Expression of pro-inflammatory cytokine and chemokine mRNA upon experimental spinal cord injury in mouse: an in situ hybridization study

Regeneration following spinal cord injury, from experimental models to humans: where are we?

Regeneration in the adult CNS following injury is extremely limited. Traumatic spinal cord injury causes a permanent neurological deficit followed by a very limited recovery due to failed regeneration attempts. In fact, it is now clear that the spinal cord intrinsically has the potential to regenerate, but cellular loss and the presence of an inhibitory environment strongly limit tissue regeneration and functional recovery. The molecular mechanisms responsible for failed regeneration are starting to be unveiled. This gain in knowledge led to the design of therapeutic strategies aimed to limit the tissue scar, to enhance the proregeneration versus the inhibitory environment, and to replace tissue loss, including the use of stem cells. They have been very successful in several animal models, although results are still controversial in humans. Nonetheless, novel experimental approaches hold great promise for use in humans.

Influence of local environment on the differentiation of neural stem cells engrafted onto the injured spinal cord

OBJECTIVES

In vitro, neural stem cells (NSCs) proliferate as undifferentiated spheroids and differentiate into neurons, astrocytes and oligodendrocytes. These features make NSCs suitable for spinal cord (SC) reconstruction. However, in vivo experiments have demonstrated that in the injured SC transplanted NSCs either remain undifferentiated or differentiate into the astrocytic phenotype. The microenvironment of the injured SC is believed to play a crucial role in driving the differentiation of the engrafted NSCs. Here, we tested the hypothesis that inflammatory cytokines (ICs) may be involved in the restricted differentiation of NSCs after grafting onto the injured SC.

METHODS

As the first step, we used immunohistochemistry to analyse the expression of tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta and interferon (IFN)-gamma in the normal SC of mice and following traumatic injury. Then, we investigated whether a combination of TNF-alpha, IL-1beta and IFN-gamma may affect the phenotype of murine NSCs in vitro.

RESULTS

We found that TNF-alpha, IL-1beta and IFN-gamma, which are absent in the normal SC, are all expressed in the injured SC and the expression of these cytokines follows a timely tuned fashion with IFN-gamma being detectable as long as 4 weeks after injury. In culture, exposure of proliferating NSCs to a combination of TNF-alpha, IL-1beta and IFN-gamma was per se sufficient to induce the astrocytic differentiation of these cells even in the absence of serum.

CONCLUSIONS

In the traumatically injured SC, differentiation of engrafted NSCs is restricted towards the astrocytic lineage because of the inflammatory environment. ICs are likely to play a major role in differentiation of NSCs in the in vivo conditions.

Inflammatory and apoptotic signaling after spinal cord injury

Central nervous system (CNS) destruction in spinal cord injury (SCI) is caused by a complex series of cellular and molecular events. Recent studies have concentrated on signaling by receptors in the tumor necrosis factor receptor (TNFR) superfamily that mediate diverse biological outcomes ranging from inflammation to apoptosis. From the perspective of basic science research, understanding how receptor signaling mediates these divergent responses is critical in clarifying events underlying irreversible cell injury in clinically relevant models of SCI. From a clinical perspective, this work also provides novel targets for the development of therapeutic agents that have the potential to protect the spinal cord from irreversible damage and promote functional recovery. In this review, we discuss how the formation of alternate signaling complexes and receptor membrane localization after SCI can influence life and death decisions of cells stimulated through two members of the TNFR superfamily, Fas/CD95 and TNFR1.

Up-regulation of TNFalpha in DRG satellite cells following lumbar facet joint injury in rats

The rat L5/6 facet joint, from which low back pain can originate, is multisegmentally innervated from the L1 to L5 dorsal root ganglia (DRG). Sensory fibers from the L1 and L2 DRG are reported to non-segmentally innervate the paravertebral sympathetic trunks, while those from the L3 to L5 DRGs segmentally innervate the L5/6 facet joint. Tumor necrosis factor alpha (TNFalpha) is a mediator of peripheral and central nervous system inflammatory response and plays a crucial role in injury and its pathophysiology. In the current study, change in TNFalpha in sensory DRG neurons innervating the L5/6 facet joint following facet joint injury was investigated in rats using a retrograde neurotransport method and immunohistochemistry. Neurons innervating the L5/6 facet joints, retrogradely labeled with fluoro-gold (FG), were distributed throughout DRGs from L1 to L5. Most DRG FG-labeled neurons innervating L5/6 facet joints were immunoreactive (IR) for TNFalpha before and after injury. In the DRG, glial fibrillary acidic protein (GFAP)-IR satellite cells emerged and surrounded neurons innervating L5/6 facet joints after injury. These satellite cells were also immunoreactive for TNFalpha. The numbers of activated satellite cells and TNFalpha-IR satellite cells were significantly higher in L1 and L2 DRG than in L3, L4, and L5 DRG. These data suggest that up-regulation of glial TNFalpha may be involved in the pathogenesis of facet joint pain.

Minocycline neuroprotects, reduces microgliosis, and inhibits caspase protease expression early after spinal cord injury

Minocycline, a clinically used tetracycline for over 40 years, crosses the blood-brain barrier and prevents caspase up-regulation. It reduces apoptosis in mouse models of Huntington's disease and familial amyotrophic lateral sclerosis (ALS) and is in clinical trial for sporadic ALS. Because apoptosis also occurs after brain and spinal cord (SCI) injury, its prevention may be useful in improving recovery. We analyzed minocycline's neuroprotective effects over 28 days following contusion SCI and found significant functional recovery compared to tetracycline. Histology, immunocytochemistry, and image analysis indicated statistically significant tissue sparing, reduced apoptosis and microgliosis, and less activated caspase-3 and substrate cleavage. Since our original report in abstract form, others have published both positive and negative effects of minocycline in various rodent models of SCI and with various routes of administration. We have since found decreased tumor necrosis factor-alpha, as well as caspase-3 mRNA expression, as possible mechanisms of action for minocycline's ameliorative action. These results support reports that modulating apoptosis, caspases, and microglia provide promising therapeutic targets for prevention and/or limiting the degree of functional loss after CNS trauma. Minocycline, and more potent chemically synthesized tetracyclines, may find a place in the therapeutic arsenal to promote recovery early after SCI in humans.

Tumor necrosis factor-immunoreactive cells and PGP 9.5-immunoreactive nerve fibers in vertebral endplates of patients with discogenic low back Pain and Modic Type 1 or Type 2 changes on MRI

STUDY DESIGN

Immunohistochemistry for tumor necrosis factor (TNF) and protein gene product (PGP) 9.5 in vertebral endplates of patients with discogenic low back pain and Modic Type 1 or Type 2 endplate changes on MRI.

OBJECTIVES

To examine whether inflammatory cytokines and nerve in-growth into the vertebral endplate are associated with discogenic low back pain.

SUMMARY AND BACKGROUND DATA

Degenerated discs and endplate abnormalities can be a cause of discogenic low back pain. However, the presence of TNF-immunoreactive cells and PGP 9.5-immunoreactive nerve fibers has not been studied in patients with discogenic low back pain and endplate changes on MRI.

METHODS

Eighteen endplates showing either normal intensity signals on MRI (endplate change -), Modic Type 1 signals (low intensity on T1-weighted spin-echo images), or Modic Type 2 signals (high intensity) from patients with discogenic low back pain (n = 14) or controls requiring surgery for other back problems (n = 4; scoliosis and traumatic injury of vertebra) were harvested during surgery. Endplates were immunostained using antibodies to TNF and PGP 9.5 and immunostained cells and nerve fibers in the endplates were counted.

RESULTS

Vertebral endplates from patients with Modic Type 1 or Type 2 endplate changes on MRI had significantly more PGP 9.5-immunoreactive nerve fibers and TNF-immunoreactive cells in comparison with patients with normal endplates on MRI (P < 0.01). The number of TNF-immunoreactive cells in endplates exhibiting Modic Type 1 changes was significantly higher than in endplates exhibiting Modic Type 2 changes (P < 0.05).

CONCLUSIONS

The results suggest that endplate abnormalities are related to inflammation and axon growth induced by TNF. TNF expression and PGP 9.5-positive nerve in-growth in abnormal endplates may be a cause of low back pain.

Expression of two temporally distinct microglia-related gene clusters after spinal cord injury

The dual role of microglia in cytotoxicity and neuroprotection is believed to depend on the specific, temporal expression of microglial-related genes. To better clarify this issue, we used high-density oligonucleotide microarrays to examine microglial gene expression after spinal cord injury (SCI) in rats. We compared expression changes at the lesion site, as well as in rostral and caudal regions after mild, moderate, or severe SCI. Using microglial-associated anchor genes, we identified two clusters with different temporal profiles. The first, induced by 4 h postinjury to peak between 4 and 24 h, included interleukin-1beta, interleukin-6, osteopontin, and calgranulin, among others. The second was induced 24 h after SCI, and peaked between 72 h and 7 days; it included C1qB, Galectin-3, and p22(phox). These two clusters showed similar expression profiles regardless of injury severity, albeit with slight decreases in expression in mild or severe injury vs. moderate injury. Expression was also decreased rostral and caudal to the lesion site. We validated the expression of selected cluster members at the mRNA and protein levels. In addition, we demonstrated that stimulation of purified microglia in culture induces expression of C1qB, Galectin-3, and p22(phox). Finally, inhibition of p22(phox) activity within microglial cultures significantly suppressed proliferation in response to stimulation, confirming that this gene is involved in microglial activation. Because microglial-related factors have been implicated both in secondary injury and recovery, identification of temporally distinct clusters of genes related to microglial activation may suggest distinct roles for these groups of factors.

