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

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.

CSPG is a secreted factor that stimulates neural stem cell survival possibly by enhanced EGFR signaling

Understanding how autocrine/paracrine factors regulate neural stem cell (NSC) survival and growth is fundamental to the utilization of these cells for therapeutic applications and as cellular models for the brain. In vitro, NSCs can be propagated along with neural progenitors (NPs) as neurospheres (nsphs). The nsph conditioned medium (nsph-CM) contains cell-secreted factors that can regulate NSC behavior. However, the identity and exact function of these factors within the nsph-CM has remained elusive. We analyzed the nsph-CM by mass spectrometry and identified DSD-1-proteoglycan, a chondroitin sulfate proteoglycan (CSPG), apolipoprotein E (ApoE) and cystatin C as components of the nsph-CM. Using clonal assays we show that CSPG and ApoE are responsible for the ability of the nsph-CM to stimulate nsph formation whereas cystatin C is not involved. Clonal nsphs generated in the presence of CSPG show more than four-fold increase in NSCs. Thus CSPG specifically enhances the survival of NSCs. CSPG also stimulates the survival of embryonic stem cell (ESC)-derived NSCs, and thus may be involved in the developmental transition of ESCs to NSCs. In addition to its role in NSC survival, CSPG maintains the three dimensional structure of nsphs. Lastly, CSPG's effects on NSC survival may be mediated by enhanced signaling via EGFR, JAK/STAT3 and PI3K/Akt pathways.

Influence of glial-derived matrix molecules, especially chondroitin sulfates, on neurite growth and survival of cultured mouse embryonic motoneurons

Mechanisms controlling neuronal survival and regeneration play an important role during development, after birth, and under lesion conditions. Isolated embryonic mouse motoneurons have been a useful tool for studying such basic mechanisms. These cultured motoneurons depend on extracellular matrix (ECM) molecules, which are potent mediators of survival and axonal growth and guidance in the CNS and in vitro, exhibiting either attractive or repellent guidance cues. Additionally, ECM proteoglycans and glycoproteins are components of the glial scar acting as a growth barrier for regenerating axons. Compared with CNS axon outgrowth, less is known about the cues that guide motoneurons toward their peripheral targets. Because we are interested in the effects of glial-derived chondroitin sulfate proteoglycans (CSPGs), we have worked out a model system for investigating the influences of glial-derived matrix molecules on motoneuron outgrowth and survival. We used cultured embryonic mouse motoneurons to investigate axon growth effects of matrix molecules produced by the glial-derived cell lines A7, Neu7, and Oli-neu primary astrocytes as well as the immortalized Schwann cell line IMS32. The results indicate that molecules of the ECM, especially chondroitin sulfates, play an important role as axon growth-promoting cues. We could demonstrate a modifying effect of the matrix components on motoneuron survival and caspase3-induced apoptosis.

Functions of chondroitin sulfate and heparan sulfate in the developing brain

Chondroitin sulfate and heparan sulfate proteoglycans are major components of the cell surface and extracellular matrix in the brain. Both chondroitin sulfate and heparan sulfate are unbranched highly sulfated polysaccharides composed of repeating disaccharide units of glucuronic acid and N-acetylgalactosamine, and glucuronic acid and N-acetylglucosamine, respectively. During their biosynthesis in the Golgi apparatus, these glycosaminoglycans are highly modified by sulfation and C5 epimerization of glucuronic acid, leading to diverse heterogeneity in structure. Their structures are strictly regulated in a cell type-specific manner during development partly by the expression control of various glycosaminoglycan-modifying enzymes. It has been considered that specific combinations of glycosaminoglycan-modifying enzymes generate specific functional microdomains in the glycosaminoglycan chains, which bind selectively with various growth factors, morphogens, axon guidance molecules and extracellular matrix proteins. Recent studies have begun to reveal that the molecular interactions mediated by such glycosaminoglycan microdomains play critical roles in the various signaling pathways essential for the development of the brain.

Upregulation of CSPG3 accompanies neuronal progenitor proliferation and migration in EAE

The molecular identities of signals that regulate the CNS lesion remodeling remain unclear. Herein, we report for the first time that extracellular matrix chondroitin sulphate proteoglycan, CSPG3 (neurocan) is upregulated after primary inflammatory injury. EAE was induced using myelin oligodendrocyte glycoprotein (MOG) (35-55) which was characterized by massive polymorphonuclear cell infiltration and loss of myelin basic protein expression along with steep decrease of CNPase. Periventricular white matter (PVWM) and cortex presented with astrogliosis evidenced by increased Glial fibrillary acidic protein (GFAP) immunoreactivity 20 days post immunization (p.i). Neuronal progenitor cell (NPC) proliferation increased after first acute episode in the subventricular zone (SVZ), corpus callosum, and cortex, indicating migration of cells to structures other than rostral migration stream and olfactory bulb, which is indicative of cell recruitment for repair process and was confirmed by presence of thin myelin sheaths in the shadow plaques. Earlier CSPG3 has been demonstrated to impede regeneration. We observed neuroinflammation-induced up-regulation of the CSPG3 expression in two most affected regions viz. PVWM and cortex after proliferation and migration of NPCs. Our results show possible role of reactive astrogliosis in lesion remodeling and redefine the relation between inflammation and endogenous cellular repair which can aid in designing of newer therapeutic strategies.

