Proteoglycans in the developing brain: new conceptual insights for old proteins

Paxillin phosphorylation counteracts proteoglycan-mediated inhibition of axon regeneration

In the adult central nervous system, the tips of axons severed by injury are commonly transformed into dystrophic endballs and cease migration upon encountering a rising concentration gradient of inhibitory proteoglycans. However, intracellular signaling networks mediating endball migration failure remain largely unknown. Here we show that manipulation of protein kinase A (PKA) or its downstream adhesion component paxillin can reactivate the locomotive machinery of endballs in vitro and facilitate axon growth after injury in vivo. In dissociated cultures of adult rat dorsal root ganglion neurons, PKA is activated in endballs formed on gradients of the inhibitory proteoglycan aggrecan, and pharmacological inhibition of PKA promotes axon growth on aggrecan gradients most likely through phosphorylation of paxillin at serine 301. Remarkably, pre-formed endballs on aggrecan gradients resume forward migration in response to PKA inhibition. This resumption of endball migration is associated with increased turnover of adhesive point contacts dependent upon paxillin phosphorylation. Furthermore, expression of phosphomimetic paxillin overcomes aggrecan-mediated growth arrest of endballs, and facilitates axon growth after optic nerve crush in vivo. These results point to the importance of adhesion dynamics in restoring endball migration and suggest a potential therapeutic target for axon tract repair.

Epiphycan from salmon nasal cartilage is a novel type of large leucine-rich proteoglycan

Chum salmon (Oncorhynchus keta) nasal cartilage was examined by next-generation DNA sequencing and mass spectrometric analyses, and 14 types of proteoglycans including epiphycan (EPY) were found. A cDNA encoding EPY was cloned and sequenced. The cDNA encoded 589 amino acids comprised a glycosaminoglycan (GAG) domain containing 55 potential GAG-modified sites (Ser-Gly and/or Gly-Ser), a cysteine cluster and 6 leucine-rich repeats. EPY was purified from salmon nasal cartilage and the structure of the GAG was characterized. As a result of unsaturated disaccharide analysis, GAG was found to be composed of chondroitin 6-sulfate (58.0%), chondroitin 4-sulfate (26.5%) and non-sulfated chondroitin (15.3%). The average molecular weight of GAG was estimated to be 3.0 × 10(4). Ser-100 and Ser-103 were identified as serine residues substituted by GAG chains by chemical modification and mass spectrometric analysis. More than 50 serine residues were assumed to be substituted by GAG chains. EPY is heavily substituted by chondroitin sulfate, giving an overall molecular weight of just under 2 × 10(6). EPY from salmon nasal cartilage is a novel type of large leucine-rich proteoglycan.

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.

New hypothesis of chronic back pain: low pH promotes nerve ingrowth into damaged intervertebral disks

The pathogenesis of low back pain is still elusive. Here, we proposed a new hypothesis that low pH is a possible cause of the development and progression of low back pain. We propose that low pH promotes the production of the inflammatory mediators and the depletion of proteoglycan in the damaged intervertebral disk. The inflammation response, evoked by the dorsal root ganglia, changes the delicate nutrient balance in the nucleus, resulting in a vicious cycle and leading to choronic back pain. Our hypothesis may explain many of the available clinical and experimental data on low back pain, thus it may help elucidate the pathogenesis of low back pain and improve clinical management.

Spatio-temporal characterization of the pleiotrophinergic system in mouse cerebellum: evidence for its key role during ontogenesis

The development of the central nervous system requires an appropriate micro-environment that is conditioned by a combination of various extracellular components. Most of the known signaling factors, such as neurotransmitters or neuropeptides, are soluble and diffuse into the extracellular matrix. However, other secreted molecules like proteoglycans or glycosaminoglycans anchor in the extracellular matrix to influence cerebral ontogenesis. As such, pleiotrophin (PTN), which binds the proteoglycans syndecan-3 (SDC3) and protein tyrosine phosphatase zeta (PTPζ), has been described as a pro-migratory and a pro-differentiating secreted cytokine on cortical neurons. In rat cerebellum, PTN is highly expressed during the first postnatal week, suggesting that this cytokine could participate to the development of the cerebellar cortex. According to this hypothesis, our spatio-temporal cartography of PTN, PTPζ and SDC3 indicated that, in mouse, the PTNergic system was present in the cerebellum at least from the first postnatal day (P0). Until P12, PTN was mainly expressed by granule cell precursors and located in the extracellular matrix, while SDC3 was expressed by Purkinje cells, Golgi cells and granule cell precursors, and PTPζ was present on Purkinje cells and Bergmann fibers. In vitro studies confirmed the presence of SDC3 on immature granule cells and demonstrated that PTN could stimulate directly their velocity in culture. In contrast, subarachnoidal injection of PTN in the cerebellum significantly reduced the rate of migration of granule cells, exacerbated their apoptosis and induced an atrophy of the Purkinje cell dendritic tree. Since differentiated granule cells did not express SDC3 or PTPζ, the PTN effect observed on migration and apoptosis may be indirectly mediated by Purkinje and/or Bergmann cells. From P21 to adulthood, the distribution of PTN, SDC3 and PTPζ changed and their expression dramatically decreased even if they were still detectable. PTN and SDC3 immunolabeling was restricted around Purkinje cell bodies and Golgi cells, whereas PTPζ was located around interneurons. These data suggested that, in the cerebellum of adult mice, PTN participates to the perineuronal nets that control neuronal plasticity. To conclude, the present work represents the first spatio-temporal characterization of the PTNergic system in the mouse cerebellum and indicates that PTN may contribute to cerebellum ontogenesis during the postnatal development as well as to neuronal plasticity at adulthood.

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.

Chondroitin sulfate proteoglycans in demyelinated lesions impair remyelination

OBJECTIVE

Failure of remyelination is a critical impediment to recovery in multiple sclerosis (MS). Chondroitin sulfate proteoglycans (CSPGs) have been reported to accumulate in MS lesions, and we thus examined the functional roles of CSPGs on oligodendrocyte precursor cells (OPCs), oligodendrocytes, and remyelination.

