Immunohistochemical localization of CNTFRalpha in adult mouse retina and optic nerve following intraorbital nerve crush: evidence for the axonal loss of a trophic factor receptor after injury

Intravitreal Co-Administration of GDNF and CNTF Confers Synergistic and Long-Lasting Protection against Injury-Induced Cell Death of Retinal Ganglion Cells in Mice

We have recently demonstrated that neural stem cell-based intravitreal co-administration of glial cell line-derived neurotrophic factor (GDNF) and ciliary neurotrophic factor (CNTF) confers profound protection to injured retinal ganglion cells (RGCs) in a mouse optic nerve crush model, resulting in the survival of ~38% RGCs two months after the nerve lesion. Here, we analyzed whether this neuroprotective effect is long-lasting and studied the impact of the pronounced RGC rescue on axonal regeneration. To this aim, we co-injected a GDNF- and a CNTF-overexpressing neural stem cell line into the vitreous cavity of adult mice one day after an optic nerve crush and determined the number of surviving RGCs 4, 6 and 8 months after the lesion. Remarkably, we found no significant decrease in the number of surviving RGCs between the successive analysis time points, indicating that the combined administration of GDNF and CNTF conferred lifelong protection to injured RGCs. While the simultaneous administration of GDNF and CNTF stimulated pronounced intraretinal axon growth when compared to retinas treated with either factor alone, numbers of regenerating axons in the distal optic nerve stumps were similar in animals co-treated with both factors and animals treated with CNTF only.

Target-Derived Neurotrophic Factor Deprivation Puts Retinal Ganglion Cells on Death Row: Cold Hard Evidence and Caveats

Glaucoma and other optic neuropathies are characterized by axonal transport deficits. Axonal cargo travels back and forth between the soma and the axon terminus, a mechanism ensuring homeostasis and the viability of a neuron. An example of vital molecules in the axonal cargo are neurotrophic factors (NTFs). Hindered retrograde transport can cause a scarcity of those factors in the retina, which in turn can tilt the fate of retinal ganglion cells (RGCs) towards apoptosis. This postulation is one of the most widely recognized theories to explain RGC death in the disease progression of glaucoma and is known as the NTF deprivation theory. For several decades, research has been focused on the use of NTFs as a novel neuroprotective glaucoma treatment. Until now, results in animal models have been promising, but translation to the clinic has been highly disappointing. Are we lacking important knowledge to lever NTF therapies towards the therapeutic armamentarium? Or did we get the wrong end of the stick regarding the NTF deprivation theory? In this review, we will tackle the existing evidence and caveats advocating for and against the target-derived NTF deprivation theory in glaucoma, whilst digging into associated therapy efforts.

Pronounced synergistic neuroprotective effect of GDNF and CNTF on axotomized retinal ganglion cells in the adult mouse

Neuroprotection is among the potential treatment options for glaucoma and other retinal pathologies characterized by the loss of retinal ganglion cells (RGCs). Here, we examined the impact of a neural stem (NS) cell-based intravitreal co-administration of two neuroprotective factors on the survival of axotomized RGCs. To this aim we used lentiviral vectors to establish clonal NS cell lines ectopically expressing either glial cell line-derived neurotrophic factor (GDNF) or ciliary neurotrophic factor (CNTF). The modified NS cell lines were intravitreally injected either separately or as a 1:1 mixture into adult mice one day after an optic nerve lesion, and the number of surviving RGCs was determined in retinal flat-mounts two, four and eight weeks after the lesion. For the transplantation experiments, we selected a GDNF- and a CNTF-expressing NS cell line that promoted the survival of axotomized RGCs with a similar efficacy. Eight weeks after the lesion, GDNF-treated retinas contained 3.8- and CNTF-treated retinas 3.7-fold more RGCs than control retinas. Of note, the number of surviving RGCs was markedly increased when both factors were administered simultaneously, with 14.3-fold more RGCs than in control retinas eight weeks after the lesion. GDNF and CNTF thus potently and synergistically rescued RGCs from axotomy-induced cell death, indicating that combinatorial neuroprotective approaches represent a promising strategy to effectively promote the survival of RGCs under pathological conditions.

