Axonal and nonneuronal cell responses to spinal cord injury in mice lacking glial fibrillary acidic protein

AAV Vector Mediated Delivery of NG2 Function Neutralizing Antibody and Neurotrophin NT-3 Improves Synaptic Transmission, Locomotion, and Urinary Tract Function after Spinal Cord Contusion Injury in Adult Rats

NG2 is a structurally unique transmembrane chondroitin sulfate proteoglycan (CSPG). Its role in damaged spinal cord is dual. NG2 is considered one of key inhibitory factors restricting axonal growth following spinal injury. Additionally, we have recently detected its novel function as a blocker of axonal conduction. Some studies, however, indicate the importance of NG2 presence in the formation of synaptic contacts. We hypothesized that the optimal treatment would be neutralization of inhibitory functions of NG2 without its physical removal. Acute intraspinal injections of anti-NG2 monoclonal antibodies reportedly prevented an acute block of axonal conduction by exogenous NG2. For prolonged delivery of NG2 function neutralizing antibody, we have developed a novel gene therapy: adeno-associated vector (AAV) construct expressing recombinant single-chain variable fragment anti-NG2 antibody (AAV-NG2Ab). We examined effects of AAV-NG2Ab alone or in combination with neurotrophin NT-3 in adult female rats with thoracic T10 contusion injuries. A battery of behavioral tests was used to evaluate locomotor function. In vivo single-cell electrophysiology was used to evaluate synaptic transmission. Lower urinary tract function was assessed during the survival period using metabolic chambers. Terminal cystometry, with acquisition of external urethral sphincter activity and bladder pressure, was used to evaluate bladder function. Both the AAV-NG2Ab and AAV-NG2Ab combined with AAV-NT3 treatment groups demonstrated significant improvements in transmission, locomotion, and bladder function compared with the control (AAV-GFP) group. These functional improvements associated with improved remyelination and plasticity of 5-HT fibers. The best results were observed in the group that received combinational AAV-NG2Ab+AAV-NT3 treatment.SIGNIFICANCE STATEMENT We recently demonstrated beneficial, but transient, effects of neutralization of the NG2 proteoglycan using monoclonal antibodies delivered intrathecally via osmotic mini-pumps after spinal cord injury. Currently, we have developed a novel gene therapy tool for prolonged and clinically relevant delivery of a recombinant single-chain variable fragment anti-NG2 antibody: AAV-rh10 serotype expressing scFv-NG2 (AAV-NG2Ab). Here, we examined effects of AAV-NG2Ab combined with transgene delivery of Neurotrophin-3 (AAV-NT3) in adult rats with thoracic contusion injuries. The AAV-NG2Ab and AAV-NG2Ab+AAV-NT3 treatment groups demonstrated significant improvements of locomotor function and lower urinary tract function. Beneficial effects of this novel gene therapy on locomotion and bladder function associated with improved transmission to motoneurons and plasticity of axons in damaged spinal cord.

RNAi-mediated suppression of vimentin or glial fibrillary acidic protein prevents the establishment of Müller glial cell hypertrophy in progressive retinal degeneration

Gliosis is a complex process comprising upregulation of intermediate filament (IF) proteins, particularly glial fibrillary acidic protein (GFAP) and vimentin, changes in glial cell morphology (hypertrophy) and increased deposition of inhibitory extracellular matrix molecules. Gliosis is common to numerous pathologies and can have deleterious effects on tissue function and regeneration. The role of IFs in gliosis is controversial, but a key hypothesized function is the stabilization of glial cell hypertrophy. Here, we developed RNAi approaches to examine the role of GFAP and vimentin in vivo in a murine model of inherited retinal degeneration, the Rhodopsin knockout (Rho-/- ) mouse. Specifically, we sought to examine the role of these IFs in the establishment of Müller glial hypertrophy during progressive degeneration, as opposed to (more commonly assessed) acute injury. Prevention of Gfap upregulation had a significant effect on the morphology of reactive Müller glia cells in vivo and, more strikingly, the reduction of Vimentin expression almost completely prevented these cells from undergoing degeneration-associated hypertrophy. Moreover, and in contrast to studies in knockout mice, simultaneous suppression of both GFAP and vimentin expression led to severe changes in the cytoarchitecture of the retina, in both diseased and wild-type eyes. These data demonstrate a crucial role for Vimentin, as well as GFAP, in the establishment of glial hypertrophy and support the further exploration of RNAi-mediated knockdown of vimentin as a potential therapeutic approach for modulating scar formation in the degenerating retina.

Discrepancy in the Usage of GFAP as a Marker of Satellite Glial Cell Reactivity

Satellite glial cells (SGCs) surrounding the neuronal somas in peripheral sensory ganglia are sensitive to neuronal stressors, which induce their reactive state. It is believed that such induced gliosis affects the signaling properties of the primary sensory neurons and is an important component of the neuropathic phenotype leading to pain and other sensory disturbances. Efforts to understand and manipulate such gliosis relies on reliable markers to confirm induced SGC reactivity and ultimately the efficacy of targeted intervention. Glial fibrillary acidic protein (GFAP) is currently the only widely used marker for such analyses. However, we have previously described the lack of SGC upregulation of GFAP in a mouse model of sciatic nerve injury, suggesting that GFAP may not be a universally suitable marker of SGC gliosis across species and experimental models. To further explore this, we here investigate the regulation of GFAP in two different experimental models in both rats and mice. We found that whereas GFAP was upregulated in both rodent species in the applied inflammation model, only the rat demonstrated increased GFAP in SGCs following sciatic nerve injury; we did not observe any such GFAP upregulation in the mouse model at either protein or mRNA levels. Our results demonstrate an important discrepancy between species and experimental models that prevents the usage of GFAP as a universal marker for SGC reactivity.

Dual roles of astrocytes in plasticity and reconstruction after traumatic brain injury

Traumatic brain injury (TBI) is one of the leading causes of fatality and disability worldwide. Despite its high prevalence, effective treatment strategies for TBI are limited. Traumatic brain injury induces structural and functional alterations of astrocytes, the most abundant cell type in the brain. As a way of coping with the trauma, astrocytes respond in diverse mechanisms that result in reactive astrogliosis. Astrocytes are involved in the physiopathologic mechanisms of TBI in an extensive and sophisticated manner. Notably, astrocytes have dual roles in TBI, and some astrocyte-derived factors have double and opposite properties. Thus, the suppression or promotion of reactive astrogliosis does not have a substantial curative effect. In contrast, selective stimulation of the beneficial astrocyte-derived molecules and simultaneous attenuation of the deleterious factors based on the spatiotemporal-environment can provide a promising astrocyte-targeting therapeutic strategy. In the current review, we describe for the first time the specific dual roles of astrocytes in neuronal plasticity and reconstruction, including neurogenesis, synaptogenesis, angiogenesis, repair of the blood-brain barrier, and glial scar formation after TBI. We have also classified astrocyte-derived factors depending on their neuroprotective and neurotoxic roles to design more appropriate targeted therapies.

