Laminin and s-laminin are produced and released by astrocytes, Schwann cells, and schwannomas in culture

Blood-Brain Barrier Dysfunction and Astrocyte Senescence as Reciprocal Drivers of Neuropathology in Aging

As the most abundant cell types in the brain, astrocytes form a tissue-wide signaling network that is responsible for maintaining brain homeostasis and regulating various brain activities. Here, we review some of the essential functions that astrocytes perform in supporting neurons, modulating the immune response, and regulating and maintaining the blood–brain barrier (BBB). Given their importance in brain health, it follows that astrocyte dysfunction has detrimental effects. Indeed, dysfunctional astrocytes are implicated in age-related neuropathology and participate in the onset and progression of neurodegenerative diseases. Here, we review two mechanisms by which astrocytes mediate neuropathology in the aging brain. First, age-associated blood–brain barrier dysfunction (BBBD) causes the hyperactivation of TGFβ signaling in astrocytes, which elicits a pro-inflammatory and epileptogenic phenotype. Over time, BBBD-associated astrocyte dysfunction results in hippocampal and cortical neural hyperexcitability and cognitive deficits. Second, senescent astrocytes accumulate in the brain with age and exhibit a decreased functional capacity and the secretion of senescent-associated secretory phenotype (SASP) factors, which contribute to neuroinflammation and neurotoxicity. Both BBBD and senescence progressively increase during aging and are associated with increased risk of neurodegenerative disease, but the relationship between the two has not yet been established. Thus, we discuss the potential relationship between BBBD, TGFβ hyperactivation, and senescence with respect to astrocytes in the context of aging and disease and identify future areas of investigation in the field.

Isolation and culturing of primary mouse astrocytes for the analysis of focal adhesion dynamics

Primary astrocytes have gained attention as an important model for in vitro biological and biochemical research in the last decades. In this protocol, we describe a fast and cost-effective technique for isolating, culturing, and maintaining primary mouse astrocytes at ∼ 80% purity levels, which can be used in in vitro studies for migration and focal adhesion dynamics. In addition, we present an optimized transfection and manual quantification approach for focal adhesion analysis in fixed and living cells.

For complete details on the use and execution of this protocol, please refer to Kusuluri et al. (2021).

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High purity of primary mouse astrocyte isolation without commercial kits

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Isolated mouse primary astrocytes are functional for downstream applications

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Quantitative analysis of focal adhesion properties in fixed and living astrocytes

Schwann cells: Rescuers of central demyelination

The presence of peripheral myelinating cells in the central nervous system (CNS) has gained the neurobiologist attention over the years. Despite the confirmed presence of Schwann cells in the CNS in pathological conditions, and the long list of their beneficial effects on central remyelination, the cues that impede or allow Schwann cells to successfully conquer and remyelinate central axons remain partially undiscovered. A better knowledge of these factors stands out as crucial to foresee a rational therapeutic approach for the use of Schwann cells in CNS repair. Here, we review the diverse origins of Schwann cells into the CNS, both peripheral and central, as well as the CNS components that inhibit Schwann survival and migration into the central parenchyma. Namely, we analyze the astrocyte- and the myelin-derived components that restrict Schwann cells into the CNS. Finally, we highlight the unveiled mode of invasion of these peripheral cells through the central environment, using blood vessels as scaffolds to pave their ways toward demyelinated lesions. In short, this review presents the so far uncovered knowledge of this complex CNS-peripheral nervous system (PNS) relationship.

Fibrous Materials Made of Poly(ε-caprolactone)/Poly(ethylene oxide)-b-Poly(ε-caprolactone) Blends Support Neural Stem Cells Differentiation

In this work, we design and produce micron-sized fiber mats by blending poly(ε-caprolactone) (PCL) with small amounts of block copolymers poly(ethylene oxide)_m-block-poly(ε-caprolactone)_n (PEO_m-b-PCL_n) using electrospinning. Three different PEO_m-b-PCL_n block copolymers, with different molecular weights of PEO and PCL, were synthesized by ring opening polymerization of ε-caprolactone using PEO as initiator and stannous octoate as catalyst. The polymer blends were prepared by homogenous solvent mixing using dichloromethane for further electrospinning procedures. After electrospinning, it was found that the addition to PCL of the different block copolymers produced micron-fibers with smaller width, equal or higher hydrophilicity, lower Young modulus, and rougher surfaces, as compared with micron-fibers obtained only with PCL. Neural stem progenitor cells (NSPC), isolated from rat brains and grown as neurospheres, were cultured on the fibrous materials. Immunofluorescence assays showed that the NSPC are able to survive and even differentiate into astrocytes and neurons on the synthetic fibrous materials without any growth factor and using the fibers as guidance. Disassembling of the cells from the NSPC and acquisition of cell specific molecular markers and morphology progressed faster in the presence of the block copolymers, which suggests the role of the hydrophilic character and porous topology of the fiber mats.

Phospholipase A2 is involved in galactosylsphingosine-induced astrocyte toxicity, neuronal damage and demyelination

Krabbe disease is a fatal rare inherited lipid storage disorder affecting 1:100,000 births. This illness is caused by mutations in the galc gene encoding for the enzyme galactosylceramidase (GALC). Dysfunction of GALC has been linked to the toxic build-up of the galactolipid, galactosylsphingosine (psychosine), which induces cell death of oligodendrocytes. Previous studies show that phospholipase A2 (PLA2) may play a role in psychosine induce cell death. Here, we demonstrate that non-selective inhibition of cPLA2/sPLA2 and selective inhibition of cPLA2, but not sPLA2, also attenuates psychosine-induced cell death of human astrocytes. This study shows that extracellular calcium is required for psychosine induced cell death, but intracellular calcium release, reactive oxygen species or release of soluble factors are not involved. These findings suggest a cell autonomous effect, at least in human astrocytes. Supporting a role for PLA2 in psychosine-induced cell death of oligodendrocytes and astrocytes, the results show inhibition of PLA2 attenuates psychosine-induced decrease in the expression of astrocyte marker vimentin as well as myelin basic protein (MBP), myelin oligodendrocyte glycoprotein (MOG) and the neuronal marker SMI-32 in organotypic slice cultures. These findings provide further mechanistic details of psychosine-induced death of glia and suggest a role for PLA2 in the process. This work also supports the proposal that novel drugs for Krabbe disease may require testing on astrocytes as well as oligodendrocytes for more holistic prediction of pre-clinical and clinical efficacy.

Transplantation of PDGF-AA-Overexpressing Oligodendrocyte Precursor Cells Promotes Recovery in Rat Following Spinal Cord Injury

Our previous study showed that Schwann cells (SCs) promote survival, proliferation and migration of co-transplanted oligodendrocyte progenitor cells (OPCs) and neurological recovery in rats with spinal cord injury (SCI). A subsequent in vitro study confirmed that SCs modulated OPC proliferation and migration by secreting platelet-derived growth factor (PDGF)-AA and fibroblast growth factor-2 (FGF)-2. We also found that PDGF-AA stimulated OPC proliferation and their differentiation into oligodendrocytes (OLs) at later stages. We therefore speculated that PDGF-AA administration can exert the same effect as SC co-transplantation in SCI repair. To test this hypothesis, in this study we investigated the effect of transplanting PDGF-AA-overexpressing OPCs in a rat model of SCI. We found that PDGF-AA overexpression in OPCs promoted their survival, proliferation, and migration and differentiation into OLs in vivo. OPCs overexpressing PDGF-AA were also associated with increased myelination and tissue repair after SCI, leading to the recovery of neurological function. These results indicate that PDGF-AA-overexpressing OPCs may be an effective treatment for SCI.

