Characterization of new cell permeable C3-like proteins that inactivate Rho and stimulate neurite outgrowth on inhibitory substrates

Extracellular vesicles from UTX-knockout endothelial cells boost neural stem cell differentiation in spinal cord injury

BACKGROUND

Vascular endothelial cells are pivotal in the pathophysiological progression following spinal cord injury (SCI). The UTX (Ubiquitously Transcribed Tetratripeptide Repeat on Chromosome X) serves as a significant regulator of endothelial cell phenotype. The manipulation of endogenous neural stem cells (NSCs) offers a compelling strategy for the amelioration of SCI.

METHODS

Two mouse models were used to investigate SCI: NSCs lineage-traced mice and mice with conditional UTX knockout (UTX KO) in endothelial cells. To study the effects of UTX KO on neural differentiation, we harvested extracellular vesicles (EVs) from both UTX KO spinal cord microvascular endothelial cells (SCMECs) and negative control SCMECs. These EVs were then employed to modulate the differentiation trajectory of endogenous NSCs in the SCI model.

RESULTS

In our NSCs lineage-traced mice model of SCI, a marked decrease in neurogenesis was observed post-injury. Notably, NSCs in UTX KO SCMECs mice showed enhanced neuronal differentiation compared to controls. RNA sequencing and western blot analyses revealed an upregulation of L1 cell adhesion molecule (L1CAM), a gene associated with neurogenesis, in UTX KO SCMECs and their secreted EVs. This aligns with the observed promotion of neurogenesis in UTX KO conditions. In vivo administration of L1CAM-rich EVs from UTX KO SCMECs (KO EVs) to the mice significantly enhanced neural differentiation. Similarly, in vitro exposure of NSCs to KO EVs resulted in increased activation of the Akt signaling pathway, further promoting neural differentiation. Conversely, inhibiting Akt phosphorylation or knocking down L1CAM negated the beneficial effects of KO EVs on NSC neuronal differentiation.

CONCLUSIONS

In conclusion, our findings substantiate that EVs derived from UTX KO SCMECs can act as facilitators of neural differentiation following SCI. This study not only elucidates a novel mechanism but also opens new horizons for therapeutic interventions in the treatment of SCI. Video Abstract.

Magnetic spatiotemporal control of SOS1 coupled nanoparticles for guided neurite growth in dopaminergic single cells

The axon regeneration of neurons in the brain can be enhanced by activating intracellular signaling pathways such as those triggered by the membrane-anchored Rat sarcoma (RAS) proto-oncogene. Here we demonstrate the induction of neurite growth by expressing tagged permanently active Harvey-RAS protein or the RAS-activating catalytic domain of the guanine nucleotide exchange factor (SOS1cat), in secondary dopaminergic cells. Due to the tag, the expressed fusion protein is captured by functionalized magnetic nanoparticles in the cytoplasm of the cell. We use magnetic tips for remote translocation of the SOS1cat-loaded magnetic nanoparticles from the cytoplasm towards the inner face of the plasma membrane where the endogenous Harvey-RAS protein is located. Furthermore, we show the magnetic transport of SOS1cat-bound nanoparticles from the cytoplasm into the neurite until they accumulate at its tip on a time scale of minutes. In order to scale-up from single cells, we show the cytoplasmic delivery of the magnetic nanoparticles into large numbers of cells without changing the cellular response to nerve growth factor. These results will serve as an initial step to develop tools for refining cell replacement therapies based on grafted human induced dopaminergic neurons loaded with functionalized magnetic nanoparticles in Parkinson model systems.

Clostridial C3 Toxins Enter and Intoxicate Human Dendritic Cells

C3 protein toxins produced by Clostridium (C.) botulinum and C. limosum are mono-ADP-ribosyltransferases, which specifically modify the GTPases Rho A/B/C in the cytosol of monocytic cells, thereby inhibiting Rho-mediated signal transduction in monocytes, macrophages, and osteoclasts. C3 toxins are selectively taken up into the cytosol of monocytic cells by endocytosis and translocate from acidic endosomes into the cytosol. The C3-catalyzed ADP-ribosylation of Rho proteins inhibits essential functions of these immune cells, such as migration and phagocytosis. Here, we demonstrate that C3 toxins enter and intoxicate dendritic cells in a time- and concentration-dependent manner. Both immature and mature human dendritic cells efficiently internalize C3 exoenzymes. These findings could also be extended to the chimeric fusion toxin C2IN-C3lim. Moreover, stimulated emission depletion (STED) microscopy revealed the localization of the internalized C3 protein in endosomes and emphasized its potential use as a carrier to deliver foreign proteins into dendritic cells. In contrast, the enzyme C2I from the binary C. botulinum C2 toxin was not taken up into dendritic cells, indicating the specific uptake of C3 toxins. Taken together, we identified human dendritic cells as novel target cells for clostridial C3 toxins and demonstrated the specific uptake of these toxins via endosomal vesicles.

Traumatic Brain Injuries: Pathophysiology and Potential Therapeutic Targets

Traumatic brain injury (TBI) remains one of the leading causes of morbidity and mortality amongst civilians and military personnel globally. Despite advances in our knowledge of the complex pathophysiology of TBI, the underlying mechanisms are yet to be fully elucidated. While initial brain insult involves acute and irreversible primary damage to the parenchyma, the ensuing secondary brain injuries often progress slowly over months to years, hence providing a window for therapeutic interventions. To date, hallmark events during delayed secondary CNS damage include Wallerian degeneration of axons, mitochondrial dysfunction, excitotoxicity, oxidative stress and apoptotic cell death of neurons and glia. Extensive research has been directed to the identification of druggable targets associated with these processes. Furthermore, tremendous effort has been put forth to improve the bioavailability of therapeutics to CNS by devising strategies for efficient, specific and controlled delivery of bioactive agents to cellular targets. Here, we give an overview of the pathophysiology of TBI and the underlying molecular mechanisms, followed by an update on novel therapeutic targets and agents. Recent development of various approaches of drug delivery to the CNS is also discussed.

