Transient blockade of the CD11d/CD18 integrin reduces secondary damage after spinal cord injury, improving sensory, autonomic, and motor function

Linear ordered collagen scaffolds loaded with collagen-binding neurotrophin-3 promote axonal regeneration and partial functional recovery after complete spinal cord transection

Neurotrophin-3 (NT3) is an important neurotrophic factor for spinal cord injury (SCI) repair. However, constant exchange of cerebrospinal fluid often decreases the effective dosage of NT3 at the targeted injury site. In the present study, a recombinant collagen-binding NT3 (CBD-NT3), consisting of a collagen-binding domain (CBD) and native NT3, was constructed. Linear rat-tail collagen (LRTC) was used as a physical carrier for CBD-NT3 to construct a LRTC/C3 system. The collagen-binding ability of CBD-NT3 was verified, and the bioactivity of CBD-NT3 was assayed with neurite outgrowth of dorsal root ganglia (DRG) explants and DRG cells in vitro. After complete spinal cord transection in rats, LRTC/CBD-NT3 or the LRTC/NT3 system was transplanted into the injury site. Hindlimb locomotion recovery was closely observed using the Basso-Beattie-Bresnahan (BBB) locomotor rating scale and the grid walk test. Significant improvement was observed in the LRTC/CBD-NT3 group. The results of regenerating nerve fiber and anterograde tracing of biotinylated dextran amine (BDA)-labeled corticospinal tract (CST) fibers demonstrated axonal regeneration of LRTC/CBD-NT3 in the injured spinal cord. Serotonin fiber regrowth also illustrated the effectiveness of LRTC/CBD-NT3. Thus, collagen-binding NT3 with LRTC may provide an effective method for treating SCI.

A systematic review of non-invasive pharmacologic neuroprotective treatments for acute spinal cord injury

An increasing number of therapies for spinal cord injury (SCI) are emerging from the laboratory and seeking translation into human clinical trials. Many of these are administered as soon as possible after injury with the hope of attenuating secondary damage and maximizing the extent of spared neurologic tissue. In this article, we systematically review the available pre-clinical research on such neuroprotective therapies that are administered in a non-invasive manner for acute SCI. Specifically, we review treatments that have a relatively high potential for translation due to the fact that they are already used in human clinical applications, or are available in a form that could be administered to humans. These include: erythropoietin, NSAIDs, anti-CD11d antibodies, minocycline, progesterone, estrogen, magnesium, riluzole, polyethylene glycol, atorvastatin, inosine, and pioglitazone. The literature was systematically reviewed to examine studies in which an in-vivo animal model was utilized to assess the efficacy of the therapy in a traumatic SCI paradigm. Using these criteria, 122 studies were identified and reviewed in detail. Wide variations exist in the animal species, injury models, and experimental designs reported in the pre-clinical literature on the therapies reviewed. The review highlights the extent of investigation that has occurred in these specific therapies, and points out gaps in our knowledge that would be potentially valuable prior to human translation.

CD11d integrin blockade reduces the systemic inflammatory response syndrome after spinal cord injury

Traumatic injury to the spinal cord triggers a systemic inflammatory response syndrome (SIRS), in which inflammatory cells from the circulation invade organs such as the liver, lung and kidney, leading to damage of these organs. Our previous study (Gris, et al, Exp. Neurol, 2008) demonstrated that spinal cord injury (SCI) activates circulating neutrophils that then invade the lung and kidney from 2 to 24 h after injury, increasing myeloperoxidase activity, cyclooxygenase-2 and matrix metalloproteinase-9 expression and lipid peroxidation in these organs. The present study was designed to ascertain whether a treatment that limits the influx of leukocytes into the injured spinal cord would also be effective in reducing the SIRS after SCI. This treatment is intravenous delivery of a monoclonal antibody (mAb) against the CD11d subunit of the CD11d/CD18 integrin expressed by neutrophils and monocytes. We delivered the anti-CD11d mAb at 2 h post moderate clip compression SCI at the 4th or 12th thoracic segments and assessed inflammation, oxidative activity and cellular damage within the lung, kidney and liver at 12 h post-injury. In some analyses we compared high and low thoracic injuries to evaluate the importance of injury level on the intensity of the SIRS. After T4 injury, treatment with the anti-integrin mAb reduced the presence of neutrophils and macrophages in the lung, with associated decreases in expression of NF-κB and oxidative enzymes and in the concentration of free radicals in this organ. The treatment also reduced lipid peroxidation, protein nitration and cell death in the lung. The anti-CD11d treatment also reduced the inflammatory cells within the kidney after T4 injury, as well as the free radical concentration and amount of lipid peroxidation. In the liver, the mAb treatment reduced the influx of neutrophils but most of the other measures examined were unaffected by SCI. The inflammatory responses within the lung and kidney were often greater after T4 than T12 injury. Clinical studies show that SIRS, with its associated organ failure, contributes significantly to the morbidity and mortality of SCI patients. This anti-integrin treatment may block the onset of SIRS after SCI.

Potential Therapeutic Targets for PPARgamma after Spinal Cord Injury

Traumatic injury to the spinal cord results in multiple anatomical, physiological, and functional deficits as a result of local neuronal and glial cell death as well as loss of descending and ascending axons traversing the injury site. The many different mechanisms thought to contribute to protracted secondary cell death and dysfunction after spinal cord injury (SCI) are potential therapeutic targets. Agents that bind and activate the transcription factor peroxisome proliferator-activated receptor-γ (PPAR-γ) show great promise for minimizing or preventing these deleterious cascades in other models of CNS disorders. This review will summarize the major secondary injury cascades occurring after SCI and discuss data from experimental CNS injury and disease models showing the exciting potential for PPARγ therapies after SCI.

TGF-β1 affects endothelial cell interaction with macrophages and T cells leading to the development of cerebrovascular amyloidosis

Astrocyte-endothelial cell (EC) interactions play a major role in the function of the neurovascular unit. Dysfunction in these interactions may lead to amyloid accumulation in blood vessels and may cause microhemorrhage and cognitive impairment. Transforming growth factor-β1 (TGF-β1) expression levels positively correlate with the degree of cerebrovascular amyloid in Alzheimer's disease (AD) cases. Furthermore, expression of TGF-β1 driven by the GFAP promoter in mice leads to an age-related deposition of amyloid, such as β-amyloid (Aβ), around cerebral blood vessels. Here, we demonstrate that TGF-β1 affects the cross talk between EC and inflammation, leading to a reduction in macrophage activity as measured by protein levels and migration ability. Changes in EC secreted factors following TGF-β1 stimulation also affect CD4(+) T cell activation, as shown by a reduction in the levels of IFN-γ. Moreover, while medium from EC can stimulate macrophages to clear insoluble cerebrovascular amyloid from an AD mouse brain, pre-incubation of EC with TGF-β1 reduces the ability of EC to affect macrophage activity. Our findings support the importance of cross talk between EC, macrophages and CD4(+) T cells in preventing cerebrovascular amyloid deposition. Understanding EC-immune system interactions may pave the way to new therapeutic approaches for cerebrovascular amyloidosis diseases.

