Laminin is associated with the "neurite outgrowth-promoting factors" found in conditioned media

Establishing neuronal polarity: microtubule regulation during neurite initiation

The initiation of nascent projections, or neurites, from the neuronal cell body is the first stage in the formation of axons and dendrites, and thus a critical step in the establishment of neuronal architecture and nervous system development. Neurite formation relies on the polarized remodelling of microtubules, which dynamically direct and reinforce cell shape, and provide tracks for cargo transport and force generation. Within neurons, microtubule behaviour and structure are tightly controlled by an array of regulatory factors. Although microtubule regulation in the later stages of axon development is relatively well understood, how microtubules are regulated during neurite initiation is rarely examined. Here, we discuss how factors that direct microtubule growth, remodelling, stability and positioning influence neurite formation. In addition, we consider microtubule organization by the centrosome and modulation by the actin and intermediate filament networks to provide an up-to-date picture of this vital stage in neuronal development.

Engineering Fiber-Based Nervous Tissue Constructs for Axon Regeneration

Biomaterial-based scaffolds used in nerve conduits including channels for confining regenerating axons and 3-dimensional (3D) gels as substrates for growth have made improvements in models of nerve repair. Many biomaterial strategies, however, continue to fall short of autologous nerve grafts, which remain the current gold standard in repairing severe nerve lesions (<20 mm). Intraluminal nerve conduit fibers have also shown considerable promise in directing regenerating axons in vitro and in vivo and have gained increasing interest for nerve repair. It is unknown, however, how growing axons respond to a fiber when encountered in a 3D environment. In this study, we considered a construct consisting of a compliant collagen hydrogel matrix and a fiber component to assess contact-guided axon growth. We investigated preferential axon outgrowth on synthetic and natural polymer fibers by utilizing small-diameter microfibers of poly-L-lactic acid and type I collagen representing 2 different fiber stiffnesses. We found that axons growing freely in a 3D hydrogel culture preferentially attach, turn and follow fibers with outgrowth rates and distances that far exceed outgrowth in a hydrogel alone. Wet-spun type I collagen from rat tail tendon performed the best, associated with highly aligned and accelerated outgrowth. This study also evaluated the response of dorsal root ganglion neurons from adult rats to provide data more relevant to axon regenerative potential in nerve repair. We found that ECM treatments on fibers enhanced the regeneration of adult axons indicating that both the physical and biochemical presentation of the fibers are essential for enhancing axon guidance and growth.

Facile Synthesis of a 3,4-Ethylene-Dioxythiophene (EDOT) Derivative for Ease of Bio-Functionalization of the Conducting Polymer PEDOT

In the pursuit of conducting polymer based bio-functional devices, a cost-effective and high yield synthesis method for a versatile monomer is desired. We report here a new synthesis strategy for a versatile monomer 2-methylene-2,3-dihydrothieno (3,4-b) (1,4) dioxine, or 3,4-ethylenedioxythiophene with a exomethylene side group (EDOT-EM). Compared to the previously reported synthesis route, the new strategy uses less steps, with faster reaction rate, and higher yield. The presence of EM group opens up endless possibility for derivatization via either hydro-alkoxy addition or thiol-ene click chemistry. EDOT-EM could be polymerized into stable and low impedance PEDOT-EM polymer using electro-polymerization method on different conducting substrates at both macro and micro scales. Facile post-functionalization of PEDOT-EM with molecules of varying size and functionality (from small molecules to DNAs and proteins) was achieved. The new synthetic route of EDOT-EM and the ease of post-functionalization of PEDOT-EM will greatly accelerate the use of conducting polymer in a broad range of organic electronics and bioelectronics applications.

Mesenchymal stromal cells from umbilical cord Wharton's jelly trigger oligodendroglial differentiation in neural progenitor cells through cell-to-cell contact

BACKGROUND AIMS

Wharton's jelly mesenchymal stromal cells (WJ-MSCs) might be ideal candidates to treat perinatal brain damage. Their secretome has been shown to have beneficial effects on neuroregeneration, in part through interaction with neural progenitor cells (NPCs). However, it remains unclear whether cell-to-cell contact decisively contributes to this positive effect. The objective of this study was to elucidate the mechanism through which differentiation in NPCs is triggered after exposure to WJ-MSCs. Furthermore, given that WJ-MSCs can be derived from term (tWJ-MSCs) or preterm (ptWJ-MSCs) deliveries and that WJ-MSCs might be used for transplantations independent of gestational age, the influence of tWJ-MSCs versus ptWJ-MSCs on the differentiation capacities of NPCs was studied.

METHODS

The effect of tWJ-MSCs and ptWJ-MSCs on the expression of neuroglial markers in NPCs was assessed in co-culture (CC), conditioned medium (CM) or transwell CC experiments by immunocytochemistry, real-time polymerase chain reaction and Western blot. Additionally, mass spectrometry was used to study their secretomes.

RESULTS

NPCs showed an increased expression of glial markers after CC with WJ-MSCs or exposure to WJ-MSC-CMs. CC had a more prominent effect on the expression of glial markers compared with CM or transwell CCs. tWJ-MSCs more strongly induced the expression of mature oligodendroglial markers compared with ptWJ-MSCs. A possible role in enhancing this maturation could be attributed to the laminin α2-subunit.

CONCLUSIONS

Cell-to-cell contact between WJ-MSCs and NPCs induces oligodendrogenesis on NPCs, whereas trophic factor secretion is sufficient to promote astrogenesis. Thus, transplanting WJ-MSCs may promote endogenous neuroregeneration in perinatal brain damage.

Comparison of repair of peripheral nerve transection in predegenerated muscle with and without a vein graft

BACKGROUND

Despite substantial research into the topic and valiant surgical efforts, reconstruction of peripheral nerve injury remains a challenging surgery. This study was conducted to evaluate the effectiveness of axonal regeneration of a transected sciatic nerve through a vein conduit containing degenerated skeletal muscle compared with axonal regeneration in a transected sciatic nerve through degenerated skeletal muscle alone.

METHODS

In two of the three experimental rat groups, 10 mm of the left sciatic nerve was transected and removed. The proximal and distal ends of the transected sciatic nerve were then approximated and surrounded with either (a) a degenerated skeletal muscle graft; or (b) a graft containing both degenerated skeletal muscle and vein. In the group receiving the combined vein and skeletal muscle graft, the vein walls were subsequently sutured to the proximal and distal nerve stump epineurium. Sciatic functional index (SFI) was used for assessment of functional recovery. Tracing study and histological procedures were used to assess axonal regeneration.

RESULTS

At 60 days, the gait functional recovery as well as the mean number of myelinated axons in the middle and distal parts of the sciatic nerve significantly increased in the group with the vein graft compared to rats with only the muscular graft (P < 0.05). Mean diameter of myelinated nerve fiber of the distal sciatic nerve was also improved with the vein graft compared to the muscle graft alone (P < 0.05). The mean number of DiI-labeled motor neurons in the L4-L5 spinal segment increased in the vein with muscle group but was not significantly different between the two groups.

CONCLUSIONS

These findings demonstrated that a graft consisting of not only predegenerated muscle, but also predegenerated muscle with vein more effectively supported nerve regeneration, thus promoting functional recovery after sciatic nerve injury in rats.

