Time-dependent effect of combination therapy with erythro- poietin and granulocyte colony-stimulating factor in a mouse model of hypoxic-ischemic brain injury

Erythropoietin （EPO） and granulocyte colony- stimulating factor （G-CSF） are likely to play broad roles in the brain. We investigated the effects of combination therapy with EPO and G-CSF in hypoxic- ischemic brain injury during the acute, subacute, and chronic phases. A total of 79 C57BL/6 mice with hypoxic-ischemic brain injury were randomly assigned acute （days 1-5）, subacute （days 11-15）and chronic （days 28-32） groups. All of them were treated with G-CSF （250 μg/kg） and EPO （5 000 U/kg） or saline daily for 5 consecutive days. Behavioral assessments and immunohistochemistry for angiogenesis, neuro- genesis, and astrogliosis were performed with an 8-week follow-up. Hypoxia-inducible factor-1 （HIF-1） was also measured by Western blot analysis. The results showed that the combination therapy with EPO and G-CSF in the acute phase significantly improved rotarod performance and forelimb-use symmetry compared to the other groups, while subacute EPO and G-CSF therapy exhibited a modest improvement compared with the chronic saline controls. The acute treatment significantly increased the density of CD31^＋（PECAM-1） and a-smooth muscle actin^＋ vessels in the frontal cortex and striatum, increased BrdU^＋/PSA- NCAM^＋ neurogenesis in the subventricular zone, and decreased astroglial density in the striatum. Furthermore, acute treatment significantly increased the HIF-1 expression in the cytosol and nucleus, whereas chronic treatment did not change the HIF-1 expression, consistent with the behavioral outcomes. These results indicate that the induction of HIF-1 expression by combination therapy with EPO and G-CSF synergistically enhances not only behavioral function but also neurogenesis and angiogenesis while decreasing the astroglial response in a time- dependent manner.     

Transforming growth factor beta 1, a cytokine with regenerative functions

We review the biology and role of transforming growth factor beta 1(TGF-β1) in peripheral nerve injury and regeneration, as it relates to injuries to large nerve trunks(i.e., sciatic nerve, brachial plexus), which often leads to suboptimal functional recovery. Experimental studies have suggested that the reason for the lack of functional recovery resides in the lack of sufficient mature axons reaching their targets, which is a result of the loss of the growth-supportive environment provided by the Schwann cells in the distal stump of injured nerves. Using an established chronic nerve injury and delayed repair animal model that accurately mimics chronic nerve injuries in humans, we summarize our key findings as well as others to better understand the pathophysiology of poor functional recovery. We demonstrated that 6 month TGF-β1 treatment for chronic nerve injury significantly improved Schwann cell capacity to support axonal regeneration. When combined with forskolin, the effect was additive, as evidenced by a near doubling of regenerated axons proximal to the repair site. We showed that in vivo application of TGF-β1 and forskolin directly onto chronically injured nerves reactivated chronically denervated Schwann cells, induced their proliferation, and upregulated the expression of regeneration-associated proteins. The effect of TGF-β1 and forskolin on old nerve injuries is quite impressive and the treatment regiment appears to mediate a growth-supportive milieu in the injured peripheral nerves. In summary, TGF-β1 and forskolin treatment reactivates chronically denervated Schwann cells and could potentially be used to extend and prolong the regenerative responses to promote axonal regeneration.     