Inflammatory phenotyping identifies CD11d as a gene markedly induced in white adipose tissue in obese rodents and women

In severe obesity, white adipose tissue (WAT) inflammation and macrophage infiltration are thought to contribute to WAT and whole-body insulin resistance. Specific players involved in triggering and maintaining inflammation (i.e. those regulating adipokine release and WAT macrophage recruitment, retention, or function) remain to be fully elaborated, and the degree to which moderate obesity promotes WAT inflammation remains to be clarified further. Therefore, we characterized adiposity and metabolic phenotypes in adult male C57BL/6J mice fed differing levels of dietary fat (10, 45, and 60% of energy) for 12 wk, concurrent with determinations of WAT inflammation markers and mRNA expression of leukocyte-derived integrins (CD11b, CD11c, CD11d) involved in macrophage extravasation and tissue macrophage homing/retention. As expected, a lard-based, very high-fat diet (60% energy) significantly increased adiposity and glucose intolerance compared with 10% fat-fed controls, coincident with higher retroperitoneal (RP) WAT transcript levels for proinflammatory factors and macrophage markers, including TNFα and CD68 mRNA, which were ~3- and ~15-fold of control levels, respectively (P < 0.001). Mice fed the 45% fat diet had more moderate obesity, less glucose intolerance, and lower WAT macrophage/inflammatory marker mRNA abundances compared with 60% fat-fed mice; TNFα and CD68 mRNA levels were ~2- and ~5-fold of control levels (P < 0.01). Relative WAT expression of CD11d was massively induced by obesity to an extent greater than any other inflammatory marker (to >300-fold of controls in the 45 and 60% fat groups) (P < 0.0001) and this induction was WAT specific. Because we found that CD11d expression also increased in RP-WAT of Zucker obese rats and in the subcutaneous WAT of obese adult women, this appears to be a common feature of obesity. Observed correlations of WAT macrophage transcript marker abundances with body weight in lean to modestly obese mice raises an interesting possibility that the activities of at least some WAT macrophages are closely linked to the normal adipose remodeling that is a requisite for changes in WAT energy storage capacity.

A selective phosphodiesterase-4 inhibitor reduces leukocyte infiltration, oxidative processes, and tissue damage after spinal cord injury

We tested the hypothesis that a selective phosphodiesterase type 4 inhibitor (PDE4-I; IC486051) would attenuate early inflammatory and oxidative processes following spinal cord injury (SCI) when delivered during the first 3 days after injury. Rats receiving a moderately severe thoracic-clip-compression SCI were treated with the PDE4-I (0.5, 1.0, and 3.0 mg/kg IV) in bolus doses from 2-60 h post-injury. Doses at 0.5 mg/kg and 1.0 mg/kg significantly decreased myeloperoxidase (MPO) enzymatic activity (neutrophils), expression of a neutrophil-associated protein and of ED-1 (macrophages), and estimates of lipid peroxidation in cord lesion homogenates at 24 h and 72 h post-injury by 25-40%. The 3.0 mg/kg dose had small or no effects on these measures. The PDE4-I treatment (0.5 or 1.0 mg/kg) reduced expression of the oxidative enzymes gp91(phox), inducible nitric oxide synthase, and cyclooxygenase-2, and diminished free radical generation by up to 40%. Treatment with 0.5 mg/kg PDE4-I improved motor function (as assessed by the Basso-Beattie-Bresnahan scale) significantly from 4-8 weeks after SCI (average difference 1.3 points). Mechanical allodynia elicited from the hindpaw decreased by up to 25%. The PDE4-I treatment also increased white matter volume near the lesion at 8 weeks after SCI. In conclusion, the PDE4-I reduced key markers of oxidative stress and leukocyte infiltration, producing cellular protection, locomotor improvements, and a reduction in neuropathic pain. Early inhibition of PDE4 is neuroprotective after SCI when given acutely and briefly at sufficient doses.

Emerging concepts in myeloid cell biology after spinal cord injury

Traumatic spinal cord injury (SCI) affects the activation, migration, and function of microglia, neutrophils and monocyte/macrophages. Because these myeloid cells can positively and negatively affect survival of neurons and glia, they are among the most commonly studied immune cells. However, the mechanisms that regulate myeloid cell activation and recruitment after SCI have not been adequately defined. In general, the dynamics and composition of myeloid cell recruitment to the injured spinal cord are consistent between mammalian species; only the onset, duration, and magnitude of the response vary. Emerging data, mostly from rat and mouse SCI models, indicate that resident and recruited myeloid cells are derived from multiple sources, including the yolk sac during development and the bone marrow and spleen in adulthood. After SCI, a complex array of chemokines and cytokines regulate myelopoiesis and intraspinal trafficking of myeloid cells. As these cells accumulate in the injured spinal cord, the collective actions of diverse cues in the lesion environment help to create an inflammatory response marked by tremendous phenotypic and functional heterogeneity. Indeed, it is difficult to attribute specific reparative or injurious functions to one or more myeloid cells because of convergence of cell function and difficulties in using specific molecular markers to distinguish between subsets of myeloid cell populations. Here we review each of these concepts and include a discussion of future challenges that will need to be overcome to develop newer and improved immune modulatory therapies for the injured brain or spinal cord.

Bioengineered scaffolds for spinal cord repair

Spinal cord injury can lead to devastating and permanent loss of neurological function, affecting all levels below the site of trauma. Unfortunately, the injured adult mammalian spinal cord displays little regenerative capacity and little functional recovery in large part due to a tissue environment that is nonpermissive for regenerative axon growth. Artificial tissue repair scaffolds may provide a physical guide to allow regenerative axon growth that bridges the lesion cavity and restores functional neural connectivity. By integrating different strategies, including the use of various biomaterials and microstructures as well as incorporation of bioactive molecules and living cells, combined or synergistic effects for spinal cord repair through regenerative axon growth may be achieved. This article briefly reviews the development of bioengineered scaffolds for spinal cord repair, focusing on spinal cord injury and the subsequent cellular response, scaffold materials, fabrication techniques, and current therapeutic strategies. Key issues and challenges are also identified and discussed along with recommendations for future research.

Cellular and molecular insights into neuropathy-induced pain hypersensitivity for mechanism-based treatment approaches

Neuropathic pain is currently being treated by a range of therapeutic interventions that above all act to lower neuronal activity in the somatosensory system (e.g. using local anesthetics, calcium channel blockers, and opioids). The present review highlights novel and often still largely experimental treatment approaches based on insights into pathological mechanisms, which impact on the spinal nociceptive network, thereby opening the 'gate' to higher brain centers involved in the perception of pain. Cellular and molecular mechanisms such as ectopia, sensitization of nociceptors, phenotypic switching, structural plasticity, disinhibition, and neuroinflammation are discussed in relation to their involvement in pain hypersensitivity following either peripheral neuropathies or spinal cord injury. A mechanism-based treatment approach may prove to be successful in effective treatment of neuropathic pain, but requires more detailed insights into the persistence of cellular and molecular pain mechanisms which renders neuropathic pain unremitting. Subsequently, identification of the therapeutic window-of-opportunities for each specific intervention in the particular peripheral and/or central neuropathy is essential for successful clinical trials. Most of the cellular and molecular pain mechanisms described in the present review suggest pharmacological interference for neuropathic pain management. However, also more invasive treatment approaches belong to current and/or future options such as neuromodulatory interventions (including spinal cord stimulation) and cell or gene therapies, respectively.

Anti-neuroinflammatory and neurotrophic effects of combined therapy with annexin II and Reg-2 on injured spinal cord

The present study was designed to investigate the neuroprotective effects of Ca(2+)-dependent phospholipid-binding protein annexin II and a secreted protein Reg-2 (regeneration gene protein 2) in spinal cord injury (SCI) model produced by contusion SCI at T(9) using the weight drop method. The agents were delivered intrathecally with Alzet miniosmotic pumps. We found that annexin II and Reg-2 remarkably reduced neuronal death, attenuated tissue damage and alleviated detrimental inflammation in vivo; meanwhile, a significant increase in white matter sparing and myelination area was observed. The propriospinal axons and long-distance supraspinal pathways were protected by the treatments as revealed by retrograde tracing. Basso Beattie Bresnahan locomotor rating scores also revealed a measurable behavioral improvement. However, no evident behavioral improvements in locomotor performance were achieved by the combined treatment with annexin II and Reg-2, compared with the separate treatment with annexin II and Reg-2.

SDF1 in the dorsal corticospinal tract promotes CXCR4+ cell migration after spinal cord injury

Background

Stromal cell-derived factor-1 (SDF1) and its major signaling receptor, CXCR4, were initially described in the immune system; however, they are also expressed in the nervous system, including the spinal cord. After spinal cord injury, the blood brain barrier is compromised, opening the way for chemokine signaling between these two systems. These experiments clarified prior contradictory findings on normal expression of SDF1 and CXCR4 as well as examined the resulting spinal cord responses resulting from this signaling.