Extracellular matrix plasticity and GABAergic inhibition of prefrontal cortex pyramidal cells facilitates relapse to heroin seeking

Successful treatment of drug addiction is hampered by high relapse rates during periods of abstinence. Neuroadaptation in the medial prefrontal cortex (mPFC) is thought to have a crucial role in vulnerability to relapse to drug seeking, but the molecular and cellular mechanisms remain largely unknown. To identify protein changes that contribute to relapse susceptibility, we investigated synaptic membrane fractions from the mPFC of rats that underwent 21 days of forced abstinence following heroin self-administration. Quantitative proteomics revealed that long-term abstinence from heroin self-administration was associated with reduced levels of extracellular matrix (ECM) proteins. After extinction of heroin self-administration, downregulation of ECM proteins was also present in the mPFC, as well as nucleus accumbens (NAc), and these adaptations were partially restored following cue-induced reinstatement of heroin seeking. In the mPFC, these ECM proteins are condensed in the perineuronal nets that exclusively surround GABAergic interneurons, indicating that ECM adaptation might alter the activity of GABAergic interneurons. In support of this, we observed an increase in the inhibitory GABAergic synaptic inputs received by the mPFC pyramidal cells after the re-exposure to heroin-conditioned cues. Recovering levels of ECM constituents by metalloproteinase inhibitor treatment (FN-439; i.c.v.) prior to a reinstatement test attenuated subsequent heroin seeking, suggesting that the reduced synaptic ECM levels during heroin abstinence enhanced sensitivity to respond to heroin-conditioned cues. We provide evidence for a novel neuroadaptive mechanism, in which heroin self-administration-induced adaptation of the ECM increased relapse vulnerability, potentially by augmenting the responsivity of mPFC GABAergic interneurons to heroin-associated stimuli.

Nanofibers in a hyaluronan-based pericellular matrix

The extracellular matrix of the brain is a highly organized hyaluronan-based supramolecular assembly that is involved in neuronal pathfinding, cell migration, synaptogenesis and neuronal plasticity. Here, we analyze the structure of the hyaluronan-rich pericellular matrix of an oligodendroglial precursor cell line using helium ion beam scanning microscopy at a subnanometer resolution. We find that thin nanofibers are the ultimate building elements of this oligodendroglial pericellular matrix. These structures may participate in the regulation of oligodendroglial maturation and motility.

Perineuronal net formation and structure in aggrecan knockout mice

Perineuronal nets (PNNs) are specialized substructures of the neural extracellular matrix (ECM) which envelop the cell soma and proximal neurites of particular sets of neurons with apertures at sites of synaptic contact. Previous studies have shown that PNNs are enriched with chondroitin sulfate proteoglycans (CSPGs) and hyaluronan, however, a complete understanding of their precise molecular composition has been elusive. In addition, identifying which specific PNN components are critical to the formation of this structure has not been demonstrated. Previous work in our laboratory has demonstrated that the CSPG, aggrecan, is a key activity-dependent component of PNNs in vivo. In order to assess the contribution of aggrecan to PNN formation, we utilized cartilage matrix deficiency (cmd) mice, which lack aggrecan. Herein, we utilized an in vitro model, dissociated cortical culture, and an ex vivo model, organotypic slice culture, to specifically investigate the role aggrecan plays in PNN formation. Our work demonstrates that staining with the lectin, Wisteria floribunda agglutinin (WFA), considered a broad PNN marker, is eliminated in the absence of aggrecan, suggesting the loss of PNNs. However, in contrast, we found that the expression patterns of other PNN markers, including hyaluronan and proteoglycan link protein 1 (HAPLN1), tenascin-R, brevican, and hyaluronan are unaffected by the absence of aggrecan. Lastly, we determined that while all PNN components are bound to the surface in a hyaluronan-dependent manner, only HAPLN1 remains attached to the cell surface when neurons are treated with chondroitinase. These results suggest a different model for the molecular association of PNNs to the cell surface. Together our work has served to assess the contribution of aggrecan to PNN formation while providing key evidence concerning the molecular composition of PNNs in addition to determining how these components ultimately form PNNs.

Differential involvement of the extracellular 6-O-endosulfatases Sulf1 and Sulf2 in brain development and neuronal and behavioural plasticity

The extracellular sulfatases Sulf1 and Sulf2 remove specific 6-O-sulfate groups from heparan sulfate, thereby modulating numerous signalling pathways underlying development and homeostasis. In vitro data have suggested that the two enzymes show functional redundancy. To elucidate their in vivo functions and to further address the question of a putative redundancy, we have generated Sulf1- and Sulf2-deficient mice. Phenotypic analysis of these animals revealed higher embryonic lethality of Sulf2 knockout mice, which can be associated with neuroanatomical malformations during embryogenesis. Sulf1 seems not to be essential for developmental or postnatal viability, as mice deficient in this sulfatase show no overt phenotype. However, neurite outgrowth deficits were observed in hippocampal and cerebellar neurons of both mutant mouse lines, suggesting that not only Sulf2 but also Sulf1 function plays a role in the developing nervous system. Behavioural analysis revealed differential deficits with regard to cage activity and spatial learning for Sulf1- and Sulf2-deficient mouse lines. In addition, Sulf1-specific deficits were shown for synaptic plasticity in the CA1 region of the hippocampus, associated with a reduced spine density. These results reveal that Sulf1 and Sulf2 fulfil non-redundant functions in vivo in the development and maintenance of the murine nervous system.

Opposing functions of chondroitin sulfate and heparan sulfate during early neuronal polarization

Axon-dendrite polarity of neurons is essential for information processing in the nervous system. Here we studied the functions of chondroitin sulfate (CS) and heparan sulfate (HS) in neuronal polarization using cultured dissociated hippocampal neurons. Immunohistochemical analyses of early cultured neurons indicated the distribution of these glycosaminoglycans to be quite different. While CS epitopes were accumulated in the focal contacts present in axons and cell bodies, those of HS were detected ubiquitously on the cell surface including on dendrites and axons. Treatment with chondroitinase (CHase) ABC, which degrades CS, and knockdown of a CS sulfotransferase, N-acetylgalactosamine 4-sulfate 6-O-sulfotransferase (4,6-ST), which is involved in the biosynthesis of oversulfated structures, induced the formation of multiple axons in hippocampal neurons. Time-lapse recordings revealed the multiple axons of CHase ABC-treated neurons to be highly unstable, extending and retracting, repeatedly. CHase ABC-treatments suggested that CS is involved in the formation of phosphorylated focal adhesion kinase-positive focal contacts. Thus, CS may enhance integrin signaling in the nascent axons, supporting axon specification. On the other hand, when neurons were treated with heparitinases that specifically degrade HS, neurons with a single axon increased. The axons of HSase-treated neurons extended steadily and showed almost no retraction. These results suggest that CS stabilizes and HS destabilizes the growth of axons in an opposing manner, contributing to early neuronal polarization.

