Differential expression of several molecules of the extracellular matrix in functionally and developmentally distinct regions of rat spinal cord

Low oral dose of 4-methylumbelliferone reduces glial scar but is insufficient to induce functional recovery after spinal cord injury

Spinal cord injury (SCI) induces the upregulation of chondroitin sulfate proteoglycans (CSPGs) at the glial scar and inhibits neuroregeneration. Under normal physiological condition, CSPGs interact with hyaluronan (HA) and other extracellular matrix on the neuronal surface forming a macromolecular structure called perineuronal nets (PNNs) which regulate neuroplasticity. 4-methylumbelliferone (4-MU) is a known inhibitor for HA synthesis but has not been tested in SCI. We first tested the effect of 4-MU in HA reduction in uninjured rats. After 8 weeks of 4-MU administration at a dose of 1.2 g/kg/day, we have not only observed a reduction of HA in the uninjured spinal cords but also a down-regulation of CS glycosaminoglycans (CS-GAGs). In order to assess the effect of 4-MU in chronic SCI, six weeks after Th8 spinal contusion injury, rats were fed with 4-MU or placebo for 8 weeks in combination with daily treadmill rehabilitation for 16 weeks to promote neuroplasticity. 4-MU treatment reduced the HA synthesis by astrocytes around the lesion site and increased sprouting of 5-hydroxytryptamine fibres into ventral horns. However, the current dose was not sufficient to suppress CS-GAG up-regulation induced by SCI. Further adjustment on the dosage will be required to benefit functional recovery after SCI.

The Role and Modulation of Spinal Perineuronal Nets in the Healthy and Injured Spinal Cord

Rather than being a stable scaffold, perineuronal nets (PNNs) are a dynamic and specialized extracellular matrix involved in plasticity modulation. They have been extensively studied in the brain and associated with neuroprotection, ionic buffering, and neural maturation. However, their biological function in the spinal cord and the effects of disrupting spinal PNNs remain elusive. The goal of this review is to summarize the current knowledge of spinal PNNs and their potential in pathological conditions such as traumatic spinal cord injury (SCI). We also highlighted interventions that have been used to modulate the extracellular matrix after SCI, targeting the glial scar and spinal PNNs, in an effort to promote regeneration and stabilization of the spinal circuits, respectively. These concepts are discussed in the framework of developmental and neuroplastic changes in PNNs, drawing similarities between immature and denervated neurons after an SCI, which may provide a useful context for future SCI research.

Microglia Dynamics and Interactions with Motoneurons Axotomized After Nerve Injuries Revealed By Two-Photon Imaging

The significance of activated microglia around motoneurons axotomized after nerve injuries has been intensely debated. In particular, whether microglia become phagocytic is controversial. To resolve these issues we directly observed microglia behaviors with two-photon microscopy in ex vivo spinal cord slices from CX3CR1-GFP mice complemented with confocal analyses of CD68 protein. Axotomized motoneurons were retrogradely-labeled from muscle before nerve injuries. Microglia behaviors close to axotomized motoneurons greatly differ from those within uninjured motor pools. They develop a phagocytic phenotype as early as 3 days after injury, characterized by frequent phagocytic cups, high phagosome content and CD68 upregulation. Interactions between microglia and motoneurons changed with time after axotomy. Microglia first extend processes that end in phagocytic cups at the motoneuron surface, then they closely attach to the motoneuron while extending filopodia over the cell body. Confocal 3D analyses revealed increased microglia coverage of the motoneuron cell body surface with time after injury and the presence of CD68 granules in microglia surfaces opposed to motoneurons. Some microglia formed macroclusters associated with dying motoneurons. Microglia in these clusters display the highest CD68 expression and associate with cytotoxic T-cells. These observations are discussed in relation to current theories on microglia function around axotomized motoneurons.

