Synthesis and effects of basement membrane components in cultured rat Schwann cells

Development of a magnetically aligned regenerative tissue-engineered electronic nerve interface for peripheral nerve applications

Peripheral nerve injuries can be debilitating to motor and sensory function, with severe cases often resulting in complete limb amputation. Over the past two decades, prosthetic limb technology has rapidly advanced to provide users with crude motor control of up to 20° of freedom; however, the nerve-interfacing technology required to provide high movement selectivity has not progressed at the same rate. The work presented here focuses on the development of a magnetically aligned regenerative tissue-engineered electronic nerve interface (MARTEENI) that combines polyimide "threads" encapsulated within a magnetically aligned hydrogel scaffold. The technology exploits tissue-engineered strategies to address concerns over traditional peripheral nerve interfaces including poor axonal sampling through the nerve and rigid substrates. A magnetically templated hydrogel is used to physically support the polyimide threads while also promoting regeneration in close proximity to the electrode sites on the polyimide. This work demonstrates the utility of magnetic templating for use in tuning the mechanical properties of hydrogel scaffolds to match the stiffness of native nerve tissue while providing an aligned substrate for Schwann cell migration in vitro. MARTEENI devices were fabricated and implanted within a 5-mm-long rat sciatic-nerve transection model to assess regeneration at 6 and 12 weeks. MARTEENI devices do not disrupt tissue remodeling and show axon densities equivalent to fresh tissue controls around the polyimide substrates. Devices are observed to have attenuated foreign-body responses around the polyimide threads. It is expected that future studies with functional MARTEENI devices will be able to record and stimulate single axons with high selectivity and low stimulation regimes.

Vitamin C regulates Schwann cell myelination by promoting DNA demethylation of pro-myelinating genes

Ascorbic acid (vitamin C) is critical for Schwann cells to myelinate peripheral nerve axons during development and remyelination after injury. However, its exact mechanism remains elusive. Vitamin C is a dietary nutrient that was recently discovered to promote active DNA demethylation. Schwann cell myelination is characterized by global DNA demethylation in vivo and may therefore be regulated by vitamin C. We found that vitamin C induces a massive transcriptomic shift (n = 3,848 genes) in primary cultured Schwann cells while simultaneously producing a global increase in genomic 5-hydroxymethylcytosine (5hmC), a DNA demethylation intermediate which regulates transcription. Vitamin C up-regulates 10 pro-myelinating genes which exhibit elevated 5hmC content in both the promoter and gene body regions of these loci following treatment. Using a mouse model of human vitamin C metabolism, we found that maternal dietary vitamin C deficiency causes peripheral nerve hypomyelination throughout early development in resulting offspring. Additionally, dietary vitamin C intake regulates the expression of myelin-related proteins such as periaxin (PRX) and myelin basic protein (MBP) during development and remyelination after injury in mice. Taken together, these results suggest that vitamin C cooperatively promotes myelination through 1) increased DNA demethylation and transcription of pro-myelinating genes, and 2) its known role in stabilizing collagen helices to form the basal lamina that is necessary for myelination.

Bioprinting: From Tissue and Organ Development to in Vitro Models

Bioprinting techniques have been flourishing in the field of biofabrication with pronounced and exponential developments in the past years. Novel biomaterial inks used for the formation of bioinks have been developed, allowing the manufacturing of in vitro models and implants tested preclinically with a certain degree of success. Furthermore, incredible advances in cell biology, namely, in pluripotent stem cells, have also contributed to the latest milestones where more relevant tissues or organ-like constructs with a certain degree of functionality can already be obtained. These incredible strides have been possible with a multitude of multidisciplinary teams around the world, working to make bioprinted tissues and organs more relevant and functional. Yet, there is still a long way to go until these biofabricated constructs will be able to reach the clinics. In this review, we summarize the main bioprinting activities linking them to tissue and organ development and physiology. Most bioprinting approaches focus on mimicking fully matured tissues. Future bioprinting strategies might pursue earlier developmental stages of tissues and organs. The continuous convergence of the experts in the fields of material sciences, cell biology, engineering, and many other disciplines will gradually allow us to overcome the barriers identified on the demanding path toward manufacturing and adoption of tissue and organ replacements.

Synergistic Effect of Laminin and Epidermal Growth Factor on Biological and Morphological Properties of Co-Cultured Myoblasts and Fibroblasts

BACKGROUND

One of the long-standing problems of myoblasts in vitro expansion is slow cell migration and this causes fibroblast population to exceed myoblasts. In this study, we investigated the synergistic effect of laminin and epidermal growth factor (EGF) on co-cultured myoblasts and fibroblasts for cell attachment, proliferation and migration.

METHODS

Skeletal human muscle cells were cultured in four different conditions; control, EGF, laminin (Lam) and laminin EGF (Lam + EGF). Using live imaging system, their cellular properties; attachment, migration and growth were exposed to Rho kinase inhibitor, Y-27632, and EGF-receptor (EGF-R) inhibitor, gefitinib were measured.

RESULTS

Myoblast migration and proliferation was enhanced significantly by synergistic stimulation of laminin and EGF (0.61 ± 0.14 µm/min, 0.008 ± 0.001 h^-1) compare to that by EGF alone (0.26 ± 0.13 µm/min, 0.004 ± 0.0009 h^-1). However, no changes in proliferation and migration were observed for fibroblasts among the culture conditions. Inhibition of Rho kinase resulted in the increase of the myoblast migration on the laminin-coated surface with EGF condition (0.64 ± 0.18 µm/min). Compared to the untreated conditions, myoblasts cultured on the laminin-coated surface and EGF demonstrated elongated morphology, and average cell length increase significantly. In contrast, inhibition of EGF-R resulted in the decrease of myoblast migration on the laminin coated surface with EGF supplemented condition (0.43 ± 0.05 µm/min) in comparison to the untreated control (0.53 ± 0.05 µm/min).

CONCLUSION

Laminin and EGF preferentially enhance the proliferation and migration of myoblasts, and Rho kinase and EGF-R play a role in this synergistic effect. These results will be beneficial for the propagation of skeletal muscle cells for clinical applications.

Dendritic Effects of Injectable Biodegradable Thermogels on Pharmacotherapy of Inflammatory Glaucoma-Associated Degradation of Extracellular Matrix

The development of advanced drug delivery systems with extensively sustained release and multiple functions is highly imperative for effective attenuation of the degradation of ocular extracellular matrix that is associated with inflammatory glaucoma. Here, the generation of amine-terminated polyamidoamine dendrimers in an injectable biodegradable thermogel is demonstrated to be important for achieving prolonged drug release profiles and potent anti-inflammatory effects. Among various generations (Gx, x = 0, 1, 3, 5), third-generation G3 is proved as the most effective material for optimizing the synergistic effects of gelatin and poly(N-isopropylacrylamide) and generating a thermogel with the highest biodegradation resistance, the best drug encapsulation/extended-release performance, and the best ability to reduce the elevated expression of inflammatory molecules. A pharmacotherapy based on intracameral injection of thermogels coloaded with pilocarpine and ascorbic acid results in effective alleviation of progressive glaucoma owing to the anti-inflammatory activity and long-acting drug release (above a therapeutic level of 10 µg mL^-1 over 80 days) of thermogels, which simultaneously suppress inflammation and stimulate regeneration of stromal collagen and retinal laminin. These findings on the dendritic effects of rationally designed injectable biomaterials with potent anti-inflammatory effects and controlled drug release demonstrate great promise of their use for pharmacological treatment of progressive glaucoma.