METHODS

We evaluated the expression of CSPGs in lysolecithin-injected mouse spinal cord, an animal model of demyelination and spontaneous remyelination. The functional impact of CSPGs on OPCs and remyelination was investigated using cultured adult murine and human OPCs and by treating demyelinated mice with xyloside to reduce the CSPG deposition that occurred following injury.

RESULTS

Early and robust upregulation of CSPGs following lysolecithin-induced demyelination was cleared during remyelination. In culture, CSPGs anchored onto the substratum reduced the adhesion of mouse and human OPCs and their subsequent morphological differentiation into process-bearing oligodendrocytes. Soluble CSPGs added to already adherent OPCs reduced the development of processes, whereas the acquisition of mature myelin proteins was unimpeded. Stripe assays of alternating CSPG and control substrata confirmed the nonpermissive nature of CSPGs for OPC adhesion and morphological differentiation. Enzymatic degradation of CSPGs with chondroitinase ABC was sufficient to overcome CSPG-dependent inhibition of human oligodendrocytes. Finally, in vivo xyloside treatment to reduce CSPG synthesis in lysolecithin-demyelinated mice increased numbers of OPCs and oligodendrocytes in lesions, and culminated in improved remyelination.

INTERPRETATION

These results identify CSPGs as a nonpermissive substrate for OPCs and oligodendrocytes, and as a prominent impediment to remyelination. The data suggest the requirement for the neutralization of CSPGs for repair after demyelination.

Corneal sulfated glycosaminoglycans and their effects on trigeminal nerve growth cone behavior in vitro: roles for ECM in cornea innervation

PURPOSE

Sensory trigeminal nerve growth cones innervate the cornea in a highly coordinated fashion. The purpose of this study was to determine if extracellular matrix glycosaminoglycans (ECM-GAGs), including keratan sulfate (KS), dermatan sulfate (DS), and chondroitin sulfate A (CSA) and C (CSC), polymerized in developing eyefronts, may provide guidance cues to nerves during cornea innervation.

METHODS

Immunostaining using antineuron-specific-β-tubulin and monoclonal antibodies for KS, DS, and CSA/C was performed on eyefronts from embryonic day (E) 9 to E14 and staining visualized by confocal microscopy. Effects of purified GAGs on trigeminal nerve growth cone behavior were tested using in vitro neuronal explant cultures.

RESULTS

At E9 to E10, nerves exiting the pericorneal nerve ring grew as tight fascicles, advancing straight toward the corneal stroma. In contrast, upon entering the stroma, nerves bifurcated repeatedly as they extended anteriorly toward the epithelium. KS was localized in the path of trigeminal nerves, whereas DS and CSA/C-rich areas were avoided by growth cones. When E10 trigeminal neurons were cultured on different substrates comprised of purified GAG molecules, their neurite growth cone behavior varied depending on GAG type, concentration, and mode of presentation (immobilized versus soluble). High concentrations of immobilized KS, DS, and CSA/C inhibited neurite growth to varying degrees. Neurites traversing lower, permissive concentrations of immobilized DS and CSA/C displayed increased fasciculation and decreased branching, whereas KS caused decreased fasciculation and increased branching. Enzymatic digestion of sulfated GAGs canceled their effects on trigeminal neurons.

CONCLUSIONS

Data herein suggest that GAGs may direct the movement of trigeminal nerve growth cones innervating the cornea.

Gene delivery to overcome astrocyte inhibition of axonal growth: an in vitro model of the glial scar

After injury to the central nervous system, a glial scar develops that physically and biochemically inhibits axon growth. In the scar, activated astrocytes secrete inhibitory extracellular matrix, of which chondroitin sulfate proteoglycans (CSPGs) are considered the major inhibitory component. An inhibitory interface of CSPGs forms around the lesion and prevents axons from traversing the injury, and decreasing CSPGs can enhance axon growth. In this report, we established an in vitro interface model of activated astrocytes and subsequently investigated gene delivery as a means to reduce CSPG levels and enhance axon growth. In the model, a continuous interface of CSPG producing astrocytes was created with neurons seeded opposite the astrocytes, and neurite crossing, stopping, and turning were evaluated as they approached the interface. We investigated the efficacy of lentiviral delivery to degrade or prevent the synthesis of CSPGs, thereby removing CSPG inhibition of neurite growth. Lentiviral delivery of RNAi targeting two key CSPG synthesis enzymes, chondroitin polymerizing factor and chondroitin synthase-1, decreased CSPGs, and reduced inhibition by the interface. Degradation of CSPGs by lentiviral delivery of chondroitinase also resulted in less inhibition and more neurites crossing the interface. These results indicate that the interface model provides a tool to investigate interventions that reduce inhibition by CSPGs, and that gene delivery can be effective in promoting neurite growth across an interface of CSPG producing astrocytes.

Unique features of extracellular matrix in the mouse medial nucleus of trapezoid body--implications for physiological functions

The medial nucleus of the trapezoid body (MNTB) is a vital structure of sound localization circuits in the auditory brainstem. Each principal cell of MNTB is contacted by a very large presynaptic glutamatergic terminal, the calyx of Held. The MNTB principal cells themselves are surrounded by extracellular matrix components forming prominent perineuronal nets (PNs). Throughout the CNS, PNs, which form lattice-like structures around the somata and proximal dendrites, are associated with distinct types of neurons. PNs are highly enriched in hyaluronan and chondroitin sulfate proteoglycans therefore providing a charged surface structure surrounding the cell body and proximal neurites of these neurons. The localization and composition of PNs have lead investigators to a number of hypotheses about their functions including: creating a specific extracellular ionic milieu around these neurons, stabilizing synapses, and influencing the outgrowth of axons. However, presently the precise functions of PNs are still quite unclear primarily due to the lack of an ideal experimental model system that is highly enriched in PNs and in which the synaptic transmission properties can be precisely measured. The MNTB principal cells could offer such a model, since they have been extensively characterized electrophysiologically. However, extracellular matrix (ECM) in these neurons has not yet been precisely detailed. The present study gives a detailed examination of the ECM organization and structural differences in PNs of the mouse MNTB. The different PN components and their distribution pattern are scrutinized throughout the MNTB. The data are complemented by electron microscopic investigations of the unique ultrastructural localization of PN-components and their interrelation with distinct pre- and postsynaptic MNTB cell structures. Therefore, we believe this work identifies the MNTB as an ideal system for studying PN function.

