Compartmentalized Platforms for Neuro-Pharmacological Research

Multiple Labeling of Compartmentalized Cortical Neurons in Microfluidic Chambers

Neurons are complex cells with two distinct compartments: the somatodendritic and the axonal domains. Because of their polarized morphology, it is challenging to study the differential cellular and molecular mechanisms that occur in axons and impact the soma and dendrites using conventional in vitro culture systems. Compartmentalized cultures offer a solution by physically and chemically separating the axonal from the somatodendritic domain of neurons. The microfluidic chamber model presented in this work is valuable for studying these mechanisms in primary cortical cultures derived from rat and mouse. In addition, this chamber model is compatible with various microscopy methods, such as phase contrast, and fluorescence imaging of living and fixed cells. Key features • Preparation and attachment of PDMS microfluidic chambers to glass coverslips. • Primary culture of cortical neurons and plating cortical neurons in microfluidic chamber. • Confirmation of compartmentalization using the retrograde transport of the fluorescently labeled form of cholera toxin subunit B (f-Ctb). • Immunofluorescence and multilabeling of compartmentalized cortical neurons. • Retrograde transport of fluorescently labeled BDNF.

Corneal neuroepithelial compartmentalized microfluidic chip model for evaluation of toxicity-induced dry eye

Part of the lacrimal functional unit, the cornea protects the ocular surface from numerous environmental aggressions and xenobiotics. Toxicological evaluation of compounds remains a challenge due to complex interactions between corneal nerve endings and epithelial cells. To this day, models do not integrate the physiological specificity of corneal nerve endings and are insufficient for the detection of low toxic effects essential to anticipate Toxicity-Induced Dry Eye (TIDE). Using high-content imaging tool, we here characterize toxicity-induced cellular alterations using primary cultures of mouse trigeminal sensory neurons and corneal epithelial cells in a compartmentalized microfluidic chip. We validate this model through the analysis of benzalkonium chloride (BAC) toxicity, a well-known preservative in eyedrops, after a single (6h) or repeated (twice a day for 15 min over 5 days) topical 5.10-4% BAC applications on the corneal epithelial cells and nerve terminals. In combination with high-content image analysis, this advanced microfluidic protocol reveal specific and tiny changes in the epithelial cells and axonal network as well as in trigeminal cells, not directly exposed to BAC, with ATF3/6 stress markers and phospho-p44/42 cell activation marker. Altogether, this corneal neuroepithelial chip enables the evaluation of toxic effects of ocular xenobiotics, distinguishing the impact on corneal sensory innervation and epithelial cells. The combination of compartmentalized co-culture/high-content imaging/multiparameter analysis opens the way for the systematic analysis of toxicants but also neuroprotective compounds.

Podocyte-Parietal Epithelial Cell Interdependence in Glomerular Development and Disease

Podocytes and parietal epithelial cells (PECs) are among the few principal cell types within the kidney glomerulus, the former serving as a crucial constituent of the kidney filtration barrier and the latter representing a supporting epithelial layer that adorns the inner wall of Bowman's capsule. Podocytes and PECs share a circumscript developmental lineage that only begins to diverge during the S-shaped body stage of nephron formation-occurring immediately before the emergence of the fully mature nephron. These two cell types, therefore, share a highly conserved gene expression program, evidenced by recently discovered intermediate cell types occupying a distinct spatiotemporal gene expression zone between podocytes and PECs. In addition to their homeostatic functions, podocytes and PECs also have roles in kidney pathogenesis. Rapid podocyte loss in diseases, such as rapidly progressive GN and collapsing and cellular subtypes of FSGS, is closely allied with PEC proliferation and migration toward the capillary tuft, resulting in the formation of crescents and pseudocrescents. PECs are thought to contribute to disease progression and severity, and the interdependence between these two cell types during development and in various manifestations of kidney pathology is the primary focus of this review.