An In-Silico Sequence-Structure-Function Analysis of the N-Terminal Lobe in CT Group Bacterial ADP-Ribosyltransferase Toxins

The C3-like toxins are single-domain proteins that represent a minimal mono-ADP-ribosyl transferase (mART) enzyme with a simple model scaffold for the entire cholera toxin (CT)-group. These proteins possess a single (A-domain) that modifies Rho proteins. In contrast, C2-like toxins require a binding/translocation partner (B-component) for intoxication. These are A-only toxins that contain the E-x-E motif, modify G-actin, but are two-domains with a C-domain possessing enzymatic activity. The N-domain of the C2-like toxins is unstructured, and its function is currently unknown. A sequence-structure-function comparison was performed on the N-terminal region of the mART domain of the enzymatic component of the CT toxin group in the CATCH fold (3.90.210.10). Special consideration was given to the N-domain distal segment, the α-lobe (α₁–α₄), and its different roles in these toxin sub-groups. These results show that the role of the N-terminal α-lobe is to provide a suitable configuration (i) of the α₂–α₃ helices to feature the α3-motif that has a role in NAD⁺ substrate binding and possibly in the interaction with the protein target; (ii) the α₃–α₄ helices to provide the α_3/4-loop with protein-protein interaction capability; and (iii) the α₁-N_tail that features specialized motif(s) according to the toxin type (A-only or A-B toxins) exhibiting an effect on the catalytic activity via the ARTT-loop, with a role in the inter-domain stability, and with a function in the binding and/or translocation steps during the internalization process.

Combinatorial Therapies After Spinal Cord Injury: How Can Biomaterials Help?

Traumatic spinal cord injury (SCI) results in an immediate loss of motor and sensory function below the injury site and is associated with a poor prognosis. The inhibitory environment that develops in response to the injury is mainly due to local expression of inhibitory factors, scarring and the formation of cystic cavitations, all of which limit the regenerative capacity of endogenous or transplanted cells. Strategies that demonstrate promising results induce a change in the microenvironment at- and around the lesion site to promote endogenous cell repair, including axonal regeneration or the integration of transplanted cells. To date, many of these strategies target only a single aspect of SCI; however, the multifaceted nature of SCI suggests that combinatorial strategies will likely be more effective. Biomaterials are a key component of combinatorial strategies, as they have the potential to deliver drugs locally over a prolonged period of time and aid in cell survival, integration and differentiation. Here we summarize the advantages and limitations of widely used strategies to promote recovery after injury and highlight recent research where biomaterials aided combinatorial strategies to overcome some of the barriers of spinal cord regeneration.

C3 transferase gene therapy for continuous conditional RhoA inhibition

Regrowth inhibitory molecules prevent axon regeneration in the adult mammalian central nervous system (CNS). RhoA, a small GTPase in the Rho family, is a key intracellular switch that mediates the effects of these extracellular regrowth inhibitors. The bacterial enzyme C3-ADP ribosyltransferase (C3) selectively and irreversibly inhibits the activation of RhoA and stimulates axon outgrowth and regeneration. However, effective intracellular delivery of the C3 protein in vivo is limited by poor cell permeability and a short duration of action. To address this, we have developed a gene therapy approach using viral vectors to introduce the C3 gene into neurons or neuronal progenitors. Our vectors deliver C3 in a cell-autonomous (endogenous) or a cell-nonautonomous (secretable/permeable) fashion and promote in vitro process outgrowth on inhibitory chondroitin sulfate proteoglycan substrate. Further conditional control of our vectors was achieved via the addition of a Tet-On system, which allows for transcriptional control with doxycycline administration. These vectors will be crucial tools for promoting continued axonal regeneration after CNS injuries or neurodegenerative diseases.

Detection and Quantification of ADP-Ribosylated RhoA/B by Monoclonal Antibody

Clostridium botulinum exoenzyme C3 is the prototype of C3-like ADP-ribosyltransferases that modify the GTPases RhoA, B, and C. C3 catalyzes the transfer of an ADP-ribose moiety from the co-substrate nicotinamide adenine dinucleotide (NAD) to asparagine-41 of Rho-GTPases. Although C3 does not possess cell-binding/-translocation domains, C3 is able to efficiently enter intact cells, including neuronal and macrophage-like cells. Conventionally, the detection of C3 uptake into cells is carried out via the gel-shift assay of modified RhoA. Since this gel-shift assay does not always provide clear, evaluable results an additional method to confirm the ADP-ribosylation of RhoA is necessary. Therefore, a new monoclonal antibody has been generated that specifically detects ADP-ribosylated RhoA/B, but not RhoC, in Western blot and immunohistochemical assay. The scFv antibody fragment was selected by phage display using the human naive antibody gene libraries HAL9/10. Subsequently, the antibody was produced as scFv-Fc and was found to be as sensitive as a commercially available RhoA antibody providing reproducible and specific results. We demonstrate that this specific antibody can be successfully applied for the analysis of ADP-ribosylated RhoA/B in C3-treated Chinese hamster ovary (CHO) and HT22 cells. Moreover, ADP-ribosylation of RhoA was detected within 10 min in C3-treated CHO wild-type cells, indicative of C3 cell entry.

Retinal ganglion cell dendrite pathology and synapse loss: Implications for glaucoma

Dendrites are exquisitely specialized cellular compartments that critically influence how neurons collect and process information. Retinal ganglion cell (RGC) dendrites receive synaptic inputs from bipolar and amacrine cells, thus allowing cell-to-cell communication and flow of visual information. In glaucoma, damage to RGC axons results in progressive neurodegeneration and vision loss. Recent data indicate that axonal injury triggers rapid structural alterations in RGC dendritic arbors, prior to manifest axonal loss, which lead to synaptic rearrangements and functional deficits. Here, we provide an update on recent work addressing the role of RGC dendritic degeneration in models of acute and chronic optic nerve damage as well as novel mechanisms that regulate RGC dendrite stability. A better understanding of how defects in RGC dendrites contribute to neurodegeneration in glaucoma might provide new insights into disease onset and progression, while informing the development of novel therapies to prevent vision loss.

Novel therapeutic uses and formulations of botulinum neurotoxins: a patent review (2012 - 2014)

INTRODUCTION

Botulinum neurotoxins (BoNTs) are among the most toxic of known biological molecules and function as acetylcholine release inhibitors and neuromuscular blocking agents. Paradoxically, these properties also make them valuable therapeutic agents for the treatment of movement disorders, urological conditions and hypersecretory disorders. Greater understanding of their molecular mechanism of action and advances in protein engineering has led to significant efforts to improve and expand their function with a view towards broadening their therapeutic potential.

AREAS COVERED

Searches of Espacenet and Google Patent have revealed a number of patents related to BoNTs. This review will focus on novel therapeutic uses and formulations disclosed during 2012 - 2014. The seven patents discussed will include nanoformulations of FDA-approved BoNTs, additional BoNT subtypes and novel BoNT variants and chimeras created through protein engineering. Supporting patents and related publications are also briefly discussed.

