Laminin and the mechanism of neuronal outgrowth

In vivo enhancement of sensory perception recovery in a tissue-engineered skin enriched with laminin

The use of autologous reconstructed skin appears to be a promising treatment for the permanent coverage of deep and extensive burns. However, the capability of reconstructed skin transplanted on wounds to promote recovery of sensory perception is a major concern. Our aim was to assess the effect of laminin on cutaneous nerve regeneration. We prepared collagen-chitosan sponges enriched with 0, 1, 10 or 50 microg of laminin/sponge to produce tissue-engineered reconstructed skins by culture of human fibroblasts and keratinocytes, then grafted on the back of athymic mice for 120 days. Immunohistochemical studies demonstrated that there were 7 times more neurofilament 150 kD-positive nerve fibers migrating in the graft in the samples enriched with 10 microg laminin/sponge, compared to reconstructed skin without laminin, 120 days after graft. A significant improvement in the current perception threshold of the Abeta and Adelta nerve fibers was measured using a Neurometer in all grafts enriched with laminin. In addition, the type C nerve fibers reached an identical current perception threshold than mouse skin, in all reconstructed skins enriched or not with laminin. We conclude that the use of a tissue-engineered autologous skin graft enriched with laminin has the potential to efficiently optimize cutaneous sensory nerve regeneration in vivo.

Overexpression of PrPC by adenovirus-mediated gene targeting reduces ischemic injury in a stroke rat model

Prion diseases are induced by pathologically misfolded prion protein (PrPSc), which recruit normal sialoglycoprotein PrPC by a template-directed process. In this study, we investigated the expression of PrPC in a rat model of cerebral ischemia to more fully understand its physiological role. Immunohistochemical analysis demonstrated that PrPC-immunoreactive cells increased significantly in the penumbra of ischemic rat brain compared with the untreated brain. Western blot analysis showed that PrPC protein expression increased in ischemic brain tissue in a time-dependent manner. In addition, PrPC protein expression was seen to colocalize with neuron, glial, and vascular endothelial cells in the penumbric region of the ischemic brain. Overexpression of PrPC by injection of rAd (replication-defective recombinant adenoviral)-PGK (phosphoglycerate kinase)-PrPC-Flag into ischemic rat brain improved neurological behavior and reduced the volume of cerebral infarction, which is supportive of a role for PrPC in the neuroprotective adaptive cellular response to ischemic lesions. Concomitant upregulation of PrPC and activated extracellular signal-regulated kinase (ERK1/2) under hypoxia-reoxygenation in primary cortical cultures was shown to be dependent on ERK1/2 phosphorylation. During hypoxia-reoxygenation, mouse neuroblastoma cell line N18 cells transfected with luciferase rat PrPC promoter reporter constructs, containing the heat shock element (HSE), expressed higher luciferase activities (3- to 10-fold) than those cells transfected with constructs not containing HSE. We propose that HSTF-1 (hypoxia-activated transcription factor), phosphorylated by ERK1/2, may in turn interact with HSE in the promoter of PrPC resulting in gene expression of the prion gene. In summary, we conclude that upregulation of PrPC expression after cerebral ischemia and hypoxia exerts a neuroprotective effect on injured neural tissue. This study suggests that PrPC has physiological relevance to cerebral ischemic injury and could be useful as a therapeutic target for the treatment of cerebral ischemia.

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

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

Survival and differentiation of embryonic neural explants on different biomaterials

Biomaterials prepared from polyacrylamide, ethyl acrylate (EA), and hydroxyethyl acrylate (HEA) in various blend ratios, methyl acrylate and chitosan, were tested in vitro as culture substrates and compared for their ability to be colonized by the cells migrating from embryonic brain explants. Neural explants were isolated from proliferative areas of the medial ganglionic eminence and the cortical ventricular zone of embryonic rat brains and cultured in vitro on the different biomaterials. Chitosan, poly(methyl acrylate), and the 50% wt copolymer of EA and HEA were the most suitable substrates to promote cell attachment and differentiation of the neural cells among those tested. Immunofluorescence microscopy analysis showed that progenitor cells had undergone differentiation and that the resulting glial and neuronal cells expressed their intrinsic morphological characteristics in culture.

A heterogeneous immunofluorescence staining for laminin-1 and related basal lamina molecules in the dorsal root ganglia following constriction nerve injury

The bodies of primary sensory neurons and their satellite glial cells (SGCs) are limited by the basal laminae from extracellular matrix of the dorsal root ganglia (DRG). The basal laminae displayed uniform immunofluorescence staining for laminin-1 in the sections of rat intact (naive) DRG. A proximal or distal ligature of the spinal nerves resulted in a heterogeneous immunostaining for laminin-1 around neuron-SGC units in the sections of the corresponding DRG. The pattern of irregular laminin-1 immunofluorescence was more extensive in the ipsilateral than the contralateral DRG of the operated rats. The immunofluorescence for laminin-1 exactly coincided with binding of Concanavalin-A as well as immunostaining for type IV collagen in both naive DRG and DRG affected by nerve ligature. Nidogen immunostaining decreased or fully disappeared at the surface of the SGCs consistently with immunofluorescence staining for laminin-1, but retained or increased in the endothelial cells and ED-1 positive cells invaded the DRG affected by nerve ligature. The results indicate an alteration of the content of basal laminae surrounding the bodies of primary sensory neurons and their SGSs following nerve constriction injury. A modulation of the basal laminae may be related with other cellular and molecular alterations related with peripheral neuropathic pain, for example, expansion of sympathetic sprouts.

Neurite bridging across micropatterned grooves

After injury, regenerating axons must navigate complex, three-dimensional (3D) microenvironments. Topographic guidance of neurite outgrowth has been demonstrated in vitro with culture substrates that contain micropatterned features on the nanometer-micron scale. In this study we report the ability of microfabricated biomaterials to support neurite extension across micropatterned grooves with feature sizes on the order of tens of microns, sizes relevant to the design of biomaterials and tissue engineering scaffolds. Neonatal rat dorsal root ganglion (DRG) neurons were cultured on grooved substrates of poly(dimethyl siloxane) coated with poly-L-lysine and laminin. Here we describe an unusual capability of a subpopulation of DRG neurons to extend neurites that spanned across the grooves, with no underlying solid support. Multiple parameters influenced the formation of bridging neurites, with the highest numbers of bridges observed under the following experimental conditions: cell density of 125,000 cells per sample, groove depth of 50 microm, groove width of 30 microm, and plateau width of 200 microm. Bridges were formed as neurites extended from a neuron in a groove, contacted adjacent plateaus, pulled the neuron up to become suspended over the groove, and the soma translocated to the plateau. These studies are of interest to understanding cytoskeletal dynamics and designing biomaterials for 3D axon guidance.