Expression of insulin-like growth factor I by astrocytes in response to injury

Astrocytes are known to express several growth factors in response to injury and neurological disease. Insulin-like growth factor I (IGF-I) induces astrocytes to divide in vitro and is expressed by developing, but not adult astrocytes both in vivo and in vitro. We tested whether IGF-I is re-expressed by reactive astrocytes in response to injury. We found that astrocytes surrounding the lesioned parenchyma after introduction of a cannula through the cerebral cortex, hippocampus and midbrain contain high levels of immunoreactive IGF-I, as determined by immunocytochemistry using a highly sensitive and specific anti-IGF-I monoclonal antibody. Interestingly, the contralateral hippocampus also contained IGF-I positive astrocytes although in substantial lower numbers. Intact animals showed no detectable IGF-I immunoreactivity in astrocytes. IGF-I was detected at the first time point tested after the lesion was made, 1 week, and for at least 1 month thereafter. Reactive astrocytes expressing high levels of glial fibrillary acidic protein were found in a much wider distribution all along the lesioned area and beyond. We conclude that mechanical injury of the brain induces a specific pattern of expression of IGF-I by a subpopulation of astrocytes. These findings suggest that IGF-I is participating in the response of astrocytes to injury.     

In vivo response to vascular injury in the absence of factor IX: examination in factor IX knockout mice

INTRODUCTION: Recently, in vitro models of coagulation have called into question the traditional conception of Factor IX as an intrinsic pathway protein, essential to propagation of coagulation but not central to the initiation of hemostatic plug, which has been thought instead to involve TF/FVIIa interactions with factor X and platelets. We hypothesized that the activation of factor IX, and its role in a factor IXa/FVIIa "tenase" complex leading to thrombin generation, plays a more important role than that of TF/FVIIa complex activation of factor X in the early hemostatic response to vascular injury. In vivo modeling is possible because of the generation of factor IX(-/-) mice. MATERIALS AND METHODS: We used two models of arterial vascular injury, histological examination following mechanical carotid artery disruption and intravital microscopy of a mesenteric arteriole subsequent to ferric chloride arteriolar injury to examine mice having complete deficiency of factor IX (FIX(-/-)). RESULTS: Both injury models demonstrate that platelet rich thrombi /hemostatic plug in FIX(-/-) mice is dramatically reduced as compared to wild type mice under conditions of high shear; in fact, no platelet thrombi (>20 mum) were observed in the intravital experiments. Interestingly, the platelet defect is more striking than that described in mice lacking fibrinogen and/or von Willebrand factor. CONCLUSIONS: The results suggest TF/FVIIa-->FX pathway is insufficient for effective platelet aggregation in the presence of high flow, requiring factor IX at the convergence of both intrinsic and extrinsic pathways. Following platelet adhesion, factor IX is required for normal platelet aggregation in vivo, as well as thrombin generation and propagation of occlusive thrombus at the site of vascular injury.     

Granulocyte colony-stimulating factor promotes growth of processes,growth associated protein 43 and microtubule-associated protein 2 expression in cultured rat retinal ganglion cells in vitro

Following granulocyte colony-stimulating factor (G-CSF) treatment,the growth of processes in cul-tured rat retinal ganglion cells (RGCs) in vitro,expression of growth associated protein 43,and expression of microtubule-associated protein 2 mRNA expression were significantly increased.In contrast,RhoA/Rock protein content was significantly reduced by G-CSF treatment.These results indicate that G-CSF promotes the growth of processes in RGCs and increases the expression of growth-associated protein 43 and micr...     

Time-dependent effect of combination therapy with erythropoietin and granulocyte colony-stimulating factor in a mouse model of hypoxic-ischemic brain injury

