho/ROCK） pathway is a major signaling pathway in the central nervous system, transducing inhibitory signals to block regeneration. After central nervous system damage, the main cause of impaired regeneration is the presence of factors that strongly inhibit regeneration in the surrounding microenvironment. These factors signal through the Rho/ROCK signaling pathway to inhibit regeneration. Therefore, a thorough understanding of the Rho/ROCK signaling pathway is crucial for advancing studies on regeneration and repair of the injured central nervous system.

Neurofilament proteins in axonal regeneration and neurodegenerative diseases

Neurofilament protein is a component of the mature neuronal cytoskeleton, and it interacts with the zygosome, which is mediated by neurofilament-related proteins. Neurofilament protein regulates enzyme function and the structure of linker proteins. In addition, neurofilament gene expression plays an important role in nervous system development. Previous studies have shown that neurofilament gene transcriptional regulation is crucial for neurofilament protein expression, especially in axonal regeneration and degenerative diseases. Post-transcriptional regulation increased neurofilament protein gene transcription during axonal regeneration, ultimately resulting in a pattern of neurofilament protein expression. An expression imbalance of post-transcriptional regulatory proteins and other disorders could lead to amyotrophic lateral sclerosis or other neurodegenerative diseases. These findings indicated that after transcription, neurofilament protein regulated expression of related proteins and promoted regeneration of damaged axons, suggesting that regulation disorders could lead to neurodegenerative diseases.

Environmental enrichment combined with fasudil promotes motor function recovery and axonal regeneration after stroke

Fasudil,a Rho-associated protein kinase(ROCK)inhibitor,has a protective effect on the central nervous system.In addition,environmental enrichment is a promising technique for inducing the recovery of motor impairments in ischemic stroke models.The present study aimed to explore whether environmental enrichment combined with fasudil can facilitate motor function recovery and induce cortical axonal regeneration after stroke.First,a mouse model of ischemic cerebral stroke was established by photochemical embolization of the left sensorimotor cortex.Fasudil solution(10 mg/kg per day)was injected intraperitoneally for 21 days after the photothrombotic stroke.An environmental enrichment intervention was performed on days 7-21 after the photothrombotic stroke.The results revealed that environmental enrichment combined with fasudil improved motor function,increased growth-associated protein 43 expression in the infarcted cerebral cortex,promoted axonal regeneration on the contralateral side,and downregulated ROCK,p-LIM domain kinase(LIMK)1,and p-cofilin expression.The combined intervention was superior to monotherapy.These findings suggest that environmental enrichment combined with fasudil treatment promotes motor recovery after stroke,at least partly by stimulating axonal regeneration.The underlying mechanism might involve ROCK/LIMK1/cofilin pathway regulation.This study was approved by the Institutional Animal Care and Use Committee of Fudan University,China(approval No.20160858A232)on February 24,2016.

Laminin-coated multifilament entubulation, combined with Schwann cells and glial cell line-derived neurotrophic factor, promotes unidirectional axonal regeneration in a rat model of thoracic spinal cord hemisection

Biomaterial bridging provides physical substrates to guide axonal growth across the lesion.To achieve efficient directional guidance,combinatory strategies using permissive matrix,cells and trophic factors are necessary.In the present study,we evaluated permissive effect of poly(acrylonitrile-co-vinyl chloride)guidance channels filled by different densities of laminin-precoated unidirectional polypropylene filaments combined with Schwann cells,and glial cell line-derived neurotrophic factor for axonal regeneration through a T10 hemisected spinal cord gap in adult rats.We found that channels with filaments significantly reduced the lesion cavity,astrocytic gliosis,and inflammatory responses at the graft-host boundaries.The laminin coated low density filament provided the most favorable directional guidance for axonal regeneration which was enhanced by co-grafting of Schwann cells and glial cell line-derived neurotrophic factor.These results demonstrate that the combinatorial strategy of filament-filled guiding scaffold,adhesive molecular laminin,Schwann cells,and glial cell line-derived neurotrophic factor,provides optimal topographical cues in stimulating directional axonal regeneration following spinal cord injury.This study was approved by Indiana University Institutional Animal Care and Use Committees(IACUC#:11011)on October 29,2015.

Axonal regeneration and sprouting as a potential therapeutic target for nervous system disorders

Nervous system disorders are prevalent health issues that will only continue to increase in frequency as the population ages.Dying-back axonopathy is a hallmark of many neurologic diseases and leads to axonal disconnection from their targets,which in turn leads to functional impairment.During the course of many of neurologic diseases,axons can regenerate or sprout in an attempt to reconnect with the target and restore synapse function.In amyotrophic lateral sclerosis(ALS),distal motor axons retract from neuromuscular junctions early in the disease-course before significant motor neuron death.There is evidence of compensatory motor axon sprouting and reinnervation of neuromuscular junctions in ALS that is usually quickly overtaken by the disease course.Potential drugs that enhance compensatory sprouting and encourage reinnervation may slow symptom progression and retain muscle function for a longer period of time in ALS and in other diseases that exhibit dying-back axonopathy.There remain many outstanding questions as to the impact of distinct disease-causing mutations on axonal outgrowth and regeneration,especially in regards to motor neurons derived from patient induced pluripotent stem cells.Compartmentalized microfluidic chambers are powerful tools for studying the distal axons of human induced pluripotent stem cells-derived motor neurons,and have recently been used to demonstrate striking regeneration defects in human motor neurons harboring ALS disease-causing mutations.Modeling the human neuromuscular circuit with human induced pluripotent stem cells-derived motor neurons will be critical for developing drugs that enhance axonal regeneration,sprouting,and reinnervation of neuromuscular junctions.In this review we will discuss compensatory axonal sprouting as a potential therapeutic target for ALS,and the use of compartmentalized microfluidic devices to find drugs that enhance regeneration and axonal sprouting of motor axons.

