Intact aggrecan and fragments generated by both aggrecanse and metalloproteinase-like activities are present in the developing and adult rat spinal cord and their relative abundance is altered by injury

Neonatal Zika virus infection causes transient perineuronal net degradation

Perineuronal nets (PNNs) form a specialized extracellular matrix that predominantly surrounds parvalbumin (PV)-expressing GABAergic inhibitory interneurons and help regulate neuronal activity. Their formation early in the postnatal period is regulated by neuronal signaling and glial activation raising concerns that part of the long-term effects ascribed to perinatal viral infections could be mediated by altered PNN formation. Previously, we developed a model of neonatal Zika virus (ZIKV) infection where mice have lifelong neurological sequelae that includes motor disfunction and reduced anxiety coupled with a persistent low-grade expression in proinflammatory markers despite resolving the acute infection. Here, we demonstrate that ZIKV infection to P1 neonatal mice results in a reduction of PNN formation during the acute disease with significant reduction in Wisteria floribunda agglutinin (WFA) staining at the peak of infection [15 days post infection (dpi)] that persisted after the symptoms resolved (30 dpi). At 60 dpi, when there is residual inflammation in the CNS, the number of WFA⁺ cells and the level of WFA staining as well as levels of aggrecan and brevican in the brains of convalescent mice were not different from those in uninfected controls, however, there was increased frequency of PNNs with an immature phenotype. Over time the impact of the perinatal infection became less evident and there were no clear differences in PNN morphology between the groups at 1 year post infection. Of note, the reduction in PNNs during acute ZIKV infection was not associated with decreased mRNA levels of aggrecan or brevican, but increased levels of degraded aggrecan and brevican indicating increased PNN degradation. These changes were associated with increased expression of matrix metalloproteinase 12 (MMP12) and MMP19, but not MMP9, a disintegrin and metalloproteinase with thrombospondin motifs 4 (ADAMTS4) or ADAMTS5. Together our findings indicate that infection at the time of PNN development interferes with PNN formation, but the nets can reform once the infection and inflammation subside.

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.

ADAMTS-5: A difficult teenager turning 20

A Disintegrin And Metalloproteinase with ThromboSpondin motif (ADAMTS)-5 was identified in 1999 as one of the enzymes responsible for cleaving aggrecan, the major proteoglycan in articular cartilage. Studies in vitro, ex vivo and in vivo have validated ADAMTS-5 as a target in osteoarthritis (OA), a disease characterized by extensive degradation of aggrecan. For this reason, it attracted the interest of many research groups aiming to develop a therapeutic treatment for OA patients. However, ADAMTS-5 proteoglycanase activity is not only involved in the dysregulated aggrecan proteolysis, which occurs in OA, but also in the physiological turnover of other related proteoglycans. In particular, versican, a major ADAMTS-5 substrate, plays an important structural role in heart and blood vessels and its proteolytic processing by ADAMTS-5 must be tightly regulated. On the occasion of the 20th anniversary of the discovery of ADAMTS-5, this review looks at the evidence for its detrimental role in OA, as well as its physiological turnover of cardiovascular proteoglycans. Moreover, the other potential functions of this enzyme are highlighted. Finally, challenges and emerging trends in ADAMTS-5 research are discussed.

Keratan Sulphate in the Tumour Environment

Keratan sulphate (KS) is a bioactive glycosaminoglycan (GAG) of some complexity composed of the repeat disaccharide D-galactose β1→4 glycosidically linked to N-acetyl glucosamine. During the biosynthesis of KS, a family of glycosyltransferase and sulphotransferase enzymes act sequentially and in a coordinated fashion to add D-galactose (D-Gal) then N-acetyl glucosamine (GlcNAc) to a GlcNAc acceptor residue at the reducing terminus of a nascent KS chain to effect chain elongation. D-Gal and GlcNAc can both undergo sulphation at C6 but this occurs more frequently on GlcNAc than D-Gal. Sulphation along the developing KS chain is not uniform and contains regions of variable length where no sulphation occurs, regions which are monosulphated mainly on GlcNAc and further regions of high sulphation where both of the repeat disaccharides are sulphated. Each of these respective regions in the KS chain can be of variable length leading to KS complexity in terms of chain length and charge localization along the KS chain. Like other GAGs, it is these variably sulphated regions in KS which define its interactive properties with ligands such as growth factors, morphogens and cytokines and which determine the functional properties of tissues containing KS. Further adding to KS complexity is the identification of three different linkage structures in KS to asparagine (N-linked) or to threonine or serine residues (O-linked) in proteoglycan core proteins which has allowed the categorization of KS into three types, namely KS-I (corneal KS, N-linked), KS-II (skeletal KS, O-linked) or KS-III (brain KS, O-linked). KS-I to -III are also subject to variable addition of L-fucose and sialic acid groups. Furthermore, the GlcNAc residues of some members of the mucin-like glycoprotein family can also act as acceptor molecules for the addition of D-Gal and GlcNAc residues which can also be sulphated leading to small low sulphation glycoforms of KS. These differ from the more heavily sulphated KS chains found on proteoglycans. Like other GAGs, KS has evolved molecular recognition and information transfer properties over hundreds of millions of years of vertebrate and invertebrate evolution which equips them with cell mediatory properties in normal cellular processes and in aberrant pathological situations such as in tumourogenesis. Two KS-proteoglycans in particular, podocalyxin and lumican, are cell membrane, intracellular or stromal tissue-associated components with roles in the promotion or regulation of tumour development, mucin-like KS glycoproteins may also contribute to tumourogenesis. A greater understanding of the biology of KS may allow better methodology to be developed to more effectively combat tumourogenic processes.

Spatiotemporal distribution of chondroitin sulfate proteoglycans after optic nerve injury in rodents

The accumulation of chondroitin sulfate proteoglycans (CSPGs) in the glial scar following acute damage to the central nervous system (CNS) limits the regeneration of injured axons. Given the rich diversity of CSPG core proteins and patterns of GAG sulfation, identifying the composition of these CSPGs is essential for understanding their roles in injury and repair. Differential expression of core proteins and sulfation patterns have been characterized in the brain and spinal cord of mice and rats, but a comprehensive study of these changes following optic nerve injury has not yet been performed. Here, we show that the composition of CSPGs in the optic nerve and retina following optic nerve crush (ONC) in mice and rats exhibits an increase in aggrecan, brevican, phosphacan, neurocan and versican, similar to changes following spinal cord injury. We also observe an increase in inhibitory 4-sulfated (4S) GAG chains, which suggests that the persistence of CSPGs in the glial scar opposes the growth of CNS axons, thereby contributing to the failure of regeneration and recovery of function.

Sensory deafferentation modulates and redistributes neurocan in the rat auditory brainstem

INTRODUCTION

Cochlear ablation causing sensory deafferentation (SD) of the cochlear nucleus triggers complex re-arrangements in the cellular and molecular communication networks of the adult mammalian central auditory system. Participation of the extracellular matrix (ECM) in these processes is not well understood.

METHODS

We investigated consequences of unilateral SD for the expression and distribution of the chondroitin sulfate proteoglycans, neurocan (Ncan) and aggrecan (Agg), alongside various plasticity markers in the auditory brainstem of the adult rat using immunohistochemical techniques.

RESULTS

In the deafferented ventral cochlear nucleus (VCN), Ncan expression increased massively within 3 postoperative days (POD), but rapidly decreased thereafter. Agg showed a similar but less pronounced progression. Decrease in Ncan was spatially and temporally related to the re-innervation of VCN documented by the emergence of growth-associated protein Gap43 contained in nerve fibers and presynaptic boutons. Concurrently, astrocytes grew and expressed matrix metalloproteinase-2 (MMP2), an enzyme known to emerge only under re-innervation of VCN. MMP2 is capable of cleaving both Ncan and Agg when released. A transient modulation of the ECM in the central inferior colliculus on the side opposite to SD occurred by POD1. Modulations of glutamatergic synapses and Gap43 expression were detected, reflecting state changes of the surrounding tissue induced by transsynaptic effects of SD.

CONCLUSIONS

The ECM variously participates in adaptive responses to sudden deafness by SD on several levels along the central auditory pathway, with a striking spatial and temporal relationship of Ncan modulation to astrocytic activation and to synaptogenesis.