Erythropoietin (EPO) and granulocyte colonystimulating factor (G-CSF) are likely to play broad roles in the brain. We investigated the effects of combination therapy with EPO and G-CSF in hypoxicischemic brain injury during the acute, subacute, and chronic phases. A total of 79 C57BL/6 mice with hypoxic-ischemic brain injury were randomly assigned acute (days 1–5), subacute (days 11–15) and chronic (days 28–32) groups. All of them were treated with G-CSF (250 μg/kg) and EPO (5 000 U/kg) or saline daily for 5 consecutive days. Behavioral assessments and immunohistochemistry for angiogenesis, neurogenesis, and astrogliosis were performed with an 8-week follow-up. Hypoxia-inducible factor-1 (HIF-1) was also measured by Western blot analysis. The results showed that the combination therapy with EPO and G-CSF in the acute phase significantly improved rotarod performance and forelimb-use symmetry compared to the other groups, while subacute EPO and G-CSF therapy exhibited a modest improvement compared with the chronic saline controls. The acute treatment significantly increased the density of CD31⁺ (PECAM-1) and α-smooth muscle actin⁺ vessels in the frontal cortex and striatum, increased BrdU⁺/PSANCAM⁺ neurogenesis in the subventricular zone, and decreased astroglial density in the striatum. Furthermore, acute treatment significantly increased the HIF-1 expression in the cytosol and nucleus, whereas chronic treatment did not change the HIF-1 expression, consistent with the behavioral outcomes. These results indicate that the induction of HIF-1 expression by combination therapy with EPO and G-CSF synergistically enhances not only behavioral function but also neurogenesis and angiogenesis while decreasing the astroglial response in a timedependent manner.     

Granulocyte colony‐stimulating factor improves neuron survival in experimental spinal cord injury by regulating nucleophosmin‐1 expression

Granulocyte colony‐stimulating factor (G‐CSF) and its related mechanisms were investigated to assess the potential for this factor to exert neuroprotective effects against spinal cord injury in mice. Recombinant human granulocyte colony‐stimulating factor (rhG‐CSF) was injected into mice spinal cord hemisection models. Locomotor activity was assessed by using the Basso‐Bettie‐Bresnahan scale. Neurons isolated from spinal cords were cultured in vitro and used in a neuronal mechanical injury model. Three treatment groups were compared with this model, 1) G‐CSF, 2) G‐CSF + NSC348884 (a nucleophosmin 1‐specific inhibitor), and 3) NSC348884. Immunofluorescence staining and Western blotting were performed to analyze the expression of G‐CSF and nucleophosmin 1 (Npm1). TUNEL staining was performed to analyze apoptosis after G‐CSF treatment. We found that the G‐CSF receptor (G‐CSFR) and Npm1 were expressed in neurons and that Npm1 expression was induced after G‐CSF treatment. G‐CSF inhibited neuronal apoptosis. NSC348884 induced p53‐dependent cell apoptosis and partially blocked the neuroprotective activity of G‐CSF on neurons in vitro. G‐CSF promoted locomotor recovery and demonstrated neuroprotective effects in an acute spinal cord injury model. The mechanism of G‐CSF's neuroprotection may be related in part to attenuating neuronal apoptosis by NPM1. © 2014 Wiley Periodicals, Inc.     

Ciliary neurotrophic factor activates spinal cord astrocytes, stimulating their production and release of fibroblast growth factor-2, to increase motor neuron survival.

At focal CNS injury sites, several cytokines accumulate, including ciliary neurotrophic factor (CNTF) and interleukin-1beta (IL-1beta). Additionally, the CNTF alpha receptor is induced on astrocytes, establishing an autocrine/paracrine loop. How astrocyte function is altered as a result of CNTF stimulation remains incompletely characterized. Here, we demonstrate that direct injection of CNTF into the spinal cord increases GFAP expression and astroglial size and that primary cultures of spinal cord astrocytes treated with CNTF, IL-1beta, or leukemia inhibitory factor exhibit nuclear hypertrophy comparable to that observed in vivo. Using a coculture bioassay, we further demonstrate that CNTF treatment of astrocytes increases their ability to support ChAT(+) ventral spinal cord neurons (presumably motor neurons) more than twofold compared with untreated astrocytes. Also, the complexity of neurites was significantly increased in neurons cultured with CNTF-treated astrocytes compared with untreated astrocytes. RT-PCR analysis demonstrated that CNTF increased levels of FGF-2 and nerve growth factor (NGF) mRNA and that IL-1beta increased NGF and hepatocyte growth factor mRNA levels. Furthermore, both CNTF and IL-1beta stimulated the release of FGF-2 from cultured spinal cord astrocytes. These findings demonstrate that cytokine-activated astrocytes better support CNS neuron survival via the production of neurotrophic molecules. We also show that CNTF synergizes with FGF-2, but not epidermal growth factor, to promote DNA synthesis in spinal cord astrocyte cultures. The significance of these findings is discussed by presenting a new model depicting the sequential activation of astrocytes by cytokines and growth factors in the context of CNS injury and repair.     

