Interactions of neurons with topographic nano cues affect branching morphology mimicking neuron–neuron interactions

3D Printing-Enabled Nanoparticle Alignment: A Review of Mechanisms and Applications

3D printing (additive manufacturing (AM)) has enormous potential for rapid tooling and mass production due to its design flexibility and significant reduction of the timeline from design to manufacturing. The current state-of-the-art in 3D printing focuses on material manufacturability and engineering applications. However, there still exists the bottleneck of low printing resolution and processing rates, especially when nanomaterials need tailorable orders at different scales. An interesting phenomenon is the preferential alignment of nanoparticles that enhance material properties. Therefore, this review emphasizes the landscape of nanoparticle alignment in the context of 3D printing. Herein, a brief overview of 3D printing is provided, followed by a comprehensive summary of the 3D printing-enabled nanoparticle alignment in well-established and in-house customized 3D printing mechanisms that can lead to selective deposition and preferential orientation of nanoparticles. Subsequently, it is listed that typical applications that utilized the properties of ordered nanoparticles (e.g., structural composites, heat conductors, chemo-resistive sensors, engineered surfaces, tissue scaffolds, and actuators based on structural and functional property improvement). This review's emphasis is on the particle alignment methodology and the performance of composites incorporating aligned nanoparticles. In the end, significant limitations of current 3D printing techniques are identified together with future perspectives.

Anisometric Microstructures to Determine Minimal Critical Physical Cues Required for Neurite Alignment

In nerve regeneration, scaffolds play an important role in providing an artificial extracellular matrix with architectural, mechanical, and biochemical cues to bridge the site of injury. Directed nerve growth is a crucial aspect of nerve repair, often introduced by engineered scaffolds imparting linear tracks. The influence of physical cues, determined by well-defined architectures, has been mainly studied for implantable scaffolds and is usually limited to continuous guiding features. In this report, the potential of short anisometric microelements in inducing aligned neurite extension, their dimensions, and the role of vertical and horizontal distances between them, is investigated. This provides crucial information to create efficient injectable 3D materials with discontinuous, in situ magnetically oriented microstructures, like the Anisogel. By designing and fabricating periodic, anisometric, discreet guidance cues in a high-throughput 2D in vitro platform using two-photon lithography techniques, the authors are able to decipher the minimal guidance cues required for directed nerve growth along the major axis of the microelements. These features determine whether axons grow unidirectionally or cross paths via the open spaces between the elements, which is vital for the design of injectable Anisogels for enhanced nerve repair.

Guiding the Patterned Growth of Neuronal Axons and Dendrites Using Anisotropic Micropillar Scaffolds

The patterning of axonal and dendritic growth is an important topic in neural tissue engineering and critical for generating directed neuronal networks in vitro. Evidence shows that artificial micro/nanotopography can better mimic the environment for neuronal growth in vivo. However, the potential mechanisms by which neurons interact with true three dimensional (3D) topographical cues and form directional networks are unclear. Herein, 3D micropillar scaffolds are designed to guide the growth of neural stem cells and hippocampal neurons in vitro. Discontinuous and anisotropic micropillars are fabricated by femtosecond direct laser writing to form patterned scaffolds with various spacings and heights, which are found to affect the branching and orientation of axons and dendrites. Interestingly, axons and dendrites tend to grow on an array of 3D micropillar scaffolds of the same height and form functionally connected neuronal networks, as reflected by synchronous neuronal activity visualized by calcium imaging. This method may represent a promising tool for studying neuron behavior and directed neuronal networks in a 3D environment.

Engineered Microsystems for Spheroid and Organoid Studies

3D in vitro model systems such as spheroids and organoids provide an opportunity to extend the physiological understanding using recapitulated tissues that mimic physiological characteristics of in vivo microenvironments. Unlike 2D systems, 3D in vitro systems can bridge the gap between inadequate 2D cultures and the in vivo environments, providing novel insights on complex physiological mechanisms at various scales of organization, ranging from the cellular, tissue-, to organ-levels. To satisfy the ever-increasing need for highly complex and sophisticated systems, many 3D in vitro models with advanced microengineering techniques have been developed to answer diverse physiological questions. This review summarizes recent advances in engineered microsystems for the development of 3D in vitro model systems. The relationship between the underlying physics behind the microengineering techniques, and their ability to recapitulate distinct 3D cellular structures and functions of diverse types of tissues and organs are highlighted and discussed in detail. A number of 3D in vitro models and their engineering principles are also introduced. Finally, current limitations are summarized, and perspectives for future directions in guiding the development of 3D in vitro model systems using microengineering techniques are provided.