Acoustic sensor for monitoring adhesion of Neuro-2A cells in real-time

Neuronal adhesion plays a fundamental role in growth, migration, regeneration and plasticity of neurons. However, current methods for studying neuronal adhesion cannot monitor this phenomenon quantitatively in real-time. In this work, we demonstrate the use of an acoustic sensor to measure adhesion of neuro-blastoma cells (Neuro-2A) in real-time. An acoustic sensor consisting of a quartz crystal sandwiched between gold electrodes was placed in a flow cell and filled with 600 microl of phosphate buffered saline (PBS). Two sets of in vitro experiments were performed using sensors that had uncoated gold electrodes and sensors that were coated with a known neuronal adhesion promoter (poly-l-lysine or PLL). The instantaneous resonant frequency and the equivalent motional resistance of the acoustic sensor were monitored every second. Cell Tracker was used to confirm neuronal adhesion to the surface. Addition of 10 microl of media and Neuro-2A cells into the above set-up elicited exponential changes in the resonant frequency and motional resistance of the quartz crystal with time to reach steady state in the range of 2-11 h. The steady-state change in resonant frequency in response to addition of neurons was linearly related to the number of Neuro-2A cells added (R2=0.94). Acoustic sensors coated with the adhesion promoter, PLL showed a much higher change in resonant frequency for approximately the same number of neurons. We conclude that the acoustic sensor has sufficient sensitivity to monitor neuronal adhesion in real-time. This has potential applications in the study of mechanisms of neuron-substrate interactions and the effect of molecular modulators in the extra cellular matrix.

Growth of human stem cell-derived neurons on solid three-dimensional polymers

Understanding neural differentiation and the development of complex neurite networks in three-dimensional matrices is critical for neural tissue engineering in vitro. In this study we describe for the first time the growth of human stem cell-derived neurons on solid polystyrene matrices coated with bioactive molecules. Highly porous foams were prepared from poly(styrene/divinylbenzene) using a high internal phase emulsion (HIPE) as a template to create the porous structure. The resulting polyHIPE matrices were readily coated with aqueous-based solutions including poly-d-lysine and laminin. Human neurons adhered well to poly-d-lysine coated surfaces and extended neural processes, however, neurite outgrowth was particularly enhanced when polymers also received a coating of laminin. These data clearly demonstrate the potential use of solid polystyrene scaffolds to create three-dimensional environments for cell growth and differentiation. We propose that these robust and stable matrices can be conveniently and routinely used in the tissue culture laboratory to study the behaviour of cells grown in three-dimensions.

Schwann cells and endoneurial extracellular matrix molecules as potential cues for sorting of regenerated axons: a review

Besides very well elaborated microsurgical management of severed peripheral nerves, the clinical results of functional recovery following surgical repair of mixed nerves are disappointing. An improvement of functional recovery after peripheral nerve lesion requires the accurate regeneration of axons to their original target tissues and structures. Therefore, better clinical results could be obtained by a greater understanding of the cellular and molecular biology of selective nerve regeneration. The studies concerning Schwann cells and their endoneurial extracellular matrix as potent cues for selective promotion and influence of regenerating motor and sensory axons are reviewed. Knowledge of the sorting mechanisms of regenerated motor and sensory axons is needed not only for improvement of functional recovery, but also for the development of biocompatible nerve prostheses.

Differential upregulation of extracellular matrix molecules associated with the appearance of granule cell dispersion and mossy fiber sprouting during epileptogenesis in a murine model of temporal lobe epilepsy

We have investigated changes in the extracellular matrix of the hippocampus associated with the early progression of epileptogenesis in a murine model of temporal lobe epilepsy using immunohistochemistry. In the first week following intrahippocampal injection of the glutamate agonist, domoate, there is a latent period at the end of which begins a sequential upregulation of extracellular matrix (ECM) molecules in the granule cell layer of the dentate gyrus, beginning with neurocan and tenascin-C. This expression precedes the characteristic dispersion of the granule cell layer which is evident at 14 days post-injection when the first recurrent seizures can be recorded. At this stage, an upregulation of the chondroitin sulfate proteoglycan, phosphacan, the DSD-1 chondroitin sulfate motif, and the HNK-1 oligosaccharide are also observed. The expression of these molecules is localized differentially in the epileptogenic dentate gyrus, especially in the sprouting molecular layer, where a strong upregulation of phosphacan, tenascin-C, and HNK-1 is observed but there is no expression of the proteoglycan, neurocan, nor of the DSD-1 chondroitin sulfate motif. Hence, it appears that granule cell layer dispersion is accompanied by a general increase in the ECM, while mossy fiber sprouting in the molecular layer is associated with a more restricted repertoire. In contrast to these changes, the expression of the ECM glycoproteins, laminin and fibronectin, both of which are frequently implicated in tissue remodelling events, showed no changes associated with either granule cell dispersion or mossy fiber sprouting, indicating that the epileptogenic plasticity of the hippocampus is accompanied by ECM interactions that are characteristic of the CNS.

The neuroprotective KDI domain of γ1-laminin is a universal and potent inhibitor of ionotropic glutamate receptors

Previous work from this laboratory indicates that the KDI (Lys-Asp-Ile) domain of gamma 1-laminin promotes functional regeneration of adult rat spinal cord injuries and protects adult rat hippocampal neurons against massive neuronal death induced by intracerebral injection of the glutamate analogue kainic acid. In the present study, we used patch clamp recordings on cultured human embryonic neocortical neurons and HEK 293 cells expressing recombinant glutamate receptor subunits to study a putative interaction of the KDI with the glutamate system. We show that the KDI domain of gamma 1-laminin is a universal and potent inhibitor of AMPA, kainate, and NMDA subclasses of glutamate receptors, with a noncompetitive action on the AMPA receptor channel activity. Glutamate neurotoxicity plays a key role in both CNS trauma and neurodegenerative disorders, so this unexpected, novel function of the gamma 1-laminin-derived tripeptide may prove clinically valuable in treatment of CNS trauma and/or disease.

Neurite outgrowth on well-characterized surfaces: preparation and characterization of chemically and spatially controlled fibronectin and RGD substrates with good bioactivity

Study of axonal growth and ligand-receptor interactions requires specificity and careful characterization of the biomaterial substrates to which the neurons bind. It would be impossible to predict the effects of important variables such as composition, surface density, spatial distribution, and conformation of the ligands on axonal growth of a neuron without highly specific surface characterization. Here, we compare two methods of surface modification (hereafter referred to as "Heterobifunctional Crosslinker" and "Pluronics" methods) used for immobilization of fibronectin (FN) and FN-derived, RGD-containing peptides to the substrates. We also characterized their performance in neurite outgrowth experiments. Various surface analytical techniques such as contact angle measurement, XPS, and time-of-flight secondary ion mass spectrometry (TOF-SIMS) were used for the analysis of the substrates at each step of the two different chemistries involved. FN-patterned surfaces were created by micro-contact printing methods and confirmed by imaging TOF-SIMS, and AFM techniques. After immobilization of FN and/or FN-derived RGD-containing peptide, including the formation of micron-scale patterns of FN, the modified surfaces were plated with neurons from postnatal rat dorsal root ganglia (DRG) and incubated in serum-free medium. Both the peptide- and/or protein-modified substrates supported significantly greater neurite outgrowth than controls, and outgrowth on both substrate chemistries was inhibited by the addition of soluble RGD peptide. Patterned FN surfaces were successful in spatially controlling the neuron attachment and outgrowth.

Differential regulation of laminin b1 transgene expression in the neonatal and adult mouse brain

Laminins are the major glycoproteins present in basement membrane, a type of extracellular matrix. We showed that the LAMB1 gene, which encodes the laminin beta1 subunit, is transcriptionally activated by retinoic acid in embryonic stem cells. However, little information is available concerning LAMB1 developmental regulation and spatial expression in the adult mouse brain. In this study we used transgenic mice expressing different lengths of LAMB1 promoter driving beta-galactosidase to investigate developmental and adult transcriptional regulation in the regions of the brain in which the laminin beta1 protein is expressed. CNS expression was not observed in transgenic mice carrying a 1.4LAMB1betagal construct. Mice carrying a 2.5LAMB1betagal construct expressed the LAMB1 transgene, as assayed by X-gal staining, only in the molecular layer of the neonatal cerebellum. In contrast, a 3.9LAMB1betagal transgene showed broad regional expression in the adult mouse brain, including the hippocampus, entorhinal cortex, colliculi, striatum, and substantia nigra. Similar expression patterns were observed for the endogenous laminin beta1 protein and for the 3.9LAMB1betagal transgene, analyzed with an antibody against the beta-galactosidase protein. The 3.9LAMB1betagal transgene expression in the hippocampal tri-synaptic circuit suggests a role for the LAMB1 gene in learning and memory.