Dab2 attenuates brain injury in APP/PS1 mice via targeting transforming growth factor-beta/SMAD signaling简

Transforming growth factor-beta(TGF-β)type II receptor(TβRII)levels are extremely low in the brain tissue of patients with Alzheimer’s disease.This receptor inhibits TGF-β1/SMAD signaling and thereby aggravates amyolid-beta deposition and neuronal injury.Dab2,a specific adapter protein,protects TβRII from degradation and ensures the effective conduction of TGF-β1/SMAD signaling.In this study,we used an adenoviral vector to overexpress the Dab2 gene in the mouse hippocampus and investigated the regulatory effect of Dab2 protein on TGF-β1/SMAD signaling in a mouse model of Alzheimer’s disease,and the potential neuroprotective effect.The results showed that the TβRII level was lower in APP/PS1 mouse hippocampus than in normal mouse hippocampus.After Dab2 expression,hippocampal TβRII and p-SMAD2/3 levels were significantly increased,while amyloid-beta deposition,microglia activation,tumor necrosis factor-βand interleulin-6 levels and neuronal loss were significantly attenuated in APP/PS1 mouse brain tissue.These results suggest that Dab2 can exhibit neuroprotective effects in Alzheimer’s disease by regulating TGF-β1/SMAD signaling.     

Differential expression of fibroblast growth factor-2 and fibroblast growth factor receptor 1 in a scarring and nonscarring model of CNS injury in the rat

Injury to the adult brain results in abortive axon regeneration and the deposition of a dense fibrous glial scar. Therapeutic strategies to promote postinjury axon regeneration are likely to require antiscarring strategies. In neonatal brain wounds, scar material is not laid down and axons grow across the lesion site, either by de novo growth or regeneration. To achieve the therapeutic goal of recapitulating the nonscarring neonatal response in the injured adult, an understanding of how ontogenic differences in scarring reflect developmental diversities in the trophic response to injury is required. Fibrobast growth factor-2 (FGF-2) expression is developmentally regulated and has been implicated as a regulator of the wounding response of the adult rat central nervous system. We have investigated the expression of FGF-2 and fibroblast growth factor receptor 1 (FGFR1) after penetrating lesions to the cerebral cortex of 5 days post partum (dpp) (nonscarring) and 16 dpp and adult (scarring) rats. In situ hybridization, immunohistochemistry and Western blotting showed robust and sustained increases in FGF-2 and FGFR1 mRNA and protein in reactive astrocytes around the lesion in scarring rats, a response that was attenuated substantially in the nonscarring neonate. These results demonstrate that changes in astrocyte FGF-2 and FGFR1 expression are coincident with the establishment of a mature pattern of glial scarring after injury in the maturing central nervous system, but it is premature to infer a causal relationship without further experiments.     

Angiogenic and inflammatory responses following skeletal muscle injury are altered by immune neutralization of endogenous basic fibroblast growth factor, insulin-like growth factor-1 and transforming growth factor-β1

Injured skeletal muscle degeneration comprises early microvascular changes and inflammatory cell infiltration, possibly under the control of several growth factors. We have studied the role of basic fibroblast growth factor (bFGF), insulin-like growth factor-1 (IGF1), and transforming growth factor beta-1 (TGFβ1), by injecting specific anti-growth factor neutralizing antibodies into mouse extensor digitorum longus muscle at the time of injury (denervation and devascularization). Four days later, at the height of damaged myofiber phagocytosis, we assessed quantitatively revascularization, phagocytic activity, and inflammation. The immune neutralization of bFGF reduced the number of capillaries, macrophages and mast cells, and delayed necrotic myofiber phagocytosis. The immune neutralization of IGF1 or TGFβ1 promoted muscle revascularization, macrophage infiltration and necrotic myofiber phagocytosis. While IGF1 neutralization reduced the number of mast cells and did not modify that of T-cells or neutrophils, TGFβ1 neutralization increased the number of all of these cells. This study strongly suggests differing roles for bFGF, IGF1 and TGFβ1 in angiogenic and inflammatory responses during muscle degeneration, apart from their known effects on the behaviour of myogenic cells.     