Brief Electrical Stimulation Triggers an Effective Regeneration of Leech CNS

The search for therapeutic strategies to promote neuronal regeneration following injuries toward functional recovery is of great importance. Brief low-frequency electrical stimulation (ES) has been reported as a useful method to improve neuronal regeneration in different animal models; however, the effect of ES on single neuron behavior has not been shown. Here, we study the effect of brief ES on neuronal regeneration of the CNS of adult medicinal leeches. Studying the regeneration of selected sets of identified neurons allow us to quantify the ES effect per cell type at the single-cell level. Chains of the CNS that were subjected to cut injury were observed for 3 d, and the spontaneous regeneration was compared with the electrically stimulated injured chains. We show that the ES improves the efficiency of regeneration of Retzius cells, as larger masses of the total branching tree traverse the injury site with better directed growth with no effect on the average branching tree length. No antero-posterior polarity was found along regeneration within the leech CNS. Moreover, the microglial cell distribution was examined revealing more microglial cells in proximity to the stimulation site compared with non-stimulated. Our results lay a foundation for future ES-based neuroregenerative therapies.

Neuro-taxis: Neuronal movement in gradients of chemical and physical environments

Environmental chemical and physical cues dynamically interact with migrating neurons and sprouting axons, and in particular, the gradients of environmental cues are regarded as one of the factors intimately involved in the neuronal movement. Since a growth cone was first described by Cajal, more than one century ago, chemical gradients have been suggested as one of the mechanisms by which the neurons determine proper paths and destinations. However, the gradients of physical cues, such as stiffness and topography, which also interact constantly with the neurons and their axons as a component of the extracellular environments, have rarely been noted regarding the guidance of neurons, despite their gradually increasingly reported influences in the case of nonneuronal-cell migration. In this review, we discuss chemical (i.e., chemo- and hapto-) and physical (i.e., duro-) taxis phenomena on the movement of neurons including axonal elongation. In addition, we suggest topotaxis, the most recently proposed physical-taxis phenomenon, as another potential mechanism in the neuronal movement, based on the reports of neuronal recognition of and responses to nanotopography.

Large-scale acoustic-driven neuronal patterning and directed outgrowth

Acoustic manipulation is an emerging non-invasive method enabling precise spatial control of cells in their native environment. Applying this method for organizing neurons is invaluable for neural tissue engineering applications. Here, we used surface and bulk standing acoustic waves for large-scale patterning of Dorsal Root Ganglia neurons and PC12 cells forming neuronal cluster networks, organized biomimetically. We showed that by changing parameters such as voltage intensity or cell concentration we were able to affect cluster properties. We examined the effects of acoustic arrangement on cells atop 3D hydrogels for up to 6 days and showed that assembled cells spontaneously grew branches in a directed manner towards adjacent clusters, infiltrating the matrix. These findings have great relevance for tissue engineering applications as well as for mimicking architectures and properties of native tissues.

Comparing Transcriptome Profiles of Neurons Interfacing Adjacent Cells and Nanopatterned Substrates Reveals Fundamental Neuronal Interactions

Developing neuronal axons are directed by chemical and physical signals toward a myriad of target cells. According to current dogma, the resulting network architecture is critically shaped by electrical interconnections, the synapses; however, key mechanisms translating neuronal interactions into neuronal growth behavior during network formation are still unresolved. To elucidate these mechanisms, we examined neurons interfacing nanopatterned substrates and compared them to natural interneuron interactions. We grew similar neuronal populations under three connectivity conditions, (1) the neurons are isolated, (2) the neurons are interconnected, and (3) the neurons are connected only to artificial substrates, then quantitatively compared both the cell morphologies and the transcriptome-expression profiles. Our analysis shows that whereas axon-guidance signaling pathways in isolated neurons are predominant, in isolated neurons interfacing nanotopography, these pathways are downregulated, similar to the interconnected neurons. Moreover, in nanotopography, interfacing neuron genes related to synaptogenesis and synaptic regulation are highly expressed, that is, again resembling the behavior of interconnected neurons. These molecular findings demonstrate that interactions with nanotopographies, although not leading to electrical coupling, play a comparable functional role in two major routes, neuronal guidance and network formation, with high relevance to the design of regenerative interfaces.