Signaling of extracellular matrices for tissue regeneration and therapeutics

Cells receive important regulatory signals from their extracellular matrix (ECM) and the physical property of the ECM regulates important cellular behaviors like cell proliferation, migration and differentiation. A large part of tissue formation and regeneration depends on cellular interaction with its ECM. A comprehensive understanding of the mechanistic biochemical pathway of the ECM components is necessary for the design of a biomaterial scaffold for tissue engineering. Depending on the type of tissue, the ECM requirement might be different and this would influence its downstream intracellular cell signaling. Here, we reviewed the ECM and its signaling pathway by discussing: 1) classification of the ECM into hard, elastic and soft tissue based on its physical properties, 2) proliferation and differentiation control of the ECM, 3) roles of membrane receptor and its intracellular regulation factor, 4) ECM remodeling via inside-out signaling. By providing a comprehensive overview of the ECM's role in mechanotransduction and the self-regulatory effect of cells back on the ECM, we hope to provide a better insight of the physical and biochemical cues from the ECM. A sound understanding on the in vivo ECM has implication on the choice of materials and surface coating of biomimetic scaffolds used for tissue regeneration and therapeutics in a cell-free scaffold.

Vascular β-amyloid and early astrocyte alterations impair cerebrovascular function and cerebral metabolism in transgenic arcAβ mice

Cerebrovascular lesions related to congophilic amyloid angiopathy (CAA) often accompany deposition of β-amyloid (Aβ) in Alzheimer's disease (AD), leading to disturbed cerebral blood flow and cognitive dysfunction, posing the question how cerebrovascular pathology contributes to the pathology of AD. To address this question, we characterised the morphology, biochemistry and functionality of brain blood vessels in transgenic arctic β-amyloid (arcAβ) mice expressing human amyloid precursor protein (APP) with both the familial AD-causing Swedish and Arctic mutations; these mice are characterised by strong CAA pathology. Mice were analysed at early, mid and late-stage pathology. Expression of the glucose transporter GLUT1 at the blood-brain barrier (BBB) was significantly decreased and paralleled by impaired in vivo blood-to-brain glucose transport and reduced cerebral lactate release during neuronal activation from mid-stage pathology onwards. Reductions in astrocytic GLUT1 and lactate transporters, as well as retraction of astrocyte endfeet and swelling consistent with neurovascular uncoupling, preceded wide-spread β-amyloid plaque pathology. We show that CAA at later disease stages is accompanied by severe morphological alterations of brain blood vessels including stenoses, BBB leakages and the loss of vascular smooth muscle cells (SMCs). Together, our data establish that cerebrovascular and astrocytic pathology are paralleled by impaired cerebral metabolism in arcAβ mice, and that astrocyte alterations occur already at premature stages of pathology, suggesting that astrocyte dysfunction can contribute to early behavioural and cognitive impairments seen in these mice.

Analysis of Schwann-astrocyte interactions using in vitro assays

Schwann cells are one of the commonly used cells in repair strategies following spinal cord injuries. Schwann cells are capable of supporting axonal regeneration and sprouting by secreting growth factors (1,2) and providing growth promoting adhesion molecules (3) and extracellular matrix molecules (4). In addition they myelinate the demyelinated axons at the site of injury (5). However following transplantation, Schwann cells do not migrate from the site of implant and do not intermingle with the host astrocytes (6,7). This results in formation of a sharp boundary between the Schwann cells and astrocytes, creating an obstacle for growing axons trying to exit the graft back into the host tissue proximally and distally. Astrocytes in contact with Schwann cells also undergo hypertrophy and up-regulate the inhibitory molecules (8-13). In vitro assays have been used to model Schwann cell-astrocyte interactions and have been important in understanding the mechanism underlying the cellular behaviour. These in vitro assays include boundary assay, where a co-culture is made using two different cells with each cell type occupying different territories with only a small gap separating the two cell fronts. As the cells divide and migrate, the two cellular fronts get closer to each other and finally collide. This allows the behaviour of the two cellular populations to be analyzed at the boundary. Another variation of the same technique is to mix the two cellular populations in culture and over time the two cell types segregate with Schwann cells clumped together as islands in between astrocytes together creating multiple Schwann-astrocyte boundaries. The second assay used in studying the interaction of two cell types is the migration assay where cellular movement can be tracked on the surface of the other cell type monolayer (14,15). This assay is commonly known as inverted coverslip assay. Schwann cells are cultured on small glass fragments and they are inverted face down onto the surface of astrocyte monolayers and migration is assessed from the edge of coverslip. Both assays have been instrumental in studying the underlying mechanisms involved in the cellular exclusion and boundary formation. Some of the molecules identified using these techniques include N-Cadherins 15, Chondroitin Sulphate proteoglycans(CSPGs) (16,17), FGF/Heparin (18), Eph/Ephrins(19). This article intends to describe boundary assay and migration assay in stepwise fashion and elucidate the possible technical problems that might occur.

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

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

The astrocyte odyssey

Neurons have long held the spotlight as the central players of the nervous system, but we must remember that we have equal numbers of astrocytes and neurons in the brain. Are these cells only filling up the space and passively nurturing the neurons, or do they also contribute to information transfer and processing? After several years of intense research since the pioneer discovery of astrocytic calcium waves and glutamate release onto neurons in vitro, the neuronal-glial studies have answered many questions thanks to technological advances. However, the definitive in vivo role of astrocytes remains to be addressed. In addition, it is becoming clear that diverse populations of astrocytes coexist with different molecular identities and specialized functions adjusted to their microenvironment, but do they all belong to the umbrella family of astrocytes? One population of astrocytes takes on a new function by displaying both support cell and stem cell characteristics in the neurogenic niches. Here, we define characteristics that classify a cell as an astrocyte under physiological conditions. We will also discuss the well-established and emerging functions of astrocytes with an emphasis on their roles on neuronal activity and as neural stem cells in adult neurogenic zones.

Enzymes that synthesize the IB4 epitope are not sufficient to impart IB4 binding in dorsal root ganglia of rat

The isolectin B4 (IB4) stains a subset of small and medium-sized dorsal root ganglion (DRG) neurons by binding to terminal alpha-galactose on glycoproteins and glycolipids. The enzymes alpha(1,3)galactosyltransferase (1,3GT) and isoglobotriaosylceramide synthase (iGb3S) synthesize the galactose-alpha(1,3)-galactose group, which is the most common carbohydrate containing terminal alpha-galactose. 1,3GT preferentially glycosylates proteins whereas iGb3S glycosylates lipids. We generated antibodies against rat 1,3GT and iGb3S that were used for immunohistochemical staining of DRG cells. Virtually all neurons that bound IB4 expressed both enzymes, suggesting that IB4 binds to both glycoproteins and glycolipids in IB4-positive neurons. 1,3GT immunoreactivity was observed in small and medium-sized neurons and satellite cells. iGb3S immunoreactivity was observed in neurons of varying sizes. Many neurons that expressed these enzymes did not bind IB4. Additionally, the majority of neurons that expressed substance P expressed both enzymes but did not bind IB4. Ultrastructual studies revealed that 1,3GT was predominantly associated with the Golgi apparatus, whereas iGb3S was found near the Golgi apparatus and in large, clear vesicles throughout the soma. These data suggest that, although expression of 1,3GT and/or iGb3S appears to be necessary for IB4 binding, expression of these enzymes is not sufficient to impart IB4 binding.