Demystifying the extracellular matrix and its proteolytic remodeling in the brain: structural and functional insights

The extracellular matrix (ECM) plays diverse roles in several physiological and pathological conditions. In the brain, the ECM is unique both in its composition and in functions. Furthermore, almost all the cells in the central nervous system contribute to different aspects of this intricate structure. Brain ECM, enriched with proteoglycans and other small proteins, aggregate into distinct structures around neurons and oligodendrocytes. These special structures have cardinal functions in the normal functioning of the brain, such as learning, memory, and synapse regulation. In this review, we have compiled the current knowledge about the structure and function of important ECM molecules in the brain and their proteolytic remodeling by matrix metalloproteinases and other enzymes, highlighting the special structures they form. In particular, the proteoglycans in brain ECM, which are essential for several vital functions, are emphasized in detail.

Quantitative changes in perineuronal nets in development and posttraumatic condition

Perineuronal net (PNN) is a highly structured portion of the CNS extracellular matrix (ECM) regulating synaptic plasticity and a range of pathologic conditions including posttraumatic regeneration and epilepsy. Here we studied Wisteria floribunda agglutinin-stained histological sections to quantify the PNN size and enrichment of chondroitin sulfates in mouse brain and spinal cord. Somatosensory cortex sections were examined during the period of PNN establishment at postnatal days 14, 21 and 28. The single cell PNN size and the chondroitin sulfate intensity were quantified for all cortex layers and specifically for the cortical layer IV which has the highest density of PNN-positive neurons. We demonstrate that the chondroitin sulfate proteoglycan staining intensity is increased between P14 and P28 while the PNN size remains unchanged. We then addressed posttraumatic changes of the PNN expression in laminae 6 and 7 of cervical spinal cord following hemisection injury. We demonstrate increase of the chondroitin sulfate content at 1.6-1.8 mm rostrally from the injury site and increase of the density of PNN-bearing cells at 0.4-1.2 mm caudally from the injury site. We further demonstrate decrease of the single cell PNN area at 0.2 mm caudally from the injury site suggesting that the PNN ECM takes part in the posttraumatic tissue rearrangement in the spinal cord. Our results demonstrate new insights on the PNN structure dynamics in the developing and posttraumatic CNS.

Perineuronal Nets in Spinal Motoneurones: Chondroitin Sulphate Proteoglycan around Alpha Motoneurones

Perineuronal nets (PNNs) are extracellular matrix structures surrounding neuronal sub-populations throughout the central nervous system, regulating plasticity. Enzymatically removing PNNs successfully enhances plasticity and thus functional recovery, particularly in spinal cord injury models. While PNNs within various brain regions are well studied, much of the composition and associated populations in the spinal cord is yet unknown. We aim to investigate the populations of PNN neurones involved in this functional motor recovery. Immunohistochemistry for choline acetyltransferase (labelling motoneurones), PNNs using Wisteria floribunda agglutinin (WFA) and chondroitin sulphate proteoglycans (CSPGs), including aggrecan, was performed to characterise the molecular heterogeneity of PNNs in rat spinal motoneurones (Mns). CSPG-positive PNNs surrounded ~70–80% of Mns. Using WFA, only ~60% of the CSPG-positive PNNs co-localised with WFA in the spinal Mns, while ~15–30% of Mns showed CSPG-positive but WFA-negative PNNs. Selective labelling revealed that aggrecan encircled ~90% of alpha Mns. The results indicate that (1) aggrecan labels spinal PNNs better than WFA, and (2) there are differences in PNN composition and their associated neuronal populations between the spinal cord and cortex. Insights into the role of PNNs and their molecular heterogeneity in the spinal motor pools could aid in designing targeted strategies to enhance functional recovery post-injury.

Casting a Wide Net: Role of Perineuronal Nets in Neural Plasticity

Perineuronal nets (PNNs) are unique extracellular matrix structures that wrap around certain neurons in the CNS during development and control plasticity in the adult CNS. They appear to contribute to a wide range of diseases/disorders of the brain, are involved in recovery from spinal cord injury, and are altered during aging, learning and memory, and after exposure to drugs of abuse. Here the focus is on how a major component of PNNs, chondroitin sulfate proteoglycans, control plasticity, and on the role of PNNs in memory in normal aging, in a tauopathy model of Alzheimer's disease, and in drug addiction. Also discussed is how altered extracellular matrix/PNN formation during development may produce synaptic pathology associated with schizophrenia, bipolar disorder, major depression, and autism spectrum disorders. Understanding the molecular underpinnings of how PNNs are altered in normal physiology and disease will offer insights into new treatment approaches for these diseases.