Aligning Synthetic Hippocampal Neural Circuits via Self-Rolled-Up Silicon Nitride Microtube Arrays

Directing neurons to form predetermined circuits with the intention of treating neurological disorders and neurodegenerative diseases is a fundamental goal and current challenge in neuroengineering. Until recently, only neuronal aggregates were studied and characterized in culture, which can limit information gathered to populations of cells. In this study, we use a substrate constructed of arrays of strain-induced self-rolled-up membrane 3D architectures. This results in changes in the neuronal architecture and altered growth dynamics of neurites. Hippocampal neurons from postnatal rats were cultured at low confluency (∼250 cells mm^-2) on an array of transparent rolled-up microtubes (μ-tubes; 4-5 μm diameter) of varying topographical arrangements. Neurite growth on the μ-tubes was characterized and compared to controls in order to establish a baseline for alignment imposed by the topography. Compared to control substrates, neurites are significantly more aligned toward the 0° reference on the μ-tube array. Pitch (20-60 and 100 μm) and μ-tube length (30-80 μm) of array elements were also varied to investigate their impact on neurite alignment. We found that alignment was improved by the gradient pitch arrangement and with longer μ-tubes. Application of this technology will enhance the ability to construct intentional neural circuits through array design and manipulation of individual neurons and can be adapted to address challenges in neural repair, reinnervation, and neuroregeneration.

Nanotopography-Promoted Formation of Axon Collateral Branches of Hippocampal Neurons

Axon collateral branches, as a key structural motif of neurons, allow neurons to integrate information from highly interconnected, divergent networks by establishing terminal boutons. Although physical cues are generally known to have a comprehensive range of effects on neuronal development, their involvement in axonal branching remains elusive. Herein, it is demonstrated that the nanopillar arrays significantly increase the number of axon collateral branches and also promote their growth. Immunostaining and biochemical analyses indicate that the physical interactions between the nanopillars and the neurons give rise to lateral filopodia at the axon shaft via cytoskeletal changes, leading to the formation of axonal branches. This report, demonstrates that nanotopography regulates axonal branching, and provides a guideline for the design of sophisticated neuron-based devices and scaffolds for neuro-engineering.

Zebrafish extracellular matrix improves neuronal viability and network formation in a 3-dimensional culture

Mammalian central nervous system (CNS) has limited capacity for regeneration. CNS injuries cause life-long debilitation and lead to $50 billion in healthcare costs in U.S. alone each year. Despite numerous efforts in the last few decades, CNS-related injuries remain as detrimental as they were 50 years ago. Some functional recovery can occur, but most regeneration are limited by an extracellular matrix (ECM) that actively inhibits axonal repair and promotes glial scarring. In most tissues, the ECM is an architectural foundation that plays an active role in supporting cellular development and regenerative response after injury. In mammalian CNS, however, this is not the case - its composition is not conducive for regeneration, with various molecules restricting plasticity and neuronal growth. In fact, the CNS ECM alters its composition dramatically following injury to restrict regeneration and to prioritize containment of injury as well as preservation of intact neural circuitry. This leads us to hypothesize that the inhibitory extracellular environment needs be modified or supplemented to be more regeneration-permissive for significant CNS regeneration. Mammalian nervous tissue cannot provide such ECM, and synthesizing it in a laboratory is beyond current technology. Evolutionarily lower species possess remarkably regenerative neural tissue. For example, small fresh-water dwelling zebrafish (Danio rerio) can regenerate severed spinal cord, re-gaining full motor function in a week. We believe their ECM contributes to its regenerative capability and that it can be harnessed to induce more regeneration in mammalian CNS. This study shows that ECM derived from zebrafish brains promotes more neuronal survival and axonal network formation than the widely studied and available ECM derived from mammalian tissues such as porcine brains, porcine urinary bladder, and rat brains. We believe its regenerative potential, combined with its affordability, easy handling, and fast reproduction, will make zebrafish an excellent candidate as a novel ECM source.