Extracellular matrix in multiple sclerosis lesions: Fibrillar collagens, biglycan and decorin are upregulated and associated with infiltrating immune cells

Extracellular matrix (ECM) proteins can modify immune reactions, e.g. by sequestering or displaying growth factors and by interacting with immune and glial cells. Here we quantified by quantitative polymerase chain reaction (qPCR) expression of 50 ECM components and 34 ECM degrading enzymes in multiple sclerosis (MS) active and inactive white matter lesions. COL1A1, COL3A1, COL5A1 and COL5A2 chains were induced strongly in active lesions and even more in inactive lesions. These chains interact to form collagen types I, III and V, which are fibrillar collagens. Biglycan and decorin, which can decorate fibrillar collagens, were also induced strongly. The fibrillar collagens, biglycan and decorin were largely found between the endothelium and astrocytic glia limitans in the perivascular space where they formed a meshwork which was closely associated with infiltrating immune cells. In active lesions collagen V was also seen in the heavily infiltrated parenchyma. Fibrillar collagens I and III inhibited in vitro human monocyte production of CCL2 (MCP-1), an inflammatory chemokine involved in recruitment of immune cells. Together, ECM changes in lesions with different activities were quantified and proteins forming a perivascular fibrosis were identified. Induced fibrillar collagens may contribute to limiting enlargement of MS lesions by inhibiting the production of CCL2 by monocytes.

Chemical properties of the extracellular matrix of the snail nervous system: a comprehensive study using a combination of histochemical techniques

The extracellular matrix (ECM) consists of various types of protein and carbohydrate polymers with red-ox and acid-base properties that have a crucial impact on tissue homeostasis. In the present study, a combination of both frequently applied and also specialized histochemical staining methods were used to reveal the chemical properties of the ECM of the snail central nervous system (CNS) which has a long been favored experimental model for comparative neurobiologists. Reactions such as silver ion reduction to label oxidative elements and different protein fibers, visible and fluorescent periodic-Schiff (PAS) reaction for the detection of unbranched chain of carbohydrates, and cationic dyes (acridine orange and alcian blue) for differentiating acidic carbohydrates were used. Illumination of sections stained with toluidine blue at pH 4.0 by a fluorescent light (lambda ex546/em580 nm), visualized components of the extraneural space (ECM molecules and glial cells) of the adult and also the developing CNS. Silver, toluidine blue and azure A were used to detect specific molecule bands in CNS extracts separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Some molecules showed both negative character and had carbohydrate side chains revealed by the Solanum tuberosum lectin probe. In a comparison of a freshwater aquatic (Lymnaea stagnalis) and a terrestrial (Helix pomatia) species, the ECM showed similarities in the composition of the periganglionic sheath and interperikaryonal space. The sheath was rich in alcian blue-positive sulfated proteoglycans infiltrated the space between collagen and reticular fibers, whereas in the interperikaryonal space PAS- and acridine orange-positive neutral and weakly acidic carbohydrates were detected. The ganglionic neuropil was mostly filled with PAS-positive material, but negatively charged sulfated and carboxylated molecules detected by acridine orange and alcian blue were present only in Helix. A low carbohydrate content was also found in the neuropil of both adult and developing Lymnaea, but most of the ECM components appeared only during the postembryonic juvenile stages. Comparing the SDS-PAGE of the periganglionic sheath and neural tissue extracts, toluidine blue (pH 4.0) and azure A (pH 2.0) revealed negatively charged molecules; some were found in both fractions. These results show, for the first time, the general chemical characteristics of the ECM of the snail CNS, indicating differences in the composition of the ganglion neuropil between aquatic and terrestrial species. Hence, a different strategy for retaining water by the neural tissue is suggested in species living in different environments.

Abnormal post-translational and extracellular processing of brevican in plaque-bearing mice over-expressing APPsw

Aggregation of amyloid-beta (Abeta) in the forebrain of Alzheimer's disease (AD) subjects may disturb the molecular organization of the extracellular microenvironment that modulates neural and synaptic plasticity. Proteoglycans are major components of this extracellular environment. To test the hypothesis that Abeta, or another amyloid precursor protein (APP) dependent mechanism modifies the accumulation and/or turnover of extracellular proteoglycans, we examined whether the expression and processing of brevican, an abundant extracellular, chondroitin sulfate (CS)-bearing proteoglycan, were altered in brains of Abeta-depositing transgenic mice (APPsw - APP gene bearing the Swedish mutation) as a model of AD. The molecular size of CS chains attached to brevican was smaller in hippocampal tissue from APPsw mice bearing Abeta deposits compared to non-transgenic mice, likely because of changes in the CS chains. Also, the abundance of the major proteolytic fragment of brevican was markedly diminished in extracts from several telencephalic regions of APPsw mice compared to non-transgenic mice, yet these immunoreactive fragments appeared to accumulate adjacent to the plaque edge. These results suggest that Abeta or APP exert inhibitory effects on proteolytic cleavage mechanisms responsible for synthesis and turnover of proteoglycans. As proteoglycans stabilize synaptic structure and inhibit molecular plasticity, defective brevican processing observed in Abeta-bearing mice and potentially end-stage human AD, may contribute to deficient neural plasticity.