MEGF9: a novel transmembrane protein with a strong and developmentally regulated expression in the nervous system

MEGF9 [multiple EGF (epidermal growth factor)-like-domains 9], a novel transmembrane protein with multiple EGF-like repeats, is predominantly expressed in the developing and adult CNS (central nervous system) and PNS (peripheral nervous system). The domain structure of MEGF9 consists of an N-terminal region with several potential O-glycosylation sites followed by five EGF-like domains, which are highly homologous with the short arms of laminins. Following one single pass transmembrane domain, a highly conserved short intracellular domain with potential phosphorylation sites is present. The protein was recombinantly expressed and characterized as a tissue component. To study the expression pattern further, immunohistochemistry was performed and staining was detected in Purkinje cells of the cerebellum and in glial cells of the PNS. Additional expression was observed in the epidermal layer of skin, papillae of the tongue and the epithelium of the gastrointestinal tract. By immunoelectron microscopy, MEGF9 was detected in glial cells of the sciatic nerve facing the basement membrane. MEGF9 represents a novel putative receptor, expressed in neuronal and non-neuronal tissues, that is regulated during development and could function as a guidance or signalling molecule.

Transplantation of Schwann cells and/or olfactory ensheathing glia into the contused spinal cord: Survival, migration, axon association, and functional recovery

Schwann cells (SCs) and olfactory ensheathing glia (OEG) have shown promise for spinal cord injury repair. We sought their in vivo identification following transplantation into the contused adult rat spinal cord at 1 week post-injury by: (i) DNA in situ hybridization (ISH) with a Y-chromosome specific probe to identify male transplants in female rats and (ii) lentiviral vector-mediated expression of EGFP. Survival, migration, and axon-glia association were quantified from 3 days to 9 weeks post-transplantation. At 3 weeks after transplantation into the lesion, a 60-90% loss of grafted cells was observed. OEG-only grafts survived very poorly within the lesion (<5%); injection outside the lesion led to a 60% survival rate, implying that the injury milieu was hostile to transplanted cells and or prevented their proliferation. At later times post-grafting, p75(+)/EGFP(-) cells in the lesion outnumbered EGFP(+) cells in all paradigms, evidence of significant host SC infiltration. SCs and OEG injected into the injury failed to migrate from the lesion. Injection of OEG outside of the injury resulted in their migration into the SC-injected injury site, not via normal-appearing host tissue but along the pia or via the central canal. In all paradigms, host axons were seen in association with or ensheathed by transplanted glia. Numerous myelinated axons were found within regions of grafted SCs but not OEG. The current study details the temporal survival, migration, axon association of SCs and OEG, and functional recovery after grafting into the contused spinal cord, research previously complicated due to a lack of quality, long-term markers for cell tracking in vivo.

Laminins containing the beta2 chain modulate the precise organization of CNS synapses

Synapses are formed and stabilized by concerted interactions of pre-, intra-, and post-synaptic components; however, the precise nature of the intrasynaptic components in the CNS remains obscure. Potential intrasynaptic components include extracellular matrix molecules such as laminins; here, we isolate beta2-containing laminins, including perhaps laminins 13 (alpha3beta2gamma3) and 14 (alpha4beta2gamma3), from CNS synaptosomes suggesting a role for these molecules in synaptic organization. Indeed, hippocampal synapses that form in vivo in the absence of these laminins are malformed at the ultrastructural level and this malformation is replicated in synapses formed in vitro, where laminins are provided largely by the post-synaptic neuron. This recapitulation of the in vivo function of laminins in vitro suggests that the malformations are a direct consequence of the removal of laminins from the synapse. Together, these results support a role for neuronal laminins in the structural integrity of central synapses.

A rapid exocytosis mode in chromaffin cells with a neuronal phenotype

We have used astrocyte-conditioned medium (ACM) to promote the transdifferentiation of bovine chromaffin cells and study modifications in the exocytotic process when these cells acquire a neuronal phenotype. In the ACM-promoted neuronal phenotype, secretory vesicles and intracellular Ca2+ rise were preferentially distributed in the neurite terminals. Using amperometry, we observed that the exocytotic events also occurred mainly in the neurite terminals, wherein the individual exocytotic events had smaller quantal size than in undifferentiated cells. Additionally, duration of pre-spike current was significantly shorter, suggesting that ACM also modifies the fusion pore stability. After long exposure (7-9 days) to ACM, the kinetics of catecholamine release from individual vesicles was markedly accelerated. The morphometric analysis of vesicle diameters suggests that the rapid exocytotic events observed in neurites of ACM-treated cells correspond to the exocytosis of large dense-core vesicles (LDCV). On the other hand, experiments performed in EGTA-loaded cells suggest that ACM treatment promotes a better coupling between voltage-gated calcium channels (VGCC) and LDCV. Thus, our findings reveal that ACM promotes a neuronal phenotype in chromaffin cells, wherein the exocytotic kinetics is accelerated. Such rapid exocytosis mode could be caused at least in part by a better coupling between secretory vesicles and VGCC.

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.

Regulation of cerebellar neuronal migration and neurite outgrowth by thyroxine and 3,3',5'-triiodothyronine

The timing of granule cell migration in the developing cerebellum is regulated by thyroid hormone. Granule cell migration depends on the recognition of extracellular neuronal guidance molecule(s), such as laminin, and this, in turn, requires cell surface adhesion molecules (integrins) that are anchored on the cell membrane by the actin cytoskeleton. While many of the actions of thyroid hormone, specifically 3,5,3'-triiodothyronine (T3), are mediated by regulated gene expression, both thyroxine (T4) and 3,3',5'-triiodothyronine (rT3) also exert direct, positive control of the quantity of polymerized actin in cultured astrocytes without affecting gene expression. T4-dependent actin polymerization has been shown to (i) participate in the immobilization of laminin to the cell surface, (ii) help deposit laminin in the molecular layer of the developing cerebellum, and (iii) anchor integrin(s) that recognize laminin present in the extracellular matrix. In this study, we show that both T4 and rT3, but not T3, directly regulate the F-actin content of elongating neurites of cerebellar neurons. T4 and rT3 also promoted extensive granule cell migration from cerebellar explants, as well as, dense cell clustering and extensive neuronal process formation when granule cells were grown on a laminin-coated surface. Both granule cell migration and neuronal process outgrowth were markedly attenuated by the addition of integrin-blocking antibodies or binding peptides, by the absence of thyroid hormone or the presence of T3. These data suggest that the T4-dependent actin polymerization in developing neurons is necessary for these migrating cells to recognize the laminin guidance molecule, thereby providing a novel molecular mechanism for the profound influence of thyroid hormone on brain development that is independent of regulated gene expression.

