Transgenic inhibition of astroglial NF-kappa B leads to increased axonal sparing and sprouting following spinal cord injury

From demyelination to remyelination: the road toward therapies for spinal cord injury

Myelin integrity is crucial for central nervous system (CNS) physiology while its preservation and regeneration after spinal cord injury (SCI) is key to functional restoration. Disturbance of nodal organization acutely after SCI exposes the axon and triggers conduction block in the absence of overt demyelination. Oligodendrocyte (OL) loss and myelin degradation follow as a consequence of secondary damage. Here, we provide an overview of the major biological events and underlying mechanisms leading to OL death and demyelination and discuss strategies to restrain these processes. Another aspect which is critical for SCI repair is the enhancement of endogenously occurring spontaneous remyelination. Recent findings have unveiled the complex roles of innate and adaptive immune responses in remyelination and the immunoregulatory potential of the glial scar. Moreover, the intimate crosstalk between neuronal activity, oligodendrogenesis and myelination emphasizes the contribution of rehabilitation to functional recovery. With a view toward clinical applications, several therapeutic strategies have been devised to target SCI pathology, including genetic manipulation, administration of small therapeutic molecules, immunomodulation, manipulation of the glial scar and cell transplantation. The implementation of new tools such as cellular reprogramming for conversion of one somatic cell type to another or the use of nanotechnology and tissue engineering products provides additional opportunities for SCI repair. Given the complexity of the spinal cord tissue after injury, it is becoming apparent that combinatorial strategies are needed to rescue OLs and myelin at early stages after SCI and support remyelination, paving the way toward clinical translation.

Neurological recovery and antioxidant effects of curcumin for spinal cord injury in the rat: a network meta-analysis and systematic review

Spinal cord injury (SCI) is a devastating condition affecting young, healthy individuals worldwide. Existing agents have inadequate therapeutic efficacy, and some are associated with side effects. Our objective is to summarize and critically assess the neurological recovery and antioxidant effects of curcumin for treatment of SCI in rat models. PubMed, Embase, and Chinese databases were searched from their inception date to February 2014. Two reviewers independently selected animal studies that evaluated neurological recovery and antioxidant effects of curcumin, compared to placebo, in rats with SCI, extracted data, and assessed the methodological quality. A pair-wise analysis and a network meta-analysis were performed. Eight studies with adequate randomization were selected and included in the systematic review. Two studies had a higher methodological quality. Overall, curcumin appears to significantly improve neurological function, as assessed using the Basso, Beattie, Bresnahan (BBB) locomotor rating scale (four studies, n=132; pooled mean difference [MD]=3.09; 95% confidence interval [CI], 3.40-4.45; p=0.04), in a random-effects model and decrease malondialdehyde (MDA) using a fixed-effects model (four studies, n=56; pooled MD=-1.00; 95% CI=-1.59 to -0.42; p=0.00008). Effect size, assessed using the BBB scale, increased gradually with increasing curcumin dosage. The difference between low- and high-dose curcumin using the BBB scale was statistically significant. Neurological recovery and antioxidant effects of curcumin were observed in rats with SCI despite poor study methodological quality.

Astrocyte reactivity and reactive astrogliosis: costs and benefits

Astrocytes are the most abundant cells in the central nervous system (CNS) that provide nutrients, recycle neurotransmitters, as well as fulfill a wide range of other homeostasis maintaining functions. During the past two decades, astrocytes emerged also as increasingly important regulators of neuronal functions including the generation of new nerve cells and structural as well as functional synapse remodeling. Reactive gliosis or reactive astrogliosis is a term coined for the morphological and functional changes seen in astroglial cells/astrocytes responding to CNS injury and other neurological diseases. Whereas this defensive reaction of astrocytes is conceivably aimed at handling the acute stress, limiting tissue damage, and restoring homeostasis, it may also inhibit adaptive neural plasticity mechanisms underlying recovery of function. Understanding the multifaceted roles of astrocytes in the healthy and diseased CNS will undoubtedly contribute to the development of treatment strategies that will, in a context-dependent manner and at appropriate time points, modulate reactive astrogliosis to promote brain repair and reduce the neurological impairment.

Intra-Spinal Bone Marrow Mononuclear Cells Transplantation Inhibits the Expression of Nuclear Factor-κB in Acute Transection Spinal Cord Injury in Rats

Objective

To assess the effect of bone marrow mononuclear cells (BMMNCs) transplantation in the expression of nuclear factor-κB (NF-κB) in spinal cord injury (SCI) in rats.

Methods

BMMNCs were isolated from tibia and femur by a density gradient centrifugation. After establishment of acute transection SCI, rats were divided into experiment (BMMNCs), experiment control (0.1 M PBS infused) and sham surgery groups (laminectomy without any SCI). Locomotor function was assessed weekly for 5 weeks post-injury using BBB locomotor score and urinary bladder function daily for 4 weeks post-injury. Activity of NF-κB in spinal cord was assessed by immunohistochemistry and reverse transcriptase polymerase chain reaction.

Results

At each time point post-injury, sham surgery group had significantly higher Basso, Beattie, Bresnahan locomotor and urinary bladder function scores than experiment and experiment control group (p<0.05). At subsequent time interval there were gradual improvement in both experiment and experiment control group, but experiment group had higher score in comparison to experiment control group (p<0.05). Comparisons were also made for expression of activated NF-κB positive cells and level of NF-κB messenger RNA in spinal cord at various time points between the groups. Activated NF-κB immunoreactivity and level of NF-κB mRNA expression were significantly higher in control group in comparison to experiment and sham surgery group (p<0.05).

Conclusion

BMMNCs transplantation attenuates the expression of NF-κB in injured spinal cord tissue and thus helps in recovery of neurological function in rat models with SCI.