The perineuronal net component of the extracellular matrix in plasticity and epilepsy

During development the extracellular matrix (ECM) of the central nervous system (CNS) facilitates proliferation, migration, and synaptogenesis. In the mature nervous system due to changes in the ECM it provides structural stability and impedes proliferation, migration, and synaptogensis. The perineuronal net (PN) is a specialized ECM structure found primarily surrounding inhibitory interneurons where it forms a mesh-like structure around points of synaptic contact. The PN organizes the extracellular space by binding multiple components of the ECM and bringing them into close proximity to the cell membrane, forming dense aggregates surrounding synapses. The PN is expressed late in postnatal development when the nervous system is in the final stages of maturation and the critical periods are closing. Once fully expressed the PN envelopes synapses and leads to decreased plasticity and increases synaptic stability in the CNS. Disruptions in the PN have been studied in a number of disease states including epilepsy. Epilepsy is one of the most common neurologic disorders characterized by excessive neuronal activity which results in recurrent spontaneous seizures. A shift in the delicate balance between excitation and inhibition is believed to be one of the underlying mechanisms in the development of epilepsy. During epileptogenesis, the brain undergoes numerous changes including synaptic rearrangement and axonal sprouting, which require structural plasticity. Because of the PNs location around inhibitory cells and its role in limiting plasticity, the PN is an important candidate for altering the progression of epilepsy. In this review, an overview of the ECM and PN in the CNS will be presented with special emphasis on potential roles in epileptogenesis.

Astrocytes as a source for extracellular matrix molecules and cytokines

Research of the past 25 years has shown that astrocytes do more than participating and building up the blood-brain barrier and detoxify the active synapse by reuptake of neurotransmitters and ions. Indeed, astrocytes express neurotransmitter receptors and, as a consequence, respond to stimuli. Within the tripartite synapse, the astrocytes owe more and more importance. Besides the functional aspects the differentiation of astrocytes has gained a more intensive focus. Deeper knowledge of the differentiation processes during development of the central nervous system might help explaining and even help treating neurological diseases like Alzheimer’s disease, Amyotrophic lateral sclerosis, Parkinsons disease, and psychiatric disorders in which astrocytes have been shown to play a role. Specific differentiation of neural stem cells toward the astroglial lineage is performed as a multi-step process. Astrocytes and oligodendrocytes develop from a multipotent stem cell that prior to this has produced primarily neuronal precursor cells. This switch toward the more astroglial differentiation is regulated by a change in receptor composition on the cell surface and responsiveness to Fibroblast growth factor and Epidermal growth factor (EGF). The glial precursor cell is driven into the astroglial direction by signaling molecules like Ciliary neurotrophic factor, Bone Morphogenetic Proteins, and EGF. However, the early astrocytes influence their environment not only by releasing and responding to diverse soluble factors but also express a wide range of extracellular matrix (ECM) molecules, in particular proteoglycans of the lectican family and tenascins. Lately these ECM molecules have been shown to participate in glial development. In this regard, especially the matrix protein Tenascin C (Tnc) proved to be an important regulator of astrocyte precursor cell proliferation and migration during spinal cord development. Nevertheless, ECM molecules expressed by reactive astrocytes are also known to act mostly in an inhibitory fashion under pathophysiological conditions. Thus, we further summarize resent data concerning the role of chondroitin sulfate proteoglycans and Tnc under pathological conditions.

Expression of ADAMTS-1, ADAMTS-4, ADAMTS-5 and TIMP3 by hepatocellular carcinoma cell lines

Little is known about the expression or role of ADAMTS-1, -4 and -5 and their endogenous inhibitor TIMP3 in the liver in physiological and pathological conditions. Their expression was, therefore, investigated in the hepatocellular carcinoma cell lines HepG2 and HuH-7 using qRT-PCR and western blotting, and their cellular localisation by immunocytochemistry. Cytokine treatments were used to assess mRNA and protein modulation. ADAMTS-1, -4, -5 and TIMP3 mRNA and protein were detected in both HepG2 and HuH-7 cells. IL-1β and IL-6 treatments significantly modulated ADAMTS-1 mRNA expression and IL-1β treatment ADAMTS-4 mRNA expression in HepG2 cells. Modulations of mRNA by ≥ 5-fold did not translate to increased protein expression. This study showed that ADAMTS-1, -4, -5 and TIMP3 were expressed at differential levels in hepatocellular carcinoma cell lines. The pro-inflammatory cytokines IL-1β, TNF-α or IL-6 induced changes in mRNA expression, although these did not translate to the protein level.

The brain's extracellular matrix and its role in synaptic plasticity

The extracellular matrix (ECM) of the brain has important roles in regulating synaptic function and plasticity. A juvenile ECM supports the wiring of neuronal networks, synaptogenesis, and synaptic maturation. The closure of critical periods for experience-dependent shaping of neuronal circuits coincides with the implementation of a mature form of ECM that is characterized by highly elaborate hyaluronan-based structures, the perineuronal nets (PNN), and PNN-like perisynaptic ECM specializations. In this chapter, we will focus on some recently reported aspects of ECM functions in brain plasticity. These include (a) the discovery that the ECM can act as a passive diffusion barrier for cell surface molecules including neurotransmitter receptors and in this way compartmentalize cell surfaces, (b) the specific functions of ECM components in actively regulating synaptic plasticity and homeostasis, and (c) the shaping processes of the ECM by extracellular proteases and in turn the activation particular signaling pathways.

Deconstructing the perineuronal net: cellular contributions and molecular composition of the neuronal extracellular matrix

Perineuronal nets (PNNs) are lattice-like substructures of the neural extracellular matrix that enwrap particular populations of neurons throughout the central nervous system. Previous work suggests that this structure plays a major role in modulating developmental neural plasticity and brain maturation. Understanding the precise role of these structures has been hampered by incomplete comprehension of their molecular composition and cellular contributions to their formation, which is studied herein using primary cortical cell cultures. By defining culture conditions to reduce (cytosine-β-d-arabinofuranoside/AraC addition) or virtually eliminate (elevated potassium chloride (KCl) and AraC application) glia, PNN components impacted by this cell type were identified. Effects of depolarizing KCl concentrations alone were also assessed. Our work identified aggrecan as the primary neuronal component of the PNN and its expression was dramatically up-regulated by both depolarization and glial cell inhibition and additionally, the development of aggrecan-positive PNNs was accelerated. Surprisingly, most of the other PNN components tested were made in a glial-dependent manner in our culture system. Interestingly, in the absence of these glial-derived components, an aggrecan- and hyaluronan-reactive PNN developed, demonstrating that these two components are sufficient for base PNN assembly. Other components were expressed in a glial-dependent manner. Overall, this work provides deeper insight into the complex interplay between neurons and glia in the formation of the PNN and improves our understanding of the molecular composition of these structures.

