Brain Slice Derived Nerve Fibers Grow along Microcontact Prints and are Stimulated by Beta-Amyloid(42)

BACKGROUND

Alzheimer's disease is characterized by extracellular beta-amyloid plaques, intraneuronal tau neurofibrillary tangles and excessive neurodegeneration. The mechanisms of neuron degeneration and the potential of these neurons to form new nerve fibers for compensation remain elusive. The present study aimed to evaluate the impact of beta-amyloid and tau on new formations of nerve fibers from mouse organotypic brain slices connected to collagen-based microcontact prints.

METHODS

Organotypic brain slices of postnatal day 8-10 wild-type mice were connected to established collagen-based microcontact prints loaded with polyornithine to enhance nerve fiber outgrowth. Human beta-amyloid(42) or P301S mutated aggregated tau was co-loaded to the prints. Nerve fibers were immunohistochemically stained with neurofilament antibodies. The physiological activity of outgrown neurites was tested with neurotracer MiniRuby, voltage-sensitive dye FluoVolt, and calcium-sensitive dye Rhod-4.

RESULTS

Immunohistochemical staining revealed newly formed nerve fibers extending along the prints derived from the brain slices. While collagen-only microcontact prints stimulated nerve fiber growth, those loaded with polyornithine significantly enhanced nerve fiber outgrowth. Beta-amyloid(42) significantly increased the neurofilament-positive nerve fibers, while tau had only a weak effect. MiniRuby crystals, retrogradely transported along these newly formed nerve fibers, reached the hippocampus, while FluoVolt and Rhod-4 monitored electrical activity in newly formed nerve fibers.

CONCLUSIONS

Our data provide evidence that intact nerve fibers can form along collagen-based microcontact prints from mouse brain slices. The Alzheimer's peptide beta-amyloid(42) stimulates this growth, hinting at a neuroprotective function when physiologically active. This "brain-on-chip" model may offer a platform for screening bioactive factors or testing drug effects on nerve fiber growth.

A Poly-D-lysine-Coated Coralline Matrix Promotes Hippocampal Neural Precursor Cells' Differentiation into GFAP-Positive Astrocytes

A major goal of regenerative medicine of the central nervous system is to accelerate the regeneration of nerve tissue, where astrocytes, despite their positive and negative roles, play a critical role. Thus, scaffolds capable of producing astrocytes from neural precursor cells (NPCs) are most desirable. Our study shows that NPCs are converted into reactive astrocytes upon cultivation on coralline-derived calcium carbonate coated with poly-D-lysine (PDL-CS). As shown via nuclei staining, the adhesion of neurospheres containing hundreds of hippocampal neural cells to PDL-CS resulted in disaggregation of the cell cluster as well as the radial migration of dozens of cells away from the neurosphere core. Migrating cells per neurosphere averaged 100 on PDL-CS, significantly higher than on uncoated CS (28), PDL-coated glass (65), or uncoated glass (20). After 3 days of culture on PDL-CS, cell migration plateaued and remained stable for four more days. In addition, NPCs expressing nestin underwent continuous morphological changes from round to spiky, extending and elongating their processes, resembling activated astrocytes. The extension of the process increased continuously during the maturation of the culture and doubled after 7 days compared to day 1, whereas bifurcation increased by twofold during the first 3 days before plateauing. In addition, nestin positive cells' shape, measured through the opposite circularity level correlation, decreased approximately twofold after three days, indicating spiky transformation. Moreover, nestin-positive cells co-expressing GFAP increased by 2.2 from day 1 to 7, reaching 40% of the NPC population on day 7. In this way, PDL-CS promotes NPC differentiation into reactive astrocytes, which could accelerate the repair of neural tissue.

Spatial confinement: A spur for axonal growth

The concept of spatial confinement is the basis of cell positioning and guidance in in vitro studies. In vivo, it reflects many situations faced during embryonic development. In vitro, spatial confinement of neurons is achieved using different technological approaches: adhesive patterning, topographical structuring, microfluidics and the use of hydrogels. The notion of chemical or physical frontiers is particularly central to the behaviors of growth cones and neuronal processes under confinement. They encompass phenomena of cell spreading, boundary crossing, and path finding on surfaces with different adhesive properties. However, the most universal phenomenon related to confinement, regardless of how it is implemented, is the acceleration of neuronal growth. Overall, a bi-directional causal link emerges between the shape of the growth cone and neuronal elongation dynamics, both in vivo and in vitro. The sensing of adhesion discontinuities by filopodia and the subsequent spatial redistribution and size adaptation of these actin-rich filaments seem critical for the growth rate in conditions in which adhesive contacts and actin-associated clutching forces dominate. On the other hand, the involvement of microtubules, specifically demonstrated in 3D hydrogel environments and leading to ameboid-like locomotion, could be relevant in a wider range of growth situations. This review brings together a literature collected in distinct scientific fields such as development, mechanobiology and bioengineering that highlight the consequences of confinement and raise new questions at different cellular scales. Its ambition is to stimulate new research that could lead to a better understanding of what gives neurons their ability to establish and regulate their exceptional size.

