Specific inhibition of the JNK pathway promotes locomotor recovery and neuroprotection after mouse spinal cord injury

In toto imaging of glial JNK signaling during larval zebrafish spinal cord regeneration

Identification of signaling events that contribute to innate spinal cord regeneration in zebrafish can uncover new targets for modulating injury responses of the mammalian central nervous system. Using a chemical screen, we identify JNK signaling as a necessary regulator of glial cell cycling and tissue bridging during spinal cord regeneration in larval zebrafish. With a kinase translocation reporter, we visualize and quantify JNK signaling dynamics at single-cell resolution in glial cell populations in developing larvae and during injury-induced regeneration. Glial JNK signaling is patterned in time and space during development and regeneration, decreasing globally as the tissue matures and increasing in the rostral cord stump upon transection injury. Thus, dynamic and regional regulation of JNK signaling help to direct glial cell behaviors during innate spinal cord regeneration.

Mechanisms and repair strategies for white matter degeneration in CNS injury and diseases

White matter degeneration is an important pathophysiological event of the central nervous system that is collectively characterized by demyelination, oligodendrocyte loss, axonal degeneration and parenchymal changes that can result in sensory, motor, autonomic and cognitive impairments. White matter degeneration can occur due to a variety of causes including trauma, neurotoxic exposure, insufficient blood flow, neuroinflammation, and developmental and inherited neuropathies. Regardless of the etiology, the degeneration processes share similar pathologic features. In recent years, a plethora of cellular and molecular mechanisms have been identified for axon and oligodendrocyte degeneration including oxidative damage, calcium overload, neuroinflammatory events, activation of proteases, depletion of adenosine triphosphate and energy supply. Extensive efforts have been also made to develop neuroprotective and neuroregenerative approaches for white matter repair. However, less progress has been achieved in this area mainly due to the complexity and multifactorial nature of the degeneration processes. Here, we will provide a timely review on the current understanding of the cellular and molecular mechanisms of white matter degeneration and will also discuss recent pharmacological and cellular therapeutic approaches for white matter protection as well as axonal regeneration, oligodendrogenesis and remyelination.

JNK3 as Therapeutic Target and Biomarker in Neurodegenerative and Neurodevelopmental Brain Diseases

The c-Jun N-terminal kinase 3 (JNK3) is the JNK isoform mainly expressed in the brain. It is the most responsive to many stress stimuli in the central nervous system from ischemia to Aβ oligomers toxicity. JNK3 activity is spatial and temporal organized by its scaffold protein, in particular JIP-1 and β-arrestin-2, which play a crucial role in regulating different cellular functions in different cellular districts. Extensive evidence has highlighted the possibility of exploiting these adaptors to interfere with JNK3 signaling in order to block its action. JNK plays a key role in the first neurodegenerative event, the perturbation of physiological synapse structure and function, known as synaptic dysfunction. Importantly, this is a common mechanism in many different brain pathologies. Synaptic dysfunction and spine loss have been reported to be pharmacologically reversible, opening new therapeutic directions in brain diseases. Being JNK3-detectable at the peripheral level, it could be used as a disease biomarker with the ultimate aim of allowing an early diagnosis of neurodegenerative and neurodevelopment diseases in a still prodromal phase.

Motor neuron loss in SMA is not associated with somal stress-activated JNK/c-Jun signaling

A pathological hallmark of spinal muscular atrophy (SMA) is severe motor neuron (MN) loss, which results in muscle weakness and often infantile or childhood mortality. Although it is well established that deficient expression of survival motor neuron (SMN) protein causes SMA, the molecular pathways that execute MN cell death are poorly defined. The c-Jun NH2-terminal kinases (JNKs) are stress-activated kinases with multiple substrates including c-Jun, which can be activated during neuronal injury and neurodegenerative disease leading to neuronal apoptosis. Recently, increased JNK-c-Jun signaling was reported in SMA raising the possibility that JNK inhibitors could be a novel treatment for this disease. We examined JNK-c-Jun activity in SMA mouse and human cultured cells and tissues. Anisomycin treatment of human SMA fibroblasts and sciatic nerve ligation in SMA mice provoked robust phosphorylated-c-Jun (p-c-Jun) expression indicating that SMN-deficiency does not prevent activation of the stress-induced JNK-c-Jun signaling pathway. Despite retained capacity to activate JNK-c-Jun, we observed no basal increase of p-c-Jun levels in SMA compared to control cultured cells, human or mouse spinal cord tissues, or mouse MNs during the period of MN loss in severe SMA model mice. In both controls and SMA, ~50% of α-MN nuclei express p-c-Jun with decreasing expression during the early postnatal period. Together these studies reveal no evidence of stress-activated JNK-c-Jun signaling in MNs of SMA mice or human tissues, but do highlight the important role of JNK-c-Jun activity during normal MN development raising caution about JNK antagonism in this pediatric neuromuscular disease.