Identification of some lectin IB4 binding proteins in rat dorsal root ganglia

Lectins are proteins that bind to glycoproteins and glycolipids. The isolectin Griffonia simplicifolia I-B4 (IB4) recognizes terminal alpha-galactose and binds to a subset of small and medium-sized neurons in the dorsal root ganglia (DRG). Using one and two-dimensional gel electrophoresis, we have identified several proteins that bind IB4 in sciatic nerve, dorsal horn, and DRG. Treatment with the enzyme alpha-galactosidase reduces IB4 binding, strongly suggesting the binding is specific for the IB4 epitope. Mass spectrometric analysis of tryptic digests of alpha-galactosidase sensitive bands identified three proteins that bind IB4: the laminin beta 2 chain and the light and medium subunits of neurofilaments.

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.

Modulation of glial glutamate transport through cell interactions with the extracellular matrix

Glial glutamate transport plays a pivotal role in maintaining glutamate homeostasis in the central nervous system. Expression of glutamate transporters is highly regulated during brain development, and a number of pathological conditions are associated with deficits in expression and/or function of glutamate transports. While several soluble factors have been shown to regulate the expression of glutamate transporter, the contribution of cell-cell interaction and cell-environmental interaction in the regulation of glutamate transport is unknown. Extracellular matrix (ECM) molecules are essential components in cell-cell and cell-environmental interactions, and the ECM has been shown to play critical role in normal development and during brain pathogenesis. We, therefore, investigated the possibility that ECM molecules may regulate astrocytic glutamate transport. Therefore, we cultured rat cortical astrocytes with different ECMs and determined expression levels of the two astrocytic glutamate transporters GLT-1 and GLAST by Western Blot and determined transporter activity through measurements of 3H-D-aspartate uptake. Astrocytes grown on poly-ornithine or poly-D/L-lysine showed approximately two-fold higher GLT-1 expression than sister cells grown on plastic dishes without ECM. Naturally occurring ECM's, including laminin and collagen, showed a dose-dependent regulation of GLT-1 protein expression. These effects were specific for GLT-1 as GLAST expression was unaffected by different ECMs. Surprisingly, however, none of the examined ECMs altered the apparent glutamate uptake activity. In probing blots side-by-side for expression of Na(+)/K(+)-ATPase, we found that ECMs affected expression of Na(+)/K(+)-ATPase and GLT-1 in a reciprocal fashion. Poly-ornithine, for example, enhanced GLT-1 expression, but reduced expression of Na(+)/K(+)-ATPase. Na(+) transport may, thus, be a limiting factor for glutamate uptake.

Laminin expression in adult and developing retinae: evidence of two novel CNS laminins

Components of the extracellular matrix exert myriad effects on tissues throughout the body. In particular, the laminins, a family of heterotrimeric extracellular glycoproteins, have been shown to affect tissue development and integrity in such diverse organs as the kidney, lung, skin, and nervous system. Of these, we have focused on the roles that laminins play in the differentiation and maintenance of the nervous system. Here, we examine the expression of all known laminin chains within one component of the CNS, the retina. We find seven laminin chains-alpha3, alpha4, alpha5, beta2, beta3, gamma2, and gamma3-outside the retinal basement membranes. Anatomically, these chains are coexpressed in one or both of two locations: the matrix surrounding photoreceptors and the first synaptic layer where photoreceptors synapse with retinal interneurons. Biochemically, four of these chains are coisolated from retinal extracts in two independent complexes, confirming that two novel heterotrimers-alpha4beta2gamma3 and alpha5beta2gamma3-are present in the retinal matrix. During development, all four of these chains, along with components of laminin 5 (the alpha3, beta3, and gamma2 chains) are also expressed at sites at which they could exert important effects on photoreceptor development. Together, these data suggest the existence of two novel laminin heterotrimers in the CNS, which we term here laminin 14 (composed of the alpha4, beta2, and gamma3 chains) and laminin 15 (composed of the alpha5, beta2, and gamma3 chains), and lead us to hypothesize that these laminins, along with laminin 5, may play roles in photoreceptor production, stability, and synaptic organization.

Expansion of adult Schwann cells from mouse predegenerated peripheral nerves

We present an effective technique for culture and expansion of Schwann cells (SC) from adult peripheral nerves. Cultures from adult mouse sciatic nerves (one to six nerves per culture) in defined medium showed markedly higher purity and density of SC when the nerve was predegenerated in vivo for 7 days than when it was harvested fresh. SC from degenerated nerves were then cultured in defined media conditioned by primary cultures of adult SC. The best results were obtained with a conditioned medium supplemented with 1% fetal calf serum. In these conditions the purity of SC was about 90% and the density about 190 cell/mm(2) by 7-10 days in vitro. These findings indicate that adult SC can be expanded from small preinjured nerve fragments in a short time period to provide a source of SC for autologous cellular transplants.

Role of Schwann cells in retinal ganglion cell axon regeneration

It is a well known fact that the injured PNS can successfully regenerate, on the other hand, the CNS such as retinal ganglion cell (RGC) axons of adult mammals is incapable of regeneration. After injury, RGC axons rapidly degenerate and most cell bodies go through the process of cell death, while glial cells at the site of injury undergo a series of responses which underlie the so-called glial scar formation. However, it has become apparent that RGCs do have an intrinsic capacity to regenerate which can be elicited by experimental replacement of the inhibitory glial environment with a permissive peripheral nerve milieu. Schwann cells are a major component of the PNS and play a role in regeneration, by producing various kinds of functional substances such as diffusible neurotrophic factors, extracellular matrix and cell adhesion molecules. RGC regeneration can be induced by cooperation of these substances. The contact of RGC axons to Schwann cells based upon the structural and molecular linkages seems to be indispensable for the stable and successful regeneration. In addition to cell adhesion molecules such as NCAM and L1, data from our laboratory show that Schwann cells utilize short focal tight junctions to provide morphological stabilization of the contact with the elongating axon, as well as a small scale of gap junctions to facilitate traffic of substances between them. Moreover, our results show that modifications of functional properties in neighboring glial cells of optic nerve are induced by transplantation of Schwann cells. Astrocytes usually considered to form a glial scar guide the regenerating axons in cooperation with Schwann cells. A decrease of the oligodendrocyte marker O4 and migration of ED-1 positive macrophages is observed within the optic nerve stump. Accordingly, RGC regeneration is not a simple phenomenon of axonal elongation on the Schwann cell membrane, but is based on direct and dynamic communication between the axon and the Schwann cell, and is also accompanied by changes and responses among the glial cell populations, which may be partly associated with the mechanisms of optic nerve regeneration.

Astrocytes prevent neuronal death induced by reactive oxygen and nitrogen species

Reactive oxygen and nitrogen species (RO/NS) such as nitric oxide (NO), hydroxyl radical (OH.), and superoxide anion (O(2)(-)) are generated in a variety of neuropathological processes and damage neurons. In the present study, we investigated the neuroprotective effects of rat astrocytes against RO/NS-induced damage using neuron-glia cocultures, and the effects were compared to those of microglial cells. Sodium nitroprusside (SNP), 3-morpholinosydnonimine (SIN-1), and FeSO(4) were used to generate NO, O(2)(-) and NO, and OH., respectively. Solely cultured neurons, which were transiently exposed to these agents, degenerated, possibly through apoptotic mechanisms as revealed by in situ detection of DNA fragmentation, whereas neurons cocultured with either astrocytes or microglial cells were viable even after exposure to RO/NS. In contrast, most neurons cocultured with meningeal fibroblasts degenerated. Astrocyte-conditioned medium partially attenuated RO/NS-induced neuronal damage. When neurons were cultured on astrocyte-derived extracellular matrix (AsECM), neuronal death induced by SNP and FeSO(4) was almost completely inhibited. AsECM contained significant amounts of laminin and fibronectin, and pure fibronectin and laminin also protected neurons against RO/NS-induced damage in the same manner as AsECM. These results suggest that astrocytes can protect neurons against RO/NS-induced damage by secreting soluble and insoluble factors.