Modeling Neurodegenerative Diseases Using In Vitro Compartmentalized Microfluidic Devices

The human brain is a complex organ composed of many different types of cells interconnected to create an organized system able to efficiently process information. Dysregulation of this delicately balanced system can lead to the development of neurological disorders, such as neurodegenerative diseases (NDD). To investigate the functionality of human brain physiology and pathophysiology, the scientific community has been generated various research models, from genetically modified animals to two- and three-dimensional cell culture for several decades. These models have, however, certain limitations that impede the precise study of pathophysiological features of neurodegeneration, thus hindering therapeutical research and drug development. Compartmentalized microfluidic devices provide in vitro minimalistic environments to accurately reproduce neural circuits allowing the characterization of the human central nervous system. Brain-on-chip (BoC) is allowing our capability to improve neurodegeneration models on the molecular and cellular mechanism aspects behind the progression of these troubles. This review aims to summarize and discuss the latest advancements of microfluidic models for the investigations of common neurodegenerative disorders, such as Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis.

Comparison of axon extension: PTFE versus PLA formed by a 3D printer

Three-dimensional (3D) printers mainly create 3D objects by stacking thin layers of material. The effect of the tools created using the fused deposition modeling (FDM) 3D printer on nerve cells remains unclear. In this study, the effects of polytetrafluoroethylene (PTFE) models and two different types of polylactic acid (PLA) models (white or natural), were created using the FDM 3D printer on axon extension were compared using the Campenot chamber. Neurons were isolated from the dorsal root ganglia and added to the central compartment of the Campenot chambers after isolation, processing, and culturing. On day 7, after the initiation of the culture, the difference of the axon extensions to the side compartments of each group was confirmed. We also compared the pH and the amount of leakage when each of these chambers was used. The PLA was associated with a shorter axon extension than the PTFE (white p = 0.0078, natural p = 0.00391). No difference in the pH was observed (p = 0.347), but there was a significant difference on multiple group comparison (p = 0.0231) in the amount of leakage of the medium. PTFE was found to be a more suitable material for culturing attachments.

Use of Microfluidics Chambers to Image Axonal transport in Adult Sensory Neurons

Transport of cargoes along axons is crucial for ensuring effective neuronal function and survival. Lysosomes, which are membrane-bound organelles responsible for the degradation of macromolecules, are among the many cargoes being transported. Compartmentalized systems that allow for the separation of the somatic compartment from the axonal network, are widely used in the field of neurobiology and in the study of axonal transport in particular. Among the various solutions available, microfluidics chambers that take advantage of fluidic separation between different compartments, have seen widespread adoption. Said chambers are made of polydimethylsiloxane (PDMS), a transparent, gas permeable compound, which is compatible with fluorescence microscopy, and have significantly positively impacted cellular neuroscience, drastically increasing our understanding of axonal peripheral signaling. Here we describe a two-layered microfluidics chamber, engineered to allow for the culture of adult sensory neurons. This device was designed to promote the proper placement of adult sensory neurons in the somatic chamber in proximity of the microgrooves. We detail the production of the master mold, how to fabricate and assemble the device and how to disaggregate and load the cells in it. In addition, we provide details on how to conduct and analyze an axonal transport experiment using a custom made script in MATLAB designed by our laboratory.

Development of an Axon-Guiding Aligned Nanofiber-Integrated Compartmentalized Microfluidic Neuron Culture System

Microfluidic-based neuron cell culture systems have recently gained a lot of attention due to their efficiency in supporting the spatial and temporal control of cellular microenvironments. However, the lack of axon guidance is the key limitation in current culture systems. To combat this, we have developed electrospun aligned nanofiber-integrated compartmentalized microfluidic neuron culture systems (NIMSs), where the nanofibers have enabled axonal guidance and stability. The resulting platform significantly improved axon alignment, length, and stability for both rat primary embryonic motor neurons (MNs) and dorsal root ganglia (DRG) neurons compared to the conventional glass-based microfluidic systems (GMSs). The results showed that axonal growth covered more than two times the area on the axonal chamber of NIMSs compared to the area covered for GMSs. Overall, this platform can be used as a valuable tool for fundamental neuroscience research, drug screening, and biomaterial testing.