Comparison of the regeneration induced by acellular nerve allografts processed with or without chondroitinase in a rat model

There have been various studies about the acellular nerve allograft (ANA) as the alternative of autologous nerve graft in the treatment of peripheral nerve defects. As well as the decellularization process methods of ANA, the various enhancement methods of regeneration of the grafted ANA were investigated. The chondroitin sulfate proteoglycans (CSPGs) inhibit the action of laminin which is important for nerve regeneration in the extracellular matrix of nerve. Chondroitinase ABC (ChABC) has been reported that it enhances the nerve regeneration by degradation of CSPGs. The present study compared the regeneration of ANA between the processed without ChABC group and the processed with ChABC group in a rat sciatic nerve 15 mm gap model. At 12 weeks postoperatively, there was not a significant difference in the histomorphometric analysis. In the functional analysis, there were no significant differences in maximum isometric tetanic force, wet muscle weight of tibialis anterior. The processed without ChABC group had better result in ankle contracture angle significantly. In conclusion, there were no significant differences in the regeneration of ANA between the processed without ChABC group and the processed with ChABC group.

Schwann Cell Precursors; Multipotent Glial Cells in Embryonic Nerves

The cells of the neural crest, often referred to as neural crest stem cells, give rise to a number of sub-lineages, one of which is Schwann cells, the glial cells of peripheral nerves. Crest cells transform to adult Schwann cells through the generation of two well defined intermediate stages, the Schwann cell precursors (SCP) in early embryonic nerves, and immature Schwann cells (iSch) in late embryonic and perinatal nerves. SCP are formed when neural crest cells enter nascent nerves and form intimate relationships with axons, a diagnostic feature of glial cells. This involves large-scale changes in gene expression, including the activation of established glial cell markers. Like early glia in the CNS, radial glia, SCP retain developmental multipotency and contribute to other crest-derived lineages during embryonic development. SCP, as well as closely related cells termed boundary cap cells, and later stages of the Schwann cell lineage have all been implicated as the tumor initiating cell in NF1 associated neurofibromas. iSch are formed from SCP in a process that involves the appearance of additional differentiation markers, autocrine survival circuits, cellular elongation, a formation of endoneurial connective tissue and basal lamina. Finally, in peri- and post-natal nerves, iSch are reversibly induced by axon-associated signals to form the myelin and non-myelin Schwann cells of adult nerves. This review article discusses early Schwann cell development in detail and describes a large number of molecular signaling systems that control glial development in embryonic nerves.

The mechanism of neuroprotective action of natural compounds

Disturbance of cerebral redox homeostasis is the primary cause of human neurodegenerative disorders, such as Parkinson's disease or Alzheimer's disease. Well known experimental research demonstrates that oxidative stress is a main cause of cell death. A high concentration of reactive oxygen and nitrogen species leads to damage of a lot of proteins, lipids and also DNA. Synthetic compounds used for the treatment in the neurodegenerative diseases failed to meet the hopes they had raised and often exhibit a number of side effects. Therefore, in recent years interest in natural compounds derived from plants appears to be on the rise. This review describes a few natural compounds (1MeTIQ, resveratrol, curcumin, vitamin C and Gingko biloba) which revealed neuroprotective potential both in experimental studies and clinical trials. 1MeTIQ has a privileged position because, as opposed to the remaining compounds, it is an endogenous amine synthesized in human and animal brain. Based on evidence from research, it seems that a common protective mechanism for all the above-mentioned natural compounds relies on their ability to inhibit or even scavenge the excess of free radicals generated in oxidative and neurotoxin-induced processes in nerve cells of the brain. However, it was demonstrated that further different molecular processes connected with neurotoxicity (e.g. the inhibition of mitochondrial complex I, activation of caspase-3, apoptosis) follow later and are initiated by the reactive oxygen species. What is more, these natural compounds are able to inhibit further stages of apoptosis triggered by neurotoxins in the brain.

■ REVIEW : Gene Expression in Nerve Regeneration

Injury of peripheral nerve in mammals leads to a complex but stereotypical pattern of histological events that comprise a highly reproducible sequence of degenerative reactions (Wallerian degeneration) succeeded by regenerative responses. These reactions are based on a corresponding sequence of cellular and mo lecular interactions that, in turn, reflect the differential expression of specific genes with functions in nerve degeneration and repair. We report on more than 60 genes and their products that show a specific pattern of regulation following peripheral nerve lesion. The group of regulated genes encoding, e.g., transcription factors, growth factors and their receptors, cytokines, neuropeptides, myelin proteins and lipid carriers, and cytoskeletal proteins as well as extracellular matrix and cell adhesion molecules. We describe and compare the distinct time-courses and cellular origin of expression and further discuss established or putative mo lecular interrelationships and functions with respect to the contribution of these genes/gene products to the molecular regeneration program of the PNS. NEUROSCIENTIST 3:112-122, 1997

The epigenetic role of vitamin C in health and disease

Recent advances have uncovered a previously unknown function of vitamin C in epigenetic regulation. Vitamin C exists predominantly as an ascorbate anion under physiological pH conditions. Ascorbate was discovered as a cofactor for methylcytosine dioxygenases that are responsible for DNA demethylation, and also as a likely cofactor for some JmjC domain-containing histone demethylases that catalyze histone demethylation. Variation in ascorbate bioavailability thus can influence the demethylation of both DNA and histone, further leading to different phenotypic presentations. Ascorbate deficiency can be presented systematically, spatially and temporally in different tissues at the different stages of development and aging. Here, we review how ascorbate deficiency could potentially be involved in embryonic and postnatal development, and plays a role in various diseases such as neurodegeneration and cancer through epigenetic dysregulation.

Regulation of the Epigenome by Vitamin C

Emerging evidence suggests that ascorbate, the dominant form of vitamin C under physiological pH conditions, influences activity of the genome via regulating epigenomic processes. Ascorbate serves as a cofactor for Ten-eleven translocation (TET) dioxygenases that catalyze the oxidation of 5-methylcytosine (5mC) into 5-hydroxymethylcytosine (5hmC), and further to 5-formylcytosine (5fC) and to 5-carboxylcytosine (5caC), which are ultimately replaced by unmodified cytosine. The Jumonji C (JmjC)-domain-containing histone demethylases also require ascorbate as a cofactor for histone demethylation. Thus, by primarily participating in the demethylation of both DNA and histones, ascorbate appears to be a mediator of the interface between the genome and environment. Furthermore, redox status has a profound impact on the bioavailability of ascorbate in the nucleus. In order to bridge the gap between redox biology and genomics, we suggest an interdisciplinary research field that can be termed redox genomics to study dynamic redox processes in health and diseases. This review examines the evidence and potential molecular mechanism of ascorbate in the demethylation of the genome, and it highlights potential epigenetic roles of ascorbate in various diseases.

Interactive relationship between basement-membrane development and sarcomerogenesis in single cardiomyocytes

The cardiac basement membrane (BM), the highly organized layer of the extracellular matrix (ECM) on the external side of the sarcolemma, is mainly composed of laminin and collagen IV, which assemble a dense, well-organized network to surround the surface of each adult cardiomyocyte. The development of the cardiac BM plays a key role in organogenesis of the myocardium through interactions between sarcomeres and integrins. Because of the complicated structure of cardiac muscle fibers and lack of a proper investigation method, the detailed interactions among BM development, sarcomeric growth, and integrin expression remain unclear. In this study, freshly isolated 3-day neonatal cardiomyocytes (CMs) were cultured on aligned collagen, which mimics the in vivo ECM structure and induces neonatal CMs to grow into rod-like shapes. Then double fluorescence-immunostained laminin and α-actinin or integrin β1 on neonatal CMs cultured 4-72 h were imaged using a confocal microscope, and the spatial relationship between laminin deposition and α-actinin expression was evaluated by colocalization analysis. At 4h, laminin was deposited around Z-bodies (dot-shaped α-actinin) and integrins; from 18-to-72 h, its gradual colocalization with Z-lines (line-shaped α-actinin) and integrins increased Pearson׳s coefficient; this indicates that development of the BM network from the neonatal stage to adulthood is closely related to sarcomeric formation via integrin-mediated interactions.

