Myelinating cocultures of rodent stem cell line-derived neurons and immortalized Schwann cells

Laser-Structured Si and PLGA Inhibit the Neuro2a Differentiation in Mono- and Co-Culture with Glia

BACKGROUND

The first step towards a successful neural tissue engineering therapy is the development of an appropriate scaffold and the in vitro study of the cellular response onto it.

METHODS

Here, we fabricated nano- and micro- patterned Si surfaces via direct ultrafast laser irradiation, as well as their replicas in the biodegradable poly(lactide-co-glycolide), in order to use them as culture substrates for neuronal cells. The differentiation of neuro2a cells on the Si platforms and their replicas was studied both in a mono-culture and in a co-culture with glial cells (Schwann-SW10).

RESULTS

It was found that the substrate's roughness inhibits the differentiation of the neuronal cells even in the presence of the differentiation medium, and the higher the roughness is, the more the differentiation gets limited.

CONCLUSION

Our results highlight the importance of the substrate's topography for the controlled growth and differentiation of the neuronal cells and their further study via protein screening methods could shed light on the factors that lead to limited differentiation; thus, contributing to the long standing request for culture substrates that induce cells to differentiate.

Praja1 RING-finger E3 ubiquitin ligase is a common suppressor of neurodegenerative disease-associated protein aggregation

The formation of misfolded protein aggregates is one of the pathological hallmarks of neurodegenerative diseases. We have previously demonstrated the cytoplasmic aggregate formation of adenovirally expressed transactivation response DNA-binding protein of 43 kDa (TDP-43), the main constituent of neuronal cytoplasmic aggregates in cases of amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD), in cultured neuronal cells under the condition of proteasome inhibition. The TDP-43 aggregate formation was markedly suppressed by co-infection of adenoviruses expressing heat shock transcription factor 1 (HSF1), a master regulator of heat shock response, and Praja1 RING-finger E3 ubiquitin ligase (PJA1) located downstream of the HSF1 pathway. In the present study, we examined other reportedly known E3 ubiquitin ligases for TDP-43, i.e. Parkin, RNF112 and RNF220, but failed to find their suppressive effects on neuronal cytoplasmic TDP-43 aggregate formation, although they all bind to TDP-43 as verified by co-immunoprecipitation. In contrast, PJA1 also binds to adenovirally expressed wild-type and mutated fused in sarcoma, superoxide dismutase 1, α-synuclein and ataxin-3, and huntingtin polyglutamine proteins in neuronal cultures and suppressed the aggregate formation of these proteins. These results suggest that PJA1 is a common sensing factor for aggregate-prone proteins to counteract their aggregation propensity, and could be a potential therapeutic target for neurodegenerative diseases that include ALS, FTLD, Parkinson's disease and polyglutamine diseases.

Anisotropic scaffolds for peripheral nerve and spinal cord regeneration

The treatment of long-gap (>10 mm) peripheral nerve injury (PNI) and spinal cord injury (SCI) remains a continuous challenge due to limited native tissue regeneration capabilities. The current clinical strategy of using autografts for PNI suffers from a source shortage, while the pharmacological treatment for SCI presents dissatisfactory results. Tissue engineering, as an alternative, is a promising approach for regenerating peripheral nerves and spinal cords. Through providing a beneficial environment, a scaffold is the primary element in tissue engineering. In particular, scaffolds with anisotropic structures resembling the native extracellular matrix (ECM) can effectively guide neural outgrowth and reconnection. In this review, the anatomy of peripheral nerves and spinal cords, as well as current clinical treatments for PNI and SCI, is first summarized. An overview of the critical components in peripheral nerve and spinal cord tissue engineering and the current status of regeneration approaches are also discussed. Recent advances in the fabrication of anisotropic surface patterns, aligned fibrous substrates, and 3D hydrogel scaffolds, as well as their in vitro and in vivo effects are highlighted. Finally, we summarize potential mechanisms underlying the anisotropic architectures in orienting axonal and glial cell growth, along with their challenges and prospects.