Cationic Arginine-Rich Peptides (CARPs): A Novel Class of Neuroprotective Agents With a Multimodal Mechanism of Action

There are virtually no clinically available neuroprotective drugs for the treatment of acute and chronic neurological disorders, hence there is an urgent need for the development of new neuroprotective molecules. Cationic arginine-rich peptides (CARPs) are an expanding and relatively novel class of compounds, which possess intrinsic neuroprotective properties. Intriguingly, CARPs possess a combination of biological properties unprecedented for a neuroprotective agent including the ability to traverse cell membranes and enter the CNS, antagonize calcium influx, target mitochondria, stabilize proteins, inhibit proteolytic enzymes, induce pro-survival signaling, scavenge toxic molecules, and reduce oxidative stress as well as, having a range of anti-inflammatory, analgesic, anti-microbial, and anti-cancer actions. CARPs have also been used as carrier molecules for the delivery of other putative neuroprotective agents across the blood-brain barrier and blood-spinal cord barrier. However, there is increasing evidence that the neuroprotective efficacy of many, if not all these other agents delivered using a cationic arginine-rich cell-penetrating peptide (CCPPs) carrier (e.g., TAT) may actually be mediated largely by the properties of the carrier molecule, with overall efficacy further enhanced according to the amino acid composition of the cargo peptide, in particular its arginine content. Therefore, in reviewing the neuroprotective mechanisms of action of CARPs we also consider studies using CCPPs fused to a putative neuroprotective peptide. We review the history of CARPs in neuroprotection and discuss in detail the intrinsic biological properties that may contribute to their cytoprotective effects and their usefulness as a broad-acting class of neuroprotective drugs.

DUSP19 mediates spinal cord injury-induced apoptosis and inflammation in mouse primary microglia cells via the NF-kB signaling pathway

Objective: Spinal cord injury (SCI) is a common injury that seriously threatens human health. NF-κB may be involved in the secondary injury of SCI that is mediated by inflammation and aggravates damage. Our study was aimed to investigate the role of NF-κB signaling in DUSP19-mediated cleaved Caspase-3 expression and the release of inflammatory factors in vivo and in vitro.Materials and Methods: DUSP19 mRNA expression and the content of IL-6 and IL-8 in patients with traumatic SCI (TSCI) were measured by real-time PCR and ELISA, respectively. The levels of p-NF-κBp65, NF-κBp65 and cleaved Caspase-3 expression and the concentrations of IL-6 and IL-8 were measured by western blotting and ELISA, respectively.Results: Patients with TSCI showed lower DUSP19 expression and higher concentration of IL-6 and IL-8 compared with healthy controls. DUSP19 overexpression inhibited p-NF-κBp65 level, cleaved Caspase-3 expression, and production of IL-8 and IL-6 in the mice induced by TSCI. DUSP19 silencing increased p-NF-κBp65 level, cleaved Caspase-3 expression, and concentration of IL-6 and IL-8 in mouse primary microglia cells. DUSP19 overexpression had an inverse effect. Importantly, DUSP19 silencing and overexpression mediated p-NF-κBp65 level, cleaved Caspase-3 expression, and concentration of IL-6 and IL-8 in mouse primary microglia cells were reversed by NF-κB inhibitor pyrrolidine dithiocarbamate (PDTC) and NF-κB activator 12-myristate 13-acetate (PMA), respectively.Conclusion: These results suggested that DUSP19-mediated SCI-induced apoptosis and inflammation via NF-κB signaling and might therefore serve as a potential therapeutic target for SCI.

JNK Signaling Pathway Involvement in Spinal Cord Neuron Development and Death

The c-Jun NH2-terminal protein kinase (JNK) is a Janus-faced kinase, which, in the nervous system, plays important roles in a broad range of physiological and pathological processes. Three genes, encoding for 10 JNK isoforms, have been identified: jnk1, jnk2, and jnk3. In the developing spinal cord, JNK proteins control neuronal polarity, axon growth/pathfinding, and programmed cell death; in adulthood they can drive degeneration and regeneration, after pathological insults. Indeed, recent studies have highlighted a role for JNK in motor neuron (MN) diseases, such as amyotrophic lateral sclerosis and spinal muscular atrophy. In this review we discuss how JNK-dependent signaling regulates apparently contradictory functions in the spinal cord, in both the developmental and adult stages. In addition, we examine the evidence that the specific targeting of JNK signaling pathway may represent a promising therapeutic strategy for the treatment of MN diseases.

Roles of extra-cellular signal-regulated protein kinase 5 signaling pathway in the development of spinal cord injury

Background:

In consideration of characteristics and functions, extra-cellular signal-regulated protein kinase 5 (ERK5) signaling pathway could be a new target for spinal cord injury (SCI) treatment. Our study aimed to evaluate the roles of ERK5 signaling pathway in secondary damage of SCI.

