Minimal essential length of Clostridium botulinum C3 peptides to enhance neuronal regenerative growth and connectivity in a non-enzymatic mode

Clostridium botulinum C3bot mediated effects on cytokine-induced psoriasis-like phenotype in full-thickness skin model

Clostridium botulinum C3 exoenzyme (C3bot) exclusively inhibits RhoA, B and C by ADP-ribosylation and is therefore used as a cell-permeable tool for investigating the cellular role of these Rho-GTPases. Rho-GTPases represent a molecular switch integrating different receptor signalling to downstream cascades including transcriptional cascades that regulate various cellular processes, such as regulation of actin cytoskeleton and cell proliferation. C3bot-induced inhibition of RhoA leads to reorganization of the actin cytoskeleton, morphological changes, and inhibition of cell proliferation as well as modulation of inflammatory response. In this study, we characterized the C3bot-mediated effects on a full-thickness skin model exhibiting a psoriasis-like phenotype through the addition of cytokines. Indeed, after the addition of cytokines, a decrease in epidermal thickness, parakeratosis, and induction of IL-6 was detected. In the next step, it was studied whether C3bot caused a reduction in the cytokine-induced psoriasis-like phenotypes. Basal addition of C3bot after cytokine induction of the full-thickness skin models caused less epidermal thinning and reduced IL-6 abundance. Simultaneous basal incubation with cytokines and C3bot, IL-6 abundance was inhibited, but epidermal thickness was only moderately affected. When C3bot was added apically to the skin model, IL-6 abundance was reduced, but no further effects on the psoriasis-like phenotype of the epidermis were observed. In summary, C3bot inhibits the cytokine-induced expression of IL-6 and thus may have an impact on the pro-inflammatory immune response in the psoriasis-like phenotype.

Enhancement of Phosphorylation and Transport Activity of the Neuronal Glutamate Transporter Excitatory Amino Acid Transporter 3 by C3bot and a 26mer C3bot Peptide

In primary murine hippocampal neurons we investigated the regulation of EAAT3-mediated glutamate transport by the Clostridium botulinum C3 transferase C3bot and a 26mer peptide derived from full length protein. Incubation with either enzyme-competent C3bot or enzyme-deficient C3bot156–181 peptide resulted in the upregulation of glutamate uptake by up to 22% compared to untreated cells. A similar enhancement of glutamate transport was also achieved by the classical phorbol-ester-mediated activation of protein kinase C subtypes. Yet comparable, effects elicited by C3 preparations seemed not to rely on PKCα, γ, ε, or ζ activation. Blocking of tyrosine phosphorylation by tyrosine kinase inhibitors prevented the observed effect mediated by C3bot and C3bot 26mer. By using biochemical and molecular biological assays we could rule out that the observed C3bot and C3bot 26mer-mediated effects solely resulted from enhanced transporter expression or translocation to the neuronal surface but was rather mediated by transporter phosphorylation at tyrosine residues that was found to be significantly enhanced following incubation with either full length protein or the 26mer C3 peptide.

Integrin Signaling in the Central Nervous System in Animals and Human Brain Diseases

The integrin family is involved in various biological functions, including cell proliferation, differentiation and migration, and also in the pathogenesis of disease. Integrins are multifunctional receptors that exist as heterodimers composed of α and β subunits and bind to various ligands, including extracellular matrix (ECM) proteins; they are found in many animals, not only vertebrates (e.g., mouse, rat, and teleost fish), but also invertebrates (e.g., planarian flatworm, fruit fly, nematodes, and cephalopods), which are used for research on genetics and social behaviors or as models for human diseases. In the present paper, we describe the results of a phylogenetic tree analysis of the integrin family among these species. We summarize integrin signaling in teleost fish, which serves as an excellent model for the study of regenerative systems and possesses the ability for replacing missing tissues, especially in the central nervous system, which has not been demonstrated in mammals. In addition, functions of astrocytes and reactive astrocytes, which contain neuroprotective subpopulations that act in concert with the ECM proteins tenascin C and osteopontin via integrin are also reviewed. Drug development research using integrin as a therapeutic target could result in breakthroughs for the treatment of neurodegenerative diseases and brain injury in mammals.