Measuring Ciliary Neurotrophic Factor (CNTF) in Lacrimal Fluid Using Optimized Commercial ELISA

The concentration of ciliary neurotrophic factor (CNTF) was measured in lacrimal fluid (LF) using Human CNTF Quantikine ELISA kit (“R&D Systems”, USA) on a ChemWell 2910 automatic analyzer (“Awareness Technology Inc.”, USA). We initially attempted to use commercial kits, designed for serum and plasma CNTF detection, to quantify lacrimal CNTF. The results, however, were rarely above the minimum detection level of the kits, most likely due to matrix complexity and low concentrations of CNTF in diluted LF (LF had to be diluted because of the small volume of collected samples). The optimal sensitivity and the lowest background for the best minimum quantifiable value were determined empirically. Phosphate buffer solution containing 1% bovine serum albumin was selected as an optimal diluent for CNTF measurements in small fluid samples. A standard curve was produced using the calibrating solutions 0-250 pg/ml. Acid treatment of LF samples before the analysis allowed to increase the detectable concentration of the CNTF two-fold. The 1:3 dilution was selected based on the available volume of collected LF and a reasonable variation coefficient. The described protocol allowed to develop a sandwich ELISA optimized for lacrimal CNTF.

Rapid monocyte infiltration following retinal detachment is dependent on non-canonical IL6 signaling through gp130

BACKGROUND

Retinal detachment (RD) can lead to proliferative vitreoretinopathy (PVR), a leading cause of intractable vision loss. PVR is associated with a cytokine storm involving common proinflammatory molecules like IL6, but little is known about the source and downstream signaling of IL6 and the consequences for the retina. Here, we investigated the early immune response and resultant cytokine signaling following RD in mice.

METHODS

RD was induced in C57BL/6 J and IL6 knockout mice, and the resulting inflammatory response was examined using immunohistochemistry and flow cytometry. Cytokines and signaling proteins of vitreous and retinas were quantified by multiple cytokine arrays and Western blotting. To attempt to block IL6 signaling, a neutralizing antibody of IL6 receptor α (IL6Rα) or IL6 receptor β (gp-130) was injected intravitreally immediately after RD.

RESULTS

Within one day of RD, bone marrow-derived Cd11b + monocytes had extravasated from the vasculature and lined the vitreal surface of the retina, while the microglia, the resident macrophages of the retina, were relatively unperturbed. Cytokine arrays and Western blot analysis revealed that this sterile inflammation did not cause activation of IL6 signaling in the neurosensory retina, but rather only in the vitreous and aqueous humor. Monocyte infiltration was inhibited by blocking gp130, but not by IL6 knockout or IL6Rα blockade.

CONCLUSIONS

Together, our results demonstrate that monocytes are the primary immune cell mediating the cytokine storm following RD, and that any resulting retinal damage is unlikely to be a direct result of retinal IL6 signaling, but rather gp130-mediated signaling in the monocytes themselves. These results suggest that RD should be treated immediately, and that gp130-directed therapies may prevent PVR and promote retinal healing.