Methods:

We randomly divided 70 healthy Wistar rats into five groups: ten in the blank group, 15 in the sham surgery + BIX02188 (sham + B) group, 15 in the sham surgery + dimethyl sulfoxide (DMSO; sham + D) group, 15 in the SCI + BIX02188 (SCI + B) group, and 15 in the SCI + DMSO (SCI + D) group. BIX02188 is a specific inhibitor of the ERK5 signaling pathway. SCI was induced by the application of vascular clips (with the force of 30 g) to the dura on T10 level, while rats in the sham surgery group underwent only T9-T11 laminectomy. BIX02188 or DMSO was intra-thecally injected at 1, 6, and 12 h after surgery or SCI. Spinal cord samples were taken for testing at 24 h after surgery or SCI.

Results:

Expression of phosphorylated-ERK5 (p-ERK5) significantly increased after SCI. Application of BIX02188 indeed inhibited ERK5 signaling pathway and reduced the degree of spinal cord tissue injury, neutrophil infiltration and proinflammatory cytokine expression, nuclear factor-κB (NF-κB) activation and apoptosis (measured by TdT-mediated 2′-deoxyuridine 5′-triphosphate nick-end labeling, expression of Fas-ligand, BCL2-associated X [Bax], and B-cell lymphoma-2 [Bcl-2]). Double immunofluorescence revealed activation of ERK5 in neurons and microglia after SCI.

Conclusion:

ERK5 signaling pathway was activated in spinal neurons and microglia, contributing to secondary injury of SCI. Moreover, inhibition of ERK5 signaling pathway could alleviate the degree of SCI, which might be related to its regulation of infiltration of inflammatory cells and release of inflammatory cytokines, expression of NF-κB and cell apoptosis.

Silencing of the MEKK2/MEKK3 Pathway Protects against Spinal Cord Injury via the Hedgehog Pathway and the JNK Pathway

Spinal cord injury (SCI) is a devastating medical condition, often accompanied by motor and sensory dysfunction. The Hedgehog (Hh) pathway has a protective role in pathological injury after SCI. However, the specific mechanism remains unclear. The present study aimed to confirm the effects of the mitogen-activated protein kinase kinase-2 (MEKK2)/MEKK3/JNK/Hh pathway on SCI. SCI rat models were established and then inoculated with plasmids overexpressing MEKK2/MEKK3 or with small interfering RNA (siRNA) against MEKK2/MEKK3. The expression of MEKK2 and -3 was detected in dorsal root ganglia (DRG) cells. The motor function of hindlimbs, the expression of the c-Jun N-terminal kinase (JNK)- and Hh-pathway-related genes, and the level of neurofilament-200 (NF-200) and glial fibrillary acidic protein (GFAP) were measured. MEKK2 and -3 were expressed at a high level in DRG cells. The silencing of MEKK2/MEKK3 in rats caused an increase in the expression of glioma-associated oncogene homolog-1 (Gli-1), Nestin, smoothened (Smo), and Sonic Hedgehog (Shh). The Basso, Beattie, and Bresnahan (BBB) rating and the level of NF-200 protein also increased. However, the expression of monocyte chemoattractant protein-1 (MCP-1), macrophage inflammatory protein-1β (MIP-1β), MIP-3α, p-JNK/JNK, and p-c-Jun/c-Jun and the level of GFAP were reduced. Downregulation of MEKK2/MEKK3 ameliorated the symptoms of SCI by promoting neural progenitor cell differentiation via activating the Hh pathway and disrupting the JNK pathway. The findings in this study reveal a potential biomarker for SCI treatment.

RETRACTED: Tanshinone IIA alleviates oxidative damage after spinal cord injury in vitro and in vivo through up-regulating miR-124

This article has been retracted: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/about/our-business/policies/article-withdrawal). This article has been retracted at the request of the Corresponding Author with the agreement of the editor. The authors used DMSO (dimethyl sulfoxide) to dissolve tanshinone IIA in this experiment, but even after dilution, DMSO also can induce toxicity of PC12 cells, which also can affect the result of the experiment. After discussion, the authors found that sulfotanshinone sodium injection can be used to replace tanshinone II A, which is both an aqueous solution and has been clinically proved to be an ideal substitute. Further, in error, the authors used 0μM /12.5μM /50μM /100μM /200μM H2O2 to stimulate oxidative injury as in figure 1A, but missed 25μM H2O2, which may also affect the experimental results.