Comparative analysis of lesion development and intraspinal inflammation in four strains of mice following spinal contusion injury

Susceptibility to neuroinflammatory disease is influenced in part by genetics. Recent data indicate that survival of traumatized neurons is strain dependent and influenced by polygenic loci that control resistance/susceptibility to experimental autoimmune encephalomyelitis (EAE), a model of CNS autoimmune disease. Here, we describe patterns of neurodegeneration and intraparenchymal inflammation after traumatic spinal cord injury (SCI) in mice known to exhibit varying degrees of EAE susceptibility [EAE-resistant (r) or EAE-susceptible (s) mice]. Spinal cords from C57BL/6 (EAE-s), C57BL/10 (EAE-r), BALB/c (EAE-r), and B10.PL (EAE-s) mice were prepared for stereological and immunohistochemical analysis at 6 hours or 3, 7, 14, 28, or 42 days following midthoracic (T9) spinal contusion injury. In general, genetic predisposition to EAE predicted the magnitude of intraparenchymal inflammation but not lesion size/length or locomotor recovery. Specifically, microglia/macrophage activation, recruitment of neutrophils and lymphocytes, and de novo synthesis of MHC class II were greatest in C57BL/6 mice and least in BALB/c mice at all times examined. However, lesion volume and axial spread of neurodegeneration were similar in C57BL/6 and BALB/c mice and were significantly greater than in C57BL/10 or B10.PL mice. Strains with marked intraspinal inflammation also developed the most intense lesion fibrosis. Thus, strain-dependent neuroinflammation was observed after SCI, but without a consistent relationship to EAE susceptibility or lesion progression. Only in C57BL/6 mice was the magnitude of intraspinal inflammation predictive of secondary neurodegeneration, functional recovery, or fibrosis.

Molecular control of physiological and pathological T-cell recruitment after mouse spinal cord injury

The intraspinal cues that orchestrate T-cell migration and activation after spinal contusion injury were characterized using B10.PL (wild-type) and transgenic (Tg) mice with a T-cell repertoire biased toward recognition of myelin basic protein (MBP). Previously, we showed that these strains exhibit distinct anatomical and behavioral phenotypes. In Tg mice, MBP-reactive T-cells are activated by spinal cord injury (SCI), causing more severe axonal injury, demyelination, and functional impairment than is found in non-Tg wild-type mice (B10.PL). Conversely, despite a robust SCI-induced T-cell response in B10.PL mice, no overt T-cell-mediated pathology was evident. Here, we show that chronic intraspinal T-cell accumulation in B10.PL and Tg mice is associated with a dramatic and sustained increase in CXCL10/IP-10 and CCL5/RANTES mRNA expression. However, in Tg mice, chemokine mRNA were enhanced 2- to 17-fold higher than in B10.PL mice and were associated with accelerated intraspinal T-cell influx and enhanced CNS macrophage activation throughout the spinal cord. These data suggest common molecular pathways for initiating T-cell responses after SCI in mice; however, if T-cell reactions are biased against MBP, molecular and cellular determinants of neuroinflammation are magnified in parallel with exacerbation of neuropathology and functional impairment.

Activation of JAK/STAT signalling in neurons following spinal cord injury in mice

The Janus kinase (JAK)/signal transducer and activator of transcription (STAT) signalling pathway is one of the most important in transducing signals from the cell surface to the nucleus in response to cytokines. In the present study, we investigated chronological alteration and cellular location of JAK1, STAT3, phosphorylated (p)-Tyr1022/1023-JAK1, p-Tyr705-STAT3, and interleukin-6 (IL-6) following spinal cord injury (SCI) in mice. Western blot analysis showed JAK1 to be significantly phosphorylated at Tyr1022/1023 from 6 h after SCI, peaking at 12 h and gradually decreasing thereafter, accompanied by phosphorylation of STAT3 at Tyr705 with a similar time course. ELISA analysis showed the concentration of IL-6 in injured spinal cord to also significantly increase from 3 h after SCI, peaking at 12 h, then gradually decreasing. Immunohistochemistry revealed p-Tyr1022/1023-JAK1, p-Tyr705-STAT3, and IL-6 to be mainly expressed in neurons of the anterior horns at 12 h after SCI. Pretreatment with a JAK inhibitor, AG-490, suppressed phosphorylation of JAK1 and STAT3 at 12 h after SCI, reducing recovery of motor functions. These findings suggest that SCI at the acute stage produces IL-6 mainly in neurons of the injured spinal cord, which activates the JAK/STAT pathway, and that this pathway may be involved with neuronal response to SCI.

Post-conditioning with lipopolysaccharide reduces the inflammatory infiltrate to the injured brain and spinal cord: a potential neuroprotective treatment

Systemic infection often accompanies or precedes acute brain injury, but it remains unclear how the systemic response contributes to outcome. To examine this problem we have microinjected recombinant interleukin-1beta (IL-1beta), a cytokine associated with acute brain injury, into the rat brain parenchyma and either preceded or followed this challenge with the intravenous injection of lipopolysaccharide (LPS), which mimics systemic inflammatory response syndrome. The microinjection of IL-1beta alone into the brain parenchyma gives rise to leukocyte mobilization in the blood, and to the delayed recruitment of neutrophils and monocytes to the brain with no evidence of blood-brain barrier breakdown or overt neuronal cell death. Systemic LPS pre-conditioning resulted in a dose-dependent reduction both in the number of circulating leukocytes and in the number of leukocytes recruited to the brain parenchyma after 12 h. Surprisingly, LPS given two hours after injury was equally effective in reducing the recruitment of leukocytes to the brain, which is more relevant to the management of clinical disease. In a more clinically relevant model of spinal cord injury, intravenous LPS post-conditioning also reduced the numbers of leukocytes mobilized in the blood and recruited to the spinal cord and thus limited the breakdown of the blood-spinal cord barrier. The effects appear to be specific to LPS, as they were not observed after intravenous IL-1beta pre-conditioning. Our studies suggest that individual pro-inflammatory conditioning strategies may protect the injured central nervous system from the damaging consequences of leukocyte recruitment and may provide scope for novel therapeutic intervention.

Activation of p38 and p42/44 MAP kinase in neuropathic pain: Involvement of VPAC2 and NK2 receptors and mediation by spinal glia

Activation of intracellular signaling pathways involving p38 and p42/44 MAP kinases may contribute importantly to synaptic plasticity underlying spinal neuronal sensitization. Inhibitors of p38 or p42/44 pathways moderately attenuated responses of dorsal horn neurons evoked by mustard oil but not brush and alleviated the behavioral reflex sensitization seen following nerve injury. Activation of p38 and p42/44 MAP kinases in spinal cord ipsilateral to constriction injury was reduced by antagonists of NMDA, VPAC2 and NK2 (but not related) receptors, the glial inhibitor propentofylline and inhibitors of TNF-alpha. A VPAC2 receptor agonist enhanced p38 phosphorylation and caused behavioral reflex sensitization in naïve animals that could be blocked by co-administration of p38 inhibitor. Conversely, an NK2 receptor agonist activated p42/44 and caused behavioral sensitization that could be prevented by co-administration of p42/44 inhibitor. Thus, spinal p38 and p42/44 MAP kinases are activated in neuropathic pain states by mechanisms involving VPAC2, NK2, NMDA receptors and glial cytokine production.

The nitrosteroid NCX 1015, a prednisolone derivative, improves recovery of function in rats after spinal cord injury

Glucocorticoids, given at high-doses, improve recovery of function after spinal cord injury (SCI) in animals. However, side effects combined with a limited efficacy in clinical trials have restricted their usefulness for treatment of SCI patients. Recent studies have shown that incorporation of the nitric oxide releasing moiety into the glucocorticoid structure enhances anti-inflammatory properties and reduces side effects. One compound, a derivative of prednisolone (PRE), (NCX 1015, prednisolone 21 [(4'nitrooxymethyl)benzoate]), has interesting pharmacological properties. Therefore, we investigated its effects on apoptosis and recovery of function in rats after SCI. Rats received subcutaneously vehicle, NCX 1015 or PRE (37 micromol/kg, each) 3.5 h after a standardized thoracic lesion. The treatment was continued once a day for 3 days and the effect of both steroids on apoptosis was examined by immunohistochemistry 24 h after the last injection. NCX 1015 but not PRE reduced TUNEL and activated caspase 3 in both white and ventral gray matter as well as tumor necrosis factor immunoreactivity in ventral horn motorneurons, suggesting that NCX 1015 reduces SCI-induced apoptosis. The effect of NCX 1015 on motor function was then examined by a standard locomotion rating scale (BBB) starting at 1 day after injury and continuing up to 14 days. NCX 1015 improved significantly locomotor activity by 4 days after injury, whereas PRE had an effect equivalent to that of vehicle, thus providing a correlation between the antiapoptotic effect of NCX1015 and its ability to improve recovery of function. The data suggest that NCX 1015 might be a novel experimental therapeutic compound for recovery of function in SCI patients.