Methods

These experiments examined the expression and function of SDF1 and CXCR4 in the normal and injured adult mouse spinal cord primarily using CXCR4-EGFP and SDF1-EGFP transgenic reporter mice.

Results

In the uninjured spinal cord, SDF1 was expressed in the dorsal corticospinal tract (dCST) as well as the meninges, whereas CXCR4 was found only in ependymal cells surrounding the central canal. After spinal cord injury (SCI), the pattern of SDF1 expression did not change rostral to the lesion but it disappeared from the degenerating dCST caudally. By contrast, CXCR4 expression changed dramatically after SCI. In addition to the CXCR4+ cells in the ependymal layer, numerous CXCR4+ cells appeared in the peripheral white matter and in the dorsal white matter localized between the dorsal corticospinal tract and the gray matter rostral to the lesion site. The non-ependymal CXCR4+ cells were found to be NG2+ and CD11b+ macrophages that presumably infiltrated through the broken blood-brain barrier. One population of macrophages appeared to be migrating towards the dCST that contains SDF1 rostral to the injury but not towards the caudal dCST in which SDF1 is no longer present. A second population of the CXCR4+ macrophages was present near the SDF1-expressing meningeal cells.

Conclusions

These observations suggest that attraction of CXCR4+ macrophages is part of a programmed response to injury and that modulation of the SDF1 signaling system may be important for regulating the inflammatory response after SCI.

Spinal cord injury therapies in humans: an overview of current clinical trials and their potential effects on intrinsic CNS macrophages

INTRODUCTION

Macrophage activation is a hallmark of spinal cord injury (SCI) pathology. CNS macrophages, derived from resident microglia and blood monocytes, are ubiquitous throughout the injured spinal cord, and respond to signals in the lesion environment by changing their phenotype and function. Depending on their phenotype and activation status, macrophages may initiate secondary injury mechanisms and/or promote CNS regeneration and repair.

AREAS COVERED

This review provides a comprehensive overview of current SCI clinical trials that are intended to promote neuroprotection, axon regeneration or cell replacement. None of these potential therapies were developed with the goal of influencing macrophage function; however, it is likely that each will have direct or indirect effects on CNS macrophages. The potential impact of each trial is discussed in the context of CNS macrophage biology.

EXPERT OPINION

Activation of CNS macrophages is an inevitable consequence of traumatic SCI. Given that these cells are exquisitely sensitive to changes in microenvironment, any intervention that affects tissue integrity and/or the composition of the cellular milieu will undoubtedly affect CNS macrophages. Thus, it is important to understand how current clinical trials will affect intrinsic CNS macrophages.

A murine model of hypertonic saline as a treatment for acute spinal cord injury: effects on autonomic outcome

Object

Spinal cord injury (SCI) continues to be a problem without a definitive cure. Research based on improved understanding of the immunological aspects of SCI has revealed targets for treating and ameliorating the extent of secondary injury. Hypertonic saline (HTS), a substance both easy to create and to transport, has been investigated as an immunologically active material that can be used in a clinically relevant interval after injury. In this pilot study, HTS was investigated in a murine model for its abilities to ameliorate secondary injury after a severe spinal cord contusion.

Methods

Female C57Bl/6 mice with severe T8–10 contusion injuries were used as the model subjects. A group of 41 mice were studied in a blinded fashion. Mice received treatments with HTS (HTS, 7.5%) or normal saline solution (NSS, 0.9%) at 2 discreet time points (3 and 24 hours after injury.) A separate group of 9 untreated animals were also used as controls. Animals were assessed for autonomic outcome (bladder function). In a group of 33 mice, histological assessment (cellular infiltration) was also measured.

Results

Bladder function was found to be improved significantly in those treated with HTS compared with those who received NSS and also at later treatment times (24 hours) than at earlier treatment times (3 hours). Decreased cellular infiltration in each group correlated with bladder recovery.

Conclusions

The increased effectiveness of later administration time of the more osmotically active and immunomodulatory substance (HTS) suggests that interaction with events occurring around 24 hours after injury is critical. These events may be related to the invasion of leukocytes peaking at 8–24 hours postinjury and/or the peak benefit time of subject rehydration.

CD47 knockout mice exhibit improved recovery from spinal cord injury

Recent data have implicated thrombospondin-1 (TSP-1) signaling in the acute neuropathological events that occur in microvascular endothelial cells (ECs) following spinal cord injury (SCI) (Benton et al., 2008b). We hypothesized that deletion of TSP-1 or its receptor CD47 would reduce these pathological events following SCI. CD47 is expressed in a variety of tissues, including vascular ECs and neutrophils. CD47 binds to TSP-1 and inhibits angiogenesis. CD47 also binds to the signal regulatory protein (SIRP)α and facilitates neutrophil diapedesis across ECs to sites of injury. After contusive SCI, TSP-1(-/-) mice did not show functional improvement compared to wildtype (WT) mice. CD47(-/-) mice, however, exhibited functional locomotor improvements and greater white matter sparing. Whereas targeted deletion of either CD47 or TSP-1 improved acute epicenter vascularity in contused mice, only CD47 deletion reduced neutrophil diapedesis and increased microvascular perfusion. An ex vivo model of the CNS microvasculature revealed that CD47(-/-)-derived microvessels (MVs) prominently exhibit adherent WT or CD47(-/-) neutrophils on the endothelial lumen, whereas WT-derived MVs do not. This implicates a defect in diapedesis mediated by the loss of CD47 expression on ECs. In vitro transmigration assays confirmed the role of SIRPα in neutrophil diapedesis through EC monolayers. We conclude that CD47 deletion modestly, but significantly, improves functional recovery from SCI via an increase in vascular patency and a reduction of SIRPα-mediated neutrophil diapedesis, rather than the abrogation of TSP-1-mediated anti-angiogenic signaling.

Anti-CD11d monoclonal antibody treatment for rat spinal cord compression injury

This study was initiated due to an NIH "Facilities of Research-Spinal Cord Injury" contract to support independent replication of published studies. Transient blockage of the CD11d/CD18 integrin has been reported to reduce secondary neuronal damage as well as to improve functional recovery after spinal cord injury (SCI) in rats. The purpose of this study was to determine whether treatment with an anti-CD11d monoclonal antibody (mAb) would improve motor performance, reduce pain and histopathological damage in animals following clip-compression injury as reported. Adult male Wistar rats (250g) were anesthetized with isoflurane, and the T12 spinal cord exposed by T10 and T11 dorsal laminectomies followed by a 60s period of clip compression utilizing a 35g clip. Control animals received an isotype-matched irrelevant antibody (1B7) while the treated group received the anti-CD11d mAb (217L; 1.0mg/kg) systemically. Open-field locomotion and sensory function were assessed and animals were perfusion-fixed at twelve weeks after injury for quantitative histopathological analysis. As compared to 1B7, 217L treated animals showed an overall non-significant trend to better motor recovery. All animals showed chronic mechanical allodynia and anti-CD11d mAb treatment did not significantly prevent its development. Histopathological analysis demonstrated severe injury to gray and white matter after compression with a non-significant trend in anti-CD11d protection compared to control animals for preserved myelin. Although positive effects with the anti-CD11d mAb treatment have been reported after compressive SCI, it is suggested that this potential treatment requires further investigation before clinical trials in spinal cord injured patients are implemented.