Pre-Injection of Small Interfering RNA (siRNA) Promotes c-Jun Gene Silencing and Decreases the Survival Rate of Axotomy-Injured Spinal Motoneurons in Adult Mice

Brachial plexus injury is a common clinical peripheral nerve trauma. A series of genes in motoneurons were activated in the corresponding segments of the spinal cord after brachial plexus roots axotomy. The spatial and temporal expression of these genes directly affects the speed of motoneuron axon regeneration and precise target organ reinnervation. In a previous study, we observed the overexpression of c-Jun in motoneurons of the spinal cord ventral horn after brachial plexus injury in rats. However, the relevance of c-Jun expression with respect to the fate of axotomy-induced branchial plexus injury in adult mice remains unknown. In the present study, we explored the function of c-Jun in motoneuron recovery after axotomy. We pre-injected small interfering RNA (siRNA) to knockdown c-Jun expression in mice and examined the effects of the overexpression of c-Jun in motoneurons after the axotomy of the brachial plexus in vivo. Axotomy induced c-Jun overexpression in the ventral horn motoneurons of adult mice from 3 to 14 days after injury. In addition, the pre-injection of siRNA transiently inhibited c-Jun expression and decreased the survival rate of axotomy-injured motoneurons. These findings indicate that the axotomy-induced overexpression of c-Jun plays an important role in the survival of ventral horn motoneurons in adult mice. In addition, the pre-injection of c-Jun siRNA through the brachial plexus stem effectively adjusts c-Jun gene expression at the ipsilateral side.

Stress-Activated Protein Kinases in Spinal Cord Injury: Focus on Roles of p38

Spinal cord injury (SCI) consists of three phases-acute, secondary, and chronic damages-and limiting the development of secondary damage possibly improves functional recovery after SCI. A major component of the secondary phase of SCI is regarded as inflammation-triggered events: induction of cytokines, edema, microglial activation, apoptosis of cells including oligodendrocytes and neurons, demyelination, formation of the astrocytic scar, and so on. Two major stress-activated protein kinases (SAPKs)-c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (p38 MAPK)-are activated in various types of cells in response to cellular stresses such as apoptotic stimuli and inflammatory waves. In animal models of SCI, inhibition of either JNK or p38 has been shown to promote neuroprotection-associated functional recovery. Here, we provide an overview on the roles of SAPKs in SCI and, in particular, the pathological role of p38 will be discussed as a promising target for therapeutic intervention in SCI.

Role of C-Jun N-terminal Kinase in Hepatocellular Carcinoma Development

Hepatocellular carcinoma (HCC) is among the most frequently occurring cancers and the leading causes of cancer mortality worldwide. Identification of the signaling pathways regulating liver carcinogenesis is critical for developing novel chemoprevention and targeted therapies. C-Jun N-terminal kinase (JNK) is a member of a larger group of serine/threonine (Ser/Thr) protein kinases known as the mitogen-activated protein kinase (MAPK) family. JNK is an important signaling component that converts external stimuli into a wide range of cellular responses, including cell proliferation, differentiation, survival, migration, invasion, and apoptosis, as well as the development of inflammation, fibrosis, cancer growth, and metabolic diseases. Because of the essential roles of JNK in these cellular functions, deregulated JNK is often found to contribute to the development of HCC. Recently, the functions and molecular mechanisms of JNK in HCC development have been addressed using mouse models and human HCC cell lines. Furthermore, recent studies demonstrate that the activation of JNK by oncogenes can promote the development of cancers by regulating the transforming growth factor (TGF)-β/Smad pathway, which makes the oncogenes/JNK/Smad signaling pathway an attractive target for cancer therapy. Additionally, JNK-targeted therapy has a broad potential for clinical applications. In summary, we are convinced that promising new avenues for the treatment of HCC by targeting JNK are on the horizon, which will undoubtedly lead to better, more effective, and faster therapies in the years to come.

Functional integration of complex miRNA networks in central and peripheral lesion and axonal regeneration

New players are emerging in the game of peripheral and central nervous system injury since their physiopathological mechanisms remain partially elusive. These mechanisms are characterized by several molecules whose activation and/or modification following a trauma is often controlled at transcriptional level. In this scenario, microRNAs (miRNAs/miRs) have been identified as main actors in coordinating important molecular pathways in nerve or spinal cord injury (SCI). miRNAs are small non-coding RNAs whose functionality at network level is now emerging as a new level of complexity. Indeed they can act as an organized network to provide a precise control of several biological processes. Here we describe the functional synergy of some miRNAs in case of SCI and peripheral damage. In particular we show how several small RNAs can cooperate in influencing simultaneously the molecular pathways orchestrating axon regeneration, inflammation, apoptosis and remyelination. We report about the networks for which miRNA-target bindings have been experimentally demonstrated or inferred based on target prediction data: in both cases, the connection between one miRNA and its downstream pathway is derived from a validated observation or is predicted from the literature. Hence, we discuss the importance of miRNAs in some pathological processes focusing on their functional structure as participating in a cooperative and/or convergence network.