Deletion of Krüppel-like factor-4 promotes axonal regeneration in mammals

Axonal regeneration plays an important role in functional recovery after nervous system damage.However,after axonal injury in mammals,regeneration is often poor.The deletion of Krüppel-like factor-4(Klf4)has been shown to promote axonal regeneration in retinal ganglion cells.However,the effects of Klf4 deletion on the corticospinal tract and peripheral nervous system are unknown.In this study,using a mouse model of sciatic nerve injury,we show that the expression of Klf4 in dorsal root ganglion sensory neurons was significantly reduced after peripheral axotomy,suggesting that the regeneration of the sciatic nerve is associated with Klf4.In vitro,dorsal root ganglion sensory neurons with Klf4 knockout exhibited significantly enhanced axonal regeneration.Furthermore,the regeneration of the sciatic nerve was enhanced in vivo following Klf4 knockout.Finally,AAV-Cre virus was used to knockout the Klf4 gene in the cortex.The deletion of Klf4 enhanced regeneration of the corticospinal tract in mice with spinal cord injury.Together,our findings suggest that regulating KLF4 activity in neurons is a potential strategy for promoting axonal regeneration and functional recovery after nervous system injury.This study was approved by the Animal Ethics Committee at Soochow University,China(approval No.SUDA20200316A01).

Targeted tissue engineering:hydrogels with linear capillary channels for axonal regeneration after spinal cord injury

Spinal cord injury（SCI）frequently results in the permanent loss of function below the level of injury due to the failure of axonal regeneration in the adult mammalian central nervous system（CNS）.The limited intrinsic growth capacity of adult neurons,a lack of growth-promoting factors and the multifactorial inhibitory microenvironment around the lesion site contribute to the lack of axonalregeneration. Strategies such as transplantation of cells,

Effect of salviae miltiorrhizae and ligustrazine hydrochloride injection on axonal regeneration and nerve growth factor expression in a rat model of sciatic nerve injury

BACKGROUND： Studies have shown that both salviae miltiorrhizae and ligustrazine can promote protein expression of nerve growth factor （NGF） and regeneration of peripheral nerve. OBJECTIVE： To verify the effect of salviae miltiorrhizae and ligustrazine hydrochloride injection on axonal regeneration and NGF protein expression in a rat model of sciatic nerve injury. DESIGN, TIME AND SETTING： A randomized, controlled, animal experiment was performed at the Laboratory of Traditional Chinese Medicine and the Institute of Bioengineering of Jinan University from July to December 2008. MATERIALS： Salviae miltiorrhizae and ligustrazine hydrochloride injection （containing 20 mg salviae miJtiorrhizae and 100 mg ligustrazine per 100 mL injection） was provided by Guizhou Baite Pharmaceutical, China; salviae miltiorrhizae and ligustrazine decoctions （containing 1 g raw drug per 1 mL decoction） were provided by Guangzhou Baiyunshan Factory for Traditional Chinese Medicine, China; rabbit-anti-rat NGF monoclonal antibody was provided by Beijing Biosynthesis Biotechnology, China. METHODS： A total of 80 healthy, male, Sprague Dawley rats were used to establish a sciatic nerve injury model via neurotomy, and were then randomly assigned to 4 groups： salviae miltiorrhizae and ligustrazine hydrochloride injection group （intraperitoneal injection of 35 mL/kg per day salviae miltiorrhizae and ligustrazine hydrochloride injection）, saIviae miltiorrhizae group （intragastric peffusion of 2 mL salviae miltiorrhizae）, ligustrazine group （intragastric peffusion of 2 mL ligustrazine）, and model group （intraperitoneal injection of 35 mL/kg per day saline）, with 20 rats in each group. Thereafter, rats in each group were then divided into 4 subgroups according to varying time points of 1, 2, 4, and 8 weeks post-surgery, with 5 rats in each subgroup. MAIN OUTCOME MEASURES： Axons were quantified using chromotrope 2R-brilliant green and silver staining combined with image analysis to calculate the axonal regeneration rate; NGF expression was detected using immunohistochemistry and Western blot analysis; toe interspace was measured by behavior at 4 and 8 weeks. RESULTS： With increasing time after sciatic nerve expression, and toe interspace gradually increased njury, the axonal regeneration rate, NGF protein At 4 and 8 weeks post-surgery, axonal regeneration rate and NGF protein expression were significantly increased in the injured tissue of the salviae miltiorrhizae and ligustrazine hydrochloride injection, salviae miltiorrhizae, and ligustrazine groups, compared with the model group （P 〈 0.05 or P 〈 0.01）, and toe interspace was remarkably enlarged （P 〈 0.05 or P 〈 0.01）, especially in the salviae miltiorrhizae and ligustrazine hydrochloride injection group. CONCLUSION： Salviae miltiorrhizae and ligustrazine hydrochloride injection promoted axonal regeneration and NGF protein expression in the injured sciatic nerve, and also enhanced neurofunctional recovery. Its effect was superior to salviae miltiorrhizae or ligustrazine alone.