The neuroprotective effects of Reg-2 following spinal cord transection injury

This study was designed to elucidate the potential neuroprotective effects of Reg-2 (regeneration gene protein 2) in a rodent model of spinal cord transection injury at the ninth thoracic level. Reg-2 at 100 and 500 μg, recombinant rat ciliary neurotrophic factor, or vehicle were delivered intrathecally using Alzet miniosmotic pumps. We found that Reg-2 treatment significantly reduced neuronal death in the spinal cord. There was also an attenuation of inflammation at the injury site and an increase in white matter sparing and retained myelination. Retrograde tracing revealed that Reg-2 protected axons of long descending pathways at 6 weeks post-SCI, and the number of FluoroGold-labeled neurons in spinal and supraspinal regions was also significantly increased. Immunofluorescent staining confirmed that the spared white matter contained neurofilament-positive axons. Moreover, behavioral improvements were revealed by Basso Beattie Bresnahan locomotor rating scores and grid-walk analysis. These results suggest that Reg-2 might promote functional recovery by increasing axonal growth, inhibiting neuronal apoptosis, and attenuating spinal cord secondary injury after SCI.

Schwann cell coculture improves the therapeutic effect of bone marrow stromal cells on recovery in spinal cord-injured mice

Studies of bone marrow stromal cells (MSCs) transplanted into the spinal cord-injured rat give mixed results: some groups report improved locomotor recovery while others only demonstrate improved histological appearance of the lesion. These studies show no clear correlation between neurological improvements and MSC survival. We examined whether MSC survival in the injured spinal cord could be enhanced by closely matching donor and recipient mice for genetic background and marker gene expression and whether exposure of MSCs to a neural environment (Schwann cells) prior to transplantation would improve their survival or therapeutic effects. Mice underwent a clip compression spinal cord injury at the fourth thoracic level and cell transplantation 7 days later. Despite genetic matching of donors and recipients, MSC survival in the injured spinal cord was very poor (∼1%). However, we noted improved locomotor recovery accompanied by improved histopathological appearance of the lesion in mice receiving MSC grafts. These mice had more white and gray matter sparing, laminin expression, Schwann cell infiltration, and preservation of neurofilament and 5-HT-positive fibers at and below the lesion. There was also decreased collagen and chondroitin sulphate proteoglycan deposition in the scar and macrophage activation in mice that received the MSC grafts. The Schwann cell cocultured MSCs had greater effects than untreated MSCs on all these indices of recovery. Analyses of chemokine and cytokine expression revealed that MSC/Schwann cell cocultures produced far less MCP-1 and IL-6 than MSCs or Schwann cells cultured alone. Thus, transplanted MSCs may improve recovery in spinal cord-injured mice through immunosuppressive effects that can be enhanced by a Schwann cell coculturing step. These results indicate that the temporary presence of MSCs in the injured cord is sufficient to alter the cascade of pathological events that normally occurs after spinal cord injury, generating a microenvironment that favors improved recovery.

Mitogen-activated protein kinase-activated protein kinase 2 (MK2) contributes to secondary damage after spinal cord injury

The inflammatory response contributes importantly to secondary tissue damage and functional deficits after spinal cord injury (SCI). In this work, we identified mitogen-activated protein kinase (MAPK)-activated protein kinase 2 (MAPKAPK2 or MK2), a downstream substrate of p38 MAPK, as a potential target using microarray analysis of contused spinal cord tissue taken at the peak of the inflammatory response. There was increased expression and phosphorylation of MK2 after SCI, with phospho-MK2 expressed in microglia/macrophages, neurons and astrocytes. We examined the role of MK2 in spinal cord contusion injury using MK2(-/-) mice. These results show that locomotor recovery was significantly improved in MK2(-/-) mice, compared with wild-type controls. MK2(-/-) mice showed reduced neuron and myelin loss, and increased sparing of serotonergic fibers in the ventral horn caudal to the injury site. We also found differential expression of matrix metalloproteinase-2 and 9 in MK2(-/-) and wild-type mice after SCI. Significant reduction was also seen in the expression of proinflammatory cytokines and protein nitrosylation in the injured spinal cord of MK2(-/-) mice. Our previous work has shown that macrophages lacking MK2 have an anti-inflammatory phenotype. We now show that there is no difference in the number of macrophages in the injured spinal cord between the two mouse strains and little if any difference in their phagocytic capacity, suggesting that macrophages lacking MK2 have a beneficial phenotype. These findings suggest that a lack of MK2 can reduce tissue damage after SCI and improve locomotor recovery. MK2 may therefore be a useful target to treat acute SCI.

Inhibition of CXCR1 and CXCR2 chemokine receptors attenuates acute inflammation, preserves gray matter and diminishes autonomic dysreflexia after spinal cord injury

STUDY DESIGN

Female Wistar rats (225 g) underwent spinal cord injury (SCI) at the T4 segment and were assigned to one of the three groups treated with: (1) saline; (2) 7.5 mg kg(-1) Reparixin; or (3) 15 mg kg(-1) Reparixin. Reparixin is a small molecule, allosteric noncompetitive inhibitor of CXCR1 and CXCR2 chemokine receptors involved in inflammation.

METHODS

Spinal cord homogenates at 12 and 72 h post-SCI were assayed for tumor necrosis factor α (TNF-α) and cytokine-induced neutrophil chemoattractant (CINC)-1 using enzyme-linked immunosorbant assay (ELISA). Myeloperoxidase activity and western blots for CD68, Fas and p75 content were used to assess inflammation and death receptor ligands, respectively. Histopathology and neurological outcomes were assessed by immunohistochemistry, locomotion scoring and cardiovascular measurement of autonomic dysreflexia 4 weeks post-SCI.

RESULTS

Both 7.5 and 15 mg kg(-1) doses of Reparixin reduced levels of TNF-α and CINC-1 72 h post-SCI and decreased macrophage (CD68) content in the spinal cord lesion. Only 15 mg kg(-1) Reparixin reduced both Fas and p75 levels in the spinal cord compared with untreated SCI. We observed a reduced lesion area and increased neuron number in the gray matter of Reparixin-treated rats. Hindlimb motor scores at 7 and 28 days post-SCI were improved by 15 mg kg(-1) Reparixin treatment. Both 7.5 and 15 mg kg(-1) Reparixin reduced development of autonomic dysreflexia 4 weeks post-SCI. The change in mean arterial pressure, induced by cutaneous or visceral stimulation, was reduced by 40-50%.

CONCLUSION

Acute treatment with 15 mg kg(-1) Reparixin reduces acute inflammation and is associated with minor improvements in motor function and a significant reduction in the severity of autonomic dysreflexia.

Validity of acute and chronic tactile sensory testing after spinal cord injury in rats

Spinal cord injury (SCI) impairs sensory systems causing allodynia. Measuring the development of allodynia in rodent models of SCI is challenging due to spinal shock and marked motor impairments. Assessment of SCI-induced allodynia is not standardized across labs, making interpretation of results difficult. Therefore, we validated sensory threshold assessment after SCI and developed a novel assessment of allodynia prior to motor recovery in a rat SCI model. One hundred fifty-six Sprague-Dawley rats received T8 laminectomy or mild to moderate SCI using the OSU SCI device (0.3 mm to 1.3 mm cord displacement). To determine tactile thresholds, von Frey hairs (VFH) were applied in Up-Down or ascending order to the dorsal or plantar hindpaw. The most efficient and valid procedures that maintain high sensitivity and specificity were identified. Ten Up-Down VFH applications yielded stable thresholds; reducing the risk of threshold decay and unnecessary exposure to painful stimuli. Importantly, distraction of SCI-rats with food revealed differential decay of thresholds than when distraction is not provided. The new test uses dorsal VFH stimulation and is independent of trunk or hindlimb control. Acute dorsal VFH thresholds collected before recovery of hindlimb weight support accurately predicted plantar VFH thresholds measured at late timepoints (chi(2)=8.479; p<0.05). Thus, standardized testing early after SCI using the dorsal VFH test or later using 10 stimuli in the Up-Down test produces valid measures of tactile sensation across many SCI severities. Early detection of allodynia in experimental SCI will allow identification of mechanisms responsible for pain development and determine targets for therapeutic interventions.