Accumulation of Extracellular Matrix in Advanced Lesions of Canine Distemper Demyelinating Encephalitis

In demyelinating diseases, changes in the quality and quantity of the extracellular matrix (ECM) may contribute to demyelination and failure of myelin repair and axonal sprouting, especially in chronic lesions. To characterize changes in the ECM in canine distemper demyelinating leukoencephalitis (DL), histochemical and immunohistochemical investigations of formalin-fixed paraffin-embedded cerebella using azan, picrosirius red and Gomori`s silver stain as well as antibodies directed against aggrecan, type I and IV collagen, fibronectin, laminin and phosphacan showed alterations of the ECM in CDV-infected dogs. A significantly increased amount of aggrecan was detected in early and late white matter lesions. In addition, the positive signal for collagens I and IV as well as fibronectin was significantly increased in late lesions. Conversely, the expression of phosphacan was significantly decreased in early and more pronounced in late lesions compared to controls. Furthermore, a set of genes involved in ECM was extracted from a publically available microarray data set and was analyzed for differential gene expression. Gene expression of ECM molecules, their biosynthesis pathways, and pro-fibrotic factors was mildly up-regulated whereas expression of matrix remodeling enzymes was up-regulated to a relatively higher extent. Summarized, the observed findings indicate that changes in the quality and content of ECM molecules represent important, mainly post-transcriptional features in advanced canine distemper lesions. Considering the insufficiency of morphological regeneration in chronic distemper lesions, the accumulated ECM seems to play a crucial role upon regenerative processes and may explain the relatively small regenerative potential in late stages of this disease.

The extracellular matrix molecule brevican is an integral component of the machinery mediating fast synaptic transmission at the calyx of Held

KEY POINTS

The proteoglycan brevican is a major component of the extracellular matrix of perineuronal nets and is highly enriched in the perisynaptic space suggesting a role for synaptic transmission. We have introduced the calyx of Held in the auditory brainstem as a model system to study the impact of brevican on dynamics and reliability of synaptic transmission. In vivo extracellular single-unit recordings at the calyx of Held in brevican-deficient mice yielded a significant increase in the action potential (AP) transmission delay and a prolongation of pre- and postsynaptic APs. The changes in dynamics of signal transmission were accompanied by the reduction of presynaptic vGlut1 and ultrastructural changes in the perisynaptic space. These data show that brevican is an important mediator of fast synaptic transmission at the calyx of Held.

ABSTRACT

The extracellular matrix is an integral part of the neural tissue. Its most conspicuous manifestation in the brain are the perineuronal nets (PNs) which surround somata and proximal dendrites of distinct neuron types. The chondroitin sulfate proteoglycan brevican is a major component of PNs. In contrast to other PN-comprising proteoglycans (e.g. aggrecan and neurocan), brevican is mainly expressed in the perisynaptic space closely associated with both the pre- and postsynaptic membrane. This specific localization prompted the hypothesis that brevican might play a role in synaptic transmission. In the present study we specifically investigated the role of brevican in synaptic transmission at a central synapse, the calyx of Held in the medial nucleus of the trapezoid body, by the use of in vivo electrophysiology, immunohistochemistry, biochemistry and electron microscopy. In vivo extracellular single-unit recordings were acquired in brevican-deficient mice and the dynamics and reliability of synaptic transmission were compared to wild-type littermates. In knockout mice, the speed of pre-to-postsynaptic action potential (AP) transmission was reduced and the duration of the respective pre- and postsynaptic APs increased. The reliability of signal transmission, however, was not affected by the lack of brevican. The changes in dynamics of signal transmission were accompanied by the reduction of (i) presynaptic vGlut1 and (ii) the size of subsynaptic cavities. The present results suggest an essential role of brevican for the functionality of high-speed synaptic transmission at the calyx of Held.