Interpreting the Entire Connectivity of Individual Neurons in Micropatterned Neural Culture With an Integrated Connectome Analyzer of a Neuronal Network (iCANN)

The function of a neural circuit can be determined by the following: (1) characteristics of individual neurons composing the circuit, (2) their distinct connection structure, and (3) their neural circuit activity. However, prior research on correlations between these three factors revealed many limitations. In particular, profiling and modeling of the connectivity of complex neural circuits at the cellular level are highly challenging. To reduce the burden of the analysis, we suggest a new approach with simplification of the neural connection in an array of honeycomb patterns on 2D, using a microcontact printing technique. Through a series of guided neuronal growths in defined honeycomb patterns, a simplified neuronal circuit was achieved. Our approach allowed us to obtain the whole network connectivity at cellular resolution using a combination of stochastic multicolor labeling via viral transfection. Therefore, we were able to identify several types of hub neurons with distinct connectivity features. We also compared the structural differences between different circuits using three-node motif analysis. This new model system, iCANN, is the first experimental model of neural computation at the cellular level, providing neuronal circuit structures for the study of the relationship between anatomical structure and function of the neuronal network.

Polylysine-decorated macroporous microcarriers laden with adipose-derived stem cells promote nerve regeneration in vivo

Cell transplantation is an effective strategy to improve the repair effect of nerve guide conduits (NGCs). However, problems such as low loading efficiency and cell anoikis undermine the outcomes. Microcarriers are efficient 3D cell culture scaffolds, which can also prevent cell anoikis by providing substrate for adhesion during transplantation. Here, we demonstrate for the first time microcarrier-based cell transplantation in peripheral nerve repair. We first prepared macroporous chitosan microcarriers (CSMCs) by the emulsion-phase separation method, and then decorated the CSMCs with polylysine (pl-CSMCs) to improve cell affinity. We then loaded the pl-CSMCs with adipose-derived stem cells (ADSCs) and injected them into electrospun polycaprolactone/chitosan NGCs to repair rat sciatic nerve defects. The ADSCs-laden pl-CSMCs effectively improved nerve regeneration as demonstrated by evaluation of histology, motor function recovery, electrophysiology, and gastrocnemius recovery. With efficient cell transplantation, convenient operation, and the multiple merits of ADSCs, the ADSCs-laden pl-CSMCs hold good potential in peripheral nerve repair.

Interaction of micropatterned topographical and biochemical cues to direct neurite growth from spiral ganglion neurons

Functional outcomes with neural prosthetic devices, such as cochlear implants, are limited in part due to physical separation between the stimulating elements and the neurons they stimulate. One strategy to close this gap aims to precisely guide neurite regeneration to position the neurites in closer proximity to electrode arrays. Here, we explore the ability of micropatterned biochemical and topographic guidance cues, singly and in combination, to direct the growth of spiral ganglion neuron (SGN) neurites, the neurons targeted by cochlear implants. Photopolymerization of methacrylate monomers was used to form unidirectional topographical features of ridges and grooves in addition to multidirectional patterns with 90^o angle turns. Microcontact printing was also used to create similar uni- and multi-directional patterns of peptides on polymer surfaces. Biochemical cues included peptides that facilitate (laminin, LN) or repel (EphA4-Fc) neurite growth. On flat surfaces, SGN neurites preferentially grew on LN-coated stripes and avoided EphA4-Fc-coated stripes. LN or EphA4-Fc was selectively adsorbed onto the ridges or grooves to test the neurite response to a combination of topographical and biochemical cues. Coating the ridges with EphA4-Fc and grooves with LN lead to enhanced SGN alignment to topographical patterns. Conversely, EphA4-Fc coating on the grooves or LN coating on the ridges tended to disrupt alignment to topographical patterns. SGN neurites respond to combinations of topographical and biochemical cues and surface patterning that leverages both cues enhance guided neurite growth.