Loss of hsp70.1 Decreases Functional Motor Recovery after Spinal Cord Injury in Mice

Heat shock proteins (HSPs) are specifically induced by various forms of stress. Hsp70.1, a member of the hsp70 family is known to play an important role in cytoprotection from stressful insults. However, the functional role of Hsp70 in motor function after spinal cord injury (SCI) is still unclear. To study the role of hsp70.1 in motor recovery following SCI, we assessed locomotor function in hsp70.1 knockout (KO) mice and their wild-type (WT) mice via the Basso, Beattie and Bresnahan (BBB) locomotor rating scale, before and after spinal hemisection at T13 level. We also examined lesion size in the spinal cord using Luxol fast blue/cresyl violet staining. One day after injury, KO and WT mice showed no significant difference in the motor function due to complete paralysis following spinal hemisection. However, when it compared to WT mice, KO mice had significantly delayed and decreased functional outcomes from 4 days up to 21 days after SCI. KO mice also showed significantly greater lesion size in the spinal cord than WT mice showed at 21 days after spinal hemisection. These results suggest that Hsp70 has a protective effect against traumatic SCI and the manipulation of the hsp70.1 gene may help improve the recovery of motor function, thereby enhancing neuroprotection after SCI.

Injured mice at the gym: review, results and considerations for combining chondroitinase and locomotor exercise to enhance recovery after spinal cord injury

Exercise provides a number of important benefits after spinal cord injury in clinical studies and animal models. However, the amount of functional improvement in overground locomotion obtained with exercise alone has been limited thus far, for reasons that are still poorly understood. One hypothesis is that the complex network of endogenous extracellular matrix components, including chondroitin sulfate proteoglycans (CSPGs), can inhibit exercise-induced remodeling and limit plasticity of spared circuitry in the adult central nervous system. Recent animal studies have shown that chondroitinase ABC (ChABC) can enhance plasticity in the adult nervous system by cleaving glycosaminoglycan sidechains from CSPGs. In this article we review the current literature on plasticity observed with locomotor training and following degradation of CSPGs with ChABC and then present a rationale for the use of exercise combined with ChABC to promote functional recovery after spinal cord injury. We also present results of a preliminary study that tested the simplest approach for combining these treatments; use of a single intraparenchymal injection of ChABC administered to the lumbar enlargement of mice with voluntary wheel running exercise after a mid-thoracic spinal contusion injury. The results are negative, yet serve to highlight limitations in our understanding of the most effective protocols for combining these approaches. Further work is directed to identify the timing, type, and quantity of exercise and pharmacological interventions that can be used to maximize functional improvements by strengthening appropriate synaptic connections.

Anti-IL-6-receptor antibody promotes repair of spinal cord injury by inducing microglia-dominant inflammation

We previously reported the beneficial effect of administering an anti-mouse IL-6 receptor antibody (MR16-1) immediately after spinal cord injury (SCI). The purpose of our present study was to clarify the mechanism underlying how MR16-1 improves motor function after SCI. Quantitative analyses of inflammatory cells using flow cytometry, and immunohistochemistry with bone marrow-chimeric mice generated by transplanting genetically marked purified hematopoietic stem cells, revealed that MR16-1 dramatically switched the central player in the post-traumatic inflammation, from hematogenous macrophages to resident microglia. This change was accompanied by alterations in the expression of relevant cytokines within the injured spinal cord; the expression of recruiting chemokines including CCL2, CCL5, and CXCL10 was decreased, while that of Granulocyte/Macrophage-Colony Stimulating Factor (GM-CSF), a known mitogen for microglia, was increased. We also showed that the resident microglia expressed higher levels of phagocytic markers than the hematogenous macrophages. Consistent with these findings, we observed significantly decreased tissue damage and reduced levels of myelin debris and Nogo-A, the axonal growth inhibitor, by MR16-1 treatment. Moreover, we observed increased axonal regeneration and/or sprouting in the MR16-1-treated mice. Our findings indicate that the functional improvement elicited by MR16-1 involves microglial functions, and provide new insights into the role of IL-6 signaling in the pathology of SCI.

Comparison of immunopathology and locomotor recovery in C57BL/6, BUB/BnJ, and NOD-SCID mice after contusion spinal cord injury

Studies of cell transplantation therapeutics in animal models of traumatic spinal cord injury (SCI) are often hampered by partial or complete rejection of the graft by the host. Pharmacological immunosuppression is rarely sufficient to prevent rejection. Further, the immunological niche created by both the host immune response and immunosuppressant drugs could hypothetically influence the proliferation, differentiation, and fate of transplanted progenitor/stem cells. To avoid these confounds, we have previously used the constitutively immunodeficient non-obese diabetic severe combined immunodeficient (NOD-SCID) mouse as a model for transplantation studies following SCI. In the current study, we compare behavioral and histological recovery in NOD-SCID, C57BL/6, and BUB/BnJ mice of both sexes to better facilitate interpretation of data from studies using NOD-SCID mice. Of the strains examined, NOD-SCID mice exhibited the greatest locomotor recovery in the open field; no sex differences were detected in locomotor recovery in any of the strains. Stereologic estimation of the number of infiltrated neutrophils showed more cells in C57BL/6 mice than NOD-SCID mice, with BUB/BnJ mice having an intermediate number. The volume of macrophages/microglia did not differ between strains or sexes, though more rostral-caudal spreading was observed in C57BL/6 and BUB/BnJ than NOD-SCID mice. No significant differences were detected in lesion volume. Taken together these findings demonstrate that relative to other strains, NOD-SCID mice have both similar primary lesion volume and cellular inflammatory parameters after SCI, and support the applicability of the model for neurotransplantation studies.

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.

ProBDNF inhibits infiltration of ED1+ macrophages after spinal cord injury

The central nervous system (CNS) does not regenerate partly due to the slow clearance of debris from the degenerated myelin sheath by Wallerian degeneration. The mechanism underlying the inefficiency in myelin clearance is not clear. Here we showed that endogenous proBDNF may inhibit the infiltration of ED1+ inflammatory cells after spinal cord injury. After injury, proBDNF and its receptors sortilin and p75NTR are expressed in the spinal cord as determined by Western blots and immunocytochemistry. ProBDNF and mature BDNF were released from macrophages in vitro. Macrophages in vivo (ED1+) and isolated in vitro (CD11b+) express moderate levels of proBDNF, sortilin and p75NTR. ProBDNF suppressed the migration of isolated macrophages in vitro and the antibody to proBDNF enhanced the migration. Suppression of proBDNF in vivo by administering the antiserum to the prodomain of BDNF after spinal cord injury (SCI) increased the infiltration of macrophages and increased number of neurons in the injured cord. BBB tests showed that the treatment of the antibody to proBDNF improved the functional recovery after spinal cord injury. Our data suggest that proBDNF is a suppressing factor for macrophage migration and infiltration and may play a detrimental role after SCI.

Spinal cord injury I: A synopsis of the basic science

Substantial knowledge has been gained in the pathological findings following naturally occurring spinal cord injury (SCI) in dogs and cats. The molecular mechanisms involved in failure of neural regeneration within the central nervous system, potential therapeutics including cellular transplantation therapy, neural plasticity, and prognostic indicators of recovery from SCI have been studied. This 2-part review summarizes 1) basic science perspectives regarding treating and curing spinal cord injury, 2) recent studies that shed light on prognosis and recovery from SCI, 3) current thinking regarding standards of care for dogs with SCI, 4) experimental approaches in the laboratory setting, and 5) current clinical trials being conducted in veterinary medicine. Part I presents timely information on the pathophysiology of spinal cord injury, challenges associated with promoting regeneration of neurons of the central nervous system, and experimental approaches aimed at developing treatments for spinal cord injury.