Sialic acid residues on astrocytes regulate neuritogenesis by controlling the assembly of laminin matrices

In the developing nervous system migrating neurons and growing axons are guided by diffusible and/or substrate-bound cues, such as extracellular matrix-associated laminin. In a previous work we demonstrated that laminin molecules could self-assemble in two different manners, giving rise to matrices that could favor either neuritogenesis or proliferation of cortical precursor cells. We investigated whether the ability of astrocytes to promote neuritogenesis of co-cultivated neurons was modulated by the assembling mode of the laminin matrix secreted by them. We compared the morphologies and neuritogenic potentials of laminin deposited by in vitro-differentiated astrocytes obtained from embryonic or neonatal rat brain cortices. We showed that, while permissive astrocytes derived from embryonic brain produced a flat laminin matrix that remained associated to the cell surface, astrocytes derived from newborn brain secreted a laminin matrix resembling a fibrillar web that protruded from the cell plane. The average neurite lengths obtained for E16 neurons cultured on each astrocyte layer were 198+/-22 and 123+/-13 microm, respectively. Analyses of surface-associated electrostatic potentials revealed that embryonic astrocytes presented a pI of -2.8, while in newborn cells this value was -3.8. Removal of the sialic acid groups on the embryonic monolayer by neuraminidase treatment led to the immediate release of matrix-associated laminin. Interestingly, laminin reassembled 1 hour after neuraminidase removal converted to the features of the newborn matrix. Alternatively, treatment of astrocytes with the cholesterol-solubilizing detergent methyl-beta-cyclodextrin also resulted in release of the extracellular laminin. To test the hypothesis that sialic-acid-containing lipids localized at cholesterol-rich membrane domains could affect the process of laminin assembly, we devised a cell-free assay where laminin polymerization was carried out over artificial lipid films. Films of either a mixture of gangliosides or pure ganglioside GT1b induced formation of matrices of morpho-functional features similar to the matrices deposited by embryonic astrocytes. Conversely, films of phosphatidylcholine or ganglioside GM1 led to the formation of bulky laminin aggregates that lacked a defined structure. We propose that the expression of negative lipids on astrocytes can control the extracellular polymerization of laminin and, consequently, the permissivity to neuritogenesis of astrocytes during development.

Acetylcholinesterase-Abeta complexes are more toxic than Abeta fibrils in rat hippocampus: effect on rat beta-amyloid aggregation, laminin expression, reactive astrocytosis, and neuronal cell loss

Neuropathological changes generated by human amyloid-beta peptide (Abeta) fibrils and Abeta-acetylcholinesterase (Abeta-AChE) complexes were compared in rat hippocampus in vivo. Results showed that Abeta-AChE complexes trigger a more dramatic response in situ than Abeta fibrils alone as characterized by the following features observed 8 weeks after treatment: 1). amyloid deposits were larger than those produced in the absence of AChE. In fact, AChE strongly stimulates rat Abeta aggregation in vitro as shown by turbidity measurements, Congo Red binding, as well as electron microscopy, suggesting that Abeta-AChE deposits observed in vivo probably recruited endogenous Abeta peptide; 2). the appearance of laminin expressing neurons surrounding Abeta-AChE deposits (such deposits are resistant to disaggregation by laminin in vitro); 3). an extensive astrocytosis revealed by both glial fibrillary acidic protein immunoreactivity and number counting of reactive hypertrophic astrocytes; and 4). a stronger neuronal cell loss in comparison with Abeta-injected animals. We conclude that the hippocampal injection of Abeta-AChE complexes results in the appearance of some features reminiscent of Alzheimer-like lesions in rat brain. Our studies are consistent with the notion that Abeta-AChE complexes are more toxic than Abeta fibrils and that AChE triggered some of the neurodegenerative changes observed in Alzheimer's disease brains.

Modelling neuroinflammatory phenotypes in vivo

Inflammation of the central nervous system is an important but poorly understood part of neurological disease. After acute brain injury or infection there is a complex inflammatory response that involves activation of microglia and astrocytes and increased production of cytokines, chemokines, acute phase proteins, and complement factors. Antibodies and T lymphocytes may be involved in the response as well. In neurodegenerative disease, where injury is more subtle but consistent, the inflammatory response is continuous. The purpose of this prolonged response is unclear, but it is likely that some of its components are beneficial and others are harmful. Animal models of neurological disease can be used to dissect the specific role of individual mediators of the inflammatory response and assess their potential benefit. To illustrate this approach, we discuss how mutant mice expressing different levels of the cytokine transforming growth factor beta-1 (TGF-beta1), a major modulator of inflammation, produce important neuroinflammatory phenotypes. We then demonstrate how crosses of TGF-beta1 mutant mice with mouse models of Alzheimer's disease (AD) produced important new information on the role of inflammation in AD and on the expression of different neuropathological phenotypes that characterize this disease.

Loss of TGF-beta 1 leads to increased neuronal cell death and microgliosis in mouse brain

TGF-beta1 is a key regulator of diverse biological processes in many tissues and cell types, but its exact function in the developing and adult mammalian CNS is still unknown. We report that lack of TGF-beta1 expression in neonatal Tgfb1(-/-) mice results in a widespread increase in degenerating neurons accompanied by reduced expression of synaptophysin and laminin and a prominent microgliosis. Lack of TGF-beta1 also strongly reduces survival of primary neurons cultured from Tgfb1(-/-) mice. TGF-beta1 deficiency in adult Tgfb1(-/+) mice results in increased neuronal susceptibility to excitotoxic injury, whereas astroglial overexpression of TGF-beta1 protects adult mice against neurodegeneration in acute, excitotoxic and chronic injury paradigms. This study reveals a nonredundant function for TGF-beta1 in maintaining neuronal integrity and survival of CNS neurons and in regulating microglial activation. Because individual TGF-beta1 expression levels in the brain vary considerably between humans, this finding could have important implications for susceptibility to neurodegeneration.

Laminin gamma1 is critical for Schwann cell differentiation, axon myelination, and regeneration in the peripheral nerve

Laminins are heterotrimeric extracellular matrix proteins that regulate cell viability and function. Laminin-2, composed of alpha2, beta1, and gamma1 chains, is a major matrix component of the peripheral nervous system (PNS). To investigate the role of laminin in the PNS, we used the Cre-loxP system to disrupt the laminin gamma1 gene in Schwann cells. These mice have dramatically reduced expression of laminin gamma1 in Schwann cells, which results in a similar reduction in laminin alpha2 and beta1 chains. These mice exhibit motor defects which lead to hind leg paralysis and tremor. During development, Schwann cells that lack laminin gamma1 were present in peripheral nerves, and proliferated and underwent apoptosis similar to control mice. However, they were unable to differentiate and synthesize myelin proteins, and therefore unable to sort and myelinate axons. In mutant mice, after sciatic nerve crush, the axons showed impaired regeneration. These experiments demonstrate that laminin is an essential component for axon myelination and regeneration in the PNS.