Müller glia reactivity follows retinal injury despite the absence of the glial fibrillary acidic protein gene in Xenopus

Intermediate filament proteins are structural components of the cellular cytoskeleton with cell-type specific expression and function. Glial fibrillary acidic protein (GFAP) is a type III intermediate filament protein and is up-regulated in glia of the nervous system in response to injury and during neurodegenerative diseases. In the retina, GFAP levels are dramatically increased in Müller glia and are thought to play a role in the extensive structural changes resulting in Müller cell hypertrophy and glial scar formation. In spite of similar changes to the morphology of Xenopus Müller cells following injury, we found that Xenopus lack a gfap gene. Other type III intermediate filament proteins were, however, significantly induced following rod photoreceptor ablation and retinal ganglion cell axotomy. The recently available X. tropicalis and X. laevis genomes indicate a small deletion most likely resulted in the loss of the gfap gene during anuran evolution. Lastly, a survey of representative species from all three extant amphibian orders including the Anura (frogs, toads), Caudata (salamanders, newts), and Gymnophiona (caecilians) suggests that deletion of the gfap locus occurred in the ancestor of all Anura after its divergence from the Caudata ancestor around 290 million years ago. Our results demonstrate that extensive changes in Müller cell morphology following retinal injury do not require GFAP in Xenopus, and other type III intermediate filament proteins may be involved in the gliotic response.

Glial fibrillary acidic protein: from intermediate filament assembly and gliosis to neurobiomarker

Glial fibrillary acidic protein (GFAP) is an intermediate filament (IF) III protein uniquely found in astrocytes in the central nervous system (CNS), non-myelinating Schwann cells in the peripheral nervous system (PNS), and enteric glial cells. GFAP mRNA expression is regulated by several nuclear-receptor hormones, growth factors, and lipopolysaccharides (LPSs). GFAP is also subject to numerous post-translational modifications (PTMs), while GFAP mutations result in protein deposits known as Rosenthal fibers in Alexander disease. GFAP gene activation and protein induction appear to play a critical role in astroglial cell activation (astrogliosis) following CNS injuries and neurodegeneration. Emerging evidence also suggests that, following traumatic brain and spinal cord injuries and stroke, GFAP and its breakdown products are rapidly released into biofluids, making them strong candidate biomarkers for such neurological disorders.

Role of GFAP in CNS injuries

The role of GFAP in CNS injury is reviewed as revealed by studies using GFAP null mice. In order to provide background information for these studies, the effects of absence of GFAP in the uninjured astrocyte are also described. Activities attributable to GFAP include suppressing neuronal proliferation and neurite extension in the mature brain, forming a physical barrier to isolate damaged tissue, regulating blood flow following ischemia, contributing to the blood-brain barrier, supporting myelination, and providing mechanical strength. However, findings for many of these roles have been variable among laboratories, pointing to the presence of unappreciated complexity in GFAP function. One complexity may be regional differences in GFAP activities; others are yet to be discovered.

Neutralization of inhibitory molecule NG2 improves synaptic transmission, retrograde transport, and locomotor function after spinal cord injury in adult rats

NG2 belongs to the family of chondroitin sulfate proteoglycans that are upregulated after spinal cord injury (SCI) and are major inhibitory factors restricting the growth of fibers after SCI. Neutralization of NG2's inhibitory effect on axon growth by anti-NG2 monoclonal antibodies (NG2-Ab) has been reported. In addition, recent studies show that exogenous NG2 induces a block of axonal conduction. In this study, we demonstrate that acute intraspinal injections of NG2-Ab prevented an acute block of conduction by NG2. Chronic intrathecal infusion of NG2-Ab improved the following deficits induced by chronic midthoracic lateral hemisection (HX) injury: (1) synaptic transmission to lumbar motoneurons, (2) retrograde transport of fluororuby anatomical tracer from L5 to L1, and (3) locomotor function assessed by automated CatWalk gait analysis. We collected data in an attempt to understand the cellular and molecular mechanisms underlying the NG2-Ab-induced improvement of synaptic transmission in HX-injured spinal cord. These data showed the following: (1) that chronic NG2-Ab infusion improved conduction and axonal excitability in chronically HX-injured rats, (2) that antibody treatment increased the density of serotonergic axons with ventral regions of spinal segments L1-L5, (3) and that NG2-positive processes contact nodes of Ranvier within the nodal gap at the location of nodal Na(+) channels, which are known to be critical for propagation of action potentials along axons. Together, these results demonstrate that treatment with NG2-Ab partially improves both synaptic and anatomical plasticity in damaged spinal cord and promotes functional recovery after HX SCI. Neutralizing antibodies against NG2 may be an excellent way to promote axonal conduction after SCI.

The effect of glial fibrillary acidic protein expression on neurite outgrowth from retinal explants in a permissive environment

Background

Increased expression of glial fibrillary acidic protein (GFAP) within macroglia is commonly seen as a hallmark of glial activation after damage within the central nervous system, including the retina. The increased expression of GFAP in glia is also considered part of the pathologically inhibitory environment for regeneration of axons from damaged neurons. Recent studies have raised the possibility that reactive gliosis and increased GFAP cannot automatically be assumed to be negative events for the surrounding neurons and that the context of the reactive gliosis is critical to whether neurons benefit or suffer. We utilized transgenic mice expressing a range of Gfap to titrate the amount of GFAP in retinal explants to investigate the relationship between GFAP concentration and the regenerative potential of retinal ganglion cells.

Findings

Explants from Gfap^-/- and Gfap^+/- mice did not have increased neurite outgrowth compared with Gfap^+/+ or Gfap over-expressing mice as would be expected if GFAP was detrimental to axon regeneration. In fact, Gfap over-expressing explants had the most neurite outgrowth when treated with a neurite stimulatory media. Transmission electron microscopy revealed that neurites formed bundles, which were surrounded by larger cellular processes that were GFAP positive indicating a close association between growing axons and glial cells in this regeneration paradigm.

Conclusions

We postulate that glial cells with increased Gfap expression support the elongation of new neurites from retinal ganglion cells possibly by providing a scaffold for outgrowth.

Distinct spatio-temporal extracellular matrix accumulation within demyelinated spinal cord lesions in Theiler's murine encephalomyelitis

The accumulation of extracellular matrix (ECM) and glial scar formation are considered important factors for the failure of regeneration in central nervous system (CNS) injury and multiple sclerosis. Theiler's murine encephalomyelitis (TME) as a model of multiple sclerosis served to evaluate the spatio-temporal course of ECM alterations in demyelinating conditions. Microarray analysis revealed only mildly upregulated gene expression of ECM molecules, their biosynthesis pathways and pro-fibrotic factors, while upregulation of matrix remodeling enzymes was more prominent. Immunohistochemistry demonstrated progressive accumulation of chondroitin sulfate proteoglycans, glycoproteins and collagens within demyelinated TME lesions, paralleling the development of astrogliosis. Deposition of collagen IV, laminin, perlecan and tenascin-C started 28 days postinfection (dpi), collagen I, decorin, entactin and neurocan accumulated from 56 dpi on, and fibronectin from 98 dpi on. The basement membrane (BM) molecules collagen IV, entactin, fibronectin, laminin and perlecan showed perivascular and parenchymal deposition, while the non-BM components collagen I, decorin, neurocan and tenascin-C only accumulated in a nonvascular pattern in demyelinated areas. Contrary, phosphacan expression progressively decreased during TME. The immunoreactivity of aggrecan and brevican remained unchanged. The spatio-temporal association of matrix accumulation with astrogliosis suggests a mainly astrocytic origin of ECM deposits, which in turn may contribute to remyelination failure in TME.

