Repulsive Guidance Research Articles

An antibody to RGMa promotes regeneration of cochlear synapses after noise exposure

Auditory neuropathy is caused by the loss of afferent input to the brainstem via the components of the neural pathway comprising inner hair cells and the first order neurons of the spiral ganglion. Recent work has identified the synapse between cochlear primary afferent neurons and sensory hair cells as a particularly vulnerable component of this pathway. Loss of these synapses due to noise exposure or aging results in the pathology identified as hidden hearing loss, an initial stage of cochlear dysfunction that goes undetected in standard hearing tests. We show here that repulsive axonal guidance molecule a (RGMa) acts to prevent regrowth and synaptogenesis of peripheral auditory nerve fibers with inner hair cells. Treatment of noise-exposed animals with an anti-RGMa blocking antibody regenerated inner hair cell synapses and resulted in recovery of wave-I amplitude of the auditory brainstem response, indicating effective reversal of synaptopathy.

Inhibition of repulsive guidance molecule-a protects dopaminergic neurons in a mouse model of Parkinson\u2019s disease

Repulsive guidance molecule-a (RGMa), a glycosylphosphatidylinositol-anchored membrane protein, has diverse functions in axon guidance, cell patterning, and cell survival. Inhibition of RGMa attenuates pathological dysfunction in animal models of central nervous system (CNS) diseases including spinal cord injury, multiple sclerosis, and neuromyelitis optica. Here, we examined whether antibody-based inhibition of RGMa had therapeutic effects in a mouse model of Parkinson’s disease (PD). We treated mice with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and found increased RGMa expression in the substantia nigra (SN). Intraventricular, as well as intravenous, administration of anti-RGMa antibodies reduced the loss of tyrosine hydroxylase (TH)-positive neurons and accumulation of Iba1-positive microglia/macrophages in the SN of MPTP-treated mice. Selective expression of RGMa in TH-positive neurons in the SN-induced neuronal loss/degeneration and inflammation, resulting in a progressive movement disorder. The pathogenic effects of RGMa overexpression were attenuated by treatment with minocycline, which inhibits microglia and macrophage activation. Increased RGMa expression upregulated pro-inflammatory cytokine expression in microglia. Our observations suggest that the upregulation of RGMa is associated with the PD pathology; furthermore, inhibitory RGMa antibodies are a potential therapeutic option.

Phosphorylation of Collapsin Response Mediator Protein 1 (CRMP1) at Tyrosine 504 residue regulates Semaphorin 3A-induced cortical dendritic growth.

Collapsin response mediator proteins (CRMPs) have been identified as mediating proteins of repulsive axon guidance cue Semaphorin-3A (Sema3A). Phosphorylation of CRMPs plays a crucial role in the Sema3A signaling cascade. It has been shown that Fyn phosphorylates CRMP1 at Tyrosine 504 residue (Tyr504); however, the physiological role of this phosphorylation has not been examined. We found that CRMP1 was the most strongly phosphorylated by Fyn among the five members of CRMPs. We confirmed Tyr504 phosphorylation of CRMP1 by Fyn. Immunocytochemistry of mouse dorsal root ganglion (DRG) neurons showed that phosphotyrosine signal in the growth cones was transiently increased in the growth cones upon Sema3A stimulation. Tyr504-phosphorylated CRMP1 also tended to increase after Sema3A simulation. Ectopic expression of a single amino acid mutant of CRMP1 replacing Tyr504 with phenylalanine (CRMP1-Tyr504Phe) suppressed Sema3A-induced growth cone collapse response in chick DRG neurons. CRMP1-Tyr504Phe expression in mouse hippocampal neurons also suppressed Sema3A but not Sema3F-induced growth cone collapse response. Immunohistochemistry showed that Tyr504-phosphorylated CRMP1 was present in the cell bodies and in the dendritic processes of mouse cortical neurons. CRMP1-Tyr504Phe suppressed Sema3A-induced dendritic growth of primary cultured mouse cortical neurons as well as the dendritic development of cortical pyramidal neurons in vivo. Fyn± ; Crmp1± double heterozygous mutant mice exhibited poor development of cortical layer V basal dendrites, which was the similar phenotype observed in Sema3a-/- , Fyn-/- , and Crmp1-/- mice. These findings demonstrate that Tyr504 phosphorylation of CRMP1 by Fyn is an essential step of Sema3A-regulated dendritic development of cortical pyramidal neurons. (247 words).

