Proliferation and differentiation of a transfected Schwann cell line is altered by an artificial basement membrane

Systematic Comparison of Commercial Hydrogels Revealed That a Synergy of Laminin and Strain-Stiffening Promotes Directed Migration of Neural Cells

Hydrogels have shown potential in replacing damaged nerve tissue, but the ideal hydrogel is yet to be found. In this study, various commercially available hydrogels were compared. Schwann cells, fibroblasts, and dorsal root ganglia neurons were seeded on the hydrogels, and their morphology, viability, proliferation, and migration were examined. Additionally, detailed analyses of the gels' rheological properties and topography were conducted. Our results demonstrate vast differences on cell elongation and directed migration on the hydrogels. Laminin was identified as the driver behind cell elongation and in combination with a porous, fibrous, and strain-stiffening matrix structure responsible for oriented cell motility. This study improves our understanding of cell-matrix interactions and thereby facilitates tailored fabrication of hydrogels in the future.

Generation of Microtumors Using 3D Human Biogel Culture System and Patient-derived Glioblastoma Cells for Kinomic Profiling and Drug Response Testing

The use of patient-derived xenografts for modeling cancers has provided important insight into cancer biology and drug responsiveness. However, they are time consuming, expensive, and labor intensive. To overcome these obstacles, many research groups have turned to spheroid cultures of cancer cells. While useful, tumor spheroids or aggregates do not replicate cell-matrix interactions as found in vivo. As such, three-dimensional (3D) culture approaches utilizing an extracellular matrix scaffold provide a more realistic model system for investigation. Starting from subcutaneous or intracranial xenografts, tumor tissue is dissociated into a single cell suspension akin to cancer stem cell neurospheres. These cells are then embedded into a human-derived extracellular matrix, 3D human biogel, to generate a large number of microtumors. Interestingly, microtumors can be cultured for about a month with high viability and can be used for drug response testing using standard cytotoxicity assays such as 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and live cell imaging using Calcein-AM. Moreover, they can be analyzed via immunohistochemistry or harvested for molecular profiling, such as array-based high-throughput kinomic profiling, which is detailed here as well. 3D microtumors, thus, represent a versatile high-throughput model system that can more closely replicate in vivo tumor biology than traditional approaches.

Nerve regeneration with aid of nanotechnology and cellular engineering

Repairing nerve defects with large gaps remains one of the most operative challenges for surgeons. Incomplete recovery from peripheral nerve injuries can produce a diversity of negative outcomes, including numbness, impairment of sensory or motor function, possibility of developing chronic pain, and devastating permanent disability. In the last few years, numerous microsurgical techniques, such as coaptation, nerve autograft, and different biological or polymeric nerve conduits, have been developed to reconstruct a long segment of damaged peripheral nerve. A few of these techniques are promising and have become popular among surgeons. Advancements in the field of tissue engineering have led to development of synthetic nerve conduits as an alternative for the nerve autograft technique, which is the current practice to bridge nerve defects with gaps larger than 30 mm. However, to date, despite significant progress in this field, no material has been found to be an ideal alternative to the nerve autograft. This article briefly reviews major up-to-date published studies using different materials as an alternative to the nerve autograft to bridge peripheral nerve gaps in an attempt to assess their ability to support and enhance nerve regeneration and their prospective drawbacks, and also highlights the promising hope for nerve regeneration with the next generation of nerve conduits, which has been significantly enhanced with the tissue engineering approach, especially with the aid of nanotechnology in development of the three-dimensional scaffold. The goal is to determine potential alternatives for nerve regeneration and repair that are simply and directly applicable in clinical conditions.