Asymmetric, nano-textured surfaces influence neuron viability and polarity

Three dimensional, nanostructured surfaces have attracted considerable attention in biomedical research since they have proven to represent a powerful platform to influence cell fate. In particular, nanorods and nanopillars possess great potential for the control of cell adhesion and differentiation, gene and biomolecule delivery, optical and electrical stimulation and recording, as well as cell patterning. Here, we investigate the influence of asymmetric poly(dichloro-p-xylene) (PPX) columnar films on the adhesion and maturation of cortical neurons. We show that nanostructured films with dense, inclined polymer columns can support viable primary neuronal culture. The cell-nanostructure interface is characterized showing a minimal cell penetration but strong adhesion on the surface. Moreover, we quantify the influence of the nano-textured surface on the neural development (soma size, neuritogenesis, and polarity) in comparison to a planar PPX sample. We demonstrate that the nanostructures facilitates an enhancement in neurite branching as well as elongation of axons and growth cones. Furthermore, we show for the first time that the asymmetric orientation of polymeric nanocolumns strongly influences the initiation direction of the axon formation. These results evidence that 3D nano-topographies can significantly change neural development and can be used to engineer axon elongation. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 1634-1645, 2018.

Topographical impact of silver nanolines on the morphology of neuronal SH-SY5Y Cells

An extracellular environment is critical in neuronal development and growth. Changes in neuronal morphology, neuron adhesion, and even the rate of neurite formation, can be modified by both the chemical and physical properties of interfacing substrates. Topography has a major impact on neuronal growth. Neuronal behavior and morphology are affected by the size, shape and pattern of the topographic elements. Combining topography with active materials may lead to enhanced influence. This paper demonstrates the effects of silver nanolines (AgNLs) on the growth pattern of SH-SY5Y cells. The morphology of the cells atop the nanotopographical substrates is measured, revealing a significant promoting effect. The number of neurites initiating from the soma is larger in SH-SY5Y cells plated on AgNLs than in control samples. The cells also exhibit an increase in neurite branching points towards more complex structures. These results indicate that substrates decorated with nanotopography affect cellular growth in a way that may be useful for enhanced regeneration, opening new possibilities for electrode and implant design.

Synergistic Toxicity of the Neurometabolites Quinolinic Acid and Homocysteine in Cortical Neurons and Astrocytes: Implications in Alzheimer's Disease

The brain of patients affected by Alzheimer's disease (AD) develops progressive neurodegeneration linked to the formation of proteins aggregates. However, their single actions cannot explain the extent of brain damage observed in this disorder, and the characterization of co-adjuvant involved in the early toxic processes evoked in AD is essential. In this line, quinolinic acid (QUIN) and homocysteine (Hcy) appear to be involved in the AD neuropathogenesis. Herein, we investigate the effects of QUIN and Hcy on early toxic events in cortical neurons and astrocytes. Exposure of primary cortical cultures to these neurometabolites for 24 h induced concentration-dependent neurotoxicity. In addition, QUIN (25 μM) and Hcy (30 μM) triggered ROS production, lipid peroxidation, diminished of Na⁺,K⁺-ATPase activity, and morphologic alterations, culminating in reduced neuronal viability by necrotic cell death. In astrocytes, QUIN (100 μM) and Hcy (30 μM) induced caspase-3-dependent apoptosis and morphologic alterations through oxidative status imbalance. To establish specific mechanisms, we preincubated cell cultures with different protective agents. The combined toxicity of QUIN and Hcy was attenuated by melatonin and Trolox in neurons and by NMDA antagonists and glutathione in astrocytes. Cellular death and morphologic alterations were prevented when co-culture was treated with metabolites, suggesting the activation of protector mechanisms dependent on soluble factors and astrocyte and neuron communication through gap junctions. These findings suggest that early damaging events involved in AD can be magnified by synergistic toxicity of the QUIN and Hcy. Therefore, this study opens new possibilities to elucidate the molecular mechanisms of neuron-astrocyte interactions and their role in neuroprotection against QUIN and Hcy.

Kynurenic Acid Prevents Cytoskeletal Disorganization Induced by Quinolinic Acid in Mixed Cultures of Rat Striatum

Kynurenic acid (KYNA) is a neuroactive metabolite of tryptophan known to modulate a number of mechanisms involved in neural dysfunction. Although its activity in the brain has been widely studied, the effect of KYNA counteracting the actions of quinolinic acid (QUIN) remains unknown. The present study aims at describing the ability of 100 μM KYNA preventing cytoskeletal disruption provoked by QUIN in astrocyte/neuron/microglia mixed culture. KYNA totally preserved cytoskeletal organization, cell morphology, and redox imbalance in mixed cultures exposed to QUIN. However, KYNA partially prevented morphological alteration in isolated primary astrocytes and failed to protect the morphological alterations of neurons caused by QUIN exposure. Moreover, KYNA prevented QUIN-induced microglial activation and upregulation of ionized calcium-binding adapter molecule 1 (Iba-1) and partially preserved tumor necrosis factor-α (TNF-α) level in mixed cultures. TNF-α level was also partially preserved in astrocytes. In addition to the mechanisms dependent on redox imbalance and microglial activation, KYNA prevented downregulation of connexin-43 and the loss of functionality of gap junctions (GJs), preserving cell-cell contact, cytoskeletal organization, and cell morphology in QUIN-treated cells. Furthermore, the toxicity of QUIN targeting the cytoskeleton of mixed cultures was not prevented by the N-methyl-D-aspartate (NMDA) antagonist MK-801. We suggest that KYNA protects the integrity of the cytoskeleton of mixed cultures by complex mechanisms including modulating microglial activation preventing oxidative imbalance and misregulated GJs leading to disrupted cytoskeleton in QUIN-treated cells. This study contributed to elucidate the molecular basis of KYNA protection against QUIN toxicity.