Role of cyclic AMP in the eye with glaucoma

Glaucoma is characterized by a slow and progressive degeneration of the optic nerve, including retinal ganglion cell (RGC) axons in the optic nerve head (ONH), leading to visual impairment. Despite its high prevalence, the biological basis of glaucoma pathogenesis still is not yet fully understood, and the factors contributing to its progression are currently not well characterized. Intraocular pressure (IOP) is the only modifiable risk factor, and reduction of IOP is the standard treatment for glaucoma. However, lowering IOP itself is not always effective for preserving visual function in patients with primary open-angle glaucoma. The second messenger cyclic adenosine 3′,5′-monophosphate (cAMP) regulates numerous biological processes in the central nervous system including the retina and the optic nerve. Although recent studies revealed that cAMP generated by adenylyl cyclases (ACs) is important in regulating aqueous humor dynamics in ocular tissues, such as the ciliary body and trabecular meshwork, as well as cell death and growth in the retina and optic nerve, the functional role and significance of cAMP in glaucoma remain to be elucidated. In this review, we will discuss the functional role of cAMP in aqueous humor dynamics and IOP regulation, and review the current medications, which are related to the cAMP signaling pathway, for glaucoma treatment. Also, we will further focus on cAMP signaling in RGC growth and regeneration by soluble AC as well as ONH astrocytes by transmembrane ACs to understand its potential role in the pathogenesis of glaucoma neurodegeneration

Hyper-IL-6: a potent and efficacious stimulator of RGC regeneration

Mature retinal ganglion cells (RGCs) normally fail to regenerate injured axons and die soon after optic nerve injury. Research over the last two decades has demonstrated that application of IL-6-like cytokines or activation of respective downstream signaling pathways promote neuroprotection and optic nerve regeneration. However, the overall beneficial effects of natural cytokines remain usually rather moderate, possibly due to intrinsic signaling pathway inhibitors, such as PTEN or SOCS3, or a limited expression of specific cytokine receptors in RGCs. It was recently demonstrated that directly targeting the gp130 receptor, a common signalling receptor of all IL-6-like cytokines, induces stronger RGC axon regeneration in vitro and in vivo than other known growth-promoting treatments such as inflammatory stimulation or PTEN knockout. Remarkably, continuous expression of hyper-IL-6 (hIL-6) upon intravitreal AAV injection after nerve injury enables long-distance axon regeneration, with some axons growing through the optic chiasm 6 weeks after optic nerve injury. Thus, AAV-mediated hIL-6 delivery is so far one of the strongest single, post-injury treatments for the promotion of optic nerve regeneration and may be suitable for the development of novel, clinically applicable therapeutic treatments for human patients.

Retinal regeneration mechanisms linked to multiple cancer molecules: A therapeutic conundrum

Over the last decade, a large number of research articles have been published demonstrating regeneration and/or neuroprotection of retinal ganglion cells following manipulation of specific genetic and molecular targets. Interestingly, of the targets that have been identified to promote repair following visual system damage, many are genes known to be mutated in different types of cancer. This review explores recent literature on the potential for modulating cancer genes as a therapeutic strategy for visual system repair and looks at the potential clinical challenges associated with implementing this type of therapy. We also discuss signalling mechanisms that have been implicated in cancer and consider how similar mechanisms may improve axonal regeneration in the optic nerve.

Boosting Central Nervous System Axon Regeneration by Circumventing Limitations of Natural Cytokine Signaling

Retinal ganglion cells (RGCs) do not normally regenerate injured axons, but die upon axotomy. Although IL-6-like cytokines are reportedly neuroprotective and promote optic nerve regeneration, their overall regenerative effects remain rather moderate. Here, we hypothesized that direct activation of the gp130 receptor by the designer cytokine hyper-IL-6 (hIL-6) might induce stronger RGC regeneration than natural cytokines. Indeed, hIL-6 stimulated neurite growth of adult cultured RGCs with significantly higher efficacy than CNTF or IL-6. This neurite growth promoting effect could be attributed to stronger activation of the JAK/STAT3 and PI3K/AKT/mTOR signaling pathways and was also observed in peripheral dorsal root ganglion neurons. Moreover, hIL-6 abrogated axon growth inhibition by central nervous system (CNS) myelin. Remarkably, continuous hIL-6 expression upon RGC-specific AAV transduction after optic nerve crush exerted stronger axon regeneration than other known regeneration promoting treatments such as lens injury and PTEN knockout, with some axons growing through the optic chiasm 6 weeks after optic nerve injury. Combination of hIL-6 with RGC-specific PTEN knockout further enhanced optic nerve regeneration. Therefore, direct activation of gp130 signaling might be a novel, clinically applicable approach for robust CNS repair.