Role of chondroitin sulfate proteoglycans in axonal conduction in Mammalian spinal cord

Chronic unilateral hemisection (HX) of the adult rat spinal cord diminishes conduction through intact fibers in the ventrolateral funiculus (VLF) contralateral to HX. This is associated with a partial loss of myelination from fibers in the VLF (Arvanian et al., 2009). Here, we again measured conduction through the VLF using electrical stimulation while recording the resulting volley and synaptic potentials in target motoneurons. We found that intraspinal injection of chondroitinase-ABC, known to digest chondroitin sulfate proteoglycans (CSPGs), prevented the decline of axonal conduction through intact VLF fibers across from chronic T10 HX. Chondroitinase treatment was also associated with behavior suggestive of an improvement of locomotor function after chronic HX. To further study the role of CSPGs in axonal conduction, we injected three purified CSPGs, NG2 and neurocan, which increase in the vicinity of a spinal injury, and aggrecan, which decreases, into the lateral column of the uninjured cord at T10 in separate experiments. Intraspinal injection of NG2 acutely depressed axonal conduction through the injected region in a dose-dependent manner. Similar injections of saline, aggrecan, or neurocan had no significant effect. Immunofluorescence staining experiments revealed the presence of endogenous and exogenous NG2 at some nodes of Ranvier. These results identify a novel acute action of CSPGs on axonal conduction in the spinal cord and suggest that antagonism of proteoglycans reverses or prevents the decline of axonal conduction, in addition to stimulating axonal growth.

The molecular cloning of glial fibrillary acidic protein in Gekko japonicus and its expression changes after spinal cord transection

The glial fibrillary acidic protein (GFAP) is an astrocyte-specific member of the class III intermediate filament proteins. It is generally used as a specific marker of astrocytes in the central nervous system (CNS). We isolated a GFAP cDNA from the brain and spinal cord cDNA library of Gekko japonicus, and prepared polyclonal antibodies against gecko GFAP to provide useful tools for further immunochemistry studies. Both the real-time quantitative PCR and western blot results revealed that the expression of GFAP in the spinal cord after transection increased, reaching its maximum level after 3 days, and then gradually decreased over the rest of the 2 weeks of the experiment. Immunohistochemical analyses demonstrated that the increase in GFAP-positive labeling was restricted to the white matter rather than the gray matter. In particular, a slight increase in the number of GFAP positive star-shaped astrocytes was detected in the ventral and lateral regions of the white matter. Our results indicate that reactive astrogliosis in the gecko spinal cord took place primarily in the white matter during a short time interval, suggesting that the specific astrogliosis evaluated by GFAP expression might be advantageous in spinal cord regeneration.

EphA4 deficient mice maintain astroglial-fibrotic scar formation after spinal cord injury

One important aspect of recovery and repair after spinal cord injury (SCI) lies in the complex cellular interactions at the injury site that leads to the formation of a lesion scar. EphA4, a promiscuous member of the EphA family of repulsive axon guidance receptors, is expressed by multiple cell types in the injured spinal cord, including astrocytes and neurons. We hypothesized that EphA4 contributes to aspects of cell-cell interactions at the injury site after SCI, thus modulating the formation of the astroglial-fibrotic scar. To test this hypothesis, we studied tissue responses to a thoracic dorsal hemisection SCI in an EphA4 mutant mouse line. We found that EphA4 expression, as assessed by beta-galactosidase reporter gene activity, is associated primarily with astrocytes in the spinal cord, neurons in the cerebral cortex and, to a lesser extent, spinal neurons, before and after SCI. However, we did not observe any overt reduction of glial fibrillary acidic protein (GFAP) expression in the injured area of EphA4 mutants in comparison with controls following SCI. Furthermore, there was no evident disruption of the fibrotic scar, and the boundary between reactive astrocytes and meningeal fibroblasts appeared unaltered in the mutants, as were lesion size, neuronal survival and inflammation marker expression. Thus, genetic deletion of EphA4 does not significantly alter the astroglial response or the formation of the astroglial-fibrotic scar following a dorsal hemisection SCI in mice. In contrast to what has been proposed, these data do not support a major role for EphA4 in reactive astrogliosis following SCI.

Adult NG2+ cells are permissive to neurite outgrowth and stabilize sensory axons during macrophage-induced axonal dieback after spinal cord injury

We previously demonstrated that activated ED1+ macrophages induce extensive axonal dieback of dystrophic sensory axons in vivo and in vitro. Interestingly, after spinal cord injury, the regenerating front of axons is typically found in areas rich in ED1+ cells, but devoid of reactive astrocyte processes. These observations suggested that another cell type must be present in these areas to counteract deleterious effects of macrophages. Cells expressing the purportedly inhibitory chondroitin sulfate proteoglycan NG2 proliferate in the lesion and intermingle with macrophages, but their influence on regeneration is highly controversial. Our in vivo analysis of dorsal column crush lesions confirms the close association between NG2+ cells and injured axons. We hypothesized that NG2+ cells were growth promoting and thereby served to increase axonal stability following spinal cord injury. We observed that the interactions between dystrophic adult sensory neurons and primary NG2+ cells derived from the adult spinal cord can indeed stabilize the dystrophic growth cone during macrophage attack. NG2+ cells expressed high levels of laminin and fibronectin, which promote neurite outgrowth on the surface of these cells. Our data also demonstrate that NG2+ cells, but not astrocytes, use matrix metalloproteases to extend across a region of inhibitory proteoglycan, and provide a permissive bridge for adult sensory axons. These data support the hypothesis that NG2+ cells are not inhibitory to regenerating sensory axons and, in fact, they may provide a favorable substrate that can stabilize the regenerating front of dystrophic axons in the inhibitory environment of the glial scar.

Spinal cord injury: emerging beneficial role of reactive astrocytes' migration

Spinal cord injury (SCI), despite considerable progress in palliative care, has currently no satisfying therapeutic leading to functional recovery. Inability of central nervous system severed axons to regenerate after injury is considered to originate from both limited intrinsic capabilities of neurons and inhibitory effect of the local environment. Precisely, the so-called "glial scar" formed by reactive astrocytes in response to injury exerts a well-known axon-outgrowth inhibitory effect. However, recent studies revealed that role of reactive astrocytes after SCI is more complex. During the first weeks after injury, reactive astrocytes indeed protect the tissue and contribute to a spontaneous relative functional recovery. Compaction of the lesion center and seclusion of inflammatory cells by migrating reactive astrocytes seem to underlie this beneficial effect. Stimulation of reactive astrocytes migration in the sub-acute phase of SCI might thus represent a new approach to improve the functional outcome of patients.

Netrin-1 is a novel myelin-associated inhibitor to axon growth

We investigated the influence of the bifunctional guidance molecule netrin-1 on axonal growth in the injured adult spinal cord. In the adult, netrin-1 is expressed on mature oligodendrocytes, cells of the central canal, and the meninges. Netrin-1 protein in white matter is selectively enriched adjacent to paranodal loops of myelin in nodes of Ranvier. The repulsion-mediating netrin-1 uncoordinated-5 (UNC5) receptors are expressed by neurons of the corticospinal and rubrospinal projections, and by intrinsic neurons of the spinal cord, both before and after spinal cord injury. Neutralization of netrin-1 in myelin prepared from adult rat spinal cord using UNC5 receptor bodies increases neurite outgrowth from UNC5-expressing spinal motor neurons in vitro. Furthermore, axon regeneration is inhibited in a netrin-1-enriched zone, devoid of other myelin-associated inhibitors, within spinal cord lesion sites in vivo. We conclude that netrin-1 is a novel oligodendrocyte-associated inhibitor that can contribute to axonal growth failure after adult spinal cord injury.