Novel Lipid-Oligonucleotide Conjugates Containing Long-Chain Sulfonyl Phosphoramidate Groups: Synthesis and Biological Properties

New lipid conjugates of DNA and RNA incorporating one to four [(4-dodecylphenyl)sulfonyl]phosphoramidate or (hexadecylsulfonyl)phosphoramidate groups at internucleotidic positions near the 3′ or 5′-end were synthesized and characterized. Low cytotoxicity of the conjugates and their ability to be taken up into cells without transfection agents were demonstrated. Lipid-conjugated siRNAs targeting repulsive guidance molecules a (RGMa) have shown a comparable gene silencing activity in PK-59 cells to unmodified control siRNA when delivered into the cells via Lipofectamine mediated transfection.

Involvement of Netrins and Their Receptors in Neuronal Migration in the Cerebral Cortex

In mammals, excitatory cortical neurons develop from the proliferative epithelium and progenitor cells in the ventricular zone and subventricular zone, and migrate radially to the cortical plate, whereas inhibitory GABAergic interneurons are born in the ganglionic eminence and migrate tangentially. The migration of newly born cortical neurons is tightly regulated by both extracellular and intracellular signaling to ensure proper positioning and projections. Non-cell-autonomous extracellular molecules, such as growth factors, axon guidance molecules, extracellular matrix, and other ligands, play a role in cortical migration, either by acting as attractants or repellents. In this article, we review the guidance molecules that act as cell–cell recognition molecules for the regulation of neuronal migration, with a focus on netrin family proteins, their receptors, and related molecules, including neogenin, repulsive guidance molecules (RGMs), Down syndrome cell adhesion molecule (DSCAM), fibronectin leucine-rich repeat transmembrane proteins (FLRTs), and draxin. Netrin proteins induce attractive and repulsive signals depending on their receptors. For example, binding of netrin-1 to deleted in colorectal cancer (DCC), possibly together with Unc5, repels migrating GABAergic neurons from the ventricular zone of the ganglionic eminence, whereas binding to α3β1 integrin promotes cortical interneuron migration. Human genetic disorders associated with these and related guidance molecules, such as congenital mirror movements, schizophrenia, and bipolar disorder, are also discussed.

Curcumin mediates repulsive guidance molecule B (RGMb) in the treatment mechanism of renal fibrosis induced by unilateral ureteral obstruction

In this study, we explored the role and mechanism of repulsive guidance molecule B (RGMb, also known as Dragon) in the protective effects of curcumin against renal fibrosis and verified Dragon’s effect on renal tubular epithelial cell apoptosis and cell programmability. Unilateral ureteral obstruction (UUO) was surgically induced in rats to establish a model of renal interstitial fibrosis (RIF). The rats were then treated with curcumin. Curcumin prominently decreased the serum creatinine (SCr) and blood urea nitrogen (BUN) levels, and also improved the tubular injury in the UUO-induced rats. Curcumin significantly downregulated the TGF-β1, P-Smad2/3, cleaved caspase-3, cleaved caspase-8 and Dragon levels. Dragon knockdown also markedly reduced the TGF-β1, P-Smad2/3, Smad2/3, cleaved caspase-3, cleaved caspase-8, fibronectin, collagen I, collagen IV, vimentin, and α-SMA expression levels. Conversely, Dragon overexpression caused higher expression levels of these proteins, and curcumin reversed this effect. Furthermore, Dragon knockdown increased the E-cadherin levels, whereas Dragon overexpression decreased these levels. Overexpressing Dragon significantly decreased the cell viability, and curcumin reversed this effect. In conclusion, curcumin acted on Dragon and attenuated RIF in UUO rat models. Curcumin downregulated the TGF-β1/Smad signaling pathway and inhibited Dragon and fibrogenic molecules in both rats and HK-2 cells.

The expression of repulsive guidance molecule a after traumatic brain injury: Time-course changes in gene expression in a murine model of controlled cortical impact.

