Neuronal differentiation and extensive migration of human neural precursor cells following co-culture with rat auditory brainstem slices

Integration of Functional Human Auditory Neural Circuits Based on a 3D Carbon Nanotube System

The physiological interactions between the peripheral and central auditory systems are crucial for auditory information transmission and perception, while reliable models for auditory neural circuits are currently lacking. To address this issue, mouse and human neural pathways are generated by utilizing a carbon nanotube nanofiber system. The super-aligned pattern of the scaffold renders the axons of the bipolar and multipolar neurons extending in a parallel direction. In addition, the electrical conductivity of the scaffold maintains the electrophysiological activity of the primary mouse auditory neurons. The mouse and human primary neurons from peripheral and central auditory units in the system are then co-cultured and showed that the two kinds of neurons form synaptic connections. Moreover, neural progenitor cells of the cochlea and auditory cortex are derived from human embryos to generate region-specific organoids and these organoids are assembled in the nanofiber-combined 3D system. Using optogenetic stimulation, calcium imaging, and electrophysiological recording, it is revealed that functional synaptic connections are formed between peripheral neurons and central neurons, as evidenced by calcium spiking and postsynaptic currents. The auditory circuit model will enable the study of the auditory neural pathway and advance the search for treatment strategies for disorders of neuronal connectivity in sensorineural hearing loss.

Optogenetically modified human embryonic stem cell-derived otic neurons establish functional synaptic connection with cochlear nuclei

Spiral ganglia neurons (SGNs) impairment can cause deafness. One important therapeutic approach involves utilizing stem cells to restore impaired auditory circuitry. Nevertheless, the inadequate implementation of research methodologies poses a challenge in accurately assessing the functionality of derived cells within the circuit. Here, we describe a novel method for converting human embryonic stem cells (hESCs) into otic neurons (ONs) and assess their functional connectivity using an optogenetic approach with cells or an organotypic slice of rat cochlear nucleus (CN) in coculture. Embryonic stem cell-derived otic neurons (eONs) exhibited SGN marker expression and generated functional synaptic connection when cocultured with cochlear nucleus neurons (CNNs). Synapsin 1 and VGLUT expression are found in the cochlear nucleus of brain slices, where eONs projected processes during the coculture of eONs and CN brain slices. Action potential spikes and INa+/IK+ of CNNs increased in tandem with light stimulations to eONs. These findings provide further evidence that eONs may be a candidate source to treat SGN-deafness.

The Biological Behaviors of Neural Stem Cell Affected by Microenvironment from Host Organotypic Brain Slices under Different Conditions

Therapeutic strategies based on neural stem cells (NSCs) transplantation bring new hope for neural degenerative disorders, while the biological behaviors of NSCs after being grafted that were affected by the host tissue are still largely unknown. In this study, we engrafted NSCs that were isolated from a rat embryonic cerebral cortex onto organotypic brain slices to examine the interaction between grafts and the host tissue both in normal and pathological conditions, including oxygen-glucose deprivation (OGD) and traumatic injury. Our data showed that the survival and differentiation of NSCs were strongly influenced by the microenvironment of the host tissue. Enhanced neuronal differentiation was observed in normal conditions, while significantly more glial differentiation was observed in injured brain slices. The process growth of grafted NSCs was guided by the cytoarchitecture of host brain slices and showed the distinct difference between the cerebral cortex, corpus callosum and striatum. These findings provided a powerful resource for unraveling how the host environment determines the fate of grafted NSCs, and raise the prospect of NSCs transplantation therapy for neurological diseases.

