Attenuation of scratch-induced reactive astrogliosis by novel EphA4 kinase inhibitors

Long-term impact of maternal obesity on the gliovascular unit and ephrin signaling in the hippocampus of adult offspring

BACKGROUND

Children born to obese mothers are at increased risk of developing mood disorders and cognitive impairment. Experimental studies have reported structural changes in the brain such as the gliovascular unit as well as activation of neuroinflammatory cells as a part of neuroinflammation processing in aged offspring of obese mothers. However, the molecular mechanisms linking maternal obesity to poor neurodevelopmental outcomes are not well established. The ephrin system plays a major role in a variety of cellular processes including cell-cell interaction, synaptic plasticity, and long-term potentiation. Therefore, in this study we determined the impact of maternal obesity in pregnancy on cortical, hippocampal development, vasculature and ephrin-A3/EphA4-signaling, in the adult offspring in mice.

METHODS

Maternal obesity was induced in mice by a high fat/high sugar Western type of diet (HF/HS). We collected brain tissue (prefrontal cortex and hippocampus) from 6-month-old offspring of obese and lean (control) dams. Hippocampal volume, cortical thickness, myelination of white matter, density of astrocytes and microglia in relation to their activity were analyzed using 3-D stereological quantification. mRNA expression of ephrin-A3, EphA4 and synaptic markers were measured by qPCR in the brain tissue. Moreover, expression of gap junction protein connexin-43, lipocalin-2, and vascular CD31/Aquaporin 4 were determined in the hippocampus by immunohistochemistry.

RESULTS

Volume of hippocampus and cortical thickness were significantly smaller, and myelination impaired, while mRNA levels of hippocampal EphA4 and post-synaptic density (PSD) 95 were significantly lower in the hippocampus in the offspring of obese dams as compared to offspring of controls. Further analysis of the hippocampal gliovascular unit indicated higher coverage of capillaries by astrocytic end-feet, expression of connexin-43 and lipocalin-2 in endothelial cells in the offspring of obese dams. In addition, offspring of obese dams demonstrated activation of microglia together with higher density of cells, while astrocyte cell density was lower.

CONCLUSION

Maternal obesity affects brain size, impairs myelination, disrupts the hippocampal gliovascular unit and decreases the mRNA expression of EphA4 and PSD-95 in the hippocampus of adult offspring. These results indicate that the vasculature-glia cross-talk may be an important mediator of altered synaptic plasticity, which could be a link between maternal obesity and neurodevelopmental/neuropsychiatric disorders in the offspring.

Unraveling Axon Guidance during Axotomy and Regeneration

During neuronal development and regeneration axons extend a cytoskeletal-rich structure known as the growth cone, which detects and integrates signals to reach its final destination. The guidance cues “signals” bind their receptors, activating signaling cascades that result in the regulation of the growth cone cytoskeleton, defining growth cone advance, pausing, turning, or collapse. Even though much is known about guidance cues and their isolated mechanisms during nervous system development, there is still a gap in the understanding of the crosstalk between them, and about what happens after nervous system injuries. After neuronal injuries in mammals, only axons in the peripheral nervous system are able to regenerate, while the ones from the central nervous system fail to do so. Therefore, untangling the guidance cues mechanisms, as well as their behavior and characterization after axotomy and regeneration, are of special interest for understanding and treating neuronal injuries. In this review, we present findings on growth cone guidance and canonical guidance cues mechanisms, followed by a description and comparison of growth cone pathfinding mechanisms after axotomy, in regenerative and non-regenerative animal models.

Replicating infant-specific reactive astrocyte functions in the injured adult brain

Infants and adults respond differently to brain injuries. Specifically, improved neuronal sparing along with reduced astrogliosis and glial scarring often observed earlier in life, likely contributes to improved long-term outcomes. Understanding the underlying mechanisms could enable the recapitulation of neuroprotective effects, observed in infants, to benefit adults after brain injuries. We reveal that in primates, Eph/ ephrin signaling contributes to age-dependent reactive astrocyte behavior. Ephrin-A5 expression on astrocytes was more protracted in adults, whereas ephrin-A1 was only expressed on infant astrocytes. Furthermore, ephrin-A5 exacerbated major hallmarks of astrocyte reactivity via EphA2 and EphA4 receptors, which was subsequently alleviated by ephrin-A1. Rather than suppressing reactivity, ephrin-A1 signaling shifted astrocytes towards GAP43+ neuroprotection, accounting for improved neuronal sparing in infants. Reintroducing ephrin-A1 after middle-aged focal ischemic injury significantly attenuated glial scarring, improved neuronal sparing and preserved circuitry. Therefore, beneficial infant mechanisms can be recapitulated in adults to improve outcomes after CNS injuries.