Proteolytic Remodeling of Perineuronal Nets: Effects on Synaptic Plasticity and Neuronal Population Dynamics

The perineuronal net (PNN) represents a lattice-like structure that is prominently expressed along the soma and proximal dendrites of parvalbumin- (PV-) positive interneurons in varied brain regions including the cortex and hippocampus. It is thus apposed to sites at which PV neurons receive synaptic input. Emerging evidence suggests that changes in PNN integrity may affect glutamatergic input to PV interneurons, a population that is critical for the expression of synchronous neuronal population discharges that occur with gamma oscillations and sharp-wave ripples. The present review is focused on the composition of PNNs, posttranslation modulation of PNN components by sulfation and proteolysis, PNN alterations in disease, and potential effects of PNN remodeling on neuronal plasticity at the single-cell and population level.

RNAi-mediated ephrin-B2 silencing attenuates astroglial-fibrotic scar formation and improves spinal cord axon growth

AIMS

Astroglial-fibrotic scar formation following central nervous system injury can help repair blood-brain barrier and seal the lesion, whereas it also represents a strong barrier for axonal regeneration. Intensive preclinical efforts have been made to eliminate/reduce the inhibitory part and, in the meantime, preserve the beneficial role of astroglial-fibrotic scar.

METHODS

In this study, we established an in vitro system, in which coculture of astrocytes and meningeal fibroblasts was treated with exogenous transforming growth factor-β1 (TGF-β1) to form astroglial-fibrotic scar-like cell clusters, and thereby evaluated the efficacy of RNAi targeting ephrin-B2 in preventing scar formation from the very beginning. We further tested the effect of RNAi-based mitigation of astroglial-fibrotic scar on spinal axon outgrowth on a custom-made microfluidic platform.

RESULTS

We found that siRNA targeting ephrin-B2 significantly reduced both the number and the diameter of cell clusters induced by TGF-β1 and diminished the expression of aggrecan and versican in the coculture, and allowed for significantly longer extension of outgrowing spinal cord axons into astroglial-fibrotic scar as assessed on the microfluidic platform.

CONCLUSIONS

These results suggest that astroglial-fibrotic scar formation and particularly the expression of aggrecan and versican could be mitigated by ephrin-B2 specific siRNA, thus improving the microenvironment for spinal axon regeneration.

Tumor Necrosis Factor-stimulated Gene-6 (TSG-6) Is Constitutively Expressed in Adult Central Nervous System (CNS) and Associated with Astrocyte-mediated Glial Scar Formation following Spinal Cord Injury

Tumor necrosis factor (TNF)-stimulated gene-6 (TSG-6) binds to hyaluronan and can reorganize/stabilize its structure, also enhancing the binding of this glycosaminoglycan to its cell surface receptor, CD44. TSG-6 is rapidly up-regulated in response to inflammatory cytokines protecting tissues from the damaging effects of inflammation. Despite TSG-6 treatment having been shown to improve outcomes in an experimental model of traumatic brain injury, TSG-6 expression has not been extensively studied in the central nervous system (CNS). We hereby analyzed the expression profile of TSG-6 in the developing CNS and following injury. We show that TSG-6 is expressed in the rat CNS by GFAP(+) and CD44(+) astrocytes, solely in the mature brain and spinal cord, and is not present during the development of the CNS. TSG-6(-/-) mice present a reduced number of GFAP(+) astrocytes when compared with the littermate TSG-6(+/-) mice. TSG-6 expression is drastically up-regulated after injury, and the TSG-6 protein is present within the glial scar, potentially coordinating and stabilizing the formation of this hyaluronan-rich matrix. This study shows that TSG-6 is expressed in the CNS, suggesting a role for TSG-6 in astrocyte activation and tissue repair. We hypothesize that within this context TSG-6 could participate in the formation of the glial scar and confer anti-inflammatory properties. Further studies are required to elucidate the therapeutic potential of targeting TSG-6 after CNS injury to promote its protective effects while reducing the inhibitory properties of the glial scar in axon regeneration.

Expression of ADAMTS-1, -4, -5 and TIMP-3 in normal and multiple sclerosis CNS white matter

ADAMTS (a disintegrin and metalloproteinase with thrombospondin motifs) -1, -4 and -5 proteases have been identified in the CNS at the mRNA level. These glutamyl endopeptidases, inhibited by tissue inhibitor of metalloproteinases (TIMP)-3, are key enzymes in the degradation of the aggregating chondroitin sulphate proteoglycans (CSPGs), and may therefore play a role in CNS extracellular matrix (ECM) changes in multiple sclerosis (MS). We have investigated ADAMTS and TIMP-3 expression in normal and MS CNS white matter by real-time RT-PCR, western blotting and immunohistochemistry. We report for the first time the presence of ADAMTS-1, -4 and -5 in normal and MS white matter. Levels of ADAMTS-1 and -5 mRNA were decreased in MS compared to normal tissue, with no significant change in ADAMTS-4 mRNA levels. Protein levels of ADAMTS-4 were significantly higher in MS tissue compared to normal tissue. Immunohistochemical studies demonstrated that ADAMTS-4 was associated predominantly with astrocytes with increased expression within MS lesions. TIMP-3 mRNA was significantly decreased in MS compared to controls. These studies suggest a role for ADAMTS-4 in the pathogenesis of MS. Further studies on the activity of ADAMTS-4 will enable a better understanding of its role in the turnover of the ECM of white matter in MS.

Proteoglycans of reactive rat cortical astrocyte cultures: abundance of N-unsubstituted glucosamine-enriched heparan sulfate

"Reactive" astrocytes and other glial cells in the injured CNS produce an altered extracellular matrix (ECM) that influences neuronal regeneration. We have profiled the glycosaminoglycan (GAG) component of proteoglycans (PGs) produced by reactive neonatal rat cortical astrocytes, and have quantified their neurite-outgrowth inhibitory activity. PGs extracted from cell layers and medium were fractionated on DEAE-Sephacel with a gradient of NaCl from 0.15 to 1.0 M. Monosaccharide analysis of the major peaks eluting at 0.6 M NaCl indicated an excess of GlcNH₂ to GalNH₂, suggesting an approximate HS/CS ratio of 6.2 in the cell layer and 4.2 in the medium. Chondroitinase ABC-generated disaccharide analysis of cell and medium PGs showed a >5-fold excess of chondroitin 4-sulfate over chondroitin 6-sulfate. Heparin lyase-generated disaccharides characteristic of the highly sulfated S-domain regions within HS were more abundant in cell layer than medium-derived PGs. Cell layer and medium HS disaccharides contained ~20% and ~40% N-unsubstituted glucosamine respectively, which is normally rare in HS isolated from most tissues. NGF-stimulated neurite outgrowth assays using NS-1 (PC12) neuronal cells on adsorbed substrata of PGs isolated from reactive astrocyte medium showed pronounced inhibition of neurite outgrowth, and aggregation of NS-1 cells. Cell layer PGs from DEAE-Sephacel pooled fractions having high charge density permitted greater NGF-stimulated outgrowth than PGs with lower charge density. Our results indicate the synthesis of both inhibitory and permissive PGs by activated astrocytes that may correlate with sulfation patterns and HS/CS ratios.

Extracellular matrix regulation of inflammation in the healthy and injured spinal cord

Throughout the body, the extracellular matrix (ECM) provides structure and organization to tissues and also helps regulate cell migration and intercellular communication. In the injured spinal cord (or brain), changes in the composition and structure of the ECM undoubtedly contribute to regeneration failure. Less appreciated is how the native and injured ECM influences intraspinal inflammation and, conversely, how neuroinflammation affects the synthesis and deposition of ECM after CNS injury. In all tissues, inflammation can be initiated and propagated by ECM disruption. Molecules of ECM newly liberated by injury or inflammation include hyaluronan fragments, tenascins, and sulfated proteoglycans. These act as "damage-associated molecular patterns" or "alarmins", i.e., endogenous proteins that trigger and subsequently amplify inflammation. Activated inflammatory cells, in turn, further damage the ECM by releasing degradative enzymes including matrix metalloproteinases (MMPs). After spinal cord injury (SCI), destabilization or alteration of the structural and chemical compositions of the ECM affects migration, communication, and survival of all cells - neural and non-neural - that are critical for spinal cord repair. By stabilizing ECM structure or modifying their ability to trigger the degradative effects of inflammation, it may be possible to create an environment that is more conducive to tissue repair and axon plasticity after SCI.