Role of the basement membrane in regulation of cardiac electrical properties

In the heart muscle, each adult cardiomyocyte is enclosed by a basement membrane (BM). This innermost extracellular matrix is a layered assembly of laminin, collagen IV, glycoproteins, and proteoglycans. In this study, the role of the BM network in regulation of the electrical properties of neonatal cardiomyocytes (NCMs) cultured on an aligned collagen I gel was investigated using a multielectrode array (MEA). A laminin antibody was added to the culture medium for 48-120 h to conjugate newly secreted laminin. Then, morphology of the NCMs on an MEA was monitored using a phase contrast microscope, and the BM network that was immunocytostained for laminin was imaged using a fluorescence microscope. When the BM laminin was absent in this culture model, dramatic changes in NCM morphology were observed. Simultaneously, the MEA-recorded cardiac field potential showed changes compared to that from the control groups: The period of contraction shortened to 1/2 of that from the control groups, and the waveform of the calcium influx shifted from a flat plateau to a peak-like waveform, indicating that the electrical properties of the NCMs were closely related to the components and distribution of the BM network.

Recombinant spider silk with cell binding motifs for specific adherence of cells

Silk matrices have previously been shown to possess general properties governing cell viability. However, many cell types also require specific adhesion sites for successful in vitro culture. Herein, we have shown that cell binding motifs can be genetically fused to a partial spider silk protein, 4RepCT, without affecting its ability to self-assemble into stable matrices directly in a physiological-like buffer. The incorporated motifs were exposed in the formed matrices, and available for binding of integrins. Four different human primary cell types; fibroblasts, keratinocytes, endothelial cells and Schwann cells, were applied to the matrices and investigated under serum-free culture conditions. Silk matrices with cell binding motifs, especially RGD, were shown to promote early adherence of cells, which formed stress fibers and distinct focal adhesion points. Schwann cells acquired most spread-out morphology on silk matrices with IKVAV, where significantly more viable cells were found, also when compared to wells coated with laminin. This strategy is thus suitable for development of matrices that allow screening of various cell binding motifs and their effect on different cell types.

Role of fibronectin in topographical guidance of neurite extension on electrospun fibers

Bridging of long peripheral nerve gaps remains a significant clinical challenge. Electrospun nanofibers have been used to direct and enhance neurite extension in vitro and in vivo. While it is well established that oriented fibers influence neurite outgrowth and Schwann cell migration, the mechanisms by which they influence these cells are still unclear. In this study, thin films consisting of aligned poly-acrylonitrile methylacrylate (PAN-MA) fibers or solvent casted smooth, PAN-MA films were fabricated to investigate the potential role of differential protein adsorption on topography-dependent neural cell responses. Aligned nanofiber films promoted enhanced adsorption of fibronectin compared to smooth films. Studies employing function-blocking antibodies against cell adhesion motifs suggest that fibronectin plays an important role in modulating Schwann cell migration and neurite outgrowth from dorsal root ganglion (DRG) cultures. Atomic Force Microscopy demonstrated that aligned PAN-MA fibers influenced fibronectin distribution, and promoted aligned fibronectin network formation compared to smooth PAN-MA films. In the presence of topographical cues, Schwann cell-generated fibronectin matrix was also organized in a topographically sensitive manner. Together these results suggest that fibronectin adsorption mediated the ability of topographical cues to influence Schwann cell migration and neurite outgrowth. These insights are significant to the development of rational approaches to scaffold designs to bridge long peripheral nerve gaps.

The potentiation of peripheral nerve sheaths in regeneration and repair

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

The extracellular-matrix protein matrilin 2 participates in peripheral nerve regeneration

Matrilins are adaptor proteins of the extracellular matrix involved in the formation of both collagen-dependent and collagen-independent filamentous networks. Although their molecular structure and binding partners have been characterized, the functional roles of the four matrilin family members in vivo are still largely unknown. Here, we show that matrilin 2, expressed in pre-myelinating Schwann cells during normal development, profoundly influences the behaviour of glial cells and neurons in vitro. When offered as a uniform substrate, matrilin 2 increased neurite outgrowth of dorsal root ganglia (DRG) neurons and enhanced the migration of both cell line- and embryonic DRG-derived Schwann cells. Vice versa, axonal outgrowth and cell migration were decreased in DRG cultures prepared from matrilin-2-deficient mice compared with wild-type (wt) cultures. In stripe assays, matrilin 2 alone was sufficient to guide axonal growth and, interestingly, axons favoured the combination of matrilin 2 and laminin over laminin alone. In vivo, matrilin 2 was strongly upregulated in injured peripheral nerves of adult wild-type mice and failure of protein upregulation in knockout mice resulted in delayed regrowth of regenerating axons and delayed time-course of functional recovery. Strikingly, the functional recovery 2 months after nerve injury was inferior in matrilin-2-deficient mice compared with wild-type littermates, although motoneuron survival, quality of axonal regeneration, estimated by analyses of axonal diameters and degrees of myelination, and Schwann cell proliferation were not influenced by the mutation. These results show that matrilin 2 is a permissive substrate for axonal growth and cell migration, and that it is required for successful nerve regeneration.

Regulation of Schwann cell function by the extracellular matrix

Laminins and collagens are extracellular matrix proteins that play essential roles in peripheral nervous system development. Laminin signals regulate Schwann cell proliferation and survival as well as actin cytoskeleton dynamics, which are essential steps for radial sorting and myelination of peripheral axons by Schwann cells. Collagen and their receptors promote Schwann cell adhesion, spreading, and myelination as well as neurite outgrowth. In this article, we will review the recent advances in the studies of laminin and collagen function in Schwann cell development.

Laminins in peripheral nerve development and muscular dystrophy

Laminins are extracellular matrix (ECM) proteins that play an important role in cellular function and tissue morphogenesis. In the peripheral nervous system (PNS), laminins are expressed in Schwann cells and participate in their development. Mutations in laminin subunits expressed in the PNS and in skeleton muscle may cause peripheral neuropathies and muscular dystrophy in both humans and mice. Recent studies using gene knockout technology, such as cell-type specific gene targeting techniques, revealed that laminins and their receptors mediate Schwann cell and axon interactions. Schwann cells with disrupted laminin expression exhibit impaired proliferation and differentiation and also undergo apoptosis. In this review, we focus on the potential molecular mechanisms by which laminins participate in the development of Schwann cells.