Combination scaffolds of salmon fibrin, hyaluronic acid, and laminin for human neural stem cell and vascular tissue engineering

Human neural stem/progenitor cells (hNSPCs) are good candidates for treating central nervous system (CNS) trauma since they secrete beneficial trophic factors and differentiate into mature CNS cells; however, many cells die after transplantation. This cell death can be ameliorated by inclusion of a biomaterial scaffold, making identification of optimal scaffolds for hNSPCs a critical research focus. We investigated the properties of fibrin-based scaffolds and their effects on hNSPCs and found that fibrin generated from salmon fibrinogen and thrombin stimulates greater hNSPC proliferation than mammalian fibrin. Fibrin scaffolds degrade over the course of a few days in vivo, so we sought to develop a novel scaffold that would retain the beneficial properties of fibrin but degrade more slowly to provide longer support for hNSPCs. We found combination scaffolds of salmon fibrin with interpenetrating networks (IPNs) of hyaluronic acid (HA) with and without laminin polymerize more effectively than fibrin alone and generate compliant hydrogels matching the physical properties of brain tissue. Furthermore, combination scaffolds support hNSPC proliferation and differentiation while significantly attenuating the cell-mediated degradation seen with fibrin alone. HNSPCs express two fibrinogen-binding integrins, αVβ1 and α5β1, and several laminin binding integrins (α7β1, α6β1, α3β1) that can mediate interaction with the scaffold. Lastly, to test the ability of scaffolds to support vascularization, we analyzed human cord blood-derived endothelial cells alone and in co-culture with hNSPCs and found enhanced vessel formation and complexity in co-cultures within combination scaffolds. Overall, combination scaffolds of fibrin, HA, and laminin are excellent biomaterials for hNSPCs.

STATEMENT OF SIGNIFICANCE

Interest has increased recently in the development of biomaterials as neural stem cell transplantation scaffolds to treat central nervous system (CNS) injury since scaffolds improve survival and integration of transplanted cells. We report here on a novel combination scaffold composed of fibrin, hyaluronic acid, and laminin to support human neural stem/progenitor cell (hNSPC) function. This combined biomaterial scaffold has appropriate physical properties for hNSPCs and the CNS, supports hNSPC proliferation and differentiation, and attenuates rapid cell-mediated scaffold degradation. The hNSPCs and scaffold components synergistically encourage new vessel formation from human endothelial cells. This work marks the first report of a combination scaffold supporting human neural and vascular cells to encourage vasculogenesis, and sets a benchmark for biomaterials to treat CNS injury.

Matrix Metalloproteinase-9 Regulates Neuronal Circuit Development and Excitability

In early postnatal development, naturally occurring cell death, dendritic outgrowth, and synaptogenesis sculpt neuronal ensembles into functional neuronal circuits. Here, we demonstrate that deletion of the extracellular proteinase matrix metalloproteinase-9 (MMP-9) affects each of these processes, resulting in maladapted neuronal circuitry. MMP-9 deletion increases the number of CA1 pyramidal neurons but decreases dendritic length and complexity. Parallel changes in neuronal morphology are observed in primary visual cortex and persist into adulthood. Individual CA1 neurons in MMP-9(-/-) mice have enhanced input resistance and a significant increase in the frequency, but not amplitude, of miniature excitatory postsynaptic currents (mEPSCs). Additionally, deletion of MMP-9 significantly increases spontaneous neuronal activity in awake MMP-9(-/-) mice and enhances response to acute challenge by the excitotoxin kainate. Our data document a novel role for MMP-9-dependent proteolysis: the regulation of several aspects of circuit maturation to constrain excitability throughout life.

Uncultured undifferentiated adipose-derived nucleated cell fractions combined with inside-out artery graft accelerate sciatic nerve regeneration and functional recovery

Effects of transplantation of adipose-derived nucleated cell fractions (ADNCs) on sciatic nerve regeneration were studied. A 10-mm sciatic nerve defect was bridged using artery graft filled with ADNCs. In control group, artery graft was filled with saline alone. Regenerated nerve fibres were studied for 12 weeks. In sham-operated group, sciatic nerve was only exposed and manipulated. Behavioural and functional studies confirmed faster recovery of regenerated axons in ADNCs transplanted animals than in control group (P<0.05). At the end of study period, animals in ADNCs transplanted group achieved a sciatic functional index (SFI) value of -31.6 ± -3.14, whereas in control group a value of -42.5 ± -3.7 was found. Gastrocnemius muscle mass in ADNCs transplanted animals was found to be significantly higher than that in control group (P=0.001). Morphometric indices of regenerated fibres showed the number and diameter of myelinated fibres to be significantly higher in ADNCs transplanted animals than in control group (P=0.001). On immunohistochemistry, there was more positive staining of S100 in the ADNCs transplanted animals than in control group. ADNCs transplantation into an artery graft could be considered a readily accessible technique that improves functional recovery of sciatic nerve.

Sciatic nerve regeneration induced by transplantation of in vitro bone marrow stromal cells into an inside-out artery graft in rat

Traumatic injury to peripheral nerves results in considerable motor and sensory disability. Several research groups have tried to improve the regeneration of traumatized nerves by invention of favorable microsurgery. Effect of undifferentiated bone marrow stromal cells (BMSCs) combined with artery graft on peripheral nerve regeneration was studied using a rat sciatic nerve regeneration model. A 10-mm sciatic nerve defect was bridged using an artery graft (IOAG) filled with undifferentiated BMSCs (2 × 10(7) cells/mL). In control group, the graft was filled with phosphated buffer saline alone. The regenerated fibers were studied 4, 8 and 12 weeks after surgery. Assessment of nerve regeneration was based on behavioral, functional (Walking Track Analysis), electrophysiological, histomorphometric and immuohistochemical (Schwann cell detection by S-100 expression) criteria. The behavioral, functional and electrophysiological studies confirmed significant recovery of regenerated axons in IOAG/BMSC group (P < 0.05). Quantitative morphometric analyses of regenerated fibers showed the number and diameter of myelinated fibers in IOAG/BMSC group were significantly higher than in the control group (P < 0.05). This demonstrates the potential of using undifferentiated BMSCs combined with artery graft in peripheral nerve regeneration without limitations of donor-site morbidity associated with isolation of Schwann cells. It is also cost saving due to reduction in interval from tissue collection until cell injection, simplicity of laboratory procedures compared to differentiated BMSCs and may have clinical implications for the surgical management of patients after facial nerve transection.

Effect of local administration of insulin-like growth factor I combined with inside-out artery graft on peripheral nerve regeneration

The objective was to assess the effect of topically administered insulin-like growth factor (IGF I) on peripheral nerve regeneration and functional recovery. Eighty male healthy white Wistar rats were divided into four experimental groups (n=20), randomly: in transected group (TC), the left sciatic nerve was transected and stumps were fixed in the adjacent muscle. In treatment group, defect was bridged using an inside-out artery graft (IOAG/IGF) filled with 10 μL IGF I (100 ng/kg). In artery graft group (IOAG), the graft was filled with phosphate-buffered saline alone. In sham-operated group (SHAM), sciatic nerve was exposed and manipulated. Each group was subdivided into five subgroups of five animals each and regenerated nerve fibres were studied 4, 8, 12 and 16 weeks after surgery. Behavioural testing, sciatic nerve functional study, gastrocnemius muscle mass and morphometric indices confirmed faster recovery of regenerated axons in IOAG/IGF than IOAG group (P<0.05). In immunohistochemistry, location of reactions to S-100 in IOAG/IGF was clearly more positive than that in IOAG group. When loaded in an artery graft, IGF I accelerated and improved functional recovery and morphometric indices of sciatic nerve.