Interactions of Neurons with Physical Environments

Nerve growth strongly relies on multiple chemical and physical signals throughout development and regeneration. Currently, a cure for injured neuronal tissue is an unmet need. Recent advances in fabrication technologies and materials led to the development of synthetic interfaces for neurons. Such engineered platforms that come in 2D and 3D forms can mimic the native extracellular environment and create a deeper understanding of neuronal growth mechanisms, and ultimately advance the development of potential therapies for neuronal regeneration. This progress report aims to present a comprehensive discussion of this field, focusing on physical feature design and fabrication with additional information about considerations of chemical modifications. We review studies of platforms generated with a range of topographies, from micro-scale features down to topographical elements at the nanoscale that demonstrate effective interactions with neuronal cells. Fabrication methods are discussed as well as their biological outcomes. This report highlights the interplay between neuronal systems and the important roles played by topography on neuronal differentiation, outgrowth, and development. The influence of substrate structures on different neuronal cells and parameters including cell fate, outgrowth, intracellular remodeling, gene expression and activity is discussed. Matching these effects to specific needs may lead to the emergence of clinical solutions for patients suffering from neuronal injuries or brain-machine interface (BMI) applications.

Mechanically Oriented 3D Collagen Hydrogel for Directing Neurite Growth

Recent studies in the field of neuro-tissue engineering have demonstrated the promising effects of aligned contact guidance cue to scaffolds of enhancement and direction of neuronal growth. In vivo, neurons grow and develop neurites in a complex three-dimensional (3D) extracellular matrix (ECM) surrounding. Studies have utilized hydrogel scaffolds derived from ECM molecules to better simulate natural growth. While many efforts have been made to control neuronal growth on 2D surfaces, the development of 3D scaffolds with an elaborate oriented topography to direct neuronal growth still remains a challenge. In this study, we designed a method for growing neurons in an aligned and oriented 3D collagen hydrogel. We aligned collagen fibers by inducing controlled uniaxial strain on gels. To examine the collagen hydrogel as a suitable scaffold for neuronal growth, we evaluated the physical properties of the hydrogel and measured collagen fiber properties. By combining the neuronal culture in 3D collagen hydrogels with strain-induced alignment, we were able to direct neuronal growth in the direction of the aligned collagen matrix. Quantitative evaluation of neurite extension and directionality within aligned gels was performed. The analysis showed neurite growth aligned with collagen matrix orientation, while maintaining the advantageous 3D growth.

Astrocyte-neuron interaction in diphenyl ditelluride toxicity directed to the cytoskeleton

Diphenylditelluride (PhTe)₂ is a neurotoxin that disrupts cytoskeletal homeostasis. We are showing that different concentrations of (PhTe)₂ caused hypophosphorylation of glial fibrillary acidic protein (GFAP), vimentin and neurofilament subunits (NFL, NFM and NFH) and altered actin organization in co-cultured astrocytes and neurons from cerebral cortex of rats. These mechanisms were mediated by N-methyl-d-aspartate (NMDA) receptors without participation of either L-type voltage-dependent calcium channels (L-VDCC) or metabotropic glutamate receptors. Upregulated Ca²⁺ influx downstream of NMDA receptors activated Ca²⁺-dependent protein phosphatase 2B (PP2B) causing hypophosphorylation of astrocyte and neuron IFs. Immunocytochemistry showed that hypophosphorylated intermediate filaments (IF) failed to disrupt their organization into the cytoskeleton. However, phalloidin-actin-FITC stained cytoskeleton evidenced misregulation of actin distribution, cell spreading and increased stress fibers in astrocytes. βIII tubulin staining showed that neurite meshworks are not altered by (PhTe)₂, suggesting greater susceptibility of astrocytes than neurons to (PheTe)₂ toxicity. These findings indicate that signals leading to IF hypophosphorylation fail to disrupt the cytoskeletal IF meshwork of interacting astrocytes and neurons in vitro however astrocyte actin network seems more susceptible. Our findings support that intracellular Ca²⁺ is one of the crucial signals that modulate the action of (PhTe)₂ in co-cultured astrocytes and neurons and highlights the cytoskeleton as an end-point of the neurotoxicity of this compound. Cytoskeletal misregulation is associated with cell dysfunction, therefore, the understanding of the molecular mechanisms mediating the neurotoxicity of this compound is a matter of increasing interest since tellurium compounds are increasingly released in the environment.