Neuronal differentiation of dental pulp stem cells from human permanent and deciduous teeth following coculture with rat auditory brainstem slices

Sensorineural hearing loss is a common disability found worldwide which is associated with a degeneration of spiral ganglion neurons (SGN). It is a challenge to restore SGN due to the permanent degeneration and viability of SGN is requisite for patients to receive an advantage from hearing aid devices. Human dental pulp stem cells (DPSC) and stem cells from human exfoliated deciduous teeth (SHED) are self-renewing stem cells that originate from the neural crest during development. These stem cells have a high potential for neuronal differentiation. This is primarily due to their multilineage differentiation potential and their relative ease of access. Previously, we have shown the ability of these stem cell types to differentiate into spiral ganglion neuron-like cells. In this study, we induced the cells into neural precursor cells (NPC) and cocultured with auditory brainstem slice (ABS) encompassing cochlear nucleus by the Stoppini method. We also investigated their ability to differentiate after 2 weeks and 4 weeks in coculture. Neuronal differentiation of DPSC-NPC and SHED-NPC was higher expression of specific markers to SGN, TrkB, and Gata3, compared to monoculture. The cells also highly expressed synaptic vesicle protein (SV2A) and exhibited intracellular calcium oscillations. Our findings demonstrated the possibility of using DPSCs and SHEDs as an autologous stem cell-based therapy for sensorineural hearing loss patients.

Organotypic Cocultures of Human Pluripotent Stem Cell Derived-Neurons with Mammalian Inner Ear Hair Cells and Cochlear Nucleus Slices

Stem cells have been touted as a source of potential replacement neurons for inner ear degeneration for almost two decades now; yet to date, there are few studies describing the use of human pluripotent stem cells (hPSCs) for this purpose. If stem cell therapies are to be used clinically, it is critical to validate the usefulness of hPSC lines in vitro and in vivo. Here, we present the first quantitative evidence that differentiated hPSC-derived neurons that innervate both the inner ear hair cells and cochlear nucleus neurons in coculture, with significantly more new synaptic contacts formed on target cell types. Nascent contacts between stem cells and hair cells were immunopositive for both synapsin I and VGLUT1, closely resembling expression of these puncta in endogenous postnatal auditory neurons and control cocultures. When hPSCs were cocultured with cochlear nucleus brainstem slice, significantly greater numbers of VGLUT1 puncta were observed in comparison to slice alone. New VGLUT1 puncta in cocultures with cochlear nucleus slice were not significantly different in size, only in quantity. This experimentation describes new coculture models for assessing auditory regeneration using well-characterised hPSC-derived neurons and highlights useful methods to quantify the extent of innervation on different cell types in the inner ear and brainstem.

Directed Differentiation of Human Embryonic Stem Cells Toward Placode-Derived Spiral Ganglion-Like Sensory Neurons

The ability to generate spiral ganglion neurons (SGNs) from stem cells is a necessary prerequisite for development of cell-replacement therapies for sensorineural hearing loss. We present a protocol that directs human embryonic stem cells (hESCs) toward a purified population of otic neuronal progenitors (ONPs) and SGN-like cells. Between 82% and 95% of these cells express SGN molecular markers, they preferentially extend neurites to the cochlear nucleus rather than nonauditory nuclei, and they generate action potentials. The protocol follows an in vitro stepwise recapitulation of developmental events inherent to normal differentiation of hESCs into SGNs, resulting in efficient sequential generation of nonneuronal ectoderm, preplacodal ectoderm, early prosensory ONPs, late ONPs, and cells with cellular and molecular characteristics of human SGNs. We thus describe the sequential signaling pathways that generate the early and later lineage species in the human SGN lineage, thereby better describing key developmental processes. The results indicate that our protocol generates cells that closely replicate the phenotypic characteristics of human SGNs, advancing the process of guiding hESCs to states serving inner-ear cell-replacement therapies and possible next-generation hybrid auditory prostheses. © Stem Cells Translational Medicine 2017;6:923-936.

Cochlear nucleus whole mount explants promote the differentiation of neuronal stem cells from the cochlear nucleus in co-culture experiments