Perineuronal and perisynaptic extracellular matrix in the human spinal cord

Extracellular matrix (ECM) forms an active interface around neurons of the central nervous system (CNS). Whilst the components, chemical heterogeneity and cellular recruitment of this intercellular assembly in various parts of the brain have been discussed in detail, the spinal cord received limited attention in this context. This is in sharp contrast to its clinical relevance since the overall role of ECM especially that of its chondroitin sulphate-based proteoglycan components (CSPGs) was repeatedly addressed in neuropathology, regeneration, CNS repair and therapy models. Based on two post-mortem human specimen, this study gives the first and detailed description of major ECM components of the human spinal cord. Immunohistochemical investigations were restricted to the systematic mapping of aggrecan, brevican, proteoglycan link-protein as well as tenascin-R and hyaluronan containing matrices in the whole cranio-caudal dimension of the human spinal cord. Other proteoglycans like versican, neurocan and NG2 were exemplarily investigated in restricted areas. We show the overall presence of tenascin-R and hyaluronan in both white and grey matters whereas aggrecan, proteoglycan link-protein and brevican were restricted to the grey matter. In the grey matter, the ECM formed aggrecan-based perineuronal nets in the ventral and lateral horns but established single perisynaptic assemblies, axonal coats (ACs), containing link-protein and brevican in all regions except of the Lissauer's zone. Intersegmental differences were reflected in the appearance of segment-specific nuclei but not in overall matrix distribution pattern or chemical heterogeneity. Perineuronal nets were typically associated with long-range projection neurons including cholinergic ventral horn motorneurons or dorsal spinocerebellar tract neurons of the Clarke-Stilling nuclei. Multiple immunolabelling revealed that nociceptive afferents were devoid of individual matrix assemblies unlike glycinergic or GABAergic synapses. The detailed description of ECM distribution in the human spinal cord shall support clinical approaches in injury and regenerative therapy.

The perineuronal net and the control of CNS plasticity

Perineuronal nets (PNNs) are reticular structures that surround the cell body of many neurones, and extend along their dendrites. They are considered to be a specialized extracellular matrix in the central nervous system (CNS). PNN formation is first detected relatively late in development, as the mature synaptic circuitry of the CNS is established and stabilized. Its unique distribution in different CNS regions, the timing of its establishment, and the changes it undergoes after injury all point toward diverse and important functions that it may be performing. The involvement of PNNs in neuronal plasticity has been extensively studied over recent years, with developmental, behavioural, and functional correlations. In this review, we will first briefly detail the structure and organization of PNNs, before focusing our discussion on their unique roles in neuronal development and plasticity. The PNN is an important regulator of CNS plasticity, both during development and into adulthood. Production of critical PNN components is often triggered by appropriate sensory experiences during early postnatal development. PNN deposition around neurones helps to stabilize the established neuronal connections, and to restrict the plastic changes due to future experiences within the CNS. Disruption of PNNs can reactivate plasticity in many CNSs, allowing activity-dependent changes to once again modify neuronal connections. The mechanisms through which PNNs restrict CNS plasticity remain unclear, although recent advances promise to shed additional light on this important subject.