Interaction of reactive astrocytes with type I collagen induces astrocytic scar formation through the integrin-N-cadherin pathway after spinal cord injury

Central nervous system (CNS) injury transforms naive astrocytes into reactive astrocytes, which eventually become scar-forming astrocytes that can impair axonal regeneration and functional recovery. This sequential phenotypic change, known as reactive astrogliosis, has long been considered unidirectional and irreversible. However, we report here that reactive astrocytes isolated from injured spinal cord reverted in retrograde to naive astrocytes when transplanted into a naive spinal cord, whereas they formed astrocytic scars when transplanted into injured spinal cord, indicating the environment-dependent plasticity of reactive astrogliosis. We also found that type I collagen was highly expressed in the spinal cord during the scar-forming phase and induced astrocytic scar formation via the integrin-N-cadherin pathway. In a mouse model of spinal cord injury, pharmacological blockade of reactive astrocyte-type I collagen interaction prevented astrocytic scar formation, thereby leading to improved axonal regrowth and better functional outcomes. Our findings reveal environmental cues regulating astrocytic fate decisions, thereby providing a potential therapeutic target for CNS injury.

Non cell-autonomous role of DCC in the guidance of the corticospinal tract at the midline

DCC, a NETRIN-1 receptor, is considered as a cell-autonomous regulator for midline guidance of many commissural populations in the central nervous system. The corticospinal tract (CST), the principal motor pathway for voluntary movements, crosses the anatomic midline at the pyramidal decussation. CST fails to cross the midline in Kanga mice expressing a truncated DCC protein. Humans with heterozygous DCC mutations have congenital mirror movements (CMM). As CMM has been associated, in some cases, with malformations of the pyramidal decussation, DCC might also be involved in this process in human. Here, we investigated the role of DCC in CST midline crossing both in human and mice. First, we demonstrate by multimodal approaches, that patients with CMM due to DCC mutations have an increased proportion of ipsilateral CST projections. Second, we show that in contrast to Kanga mice, the anatomy of the CST is not altered in mice with a deletion of DCC in the CST. Altogether, these results indicate that DCC controls CST midline crossing in both humans and mice, and that this process is non cell-autonomous in mice. Our data unravel a new level of complexity in the role of DCC in CST guidance at the midline.

Inhibition of p21-Activated Kinase 1 by IPA-3 Promotes Locomotor Recovery After Spinal Cord Injury in Mice

STUDY DESIGN

Ninety-six male adult CD-1 mice were randomly divided into sham, spinal cord injury (SCI) + vehicle, and SCI + IPA-3 groups. Expression of matrix metalloproteinase (MMP)-2 and MMP-9, production of tumor necrosis factors (TNF)-α and interleukin (IL)-1β, tissue edema, blood-spinal cord barrier penetrability, neural cell apoptosis, and neurological function recovery were measured.

OBJECTIVE

The aim of the study was to evaluate the effect of specific inhibition of p21-activated kinase 1 (PAK1) by IPA-3 on SCI and the underlying mechanisms thereof.

SUMMARY OF BACKGROUND DATA

SCI is a devastating clinical condition that may result in long-lasting and deteriorating functional deficits. The major goal of SCI treatment is to limit the development of secondary injury. IPA-3, a PAK1 inhibitor, exhibited neuroprotection against secondary damage after traumatic brain injury and subarachnoid hemorrhage (SAH).

METHODS

MMP-2, MMP-9, and cleaved caspase-3 expression were assessed by Western blot. Inflammatory cytokines TNF-α and IL-1β were detected by enzyme-linked immunosorbent assay (ELISA). The blood-spinal cord barrier disruption was measured by water content and Evans blue extravasation of the spinal cord. Neuronal apoptosis was evaluated by Nissl staining and Terminal-deoxynucleoitidyl Transferase Mediated Nick End Labeling (TUNEL) assay. The locomotor behavior of hind limb was evaluated by Basso Mouse Scale (BMS) at 1, 3, 7, 14, and 28 days post-injury.

RESULTS

Compared with SCI + vehicle mice, IPA-3 treatment showed decreased p-PAK1, MMP-2, MMP-9, cleaved caspase-3, TNF-α, and IL-1β expression. Moreover, inhibition of PAK1 by IPA-3 reduced spinal cord water content and Evans blue extravasation, increased neuronal survival, and reduced TUNEL-positive cells at 24 hours after SCI. Furthermore, IPA-3 improved spinal cord functional recovery 7 days after SCI.

CONCLUSION

Inhibition of PAK1 by IPA-3 promoted recovery of neurological function, possibly by downregulating the expression of MMP-2, MMP-9, TNF-α, and IL-1β. Our data suggest that PAK1 may be a potential therapeutic target in patients with SCI.

LEVEL OF EVIDENCE

1.