Peptide-modified alginate surfaces as a growth permissive substrate for neurite outgrowth

Different strategies are being investigated for treatment of spinal cord injuries, one of the most promising being application of neurotrophic factors, which have been shown to prevent neuronal death and stimulate regeneration of injured axons. Ex vivo gene therapy has emerged as the leading delivery method at the site of the injury, and we have shown previously that encapsulating genetically engineered fibroblasts in an immunoprotective alginate capsule can permit implantation of the factor-secreting cells without need for immunosuppression. This strategy could be greatly enhanced by providing the sprouting neurons with a permissive substrate upon which to attach and grow. We report here studies on the modification of an alginate gel surface by either coating it with laminin or by covalent attachment of YIGSR peptide. Using NB2a neuroblastoma cells, we found that native alginate elicited minimal cell attachment ( approximately 1.5%); however, YIGSR-alginate conjugate elicited a fivefold increase in numbers of cells attached using peptide ratios of 0.5 and 1 mg/g alginate, ranging from 9.5% of the cells at the lower ratio, to about 44% at the higher. Only a further 19% increase was obtained at an increased peptide density of 2 mg/g alginate ( approximately 63% over control). Laminin-coated gels showed approximately 60% cell attachment. However, laminin coating did not stimulate differentiation and neurite growth, whereas both numbers and lengths of outgrowths increased with increasing peptide density on peptide-modified alginate. We demonstrate here the ability of the peptide-modified alginate gels to allow adhesion of NB2a neuroblastoma cells and to promote neurite outgrowth from these cells when attached to the peptide-modified alginate surface. Also, we show that the adhesion of NB2a neuroblastoma cells and neurite outgrowth from the attached cells is a function of the peptide density on the gel surface.

Differentiation and tropic/trophic effects of exogenous neural precursors in the adult spinal cord

The fate of exogenous neural stem cells (NSCs) in the environment of the adult nervous system continues to be a matter of debate. In the present study, we report that cells of the murine NSC clone C17.2, when grafted into the lumbar segments of the spinal cord of adult rats, survive and undergo partial differentiation. C17.2 cells migrate avidly toward axonal tracts and nerve roots and differentiate into nonmyelinating ensheathing cells. Notably, C17.2 cells induce the de novo formation of host axon tracts aiming at graft innervation. Differentiation and inductive properties of C17.2 cells are independent of the presence of lesions in the spinal cord. The tropic/trophic interactions of C17.2 NSCs with host axons, the avid C17.2 cell-host axon contacts, and the ensheathing properties of these cells are related to their complex molecular profile, which includes the expression of trophic cytokines and neurotrophins such as glial cell line-derived neurotrophic factor and brain-derived neurotrophic factor, glial growth factor receptors such as ErbB-2; and PASK, the mammalian homologue of the fray gene that is involved in axon ensheathment. These results show that NSCs might not only play a critical supportive role in repairing axonal injury in the adult spinal cord but also can be used as probes for exploring the molecular underpinnings of the regenerative potential of the mature nervous system after injury.

Extracellular matrix and matrix metalloproteinases in sciatic nerve

Although matrix metalloproteinases (MMPs) are increasingly being implicated in several pathologies of the nervous system, it is not yet clear what role they play in normal neurobiological processes. We review the expression of extracellular matrix (ECM) components as well as MMPs and tissue inhibitors of metalloproteinases (TIMPs) in the peripheral nervous system. We explore the expression of certain MMPs and the four TIMPs at the mRNA level in the postnatal mouse sciatic nerve. In addition, we have used substrate gel and in situ zymography to determine levels of MMP-2 and -9 and TIMP activity in rat sciatic nerve after crush and during regeneration. A rapid and transient increase in MMP-9 localised at and immediately distal to the site of injury was observed, whereas an increase in MMP-2 activity was delayed, prolonged, and extended proximal and distal to the injury site. This activity coincides with periods of axonal elongation, suggesting that it could act to facilitate axonal extension along the nerve matrix. We also detected multiple species of gelatinolytic inhibitory activity, including TIMP-1 and -3 in control and injured nerve. These activities probably act to prevent uncontrolled gelatinolytic activity, maintaining nerve integrity at the level essential for axonal regrowth.

N-terminal α-dystroglycan binds to different extracellular matrix molecules expressed in regenerating peripheral nerves in a protein-mediated manner and promotes neurite extension of PC12 cells

alpha-dystroglycan is a cell surface receptor that is expressed in many tissues including the nervous system. The study shows that a recombinant, non-glycosylated N-terminal fragment of alpha-dystroglycan comprising residues 30 to 315 [alphaDG (30-315)] bound to laminin-2/-4 and laminin-1, fibronectin and fibrinogen, all molecules highly upregulated in the regenerating peripheral nerve. The interaction was concentration dependent and saturable and could not be inhibited by heparin suggesting only minor involvement of sulfated carbohydrate moieties. In contrast to published data, addition of bivalent cations increased the binding affinity by only ten fold.alphaDG (30-315) promotes neurite extension of PC12 cells in a similar amount as described for laminin isoforms and could be inhibited in a concentration dependent manner by alphaDG (30-315) itself, soluble laminin-1, partially by heparin, EDTA, and an RGD-peptide. Furthermore, co-immunoprecipitations between alpha-dystroglycan and beta1-integrin from PC12 cell surfaces suggested complex interactions between neuronal dystroglycan, integrins, and the ECM that induce neurite extension in vitro.

Disappearance of the post-lesional laminin immunopositivity of brain vessels is parallel with the formation of gliovascular junctions and common basal lamina. A double-labelling immunohistochemical study

Previous studies revealed that during development the laminin immunopositivity gradually disappeared from the brain vessels, but temporarily re-appeared in them around lesions. The question of the present study was the correlation between the post-lesional vascular immunopositivity to laminin and the glial reaction. Following stab wounds, double fluorescent immunohistochemical labelling was performed against laminin (using a polyclonal antiserum against laminin 1) and glial fibrillary acidic protein. A number of vessels exhibited intense immunopositivity to laminin within the lesioned tissue. Where these laminin immunopositive vessels entered the perilesional brain substance, the astroglia formed contacts on them, and the separate vascular and glial basal laminae fused. The disappearance of the post-lesional laminin immunopositivity seemed to coincide with these phenomena. When monoclonal antibodies were applied against the beta1 and gamma1 laminin chains, vessels proved to be immunopositive at the lesion, but none in the intact brain tissue. No immunoreactivity was detected in the cases of alpha2 and beta2 chains. The results suggest that the disappearance of laminin immunopositivity may be attributed to that the epitopes become inaccessible for antibodies owing to the formation of gliovascular junctions and common basal lamina between astroglia and vessel. The possible role of an alteration in the laminin composition and the effect of fixation are discussed.

Axolotl pronephric duct migration requires an epidermally derived, laminin 1-containing extracellular matrix and the integrin receptor alpha6beta1

The epidermis overlying the migrating axolotl pronephric duct is known to participate in duct guidance. This epidermis deposits an extracellular matrix onto the migrating duct and its pathway that is a potential source of directional guidance cues. The role of this matrix in pronephric duct guidance was assayed by presenting matrix deposited on microcarriers directly to migrating pronephric ducts in situ. We found that reorientation of extracellular-matrix-bearing carriers prior to their presentation to migrating ducts caused a corresponding reorientation of pronephric duct migration. Subepidermal microinjection of function-blocking antibodies against alpha6 integrin, beta1 integrin or the laminin-1/E8 domain recognized by alpha6beta1 integrin, all of which were detected and localized here, inhibited pronephric duct migration. Moreover, pre-exposure to anti-laminin-1/E8 function-blocking antibody prevented reoriented carriers of epidermally deposited matrix from reorienting pronephric duct migration. These results are incorporated into an integrated model of pronephric duct guidance consistent with all present evidence, proposing roles for the previously implicated glial cell-line derived neurotrophic factor and its receptor as well as for laminin 1 and alpha6beta1 integrin.