Vimentin-positive astrocytes in canine distemper: a target for canine distemper virus especially in chronic demyelinating lesions?

In canine distemper demyelinating leukoencephalitis (DL), caused by canine distemper virus (CDV), astrocytes represent the main virus target. In these cells, glial fibrillary acidic protein (GFAP) is the main intermediate filament, whereas vimentin occurs early in the astrocytic lineage and is replaced gradually by GFAP. To further characterize the role of astrocytic infection in dogs with DL, an animal model for multiple sclerosis, formalin-fixed paraffin-embedded cerebella were investigated immunohistochemically and by immunofluorescence. The expression and morphological alterations of these intermediate filaments were also determined by immunofluorescence studies of CDV-infected canine mixed brain cell cultures. In acute distemper lesions, the astrocytic response was mainly composed of GFAP- and CDV-positive cells. In contrast, vimentin-positive astrocyte-like cells were present in advanced lesions, which represented the main cell type harboring the pathogen, indicating a change in cell tropism and/or susceptibility of glial cells during lesion progression in CDV encephalomyelitis. Canine cell cultures were composed of GFAP-positive astrocytes, vimentin-positive cells and other glial cells. Following infection with the CDV-R252 strain, GFAP-positive astrocytes, especially multinucleated syncytial giant cells, displayed a disrupted cytoskeleton, whereas vimentin-positive cells though more frequently infected did not show any alteration in the filament network. This indicates increased vulnerability of mature GFAP-positive astrocytes compared to immature, vimentin-positive astrocytes. The latter, however, exhibited increased susceptibility to CDV. To conclude, the present findings indicate a change in cell tropism of CDV and/or the occurrence of less differentiated astrocytes representing a permanent source for virus infection and spread in advanced lesions of DL.

Extracellular adenosine triphosphate induces glutamate transporter-1 expression in hippocampus

ATP can be significantly released following various brain insults and activates the extracellular signal-regulated protein kinase (ERK) pathway in astrocytes. Glutamate transporter-1 (GLT1) is the major forebrain astroglial glutamate transporter and its expression is stimulated also via ERK1/2 phosphorylation. We thus hypothesized that extracellular ATP could be a signal to GLT1 modulation in hippocampal slices obtained from rat. We indeed observed by western blot analysis that, after 1 mM ATP exposure, GLT1 expression, but not the glutamate-aspartate transporter, was enhanced. At the same time, high ATP induced significant rates of cell death in piramidal and granule cell layers, as shown by propidium iodide uptake, and increased glutamate uptake through GLT1 transporter. Also using confocal laser-scanning microscopy, we observed that ATP induced a vigorous and extensive GLT1-labeling on glial fibrillary acidic protein-positive cells. This stimulation was abolished by purine/pyrimidine nucleotide receptor antagonists and by MEK1/2 inhibitor. The present study demonstrates a novel mechanism of GLT1 regulation by extracellular ATP, reinforcing the evidence of cross talk between glutamatergic and purinergic systems.

Behavioral, histological, and ex vivo magnetic resonance imaging assessment of graded contusion spinal cord injury in mice

This study characterized the Infinite Horizon (IH) Impactor for use in mouse models of contusion spinal cord injury (SCI), and investigated the feasibility and reliability of using magnetic resonance imaging (MRI) as a method to accurately measure lesion volume after mouse contusion SCI. Eight-week-old female C57Bl/6 mice received a mild (30 kilodyne), moderate (50 kilodyne), or severe (70 kilodyne) contusion injury at the T9 vertebral level. Uninjured control mice received a T9 laminectomy only. Functional recovery was assessed using the Basso, Beattie, Bresnahan (BBB) and Basso Mouse Scale (BMS) open-field locomotor rating scales. Next, 4% paraformaldehyde-perfused spinal cords were collected between the T6 and T12 spinal roots, and stored in phosphate-buffered saline (PBS) at 4 degrees C until MRI analysis. MRI lesion volumes were determined using T1-weighted images on a 7-Tesla MRI. Histology was performed on 20-microm polyester wax-embedded sections processed from the same spinal cords for stereological determination of fibronectin lesion volume and myelin basic protein spared white matter volume. Area of spared white matter at the epicenter was also analyzed. The results demonstrated that the IH Impactor produced precise, graded contusion SCI in mice. Lesion volumes were positively correlated with force of impact, and negatively correlated with spared white matter and functional recovery. Additionally, similar lesion volumes were detected using fibronectin staining and MRI analysis, although MRI may be more sensitive for milder injuries. These results give researchers more options in how to analyze spinal cord injuries in animal models.

Adeno-associated virus-mediated L1 expression promotes functional recovery after spinal cord injury

Paucity of permissive molecules and abundance of inhibitory molecules in the injured spinal cord of adult mammals prevent axons from successful regeneration and, thus, contribute to the failure of functional recovery. Using an adeno-associated viral (AAV) vector, we expressed the regeneration-promoting cell adhesion molecule L1 in both neurons and glia in the lesioned spinal cord of adult mice. Exogenous L1, detectable already 1 week after thoracic spinal cord compression and immediate vector injection, was expressed at high levels up to 5 weeks, the longest time-period studied. Dissemination of L1-transduced cells throughout the spinal cord was wide, spanning over more than 10 mm rostral and 10 mm caudal to the lesion scar. L1 was not detectable in the fibronectin-positive lesion core. L1 overexpression led to improved stepping abilities and muscle coordination during ground locomotion over a 5-week observation period. Superior functional improvement was associated with enhanced reinnervation of the lumbar spinal cord by 5-HT axons. Corticospinal tract axons did not regrow beyond the lesion scar but extended distally into closer proximity to the injury site in AAV-L1-treated compared with control mice. The expression of the neurite outgrowth-inhibitory chondroitin sulphate proteoglycan NG2 was decreased in AAV-L1-treated spinal cords, along with reduction of the reactive astroglial marker GFAP. In vitro experiments confirmed that L1 inhibits astrocyte proliferation, migration, process extension and GFAP expression. Analyses of intracellular signalling indicated that exogenous L1 activates diverse cascades in neurons and glia. Thus, AAV-mediated L1 overexpression appears to be a potent means to favourably modify the local environment in the injured spinal cord and promote regeneration. Our study demonstrates a clinically feasible approach of promising potential.

The role of astrocytes and complement system in neural plasticity

In neurotrauma, brain ischemia or neurodegenerative diseases, astrocytes become reactive (which is known as reactive gliosis) and this is accompanied by an altered expression of many genes. Two cellular hallmarks of reactive gliosis are hypertrophy of astrocyte processes and the upregulation of the part of the cytoskeleton known as intermediate filaments, which are composed of nestin, vimentin, and GFAP. Our aim has been to better understand the function of reactive astrocytes in CNS diseases. Using mice deficient for astrocyte intermediate filaments (GFAP(-/-)Vim(-/-)), we were able to attenuate reactive gliosis and slow down the healing process after neurotrauma. We demonstrated the key role of reactive astrocytes in neurotrauma-at an early stage after neurotrauma, reactive astrocytes have a neuroprotective effect; at a later stage, they facilitate the formation of posttraumatic glial scars and inhibit CNS regeneration, specifically, they seem to compromise neural graft survival and integration, reduce the extent of synaptic regeneration, inhibit neurogenesis in the old age, and inhibit regeneration of severed CNS axons. We propose that reactive astrocytes are the future target for the therapeutic strategies promoting regeneration and plasticity in the brain and spinal cord in various disease conditions. Through its involvement in inflammation, opsonization, and cytolysis, complement protects against infectious agents. Although most of the complement proteins are synthesized in CNS, the role of the complement system in the normal or ischemic CNS remains unclear. Complement activiation in the CNS has been generally considered as contributing to tissue damage. However, growing body of evidence suggests that complement may be a physiological neuroprotective mechanism as well as it may participate in maintenance and repair of the adult brain.