Chondroitin sulfate proteoglycans inhibit oligodendrocyte myelination through PTPσ

CNS damage often results in demyelination of spared axons due to oligodendroglial cell death and dysfunction near the injury site. Although new oligodendroglia are generated following CNS injury and disease, the process of remyelination is typically incomplete resulting in long-term functional deficits. Chondroitin sulfate proteoglycans (CSPGs) are upregulated in CNS grey and white matter following injury and disease and are a major component of the inhibitory scar that suppresses axon regeneration. CSPG inhibition of axonal regeneration is mediated, at least in part, by the protein tyrosine phosphatase sigma (PTPσ) receptor. Recent evidence demonstrates that CSPGs inhibit OL process outgrowth, however, the means by which their effects are mediated remains unclear. Here we investigate the role of PTPσ in CSPG inhibition of OL function. We found that the CSPGs, aggrecan, neurocan and NG2 all imposed an inhibitory effect on OL process outgrowth and myelination. These inhibitory effects were reversed by degradation of CSPGs with Chondroitinase ABC prior to OL exposure. RNAi-mediated down-regulation of PTPσ reversed the inhibitory effect of CSPGs on OL process outgrowth and myelination. Likewise, CSPG inhibition of process outgrowth and myelination was significantly reduced in cultures containing PTPσ(-/-) OLs. Finally, inhibition of Rho-associated kinase (ROCK) increased OL process outgrowth and myelination during exposure to CSPGs. These results suggest that in addition to their inhibitory effects on axon regeneration, CSPGs have multiple inhibitory actions on OLs that result in incomplete remyelination following CNS injury. The identification of PTPσ as a receptor for CSPGs, and the participation of ROCK downstream of CSPG exposure, reveal potential therapeutic targets to enhance white matter repair in the damaged CNS.

ADAMTS1, ADAMTS5, ADAMTS9 and aggrecanase-generated proteoglycan fragments are induced following spinal cord injury in mouse

ADAMTS (a disintegrin and metalloproteinase with thrombospondin motifs) proteinases are involved in a variety of biological processes such as angiogenesis, cancer and arthritis. ADAMTSs appears to be responsible for the cleavage of proteoglycans in several tissues including brain and cartilage. Chondroitin sulfate proteoglycans (CSPGs) maintains the integrity of the brain extracellular matrix and major inhibitory contributors for glial scar and neural plasticity. The activity of aggrecanases in the central nervous system (CNS) has been reported. ADAMTSs are an enzyme degrading CSPGs in the brain. However, there is a little knowledge regarding ADAMTSs in the CNS. We investigated the expression levels of ADAMTSs mRNAs by RT-PCR after spinal cord injury in mouse. Transcripts encoding 4 of the 19 known ADAMTSs were evaluated in the mouse spinal cord following injury. ADAMTS1, -5 and -9 expression levels were found to be upregulated. No change was observed in ADAMTS4 expression. By means of immunohistochemistry, ADAMTSs were detected in the astrocytes implying its cellular source in SCI. Western blot analyses indicated that aggrecanase-generated proteoglycan fragments are produced after SCI.

Lectican proteoglycans, their cleaving metalloproteinases, and plasticity in the central nervous system extracellular microenvironment

The extracellular matrix (ECM) in the central nervous system actively orchestrates and modulates changes in neural structure and function in response to experience, after injury, during disease, and with changes in neuronal activity. A component of the multi-protein, ECM aggregate in brain, the chondroitin sulfate (CS)-bearing proteoglycans (PGs) known as lecticans, inhibit neurite outgrowth, alter dendritic spine shape, elicit closure of critical period plasticity, and block target reinnervation and functional recovery after injury as the major component of a glial scar. While removal of the CS chains from lecticans with chondroitinase ABC improves plasticity, proteolytic cleavage of the lectican core protein may change the conformation of the matrix aggregate and also modulate neural plasticity. This review centers on the roles of the lecticans and the endogenous metalloproteinase families that proteolytically cleave lectican core proteins, the matrix metalloproteinases (MMPs) and a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTSs), in neural plasticity. These extracellular metalloproteinases modulate structural neural plasticity-including changes in neurite outgrowth and dendritic spine remodeling-and synaptic plasticity. Some of these actions have been demonstrated to occur via cleavage of the PG core protein. Other actions of the proteases include cleavage of non-matrix substrate proteins, whereas still other actions may occur directly at the cell surface without proteolytic cleavage. The data convincingly demonstrate that metalloproteinases modulate physiological and pathophysiological neural plasticity.

Localization and developmental expression patterns of CSPG-cs56 (aggrecan) in normal and dystrophic retinas in two rat strains

Proteoglycans have a number of important functions in the central nervous system. Aggrecan (hyaluronan-binding proteoglycan, CSPG-cs56) is found in the extracellular matrix of cartilage as well as in the developing brain. We compared the postnatal distribution of CSPG-cs56 in Long Evans (LE) and Royal College of Surgeons (RCS) rat retinas to determine if this proteoglycan played a role in the development of dystrophic retinas. CSPG-cs56 expression was examined in rat retinas aged between birth (postnatal day 0, P0) and P150 using immunofluorescence and Western-blots. Immunofluorescence was quantified using ImageJ. GFAP staining was used to compare Müller cell labeling and the distribution of CSPG-cs56. Both rat strains showed a significant rise in total retinal CSPG-cs56 between P0 and P21; values peaked on P21 in LE rats and P14 in RCS rats. CSPG-cs56 then significantly decreased to lower levels (P35) in both strains before reaching significantly higher levels by P90-P150. CSPG-cs56 positive staining was present in the ganglion cell layer at birth and clear layering of the inner plexiform layer was seen between P7 and P21 due to dendritic staining of retinal ganglion cells. Staining was less intense and diffuse within the outer plexiform over a similar time-course. Light CSPG-cs56 labeling in the region of the outer segments was present at (P14) and became more intense as the retina approached maturity. CSPG-cs56 in the outer segments was the main contributor to the higher expression in older animals. Substantial differences in CSPG-cs56 labeling were not seen between LE and RCS rats. There was no evidence to suggest that Müller cells were the source of CSPG-cs56 in either rat strain, although their staining distributions had a degree of overlap. The lack of significant differences between LE and RCS rats indicates that CSPG-cs56 may not be involved in the degenerative process or the reorganization of the RCS rat retina. We suggest that the main role of CPSG-cs56 is to maintain retinal ganglion cell dendritic structure in the inner plexiform layer and is closely related to providing adequate support and flexibility for the photoreceptor outer segments, which is necessary to maintain their function.

Alterations in chondroitin sulfate proteoglycan expression occur both at and far from the site of spinal contusion injury

Chondroitin sulfate proteoglycans (CSPGs) present an inhibitory barrier to axonal growth and plasticity after trauma to the central nervous system. These extracellular and membrane bound molecules are altered after spinal cord injuries, but the magnitude, time course, and patterns of expression following contusion injury have not been fully described. Western blots and immunohistochemistry were combined to assess the expression of four classically inhibitory CSPGs, aggrecan, neurocan, brevican and NG2, at the lesion site and in distal segments of cervical and thoracic spinal cord at 3, 7, 14 and 28 days following a severe mid-thoracic spinal contusion. Total neurocan and the full-length (250 kDa) isoform were strongly upregulated both at the lesion epicenter and in cervical and lumbar segments. In contrast, aggrecan and brevican were sharply reduced at the injury site and were unchanged in distal segments. Total NG2 protein was unchanged across the injury site, while NG2+ profiles were distributed throughout the lesion site by 14 days post-injury (dpi). Far from the lesion, NG2 expression was increased at lumbar, but not cervical spinal cord levels. To determine if the robust increase in neurocan at the distal spinal cord levels corresponded to regions of increased astrogliosis, neurocan and GFAP immunoreactivity were measured in gray and white matter regions of the spinal enlargements. GFAP antibodies revealed a transient increase in reactive astrocyte staining in cervical and lumbar cord, peaking at 14 dpi. In contrast, neurocan immunoreactivity was specifically elevated in the cervical dorsal columns and in the lumbar ventral horn and remained high through 28 dpi. The long lasting increase of neurocan in gray matter regions at distal levels of the spinal cord may contribute to the restriction of plasticity in the chronic phase after SCI. Thus, therapies targeted at altering this CSPG both at and far from the lesion site may represent a reasonable addition to combined strategies to improve recovery after SCI.