Repulsive guidance molecule a (RGMa) is a key protein that negatively regulates neuronal regeneration as its inhibition enhances axonal growth and promotes functional recovery in animal models of spinal cord injury. However, the role of RGMa in traumatic brain injury (TBI) remains elusive. This study aimed to clarify TBI-responsive RGMa expression in a murine model. Adult male C57BL/6J mice were subjected to controlled cortical impact. Brains were extracted 6 hours and 1, 3, 7, 14 and 21 days after injury (n = 6 in each group). Changes in the messenger RNA (mRNA) expression of RGMa and its receptor, neogenin, were evaluated by quantitative polymerase chain reaction in the damaged area of the cortex and contralateral cortex, along with expression measurement of inflammation-related molecules. Neurological deficit was also assessed by the cylinder test. Neurological score was consistently lower in the TBI group compared to the sham group throughout the experimental period. The mRNA expressions of representative inflammatory cytokine TNF-α and chemokine receptor CCR2 were remarkably increased in the injured cortex on day 1 and gradually decreased over time, although remaining at higher values at least until day 14. The mRNA expressions of RGMa and neogenin were significantly suppressed in the damaged cortex until day 3. Interestingly, RGMa expression was suppressed most on day 1 and recovered over time. In the acute phase of TBI, gene expression of inflammatory cytokines significantly increased, and gene expressions of RGMa and neogenin significantly decreased in the inflammatory milieu of the damaged area. Despite the subsequent remission of inflammation, RGMa gene expression recovered to the normal level 1 week after TBI. Intrinsic regenerative response to acute brain injury might be hampered by the following recovery of RGMa expression, hinting at the possibility of functional RGMa inhibition as a new, effective maneuver against TBI.

Serotonin functions as a bidirectional guidance molecule regulating growth cone motility.

The neurotransmitter serotonin has been implicated in a range of complex neurological disorders linked to alterations of neuronal circuitry. Serotonin is synthesized in the developing brain before most neuronal circuits become fully functional, suggesting that serotonin might play a distinct regulatory role in shaping circuits prior to its function as a classical neurotransmitter. In this study, we asked if serotonin acts as a guidance cue by examining how serotonin alters growth cone motility of rodent sensory neurons in vitro. Using a growth cone motility assay, we found that serotonin acted as both an attractive and repulsive guidance cue through a narrow concentration range. Extracellular gradients of 50µM serotonin elicited attraction, mediated by the serotonin 5-HT2a receptor while 100µM serotonin elicited repulsion mediated by the 5-HT1b receptor. Importantly, high resolution imaging of growth cones indicated that these receptors signalled through their canonical pathways of endoplasmic reticulum-mediated calcium release and cAMP depletion, respectively. This novel characterisation of growth cone motility in response to serotonin gradients provides compelling evidence that secreted serotonin acts at the molecular level as an axon guidance cue to shape neuronal circuit formation during development.

Elevated repulsive guidance molecule-a mRNA in peripheral blood mononuclear cells are associated with impaired leptomeningeal collaterals in patients with middle cerebral artery occlusions.

In the event of middle cerebral artery occlusion (MCAO), leptomeningeal collaterals (LMCs) play a crucial role in determining the survival of brain tissue distal to occlusion. Previous findings indicated that genes controlling arteriogenesis can impact the extent of LMCs. Therefore, probe for potential genetic parameters correlating of arteriogenesis may be clinically useful in predicting LMCs status in MCAO. During the screening process, we focused on repulsive guidance molecule a (RGMa), which has been reported to play a negative role in angiogenesis after stroke by decreasing the proliferation, migration, and tube formation of endothelial cells (ECs) in vivo and in vitro. Indeed, endothelial function plays a main role in arteriogenesis and is essential in determining the LMCs status. Therefore, in present study, we aimed to testify the hypothesis that RGMa might be associated with LMCs status in MCAO. We prospectively enrolled patients with acute M1 MCA +/- intracranial internal carotid artery (ICA) occlusions (n=96) and healthy controls (n=33). Status of LMCs was evaluated according to computed tomographic angiography (CTA) on admission. Baseline RGMa mRNA expression was quantified by using quantitative real-time PCR. Patients with poor LMCs showed significantly higher RGMa mRNA levels than patients with good LMCs status (P=0.001) as well as healthy controls (P=0.002), respectively; whereas good LMCs group showed similar baseline RGMa levels than controls (P=1.000). RGMa mRNA level and baseline NIHSS score were independent predictors for impaired LMCs. In MCAO patients, elevated PBMCs RGMa mRNA levels were associated with impaired LMCs status, indicating that measurement of RGMa mRNA expression in the early phase of stroke, together with other clinical approaches, was logically expected to be useful for predicting LMCs status. Moreover, a role for RGMa in leptomeningeal arteriogenesis following ischemic stroke can be hypothesized.