Schwann cell-specific ablation of laminin gamma1 causes apoptosis and prevents proliferation

To investigate the function of laminin in peripheral nerve development, we specifically disrupted the laminin gamma1 gene in Schwann cells. Disruption of laminin gamma1 gene expression resulted in depletion of all other laminin chains known to be expressed in Schwann cells. Schwann cells lacking laminin do not extend processes required for initiating axonal sorting and mediating axon-Schwann cell interaction. They fail to downregulate Oct-6 and arrest at the premyelinating stage. The impaired axon-Schwann cell interaction prevents phosphorylation of beta-neuregulin-1 receptors and results in decreased cell proliferation. Postnatally, laminin-null Schwann cells exhibit reduced phosphatidylinositol 3 (PI3)-kinase activity and activation of caspase cascades, leading to apoptosis. Injection of a laminin peptide into mutant sciatic nerves partially restores PI3-kinase activity and reduces apoptotic signals. These results demonstrate the following: (1) that laminin initiates axonal sorting and mediates axon-Schwann cell interactions required for Schwann cell proliferation and differentiation, and (2) that laminin provides a PI3-kinase/Akt-mediated Schwann cell survival signal.

Impeded interaction between Schwann cells and axons in the absence of laminin alpha4

The Schwann cell basal lamina (BL) is required for normal myelination. Loss or mutations of BL constituents, such as laminin-2 (alpha2beta1gamma1), lead to severe neuropathic diseases affecting peripheral nerves. The function of the second known laminin present in Schwann cell BL, laminin-8 (alpha4beta1gamma1), is so far unknown. Here we show that absence of the laminin alpha4 chain, which distinguishes laminin-8 from laminin-2, leads to a disturbance in radial sorting, impaired myelination, and signs of ataxia and proprioceptive disturbances, whereas the axonal regenerative capacity is not influenced. In vitro studies show poor axon growth of spinal motoneurons on laminin-8, whereas it is extensive on laminin-2. Schwann cells, however, extend longer processes on laminin-8 than on laminin-2, and, in contrast to the interaction with laminin-2, solely use the integrin receptor alpha6beta1 in their interaction with laminin-8. Thus, laminin-2 and laminin-8 have different critical functions in peripheral nerves, mediated by different integrin receptors.

Adhesion and proliferation of human Schwann cells on adhesive coatings

Attachment to and proliferation on the substrate are deemed important considerations when Schwann cells (SCs) are to be seeded in synthetic nerve grafts. Attachment is a prerequisite for the SCs to survive and fast proliferation will yield large numbers of SCs in a short time, which appears promising for stimulation of peripheral nerve regeneration. The aim of the present study was to compare the adhesion and proliferation of human Schwann cells (HSCs) on different substrates. The following were selected for their suitability as an internal coating of synthetic nerve grafts; the extracellular matrix proteins fibronectin, laminin and collagen type I and the poly-electrolytes poly(d-lysine) (PDL) and poly(ethylene-imine) (PEI). On all coatings, attachment of HSCs was satisfactory and comparable, indicating that this factor is not a major consideration in choosing a suitable coating. Proliferation was best on fibronectin, laminin and PDL, and worst on collagen type I and PEI. Since nerve regeneration is enhanced by laminin and/or fibronectin, these are preferred as coatings for synthetic nerve grafts seeded with SCs.

Oriented astroglial cell growth on micropatterned polystyrene substrates

In an effort to develop a permissive environment for neural stem cell differentiation, directional growth of astrocytes has been achieved on polymer substrates in vitro. Manipulating a combination of physical and chemical cues, astrocyte adhesion and alignment in vitro were examined. To provide physical guidance, micropatterned polymer substrates of polystyrene (PS) were fabricated. Laminin was selectively adsorbed onto the grooves of the patterned surface. Rat type-1 astrocytes were seeded onto the micropatterned PS substrates, and the effects of substrate topography and the adsorption of laminin to the PS substrates on the behavior and morphology of the astrocytes were explored. The astrocytes were found to align parallel to the micropatterned grooves at initial seeding densities of approximately 7500, 13,000, and 20,000 cells/cm(2) due to the effects of the physical and chemical guidance mechanisms. Adsorbing laminin in the microgrooves of the micropatterned PS substrates improved cell adhesion and spreading of cytoskeletal filaments significantly. At these initial seeding densities, over 85% astrocyte alignment in the direction of the grooves was achieved on the micropatterned PS substrates with laminin adsorbed in the grooves. This combination of guidance cues has the potential to provide a permissive substrate for in vivo regeneration within the central nervous system.

Immunohistochemical and Ultrastructural Comparative Study of External Lamina Structure in 31 Cases of Cellular, Classical, and Melanotic Schwannomas

Unlike most soft tissue tumors, schwannoma is characterized by the presence of distinct linear, frequently duplicated external lamina (EL). Although electron microscopy remains the gold standard for demonstrating this unique feature and distinguishing its morphologic variants from mimickers, the use of two anti-EL antibodies, laminin and type IV collagen, appears to supersede electron microscopy in terms of current practice. To determine whether immunohistochemical expression correlates with ultrastructural findings, 10 cellular schwannomas, 18 classic schwannomas, and 3 melanotic schwannomas were evaluated ultrastructurally and immunohistochemically using antibodies to type IV collagen and laminin. Immunohistochemically, a moderate to strong intensity in more than 50% of tumor cells was detected using either antibody in most cases of cellular schwannomas (70%), the Antoni A areas of classic schwannomas (78%), and melanotic schwannomas (67%). Ultrastructurally, the presence of diffusely continuous, duplicated EL was observed in 30% of cellular schwannomas and 56% of classic schwannomas, while 50% of cellular schwannomas and 22% of classic schwannomas showed either continuous simple EL or discontinuous but duplicated EL alone. In addition, two cellular schwannomas (20%) and four classic schwannomas (22.2%) had only a simple layer of EL in focal areas. In contrast to the distinct immunostaining surrounding individual cells seen in the former two subtypes, all three melanotic schwannomas displayed a biphasic-staining pattern of the EL (ie, individual cell and nested), which was confirmed at the ultrastructural level. The authors found a significant difference in intensity between the Antoni A and B areas of classic schwannomas using both laminin and type IV collagen. In addition, the intensities of laminin and type IV collagen in the Antoni A areas of classic schwannomas were significantly stronger compared with those of cellular schwannomas. Nevertheless, there was no significant difference either between two antibodies or between cellular and classic variants with regard to the extent of immunoreaction. Only in classic schwannomas did the extent of immunoreaction against both laminin and type IV collagen correlate significantly with the ultrastructural EL distribution pattern (diffusely continuous vs. discontinuous). However, this association was not detected in cases of cellular schwannomas. On the other hand, the intensities of laminin and type IV collagen did not correlate with the ultrastructural thickness of EL, irrespective of the morphologic subtypes. In conclusion, both type collagen IV and laminin are still reliable markers of EL in various types of schwannomas. Schwannomas exhibiting a monolayered EL are as strong in immunoreaction as those displaying reduplicated/thickened EL, indicating that a single layer of EL is thick enough to be identified by both antibodies with sufficient sensitivity. The peculiar biphasic EL pattern seen in melanotic schwannoma remains under-recognized, which may lead to misdiagnosis as malignant melanomas, especially in limited biopsy specimens.

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

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

Microglia enhance dorsal root ganglion outgrowth in Schwann cell cultures

Transplantation of cellular populations to facilitate regrowth of damaged axons is a common experimental therapy for spinal cord injury. Schwann cells (SC) or microglia grafted into injury sites can promote axonal regrowth of central projections of dorsal root ganglion (DRG) sensory neurons. We sought to determine whether the addition of microglia or microglia-derived secretory products alters DRG axon regrowth upon cultures of SC. Rat DRG explants were grown on monolayers consisting of either SC, microglia, SC exposed to microglia-conditioned medium (MCM), or co-cultures with different relative concentrations of microglia. Image analysis revealed that, compared to SC alone, the extent of neurite outgrowth was significantly greater on SC-microglia co-cultures. Immunocytochemistry for extracellular matrix molecules showed that microglial cells stained positively for growth-promoting thrombospondin, whereas laminin and the inhibitory chondroitin sulfate proteoglycans (CSPGs) were localized primarily to SC. Notably, immunoreactivity for CSPGs appeared reduced in areas associated with DRG outgrowth in co-cultures and SC exposed to MCM. These results show that microglia or their secreted products can augment SC-mediated DRG regrowth in vitro, indicating that co-grafting SC with microglia provides a novel approach to augment sensory fiber regeneration after spinal cord injury.