Role of chondroitin sulfate C in the action of anthrax toxin

Anthrax toxin is produced by Bacillus anthracis, the causative agent of anthrax, and is responsible for the majority of disease symptoms. The toxin consists of 3 proteins, protective antigen (PA), lethal factor (LF), and edema factor (EF), which combine to form lethal and edema toxin. Glycosaminoglycans, which are present on the surface of cells, were investigated with regard to their role in toxicity resulting from anthrax toxin exposure. Lethal toxin-induced cytotoxicity of the RAW 264.7 cells was significantly inhibited by the addition of chondroitin sulfate C as determined by the MTT assay. By contrast, several other glycosaminoglycans, including heparin, heparan sulfate, and dermatan sulfate did not show significant levels of inhibition. Studies utilizing fluorescence-labeled PA demonstrated decreased PA binding to RAW 264.7 cells with the addition of chondroitin sulfate C. Formation of PA oligomers at the surface of cells after binding was also inhibited by chondroitin sulfate C. Interestingly, enzymatic degradation of endogenous chondroitin sulfate C from the cell surface with chondroitinase ABC was accompanied by increased sensitivity to the toxin. These findings were further confirmed by pretreating cells with sodium chlorate to reduce the degree of cell surface glycosaminoglycans sulfation. In addition, chondroitin sulfate C effectively inhibits edema toxin-induced cAMP accumulation in cells. Our results indicate that chondroitin sulfate C may play an important role in the toxicity of anthrax toxin.

The phenotype of a germline mutation in PIGA: the gene somatically mutated in paroxysmal nocturnal hemoglobinuria

Phosphatidylinositol glycan class A (PIGA) is involved in the first step of glycosylphosphatidylinositol (GPI) biosynthesis. Many proteins, including CD55 and CD59, are anchored to the cell by GPI. Loss of CD55 and CD59 on erythrocytes causes complement-mediated lysis in paroxysmal nocturnal hemoglobinuria (PNH), a disease that manifests after clonal expansion of hematopoietic cells with somatic PIGA mutations. Although somatic PIGA mutations have been identified in many PNH patients, it has been proposed that germline mutations are lethal. We report a family with an X-linked lethal disorder involving cleft palate, neonatal seizures, contractures, central nervous system (CNS) structural malformations, and other anomalies. An X chromosome exome next-generation sequencing screen identified a single nonsense PIGA mutation, c.1234C>T, which predicts p.Arg412(∗). This variant segregated with disease and carrier status in the family, is similar to mutations known to cause PNH as a result of PIGA dysfunction, and was absent in 409 controls. PIGA-null mutations are thought to be embryonic lethal, suggesting that p.Arg412(∗) PIGA has residual function. Transfection of a mutant p.Arg412(∗) PIGA construct into PIGA-null cells showed partial restoration of GPI-anchored proteins. The genetic data show that the c.1234C>T (p.Arg412(∗)) mutation is present in an affected child, is linked to the affected chromosome in this family, is rare in the population, and results in reduced, but not absent, biosynthesis of GPI anchors. We conclude that c.1234C>T in PIGA results in the lethal X-linked phenotype recognized in the reported family.

Chondroitin sulfate "wobble motifs" modulate maintenance and differentiation of neural stem cells and their progeny

Chondroitin sulfate/dermatan sulfate (CS/DS) proteoglycans, major components of the central nervous system, have the potential to interact with a wide range of growth factors and neurotrophic factors that influence neuronal migration, axon guidance pathways, and neurite outgrowth. Recent studies have also revealed the role of CS/DS chains in the orchestration of the neural stem/progenitor cell micromilieu. Individual functional proteins recognize a set of multiple overlapping oligosaccharide sequences decorated to give different sulfation patterns, which are termed here "wobble CS/DS oligosaccharide motifs," and induce signaling pathways essential for the proliferation, self-renewal, and cell lineage commitment of neural stem/progenitor cells.

Molecular properties of water-unextractable proteoglycans from Hypsizygus marmoreus and their in vitro immunomodulatory activities

Four proteoglycans were sequentially extracted from Hypsizygus marmoreus using 0.1 M NaOH (alkali-soluble proteoglycans [F1] and alkali-insoluble proteoglycans [F3]) and 0.1 M HCl (acid-soluble proteoglycans [F2] and acid-insoluble proteoglycans [F4]), and their structures and immunomodulatory activities were investigated. The proteoglycans were found to contain carbohydrates (19.8-82.4%) with various amounts of proteins (7.7-67.3%), and glucose was the major monosaccharide unit present, along with trace amounts of galactose. The molecular weights (Mw) and the radius of gyration (Rg) of these proteoglycans showed ranges of 16 × 10(4)-19,545 × 10(4) g/mol and 35-148 nm, respectively, showing significant variations in their molecular conformations. The backbones of F1 and F2 were mainly connected through a-(1→3), (1→4) and b-(1→6)-glycosidic linkages with some branches. The F1 and F2 proteoglycans significantly stimulated Raw264.7 cells to release nitric oxide (NO), prostaglandin E2 (PGE(2)) and various cytokines, such as IL-1β, TNF-α and IL-6 by inducing their mRNA expressions.