Ketoprofen combined with artery graft entubulization improves functional recovery of transected peripheral nerves

The objective was to assess the local effect of ketoprofen on sciatic nerve regeneration and functional recovery. Eighty healthy male white Wistar rats were randomized into four experimental groups of 20 animals each: In the transected group (TC), the left sciatic nerve was transected and nerve cut ends were fixed in the adjacent muscle. In the treatment group the defect was bridged using an artery graft (AG/Keto) filled with 10 microliter ketoprofen (0.1 mg/kg). In the artery graft group (AG), the graft was filled with phosphated-buffer saline alone. In the sham-operated group (SHAM), the sciatic nerve was exposed and manipulated. Each group was subdivided into four subgroups of five animals each and regenerated nerve fibres were studied at 4, 8, 12 and 16 weeks post operation. Behavioural testing, sciatic nerve functional study, gastrocnemius muscle mass and morphometric indices showed earlier regeneration of axons in AG/Keto than in AG group (p < 0.05). Immunohistochemical study clearly showed more positive location of reactions to S-100 in AG/Keto than in AG group. When loaded in an artery graft, ketoprofen improved functional recovery and morphometric indices of the sciatic nerve. Local usage of this easily accessible therapeutic medicine is cost saving and avoids the problems associated with systemic administration.

Regulation by lipocalin-2 of neuronal cell death, migration, and morphology

A secreted protein, lipocalin-2 (LCN2), has been previously shown to regulate a variety of cellular phenotypes such as cell death, migration, and morphology. The role of LCN2, however, appears to be different depending on the cellular context. Here, we investigated how LCN2 influences neuronal phenotypes by using primary cortical neuronal cell cultures and neuroblastoma cell lines as a model. When exposed to LCN2 protein, neurons and neuroblastoma cells were sensitized to cell death evoked by nitric oxide, oxidative stress, and tumor necrosis factor-α (TNF-α). A forced expression of lcn2 in glia enhanced neuronal cell death in cocultures of glia and neurons, indicating that both exogenous protein addition and endogenous expression of lcn2 give rise to similar results. Iron and BCL2-interacting mediator of cell death (BIM) protein were involved in LCN2-induced cell death sensitization, based on the studies using iron donor, chelator, siderophore, and short hairpin RNA (shRNA)-mediated knockdown of bim expression. Furthermore, cell migration assay and immunofluorescence microscopic observation revealed that LCN2 accelerated neuronal motility and process extension, suggesting multiple roles for LCN2 in the regulation of neuronal cell death, migration, and morphology.

Transferrin receptor-1 suppresses neurite outgrowth in neuroblastoma Neuro2A cells

Transferrin receptor-1 (TfR1) is a cell membrane-associated glycoprotein responsible for incorporation of the iron bound to transferrin through an endocytotic process from the circulating blood. Iron is believed to play a dual role as an active center of the electron transfer system in mitochondria and as an endogenous cytotoxin through promoted generation of reactive oxygen species in different eukaryotic cells. In this study, we evaluated expression profiles of different genes related to iron mobilization across plasma membranes in neuronal cells. Marked mRNA expression was seen for various iron-related genes such as TfR1 in cultured mouse neocortical neurons, while TfR1 mRNA levels were more than doubled during culture from 3 to 6days. In mouse embryonal carcinoma P19 cells endowed to differentiate into neuronal and astroglial lineages, a transient increase was seen in both mRNA and corresponding protein for TfR1 in association with neuronal marker expression during culture with all-trans retinoic acid (ATRA). In neuronal Neuro2A cells cultured with ATRA, moreover, neurite was elongated together with increased expression of both mRNA and protein for TfR1. Overexpression of TfR1 significantly decreased the length of neurite elongated, however, while significant promotion was invariably seen in the neurite elongation in Neuro2A cells transfected with TfR1 siRNA as well as in Neuro2A cells cultured with an iron chelator. These results suggest that TfR1 would be highly expressed by neurons rather than astroglia to play a negative role in the neurite outgrowth after the incorporation of circulating transferrin in the brain.

The effect of chondroitinase on nerve regeneration following composite tissue allotransplantation

PURPOSE

To improve the degree of functional return and sensibility provided by composite tissue allotransplantation, enhanced nerve regeneration is essential. Chondroitin sulfate proteoglycans are found in the extracellular matrix of nerves and inhibit regenerating axons after injury. Treatment with chondroitinase to remove chondroitin sulfate proteoglycans has been shown to improve nerve regeneration in isolated nerve graft and transection-and-repair models. This study assesses the efficacy of chondroitinase as a neurotherapeutic agent in the setting of composite tissue allotransplantation.

METHODS

Adult Lewis rats received either orthotopic hind limb transplants from Brown Norway rat donors (n = 12) or sciatic nerve transection and repair (n = 6). Following approximation of the sciatic nerve, half the animals received intraneural injections of chondroitinase in saline and the other half received intraneural injections of saline alone. Five weeks after transplantation, we killed the animals and analyzed nerves with nonbiased quantitative nerve histomorphometry. One day after transection and repair, we killed animals and harvested sciatic nerves for immunohistochemical staining of cleaved chondroitin sulfate proteoglycans epitope and laminin. We used unpaired t-tests for statistical analysis.

RESULTS

Distal to the suture line, chondroitinase-treated animals demonstrated statistically greater total number of fibers and nerve density compared with controls. There were no statistically significant differences in fiber number or nerve density proximal to the suture line or in fiber widths. We observed staining of cleaved chondroitin sulfate proteoglycan epitopes only in treated animals, with no differences observed in the degree of laminin staining.

CONCLUSIONS

Intraneural injection of chondroitinase cleaved inhibitory chondroitin sulfate proteoglycans without disrupting proregenerative laminin and resulted in enhanced nerve regeneration after composite tissue allotransplantation. Studies at later time points are needed to assess whether this enhanced nerve regeneration will produce improved functional return.

Extracellular matrix: functions in the nervous system

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

Guiding neuron development with planar surface gradients of substrate cues deposited using microfluidic devices

Wiring the nervous system relies on the interplay of intrinsic and extrinsic signaling molecules that control neurite extension, neuronal polarity, process maturation and experience-dependent refinement. Extrinsic signals establish and enrich neuron-neuron interactions during development. Understanding how such extrinsic cues direct neurons to establish neural connections in vitro will facilitate the development of organized neural networks for investigating the development and function of nervous system networks. Producing ordered networks of neurons with defined connectivity in vitro presents special technical challenges because the results must be compliant with the biological requirements of rewiring neural networks. Here we demonstrate the ability to form stable, instructive surface-bound gradients of laminin that guide postnatal hippocampal neuron development in vitro. Our work uses a three-channel, interconnected microfluidic device that permits the production of adlayers of planar substrates through the combination of laminar flow, diffusion and physisorption. Through simple flow modifications, a variety of patterns and gradients of laminin (LN) and fluorescein isothiocyanate-conjugated poly-l-lysine (FITC-PLL) were deposited to present neurons with an instructive substratum to guide neuronal development. We present three variations in substrate design that produce distinct growth regimens for postnatal neurons in dispersed cell cultures. In the first approach, diffusion-mediated gradients of LN were formed on cover slips to guide neurons toward increasing LN concentrations. In the second approach, a combined gradient of LN and FITC-PLL was produced using aspiration-driven laminar flow to restrict neuronal growth to a 15 microm wide growth zone at the center of the two superimposed gradients. The last approach demonstrates the capacity to combine binary lines of FITC-PLL in conjunction with surface gradients of LN and bovine serum albumin (BSA) to produce substrate adlayers that provide additional levels of control over growth. This work demonstrates the advantages of spatio-temporal fluid control for patterning surface-bound gradients using a simple microfluidics-based substrate deposition procedure. We anticipate that this microfluidics-based patterning approach will provide instructive patterns and surface-bound gradients to enable a new level of control in guiding neuron development and network formation.