Delayed rectifier K currents in NF1 Schwann cells. Pharmacological block inhibits proliferation

K+(K) currents are related to the proliferation of many cell types and have a relationship to second messenger pathways implicated in regulation of the cell cycle in development and certain disease states. We examined the role of K currents in Schwann cells (SC) cultured from tumors that arise in the human disease neurofibromatosis type 1 (NF1). Comparisons were made between whole cell voltage clamp recordings from normal human SC cultures and from neurofibroma cultures and malignant peripheral nerve sheath tumor (MPNST) cell lines. The outward K currents of normal and tumor cells could be divided into three types based on pharmacology and macroscopic inactivation: (1) "A type" current blocked by 4-aminopyridine, (2) delayed rectifier (DR) current blocked by tetraethylammonium, and (3) biphasic current consisting of a combination of these two current types. The DR K current was present in MPNST- and neurofibroma-derived SC, but not in quiescent, nondividing, normal SC. DR currents were largest in MPNST-derived SC (50 pA/pF vs. 2.1-4.9 pA/pF in dividing and quiescent normal SC). Normal SC cultures had significantly more cells with A type current than cultures of MPNST and the plexiform neurofibroma. Conversely, MPNST and plexiform neurofibroma cultures had significantly more SC with DR current than did normal cultures, and these DR currents were significantly larger. In addition, the plexiform neurofibroma culture had significantly more cells with DR current than the dermal neurofibroma culture. K currents in SC from normal NF1 SC cultures had current abundances similar to GGF-exposed normal SC and the plexiform neurofibroma. We have established a link between DR K current blockade via TEA analogs and inhibition of proliferation of NF1 SC in vitro. In addition, a farnysyl transferase inhibitor (FTI), a blocker of Ras activation, blocked cell proliferation without blocking K currents in all cultures except a plexiform neurofibroma, suggesting that regulation of proliferation in neoplastic and normal SC in vitro is complex.

Laminin chains in rat and human peripheral nerve: distribution and regulation during development and after axonal injury

During nerve growth, axons are dependent upon contact with matrix components, such as laminins, for elongation, guidance, and trophic support. Semiquantitative in situ hybridization histochemistry and immunohistochemistry (IHC) were used to identify laminin chains in normal peripheral nerves, during postnatal development, after sciatic nerve transection (SNT), and after sciatic nerve crush (SNC). Laminin alpha2, alpha4, beta1, beta2, and gamma1 chain mRNAs were all expressed at high levels in newborn rat sciatic nerves with declining levels during later developmental stages. At the adult stage, no laminin chain mRNA was detectable. Of interest, the mRNA levels for alpha4 chain declined faster than those for alpha2. After SNT, laminin alpha2, alpha4, beta1, and gamma1 mRNA levels were up-regulated at the site of the injury, with the most profound reaction in the proximal nerve stump. Laminin alpha2 and alpha4 chains differed in that the mRNA levels of alpha4 were up-regulated earlier and declined quicker, whereas alpha2 had a later onset, with high levels remaining even after 6 weeks. After SNC, there was an initial up-regulation of the same laminin chain mRNAs as after SNT in the nerve, however, less intense, and at 6 weeks after SNC, all laminin mRNA levels studied had returned to normal. IHC of adult human normal and transected peripheral nerves stained positive for laminin alpha2, alpha4, beta1, and gamma1 chains in close relation to neurofilament labeled axons. Laminin alpha3, alpha4, alpha5, beta1, beta2, and gamma1 chains were found in blood vessel-like structures and alpha3, alpha4, alpha5, beta2, and gamma1 in the perineurium. These results and a previously published description of integrin regulation in spinal motoneurons suggest that both laminin-2 (alpha2beta1gamma1) and laminin-8 (alpha4beta1gamma1) are important for the postnatal nerve development and axonal regeneration after injury and that laminin-8 may have important functions especially early postnatally and early after adult nerve lesion.

Expression of dystroglycan and the laminin-alpha 2 chain in the rat peripheral nerve during development

In Schwann cells, the transmembrane glycoprotein beta-dystroglycan comprises the dystroglycan complex, together with the extracellular glycoprotein alpha-dystroglycan, which binds laminin-2 (alpha 2/beta 1/gamma 1), a major component of the Schwann cell basal lamina. To provide clues to the biological functions of the interaction of the dystroglycan complex with laminin-2 in peripheral nerves, we investigated the expression of beta-dystroglycan and the laminin-alpha 2 chain in rat sciatic nerve during development by immunoblot, immunofluorescence, and immunoelectron microscopic studies. The expression of beta-dystroglycan and the laminin-alpha 2 chain in the rat sciatic nerve was low and not confined to the Schwann cell outer membrane from embryonic day 18 to birth, when there was only an immature basal lamina assembly and no compact myelin formation by Schwann cells. However, the expression of these proteins increased markedly and became clearly localized to the Schwann cell outer membrane between birth and postnatal day 7, when both basal lamina assembly and compact myelin formation by Schwann cells progressed rapidly. From postnatal day 7 to adult, there was no remarkable change in the expression of these proteins. Our results support the hypothesis that the dystroglycan complex functions as an adhesion apparatus, binding the Schwann cell outer membrane with the basal lamina, and suggest that the dystroglycan complex plays a role in Schwann cell myelination through its interaction with laminin-2.

Contraction of collagen-glycosaminoglycan matrices by peripheral nerve cells in vitro

The objective of this study was to investigate the contractile behavior of peripheral nerve support cells in collagen-glycosaminoglycan (GAG) matrices in vitro. Contractile fibroblasts (myofibroblasts) are known to participate in wound contraction during healing of selected connective tissues (viz., dermis), but little is known about the activity of non-muscle contractile cells during healing of peripheral nerves. Explants from adult rat sciatic nerves were placed onto collagen-GAG matrix disks and maintained in culture for up to 30 days. Groups of collagen-GAG matrices were tested that differed in average pore diameter and in degree of cross-linking. Cell migration from nerve explants into the matrices was examined, and immunohistochemical staining was used to identify cells expressing a contractile actin isoform (alpha-smooth muscle actin; alpha-SMA) and Schwann cells (S-100). Geometric contraction of matrix disks was quantified every five days as the percent reduction in disk diameter. The amount of contraction of matrix disks was significantly affected by the degree of cross-linking. Cell migration into the matrices and the distribution of cells staining for alpha-SMA or S-100 was not affected by matrix parameters. These studies demonstrate that cells from peripheral nerve explants were capable of adopting a contractile phenotype and causing geometric contraction of matrices in vitro and suggest that contractile processes may be important during nerve wound healing in vivo.