Compartmentalized microfluidic chambers enable long-term maintenance and communication between human pluripotent stem cell-derived forebrain and midbrain neurons

Compartmentalized microfluidic devices are becoming increasingly popular and have proven to be valuable tools to probe neurobiological functions that are inherently difficult to study using traditional approaches. The ability of microfluidic devices to compartmentalize neurons offers considerable promise for disease modeling and drug discovery. Rodent cortical neurons/neural progenitors are commonly used in such studies but, while these cells mature rapidly, they do not possess the same receptors, ion channels and transport proteins found in human cortical neurons. Human pluripotent stem cell derived neurons offer a human phenotype, but their slow maturation offsets this phenotypic advantage, particularly over long-term culture where overgrowth and subsequent death of neurons may be a problem. In this work, we integrate the use of Matrigel as a 3D cell culture scaffold that enables high cell seeding density over a small fraction of the culture surface. This approach, in an open chamber microfluidic system, enables culture over a five-month period without the use of growth inhibitors. Matrigel was also uniquely utilized to hinder agonist diffusion across microchannels. We demonstrate the development of neuron-to-neuron communication networks by showing that electrical stimulation or the unilateral addition of agonists to one chamber resulted in activation of neurons in the adjacent chamber. Lastly, using a delayed neuron seeding strategy, we show that we can foster essentially one-way communication between separate populations of human forebrain and midbrain dopaminergic neuron containing cultures.

Microfabricated Devices for Confocal Microscopy on Biological Samples

Microfabricated devices have found applications in a range of biomedical research problems in recent years, with thousands of research papers published and multiple commercial devices now available. This chapter is intended to provide an overview of the available options for devices compatible with confocal microscopy, including an overview of fabrication techniques and some examples of device use. Although there are times when off-the-shelf devices are well suited for the problem at hand, in some cases customized devices are necessary or more convenient. Protocols for researchers who wish to make their own devices are outlined below; although fabricating templates for devices requires some specialized equipment, making PDMS or hydrogel devices from templates can be done in a standard laboratory setting.

Integrating Biosensors in Organs-on-Chip Devices: A Perspective on Current Strategies to Monitor Microphysiological Systems

Organs-on-chip (OoC), often referred to as microphysiological systems (MPS), are advanced in vitro tools able to replicate essential functions of human organs. Owing to their unprecedented ability to recapitulate key features of the native cellular environments, they represent promising tools for tissue engineering and drug screening applications. The achievement of proper functionalities within OoC is crucial; to this purpose, several parameters (e.g., chemical, physical) need to be assessed. Currently, most approaches rely on off-chip analysis and imaging techniques. However, the urgent demand for continuous, noninvasive, and real-time monitoring of tissue constructs requires the direct integration of biosensors. In this review, we focus on recent strategies to miniaturize and embed biosensing systems into organs-on-chip platforms. Biosensors for monitoring biological models with metabolic activities, models with tissue barrier functions, as well as models with electromechanical properties will be described and critically evaluated. In addition, multisensor integration within multiorgan platforms will be further reviewed and discussed.

Nanogrooves for 2D and 3D Microenvironments of SH-SY5Y Cultures in Brain-on-Chip Technology

Brain-on-chip (BOC) technology such as nanogrooves and microtunnel structures can advance in vitro neuronal models by providing a platform with better means to maintain, manipulate and analyze neuronal cell cultures. Specifically, nanogrooves have been shown to influence neuronal differentiation, notably the neurite length and neurite direction. Here, we have drawn new results from our experiments using both 2D and 3D neuronal cell culture implementing both flat and nanogrooved substrates. These are used to show a comparison between the number of cells and neurite length as a first indicator for valuable insights into baseline values and expectations that can be generated from these experiments toward design optimization and predictive value of the technology in our BOC toolbox. Also, as a new step toward neuronal cell models with multiple compartmentalized neuronal cell type regions, we fabricated microtunnel devices bonded to both flat and nanogrooved substrates to assess their compatibility with neuronal cell culture. Our results show that with the current experimental protocols using SH-SY5Y cells, we can expect 200 – 400 cells with a total neurite length of approximately 4,000–5,000 μm per 1 mm² within our BOC devices, with a lower total neurite length for 3D neuronal cell cultures on flat substrates only. There is a statistically significant difference in total neurite length between 2D cell culture on nanogrooved substrates versus 3D cell culture on flat substrates. As extension of our current BOC toolbox for which these indicative parameters would be used, the microtunnel devices show that culture of SH-SY5Y was feasible, though a limited number of neurites extended into microtunnels away from the cell bodies, regardless of using nanogrooved or flat substrates. This shows that the novel combination of microtunnel devices with nanogrooves can be implemented toward neuronal cell cultures, with future improvements to be performed to ensure neurites extend beyond the confines of the wells between the microtunnels. Overall, these results will aid toward creating more robust BOC platforms with improved predictive value. In turn, this can be used to better understand the brain and brain diseases.