Adamts5 deletion blocks murine dermal repair through CD44-mediated aggrecan accumulation and modulation of transforming growth factor β1 (TGFβ1) signaling

ADAMTS5 has been implicated in the degradation of cartilage aggrecan in human osteoarthritis. Here, we describe a novel role for the enzyme in the regulation of TGFβ1 signaling in dermal fibroblasts both in vivo and in vitro. Adamts5(-/-) mice, generated by deletion of exon 2, exhibit impaired contraction and dermal collagen deposition in an excisional wound healing model. This was accompanied by accumulation in the dermal layer of cell aggregates and fibroblastic cells surrounded by a pericellular matrix enriched in full-length aggrecan. Adamts5(-/-) wounds exhibit low expression (relative to wild type) of collagen type I and type III but show a persistently elevated expression of tgfbRII and alk1. Aggrecan deposition and impaired dermal repair in Adamts5(-/-) mice are both dependent on CD44, and Cd44(-/-)/Adamts5(-/-) mice display robust activation of TGFβ receptor II and collagen type III expression and the dermal regeneration seen in WT mice. TGFβ1 treatment of newborn fibroblasts from wild type mice results in Smad2/3 phosphorylation, whereas cells from Adamts5(-/-) mice phosphorylate Smad1/5/8. The altered TGFβ1 response in the Adamts5(-/-) cells is dependent on the presence of aggrecan and expression of CD44, because Cd44(-/-)/Adamts5(-/-) cells respond like WT cells. We propose that ADAMTS5 deficiency in fibrous tissues results in a poor repair response due to the accumulation of aggrecan in the pericellular matrix of fibroblast progenitor cells, which prevents their transition to mature fibroblasts. Thus, the capacity of ADAMTS5 to modulate critical tissue repair signaling events suggests a unique role for this enzyme, which sets it apart from other members of the ADAMTS family of proteases.

Plasticity after spinal cord injury: relevance to recovery and approaches to facilitate it

Motor, sensory, and autonomic functions can spontaneously return or recover to varying extents in both humans and animals, regardless of the traumatic spinal cord injury (SCI) level and whether it was complete or incomplete. In parallel, adverse and painful functions can appear. The underlying mechanisms for all of these diverse functional changes are summarized under the term plasticity. Our review will describe what is known regarding this phenomenon after traumatic SCI and focus on its relevance to motor and sensory recovery. Although it is still somewhat speculative, plasticity can be found throughout the neuraxis and includes various changes ranging from alterations in the properties of spared neuronal circuitries, intact or lesioned axon collateral sprouting, and synaptic rearrangements. Furthermore, we will discuss a selection of potential approaches for facilitating plasticity as possible SCI treatments. Because a mechanism underlying spontaneous plasticity and recovery might be motor activity and the related neuronal activity, activity-based therapies are being used and investigated both clinically and experimentally. Additional pharmacological and gene-delivery approaches, based on plasticity being dependent on the delicate balance between growth inhibition and promotion as well as the basic intrinsic growth ability of the neurons themselves, have been found to be effective alone and in combination with activity-based therapies. The positive results have to be tempered with the reality that not all plasticity is beneficial. Therefore, a tremendous number of questions still need to be addressed. Ultimately, answers to these questions will enhance plasticity's potential for improving the quality of life for persons with SCI.

Schwann cell migration is integrin-dependent and inhibited by astrocyte-produced aggrecan

Schwann cells transplantation has considerable promise in spinal cord trauma to bridge the site of injury and for remyelination in demyelinating conditions. They support axonal regeneration and sprouting by secreting growth factors and providing a permissive surface and matrix molecules while shielding axons from the inhibitory environment of the central nervous system. However, following transplantation Schwann cells show limited migratory ability and they are unable to intermingle with the host astrocytes. This in turn leads to formation of a sharp boundary and an abrupt transition between the Schwann cell graft and the host tissue astrocytes, therefore preventing regenerating axons from exiting the graft. The objective of this study was to identify inhibitory elements on astrocytes involved in restricting Schwann cell migration. Using in vitro assays of cell migration, we show that aggrecan produced by astrocytes is involved in the inhibition of Schwann cell motility on astrocytic monolayers. Knockdown of this proteoglycan in astrocytes using RNAi or digestion of glycosaminglycan chains on aggrecan improves Schwann cell migration. We further show aggrecan mediates its effect by disruption of integrin function in Schwann cells, and that the inhibitory effects of aggrecan can overcome by activation of Schwann cell integrins.

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.

Traumatic brain injury results in disparate regions of chondroitin sulfate proteoglycan expression that are temporally limited

Axonal injury is a major hallmark of traumatic brain injury (TBI), and it seems likely that therapies directed toward enhancing axon repair could potentially improve functional outcomes. One potential target is chondroitin sulfate proteoglycans (CSPGs), which are major axon growth inhibitory molecules that are generally, but not always, up-regulated after central nervous system injury. The current study was designed to determine temporal changes in cerebral cortical mRNA or protein expression levels of CSPGs and to determine their regional localization and cellular association by using immunohistochemistry in a controlled cortical impact model of TBI. The results showed significant increases in versican mRNA at 4 and 14 days after TBI but no change in neurocan, aggrecan, or phosphacan. Semiquantitative Western blot (WB) analysis of cortical CSPG protein expression revealed a significant ipsilateral decrease of all CSPGs at 1 day after TBI. Lower CSPG protein levels were sustained until at least 14 days, after which the levels began to normalize. Immunohistochemistry data confirm previous reports of regional increases in CSPG proteins after CNS injury, seen primarily within the developing glial scar after TBI, but also corroborate the WB data by revealing wide areas of pericontusional tissue that are deficient in both extracellular and perineuronal net-associated CSPGs. Given the evidence that CSPGs are largely inhibitory to axonal growth, we interpret these data to indicate a potential for regional spontaneous plasticity after TBI. If this were the case, the gradual normalization of CSPG proteins over time postinjury would suggest that this may be temporally as well as regionally limited.

Adipose-derived stem cells from pregnant women show higher proliferation rate unrelated to estrogen

BACKGROUND

Adipose tissue contains an abundant population of multipotent adipose-derived stem cells (ASCs) and has been an excellent source of mesenchymal stem cells for cell therapy and tissue engineering. To ensure successful cell therapies, consistency of stem cell performance across donors is critical. However, the effect of the donor's reproductive status on ASC proliferation rate and differentiation capacity is undefined.

METHODS

We investigated whether the yield and function of ASCs are affected by the woman's reproductive status: pregnancy, premenopause or menopause. ASCs were isolated from the abdomen of 15 women and their proliferation rates and differentiation capacities were compared by cell count. The capacity of ASCs to differentiate into the chondrogenic lineage was investigated by quantitative real-time polymerase chain reaction and immunohistochemistry.

RESULTS

There was no significant difference in the differentiation capacity between the three groups, whereas the proliferation rate of ASCs from pregnant women was significantly higher than from the other two groups (P < 0.05). The proliferation rate of ASCs after estrogen treatment remained unchanged.

CONCLUSIONS

Despite the higher proliferation rate in pregnant women, ASCs showed consistency in cell differentiation capacity and were unaffected by donor status. This suggests that factors other than estrogen are responsible for the difference in proliferation.

Extracellular matrix of the central nervous system: from neglect to challenge

The basic concept, that specialized extracellular matrices rich in hyaluronan, chondroitin sulfate proteoglycans (aggrecan, versican, neurocan, brevican, phosphacan), link proteins and tenascins (Tn-R, Tn-C) can regulate cellular migration and axonal growth and thus, actively participate in the development and maturation of the nervous system, has in recent years gained rapidly expanding experimental support. The swift assembly and remodeling of these matrices have been associated with axonal guidance functions in the periphery and with the structural stabilization of myelinated fiber tracts and synaptic contacts in the maturating central nervous system. Particular interest has been focused on the putative role of chondroitin sulfate proteoglycans in suppressing central nervous system regeneration after lesions. The axon growth inhibitory properties of several of these chondroitin sulfate proteoglycans in vitro, and the partial recovery of structural plasticity in lesioned animals treated with chondroitin sulfate degrading enzymes in vivo have significantly contributed to the increased awareness of this long time neglected structure.

Aggrecan components differentially modulate nerve growth factor-responsive and neurotrophin-3-responsive dorsal root ganglion neurite growth

Aggrecan is one of the major chondroitin sulfate proteoglycans (CSPGs) expressed in the central nervous system. The signaling pathways activated downstream of cell interaction with aggrecan and with CSPGs in general and the importance of chondroitin sulfate-glycosaminoglycan side chains in their inhibition are unclear. Therefore, to analyze the effect of different components of aggrecan in inhibiting neurite growth, neurite outgrowth was quantified in an in vitro model in which chick dorsal root ganglion (DRG) explants were grown on substrates containing aggrecan bound to hyaluronan and link protein as a macromolecular aggregate, aggrecan monomers, hyaluronan, or ChABC-treated aggrecan. Aggrecan aggregate, aggrecan monomer, and hyaluronan inhibited neurite outgrowth from nerve growth factor (NGF)- and neurotrophin-3 (NT3)-responsive DRG neurons. Aggrecan inhibition was dependent on its chondroitin sulfate-glycosaminoglycans, as ChABC digestion alleviated neurite inhibition because of aggrecan. Growth cones displayed full or partial collapse on aggrecan aggregate, hyaluronan, and ChABC-treated aggrecan. Inhibition of Rho kinase (ROCK) with Y27632 increased neurite growth on some but not all of the aggrecan components tested. With NGF in the culture medium, Y27632 increased neurite outgrowth on aggrecan aggregate, monomers, and ChABC-treated aggrecan, but not on hyaluronan. The ROCK inhibitor also increased NT3-responsive outgrowth on aggrecan aggregate and hyaluronan, but not on ChABC-treated aggrecan. This study showed that the matrix proteoglycan aggrecan and its components have multiple effects on neurite outgrowth and that some of these effects involve the Rho/ROCK pathway.