EXPERT OPINION

The clinical and commercial success of BoNTs has prompted investigation into novel BoNTs or BoNT-mediated chimeras with promising in vitro results. Distinct strategies including the use of nanoformulations and targeted delivery have been implemented to identify new indication and improved functionality. Greater understanding of their systemic exposure, efficacy and safety profiles will be required for further development.

Myelin Lipids Inhibit Axon Regeneration Following Spinal Cord Injury: a Novel Perspective for Therapy

Lack of axon regeneration following spinal cord injury has been mainly ascribed to the inhibitory environment of the injury site, i.e., to chondroitin sulfate proteoglycans (CSPGs) and myelin-associated inhibitors (MAIs). Here, we used shiverer (shi) mice to assess axon regeneration following spinal cord injury in the presence of MAIs and CSPG but in the absence of compact myelin. Although in vitro shi neurons displayed a similar intrinsic neurite outgrowth to wild-type neurons, in vivo, shi fibers had increased regenerative capacity, suggesting that the wild-type spinal cord contains additional inhibitors besides MAIs and CSPG. Our data show that besides myelin protein, myelin lipids are highly inhibitory for neurite outgrowth and suggest that this inhibitory effect is released in the shi spinal cord given its decreased lipid content. Specifically, we identified cholesterol and sphingomyelin as novel myelin-associated inhibitors that operate through a Rho-dependent mechanism and have inhibitory activity in multiple neuron types. We further demonstrated the inhibitory action of myelin lipids in vivo, by showing that delivery of 2-hydroxypropyl-β-cyclodextrin, a drug that reduces the levels of lipids specifically in the injury site, leads to increased axon regeneration of wild-type (WT) dorsal column axons following spinal cord injury. In summary, our work shows that myelin lipids are important modulators of axon regeneration that should be considered together with protein MAIs as critical targets in strategies aiming at improving axonal growth following injury.

Spinal cord regeneration

Three theories of regeneration dominate neuroscience today, all purporting to explain why the adult central nervous system (CNS) cannot regenerate. One theory proposes that Nogo, a molecule expressed by myelin, prevents axonal growth. The second theory emphasizes the role of glial scars. The third theory proposes that chondroitin sulfate proteoglycans (CSPGs) prevent axon growth. Blockade of Nogo, CSPG, and their receptors indeed can stop axon growth in vitro and improve functional recovery in animal spinal cord injury (SCI) models. These therapies also increase sprouting of surviving axons and plasticity. However, many investigators have reported regenerating spinal tracts without eliminating Nogo, glial scar, or CSPG. For example, many motor and sensory axons grow spontaneously in contused spinal cords, crossing gliotic tissue and white matter surrounding the injury site. Sensory axons grow long distances in injured dorsal columns after peripheral nerve lesions. Cell transplants and treatments that increase cAMP and neurotrophins stimulate motor and sensory axons to cross glial scars and to grow long distances in white matter. Genetic studies deleting all members of the Nogo family and even the Nogo receptor do not always improve regeneration in mice. A recent study reported that suppressing the phosphatase and tensin homolog (PTEN) gene promotes prolific corticospinal tract regeneration. These findings cannot be explained by the current theories proposing that Nogo and glial scars prevent regeneration. Spinal axons clearly can and will grow through glial scars and Nogo-expressing tissue under some circumstances. The observation that deleting PTEN allows corticospinal tract regeneration indicates that the PTEN/AKT/mTOR pathway regulates axonal growth. Finally, many other factors stimulate spinal axonal growth, including conditioning lesions, cAMP, glycogen synthetase kinase inhibition, and neurotrophins. To explain these disparate regenerative phenomena, I propose that the spinal cord has evolved regenerative mechanisms that are normally suppressed by multiple extrinsic and intrinsic factors but can be activated by injury, mediated by the PTEN/AKT/mTOR, cAMP, and GSK3b pathways, to stimulate neural growth and proliferation.

A ROCK Inhibitor Blocks the Inhibitory Effect of Chondroitin Sulfate Proteoglycan on Morphological Changes of Mesenchymal Stromal/Stem Cells into Neuron-Like Cells

Chondroitin sulfate proteoglycan (CSPG) inhibits neurite outgrowth of various neuronal cell types, and CSPG-associated inhibition of neurite outgrowth is mediated by the Rho/ROCK pathway. Mesenchymal stromal/stem cells (MSCs) have the potential to differentiate into neuron-like cells under specific conditions and have been shown to differentiate into neuron-like cells by co-treatment with the ROCK inhibitor Y27632 and the hypoxia condition mimicking agent CoCl2. In this study, we addressed the hypothesis that a ROCK inhibitor might be beneficial to regenerate neurons during stem cell therapy by preventing transplanted MSCs from inhibition by CSPG in damaged tissues. Indeed, dose-dependent inhibition by CSPG pretreatment was observed during morphological changes of Wharton's jelly-derived MSCs (WJ-MSCs) induced by Y27632 alone. The formation of neurite-like structures was significantly inhibited when WJ-MSCs were pre-treated with CSPG before induction under Y27632 plus CoCl2 conditions, and pretreatment with a protein kinase C inhibitor reversed such inhibition. However, CSPG treatment resulted in no significant inhibition of the WJ-MSC morphological changes into neuron-like cells after initiating induction by Y27632 plus CoCl2. No marked changes were detected in expression levels of neuronal markers induced by Y27632 plus CoCl2 upon CSPG treatment. CSPG also blocked the morphological changes of human bone marrow-derived MSCs into neuron-like cells under other neuronal induction condition without the ROCK inhibitor, and Y27632 pre-treatment blocked the inhibitory effect of CSPG. These results suggest that a ROCK inhibitor can be efficiently used in stem cell therapy for neuronal induction by avoiding hindrance from CSPG.

Multifaceted neuro-regenerative activities of human dental pulp stem cells for functional recovery after spinal cord injury

Spinal cord injury (SCI) often leads to persistent functional deficits due to the loss of neurons and glia and to limited axonal regeneration after such injury. Recently, three independent groups have reported marked recovery of hindlimb locomotor function after the transplantation of human adult dental pulp stem cells (DPSCs) and stem cells from human exfoliated deciduous teeth (SHEDs) into rats or mice with acute, sub-acute or chronic SCI. This review summarizes the primary characteristics of human dental pulp stem cells and their therapeutic benefits for treating SCI. Experimental data from multiple preclinical studies suggest that pulp stem cells may promote functional recovery after SCI through multifaceted neuro-regenerative activities.