Social stress increases expression of hemoglobin genes in mouse prefrontal cortex

BACKGROUND

In order to better understand the effects of social stress on the prefrontal cortex, we investigated gene expression in mice subjected to acute and repeated social encounters of different duration using microarrays.

RESULTS

The most important finding was identification of hemoglobin genes (Hbb-b1, Hbb-b2, Hba-a1, Hba-a2, Beta-S) as potential markers of chronic social stress in mice. Expression of these genes was progressively increased in animals subjected to 8 and 13 days of repeated stress and was correlated with altered expression of Mgp (Mglap), Fbln1, 1500015O10Rik (Ecrg4), SLC16A10, and Mndal. Chronic stress increased also expression of Timp1 and Ppbp that are involved in reaction to vascular injury. Acute stress did not affect expression of hemoglobin genes but it altered expression of Fam107a (Drr1) and Agxt2l1 (Etnppl) that have been implicated in psychiatric diseases.

CONCLUSIONS

The observed up-regulation of genes associated with vascular system and brain injury suggests that stressful social encounters may affect brain function through the stress-induced dysfunction of the vascular system.

BDNF treatment and extended recovery from optic nerve trauma in the cat

PURPOSE

We examined the treatment period necessary to restore retinal and visual stability following trauma to the optic nerve.

METHODS

Cats received unilateral optic nerve crush and no treatment (NT), treatment of the injured eye with brain-derived neurotrophic factor (BDNF), or treatment of the injured eye combined with treatment of visual cortex for 2 or 4 weeks. After 1-, 2-, 4-, or 6-week survival periods, pattern electroretinograms (PERGs) were obtained and retinal ganglion cell (RGC) survival determined.

RESULTS

In the peripheral retina, RGC survival for NT, eye only, and eye + cortex animals was 55%, 78%, and 92%, respectively, at 1 week, and 31%, 60%, and 93%, respectively, at 2 weeks. PERGs showed a similar pattern of improvement. After 4 weeks, RGC survival was 7%, 29%, and 53% in each group, with PERGs in the dual-treated animals similar to the 1- to 2-week animals. For area centralis (AC), the NT, eye only, and eye + cortex animals showed 47%, 78%, and 82% survival, respectively, at 2 weeks, and 13%, 54%, and 81% survival, respectively, at 4 weeks. Removing the pumps at 2 weeks resulted in ganglion cell survival levels of 76% and 74% in the AC at 4 and 6 weeks postcrush, respectively. The PERGs from 2-week treated, but 4- and 6-week survival animals were comparable to those of the 2-week animals.

CONCLUSIONS

Treating the entire central visual pathway is important following optic nerve trauma. Long-term preservation of central vision may be achieved with as little as 2 weeks of treatment using this approach.

Glial cells activation potentially contributes to the upregulation of stromal cell-derived factor-1α after optic nerve crush in rats