Plasminogen enhances neuritogenesis on laminin-1

Proteins of the plasminogen activation system are broadly expressed throughout the nervous system, and key roles for these proteins in neuronal function have been demonstrated. Recent reports have established that plasminogen is synthesized in neuroendocrine tissues, making this protein and the proteolytic activity of the product of its activation, plasmin, available at sites separated anatomically from circulating, hepatocyte-derived plasminogen. Results with plasminogen-deficient humans and mice suggest a role for plasminogen in neuritogenesis. To elucidate the role of the plasminogen activation system in these processes, the function of plasminogen during neuritogenesis and neurite outgrowth was studied. It is shown here that plasminogen participates in neuritogenesis, as plasmin inhibitors reduced both neurite outgrowth and neurite length in PC-12 cells. The addition of exogenous plasminogen enhanced neurite outgrowth and neurite length in both PC-12 cells and primary cortical neurons. The proteolytic activity of plasmin was required, since mutation of the catalytic serine residue completely abolished the stimulatory activity. Furthermore, mutation of the lysine binding site within kringle 5 of the plasminogen molecule also reduced the neuritogenic activity of plasminogen. Additionally, we demonstrate that plasminogen specifically bound to laminin-1, the interaction resulted in increased plasminogen activation by tissue-type plasminogen activator, and was dependent on a functional lysine binding site within plasminogen kringle 5. Moreover, during NGF-induced neuritogenesis, laminin-1 was degraded, and this cleavage was catalyzed by plasmin. This study provides the first direct evidence that plasminogen participates in neurite outgrowth and also suggests that laminin-1 degradation by plasmin contributes to the process of neuritogenesis.

Isolation and culture of post-natal mouse cerebellar granule neuron progenitor cells and neurons

The cerebellar cortex is a well described structure that provides unique opportunities for studying neuronal properties and development^1,2. Of the cerebellar neuronal types (granule cells, Purkinje cells and inhibitory interneurons), granule neurons are by far the most numerous and are the most abundant type of neurons in the mammalian brain. In rodents, cerebellar granule neurons are generated during the first two post-natal weeks from progenitor cells in the outermost layer of the cerebellar cortex, the external granule layer (EGL). The protocol presented here describes techniques to enrich and culture granule neurons and their progenitor cells from post-natal mouse cerebellum. We will describe procedures to obtain cultures of increasing purity^3,4, which can be used to study the differentiation of proliferating progenitor cells into granule neurons^5,6. Once the progenitor cells differentiate, the cultures also provide a homogenous population of granule neurons for experimental manipulation and characterization of phenomena such as synaptogenesis, glutamate receptor function⁷, interaction with other purified cerebellar cells^8,9 or cell death⁷.

Modulation of neuritogenesis by astrocyte muscarinic receptors

Astrocytes have been shown to release factors that have promoting or inhibiting effects on neuronal development. However, mechanisms controlling the release of such factors from astrocytes are not well established. Astrocytes express muscarinic receptors whose activation stimulates a robust intracellular signaling, although the role of these receptors in glial cells is not well understood. Acetylcholine and acetylcholine receptors are present in the brain before synaptogenesis occurs and are believed to be involved in neuronal maturation. The present study was undertaken to investigate whether stimulation of muscarinic receptors in astrocytes would modulate neurite outgrowth in hippocampal neurons. Rat hippocampal neurons, co-cultured with rat cortical astrocytes previously exposed to the cholinergic agonist carbachol, displayed longer neurites. The effect of carbachol in astrocytes was due to the activation of M3 muscarinic receptors. Exposure of astrocytes to carbachol increased the expression of the extracellular matrix proteins fibronectin and laminin-1 in these cells. This effect was mediated in part by an increase in laminin-1 and fibronectin mRNA levels and in part by the up-regulation of the production and release of plasminogen activator inhibitor-1, an inhibitor of the proteolytic degradation of the extracellular matrix. The inhibition of fibronectin activity strongly reduced the effect of carbachol on the elongation of all the neurites, whereas inhibition of laminin-1 activity reduced the elongation of minor neurites only. Plasminogen activator inhibitor-1 also induced neurite elongation through a direct effect on neurons. Taken together, these results demonstrate that cholinergic muscarinic stimulation of astrocytes induces the release of permissive factors that accelerate neuronal development.

Neurite guidance on protein micropatterns generated by a piezoelectric microdispenser

In this study, we developed a microdispenser technique in order to create protein patterns for guidance of neurites from cultured adult mouse dorsal root ganglia (DRG). The microdispenser is a micromachined silicon device that ejects 100 picolitre droplets and has the ability to position the droplets with a precision of 6-8 microm. Laminin and bovine serum albumin (BSA) was used to create adhesive and non-adhesive protein lines on polystyrene surfaces (cell culture dishes). Whole-mounted DRGs were then positioned close to the patterns and neurite outgrowth was monitored. The neurites preferred to grow on laminin lines as compared to the unpatterned plastic. When patterns were made from BSA the neurites preferred to grow in between the lines on the unpatterned plastic surface. We conclude that microdispensing can be used for guidance of sensory neurites. The advantages of microdispensing is that it is fast, flexible, allows deposition of different protein concentrations and enables patterning on delicate surfaces due to its non-contact mode of operation. It is conceivable that microdispensing can be utilized for the creation of protein patterns for guiding neurites to obtain in vitro neural networks, in tissue engineering or rapid screening for guiding proteins.

Effect of filament diameter and extracellular matrix molecule precoating on neurite outgrowth and Schwann cell behavior on multifilament entubulation bridging devicein vitro

At present there is no clinically effective treatment for injuries or pathological processes that disrupt the continuity of axons in the mature central nervous system. However, a number of studies suggest that a tremendous potential exists for developing biomaterial based therapies. In particular, biomaterials in the form of bridging substrates have been shown to support at least some level of axonal regeneration across the lesion site, but display a limited capacity for directing axons toward their targets. To improve the directionality and outgrowth rate of the axonal regeneration process, filaments and tubes appear promising, but the technology is far from optimized. As a step toward optimization, the influence of filament diameter and various extracellular matrix coatings on nerve regeneration was evaluated in this article using a dorsal root ganglion (DRG) explant model. An increasing pattern of alignment and outgrowth of neurites in the direction parallel the long axis of the packed filament bundles with decreasing filament diameters ranging from supracellular and beyond (500 to 100 mum), cellular (30 mum), down to subcellular size (5 mum) was observed. Such effects became most prominent on filament bundles with individual filament diameters in the range of cellular size and below (5 and 30 mum) where highly directional and robust neuronal outgrowth was achieved. In addition, laminin-coated filaments that approached the size of spinal axons support significantly longer regenerative outgrowth than similarly treated filaments of larger diameter, and exceed outgrowth distance on similarly sized filaments treated with fibronectin. These data suggested the feasibility of using a multifilament entubulation bridging device for supporting directional axonal regeneration.