Silencing miR-20a-5p inhibits axonal growth and neuronal branching and prevents epileptogenesis through RGMa-RhoA-mediated synaptic plasticity.

Epileptogenesis is a potential process. Mossy fibre sprouting (MFS) and synaptic plasticity promote epileptogenesis. Overexpression of repulsive guidance molecule a (RGMa) prevents epileptogenesis by inhibiting MFS. However, other aspects underlying the RGMa regulatory process of epileptogenesis have not been elucidated. We studied whether RGMa could be modulated by microRNAs and regulated RhoA in epileptogenesis. Using microRNA databases, we selected four miRNAs as potential candidates. We further experimentally confirmed miR‐20a‐5p as a RGMa upstream regulator. Then, in vitro, by manipulating miR‐20a‐5p and RGMa, we investigated the regulatory relationship between miR‐20a‐5p, RGMa and RhoA, and the effects of this pathway on neuronal morphology. Finally, in the epilepsy animal model, we determined whether the miR‐20a‐5p‐RGMa‐RhoA pathway influenced MFS and synaptic plasticity and then modified epileptogenesis. Our results showed that miR‐20a‐5p regulated RGMa and that RGMa regulated RhoA in vitro. Furthermore, in primary hippocampal neurons, the miR‐20a‐5p‐RGMa‐RhoA pathway regulated axonal growth and neuronal branching; in the PTZ‐induced epilepsy model, silencing miR‐20a‐5p prevented epileptogenesis through RGMa‐RhoA‐mediated synaptic plasticity but did not change MFS. Overall, we concluded that silencing miR‐20a‐5p inhibits axonal growth and neuronal branching and prevents epileptogenesis through RGMa‐RhoA‐mediated synaptic plasticity in the PTZ‐induced epilepsy model, thereby providing a possible strategy to prevent epileptogenesis.

Integrating Chemistry and Mechanics: The Forces Driving Axon Growth.

The brain is our most complex organ. During development, neurons extend axons, which may grow over long distances along well-defined pathways to connect to distant targets. Our current understanding of axon pathfinding is largely based on chemical signaling by attractive and repulsive guidance cues. These cues instruct motile growth cones, the leading tips of growing axons, where to turn and where to stop. However, it is not chemical signals that cause motion-motion is driven by forces. Yet our current understanding of the mechanical regulation of axon growth is very limited. In this review, I discuss the origin of the cellular forces controlling axon growth and pathfinding, and how mechanical signals encountered by growing axons may be integrated with chemical signals. This mechanochemical cross talk is an important but often overlooked aspect of cell motility that has major implications for many physiological and pathological processes involving neuronal growth.

Delayed administration of the human anti-RGMa monoclonal antibody elezanumab promotes functional recovery including spontaneous voiding after spinal cord injury in rats