Cell type-specific signaling function of RhoA GTPase: lessons from mouse gene targeting

RhoA GTPase is a key intracellular regulator of actomyosin dynamics and other cell functions, including adhesion, proliferation, survival, and gene expression. Most of our knowledge of RhoA signaling function is from studies in immortalized cell lines utilizing inhibitors or dominant mutant overexpression, both of which are limited in terms of specificity, dosage, and clonal variation. Recent mouse gene targeting studies of rhoA and its regulators/effectors have revealed cell type-specific signaling mechanisms in the context of mammalian physiology. The new knowledge may present therapeutic opportunities for the rational targeting of RhoA signaling-mediated pathophysiologies.

Effect of Y-27632 on the cultured retinal neurocytes of rats

AIM

To investigate the effect of Y-27632 on the survival and neurite outgrowth of the cultured retinal neurocytes.

METHODS

After the postnatal day 2-3, Sprague-Dawley retinal neurocytes were cultured for 48 hours, the culture media was replaced with serum-free media (control group) and serum-free media contained 30µmol/L Y-27632 (Y-27632 group), and the cells were continually cultured another 48 hours. The cultured retinal neurocytes were identified with anti-neuron specific enolase (NSE) immunocytochemistry. The survival state of those cells was estimated by MTT assay, and the neurite outgrowth of those cells was evaluated by the computerized image-analysis system.

RESULTS

Compared with the control group, the absorbance values of cells survival in Y-27632 group increased 12.90% and 33.33% respectively after 72 and 96 hours culture. Y-27632 had no significant effect on the diameter of cultured retinal neurocytes. Compared with the control group, Y-27632 induced a stable improvement of neurite outgrowth of retinal neurocytes after 72 and 96 hours culture (P=0.001).

CONCLUSION

Y-27632 could promote the survival and neurite outgrowth of the early postnatal cultured retinal neurocytes.

Y-39983 downregulates RhoA/Rho-associated kinase expression during its promotion of axonal regeneration

Y-39983, a selective Rho-associated kinase (ROCK) inhibitor, promotes axonal regeneration of damaged retinal ganglion cells (RGCs). The present study investigated the effects of Y-39983 on RhoA/ROCK expression during promotion of axonal regeneration using a rat optic nerve crush (ONC) model. Herein, we demonstrated that Y-39983 significantly enhanced the survival and axonal regeneration of RGCs after ONC. Using a pull‑down assay and affinity precipitation to examine the activity of RhoA, we detected the decreased expression of active-RhoA after using Y-39983. The expression of ROCK1 and ROCK2 was significantly decreased as demonstrated by RT-PCR, immunohistochemistry and western blot analysis. The downregulation of active-RhoA, ROCK1 and ROCK2 expression by Y-39983 coincided with the appearance of larger numbers of regenerating axons. In conclusion, Y-39983 downregulated the expression of active-RhoA, ROCK1 and ROCK2 during its promotion of axonal regeneration.

Rho-independent stimulation of axon outgrowth and activation of the ERK and Akt signaling pathways by C3 transferase in sensory neurons

Peripheral nerve injury triggers the activation of RhoA in spinal motor and peripheral sensory neurons. RhoA activates a number of effector proteins including the Rho-associated kinase, ROCK, which targets the cytoskeleton and leads to inhibition of neurite outgrowth. Blockade of the Rho/ROCK pathway by pharmacological means improves axon regeneration after experimental injury. C3_bot transferase, an exoenzyme produced by Clostridium botulinum, inactivates RhoA by ADP-ribosylation. It has been successfully applied in experimental CNS lesions to facilitate axon regeneration. Up to now it was not investigated thoroughly whether C3_bot exerts positive effects on peripheral axon regeneration as well. In the present study, recombinant membrane permeable C3_bot produced a small, but significant, axon outgrowth effect on peripheral sensory neurons dissociated from adult dorsal root ganglia (DRG) of the rat. Neuronal overexpression of C3, however, did not enhance axonal growth. Moreover, transfection of plasmids encoding dominant negative RhoA or RhoA specific shRNAs failed to increase axonal growth. Furthermore, we show that the C3_bot mutant, C3_E174Q, which lacks RhoA inhibitory activity, still stimulates axonal growth. When analyzing possible signaling mechanisms we found that extracellular signal-regulated kinase (ERK) and Akt are activated by C3_bot and ERK is induced by the C3_E174Q mutant. Upregulation of kinase activities by C3_bot occurs significantly faster than inactivation of RhoA indicating a RhoA-independent pathway of action by C3_bot. The induction of ERK signaling by C3_bot was detected in embryonic hippocampal neurons, too. Taken together, although RhoA plays a central role for inhibition of axon outgrowth by myelin-derived inhibitors, it does not interfere with axonal growth of sensory neurons on a permissive substrate in vitro. C3_bot blocks neuronal RhoA activity, but its positive effects on axon elongation and branching appear to be mediated by Rho independent mechanisms involving activation of axon growth promoting ERK and Akt kinases.

Targeting Rho GTPase signaling for cancer therapy

Accumulating evidence from basic and clinical studies supports the concept that signaling pathways downstream of Rho GTPases play important roles in tumor development and progression. As a result, there has been considerable interest in the possibility that specific proteins in these signal transduction pathways could be potential targets for cancer therapy. A number of inhibitors targeting critical effector proteins, activators or the Rho GTPases themselves, have been developed. We will review the strategies currently being used to develop inhibitors of Rho GTPases and downstream signaling kinases and discuss candidate entities. Although molecularly targeted drugs that inhibit Rho GTPase signaling have not yet been widely adopted for clinical use, their potential value as cancer therapeutics continues to drive considerable pharmaceutical research and development.

Human dental pulp-derived stem cells promote locomotor recovery after complete transection of the rat spinal cord by multiple neuro-regenerative mechanisms

Spinal cord injury (SCI) often leads to persistent functional deficits due to loss of neurons and glia and to limited axonal regeneration after injury. Here we report that transplantation of human dental pulp stem cells into the completely transected adult rat spinal cord resulted in marked recovery of hind limb locomotor functions. Transplantation of human bone marrow stromal cells or skin-derived fibroblasts led to substantially less recovery of locomotor function. The human dental pulp stem cells exhibited three major neuroregenerative activities. First, they inhibited the SCI-induced apoptosis of neurons, astrocytes, and oligodendrocytes, which improved the preservation of neuronal filaments and myelin sheaths. Second, they promoted the regeneration of transected axons by directly inhibiting multiple axon growth inhibitors, including chondroitin sulfate proteoglycan and myelin-associated glycoprotein, via paracrine mechanisms. Last, they replaced lost cells by differentiating into mature oligodendrocytes under the extreme conditions of SCI. Our data demonstrate that tooth-derived stem cells may provide therapeutic benefits for treating SCI through both cell-autonomous and paracrine neuroregenerative activities.