Discordant localization of WFA reactivity and brevican/ADAMTS-derived fragment in rodent brain

Background

Proteoglycan (PG) in the extracellular matrix (ECM) of the central nervous system (CNS) may act as a barrier for neurite elongation in a growth tract, and regulate other characteristics collectively defined as structural neural plasticity. Proteolytic cleavage of PGs appears to alter the environment to one favoring plasticity and growth. Brevican belongs to the lectican family of aggregating, chondroitin sulfate (CS)-bearing PGs, and it modulates neurite outgrowth and synaptogenesis. Several ADAMTSs (a disintegrin and metalloproteinase with thrombospondin motifs) are glutamyl-endopeptidases that proteolytically cleave brevican. The purpose of this study was to localize regions of adult CNS that contain a proteolytic-derived fragment of brevican which bears the ADAMTS-cleaved neoepitope sequence. These regions were compared to areas of Wisteria floribunda agglutin (WFA) reactivity, a common reagent used to detect "perineuronal nets" (PNNs) of intact matrix and a marker which is thought to label regions of relative neural stability.

Results

WFA reactivity was found primarily as PNNs, whereas brevican and the ADAMTS-cleaved fragment of brevican were more broadly distributed in neuropil, and in particular regions localized to PNNs. One example is hippocampus where the ADAMTS-cleaved brevican fragment is found surrounding pyramidal neurons, in neuropil of stratum oriens/radiatum and the lacunosum moleculare. The fragment was less abundant in the molecular layer of the dentate gyrus. Mostly PNNs of scattered interneurons along the pyramidal layer were identified by WFA. In lateral thalamus, the reticular thalamic nucleus stained abundantly with WFA whereas ventral posterior nuclei were markedly immunopositive for ADAMTS-cleaved brevican. Using Western blotting techniques, no common species were reactive for brevican and WFA.

Conclusion

In general, a marked discordance was observed in the regional localization between WFA and brevican or the ADAMTS-derived N-terminal fragment of brevican. Functionally, this difference may correspond to regions with varied prevalence for neural stability/plasticity.

Chondroitinase ABC has a long-lasting effect on chondroitin sulphate glycosaminoglycan content in the injured rat brain

Chondroitin sulphate proteoglycans (CSPGs) are axon growth inhibitory molecules present in the glial scar that play a part in regeneration failure after damage to the CNS and which restrict CNS plasticity. Removal of chondroitin sulphate glycosaminoglycan (GAG) chains with chondroitinase-ABC (chABC) in models of CNS injury promotes both axon regeneration and plasticity. We have analysed the immediate and long-term effects of a single injection of chABC on CSPGs, GAGs and axon regeneration. We made unilateral nigrostriatal lesions in adult rats accompanied by an adjacent infusion of either chABC or a bacterial-derived control enzyme (penicillinase). Within 24 h of chABC treatment there was digestion of GAGs, including hyaluronan, and a reduction in neurocan in an area extending 1.5 mm around the injection site. Around 50% of GAG is inaccessible to chABC digestion, even in tissue digested in vitro, which probably represents intracellular stores. In control penicillinase treated animals, total GAGs recovered from the lesioned brains were up-regulated by 4-fold 7 days after injury and gradually decreased to normal at 28 days post-lesion. In chondroitinase-treated animals, the total GAG remained at low level throughout the 28-day experimental period. This suggests the persistence of active chABC for at least 10 days after injection which is able to digest CSPGs released from cells during this time. This was confirmed by immunological detection of enzyme for 10 days and by retrieval of active enzyme from the brain at 10 days after injection. Our results suggest that a single injection of chABC can produce an environment conducive to CNS repair for over 10 days.

Aggrecanolysis in human osteoarthritis: confocal localization and biochemical characterization of ADAMTS5-hyaluronan complexes in articular cartilages

OBJECTIVE

Human osteoarthritis (OA) is characterized by aggrecanase-mediated depletion of cartilage aggrecan. We have examined the abundance, location and some biochemical properties of the six known aggrecanases (A disintegrin and metalloproteinase with thrombospondin-like motifs 1 (ADAMTS1) 4, 5, 8, 9 and 15) in normal and OA human cartilages.

METHODS

Formalin-fixed, ethylenediamine tetraacetic acid (EDTA)-decalcified sections of full-depth cartilage from human OA tibial plateaus and normal control samples were studied by confocal imaging. Probes included specific antibodies to aggrecanases and two aggrecan epitopes, as well as biotinylated hyaluronan binding protein (HABP) for hyaluronan (HA) visualization. Cartilage extracts were analyzed by Western blot for the individual proteinases and aggrecan fragments.

RESULTS

ADAMTS5 was present in association with cells throughout normal cartilage and was markedly increased in OA, particularly in clonal groups in the superficial and transitional zones, where it was predominantly co-localized with HA. Consistent with the confocal analysis, a high molecular weight complex of ADAMTS5 and HA was isolated from human OA cartilage by isotonic salt extraction and chromatography on Superose 6. The complex eluted with an apparent molecular size of about 2x10(6) and contained major ADAMTS5 forms of 150, 60, 40 and 30kDa. The yield of most forms on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) was markedly enhanced by prior digestion of the complex with either Streptomyces hyaluronidase or chondroitinase ABC.

CONCLUSION

ADAMTS5 abundance and distribution in human OA cartilages is consistent with a central role for this enzyme in destructive aggrecanolysis. HA-dependent sequestration of ADAMTS5 in the pericellular matrix may be a mechanism for regulating the activity of this proteinase in human OA cartilage.

How does chondroitinase promote functional recovery in the damaged CNS?

A number of recent studies have established that the bacterial enzyme chondroitinase ABC promotes functional recovery in the injured CNS. The issue of how it works is rarely addressed, however. The effects of the enzyme are presumed to be due to the degradation of inhibitory chondroitin sulphate GAG chains. Here we review what is known about the composition, structure and distribution of the extracellular matrix in the CNS, and how it changes in response to injury. We summarize the data pertaining to the ability of chondroitinase to promote functional recovery, both in the context of axon regeneration and the reactivation of plasticity. We also present preliminary data on the persistence of the effects of the enzyme in vivo, and its hyaluronan-degrading activity in CNS homogenates in vitro. We then consider precisely how the enzyme might influence functional recovery in the CNS. The ability of chondroitinase to degrade hyaluronan is likely to result in greater matrix disruption than the degradation of chondroitin sulphate alone.

The role of chondroitin sulfate proteoglycans in regeneration and plasticity in the central nervous system

Chondroitin sulfate proteoglycans (CSPGs) consist of a core protein and glycosaminoglycan (GAG) chains. There is enormous structural diversity among CSPGs due to variation in the core protein, the number of GAG chains and the extent and position of sulfation. Most CSPGs are secreted from cells and participate in the formation of the extracellular matrix (ECM). CSPGs are able to interact with various growth-active molecules and this may be important in their mechanism of action. In the normal central nervous system (CNS), CSPGs have a role in development and plasticity during postnatal development and in the adult. Plasticity is greatest in the young, especially during critical periods. CSPGs are crucial components of perineuronal nets (PNNs). PNNs have a role in closure of the critical period and digestion of PNNs allows their re-opening. In the adult, CSPGs play a part in learning and memory and the hypothalamo-neurohypophysial system. CSPGs have an important role in CNS injuries and diseases. After CNS injury, CSPGs are the major inhibitory component of the glial scar. Removal of CSPGs improves axonal regeneration and functional recovery. CSPGs may also be involved in the pathological processes in diseases such as epilepsy, stroke and Alzheimer's disease. Several possible methods of manipulating CSPGs in the CNS have recently been identified. The development of methods to remove CSPGs has considerable therapeutic potential in a number of CNS disorders.

Bone morphogenetic proteins promote gliosis in demyelinating spinal cord lesions

OBJECTIVE

To determine the role of bone morphogenetic proteins (BMPs) in stimulating glial scar formation in demyelinating lesions of the adult spinal cord.