Thyroid hormone regulates the extracellular organization of laminin on astrocytes

Astrocytes produce laminin, a key extracellular matrix guidance molecule in the developing brain. Laminin is bound to transmembrane receptors on the surface of astrocytes known as integrins, which are, in turn, bound to the microfilament meshwork inside the astrocyte. Previous studies have shown that T4 regulates the pattern of integrin distribution in astrocytes by modulating the organization of the microfilaments. In this study, the effect of thyroid hormone on the secretion and topology of laminin in astrocytes was examined. Linear arrays of secreted laminin were observed on the surface of the T4-treated astrocytes within 10 h after seeding the cells onto poly-D-lysine-coated coverslips and became an organized meshwork by 24 h. In contrast, little if any laminin was identified on the surface of either hormone-deficient or T3-treated cells until 36 h after seeding and then was restricted to punctate deposits. Secretion of laminin into the medium by hormone-deficient and T3-treated cells was significantly greater than that by T4-treated cells. Conversely, deposition of laminin into the extracellular matrix was significantly greater in T4-treated cells than in hormone-deficient and T3-treated cells. Thyroid hormone had no effect on the production of laminin by astrocytes. These data show that T4 regulates the extracellular deposition and organization of laminin on the surface of astrocytes and provide a mechanism by which this morphogenic hormone can influence neuronal migration and axonal projection in the developing brain.

Morphological differentiation of microglial cells in culture: involvement of insoluble factors derived from astrocytes

It is believed that ramified resting microglial cells in the brain are differentiated from macrophage-like ameboid cells, although the mechanism for the differentiation is not fully understood. In the present study, we investigated whether the differentiation of microglial cells is observable in mixed brain cell culture prepared from newborn rat forebrains. In confluent mixed brain cell culture, both ramified and ameboid microglial cells were simultaneously present. The ramified cells were located in or under the astrocyte monolayer, while the ameboid cells were over the layer as revealed by confocal laser scan microscopy. The majority of ramified cells appeared after the astrocyte layer was completely formed and they downregulated the expression of the major histocompatibility complex antigen. Fibronectin was detected around ramified microglial cells, and laminin was also present in the astrocyte monolayer in mixed brain cell culture, while both proteins were not distributed near ameboid cells over the monolayer. When purified microglial cells were cultured on astrocyte-derived extracellular matrix in serum-free medium, they ramified. These results show that the differentiation of microglial cells is observable in culture and that astrocytes may play pivotal roles in the differentiation mainly by secreting insoluble factors.

Thyroid hormone regulates the expression of laminin in the developing rat cerebellum

In the rat cerebellum, migration of neurons from the external granular layer to the internal granular layer occurs postnatally and is dependent upon the presence of thyroid hormone. In hypothyroidism, many neurons fail to complete their migration and die. Key guidance signals to these migrating neurons are provided by laminin, an extracellular matrix protein that is fixed to the surface of astrocytes. Expression of laminin in the brain is developmentally timed to coincide with neuronal growth spurts. In this study, we examined the role of thyroid hormone on the expression and distribution of laminin in the rat cerebellum. We show that laminin content steadily increased 2- to 3-fold from birth to maximal levels on postnatal day 8-10 then steadily decreased to a plateau by postnatal day 12 in the euthyroid cerebellum. Immunoreactive laminin appeared in the molecular layer of the euthyroid cerebellum by postnatal day 4, reached maximal intensity by postnatal day 8-10, and was gone by postnatal day 14. In contrast, laminin content in the hypothyroid cerebellum remained unchanged from birth until postnatal day 10 and then increased to maximal levels over the next two days; maximal levels were approximately 35% less than those levels in the euthyroid cerebellum. Laminin staining did not appear in the molecular layer of the hypothyroid rat cerebellum until postnatal day 10, reached maximal intensity by postnatal day 15 and disappeared by postnatal day 18, despite the continued presence granular neurons in the external granular layer. These data indicate that the disruption of the timing of the appearance and regional distribution of laminin in the absence of thyroid hormone may play a major role in the profound derangement of neuronal migration observed in the cretinous brain.

"...those left behind." Biology and oncology of invasive glioma cells

Although significant technical advances in surgical and radiation treatment for brain tumors have emerged in recent years, their impact on clinical outcome for patients has been disappointing. A fundamental source of the management challenge presented by glioma patients is the insidious propensity of the malignant cells to invade into adjacent normal brain. Invasive tumor cells escape surgical removal and geographically dodge lethal radiation exposure. Recent improved understanding of the biochemistry and molecular determinants of glioma cell invasion provide valuable insight to the underlying biological features of the disease, as well as illuminating possible new therapeutic targets. Heightened commitment to migrate and invade is accompanied by a glioma cell's reduced proliferative activity. The microenvironmental manipulations coincident to invasion and migration may also impact the glioma cell's response to cytotoxic treatments. These collateral aspects of the glioma cell invasive phenotype should be further explored and exploited as novel antiglioma therapies.

Association of adhesive macromolecules with terminal sprouts at the neuromuscular junction after botulinum treatment

Small quantities of botulinum toxin (BTX) are useful in the treatment of certain movement disorders, such as laryngeal spasmodic dysphonia, blepharospasm, and cervical dystonia. However, the corrective paralytic effects of BTX are only temporary, in part because of the formation of remodeled neuromuscular junctions. Here, we questioned whether various factors within and near the neuromuscular junction could contribute to the remodeling seen after BTX treatment. BTX was injected subcutaneously in the region of the levator auris longus muscle. At 1-week intervals, levator auris longus muscles were removed and examined histochemically. As previously described, BTX treatment results in a progressive elongation of end plates. The neural cell adhesion molecule was not associated with the elongated end plates but was associated with the BTX-induced nerve sprouts after long intervals (3 to 4 weeks). Similarly, after BTX, laminin-1 (composed of alpha 1, beta 1, and gamma 1 chains) reactivity was associated with the nerve sprouts, but not with the end plates. Laminin beta 2 reactivity at the end plate dispersed somewhat within 1 week but remained diffusely associated with the elongating end plates for up to 5 weeks. Together these results suggest that neural cell adhesion molecule and laminins may participate in the sprouting observed after BTX treatment and that alterations in laminin beta 2 expression may participate in initial loss of contacts.

