Rapid generation of functional engineered 3D human neuronal assemblies: network dynamics evaluated by micro-electrodes arrays

Enhanced electrophysiological activity and neurotoxicity screening of environmental chemicals using 3D neurons from human neural precursor cells purified with PSA-NCAM

The assessment of neurotoxicity for environmental chemicals is of utmost importance in ensuring public health and environmental safety. Multielectrode array (MEA) technology has emerged as a powerful tool for assessing disturbances in the electrophysiological activity. Although human embryonic stem cell (hESC)-derived neurons have been used in MEA for neurotoxicity screening, obtaining a substantial and sufficiently active population of neurons from hESCs remains challenging. In this study, we successfully differentiated neurons from a large population of human neuronal precursor cells (hNPC) purified using a polysialylated neural cell adhesion molecule (PSA-NCAM), referred to as hNPCPSA-NCAM+. The functional characterization demonstrated that hNPCPSA-NCAM+-derived neurons improve functionality by enhancing electrophysiological activity compared to total hNPC-derived neurons. Furthermore, three-dimensional (3D) neurons derived from hNPCPSA-NCAM+ exhibited reduced maturation time and enhanced electrophysiological activity on MEA. We employed subdivided population analysis of active mean firing rate (MFR) based on electrophysiological intensity to characterize the electrophysiological properties of hNPCPSA-NCAM+-3D neurons. Based on electrophysiological activity including MFR and burst parameters, we evaluated the sensitivity of hNPCPSA-NCAM+-3D neurons on MEA to screen both inhibitory and excitatory neuroactive environmental chemicals. Intriguingly, electrophysiologically active hNPCPSA-NCAM+-3D neurons demonstrated good sensitivity to evaluate neuroactive chemicals, particularly in discriminating excitatory chemicals. Our findings highlight the effectiveness of MEA approaches using hNPCPSA-NCAM+-3D neurons in the assessment of neurotoxicity associated with environmental chemicals. Furthermore, we emphasize the importance of selecting appropriate signal intensity thresholds to enhance neurotoxicity prediction and screening of environmental chemicals.

A NSC-34 cell line-derived spheroid model: Potential and challenges for in vitro evaluation of neurodegeneration

Three-dimensional (3D) spheroid models aim to bridge the gap between traditional two-dimensional (2D) cultures and the complex in vivo tissue environment. These models, created by self-clustering cells to mimic a 3D environment with surrounding extracellular framework, provide a valuable research tool. The NSC-34 cell line, generated by fusing mouse spinal cord motor neurons and neuroblastoma cells, is essential for studying neurodegenerative diseases like amyotrophic lateral sclerosis (ALS), where abnormal protein accumulation, such as TAR-DNA-binding protein 43 (TDP-43), occurs in affected nerve cells. However, NSC-34 behavior in a 3D context remains underexplored, and this study represents the first attempt to create a 3D model to determine its suitability for studying pathology. We generated NSC-34 spheroids using a nonadhesive hydrogel-based template and characterized them for 6 days. Light microscopy revealed that NSC-34 cells in 3D maintained high viability, a distinct round shape, and forming stable membrane connections. Scanning electron microscopy identified multiple tunnel-like structures, while ultrastructural analysis highlighted nuclear bending and mitochondria alterations. Using inducible GFP-TDP-43-expressing NSC-34 spheroids, we explored whether 3D structure affected TDP-43 expression, localization, and aggregation. Spheroids displayed nuclear GFP-TDP-43 expression, albeit at a reduced level compared with 2D cultures and generated both TDP-35 fragments and TDP-43 aggregates. This study sheds light on the distinctive behavior of NSC-34 in 3D culture, suggesting caution in the use of the 3D model for ALS or TDP-43 pathologies. Yet, it underscores the spheroids' potential for investigating fundamental cellular mechanisms, cell adaptation in a 3D context, future bioreactor applications, and drug penetration studies. RESEARCH HIGHLIGHTS: 3D spheroid generation: NSC-34 spheroids, developed using a hydrogel-based template, showed high viability and distinct shapes for 6 days. Structural features: advanced microscopy identified tunnel-like structures and nuclear and mitochondrial changes in the spheroids. Protein dynamics: the study observed how 3D structures impact TDP-43 behavior, with altered expression but similar aggregation patterns to 2D cultures. Research implications: this study reveals the unique behavior of NSC-34 in 3D culture, suggests a careful approach to use this model for ALS or TDP-43 pathologies, and highlights its potential in cellular mechanism research and drug testing applications.

Long-termin vitroculture of 3D brain tissue model based on chitosan thermogel

Methods for studying brain function and disease heavily rely onin vivoanimal models,ex-vivotissue slices, and 2D cell culture platforms. These methods all have limitations that significantly impact the clinical translatability of results. Consequently, models able to better recapitulate some aspects ofin vivohuman brain are needed as additional preclinical tools. In this context, 3D hydrogel-basedin vitromodels of the brain are considered promising tools. To create a 3D brain-on-a-chip model, a hydrogel capable of sustaining neuronal maturation over extended culture periods is required. Among biopolymeric hydrogels, chitosan-β-glycerophosphate (CHITO-β-GP) thermogels have demonstrated their versatility and applicability in the biomedical field over the years. In this study, we investigated the ability of this thermogel to encapsulate neuronal cells and support the functional maturation of a 3D neuronal network in long-term cultures. To the best of our knowledge, we demonstrated for the first time that CHITO-β-GP thermogel possesses optimal characteristics for promoting neuronal growth and the development of an electrophysiologically functional neuronal network derived from both primary rat neurons and neurons differentiated from human induced pluripotent stem cells (h-iPSCs) co-cultured with astrocytes. Specifically, two different formulations were firstly characterized by rheological, mechanical and injectability tests. Primary nervous cells and neurons differentiated from h-iPSCs were embedded into the two thermogel formulations. The 3D cultures were then deeply characterized by immunocytochemistry, confocal microscopy, and electrophysiological recordings, employing both 2D and 3D micro-electrode arrays. The thermogels supported the long-term culture of neuronal networks for up to 100 d. In conclusion, CHITO-β-GP thermogels exhibit excellent mechanical properties, stability over time under culture conditions, and bioactivity toward nervous cells. Therefore, they are excellent candidates as artificial extracellular matrices in brain-on-a-chip models, with applications in neurodegenerative disease modeling, drug screening, and neurotoxicity evaluation.

Human-Derived Cortical Neurospheroids Coupled to Passive, High-Density and 3D MEAs: A Valid Platform for Functional Tests

With the advent of human-induced pluripotent stem cells (hiPSCs) and differentiation protocols, methods to create in-vitro human-derived neuronal networks have been proposed. Although monolayer cultures represent a valid model, adding three-dimensionality (3D) would make them more representative of an in-vivo environment. Thus, human-derived 3D structures are becoming increasingly used for in-vitro disease modeling. Achieving control over the final cell composition and investigating the exhibited electrophysiological activity is still a challenge. Thence, methodologies to create 3D structures with controlled cellular density and composition and platforms capable of measuring and characterizing the functional aspects of these samples are needed. Here, we propose a method to rapidly generate neurospheroids of human origin with control over cell composition that can be used for functional investigations. We show a characterization of the electrophysiological activity exhibited by the neurospheroids by using micro-electrode arrays (MEAs) with different types (i.e., passive, C-MOS, and 3D) and number of electrodes. Neurospheroids grown in free culture and transferred on MEAs exhibited functional activity that can be chemically and electrically modulated. Our results indicate that this model holds great potential for an in-depth study of signal transmission to drug screening and disease modeling and offers a platform for in-vitro functional testing.