EphA4 Obstructs Spinal Cord Neuron Regeneration by Promoting Excessive Activation of Astrocytes

Studies have found that molecular targets that regulate tissue development are also involved in regulating tissue regeneration. Erythropoietin-producing hepatocyte A4 (EphA4) not only plays a guiding role in neurite outgrowth during the development of the central nervous system (CNS) but also induces injured axon retraction and inhibits axon regeneration after spinal cord injury (SCI). EphA4 targets several ephrin ligands (including ephrin-A and ephrin-B) and is involved in cortical cell migration, axon guidance, synapse formation and astrocyte function. However, how EphA4 affects axon regeneration after SCI remains unclear. This study focuses on the effect and mechanism of EphA4-regulated astrocyte function in neuronal regeneration after SCI. Our research found that EphA4 expression increased significantly after SCI and peaked at 3 days post-injury; accordingly, we identified the cellular localization of EphA4 and ephrin-B ligands in neurons and astrocytes after SCI. EphA4 was mainly expressed on the surface of neurons, ephrin-B1 and ephrin-B3 were mainly localized on astrocytes, and ephrin-B2 was distributed on both neurons and astrocytes. To further elucidate the effect of EphA4 on astrocyte function after SCI, we detected the related cytokines secreted by astrocytes in vivo. We found that the levels of neurotrophic factors including nerve growth factor (NGF) and basic fibroblast growth factor (bFGF) increased significantly after SCI (NGF peaked at 3 days and bFGF peaked at 7 days); the expression of laminin and fibronectin increased gradually after SCI; the expression of inflammatory factors [interleukin (IL)-1β and IL-6] increased significantly from 4 h to 7 days after SCI; and the levels of glial fibrillary acidic protein (GFAP), a marker of astrocyte activation, and chondroitin sulphate proteoglycan (CSPG), the main component of glial scars, both peaked at 7 days after SCI. Using a damaged astrocyte model in vitro, we similarly found that the levels of related cytokines increased after injury. Consequently, we observed the effect of damaged astrocytes on neurite outgrowth and regeneration, and the results showed that damaged astrocytes hindered neurite outgrowth and regeneration; however, the inhibitory effect of injured astrocytes on neurite regeneration was reduced following ephrin-B receptor knockdown or inflammatory inhibition at 24 h after astrocyte injury. Our results showed that EphA4 regulates the secretion of neurotrophic factors, adhesion molecules, inflammatory factors and glial scar formation by binding with the ligand ephrin-B located on the surface of astrocytes. EphA4 affects neurite outgrowth and regeneration after SCI by regulating astrocyte function.

Systematic analysis of purified astrocytes after SCI unveils Zeb2os function during astrogliosis

Spinal cord injury (SCI) is one of the most devastating neural injuries without effective therapeutic solutions. Astrocytes are the predominant component of the scar. Understanding the complex contributions of reactive astrocytes to SCI pathophysiologies is fundamentally important for developing therapeutic strategies. We have studied the molecular changes in the injury environment and the astrocyte-specific responses by astrocyte purification from injured spinal cords from acute to chronic stages. In addition to protein-coding genes, we have systematically analyzed the expression profiles of long non-coding RNAs (lncRNAs) (>200 bp), which are regulatory RNAs that play important roles in the CNS. We have identified a highly conserved lncRNA, Zeb2os, and demonstrated using functional assays that it plays an important role in reactive astrogliosis through the Zeb2os/Zeb2/Stat3 axis. These studies provide valuable insights into the molecular basis of reactive astrogliosis and fill the knowledge gap regarding the function(s) of lncRNAs in astrogliosis and SCI.