Quinolinic acid neurotoxicity: Differential roles of astrocytes and microglia via FGF-2-mediated signaling in redox-linked cytoskeletal changes

QUIN is a glutamate agonist playing a role in the misregulation of the cytoskeleton, which is associated with neurodegeneration in rats. In this study, we focused on microglial activation, FGF2/Erk signaling, gap junctions (GJs), inflammatory parameters and redox imbalance acting on cytoskeletal dynamics of the in QUIN-treated neural cells of rat striatum. FGF-2/Erk signaling was not altered in QUIN-treated primary astrocytes or neurons, however cytoskeleton was disrupted. In co-cultured astrocytes and neurons, QUIN-activated FGF2/Erk signaling prevented the cytoskeleton from remodeling. In mixed cultures (astrocyte, neuron, microglia), QUIN-induced FGF-2 increased level failed to activate Erk and promoted cytoskeletal destabilization. The effects of QUIN in mixed cultures involved redox imbalance upstream of Erk activation. Decreased connexin 43 (Cx43) immunocontent and functional GJs, was also coincident with disruption of the cytoskeleton in primary astrocytes and mixed cultures. We postulate that in interacting astrocytes and neurons the cytoskeleton is preserved against the insult of QUIN by activation of FGF-2/Erk signaling and proper cell-cell interaction through GJs. In mixed cultures, the FGF-2/Erk signaling is blocked by the redox imbalance associated with microglial activation and disturbed cell communication, disrupting the cytoskeleton. Thus, QUIN signal activates differential mechanisms that could stabilize or destabilize the cytoskeleton of striatal astrocytes and neurons in culture, and glial cells play a pivotal role in these responses preserving or disrupting a combination of signaling pathways and cell-cell interactions. Taken together, our findings shed light into the complex role of the active interaction of astrocytes, neurons and microglia in the neurotoxicity of QUIN.

Calcium signaling mechanisms disrupt the cytoskeleton of primary astrocytes and neurons exposed to diphenylditelluride

BACKGROUND

Diphenylditelluride (PhTe)2 is a potent neurotoxin disrupting the homeostasis of the cytoskeleton.

METHODS

Cultured astrocytes and neurons were incubated with (PhTe)2, receptor antagonists and enzyme inhibitors followed by measurement of the incorporation of [32P]orthophosphate into intermediate filaments (IFs).

RESULTS

(PhTe)2 caused hyperphosphorylation of glial fibrillary acidic protein (GFAP), vimentin and neurofilament subunits (NFL, NFM and NFH) from primary astrocytes and neurons, respectively. These mechanisms were mediated by N-methyl-d-aspartate (NMDA) receptors, L-type voltage-dependent calcium channels (L-VDCCs) as well as metabotropic glutamate receptors upstream of phospholipase C (PLC). Upregulated Ca(2+) influx activated protein kinase A (PKA) and protein kinase C (PKC) in astrocytes causing hyperphosphorylation of GFAP and vimentin. Hyperphosphorylated (IF) together with RhoA-activated stress fiber formation, disrupted the cytoskeleton leading to altered cell morphology. In neurons, the high intracellular Ca(2+) levels activated the MAPKs, Erk and p38MAPK, beyond PKA and PKC, provoking hyperphosphorylation of NFM, NFH and NFL.

CONCLUSIONS

Our findings support that intracellular Ca(2+) is one of the crucial signals that modulate the action of (PhTe)2 in isolated cortical astrocytes and neurons modulating the response of the cytoskeleton against the insult.

GENERAL SIGNIFICANCE

Cytoskeletal misregulation is associated with neurodegeneration. This compound could be a valuable tool to induce molecular changes similar to those found in different pathologies of the brain.