A peptide derived from a neurite outgrowth-promoting domain on the gamma 1 chain of laminin modulates the electrical properties of neocortical neurons

Laminins form a family of large multidomain glycoproteins of the extracellular matrix. The cellular distribution of laminin immunoreactivity in the adult mammalian central nervous system suggests an important role for laminins in mature brain function in addition to their role during brain development. To characterize the effects of this group of extracellular matrix molecules on mature brain function, intracellular recording techniques were applied to in vitro slice preparations of the rat neocortex. The experiments show that a peptide homologous to the C-terminal part of the gamma 1 chain of laminin modulates the electrical activity of pyramidal neurons in the adult neocortex of the rat. The peptide is part of the neurite outgrowth-promoting domain of the gamma 1 chain on the E8 fragment of laminin and it displays the neurite outgrowth-promoting activity of the native laminin molecule. Perfusion of in vitro brain slices with the peptide increased the input resistance of the neuronal membrane. In addition, a rise in inward rectification could be observed. These events were accompanied by a strong increase in direct excitability of the treated neurons. Immunohistochemistry techniques were applied to sections of the adult rat neocortex and hippocampus to demonstrate the presence of both the neurite outgrowth-promoting domain and the native laminin in the adult brain. An antiserum raised against the neurite outgrowth-promoting domain on the gamma 1 chain of laminin, which also recognized the free synthetic peptide, showed immunoreactivity on neurons. In addition, a population of glial fibrillary acidic protein-positive astrocytes in the hippocampus displayed immunoreactivity for this antibody. These results were confirmed by using several antibodies directed against the whole laminin-1 molecule. Neurons in the neocortex and hippocampus, as well as astrocytes in the hippocampus, demonstrated immunoreactivity for antibodies directed against the whole laminin-1 molecule. The results suggest that laminins containing the gamma 1 chain have the potential to modulate neuronal activity. This effect may be mediated either by direct cell-cell contact from surrounding cells, or through the neuronal expression of laminin or laminin-like molecules which are inserted into the neuronal cell membrane.

Spatiotemporal patterns of expression of extracellular matrix molecules in the developing and adult rat olfactory system

Using immunocytochemical methods, we have examined extensively the spatial and temporal patterns of expression of three extracellular matrix molecules-laminin, fibronectin, and type IV collagen-in the embryonic, postnatal (days 2 and 11) and adult rat olfactory system. The study started at embryonic day 14 when olfactory fibres and their associated migrating cells course through the nasal mesenchyme. From embryonic day 14 to the adult, a sheet-like pattern of labelling for laminin, fibronectin and type IV collagen was observed along the basal surface of the olfactory epithelium and around the telencephalon. This type of labelling was continuous around the telencephalic vesicle, whereas it appeared disrupted in the basal lamina of the olfactory epithelium to permit exit of the olfactory axons and their associated migrating cells into the mesenchyme. From embryonic day 14 to day 20, punctate labelling for the three molecules studied was observed along the mesenchymal olfactory pathway, the ventral part of the olfactory bulb, the olfactory nerve layer and the presumptive glomerular layer, respectively. By embryonic day 17, the punctate labelling initially detected in the mesenchymal olfactory pathway was replaced by a sheet-like pattern related to the mature basal lamina surrounding the olfactory axon fascicles. Punctate labelling for laminin and type IV collagen persisted in the olfactory nerve layer and around the glomeruli through adult life whereas that of fibronectin declined and disappeared by postnatal day 2. The spatiotemporal distribution of the punctate pattern for laminin, fibronectin and type IV collagen observed in the embryonic olfactory system suggests a role in delineating the pathway for olfactory axon elongation. The continuous expression of laminin and type IV collagen in the adult olfactory bulb may be related to the regenerative activity and high plasticity of the olfactory system.

Identification of the cellular source of laminin beta2 in adult and developing vertebrate retinae

The interphotoreceptor matrix (IPM) is a specialized extracellular matrix that surrounds the inner and outer segments of photoreceptors. This matrix contains molecules that may be important in directing photoreceptor differentiation and survival. For example, one molecule that we have previously identified as a component of the IPM, laminin beta2 (formerly known as s-laminin), is implicated in the differentiation of rod photoreceptor cells. Developmentally, laminin beta2 is present before rod birth in a position that is consistent with a role in directing rod differentiation; it is found, in both the rat and skate, in the ventricular space that ultimately becomes the IPM. In this study, we identify the source of laminin beta2 in the adult and developing retina. Both immunohistochemistry in the adult skate retina and in situ hybridizations in the adult rat retina reveal that laminin beta2 is produced by Müller cells. In addition, in the skate but not the rat retina, retinal pigment epithelial cells may be an alternative source of laminin beta2. During development, however, laminin beta2 is present before the birth of Müller glial cells; at this stage of development, laminin beta2 RNA is present within the neuroepithelial layer in a pattern that is consistent with its production by neuroepithelial cells.

Extracellular matrix proteins expressed by human adult astrocytes in vivo and in vitro: an astrocyte surface protein containing the CS1 domain contributes to binding of lymphoblasts

Primary cultures of human astrocytes, expressing glial fibrillary acidic protein (GFAP), were obtained from postmortem brain tissue samples. These cultured astrocytes produced an extracellular matrix (ECM), containing laminin (Ln) and fibronectin (Fn), as shown with specific antibodies. The perinuclear staining observed in these cells indicated that these proteins were de novo synthesized. Monoclonal antibody (mAb) 90.45, which recognizes the CS1 sequence found in an alternatively spliced form of Fn, also stained cultured astrocytes. Immunohistochemical analysis of normal human brain tissue showed positive staining for the CS1 domain, both on protoplasmic and fibrous astrocytes located in the gray and white matter. In contrast to cultured astrocytes, no immunoreactivity for Ln or Fn was found on astrocytes in normal human brain tissue. These in situ data indicate that the CS1 domain expressed by astrocytes is not part of a splicing variant of Fn. Western blot analysis confirmed that the CS1 domain expressed by cultured human astrocytes is part of an astrocyte protein which is different from human Fn. The CS1 domain is a known ligand for the adhesion receptor alpha4beta1 (VLA-4). We found that the human lymphoma cell lines Jurkat and Ramos, which express alpha4beta1, bound to cultured human astrocytes, and that this interaction could be partly blocked by mAb 90.45 or a synthetic CS1 peptide. Thus, the novel CS1-containing surface protein expressed by astrocytes in vitro and in vivo, contributes to binding of lymphoblasts, and therefore may be a relevant adhesion molecule for the recruitment of alpha4-integrin expressing leukocytes into the central nervous system (CNS).

Regulation of CD44 in the regenerating mouse facial motor nucleus

CD44 is a cell adhesion molecule which plays an important role in cell movement and adhesion, e.g. in lymphocyte homing and tumour metastasis. Here we studied the expression of CD44 mRNA and protein immunoreactivity in the facial nucleus after nerve injury and during the ensuing regeneration. Transection of the facial nerve led to a strong up-regulation of CD44, peaking 4 days after injury on the motoneurons of the axotomized facial nucleus. Use of the polymerase chain reaction confirmed the de novo expression of CD44 and detected only the standard haematopoietic CD44 isoform. Western blotting also detected the 76 kDa protein subtype, in line with the predicted size of the haematopoietic CD44 variant. At the ultrastructural level, CD44 immunoreactivity was restricted to the surface of the neuronal perikarya, their dendrites and axons. It was not seen in the adjacent activated astrocytes, microglia or vascular endothelia. This study shows strong up-regulation of the cell adhesion molecule CD44 on the regenerating motoneurons in the axotomized facial nucleus. These data suggest that CD44 may play a role in neurite outgrowth, in synaptic stripping or in the adhesion of activated glial cells to the perikaryal surface of the axotomized motoneurons.