Potentiation of Brain-Derived Neurotrophic Factor-Induced Protection of Spiral Ganglion Neurons by C3 Exoenzyme/Rho Inhibitor

Preservation of the excitability of spiral ganglion neurons (SGN) may contribute to an improved speech perception after cochlear implantation. Thus, the application of exogenous neurotrophic factors such as the neurotrophin brain-derived neurotrophic factor (BDNF) to increase SGN survival in vitro and in vivo is a promising pharmacological approach in cochlear implant (CI) research. Due to the difficult pharmacokinetic profile of proteins such as BDNF, there is a quest for small molecules to mediate the survival of SGN or to increase the efficacy of BDNF. The C3 exoenzyme from Clostridium botulinum could be a potential new candidate for the protection and regeneration of SGN. Inhibition of the RhoA GTPase pathway which can be mediated by C3 is described as a promising strategy to enhance axonal regeneration and to exert pro-survival signals in neurons. Nanomolar concentrations of C3, its enzymatically inactive form C3^E174Q, and a 26mer C-terminal peptide fragment covering amino acid 156–181 (C3^156-181) potentiated the neuroprotective effect on SGN mediated by BDNF in vitro. The neuroprotective effect of C3/BDNF was reduced to the neuroprotective effect of BDNF alone after the treatment with wortmannin, an inhibitor of the phosphatidylinositol-3-kinase (PI3K).The exoenzyme C3 (wild-type and enzyme-deficient) and the C3 peptide fragment C3^154–181 present novel biologically active compounds for the protection of the SGN. The exact underlying intracellular mechanisms that mediate the neuroprotective effect are not clarified yet, but the combination of BDNF (TrkB stimulation) and C3 exoenzyme (RhoA inhibition) can be used to protect SGN in vitro.

The Higher Sensitivity of GABAergic Compared to Glutamatergic Neurons to Growth-Promoting C3bot Treatment Is Mediated by Vimentin

The current study investigates the neurotrophic effects of Clostridium botulinum C3 transferase (C3bot) on highly purified, glia-free, GABAergic, and glutamatergic neurons. Incubation with nanomolar concentrations of C3bot promotes dendrite formation as well as dendritic and axonal outgrowth in rat GABAergic neurons. A comparison of C3bot effects on sorted mouse GABAergic and glutamatergic neurons obtained from newly established NexCre;Ai9xVGAT Venus mice revealed a higher sensitivity of GABAergic cells to axonotrophic and dendritic effects of C3bot in terms of process length and branch formation. Protein biochemical analysis of known C3bot binding partners revealed comparable amounts of β1 integrin in both cell types but a higher expression of vimentin in GABAergic neurons. Accordingly, binding of C3bot to GABAergic neurons was stronger than binding to glutamatergic neurons. A combinatory treatment of glutamatergic neurons with C3bot and vimentin raised the amount of bound C3bot to levels comparable to the ones in GABAergic neurons, thereby confirming the specificity of effects. Overall, different surface vimentin levels between GABAergic and glutamatergic neurons exist that mediate neurotrophic C3bot effects.

SCISSOR-Spinal Cord Injury Study on Small molecule-derived Rho inhibition: a clinical study protocol

INTRODUCTION

The approved analgesic and anti-inflammatory drugs ibuprofen and indometacin block the small GTPase RhoA, a key enzyme that impedes axonal sprouting after axonal damage. Inhibition of the Rho pathway in a central nervous system-effective manner requires higher dosages compared with orthodox cyclooxygenase-blocking effects. Preclinical studies on spinal cord injury (SCI) imply improved motor recovery after ibuprofen/indometacin-mediated Rho inhibition. This has been reassessed by a meta-analysis of the underlying experimental evidence, which indicates an overall effect size of 20.2% regarding motor outcome achieved after ibuprofen/indometacin treatment compared with vehicle controls. In addition, ibuprofen/indometacin may also limit sickness behaviour, non-neurogenic systemic inflammatory response syndrome (SIRS), neuropathic pain and heterotopic ossifications after SCI. Consequently, 'small molecule'-mediated Rho inhibition after acute SCI warrants clinical investigation.

METHODS AND ANALYSIS

Protocol of an investigator-initiated clinical open-label pilot trial on high-dose ibuprofen treatment after acute traumatic, motor-complete SCI. A sample of n=12 patients will be enrolled in two cohorts treated with 2400 mg/day ibuprofen for 4 or 12 weeks, respectively. The primary safety end point is an occurrence of serious adverse events, primarily gastroduodenal bleedings. Secondary end points are pharmacokinetics, feasibility and preliminary effects on neurological recovery, neuropathic pain and heterotopic ossifications. The primary safety analysis is based on the incidence of severe gastrointestinal bleedings. Additional analyses will be mainly descriptive and casuistic.