Rescuing vasculature with intravenous angiopoietin-1 and alpha v beta 3 integrin peptide is protective after spinal cord injury

Blood vessel loss and inflammation cause secondary degeneration following spinal cord injury. Angiopoietin-1 through the Tie2 receptor, and other ligands through alphavbeta3 integrin, promote endothelial cell survival during developmental or tumour angiogenesis. Here, daily intravenous injections with an alphavbeta3-binding peptide named C16 or an angiopoietin-1 mimetic following a spinal cord contusion at thoracic level 9 in mice rescued epicentre blood vessels, white matter and locomotor function, and reduced detrimental inflammation. Preserved vascularity and reduced inflammation correlated with improved outcomes. C16 and angiopoietin-1 reduced leukocyte transmigration in vitro. Growth factor receptors and integrins facilitate each others' function. Therefore, angiopoietin-1 and C16 were combined and the effects were additive, resulting in almost complete functional recovery. The treatment had lasting effects when started 4 h following injury and terminated after one week. These results identify alphavbeta3 integrin and the endothelial-selective angiopoietin-1 as vascular and inflammatory regulators that can be targeted in a clinically relevant manner for neuroprotection after central nervous system trauma.

FTY720 reduces inflammation and promotes functional recovery after spinal cord injury

A robust and complex inflammatory cascade is known to be a prominent component of secondary injury following spinal cord injury (SCI). Specifically, the concept of trauma-induced autoimmunity has linked the lymphocyte population with neural tissue injury and neurologic deficit. FTY720, a sphingosine receptor modulator that sequesters lymphocytes in secondary lymphoid organs, has been shown to be effective in the treatment of a variety of experimental autoimmune disorders. Accordingly, by reducing lymphocyte infiltration into the spinal cord following SCI, this novel immunomodulator may enhance tissue preservation and functional recovery. In the present study, a moderate to severe contusion SCI was simulated in adult Long-Evans hooded rats. Using flow cytometry we showed that daily FTY720 treatment dramatically reduced T-cell infiltration into the SCI lesion site at 4 and 7 days post-injury, while other inflammatory cell populations were relatively unaltered. To assess functional recovery, three groups of injured animals (treated, vehicle, and injury only) were evaluated weekly for hindlimb recovery. Animals in the treated group consistently exhibited higher functional scores than animals in the control groups after 2 weeks post-injury. This finding was associated with a greater degree of white matter sparing at the lesion epicenter when cords were later sectioned and stained. Furthermore, treated animals were found to exhibit improved bladder function and a reduced incidence of hemorrhagic cystitis compared to control counterparts. Collectively these results demonstrate the neuroprotective potential of FTY720 treatment after experimental SCI.

Synergistic effects of transplanted adult neural stem/progenitor cells, chondroitinase, and growth factors promote functional repair and plasticity of the chronically injured spinal cord

The transplantation of neural stem/progenitor cells (NPCs) is a promising therapeutic strategy for spinal cord injury (SCI). However, to date NPC transplantation has exhibited only limited success in the treatment of chronic SCI. Here, we show that chondroitin sulfate proteoglycans (CSPGs) in the glial scar around the site of chronic SCI negatively influence the long-term survival and integration of transplanted NPCs and their therapeutic potential for promoting functional repair and plasticity. We targeted CSPGs in the chronically injured spinal cord by sustained infusion of chondroitinase ABC (ChABC). One week later, the same rats were treated with transplants of NPCs and transient infusion of growth factors, EGF, bFGF, and PDGF-AA. We demonstrate that perturbing CSPGs dramatically optimizes NPC transplantation in chronic SCI. Engrafted NPCs successfully integrate and extensively migrate within the host spinal cord and principally differentiate into oligodendrocytes. Furthermore, this combined strategy promoted the axonal integrity and plasticity of the corticospinal tract and enhanced the plasticity of descending serotonergic pathways. These neuroanatomical changes were also associated with significantly improved neurobehavioral recovery after chronic SCI. Importantly, this strategy did not enhance the aberrant synaptic connectivity of pain afferents, nor did it exacerbate posttraumatic neuropathic pain. For the first time, we demonstrate key biological and functional benefits for the combined use of ChABC, growth factors, and NPCs to repair the chronically injured spinal cord. These findings could potentially bring us closer to the application of NPCs for patients suffering from chronic SCI or other conditions characterized by the formation of a glial scar.

Embryonic stem cells promote motor recovery and affect inflammatory cell infiltration in spinal cord injured mice

The purpose of this study was to determine the fate and the effects of undifferentiated embryonic stem cells (ESCs) in mice after contusive lesion of the spinal cord (SCI). Reproducible traumatic lesion to the cord was performed at T8 level by means of the Infinite Horizon Device, and was followed by intravenous injection of one million of undifferentiated ESCs through the tail vein within 2 h from the lesion. The ESCs-treated animals showed a significant improvement of the recovery of motor function 28 days after lesion, with an average score of 4.61+/-0.13 points of the Basso Mouse Scale (n=14), when compared to the average score of vehicle treated mice, 3.58+/-0.23 (n=10). The number of identified ESCs found at the lesion site was 0.6% of the injected cells at 1 week after transplantation, and further reduced to 0.04% at 1 month. It is, thus, apparent that the promoted hind-limb recovery cannot be correlated to a substitution of the lost tissue performed by the exogenous ESC. The extensive evaluation of production of several neuroprotective and inflammatory cytokines did not reveal any effect by ESC-treatment, but unexpectedly the number of invading macrophages and neutrophils was greatly reduced. This may explain the improved preservation of lesion site ventral myelin, at both 1 week (29+/-11%) and 1 month (106+/-14%) after injury. No teratoma formation was observed, although an inappropriate colonization of the sacral cord by differentiated nestin- and beta-tubulin III-positive ESCs was detected.

Quantitative analysis of cellular inflammation after traumatic spinal cord injury: evidence for a multiphasic inflammatory response in the acute to chronic environment

Traumatic injury to the central nervous system results in the disruption of the blood brain/spinal barrier, followed by the invasion of cells and other components of the immune system that can aggravate injury and affect subsequent repair and regeneration. Although studies of chronic neuroinflammation in the injured spinal cord of animals are clinically relevant to most patients living with traumatic injury to the brain or spinal cord, very little is known about chronic neuroinflammation, though several studies have tested the role of neuroinflammation in the acute period after injury. The present study characterizes a novel cell preparation method that assesses, quickly and effectively, the changes in the principal immune cell types by flow cytometry in the injured spinal cord, daily for the first 10 days and periodically up to 180 days after spinal cord injury. These data quantitatively demonstrate a novel time-dependent multiphasic response of cellular inflammation in the spinal cord after spinal cord injury and are verified by quantitative stereology of immunolabelled spinal cord sections at selected time points. The early phase of cellular inflammation is comprised principally of neutrophils (peaking 1 day post-injury), macrophages/microglia (peaking 7 days post-injury) and T cells (peaking 9 days post-injury). The late phase of cellular inflammation was detected after 14 days post-injury, peaked after 60 days post-injury and remained detectable throughout 180 days post-injury for all three cell types. Furthermore, the late phase of cellular inflammation (14-180 days post-injury) did not coincide with either further improvements, or new decrements, in open-field locomotor function after spinal cord injury. However, blockade of chemoattractant C5a-mediated inflammation after 14 days post-injury reduced locomotor recovery and myelination in the injured spinal cord, suggesting that the late inflammatory response serves a reparative function. Together, these data provide new insight into cellular inflammation of spinal cord injury and identify a surprising and extended multiphasic response of cellular inflammation. Understanding the role of this multiphasic response in the pathophysiology of spinal cord injury could be critical for the design and implementation of rational therapeutic treatment strategies, including both cell-based and pharmacological interventions.