Fluoxetine and Riluzole Mitigates Manganese-Induced Disruption of Glutamate Transporters and Excitotoxicity via Ephrin-A3/GLAST-GLT-1/Glu Signaling Pathway in Striatum of Mice

Manganese (Mn) is an essential element required for many biological processes and systems in the human body. Mn intoxication increases brain glutamate (Glu) levels causing neuronal damage. Recent studies have reported that ephrin-A3 regulates this glutamate transporter. However, none has explored the role of this crucial molecule in Mn-induced excitotoxicity. The present study investigated whether ephrin-A3/GLAST-GLT-1/Glu signaling pathway participates in Mn-induced excitotoxicity using astrocytes and Kunming mice. The mechanisms were explored using fluoxetine (ephrin-A3 inhibitor) and riluzole (a Glu release inhibitor). Firstly, we demonstrated that Mn exposure (500 μM or 50 mg/kg MnCl₂) significantly increased Mn, ephrin-A3, and Glu levels, and inhibited Na⁺-K⁺ ATPase activity, as well as mRNA and protein levels of GLAST and GLT-1. Secondly, we found that astrocytes and mice pretreated with fluoxetine (100 μM or 15 mg/kg) and riluzole (100 μM or 32 μmol/kg) prior to Mn exposure had lower ephrin-A3 and Glu levels, but higher Na⁺-K⁺ ATPase activity, expression levels of GLAST and GLT-1 than those exposed to 500 μM or 50 mg/kg MnCl₂. Moreover, the morphology of cells and the histomorphology of mice striatum were injured. Results showed that pretreatment with fluoxetine and riluzole attenuated the Mn-induced motor dysfunctions. Together, these results suggest that the ephrin-A3/GLAST-GLT-1/Glu signaling pathway participates in Mn-induced excitotoxicity, and fluoxetine and riluzole can mitigate the Mn-induced excitotoxicity in mice brain.

Effects of miR-219/miR-338 on microglia and astrocyte behaviors and astrocyte-oligodendrocyte precursor cell interactions

MiR-219 and miR-338 (miR-219/miR-338) are oligodendrocyte-specific microRNAs. The overexpression of these miRs in oligodendrocyte precursor cells promotes their differentiation and maturation into oligodendrocytes, which may enhance axonal remyelination after nerve injuries in the central nervous system (CNS). As such, the delivery of miR-219/miR-338 to the CNS to promote oligodendrocyte precursor cell differentiation, maturation and myelination could be a promising approach for nerve repair. However, nerve injuries in the CNS also involve other cell types, such as microglia and astrocytes. Herein, we investigated the effects of miR-219/miR-338 treatment on microglia and astrocytes in vitro and in vivo. We found that miR-219/miR-338 diminished microglial expression of pro-inflammatory cytokines and suppressed astrocyte activation. In addition, we showed that miR-219/miR-338 enhanced oligodendrocyte precursor cell differentiation and maturation in a scratch assay paradigm that re-created a nerve injury condition in vitro. Collectively, our results suggest miR-219/miR-338 as a promising treatment for axonal remyelination in the CNS following nerve injuries. All experimental procedures were approved by the Institutional Animal Care and Use Committee (IACUC), Nanyang Technological University (approval No. A0309 and A0333) on April 27, 2016 and October 8, 2016.

Axon Guidance Molecules Guiding Neuroinflammation

Axon guidance molecules (AGMs), such as Netrins, Semaphorins, and Ephrins, have long been known to regulate axonal growth in the developing nervous system. Interestingly, the chemotactic properties of AGMs are also important in the postnatal period, such as in the regulation of immune and inflammatory responses. In particular, AGMs play pivotal roles in inflammation of the nervous system, by either stimulating or inhibiting inflammatory responses, depending on specific ligand-receptor combinations. Understanding such regulatory functions of AGMs in neuroinflammation may allow finding new molecular targets to treat neurodegenerative diseases, in which neuroinflammation underlies aetiology and progression.

EphrinB3 restricts endogenous neural stem cell migration after traumatic brain injury

Traumatic brain injury (TBI) leads to a series of pathological events that can have profound influences on motor, sensory and cognitive functions. Conversely, TBI can also stimulate neural stem/progenitor cell proliferation leading to increased numbers of neuroblasts migrating outside their restrictive neurogenic zone to areas of damage in support of tissue integrity. Unfortunately, the factors that regulate migration are poorly understood. Here, we examine whether ephrinB3 functions to restrict neuroblasts from migrating outside the subventricular zone (SVZ) and rostral migratory stream (RMS). We have previously shown that ephrinB3 is expressed in tissues surrounding these regions, including the overlying corpus callosum (CC), and is reduced after controlled cortical impact (CCI) injury. Our current study takes advantage of ephrinB3 knockout mice to examine the influences of ephrinB3 on neuroblast migration into CC and cortex tissues after CCI injury. Both injury and/or ephrinB3 deficiency led to increased neuroblast numbers and enhanced migration outside the SVZ/RMS zones. Application of soluble ephrinB3-Fc molecules reduced neuroblast migration into the CC after injury and limited neuroblast chain migration in cultured SVZ explants. Our findings suggest that ephrinB3 expression in tissues surrounding neurogenic regions functions to restrict neuroblast migration outside the RMS by limiting chain migration.