Genetic mouse models for studying inhibitors of spinal axon regeneration

The laboratory mouse has emerged as a primary model organism for studying axon regeneration after experimental spinal cord injury, owing to its genetic amenability. Mutant mouse models are contributing significantly to our understanding of the molecular mechanisms of axon regeneration failure in the adult mammalian central nervous system (CNS), in particular regarding the role of axon-growth inhibitors. Here, we discuss recent advances in understanding axon regeneration failure that have been made using genetically modified mice, focusing on the inhibitory influences in the CNS, and we illustrate the advantages of using the mouse as a surrogate organism to study axon regeneration and spinal cord repair.

Characterization of non-neuronal elements within fibronectin mats implanted into the damaged adult rat spinal cord

Previous studies have shown that mats made from fibronectin (FN) integrate well into spinal cord lesion sites and support extensive axonal growth. Using immunohistochemistry, we have investigated the non-neuronal factors that contribute to these properties. Extensive vascularization was observed in FN mats by 1 week along with heavy macrophage infiltration by 3 days post-implantation. By 1 week post-implantation, laminin tubules had formed and were associated with axons and p75 immunoreactive Schwann cells. By 4 weeks post-implantation, most axons were associated with Schwann cell derived myelin. Few oligodendrocytes were present within the mat, even with an increase in the number of oligodendrocyte precursors around the implant site by 7 days post-implantation. Astrocyte proliferation also occurred in the intact tissue, with a prominent glial scar forming around the implant within 4 weeks. However, by 2 months post-implantation astrocytes were present in the FN implant site and were intermingled with the axons. Axonal ingrowth and integration of the FN mats is probably due to the ability of FN mats to support and organize infiltration of Schwann cells and deposition of laminin. At later time points, myelinated axons remain in the implant site, even after other elements (e.g. macrophages and laminin) have disappeared. Both of these properties are likely to be important in the design of biomaterial bridges for CNS regeneration.

Astrocyte activation and reactive gliosis

Astrocytes become activated (reactive) in response to many CNS pathologies, such as stroke, trauma, growth of a tumor, or neurodegenerative disease. The process of astrocyte activation remains rather enigmatic and results in so-called "reactive gliosis," a reaction with specific structural and functional characteristics. In stroke or in CNS trauma, the lesion itself, the ischemic environment, disrupted blood-brain barrier, the inflammatory response, as well as in metabolic, excitotoxic, and in some cases oxidative crises--all affect the extent and quality of reactive gliosis. The fact that astrocytes function as a syncytium of interconnected cells both in health and in disease, rather than as individual cells, adds yet another dimension to this picture. This review focuses on several aspects of astrocyte activation and reactive gliosis and discusses its possible roles in the CNS trauma and ischemia. Particular emphasis is placed on the lessons learnt from mouse genetic models in which the absence of intermediate filament proteins in astrocytes leads to attenuation of reactive gliosis with distinct pathophysiological and clinical consequences.

Astrocyte intermediate filaments in CNS pathologies and regeneration

Astroglial cells are the most abundant cells in the mammalian central nervous system (CNS), yet our knowledge about their function in health and disease has been limited. This review focuses on the recent work addressing the function of intermediate filaments in astroglial cells under severe mechanical or osmotic stress, in hypoxia, and in brain and spinal cord injury. Recent data show that when astrocyte intermediate filaments are genetically ablated in mice, reactive gliosis is attenuated and the course of several CNS pathologies is altered, while the signs of CNS regeneration become more prominent. GFAP is the principal astrocyte intermediate filament protein and dominant mutations in the GFAP gene have been shown to lead to Alexander disease, a fatal neurodegenerative condition in humans.

Long-term changes in the molecular composition of the glial scar and progressive increase of serotoninergic fibre sprouting after hemisection of the mouse spinal cord

The scarring process occurring after adult central nervous system injury and the subsequent increase in the expression of certain extracellular matrix molecules are known to contribute to the failure of axon regeneration. This study provides an immunohistochemical analysis of temporal changes (8 days to 1 year) in the cellular and molecular response of the Swiss mouse spinal cord to a dorsal hemisection and its correlation with the axonal growth properties of a descending pathway, the serotoninergic axons. In this lesion model, no cavity forms at the centre of the lesion. Instead, a dense fibronectin-positive tissue matrix occupies the centre of the lesion, surrounded by a glial scar mainly constituted by reactive astrocytes. NG2 proteoglycan and tenascin-C, potential axon growth inhibitors, are constantly associated with the central region. In the glial scar, tenascin-C is never observed and the expression of chondroitin sulphate proteoglycans (revealed with CS-56 and anti-NG2 antibodies) highly increases in the week following injury to progressively return to their control level. In parallel, there is an increasing expression of the polysialilated neural cell adhesion molecule by reactive astrocytes. These molecular changes are correlated with a sprouting process of serotoninergic axons in the glial scar, except in a small area in contact with the central region. All these observations suggest that while a part of the glial scar progressively becomes permissive to axon regeneration after mouse spinal cord injury, the border of the glial scar, in contact with the fibronectin-positive tissue matrix, is the real barrier to prevent axon regeneration.

Glial fibrillary acidic protein gene promoter is differently modulated by transforming growth factor-beta 1 in astrocytes from distinct brain regions

The expression of glial fibrillary acidic protein (GFAP), the major intermediate filament protein of mature astrocytes, is regulated under developmental and pathological conditions. Recently, we have investigated GFAP gene modulation by using a transgenic mouse bearing part of the GFAP gene promoter linked to the beta-galactosidase reporter gene. We demonstrated that cerebral cortex neurons activate the GFAP gene promoter, inducing transforming growth factor-beta 1 (TGF-beta 1) secretion by astrocytes. Here, we report that cortical neurons or conditioned medium derived from them do not activate the GFAP gene promoter of transgenic astrocytes derived from midbrain and cerebellum suggesting a neuroanatomical regional specificity of this phenomenon. Surprisingly, they do induce synthesis of TGF-beta 1 by these cells. Western blot and immunocytochemistry assays revealed wild distribution of TGF receptor in all subpopulations of astrocytes and expression of TGF-beta 1 in neurons derived from all regions, thus indicating that the unresponsiveness of the cerebellar and midbrain GFAP gene to TGF-beta 1 is not due to a defect in TGF-beta 1 signalling. Together, our data highlight the great complexity of neuron-glia interactions and might suggest a distinct mechanism underlying modulation of the GFAP gene in the heterogeneous population of astrocytes throughout the central nervous system.

Molecular approaches to spinal cord repair

Axon growth inhibitors associated with myelin and the glial scar contribute to the failure of axon regeneration in the injured adult mammalian central nervous system (CNS). A number of these inhibitors, their receptors, and signaling pathways have been identified. These inhibitors can now be neutralized by a variety of approaches that point to the possibility of developing new therapeutic strategies to stimulate regeneration after spinal cord injury.