Protective effects of Vitamin C against spinal cord injury-induced renal damage through suppression of NF-κB and proinflammatory cytokines

Spinal cord injury [SCI] leads to complex cellular and molecular interactions which affects various organ systems. The present study focused on determining the protection offered by Vitamin C against spinal injury-induced kidney damage in wistar rats. The experimental protocol was performed with three groups; Sham, SCI and Vitamin C [20 mg/kg/bw] followed by SCI. The kidney tissue was investigated for oxidative stress parameters [reactive oxygen species, protein carbonyl, sulphydryl content, thiobarbituric acid reactive species [TBARS], and myeloperoxidase activity] and antioxidant status [glutathione, superoxide dismutase, catalase, glutathione peroxidase, glutathione-S-transferase activity]. Further, inflammation studies were performed by analyzing expression of NF-κB, cycloxygenase-2, iNOS through western blot analysis and inflammatory cytokines by TNF-α and IL-1β levels. The present study shows clear evidence that Vitamin C treatment abrogated spinal injury-induced oxidative stress and inflammatory responses and enhanced the antioxidant status. Thus, the protection offered by Vitamin C against spinal cord injury-induced kidney damage is attributed to its anti-oxidant and anti-inflammatory effects.

Cytokine pathways regulating glial and leukocyte function after spinal cord and peripheral nerve injury

Injury to the nervous system causes the almost immediate release of cytokines by glial cells and neurons. These cytokines orchestrate a complex array of responses leading to microgliosis, immune cell recruitment, astrogliosis, scarring, and the clearance of cellular debris, all steps that affect neuronal survival and repair. This review will focus on cytokines released after spinal cord and peripheral nerve injury and the primary signalling pathways triggered by these inflammatory mediators. Notably, the following cytokine families will be covered: IL-1, TNF, IL-6-like, TGF-β, and IL-10. Whether interfering with cytokine signalling could lead to novel therapies will also be discussed. Finally, the review will address whether manipulating the above-mentioned cytokine families and signalling pathways could exert distinct effects in the injured spinal cord versus peripheral nerve.

Protective Effect of a cAMP Analogue on Behavioral Deficits and Neuropathological Changes in Cuprizone Model of Demyelination

Multiple sclerosis (MS) is an inflammatory demyelinating disease that leads to neuronal cell loss. Cyclic AMP and its analogs are well known to decrease inflammation and apoptosis. In the present study, we examined the effects of bucladesine, a cell-permeable analogue of cyclic adenosine monophosphate (cAMP), on myelin proteins (PLP, PMP-22), inflammation, and apoptotic, as well as anti-apoptotic factors in cuprizone model of demyelination. C57BL/6J mice were fed with chow containing 0.2% copper chelator cuprizone or vehicle by daily oral gavage for 5 weeks to induce reversible demyelination predominantly of the corpus callosum. Bucladesine was administered intraperitoneally at different doses (0.24, 0.48, or 0.7 μg/kg body weight) during the last 7 days of 5-week cuprizone treatment. Bucladesine exhibited a protective effect on myelination. Furthermore, bucladesine significantly decreased the production of interleukin-6 pro-inflammatory mediator as well as nuclear factor-κB activation and reduced the mean number of apoptotic cells compared to cuprizone-treated mice. Bucladesine also decreased production of caspase-3 as well as Bax and increased Bcl-2 levels. Our data revealed that enhancement of intracellular cAMP prevents demyelination and plays anti-inflammatory and anti-apoptotic properties in mice cuprizone model of demyelination. This suggests the modulation of intracellular cAMP as a potential target for treatment of MS.

Fingolimod may support neuroprotection via blockade of astrocyte nitric oxide

OBJECTIVE

Although astrocytes participate in glial scar formation and tissue repair, dysregulation of the NFκB pathway and of nitric oxide (NO) production in these glia cells contributes to neuroinflammation and neurodegeneration. Here we investigated the role of the crosstalk between sphingosine-1-phosphate (S1P) and cytokine signaling cascades in astrocyte activation and inflammation-mediated neurodegeneration, and addressed the effects of fingolimod on astrocyte-neuron interaction and NO synthesis in vivo.

METHODS

Immunohistochemistry, immunofluorescence, and confocal microscopy were used to detect S1P receptors, interleukin (IL) 1R, IL17RA, and nitrosative stress in multiple sclerosis (MS) plaques, experimental autoimmune encephalomyelitis (EAE) spinal cord, and the spinal cord of fingolimod-treated EAE mice. An in vitro model was established to study the effects of S1P, IL1, and IL17 stimulation on NFkB translocation and NO production in astrocytes, on spinal neuron survival, and on astrocyte-neuron interaction. Furthermore, fingolimod efficacy in blocking astrocyte-mediated neurodegeneration was evaluated.

RESULTS

We found coordinated upregulation of IL1R, IL17RA, S1P1, and S1P3 together with nitrosative markers in astrocytes within MS and EAE lesions. In vitro studies revealed that S1P, IL17, and IL1 induced NFκB translocation and NO production in astrocytes, and astrocyte conditioned media triggered neuronal death. Importantly, fingolimod blocked the 2 activation events evoked in astrocytes by either S1P or inflammatory cytokines, resulting in inhibition of astrocyte-mediated neurodegeneration. Finally, therapeutic administration of fingolimod to EAE mice hampered astrocyte activation and NO production.

INTERPRETATION

A neuroprotective effect of fingolimod in vivo may result from its inhibitory action on key astrocyte activation steps.

Scar-modulating treatments for central nervous system injury

Traumatic injury to the adult mammalian central nervous system (CNS) leads to complex cellular responses. Among them, the scar tissue formed is generally recognized as a major obstacle to CNS repair, both by the production of inhibitory molecules and by the physical impedance of axon regrowth. Therefore, scar-modulating treatments have become a leading therapeutic intervention for CNS injury. To date, a variety of biological and pharmaceutical treatments, targeting scar modulation, have been tested in animal models of CNS injury, and a few are likely to enter clinical trials. In this review, we summarize current knowledge of the scar-modulating treatments according to their specific aims: (1) inhibition of glial and fibrotic scar formation, and (2) blockade of the production of scar-associated inhibitory molecules. The removal of existing scar tissue is also discussed as a treatment of choice. It is believed that only a combinatorial strategy is likely to help eliminate the detrimental effects of scar tissue on CNS repair.