Four steps to optic nerve regeneration

The failure of the optic nerve to regenerate after injury or in neurodegenerative disease remains a major clinical and scientific problem. Retinal ganglion cell (RGC) axons course through the optic nerve and carry all the visual information to the brain, but after injury, they fail to regrow through the optic nerve and RGC cell bodies typically die, leading to permanent loss of vision. There are at least 4 hurdles to overcome in preserving RGCs and regenerating their axons: 1) increase RGC survival, 2) overcome the inhibitory environment of the optic nerve, 3) enhance RGC intrinsic axon growth potential, and 4) optimize the mapping of RGC connections back into their targets in the brain.

Citron kinase controls abscission through RhoA and anillin

The small GTPase RhoA plays a crucial role in the different stages of cytokinesis, including contractile ring formation, cleavage furrow ingression, and midbody abscission. Citron kinase (CIT-K), a protein required for cytokinesis and conserved from insects to mammals, is currently considered a cytokinesis-specific effector of active RhoA. In agreement with previous observations, we show here that, as in Drosophila cells, CIT-K is specifically required for abscission in mammalian cells. However, in contrast with the current view, we provide evidence that CIT-K is an upstream regulator rather than a downstream effector of RhoA during late cytokinesis. In addition, we show that CIT-K is capable of physically and functionally interacting with the actin-binding protein anillin. Active RhoA and anillin are displaced from the midbody in CIT-K-depleted cells, while only anillin, but not CIT-K, is affected if RhoA is inactivated in late cytokinesis. The overexpression of CIT-K and of anillin leads to abscission delay. However, the delay produced by CIT-K overexpression can be reversed by RhoA inactivation, while the delay produced by anillin overexpression is RhoA-independent. Altogether, these results indicate that CIT-K is a crucial abscission regulator that may promote midbody stability through active RhoA and anillin.

The lipid sulfatide is a novel myelin-associated inhibitor of CNS axon outgrowth

CNS myelin is strongly inhibitory to growing axons and is thought to be a major contributor to CNS axon regenerative failure. Although a number of proteins present in myelin, including Nogo, MAG, and oligodendrocyte-myelin glycoprotein (OMgp), have been identified as myelin-associated inhibitors, studies of mice lacking these genes suggest that additional inhibitors present in CNS myelin remain to be identified. Here we have investigated the hypothesis that myelin lipids contribute to CNS regenerative failure. We identified sulfatide, a major constituent of CNS myelin, as a novel myelin-associated inhibitor of neurite outgrowth. Sulfatide, but not galactocerebroside or ceramide, strongly inhibited the neurite outgrowth of retinal ganglion cells (RGCs) when used as a purified lipid substrate. The mechanism involved in sulfatide-mediated inhibition may share features with other known inhibitors, because the Rho inhibitor C3 transferase lessened these effects. Myelin in which sulfatide was lacking or blocked using specific antibodies was significantly less inhibitory to RGC neurite outgrowth in vitro than was wild-type myelin, indicating that sulfatide is a major component of the inhibitory activity of CNS myelin. Mice unable to make sulfatide did not regenerate RGC axons more robustly after optic nerve crush than wild-type littermates under normal conditions but did exhibit a small but significant enhancement in the extent of zymosan-induced regeneration. These results demonstrate that specific lipids can powerfully inhibit axon growth, identify sulfatide as a novel myelin-associated axon growth inhibitor, and provide evidence that sulfatide inhibition contributes to axon regenerative failure in vivo.

Anti-ganglioside antibody-mediated activation of RhoA induces inhibition of neurite outgrowth

Anti-ganglioside antibodies (Abs) are strongly associated with axonal forms of Guillain Barré syndrome (GBS). Some studies indicate that these Abs, including those with GD1a reactivity, are associated with poor prognosis and/or incomplete recovery. We recently demonstrated that a disease-relevant anti-ganglioside Ab with GD1a reactivity inhibits axon regeneration after PNS injury in an animal model (Lehmann et al., 2007). An implication of these findings is that anti-GD1a Abs can mediate inhibition of axon regeneration and limit recovery in some patients with GBS. The downstream inhibitory intracellular signaling that mediates anti-ganglioside Ab-induced axon inhibition remains unclear. In the current study, we show that disease-relevant and GBS patient's anti-ganglioside Abs can inhibit neurite outgrowth in dissociated primary neuronal cultures. Activation of small GTPase RhoA and its key downstream effector Rho kinase (ROCK) are critical mediators of growth cone and neurite outgrowth inhibition. Therefore, we examined the role of these intracellular signaling molecules in our primary neuronal cultures by molecular and pharmacologic approaches. Our results show that the Ab-mediated inhibition of neurite outgrowth involves the activation of RhoA and ROCK pathway and this activation is through the engagement of specific cell-surface gangliosides by Abs. In summary, these studies directly link patient autoantibodies to an intracellular inhibitory signaling pathway involved in anti-ganglioside Ab-mediated inhibition of neurite outgrowth.

Sustained delivery of activated Rho GTPases and BDNF promotes axon growth in CSPG-rich regions following spinal cord injury

BACKGROUND

Spinal cord injury (SCI) often results in permanent functional loss. This physical trauma leads to secondary events, such as the deposition of inhibitory chondroitin sulfate proteoglycan (CSPG) within astroglial scar tissue at the lesion.

METHODOLOGY/PRINCIPAL FINDINGS

We examined whether local delivery of constitutively active (CA) Rho GTPases, Cdc42 and Rac1 to the lesion site alleviated CSPG-mediated inhibition of regenerating axons. A dorsal over-hemisection lesion was created in the rat spinal cord and the resulting cavity was conformally filled with an in situ gelling hydrogel combined with lipid microtubes that slowly released constitutively active (CA) Cdc42, Rac1, or Brain-derived neurotrophic factor (BDNF). Treatment with BDNF, CA-Cdc42, or CA-Rac1 reduced the number of GFAP-positive astrocytes, as well as CSPG deposition, at the interface of the implanted hydrogel and host tissue. Neurofilament 160kDa positively stained axons traversed the glial scar extensively, entering the hydrogel-filled cavity in the treatments with BDNF and CA-Rho GTPases. The treated animals had a higher percentage of axons from the corticospinal tract that traversed the CSPG-rich regions located proximal to the lesion site.