Axon microdissection and transcriptome profiling reveals the in vivo RNA content of fully differentiated myelinated motor axons

Axonal protein synthesis has been shown to play a role in developmental and regenerative growth, as well as in the maintenance of the axoplasm in a steady state. Recent studies have begun to identify the mRNAs localized in axons, which could be translated locally under different conditions. Despite that by now hundreds or thousands of mRNAs have been shown to be localized into the axonal compartment of cultured neurons in vitro, knowledge of which mRNAs are localized in mature myelinated axons is quite limited. With the purpose of characterizing the transcriptome of mature myelinated motor axons of peripheral nervous systems, we modified the axon microdissection method devised by Koenig, enabling the isolation of the axoplasm RNA to perform RNA-seq analysis. The transcriptome analysis indicates that the number of RNAs detected in mature axons is lower in comparison with in vitro data, depleted of glial markers, and enriched in neuronal markers. The mature myelinated axons are enriched for mRNAs related to cytoskeleton, translation, and oxidative phosphorylation. Moreover, it was possible to define core genes present in axons when comparing our data with transcriptomic data of axons grown in different conditions. This work provides evidence that axon microdissection is a valuable method to obtain genome-wide data from mature and myelinated axons of the peripheral nervous system, and could be especially useful for the study of axonal involvement in neurodegenerative pathologies of motor neurons such as amyotrophic lateral sclerosis (ALS) and spinal muscular atrophies (SMA).

Evidence for cell-contact factor involvement in neurite outgrowth of dorsal root ganglion neurons stimulated by Schwann cells

NEW FINDINGS

What is the central question of this study? Although the factors secreted from Schwann cells that promote axonal growth in the peripheral nervous system have been well studied, the effect of cell-contact factors on Schwann cells remains to be determined. What is the main finding and its importance? This study demonstrates that Schwann cells stimulate neurite outgrowth by direct contact with neurites and by secreting factors. Notably, the effect of cell-contact factors in neurite outgrowth is comparable to that of secreted factors, indicating that the identification of cell surface molecules on Schwann cells that promote neurite outgrowth could lead to development of a new therapy for peripheral nervous system injury.

ABSTRACT

Schwann cells (SCs) play a variety of roles in the regeneration process after injury to the peripheral nervous system. The factors secreted from SCs that promote axonal growth have been well studied. However, the involvement of cell-contact factors on SCs remains to be determined. Here, we demonstrate a significant contribution of a cell-contact mechanism in the effect of SCs on promotion of neuronal outgrowth. Neurite outgrowth of adult sensory neurons from dorsal root ganglia was quantified during co-culture with adult SCs. Direct contact of SCs with neurons was eliminated by culturing SCs on an insert placed in the same well; this resulted in a 51% reduction in the length of neurite outgrowth. In addition, when dorsal root ganglion neurons were cultured on sparsely seeded SCs, neurons that made contact with SCs on their neurites had 118% longer neurites than neurons that lacked contacts with SCs. Collectively, these findings provide evidence that SCs stimulate neurite outgrowth via direct contact with neurites in addition to secreting factors. The identification of cell surface molecules on SCs that promote neurite outgrowth could lead to development of a new therapy for peripheral nervous system injury.