The cochlear nucleus is the first brainstem nucleus to receive sensory input from the cochlea. Depriving this nucleus of auditory input leads to cellular and molecular disorganization which may potentially be counteracted by the activation or application of stem cells. Neuronal stem cells (NSCs) have recently been identified in the neonatal cochlear nucleus and a persistent neurogenic niche was demonstrated in this brainstem nucleus until adulthood. The present work investigates whether the neurogenic environment of the cochlear nucleus can promote the survival of engrafted NSCs and whether cochlear nucleus-derived NSCs can differentiate into neurons and glia in brain tissue. Therefore, cochlear nucleus whole-mount explants were co-cultured with NSCs extracted from either the cochlear nucleus or the hippocampus and compared to a second environment using whole-mount explants from the hippocampus. Factors that are known to induce neuronal differentiation were also investigated in these NSC-explant experiments. NSCs derived from the cochlear nucleus engrafted in the brain tissue and differentiated into all cells of the neuronal lineage. Hippocampal NSCs also immigrated in cochlear nucleus explants and differentiated into neurons, astrocytes and oligodendrocytes. Laminin expression was up-regulated in the cochlear nucleus whole-mounts and regulated the in vitro differentiation of NSCs from the cochlear nucleus. These experiments confirm a neurogenic environment in the cochlear nucleus and the capacity of cochlear nucleus-derived NSCs to differentiate into neurons and glia. Consequently, the presented results provide a first step for the possible application of stem cells to repair the disorganization of the cochlear nucleus, which occurs after hearing loss.

Effects of ROCK inhibitor Y27632 and EGFR inhibitor PD168393 on human neural precursors co-cultured with rat auditory brainstem explant

Hearing function lost by degeneration of inner ear spiral ganglion neurons (SGNs) in the auditory nervous system could potentially be compensated by cellular replacement using suitable donor cells. Donor cell-derived neuronal development with functional synaptic formation with auditory neurons of the cochlear nucleus (CN) in the brainstem is a prerequisite for a successful transplantation. Here a rat auditory brainstem explant culture system was used as a screening platform for donor cells. The explants were co-cultured with human neural precursor cells (HNPCs) to determine HNPCs developmental potential in the presence of environmental cues characteristic for the auditory brainstem region in vitro. We explored effects of pharmacological inhibition of GTPase Rho with its effector Rho-associated kinase (ROCK) and epidermal growth factor receptor (EGFR) signaling on the co-cultures. Pharmacological agents ROCK inhibitor Y27632 and EGFR blocker PD168393 were tested. Effect of the treatment on explant penetration by green fluorescent protein (GFP)-labeled HNPCs was evaluated based on the following criteria: number of GFP-HNPCs located within the explant; distance migrated by the GFP-HNPCs deep into the explant; length of the GFP+/neuronal class III β-tubulin (TUJ1)+ processes developed and phenotypes displayed. In a short 2-week co-culture both inhibitors had growth-promoting effects on HNPCs, prominent in neurite extension elongation. Significant enhancement of migration and in-growth of HNPCs into the brain slice tissue was only observed in Y27632-treated co-cultures. Difference between Y27632- and PD168393-treated HNPCs acquiring neuronal fate was significant, though not different from the fates acquired in control co-culture. Our data suggest the presence of inhibitory mechanisms in the graft-host environment of the auditory brainstem slice co-culture system with neurite growth arresting properties which can be modulated by administration of signaling pathways antagonists. Therefore the co-culture system can be utilized for screens of donor cells and compounds regulating neuronal fate determination.

Human-induced pluripotent stem cells: potential for neurodegenerative diseases

The cell biology of human neurodegenerative diseases has been difficult to study till recently. The development of human induced pluripotent stem cell (iPSC) models has greatly enhanced our ability to model disease in human cells. Methods have recently been improved, including increasing reprogramming efficiency, introducing non-viral and non-integrating methods of cell reprogramming, and using novel gene editing techniques for generating genetically corrected lines from patient-derived iPSCs, or for generating mutations in control cell lines. In this review, we highlight accomplishments made using iPSC models to study neurodegenerative disorders such as Huntington's disease, Parkinson's disease, Amyotrophic Lateral Sclerosis, Fronto-Temporal Dementia, Alzheimer's disease, Spinomuscular Atrophy and other polyglutamine diseases. We review disease-related phenotypes shown in patient-derived iPSCs differentiated to relevant neural subtypes, often with stressors or cell "aging", to enhance disease-specific phenotypes. We also discuss prospects for the future of using of iPSC models of neurodegenerative disorders, including screening and testing of therapeutic compounds, and possibly of cell transplantation in regenerative medicine. The new iPSC models have the potential to greatly enhance our understanding of pathogenesis and to facilitate the development of novel therapeutics.