Astrocytic TGF-β signaling limits inflammation and reduces neuronal damage during central nervous system Toxoplasma infection

The balance between controlling infection and limiting inflammation is particularly precarious in the brain because of its unique vulnerability to the toxic effects of inflammation. Astrocytes have been implicated as key regulators of neuroinflammation in CNS infections, including infection with Toxoplasma gondii, a protozoan parasite that naturally establishes a chronic CNS infection in mice and humans. In CNS toxoplasmosis, astrocytes are critical to controlling parasite growth. They secrete proinflammatory cytokines and physically encircle parasites. However, the molecular mechanisms used by astrocytes to limit neuroinflammation during toxoplasmic encephalitis have not yet been identified. TGF-β signaling in astrocytes is of particular interest because TGF-β is universally upregulated during CNS infection and serves master regulatory and primarily anti-inflammatory functions. We report in this study that TGF-β signaling is activated in astrocytes during toxoplasmic encephalitis and that inhibition of astrocytic TGF-β signaling increases immune cell infiltration, uncouples proinflammatory cytokine and chemokine production from CNS parasite burden, and increases neuronal injury. Remarkably, we show that the effects of inhibiting astrocytic TGF-β signaling are independent of parasite burden and the ability of GFAP(+) astrocytes to physically encircle parasites.

Role of nuclear factor kappa B in central nervous system regeneration

Activation of nuclear factor kappa B (NF-κB) is a hallmark of various central nervous system (CNS) pathologies. Neuron-specific inhibition of its transcriptional activator subunit RelA, also referred to as p65, promotes neuronal survival under a range of conditions, i.e., for ischemic or excitotoxic insults. In macro- and microglial cells, post-lesional activation of NF-κB triggers a growth-permissive program which contributes to neural tissue inflammation, scar formation, and the expression of axonal growth inhibitors. Intriguingly, inhibition of such inducible NF-κB in the neuro-glial compartment, i.e., by genetic ablation of RelA or overexpression of a transdominant negative mutant of its upstream regulator IκBα, significantly enhances functional recovery and promotes axonal regeneration in the mature CNS. By contrast, depletion of the NF-κB subunit p50, which lacks transcriptional activator function and acts as a transcriptional repressor on its own, causes precocious neuronal loss and exacerbates axonal degeneration in the lesioned brain. Collectively, the data imply that NF-κB orchestrates a multicellular program in which κB-dependent gene expression establishes a growth-repulsive terrain within the post-lesioned brain that limits structural regeneration of neuronal circuits. Considering these subunit-specific functions, interference with the NF-κB pathway might hold clinical potentials to improve functional restoration following traumatic CNS injury.

Stem cell therapy and curcumin synergistically enhance recovery from spinal cord injury

Acute traumatic spinal cord injury (SCI) is marked by the enhanced production of local cytokines and pro-inflammatory substances that induce gliosis and prevent reinnervation. The transplantation of stem cells is a promising treatment strategy for SCI. In order to facilitate functional recovery, we employed stem cell therapy alone or in combination with curcumin, a naturally-occurring anti-inflammatory component of turmeric (Curcuma longa), which potently inhibits NF-κB. Spinal cord contusion following laminectomy (T9–10) was performed using a weight drop apparatus (10 g over a 12.5 or 25 mm distance, representing moderate or severe SCI, respectively) in Sprague-Dawley rats. Neural stem cells (NSC) were isolated from subventricular zone (SVZ) and transplanted at the site of injury with or without curcumin treatment. Functional recovery was assessed by BBB score and body weight gain measured up to 6 weeks following SCI. At the conclusion of the study, the mass of soleus muscle was correlated with BBB score and body weight. Stem cell therapy improved recovery from moderate SCI, however, it had a limited effect on recovery after severe SCI. Curcumin stimulated NSC proliferation in vitro, and in combination with stem cell therapy, induced profound recovery from severe SCI as evidenced by improved functional locomotor recovery, increased body weight, and soleus muscle mass. These findings demonstrate that curcumin in conjunction with stem cell therapy synergistically improves recovery from severe SCI. Furthermore, our results indicate that the effect of curcumin extends beyond its known anti-inflammatory properties to the regulation of stem cell proliferation.

Inhibition of NADPH oxidase activation in oligodendrocytes reduces cytotoxicity following trauma

Spinal cord injury is a debilitating neurological disorder that initiates a cascade of cellular events that result in a period of secondary damage that can last for months after the initial trauma. The ensuing outcome of these prolonged cellular perturbations is the induction of neuronal and glial cell death through excitotoxic mechanisms and subsequent free radical production. We have previously shown that astrocytes can directly induce oligodendrocyte death following trauma, but the mechanisms regulating this process within the oligodendrocyte remain unclear. Here we provide evidence demonstrating that astrocytes directly regulate oligodendrocyte death after trauma by inducing activation of NADPH oxidase within oligodendrocytes. Spinal cord injury resulted in a significant increase in oxidative damage which correlated with elevated expression of the gp91 phox subunit of the NADPH oxidase enzyme. Immunohistochemical analysis confirmed the presence of gp91 phox in oligodendrocytes in vitro and at 1 week following spinal cord injury. Exposure of oligodendrocytes to media from injured astrocytes resulted in an increase in oligodendrocyte NADPH oxidase activity. Inhibition of NADPH oxidase activation was sufficient to attenuate oligodendrocyte death in vitro and at 1 week following spinal cord injury, suggesting that excitotoxicity of oligodendrocytes after trauma is dependent on the intrinsic activation of the NADPH oxidase enzyme. Acute administration of the NADPH oxidase inhibitor apocynin and the alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate channel blocker 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo[f]quinoxaline-2,3-dione significantly improved locomotor behavior and preserved descending axon fibers following spinal cord injury. These studies lead to a better understanding of oligodendrocyte death after trauma and identify potential therapeutic targets in disorders involving demyelination and oligodendrocyte death.

Inhibition of astroglial NF-κB enhances oligodendrogenesis following spinal cord injury

BACKGROUND

Astrocytes are taking the center stage in neurotrauma and neurological diseases as they appear to play a dominant role in the inflammatory processes associated with these conditions. Previously, we reported that inhibiting NF-κB activation in astrocytes, using a transgenic mouse model (GFAP-IκBα-dn mice), results in improved functional recovery, increased white matter preservation and axonal sparing following spinal cord injury (SCI). In the present study, we sought to determine whether this improvement, due to inhibiting NF-κB activation in astrocytes, could be the result of enhanced oligodendrogenesis in our transgenic mice.

