EphB3: an endogenous mediator of adult axonal plasticity and regrowth after CNS injury

CHD2 Regulates Neuron-Glioma Interactions in Pediatric Glioma

High-grade gliomas (HGG) are deadly diseases for both adult and pediatric patients. Recently, it has been shown that neuronal activity promotes the progression of multiple subgroups of HGG. However, epigenetic mechanisms that govern this process remain elusive. Here we report that the chromatin remodeler chromodomain helicase DNA-binding protein 2 (CHD2) regulates neuron-glioma interactions in diffuse midline glioma (DMG) characterized by onco-histone H3.1K27M. Depletion of CHD2 in H3.1K27M DMG cells compromises cell viability and neuron-to-glioma synaptic connections in vitro, neuron-induced proliferation of H3.1K27M DMG cells in vitro and in vivo, activity-dependent calcium transients in vivo, and extends the survival of H3.1K27M DMG-bearing mice. Mechanistically, CHD2 coordinates with the transcription factor FOSL1 to control the expression of axon-guidance and synaptic genes in H3.1K27M DMG cells. Together, our study reveals a mechanism whereby CHD2 controls the intrinsic gene program of the H3.1K27M DMG subtype, which in turn regulates the tumor growth-promoting interactions of glioma cells with neurons. Significance: Neurons drive the proliferation and invasion of glioma cells. Here we show that chromatin remodeler chromodomain helicase DNA-binding protein 2 controls the epigenome and expression of axon-guidance and synaptic genes, thereby promoting neuron-induced proliferation of H3.1K27M diffuse midline glioma and the pathogenesis of this deadly disease.

Circular RNA circRest regulates manganese induced cell apoptosis by targeting the mmu-miR-6914-5p/Ephb3 axis

Overexposure to manganese (Mn) can lead to neurotoxicity, the underlying mechanisms remain incompletely understood. Circular RNAs (circRNAs) have emerged as important regulators in various biological processes. It is plausible that circRNAs may be involved in the biological mechanisms underlying Mn caused neurotoxicity. Here, circRest was downregulated in Mn-exposed mouse neuroblastoma cells (N2a cells) by RNA sequencing and quantitative real-time PCR. When circRest was overexpressed, it led to an increase in cell viability and a decrease in apoptosis following Mn exposure. Conversely, silencing circRest resulted in opposite effects in N2a cells. Further investigation revealed that circRest acts as a mmu-miR-6914-5p sponge, and mmu-miR-6914-5p could bind and inhibit Ephb3, thereby promoting apoptosis in N2a cells. This was confirmed through RNA antisense purification and dual luciferase reporter assays. Additionally, the circRest/mmu-miR-6914-5p/Ephb3 axis may influence memory and learning in mice following Mn exposure. In conclusion, our study uncovers a novel mechanism by which circRest may attenuate Mn caused neurotoxicity via the mmu-miR-6914-5p/Ephb3 axis.

Role and mechanism of EphB3 in epileptic seizures and epileptogenesis through Kalirin

BACKGROUND

The EphB receptor tyrosine kinase family participates in intricate signaling pathways that orchestrate neural networks, guide neuronal axon development, and modulate synaptic plasticity through interactions with surface-bound ephrinB ligands. Additionally, Kalirin, a Rho guanine nucleotide exchange factor, is notably expressed in the postsynaptic membrane of excitatory neurons and plays a role in synaptic morphogenesis. This study postulates that Kalirin may act as a downstream effector of EphB3 in epilepsy. This investigation focuses on understanding the link between EphB3 and epilepsy.

MATERIALS AND METHODS

Chronic seizure models using LiCl-pilocarpine (LiCl/Pilo) and pentylenetetrazol were developed in rats. Neuronal excitability was gauged through whole-cell patch clamp recordings on rat hippocampal slices. Real-time PCR determined Kalirin's mRNA expression, and Western blotting was employed to quantify EphB3 and Kalirin protein levels. Moreover, dendritic spine density in epileptic rats was evaluated using Golgi staining.

RESULTS

Modulation of EphB3 functionality influenced acute seizure severity, latency duration, and frequency of spontaneous recurrent seizures. Golgi staining disclosed an EphB3-driven alteration in dendritic spine density within the hippocampus of epileptic rats, underscoring its pivotal role in the reconfiguration of hippocampal neural circuits. Furthermore, our data propose Kalirin as a prospective downstream mediator of the EphB3 receptor.

CONCLUSIONS

Our findings elucidate that EphB3 impacts the action potential dynamics in isolated rat hippocampal slices and alters dendritic spine density in the inner molecular layer of epileptic rat hippocampi, likely through Kalirin-mediated pathways. This hints at EphB3's significant role in shaping excitatory circuit loops and recurrent seizure activity via Kalirin.

Platelet formation and activation are influenced by neuronal guidance proteins

Platelets are anucleate blood cells derived from megakaryocytes. They link the fundamental functions of hemostasis, inflammation and host defense. They undergo intracellular calcium flux, negatively charged phospholipid translocation, granule release and shape change to adhere to collagen, fibrin and each other, forming aggregates, which are key to several of their functions. In all these dynamic processes, the cytoskeleton plays a crucial role. Neuronal guidance proteins (NGPs) form attractive and repulsive signals to drive neuronal axon navigation and thus refine neuronal circuits. By binding to their target receptors, NGPs rearrange the cytoskeleton to mediate neuron motility. In recent decades, evidence has indicated that NGPs perform important immunomodulatory functions and influence platelet function. In this review, we highlight the roles of NGPs in platelet formation and activation.

Cannabigerol Activates Cytoskeletal Remodeling via Wnt/PCP in NSC-34: An In Vitro Transcriptional Study

Cannabigerol (CBG) is a non-psychoactive phytocannabinoid present in the Cannabis sativa L. plant. In our study, CBG at the concentration of 10 µM was used to treat NSC-34 motor neuron-like cells. The aim of the study was to evaluate the effects of CBG on NSC-34 cells, using next-generation sequencing (NGS) technology. Analysis showed the activation of the WNT/planar cell polarity (PCP) pathway and Ephrin-Eph signaling. The results revealed that CBG increases the expression of genes associated with the onset process of cytoskeletal remodeling and axon guidance.

Detection of repeat expansions in large next generation DNA and RNA sequencing data without alignment

Bioinformatic methods for detecting short tandem repeat expansions in short-read sequencing have identified new repeat expansions in humans, but require alignment information to identify repetitive motif enrichment at genomic locations. We present superSTR, an ultrafast method that does not require alignment. superSTR is used to process whole-genome and whole-exome sequencing data, and perform the first STR analysis of the UK Biobank, efficiently screening and identifying known and potential disease-associated STRs in the exomes of 49,953 biobank participants. We demonstrate the first bioinformatic screening of RNA sequencing data to detect repeat expansions in humans and mouse models of ataxia and dystrophy.