CONCLUSION

Local delivery of CA-Cdc42, CA-Rac1, and BDNF may have a significant therapeutic role in overcoming CSPG-mediated regenerative failure after SCI.

The effects of combining chondroitinase ABC and NEP1-40 on the corticospinal axon growth in organotypic co-cultures

The area surrounding the injured spinal cord is a non-permissive milieu for axonal growth due to the inhibitory factors, especially chondroitin sulfate proteoglycan (CSPG) and Nogo. Recent studies have reported that chondroitinase ABC (ChABC) or Nogo-66(1-40) antagonist peptide (NEP1-40) promote axonal growth after spinal cord injury. But no study has addressed the effects on spinal cord injury of combining ChABC and NEP1-40. Previously, we described an organotypic co-culture system using the brain cortex and spinal cord from neonatal rats. In this study, we examined whether the combination of ChABC and NEP1-40 creates an action that promotes corticospinal axon growth in organotypic co-cultures. Organotypic co-cultures of brain and spinal cord were prepared from rats, and ChABC or NEP1-40 was delivered to them. To examine the effects of this combination these two drugs were applied together. We counted the number of labeled axons with DiI and assessed the immunoreactivity of CSPG and Nogo. Axonal growth was enhanced by infusing ChABC or NEP1-40 compared with that in the control group, whereas synergistic effects of combined administration of ChABC and NEP1-40 on axonal growth were not observed. There is a possibility that ChABC and NEP1-40 affect the same intracellular pathways and have no synergistic influence on axonal growth.

Spinal interneuron axons spontaneously regenerate after spinal cord injury in the adult feline

It is well established that long, descending axons of the adult mammalian spinal cord do not regenerate after a spinal cord injury (SCI). These axons do not regenerate because they do not mount an adequate regenerative response and growth is inhibited at the injury site by growth cone collapsing molecules, such as chondroitin sulfate proteoglycans (CSPGs). However, whether axons of axotomized spinal interneurons regenerate through the inhibitory environment of an SCI site remains unknown. Here, we show that cut axons from adult mammalian spinal interneurons can regenerate through an SCI site and form new synaptic connections in vivo. Using morphological and immunohistochemical analyses, we found that after a midsagittal transection of the adult feline spinal cord, axons of propriospinal commissural interneurons can grow across the lesion despite a close proximity of their growth cones to CSPGs. Furthermore, using immunohistochemical and electrophysiological analyses, we found that the regenerated axons conduct action potentials and form functional synaptic connections with motoneurons, thus providing new circuits that cross the transected commissures. Our results show that interneurons of the adult mammalian spinal cord are capable of spontaneous regeneration after injury and suggest that elucidating the mechanisms that allow these axons to regenerate may lead to useful new therapeutic strategies for restoring function after injury to the adult CNS.

Ibuprofen enhances recovery from spinal cord injury by limiting tissue loss and stimulating axonal growth

The GTP-binding protein RhoA regulates microfilament dynamics in many cell types and mediates the inhibition of axonal regeneration by myelin and chondroitin sulfate proteoglycans. Unlike most other nonsteroidal anti-inflammatory drugs, ibuprofen suppresses basal RhoA activity (Zhou et al., 2003). A recent report suggested that ibuprofen promotes corticospinal axon regeneration after spinal cord injury (Fu et al., 2007). Here, we confirm that ibuprofen reduces ligand-induced Rho signaling and myelin-induced inhibition of neurite outgrowth in vitro. Following 4 weeks of subcutaneous administration of ibuprofen, beginning 3 days after spinal cord contusion, animals recovered walking function to a greater degree, with twice as many rats achieving a hind limb weight-bearing status. We examined the relative role of tissue sparing, axonal sprouting, and axonal regeneration in the action of ibuprofen. Histologically, ibuprofen-treated animals display an increase in spared tissue without an alteration in astrocytic or microglial reaction. Ibuprofen increases axonal sprouting from serotonergic raphespinal axons, and from rostral corticospinal fibers in the injured spinal cord, but does not permit caudal corticospinal regeneration after spinal contusion. Treatment of mice with complete spinal cord transection demonstrates long-distance raphespinal axon regeneration in the presence of ibuprofen. Thus, administration of ibuprofen improves the recovery of rats from a clinically relevant spinal cord trauma by protecting tissue, stimulating axonal sprouting, and allowing a minor degree of raphespinal regeneration.

New perspectives for the treatment options in spinal cord injury

Spinal cord injury (SCI) is a serious clinical disorder that leads to lifetime disability for which no suitable therapeutic agents are available so far. Further research is needed to understand the basic mechanisms of spinal cord pathology that results in permanent disability and poses a heavy burden on our society. In the past, a lot of effort was placed on improving functional outcome with the help of various therapeutic agents, however less attention has been paid on the development and propagation of spinal cord pathology over time. Thus, it is still unclear whether improvement of functional outcome is related to spinal cord pathology or vice versa. Few drugs are able to influence functional outcome without having any improvement on cord pathology. Some drugs, however, can lessen cord pathology but fail to influence the functional outcome. The goal of future treatment options for SCI is therefore to find suitable new drugs or a combination of existing drugs and to use various cellular transplants, neurotrophic factors, myelin-inhibiting factors, tissue engineering and nano-drug delivery to improve both the functional and the pathological outcome in the inured patient. This review deals with the key aspects of the latest treatments for SCI and suggests some possible future therapeutic measures to enhance healthcare in clinical situations.