METHODS

To assess oligodendrogenesis in GFAP-IκBα-dn compared to wild-type (WT) littermate mice following SCI, we used bromodeoxyuridine labeling along with cell-specific immuno-histochemistry, confocal microscopy and quantitative cell counts. To further gain insight into the underlying molecular mechanisms leading to increased white matter, we performed a microarray analysis in naïve and 3 days, 3 and 6 weeks following SCI in GFAP-IκBα-dn and WT littermate mice.

RESULTS

Inhibition of astroglial NF-κB in GFAP-IκBα-dn mice resulted in enhanced oligodendrogenesis 6 weeks following SCI and was associated with increased levels of myelin proteolipid protein compared to spinal cord injured WT mice. The microarray data showed a large number of differentially expressed genes involved in inflammatory and immune response between WT and transgenic mice. We did not find any difference in the number of microglia/leukocytes infiltrating the spinal cord but did find differences in their level of expression of toll-like receptor 4. We also found increased expression of the chemokine receptor CXCR4 on oligodendrocyte progenitor cells and mature oligodendrocytes in the transgenic mice. Finally TNF receptor 2 levels were significantly higher in the transgenic mice compared to WT following injury.

CONCLUSIONS

These studies suggest that one of the beneficial roles of blocking NF-κB in astrocytes is to promote oligodendrogenesis through alteration of the inflammatory environment.

Inflammatory consequences in a rodent model of mild traumatic brain injury

Mild traumatic brain injury (mTBI), particularly mild "blast type" injuries resulting from improvised exploding devices and many sport-caused injuries to the brain, result in long-term impairment of cognition and behavior. Our central hypothesis is that there are inflammatory consequences to mTBI that persist over time and, in part, are responsible for resultant pathogenesis and clinical outcomes. We used an adaptation (1 atmosphere pressure) of a well-characterized moderate-to-severe brain lateral fluid percussion (LFP) brain injury rat model. Our mild LFP injury resulted in acute increases in interleukin-1α/β and tumor necrosis factor alpha levels, macrophage/microglial and astrocytic activation, evidence of heightened cellular stress, and blood-brain barrier (BBB) dysfunction that were evident as early as 3-6 h postinjury. Both glial activation and BBB dysfunction persisted for 18 days postinjury.

Reduced extracellular zinc levels facilitate glutamate-mediated oligodendrocyte death after trauma

Spinal cord injury results in irreversible paralysis, axonal injury, widespread oligodendrocyte death, and white matter damage. Although the mechanisms underlying these phenomena are poorly understood, previous studies from our laboratory indicate that inhibiting activation of the nuclear factor-κB transcription factor in astrocytes reduces white matter damage and improves functional recovery following spinal cord injury. In the current study, we demonstrate that activation of the nuclear factor-κB transcription factor within astrocytes results in a significant increase in oligodendrocyte death following trauma by reducing extracellular zinc levels and inducing glutamate excitotoxicity. By using an ionotropic glutamate receptor antagonist (CNQX), we show that astroglial nuclear factor-κB-mediated oligodendrocyte death is dependent on glutamate signaling despite no change in extracellular glutamate concentrations. Further analysis demonstrated a reduction in levels of extracellular zinc in astrocyte cultures with functional nuclear factor-κB signaling following trauma. Cotreatment of oligodendrocytes with glutamate and zinc showed a significant increase in oligodendrocyte toxicity under low-zinc conditions, suggesting that the presence of zinc at specific concentrations can prevent glutamate excitotoxicity. These studies demonstrate a novel role for zinc in regulating oligodendrocyte excitotoxicity and identify new therapeutic targets to prevent oligodendrocyte cell death in central nervous system trauma and disease.

Effects of combining methylprednisolone with rolipram on functional recovery in adult rats following spinal cord injury

Methylprednisolone (MP) has been widely used as a standard therapeutic agent for the treatment of spinal cord injury (SCI). Because of its controversial beneficial effects, the combination of MP and other pharmacological agents aimed at enhancing functional recovery is desirable. The phosphodiesterase 4 (PDE4) inhibitor rolipram has been implicated in promotion of regeneration due to elevating cAMP. In the present study, we sought to determine the effects of MP and rolipram, administered in combination, after spinal cord injury (SCI) in adult rats. Here we show that in vitro administration of rolipram and MP significantly increased neuron survival and promoted neurite outgrowth of neurons on the inhibitory substrate CSPGs by upregulation of MMP-2 expression; in vivo administration of rolipram and MP inhibited CSPG expression and increase CSPG digestion after rat SCI. Rolipram and MP combining treatment promoted significant neuroprotection through reduced motoneuron death, minimized lesion cavity, and increased regeneration of lesioned corticospinal tract (CST) axons beyond the lesion site after SCI. Enhanced functional recovery was also observed. Overall, our study strongly suggested that the combination treatment of MP and rolipram may represent a promising strategy for clinically applicable pharmacological therapy for rapid initiation of neuroprotection after SCI.

Astrocytes: conductors of the Alzheimer disease neuroinflammatory symphony

Alzheimer disease (AD) is the most prevalent cause of dementia in humans, and the symptoms are commonly manifested after the seventh decade of life. Numerous pathological changes have been described in the postmortem brains of AD patients, including senile plaques, neurofibrillary tangles, neuroinflammation, synapse loss, and neuronal death. Reactive astrocytes surrounding senile plaques seem to be responsible for the ongoing inflammatory process in the disease through the release of cytokines and other toxic products. However, little is known about the regulation of these cells in the AD brain. Here we discuss the potential translational impact of the recent findings of Carrero and colleagues, published in Experimental Neurology, that shows the underlying molecular mechanism of astrocyte activation in response to β-amyloid (Aβ). Likewise, the relevance of pro-inflammatory mediators tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), cyclooxygenase-2 (COX-2) and nuclear factor-κB (NF-κB), as integral players in disease progression will be discussed.