Stromal cell-derived factor-1α (SDF-1α) plays an important role after injury. However, little is known regarding its temporal and spatial expression patterns or how it interacts with glial cells after optic nerve crush injury. We characterized the temporal and spatial expression pattern of SDF-1α in the retina and optic nerve following optic nerve crush and demonstrated that SDF-1α is localized to the glial cells that are distributed in the retina and optic nerve. CXCR4, the receptor for SDF-1α, is expressed along the ganglion cell layer (GCL). The relative expression levels of Sdf-1α mRNA and SDF-1α protein in the retina and optic nerve 1, 2, 3, 5, 7, 10 and 14 days after injury were determined using real-time polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay, respectively, and the Cxcr4 mRNA expression was determined using real-time PCR. Immunofluorescence and immunohistochemical approaches were used to detect the localization of SDF-1α and CXCR4 after injury. The upregulation of Sdf-1α and Cxcr4 mRNA was detected as early as day one after injury in the retina and day two in the optic nerve, the expression peaks 5-7 days after injury. The expression of Sdf-1α and Cxcr4 mRNA was maintained for at least 14 days after the optic nerve crush injury. Furthermore, SDF-1α-positive zones were distributed locally in the reactive glial cells, which suggested potential autocrine stimulation. CXCR4 was mainly expressed in the GCL, which was also adjacent to the the glial cells. These findings suggest that following optic nerve crush, the levels of endogenous SDF-1α and CXCR4 increase in the retina and optic nerve, where activated glial cells may act as a source of increased SDF-1α protein.

Stimulating axonal regeneration of mature retinal ganglion cells and overcoming inhibitory signaling

Like other neurons of the central nervous system (CNS), retinal ganglion cells (RGCs) are normally unable to regenerate injured axons and instead undergo apoptotic cell death. This regenerative failure leads to lifelong visual deficits after optic nerve damage and is partially attributable to factors located in the inhibitory environment of the forming glial scar and myelin as well as to an insufficient intrinsic ability for axonal regrowth. In addition to its ophthalmological relevance, the optic nerve has long been used as a favorable paradigm for studying regenerative failure in the CNS as a whole. Findings over the last 15 years have shown that, under certain circumstances, mature RGCs can be transformed into an active regenerative state enabling these neurons to survive axotomy and to regenerate axons in the optic nerve. Moreover, combinatorial treatments overcoming the inhibitory environment of the glial scar and optic nerve myelin, together with approaches activating the intrinsic growth program, can further enhance the amount of regeneration in vivo. These findings are encouraging and open the possibility that clinically meaningful regenerationmay become achievable in the future.

Soluble adenylyl cyclase activity is necessary for retinal ganglion cell survival and axon growth

cAMP is a critical second messenger mediating activity-dependent neuronal survival and neurite growth. We investigated the expression and function of the soluble adenylyl cyclase (sAC, ADCY10) in CNS retinal ganglion cells (RGCs). We found sAC protein expressed in multiple RGC compartments including the nucleus, cytoplasm and axons. sAC activation increased cAMP above the level seen with transmembrane adenylate cyclase (tmAC) activation. Electrical activity and bicarbonate, both physiologic sAC activators, significantly increased survival and axon growth, whereas pharmacologic or siRNA-mediated sAC inhibition dramatically decreased RGC survival and axon growth in vitro, and survival in vivo. Conversely, RGC survival and axon growth were unaltered in RGCs from AC1/AC8 double knock-out mice or after specifically inhibiting tmACs. These data identify a novel sAC-mediated cAMP signaling pathway regulating RGC survival and axon growth, and suggest new neuroprotective or regenerative strategies based on sAC modulation.

Receptor tyrosine kinases: molecular switches regulating CNS axon regeneration

The poor or lack of injured adult central nervous system (CNS) axon regeneration results in devastating consequences and poor functional recovery. The interplay between the intrinsic and extrinsic factors contributes to robust inhibition of axon regeneration of injured CNS neurons. The insufficient or lack of trophic support for injured neurons is considered as one of the major obstacles contributing to their failure to survive and regrow their axons after injury. In the CNS, many of the signalling pathways associated with neuronal survival and axon regeneration are regulated by several classes of receptor tyrosine kinases (RTK) that respond to a variety of ligands. This paper highlights and summarises the most relevant recent findings pertinent to different classes of the RTK family of molecules, with a particular focus on elucidating their role in CNS axon regeneration.