Calcium channel inhibition-mediated axonal stabilization improves axonal regeneration after optic nerve crush

Axonal projections are specialized neuronal compartments and the longest parts of neurons.Axonal degeneration is a common pathological feature in many neurodegenerative disorders,such as Parkinson’s disease,amyotrophic lateral sclerosis,glaucoma,as well as in traumatic lesions of the central nervous system（CNS）,such as spinal cord injury.

ROCK inhibition as a novel potential strategy for axonal regeneration in optic neuropathies

Optic neuropathies or optic nerve diseases are a frequent cause of permanent vision loss that can occur after inflammation,ischemia,infection,tumors,trauma and/or an elevated pressure inside the eye（also called intraocular pressure or IOP）.

Restoring axonal localization and transport of transmembrane receptors to promote repair within the injured CNS: a critical step in CNS regeneration

Each neuronal subtype is distinct in how it develops,responds to environmental cues,and whether it is capable of mounting a regenerative response following injury.Although the adult central nervous system（CNS） does not regenerate,several experimental interventions have been trialled with successful albeit limited instances of axonal repair.We highlight here some of these approaches including extracellular matrix（ECM） modification,cellular grafting,gene therapy-induced replacement of proteins,as well as application of biomaterials.We also review the recent report demonstrating the failure of axonal localization and transport of growth-promoting receptors within certain classes of mature neurons.More specifically,we discuss an inability of integrin receptors to localize within the axonal compartment of mature motor neurons such as in the corticospinal and rubrospinal tracts,whereas in immature neurons of those pathways and in mature sensory tracts such as in the optic nerve and dorsal column pathways these receptors readily localize within axons.Furthermore we assert that this failure of axonal localization contributes to the intrinsic inability of axonal regeneration.We conclude by highlighting the necessity for both combined therapies as well as a targeted approach specific to both age and neuronal subtype will be required to induce substantial CNS repair.

Rabs and axonal regeneration

Membrane trafficking processes are presumably vital for axonal regeneration after injury, but mechanistic understanding in this regard has been sparse. A recent loss-of-function screen had been carried out for factors important for axonal regeneration by cultured cortical neurons and the results suggested that the activity of a number of Rab GTPases might act to restrict axonal regeneration. A loss of Rab27b, in particular, is shown to enhance axonal regeneration in vitro, as well as in C. elegans and mouse central nervous system injury models in vivo. Possible mechanisms underlying this new finding, which has important academic and translational implication, are discussed.

Erythropoietin upregulates growth associated protein-43 expression and promotes retinal ganglion cell axonal regeneration in vivo after optic nerve crush

In this study, we established a rat model of optic nerve crush to explore the effects of erythropoietin on retinal ganglion cell axonal regeneration. At 15 days after injury in erythropoietin treated rats, retinal ganglion cell densities in regions corresponding to the 1/6, 3/6 and 5/6 ratios of the retinal radius were significantly increased. In addition, the number of growth associated protein-43 positive axons was significantly increased at different distances （50, 250 and 500 pm） from the crush site after erythropoietin treatment. Erythropoietin significantly increased growth associated protein-43 protein levels in the retina after crush injury, as determined by westem blot and immunofluorescence analysis. These results demonstrate that erythropoietin protects injured retinal ganglion cells and promotes axonal regeneration.

Acetylation as a mechanism that regulates axonal regeneration

The capacity for adult axons to regenerate after injury is diminished compared with developing axons.In the case of central nervous system（CNS）axons,injury causes a total failure to regenerate.This failure is due to both the intrinsic developmental decrease in growth capacity and the extrinsic inhibitory environment formed because of the injury.

Microfluidic systems for axonal growth and regeneration research

Damage to the adult mammalian central nervous system （CNS） often results in persistent neurological deficits with limited recovery of functions. The past decade has seen in- creasing research efforts in neural regeneration research with the ultimate goal of achieving functional recovery. Many studies have focused on prevention of further neural damage and restoration of functional connections that are com- promised after iniurY or pathological damage.

Manipulating extrinsic and intrinsic obstacles to axonal regeneration after spinal cord injury

Spinal cord injury（SCI）is a traumatic event that can lead to permanent motor and sensory deficits.After the initial trauma,axons of surviving neurons rapidly retract.While there may be a small degree of abortive sprouting,virtually all attempts at robust regrowth across the lesion site ultimately fail.Thus,neurons below the level of the injury are permanently disconnected from their normal input,resulting in persistent loss of function.