Roles of STEF/Tiam1, guanine nucleotide exchange factors for Rac1, in regulation of growth cone morphology

Rho family GTPases are suggested to be pivotal for growth cone behavior, but regulation of their activities in response to environmental cues remains elusive. Here, we describe roles of STEF and Tiam1, guanine nucleotide exchange factors for Rac1, in neurite growth and growth cone remodeling. We reveal that, in primary hippocampal neurons, STEF/Tiam1 are localized within growth cones and essential for formation of growth cone lamellipodia, eventually contributing to neurite growth. Furthermore, experiments using a dominant-negative form demonstrate that STEF/Tiam1 mediate extracellular laminin signals to activate Rac1, promoting neurite growth in N1E-115 neuroblastoma cells. STEF/Tiam1 are revealed to mediate Cdc42 signal to activate Rac1 during lamellipodial formation. We also show that RhoA inhibits the STEF/Tiam1-Rac1 pathway. These data are used to propose a model that extracellular and intracellular information is integrated by STEF/Tiam1 to modulate the balance of Rho GTPase activities in the growth cone and, consequently, to control growth cone behavior.

The hippocampal laminin matrix is dynamic and critical for neuronal survival

Laminins are extracellular matrix proteins that participate in neuronal development, survival, and regeneration. During excitotoxin challenge in the mouse hippocampus, neuron interaction with laminin-10 (alpha5,beta1,gamma1) protects against neuronal death. To investigate how laminin is involved in neuronal viability, we infused laminin-1 (alpha1,beta1,gamma1) into the mouse hippocampus. This infusion specifically disrupted the endogenous laminin layer. This disruption was at least partially due to the interaction of the laminin-1 gamma1 chain with endogenous laminin-10, because infusion of anti-laminin gamma1 antibody had the same effect. The disruption of the laminin layer by laminin-1 1) did not require the intact protein because infusion of plasmin-digested laminin-1 gave similar results; 2) was posttranscriptional, because there was no effect on laminin mRNA expression; and 3) occurred in both tPA(-/-) and plasminogen(-/-) mice, indicating that increased plasmin activity was not responsible. Finally, although tPA(-/-) mice are normally resistant to excitotoxin-induced neurodegeneration, disruption of the endogenous laminin layer by laminin-1 or anti-laminin gamma1 antibody renders the tPA(-/-) hippocampal neurons sensitive to kainate. These results demonstrate that neuron interactions with the deposited matrix are not necessarily recapitulated by interactions with soluble components and that the laminin matrix is a dynamic structure amenable to modification by exogenous molecules.

Expression of laminin chains by central neurons: analysis with gene and protein trapping techniques

Laminins exert numerous effects on neurons in vitro, but expression of laminin subunit genes by neurons in vivo remains controversial. To reexamine this issue, we generated mice from ES cells in which the laminin alpha1, alpha5, beta1, and gamma1 genes had been "trapped" by insertion of a histochemically detectable selectable marker, betageo (beta-galactosidase fused to neomycin phosphotransferase). The presence of laminin-betageo fusion proteins was assayed histochemically and immunochemically, revealing expression of laminin beta1 and gamma1 genes, but not alpha chain genes, by defined subsets of neurons in brain and retina. We also used the gene traps in a novel way to assay expression of endogenous laminin subunits, which were barely detectable by ordinary immunohistochemical methods. The trapping vector included a transmembrane domain that anchors proteins otherwise destined for secretion. Laminin alpha/beta/gamma heterotrimers are assembled intracellularly, and we show that the trapped laminin gamma1 fusion protein "co-trapped" endogenous beta1 intracellularly. The laminin gamma1 fusion was also able to co-trap transgene-derived alpha chains, but we detected no co-trapped endogenous alpha chains. The co-trapping method may be generally useful for identifying proteins or isolating protein complexes associated with trapped gene products.

Rit promotes MEK-independent neurite branching in human neuroblastoma cells

Rit, by sequence homology, is a member of the Ras subfamily of small guanine triphosphatases (GTPases). In PC6 cells, Rit signals through pathways both common to and different from those activated by Ras to promote cell survival and neurite outgrowth. However, the specific morphological changes induced by Rit in human cells are not known. Here, we show in a human neuronal model that Rit increases neurite outgrowth and branching through MEK-dependent and MEK-independent signaling mechanisms, respectively. Adenoviral expression of wild-type or constitutively active Rit increased neurite initiation, elongation and branching on endogenous matrix or a purified laminin-1 substratum of SH-SY5Y cells as assessed using image analysis. This outgrowth was morphologically distinct from that promoted by constitutively active Ras or Raf (evidenced by increased branching and elongation). Constitutively active Rit increased phosphorylation of ERK 1/2, but not Akt, and the MEK inhibitor PD 098059 blocked constitutively active Rit-induced neurite initiation but not elongation or branching. These results suggest that Rit plays a key role in human neuronal development and regeneration through activating both known and as yet undefined signaling pathways.

Concentration-dependent actions of glial chondroitin sulfate on the neuritic growth of midbrain neurons

Astrocytes located in two distinct regions of midbrain differ in their neuritic growth support abilities. Midbrain neurons cultured onto astrocyte monolayers from the lateral (L) region develop long and branched neurites while neurons cultured onto astrocyte monolayers from the medial (M) region develop short or no neurites. The extracellular matrix of these astrocytes has an important role in promoting or inhibiting the growth of these neurons. Differences on the compartmental distribution, as well as on the concentration of GAGs of L and M astrocytes, may be related to their differential capacity of supporting neuritic growth. Indeed, enzymatic digestion of heparan sulfate (HS) and chondroitin sulfate (CS) chains also pointed to an important function for GAGs on axon navigation. In order to better characterize the role of CS on the growth of midbrain neurites, we treated L and M astrocyte monolayers with 1 mM of beta-D-xyloside. Under these conditions, astrocytes oversynthesized and secreted CS protein-free chains to the culture medium. M astrocytes had a significant reduction in their neuritic growth-inhibiting ability after xyloside treatment, suggesting a promoting role for soluble CS in neuritic growth. Chondroitin 4-sulfate (CS-4) added in different concentrations to M astrocyte cultures turned this glia into a permissive substrate, acting in a linear way as far as the largest neurite was concerned. However, a U-shaped dose-effect curve on neurite growth resulted from the similar treatment of L astrocytes. These results suggest that glial CS-4 could be involved in the neurite growth modulating properties of midbrain neurons in a complex concentration-dependent way.