EZH2-mediated epigenetic suppression of EphB3 inhibits gastric cancer proliferation and metastasis by affecting E-cadherin and vimentin expression

EphB3 is a member of the EPH family of receptors and has been found to play a role in the carcinogenesis of some human cancers. However, its expression and clinical significance in gastric cancer (GC) have not been well documented. In the present study, we detected the expression of EphB3 in GC and adjacent noncancerous tissues and explored its relationships with the clinicopathological features and prognosis of GC patients. It was found that EphB3 silenced GC cells epigenetically by direct transcriptional repression of GC cells via polycomb group protein EZH2 mediation. EphB3 was downregulated in GC cells and tissues, and EphB3 depletion promoted GC cell growth and invasion, while ectopic overexpression of EphB3 produced a significant anti-tumor effect. EphB3 was found to be involved in epithelial-mesenchymal transition by regulating E-cadherin and vimentin expression. In addition, patients with reduced EphB3 expression had shorter disease-free survival (DFS), indicating that EphB3 may prove to be a biomarker for prognosis of GC. These results demonstrated that EphB3 functioned as a tumor-suppressor and prognostic biomarker in GC.

Exploring Optic Nerve Axon Regeneration

Background:

Traumatic optic nerve injury is a leading cause of irreversible blindness across the world and causes progressive visual impairment attributed to the dysfunction and death of retinal ganglion cells (RGCs). To date, neither pharmacological nor surgical interventions are sufficient to halt or reverse the progress of visual loss. Axon regeneration is critical for functional recovery of vision following optic nerve injury. After optic nerve injury, RGC axons usually fail to regrow and die, leading to the death of the RGCs and subsequently inducing the functional loss of vision. However, the detailed molecular mechanisms underlying axon regeneration after optic nerve injury remain poorly understood.

Methods:

Research content related to the detailed molecular mechanisms underlying axon regeneration after optic nerve injury have been reviewed.

Results:

The present review provides an overview of regarding potential strategies for axonal regeneration of RGCs and optic nerve repair, focusing on the role of cytokines and their downstream signaling pathways involved in intrinsic growth program and the inhibitory environment together with axon guidance cues for correct axon guidance. A more complete understanding of the factors limiting axonal regeneration will provide a rational basis, which contributes to develop improved treatments for optic nerve regeneration. These findings are encouraging and open the possibility that clinically meaningful regeneration may become achievable in the future.

Conclusion:

Combination of treatments towards overcoming growth-inhibitory molecules and enhancing intrinsic growth capacity combined with correct guidance using axon guidance cues is crucial for developing promising therapies to promote axon regeneration and functional recovery after ON injury.

Differential Expression Patterns of Eph Receptors and Ephrin Ligands in Human Cancers

Eph receptors constitute the largest family of receptor tyrosine kinases, which are activated by ephrin ligands that either are anchored to the membrane or contain a transmembrane domain. These molecules play important roles in the development of multicellular organisms, and the physiological functions of these receptor-ligand pairs have been extensively documented in axon guidance, neuronal development, vascular patterning, and inflammation during tissue injury. The recognition that aberrant regulation and expression of these molecules lead to alterations in proliferative, migratory, and invasive potential of a variety of human cancers has made them potential targets for cancer therapeutics. We present here the involvement of Eph receptors and ephrin ligands in lung carcinoma, breast carcinoma, prostate carcinoma, colorectal carcinoma, glioblastoma, and medulloblastoma. The aberrations in their abundances are described in the context of multiple signaling pathways, and differential expression is suggested as the mechanism underlying tumorigenesis.

Overlapping Mechanisms of Peripheral Nerve Regeneration and Angiogenesis Following Sciatic Nerve Transection

Peripheral nervous system owns the ability of self-regeneration, mainly in its regenerative microenvironment including vascular network reconstruction. More recently, more attentions have been given to the close relationship between tissue regeneration and angiogenesis. To explore the overlap of molecular mechanisms and key regulation molecules between peripheral nerve regeneration and angiogenesis post peripheral nerve injury, integrative and bioinformatic analysis was carried out for microarray data of proximal stumps after sciatic nerve transection in SD rats. Nerve regeneration and angiogenesis were activated at 1 day immediately after sciatic nerve transection simultaneously. The more obvious changes of transcription regulators and canonical pathways suggested a phase transition between 1 and 4 days of both nerve regeneration and angiogenesis after sciatic nerve transection. Furthermore, 16 differentially expressed genes participated in significant biological processes of both nerve regeneration and angiogenesis, a few of which were validated by qPCR and immunofluorescent staining. It was demonstrated that STAT3, EPHB3, and Cdc42 co-expressed in Schwann cells and vascular endothelial cells to play a key role in regulation of nerve regeneration and angiogenesis simultaneously response to sciatic nerve transection. We provide a framework for understanding biological processes and precise molecular correlations between peripheral nerve regeneration and angiogenesis after peripheral nerve transection. Our work serves as an experimental basis and a valuable resource to further understand molecular mechanisms that define nerve injury-induced micro-environmental variation for achieving desired peripheral nerve regeneration.

EphB3 protein is associated with histological grade and FIGO stage in ovarian serous carcinomas

Eph (Erythropoietin-producing human hepatocellular carcinoma cell) is the largest subfamily of receptor tyrosine kinases. Eph receptors and their ephrin ligands are involved in embryonic development and physiological processes. Aberrant expression of Eph/ephrin may contribute to a variety of diseases including cancer. EphB3 is a member of Eph receptors and has been found to play roles in carcinogenesis of some types of human cancer. But, its expression and clinical significance in ovarian serous carcinoma have not been well investigated and are unknown. In this study, a set of ovarian tissues including normal fallopian tube, serous borderline tumor, and serous carcinoma were subjected to immunohistochemistry using a specific polyclonal antibody for EphB3. The relationship between EphB3 expression and clinicopathological parameters was statistically analyzed. EphB3 was strongly expressed in all fallopian tube specimens (19/19, 100%). EphB3 was negatively or weekly expressed in 1 of 17 (5.8%) in borderline tumors and 26 of 50 (52.0%) in serous carcinomas, moderately expressed in 7 of 17 (41.2%) in borderline tumors and 14 of 50 (28%) in serous carcinomas, and strongly expressed in 9 17 (52.9%) in borderline tumors and 10 of 50 (20%) in serous carcinomas. EphB3 expression is significantly reduced in serous carcinomas compared with normal fallopian tubes and borderline tumors (p < 0.001). EphB3 expression is negatively associated with histological grade (p < 0.001, r_s = -0.613) and FIGO stage (p = 0.001, r_s = -0.464) of serous carcinomas. Our results show EphB3 protein lost in ovarian serous carcinoma and is associated with tumor grade and FIGO stage, which indicate EphB3 protein may play a role in carcinogenesis of ovarian serous carcinoma and may be used as a molecular marker for prognosis.