Functionalization of TiO2 sol-gel derived films for cell confinement

The neuroscience field has increased enormously over the last decades, achieving the possible real application of neuronal cultures not only for reproducing neural architectures resembling in vivo tissues, but also for the development of functional devices. In this context, surface patterning for cell confinement is crucial, and new active materials together with new protocols for preparing substrates suitable for confining cells, guiding their processes in the desired configuration are extremely appreciated. Here, TiO₂ sol-gel derived films were selected as proof-of-concept materials to grow neurons in suitable confined configurations, taking advantage of the biocompatible properties of modified TiO₂ substrates. TiO₂ sol-gel derived films were made compatible with the growth of neurons thanks to a stable and controlled poly-lysine coating, obtained by silanization chemistry and streptavidin-biotin interactions. Moreover, a spotting protocol, here described and optimized, allowed the simple preparation of arrays of neurons, where cell adhesion was guided in specific areas and the neurites development driven in the desired arrangement. The resulting arrays were successfully tested for the growth and differentiation of neurons, demonstrating the possible adhesion of cells in specific areas of the film, therefore paving the way to applications such as the direct growth of excitable cells nearby electrodes of devices, with an evident enhancement of cell-electrodes communication.

Engineering Biocompatible Interfaces via Combinations of Oxide Films and Organic Self-Assembled Monolayers

In this paper, we demonstrate that cell adhesion and neuron maturation can be guided by patterned oxide surfaces functionalized with organic molecular layers. It is shown that the difference in the surface potential of various oxides (SiO₂, Ta₂O₅, TiO₂, and Al₂O₃) can be increased by functionalization with a silane, (3-aminopropyl)-triethoxysilane (APTES), which is deposited from the gas phase on the oxide. Furthermore, it seems that only physisorbed layers (no chemical binding) can be achieved for some oxides (Ta₂O₅ and TiO₂), whereas self-assembled monolayers (SAM) form on other oxides (SiO₂ and Al₂O₃). This does not only alter the surface potential but also affects the neuronal cell growth. The already high cell density on SiO₂ is increased further by the chemically bound APTES SAM, whereas the already low cell density on Ta₂O₅ is even further reduced by the physisorbed APTES layer. As a result, the cell density is ∼8 times greater on SiO₂ compared to Ta₂O₅, both coated with APTES. Furthermore, neurons form the typical networks on SiO₂, whereas they tend to cluster to form neurospheres on Ta₂O₅. Using lithographically patterned Ta₂O₅ layers on SiO₂ substrates functionalized with APTES, the guided growth can be transferred to complex patterns. Cell cultures and molecular layers can easily be removed, and the cell experiment can be repeated after functionalization of the patterned oxide surface with APTES. Thus, the combination of APTES-functionalized patterned oxides might offer a promising way of achieving guided neuronal growth on robust and reusable substrates.

Manipulating nanoscale structure to control functionality in printed organic photovoltaic, transistor and bioelectronic devices

Printed electronics is simultaneously one of the most intensely studied emerging research areas in science and technology and one of the fastest growing commercial markets in the world today. For the past decade the potential for organic electronic (OE) materials to revolutionize this printed electronics space has been widely promoted. Such conviction in the potential of these carbon-based semiconducting materials arises from their ability to be dissolved in solution, and thus the exciting possibility of simply printing a range of multifunctional devices onto flexible substrates at high speeds for very low cost using standard roll-to-roll printing techniques. However, the transition from promising laboratory innovations to large scale prototypes requires precise control of nanoscale material and device structure across large areas during printing fabrication. Maintaining this nanoscale material control during printing presents a significant new challenge that demands the coupling of OE materials and devices with clever nanoscience fabrication approaches that are adapted to the limited thermodynamic levers available. In this review we present an update on the strategies and capabilities that are required in order to manipulate the nanoscale structure of large area printed organic photovoltaic (OPV), transistor and bioelectronics devices in order to control their device functionality. This discussion covers a range of efforts to manipulate the electroactive ink materials and their nanostructured assembly into devices, and also device processing strategies to tune the nanoscale material properties and assembly routes through printing fabrication. The review finishes by highlighting progress in printed OE devices that provide a feedback loop between laboratory nanoscience innovations and their feasibility in adapting to large scale printing fabrication. The ability to control material properties on the nanoscale whilst simultaneously printing functional devices on the square metre scale is prompting innovative developments in the targeted nanoscience required for OPV, transistor and biofunctional devices.