Brain phenotype of carbonic anhydrase IX-deficient mice

Preliminary observations have suggested mild behavioral changes and a morphological disruption of brain histology in 1.5-year-old carbonic anhydrase IX (CA IX)-deficient (Car9 (-/-)) mice. These findings led us to design a 1-year follow-up study in which the behavior and brain histology of Car9 (-/-) and wild-type mice were monitored. Morphological analysis revealed vacuolar degenerative changes in the brains of Car9 (-/-) mice. The changes became visible at the age of eight to ten months. Behavioral tests showed that the Car9 (-/-) mice exhibited abnormal locomotor activity and poor performance in a memory test. To further identify the transcriptomic responses to CA IX deficiency in the brain, genome-wide cDNA microarray analyses were performed. Thirty-one and 37 genes were significantly up- or down-regulated, respectively, in the brain of Car9 (-/-) mice compared to the wild-type mice. Functional annotation revealed that the genes with increased expression were involved in several processes, such as RNA metabolism, and the genes with reduced expression were implicated in other important processes, including the regulation of cellular ion homeostasis. Notably, the biological processes "behavior" and "locomotory behavior" were the two prominent terms overrepresented among the down-regulated genes, which is consistent with the behavioral phenotype. These results suggest that CA IX may directly or indirectly play novel functions in brain tissue. Furthermore, the brain phenotype of Car9 (-/-) mice seems to be age-dependent. The results indicate that the functional changes precede the microscopic alterations in the brains of Car9 (-/-) mice.

Relationships between gene expression and brain wiring in the adult rodent brain

We studied the global relationship between gene expression and neuroanatomical connectivity in the adult rodent brain. We utilized a large data set of the rat brain “connectome” from the Brain Architecture Management System (942 brain regions and over 5000 connections) and used statistical approaches to relate the data to the gene expression signatures of 17,530 genes in 142 anatomical regions from the Allen Brain Atlas. Our analysis shows that adult gene expression signatures have a statistically significant relationship to connectivity. In particular, brain regions that have similar expression profiles tend to have similar connectivity profiles, and this effect is not entirely attributable to spatial correlations. In addition, brain regions which are connected have more similar expression patterns. Using a simple optimization approach, we identified a set of genes most correlated with neuroanatomical connectivity, and find that this set is enriched for genes involved in neuronal development and axon guidance. A number of the genes have been implicated in neurodevelopmental disorders such as autistic spectrum disorder. Our results have the potential to shed light on the role of gene expression patterns in influencing neuronal activity and connectivity, with potential applications to our understanding of brain disorders. Supplementary data are available at http://www.chibi.ubc.ca/ABAMS.

We tested the idea that the “wiring diagram” of the adult brain has a relationship with where genes are expressed. We were inspired by similar work carried out by groups examining the nematode worm Caenorhabditis elegans. By using large-scale databases of brain connectivity and gene expression in rodents, we found that many genes involved in the development of the brain show correlations with anatomical connectivity patterns. Some of the genes we found have been implicated in disorders such as autism, which is suspected to affect brain wiring. While the biological causes of the patterns we found are not yet known, we believe they provide new insight into the patterns of gene expression in the brain and will spur further study of this problem.

Investigating regeneration and functional integration of CNS neurons: lessons from zebrafish genetics and other fish species

Zebrafish possess a robust, innate CNS regenerative ability. Combined with their genetic tractability and vertebrate CNS architecture, this ability makes zebrafish an attractive model to gain requisite knowledge for clinical CNS regeneration. In treatment of neurological disorders, one can envisage replacing lost neurons through stem cell therapy or through activation of latent stem cells in the CNS. Here we review the evidence that radial glia are a major source of CNS stem cells in zebrafish and thus activation of radial glia is an attractive therapeutic target. We discuss the regenerative potential and the molecular mechanisms thereof, in the zebrafish spinal cord, retina, optic nerve and higher brain centres. We evaluate various cell ablation paradigms developed to induce regeneration, with particular emphasis on the need for (high throughput) indicators that neuronal regeneration has restored sensory or motor function. We also examine the potential confound that regeneration imposes as the community develops zebrafish models of neurodegeneration. We conclude that zebrafish combine several characters that make them a potent resource for testing hypotheses and discovering therapeutic targets in functional CNS regeneration. This article is part of a Special Issue entitled Zebrafish Models of Neurological Diseases.