Light promotes regeneration and functional recovery and alters the immune response after spinal cord injury

BACKGROUND AND OBJECTIVES

Photobiomodulation (PBM) has been proposed as a potential therapy for spinal cord injury (SCI). We aimed to demonstrate that 810 nm light can penetrate deep into the body and promote neuronal regeneration and functional recovery.

STUDY DESIGN/MATERIALS AND METHODS

Adult rats underwent a T9 dorsal hemisection, followed by treatment with an 810 nm, 150 mW diode laser (dosage = 1,589 J/cm2). Axonal regeneration and functional recovery were assessed using single and double label tract tracing and various locomotor tasks. The immune response within the spinal cord was also assessed.

RESULTS

PBM, with 6% power penetration to the spinal cord depth, significantly increased axonal number and distance of regrowth (P < 0.001). PBM also returned aspects of function to baseline levels and significantly suppressed immune cell activation and cytokine/chemokine expression.

CONCLUSION

Our results demonstrate that light, delivered transcutaneously, improves recovery after injury and suggests that light will be a useful treatment for human SCI.

Strategies to promote neural repair and regeneration after spinal cord injury

STUDY DESIGN

Retrospective review of current literature regarding neuroprotection and axonal regeneration therapies for acute spinal cord injury.

OBJECTIVES

To provide an update for spine clinicians of the emerging therapeutic strategies for promoting neural repair and regeneration after spinal cord injury.

SUMMARY OF BACKGROUND DATA

The neuroscientific community has generated a number of novel potential treatments for spinal injuries, some of which have entered clinical trials. Clinicians who manage spinal cord trauma are likely to encounter patients and their families who have questions or wish to be involved in these emerging treatments.

METHODS

Literature review, with particular focus on currently used medications that may have neuroprotective potential in spinal cord injury, and axonal regeneration strategies that are emerging in preliminary human clinical trials.

RESULTS

A number of medications such as erythropoietin and minocycline have demonstrated neuroprotective properties in animal models of spinal cord injury, and their long-established safety in humans make them appealing candidates for clinical trials. Human experience with novel neuroprotective and axonal regeneration strategies is growing around the world, and the peer-reviewed reporting of this is anxiously awaited.

CONCLUSIONS

The initiation of human clinical trials for spinal cord-injured patients heralds great hope that effective therapies will be forthcoming, although a great deal remains to be learned. Clinicians must provide leadership in the epidemiologic design and rigor of these initial forays into human evaluation.

Regional energy metabolism following short-term neural stem cell transplantation into the injured spinal cord

Stem cells have been shown to partly restore central nervous system (CNS) function after transplantation into the injured CNS. However, little is known about their influence on acute energy metabolism after spinal cord injury. The present study was designed to analyze regional changes in energy metabolites. Young adult mice were subjected to laminectomy with subsequent hemisection at the L2/3 vertebral level. Immediately thereafter a stable clone of murine neural stem cells (NSCs) was injected into the lesion site. After 4 and 24 h, spinal cords were removed and ATP, glucose, and lactate were analyzed by a bioluminescence approach in serial sections and compared to a laminectomized (intact control), hemisected-only or hemisected vehicle-injected control group. At both time points, ATP content of the hemisected group in the tissue segments adjacent to the lesion was increased when compared to the laminectomized control. At the lesion site ATP content decreased significantly at 24 h in the cell-transplanted group when compared to the laminectomized control group. Glucose content decreased at the lesion site and in segments adjacent to the lesion at both time points and in all experimental groups when compared to the laminectomized control group. Lactate content decreased significantly at 4 h in the caudal segments of the vehicle-injected group and in both adjacent segments of the transplanted group when compared to the laminectomized control. At the lesion site, lactate content decreased significantly at 4 and 24 h in the cell-transplanted group, when compared to the laminectomized control. The area of ATP decline at the lesion site 24 h postinjury was significantly lower in the vehicle control group as compared to the hemisected or transplanted group. The decrease in glucose combined with an increase in ATP in the lesion-adjacent segments may indicate that the tissue responds with an increased use of glucose to support itself with sufficient ATP. The significant decrease in glucose, lactate, and ATP in the cell-transplanted group at 24 h may indicate a high metabolic need of the stem cells. The lower area of ATP decline 24 h after vehicle administration suggests that the vehicle solution washes out toxic mediators, thus ameliorating hemisection-dependent secondary tissue damage.

Interleukin-1 beta induction of neuron apoptosis depends on p38 mitogen-activated protein kinase activity after spinal cord injury

AIM

Interleukin-1 beta (IL-1beta) has been implicated as an extracellular signal in the initiation of apoptosis in neurons and oligodendrocytes after spinal cord injury (SCI). To further characterize the apoptotic cascade initiated by IL-1beta after SCI, we examined the expression of IL-1beta, p38 mitogen-activated protein kinase (p38 MAPK) and caspase-3 after SCI, and further investigated whether p38 MAPK was involved in neuron apoptosis induced by IL-1beta.

METHODS

Adult rats were given contusion SCI at the T-10 vertebrae level with a weight-drop impactor (10 g weight dropped 25.0 mm). The expression levels of IL-1beta, p38 MAPK and caspase-3 after SCI were assessed with Western blots, immunohistochemistry staining, and real time reverse transcription polymerase chain reactions (RT-PCR). Neuron apoptosis was assessed with the terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-biotin nick end labeling (TUNEL) method.

RESULTS

Increased levels of IL-1beta and p38 MAPK were observed soon after injury, with a peak in expression levels within 6 h of injury. By 24 h after injury, caspase-3 expression was markedly increased in the injured spinal cord. TUNEL-positive cells were first observed in the lesioned area 6 h after SCI. The largest number of TUNEL-positive cells was observed at 24 h post-SCI. Intrathecal injection of the IL-1 receptor antagonist IL-1Ra significantly reduced expression of p38 MAPK and caspase-3, and reduced the number of TUNEL-positive cells. Moreover, intrathecal injection of an inhibitor of p38 MAPK, SB203580, also significantly reduced the expression of caspase-3, and reduced the number of TUNEL-positive cells in the injured spinal cord.

CONCLUSION

The p38MAPK signaling pathway plays an important role in IL-1beta mediated induction of neuron apoptosis following SCI in rats.

Lineage-restricted neural precursors survive, migrate, and differentiate following transplantation into the injured adult spinal cord

Fetal spinal cord from embryonic day 14 (E14/FSC) has been used for numerous transplantation studies of injured spinal cord. E14/FSC consists primarily of neuronal (NRP)- and glial (GRP)-restricted precursors. Therefore, we reasoned that comparing the fate of E14/FSC with defined populations of lineage-restricted precursors will test the in vivo properties of these precursors in CNS and allow us to define the sequence of events following their grafting into the injured spinal cord. Using tissue derived from transgenic rats expressing the alkaline phosphatase (AP) marker, we found that E14/FSC exhibited early cell loss at 4 days following acute transplantation into a partial hemisection injury, but the surviving cells expanded to fill the entire injury cavity by 3 weeks. E14/FSC grafts integrated into host tissue, differentiated into neurons, astrocytes, and oligodendrocytes, and demonstrated variability in process extension and migration out of the transplant site. Under similar grafting conditions, defined NRP/GRP cells showed excellent survival, consistent migration out of the injury site and robust differentiation into mature CNS phenotypes, including many neurons. Few immature cells remained at 3 weeks in either grafts. These results suggest that by combining neuronal and glial restricted precursors, it is possible to generate a microenvironmental niche where emerging glial cells, derived from GRPs, support survival and neuronal differentiation of NRPs within the non-neurogenic and non-permissive injured adult spinal cord, even when grafted into acute injury. Furthermore, the NRP/GRP grafts have practical advantages over fetal transplants, making them attractive candidates for neural cell replacement.

Attenuation of acute inflammatory response by atorvastatin after spinal cord injury in rats

Spinal cord injury (SCI) is a devastating and complex clinical condition involving proinflammatory cytokines and nitric oxide toxicity that produces a predictable pattern of progressive injury entailing neuronal loss, axonal destruction, and demyelination at the site of impact. The involvement of proinflammatory cytokines and inducible nitric oxide synthase (iNOS) in exacerbation of SCI pathology is well documented. We have reported previously the antiinflammatory properties and immunomodulatory activities of statins (3-hydroxy-3-methylglutaryl [HMG]-CoA reductase inhibitors) in the animal model of multiple sclerosis, experimental allergic encephalitis (EAE). The present study was undertaken to investigate the efficacy of atorvastatin (Lipitor; LP) treatment in attenuating SCI-induced pathology. Immunohistochemical detection and real-time PCR analysis showed increased expression of iNOS, tumor necrosis factor alpha (TNFalpha) and interleukin 1beta (IL-1beta) after SCI. In addition, neuronal apoptosis was detected 24 hr after injury followed by a profound increase in ED1-positive inflammatory infiltrates, glial fibrillary acidic protein (GFAP)-positive reactive astrocytes, and oligodendrocyte apoptosis by 1 week after SCI relative to control. LP treatment attenuated the SCI-induced iNOS, TNFalpha, and IL-1beta expression. LP also provided protection against SCI-induced tissue necrosis, neuronal and oligodendrocyte apoptosis, demyelination, and reactive gliosis. Furthermore, rats treated with LP scored much higher on the locomotor rating scale after SCI (19.13 +/- 0.53) than did untreated rats (9.04 +/- 1.22). This study therefore reports the beneficial effect of atorvastatin for the treatment of SCI-related pathology and disability.