Regenerating islet-derived 1α (Reg-1α) protein is new neuronal secreted factor that stimulates neurite outgrowth via exostosin Tumor-like 3 (EXTL3) receptor

Regenerating islet-derived 1α (Reg-1α)/lithostathine, a member of a family of secreted proteins containing a C-type lectin domain, is expressed in various organs and plays a role in proliferation, differentiation, inflammation, and carcinogenesis of cells of the digestive system. We previously reported that Reg-1α is overexpressed during the very early stages of Alzheimer disease, and Reg-1α deposits were detected in the brain of patients with Alzheimer disease. However, the physiological function of Reg-1α in neural cells remains unknown. Here, we show that Reg-1α is expressed in neuronal cell lines (PC12 and Neuro-2a) and in rat primary hippocampal neurons (E17.5). Reg-1α is mainly localized around the nucleus and at the membrane of cell bodies and neurites. Transient overexpression of Reg-1α or addition of recombinant Reg-1α significantly increases the number of cells with longer neurites by stimulating neurite outgrowth. These effects are abolished upon down-regulation of Reg-1α by siRNA and following inhibition of secreted Reg-1α by antibodies. Moreover, Reg-1α colocalizes with exostosin tumor-like 3 (EXTL3), its putative receptor, at the membrane of these cells. Overexpression of EXTL3 increases the effect of recombinant Reg-1α on neurite outgrowth, and Reg-1α is not effective when EXTL3 overexpression is down-regulated by shRNA. Our findings indicate that Reg-1α regulates neurite outgrowth and suggest that this effect is mediated by its receptor EXTL3.

Dermatan sulfotransferase Chst14/D4st1, but not chondroitin sulfotransferase Chst11/C4st1, regulates proliferation and neurogenesis of neural progenitor cells

Chondroitin sulfates (CSs) and dermatan sulfates (DSs) are enriched in the microenvironment of neural stem cells (NSCs) during development and in the adult neurogenic niche, and have been implicated in mechanisms governing neural precursor migration, proliferation and differentiation. In contrast to previous studies, in which a chondroitinaseABC-dependent unselective deglycosylation of both CSs and DSs was performed, we used chondroitin 4-O-sulfotransferase-1 (Chst11/C4st1)- and dermatan 4-O-sulfotransferase-1 (Chst14/D4st1)-deficient NSCs specific for CSs and DSs, respectively, to investigate the involvement of specific sulfation profiles of CS and DS chains, and thus the potentially distinct roles of CSs and DSs in NSC biology. In comparison to wild-type controls, deficiency for Chst14 resulted in decreased neurogenesis and diminished proliferation of NSCs accompanied by increased expression of GLAST and decreased expression of Mash-1, and an upregulation of the expression of the receptors for fibroblast growth factor-2 (FGF-2) and epidermal growth factor (EGF). By contrast, deficiency in Chst11 did not influence NSC proliferation, migration or differentiation. These observations indicate for the first time that CSs and DSs play distinct roles in the self-renewal and differentiation of NSCs.

Perisynaptic aggrecan-based extracellular matrix coats in the human lateral geniculate body devoid of perineuronal nets

The extracellular matrix surrounds different neuronal compartments in the mature nervous system. In a variety of vertebrates, most brain regions are loaded with a distinct type of extracellular matrix around the somatodendritic part of neurons, termed perineuronal nets. The present study reports that chondrotin sulfate proteoglycan-based matrix is structured differently in the human lateral geniculate body. Using various chondrotin sulfate proteoglycan-based extracellular matrix antibodies, we show that perisomatic matrix labeling is rather weak or absent, whereas dendrites are contacted by axonal coats appearing as small, oval structures. Confocal laser scanning microscopy and electron microscopy demonstrated that these typical structures are associated with synaptic loci on dendrites. Using multiple labelings, we show that different chondrotin sulfate proteoglycan components of the extracellular matrix do not associate exclusively with neuronal structures but possibly associate with glial structures as well. Finally, we confirm and extend previous findings in primates that intensity differences of various extracellular matrix markers between magno- and parvocellular layers reflect functional segregation between these layers in the human lateral geniculate body.

Training and anti-CSPG combination therapy for spinal cord injury

Combining different therapies is a promising strategy to promote spinal cord repair, by targeting axon plasticity and functional circuit reconnectivity. In particular, digestion of chondroitin sulphate proteoglycans at the site of the injury by the activity of the bacterial enzyme chondrotinase ABC, together with the development of intensive task specific motor rehabilitation has shown synergistic effects to promote behavioural recovery. This review describes the mechanisms by which chondroitinase ABC and motor rehabilitation promote neural plasticity and we discuss their additive and independent effects on promoting behavioural recovery.

LC-MS(n) analysis of isomeric chondroitin sulfate oligosaccharides using a chemical derivatization strategy

Improved methods for structural analyses of glycosaminoglycans (GAGs) are required to understand their functional roles in various biological processes. Major challenges in structural characterization of complex GAG oligosaccharides using liquid chromatography-mass spectrometry (LC-MS) include the accurate determination of the patterns of sulfation due to gas-phase losses of the sulfate groups upon collisional activation and inefficient on-line separation of positional sulfation isomers prior to MS/MS analyses. Here, a sequential chemical derivatization procedure including permethylation, desulfation, and acetylation was demonstrated to enable both on-line LC separation of isomeric mixtures of chondroitin sulfate (CS) oligosaccharides and accurate determination of sites of sulfation by MS(n). The derivatized oligosaccharides have sulfate groups replaced with acetyl groups, which are sufficiently stable to survive MS(n) fragmentation and reflect the original sulfation patterns. A standard reversed-phase LC-MS system with a capillary C18 column was used for separation, and MS(n) experiments using collision-induced dissociation (CID) were performed. Our results indicate that the combination of this derivatization strategy and MS(n) methodology enables accurate identification of the sulfation isomers of CS hexasaccharides with either saturated or unsaturated nonreducing ends. Moreover, derivatized CS hexasaccharide isomer mixtures become separable by LC-MS method due to different positions of acetyl modifications.

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.

Chondroitin sulphate proteoglycans: key modulators of spinal cord and brain plasticity

Chondroitin sulphate proteoglycans (CSPGs) are a family of inhibitory extracellular matrix molecules that are highly expressed during development, where they are involved in processes of pathfinding and guidance. CSPGs are present at lower levels in the mature CNS, but are highly concentrated in perineuronal nets where they play an important role in maintaining stability and restricting plasticity. Whilst important for maintaining stable connections, this can have an adverse effect following insult to the CNS, restricting the capacity for repair, where enhanced synapse formation leading to new connections could be functionally beneficial. CSPGs are also highly expressed at CNS injury sites, where they can restrict anatomical plasticity by inhibiting sprouting and reorganisation, curbing the extent to which spared systems may compensate for the loss function of injured pathways. Modification of CSPGs, usually involving enzymatic degradation of glycosaminoglycan chains from the CSPG molecule, has received much attention as a potential strategy for promoting repair following spinal cord and brain injury. Pre-clinical studies in animal models have demonstrated a number of reparative effects of CSPG modification, which are often associated with functional recovery. Here we discuss the potential of CSPG modification to stimulate restorative plasticity after injury, reviewing evidence from studies in the brain, the spinal cord and the periphery.