Integrin-mediated dendrite branch maintenance requires Abelson (Abl) family kinases

Dendrite arbor structure is a critical determinant of nervous system function that must be actively maintained throughout life, but the signaling pathways that regulate dendrite maintenance are essentially unknown. We report that the Abelson (Abl) and Abl-related gene (Arg) nonreceptor tyrosine kinases are required for maintenance of cortical dendrites in the mouse brain. arg-/- cortical dendrites initially develop normally and are indistinguishable from wild-type dendrites at postnatal day 21. Dendrite branches are not efficiently maintained in arg-/- neurons, leading to a reduction in dendrite arbor size by early adulthood. More severe dendrite loss is observed in abl-/-arg-/- neurons. Elevation of Arg kinase activity in primary cortical neurons promotes axon and dendrite branching. Activation of integrin receptors by adhesion to laminin-1 or Semaphorin 7A also promotes neurite branching in cortical neurons, but this response is absent in arg-/- neurons because of the reduced dynamic behavior of mutant neurite branches. These data suggest that integrin signaling through Abl and Arg support cortical dendrite branch maintenance by promoting dendrite branch dynamics in response to adhesive cues.

Functional analysis of SIRPα in the growth cone

The `signal regulatory protein' SIRPα is an Ig superfamily, transmembrane glycoprotein with a pair of cytoplasmic domains that can bind the phosphatase SHP-2 when phosphorylated on tyrosine. SIRPα is prominent in growth cones of rat cortical neurons and located, together with the tetraspanin CD81, in the growth cone periphery. SIRPα is dynamically associated with Triton-X-100-sensitive, but Brij-98-resistant, lipid microdomains, which also contain CD81. Challenge of growth cones with the integrin-binding extracellular-matrix (ECM) protein, laminin, or with the growth factors, IGF-1 or BDNF, increases SIRPα phosphorylation and SHP-2 binding rapidly and transiently, via Src family kinase activation; phosphorylated SIRPα dissociates from the lipid microdomains. A cytoplasmic tail fragment of SIRPα (cSIRPα), when expressed in primary cortical neurons, also is phosphorylated and binds SHP-2. Expression of wild-type cSIRPα, but not of a phosphorylation-deficient mutant, substantially decreases IGF-1-stimulated axonal growth on laminin. On poly-D-lysine and in control conditions, axonal growth is slower than on laminin, but there is no further reduction in growth rate induced by the expression of cSIRPα. Thus, the effect of cSIRPα on axon growth is dependent upon integrin activation by laminin. These results suggest that SIRPα functions in the modulation of axonal growth by ECM molecules, such as laminin.

Beneficial effect of nerve growth factor-7S on peripheral nerve regeneration through inside-out vein grafts: An experimental study

This study investigated the effect of local administration of nerve growth factor-7S (NGF-7S) on the axonal regrowth of mixed peripheral nerves through inside-out vein grafts. Sixty male Wistar rats were randomized into two groups (n = 30). A defect 12 mm long in the right sciatic nerve was created and repaired with an inside-out vein graft from the right jugular vein. NGF-7S (group A) or phosphate-buffered saline (group B; control) was locally administered daily during the first 3 weeks. Walking-track analysis and electrophysiological and histological-morphometric studies were carried out 4, 6, 8, 10, and 12 weeks postoperatively (subgroups a, b, c, d, and e, respectively, n = 6 each). Data analysis showed that 1) the recovery of motor function, as measured by walk pattern analysis and evoked muscle action potential, and 2) the orientation, number, myelin thickness, and diameter of myelinated fibers were better in the NGF-7S than in the control group. These findings present strong evidence of the beneficial effect of NGF-7S on peripheral nerve regeneration through inside-out vein grafts.

Characterization of PC12 cell proliferation and differentiation-stimulated by ECM adhesion proteins and neurotrophic factors

Among the various elements which influence axonal outgrowth in vivo is the physicochemical interaction of actively outgrowing nerve fibers with the various substrata they encounter during differentiation. Several experiments have explored the role of the extracellular matrix (ECM) in the control of neuronal differentiation. The nature, however, of the interactions between neurons and components of the ECM during regeneration and development are largely a matter of speculation. Although previous studies have already explored the influence of a number of ECM adhesion proteins and neurotrophic factors on neurite outgrowth, none have been carried in a systematic approach that allows for the simultaneous comparison of different surface conditions in relation to different neurotrophic factors. Motivated by the necessity of establishing controlled environments that allow for the rational design of stable neuronal/biomaterial interfaces, the long-term effects of NGF and FGF-2 on the behavior of PC12 cells plated on collagen and laminin modified surfaces were evaluated. A pheochromocytoma cell line derived from transplantable rat adrenal medulla, PC12 cells have been commonly employed as an instructive model for studying the underlying mechanisms of neuronal differentiation. Long-term characterization of PC12 proliferation and neuronal differentiation for an experimental duration of 7-22 days was achieved by both qualitatively and quantitatively assaying for cell count, neurite number, neurite mean length, and neurite stability. Neurite stability was determined in terms of resistance to loss after neurotrophic factor (NGF/FGF-2) withdrawal. The present findings demonstrate that ECM adhesion proteins collagen and laminin are equally effective in promoting PC12 proliferation. It was noted as well that NGF supplemented collagen cultures are significantly more efficient in providing long-term support to PC12 differentiation in terms of neurite number, mean length, and stability.

EphA4 provides repulsive signals to developing cochlear ganglion neurites mediated through ephrin-B2 and -B3

The ephrins and Eph receptors make up two large families of bi-directional signaling molecules that are known to play a role in the development of the nervous system. Recently, expression of EphA4 in the developing cochlea was shown, with strong expression in cells lining the osseous spiral lamina (OSL) through which afferent dendrites must pass to reach the organ of Corti (OC). It was also demonstrated that ephrin-B2 and -B3, both of which are known to interact with EphA4, are expressed by spiral ganglion (SG) neurons. To investigate the functional role of EphA4 in the development of inner ear neurons, neonatal rat SG explants were cultured for 72 hours on uniformly coated surfaces or near stripes of EphA4/IgG-Fc-chimera. Control explants were cultured on or near IgG-Fc and EphA1/IgG-Fc-chimera. To assess the roles of ephrin-B2 and -B3 in EphA4 signaling, SG explants were cultured with or without anti-ephrin-B2 and/or -B3 blocking antibodies. Growth patterns of SG neurites at the border of EphA4 receptor stripes showed repulsion, characterized by turning, stopping and/or reversal. In the case of IgG-Fc and EphA1, the neurites grew straight onto the stripes. Treatment with either anti-ephrin-B2 or -B3 blocking antibodies significantly reduced the repulsive effect of an EphA4 stripe. Moreover, when both antibodies were used together, neurites crossed onto EphA4 stripes with no evidence of repulsion. The results suggest that EphA4 provides repulsive signals to SG neurites in the developing cochlea, and that ephrin-B2 and -B3 together mediate this response.

Inside-out vein graft and inside-out artery graft in rat sciatic nerve repair

Although veins and arteries present similar wall structures, there are differences which may be relevant in peripheral nerve reconstruction. Inside-out vein grafts (IOVG) have been satisfactorily used to repair both motor and sensitive nerves. However, the inside-out artery graft (IOAG) is a new technique and not fully investigated. Our study presents comparative morphological data on nerve regeneration achieved with IOVG and IOAG in the repair of Wistar rat sciatic nerves. Jugular veins and aorta arteries were harvested from donor animals and used "inside-out" to bridge a 10-mm gap. Animals were sacrificed at 10 weeks to evaluate nerve regeneration. Both techniques presented great variability in nervous tissue, though some animals showed satisfactory results. Different intensities of scarring processes might have interfered with nerve regeneration. Although IOVG and IOAG techniques showed similar morphometric results, in general, IOVG presented a closer-to-normal nerve organization than IOAG.