Neuroprotective effects of sulforaphane after contusive spinal cord injury

Traumatic spinal cord injury (SCI) leads to oxidative stress, calcium mobilization, glutamate toxicity, the release of proinflammatory factors, and depletion of reduced glutathione (GSH) at the site of injury. Induction of the Keap1/Nrf2/ARE pathway can alleviate neurotoxicity by protecting against GSH depletion, oxidation, intracellular calcium overload, mitochondrial dysfunction, and excitotoxicity. Sulforaphane (SF), an isothiocyanate derived from broccoli, is a potent naturally-occurring inducer of the Keap1/Nrf2/ARE pathway, leading to upregulation of genes encoding cytoprotective proteins such as NAD(P)H: quinone oxidoreductase 1, and GSH-regulatory enzymes. Additionally, SF can attenuate inflammation by inhibiting the nuclear factor-κB (NF-κB) pathway, and the enzymatic activity of the proinflammatory cytokine macrophage inhibitory factor (MIF). Our study examined systemic administration of SF in a rat model of contusion SCI, in an effort to utilize its indirect antioxidant and anti-inflammatory properties to decrease secondary injury. Two doses of SF (10 or 50 mg/kg) were administered at 10 min and 72 h after contusion SCI. SF (50 mg/kg) treatment resulted in both acute and long-term beneficial effects, including upregulation of the phase 2 antioxidant response at the injury site, decreased mRNA levels of inflammatory cytokines (i.e., MMP-9) in the injured spinal cord, inactivation of urinary MIF tautomerase activity, enhanced hindlimb locomotor function, and an increased number of serotonergic axons caudal to the lesion site. These findings demonstrate that SF provides neuroprotective effects in the spinal cord after injury, and could be a candidate for therapy of SCI.

Transgenic inhibition of astroglial NF-κB protects from optic nerve damage and retinal ganglion cell loss in experimental optic neuritis

Background

Optic neuritis is an acute, demyelinating neuropathy of the optic nerve often representing the first appreciable symptom of multiple sclerosis. Wallerian degeneration of irreversibly damaged optic nerve axons leads to death of retinal ganglion cells, which is the cause of permanent visual impairment. Although the specific mechanisms responsible for triggering these events are unknown, it has been suggested that a key pathological factor is the activation of immune-inflammatory processes secondary to leukocyte infiltration. However, to date, there is no conclusive evidence to support such a causal role for infiltrating peripheral immune cells in the etiopathology of optic neuritis.

Methods

To dissect the contribution of the peripheral immune-inflammatory response versus the CNS-specific inflammatory response in the development of optic neuritis, we analyzed optic nerve and retinal ganglion cells pathology in wild-type and GFAP-IκBα-dn transgenic mice, where NF-κB is selectively inactivated in astrocytes, following induction of EAE.

Results

We found that, in wild-type mice, axonal demyelination in the optic nerve occurred as early as 8 days post induction of EAE, prior to the earliest signs of leukocyte infiltration (20 days post induction). On the contrary, GFAP-IκBα-dn mice were significantly protected and showed a nearly complete prevention of axonal demyelination, as well as a drastic attenuation in retinal ganglion cell death. This correlated with a decrease in the expression of pro-inflammatory cytokines, chemokines, adhesion molecules, as well as a prevention of NAD(P)H oxidase subunit upregulation.

Conclusions

Our results provide evidence that astrocytes, not infiltrating immune cells, play a key role in the development of optic neuritis and that astrocyte-mediated neurotoxicity is dependent on activation of a transcriptional program regulated by NF-κB. Hence, interventions targeting the NF-κB transcription factor in astroglia may be of therapeutic value in the treatment of optic neuritis associated with multiple sclerosis.

Genomic analysis of reactive astrogliosis

Reactive astrogliosis is characterized by a profound change in astrocyte phenotype in response to all CNS injuries and diseases. To better understand the reactive astrocyte state, we used Affymetrix GeneChip arrays to profile gene expression in populations of reactive astrocytes isolated at various time points after induction using two mouse injury models, ischemic stroke and neuroinflammation. We find reactive gliosis consists of a rapid, but quickly attenuated, induction of gene expression after insult and identify induced Lcn2 and Serpina3n as strong markers of reactive astrocytes. Strikingly, reactive astrocyte phenotype strongly depended on the type of inducing injury. Although there is a core set of genes that is upregulated in reactive astrocytes from both injury models, at least 50% of the altered gene expression is specific to a given injury type. Reactive astrocytes in ischemia exhibited a molecular phenotype that suggests that they may be beneficial or protective, whereas reactive astrocytes induced by LPS exhibited a phenotype that suggests that they may be detrimental. These findings demonstrate that, despite well established commonalities, astrocyte reactive gliosis is a highly heterogeneous state in which astrocyte activities are altered to respond to the specific injury. This raises the question of how many subtypes of reactive astrocytes exist. Our findings provide transcriptome databases for two subtypes of reactive astrocytes that will be highly useful in generating new and testable hypotheses of their function, as well as for providing new markers to detect different types of reactive astrocytes in human neurological diseases.

Innate immunity in the central nervous system

Immune responses in the CNS are common, despite its perception as a site of immune privilege. These responses can be mediated by resident microglia and astrocytes, which are innate immune cells without direct counterparts in the periphery. Furthermore, CNS immune reactions often take place in virtual isolation from the innate/adaptive immune interplay that characterizes peripheral immunity. However, microglia and astrocytes also engage in significant cross-talk with CNS-infiltrating T cells and other components of the innate immune system. Here we review the cellular and molecular basis of innate immunity in the CNS and discuss what is known about how outcomes of these interactions can lead to resolution of infection, neurodegeneration, or neural repair depending on the context.