Extracellular matrix abnormalities in schizophrenia

Emerging evidence points to the involvement of the brain extracellular matrix (ECM) in the pathophysiology of schizophrenia (SZ). Abnormalities affecting several ECM components, including Reelin and chondroitin sulfate proteoglycans (CSPGs), have been described in subjects with this disease. Solid evidence supports the involvement of Reelin, an ECM glycoprotein involved in corticogenesis, synaptic functions and glutamate NMDA receptor regulation, expressed prevalently in distinct populations of GABAergic neurons, which secrete it into the ECM. Marked changes of Reelin expression in SZ have typically been reported in association with GABA-related abnormalities in subjects with SZ and bipolar disorder. Recent findings from our group point to substantial abnormalities affecting CSPGs, a main ECM component, in the amygdala and entorhinal cortex of subjects with schizophrenia, but not bipolar disorder. Striking increases of glial cells expressing CSPGs were accompanied by reductions of perineuronal nets, CSPG- and Reelin-enriched ECM aggregates enveloping distinct neuronal populations. CSPGs developmental and adult functions, including neuronal migration, axon guidance, synaptic and neurotransmission regulation are highly relevant to the pathophysiology of SZ. Together with reports of anomalies affecting several other ECM components, these findings point to the ECM as a key component of the pathology of SZ. We propose that ECM abnormalities may contribute to several aspects of the pathophysiology of this disease, including disrupted connectivity and neuronal migration, synaptic anomalies and altered GABAergic, glutamatergic and dopaminergic neurotransmission.

In vitro modeling of perineuronal nets: hyaluronan synthase and link protein are necessary for their formation and integrity

We have previously shown that all perineuronal nets (PNNs) bearing neurons express a hyaluronan synthase (HAS), a link protein (usually cartilage link protein-1; Crtl1) and a chondroitin sulfate proteoglycan (usually aggrecan). Animal lacking Crtl1 in the CNS lacks normal PNNs. PNNs are implicated in the control of neuronal plasticity, and interventions to modulate PNN formation will be useful for manipulating plasticity. We have developed an in vitro model which demonstrates how the structural components of PNNs trigger their formation, using human embryonic kidney cells, which do not normally produce a pericellular matrix. Expression of HAS3 leads to the production of a diffuse matrix. It was converted into a compact PNN-like structure when the cells also expressed Crtl1 and aggrecan. This matrix was stained by Wisteria floribunda, contained Crtl1 and aggrecan, and like PNNs, could only be solubilized in 6 M urea. In the absence of hyaluronan produced by HAS3, aggrecan and Crtl1 dissipated into the medium, but when the cells were transfected to produce a hyaluronan matrix, Crtl1 and aggrecan were incorporated into it. Cells lacking any one of these molecules showed impaired integrity of the PNNs. Cells expressing HAS3 and Crtl1 were able to incorporate exogenous aggrecan into their pericellular matrix.

Sporadic ALS has compartment-specific aberrant exon splicing and altered cell-matrix adhesion biology

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by progressive weakness from loss of motor neurons. The fundamental pathogenic mechanisms are unknown and recent evidence is implicating a significant role for abnormal exon splicing and RNA processing. Using new comprehensive genomic technologies, we studied exon splicing directly in 12 sporadic ALS and 10 control lumbar spinal cords acquired by a rapid autopsy system that processed nervous systems specifically for genomic studies. ALS patients had rostral onset and caudally advancing disease and abundant residual motor neurons in this region. We created two RNA pools, one from motor neurons collected by laser capture microdissection and one from the surrounding anterior horns. From each, we isolated RNA, amplified mRNA, profiled whole-genome exon splicing, and applied advanced bioinformatics. We employed rigorous quality control measures at all steps and validated findings by qPCR. In the motor neuron enriched mRNA pool, we found two distinct cohorts of mRNA signals, most of which were up-regulated: 148 differentially expressed genes (P ≤ 10⁻³) and 411 aberrantly spliced genes (P ≤ 10⁻⁵). The aberrantly spliced genes were highly enriched in cell adhesion (P ≤ 10⁻⁵⁷), especially cell–matrix as opposed to cell–cell adhesion. Most of the enriching genes encode transmembrane or secreted as opposed to nuclear or cytoplasmic proteins. The differentially expressed genes were not biologically enriched. In the anterior horn enriched mRNA pool, we could not clearly identify mRNA signals or biological enrichment. These findings, perturbed and up-regulated cell–matrix adhesion, suggest possible mechanisms for the contiguously progressive nature of motor neuron degeneration. Data deposition: GeneChip raw data (CEL-files) have been deposited for public access in the Gene Expression Omnibus (GEO), www.ncbi.nlm.nih.gov/geo, accession number GSE18920.