Schwann cell type V collagen inhibits axonal outgrowth and promotes Schwann cell migration via distinct adhesive activities of the collagen and noncollagen domains

Previously, we reported the cloning of alpha4 type V collagen, a novel member of the collagen type V gene family that is expressed by Schwann cells in developing peripheral nerves (Chernousov et al., 2000). The present study was performed to investigate the effects of this collagen on the adhesion and migration of premyelinating Schwann cells and neurite outgrowth from embryonic dorsal root ganglion neurons. Purified alpha4(V)-containing collagen isolated from Schwann cell conditioned medium (collagen type V(SC)) promoted migration of Schwann cells but inhibited outgrowth of axons from rat embryo dorsal root ganglia. Collagen type V(SC) blocked axonal outgrowth in the presence of otherwise active substrates such as collagen type IV, indicative of active inhibition. The noncollagen N-terminal domain of alpha4(V) promoted Schwann cell adhesion, spreading, and migration. These processes were inhibited by soluble heparin but not by function-blocking antibodies against alpha1- and alpha2-integrins. The collagen domain of pepsin-digested collagen type V was poorly adhesive for Schwann cells. The type V collagen domain but not the alpha4(V) N-terminal domain blocked neurite outgrowth from dorsal root ganglion neurons. In cocultures of dorsal root ganglion neurons and Schwann cells, collagen type V(SC) promoted axon fasciculation and association of axons with Schwann cells. These results suggest that in embryonic peripheral nerves, collagen type V(SC) plays a dual role in regulating cell migration. This represents a heretofore unrecognized function of peripheral nerve collagen fibrils in regulating patterns of peripheral nerve growth during development.

A comparison of caveolae and caveolin-1 to folate receptor alpha in retina and retinal pigment epithelium

Caveolae are flask-shaped membrane invaginations present in most mammalian cells. They are distinguished by the presence of a striated coat composed of the protein, caveolin. Caveolae have been implicated in numerous cellular processes, including potocytosis in which caveolae are hypothesized to co-localize with folate receptor alpha and participate in folate uptake. Our laboratory has recently localized folate receptor alpha to the basolateral surface of the retinal pigment epithelium (RPE). It is present also in many other cells of the retina. In the present study, we asked whether caveolae were present in the RPE, and if so, whether their pattern of distribution was similar to folate receptor alpha. We also examined the distribution pattern of caveolin-1, which can be a marker of caveolae. Extensive electron microscopical analysis revealed caveolae associated with endothelial cells. However, none were detected in intact or cultured RPE. Laser scanning confocal microscopical analysis of intact RPE localized caveolin-1 to the apical and basal surfaces, a distribution unlike folate receptor alpha. Western analysis confirmed the presence of caveolin-1 in cultured RPE cells and laser scanning confocal microscopy localized the protein to the basal plasma membrane of the RPE, a distribution like that of folate receptor alpha. This distribution was confirmed by electron microscopic immunolocalization. The lack of caveolae in the RPE suggests that these structures may not be essential for folate internalization in the RPE.

Attachment of A-431 cells on immobilized antibodies to the EGF receptor promotes cell spreading and reorganization of the microfilament system

EGF-like sequences, inherent in a number of extracellular matrix proteins, participate in cell adhesion. It is possible that interactions of these sequences with EGF receptors (EGFR) affect actin filament organization. It was shown previously [Khrebtukova et al., 1991: Exp. Cell Res. 194:48-55] that antibodies specific to EGFR induce capping of these receptors and redistribution of cytoskeletal proteins in A-431 cells. Here we report that A-431 cells attach and spread on solid substrata coated with antibodies to EGFR, even in the absence of serum. Thus, EGFR can act as an adhesion protein and promote microfilament reorganization. Binding of the cells to the EGFR-antibody resulted in the formation of a unique cell shape characterized by numerous, actin-based filopodia radiating from the cell body, but without membrane ruffles. There was also a conspicuous circular belt of actin-containing fibers inside the cell margin, and many irregular actin aggregates in the perinuclear area. The morphologies and actin distributions in A-431 cells spread on fibronectin or laminin 2/4 were very different. On fibronectin, cells had polygonal shapes with numerous stress-fibers and thick actin-containing fibers along the cell edges. On laminin-covered substrata, the cells became fusiform and acquired broad leading lamellae with ruffles. In these cells, there were also a few bundles of filaments running the whole length of the cell body, and shorter bundles extending through the leading lamellae towards the membrane ruffles in the cell edge. These effects and those seen with immobilized EGF suggest that different ligand/receptor complexes induce specific reorganizations of the microfilament system.

Schwannosis: role of gliosis and proteoglycan in human spinal cord injury

Schwannosis (aberrant proliferation of Schwann cells and nerve fibers) has been reported following spinal cord injury (SCI). In this study, we examined the incidence of schwannosis following human SCI, and investigated its relationship to gliosis. We found evidence of schwannosis in 32 out of 65 cases (48%) of human SCI that survived 24 h to 24 years after injury; this incidence rose to 82% in those patients who survived for more than 4 months. Schwannosis was not observed in cases that survived less than 4 months after injury. In affected cases, it was generally noted in areas that had low immunoreactivity for glial fibrillary acidic protein (GFAP), suggesting that reduced gliosis might have contributed to the aberrant proliferation of Schwann cells following SCI. Since chondroitin sulfate proteoglycan (CSPG) has been proposed to play a role in Schwann cell/glial interaction, we performed immunohistochemical staining for CSPG to investigate its potential relationship with schwannosis. CSPG in the injured cord was generally associated with the blood vessel walls, but was also sometimes noted in reactive astrocytes. In SCI with schwannosis, CSPG staining was more prominent and confined largely to the extracellular matrix and basal lamina of proliferating Schwann cells. Our study suggests that Schwann cells, which may have been displaced from spinal roots and introduced into the injured cord through a break in the pial surface, are capable of proliferating and producing CSPG, particularly in the setting of reduced gliosis. Since CSPG has been associated with inhibition of neurite outgrowth, its increased production by aberrant Schwann cells may impair spinal cord regeneration after injury.

p200, a collagen secreted by Schwann cells, is expressed in developing nerves and in adult nerves following axotomy

Previously we reported that cultured rat Schwann cells secrete p200, a collagen-like heparin-binding adhesive glycoprotein with a restricted pattern of expression. Here we report that p200 is secreted as a stable trimer, but only after treatment of Schwann cells with ascorbic acid, and was deposited in the fibrillar extracellular matrix. Heparin and heparitinase treatment inhibited incorporation of p200 into extracellular matrix, suggesting the involvement of Schwann cell heparan sulfate proteoglycans in this process. Pepsin digestion revealed that p200 secreted by ascorbate-treated cells contains a collagenous domain of approximately 140 kDa. Immunofluorescent staining of rat embryos at different ages showed that p200 first appeared between embryonic days 15 and 18, and was confined to peripheral nerves. Staining of adult peripheral nerve was negative, but p200 expression was induced in adult sciatic nerve following nerve transection. These data suggest that p200 carries out unique functions during peripheral nerve development and regeneration and that its expression by Schwann cells is regulated by axon-Schwann cell interaction.