Astrocytic Ephrin-B1 Regulates Synapse Remodeling Following Traumatic Brain Injury

Traumatic brain injury (TBI) can result in tissue alterations distant from the site of the initial injury, which can trigger pathological changes within hippocampal circuits and are thought to contribute to long-term cognitive and neuropsychological impairments. However, our understanding of secondary injury mechanisms is limited. Astrocytes play an important role in brain repair after injury and astrocyte-mediated mechanisms that are implicated in synapse development are likely important in injury-induced synapse remodeling. Our studies suggest a new role of ephrin-B1, which is known to regulate synapse development in neurons, in astrocyte-mediated synapse remodeling following TBI. Indeed, we observed a transient upregulation of ephrin-B1 immunoreactivity in hippocampal astrocytes following moderate controlled cortical impact model of TBI. The upregulation of ephrin-B1 levels in hippocampal astrocytes coincided with a decline in the number of vGlut1-positive glutamatergic input to CA1 neurons at 3 days post injury even in the absence of hippocampal neuron loss. In contrast, tamoxifen-induced ablation of ephrin-B1 from adult astrocytes in ephrin-B1^loxP/yERT2-Cre^GFAP mice accelerated the recovery of vGlut1-positive glutamatergic input to CA1 neurons after TBI. Finally, our studies suggest that astrocytic ephrin-B1 may play an active role in injury-induced synapse remodeling through the activation of STAT3-mediated signaling in astrocytes. TBI-induced upregulation of STAT3 phosphorylation within the hippocampus was suppressed by astrocyte-specific ablation of ephrin-B1 in vivo, whereas the activation of ephrin-B1 in astrocytes triggered an increase in STAT3 phosphorylation in vitro. Thus, regulation of ephrin-B1 signaling in astrocytes may provide new therapeutic opportunities to aid functional recovery after TBI.

Regulation of axon regeneration by the RNA repair and splicing pathway

Mechanisms governing a neuron’s regenerative ability are important but not well understood. We identified Rtca, RNA 3′-terminal phosphate cyclase, as an inhibitor for axon regeneration. Removal of dRtca cell-autonomously enhanced axon regrowth in the Drosophila central nervous system, whereas its overexpression reduced axon regeneration in the periphery. Rtca along with the RNA ligase Rtcb and its catalyst Archease operate in the RNA repair/splicing pathway important for stress induced mRNA splicing, including that of Xbp1, a cellular stress sensor. dRtca and dArchease had opposing effects on Xbp1 splicing, and deficiency of dArchease or Xbp1 impeded axon regeneration in Drosophila. Moreover, overexpressing mammalian Rtca in cultured rodent neurons reduced axonal complexity in vitro, whereas reducing its function promoted retinal ganglion cell axon regeneration after optic nerve crush in mice. Our study thus links axon regeneration to cellular stress and RNA metabolism, revealing new potential therapeutic targets for treating nervous system trauma.

Central nervous system regenerative failure: role of oligodendrocytes, astrocytes, and microglia

Animal studies are now showing the exciting potential to achieve significant functional recovery following central nervous system (CNS) injury by manipulating both the inefficient intracellular growth machinery in neurons, as well as the extracellular barriers, which further limit their regenerative potential. In this review, we have focused on the three major glial cell types: oligodendrocytes, astrocytes, and microglia/macrophages, in addition to some of their precursors, which form major extrinsic barriers to regrowth in the injured CNS. Although axotomized neurons in the CNS have, at best, a limited capacity to regenerate or sprout, there is accumulating evidence that even in the adult and, especially after boosting their growth motor, neurons possess the capacity for considerable circuit reorganization and even lengthy regeneration when these glial obstacles to neuronal regrowth are modified, eliminated, or overcome.

Molecular mechanisms underlying the effects of acupuncture on neuropathic pain

Acupuncture has been used to treat neuropathic pain for a long time, but its mechanisms of action remain unknown. In this study, we observed the effects of electroacupuncture and manual acu-puncture on neuropathic pain and on ephrin-B/EphB signaling in rats models of chronic constriction injury-induced neuropathic pain. The results showed that manual acupuncture and elec-puncture significantly reduced mechanical hypersensitivity following chronic constriction injury, es-pecially electroacupuncture treatment. Real-time PCR results revealed that ephrin-B1/B3 and EphB1/B2 mRNA expression levels were significantly increased in the spinal dorsal horns of chronic constriction injury rats. Electroacupuncture and manual acupuncture suppressed the high sion of ephrin-B1 mRNA, and elevated EphB3/B4 mRNA expression. Electroacupuncture signifi-cantly enhanced the mRNA expression of ephrin-B3 and EphB3/B6 in the dorsal horns of neuro-pathic pain rats. Western blot results revealed that electroacupuncture in particular, and manual acupuncture, significantly up-regulated ephrin-B3 protein levels in rat spinal dorsal horns. The re-sults of this study suggest that acupuncture could activate ephrin-B/EphB signaling in neuropathic pain rats and improve neurological function.

Lost in the jungle: new hurdles for optic nerve axon regeneration

The poor regenerative capacity of injured central nervous system (CNS) axons leads to permanent neurological deficits after brain, spinal cord, or optic nerve lesions. In the optic nerve, recent studies showed that stimulation of the cytokine or mammalian target of rapamycin (mTOR) signaling pathways potently enhances sprouting and regeneration of injured retinal ganglion cell axons in adult mice, but does not allow the majority of axons to reach their main cerebral targets. New analyses have revealed axon navigation defects in the optic nerve and at the optic chiasm under conditions of strong growth stimulation. We propose that a balanced growth stimulatory treatment will have to be combined with guidance factors and suppression of local growth inhibitory factors to obtain the full regeneration of long CNS axonal tracts.

Glial scar and immune cell involvement in tissue remodeling and repair following acute CNS injuries

Inadequate axonal regeneration is a common phenomenon occurring following acute injury to the central nervous system (CNS), and is often associated with permanent neurological deficits. The injured axons attempting to regenerate face the inhospitable environment of the CNS scar, which can hinder axonal growth and sprouting. In addition, in response to the insult, intense activation and infiltration of immune cells take place. Both the scar tissue and immune response, which have received a bad reputation in the context of CNS repair are essential for the overall recovery from CNS injuries, but are not optimally controlled. The glial scar contributes to protection of the spared neural tissues by establishing a boundary between damaged and salvageable tissue, and by educating the immune cells to promote the healing of the CNS tissue. In turn, the immune cells, and in particular the infiltrating macrophages, exert several functions at the lesion site, including resolution of the microglial response, control of scar tissue degradation, and production of growth factors; thereby, promoting neuronal survival, axonal regeneration, and tissue remodeling. As axonal regeneration and tissue remodeling are viewed as critical steps for the overall functional recovery following CNS injury, a detailed understanding of the mechanisms underlying the timely formation and degradation of the CNS scar, and its crosstalk with the inflammatory response, are of great importance, both biologically and clinically.