Matrigel supports survival and neuronal differentiation of grafted embryonic stem cell-derived neural precursor cells

Cell replacement therapy holds great promise as a means of treating neurological disorders, including Parkinson's disease. However, one of the major obstacles to the success of this treatment is the low survival rate of grafted cells, which probably results from mechanical damage, acute inflammation, and immunological rejection. To overcome this problem, we investigated the effect of different types of extracellular matrix (ECM) on the survival and differentiation of embryonic stem (ES) cell-derived neural precursor cells (NPCs). We tested materials from natural sources, including collagen, ornithine/laminin, and growth factor-reduced Matrigel (gfrMG), as well as the synthetic biomaterial PuraMatrix, which consists of self-assembling polypeptides. GfrMG efficiently supported cell survival, migration, and neurite outgrowth in vitro and promoted proliferation of grafted cells in vivo, resulting in larger graft volume and an increase in the number of TH-positive dopaminergic neurons in the graft. GfrMG did not induce dopaminergic differentiation directly; rather, it reduced the invasion of pan-leukocytic CD45-positive cells into the graft. Insofar as the inflammatory or immune response in the host brain inhibits neuronal differentiation of grafted NPCs, gfrMG may increase the number of TH-positive cells by suppressing this effect. Thus, gfrMG appears to provide a suitable scaffold that supports survival and differentiation of NPCs. However, because it is derived from mouse sarcomas, a human-derived matrix or synthetic biomaterial must be developed for clinical applications.

Fibrin matrix for suspension of regenerative cells in an artificial nerve conduit

Peripheral nerve injury presents with specific problems of neuronal reconstructions, and from a clinical viewpoint a tissue engineering approach would facilitate the process of repair and regeneration. We have previously used artificial nerve conduits made from bioresorbable poly-3-hydroxybutyrate (PHB) in order to refine the ways in which peripheral nerves are repaired and reconnected to the target muscles and skin. The addition of Schwann cells (SC) or differentiated mesenchymal stem cells (dMSC) to the conduits enhances regeneration. In this study, we have used a matrix based on fibrin (Tisseel) to fill optimally the nerve-conduits with cells. In vitro analysis showed that both SC and MSC adhered significantly better to PHB in the presence of fibrin and cells continued to maintain their differentiated state. Cells were more optimally distributed throughout the conduit when seeded in fibrin than by delivery in growth medium alone. Transplantation of the nerve conduits in vivo showed that cells in combination with fibrin matrix significantly increased nerve regeneration distance (using PGP9.5 and S100 distal and proximal immunohistochemistry) when compared with empty PHB conduits. This study shows the beneficial combinatory effect of an optimised matrix, cells and conduit material as a step towards bridging nerve gaps which should ultimately lead to improved functional recovery following nerve injury.

Aging Schwann cells in vitro

Schwann cells (SCs) can support the regeneration of lesioned fiber tracts of the peripheral and central nervous system and have been transplanted alone or in combination with synthetic nerve guides. For neuronal tissue engineering purposes, the cells must be isolated from small biopsies and expanded in vitro. In this study we analyze the impact of cell expansion on 9 different cell parameters, comparing short- and long-term cultured rat SCs, which we refer to as 'young' and 'old' or 'aged' cells, respectively. In comparison to young SCs, old SCs doubled the axonal outgrowth from dorsal root ganglion explants and displayed only one-third as much adhesion to the gray and white matter of spinal cord cryosections. In a 3-dimensional extracellular matrix the two cell populations showed very different cellular responses with regard to cell morphology and cell-cell adhesion. Cell proliferation of old SCs was independent of serum components and was not hampered by contact inhibition. In addition, population doubling times were reduced by a factor of almost three compared to those of young SCs. Despite considerable karyotype changes, with an average of 68.7 chromosomes versus 42 in native rat cells, old SCs did not show any increase in telomerase activity and loss of anchorage dependence--characteristics that are typical of tumor cells. The data also provide biological insights into which cell characteristics (proliferation and adhesion, for example) are functionally clustered and either change or remain constant with aging in vitro. Though the data indicate a lack of tumorigenic transformation coupled with increased neurite outgrowth-promoting activity after extensive SC expansion in vitro, thus suggesting better regeneration qualities, we strongly recommend that in vitro aged rat SCs (>11 passages) should not be employed for tissue engineering.