Activity-dependent remodeling of chondroitin sulfate proteoglycans extracellular matrix in the hypothalamo-neurohypophysial system

The hypothalamo-neurohypophysial system (HNS) consisting of arginine vasopressin (AVP) and oxytocin (OXT) magnocellular neurons shows the structural plasticity including the rearrangement of synapses, dendrites, and neurovascular contacts during chronic physiological stimulation. In this study, we examined the remodeling of chondroitin sulfate proteoglycans (CSPGs), main extracellular matrix (ECM), in the HNS after salt loading known as a chronic stimulation to cause the structural plasticity. In the supraoptic nucleus (SON), confocal microscopic observation revealed that the immunoreactivity of 6B4 proteoglycans (PG) was observed mainly at AVP-positive magnocellular neurons but that of neurocan was seen chiefly at OXT-positive magnocellular neurons. The immunoreactivity of phosphacan and aggrecan was seen at both AVP- and OXT-positive magnocellular neurons. Electron microscopic observation further showed that the immunoreactivity of phosphacan and neurocan was observed at astrocytic processes to surround somata, dendrites, and terminals, but not synaptic junctions. In the neurohypophysis (NH), the immunoreactivity of phosphacan, 6B4 PGs, and neurocan was observed at AVP-positive magnocellular terminals, but the reactivity of Wisteria floribunda agglutinin lectin was seen at OXT-positive ones. The immunoreactivity of versican was found at microvessel and that of aggrecan was not detected in the NH. Quantitative morphometrical analysis showed that the chronic physiological stimulation by 7-day salt loading decreased the level of 6B4 PGs in the SON and the level of phosphacan, 6B4 PGs, and neurocan in the NH. These results suggest that the extracellular microenvironment of CSPGs is different between AVP and OXT magnocellular neurons and activity-dependent remodeling of CSPGs could be involved in the structural plasticity of the HNS.

Contributions of astrocytes to synapse formation and maturation - Potential functions of the perisynaptic extracellular matrix

The concept of the tripartite synapse proposes that in addition to the presynapse and the postsynaptic membrane closely apposed processes of astrocytes constitute an integral part of the synapse. Accordingly, astrocytes may influence synaptic activity by various ways. Thus glia- and neuron-derived neurotrophins, cytokines and metabolites influence neuronal survival, synaptic activity and plasticity. Beyond these facts, the past years have shown that astrocytes are required for synaptogenesis, the structural maintenance and proper functioning of synapses. In particular, astrocytes seem to play a key role in the organization of the brain's extracellular matrix (ECM) - most prominently the so-called perineuronal nets (PNNs), complex macromolecular assemblies of ECM components. Due to progress in cellular and molecular neurosciences, it has been possible to decipher the composition of ECM structures and to obtain insight into their function(s) and underlying mechanisms. It appears that PNN-related structures are involved in regulating the sprouting and pruning of synapses, which represents an important morphological correlate of synaptic plasticity in the adult nervous system. Perturbation assays and gene elimination by recombinant techniques have provided clear indications that astrocyte-derived ECM components, e.g. the tenascins and chondroitinsulfate proteoglycans (CSPGs) of the lectican family participate in these biological functions. The present review will discuss the glia-derived glycoproteins and CSPGs of the perisynaptic ECM, their neuronal and glial receptors, and in vitro assays to test their physiological functions in the framework of the synapse, the pivotal element of communication in the central nervous system.

Rapid assembly of functional presynaptic boutons triggered by adhesive contacts

CNS synapse assembly typically follows after stable contacts between "appropriate" axonal and dendritic membranes are made. We show that presynaptic boutons selectively form de novo following neuronal fiber adhesion to beads coated with poly-d-lysine (PDL), an artificial cationic polypeptide. As demonstrated by atomic force and live confocal microscopy, functional presynaptic boutons self-assemble as rapidly as 1 h after bead contact, and are found to contain a variety of proteins characteristic of presynaptic endings. Interestingly, presynaptic compartment assembly does not depend on the presence of a biological postsynaptic membrane surface. Rather, heparan sulfate proteoglycans, including syndecan-2, as well as others possibly adsorbed onto the bead matrix or expressed on the axon surface, are required for assembly to proceed by a mechanism dependent on the dynamic reorganization of F-actin. Our results indicate that certain (but not all) nonspecific cationic molecules like PDL, with presumably electrostatically mediated adhesive properties, can effectively bypass cognate and natural postsynaptic ligands to trigger presynaptic assembly in the absence of specific target recognition. In contrast, we find that postsynaptic compartment assembly depends on the prior presence of a mature presynaptic ending.

Dietary fats, cerebrovasculature integrity and Alzheimer's disease risk

An emerging body of evidence is consistent with the hypothesis that dietary fats influence Alzheimer's disease (AD) risk, but less clear is the mechanisms by which this occurs. Alzheimer's is an inflammatory disorder, many consider in response to fibrillar formation and extracellular deposition of amyloid-beta (Abeta). Alternatively, amyloidosis could notionally be a secondary phenomenon to inflammation, because some studies suggest that cerebrovascular disturbances precede amyloid plaque formation. Hence, dietary fats may influence AD risk by either modulating Abeta metabolism, or via Abeta independent pathways. This review explores these two possibilities taking into consideration; (i) the substantial affinity of Abeta for lipids and its ordinary metabolism as an apolipoprotein; (ii) evidence that Abeta has potent vasoactive properties and (iii) studies which show that dietary fats modulate Abeta biogenesis and secretion. We discuss accumulating evidence that dietary fats significantly influence cerebrovascular integrity and as a consequence altered Abeta kinetics across the blood-brain barrier (BBB). Specifically, chronic ingestion of saturated fats or cholesterol appears to results in BBB dysfunction and exaggerated delivery from blood-to-brain of peripheral Abeta associated with lipoproteins of intestinal and hepatic origin. Interestingly, the pattern of saturated fat/cholesterol induced cerebrovascular disturbances in otherwise normal wild-type animal strains is analogous to established models of AD genetically modified to overproduce Abeta, consistent with a causal association. Saturated fats and cholesterol may exacerbate Abeta induced cerebrovascular disturbances by enhancing exposure of vessels of circulating Abeta. However, presently there is no evidence to support this contention. Rather, SFA and cholesterol appear to more broadly compromise BBB integrity with the consequence of plasma protein leakage into brain, including lipoprotein associated Abeta. The latter findings are consistent with the concept that AD is a dietary-fat induced phenotype of vascular dementia, reflecting the extraordinary entrapment of peripherally derived lipoproteins endogenously enriched in Abeta. Rather than being the initiating trigger for inflammation in AD, accumulation of extracellular lipoprotein-Abeta may be a secondary amplifier of dietary induced inflammation, or possibly, simply be consequential. Clearly, delineating the mechanisms by which dietary fats increase AD risk may be informative in developing new strategies for prevention and treatment of AD.