Sputtering of Electrospun Polymer-Based Nanofibers for Biomedical Applications: A Perspective

Electrospinning has gained wide attention recently in biomedical applications. Electrospun biocompatible scaffolds are well-known for biomedical applications such as drug delivery, wound dressing, and tissue engineering applications. In this review, the synthesis of polymer-based fiber composites using an electrospinning technique is discussed. Formerly, metal particles were then deposited on the surface of electrospun fibers using sputtering technology. Key nanometals for biomedical applications including silver and copper nanoparticles are discussed throughout this review. The formulated scaffolds were found to be suitable candidates for biomedical uses such as antibacterial coatings, surface modification for improving biocompatibility, and tissue engineering. This review briefly mentions the characteristics of the nanostructures while focusing on how nanostructures hold potential for a wide range of biomedical applications.

Accelerated Development of Hippocampal Neurons and Limited Adhesion of Astrocytes on Negatively Charged Surfaces

This work examines the development of primary neurons and astrocytes on thoroughly controlled functional groups. Negatively charged surfaces presenting carboxylate (COO^-) or sulfonate (SO₃^-) groups prove beneficial to neuronal behavior, in spite of their supposed repulsive electrostatic interactions with cellular membranes. The adhesion and survival of primary hippocampal neurons on negatively charged surfaces are comparable to or slightly better than those on positively charged (poly-d-lysine-coated) surfaces, and neuritogenesis and neurite outgrowth are accelerated on COO^- and SO₃^- surfaces. Moreover, such favorable influences of the negatively charged surfaces are only seen in neurons but not for astrocytes. Our results indicate that the in vitro developmental behavior of primary hippocampal neurons is sophisticatedly modulated by angstrom-sized differences in chemical structure or the charge density of the surface. We believe that this work provides new implications for understanding neuron-material interfaces as well as for establishing new ways to fabricate neuro-active surfaces.

Microenvironments to study migration and somal translocation in cortical neurons

Migrating post-mitotic neurons of the developing cerebral cortex undergo terminal somal translocation (ST) when they reach their final destination in the cortical plate. This process is crucial for proper cortical layering and its perturbation can lead to brain dysfunction. Here we present a reductionist biomaterials platform that faithfully supports and controls the distinct phases of terminal ST in vitro. We developed microenvironments with different adhesive molecules to support neuronal attachment, neurite extension, and migration in distinct manners. Efficient ST occurred when the leading process of migratory neurons crossed from low-to high-adhesive areas on a substrate, promoting spreading of the leading growth cone. Our results indicate that elementary adhesive cell-substrate interactions strongly influence migratory behavior and the final positioning of neurons during their developmental journey. This in vitro model allows advanced experimentation to reveal the microenvironmental requirements underlying cortical layer development and disorders.

Modification of porous PLGA microspheres by poly-l-lysine for use as tissue engineering scaffolds

Due to their good biocompatibility, biodegradability and special shapes, porous poly(lactic-co-glycolic acid) (PLGA) microspheres show a wide application in the field of tissue engineering. Herein we demonstrate a simple and low-cost method for modifying porous PLGA microspheres with poly-l-lysine (PLL) to promote cell growth on the microspheres. Porous PLGA microspheres were first treated by sodium hydroxide (NaOH) solution to introduce carboxyl groups on their surface. Then, the hydrolyzed microspheres (PLGA-H) were immerged in PLL solution to yield PLL-impregnated microspheres (PLGA-PLL). Cell experiments showed that although the cytotoxicity of microspheres was slightly increased after PLL modification, their cell viability was still higher than 85%. Compared with PLGA and PLGA-H microspheres, PLGA-PLL microspheres were more favorable for MG63 cell to attach and proliferate due to their increased initial cell attachment numbers and enhanced cell-matrix interactions. This new modification method of porous PLGA microspheres proposes a route toward efficient repair of tissue defects at reduced risk and cost level.

Toluene disruption of the functions of L1 cell adhesion molecule at concentrations associated with occupational exposures

BACKGROUND

Prenatal toluene exposure can cause neurodevelopmental disabilities similar to fetal alcohol syndrome. Both share neuroanatomic pathologies similar to children with mutations in L1 cell adhesion molecule (L1). L1 mediates neurite outgrowth (NOG) via signaling through ERK1/2, which require trafficking of L1 through lipid rafts. Our objective is to determine if toluene inhibits L1-mediated NOG and toluene inhibits L1 signaling at concentrations achieved during occupational exposure.