Interleukin-1β exacerbates and interleukin-1 receptor antagonist attenuates neuronal injury and microglial activation after excitotoxic damage in organotypic hippocampal slice cultures

The effects of interleukin (IL)-1beta and IL-1 receptor antagonist (IL-1ra) on neurons and microglial cells were investigated in organotypic hippocampal slice cultures (OHSCs). OHSCs obtained from rats were excitotoxically lesioned after 6 days in vitro by application of N-methyl-D-aspartate (NMDA) and treated with IL-1beta (6 ng/mL) or IL-1ra (40, 100 or 500 ng/mL) for up to 10 days. OHSCs were then analysed by bright field microscopy after hematoxylin staining and confocal laser scanning microscopy after labeling of damaged neurons with propidium iodide (PI) and fluorescent staining of microglial cells. The specificity of PI labeling of damaged neurons was validated by triple staining with neuronal and glial markers and it was observed that PI accumulated in damaged neurons only but not in microglial cells or astrocytes. Treatment of unlesioned OHSCs with IL-1beta did not induce neuronal damage but caused an increase in the number of microglial cells. NMDA lesioning alone resulted in a massive increase in the number of microglial cells and degenerating neurons. Treatment of NMDA-lesioned OHSCs with IL-1beta exacerbated neuronal cell death and further enhanced microglial cell numbers. Treatment of NMDA-lesioned cultures with IL-1ra significantly attenuated NMDA-induced neuronal damage and reduced the number of microglial cells, whereas application of IL-1ra in unlesioned OHSCs did not induce significant changes in either cell population. Our findings indicate that: (i) IL-1beta directly affects the central nervous system and acts independently of infiltrating hematogenous cells; (ii) IL-1beta induces microglial activation but is not neurotoxic per se; (iii) IL-1beta enhances excitotoxic neuronal damage and microglial activation and (iv) IL-1ra, even when applied for only 4 h, reduces neuronal cell death and the number of microglial cells after excitotoxic damage.

Neural precursor cells can be delivered into the injured cervical spinal cord by intrathecal injection at the lumbar cord

Neural precursor cells (NPCs) are promising grafts for treatment of traumatic CNS injury and neurodegenerative disorders because of their potential to differentiate into neurons and glial cells. When designing clinical protocols for NPC transplantation, it is important to develop alternatives to direct parenchymal injection, particularly at the injury site. We reasoned that since it is minimally invasive, intrathecal delivery of NPCs at lumbar spinal cord (lumbar puncture) represents an important and clinically applicable strategy. We tested this proposition by examining whether NPCs can be delivered to the injured cervical spinal cord via lumbar puncture using a mixed population of neuronal-restricted precursors (NRPs) and glial-restricted precursors (GRPs). For reliable tracking, the NPCs were derived from the embryonic spinal cord of transgenic donor rats that express the marker gene, human placental alkaline phosphatase, under the control of the ubiquitous Rosa 26 promoter. We found that mixed NRP/GRP grafts can be efficiently delivered to a cervical hemisection injury site by intrathecal delivery at the lumbar cord. Similar to direct parenchymal injections, transplanted NRP/GRP cells survive at the injury cavity for at least 5 weeks post-engraftment, migrate into intact spinal cord along white matter tracts and differentiate into all three mature CNS cell types, neurons, astrocytes, and oligodendrocytes. Furthermore, very few graft-derived cells localize to areas outside the injury site, including intact spinal cord and brain. These results demonstrate the potential of delivering lineage-restricted NPCs using the minimally invasive lumbar puncture method for the treatment of spinal cord injury.

Activation of complement pathways after contusion-induced spinal cord injury

Previous studies have shown that a cellular inflammatory response is initiated, and inflammatory cytokines are synthesized, following experimental spinal cord injury (SCI). In the present study, we tested the hypothesis that the complement cascade, a major component of both the innate and adaptive immune response, is also activated following experimental SCI. We investigated the pathways, cellular localization, timecourse, and degree of complement activation in rat spinal cord following acute contusion-induced SCI using the New York University (NYU) weight drop impactor. Mild and severe injuries (12.5 and 50 mm drop heights) at 1, 7, and 42 days post injury time points were evaluated. Classical (C1q and C4), alternative (Factor B) and terminal (C5b-9) complement pathways were strongly activated within 1 day of SCI. Complement protein immunoreactivity was predominantly found in cell types vulnerable to degeneration, neurons and oligodendrocytes, and was not generally observed in inflammatory or astroglial cells. Surprisingly, immunoreactivity for complement proteins was also evident 6 weeks after injury, and complement activation was observed as far as 20 mm rostral to the site of injury. Axonal staining by C1q and Factor B was also observed, suggesting a potential role for the complement cascade in demyelination or axonal degeneration. These data support the hypothesis that complement activation plays a role in SCI.

Severity-dependent expression of pro-inflammatory cytokines in traumatic spinal cord injury in the rat

The post-traumatic inflammatory response in acute spinal cord contusion injury was studied in the rat. Mild and severe spinal cord injury (SCI) was produced by dropping a 10 g weight from 3 and 12 cm at the T12 vertebral level. Increased immunoreactivity of TNF-alpha in mild and severe SCI was detected in neurons at 1 h post-injury, and in neurons and microglia at 6 h post-injury, with a less significant increase in mild SCI. Expression was short-lived and declined sharply by 1 d post-injury. RT-PCR showed an early significant up-regulation of IL-1 beta, IL-6 and TNF-alpha mRNAs, maximal at 6 h post-injury with return to control levels by 24 h post-injury, the changes being less statistically significantly in mild SCI. Western blot showed early transient increases of IL-1 beta, IL-6 and TNF-alpha proteins in severe SCI but not mild SCI. Immunocytochemical, western blotting and RT-PCR analyses suggest that endogenous cells (neurons and microglia) in the spinal cord, not blood-borne leucocytes, contribute to IL-1 beta, IL-6 and TNF-alpha production in the post-traumatic inflammatory response and that their up-regulation is greater in severe than mild SCI.

Methylprednisolone Inhibits Production of Interleukin-1?? and Interleukin-6 in the Spinal Cord Following Compression Injury in Rats

Interleukin-1beta (IL-1beta) and interleukin-6 (IL-6) are major inflammatory cytokines produced after spinal cord injury (SCI). This study sought to evaluate the effects of methylprednisolone (MP) on IL-1beta and IL-6 protein in spinal cord tissue following SCI. Halothane-anesthetized, female Sprague-Dawley rats weighing (280-320 g) underwent laminectomy at T7-T8. No lesions were produced in animals in the saline control and MP control groups. SCI was induced by temporary placement of an aneurysm clip at T7-T8, with a closing pressure of 55 g at the spinal level of T7-T8, resulting in spinal cord compression for one minute. Animals with SCI were treated with MP (30 mg/kg sc) or an equal volume of saline. IL-1beta and IL-6 spinal cord protein were measured by enzyme-linked immunosorbent assays (ELISA). Data were summarized as mean +/- SD and compared by two-way analysis of variance (ANOVA). IL-1beta and IL-6 levels were elevated in the SCI + Saline animals (P < 0.01) compared with saline control, MP control, and SCI + MP-treated animals. The rise in IL-1beta and IL-6 levels after SCI was blunted after administration of MP, suggesting an interaction between glucocorticosteroids and the cytokine cascade after spinal cord trauma. Further evaluation of the effects of MP on the cytokine cascade may be important in assessing whether or not the anti-inflammatory effects of glucocorticosteroids confer neuroprotection after SCI.

Poly(adenosine diphosphate ribose) polymerase inhibition modulates spinal cord dysfunction after thoracoabdominal aortic ischemia-reperfusion

OBJECTIVE

Spinal cord injury (SCI) remains a source of morbidity after thoracoabdominal aortic reconstruction. These studies were designed to determine whether PJ34, a novel ultrapotent inhibitor of the nuclear enzyme poly(adenosine diphosphate ribose) polymerase (PARP) could modulate neurologic injury after thoracic aortic ischemia reperfusion (TAR) in a murine model of SCI.