A microfabricated multi-compartment device for neuron and Schwann cell differentiation

Understanding the complex communication between different cell populations and their interaction with the microenvironment in the central and peripheral nervous systems is fundamental in neuroscience research. The development of appropriate in vitro approaches and tools, able to selectively analyze and/or probe specific cells and cell portions (e.g., axons and cell bodies in neurons), driving their differentiation into specific cell phenotypes, has become therefore crucial in this direction. Here we report a multi-compartment microfluidic device where up to three different cell populations can be cultured in a fluidically independent circuit. The device allows cell migration across the compartments and their differentiation. We showed that an accurate choice of the device geometrical features and cell culture parameters allows to (1) maximize cell adhesion and proliferation of neuron-like human cells (SH-SY5Y cells), (2) control the inter-compartment cell migration of neuron and Schwann cells, (3) perform long-term cell culture studies in which both SH-SY5Y cells and primary rat Schwann cells can be differentiated towards specific phenotypes. These results can lead to a plethora of in vitro co-culture studies in the neuroscience research field, where tuning and investigating cell-cell and cell-microenvironment interactions are essential.

Generation of High-Yield, Functional Oligodendrocytes from a c-myc Immortalized Neural Cell Line, Endowed with Staminal Properties

Neural stem cells represent a powerful tool to study molecules involved in pathophysiology of Nervous System and to discover new drugs. Although they can be cultured and expanded in vitro as a primary culture, their use is hampered by their heterogeneity and by the cost and time needed for their preparation. Here we report that mes-c-myc A1 cells (A1), a neural cell line, is endowed with staminal properties. Undifferentiated/proliferating and differentiated/non-proliferating A1 cells are able to generate neurospheres (Ns) in which gene expression parallels the original differentiation status. In fact, Ns derived from undifferentiated A1 cells express higher levels of Nestin, Kruppel-like factor 4 (Klf4) and glial fibrillary protein (GFAP), markers of stemness, while those obtained from differentiated A1 cells show higher levels of the neuronal marker beta III tubulin. Interestingly, Ns differentiation, by Epidermal Growth Factors (EGF) and Fibroblast Growth Factor 2 (bFGF) withdrawal, generates oligodendrocytes at high-yield as shown by the expression of markers, Galactosylceramidase (Gal-C) Neuron-Glial antigen 2 (NG2), Receptor-Interacting Protein (RIP) and Myelin Basic Protein (MBP). Finally, upon co-culture, Ns-A1-derived oligodendrocytes cause a redistribution of contactin-associated protein (Caspr/paranodin) protein on neuronal cells, as primary oligodendrocytes cultures, suggesting that they are able to form compact myelin. Thus, Ns-A1-derived oligodendrocytes may represent a time-saving and low-cost tool to study the pathophysiology of oligodendrocytes and to test new drugs.

An efficient neuron-astrocyte differentiation protocol from human embryonic stem cell-derived neural progenitors to assess chemical-induced developmental neurotoxicity

Human embryonic stem cell neuronal differentiation models provide promising in vitro tools for the prediction of developmental neurotoxicity of chemicals. Such models mimic essential elements of human relevant neuronal development, including the differentiation of a variety of brain cell types and their neuronal network formation as evidenced by specific gene and protein biomarkers. However, the reproducibility and lengthy culture duration of cell models present drawbacks and delay regulatory implementation. Here we present a relatively short and robust protocol to differentiate H9-derived neural progenitor cells (NPCs) into a neuron-astrocyte co-culture. When frozen-stored NPCs were re-cultured and induced into neuron-astrocyte differentiation, they showed gene- and protein expression typical for these cells, and most notably they exhibited spontaneous electrical activity within three days of culture as measured by a multi-well micro-electrode array. Modulating the ratio of astrocytes and neurons through different growth factors including glial cell line-derived neurotrophic factor (GDNF), brain-derived neurotrophic factor (BDNF), and ciliary neurotrophic factor (CNTF) did not compromise the ability to develop spontaneous electrical activity. This robust neuronal differentiation model may serve as a functional component of a testing strategy for unravelling mechanisms of developmental neurotoxicity.

Praja1 RING-finger E3 ubiquitin ligase suppresses neuronal cytoplasmic TDP-43 aggregate formation

Transactivation response DNA-binding protein of 43 kDa (TDP-43) is a major constituent of cytoplasmic aggregates in neuronal and glial cells in cases of amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD). We have previously shown neuronal cytoplasmic aggregate formation induced by recombinant adenoviruses expressing human wild-type and C-terminal fragment (CTF) TDP-43 under the condition of proteasome inhibition in vitro and in vivo. In the present study, we demonstrated that the formation of the adenoviral TDP-43 aggregates was markedly suppressed in rat neural stem cell-derived neuronal cells by co-infection of an adenovirus expressing heat shock transcription factor 1 (HSF1), a master regulator of heat shock response. We performed DNA microarray analysis and searched several candidate molecules, located downstream of HSF1, which counteract TDP-43 aggregate formation. Among these, we identified Praja 1 RING-finger E3 ubiquitin ligase (PJA1) as a suppressor of phosphorylation and aggregate formation of TDP-43. Co-immunoprecipitation assay revealed that PJA1 binds to CTF TDP-43 and the E2-conjugating enzyme UBE2E3. PJA1 also suppressed formation of cytoplasmic phosphorylated TDP-43 aggregates in mouse facial motor neurons in vivo. Furthermore, phosphorylated TDP-43 aggregates were detected in PJA1-immunoreactive human ALS motor neurons. These results indicate that PJA1 is one of the principal E3 ubiquitin ligases for TDP-43 to counteract its aggregation propensity and could be a potential therapeutic target for ALS and FTLD.