Toward spinal cord injury repair strategies: peptide surface modification of expanded poly(tetrafluoroethylene) fibers for guided neurite outgrowth in vitro

Expanded poly(tetrafluoroethylene) fibers were surface modified using an ultraviolet-activated mercury/ammonia reaction to yield amine-functional groups for the coupling of laminin-derived cell adhesive peptides CYIGSR, CDPGYIGSR, CIKVAV, and CQAASIKVAV. Surface elemental composition, determined by X-ray photoelectron spectroscopy, and radiolabeling data indicated that the amount of peptide introduced was approximately equivalent regardless of peptide type, yet mixed peptide surfaces had approximately 60% YIGSR and 40% IKVAV. The peptide-modified surfaces were compared in terms of the response of dorsal root ganglia with neurite length and number of cells attached to each fiber measured. All peptide-functionalized surfaces had a greater cellular response than the aminated ePTFE and ePTFE controls. Surfaces modified with extended peptide sequences CDPGYIGSR and CQAASIKVAV demonstrated a greater cellular response than those modified with the shorter peptide sequences CYIGSR and CIKVAV, respectively, likely because the extended peptides more closely mimic the three-dimensional conformation that the peptides maintain in laminin. Differences in neurite extension were evident among the peptide-functionalized surfaces, with the longest neurites observed on surfaces modified with both CQAASIKVAV and CDPGYIGSR. The "guidance capacity" of the fibers as a function of fiber diameter was investigated in terms of length and directionality of neurite outgrowth. As fiber diameter decreased (from 100+ to 10 microm), the neurites tended to grow to a greater degree down the length of the fiber. The thinnest fibers (with diameters <20 microm) extended shorter neurites than the fibers with a wider diameter. Combining neurite length with guidance indicated that of the fiber diameters investigated, the optimal fiber diameter for neurite guidance was between 30 and 50 microm.

Laminin chain expression suggests that laminin-10 is a major isoform in the mouse hippocampus and is degraded by the tissue plasminogen activator/plasmin protease cascade during excitotoxic injury

Laminins are important components of the extracellular matrix, and participate in neuronal development, survival and regeneration. The tissue plasminogen activator/plasmin extracellular protease cascade and downstream laminin degradation are implicated in excitotoxin-induced neuronal degeneration. To determine which specific laminin chains are involved, we investigated the expression of laminins in the hippocampus, and the cell types expressing them. Reverse transcription-PCR demonstrated that the messenger RNAs for all laminin chains could be detected in the hippocampus. To determine the localization of laminin chain expression, immunostaining was used. This method showed that alpha5, beta1 and gamma1 are most highly expressed in the neuronal cell layers. Immunoblotting confirmed the hippocampal expression of the chains alpha5, beta1 and gamma1, and RNA in situ hybridization showed a neuronal expression pattern of alpha5, beta1 and gamma1. At early time points following intrahippocampal injection of kainate, alpha5, beta1 and gamma1 chain immunoreactivities were lost. In addition, tissue plasminogen activator-deficient mice, which are resistant to kainate-induced neuronal death, show no significant change in laminins alpha5, beta1 and gamma1 after intrahippocampal kainate injection. Taken together, these results suggest that laminin-10 (alpha5-beta1-gamma1) comprises a major neuronal laminin in the mouse hippocampus, and is degraded before neuronal death during excitotoxic injury by the tissue plasminogen activator/plasmin protease cascade. By identifying a neuronal laminin (laminin-10) that participates in neuronal degeneration after excitotoxic injury, this study clarifies the molecular definition of the extracellular matrix in the hippocampus and further defines a pathway for mechanisms of neuronal death.

Involvement of alpha7beta1 integrin in the conditioning-lesion effect on sensory axon regeneration

Conditioning lesions of peripheral nerves improve axonal regeneration after injury and involve changes in expression of proteins required for axonal growth. Integrin alpha7beta1 expression in motor and sensory neurons increases following nerve lesions and motor axon regeneration is impaired in alpha7 integrin KO mice (J. Neurosci. 20, 1822-1830). To investigate the role of alpha7beta1 integrin in sensory axon regeneration, dorsal root ganglia of adult mice were cultured in gels of laminin-rich extracellular matrix (Matrigel) or collagen. Normal dorsal root ganglia in Matrigel or collagen supplemented with laminin showed spontaneous axonal outgrowth, which was greatly increased in conditioned preparations, but only in the presence of laminin. Conditioned dorsal root ganglia from normal mice cultured with a blocking antibody to beta1 integrin and from alpha7 integrin KO mice showed reduced axonal growth in both Matrigel- and laminin-supplemented collagen gels. Enhanced axonal regeneration after conditioning lesions therefore involves increased responsiveness to laminin and integrin alpha7beta1 expression.

Collapsin response mediator proteins of neonatal rat brain interact with chondroitin sulfate

Chondroitin sulfate proteoglycans are structurally and functionally important components of the extracellular matrix of the central nervous system. Their expression in the developing mammalian brain is precisely regulated, and cell culture experiments implicate these proteoglycans in the control of cell adhesion, neuron migration, neurite formation, neuronal polarization, and neuron survival. Here, we report that a monoclonal antibody against chondroitin sulfate-binding proteins from neonatal rat brain recognizes collapsin response mediator protein-4 (CRMP-4), which belongs to a family of proteins involved in collapsin/semaphorin 3A signaling. Soluble CRMPs from neonatal rat brain bound to chondroitin sulfate affinity columns, and CRMP-specific antisera co-precipitated chondroitin sulfate. Moreover, chondroitin sulfate and CRMP-4 were found to be localized immuno-histochemically in overlapping distributions in the marginal zone and the subplate of the cerebral cortex. CRMPs are released to culture supernatants of NTera-2 precursor cells and of neocortical neurons after cell death, and CRMP-4 is strongly expressed in the upper cortical plate of neonatal rat where cell death is abundant. Therefore, naturally occurring cell death is a plausible mechanism that targets CRMPs to the extracellular matrix at certain stages of development. In summary, our data indicate that CRMPs, in addition to their role as cytosolic signal transduction molecules, may subserve as yet unknown functions in the developing brain as ligands of the extracellular matrix.

Structure of laminin substrate modulates cellular signaling for neuritogenesis

Laminin, a major component of basement membranes, can self-assemble in vitro into a typical mesh-like structure, according to a mass-action-driven process. Previously, we showed that pH acidification dramatically increased the efficiency of laminin self-assembly, practically abolishing the necessity for a minimal protein concentration. Here we have characterized the morphologies of laminin matrices produced in either neutral or acidic conditions and compared their capacities to induce neuritogenesis of rat embryonic cortical neurons. Although laminin matrices formed in neutral buffer presented aggregates of heterogeneous morphology, the acidic matrix consisted of a homogeneous hexagonal sheet-like structure. The latter was comparable to the matrix assembled in vivo at the inner limiting membrane of the retina in newborn rats, shown here, and to matrices secreted by cultivated cells, shown elsewhere. The average neurite length of cortical neurons plated on acidic matrices was 244.9 micro m, whereas on neutral matrices this value dropped to 104.1 micro m. Increased neuritogenesis on the acidic matrix seemed to be associated with a higher degree of neuronal differentiation, since cell proliferation was immediately arrested upon plating, whereas on neutral matrices, the cell number increased six-fold within 24 hours. Investigation of the mechanisms mediating neurite outgrowth on each condition revealed that the extensive neuritogenesis observed on the acidic matrix involved activation of protein kinase A, whereas moderate neuritogenesis on neutral laminin was mediated by activation of protein kinase C and/or myosin light-chain kinase. Explants of cerebral cortex from P2 rats did not grow on the neutral laminin substrate but presented extensive cell migration and neurite outgrowth on the acidic laminin matrix. We propose that laminin can self-assemble independently of cell contact and that the assembling mode differentially modulates neuritogenesis and neuroplasticity.