Versican V0 and V1 direct the growth of peripheral axons in the developing chick hindlimb

Peanut agglutinin-binding disaccharides and chondroitin sulfate mark transient mesenchymal barriers to advancing motor and sensory axons innervating the hindlimbs during chick development. Here we show that the vast majority of these carbohydrates are at the critical stage and location attached to the versican splice variants V0 and V1. We reveal that the isolated isoforms of this extracellular matrix proteoglycan suppress axon extension at low concentrations and induce growth cone collapse and rapid retraction at higher levels. Moreover, we demonstrate that versican V0 and/or V1, recombinantly expressed in collagen-I gels or ectopically deposited in the hindlimbs of chicken embryos in ovo, cause untimely defasciculation and axon stalling. Consequently, severe disturbances of nerve patterning are observed in the versican-treated embryos. Our experiments emphasize the inhibitory capacity of versicans V0 and V1 in axonal growth and evidence for their function as basic guidance cues during development of the peripheral nervous system.

Chondroitin sulfate proteoglycans regulate astrocyte-dependent synaptogenesis and modulate synaptic activity in primary embryonic hippocampal neurons

It has been shown that astrocyte-derived extracellular matrix (ECM) is important for formation and maintenance of CNS synapses. In order to study the effects of glial-derived ECM on synaptogenesis, E18 rat hippocampal neurons and primary astrocytes were co-cultivated using a cell-insert system. Under these conditions, neurons differentiated under low density conditions (3500 cells/cm(2) ) in defined, serum-free medium and in the absence of direct, membrane-mediated neuron-astrocyte interactions. Astrocytes promoted the formation of structurally intact synapses, as documented by the co-localisation of bassoon- and ProSAP1/Shank2-positive puncta, markers of the pre- and postsynapse, respectively. The development of synapses was paralleled by the emergence of perineuronal net (PNN)-like structures that contained various ECM components such as hyaluronic acid, brevican and neurocan. In order to assess potential functions for synaptogenesis, the ECM was removed by treatment with hyaluronidase or chondroitinase ABC. Both enzymes significantly enhanced the number of synaptic puncta. Whole-cell voltage-clamp recordings of control and enzyme-treated hippocampal neurons revealed that chondroitinase ABC treatment led to a significant decrease in amplitude and a reduced charge of miniature excitatory postsynaptic currents, whereas inhibitory postsynaptic currents were not affected. When the response to the application of glutamate was measured, a reduced sensitivity could be detected and resulted in decreased currents in response to the excitatory neurotransmitter. These findings are consistent with the interpretation that the ECM partakes in the regulation of the density of glutamate receptors in subsynaptic sites.

Chondroitinase activity can be transduced by a lentiviral vector in vitro and in vivo

The bacterial enzyme chondroitinase ABC (ChABC), which cleaves chondroitin sulfate glycosaminoglycan chains, can degrade inhibitory scar tissue formed following spinal cord injury, thereby promoting axonal growth and regeneration. However, delivering the active enzyme for prolonged periods presents practical limitations. To overcome these problems, we prepared a lentiviral vector (LV) encoding chondroitinase AC (Chase) together with the green fluorescent protein (GFP) reporter (Chase/LV) and demonstrated its expression and enzymatic activity in vitro and in vivo. Neural precursor cells infected with Chase/LV expressed the GFP reporter at levels that increased dramatically with time in culture. Enzymatic activity from the supernatant of the infected cells was demonstrated by dot blot assay using an antibody that recognizes the digested form of CSPG and was compared with the bacterial ChABC enzyme. Chick DRG cultures plated adjacent to the CSPG border and incubated with supernatant from Chase/LV-infected cells showed neurites growing into the CSPG area, a response similar to that after treatment with ChABC. In contrast, in control cultures, the neurites turned to avoid the inhibitory CSPG interface. Degradation of CSPG in these cultures was confirmed by specific CSPG antibodies. A single injection of Chase/LV into the spinal cord resulted in sustained secretion of the enzyme, whose activity was detected for 8 weeks by expression of GFP and evidence of the digested form of CSPG. This study demonstrates the efficacy of the Chase/LV vector and its potential as a therapeutic tool to reduce scar inhibition and promote axonal growth and repair following central nervous system injury.

Proteoglycan-specific molecular switch for RPTPσ clustering and neuronal extension

Heparan and chondroitin sulfate proteoglycans (HSPGs and CSPGs, respectively) regulate numerous cell surface signaling events, with typically opposite effects on cell function. CSPGs inhibit nerve regeneration through receptor protein tyrosine phosphatase sigma (RPTPσ). Here we report that RPTPσ acts bimodally in sensory neuron extension, mediating CSPG inhibition and HSPG growth promotion. Crystallographic analyses of a shared HSPG-CSPG binding site reveal a conformational plasticity that can accommodate diverse glycosaminoglycans with comparable affinities. Heparan sulfate and analogs induced RPTPσ ectodomain oligomerization in solution, which was inhibited by chondroitin sulfate. RPTPσ and HSPGs colocalize in puncta on sensory neurons in culture, whereas CSPGs occupy the extracellular matrix. These results lead to a model where proteoglycans can exert opposing effects on neuronal extension by competing to control the oligomerization of a common receptor.

Carbohydrates for improving the cognitive performance of independent-living older adults with normal cognition or mild cognitive impairment

BACKGROUND

Mild cognitive impairment (MCI) is an intermediate state between normal cognition and dementia in which daily function is largely intact. This condition may present an opportunity for research into the prevention of dementia. Carbohydrate is an essential and easily accessible macronutrient which influences cognitive performance. A better understanding of carbohydrate-driven cognitive changes in normal cognition and mild cognitive impairment may suggest ways to prevent or reduce cognitive decline.