Connexin 43 stabilizes astrocytes in a stroke-like milieu to facilitate neuronal recovery

AIM

Connexin 43 (Cx43) is a member of connexin family mainly expressed in astrocytes, which forms gap junctions and hemichannels and maintains the normal shape and function of astrocytes. In this study we investigated the role of Cx43 in astrocytes in facilitating neuronal recovery during ischemic stroke.

METHODS

Primary culture of astrocytes or a mixed culture of astrocytes and cortical neurons was subjected to oxygen glucose deprivation and reperfusion (OGD/R). The expression of Cx43 and Ephrin-A4 in astrocytes was detected using immunocytochemical staining and Western blot assays. Intercellular Ca(2+) concentration was determined with Fluo-4 AM fluorescent staining. Middle cerebral artery occlusion (MCAO) model rats were used for in vivo studies.

RESULTS

OGD/R treatment of cultured astrocytes caused a decrement of Cx43 expression and translocation of Cx43 from cell membrane to cytoplasm, accompanied by cell retraction. Furthermore, OGD/R increased intracellular Ca(2+) concentration, activated CaMKII/CREB pathways and upregulated expression of Ephrin-A4 in the astrocytes. All these changes in OGD/R-treated astrocytes were alleviated by overexpression of Cx43. In the cortical neurons cultured with astrocytes, OGD/R inhibited the neurite growth, whereas overexpression of Cx43 or knockdown of Ephrin-A4 in astrocytes restored the neurite growth. In MCAO model rats, neuronal recovery was found to be correlated with the recuperation of Cx43 and Ephrin-A4 in astrocytes.

CONCLUSION

Cx43 can stabilize astrocytes and facilitate the resistance to the deleterious effects of a stroke-like milieu and promote neuronal recovery.

Development and structural analysis of a nanomolar cyclic peptide antagonist for the EphA4 receptor

The EphA4 receptor is highly expressed in the nervous system, and recent findings suggest that its signaling activity hinders neural repair and exacerbates certain neurodegenerative processes. EphA4 has also been implicated in cancer progression. Thus, EphA4 inhibitors represent potential therapeutic leads and useful research tools to elucidate the role of EphA4 in physiology and disease. Here, we report the structure of a cyclic peptide antagonist, APY, in complex with the EphA4 ligand-binding domain (LBD), which represents the first structure of a cyclic peptide bound to a receptor tyrosine kinase. The structure shows that the dodecameric APY efficiently occupies the ephrin ligand-binding pocket of EphA4 and promotes a "closed" conformation of the surrounding loops. Structure-guided relaxation of the strained APY β-turn and amidation of the C terminus to allow an additional intrapeptide hydrogen bond yielded APY-βAla8.am, an improved APY derivative that binds to EphA4 with nanomolar affinity. APY-βAla8.am potently inhibits ephrin-induced EphA4 activation in cells and EphA4-dependent neuronal growth cone collapse, while retaining high selectivity for EphA4. The two crystal structures of APY and APY-βAla8.am bound to EphA4, in conjunction with secondary phage display screens, highlighted peptide residues that are essential for EphA4 binding as well as residues that can be modified. Thus, the APY scaffold represents an exciting prototype, particularly since cyclic peptides have potentially favorable metabolic stability and are emerging as an important class of molecules for disruption of protein-protein interactions.