Role of transverse bands in maintaining paranodal structure and axolemmal domain organization in myelinated nerve fibers: effect on longevity in dysmyelinated mutant mice

The consequences of dysmyelination are poorly understood and vary widely in severity. The shaking mouse, a quaking allele, is characterized by severe central nervous system (CNS) dysmyelination and demyelination, a conspicuous action tremor, and seizures in approximately 25% of animals, but with normal muscle strength and a normal lifespan. In this study we compare this mutant with other dysmyelinated mutants including the ceramide sulfotransferase deficient (CST-/-) mouse, which are more severely affected behaviorally, to determine what might underlie the differences between them with respect to behavior and longevity. Examination of the paranodal junctional region of CNS myelinated fibers shows that "transverse bands," a component of the junction, are present in nearly all shaking paranodes but in only a minority of CST-/- paranodes. The number of terminal loops that have transverse bands within a paranode and the number of transverse bands per unit length are only moderately reduced in the shaking mutant, compared with controls, but markedly reduced in CST-/- mice. Immunofluorescence studies also show that although the nodes of the shaking mutant are somewhat longer than normal, Na(+) and K(+) channels remain separated, distinguishing this mutant from CST-/- mice and others that lack transverse bands. We conclude that the essential difference between the shaking mutant and others more severely affected is the presence of transverse bands, which serve to stabilize paranodal structure over time as well as the organization of the axolemmal domains, and that differences in the prevalence of transverse bands underlie the marked differences in progressive neurological impairment and longevity among dysmyelinated mouse mutants.

Optic nerve and vitreal inflammation are both RGC neuroprotective but only the latter is RGC axogenic

Intravitreal inflammation, induced by either lens injury, or intravitreal injection of zymosan (IVZ), protects RGC from apoptosis and stimulates axon regeneration after optic nerve transection. Here, we investigate the differential effects of intra-optic nerve zymosan (ONZ) and IVZ injections on RGC neuroprotection and axogenesis. After both IVZ and ONZ injection, zymosan-induced inflammation promoted a similar 4-/5-fold enhancement in RGC survival, compared to optic nerve transected controls, but only IVZ promoted RGC axon regeneration. IVZ was the most effective in activating retinal astrocyte/Müller cells while regulated intramembraneous proteolysis (RIP) of p75(NTR) and inactivation of Rho (key components of the axon growth inhibitory signalling cascade) occurred in both ONZ and IVZ, but only in the latter did RGC axons regenerate. We suggest that neuroprotective factors may be transported to RGC somata by retrograde transport after ONZ and diffuse into the retina after IVZ injection, but an axogenic agent is required to initiate and maintain disinhibited RGC axon regeneration that may be an exclusive property of a Müller cell-derived factor released after IVZ.

CNTF induces photoreceptor neuroprotection and Müller glial cell proliferation through two different signaling pathways in the adult zebrafish retina