Propitious Therapeutic Modulators to Prevent Blood-Spinal Cord Barrier Disruption in Spinal Cord Injury

The blood-spinal cord barrier (BSCB) is a specialized protective barrier that regulates the movement of molecules between blood vessels and the spinal cord parenchyma. Analogous to the blood-brain barrier (BBB), the BSCB plays a crucial role in maintaining the homeostasis and internal environmental stability of the central nervous system (CNS). After spinal cord injury (SCI), BSCB disruption leads to inflammatory cell invasion such as neutrophils and macrophages, contributing to permanent neurological disability. In this review, we focus on the major proteins mediating the BSCB disruption or BSCB repair after SCI. This review is composed of three parts. Section 1. SCI and the BSCB of the review describes critical events involved in the pathophysiology of SCI and their correlation with BSCB integrity/disruption. Section 2. Major proteins involved in BSCB disruption in SCI focuses on the actions of matrix metalloproteinases (MMPs), tumor necrosis factor alpha (TNF-α), heme oxygenase-1 (HO-1), angiopoietins (Angs), bradykinin, nitric oxide (NO), and endothelins (ETs) in BSCB disruption and repair. Section 3. Therapeutic approaches discusses the major therapeutic compounds utilized to date for the prevention of BSCB disruption in animal model of SCI through modulation of several proteins.

Drug delivery, cell-based therapies, and tissue engineering approaches for spinal cord injury

Spinal cord injury (SCI) results in devastating neurological and pathological consequences, causing major dysfunction to the motor, sensory, and autonomic systems. The primary traumatic injury to the spinal cord triggers a cascade of acute and chronic degenerative events, leading to further secondary injury. Many therapeutic strategies have been developed to potentially intervene in these progressive neurodegenerative events and minimize secondary damage to the spinal cord. Additionally, significant efforts have been directed toward regenerative therapies that may facilitate neuronal repair and establish connectivity across the injury site. Despite the promise that these approaches have shown in preclinical animal models of SCI, challenges with respect to successful clinical translation still remain. The factors that could have contributed to failure include important biologic and physiologic differences between the preclinical models and the human condition, study designs that do not mirror clinical reality, discrepancies in dosing and the timing of therapeutic interventions, and dose-limiting toxicity. With a better understanding of the pathobiology of events following acute SCI, developing integrated approaches aimed at preventing secondary damage and also facilitating neuroregenerative recovery is possible and hopefully will lead to effective treatments for this devastating injury. The focus of this review is to highlight the progress that has been made in drug therapies and delivery systems, and also cell-based and tissue engineering approaches for SCI.

Proinflammatory cytokines downregulate connexin 43-gap junctions via the ubiquitin-proteasome system in rat spinal astrocytes

Astrocytic gap junctions formed by connexin 43 (Cx43) are crucial for intercellular communication between spinal cord astrocytes. Various neurological disorders are associated with dysfunctional Cx43-gap junctions. However, the mechanism modulating Cx43-gap junctions in spinal astrocytes under pathological conditions is not entirely clear. A previous study showed that treatment of spinal astrocytes in culture with pro-inflammatory cytokines tumor necrosis factor-α (TNF-α) and interferon-γ (IFN-γ) decreased both Cx43 expression and gap junction intercellular communication (GJIC) via a c-jun N-terminal kinase (JNK)-dependent pathway. The current study further elaborates the intracellular mechanism that decreases Cx43 under an inflammatory condition. Cycloheximide chase analysis revealed that TNF-α (10 ng/ml) alone or in combination with IFN-γ (5 ng/ml) accelerated the degradation of Cx43 protein in cultured spinal astrocytes. The reduction of both Cx43 expression and GJIC induced by a mixture of TNF-α and IFN-γ were blocked by pretreatment with proteasome inhibitors MG132 (0.5 μM) and epoxomicin (25 nM), a mixture of TNF-α and IFN-γ significantly increased proteasome activity and Cx43 ubiquitination. In addition, TNF-α and IFN-γ-induced activation of ubiquitin-proteasome systems was prevented by SP600125, a JNK inhibitor. Together, these results indicate that a JNK-dependent ubiquitin-proteasome system is induced under an inflammatory condition that disrupts astrocytic gap junction expression and function, leading to astrocytic dysfunction and the maintenance of the neuroinflammatory state.

Neuroprotective peptides fused to arginine-rich cell penetrating peptides: Neuroprotective mechanism likely mediated by peptide endocytic properties

Several recent studies have demonstrated that TAT and other arginine-rich cell penetrating peptides (CPPs) have intrinsic neuroprotective properties in their own right. Examples, we have demonstrated that in addition to TAT, poly-arginine peptides (R8 to R18; containing 8-18 arginine residues) as well as some other arginine-rich peptides are neuroprotective in vitro (in neurons exposed to glutamic acid excitotoxicity and oxygen glucose deprivation) and in the case of R9 in vivo (after permanent middle cerebral artery occlusion in the rat). Based on several lines of evidence, we propose that this neuroprotection is related to the peptide's endocytosis-inducing properties, with peptide charge and arginine residues being critical factors. Specifically, we propose that during peptide endocytosis neuronal cell surface structures such as ion channels and transporters are internalised, thereby reducing calcium influx associated with excitotoxicity and other receptor-mediated neurodamaging signalling pathways. We also hypothesise that a peptide cargo can act synergistically with TAT and other arginine-rich CPPs due to potentiation of the CPPs endocytic traits rather than by the cargo-peptide acting directly on its supposedly intended intracellular target. In this review, we systematically consider a number of studies that have used CPPs to deliver neuroprotective peptides to the central nervous system (CNS) following stroke and other neurological disorders. Consequently, we critically review evidence that supports our hypothesis that neuroprotection is mediated by carrier peptide endocytosis. In conclusion, we believe that there are strong grounds to regard arginine-rich peptides as a new class of neuroprotective molecules for the treatment of a range of neurological disorders.