Dendrite formation of cerebellar Purkinje cells

During postnatal cerebellar development, Purkinje cells form the most elaborate dendritic trees among neurons in the brain, which have been of great interest to many investigators. This article overviews various examples of cellular and molecular mechanisms of formation of Purkinje cell dendrites as well as the methodological aspects of investigating those mechanisms.

The subependymal zone neurogenic niche: a beating heart in the centre of the brain: how plastic is adult neurogenesis? Opportunities for therapy and questions to be addressed

The mammalian brain is a remarkably complex organ comprising millions of neurons, glia and various other cell types. Its impressive cytoarchitecture led to the long standing belief that it is a structurally static organ and thus very sensitive to injury. However, an area of striking structural flexibility has been recently described at the centre of the brain. It is the subependymal zone of the lateral wall of the lateral ventricles. The subependymal zone--like a beating heart--continuously sends new cells to different areas of the brain: neurons to the olfactory bulbs and glial cells to the cortex and the corpus callosum. Interestingly, the generation and flow of cells changes in response to signals from anatomically remote areas of the brain or even from the external environment of the organism, therefore indicating that subependymal neurogenesis--as a system--is integrated in the overall homeostatic function of the brain. In this review, it will be attempted to describe the fundamental structural and functional characteristics of the subependymal neurogenic niche and to summarize the available evidence regarding its plasticity. Special focus is given on issues such as whether adult neural stem cells are activated after neurodegeneration, whether defects in neurogenesis contribute to neuropathological conditions and whether monitoring changes in neurogenic activity can have a diagnostic value.

Development of hyaluronic acid-based scaffolds for brain tissue engineering

Three-dimensional biodegradable porous scaffolds play vital roles in tissue engineering. In this study, a hyaluronic acid-collagen (HA-Coll) sponge with an open porous structure and mechanical behavior comparable to brain tissue was developed. HA-Coll scaffolds with different mixing ratios were prepared by a freeze-drying technique and crosslinked with water-soluble carbodiimide to improve mechanical stability. The pore structure of the samples was evaluated by light and scanning electron microscopy, and the mechanical behavior was analyzed by mechanical compression and tension testing. The degree of crosslinking was determined by the water absorption and trinitrobenzene sulfonic assay, and the HA content was determined by a carbazole assay. The results showed that HA-Coll scaffolds containing an open porous structure with a homogeneous pore size distribution could be fabricated. Certain features of the mechanical properties of HA-Coll scaffolds prepared with a Coll:HA mixing ratio of 1:2, and pure HA sponges, were comparable with brain tissue. Neural stem cells (NSCs) were expanded in number in monolayer culture and then seeded onto the three-dimensional scaffolds in order to investigate the effects of the different types of scaffolds on neurogenic induction of the cells. This study contributes to the understanding of the effects of HA content and crosslink treatment on pore characteristics, and mechanical behavior essential for the design of HA-Coll scaffolds suitable for NSC growth and differentiation for brain tissue engineering.

Influence of aging on chondroitin sulfate proteoglycan expression and neural stem/progenitor cells in rat brain and improving effects of a herbal medicine, yokukansan

There is evidence of structural and functional deterioration in the brain, including the prefrontal cortex (PFC) and hippocampus, during the normal aging process in animals and humans. Extracellular matrix-associated glycoproteins, such as chondroitin sulfate proteoglycans (CSPGs), are involved in not only maintaining the structures and functions of adult neurons, but also regulating the proliferation, migration, and neurite outgrowth of neural stem cells in the brain. On the other hand, a herbal medicine, yokukansan (YKS), is used in a variety of clinical situations for treating symptoms associated with age-related neurodegenerative disorders such as Alzheimer's disease, but its pharmacological properties have not been fully understood. The present study was designed to clarify the influence of aging and the improving effects of YKS on the expression of aggrecan, a major molecule of CSPGs, and on the proliferation and migration of neural stem/progenitor cells identified by bromodeoxyuridine (BrdU) incorporation in the PFC and hippocampus including the dentate gyrus. Aged rats (24 months old) showed a significant increase in aggrecan expression throughout the PFC and in the hippocampus particularly in the CA3 subfield, but not the dentate gyrus compared to young rats (5 months old), evaluated by the immunohistochemical method. YKS treatment decreased the age-related increase in aggrecan expression as well as normal expression in young rats. Aged rats also showed a decreased number of BrdU-labeled cells in the PFC and hippocampus, and these decreases were improved by YKS treatment, which also increased the numbers in young rats. These results suggest that aging influences the microenvironment for adult and immature neurons in the brain, which may affect the proliferation and migration of neural stem/progenitor cells, and YKS has pharmacological potency for these age-related events. These findings help to understand the physiology and pathology of the aged brain and provide an anti-aging strategy for the brain.