Rho inhibition recruits DCC to the neuronal plasma membrane and enhances axon chemoattraction to netrin 1

Molecular cues, such as netrin 1, guide axons by influencing growth cone motility. Rho GTPases are a family of intracellular proteins that regulate the cytoskeleton, substrate adhesion and vesicle trafficking. Activation of the RhoA subfamily of Rho GTPases is essential for chemorepellent axon guidance; however, their role during axonal chemoattraction is unclear. Here, we show that netrin 1, through its receptor DCC, inhibits RhoA in embryonic spinal commissural neurons. To determine whether netrin 1-mediated chemoattraction requires Rho function, we inhibited Rho signaling and assayed axon outgrowth and turning towards netrin 1. Additionally, we examined two important mechanisms that influence the guidance of axons to netrin 1: substrate adhesion and transport of the netrin receptor DCC to the plasma membrane. We found that inhibiting Rho signaling increased plasma membrane DCC and adhesion to substrate-bound netrin 1, and also enhanced netrin 1-mediated axon outgrowth and chemoattractive axon turning. Conversely, overexpression of RhoA or constitutively active RhoA inhibited axonal responses to netrin 1. These findings provide evidence that Rho signaling reduces axonal chemoattraction to netrin 1 by limiting the amount of plasma membrane DCC at the growth cone, and suggest that netrin 1-mediated inhibition of RhoA activates a positive-feedback mechanism that facilitates chemoattraction to netrin 1. Notably, these findings also have relevance for CNS regeneration research. Inhibiting RhoA promotes axon regeneration by disrupting inhibitory responses to myelin and the glial scar. By contrast, we demonstrate that axon chemoattraction to netrin 1 is not only maintained but enhanced, suggesting that this might facilitate directing regenerating axons to appropriate targets.

Inhibition of the Rho/ROCK pathway reduces apoptosis during transplantation of embryonic stem cell-derived neural precursors

Rho-GTPase has been implicated in the apoptosis of many cell types, including neurons, but the mechanism by which it acts is not fully understood. Here, we investigate the roles of Rho and ROCK in apoptosis during transplantation of embryonic stem cell-derived neural precursor cells. We find that dissociation of neural precursors activates Rho and induces apoptosis. Treatment with the Rho inhibitor C3 exoenzyme and/or the ROCK inhibitor Y-27632 decreases the amount of dissociation-induced apoptosis (anoikis) by 20-30%. Membrane blebbing, which is an early morphological sign of apoptosis; cleavage of caspase-3; and release of cytochrome c from the mitochondria are also reduced by ROCK inhibition. These results suggest that dissociation of neural precursor cells elicits an intrinsic pathway of cell death that is at least partially mediated through the Rho/ROCK pathway. Moreover, in an animal transplantation model, inhibition of Rho and/or ROCK suppresses acute apoptosis of grafted cells. After transplantation, tumor necrosis factor-alpha and pro-nerve growth factor are strongly expressed around the graft. ROCK inhibition also suppresses apoptosis enhanced by these inflammatory cytokines. Taken together, these results indicate that inhibition of Rho/ROCK signaling may improve survival of grafted cells in cell replacement therapy.

Emerging drugs for spinal cord injury

BACKGROUND

This review summarizes several promising pharmacological approaches for the therapeutic management of traumatic spinal cord injury (SCI), which are either in early-phase clinical trials or nearing clinical translation.

OBJECTIVE

This review provides the reader with an understanding of the key pathophysiological mechanisms that contribute to neurological deficits after SCI. Through discussion of the mechanism(s) of action of the selected therapeutic approaches potentially important targets to aid further drug discovery will be highlighted.

METHODS

Systematic literature review of the pre-clinical literature and clinical SCI trials related to neuroprotective, immunomodulatory and regenerative therapeutic approaches.

RESULTS/CONCLUSION

The next decade will witness an unprecedented number of clinical trials which will seek to translate key biomedical research discoveries. The promising drug-based therapeutic approaches include regenerative strategies to neutralize myelin-mediated neurite outgrowth inhibition, neuroprotective strategies to reduce apoptotic triggers, the targeting of cationic/glutamatergic toxicity, anti-inflammatory strategies and the use of approaches to stabilize disrupted cell membranes.

Cellular uptake mechanisms and potential therapeutic utility of peptidic cell delivery vectors: progress 2001-2006

Cell delivery vectors (CDVs) are short amphipathic and cationic peptides and peptide derivatives, usually containing multiple lysine and arginine residues. They possess inherent membrane activity and can be conjugated or complexed with large impermeable macromolecules and even microscopic particles to facilitate cell entry. Various mechanisms have been proposed but it is now becoming clear that the main port of entry into cells of such CDV constructs involves adsorptive-mediated endocytosis rather than direct penetration of the plasma membrane. It is still unclear, however, how and to what extent CDV constructs are capable of exiting endosomal compartments and reaching their intended cellular site of action, usually the cytosol or the nucleus. Furthermore, although many CDVs can mediate cellular uptake of their cargo and appear comparatively non-toxic to cells in tissue culture, the utility of CDVs for in vivo applications remains poorly understood. Whatever the mechanisms of cell entry and disposition, the overriding question as far as potential pharmacological application of CDV conjugates is concerned is whether or not a therapeutic margin can be achieved by their administration. Such a margin will only result if the intracellular concentration in the target tissues necessary to elicit the biological effect of the CDV cargo can be achieved at systemic CDV exposure levels that are non-toxic to both target and bystander cells. It is proposed that the focus of CDV research now be shifted from mechanistic in vitro studies with labeled but otherwise unconjugated CDVs to in vivo pharmacological and toxicological studies using CDV-derivatized and other cationized forms of inherently non-permeable macromolecules of true therapeutic interest.

Integrin signaling is integral to regeneration

The inability of the adult injured mammalian spinal cord to successfully regenerate is not well understood. Studies suggest that both extrinsic and intrinsic factors contribute to regeneration failure. In this review, we focus on intrinsic factors that impact regeneration, in particular integrin receptors and their downstream signaling pathways. We discuss studies that address the impact of integrins and integrin signaling pathways on growth cone guidance and motility and how lessons learned from these studies apply to spinal cord regeneration in vivo.

Purkinje cell survival in organotypic cultures: Implication of Rho and its downstream effector ROCK

Organotypic cultures of postnatal day 1 (P1) to P7 mouse cerebella are well-established models for studying cell survival. In the present work, we investigate the involvement of the Rho/ROCK intracellular pathway in Purkinje cell survival by using organotypic cultures of P3 Swiss mice. Specific inhibitors of Rho or ROCK were applied at different concentrations to the slice cultures, which were maintained for 5 days in vitro. We show that the bacterial exoenzyme C3 transferase, a specific inhibitor of the small GTPase Rho, increases Purkinje cell survival. There is a 4.5- and 2.5-fold increase in Purkinje cell survival when C3 intracellular uptake is promoted either by the PEP-1 peptide or by the C2IN carrier protein, respectively, and not with the commonly used TAT peptide. Moreover, treatment with Y27632 and H-1152, two specific inhibitors of the Rho kinase ROCK, also strongly reduces apoptotic cell death and results in 6.5- and 8.5-fold increases in cell survival, respectively. In immunohistochemical analysis, we also show that H-1152 did not change either glial fibrillary acidic protein or isolectin-B4 staining, indicating that this compound did not alter the cellular composition in our cultures. Thus, our data demonstrate that inhibition of Rho and its downstream effector ROCK may be used to enhance cell survival in neurodegenerative diseases.