Hypoxic induction of vascular endothelial growth factor is selectively impaired in mice carrying the mutant SOD1 gene

Localization and hypoxic induction of vascular endothelial growth factor (VEGF) was examined in the spinal cord of transgenic mice carrying a mutation in the superoxide dismutase 1 gene. Immunohistochemical and immunofluorescent study demonstrated that VEGF is mainly expressed in motor neurons before and after hypoxia. Baseline expression of VEGF was higher in transgenic (Tg) mice than in wild-type (Wt) littermates. However, VEGF was hardly induced after hypoxia in Tg mice, whereas Wt mice showed an approximate nine-fold increase. Impaired VEGF induction was evident in Tg mice at 12 weeks of age, when they were still presymptomatic. In contrast, baseline and hypoxic expression of brain-derived neurotrophic factor and glial cell line-derived neurotrophic factor did not differ between Tg and Wt mice. Thus, the present study demonstrates that hypoxic induction of VEGF in Tg mice is selectively impaired from a very early stage, suggesting profound involvement in the pathogenesis of motor neuron degeneration in this animal model of amyotrophic lateral sclerosis.     

Transforming growth factor β as a neuronoglial signal during peripheral nervous system response to injury

In contrast to the central nervous system (CNS), the peripheral nervous system (PNS) displays an important regenerative ability which is dependent, at least in part, on Schwann cell properties. The mechanisms which stimulate Schwann cells to adapt their behavior after a lesion to generate adequate conditions for PNS regeneration remain unknown. In this work, we report that adult rat dorsal root ganglion (DRG) neurons are able, after a lesion performed in vivo or when they are dissociated and cultured in vitro, to synthesize transforming growth factor β (TGFβ), a pleiotropic growth factor implicated in wound healing processes and in carcinogenesis. This TGFβ is tentatively identified as the β-1 isoform. Adult rat DRG neurons release a biologically active form of TGFβ which is able to elicit multiple Schwann cell responses including a stimulation to proliferate. Moreover, purified TGFβ-1 produces a Schwann cell morphology alteration and decreases the secretion of tissue-type plasminogen activator (tPA) and enhances the secretion of plasminogen activator inhibitor (PAI) by Schwann cells. This generates conditions which are thought to favor a successful neuritic regrowth. Furthermore, purified TGFβ-1 stimulates type IV collagen mRNA expression in Schwann cells. This subtype of collagen is associated with the process of myelinization. Finally, TGFβ-1 decreases nerve growth factor (NGF) mRNA expression by Schwann cells, an effect which could participate in the maintenance of a distoproximal NGF gradient during nerve regeneration. We propose that neuronal TGFβ plays an essential role as a neuronoglial signal that modulates the response of Schwann cells to injury and participates in the successful regeneration processes observed in the PNS. © 1993 Wiley-Liss, Inc.     