The blood-brain barrier as a target in traumatic brain injury treatment

Traumatic brain injury (TBI) is one of the most frequent causes of death in the young population. Several clinical trials have unsuccessfully focused on direct neuroprotective therapies. Recently immunotherapeutic strategies shifted into focus of translational research in acute CNS diseases. Cross-talk between activated microglia and blood-brain barrier (BBB) could initiate opening of the BBB and subsequent recruitment of systemic immune cells and mediators into the brain. Stabilization of the BBB after TBI could be a promising strategy to limit neuronal inflammation, secondary brain damage and acute neurodegeneration. This review provides an overview on the pathophysiology of TBI and brain edema formation including definitions and classification of TBI, current clinical treatment strategies, as well as current understanding on the underlying cellular processes. A summary of in vivo and in vitro models to study different aspects of TBI is presented. Three mechanisms proposed for stabilization of the BBB, myosin light chain kinases, glucocorticoid receptors and peroxisome proliferator-activated receptors are reviewed for their influence on barrier-integrity and outcome after TBI. In conclusion, the BBB is recommended as a promising target for the treatment of traumatic brain injury, and it is suggested that a combination of BBB stabilization and neuroprotectants may improve therapeutic success.

Ephrin-A3 reverse signaling regulates hippocampal neuronal damage and astrocytic glutamate transport after transient global ischemia

Increasing evidence indicates that the Eph receptors and their ephrin ligands are involved in the regulation of interactions between neurons and astrocytes. Moreover, astrocytic ephrin-A3 reverse signaling mediated by EphA4 receptors is necessary for controlling the abundance of glial glutamate transporters. However, the role of ephrin-A3 reverse signaling in astrocytic function and neuronal death under ischemic conditions remains unclear. In the present study, we found that the EphA4 receptor and its ephrin-A3 ligand, which were distributed in neurons and astrocytes, respectively, in the hippocampus showed a coincident up-regulation of protein expression in the early stage of ischemia. Application of clustered EphA4 decreased the expressions of astrocytic glutamate transporters together with astrocytic glutamate uptake capacity through activating ephrin-A3 reverse signaling. In consequence, neuronal loss was aggravated in the CA1 region of the hippocampus accompanied by impaired hippocampus-dependent spatial memory when clustered EphA4 treatment was administered prior to transient global ischemia. These findings indicate that EphA4-mediated ephrin-A3 reverse signaling is a crucial mechanism for astrocytes to control glial glutamate transporters and prevent glutamate excitotoxicity under pathological conditions. Astrocytic ephrin-A3 reverse signaling mediated by EphA4 receptor is necessary for controlling the abundance of glial glutamate transporters under physiological conditions. However, the role of ephrin-A3 reverse signaling in astrocytic function and neuronal death under ischemic conditions remains unclear. We found EphA4-mediated ephrin-A3 reverse signaling to be a crucial mechanism for astrocytes to control glial glutamate transporters and protect hippocampal neurons from glutamate excitotoxicity under ischemic conditions, this cascade representing a potential therapeutic target for stroke.

Involvement of p38 MAPK in reactive astrogliosis induced by ischemic stroke

Reactive astrogliosis is an essential feature of astrocytic response to all forms of central nervous system (CNS) injury and disease, which may benefit or harm surrounding neural and non-neural cells. Despite extensive study, its molecular triggers remain largely unknown in term of ischemic stroke. In the current study we investigated the role p38 mitogen-activated protein kinase (MAPK) in astrogliosis both in vitro and in vivo. In a mouse model of middle cerebral artery occlusion (MCAO), p38 MAPK activation was observed in the glia scar area, along with increased glial fibrillary acidic protein (GFAP) expression. In primary astrocyte cultures, hypoxia and scratch injury-induced astrogliosis was attenuated by both p38 inhibition and knockout of p38 MAPK. In addition, both knockout and inhibition of p38 MAPK also reduced astrocyte migration, but did not affect astrocyte proliferation. In a mouse model of permanent MCAO, no significant difference in motor function recovery and lesion volume was observed between conditional GFAP/p38 MAPK knockout mice and littermates. While a significant reduction of astrogliosis was observed in the GFAP/p38 knockout mice compared with the littermates. Our findings suggest that p38 MAPK signaling pathway plays an important role in the ischemic stroke-induced astrogliosis and thus may serve as a novel target to control glial scar formation.

Genome-wide association study identifies ephrin type A receptors implicated in paclitaxel induced peripheral sensory neuropathy

BACKGROUND

Peripheral neuropathy is the dose limiting toxicity of paclitaxel, a chemotherapeutic drug widely used to treat solid tumours. This toxicity exhibits great inter-individual variability of unknown origin. The present study aimed to identify genetic variants associated with paclitaxel induced neuropathy via a whole genome approach.