Differential expression of receptor protein tyrosine phosphatases accompanies the reorganisation of the retina upon laser lesion

The regulation of protein phosphorylation plays an essential role in virtually all aspects of eukaryotic development. Beginning with the regulation of the cell cycle to cellular proliferation and differentiation, the delicate balance between the phosphorylating activity of kinases and the dephosphorylation by phosphatases controls the outcome of many signal transduction cascades. The generation of cellular diversity occurs in an environment that is structured by the extracellular matrix (ECM) which forms a surrounding niche for stem and progenitor cells. Cell-cell and cell-matrix interactions elicit specific signaling pathways that control cellular behavior. In pathological situations such as neural degenerating diseases, gene expression patterns and finally the composition of the ECM change dramatically. This leads to changes of cell behavior and finally results in the failure of regeneration and functional restoration in the adult central nervous system. In order to study the roles of tyrosine phosphatases and ECM in this context, we analyzed the effects of laser-induced retinal injury on the regulation of the receptor protein tyrosine phosphatases (RPTP) RPTPBr7, Phogrin and RPTPbeta/zeta. The latter occurs in several isoforms, including the soluble released chondroitin sulfate proteoglycan phosphacan that is expressed in the developing retina. The receptor variants RPTPbeta/zeta(long) and RPTPbeta/zeta(short) may serve as receptors of tenascin-proteins and serve as modulators of cell intrinsic signaling in response to the ECM. Using quantitative real-time RT-PCR analysis, we show here a time-dependent pattern of gene expression of these molecules following laser lesions of the retina.

Versican V2 assembles the extracellular matrix surrounding the nodes of ranvier in the CNS

The CNS-restricted versican splice-variant V2 is a large chondroitin sulfate proteoglycan incorporated in the extracellular matrix surrounding myelinated fibers and particularly accumulating at nodes of Ranvier. In vitro, it is a potent inhibitor of axonal growth and therefore considered to participate in the reduction of structural plasticity connected to myelination. To study the role of versican V2 during postnatal development, we designed a novel isoform-specific gene inactivation approach circumventing early embryonic lethality of the complete knock-out and preventing compensation by the remaining versican splice variants. These mice are viable and fertile; however, they display major molecular alterations at the nodes of Ranvier. While the clustering of nodal sodium channels and paranodal structures appear in versican V2-deficient mice unaffected, the formation of the extracellular matrix surrounding the nodes is largely impaired. The conjoint loss of tenascin-R and phosphacan from the perinodal matrix provide strong evidence that versican V2, possibly controlled by a nodal receptor, organizes the extracellular matrix assembly in vivo.

Calcium diffusion enhanced after cleavage of negatively charged components of brain extracellular matrix by chondroitinase ABC

The concentration of extracellular calcium plays a critical role in synaptic transmission and neuronal excitability as well as other physiological processes. The time course and extent of local fluctuations in the concentration of this ion largely depend on its effective diffusion coefficient (D*) and it has been speculated that fixed negative charges on chondroitin sulphate proteoglycans (CSPGs) and other components of the extracellular matrix may influence calcium diffusion because it is a divalent cation. In this study we used ion-selective microelectrodes combined with pressure ejection or iontophoresis of ions from a micropipette to quantify diffusion characteristics of neocortex and hippocampus in rat brain slices. We show that D* for calcium is less than the value predicted from the behaviour of the monovalent cation tetramethylammonium (TMA), a commonly used diffusion probe, but D* for calcium increases in both brain regions after the slices are treated with chondroitinase ABC, an enzyme that predominantly cleaves chondroitin sulphate glycans. These results suggest that CSPGs do play a role in determining the local diffusion properties of calcium in brain tissue, most likely through electrostatic interactions mediating rapid equilibrium binding. In contrast, chondroitinase ABC does not affect either the TMA diffusion or the extracellular volume fraction, indicating that the enzyme does not alter the structure of the extracellular space and that the diffusion of small monovalent cations is not affected by CSPGs in the normal brain ionic milieu. Both calcium and CSPGs are known to have many distinct roles in brain physiology, including brain repair, and our study suggests they may be functionally coupled through calcium diffusion properties.

Agrin, aquaporin-4, and astrocyte polarity as an important feature of the blood-brain barrier

The blood-brain barrier (BBB) does not exclusively refer to brain endothelial cells, which are the site of the barrier proper. In the past few years, it has become increasingly clear that BBB endothelial cells depend considerably on the brain microenvironment to a degree exceeding the environmental influence in other organs. The concept of the BBB has been continuously developed over the decades, culminating now in the recognition that endothelial cell function in the brain is not limited to simply mediating energy and oxygen transfer between blood and neural tissue. Endothelial cells are rather "Janus-headed beings" that are active partners of both luminal molecules and cells, as well as subendothelial cells such as pericytes, astrocytes, and neurons. In this overview, the authors present and discuss both the role of astroglial cells in managing the BBB and aspects of pathological alterations in the brain as far as the BBB is involved. After a brief introduction of the BBB that describes the structure and function of the brain capillary endothelial cells, the authors report on both the water channel protein aquaporin-4 (AQP4) in astrocytes and the extracellular matrix between astrocytes/pericytes and endothelial cells. The AQP4 has an important impact on the homeostasis in the brain parenchyma; however, the mechanistic cascade from the composition of the astrocyte membrane to the maintenance of BBB properties in the endothelial cells, including their tight junction formation, is still completely unknown.