Plasticity in the Injured Brain

Changes in brain circuits occur within specific paradigms of action in the adult brain. These paradigms include changes in behavioral activity patterns, alterations in environmental experience, and direct brain injury. Each of these paradigms can produce axonal sprouting, dendritic morphology changes, and alterations in synaptic connectivity. Activity-, experience-, and injury-dependent plasticity alter neuronal network function and behavioral output, and in the case of brain injury, may produce neurological recovery. The molecular substrate for adult neuronal plasticity overlaps in these three paradigms in key signaling pathways. These common pathways for adult plasticity suggest common mechanisms for activity-, experience-, and injury-dependent plasticity. These common pathways may also interact to enhance or impede each other during adult recovery of function after injury. This review focuses on common molecular changes evoked during the process of adult neuronal plasticity, with a focus on neural repair in stroke.

Three-dimensional evaluation of retinal ganglion cell axon regeneration and pathfinding in whole mouse tissue after injury

Injured retinal ganglion cell (RGC) axons do not regenerate spontaneously, causing loss of vision in glaucoma and after trauma. Recent studies have identified several strategies that induce long distance regeneration in the optic nerve. Thus, a pressing question now is whether regenerating RGC axons can find their appropriate targets. Traditional methods of assessing RGC axon regeneration use histological sectioning. However, tissue sections provide fragmentary information about axonal trajectory and termination. To unequivocally evaluate regenerating RGC axons, here we apply tissue clearance and light sheet fluorescence microscopy (LSFM) to image whole optic nerve and brain without physical sectioning. In mice with PTEN/SOCS3 deletion, a condition known to promote robust regeneration, axon growth followed tortuous paths through the optic nerve, with many axons reversing course and extending towards the eye. Such aberrant growth was prevalent in the proximal region of the optic nerve where strong astroglial activation is present. In the optic chiasms of PTEN/SOCS3 deletion mice and PTEN deletion/Zymosan/cAMP mice, many axons project to the opposite optic nerve or to the ipsilateral optic tract. Following bilateral optic nerve crush, similar divergent trajectory is seen at the optic chiasm compared to unilateral crush. Centrally, axonal projection is limited predominantly to the hypothalamus. Together, we demonstrate the applicability of LSFM for comprehensive assessment of optic nerve regeneration, providing in-depth analysis of the axonal trajectory and pathfinding. Our study indicates significant axon misguidance in the optic nerve and brain, and underscores the need for investigation of axon guidance mechanisms during optic nerve regeneration in adults.

Macrophages in inflammatory multiple sclerosis lesions have an intermediate activation status

Background

Macrophages play a dual role in multiple sclerosis (MS) pathology. They can exert neuroprotective and growth promoting effects but also contribute to tissue damage by production of inflammatory mediators. The effector function of macrophages is determined by the way they are activated. Stimulation of monocyte-derived macrophages in vitro with interferon-γ and lipopolysaccharide results in classically activated (CA/M1) macrophages, and activation with interleukin 4 induces alternatively activated (AA/M2) macrophages.

Methods

For this study, the expression of a panel of typical M1 and M2 markers on human monocyte derived M1 and M2 macrophages was analyzed using flow cytometry. This revealed that CD40 and mannose receptor (MR) were the most distinctive markers for human M1 and M2 macrophages, respectively. Using a panel of M1 and M2 markers we next examined the activation status of macrophages/microglia in MS lesions, normal appearing white matter and healthy control samples.

Results

Our data show that M1 markers, including CD40, CD86, CD64 and CD32 were abundantly expressed by microglia in normal appearing white matter and by activated microglia and macrophages throughout active demyelinating MS lesions. M2 markers, such as MR and CD163 were expressed by myelin-laden macrophages in active lesions and perivascular macrophages. Double staining with anti-CD40 and anti-MR revealed that approximately 70% of the CD40-positive macrophages in MS lesions also expressed MR, indicating that the majority of infiltrating macrophages and activated microglial cells display an intermediate activation status.

Conclusions

Our findings show that, although macrophages in active MS lesions predominantly display M1 characteristics, a major subset of macrophages have an intermediate activation status.

EphB2 signaling regulates lesion-induced axon sprouting but not critical period length in the postnatal auditory brainstem

Background

Studies of developmental plasticity may provide insight into plasticity during adulthood, when neural circuitry is less responsive to losses or changes in input. In the mammalian auditory brainstem, globular bushy cell axons of the ventral cochlear nucleus (VCN) innervate the contralateral medial nucleus of the trapezoid body (MNTB) principal neurons. VCN axonal terminations in MNTB, known as calyces of Held, are very large and specialized for high-fidelity transmission of auditory information. Following unilateral deafferentation during postnatal development, VCN axons from the intact side form connections with novel targets, including the ipsilateral MNTB. EphB signaling has been shown to play a role in this process during the first postnatal week, but mechanisms involved in this reorganization during later developmental periods remain unknown.

Results

We found that EphB2 signaling reduces the number of induced ipsilateral projections to the MNTB after unilateral VCN removal at postnatal day seven (P7), but not after removal of the VCN on one side at P10, after the closure of the critical period for lesion-induced innervation of the ipsilateral MNTB.

Conclusions

Results from this study indicate that molecular mechanisms involved in the development of circuitry may also play a part in rewiring after deafferentation during development, but do not appear to regulate the length of critical periods for plasticity.

Inactivation of the microRNA-183/96/182 cluster results in syndromic retinal degeneration

The microRNA-183/96/182 cluster is highly expressed in the retina and other sensory organs. To uncover its in vivo functions in the retina, we generated a knockout mouse model, designated "miR-183C(GT/GT)," using a gene-trap embryonic stem cell clone. We provide evidence that inactivation of the cluster results in early-onset and progressive synaptic defects of the photoreceptors, leading to abnormalities of scotopic and photopic electroretinograms with decreased b-wave amplitude as the primary defect and progressive retinal degeneration. In addition, inactivation of the miR-183/96/182 cluster resulted in global changes in retinal gene expression, with enrichment of genes important for synaptogenesis, synaptic transmission, photoreceptor morphogenesis, and phototransduction, suggesting that the miR-183/96/182 cluster plays important roles in postnatal functional differentiation and synaptic connectivity of photoreceptors.