Ciliary neurotrophic factor (CNTF) acts in several processes in the vertebrate retina, including neuroprotection of photoreceptors in the stressed adult retina and regulation of neuronal progenitor cell proliferation during retinal development. However, the signaling pathway it utilizes (Jak/Stat, MAPK, or Akt) in these processes is ambiguous. Because dark-adapted albino zebrafish exhibit light-induced rod and cone cell death and subsequently regenerate the lost photoreceptor cells, zebrafish should be a useful model to study the role of CNTF in both neuroprotection and neuronal progenitor cell proliferation. We therefore investigated the potential roles of CNTF in both the undamaged and light-damaged adult zebrafish retinas. Intraocular injection of CNTF suppressed light-induced photoreceptor cell death, which then failed to exhibit the regeneration response that is marked by proliferating Müller glia and neuronal progenitor cells. Inhibiting the MAPK signaling pathway, but neither the Stat3 nor Akt pathways, significantly reduced the CNTF-mediated neuroprotection of light-induced photoreceptor cell death. Intraocular injection of CNTF into non-light-treated (undamaged) eyes mimicked constant intense light treatment by increasing Stat3 expression in Müller glia followed by increasing the number of proliferating Müller glia and neuronal progenitors. Knockdown of Stat3 expression in the CNTF-injected non-light-treated retinas significantly reduced the number of proliferating Müller glia, while coinjection of CNTF with either MAPK or Akt inhibitors did not inhibit the CNTF-induced Müller glia proliferation. Thus, CNTF utilizes a MAPK-dependant signaling pathway in neuroprotection of light-induced photoreceptor cell death and a Stat3-dependant signaling pathway to stimulate Müller glia proliferation.

CNTF protects oligodendrocytes from ammonia toxicity: intracellular signaling pathways involved

In pediatric patients, hyperammonemia can provoke irreversible damages to developing CNS like cortical atrophy, ventricular enlargement, demyelination or gray and white matter hypodensities which are concordant with alterations of neurons and oligodendrocytes. Cerebral injury triggers endogenous protective mechanisms that can prevent or limit brain damage. Understanding these mechanisms may lead to new therapeutic strategies. We investigated whether ciliary neurotrophic factor (CNTF), a cytokine-like protein expressed by astrocytes and described as an injury-associated survival factor, was up-regulated by ammonia in developing reaggregated 3D brain cell cultures. We showed that CNTF is up-regulated by ammonia exposure, through mediation of p38 MAPK activation in astrocytes. We also observed that SAPK/JNK and Erk1/2 activations in oligodendrocytes and neurons, respectively, also play indirect roles in CNTF synthesis by astrocytes. Co-treatment with exogenous CNTF demonstrated strong protective effects on oligodendrocytes, but not on neurons, against ammonia toxicity. These protective effects involved JAK/STAT, SAPK/JNK and c-jun proteins.

Chronically increased ciliary neurotrophic factor and fibroblast growth factor-2 expression after spinal contusion in rats

Demyelination and oligodendrocyte loss following spinal cord injury (SCI) are well documented. Recently, we showed oligodendrocyte progenitor cell (OPC) accumulation and robust oligodendrocyte genesis occurring along SCI lesion borders. We have since begun investigating potential mechanisms for this endogenous repair response. Here, we examined ciliary neurotrophic factor (CNTF) and fibroblast growth factor-2 (FGF-2) expression, because both factors alter progenitor proliferation and differentiation and are increased in several CNS disorders. We hypothesized that CNTF and FGF-2 would increase after SCI, especially in regions of enhanced oligogenesis. First, CNTF protein was quantified using Western blots, which revealed that CNTF protein continually rose through 28 days post injury (dpi). Next, by using immunohistochemistry, we examined the spatiotemporal expression of CNTF in cross-sections spanning the injury site. CNTF immunoreactivity was observed on astrocytes and oligodendrocytes in naïve and contused spinal cords. Significantly increased CNTF was detected in spared white and gray matter between 5 and 28 dpi compared with uninjured controls. By 28 dpi, CNTF expression was significantly higher along lesion borders compared with outlying spared tissue; a similar distribution of phosphorylated STAT3, a transcription factor up-regulated by CNTF and to a lesser extent FGF-2, was also detected. Because CNTF can potentiate FGF-2 expression, we examined the distribution of FGF-2+ cells. Significantly more FGF-2+ cells were noted along lesion borders at 7 and 28 dpi. Thus, both CNTF and FGF-2 are present in regions of elevated OPC proliferation and oligodendrocyte generation after SCI and therefore may play a role in injury-induced gliogenesis.