Tenascins and their implications in diseases and tissue mechanics

Tenascins are glycoproteins found in the extracellular matrix (ECM) of many tissues. Their role is not only to support the tissue structurally but also to regulate the fate of the different cell types populating the ECM. For instance, tenascins are required when active tissue modeling during embryogenesis or re-modeling after injury occurs. Interestingly, the four members of the tenascin family, tenascin-C, -X, -R and -W, show different and often mutually exclusive expression patterns. As a consequence, these structurally related proteins display distinct functions and are associated with distinct pathologies. The present review aims at presenting the four members of the tenascin family with respect to their structure, expression patterns and implications in diseases and tissue mechanics.

Differential distribution of aggrecan isoforms in perineuronal nets of the human cerebral cortex

Aggrecan is a component of the CNS extracellular matrix (ECM) and we show here that the three primary alternative spliced transcripts of the aggrecan gene found in cartilage are also present in the adult CNS. Using a unique panel of core protein-directed antibodies against human aggrecan we further show that different aggrecan isoforms are deposited in perineuronal nets (PNNs) and neuropil ECM of Brodmann’s area 6 of the human adult cerebral cortex. According to their distribution pattern, the identified cortical aggrecan isoforms were subdivided into five clusters spanning from cluster 1, comprised isoforms that appeared widespread throughout the cortex, to cluster 5, which was an aggrecan-free subset. Comparison of brain and cartilage tissues showed a different relative abundance of aggrecan isoforms, with cartilage-specific isoforms characterizing cluster 5, and PNN-associated isoforms lacking keratan sulphate chains. In the brain, isoforms of cluster 1 were disclosed in PNNs surrounding small-medium interneurons of layers II–V, small-medium pyramidal neurons of layers III and V and large interneurons of layer VI. Aggrecan PNNs enveloped both neuron bodies and neuronal processes, encompassing pre-terminal nerve fibres, synaptic boutons and terminal processes of glial cells and aggrecan was also observed in continuous ‘coats’ associated with satellite, neuron-associated cells of a putative glial nature. Immunolabelling for calcium-binding proteins and glutamate demonstrated that aggrecan PNNs were linked to defined subsets of cortical interneurons and pyramidal cells. We suggest that in the human cerebral cortex, discrete, layer-specific PNNs are assembled through the participation of selected aggrecan isoforms that characterize defined subsets of cortical neurons.

Accumulation of chondroitin sulfate proteoglycans in the microenvironment of spinal motor neurons in amyotrophic lateral sclerosis transgenic rats

Chondroitin sulfate proteoglycans (CSPGs) are the major components of extracellular matrix in the central nervous system. In the spinal cord under various types of injury, reactive gliosis emerges in the lesion accompanied by CSPG up-regulation. Several types of CSPG core proteins and their side chains have been shown to inhibit axonal regeneration in vitro and in vivo. In the present study, we examined spatiotemporal expression of CSPGs in the spinal cord of transgenic (Tg) rats with His46Arg mutation in the Cu/Zn superoxide dismutase gene, a model of amyotrophic lateral sclerosis (ALS). Immunofluorescence disclosed a significant up-regulation of neurocan, versican, and phosphacan in the ventral spinal cord of Tg rats compared with age-matched controls. Notably, Tg rats showed progressive and prominent accumulation of neurocan even at the presymptomatic stage. Immunoblotting confirmed the distinct increase in the levels of both the full-length neurocan and their fragment isoforms. On the other hand, the up-regulation of versican and phosphacan peaked at the early symptomatic stage, followed by diminishment at the late symptomatic stage. In addition, double immunofluorescence revealed a colocalization between reactive astrocytes and immunoreactivities for neurocan and phosphacan, especially around residual large ventral horn neurons. Thus, reactive astrocytes are suggested to be participants in the CSPG accumulation. Although the possible neuroprotective involvement of CSPG remains to be investigated, the present results suggest that both the reactive astrocytes and the differential accumulation of CSPGs may create a nonpermissive microenvironment for neural regeneration in neurodegenerative diseases such as ALS.