Modulators of axonal growth and guidance at the brain midline with special reference to glial heparan sulfate proteoglycans

Bilaterally symmetric organisms need to exchange information between the left and right sides of their bodies to integrate sensory input and to coordinate motor control. Thus, an important choice point for developing axons is the Central Nervous System (CNS) midline. Crossing of this choice point is influenced by highly conserved, soluble or membrane-bound molecules such as the L1 subfamily, laminin, netrins, slits, semaphorins, Eph-receptors and ephrins, etc. Furthermore, there is much circumstantial evidence for a role of proteoglycans (PGs) or their glycosaminoglycan (GAG) moieties on axonal growth and guidance, most of which was derived from simplified models. A model of intermediate complexity is that of cocultures of young neurons and astroglial carpets (confluent cultures) obtained from medial and lateral sectors of the embryonic rodent midbrain soon after formation of its commissures. Neurite production in these cocultures reveals that, irrespective of the previous location of neurons in the midbrain, medial astrocytes exerted an inhibitory or non-permissive effect on neuritic growth that was correlated to a higher content of both heparan and chondroitin sulfates (HS and CS). Treatment with GAG lyases shows minor effects of CS and discloses a major inhibitory or non-permissive role for HS. The results are discussed in terms of available knowledge on the binding of HSPGs to interative proteins and underscore the importance of understanding glial polysaccharide arrays in addition to its protein complement for a better understanding of neuron-glial interactions.

The biology of the cellular prion protein

Prions are the etiological agents for infectious degenerative encephalopaties acting by inducing conformational changes in the cellular prion protein (PrPc), which is a cell membrane GPI anchored glycoprotein. Besides its conservation among species and expression in most tissues, and in particular, in high levels in the nervous system, the role for cellular prion protein remained obscure for some time. Initial skepticism about such a role was mainly due to the absence of a gross phenotype alteration in cellular prion protein null mice. In the last few years, some possible biological functions for cellular prion protein have been described. Copper binds to the molecule and the resulting complex may be responsible for cell protection against oxidative stress. Cellular prion protein is also a high-affinity ligand for laminin, and induces neuronal cell adhesion, neurite extension and maintenance. The binding site resides in a carboxy-terminal peptide of the gamma-1 chain, which is very conserved among all laminin types, indicating that this interaction may be relevant in other tissues besides the brain. Moreover, cellular prion protein association with a peptide that mimics a putative ligand at the cell surface, p66, triggers neuroprotective signals through a cAMP/PKA-dependent pathway. Since PrPc recycles from membrane to an intracellular compartment, which is induced by copper binding, it is also possible that the internalization mechanism allows switching off elicited signals.

Mechanistic distinctions between agrin and laminin-1 induced aggregation of acetylcholine receptors

BACKGROUND

One of the earliest steps in synaptogenesis at the neuromuscular junction is the aggregation of nicotinic acetylcholine receptors at the postsynaptic membrane. This study presents quantitative analyses of receptor and alpha-Dystroglycan aggregation in response to agrin and laminin-1, alone or in combination.

RESULTS

Both laminin and agrin increased overall expression of receptors on the plasma membrane. Following a 24 hour exposure, agrin increased the number of receptor aggregates but did not affect the number of alpha-Dystroglycan aggregates, while the reverse was true of laminin-1. Laminin also increased receptor concentration within aggregates, while agrin had no such effect. Finally, the spatial distribution of aggregates was indistinguishable from random in the case of laminin, while agrin induced aggregates were closer together than predicted by a random model.

CONCLUSIONS

Agrin and laminin-1 both increase acetylcholine receptor aggregate size after 24 hours, but several lines of evidence indicate that this is achieved via different mechanisms. Agrin and laminin had different effects on the number and density of receptor and alpha-Dystroglycan aggregates. Moreover the random distribution of laminin induced (as opposed to agrin induced) receptor aggregates suggests that the former may influence aggregate size by simple mass action effects due to increased receptor expression.

Cellular prion protein: implications in seizures and epilepsy

1. Cellular prion (PrPc) is a plasma membrane protein involved with copper uptake, protection against oxidative stress, cell adhesion, differentiation, signaling, and survival in the central nervous system. 2. Deletion of PrPc gene (Pmp) in mice enhances sensitivity to seizures in vivo and neuronal excitability in vitro which can be related to: (i) disrupted Ca(+2)-activated K+ currents, with loss of IHAP conductance in hippocampus; (ii) abnormal GABA-A inhibition in the hippocampus; (iii) mossy fiber reorganization in the hippocampus; (iv) changes in ectonucleotidases in both hippocampus and neocortex; and (v) higher levels of neocortical and subcortical oxidative stress. Moreover, postnatal Prnp knockout mice showed a significant reduction of after hyperpolarization potentials in hippocampal CA1 cells. 3. Taken together, these findings suggest that loss of PrPc function contributes to the hyperexcitable and synchronized activities underlying epileptic seizures generated in neocortex and hippocampus. Hence, the role of PrPc on human symptomatic, cryptogenic or idiopathic epileptic syndromes deserves further investigation.

The critical role of basement membrane-independent laminin gamma 1 chain during axon regeneration in the CNS

We have addressed the question of whether a family of axon growth-promoting molecules known as the laminins may play a role during axon regeneration in the CNS. A narrow sickle-shaped region containing a basal lamina-independent form of laminin exists in and around the cell bodies and proximal portion of the apical dendrites of CA3 pyramidal neurons of the postnatal hippocampus. To understand the possible function of laminin in axon regeneration within this pathway, we have manipulated laminin synthesis at the mRNA level in a slice culture model of the lesioned mossy system. In this model early postnatal mossy fibers severed near the hilus can regenerate across the lesion and elongate rapidly within strata lucidum and pyramidale. In slice cultures of the postnatal day 4 hippocampus, 2 d before lesion and then continuing for 1-5 d after lesion, translation of the gamma1 chain product of laminin was reduced by using antisense oligodeoxyribonucleotides and DNA enzymes. In the setting of the lesioned organotypic hippocampal slice, astroglial repair of the lesion and overall glial patterning were unperturbed by the antisense or DNA enzyme treatments. However, unlike controls, in the treated, lesioned slices the vast majority of regenerating mossy fibers could not cross the lesion site; those that did were very much shorter than usual, and they took a meandering course. In a recovery experiment in which the DNA enzyme or antisense oligos were washed away, laminin immunoreactivity returned and mossy fiber regeneration resumed. These results demonstrate the critical role of laminin(s) in an axon regeneration model of the CNS.

Laminets: laminin- and netrin-related genes expressed in distinct neuronal subsets

Laminins and netrins are families of related secreted proteins known to play critical roles in guiding the growth of peripheral and central axons, respectively. Here we report the identification of two novel cell surface glycoproteins that we name laminets because they resemble both laminins and netrins. Laminet-1 and -2 are selectively expressed in neurons, each in a distinct subset that includes populations in forebrain, midbrain, hindbrain, spinal cord, and spinal ganglia. In several forebrain regions, including main relays of the central olfactory pathway, laminet-1 and -2 are expressed in nonoverlapping neuronal subsets. Both laminets are subject to alternative splicing which, in the case of laminet-1, generates at least 10 distinct isoforms, each of which contains a unique combination of potential binding sites for ligands or counterreceptors. Their complex patterns of distribution and isoform diversity, along with their homology to known axon guidance molecules, suggest that laminets contribute to the patterning of neuronal connections.