Alginate hydrogel and matrigel as potential cell carriers for neurotransplantation

Development of biosynthetic conduits carrying extracellular matrix molecules and cell lines expressing neurotrophic growth factors represents a novel and promising strategy for spinal cord and peripheral nerve repair. In the present in vitro study, the compatibility and growth-promoting effects of (i) alginate hydrogel, (ii) alginate hydrogel complemented with fibronectin, and (iii) matrigel were compared between olfactory ensheathing cells (OECs), Schwann cells (SCs), and bone marrow stromal cells (BMSCs). Neurite outgrowth from embryonic dorsal root ganglia (DRG) neurons was used to assess the efficacy of the hydrogels alone or in combination with cultured cells to promote axonal regeneration. The result showed that alginate hydrogel transformed OECs, SCs, and BMSCs into atypical cells with spherical shape and inhibited their metabolic activity. Combination of alginate hydrogel with fibronectin promoted only OECs proliferation. Alginate hydrogel also inhibited outgrowth of DRG neurites, although this effect was attenuated by addition of fibronectin, SCs, or BMSCs. In contrast, matrigel stimulated cell proliferation, preserved the typical morphological features of the cultured cells and induced massive sprouting of DRG neurites. Addition of cultured cells to matrigel did not further improve DRG neurite outgrowth. The present findings suggest that addition of extracellular matrix should be considered when engineering biosynthetic scaffolds on the basis of alginate hydrogels.

A novel use of alginate hydrogel as Schwann cell matrix

The use of bioresorbable conduits supplemented with Schwann cells (SCs) is a promising tissue engineering technique to replace nerve grafting. Alginate hydrogel (AH), as a SC tissue engineering matrix, has many advantages over previously used matrices but has not been evaluated for this purpose. In this study, the viability and proliferation of SCs together with SC function in AH was evaluated in vitro. AlamarBlue cell assay was used to monitor the viability of SCs in AH and compared to SC viability in collagen gel, fibrin glue, hyaluronic acid, Matrigel, and standard culture plate over 5 days in culture. The results showed that the viability and growth of SCs in different matrices over the culture period did not significantly differ to culture plate culture. SC function when suspended in AH was monitored using chick embryo dorsal root ganglia (CDRG) growth assay. Growth of CDRG in AH with or without SCs was compared to CDRG growth without AH matrix. After 3 days in culture, the mean length of neurite sprouting was measured. The results showed that there was neurite growth in AH but was reduced to 43% of control. The neurite growth in AH was, however, enhanced by 170% when SCs were suspended in the gel. In conclusion, AH supported SC viability and function in vitro and may be useful in peripheral nerve tissue engineering in reconstructive procedures.

In vitro techniques for the assessment of neurotoxicity

Risk assessment is a process often divided into the following steps: a) hazard identification, b) dose-response assessment, c) exposure assessment, and d) risk characterization. Regulatory toxicity studies usually are aimed at providing data for the first two steps. Human case reports, environmental research, and in vitro studies may also be used to identify or to further characterize a toxic hazard. In this report the strengths and limitations of in vitro techniques are discussed in light of their usefulness to identify neurotoxic hazards, as well as for the subsequent dose-response assessment. Because of the complexity of the nervous system, multiple functions of individual cells, and our limited knowledge of biochemical processes involved in neurotoxicity, it is not known how well any in vitro system would recapitulate the in vivo system. Thus, it would be difficult to design an in vitro test battery to replace in vivo test systems. In vitro systems are well suited to the study of biological processes in a more isolated context and have been most successfully used to elucidate mechanisms of toxicity, identify target cells of neurotoxicity, and delineate the development and intricate cellular changes induced by neurotoxicants. Both biochemical and morphological end points can be used, but many of the end points used can be altered by pharmacological actions as well as toxicity. Therefore, for many of these end points it is difficult or impossible to set a criterion that allows one to differentiate between a pharmacological and a neurotoxic effect. For the process of risk assessment such a discrimination is central. Therefore, end points used to determine potential neurotoxicity of a compound have to be carefully selected and evaluated with respect to their potential to discriminate between an adverse neurotoxic effect and a pharmacologic effect. It is obvious that for in vitro neurotoxicity studies the primary end points that can be used are those affected through specific mechanisms of neurotoxicity. For example, in vitro systems may be useful for certain structurally defined compounds and mechanisms of toxicity, such as organophosphorus compounds and delayed neuropathy, for which target cells and the biochemical processes involved in the neurotoxicity are well known. For other compounds and the different types of neurotoxicity, a mechanism of toxicity needs to be identified first. Once identified, by either in vivo or in vitro methods, a system can be developed to detect and to evaluate predictive ability for the type of in vivo neurotoxicity produced. Therefore, in vitro tests have their greatest potential in providing information on basic mechanistic processes in order to refine specific experimental questions to be addressed in the whole animal.