Muscle regeneration following injury can be modified in vivo by immune neutralization of basic fibroblast growth factor, transforming growth factor β1 or insulin-like growth factor I

Previous in vitro studies pointed out the role played by several growth factors (basic fibroblast growth factor or bFGF, transforming growth factor beta-1 or TGFβ1, insulin-like growth factor-I or IGF-I) on the proliferation, the differentiation and the fusion of myogenic precursor cells. We attempted to modify the muscle regeneration which follows the denervation-devascularization of extensor digitorum longus in mice, by acting on the growth factors which are possibly involved in this process. The injection of neutralizing antibodies against either bFGF or IGF-I into the muscle at the time of lesion reduced the number and diameter of regenerating myofibres, suggesting a delay in proliferation and/or fusion of activated satellite cells. The neutralization of TGFβ1 led to an increased number of small regenerating myofibres, which would be due to the promoting effects of the remaining growth factors (i.e. bFGF and IGF-I) on myoblast proliferation. These contrasted results strongly suggest that the growth factors regulate in vivo muscle regeneration and would be accessible tools for future therapy of muscular disorders.     

Astrocytic ceruloplasmin expression,which is induced by IL-1beta and by traumatic brain injury,increases in the absence of the IL-1 type 1 receptor

IL-1alpha and IL-1beta are induced immediately after insults to the brain, and signaling through the type 1 IL-1 receptor is essential for a normal microglial and astroglial response to injury. To better understand which genes are induced in astrocytes by IL-1beta, we used the unbiased technique of differential display to analyze mouse astroglial gene expression after IL-1beta treatment. Two novel genes were induced, as well as the gene for ceruloplasmin, a ferroxidase with antioxidant properties. Ceruloplasmin was analyzed further by Northern and Western blot. RNA and protein levels of ceruloplasmin were increased when astrocytes were treated with IL-1beta. To determine whether the IL-1 type 1 receptor (IL-1R1) is essential for the injury-induced expression of ceruloplasmin, a Western blot analysis was performed after a traumatic brain injury on mice that were IL-1R1-deficient. Ceruloplasmin increased significantly above controls after injury; however, injury-induced levels of ceruloplasmin were lower in IL-1R1-deficient (2.7-fold increase) than in the wild-type animals (3.5-fold increase). These data indicate that while IL-1R1 deletion has a slight effect on ceruloplasmin expression, it is not essential for either the basal or the induced expression of ceruloplasmin in vivo. Since ceruloplasmin buffers free copper, oxidizes ferrous iron, and catalyzes the dismutation of free radicals, increased levels of ceruloplasmin likely protect neurons and glia from sustaining damage after injury. Furthermore, as the IL-1R1 has been proposed to be a target for achieving neuroprotection after injury, these data suggest that the protection afforded by ceruloplasmin will be retained even when the IL-1R1 is antagonized.     

Nerve growth factor response to excitotoxic lesion of the cholinergic basal forebrain is slightly impaired in aged rats

Nerve growth factor (NGF) promotes survival and function of basal forebrain cholinergic neurons. We studied NGF and choline acetyltransferase (ChAT) activity after partial quisqualic acid induced lesions of the basal forebrain in 3 and 27 months-old rats, in order to investigate whether NGF-related regeneration is disturbed in old age. 2 weeks post lesion, ChAT activity decreased by 25 to 32% in adult and old rats. 3 months post lesion, the ChAT deficit receded in adult rats, but remained unchanged in old rats. 2 weeks post lesion, NGF levels were reduced by 36 to 44%, but there was no significant difference between adult and old rats. 3 months post lesion, we found increased NGF levels by 44% in the posterior cortex of adult rats. These results indicate that the compensatory NGF increase in the posterior cortex after partial cholinergic lesion of the basal forebrain is slightly impaired in old age.     

PET imaging of colony-stimulating factor 1 receptor: A head-to-head comparison of a novel radioligand, 11C-GW2580, and 11C-CPPC,in mouse models of acute and chronic neuroinflammation and a rhesus monkey