Inhibitors of c-Jun N-terminal kinases: an update

The c-Jun N-terminal kinases (JNKs) are serine/threonine kinases implicated in the pathogenesis of various diseases. Recent advances in the development of novel inhibitors of JNKs will be reviewed. Significant progress in the design of JNK inhibitors displaying selectivity versus other kinases has been achieved within the past 4 years. However, the development of isoform selective JNK inhibitors is still an open task.

Subconjunctival injection of XG-102, a JNK inhibitor peptide, in patients with intraocular inflammation: a safety and tolerability study

PURPOSE

We aimed to investigate the safety, tolerability, and systemic diffusion of a single escalating dose of XG-102 (a 31-D-amino-acid peptide inhibiting JNK pathway activation), administered subconjunctivally in the treatment of post-surgery or post-trauma intraocular inflammation.

METHODS

This is a dose-escalating, tolerance Phase Ib study. Twenty patients with post-surgery or post-traumatic intraocular inflammation were assigned to 1 of the 4 dose escalating (45, 90, 450, or 900 μg XG-102) groups of 5 patients each. Patients were evaluated at 24, 48 h, 8, and 28 days following the administration of XG-102, including laboratory tests, standard eye examinations, vital signs, and occurrence of adverse events. A single plasma quantification of XG-102 was performed 30 min after administration, according to previous pharmacokinetics studies performed on volunteers.

RESULTS

A total of 17 non-serious adverse events, considered unrelated to the study treatment, were reported for 10 patients. The adverse event incidence was not related to the drug dose. All patients experienced a decrease in intraocular inflammation as of 24 h post-administration and this decrease was sustained up to 28 days thereafter. No patient required local injection or systemic administration of corticoids following the administration of XG-102. XG-102 was undetectable in the first 3 dose groups. In the fourth-dose group (900 μg) the XG-102 plasma levels were above the limit of detection for 3 patients and above the limit of quantification for 1 patient.

CONCLUSIONS

In this first clinical trial using XG-102, administered as a single subconjunctival injection as adjunct therapy, in patients with recent post-surgery or post-trauma intraocular inflammation is safe and well tolerated. Further studies are required to evaluate its efficacy.

Cell-based peptide screening to access the undruggable target space

Only 20-30% of drug target proteins can be accessed by common drug classes, like small molecules or therapeutic antibodies. The vast majority of the remaining proteins are considered "undruggable" and include drug target proteins, like transcription factors, scaffold or adapter proteins, which play important roles in disease. However over the last years innovative compound classes including nucleotide derived drugs (e.g. siRNA, antisense), macrocyclic compounds and cell-permeable peptides matured significantly and hold now the potential to modulate these hard to access target proteins for therapeutic use. This article will focus on the discovery of cell-permeable peptides and discuss intracellular screening systems for peptides, which yield highly relevant peptides, because peptide selection takes place in eukaryotic cells, under conditions, which are very similar to the later therapeutic use.

Determination of tissue levels of a neuroprotectant drug: the cell permeable JNK inhibitor peptide

INTRODUCTION

Cell permeable peptides (CPPs) represent a novel tool for the delivery of bioactive molecules into scarcely accessible organs, such as the brain. CPPs have been successfully used in pre-clinical studies for a variety of diseases, ranging from cancer to neurological disorders. However, the mechanisms by which CPPs cross biological membranes, as well as their pharmacokinetic properties, have been poorly explored due to the lack of specific and sensitive analytical methods.

METHODS

In this paper we describe a protocol to quantitatively determine the amount of CPPs in in vitro and in vivo experimental models. To this end we selected the peptide D-JNKI1 that was shown to prevent neurodegeneration in both acute and chronic degenerative disorders. This method allows an accurate quantitative analysis of D-JNKI1 in both neuronal lysates and tissue homogenates using mass spectrometry and stable isotope dilution approach.

RESULTS

We found that D-JNKI1 crosses cellular membranes with fast kinetics, through an active and passive mechanism. After acute intraperitoneal (ip) administration of D-JNKI1 in mice, the peptide was found in the main organs with particular regard to the liver and kidney. Interestingly, D-JNKI1 crosses the blood brain barrier (BBB) and reaches the brain, where it remains for one week.

DISCUSSION

The challenge lies in developing the clinical application of therapeutic cell permeable peptides. Discerning pharmacokinetic properties is a high priority to produce a powerful therapeutic strategy. Overall, our data shed light on the pharmacokinetic properties of D-JNKI1 and supports its powerful neuroprotective effect.