Magnetic resonance imaging assessment of macrophage accumulation in mouse brain after experimental traumatic brain injury

Macrophages contribute to secondary damage and repair after central nervous system (CNS) injury. Micron-sized paramagnetic iron oxide (MPIO) particles can label macrophages in situ, facilitating three-dimensional (3D) mapping of macrophage accumulation following traumatic brain injury (TBI), via ex vivo magnetic resonance microscopy (MRM) and in vivo monitoring with magnetic resonance imaging (MRI). MPIO particles were injected intravenously (iv; 4.5 mg Fe/Kg) in male C57BL/6J mice (n = 21). A controlled cortical impact (CCI) was delivered to the left parietal cortex. Five protocols were used in naive and injured mice to assess feasibility, specificity, and optimal labeling time. In vivo imaging was carried out at 4.7 Tesla (T). Brains were then excised for 3D MRM at 11.7 T. Triple-label immunofluorescence (MPIO via Dragon Green, macrophages via F480, and nuclei via 4,6-diamidino-2-phenylindole [DAPI]) of brain sections confirmed MPIO particles within macrophages. MRM of naives showed an even distribution of a small number of MPIO-labeled macrophages in the brain. MRM at 48-72 h after CCI and MPIO injection revealed MPIO-labeled macrophages accumulated in the trauma region. When MPIO particles were injected 6 days before CCI, MRM 48 h after CCI also revealed labeled cells at the injury site. In vivo studies of macrophage accumulation by MRI suggest that this approach is feasible, but requires additional optimization. We conclude that MPIO labeling and ex vivo MRM mapping of macrophage accumulation for assessment of TBI is readily accomplished. This new technique could serve as an adjunct to conventional MR approaches by defining inflammatory mechanisms and therapeutic efficacy of anti-inflammatory agents in experimental TBI.

Timing and duration of anti-alpha4beta1 integrin treatment after spinal cord injury: effect on therapeutic efficacy

OBJECT

After spinal cord injury (SCI) leukocytes infiltrate the injured cord, causing significant damage and further impairment of functional recovery. The leukocyte integrin alpha4beta1 is crucial for their entry. The authors previously demonstrated that an anti-alpha4 monoclonal antibody (mAb) treatment attenuates leukocyte infiltration, improves motor and autonomic function, and reduces neuropathic pain when administered at 2 hours and 24 hours after SCI.

METHODS

The authors conducted 2 preclinical studies: the first determined effects of treatment commencing at 6 hours, a clinically relevant time after injury, and the second examined effects of long-lasting treatment (28 days) on neurological recovery after SCI, as current clinically used anti-inflammatory monoclonal antibodies have such longevity. In the first study (timing study), rats were treated with anti-alpha4 or control mAb (intravenously) at 6 hours and 48 hours after moderate (35 g) thoracic compression SCI. Effects on intraspinal inflammation and oxidative injury were assessed at 3 and 7 days after SCI; motor function and pain were examined for 6 weeks. In the second study (duration study), anti-alpha4 mAb was administered starting 2 hours after SCI and subsequently every 3 days for 4 weeks (total of 8 doses), using a schedule of decreasing doses to resemble the pharmacodynamics of long-lasting antibodies used clinically. Motor function and pain were examined for 6 weeks. Lesions were assessed for tissue sparing and inflammation at 6 weeks by histological examination and MR imaging.

RESULTS

Anti-alpha4 mAb treatment at 6 hours and 48 hours after SCI (timing study) significantly decreased neutrophil and monocyte/macrophage influx at 3 days by 36% and 20%, respectively, but had no effect by at 7 days after SCI. Antibody treatment significantly reduced intraspinal myeloperoxidase activity by 48% and lipid peroxidation by 27% at 3 days post-injury. The treatment did not improve locomotor function but reduced mechanical allodynia elicited from the trunk and hind paw by ~50% at 3-6 weeks after SCI. In contrast, long-term mAb treatment commencing at 2 hours after SCI (duration study) significantly improved locomotor function at 2-6 weeks after SCI, (mean BBB scores +/- SE: treated rats, 8.3 +/- 0.16; controls, 7.3 +/- 0.2 at 6 weeks). At 3-6 weeks, mAb treatment decreased mechanical allodynia elicited from the trunk and hind paw by ~55%. This recovery correlated with 30% more myelin-containing white matter in treated rats than controls at 6 weeks. The lesion cavity was smaller in the treated rats when assessed by both histological (-37%) and imaging (-50%) methods. The accumulation of ED1-immunoreactive microglia/macrophages at the lesion was similar in treated and control rats.

CONCLUSIONS

Although delayed treatment reduced intraspinal inflammation and pain, motor function was not improved, revealing decreased efficacy at the more clinically feasibly treatment onset. Long-term anti-alpha4 mAb treatment starting 2 hours after SCI improved neurological outcomes, with tissue sparing near the lesion and no impairment of the late immune response to injury. These findings reveal no disadvantage of long-lasting immunosuppression by the treatment but show that efficacy depends upon very early delivery.

Blockade of interleukin-6 signaling suppressed cochlear inflammatory response and improved hearing impairment in noise-damaged mice cochlea

Hearing impairment can be the cause of serious socio-economic disadvantages. Recent studies have shown inflammatory responses in the inner ear co-occur with various damaging conditions including noise-induced hearing loss. We reported pro-inflammatory cytokine interleukin-6 (IL-6) was induced in the cochlea 6h after noise exposure, but the pathophysiological implications of this are still obscure. To address this issue, we investigated the effects of IL-6 inhibition using the anti-IL-6 receptor antibody (MR16-1). Noise-exposed mice were treated with MR16-1 and evaluated. Improved hearing at 4kHz as measured by auditory brainstem response (ABR) was noted in noise-exposed mice treated with MR16-1. Histological analysis revealed the decrease in spiral ganglion neurons was ameliorated in the MR16-1-treated group, while no significant change was observed in the organ of Corti. Immunohistochemistry for Iba1 and CD45 demonstrated a remarkable reduction of activated cochlear macrophages in spiral ganglions compared to the control group when treated with MR16-1. Thus, MR16-1 had protective effects both functionally and pathologically for the noise-damaged cochlea primarily due to suppression of neuronal loss and presumably through alleviation of inflammatory responses. Anti-inflammatory cytokine therapy including IL-6 blockade would be a feasible novel therapeutic strategy for acute sensory neural hearing loss.

beta2-integrins in demyelinating disease: not adhering to the paradigm

The beta(2)-integrins are a subfamily of integrins expressed on leukocytes that play an essential role in leukocyte trafficking, activation, and many other functions. Studies in EAE, the animal model for multiple sclerosis, show differential requirements for beta(2)-integrins in this disease model, ranging from critical in the case of LFA-1 (CD11a/CD18) to unimportant in the case of CD11d/CD18. Importantly, expression of beta(2)-integrins on T cell subsets provides some clues as to the function(s) these adhesion molecules play in disease development. For example, transferred EAE studies have shown that Mac-1 (CD11b/CD18) expression on alphabeta T cells is critical for disease development, and the absence of LFA-1 on Tregs in recipient mice results in exacerbated disease. In this review, we summarize recent findings regarding the role of beta(2)-integrins in demyelinating disease and new information about the role of beta(2)-integrins with respect to alterations in Treg numbers and function. In addition, we discuss the potential for targeting beta(2)-integrins in human demyelinating disease in light of the recent animal model studies.

Identification of two distinct macrophage subsets with divergent effects causing either neurotoxicity or regeneration in the injured mouse spinal cord

Macrophages dominate sites of CNS injury in which they promote both injury and repair. These divergent effects may be caused by distinct macrophage subsets, i.e., "classically activated" proinflammatory (M1) or "alternatively activated" anti-inflammatory (M2) cells. Here, we show that an M1 macrophage response is rapidly induced and then maintained at sites of traumatic spinal cord injury and that this response overwhelms a comparatively smaller and transient M2 macrophage response. The high M1/M2 macrophage ratio has significant implications for CNS repair. Indeed, we present novel data showing that only M1 macrophages are neurotoxic and M2 macrophages promote a regenerative growth response in adult sensory axons, even in the context of inhibitory substrates that dominate sites of CNS injury (e.g., proteoglycans and myelin). Together, these data suggest that polarizing the differentiation of resident microglia and infiltrating blood monocytes toward an M2 or "alternatively" activated macrophage phenotype could promote CNS repair while limiting secondary inflammatory-mediated injury.