Shiga toxin 1 induces on lipopolysaccharide-treated astrocytes the release of tumor necrosis factor-alpha that alter brain-like endothelium integrity

The hemolytic uremic syndrome (HUS) is characterized by hemolytic anemia, thrombocytopenia and renal dysfunction. The typical form of HUS is generally associated with infections by Gram-negative Shiga toxin (Stx)-producing Escherichia coli (STEC). Endothelial dysfunction induced by Stx is central, but bacterial lipopolysaccharide (LPS) and neutrophils (PMN) contribute to the pathophysiology. Although renal failure is characteristic of this syndrome, neurological complications occur in severe cases and is usually associated with death. Impaired blood-brain barrier (BBB) is associated with damage to cerebral endothelial cells (ECs) that comprise the BBB. Astrocytes (ASTs) are inflammatory cells in the brain and determine the BBB function. ASTs are in close proximity to ECs, hence the study of the effects of Stx1 and LPS on ASTs, and the influence of their response on ECs is essential. We have previously demonstrated that Stx1 and LPS induced activation of rat ASTs and the release of inflammatory factors such as TNF-α, nitric oxide and chemokines. Here, we demonstrate that rat ASTs-derived factors alter permeability of ECs with brain properties (HUVECd); suggesting that functional properties of BBB could also be affected. Additionally, these factors activate HUVECd and render them into a proagregant state promoting PMN and platelets adhesion. Moreover, these effects were dependent on ASTs secreted-TNF-α. Stx1 and LPS-induced ASTs response could influence brain ECs integrity and BBB function once Stx and factors associated to the STEC infection reach the brain parenchyma and therefore contribute to the development of the neuropathology observed in HUS.

Hemolytic-uremic syndrome (HUS) is generally caused by Shiga toxin (Stx)-producing Escherichia coli but bacterial lipopolysaccharide (LPS) and neutrophils (PMN) contribute to the pathophysiology. Acute renal failure is the main feature of HUS, but in severe cases, patients develop neurological complications, which are usually associated with death. Although the mechanisms of neurological damage remain uncertain, alterations/injury of brain endothelial cells (ECs) which constitute the blood-brain barrier (BBB) is clear. Astrocytes (ASTs) are inflammatory cells enclosing ECs and are responsible of the normal function of the barrier. We have recently demonstrated that Stx1, one of the most common types of Stx, induce an inflammatory response in LPS-treated ASTs. We then study the effects of factors released by ASTs in response to LPS and/or Stx1 on brain-like ECs. We demonstrate that Stx1 induces in LPS-treated ASTs the release of factors that alter brain properties in ECs, including the permeability; turning them more susceptible to Stx1 toxic effects. Furthermore, they activate ECs, neutrophils (PMN) and platelets and render ECs into a proagregant state promoting PMN and platelet adhesion. Our results suggest that ASTs could influence brain ECs integrity and BBB function once Stx in combination with bacterial factors reach the brain parenchyma.

Stimulation of the neurotrophin receptor TrkB on astrocytes drives nitric oxide production and neurodegeneration

Neurotrophin growth factors support neuronal survival and function. In this study, we show that the expression of the neurotrophin receptor TrkB is induced on astrocytes in white matter lesions in multiple sclerosis (MS) patients and mice with experimental autoimmune encephalomyelitis (EAE). Surprisingly, mice lacking TrkB specifically in astrocytes were protected from EAE-induced neurodegeneration. In an in vitro assay, astrocytes stimulated with the TrkB agonist brain-derived neurotrophic factor (BDNF) released nitric oxide (NO), and conditioned medium from activated astrocytes had detrimental effects on the morphology and survival of neurons. This neurodegenerative process was amplified by NO produced by neurons. NO synthesis in the central nervous system during EAE depended on astrocyte TrkB. Together, these findings suggest that TrkB expression on astrocytes may represent a new target for neuroprotective therapies in MS.

Recovery from spinal cord injury using naturally occurring antiinflammatory compound curcumin: laboratory investigation

OBJECT

Spinal cord injury (SCI) is a debilitating disease. Primary SCI results from direct injury to the spinal cord, whereas secondary injury is a side effect from subsequent edema and ischemia followed by activation of proinflammatory cytokines. These cytokines activate the prosurvival molecule nuclear factor-κB and generate obstacles in spinal cord reinnervation due to gliosis. Curcumin longa is an active compound found in turmeric, which acts as an antiinflammatory agent primarily by inhibiting nuclear factor-κB. Here, the authors study the effect of curcumin on SCI recovery.

METHODS

Fourteen female Sprague-Dawley rats underwent T9-10 laminectomy and spinal cord contusion using a weight-drop apparatus. Within 30 minutes after contusion and weekly thereafter, curcumin (60 mg/kg/ml body weight in dimethyl sulfoxide) or dimethyl sulfoxide (1 ml/kg body weight) was administered via percutaneous epidural injection at the injury site. Spinal cord injury recovery was assessed weekly by scoring hindlimb motor function. Animals were killed 6 weeks postcontusion for histopathological analysis of spinal cords and soleus muscle weight evaluation.

RESULTS

Curcumin-treated rats had improved motor function compared with controls starting from Week 1. Body weight gain significantly improved, correlating with improved Basso-Beattie-Bresnahan scores. Soleus muscle weight was greater in curcumin-treated rats than controls. Histopathological analysis validated these results with increased neural element mass with less gliosis at the contusion site in curcumin-treated rats than controls.

CONCLUSIONS

Epidural administration of curcumin resulted in improved recovery from SCI. This occurred with no adverse effects noted in experimental animals. Therefore, curcumin treatment may translate into a novel therapy for humans with SCI.

Nuclear factor-κB activation in Schwann cells regulates regeneration and remyelination

Schwann cells (SCs) are crucial for peripheral nerve development and regeneration; however, the intrinsic regulatory mechanisms governing postinjury responses are poorly understood. Activation and deacetylation of nuclear factor-κB (NF- κB) in SCs have been implicated as prerequisites for peripheral nerve myelination. Using GFAP-IκBα-dn mice in which NF- κB transcriptional activation is inhibited in SCs, we found no discernable differences in the quantity or structure of myelinated axons in adult facial nerves. Following crush injury, axonal regeneration was impaired at 31 days and significantly enhanced at 65 days in transgenic animals. Compact remyelination and Remak bundle organization were significantly compromised at 31 days and restored by 65 days post injury. Together, these data indicate that inhibition of NF-κB activation in SCs transiently delays axonal regeneration and compact remyelination. Manipulating the temporal activation of nuclear factor-κB in Schwann cells may offer new therapeutic avenues for PNS and CNS regeneration.