OBJECTIVES

To assess the effectiveness of carbohydrates in improving cognitive function in older adults.

SEARCH STRATEGY

We searched ALOIS, the Cochrane Dementia and Cognitive Improvement Group Specialized Register on 22 June 2010 using the terms: carbohydrates OR carbohydrate OR monosaccharides OR disaccharides OR oligosaccharides OR polysaccharides OR CARBS. ALOIS contains records from all major healthcare databases (The Cochrane Library, MEDLINE, EMBASE, PsycINFO, CINAHL, LILACS) as well as from many trial databases and grey literature sources.

SELECTION CRITERIA

All randomised controlled trials (RCT) that have examined the efficacy of any form of carbohydrates in normal cognition and MCI.

DATA COLLECTION AND ANALYSIS

One review author selected and retrieved relevant articles for further assessment. The remaining authors independently assessed whether any of the retrieved trials should be included. Disagreements were resolved by discussion. 

MAIN RESULTS

There is no suitable RCT of any form of carbohydrates involving independent-living older adults with normal cognition or mild cognitive impairment.

AUTHORS' CONCLUSIONS

There are no suitable RCTs on which to base any recommendations about the use of any form of carbohydrate for enhancing cognitive performance in older adults with normal cognition or mild cognitive impairment. More studies of many different carbohydrates are needed to tease out complex nutritional issues and further evaluate memory improvement.

Chondroitinase ABC I-mediated enhancement of oncolytic virus spread and antitumor efficacy

PURPOSE

The inhibitory role of secreted chondroitin sulfate proteoglycans on oncolytic viral (OV) therapy was examined. Chondroitinase ABC (Chase-ABC) is a bacterial enzyme that can remove chondroitin sulfate glycosaminoglycans from proteoglycans without any deleterious effects in vivo. We examined the effect of Chase-ABC on OV spread and efficacy.

EXPERIMENTAL DESIGN

Three-dimensional glioma spheroids placed on cultured brain slices were utilized to evaluate OV spread. Replication-conditional OV-expressing Chase-ABC (OV-Chase) was engineered using HSQuik technology and tested for spread and efficacy in glioma spheroids. Subcutaneous and intracranial glioma xenografts were utilized to compare antitumor efficacy of OV-Chase, rHsvQ (control), and PBS. Titration of viral particles was performed from OV-treated subcutaneous tumors. Glioma invasion was assessed in collagen-embedded glioma spheroids in vitro and in intracranial tumors. All statistical tests were two sided.

RESULTS

Treatment with Chase-ABC in cultured glioma cells significantly enhanced OV spread in glioma spheroids grown on brain slices (P < 0.0001). Inoculation of subcutaneous glioma xenografts with Chase-expressing OV significantly increased viral titer (>10 times, P = 0.0008), inhibited tumor growth, and significantly increased overall animal survival (P < 0.006) compared with treatment with parental rHsvQ virus. Single OV-Chase administration in intracranial xenografts also resulted in longer median survival of animals than rHsvQ treatment (32 vs. 21 days, P < 0.018). Glioma cell migration and invasion were not increased by OV-Chase treatment.

CONCLUSIONS

We conclude that degradation of glioma extracellular matrix with OV-expressing bacterial Chase-ABC enhanced OV spread and antitumor efficacy.

Fine-tuning of cell signaling by glypicans

Signaling peptides of the extracellular environment regulate cell biological processes underlying embryonic development, tissue homeostasis, and pathophysiology. The heparan sulphate proteoglycans, glypicans, have evolved as essential modulators of key regulatory proteins such as Wnt, Bmp, Fgf, and Shh. By acting on signal spreading and receptor activation, glypicans can control signal read-out and fate in targeted cells. Genetic and embryological studies have highlighted that glypicans act in a temporal and spatially regulated manner to modulate distinct cellular events. However, alterations of glypican function underlie human congenital malformations and cancer. Recent reports are starting to reveal their mechanism of action and how they can ensure tight modulation of cell signaling.

Colocalisation of plasma derived apo B lipoproteins with cerebral proteoglycans in a transgenic-amyloid model of Alzheimer's disease

Alzheimer's disease (AD) is characterized by cerebral proteinaceous deposits comprised of amyloid beta (Aβ). Evidence suggests that enhanced blood-to-brain delivery of Aβ occurs when plasma concentration is increased, exacerbating amyloidosis. In blood, significant Aβ is associated with apolipoprotein (apo) B lipoproteins. In this study, immunofluorescent microscopy was utilised to explore if there is an association between apo B lipoproteins and proteoglycan expression within Aβ-rich plaques in transgenic-amyloid mice. Focal accumulation of apo B was found with Aβ-plaque in APP/PS1 mice. There was enrichment in the proteoglycans, agrin, perlecan, biglycan and decorin within the core of dense Aβ-plaque. Perlecan, biglycan and decorin were positively associated with apo B lipoprotein abundance within amyloid plaque consistent with a cause-for-retention effect. These findings show that proteoglycans are an integral component of Aβ deposits in APP/PS1 mice. This study suggests that some proteoglycans contribute to Aβ retention, whilst other proteoglycans have different functions in the aetiology of AD.

Differential gene expression of multiple chondroitin sulfate modification enzymes among neural stem cells, neurons and astrocytes

Chondroitin sulfate/dermatan sulfate (CS/DS) polysaccharides have been reported to play a crucial role in the proliferation and maintenance of neural stem cells (NSCs). However, little is known about the structural changes and functional role of CS/DS chains in the differentiation of NSCs. Western blots of NSCs, neurons and astrocytes in culture, with three CS-polysaccharide antibodies of different specificities, revealed marked differences in CS structure among the three cell types. To confirm this finding, we measured gene expression levels of CS sulfotransferases and C5-epimerase in these cell types, as these are responsible for producing the high structural diversity of CS/DS. Expressions of chondroitin 4-O-sulfotransferase, chondroitin 6-O-sulfotransferase, and N-acetylgalactosamine 4-sulfate 6-O-sulfotransferase mRNAs were low in cultures of differentiated neural cells, such as neurons and astrocytes, in comparison to NSCs. In contrast, expressions of uronyl 2-O-sulfotransferase and C5-epimerase mRNAs were higher in the differentiated neural cells than NSCs. Thus, we first provide evidence to support the hypothesis that CS/DS undergoes structural changes during NSC differentiation. The structural changes in CS/DS may be implicated in the regulation of NSC differentiation through interactions with growth/neurotrophic factors and cytokines.