METHODS

The dorsal columns of adult rats were injected with lysolecithin to induce a local demyelinating lesion. Levels of BMP4 and BMP7 proteins were assayed and compared with glial fibrillary acidic protein expression in the injury area. BMP-responsive cells were identified by expression of phosphorylated Smad1/5/8. Cultures of mature spinal cord astrocytes were treated with BMP4, and levels of chondroitin sulphate proteoglycans (CSPGs) were measured. The effect of BMP4 on CSPG gene regulation was determined by real-time polymerase chain reaction for CSPG core proteins.

RESULTS

BMP4 and BMP7 increase rapidly at the site of demyelination, and astrocytes surrounding the lesion increase expression of phosphorylated Smad1/5/8. Cultured mature astrocytes respond directly to BMPs with Smad1 translocation to the nucleus, increased phosphorylated Smad1/5/8, and increases in glial fibrillary acidic protein and CSPG expression. BMP treatment also increased CSPG messenger RNA for CSPG core proteins, including aggrecan and neurocan. Increases in CSPG expression in astrocytes by BMPs were blocked by the inhibitor noggin. Injections of BMP4 or BMP7 into the dorsal columns in the absence of demyelination led to increases in CSPG expression.

INTERPRETATION

Local increases in BMPs at the site of a demyelinating lesion causes upregulation of gliosis, glial scar formation, and heightened expression of CSPGs such as neurocan and aggrecan that may inhibit remyelination.

Dynamic role of kallikrein 6 in traumatic spinal cord injury

Kallikrein 6 (K6) is a member of the kallikrein gene family that comprises 15 structurally and functionally related serine proteases. In prior studies we showed that, while this trypsin-like enzyme is preferentially expressed in neurons and oligodendroglia of the adult central nervous system (CNS), it is up-regulated at sites of injury due to expression by infiltrating immune and resident CNS cells. Given this background we hypothesized that K6 is a key contributor to the pathophysiology of traumatic spinal cord injury (SCI), influencing neural repair and regeneration. Examination of K6 expression following contusion injury to the adult rat cord, and in cases of human traumatic SCI, indicated significant elevations at acute and chronic time points, not only at the injury site but also in cord segments above and below. Elevations in K6 were particularly prominent in macrophages, microglia and reactive astrocytes. To determine potential effects of elevated K6 on the regeneration environment, the ability of neurons to adhere to and extend processes on substrata which had been exposed to recombinant K6 was examined. Limited (1 h) or excess (24 h) K6-mediated proteolytic digestion of a growth-facilitatory substrate, laminin, significantly decreased neurite outgrowth. By contrast, similar hydrolysis of a growth-inhibitory substrate, aggrecan, significantly increased neurite extension and cell adherence. These data support the hypothesis that K6 enzymatic cascades mediate events secondary to spinal cord trauma, including dynamic modification of the capacity for axon outgrowth.

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

We have examined the regional distribution of several chondroitin sulfate proteoglycans (neurocan, brevican, versican, aggrecan, phosphacan), of their glycosaminoglycan moieties, and of tenascin-R in the spinal cord of adult rat. The relationships of these molecules with glial and neuronal populations, identified with appropriate markers, were investigated by using multiple fluorescence labeling combined with confocal microscopy. The results showed that the distribution of the examined molecules was similar at all spinal cord levels but displayed area-specific differences along the dorso-ventral axis, delimiting functionally and developmentally distinct areas. In the gray matter, laminae I and II lacked perineuronal nets (PNNs) of extracellular matrix and contained low levels of chondroitin sulfate glycosaminoglycans (CS-GAGs), brevican, and tenascin-R, possibly favoring the maintenance of local neuroplastic properties. Conversely, CS-GAGs, brevican, and phosphacan were abundant, with numerous thick PNNs, in laminae III-VIII and X. Motor neurons (lamina IX) were surrounded by PNNs that contained all molecules investigated but displayed various amounts of CS-GAGs. Double-labeling experiments showed that the presence of PNNs could not be unequivocally related to specific classes of neurons, such as motor neurons or interneurons identified by their expression of calcium-binding proteins (parvalbumin, calbindin, calretinin). However, a good correlation was found between PNNs rich in CS-GAGs and the neuronal expression of the Kv3.1b subunit of the potassium channel, a marker of fast-firing neurons. This observation confirms the correlation between the electrophysiological properties of these neurons and the specific composition of their microenvironment.

From barriers to bridges: chondroitin sulfate proteoglycans in neuropathology

Emerging studies have revealed new roles for the neural extracellular matrix in neuropathologies. The structure of this matrix is unusual and uniquely enriched in chondroitin sulfate proteoglycans, particularly those of the lectican family. Historically, lecticans have attracted considerable interest in the normal and injured brain for their prominent roles as inhibitors of cellular motility, neurite extension and synaptic plasticity. However, these molecules are structurally heterogeneous, have distinct expression patterns and mediate unique interactions, suggesting that they might have other functions in addition to their traditional role as chemorepulsants. Here, we review recent work demonstrating unique modifications and structural microheterogeneity of the lecticans in the diseased CNS, which might relate to novel roles of these molecules in neuropathologies.

Effects of covalently attached chondroitin sulfate on aggrecan cleavage by ADAMTS-4 and MMP-13

Aggrecan is degraded by several aggrecanase-1 (ADAMTS-4) isoforms differing in the number of sulfated glycosaminoglycan (sGAG)-binding motifs. ADAMTS-4 and MMPs cleave aggrecan more efficiently within the chondroitin sulfate (CS)-rich region than the interglobular domain (IGD). We investigated the influence of CS on aggrecan core protein cleavage by ADAMTS-4 (p68) and (p40) as well as MMP-13, which has no recognizable GAG-binding sites. Chondroitinase ABC-treated cartilage aggrecan was cleaved with ADAMTS-4 (p68) less efficiently than CS-substituted aggrecan within the CS-2 domain. Keratanase-treated aggrecan exhibited reduced IGD cleavage, but when both CS and KS were removed, the IGD cleavage was restored. This result suggests that KS in the IGD may compete with CS for ADAMTS-4 (p68) binding. In the absence of KS, however, p68 binding was shifted to the CS-2 domain. CS-deficient full-length recombinant aggrecan (rbAgg) was produced by chondroitinase ABC treatment, or by expression in the xylosyltransferase-deficient CHO-pgsA745 cell line. When digested with the ADAMTS-4 (p68), each of these preparations exhibited reduced CS-2 domain cleavage compared to CS-substituted CHO-K1 cell-derived aggrecan. Additionally, CS-deficient rbAgg showed increased IGD scission prior to cleavage within the CS-2 domain. ADAMTS-4 (p40) readily cleaved both rbAggs within the IGD, but cleaved poorly within the CS-2 domain, indicating little CS dependence. MMP-13, in contrast, cleaved the CS region and the IGD of both CS-substituted and CS-deficient rbAgg equally well. These data indicate that covalently bound CS enhances ADAMTS-4-mediated cleavage within the CS-rich region. MMP-13 also cleaves preferentially within the CS-region, but by an apparently CS-independent mechanism.

ADAMTS5-mediated aggrecanolysis in murine epiphyseal chondrocyte cultures

OBJECTIVE

Aggrecan degradation by aggrecanases [a disintegrin and metalloproteinase with thrombospondin-like motifs (ADAMTS) 1, 4, 5, 8, 9, 15] is considered to initiate much of the cartilage pathology seen in human arthritis, however, the proteinase responsible and its mode of control is unclear. The present work was done to examine mechanisms of aggrecanase control in a novel murine epiphyseal cell system and to determine whether ADAMTS5 alone is responsible for aggrecanolysis by these cells.

METHODS

Epiphyseal cells from 4-day-old mice (wild type, TS-5 (-/-), CD44(-/-), syndecan-1(-/-), membrane type-4 matrix metalloproteinase [MT4MMP(-/-)]) were maintained in non-adherent aggregate cultures and aggrecanolysis studied by biochemical and histochemical methods. Confocal immunolocalization analyses were done with specific probes for ADAMTS5, hyaluronan (HA) and aggrecanase-generated fragments of aggrecan.

RESULTS

Aggrecanolysis by these cells was specifically aggrecanase-mediated and it occurred spontaneously without the need for addition of catabolic stimulators. Chondrocytes from ADAMTS5-null mice were aggrecanase-inactive whereas all other mutant cells behaved as wild type in this regard suggesting that ADAMTS5 activity is not controlled by CD44, syndecan-1 or MT4MMP in this system. Immunohistochemical analysis supported the central role for ADAMTS5 in the degradative pathway and indicated that aggrecanolysis occurs primarily in the HA-poor pericellular region in these cultures.