Robust neural integration from retinal transplants in mice deficient in GFAP and vimentin

With recent progress in neuroscience and stem-cell research, neural transplantation has emerged as a promising therapy for treating CNS diseases. The success of transplantation has been limited, however, by the restricted ability of neural implants to survive and establish neuronal connections with the host. Little is known about the mechanisms responsible for this failure. Neural implantation triggers reactive gliosis, a process accompanied by upregulation of intermediate filaments in astrocytes and formation of astroglial scar tissue. Here we show that the retinas of adult mice deficient in glial fibrillary acidic protein and vimentin, and consequently lacking intermediate filaments in reactive astrocytes and Müller cells, provide a permissive environment for grafted neurons to migrate and extend neurites. The transplanted cells integrated robustly into the host retina with distinct neuronal identity and appropriate neuronal projections. Our results indicate an essential role for reactive astroglial cells in preventing neural graft integration after transplantation.

Axonal plasticity and functional recovery after spinal cord injury in mice deficient in both glial fibrillary acidic protein and vimentin genes

The lack of axonal regeneration in the injured adult mammalian spinal cord leads to permanent functional disabilities. The inability of neurons to regenerate their axon is appreciably due to an inhospitable environment made of an astrocytic scar. We generated mice knock-out for glial fibrillary acidic protein and vimentin, the major proteins of the astrocyte cytoskeleton, which are upregulated in reactive astrocytes. These animals, after a hemisection of the spinal cord, presented reduced astroglial reactivity associated with increased plastic sprouting of supraspinal axons, including the reconstruction of circuits leading to functional restoration. Therefore, improved anatomical and functional recovery in the absence of both proteins highlights the pivotal role of reactive astrocytes in axonal regenerative failure in adult CNS and could lead to new therapies of spinal cord lesions.

Increased adenine nucleotide translocator 1 in reactive astrocytes facilitates glutamate transport

A hallmark of central nervous system (CNS) pathology is reactive astrocyte production of the chronic glial scar that is inhibitory to neuronal regeneration. The reactive astrocyte response is complex; these cells also produce neurotrophic factors and are responsible for removal of extracellular glutamate, the excitatory neurotransmitter that rises to neurotoxic levels in injury and disease. To identify genes expressed by reactive astrocytes, we employed an in vivo model of the glial scar and differential display PCR and found an increase in the level of Ant1, a mitochondrial ATP/ADP exchanger that facilitates the flux of ATP out of the mitochondria. Ant1 expression in reactive astrocytes is regulated by transforming growth factor-beta1, a pluripotent CNS injury-induced cytokine. The significance of increased Ant1 is evident from the observation that glutamate uptake is significantly decreased in astrocytes from Ant1 null mutant mice while a specific Ant inhibitor reduces glutamate uptake in wild-type astrocytes. Thus, the astrocytic response to CNS injury includes an apparent increase in energy mobilization capacity by Ant1 that contributes to neuroprotective, energy-dependent glutamate uptake.

Vaccination stimulates retinal ganglion cell regeneration in the adult optic nerve

We examined whether vaccination of adult rats with spinal cord homogenate (SCH) can promote regeneration of retinal ganglion cells (RGCs) after microcrush lesion of the optic nerve. Injured animals vaccinated with SCH showed axon growth into the optic nerve and such regeneration was not observed in animals vaccinated with liver homogenate (LH). Regeneration was not a consequence of neuroprotection since our vaccine did not protect RGCs from axotomy-induced cell death. Sera of vaccinated animals were tested for antibodies against myelin-associated glycoprotein, NogoA, Nogo-66 receptor, or chondroitin sulphate proteoglycans (CSPG), but no significant levels were detected. Antibodies to myelin basic protein were present in the serum of some SCH-vaccinated animals. In culture, serum from SCH-vaccinated animals promoted RGC growth on myelin but not on CSPG. Our results show that the effect of the pro-regenerative vaccine is mediated by antibodies to SCH. However, we were not able to detect a significant immune reaction to growth inhibitory proteins, suggesting alternative mechanisms for the success of vaccination to promote regeneration.

Neuro-glia interaction effects on GFAP gene: a novel role for transforming growth factor-beta1

Central nervous system (CNS) development is highly guided by microenvironment cues specially provided by neuron-glia interactions. By using a transgenic mouse bearing part of the gene promoter of the astrocytic maturation marker GFAP (glial fibrillary acidic protein) linked to the beta-galactosidase (beta-Gal) reporter gene, we previously demonstrated that cerebral cortical neurons increase transgenic beta-Gal astrocyte number and activate GFAP gene promoter by secretion of soluble factors in vitro. Here, we identified TGF-beta1 as the major mediator of this event. Identification of TGF-beta1 in neuronal and astrocyte extracts revealed that both cell types might synthesize this factor, however, addition of neurons to astrocyte monolayers greatly increased TGF-beta1 synthesis and secretion by astrocytes. Further, by exploiting the advantages of cell culture system we investigated the influence of neuron and astrocyte developmental stage on such interaction. We demonstrated that younger neurons derived from 14 embryonic days wild-type mice were more efficient in promoting astrocyte differentiation than those derived from 18 embryonic days mice. Similarly, astrocytes also exhibited timed-schedule developed responsiveness to neuronal influence with embryonic astrocytes being more responsive to neurons than newborn and late postnatal astrocytes. RT-PCR assays identified TGF-beta1 transcripts in young but not in old neurons, suggesting that inability to induce astrocyte differentiation is related to TGF-beta1 synthesis and secretion. Our work reveals an important role for neuron-glia interactions in astrocyte development and strongly implicates the involvement of TGF-beta1 in this event.

Development and characterization of a novel, graded model of clip compressive spinal cord injury in the mouse: Part 1. Clip design, behavioral outcomes, and histopathology

In order to take advantage of various genetically manipulated mice available to study the pathophysiology of spinal cord injury (SCI), we adapted an extradural clip compression injury model to the mouse (FEJOTA mouse clip). The dimensions of the modified aneurysm clip blades were customized for application to the mouse spinal cord. Three clips with different springs were made to produce differing magnitudes of closing force (3, 8, and 24 g). The clips were calibrated regularly to ensure that the closing force remained constant. The surgical procedure involved a laminectomy at T3 and T4, followed by extradural application of the clip at this level for 1 min to produce SCI. Three injury severities (3, 8, and 24 g), sham (passage of dissector extradurally at T3-4), and transection control groups were examined (n = 12/group). Quantitative behavioural assessments using the Basso, Beattie, and Bresnahan (BBB; H > 46; df = 4; p < 0.001; Kruskal-Wallis one-way ANOVA) and inclined plane (IP; F = 123; df = 4; p < 0.0001; two-way repeated measures ANOVA) tests showed a significant graded increase in neurological deficits with increasing severity of injury. By day 14, the motor recovery of the mice plateaued. Qualitative examination of the injury site morphology indicated that microcystic cavitation, degenerating axons, and robust astrogliosis were characteristic of the murine response to clip compressive SCI. Morphometric analyses of H&E/Luxol Fast Blue stained sections at every 50 microm from the injury epicenter indicated that with greater injury severity there was a progressive decrease in residual tissue (F = 220, df = 3; p < 0.0001; two-way ANOVA). In addition, statistically significant differences were found in the amount of residual tissue at the injury epicenter between all of the injury severities (p < 0.05, SNK test). This novel, graded compressive model of SCI will facilitate future studies of the pathological mechanisms of SCI using transgenic and knockout murine systems.