Glial activation in the spinal ventral horn caudal to cervical injury

Microglia and astrocytes play complex roles following spinal cord injury (SCI), contributing to inflammatory processes that both exacerbate injury and promote functional recovery by supporting neuro-protection and neuroplasticity. The crossed phrenic phenomenon (CPP) is an example of respiratory plasticity in which C(2) cervical hemisection (C(2)HS) strengthens crossed-spinal synaptic pathways to phrenic motor neurons ipsilateral to injury. We hypothesized that microglia and astrocytes are activated in the phrenic motor nucleus caudal and ipsilateral to C(2)HS, suggesting their potential for involvement in the CPP. To test this hypothesis, an incomplete cervical spinal hemisection (C(2) lateral injury; C(2)LI) was performed, and rats were allowed to recover for 1, 3, 14 or 28 days before collecting perfused spinal tissues. Microglia (via OX42) and astrocytes [via glial fibrillary acidic protein (GFAP)] were visualized with immunofluorescence microscopy in the C(4)-C(5) ventral horn, the region encompassing most of the phrenic motor nucleus. OX42-occupied fractional area ipsilateral to injury increased with C(2)LI (vs. sham) at 1 (12.5±1.8%, p<0.001), 3 (29.0±1.9%, p<0.001), 14 (26.1±3.1%, p<0.001) and 28 (19.2±2.0%, p<0.001) days post-C(2)LI. GFAP-occupied fractional area also increased with C(2)LI at 3 (24.4±3.2%, p<0.001) and 14 (16.8±8.3%, p=0.012) days, but not at 1 (6.2±3.9%, p=0.262) or 28 (10.6±3.9%, p=0.059) days post-C(2)LI. Thus, microglia and astrocytes are activated in the phrenic motor nucleus caudal to C(2)LI, suggesting that they play a role in functional deficits and/or recovery following spinal injury.

Astroglial inhibition of NF-κB does not ameliorate disease onset and progression in a mouse model for amyotrophic lateral sclerosis (ALS)

Motor neuron death in amyotrophic lateral sclerosis (ALS) is considered a “non-cell autonomous” process, with astrocytes playing a critical role in disease progression. Glial cells are activated early in transgenic mice expressing mutant SOD1, suggesting that neuroinflammation has a relevant role in the cascade of events that trigger the death of motor neurons. An inflammatory cascade including COX2 expression, secretion of cytokines and release of NO from astrocytes may descend from activation of a NF-κB-mediated pathway observed in astrocytes from ALS patients and in experimental models. We have attempted rescue of transgenic mutant SOD1 mice through the inhibition of the NF-κB pathway selectively in astrocytes. Here we show that despite efficient inhibition of this major pathway, double transgenic mice expressing the mutant SOD1^G93A ubiquitously and the dominant negative form of IκBα (IκBαAA) in astrocytes under control of the GFAP promoter show no benefit in terms of onset and progression of disease. Our data indicate that motor neuron death in ALS cannot be prevented by inhibition of a single inflammatory pathway because alternative pathways are activated in the presence of a persistent toxic stimulus.

The role of propriospinal interneurons in recovery from spinal cord injury

Over one hundred years ago, Sir Charles Sherrington described a population of spinal cord interneurons (INs) that connect multiple spinal cord segments and participate in complex or 'long' motor reflexes. These neurons were subsequently termed propriospinal neurons (PNs) and are known to play a crucial role in motor control and sensory processing. Recent work has shown that PNs may also be an important substrate for recovery from spinal cord injury (SCI) as they contribute to plastic reorganisation of spinal circuits. The location, inter-segmental projection pattern and sheer number of PNs mean that after SCI, a significant number of them are capable of 'bridging' an incomplete spinal cord lesion. When these properties are combined with the capacity of PNs to activate and coordinate locomotor central pattern generators (CPGs), it is clear they are ideally placed to assist locomotor recovery. Here we summarise the anatomy, organisation and function of PNs in the uninjured spinal cord, briefly outline the pathophysiology of SCI, describe how PNs contribute to recovery of motor function, and finally, we discuss the mechanisms that underlie PN plasticity. We propose there are two major challenges for PN research. The first is to learn more about ways we can promote PN plasticity and manipulate the 'hostile' micro-environment that limits regeneration in the damaged spinal cord. The second is to study the cellular/intrinsic properties of PNs to better understand their function in both the normal and injured spinal cord. This article is part of a Special Issue entitled 'Synaptic Plasticity & Interneurons'.

Signaling pathways in reactive astrocytes, a genetic perspective

Reactive astrocytes are associated with a vast array of central nervous system (CNS) pathologies. The activation of astrocytes is characterized by changes in their molecular and morphological features, and depending on the type of damage can also be accompanied by inflammatory responses, neuronal damage, and in severe cases, scar formation. Although reactive astrogliosis is the normal physiological response essential for containing damage, it can also have detrimental effects on neuronal survival and axon regeneration, particularly in neurodegenerative diseases. It is believed that progressive changes in astrocytes as they become reactive are finely regulated by complex intercellular and intracellular signaling mechanisms. However, these have yet to be sorted out. Much has been learned from gain-of-function approaches in vivo and culture paradigms, but in most cases, loss-of-function genetic studies, which are a critical complementary approach, have been lacking. Understanding which signaling pathways are required to control different aspects of astrogliosis will be necessary for designing therapeutic strategies to improve their beneficial effects and limit their detrimental ones in CNS pathologies. In this article, we review recent advances in the mechanisms underlying the regulation of aspects of astrogliosis, with the main focus on the signaling pathways that have been studied using loss-of-function genetic mouse models.