Decorin promotes robust axon growth on inhibitory CSPGs and myelin via a direct effect on neurons

Inhibitory chondroitin sulfate proteoglycans (CSPGs) and myelin-associated molecules are major impediments to axon regeneration within the adult central nervous system (CNS). Decorin infusion can however suppress the levels of multiple inhibitory CSPGs and promote axon growth across spinal cord injuries [Davies, J.E., Tang, X., Denning, J.W., Archibald, S.J., and Davies, S.J., 2004. Decorin suppresses neurocan, brevican, phosphacan and NG2 expression and promotes axon growth across adult rat spinal cord injuries. Eur. J. Neurosci. 19, 1226-1242]. A question remained as to whether decorin can also increase axon growth on inhibitory CSPGs and myelin via a direct effect on neurons. We have therefore conducted an in vitro analysis of neurite extension by decorin-treated adult dorsal root ganglion (DRG) neurons cultured on substrates of inhibitory CSPGs or myelin membranes mixed with laminin. Decorin treatment promoted 14.5 and 5-fold increases in average neurite length/neuron over untreated controls on CSPGs or myelin membranes respectively. In addition to suppressing inhibitory scar formation, our present data shows that decorin can directly boost the ability of neurons to extend axons within CSPG or myelin rich environments.

Distribution and synthesis of extracellular matrix proteoglycans, hyaluronan, link proteins and tenascin-R in the rat spinal cord

Perineuronal nets (PNNs) are dense extracellular matrix (ECM) structures that form around many neuronal cell bodies and dendrites late in development. They contain several chondroitin sulphate proteoglycans (CSPGs), hyaluronan, link proteins and tenascin-R. Their time of appearance correlates with the ending of the critical period for plasticity, and they have been implicated in this process. The distribution of PNNs in the spinal cord was examined using Wisteria floribunda agglutinin lectin and staining for chondroitin sulphate stubs after chondroitinase digestion. Double labelling with the neuronal marker, NeuN, showed that PNNs were present surrounding approximately 30% of motoneurons in the ventral horn, 50% of large interneurons in the intermediate grey and 20% of neurons in the dorsal horn. These PNNs formed in the second week of postnatal development. Immunohistochemical staining demonstrated that the PNNs contain a mixture of CSPGs, hyaluronan, link proteins and tenascin-R. Of the CSPGs, aggrecan was present in all PNNs while neurocan, versican and phosphacan/RPTPbeta were present in some but not all PNNs. In situ hybridization showed that aggrecan and cartilage link protein (CRTL 1) and brain link protein-2 (BRAL 2) are produced by neurons. PNN-bearing neurons express hyaluronan synthase, and this enzyme and phosphacan/RPTPbeta may attach PNNs to the cell surface. During postnatal development the expression of link protein and aggrecan mRNA is up-regulated at the time of PNN formation, and these molecules may therefore trigger their formation.

Chronic erythropoietin-mediated effects on the expression of astrocyte markers in a rat model of contusive spinal cord injury