CONCLUSION

These findings are consistent with published in vivo studies showing that single-gene ADAMTS5 ablation confers significant protection on cartilage in murine arthritis. We propose that this culture system and the analytical approaches described provide a valuable framework to further delineate the expression, activity and control of ADAMTS-mediated aggrecanolysis in human arthritis.

Distribution patterns of the anti-angiogenic protein ADAMTS-1 during rat development

A disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS-1) belongs to the large ADAM family of proteins. ADAMTS-1 contains a metalloproteinase domain, a disintegrin domain and three thrombospondin-like repeats but unlike ADAMs lacks a transmembrane domain. For the elucidation of the biological functions of ADAMTS-1, we raised new antibodies against ADAMTS-1. We show an accumulation of ADAMTS-1 protein at the basal lamina of rat embryonal epithelia of intestines, nasal cavity, choroid plexus, skin and in intracellular storage vesicles of epithelial cells. ADAMTS-1 protein seems to play a role in the development of the neuronal system, adipose tissue, muscle, heart, liver and adrenal glands. At the time of birth its presence is reduced in most organs. However, in the developing bone as well as in the skin, labelling increased towards late embryonal development. Immunoblots revealed a strong presence of a 62 kDa ADAMTS-1 fragment in kidneys, adrenal glands, lungs, intestines and heart. ADAMTS-1 was also present in the corresponding adult rat organs, but in more restricted distribution patterns. It was typically found in principal cells of collecting ducts, of the renal medulla, in ependymal cells of the ventricles and in some neurons. The results were confirmed by real-time PCR. The specific distribution pattern of ADAMTS-1 in a variety of organs during embryogenesis suggests a role of the molecule in tissue remodelling, vasculogenesis and angiogenesis.

Human osteoarthritis synovial fluid and joint cartilage contain both aggrecanase- and matrix metalloproteinase-generated aggrecan fragments

OBJECTIVE

To identify the major aggrecanase- and matrix metalloproteinase (MMP)-generated aggrecan fragments in human osteoarthritis (OA) synovial fluid and in human OA joint cartilage.

METHOD

Aggrecan fragments were prepared by CsCl gradient centrifugation. Fragment distributions were compared with aggrecanase-1 (ADAMTS-4) and MMP-3 digested human aggrecan by analysis with neoepitope antibodies and an anti-G1 domain antibody, using Western immuno-blots.

RESULTS

The overall fragment pattern of OA synovial fluid aggrecan was similar to the fragment pattern of cartilage aggrecan cleaved in vitro by ADAMTS-4. However, multiple glycosaminoglycan (GAG) containing aggrecanase and MMP-generated aggrecan fragments were identified in OA synovial fluid and some of these fragments were produced by the action of both types of proteinases. The synovial fluid content of large size aggrecan fragments with (374)ARGS- and (342)FFGV- N-terminals was about 107 and 40 pmoles per ml, respectively, out of a total concentration of aggrecan fragments of about 185 pmoles per ml. OA synovial fluid contained insignificant amounts of the G1-IPEN(341) fragment as compared to the G1-TEGE(373) fragment, while OA cartilage contained significant amounts of both fragments. OA cartilage contained several GAG-containing aggrecan fragments with N-terminals of G1- or (342)FFGV- but no fragments with an N-terminal of (374)ARGS-.

CONCLUSIONS

The overall pattern of aggrecan fragments in human OA synovial fluid and cartilage supports an important role for aggrecanase in aggrecan degradation. However, the fragment patterns and their differential distribution between cartilage and synovial fluid are consistent with the existence of at least two proteolytic pathways for aggrecan degradation in human OA, generating both (342)FFGV- and (374)ARGS-fragments.

A disintegrin and metalloprotease 21 (ADAM21) is associated with neurogenesis and axonal growth in developing and adult rodent CNS

We have reported that alpha6beta1 integrin regulates the directed migration of neuroblasts from the adult rodent subventricular zone (SVZ) through the rostral migratory stream (RMS). ADAM (a disintegrin and metalloprotease) proteins bind integrins. Here, we show that ADAM21, but not ADAM2, -3, -9, -10, -12, -15, or -17, is expressed in adult rats and mice by ependyma and SVZ cells with long basal processes, and in radial glia at early postnatal times. ADAM21-positive processes projected into the RMS, contacted blood vessels, and were present within the RMS intermingled with neuroblasts up to where neuroblasts start their radial migration and differentiation in the olfactory bulb. Tissue inhibitors of metalloproteases (TIMPs) 1, 2, and 3 are present in the ependymal layer but not in the SVZ and RMS. Thus, ADAM21 could regulate neurogenesis and guide neuroblast migration through cleavage-dependent activation of proteins and integrin binding. ADAM21 is also present in growing axonal tracts during postnatal development and in growing primary olfactory axons in adults. In the olfactory nerve layer, ADAM21 often, but not always, colocalizes with OMP, a marker of mature olfactory neurons, but is not colocalized with the immature marker betaIII-tubulin. This suggests that ADAM21 is involved in the final axonal outgrowth phase and/or synapse formation. TIMP3 is present in periglomerular neurons, where it could restrict ADAM21-mediated axonal growth to the glomeruli. ADAM21's unique disintegrin and metalloprotease sequences and its restricted expression suggest that it might be a good target for influencing neurogenesis and neuronal plasticity.

Focal cerebral ischemia induces changes in both MMP-13 and aggrecan around individual neurons

INTRODUCTION

To test the hypothesis that matrix metalloprotease-13 (MMP-13) and aggrecan may play roles in post-ischemic neuronal pathophysiology, we examined the impact of middle cerebral artery occlusion/reperfusion (MCAO/R) on the abundance of these proteins in different regions of the infarct by immunohistochemistry (IHC) and Western blotting (WB).

METHODS

The effect of MCAO/R on the abundance of MMP-13 and aggrecan was examined in 23 Wistar rats using antibodies against MMP-13 and aggrecan. BrdU was administered the last 2 days of the experiment. The cellular source of the respective antigens was examined with fluorescent double labeling using the neuronal marker NeuN. Sections were also stained for BrdU. The ischemic zone was defined by MRI on T2-weighted images and also on the tissue sections with the help of H and E counterstain. WB was performed for MMP-13.

RESULTS

MMP-13 protein is highly induced in ischemic brain and is associated with neurons, whereas aggrecan is associated with the perineuronal matrix in non-ischemic brain. After 3 days of cerebral ischemia, the number of MMP-13 positive neurons in the periphery of the ischemic lesion increased compared to the respective area in the non-ischemic brain with a peak on day 7. A stronger staining for aggrecan was observed around MMP-13 positive neurons compared with other neurons. The majority of the MMP-13 positive neurons in normal non-ischemic brain were also NeuN positive. BrdU was incorporated into MMP-13 positive neurons in the periphery of the infarct. WB confirmed this results by detecting MMP-13 bands in ischemic brains and activated MMP-13 up to 14 days after ischemia.

CONCLUSIONS

There is a close spatial association of MMP-13 and aggrecan around individual neurons. Both MMP-13 and aggrecan appear to be involved in perineuronal matrix remodeling suggesting a role in neuronal reorganization after cerebral ischemia.

Decomposition and long-lasting downregulation of extracellular matrix in perineuronal nets induced by focal cerebral ischemia in rats

The upregulation of extracellular matrix components, especially chondroitin sulfate proteoglycans, after brain injury and stroke is known to accompany the glial reaction, forming repellent scars that hinder axonal growth and the reorganization of the injured neuronal networks. The extracellular matrix associated with perineuronal nets (PNs) in the primarily injured and remote regions has not yet been systematically analyzed. We use the model of permanent middle cerebral artery occlusion (MCAO) to investigate the acute and long-lasting consequences of ischemia for PNs, related to the damage of neurons and reactions of glial cells, in spontaneously hypertensive rats. Extracellular matrix components associated with PNs around cortical interneurons and neurons in thalamic nuclei were characterized 1, 7, 14, and 35 days after MCAO, using Wisteria floribunda agglutinin (WFA) staining and immunocytochemistry. The degradation of PNs in the infarct core was initiated by loss of WFA-binding matrix components, indicating the cleavage of glycosaminoglycan chains of chondroitin sulfate proteoglycans. Immunostaining showed the subsequent removal of proteoglycan core proteins within the extending microglia/macrophage invasion zone lasting for 2 weeks after MCAO. In the cortical periinfarct region, delineated by an astrocytic scar against the infarct core, the number of WFA-stained and proteoglycan core protein-immunoreactive PNs was permanently reduced. In the homolateral ventroposterior thalamus, the delayed decrease in perineuronal matrix was related to the distribution pattern of activated microglia and massive neuronal degeneration. It can be concluded from these results that complementary to the known upregulation of matrix components in the glial scar, deficits in the expression of the neuron-associated extracellular matrix develop in the periinfarct and remote regions. These deficits may contribute to the long-lasting functional impairments after stroke.