NF-κB in the mechanism of brain edema in acute liver failure: studies in transgenic mice

Astrocyte swelling and brain edema are major complications of the acute form of hepatic encephalopathy (acute liver failure, ALF). While elevated brain ammonia level is a well-known etiological factor in ALF, the mechanism by which ammonia brings about astrocyte swelling is not well understood. We recently found that astrocyte cultures exposed to ammonia activated nuclear factor-κB (NF-κB), and that pharmacological inhibition of such activation led to a reduction in astrocyte swelling. Although these findings suggest the involvement of NF-κB in astrocyte swelling in vitro, it is not known whether NF-κB contributes to the development of brain edema in ALF in vivo. Furthermore, pharmacological agents used to inhibit NF-κB may have non-specific effects. Accordingly, we used transgenic (Tg) mice that have a functional inactivation of astrocytic NF-κB and examined whether these mice are resistant to ALF-associated brain edema. ALF was induced in mice by treatment with the hepatotoxin thioacetamide (TAA). Wild type (WT) mice treated with TAA showed a significant increase in brain water content (1.65%) along with prominent astrocyte swelling and spongiosis of the neuropil, consistent with the presence of cytotoxic edema. These changes were not observed in Tg mice treated with TAA. Additionally, WT mice with ALF showed an increase in inducible nitric oxide synthase (iNOS) immunoreactivity in astrocytes from WT mice treated with TAA (iNOS is known to be activated by NF-κB and to contribute to cell swelling). By contrast, Tg mice treated with TAA did not exhibit brain edema, histological changes nor an increase in iNOS immunoreactivity. We also examined astrocytes cultures derived from Tg mice to determine whether these cells exhibit a lesser degree of swelling and cytopathological changes following exposure to ammonia. Astrocyte cultures derived from Tg mice showed no cell swelling nor morphological abnormalities when exposed to ammonia for 24h. By contrast, ammonia significantly increased cell swelling (31.7%) in cultured astrocytes from WT mice and displayed cytological abnormalities. Moreover, we observed a lesser increment in iNOS and NADPH oxidase activity (the latter is also known to be activated by NF-κB and to contribute to astrocyte swelling) in astrocyte cultures from Tg mice treated with ammonia, as compared to ammonia-treated WT mice astrocytes. These findings strongly suggest that activation of NF-κB is a critical factor in the development of astrocyte swelling/brain edema in ALF.

Astrocytes initiate inflammation in the injured mouse spinal cord by promoting the entry of neutrophils and inflammatory monocytes in an IL-1 receptor/MyD88-dependent fashion

CNS injury stimulates the expression of several proinflammatory cytokines and chemokines, some of which including MCP-1 (also known as CCL2), KC (CXCL1), and MIP-2 (CXCL2) act to recruit Gr-1(+) leukocytes at lesion sites. While earlier studies have reported that neutrophils and monocytes/macrophages contribute to secondary tissue loss after spinal cord injury (SCI), recent work has shown that depletion of Gr-1(+) leukocytes compromised tissue healing and worsened functional recovery. Here, we demonstrate that astrocytes distributed throughout the spinal cord initially contribute to early neuroinflammation by rapidly synthesizing MCP-1, KC, and MIP-2, from 3 up to 12h post-SCI. Chemokine expression by astrocytes was followed by the infiltration of blood-derived immune cells, such as type I "inflammatory" monocytes and neutrophils, into the lesion site and nearby damaged areas. Interestingly, astrocytes from mice deficient in MyD88 signaling produced significantly less MCP-1 and MIP-2 and were unable to synthesize KC. Analysis of the contribution of MyD88-dependent receptors revealed that the astrocytic expression of MCP-1, KC, and MIP-2 was mediated by the IL-1 receptor (IL-1R1), and not by TLR2 or TLR4. Flow cytometry analysis of cells recovered from the spinal cord of MyD88- and IL-1R1-knockout mice confirmed the presence of significantly fewer type I "inflammatory" monocytes and the almost complete absence of neutrophils at 12h and 4days post-SCI. Together, these results indicate that MyD88/IL-1R1 signals regulate the entry of neutrophils and, to a lesser extent, type I "inflammatory" monocytes at sites of SCI.

Beneficial effects of secretory leukocyte protease inhibitor after spinal cord injury

Secretory leukocyte protease inhibitor is a serine protease inhibitor produced by various cell types, including neutrophils and activated macrophages, and has anti-inflammatory properties. It has been shown to promote wound healing in the skin and other non-neural tissues, however, its role in central nervous system injury was not known. We now report a beneficial role for secretory leukocyte protease inhibitor after spinal cord injury. After spinal cord contusion injury in mice, secretory leukocyte protease inhibitor is expressed primarily by astrocytes and neutrophils but not macrophages. We show, using transgenic mice over-expressing secretory leukocyte protease inhibitor, that this molecule has an early protective effect after spinal cord contusion injury. Furthermore, wild-type mice treated for the first week after spinal cord contusion injury with recombinant secretory leukocyte protease inhibitor exhibit sustained improvement in locomotor control and reduced secondary tissue damage. Recombinant secretory leukocyte protease inhibitor injected intraperitoneally localizes to the nucleus of circulating leukocytes, is detected in the injured spinal cord, reduces activation of nuclear factor-kappaB and expression of tumour necrosis factor-alpha. Administration of recombinant secretory leukocyte protease inhibitor might therefore be useful for the treatment of acute spinal cord injury.

Astrocytes in the damaged brain: molecular and cellular insights into their reactive response and healing potential

Long considered merely a trophic and mechanical support to neurons, astrocytes have progressively taken the center stage as their ability to react to acute and chronic neurodegenerative situations became increasingly clear. Reactive astrogliosis starts when trigger molecules produced at the injury site drive astrocytes to leave their quiescent state and become activated. Distinctive morphological and biochemical features characterize this process (cell hypertrophy, upregulation of intermediate filaments, and increased cell proliferation). Moreover, reactive astrocytes migrate towards the injured area to constitute the glial scar, and release factors mediating the tissue inflammatory response and remodeling after lesion. A novel view of astrogliosis derives from the finding that subsets of reactive astrocytes can recapitulate stem cell/progenitor features after damage, fostering the concept of astroglia as a promising target for reparative therapies. But which biochemical/signaling pathways modulate astrogliosis with respect to both the time after injury and the type of damage? Are reactive astrocytes overall beneficial or detrimental for neuroprotection and tissue regeneration? This debate has been animating this research field for several years now, and an integrated view on the results obtained and the possible future perspectives is needed. With this Commentary article we have attempted to answer the above-mentioned questions by reviewing the current knowledge on the molecular mechanisms controlling and sustaining the reaction of astroglia to injury and its stem cell-like properties. Moreover, the cellular/molecular mechanisms supporting the detrimental or beneficial features of astrogliosis have been scrutinized to gain insights on possible pharmacological approaches to enhance astrocyte neuroprotective activities.