Colony-stimulating factor 1 receptor (CSF1R) is a specific biomarker for microglia. In this study, we developed a novel PET radioligand for CSF1R, ¹¹C-GW2580, and compared it to a reported CSF1R tracer, ¹¹C-CPPC, in mouse models of acute and chronic neuroinflammation and a rhesus monkey. Dynamic ¹¹C-GW2580- and ¹¹C-CPPC-PET images were quantified by reference tissue-based models and standardized uptake value ratio. Both tracers exhibited increased uptake in the lesioned striata of lipopolysaccharide-injected mice and in the forebrains of App^{NL-G-F/NL-G-F}-knock-in mice, spatially in agreement with an increased 18-kDa translocator protein radioligand retention. Moreover, ¹¹C-GW2580 captured changes in CSF1R availability more sensitively than ¹¹C-CPPC, with a larger dynamic range and a smaller inter-individual variability, in these model animals. PET imaging of CSF1R in a rhesus monkey displayed moderate-to-high tracer retention in the brain at baseline. Homologous blocker (i. e. unlabeled tracer) treatment reduced the uptake of ¹¹C-GW2580 by ∼30% in all examined brain regions except for centrum semi-ovale white matter, but did not affect the retention of ¹¹C-CPPC. In summary, our results demonstrated that ¹¹C-GW2580-PET captured inflammatory microgliosis in the mouse brain with higher sensitivity than a reported radioligand, and displayed saturable binding in the monkey brain, potentially providing an imaging-based quantitative biomarker for reactive microgliosis.     

Role of tumor necrosis factor receptor-1 in the death of retinal ganglion cells following optic nerve crush injury in mice

To assess the specific role of tumor necrosis factor (TNF) death receptor signaling in the induction of retinal ganglion cell (RGC) death, optic nerves of mice deficient for TNF receptor-1 (TNF-R1-/-) and control mice (C57BL/6J) were unilaterally subjected to crush injury. Counts of RGCs and their axons 6 weeks after the injury demonstrated that their loss was significantly less in TNF-R1-/- mice compared to controls. The most prominent decrease in neuronal loss detected in TNF-R1-/- mice was beyond the initial 2-week period after the injury. This time period was correlated with the period of glial activation and increased glial immunolabeling for TNF-alpha in these eyes. No further protection against neuronal loss was detectable in TNF-R1-/- mice treated with D-JNKI1, a specific inhibitor of c-Jun N-terminal protein kinase (JNK). However, anti-JNK treatment of control animals provided a significant protection against neuronal loss during the same secondary degeneration period. Phospho-JNK immunolabeling of RGCs in control mice subjected to optic nerve crush significantly decreased following their treatment with D-JNKI1, and anti-JNK treatment protected RGCs from degeneration in these animals, similar to the lack of TNF-R1. These findings provide evidence that TNF death receptor signaling is involved in the secondary degeneration of RGCs following optic nerve injury, and is associated with JNK signaling. Since secondarily degenerating neurons are viable targets for neuroprotection, inhibition of TNF death receptor signaling may be an effective strategy to protect RGCs in several neurodegenerative injuries.     

Interleukin-6 (IL6) and cellular response to facial nerve injury: effects on lymphocyte recruitment, early microglial activation and axonal outgrowth in IL6-deficient mice

Nerve injury triggers numerous changes in the injured neurons and surrounding non-neuronal cells. Of particular interest are molecular signals that play a role in the overall orchestration of this multifaceted cellular response. Here we investigated the function of interleukin-6 (IL6), a multifunctional neurotrophin and cytokine rapidly expressed in the injured nervous system, using the facial axotomy model in IL6-deficient mice and wild-type controls. Transgenic deletion of IL6 caused a massive decrease in the recruitment of CD3-positive T-lymphocytes and early microglial activation during the first 4 days after injury in the axotomized facial nucleus. This was accompanied by a more moderate reduction in peripheral regeneration at day 4, lymphocyte recruitment (day 14) and enhanced perikaryal sprouting (day 14). Motoneuron cell death, phagocytosis by microglial cells and recruitment of granulocytes and macrophages into injured peripheral nerve were not affected. In summary, IL6 lead to a variety of effects on the cellular response to neural trauma. However, the particularly strong actions on lymphocytes and microglia suggest that this cytokine plays a central role in the initiation of immune surveillance in the injured central nervous system.