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.

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.

Extracellular matrix proteins inhibit proliferation, upregulate migration and induce morphological changes in human glioma cell lines

The influence of an artificial basement membrane (BM), Matrigel, and four individual extracellular matrix proteins, fibronectin, laminin, collagen I and vitronectin, on cell proliferation, morphology and migration was assessed in four glioma cell lines. Matrigel and individual BM proteins differentially inhibited cell proliferation of all cell lines studied. In addition, Matrigel was found to induce extensive morphological changes in glioma cells. Polycarbonate filters, of 8-microns porosity in modified Boyden chambers, were used to assess the chemoattraction activity of Matrigel and the individual proteins on glioma cells. All these components were found to stimulate cell migration, albeit to different extents but laminin proved to be the most effective chemoattractant for glioma cells in vitro. These data suggest that basement membrane proteins may inhibit proliferation and stimulate migration in order to facilitate invasion.

Association of glucocerebroside homolog biosynthesis with Schwann cell proliferation

The biosynthesis of myelin-associated glycolipids was studied in quiescent secondary cultures of Schwann cells and in rapidly proliferating population of transfected Schwann cells (TSC) by in vitro incorporation of [3H]galactose. The TSC demonstrated a marked increase (> 10-fold) in [3H]galactose incorporation when compared to quiescent Schwann cells. The level (or amount) of [3H]galactose incorporation into lipids is dependent upon the number of TSC in culture. The majority of 3H-labeled lipids were oligohexosylceramides (GL-2, GL-3, and GL-4). Substrates that inhibit TSC proliferation, collagen type I and Matrigel, and artificial basement membrane, decrease the [3H]galactose incorporation by 25% and 80%, respectively. Our results indicate that the synthesis of glucocerebroside and its homologs is associated with Schwann cell proliferation.

Establishment and neurite outgrowth properties of neonatal and adult rat olfactory bulb glial cell lines

Two glial cell types surround olfactory axons and glomeruli in the olfactory bulb (OB) and may influence synapse development and regeneration. OB astrocytes resemble type-1 astrocytes, and OB ensheathing cells resemble non-myelinating Schwann cells. We have produced clonal OB astrocyte and ensheathing cell lines from rat neonatal and adult OB cultures by SV40 large T antigen transduction. These cell lines have been characterized by morphology, growth characteristics, immunophenotype, and ability to promote neurite outgrowth in vitro. Neonatal and adult ensheathing cell lines were found to support higher neurite outgrowth than OB astrocyte lines. Neonatal OB astrocyte lines were of two types, high and low outgrowth support. The low support astrocyte lines express J1 and a chondroitin sulfate-containing proteoglycan as do astrocytes encircling the neonatal glomeruli in vivo. The adult OB astrocyte cell lines supported lower levels of outgrowth than adult ensheathing cell lines. These results are consistent with a positive role for ensheathing cells in OB synapse regeneration, in vivo. Further, based on our results, we hypothesize that ensheathing cells and high-outgrowth astrocytes facilitate axon growth in vivo, while low outgrowth astrocytes inhibit axon growth and may facilitate glomerulus formation.