Low density culture of mammalian primary neurons in compartmentalized microfluidic devices

This paper demonstrates the fabrication of a compartmentalized microfluidic device with docking sites to position a single neuron or a cluster of 5-6 neurons along with varying length of microgrooves and the optimization process for culturing primary mammalian neurons at low densities. The principle of centrifugation was employed to situate cells in desired locations followed by the application of a fluid flow to remove the extra or unwanted cells lying in the vicinity of the located neurons. The neuronal cell density was optimized by seeding 10³ cells and 10⁴ cells/microfluidic device. The speed of centrifugation was optimized as 1500 rpm for 1 min and a cell density of greater than or equal to 10⁴ cells/microfluidic device was found to be suitable for loading maximum number of docking sites. The outcomes of the simulated experiments was found to be in compliance with the experimemtal verifications. Furthermore, the cells cultured within the microfluidic device were assessed for immunocytochemical staining and the axonal growth was quantified with the help of an Axofluidic software. Although, several in vitro microfluidic platforms have been developed that facilitate the investigations where communication between neurons or between neurons and other cell types is concerned, none of the partitioned devices so far has reported the presence of docking sites along with an array of grooves of varying lengths. These physically connected but fluidically isolated compartmentalized microfluidic devices may serve us in analysing the activity of a low density of neurons and the influence of axonal length in setting up a communication with other cell type.This platform is useful to gain insights into the processes of synapse formation, axonal guidance, cell-cell interaction, to name a few.

Neural microphysiological systems for in vitro modeling of peripheral nervous system disorders

PNS disease pathology is diverse and underappreciated. Peripheral neuropathy may result in sensory, motor or autonomic nerve dysfunction and can be induced by metabolic dysfunction, inflammatory dysfunction, cytotoxic pharmaceuticals, rare hereditary disorders or may be idiopathic. Current preclinical PNS disease research relies heavily on the use of rodent models. In vivo methods are effective but too time-consuming and expensive for high-throughput experimentation. Conventional in vitro methods can be performed with high throughput but lack the biological complexity necessary to directly model in vivo nerve structure and function. In this review, we survey in vitro PNS model systems and propose that 3D-bioengineered microphysiological nerve tissue can improve in vitro–in vivo extrapolation and expand the capabilities of in vitro PNS disease modeling.

Morphometric and computational assessments to evaluate neuron survival and maturation within compartmentalized microfluidic devices: The influence of design variation on diffusion-driven nutrient transport

Burgeoning use of segregated microfluidic platforms that parse somas and neurites into discrete compartments is fueling unique examinations of neuronal structure and physiology in a manner impossible to achieve with non-compartmentalized systems. However, even though this line of axon-soma polarizing microfluidic devices stems from the same general design of a Campenot chamber set-up, slight deviations in device geometry appear to induce vastly different nutrient transport profiles that influence neuron survival and maturation. Here we examine the uptake of nerve growth factor (NGF) by a pheochromocytoma PC12 cell line cultured using two Campenot-like device designs, a "Standard" layout, representative of a commercial device, and a custom "Notch" layout, predicted to encourage more efficient nutrient transfer that gives rise to sustained neuron viability and extensive neurite elaboration. Exploiting in vitro culture schemes coupled with computational analyses, we identify the influence of device design geometry on the interplay between neuronal survival and maturation, gauged from morphometric assessments and the spatiotemporal distribution of NGF. Computer simulations of NGF transport within the devices revealed that the microfluidic neuron culture system is highly sensitive to change, where nutrient transport is intricately linked to device geometry and cell plating density, and premature depletion of nutrients is observed if specific design criteria are not met. This study underscores the importance of validating specific device geometries for a particular neuro-based assessment, while showcasing computational modeling as a powerful tool to achieve this goal.

Modeling PNS and CNS Myelination Using Microfluidic Chambers

Modeling myelination in vitro allows mechanistic study of developmental myelination and short-term myelin maintenance, but analyses possible to carry out using currently available models are usually limited because of high cell density and the lack of separation between neurons and myelinating cells. Furthermore, regeneration studies of myelinated systems after lesion require compartmentalization of neuronal cell bodies, axons, and myelinating cells. Here we describe a compartmentalized method using microfluidics that allows live-cell imaging at the single-cell level to follow short- and long-term dynamic interactions of neurons and myelinating cells and large-scale analyses, e.g., RNA sequencing on pure or highly enriched neurons or myelinating cells, separately.