Mature bovine articular cartilage contains abundant aggrecan that is C-terminally truncated at Ala719-Ala720, a site which is readily cleaved by m-calpain

Extracts of normal mature articular cartilage contain aggrecan molecules which bear the G1 domain (the N-terminal globular domain of aggrecan) and are C-terminally truncated by proteolysis at a number of sites. A proportion of these molecules are generated by an aggrecanase and/or matrix-metalloproteinase-mediated cleavage in the IGD (interglobular domain between the G1 and G2 domains of aggrecan). However, the proteinase(s) responsible for formation of the majority of the larger G1-G2 and glycosaminoglycan-bearing truncated species is (are) unknown. N-terminal sequencing of aggrecan core fragments generated by m-calpain digestion of bovine aggrecan has identified four novel cleavage sites: one within the CS (chondroitin sulphate)-1 domain (at one or more of the bonds Ser1229-Val1230, Ser1249-Val1250, Ser1287-Val1288, Gly1307-Val1308 and Ser1346-Val1347), two within the IGD (at bonds Ala474-Ala475 and Gly365-Gly366) and one within the KS (keratan sulphate) domain (at Ala719-Ala720). A new monoclonal antibody (SK-28) to the C-terminal neoepitope at M710VTQVGPGVA719 showed that aggrecan products generated by this cleavage are present in high abundance in mature bovine articular cartilage extracts. We conclude that m-calpain, or an unidentified proteinase with the capacity to cleave at the same site, is active during aggrecan biosynthesis/secretion by mature chondrocytes or in the matrix of mature bovine articular cartilage in vivo.

Protease degradomics: mass spectrometry discovery of protease substrates and the CLIP-CHIP, a dedicated DNA microarray of all human proteases and inhibitors

The biological role of most proteases in vivo is largely unknown. Therefore, to develop robust techniques to analyze the protease degradome in cells and tissues and to elucidate their substrate degradomes we have developed a dedicated and complete human protease and inhibitor microarray that we have called the CLIP-CHIP Oligonucleotides (70-mers) for identifying all 715 human proteases, inactive homologs and inhibitors were spotted in triplicate onto glass slides with a dedicated subarray containing oligonucleotides for specific human breast carcinoma genes. Initial analyses revealed the elevated expression of a number of proteases in invasive ductal cell carcinoma including ADAMTS17, carboxypeptidases A5 and M, tryptase-gamma and matriptase-2. Matrix metalloproteinases (MMPs) showed a restricted expression pattern in both normal and cancerous breast tissues with most expressed at low levels. However, of the several MMPs expressed in significant quantities, the carcinoma samples showed only slightly elevated amounts other than for MMP-28 which was strongly elevated. To discover new protease substrates we developed a novel yeast two-hybrid approach we term 'inactive catalytic domain capture' (ICDC). Here, an inactive mutant protease catalytic domain lacking the propeptide was used as a yeast two hybrid bait to screen a human fibroblast cDNA library for interactor proteins as a substrate trap. Wnt-induced signaling protein-2 (WISP-2) was identified by ICDC and was biochemically confirmed as a new MMP substrate. In another approach we used isotope-coded affinity tag (ICAT) labeling with tandem mass spectrometry to quantitate the levels of secreted or shed extracellular proteins in MDA-MB-231 breast carcinoma cell cultures in the presence or absence of membrane type 1-MMP (MT1-MMP) overexpression. By this proteomic approach we identified and biochemically confirmed that IL-8, the serine protease inhibitor SLPI, the death receptor-6, pro-TNF-alpha and CTGF are novel substrates of MT1-MMP. The utility and quantitative nature of ICAT with MS/MS analysis as a new screen for protease substrate discovery based on detection of cleaved or shed substrate products should be readily adaptable to other classes of protease for assessing proteolytic function in a cellular context.

Destruction of extracellular matrix proteoglycans is pervasive in simian retroviral neuroinfection

Disruption of the perineuronal matrix has been reported in human immunodeficiency virus (HIV) encephalitis. To better understand the extent of matrix disruption during lentiviral encephalitis, we characterized the extracellular matrix (ECM) damage in brains of 12 macaques infected with simian immunodeficiency virus (SIV). Matrix integrity was assessed by Wisteria floribunda lectin histochemistry. Confocal microscopy was used to quantify matrix loss, macrophage infiltration, and synaptic damage. Disruption of brain ECM was present shortly after retroviral infection, preceding parenchymal macrophage infiltration. In agreement with previous observations, reduced staining of presynaptic and postsynaptic proteins in SIV encephalitis occurred concurrently with matrix abnormalities. Lentiviral infection induced microglial and macrophage expression of two disintegrins and metalloproteinases with thrombospondin motifs (ADAMTS-1 and ADAMTS-4), with high substrate specificity for matrix proteoglycans. Matrix damage is pervasive during SIV neuroinfection, which suggests interventions to conserve brain matrix proteoglycans might avert or delay retroviral-induced neurodegeneration.

Regulation of RPTPbeta/phosphacan expression and glycosaminoglycan epitopes in injured brain and cytokine-treated glia

Several chondroitin sulfate proteoglycans (CSPGs) are upregulated after CNS injury and are thought to limit axonal regeneration in the adult mammalian CNS. Therefore, we examined the expression of the CSPG, receptor protein tyrosine phosphatase beta (RPTPbeta)/phosphacan, after a knife lesion to the cerebral cortex and after treatment of glial cultures with regulatory factors. The three splice variants of this CSPG gene, the secreted isoform, phosphacan, and the two transmembrane isoforms, the long and short RPTPbeta, were examined. Western blot and immunostaining analysis of injured and uninjured tissue revealed a transient decrease of phosphacan protein levels, but not of short RPTPbeta, in the injured tissue from 1 to 7 days postlesion (dpl). By real time RT-PCR, we show that phosphacan and long RPTPbeta mRNA levels are transiently down-regulated at 2 dpl, unlike those of short RPTPbeta which increased after 4 dpl. In contrast to the core glycoprotein, the phosphacan chondroitin sulfate (CS) glycosaminoglycan epitope DSD-1 was up-regulated after 7 dpl. Phosphacan was expressed by cultivated astrocytes and oligodendrocyte precursors but was more glycanated in oligodendrocyte precursors, which produce more of DSD-1 epitope than astrocytes. Epidermal growth factor/transforming growth factor alpha strongly increased the astrocytic expression of long RPTPbeta and phosphacan and slightly the short RPTPbeta protein levels, while interferon gamma and tumor necrosis factor alpha reduced astrocytic levels of phosphacan, but not of the receptor forms. Examining the effects of phosphacan on axon growth from rat E17 cortical neurons, we found that phosphacan stimulates outgrowth in a largely CS dependent manner, while it blocks the outgrowth-promoting effects of laminin through an interaction that is not affected by removal of the CS chains. These results demonstrate complex injury-induced modifications in phosphacan expression and glycanation that may well influence axonal regeneration and repair processes in the damaged CNS.

Intact aggrecan and chondroitin sulfate-depleted aggrecan core glycoprotein inhibit axon growth in the adult rat spinal cord

Aggrecan is a chondroitin sulfate (CS)/keratan sulfate (KS)-substituted proteoglycan (PG) abundant in cartilage which is also present within the mammalian embryonic, adult, and injured adult central nervous system (CNS). Although its role within the CNS is not clear, cell culture studies show that when substituted with CS, aggrecan inhibits neurite extension. To better understand the inhibitory effect of aggrecan on injured adult axons in vivo, we developed a model to independently test intact aggrecan and CS-depleted aggrecan core glycoprotein. Acute rat spinal cord hemisection cavities were filled with a growth-promoting matrix, Matrigel, and severed dorsal rootlets were placed into this matrix. This created an assay in which axons readily grew. The extent of ingrowth in this baseline assay was compared to the ingrowth in Matrigel loaded with intact aggrecan or the purified core glycoprotein of aggrecan. Our results show that both intact aggrecan and equivalent concentrations of the core glycoprotein component significantly inhibit axonal growth in this model system. These results confirm that aggrecan can inhibit the growth of adult axons in vivo and suggest that the inhibitory effects of aggrecan may be mediated, at least in part, by structures located on the core glycoprotein in the absence of the bulk of the CS chains.