METHODS

Forty-one anesthetized male mice were subject to thoracic aortic occlusion (11 minutes) through a cervical mediastinotomy followed by 48 hours of reperfusion (TAR) under normothermic conditions. PJ34-treated mice (PJ, n = 12) were given 10 mg/kg PJ34 intraperitoneally 1 hour before ischemia and 1 hour after unclamping. The control group (UN, n = 21) received normal saline intraperitoneally 1 hour before ischemia and 1 hour after unclamping. Sham animals (n = 10) were subject to thoracic aortic exposure with no aortic clamping and similar intraperitoneal normal saline injections. PARP-1-/- (KO, n = 8) mice were subjected to the same conditions as the UN mice. Blinded observers rated murine neurologic status after TAR by using an established rodent paralysis scoring system. Murine spinal cords were subjected to cytokine (GRO-1) protein analysis as a marker of inflammation and immunohistochemical analysis (hematoxylin-eosin and PAR staining). Paralysis scores (PS) and GRO-1 levels were compared with analysis of variance, and survival data were compared with chi 2 .

RESULTS

Immediately after TAR, UN and PJ mice had severe neurologic dysfunction (PS = 5.8 +/- 0.1 and 4.6 +/- 0.6, respectively; P > .05), which was significantly worse than the KO mice (PS = 1.0 +/- 0.7, P < .001). After 6, 24, and 48 hours KO mice had no discernable neurologic injury (PS = 0). Six hours after TAR, PJ mice significantly improved (PS = 1.1 +/- 0.73, P < .001) and remained improved at 24 (PS = 0.7 +/- 0.6) and 48 hours (PS = 0.6 +/- 0.6). UN mice did not improve their PS, and Sham mice showed no neurologic abnormality at any time during these experiments. The mortality at 48 hours was 0% for PJ and KO mice, 43% for UN (P = .012), and 0% for Sham. GRO-1 levels were significantly decreased in PJ and KO versus UN mice (UN, 583 +/- 119 vs PJ, 5.8 +/- 0 vs KO, 5.3 +/- 1.4 mg/pg; P < .0001). Immunohistochemistry showed evidence of decreased PAR staining and ventral motor neuron injury in PJ mice.

CONCLUSIONS

Genetic deletion of PARP or inhibition of its activity (PJ34) rescued neurologic function in mice subjected to TAR. PARP inhibition might represent a novel therapeutic approach for prevention of SCI after TAR.

Inhibition of tumour necrosis factor-alpha by antisense targeting produces immunophenotypical and morphological changes in injury-activated microglia and macrophages

Microglia respond in a stereotypical pattern to a diverse array of pathological states. These changes are coupled to morphological and immunophenotypical alterations and the release of a variety of reactive species, trophic factors and cytokines that modify both microglia and their cellular environment. We examined whether a microglial-produced cytokine, tumour necrosis factor-alpha (TNF-alpha), was involved in the maintenance of microglial activation after spinal cord injury by selective inhibition using TNF-alpha antisense deoxyoligonucleotides (ASOs). Microglia and macrophages harvested from 3 d post-contused rat spinal cord were large and rounded (86.3 +/- 9.6%). They were GSA-IB4-positive (GSA-IB4(+)) (Griffonia simplicifolia lectin, microglia specific; 94.8 +/- 5.1%), strongly OX-42 positive (raised against a type 3 complement/integrin receptor, CD11b; 78.9 +/- 9.1%), ED-1 positive (a lysosomal marker shown to correlate well with immune cell activation; 97.2 +/- 2.6%) and IIA positive (antibody recognizes major histocompatibility complex II; 57.2 +/- 5.6%), indicative of fully activated cells, for up to 48 h after plating. These cells also secreted significant amounts of TNF-alpha (up to 436 pg/microg total protein, 16 h). Fluoroscein isothiocyanate-labelled TNF-alpha ASOs (5, 50 and 200 nm) added to the culture medium were taken up very efficiently into the cells (> 90% cells) and significantly reduced TNF-alpha production by up to 92% (26.5 pg/microg total protein, 16 h, 200 nm TNF-alpha ASOs). Furthermore, few of the treated cells at this time were round (5.4 +/- 2.7%), having become predominantly spindle shaped (74.9 +/- 6.3%) or stellate (21.4 +/- 2.7%); immunophenotypically, although all of them remained GSA-IB4 positive (91.6 +/- 6.2%), many were weakly OX-42 positive and few expressed either ED-1 (12.9 +/- 2.5%) or IIA (19.8 +/- 7.4%). Thus, the secretion of TNF-alpha early in spinal cord injury may be involved in autoactivating microglia/macrophages. However, at the peak of microglial activation after injury, the activation state of microglia/macrophages is not stable and this process may still be reversible by blocking TNF-alpha.

A novel role of lactosylceramide in the regulation of tumor necrosis factor alpha-mediated proliferation of rat primary astrocytes. Implications for astrogliosis following neurotrauma

The present study describes the role of glycosphingolipids in neuroinflammatory disease and investigates tumor necrosis factor alpha (TNFalpha)-induced astrogliosis following spinal cord injury. Astrogliosis is the hallmark of neuroinflammation and is characterized by proliferation of astrocytes and increased glial fibrillary acidic protein (GFAP) gene expression. In primary astrocytes, TNFalpha stimulation increased the intracellular levels of lactosylceramide (LacCer) and induced GFAP expression and astrocyte proliferation. D-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol.HCl (PDMP), a glucosylceramide synthase and LacCer synthase (GalT-2) inhibitor, inhibited astrocyte proliferation and GFAP expression, which were reversed by exogenous supplementation of LacCer but not by other glycosphingolipids. TNFalpha caused a rapid increase in the activity of GalT-2 and synthesis of LacCer. Silencing of GalT-2 gene using antisense oligonucleotides also attenuated the proliferation of astrocytes and GFAP expression. The PDMP and antisense-mediated inhibition of proliferation and GFAP expression was well correlated with decreased Ras/ERK1/2 pathway activation. Furthermore, TNFalpha-mediated astrocyte proliferation and GFAP expression was also inhibited by LY294002, a phosphatidylinositol 3-kinase inhibitor, which was reversed by exogenous LacCer. LY294002 also inhibited TNFalpha-induced GalT-2 activation and LacCer synthesis, suggesting a phosphatidylinositol 3-kinase-mediated regulation of GalT-2. In vivo, PDMP treatment attenuated chronic ERK1/2 activation and spinal cord injury (SCI)-induced astrocyte proliferation with improved functional recovery post-SCI. Therefore, the in vivo studies support the conclusions drawn from cell culture studies and provide evidence for the role of LacCer in TNFalpha-induced astrogliosis in a rat model of SCI. To our knowledge, this is the first report demonstrating the role of LacCer in the regulation of TNFalpha-induced proliferation and reactivity of primary astrocytes.

Microglia as potential contributors to motor neuron injury in amyotrophic lateral sclerosis

The central nervous system (CNS) is equipped with a variety of cell types, all of which are assigned particular roles during the development, maintenance, function and repair of neural tissue. One glial cell type, microglia, deserves particular attention, as its role in the healthy or injured CNS is incompletely understood. Evidence exists for both regenerative and degenerative functions of these glial cells during neuronal injury. This review integrates the current knowledge of the role of microglia in an adult-onset neurodegenerative disease, amyotrophic lateral sclerosis (ALS), and pays particular attention to the possible mechanisms of initiation and propagation of neuronal damage during disease onset and progression. Microglial cell properties, behavior and detected inflammatory reactions during the course of the disease are described. The neuroinflammatory changes that occur in a mouse model of ALS are summarized. The understanding of microglial function in the healthy and injured CNS could offer better diagnostic as well as therapeutic approaches for prevention, retardation, or repair of neural tissue degeneration.

Differential gene expression after complete spinal cord transection in adult rats: an analysis focused on a subchronic post-injury stage

In an attempt to characterize changes in transcription after a sub-chronic spinal cord injury (SCI), we investigated gene expression profiles using cDNA microarray. Among 7523 genes and expressed sequence tags (ESTs) examined, 444 transcripts, including 218 genes and 226 ESTs, were identified to be either up-regulated (373 of 444) or down-regulated (71 of 444) greater than 2.0-fold in the spinal cord at 14 days after a complete spinal transection at the 11th thoracic level in adult rats. Based on their potential function, these differentially expressed genes were categorized into seven classes which include cell division-related protein, channels and receptors, cytoskeletal elements, extracellular matrix proteins, metalloproteinases and inhibitors, growth-associated molecules, metabolism, intracellular transducers and transcription factors, as well as others. Strong expressional changes were found in all classes revealing the complexity and diversity of gene expression profiles following SCI. We verified array results with RT-PCR for eight genes, Northern blotting for nine genes, and in situ hybridization for one gene and immunohistochemistry for four genes. These analyses confirmed, to a large extent, that the array results have accurately reflected the molecular changes occurring at 14 days post-SCI. Importantly, the current study has identified a number of genes, including annexins, heparin-binding growth-associated protein (HB-GAM), P9ka (S100A4), matrix metalloproteinases, and lysozyme, that may shed new light on SCI-related inflammation, neuroprotection, neurite-outgrowth, synaptogenesis, and astrogliosis. In conclusion, the identification of molecular changes using the large-scale microarray analysis may lead to a better understanding of underlying mechanisms, thus, the development of new repair strategies for SCI.