Regulation of endogenous neural stem/progenitor cells for neural repair-factors that promote neurogenesis and gliogenesis in the normal and damaged brain

Neural stem/precursor cells in the adult brain reside in the subventricular zone (SVZ) of the lateral ventricles and the subgranular zone (SGZ) of the dentate gyrus in the hippocampus. These cells primarily generate neuroblasts that normally migrate to the olfactory bulb (OB) and the dentate granule cell layer respectively. Following brain damage, such as traumatic brain injury, ischemic stroke or in degenerative disease models, neural precursor cells from the SVZ in particular, can migrate from their normal route along the rostral migratory stream (RMS) to the site of neural damage. This neural precursor cell response to neural damage is mediated by release of endogenous factors, including cytokines and chemokines produced by the inflammatory response at the injury site, and by the production of growth and neurotrophic factors. Endogenous hippocampal neurogenesis is frequently also directly or indirectly affected by neural damage. Administration of a variety of factors that regulate different aspects of neural stem/precursor biology often leads to improved functional motor and/or behavioral outcomes. Such factors can target neural stem/precursor proliferation, survival, migration and differentiation into appropriate neuronal or glial lineages. Newborn cells also need to subsequently survive and functionally integrate into extant neural circuitry, which may be the major bottleneck to the current therapeutic potential of neural stem/precursor cells. This review will cover the effects of a range of intrinsic and extrinsic factors that regulate neural stem/precursor cell functions. In particular it focuses on factors that may be harnessed to enhance the endogenous neural stem/precursor cell response to neural damage, highlighting those that have already shown evidence of preclinical effectiveness and discussing others that warrant further preclinical investigation.

Eph/Ephrin signaling in injury and inflammation

The Eph/ephrin receptor-ligand system plays an important role in embryogenesis and adult life, principally by influencing cell behavior through signaling pathways, resulting in modification of the cell cytoskeleton and cell adhesion. There are 10 EphA receptors, and six EphB receptors, distinguished on sequence difference and binding preferences, that interact with the six glycosylphosphatidylinositol-linked ephrin-A ligands and the three transmembrane ephrin-B ligands, respectively. The Eph/ephrin proteins, originally described as developmental regulators that are expressed at low levels postembryonically, are re-expressed after injury to the optic nerve, spinal cord, and brain in fish, amphibians, rodents, and humans. In rodent spinal cord injury, the up-regulation of EphA4 prevents recovery by inhibiting axons from crossing the injury site. Eph/ephrin proteins may be partly responsible for the phenotypic changes to the vascular endothelium in inflammation, which allows fluid and inflammatory cells to pass from the vascular space into the interstitial tissues. Specifically, EphA2/ephrin-A1 signaling in the lung may be responsible for pulmonary inflammation in acute lung injury. A role in T-cell maturation and chronic inflammation (heart failure, inflammatory bowel disease, and rheumatoid arthritis) is also reported. Although there remains much to learn about Eph/ephrin signaling in human disease, and specifically in injury and inflammation, this area of research raises the exciting prospect that novel therapies will be developed that precisely target these pathways.

Eph-2B, acting as an extracellular ligand, induces differentiation markers in epidermal keratinocytes

In the bi-directional signaling system comprising ephrins (EFNs) and ephrin receptors (Ephs), both EFNs and Ephs simultaneously function both as ligands and as receptors. Importantly, the EFN/Eph system is deregulated in human cancers and has been implicated in the metastatic processes because of its effects on the adhesion and migration of epithelial cells. The idiosyncratic function of Ephs, membrane-bound receptor kinases, as extracellular signaling ligands, has not been extensively studied. This prompted us to explore the transcriptional targets regulated by Ephs acting solely as ligands. To define the ligand function of EphB2 in human epidermal keratinocytes, we treated these cells with EphB2 as Fc-conjugate dimmers, which thus act exclusively as extracellular ligands. We compared the EphB2 and EFNA4 effects during a 48 h time course, using transcriptional profiling. We found that EphB2, acting as a ligand, promotes epidermal differentiation. For example, EphB2 induces expression of markers of epidermal differentiation, including keratins KRT1 and KRT10, SPRRs, desmosomal proteins and cell cycle inhibitors, while suppressing basal layer markers, integrins and cell cycle proteins. The effects of EphB2 are delayed relative to those of EFNA4. Unlike EFNA4, EphB2 did not induce lipid metabolism proteins, this particular aspect of epidermal differentiation seems not to be regulated by EphB2. Our results define the transcriptional targets of the reverse signaling by EphB2 acting exclusively as a ligand and begin to characterize this intriguing function of Ephs.

Myelin-derived ephrinB3 restricts axonal regeneration and recovery after adult CNS injury

Recovery of neurological function after traumatic injury of the adult mammalian central nervous system is limited by lack of axonal growth. Myelin-derived inhibitors contribute to axonal growth restriction, with ephrinB3 being a developmentally important axonal guidance cue whose expression in mature oligodendrocytes suggests a role in regeneration. Here we explored the in vivo regeneration role of ephrinB3 using mice lacking a functional ephrinB3 gene. We confirm that ephrinB3 accounts for a substantial portion of detergent-resistant myelin-derived inhibition in vitro. To assess in vivo regeneration, we crushed the optic nerve and examined retinal ganglion fibers extending past the crush site. Significantly increased axonal regeneration is detected in ephrinB3(-/-) mice. Studies of spinal cord injury in ephrinB3(-/-) mice must take into account altered spinal cord development and an abnormal hopping gait before injury. In a near-total thoracic transection model, ephrinB3(-/-) mice show greater spasticity than wild-type mice for 2 mo, with slightly greater hindlimb function at later time points, but no evidence for axonal regeneration. After a dorsal hemisection injury, increased corticospinal and raphespinal growth in the caudal spinal cord are detected by 6 wk. This increased axonal growth is accompanied by improved locomotor performance measured in the open field and by kinematic analysis. Thus, ephrinB3 contributes to myelin-derived axonal growth inhibition and limits recovery from adult CNS trauma.

Inflammation and axon regeneration

PURPOSE OF REVIEW

The inflammatory response that accompanies neural injury involves multiple cell types and effector molecules with both positive and negative effects. Inflammation is essential for normal regeneration in the peripheral nervous system, and here we review evidence that augmenting inflammation can enhance regeneration in areas of the central nervous system in which it normally does not occur.

RECENT FINDINGS

Within the spinal cord, inflammation enables transplanted sensory neurons to regenerate lengthy axons and enhances the ability of a trophic factor to promote corticospinal tract sprouting. Induction of inflammation in the eye supports survival of retinal ganglion cells and enables them to regenerate injured axons through the optic nerve. These effects are linked to an atypical trophic factor, oncomodulin, along with other, better known molecules. Induction of inflammation within dorsal root ganglia, when combined with other treatments, enables peripheral sensory neurons to regenerate axons into the spinal cord. However, inflammation also has negative effects that impede recovery.

SUMMARY

In light of the importance of inflammation for neural repair, it is important to identify the specific cell types and molecules responsible for the positive and negative effects of inflammation and to develop treatments that tip the balance to favor repair.