Disturbance of hippocampal long-term potentiation after transient ischemia in GFAP deficient mice

GFAP (glial fibrillary acidic protein) is an intermediate filament protein found exclusively in the astrocytes of the central nervous system. We studied the role of GFAP in the neuronal degeneration in the hippocampus after transient ischemia using knockout mice. Wild-type C57 Black/6 (GFAP(+/+)) mice and mutant (GFAP(-/-)) mice were subjected to occlusion of both carotid arteries for 5-15 min. Hippocampal slices were prepared 3 days after reperfusion and the field excitatory postsynaptic potentials (fEPSP) in the CA1 were recorded. High frequency stimulation induced robust long-term potentiation (LTP) in GFAP(-/-), as in GFAP(+/+) mice. After ischemia, however, the LTP in GFAP(-/-) was significantly depressed. Similarly, paired pulse facilitation (PPF) displayed little difference between GFAP(+/+) and GFAP(-/-), but after ischemia, the PPF in GFAP(-/-) showed a depression. Histological study revealed that loss of CA1 and CA3 pyramidal neurons after ischemia was marked in GFAP(-/-). MAP2 (dendritic) immunostaining in the post-ischemic hippocampus showed little difference but NF200 (axonal) immunoreactivity was reduced in GFAP(-/-). S100beta (glial) immunoreactivity was similar in the post-ischemic hippocampus of the GFAP(+/+) and GFAP(-/-), indicating that reactive astrocytosis did not require GFAP. Our results suggest that GFAP has an important role in astrocyte-neural interactions and that ischemic insult impairs LTP and accelerates neuronal death.

Inactivation of the glial fibrillary acidic protein gene, but not that of vimentin, improves neuronal survival and neurite growth by modifying adhesion molecule expression

Intermediate filaments (IFs) are a major component of the cytoskeleton in astrocytes. Their role is far from being completely understood. Immature astrocytes play a major role in neuronal migration and neuritogenesis, and their IFs are mainly composed of vimentin. In mature differentiated astrocytes, vimentin is replaced by the IF protein glial fibrillary acidic protein (GFAP). In response to injury of the CNS in the adult, astrocytes become reactive, upregulate the expression of GFAP, and reexpress vimentin. These modifications contribute to the formation of a glial scar that is obstructive to axonal regeneration. Nevertheless, astrocytes in vitro are considered to be the ideal substratum for the growth of embryonic CNS axons. In the present study, we have examined the potential role of these two major IF proteins in both neuronal survival and neurite growth. For this purpose, we cocultured wild-type neurons on astrocytes from three types of knock-out (KO) mice for GFAP or/and vimentin in a neuron-astrocyte coculture model. We show that the double KO astrocytes present many features of immaturity and greatly improve survival and neurite growth of cocultured neurons by increasing cell-cell contact and secreting diffusible factors. Moreover, our data suggest that the absence of vimentin is not a key element in the permissivity of the mutant astrocytes. Finally, we show that only the absence of GFAP is associated with an increased expression of some extracellular matrix and adhesion molecules. To conclude, our results suggest that GFAP expression is able to modulate key biochemical properties of astrocytes that are implicated in their permissivity.

Modulating astrogliosis after neurotrauma

Traumatic injury to the adult central nervous system (CNS) results in a rapid response from resident astrocytes, a process often referred to as reactive astrogliosis or glial scarring. The robust formation of the glial scar and its associated extracellular matrix (ECM) molecules have been suggested to interfere with any subsequent neural repair or CNS axonal regeneration. A series of recent in vivo experiments has demonstrated a distinct inhibitory influence of the glial scar on axonal regeneration. Here we review several experimental strategies designed to elucidate the roles of astrocytes and their associated ECM molecules after CNS damage, including astrocyte ablation techniques, transgenic approaches, and alterations in the deposition of the ECM. In the short term, mediators that modulate the inflammatory mechanisms responsible for eliciting astrogliotic scarring hold strong potential for establishing a favorable environment for neuronal repair. In the future, the conditional (inducible) genetic manipulation of astrocytes holds promise for further increasing our understanding of the functional biology of astrocytes as well as opening new therapeutic windows. Nevertheless, it is most likely that, to obtain long distance axonal regeneration within the injured adult CNS, a combinatorial approach involving different repair strategies, including but not limited to astrogliosis modulation, will be required.

Effects of age on gene expression during estrogen-induced synaptic sprouting in the female rat

Age and estrogen treatment influenced fiber outgrowth and compensatory neuronal sprouting after unilateral entorhinal cortex lesions (ECL) which model Alzheimer disease-like deafferentation in the dentate gyrus of the hippocampus. In young F344 rats (3 months old), ovariectomy (OVX) decreased reactive fiber outgrowth by 60%. Sprouting in middle-aged rats (18 months old) was reduced in intact females; no further reduction was caused by OVX. Several astrocyte mRNAs were measured in the dentate gyrus of young and middle-aged female rats in three different estrogen states (sham OVX, OVX, or OVX + estradiol) 1 week after ECL. Glial fibrillary acidic protein (GFAP) mRNA was twofold greater in middle-aged rats than young, although both ages showed threefold increases in response to ECL. In prior studies GFAP was found to be decreased by estradiol treatment 3-4 days after ECL; in this study GFAP mRNA had returned to sham OVX levels in young rats by 7 days post-ECL. Surprisingly, estradiol treatment increased GFAP mRNA levels by 25% above OVX in middle-aged rats. Apolipoprotein E (apoE) mRNA was decreased 20% by age in the dentate, although both age groups showed a 25% increase in apoE mRNA in response to ECL. Apolipoprotein J (apoJ) mRNA was increased 20% in the dentate gyrus of middle-aged rats, and both age groups responded to ECL with a 65% increase in apoJ mRNA. The estrogen state did not alter levels of either apolipoprotein mRNA in the deafferented dentate. The data suggest that the estrogen-induced decrease of GFAP in response to lesions does not persist at 7 days post-ECL during sprouting. Overall effects of age on the dentate gyrus include elevated GFAP mRNA and decreased apoE mRNA. The cortical wound site showed consistent enhancement of GFAP mRNA in both age groups by estradiol above sham OVX and greater responses in middle-aged rats.

Immunocytochemical basis for a meningeo-glial network

Evidence is presented here for a cellular network that courses through all layers of meninges, the vasculature of both the brain and meninges, and extends into the brain parenchyma. Confocal mapping of calcium-binding protein S100beta immunoreactivity (S100beta-ir) and of the intermediate filament vimentin-ir through serial sections of the meningeal-intact adult rat brain revealed this network. In all tissues examined, S100beta-ir and vimentin-ir were primarily colocalized, and were found in cells with elongated processes through which these cells contacted one another to form a network. The location of labeling and the morphology of the cells labeled were consistent with the possibility that this network consists of fibroblasts in the meninges and the walls of large blood vessels, of pericytes at the level of capillaries, and of ependymocytes and a population of astrocytes in the brain parenchyma. At many sites along the borders of the brain parenchyma itself and of the brain blood vessels, it was possible to detect S100beta-ir and vimentin-ir cell processes that cross the basal laminae. This suggested the probable means by which the S100beta-ir cells of the extraparenchymal tissues anatomically contact the cells that express the same markers in the brain. Privileged anatomical relationships of the S100beta/vimentin network with the glial fibrillary acidic protein (GFAP) astrocytes further suggested that, together, they form the structural basis for a general meningeo-glial network. This organization challenges the current model of brain architecture, calls for a reconsideration of the role of meninges and vascular tissues, and appears to reflect the existence of hitherto unsuspected systems of communication.