METHODS

Concentrations of toluene reflective of blood concentrations achieved in solvent abusers and occupational settings are used. Cerebellar granule neurons (CGN) harvested from postnatal day 6 rat pups are plated on coverslips coated with poly-L-lysine (PLL) alone or PLL followed by laminin. L1 is added to the media of CGN plated on PLL alone. Toluene is added 2 h after plating. Cells are fixed at 24 h and neurite length is measured. ERK1/2 activation by L1 in CGN is analyzed by immunoblot.

RESULTS

Toluene significantly reduced mean neurite length of CGN exposed to L1 but not laminin. Toluene significantly reduced L1-mediated ERK1/2 phosphorylation.

CONCLUSION

Results suggest that toluene inhibits L1-lipid raft interactions at occupationally relevant concentrations and may lead to a fetal solvent spectrum disorder similar to fetal alcohol spectrum disorder.

Synaptic compartmentalization by micropatterned masking of a surface adhesive cue in cultured neurons

Functions of neuronal circuit are fundamentally modulated by its quality and quantity of connections. Assessment of synapse, the basic unit for a neuronal connection, is labor-intensive and time-consuming in conventional culture systems, due to the small size and the spatially random distribution. In the present study, we propose a novel 'synapse compartmentalization' culture system, in which synapses are concentrated at controlled locations. We fabricated a negative dot array pattern by coating the entire surface with poly-l-lysine (PLL) and subsequent microcontact printing of 1) substrates which mask positive charge of PLL (Fc, BSA and laminin), or 2) a chemorepulsive protein (Semaphorin 3F-Fc). By combination of physical and biological features of these repulsive substrates, functional synapses were robustly concentrated in the PLL-coated dots. This synapse compartmentalization chip can be combined with the various high-throughput assay formats based on the synaptic morphology and function. Therefore, this quantifiable and controllable dot array pattern by microcontact printing will be potential useful for bio-chip platforms for the high-density assays used in synapse-related neurobiological studies.

A microfluidic method for dopamine uptake measurements in dopaminergic neurons

Dopamine (DA) is a classical neurotransmitter and dysfunction in its synaptic handling underlies many neurological disorders, including addiction, depression, and neurodegeneration. A key to understanding DA dysfunction is the accurate measurement of dopamine uptake by dopaminergic neurons. Current methods that allow for the analysis of dopamine uptake rely on standard multiwell-plate based ELISA, or on carbon-fibre microelectrodes used in in vivo recording techniques. The former suffers from challenges associated with automation and analyte degradation, while the latter has low throughput and is not ideal for laboratory screening. In response to these challenges, we introduce a digital microfluidic platform to evaluate dopamine homeostasis in in vitro neuron culture. The method features voltammetric dopamine sensors with limit of detection of 30 nM integrated with cell culture sites for multi-day neuron culture and differentiation. We demonstrate the utility of the new technique for DA uptake assays featuring in-line culture and analysis, with a determination of uptake of approximately ∼32 fmol in 10 min per virtual microwell (each containing ∼200 differentiated SH-SY5Y cells). We propose that future generations of this technique will be useful for drug discovery for neurodegenerative disease as well as for a wide range of applications that would benefit from integrated cell culture and electroanalysis.

Effects of ECM protein micropatterns on the migration and differentiation of adult neural stem cells

The migration and differentiation of adult neural stem cells (aNSCs) are believed to be strongly influenced by the spatial distribution of extracellular matrix (ECM) proteins in the stem cell niche. In vitro culture platform, which involves the specific spatial distribution of ECM protein, could offer novel tools for better understanding of aNSC behavior in the spatial pattern of ECM proteins. In this work, we applied soft-lithographic technique to design simple and reproducible laminin (LN)-polylysine cell culture substrates and investigated how aNSCs respond to the various spatial distribution of laminin, one of ECM proteins enriched in the aNSC niche. We found that aNSC preferred to migrate and attach to LN stripes, and aNSC-derived neurons and astrocytes showed significant difference in motility towards LN stripes. By changing the spacing of LN stripes, we were able to control the alignment of neurons and astrocytes. To the best of our knowledge, this is the first time to investigate the differential cellular responses of aNSCs on ECM protein (LN) and cell adhesive synthetic polymer (PDL) using surface micropatterns. Our findings would provide a deeper understanding in astrocyte-neuron interactions as well as ECM-stem cell interactions.