Spinal cord injury (SCI) often results in permanent functional loss due to a series of degenerative events including cell death, axonal damage, and the upregulation of inhibitory proteins that impede regeneration. Repulsive Guidance Molecule A (RGMa) is a potent inhibitor of axonal growth that is rapidly upregulated following injury in both the rodent and human central nervous system (CNS). Previously, we showed that monoclonal antibodies that specifically block inhibitory RGMa signaling promote neuroprotective and regenerative effects when administered acutely in a clinically relevant rat model of thoracic SCI. However, it is unknown whether systemic administration of RGMa blocking antibodies are effective for SCI after delayed administration. Here, we administered elezanumab, a human monoclonal antibody targeting RGMa, intravenously either acutely or at 3 h or 24 h following thoracic clip impact-compression SCI. Rats treated with elezanumab acutely and at 3 h post-injury showed improvements in overground locomotion and fine motor function and gait. Rats treated 24 h post-SCI trended towards better recovery demonstrating significantly greater stride length and swing speed. Treated rats also showed greater tissue preservation with reduced lesion areas. As seen with acute treatment, delayed administration of elezanumab at 3 h post-SCI also increased perilesional neuronal sparing and serotonergic and corticospinal axonal plasticity. In addition, all elezanumab treated rats showed earlier spontaneous voiding ability and less post-trauma bladder wall hypertrophy. Together, our data demonstrate the therapeutic efficacy of delayed systemic administration of elezanumab in a rat model of SCI, and uncovers a new role for RGMa inhibition in bladder recovery following SCI.

Repulsive guidance molecules lock growth differentiation factor 5 in an inhibitory complex

Repulsive guidance molecules (RGMs) are cell surface proteins that regulate the development and homeostasis of many tissues and organs, including the nervous, skeletal, and immune systems. They control fundamental biological processes, such as migration and differentiation by direct interaction with the Neogenin (NEO1) receptor and function as coreceptors for the bone morphogenetic protein (BMP)/growth differentiation factor (GDF) family. We determined crystal structures of all three human RGM family members in complex with GDF5, as well as the ternary NEO1-RGMB-GDF5 assembly. Surprisingly, we show that all three RGMs inhibit GDF5 signaling, which is in stark contrast to RGM-mediated enhancement of signaling observed for other BMPs, like BMP2. Despite their opposite effect on GDF5 signaling, RGMs occupy the BMP type 1 receptor binding site similar to the observed interactions in RGM-BMP2 complexes. In the NEO1-RGMB-GDF5 complex, RGMB physically bridges NEO1 and GDF5, suggesting cross-talk between the GDF5 and NEO1 signaling pathways. Our crystal structures, combined with structure-guided mutagenesis of RGMs and BMP ligands, binding studies, and cellular assays suggest that RGMs inhibit GDF5 signaling by competing with GDF5 type 1 receptors. While our crystal structure analysis and in vitro binding data initially pointed towards a simple competition mechanism between RGMs and type 1 receptors as a possible basis for RGM-mediated GDF5 inhibition, further experiments utilizing BMP2-mimicking GDF5 variants clearly indicate a more complex mechanism that explains how RGMs can act as a functionality-changing switch for two structurally and biochemically similar signaling molecules.

Bone morphogenetic protein receptors: Structure, function and targeting by selective small molecule kinase inhibitors.

Bone morphogenetic proteins (BMPs) are secreted cytokines that control the fate and function of many different cell types. They exert their cellular responses via heteromeric complexes of specific BMP type I and type II serine/threonine kinase receptors, e.g. BMPRIA and BMPRII. Three type II and four type I receptors, also termed activin receptor-like kinases (ALKs), have been identified. The constitutively active type II kinase phosphorylates the type I receptor, which upon activation initiates intracellular signaling by phosphorylating SMAD effectors. Auxiliary cell surface receptors without intrinsic enzymatic motifs, such as Endoglin and Repulsive guidance molecules (RGM), can fine-tune signaling by regulating the interaction of the BMP ligands with the BMPRs. The functional annotation of the BMPR encoding genes has helped to understand underlying mechanisms of diseases in which these genes are mutated. Loss of function mutations in BMPRII, Endoglin or RGMc are causally linked to pulmonary arterial hypertension, hereditary hemorrhagic telangiectasia and juvenile hemochromatosis, respectively. In contrast, gain of function mutations in ACVR1, encoding ALK2, are linked to Fibrodysplasia ossificans progressiva and diffuse intrinsic pontine glioma. Here, we discuss BMPR identification, structure and function in health and disease. Moreover, we highlight the therapeutic promise of small chemical compounds that act as selective BMPR kinase inhibitors to normalize overactive BMPR signaling.

Shootin-1 is required for nervous system development in zebrafish.