Involvement of EphB/Ephrin-B signaling in axonal survival in mouse experimental glaucoma

PURPOSE

To examine the functional significance of EphB/ephrin-B upregulation in mouse experimental glaucoma.

METHODS

In a loss-of-function approach, mouse mutants lacking EphB2 (EphB2(-/-)) or EphB3 (EphB3(-/-)) protein, and mutants expressing EphB2 truncated in the C-terminus (EphB2(lacZ/lacZ)) were subjected to laser-induced ocular hypertension (LIOH), an experimental mouse model of glaucoma. The number of optic nerve axons was counted in paraphenylenediamine (PPD)-stained sections and compared between EphB mutants and wild type littermates. In a gain-of-function approach, retina/optic nerve explants obtained from LIOH-treated animals were exposed to EphB2-Fc recombinant proteins or Fc control proteins. Tissue sections through the optic nerve head (ONH) were labeled with neuron-specific anti-tubulin β-III antibody to determine axonal integrity.

RESULTS

Both EphB2 and EphB3 null mutant mice exhibited more severe axonal degeneration than wild type littermates after treatment with LIOH. Mutant mice in which the C-terminal portion of EphB2 is truncated had an intermediate phenotype. Application of EphB2-Fc recombinant protein to LIOH-treated optic nerve explants resulted in greater sparing of tubulin β-III-containing retinal ganglion cell (RGC) axons.

CONCLUSIONS

These results provide genetic evidence in mice that both EphB/ephrin-B forward and reverse signaling feed into an endogenous pathway to moderate the effects of glaucomatous insult on RGC axons. LIOH-induced axon loss is maintained in retina/optic nerve explants after removal from an ocular hypertensive environment. Exogenous application of EphB2 protein enhances RGC axon survival in explants, suggesting that modulation of Eph/ephrin signaling may be of therapeutic interest.

Chemical priming for spinal cord injury: a review of the literature. Part I-factors involved

INTRODUCTION

There are significant differences between the propensity of neural regeneration between the central and peripheral nervous systems.

MATERIALS AND METHODS

Following a review of the literature, we describe the role of growth factors, guiding factors, and neurite outgrowth inhibitors in the physiology and development of the nervous system as well as the pathophysiology of the spinal cord. We also detail their therapeutic role as well as those of other chemical substances that have recently been found to modify regrowth following cord injury.

CONCLUSIONS

Multiple factors appear to have promising futures for the possibility of improving spinal cord injury following injury.

Growth-associated protein-43 and ephrin B3 induction in the brain of adult SIV-infected rhesus macaques

Understanding the mechanisms of neuronal regeneration and repair in the adult central nervous system is a vital area of research. Using a rhesus lentiviral encephalitis model, we sought to determine whether recovery of neuronal metabolism after injury coincides with the induction of two important markers of synaptodendritic repair: growth-associated protein-43 (GAP-43) and ephrin B3. We examined whether the improvement of neuronal metabolism with combined anti-retroviral therapy (cART) after simian immunodeficiency virus (SIV) infection in rhesus macaques involved induction of GAP-43, also known as neuromodulin, and ephrin B3, both implicated in axonal pathfinding during neurodevelopment and regulation of synapse formation, neuronal plasticity, and repair in adult brain. We utilized magnetic resonance spectroscopy to demonstrate improved neuronal metabolism in vivo in adult SIV-infected cART animals compared to untreated and uninfected controls. We then assessed levels of GAP-43, ephrin B3, and synaptophysin, a pre-synaptic marker, in three brain regions important for cognitive function, cortex, hippocampus, and putamen, by quantitative real-time RT-PCR and immunohistochemistry. Here we demonstrate that (1) GAP-43 mRNA and protein are induced with SIV infection, (2) GAP-43 protein is higher in the hippocampus outer molecular layer in SIV-infected animals that received cART compared to those that did not, and (3) activated microglia and infiltrating SIV-infected macrophages express abundant ephrin B3, an important axonal guidance molecule. We propose a model whereby SIV infection triggers events that lead to induction of GAP-43 and ephrin B3, and that short-term cART results in increased magnitude of repair mechanisms especially in the hippocampus, a region known for high levels of adult plasticity.

Mutations in zebrafish lrp2 result in adult-onset ocular pathogenesis that models myopia and other risk factors for glaucoma

The glaucomas comprise a genetically complex group of retinal neuropathies that typically occur late in life and are characterized by progressive pathology of the optic nerve head and degeneration of retinal ganglion cells. In addition to age and family history, other significant risk factors for glaucoma include elevated intraocular pressure (IOP) and myopia. The complexity of glaucoma has made it difficult to model in animals, but also challenging to identify responsible genes. We have used zebrafish to identify a genetically complex, recessive mutant that shows risk factors for glaucoma including adult onset severe myopia, elevated IOP, and progressive retinal ganglion cell pathology. Positional cloning and analysis of a non-complementing allele indicated that non-sense mutations in low density lipoprotein receptor-related protein 2 (lrp2) underlie the mutant phenotype. Lrp2, previously named Megalin, functions as an endocytic receptor for a wide-variety of bioactive molecules including Sonic hedgehog, Bone morphogenic protein 4, retinol-binding protein, vitamin D-binding protein, and apolipoprotein E, among others. Detailed phenotype analyses indicated that as lrp2 mutant fish age, many individuals—but not all—develop high IOP and severe myopia with obviously enlarged eye globes. This results in retinal stretch and prolonged stress to retinal ganglion cells, which ultimately show signs of pathogenesis. Our studies implicate altered Lrp2-mediated homeostasis as important for myopia and other risk factors for glaucoma in humans and establish a new genetic model for further study of phenotypes associated with this disease.

Complex genetic inheritance, including variable penetrance and severity, underlies many common eye diseases. In this study, we present analysis of a zebrafish mutant, bugeye, which shows complex inheritance of multiple ocular phenotypes that are known risk factors for glaucoma, including high myopia, elevated intraocular pressure, and up-regulation of stress-response genes in retinal ganglion cells. Molecular genetic analysis revealed that mutations in low density lipoprotein receptor-related protein 2 (lrp2) underlie the mutant phenotypes. Lrp2 is a large transmembrane protein expressed in epithelia of the eye. It facilitates transport and clearance of multiple secreted bioactive factors through receptor-mediated endocytosis. Glaucoma, a progressive blinding disorder, usually presents in adulthood and is characterized by optic nerve damage followed by ganglion cell death. In bugeye/lrp2 mutants, ganglion cell death was significantly elevated, but surprisingly moderate, and therefore they do not model this endpoint of glaucoma. As such, bugeye/lrp2 mutants should be considered valuable as a genetic model (A) for buphthalmia, myopia, and regulated eye growth; (B) for identifying genes and pathways that modify the observed ocular phenotypes; and (C) for studying the initiation of retinal ganglion cell pathology in the context of high myopia and elevated intraocular pressure.