The potentiation of peripheral nerve sheaths in regeneration and repair

Traumatic injury to the nervous system often results in life changing loss of neurological function. Spontaneous neural regeneration occurs rarely and the outcome of therapeutic intervention is most often unacceptable. An intensive effort is underway to improve methods and technologies for nervous system repair. To date, the most success has been attained in the outcomes of peripheral nerve restoration. The importance of the peripheral nerve sheaths in successful nerve regeneration has been long recognized. In particular, Schwann cells and their basal laminae play a central role in axon development, maintenance, physiology, and response to injury. The endoneurial basal lamina is rich in components that promote axonal growth. It is now evident that the bioactivities of these components are counterbalanced by various factors that impede axonal growth. The growth-promoting potential of peripheral nerve is realized in the degenerative processes that occur distal to a lesion. This potentiation involves precise spatiotemporal alterations in the balance of antagonistic regulators of axonal growth. Experimental alteration of nerve sheath composition can also potentiate nerve and improve key features of nerve regeneration. For instance, enzymatic degradation of inhibitory chondroitin sulfate proteoglycan mimics endogenous processes that potentiate degenerated nerve and improves the outcome of direct nerve repair and grafting in animal models. This review provides a perspective of the essential role that peripheral nerve sheaths play in regulating axonal regeneration and focuses on discoveries leading to the inception and development of novel therapies for nerve repair.

Agrin defines polarized distribution of orthogonal arrays of particles in astrocytes

Accumulating evidence indicates that agrin, a heparan sulphate proteoglycan of the extracellular matrix, plays a role in the organization and maintenance of the blood-brain barrier. This evidence is based on the differential effects of agrin isoforms on the expression and distribution of the water channel protein, aquaporin-4 (AQP4), on the swelling capacity of cultured astrocytes of neonatal mice and on freeze-fracture data revealing an agrin-dependent clustering of orthogonal arrays of particles (OAPs), the structural equivalent of AQP4. Here, we show that the OAP density in agrin-null mice is dramatically decreased in comparison with wild-types, by using quantitative freeze-fracture analysis of astrocytic membranes. In contrast, anti-AQP4 immunohistochemistry has revealed that the immunoreactivity of the superficial astrocytic endfeet of the agrin-null mouse is comparable with that in wild-type mice. Moreover, in vitro, wild-type and agrin-null astrocytes cultured from mouse embryos at embryonic day 19.5 differ neither in AQP4 immunoreactivity, nor in OAP density in freeze-fracture replicas. Analyses of brain tissue samples and cultured astrocytes by reverse transcription with the polymerase chain reaction have not demonstrated any difference in the level of AQP4 mRNA between wild-type astrocytes and astrocytes from agrin-null mice. Furthermore, we have been unable to detect any difference in the swelling capacity between wild-type and agrin-null astrocytes. These results clearly demonstrate, for the first time, that agrin plays a pivotal role for the clustering of OAPs in the endfoot membranes of astrocytes, whereas the mere presence of AQP4 is not sufficient for OAP clustering.

Drosophila multiplexin (Dmp) modulates motor axon pathfinding accuracy

Multiplexins are multidomain collagens typically composed of an N-terminal thrombospondin-related domain, an interrupted triple helix and a C-terminal endostatin domain. They feature a clear regulatory function in the development of different tissues, which is chiefly conveyed by the endostatin domain. This domain can be found in proteolytically released monomeric and trimeric versions, and their diverse and opposed effects on the migratory behavior of epithelial and endothelial cell types have been demonstrated in cell culture experiments. The only Drosophila multiplexin displays specific features of both vertebrate multiplexins, collagens XV and XVIII. We characterized the Drosophila multiplexin (dmp) gene and found that three main isoforms are expressed from it, one of which is the monomeric endostatin version. Generation of dmp deletion alleles revealed that Dmp plays a role in motor axon pathfinding, as the mutants exhibit ventral bypass defects of the intersegmental nerve b (ISNb) similar to other motor axon guidance mutants. Transgenic overexpression of monomeric endostatin as well as of full-length Dmp, but not trimeric endostatin, were able to rescue these defects. In contrast, trimeric endostatin increased axon pathfinding accuracy in wild type background. We conclude that Dmp plays a modulating role in motor axon pathfinding and may be part of a buffering system that functions to avoid innervation errors.

Expression of syndecan-2 in the amoeboid microglial cells and its involvement in inflammation in the hypoxic developing brain

The present study examined the expression of heparan sulphate proteoglycan, syndecan-2 (Sdc-2) in the corpus callosum and the amoeboid microglial cells (AMC) in the neonatal rat brain in response to hypoxia. In 1-day old Wistar rats subjected to hypoxia the mRNA and protein expression of Sdc-2 in the corpus callosum, heavily populated by AMC, was increased up to 3 days after the hypoxic exposure. Immunoexpression of Sdc-2 was localized in AMC as confirmed by double labeling using microglial marker. Primary cultures of microglial cells subjected to hypoxia showed a significant increase in Sdc-2 expression. Application of Sdc-2 to microglial cultures under hypoxia increased the release of tumor necrosis factor-alpha, interleukin-1beta, chemokine (C-C motif) ligand 2 (CCL2), and chemokine (C-X-C motif) ligand 12 (CXCL12) by the microglial cells. Additionally, Sdc-2 enhanced the production of reactive oxygen species (ROS) by microglia subjected to hypoxia. Edaravone [3-methyl-1phenyl-2-pyrazolin-5-one], an antioxidant drug, suppressed the hypoxia- and Sdc-2-induced increased production of cytokines, chemokines, and ROS. In the light of these findings, we suggest that Sdc-2 plays an important role in microglial production of inflammatory cytokines, chemokines, and ROS in hypoxic conditions. In this connection, edaravone suppressed the hypoxia- and Sdc-2-induced increased cytokine and ROS production suggesting its therapeutic potential in ameliorating neuroinflammation.