Body weight, limb size, and muscular properties of early paraplegic mice

Patients with spinal cord injury (SCI) typically experience body weight loss, motor function deficits, and a general decline of physical fitness. Animal models with these characteristics can serve to study the detailed adaptive changes following SCI. In the present study, we report the use of an adult paraplegic mouse model to study SCI-induced changes. We characterized the early effects of complete thoracic spinal cord transection on (1) whole body weight, (2) forelimb and hindlimb weight and volume, and (3) contractile properties of hindlimb extensor muscle. Drastic changes were found at 7 days post-spinal cord transection. These included a 24% loss in whole body weight accompanied by a large decrease of weight and volume in the forelimbs and the hindlimbs. We also observed in the soleus muscle, a 32% decrease in mass and maximal tetanic tension (Po) as well as a 21% and 48% increase in time-to-peak tension (TPT) and half-relaxation time (1/2 RT) respectively. After 28 days, all of the changes remained, except for 1/2 RT and TPT which nearly returned to control levels. Altogether, the results reveal that large changes in body weight, limb size and musculoskeletal properties occur within only one week after complete spinal cord transection. The use of paraplegic mouse models may provide new therapeutic approaches to restore motor and locomotor functions after SCI.

Antithrombin Reduces Compression-Induced Spinal Cord Injury in Rats

Antithrombin (AT), a natural anticoagulant, has been shown to exert anti-inflammatory activity by promoting the endothelial production of prostaglandin I2 (PGI2), thereby reducing tissue injury. To examine whether AT prevents post-traumatic spinal cord injury (SCI), a pathologic condition in which activated neutrophils are critically involved, we tested the effect of AT on SCI induced by compression trauma in rats. Intravenous administration of AT, either before or after the induction of SCI, significantly reduced SCI-related motor disturbances in these animals. AT also significantly inhibited both intramedullary hemorrhage and the decrease in the number of motor neurons following SCI, and inhibited the accumulation of neutrophils in the damaged segment of the spinal cord by inhibiting the increase in transcription of tumor necrosis factor-alpha (TNF-alpha). AT significantly enhanced the increase in the tissue level of 6-keto-PGF1alpha, a stable metabolite of PGI2, at the injured segment of the cord. These therapeutic effects of AT may not depend on its anticoagulant effect. AT did not show any effects in animals pretreated with indomethacin, a potent inhibitor of prostaglandin synthesis, and iloprost, a stable PGI2 analog, produced effects similar to those of AT. Furthermore, intravenously administered AT accumulated selectively at the injured segment of the spinal cord, where thrombin generation might be increased. These findings suggest that AT may reduce the effects of compression trauma-induced SCI by inhibiting neutrophil activation as a consequence of the AT-mediated inhibition of TNF-alpha production. Such therapeutic effects of AT might be mediated by its promoting the endothelial release of PGI2. These findings strongly suggest AT as a potential agent for treating SCI in the clinical setting.

Potent pro-inflammatory actions of leukemia inhibitory factor in the spinal cord of the adult mouse

Injury in the peripheral or central nervous systems causes a significant rise in the levels of the pleiotropic cytokine leukemia inhibitory factor (LIF). This increase influences cell survival, reactive gliosis and inflammatory responses. Since prior work has focused primarily on peripheral nerve and brain, little is known about the role of LIF in the spinal cord injury response. We address this issue by examining the effects of injury in the LIF knockout (KO) mouse, as well as using an adenoviral vector to over-express LIF in the spinal cord of adult mice. We find that LIF over-expression results in a dramatic rise in cell proliferation, primarily in microglia/macrophages. Astrocytes are not stimulated to proliferate but are activated by the elevated LIF. LIF over-expression also causes the development of severe hindlimb motor dysfunction, an effect mediated by the enhanced activation of microglia/macrophages, as inhibiting microglial activation with minocycline attenuates these motor deficits. Conversely, proliferation is significantly diminished and the microglial/macrophage response to spinal cord injury is much less in the LIF KO compared to wild type (WT). Thus, LIF is a potent pro-inflammatory factor in the adult spinal cord and represents a potential target for the manipulation of inflammatory reactions after spinal cord injury.

Src Family Kinase Inhibitor PP1 Reduces Secondary Damage after Spinal Cord Compression in Rats

The synthetic pyrazolopyrimidine, 4-amino-5-(4-methylphenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP1) is a novel, potent, and selective inhibitor of Src family tyrosine kinases. Vascular permeability appears to be mediated by vascular endothelial growth factor (VEGF), which requires the activation of downstream Src family kinases to exert its function. This study investigates the effects of PP1 on vascular permeability and inflammatory response in a rat spinal cord compression model. Ten minutes after compression, PP1 (PP1 group) or the vehicle only (control group) was administered. On days 1, 3, and 7 after compression, the spinal cords were removed and examined histopathologically to determine the expression of VEGF and the extent of edema and inflammation. The dryweight method was used to measure the water content of the spinal cords. The mRNA levels of tumor necrosis factor a (TNFalpha) and interleukin 1beta (IL-1beta), which is related to inflammatory responses, were measured with a real-time polymerase chain reaction (RT-PCR) system 6 h after compression. Although VEGF expression was similar in both groups, the extent of contusional lesion in the PP1 group was reduced by approximately 35% on day 3. Moreover, the water content on days 1, 3, and 7 was significantly reduced and macrophage infiltration on days 3 and 7 was dramatically reduced in the PP1 group. TNF and IL-1beta mRNA expression in the PP1 group were also significantly reduced. These results indicate that PP1 reduces secondary damage after spinal cord injury.

The Role of Excitotoxicity in Secondary Mechanisms of Spinal Cord Injury: A Review with an Emphasis on the Implications for White Matter Degeneration

Following an initial impact after spinal cord injury (SCI), there is a cascade of downstream events termed 'secondary injury', which culminate in progressive degenerative events in the spinal cord. These secondary injury mechanisms include, but are not limited to, ischemia, inflammation, free radical-induced cell death, glutamate excitotoxicity, cytoskeletal degradation and induction of extrinsic and intrinsic apoptotic pathways. There is emerging evidence that glutamate excitotoxicity plays a key role not only in neuronal cell death but also in delayed posttraumatic spinal cord white matter degeneration. Importantly however, the differences in cellular composition and expression of specific types of glutamate receptors in grey versus white matter require a compartmentalized approach to understand the mechanisms of secondary injury after SCI. This review examines mechanisms of secondary white matter injury with particular emphasis on glutamate excitotoxicity and the potential link of this mechanism to apoptosis. Recent studies have provided new insights into the mechanisms of glutamate release and its potential targets, as well as the downstream pathways associated with glutamate receptor activation in specific types of cells. Evidence from molecular and functional expression of glutamatergic AMPA receptors in white matter glia (and possibly axons), the protective effects of AMPA/kainate antagonists in posttraumatic white matter axonal function, and the vulnerability of oligodendrocytes to excitotoxic cell death suggest that glutamate excitotoxicity is associated with oligodendrocyte apoptosis. The latter mechanism appears key to glutamatergic white matter degeneration after SCI and may represent an attractive therapeutic target.

The significance of vasoactive intestinal peptide in immunomodulation

First identified by Said and Mutt some 30 years ago, the vasoactive intestinal peptide (VIP) was originally isolated as a vasodilator peptide. Subsequently, its biochemistry was elucidated, and within the 1st decade, their signature features as a neuropeptide became consolidated. It did not take long for these insights to permeate the field of immunology, out of which surprising new attributes for VIP were found in the last years. VIP is rapidly transforming into something more than a mere hormone. In evolving scientifically from a hormone to a novel agent for modifying immune function and possibly a cytokine-like molecule, VIP research has engaged many physiologists, molecular biologists, biochemists, endocrinologists, and pharmacologists and it is a paradigm to explore mutual interactions between neural and neuroendocrine links in health and disease. The aim of this review is firstly to update our knowledge of the cellular and molecular events relevant to VIP function on the immune system and secondly to gather together recent data that support its role as a type 2 cytokine. Recognition of the central functions VIP plays in cellular processes is focusing our attention on this "very important peptide" as exciting new candidates for therapeutic intervention and drug development.

Degenerative and regenerative mechanisms governing spinal cord injury

Spinal cord injury (SCI) is a major cause of disability, and at present, there is no universally accepted treatment. The functional decline following SCI is contributed to both direct mechanical injury and secondary pathophysiological mechanisms that are induced by the initial trauma. These mechanisms initially involve widespread haemorrhage at the site of injury and necrosis of central nervous system (CNS) cellular components. At later stages of injury, the cord is observed to display reactive gliosis. The actions of astrocytes as well as numerous other cells in this response create an environment that is highly nonpermissive to axonal regrowth. Also manifesting important effects is the immune system. The early recruitment of neutrophils and at later stages, macrophages to the site of insult cause exacerbation of injury. However, at more chronic stages, macrophages and recruited T helper cells may potentially be helpful by providing trophic support for neuronal and non-neuronal components of the injured CNS. Within this sea of injurious mechanisms, the oligodendrocytes appear to be highly vulnerable. At chronic stages of SCI, a large number of oligodendrocytes undergo apoptosis at sites that are distant to the vicinity of primary injury. This leads to denudement of axons and deterioration of their conductive abilities, which adds significantly to functional decline. By indulging into the molecular mechanisms that cause oligodendrocyte apoptosis and identifying potential targets for therapeutic intervention, the prevention of this apoptotic wave will be of tremendous value to individuals living with SCI.