Cellular prion protein: on the road for functions

Cellular prion (PrPc) is a plasma membrane glycosyphosphatidylinositol-anchored protein present in neurons but also in other cell types. Protein conservation among species suggests that PrPc may have important physiological roles. Cellular and molecular approaches have established several novel features of the regulation of PrPc expression, cellular trafficking as well as its participation in copper uptake, protection against oxidative stress, cell adhesion, differentiation, signaling and cell survival. It is therefore likely that PrPc plays pleiotropic roles in neuronal and non-neuronal cells, and as such the loss of function of PrPc may be an important component of various diseases.

Nervous system pathology: the fibrin perspective

Studies of extracellular matrix (ECM) biology in the nervous system have mainly focused on laminin, fibronectin and tenascin-R, proteins that are present during nervous system development and normal function. However, during disease, fibrin, which physiologically is not present in the nervous tissue, is detected at nervous tissue lesions. This review summarizes evidence that correlates fibrin deposition with neuropathology and presents recent findings on cellular mechanisms and intracellular signaling pathways regulated by fibrin that might contribute to nervous system disease.

Promotion of neural cell adhesion by electrochemically generated and functionalized polymer films

New strategies for spatially controllable cell adhesion have been developed for brain cells from embryonic chicken. They are based on electrochemically active phenol and pyrrole derivatives, and can be used for the selective coverage of electroconductive substrates. Besides mimicking standard laminin-related adhesion promoting mechanisms by means of an electroactive monomer-linked 18-peptide segment from laminin (SRARKQAASIKVAVSADR), electrochemically generated thin (6-30 nm) polymer films of 3-hydroxybenzyl-hydrazine (3HBH) and 2-(3-hydroxyphenyl)-ethanol (2(3HP)E) with and without mechanically entrapped or covalently linked D-lysine have proved to promote cell adhesion in serum-free medium on indium-doped tin oxide (ITO) substrates during the first 6 culturing days in vitro. The effectiveness of the peptide was strongly density-dependent. Unexpectedly, laminin itself or a combination of laminin and poly-D-lysine (PDL) did not promote cell adhesion and neuron differentiation in serum-free cultures on ITO. However, they worked perfectly well on regular polystyrene substrates in serum-free medium or on ITO when medium with serum was used. This finding might suggest that the adhesion efficiency of laminin does not depend only on the kind of medium supplement but also on the type of substrate. In contrast, the adhesion-promoting properties of "artificial" polymeric films seemed to be based on a more direct cell-film interaction, with the film masking the substrate properties.

Array analysis of the genes regulated during neuronal differentiation of human embryonal cells

Recent advances in genetic technology have provided a new platform on which the simultaneous analysis of a large number of genes is possible in a rapid and efficient fashion. To assess the differential expression of human genes during neuronal differentiation, we compared the transcript profiles of undifferentiated, partially differentiated, and fully differentiated NT2/D1 cultures with cDNA expression arrays. Approximately 75 genes (13% of the gene array pool) were differentially expressed during neuronal development of NT2/D1 cells. Genes coding for pyruvate kinase M2 isozyme, clathrin assembly proteins, calmodulin, fibronectin, laminin, thymosin β-10, and many others were upregulated as NT2/D1 cells differentiated into neurons. In contrast, several kinases, phosphatases, and G-protein coupled receptor genes showed downregulation upon neuronal differentiation. The information provided here is an invaluable reference for characterizing the phenotype of these cells. This information can also be used in cell therapy and transplantation in which the graft microenvironment and interaction with the host tissue is crucial.Key words: Atlas cDNA expression arrays, differentiation, neurodevelopment, neuron, NT2/D1 cells.

Extracellular matrix in development of the early embryo

The extracellular matrix interacts with cells and promotes and regulates cellular functions such as adhesion, migration, proliferation, differentiation, and morphogenesis. Extracellular molecules are linked to one another by multiple binding domains and form a stable, multifunctional matrix. Cells respond to the extracellular matrix through plasma membrane receptors, which include integrin and non-integrin receptors. The regulation of these interactions requires the coordination of a multiplicity of signals both spatially and temporally.

Insights into the physiological function of cellular prion protein

Prions have been extensively studied since they represent a new class of infectious agents in which a protein, PrPsc (prion scrapie), appears to be the sole component of the infectious particle. They are responsible for transmissible spongiform encephalopathies, which affect both humans and animals. The mechanism of disease propagation is well understood and involves the interaction of PrPsc with its cellular isoform (PrPc) and subsequently abnormal structural conversion of the latter. PrPc is a glycoprotein anchored on the cell surface by a glycosylphosphatidylinositol moiety and expressed in most cell types but mainly in neurons. Prion diseases have been associated with the accumulation of the abnormally folded protein and its neurotoxic effects; however, it is not known if PrPc loss of function is an important component. New efforts are addressing this question and trying to characterize the physiological function of PrPc. At least four different mouse strains in which the PrP gene was ablated were generated and the results regarding their phenotype are controversial. Localization of PrPc on the cell membrane makes it a potential candidate for a ligand uptake, cell adhesion and recognition molecule or a membrane signaling molecule. Recent data have shown a potential role for PrPc in the metabolism of copper and moreover that this metal stimulates PrPc endocytosis. Our group has recently demonstrated that PrPc is a high affinity laminin ligand and that this interaction mediates neuronal cell adhesion and neurite extension and maintenance. Moreover, PrPc-caveolin-1 dependent coupling seems to trigger the tyrosine kinase Fyn activation. These data provide the first evidence for PrPc involvement in signal transduction.

Interactions of laminin with the amyloid beta peptide. Implications for Alzheimer's disease

Extensive neuronal cell loss is observed in Alzheimer's disease. Laminin immunoreactivity colocalizes with senile plaques, the characteristic extracellular histopathological lesions of Alzheimer brain, which consist of the amyloid beta (A(beta)) peptide polymerized into amyloid fibrils. These lesions have neurotoxic effects and have been proposed to be a main cause of neurodegeneration. In order to understand the pathological significance of the interaction between laminin and amyloid, we investigated the effect of laminin on amyloid structure and toxicity. We found that laminin interacts with the A(beta)1-40 peptide, blocking fibril formation and even inducing depolymerization of preformed fibrils. Protofilaments known to be intermediate species of A(beta) fibril formation were also detected as intermediate species of laminin-induced A(beta) fibril depolymerization. Moreover, laminin-amyloid interactions inhibited the toxic effects on rat primary hippocampal neurons. As a whole, our results indicate a putative anti-amyloidogenic role of laminin which may be of biological and therapeutic interest for controlling amyloidosis, such as those observed in cerebral angiopathy and Alzheimer's disease.

Neurons and glial cells of the embryonic human brain and spinal cord express multiple and distinct isoforms of laminin

We have identified by immunocytochemistry, Western blotting, and RT-PCR the isoforms of laminin expressed by glial cells and neurons cultured from human embryonic brain and spinal cord. We show that most of the known laminins are present in human neurons and glial cells. Importantly, Western analysis demonstrates that the isoforms of laminin present in embryonic human brain differ from those expressed in human spinal cord. Neurons of the brain and spinal cord also express their distinct and characteristic isoforms of laminin compared to the glial cells of the same CNS regions. These results suggest that, in addition to the known laminins, several novel isoforms may exist in the human embryonic CNS. The observed differences between the isoforms of laminin in brain and spinal cord neurons and glial cells may result from primary structural changes or from posttranslational modifications, e.g., variations in glycosylation. Thus, identification of these novel laminins and determination of their function(s) should further our understanding of the mechanisms of aging, disease, and trauma in the human CNS.