Gold Nanoparticle-Decorated Scaffolds Promote Neuronal Differentiation and Maturation

Engineered 3D neuronal networks are considered a promising approach for repairing the damaged spinal cord. However, the lack of a technological platform encouraging axonal elongation over branching may jeopardize the success of such treatment. To address this issue we have decorated gold nanoparticles on the surface of electrospun nanofiber scaffolds, characterized the composite material, and investigated their effect on the differentiation, maturation, and morphogenesis of primary neurons and on an immature neuronal cell line. We have shown that the nanocomposite scaffolds have encouraged a longer outgrowth of the neurites, as judged by the total length of the branching trees and the length and total distance of neurites. Moreover, neurons grown on the nanocomposite scaffolds had less neurites originating out of the soma and lower number of branches. Taken together, these results indicate that neurons cultivated on the gold nanoparticle scaffolds prefer axonal elongation over forming complex branching trees. We envision that such cellular constructs may be useful in the future as implantable cellular devices for repairing damaged neuronal tissues, such as the spinal cord.

Remote Magnetic Orientation of 3D Collagen Hydrogels for Directed Neuronal Regeneration

Hydrogel matrices are valuable platforms for neuronal tissue engineering. Orienting gel fibers to achieve a directed scaffold is important for effective functional neuronal regeneration. However, current methods are limited and require treatment of gels prior to implantation, ex-vivo, without taking into consideration the pathology in the injured site. We have developed a method to control gel orientation dynamically and remotely in situ. We have mixed into collagen hydrogels magnetic nanoparticles then applied an external magnetic field. During the gelation period the magnetic particles aggregated into magnetic particle strings, leading to the alignment of the collagen fibers. We have shown that neurons within the 3D magnetically induced gels exhibited normal electrical activity and viability. Importantly, neurons formed elongated cooriented morphology, relying on the particle strings and fibers as supportive cues for growth. The ability to inject the mixed gel directly into the injured site as a solution then to control scaffold orientation remotely opens future possibilities for therapeutic engineered scaffolds.

Impaired Neurite Contact Guidance in Ubiquitin Ligase E3a (Ube3a)-Deficient Hippocampal Neurons on Nanostructured Substrates

Recent discoveries indicate that during neuronal development the signaling processes that regulate extracellular sensing (e.g., adhesion, cytoskeletal dynamics) are important targets for ubiquitination-dependent regulation, in particular through E3 ubiquitin ligases. Among these, Ubiquitin E3a ligase (UBE3A) has a key role in brain functioning, but its function and how its deficiency results in the neurodevelopmental disorder Angelman syndrome is still unclear. Here, the role of UBE3A is investigated in neurite contact guidance during neuronal development, in vitro. The microtopography sensing of wild-type and Ube3a-deficient hippocampal neurons is studied by exploiting gratings with different topographical characteristics, with the aim to compare their capabilities to read and follow physical directional stimuli. It is shown that neuronal contact guidance is defective in Ube3a-deficient neurons, and this behavior is linked to an impaired activation of the focal adhesion signaling pathway. Taken together, the results suggest that the neuronal contact sensing machinery might be affected in Angelman syndrome.

Magnetic micro-device for manipulating PC12 cell migration and organization

Directing neuronal migration and growth has an important impact on potential post traumatic therapies. Magnetic manipulation is an advantageous method for remotely guiding cells. In the present study, we have generated highly localized magnetic fields with controllable magnetic flux densities to manipulate neuron-like cell migration and organization at the microscale level. We designed and fabricated a unique miniaturized magnetic device composed of an array of rectangular ferromagnetic bars made of permalloy (Ni80Fe20), sputter-deposited onto glass substrates. The asymmetric shape of the magnets enables one to design a magnetic landscape with high flux densities at the poles. Iron oxide nanoparticles were introduced into PC12 cells, making the cells magnetically sensitive. First, we manipulated the cells by applying an external magnetic field. The magnetic force was strong enough to direct PC12 cell migration in culture. Based on time lapse observations, we analysed the movement of the cells and estimated the amount of MNPs per cell. We plated the uploaded cells on the micro-patterned magnetic device. The cells migrated towards the high magnetic flux zones and aggregated at the edges of the patterned magnets, corroborating that the cells with magnetic nanoparticles are indeed affected by the micro-magnets and attracted to the bars' magnetic poles. Our study presents an emerging method for the generation of pre-programmed magnetic micro-'hot spots' to locate and direct cellular growth, setting the stage for implanted magnetic devices.