Semaphorin6A (Sema6A) and its PlexinA2 (PlxnA2) receptor canonically function as repulsive axon guidance cues. To understand downstream signaling mechanisms, we performed a microarray screen and identified the "clutch molecule" shootin-1 (shtn-1) as a transcriptionally repressed target. Shtn-1 is a key proponent of cell migration and neuronal polarization and must be regulated during nervous system development. The mechanisms of Shtn-1 regulation and the phenotypic consequences of loss of repression are poorly understood. We demonstrate shtn-1 overexpression results in impaired migration of the optic vesicles, lack of retinal pigmented epithelium, and pathfinding errors of retinotectal projections. We also observed patterning defects in the peripheral nervous system. Importantly, these phenotypes were rescued by overexpressing PlxnA2. We demonstrate a functional role for repression of shtn-1 by PlxnA2 in development of the eyes and peripheral nervous system in zebrafish. These results demonstrate that careful regulation of shtn-1 is critical for development of the nervous system.

Modular and Distinct Plexin-A4/FARP2/Rac1 Signaling Controls Dendrite Morphogenesis

Diverse neuronal populations with distinct cellular morphologies coordinate the complex function of the nervous system. Establishment of distinct neuronal morphologies critically depends on signaling pathways that control axonal and dendritic development. The Sema3A-Nrp1/PlxnA4 signaling pathway promotes cortical neuron basal dendrite arborization but also repels axons. However, the downstream signaling components underlying these disparate functions of Sema3A signaling are unclear. Using the novel PlxnA4KRK-AAA knock-in male and female mice, generated by CRISPR/cas9, we show here that the KRK motif in the PlxnA4 cytoplasmic domain is required for Sema3A-mediated cortical neuron dendritic elaboration but is dispensable for inhibitory axon guidance. The RhoGEF FARP2, which binds to the KRK motif, shows identical functional specificity as the KRK motif in the PlxnA4 receptor. We find that Sema3A activates the small GTPase Rac1, and that Rac1 activity is required for dendrite elaboration but not axon growth cone collapse. This work identifies a novel Sema3A-Nrp1/PlxnA4/FARP2/Rac1 signaling pathway that specifically controls dendritic morphogenesis but is dispensable for repulsive guidance events. Overall, our results demonstrate that the divergent signaling output from multifunctional receptor complexes critically depends on distinct signaling motifs, highlighting the modular nature of guidance cue receptors and its potential to regulate diverse cellular responses.SIGNIFICANCE STATEMENT The proper formation of axonal and dendritic morphologies is crucial for the precise wiring of the nervous system that ultimately leads to the generation of complex functions in an organism. The Semaphorin3A-Neuropilin1/Plexin-A4 signaling pathway has been shown to have multiple key roles in neurodevelopment, from axon repulsion to dendrite elaboration. This study demonstrates that three specific amino acids, the KRK motif within the Plexin-A4 receptor cytoplasmic domain, are required to coordinate the downstream signaling molecules to promote Sema3A-mediated cortical neuron dendritic elaboration, but not inhibitory axon guidance. Our results unravel a novel Semaphorin3A-Plexin-A4 downstream signaling pathway and shed light on how the disparate functions of axon guidance and dendritic morphogenesis are accomplished by the same extracellular ligand in vivo.

Intrinsic and extrinsic mechanisms regulating neuronal dendrite morphogenesis

Neurons are the structural and functional unit of the nervous system. Precisely regulated dendrite morphogenesis is the basis of neural circuit assembly. Numerous studies have been conducted to explore the regulatory mechanisms of dendritic morphogenesis. According to their action regions, we divide them into two categories: the intrinsic and extrinsic regulators of neuronal dendritic morphogenesis. Intrinsic factors are cell type-specific transcription factors, actin polymerization or depolymerization regulators and regulators of the secretion or endocytic pathways. These intrinsic factors are produced by neuron itself and play an important role in regulating the development of dendrites. The extrinsic regulators are either secreted proteins or transmembrane domain containing cell adhesion molecules. They often form receptor-ligand pairs to mediate attractive or repulsive dendritic guidance. In this review, we summarize recent findings on the intrinsic and external molecular mechanisms of dendrite morphogenesis from multiple model organisms, including Caenorhabditis elegans, Drosophila and mice. These studies will provide a better understanding on how defective dendrite development and maintenance are associated with neurological diseases.