The heparan sulfate proteoglycan agrin modulates neurite outgrowth mediated by FGF-2

Although the role of agrin in the formation of the neuromuscular junction is well established, other functions for agrin have remained elusive. The present study was undertaken to assess the role of agrin in neurite outgrowth mediated by the heparin-binding growth factor basic fibroblast growth factor (FGF-2), which we have shown previously to bind to agrin with high affinity and that has been shown to mediate neurite outgrowth from a number of neuronal cell types. Using both an established neuronal cell line, PC12 cells, and primary chick retina neuronal cultures, we find that agrin potentiates the ability of FGF-2 to stimulate neurite outgrowth. In PC12 cells and retinal neurons agrin increases the efficacy of FGF-2 stimulation of neurite outgrowth mediated by the FGF receptor, as an inhibitor of the FGF receptor abolished neurite outgrowth in the presence of agrin and FGF-2. We also examined possible mechanisms by which agrin may modulate neurite outgrowth, analyzing ERK phosphorylation and c-fos phosphorylation. These studies indicate that agrin augments a transient early phosphorylation of ERK in the presence of FGF-2, and augments and sustains FGF-2 mediated increases in c-fos phosphorylation. These data are consistent with established mechanisms where heparan sulfate proteoglycans such as agrin may increase the affinity between FGF-2 and the FGF receptor. In summary, our studies suggest that neural agrin contributes to the establishment of axon pathways by modulating the function of neurite promoting molecules such as FGF-2.

Axonal Growth on Solubilized and Reconstituted Matrix from the Embryonic Chicken Retina Inner Limiting Membrane

Basal laminae, thin sheets of extracellular matrix covering the basal side of all neuroepithelia, are strongly supportive for neurite outgrowth in vitro and may provide a permissive environment for growing neurites in vivo. To gain information about the biological activity and composition of in situ-derived basal laminae the inner limiting membranes from embryonic day (E) 7 to E11 chick and quail retinae were isolated. The basal laminae were solubilized with high-molar guanidine hydrochloride or urea, and the solubilized proteins reconstituted by dialysis. The matrix proteins were spotted or dried onto nitrocellulose or polylysine-coated dishes. When explants from retina or from dorsal root ganglia were incubated on the protein spots, neurite extension was very robust, at a level as high as on authentic basal lamina. Extracts from the pigment epithelial basement membrane did not support neurite extension. Western blot analysis showed that the explant from the retinal inner limiting membrane contained predominantly basal lamina-type proteins, such as laminin, collagen type IV and heparan sulphate proteoglycan, whereas the matrix extract from the pigment epithelium contained predominantly mesenchymal-type proteins, like collagen type I and tenascin. JG22, a beta1 integrin antibody that inhibited neurite extension on EHS tumour laminin substrate, had no effect on neurite outgrowth on retinal basal lamina matrix, indicating that embryonic basal laminae contain other or additional growth promoting substrate molecules.

Nerve growth factor is expressed in rat femoral vein

PURPOSE

Entubulization is a well known method of nerve repair for defects too large to be reconstructed by direct suturing without tension. Vein grafts and alloplastic tubes have been used for entubulization in peripheral and cranial nerves, but the mechanism by which they promote healing is poorly understood. The overall hypothesis of this laboratory is that nerve growth factor (NGF) plays an important role in nerve regeneration after entubulization with a vein graft. The purpose of this pilot study was to localize NGF protein expression in the rat femoral vein.

MATERIALS AND METHODS

Sciatic nerves and femoral veins were harvested from adult male Sprague-Dawley rats. Femoral arteries were also collected and used for comparison and validation of the analysis. All specimens were fixed in paraformaldehyde and embedded in paraffin. Specimens were either stained with hematoxylin and eosin or used for immunohistochemical reaction with anti-NGF antibody.

RESULTS

Sciatic nerve was used as a positive control to identify the monofascicular architecture with hematoxylin and eosin and to document the positive immunohistochemical reaction. NGF immunoreactivity was present in the tunica intima and tunica adventitia of femoral vein and artery but not in the tunica media.

CONCLUSION

The results of this pilot study indicate that NGF is detectable in both the intimal and adventitial layers of the rat femoral vein and artery but not in the smooth muscle wall. These findings suggest that vein grafts could potentially promote nerve regeneration by supplying NGF to the injured nerve.

Relationship between sprouting axons, proteoglycans and glial cells following unilateral nigrostriatal axotomy in the adult rat

Proteoglycans may modulate axon growth in the intact and injured adult mammalian CNS. Here we investigate the distribution and time course of deposition of a range of proteoglycans between 4 and 14 days following unilateral axotomy of the nigrostriatal tract in anaesthetised adult rats. Immunolabelling using a variety of antibodies was used to examine the response of heparan sulphate proteoglycans, chondroitin sulphate proteoglycans and keratan sulphate proteoglycans. We observed that many proteoglycans became abundant between 1 and 2 weeks post-axotomy. Heparan sulphate proteoglycans were predominantly found within the lesion core (populated by blood vessels, amoeboid macrophages and meningeal fibroblasts) whereas chondroitin sulphate proteoglycans and keratan sulphate proteoglycans were predominantly found in the lesion surround (populated by reactive astrocytes, activated microglia and adult precursor cells). Immunolabelling indicated that cut dopaminergic nigral axons sprouted prolifically within the lesion core but rarely grew into the lesion surround. We conclude that sprouting of cut dopaminergic nigral axons may be supported by heparan sulphate proteoglycans but restricted by chondroitin sulphate proteoglycans and keratan sulphate proteoglycans.

Retinal ganglion cells do not extend axons by default: promotion by neurotrophic signaling and electrical activity

We investigate the signaling mechanisms that induce retinal ganglion cell (RGC) axon elongation by asking whether surviving neurons extend axons by default. We show that bcl-2 overexpression is sufficient to keep purified RGCs alive in the absence of any glial or trophic support. The bcl-2-expressing RGCs do not extend axons or dendrites unless signaled to do so by single peptide trophic factors. Axon growth stimulated by peptide trophic factors is remarkably slow but is profoundly potentiated by physiological levels of electrical activity spontaneously generated within embryonic explants or mimicked on a multielectrode silicon chip. These findings demonstrate that these surviving neurons do not constitutively extend axons and provide insight into the signals that may be necessary to promote CNS regeneration.

Inside-out versus standard artery graft to repair a sensory nerve in rats

It is known that a vein graft provides a good microenvironment for axon regeneration in motor peripheral nerves, but the use of artery graft for regeneration of sensory nerves is controversial. We sectioned the saphenous nerve and repaired it by using heterologous inside-out and standard artery graft techniques in rats. After 4, 12, and 20 weeks, the graft and the distal stump were observed under electron microscopy. In each period studied, the pattern, diameters, and thickness of the myelin sheaths of the regenerated axons were measured in the graft and distal stump. There was capillary invasion in both the graft and distal stump, especially in the inside-out artery graft group. Regenerated nerve fibers were prominent in both heterologous artery grafts 4 weeks after the surgical procedures. Conversely, in the distal stump, regenerated nerve fibers were observed only after 12 weeks. In both the inside-out artery graft and standard artery graft, no statistical difference in the diameters and thickness of the myelinated fibers after 20 weeks was observed.