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Cellular therapies play a critical role in the treatment of spinal cord injury (SCI). Compared with cell-seeded conduits, fully cellular grafts have more similarities with autografts, and thus might result in better regeneration effects. In this study, we fabricated Schwann cell (SC)-neural stem cell (NSC) core–shell alginate hydrogel fibers in a coaxial extrusion manner. The rat SC line RSC96 and mouse NSC line NE-4C were used in this experiment. Fully cellular components were achieved in the core portion and the relative spatial positions of these two cells partially mimic the construction of nerve fibers in vivo. SCs were demonstrated to express more genes of neurotrophic factors in alginate shell. Enhanced proliferation and differentiation tendency of NSCs was observed when they were co-cultured with SCs. This model has strong potential for application in SCI repair.

Engineering a platform for nerve regeneration with direct application to nerve repair technology

The development of effective treatment options for repair of peripheral nerves is complicated by lack of knowledge concerning the interactions between cells and implants. A promising device, the multichannel scaffold, incorporates microporous channels, aligning glia and directing axonal growth across a nerve gap. To enhance clinical outcomes of nerve repair, a platform, representative of current implant technology, was engineered which 1) recapitulated key device features (porosity and linearity) and 2) demonstrated remyelination of adult neurons. The in vitro platform began with the study of Schwann cells on porous polycaprolactone (PCL) and poly(lactide co-glycolide) (PLGA) substrates. Surface roughness determined glial cell attachment, and an additional layer of topography, 40 μm linear features, aligned Schwann cells and axons. In addition, direct co-culture of sensory neurons with Schwann cells significantly increased neurite outgrowth, compared to neurons cultured alone (naive or pre-conditioned). In contrast to the control substrate (glass), on porous PCL substrates, Schwann cells differentiated into a mature myelinating phenotype, expressing Oct-6, MPZ and MBP. The direct applicability of this platform to nerve implants, including its response to physiological cues, allows for optimization of cell-material interactions, close observation of the regeneration process, and the study of therapeutics, necessary to advance peripheral nerve repair technology.

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.

Establishment of a myelinating co-culture system with a motor neuron-like cell line NSC-34 and an adult rat Schwann cell line IFRS1

Co-culture models of neurons and Schwann cells have been utilized for the study of myelination and demyelination in the peripheral nervous system; in most of the previous studies, however, these cells were obtained by primary culture with embryonic or neonatal animals. A spontaneously immortalized Schwann cell line IFRS1 from long-term cultures of adult Fischer rat peripheral nerves has been shown to retain fundamental ability to myelinate neurites in co-cultures with adult rat dorsal root ganglion neurons and nerve growth factor-primed PC12 cells. Our current investigation focuses on the establishment of stable co-culture system with IFRS1 cells and NSC-34 motor neuron-like cells. NSC-34 cells were seeded at a low density (2 × 10³/cm²) and maintained for 5-7 days in serum-containing medium supplemented with non-essential amino acids and brain-derived neurotrophic factor (BDNF; 10 ng/mL). Upon observation of neurite outgrowth under a phase-contrast microscope, the NSC-34 cells were exposed to an anti-mitotic agent mitomycin C (1 µg/mL) for 12-16 h, then co-cultured with IFRS1 cells (2 × 10⁴/cm²), and maintained in serum-containing medium supplemented with ascorbic acid (50 µg/mL), BDNF (10 ng/mL), and ciliary neurotrophic factor (10 ng/mL). Double immunofluorescence staining carried out at day 28 of the co-culture showed myelin protein (P0 or PMP22)-immunoreactive IFRS1 cells surrounding the βIII tubulin-immunoreactive neurites. This co-culture system can be a beneficial tool to study the pathogenesis of motor neuron diseases (e.g., amyotrophic lateral sclerosis, Charcot-Marie-Tooth diseases, and immune-mediated demyelinating neuropathies) and novel therapeutic approaches against them.