Infiltrating blood-derived macrophages are vital cells playing an anti-inflammatory role in recovery from spinal cord injury in mice

BACKGROUND

Although macrophages (MPhi) are known as essential players in wound healing, their contribution to recovery from spinal cord injury (SCI) is a subject of debate. The difficulties in distinguishing between different MPhi subpopulations at the lesion site have further contributed to the controversy and led to the common view of MPhi as functionally homogenous. Given the massive accumulation in the injured spinal cord of activated resident microglia, which are the native immune occupants of the central nervous system (CNS), the recruitment of additional infiltrating monocytes from the peripheral blood seems puzzling. A key question that remains is whether the infiltrating monocyte-derived MPhi contribute to repair, or represent an unavoidable detrimental response. The hypothesis of the current study is that a specific population of infiltrating monocyte-derived MPhi is functionally distinct from the inflammatory resident microglia and is essential for recovery from SCI.

METHODS AND FINDINGS

We inflicted SCI in adult mice, and tested the effect of infiltrating monocyte-derived MPhi on the recovery process. Adoptive transfer experiments and bone marrow chimeras were used to functionally distinguish between the resident microglia and the infiltrating monocyte-derived MPhi. We followed the infiltration of the monocyte-derived MPhi to the injured site and characterized their spatial distribution and phenotype. Increasing the naïve monocyte pool by either adoptive transfer or CNS-specific vaccination resulted in a higher number of spontaneously recruited cells and improved recovery. Selective ablation of infiltrating monocyte-derived MPhi following SCI while sparing the resident microglia, using either antibody-mediated depletion or conditional ablation by diphtheria toxin, impaired recovery. Reconstitution of the peripheral blood with monocytes resistant to ablation restored the lost motor functions. Importantly, the infiltrating monocyte-derived MPhi displayed a local anti-inflammatory beneficial role, which was critically dependent upon their expression of interleukin 10.

CONCLUSIONS

The results of this study attribute a novel anti-inflammatory role to a unique subset of infiltrating monocyte-derived MPhi in SCI recovery, which cannot be provided by the activated resident microglia. According to our results, limited recovery following SCI can be attributed in part to the inadequate, untimely, spontaneous recruitment of monocytes. This process is amenable to boosting either by active vaccination with a myelin-derived altered peptide ligand, which indicates involvement of adaptive immunity in monocyte recruitment, or by augmenting the naïve monocyte pool in the peripheral blood. Thus, our study sheds new light on the long-held debate regarding the contribution of MPhi to recovery from CNS injuries, and has potentially far-reaching therapeutic implications.

The extracellular domain of CD11d regulates its cell surface expression

A mAb targeting the CD11d subunit of the leukocyte integrin CD11d/CD18 decreases intraspinal inflammation and oxidative damage leading to improved neurological outcomes in rodent models of SCI. CD11d/CD18 is the fourth member of the beta2-integrin family. Current evidence indicates that CD11d/CD18 is regulated differently than other beta2-integrins, suggesting that CD11d(+) leukocytes play a distinct role in inflammation. Although the transcriptional control of CD11d expression has been evaluated, control of the intracellular distribution of CD11d has not been addressed. For this reason and as a result of the potential of CD11d as a therapeutic target for SCI and possibly other CNS injuries, we investigated the intracellular localization and surface expression of CD11d in cultured cells. CD11d and CD18 were fused at their C-termini with YFP and mRFP, respectively. Flow cytometry and confocal microscopy demonstrated that rCD11d-YFP is expressed on the cell surface of leukocyte cell lines expressing CD18. In contrast, in heterologous cell lines, CD11d-YFP is retained intracellularly in the TGN. Coexpression of CD11d-YFP and CD18-mRFP relieves this intracellular restriction and allows the CD11d/CD18 heterodimer to be surface-expressed. Based on domain-swapping experiments with CD25, the extracellular domain of CD11d is required and sufficient for the observed intracellular retention in heterologous cells. Furthermore, the transmembrane and C-terminus are also required for proper heterodimerization with CD18 and localization to the plasma membrane. These findings suggest that multiple CD11d domains play a role in controlling intracellular location and association with CD18.

Depletion of Ly6G/Gr-1 leukocytes after spinal cord injury in mice alters wound healing and worsens neurological outcome

Spinal cord injury (SCI) induces a robust inflammatory response and the extravasation of leukocytes into the injured tissue. To further knowledge of the functions of neuroinflammation in SCI in mice, we depleted the early arriving neutrophils using an anti-Ly6G/Gr-1 antibody. Complete blood counts revealed that neutrophils increased approximately 3-fold over uninjured controls and peaked at 6-12 h after injury, and that anti-Ly6G/Gr-1 treatment reduced circulating neutrophils by >90% at these time points. Intravital and spinning disk confocal microscopy of the exposed posterior vein and postcapillary venules showed a significant reduction in rolling and adhering neutrophils in vivo after anti-Ly6G/Gr-1 treatment; this was accompanied by a parallel reduction in neutrophil numbers within the injured spinal cord at 24 and 48 h as determined by flow cytometry. The evolution of astrocyte reactivity, a wound healing response, was reduced in anti-Ly6G/Gr-1-treated mice, which also had less spared white matter and axonal preservation compared with isotype controls. These histological outcomes may be caused by alterations of growth factors and chemokines important in promoting wound healing. Importantly, anti-Ly6G/Gr-1 treatment worsened behavioral outcome as determined using the Basso Mouse Scale and subscores. Although the spectrum of cells affected by anti-Ly6G/Gr-1 antibody treatment cannot be fully ascertained at this point, the correspondence of neutrophil depletion and worsened recovery suggests that neutrophils promote recovery after SCI through wound healing and protective events that limit lesion propagation.

Blockade of the 5-HT3 receptor for days causes sustained relief from mechanical allodynia following spinal cord injury

Chronic neuropathic pain is a frequent, serious outcome of spinal cord injury (SCI) that is highly refractory to treatment. Serotonin can contribute to neuropathic pain after SCI, as suggested by our previous observation that transient blockade of the 5-HT(3) receptor by intrathecal injections of the antagonist ondansetron reduces mechanical allodynia after SCI in rats. The current study determined whether intrathecal or intravenous infusion of ondansetron for 3 or 7 days, respectively, could cause sustained blockade of mechanical allodynia at and below the level of a twelfth thoracic clip compression injury in rats. Intrathecal 3-day infusion of ondansetron (2.0 microg/hr), targeted to the cord rostral to the SCI and commencing at 28 days after SCI, decreased at-level mechanical allodynia by 40% and below-level allodynia by 60% compared with saline-treated rats (controls). This reduction was sustained throughout drug delivery and for 1 day afterward. During the next 3 days, allodynia gradually returned toward the values of saline-treated rats. An initial experiment showed that bolus intravenous injections of ondansetron (20-100 microg) at 28 days after SCI decreased both at- and below-level allodynia for 90-120 min. Intravenous 7-day infusions (20 microg/hr), commencing at 28 days after SCI, significantly decreased at-level allodynia by 48% and below-level allodynia by 51% compared with controls. This reduction of allodynia lasted throughout the infusion and for 1-3 days afterward while pain responses gradually approached those of controls. These findings suggest a potential role of 5-HT(3) receptor antagonism in the relief of neuropathic pain after SCI in humans.

Gene expression profiling in anti-CD11d mAb-treated spinal cord-injured rats

Acute administration of a mononclonal antibody (mAb) raised against the CD11d subunit of the leukocyte CD11d/CD18 integrin after spinal cord injury (SCI) in the rat greatly improves neurological outcomes. We have profiled gene expression in anti-CD11d and isotyped-matched control mAb-treated rats after SCI. Microarray analysis demonstrated reduced expression of pro-inflammatory cytokines and increased expression of inflammatory mediators that promote wound healing and the expression of scar proteins predicted to improve nerve growth. These changes in gene expression may reflect changes in the types of macrophages that populate the lesions in anti-CD11d mAb-treated rats.