The use of conventional and invaginated autologous vein grafts for nerve repair by means of entubulation

Nerve repair by entubulation has re-emerged recently as a possible means of enhancing the microenvironment at the site of repair by inclusion within the tube of various trophic factors. To this end, a modification of the vein-graft technique has been used by turning it inside out before repair, to expose the adventitial surface to the regenerating axons. A comparative study of standard vein grafting versus the inside-out technique was carried out in two equal-sized groups of inbred Lewis rats. Jugular vein isografts were derived from litter mates. The sciatic nerve was transected and repaired by entubulation using the standard vein graft in one group and the inside-out graft in the other group. Morpho-metric and electrophysiological assessment were carried out 3 months after repair. When the animals were assessed it was found that both the standard-vein-graft group and the inside-out group exhibited a reduction in all of the morphometric and electrophysiological variables when compared to normal nerves. The mean axon diameter, fibre diameter and myelin sheath thickness were, however, found to be greater in the group that underwent the inside-out repair. The superior morphometric results seen in the inside-out group were not matched by improved electrophysiological performance. It is concluded that the use of the inside-out technique confers no functional benefit over standard vein grafting.

Integrins as receptors for laminins

Laminins are a family of trimeric glycoproteins present in the extracellular matrix and the major constituents of basement membranes. Integrins are alpha beta transmembrane receptors that play critical roles in both cell-matrix and cell-cell adhesion. Several members of the integrin family, including alpha 1 beta 1, alpha 2 beta 1, alpha 3 beta 1, alpha 6 beta 1, alpha 7 beta 1 and alpha 6 beta 4 heterodimers serve as laminin receptors on a variety of cell types. This review summarizes recent advances in understanding the involvement of individual integrins in cell interactions with laminins and the roles of laminin-binding integrins in adhesion-mediated events in vertebrates, including embryonic development, cell migration and tumor cell invasiveness, cell proliferation and differentiation, as well as basement membrane assembly. We discuss the regulation of integrin function via alternative splicing of cytoplasmic domains of alpha and beta subunits of the integrin receptors for laminins and present examples of functional collaboration between laminin-binding integrins and non-integrin laminin receptors. Advances in our understanding of the laminin-binding integrins continue to demonstrate the essential roles these receptors play in maintaining cell polarity and tissue architecture.

Laminin inhibition of beta-amyloid protein (Abeta) fibrillogenesis and identification of an Abeta binding site localized to the globular domain repeats on the laminin a chain

beta-Amyloid protein (Abeta) is a major component of neuritic plaques and cerebrovascular amyloid deposits in the brains of patients with Alzheimer's disease (AD). Inhibitors of Abeta fibrillogenesis are currently sought as potential future therapeutics for AD and related disorders. In the present study, the basement membrane protein laminin was found to bind Abeta 1-40 with a single dissociation constant, K(d) = 2.7 x 10(-9) M, and serve as a potent inhibitor of Abeta fibril formation. 25 microM of Abeta 1-40 was incubated at 37 degrees C for 1 week in the presence of 100 nM of laminin or other basement membrane components, including perlecan, type IV collagen, and fibronectin to determine their effects on Abeta fibril formation as evaluated by thioflavin T fluorometry. Of all the basement membrane components tested, laminin demonstrated the greatest inhibitory effect on Abeta-amyloid fibril formation, causing a ninefold inhibition at 1 and 3 days and a 21-fold inhibition at 1 week. The inhibitory effects of laminin on Abeta fibrillogenesis occurred in a dose-dependent manner and were still effective at lower concentrations. The inhibitory effects of laminin on Abeta 1-40 fibril formation was confirmed by negative stain electron microscopy, whereby laminin caused an almost complete inhibition of Abeta fibril formation and assembly by 3 days, resulting in the appearance of primarily amorphous nonfibrillar material. Laminin also caused partial disassembly of preformed Abeta-amyloid fibrils following 4 days of coincubation. Laminin was not effective as an inhibitor of islet amyloid polypeptide fibril formation, suggesting that laminin's amyloid inhibitory effects were Abeta-specific. To identify a potential Abeta-binding site(s) on laminin, laminin was first digested with V8, trypsin, or elastase. An Abeta-binding elastase digestion product of approximately 120-130 kDa was found. In addition, a approximately 55 kDa fragment derived from V8 and elastase-digested laminin interacted with biotinylated Abeta 1-40. Amino acid sequencing of the approximately 55 kDa fragment identified a conformationally dependent Abeta-binding site within laminin localized to the globular repeats on the laminin A chain. These studies demonstrate that laminin not only binds Abeta with relatively high affinity but is a potent inhibitor of Abeta-amyloid fibril formation. In addition, further identification of an Abeta-binding domain within the globular repeats on the laminin A chain may lead to the design of new therapeutics for the inhibition of Abeta fibrillogenesis.

Separation of neural induction and neurulation in Xenopus

Cellular interactions with laminin are important for numerous morphogenetic events. In Xenopus, the first of these is neurulation. The integrin alpha6 subunit mediates an attachment of the cells of the neural plate to the underlying basal lamina. A disruption of this interaction results in embryos that fail to neurulate (T. E. Lallier et al., 1996, Development 122, 2539-2554). Here we provide evidence supporting the specificity of this phenomenon and characterize developmental events as either disrupted or unaffected by a perturbation of alpha6 integrin expression. First, reduction of alpha6 integrin expression does not halt mitotic division throughout the embryo, indicating that the neural defects observed are not simply a global perturbation of all developmental processes. Second, a gene associated with dorsal mesoderm formation, brachyury, is expressed normally in alpha6 integrin-perturbed embryos. Third, the expression of BMP4, noggin, chordin, and follistatin, all of which are critical for neural induction, are at near normal levels. In addition, several genes expressed shortly after neural induction (N-CAM, nrp1, and Xanf1) are not perturbed in nonneurulating embryos. Interestingly, expression of one neural-specific gene (synaptobrevin), which is normally detectable late in neurulation, is abolished in these alpha6 integrin-perturbed embryos. Furthermore, the spatial expression of several transcripts is expanded in alpha6 integrin-perturbed embryos (orthodenticle and engrailed). Taken together, these data indicate that while alpha6 integrin-mediated interactions with laminin are required for neurulation, they are not required for the initial processes of neural induction. However, these cell-extracellular matrix interactions appear to be important in later inductive events and rostrocaudal patterning of the neural tube.

Hyaluronic acid enhances peripheral nerve regeneration in vivo

Hyaluronic acid has been shown to enhance peripheral nerve regeneration in vitro. It has been proposed that, during the fibrin matrix phase of regeneration, hyaluronic acid organizes the extracellular matrix into a hydrated open lattice, thereby facilitating migration of the regenerating axons. Hyaluronic acid solutions and saline control solutions were injected into a nerve guide spanning a transected gap in the sciatic nerve of Sprague-Dawley rats (five in each group). Nerve conduction velocities were measured at 4 weeks by electromyography (EMG) before sacrifice of the animals. These studies demonstrated increased conduction velocities in the hyaluronic acid group compared with control animals (P = 0.006). After the animals were sacrificed, regenerated axon cables were quantified histologically, and axon branching was delineated by retrograde tracer analysis. In addition, the hyaluronic acid group showed an increase in myelinated axon counts at 4 weeks (P= 0.03). An increase in retrograde flow was demonstrated in the hyaluronic acid groups compared with animals receiving saline solution.