Laminins of the adult mammalian CNS; laminin-alpha2 (merosin M-) chain immunoreactivity is associated with neuronal processes

Laminins are glycoproteins with three subunits, i.e. a longer alpha chain, a shorter beta chain and a shorter gamma chain. Well-characterized laminins are laminin-1 (EHS laminin; alpha1-beta1-gamma1), laminin-2 (merosin; alpha2-beta1-gamma1), laminin-3 (alpha1-beta2-gamma1) and laminin-4 (alpha2-beta2-gamma1). The present study shows that in the adult mammalian CNS (rat, rabbit, pig and monkey) alpha2 chain immunoreactivity is associated most evidently with neuronal fibers and punctate, potentially synaptic, structures of limbic brain regions. Third ventricle tanycytes and ensheathing cells of the olfactory nerve also express intense alpha2 chain immunoreactivity. Immunostaining for gamma1 chain is present throughout the central nervous system (CNS) in essentially all neuronal cell bodies and their most proximal processes. Immunoreactivity for all chains investigated (alpha1, alpha2, beta1, beta2 and gamma1) were present around blood vessels, especially evident in lightly fixed tissues. The finding that, other than blood vessels, neurons and other structures exhibited immunoreactivity for only one or two (and not three) chains, suggests that variant forms of laminin with yet undiscovered chains or other configurations than the heterotrimeric form are present in the CNS. The association of alpha2-like immunoreactivity with neuronal fibers and synaptic structures is of great interest in light of the known neurite-promoting and cell attachment activities of laminin-2.

Differential laminin isoform expression in the developing rat olfactory system

Members of the laminin family influence mammalian cells in a variety of ways, mediating adhesion, proliferation, migration, and growth of neuronal processes. Specific laminin domains act through a number of cellular interaction sites to mediate these activities. In the developing olfactory system, axons grow from the olfactory epithelium to synaptic sites in the olfactory bulb a matrix rich in laminins and known mediators of laminin-axon interactions include integrins and a galectin-1/glycoconjugate adhesion system. Using biochemistry, immunocytochemistry, and in situ hybridization, we identified alpha 2, alpha 3, beta 1, beta 2 and gamma 1 laminin isoforms in the late embryonic and neonatal rat olfactory system. However, alpha 1-containing laminin could not be detected in association with olfactory neurons. Immunocytochemistry revealed that beta 2 laminin is preferentially expressed in the ventral and lateral nerve layer of the olfactory bulb and in the main olfactory axon tracks, but is undetectable in the accessory system during embryonic and early postnatal development. In contrast, beta 1 and gamma 1 laminins are evenly distributed throughout the olfactory bulb and in both the main and accessory olfactory axon tracks. The differential localization of laminin chains in vivo is likely to have functional significance for the development and maintenance of the olfactory system.

Neuritic outgrowth associated with astroglial phenotypic changes induced by antisense glial fibrillary acidic protein (GFAP) mRNA in injured neuron-astrocyte cocultures

In the adult CNS, axons fail to regenerate after injury. Among the cell interactions that lead to this failure are those developed with astrocytes. In an effort to elucidate the mechanisms underlying these negative interactions, we have used astrocytes treated with antisense glial fibrillary acidic protein (GFAP) mRNA to inhibit the formation of gliofilaments, indispensable for the astroglial morphological response to injury, and have studied their permissivity for neuritic outgrowth. In a neuron-astrocyte coculture, a mechanical lesion led to hypertrophy of astrocytes neighboring the lesion. Neuronal cell bodies and neurites were absent both from the area of lesion and from its surroundings. Reactive astrocytes appeared, therefore, to be a nonpermissive substrate. Transfection that used antisense GFAP mRNA blocked astroglial morphological changes and was characterized by both a persistence of neuronal cell bodies in the vicinity of the lesion site and a growth of neurites into the same region. These morphological differences were associated with a 46% decrease in the GFAP translation capacity and a 50% increase in the concentration of GAP-43 in the treated cultures. Neurons were associated mainly with an extracellular laminin network, which was predominant at the lesion site in treated cocultures. In contrast, those astrocytes highly laminin-immunoreactive appeared to be a nonpermissive substrate for neurons. These results show that inhibition in GFAP synthesis, leading to a reduction of astroglial hypertrophy, relieves the blockade of neuritic outgrowth that normally is observed after a lesion. The mechanisms may involve changes in the secretion of extracellular matrix molecules by astrocytes.

Distribution of the ten known laminin chains in the pathways and targets of developing sensory axons

Laminins are heterotrimers of alpha, beta, and gamma chains. At present, five alpha, three beta, and two gamma chains have been described. The best characterized laminin (laminin 1 = alpha 1, beta 1, gamma 1) promotes neurite outgrowth from virtually all classes of developing neurons, implying that laminins may serve as axon guidance molecules in vivo. Moreover, different laminin trimers exert distinct effects on subsets of laminin-1-responsive cells, suggesting that isoform diversity may underlie some axonal choices in vivo. As a first step toward evaluating these hypotheses, we have documented the expression patterns of all 10-known laminin chains in the peripheral nervous system and spinal cord of the murine embryo. The alpha 2, alpha 4, beta 1, and gamma 1 chains are expressed in peripheral axonal pathways by embryonic day (E) 11.5, when sensory and motor axonal outgrowth is underway. Thus, laminins (but not laminin 1) may promote peripheral axonal outgrowth. By E 13.5, laminin chains are differentially expressed in the limb-bud, with prominent expression of alpha 2 and alpha 4 in muscle and of alpha 3 and alpha 5 in skin. This pattern raises the possibility that laminin isoform diversity contributes to the ability of cutaneous and muscle sensory axons to distinguish their targets. Later in development, some chains (e.g., alpha 2, alpha 4, and beta 1) are downregulated in peripheral nerve while others (e.g., gamma 1), continue to be expressed by Schwann cells into adulthood. In contrast to peripheral nerves and ganglia, laminin chains are expressed at low levels, if at all, in the developing spinal cord gray matter.

Different voltage-gated sodium currents are expressed by human neuroblastoma NB69 cells when cultured in defined serum-free and in astroglial-conditioned media

Voltage-gated Na+ currents (INa) were analysed with the whole-cell patch-clamp technique in human neuroblastoma NB69 cells plated in serum-free "defined" medium (DM) or in "astroglial-conditioned" medium (CM). Cells survived in both media and expressed the microtubule associated protein 1A, indicating neuron-like differentiation. Two INa types with different time-, voltage-dependent properties and tetrodotoxin (TTX) sensitivities were expressed in DM and CM. The INa in DM-plated cells was present from day 4 and its surface density increased from 11 pA/pF (days 5-7) to 68 pA/pF (days 15-30). The underlying conductance (GNa) half-activated (V0A) at -24 mV. INa inactivation was fitted by single exponentials with 7.5 ms time constant (th) at the -35 mV half-inactivation voltage (V0I). INa was not affected by 10 nM, was reduced (65%) by 100 nM, and not completely abolished (92%) by 300 nM tetrodotoxin (TTX). The INa of CM-plated cells appeared at day 3-4 and its surface density increased from 14 pA/pF (days 3-6) to 28 pA/pF (days 11-14). The GNa V0A was -29 mV and inactivation was fitted by single exponentials with 2.6 ms that the -58 mV V0I. This INa was reduced (55%) by 10 nM and totally abolished by 100 nM tetrodotoxin (TTX). In conclusion, NB69 cells displayed a slow, "TTX-resistant," or a fast, "TTX-sensitive" INa in DM and CM, respectively, suggesting that the CM contained diffusible trophic factors of astroglial origin that induced the expression of a different Na+ channel type. About half of the CM- and DM-plated cells also displayed a persistent Na+ current (INaP).