Schwann cells use a novel collagen-dependent mechanism for fibronectin fibril assembly

Cultured rat Schwann cells were stimulated to deposit fibrillar extracellular matrix by treatment with ascorbic acid in the absence of nerve cells. Immunofluoresence staining of the matrix showed that it contains collagens types I and IV, fibronectin and perlecan but not laminin. Collagen type IV, fibronectin and perlecan co-distributed completely in the matrix fibrils, whereas collagen type I was present in only a subset of these fibrils. Time course studies indicated that collagen type I fibrils appear at late stages of matrix formation. Digestion of Schwann cell extracellular matrix with collagenase effectively disrupted most of the matrix including fibronectin fibrils. This was in contrast with fibroblasts, where collagenase treatment removed collagen with no visible effect on fibronectin fibrils. alpha5 integrin was expressed on the cell surface of Schwann cells and partially codistributed with fibronectin-containing fibrils. This suggests that the inability of Schwann cells to deposit fibronectin-containing matrix through a conventional, collagen-independent mechanism was not due to the lack of fibronectin-binding integrins on their cell surface. Polyclonal anti-fibronectin antibodies inhibited the deposition of fibronectin into the matrix fibrils, whereas collagen type IV fibrils were generally unaffected. Growth of Schwann cells on collagen type IV-coated substrate in the absence of ascorbate induced deposition of fine fibronectin fibrils. These results suggest that Schwann cells use an apparently novel, collagen type IV-dependent mechanism for the deposition of fibronectin into their extracellular matrix.

Effects of transforming growth factor-beta1 and basic fibroblast growth factor on proliferation of cell cultures derived from human vestibular nerve schwannoma

The influence of transforming growth factor-beta1 (TGF-beta1) and basic fibroblast growth factor (bFGF) on growth of cell cultures derived from unilateral vestibular nerve schwannomas was investigated. Cell cultures were initiated from 9 schwannomas and characterized immunocytochemically with antibodies against S-100 and type IV collagen. The effects of TGF-beta1 and bFGF on DNA synthesis in chemically defined serum-free medium were assessed by measuring the incorporation of 5-bromo-2'-deoxy-uridine (BRDU) into cellular DNA. Cell proliferation was evaluated with an electronic cell counter. Reverse transcription polymerase chain reaction (RT-PCR) was performed using oligonucleotide primers specific for TGF-beta1 and TGF-beta2. TGF-beta1 stimulated DNA synthesis in a dose dependent manner. Maximal stimulation was observed at a concentration of 1 ng/ml, which induced a nearly 2-fold increase in DNA content. This effect was not seen when TGF-beta1 was added in the presence of neutralizing antibodies. In addition, antibodies against TGF-beta1 significantly reduced DNA synthesis in control cultures without supplemented exogenous growth factors. bFGF alone had no significant effects on DNA synthesis. In contrast, when TGF-beta1 and bFGF were added together, the mitogenic response was much greater than produced by TGF-beta1 alone. RT-PCR showed that the cultured cells expressed mRNA for both TGF-beta1 and TGF-beta2. We hypothesize that TGF-beta1 is an autocrine growth factor for human vestibular nerve schwannomas in culture. A similar mechanism might be involved in the growth of these tumors in situ.

Role of axonal components during myelination

Myelination is a multistep ordered process whereby Schwann cells in the peripheral nervous system (PNS) and oligodendrocytes in the central nervous system (CNS), produce and extend membranous processes that envelop axons. Mechanisms that regulate this complex process are not well understood. Advances in deciphering the regulatory components of myelination have been carried out primarily in the PNS and although the mechanisms for triggering and directing myelination are not known, it is well established that myelination does not occur in the absence of axons or axon/neuron-derived factors. This appears to be true both in PNS and CNS. Progress in understanding CNS myelinogenesis has been relatively slow because of the unavailability of a suitable culture system, which, in turn, is partly due to complexity in the cellular organization of the CNS. Though the myelin composition differs between PNS and CNS, the regulation of myelination seems to parallel rather than differ between these two systems. This article reviews the regulatory role of axonal components during myelination. The first half consists of an overview of in vitro and in vivo studies carried out in the nervous system. The second half discusses the use of a cerebellar slice culture system and generation of anti-axolemma monoclonal antibodies to investigate the role of axonal membrane components that participate in myelination. It also describes the characterization of an axonal protein involved in myelination.

Activity of cyclic AMP phosphodiesterases and adenylyl cyclase in peripheral nerve after crush and permanent transection injuries

Recent studies demonstrate that cAMP levels are tightly controlled during demyelination and remyelination in Schwann cells as cAMP decreases to 8-10% of normal following both sciatic nerve crush or permanent transection injury and only begins to increase in the crushed nerve after remyelination (Poduslo, J. F., Walikonis, R. S., Domec, M., Berg, C. T., and Holtz-Heppelmann, C. J. (1995) J. Neurochem. 65, 149-159). To investigate the mechanisms responsible for this change in cAMP levels, cAMP phosphodiesterase (PDE) and adenylyl cyclase activities were determined before and after sciatic nerve injury. Basal cAMP PDE activity in soluble endoneurial homogenates of normal nerve was 34.9 +/- 1.9 pmol/mg of protein/min (chi +/- S.E.; n = 10). This activity increased about 3-fold within 6 days following both injuries. Basal PDE activity remained elevated in the transected nerve, but declined to 70 pmol/mg of protein/min in the crushed nerve at 21 and 35 days following injury. Isozyme-specific inhibitors and stimulators were used to identify the PDE families in the sciatic nerve. The low Km cAMP-specific (PDE4) and the Ca2+/calmodulin-stimulated (PDE1) families were found to predominate in assays using endoneurial homogenates. The PDE4 inhibitor rolipram also increased cAMP levels significantly after incubation of endoneurial tissue with various isozyme-specific inhibitors, indicating that PDE4 plays a major role in determining cAMP levels. PDE4 mRNA was localized by in situ hybridization to cells identified as Schwann cells by colabeling of S100, a Schwann cell specific protein. Adenylyl cyclase activity declined following injury, from 3.7 pmol/mg of protein/min in normal nerve to 0.70 pmol/mg/min by 7 days following injury. Both decreased synthesis and increased degradation contribute, therefore, to the reduced levels of cAMP following peripheral nerve injury and are likely critical to the process of Wallerian degeneration.

Which direction do nevus cells move? Abtropfung reexamined

In 1893, Unna published his theory of Abtropfung in which he suggested that melanocytic nevus cells originate in the epidermis and drop off into the dermis. We studied 3,534 nevi from patients of all ages to reassess this almost sacred concept. If Unna was correct, one would expect that in childhood most nevi would be junctional, while in late adult life almost all nevi would be intradermal. In our series, no child under age 10 had a purely junctional nevus, 52% had compound nevi, and 48% had dermal nevi. In patients older than age 60, 12% had junctional nevi, 23% had compound nevi, and 65% had dermal nevi. Our data fail to support the concept of Abtropfung; they fit better with the contradictory theory of upward migration of nevus cells.

Insulin-like growth factor-I (IGF-I) and IGF binding protein-5 in Schwann cell differentiation

Schwann cells (SCs) are the myelin producing cells of the peripheral nervous system. During development, SCs cease proliferation and differentiate into either a myelin-forming or non-myelin forming mature phenotype. We are interested in the role of insulin-like growth factor-I (IGF-I) in SC development. We have shown previously SCs proliferate in response to IGF-I in vitro. In the current study, we investigated the role of IGF-I in SC differentiation. SC differentiation was determined by morphological criteria and expression of myelin proteins. Addition of 1 mM 8-bromo cyclic AMP (cAMP) or growth on Matrigel matrix decreased proliferation and induced differentiation of SCs. IGF-I enhanced both cAMP and Matrigel matrix-induced SC differentiation, as assessed by both morphological criteria and myelin gene expression. Cultured SCs also express IGF binding protein-5 (IGFBP-5), which can modulate the actions of IGF-I. We examined the expression of IGFBP-5 during SC differentiation. Both cAMP and Matrigel matrix treatment enhanced IGFBP-5 protein expression and cAMP increased IGFBP-5 gene expression five fold. These findings suggest IGF-I potentiates SC differentiation. The concomitant up-regulation of IGFBP-5 may play a role in targeting IGF-I to SCs and thus increase local IGF-I bioavailability.