Inside-out vs. standard vein graft to repair a sensory nerve in rats

Nerve regeneration in a sensory nerve was obtained by the application of different techniques: inside-out vein graft (IOVG group) and standard vein graft (SVG group). These techniques provide a good microenvironment for axon regeneration in motor nerves, but their efficiency for regeneration of sensory nerves is controversial. The saphenous nervtce was sectioned and repaired by the inside-out and standard vein graft techniques in rats. After 4, 12, and 20 weeks the graft and the distal stump were observed under electron microscopy. In each studied period, the pattern, diameters, and thickness of the myelin sheaths of the regenerated axons were measured in the graft and distal stump. A comparative study about the regenerated nerve fibers by these two different techniques was performed. Regenerated nerve fibers were prominent in both vein grafts 4 weeks after the surgical procedures. On the other hand, in the distal stump, regenerated nerve fibers were observed only from 12 weeks. In both inside-out vein graft and standard vein graft statistical difference was not observed about the diameters and thickness of the myelinated fibers after 20 weeks. On the other hand, the inside-out group had greater regenerated axon number when compared to the standard group. There is a capillary invasion in both graft and distal stump, especially in the IOVG group. The regenerated axons follow these capillaries all the time like satellite microfascicles. After 20 weeks, the diameters of regenerated fibers repaired by the standard vein graft technique were closer to the normal fibers compared to the inside-out vein graft. On the other hand, the pattern of these regenerated axons was better in the IOVG group.

Diabetic neuropathy: pathogenesis and therapy

Diabetic neuropathies are complex, heterogeneous disorders that encompass a wide range of abnormalities affecting both peripheral and autonomic nervous systems, causing considerable morbidity and mortality. Treatment should be based upon the underlying etiology and not symptoms alone, although symptomatic therapy is needed. Neuropathies may be focal or diffuse, proximal or distal, and involve somatic and autonomic nerves. Focal syndromes are classified as (1) entrapment syndromes or (2) mononeuropathies. Entrapment syndromes are treated by means of relieving compression within confined spaces. Mononeuropathies are due to a vascular insult and resolve spontaneously. They are best treated by supportive therapy. Proximal neuropathies are usually due to an inflammatory, vasculitic, or autoimmune condition and are best treated with specific therapies for the underlying disorder based on biopsy findings. Therapies for distal polyneuropathies include metabolic treatments (e.g., aldose reductase inhibitors, aminoguanidine, gamma-linolenic acid), autoimmune therapies, and nerve growth factors. No definitive treatment is available for painful diabetic neuropathy. Several medications have been used, among them tricyclic antidepressants, antiepileptic drugs, phenothiazines, calcitonin, local anesthetics, nonsteroidal anti-inflammatory drugs, and dextromethorphan. Nonpharmacologic therapies include surgical sympathectomy, spinal cord blockade, electrical spinal cord stimulation, and prostaglandin.

DSD-1-proteoglycan is the mouse homolog of phosphacan and displays opposing effects on neurite outgrowth dependent on neuronal lineage

DSD-1-PG is a chondroitin sulfate proteoglycan (CSPG) expressed by glial cells that can promote neurite outgrowth from rat embryonic mesencephalic (E14) and hippocampal (E18) neurons, an activity that is associated with the CS glycosaminoglycans (GAGs). Further characterization of DSD-1-PG has included sequencing of peptides from the core protein and the cloning of the corresponding cDNA using polyclonal antisera against DSD-1-PG to screen phage expression libraries. On the basis of these studies we have identified DSD-1-PG as the mouse homolog of phosphacan, a neural rat CSPG. Monoclonal antibodies 3H1 and 3F8 against carbohydrate residues on rat phosphacan recognize these epitopes on DSD-1-PG. The epitopes of the antibodies, L2/HNK-1 and L5/Lewis-X, which have been implicated in functional interactions, are also found on DSD-1-PG. Although DSD-1-PG has previously been shown to promote neurite outgrowth, its upregulation after stab wounding of the CNS and its localization in regions that are considered boundaries to axonal extension suggested that it may also have inhibitory functions. Neonatal dorsal root ganglion (DRG) explants grown on a rich supportive substrate (laminin) with and without DSD-1-PG were strikingly inhibited by the proteoglycan. The inhibitory effects of DSD-1-PG on the DRG explants were not relieved by removal of the CS GAGs, indicating that this activity is associated with the core glycoprotein. The neurite outgrowth from embryonic hippocampal neurons on laminin was not affected by the addition of DSD-1-PG. This indicates that DSD-1-PG/mouse phosphacan can have opposing effects on the process of neurite outgrowth dependent on neuronal lineage.

Identification of extracellular matrix ligands for the heparan sulfate proteoglycan agrin

Agrin is a major brain heparan sulfate proteoglycan which is expressed in nearly all basal laminae and in early axonal pathways of the developing central nervous system. To further understand agrin's function during nervous system development, we have examined agrin's ability to interact with several heparin-binding extracellular matrix proteins. Our data show that agrin binds FGF-2 and thrombospondin by a heparan sulfate-dependent mechanism, merosin and laminin by both heparan sulfate-dependent and -independent mechanisms, and tenascin solely via agrin's protein core. Furthermore, agrin's heparan sulfate side chains encode a specificity in interactions with heparin-binding molecules since fibronectin and the cell adhesion molecule L1 do not bind agrin. Surface plasmon resonance studies (BIAcore) reveal a high affinity for agrin's interaction with FGF-2 and merosin (2.5 and 1.8 nM, respectively). Demonstrating a biological significance for these interactions, FGF-2, laminin, and tenascin copurify with immunopurified agrin and immunohistochemistry reveals a partial codistribution of agrin and its ECM ligands in the chick developing visual system. These studies and our previous studies, showing that merosin and NCAM also colocalize with agrin, provide evidence that agrin plays a crucial role in the function of the extracellular matrix and suggest a role for agrin in axon pathway development.

DSD-1-proteoglycan is the mouse homolog of phosphacan and displays opposing effects on neurite outgrowth dependent on neuronal lineage

DSD-1-PG is a chondroitin sulfate proteoglycan (CSPG) expressed by glial cells that can promote neurite outgrowth from rat embryonic mesencephalic (E14) and hippocampal (E18) neurons, an activity that is associated with the CS glycosaminoglycans (GAGs). Further characterization of DSD-1-PG has included sequencing of peptides from the core protein and the cloning of the corresponding cDNA using polyclonal antisera against DSD-1-PG to screen phage expression libraries. On the basis of these studies we have identified DSD-1-PG as the mouse homolog of phosphacan, a neural rat CSPG. Monoclonal antibodies 3H1 and 3F8 against carbohydrate residues on rat phosphacan recognize these epitopes on DSD-1-PG. The epitopes of the antibodies, L2/HNK-1 and L5/Lewis-X, which have been implicated in functional interactions, are also found on DSD-1-PG. Although DSD-1-PG has previously been shown to promote neurite outgrowth, its upregulation after stab wounding of the CNS and its localization in regions that are considered boundaries to axonal extension suggested that it may also have inhibitory functions. Neonatal dorsal root ganglion (DRG) explants grown on a rich supportive substrate (laminin) with and without DSD-1-PG were strikingly inhibited by the proteoglycan. The inhibitory effects of DSD-1-PG on the DRG explants were not relieved by removal of the CS GAGs, indicating that this activity is associated with the core glycoprotein. The neurite outgrowth from embryonic hippocampal neurons on laminin was not affected by the addition of DSD-1-PG. This indicates that DSD-1-PG/mouse phosphacan can have opposing effects on the process of neurite outgrowth dependent on neuronal lineage.