The pivotal role of RhoA GTPase in the molecular signaling of axon growth inhibition after CNS injury and targeted therapeutic strategies

The dogma that the adult central nervous system (CNS) is nonpermissive to axonal regeneration is beginning to fall in the face of increased understanding of the molecular and cellular biology of axon outgrowth. It is now appreciated that axon growth is regulated by a combination of extracellular factors related to the milieu of the developing or adult CNS and the presence of injury, and intracellular factors related to the "growth state" of the developing or regenerating neuron. Several critical points of convergence within the developing or regenerating neuron for mediating intracellular cell signaling effects on the growth cone cytoskeleton have been identified, and their modulation has produced marked increases in axon outgrowth within the "nonpermissive" milieu of the adult injured CNS. One such critical convergence point is the small GTPase RhoA, which integrates signaling events produced by both myelin-associated inhibitors (e.g., NogoA) and astroglial-derived inhibitors (chondroitin sulfate proteoglycans) and regulates the activity of downstream effectors that modulate cytoskeletal dynamics within the growth cone mediating axon outgrowth or retraction. Inhibition of RhoA has been associated with increased outgrowth on nonpermissive substrates in vitro and increased axon regeneration in vivo. We are developing lentiviral vectors that modulate RhoA activity, allowing more long-term expression than is possible with current approaches. These vectors may be useful in regenerative strategies for spinal cord injury, brain injury, and neurodegenerative diseases including Parkinson's disease, Alzheimer's disease, and Huntington's disease.

Myelin-associated inhibitory signaling and strategies to overcome inhibition

Numerous studies in the last two decades have resulted in significant progress in our understanding of the role of inhibitors on axonal regeneration and conditions that influence mature neurons to regrow in an inhibitory environment. These studies have revealed putative therapeutic targets and strategies to interfere in the inhibitory signaling cascade and promote axonal regeneration. Some agents that were successful in animal models are now being tested in human patients. All of these advances have raised hope of a cure for an injury that was once thought to be 'an ailment for which nothing is done' (Quote from Edwin Smith surgical papyrus, 1600BC).

How does chondroitinase promote functional recovery in the damaged CNS?

A number of recent studies have established that the bacterial enzyme chondroitinase ABC promotes functional recovery in the injured CNS. The issue of how it works is rarely addressed, however. The effects of the enzyme are presumed to be due to the degradation of inhibitory chondroitin sulphate GAG chains. Here we review what is known about the composition, structure and distribution of the extracellular matrix in the CNS, and how it changes in response to injury. We summarize the data pertaining to the ability of chondroitinase to promote functional recovery, both in the context of axon regeneration and the reactivation of plasticity. We also present preliminary data on the persistence of the effects of the enzyme in vivo, and its hyaluronan-degrading activity in CNS homogenates in vitro. We then consider precisely how the enzyme might influence functional recovery in the CNS. The ability of chondroitinase to degrade hyaluronan is likely to result in greater matrix disruption than the degradation of chondroitin sulphate alone.

A role for Nogo receptor in macrophage clearance from injured peripheral nerve

We report a role for Nogo receptors (NgRs) in macrophage efflux from sites of inflammation in peripheral nerve. Increasing numbers of macrophages in crushed rat sciatic nerves express NgR1 and NgR2 on the cell surface in the first week after injury. These macrophages show reduced binding to myelin and MAG in vitro, which is reversed by NgR siRNA knockdown and by inhibiting Rho-associated kinase. Fourteen days after sciatic nerve crush, regenerating nerves with newly synthesized myelin have fewer macrophages than cut/ligated nerves that lack axons and myelin. Almost all macrophages in the cut/ligated nerves lie within the Schwann cell basal lamina, while in the crushed regenerating nerves the majority migrate out. Furthermore, crush-injured nerves of NgR1- and MAG-deficient mice and Y-27632-treated rats show impaired macrophage efflux from Schwann cell basal lamina containing myelinated axons. These data have implications for the resolution of inflammation in peripheral nerve and CNS pathologies.

Recapitulate development to promote axonal regeneration: good or bad approach?

In the past decade there has been an explosion in our understanding, at the molecular level, of why axons in the adult, mammalian central nervous system (CNS) do not spontaneously regenerate while their younger counterparts do. Now a number of inhibitors of axonal regeneration have been described, some of the receptors they interact with to transduce the inhibitory signal are known, as are some of the steps in the signal transduction pathway that is responsible for inhibition. In addition, developmental changes in the environment and in the neurons themselves are also now better understood. This knowledge in turn reveals novel, putative sites for drug development and therapeutic intervention after injury to the brain and spinal cord. The challenge now is to determine which of these putative treatments are the most effective and if they would be better applied in combination rather than alone. In this review I will summarize what we have learnt about these molecules and how they signal. Importantly, I will also describe approaches that have been shown to block inhibitors and encourage regeneration in vivo. I will also speculate on what the differences are between the neonatal and adult CNS that allow the former to regenerate and the latter not to.

Structural and functional recovery elicited by combined putrescine and aminoguanidine treatment after aspirative lesion of the fimbria-fornix and overlying cortex in the adult rat

Damage to the adult CNS often causes permanent deficits. Based on a lesion model of septohippocampal pathway aspiration in the rat, we attempted to promote neuronal cell survival and post-traumatic recovery by using a pharmacological treatment combining aminoguanidine and putrescine (AGP). The functional recovery was followed over 15 weeks before morphological analysis. AGP treatment produced a persistent attenuation (approximately 50%) of the lesion-induced hyperactivity, a reduction (approximately 60%) in the sensorimotor impairments and an improved performance in the water-maze task which did not, however, rely upon improved memory capabilities. AGP weakened the lesion-induced decrease in ChAT-positive neurons in the medial septum and the extent of thalamic retrograde necrosis (by approximately 30% in each case) and resulted in a partial cholinergic reinnervation of the dentate gyrus. These promising results support the idea that coadministration of putrescine and aminoguanidine might become a potent way to foster structural and functional recovery (or compensation) in the adult mammalian CNS after injury.