METHODS

A genome-wide association study (GWAS) was performed in 144 white European patients uniformly treated with paclitaxel/carboplatin and for whom detailed data on neuropathy was available. Per allele single nucleotide polymorphism (SNP) associations were assessed by Cox regression, modelling the cumulative dose of paclitaxel up to the development of grade 2 sensory neuropathy.

RESULTS

The strongest evidence of association was observed for the ephrin type A receptor 4 (EPHA4) locus (rs17348202, p=1.0×10(-6)), and EPHA6 and EPHA5 were among the top 25 and 50 hits (rs301927, p=3.4×10(-5) and rs1159057, p=6.8×10(-5)), respectively. A meta-analysis of EPHA5-rs7349683, the top marker for paclitaxel induced neuropathy in a previous GWAS (r(2)=0.79 with rs1159057), gave a hazard ratio (HR) estimate of 1.68 (p=1.4×10(-9)). Meta-analysis of the second hit of this GWAS, XKR4-rs4737264, gave a HR of 1.71 (p=3.1×10(-8)). Imputed SNPs at LIMK2 locus were also strongly associated with this toxicity (HR=2.78, p=2.0×10(-7)).

CONCLUSIONS

This study provides independent support of EPHA5-rs7349683 and XKR4-rs4737264 as the first markers of risk of paclitaxel induced neuropathy. In addition, it suggests that other EPHA genes also involved in axonal guidance and repair following neural injury, as well as LIMK2 locus, may play an important role in the development of this toxicity. The identified SNPs could form the basis for individualised paclitaxel chemotherapy.

EphA4 receptor tyrosine kinase is a modulator of onset and disease severity of experimental autoimmune encephalomyelitis (EAE)

The EphA4 receptor tyrosine kinase is a major regulator of axonal growth and astrocyte reactivity and is a possible inflammatory mediator. Given that multiple sclerosis (MS) is primarily an inflammatory demyelinating disease and in mouse models of MS, such as experimental autoimmune encephalomyelitis (EAE), axonal degeneration and reactive gliosis are prominent clinical features, we hypothesised that endogenous EphA4 could play a role in modulating EAE. EAE was induced in EphA4 knockout and wildtype mice using MOG peptide immunisation and clinical severity and histological features of the disease were then compared in lumbar spinal cord sections. EphA4 knockout mice exhibited a markedly less severe clinical course than wildtype mice, with a lower maximum disease grade and a slightly later onset of clinical symptoms. Numbers of infiltrating T cells and macrophages, the number and size of the lesions, and the extent of astrocytic gliosis were similar in both genotypes; however, EphA4 knockout mice appeared to have decreased axonal pathology. Blocking of EphA4 in wildtype mice by administration of soluble EphA4 (EphA4-Fc) as a decoy receptor following induction of EAE produced a delay in onset of clinical symptoms; however, most mice had clinical symptoms of similar severity by 22 days, indicating that EphA4 blocking treatment slowed early EAE disease evolution. Again there were no apparent differences in histopathology. To determine whether the role of EphA4 in modulating EAE was CNS mediated or due to an altered immune response, MOG primed T cells from wildtype and EphA4 knockout mice were passively transferred into naive recipient mice and both were shown to induce disease of equivalent severity. These results are consistent with a non-inflammatory, CNS specific, deleterious effect of EphA4 during neuroinflammation that results in axonal pathology.

Partial change in EphA4 knockout mouse phenotype: loss of diminished GFAP upregulation following spinal cord injury

In a previous study we found that the EphA4 receptor inhibits regeneration following spinal cord injury by blocking regrowth of axons and regulation of astrocyte reactivity. In our original studies using EphA4 null mice [Goldshmit et al., J. Neurosci., 2004] we found attenuated astrocyte reactivity following spinal cord injury. Several other studies have now supported the role of EphA4 in regulating neural regeneration but a recent study [Herrmann et al., Exp. Neurol., 2010] did not find an effect of EphA4 on astrocyte reactivity. Re-examination of astrocytic gliosis following injury in our current cohort of EphA4 null mice revealed that they no longer showed attenuation of astrocyte reactivity, however other EphA4 null mouse phenotypes, such as decreased size of the dorsal funiculus were unaltered. We hypothesised that long-term breeding on the C57Bl/6 background may influence the EphA4-mediated astrocyte phenotype and compared astrocytic gliosis at 4 days following spinal cord injury in wildtype and EphA4 null mice on the C57Bl/6 background and backcrossed C57Bl/6×129Sv(F2) mice, as well as wildtype 129Sv mice. 129Sv mice had increased GFAP expression and increased numbers of reactive GFAP astrocytes compared to C57Bl/6 mice. There was no significant effect of EphA4 deletion on GFAP expression in C57Bl/6 mice or the F2 crosses other than a moderately decreased number of EphA4 null astrocytes in C57Bl/6 mice using one of two antibodies. Therefore, there has been an apparent change in EphA4-mediated astroglial phenotype associated with long term breeding of the EphA4 colony but it does not appear to be influenced by background mouse strain.