In vivo injection of fibroblast growth factor-2 into the cisterna magna induces glypican-6 expression in mouse brain tissue

The proteoglycans (PGs) are multifunctional macromolecules composed of a core polypeptide and a variable number of glycosaminoglycan chains. In the nervous system, PGs regulate the structural organization of the extracellular matrix (ECM) and modulate growth factor activities and cell proliferation and migration. Most cortical neurons are generated from neural precursor cells that reside in the ventricular zone of the embryonic brain. The proliferation and differentiation of neural precursor cells are regulated by various growth and neurotrophic factors. Fibroblast growth factor-2 (FGF-2) is an important mitogen for cortical neural precursor cells, and glypicans regulate the action of FGF-2 on neural precursor cells. Glypican-6 is one of the most abundant ECM molecules in the brain. In this study the effects of FGF-2 on glypican-6 expression in brain tissue have been investigated. FGF-2 was injected into the cerebrospinal fluid (CSF) through the cisterna magna of mouse pups. Using Western blotting, it was shown that the expression of glypican-6 is increased in response to infusion of FGF-2 into the CSF. The injection of anti-FGF-2 antibody into the cisterna magna decreased glypican-6 expression in brain tissue. The results from this study suggest that glypican-6 is important in regulating FGF-2 activity during cerebral cortical development.

Chondroitinase ABC-mediated plasticity of spinal sensory function

Experimental therapeutics designed to enhance recovery from spinal cord injury (SCI) primarily focus on augmenting the growth of damaged axons by elevating their intrinsic growth potential and/or by nullifying the influence of inhibitory proteins present in the mature CNS. However, these strategies may also influence the wiring of intact pathways. The direct contribution of such effects to functional restoration after injury has been mooted, but as yet not been described. Here, we provide evidence to support the hypothesis that reorganization of intact spinal circuitry enhances function after SCI. Adult rats that underwent unilateral cervical spared-root lesion (rhizotomy of C5, C6, C8, and T1, sparing C7) exhibited profound sensory deficits for 4 weeks after injury. Delivery of a focal intraspinal injection of the chondroitin sulfate proteoglycan-degrading enzyme chondroitinase ABC (ChABC) was sufficient to restore sensory function after lesion. In vivo electrophysiological recordings confirm that behavioral recovery observed in ChABC-treated rats was consequent on reorganization of intact C7 primary afferent terminals and not regeneration of rhizotomized afferents back into the spinal cord within adjacent segments. These data confirm that intact spinal circuits have a profound influence on functional restoration after SCI. Furthermore, comprehensive understanding of these targets may lead to therapeutic interventions that can be spatially tailored to specific circuitry, thereby reducing unwanted maladaptive axon growth of distal pathways.

Looking beyond development: maintaining nervous system architecture

Neuronal circuitries established in development must persist throughout life. This poses a serious challenge to the structural integrity of an embryonically patterned nervous system as an animal dramatically increases its size postnatally, remodels parts of its anatomy, and incorporates new neurons. In addition, body movements, injury, and ageing generate physical stress on the nervous system. Specific molecular pathways maintain intrinsic properties of neurons in the mature nervous system. Other factors ensure that the overall organization of entire neuronal ensembles into ganglia and fascicles is appropriately maintained upon external challenges. Here, we discuss different molecules underlying these neuronal maintenance mechanisms, with a focus on lessons learned from the nematode Caenorhabditis elegans.

Cell adhesion to agrin presented as a nanopatterned substrate is consistent with an interaction with the extracellular matrix and not transmembrane adhesion molecules

BACKGROUND

Molecular spacing is important for cell adhesion in a number of ways, ranging from the ordered arrangement of matrix polymers extracellularly, to steric hindrance of adhesion/signaling complexes intracellularly. This has been demonstrated using nanopatterned RGD peptides, a canonical extracellular matrix ligand for integrin interactions. Cell adhesion was greatly reduced when the RGD-coated nanoparticles were separated by more than 60 nm, indicating a sharp spacing-dependent threshold for this form of cell adhesion.

RESULTS

Here we show a similar dependence of cell adhesion on the spacing of agrin, a protein that exists as both a secreted, matrix-bound form and a type-2 transmembrane form in vivo. Agrin was presented as a substrate for cell adhesion assays by anchoring recombinant protein to gold nanoparticles that were arrayed at tunable distances onto glass coverslips. Cells adhered well to nanopatterned agrin, and when presented as uniformly coated substrates, adhesion to agrin was comparable to other well-studied adhesion molecules, including N-Cadherin. Adhesion of both mouse primary cortical neurons and rat B35 neuroblastoma cells showed a spacing-dependent threshold, with a sharp drop in adhesion when the space between agrin-coated nanoparticles increased from 60 to 90 nm. In contrast, adhesion to N-Cadherin decreased gradually over the entire range of distances tested (uniform, 30, 60, 90, and 160 nm). The spacing of the agrin nanopattern also influenced cell motility, and peptide competition suggested adhesion was partially integrin dependent. Finally, differences in cell adhesion to C-terminal agrin fragments of different lengths were detected using nanopatterned substrates, and these differences were not evident using uniformly coated substrates.

CONCLUSION

These results suggest nanopatterned substrates may provide a physiological presentation of adhesive substrates, and are consistent with cells adhering to agrin through a mechanism that more closely resembles an interaction with the extracellular matrix than a transmembrane adhesion molecule.

Chondroitin-4-sulfation negatively regulates axonal guidance and growth

Glycosaminoglycan (GAG) side chains endow extracellular matrix proteoglycans with diversity and complexity based upon the length, composition and charge distribution of the polysaccharide chain. Using cultured primary neurons, we show that specific sulfation in the GAG chains of chondroitin sulfate mediates neuronal guidance cues and axonal growth inhibition. Chondroitin-4-sulfate (CS-A), but not chondroitin-6-sulfate (CS-C), exhibits a strong negative guidance cue to mouse cerebellar granule neurons. Enzymatic and gene-based manipulations of 4-sulfation in the GAG side chains alter their ability to direct growing axons. Furthermore, 4-sulfated chondroitin sulfate GAG chains are rapidly and significantly increased in regions that do not support axonal regeneration proximal to spinal cord lesions in mice. Thus, our findings show that specific sulfation along the carbohydrate backbone carries instructions to regulate neuronal function.