Genetic dissection of axon regeneration

Axon regeneration has long been studied in vertebrate model organisms and neuronal cultures. Recent development of axon regeneration paradigms in genetic model organisms, such as Caenorhabditis elegans, Drosophila and zebrafish, has opened an exciting field for in vivo functional dissection of regeneration pathways. Studies in these organisms have discovered essential genes and pathways for axon regrowth. The conservation of these genes crossing animal phyla suggests mechanistic relevance to higher organisms. The power of genetic approaches in these organisms makes large-scale genetic and pharmacological screens feasible and can greatly accelerate the mechanistic understanding of axon regeneration.

Lack of axonal sprouting of spared propriospinal fibers caudal to spinal contusion injury is attributed to chronic axonopathy

We have previously shown that a small percentage of long descending propriospinal tract (LDPT) axons are spared, whereas few short thoracic propriospinal (TPS) fibers survive 2 weeks following severe (50 mm weight drop) low thoracic spinal cord contusion injury (SCI). Here, we extended those findings to a moderate (25 mm weight drop) T9 SCI and assessed the effects of this lesion severity on propriospinal tract fibers at different time periods after injury. We anterogradely labeled fibers with fluororuby (FR) or WGA-HRP to determine their location and number 2, 4, 6, and 16 weeks post-SCI. Findings were compared with non-injured controls. At chronic time points, surviving FR-labeled LDPT fibers rostral to the injury remained as reactive endings or as putative regenerative sprouts. Caudal to the injury, spared LDPT fibers ran along a rim of lateral and ventral white matter, and ended as small abnormal-appearing putative terminal boutons or reactive endings within the intermediate gray matter of lumbosacral cord, with little axonal arborization and no evidence of injury-induced sprouting. One striking difference in the WGA-HRP experimental operates was the increased density of labeling of spared axons within the white matter caudal to the injury compared to controls. This labeling pattern was reminiscent of the labeling found after axotomy in studies by others, and raises a question as to contusion injury-induced impaired axonal transport. We hypothesize that axonal sprouting of axons after partial spinal cord injury seen in previous investigations was not found in the present investigation because of the additional pathological effects of contusion injury, similar to what is observed after traumatic brain injury.

Laser-induced ocular hypertension in albino CD-1 mice

PURPOSE

To establish a laser-induced model of ocular hypertension (LIOH) in albino CD-1 mice and to characterize the sequence of pathologic events triggered by intraocular pressure (IOP) elevation.

METHODS

LIOH was induced unilaterally in CD-1 mice by laser photocoagulation of limbal and episcleral veins 270 degrees to 300 degrees circumferentially, sparing the nasal aspect and the long ciliary arteries. IOP was measured with a rebound tonometer. Hematoxylin and eosin-stained plastic sections were used for morphometric analysis of retinal layers, and retinal whole-mounts were immunostained with anti-Brn-3b to quantify retinal ganglion cell (RGC) gene expression ion and density. Axonal and myelin morphologies were characterized using appropriate antibodies, and axon counts were obtained from paraphenylenediamine-stained optic nerve sections.

RESULTS

LIOH resulted in IOP doubling within 4 hours after laser treatment, which returned to normal by 7 days. Axon degenerative changes, reactive plasticity, and aberrant regrowth were detected at the optic nerve head (ONH) as early as 4 days after treatment. By 7 days, axon number was significantly reduced in the myelinated optic nerve, with concurrent signs of myelin degradation. At 14 days, Brn-3b(+) RGC density was reduced, with neuronal loss confined to the RGC layer and no apparent effects on other retinal layers.

CONCLUSIONS

Laser photocoagulation of limbal and episcleral veins induces transient ocular hypertension in albino CD-1 mice. The ensuing retinal and optic nerve pathologic events recapitulated key features of glaucoma and placed ONH RGC axon responses as an early manifestation of damage. LIOH in albino mice may be useful as a mouse model to examine mechanisms of RGC and axon glaucomatous injury.

Axonal/glial upregulation of EphB/ephrin-B signaling in mouse experimental ocular hypertension

PURPOSE

To use a laser-induced ocular hypertension (LIOH) mouse model to examine the optic nerve head (ONH) expression of EphB/ephrin-B, previously shown to be upregulated in glaucomatous DBA/2J mice. To relate ephrin-B reverse signaling with states of axonal response to disease.

METHODS

LIOH was induced unilaterally in CD-1 mice by laser photocoagulation of limbal and episcleral veins. Intraocular pressure (IOP) was measured with a tonometer. EphB/ephrin-B mRNA expression was assessed by in situ hybridization on eyecup cryosections and real-time PCR. Cell specific markers were used to identify the cellular origin of EphB/ephrin-B expression. Activation of ephrin-B signaling was investigated with a phosphospecific antibody on cryosections and retinal whole-mounts.

RESULTS

Upregulation of EphB/ephrin-B expression occurred early within a day of IOP elevation. A transient increase of phosphorylation-dependent ephrin-B (pEB) reverse signaling was observed in ONH axons, microglia, and some astrocytes. Morphologically unaffected retinal ganglion cell (RGC) axons differed from axons with reactive aberrant trajectories by exhibiting increased pEB activation, whereas pEB levels in morphologically affected axons were comparable to those of controls.

CONCLUSIONS

An Eph-ephrin signaling network is activated at the ONH after LIOH in CD-1 mice, either before or coincident with the initial morphologic signs of RGC axon damage reported previously. Of note, ephrin-B reverse signaling was transiently upregulated in RGC axons at the ONH early in their response to IOP elevation but was downregulated in axons that had been damaged by glaucomatous injury and exhibited aberrant trajectories. Ephrin-B reverse signaling may mark RGC axons for damage or confer a protective advantage against injury.

Structure-activity relationship study of EphB3 receptor tyrosine kinase inhibitors

A structure-activity relationship study for a 2-chloroanilide derivative of pyrazolo[1,5-a]pyridine revealed that increased EphB3 kinase inhibitory activity could be accomplished by retaining the 2-chloroanilide and introducing a phenyl or small electron donating substituents to the 5-position of the pyrazolo[1,5-a]pyridine. In addition, replacement of the pyrazolo[1,5-a]pyridine with imidazo[1,2-a]pyridine was well tolerated and resulted in enhanced mouse liver microsome stability. The structure-activity relationship for EphB3 inhibition of both heterocyclic series was similar. Kinase inhibitory activity was also demonstrated for representative analogs in cell culture. An analog (32, LDN-211904) was also profiled for inhibitory activity against a panel of 288 kinases and found to be quite selective for tyrosine kinases. Overall, these studies provide useful molecular probes for examining the in vitro, cellular and potentially in vivo kinase-dependent function of EphB3 receptor.