Lentivirally administered glial cell line-derived neurotrophic factor promotes post-ischemic neurological recovery, brain remodeling and contralesional pyramidal tract plasticity by regulating axonal growth inhibitors and guidance proteins

Owing to its potent longterm neuroprotective and neurorestorative properties, glial cell line-derived neurotrophic factor (GDNF) is currently studied in neurodegenerative disease clinical trials. However, little is known about the longterm effect of GDNF on neurological recovery, brain remodeling and neuroplasticity in the post-acute phase of ischemic stroke. In a comprehensive set of experiments, we examined the effects of lentiviral GDNF administration after ischemic stroke. GDNF reduced neurological deficits, neuronal injury, blood-brain barrier permeability in the acute phase in mice. As compared with control, enhanced motor-coordination and spontaneous locomotor activity were noted in GDNF-treated mice, which were associated with increased microvascular remodeling, increased neurogenesis and reduced glial scar formation in the peri-infarct tissue. We observed reduced brain atrophy and increased plasticity of contralesional pyramidal tract axons that crossed the midline in order to innervate denervated neurons in the ipsilesional red and facial nuclei. Contralesional axonal plasticity by GDNF was associated with decreased abundance of the axonal growth inhibitors brevican and versican in contralesional and ipsilesional brain tissue, reduced abundance of the growth repulsive guidance molecule ephrin b1 in contralesional brain tissue, increased abundance of the midline growth repulsive protein Slit1 in contralesional brain tissue and reduced abundance of Slit1's receptor Robo2 in ipsilesional brain tissue. These data indicate that GDNF potently induces longterm neurological recovery, peri-infarct brain remodeling and contralesional neuroplasticity, which are associated with the fine-tuned regulation of axonal growth inhibitors and guidance molecules that facilitate the growth of contralesional corticofugal axons in the direction to the ipsilesional hemisphere.

Long-distance regressive signaling in neural development and disease.

Nervous system development proceeds via well-orchestrated processes involving a balance between progressive and regressive events including stabilization or elimination of axons, synapses, and even entire neurons. These progressive and regressive events are driven by functionally antagonistic signaling pathways with the dominant pathway eventually determining whether a neural element is retained or removed. Many of these developmental sculpting events are triggered by final target innervation necessitating a long-distance mode of communication. While long-distance progressive signaling has been well characterized, particularly for neurotrophic factors, there remains relatively little known about how regressive events are triggered from a distance. Here we discuss the emergent phenomenon of long-distance regressive signaling pathways. In particular, we will cover (a) progressive and regressive cues known to be employed after target innervation, (b) the mechanisms of long-distance signaling from an endosomal platform, (c) recent evidence that long-distance regressive cues emanate from platforms like death receptors or repulsive axon guidance receptors, and (d) evidence that these pathways are exploited in pathological scenarios. This article is categorized under: Nervous System Development > Vertebrates: General Principles Signaling Pathways > Global Signaling Mechanisms Establishment of Spatial and Temporal Patterns > Cytoplasmic Localization.

Repulsive Guidance Molecule A Suppresses Adult Neurogenesis.

SummaryRepulsive guidance molecule A (RGMa) is a glycosylphosphatidylinositol-anchored glycoprotein that exhibits repulsive neurite guidance and regulates neuronal differentiation and survival during brain development. However, the function of RGMa in the adult brain is unknown. Here, we show that RGMa is expressed in the adult hippocampus and provide evidence that RGMa signaling suppresses adult neurogenesis. Knockdown of RGMa in the dentate gyrus increased the number of surviving newborn neurons; however, these cells failed to properly migrate into the granular cell layer. In vitro, RGMa stimulation of adult neural stem cells suppressed neurite outgrowth of newborn neurons, which could be prevented by knockdown of the multifunctional receptor neogenin, as well as pharmacological inhibition of the downstream target Rho-associated protein kinase. These findings present a function for RGMa in the adult brain and add to the intricate molecular network that regulates adult brain plasticity.