ETHICS AND DISSEMINATION

The clinical trial protocol was approved by the responsible German state Ethics Board, and the Federal Institute for Drugs and Medical Devices. The study complies with the Declaration of Helsinki, the principles of Good Clinical Practice and all further applicable regulations. This safety and pharmacokinetics trial informs the planning of a subsequent randomised controlled trial. Regardless of the result of the primary and secondary outcome assessments, the clinical trial will be reported as a publication in a peer-reviewed journal.

TRIAL REGISTRATION NUMBER

NCT02096913; Pre-results.

Mast cells promote scar remodeling and functional recovery after spinal cord injury via mouse mast cell protease 6

An important barrier for axon regeneration and recovery after traumatic spinal cord injury (SCI) is attributed to the scar that is formed at the lesion site. Here, we investigated the effect of mouse mast cell protease (mMCP) 6, a mast cell (MC)-specific tryptase, on scarring and functional recovery after a spinal cord hemisection injury. Functional recovery was significantly impaired in both MC-deficient and mMCP6-knockout (mMCP6(-/-)) mice after SCI compared with wild-type control mice. This decrease in locomotor performance was associated with an increased lesion size and excessive scarring at the injury site. Axon growth-inhibitory chondroitin sulfate proteoglycans and the extracellular matrix components fibronectin, laminin, and collagen IV were significantly up-regulated in MC-deficient and mMCP6(-/-) mice, with an increase in scar volume between 23 and 32%. A degradation assay revealed that mMCP6 directly cleaves fibronectin and collagen IV in vitro In addition, gene expression levels of the scar components fibronectin, aggrecan, and collagen IV were increased up to 6.8-fold in mMCP6(-/-) mice in the subacute phase after injury. These data indicate that endogenous mMCP6 has scar-suppressing properties after SCI via indirect cleavage of axon growth-inhibitory scar components and alteration of the gene expression profile of these factors.-Vangansewinkel, T., Geurts, N., Quanten, K., Nelissen, S., Lemmens, S., Geboes, L., Dooley, D., Vidal, P. M., Pejler, G., Hendrix, S. Mast cells promote scar remodeling and functional recovery after spinal cord injury via mouse mast cell protease 6.

Clostridial C3 Toxins Target Monocytes/Macrophages and Modulate Their Functions

The C3 enzymes from Clostridium (C.) botulinum (C3bot) and Clostridium limosum (C3lim) are single chain protein toxins of about 25 kDa that mono-ADP-ribosylate Rho-A, -B, and -C in the cytosol of mammalian cells. We discovered that both C3 proteins are selectively internalized into the cytosol of monocytes and macrophages by an endocytotic mechanism, comparable to bacterial AB-type toxins, while they are not efficiently taken up into the cytosol of other cell types including epithelial cells and fibroblasts. C3-treatment results in disturbed macrophage functions, such as migration and phagocytosis, suggesting a novel function of clostridial C3 toxins as virulence factors, which selectively interfere with these immune cells. Moreover, enzymatic inactive C3 protein serves as a transport system to selectively deliver pharmacologically active molecules into the cytosol of monocytes/macrophages without damaging these cells. This review addresses also the generation of C3-based molecular tools for experimental macrophage pharmacology and cell biology as well as the exploitation of C3 for development of novel therapeutic strategies against monocyte/macrophage-associated diseases.

Absence of IL-1β positively affects neurological outcome, lesion development and axonal plasticity after spinal cord injury

Precise crosstalk between the nervous and immune systems is important for neuroprotection and axon plasticity after injury. Recently, we demonstrated that IL-1β acts as a potent inducer of neurite outgrowth from organotypic brain slices in vitro, suggesting a potential function of IL-1β in axonal plasticity. Here, we have investigated the effects of IL-1β on axon plasticity during glial scar formation and on functional recovery in a mouse model of spinal cord compression injury (SCI). We used an IL-1β deficiency model (IL-1βKO mice) and administered recombinant IL-1β. In contrast to our hypothesis, the histological analysis revealed a significantly increased lesion width and a reduced number of corticospinal tract fibers caudal to the lesion center after local application of recombinant IL-1β. Consistently, the treatment significantly worsened the neurological outcome after SCI in mice compared with PBS controls. In contrast, the absence of IL-1β in IL-1βKO mice significantly improved recovery from SCI compared with wildtype mice. Histological analysis revealed a smaller lesion size, reduced lesion width and greatly decreased astrogliosis in the white matter, while the number of corticospinal tract fibers increased significantly 5 mm caudal to the lesion in IL-1βKO mice relative to controls. Our study for the first time characterizes the detrimental effects of IL-1β not only on lesion development (in terms of size and glia activation), but also on the plasticity of central nervous system axons after injury.

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.