Using a standardized rat model of contusive spinal cord injury (SCI; [Gorio A, Gokmen N, Erbayraktar S, Yilmaz O, Madaschi L, Cichetti C, Di Giulio AM, Vardar E, Cerami A, Brines M (2002) Recombinant human erythropoietin counteracts secondary injury and markedly enhances neurological recovery from experimental spinal cord trauma. Proc Natl Acad Sci U S A 99:9450-9455]), we previously showed that the administration of recombinant human erythropoietin (rhEPO) improves both tissue sparing and locomotory outcome. In the present study, to better understand rhEPO-mediated effects on chronic astrocyte response to SCI in rat, we have used immunocytochemical methods combined with confocal and electron microscopy to investigate, 1 month after injury, the effects of a single rhEPO administration on the expression of a) aquaporin 4 (AQP4), the main astrocytic water channel implicated in edema development and resolution, and two molecules (dystrophin and syntrophin) involved in its membrane anchoring; b) glial fibrillary acidic protein (GFAP) and vimentin as markers of astrogliosis; c) chondroitin sulfate proteoglycans of the extracellular matrix which are upregulated after SCI and can inhibit axonal regeneration and influence neuronal and glial properties. Our results show that rhEPO administration after SCI modifies astrocytic response to injury by increasing AQP4 immunoreactivity in the spinal cord, but not in the brain, without apparent modifications of dystrophin and syntrophin distribution. Attenuation of astrogliosis, demonstrated by the semiquantitative analysis of GFAP labeling, was associated with a reduction of phosphacan/RPTP zeta/beta, whereas the levels of lecticans remained unchanged. Finally, the relative volume of a microvessel fraction was significantly increased, indicating a pro-angiogenetic or a vasodilatory effect of rhEPO. These changes were consistently associated with remarkable reduction of lesion size and with improvement in tissue preservation and locomotor recovery, confirming previous observations and underscoring the potentiality of rhEPO for the therapeutic management of SCI.

Brevican and phosphacan expression and localization following transient middle cerebral artery occlusion in the rat

The ECM (extracellular matrix) is a complex molecular framework that provides physical support to cells and tissues, while also providing signals for cell growth, migration, differentiation and survival. The ECM of the CNS (central nervous system) is unusual in that it is rich in CSPGs (chondroitin sulfate proteoglycans), hyaluronan and tenascins. The CSPGs are widely expressed throughout the developing and adult CNS and have a role in guiding or limiting neurite outgrowth and cell migration. Alterations in the synthesis or breakdown of the ECM may contribute to disease processes. Here, we examine changes in the brain-specific CSPGs, brevican and phosphacan, following transient middle cerebral artery occlusion, a model of stroke in the rat. We have investigated their expression at various time points as well as their spatial relationship with ADAMTS-4 (adisintegrin and metalloprotease with thrombospondin motifs 4). The co-localization of ADAMTS or its activity may indicate a functional role for this matrix–protease pair in degeneration/regeneration processes that occur in stroke.

Differential expression of phosphacan/RPTPβ isoforms in the developing mouse visual system

The chondroitin sulfate proteoglycan DSD-1-PG/phosphacan represents one of four splice variants of receptor-protein-tyrosine-phosphatase-beta/zeta (RPTPbeta/zeta). This receptor is expressed by glial cells and occurs in two isoforms, RPTPbeta(long) and RPTPbeta(short). The secreted forms phosphacan and phosphacan short isoform (PSI) bind to extracellular matrix and adhesion molecules and might mediate astroglial effects on neuronal differentiation. Phosphacan and RPTPbeta(long) both carry the DSD-1 epitope, a glycosaminoglycan modification that is involved in stimulating neurite outgrowth of embryonic rat mesencephalic and hippocampal neurons in a polycationic environment. Additionally, phosphacan inhibits neurite outgrowth of embryonic DRG neurons in the presence of laminin. In the light of these functional properties we examined the expression patterns of the DSD-1 epitope and phosphacan isoforms in the developing mouse visual system. During retinal development the DSD-1 epitope appears around embryonic day (E)13, peaks around postnatal day (P)6, and is downregulated from P9 to adolescence. By comparison, the phosphacan core protein is first detectable at E12, reaches maximal levels around P14, and persists, although at lower levels, to adulthood. The DSD-1 epitope is restricted to the nerve fiber and the inner plexiform layers. In contrast, the phosphacan core protein immunoreactivity extends from the nerve fiber layer to the outer plexiform layer. The level of expression of the phosphacan/RPTPbeta gene was investigated by reverse-transcriptase polymerase chain reaction. These experiments suggest that there is a shift in the expression patterns of the different phosphacan/RPTPbeta isoforms during late embryonic and postnatal development. In situ hybridization experiments support the conclusion that at least one of the phosphacan/RPTPbeta isoforms in the retina is expressed by neurons.