The JNK inhibitor, SP600125, potentiates the glial response and cell death induced by methamphetamine in the mouse striatum

This study investigates the effect of the selective Jun NH2-terminal kinase 1/2 (JNK1/2) inhibitor, (SP600125) on the striatal dopamine nerve terminal loss and on the increased interleukin-15 (IL-15) expression and glial response induced by methamphetamine (METH). Mice were given repeated low doses of METH (4 mg/kg, i.p., three times separated by 3 h) and killed 24 h or 7 d after the last dose. SP600125 (30 mg/kg, i.p) was administered 30 min before the last METH injection. Results indicate that METH produced dopaminergic axonal neurotoxicity reflected as a marked decrease in the striatal density of tyrosine hydroxylase-immunoreactive (TH-ir) fibres and dopamine transporter-immunoreactivity (DAT-ir) 24 h after dosing. These effects were not modified by SP600125. This compound also failed to prevent the long-term loss of dopamine levels and DAT observed 7 d following METH injection. Nevertheless, SP600125 potentiated METH-induced striatal cell loss reflected by an increase in Fluoro-Jade immunostaining, cleaved capase-3 immunoreactivity and the number of terminal deoxyncleotidyl transferase-mediated dUTP nick end labelling (TUNEL) positive cells. In line with a deleterious effect of JNK1/2 inhibition, SP600125 increased the astroglial and microglial response induced by METH and interfered with drug-induced IL-15 expression. Together these data indicate that, not only does SP600125 fail to protect against the dopaminergic damage induced by METH but also, in fact, it potentiates the glial response and the non-dopaminergic striatal cell loss caused by the drug.

XG-102 administered to healthy male volunteers as a single intravenous infusion: a randomized, double-blind, placebo-controlled, dose-escalating study

The aim of the study is to evaluate the safety, tolerability and pharmacokinetics (PK) of the JNK inhibitor XG-102 in a randomized, double blind, placebo controlled, sequential ascending dose parallel group Phase 1 Study. Three groups of male subjects received as randomly assigned ascending single XG-102 doses (10, 40, and 80 μg/kg; 6 subjects per dose) or placebo (2 subjects per dose) as an intravenous (IV) infusion over 60 min. Safety and tolerability were assessed by physical examination, vital signs, electrocardiography, eye examination, clinical laboratory tests and adverse events (AEs). PK was analyzed using noncompartmental methods. All reported AEs were mild to moderate and neither their number nor their distribution by System Organ Class suggest a dose relationship. Only headache and fatigue were considered probably or possibly study drug related. Headache frequency was similar for active and placebo, consequently this was not considered to be drug related but probably to study conditions. The other examinations did not show clinically relevant deviations or trends suggesting a XG-102 relationship. Geometric mean half-life was similar among doses, ranging from 0.36 to 0.65 h. Geometric mean XG-102 AUC_0–last increased more than linearly with dose, 90% confidence intervals (CIs) did not overlap for the two highest doses. Geometric mean dose normalized C_max values suggest a more than linear increase with dose but 90% CIs overlap. It may be concluded that XG-102 single IV doses of 10–80 μg/kg administered over 1 h to healthy male subjects were safe and well tolerated.

Analgesic effect of acupuncture is mediated via inhibition of JNK activation in astrocytes after spinal cord injury

Acupuncture (AP) has been used worldwide to relieve pain. However, the mechanism of action of AP is poorly understood. Here, we found that AP relieved neuropathic pain (NP) by inhibiting Jun-N-terminal kinase (JNK) activation in astrocytes after spinal cord injury (SCI). After contusion injury which induces the below-level (L4-L5) NP, Shuigou (GV26) and Yanglingquan (GB34) acupoints were applied. At 31 d after injury, both mechanical allodynia and thermal hyperalgesia were significantly alleviated by AP applied at GV26 and GB34. Immunocytochemistry revealed that JNK activation was mainly observed in astrocytes after injury. AP inhibited JNK activation in astrocytes at L4-L5 level of spinal cord. The level of p-c-Jun known, a downstream molecule of JNK, was also decreased by AP. In addition, SCI-induced GFAP expression, a marker for astrocytes, was decreased by AP as compared to control groups. Especially, the number of hypertrophic, activated astrocytes in laminae I–II of dorsal horn at L4-5 was markedly decreased by AP treatment when compared with vehicle and simulated AP-treated groups. When animals treated with SP600125, a specific JNK inhibitor, after SCI, both mechanical allodynia and thermal hyperalgesia were significantly attenuated by the inhibitor, suggesting that JNK activation is likely involved in SCI-induced NP. Also, the expression of chemokines which is known to be mediated through JNK pathway was significantly decreased by AP and SP600125 treatment. Therefore, our results indicate that analgesic effect of AP is mediated in part by inhibiting JNK activation in astrocytes after SCI.