TNF-alpha and TNF-alpha receptor type 1 upregulation in glia and neurons after peripheral nerve injury: studies in murine DRG and spinal cord

OBJECTIVES

The purpose of the current study was to evaluate changes in tumor necrosis factor-alpha (TNF-alpha ) and TNF-alpha receptor 1 (p55 receptor) using double fluorescent immunohistochemistry in glial and neural cells in the dorsal root ganglion and spinal cord after sciatic nerve injury in mice. SUMMARY OF BACKGROUND DATA.: TNF-alpha is a primary mediator of the inflammatory response and is primarily synthesized and released in the nervous system by macrophages and Schwann cells following peripheral nerve injury. TNF-alpha is also released from astrocytes and microglia in the central nervous system, where it plays a crucial role in the pathophysiology of injury.

METHODS

Sixteen female mice were used. Under anesthesia, the left sciatic nerve was crushed. At 3, 5, and 14 days after surgery, the spinal cord at the level of L5 and the left L5 DRG were removed and processed for immunohistochemistry. Tissue sections were double stained with antibodies to either glial fibrillary acidic protein (GFAP; marker for astrocytes or satellite cells) or NeuN (marker for neurons), and TNF or p55 receptor. RESULTS.: In the dorsal root ganglion, GFAP-immunoreactive (IR) satellite cells became evident after injury and were also immunoreactive for both TNF-alpha and p55 receptor. Dorsal root ganglion neurons expressed p55 receptor after injury. TNF-alpha and GFAP-IR satellite cells surrounded p55-IR neurons. Furthermore, the number of GFAP-IR astrocytes dramatically increased in the spinal cord after nerve injury, and some astrocytes were also TNF-alpha -IR and p55 receptor-IR. TNF-alpha -1R astrocytes were seen around p55 receptor-IR neurons.

CONCLUSIONS

These data demonstrate that upregulation of glial TNF-alpha is associated with the expression of the p55 receptor on adjacent neurons. This association may have induced the expression of several cytokines and immediate early genes in dorsal root ganglion and spinal cord neurons via the TNF signaling pathway. These findings may be related to the pathogenesis of neuropathic pain.

Early expression and cellular localization of proinflammatory cytokines interleukin-1beta, interleukin-6, and tumor necrosis factor-alpha in human traumatic spinal cord injury

STUDY DESIGN

Post-traumatic inflammatory response was studied in 11 human cases of acute spinal cord contusion injury.

OBJECTIVES

To examine the inflammatory cellular response and the immunocytochemical expression and localization of interleukin-1beta, interleukin-6, and tumor necrosis factor-alpha in human spinal cord after contusion injury.

SUMMARY OF BACKGROUND DATA

: The post-traumatic inflammatory response plays an important role in secondary injury mechanisms after spinal cord injury, and interleukin-1beta, interleukin-6, and tumor necrosis factor-alpha are key inflammatory mediators.

METHODS

: The study group comprised 11 patients with spinal cord contusion injury and 2 normal individuals. Histologic and immunocytochemical assessments were undertaken to evaluate the inflammatory cellular response and the immunoexpression of interleukin-1beta, interleukin-6, and tumor necrosis factor-alpha in the injured human spinal cord. The cellular sources of interleukin-1beta, interleukin-6, and tumor necrosis factor-alpha were elucidated by immunofluorescence double-labeled confocal imaging.

RESULTS

: Increased immunoreactivity of interleukin-1beta, interleukin-6, and tumor necrosis factor-alpha was detected in neurons 0.5 hour after injury, and in neurons and microglia 5 hours after injury, but the expression of these proinflammatory cytokines was short-lived and declined sharply to baseline by 2 days after injury. In the inflammatory cellular response, as early as 0.5 hour after spinal cord injury, activated microglia were detected, and axonal swellings and axons were surrounded by microglial processes. Numerous neutrophils appeared in the injured cord 1 day after injury, and then their number declined dramatically, whereas macrophages progressively increased after day 1.

CONCLUSIONS

Endogenous cells (neurons and microglia) in the human spinal cord, not the blood-borne leukocytes, contribute to the early production of interleukin-1beta, interleukin-6, and tumor necrosis factor-alpha in the post-traumatic inflammatory response, and microglia are involved the early response to traumatic axonal injury.

Spinal cord injury induces lesional expression of the proinflammatory and antiangiogenic cytokine EMAP II

Inflammatory cellular responses to spinal cord injury are promoted by proinflammatory messengers. We have analyzed expression of endothelial monocyte activating polypeptide II (EMAP II), a proinflammatory, antiangiogenic cytokine in rats after spinal cord injury (SCI) in comparison to normal rat spinal cords. Immunohistochemical analysis demonstrated a highly significant (p < 0.0001) accumulation of EMAP II(+) microglia/macrophages at the lesion site compared to remote areas and uninjured controls. After peaking at day 3, EMAP II(+) microglia/macrophage cell numbers declined gradually until day 28 after SCI-but still remained elevated. Further, EMAP II(+) cells formed clusters in perivascular Virchow-Robin spaces reaching a maximum at day 3. Prolonged accumulation of EMAP II(+), ED1(+) microglia/macrophages suggest a role of EMAP II in the pathophysiology of secondary injury following SCI.

Inflammation, degeneration and regeneration in the injured spinal cord: insights from DNA microarrays

GeneChip microarrays have recently been introduced to the field of neurobiology to identify and monitor the expression levels of thousands of genes simultaneously. This powerful technique is now used for studying the pathophysiology of CNS injuries including spinal cord lesions. Early stages after injury are characterized by the strong upregulation of genes involved in transcription and inflammation and a general downregulation of structural proteins and proteins involved in neurotransmission. Later, an increase in the expression of growth factors, axonal guidance factors, extracellular matrix molecules and angiogenic factors reflects the attempts for repair, while upregulation of stress genes and proteases and downregulation of cytoskeletal and synaptic mRNA reflect the struggle of the tissue to survive. DNA microarrays have the potential to aid discovery of new targets for neuroprotective or restorative therapeutic approaches

Differences in cytokine gene expression profile between acute and secondary injury in adult rat spinal cord

It is likely that the environment within the injured spinal cord influences the capacity of fetal spinal cord transplants to support axonal growth. We have recently demonstrated that fetal spinal cord transplants and neurotrophin administration support axonal regeneration after spinal cord transection, and that the distance and amount of axonal growth is greater when these treatments are delayed by several weeks after injury. In this study, we sought to determine whether differences in inflammatory mediators exist between the acutely injured spinal cord and the spinal cord after a second injury and re-section, which could provide a more favorable environment for the axonal re-growth. The results of this study show a more rapid induction of transforming growth factor (TGF) beta1 mRNA expression in the re-injured spinal cord than the acutely injured spinal cord and an attenuation of proinflammatory cytokine mRNA expression. Furthermore, there was a rapid recruitment of activated microglia/macrophages in the degenerating white matter rostral and caudal to the injury but fewer within the lesion site itself. These findings suggest that the augmentation of TGFbeta-1 gene expression and the attenuation of pro-inflammatory cytokine gene expression combined with an altered distribution of activated microglia/macrophages in the re-injured spinal cord might create a more favorable milieu for transplants and axonal regrowth as compared to the acutely injured spinal cord.

Expression of pro-inflammatory cytokine and caspase genes promotes neuronal apoptosis in pontine reticular formation after spinal cord transection

We identified apoptotic neurons in pontine reticular formation (PRF), the origin of pontine reticulospinal fibers, in adult Sprague-Dawley rats after complete spinal cord transection (SCT) at T8 level. SCT also increased the expression in PRF of tumor necrosis factor-alpha (TNF-alpha), interleukin (IL)-1beta, IL-6, caspase-1, or caspase-3 mRNA. This was followed by an augmented expression of activated caspase-3 protein, an increase in caspase-3 activity, and expression of a cleaved fragment of poly(ADP-ribose) polymerase (PARP), a proteolytic substrate of the activated caspase-3. Microinjection bilaterally into the PRF of an antiserum against TNF-alpha attenuated the expression of IL-6 mRNA and up-regulation of caspase-3 mRNA, and a caspase-3 inhibitor, DEVD-CHO, suppressed the augmentation in activated caspase-3 or cleaved PARP expression after SCT. Both treatments also reduced the number of SCT-induced apoptotic PRF neurons. We conclude that PRF neurons in adult mammalian brain may actively degrade themselves after SCT through apoptosis, via signaling processes that involve activation of proinflammatory cytokine genes and the intracellular caspase-3 pathway.