Substrates coated with silver nanoparticles as a neuronal regenerative material

Much effort has been devoted to the design of effective biomaterials for nerve regeneration. Here, we report the novel use of silver nanoparticles (AgNPs) as regenerative agents to promote neuronal growth. We grew neuroblastoma cells on surfaces coated with AgNPs and studied the effect on the development of the neurites during the initiation and the elongation growth phases. We find that the AgNPs function as favorable anchoring sites, and the growth on the AgNP-coated substrates leads to a significantly enhanced neurite outgrowth. Cells grown on substrates coated with AgNPs have initiated three times more neurites than cells grown on uncoated substrates, and two times more than cells grown on substrates sputtered with a plain homogenous layer of silver. The growth of neurites on AgNPs in the elongation phase was enhanced as well. A comparison with substrates coated with gold nanoparticles (AuNPs) and zinc oxide nanoparticles (ZnONPs) demonstrated a clear silver material-driven promoting effect, in addition to the nanotopography. The growth on substrates coated with AgNPs has led to a significantly higher number of initiating neurites when compared to substrates coated with AuNPs or ZnONPs. All nanoparticle-coated substrates affected and promoted the elongation of neurites, with a significant positive maximal effect for the AgNPs. Our results, combined with the well-known antibacterial effect of AgNPs, suggest the use of AgNPs as an attractive nanomaterial – with dual activity – for neuronal repair studies.

Interaction of leech neurons with topographical gratings: comparison with rodent and human neuronal lines and primary cells

Controlling and improving neuronal cell migration and neurite outgrowth are critical elements of tissue engineering applications and development of artificial neuronal interfaces. To this end, a promising approach exploits nano/microstructured surfaces, which have been demonstrated to be capable of tuning neuronal differentiation, polarity, migration and neurite orientation. Here, we investigate the neurite contact guidance of leech neurons on plastic gratings (GRs; anisotropic topographies composed of alternating lines of grooves and ridges). By high-resolution microscopy, we quantitatively evaluate the changes in tubulin cytoskeleton organization and cell morphology and in the neurite and growth cone development. The topography-reading process of leech neurons on GRs is mediated by filopodia and is more responsive to 4-µm-period GRs than to smaller period GRs. Leech neuron behaviour on GRs is finally compared and validated with several other neuronal cells, from murine differentiated embryonic stem cells and primary hippocampal neurons to differentiated human neuroblastoma cells.

Nanoimprinting of topographical and 3D cell culture scaffolds

The extracellular matrix exhibits several nanostructures such as fibers, filaments, nanopores and ridges that can be mimicked by topographical and 3D substrates for cell and tissue cultures for an environment closer to in vivo conditions. This review summarizes and discusses a growing number of reports employing nanoimprint lithography to obtain such scaffolds. The different nanoimprint lithography methods as well as their advantages and disadvantages are described and special attention is paid to cell culture applications. We discuss the impact of materials, nanotopography, size, geometry, fabrication method, and cell type on growth guidance and differentiation. We present examples of cell guidance, inhibition of cell growth, cell pinning and engineering of 3D cell sheets or spheroids. As current applications are limited and not systematically compared for various cell types, this review only suggests promising substrates for particular applications. Future possible directions are also proposed in which this field may proceed.

Two-photon polymerization of sub-micrometric patterned surfaces: investigation of cell-substrate interactions and improved differentiation of neuron-like cells

Direct Laser Writing (DLW) is an innovative tool that allows the photofabrication of high resolution 3D structures, which can be successfully exploited for the study of the physical interactions between cells and substrates. In this work, we focused our attention on the topographical effects of submicrometric patterned surfaces fabricated via DLW on neuronal cell behavior. In particular, we designed, prepared, and characterized substrates based on aligned ridges for the promotion of axonal outgrowth and guidance. We demonstrated that both rat PC12 neuron-like cells and human SH-SY5Y derived neurons differentiate on parallel 2.5 μm spaced submicrometric ridges, being characterized by strongly aligned and significantly longer neurites with respect to those differentiated on flat control substrates, or on more spaced (5 and 10 μm) ridges. Furthermore, we detected an increased molecular differentiation toward neurons of the SH-SY5Y cells when grown on the submicrometric patterned substrates. Finally, we observed that the axons can exert forces able of bending the ridges, and we indirectly estimated the order of magnitude of these forces thanks to scanning probe techniques. Collectively, we showed as submicrometric structures fabricated by DLW can be used as a useful tool for the study of the axon mechanobiology.