Involvement of glial fibrillary acidic protein (GFAP) expressed in astroglial cells in circadian rhythm under constant lighting conditions in mice

To clarify the role of glial fibrillary acidic protein (GFAP)-expressed glial cells in the circadian clock, we examined GFAP expression in the suprachiasmatic nucleus (SCN) and the intergeniculate leaflet (IGL) under various lighting conditions in mice. We demonstrated that GFAP expression did not show daily change in the SCN under a light-dark cycle; however, long-term housing under constant lighting conditions led to dramatic changes in GFAP expression, i.e., a decrease in the SCN and an increase in the IGL. Furthermore, mice that had a targeted deletion in the GFAP gene (GFAP mutant mice) showed longer and more arrhythmic circadian activity rhythms in constant lighting conditions than wild-type mice, while GFAP mutant mice exhibited stable circadian rhythms both in a light-dark cycle and constant darkness, and showed normal entrainment to environmental light stimuli. These results suggest that the GFAP-expressed astroglial cells in the SCN and the IGL may have some role in circadian oscillation under constant lighting conditions.

Chondroitinase ABC promotes axonal regeneration of Clarke's neurons after spinal cord injury

We examined whether enzymatic digestion of chondroitin sulfate (CS) promoted the axonal regeneration of neurons in Clarke's nucleus (CN) into a peripheral nerve (PN) graft following injury of the spinal cord. After hemisection at T11, a segment of PN graft was implanted at the lesion site. Either vehicle, brain-derived neurotrophic factor (BDNF) or chondroitinase ABC was applied at the implantation site. The postoperative survival period was 4 weeks. Treatment with vehicle or BDNF did not promote the axonal regeneration of CN neurons into the PN graft. Application of 2.5 unit/ml chondroitinase ABC resulted in a significant increase (12.8%) in the number of regenerated CN neurons. Double labeling with Fluoro-Gold and NADPH-diaphorase histochemistry showed that the regenerated CN neurons did not express nitric oxide synthase (NOS). Our results suggest that CS is inhibitory to the regeneration of CN neurons following injury of the spinal cord.

Traumatic spinal cord injury produced by controlled contusion in mouse

Previous work from this laboratory has described a rat spinal cord injury (SCI) model in which the mid-thoracic spinal cord is subjected to a single rapid and calibrated displacement at the site of a dorsal laminectomy. Injury is initiated at the tip of a vertical shaft driven by an electromagnetic shaker. Transducers arranged in series with the shaft record the patterns of displacement and force during the impact sequence. In the present study, this device and the relevant surgical procedures were adapted to produce a spinal contusion injury model in laboratory mice. The signal generator for the injury device has also been converted to a computer-controlled interface to permit extension of the model to other laboratories. Mice were subjected to SCI across a range of severities by varying the amplitude of displacement and the magnitude of measured preload force on the dural surface. A moderate injury produced by displacement of 0.5 mm over 25 msec resulted in initial paralysis and recovery of locomotion with chronic deficits in hindlimb function. The magnitude of the peak force, impulse, power, and energy generated at impact were correlated with behavioral outcome at 1 day postinjury, while peak displacement and impulse were the best predictors of behavioral outcome at 28 days postinjury. The shape of the force recording proved to be a highly sensitive measure of subtle variations in the spinal compartment that were otherwise difficult to detect in this small species. The results demonstrate that the electromagnetic spinal cord injury device (ESCID) can be used to produce a well-controlled contusion injury in mice. The unique features of controlled displacement and monitoring of the biomechanical parameters at the time of impact provide advantages of this model for reducing outcome variability. Use of this model in mice with naturally occurring and genetically engineered mutations will facilitate understanding of the molecular mechanisms of pathophysiology following traumatic spinal cord injury.

A therapeutic vaccine approach to stimulate axon regeneration in the adult mammalian spinal cord

Axon growth inhibitors associated with myelin play an important role in the failure of axon regeneration in the adult mammalian central nervous system (CNS). Several inhibitors are present in the mature CNS. We now present a novel therapeutic vaccine approach in which the animals' own immune system is stimulated to produce polyclonal antibodies that block myelin-associated inhibitors without producing any detrimental cellular inflammatory responses. Adult mice immunized in this manner showed extensive regeneration of large numbers of axons of the corticospinal tracts after dorsal hemisection of the spinal cord. The anatomical regeneration led to recovery of certain hind limb motor functions. Furthermore, antisera from immunized mice were able to block myelin-derived inhibitors and promote neurite growth on myelin in vitro.

Common myofibroblastic features of newborn rat astrocytes and cirrhotic rat liver stellate cells in early cultures and in vivo

Double-immunolabelling techniques were employed to investigate the distribution of smooth muscle alpha-actin (actin) in glial fibrillary acidic protein (GFAP)-positive cells in rat brain during early postnatal development and maturation and in glial primary culture derived from newborn rat brain. In addition the expression of desmin was studied in the glial primary cultures as a function of the differentiation of the cells. Comparison of the cultured astroglial cells at an early age with hepatic stellate cells derived from CCl4-induced cirrhotic rat liver, revealed features of the astrocytic cytoskeleton characteristic of myofibroblastic cells, i.e., strong expression of both myofibroblastic markers, actin and desmin. In astroglial cells with an initial morphology reminiscent of fibroblasts the non-filamentous perinuclear immunoreaction of GFAP increased with time at the expense of actin and, partially, desmin. GFAP filaments were spread throughout the cytoplasm of the cells which acquired stellate morphology. The alterations in the morphology of the cells and the distribution and intensity of staining for GFAP and actin during the differentiation of astrocytes in culture were similar to those observed in astrocytes during the maturation of the brain. In astrocytes from a newborn brain as well as in cirrhotic hepatic stellate cells, the area of immunoreaction of GFAP was reduced and confined mainly to the nuclear region. In contrast, the cells expressed actin throughout the cytoplasm. These findings may hint at a similar function of these regionally specialized perivascular myofibroblastic cells in a normal brain and diseased liver and at inverse organ-specific functions which the cells fulfill under non-pathological conditions in vivo.

Glial fibrillary acidic protein (GFAP): modulation by growth factors and its implication in astrocyte differentiation

Intermediate filament (IF) proteins constitute an extremely large multigene family of developmentally and tissue-regulated cytoskeleton proteins abundant in most vertebrate cell types. Astrocyte precursors of the CNS usually express vimentin as the major IF. Astrocyte maturation is followed by a switch between vimentin and glial fibrillary acidic protein (GFAP) expression, with the latter being recognized as an astrocyte maturation marker. Levels of GFAP are regulated under developmental and pathological conditions. Upregulation of GFAP expression is one of the main characteristics of the astrocytic reaction commonly observed after CNS lesion. In this way, studies on GFAP regulation have been shown to be useful to understand not only brain physiology but also neurological disease. Modulators of GFAP expression include several hormones such as thyroid hormone, glucocorticoids and several growth factors such as FGF, CNTF and TGF beta, among others. Studies of the GFAP gene have already identified several putative growth factor binding domains in its promoter region. Data obtained from transgenic and knockout mice have provided new insights into IF protein functions. This review highlights the most recent studies on the regulation of IF function by growth factors and hormones.