Differential gene expression in the EphA4 knockout spinal cord and analysis of the inflammatory response following spinal cord injury

Mice lacking the axon guidance molecule EphA4 have been shown to exhibit extensive axonal regeneration and functional recovery following spinal cord injury. To assess mechanisms by which EphA4 may modify the response to neural injury a microarray was performed on spinal cord tissue from mice with spinal cord injury and sham injured controls. RNA was purified from spinal cords of adult EphA4 knockout and wild-type mice four days following lumbar spinal cord hemisection or laminectomy only and was hybridised to Affymetrix All-Exon Array 1.0 GeneChips™. While subsequent analyses indicated that several pathways were altered in EphA4 knockout mice, of particular interest was the attenuated expression of a number of inflammatory genes, including Arginase 1, expression of which was lower in injured EphA4 knockout compared to wild-type mice. Immunohistological analyses of different cellular components of the immune response were then performed in injured EphA4 knockout and wildtype spinal cords. While numbers of infiltrating CD3+ T cells were low in the hemisection model, a robust CD11b+ macrophage/microglial response was observed post-injury. There was no difference in the overall number or spread of macrophages/activated microglia in injured EphA4 knockout compared to wild-type spinal cords at 2, 4 or 14 days post-injury, however a lower proportion of Arginase-1 immunoreactive macrophages/activated microglia was observed in EphA4 knockout spinal cords at 4 days post-injury. Subtle alterations in the neuroinflammatory response in injured EphA4 knockout spinal cords may contribute to the regeneration and recovery observed in these mice following injury.

Models of CNS injury in the nonhuman primate: A new era for treatment strategies

Central nervous system (CNS) injuries affect all levels of society indiscriminately, resulting in functional and behavioral deficits with devastating impacts on life expectancies, physical and emotional wellbeing. Considerable literature exists describing the pathophysiology of CNS injuries as well as the cellular and molecular factors that inhibit regrowth and regeneration of damaged connections. Based on these data, numerous therapeutic strategies targeting the various factors of repair inhibition have been proposed and on-going assessment has demonstrated some promising results in the laboratory environ. However, several of these treatment strategies have subsequently been taken into clinical trials but demonstrated little to no improvement in patient outcomes. As a result, options for clinical interventions following CNS injuries remain limited and effective restorative treatment strategies do not as yet exist. This review discusses some of the current animal models, with focus on nonhuman primates, which are currently being modeled in the laboratory for the study of CNS injuries. Last, we review the current understanding of the mechanisms underlying repair/regrowth inhibition and the current trends in experimental treatment strategies that are being assessed for potential translation to clinical applications.

Fragment based lead discovery of small molecule inhibitors for the EPHA4 receptor tyrosine kinase

The in silico identification, optimization and crystallographic characterization of a 6,7,8,9-tetrahydro-3H-pyrazolo[3,4-c]isoquinolin-1-amine scaffold as an inhibitor for the EPHA4 receptor tyrosine kinase is described. A database containing commercially available compounds was subjected to an in silico screening procedure which was focused on finding novel, EPHA4 hinge binding fragments. This resulted in the identification of 6,7,8,9-tetrahydro-3H-pyrazolo[3,4-c]isoquinolin-1-amine derivatives as EPHA4 inhibitors. Hit exploration yielded a compound with 2 μM (IC(50)) affinity for the EPHA4 receptor tyrosine kinase domain. Soaking experiments into a crystal of the EPHA4 kinase domain gave a 2.11Å X-ray structure of the EPHA4 - inhibitor complex, which confirmed the binding mode of the scaffold as proposed by the initial in silico work. The results underscore the strength of fragment based in silico screening as a tool for the discovery of novel lead compounds as small molecule kinase inhibitors.