Compartmentalization from the outside: the extracellular matrix and functional microdomains in the brain

The extracellular matrix (ECM) of the central nervous system is well recognized as a migration and diffusion barrier that allows for the trapping and presentation of growth factors to their receptors at the cell surface. Recent data highlight the importance of ECM molecules as synaptic and perisynaptic scaffolds that direct the clustering of neurotransmitter receptors in the postsynaptic compartment and that present barriers to reduce the lateral diffusion of membrane proteins away from synapses. The ECM also contributes to the migration and differentiation of stem cells in the neurogenic niche and organizes the polarized localization of ion channels and transporters at contacts between astrocytic processes and blood vessels. Thus, the ECM contributes to functional compartmentalization in the brain.

Distribution and classification of aggrecan-based extracellular matrix in the thalamus of the rat

Extracellular matrix molecules take part in functional isolation and stabilization of neuronal compartments but form a vivid interface between neuronal elements at the same time. Previous studies have shown that the accumulation of extracellular matrix, especially its typical phenotypic form, termed perineuronal nets, correlates not only with the functional properties of the single neuron but also with the functional properties of the whole brain area. In contrast to recent advances in investigating neocortex, the present study mapped the occurrence and phenotypic appearance of aggrecan-based matrix accumulation throughout the rat thalamus. Results showed that divisions of thalamus that relay information to cortical fields known rather for their plastic properties exibit a poor matrix immunoreactivity, whereas matrix accumulation is more enhanced in nuclei connected to primary cortical regions. In addition to perineuronal nets, extracellular matrix condensed in another peculiar form, in 2-5-μm, large, round or oval structures, as described by Brückner et al. ([ 2008] Neuroscience 151:489-504) as axonal coats (ACs). Multiple labelling experiments showed that specific excitatory afferents were not ensheathed with these structures. At the same time, inhibitory endings were occasionally enwrapped in ACs. Electron microscopic analysis showed that aggrecan-immunoreactive profiles were present mostly around inhibitory terminals but also in all neuronal compartments. We suggest that aggrecan-based extracellular matrix is formed by both pre- and postsynaptic elements and is preferably associated with inhibitory terminals in the extracellular space.

Extracellular matrix: functions in the nervous system

An astonishing number of extracellular matrix glycoproteins are expressed in dynamic patterns in the developing and adult nervous system. Neural stem cells, neurons, and glia express receptors that mediate interactions with specific extracellular matrix molecules. Functional studies in vitro and genetic studies in mice have provided evidence that the extracellular matrix affects virtually all aspects of nervous system development and function. Here we will summarize recent findings that have shed light on the specific functions of defined extracellular matrix molecules on such diverse processes as neural stem cell differentiation, neuronal migration, the formation of axonal tracts, and the maturation and function of synapses in the peripheral and central nervous system.

Biochemical and thermodynamic characterization of mutated β1,4-galactosyltransferase 7 involved in the progeroid form of the Ehlers-Danlos syndrome

Three mutations of the B4GALT7 gene [encoding β1,4-GalT7 (β1,4-galactosyltransferase 7)], corresponding to A186D, L206P and R270C, have been identified in patients with the progeroid form of the Ehlers-Danlos syndrome and are described as being associated with the reduction or loss of β1,4-GalT7 activity. However, the molecular basis of the reduction or loss of activity remained to be determined. In the present study, wild-type, A186D, L206P and R270C β1,4-GalT7 were expressed in CHO618 cells as membrane proteins and in Escherichia coli as soluble proteins fused to MBP (maltose-binding protein). The ability of the expressed proteins to transfer galactose from donor to acceptor substrates was systematically characterized by kinetic analysis. The physicochemical properties of soluble proteins were explored by isothermal titration calorimetry, which is a method of choice when determining the thermodynamic parameters of the binding of substrates. Together, the results showed that: (i) the L206P mutation abolished the activity when L206P β1,4GalT7 was either inserted in the membrane or expressed as a soluble MBP-full-length fusion protein; (ii) the A186D mutation weakly impaired the binding of the donor substrate; and (iii) the R270C mutation strongly impaired the binding of the acceptor substrate. Moreover, the ex vivo consequences of the mutations were investigated by evaluating the priming efficiency of xylosides on GAG (glycosaminoglycan) chain initiation. The results demonstrate a quantitative effect on GAG biosynthesis, depending on the mutation; GAG biosynthesis was fully inhibited by the L206P mutation and decreased by the R270C mutation, whereas the A186D mutation did not affect GAG biosynthesis severely.

IFN-beta pharmacogenomics in multiple sclerosis

Multiple sclerosis (MS) is a condition of the CNS marked by inflammation and neurodegeneration. Interferon (IFN)-beta was the first, and still is the main, immunomodulatory treatment for MS. Its clinical efficacy is limited, and a proportion of patients, ranging between 20-55%, do not respond to the therapy. Identification and subsequently, implementation in the clinic of biomarkers predictive for individual therapeutic response would facilitate improved patient care in addition to ensuring a more rational provision of this therapy. In this article, we summarize the main findings from studies addressing the pharmacogenomics of clinical response to IFN-beta in MS by either whole-genome association scans, candidate gene or transcriptomics studies. Whole-genome DNA association screens have revealed a high representation of brain-specific genes, and have hinted toward both extracellular ligand-gated ion channels and type I IFNs pathway genes as important categories of genetic IFN-beta response modifiers. One hit, glypican 5 (GPC5), was recently replicated in an independent study of IFN-beta responsiveness. Recent RNA transcriptomics studies have revealed the occurrence of a pre-existing type I IFN gene-expression signature, composed of genes that are predominantly induced by type I IFNs, as a potential contributing feature of poor response to therapy. Thus, while the outlines of a complex polygenic mechanism are gradually being uncovered, the main challenges for the near future will reside in the robust validation of identified response-modifying genes as well as in the decipherment of the mechanistic relationships between these genes and clinical response to IFN-beta.