Vasoactive intestinal peptide prevents activated microglia-induced neurodegeneration under inflammatory conditions: potential therapeutic role in brain trauma

In most neurodegenerative disorders, including multiple sclerosis, Parkinson's disease, and Alzheimer's disease, a massive neuronal cell death occurs as a consequence of an uncontrolled inflammatory response, where activated microglia and its cytotoxic agents play a crucial pathologic role. Because current treatments for these diseases are not effective, several regulatory molecules termed "microglia-deactivating factors" recently have been the focus of considerable research. Vasoactive intestinal peptide (VIP) is a neuropeptide with a potent anti-inflammatory effect, which has been found to protect from other inflammatory disorders, such as endotoxic shock and rheumatoid arthritis. In the present study, we investigate the effect of VIP on inflammation-mediated neurodegeneration in vitro and in vivo as well as on the putative neuroprotective effect of VIP on experimental pathological conditions in which central nervous system (CNS) inflammation is involved, such as brain trauma. The involvement of activated microglia and their derived cytotoxic products is also studied. VIP has a clear neuroprotective effect on inflammatory conditions by inhibiting the production of microglia-derived proinflammatory factors (tumor necrosis factor alpha, interleukin-1beta, nitric oxide). In this sense, VIP prevents neuronal cell death following brain trauma by reducing the inflammatory response of neighboring microglia. Therefore, VIP emerges as a valuable neuroprotective agent for the treatment of pathologic conditions of the CNS where inflammation-induced neurodegeneration occurs.

The immunosuppressant mycophenolate mofetil attenuates neuronal damage after excitotoxic injury in hippocampal slice cultures

In this study we investigated whether treatment with the immunosuppressant mycophenolate mofetil (MMF) has beneficial effects on neuronal damage after excitotoxic injury. Organotypic hippocampal slice culture (OHSC), lesioned by the application of N-methyl-d-aspartate (NMDA) after 6 days in vitro, showed an improved preservation of the hippocampal cytoarchitecture after continuous treatment with MMF for 3 further days (10 or 100 micro g/mL). Treatment with NMDA and MMF (100 microg/mL) reduced the number of damaged propidium iodide (PI)+ neurons by 50.7% and the number of microglial cells by 52%. Continuous treatment of lesioned OHSCs with MMF for 3 days almost abrogated the glial proliferative response, reflected by the 91.5% reduction in the number of bromo-desoxy-uridine (BrdU)-labelled microglial cells and astrocytes. Microglial cells in MMF-treated OHSCs contained fragmented nuclei, indicating apoptotic cell death, an effect which was also found in isolated microglial cells treated with MMF. The beneficial effect of MMF on neuronal survival apparently does not reflect a direct antiexcitotoxic effect, as short-term treatment of OHSCs with NMDA and MMF for 4 h did not reduce the number of PI+ neurons. In conclusion, MMF inhibits proliferation and activation of microglia and astrocytes and protects neurons after excitotoxic injury.

Rats and mice exhibit distinct inflammatory reactions after spinal cord injury

Spinal contusion pathology in rats and mice is distinct. Cystic cavities form at the impact site in rats while a dense connective tissue matrix occupies the injury site in mice. Because inflammatory cells coordinate mechanisms of tissue injury and repair, we evaluated whether the unique anatomical presentation in spinally injured rats and mice is associated with a species-specific inflammatory response. Immunohistochemistry was used to compare the leukocytic infiltrate between rats and mice. Microglia/macrophage reactions were similar between species; however, the onset and magnitude of lymphocyte and dendritic cell (DC) infiltration were markedly different. In rats, T-cell numbers were highest between 3 and 7 days postinjury and declined by 50% over the next 3 weeks. In mice, significant T-cell entry was not evident until 14 days postinjury, with T-cell numbers doubling between 2 and 6 weeks. Dendritic cell influx paralleled T-cell infiltration in rats but was absent in mouse spinal cord. De novo expression of major histocompatability class II molecules was increased in both species but to a greater extent in mice. Unique to mice were cells that resembled lymphocytes but did not express lymphocyte-specific markers. These cells extended from blood vessels within the fibrotic tissue matrix and expressed fibronectin, collagen I, CD11b, CD34, CD13, and CD45. This phenotype is characteristic of fibrocytes, specialized blood-borne cells involved in wound healing and immunity. Thus, species-specific neuroinflammation may contribute to the formation of distinct tissue environments at the site of spinal cord injury in mice and rats.

Post-traumatic inflammation following spinal cord injury

Inflammatory reaction following a spinal cord injury (SCI) contributes substantially to secondary effects, with both beneficial and devastating effects. This review summarizes the current knowledge concerning the structural features (vascular, cellular, and biochemical events) of SCI and gives an overview of the regulation of post-traumatic inflammation.

Trauma-induced tumorigenesis of cells implanted into the rat spinal cord

OBJECT

Findings in several clinical cases have suggested a correlation between tumor formation and previous injury to the central nervous system (CNS); however, the relationship between trauma and tumorigenesis has not been investigated well experimentally. In this study the authors provide evidence correlating tumorigenesis with trauma in the rat spinal cord.

METHODS

A glial cell line, C6R-G/H, which expresses green fluorescent protein (GFP) and hygromycin phosphotransferase (HPT), was implanted into normal and injured rat spinal cords. In all rats in which the cells were implanted into an injured site, locomotor function deteriorated and histological analysis demonstrated glioblastoma multiforme by 6 weeks; tumorigenesis was correlated with a loss of both GFP expression and resistance to hygromycin treatment. In contrast, no evidence of tumor formation was found at 6 weeks in rats in which the cells were implanted into healthy tissue. When C6R-G/H cells were treated with contused spinal cord extract in culture before implantation, they lost GFP expression and hygromycin resistance, and later formed tumors after implantation into normal spinal cord.

CONCLUSIONS

The findings of this study indicate that trauma can induce tumorigenesis. Implantation of C6R-G/H cells into traumatized spinal cords resulted in their transformation, which was signaled by loss of GFP expression and hygromycin resistance accompanied by tumor formation. Exposure to extracts derived from injured spinal cord produced similar transformation and gene expression changes, as well as tumor formation after such cells were implanted into normal cords. Care, therefore, should be taken when cells are implanted into an injured CNS because of potential mutagenesis due to trauma-induced factors.

Increased hippocampal uptake of tumor necrosis factor alpha and behavioral changes in mice

Brain trauma may alter the function of the blood-brain barrier (BBB) and affect psychomotor activity. We have shown that the transport system for tumor necrosis factor alpha (TNF alpha) at the BBB undergoes regulatory changes after spinal cord injury. In this study, we show in CD1 mice that mild trauma by weight-drop to the right temporal region specifically increases the uptake of blood-borne TNF alpha. This increase, measured by use of radiolabeled murine TNF alpha, occurred only in the right hippocampus 24 h after injury and returned to normal at 1 week. There was no increase in the uptake of the vascular marker albumin at 1 h, 24 h, or 1 week postinjury, indicating that the BBB remained relatively intact. Human interleukin-1 beta, which does not cross the BBB by saturable transport, showed no significant changes in brain uptake after trauma. Therefore, the selective entry of TNF alpha in the injured right hippocampus may be explained by enhanced transport across the BBB. To explore the functional relevance of this transport regulation, we measured mouse behavior by the staircase test. The number of rearings, mainly reflective of exploratory behavior, decreased at 1 h and 1 day after injury but increased at 1 week after a 30-g weight-drop injury. The number of stairs ascended, mainly indicative of locomotor activity, was unchanged at all times tested. We conclude that mild, blunt brain trauma involving the hippocampus causes specific upregulation of TNF alpha transport and a selective change in exploratory behavior. Although no causal relationship can be established at this time, the behavioral changes might be related to the increased TNF alpha transport after trauma.

Vasoactive intestinal peptide and pituitary adenylate cyclase-activating polypeptide inhibit the production of inflammatory mediators by activated microglia

Microglia play a central role in the regulation of immune and inflammatory activities, as well as tissue remodeling in the central nervous system. However, activation of microglia is a histopathological hallmark of several neurodegenerative diseases. Pathological microglial activation is believed to contribute to progressive damage in neurodegenerative diseases through the release of proinflammatory and/or cytotoxic factors, including tumor necrosis factor alpha (TNF-alpha), interleukin (IL)-1beta, IL-6, IL-12, and nitric oxide (NO). Hence, it is important to unravel mechanisms regulating microglia activation of inflamed brain parenchyma to provide insights into efficient therapeutic intervention. This study examines the role of two anti-inflammatory neuropeptides, the vasoactive intestinal peptide (VIP) and the pituitary adenylate cyclase-activating polypeptide (PACAP) on the production of various proinflammatory factors by endotoxin-stimulated microglia. VIP and PACAP inhibit TNF-alpha, IL-1beta, IL-6, and NO production by lipopolysaccharide (LPS)-activated microglia. The specific type 1 VIP receptor mediates the inhibitory effect of VIP/PACAP, and cyclic adenosine monophosphate is the major, second messenger involved. VIP and PACAP regulate the production of these proinflammatory factors at a transcriptional level by inhibiting p65 nuclear translocation and nuclear factor-kappaB-DNA binding. This effect is mediated, as neuropeptides stabilize the inhibitor IkappaB by inhibiting LPS-induced IkappaB-kinase activity. Therefore, the inhibitory effects on the production of proinflammatory mediators define VIP and PACAP as "microglia-deactivating factors" with significant, therapeutical potential for inflammatory/degenerative brain disorders.