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Abstract Background Microelectrode array (MEA) systems are valuable for in vitro assessment of neurotoxicity and drug efficiency. However, several difficulties such as protracted functional maturation and high experimental costs hinder the use of MEA analysis requiring human induced pluripotent stem cells (hiPSCs). Neural network functional parameters are also needed for in vitro to in vivo extrapolation. Methods In the present study, we produced a cost effective nanofiber culture platform, the SCAD device, for long-term culture of hiPSC-derived neurons and primary peripheral neurons. The notable advantage of SCAD device is convenient application on multiple MEA systems for neuron functional analysis. Results We showed that the SCAD device could promote functional maturation of cultured hiPSC-derived neurons, and neurons responded appropriately to convulsant agents. Furthermore, we successfully analyzed parameters for in vitro to in vivo extrapolation, i.e., low-frequency components and synaptic propagation velocity of the signal, potentially reflecting neural network functions from neurons cultured on SCAD device. Finally, we measured the axonal conduction velocity of peripheral neurons. Conclusions: Neurons cultured on SCAD devices might constitute a reliable in vitro platform to investigate neuron functions, drug efficacy and toxicity, and neuropathological mechanisms by MEA.

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative motor neuron (MN) disease. The gene encoding superoxide dismutase 1 (SOD1) is a causative element of familial ALS. Animal ALS models involving SOD1 gene mutations are widely used to study the underlying mechanisms of disease and facilitate drug discovery. Unfortunately, most drug candidates have failed in clinical trials, potentially due to species differences among rodents and humans. It is unclear, however, whether there are different responses to drugs among the causative genes of ALS or their associated mutations. In this study, to evaluate different SOD1 mutations, we generated SOD1-ALS models derived from human embryonic stem cells with identical genetic backgrounds, except for the overexpression of mutant variants of SOD1. The overexpression of mutant SOD1 did not affect pluripotency or MN differentiation. However, mutation-dependent reductions in neurite length were observed in MNs. Moreover, experiments investigating the effects of specific compounds revealed that each ALS model displayed different responses with respect to MN neurite length. These results suggest that SOD1 mutations could be classified based the response of MNs to drug treatment. This classification could be useful for the development of mutant-specific strategies for drug discovery and clinical trials.

BACKGROUND: There are no cures or efficacious treatments for severe motor neuron diseases. It is extremely difficult to obtain naïve spinal motor neurons (sMNs) from human tissues for research due to both technical and ethical reasons. Human embryonic stem cells (hESCs) are alternative sources. Several methods for MN differentiation have been reported. However, efficient production of naïve sMNs and culture cost were not taken into consideration in most of the methods. METHODS/PRINCIPAL FINDINGS: We aimed to establish protocols for efficient production and enrichment of sMNs derived from pluripotent stem cells. Nestin+ neural stem cell (NSC) clusters were induced by Noggin or a small molecule inhibitor of BMP signaling. After dissociation of NSC clusters, neurospheres were formed in a floating culture containing FGF2. The number of NSCs in neurospheres could be expanded more than 30-fold via several passages. More than 33% of HB9+ sMN progenitor cells were observed after differentiation of dissociated neurospheres by all-trans retinoic acid (ATRA) and a Shh agonist for another week on monolayer culture. HB9+ sMN progenitor cells were enriched by gradient centrifugation up to 80% purity. These HB9+ cells differentiated into electrophysiologically functional cells and formed synapses with myotubes during a few weeks after ATRA/SAG treatment. CONCLUSIONS AND SIGNIFICANCE: The series of procedures we established here, namely neural induction, NSC expansion, sMN differentiation and sMN purification, can provide large quantities of naïve sMNs derived from human and monkey pluripotent stem cells. Using small molecule reagents, reduction of culture cost could be achieved.