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.

Role of extracellular matrix proteins in regulation of human glioma cell invasion in vitro

Primary brain tumors lack the metastatic behavior that is in part believed to be promoted by the extracellular matrix (ECM) components of the basement membrane. This study was intended to examine the influence of the ECM components present in the basement membrane that may act as natural barriers to tumor cell invasion. We examined the effect of type I and type IV collagens, fibronectin, laminin, and hyaluronic acid on the migration and invasion of four established glioblastoma cell lines, SNB19, U251, UWR1, and UWR2. Lower concentrations of all the ECM components induced the migration and invasion of all the cell lines. However, in the case of SNB19, laminin inhibited both migration and invasion in a concentration-dependent manner. We have also examined the influence of individual ECM components on the migration of cells from a spheroid to a monolayer on ECM component-coated coverslips. Consistent with the invasion studies using the modified Boyden chamber assays, lower concentrations of ECM components induced the migration of cells from spheroids to monolayer. Again, laminin inhibited the migration of cells from SNB19 spheroids. These results indicate that ECM components induce the invasion of glioma cells, apart from components like laminin, which may act as natural inhibitors.

Extracellular matrix upregulates synthesis of glucosylceramide-based glycosphingolipids in primary Schwann cells

The formation of basement membrane around Schwann cells that are in contact with axons is necessary for Schwann cell differentiation and myelin formation in the peripheral nervous system. However, primary Schwann cells grown on basement membrane in the absence of neuronal influence show increased proliferation rather than differentiation, which implies that the signals generated by Schwann cell-basement membrane interactions are multipotential. We examined the effect of matrigel, an exogenous basement membrane preparation, and other extracellular matrix growth surfaces on primary Schwann cells to determine if the resulting interactions play a role in the control of glycosphingolipid synthesis. Isolated primary Schwann cells grown on a thin layer of matrigel rapidly adhered to the surface and exhibited a greater degree of cell spreading when compared to cells grown on the nonspecific substrate polylysine. Labeling of the cells with [3H]galactose between 24 and 48 hr after plating revealed that the incorporation of [3H]galactose into glucosylceramide-based glycosphingolipids increased from 1.5-3-fold on matrigel in comparison to cells grown on polylysine. The major labeled glycolipids under both conditions were GM3 ganglioside and two neutral glycolipids that comigrated with GbOse4Cer (GalNAc beta 1-3Gal alpha 1-4Gal beta 1-1Cer) and GbOse5Cer (GalNAc alpha 1-3Gal-NAc beta 1-3Gal alpha 1-4Gal beta 1-4Glc beta 1-1Cer) standards. There was little or no increase in the incorporation of [3H]leucine, [3H]galactose, or [3H]glucosamine into proteins or [3H]palmitic acid into phospholipids, free ceramides, or sphingomyelin, suggesting that the matrigel-induced increase in the synthesis of the glycolipids was selective. In the absence of serum, there was little or no difference in the levels of glycolipid labeling between cells grown on the two substrata, demonstrating that serum factors were required for matrigel to have this effect. When cells were grown on surfaces coated with individual extracellular matrix components, those cells grown on laminin and collagen IV showed an increase in glycolipid labeling similar to that produced by matrigel, while labeling increased to a lesser degree for the other components tested. Thus, the signals generated by interactions between Schwann cells and basement membrane, particularly the laminin and collagen IV constituents, contribute to the regulation of glycolipid synthesis which in turn may affect cell morphology and proliferation.

Schwann cells secrete a novel collagen-like adhesive protein that binds N-syndecan

A heparin-binding glycoprotein was purified from conditioned medium of cultured rat Schwann cells. The protein, p200, which has an apparent molecular mass of approximately 200 kDa, was identified by its ability to bind the cell surface heparan sulfate proteoglycan N-syndecan (syndecan-3) in a membrane overlay assay. Soluble heparin but not chondroitin sulfate inhibited the binding, suggesting the involvement of heparan sulfate chains of proteoglycan in the interaction. Purified p200 promoted the attachment and spreading of Schwann cells. Adhesion to p200 was blocked by heparin, suggesting that heparan sulfate proteoglycans are cell surface receptors for p200. The tissue distribution of p200 was determined by immunoblot analysis with anti-p200 antibodies. Among neonatal rat tissues examined p200 was detected only in sciatic nerve and, at lower levels, in skeletal muscle. p200 expression in sciatic nerve was detectable only during the first 2-3 weeks of postnatal development and was not detected in adult rats. Immunofluorescent staining of rat sciatic nerve showed that p200 was localized in the extracellular matrix surrounding individual Schwann cells-axon units. Two tryptic peptides from p200 were purified and sequenced. These contained multiple GXX collagen-like repeats. Bacterial collagenase digestion of p200 produced a product with an apparent molecular mass of approximately 90 kDa. These data suggest that Schwann cells secrete an apparently novel collagen-like adhesive protein that interacts with cells through cell surface heparan sulfate proteoglycans.

Immunohistochemical localization of extracellular matrix proteins in human glioma, both in vivo and in vitro

Expression of type IV collagen, fibronectin and laminin in various types of primary human brain tumor sections and normal brain tissue sections as well as cultured glioma cell lines was examined by an immunofluorescence technique. Type IV collagen, fibronectin, and laminin were mainly localized to the basement membrane of the vasculature in glioblastoma, anaplastic astrocytoma, low grade glioma, and in normal brain. However, positive staining for all the extracellular matrix (ECM) components tested was found only in glioblastoma sections both in the cells and in the ECM. In all other tumor types and in normal brain tissue, the cells did not stain for any of the ECM components. Four glioblastoma cell lines and autologous ECM synthesized by respective glioblastoma cell lines also showed positive staining for type IV collagen, fibronectin and laminin in vitro. These results suggest that glioblastoma cells both in vitro and in vivo express the extracellular matrix components that are involved in the regulation of tumor cell invasion.

Specific induction of cell motility on laminin by alpha 7 integrin

Laminin, the major glycoprotein of basement membranes, actively supports cell migration in development, tissue repair, tumor growth, metastasis, and other pathological processes. Previously we have shown that the locomotion of murine skeletal myoblasts is specifically and significantly enhanced on laminin but not on other matrix proteins. One of the major laminin receptors of myoblasts is the alpha 7 beta 1 integrin, which was first described in human MeWo melanoma cells and Rugli glioblastoma cells. In order to investigate and directly test the role of the alpha 7 integrin in cell migration on laminin, we expressed the murine alpha 7B splice variant in human 293 kidney cells and 530 melanoma cells which cannot migrate on laminin and are devoid of endogenous alpha 7. Northern blotting of the transfected cells showed that the alpha 7 mRNA was expressed efficiently, and the protein was detected on the cell surface by immunofluorescence and fluorescence-activated cell sorter analysis. Cell motility measurements by computer-assisted time-lapse videomicroscopy of the alpha 7-transfected cells revealed an 8-10-fold increase in motility on laminin-1 and its E8 fragment, but not on fibronectin. Mock-transfected cells did not migrate significantly of alpha 7-transfected 293 cells through laminin-coated filters in a Boyden chamber assay was significantly enhanced in comparison to mock transfected cells. These findings prove that alpha 7 integrin expression confers a gain of function-motile phenotype to immobile cells and may be responsible for transduction of the laminin-induced cell motility.