Laminins in the adult and aged brain

Only recently have we become aware of the diversity of laminins in adult brain. In vascular basement membranes, the expression of at least five laminin chains has been demonstrated, suggesting the presence of several laminin variants. Recent ultrastructural evidence for heterogeneity of laminin expression in vascular basement membranes is an exciting finding, and points to structural and functional diversity of the basement membranes around cerebral blood vessels. Neuronal laminin-like immunoreactivity in the adult brain is a consistent observation, but does not fit well in the current understanding of the physiology and biochemistry of the heterotrimeric laminins. Nevertheless, the unique localization of putative neuronal laminins warrants their further characterization. The structure and function of laminins produced by reactive astrocytes in the lesioned adult brain and that seen in the brains of Alzheimer disease (AD) patients are not yet resolved. The possibility that these laminins play an important role in the CNS response to injury and pathophysiology of AD is expected to be a fruitful investigation. The next decade should see very significant advances in the characterization of brain laminins and, hopefully, in the elucidation of functional correlates to the structural diversity of laminins in brain.

Laminin alpha 2 is a component of brain capillary basement membrane: reduced expression in dystrophic dy mice

In the present study we demonstrate low level expression of the laminin alpha 2 chain in brain and localize the alpha 2 protein to the capillary basement membrane. While in peripheral basement membranes the laminin alpha 1 and alpha 2 chains have an almost mutually exclusive distribution, the present results suggest both alpha 1 and alpha 2 in the cerebral capillary basement membrane. Towards elucidating the function of alpha 2 in brain, we have performed ultrastructural analysis of the capillary basement membrane in dystrophic dy mice, which show a 70-90% and > 95% reduction of alpha 2 messenger RNA compared to heterozygous and wild-type mice, respectively, and show a nearly total absence of the alpha 2 protein by immunofluorescence. In contrast to the muscle and Schwann cell basement membrane, where alpha 2 deficiency causes structural basement membrane abnormalities, the present results show that the lack of the alpha 2 subunit in the cerebral capillary basement membrane is not detrimental to its structure. This observation might be explained by the fact that the cerebral capillary basement membrane expresses both alpha chains and therefore exhibits structural redundancy.

Some unusual responses of astrocytes to ghost tangles in a long duration case of juvenile Alzheimer's disease: an electron microscopic study

The ghost tangles (GTs) in usual Alzheimer's disease are separated into small bundles of abnormal straight filaments by many invading astrocytic processes lacking a basal lamina (BL). An electron microscopic study of GTs in the Ammon's horn of a case of juvenile Alzheimer's disease of 25 years' duration, however, revealed that only a small number of astrocytic processes had infiltrated the GTs, resulting in the GTs being composed of large bundles. Moreover, the majority of glial processes that had invaded or apposed GTs possessed an interrupted but still fairly well-developed BL with hemidesmosome-like profiles. Although pia-arachnoid cells are required for astrocytes to form a continuous BL, astrocytes can have a segmental BL on their surface facing even empty intercellular spaces within the brain parenchyma. The much greater frequency and better development of the GT-associated BL in our case indicate that the GT filaments somehow increased the ability of astrocytes to form a BL. On the other hand, the scarcity of GT-invading astrocytic processes implies that many of the glial processes that had once penetrated GTs had been withdrawn, with the result that GTs escaped expectable endocyto-phagocytosis by astrocytes.

The dynamics of beta 1 integrin expression during peripheral nerve regeneration

The aim of the present study was to examine the expression of beta 1 integrin subunit after peripheral nerve transection. After sciatic nerve transection two experimental procedures were used; changes in the freely regenerating rat sciatic nerve were compared to a situation in which spontaneous regeneration was prevented by suturing both ends of the nerve to the muscle next to the point of transection. Specimens for morphological analysis were collected 6 h, 1, 3, 5, 7 days and 2, 4, 6 and 8 weeks after the axotomy. Sections from the proximal (two zones) and distal (three zones) stumps next to the point of transection were stained with antibodies against beta 1 integrin subunit, macrophages, collagen types I and III, and S-100 protein. The control nerves showed beta 1 integrin-stained cells in the perineurium and vasa nervorum but the endoneurium was negative. Positively stained endoneurial fibroblast-like cells could be seen in the proximal part of the nerve already at 24 h after transection. The number of these positively stained cells increased steadily; they were most numerous 4 weeks after transection in the distal zone 2. Subsequently, the number of positively stained endoneural cells declined sharply and 8 weeks after transection no positively stained cells could be found. The morphological appearance and the immunohistochemical properties of the cells suggest that the majority of beta 1 integrin-positive cells are endoneurial fibroblast-like cells. Thus, the process appeared to be dynamic, starting from the proximal part and continuing to the distal parts, and was similar in both experimental groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Interaction of chromosome-6-encoded dystrophin related protein with the extracellular matrix

Dystrophin-related protein/utrophin is a large, cytoskeletal protein that shares significant sequence similarity with dystrophin. Dystrophin-related protein is known to be enriched where cell-extracellular matrix contacts are well defined; however, the mechanism of dystrophin-related protein enrichment and its functional role(s) at these sites are yet to be defined. Here, we demonstrate that dystrophin-related protein is concentrated in patches of astrocyte membrane in apposition with the extracellular matrix and that the distribution of dystrophin-related protein is temporally modulated by the extracellular matrix constituent laminin. Furthermore, we demonstrate the existence of a specific biochemical association between dystrophin-related protein and laminin in astrocytes. In these astrocytes, the depletion of dystrophin-related protein by the use of antisense dystrophin-related protein oligonucleotides causes marked reduction in the formation of functional substratum-membrane attachments. Taken together, these data suggest that dystrophin-related protein may function in the generation and maintenance of regional substratum-associated membrane specializations, such as those found at the blood-brain barrier.

Astrocytes: form, functions, and roles in disease

Astrocytes, once relegated to a mere supportive role in the central nervous system, are now recognized as a heterogeneous class of cells with many important and diverse functions. Major astrocyte functions can be grouped into three categories: guidance and support of neuronal migration during development, maintenance of the neural microenvironment, and modulation of immune reactions by serving as antigen-presenting cells. The concept of astrocytic heterogeneity is critical to understanding the functions and reactions of these cells in disease. Astrocytes from different regions of the brain have diverse biochemical characteristics and may respond in different ways to a variety of injuries. Astrocytic swelling and hypertrophy-hyperplasia are two common reactions to injury. This review covers the morphologic and pathophysiologic findings, time course, and determinants of these two responses. In addition to these common reactions, astrocytes may play a primary role in certain diseases, including epilepsy, neurological dysfunction in liver disease, neurodegenerative disorders such as Parkinson's and Huntington's diseases, and demyelination. Evidence supporting primary involvement of astrocytes in these diseases will be considered.