The role of macrophages in optic nerve regeneration

Following injury to the nervous system, the activation of macrophages, microglia, and T-cells profoundly affects the ability of neurons to survive and to regenerate damaged axons. The primary visual pathway provides a well-defined model system for investigating the interactions between the immune system and the nervous system after neural injury. Following damage to the optic nerve in mice and rats, retinal ganglion cells, the projection neurons of the eye, normally fail to regenerate their axons and soon begin to die. Induction of an inflammatory response in the vitreous strongly enhances the survival of retinal ganglion cells and enables these cells to regenerate lengthy axons beyond the injury site. T cells modulate this response, whereas microglia are thought to contribute to the loss of retinal ganglion cells in this model and in certain ocular diseases. This review discusses the complex and sometimes paradoxical actions of blood-borne macrophages, resident microglia, and T-cells in determining the outcome of injury in the primary visual pathway.

Another barrier to regeneration in the CNS: activated macrophages induce extensive retraction of dystrophic axons through direct physical interactions

Injured axons of the adult CNS undergo lengthy retraction from the initial site of axotomy after spinal cord injury. Macrophage infiltration correlates spatiotemporally with this deleterious phenomenon, but the direct involvement of these inflammatory cells has not been demonstrated. In the present study, we examined the role of macrophages in axonal retraction within the dorsal columns after spinal cord injury in vivo and found that retraction occurred between days 2 and 28 after lesion and that the ends of injured axons were associated with ED-1+ cells. Clodronate liposome-mediated depletion of infiltrating macrophages resulted in a significant reduction in axonal retraction; however, we saw no evidence of regeneration. We used time-lapse imaging of adult dorsal root ganglion neurons in an in vitro model of the glial scar to examine macrophage-axon interactions and observed that adhesive contacts and considerable physical interplay between macrophages and dystrophic axons led to extensive axonal retraction. The induction of retraction was dependent on both the growth state of the axon and the activation state of the macrophage. Only dystrophic adult axons were susceptible to macrophage "attack." Unlike intrinsically active cell line macrophages, both primary macrophages and microglia required activation to induce axonal retraction. Contact with astrocytes had no deleterious effect on adult dystrophic axons, suggesting that the induction of extensive retraction was specific to phagocytic cells. Our data are the first to indicate a direct role of activated macrophages in axonal retraction by physical cell-cell interactions with injured axons.

Repulsive Wnt signaling inhibits axon regeneration after CNS injury

Failure of axon regeneration in the mammalian CNS is attributable in part to the presence of various inhibitory molecules, including myelin-associated proteins and proteoglycans enriched in glial scars. Here, we evaluate whether axon guidance molecules also regulate regenerative growth after injury in adulthood. Wnts are a large family of axon guidance molecules that can attract ascending axons and repel descending axons along the length of the developing spinal cord. Their expression (all 19 Wnts) is not detectable in normal adult spinal cord by in situ hybridization. However, three of them are clearly reinduced after spinal cord injury. Wnt1 and Wnt5a, encoding potent repellents of the descending corticospinal tract (CST) axons, were robustly and acutely induced broadly in the spinal cord gray matter after unilateral hemisection. Ryk, the conserved repulsive Wnt receptor, was also induced in the lesion area, and Ryk immunoreactivity was found on the lesioned CST axons. Wnt4, which attracts ascending sensory axons in development, was acutely induced in areas closer to the lesion than Wnt1 and Wnt5a. Injection of function-blocking Ryk antibodies into the dorsal bilateral hemisectioned spinal cord either prevented the retraction of CST axons or promoted their regrowth but clearly enhanced the sprouting of CST collateral branches around and beyond the injury site. Therefore, repulsive Wnt signaling may be a cause of cortical spinal tract axon retraction and inhibits axon sprouting after injury.

Eph receptors and ephrin signaling pathways: a role in bone homeostasis

The maintenance of bone homeostasis is tightly controlled, and largely dependent upon cellular communication between osteoclasts and osteoblasts, and the coupling of bone resorption to bone formation. This tight coupling is essential for the correct function and maintenance of the skeletal system, repairing microscopic skeletal damage and replacing aged bone. A range of pathologic diseases, including osteoporosis and cancer-induced bone disease, disrupt this coupling and cause subsequent alterations in bone homeostasis. Eph receptors and their associated ligands, ephrins, play critical roles in a number of cellular processes including immune regulation, neuronal development and cancer metastasis. Eph receptors are also expressed by cells found within the bone marrow microenvironment, including osteoclasts and osteoblasts, and there is increasing evidence to implicate this family of receptors in the control of normal and pathological bone remodeling.

Activation of peripheral ephrinBs/EphBs signaling induces hyperalgesia through a MAPKs-mediated mechanism in mice

EphBs receptors and ephrinBs ligands are present in the adult brain and peripheral tissue and play a critical role in modulating multiple aspects of physiology and pathophysiology. Ours and other studies have demonstrated that spinal ephrinBs/EphBs signaling was involved in the modulation of nociceptive information and central sensitization. However, the role of ephrinBs/EphBs signaling in peripheral sensitization is poorly understood. This study shows that intraplantar (i.pl.) injection of ephrinB1-Fc produces a dose- and time-dependent thermal and mechanical hyperalgesia and the increase of spinal Fos protein expression in mice, which can be partially prevented by pre-treatment with EphB1-Fc. EphrinB1-Fc-induced hyperalgesia is accompanied with the NMDA receptor-mediated increase of expression in peripheral and spinal phosphorylated mitogen-activated protein kinases (phospho-MAPKs) including p-p38, pERK and pJNK, and also is prevented or reversed by the inhibition of peripheral and spinal MAPKs. Furthermore, in formalin inflammation pain model, pre-inhibition of EphBs receptors by the injection of EphB1-Fc reduces pain behavior, which is accompanied by the decreased expression of peripheral p-p38, pERK and pJNK. These data provide evidence that ephrinBs may act as a prominent contributor to peripheral sensitization, and demonstrate that activation of peripheral ephrinBs/EphBs system induces hyperalgesia through a MAPKs-mediated mechanism.

Alpha-crystallin protected axons from optic nerve degeneration after crushing in rats

In mature mammals, optic nerve injury results in apoptosis of retinal ganglion cells. The literature confirms that lens injury enhances retinal ganglion cells survival, but the mechanism is not very clear. Using silver staining method and computer image analysis techniques, the effect of alpha-crystallin, a major component of the lens in the survival of retinal ganglion cell axons, was investigated in vivo after intravitreal injections. The results showed that enhanced survival of axotomized axons was observed beyond the crush site after a single intravitreal administration of alpha-crystallin at the time of axotomy. Axonal density of the retinal ganglion cell was significantly greater than in the untreated controls until 2 weeks after injection. This effect declined by 4 weeks after injection but survival of axons remained greater than controls. These findings indicate that alpha-crystallin plays a key role in protecting axons after optic nerve injury.